Process for preparation of polycarbonates

Abstract

The invention relates to the use of ultraviolet-stable compounds comprising at least one benzotriazole group as heat stabilizers in polycarbonates produced by a melt transesterification process, the melt transesterification process includes reacting a diaryl carbonate and a bisphenol under catalysis of a catalyst and quenching the catalyst with a quenching agent.

Description

[0001] The invention relates to the use of UV-stabilizing compounds comprising at least one benzotriazole group in polycarbonates and to a process for preparing polycarbonates.

[0002] Polycarbonates are generally prepared using two different techniques. In the first technique, which is called interfacial technology or interfacial method, phosgene reacts with bisphenol A (BPA) in the liquid phase. In this method, the aromatic polycarbonate chain will grow, that is, the molecular weight will increase, until the reaction is stopped by adding a chain terminator (also called an end-capping agent). Typically, such end-capping agents are monohydroxy compounds, such as phenol. Due to the nature of the interfacial technology, the end-capping level of aromatic polycarbonates is very high, which means that the aromatic polycarbonate obtained via the interfacial technology will have a relatively small amount of terminal hydroxyl groups at the end of the aromatic polycarbonate chain. Therefore, such aromatic polycarbonates generally have very good initial color and long-term thermal stability. The long-term stability is at least partially attributed to the absence of catalysts or catalyst residues, because the catalysts or catalyst residues are generally removed from the reaction mixture before the polycarbonate polymer is isolated. Although this method produces the desired polymer, there are also disadvantages associated with it. For example, phosgene is highly toxic and therefore causes safety issues. In addition, dichloromethane, which is often used as a solvent in the interfacial method, also causes environmental concerns. Polycarbonates prepared using the interfacial method are referred to as interfacial polycarbonates in this article.

[0003] Another well-known technology for preparing aromatic polycarbonates is the so-called melt technology, sometimes also referred to as melt transesterification, melt process or melt polycondensation technology. In the melt technology or melt process, a bisphenol, usually bisphenol A (BPA), reacts with a carbonate, usually diphenyl carbonate (DPC) in the melt phase. The reaction between DPC and BPA releases phenol, which needs to be removed from the reaction mixture in order to carry out the polymerization reaction. Typically, the melt process is carried out in multiple stages with increasing temperature and decreasing pressure until the desired molecular weight is obtained. Due to the nature of the melt process, the resulting aromatic polycarbonate usually has a significantly larger amount of terminal hydroxyl groups. As a result, the obtained aromatic polycarbonate has lower long-term thermal stability properties than the aromatic polycarbonate prepared by the interfacial process. In addition to the higher content of free hydroxyl groups in the melt polycarbonate, the polycarbonate leaving the final reactor still contains active catalyst. In order to improve the long-term stability of polycarbonate, it is known to use a catalyst deactivating compound (generally referred to as a quencher) to deactivate the catalyst. The polycarbonate produced by the melt process is referred to as melt polycarbonate in this article.

[0004] US2018 / 371208 discloses an article formed from a composition, the composition comprising: a molten polycarbonate resin derived from diphenyl carbonate; and tristearic acid glyceryl mixed with the molten polycarbonate resin, wherein the molten polycarbonate resin exhibits a melt volume rate between about 18 cubic centimeters / 10 minutes and about 22 cubic centimeters / 10 minutes, wherein the molten polycarbonate resin of the composition exhibits a fries concentration of less than about 800 ppm, wherein the article formed from the composition exhibits a melt volume rate between about 9.5 KJ / m 2 and about 13KJ / m 2 The composition has an Izod impact property of between about 10% and about 20% based on ISO 180 at room temperature at a thickness of 4 mm, and wherein an article formed from the composition exhibits a weathering value of less than about 12 delta yellowness index when tested in accordance with ISO 4892 at an exposure time of 2000 hours.

[0005] US2019 / 382557 discloses a molded article comprising: a polycarbonate resin produced by an interfacial polymerization process and having an end-capping level of at least about 98%; an ultraviolet (UV) absorbing component; a thermal stabilizer component; and an acid stabilizer component, wherein when molded under abusive molding conditions, the molded article comprises a ratio of bound UV absorbing component to free UV absorbing component of less than about 1.0.

[0006] US2004 / 063825 discloses an aromatic-aliphatic copolycarbonate resin composition comprising 100 parts by weight of an aromatic-aliphatic copolycarbonate, 0.001 to 0.5 parts by weight of a benzotriazole ultraviolet absorber, and 0.005 to 0.1 parts by weight of at least one of the phosphorus antioxidants represented by the following formulae (1) to (3):

[0007]

[0008] (wherein R1 to R6 represent a hydrogen atom, an alkyl group having 1 to 18 carbon atoms or an oxyalkyl group having 1 to 18 carbon atoms, provided that R1 to R6 may be the same or different; n represents the number of substituents and is an integer from 0 to 4).

[0009] US2016 / 362537 discloses a method for making a thermoplastic composition, comprising melt polymerizing polycarbonate, extruding and melt filtering the polycarbonate to form a melt-filtered polycarbonate; forming a thermoplastic composition comprising the melt-filtered polycarbonate, 0.03 to 0.05 weight percent of a triglyceride release agent, and 0.10 to 0.14 weight percent of a UV stabilizer; wherein the weight percents are based on the total weight of the composition; and extruding the thermoplastic composition.

[0010] The inventors observed that the addition of a quencher to molten polycarbonate resulted in higher initial color values, also referred to herein as a* values ​​or “cookie values.” Thus, the inventors observed that higher amounts of quencher resulted in higher a* values.

[0011] In view of this, it was an object of the present invention to provide a polycarbonate which has not only good initial color values ​​but also long-term color stability.

[0012] To this end, the present inventors have surprisingly found that the addition of relatively small amounts of ultraviolet (UV) stabilizing compounds having benzotriazole groups (also referred to as UV stabilizers) unexpectedly leads to lower initial color values.

[0013] The present invention therefore relates to the use of a UV-stable compound comprising at least one benzotriazole group as a heat stabilizer in polycarbonate prepared by a melt transesterification process comprising reacting a diaryl carbonate and a bisphenol in the presence of a catalyst and quenching the catalyst with a quencher.

[0014] More particularly, the present invention relates to the use of a UV stabilizing compound comprising at least one benzotriazole group as an additive in a polycarbonate prepared by a melt transesterification process comprising reacting a diaryl carbonate and a bisphenol in the presence of a catalyst and quenching the catalyst with a quencher, for producing an article having a lower a* value than an otherwise identical polycarbonate not comprising said compound.

[0015] According to the present invention, the method for preparing polycarbonate comprises:

[0016] - reacting diaryl carbonate and bisphenol in the presence of a catalyst in at least two continuous reactors to form a molten polycarbonate stream,

[0017] - adding a quencher and a UV stabilizing compound comprising at least one benzotriazole group to the molten polycarbonate stream,

[0018] - extruding a molten polycarbonate stream into one or more strands,

[0019] -Optionally cool one or more strands

[0020] - granulating the strands,

[0021] wherein the molar ratio of quencher to catalyst is from 0.9 to 10.0, preferably from 1.0 to 5.0, more preferably from 1.0 to 2.0, and wherein the amount of the UV stabilizing compound is from 500 to 5000 ppm by weight based on the weight of the polycarbonate.

[0022] Polycarbonate

[0023] The polycarbonate is preferably an aromatic polycarbonate obtained by reacting bisphenols and diaryl carbonates, wherein the bisphenol is preferably bisphenol A (BPA) and the diaryl carbonate is preferably diphenyl carbonate (DPC). Other types of bisphenols and / or mixtures of bisphenol A and further bisphenols can also be used. The aromatic polycarbonate is preferably a linear aromatic polycarbonate, which means that the melt transesterification is carried out based on bisphenols and diaryl carbonates in the absence of any branching agents, such as, for example, polyfunctional alcohols. For the purposes of the present invention, the melt polycarbonate may however be branched or linear.

[0024] Despite what has been mentioned above, it is well known that the melt transesterification process for the preparation of polycarbonates, in which BPA and DPC react under molten conditions to release phenol, results in a certain amount of branching, known as Fries branches. The amount of Fries branches depends inter alia on the type and amount of transesterification catalyst used and on the reaction conditions applied, in particular temperature, pressure and residence time. Thus, in the context of the present invention, linear polycarbonates will contain a certain amount of Fries branches. However, it is to be understood that in the present invention it is preferred to prepare the polycarbonates in the absence of branching agents, i.e. in the absence of agents comprising three or more functional groups, which introduce branches or even crosslinking into the polycarbonate.

[0025] The polycarbonate is preferably a bisphenol A polycarbonate homopolymer.

[0026] The amount of Fries branches may be from 300 to 3000 ppm, preferably from 500 to 2000 ppm, more preferably from 600 to 1200 ppm. The term "Fries branches" is known to the skilled person and refers in particular to structures as disclosed in EP2174970 and reproduced below as structures (1) to (5), but may also include more branched structures.

[0027]

[0028] WO 2011 / 120921 discloses that units such as those disclosed in EP 217940 are Fries branch species. Methods for determining the amount of Fries branches are known to the skilled person and generally involve subjecting the polycarbonate to methanolysis followed by HPLC chromatography to identify the total amount of Fries structures. Additionally, NMR techniques may be used to determine the type and amount of these Fries structures, such as the corresponding amounts of linear and branched Fries structures.

[0029] The polycarbonate preferably has a weight average molecular weight (Mw) of 15,000 to 60,000 g / mol as determined by GPC based on polystyrene standards.

[0030] The polycarbonate preferably has a melt volume rate (MVR) of 3 to 30 cc / 10 min, as determined according to ISO 1133 (300° C., 1.2 kg).

[0031] Manufacturing method

[0032] The method for producing molten polycarbonate is not limited per se. In general, the melt process includes the use of multiple reactors, wherein the elevated temperature and lower pressure are usually applied, so that the condensation reaction is continued by removing the condensation byproducts (usually phenol). Higher temperatures are not only used to promote the reaction, but also to cope with the increasing viscosity of the polymer being formed. Therefore, the method disclosed herein relates to a multi-stage method for preparing polycarbonate, including a monomer mixing stage, an oligomerization stage and a polymerization stage. However, the method may include other stages, such as specifically a post-processing stage, in which the polycarbonate obtained by the polymerization stage is fed to an extruder, extruded into strands, and then strands are continuously cut into pellets. An extruder provides the possibility of adding more materials to the polycarbonate directly received from the final reactor.

[0033] Preferably, use Figure 1 The method and apparatus schematically shown in the present invention are used to prepare polycarbonate, but it should not be considered as limiting the present invention. The following description will be based on BPA and DPC as raw materials, but the skilled person will understand that the description is also applicable to other types of bisphenols, bisphenol mixtures, other types of diaryl carbonates and diaryl carbonate mixtures.

[0034] The monomer mixing stage comprises the mixing of the monomers, namely bisphenols and diaryl carbonates, or more specifically BPA and DPC. The plant for preparing polycarbonates may be part of an integrated site, and the BPA and DPC may come directly from the plant (which produces the monomers in solid or molten form) on site. However, the present invention is not limited to this embodiment, and BPA and DPC (or any other bisphenols and diaryl carbonates) may also be obtained from an external source and added to the plant using appropriate feeding equipment in the monomer mixing stage and when any optional pretreatments such as melting, filtering, purification, solvent removal, etc. are applied.

[0035] refer to Figure 1, BPA and DPC are added to the monomer mixing device 10 as feed streams A and B1, respectively. The ratio of DPC to BPA in the monomer mixing device is kept fixed. The β catalyst is added to the monomer mixing device 10 via feed stream C. The monomer mixing device is equipped with a suitable agitator to ensure a uniform concentration of the components in the device. The monomer mixing device 10 can be maintained at a temperature of 160 to 180° C. and approximately atmospheric pressure. The feed stream leaving the monomer mixing device 10 is fed to the first oligomerization reactor 20. Due to process flexibility, an additional amount of DPC is optionally added as feed stream B2. The α catalyst is added as feed stream D. The monomer mixture is reacted for a certain time in the oligomerization reactor 20 in the oligomerization stage. Generally speaking, the oligomerization reactor 20 is a continuous stirred tank reactor.

[0036] The oligomerization reactor 20 is operated at a temperature of 230 to 260° C. and a pressure of 140 to 200 mbar. An overhead stream comprising phenol by-product and optionally monomers or other low molecular weight reaction products is removed via stream 70 and fed to column 50, which separates phenol from the overhead stream. Phenol is then removed via overhead stream E for further purification and / or use, while the bottoms stream is optionally fed back to the reactor 20 as stream 71. The bottom portion of column 50 may also be further purified off-line or may be purged.

[0037] The mixture leaving the reactor 20 is fed to the second oligomerization reactor 21 for further reaction. The second oligomerization reactor 21 is operated at a temperature of 270 to 290° C. and a pressure of 30 to 50 mbar. Phenol by-product is removed from the second reactor 21 as stream E. The second oligomerization reactor 20 can also be a continuous stirred tank reactor.

[0038] The oligomerization reactors 20 and 21 constitute an oligomerization stage, and the polycarbonate oligomer stream produced is fed to the first polymerization reactor 30 and then to the second polymerization reactor 31. Reactor 30 is operated at a temperature of 290 to 315°C and a pressure of 1 to 5 mbar. Then, the stream of the first polymerization reactor 30 is fed to the second polymerization reactor 31, which is operated at a temperature of 290 to 315°C and a pressure of 0.3 to 1.5 mbar. The temperature in reactor 31 is generally higher than the temperature in reactor 30, and the pressure in reactor 31 is generally lower than the pressure in reactor 30. Similar to the oligomerization stage, phenol by-products are removed from reactors 30 and 31. Polymerization reactors 30 and 31 together constitute a polymerization stage. As known to those skilled in the art, different types of reactors can be used.

[0039] The polymer leaving the second polymerization reactor 31 is fed to an extruder 40 where it is combined with one or more additives indicated by I. A stream of a catalyst deactivator or quencher is added via stream 16. The extruded stream is passed through a melt filter 60 and then extruded into strands and cut into pellets. For the avoidance of doubt, it is noted that the location for adding the catalyst quencher is not limited to stream 16 and other locations may be equally suitable. The quencher may be combined with the polycarbonate upstream, downstream or together with the additive. Additives include UV stabilizing compounds containing at least one benzotriazole group, as discussed herein.

[0040] The additive stream may also include a (mechanically) recycled polycarbonate stream, preferably in pellet or powder form, and the UV-stabilizing compound comprising at least one benzotriazole group is preferably contained in the recycled polycarbonate. In other words, the UV-stabilizing compound comprising at least one benzotriazole group can be combined with polycarbonate in an extruder by a masterbatch comprising or consisting of recycled polycarbonate as a carrier resin, the carrier resin comprising the UV-stabilizing compound. Therefore, it is preferred that in the process disclosed herein, polycarbonate is fed from the final reactor to the extruder, and wherein a certain amount of recycled polycarbonate is combined with the polycarbonate in the extruder, the UV-stabilizing compound being at least partially contained in the recycled polycarbonate.

[0041] The UV-stabilizing compound comprising at least one benzotriazole group can also be added as a separate stream.

[0042] Note that although Figure 1 Polymerisation reactors 30 and 31 are shown as horizontal polymerisation units, but these reactors may each independently be vertical reactors such as the known wire wetting fallpolymerisation type reactors.

[0043] Figure 1The method indicated in is shown as a single production line. However, it is possible to divide the line into two or more parallel lines at any point in the method, wherein each line operates under the same or different conditions including monomer mixture composition, temperature, pressure, residence time, etc. By way of example, the stream leaving the oligomerization reactor 21 can be divided into two or more different streams, after which each stream is polymerized using, for example, different conditions in one or more polymerization reactors, thereby resulting in the parallel preparation of different grades of polycarbonate. Another possibility is to divert the stream leaving the final polymerization reactor 31 and then feed the polycarbonate stream to different extruders. An option in this embodiment is to add chain scissors via stream 16 and / or use different additives in the extruder so as to prepare different grades in parallel. Finally, the monomer mixing device can supply any number of oligomerization and polymerization lines.

[0044] remove Figure 1 In addition to the specific configuration shown in , the method of the present invention is carried out under one or more of the following preferred conditions.

[0045] Preferably the monomer mixing stage includes the addition of a beta catalyst, wherein the beta catalyst is a quaternary ammonium compound or a quaternary phosphonium compound or a mixture thereof.

[0046] Beta Catalyst

[0047] The quaternary ammonium compound may be one or more compounds having the structure (R1)4N + X - An organic ammonium compound, wherein each R1 is the same or different and is C1-C 20 Alkyl, C4-C 20 Cycloalkyl or C6-C 20 Aryl; and X - For organic or inorganic anions, for example hydroxide, halide, carboxylate, sulfonate, sulfate, formate, carbonate or bicarbonate. Some non-limiting examples of organic quaternary ammonium compounds include tetramethylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium acetate, tetramethylammonium formate, tetrabutylammonium acetate, and combinations comprising two or more of the foregoing. Usually tetramethylammonium hydroxide is used.

[0048] The quaternary phosphonium compound may be of the structure (R2)4P + X - An organic phosphonium compound, wherein each R2 is the same or different and is C 1-20 Alkyl, C4-C 20 Cycloalkyl or C6-C 20 Aryl; and X -is an organic or inorganic anion, for example hydroxide, phenol, halide, carboxylate such as acetate or formate, sulfonate, sulfate, formate, carbonate or bicarbonate. - In the case of polyvalent anions such as carbonate or sulfate, it is understood that the positive and negative charges in the quaternary ammonium and quaternary phosphonium structures are appropriately balanced. For example, in the case where each R2 is independently methyl and X- is carbonate, it is understood that X - Indicates 2(CO3 2- ).

[0049] Examples of the organic quaternary phosphonium compound include tetramethylphosphonium hydroxide, tetramethylphosphonium acetate, tetramethylphosphonium formate, tetrabutylphosphonium hydroxide, tetraphenylphosphonium acetate (TPPA), tetraphenylphosphonium phenolate (TPPP), tetraethylphosphonium acetate, tetrapropylphosphonium acetate, tetrabutylphosphonium acetate (TBPA), tetrapentylphosphonium acetate, tetrahexylphosphonium acetate, tetraheptylphosphonium acetate, tetraoctylphosphonium acetate, tetradecylphosphonium acetate, Tetrakis(dodecyl)phosphonium acetate, tetratolylphosphonium acetate, tetramethylphosphonium benzoate, tetraethylphosphonium benzoate, tetrapropylphosphonium benzoate, tetraphenylphosphonium benzoate, tetraethylphosphonium formate, tetrapropylphosphonium formate, tetraphenylphosphonium formate, tetramethylphosphonium propionate, tetraethylphosphonium propionate, tetrapropylphosphonium propionate, tetramethylphosphonium butyrate, tetraethylphosphonium butyrate, and tetrapropylphosphonium butyrate, and combinations comprising two or more of the foregoing.

[0050] The quaternary catalyst may comprise TPPP, TPPA, TBPA or a combination comprising one or both of the foregoing. In a preferred embodiment, the beta catalyst, ie, the quaternary catalyst, is tetrabutylphosphonium acetate (TBPA).

[0051] The amount of quaternary catalyst employed is generally based on the total moles of dihydroxy compounds employed in the polymerization reaction. When referring to the ratio of the quaternary catalyst, such as the phosphonium salt, to all dihydroxy compounds employed in the polymerization reaction, it is convenient to refer to the moles of the phosphonium salt per mole of one or more dihydroxy compounds, meaning the moles of the phosphonium salt divided by the sum of the moles of each individual dihydroxy compound present in the reaction mixture. The amount of beta catalyst, i.e., quaternary catalyst (e.g., organic ammonium or phosphonium salt), employed will generally be 1×10 mol / L per total mole of dihydroxy compounds in the reaction mixture. -2 Up to 1×10 -5 Specifically, 1×10 -3 Up to 1×10 -4 Moore.

[0052] The quaternary catalyst preferably contains no metal compounds, which may be present as impurities. In particular, the quaternary catalyst comprises at most 500 ppm, preferably at most 50 ppm, of sodium and at most 100, preferably at most 50 ppm, of potassium, based on the total weight of the quaternary catalyst.

[0053] The quaternary catalyst may be added just upstream of the monomer mixing device, and / or directly into the monomer mixing device, and / or directly into the oligomerization reactor.

[0054] Alpha Catalyst

[0055] The alpha catalyst is an alkali containing catalyst comprising a source of one or both of alkali metal ions and alkaline earth metal ions. The source of these ions may include alkaline earth metal hydroxides, such as magnesium hydroxide and calcium hydroxide. The source of alkali metal ions may include alkali metal hydroxides, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and a combination comprising two or more of the foregoing. Examples of alkaline earth metal hydroxides are calcium hydroxide, magnesium hydroxide, and a combination comprising two or more of the foregoing. The alkaline catalyst may comprise sodium hydroxide. The alkaline catalyst will generally be present in an amount sufficient to provide 1×10 -2 Up to 1×10 -8 Mole, specifically 1×10 -4 Up to 1×10 -7 Molar amounts of metal hydroxide are used.

[0056] Other possible sources of alkaline earth and alkali metal ions include salts of carboxylic acids (such as sodium acetate) and derivatives of ethylenediaminetetraacetic acid (EDTA) (such as EDTA tetrasodium salt and EDTA magnesium disodium salt), and combinations comprising at least one of the foregoing. For example, the alkaline catalyst may comprise one or more alkali metal salts of carboxylic acids, one or more alkaline earth metal salts of carboxylic acids, or a combination comprising at least one of the foregoing. In another example, the alkaline catalyst comprises Na2Mg EDTA or a salt thereof.

[0057] The basic catalyst may also or alternatively comprise one or more salts of a non-volatile inorganic acid. For example, the basic catalyst may comprise one or more salts of a non-volatile inorganic acid, such as NaH2PO3, NaH2PO4, Na2HPO3, KH2PO4, CsH2PO4, Cs2HPO4 and a combination comprising two or more of the foregoing. Alternatively or in addition, the basic catalyst may comprise one or more mixed alkali metal salts of phosphoric acid, such as NaKHPO4, CsNaHPO4, CsKHPO4 and a combination comprising two or more of the foregoing. The basic catalyst may comprise KNaHPO4, wherein the molar ratio of Na to K is 0.5 to 2.

[0058] The basic catalyst is preferably added downstream of the monomer mixing device and can, for example, be added upstream of one or more oligomerization and / or polymerization reactors and / or directly into one or more oligomerization and / or polymerization reactors.

[0059] Basic catalysts (i.e., alpha catalysts) are generally more thermally stable transesterification catalysts than quaternary catalysts (i.e., beta catalysts), and can therefore be used throughout the transesterification period, including during oligomerization and after oligomerization, e.g., in a polymerization reactor, during polymerization. Nearly all of the basic catalyst (e.g., more than 80 wt. %, specifically more than 90 wt. %) survives the polymerization process. Such catalysts can thus be used to catalyze additional and generally undesirable reactions downstream of the polymerization process, such as in an extruder, or even in post-processing of the resulting polycarbonate.

[0060] To inhibit such other reactions, a catalyst quencher may be added to deactivate, i.e., quench, the basic catalyst. Thus, the method of the present invention comprises adding a quencher to the last polymerization reactor of the polymerization reactor and / or to the extruder to at least partially deactivate the catalyst in the polycarbonate. The quencher may comprise a sulfonate, such as an alkyl sulfonate having the formula R3SO3R4, wherein R3 is hydrogen, C1-C 12 Alkyl, C6-C 18 Aryl or C7-C 19 Alkyl aryl, and R4 is C1-C 12 Alkyl, C6-C 18 Aryl or C7-C 19 Alkaryl. Examples of alkyl sulfonates include benzenesulfonate, p-toluenesulfonate, methyl benzenesulfonate, ethyl benzenesulfonate, n-butyl benzenesulfonate, octyl benzenesulfonate and phenyl benzenesulfonate, methyl p-toluenesulfonate, ethyl p-toluenesulfonate, n-butyl p-toluenesulfonate, octyl p-toluenesulfonate and phenyl p-toluenesulfonate. Sulfonates may include alkyl p-toluenesulfonates, such as n-butyl p-toluenesulfonate.

[0061] The preferred amount of quencher is such that the molar ratio of quencher to catalyst is preferably 0.9 to 10.0, preferably 0.9 to 5.0 or 0.9 to 3.5, more preferably 1.0 to 5.0, even more preferably 1.0 to 3.5, even more preferably 1.0 to 1.5. The amount of quencher is determined based on the amount of alpha catalyst, since beta catalysts generally cannot survive the process conditions in the final polymerization reaction.

[0062] Typically, the quencher is added in an amount of 0.5 to 5 ppm, preferably 0.5 to 2 ppm, more preferably 0.5 to 1.5 ppm, more preferably 0.8 to 1.2 ppm based on the weight of the polycarbonate. Higher amounts of quenchers can result in poorer initial color of the resulting polycarbonate, i.e., higher cookie values.

[0063] The quencher may be added as a liquid or solid at one or more locations in the melt preparation of the polycarbonate.The quencher may be part of a composition that also includes a liquid carrier, a solid carrier, or a solvent.

[0064] The preferred catalyst quencher is n-butyl p-toluenesulfonate.

[0065] In one embodiment, the process of the invention does not include the addition of an alpha catalyst, and only a beta catalyst which is a quaternary phosphonium compound, such as, in particular, TPPP.

[0066] Preferably, in the methods for preparing polycarbonates disclosed herein, in several aspects thereof, acid stabilizers, such as phosphorous acid, are not added to the polycarbonate. Such acids may be added to improve thermal stability. For the avoidance of doubt, it is noted that quenchers such as n-butyl p-toluenesulfonate should not be considered acid stabilizers.

[0067] The monomer mixing stage is preferably conducted at a temperature of 100 to 250° C., specifically 150 to 200° C., more specifically 165 to 185° C. The pressure in the monomer mixing stage is preferably substantially atmospheric pressure, such as 900 to 1100 mbar.

[0068] The oligomerization stage is preferably carried out in two steps, wherein in the first step the temperature is from 230 to 260° C. and the pressure is from 140 to 200 mbar; and wherein in the second step the temperature is higher than in the first step and is from 260 to 290° C. and the pressure is from 30 to 50 mbar.

[0069] The weight average molecular weight of the oligomers produced from the oligomerization stage is preferably at most 12,000, preferably from 8,000 to 12,000 Daltons, as determined based on polystyrene standards.

[0070] The polymerization stage is preferably carried out in two steps, wherein in the first step the temperature is from 290 to 315° C. and the pressure is from 1 to 5 mbar, and wherein in the second step the temperature is from 290 to 315° C. and the pressure is from 0.3 to 1.5 mbar.

[0071] according to Figure 1 An exemplary process of the invention, preferably the oligomerization stage consists of preparing carbonate oligomers in two oligomerization reactors, and wherein the polymerization stage consists of preparing polycarbonate in two polymerization reactors.

[0072] More preferably the process comprises the step of melt filtering the polycarbonate from the last of the polymerization reactors and feeding the polycarbonate to a finishing extruder.

[0073] In a preferred embodiment of the process of the present invention, the bisphenol is bisphenol A, the diaryl carbonate is diphenyl carbonate, the beta catalyst is added in the monomer mixing stage, and the alpha catalyst is added before the monomer mixture prepared in the monomer mixing device is fed to the first oligomerization reactor.

[0074] In a preferred embodiment of the method of the present invention, the bisphenol is bisphenol A, the diaryl carbonate is diphenyl carbonate, the alpha catalyst is NaKHPO4 or NaOH, the beta catalyst is tetrabutylphosphonium acetate, and the quencher is n-butyl p-toluenesulfonate.

[0075] UV stabilizers

[0076] The UV stabilizer according to aspects of the invention disclosed herein is preferably selected from

[0077]

[0078] and combinations of two or more of these compounds.

[0079] The present invention also relates to articles comprising or consisting of a polycarbonate obtained or obtainable by the process disclosed herein.

[0080] Likewise, the present invention relates to making such an article comprising preparing a polycarbonate according to the method disclosed herein and molding the polycarbonate at a temperature of 280 to 350° C., preferably at least 300° C., for example 300 to 350° C. or 300 to 330° C. A molding temperature of at least 300° C. is preferred for polycarbonates having a relatively low MVR, such as up to 8 cc / 10 min, measured according to ISO 1133 (300° C., 1.2 kg).

[0081] Cookie value (a*)

[0082] The biscuit value (a* value) is determined by the so-called biscuit test, in which 10 grams of polycarbonate are placed in an aluminum baking pan with a diameter of about 7 cm for biscuit baking and subjected to a heat aging test. The "biscuit test" is an in-house test for the rapid determination of the heat resistance of polycarbonate materials.

[0083] The baking tray was placed in an oven for 120 minutes at 250°C under normal atmosphere. The polycarbonate melted, forming a disc-shaped plate at the bottom of the cookie tray. The "cookie value", i.e., the a* value, of the plate when cooled to room temperature was measured according to standard ASTM D1925. The reported a* value is the numerical average of the a* values ​​measured on three different plates.

[0084] The present invention will be further illustrated based on the following non-limiting examples.

[0085] Material

[0086] Table 1

[0087]

[0088] The following compositions based on the same polycarbonate (PC) were prepared and subjected to the Cookie Test. The reported values ​​are the average of three measurements. Table 2 shows the Cookie values ​​(a*) for compositions containing UV1 as UV stabilizer.

[0089] Table 2

[0090]

[0091] The graph of this data is Figure 2 shown.

[0092] From the data, it can be seen that for compositions without UV additives, the a* value increases with increasing amounts of quencher added to the polycarbonate. It can also be further observed that the addition of UV1 additives can at least partially mitigate the increase in a* value caused by the addition of quenchers.

[0093] As shown in Tables 2 and 3 below, similar effects were observed for UV2 and UV3.

[0094] Table 3

[0095]

[0096] The graph of this data is Figure 3 shown.

[0097] Table 3

[0098]

[0099] The graph of this data is Figure 4 shown.

[0100] Experimental data show that a UV-stable compound containing at least one benzotriazole group can be successfully used as a heat stabilizer in polycarbonate prepared by a melt transesterification process comprising reacting a diaryl carbonate and a bisphenol in the presence of a catalyst and quenching the catalyst with a quencher. Addition of such a UV stabilizer reduces the cookie value, indicating that the yellowing of the polycarbonate upon heat aging is improved.

Claims

1. Use of a UV-stable compound comprising at least one benzotriazole group as a heat stabilizer in polycarbonate prepared by a melt transesterification process comprising reacting a diaryl carbonate and a bisphenol in the presence of a catalyst and quenching the catalyst with a quencher.

2. Use of a UV-stabilizing compound comprising at least one benzotriazole group as an additive in a polycarbonate prepared by a melt transesterification process comprising reacting a diaryl carbonate and a bisphenol in the presence of a catalyst and quenching the catalyst with a quencher, for producing an article having a lower a* value than an otherwise identical polycarbonate not comprising the UV-stabilizing compound, wherein the a* value is determined according to the method described in the specification.

3. A method for preparing a molten polycarbonate, comprising: - reacting diaryl carbonate and bisphenol in the presence of a catalyst in at least two continuous reactors to form a molten polycarbonate stream, - adding a quencher and a UV stabilizing compound comprising at least one benzotriazole group to the molten polycarbonate stream, - extruding the molten polycarbonate stream into one or more strands, - optionally cooling the strand or strands, - granulating the strands, wherein the molar ratio of the quencher to the catalyst is 1.0 to 5.0, preferably 1.0 to 2.0, and wherein the amount of the UV stabilizing compound is 500 to 5000 ppm by weight based on the weight of the polycarbonate.

4. The method of claim 3, wherein the polycarbonate has a lower a* value than a polycarbonate prepared by an otherwise identical process without the addition of the UV stabilizing compound, wherein the a* value is determined according to the method described in the specification.

5. The process according to claim 3 or 4, wherein the polycarbonate is fed from a final reactor to an extruder, and wherein the quenching agent is added in the final reactor and / or in the extruder.

6. The method according to any one or more of claims 3-5, wherein the UV stabilizing compound is added to the extruder.

7. The method according to any one or more of claims 3-6, wherein the UV stabilizing compound is selected from and combinations of two or more of these compounds.

8. The method according to any one or more of claims 3 to 7, wherein the amount of quencher is up to 1.8 ppm, preferably 0.5 to 1.5 ppm, more preferably 0.8 to 1.2 ppm, based on the weight of the polycarbonate.

9. The method of any one or more of claims 3-8, wherein the quencher comprises butyl p-toluenesulfonate.

10. The process according to any one or more of claims 3 to 8, wherein no acid stabilizers, preferably no phosphoric acid, are added to the polycarbonate.

11. The method of any one of claims 3 to 9, wherein the polycarbonate is fed from a final reactor to an extruder, and wherein an amount of recycled polycarbonate is combined with the polycarbonate in the extruder, the UV stabilizing compound being at least partially contained in the recycled polycarbonate.

12. The use according to claim 1 or 2 or the method according to any one of claims 3 to 11, wherein the bisphenol consists of bisphenol A and the diaryl carbonate consists of diphenyl carbonate.

13. Article comprising or consisting of a polycarbonate obtained or obtainable by a process according to any one or more of claims 3 to 12.

14. Process for producing an article according to claim 13, comprising preparing a polycarbonate according to any one or more of claims 3 to 12 and moulding the polycarbonate at a temperature of at least 280°C, preferably at least 300°C.

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