Method for producing foam particles made of thermoplastic elastomers with polyamide segments

Abstract

A process for producing foam particles composed of thermoplastic elastomers having polyamide segments, comprising the steps: (a) production of a suspension of pellets of the thermoplastic elastomer in a suspension medium, (b) addition of a blowing agent, (c) impregnation of the pellets with the blowing agent by heating of the suspension in a pressure vessel to an impregnation temperature IMT at an impregnation pressure IMP, depressurization of the suspension by emptying of the pressure vessel via a depressurization device and work-up of the foam particles obtained, and also foam particles obtainable by the process.

Claims

1. A process for producing foam particles composed of one or more thermoplastic elastomers having polyamide segments, the process comprising: adding a blowing agent to a suspension of pellets of a polymer in a suspension medium; impregnating the pellets with the blowing agent by heating the suspension in a pressure vessel to an impregnation temperature IMT, which is from 80 to 180? C., at an impregnation pressure IMP in the range of from 500 to 3010 kPa absolute; depressurizing the suspension by emptying the pressure vessel with a depressurization device, thereby obtaining foam particles; and obtaining a foam molding by fusing the foam particles with steam at a gauge pressure of from 80 to 150 kPa, wherein the polymer content in the pellets consists of the one or more thermoplastic elastomers having polyamide segments; wherein the process is a batchwise process; (a) wherein the blowing agent consists of carbon dioxide; (b) wherein the foam particles have a bulk density of from 20 to 250 kg/m.sup.3; wherein the impregnating by heating the suspension, is followed by keeping the suspension at a temperature of from 2? C. above the impregnation temperature (IMT) to 5? C. below the impregnation temperature (IMT) for a period of from 2 to 100 minutes; wherein the blowing agent is used in amounts of from 1 to 50% by weight, based on the weight of the pellets; wherein the thermoplastic elastomer having polyamide is a polyether block amide (PEBA); wherein the PEBA consists of flexible polytetrahydrofuran and crystalline polyamide 12 units; and wherein the PEBA has 19.8 to 25.4% by weight polyamide blocks.

2. The process according to claim 1, wherein the pellets have an average mass of from 1 to 50 mg.

3. The process according to claim 1, wherein the suspension medium comprises water.

4. The process according to claim 1, wherein the depressurizing of the suspension is effected by emptying the pressure vessel with a ball valve into an expansion vessel.

5. The process according to claim 1, wherein, during the depressurizing, the suspension is brought into contact with a liquid coolant downstream of the depressurization device.

6. The process according to claim 1, wherein the foam molding has a ball rebound resilience of at least 55%, as measured in accordance with DIN EN ISO 8307.

7. The process according to claim 1, wherein the foam molding has a bulk density of 200 to 300 kg/m.sup.3.

8. The process according to claim 1, wherein the foam particles have a bulk density of 120 to 250 kg/m.sup.3.

9. The process according to claim 1, wherein the foam particles have a bulk density of 150 to 250 kg/m.sup.3.

10. The process according to claim 1, wherein the suspension is kept at a temperature of from 2? C. above the impregnation temperature (IMT) to 5? C. below the impregnation temperature (IMT) for a period of from 2 to 20 minutes.

11. The process according to claim 1, wherein the blowing agent is used in an amount of 12-50% by weight of the pellets.

Description

EXAMPLES

(1) Test Methods:

(2) The following test methods and parameters were used, inter alia, to characterize the raw materials used and also the resulting foam particles and moldings:

(3) Melting Point Determination by Means of DSC:

(4) Procedure in accordance with ISO 11357-3 (German version of Apr. 1, 2013) using a DSC Q100 from TA Instruments. To determine the melting point of the thermoplastic elastomers used or of other thermoplastic elastomers according to the invention in pellet form, 3-5 mg are heated at a heating rate of 20? C./min in a 1.sup.st run between 20? C. and 200? C., subsequently cooled at 10? C./min to 20? C., followed by a further heating cycle (2.sup.nd run) at a heating rate of 10? C./min. The temperature of the peak maximum in the 2.sup.nd run was reported as melting point.

(5) Crystalline Structure by DSC:

(6) To characterize the crystalline structure of the compact thermoplastic elastomer or the expanded foam particles, 3-5 mg are heated at a heating rate of 20? C./min between 20? C. and 200? C. and the resulting heat flow is determined.

(7) Bulk Density:

(8) The determination was carried out by a method based on DIN EN ISO 60: 2000-1. Here, the foam particles were introduced into a measuring cylinder having a known volume with the aid of a funnel having a predetermined geometry (completely filled with bulk material), the excess of the bulk material was struck off from the measuring cylinder by means of a straight-edged bar and the contents of the measuring cylinder were determined by weighing.

(9) The funnel used has a height of 40 cm, an opening angle of 35? C. and an outlet having a diameter of 50 mm. The measuring cylinder had an internal diameter of 188 mm and a volume of 10 l.

(10) The bulk density (BD) is given by the mass of the bed [kg]/0.01 [m.sup.3].

(11) The average of 3 measurements in kg/m.sup.3 was reported as bulk density.

(12) Degree of Compaction DC

(13) The degree of compaction DC is the ratio of density of the molding (M density) to bulk density (BD). DC=M density [kg/m.sup.3]/BD [kg/m.sup.3].

(14) Hot Storage

(15) The test specimens (180?60?M density mm) were placed in an oven which had been preheated to the appropriate storage temperature (110? C.) and stored at this temperature for 96 hours.

(16) Assessment of the Surfaces/Edges as Follows:

(17) The surface and edge of the test specimens was assessed every 24 hours during the storage time according to a scale of grades. For this purpose, the test specimens were briefly taken from the oven.

(18) TABLE-US-00001 Evaluation Grade No change 1 Abrasion at edge 2 Disintegration of edge 3 Disintegration of the edge 4 plus 0 to 5 mm deep damage to the surface Disintegration of the edge 5 plus 5 to 10 mm deep damage to the surface Sample disintegrates under 6 gentle thumb pressure

(19) After the end of the hot storage, the test specimens were carefully taken from the oven, stored at room temperature for 24 hours under room conditions and the change in dimensions was subsequently measured by means of the sliding caliber.

(20) The change in dimensions (length, width, height) is calculated according to the following formula:
CD=[(Lo?L1)/Lo)]?100 CD=change in dimension in % Lo=original dimension L1=dimension after hot storage

(21) The heat resistance was satisfactory (OK) when surfaces and edges did not display any changes and the average change in dimensions over length, width and height was <10%. It is limited when this change in dimensions is achieved only in the case of storage at lower temperatures.

(22) Starting Materials

(23) A TPA-EE, i.e. a polyether block amide (PEBA), was used as thermoplastic polyamide elastomer (TPA) in the examples according to the invention. Such products are supplied, for example, by Arkema Speciality Polyamides under the tradename PEBAX. The products listed in table 1 consist of flexible polytetrahydrofuran and crystalline polyamide units (PA-12).

(24) TABLE-US-00002 TABLE 1 thermoplastic polyamide elastomers used 2533 3533 4033 7233 Pebax SA 01 SA 01 SA 01 SA 01 Density [g/cm.sup.3] ISO 1183 1.00 1.00 1.00 1.01 Melting point [? C.] ISO 11357 134 144 160 174 Vicat temperature (at 1 ISO 306 58 77 131 164 daN) [? C.] Hardness [Shore A/ ISO 868 77/27 82/33 90/42 -/69 Shore D] Characterization by described methods Pellets, particle weights 18 21 21 17 [mg] Pellets, bulk density 602 589 614 588 [kg/m.sup.3] DSC Tmax (1.sup.st run) [? C.] 70/142 78/149 -/164 -/171 Elemental analysis (EA) N 1.4 1.8 3.4 6.6 [%] Proportion of PA block 19.8 25.4 48.0 93.1 [%] by weight] (calculated from N from EA)
Production of the Expanded Thermoplastic Elastomer

General Experimental Description

(25) Pellets having a particle weight of about 19 mg, whose composition is described in table 1, were used.

Examples 1-4 and 6-13

(26) The experiments were carried out with a degree of fill of the vessel of 80% and a phase ratio of 0.41.

(27) 100 parts by weight (corresponding to 28.5% by weight, based on the total suspension without blowing agent) of the pellets, 245 parts by weight (corresponding to 69.6% by weight, based on the total suspension without blowing agent) of water, 6.7 parts by weight (corresponding to 1.9% by weight, based on the total suspension without blowing agent) of calcium carbonate, 0.13 part by weight (corresponding to 0.04% by weight, based on the total suspension without blowing agent) of a surface-active substance (Lutensol AT 25) and the appropriate amount of butane as blowing agent (based on the amount of pellets used) were heated while stirring. Nitrogen was then additionally injected at a temperature of the liquid phase of 50? C. and the internal pressure was set to a previously defined pressure (800 kPa). Depressurization is subsequently carried out via a depressurization apparatus after attainment of the impregnation temperature (IMT) and optionally after a hold time (HT) and at the impregnation pressure (IMP) set at the end. The gas space is here brought to a predetermined expression pressure and kept constant during the depressurization. The depressurization jet can optionally be cooled by means of a particular volume flow of water having a particular temperature (water quench) downstream of the depressurization apparatus. In examples 1-4 and 10, cooling was carried out using an amount of water at 25? C. which corresponds to the ratio (mass of quenching water)/(mass of suspension medium)=0.85.

(28) After removal of the suspension aid (dispersant and soap) and drying, the bulk density (BD) of the resulting particles is measured.

Example 5

(29) As for examples 1-4, but 12% by weight of CO.sub.2 are used instead of butane as blowing agent and no additional nitrogen is injected.

Example 14

(30) The experiment was carried out with a degree of fill of the vessel of 70% and a phase ratio of 0.27.

(31) 100 parts by weight (corresponding to 21.2% by weight, based on the total suspension without blowing agent) of the pellets, 365 parts by weight (corresponding to 77.4% by weight, based on the total suspension without blowing agent) of water, 6.7 parts by weight (corresponding to 1.4% by weight, based on the total suspension without blowing agent) of calcium carbonate, 0.14 part by weight (corresponding to 0.03% by weight, based on the total suspension without blowing agent) of a surface-active substance (Lutensol AT 25) and the appropriate amount of butane as blowing agent (based on the amount of pellets used) were heated while stirring. No additional injection of nitrogen was carried out at 50? C. Depressurization is subsequently carried out via a depressurization apparatus after attainment of the impregnation temperature (IMT) and optionally after a hold time (HT) and at the impregnation pressure (IMP) set at the end. The gas space is here brought to a predetermined expression pressure (3700 kPa) and kept constant during the depressurization.

(32) After removal of the suspension aid (dispersant and soap) and drying, the bulk density (BD) of the resulting foam particles is measured.

Examples 15 and 16

(33) The experiments were carried out with a degree of fill of the vessel of 80% and a phase ratio of 0.31.

(34) 100 parts by weight (corresponding to 23.4% by weight, based on the total suspension without blowing agent) of the pellets, 320 parts by weight (corresponding to 75.0% by weight, based on the total suspension without blowing agent) of water, 6.7 parts by weight (corresponding to 1.6% by weight, based on the total suspension without blowing agent) of calcium carbonate, 0.13 part by weight (corresponding to 0.03% by weight, based on the total suspension without blowing agent) of a surface-active substance (Lutensol AT 25) and the appropriate amount of butane as blowing agent (based on the amount of pellets used) were heated while stirring.

(35) In the case of example 15, no additional nitrogen is injected. In the case of example 16, nitrogen was additionally injected and the internal pressure set to a previously defined pressure (800 kPa) at a temperature of the liquid phase of 50? C.

(36) The further course of the experiment is as in example 14.

(37) The experimental parameters (blowing agent, amount of blowing agent, impregnation temperature (IMT), impregnation pressure (IMP), expression pressure) and the resulting bulk density (BD) for examples 1 to 16 according to the invention are reported in table 2.

(38) The phase ratio is defined as the ratio of pellets, measured in kilograms, to suspension medium, which is preferably water, likewise in kilograms.

(39) The hold time (HT) is defined as the time [min] for which the temperature of the liquid phase is in a temperature range from 5? C. below the IMT to 2? C. above the IMT.

(40) Production of the Moldings:

(41) The production of the moldings was carried out on a commercial automatic EPP molding machine (model K68 from Kurtz GmbH). Cuboidal test specimens having different thicknesses were produced using tools having the dimensions 315?210?25 mm and 315*210*20 mm. The moldings were produced by the pressure filling process or the crack filling process. After production of the moldings, the moldings were stored at 60? C. for 16 hours.

(42) The results of the subsequent tests on the moldings are reported in table 3.

(43) TABLE-US-00003 TABLE 2 Experimental parameters for examples 1 to 16 T [? C.] Blowing of the Bulk agent suspension Hold Expression density Blowing contents at N.sub.2 IMT time IMP pressure Water BD Example Type of pellets agent [% by weight] introduction [? C.] [min] [kPa] [kPa] quench [kg/m.sup.3] Example 1 Pebax 2533 SA 01 Butane 24.0 50 100.0 2 1970 3400 yes 94 Example 2 Pebax 2533 SA 01 Butane 24.0 50 95.0 2 1830 3400 yes 141 Example 3 Pebax 2533 SA 01 Butane 24.0 50 90.0 15 1670 3400 yes 213 Example 4 Pebax 2533 SA 01 Butane 24.0 50 95.0 13 1800 3400 yes 104 Example 5 Pebax 2533 SA 01 CO.sub.2 12.0 100.0 11 3010 3700 yes 215 Example 6 Pebax 3533 SA 01 Butane 24.0 50 100.0 4 1810 3400 no 206 Example 7 Pebax 3533 SA 01 Butane 24.0 50 103.0 20 1960 3400 no 136 Example 8 Pebax 3533 SA 01 Butane 24.0 50 105.5 17 2020 3400 no 107 Example 9 Pebax 3533 SA 01 Butane 24.0 50 106.5 15 2030 3400 no 92 Example 10 Pebax 3533 SA 01 Butane 24.0 50 106.5 17 2020 3400 yes 131 Example 11 Pebax 4033 SA 01 Butane 24.0 50 132.0 3 2750 3700 no 81 Example 12 Pebax 4033 SA 01 Butane 24.0 50 135.0 3 2780 3700 no 40 Example 13 Pebax 4033 SA 01 Butane 24.0 50 130.0 3 2880 3700 no 113 Example 14 Pebax 7233 SA 01 Butane 24.0 156.0 3 2350 3700 no 84 Example 15 Pebax 7233 SA 01 Butane 24.0 156.0 3 2960 3700 no 36 Example 16 Pebax 7233 SA 01 Butane 24.0 50 152.0 3 3530 3700 no 48

(44) TABLE-US-00004 TABLE 3 Tests on moldings produced from foam particles from examples 1 to 16 Density of the Tensile Compressive Elongation Rebound molding stress stress at break resilience [kg/m.sup.3] [kPa] [kPa] [%] [%] DIN EN ISO DIN EN ISO DIN EN ISO 844 DIN EN ISO DIN EN ISO Foam 845 1798 (Nov. 1, 2014) 1798 8307 particles (Oct. 1, (Apr. 1, at 50% (Apr. 1, (Jan. 1, Molding (table 2) DC 2009) 2008) compression 2008) 2008) Heat resistance M-1 Example 1 2.1 200 400 165 75 69 n.d. M-2 Example 2 1.8 260 450 300 75 68 limited (OK at 90? C.) M-4 Example 4 2.0 210 250 165 55 73 n.d. M-5 Example 5 2.0 410 980 650 138 66 n.d. M-7 Example 7 2.1 280 490 380 56 75 OK (CD < 10%) M-8 Example 8 2.0 215 200 250 26 75 n.d. M-9 Example 9 2.4 220 450 260 58 73 OK (CD < 10%) M-10 Example 10 2.1 280 480 390 55 74 OK (CD < 10%) M-11 Example 11 1.9 150 530 360 35 65 OK (CD < 1%) M-12 Example 12 2.4 95 350 170 45 64 n.d. M-13 Example 13 1.7 190 490 500 35 61 OK (CD < 1%) M-16 Example 16 4.0 160 200 450 20 45 OK (CD < 1%) n.d. not determined M-5 and M-16 were produced by the crack filling process.