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
2002-06-13
2003-10-28
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...
C560S025000, C560S027000
Reexamination Certificate
active
06639040
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a continuous process for the production of allophanate-modified diphenylmethane diisocyanates having an NCO group content of 19 to 32% by weight and an urethane content of less than 2 area % as determined by GPC analysis. The process comprises (1) continuously reacting (a) diphenylmethane diisocyanate and (b) an alcohol, in the presence of (c) at least 25 ppm of an allophanate catalyst, based on the combined weight of the diphenylmethane diisocyanate and the alcohol, in a reactor in an oxygen-free environment; (2) continuously treating the product exiting the reactor with a catalyst stopper at the reaction temperature; and (3) cooling the resultant product. The allophanate catalyst can be dissolved in either the diphenylmethane diisocyanate or in the alcohol.
Allophanate-modified di- and poly-isocyanates are known and described in, for example, U.S. Pat. Nos. 4,160,080, 4,738,991, 4,866,103, 5,319,053 and GB 994,890.
U.S. Pat. No. 4,160,080 discloses a process for the preparation of allophanates which containing aliphatically and/or cycloaliphatically bound isocyanate groups in which compounds containing urethane groups are reacted with polyisocyanates having aliphatic and/or cycloaliphatic isocyanate groups, in the presence of a strong acid. The process is generally conducted at a temperature of from 90 to 140° C. for about 4 to about 20 hours. All of the working examples describe a batch process.
Storage-stable polyisocyanates having allophanate linkages are disclosed by U.S. Pat. No. 4,738,991. These polyisocyanates containing allophanate linkages are prepared by reacting an organic polyisocyanate with a mono- or polyhydric compound in the presence of an organo-metallic catalyst. The catalyst is then deactivated by a compound such as an inorganic acid, an organic acid, an organic chloroformate or an organic acid chloride. Only a batch process is described. All of the examples use toluene diisocyanate with ethylene glycol to form the polyisocyanates having allophanate linkages.
Polyisocyanate compositions are disclosed in U.S. Pat. No. 4,8661,103. These polyisocyanates comprise the reaction product of an alcohol or thiol having an average functionality of from about 1.5 to about 4 and an average equivalent weight of at least 500 with at least 2 equivalents per hydroxyl and/or thiol equivalent of an organic poly-isocyanate (including the 4,4′- and 2,4′- isomers of diphenylmethane diisocyanate) under conditions such that at least about 20% of the initially formed urethane and/or thiourethane groups are converted to allophanate and/or thioallophanate groups. The only working example illustrating the preparation of an allophanate modified isocyanate uses a batch process.
U.S. Pat. No. 5,319,053 discloses stable, liquid, allophanate-modified diphenylmethane diisocyanates having NCO group contents of 12 to 32.5% by weight, and prepolymers of these stable, liquid, allophanate-modified diphenylmethane diisocyanates. Batch processes for the production of these products are also disclosed. The allophanate-modified diphenylmethane diisocyanates of this reference may be prepared by (1) pre-reacting the diphenylmethane diisocyanate with an aliphatic alcohol to form a urethane, which is subsequently converted to an allophanate; or (2) reacting the aliphatic alcohol, diphenylmethane diisocyanate and catalyst to form the allophanate directly. Although the batch process described therein has been used successfully in commercial operations, it is desirable to produce substantially identical products via a continuous process due to lower costs, resulting from smaller reactors having substantially higher throughput.
Allophanate modified polyisocyanates are also disclosed in GB 994,890. These are obtained by reacting an amount in excess of n moles of an organic diisocyanate with one mole of a urethane isocyanate of the specified formulation, with the reaction being carried out under conditions such that substantially one molecule of diisocyanate reacts with each urethane group present, as indicated by the measured isocyanate group content of the reaction mixture. Suitable conditions for the reaction include heat alone, or in the presence of a catalyst such as, for example, a metal carboxylate, a metal chelate or a tertiary amine. Only batch processes are described for the preparation of allophanate-modified isocyanates.
Advantages of the present invention include a novel method of preparing, at various NCO group contents, a consistent allophanate product at a lower cost from MDI and alcohols in the presence of an allophanate catalyst using inexpensive equipment. The present invention also describes the most probable method for introduction of the allophanate catalyst and the limitations of using MDI as a vehicle to deliver the allophanate catalyst.
SUMMARY OF THE INVENTION
This invention relates to a continuous process for the production of allophanate modified diphenylmethane diisocyanates having NCO group contents of from about 19 to about 32% by weight, and having a urethane content of less than 2 area % by GPC analysis. This process comprises:
(1) continuously reacting
(a) diphenylmethane diisocyanate comprising
(i) from about 0 to about 60% by weight of 2,4′-diphenylmethane diisocyanate,
(ii) less than about 6% by weight of 2,2′-diphenylmethane diisocyanate, and
(iii) the balance being 4,4′-diphenylmethane diisocyanate, with the sum of the %'s of (a)(i), (a)(ii) and (a)(iii) totaling 100% by weight of (a), the diphenylmethane diisocyanate; and
(b) an alcohol; in the presence of
(c) at least 25 ppm of an allophanate catalyst, based on the combined weight of the diphenylmethane diisocyanate and the alcohol;
in at least one reactor at a temperature of from 80 to 110° C., preferably 90 to 100° C., most preferably about 90° C., for about 0.5 to 4 hours, preferably 1 to 2 hours and most preferably about 1 to about 1.5 hours, in an oxygen free environment (preferably in the presence of an inert gas such as, for example, nitrogen;
(2) continuously treating the product exiting the reactor with a catalyst stopper, with the stopper being present in an amount such that there is at least 1 mole of stopper for each mole of catalyst and more preferably from 1 mole to 4 moles of stopper for each mole of catalyst, and the stopper being added at the reaction temperature; and
(3) cooling the resultant product, preferably to a temperature of from about 25 to about 30° C.
DETAILED DESCRIPTION OF THE INVENTION
The continuous process of the present invention can be performed, for example, in at least one reactor, wherein the reactants are continuously fed into the reactor and the product continuously exits the reactor. It is preferred to use either a plug-flow reactor, or a cascade overflow reactor system. In cascade-overflow reactor system, it is preferred that the system comprise at least two (2) reactors, more preferably from two (2) to four (4) reactors, and most preferably three (3) reactors.
Suitable reaction temperatures for the first step, i.e. continuously reacting diphenylmethane diisocyanate with an alcohol, in the present process are from about 80 to about 110° C., preferably from about 90 to about 100° C. and most preferably about 90° C., for time periods of from about 0.5 to about 4 hours, preferably about 1 to about 2 hours, and most preferably about 1 to about 1.5 hours. These residence times represent the total reaction time for all reactors present.
Suitable reactor systems and feed systems for the present continuous process have oxygen-free environments. It is preferred that the entire system including feed systems as well as the reactors are purged with an inert gas. Some examples of inert gases suitable for this purpose include compounds such as nitrogen, helium, neon, argon, etc. Nitrogen is a particularly preferred inert gas for the present invention.
Suitable (a) diphenylmethane diisocyanates for the present process include those which comprise:
(i) from about 0 to about 60% by weight, preferably from
Kemp, II Hersel T.
Miller William E.
Slack William E.
Bayer Corporation
Brown N. Denise
Gil Joseph C.
Gorr Rachel
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