Process for the continuous preparation of melt processable...

Details Process for the continuous preparation of melt processable... Process for the continuous preparation of melt processable...

2000-05-17

2002-03-12

Gorr, Rachel (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...

C528S083000, C528S085000, C264S211210

Reexamination Certificate

active

06355762

ABSTRACT:

The invention relates to a process for the continuous preparation of melt processable polyurethanes in a static mixer with improved softening behaviour.
Thermoplastic polyurethane elastomers (TPU) are by no means new. They are of industrial importance in view of the combination of high-quality mechanical properties and the well known advantages of inexpensive melt processability. Due to the use of different chemical constituents, a wide variation of mechanical properties may be obtained. A review of TPUs, their properties and applications, is given, e.g., in Kunststoffe 68 (1978), pages 819 to 825 or Kautschuk, Gummi, Kunststoffe 35 (1982), pages 568 to 584.
TPUs are synthesised from linear polyols, mostly polyester or polyether polyols, organic diisocyanates and short-chain diols (chain extenders). In addition, catalysts may be added to accelerate the formation reaction. In order to adjust the properties, the constituents may be varied in relatively wide molar ratios. Molar ratios of polyols to chain extenders from 1:1 to 1:12 have proved suitable. As a result, products ranging from 70 Shore A to 75 Shore D are obtained.
The synthesis of melt processable polyurethane elastomers may take place either in steps (prepolymer metering process) or by the simultaneous reaction of all the components in one step (one-shot metering process).
The TPUs may be prepared continuously or batchwise. The most well known industrial production processes are the belt process (GB-A 1 057 018) and the extruder process (DE-A 19 64 834, DE-A 23 02 564 and DE-A 20 59 570). In the extruder process, the starting materials are metered into a screw reactor where polyaddition takes place, and are converted to a uniform granular form. The extruder process is comparatively simple but has the disadvantage that the homogeneity of the products thus produced is not sufficient for many applications in view of the fact that mixing and reaction proceed simultaneously. In addition, the softening behaviour of the TPUs and the moulded articles produced from them is limited. TPUs which melt readily, of the kind used e.g. for hot melt films or sintered products, can be prepared only to a limited extent, if at all, by this process.
Moreover, preparation processes are known from the literature in which the starting materials are initially mixed in a mixing zone at low temperatures at which no poly-addition occurs, and then react together in a reaction zone which has the desired reaction temperature. The mixing and reaction zone is designed preferably as a static mixer.
In DE-A 28 23 762, homogeneous products are obtained by the “one-shot process”. In EP-A 747 409, metering takes place by the prepolymer process and homogenous TPUs with improved mechanical properties are obtained.
The object was, therefore, to provide a simple process with which it is possible to prepare homogeneous TPUs with improved softening behaviour in an inexpensive and technically simple manner.
Surprisingly, this object was achieved by preparing TPUs continuously in a static mixer, in which the entire TPU reaction is carried out substantially in the “one-shot metering process”, under special process conditions. Homogeneous TPU products with markedly better melting properties are obtained with this process.
The invention provides a process for the continuous preparation of melt processable, homogeneous polyurethane elastomers with improved softening behaviour, in which
one or more polyisocyanates (A) and
a mixture (B) having Zerewitinoff active hydrogen atoms of
B1) 1 to 85 equivalent %, based on the isocyanate groups in (A), of one or more compounds with on average at least 1.8 and at most 2.2 Zerewitinoff active hydrogen atoms per molecule and an average molecular weight {overscore (M)}
n
from 450 to 5000 g/mole,
B2) 15 to 99 equivalent %, based on the isocyanate groups in (A), of one or more chain extenders with on average at least 1.8 and at most 2.2 Zerewitinoff active hydrogen atoms per molecule and a molecular weight from 60 to 400 g/mole, and
0 to 20 wt. %, based on the total quantity of TPU, of further auxiliaries and additives (C),
wherein the components A) and B) are used in an NCO:OH ratio of 0.9:1 to 1.:1,
are homogeneously mixed in a static mixer at a shear rate of >500 sec
−1
and <50,000 sec
−1
within a maximum of 1 second, the reaction mixture thus prepared is metered into an extruder, optionally via a second static mixer, and optionally auxiliaries and/or further components are incorporated, characterised in that the polyisocyanate (A) and the mixture (B) each have a temperature of >170° C. and <250° C. the reaction takes place substantially in the first static mixer with a conversion of >90%, based on component A), and the reaction mixture leaves the first static mixer at a temperature of >240° C. and <350° C.
Examples of suitable organic polyisocyanates (A) include aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, as described e.g. in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136.
More specifically, examples include: aliphatic diisocyanates such as hexamethylene diisocyanate, cycloaliphatic diisocyanates such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4- and 2,6-cyclohexane diisocyanate and the corresponding isomer mixtures, 4,4′-2,4′- and 2,2′-dicyclohexylmethane diisocyanate and the corresponding isomer mixtures and aromatic diisocyanates such as toluene 2,4-diisocyanate, mixtures of toluene 2,4- and 2,6-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 and/or 2,4′-diphenylmethane diisocyanates, 4,4′-diisocyananatodiphenylethane-(1,2) and 1,5-naphthylene diisocyanate. Diphenyl-methane diisocyanate isomer mixtures with 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 in preference. The diisocyanates mentioned may be used individually or in the form of mixtures. They may also be used together with up to 15% (based on total diisocyanate) but at most that amount of a polyisocyanate required to obtain a melt processable product. Examples are triphenylmethane-4,4′4″-triisocyanate and polyphenylpolymethylene poly-isocyanates.
Linear hydroxyl-terminated polyols with on average 1.8 to 3.0, preferably to 2.2 Zerewitinoff active hydrogen atoms per molecule and with a molecular weight from 450 to 5000 g/mole are used as component B1). Due to production conditions, said polyols often contain small amounts of non-linear compounds. The term “substantially linear polyols” is often, therefore, used. Polyester, polyether, polycarbonate diols or mixtures thereof are preferred.
Suitable polyether diols may be prepared by reacting one or more alkylene oxides with 2 to 4 carbon atoms in the alkylene radical with a starter molecule which contains two active hydrogen atoms in the bound state. Examples of suitable alkylene oxides include: ethylene oxide, 1,2-propylene oxide, epichlorohydrin and 1,2-butylene oxide and 2,3-butylene oxide. Ethylene oxide, propylene oxide and mixtures of 1,2-propylene oxide and ethylene oxide are used in preference. The alkylene oxides may be used individually, in alternating succession or as mixtures. Examples of suitable starter molecules include: water, aminoalcohols such as N-alkyl diethanolamines, for example, N-methyl diethanolamine, and diols such as ethylene glycol, 1,3-propylene glycol, butane 1,4-diol and hexane 1,6-diol. Optionally, mixtures of starter molecules may also be used. Suitable polyetherols are also the hydroxyl group-containing polymerisation products of tetrahydrofuran. Trifunctional polyethers may also be used in proportions from 0 to 30 wt. %, based on the bifunctional polyethers, but at

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