Process of making a vinyl ester based polymer latex composition
The present invention relates to a vinyl ester based polymer latex composition obtainable by free radical emulsion polymerization in substantial absence of a protective colloid and in the presence of no or small amounts of a surfactant, and to a process of making the same. The invention further pertains to a dispersion incorporating said vinyl ester based polymer latex composition, products comprising said dispersion, and various uses of the dispersion.
1. An emulsion polymerization process for producing a vinyl ester based polymer latex in an aqueous medium, said polymer comprising polymerized units of:
(a) 40-95.3 wt. % vinyl ester monomer
(b) 5-30 wt. % ethylene monomer
(c) 1-10 wt. % post-crosslinking monomer,
(d) 0.2-2 wt. % vinyl sulfonate monomer, and
(e) 0.5-2 wt. % unsaturated carboxylic acid monomer,
based on the total weight of monomers,
wherein the process is carried out substantially in the absence of any added protective colloid and in the presence of from 0 to 1.0 wt. % of surfactant, based on the total weight of the monomers,
wherein the process comprises
(i) a first stage of providing an initial reactor charge comprising an aqueous phase comprising
a) 10-30 wt. % of the vinyl ester monomer, based on total weight of vinyl ester monomer,
b) at least 50 wt. % of the ethylene monomer, based on total weight of ethylene monomer,
c) 5-25 wt. % of the post-crosslinking monomer, based on the total weight of post-crosslinking monomer, and
d) 50-100 wt. % of the vinyl sulfonate monomer, based on total weight of vinyl sulfonate monomer, and
(ii) a second stage of feeding any remaining monomers and optionally a polymerization initiator system in one or more feeds to the initial charge,
wherein the vinyl ester polymer latex has a solids content of at least 20 wt. %.
2. The process of claim 1 wherein surfactant is present at 0-0.1 wt. % based on the total weight of monomers.
3. The process of claim 1 wherein the initial reactor charge contains no surfactant.
4. The process of claim 1 wherein said second stage comprises polymerization substantially carried out at a pH≦3.
5. The process of claim 1 wherein the vinyl ester based polymer latex further comprises polymerized units of:
(f) 0-30 wt. % of at least one copolymerizable monomer selected from the group consisting of monomers X, Y, and Z,
wherein all percentages are based on the total weight of monomers, and the total weight of monomers is 100 wt. %, and wherein
(f1) monomer X is selected from the group consisting of C 1-10 alkyl acrylate monomers and mixtures thereof,
(f2) monomer Y is selected from the group consisting of vinyl-C 5-18 acyl esters, unsaturated dicarboxylic acid C 1-10 mono and dialkyl esters, unsaturated dicarboxylic acid anhydrides, unsaturated dicarboxylic acid mono- or diacid halides, and mixtures thereof, and
(f3) monomer Z is selected from the group consisting of a monoethylenically unsaturated, water soluble functional monomers, polyethylenically unsaturated pre-crosslinking monomers, chain transfer agents, and mixtures thereof.
6. The process of claim 5 wherein
monomer (a) comprises vinyl acetate,
monomer (c) comprises N-methylol acrylamide
monomer (d) comprises sodium vinyl sulfonate,
monomer (e) comprises acrylic acid, and
monomer (f) comprises:
(f1) 0-1.5 wt. % butyl acrylate
(f2) 0-6 wt. % vinyl versatate
(f3) 0-2 wt. % 2-acrylamido-propanesulfonate-sodium salt.
7. The process of claim 6 wherein the initial reactor charge contains no surfactant.
8. The process of claim 6 wherein said second stage comprises polymerization substantially carried out at a pH≦3.