Latex comprising water and a styrenic block copolymer and a process for preparing articles therefrom
View Patent ↗Articles with enhanced tensile strength and comfort are prepared from a latex comprising water and a styrenic block copolymer, wherein the styrenic block copolymer has 2 or more poly(vinyl aromatic) blocks and at least one block of polymerized conjugated diene, wherein the styrenic block copolymer has a weight average molecular weight of 150,000 to 250,000, the poly(vinyl aromatic) blocks have a weight average molecular weight ranging from 9,000 to 15,000, and the content of poly(vinylaromatic) blocks in the styrenic block copolymer ranges from 8 to 15% wt, based on the total styrenic block copolymer, by a process which comprises coating a surface with the latex to obtain a film, wherein the latex comprises a vulcanizing agent. The invention also provides a latex comprising such a styrenic block copolymer and a vulcanizing agent, as well as a styrenic block copolymer that is particularly suitable for use in such a latex.
1. A latex comprising water and a styrenic block copolymer, wherein the styrenic block copolymer has 2 or more poly(vinyl aromatic) blocks, said poly(vinyl aromatic) blocks are a polystyrene block, containing less than 5 wt % of copolymerizable monomer, based on the weight of poly(vinyl aromatic) block and at least one block of polymerized conjugated diene, said conjugated diene is a polyisoprene block, containing less than 5 wt % of copolymerizable monomer, based on the weight of block polymerized conjugated diene, wherein the styrenic block copolymer has a weight average molecular weight of 170,000 to 220,000, the poly(vinyl aromatic) blocks have a weight average molecular weight ranging from 9,000 to 14,000, and the content of poly(vinylaromatic) blocks in the styrenic block copolymer ranges from 9 to 14% wt, based on the total styrenic block copolymer, and a vulcanising agent.
2. A latex according to claim 1 , wherein the vulcanising agent comprises a sulphur compound and, optionally, one or more accelerators.
3. A latex according to claim 2 , wherein one or more accelerators are used and are selected from the group consisting of sulphenamide compounds, thiazole compounds, thiuram compounds, dithiocarbamates, xanthates and guanidines.
4. A latex according to claim 2 , wherein the sulphur compound has been selected from the group consisting of sulphur, thiuram sulphides, dithiodimorpholine, caprolactam disulphide, dialkylthiophosphoryl disulphide, diisopropylxanthogen polysulphide, and mixtures thereof.
5. A latex according claim 2 , wherein the amount of the sulphur compound ranges from 0.2 to 4 parts by weight per hundred parts by weight of the combination of water and styrenic block copolymer.
6. A latex according to claim 1 , wherein the styrenic block copolymer is of the general formula A-B-A, wherein each block A independently is a poly(vinyl aromatic) block, and wherein block B is a block of polymerized conjugated diene, wherein each block independently is a homopolymer block or a copolymer block, and optionally a block B is partly hydrogenated.
7. A latex according to claim 1 , wherein the styrenic block copolymer has been prepared by sequential polymerization of
(i) a vinyl aromatic monomer or a mixture (a) composed for at least 95 wt % of a vinyl aromatic monomer and at most 5 wt % of a copolymerizable monomer, based on the weight of the mixture (a),
(ii) a conjugated diene or a mixture (b) composed for at least 95 wt % of a conjugated diene, and at most 5 wt % of a copolymerizable monomer based on the weight of the mixture (b), and
(iii) a vinyl aromatic monomer or a mixture (c) composed for at least 95 wt % of a vinyl aromatic monomer and at most 5 wt % of a copolymerizable monomer based on the weight of the mixture (c).
8. The latex according to claim 1 , wherein the latex comprises from 20 to 80% by weight of styrenic block copolymer, based on the weight of the combination of water and styrenic block copolymer.
9. A process for preparing articles from a latex according to claim 1 , which process comprises coating a surface with the latex to obtain a film.
10. An article prepared from the latex of claim 1 , in the form of a glove, catheter or condom.
11. Cured, vulcanized latex comprising a styrenic block copolymer comprising 2 or more poly(vinyl aromatic) blocks and at least one block of polymerized conjugated diene, wherein the styrenic block copolymer has a weight average molecular weight of 170,000 to 220,000, the poly(vinyl aromatic) blocks have a weight average molecular weight ranging from 9,000 to 14,000, and the content of poly(vinylaromatic) blocks in the styrenic block copolymer ranges from 9 to 14% wt, based on the total styrenic block copolymer, said cured, vulcanized latex has a tensile strength ≧23.9 but ≦33.9 MPa, and said latex has a 10% Young's Modulus ≧0.22 but ≦0.25 MPa, according to ASTM D412 and ASTM D3577.