Method for producing post-foaming polycarbonate beads, and corresponding polycarbonate beads

Abstract

The present invention relates to a method for producing re-foaming polycarbonate beads and the corresponding beads themselves, which can be used as propellant-free beads for producing molded parts, and even molded parts having complex 3D shapes, in a drop-in technique at an average pressure of 4 to 6 bar in a steam molding machine already used in EPP manufacturing, and which result in molded parts having an excellent dense and closed surface structure.

Description

[Technical Field]

[0001] This invention relates to post-foaming polycarbonate beads (particle foams), a manufacturing process for these polycarbonate beads, and molded articles obtained from these polycarbonate beads, as well as the corresponding manufacturing processes. [Background technology]

[0002] Particulate foams, and in this specification in particular EPS, EPP, and E-TPU, are becoming increasingly important. Modern technology now makes it possible to manufacture particulate foams of reliable quality and to use these foams to produce parts with advantageous properties. Their lower bulk density compared to "simple" thermoplastics opens up new application areas for foam materials or allows conventional applications to be achieved with significant weight reduction. Therefore, foamed thermoplastics are attractive materials, especially for lightweight applications, provided that the application-specific properties are sufficiently good. Recent mold developments have made it possible to manufacture visible parts made of foamed thermoplastics that are significantly lighter while having a surface appearance that makes them a true substitute for corresponding injection-molded parts. Due to their low material consumption, foam materials are also attractive from a sustainability standpoint, and furthermore, as an additional effect when used as thermal insulation or soundproofing material for noise reduction, they can generally contribute to energy savings due to their good thermal insulation properties.

[0003] There are already existing literature descriptions of polycarbonate particulate foams. Particulate foams made from engineering thermoplastics are of interest in the automotive industry, for example, due to their properties such as high thermal stability and good fire resistance. EPC is a particulate foam for high-temperature applications where conventional polymer foams such as EPP do not function. Patent Document 1 describes a process for producing polycarbonate foam from polycarbonate, in which a transesterification catalyst is added to aromatic polycarbonate in combination with aromatic polycarbonate acid or water, optionally together with aliphatic hydroxycarboxylic acid and / or aliphatic alcohol. This results in controlled partial decomposition of polycarbonate accompanied by the release of CO2, which helps to foam the remaining polycarbonate. The polycarbonate foam described in Patent Document 1 has a density of approximately 0.4 g / cm³. 3 ~0.8g / cm 3 It has a density of .

[0004] Patent Document 2 describes polyester foams and also explicitly considers polycarbonate foams that have good processability in addition to low density. For the production of these particulate foams, a starting polymer material is selected in which the degree of crystallinity, as reflected by the enthalpy of fusion, glass transition temperature, and melting temperature is within a certain range. The process for producing the particulate foam includes providing the corresponding starting polymer component in a molten state, mixing a blowing agent component and optionally one or more additives into the molten material, extrusion, and pelletizing the blowing agent-containing molten material in water under high pressure of 1 bar to 20 bar. Patent Document 2 also describes a principled option of stabilizing the extrusion operation by increasing the molecular weight, for example by adding a chain extender, but does not specify the amount. Furthermore, no further requirements are imposed on the polymer used in Patent Document 2.

[0005] Patent Document 3 describes a process for producing foamed particles from aromatic polycarbonate by extruding aromatic polycarbonate, pelletizing it, impregnating it with carbon dioxide as a foaming agent, foaming the particles, and then molding the particles to obtain a foamed molded product.

[0006] The processing of particulate foam containing polycarbonate beads into molded articles can be carried out through several processes, for example, by variothermal means (thermal means by heating) or by an established steam process, preferably a steam process as specified herein. In the steam process, pressurized steam is used in a steam molding machine, i.e., the temperature in the steam is increased by high pressure, so that the particle surface is partially melted or softened, thereby resulting in interdiffusion of polymer chains between different beads and consequently the aggregation of the beads. For high welding quality between polycarbonate beads, steam pressures of 7 to 11 bar (165.0°C to 184.1°C), more preferably 8 to 10 bar (170.4°C to 179.9°C), have been required for EPC. Good cohesiveness between particles and a low proportion of macropores / gaps, i.e., cavities between particles in the part due to insufficient filling, are necessary for the good mechanical properties of the resulting molded article. Homogeneous production of molded articles is ensured by overfilling the mold, but this is limited to simple shapes. Therefore, it remains impossible to mold complex 3D parts from polycarbonate beads.

[0007] Molding machines already in practical use for EPP (expanded polypropylene) or EPS (expanded polystyrene) can be divided into three operating ranges: "low pressure" up to 2 bar, "medium pressure" 3 to 10 bar, and "high pressure" 11 to 20 bar. Low-pressure molding machines reach a temperature of 120°C at a maximum vapor pressure of 2 bar and are suitable only for welding EPS. In the case of steam molding machines, firstly, there is a correlation between energy consumption, and therefore operating costs, and the operating pressure range; secondly, the vapor pressure determines the vapor temperature and therefore the processability of the polymer. For this reason, welding service providers and their molding machines specialize in processing EPP in a pressure range of 3 to 6 bar, usually 3 to 4 bar. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] German Patent Application Publication No. 4100200 [Patent Document 2] European Patent Application Publication No. 2603549 [Patent Document 3] European Patent Application Publication No. 3858906 [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, the challenge was to provide polycarbonate beads that can form high-quality molded articles, and especially high-quality molded articles with complex 3D molded article shapes, by processing with steam at a moderate vapor pressure in the range of 4 bar to 6 bar. The vapor pressure in the mold is preferably determined by a pressure sensor in accordance with DIN 16086:2006-01. [Means for solving the problem]

[0010] Surprisingly, it has been newly discovered that molded articles, particularly 3D molded articles, made from "polycarbonate beads" (polycarbonate particle foam) can be obtained at moderate vapor pressures of 4 to 6 bar, especially 4 bar (= absolute pressure of water vapor), only when the optimal ratio between the molecular weight of the aromatic polycarbonate present in the polycarbonate beads and the branched polymer topology is established through a temperature and residence time-dependent reaction with a chain extender, and the beads are frozen in an entropically non-equilibrium state, which is achieved by "quenching," i.e., rapid cooling. It is hypothesized that the polymer chains in the beads obtained by the process of the present invention are aligned by shear and temperature and have oriented polymer chains frozen in this state. When energy is again supplied, here by vapor, the polymer chains return to an entropically more favorable state of entangled polymers with random orientation of chains.

[0011] The chain extender makes it possible to achieve a high melting temperature T, T1 = (T g +110℃)~T2=(T g (+170℃) (T g Post-foaming can only be achieved by reactive particle foaming extrusion at the glass transition temperature of aromatic polycarbonate (T), and possibly by the immobilization of the branched polymer topology on the particle surface, which is in a sheared and oriented entropically non-equilibrium state. Post-foaming of particles in the process of steam welding is made possible by relaxation of entropically unfavorably immobilized branching / crosslinking on the particle surface of polycarbonate beads, without further post-treatment and especially without subsequent gas filling. Those skilled in the art will recognize that "particle foaming extrusion" in the prior art is a complete or partial extrusion process involving the addition of a foaming gas and the subsequent generation of foamed particles by pelletizing and cooling, wherein, in the case of amorphous thermoplastics, the melting temperature at the nozzle is T g +10℃~T g +70℃(T gIt will be understood to mean those carried out at the glass transition temperature of the polymer material). In the present specification, both the content of the OH end groups of the aromatic polycarbonate used and the ratio of the OH end groups to the reactive groups of the chain extender play an important role, similar to the residence time of the reactive mixture of the aromatic polycarbonate and the chain extender in the molten state.

[0012] Therefore, the present invention provides a) Continuous particle foam extrusion of a plasticized mixture in an extrusion process, wherein the mixture comprises the following components: i) an aromatic polycarbonate having a content of OH end groups of at least 350 ppm as measured by 1H NMR spectroscopy using dichloromethane as a solvent at room temperature, based on the total weight of the aromatic polycarbonate, and 1 an aromatic polycarbonate, and ii) a chain extender suitable for OH groups, wherein the aromatic polycarbonate and the chain extender suitable for OH groups are used in a molar ratio such that 0.64 mol to 1.10 mol of reactive groups of the chain extender are used per 1 mol of OH end groups of the polycarbonate, and iii) a physical foaming agent, and containing T1 = (T g + 110 °C) to T2 = (T g + 170 °C) (where T g is the glass transition temperature of the aromatic polycarbonate) at a temperature T of the plasticized mixture, a continuous particle foam extrusion step in which the residence time of the aromatic polycarbonate and the chain extender suitable for OH groups in the molten state is at least 4 minutes, and b) a subsequent underwater pelletizing step of the foam-containing melt at a water temperature of T3 = (T g - 90 °C) to T4 = (T g - 55 °C) (where T g is the glass transition temperature of the aromatic polycarbonate) under non-pressurized water or under pressurized water up to a maximum of 3.5 bar, to produce post-foamable foamed polycarbonate beads.

[0013] The final pelletizing process yields foamed polycarbonate beads that, after a gas exchange, are free of the blowing agent. Therefore, the final product obtained from the above process is foamed polycarbonate beads free of the blowing agent. Removal of any remaining blowing agent present at the time of pelletizing occurs without further intervention during simple storage of the beads after the process; typically, less than an hour is sufficient for the beads to become completely free of the blowing agent, i.e., for complete gas exchange to occur. However, it is equally possible to remove the blowing agent more rapidly by exposing the beads to high temperatures in a controlled manner. Storage at high temperatures of 120°C for several days does not adversely affect the subsequent post-foaming properties during the vapor diffusion welding process.

[0014] The OH-terminal group content was determined by evaluating the ratio of the integral signals at 6.68 ppm (two aromatic protons in the ortho position relative to the phenol OH group) and 1.68 ppm (six methyl protons of the bisphenol A unit), using dichloromethane as the solvent at room temperature. 1 It is measured by 1H NMR spectroscopy.

[0015] The glass transition temperature is determined according to DIN EN ISO 11357-1:2017.

[0016] "Plasticizing mixture" means a polymer molten material in which its constituent components are uniformly distributed. The polymer molten material can be, for example, taken directly from the polymerization reactor as newly polymerized material, or introduced directly from there to a mixing extruder. In the mixing extruder, chain extenders, blowing agents, and optionally additives are finally introduced at various points. The given temperature range for the plasticizing mixture means the temperature range in which the molten material exists from plasticization until it exits the nozzle. For example, it will be clear that even if the temperature of the intake zone of the extruder is lower, it is still within the scope of the present invention. Similarly, as long as the temperature of the final zone in particle foaming extrusion is within the given range, the presence of one or more higher temperature zones somewhere in the extruder does not deviate from the overall concept of the present invention. However, it is preferable that particle foaming extrusion is performed only in zones within the specified temperature range.

[0017] Unless explicitly stated otherwise, all amounts expressed in ppm in this invention should be considered as weight ratios.

[0018] In accordance with the present invention, "up to" and "maximum" mean that the given range includes the respective limit values.

[0019] There are minimum values ​​for the amount of OH-terminal groups and even the concentration of chain extenders, but in the case of particulate foam production, T1 = (T g +110℃)~T2=(T g (+170℃), preferably T1=(T g (T)~T2=(T g (+160℃), more preferably T1=(T g +130℃)~T2=(T g There is also a maximum concentration for foam extrusion at high melting temperatures T in the extruder and nozzle (=molding outlet opening) in the range of +150℃, which is 200 kg / m³ determined according to the buoyancy principle according to DIN EN ISO 845:2009-10. 3 ~350 kg / m 3 Beads are manufactured for polycarbonate molded articles having good mechanical properties within a density range.

[0020] The number of OH groups in aromatic polycarbonate significantly affects whether the resulting molded article can produce beads with good mechanical properties at low density. Too many OH groups in the polycarbonate leads to excessively high reactivity, ultimately resulting in rearrangement reactions of the polycarbonate chains, a decrease in molecular weight due to excessively rapid branching and a corresponding excessively rapid increase in viscosity (excessively high shear input), and yellowing. On the other hand, too few OH groups in the polycarbonate result in insufficient or no reaction with the chain extender. However, this also means that a good particulate foam with sufficient mechanical properties cannot be obtained. Instead, the particulate foam will have many broken and collapsed cells.

[0021] According to the present invention, the OH-terminal group content of the aromatic polycarbonate used in the method of the present invention 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 and not aromatic polycarbonate-based compositions. To achieve such terminal group content, preferably more than 70% by weight of SPC is used based on the total weight of the aromatic polycarbonate used, more preferably at least 80% by weight of SPC is used based on the total weight of the aromatic polycarbonate used, and most preferably only SPC is used as the aromatic polycarbonate for the production of polycarbonate beads.

[0022] The concentration of the chain extender is also important. Too much chain extender leads to an unworkable material due to excessively high viscosity resulting from an excessive increase in the molecular weight of the polycarbonate. Too little chain extender does not result in a significant increase in molecular weight, and therefore an insufficient increase in pressure (the viscosity of PC is too low with no / insufficient chain extender at 300°C), ultimately resulting in inferior mechanical properties of the final molded article, given that the reaction between the chain extender and polycarbonate is a function of time and temperature. For example, in the case of bisphenol A homopolycarbonate, the foaming extrusion process is T 1ハウジング =T g +100℃~T 2ハウジング =T g Housing temperature T of +150℃ ハウジング , and about T after the foaming agent has been mixed and dissolved g The process is preferably carried out at a melting temperature T of +(110℃~170℃). Production of particulate foam without cooling results in dense, collapsed particles. Depending on the process control, cooling causes stabilization and solidification of the foam structure, leading to a rapid cessation of foam expansion. Higher temperatures in the process allow for the utilization of the full foaming potential of the formulation under cooling by compensating for excessively rapid cooling / solidification. However, at these temperature profiles, the pressure on the die plate without a chain extender is 80-90 bar. The use of a chain extender increases the pressure on the die plate to 140-180 bar, preferably 150-160 bar. Production of particulate foam is impossible under these process conditions (temperature) without appropriate chain extension and therefore without an additional increase in viscosity.

[0023] In order for the resulting polycarbonate beads to have good properties, it has been found that the molar ratio of the chain extender's reactive groups to 1 mole of polycarbonate OH-terminated groups is 0.64 mol to 1.10 mol, preferably 0.71 mol to 1.0 mol, more preferably 0.96 mol, even more preferably 0.8 mol to 0.9 mol, and especially 0.82 mol to 0.90 mol (in continuous processes, metered addition is performed based on the processing volume), which is essential for the present invention.

[0024] Preferably, the content of OH-terminated groups in the aromatic polycarbonate is such that when dichloromethane is used as the solvent at room temperature. 1 If the concentration is measured by 1H NMR spectroscopy between 400 ppm and 550 ppm, then 0.71 mol to 0.96 mol of reactive chain extender groups are used per mole of OH-terminal groups of polycarbonate.

[0025] It will be clear that the molar ratio of the OH-terminated groups of the polycarbonate to the reactive groups of the chain extender, as defined in the claims, needs to be adjusted according to process control. In continuous procedures, the adjustment based on the processing rate of the concentration (mol / h:mol / h ratio) is appropriately performed.

[0026] The use of chain extenders increases the molar mass of polycarbonate to a range of 40,000 g / mol to 230,000 g / mol, preferably 50,000 g / mol to 160,000 g / mol, which is related to an additional increase of about 60 to 100 bar of pressure on the die plate at the temperature in which the polycarbonate is in a plasticized state. Suitable chain extenders are, in principle, amines, carboxyl compounds, maleic anhydride modified compounds, epoxy functionalized compounds, oxazolines, carbodiimides, and / or functionalized polymers based on, for example, acrylates and / or styrene, having the corresponding functional groups. Such compounds can be used alone or in mixtures. Such groups are, for example, amine 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 that can react with the OH-terminal groups of polycarbonate to increase the chain length. Preferred chain extenders are particularly epoxy-functionalized compounds, most preferably epoxy-functionalized styrene-acrylic polymers, which are supplied from BASF SE, for example, as Joncryl additives, e.g., Joncryl ADR 4368, ADR 4400, ADR 4468. The amount / weight of the chain extender must be adapted to the aromatic polycarbonate so that 0.64 mol to 1.10 mol, preferably 0.71 mol to 1.0 mol, more preferably up to 0.96 mol, even more preferably 0.8 mol to 0.9 mol, and especially 0.82 mol to 0.90 mol of reactive groups of the chain extender are used per mole of OH-terminated groups of the polycarbonate. For example, if the amount of chain extender is obtained by starting with an aromatic polycarbonate having 350 ppm to 600 ppm of OH-terminated groups and reacting it with a chain extender having an epoxy equivalent of 310 g / mol, such as Joncryl ADR 4468, at a concentration of 0.4% to 1.2% by weight, preferably 0.5% to 1.0% by weight, more preferably 0.7% to 0.9% by weight, then the ratio of reactive groups in this range can be achieved based on the resulting overall composition (an aromatic polycarbonate-based composition, i.e., one containing the chain extender in addition to any blending partners and any additives).By controlling and adjusting the molar ratio from 1 mol:0.64 mol to 1.10 mol, a molecular weight range of 50,000 g / mol to 160,000 g / mol, preferably 155,000 g / mol, can be achieved as described.

[0027] The method of the present invention may be a one-step, two-step, or even three or more-step extrusion process. The reaction that increases molecular weight can be carried out through multiple extrusion steps with sufficient residence time. In the case of some steps, the residence time includes the cumulative time, i.e., the total time until discharge of the polymer-chain extender mixture in the molten state where the reaction that increases molecular weight can occur.

[0028] If the process is a two-step process, the molecular weight of the polymer is increased in the first extrusion step in the presence of a chain extender, yielding pelletized polycarbonate as the first product. In the second extrusion step, foaming is carried out with a physical blowing agent, preferably carbon dioxide, and as a result of subsequent pelletizing in water, the polycarbonate beads of the present invention are finally obtained.

[0029] According to the present invention, a minimum residence time of 4 minutes is assumed. Depending on the system configuration, the upper limit is due to the maximum processable viscosity. There is a maximum value for molecular weight increase reactions, which are a function of temperature and time. Theoretically, the mixture can be reacted completely. Therefore, the viscosity will be correspondingly high. In this regard, the system may stop due to excessively high viscosity, or the polymer chains may be mechanically broken again if operation continues. Residence times of up to 15 minutes, preferably up to 420 seconds, are typically manageable without problems.

[0030] The molten material, after being mixed with a foaming agent and dissolved, passes through the nozzle plate at the outlet opening of the extruder, generally T1=(T g +110℃)~T2=(T g (+170℃), preferably T1=(T g (T)~T2=(T g (+160℃), more preferably T1=(T g +130℃)~T2=(T gThe extrusion is performed at a molten material temperature T in the range of +150°C. The nozzle plate temperature is preferably T to further prevent the nozzle from freezing due to the cooling of the polymer molten material, thus ensuring constant polymer pelletization and achieving appropriate foaming expansion at the maximum expansion potential. g The temperature is set to +(130℃~150℃).

[0031] For single-hole nozzles, the diameter of the nozzle opening is preferably in the range of 0.8 mm to 3 mm, and more preferably in the range of 1.0 mm to 2.4 mm. For multi-hole nozzles, the nozzle diameter is preferably 0.4 mm to 0.8 mm, and more preferably 0.6 mm.

[0032] Pelletization is performed by a die plate at the outlet opening of the extruder, where the material is extruded and then cut to a certain length. Cutting to a certain length is achieved by a cutting device, which is typically located immediately downstream of the molding tool through which the material is extruded.

[0033] The pelletization of the molten material at the end of the process of the present invention is carried out by underwater pelletization at a pressure in a water circuit of 0 to 3.5 bar, preferably 1 to 2 bar, i.e., underwater pelletization is carried out without additional pressurization of water or at a pressurization of up to 3.5 bar. As the molten material exits the nozzle, the polycarbonate material undergoes a pressure drop of 140 to 180 bar, preferably 150 to 160 bar, to the pressure set in the water circuit of up to 3.5 bar, rather than a complete decompression to atmospheric pressure. The material does not foam as much as expected based on the amount of blowing agent available, but instead quenches in an entropically non-equilibrium state, which causes subsequent post-foaming of the beads. A physical blowing agent, such as carbon dioxide, expands the polycarbonate material as the gas diffuses from the polymer molten material. After a certain period of time, complete or near-complete gas exchange occurs, and as a result, only the normal air composition may be present in the foamed polycarbonate in pelletized form, i.e., polycarbonate beads. Therefore, polycarbonate beads "do not contain foaming agents."

[0034] For carrying out reactive particle foam extrusion, the following configurations with sufficient residence time can be used, but are not limited to these: a) Polymerization reactor / (static) extruder / mixer / gas metering system / melt pump / pelletizer b) Extruders (twin-screw / single-screw) / Gas metering systems / Pelletizers c) Extruders (twin-screw / single-screw) / Gas metering systems / Static mixers / Pelletizers d) Extruders (twin-screw / single-screw) / Gas metering systems / Heat exchangers / Pelletizers e) Extruders (twin-screw / single-screw) / Gas metering systems / Static mixers / Heat exchangers / Pelletizers f) Twin-screw extruders / Gas metering systems / Single-screw extruders / Pelletizers g) Twin-screw extruders / Gas metering systems / Single-screw extruders / Melt pumps / Pelletizers h) Twin-screw extruder / Gas metering system / Melting pump / Heat exchanger / Melting pump / Pelletizer i) Twin-screw extruders / gas metering systems / heat exchangers / melting pumps / pelletizers.

[0035] The extrusion process can be carried out in one or more stages.

[0036] In detail, the process can be carried out in various configurations. Key steps in the process include melting the aromatic polycarbonate composition, optionally adding a nucleating agent (talc, especially nanoscale talc, graphite, carbon black, pigment, etc.), administering a foaming agent via a liquid injection system (e.g., Lewa GmbH (Germany)) or a compression unit (high-pressure unit) (e.g., Maximator GmbH (Germany)), optionally cooling, e.g., appropriate die plate shaping, addition of reactive macromonomers, or pressure increase to the die plate via technical aids such as a breaker plate or melting pump (pressure is preferably increased by the addition of reactive macromonomers or the use of technical aids), and finally, chopping of pellets / beads via pelletizing in a liquid medium, hot chopping, or pelletizing in a gas (gas mixtures can also be used). Note that the liquid medium used here may be an aqueous medium, or alternative media such as glycerin or glycerol.

[0037] For carrying out the process of the present invention, a configuration comprising a twin-screw, a gas metering system, a melting pump, a heat exchanger, a second melting pump, and underwater pelletization is particularly preferred. In this case, the twin-screw is more preferably used for plasticizing the aromatic polycarbonate composition and mixing the physical blowing agent and the chain extender, and the heat exchanger is used for residence time and molecular weight increase reactions.

[0038] The metering and addition of the physicoblasting agent to the molten material, which contains aromatic polycarbonate and chain extender reacting throughout the entire process, is more preferably carried out in the last third of the first extrusion unit (depending on the structure). Mixing is preferably carried out so that the polymer molten material ultimately contains a uniformly distributed amount of the physicoblasting agent, where the proportion of the physicoblasting agent in the mixture is preferably 1.0% to 2.3% by weight, more preferably 1.2% to 1.7% by weight, more preferably 1.3% to 1.5% by weight, based on the total weight of the polymer molten material (= polycarbonate composition) and chain extender, and for N2, it 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.

[0039] To initiate foam cell formation for a finer and more homogeneous cell morphology, nucleating agents such as talc, particularly nanoscale talc, graphite, carbon black, and pigments are added at a low concentration of 0.1% to 1.0% by weight, more preferably 0.15% to 0.5% by weight, and more preferably 0.2% to 0.3% by weight, based on the overall composition obtained with the polycarbonate-based composition and chain extender.

[0040] In principle, any blowing agent commonly used for foaming thermoplastics can be used as a physical blowing agent. Examples here include propane, butane, n-pentane, and isopentane, but also include similar aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, aliphatic alcohols, carbon dioxide, nitrogen, compressed air, inert gases such as argon or helium, and others. "Air" at atmospheric pressure is not considered a blowing agent for the purposes of this invention. According to this invention, "compressed air" means air at a pressure higher than atmospheric pressure. Combinations of two or more of these 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 are not only free from toxicological and environmental concerns but also do not promote fire. Nitrogen, carbon dioxide, or mixtures thereof are particularly preferred, with carbon dioxide being the most preferred.

[0041] When 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 molten material containing the chain extender and additives (i.e., the chain extender in addition to the polycarbonate composition).

[0042] When carbon dioxide is used as a physical blowing agent, preferably 1.0% to 2.3% by weight, more preferably 1.2% to 1.7% by weight, and more preferably 1.3% to 1.5% by weight of carbon dioxide is used based on the polymer molten material containing the chain extender and additives.

[0043] The process of the present invention allows for the production of post-foamed polycarbonate beads, which, compared to conventional post-foamed beads, do not contain a foaming agent. According to the present invention, "beads" typically refer to foamed pellets (= granular foams) having a maximum density of 50% or less of the unfoamed starting material (aromatic polycarbonate composition). The use of granular foamed polycarbonate combines the lightweight and impact-resistant properties of the material with a higher continuous operating temperature (e.g., stability in cationic electrodeposition coating processes) compared to PP, ABS, PE, or PA6, enabling a significant reduction in the weight of some vehicle components, as well as a reduction in 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 wider range of application fields, particularly those requiring thermal insulation at high temperatures.

[0044] The present invention also provides post-foaming polycarbonate beads produced by the process of the present invention. Accordingly, the present invention provides weight-average molecular weight M of polycarbonate ranging from 50,000 g / mol to 160,000 g / mol, as determined by GPC measurement in dichloromethane calibrated against a bisphenol A polycarbonate standard. w A foamed polycarbonate bead without a foaming agent, wherein the foamed polycarbonate bead is post-foaming and exhibits post-foaming of 20% to 60% by volume when welded at 4 bar in a steam-based process without pretreatment of the beads, wherein the foamed polycarbonate bead is subject to the following conditions: Q = δ / M w = 3.20 × 10 -4 ~1.93 × 10 -3 (degrees·mol / g) (In the formula, δ is the complex shear modulus |G) * This is the phase angle in the Van Gurp-Palmen plot, determined at |=3000 Pa and a temperature of 240°C, where δ < 78.0 degrees, and M w This relates to foamed polycarbonate beads that do not contain foaming agents, as described above.

[0045] The present invention also provides a process for manufacturing molded articles from polycarbonate beads, particularly molded articles having complex 3D shapes, and corresponding molded articles.

[0046] The aromatic polycarbonate present in the foamed polycarbonate beads of the present invention, which do not contain a foaming agent, has a weight-average molecular weight of 50,000 g / mol to 160,000 g / mol, as determined by GPC in dichloromethane calibrated against a bisphenol A polycarbonate standard. The aromatic polycarbonate is the main component of the thermoplastic material constituting the polycarbonate beads of the present invention, obtained by the process of the present invention.

[0047] The starting material for the production of the beads of the present invention in the process of the present invention is an aromatic polycarbonate, preferably in the form of an aromatic polycarbonate composition. According to the present invention, "in the form of an aromatic polycarbonate composition" does not mean that an already formulated composition must be directly supplied to the extruder in which particle foaming extrusion is performed. While this is possible, it is also possible to supply the various components of the aromatic polycarbonate composition to the extruder via individual metering elements. "Aromatic polycarbonate composition" simply means that the material constituting the polycarbonate beads may be any desired advanced formulation in which appropriate additives are optionally added to polycarbonate.

[0048] In the context of the present invention, the term "aromatic polycarbonate" is considered to mean both aromatic homopolycarbonates and aromatic copolycarbonates. These polycarbonates may be linear or branched, as is known.

[0049] The polycarbonates present in the composition are prepared by known methods from dihydroxyaryl compounds, carbon dioxide derivatives, and optionally chain arresters and branching agents.

[0050] Details of the preparation of polycarbonate have been described in numerous patent specifications over the past 40 years. For example, Schnell, "Chemistry and Physics of Polycarbonates", Polymer Reviews, Volume 9, Interscience Publishers, New York, London, Sydney 1964, D. Freitag, U. Grigo, PR Mueller, H. Nouvertne, 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 PR Mueller "Polycarbonate" [Polycarbonates] in Becker / Braun, Kunststoff-Handbuch [Plastics Handbook], volume 3 / 1, Polycarbonate, Polyacetale, Polyester, Celluloseester [Polycarbonates, Polyacetals, Polyesters, Cellulose Esters], Carl Hanser Verlag Munich, Vienna 1992, pages 117 to 299.

[0051] Aromatic polycarbonates are prepared, for example, by an interfacial process reaction between a dihydroxyaryl compound and a carbonyl halogen, preferably phosgene, and / or an aromatic dihalogenated dicarbonyl, preferably a dihalogenated benzenedicarbonyl, optionally using a chain arrestor and optionally a trifunctional or higher branching agent. Similarly, they can also be prepared by reacting a dihydroxyaryl compound with, for example, diphenyl carbonate via melt polymerization. According to the present invention, it is preferable to use polycarbonates prepared by melt polymerization, the so-called "transesterification method." The polycarbonates used according to the present invention have 350 ppm to 600 ppm of OH-terminated groups, and this value refers to the polycarbonate as the polymer itself without additives. The amount of OH-terminated groups is based on the total amount of polycarbonate used. It is also possible to use a mixture of polycarbonates obtained by melt polymerization and polycarbonates obtained by the interfacial method, provided that the total concentration of OH-terminated groups in the polycarbonates used is within the specified range. However, it is particularly preferable to use only polycarbonates prepared by melt polymerization.

[0052] Dihydroxyaryl compounds suitable for the preparation of polycarbonates include, for example, hydroquinone, resorcinol, dihydroxydiphenyl, bis(hydroxyphenyl)alkane, bis(hydroxyphenyl)cycloalkane, bis(hydroxyphenyl)sulfide, bis(hydroxyphenyl)ether, bis(hydroxyphenyl)ketone, bis(hydroxyphenyl)sulfone, bis(hydroxyphenyl)sulfoxide, α,α'-bis(hydroxyphenyl)diisopropylbenzene, phthaliumidines derived from isatin or phenolphthalein derivatives, and their cyclic alkylated, cyclic arylated, and cyclic halogenated compounds.

[0053] Preferred dihydroxyaryl compounds include 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, 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)~(III): [ka] (In the formula, R' represents C1-C4 alkyl, aralkyl, or aryl, preferably methyl or phenyl, most preferably methyl, in each case.)

[0054] 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 dimethylbisphenol A, as well as bisphenols of formulas (I), (II), and (III).

[0055] These and other suitable dihydroxyaryl compounds are, for example, U.S. Patent Nos. 3028635, 2999825, 3148172, 2991273, 3271367, 4982014, and 2999846, German Patent Publication Nos. 1570703, 2063050, 2036052, 2211956, and 3832396, French Patent Publication No. 1561518, and the research paper "H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York" This is described in 1964, as well as in Japanese Patent Publication Nos. Sho 61 (1986)-62039, Sho 61 (1986)-62040, and Sho 61 (1986)-105550.

[0056] In the case of homopolycarbonates, only one type of dihydroxyaryl compound is used, while in the case of copolicarbonates, two or more types of dihydroxyaryl compounds are used.

[0057] Examples of suitable carbonate derivatives include phosgene or diphenyl carbonate.

[0058] Suitable chain-stopping agents that can be used in the manufacture of polycarbonates include monophenols. Examples of suitable monophenols include phenol itself, alkylphenols such as cresol, p-tert-butylphenol, isooctylphenol, cumylphenol, and mixtures thereof.

[0059] Preferred chain arrestors are linear or branched chains C1-C1 30 -A phenol monosubstituted or polysubstituted with an alkyl radical, preferably unsubstituted or tert-butyl substituted. Particularly preferred chain arresters are phenol, cumylphenol, and / or p-tert-butylphenol.

[0060] The amount of chain arrester used is preferably 0.1 mol% to 5 mol%, based on the moles of the dihydroxyaryl compound used in each case. The chain arrester can be added before, during, or after the reaction with the carbonic acid derivative.

[0061] Suitable branching agents are compounds with three or more functionalities known in polycarbonate chemistry, particularly those having three or more phenol OH groups.

[0062] Examples of suitable branching agents include 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'-methylbenzyl)-4-methylphenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane, tetra(4-hydroxyphenyl)methane, tetra(4-(4-hydroxyphenylisopropyl)phenoxy)methane, and 1,4-bis((4',4''-dihydroxytriphenyl)methyl)benzene, and 3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.

[0063] The amount of branching agent used is preferably 0.05 mol% to 2.00 mol%, based on the moles of the dihydroxyaryl compound used in each case.

[0064] The branching agent can be added either by forming an initial input in the aqueous alkaline phase with the dihydroxyaryl compound and the chain termination agent, or by dissolving it in an organic solvent before phosgenation. In the transesterification process, the branching agent is used together with the dihydroxyaryl compound.

[0065] Particularly preferred polycarbonates include homopolycarbonates based on bisphenol A, copolycarbonates based on 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and 4,4'-dihydroxydiphenyl, and copolycarbonates based on two monomers, bisphenol A and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, as well as formulas (I), (II), and (III): [ka] The polycarbonate is a homopolycarbonate or copolicarbonate derived from a dihydroxyaryl compound of a C1-C4 alkyl, aralkyl, or aryl group, preferably methyl or phenyl, most preferably methyl, and particularly from bisphenol A. Most preferably, the polycarbonate composition contains a bisphenol A-based polycarbonate, and the polycarbonate in the polycarbonate composition is very preferably a bisphenol A-based homopolycarbonate.

[0066] General formula (1a): [ka] (In the formula, R 5 This is hydrogen or C1-C4 alkyl, C1-C3 alkoxy, preferably hydrogen; methoxy or methyl. R 6 , R 7 , R 8 , and R 9 These are, independently, C1-C4 alkyl or C6-C 12 -aryl, preferably methyl or phenyl, Y consists of single bonds, -SO2-, -S-, -CO-, -O-, C1~C6-alkylene, C2~C5-alkylidene, and C6~C 12-Arylene (which may optionally be condensed to a further aromatic ring containing a heteroatom) or a C5-C6-cycloalkylidene radical which may be monosubstituted or polysubstituted with a C1-C4-alkyl group, preferably a single bond, -O-, isopropylidene, or a C5-C6-cycloalkylidene radical which may be monosubstituted or polysubstituted with a C1-C4-alkyl group. V is oxygen, C2-C6-alkylene, or C3-C6-alkylidene, preferably oxygen or C3-alkylene. p, q, and r are each independently either 0 or 1. When q=0, W is a single bond; when q=1 and r=0, W is oxygen, C2-C6 alkylene, or C3-C6 alkylidene, preferably oxygen or C3 alkylene. When q=1 and r=1, W and V are independently C2-C6-alkylene or C3-C6-alkylidene, preferably C3-alkylene. Z is a C1-C6 alkylene, preferably a C2 alkylene. o is the average number of repeating units, preferably 10 to 100, between 10 and 500. Copolycarbonates produced using diphenols (where m is the average number of repeating units, preferably 1 to 6, and more preferably 1.5 to 5) are also preferred. It is equally possible to use diphenols in which two or more siloxane blocks of general formula (1a) are bonded to each other via terephthalic acid and / or isophthalic acid to form ester groups.

[0067] Equations (2) and (3): [ka] (In the formula, R1 is hydrogen, C1-C4 alkyl, preferably hydrogen or methyl, particularly preferably hydrogen.) R2 is independently an aryl or alkyl, preferably methyl. X is a single bond, -SO2-, -CO-, -O-, -S-, C1~C6 alkylene, C2~C5 alkylidene, or C6~C12 It is an arylene, which may optionally be condensed with a further aromatic ring containing a heteroatom. X is preferably a single bond, C1-C5 alkylene, C2-C5 alkylidene, C5-C 12 Cycloalkylidenes, -O-, -SO-, -CO-, -S-, -SO2-, more preferably X is a single bond, isopropylidene, C5~C 12 Cycloalkylidene or oxygen, very preferably isopropylidene, n is an average number between 10 and 400, preferably between 10 and 100, and particularly preferably between 15 and 50. (where m is an average number of 1 to 10, preferably 1 to 6, and most preferably 1.5 to 5) (poly)siloxanes are particularly preferred.

[0068] The siloxane block also preferably has the following structure: [ka] (Here, a in formulas (IV), (V), and (VI) may be derived from the average number of 10 to 400, preferably 10 to 100, and more preferably 15 to 50.)

[0069] It is equally preferable that at least two identical or different siloxane blocks of general formula (IV), general formula (V), or general formula (VI) are bonded to each other via terephthalic acid and / or isophthalic acid to form an ester group.

[0070] In equation (1a), p=0, V is C3-alkylene, r=1, Z is C2-alkylene, R 8 and R 9 is methyl, q=1, W is C3-alkylene, m=1, R 5 is hydrogen or C1-C4 alkyl, preferably hydrogen or methyl, R 6 and R 7 It is equally preferable when each of them is independently a C1-C4 alkyl group, preferably a methyl group, and o is 10-500.

[0071] Copolycarbonates having monomer units of formula (1a), and in particular their preparation, are also described in International Publication No. 2015 / 052106.

[0072] Copolycarbonates having monomer units of formula (IV), and in particular their preparations, are also described in International Publication No. 2015 / 052106.

[0073] In principle, one or more additives can be added directly to the aromatic polycarbonate, or in practice, to the polycarbonate used as the starting material in the process of the present invention. However, one or more additives can also be supplied to the aromatic polycarbonate in an extruder, preferably together with a chain extender, only during the execution of the process of the present invention. If only one extrusion stage is used, incorporation via a side extruder is not possible in the process of the present invention because the foaming agent is present in the molten material and therefore escapes through the side feed. However, if an airtight side feed is available, the introduction of additives in this manner would be possible. Additives can also be introduced by powder premix or as a masterbatch. Liquid additives can always be injected at any point in the process, preferably in the area of ​​a static or dynamic mixing unit, as long as sufficient homogenization is still possible. Additives can also be added in the first stage, followed by the foaming agent in the second stage. In that case, it is also possible to add the additives via a side extruder.

[0074] A mixture of aromatic polycarbonate as a starting material, an optional blending partner, and any additives is referred to as an "aromatic polycarbonate composition." In process step a, either aromatic polycarbonate "alone" or aromatic polycarbonate as an aromatic polycarbonate composition may be used. When an aromatic 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. Very preferably, the "aromatic polycarbonate composition" does not contain a blending partner to the polycarbonate, and instead, only aromatic polycarbonate is used in the process of the present invention for producing polycarbonate beads, except for any additives that are conventional to polycarbonate.

[0075] Further additives conventionally added to polycarbonates include, in particular, heat stabilizers, flame retardants, antioxidants, mold release agents, drip inhibitors, e.g., polytetrafluoroethylene (Teflon®) or SAN-encapsulated PTFE (e.g., Blendex 449), UV absorbers, IR absorbers, impact resistance modifiers, antistatic agents, fluorescent whitening agents, fillers such as talc and quartz, light scattering agents, transesterification inhibitors, compatibilizers, nucleating agents, colorants, pigments, e.g., titanium dioxide, carbon black, chemical blowing agents, and / or laser marking additives, in amounts conventionally used for polycarbonate compositions. Such additives are described, for example, in European Patent Application Publication No. 0839623, International Publication No. 96 / 15102, European Patent Application Publication No. 0500496, or "Plastics Additives Handbook", Hans Zweifel, 5th Edition 2000, Hanser Verlag, Munich. These additives may be added individually or in mixtures. It will be understood that such additives may be added only in such amounts, provided that they do not have a significant adverse effect on the production of beads by the process of the present invention.

[0076] The additives are preferably selected from the group consisting of heat stabilizers, flame retardants, antioxidants, mold release agents, colorants, pigments, drip inhibitors, UV absorbers, IR absorbers, nucleating agents, impact resistance modifiers, antistatic agents, fluorescent whitening agents, light scattering agents, transesterification inhibitors, compatibilizers, and / or additives for laser marking.

[0077] The aromatic polycarbonate or aromatic polycarbonate-based composition is preferably determined according to ISO 1133:2012-3 (test temperature 300°C, mass 1.2 kg), with a maximum length of 14 cm. 3 (10 minutes), more preferably up to 12 cm 3 (10 minutes), more preferably 5 cm 3 / (10 minutes)~9cm 3 (10 minutes), most preferably 5.5 cm 3 / (10 minutes)~6.5cm 3It has a melt volume flow rate MVR of / (10 min).

[0078] The aromatic polycarbonate used in the process of the present invention may be polycarbonate, or a mixture of two or more aromatic polycarbonates, provided that the total OH-terminated group content of the polycarbonates used is within the scope of the present invention. The OH-terminated group content should be understood in relation to the aromatic polycarbonate, not the aromatic polycarbonate composition. It is also possible to use recycled polycarbonate after consumer or industrial use. Suitable recycled materials can be supplied to the extruder in the form of pellets or pulverized material. It is also possible to use recycled materials only as part of the aromatic polycarbonate.

[0079] The foamed polycarbonate beads of the present invention are foaming agent-free beads. "Foaming agent-free" means that at the time of further processing after gas exchange, only ambient air is present in the foaming cells. Nevertheless, the foamed polycarbonate beads of the present invention exhibit considerable post-foaming, for example, in a vapor diffusion welding process. This is because their cell walls and particle surfaces are frozen by water pelletization through quenching in an entropically non-equilibrium state.

[0080] The polycarbonate beads produced by the process of the present invention have a spherical or at least substantially spherical shape. Here, "substantially spherical" means that, when a sphere is drawn by axes of equal length directed from a common origin into space, the variation in the axial length of the spherical particles from the ideal state of a sphere is at most 20% along the axes that define the radius of the sphere in all spatial directions.

[0081] The post-foamed polycarbonate beads of the present invention preferably have an average particle size of 1.0 mm to 3.2 mm, preferably 2 mm to 2.6 mm, which is determined by a Camsizer according to ISO 13322-2. This can be established by selecting an appropriate die plate shape, i.e., nozzle size in the extruder, i.e., pore diameter and die land, as well as by the processing rate, blade speed, and composition of the foaming agent-containing molten material.

[0082] The polycarbonate beads have an open-cell content of up to 20%, preferably up to 16%, more preferably up to 15%, and even more preferably up to 10%, as determined according to DIN EN ISO 4590:2016-12. More than 80%, preferably more than 84%, and more preferably more than 90% of the cells are intact in the beads, i.e., the individual cell structures in these beads share walls with at least three other structural elements (cells), and there are no more than two broken cell walls per single cell. Thus, the polycarbonate beads have intact ("closed-cell") or at least a majority intact cells, and therefore, molded foam articles having a very uniform and flat surface and homogeneous welding of the beads can be produced from polycarbonate beads.

[0083] The particle density of the beads before foaming, determined according to the buoyancy principle in ASTM-D-792:2020-07, is 300 kg / m³. 3 ~620 kg / m 3 That is the case.

[0084] The phase angle of the polycarbonate beads in the Van Gurp-Palmen plot was determined as described in the examples, and the complex shear modulus |G * At a pressure of 3000 Pa and a temperature of 240°C, the temperature is less than 78.0°C, preferably between 64°C and 78.0°C, and more preferably between 71°C and 75°C.

[0085] Post-foaming polycarbonate beads without a foaming agent have a quotient of 3.20 × 10⁻⁶ between this phase angle and the weight-average molecular weight of the polycarbonate in this Van Gurp-Palmen plot. -4 ~1.93 × 10 -3 (degrees·mol / g), preferably 4.5 × 10⁻⁶ -4 ~1.52 × 10 -3 The condition is (degrees·mol / g).

[0086] For the manufacture of molded articles / parts, foamed particles can be welded to each other by variothermal means (thermal means by heating) or, preferably, by a steam molding machine. In a steam molding machine, the particle surface is partially melted or softened using high-pressure steam (i.e., high-temperature steam), which leads to interdiffusion of polymer chains between different beads and, consequently, aggregation of the beads. Good aggregation between particles and a low proportion of macropores / gaps, i.e., cavities between particles, in the part due to insufficient filling are necessary to ensure good mechanical properties. The processing from foamed beads to a finished part is carried out in five steps in the molding machine: 1) complete or partial closure of the mold, 2) filling of the mold, followed by complete closure if necessary, 3) welding of particles, 4) cooling and stabilization, and 5) removal of the molded article. Two methods are identified here: the crack gap method and the pressure filling method. In the pressurized filling method, the mold is first closed, then the particles are drawn out of the container by air pressure and injected into the mold by an injector at approximately 3 bar, where they are compressed. The particles expand within the mold, resulting in better cavity filling (equivalent to approximately 10% overfilling in the crack gap method). In the crack gap method, the mold is not completely closed, but a certain percentage of the cavity is left open. Next, the mold is filled with particles so that the mold is overfilled by a certain percentage (10% to 20% by volume in the current EPC method). Then, the mold is closed and the particles are compressed to the target thickness. If the target thickness of the part is, for example, 20 mm, the mold cavity is further opened, for example, by 4 mm (= 20% by volume), and filled with polycarbonate beads. Next, the mold is shrunk to the 20 mm part thickness. This step is important to achieve a uniform distribution of beads within the mold. In the third step, the beads fuse together as steam flows through the mold according to a predetermined procedure. During steam treatment, the beads form physical bonds through the interdiffusion of polymer chains between adjacent particles. To ensure high-quality welding between particles, current EPCs require the use of 7 to 11 bar, more preferably 8 to 10 bar.In a steam-based welding process, where overfilling is not possible and underfilling may occur due to post-foaming of the beads, the air between the beads is first expelled and the mold is preheated. While the valve is open, the steam flows parallel to the mold. In the second step, the steam flows through the mold. This is called cross-steaming. During this step, the steam inlet and outlet valves, located on opposite sides of each other, are open. To ensure a very uniform temperature distribution and uniform welding quality throughout the part, it is preferable to steam treat the mold from both sides. Finally, with the outlet valve closed, steam is introduced into the steam chamber at a specific pressure to improve surface quality by forming a skin layer (autoclave steaming). In the fourth step, the molded article is cooled. This is crucial for dimensional accuracy. If the part is removed without cooling, further expansion of the particles may occur, resulting in deviation from the original dimensions. For cooling, water is sprayed onto the mold until it reaches a temperature of approximately 80°C. After molding and cooling, in the final step, the part is removed, preferably by compressed air and a mechanical ejector.

[0087] Molded articles can be advantageously manufactured from the foaming agent-free foamed polycarbonate beads of the present invention using a standard vapor diffusion welding process. Here, “standard” means that this is an established process in machinery already used to manufacture molded articles from other polymer foams by a vapor diffusion welding process. This is preferably a drop-in technique for EPP welding processes, meaning that the post-foamed polycarbonate beads can be processed into molded articles in plants typically used for manufacturing molded articles from foamed polypropylene, which can utilize the process known by EPP. Thus, polycarbonate beads can be converted into molded articles, even those with complex shapes, by filling the corresponding cavities, ultimately requiring only one corresponding step. Subsequent dimensional cutting (which is still frequently required and generates associated waste), known with extruded foams, is unnecessary. Furthermore, polycarbonate beads are easier to transport than the often bulky sheets of available extruded foams.

[0088] Therefore, the molded articles of the present invention are preferably manufactured from the post-foaming polycarbonate beads of the present invention by vapor diffusion welding at an average vapor pressure of 4 bar to 6 bar, more preferably 4.0 bar to 4.5 bar, and particularly 4 bar.

[0089] Due to the spherical or nearly spherical shape of the beads, a molded article having a dense, continuous surface can be obtained.

[0090] When the polycarbonate beads of the present invention are used as obtained by the process of the present invention without further pretreatment after manufacturing, the polycarbonate beads still exhibit post-foaming of 20% to 60% by volume, preferably 30% to 50% by volume, in a steam diffusion welding process in water vapor at 4 bar, even though they do not contain a foaming agent.

[0091] The molded articles of the present invention, i.e., sheets and those having complex 3D shapes, have a dense, continuous surface and, in bending tests, exhibit a bending strain at a maximum force of at least 5.0%, preferably at least 5.5%, as determined according to ISO 1209-2:2007, where "according to" means that the sample thickness was 10 mm, the support width was 100 mm, and the outer skin of the sample was removed. The welded sheets cannot be broken by hand, regardless of the force applied by the tester (sheet dimensions in these tests: 300 × 200 × 15 mm). 3 ).

[0092] The part density of the corresponding molded article is determined according to DIN EN ISO 845:2009-10, preferably 200 kg / m³. 3 ~350 kg / m 3 That is the case.

[0093] The corresponding molded articles of the present invention can be used in the automotive industry, transportation, construction industry, aerospace industry, packaging industry, and generally in lightweight and / or composite structures. Molded articles that can be made from polycarbonate beads include not only sheets but also complex three-dimensional parts.

[0094] Molded articles consisting solely of or containing the polycarbonate beads of the present invention are particularly suitable as visible parts in various application fields, which can also be upgraded with laser textures. Examples include dashboard or interior trim elements, soundproofing elements, such as filling elements for carpets in the footwells of automobiles, core materials or supporting foam parts for composite materials, such as body insulation for vehicles, especially electric vehicles, insulation in the HVAC field (heating, ventilation, air conditioning), high-temperature insulation in industrial, residential and building technology or transportation, barriers and insulation materials, packaging, lightweight structural elements, wind turbine blades, and facade components. [Modes for carrying out the invention] [Examples]

[0095] 1. Description of raw materials and test methods a) Raw materials PC-1: Aromatic polycarbonate based on bisphenol A, with an MVR of 6 cm². 3 The process is (10 minutes) (300℃ / 1.2kg, ISO 1133-1:2011), and the softening temperature (VST / B 120; ISO 306:2013) is 149℃. g This is determined according to DIN EN ISO 11357-1:2017: 148℃. w The concentration was determined as described above, approximately 30900 g / mol. It contains 0.06% heat stabilizer and 0.1% UV stabilizer. The OH-terminated group content was determined using dichloromethane as the solvent at room temperature. 1 Determined by 1H NMR spectroscopy: 470 ppm. Manufactured via melt condensation (SPC) method.

[0096] PC-2: Aromatic polycarbonate based on bisphenol A, with an MVR of 6 cm². 3 The process is (10 minutes) (300℃ / 1.2kg, ISO 1133-1:2011), and the softening temperature (VST / B 120; ISO 306:2013) is 150℃. g This is determined according to DIN EN ISO 11357-1:2017: 148℃. w The concentration was determined as described above, approximately 30,900 g / mol at 28 kDa (MALLS). The OH-terminal group content was determined using dichloromethane as the solvent at room temperature. 1 Determined by 1H NMR spectroscopy (as above): 60 ppm. Manufactured via interfacial condensation (LPC) method.

[0097] CE-1: A commercially available polyfunctional chain extender (Joncryl ADR 4468) manufactured by BASF SE, based on a styrene / acrylic polymer having epoxy-reactive groups, with an average molecular weight (in orthodichlorobenzene, gel permeation chromatography at 150°C, polystyrene calibrated) M w = 7250 g / mol, epoxy equivalent 310 g / mol (determined according to DIN EN 1877-1:2000-12), glass transition temperature Tg The temperature at which it rises is 59°C, and the decomposition temperature is 350°C (determined according to DIN EN ISO 11357-1:2017).

[0098] b) Test method The bending strain at maximum force was determined according to ISO 1209-2:2007, where "according to" means that the sample thickness was 10 mm, the support width was 100 mm, and the outer skin layer of the sample was removed.

[0099] The molecular weight was determined by GPC measurement in dichloromethane, calibrated against a bisphenol A polycarbonate standard according to DIN EN ISO 16014-3:2019.

[0100] The density of the particles was determined according to the buoyancy principle in ASTM-D-792:2020-07, and the density of the molded articles was determined according to DIN EN ISO 845:2009-10.

[0101] Van Gurp-Palmen plot: Value of the phase angle.

[0102] The foamed polycarbonate beads were dried in an oven at 110 °C under vacuum for at least 20 hours. To ensure uniform drying, the amount in the drying container was limited to just cover the bottom of the container with a layer of beads. The thus dried sample was placed in a press mask with a diameter of 25 mm and pressed in a P / O / Weber PW 20 laboratory press at 200 °C into a transparent test piece with a thickness of 1.6 mm without visible gas mixing. Then, the sample was cooled to room temperature and immediately transferred to an ARES G2 rheometer manufactured by TA Instruments preheated to 240 °C. After heating for 2 minutes, a small vertical resistance was applied for a short time to ensure very good contact between the rheometer tool and the molten sample. As soon as the measurement gap decreased to 1.5 mm, the vertical resistance was decreased to 0. The extra material at the edge extruded by the measurement die was removed by hand. After temperature control for 120 seconds, a test piece with a thickness of 1.5 mm and a diameter of 25 mm was analyzed at 240 °C under a vibration load with a deformation rate of 0.4% from a frequency of 100 Hz to 0.001 Hz. To prevent the reaction between the sample and oxygen during the handling and measurement of the sample, the rheometer convection furnace was purged with nitrogen gas. After the measurement at 240 °C, the temperature in the oven was lowered to 230 °C and the measurement was repeated with an elongation of 0.3%. Next, the temperature was lowered to 220 °C and the measurement was repeated with an elongation of 0.2%. In the next step, the temperature was lowered to 210 °C and the measurement was repeated with an elongation of 0.12%. Subsequently, the temperature was lowered to 205 °C and the measurement was repeated with an elongation of 0.1%. Next, the sample was taken out of the rheometer. No bubbles were observed in the visual inspection of the sample.

[0103] Using the results of rheological measurements at different temperatures, namely, the storage shear modulus G’, the loss shear modulus G’’, and the phase angle δ(=arctan(G’’ / G’)), the measured phase angle δ was plotted against the complex shear modulus |G * |=√((G’) 2 +(G’’) 2 ) to create a so-called "Van Gurp-Palmen plot". Using this plot, the phase angle at G * [MPa]=3000 Pa was determined.

[0104] The open-cell content was determined according to DIN EN ISO 4590:2016-12.

[0105] The cell diameter was determined by SEM (ASTM E1508-12a:2019).

[0106] The bead size distribution was determined using Camsizer.

[0107] For the example, a topology image of the manufactured molded article (see figure) was also created. The corresponding height profile was created using image processing software based on a photograph of the molded article. For this purpose, the photograph was converted to a 16-bit grayscale image, and a representative area of ​​2 cm × 2 cm was selected. For this area, a 3D surface plot (top view) with a maximum grid size of 1024 and smoothing of 200 was created, as well as a wireframe surface plot (height profile image) with a polygon multiplier of 100%.

[0108] c) Procedure Tests to identify suitable materials The tests described below were carried out using a twin-screw extruder-gas metering system-single-screw extruder-melt pump-water pelletization configuration. Example i) describes a series of tests in which the OH concentration (ppm) of polycarbonate was gradually decreased while keeping the reactive components constant.

[0109] i) A twin-screw extruder (Extruder A) (43D) manufactured by Reifenhaeuser (Troisdorf, Germany) was operated at a rate of 35 kg / h, profile temperatures of 100°C to 160°C (Housing 1 to Housing 3), 240°C (Housing 4) to 280°C (Housing 5 to Housing 10), and a speed of 100 rpm. In addition, chain extender 1 was added at a fixed concentration of 0.7 wt%. In this series, the molar ratio of reactive groups OH:epoxy was varied from 1:0.82 to 1:1.47 (OH:epoxy, in all cases mol) by changing the proportion of the second polycarbonate (Table 1). The melting temperature was 10°C to 20°C higher than the housing temperature throughout the system (from the melting zone of the twin-screw to the die plate). The foaming agent was supplied at position 6 at a CO2 level of 1.3 wt% by Maximator (Maximator GmbH (Germany)) and / or metering station (Lewa GmbH (Germany)). Starting from position 5, the pressure profile within the twin-screw gradually increased from 45 bar at 100 wt% SPC, reaching 270 bar at the extruder tip. Adding PC-2, a PC component with fewer OH-terminated groups, resulted in a slight increase in the pressure profile to 275 bar at the initial 10% level. Further addition of PC components with fewer OH-terminated groups, exceeding 20 wt%, decreased the pressure profile. The molten material was transported to a single-screw extruder (Reifenhaeuser) (Extruder B) via a transfer pipe (290°C). Extruder B was also operated at a continuous housing temperature of 280°C, a processing rate of 35 kg / h, and a speed of 26 rpm. The melting pump was operated under pressure control with a back pressure of 110 bar and a temperature of 280°C. The pressure downstream of the melting pump was determined by the reactive polycarbonate content and decreased with the exogenous matrix content (details are shown in Table 1). The divertor and die plate are also set to a temperature of 280°C, and the melting temperature in the divertor and die plate is T g +140℃~T gThe temperature was +150°C. The UWP (EUP 50) and die plate were manufactured by ECON (Econ GmbH, Austria). The die plate consisted of five single-hole inserts with a diameter of 2.2 mm and a die land of 3.49 mm. The residence time of the molten material between the intake and outlet was approximately 7 to 10 minutes. Downstream of the outlet, the molten material was separated by a 6-blade knife rotating at 1500 rpm and transported by a chilled water circuit at 70°C to 80°C (28 m³). 3 ( / h). The roundness of the particles gradually decreased, and the foam density increased.

[0110] If the concentration of polycarbonate at the OH-terminated groups is too low, specifically below 350 ppm, the manufacturing process collapses with a reactive group molar ratio of 1:1.12 (OH:epoxy, each in moles) (outside the scope of the claims). The increase in molecular weight no longer occurs to a sufficient degree, and therefore the viscosity of the molten mixture, and thus the pressure at the die plate, is no longer sufficient for a homogeneous particle foam. The resulting particles become more elongated in shape and non-uniform in shape and appearance as the foam density increases (smaller pressure drop) (as a result of decreased viscosity and the accompanying changes in flow properties) (Table 2). Such particles can no longer be welded sufficiently well within the pressure range of 7 bar to 11 bar. The parts lack a continuous surface and have many sink points / cavities, resulting in reduced thermal conductivity, increased stiffness, a clear decrease in maximum bending strain, and reduced puncture performance (Tables 2 and 3).

[0111] The manufactured particles are processed using a Teubert TVZ162 / 100PP molding machine (Teubert Maschinenbau GmbH (Germany)) to a density of 200 ± 10 kg / m³. 3 , shape 300×200×15mm 3Parts were processed. From the concentration study to identify the appropriate materials, the pressure required for welding of EPC was in the range of 7 bar to 10 bar. Finally, the characteristics of the parts were determined. To visualize the morphology, measurements were carried out using a scanning electron microscope (SEM, model: JEOL JSM - 6510 (Borken, Germany)) on graphite sputtered samples. Dynamic mechanical analysis (DMA) was performed using a Gabo Eplexor 500N manufactured by NETZSCH GmbH (Selb, Germany) on samples of 15×15×15 mm 3 at a temperature range of -25°C to 250°C, a heating rate of 1 K / min, in pressure adjustment mode, with amplitudes of 5% (static) and 2% (dynamic) of the sample height, a frequency of 1 Hz, and in pressure mode. Mechanical property evaluation was carried out using pressure tests, tensile tests, and three - point bending tests (at room temperature, 80°C, and 110°C), as well as puncture tests (RT). The pressure test was carried out using a Zwick Z020 universal testing machine manufactured by Zwick & Roell (Ulm, Germany) in accordance with DIN EN ISO 844:2014 - 11, using a 10 kN load cell on samples of the shape of 15×15×15 mm 3 up to 60% compression. The three - point bending was carried out using the same universal testing machine at 10 mm / min and using a 20 kN load cell based on ISO 1209 - 1:2007 - 05. The samples were prepared by removing the skin layer to eliminate the influence of the dense boundary layer and the shape was adjusted to 120×25×10 mm 3 The tensile measurement of the parts was carried out using a Zwick Z050 universal testing machine (Zwick & Roell (Ulm, Germany)) in accordance with ISO 1926:2009, with a sample shape of 140(30 + 80 + 30)×80×15 mm 3 and using a 20 kN load cell. The puncture property evaluation was carried out using a Fractovis Plus drop - weight tester manufactured by Instron Ceast (Pianezza, Italy) with a maximum energy of 40 J, a puncture speed of 4.4 m / s (in accordance with DIN EN ISO 6603 - 2:2002 - 04), and a sample shape of 60×60×15 mm 3 All mechanical property evaluations were carried out at room temperature, 80°C, and 110°C, and in all cases, an intermediate step of 10 minutes was provided for temperature adjustment before measurement. All parts were approximately 200 kg / m3 The analysis was performed at the same density. Thermal conductivity measurements were taken using a NETZSCH (Selb, Germany) HFM 446 Lambda instrument at -10°C, 10°C, 25°C, 50°C, and 70°C.

[0112] The OH value of polymers was determined using dichloromethane as a solvent at room temperature. 1 This was confirmed by evaluating the ratio of the integral signals at 6.68 ppm (two aromatic protons in the ortho position relative to the phenol OH group) and 1.68 ppm (six methyl protons of the bisphenol A unit) using 1H NMR spectroscopy.

[0113] [Table 1]

[0114] [Table 2]

[0115] These tests indicated that the starting material to be used for further testing should be based on the total weight of aromatic polycarbonates, using dichloromethane as the solvent at room temperature. 1 Measurements by 1H NMR spectroscopy revealed that the aromatic polycarbonate contains at least 350 ppm of OH-terminal groups, and that a sufficient amount of chain extender should be used so that 0.64 mol to 1.10 mol of reactive groups of the chain extender are used per mole of OH-terminal groups of the polycarbonate.

[0116] Example 1 of the present invention System configuration: ZSK 26 MC type twin-screw extruder (manufactured by Coperion GmbH) (44D), gas metering station (manufactured by Promix Solutions GmbH), heat exchanger, followed by a melting pump (manufactured by Maag-Germany GmbH), and LPU type submersible pelletizer (manufactured by Maag-Germany GmbH). Die plate shape: two holes with a diameter of 2.4 mm, die land 12.7 mm, blade speed 4500 rpm (7-blade knife).

[0117] Composition: 99.3 wt% aromatic polycarbonate PC-1, 0.7 wt% polyfunctional chain extender CE-1, 1.3 wt% CO2. The molar ratio of reactive groups, polycarbonate OH groups: epoxy, is 1 mol:0.82 mol.

[0118] Process: The processing rate was 20 kg / h, and the set temperatures for the extruder and heat exchanger were 285°C. The extruder speed was 230 rpm. The melting pressure inside the extruder was 64 bar. The melting temperature upstream of the diverter was 290°C. The die plate temperature was 330°C, and the melting pressure was 177 bar. The process water temperature was 92°C, and the water pressure was 2.5 bar. The residence time in the system was 400 seconds.

[0119] Results: Average diameter 2.4mm-2.6mm, particle density 505kg / m³ due to buoyancy principle. 3 , average cell diameter 82 μm, open-cell content 6%, phase angle 72 degrees in Van Gurp-Palmen plot, and 4.65 × 10 -4 Particles with a quotient Q of (degrees·mol / g) were obtained. The particles were weldable at 4 bar in a "standard" vapor diffusion welding process, with a post-foaming rate of 47 vol% (100% - (100 × post-weld density / pre-weld density)) and a part density of 270 kg / m³. 3 The resulting molded articles had a dense, continuous surface (Table 3), could not be broken by hand, and exhibited a bending strain of 6.4% at maximum force in bending tests.

[0120] Example 2 of the present invention Modifications from Embodiment 1 of the present invention: System configuration: An additional melting pump (Maag-Germany GmbH) was installed upstream of the heat exchanger. The die plate shape had three holes with a diameter of 1.8 mm, a die land of 11 mm, and a blade speed of 4700 rpm.

[0121] Process: The die plate temperature was 330°C and the melting pressure was 162 bar. The process water temperature was 91°C and the water pressure was 2 bar. The residence time in the system was 420 seconds.

[0122] Results: average diameter 2.0mm~2.2mm, particle density 614kg / m 3 , average cell diameter 54 μm, open-cell content 4%, phase angle 72 degrees in Van Gurp-Palmen plot, and 8.0 × 10 -4 Particles with a quotient Q of (degrees·mol / g) were obtained. The particles were weldable at 4 bar in a "standard" vapor diffusion welding process, with a post-foaming of 46 volume%, and a part density of 330 kg / m³. 3 The resulting molded articles had a dense, continuous surface (Table 3), could not be broken by hand, and exhibited a bending strain of 5.8% at maximum force in bending tests.

[0123] Example 3 of the present invention Modifications from Embodiment 1 of the present invention: System configuration: An additional melting pump (Maag-Germany GmbH) was installed upstream of the heat exchanger. The blade speed was 4700 rpm.

[0124] Process: The extruder speed was 150 rpm. The melting temperature upstream of the diverter was 285°C. The die plate temperature was 335°C and the melting pressure was 189 bar. The process water temperature was 85°C and the water pressure was 1.5 bar. The residence time in the system was 460 seconds.

[0125] Results: average diameter 2.4mm~2.6mm, particle density 485kg / m 3, average cell diameter 43 μm, open-cell content 4%, phase angle 71 degrees, and 9.47 × 10⁻⁶ -4 Particles with a quotient Q of (degrees·mol / g) were obtained. The particles were weldable at 4 bar in a "standard" vapor diffusion welding process, with a post-foaming of 36 volume%, resulting in a part density of 310 kg / m³. 3 The resulting molded articles had a dense, continuous surface (Table 3), could not be broken by hand, and exhibited a bending strain of 6.6% at maximum force in bending tests (according to ISO 1209-2:2007).

[0126] Example 4 of the present invention Modifications from Embodiment 1 of the present invention: System configuration: An additional melting pump (Maag-Germany GmbH) was installed upstream of the heat exchanger. The blade speed was 4700 rpm.

[0127] Process: The processing rate was 24 kg / h. The melting temperature upstream of the diverter was 284°C. The die plate temperature was 335°C and the melting pressure was 177 bar. The process water temperature was 85°C and the water pressure was 1.8 bar. The residence time in the system was 350 seconds.

[0128] Results: average diameter 2.6mm~3.2mm, particle density 425kg / m 3 , average cell diameter 43 μm, open-cell content 15%, phase angle 74 degrees, and 1.52 × 10⁻⁶ -3 Particles with a quotient Q of (degrees·mol / g) were obtained. The particles were weldable at 4 bar in a "standard" vapor diffusion welding process, and after 31 volume% post-foaming, the part density was 290 kg / m³. 3 The resulting molded articles had a dense, continuous surface (Table 3), could not be broken by hand, and exhibited a bending strain of 6.0% at maximum force in bending tests.

[0129] Comparative Example 1 Modifications from Embodiment 1 of the present invention: System configuration: No heat exchanger in the process.

[0130] Process: The die plate temperature was 330°C and the melting pressure was 137 bar. The process water temperature was 85°C and the water pressure was 3.5 bar. The residence time in the system was very short, at 90 seconds.

[0131] Results: average diameter 2.6mm~2.8mm, particle density 490kg / m 3 , average cell diameter 41 μm, open-cell content 45%, phase angle 79 degrees, and 1.95 × 10 outside the scope of the claims -3 A particle with a quotient Q of (degrees·mol / g) was obtained.

[0132] Despite 34% post-foaming, the particles exhibited poor weldability at 4 bar in a "standard" vapor diffusion welding process. The molecular weight-to-chain branching ratio was outside the optimal range. Insufficient molar mass and insufficient chain branching resulted in low melt strength and therefore insufficient morphological stabilization, which led to a high open-cell content and poor weldability. The molded articles obtained from this example consisted of somewhat loosely aggregated particles, with a part density of 320 kg / m³. 3 These samples lacked a dense, closed surface (Table 3), could be broken by hand, and exhibited a bending strain of 2.1% at maximum force in bending tests.

[0133] Comparative Example 2 Modifications from Embodiment 1 of the present invention: System configuration: An additional melting pump (Maag-Germany GmbH) was installed upstream of the heat exchanger. The die plate shape consisted of two holes with a diameter of 2.8 mm and a die lanyard of 6 mm.

[0134] Composition: 99.5% by weight aromatic polycarbonate PC-1, 0.5% by weight polyfunctional chain extender CE-1, 1.3% by weight CO2. The molar ratio of reactive groups, polycarbonate OH groups: epoxy, is 1 mol:0.59 mol.

[0135] Process: The processing rate was 24 kg / h. The die plate temperature was 330°C and the melting pressure was 130 bar. The process water temperature was 91°C and the water pressure was 2 bar. The residence time in the system was 430 seconds.

[0136] Results: average diameter 2.4mm~2.6mm, particle density 370kg / m 3 , average cell diameter 81 μm, open-cell content 40%, phase angle 84 degrees, and 2.71 × 10 outside the scope of the claims -3 A particle with a quotient Q of (degrees·mol / g) was obtained.

[0137] The particles were unweldable at 4 bar in a "standard" vapor diffusion welding process, showed no post-foaming, and collapsed in the mold as a result of an insufficient molar ratio of reactive groups for the chemical molecular weight increase reaction at a residence time of 430 seconds. The resulting molded articles consisted of loosely aggregated particles, lacked a dense, continuous surface (Table 3), and broke under their own weight (at the lowest possible load). Bending tests reported a bending strain of 0% at maximum force for this material.

[0138] The following is a summary of the experimental results obtained (Table 3).

[0139] [Table 3]

Claims

1. a) A continuous particle foaming extrusion process of a plasticizing mixture in an extrusion process, The mixture consists of the following components: i) Aromatic polycarbonate, where dichloromethane is used as the solvent at room temperature, based on the total weight of the aromatic polycarbonate. １ Aromatic polycarbonates having at least 350 ppm of OH-terminated groups, as measured by 1H NMR spectroscopy, ii) A chain extender suitable for OH groups, wherein the aromatic polycarbonate and the chain extender suitable for the OH groups are used in a molar ratio such that 0.64 mol to 1.10 mol of the reactive group of the chain extender is used per 1 mol of OH-terminated groups of the polycarbonate, iii) Physical foaming agent, It contains, T １ = (T ｇ +110℃) ~ T ２ = (T ｇ +170℃) (in the formula, T ｇ At the temperature T of the plasticizing mixture (where is the glass transition temperature of aromatic polycarbonate), A continuous particle foaming extrusion process in which the residence time in the molten state of the aromatic polycarbonate and the chain extender suitable for the OH group is at least 4 minutes, b) T ３ = (T ｇ - 90°C) to T ４ = (T ｇ - 55°C) (where T ｇ is the glass transition temperature of the aromatic polycarbonate) at the water temperature, under non-pressurized water or under pressurized water up to a maximum of 3.5 bar, in the subsequent underwater pelletization process of the foaming agent-containing melt, a process for producing post-foaming foamed polycarbonate beads.

2. The process according to claim 1, wherein the residence time of the mixture in a molten state is at least 5.5 minutes.

3. The process according to claim 1 or 2, wherein 0.8 mol to 1.0 mol of reactive groups of a chain extender are used per mol of OH-terminated groups of polycarbonate.

4. The process according to any one of claims 1 to 3, wherein the pelletization of the foaming agent-containing molten material in water is carried out under a water pressure of 1.5 bar to 2.5 bar.

5. The process according to any one of claims 1 to 4, wherein the average particle size of the post-foamed polycarbonate beads is adjusted to 1.0 mm to 3.2 mm, preferably 2 mm to 2.6 mm.

6. The process according to any one of claims 1 to 5, wherein the beads obtained by step b are stored before further processing until complete gas exchange occurs.

7. The weight-average molecular weight M of polycarbonates ranging from 50,000 g / mol to 160,000 g / mol, as determined by GPC measurement in dichloromethane calibrated against a bisphenol A polycarbonate standard. ｗ A foamed polycarbonate bead having a foaming agent-free property, The foamed polycarbonate beads are post-foaming, and are characterized by exhibiting 20% ​​to 60% post-foaming when welded in steam at 4 bar without any pretreatment of the beads. The aforementioned foamed polycarbonate beads meet the following conditions: Q = δ / M ｗ = 3.20×10 －４ ~1.93×10 －３ (degree·mol / g) (In the formula, δ is the complex shear modulus |G) ＊ This is the phase angle in the Van Gurp-Palmen plot, determined at | = 3000 Pa and a temperature of 240°C, where δ < 78.0 degrees. M ｗ Foamed polycarbonate beads without foaming agents, as described above.

8. The foamed polycarbonate beads without a foaming agent according to claim 7, wherein the polycarbonate beads are spherical or nearly spherical, and "nearly spherical" means that, when a sphere is drawn by axes of equal length directed from a common origin into space, the variation in the axial length of the spherical particles from the ideal state of a sphere is at most 20% along the axes that define the radius of the sphere in all spatial directions.

9. Complex shear modulus | G ＊ The foamed polycarbonate beads without a foaming agent according to claim 7 or 8, wherein the phase angle δ in the Van Gurp-Palmen plot, determined by | = 3000 Pa and a temperature of 240°C, is between 64 degrees and less than 78.0 degrees.

10. Complex shear modulus | G ＊ The foamed polycarbonate beads according to any one of claims 7 to 9, wherein the phase angle δ in the Van Gurp-Palmen plot, determined by | = 3000 Pa and a temperature of 240°C, is less than 75 degrees.

11. The foamed polycarbonate beads according to any one of claims 7 to 10, wherein the foamed polycarbonate beads have a maximum open-cell content of 20%, as determined in accordance with DIN EN ISO 4590:2016-12.

12. The foamed polycarbonate beads according to any one of claims 7 to 11, wherein the polycarbonate beads have a maximum open-cell content of 15%, as determined in accordance with DIN EN ISO 4590:2016-12.

13. The foamed polycarbonate beads according to any one of claims 7 to 12, wherein the polycarbonate beads exhibit 30% to 50% post-foaming when welded in steam at 4 bar without pretreatment of the beads.

14. A molded article manufactured from foamed polycarbonate beads that do not contain the foaming agent described in any one of claims 7 to 13.

15. A process for manufacturing a molded article according to claim 14, wherein the molded article is manufactured by steam with an average absolute vapor pressure of 4 to 6 bar.

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