Aliphatic thermoplastic polyurethanes, a process for...

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...

Reexamination Certificate

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C528S048000, C528S080000, C528S083000

Reexamination Certificate

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06559266

ABSTRACT:

This invention relates to aliphatic thermoplastic polyurethanes (TPUs) which exhibit improved properties, to a process for producing them and to the use thereof.
The current requirements which are imposed on materials for use in the interior trim of motor vehicles, particularly for surface mouldings for instrument panels (IPs), are very complex, especially if the passenger airbag is designed as an invisible, integral component of the IP. This means that the only materials which can be used are those which fulfil the complex combination of this range of requirements, such as stability to light, heat and hydrolysis, for example, and which also fulfil the requirement of allowing the passenger airbag to open, even at temperatures of −30° C. and below, without a brittle reaction. If only one of these essential conditions of the range of requirements of the automobile industry is not complied with, the material is not suitable for this application.
Aromatic thermoplastic polyurethanes (aromatic TPUs) are not stable to light due to their synthesis from aromatic diisocyanates. When colours are incorporated in mouldings, a strong yellowing effect occurs due to the effect of light, and even black mouldings exhibit changes in colour and in their degree of gloss.
DE-C 42 03 307 describes a thermoplastic polyurethane moulding composition in the form of a sinterable powder for the production of embossed sintered sheeting, wherein the powder is produced solely from linear, aliphatic components. The polyol component is composed of 60 to 80 parts by weight of an aliphatic polycarbonate diol with a molecular weight M
n
of 2000, and of 40 to 20 parts by weight of a polydiol based on adipic acid, hexanediol and neopentyl glycol with a molecular weight M
n
of 2000. 1,6-hexamethylene diisocyanate is used in an equivalent ratio from 2.8:1.0 to 4.2:1.0 with respect to the polyol mixture and 1,4-butanediol is used as a chain extender, wherein the equivalent ratio of the 1,4-butanediol with respect to the polyol mixture ranges from 1.3:1.0 to 3.3:1.0. This moulding composition fulfils all the requirements with regard to its stability to light, heat, hydrolysis and embossing, but has the disadvantage, due to its T
G
of ≧−45° C., that it is too brittle in passenger airbag sudden inflation tests at −30° C. (some automobile companies require this level of flexibility when cold), which is why this material is unsuitable for this application (IPs comprising an integral, invisible passenger airbag).
U.S. Pat. No. 5,824,738 describes an aliphatic TPU which is stable to light and which is distinguished by only very slight yellowing even after intensive artificial weathering. The light-stable TPU which is described there consists of a critical combination of a UV stabiliser, antioxidant and pigment. These light-stable TPUs based on H
12
-MDI do in fact have a very low T
G
of about −68° C., but do not fulfil the requirements of most automobile companies as regards stability during hot storage.
The object of the present invention was therefore to provide thermoplastic polyurethanes (TPUs) which are stable to light, heat and hydrolysis and which do not tend to exhibit brittleness at low temperatures, and to provide a process for the production thereof.
It has been possible to achieve this object by means of the thermoplastic polyurethanes according to the invention.
The present invention relates to light-stable, aliphatic, thermoplastic polyurethanes having an ultimate tensile strength and an elongation at break after hot storage (500 hours at 120° C.) which amount to at least 60% (preferably at least 70%) of the initial ultimate tensile strength and elongation at break before hot storage, and having a glass transition temperature T
G
(as measured by means of dynamic mechanical analysis (DMS) in tensile mode, which is described in more detail below) of less than or equal to −50° C., and having an ultimate tensile strength and an elongation at break after hydrolytic storage (at 80° C. and after 7 days) which amount to at least 80% (preferably at least 85%) of the initial ultimate tensile strength and initial elongation before hydrolytic storage, and having a hardness of 70 to 95 Shore A. (preferably 70 to 90 Shore A).
The test conditions for hydrolytic storage and hot storage are defined in more detail below.
Therefore, the only TPUs which are suitable are those which exhibit a decrease in ultimate tensile strength and elongation at break after hot storage (500 hours at 120° C.) of less than 40% (preferably less than 30%) and which a the same time exhibit a decrease in their ultimate tensile strength and elongation at break after hydrolytic storage (80° C. for 7 days) of less than 20% (preferably less than 15%).
The aliphatic thermoplastic polyurethanes according to the invention are preferably obtainable from
A) aliphatic diisocyanates selected from the group consisting of hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (hydrogenated MDI) or isophorone diisocyanate (IPDI) or mixtures thereof,
B) a mixture of polyether polyol having a number average molecular weight of 600 to 10,000 g/mol with a polyester polyol having a number average molecular weight of 600 to 10,000 g/mol,
C) a chain extender with an average molecular weight of 60 to 500 g/mol,
D) UV stabilisers in an amount from 0.4 to 0.9% by weight with respect to A)+B)+C),
E) antioxidants in an amount from 0.2 to 5.0% by weight with respect to A)+B)+C),
F) anti-hydrolysis agents (such as carbodiimides for example) in an amount from 0 to 2.0% by weight, preferably from 0.2 to 2.0% by weight, with respect to the polyester polyol,
G) optionally catalysts, and
H) optionally customary adjuvant substances and additives,
wherein the equivalent ratio of diisocyanate A) to polyol B) is between 1.5:1.0 and 10:1.0 and wherein the NCO characteristic number (formed from the quotient comprising the equivalent ratio of isocyanate groups divided by the sum of the hydroxyl groups from the polyol and the chain extender, multiplied by 100) ranges from 95 to 105.
When polycaprolactone diol is used as a polyester polyol, an anti-hydrolysis agent is not required. Polycaprolactone diol (polyester polyol) can be used without a polyether polyol.
The above sequence of components A to H does not imply any statement regarding the production of the TPUs according to the invention. The TPUs according to the invention can be produced by any conventional process.
The TPUs according to the invention, which are based on two different aliphatic diisocyanates “A1” and “A2”, can be produced, for example, in one reaction process to form TPU “A1-2” as described below. In the known manner, however, TPU “A1” based on aliphatic diisocyanate “A1” can be produced first, and TPU “A2” based on aliphatic diisocyanate “A2” can be produced separately therefrom, wherein the remaining components B to H are identical. Thereafter, TPU “A1” and TPU “A2” are mixed in the desired ratio to form TPU “A1-A2” (e.g. in extruders or kneaders).
The TPUs according to the invention, which are based on polyol mixtures, can also be produced using polyol mixtures (polyol B1 and polyol B2) (e.g. in mixer units) to form TPU B1-2 in one reaction process, which is described in more detail below. Alternatively, and in the known manner, TPU B1 based on polyol B1 can first be produced, and TPU B2 based on polyol B2 can be produced separately therefrom, wherein the remaining components A and C to H are identical Thereafter, TPUs B 1 and B2 are mixed in the desired ratio and in the known manner (e.g. in extruders or kneaders) to form TPU B 1-2.
A mixture of 20 to 80% by weight of a polyether polyol with an average molecular weight of 1000 to 8000 g/mol and 80 to 20% by weight of a polyalkanediol adipate or of a polycaprolactone diol with an average molecular weight of 1000 to 8000 g/mol is preferably used as a polyol component.
A polycaprolactone diol with a molecular weight of 1000 to 5000 g/mol is also preferably used as a polyol component.
The polyol comp

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