Innovative Trimerization Catalyst Systems for Polyisocyanurate Foams

摘要

This paper describes the role of novel trimerization catalyst systems that improve adhesion and hydrolysis of polyester polyols for rigid polyisocyanurate (PIR) foams blown with environmentally friendly blowing agents. HCFC elimination in polyurethane (PUR) applications has been accomplished using blowing agents such as hydrofluorocarbons (HFCs), hydrocarbons (HCs), carbon dioxide (CO2) and water. In many PIR rigid foam applications however, inferior foam properties as well as deteriorated flame resistance continue to be major issues. In general, PIR rigid foams are produced through complex reactions such as trimerization of isocyanate, urethane and urea formations, which all progress simultaneously. In addition to controlling the rate of reaction, the catalyst plays an important role on the foaming profiles and resulting foam properties such as adhesive strength, dimensional stability and flame resistance. A variety of trimerization catalysts have been proposed and utilized in PIR rigid foams, however, most catalysts have some drawbacks. For instance, alkali metal compounds exhibit high trimerization activity at high temperature, which causes undesirable rise profiles and severe friability leading to poor adhesive strength. In contrast, quaternary ammonium compounds and tertiary amines provide desirable rise profiles, flow properties and moldability, however, they exhibit lower trimerization activity, which results in reduced flame resistance. As the choice of blowing agents becomes more defined, it is evident that higher water levels are utilized to reduce the system cost and minimize the use of combustible blowing agents. The another main drawback for PIR systems containing polyester polyols and water is the hydrolysis of polyester polyols, which is caused by catalyst systems. Consequently, the foam system not only becomes unstable but reactivity and physical properties are diminished. An another major problem encountered in water blown systems is the fact that it is difficult to improve adhesion properties. Tosoh Corporation has investigated the role of trimerization catalysts used in all-water, HFC and HC blown PIR foams. Moreover, Tosoh has determined the function of catalysts on the storage stability of rigid foam systems containing aromatic polyester polyols and water. This study has led to the development of new catalyst systems that improve processing of PIR rigid foams giving high trimerization conversion, excellent physical properties, improved flame resistance and flowability, and reduced friability.