Co-extruded insecticidal pet collars contain one or more active insecticidal components in a desired relationship to the skin of the animal. The outside layer (away from the skin) contains carbamate, organo-phosphate chlorinated hydrocarbon or other insecticide that is irritating to the skin, or a cholinesterase inhibitor. The inside layer acts as a barrier to the insecticide. The layers of a multi-layered collar which is prepared by extrusion may also contain different insecticidal systems. A co-extruded collar is prepared by preparing two blends which have varying concentrations of active and/or inert ingredients, depending on the end product which is desired. Each of the blends is fed into an extruder wherein the polyvinyl chloride is fused. The melt blend from extruder B is then transferred to the die of extruder A where it becomes an integral part of the extruded strip from extruder A.
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