Method for producing particle foams based on thermoplastic elastomers, by thermal bonding using microwaves

Abstract

A method for producing bead foams from foam beads based on thermoplastic elastomers, especially thermoplastic polyurethane, comprises foam beads being wetted with a polar liquid and joined together thermally in a mold via high-frequency electromagnetic radiation, especially microwave radiation, and also the bead foams obtainable therefrom.

Claims

1. A method for producing bead foams, the method comprising wetting foam beads with a polar liquid that has a boiling point in the range from 120° C. to 350° C., and joining the foam beads together thermally in a mold via high-frequency electromagnetic radiation, wherein the foam beads are obtained from at least one thermoplastic polyurethane elastomer and a blowing agent; and wherein said polar liquid comprises a glycol ester of acetic acid, a glycol ester of citric acid, a glycerol ester of acetic acid, a glycerol ester of citric acid, triethylene glycol tripropylene glycol or a mixture thereof.

2. The method according to claim 1, wherein the foam beads are joined together thermally via microwaves in the frequency range between 100 MHz and 300 GHz.

3. The method according to claim 1, wherein the foam beads have a bulk density in the range from 30 to 250 kg/m.sup.3.

4. The method according to claim 1, wherein the foam beads are wetted with the polar liquid in proportions of 0.1 to 10 wt %, based on the foam beads.

5. The method according to claim 1, wherein the polar liquid comprises 1,2,3-propanetriol triacetate, triethylene glycol, tripropylene glycol, or a mixture thereof.

Description

EXAMPLES

(1) Materials Used: E-TPU Infinergy® 32-100 U10, expanded, predominantly closed-cell foam beads based on thermoplastic polyurethane, obtained by expansion of pelletized Elastollan® from BASF Polyurethanes GmbH under pressure and high temperature, bulk densities 110 g/l and 150 g/l. Polar liquids: glycerol triacetate (triacetin, 1,2,3-propantriol triacetate) triethylene glycol tripropylene glycol tri butyl acetylcitrate Adhesive: Elastopave 6550/101 from BASF Polyurethanes GmbH, compact 2-component polyurethane system Apparatus: MLS-Ethos plus laboratory microwave system having a maximum power output of 2.5 kW.

(2) Methods of Measurement:

(3) Bulk density was determined by filling a 200 ml vessel with the expanded beads and determining the weight by weighing. An accuracy of ±5 g/l may be assumed here.

(4) The densities of the foam sheets were determined to DIN EN ISO 1183-1 A.

(5) The compressive strength of the foam sheets was measured in accordance with DIN EN ISO 3386 at 10%, 25%, 50% and 75% compression.

(6) Compression set was determined for the foam sheets (shoe foam) after conditioning (6h/50° C./50%) to ASTM D395.

(7) The rebound resilience of the foam sheets was determined to DIN 53512.

(8) Elongation at break and tensile strength were determined to DIN 53504.

Example B1

(9) 45 parts by weight of the E-TPU foam beads having a bulk density of 110 g/l were placed in a vessel together with 2.4 parts by weight of glycerol triacetate. The vessel was shaken to completely wet the E-TPU foam particles with glycerol triacetate in the course of 60 seconds.

(10) 47.4 grams of the wetted and still loose individual beads were filled into a microwaveable mold measuring 200 mm×200 mm×10 mm. A height-adjustable lid exerted slight pressure on the beads. This filled mold was placed aslant at a 30° angle on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 40 seconds, the mold was turned 180° about its vertical axis and irradiated at 400 W for a further 40 seconds, then the mold was turned about its vertical axis by a further 90° and then irradiated horizontally at 400 W for a further 40 seconds. The mold was removed from the microwave and cooled down to room temperature in a water bath. A fused-together sheet of foam could then be removed.

Example B2

(11) 55 parts by weight of the E-TPU foam beads having a bulk density of 130 g/l were placed in a vessel together with 2.8 parts by weight of glycerol triacetate. The vessel was shaken to completely wet the E-TPU foam beads with glycerol triacetate in the course of 60 seconds.

(12) 57.8 grams of the wetted and still loose individual beads were filled into a microwaveable mold measuring 200 mm×200 mm×10 mm. A height-adjustable lid exerted slight pressure on the beads. This filled mold was placed aslant at a 30° angle on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 45 seconds, the mold was turned 180° about its vertical axis and irradiated at 400 W for a further 45 seconds, then the mold was turned about its vertical axis by a further 90° and then irradiated horizontally at 400 W for a further 45 seconds. The mold was removed from the microwave and cooled down to room temperature in a water bath. A fused-together sheet of foam could then be removed.

Example B3

(13) 55 parts by weight of the E-TPU foam beads having a bulk density of 130 g/l were placed in a vessel together with 2.8 parts by weight of triethylene glycol. The vessel was shaken to completely wet the E-TPU foam beads with triethylene glycol in the course of 60 seconds.

(14) 57.8 grams of the wetted and still loose individual beads were filled into a microwaveable mold measuring 200 mm×200 mm×10 mm. A height-adjustable lid exerted slight pressure on the beads. This filled mold was placed aslant at a 30° angle on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 40 seconds, the mold was turned 180° about its vertical axis and irradiated at 400 W for a further 40 seconds, then the mold was turned about its vertical axis by a further 90° and then irradiated horizontally at 400 W for a further 40 seconds. The mold was removed from the microwave and cooled down to room temperature in a water bath. A fused-together sheet of foam could then be removed.

Example B4

(15) 55 parts by weight of the E-TPU foam beads having a bulk density of 130 g/l were placed in a vessel together with 2.8 parts by weight of tributyl acetylcitrate. The vessel was shaken to completely wet the E-TPU foam beads with tributyl acetylcitrate in the course of 60 seconds.

(16) 57.8 grams of the wetted and still loose individual beads were filled into a microwaveable mold measuring 200 mm×200 mm×10 mm. A height-adjustable lid exerted slight pressure on the beads. This filled mold was placed aslant at a 30° angle on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 45 seconds, the mold was turned 180° about its vertical axis and irradiated at 400 W for a further 45 seconds, then the mold was turned about its vertical axis by a further 90° and then irradiated horizontally at 400 W for a further 45 seconds. The mold was removed from the microwave and cooled down to room temperature in a water bath. A fused-together sheet of foam could then be removed.

(17) Comparative Test V1:

(18) 60 g of uncoated E-TPU foam beads having a density of 110 g/l were fused together using water vapor to form shaped foam articles.

(19) Comparative Test V2:

(20) 60 g of uncoated E-TPU foam beads having a density of 110 g/l were fused together using 9 wt % of an adhesive to form shaped articles of foam.

(21) Comparative Test V3:

(22) 60 g of uncoated E-TPU foam beads having a density of 110 g/l were fused together using 23 wt % of an adhesive to form shaped articles of foam.

(23) The properties of the foam sheets from Examples B1-B4 and Comparative Tests V1-V3 are summarized in table 1.

(24) The foam sheets from Examples B1 to B4 exhibit a higher rebound resilience versus the adhered foam sheets from Comparative Tests V2 and V3.

(25) It is further advantageous that the microwave fusion (Examples B1) allows lower component part weights than are possible by water vapor fusion (Comparative Test V1). An increase in the rebound resilience and a reduction in density are considered advantageous.

(26) Also of particular advantage is the high elongation at break for the foam sheets of Examples B2 and B3 versus the foam sheets fused together in standard fashion with water vapor (Comparative Test V1) and the adhered foam sheets (V2 and V3).

(27) Particularly the combination of low density, high tensile strength and elongation at break and also high rebound resilience is desirable in order to obtain lightweight component parts having good mechanical properties.

(28) TABLE-US-00001 TABLE 1 Properties of foam sheets from Examples B1-B4 and Comparative Tests V1-V3 B1 B2 B3 B4 V1 V2 V3 Compressive strength 10% [kPa] 8.3 9.6 3.4 3.9 78 20.3 26.8 Compressive strength 25% [kPa] 44.4 51.7 22.6 24.5 170 53 60.3 Compressive strength 50% [kPa] 157.3 261.7 139.7 138.0 366.7 142 156.9 Compressive strength 75% [kPa] 814 2439 1127 1183 1822 540.3 669.5 Density [g/l] 189 265 301 299 253.5 135 152 Rebound resilience [%] 58 59 56 57 70 55 55 Tensile strength [kPa] 313 599 561 499 1168 120 292 Elongation at break [%] 124 189 183 185 108 32 42