HYBRID SYSTEMS CONSISTING OF FOAMED THERMOPLASTIC ELASTOMERS AND POLYURETHANES

Abstract

The present invention relates to a hybrid material comprising a matrix of polyurethane and foamed particles of thermoplastic polyurethane comprised therein and also a process for producing such hybrid materials and the use of these hybrid materials as bicycle saddles, upholstery and shoe soles.

Claims

1. A process for producing a hybrid material comprising a matrix of polyurethane and foamed particles of thermoplastic polyurethane comprised therein, which comprises mixing a) polyisocyanates with b) compounds having hydrogen atoms which are reactive toward isocyanates, c) expandable particles (c) of thermoplastic polyurethane which comprise blowing agents in dispersed or dissolved form and, if appropriate, d) chain extenders and/or crosslinkers, e) catalysts, f) blowing agents and g) further additives and reacting the mixture to form the hybrid material, with the reaction being carried out under conditions which lead to expansion of the expandable particles (c) so that the foamed particles have a closed surface skin.

Description

PRODUCTION OF THE EXPANDABLE PARTICLES

[0106] Starting out from one mol of a polyester polyol having a number average molecular weight of 800 g/mol and based on adipic acid and 1,4-butanediol, pellets of a thermoplastic polyurethane (TPU A) having a mean particle weight of about 2 mg were produced by reaction with 0.44 mol of 1,4-butanediol and 1.44 mol of 4,4-MDI. In addition, starting out from 1 mol of polytetrahydrofuran having a number average molecular weight of 1333 g/mol, pellets of a thermoplastic polyurethane (TPU B) having a mean particle weight of likewise about 2 mg were produced analogously by reaction with 0.97 mol of 1,4-butanediol and 1.97 mol of 4,4-MDI.

[0107] In an autoclave, 100 parts by weight of the thermoplastic polyurethane A (TPU A) or B (TPU B) were in each case mixed with, in succession, 250 parts of water, 6.7 parts of tricalcium phosphate and 20 parts of n-butane while stirring and heated to the temperature indicated in table 1. The contents of the pressure vessel were then discharged and depressurized through a bottom valve, with the pressure in the vessel being kept constant by injection of further nitrogen or the blowing agent used. The foam particles were freed of adhering residues of the auxiliary by washing with nitric acid and water and air dried at 50 C.

[0108] The impregnation conditions and the bulk densities of the expanded particles obtained are shown in table 1.

TABLE-US-00001 TABLE 1 n-Butane Temperature Bulk density TPU [parts by weight] [ C.] [g/l] TPU A 20 112 300 TPU A 20 114 170 TPU B 20 119 240 TPU B 20 120 190 TPU B 20 122 140 TPU B 20 125 120

Production of a Hybrid Material as Integral Foam (Example 1)

[0109] An aluminum mold having dimensions of 20204 cm which had been heated to 50 C. was used. The mold was firstly filled to the rim with 160 g of previously expanded TPU beads and subsequently charged with 400 g of reaction mixture as shown in table 2. The matrix formulation of example 1 represents a usual polyurethane mixture for producing integral foams of medium density. The formulation for C1 represents a formulation for low-density systems in which a polymer polyol is added to obtain the mechanical properties. The mold is closed and the molding is removed after 5 minutes.

[0110] The composition and the mechanical properties of the foams are summarized in table 2:

TABLE-US-00002 TABLE 2 Composition and mechanical properties of hybrid foams (1) and conventional low-density foams (C1) Example 1 C1 Polyol 1 25.0 25.0 Polyol 2 57.0 32.9 Polyol 3 29.7 Chain extender 13.0 8.8 Water 0.6 1.1 Amine cat. 3.0 1.6 Tin cat. 0.05 0.2 Cell regulator 0.4 ExTPU + B: Iso comp. Iso 1 133.1 Iso 2 112.6 Index 98 100 Mechanical properties Density [g/l] 300 300 Density of the matrix [g/l] 550 300 Hardness [Asker C] 56-58 56-58 Split tear [N/mm] 3.8 2.4 Rebound resilience [%] 51 46

[0111] Isocyanate components. Isocyanate components used were isocyanate prepolymers based on MDI and polyetherol mixtures and having an NCO content of 13.9% (Iso 1) or 18% (Iso 2).

[0112] Polyol 1 is a polyetherol based on propylene oxide/ethylene oxide and having an OH number of 29 mg KOH/g and a functionality, based on the starter, of 2. Polyol 2 is a polyetherol based on propylene oxide/ethylene oxide and having an OH number of 27 mg KOH/g and a functionality, based on the starter, of 3. Polyol 3 is a polymer polyetherol having a solids content of 45% and an OH number of 20 mg KOH/g. The chain extender is a mixture of 1,4-butanediol and ethylene glycol. As amine catalyst, use was made of a mixture of tertiary amines in glycols. The cell regulator is a surface-active silicone polymer.

[0113] The determination of the tear propagation resistance (split tear) was carried out in accordance with ASTM D3574F.

[0114] The determination of the rebound resilience was carried out in accordance with DIN 53512.

[0115] Table 2 shows that a hybrid material as per Example 1 has, compared to the foam as per C1, a significantly improved tear propagation resistance and an improved rebound resilience at the same density and the same hardness and is therefore highly suitable for use in shoe soles.

Production of a Hybrid Material as Sheet-Like Material

[0116] An isocyanate prepolymer having an NCO content of 10% by weight was prepared from 36 parts by weight of isocyanate 1, viz. a diphenylmethane diisocyanate having an NCO content of 32.2%, 2 parts by weight of isocyanate 2, viz. a modified diphenylmethane diisocyanate having an NCO content of 29.5%, and 62 parts by weight of a polyetherol based on propylene oxide and having an OH number of 56 mg KOH/g.

[0117] 40 g of the isocyanate prepolymer (Prepo) produced and 200 g of expanded TPU beads having an average particle diameter of about 2 mm (ExTPU1) were mixed in a polypropylene bucket, capacity: 2.75 l, by means of a Vollrath stirrer at 700 revolutions per minute for 2 minutes. The mixture was subsequently introduced into a wooden frame having dimensions of 20201.5 cm and compacted to a thickness of about 1.5 cm. The sheet-like materials obtained were stored overnight in a fume hood, removed from the mold after storage for a further 24 hours under standard conditions of temperature and humidity (23 C., 50% rel. atmospheric humidity) and stored for a further 5 days under standard conditions of temperature and humidity (Example 2).

[0118] Example 3 was carried out in a manner analogous to Example 2, with 60% by weight of the expanded TPU beads being replaced by industrial recycled rubber based on a blend of styrene-butadiene rubber (SBR) and isobutene-isoprene rubber (rubber).

[0119] Example 4 was carried out in a manner analogous to Example 2, with expanded TPU beads having an average particle diameter of about 7 mm (ExTPU2) being used instead of the expanded TPU beads having an average particle diameter of about 2 mm.

[0120] Example 5 was carried out in a manner analogous to Example 4, with 40% by weight of the expanded TPU beads being replaced by industrial recycled rubber based on a blend of styrene-butadiene rubber (SBR) and isobutene-isoprene rubber.

[0121] Comparative Example 2 was carried out in a manner analogous to Example 2, with the expanded TPU beads being replaced by industrial recycled rubber based on a blend of styrene-butadiene rubber (SBR) and isobutene-isoprene rubber.

[0122] To determine the mechanical properties of the cured foam plates, four tensile bars having a width of the narrow part of 25 mm are stamped from each plate. The tensile strength and the elongation at break are determined on these tensile bars using a method based on DIN EN ISO 1856, with a width of the narrow part of 25 mm and a test speed of 100 mm/min being used as modifications of this standard. The mean of the results for each plate was subsequently calculated. The results of these measurements and the density of the test specimens are shown in Table 3.

TABLE-US-00003 Example 2 Example 3 Example 4 Example 5 C2 Ex TPU1 [parts 100 40 by weight] Ex TPU2 [parts 100 60 by weight] Rubber [parts by 60 40 100 weight] Prepo [parts by 20 20 20 20 20 weight] Tensile strength 967 282 278 348 251 [kPa] Elongation at 235 95 82 107 22 break [%] Density [kg/m.sup.3] 289.6 463.1 204.5 305.1 720.4

[0123] Table 3 shows that a hybrid material as per Examples 2 to 5 has an improved tensile strength and an improved elongation at break at a lower density compared to Comparison 2.