Light-resistant thermoplastic polyurethanes, a process for...

Details Light-resistant thermoplastic polyurethanes, a process for... Light-resistant thermoplastic polyurethanes, a process for...

2002-03-25

2003-07-22

Gorr, Rachel (Department: 1711)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S460000, C525S440030, C524S714000

Reexamination Certificate

active

06596820

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to thermoplastic compositions and more particularly to compositions containing light-resistant aliphatic polyurethane.
SUMMARY OF THE INVENTION
A thermoplastic molding composition that contains a light-resistant aliphatic thermoplastic polyurethane elastomer is disclosed. The composition which largely contains of thermoplastic polyurethanes with high molecular weights and small amounts of thermoplastic polyurethanes with low molecular weights is useful for the preparation of a variety of articles and for use as sinterable composition in powder form.
BACKGROUND OF THE INVENTION
Thermoplastic polyurethanes (TPUs) are very important industrial products because they have good elastomeric properties and may be thermoplastically processed. A wide range of variations in mechanical properties can be produced by suitable choice of the components. A review of TPUs, their properties and applications is given e.g. in
Kunststoffe
68 (1978), p. 819-825, In
Kautschuk, Gummi, Kunststoffe
35 (1982), p. 569-584 and in G. Becker, D. Braun,
Kunststoff-Handbuch
, vol. 7 “Polyurethane”, Munich, Vienna, Carl Hanser Verlag 1983. A review of methods of preparation may be found in Plastverarbeiter 40 (1989).
TPUs are mostly built up from linear polyols (macrodiols) such as polyester or polyether diols, organic diisocyanates and short-chain, mostly difunctional, alcohols (chain extenders). They may be prepared continuously or batchwise. The best known methods of preparation are the strip process and the extruder process.
Aromatic diisocyanates are usually used to build up TPUs. However, aromatic TPUs are not light-resistant. More recently, aliphatic TPUs which have been known per se for a long time have become increasingly important because these do not yellow under the effects of light and, even when provided with black coloration, do not tend to change color or degree of glossiness during use.
U.S. Pat. No. 5,824,738 describes a light-resistant aliphatic TPU which is characterised by a very low degree of yellowing, even after intensive artificial weathering. However, this light-resistant TPU, based on H
12
-MDI, has the disadvantage that it has only a relatively low resistance to heat.
EP-A 1 010 712 describes thermoplastic polyurethane elastomers which are both lightfast and thermally stable and which comply with the requirements for lighffastness and thermal stability due to their specific structure. The disadvantage of these lightfast TPUs is the low tendency of the molten TPUs to crystallise.
To produce decorative films and injection molded parts or in particular to produce flat materials from meltable, sinterable powders, flexible, light-resistant and thermally stable TPU raw materials are required by the user, which TPU materials flow well while being processed from the melt and crystallise rapidly on cooling. Products from the prior art comply with these requirements to only an inadequate extent.
Therefore, the object of the present invention was to provide aliphatic, flexible, lightfast TPUs which crystallise rapidly on cooling and which may be extruded, injection molded and blow molded without complications to make articles.
DETAILED DESCRIPTION OF THE INVENTION
This object may be achieved by the mixtures according to the invention described in detail below. Surprisingly, it was found that the addition of a low molecular weight TPU based on hexamethylene diisocyanate (HDI) to a molten, lighffast TPU leads to an early start to crystallisation during cooling and thus substantially simplifies the processing procedure.
Contrary to expectations, the good thermal stability of lighffast TPUs is not lost as a result of adding the low molecular weight TPU, although a reduction in viscosity does occur. Due to the use of the mixtures according to the invention described in greater detail below, the processability and the thermal stability are substantially improved.
Thus, the present invention provides light-resistant thermoplastic aliphatic polyurethane elastomer molding composition contains 80 to 98% relative to the weight of the composition of an aliphatic thermoplastic polyurethane (TPU Y), obtained, optionally in the presence of catalysts, from reacting
A) 100 to 60 mol. %, preferably 100 to 80 mol. %, of hexamethylene diisocyanate (HDI) and 0 to 40 mol. %, preferably 0 to 20 mol. %, of other aliphatic diisocyanates, the mol % being relative to the moles of diisocyanates,
B) polyols, preferably difunctional polyesterdiols with a number average molecular weight of 600 to 5000 g/mol, preferably 700 to 4200 g/mol, and
C) chain extenders with an average molecular weight of 60 to 500 g/mol
optionally with the addition of UV stabilisers D) in an amount of 0.4 to 0.9 wt. %, preferably 0.4 to 0.8 wt. %, with respect to [A)+B)+C)], and other conventional auxiliary substances and additives (F),
wherein the ratio by equivalents of A) to B) is 1.5:1.0 to 6.0:1.0 and wherein the characteristic value (calculated by multiplying by 100 the ratio by equivalents of isocyanate groups to the sum of the hydroxyl groups from the polyol and the chain extending agents) is 95 to 105, and 2 to 20% relative to the weight of the composition of a low molecular weight thermoplastic polyurethane (TPU X) obtained from reacting
G) hexamethylene diisocyanate (HDI),
H) diols with a number average molecular weight of 62 to 300 g/mol and
I) monofunctional alcohols as chain stoppers with a molecular weight of 32 to 300 g/mol,
wherein the molar ratio of G) to H) is 2:1 to 1.05:1, preferably 1.7:1 to 1.2:1, and wherein the characteristic value (calculated by multiplying by 100 the ratio by equivalents of isocyanate groups from G) to the sum of he hydroxyl groups from H) and I)) is 99 to 101.
The TPU Y preferably has a number average molecular weight of 20,000 g/mol to 100,000 g/mol. The TPU X preferably has a number average molecular weight of 462 g/mol to 6000 g/mol.
The TPU Y particularly preferably has 13 to 21 wt. %, preferably 14 to 18 wt. % of rigid segments (calculated from the amount of diisocyanate A) and chain extender C), with respect to the total weight of TPU Y).
The invention also provides a process for preparing light-resistant, thermoplastic polyurethane elastomer mixtures characterised in that B) and C) are mixed continuously or batchwise and then intensively blended with A) and, before during or preferably after reaction of components A), B) and C) in an extruder, the separately prepared TPU X is added and the product thus obtained is optionally granulated.
The process according to the invention is preferably performed in such a way that the reaction to prepare the TPU Y is performed continuously in the presence of a catalyst.
The TPU X is preferably prepared without a catalyst.
Polyurethane elastomer mixtures according to the invention are used to produce molded items, extrudates, films and injection molded parts. Polyurethane elastomer mixtures according to the invention may be used as sinterable and free-flowing powders in an outstanding manner to produce flat materials and blown items.
Apart from 1,6-hexamethylene diisocyanate, other aliphatic and/or cycloaliphatic diisocyanates may be used as diisocyanate A) (see Houben-Weyl, “Methoden der organischen Chemie”, vol. 20, Makromolekulare Stoffe, Georg Thieme Verlag, Stuttgart, New York, 1987, p. 1587-1593). Examples are ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane diisocyanate, cyclohexane-1,3 and -1,4 diisocyanate, and any mixture of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexan, 2,4- and 2,6-hexahydrotoluylene diisocyanate, and any mixture of these isomers, hexahydro-1,3- and/or -1,4-phenylene diisocyanate, perhydro-2,4′- and/or 4,4′-diphenylmethane diisocyanate, and norbornane diisocyanate (e.g. U.S. Pat. No. 3,492,330). In addition to 1,6-hexamethylene diisocyanate (HDI), cycloaliphatic diisocyanates such as 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI) and perhydro-2,4′-

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