Aliphatic thermoplastic polyurethanes and use thereof

Details Aliphatic thermoplastic polyurethanes and use thereof Aliphatic thermoplastic polyurethanes and use thereof

2002-09-10

2004-03-16

Niland, Patrick D. (Department: 1714)

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

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S589000, C528S044000, C528S076000, C528S080000, C528S083000, C528S084000, C528S085000

Reexamination Certificate

active

06706807

ABSTRACT:

This invention relates to aliphatic thermoplastic polyurethanes (TPU) prepared from hexamethylene diisocyanate, polytetramethylene glycol and hexanediol with improved properties.
Aromatic thermoplastic polyurethanes (aromatic TPUs) are not light-stable because they are synthesised from aromatic diisocyanates. In coloured mouldings, exposure to light brings about severe yellowing and changes in colour and degree of gloss occur even in black mouldings.
DE-C 42 03 307 describes a thermoplastic polyurethane moulding composition processable in the form of a sinterable powder for the production of grained sintered films, wherein the powder is produced exclusively from linear, aliphatic components. The polyol component is composed of 60 to 80 parts by weight of an aliphatic poly-carbonate diol having a molecular weight {overscore (M)}n of 2000 and 40 to 20 parts by weight of a polydiol based on adipic acid, hexanediol and neopentyl glycol having a molecular weight {overscore (M)}n of 2000. Preferably, 1,6-hexamethylene diisocyanate is used in an equivalence ratio of 2.8:1.0 to 4.2:1.0, relative to the polyol mixture, and 1,4-butanediol is used as the chain extender, wherein the equivalence ratio of 1,4-butanediol relative to the polydiol is 1.3:1.0 to 3.3:1.0.
This moulding composition has the disadvantage (especially for optically demanding applications) that it has a tendency to form a white deposit after storage (at room temperature and in particular during accelerated ageing tests, such as the alternating climate test, Arizona test and at elevated temperatures (60-95° C.)). The resultant deposit has the further disadvantage that it cannot readily be wiped off with a cloth.
While formation of the stated deposit is indeed reduced when 1,6-hexanediol is used as chain extender, the deposit reforms on storage at room temperature. However, this deposit may be removed by wiping with a cloth.
The object of the present invention was accordingly to provide light-stable thermoplastic polyurethanes to meet demanding optical requirements, which polyurethanes, after storage at room temperature and after accelerated ageing testing (for example after storage at 60° C.), yield mouldings which exhibit only very slight or no formation of deposits.
This object has been achieved by the thermoplastic polyurethanes according to the invention.
The present invention provides aliphatic, thermoplastic polyurethanes prepared by reacting
A) 100 to 60 mol %, preferably 100 to 70 mol %, particularly preferably 100 to 80 mol % of hexamethylene diisocyanate (HDI) and 0 to 40 mol %, preferably 0 to 30 mol %, particularly preferably 0 to 20 mol % of other aliphatic diisocyanates differing from HDI,
B) 40 to 100 wt. % of polytetramethylene glycol having a number average molecular weight of 600 to 1600 g/mol and 0 to 60 wt. % of a polyol or polyol mixture differing from polytetramethylene glycol and having a number average molecular weight of 600 to 5000 g/mol and
C) 80 to 100 wt. % of 1,6-hexanediol and 0 to 20 wt. % of a chain extender differing from 1,6-hexanediol and having a number average molecular weight of 60 to 500 g/mol.
The inventive thermoplastic polyurethane may be prepared in the presence of
D) optional catalysts and may contain
E) optional further conventional auxiliary substances and additives.
The equivalence ratio of diusocyanate A) to polyol B) is between 1.5:1.0 and 10.0:1.0 and the NCO index (formed from the quotients, multiplied by 100, of the equivalence ratios of isocyanate groups and the sum of the hydroxyl groups of polyol and chain extending agent) characterizing the TPU is 95 to 105.
The present invention furthermore provides aliphatic thermoplastic polyurethanes prepared by reacting
A) 100 to 60 mol %, preferably 100 to 70 mol %, particularly preferably 100 to 80 mol % of hexamethylene diisocyanate (HDI) and 0 to 40 mol %, preferably 0 to 30 mol %, particularly preferably 0 to 20 mol % of other aliphatic diisocyanates differing from HDI,
B) 70 to 30 wt. % of at least one polyol differing from polytetramethylene glycol and having a number average molecular weight of 600 to 5000 g/mol and 30-70 wt. % of polytetramethylene glycol having a number average molecular weight of 200 to 590 g/mol and
C) 80 to 100 wt. % of 1,6-hexanediol and 0 to 20 wt. % of a chain extender having a number average molecular weight of 60 to 500 g/mol, which differs from polytetramethylene glycol having a number average molecular weight of 200 to 590 g/mol and differs from 1,6-hexanediol,
wherein the equivalence ratio of diisocyanate A) to polyol B) is between 1.5:1.0 and 10.0:1.0 and wherein the NCO index (formed from the quotients, multiplied by 100, of the equivalence ratios of isocyanate groups and the sum of the hydroxyl groups of polyol and chain extending agent) is 95 to 105.
The preparation of the inventive TPU may be in the presence of D) catalysts and the composition may contain E) conventional additives.
The above sequence of components A to E is no indication of the method by which the TPUs according to the invention are produced. The TPUs according to the invention may be produced by various process variants, wherein these variants are mutually equivalent.
The TPUs according to the invention based on two different aliphatic diisocyanates “A1” (HDI) and “A2” (aliphatic diusocyanate differing from HDI) may, for example, be produced in a reaction process to yield TPU “A1-2”. It is, however, also possible in known manner initially to produce TPU “A1” based on the aliphatic diisocyanate “A1” and to produce separately therefrom TPU “A2” based on the aliphatic diisocyanate “A2”, wherein the other components B to E are identical. TPU “A1” and TPU “A2” are then mixed in known manner in the desired ratio to yield TPU “A1-2” (for example using extruders or kneaders).
The TPUs according to the invention based on polyol mixtures may likewise be produced by using polyol mixtures (polyol B1 and polyol B2) (for example in mixers) in a reaction process to yield TPU “B1-2”. Alternatively, it is also possible in known manner initially to produce TPU “B1” based on polyol “B1” and to produce separately therefrom TPU “B2” based on polyol “B2”, wherein the remaining components A and C to E are identical. TPUs “B1” and “B2” are then mixed in known manner in the desired ratio to yield TPU “B1-2” (for example using extruders or kneaders).
Depending upon the requirements placed upon the moulding which is produced from the TPU according to the invention, the hexamethylene diisocyanate (HDI) may be replaced in part by one or more other aliphatic diisocyanates, in particular isophorone diisocyanate (IPDI), 1,4-cyclohexane diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate, 1-methyl-2,6-cyclohexane diisocyanate and isomer mixtures thereof, 4,4′-, 2,4′- and 2,2′-dicyclohexylmethane diisocyanate and isomer mixtures thereof.
In applications having low requirements with regard to light stability, for example dark coloured moulding compositions, proportions (0 to 20 wt. %) of the aliphatic diisocyanate may even be replaced by aromatic diisocyanates. Aromatic diisocyanates are described in
Justus Liebigs Annalen der Chemie,
562, pp. 75-136. Examples are 2,4-tolylene diisocyanate, mixtures of 2,4- and 2,6-tolylene diisocyanate, 4,4′-, 2,2′- and 2,4′-diphenylmethane diisocyanate, mixtures of 2,4- and 4,4′-diphenylmethane diisocyanate, urethane-modified, liquid 2,4- and/or 4,4′-diphenylmethane diisocyanates, 4,4′-diisocyanato-1,2-diphenylethane and 1,5-naphthylene diisocyanate.
Linear hydroxyl-terminated polyols for instance polyester diol and polyether diol, having an average molecular weight of 600 to 5000 g/mol, preferably of 700 to 4200 g/mol, are used as component B2). As a result of the production process, these frequently contain small amounts of non-linear compounds. For this reason, they are often also referred to as “substantially linear polyols”.
Suitable polyester diols may be produced for example from dicarboxylic acids having 2 to 12 carbon atoms, preferably 4 to 6 carbon

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