Process for producing foams based on thermoplastic polyurethanes

Abstract

A process for producing foamed thermoplastic polyurethane particles comprises the steps of a) melting a thermoplastic polyurethane in a first extruder (E1), b) injecting a gaseous blowing agent in a second extruder (E2), c) impregnating the gaseous blowing agent homogeneously into the thermoplastic polyurethane melt in a third extruder (E3), d) extruding the impregnated thermoplastic polyurethane melt through a die plate and granulating the melt in an underwater granulation device under temperature and pressure conditions to form foamed thermoplastic polyurethane particles.

Claims

1. A process for producing foamed thermoplastic polyurethane particles, the process comprising: a) melting a thermoplastic polyurethane in a first extruder E1, which is a single screw extruder, b) injecting a gaseous blowing agent in a second extruder E2, which is a twin extruder, c) impregnating the gaseous blowing agent homogeneously into the thermoplastic polyurethane melt in a third extruder E3, which is a single screw extruder operating at a lower rotation and lower sheer rate than said second extruder E2, and d) extruding the impregnated thermoplastic polyurethane melt through a die plate and granulating the melt in an underwater granulation device under temperature and pressure conditions to form foamed thermoplastic polyurethane particles, wherein a bulk density of the foamed thermoplastic polyurethane particles formed in step d) is from 30 to 250 kg/m.sup.3.

2. The process according to claim 1, wherein the gaseous blowing agent comprises CO.sub.2, N.sub.2, or a combination of CO.sub.2 and N.sub.2.

3. The process according to claim 1, wherein a single screw extruder is used as the first extruder E1 and the third extruder E3, and a twin extruder is used as the second Extruder E2.

4. The process according to claim 1, wherein the water in the underwater granulation device has a pressure in the range from 1 to 20 bar and a temperature in the range from 10 to 50° C.

5. The process according to claim 1, wherein the bulk density of the foamed thermoplastic polyurethane particles formed in step d) is from 100 to 200 kg/m.sup.3.

6. The process according to claim 1, wherein the bulk density of the foamed thermoplastic polyurethane particles formed in step d) is from 160 to 230 kg/m.sup.3.

7. The process according to claim 1, wherein the thermoplastic polyurethane further comprises a crosslinking agent that is polyether polyol-MDI-based prepolymer.

8. The process according to claim 7, wherein the gaseous blowing agent comprises CO.sub.2, N.sub.2, or a combination of CO.sub.2 and N.sub.2.

Description

EXAMPLES

(1) Raw Materials:

(2) Elastollan 1180A (commercially available TPU of BASF SE)

(3) Elastollan 1196A (commercially available TPU of BASF Japa)

(4) Elastollan ET880 (commercially available TPU of BASF Japan)

(5) Elastollan SP9324 (commercially available TPU of BASF SE)

(6) Crosslinking agent Polyether polyol -MDI-based prepolymer

(7) Binder for TPU form

(8) Elastan® C8008 C-B: 15% /MCP

(9) Following Set-up of the machine was used for examples 1-12:

(10) 3 different types of extruders are connected and following equipment is attached respectively;

(11) 1. Dryer to the 1st extruder. 2. Gas dosing system to the 2.sup.nd extruder. 3. Underwater pelletize system to the 3rd extruders.

(12) TPU was melted in a 1st Extruder. Temperature conditions were adjusted dependent on TPU grade used.

(13) Nitrogen and/or carbon dioxide were injected into the 2.sup.nd Extruder (46 mmcp twin extruder) using injection pumps.

(14) Setting Temperature of heater zone C1 to C12 and AD (Adapter)

(15) TABLE-US-00001 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 AD 200 200 190 190 190 190 190 190 190 190 190 190 190 180 180

(16) Control conditions

(17) Rotating speed: 47 rpm

(18) Exit pressure : 7.5 MPa

(19) Blowing agents:

(20) N.sub.2: Pressure 8 MPa (0.4˜0.5% vs TPU)

(21) CO.sub.2: Pressure 4 MPa (1.1˜.4% vs TPU)

(22) A 3.sup.rd Extruder (65 mmcp single extruder with cooling able quadruple thread screw) was used for gas diffusion in the melted TPU

(23) Setting Temperature of heater zone C1 to C4 and AD (Adapter)

(24) TABLE-US-00002 Screw C1 C2 C3 C4 AD 160 170 190 190 190 180

(25) Control conditions

(26) Rotating speed: 24 rpm

(27) Entrance pressure: 8 MPa

(28) Die pressure: 9 MPa

(29) Underwatergranulation:

(30) Setting Temperature of adapter (between filter and die) and die

(31) TABLE-US-00003 Adapter Die 188 200

(32) Following Set-up of the machine was used for comparative examples 13-15:

(33) Comparative examples were used only 1 extruder which are implemented TPU melting, gas dosing and gas diffusion.

(34) Setting Temperature of heater zone C1 to C12 and AD (Adapter)

(35) TABLE-US-00004 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 AD 160 180 190 190 190 190 190 190 190 190 190 190 190 180 180

(36) Underwatergranulation:

(37) Setting Temperature of adapter (between filter and die) and die

(38) TABLE-US-00005 Adapter Die 188 200

(39) Molding Conditions:

(40) TPU-foam particles from example 1-15 were molded using PU binder Elastan C8008 and pressed 30 minutes at 80° C. Physical properties of the moldings are summarized in Table 1.

(41) Testing:

(42) Mold density and compressive strength were determined according to JIS K 6767.

(43) Tensile strength and elongation at break were determined according to JIS K 6400.

(44) Tear strength and Rebound resilience were determined according to JIS K 7311.

(45) Compression set was determined

(46) TABLE-US-00006 TABLE 1 Physical properties of Examples 1-15 Example 1 2 3 4 5 6 7 8 9 Base TPU 1180A 1180A 1196 gas CO.sub.2 CO.sub.2 + N.sub.2 CO.sub.2 melt viscosity 5.4 5.4 16 16 5.4 5.4 1.1 1.1 1.1 MFR [g/10 min] crosslinker [%] 5 5 5 — 5 5 5 5 5 particle (g/l) 170 200 170 170 160 200 160 180 190 bulk density Compressive 10% 0.05 0.06 0.05 0.05 0.03 0.07 0.11 0.12 0.13 strength 25% 0.13 0.15 0.13 0.11 0.08 0.14 0.35 0.40 0.50 50% 0.28 0.30 0.27 0.25 0.15 0.25 0.75 0.90 0.95 Compressive (MPa) 0.40 0.50 0.40 0.39 0.25 0.40 0.90 0.90 1.00 elasticity modulus rebound resilience (%) 53 53 49 47 49 50 27 26 26 Compression (%) 23 20 37 50 33 30 27 22 20 set (23° C. × 22 hr) Example 10 11 12 13 14 15 Base TPU ET880 SP9324 1180A SP9324 1196A gas CO.sub.2 CO.sub.2 CO.sub.2 + N.sub.2 CO.sub.2 + N.sub.2 CO.sub.2 + N.sub.2 melt viscosity 10.2 10.2 23 5.4 23 1.1 MFR [g/10 min] crosslinker [%] 5 5 5 — — — particle (g/l) 210 230 240 110 230 Not expanded bulk density Compressive 10% 0.05 0.06 0.07 0.03 0.05 strength 25% 0.13 0.14 0.15 0.08 0.12 50% 0.24 0.25 0.27 0.16 0.24 Compressive (MPa) 0.52 0.53 0.54 0.19 0.49 elasticity modulus rebound resilience (%) 56 56 58 57 59 Compression (%) 16 15 17 set (23° C. × 22 hr)