VINYL ESTER-BASED COPOLYMER DISPERSIONS FROM A CONTINUOUS TUBULAR EMULSION POLYMERIZATION PROCESS
Disclosed are aqueous polymer dispersions which can be used as binders in paper coating compositions. Such dispersions are made using a continuous polymerization process involving a tubular reactor with a continuous loop section and a secondary line section and comprise a polymer of polymerized copolymers (a) a vinyl ester, (b) an ethylenically unsaturated mono or di-carboxylic acid or half ester of a di-carboxylic acid, and (c) a comonomer having a multifunctional moiety.
1 . A composition comprising:
an aqueous dispersion of a polymer comprising at least the following polymerized comonomers:
vinyl acetate,
at least one ethylenically unsaturated mono or di-carboxylic acid or half ester of a di-carboxylic acid, and
at least one multifunctional comonomer,
where the dispersion is prepared by a continuous emulsion polymerization in a reactor comprising a closed loop section and a secondary line section.
2 . A composition comprising:
an aqueous dispersion of a polymer comprising at least the following polymerized comonomers:
vinyl acetate,
at least one ethylenically unsaturated mono or di-carboxylic acid or half ester of a di-carboxylic acid,
and at least one multifunctional comonomer,
where the dispersion is prepared by a continuous emulsion polymerization in a polymerization reactor comprising a first section with a circulation loop with one or more inlets for raw material, a pump for circulating a reactor charge within the circulation loop, and a secondary line section not forming a closed loop connected to a discharge of the loop section.
3 . The composition of claim 1 , wherein the volume of the secondary line section is less than twice the volume of the loop section.
4 . The composition of claim 1 , wherein the polymer further comprises ethylene polymerized with the other comonomers.
5 . The composition of claim 1 , wherein the at least one ethylenically unsaturated mono or di-carboxylic acid or half ester of a di-carboxylic acid comprises acrylic acid, vinyl acetic acid, crotonic acid, methacrylic acid, tiglic acid, maleic acid, fumaric acid, itaconic acid, maleic acid, citraconic acid, hydromuconic acid, allylmolonic acid, mono(2-ethylhexyl) maleate, monoethyl maleate, or monobutyl maleate, preferably monoethyl maleate.
6 . The composition of claim 1 , wherein the at least one multifunctional monomer comprises triallyl cyanurate, triallyl isocyanurate, diallyl maleate, diallyl fumarate, dyvinyl benzene or diallyl phthalate, preferably diallyl phthalate.
7 . The composition of claim 1 , wherein the dispersion is stabilized with anionic and/or nonionic emulsifiers which are substantially free of alkylphenol ethoxylate surfactants.
8 . The composition of claim 1 , further comprising an external crosslinker, preferably ammonium zirconium carbonate and/or potassium zirconium carbonate.
9 . The composition of claim 1 , having a solids content of from 40 wt % to 70 wt %.
10 . The composition of claim 1 , wherein the polymer comprises from 70 to 98-pphm vinyl acetate and from 2 to 30 pphm of ethylene.
11 . The composition of claim 1 , which exhibits a volume average particle size value, D v , of at least 150 nm.
12 . The composition of claim 1 , further comprising a pigment selected from the group consisting of kaolin clay, calcium carbonate, titanium dioxide, plastic pigments and combinations of said pigments.
13 . A coating formed by the composition of claim 1 , having an % IGT Dry Pick Value greater than 60% compared to the same composition prepared using a batch process.
14 . A paper or paperboard substrate coated with from about 1 g/m 2 to 30 g/m 2 of the coating composition of claim 1 .