Aliphatic, low-emission thermoplastic polyurethane molding...

Details Aliphatic, low-emission thermoplastic polyurethane molding... Aliphatic, low-emission thermoplastic polyurethane molding...

2000-06-16

2002-07-16

Sergent, Rabon (Department: 1711)

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

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C528S083000, C528S085000, C528S481000, C528S483000

Reexamination Certificate

active

06420510

ABSTRACT:

Polyurethane moulding compositions which can be melt processed in the form of sintering powders suitable for the preparation of sintered films and which are prepared exclusively from linear, aliphatic components are described. The polyol component is composed of 30 to 80 parts by weight of an aliphatic polycarbonate diol with an average molecular weight {overscore (M)}
n
of 1000 to 2200 and 70 to 20 parts by weight of a polybutane diol adipate and/or a polycaprolactone diol with an average molecular weight {overscore (M)}
n
of 1000 to 2400. Moreover, the mixture contains 1,6-hexamethylene diisocyanate in an equivalence ratio of 2.3:1.0 to 6.2:1.0, based on the polyol mixture and butane-1,4-diol as the chain extender, the equivalence ratio of the butane-1,4-diol based on the poly mixture being 1.3:1.0 to 5.2:1.0.
The NCO characteristic, formed from the quotient, multiplied by 100, of the equivalence ratios of isocyanate groups and the sum of the hydroxyl groups of polyols and chain extender, is 96 to 99.
Grained sintered films are used for the surface trim of dashboards in motor vehicles and have been produced hitherto from polyvinyl chloride, of which the chlorine content and heavy metal proportion and plasticiser content cause problems during recycling and during use in the motor vehicle. It is known, for example, that plasticisers release gases in sunlight, a fact which becomes apparent in a troublesome film on the interior of the windscreen.
The commercially available, thermoplastic polyurethanes that are used for the production of synthetic leather and also in extrusion and injection moulding processes are suitable for melt processing by the sintering powder process, but the light and temperature stability in particular of the films obtained do not meet the requirements that the automobile industry expects of films for dashboards.
Aromatic, thermoplastic polyurethanes are not light stable due to their aromatic diisocyanate constitution. In the case of light colours, considerable yellowing is brought about by the action of light, and even black films undergo a change in colour and gloss.
DE-AS 16 94 135 describes a process for the preparation of crosslinked polyurethanes from relatively high molecular weight, linear polyhydroxyl compounds which consist of a mixture of 70 to 90 wt. % of hexane diol polycarbonate which has been prepared by reaction of hexane-1,6-diol and diaryl carbonates, and 10 to 30 wt. % of mixed polyester of i.a. adipic acid, hexane-1,6-diol and 2,2′-dimethylpropane-1,3-diol diisocyanates and low molecular weight chain extender containing at least two hydrogen atoms reacting with isocyanate groups, for example, butane-1,4-diol. Exclusively aromatic diisocyanates are to be used. The crosslinking of the polyurethanes is achieved by the use of an excess of diisocyanates. In polyurethane elastomers prepared from these starting materials, the high resistance to hydrolysis caused by the polycarbonate remains intact. Moreover, such elastomers also have improved low temperature resistance and processability compared with the elastomers for the preparation of which pure hexane-1,6-diol polycarbonate was used as the polyol component. The improved processability has particular consequences in the liquid phase - for example, during the casting process-since the polyester-polycarbonate mixtures used have a lower viscosity than the pure hexane diol polycarbonate at the processing temperatures, which is why the resulting film can be cast more easily in a bubble-free manner. The products prepared by this process may be used in mechanical engineering and vehicle construction; no statements are made about their softening range and the heat resistance of their optionally profiled surfaces.
Aliphatic, thermoplastic polyurethanes based on H
12
-MDI are light-fast but their heat resistance is not sufficient for use on dashboards in motor vehicles. In view of intense solar irradiation, the interior of motor vehicles behind the glass windscreen on the dashboard rises to more than 100° C., a temperature which already lies in the softening range of these polyurethanes. Grain stability up to a temperature of 130° C. and hot light stability up to 120° C. cannot be achieved with these materials.
DE-C 42 03 307 describes a polyurethane moulding composition which can be melt processed in the form of a sintering powder for the preparation of grained sintered films, the powder being composed exclusively of linear, aliphatic components. The polyol component is composed of 60 to 80 parts by weight of an aliphatic polycarbonate diol with a molecular weight {overscore (M)}
n
of 2000 and 40 to 20 parts by weight of a polydiol based on adipic acid, hexane diol and neopentyl glycol with a molecular weight {overscore (M)}
n
of 2000. Moreover, the mixture contains 1,6-hexamethylene diisocyanate in an equivalence ratio of 2.8:1.0 to 4.2:1.0 based on the polyol mixture and butane-1,4-diol as chain extender, the equivalence ratio of the butane-1,4-diol based on the poly mixture being 1.3:1.0 to 3.3:1.0. This moulding composition has the disadvantage that the fogging behaviour does not comply with the guidelines of some automobile manufacturers.
The object of the present invention was, therefore, to find a polyurethane moulding composition which can be melt processed as a sintering powder which meets the requirements of motor vehicle manufacturers for plastics in the dashboard area and consequently has the following properties:
soft and leather-like handle;
light fastness, i.e. no yellowing under the action of light and no change in the gloss;
grain stability at temperatures up to 130° C. and hot light stability up to 120° C.;
softening range above 140° C.;
well defined melting point;
low-viscosity melt from the very melting point onwards;
high tensile strength;
tear and tear propagation resistance;
less release of low molecular weight and condensable compounds than is the case with polyurethane moulding compositions according to the state of the art;
good adhesion with the polyurethane backing foam of the instrument panel bodies.
The object according to the invention is achieved by providing a thermoplastic polyurethane moulding composition which can be processed in the form of sintering powder, which moulding composition is obtained by reaction of
100 parts by weight of a polyol mixture of
30 to 80 parts by weight of an aliphatic polycarbonate diol with an average molecular weight {overscore (M)}
n
of 1000 to 2200, preferably 1000 to 2200, and
70 to 20 parts by weight of a polybutane diol adipate or a polycaprolactone diol with an average molecular weight {overscore (M)}
n
of 1000 to 2400, preferably 1800 to 2400, and
1,6-hexamethylene diisocyanate in an equivalence ratio of 2.3:1.0 to 6.2:1.0, based on the polyol mixture, and
butane-1,4-diol as chain extender in an equivalence ratio of 1.3:1.0 to 5.2:1.0, based on the polyol mixture,
wherein the NCO characteristic, formed from the quotient, multiplied by 100, of the equivalence ratios of isocyanate groups and the sum of the hydroxyl groups of polyol mixture and chain extender, is 96 to 99.
The polyurethane moulding composition is prepared exclusively from aliphatic components, namely 100 parts by weight of a polyol mixture of 30 to 80 parts by weight of an aliphatic polycarbonate diol with an OH value of 112.2 to 51, corresponding to an average molecular weight {overscore (M)}
n
of 1000 to 2200, preferably an OH value of 62.3 to 51, corresponding to an average molecular weight {overscore (M)}
n
of 1800 to 2200, 70 to 20 parts by weight of a polybutane diol adipate or a polycaprolactone diol, in each case with an OH value of 112.2 to 46.7, corresponding to an average molecular weight {overscore (M)}
n
of 1000 to 2400, preferably an OH value of 62.3 to 46.7, corresponding to an average molecular weight {overscore (M)}
n
of 1800 to 2400, 1,6-hexamethylene diisocyanate in an equivalence ratio of 2.3:1.0 to 6.2:1.0, based on the polyol mixture, and butane-1,4-diol as chain extender in an equivalence ratio of 1.3:1.0 to 5.2:1.0, based

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