Granules based on high temperature polymers are prepared by underwater pelletization at elevated water temperatures to make (rigid) particle foams

Abstract

The invention relates to a process for the production of (hard) granular foams from a polymer composition comprising at least one polymer having a glass transition temperature according to ISO 11357-2 (July 2014) of at least 180°C using an underwater pelletizing system, wherein the polymer melt of an extruder 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, which is pelletized, and the use of these (hard) granular foams.

Description

Technical Field

[0001] The present invention relates to a method for preparing (rigid) granular foams from a polymer composition using an underwater granulation system, the polymer having a glass transition temperature of at least 180°C according to ISO 11357-2. Background Technology

[0002] Due to the high processing temperatures of engineering plastics, they can only be processed via wire rod granulation under current technology. The resulting cylindrical pellets have sharp edges. During transport and further processing, these sharp edges lead to increased dust and fine particle formation, necessitating appropriate occupational safety measures. Furthermore, the quality of the pellets is reduced because the surface may be damaged, such as by the appearance of microcracks.

[0003] These problems are addressed to some extent by underwater granulation as described in WO2005 / 056653. However, the granules obtained by this method have an increased proportion of surface defects (dents) and sometimes even internal defects (cavitation).

[0004] To remove inferior pellets, laborious downstream sorting processes are required. EP3377288 and EP2361174 describe methods for preparing plastic pellets by underwater granulation in a process chamber, where the process fluid is at a temperature above 120°C at a process pressure of at least 2.0 bar. However, the quality of the plastic pellets obtained from these methods is insufficient to meet the requirements of many applications.

[0005] In principle, there are multiple methods for preparing granular foam.

[0006] WO2019 / 038213 describes a method in which a composition consisting of 80% to 99.5% wt% PEI, 0.5% to 10% wt% foaming agent, and 0% to 10% wt% additives is processed into foamed or foamable granules by means of an extruder with an orifice plate. The temperature between the feed zone and the screw tip is preferably in the range of 320 to 400°C. Furthermore, there is generally no uniform temperature in this section; instead, there is, for example, a temperature gradient with increasing temperature in the direction of polymer melt transport. The temperature of the orifice plate is between 250 and 350°C, and the material temperature is between 230 and 360°C when exiting through the orifice plate. The foaming agent is typically loaded into the extruder. The granules then undergo foaming upon exiting the orifice plate, provided that the pressure in the underwater granulation is below the expanding force of the foaming agent. The expanded granules are then preferably further processed into granular foam moldings. Because these foam beads typically have very low density, the aforementioned method has a particularly negative impact on economical transportation. Furthermore, during the molding process, the expanded granular foam must always be compressed to avoid defects and cavities, which inevitably leads to increased density and thus reduces the potential for lightweight construction.

[0007] WO 2019 / 025245 describes a method for preparing expandable granules containing a foaming agent and based on a high-temperature thermoplastic. In this method, a polymer melt is prepared 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 a temperature between 300°C and 350°C. After adding the foaming agent to the polymer melt, the melt is cooled to a temperature between 180°C and 250°C, conveyed through a perforated plate, and granulated in an underwater granulator at a water temperature between 75°C and 99°C.

[0008] The required nozzle temperature is very high relative to the normal water temperature (which is less than 100°C). This results in a cooling effect on the nozzle and therefore a risk of the polymer melt freezing in the nozzle, especially during process startup.

[0009] A novel method for preventing polymer melt freezing in the extruder nozzle is described in Gloeckner and Müller's article "Brillianten ausdem Reaktor" published in Kunststoffe, 2, 2016. The article mentions various plastics. However, the preparation of granular foams, particularly from polymer melts containing foaming agents, is not discussed. Summary of the Invention

[0010] Technical problems to be solved

[0011] In view of the prior art, the technical problem to be solved by the present invention is to provide a new granulation method for high-temperature granular foam.

[0012] Solution

[0013] The problem is solved by providing a method for preparing (rigid) granular foam from a polymer composition comprising at least one polymer using an underwater granulation system, said polymer having a glass transition temperature of at least 180°C according to ISO 11357-2 (published July 2014), the method being characterized in that...

[0014] The polymer melt from the extruder

[0015] a) Water is supplied to a pressurized first water circuit, wherein the pressure is in the range of 0.2 to 30 bar, and the water temperature in said water circuit is in the range of 105°C to 180°C.

[0016] b) Granulation, and

[0017] c) Optionally, water is supplied to a second water circuit, which has a temperature below 100°C and operates under the following conditions.

[0018] 1) No pressure applied, or

[0019] 2) Under pressures ranging from 0.2 to 30 bar.

[0020] In one embodiment of the invention, the polymer composition may be guided into an underwater granulator as it leaves the extruder.

[0021] Here, the underwater granulator is designed to operate under a specific combination of temperature and pressure, resulting in a closed system. According to the invention, the temperature in the first water circuit is between 100°C and 200°C. This design minimizes the large temperature difference between the polymer melt and the process water in the underwater granulator. Therefore, the risk of the polymer melt freezing in the nozzle, as described in the prior art, can be prevented.

[0022] In conventional methods, polymer melt from an extruder is supplied to an underwater granulation system operating at a water temperature below 100°C. This results in the sudden cooling of the granules. Consequently, indentations or cavitation forms on the surface of the granules.

[0023] It has been surprisingly discovered that the method according to the invention produces the following result: the increased temperature level in the first water circuit prevents the formation of dents or cavitation.

[0024] According to the present invention, the pressurized first water circuit preferably operates at a pressure in the range of 0.2 to 30 bar, more preferably 5 to 30 bar, and even more preferably 3 to 10 bar. The water temperature in the first water circuit is preferably 105°C to 180°C, more preferably 115°C to 180°C.

[0025] This closed, pressurized water circulation system allows for operation at higher water temperatures while reducing operator exposure to hot water steam.

[0026] Granulation takes place in the first water circuit. This prevents the drawbacks mentioned in the prior art, such as dust formation and reduced granule quality due to scraping and sharp cut edges.

[0027] According to the invention, the obtained granules can be supplied to a second water circuit having a temperature below 100°C and operating without pressurization, or operating at a pressure of 0.2 to 30 bar.

[0028] When the second water circuit is operating under pressure according to method step c)2), the pressure level is reduced to ambient pressure before separating the granules from the process water.

[0029] The obtained granules can be supplied to the drying process.

[0030] Drying can be carried out using conventional dryers. Suitable dryers for this purpose include, for example, centrifugal dryers, circulating air dryers, compressed air dryers, impact dryers, belt dryers, adsorption dryers, rotary drum dryers with infrared heating, or dryers containing molecular sieves.

[0031] In an alternative method variation, following steps a) and b), the obtained pellets are immediately discharged from the pressurized first loop and supplied to the drying process. This is particularly interesting when the obtained pellets are to be further processed at higher temperature levels.

[0032] In another variation of the embodiment, the polymer composition containing the foaming agent can be processed by means of an extruder.

[0033] In this variant, the polymer composition is guided into the underwater granulator of the present invention as it leaves the extruder.

[0034] Here, the underwater granulator is designed to operate under a combination of temperature and pressure to prevent foaming, for example by keeping the temperature in step a) at least 5°C below the Tg of the polymer melt containing the foaming agent. This provides granules loaded with the foaming agent, which can then be foamed to the desired density by re-inputting energy and / or further processed into granular foam workpieces by optional molding.

[0035] The pressure present in the first water circuit (also known as back pressure) prevents the foaming agent from boiling, thereby preventing the granules from foaming.

[0036] The foaming agent suitable for this method is selected from volatile organic compounds, inorganic foaming agents, thermally decomposable foaming agents, and mixtures thereof, wherein the volatile organic compounds have a boiling point at standard pressure lower than the glass transition temperature of the base material.

[0037] Volatile organic compounds with boiling points below the glass transition temperature of the base material under standard pressure and which are liquid at standard temperature (i.e., 25°C, 1013 mbar) are preferably selected from non-halogenated hydrocarbons, ketones, alcohols, halogenated hydrocarbons, and mixtures thereof.

[0038] The ketone is preferably selected from acetone, methyl ethyl ketone, cyclohexanone, cyclononanone, diacetone alcohol, and mixtures thereof. More preferably, the ketone is selected from acetone, methyl ethyl ketone, and mixtures thereof.

[0039] Suitable polymers having a glass transition temperature of at least 180°C according to ISO 11357-2 are selected from polysulfones or polyimides, particularly polyethersulfone (PESU), polyphenylene sulfone (PPSU), polysulfone (PSU), polyetherimide (PEI), thermoplastic polyimides, and mixtures thereof. Particulate foams based on blends of PEI and polyetheretherketone (PEEK) are also suitable.

[0040] Unless otherwise stated, the glass transition temperature according to the invention is measured by DSC (Differential Scanning Calorimetry). Those skilled in the art will recognize that DSC provides sufficiently convincing information only when the material sample is held at a temperature at least 25°C higher than the material's highest glass transition temperature or melting temperature, but at least 20°C lower than the material's lowest decomposition temperature, after the first heating cycle. The sample is then cooled again to a temperature at least 20°C lower than the lowest glass transition temperature or melting temperature to be measured, wherein the cooling rate should not exceed 20°C / min, preferably not more than 10°C / min. After waiting for several more minutes, the actual measurement is performed, wherein the sample is heated at a heating rate typically 10°C / min or less until it is at least 20°C higher than the highest melting temperature or glass transition temperature.

[0041] In another variation of the method for preparing granular foam, the corresponding polymer composition containing a nucleating agent is processed.

[0042] This optional nucleating agent is preferably selected from talc, graphite, carbon black, titanium dioxide, and mixtures thereof. The optional nucleating agent advantageously improves the cell morphology.

[0043] The polymer composition contains 0.01 to 3% by weight, preferably 0.05 to 1% by weight, of a nucleating agent based on the total mass.

[0044] The granules prepared according to the present invention are further processed into (rigid) granular foam.

[0045] Here, (rigid) granular foam refers to foam, rigid foam, granular foam and rigid granular foam, which are prepared based on polymers having a glass transition temperature of at least 180°C according to ISO 11357-2.

[0046] Because of the improved quality of the granules, particularly the minimization of defects in or on the surface of the granules, a (rigid) granular foam with a particularly uniform pore size distribution is obtained.

[0047] The (rigid) particulate foam prepared by the method according to the invention from at least one polymer having a glass transition temperature of at least 180°C according to ISO 11357-2 can be used in the construction of spacecraft or aircraft, shipbuilding, rail vehicle construction or vehicle construction, particularly in electric vehicles, in their external components. These (rigid) particulate foams can also be used to prepare composite materials, which can also be used in the aforementioned applications.

[0048] (Rigid) granular foams made from at least one polymer having a glass transition temperature of at least 180°C according to ISO 11357-2 are also particularly suitable for introduction into the external areas of aircraft. The term "external areas" here means not only fillers in the aircraft skin, but also, in particular, fillers in the nose, tail, wings, outer doors, rudder, or rotor blades.

[0049] In particular, due to their flame-retardant properties, the (rigid) granular foam and composite materials prepared according to the present invention can also be installed in the interior space of the vehicle.

[0050] (Rigid) granular foams based on polymers having a glass transition temperature of at least 180°C according to ISO 11357-2 are particularly suitable for introduction into aircraft interior areas. Aircraft include, in particular, helicopters or even spacecraft, in addition to jet aircraft or light aircraft. Examples of installation in such aircraft interior spaces include, for example, tray tables that fold down behind passenger seats, padding for seats or interior partitions, and, for example, interior doors.

[0051] The method of the present invention and the (rigid) granular foam produced by the method are particularly suitable for high-temperature applications. Detailed Implementation

[0052] Example

[0053] Example 1

[0054] Underwater granulation of Ultem 1000 type polyetherimide

[0055] Polyetherimide (PEI) (Ultem 1000, SABIC, Netherlands) was loaded into the storage container of an extruder (automatic single-screw APME1-180). The PEI had a glass transition temperature of 217°C, as measured according to ISO 11357-2 (published July 2014). Extrusion was carried out at approximately 370-375°C and a pressure of 15 bar. The material throughput was 160 kg / h. The melt was supplied via an orifice plate to an underwater granulation system (SPHERO 70, MAAG Automatik GmbH, Germany). The pressure in the nozzle upstream of the orifice plate was approximately 195 bar. Granulation was performed using nine blades at 2000 rpm.

[0056] The underwater granulation is carried out in two process water loops. In the first high-temperature loop, the process water temperature is approximately 140°C and the pressure is approximately 4.95 bar. In the second loop, the process water temperature is approximately 70°C and the pressure is approximately 2.5 bar. The residence time in each of the two loops is approximately 8 seconds.

[0057] The granules were then dried in a centrifugal dryer (CENTRO 300, MAAG Automatik GmbH, Germany). The residual moisture content was 0.30% to 0.47%.

Claims

1. A method for preparing granular foam using an underwater granulation system, comprising a polymer composition containing at least one polymer having a glass transition temperature of at least 180°C according to ISO 11357-2 published in July 2014, wherein, The polymer melt from the extruder a) Water is supplied to a pressurized first water circuit, wherein the pressure is in the range of 0.2 to 30 bar, and the water temperature in said water circuit is in the range of 105°C to 180°C. b) Granulation; The polymer having a glass transition temperature of at least 180°C according to ISO 11357-2 is selected from polysulfone, polyimide and mixtures thereof.

2. The method for preparing granular foam using an underwater granulation system according to claim 1, characterized in that, The granular foam is rigid granular foam.

3. The method for preparing granular foam using an underwater granulation system according to claim 1 or 2, characterized in that, The polymer melt from the extruder a) Water is supplied to a pressurized first water circuit, wherein the pressure is in the range of 0.2 to 30 bar, and the water temperature in said water circuit is in the range of 105°C to 180°C. b) Granulation, and c) Supply to a second water circuit, which has a temperature below 100°C and operates under the following conditions. 1) No pressure applied, or 2) Under pressures ranging from 0.2 to 30 bar.

4. The method for preparing granular foam according to claim 1 or 2, characterized in that, The polymer having a glass transition temperature of at least 180°C according to ISO 11357-2 is selected from polyethersulfone (PESU), polyphenylsulfone (PPSU), polysulfone (PSU), thermoplastic polyimide, and mixtures thereof.

5. The method for preparing granular foam according to claim 1 or 2, characterized in that, The polymer having a glass transition temperature of at least 180°C according to ISO 11357-2 is polyetherimide (PEI).

6. The method for preparing granular foam according to claim 1 or 2, characterized in that, The polymer composition contains a foaming agent.

7. The method for preparing granular foam according to claim 6, characterized in that, The temperature in step a) is at least 5°C lower than the Tg of the polymer melt containing the foaming agent.

8. The method for preparing granular foam according to claim 6, characterized in that, The foaming agent is selected from volatile organic compounds, inorganic foaming agents, thermally decomposable foaming agents, and mixtures thereof, wherein the boiling point of the volatile organic compounds under standard pressure is lower than the glass transition temperature of the base material.

9. The method for preparing granular foam according to claim 1, characterized in that, The polymer composition contains a nucleating agent.

10. The method for preparing granular foam according to claim 9, characterized in that, The nucleating agent is selected from talc, graphite, carbon black, titanium dioxide, and mixtures of the above substances.

11. The method for preparing granular foam according to claim 1, characterized in that, After step b), the obtained granules are discharged and supplied to the drying process.

12. The method for preparing granular foam according to claim 3, characterized in that, The obtained granules are discharged after step c) and supplied to the drying process.

13. Use of particulate foam prepared by the method according to any one of claims 1-12 in the aerospace industry, shipbuilding or vehicle construction.

14. The use according to claim 13, wherein the particulate foam is used in an electric vehicle.