UV curable elastomer composition

#This invention relates to elastomeric compositions that are curable by exposure to ultraviolet (UV) radiation. In addition, this invention relates to a process for curing elastomeric seals rapidly, wherein the seals are formed by applying an uncured polymer composition directly onto a sealing element or a surface to be sealed. This invention further relates to cured articles produced by the process of the invention.

#Elastomeric compositions require a vulcanization, i.e. curing, step in order to develop the crosslinked network structure which confers optimum rubbery properties to such compositions. Typically, the curing processes are based on compression molding or transfer molding techniques wherein an elastomer, fully compounded with curing agent and other additives, is introduced into a mold that is then heated under pressure. The elevated temperatures used during the molding process cause chemical reaction of the elastomer and curative, thereby producing a crosslinked product.

#The particular raw (i.e. uncured) elastomer used to manufacture a synthetic rubber article will be selected with reference to the specific end use application and environment under which the finished article must function. For example, one will select different elastomers from among ethylene alkyl acrylate copolymer rubbers, ethylene alpha-olefin copolymer elastomers, fluoroelastomers and chlorinated elastomers depending upon whether the finished article will be exposed to oils, water, fuels, acids or bases. One will also consider the temperature range to which the article will be subjected and special requirements such as flame resistance. In addition, consideration will be given to the cure characteristics of the polymer and the ease with which defect-free parts can be produced.

#The invention is illustrated by the following specific embodiments wherein all parts are by weight unless otherwise indicated.

#A curable elastomeric composition of the invention was prepared by mixing on a rubber mill 92.5 parts of a copolymer of ethylene and methyl acrylate (ethylene content 34 wt. %, Mooney viscosity ML1+4 (100° C.) of 8), 7.5 parts trimethylolpropane triacrylate, 0.75 parts Irgacure® 1800 photoinitiator (a mixture of 75 wt. % 1-hydroxycyclohexyl phenyl ketone and 25 wt. % bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylphenylphosplhine oxide, available from Ciba-Geigy, Ltd.), and 0.5 parts Naugard® 445 antioxidant (4,4′-di(α, α-dimethyl-benzyl)diphenylamine, available from Uniroyal, Inc.). Uncured slabs of 6 mm thickness were shaped by molding in a mold coated with Teflono®fluoropolymer resin. The slabs were exposed for one and two minutes respectively to UV radiation from a medium pressure mercury lamp which emitted radiation of wavelength approximately 250-400 nm at 80 watts/cm. The distance of the samples from the lamp was 10 cm. The cured samples exhibited the properties shown in Table I.

#TABLE I Length of Exposure (Minutes) 1 2 Hardness, Shore A 46 50 Surface Facing Source Hardness, Shore A 35 42 Surface Away From Source