Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-05-13
2003-07-08
Sergent, Rabon (Department: 1711)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C544S067000, C544S222000, C548S951000, C548S952000, C560S330000, C560S336000, C560S355000, C252S182200, C252S182210
Reexamination Certificate
active
06590098
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of preparing aliphatic polyisocyanates with uretdione, isocyanurate or iminooxadiazindione structures, the isocyanates thus prepared and polyurethane paints and coatings containing them.
Oligomerization of isocyanates is a long-known, generally accepted method of modifying low molecular weight isocyanates, which are usually difunctional, in order to obtain products with advantageous application properties for example in the paint and coating sector. These oligomeric isocyanates will be referred to generally as polyisocyanates in this specification (
J. Prakt. Chem./Chem. Ztg
1994, 336, 185-200). Polyisocyanates based on aliphatic diisocyanates are normally used for light-resistant, non-yellowing paints and coatings. The term “aliphatic” refers to the carbon atoms to which the NCO groups of the monomer are bonded, i.e. the compound molecule may perfectly well contain aromatic rings, which do not carry NCO groups.
One can distinguish between different products and processes according to the type of structure mainly formed from the previously free NCO groups in the respective oligomerization reaction.
Particularly important procedures are so-called dimerization to form uretdione structures of formula 1, described for example in DE-A 16 709 720 and so-called trimerization to form isocyanate structures of formula 2, described for example in EP-A 0 010 589. In addition to the last-mentioned trimers isomeric (i.e. also trimeric) products with an iminooxadiazindione structure of formula 3 can be obtained for example according to the teaching of EP-A 0 798 299. If this specification refers to both isomeric trimers, isocyanurates and iminooxadiazindiones, it will generally be speaking of trimers or trimerized compounds, otherwise the exact term will be used.
R=difunctional substituent
Complete conversion of all monomeric diisocyanate molecules OCN-R-NCO in one reaction step would in practice lead to high molecular weight, extremely high-viscosity or gel-like products which would be useless in the paint and coatings sector, owing to further reaction of the NCO groups in ideal structures 1 to 3. In catalyzed preparation of polyisocyanates for paint the industrial procedure is therefore to convert only part of the monomer, to stop any further reaction by adding a catalyst poison (a “stopper”) then to separate the non-converted monomer. The aim is to have to separate the smallest possible proportion of non-converted monomer at the lowest possible viscosity of the low-monomer polyisocyanate paint resin, i.e. to obtain high conversion in the reaction accompanied by a high resin yield at the following processing stage with high-level properties of the polyisocyanate resins.
Dimers based on aliphatic diisocyanates have a far lower viscosity than trimers. However they have a strictly linear, i.e. NCO-difunctional structure regardless of the degree of conversion or the resin yield. Trimers on the other hand have the higher functionality required for a high crosslink-density in the polymer and consequent good stability properties thereof. Their viscosity increases very rapidly though with increasing conversion in the reaction. Compared with isomeric isocyanurates iminooxadiazindiones have far lower viscosity with the same NCO-functionality of the polyisocyanate resin (cf. Proc. of the XXIVth Fatipec Conference, Jun. 8-11, 1998, Interlaken, CH, vol. D, pp. D-136-137), though they do not reach the viscosity level of uretdiones.
In practice the products formed are not only those which give their names to the reaction (dimers in dimerization, trimers in trimerization) but nearly always the other reaction products simultaneously (trimers in dimerization, uretdiones in trimerization). However the content of these is low.
Thus trimers are always contained in the polyisocyanates accessible from the teaching of DE-A 16 70 720 (trialkylphosphine-catalyzed dimerization, cf. also comparative example 1). Their content can be increased somewhat with higher conversion (conversion-dependent selectivity) and by raising the temperature. However carbodiimides and secondary products thereof, particularly uretone imines are also formed increasingly in the latter case. The negative role of such products in the technology of aliphatic polyisocyanates and poor monomer stability in particular have been described elsewhere (cf. EP-A 798 299, p.4, line 42 to p.5, line 15). Their formation is thus undesirable in all cases and stands in the way of wide, hazard-free use of such polyisocyanates. The molar uretdione content of carbodiimide-free and uretone imine-free products prepared according to DE-A 16 70 720 is generally over 60%. In this specification the term “mol %” will, unless otherwise stated, always refer to the sum of structure-types formed by the modifying reaction (oligomerization) from the previously free NCO groups of the respective monomer. The molar content can be determined for example by NMR spectroscopic methods (cf. Examples).
Oligomerization of aliphatic diisocyanates with N-silyl compounds, described for example in EP-A 57 653, EP-A 89 297, EP-A 187 105, EP-A 197 864 and WO 99/07765 (cf. also comparative Example 2), is to a certain extent the counterpart of phosphine catalysis with the content of trimers and uretdiones reversed. One drawback here is that the selectivity of catalysis is highly dependent on conversion—the uretdione content of the polyisocyanates drops sharply as conversion increases—another is that the iminooxadiazindione content of the resins is very low, always well below 5 mol %. According to the teaching of WO 99/07765 step-by-step modification is possible through thermally induced, i.e. non-catalyzed or rather self-catalyzed uretdione formation preceding the silylamine-catalyzed trimerization. Apart from the above-mentioned general drawbacks of silylamine catalysis this procedure however has the disadvantage that thermally induced uretdione formation is a slow process, leading to long, industrially unacceptable overall reaction times, particularly if there is an attempt to obtain a higher uretdione content. The molar uretdione content of the products of WO 99/07765 is not more than 30%.
In products accessible from the teaching of EP-A 798 299, i.e. trimerized compounds with a high content of iminooxadiazindione structures, the uretdione content is similarly low (<<20 mol %) relative to the sum of isocyanurate and iminooxadiazindione structures. The selectivity of the reaction is also dependent on conversion and temperature.
Good methods for obtaining polyisocyanates for paints with the lowest possible viscosity and the highest possible NCO-functionality can be characterized as follows:
1. The trimerization reaction is interrupted at very low conversion rates as the higher-molecular type of compound with more than one isocyanurate ring per molecule, which is responsible for the increase in viscosity, is not yet very advanced then, or
2. polyisocyanates of the uretdione type are mixed with trimerized compound resins; here the uretdione component is so to speak the reactive diluent.
Yet both methods have specific disadvantages. Thus in the first method the resin yield is very small, giving rise not only to technical problems (separating a large quantity of monomer) but also to economic ones (space-time yield) and ecological drawbacks (energy consumption). When different paint resins are mixed, apart from the general drawback of having an additional step in the process it must be realized that viscosity will be increased by the build-up of molecular weight through the consecutive addition of further monomer molecules to the NCO groups of ideal structure 1 (polymer chain formation), even in the preparation of dimerized compounds with higher conversion; this is so even if the increase in viscosity is not as marked as with trimerized compounds (star-shaped progress of oligomer build-up). Hence dimerized resins which are suitable as reactive diluents are similarly produced with a relatively low resin yield.
It was an
Halpaap Reinhard
Köcher Jürgen
Laas Hans-Josef
Richter Frank
Bayer Aktiengesellschaft
Gil Joseph C.
Roy Thomas W.
Sergent Rabon
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