Organic compounds -- part of the class 532-570 series – Organic compounds – Isocyanate esters
Reexamination Certificate
1997-01-16
2004-07-20
Price, Elvis O. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Isocyanate esters
C544S193000
Reexamination Certificate
active
06765111
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a new process for the production of polyisocyanates containing isocyanurate groups by trimerizing a portion of the isocyanate groups of hexamethylene diisocyanate (referred to hereinafter as “HDI”), to the products obtained by this process, and their use, optionally in blocked form, as the isocyanate component in polyisocyanate polyaddition products, preferably polyurethane lacquers.
2. Description of the Prior Art
The use of quaternary ammonium hydroxides as catalysts for the trimerization of isocyanate groups is known and has been repeatedly described. Thus, according to JP-PS 601,337 (U.S. Pat. No. 3,487,080), quaternary ammonium hydroxides are used together with certain co-catalysts. The examples primarily describe the partial trimerization of aromatic diisocyanates. However, the partial trimerization of HDI is described in the examples.
The process according to EP-A 10,589 represents a further development of the process according to the Japanese patent specification cited above. According to this prior publication, quaternary ammonium hydroxides containing hydroxyalkyl substituents are used for the trimerization of HDI. With these catalysts, HDI can be trimerized in excellent fashion without cloudiness. The disadvantage of this process is that the hydroxyalkyl ammonium hydroxides are very difficult to produce in colorless form and have to be used in relatively large quantities of up to 0.6%. Accordingly, the end products of the process, i.e. the isocyanurate polyisocyanates freed from excess starting diisocyanate, may possibly show a yellowish coloration.
EP-A 47,452 describes the production of mixed trimers based on HDI and IPDI by a process wherein starting diisocyanates which are not freed from carbon dioxide are used, necessitating comparatively large quantities of catalysts, as can be seen from the examples.
Other known processes for the production of isocyanurate polyisocyanates based on HDI are also attended by serious disadvantages. Thus, GB-PS 920,080, DE-OS 3,100,262, DE-OS 3,219,608 or DE-OS 3,240,613 for example describe processes for the trimerization of HDI using metal-containing catalysts and co-catalysts such as phenols, alcohols or tertiary amines. The metal compounds can only be removed from the end products by very elaborate processes, if at all, and can significantly affect subsequent applications and also the stability of the end products. In addition, the use of co-catalysts containing active hydrogen atoms leads to secondary reactions in which valuable isocyanate groups are consumed. The same also applies to the process according to EP-AS 155,559, wherein ammonium salts of organic acids are used as catalysts in combination with large amounts of alcoholic compounds.
In the processes according to EP-A 57,653, EP-A 89,297 and EP-A 187,105, organosilicon catalysts are used in comparatively large quantities. These compounds also cannot be completely removed from the end product and adversely affect its use.
Accordingly, an object of the present invention is to provide a new process for the partial trimerization of the isocyanate groups of HDI which combines the following advantages:
The end products are substantially colorless, i.e., have a color value (HAZEN) according to DIN 53,409 below 100.
The end products are free from cloudiness and can be dissolved without cloudiness in any of the standard lacquer solvents.
The end products contain no metal ions.
The process can be carried out using minimal quantities of catalysts without being dependent on the use of large quantities of isocyanate-reactive co-catalysts.
It has now surprisingly been found that this object can be achieved according to the present invention as described in detail hereinafter.
SUMMARY OF THE INVENTION
The present invention is directed to a process for the production of polyisocyanates containing isocyanurate groups by trimerizing a portion of the isocyanate groups of hexamethylene diisocyanate using quaternary ammonium hydroxides corresponding to the formula
wherein
R
1
, R
2
and R
3
may be the same or different and represent alkyl radicals containing 1 to 18 carbon atoms and
R
4
is a benzyl radical,
as the trimerization catalyst, terminating the trimerization reaction at the desired degree of trimerization by adding a catalyst poison and/or by thermally deactivating the catalyst and removing unreacted hexamethylene diisocyanate to a residual content of at most 0.2% by weight, characterized in that
a) the hexamethylene diisocyanate used as starting material is freed from carbon dioxide to a residual content of less than 20 ppm (weight) and
b) the catalyst is used in a quantity of less than about 0.03% by weight, based on the weight of the hexamethylene diisocyanate used.
The present invention is also directed to the polyisocyanates containing isocyanurate groups obtained by this process and to their use, optionally blocked by blocking agents for isocyanate groups, as the isocyanate component for the production of polyisocyanate polyaddition products.
DETAILED DESCRIPTION OF THE INVENTION
The use of HDI which is substantially free from carbon dioxide as the starting material is crucially important to the present invention. The HDI used in accordance with the invention has a carbon dioxide content of less than 20 ppm (weight), preferably less than 10 ppm (weight) and more preferably less than 5 ppm (weight).
Technical HDI purified by distillation, which has previously been used for the production of polyisocyanates containing isocyanurate groups, contains considerable quantities (approximately 20 ppm to 100 ppm by weight) of carbon dioxide. Carbon dioxide can enter the HDI during the production process, for example during the phosgenation of carbonic acid salts of hexamethylenediamine. It can be taken up from the air during storage and can be formed by chemical reaction of the NCO groups, for example by forming carbodiimide groups or by reaction with moisture. HDI freshly purified by vacuum distillation contains, for example, 40 ppm carbon dioxide after 24 hours in a sealed container. HDI stored for a period of about 6 months can contain up to 0.6% by weight carbon-dioxide if the container is opened during the period of storage.
Carbon dioxide can be removed from HDI by blowing ultra-pure nitrogen or a noble gas, for example argon, for example at a temperature of about 0 to 70° C., through HDI. Although it is possible to apply a higher temperature, this does not afford any significant advantages. Carbon dioxide may also be removed by distillation in a stream of nitrogen or noble gas. The method by which the carbon dioxide is removed is not crucial to the process according to the invention. However, substantially complete removal of carbon dioxide is generally not possible merely by distillation.
The catalysts used in the process according to the invention are quaternary ammonium hydroxides corresponding to the formula
wherein
R
1
, R
2
and R
3
may be the same or different and represent alkyl radicals containing 1 to 18 carbon atoms, preferably 1 to 4 carbon atoms, more preferably methyl groups and
R
4
is a benzyl radical.
A particularly preferred catalyst is N,N,N-trimethyl-N-benzyl-ammonium hydroxide.
The quaternary ammonium hydroxides to be used in accordance with the invention and their production are known. They are commercially available either in the form of colorless substances or solutions or as already stated, only as brightly colored solutions. This natural color of the catalysts is often a disadvantage in the processes corresponding to the prior art cited above for the production of isocyanurate polyisocyanates based on HDI, because in these known processes the catalysts have to be used in comparatively large quantities. By contrast, in the process according to the invention, the natural color of the catalysts is not an important factor because the catalyst is only used in extremely low concentrations.
In the process according to the invention, the catalyst is used in a posit
Bock Manfred
Dieris Carl-Gerd
Pedain Josef
Bayer Aktiengesellschaft
Cheung Noland J.
Gil Joseph C.
Price Elvis O.
Roy Thomas W.
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