Nanosilica-organic polymer composite latex

Abstract

An aqueous dispersion comprising: (a) a latex binder, wherein the latex binder comprises: (i) about 1-25% by weight of a monomer having latent crosslinking functionality, (ii) 0.1 to about 15% of an acid functional monomer, (iii) about 1 to about 25% ethylenically functional silica, (iv) and about 35 to 97.9% other monomers; and (b) an aqueous unsaturated silane treated silica dispersion, wherein the unsaturated silane treated silica dispersion comprises colloidal ethylenically unsaturated silica particles having an average particle size less than about 100 nm.

Claims

1. An aqueous dispersion comprising a latex binder, wherein the latex binder comprises a polymerization reaction product of: (i) about 1-25% by weight of a monomer having latent crosslinking functionality, (ii) 0.1 to about 15% by weight of an acid functional monomer, (iii) about 1 to about 25% by weight of an aqueous unsaturated alkoxy silane treated silica dispersion, wherein the unsaturated alkoxy silane treated silica dispersion comprises colloidal ethylenically unsaturated silica particles having an average particle size less than about 100 nm, the colloidal ethylenically unsaturated silica particles formed by a process which comprises admixing: (a) a polyalkoxy silane having ethylenic unsaturation selected from the group consisting of 3-acryloxypropyltrimethoxysilane, 2-methacryloxyethyltrimethoxysilane, 2-acryloxyethyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 2-methacryloxyethyltriethoxysilane, 2-acryloxyethyltriethoxysilane, gamma glycidoxypropyltrimethoxysilane, gamma methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, and mixtures thereof; (b) an aqueous silica dispersion; (c) a non-ionic surfactant; and (d) a base, (iv) about 35 to 97.8% by weight other monomers, and (v) a crosslinker.

2. The coating composition of claim 1 wherein the monomer having latent crosslinking functionality comprises diacetone acrylamide.

Description

EXAMPLE 1

Preparation of Unsaturated Silane Treated Silica

(1) To a reaction vessel containing a mixture of 720 parts water, 1.1 parts ammonium hydroxide, 6 parts of a non-ionic surfactant (Antarox® BL-240 Linear alcohol ethylene oxide propylene oxide polymer from Rhodia) and 5087 parts of a silica dispersion (Ludox® AS-40 40% NVM colloidal silica from W.R. Grace), is added dropwise at room temperature with vigorous stirring, 0.536 parts gamma-methacryloxypropyltriisopropoxysilane. The temperature was then raised to 82° C. and held for 30 minutes to produce the silane treated silica. This reaction product was used as is to produce a latex polymer as shown in Example 2.

EXAMPLE 2

(2) A latex incorporating the treated silica was then prepared by the following process. To the above reaction vessel containing the silane treated silica without any additional separation or purification, a mixture of 3.5 Rhodafac® RS-610 (anionic surfactant from Rhodia) with 30 parts water and 1.8 parts ammonium hydroxide was pumped in at high speed. The temperature was maintained at 82° C. and, under a nitrogen purge, a monomer pre-emulsion 17 parts Rhodafac® RS-610, 23 parts PAM-200® (phosphate ester of polypropylene glycol monomethacrylate from Rhodia), 46 parts diacetone acrylamide, 660 parts water, 8.5 parts ammonium hydroxide, 5.6 parts methacrylic acid, 224 parts methyl methacrylate, 612 parts butyl acrylate and 253 parts styrene and an initiator solution (3.7 parts ammonium persulfate and 270 parts water) were slowly fed in over a period of 3.5 hours. The reaction mixture was maintained under agitation for 70 minutes after which the temperature was lowered to 65′C and a mixture of 1.1 parts sodium metabisulfite in 25 parts water was slowly added over a period of 1 hour and held for an additional 30 minutes to reduce residual monomers. The latex was then admixed with 17 parts adipic dihydrazide to yield a cross-linkable composite latex.

(3) For comparison, a similar latex preparation was conducted in which the silane and silica were added to the reaction vessel, but not prereacted, followed by the addition of the monomer pre-emulsion as above. This preparation became a gel-like mass within 20 hours. Another comparative example was conducted by initially adding just the silica to the reaction vessel and then incorporating the silane into the monomer pre-emulsion mixture. This reaction product also became gel-like within 2 hours.

(4) While this invention has been described by a specific number of embodiments, it is obvious that other variations and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.