Flame-retardant epoxy resin system

The matrix material for the laminates for this investigation was a typical flame retardant epoxy resin system used in PWB technology. The epoxy resin was a brominated diglycidyl ether of bisphenol-A cured with dicyandiamide and catalyzed by benzyl dimethylamine. 

Flame-retardant epoxy resins with different silicon contents were prepared using silicon-containing epoxides or silicon-containing prepolymers. The thermal stability and flame-retardant properties of the produced epoxide systems were evaluated and related to the silicon content. The char yields under nitrogen and air atmospheres increased with increase in silicon content. The authors pointed out that the silicon-containing resin has improved flame retardancy over the silicon-free resin as evidenced by the LOI. LOI values increased from 24 for a standard commercial resin to 36 for silicon-containing resins.35... 

Selecting a flame retardant for an adhesive system has many ramifications, depending on the formulation being modified, the end use, how it will be processed, and the cost/performance ratio. When one is choosing a flame retardant, characteristics such as water extraction, particle size, viscosity, toxicity, dusting, uniformity, as well as economics must be considered. The materials chosen to perform the function of flame retardation must not interfere with the final product s performance. The major problem with incorporating flame retardants in adhesives is that very often a significant amount is required, and they interfere with the other properties of the adhesive and contribute to the cost. This is why bromo bisphenol epoxy resins are often employed in flame-retardant epoxy adhesives. 

As a result of their three-dimensional crosslinked stmctures, thermosets do not soften or flow when burning. The tendency to form gaseous decomposition products is also less than with thermoplastics. Heat may cause surface charring that can prevent ignition. Unsaturated polyester resins and epoxy resin systems require flame retardants to meet the fire protection standards in the constmction, transport and electrical industries where such resins are mainly used. The flammability of epoxy resins is greater than comparable thermosets since they have a reduced tendency to carbonise. After removal of an ignition source, once alight they continue to bum on their own. 

Kubens (9) found cyanate ester resins were compatible and reactive with epoxy resins. We have confirmed this in our laboratories. Such combinations can be formulated to yield cured materials containing both triazine and oxazoline ring structures. If brominated epoxy resins are employed in such blends, flame retardant materials can be obtained containing as low as 12% bromine versus 20% bromine required to flame retard epoxy systems. Such products show promise for use in printed wiring board laminates. 

In general purpose applications competitively priced thermosets are used for the printed circuit board base material which is usually FR4 (Flame Retardant) . One of the main flame retardants used in America is to have tetrabromobisphenol-A reacted into the epoxy resin. Non-halogen systems include additives such as alumina trihydrate, alumina trihydrate/red phosphorus and aromatic phosphates. Flame retardant epoxy coatings are reported to use ammonium polyphosphate with char-forming additives. 

R.L. Markezich Flame Retardant Additives for Epoxy Resin Systems, Epoxy Resin Formulators Division Winter Meeting, February 1987. 

Novel 2,2, 6,6 -tetrabromo-3,3, 5,5 -tetramethyl-4,4 -biphenol (TBTMBP) and its epoxy derivatives [28] were synthesized to incorporate the stable meta-terminated phenol moiety into epoxy resin systems. In electronic encapsulation and laminate applications, epoxy systems derived from TBTMBP exhibit superior hydrolytic and thermal stability as compared with the conventional ortho-bromi-nated epoxy resins. These properties have resulted in an extended device life for semiconductors and a high Tg with excellent blister resistance for the printed circuit board, while meeting flame retardancy requirements as well. 

The binder system of a plastic encapsulant consists of an epoxy resin, a hardener or curing agent, and an accelerating catalyst system. The conversion of epoxies from the Hquid (thermoplastic) state to tough, hard, thermoset soHds is accompHshed by the addition of chemically active compounds known as curing agents. Flame retardants (qv), usually in the form of halogens, are added to the epoxy resin backbone because epoxy resins are inherently flammable. 

Electrical Laminates. A significant use for epoxy resins is in the manufacture of copper-clad epoxy-glass printed circuit boards. Systems are available that meet the National Electrical Manufacturers Association (NEMA), GIO, Gil, FR3, FR4, FR5 specifications. Currently the majority of boards are manufactured to the fiame-retardant FR4 specification. The flame retardance is achieved by the use of a soHd epoxy resin based on... 

Weil, E. D., and Levchik, S., A Review of Current Flame Retardant Systems for Epoxy Resins, Journal of Fire Sciences, vol. 22, January 2004, pp. 25 10. 

Although epoxy resin and hardener may be used in unmodified form in adhesive systems, most systems will consist of components that have been modified by incorporation of various additives to achieve specific effects. Formulators will add catalysts or blend hardeners to obtain a specific usable life of the mix and to control the curing temperature. Reactive diluents may be added to modify viscosity or flexibility. Fillers impart improved compression strength and reduce shrinkage and cost. Solvents may be used to reduce viscosity or improve adhesion. Various additives may be added, usually at a low percentage, to reduce aeration, improve adhesion to difficult surfaces, or minimize settlement of fillers. Depending on the application, particular properties such as flame retardency. 

Chem. Descrip. Triphenyl phosphite CAS 101-02-0 EINECS/ELINCS 202-908-4 Uses Costabilizer for PVC and other polymers such as PP vise, modifier, reactive diluent for a variety of resin systems, esp. epoxies antioxidant for syn. rubbers, butyrates flame retardant for PU foams in transesterification reactions lubricant oil additive chem. intermediate for prod, of other phosphite esters and phosphonates Features Improves adhesion, elec, props., dimensional stability Properties Colorless mobile liq. 10% P Albrite Tributyl Phosphate [Huntsman Surf. Sciences]... 

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