Metal bonding with nitrile-phenolic

Supported films of nitrile phenolic adhesives are formulated with excess phenolic resin which gives a more brittle polymer with resin on its surface. This surface excess obviates the need for priming the metal substrate with nitrile-phenolic before bonding. The brittleness of the adhesive is offset by the presence of fabric as the carrier. Solvent based nitrile phenolics contain an excess of nitrile rubber. Materials which are used as the support comprise cotton nylon polyester glass tissue paper. The support may be either woven or non-woven. 

Chlorinated rubber is also an effective bonding agent. It can be used for bonding neoprene, nitrile and natural rubbers to metals. Phenol formaldehyde resins have been used alone or in conjunction with chlorinated rubbers, but curing time is lengthy. 

The thermosetting films are employed for metal-to-metal bonding in aircraft, as well as less demanding appliance, electrical, and automotive requirements. These adhesives are hybrids designed to provide an optimum combination of shear strength, elongation, and heat resistance. Nitrile-phenolic and epoxy-nitrile are the leaders, followed by vinyl butyral-phe-nolic, epoxy-nylon, and epoxy-phenolic. The nitrile rubber in the epoxy-nitrile is a carboxyl-terminated butadiene-nitrile polymer which reacts with the epoxy at the elevated cure temperature. 

Nitrile rubber/phenolic adhesives are also quite useful in adhering rubber to various met-als, " e.g., in the manufacture of rubber covered metal rollers. Huber reported that a nitrile/phenolic adhesive composition provided excellent bonding of rubber to a magnesium roll (Table 20). Other metal bonding applications with nitrile rubber/phenolic adhesives include laminating aluminum foil to paper and then to wood, bonding abrasives to metal, and bonding polyamide to metal. 

Strength properties with impervious substrates as well as with wood. They are combined with thermoplastic polymers to provide both metal-to-metal or metal-to-paper or plastic bonding. It is postulated that the phenolic crosslinks to rubber through quinone methide intermediates by a 1-4 addition across the vinyl double bonds. Some of the main materials are NBR with 15-40% acrylonitrile in nitrile/phenolic resins and polyvinylacetal in vinyl/phenolic blends. In all cases the phenolic gives inherent strength, solvent resistance, and thermal stability to the adhesive. 

The last two items of the earlier list involve the behaviour of primers, in part chemical, in part physical, as forms of adhesives sticking the bulk adhesive to the actual metal, wood or other adherend. When dissimilar materials are to be joined, an adhesive suitable for one may not be so for the other. In these circumstances a primer for one of the substrates is chosen to be both suitable for it and compatible with the adhesive. Phenol-formaldehyde condensation products are often thus used particularly when the adhesive itself contains such material dispersed in another polymer, e.g. Redux775 (Bonded Structures, Ltd) or various epoxy-phenolic or nitrile-phenolic adhesives. Most important members of the class of coupling agents are the reactive silanes (siloxanes) and titanates. These materials have achieved their main use in the treatment of glass fibres for the manufacture of glass reinforced plastics. 

Bonding or priming should be carried out as soon as possible. Parts should be warmed slightly before bonding. Primers recommended include nitrile-phenolic, resorcinol-formaldehyde, vinyl phenolic, silane, and so on. Epoxies have been used on metallic surfaces, with the nylon being bonded to the epoxy. 

This material may not be joined to itself using solvents as there is no solvent at room temperature. Because of its inert, non-stick surface it is difficult to bond using adhesives some success with contact or hot melt adhesives. If the surface is made polar, for example by using a flame or an electrical disr charge, then this material may be bonded to metals using epoxides or nitrile-phenolic adhesives such treatments also improve printability. 

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