Production of pellets based on high-temperature polymers by underwater pelletization at elevated water temperature for the production of (rigid) particle foams

Abstract

Process for producing (rigid) bead foams by a process of underwater pelletization from a polymer composition featuring at least one polymer which has a glass transition temperature according to ISO 11357-2 (publication: 2014-07) of at least 180°C, wherein the extruder polymer melt is conveyed in a pressurized first water circuit, wherein the pressure is in the range from 0.2 to 30 bar and the water temperature in the water circuit is in the range from 105°C to 180°C, and the use of these (rigid) bead foams.

Description

[0001] Production of granules based on high-temperature polymers by underwater granulation at elevated water temperature for the production of particle (rigid) foams

[0002] Field of the invention

[0003] The present invention relates to a process for producing particle (rigid) foams from at least one polymer having a glass transition temperature according to ISO 11357-2 of at least 180°C from a polymer composition by means of underwater granulation.

[0004] State of the art

[0005] Due to their high processing temperatures, engineering plastics can currently only be processed using strand pelletizing. The resulting cylindrical pellets have sharp edges. During transport and further processing, these sharp edges lead to increased dust and fine particle formation, requiring appropriate occupational safety measures. Furthermore, the quality of the pellets is reduced, as damage to the pellet surfaces, such as microcracks, can occur.

[0006] The underwater granulation process described in W02005 / 056653 partially solves these problems. However, the granules produced with this process exhibit a higher proportion of defects on the surface (dents), and in some cases even defects within the granules (vacuoles).

[0007] Complex sorting processes are used to separate inferior granules. EP3377288 and EP2361174 describe processes for producing plastic granules using underwater granulation in a process chamber where the process fluid has a temperature above 120°C and a process pressure of at least 2.0 bar. However, the quality of the plastic granules is insufficient for many applications.

[0008] Basically, there are different procedures for producing particle foams.

[0009] WO2019 / 038213 describes a process in which a composition of 80 to 99.5 wt% PEI, 0.5 to 10 wt% blowing agent, and 0 to 10 wt% additives is processed into foamed or foamable granules using a die-cut extruder. The temperatures between the feed zone and the screw tip are preferably in a range between 320 and 400°C. Furthermore, there is usually no uniform temperature across this distance, but rather, for example, a gradient with increasing temperature in the conveying direction of the polymer melt. The temperature of the die-cut plate is between 250 and 350°C, and the melt temperature upon exiting the die-cut plate is between 230 and 360°C. The extruder is generally used to load the granules with the blowing agent. The granules then foam upon exiting the die-cut plate, provided the pressure in the underwater granulation is lower than the expansion force of the blowing agent.The expanded granulate is then preferably further processed into a particle foam molded part. Since these foam beads typically have a very low density, this process has a negative impact, especially on economical transport. Furthermore, expanded particle foams must always be compressed during molding to avoid defects and voids, which inevitably leads to an increase in density and thus a reduction in the potential for lightweight construction.

[0010] WO 2019 / 025245 describes a process for producing expandable, blowing-agent-containing granules based on high-temperature thermoplastics. A polymer melt is produced by melting a polymer with a glass transition temperature of at least 180°C and mixing it with at least one nucleating agent in an extruder at temperatures between 300°C and 350°C. After adding the blowing agent to the polymer melt, it is cooled to temperatures between 180°C and 250°C, conveyed through a die plate, and granulated in an underwater granulator with a water temperature between 75°C and 99°C.

[0011] The required nozzle temperature is very high compared to the typical water temperature, which is less than 100°C. This results in a cooling effect of the nozzle and thus in the risk of the polymer melt freezing in the nozzle, especially during process start-up.

[0012] The article "Brillians from the Reactor" by Gloeckner and Müller, published in Kunststoffe, 2, 2016, describes a new process designed to prevent the polymer melt from freezing in the extruder nozzle. Various plastics are mentioned in the article. However, the production of particle foams, especially from blowing agent-loaded polymer melts, is not discussed.

[0013] Task

[0014] The object of the present invention was to provide a new granulation process for high-temperature particle foams in view of the state of the art.

[0015] Solution

[0016] The object is achieved by providing a process for producing particle (rigid) foams by means of underwater granulation from a polymer composition with at least one polymer which has a glass transition temperature according to ISO 11357-2 (publication: 2014-07) of at least 180°C, characterized in that the polymer melt from the extruder a) is conveyed into a pressurized first water circuit, wherein the pressure is in the range from 0.2 to 30 bar and the water temperature in the water circuit is in the range from 105°C to 180°C, b) is granulated and c) is optionally fed to a second water circuit which has a temperature below 100°C and

[0017] 1) pressureless or

[0018] 2) is operated under a pressure in the range of 0.2 to 30 bar.

[0019] In one embodiment of the invention, the polymer composition can be passed into an underwater granulator upon exiting the extruder.

[0020] This is designed in such a way with regard to a combination of temperature and pressure that a closed system is created. According to the invention, the temperature of the first water circuit is 100°C to 200°C. This approach minimizes the large temperature difference between the polymer melt and the process water temperature of the underwater granulator. The risk of the polymer melt freezing at the nozzle, as described in the prior art, can thus be prevented.

[0021] In conventional processes, the polymer melt from the extruder is fed into an underwater pelletizer, which operates at a water temperature below 100°C. This leads to sudden cooling of the pellets. As a result, the pellets form dents, or vacuoles, on their surface.

[0022] Surprisingly, it was found that the process according to the invention results in the increased temperature level in the first water circuit leading to the formation of dents or vacuoles being prevented.

[0023] According to the invention, the pressurized first water circuit is preferably operated at a pressure in the range of 0.2 to 30 bar, preferably 5 to 30 bar, particularly preferably 3 to 10 bar. The water temperature in the first water circuit is preferably 105°C to 180°C, particularly preferably 115°C to 180°C.

[0024] The closed pressurized water circulation system enables work at higher water temperatures while reducing exposure of operating personnel to hot water vapors.

[0025] Granulation takes place in the first water circuit. This prevents the disadvantages of dust formation and degradation of the granulate due to scratching and sharp edges, which are common in the prior art.

[0026] According to the invention, the resulting granulate can be fed to a second water circuit that has a temperature below 100°C and is operated without pressure, alternatively at a pressure of 0.2 to 30 bar. If the second water circuit is operated under pressure according to process step c) 2), the pressure level is reduced to ambient pressure before the granulate is separated from the process water.

[0027] The resulting granules can be dried.

[0028] Drying can be carried out using conventional dryers, such as centrifugal dryers, forced-air dryers, compressed-air dryers, impact dryers, belt dryers, adsorption dryers, rotating drums with infrared heating, or dryers with molecular sieves.

[0029] An alternative process variant provides that, after process steps a) and b), the resulting granulate is directly discharged from the pressurized first circuit and sent to a drying process. This is particularly useful if the resulting granulate is to be further processed at a higher temperature level.

[0030] In a further variant of the embodiment, a polymer composition loaded with blowing agent can be processed by means of an extruder.

[0031] In this variant, the polymer composition is fed into the underwater granulator according to the invention upon exiting the extruder.

[0032] The process is designed with a combination of temperature and pressure to prevent foaming, for example, by maintaining the temperature in step a) at least 5°C below the Tg of the blowing agent-loaded polymer melt. This process produces blowing agent-loaded granules, which can later be foamed to the desired density by further energy input and / or further processed into a particle foam workpiece, optionally with molding.

[0033] The pressure present in the first water circuit, also known as counterpressure, prevents the propellant from boiling and thus prevents the granules from foaming.

[0034] The blowing agents suitable for this process are selected from the group consisting of volatile organic compounds having a boiling point at atmospheric pressure below the glass transition temperature of the base material, inorganic blowing agents, thermally decomposable blowing agents and mixtures of the aforementioned.

[0035] Preferably, the volatile organic compound having a boiling point at atmospheric pressure below the glass transition temperature of the base material and being liquid at atmospheric temperature (i.e. 25 °C, 1013 mbar) is selected from the group consisting of non-halogenated hydrocarbons, ketones, alcohols, halogenated hydrocarbons and mixtures of the aforementioned.

[0036] Preferably, the ketone is selected from acetone, methyl ethyl ketone, cyclohexanone, cyclononanone, diacetone alcohol, and mixtures of the foregoing. More preferably, the ketone is selected from acetone, methyl ethyl ketone, and mixtures of the foregoing.

[0037] Suitable polymers with a glass transition temperature according to ISO 11357-2 of at least 180°C are selected from the group of polysulfones or polyimides, in particular polyethersulfone (PESU), polyphenylsulfone (PPSU), polysulfone (PSU), polyetherimide (PEI), thermoplastic polyimides, and mixtures thereof. Particle foams based on a blend of PEI and polyetheretherketone (PEEK) are also suitable.

[0038] According to the invention, unless otherwise stated, the stated glass transition temperatures are measured using DSC (Differential Scanning Calorimetry). Those skilled in the art will appreciate that DSC is only sufficiently meaningful if, after an initial heating cycle, the temperature is at least 25 °C above the highest glass transition temperature.

[0039] Melting temperature, but at least 20 °C below the lowest decomposition temperature of a material, the material sample is held at this temperature for at least 2 minutes. Afterwards it is cooled again to a temperature that is at least 20 °C below the lowest glass transition or melting temperature to be determined, whereby the cooling rate should be a maximum of 20 °C / min, preferably a maximum of 10 °C / min. After a further waiting time of a few minutes the actual measurement is then carried out, in which the sample is heated at a heating rate of usually 10 °C / min or less to at least 20 °C above the highest melting or glass transition temperature.

[0040] In a further process variant for producing a particle foam, a corresponding polymer composition containing a nucleating agent is processed.

[0041] This optional nucleating agent is preferably selected from the group consisting of talc, graphite, carbon black, titanium dioxide, and mixtures of the foregoing. The optional nucleating agent advantageously improves cell morphology.

[0042] The polymer composition contains 0.01 to 3 wt.%, preferably 0.05 to 1 wt.% nucleating agent, based on the total mass.

[0043] The granules produced according to the invention are further processed into particle (rigid) foams.

[0044] In this context, particle (rigid) foams mean foams, rigid foams, particle foams and particle rigid foams that are produced on the basis of polymers with a glass transition temperature according to ISO 11357-2 of at least 180°C.

[0045] Due to the better quality of the granules, in particular the minimization of defects in the granules or on the surface of the granules, particle (rigid) foams with a particularly uniform pore size distribution are obtained.

[0046] The particle (rigid) foams produced by the process according to the invention, made from at least one polymer with a glass transition temperature according to ISO 11357-2 of at least 180°C, are used in the construction of spacecraft or aircraft, shipbuilding, rail vehicle construction, or vehicle construction, particularly in electromobility, in their exteriors. Furthermore, these particle (rigid) foams can be used to produce composite materials that can also be used in these applications. Furthermore, particle (rigid) foams made from at least one polymer with a glass transition temperature according to ISO 11357-2 of at least 180°C are particularly suitable for installation in the exterior of an aircraft. "Exterior" refers not only to fillings in the outer skin of an aircraft, but also, in particular, in the nose, tail, wings, outer doors, rudders, or rotor blades.

[0047] In particular, due to their low flammability, the particle (rigid) foams or composite materials produced according to the invention can also be installed in the interior of these vehicles.

[0048] The particle (rigid) foams based on polymers with a glass transition temperature of at least 180°C according to ISO 11357-2 are particularly suitable for installation in the interior of aircraft. In this context, aircraft includes not only jets or small aircraft, but also helicopters and even spacecraft. Examples of installation in the interior of such aircraft include the fold-out trays on the back of a passenger aircraft seat, the filling of a seat or partition wall, and, for example, in interior doors.

[0049] The present process and the particle (rigid) foams produced with it are particularly suitable for high-temperature applications.

[0050] Examples

[0051] Example 1

[0052] Underwater pelletizing of polyetherimide type Ultem 1000

[0053] Polyetherimide (PEI) (Ultem 1000, SABIC, Netherlands), with a glass transition temperature of 217°C, measured according to ISO 11357-2 (publication: 2014-07), is fed into the feed hopper of an extruder (Automatic Single Screw APM E1-180). Extrusion takes place at approximately 370-375°C and a pressure of 15 bar. The throughput is 160 kg / h. The melt is fed via a die plate to an underwater pelletizer (SPHERO 70, MAAG Automatik GmbH, Germany). The pressure at the die upstream of the die plate is approximately 195 bar. Pelletizing is carried out with nine knives at 2000 rpm.

[0054] Underwater granulation takes place in two process water circuits. In the first high-temperature circuit, the process water temperature is approximately 140°C at a pressure of approximately 4.95 bar. In the second circuit, the process water temperature is approximately 70°C at a pressure of approximately 2.5 bar. The residence time in each circuit is approximately 8 seconds.

[0055] The granules are then dried in a centrifugal dryer (CENTRO 300, MAAG Automatik GmbH, Germany). The residual moisture content is 0.30 to 0.47%.

Claims

Amended claims: Method for producing particle (rigid) foams by means of underwater pelletizing from a polymer composition with at least one polymer which has a glass transition temperature according to ISO 11357-2 (publication: 2014-07) of at least 180°C, characterized in that the polymer melt of the extruder a) is conveyed into a pressurized first water circuit, wherein the pressure is in the range of 0.2 to 30 bar and the water temperature in the water circuit is in the range of 105°C to 180°C, b) is pelletized.A method for producing particle / rigid foams by means of underwater granulation according to claim 1, characterized in that the polymer melt of the extruder is a) conveyed in a pressurized first water circuit, wherein the pressure is in the range of 0.2 to 30 bar and the water temperature in the water circuit is in the range of 105°C to 180°C, b) granulated and c) fed to a second water circuit which has a temperature below 100°C. 1) Pressureless or 2) Operated under pressure in the range of 0.2 to 30 bar. A process for producing particle (rigid) foams according to claim 1, characterized in that the polymer with a glass transition temperature according to ISO 11357-2 of at least 180°C is selected from the group consisting of polysulfones or polyimides, in particular polyethersulfone (PESU), polyphenylsulfone (PPSU), polysulfone (PSU), polyetherimide (PEI), thermoplastic polyimides and mixtures thereof. A process for producing particle (rigid) foams according to claim 1, characterized in that the polymer composition contains a blowing agent.

5. Method for producing particle (rigid) foams according to claim 3, characterized in that the temperature in step a) is at least 5°C below Tg of the blowing agent-loaded polymer melt.

6. Method for producing particle (rigid) foams according to claim 3, characterized in that the blowing agent is selected from the group consisting of volatile organic compounds having a boiling point at normal pressure below the glass transition temperature of the base material, inorganic blowing agents, thermally decomposable blowing agents and mixtures of the aforementioned.

7. Method for producing particle (rigid) foams according to claim 1, characterized in that the polymer composition contains a nucleating agent.

8. Method for producing particle (rigid) foams according to claim 6, characterized in that the nucleating agent is selected from the group consisting of talc, graphite, carbon black, titanium dioxide and mixtures of the aforementioned.

9. Method for producing particle (rigid) foams according to claim 1, characterized in that the granules obtained after step b) are removed and subjected to drying.

10. Method for producing particle (rigid) foams according to claim 1, characterized in that the granules obtained after step c) are removed and subjected to drying.

11. Use of particle (rigid) foams, manufactured according to the process in accordance with Claim 1, in aerospace, shipbuilding, vehicle manufacturing, in particular in electromobility.