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...
Reexamination Certificate
1998-11-10
2001-01-30
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...
C252S182200
Reexamination Certificate
active
06180743
ABSTRACT:
The present invention relates to new thermolabile protective groups for the isocyanate functional groups. It relates more particularly to a process for isocyanate masking, to the use of oximes for isocyanate masking, to masked isocyanates and to the use of the latter in the manufacture of coating.
In particular, the subject-matter of the present invention is molecular compounds constituting a unit, be it of mono-, oligo- or polymeric nature, carrying isocyanate groups, and capable of reacting with appropriate coreactants such as alcohols, phenols, amines, aminophenols or aminoalcohols, advantageously at least partially bi- or polyfunctional, which may be of mono-, oligo- or polymeric nature.
More precisely, the present invention relates to polyisocyanates in which at least some of the isocyanate functional groups are masked, or protected, by protective radicals, radicals which will sometimes be identified in the description which follows by the qualifier “masking” or “blocking”.
The present invention also relates to some of the processes for obtaining these new masked polyisocyanates.
It furthermore relates to the use of the above masked polyisocyanates in compositions for the preparation of polymers, especially of polycondensates and of crosslinked products resulting from the reaction of the said protected polyisocyanates and of nucleophilic coreactants. This preparation is that which is exploited in industrial applications, such as the coatings of all kinds and especially those on textiles, on glasses, on papers, on metals and on materials of construction, and paints.
The usefulness of the masking of isocyanate functional groups (masking sometimes referred to as blocking), or even its need, is explained by an excessively high reactivity of isocyanates at ambient temperature towards some coreactants or towards a reactive solvent or of a, generally continuous, substrate phase in the case of emulsions or suspensions, such as water. This high reactivity is often very awkward, especially in the case of some applications of polyurethanes, in particular in paints, because this demands a separate packaging and sometimes handling of the isocyanate comonomer. This results in a processing which is not very convenient.
Thus, in all the applications of polyurethanes as coatings it is of the greatest interest to have available protected isocyanates in which the isocyanate functional group is made unreactive at ambient temperature towards its coreactants, but is kept reactive at a higher temperature.
These masked isocyanate units are advantageous on a number of counts. In the first place they make it possible to propose, in the same single packaging, compositions (including emulsions and suspensions) for obtaining a coating in which the isocyanate component is stable and not very sensitive to water. It follows that it is no longer necessary to employ costly anhydrous solvents which are specific for the isocyanates and that it is possible to store the masked isocyanates for a long time, without deterioration, in conditions in which those that are free would deteriorate.
Lastly, the use of masked polyisocyanates makes it possible to reduce, or even to eliminate, the possible toxic hazard associated with the presence of free and unstable isocyanates.
The improvement in this technique of masking the isocyanate functional groups in reactive mono-, oligo- or polymer units involves the optimization, generally a lowering, of the reaction temperature, that is to say that at which the deprotection takes place, thus resulting in the intended polymerization and/or crosslinking.
More specifically, the demasking temperature must be sufficiently high for there to be no risk of reaction during the storage period, and this reaction temperature must be sufficiently low for it to be easy to carry out the polycondensation when this is desired.
In general the temperature of “release” of the isocyanates, especially aliphatic (that is to say that the carbon carrying the nitrogen has sp
3
hybridization) is too high. This implies that an attempt is made to lower this temperature of release.
Such a lowering is reflected in economic savings which are not insignificant in energy and in process duration.
It is appropriate to mention, incidentally, that the masking groups employed in the case of aromatic isocyanates are generally not directly transposable to the aliphatic isocyanates, since the temperature of “release” for the same masking group is several tens of degrees centigrade higher than that of the aromatic isocyanates.
Many blocking radicals have already been employed. Among these there may be mentioned, among others, some triazoles, imidazolines, lactams, hydroxy-nitro compounds, sodium bisulphites, isocyanate dimers, phenols, esters of acetoacetic acid and alcohols. One of the most widely employed groups is the group of dialkylketoximes, which, however, has the major disadvantage of exhibiting a high release temperature, too high for many applications.
Among these masking agents, only those for which the octanol test gives a deblocking temperature of between approximately 100° C. (two significant figures) and 180° C. (two significant figures) are regarded as true masking agents.
It is appropriate to note that the multiplicity of the parameters makes it difficult to systematize some classes.
Thus, one of the essential objectives of the present invention is to provide new polyisocyanates with blocked functional groups and which have a relatively low temperature of dissociation for a limited period and with a dissociation yield that is compatible with polymerization techniques.
Another objective of the invention is to provide new polyisocyanates with blocked functional groups, which are not toxic or only slightly so.
Another objective of the invention is to provide new polyisocyanates with masked functional groups, which are not hazardous and/or tricky to handle and apply.
Another objective of the invention is to provide new polyisocyanates with blocked functional groups, which are economical.
Another objective of the invention is to provide new polyisocyanates with blocked functional groups, providing access to optionally crosslinked polymers (or rather to polycondensates), which satisfy the application specifications.
Another objective of the invention is to provide a process for obtaining such blocked polyisocyanates.
Another objective of the invention is to provide a process for the preparation of polymers and/or crosslinked products from the said blocked polyisocyanates.
Another aim of the present invention is to provide compositions comprising masked isocyanates of the above types.
Another aim of the present invention is to provide powder compositions of the abovementioned type.
Another aim of the present invention is to provide aqueous emulsions comprising isocyanates of the above type.
Another aim of the present invention is to provide suspensions comprising isocyanates of the above type.
These aims, and others which will appear subsequently, are attained by means of masked isocyanates, advantageously diisocyanates, preferably polyisocyanates. This compound carries at least one masked isocyanate functional group capable of being obtained by the action on a free isocyanate of a compound carrying an oxime functional group where the carbon of the oxime functional group carries at least one electron-attracting functional group.
More specifically, the substituents of the carbon of the oxime functional group, and especially the said electron-attracting functional group, are chosen so that the sum of the Hammett constants &dgr;
p
is at least equal to 0.2, advantageously to 0.25, preferably to 0.3. It is additionally desirable that the substituents of the carbon of the oxime functional group should be chosen so that the sum of the Hammett constants &dgr;
p
is at most equal to 1, advantageously 0.8, preferably 0.6.
To do this, at least one of the substituents of the carbon of the oxime functional group may be chosen from the electron-attracting functional groups exhibiting a Hammett constant &dgr;
p
at most
Bernard Jean-Marie
Perroud Eug{acute over (e)}nie
Gorr Rachel
Rhodia Chimie
Seugnet Jean-Louis
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