Expanded thermoplastic polyurethane beads, production thereof and production of a molded part
Disclosed herein are expanded thermoplastic polyurethane beads polymerized from an isocyanate, an isocyanate-reactive compound having a molecular weight between 500 and 10 000 g/mol and a chain extender, wherein customary adjuvants may be additionally present, and the thermoplastic polyurethane has a hard phase fraction ranging from 0.1 to 0.95 and the hard phase fraction is defined by: Hard phase fraction = ∑ x = 1 k ( ( m KVx M KV x ) · M Iso + m KVx ) m ges where M KVx represents a molar mass of chain extender x in g/mol, m KVx represents a mass of chain extender x in g, M Ixo represents a molar mass of isocyanate in g/mol, m ges represents a total mass of all starting materials without adjuvants, and k represents a number of chain extenders. Also disclosed herein are processes for producing expanded thermoplastic polyurethanes and processes for producing molded parts therefrom.
1. Expanded thermoplastic polyurethane beads polymerized from an isocyanate, an isocyanate-reactive compound having a molecular weight between 500 and 10 000 g/mol and a chain extender,
wherein:
customary adjuvants may be additionally present;
the thermoplastic polyurethane has a hard phase fraction in the range from 0.15 to 0.5 and the hard phase fraction is defined by:
Hard
phase
fraction
=
∑
x
=
1
k
(
(
m
KVx
M
KV
x
)
·
M
Iso
+
m
KVx
)
m
ges
,
wherein:
M KVx : molar mass of chain extender x in g/mol,
m KVx : mass of chain extender x in g,
M Iso : molar mass of isocyanate in g/mol
M ges : total mass of all starting materials without adjuvants
k: number of chain extenders;
wherein said chain extender is selected from the group consisting of
1,6 hexanediol,
1,6-hexanediol and 1,4-butanediol, and
1,4-butanediol and 1,3-propanediol,
excluding 1,4-butanediol alone; and
said thermoplastic polyurethane has a melting temperature below 120° C.
2. The expanded thermoplastic polyurethane according to claim 1 , wherein the isocyanate is selected from the group consisting of trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylene diisocyanate; 2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene 1,4-diisocyanate, butylene 1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; 1,4-bis(isocyanatomethyl) cyclohexane; 1,4-cyclohexane diisocyanate; 1-methyl-2,4-cyclohexane diisocyanate; 1-methyl-2,6-cyclohexane diisocyanate; 2,2′-dicyclohexylmethane diisocyanate; 2,4′-dicyclohexylmethane diisocyanate; 4,4′-dicyclohexylmethane diisocyanate; 2,2′-diphenylmethane diisocyanate; 2,4′-diphenylmethane diisocyanate; 4,4′-diphenylmethane diisocyanate; 1,5-naphthylene diisocyanate; 2,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; diphenylmethane diisocyanate; 3,3′-dimethylbiphenyl diisocyanate; 1,2-diphenylethane diisocyanate and phenylene diisocyanate and also any desired mixture thereof.
3. The expanded thermoplastic polyurethane according to claim 1 , wherein the isocyanate-reactive compound is selected from the group consisting of a polyetherol, a polyesterol, a polybutadienol, a polycarbonateol, mixtures thereof, and block copolymers thereof.
4. The expanded thermoplastic polyurethane according to claim 1 , wherein the expanded thermoplastic polyurethane is closed cell and has a cell size in the range from 1 to 250 μm.
5. The expanded thermoplastic polyurethane according to claim 1 , wherein the expanded thermoplastic polyurethane is in the form of beads having a maximum longitudinal dimension of 1 to 25 mm.
6. A process for producing an expanded thermoplastic polyurethane according to claim 1 , the process comprising:
(a) reacting an isocyanate with an isocyanate-reactive compound and the chain extender optionally in the presence of one or more catalysts and/or adjuvants to form a polyurethane,
wherein:
amounts of isocyanate, of isocyanate-reactive compound and of chain extender are adjusted such that the thermoplastic polyurethane has a hard phase fraction in the range from 0.15 to 0.5 and the hard phase fraction is defined by:
Hard
phase
fraction
=
∑
x
=
1
k
(
(
m
KVx
M
KV
x
)
·
M
Iso
+
m
KVx
)
m
ges
,
wherein
M KVx : molar mass of chain extender x in g/mol,
M KVx : mass of chain extender x in g,
M Iso : molar mass of isocyanate in g/mol
M ges : total mass of all starting materials without adjuvants
k: number of chain extenders;
(b) cutting the polyurethane into pellets;
(c) impregnating the polyurethane with a blowing agent, wherein impregnating can be carried out before or after cutting the polyurethane into pellets; and
(d) depressurizing the blowing agent-impregnated polyurethane into the expanded thermoplastic polyurethane.
7. The process according to claim 6 , wherein the polyurethane is impregnated with the blowing agent in an extruder, the impregnated polyurethane is cut into a pellet material, and the pellet material is depressurized into expanded thermoplastic polyurethane beads immediately after cutting.
8. The process according to claim 6 , wherein the polymerizing of the polyurethane in step (a) is carried out in a first extruder or a first extruder part, impregnating of a melt is carried out in a second extruder or a second extruder part, the impregnated polyurethane is cut into a pellet material, and the pellet material is depressurized into expanded thermoplastic polyurethane beads immediately after cutting.
9. The process according to claim 6 , wherein the polyurethane polymerized in step (a) is cut into a pellet material, the pellet material is impregnated with from 0.1 to 40% by weight of a blowing agent in a tank or in an autoclave at a temperature in the range from 100 to 180° C. and a pressure in the range from 5 to 100 bar, and then the blowing agent-containing pellet material is foamed by depressurization.
10. A process for producing a molded part from the expanded thermoplastic polyurethane beads according to claim 9 , the process comprising:
(a) introducing the expanded thermoplastic polyurethane beads into a mold; and
(b) subjecting the expanded thermoplastic polyurethane beads introduced into the mold to steam, hot air or high-energy radiation whereby the expanded thermoplastic polyurethane beads incipiently melt at the surface and fuse together to form the molded part.
11. The process according to claim 10 , wherein the molded part is a shoe sole, a gymnastics mat, a body protector, a trim element in automotive construction, a sound absorber, a vibration absorber, a cushioning pad, a bicycle saddle, a toy, a tire or a tire part or a surface for an athletic running track, a sports hall or a footpath, a damping layer or a damping core in a sandwich element or a packaging item.
12. The expanded thermoplastic polyurethane according to claim 1 ,
wherein said thermoplastic polyurethane has a hard phase fraction in the range of 0.2 to 0.45.
13. The expanded thermoplastic polyurethane according to claim 1 , wherein said thermoplastic polyurethane has a storage modulus at room temperature of 5 to 100 MPa.
14. The expanded thermoplastic polyurethane according to claim 1 , wherein said expanded thermoplastic polyurethane beads have a density in a range from 20 to 350 g/l.