VULCANIZATION SYSTEMS FOR CURING BLOCK COPOLYMER LATEX FILMS
A method for the curing of aqueous latexes comprising block copolymers is disclosed. The block copolymers have the general formula A-B-A or A-B-Y-(B-A) n . The curing is conducted using vulcanization systems that are free of guanidine and thiuram compounds. The cured latexes are useful in the manufacture of elastic films, surgical, examination and electrical insulation gloves, industrial gloves and condoms.
1 . A method for curing a latex comprising water, a block copolymer, and a guanidine-free and thiuram-free vulcanization system such method comprising:
a. forming a solid film from the latex,
b. curing the film by heating to a temperature from 100° C. to less than 130° C.
2 . The method of claim 1 , where in the block copolymer comprises at least one mono-alkenyl arene block (A) and at least one conjugated diene block (B).
3 . The method of claim 2 , wherein the mono-alkenyl arene is styrene.
4 . The method of claim 2 , wherein the mono-alkenyl arene constitutes 8 to 15 wt. % of the total block copolymer.
5 . The method of claim 2 , wherein the conjugated diene is isoprene, butadiene, or mixtures thereof.
6 . The method of claim 5 , wherein the conjugated diene is isoprene.
7 . The method of claim 2 , wherein the block copolymer has the general formula
A-B-A or A-B-Y-(B-A)n where (n+1)
represents the average number of arms in a coupled polymer and n ranges from 1 to 6 and Y represents the residue of a coupling agent.
8 . The method of claim 2 , wherein the molecular weight of the A block is from 9,000 to 15,000.
9 . The method of claim 2 , wherein the molecular weight of the B block is from 75,000 to 150,000.
10 . The method of claim 7 , wherein the coupling efficiency is at least 90%.
11 . The method of claim 7 , wherein the coupling agent is γ-glycidoxy-propyl-trimethoxy-silane.
12 . The method of claim 1 , wherein the vulcanization system comprises sulfur, zinc-diethyldithio-carbamate, and zinc-2-mercapto-benzo-thiazole.
13 . The method of claim 1 , wherein the curing temperature is from 110 to 125° C.
14 . The method of claim 1 , further comprising the step of increasing the pH of the latex to 10 or greater by addition of an aqueous base before curing the film.
15 . The method of claim 1 , wherein the latex comprises from 20 to 80 wt. % of the block copolymer.
16 . An article prepared by the method of claim 1 .
17 . The article of claim 16 , which is a thin walled article or a dipped article.
18 . The article of claim 16 , which is a film, balloon, surgical glove, examination glove, electrical insulation glove, industrial glove or condom.