| 摘要 |
A soft but tough self-supporting elastomeric film having a glass transition temperature (Tg) in the range from about -20 DEG C. to about -60 DEG C., raw tensile strength of at least 300 psi, along with an elongation of at least 350% and less than 20% hysteresis loss, exhibits "snap", a characteristic of a natural rubber band. The novel film is derived from a crosslinked carboxylate latex containing from 1-20 phr of itaconic acid (IA) and at least 70 phr of one or more copolymerizable monomers one of which is an acrylate having the structure <IMAGE> (I) wherein R1 is hydrogen or methyl; R2 represents C1-C20 alkyl, C2-C7 alkylthioalkyl, or C2-C7 cyanoalkyl; and at least 40 phr of said acrylate in said film is present as an alkyl acrylate in which alkyl is C4-C8. The film can only be derived from a latex which has been formed by an emulsion polymerization process, in which at least one-half of the IA is initially charged into a reactor, and the remaining ingredients of the recipe then added gradually. This unique order of addition produces a concenration of carboxyl (COOH) groups on the surface of the latex particles which is at least twice that of COOH groups on particles of a latex formed by conventionally proportioning the monomer ingredients after initiation. This distribution of COOH groups persists in coalesced latex particles, and results in a film having higher tensile strength and toughness than might be expected in a film with such low Tg in the acrylate family.
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