METHOD FOR THE PRODUCTION OF POLYCARBONATE BEADS

Description

[0001] The invention relates to a method for producing polycarbonate beads, the polycarbonate beads obtainable by the method, and molded parts obtainable from the polycarbonate beads.

[0002] Expanded thermoplastics (EPS), particularly EPS, EPP, and E-TPU, are gaining increasing importance. Modern technology now allows for the production of high-quality expanded thermoplastics and the manufacture of components with advantageous properties. Their lower bulk density compared to "simple" thermoplastics opens up new application areas for these expanded materials, and conventional applications can be realized with significant weight savings. Expanded thermoplastics are therefore an attractive material, especially for lightweight construction applications, provided their application-specific properties are also sufficiently good. Tooling developments in recent years have made it possible to produce components with surfaces that exhibit such an aesthetically pleasing appearance that even visible parts made of expanded thermoplastics are a genuine alternative to corresponding injection-molded parts, while exhibiting a significantly lower weight.Due to the lower material consumption, expanded materials are also attractive from a sustainability point of view and can also contribute to energy savings due to generally good thermal insulation properties, for example when used as thermal insulation material or as an additional effect when used as insulation material for noise reduction.

[0003] Polycarbonate particle foams have also been described. Particle foams made of engineering thermoplastics are of interest to the automotive industry, for example, due to properties such as high temperature resistance and good fire behavior. EPC is a particle foam for high-temperature applications where conventional polymer foams like EPP fail. DE 4100200 A1 describes a process for producing polycarbonate foam from polycarbonate, in which a transesterification catalyst is added to aromatic polycarbonate in combination with aromatic polycarboxylic acids or water, optionally together with aliphatic hydroxycarboxylic acids and / or aliphatic alcohols. This results in a controlled, partial degradation of the polycarbonate with the release of CO₂, which serves to foam the remaining polycarbonate. The polycarbonate foams described in the document have densities of around 0.4 to 0.8 g / cm³.

[0004] EP 3858906 A1 discloses a process for producing expanded particles from aromatic polycarbonate by extruding aromatic polycarbonate, granulating, impregnating with carbon dioxide as a blowing agent and expanding the particles, followed by shaping the particles to obtain an expanded molded body.

[0005] EP 2603549 A1 describes polyester foams and explicitly includes polycarbonate foams in this category, which, in addition to low density, exhibit good processability. For the production of these particle foams, a starting polymer material is selected in which crystallinity, reflected by the enthalpy of fusion, glass transition temperature, and melting temperature, lies within a specific range. The process for producing the particle foams involves providing the appropriate starting polymer components in a molten state, mixing a blowing agent component and, if necessary, one or more additives into the melt, extrusion, and granulation of the blowing agent-containing melt under water at elevated pressure of 1 to 20 bar. EP 2603549 A1 also describes the general possibility of adding, for example, chain extenders to stabilize the extrusion process by increasing the molecular weight, although no specific quantity is given.Furthermore, no further requirements are placed on the polymer used.

[0006] The task was therefore to provide improved, low-density polycarbonate beads via a continuous process, from which molded parts with better mechanics could be produced.

[0007] Surprisingly, it has now been discovered that molded parts made from polycarbonate particle foams, so-called foamed "polycarbonate beads," can only be produced with sufficiently good mechanical properties if a chain extender is reacted in a specific quantity with polycarbonate containing a certain number of OH end groups. Only then is the necessary process control for good mechanical properties achieved through reactive particle foam extrusion possible, enabling foaming at high melt temperatures T1 = (Tg + 110°C) to T2 = (Tg + 170°C) (where Tg is the glass transition temperature of the aromatic polycarbonate-based composition), exceeding the usual temperature range for foam production via thermoplastic extrusion with a physical blowing agent to expand into low-density foams, and simultaneously under high pressures.According to the prior art, a "particle foam extrusion" is understood by a person skilled in the art to be a complete or partial extrusion process with the addition of a blowing gas, followed by granulation and cooling to expandable particles, in the case of amorphous thermoplastics at melt temperatures from Tg + 10 °C to Tg + 70 °C where Tg = the glass transition temperature of the polymer material.

[0008] The invention therefore relates to a method, in particular a continuous method, for the production of polycarbonate beads, comprising the following steps, preferably in this order: a) Providing a composition based on aromatic polycarbonate, wherein the aromatic polycarbonate has an OH end group content of at least 350 ppm, determined by 1H NMR spectroscopy using dichloromethane as solvent at room temperature, based on the total weight of the aromatic polycarbonate; b) Mixing the composition based on aromatic polycarbonate with a chain extender suitable for OH groups in such a molar ratio that for every 1 mol of OH end groups of the polycarbonate, 0.64 to 1.10 mol of the reactive group of the chain extender are used; c) Providing the mixture in a plasticized state; d) Mixing a physical blowing agent into the melt; e) Extruding the plasticized mixture into a particle foam at a temperature of the plasticized mixture T1 from Tg = (Tg + 110°C) to T2 = (Tg + 170°C).where Tg is the glass transition temperature of the aromatic polycarbonate-based composition, f) Granulation of the blowing agent-containing melt.

[0009] The final granulation process yields foamed polycarbonate beads.

[0010] The content of OH end groups is determined by 1< H-NMR spectroscopy with dichloromethane as solvent at room temperature by evaluating the ratio of the integrals of the signals at 6.68 ppm (two aromatic protons ortho-positioned to phenolic OH groups) and at 1.68 ppm (six methyl protons of the bisphenol A unit).

[0011] The glass transition temperature is determined according to DIN EN ISO 11357-1:2017.

[0012] "Providing the mixture in a plasticized state" means that a polymer melt is present.

[0013] Unless expressly stated otherwise, all ppm quantities in the present invention are to be understood as proportions by weight.

[0014] There is a minimum value and a maximum concentration for both the amount of OH end groups and the concentration of chain extenders for foam extrusion at high melt temperatures Tg from T1 = (Tg + 110°C) to T2 = (Tg + 170°C), preferably T1 = (Tg + 120°C) to T2 = (Tg + 160°C), and particularly preferably in the range of T1 = (Tg + 130°C) to T2 = (Tg + 150°C) for particle foam production, in order to obtain a polycarbonate particle foam with good mechanical properties in the bulk density range of 150 to 250 g / L, determined in accordance with DIN EN ISO 60:2000-01. "In accordance with" means that instead of the standardized aluminum container with known volume, a 1 L beaker was filled and its contents weighed to determine the density of the material.

[0015] The number of OH groups in the aromatic polycarbonate significantly influences whether low-density beads with good mechanical properties can be obtained in the resulting molded parts. Too many OH groups in the polycarbonate result in excessive reactivity, ultimately leading to rearrangement reactions of the polycarbonate chain, a reduction in molecular weight due to excessively rapid branching with a consequent increase in viscosity (excessive shear stress), and yellowing. Conversely, too few OH groups in the polycarbonate result in insufficient or no reaction with the chain extender. This also means that a good particle foam with sufficient mechanical properties is not obtained. Instead, the particle foam exhibits a large number of defective, collapsed cells.

[0016] According to the invention, the OH end-group content of the aromatic polycarbonate used in the process is at least 350 ppm, preferably 350 ppm to 600 ppm, more preferably 380 ppm to 580 ppm, particularly preferably 400 ppm to 550 ppm, and most preferably 450 to 550 ppm, based on the total weight of aromatic polycarbonate used. The reference quantity here is the pure aromatic polycarbonate, not the aromatic polycarbonate-based composition. To achieve such an end-group content, preferably more than 70 wt.% SPC, based on the total weight of the aromatic polycarbonate used, is used; more preferably at least 80 wt.% SPC, based on the total weight of the aromatic polycarbonate used; and most preferably, exclusively SPC is used as the aromatic polycarbonate for the production of the polycarbonate beads.

[0017] The concentration of the chain extender is also crucial. Too much chain extender leads to excessively high viscosities due to the resulting significant molecular weight increase of the polycarbonate, rendering the material unprocessable. Too little chain extender does not cause a significant molecular weight increase, resulting in insufficient pressure build-up (the viscosity of PC without / with insufficient CE at 300 °C is too low) and ultimately poorer mechanical properties. The reaction of the chain extender with the polycarbonate is a function of time and temperature. For example, the foam extrusion process for bisphenol-A-based homopolycarbonate is preferably carried out at a case temperature of Tcase = Tg + 100 °C to Tcase = Tg + 150 °C and a melt temperature Tg of approximately Tg + (110 to 170 °C) after blowing agent mixing and dissolution.Producing particle foam without cooling results in collapsed, high-density particles. Depending on the process parameters, the stabilization and solidification of the foam structure through cooling can prevent foam expansion from occurring too quickly. The high process temperatures allow the full foaming potential of the formulation to be utilized with cooling, compensating for the excessively rapid cooling / solidification. However, under these temperature profiles, the pressure at the perforated plate without chain extenders is 80–90 bar (despite the melt pump). The use of chain extenders increases the pressure at the perforated plate to 140–180 bar, preferably 150–160 bar. Without a corresponding chain extension, and thus without the additional viscosity increase, particle foam production is not possible under these process conditions (temperatures).

[0018] In order to obtain polycarbonate beads with good properties, it has proven essential to the invention that a molar ratio (in a continuous process, a throughput-related addition is made) of 1 mol of OH end groups of the polycarbonate to 0.64 - 1.10 mol, preferably 0.71 to 1.0 mol, further preferably up to 0.96 mol, even more preferably 0.8 to 0.9 mol, in particular 0.82 to 0.90 mol of the reactive group of the chain extender is used.

[0019] Preferably, if the content of the aromatic polycarbonate of OH end groups is 400 to 550 ppm, determined by 1< H-NMR spectroscopy with dichloromethane as solvent at room temperature, 0.71 to 0.96 mol of the reactive group of the chain extender are used for every 1 mol of OH end groups of the polycarbonate.

[0020] The use of a chain extender results in a molar mass increase of the polycarbonate to a range of 40,000 to 230,000 g / mol, preferably up to 100,000 g / mol, which is associated with an additional pressure increase at the perforated plate of about 60 to 100 bar at the temperatures in which polycarbonate is in a plasticized state.

[0021] In a particularly preferred embodiment according to the invention, the method is carried out continuously and comprises the following steps, preferably in this order: a) Providing a composition based on aromatic polycarbonate, wherein the aromatic polycarbonate has an OH end group content of at least 350 ppm, preferably 400 to 550 ppm, determined by 1H NMR spectroscopy with dichloromethane as solvent at room temperature, based on the total weight of the aromatic polycarbonate; b) Mixing the composition based on aromatic polycarbonate with a chain extender suitable for OH groups in an amount such that for every 1 mol of OH end groups of the polycarbonate, 0.64 to 1.10 mol, preferably 0.71 to 1.0 mol, more preferably up to 0.96 mol, and even more preferably 0.8 to 0.9 mol, in particular 0.82 to 0.90 mol of the reactive group of the chain extender (adjusted according to throughput) are used, wherein an epoxy-functionalized chain extender is used, preferably a styrene-acrylic based polymer comprising epoxy reactive groups,in particular one with an epoxy equivalent weight (EEW ​​= Epoxy Equivalent Weight) of 285 to 485 g / mol, determined according to DIN EN 1877-1:2000. c) Providing the mixture in a plasticized state, d) Mixing a physical blowing agent into the melt at a concentration of 0.1–2.3 wt.% based on the polymer melt, wherein the physical blowing agent is nitrogen, carbon dioxide, or a mixture thereof, preferably carbon dioxide, e) Extruding the plasticized mixture into a particle foam at a melt temperature T1 = (Tg + 110°C) to T2 = (Tg + 170°C), preferably at T2 = (Tg + 160°C), where Tg is the glass transition temperature of the aromatic polycarbonate-based composition, f) Granulating the blowing agent-containing melt, preferably by underwater granulation without pressurization.

[0022] The individual steps of the method according to the invention can be carried out using tools and machines known to those skilled in the art and available in plastics technology. Individual steps can also be combined if necessary.

[0023] The process for producing the polycarbonate beads can be carried out continuously or batchwise. The polymer melt can, for example, be taken directly from the polymerization reactor as freshly polymerized material or fed directly from the reactor into a mixing extruder, in which chain extenders, blowing agents, and optionally additives are introduced at various points. The process according to the invention is preferably carried out as a continuous process, because with a batch process there is a risk of the polycarbonate crystallizing.

[0024] It is understood that the required specifications regarding the ratio of the amounts of OH end groups of the polycarbonate and the reactive group of the chain extender must be adjusted according to the process parameters. In a continuous process, a throughput-related concentration adjustment (ratio mol / h : mol / h) is expediently carried out.

[0025] The process according to the invention can be a one-stage or a two-stage extrusion process. In a first extrusion step, the polymer undergoes molecular weight build-up in the presence of the chain extender, yielding polycarbonate granules as the first product. In a second extrusion step, foaming occurs with the physical blowing agent, preferably carbon dioxide. The result of the subsequent underwater granulation is the polycarbonate beads according to the invention. Granulation can then be carried out at the end of the first extrusion stage. For this purpose, the melt is extruded through a die at an exit opening of the extruder and then cut to length. Cutting to length is performed by a cutting device, which is usually located directly downstream of the die through which the material is extruded.The cutting device can be in contact with the mold or positioned at a certain distance from it. Similarly, the subsequent blowing agent injection can also take place in the same extruder, either after a certain residence time of the polycarbonate and chain extender mixture, or simultaneously with the feeding of the chain extender.

[0026] The inventive process yields polycarbonate beads, a particle foam. Due to the material's low weight and impact resistance, combined with higher continuous operating temperatures (e.g., resistance in the e-coating process) compared to PP, ABS, PE, or PA6, the use of particle-foamed polycarbonate makes it possible to significantly reduce the weight of some vehicle components and lower fuel consumption and CO₂ emissions, while maintaining its mechanical properties even at higher temperatures. Furthermore, the availability of foamed polycarbonate is expected to open up a whole range of additional application areas, especially wherever insulation is required at higher temperatures.

[0027] The invention also relates to polycarbonate beads produced according to the inventive method. A "bead" is understood to be a foamed granulate (particle foam) produced according to the invention, which typically has a maximum density of 50% of the unfoamed starting material (the aromatic polycarbonate-based composition). The polycarbonate beads obtainable by the inventive method preferably have a molar mass average, measured here as absolute molar mass, of the aromatic polycarbonate of at least 140 kDa (highly branched), particularly preferably at least 150 kDa, determined by GPC-MALLS measurement (multi-angle laser light scattering) according to DIN EN ISO 16014-5:2019-09.Simultaneously, the molar masses and molecular dimensions of the molecules are determined, and conclusions are drawn about the degree of branching of the materials. This is because branching influences the separation mechanism of the GPC (glass-plastic polycarbonate), which is reflected in the rising molar mass curve. The linear starting material is used as a reference for comparison with the foamed samples. The more branched the sample (smaller hydrodynamic volume at the same molar mass), the further the curve deviates from the ideal line of an unbranched polycarbonate. Polycarbonate material exhibiting a sufficient minimum degree of branching foams well, resulting in polycarbonate beads with good morphology, from which molded parts with good mechanical properties can then be produced.

[0028] The expanded polycarbonate particles, the "polycarbonate beads", produced according to the inventive method, have the following properties: A bulk density, depending on the continuous process, of 150 g / L to 250 g / L, preferably 180 g / L to 200 g / L, determined in the process via the bulk density in accordance with DIN EN ISO 60:1999. "In accordance with" means that instead of the standardized aluminum container with known volume, a 1 L beaker was filled and its contents weighed to determine the density of the material. A nominal diameter (depending on the process) in the range of 2 to 7 mm, preferably 2.5 to 5 mm, particularly preferably 3 mm ± 0.2 mm, the exact determination of the size distribution preferably being carried out using a cam sizer; the thermal properties (Tg of 145-150 °C) and mechanical properties of polycarbonate, e.g.with a component density of 200 kg / m³ < a flexural modulus of at least 70 MPa, a flexural strength of 2.5 MPa (ISO 6603-2:2000); a compressive modulus of 59 MPa and a compressive strength (at 10% compression) of 1.73 MPa (ISO 844-11:2014); a tensile strength of at least 1.97 MPa and an elongation at break of 8–14% (ISO 1926:2009); a mean equivalent circle diameter of the cells to the circle with the same projection area of ​​a maximum of 150 µm, preferably of a maximum of 100 µm, particularly preferably of a maximum of 80 µm, determined by SEM (ASTM E1508-12a:2019).

[0029] The size of the beads depends on the process parameters and can be influenced, among other things, by the selected nozzle size, throughput, knife speed, and composition of the blowing agent-containing melt. An example process with a nozzle size of 1.2 mm yields beads with a nominal diameter in the range of 1.8 to 3 mm. The maximum of the frequency distribution is at 2.5 mm with a distribution width of 28%, based on the mean. With a nozzle of 2.2 mm, a particle size distribution with an average diameter of 5 mm and a distribution width of 40%, based on the mean, is obtained.

[0030] The polycarbonate beads are weldable over a wide range, preferably at a water vapor pressure of 7 bar to 11 bar, particularly preferably 8 bar to 10 bar. They have a high molecular weight Mw in the range of 40,000 g / mol to 230,000 g / mol, determinable by GPC as described in the example section.

[0031] The polycarbonate beads exhibit good mechanical properties and low thermal conductivity (DIN EN 12667:2001) in the range of 45 - 47 mW / (m*K) at 10 °C and a component density of 200 ± 10 kg / m 3< .

[0032] The beads have intact ("closed-cell") or at least predominantly intact cells, which is why foam molded parts with very uniform, flat surfaces and homogeneous bead welding can be produced from the polycarbonate beads. "Predominantly" here means that preferably > 85%, and more preferably > 90% of the cells of a bead are intact; that is, in these beads, the individual cell structure is shared by at least three other structural elements (cells), and there are no more than two damaged cell walls per individual cell.

[0033] The starting material for the production of the beads according to the invention in the process according to the invention is a composition based on aromatic polycarbonate.

[0034] The term "aromatic polycarbonate" as used in the invention refers to both aromatic homopolycarbonates and aromatic copolycarbonates. The polycarbonates can be linear or branched in a known manner.

[0035] The polycarbonates contained in the compositions are produced in a known manner from dihydroxyaryl compounds, carbonic acid derivatives, optionally chain terminators and branchers.

[0036] Details of the production of polycarbonates have been laid down in numerous patent specifications for about 40 years. Examples include Schnell, "Chemistry and Physics of Polycarbonates," Polymer Reviews, Volume 9, Interscience Publishers, New York, London, Sydney 1964; D. Freitag, U. Grigo, P.R. Müller, H. Nouvertné, BAYER AG, "Polycarbonates" in Encyclopedia of Polymer Science and Engineering, Volume 11, Second Edition, 1988, pages 648-718; and finally, U. Grigo, K. Kirchner, and P.R. Müller, "Polycarbonate," in Becker / Braun, Kunststoff-Handbuch, Volume 3 / 1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299.

[0037] Aromatic polycarbonates are produced, for example, by reacting dihydroxyaryl compounds with carbonic acid halides, preferably phosgene, and / or with aromatic dicarboxylic acid dihalides, preferably benzenedicarboxylic acid dihalides, using the interface method, optionally with the use of chain terminators and optionally with the use of trifunctional or more than trifunctional branchers. Likewise, production via a melt polymerization process by reacting dihydroxyaryl compounds with, for example, diphenyl carbonate is possible. According to the invention, polycarbonate produced by the melt polymerization process, also called "transesterification," is preferably used. The polycarbonate used according to the invention has 350 to 600 ppm OH end groups, this figure referring to the polycarbonate itself, the polymer, without any additives that may be added.The amount of OH end groups refers to the total polycarbonate used. A mixture of polycarbonate obtained by melt polymerization and polycarbonate obtained by interfacial processes can also be used, as long as the total concentration of OH end groups in the polycarbonate used remains within the specified range. However, polycarbonate produced by melt polymerization is particularly preferred.

[0038] Examples of dihydroxyaryl compounds suitable for the production of polycarbonates are hydroquinone, resorcinol, dihydroxydiphenyls, bis-(hydroxyphenyl)alkanes, bis-(hydroxyphenyl)cycloalkanes, bis-(hydroxyphenyl)sulfides, bis-(hydroxyphenyl) ethers, bis-(hydroxyphenyl)ketones, bis-(hydroxyphenyl)sulfones, bis-(hydroxyphenyl)sulfoxides, α-α'-bis-(hydroxyphenyl)diisopropylbenzenes, phthalimidines derived from isatin or phenolphthalein derivatives, and their nuclear-alkylated, nuclear-arylated, and nuclear-halogenated compounds.

[0039] Preferred dihydroxyaryl compounds are 4,4'-dihydroxydiphenyl, 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A), 2,4-bis-(4-hydroxyphenyl)-2-methylbutane, 1,1-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, 2,2-bis-(3-methyl-4-hydroxyphenyl)-propane, dimethyl bisphenol A, bis-(3,5-dimethyl-4-hydroxyphenyl)-methane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone, 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane, 1,1-Bis-(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene and 1,1-Bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and bisphenols (I) to (III) in which R' stands for C 1 - to C 4 -alkyl, aralkyl or aryl, preferably for methyl or phenyl, most preferably for methyl.

[0040] Particularly preferred bisphenols are 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A), 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane, 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 4,4'-dihydroxydiphenyl and dimethyl-bisphenol A, as well as the bisphenols of formulas (I), (II) and (III).

[0041] These and other suitable dihydroxyaryl compounds are found, for example, in US 3 028 635 A, US 2 999 825 A, US 3 148 172 A, US 2 991 273 A, US 3 271 367 A, US 4 982 014 A and US 2 999 846 A, in DE 1 570 703 A, DE 2063 050 A, DE 2 036 052 A, DE 2 211 956 A and DE 3 832 396 A, in FR 1 561 518 A, in the monograph "H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964" as well as in JP 62039 / 1986 A, JP 62040 / 1986 A and JP 105550 / 1986 A described.

[0042] In the case of homopolycarbonates, only one dihydroxyaryl compound is used; in the case of copolycarbonates, several dihydroxyaryl compounds are used.

[0043] Suitable carbon dioxide derivatives include, for example, phosgene or diphenyl carbonate.

[0044] Suitable chain terminators that can be used in the production of polycarbonates are monophenols. Suitable monophenols include, for example, phenol itself, alkylphenols such as cresols, p-tert-butylphenol, isooctylphenol, cumylphenol, and mixtures thereof.

[0045] Preferred chain terminators are phenols that are single or multiple substituted with C1 to C30 alkyl groups, linear or branched, preferably unsubstituted, or with tert-butyl. Particularly preferred chain terminators are phenol, cumylphenol, and / or p-tert-butylphenol.

[0046] The amount of chain terminator to be used is preferably 0.1 to 5 mol%, based on the number of moles of dihydroxyaryl compounds used. The chain terminator can be added before, during, or after the reaction with a carbonic acid derivative.

[0047] Suitable branchers are the tri- or more than trifunctional compounds known in polycarbonate chemistry, especially those with three or more than three phenolic OH groups.

[0048] Suitable branchers include, for example, 1,3,5-tri-(4-hydroxyphenyl)benzene, 1,1,1-tri-(4-hydroxyphenyl)ethane, tri-(4-hydroxyphenyl)phenylmethane, 2,4-bis-(4-hydroxyphenylisopropyl)phenol, 2,6-bis-(2-hydroxy-5'-methyl-benzyl)-4-methylphenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane, tetra-(4-hydroxyphenyl)methane, tetra-(4-(4-hydroxyphenylisopropyl)-phenoxy)methane, 1,4-bis-((4',4"-dihydroxytriphenyl)-methyl)benzene, and 3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.

[0049] The amount of branching agents to be used, if applicable, is preferably 0.05 mol% to 2.00 mol%, based on moles of dihydroxyaryl compounds used.

[0050] The branching agents can either be placed in the aqueous alkaline phase with the dihydroxyaryl compounds and the chain terminations, or added dissolved in an organic solvent before phosgenation. In the case of the transesterification process, the branching agents are used together with the dihydroxyaryl compounds.

[0051] Particularly preferred polycarbonates are the homopolycarbonate based on bisphenol A, the copolycarbonates based on 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and 4,4'-dihydroxydiphenyl, as well as the copolycarbonates based on the two monomers bisphenol A and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and the dihydroxyaryl compounds of formulas (I), (II) and (III). in which R' stands for C 1 - to C 4 -alkyl, aralkyl or aryl, preferably for methyl or phenyl, most preferably for methyl,

[0052] Derived homo- or copolycarbonates, in particular with bisphenol A. The polycarbonate-based compositions most preferably contain bisphenol A-based polycarbonate; the polycarbonate in the polycarbonate-based compositions most preferably is bisphenol A-based homopolycarbonate.

[0053] Copolycarbonates produced using diphenols of general formula (1a) are also preferred: where R 5< for hydrogen or C 1 - to C 4 - alkyl, C 1 - to C 3 - alkoxy, preferably for hydrogen; Methoxy or methyl, R6<, R7<, R8< and R9< each independently represent C1- to C4-alkyl or C6- to C12-aryl, preferably methyl or phenyl, Y represents a single bond, SO2-, -S-, -CO-, -O-, C1- to C6-alkylene, C2- to C5-alkylidene, C6- to C12-arylene, which may optionally be condensed with aromatic rings containing further heteroatoms or a C5- to C6-cycloalkylidene residue which may be substituted once or several times with C1- to C4-alkyl, preferably a single bond, -O-, isopropylidene or a C5- to C6-cycloalkylidene residue which may be substituted once or several times with C1- to C4-alkyl, V represents Oxygen, C2- to C6-alkylenes or C3- to C6-alkylidenes, preferably for oxygen or C3-alkylenes, p, q and r each independently stand for 0 or 1 when q = 0,W represents a single bond when q = 1 and r = 0, W represents oxygen, C2- to C6-alkylenes or C3- to C6-alkylidenes, preferably oxygen or C3-alkylenes when q = 1 and r = 1, W and V each independently represent C2- to C6-alkylenes or C3- to C6-alkylidenes, preferably C3-alkylenes, Z represents a C1- to C6-alkylene, preferably a C2-alkylene, o represents an average number of repeating units of 10 to 500, preferably 10 to 100, and m represents an average number of repeating units of 1 to 10, preferably 1 to 6, more preferably 1.5 to 5. It is also possible to use diphenols in which two or more siloxane blocks of general formula (1a) are linked to each other via terephthalic acid and / or isophthalic acid to form ester groups.

[0054] Particularly preferred are (poly)siloxanes of formulas (2) and (3) where R1 represents hydrogen, C1 to C4 alkyl, preferably hydrogen or methyl, and particularly preferably hydrogen; R2 independently represents aryl or alkyl, preferably methyl; X represents a single bond, -SO2-, -CO-, -O-, -S-, C1 to C6 alkylene, C2 to C5 alkylidene, or C6 to C12 arylene, which may optionally be condensed with aromatic rings containing further heteroatoms; X preferably represents a single bond, C1 to C5 alkylene, C2 to C5 alkylidene, C5 to C12 cycloalkylidene, -O-, -SO-, -CO-, -S-, -SO2-; X particularly preferably represents a single bond, isopropylidene, C5 to C12 cycloalkylidene, or oxygen, and most preferably isopropylidene; n represents an average number of 10 to 400, preferably 10 and 100, particularly preferably 15 to 50 means and m represents an average number of 1 to 10, preferably 1 to 6 and particularly preferably 1,5 to 5 stands.

[0055] The siloxane block can also preferably be derived from the following structure. preferred (Va) or where a in formula (IV), (V) and (VI) represents an average number of 10 to 400, preferably 10 to 100 and particularly preferably 15 to 50.

[0056] It is also preferred that at least two identical or different siloxane blocks of the general formulas (IV), (V) or (VI) are linked together via terephthalic acid and / or isophthalic acid to form ester groups.

[0057] Likewise, it is preferred if in formula (1a) p = 0, V stands for C 3 alkylene, r = 1, Z stands for C 2 alkylene, R 8< and R 9< stand for methyl, q = 1, W stands for C 3 alkylene, m = 1, R 5< stands for hydrogen or C 1 to C 4 alkyl, preferably for hydrogen or methyl, R 6< and R 7< each independently stand for C 1 to C 4 alkyl, preferably for methyl and o stands for 10 to 500.

[0058] Copolycarbonates with monomer units of formula (1a) and in particular their preparation are described in WO 2015 / 052106 A2.

[0059] Copolycarbonates with monomer units of formula (IV) and in particular their production are described in WO 2015 / 052106 A2.

[0060] The aromatic polycarbonate used in the process according to the invention can be a single polycarbonate or a mixture of two or more aromatic polycarbonates, as long as the OH end group content of the total polycarbonate used is within the range specified in the invention. Post-consumer or post-industrial recycled polycarbonate can also be used. Such recycled materials can be fed to the extruder as granules or regrind. It is also possible to use recycled material only as a portion of the aromatic polycarbonate.

[0061] One or more additives can be added to the aromatic polycarbonate, specifically to the polycarbonate as used as the starting material in the process according to the invention. However, one or more additives can also be added to the aromatic polycarbonate during the extrusion process, preferably together with the chain extender. Incorporation via the side extruder is not possible in the process according to the invention if only one extrusion stage is used, since the blowing agent is present in the melt and would therefore escape through the side feed. A gas-tight side feed, however, would allow the additives to be introduced in this way. Additives can also be introduced by means of powder premixes or as a masterbatch.Liquid additives can generally be injected at any point in the process, provided sufficient homogenization can still be achieved, preferably in the area of ​​static or dynamic mixing units. Additives can also be added in a first stage and the blowing agent in a second. In this case, the additives can also be metered via a side extruder.

[0062] The mixture of aromatic polycarbonate, optionally blending partners and optionally additives as a starting material is referred to as an "aromatic polycarbonate-based composition." The use of an "aromatic polycarbonate-based composition" in process step a can thus be understood as the use of the pure polymer, but also as the use of additivated aromatic polycarbonate. If an additivated polycarbonate composition is used, it preferably contains at least 70 wt.%, more preferably at least 80 wt.%, even more preferably at least 90 wt.%, particularly preferably at least 95 wt.%, and most preferably at least 98 wt.% aromatic polycarbonate, based on the total weight of the polycarbonate composition.Most preferably, the "aromatic polycarbonate-based composition" contains no blending partners to the polycarbonate, but in the inventive process for the production of polycarbonate beads, only aromatic polycarbonate is used, except for additives that are common for polycarbonate, if any.

[0063] Other additives commonly used in polycarbonates include, in particular, thermostabilizers, flame retardants, antioxidants, release agents, anti-drip agents (such as polytetrafluoroethylene, Teflon, or SAN-encapsulated PTFE, e.g., Blendex 449), UV absorbers, IR absorbers, impact modifiers, antistatic agents, optical brighteners, fillers such as talc, light scattering agents, transesterification inhibitors, compatibility enhancers, nucleating agents, colorants, pigments (e.g., titanium dioxide, carbon black), chemical blowing agents, and / or laser marking additives, especially in the quantities typical for polycarbonate-based compositions. Such additives are described, for example, in EP-A 0 839 623, WO-A 96 / 15102, EP-A 0 500 496, or in the "Plastics Additives Handbook," Hans Zweifel, 5th Edition 2000, Hanser Verlag, Munich. These additives can be added individually or in a mixture.It is understood that only such additives and only in such quantities may be added if they do not have a significantly negative effect on the production of the beads according to the inventive method.

[0064] Preferably, the additives are selected from the group consisting of thermostabilizers, flame retardants, antioxidants, release agents, colorants, pigments, anti-drip agents, UV absorbers, IR absorbers, nucleating agents, impact modifiers, antistatic agents, optical brighteners, light scattering agents, transesterification inhibitors, compatibility enhancers and / or laser marking additives.

[0065] The aromatic polycarbonate-based composition preferably has a melt volume flow rate (MVR) of up to 14 cm³ / (10 min), more preferably up to 12 cm³ / (10 min), particularly preferably from 5 cm³ / (10 min) to 9 cm³ / (10 min), and most preferably from 5.5 cm³ / (10 min) to 6.5 cm³ / (10 min), determined according to ISO 1133:2012-3 (test temperature 300°C, mass 1.2 kg).

[0066] As part of the process according to the invention, sufficient chain extender is added to the aromatic polycarbonate used such that the molar ratio of the OH end groups of the polycarbonate is 1 to 0.64 to 1.1, preferably 0.71 to 1.0, more preferably to 0.96, and even more preferably 0.8 to 0.9, particularly 0.82 to 0.90, of the reactive groups of the chain extender. The amount of substance is preferably adjusted based on the throughput per hour. This results in polymer synthesis, and the molecular weight of the aromatic polycarbonate is increased by the formation of long-chain branches.

[0067] Suitable chain extenders include amines, carboxyl compounds, maleic anhydride-modified compounds, epoxy-functionalized compounds, oxazolines, carbodiimides, and / or functionalized polymers, such as those based on acrylates and / or styrene, that possess the appropriate functional group. Such compounds can be used alone or in mixtures. These functional groups include, for example, amine groups in amines, carboxyl groups in carboxy compounds, anhydride groups in maleic anhydride-modified compounds, epoxy groups in epoxy-functionalized compounds, or other functional groups that can react with the OH end groups of the polycarbonate to form a chain. Epoxy-functionalized compounds are particularly preferred as chain extenders, and epoxy-functionalized styrene-acrylic-based polymers, such as those marketed by BASF SE as Joncryl additives, are highly preferred.Joncryl ADR 4368, ADR 4400, ADR 4468 are offered. The amount / weight of chain extender must be adjusted to the aromatic polycarbonate so that for every 1 mol of OH end groups of the polycarbonate, 0.64 to 1.10 mol, preferably 0.71 to 1.0 mol, more preferably up to 0.96 mol, and even more preferably 0.8 to 0.9 mol, particularly 0.82 to 0.90 mol of the reactive group of the chain extender are used.

[0068] Starting, for example, from an aromatic polycarbonate with 350–600 ppm OH end groups, reacted with a chain extender having an epoxy equivalent weight of 310 g / mol, e.g., with Joncryl ADR 4468, in concentrations of 0.4–1.2 wt.%, preferably 0.5–1.0 wt.%, particularly preferably in concentrations of 0.7–0.9 wt.%, wherein the amount of chain extender is based on the resulting total composition (aromatic polycarbonate-based composition, i.e., including any blending partners and any additives, plus chain extender), the desired ranges of reactive group ratios can be achieved. By selectively adjusting the molar ratio from 1 mol to 0.64 to 1.10 mol, molecular weight ranges of 40,000 to 230,000 g / mol, preferably 50,000 to 150,000 g / mol, and particularly preferably 75,000 to 100,000 g / mol, as described, are achieved. The wide processing window makes it possible to produce components from particles with molecular weights between 40 and 150,000 g / mol.to produce 000 to 230,000 g / mol with different properties.

[0069] The following setup arrangements can be used, but are not limited to, for carrying out reactive particle foam extrusion: a) Polymerization reactor / (static) extruder / mixer / gas dosing / melt pump / granulator b) Extruder (twin / single screw) / gas dosing / granulator c) Extruder (twin / single screw) / gas dosing / static mixer / granulator d) Extruder (twin / single screw) / gas dosing / heat exchanger / granulator e) Extruder (twin / single screw) / gas dosing / static mixer / heat exchanger / granulator f) Twin screw extruder / gas dosing / single screw extruder / granulator g) Twin screw extruder / gas dosing / heat exchanger / granulator h) Twin screw extruder / gas dosing / single screw extruder / melt pump / granulator i) Twin screw extruder / gas dosing / heat exchanger / melt pump / granulator.

[0070] The extrusion process can be carried out in one or two stages.

[0071] In detail, the process can be implemented in various configurations. Key steps include: melting the aromatic polycarbonate-based composition, optionally adding nucleating agents (talc, especially nano-talc, graphite, carbon black, pigments, etc.), dosing the blowing agent via liquid dosing systems (e.g., from Lewa GmbH in Germany) or compression units (high-pressure units) (e.g., from Maximator GmbH in Germany), optionally building up pressure to the perforated plate by means of cooling, the addition of reactive macromonomers, or technical aids such as breaker plates or melt pumps (pressure build-up is preferably achieved by adding reactive macromonomers or using technical aids), and finally, the removal of the granules / beads via granulation in a liquid medium, hot removal, or sub-gas granulation, whereby gas mixtures can also be used.It should be noted that the liquid medium used here is not limited to water, but can also be an alternative medium such as glycerin or glycerol.

[0072] A tandem setup consisting of a twin screw and a single screw is particularly preferred for carrying out the process according to the invention. The twin screw is preferably used for plasticizing the aromatic polycarbonate-based composition and for incorporating the physical blowing agent and the chain extender, while the single screw is subsequently used for melt tempering. The molecular weight build-up takes place in the twin screw / first extruder and continues until exiting the die (end of the extrusion line).

[0073] The addition of the physical blowing agent to the melt, which contains the aromatic polycarbonate and the chain extender that reacts during the overall process, is particularly preferably carried out in the last third of the first extrusion unit (depending on the design). Mixing is preferably carried out such that the polymer melt ultimately contains the blowing agent in a homogeneous distribution, wherein the proportion of the physical blowing agent in the mixture is preferably 1.0 to 2.3 wt.%, more preferably 1.2 to 1.7 wt.%, and particularly preferably 1.3 to 1.5 wt.% for CO₂, and preferably 0.1 to 0.5 wt.%, more preferably 0.1 to 0.3 wt.%, and particularly preferably 0.15 to 0.25 wt.% for N₂, based on the total weight of the polymer melt (= polycarbonate-based composition) with chain extender. It should be noted that the method according to the invention does not require that step d be carried out after step b.It is also possible that the mixing of the physical propellant into the melt begins simultaneously with or overlaps in time with the addition of the chain extender.

[0074] For initiating foam cell formation to achieve a finer and more homogeneous cell morphology, nucleating agents such as talc, in particular nano-talc, graphite, carbon black, pigments and etc. are preferably added in low concentrations of 0.1 to 1.0 wt.%, more preferably 0.15 to 0.5 wt.%, and most preferably in concentrations of 0.2 to 0.3 wt.%, wherein the quantities refer to the resulting total composition of polycarbonate-based composition and chain extender.

[0075] In principle, all blowing agents commonly used for foaming thermoplastics can be employed as physical blowing agents. Examples include propane, butane, n-pentane, isopentane, as well as similar aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, aliphatic alcohols, carbon dioxide, nitrogen, air, inert gases such as argon or helium, and others. Combinations of two or more of these blowing agents can also be used. Carbon dioxide, one or more inert gases, nitrogen, air, or mixtures thereof are preferred as physical blowing agents because they are not only toxicologically and ecologically safe but also non-combustible. Nitrogen, carbon dioxide, or a mixture thereof are particularly preferred, with carbon dioxide being the most preferred.

[0076] If nitrogen is used as a physical blowing agent, preferably 0.1 to 0.5 wt.%, more preferably 0.1 to 0.3 wt.%, particularly preferably 0.15 to 0.25 wt.% and most preferably 0.15 to 0.2 wt.% nitrogen, based on the polymer melt including chain extenders and additives (i.e. polycarbonate-based composition plus chain extenders), are used.

[0077] If carbon dioxide is used as a physical blowing agent, preferably 1.0 to 2.3 wt.%, more preferably 1.2 to 1.7 wt.%, particularly preferably 1.3 - 1.5 wt.% carbon dioxide is used, based on the polymer melt including chain extenders and additives.

[0078] In the manufacturing process, illustrated here by a tandem system (configuration h), various physical blowing agents can be introduced into the polymer melt at different points, for example, by liquid dosing or high-pressure dosing. Preferably, physical blowing gases are added in the first extruder, but in the last third of the extruder to ensure optimal homogenization. Dosing at the end of the tandem system would also allow for particle formation, but the process would be less stable and the resulting particles inhomogeneous. Carbon dioxide is the most preferred blowing agent because, compared to other blowing agents used in the production of expanded thermoplastics, it has the advantage of being non-flammable and is also more cost-effective than inert gases and nitrogen.Furthermore, it can be relatively easily brought into the supercritical state (T > 31.0 °C and p > 73.8 bar), which promotes miscibility and dissolution in polycarbonate due to its low compressibility and rapid diffusivity. Therefore, when using carbon dioxide as a blowing agent in the manufacturing process according to the invention, the polycarbonate beads can be used without hesitation for components in applications involving a certain fire hazard or where outgassing is prohibited (e.g., interiors). In particular, applications in the field of e-mobility, such as body components, e.g., for composite parts, are conceivable. Specifically, noise reduction elements integrated into the vehicle floor area or insulating layers in the bodywork are possible applications.

[0079] The melt pressure should be chosen so that it is above the critical solution pressure of the physical blowing agent.

[0080] The extrusion of the melt at the extruder outlet through a die plate, after mixing and dissolving the blowing agent, generally takes place at a melt temperature T1 of (Tg + 110 °C) to T2 of (Tg + 170 °C), preferably from T1 = (Tg + 120 °C) to T2 = (Tg + 160 °C), and particularly preferably in the range of T1 = (Tg + 130 °C) to T2 = (Tg + 150 °C). The temperature of the die plate is also preferably set to a temperature of Tg + (130 to 150 °C) to prevent the die from freezing due to cooling polymer melt, thus ensuring smooth polymer granulation and achieving appropriate foam expansion with the highest possible expansion potential.

[0081] The diameter of the nozzle opening for a single-hole nozzle is preferably in the range of 0.8 to 2.2 mm, more preferably 1.0 to 1.5 mm. For multi-hole nozzles, nozzle diameters of 0.4 to 0.8 mm are preferred, particularly preferably 0.6 mm.

[0082] The granulation of the melt at the end of the process according to the invention is preferably carried out by underwater granulation and, more preferably, without additional pressurization, i.e., at atmospheric pressure. Granulation at atmospheric pressure allows the desired low densities of the polycarbonate beads to be achieved. Upon exiting the nozzle, the polycarbonate material experiences a pressure drop from 140 to 180 bar, preferably from 150 to 160 bar, to atmospheric pressure of approximately 1 bar, at which point the material begins to foam. The physical blowing agent, for example, carbon dioxide, expands the polycarbonate material, while the gas diffuses out of the polymer melt. After a certain time, a complete or almost complete gas exchange has taken place, so that only the normal composition of air remains in the granulated, expanded polycarbonate, the polycarbonate beads.

[0083] The invention also relates to a method for producing molded parts from the polycarbonate beads produced according to the inventive method, and to such molded parts.

[0084] The polycarbonate beads can be transferred into molded parts, even those with complex geometries, by filling corresponding cavities, ultimately requiring only one processing step. The subsequent cutting, often necessary with extruded foams and the associated waste, is eliminated. Furthermore, polycarbonate beads are easier to transport than the often bulky sheets of available extruded foams.

[0085] The molded parts according to the invention can be used in the automotive industry, transportation, construction, aerospace, packaging, and generally in lightweight and / or composite construction. Possible molded parts made from the polycarbonate beads include not only sheets but also complex, three-dimensionally shaped components.

[0086] Molded parts consisting of or comprising the polycarbonate beads according to the invention are in particular visible parts in various fields of application, whereby finishing with laser textures is also possible, for example dashboards or interior trim elements, soundproofing elements, foaming elements, e.g. in carpets of the footwell in cars, a core material or load-bearing foam part of composite materials, for example for body insulation for vehicles, in particular electric vehicles, in the field of HVAC (heating, air conditioning, ventilation) as insulating material, as high-temperature insulation in industry, building services engineering or in transport, insulating materials, packaging, lightweight components, rotor blades of wind turbines, facade components.

[0087] In general, molded parts made of polymer foams are primarily subjected to compressive stress. Another relevant type of stress for polymer foams is bending. Here, the component is subjected to a complex load, with the upper side under compressive stress and the lower side under tensile stress. Compression tests provide information about the application-relevant mechanical performance, while tensile and bending tests provide information about the weld quality. The components made from the polycarbonate beads obtained by the inventive method can exhibit a thermo-mechanical profile of polycarbonate (Tg of 145–150 °C), e.g.with a component density of 200 kg / m³, a flexural modulus of 59.1 ± 11.4 MPa, a flexural strength of 2.2 ± 0.3 MPa (at 23°C, ISO 1209-1:2007, modified geometry to 120 x 25 x 10 mm³); a compressive modulus of 54.7 ± 5 MPa and a compressive strength (at 10% compression) of 1.61 ± 0.12 MPa (at 23°C, DIN EN ISO 844-11:2014); a tensile strength of at least 1.97 MPa and an elongation at break of 8.4% (DIN EN ISO 1926:2009) with simultaneously good insulation performance of 45.2 ± 2 mW / (m K) at 10°C (EN ISO 8301-8:1991). Commercially available EPP particle foam, at the same density of 200 kg / m³, exhibits approximately a flexural modulus of 56.1 ± 10.8 MPa, a flexural strength of 1.85 ± 0.25 MPa, a compressive modulus of 48.4 ± 3.6 MPa, and a compressive strength (at 10% compression) of 1.51 ± 0.5 MPa.Furthermore, EPP has a tensile strength of 2.49 MPa and an elongation at break of 20.2% with a simultaneous insulation effect of 54 ± 0.2 mW / (m*K) (10 °C), whereby the determination of these values ​​is carried out as described above for EPC, a noticeably lower performance.

[0088] Because the polycarbonate beads are sometimes quite large, with average equivalent diameters (nominal diameters) of approximately 4 to 6 mm corresponding to a circle projected onto it, it is necessary to overfill the cavity in the mold by 10–20% volume-wise. The vapor-based welding process for particle foams follows the same mechanism for all particles and is described in detail in the literature, for example in Raps et al. 2015; DOI: 10.1016 / j.polymer.2014.10.078.

[0089] To produce molded parts / components, foam particles are welded together in a steam molding machine or variothermally (thermally by heating). In the steam molding machine, the particle surface is melted or softened using high-pressure steam (i.e., steam at high temperature), which leads to interdiffusion of polymer chains between different beads and resulting cohesion of the beads. Good cohesion between the particles and a low proportion of macropores / gaps, i.e., voids between particles in the component due to poor packing, are necessary to ensure favorable mechanical properties. The processing of foam beads into the finished part takes place in a molding machine in five steps: 1) Complete or partial closing of the mold, 2) Filling the mold with, if necessary,The process involves: 3) complete closing, 4) welding of the particles, 5) cooling and stabilization, and 6) ejection of the molded part. Two methods are used: the crack gap method and the pressure filling method. In the pressure filling method, the mold is first closed, then the particles are drawn from a container by air pressure and blown into the mold by an injector at approximately 3 bar, where they are compressed. The particles expand in the mold and fill the cavities more effectively (corresponding to an overfill of approximately 10% in the crack gap method). In the crack gap method, the mold is not completely closed, but a certain gap (%) remains open. The mold is then filled with particles, resulting in a certain percentage overfill (10-20% by volume for EPC). Afterward, the mold is closed, and the particles are compressed to the target thickness.For a target component thickness of, for example, 20 mm, the mold cavity is opened further, e.g., by 4 mm (= 20 vol%), filled with polycarbonate beads, and then the mold is closed to a component thickness of 20 mm. This step is crucial for achieving a homogeneous distribution of the beads within the mold. In the third step, the beads are fused together by hot steam flowing through the mold according to a fixed sequence. During the steaming process, the beads form physical bonds due to the interdiffusion of polymer chains between adjacent particles. To ensure high weld quality between the particles, pressures of 7 to 11 bar, and particularly 8 to 10 bar, are preferably used for EPC. In the steam-based welding process, the air between the beads is first purged, and the mold is preheated. Steam flows in parallel to the mold with the valves open.In the second step, steam flows through the mold, a process known as cross-steaming. During this step, the opposing steam inlet and outlet valves are open. To ensure the most homogeneous temperature distribution and consistent weld quality across the entire part, the mold is preferably steamed from both sides. Finally, with the outlet valves closed, steam at a specific pressure is introduced into the steam chamber to improve the surface quality by forming a skin (autoclave steaming). In the fourth step, the molded part is cooled, which is crucial for dimensional accuracy. If the part is ejected without cooling, further expansion of the particles is possible, leading to deviations from the original dimensions. To cool the mold, it is sprayed with water until a temperature of approximately 80 °C is reached.After forming and cooling, the part is finally ejected in the last step, preferably by means of compressed air and mechanical ejectors.

[0090] The invention is illustrated by the following figures.

[0091] They show: Fig. 1 Flow diagram of the inventive process for the production of polycarbonate beads. Fig. 2a SEM image of the foam morphology of a polycarbonate bead obtainable by the inventive process (molar reactive group ratio OH : epoxy of 1 mol : 0.82 mol for a PC 1 component with an OH end group content of 470 ppm (E1)). The OH end group content, based on the total weight of the aromatic polycarbonate used, was 470 ppm. Fig. 2bSEM image of the foam morphology of another polycarbonate bead obtainable by the inventive process (molar reactive group ratio OH : epoxy of 1 mol : 0.90 mol (based on the throughput per hour) for a PC 1 component with an OH end group content of 470 ppm (E2)). The OH end group content, based on the total weight of the aromatic polycarbonate used, was 429 ppm. Fig. 2c SEM image of the foam morphology of a non-inventive polycarbonate bead (molar reactive group ratio OH : epoxy of 1 mol : 1.12 mol (based on the throughput per hour) for a PC 1 component with an OH end group content of 470 ppm (V4)). The OH end group content, based on the total weight of the aromatic polycarbonate used, was 346 ppm. Fig. 2dSEM image of the foam morphology of another non-inventive polycarbonate bead (molar reactive group ratio OH : epoxy of 1 mol : 1.47 mol (based on the throughput per hour) for a PC 1 component with an OH end group content of 470 ppm (V6)). The OH end group content, based on the total weight of the aromatic polycarbonate used, was 264 ppm.

[0092] The in Figure 1The illustrated system for carrying out the process according to the invention is a tandem setup. This consists first of a co-rotating twin-screw extruder (A). The screws are optimized for the foaming process (e.g., two counterclockwise rotating elements for gas tightness towards the feed). In this exemplary illustration, the twin-screw extruder has 10 heated zones with corresponding temperature control and pressure monitoring, with gas dosing occurring at position 1.6 in this example. After homogenization of the melt, it is forcibly conveyed via the bypass (B) into the single screw (C). The single screw extruder has 4 heated zones with corresponding temperature control and pressure sensors. The gas-melt mixture is primarily conveyed to the melt pump and maintained at a constant temperature during this process.The subsequent melt pump (D) is responsible for generating back pressure into the upstream system (improving gas solubility) and controlling the pressure in front of the perforated plate. The homogenized melt is forced through the perforated plate, foams up, and is separated by a rotating blade and transported away by the water circuit (E) (dried and separated).

[0093] The Figures 2a to 2d SEM images show the morphologies of various polycarbonate beads produced according to the process steps of the inventive method, albeit at different molar ratios of OH end groups of the polycarbonate to epoxy groups of the chain extender ("OH to epoxy"). While in the production of the beads from the Figures 2a and 2b While aromatic polycarbonate was used in which the molar ratio OH : epoxy is within the range specified in the invention, this does not apply to the materials from the Figures 2c and 2dHere, the molar ratio of OH to epoxy in the formulation used was 1:1.12 or 1.47. The partially destroyed cell morphology and cell coalescence are clearly visible in these comparison beads. This results in a material that cannot be processed into molded parts with good mechanical properties. However, the polycarbonate beads according to the invention, produced according to the inventive method, exhibit largely intact foam cells, with the quality of the foam structure being significantly improved in the particularly preferred range of reactive group equivalents of the formulation. Examples 1. Description of raw materials and testing methods a) Raw materials Polymers:

[0094] PC1: An aromatic polycarbonate based on bisphenol A with a melting point (MVR) of 6 cm³ / (10 min) (300°C / 1.2 kg, ISO 1133-1:2011) and a softening point (VST / B 120; ISO 306:2013) of 149°C. Tg, determined according to DIN EN ISO 11357-1:2017: 148°C. Mw, determined as described below, approx. 30,900 g / mol at 28 kDa (MALLS). Containing 0.06% heat stabilizer and 0.1% UV stabilizer. OH end-group content, determined by 1H NMR spectroscopy with dichloromethane as solvent at room temperature (as described above): 470 ppm. Produced by smelting-phase condensation (SPC).

[0095] PC2:An aromatic polycarbonate based on bisphenol A with a melting point (MVR) of 6 cm³ / (10 min) (300°C / 1.2 kg, ISO 1133-1:2011) and a softening point (VST / B 120; ISO 306:2013) of 150°C. Tg, determined according to DIN EN ISO 11357-1:2017: 148°C. Mw, determined as described below, approx. 30,900 g / mol at 28 kDa (MALLS). OH end-group content, determined by 1H NMR spectroscopy with dichloromethane as solvent at room temperature (as described above): 60 ppm.

[0096] Produced via the low-pressure condensation (LPC) process.

[0097] Chain extender 1:A commercially available and multifunctional chain extender from BASF SE (Joncryl ADR 4468) based on a styrene-acrylic polymer comprising epoxy reactive groups, with a mean molecular weight (gel permeation chromatography in ortho-dichlorobenzene at 150 °C with polystyrene calibration) Mw = 7,250 g / mol, an epoxy equivalent weight of 310 g / mol, determined according to DIN EN 1877-1:2000-12, a glass transition temperature Tg of 59 °C and a decomposition temperature of 350 °C, determined according to DIN EN ISO 11357-1:2017. b) Implementation of the procedure for the examples

[0098] The process according to the invention can, in principle, be carried out using various machine setups, as previously described. The experiments described below were performed using the setup i), ii), iii) twin-screw extruder-gas metering-single-screw extruder-melt pump-underwater pelletizing, also shown in Figure 1, carried out. Example i) describes successful particle production within the claimed range, example ii) describes failed particle production due to exceeding the maximum concentration of the chain extender, example iii) describes failed particle production due to the absence of the reactive component, example iv) describes a series of experiments with the same setup and process parameters as in i) but with successive reduction of the OH concentration of the melt PCs (ppm) at a constant reactive component, and example v) describes successful particle production using an alternative setup: twin-screw extruder-static mixer / heat exchanger-melt pump-underwater pelletizing. i) A twin-screw extruder from Reifenhäuser (Troisdorf, Germany) with a 43D screw capacity was operated at a throughput of 35 kg / h, with profile temperatures of 100–160 °C (positions 1 to 3), 240 °C (position 4) to 280 °C (positions 5–10), and a rotational speed of 100 rpm. Chain extender 1 was added to the PC1 melt at a low concentration of 0.7 wt.%. This corresponds to a molar OH : Epoxy ratio of 1 : 0.82 (mol / mol). The melt temperature was 10–20 °C higher than the housing temperature. The blowing agent was supplied via a Maximator (Maximator GmbH, Germany) and / or a metering station (Lewa GmbH, Germany) at position 6 with a CO₂ content of 1.2 to 1.5 wt.%. The pressure profiles in the twin screw increased successively from position 5 from 45 bar to 310 bar at the tip of the extruder. The melt was conveyed via the transfer pipe (290 °C) into the single screw (tire houses).The extruder was also operated at a constant housing temperature of 280 °C, a throughput of 35 kg / h, and a rotational speed of 26 rpm. The melt pressure gradually decreased across the screw to the melt pump (from 250 to 120 bar). The melt pump was pressure-controlled and operated at a back pressure of 110 bar and a temperature of 280 °C. The pressure downstream of the melt pump was in the range of 160–180 bar (pressure at the die plate). The start-up diverter valve and the die plate were also set to a temperature of 280 °C, and the melt temperature ranged from (Tg + 140 °C) to (Tg + 150 °C). The UWG (EUP 50) and the die plate were manufactured by ECON (Econ GmbH, Austria). The perforated plate consisted of 5 individual perforated inserts with a diameter of 2.2 mm and a yoke length of 3.49 mm. The residence time of the melt between infeed and outfeed was approximately 7-10 minutes.After exiting the material, the melt was separated using a rotating 6-blade knife at 1500 rpm and removed by a cold water circuit at 70–80 °C (28 m³ / h). The resulting particles were rounded with a bulk density of 150–180 g / L and welded well at pressures of 8–10 bar. ii) A twin screw conveyor from Reifenhäuser (Troisdorf, Germany) with a 43D screw capacity was operated at a throughput of 17 kg / h, with profile temperatures of 160–240 °C (positions 1 to 3), 260–270 °C (positions 4 and 5), and up to 280 °C (positions 6–10), and a rotational speed of 86 rpm. Additionally, chain extender 1 was added at a high concentration of 1.5 wt.%. This corresponds to a reactive group ratio OH : Epoxy of 1 mol : 1.78 mol. The melting temperature was 10 - 20 °C higher than the casing temperature.The blowing agent was supplied via a Maximator (Maximator GmbH, Germany) and / or a dosing station (Lewa GmbH, Germany) at position 6 with a CO₂ content of 2 to 2.3 wt%. The pressure profile in the twin-screw extruder increased successively from 67 bar at position 5 to 250 bar at the top of the extruder. The melt was conveyed via the transfer pipe (290 °C) into the single-screw extruder (tire houses). The extruder was also operated at a constant housing temperature of 280 °C, a throughput of 17 kg / h, and a speed of 15 rpm. The melt pressure decreased successively along the screw to the melt pump (from 250 to 115 bar). The melt pump was pressure-controlled, operating at a back pressure of 110 bar and a temperature of 280 °C. The pressure after the melt pump was 230 bar (pressure at the perforated plate) during this process. The start-up diverter was also set to a temperature of 280 °C and the perforated plate to 320 °C.The melt temperature ranged from (Tg + 150 °C) to (Tg + 160 °C). Due to an overdose of the reactive component, the throughput had to be significantly reduced and the perforated plate temperature increased to prevent an emergency shutdown due to critical system pressure. The UWG (EUP 50) and the perforated plate were manufactured by ECON (Econ GmbH, Austria). The perforated plate consisted of five individual perforated inserts with a diameter of 2.2 mm and a clamping length of 15 mm. The residence time of the melt between inlet and outlet was approximately 7–10 minutes. After outlet, the melt was cut with a rotating 6-blade knife at 1500 rpm and removed by a cold water circuit (70–80 °C, 28 m³ / h). The manufacturing process was unstable and resulted in collapsed and shriveled particles (bulk density > 500 g / L) that could not be welded together.iii) A twin-screw extruder from Reifenhäuser (Troisdorf, Germany) with a 43D diameter was operated at a throughput of 15 kg / h, with profile temperatures of 160–240 °C (positions 1 to 3), 260–270 °C (positions 4 and 5), and up to 280 °C (positions 6–10), and a rotational speed of 85 rpm. This test series was conducted without a chain extender. The melt temperature was 10–20 °C higher than the casing temperature. Gas was supplied via a Maximator (Maximator GmbH, Germany) and / or a metering station (Lewa GmbH, Germany) at position 6 with a CO₂ content of 2 to 2.3 wt%. The pressure profiles in the twin screw increased successively from 73 bar at position 5 to 94 bar at the top of the extruder. The melt was conveyed via the transfer pipe (290 °C) into the single screw (tire houses). The extruder was also operated at a constant housing temperature of 280 °C, a throughput of 15 kg / h, and a speed of 15 rpm.The melt pressure gradually decreased across the screw conveyor to the melt pump (from 94 to 87 bar). The melt pump was pressure-controlled, operating at a dynamic pressure of 110 bar and a temperature of 280 °C. The pressure downstream of the melt pump was 90 bar (pressure at the perforated plate). The start-up diverter and the perforated plate were set to a temperature of 280 °C, and the melt temperature ranged from (Tg + 140 °C) to (Tg + 150 °C). Despite the absence of a reactive component, the process control was kept as similar as possible to that described in ii). The UWG (EUP 50) and the perforated plate were manufactured by ECON (Econ GmbH, Austria). The perforated plate consisted of five individual perforated inserts with a diameter of 2.2 mm and a clamping length of 15 mm. The residence time of the melt between inlet and outlet was approximately 7–10 minutes.After exiting the material, the melt was separated with a rotating 6-blade knife at 1500 rpm and removed by a cold water circuit at 70–80 °C (28 m³ / h). Under the given conditions, the manufacturing process was not feasible and resulted in barely expanded round particles with a very high density of 500–600 kg / m³. These particles were very difficult, if not impossible, to weld into components. iv) A twin-screw conveyor from Reifenhäuser (Troisdorf, Germany) with a 43D capacity was operated at a throughput of 35 kg / h, with profile temperatures of 100–160 °C (positions 1 to 3), 240 °C (position 4) to 280 °C (positions 5–10), and a rotational speed of 100 rpm. Additionally, chain extender 1 was added at a fixed concentration of 0.7 wt.%. In this series, the molar reactive group ratio OH : Epoxy was varied by using a different proportion of a second polycarbonate, ranging from 1 : 0.82 to 1 : 1.47 (OH : Epoxy, each in mol) (Table.1) The melt temperature was 10–20 °C higher than the casing temperature. The blowing agent was supplied via a Maximator (Maximator GmbH, Germany) and / or a dosing station (Lewa GmbH, Germany) at position 6 with a CO₂ content of 1.3 wt.%. The pressure profiles in the twin screw increased successively from position 5 from 45 bar to 270 bar at the top of the extruder for 100 wt.% SPC. The addition of a PC component with low OH end groups, PC-2, initially increased the pressure profiles slightly to 275 bar at a content of 10%. Further addition of the PC component with low OH end groups beyond 20 wt.% resulted in decreasing pressure profiles. The melt was conveyed via the transfer pipe (290 °C) into the single screw (tire houses). The extruder was also operated at a constant housing temperature of 280 °C, a throughput of 35 kg / h and a speed of 26 rpm.The melt pump was pressure-controlled and operated at a dynamic pressure of 110 bar and a temperature of 280 °C. The pressure downstream of the melt pump was determined by the reactive polycarbonate content and reduced by the foreign matrix content (detailed in Table 1). The start-up diverter and the perforated plate were also set to a temperature of 280 °C, and the melt temperature ranged from Tg + 140 °C to Tg + 150 °C. The UWG (EUP 50) and the perforated plate were manufactured by ECON (Econ GmbH, Austria). The perforated plate consisted of five individual perforated inserts with a diameter of 2.2 mm and a clamping length of 3.49 mm. The residence time of the melt between inlet and outlet was approximately 7–10 minutes. After exiting the molten material, it was separated using a rotating 6-blade knife at 1500 rpm and removed by a cold water circuit (70–80 °C, 28 m³ / h). The roundness of the particles gradually decreased, while the foam density increased.If the polycarbonate concentration of OH end groups is too low, specifically < 350 ppm, the manufacturing process breaks down with a molar reactive group ratio (OH : epoxy, each in mol) of 1 : 1.12 (outside the required range). The molecular weight build-up no longer occurs sufficiently, so the viscosities of the melt mixture, and consequently the pressures at the perforated plate, are no longer adequate for a homogeneous particle foam. The resulting particles exhibit a more elongated shape and inhomogeneity in form and appearance (due to lower viscosity and thus altered flow properties) at higher foam densities (lower pressure drop) (Table 2). The particles can no longer be welded sufficiently well in the required pressure range of 7–11 bar.The components do not have a closed surface and have many sink marks / cavities, resulting in poorer thermal conductivity, increased stiffness, significantly reduced maximum flexural strain, and poorer puncture performance (Tables 2 and 3). v) A Coperion ZSK 26 MC twin-screw extruder with a 44D die was operated at a throughput of 20 kg / h at a casing temperature of 280°C (from the melting zone), a torque of 60%, and a rotational speed of 230 rpm. Additionally, the chain extender 1 was added in low concentrations of 0.9 wt%. This corresponds to a molar reactive group ratio OH : epoxy of 1 : 0.9 - 1.1 for a PC component with a particularly preferred OH end-group content of 450 to 550 ppm and is therefore within the range of the invention.In housing 7 of the 10 housings of the twin screw conveyor, the blowing agent CO₂ was introduced via a gas dosing station (Promix Solutions GmbH, Germany) at concentrations of 1.2 to 1.5 wt%. The melting temperature of the gas-polymer mixture was 280°C (Tg + 130°C). The homogenized gas-polymer mixture was forced into the static mixer. The residence time in this mixer was 6–8 minutes. The mixer was also operated at a profile temperature of 280°C. At the end of the static mixer, a melt pump from Maag-Germany GmbH regulated the back pressure at the inlet of the melt pump to 90 bar. A pressure of 198 bar was present before the perforated plate. The melt was granulated using an underwater pelletizer (Gala). In this process, the gas-molten mixture was forced through a perforated plate with two holes into the water-filled cutting chamber. The diameter of the holes in the perforated plate was 2.4 mm.In the cutting chamber, the molten material was cut into granules by rotating blades. The blade speed was 3500 rpm. Due to the pressure drop behind the perforated plate, the granules foamed up. A pressure of 2 bar was applied to the 80–90°C hot process water flowing through the cutting chamber. Finally, the granules were dried in a centrifuge and separated. The resulting particles were round, had a smooth, homogeneous surface, a bulk density of 220–250 g / L, and welded very well. c) Testing methods

[0099] The manufactured particles were processed into components with a density of 200 ± 10 kg / m³ and a geometry of 300 × 200 × 15 mm³ using a Teubert TVZ162 / 100PP molding machine (Teubert Maschinenbau GmbH, Germany). The required welding pressure for the EPC was in the range of 7 to 10 bar. Finally, the properties of the components were determined. Scanning electron microscopy (SEM, Model: JEOL JSM-6510, Borken, Germany) was performed on graphite-sputtered samples to visualize the morphology. A dynamic mechanical analysis (DMA) was performed on a Gabo Eplexor 500N from NETZSCH GmbH, (Selb, Germany) in pressure mode on 15 × 15 × 15 mm 3< samples in the temperature range of -25 to 250 °C at a heating rate of 1 K / min in pressure-regulated mode with an amplitude of 5% (static) and 2% (dynamic) of the sample height at a frequency of 1 Hz.Mechanical characterization was performed using compression, tension, and three-point bending tests (room temperature, 80 and 110 °C) and puncture tests (room temperature). Compression tests were carried out according to DIN EN ISO 844:2014-11 on a Zwick Z020 universal testing machine from Zwick & Roell (Ulm, Germany) on specimens with a geometry of 15 × 15 × 15 mm³ and a 10 kN load cell up to 60% compression. Three-point bending was performed according to ISO 1209-1:2007-05 on the same universal testing machine at 10 mm / min and a 20 kN load cell. The specimens were skinned to eliminate the influence of the compact surface layer, and the geometry was adjusted to 120 × 25 × 10 mm³. Tensile measurements on the components were carried out according to ISO 1926:2009 on a Zwick Z050 universal testing machine (Zwick & Roell, Ulm, Germany) with a sample geometry of 140 (30+80+30) × 80 × 15 mm 3< and a 20 kN load cell.Puncture characterization was performed using a Fractovis Plus drop-bolt testing machine from Instron Ceast (Pianezza, Italy) with a maximum energy of 40 J and a penetration velocity of 4.4 m / s (based on DIN EN ISO 6603-2:2002-04) with a sample geometry of 60 × 60 × 15 mm. All mechanical characterizations were carried out at room temperature, 80 °C, and 110 °C, each with a 10-minute intermediate step for temperature acclimation before measurement. All components were tested at a density of approximately 200 kg / m³. Thermal conductivity measurements were performed on an HFM 446 Lambda measuring device from NETZSCH (Selb, Germany) at -10 °C, 10 °C, 25 °C, 50 °C, and 70 °C.

[0100] The average molecular weight MwPC-1 and PC-2 were determined by gel permeation chromatography. Calibration was performed against bisphenol A polycarbonate standards using dichloromethane as the eluent. Calibration was also performed using linear polycarbonates (from bisphenol A and phosgene) of known molar mass distribution from PSS Polymer Standards Service GmbH, Germany, and according to method 2301-0257502-09D (from 2009 in German) from Currenta GmbH & Co. OHG, Leverkusen. The eluent used was dichloromethane. The column was made of cross-linked styrene-divinylbenzene resins.

[0101] Diameter of the analytical columns: 7.5 mm; length: 300 mm. Particle sizes of the column material: 3 mm to 20 mm. Solution concentration: 0.2 wt%. Flow rate: 1.0 ml / min; solution temperature: 30°C. Injection volume: 100 ml. Detection by UV detector. The highly branched polycarbonate, produced by molecular weight build-up via the addition of a chain extender, was determined using GPC-MALLS as described above. Not all highly branched / partially cross-linked fractions could be dissolved (XYZ% insoluble), meaning that particularly high molecular weight fractions cannot be characterized using existing analytical methods. This is a known problem for those skilled in the art, so the accuracy of determining the molecular weight of highly branched polymers is limited. The previously mentioned molecular weight ranges refer accordingly to the fractions soluble in dichloromethane.

[0102] The OH numberThe polymers were determined by 1< H-NMR spectroscopy with dichloromethane as solvent at room temperature by evaluating the ratio of the integrals of the signals at 6.68 ppm (2 aromatic protons ortho-positioned to phenolic OH groups) and at 1.68 ppm (6 methyl protons of the bisphenol A unit). 2. Results Composition and analysis

[0103] Table 1: Detailed compositions and analytical results for the study of the molar ratio according to example iv) E-1 E-2 E-3 V-4 V-5 V-6 PC1 [wt.%] 99,3 89,3 79,3 69,3 59,3 49,3 PC2 [wt.%] 0 10 20 30 40 50 PC1 throughput [g / h] 34760 31280 27810 24330 20806 17380 Pressure End A-Extruder [bar] 270 275 250 288 189 176 Pressure on perforated plate [bar] 190 184 177 170 134 122 OH group content, based on the total weight of aromatic polycarbonate [ppm] 470 429 387 346 305 264 Molar ratio of the reactive OH group (PC) to the reactive group of the chain extender (1: x) 0,82 0,90 1,00 1,12 1,27 1,47 M w from GPC [g / mol] 50180 52870 95690 93175 71691 50210 M w from GPC-MALLS [kDA] 158 168 206 207 139 107 Particle density [kg / m³< ] 197 234 265 271 260 253 Mean cell diameter [µm] 100 ± 47 129 ± 77 139 ± 66 193 ± 99 193 ± 11 7 206 ± 13 4 Cell density [cells / cm³< ] 8,88·10 5< 4,12·10 5< 3,48·10 5< 1,47·10 5< 1,33·10 5< 1,18·10 5< Cell coalescence No No No Yes Yes Yes Table 2: Detailed characteristic values ​​of the compression tests, bending tests and puncture tests for the comparative study in example iv) of the EPC particle foam components EPC (E-1) EPC (V-4) Component density [kg / m³<] 200 ± 10 230 ± 15 Pressure module [MPa] 54,7 ± 5 50,9 ± 5,2 Compressive strength at 10% compression [MPa] 1,61 ± 0,12 1,90 ± 0,14 EPC (E-1) EPC (V-4) Flexural modulus [MPa] 59,1 ± 11,4 86 ± 6,4 Flexural strength [MPa] 2,2 ± 0,3 2,52 ± 0,30 Maximum bending strain [%] 8,8 ± 1,1 5,1 ± 0,7 EPC (E-1) EPC (V-4) Maximum force [N] 1688 ± 27 936 ± 107 Penetration force [N] 844 ± 29 467 ± 53 Total energy [J] 21,2 ± 3 12,2 ± 2 Total deformation [mm] 33,9 28,4 ± 7 Note: Component made of EPC (V-4) has a foam density of 230 kg / m³. / m 3< . The parameters here are original and would need to be adjusted using a factor of 0.85 for simple percentage normalization. Table 3: Complete data for the thermal conductivity of EPC (E1) and (V4). thermal conductivity / mW / (m·K) Polymer matrix PC-1 -10 °C 10 °C 25 °C 50 °C 70 °C EPC (E-1) 200 kg / m³< 200 #< 44.0 46.2 47.9 50.7 52,7 EPC (V-4) 230 kg / m³ < 200 #< 46.2 48.8 50.7 53.7 55.6 #< Thermal conductivity data of the unexpanded starting material

Claims

1. Process for producing foamed polycarbonate beads, comprising the following steps: a) providing an aromatic polycarbonate-based composition, where the aromatic polycarbonate, based on the total weight of the aromatic polycarbonate, has a content of OH end groups of at least 350 ppm, determined by 1H NMR spectroscopy with dichloromethane as solvent at room temperature, b) mixing the aromatic polycarbonate-based composition with a chain extender suitable for OH groups in such a molar ratio that 0.64-1.10 mol of the reactive group of the chain extender is used per 1 mol of OH end groups of the polycarbonate, c) providing the mixture in a plastified state, d) mixing a physical blowing agent into the melt, e) particle foam extrusion of the plastified mixture at a temperature T of T1 = (Tg + 110°C) to T2 = (Tg + 170°C), where Tg is the glass transition temperature of the aromatic polycarbonate-based composition, where the glass transition temperature is determined by dynamic differential calorimetry according to DIN EN ISO 11357-1:2017, f) pelletizing the blowing agent-containing melt.

2. Process according to Claim 1, wherein carbon dioxide is used as blowing agent.

3. Process according to Claim 1 or 2, wherein the process is performed as a continuous operation.

4. Process according to any of the preceding claims, wherein the aromatic polycarbonate-based composition from step a has a melt volume flow rate MVR of up to 12 cm3 / (10 min), determined in accordance with ISO 1133:2012-3 (test temperature 300°C, mass 1.2 kg).

5. Process according to any of the preceding claims, wherein the pelletization is a pelletization in liquid medium, by hot chopping or an under-air pelletization.

6. Process according to any of the preceding claims, wherein the pelletization is an unpressurized underwater pelletization.

7. Process according to any of the preceding claims, wherein the chain extender used is one or more epoxy-functionalized compounds.

8. Process according to any of the preceding claims, wherein 0.1-2.3% by weight of physical blowing agent is added in step d, where the stated amount is based on the total weight of aromatic polycarbonate-based composition and chain extender.

9. Process according to any of the preceding claims, wherein the aromatic polycarbonate in the composition from step a, based on the total weight of the aromatic polycarbonate, has a content of OH end groups of 350 to 600 ppm, determined by 1H NMR spectroscopy with dichloromethane as solvent at room temperature.

10. Process according to any of the preceding claims, wherein the aromatic polycarbonate in the composition from step a, based on the total weight of the aromatic polycarbonate, has a content of OH end groups of at least 380 ppm, determined by 1H NMR spectroscopy with dichloromethane as solvent at room temperature.

11. Process according to any of the preceding claims, wherein step b and step d overlap in time.

12. Process according to any of Claims 1 to 10, wherein steps a to f take place in the sequence stated.

13. Process according to any of the preceding claims, wherein the chain extender used is an epoxy-functionalized chain extender with an epoxy equivalent weight of 285 to 485 g / mol.

14. Polycarbonate beads produced by the method according to any of the preceding claims.

15. Process for producing moulded articles from the polycarbonate beads according to Claim 14, wherein the crack gap method or the pressure filling method is utilized.