Production of high temperature polymer based pellets by underwater pelletization at elevated water temperature to produce (rigid) bead foams

Abstract

A process can be used for producing (rigid) particle foams from polymer compositions containing at least one polymer having a glass transition temperature according to ISO 11357-2 of at least 180 C. with an underwater pelletization system.

Claims

1. A process for preparing expandable pellets with an underwater pelletization system from a polymer composition comprising at least one polymer having a glass transition temperature according to ISO 11357-2 published: 2014-07 of at least 180 C., the process comprising: a) conveying a polymer melt of the polymer composition from an extruder into a first water circuit that is pressurized, with a gauge pressure being within a range from 0.2 to 30 bar and a water temperature in the first water circuit being within a range from 105 C. to 180 C., and b) pelletizing, wherein the polymer composition comprises a blowing agent, further comprising: c) supplying a pelletized material from b) to a second water circuit that has a temperature below 100 C. and is operated 1) unpressurized, or 2) under a gauge pressure within a range from 0.2 to 30 bar.

2. The process for preparing expandable pellets according to claim 1, wherein the at least one polymer having a glass transition temperature according to ISO 11357-2 of at least 180 C. is selected from the group consisting of a polysulfone, a polyimide, and a mixture thereof.

3. The process for preparing expandable pellets according to claim 2, wherein the at least one polymer having a glass transition temperature according to ISO 11357-2 of at least 180 C. is selected from the group consisting of polyethersulfone (PESU), polyphenylsulfone (PPSU), polysulfone (PSU), polyetherimide (PEI), a thermoplastic polyimide, and a mixture thereof.

4. The process for preparing expandable pellets according to claim 1, wherein the temperature in a) is at least 5 C. below a Tg of the polymer melt containing the blowing agent and said at least one polymer.

5. The process for preparing expandable pellets according to claim 1, wherein the blowing agent is selected from the group consisting of a volatile organic compound having a boiling point at standard pressure below a glass transition temperature of said at least one polymer having a glass transition temperature according to ISO 11357-2 published: 2014-07 of at least 180 C., an inorganic blowing agent, a thermally decomposable blowing agent, and a mixture thereof.

6. The process for preparing expandable pellets according to claim 1, wherein the polymer composition comprises a nucleating agent.

7. The process for preparing expandable pellets according to claim 6, wherein the nucleating agent is selected from the group consisting of talc, graphite, carbon black, titanium dioxide, and a mixture thereof.

8. The process for preparing expandable pellets according to claim 1, wherein a pelletized material obtained after b) is discharged and supplied to a drying process.

9. The process for preparing expandable pellets according to claim 1, wherein a pelletized material obtained after c) is discharged and supplied to a drying process.

10. A method, comprising: installing foamed particles obtained by inputting energy into the expandable pellets produced by the process according to claim 1, in an aircraft, ship, or vehicle.

11. The method according to claim 10, wherein the vehicle is an electromobility vehicle.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Said underwater pelletizer is designed to operate at a combination of temperature and pressure such that there is a closed system present. According to the invention, the temperature in the first water circuit is 100 C. to 200 C. Through this approach, the large temperature difference between the polymer melt and the temperature of the process water in the underwater pelletizer is minimized. The risk of the polymer melt freezing in the nozzle described in the prior art can thus be averted.

(2) In the conventional process, the polymer melt from the extruder is supplied to an underwater pelletization system operated at a water temperature below 100 C. This results in abrupt cooling of the pelletized material. The pellets accordingly develop dents on the surface of the pelletized material or vacuoles.

(3) It has surprisingly been found that the procedure according to the invention has the result that the increased temperature level in the first water circuit makes it possible for the formation of dents or vacuoles to be prevented.

(4) According to the invention, the first water circuit, which is pressurized, is operated at a pressure preferably within a range from 0.2 to 30 bar, preferably 5 to 30 bar, 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.

(5) The closed, pressurized water circulation system makes working at higher water temperatures possible while at the same time reducing the exposure or the operating personnel to hot steam.

(6) Pelletization takes place in the first water circuit. This prevents the disadvantages of dust formation and the reduction in quality of the pelletized material due to scratching and sharp broken edges that are described in the prior art.

(7) According to the invention, the pelletized material obtained can be supplied to a second water circuit having a temperature below 100 C. and operated unpressurized, alternatively at a pressure of 0.2 to 30 bar.

(8) When the second water circuit according to process step c) 2) is operated under pressure, the pressure level is lowered to ambient pressure before separation of the pelletized material from the process water.

(9) The pelletized material obtained may be supplied to a drying process.

(10) Drying may be carried out using conventional dryers. Suitable for this purpose are for example centrifugal dryers, circulating-air dryers, compressed-air dryers, impact dryers, belt dryers, adsorption dryers, rotating drums with infrared heating or dryers containing molecular sieves.

(11) In an alternative process variant, the pelletized material obtained is after process steps a) and b) immediately discharged from the pressurized first circuit and supplied to a drying process. This is of particular interest when the pelletized material obtained is to undergo further treatment at a higher temperature level.

(12) In a further variant of the embodiment, a blowing agent-containing polymer composition can be processed by means of an extruder.

(13) In this variant, the polymer composition is on exiting the extruder guided into the underwater pelletizer of the invention.

(14) Said underwater pelletizer is designed to operate at a combination of temperature and pressure such that foaming is prevented from occurring, for example by the temperature in step a) being at least 5 C. below the Tg of the blowing agent-containing polymer melt. This approach affords a blowing agent-containing pelletized material that may subsequently be foamed to the desired density by a renewed input of energy and/or further processed into a particle foam workpiece by optional moulding.

(15) The pressure present in the first water circuit, also referred to as the counterpressure, prevents the blowing agent from boiling, thereby preventing the pellets from foaming.

(16) The blowing agents suitable for this process are selected from the group consisting of volatile organic compounds having a boiling point at standard pressure below the glass transition temperature of the base material, inorganic blowing agents, thermally decomposable blowing agents and mixtures of the above.

(17) The volatile organic compound having a boiling point at standard pressure below the glass transition temperature of the base material and that is liquid at standard temperature (i.e. 25 C., 1013 mbar), is preferably selected from the group consisting of non-halogenated hydrocarbons, ketones, alcohols, halogenated hydrocarbons and mixtures of the above.

(18) The ketone is preferably selected from acetone, methyl ethyl ketone, cyclohexanone, cyclononanone, diacetone alcohol and mixtures of the above. The ketone is more preferably selected from acetone, methyl ethyl ketone and mixtures of the above.

(19) Suitable polymers having 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. Also suitable are particle foams based on a blend of PEI and polyether ether ketone (PEEK).

(20) Stated glass transition temperatures are according to the invention measured by DSC (differential scanning calorimetry) unless otherwise specified. Those skilled in the art are aware that DSC is sufficiently informative only when, after a first heating cycle up to a temperature that is a minimum of 25 C. above the highest glass transition or 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 min. The sample is then cooled back down to a temperature that is at least 20 C. below the lowest glass transition or melting temperature to be determined, wherein the cooling rate should be not more than 20 C./min, preferably not more than 10 C./min. After a further wait time of a few minutes, the actual measurement is then carried out, in which the sample is heated to at least 20 C. above the highest melting or glass transition temperature at a heating rate of generally 10 C./min or less.

(21) In another variant of the process for producing a particle foam, a corresponding polymer composition comprising a nucleating agent is processed.

(22) This optional nucleating agent is preferably selected from the group consisting of talc, graphite, carbon black, titanium dioxide and mixtures of the above. The optional nucleating agent advantageously improves the cell morphology.

(23) The polymer composition contains 0.01% to 3% by weight, preferably 0.05% to 1% by weight, of nucleating agent based on the total mass.

(24) The pellets produced according to the invention are processed further into (rigid) particle foams.

(25) (Rigid) particle foams mean in this context foams, rigid foams, particle foams and rigid particle foams that are produced based on polymers having a glass transition temperature according to ISO 11357-2 of at least 180 C.

(26) As a consequence of the better quality of the pellets, in particular the minimization of defects in the pelletized material or on the surface of the pellets, (rigid) particle foams having particularly uniform pore size distribution are obtained.

(27) The (rigid) particle foams produced according to the process of the invention from at least one polymer having a glass transition temperature according to ISO 11357-2 of at least 180 C. find use in the construction of spacecraft or aircraft, in shipbuilding, rail vehicle construction or vehicle construction, particularly in electromobility, in the exterior thereof. These (rigid) particle foams can also be used to produce composite materials that can likewise find use in said applications.

(28) (Rigid) particle foams from at least one polymer having a glass transition temperature according to ISO 11357-2 of at least 180 C. are in addition particularly suitable for incorporation in aircraft exteriors too. The exterior means not just as filling in the outer skin of an aircraft, but especially also in an aircraft nose, in the tall region. In the wings, in the outside doors, in the control surfaces or in rotor blades.

(29) In particular, their low flammability means that the (rigid) particle foams and composite materials produced according to the invention can be installed in the interior of said vehicles too.

(30) (Rigid) particle foams based on polymers having a glass transition temperature according to ISO 11357-2 of at least 180 C. are particularly suitable for incorporation in aircraft interiors. Besides jets or light aircraft, aircraft especially also includes helicopters or even spacecraft. Examples of installation in the interior of such an aircraft are, for example, the trays that can be folded down on the rear side of seats in passenger aircraft, filling for a seat or an internal partition, and also, for example, in internal doors.

(31) The present process and the (rigid) particle foams generated therewith are particularly suitable for high-temperature uses.

EXAMPLES

Example 1

(32) Underwater Pelletization of Ultem 1000 Type Polyetherimide.

(33) Polyetherimide (PEI) (Ultem 1000, SABIC, the Netherlands), having a glass transition temperature of 217 C., measured according to ISO 11357-2 (published: 2014-07), is loaded into a reservoir vessel of an extruder (automatic single screw APM E1-180). The extrusion takes place at approx. 370-375 C. and a pressure of 15 bar. The throughput is 160 kg/h. The melt is supplied to an underwater pelletization system (Sphero 70, MAAG Automatlk GmbH, Germany) via a perforated plate. The pressure in the nozzle upstream of the perforated plate is approx. 195 bar. The pelletization is carried out with 9 knives at 2000 1/min.

(34) The underwater pelletization takes place in two process water circuits. In a first, high-temperature circuit, the process water temperature is approx. 140 C. at a pressure of approx. 4.95 bar. In the second circuit, the process water temperature is approx. 70 C. at a pressure of approx. 2.5 bar. The residence time in the two circuits is in each case approx. 8 s.

(35) The pelletized material is then dried in a centrifugal dryer (Centro 300, MAAG Automatik GmbH, Germany). The residual moisture content is 0.30% to 0.47%.