Thermoplastically processable polyurethane elastomers having...

Details Thermoplastically processable polyurethane elastomers having... Thermoplastically processable polyurethane elastomers having...

2001-10-01

2002-11-26

Gorr, Rachel (Department: 1711)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S710000, C528S051000

Reexamination Certificate

active

06486243

ABSTRACT:

The present invention relates to thermoplastically processable polyurethane elastomers (TPUs) having an improved intrinsic color as a result of the utilization of one or more compounds of pentaerythritol diphosphites substituted in specific manner, and to the use thereof.
Thermoplastic polyurethanes (TPUs) are widely used because they have good elastomer properties and lend themselves readily to thermoplastic further processing. A very varied range of mechanical properties may be obtained by suitable selection of components. Kunststoffe 68 (1978) 819; Kautschuk, Gummi, Kunststoffe 35, (1982) 569; G. Becker, D. Braun: Kunststoff-Handbuch [Manual of Plastics], Vol. 7, “Polyurethane [Polyurethanes]”, Munich, Vienna, Carl Hanser Verlag 1983, for example, contain an overview of TPUs and their properties and uses. An overview of processes for preparing them is given in Plastikverarbeiter [Plastic Processor] 40 (1989).
TPUs are constructed from generally linear polyols such as polyester polyols or polyether polyols, organic diisocyanates and short-chain, generally bifunctional, alcohols (chain extenders). They can be prepared in batch or continuous manner.
Thermoplastic polyurethanes are susceptible to discoloration because of the raw materials on which they are based and because of the thermal treatment to which they are twice exposed during their production and processing. Yet in many TPU applications the color of the article is an important property. Discoloration caused by heat during preparation of the TPUs or during processing by injection molding or extrusion is undesirable, in particular in the case of white or light-colored articles.
In U.S. Pat. No. 4 169 196 Ehrlich et al. describe a process for the preparation of TPUs based on 4,4′-diphenylmethane diisocyanate with a phosphorus component PX3 being utilized, in which X are aryl, aryloxy and low alkoxy groups, and with a reduced quantity of tin catalysts being utilized. A triphenyl phosphite is preferably utilized. Thermally stable, color-stable TPUs are obtained thus.
The GE Specialty Chemicals monograph (1997 by General Electrical Company) also describes specific phosphites for improving the stability in processing and the color stability of thermoplastics prepared from polyolefins, polyesters, polyvinyl chloride, polycarbonate, polystyrene, ABS, polyurethanes and other elastomers. Triphenyl phosphite, a range of tri(alkylphenyl)phosphites, a hydroxyalkyl triphosphite, two substituted pentaerythritol diphosphites
where R=stearyl and R=di(tert.-butyl)phenyl, and a substituted pentaerythritol monophosphite (R=tri(tert.-butyl)phenyl), are described.
The utilization of these phosphites reduces discoloration in thermoplastic polyurethanes during their preparation and processing.
However, the utiliation of phosphites in the preparation of TPUs also influences the reactivity (monomer reactivity) of the starting components (EP-A 0 522 340). The utilization of phosphites as color stabilizers in the preparation of TPUs is therefore problematic.
The object was to provide thermoplastically processable polyurethane elastomers which have a good intrinsic color which remains unchanged or is barely changed during preparation and/or processing.
It has now been found that TPUs having a good color (low Yellowness Index in accordance with DIN 6167) with unchanged monomer reactivity can be provided when pentaerythritol diphosphites substituted in specific manner are added to the reaction components before or during preparation of the TPUs.
The invention therefore provides light-colored thermoplastically processable polyurethane elastomers (TPUs) consisting of a reaction product which is obtainable from
A) at least one polyol having on average a minimum of 1.8 and a maximum of 3.0 Zerewitinoff-active hydrogen atoms and an average molecular weight Mn of 450 to 10000,
B) at least one organic diisocyanate and
C) at least one polyol having on average a minimum of 1.8 and a maximum of 3.0 Zerewitinoff-active hydrogen atoms and an average molecular weight Mn of 60 to 400,
wherein the NCO/OH ratio of the reaction components A), B) and C) which are used is between 0.85 and 1.2,
and from 0 to 20 wt. %, in relation to the quantity of TPU, of further auxiliary substances and additives (D),
as well as from 0.001 to 1 wt. %, in relation to the quantity of TPU, of one or more color stabilizers from the group comprising pentaerythritol diphosphites (E) corresponding to the formula (I)
wherein
R=C
6
to C
30
-alkyl, in particular C
6
to C
20
-alkyl, and Ph denotes phenyl.
The TPUs according to the invention preferably have a Yellowness Index (measured in accordance with DIN 6167) of less than 9, in particular of less than 8.
Aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic diisocyanates or any mixtures of these diisocyanates may be used as organic diisocyanates (B) (cf. HOUBEN-WEYL “Methoden der organischen Chemie” [Organic Chemistry Methods], Vol. E20 “Makromolekulare Stoffe [Macromolecular Substances]”, Georg Thieme Verlag, Stuttgart, New York 1987, pp. 1587-1593 or Justus Liebig's Annalen der Chemie [Annals of Chemistry], 562, pp. 75 to 136).
The following might be named in detail as examples: aliphatic diisocyanates such as ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,1 2-dodecane diisocyanate; cycloaliphatic diisocyanates such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate and l-methyl-2,6-cyclohexane diisocyanate as well as the corresponding isomer mixtures, 4,4′-dicyclohexylmethane diisocyanate, 2,4′-dicyclohexylmethane diisocyanate and 2,2′-dicyclohexylmethane diisocyanate as well as the corresponding isomer mixtures; furthermore aromatic diisocyanates such as 2,4-tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate and 2,2′-diphenylmethane diisocyanate, mixtures of 2,4′-diphenylmethane diisocyanate and 4,4′-diphenylmethane diisocyanate, urethane-modified liquid 4,4′-diphenylmethane diisocyanates or 2,4′-diphenylmethane diisocyanates, 4,4′-diisocyanate- 1,2-diphenylethane and 1,5-naphthylene diisocyanate. 1,6-Hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate isomer mixtures having a 4,4′-diphenylmethane diisocyanate content of more than 96 wt. % and in particular 4,4′-diphenylmethane diisocyanate and 1,5-naphthylene diisocyanate, are used for preference. The named diisocyanates may be used individually or in the form of intermixtures. They may also be used together with up to 15 mol % (in relation to total diisocyanate) of a polyisocyanate, however polyisocyanate may be added only in a quantity such that a product which is still thermoplastically processable arises. Examples of polyisocyanates are triphenylmethane-4,4′,4″-triisocyanate and poly-phenyl-polymethylene polyisocyanates.
Zerewitinoff-active polyols (A) utilized in the products according to the invention are those such as have on average a minimum of 1.8 and a maximum of 3.0 Zerewitinoff-active hydrogen atoms and an average molecular weight {overscore (M)}
n
of 450 to 10000.
Besides compounds having amino groups, thiol groups or carboxyl groups, compounds having in particular two to three, preferably two, hydroxyl groups, are included, specifically those such as have average molecular weights {overscore (M)}
n
of 450 to 6000, particularly preferably those such as have an average molecular weight {overscore (M)}
n
of 600 to 4500, for example polyesters, polyethers, polycarbonates and polyester amides having hydroxyl groups.
Suitable polyether diols may be prepared by reacting one or more alkylene oxides having 2 to 4 carbon atoms in the alkylene radical with a starter molecule which comprise

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