Electrically conductive particle foams based on thermoplastic elastomers

Abstract

Foam beads based on thermoplastic elastomers and having a coating comprising at least one electrically conductive substance, processes for producing same by coating the foam beads with an emulsion of a conductive substance in a plasticizer, and also processes for producing bead foams by joining the foam beads together thermally via high-frequency electromagnetic radiation.

Claims

1. Foam beads comprising: a base which comprises a thermoplastic elastomer; and a coating provided on a surface of the base, the coating essentially consisting of at least one electrically conductive substance, wherein a proportion of a total of the at least one electrically conductive substance ranges from 0.1 to 1 wt %, based on the foam beads.

2. The foam beads according to claim 1, wherein the thermoplastic elastomer comprises a thermoplastic polyurethane.

3. The foam beads according to claim 1, wherein the coating consists of graphite.

4. The foam beads according to claim 1, having a bulk density ranging from 30 to 250 kg/m.sup.3.

5. A process for producing the foam beads of claim 1, the process comprising coating foam beads with an emulsion of a conductive substance in a plasticizer selected from the group consisting of a phthalate, an alkylsulfonic ester, a polyether, a polyurethane, a low molecular weight polyamide, a citric ester, an adipic ester, a diisononyl 1, 2-cyclohexanedicarboxylate and a glycerol ester.

6. The process according to claim 5, wherein foam beads of a thermoplastic polyurethane are coated with an emulsion of graphite in 1,2,3-propanetriol triacetate.

7. A process for producing bead foams, the process comprising joining the foam beads of claim 1 together thermally using high-frequency electromagnetic radiation.

8. The process according to claim 7, wherein the foam beads are joined thermally using microwaves in a frequency range between 100 MHz and 300 GHz.

9. A bead foam obtainable by the process according to claim 7, wherein the bead foam has a specific volume resistivity of less than 10.sup.6 [ mm2/m].

10. A packaging or footwear, comprising the bead foam of claim 9.

11. The foam beads according to claim 1, wherein the coating consists of the at least one electrically conductive substance.

12. The foam beads according to claim 2, wherein the coating consists of graphite.

13. The foam beads according to claim 2, having a bulk density ranging from 30 to 250 kg/m.sup.3.

14. The foam beads according to claim 2, wherein the coating consists of the at least one electrically conductive substance.

Description

EXAMPLES

(1) Materials Used:

(2) 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. Graphite emulsion: emulsion of graphite of not less than 99.5% purity in triacetin (1,2,3-propanetriol triacetate) The exemplified parts by weight of graphite powder and plasticizer were stirred with a dispersing rod (Ultra Turrax) in a glass beaker until homogeneous. Iron emulsion: emulsion of carbonyl iron powder (finely dispersed iron powder deposited from the gas phase, with not less than 99% purity and a particle size below 10 m) in triacetin (1,2,3-propanetriol triacetate) The exemplified parts by weight of carbonyl iron powder and plasticizer were stirred with a dispersing rod (Ultra Turrax) in a glass beaker until homogeneous. Adhesive: Elastopave 6550/101 from BASF Polyurethanes GmbH, compact 2-component polyurethane system
Apparatus:

(3) MLS-Ethos plus laboratory microwave system having a maximum power output of 2.5 kW.

(4) Methods of Measurement:

(5) 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.

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

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

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

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

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

(11) Conductivity and specific volume resistivity were determined in accordance with DIN EN 61340.

Example B1

(12) 97 parts by weight of the E-TPU foam beads having a bulk density of 110 g/l were mixed in a vessel together with an emulsion of 0.4 part by weight of graphite and 2.6 parts by weight of triacetin on an electrical laboratory roller track. The E-TPU foam beads became enveloped with a complete, homogeneous layer of graphite in the course of 6 h.

(13) 52 grams of the loose individual beads thus enveloped were filled into a paperboard mold measuring 220 mm110 mm15 mm. The paperboard lid exerted slight pressure on the beads. This filled mold was placed upright at a 50 angle on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 90 seconds. Following a short period of cooling down, a coherent sheet of foam could be removed.

Example B2

(14) 97.9 parts by weight of the E-TPU foam beads having a bulk density of 150 g/l were mixed in a vessel together with an emulsion of 0.2 part by weight of graphite and 1.9 parts by weight of triacetin on a laboratory roller track. The E-TPU foam beads became enveloped with a complete, homogeneous layer of graphite in the course of 6 h.

(15) 60 grams of the loose individual beads thus enveloped were filled into a paperboard mold measuring 220 mm110 mm15 mm. The paperboard lid exerted slight pressure on the beads. This filled mold was placed upright at a 50 angle on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 120 seconds. Following a short period of cooling down, a coherent sheet of foam could be removed.

Example B3

(16) 97 parts by weight of the E-TPU foam beads having a bulk density of 150 g/l were mixed in a vessel together with an emulsion of 0.4 part by weight of graphite and 2.6 parts by weight of triacetin on an electrical laboratory roller track. The E-TPU foam beads became enveloped with a complete, homogeneous layer of graphite in the course of 6 h.

(17) 48 grams of the loose individual beads thus enveloped were filled into a mold of Ultrason E2010 (polyether sulfone) from BASF SE measuring 150 mm150 mm70 mm. A moveable Ultrason lid exerted slight pressure on the beads. The filled mold was placed on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 90 seconds. Following a short period of cooling down, a coherent sheet of foam could be removed.

Example B4

(18) 91.2 parts by weight of the E-TPU foam beads having a bulk density of 150 g/l were mixed in a vessel together with an emulsion of 6 parts by weight of iron carbonyl powder having a particle size <10 m and 2.8 parts by weight of triacetin on an electrical laboratory roller track. The E-TPU foam beads became enveloped with a complete, homogeneous layer of graphite in the course of 6 h.

(19) 56 grams of the loose individual beads thus enveloped were filled into a mold of Ultrason E2010 (polyether sulfone) from BASF SE measuring 150 mm150 mm70 mm. A moveable Ultrason lid exerted slight pressure on the beads. The filled mold was placed on the outer edge of the laboratory microwave turntable and irradiated at 400 watts for 110 seconds. Following a short period of cooling down, a coherent sheet of foam could be removed.

(20) Comparative Test V1:

(21) 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.

(22) Comparative Test V2:

(23) 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 foam articles.

(24) Comparative Test V3:

(25) 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 foam articles.

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

(27) The foam sheets from Examples B1 and B2 exhibit a higher rebound resilience versus the adhered foam sheets from Comparative Tests V2 and V3.

(28) It is further advantageous that the microwave fusion (Examples B1 and B2) 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. Also of particular advantage is the high electrical conductivity of the foam sheets from Examples B1 to B4 versus the foam sheets fused together in standard fashion with water vapor (Comparative Test V1) and the adhered foam sheets (V2 and V3).

(29) TABLE-US-00001 TABLE 1 Properties of foam sheets from Examples B1 and B2 and Comparative Tests V1-V3 B1 B2 B3 B4 V1 V2 V3 Compressive strength 10% [kPa] 15 30.4 78 20.3 26.8 Compressive strength 25% [kPa] 52.8 103.8 170 53 60.3 Compressive strength 50% [kPa] 151.6 275.7 366.7 142 156.9 Compressive strength 75% [kPa] 718.4 1607.3 1822 540.3 669.5 Density [g/l] 165 229 253.5 135 152 Compression set [%] (6 h/50 C./50%) 72 62 28.9 43 35 Rebound resilience [%] 59 64 70 55 55 Tensile strength [kPa] 64 294 1168 120 292 Elongation at break [%] 13 37 108 32 42 Specific volume resistivity [ mm.sup.2/m] 6.6*10.sup.3 6.3*10.sup.3 6.5*10.sup.3 4.9*10.sup.5 1.7*10.sup.11 1.3*10.sup.11 1.6*10.sup.11