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
1999-12-10
2004-01-06
Reddick, Judy M. (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...
C524S457000, C524S503000, C526S202000
Reexamination Certificate
active
06673862
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to vinyl acetate-ethylene copolymer emulsions and, more particularly, relates to high solids copolymer emulsions. High solids vinyl acetate/ethylene emulsions are characterized as having a solids level of at least 65% to about 75% by weight and having a viscosity of less than 5000 centipoises. Stabilization of high solids, e.g., vinyl acetate/ethylene (VAE) based copolymers prepared by aqueous emulsion polymerization typically has been achieved by the combined use of poly(vinyl alcohol) and nonionic surfactants.
Representative patents showing the production of vinyl acetate/ethylene emulsions and high solids vinyl acetate/ethylene emulsions are as follows:
U.S. Pat. No. 3,218,281 discloses a process for producing vinyl acetate emulsions in the presence of a water soluble emulsifying agent consisting of copolymers of vinyl acetate and polyoxyalkylene compounds, such as copolymers of vinyl acetate and polyoxyethylene glycol.
U.S. Pat. No. 4,133,791 discloses the production of ethylene containing copolymers in the presence of poly(vinyl alcohol) having a molecular weight of from 6000 to 100,000 to a solids content of from 30 to 60% by weight and then evenly distributing polyethylene glycol or a mixture of polyethylene glycol; and polyethylene/propylene glycol in the copolymer dispersion. The resultant viscosity of the dispersion is above 20 Pas.
U.S. Pat. No. 4,921,898 discloses a process for producing high solids VAE compositions by using a stabilizing amount of a poly(vinyl alcohol)/surfactant system consisting essentially of a poly(vinyl alcohol) having a 100-600 degree of polymerization and a nonionic surfactant consisting of a 30-40 ethylene oxide unit substituted alkyl phenol or a 30-40 ethylene oxide unit substituted propylene glycol.
U.S. Pat. No. 4,963,611 discloses the production of vinyl acetate emulsions for use as adhesives and paints employing a water soluble poly(vinyl alcohol) as a stabilizing agent. Example 4 shows the production of a low solids vinyl acetate homopolymer in the presence of poly(vinyl alcohol) and a polyethylene glycol having a molecular weight of 200.
U.S. Pat. No. 5,070,134 disclose a vinyl acetate/ethylene high solids emulsion utilizing a stabilizing system comprised of from 1 to 1.9 parts of poly(vinyl alcohol) having a degree of polymerization from 300 to 1000 and from 1 to 3 parts by weight of a polyoxyethylene nonionic surface active agent having an HLB of 15.5 to 17.5 per 100 parts by weight vinyl acetate.
U.S. Pat. No. 5,110,856 discloses high solids vinyl acetate/ethylene emulsions formed by polymerizing vinyl acetate and ethylene in the presence of a stabilizing system of poly(vinyl alcohol) having a degree of polymerization of 300 to 1000 and from 1 to 3% of a polyoxyethylene surface active agent having an HLB of 16.5 to 17.5.
U.S. Pat. No. 5,629,370 discloses a vinyl acetate/ethylene copolymer emulsion having a solids content of at least 65% by weight. The emulsion is prepared by polymerizing vinyl acetate and ethylene in the presence of a partially hydrolyzed poly(vinyl alcohol) and a mixture of nonionic ethoxylated alkyl phenol surfactants having an HLB of from 16 to 16.5.
EP 0 089 068 discloses a process for producing high solids >70% a viscosity of 5000 mPa·s or less utilizing a stabilizing system comprised of poly(vinyl alcohol) having a degree of hydrolysis of 88% and a polyoxyethylene oxide surfactant such as that sold under the trademark Pluronic.
BRIEF SUMMARY OF THE INVENTION
The present invention provides for the production of stable aqueous dispersions of vinyl acetate-ethylene copolymers having a solids content typically from 55 to 75% by weight and higher, preferably emulsions having a high solids content, i.e., greater than 65 wt %, preferably >70% which are useful as adhesives. They demonstrate surprisingly good speed of set and creep resistance at such high solids level. The vinyl acetate-ethylene copolymer is comprised of polymerized units of vinyl acetate and ethylene in approximately 50-95 wt % and 5-50 wt %, respectively. Optionally, other monomers may be copolymerized therewith.
The copolymers are prepared by the emulsion copolymerization of vinyl acetate and ethylene monomers in the presence of a stabilizing system consisting essentially of (1) poly(vinyl alcohol) which is 75-99+mole % hydrolyzed and has an average degree of polymerization ranging from 100-2200 and (2) a polyethylene glycol having a number average molecular weight of from 200 to 20,000.
The resulting vinyl acetate/ethylene copolymer emulsions will comprise about 55 to about 75 wt % solids, preferably from 65 to 75% solids with a viscosity of less than about 5000, typically less than 3500 cps, preferably less than about 2500 cps at 65% solids or greater and at 60 rpm (Brookfield #4 spindle at 25° C.).
Several advantages can be achieved by the invention:
increased polymer solids at viscosities comparable to lower solids emulsions;
excellent resistance to sedimentation and excellent stability of the emulsion;
accelerated bond formation and adhesive setting speed; and,
improved creep resistance versus many conventional high solids emulsions.
DETAILED DESCRIPTION OF THE INVENTION
The copolymers according to the invention typically comprise from 50-95 wt % vinyl acetate and 5-50 wt % ethylene to provide a Tg ranging from about −35 to 20° C. Preferably, the copolymer forming adhesive applications contains from 65 to 80 wt % vinyl acetate and 20 to 35 wt % ethylene on a monomer basis. Pressure sensitive adhesive applications may contain ethylene concentrations from about 35 to 45%.
The vinyl acetate-ethylene copolymers may optionally include one or more additional ethylenically unsaturated copolymerizable monomers. Exemplary of such comonomers, which may be present in amounts from 0 to 10 wt %, but preferably less than 5%, e.g., 0.5 to 5% are C
3
-C
10
alkenoic acids, such as acrylic acid, methacrylic acid, crotonic acid and isocrotonic acid and their esters with C
1
-C
18
alkanols, such as methanol, ethanol, propanol, butanol, and 2-ethylhexanol; vinyl halides such as vinyl chlorides; alpha, beta-unsaturated C
4
-C
10
alkenedioic acids such as maleic acid, fumaric acid and itaconic acid and their monoesters and diesters with the C
1
-C
18
alkanols, such as dibutyl maleate and dioctyl maleate; and nitrogen containing monoolefinically unsaturated monomers, particularly nitriles, amides, N-methylol amides, lower alkanoic acid esters of N-methylol amides, lower alkyl ethers of N-methylol amides and allylcarbamates, such as acrylonitrile, acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N-methylol allylcarbamate, and lower alkyl ethers or lower alkanoic acid esters of N-methylol acrylamide, N-methylol methacrylamide and N-methylol allylcarbamate. If any additional ethylenically unsaturated comonomer is used, about 1-5 wt % is preferred.
The stabilizing system for the copolymerization reaction consists essentially of poly(vinyl alcohol) and polyethylene glycol wherein the poly(vinyl alcohol) is present in an amount of from 1-4 wt %, preferably 2 to 3 wt % by weight of copolymer and from 1-4 wt %, preferably 2-3 wt % of the polyethylene glycol, said polyethylene glycol having a number average molecular weight of from 200 to 20,000 by weight of the copolymer. (Typically, the poly(vinyl alcohol) and polyethylene glycol are based upon the total weight of the monomers charged to the polymerization.) The poly(vinyl alcohol) which is used in the stabilizing system can be 75-99+mole % hydrolyzed, preferably 85-90 mole % and especially 87-89 mole % hydrolyzed and has a degree of polymerization ranging from 100 to 2200, preferably, 140 to 1000, and most preferably 200 to 700. Another means for assessing the degree of polymerization of the poly(vinyl alcohol) is its viscosity as a 4 wt % aqueous solution at 20° C. Suitable poly(vinyl alcohol)s will have a viscosity ranging from 2 to about 50, preferably 2.5 to 7 for higher solids emulsions.
As stated the stabil
Air Products Polymers, L.P.
Bongiorno Mary E.
Brewer Russell L.
Reddick Judy M.
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