Wax dispersions and process thereof

Details Wax dispersions and process thereof Wax dispersions and process thereof

2002-08-28

2004-12-28

Sanders, Kriellion A. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S488000, C430S137170

Reexamination Certificate

active

06835768

ABSTRACT:

The present invention is generally directed to aqueous wax dispersions and processes thereof, and which dispersions are comprised, for example, of wax particles stabilized with a hydrophilic polyester resin, and wherein the dispersions are useful for a variety of applications, such as ingredients for toners, inks, paints, or coating formulations such as a coating for articles like wood. More specifically, the present invention relates to storage/stable wax dispersions, and economical and practical methods for generating a storage/stable wax dispersion stabilized by a hydrophilic polyester resin, and wherein the wax particles have a fine particle size range, such as, for example, a particle size of from about 10 to about 500 nanometers, with particle size distribution, such as, for example, about 1.2 to about 1.6, as measured utilizing a Microtrac UPA150 particle size analyzer, or a Nicomp Analyzer. Yet, more specifically, the present invention relates to economical processes compared, for example, to solvent based or dispersion based methods for generating wax dispersions wherein the wax dispersion is obtained by utilizing a known apparatus comprised of a homogenizer connected to a reactor in a sealed and closed loop configuration; and wherein the process is comprised of homogenizing the wax in an aqueous solution containing a stabilizer, such as a hydrophilic polyester resin, and wherein the defined particle size is attained, for example, by controlling the concentration of wax, the concentration of the stabilizer, and apparatus and process variables such as temperature, pressure and time. The wax dispersion in embodiments is storage/stable, that is stable without agglomeration or settling for a substantial time, such as more than six months, and more specifically, for more than two years.
In specific embodiments, the present invention is directed to the economical preparation of a storage/stable wax dispersion stabilized with a hydrophilic polyester resin, such as a wax, selected from the group comprised of natural waxes, such a carnauba wax, paraffin wax, montan wax; synthetic waxes, such as microcrystalline polyethylene wax, polybutylene wax, polyethylene-acrylic wax, polyester wax, polyamide wax, or Fischer-Tropsch wax, mixtures thereof and the like; and wherein the wax dispersion possesses, for example, a particle size diameter of from about 10 to about 500 nanometers with a size distribution of from about 1.2 to about 1.6. The wax dispersion is preferably obtained by utilizing a known apparatus comprised of a homogenizer, such as a Gaulin 15MR available from APV Homogenizer, connected to a reactor in a sealed and closed loop configuration, such as a one gallon stainless steel jacketed reactor with steam heating and water cooling capability; heating to a temperature higher than the peak melting point of the wax to melt the wax, such as from about 10° C. or more higher than the peak melting point of the wax, and thereafter the mixture resulting is pumped through the homogenizer, which is comprised of two valves in series comprised of a primary valve that operates at high pressure, such as up to 8,000 pounds per square inch (psi), during homogenization, and a secondary valve that operates at lower pressures of up to about 1,000 pounds per square inch (psi); and wherein the homogenizer (generating emulsions or dispersions in a fluid mixture under pressure) is initially operated in a pre-emulsification mode where the primary valve is fully open and the secondary valve is partially closed to generate a pressure drop of about 800 to about 1,000 psi for a desired period of time, up to 8 theoretical passes (time for one theoretical pass is calculated by the mixture volume divided by the volumetric flow rate through the homogenizer). More specifically, for a 4 liter mixture pumped at 1 liter per minute, one theoretical pass consumes about 4 minutes; 30 minutes of pre-emulsification is equivalent to about 7.5 theoretical passes. After pre-emulsification, the primary valve is partially closed to increase the homogenizer pressure to a desired pressure of from about 3,000 psi to about 8,000 psi. Emulsification is accomplished for a number of theoretical passes of from about 5 to about 15 passes, and wherein operating at a higher pressure for a longer time period results in a smaller wax particle size in the product. After completion of emulsification, the homogenizer is disconnected and the wax dispersion in the reactor is cooled to ambient room temperature, discharged into a product container and filtered through a filter bag (typically about 1 to about 50 micron pore size). The dispersion product is analyzed for total solids content using a Sartorius MA30 moisture analyzer and average particle size and particle size distribution using the Microtrac UPA150 particle.
Aqueous wax dispersions based on polyethylene or polypropylene waxes can be prepared in principle by two methods; as primary dispersions by polymerization of ethylene or propylene in a surfactant-containing aqueous phase under super atmospheric pressure and in the presence of an initiator system, or as secondary dispersions by dispersing dispersible polyethylene or polypropylene waxes in powder form with the aid of a suitable dispersant system. Emulsifiable waxes usually contain low molecular weight polyolefin chains functionalized with carboxylate, keto or hydroxyl groups; the chains can be prepared by copolymerization of ethylene or propylene with, for example, unsaturated carboxylic acids, such as acrylic acid, or by atmospheric oxidation of polyolefin waxes. Primary dispersions generally possess particle sizes of from about 10 to about 1,000 nanometers. Dispersions having larger particles tend to undergo phase separation primarily in view of the low density and the hydrophobic nature of the polyolefin wax. In both preparation methods, solids contents of up to about 35 percent by weight can usually be achieved. Higher wax contents are achievable in relatively high amounts with difficulties.
In U.S. Pat. No. 5,723,137, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for producing a storage/stable wax dispersion by, for example, heating a mixture containing (A) about 10 percent to about 80 percent by weight of a wax, (B) about 0.5 percent to about 30 percent by weight of a hydrophilic nonionic dispersant having an HLB value of about 8 to about 18, and (C) about 1 percent to about 30 percent by weight of a hydrophobic codispersant selected from the group consisting of fatty alcohols containing about 12 to about 22 carbon atoms and partial esters of polyols containing about 3 to about 6 carbon atoms with fatty acids containing about 12 to about 22 carbon atoms, and wherein the weight ratio of component (B) to component (C) is from about 0.5:1 to about 20:1, and which process is completed in the presence of about 15 percent to about 85 percent by weight of water; heating to a temperature above the melting point of the mixture of components (A) to (C) to form a dispersion; heating the dispersion to its phase inversion temperature, and then cooling the dispersion to a temperature below its phase inversion temperature.
In U.S. Pat. No. 5,746,812, the disclosure of which is totally incorporated herein by reference, there are illustrated aqueous polyolefin wax dispersions that contain (A) from about 5 to about 65 percent by weight of polyethylene wax or polypropylene wax having a mean particle size of from about 1 to about 50 and an acid number of less than about 5 milligrams of KOH/gram of wax, and (B) from about 0.5 to about 20 percent by weight of glyceride of predominantly ethylenically monounsaturated or polyunsaturated monocarboxylic acids which may additionally contain hydroxyl groups, which glyceride has been reacted with from about 1 to about 50 mol of a 1,2-alkylene oxide of about 2 to about 4 carbon atoms as a dispersant.
In U.S. Pat. No. 5,290,654, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparati

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