Method for producing polycarbonate beads

Abstract

The invention relates to a method for producing polycarbonate beads by using a chain extender. The polycarbonate beads have a low apparent density and are suitable for the manufacture of molded articles having good surface properties and good mechanical properties.

Description

[0001] The present invention relates to a method for producing polycarbonate beads, polycarbonate beads that can be obtained by the method, and molded articles that can be obtained from the polycarbonate beads.

[0002] Particulate foams, especially EPS, EPP, and E-TPU, are becoming increasingly important. Modern technologies have made it possible to produce reliable quality particulate foams and to use these foams to create high-performance components. The lower apparent density compared to "simple" thermoplastics opens up new application areas for expanded materials, or enables significant weight reductions in traditional applications. Therefore, expanded thermoplastics are a highly attractive material, especially for lightweight manufacturing applications, provided their application-specific properties are sufficiently excellent. In recent years, advancements in molding have allowed for the production of parts with specific surface finishes, making even visible parts made of expanded thermoplastics a true alternative to their corresponding injection-molded parts, while also being significantly lighter. Expanded materials are also highly attractive in terms of sustainability due to their lower material consumption, and their generally good thermal insulation properties contribute to energy conservation, for example, when used as thermal insulation materials or as sound-absorbing materials.

[0003] Granular foams made from polycarbonate have also been described. For example, granular foams made from engineering thermoplastics are favored by the automotive industry due to properties such as high thermal stability and good fire resistance. EPC is a type of granular foam suitable for high-temperature applications, while conventional polymer foams (such as EPP) cannot meet the requirements of this application. DE4100200 A1 describes a method for producing polycarbonate foam from polycarbonate, wherein an transesterification catalyst is added to an aromatic polycarboxylic acid or water (optionally also with aliphatic hydroxycarboxylic acids and / or aliphatic alcohols). This results in the controlled partial degradation of the polycarbonate and the release of CO2, which is used to foam the remaining polycarbonate. The polycarbonate foam described in this literature has a density of about 0.4 to 0.8 g / cm³.

[0004] EP 3858906 A1 describes a method for producing expandable granules from aromatic polycarbonate by extruding the aromatic polycarbonate, granulating it, impregnating it with carbon dioxide as a foaming agent and expanding the granules, and then molding the granules to obtain an expanded molded body.

[0005] EP 2603549 A1 describes polyester foams, explicitly stating that it also includes polycarbonate foams, which are not only low in density but also possess good processability. To produce these granular foams, a starting polymer material is selected whose crystallinity (reflected by the enthalpy of melting), glass transition temperature, and melting temperature are all within a certain range. The method for producing granular foams involves providing the starting polymer components in a molten state; incorporating a blowing agent component and optionally one or more additives into the melt; extruding and granulating the blowing agent-containing melt underwater under high pressure of 1 to 20 bar. EP 2603549 A1 also describes, in principle, possible ways to increase the molecular weight to stabilize the extrusion operation by, for example, adding a chain extender (but without specifying a specific amount). Furthermore, no other requirements are made regarding the polymer used.

[0006] Therefore, the aim is to provide low-density polycarbonate beads that are an improvement over existing technologies through a continuous process, thereby enabling the production of molded products with better mechanical properties.

[0007] Surprisingly, it has now been discovered that only when a specific amount of chain extender reacts with polycarbonate containing a specific amount of OH end groups can molded articles with sufficiently good mechanical properties be obtained from polycarbonate granular foam (i.e., so-called foamed "polycarbonate beads"). Only in this way can the reactive granular foaming extrusion process control required for good mechanical properties be achieved, thereby enabling the process to achieve T1 = (T g +110℃) to T2= (T g Foaming is performed at a high melting temperature T (+170℃) and under high pressure (where T) g This is equal to the glass transition temperature of the composition based on aromatic polycarbonate, a temperature higher than the common temperature range for expanding thermoplastics into low-density foams by extruding thermoplastics and using physical foaming agents. Those skilled in the art will understand that "granular foam extrusion" according to the prior art refers to the process of extruding amorphous thermoplastics at a melt temperature of Tg +10°C to Tg +70°C (where Tg is the glass transition temperature of the amorphous thermoplastic). g =The glass transition temperature of the polymer material) is used in a process of adding foaming gas and then granulating and cooling to obtain fully or partially extruded particles.

[0008] Therefore, the subject of this invention is a method for producing polycarbonate beads, particularly a continuous method, comprising the following steps, preferably performed in the following order: a) Provides an aromatic polycarbonate-based composition, wherein, based on the total weight of the aromatic polycarbonate, the aromatic polycarbonate has an OH end-group content of at least 350 ppm, the content being determined by... 1 The 1H NMR spectroscopy method uses dichloromethane as a solvent for determination at room temperature. b) The aromatic polycarbonate-based composition is mixed with a chain extender suitable for OH groups at a molar ratio such that 1 mol of OH end groups of the carbonate uses 0.64-1.10 mol of reactive groups of the chain extender. c) Provide a mixture in a plasticized state. d) Incorporate a physical foaming agent into the melt. e) At the temperature T of the plasticized mixture, T1 = (T g + 110℃) to T2 = (T g The plasticized mixture is subjected to granular foaming extrusion at +170℃, wherein T g It is the glass transition temperature of the composition based on aromatic polycarbonate. f) Granulate the melt containing the foaming agent.

[0009] Expanded polycarbonate beads are obtained through final granulation.

[0010] The content of OH end groups was determined by using dichloromethane as a solvent at room temperature. 1 The H NMR spectroscopy method was determined by evaluating the signal integration ratio at 6.68 ppm (two aromatic protons adjacent to the OH group of the phenol) and 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] "A mixture that provides a plasticized state" means that a polymer melt is present.

[0013] Unless otherwise expressly stated, all ppm amounts in this invention should be considered as weight percentages.

[0014] There are minimum values ​​for both the number of OH end groups and the concentration of the chain extender, but for high melting temperatures T, T1 = (T g + 110℃) to T2 = (T g +170℃), preferably T is T1 = (T g +120℃) to T2= (T g +160℃), more preferably T1=(T g +130℃) to T2= (T gThe maximum concentration for producing granular foam is also achieved by foaming and extruding at +150°C, where polycarbonate granular foam with good mechanical properties in the apparent density range of 150 to 250 g / L is obtained, based on DIN EN ISO 60:2000-01. Here, "based on" means not filling a standardized aluminum container of known volume, but filling a 1-liter beaker and weighing its contents to determine the density of the material.

[0015] The number of OH groups in aromatic polycarbonates has a significant impact on the achievement of low-density beads and the resulting molded products' good mechanical properties. An excessive number of OH groups in polycarbonate indicates overly high reactivity, ultimately leading to polycarbonate chain rearrangement, a decrease in molecular weight due to excessively rapid branching, and a rapid increase in viscosity (excessive shear input) and yellowing. Conversely, an insufficient number of OH groups results in incomplete or even absent reaction with chain extenders. This, in turn, means that good granular foam with sufficient mechanical properties cannot be obtained. Instead, the granular foam will have numerous defective collapsed cells.

[0016] According to the invention, the OH end group content of the aromatic polycarbonate used in this method is at least 350 ppm, preferably 350 ppm to 600 ppm, more preferably 380 ppm to 580 ppm, more preferably 400 ppm to 550 ppm, and most preferably 450 ppm to 550 ppm, based on the total weight of the aromatic polycarbonate used. The reference values ​​here refer to pure aromatic polycarbonate, not to compositions based on aromatic polycarbonate. To achieve such end group content, it is preferable to use SPC containing more than 70% by weight of the total aromatic polycarbonate used, more preferably at least 80% by weight of the total aromatic polycarbonate used, and most preferably using only SPC as the aromatic polycarbonate for producing polycarbonate beads.

[0017] The concentration of chain extender is also important. Excessive chain extender can render the material unprocessable because excessive increase in the molecular weight of polycarbonate leads to excessively high viscosity. Insufficient chain extender fails to significantly increase the molecular weight, resulting in only insufficient pressure increase (excessively low viscosity of PC with / without insufficient CE at 300°C), ultimately leading to poor mechanical properties. The reaction between the chain extender and polycarbonate is a function of time and temperature. For bisphenol A-based homopolymer polycarbonates, the foaming extrusion process is preferably performed at a shell temperature T after the foaming agent has been mixed and dissolved. 机壳 For T 1机壳 = T g +100℃ to T 2机壳 = T g +150℃ and melting temperature T is approximately T gThe process is carried out at + (110 to 170°C). Production of uncooked granular foam results in high-density, collapsed granules. Depending on process control, stabilizing and solidifying the foam structure through cooling causes foam expansion to stop too quickly. The high temperatures in the process can compensate for the excessively rapid cooling / solidification, allowing the formulation to utilize its full foaming potential at cooling. However, at these temperature profiles, the pressure on the orifice plate is 80-90 bar without the use of a chain extender (despite the use of a melt pump). Using a chain extender increases the pressure on the orifice plate to 140-180 bar, preferably 150-160 bar. Granular foam cannot be produced under these process conditions (temperatures) without corresponding chain extension and therefore without additional viscosity increase.

[0018] To produce polycarbonate beads with good performance, it has been found that, which is crucial to the present invention, the molar ratio of 1 mol of OH end groups of polycarbonate to 0.64-1.10 mol, preferably 0.71 to 1.0 mol, more preferably 0.96 mol, and even more preferably 0.8 to 0.9 mol, particularly 0.82 to 0.90 mol of reactive groups (in a continuous process, the addition is based on throughput metering).

[0019] Preferably, if the content of OH end groups in the aromatic polycarbonate is 400 to 550 ppm (using dichloromethane as a solvent at room temperature), 1 If the OH end groups of polycarbonate are determined by ¹H NMR spectroscopy, then 0.71 to 0.96 mol of reactive groups of chain extender are used for 1 mol of OH end groups.

[0020] By using chain extenders, the molar mass of polycarbonate is increased to 40,000 to 230,000 g / mol, preferably to 100,000 g / mol, which is associated with an additional increase of about 60 to 100 bar in pressure on the perforated plate at the temperature when the polycarbonate is in a plasticized state.

[0021] In a particularly preferred embodiment of the invention, the method is performed continuously and includes the following steps, preferably in the following order: a) Provides an aromatic polycarbonate-based composition, wherein, based on the total weight of the aromatic polycarbonate, the aromatic polycarbonate has an OH end-group content of at least 350 ppm, preferably 400 to 550 ppm, which is determined by... 1 The 1H NMR spectroscopy method uses dichloromethane as a solvent for determination at room temperature. b) The aromatic polycarbonate-based composition is mixed with a chain extender suitable for OH groups at a molar ratio such that 1 mol of OH end groups of the carbonate uses 0.64-1.10 mol, preferably 0.71 to 1.0 mol, more preferably 0.96 mol, and even more preferably 0.8 to 0.9 mol, particularly 0.82 to 0.90 mol of reactive groups (based on throughput adjustment), wherein the chain extender used is an epoxy-functionalized chain extender, preferably a styrene-acrylic acid-based polymer containing epoxy reactive groups, particularly a polymer with an epoxy equivalent weight (EEW ​​= epoxy equivalent weight) of 285 to 485 g / mol, said epoxy equivalent weight being determined according to DIN EN 1877-1:2000. c) Provide a mixture in a plasticized state. d) Incorporating a physical blowing agent into the melt at a concentration of 0.1-2.3% by weight based on the polymer melt, wherein the physical blowing agent is nitrogen, carbon dioxide, or a mixture thereof, preferably carbon dioxide. e) At a melting temperature T, T1 = (T g + 110℃) to T2 = (T g +170℃), preferably T is T1 = (T g +120℃) to T2= (T g The plasticized mixture is subjected to granular foaming extrusion at +160℃, wherein T g It is the glass transition temperature of the composition based on aromatic polycarbonate. f) Granulating the melt containing the foaming agent, preferably by non-pressurized underwater granulation.

[0022] Each step of the method of the present invention can be performed using tools and machines available in plastics technology known to those skilled in the art. Alternatively, the steps can be combined.

[0023] The production of polycarbonate beads can be carried out continuously or discontinuously. For example, the polymer melt can be taken directly from the polymerization reactor as fresh polymerization material, or it can be fed directly into a mixing extruder, where chain extenders, foaming agents, and optional additives are ultimately added at different locations within the mixing extruder. The method of the present invention is preferably carried out as a continuous process because discontinuous process control carries the risk of polycarbonate crystallization.

[0024] Obviously, the molar ratio of the OH end groups of polycarbonate to the reactive groups of the chain extender specified in the claim must be adjusted according to process control. In continuous processes, concentration adjustments based on throughput (mol / h : mol / h) must be performed.

[0025] The method of the present invention can be a single-stage or two-stage extrusion method, wherein, in a first extrusion step, the molecular weight of the polymer is increased in the presence of a chain extender, and polycarbonate granules are obtained as a first product; then, in a second extrusion step, foaming is performed using a physical foaming agent (preferably carbon dioxide), wherein subsequent underwater granulation ultimately yields the polycarbonate beads of the present invention. The first extrusion step may end with granulation. For this purpose, the melt is extruded through a forming tool at the extruder outlet and then cut to length. Cutting to length is accomplished by a cutting device, which is typically located directly downstream of the forming tool of the extruded material. The cutting device here may be in contact with the forming tool or positioned at a distance from the forming tool. However, the foaming agent may subsequently be incorporated into the same extruder, either only after the mixture of polycarbonate and chain extender has resided for a certain period of time, or simultaneously with the supply of the chain extender.

[0026] The method of this invention allows for the production of polycarbonate beads, i.e., a type of granular foam. Due to the lightweight and impact-resistant properties of granular foamed polycarbonate materials, and their higher continuous operating temperature (e.g., stability during cathodic dip coating) compared to PP, ABS, PE, or PA6, the use of granular foamed polycarbonate enables significant weight reduction in some vehicle components, as well as lower fuel consumption and CO2 emissions, while maintaining mechanical properties even at higher temperatures. Furthermore, the availability of foamed polycarbonate is expected to open up a range of other applications, particularly in areas requiring thermal insulation at higher temperatures.

[0027] Therefore, the subject of this invention remains polycarbonate beads produced by the method of this invention. According to this invention, "beads" refers to foamed granules (= granular foam) whose maximum density is typically up to 50% of the unfoamed starting material (a composition based on aromatic polycarbonate). The average molar mass of the aromatic polycarbonate in the polycarbonate beads obtained by the method of this invention (here measured as an absolute molar mass) is preferably at least 140 kDa (highly branched), more preferably at least 150 kDa, determined by GPC-MALLS measurement (multi-angle laser scattering) according to DIN EN ISO 16014-5:2019-09. Simultaneously, the molar mass and molecular size are measured to determine the degree of branching of the material, as branching affects the separation mechanism of GPC, as can be seen from the rising molar mass curve. A linear starting material is used as a reference for comparison with the foamed sample. The higher the degree of branching of the sample (the smaller the hydrodynamic volume for the same molar mass), the greater the deviation of the curve from the ideal straight line of unbranched polycarbonate. Polycarbonate materials with the corresponding minimum branching degree can be well foamed to form polycarbonate beads with good morphology, which can be used to produce molded products with good mechanical properties.

[0028] Expanded polycarbonate particles, or "polycarbonate beads," produced by the method of this invention have the following properties: - Depending on continuous process control, the apparent density is 150 g / L to 250 g / L, preferably 180 g / L to 200 g / L, determined in the process based on DIN EN ISO 60:1999 by apparent density determination. Here, "based on" means not filling a standardized aluminum container of known volume, but filling a 1-liter beaker and weighing its contents to determine the density of the material. - The nominal diameter (depending on the process) is 2 to 7 mm, preferably 2.5 to 5 mm, more preferably 3 mm ± 0.2 mm; wherein the size distribution is preferably determined precisely using a Camsizer; - Thermal properties of polycarbonate (T g (for temperatures of 145-150℃) and mechanical properties, for example, in parts with a density of 200 kg / m³. 3 At that time, the flexural modulus is at least 70 MPa, the flexural strength is at least 2.5 MPa (ISO 6603-2:2000); the compressive modulus is at least 59 MPa, the compressive strength (10% compression) is at least 1.73 MPa (ISO 844-11:2014); the tensile strength is at least 1.97 MPa, and the elongation at break is at least 8-14% (ISO 1926:2009). - The average equivalent circle diameter of the bubble relative to a circle with equal projected area is at most 150 µm, preferably at most 100 µm, more preferably at most 80 µm, as determined by SEM (ASTM E1508-12a:2019).

[0029] Bead size depends on process control and is particularly susceptible to the selected nozzle size, throughput, blade speed, and composition of the foaming agent melt. Process control with a 1.2 mm nozzle size, for example, yields beads with nominal diameters ranging from 1.8 to 3 mm. The maximum frequency distribution is 2.5 mm, with a distribution width of 28% (based on average). Using a 2.2 mm nozzle yields a particle size distribution with an average diameter of 5 mm and a distribution width of 40% (based on average).

[0030] Polycarbonate beads can be welded over a wide range, preferably at 7 to 11 bar, more preferably at 8 to 10 bar of water vapor pressure. They possess a high molecular weight M of 40,000 to 230,000 g / mol. w It can be determined by GPC as described in the examples.

[0031] Polycarbonate beads exhibit good mechanical properties and a low thermal conductivity of 45-47 mW / (m*K) at 10°C (DIN EN 12667:2001) and 200±10 kg / m². 3Component density.

[0032] The beads have complete (“closed-cell”) or at least mostly complete cells, thus allowing the production of highly uniform, smooth-surfaced, and uniformly welded foam molded products from polycarbonate beads. Here, “mostly” means that preferably >85% of the cells in the beads, more preferably >90% of the cells, are complete, meaning that the individual cell structure in these beads is separated by at least three other structural units (cells), and that no more than two cell walls in each individual cell are broken.

[0033] In the method of the present invention, the starting material used to produce the beads of the present invention is a composition based on aromatic polycarbonate.

[0034] In this invention, the term "aromatic polycarbonate" refers to both aromatic homopolymers and aromatic copolymers. These polycarbonates can be linear or branched in a known manner.

[0035] The polycarbonate contained in the composition is prepared in a known manner from a dihydroxyaryl compound, a carbonate derivative, and optionally a chain terminator and a branching agent.

[0036] Over the past 40 years, numerous patent documents have detailed methods for preparing polycarbonates. See, for example, Schnell, "Chemistry and Physics of Polycarbonates", Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964; D. Freitag, U. Grigo, PR Müller, H. Nouvertné, BAYER AG, "Polycarbonates", Encyclopedia of Polymer Science and Engineering, Vol. 11, 2nd edition, 1988, pp. 648-718; and finally, U. Grigo, K. Kirchner and PR Müller, "Polycarbonate", Becker / Braun, Kunststoff-Handbuch, Vol. 3 / 1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser Verlag München, Wien 1992, pp. 117-299.

[0037] Aromatic polycarbonates can be prepared, for example, by reacting a dihydroxyaryl compound with a carbonyl halide (preferably phosgene) and / or with an aromatic dicarbonyl dihalide, preferably a phenyl dicarbonyl dihalide, according to an interfacial reaction, wherein a chain terminator is optionally used and a branching agent of trifunctionality or greater is optionally used. They can also be prepared by melt polymerization by reacting a dihydroxyaryl compound with, for example, diphenyl carbonate. According to the invention, polycarbonates prepared by melt polymerization (also known as "transesterification") are preferred. The polycarbonates used according to the invention have 350 to 600 ppm of OH end groups, wherein this value is based on the polycarbonate itself, i.e., the polymer, without optionally added additives. The OH end group content is based on the total amount of polycarbonate used. A mixture of polycarbonates obtained by melt polymerization and polycarbonates obtained by an interfacial reaction can also be used, provided that the total concentration of OH end groups in the polycarbonates used is within a specified range. However, it is particularly preferred to use only polycarbonates prepared by melt polymerization.

[0038] Dihydroxyaryl compounds suitable for preparing polycarbonates include, for example, hydroquinone, resorcinol, dihydroxybiphenyl, 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)diisopropylbenzene, benzopyrrolidones derived from indigo or phenolphthalein derivatives, and their cycloalkylated, cycloarylated, and cyclohalogenated compounds.

[0039] Preferred dihydroxyaryl compounds include 4,4'-dihydroxybiphenyl, 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, dimethylbisphenol 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, as well as bisphenol (I) to (III). In each case, R' represents a C1- to C4-alkyl, aralkyl, or aryl group, preferably methyl or phenyl, with methyl being the most preferred.

[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'-dihydroxybiphenyl and dimethylbisphenol A, as well as bisphenols of formulas (I), (II) and (III).

[0041] These and other suitable dihydroxyaryl compounds are described, 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, 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, FR 1 561 518 A, the monograph "H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964", and JP 62039 / 1986 A, JP 62040 / 1986 A and JP 105550 / 1986 A

[0042] For homopolymers, only one dihydroxy aryl compound is used; for copolymers, multiple dihydroxy aryl compounds are used.

[0043] Examples of suitable carbonate derivatives include phosgene or diphenyl carbonate.

[0044] Suitable chain terminators for the preparation of polycarbonates include monophenols. Examples of suitable monophenols include phenol itself, alkylphenols (e.g., cresol, p-tert-butylphenol, isooctylphenol, cumylphenol), and mixtures thereof.

[0045] The preferred chain terminator is a straight-chain or branched chain, preferably an unsubstituted C1 to C1 chain. 30 Alkyl groups or phenols mono- or poly-substituted with tert-butyl groups. Particularly preferred chain terminators are phenol, cumylphenol, and / or p-tert-butylphenol.

[0046] The chain terminator is preferably used in an amount of 0.1 to 5 mol%, based on the number of moles of the dihydroxyaryl compound used in each case. The chain terminator can be added before, during, or after the reaction with the carbonate derivative.

[0047] Suitable branching agents are trifunctional or more functional compounds known in polycarbonate chemistry, especially compounds with three or more phenolic OH groups.

[0048] Examples of suitable branching agents include 1,3,5-tris(4-hydroxyphenyl)benzene, 1,1,1-tris(4-hydroxyphenyl)ethane, tris(4-hydroxyphenyl)phenylmethane, 2,4-bis(4-hydroxyphenyl isopropyl)phenol, 2,6-bis(2-hydroxy-5'-methylbenzyl)-4-methylphenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane, tetra(4-hydroxyphenyl)methane, tetra(4-(4-hydroxyphenyl isopropyl)phenoxy)methane, and 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 the optional branching agent is preferably from 0.05 mol% to 2.00 mol%, based on the number of moles of the dihydroxyaryl compound used in each case.

[0050] Branching agents can be pre-loaded in an alkaline aqueous phase along with dihydroxyaryl compounds and chain terminators, or added prior to phosgenation in the form of a solution dissolved in an organic solvent. In transesterification, the branching agent is used in conjunction with the dihydroxyaryl compound.

[0051] Particularly preferred polycarbonates are homopolymers based on bisphenol A, copolymers based on 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and 4,4'-dihydroxybiphenyl, and copolymers based on the two monomers bisphenol A and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, as well as homopolymers or copolymers derived from dihydroxyaryl compounds of formulas (I), (II), and (III), especially copolymers with bisphenol A. R' is C1-C4 alkyl, aralkyl, or aryl, preferably methyl or phenyl, and very particularly preferably methyl.

[0052] Very particularly preferred, the polycarbonate-based composition comprises a bisphenol A-based polycarbonate; most preferably, the polycarbonate in the polycarbonate-based composition is a bisphenol A-based homopolymer polycarbonate.

[0053] Copolycarbonates prepared using bisphenols of general formula (1a) are also preferred: in R 5It is hydrogen or C1-C4 alkyl, C1-C3 alkoxy, preferably hydrogen; methoxy or methyl, R 6 R 7 R 8 and R 9 Each is independently C1- to C4-alkyl or C6- to C4-alkyl. 12 -Aryl, preferably methyl or phenyl Y is a single bond, SO2-, -S-, -CO-, -O-, C1- to C6-alkylene, C2- to C5-alkylidene, C6- to C 12 -Arylidene (which may optionally be fused with other aromatic rings containing heteroatoms) or a C5- to C6-cycloalkylidene group that may be mono- or poly-substituted with C1- to C4-alkyl groups, preferably a single bond, -O-, isopropylidene, or a C5- to C6-cycloalkylidene group that may be mono- or poly-substituted with C1- to C4-alkyl groups. V is an oxygen, a C2- to C6-alkylene group, or a C3- to C6-alkylidene group, preferably an oxygen or a C3-alkylene group. p, q, and r are each independently 0 or 1. When q = 0, W is a single bond; when q = 1 and r = 0, W is an oxygen, C2- to C6-alkylene, or C3- to C6-alkylidene group, preferably an oxygen or C3-alkylene group. When q = 1 and r = 1, W and V are each independently C2- to C6-alkylene or C3- to C6-alkylidene, preferably C3-alkylene. Z is a C1- to C6-alkylene group, preferably a C2-alkylene group. o is 10 to 500, preferably 10 to 100, the average number of repeating units, and m is 1 to 10, preferably 1 to 6, and more preferably 1.5 to 5, the average number of repeating units. Similarly, two or more siloxane blocks of general formula (1a) can be interconnected via terephthalic acid and / or isophthalic acid to form ester-based diphenols.

[0054] The (poly)siloxanes of formulas (2) and (3) are particularly preferred. R1 is hydrogen, C1- to C4-alkylene, preferably hydrogen or methyl, and particularly preferably hydrogen. R2 is independently aryl or alkyl, preferably methyl. X is a single bond, -SO2-, -CO-, -O-, -S-, C1- to C6-alkylene, C2- to C5-alkylidene, or C6- to C6-alkylene. 12-Aryl group, which can optionally fused with other aromatic rings containing heteroatoms. X is preferably a single bond, C1- to C5-alkylene, C2- to C5-alkylidene, C5- to C6-alkylene, C6- to C7 ... 12 -cycloalkylidene group, -O-, -SO-, -CO-, -S-, -SO2-, more preferably X is a single bond, isopropylidene group, C5- to C6-. 12 - Cycloalkylidene group or oxygen, most preferably isopropylidene group. n is a number from 10 to 400, preferably from 10 to 100, and particularly preferably an average of 15 to 50. m is 1 to 10, preferably 1 to 6, and especially preferably an average of 1.5 to 5.

[0055] Siloxane blocks can also be preferably derived from the following structures (V), preferably (Va) or In formulas (IV), (V) and (VI), a is an average of 10 to 400, preferably 10 to 100, and particularly preferably 15 to 50.

[0056] Also preferably, at least two identical or different siloxane blocks of general formula (IV), (V) or (VI) are interconnected by terephthalic acid and / or isophthalic acid to form an ester group.

[0057] Also preferably, in formula (1a), p = 0, V is a C3 alkylene group, r = 1, Z is a C2 alkylene group, and R... 8 and R 9 Methyl, q=1, W is a C3 alkylene group, m=1, R 5 It is hydrogen or C1 to C4 alkyl, preferably hydrogen or methyl, R 6 and R 7 Each of them is independently C1 to C4 alkyl, preferably methyl, and o is 10 to 500.

[0058] Copolycarbonates having monomer units of formula (1a), and in particular their preparation methods, have been described in WO 2015 / 052106 A2.

[0059] Copolycarbonates having monomer units of formula (IV), and in particular their preparation methods, have been described in WO 2015 / 052106 A2.

[0060] The aromatic polycarbonate used in the method of this invention can be a single polycarbonate or a mixture of two or more aromatic polycarbonates, provided that the OH end group content of all polycarbonates used is within the range of this invention. Polycarbonates that are recycled after consumption or industry can also be used. The corresponding recycled material can be fed into an extruder as granules or abrasives. The recycled material can also be used only as a portion of the aromatic polycarbonate.

[0061] In principle, one or more additives can be added to aromatic polycarbonates, more specifically to the polycarbonates used as starting materials in the method of the present invention. However, one or more additives may also be added to the aromatic polycarbonates only when the method of the present invention is carried out in an extruder, more specifically preferably together with a chain extender. If only one extrusion stage is used, additives cannot be added via a side extruder in the method of the present invention because the foaming agent is present in the melt and will therefore escape through the side feed port. However, an airtight side feed port can be used to introduce additives in this way. Additives can also be added via powder premixes or as masterbatches. Liquid additives can, in principle, be injected at any point in the process, as long as sufficient homogenization is still possible, preferably in static or dynamic mixing unit areas. Additives can also be added in the first stage, followed by the addition of the foaming agent in the second stage. In this case, additives can also be metered in via a side extruder.

[0062] A mixture of aromatic polycarbonate as a starting material, optional blending partners, and optional additives is referred to as an "aromatic polycarbonate-based composition." Therefore, the use of "aromatic polycarbonate-based composition" in step a of method should be understood as the use of a pure polymer, but also includes the use of aromatic polycarbonate with added additives. If an additive-added polycarbonate composition is used, it preferably contains at least 70% by weight, more preferably at least 80% by weight, even more preferably at least 90% by weight, more preferably at least 95% by weight, and most preferably at least 98% by weight of aromatic polycarbonate, based on the total weight of the polycarbonate composition. Most preferably, the "aromatic polycarbonate-based composition" does not contain any blending partners blended with polycarbonate, but uses only aromatic polycarbonate in the method of the present invention for producing polycarbonate beads, except for optional additives commonly used with polycarbonate.

[0063] Other additives commonly added to polycarbonate include, in particular, heat stabilizers, flame retardants, antioxidants, mold release agents, anti-drip agents such as Teflon or SAN-coated PTFE (e.g., Blendex 449), UV absorbers, infrared absorbers, impact modifiers, antistatic agents, fluorescent whitening agents, fillers (e.g., talc), light scattering agents, transesterification inhibitors, compatibilizers, nucleating agents, colorants, pigments (e.g., titanium dioxide, carbon black), chemical foaming agents, and / or additives for laser marking, especially in amounts typically used in polycarbonate-based compositions. Such additives are described, for example, in EP-A0 839 623, WO-A 96 / 15102, EP-A 0 500 496, or "Plastics Additives Handbook", Hans Zweifel, 5th edition, Hanser Verlag, Munich. These additives can be added individually or in combination. It should be understood that these additives and in these amounts are permitted only if they do not have a significant adverse effect on the production of beads according to the method of the present invention.

[0064] The additives are preferably selected from heat stabilizers, flame retardants, antioxidants, release agents, colorants, pigments, anti-drip agents, ultraviolet absorbers, infrared absorbers, nucleating agents, impact modifiers, antistatic agents, fluorescent whitening agents, light scattering agents, transesterification inhibitors, compatibilizers and / or additives for laser marking.

[0065] The melt volume flow rate (MVR) of the aromatic polycarbonate-based composition is preferably at most 14 cm³ / (10 min), more preferably at most 12 cm³ / (10 min), more 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), as determined according to ISO 1133:2012-3 (test temperature 300°C, mass 1.2 kg).

[0066] As part of the method of the present invention, such a large amount of chain extender is added to the aromatic polycarbonate used such that the molar ratio of the OH end groups of the polycarbonate to the reactive groups of the chain extender is 1:0.64 to 1.1, preferably 1:0.71 to 1.0, more preferably 0.96, even more preferably 1:0.8 to 0.9, and particularly 1:0.82 to 0.90. The molar amount is preferably adjusted based on the hourly throughput. This results in the polymer formation, where the molecular weight of the aromatic polycarbonate increases through the formation of long-chain branches.

[0067] Suitable chain extenders generally include amines, carboxyl compounds, maleic anhydride-modified compounds, epoxy-functionalized compounds, oxazolines, carbodiimides, and / or functionalized polymers (e.g., based on acrylates and / or styrene) with the corresponding functional groups. These compounds can be used alone or in combination. These groups include, for example, amino functional groups in amines, carboxyl functional groups in carboxyl compounds, anhydride functional groups in maleic anhydride-modified compounds, epoxy functional groups in epoxy-functionalized compounds, or other functional groups capable of reacting with the OH end groups of polycarbonate to increase chain length. Preferred chain extenders are, in particular, epoxy-functionalized compounds, most preferably epoxy-functionalized styrene-acrylate-based polymers supplied by BASF SE, for example as Joncryl additives such as Joncryl ADR 4368, ADR 4400, and ADR 4468. The amount / weight of the chain extender must be matched to the aromatic polycarbonate so that 0.64 to 1.10 mol, preferably 0.71 to 1.0 mol, more preferably 0.96 mol, even more preferably 0.8 to 0.9 mol, and particularly 0.82 to 0.90 mol of reactive groups are used per mol of OH end groups in the polycarbonate. For example, using an aromatic polycarbonate having 350-600 ppm OH end groups as a starting material, a chain extender with an epoxy equivalent weight of 310 g / mol (e.g., with Joncryl ADR 4468) at a concentration of 0.4-1.2 wt%, preferably 0.5-1.0 wt%, and more preferably 0.7-0.9 wt%, can be reacted with the chain extender at a concentration of 0.7-0.9 wt%, wherein the amount of chain extender, based on the resulting total composition (a composition based on the aromatic polycarbonate, i.e., including optional blend partners and optional additives, plus the chain extender), can achieve the range of reactive group ratios. By selectively adjusting the molar ratio to 1 mol:0.64 to 1.10 mol, a molecular weight range of 40,000 to 230,000 g / mol, preferably 50,000 to 150,000 g / mol, and more preferably 75,000 to 100,000 g / mol (as described above) is achieved. This wide processing window enables the production of components with varying properties using particles with a molecular weight of 40,000 to 230,000 g / mol.

[0068] For reactive particle foaming and extrusion, the following structural arrangements can be used, but are not limited to: a) Polymerization reactor / (static) extruder / mixer / gas metering system / melt pump / granulation b) Extruder (twin / single screw) / Gas metering system / Granulator c) Extruder (twin / single screw) / Gas metering system / Static mixer / Granulator d) Extruder (twin / single screw) / Gas metering system / Heat exchanger / Granulator e) Extruder (twin / single screw) / Gas metering system / Static mixer / Heat exchanger / Granulator f) Twin-screw extruder / gas metering system / single-screw extruder / granulator g) Twin-screw extruder / gas metering system / heat exchanger / granulator h) Twin-screw extruder / gas metering system / single-screw extruder / melt pump / granulator i) Twin-screw extruder / gas metering system / heat exchanger / melt pump / granulator.

[0069] Extrusion processes can be carried out in one or two stages.

[0070] Specifically, this process can be implemented in various arrangements. Key steps in the process include: melting the aromatic polycarbonate-based composition; optionally adding a nucleating agent (talc, particularly nano-sized talc, graphite, carbon black, pigments, etc.); metering a foaming agent via a liquid metering system (e.g., from Lewa GmbH, Germany) or a compression device (high-pressure device) (e.g., from Maximator GmbH, Germany); optionally increasing the pressure to the orifice plate by, for example, cooling, adding reactive macromolecular monomers, or by technical aids such as a crushing plate or melt pump (preferably by adding reactive macromolecular monomers or by using technical aids to increase the pressure); and finally, shredding the granules / beads by granulation in a liquid medium, thermal shredding, or gas-based granulation (where gas mixtures may also be used). It should be noted that the liquid medium used here can be not only water but also other media, such as glycerol or glycerol.

[0071] The method of the present invention is particularly preferred to use a tandem configuration consisting of a twin-screw and a single-screw. In this case, the twin-screw is further preferably used for plasticizing the aromatic polycarbonate-based composition and mixing the physical foaming agent and chain extender, while the single-screw is subsequently used for melt temperature control. The molecular weight increase has already occurred in the twin-screw / first extruder and continues until exiting the nozzle (the end of the extrusion unit).

[0072] More preferably, in the last third of the first extrusion unit (depending on the structure), the physical blowing agent is metered into the melt containing the aromatic polycarbonate and the chain extender that reacts throughout the process. It is preferred to mix thoroughly in such a way that the polymer melt contains a ultimately uniformly distributed blowing agent, wherein the proportion of the physical blowing agent in the mixture is preferably 1.0% to 2.3% by weight for CO2, more preferably 1.2% to 1.7% by weight, more preferably 1.3-1.5% by weight, and for N2 preferably 0.1% to 0.5% by weight, more preferably 0.1% to 0.3% by weight, more preferably 0.15% to 0.25% by weight, and most preferably 0.15% to 0.2% by weight, based on the total weight of the polymer melt (= polycarbonate-based composition) and the chain extender. It should be noted that the method of the present invention does not require step d to be performed after step b. Similarly, the mixing of the physical blowing agent into the melt can also begin simultaneously with or overlap with the metered addition of the chain extender.

[0073] To induce foam cell formation and obtain a finer and more uniform cell morphology, a nucleating agent, such as talc, especially nano-sized talc, graphite, carbon black, pigment, etc., is preferably added at a low concentration of 0.1% to 1.0% by weight, more preferably 0.15% to 0.5% by weight, and even more preferably 0.2% to 0.3% by weight, is added, wherein the dosage data is based on the total composition obtained from the polycarbonate-based composition and the chain extender.

[0074] In principle, the physical blowing agent used can be any blowing agent commonly used for foaming thermoplastics. Examples include propane, butane, n-pentane, isopentane, and similar aliphatic hydrocarbons, including aromatic hydrocarbons, alicyclic hydrocarbons, aliphatic alcohols, carbon dioxide, nitrogen, air, inert gases (e.g., argon or helium), etc. Combinations of two or more such blowing agents can also be used as physical blowing agents. Carbon dioxide, one or more inert gases, nitrogen, air, or mixtures thereof are preferred as physical blowing agents because they not only have no toxicological and environmental problems, but also do not support combustion. Nitrogen, carbon dioxide, or mixtures thereof are very particularly preferred, with carbon dioxide being the most preferred.

[0075] If nitrogen is used as a physical blowing agent, the amount of nitrogen used is preferably 0.1% to 0.5% by weight, more preferably 0.1% to 0.3% by weight, more preferably 0.15% to 0.25% by weight, and most preferably 0.15% to 0.2% by weight, based on the polymer melt including chain extenders and additives.

[0076] If carbon dioxide is used as a physical blowing agent, then based on the polymer melt including chain extenders and additives, it is preferred to use 1.0 to 2.3% by weight, more preferably 1.2% to 1.7% by weight, and even more preferably 1.3% to 1.5% by weight of carbon dioxide.

[0077] In the production process, taking a series-connected device (equipment h) as an example, various physical foaming agents can be introduced into the polymer melt from different locations, such as through a liquid metering system or a high-pressure metering system. The physical foaming gas is preferably added to the first extruder, but for the best possible homogenization, it is added to the last third of the extruder. Metering at the end of the series-connected device can also form particles, but the operation is less stable, and the resulting particles are uneven. The most preferred foaming agent is carbon dioxide because it is non-flammable and less expensive than inert gases and nitrogen compared to other foaming agents used in the production of expanded thermoplastics. Furthermore, it can be relatively easily converted to a supercritical state (T>31.0℃ and p>73.8 bar), which promotes its miscibility and dissolution in polycarbonate through low compressibility and rapid diffusion. Therefore, when carbon dioxide is used as the foaming agent in the production method of the present invention, the polycarbonate beads of the present invention can even be used in applications where there is a certain fire risk or where venting (interior) is not permitted, without concern. Therefore, it is particularly suitable for use in the electric vehicle field, for example, as body parts (e.g., composite material parts). Possible applications include sound-absorbing elements integrated into the vehicle floor area or thermal insulation layers in the vehicle body.

[0078] The melt pressure must be higher than the critical dissolution pressure of the physical foaming agent.

[0079] After the foaming agent is mixed in and dissolved, the melt is extruded through the nozzle plate at the extruder opening, usually at a melt temperature T of T1 = (T g +110℃) to T2= (T g +170℃), preferably T1= (T g + 120℃) to T2 = (Tg + 160℃), more preferably T1 = (T g +130℃) to T2= (T g The process is carried out at +150°C. Furthermore, the temperature of the nozzle plate is preferably set to T. g A temperature of + (130 to 150°C) is maintained to prevent the nozzle from freezing due to the cooled polymer melt, thereby ensuring smooth polymer granulation and achieving corresponding foam expansion with the highest possible expansion potential.

[0080] The nozzle opening diameter of a single-hole nozzle is preferably 0.8 to 2.2 mm, more preferably 1.0 to 1.5 mm. For a multi-hole nozzle, the nozzle diameter is preferably 0.4 to 0.8 mm, more preferably 0.6 mm.

[0081] After the method of the present invention is completed, the granulation of the melt is preferably carried out underwater, more preferably without additional pressurization, i.e., at atmospheric pressure. Granulation at atmospheric pressure allows for the achievement of the required low density of the polycarbonate beads. As the melt exits the nozzle, the pressure of the polycarbonate material drops by 140 to 180 bar, preferably 150-160 bar, until it reaches approximately 1 bar of atmospheric pressure, which causes the material to begin foaming. A physical foaming agent (e.g., carbon dioxide) causes the polycarbonate material to expand, while gas diffuses out of the polymer melt. After a period of time, the gas exchange is complete or almost complete, so that only the normal air composition is found in the subsequently granulated expanded polycarbonate (i.e., polycarbonate beads).

[0082] The subject of this invention is still the method for producing molding articles from polycarbonate beads prepared by the method of this invention, and such molding articles.

[0083] Polycarbonate beads can be transformed into molded articles by filling appropriate mold cavities, even those with complex geometries, ultimately requiring only one corresponding operation step. This eliminates the need for subsequent cutting, as is typically required with extruded foam, and the corresponding waste generated from scrap. Furthermore, polycarbonate beads are much easier to transport compared to the usually bulky extruded foam boards.

[0084] The molded articles of this invention can be used in the automotive, transportation, construction, aerospace, and packaging industries, as well as in typical lightweight and / or composite material structures. The molded articles made of polycarbonate beads can be not only sheets but also complex three-dimensional molded parts.

[0085] Molded articles composed of or containing the polycarbonate beads of the present invention are particularly visible components in various application fields, where laser texturing can also be used for enhancement, such as dashboard or interior components, sound insulation components, foam components (e.g., carpets for automotive footwells), core materials of composite materials or supporting foam components (e.g., body insulation for vehicles (especially electric vehicles), as insulation materials in the HVAC field (heating, ventilation, air conditioning), as high-temperature insulation materials in industry, housing and building technology or transportation, barrier and insulation materials, packaging, lightweight building components, rotor blades of wind turbines, and exterior wall components.

[0086] Typically, molded parts made of polymer foam are primarily subjected to compressive stress. Another relevant type of stress for polymer foam is bending. In this case, the part experiences complex stresses, with compressive stress at the top and tensile stress at the bottom. Compression testing can yield conclusions regarding application-related mechanical properties, while tensile and bending tests can yield conclusions related to weld quality. Parts made from polycarbonate beads obtained by the method of this invention can possess the thermomechanical properties of polycarbonate. g The temperature curve is 145-150℃, for example, when the component density is 200 kg / m³. 3 At 23°C, the flexural modulus is 59.1 ± 11.4 MPa, and the flexural strength is 2.2 ± 0.3 MPa (ISO 1209-1:2007). The modified geometric dimensions are 120 x 25 x 10 mm. 3 The compressive modulus is 54.7 ± 5 MPa, and the compressive strength (10% compression) is 1.61 ± 0.12 MPa (at 23°C, DIN EN ISO 844-11:2014); the tensile strength is at least 1.97 MPa, and the elongation at break is 8.4% (DIN EN ISO 1926:2009), while also exhibiting good thermal insulation performance of 45.2 ± 2 mW / (m·K) at 10°C (EN ISO8301-8:1991). Commercially available granular EPP foam, with the same density of 200 kg / m³, has a compressive modulus of 54.7 ± 5 MPa and a compressive strength (10% compression) of 1.61 ± 0.12 MPa (at 23°C, DIN EN ISO 844-11:2014); it also has good thermal insulation performance of 45.2 ± 2 mW / (m·K) at 10°C (EN ISO8301-8:1991). 3 The flexural modulus is approximately 56.1 ± 10.8 MPa, the flexural strength is 1.85 ± 0.25 MPa, the compressive modulus is 48.4 ± 3.6 MPa, and the compressive strength (10% compression) is 1.51 ± 0.5 MPa. Furthermore, the EPP has a tensile strength of 2.49 MPa, an elongation at break of 20.2%, and a thermal insulation effect of 54 ± 0.2 mW / (m*K) (10℃). These values ​​were determined in the same way as those for the EPC, but the performance is significantly lower.

[0087] Because polycarbonate beads are quite large in some cases and their average equivalent circle diameter relative to a circle of equal projected area, i.e., a nominal diameter of about 4 to 6 mm, the mold cavity needs to be filled by 10-20% (based on volume). Steam-based welding methods for granular foams follow the same mechanism for all granules and are extensively described in the literature, e.g., Raps et al. 2015; DOI: 10.1016 / j.polymer.2014.10.078.

[0088] To produce molded parts / components, foam granules are welded together in a steam molding machine or by a variable-temperature method (heating). In a steam molding machine, high-pressure steam (i.e., high-temperature steam) melts or softens the surface of the granules, causing the polymer chains between the different beads to interdiffusion and thus creating bead bonding. To ensure favorable mechanical properties, good bonding between the granules is necessary, and the proportion of large pores / gaps (i.e., cavities between granules in the part due to poor filling) must be low. In a molding machine, the foam beads are processed into finished parts through five steps: 1) fully or partially closing the mold, 2) filling the mold with optional full closure, 3) welding the granules, 4) cooling and stabilization, and 5) ejecting the molded part. Two methods are distinguished here: the slit method and the pressure filling method. In the pressure filling method, the mold is first closed, then the granules are extracted from the container by air pressure and blown into the mold with a pressure of about 3 bar using a syringe and compressed therein. The granules expand in the mold and better fill the cavity (equivalent to about 10% overfill in the slit method). In the slit method, the mold is not completely closed, but a certain gap (%) remains open. It is then filled with granules to overfill the mold at a certain percentage (10-20% by volume in the case of EPC). The mold is then closed and the granules are compressed to the target thickness. For example, if the target thickness of the part is 20 mm, the mold cavity is further opened, for example, by 4 mm, for filling (= 20% by volume) with polycarbonate beads, and then the mold is closed to a part thickness of 20 mm. This step is crucial for achieving a uniform distribution of the beads in the mold. In the third step, the beads are fused together by flowing hot steam through the mold according to a fixed procedure. During the steam treatment, the beads form physical bonds due to the interdiffusion of polymer chains between adjacent particles. To ensure high weld quality between the particles, 7 to 11 bar is preferred for EPC, more preferably 8 to 10 bar. In the steam-based welding process, air between the beads is first vented and the mold is preheated. When the valve is opened, the steam flows parallel to the mold. In the second step, steam flows through the mold; this is called cross-steam treatment. In this step, the steam inlet and outlet valves, which are opposite to each other, are opened. To ensure the temperature distribution throughout the part is as uniform as possible and the weld quality is uniform, steam treatment is preferably performed from both sides of the mold. Finally, with the outlet valve closed, steam at a specific pressure is introduced into the steam chamber to improve surface quality by forming a skin (autoclave steam treatment). In the fourth step, the molded part is cooled, which is crucial for dimensional accuracy. If the part is ejected without cooling, the particles may expand further, causing deviations from the original dimensions. To cool, water is sprayed onto the mold until the temperature reaches approximately 80°C. After molding and cooling, the part is finally ejected in the last step, preferably using compressed air and a mechanical ejector.

[0089] The present invention will be described with reference to the following figures.

[0090] It shows: Figure 1 : A flowchart of the method for producing polycarbonate beads according to the present invention.

[0091] Figure 2a SEM images of the foam morphology of polycarbonate beads obtained by the method of this invention (for PC 1 component (E1) with an OH end group content of 470 ppm, the molar ratio of reactive groups OH:epoxy is 1 mol:0.82 mol). The OH end group content is 470 ppm based on the total weight of the aromatic polycarbonate used.

[0092] Figure 2b SEM image of another polycarbonate bead foam morphology obtained by the method of the present invention (for PC 1 component (E2) with OH end group content of 470 ppm, the reactive group molar ratio of OH:epoxy is 1 mol:0.90 mol (based on hourly throughput)). The OH end group content is 429 ppm based on the total weight of the aromatic polycarbonate used.

[0093] Figure 2c SEM images of the foam morphology of polycarbonate beads not of this invention (for PC 1 component (V4) with an OH end group content of 470 ppm, the reactive group molar ratio of OH:epoxy is 1 mol:1.12 mol (based on hourly throughput)). The OH end group content is 346 ppm based on the total weight of the aromatic polycarbonate used.

[0094] Figure 2d SEM image of another non-inventive polycarbonate bead foam morphology (for PC 1 component (V6) with OH end group content of 470 ppm, the reactive group molar ratio of OH:epoxy is 1 mol:1.47 mol (based on hourly throughput)). The OH end group content is 264 ppm based on the total weight of the aromatic polycarbonate used.

[0095] Figure 1The apparatus shown for carrying out the method of the present invention is a series configuration. The apparatus first consists of a co-rotating twin-screw extruder (A). The screw needles are optimized for the foaming process (e.g., two left-handed elements are used to ensure airtightness in the inlet direction). In the exemplary illustration, the twin-screw extruder has 10 heating zones equipped with corresponding temperature and pressure monitoring, where, in this embodiment, gas metering is located at position 1.6. After homogenization, the melt is forced through a bypass (B) to a single screw (C). This single-screw extruder has 4 heating zones equipped with corresponding temperature and pressure sensors. The gas-melt mixture is first fed to a melt pump and maintained at the same temperature during this process. The subsequent melt pump (D) is tasked with generating back pressure (for better gas solubility) in the upstream equipment and controlling the pressure upstream of the orifice plate. The homogenized melt is forced through the orifice plate, foamed, separated by rotating blades, and conveyed out through the water circuit (E) (drying and cutting).

[0096] Figures 2a to 2d SEM images show the morphologies of different polycarbonate beads produced via the method steps of this invention, but with varying molar ratios of OH end groups in the polycarbonate to epoxy groups in the chain extender (“OH:epoxy”). Although aromatic polycarbonates are used in the production of... Figure 2a and 2b The beads in which the molar ratio of OH to epoxy is within the scope of this invention, but this does not apply to... Figure 2c and 2d The materials used here have OH:epoxy molar ratios of 1:1.12 and 1.47, respectively. In these comparative beads, partially disrupted cell morphology and cell adhesion are clearly visible. As a result, this material cannot be processed into molded articles with good mechanical properties. However, the polycarbonate beads of the present invention produced by the method of the present invention have substantially intact foam cells, wherein the quality of the foam structure is significantly improved within a particularly preferred range of reactive group equivalents in the formulation. Example

[0097] 1. Description of raw materials and test methods a) Raw materials polymer: PC 1: Bisphenol A-based aromatic polycarbonate, MVR of 6 cm³ / (10 min) (300℃ / 1.2 kg, ISO 1133-1:2011), softening temperature (VST / B 120; ISO 306:2013) of 149℃. Tb determined according to DIN EN ISO 11357-1:2017. g The temperature was 148℃. M was measured as described below. wAt 28 kDa (MALLS), it has a concentration of approximately 30900 g / mol. It contains 0.06% heat stabilizer and 0.1% UV stabilizer. (The last sentence appears to be incomplete and possibly refers to a different product.) 1 The OH end group content determined by 1H NMR spectroscopy using dichloromethane as solvent at room temperature (as described above) was 470 ppm.

[0098] Produced via melt condensation (SPC) method.

[0099] PC 2: Bisphenol A-based aromatic polycarbonate with an MVR of 6 cm³ / (10 min) (300 °C / 1.2 kg, ISO 1133-1:2011) and a softening temperature (VST / B 120; ISO 306:2013) of 150 °C. Tb was determined according to DIN EN ISO 11357-1:2017. g The temperature was 148℃. M was measured as described below. w At 28 kDa (MALLS), it is approximately 30900 g / mol. (By...) 1 The OH end group content was determined by 1H NMR spectroscopy using dichloromethane as a solvent at room temperature (as described above): 60 ppm.

[0100] Produced by the phase interface condensation (LPC) method.

[0101] Chain extender 1: A commercially available multifunctional chain extender (Joncryl ADR 4468) manufactured by BASF SE, based on a styrene / acrylic acid-based polymer containing reactive epoxy groups, with an average molecular weight (calibrated with polystyrene by gel permeation chromatography in o-dichlorobenzene at 150°C) M w = 7250 g / mol, epoxy equivalent weight is 310 g / mol, glass transition temperature T determined according to DIN EN 1877-1:2000-12 g The temperature is 59℃, and the decomposition temperature is 350℃, as determined according to DIN EN ISO11357-1:2017.

[0102] b) Perform the method for the embodiments The method of this invention can, in principle, be carried out using various machine setups as described above. The experiments described below are conducted using structures i), ii), and iii) a twin-screw extruder-gas metering system-single-screw extruder-melt pump-underwater granulation, as follows: Figure 1As shown. Example i) describes successful pellet production within the scope of the claims; Example ii) describes pellet production failure due to chain extender concentration exceeding the maximum value; Example iii) describes pellet production failure due to the absence of reactive components; Example iv) describes an experimental series using the same structure and process parameters as i), but with the OH concentration (ppm) of the PC melt gradually decreasing while the reactive components remained constant; Example v) describes successful pellet production using an alternative structure: twin-screw extruder - static mixer / heat exchanger - melt pump - underwater granulation.

[0103] i) A 43D twin-screw extruder from Reifenhäuser (Trösdorf, Germany) was operated at a throughput of 35 kg / h, profile temperatures of 100-160°C (positions 1-3), 240°C (position 4) to 280°C (positions 5-10), and a speed of 100 rpm. Chain extender 1 was added to the PC 1 melt at a low concentration of 0.7 wt%. This corresponds to an OH:epoxy molar ratio of 1:0.82 (mol / mol). The melt temperature was 10-20°C higher than the casing temperature. A blowing agent was added at position 6 via Maximator (Maximator GmbH, Germany) and / or via a metering station (Lewa GmbH, Germany), with a CO2 content of 1.2-1.5 wt%. From position 5, the pressure profile in the twin screw gradually increased from 45 bar to 310 bar at the extruder tip. The melt was conveyed to the single-screw extruder (Reifenhäuser) via a delivery pipe (290°C). The extruder also operates at a continuous casing temperature of 280°C, a throughput of 35 kg / h, and a rotational speed of 26 rpm. The melt pressure is gradually reduced via the screw to the melt pump (from 250 bar to 120 bar). The melt pump operates under pressure control at a back pressure of 110 bar and a temperature of 280°C. During this process, the pressure downstream of the melt pump is 160-180 bar (pressure at the orifice plate). The distributor and orifice plate temperatures are also set to 280°C, and the melt temperature is (T... g +140℃) to (T g +150℃). The UWP (EUP 50) and orifice plate are manufactured by ECON GmbH (Austria). The orifice plate consists of five single-hole inserts with a diameter of 2.2 mm and a die slot width of 3.49 mm. The residence time of the melt between the inlet and outlet is approximately 7-10 minutes. At the outlet, the melt is separated by a rotating six-blade blade at 1500 rpm and passed through a water circuit (28m) at a temperature of 70-80℃. 3 The particles are conveyed out at a pressure of 8-10 bar. The resulting particles are spherical with an apparent density of 150-180 g / L and can be well welded within a pressure range of 8-10 bar.

[0104] ii) The Reifenhäuser 43D twin-screw extruder (Trossdorf, Germany) operates at a throughput of 17 kg / h, profile temperatures of 160-240°C (positions 1 to 3), 260-270°C (positions 4 and 5) to 280°C (positions 6-10), and a speed of 86 rpm. Additionally, a high concentration of chain extender 1 (1.5 wt%) is added. This corresponds to a reactive group ratio of OH:epoxy of 1 mol:1.78 mol. The melt temperature is 10-20°C higher than the casing temperature. The blowing agent, with a CO2 content of 2-2.3 wt%, is added at position 6 via Maximator (Maximator GmbH, Germany) and / or via a metering station (Lewa GmbH, Germany). From position 5, the pressure profile in the twin screw gradually increases from 67 bar to 250 bar at the extruder tip. The melt is conveyed to the single-screw extruder (Reifenhäuser) via a delivery pipe (290°C). The extruder also operates at a continuous casing temperature of 280°C, a throughput of 17 kg / h, and a rotational speed of 15 rpm. The melt pressure is gradually reduced via the screw to the melt pump (from 250 bar to 115 bar). The melt pump operates under pressure control at a back pressure of 110 bar and a temperature of 280°C. During this process, the pressure downstream of the melt pump is 230 bar (pressure at the orifice plate). Similarly, the distributor temperature is set to 280°C, and the orifice plate temperature is set to 320°C. The melt temperature is (T... g +150℃) to (T g +160℃). Due to the over-metering of reactive components, the throughput must be significantly reduced and the orifice plate temperature increased to prevent emergency shutdown due to critical equipment pressure. The UWP (EUP 50) and orifice plate are manufactured by ECON (Econ GmbH, Austria). The orifice plate consists of five single-hole inserts with a diameter of 2.2 mm and a die groove width of 15 mm. The residence time of the melt between the inlet and outlet is approximately 7-10 minutes. Downstream of the outlet, the melt is separated by a rotating 6-blade blade at 1500 rpm and passed through a water circuit (28m) at a temperature of 70-80℃. 3 The process is unstable, resulting in collapsed and shrunken particles (apparent density > 500 g / L) that cannot be welded.

[0105] iii) A Reifenhäuser 43D twin-screw extruder (Trossdorf, Germany) was operated at a throughput of 15 kg / h, profile temperatures of 160-240°C (positions 1-3), 260-270°C (positions 4 and 5) to 280°C (positions 6-10), and a speed of 85 rpm. This experimental series was conducted without the use of chain extenders. The melt temperature was 10-20°C higher than the casing temperature. Gas was added at position 6 via a Maximator (Maximator GmbH, Germany) and / or via a metering station (Lewa GmbH, Germany), with a CO2 content of 2% to 2.3% by weight. From position 5, the pressure profile in the twin screw gradually increased from 73 bar to 94 bar at the tip of the extruder. The melt was fed into the single-screw extruder (Reifenhäuser) via a delivery pipe (290°C). The extruder was also operated at a continuous casing temperature of 280°C, a throughput of 15 kg / h, and a speed of 15 rpm. The melt pressure is gradually reduced to the melt pump via the screw (from 94 bar to 87 bar). The melt pump operates under pressure control at a back pressure of 110 bar and a temperature of 280°C. During this process, the pressure downstream of the melt pump is 90 bar (pressure at the orifice plate). The temperature of the distributor and orifice plate is set to 280°C, and the melt temperature is (T... g +140℃) to (T g +150℃). Despite the lack of reactive components, process control is kept as close as possible (ii). The UWP (EUP 50) and orifice plate are manufactured by ECON (Econ GmbH, Austria). The orifice plate consists of five single-hole inserts with a diameter of 2.2 mm and a die groove width of 15 mm. The residence time of the melt between the inlet and outlet is approximately 7-10 minutes. Downstream of the outlet, the melt is separated by a rotating six-blade blade at 1500 rpm and passed through a water circuit (28m) at 70-80℃. 3 / h) is conveyed out. Under given conditions, the production process cannot proceed, resulting in the formation of almost unexpanded material with 500-600 kg / m³. 3 Extremely high density spherical particles. They are difficult or even impossible to weld together to produce parts.

[0106] iv) The Reifenhäuser AG (Trösdorf, Germany) 43D twin-screw extruder was operated at a throughput of 35 kg / h, profile temperatures of 100-160°C (positions 1-3), 240°C (position 4) to 280°C (positions 5-10), and a speed of 100 rpm. Chain extender 1 was added at a fixed concentration of 0.7%. In this series, the molar ratio of reactive groups of the second polycarbonate, OH:epoxy, varied, more precisely, between 1:0.82 and 1:1.47 (OH:epoxy, in molars for each case) (Table 1). The melt temperature was 10-20°C higher than the die temperature. The blowing agent was added at position 6 via Maximator (Maximator GmbH, Germany) and / or via a metering station (Lewa GmbH, Germany), with a CO2 content of 1.3% by weight. From position 5, the pressure profile in the twin screw gradually increased from 45 bar to 270 bar at the extruder tip (at 100% SPC). Due to the addition of PC-2, a PC component with low OH end groups, the pressure curve initially rises slightly to 275 bar at a 10% content. Further addition of PC component with low OH end groups exceeding 20% ​​by weight causes the pressure curve to decrease. The melt is fed into a single-screw extruder (Reifenhäuser) via a delivery pipe (290°C). The extruder also operates at a continuous casing temperature of 280°C with a throughput of 35 kg / h and a speed of 26 rpm. The melt pump operates under pressure control at a back pressure of 110 bar and a temperature of 280°C. The pressure downstream of the melt pump is determined by the reactive polycarbonate content and reduced by the proportion of external matrix (see Table 1). The distributor and die are also set to a temperature of 280°C, with a melt temperature ranging from Tg + 140°C to Tg + 150°C. The UWP (EUP 50) and orifice plate are manufactured by ECON GmbH (Austria). The orifice plate consists of five single-hole inserts, each 2.2 mm in diameter and with a die groove width of 3.49 mm. The residence time of the melt between the inlet and outlet is approximately 7-10 minutes. Downstream of the outlet, a rotating six-bladed blade at 1500 rpm separates the melt and passes it through a water circuit at 70-80°C (28m). 3 The particles are conveyed out at a rate of / h. The roundness of the particles gradually decreases, and the foam density gradually increases.

[0107] If the concentration of OH end groups in the polycarbonate is too low, more precisely <350 ppm, the production process fails when the molar ratio of reactive groups (hydroxyl:epoxy, each in moles) is 1:1.12 (outside the scope of the claims). The molecular weight cannot be increased sufficiently so that the viscosity of the melt mixture and the pressure at the orifice plate are no longer sufficient to form a uniform granular foam. The resulting granules have a more elongated shape and inhomogeneity in shape and appearance at higher foam densities (lower pressure drop) (due to lower viscosity and thus altered flow properties) (Table 2). Within the 7-11 bar pressure range of the claims, the granules cannot be welded sufficiently well. These parts lack closed surfaces and have numerous shrinkage cavities / cavities, resulting in poor thermal conductivity, increased rigidity, significantly reduced maximum flexural strain, and poor puncture resistance (Tables 2 and 3).

[0108] v) A Coperion ZSK 26 MC twin-screw extruder (model 44 D) operates at a throughput of 20 kg / h at a casing temperature of 280°C (from the melt zone), 60% torque, and a rotational speed of 230 rpm. Chain extender 1 is added at a low concentration of 0.9%. This corresponds to a reactive group molar ratio of OH:epoxy of 1:0.9-1.1 for the PC component in the composition, and a particularly preferred OH end-group content of 450 to 550 ppm, thus falling within the scope of this invention. In the casings 7 to 10 of the twin-screw, blowing agent CO2 is introduced at a concentration of 1.2% to 1.5% by weight via a gas metering station (Promix Solutions GmbH, Germany). The melt temperature of the gas-polymer mixture is 280°C (=Tg + 130°C). The homogenized gas-polymer mixture is forcibly conveyed to a static mixer. The residence time in this mixer is 6-8 minutes. The mixer is also operated at a profile temperature of 280°C. At the end of the static mixer, a melt pump from Maag-Germany GmbH regulates the back pressure at the melt pump inlet to 90 bar. The pressure upstream of the orifice plate is 198 bar. The melt is granulated using an underwater granulator (Gala). The gas-melt mixture is forced through an orifice plate with two holes into a water-filled cutting chamber. The orifice diameter in the orifice plate is 2.4 mm. In the cutting chamber, the melt is cut into pellets by rotating blades at a speed of 3500 rpm. The pellets foam due to the pressure drop downstream of the orifice plate. A pressure of 2 bar is applied to the process water flowing through the cutting chamber at a temperature of 80-90°C. Finally, the pellets are dried and separated in a centrifuge. The resulting granules are spherical, with a smooth and uniform surface, an apparent density of 220-250 g / L, and are very weldable.

[0109] c) Testing methods The produced particles were processed into parts with a density of 200 ± 10 kg / m³ and dimensions of 300 × 200 × 15 mm³ using a Teubert TVZ162 / 100PP molding machine (Teubert Maschinenbau GmbH, Germany). For EPC, the required welding pressure was 7 to 10 bar. Finally, the properties of the parts were determined. To visualize the morphology, the graphite sputtered samples were measured using a scanning electron microscope (SEM, model: JEOL JSM-6510, Borken, Germany). Measurements of 15 × 15 × 15 mm samples were performed using a Gabo Eplexor 500N from NETZSCH GmbH (Selb, Germany) in pressure mode. 3 The samples underwent dynamic mechanical analysis (DMA) at a temperature range of -25 to 250 °C, a heating rate of 1 K / min, a pressure regulation mode, and amplitudes of 5% (static) and 2% (dynamic) of the sample height at a frequency of 1 Hz. Mechanical characterization was performed using pressure testing, tensile testing, three-point bending testing (room temperature, 80 and 110 °C), and puncture testing (RT). Samples with geometric dimensions of 15 × 15 × 15 mm were tested using a Zwick Z020 universal testing machine (Ulm, Germany) from Zwick & Roell, according to DIN EN ISO 844:2014-11. 3 The samples were pressure tested under a 10 kN force sensor up to 60% compression. Three-point bending tests were performed using the same universal testing machine at a rate of 10 mm / min and a 20 kN force sensor, based on ISO 1209-1:2007-05 standard. To eliminate the influence of the tight boundary layer, the samples were peeled, and the geometry was adjusted to 120 × 25 × 10 mm. 3 Tensile measurements of the components were performed using a Zwick Z050 universal testing machine (Zwick & Roell, Ulm, Germany) based on ISO 1926:2009. The sample dimensions were 140 (30+80+30) × 80 × 15 mm. 3 The force sensor was 20 kN. Puncture characteristics were tested using a Fractovis Plus drop hammer testing machine from Instron Ceast (Pianezza, Italy), with a maximum energy of 40 J and a puncture speed of 4.4 m / s (based on DIN EN ISO 6603-2:2002-04). The sample size was 60 × 60 × 15 mm. 3 All mechanical properties were tested at room temperature, 80°C, and 110°C, with a 10-minute conditioning step preceding each measurement. All components were tested at approximately 200 kg / m³. 3The test was conducted at the same density. Thermal conductivity was measured using a NETZSCH (Selb, Germany) HFM 446 Lambda measuring instrument at -10℃, 10℃, 25℃, 50℃, and 70℃.

[0110] The average molecular weight (Mw) of PC-1 and PC-2 was determined by gel permeation chromatography. Calibration was performed against bisphenol A polycarbonate standards using dichloromethane as the eluent. Calibration was performed using linear polycarbonates (formed from bisphenol A and phosgene) with known molar mass distributions from PSS Polymer Standards Service GmbH, Germany, according to Method 2301-0257502-09D (2009, German) of Currenta GmbH & Co. Leverkusen. The eluent was dichloromethane. The column assembly was cross-linked styrene-divinylbenzene resin. Analytical column diameter: 7.5 mm; length: 300 mm. Column material particle size: 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 was performed using a UV detector. For highly branched polycarbonates formed by increasing molar mass through the addition of chain extenders, determination was performed using GPC-MALLS as described above. All highly branched / partially crosslinked fractions (XYZ% insoluble) are insoluble, therefore existing analytical methods may not be able to characterize particularly high molecular weight fractions. This is a problem known to those skilled in the art, and thus the accuracy of molar mass determination in highly branched polymers is limited in its precision. The above molar mass ranges are accordingly based on the dichloromethane-soluble fraction.

[0111] The OH value of the polymer is determined by... 1 1H NMR spectroscopy at room temperature, using dichloromethane as a solvent, was determined by evaluating the integral ratio of the signals at 6.68 ppm (two aromatic protons adjacent to the OH group of the phenol) and 1.68 ppm (six methyl protons of the bisphenol A unit).

[0112] 2. Results Composition and Analysis Table 1: Analytical results of detailed composition and molar ratio studies according to Example iv). E-1 E-2 E-3 V-4 V-5 V-6 PC1 [weight%] 99.3 89.3 79.3 69.3 59.3 49.3 PC2 [weight%] 0 10 20 30 40 50 PC1 throughput [g / h] 34760 31280 27810 24330 20806 17380 The end pressure of extruder A [bar]. 270 275 250 288 189 176 Orifice plate pressure [bar] 190 184 177 170 134 122 OH group content, based on total weight of aromatic polycarbonate [ppm] 470 429 387 346 305 264 The molar ratio (1:x) of reactive OH groups (PC) to chain extender reactive groups. 0.82 0.90 1.00 1.12 1.27 1.47 <![CDATA[M from GPC w [g / mol]]]> 50180 52870 95690 93175 71691 50210 <![CDATA[M from GPC-MALLS w [kDa]]]> 158 168 206 207 139 107 <![CDATA[Particle density [kg / m 3 > 197 234 265 271 260 253 Average cell diameter [µm] 100±47 129±77 139±66 193±99 19± 117 206±134 <![CDATA[Cell density [cells / cm 3 > <![CDATA[8.88∙10 5 ]]> <![CDATA[4.12∙10 5 ]]> <![CDATA[3.48∙10 5 ]]> <![CDATA[1.47∙10 5 ]]> <![CDATA[1.33∙10 5 ]]> <![CDATA[1.18∙10 5 ]]> Foam bonding no no no yes yes yes

[0113] Table 2: Detailed characteristic values ​​of pressure, bending, and puncture tests in the comparative study of the EPC granular foam components in Example iv). EPC(E-1) EPC(V-4) <![CDATA[Component density [kg / m3 > 200±10 230±15 Compression modulus [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 Puncture force [N] 844±29 467±53 Total energy [J] 21.2±3 12.2±2 Total deformation [mm] 33.9 28.4±7 Note: The foam density of the components from EPC (V-4) is 230 kg / m³. 3 The eigenvalues ​​here are the original values, in order to... To achieve simple % standardization, a coefficient of 0.85 must be used in the calculation.

[0114] Table 3: Complete thermal conductivity data for EPC (E1) and (V4). # Thermal conductivity data of the unexpanded starting material.

Claims

1. A method for producing expanded polycarbonate beads, comprising the following steps: a) Provides an aromatic polycarbonate-based composition, wherein, based on the total weight of the aromatic polycarbonate, the aromatic polycarbonate has an OH end-group content of at least 350 ppm, the content being determined by... 1 The 1H NMR spectroscopy method uses dichloromethane as a solvent for determination at room temperature. b) The aromatic polycarbonate-based composition is mixed with a chain extender suitable for OH groups at a molar ratio such that 1 mol of OH end groups of the carbonate uses 0.64-1.10 mol of reactive groups of the chain extender. c) Provide a mixture in a plasticized state. d) Incorporate a physical foaming agent into the melt. e) At temperature T, T1 = (T g +110℃) to T2= (T g The plasticized mixture is subjected to granular foaming extrusion at +170℃, wherein T g It is the glass transition temperature of the composition based on aromatic polycarbonate. f) Granulate the melt containing the foaming agent.

2. The method of claim 1, wherein carbon dioxide is used as a foaming agent.

3. The method according to claim 1 or 2, wherein the method is performed in a continuous operation.

4. The method according to any one 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 according to ISO 1133:2012-3 (test temperature 300 °C, mass 1.2 kg).

5. The method according to any one of the preceding claims, wherein the granulation is performed as granulation in a liquid medium, as thermal shearing, or as granulation under air.

6. The method according to any one of the preceding claims, wherein the granulation is performed as unpressurized underwater granulation.

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

8. The method according to any one of the preceding claims, wherein 0.1-2.3% by weight of a physical foaming agent is incorporated in step d, wherein the amount is based on the total weight of the aromatic polycarbonate-based composition and the chain extender.

9. The method according to any one of the preceding claims, wherein the aromatic polycarbonate in the composition from step a has an OH end-group content of 350 to 600 ppm based on the total weight of the aromatic polycarbonate, the content being determined by... 1 The H NMR spectroscopy method uses dichloromethane as a solvent for determination at room temperature.

10. The method according to any one of the preceding claims, wherein the aromatic polycarbonate in the composition from step a has an OH end group content of at least 380 ppm based on the total weight of the aromatic polycarbonate, the content being determined by... 1 The H NMR spectroscopy method uses dichloromethane as a solvent for determination at room temperature.

11. The method according to any one of the preceding claims, wherein steps b and d are performed concurrently in time.

12. The method according to any one of claims 1 to 10, wherein steps a to f are performed in the stated order.

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

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

15. A method for producing molded articles from polycarbonate beads according to claim 14, wherein a slit method or a pressure filling method is used.

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