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...
Reexamination Certificate
1999-07-06
2001-06-12
Wu, David W. (Department: 1713)
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...
C524S563000, C526S065000, C526S067000, C526S073000, C526S202000, C526S331000
Reexamination Certificate
active
06245851
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
Vinyl acetate/ethylene (VAE) emulsions have been widely produced for use as adhesives, coatings, paints, and other applications. One of the recent trends in vinyl acetate/ethylene polymer emulsion technology is to increase the solids content to a level above about 65% by weight, preferably to a level of at least from 65 to 75% by weight. Customary commercial vinyl acetate/ethylene emulsions typically have a solids content of from 54-56%. The former emulsions are referred to as “high solids” emulsions and offer many advantages in addition to the fact there is more product per unit weight. Representative patents for producing batch high solids vinyl acetate/ethylene emulsions are as follows:
U.S. Pat. No. 4,921,898 discloses a process for producing vinyl acetate/ethylene copolymer emulsions having from about 65-70% solids which emulsion is prepared in the presence of a stabilizing system consisting essentially of 2-4 wt % polyvinyl alcohol having a degree of polymerization of from 100 to 600 and from about 2-4 wt % of a surfactant such as condensates of ethylene oxide and a hydrophobic base and alkylphenoxy poly(ethyleneoxy) ethanol, the surfactants being sold under the trademarks Pluronic and Igepal, respectively.
U.S. Pat. No. 5,124,394 discloses a process for producing high solids vinyl acetate/ethylene copolymers utilizing a stabilizing system consisting essentially of poly(ethyloxazoline). Optionally, a low molecular weight polyvinyl alcohol having a molar percent hydrolysis of from 75-99% and an average degree of polymerization from 100 to 600 is included as a component of the stabilizing system. Also, one can incorporate small levels of alkylphenoxy poly(ethyleneoxy) ethanols and ethylene oxides of hydrophobic bases.
U.S. Pat. No. 5,070,134 discloses a process for producing high solids vinyl acetate/ethylene emulsions having a solids content of from 65-70% by weight utilizing an emulsifying dispersant containing from 1 to 1.9 parts by weight partially saponified polyvinyl alcohol having an average polymerization degree of from 300 to 1,000 and from 1 to 3 parts by weight of a polyoxyethylene nonionic surface active agent having an HLB of from 16.5 to 17.5 per hundred parts by weight of vinyl acetate units.
U.S. Pat. No. 5,629,370 discloses a process for producing vinyl acetate/ethylene copolymers having a solids content of at least 65% by weight utilizing from 0.8 to 2 percent by weight of a fully or partially hydrolyzed polyvinyl alcohol in a mixture of nonionic, ethoxylated alkylphenol surfactants having an HLB of from 16.0 to 16.5.
Vinyl acetate/ethylene emulsions have also been prepared by continuous processes, but largely the continuous processes have been used for the production of polyvinyl acetate homopolymers and vinyl acetate/ethylene emulsions at conventional, 54-56% solid levels. Representative patents are as follows:
U.S. Pat. No. 4,164,489 discloses a continuous process for producing vinyl acetate/ethylene copolymer emulsions for use in adhesive applications. The solids content of the emulsions range from about 40-65% with a general range of between 50 and 60% solids. The stabilizer used for the polymerization consisted of polyvinyl alcohol typically having a molar hydrolysis of 87-89% and a viscosity of 21-25 cps at 4% solids at ~20° C. Initial polymerization of vinyl acetate and ethylene is carried out in the presence of a seed latex and then removing the latex from the initial polymerization vessel at a vinyl acetate monomer content of from 5-20% by weight.
U.S. Pat. No. 2,587,562 discloses a process for continuous polymerization of vinyl acetate utilizing a stabilizing system of hydroxyethyl cellulose and sodium sulfonate.
U.S. Pat. No. 3,551,396 discloses a process for producing a variety of vinyl polymers by polymerizing such vinyl monomers in a “loop” reactor. The stabilizing system employed in the loop reactor is a polyoxyethylene-polyoxypropylene copolymer.
U.S. Pat. No. 4,035,329 discloses a process for the continuous production of an ethylene/vinyl acetate copolymer in the presence of a redox catalyst system in which the oxidizing component of the redox catalyst system is in molar excess of from 3 to 10 times the presence of the reducing agent, and the monomers are added at a rate such that the unreacted vinyl monomer concentration does not exceed 15% by weight.
U.S. Pat. No. 5,442,006 discloses a process for producing vinyl acetate and acrylic dispersions having wide particle size range. A wide variety of surface active substances containing polymer are suited for stabilizing the emulsion, and these include polyvinyl alcohol, cellulose derivatives, and vinyl pyrrolidone containing copolymers as well as other nonionic, cationic, and anionic emulsifiers.
BRIEF SUMMARY OF THE INVENTION
The basic process for producing high solids vinyl acetate/ethylene emulsions comprised polymerizing vinyl acetate and ethylene, optionally including other ethylenically unsaturated monomers, in a reaction vessel in the presence of a stabilizing system. On conclusion of the polymerization the unreacted monomers are removed and product recovered. The improvement for producing a high solids vinyl acetate/ethylene aqueous emulsion comprises:
effecting polymerization in at least two backmixed reaction vessels comprised of a primary and secondary reaction vessel wherein the reactants and products are continuously and sequentially introduced and removed respectively; and
effecting polymerization in the presence of a stabilizing system consisting essentially of a low molecular weight polyvinyl alcohol having a molar hydrolysis value of from 87 to 99%.
There are significant advantages of the improved process, and these include:
an ability to eliminate conventional surfactants from the emulsion polymerization process and thus improve the potential to increase the water resistance of the vinyl acetate/ethylene polymer in its end-use applications;
an ability to remove surfactant from the polymerization process thus permitting one to improve vinyl acetate/ethylene polymer product consistency, as it is no longer necessary to carefully control the relative concentrations of two different stabilizers and their addition rate in the polymerization process;
an ability to produce low viscosity vinyl acetate/ethylene emulsions having a viscosity of <3000 cps a @ 65% solids, typically from 1000 to 3000 cps; and,
an ability to produce quality vinyl acetate/ethylene emulsions at high solids.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
The drawing is a process flow diagram of a continuous process for producing high solids vinyl acetate/ethylene emulsions.
DETAILED DESCRIPTION OF THE INVENTION
Emulsion polymerization of high solids vinyl acetate/ethylene based emulsions has generally been effected in a batch reactor in an aqueous medium under ethylene pressures not exceeding 100 atmospheres (generally from 40 to 80 atmospheres) in the presence of a catalyst and at least one emulsifying agent. In the past, the emulsifying agent comprised polyvinyl alcohol and a surfactant. The presence of polyvinyl alcohol complicates the process because conventional batch processes have not been adapted to make high solids vinyl acetate/ethylene emulsions without surfactant.
The high solids vinyl acetate/ethylene copolymers produced by the process herein contain from about 65 to 95% by weight of vinyl acetate, 5 to 35% by weight of ethylene and 0 to 15% by weight of ethylenically unsaturated monomer. The sum of the percentages of the monomers employed to form the copolymer is always 100. Preferred ranges are 15-25% by weight for ethylene and 75-85% by weight for vinyl acetate and less than 5% optional monomer.
A variety of ethylenically unsaturated monomers can be copolymerized with the vinyl acetate and ethylene to form the high solids VAE emulsions. For example, C
1-8
alkyl vinyl ethers, C
1-8
esters and amides of acrylic acid
Cordeiro Cajetan Francis
Petrocelli Francis Peter
Air Products Polymers, L.P.
Brewer Russell L.
Egwim Kelechi
Wu David W.
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