Continuous process for the production of partially blocked isocyanates
AssigneeCargill, Incorporated
InventorsK. A. Pai Panandiker, David E. Tweet
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Abstract
A method for manufacturing partially blocked isocyanate curing agents in which a polyisocyanate and a blocking agent for the polyisocyanate are separately and continuously metered into a reaction zone in predetermined nonstoichiometric proportion under reaction conditions, and in which the reaction mixture is continuously withdrawn from the reaction zone to provide a partially blocked isocyanate curing agent product. The partially blocked isocyanate curing agent product may be continuously reacted with a polyhydroxy resin coating precursor at a temperature below the unblocking temperature of the blocking agent in respect of the polyisocyanate to provide a heat curable powder coating composition.
Claims11
A method for manufacturing partially blocked isocyanate curing agents which are the reaction product of a polyfunctional isocyanate and a blocking agent for the isocyanate which is capable of splitting from the curing agent at elevated temperature to regenerate isocyanate functionality, comprising the steps of
- separately and continuously metering a polyisocyanate and a blocking agent for said polyisocyanate into a reaction zone in predetermined stoichiometric isocyanate excess to provide a reaction mixture in the reaction zone at reaction temperature,
- continuously withdrawing the reaction mixture from said reaction zone to provide a partially blocked isocyanate curing agent reaction product after maintaining said reaction mixture in the reaction zone for a time sufficient to reduce the free isocyanate content of the reaction product to at least a predetermined level indicating substantial completion of the reaction.
Dependencies are inferred from the claim text.