4-12 MATERIALS AND MOLDING METHODS 



One method of increasing the fire resistance of a laminate is to seal its surface with a 

 self-extinguishing resin. The interior of the laminate is made with ordinary polyesters but 

 its outermost plies are laid up with a self-extinguishing type. 



Air Cured Polyesters: Some types of polyester resins cure in air with a tacky or sticky 

 surface. Contact with air inhibits the curing reaction and leaves a sticky layer of uncured 

 resin on the surface of the laminate. This layer of uncured resin can be an advantage where 

 successive plies of reinforcement are laid up since it provides an effective bond for addi- 

 tional plies. The outer surface of a laminate made by the contact molding method should 

 cure with a dry or tack free surface. Resin manufacturers produce special resins capable 

 of curing tack free in contact with air (7). 



Some of the standard rigid and semi-rigid resins produced for the reinforced plastics 

 industry are air curing types and entire laminates can be made with them. 



Epoxy 



Epoxy resins are a more recent development which have found application as laminating 

 resins, adhesives and coatings. Epoxy resins are syrup-like liquids which resemble 

 polyesters in that they can be cured or polymerized into hard solids. Epoxy resins are 

 chemically very different from polyesters, exhibit greater adhesion and have higher physical 

 properties. Shrinkage during cure is also considerably lower than that of polyesters (18). 



The limited use of epoxy resins in boat manufacture can be attributed to their higher 

 cost and tendency of some of the curing agents used to cause skin irritation on contact. 

 Recently developed curing agents greatly reduce this irritant effect. Also, improved mold- 

 ing techniques, where the resin and glass fibers are simultaneously deposited on the mold 

 without appreciable contact by the operator, is increasing the usage of epoxy resin in boat 

 manufacture (11, 13, 19). 



Epoxy resins have a wide usage in fiberglass boat construction for bonding component 

 parts together and in sealing and caulking. Superior coatings and paints with epoxide com- 

 ponents have also been developed for marine use. 



For the fabrication of structural laminates, epoxy resins can be molded by the same 

 methods used for polyester resins. 



Slightly higher mechanical properties can be obtained for structural laminates molded 

 with epoxy resins as compared with polyester laminates. This is particularly essential 

 where weight and thickness criteria are of utmost importance (18). 



Catalysts 



Catalysts, in the form of pastes or liquids, are added to polyesters to start polymeriza- 

 tion or the curing reaction (7, 20, 21). Approximately 1 to 2 per cent by weight of a catalyst 

 is used in the resin. Benzoyl peroxide dispersed in dibutyl phthalate, and methyl ethyl 

 ketone peroxide are several of many organic peroxides used for this purpose. If a batch of 

 resin is catalyzed, it must be used and not returned to storage. The type and concentration 

 of catalyst used affects the rate and conditions of a curing reaction. 



