HK1051377B - Polycarbonate substrates - Google Patents

Description

Polycarbonate substrate

The invention relates to polycarbonate substrates produced on the basis of 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane, to the use thereof for producing moldings having particularly high purity and particularly high surface gloss, and to moldings producible from the polycarbonate substrates.

High-purity polycarbonates are required for some molded articles, such as motor vehicle window panes and scattering glasses for motor vehicle mirrors, where high light transmission without defects in the molded article is of particular importance.

Polycarbonates are prepared by the so-called phase boundary process, in which dihydroxydiarylalkanes in the form of their alkali metal salts are reacted with phosgene in a heterogeneous phase in the presence of inorganic bases, such as sodium hydroxide solution, and organic solvents in which the product polycarbonate is preferably soluble. During the reaction, the aqueous phase is distributed in the organic phase, after which the organic polycarbonate-containing phase is washed with an aqueous liquid, in which, inter alia, the electrolytes should be removed, and the wash liquid is then separated.

Japanese patent application JP-A-07196783 describes ｃA process for the preparation of polycarbonates in which, in order to produce advantageous color properties, the concentration of iron in the sodium hydroxide solution used should be less than 2 ppm.

It is an object of the present invention to provide an alternative improved process for the preparation of pure polycarbonate substrates and to provide polycarbonate moldings having a particularly high purity.

It has now surprisingly been found that polycarbonate moldings produced from polycarbonate substrates prepared by a special process based on 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane and having an average molecular weight of from 25.000 to 400.000 have particularly high surface gloss and purity.

The present invention therefore provides polycarbonate substrates prepared on the basis of 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane, which have less than 250, in particular less than 150, defects per square meter measured on 200 μm extruded foils.

The invention further provides moldings and foils based on polycarbonate substrates, in particular scattering glasses for motor vehicle panes and for automotive mirrors, which are produced on the basis of 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane and have less than 250, in particular less than 150, defects per square meter measured on 200 μm extruded foils.

When carried out in a particular manner, the polycarbonate substrates of the invention are obtained.

The present application therefore provides a process for preparing polycarbonates by the phase boundary process in which dihydroxydiarylalkanes in their alkali metal salt form are reacted with phosgene in the heterogeneous phase in the presence of sodium hydroxide solution and an organic solvent, characterized in that:

a) the raw materials have low contents of metals Fe, Cr, Ni, Zn, Ca, Mg, Al or their chemical homologues

b) The organic solvent is separated out

c) Post-treating the polycarbonate obtained

In the context of the present invention, low contents of the metals and their chemical homologues mean that the total metals contained in the starting materials, in particular the metals and homologues listed above, is preferably not more than 2ppm, more preferably not more than 1ppm, particularly preferably not more than 0.5ppm, very particularly preferably not more than 0.2 ppm. These limits do not apply to alkali metals.

The starting sodium hydroxide solution preferably contains a low content of said metals. In particular, the sodium hydroxide solution should contain not more than 1ppm, preferably not more than 0.5ppm, more preferably not more than 0.3ppm of alkaline earth metals and their homologues for a NaOH content of 100 wt.%. In particular, the raw sodium hydroxide solution should contain not more than 1ppm, preferably not more than 0.5ppm, more preferably not more than 0.1ppm of iron for a NaOH content of 100% by weight.

Sodium hydroxide solutions having a concentration of 20 to 55% by weight, particularly preferably 30 to 50% by weight, are preferably used in the process according to the invention.

The sodium hydroxide solutions having the above-mentioned limits can be obtained by the membrane process known from the literature.

In a preferred embodiment, in addition to the sodium hydroxide solution, the starting bisphenols, in particular bisphenols and water, very particularly preferably bisphenols, water and organic solvents, have a low metal content, in particular a low content of Fe, Cr, Ni, Zn, Ca, Mg, Al.

Also included are embodiments in which the sodium bisphenolate (solution) has been previously prepared from a sodium hydroxide solution and a bisphenol (or bisphenols).

In a preferred variant, these raw materials having a low metal content are obtained by distilling the solvent, crystallizing the bisphenol, preferably crystallizing or distilling the bisphenol several times, and using water of VE quality.

VE-water is preferably desalted, degassed and/or desilicated. As a quality criterion, for example, the electrical conductivity (overall parameter of minerals from salts still present in trace amounts in water) is used, wherein, in the process according to the invention, VE-water is characterized by an electrical conductivity of 0.2. mu.S/cm (DIN 38404C 8), SiO₂The concentration was 0.02mg/kg (VGB3.3.1.1), or lower for each of them.

The concentration of dissolved oxygen in VE-water is advantageously less than 1ppm, preferably less than 100 ppb.

In a further preferred embodiment, at least the sodium hydroxide solution, preferably also the bisphenol, particularly preferably sodium hydroxide, bisphenol and water, most preferably sodium hydroxide solution, bisphenol, water and organic solvent are filtered at least once, preferably twice, particularly preferably three times stepwise before the start of the reaction in the starting material set.

The present invention also provides a process for the preparation of polycarbonates by the phase interface process in which a dihydroxydiarylalkane in its alkali metal salt form is reacted with phosgene in a heterogeneous phase in the presence of sodium hydroxide solution and an organic solvent, which process is characterized in that:

a) the raw materials have low content of metal Fe, Cr, Ni, Zn, Ca, Mg, Al or their homologues

b) The organic solvent is separated out, and

c) the polycarbonate obtained is worked up

d) Separating the aqueous phase produced during the reaction, washing the separated organic polycarbonate phase with an aqueous solution, and

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

in a preferred embodiment, in process step d), the reaction mixture is filtered directly after the 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.

It is preferred to carry out at least two of these filtration processes, in particular to carry out all three filtration processes.

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 3 times, in particular stepwise. In the case of step-wise filtration, a coarser filter is used first, followed by a finer filter. The filtration of the two-phase medium in step (d) is preferably carried out using a coarser filter.

In process step e), the hot filtration is carried out using a filter having a smaller pore size. In this case, it is important that the polycarbonate phase is present in as homogeneous a solution as possible. This can be done by heating the organic polycarbonate phase which generally still contains residual aqueous washing liquid. At which point the wash solution was dissolved and a clear solution was formed. Previously dissolved impurities, in particular dissolved alkali metal salts, precipitate out and are filtered off.

In order to obtain a uniform solution, a well-known freezing method may be used in addition to the above-described method.

For the filtration according to the invention, membrane filters and sintered metal filters or bag filters can be used as filters. The filter typically has a pore size of 0.01 to 5 microns, preferably 0.02 to 1.5 microns, and more preferably about 0.05 to 1.0 microns. These types of filters are commercially available, for example from Pall GmbH, D-63363Dreieich, and Krebsb ö ge GmbH, D-42477 Radevmwald (SIKA-R CU1 AS).

By the combination of the methods according to the invention, a significantly improved filter life is obtained.

The performance of other process steps is generally well known. Thus, during the reaction, the aqueous phase is emulsified in the organic phase. Thereby producing droplets of different sizes. After the reaction, the organic polycarbonate-containing phase is usually washed several times with an aqueous liquid and separated from the aqueous phase as far as possible after each washing. The washing is preferably carried out with very finely filtered water having a very low metal content. The polymer solution is usually turbid after washing and separation from the washing liquid. Removing the catalyst with an aqueous liquid as a washing liquid, using dilute mineral acid such as HCl or H₃PO₄And fully deionized water for further purification. HCl or H in the wash₃PO₄The concentration of (B) may be, for example, 0.5 to 1.0% by weight. The organic phase is washed, for example and preferably 5 times.

A separating funnel, phase separator, centrifuge or coalescer or a combination of these devices, which are known in principle, can be used as phase separation device in order to separate the wash liquor from the organic phase.

The solvent is evaporated to obtain a high purity polycarbonate. The evaporation can be carried out in several evaporation stages. According to another preferred embodiment of the present invention, the solvent or a part of the solvent may be removed by spray drying, thereby obtaining a high purity polycarbonate in powder form. It is likewise possible to use the high-purity polycarbonate obtained by precipitation from an organic solution and then to dry the precipitate which has been filtered off. Extrusion, for example, is a suitable method for evaporating residual solvent. The extrusion-evaporation process is another method.

As diphenols, use may be made of 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane and 2, 2-bis- (4-hydroxyphenyl) -propane (BPA/bisphenol-A), optionally in the form of mixtures, wherein 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane is always present in an amount of more than 0.1 mol%. Preferably, the concentration of 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane is from 10 to 100 mol%. The bisphenols used according to the invention are reacted with carbonic acid compounds, in particular phosgene.

The polyester carbonates are obtained by reacting the bisphenols already described, at least one aromatic dicarboxylic acid and optionally carbon dioxide. Suitable aromatic dicarboxylic acids are, for example, phthalic acid, terephthalic acid, isophthalic acid, 3 '-or 4, 4' -biphenyldicarboxylic acid and benzophenonedicarboxylic acid.

Inert organic solvents used in the process are, for example, dichloromethane, the various dichloroethane and chloropropane compounds, chlorobenzene and chlorotoluene. Preference is given to using methylene chloride and mixtures of methylene chloride and chlorobenzene.

The reaction is accelerated by catalysts such as tertiary amines, N-alkylpiperidines or onium salts. It is preferred to use tributylamine, triethylamine and N-ethylpiperidine. 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. Isatin-biscresol may be used, for example, as a branching agent.

To prepare high purity polycarbonates, the bisphenols are dissolved in an alkaline aqueous phase, preferably sodium hydroxide solution. The chain terminators, which are optionally required for the preparation of copolycarbonates, are dissolved in an alkaline aqueous phase or are likewise added to an inert organic phase in an amount of 1.0 to 20.0 mol% per mol of bisphenol. Phosgene is then passed into a mixer containing the remaining reaction components and the polymerization is carried out.

Chain terminators which are optionally used are monophenols or monocarboxylic acids. Suitable monophenols are phenol itself, alkylphenols such as cresol, p-tert-butylphenol, p-cumylphenol, p-n-octylphenol, p-isooctylphenol, p-n-nonylphenol and p-isononylphenol, 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.

Preferred chain terminators are phenols of the 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 0.1 mole% to 5 mole%, referred to the moles of diphenols used in each case. The addition of chain terminators may be carried out before, during or after phosgenation.

Optionally, branching agents may also be added to the reaction. Preferred branching agents are trifunctional or more than trifunctional compounds known from polycarbonate chemistry, in particular compounds having three or more than three phenolic OH groups.

Branching agents are also, for example and preferably, phloroglucinol, 4, 6-dimethyl-2, 4, 6-tri- (4-hydroxyphenyl) -hept-2-ene, 4, 6-dimethyl-2, 4, 6-tri- (4-hydroxyphenyl) -heptane, 1, 3, 5-tri- (4-hydroxyphenyl) -benzene, 1, 1, 1-tri- (4-hydroxyphenyl) -ethane, tri- (4-hydroxyphenyl) -phenylmethane, 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-hydroxyphenyl) -2- (2, 4-dihydroxyphenyl) -propane, Hexa- (4- (4-hydroxyphenyl-isopropyl) -phenyl) -orthoterephthalate (Hexa- (4- (4-hydroxyphenyl-isopropyl) -phenyl) -ortherhal-hals-bereester), 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-indoline.

The amount of branching agent optionally used is likewise from 0.05 mol% to 2 mol% for the moles of bisphenol used per time.

The branching agents may be added to the aqueous alkaline phase beforehand, together with the bisphenols and the chain terminators, or dissolved in an organic solvent before phosgenation.

Some carbonate groups in the polycarbonate, up to 80 mol%, preferably from 20 to 50 mol%, may be substituted by aromatic dicarboxylic acid ester groups.

The polycarbonates according to the invention are homopolycarbonates or copolycarbonates or mixtures thereof. The polycarbonates according to the invention may be aromatic polyester carbonates or polycarbonates present in a mixture with aromatic polyester carbonates. The concept of polycarbonate denotes a polycarbonate substrate which can be obtained by the process according to the invention.

The average molecular weight M of the polycarbonate_w(determined by measuring the relative viscosity in methylene chloride at 25 ℃ at a concentration of 0.5 g of polycarbonate per 100 ml of methylene chloride) is 12,000-400,000, preferably 23,000-80,000, especially 24,000-40,000.

The moldings according to the invention produced from the high-purity polycarbonate substrates according to the invention are in particular glazings for motor vehicles and diffusing glasses for motor vehicle mirrors, where high light transmission without defects in the moldings is of particular importance. These moldings are produced by injection molding, extrusion and extrusion blow molding using the polycarbonates according to the invention having suitable molecular weights.

The moldings and foils of the invention are distinguished by a particularly low defect rate in the film laser scanning test and by a particularly low haze of less than 0.5%, in particular less than 0.4%. The moldings of the invention have a number of defects per square meter of less than 300, in particular less than 250, preferably less than 150 defects, measured on an extruded film of 200 μm.

The following examples are used to explain the present invention, but the present invention is not limited to these examples.

Examples

To prepare the polycarbonate, 1-bis- (4-hydroxyphenyl) -3, 3-dimethyl-5-methylcyclohexane (oxygen removed by 5 vacuums and nitrogen purging) and a sodium hydroxide solution were dissolved under oxygen-removing conditions in a stirred tank reactor before the dissolution and mixed with a solution of BPA in sodium hydroxide under oxygen-removing conditions (molten BPA was continuously mixed with the solution of sodium hydroxide) to prepare a disodium salt solution (57 Mol-%: 43 Mol-%) of aqueous sodium bisphenolate/1, 1-bis- (4-hydroxyphenyl) -3, 3-dimethyl-5-methylcyclohexane. The sodium hydroxide solutions used had different concentrations and purities (see table 1), wherein the original sodium hydroxide solution was further diluted to a 6.5% sodium hydroxide solution in order to dissolve the bisphenol. At this point the sodium bisphenolate solution is filtered through a 0.6 μ a filter and added to the polycarbonate reaction. After the reaction, the reaction solution was filtered through a 1.0 μ a bag filter and the wash solution was added, whereupon it was washed with 0.6% hydrochloric acid and then 5 times with filtered VE-water. The organic solution was separated from the aqueous phase and after heating the organic solution to 55 ℃ it was filtered first with a 0.6 μ a filter and then with a 0.2 μ a filter. After separation, poly-1, 1-bis- (4-hydroxyphenyl) -3, 3-dimethyl-5-methylcyclohexane-co-2, 2-bis- (4-hydroxyphenyl) -propane carbonate is obtained. The average molecular weight Mw of the polycarbonate thus obtained was 31,000.

TABLE 1

Quality of sodium hydroxide 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 amount (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 amount (ppm)	7.8	3.1	＜0.9

Filter life at different filter locations in each case:

TABLE 2

	Experiment number for preparing sodium hydroxide
				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
Final filter 1 ═ 0.6 μ a-filter final filter 2 ═ 0.2 μ a-filter	12h	3d	21d

Polycarbonate extruded films prepared from experiments 1-3 with sodium hydroxide were subjected to film laser scanning testing using known methods. The extruded film was 200 microns thick and 60 mm wide. The film was scanned in width with a He/Ne laser ("spot diameter" of 0.1 mm) at a scanning frequency of 5000Hz, and a transport speed of 5m/s in the length direction was used. All defects (above 0.10 mm diameter) causing scattering of the emitted laser light were detected using a photomultiplier tube and counted using software. The number of optical defects per kilogram of polycarbonate or per square meter of film is a measure of the surface quality of these films and the purity of the PC.

Analysis of extruded films with laser scanner
					Experimental number for preparing PC by using sodium hydroxide solution
# per square meter of surface	1	2	3
				0.10-0.30mm	194	99	53
＞0.30mm	216	128	72
				Total number of	410	227	125

Solid sheets for automotive glass and automotive headlights were prepared from the polycarbonate prepared from experiments 1-3 with sodium hydroxide solution. The polycarbonate prepared from experiment 3 using the sodium hydroxide solution had less flash fraction and higher luminous efficiency.

Color sample plaques were produced from different qualities of polycarbonate. According to ASTM D1003, the colour sample plaques have different degrees of haze, with colour sample plaques (4 mm thick) produced from the polycarbonate prepared in experiment 3 with a sodium hydroxide solution having a particularly low degree of haze of 0.4%, which results in less diffuse scattered light when used as glazing/scattering glass.

Claims (8)

1. The number of defects measured in a 200 μm extruded film prepared from a base based on 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane is less than 300/m²The polycarbonate substrate of (1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane having an average molecular weight of 25,000-400,000, which is prepared by a phase interface process in which 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane in its alkali metal salt form is reacted with phosgene in a heterogeneous phase in the presence of sodium hydroxide solution and an organic solvent, wherein

a) The raw materials have low content of metal Fe, Cr, Ni, Zn, Ca, Mg, Al or homologues thereof,

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

c) the polycarbonate obtained is subjected to a post-treatment,

d) separating the aqueous phase produced during the reaction, washing the separated organic polycarbonate phase with an aqueous solution, and

e) the washed organic polycarbonate phase is separated from the washing liquid.

2. The polycarbonate substrate according to claim 1, wherein the number of defects measured in a 200 micron extruded film is less than 250/m²。

3. Use of the polycarbonate substrate according to claim 1 or 2 for producing polycarbonate moldings.

4. A process for producing a polycarbonate molded article having a small number of defects, characterized in that a polycarbonate substrate according to claim 1 or 2 is used as a starting substrate.

5. Number of defects of less than 300/m measured on a 200 μm extruded film from a 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane-based film according to claim 1 or 2²A molded article made of the polycarbonate of (1).

6. The molding according to claim 5, having an haze of less than 0.5%.

7. Number of defects of less than 300/m measured on a 200 μm extruded film from a 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane-based film according to claim 1 or 2²And haze less than 0.5% for thin disks made of polycarbonate.

8. Number of defects of less than 300/m measured on a 200 μm extruded film from a 1, 1-bis- (4-hydroxyphenyl) -3, 3, 5-trimethylcyclohexane-based film according to claim 1 or 2²And haze less than 0.5% of polycarbonate.