Flame retardant pressure-sensitive adhesives and tapes

#This invention relates to pressure-sensitive adhesive compositions containing non-halogen intumescent flame retardant (NHIFR) additives and to flame retardant pressure-sensitive adhesive tapes.

#Pressure-sensitive adhesives find use in a wide variety of applications, such as the automotive, aerospace, construction and electrical markets, either in the form of tapes or as adhesive coatings on other backings. For many of these applications, good flame retardant properties are of considerable importance. This performance has generally been achieved by means of the incorporation of halogenated, often brominated flame retardant additives into the adhesive formulation, as disclosed for example, in U.S. Pat. No. 4,061,826. Although efficient as flame retardants, these types of materials have considerable drawbacks in terms of smoke production and toxicity concerns, relating both to combustion products and also to disposal of the compounds themselves. Hence, there is considerable momentum towards the reduction in use or replacement of these flame retardants by zero halogen alternatives.

#A further limitation of the use of halogenated flame retardants in pressure-sensitive adhesives is that during combustion they emit larger amounts of corrosive smoke. Combustion products of halogen containing materials, in particular HCl and HBr, contribute significantly to these effects. The corrosivity of smoke is of particular importance in electrical/electronic applications, since a small fire involving halogenated insulation materials may generate sufficient corrosive combustion products to cause widespread damage to other equipment not directly involved in the fire.

#The pressure-sensitive adhesive compositions may be based on a wide variety of adhesives including rubber based compositions, acrylic adhesive compositions and adhesive foams. The adhesive compositions have a wide variety of applications and are particularly suitable for use in the preparation of adhesive tapes.

#The compositions of the invention possess an excellent combination of flame retardant and adhesive characteristics. In the case where solely NHIFR additives are used, reductions in smoke emission, and also in combustion toxicity and corrosivity, representing improvements upon the art are conferred by a completely non-halogen composition. However, other flame retardants may be present and in the case where combinations of NHIFR and halogenated flame retardant additives are used together, a synergistic effect is seen in flammability performance in rubber based compositions, with a surprising reduction in the tendency to produce burning drips during combustion. In addition, such combinations permit a reduction in the loading of halogenated flame retardant additive.

#In one embodiment, the flame retardant is one or more NHIFR materials. Such materials normally contain up to three components: a carbonific, an acid forming catalyst, and a blowing agent. These three functions may be contained in only one or two chemicals. Such materials usually contain phosphorus compounds, and often also contain compounds of nitrogen, and are known as P/N flame retardants.