Blends comprising thermoplastic polyurethane

Details Blends comprising thermoplastic polyurethane Blends comprising thermoplastic polyurethane

2001-09-19

2003-05-06

Woodward, Ana (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S125000, C525S131000

Reexamination Certificate

active

06559229

ABSTRACT:

The present invention relates to blends comprising (a) thermoplastic polyurethane having a Shore hardness of from 60 A to 50 D and (b) ethylene-propylene (EPM) rubbers and/or modified ethylene-propylene (EPM) rubbers, where the weight ratio of (a): (b) is from 3:1 to 999:1, preferably from 6:1 to 100:1.
Thermoplastic polyurethanes, hereinafter also referred to as TPUS, are generally known. As materials, they are notable for high strength together with a good elasticity. In addition to these excellent properties, a high abrasion resistance is desirable for many applications. To reduce abrasion, blends of TPUs with rubbers based on ethylene-propylene polymers are described in the literature. Thus, JP-A 09 255 868 discloses general blends comprising TPU and ethylene-propylene rubbers which have been modified with aromatic, unsaturated compounds and with unsaturated substances containing polar, functional groups. In addition, a further modification is achieved by mixing the ethylene-propylene rubbers mentioned with styrene and 2-hydroxyethyl methacrylate and various additives. The weight ratio of TPU to modified rubber is 2.3:1 in the example. A disadvantage of these blends is the addition of unsaturated aromatic compounds which are undesirable in some applications. Furthermore, as a result of the high proportion of rubber these blends display, as expected, no reduction in the abrasion compared to pure TPUs. This result is consistent with findings in the case of TPU mixed with other plastics. As a rule, the arrangement of the soft segments and the hard segments, which in the TPUs leads to the excellent properties of these materials, is destroyed by mixing in further plastics. Mixing other plastics with TPU thus generally leads to a worsening of the properties compared to the pure TPU. Further TPU-rubber blends are described in JP-A 06 145 500, U.S. Pat. No. 5,149,739, J0 3035-054 and J0 3035-056.
It is an object of the present invention to develop TPU-based blends which display significantly reduced abrasion compared to pure TPUs without having disadvantages in the other properties, for example in respect of the tensile strength.
We have found that this object is achieved by the blends described at the outset.
The Shore hardnesses reported in the present application are measured in accordance with DIN 53 505.
As TPU (a) in the blends of the present invention, it is possible to use generally customary TPUs which have the hardness specified according to the present invention and can be prepared by known methods from (c) isocyanates, (d) compounds which are reactive toward isocyanates and, if desired (e) chain extenders in the presence or absence of (f) catalysts and/or (g) auxiliaries and/or additives, where the ratio of the isocyanate groups of the component (c) to the sum of isocyanate-reactive groups of the components (d) and, if used, (e) is usually from 1:0.9 to 1:1.1.
Examples of starting components and preparative methods for (a) and (b) are described below.
c) Suitable organic isocyanates (c) are preferably aliphatic, cycloaliphatic and in particular aromatic diisocyanates. Specific examples are: aliphatic diisocyanates such as hexamethylene 1,6-diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene 1,4-diisocyanate or mixtures of at least 2 of the C
6
-alkylene diisocyanates mentioned, pentamethylene 1,5-diisocyanate and butylene 1,4-diisocyanate, cycloaliphatic diisocyanates such as 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), 1,4- and/or 1,3-bis(isocyanatomethyl)cyclohexane (HXDI), cyclohexane 1,4- diisocyanate, 1-methylcyclohexane 2,4- and 2,6-diisocyanate and also the corresponding isomer mixtures, dicyclohexylmethane 4,4′-, 2,4′- and 2,2′-diisocyanate and also the corresponding isomer mixtures and preferably aromatic diisocyanates such as tolylene 2,4-diisocyanate, mixtures of tolylene 2,4- and 2,6-diisocyanate, 3,3′-dimethylbiphenyl 4,4′-diisocyanate (TODI), p-phenylene diisocyanate (PDI), m-, p-xylylene diisocyanate (XDI), diphenylmethane 4,4′-, 2,4′- and 2,2′-diisocyanate (MDI), mixtures of diphenylmethane 2,4′- and 4,4′-diisocyanate, urethane-modified liquid diphenylmethane 4,4′- and/or 2,4′-diisocyanates, 1,2-bis(4-isocyanatophenyl)ethane (EDI) and naphthylene 1,5-diisocyanate. Preference is given to using naphthylene 1,5-diisocyanate, dicyclohexylmethane 4,4′-diisocyanate, hexamethylene 1,6-diisocyanate, diphenylmethane diisocyanate isomer mixtures having a diphenylmethane 4,4′-diisocyanate content of greater than 96% by weight and, in particular, diphenylmethane 4,4′-diisocyanate and hexamethylene 1,6-diisocyanate.
d) Suitable substances (d) which are reactive toward isocyanates are, for example, polyhydroxyl compounds having molecular weights of from 500 to 8000, preferably polyetherols and polyesterols. However, other suitable isocyanate-reactive substances (d) are hydroxyl-containing polymers, for example polyacetals such as polyoxymethylenes and especially water-insoluble formals, e.g. polybutanediol formal and polyhexanediol formal, and aliphatic polycarbonates, particularly those prepared from diphenyl carbonate and 1,6-hexanediol by transesterification and having the abovementioned molecular weights. The polyhydroxyl compounds mentioned can be used as individual components or in the form of mixtures.
The mixtures for preparing the TPU or TPUs are usually based at least predominantly on bifunctional isocyanate-reactive substances, i.e. the mean functionality of the component (d) is preferably from 1.8 to 2.6, particularly preferably from 1.9 to 2.2. The TPUs are thus predominantly unbranched, i.e. predominantly uncrosslinked.
Suitable polyetherols can be prepared by known methods, for example from one or more alkylene oxides having from 2 to 4 carbon atoms in the alkylene radical and, if appropriate, an initiator molecule containing two reactive hydrogen atoms in bound form by anionic polymerization using alkali metal hydroxides such as sodium or potassium hydroxide or alkali metal alkoxides such as sodium methoxide, sodium or potassium ethoxide or potassium isopropoxide as catalysts or by cationic polymerization using Lewis acids such as antimony pentachloride, boron fluoride etherate, etc., or bleaching earth as catalysts. Examples of alkylene oxides are: ethylene oxide, 1,2-propylene oxide, tetrahydrofuran, 1,2- and 2,3-butylene oxide. Preference is given to using ethylene oxide and mixtures of 1,2-propylene oxide and ethylene oxide. The alkylene oxides can be used individually, alternately in succession or as mixtures. Examples of suitable initiator molecules are: water, aminoalcohols such as N-alkyldialkanolamines, for example N-methyldiethanolamine, and diols, e.g. alkanediols or dialkylene glycols having from 2 to 12 carbon atoms, preferably from 2 to 6 carbon atoms, for example ethanediol, 1,3-propanediol, 1,4-butanediol and 1,6-hexanediol. If desired, it is also possible to use mixtures of initiator molecules. Further suitable polyetherols are the hydroxyl-containing polymerization products of tetrahydrofuran (polyoxytetramethylene glycols).
Preference is given to using polyetherols derived from 1,2-propylene oxide and ethylene oxide in which more than 50%, preferably from 60 to 80%, of the OH groups are primary hydroxyl groups and in which at least part of the ethylene oxide is arranged as a terminal block; particular preference is given to using polyoxytetramethylene glycols.
Such polyetherols can be obtained by, for example, first polymerizing the 1,2-propylene oxide onto the initiator molecule and subsequently polymerizing on the ethylene oxide or first copolymerizing all the 1,2-propylene oxide with part of the ethylene oxide and subsequently polymerizing on the remainder of the ethylene oxide or, stepwise, first polymerizing part of the ethylene oxide onto the initiator molecule, then polymerizing on all of the 1,2-propylene oxide and then polymerizing on the remainder of the ethylene oxide.
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