Aliphatic thermoplastic polyurethanes, processes for their...

Details Aliphatic thermoplastic polyurethanes, processes for their... Aliphatic thermoplastic polyurethanes, processes for their...

1999-12-13

2003-02-11

Seidleck, James J. (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...

C528S080000, C528S083000

Reexamination Certificate

active

06518389

ABSTRACT:

The invention relates to aliphatic thermoplastic polyurethanes (TPUs) with improved properties, processes for their preparation and their use.
Aromatic thermoplastic polyurethanes (aromatic TPUs) are not stable to light because they are built up from aromatic diisocyanates. In colour formulations of shaped articles, severe yellowing develops due to the action of light, and a change in colour and degree of gloss occurs even in black shaped articles.
DE-C 42 03 307 describes a polyurethane moulding composition which can be processed thermoplastically in the form of sintered powder for the production of grained sintered films, the powder being prepared exclusively from linear, aliphatic components. The polyol component is composed of 60 to 80 parts by weight of an aliphatic polycarbonate diol having a molecular weight {overscore (M)}
n
of 2,000 and 40 to 20 parts by weight of a polydiol based on adipic acid, hexanediol and neopentylglycol having a molecular weight {overscore (M)}
n
of 2,000. 1,6-Hexamethylene-diisocyanate in an equivalent ratio of 2.8:1.0 to 4.2:1.0, based on the polyol mixture, and 1,4-butanediol as a chain-lengthening agent are employed, the equivalent ratio of the 1,4-butanediol, based on the polyol mixture, being 1.3:1.0 to 3.3:1.0. This moulding composition has the disadvantage that after storage (at room temperature and especially in an accelerated ageing test, such as the changing climate test, Arizona test and in heat (60-95° C.)) it tends towards a formation of a white deposit. This is a disadvantage in particular for applications with optical demands.
U.S. Pat. No. 5,824,738 describes a light-stable, aliphatic TPU which is distinguished by a very low yellowing even after intensive simulated weathering. The light-stable TPU described comprises on the one hand a critical combination of UV stabilizer, antioxidant and pigment, and on the other hand a polyether polyol based on propylene oxide with ethylene oxide end groups, dicyclohexylmethane-diisocyanate (hydrogenated MDI=H
12
-MDI) and 1,4-butanediol. Although these TPUs based on H
12
-MDI are stable to light, they have the disadvantage that they have only a relatively low heat stability, which is a particular disadvantage for applications e.g. inside automobiles, where a high heat resistance is required.
The object of the present invention was therefore to provide both light- and heat-stable thermoplastic polyurethanes and a process for their preparation. For high optical requirements, such as e.g. inside automobiles, there was additionally the object of providing TPUs which, after storage at room temperature and in particular after the accelerated ageing test (e.g. after storage at 60 to 95° C.), still give shaped articles which show only a slight or no formation of a deposit.
It has been possible to achieve this object with the thermoplastic polyurethanes according to the invention.
The present invention relates to aliphatic thermoplastic polyurethanes characterized in having a yellow value after having been subjected to weathering, lower than 20, preferably lower than 15, selected from the group consisting of
(i) polyurethanes having Shore A hardness of 75 to 84 and a Softening Temperature greater than 100° C., and
(ii) polyurethanes having Shore A hardness of 85 to 98 and Softening Temperature greater than 130° C.
The yellow value being determined after weathering for 504 hours in accordance with ISO 4892; the Softening Temperature, at E′=3 Mpa, determined by means of dynamic-mechanical analysis in the tensile mode, as described in more details below and the hardness values refer to measurements both before and after weaterhing for 504 hours in accordance with ISO 4892.
The aliphatic thermoplastic polyurethanes according to the invention are obtainable from
A) 100 to 60 mol %, preferably 100 to 70 mol %, particularly preferably 100 to 80 mol % hexamethylene-diisocyanate (HDI) based on the total amount of diisocyanates and 0 to 40 mol %, preferably 0 to 30 mol %, particularly preferably 0 to 20 mol % of other aliphatic diisocyanates based on the total amount of diisocyanates
B) polyester polyol having a number average molecular weight of between 600 and 5,000 g/mol, preferably 700 and 4,200 g/mol
C) chain lengthener having a number average molecular weight of 60 to 500 g/mol
D) UV stabilizers in an amount of 0.4 to 0.9 wt. %, preferably 0.4 to 0.8 wt. %, based on A)+B)+C)
E) optionally catalysts and
F) optionally further conventional auxiliary substances and additives,
wherein the equivalent ratio of diisocyanate A) to polyol B) is between 1.5:1.0 and 10.0:1.0, and wherein the NCO index (obtained from the quotient of the equivalent ratios of isocyanate groups and the sum of hydroxyl groups from the polyol and chain-lengthening agent multiplied by 100) is 95 to 105.
The TPUs according to the invention can be produced by various types of processes which are however all equally effective.
The TPUs according to the invention based on two different aliphatic diisocyanates “A1” (HDI) and “A2” (aliphatic diisocyanate), can for example (cf. also pages 10 to 14 of the present description) be produced to form an “A1/2” TPU in one reaction process. It is however also possible first of all to produce an “A1” TPU based on aliphatic diisocyanate “A1” and to produce an “A2” TPU based on aliphatic diisocyanate “A2” separately, the other components B to F being identical. Then the “A1” TPU and the “A2” TPU are mixed (e.g. in extruders or kneaders) in a known manner in the required ratio to form the “A1/2” TPU.
The TPUs based on mixtures of polyols according to the invention can also be produced in one reaction process (see also pages 10 to 14) to form a “B1/2” TPU by using mixtures of polyols (a B1 polyol and a B2 polyol) (e.g. mixed aggregates). It is also possible first of all to produce a “B1” TPU based on polyol “B1” in a known manner and then to produce a “B2” TPU based o polyol “B2” separately, the remaining components A and C to F being identical. Then the “B1” and “B2” TPUs are mixed e.g. in extruders or kneaders) in a known manner in the required ratio to form the “B1/2” TPU.
Instead of the polyester polyol B), the following polyols can be employed:
polyether polyol having a number average molecular weight of between 600 and 5,000 g/mol, preferably between 700 and 4,200 g/mol,
polycarbonate diol having a number average molecular weight of between 600 and 5,000 g/mol, preferably between 700 and 4,200 g/mol,
polyether polyol/polyester polyol mixture having a number average molecular weight of between 600 and 5,000 g/mol, preferably between 700 and 4,200 g/mol,
polyether polyol/polycarbonate diol mixture having a number average molecular weight of between 600 and 5,000 g/mol, preferably between 700 and 4,200 g/mol,
polyester polyol/polycarbonate diol mixture having a number average molecular weight of between 600 and 5,000 g/mol, preferably between 700 and 4,200 g/mol.
A mixture of 20 to 80 parts by wt. of an aliphatic polycarbonate diol having a number average molecular weight of 1,000 to 2,200 g/mol and
80 to 20 parts by wt. of a polybutanediol adipate or a polycaprolactone diol having a number average molecular weight of 1,000 to 2,400 g/mol is preferably employed as the polyol component.
The polyol component particularly preferably comprises a mixture of 30 to 70 parts by wt. of an aliphatic polycarbonate diol having a number average molecular weight of 1,000 to 2,200 g/mol and
70 to 30 parts by wt. of a polybutanediol adipate or a polycaprolactone diol having a number average molecular weight of 1,000 to 2,400 g/mol.
If the content of polybutanediol adipate in the polyol mixture is increased above 50% and there are particular requirements regarding hydrolysis, known hydrolysis stabilizers (such as e.g. carbodiimides) must be added to the polybutanediol adipate.
Suitable UV stabilizers are described in R. Gächter, H. Müller (ED.): Taschenbuch der Kunststoff-Additive [Pocket Book of Plastics Additives], 3
rd
edition, Hanser Verlag, Munich 1989, chapter “Polyurethane

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