Polyisocyanates, bonding agents

Terpene phenolic resins can also be added to solvent-borne CR adhesives to increase open tack time and to provide a softer glue line than /-butyl phenolic resins. To provide adequate hot bond strength, these resins are used in combination with a polyisocyanate curing agent. 

Typically used for the coating of polyester and polyamide substrates with plasticised PVC. Chemically one-component bonding agents (e.g. aromatic polyiso-cyanurate) and two-component bonding agents (e.g. aliphatic polyisocyanate) liquids. 

CR may also be used in dough processes employed in coated fabrics for various applications. It is important to ensure that regulations related to solvent vapors are followed for those processes where combinations of solvents such as naphtha/methyl ethyl ketone (MEK) or naphtha/toluene are employed. The solutions may contain special bonding agents, for example, polyisocyanates. Pot lifetimes of such compounds are fairly short (1 h), because of the crosslinking activity of such materials. 

A stable, blocked di- or polyisocyanate in suspension, including aqueous suspension or solution is applied alone in combination with a conventional plastic or rubber type, in combination with a di- or polyhydroxy material or in combination with a preformed polyurethane vehicle to adherend surfaces. The coating is dried, the coated adherend surfaces contacted and the assembly heated to decompose the blocked isocynate. This generates free di- or polyisocyanate which proceeds to bond the adherend directly and through reaction with the vehicle which may be a pre- or in-situ formed polyurethane. The cleaved blocking agent diffuses into the surrounding matrix or escapes into the air. 

Covalent bonding using non-sulphur vulcanizing agents such as peroxides, polyisocyanates, polyamines and p-quinone dioximes is also practised with, in many cases, network formation not requiring a double bond. Some methods of introducing covalent cross-links into polymers are indicated in Fig. 4.1. These methods are of course equally applicable to plastics, surface coatings and adhesives. 

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