Aliphatic, sinterable, thermoplastic polyurethane molding...

Details Aliphatic, sinterable, thermoplastic polyurethane molding... Aliphatic, sinterable, thermoplastic polyurethane molding...

2000-04-26

2002-06-25

Wu, David W. (Department: 1713)

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...

C524S513000, C524S515000, C524S521000, C524S522000, C524S565000

Reexamination Certificate

active

06410638

ABSTRACT:

CROSS REFERENCE TO RELATED PATENT APPLICATIONS
The present patent application claims the right of priority under 35 U.S.C. §119(a)-(d) German Patent Application No. 199 20 367.9, filed May 4, 1999.
FIELD OF THE INVENTION
The invention relates to light-stable, sinterable, thermoplastic polyurethane moulding compositions with reduced mechanical strength, improved tactile properties and improved write sensitivity, which can be processed by the powder-slush process. The moulding compositions according to the invention are particularly suitable for the production of textured sintered films for the interior trim of means of transport, particularly as a cover for airbags in motor vehicles.
BACKGROUND OF THE INVENTION
Aliphatic thermoplastic polyurethanes (TPU) for use in the interior trim of motor vehicles, e.g. in the trim of instrument panels, are already described, for example, in DE-C-42 03 307. Naturally, there is a desire to achieve a uniform appearance of the overall trim and, therefore, to produce said trim from a single material. The problem arises, however, that the common aliphatic thermoplastic polyurethanes with good light fastness and thermal stability are not suitable as a cover for airbags because of their outstanding mechanical properties, particularly the high ultimate tensile strength, particularly if the passenger airbag is designed as an invisible, integral component of the instrument panel.
A process for the preparation of crosslinked polyurethanes from diisocyanate and low molecular weight chain extender containing at least two hydrogen atoms reacting with isocyanate groups, for example, butane 1,4-diol and from relatively high molecular weight, linear polylhydroxyl compounds is described in DE-AS 16 94 135, which contain a mixture of 70 to 90 wt. % of hexane diol polycarbonate which was prepared by reaction of hexane 1,6-diot and diary carbonates, and of 10 to 30 wt. % of mixed polyester of, i.a., hexane 1,6-diol and 2,2′-dimethyl-1,3-propane diol. The crosslinking of the polyurethanes is achieved by the use of diisocyanates in excess. In polyurethane elastomers prepared from these starting materials, the high resistance to hydrolysis due to the polycarbonate remains intact. Moreover, such elastomers also exhibit, however,improved low temperature resistance and processability compared with elastomers for whose preparation the polyol component used was pure hexane 1,6-diol polycarbonate. The better processability becomes effective particularly in the liquid phase—for example in the casting process—since the polyester-polycarbonate mixtures used have a lower viscosity at the processing temperatures than the pure hexane diol polycarbonate, which is why the resulting film can more easily be cast bubble-free. The products produced according to this process may be used in mechanical engineering and vehicle production.
A polyurethane moulding compound which can be melt processed in the form of sintered powder for the production of textured sintered films is described in DE-C-42 03 307, wherein the powder is composed solely 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 equivalent ratio of 2.8:1.0 to 4.2:1.0, based on the polyol mixture, and butane 1,4-diol as chain extender, wherein the equivalent ratio of the butane 1,4-diol based on the polymixture is 1.3:1.0 to 3.3:1.0. These materials are characterised, inter alia, by a high tensile strength, tear strength and tear propagation resistance. EP-A-399 272 also discloses polyurethane films with good mechanical properties, particularly high ultimate tensile strength.
SUMMARY OF THE INVENTION
The object was, therefore, to develop materials with good light stability and thermal stability which have a lower mechanical strength than the well known thermoplastic polyurethanes. In addition, the materials obtained should, if necessary, also have improved tactile properties (“handle” or “feel”) compared with pure TPU, and improved write resistance.
It has now been found that materials with good light stability and thermal stability which have a lower mechanical strength than the well known thermoplastic polyurethanes can be obtained by modifying light-stable thermoplastic polyurethanes with certain other components.
The invention provides, therefore, sinterable, thermoplastic moulding compositions containing a thermoplastic polyurethane based on an aliphatic diisocyanate and at least one other representative of the group comprising styrene-acrylonitrile copolymer (SAN), acrylonitrile-butadiene-styrene polymer (ABS), acrylonitrile-styrene-polyacrylate rubber moulding compound (ASA), copolymers of ethylene and/or propylene and acrylic acid or methacrylic acid or sodium or zinc salts thereof, and copolymers of ethylene and/or propylene and ester of acrylic or methacrylic acid, preferably methyl, ethyl or butyl ester, and UV stabilisers and antioxidants.
DETAILED DESCRIPTION OF THE INVENTION
The moulding compositions according to the invention preferably have an ultimate tensile strength at room temperature of not more than 20 N/mm
2
, particularly preferably not more than 18 N/mm
2
and an elongation at break at room temperature of not more than 450%, particularly preferably not more than 400% (in each case measured in accordance with EN ISO 527-3/5 at tensile testing speed of 500 mm/min).
The ultimate tensile strength at −35° C. of the moulding compositions according to the invention is preferably not more than 35 N/mm
2
, particularly preferably not more than 30 N/mm
2
, and the elongation at break at −35° C. is not more than 250%, particularly preferably not more than 200% (in each case measured in accordance with EN ISO 527-3/2 at tensile testing speed of 500 mm/min).
The melt flow index (MVR) of the moulding compositions according to the invention, measured at 190° C. with a load of 2.16 kg (according to ISO 1133, method B), is preferably between 10 ml/10 min and 200 ml/10 min, particularly preferably between 20 ml/10 min and 150 ml/10 min.
Moreover, the low-temperature flexibility of the moulding compositions according to the invention is so high that the requirements of the falling ball test and the mandrel flex test at −50° C. are complied with without restriction.
In a preferred embodiment, the moulding compositions according to the invention contain
50 to 90 parts by wt. of thermoplastic polyurethane based on an aliphatic diisocyanate,
0 to 25 parts by wt. of ASA
0 to 30 parts by wt. of SAN
0 to 25 parts by wt. of ABS
0 to 25 parts by wt. of copolymers of ethylene and/or propylene and acrylic acid or methacrylic acid or sodium or zinc salts thereof, and copolymers of ethylene and/or propylene and acrylate or methacrylate or mixtures of said components
UV stabilisers and antioxidants in a quantity from 0.2 to 5.0 wt. %, preferably 0.4 to 4.0 wt. %, based on the TPU,
optionally other conventional auxiliaries and additives.
Examples for particularly preferred embodiments are moulding compositions which contain, per 100 parts by wt. of moulding compound, up to 30 parts by wt., particularly up to 20 parts by wt. of ASA.
In a further preferred embodiment, the moulding compositions according to the invention contain
70 to 90 parts by wt. of thermoplastic polyurethane based on an aliphatic diisocyanate, and
10 to 30 parts by wt. of SAN.
In a further preferred embodiment, the moulding compositions according to the invention contain
50 to 90 parts by wt. of thermoplastic polyurethane based on an aliphatic diisocyanate, and
up to 30 parts by wt. of SAN, particularly up to 20 parts by wt. of SAN and additionally up to 20 parts by wt., particularly up to 15 parts by wt. of ASA, ABS, EMA (copolymer of ethylene and methyl acrylate) or EBA (copolymer of ethylene and

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