CA1322064C

CA1322064C - Vinyl acetate-ethylene copolymer emulsions prepared in the presence of a stabilizing system of a low molecular weight polyvinyl alcohol and a surfactant

Info

Publication number: CA1322064C
Application number: CA000558636A
Authority: CA
Inventors: William Edward Lenney; John Generoso Iacoviello
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 1987-02-17
Filing date: 1988-02-10
Publication date: 1993-09-07
Anticipated expiration: 2010-09-07

Abstract

ABSTRACT
A vinyl acetate-ethylene copolymer emulsion which is about 65-70%
solids and has a viscosity of less than about 3,500 is disclosed. The emulsion is prepared by copolymerization of vinyl acetate and ethylene monomers in the presence of a stabllizing system consisting essentially of 2-4 wt%, based on vinyl acetate monomer, of a polyvinyl alcohol having a 100-600 degree of polymerization and 2-4 wt%, based on vinyl acetate monomer, of a surfactant. Such emulsions demonstrate an improved speed of set as an adhesive.

Description

t 322064 VINYL ACETATE-ETHYLENE COPOLYMER EMULSIONS PREPARED IN THE
PRESENCE OF A STABILIZING SYSTEM OF A LOW MOLECULAR ~EIGHT
POLYVINYL ALCOHOL AND A SURFACTANT

TECHNICAL FIELD
The invention relates to vinyl acetate-ethylene copolymer emulsions and more particularly relates to such copolymer emulsions prepared in the presence of a polyvinyl alcohol stabilizing agent to provide an adhesive composition.
s BACKGROUND OF THE INVENTION
A large proportion of packaging adhesives currently in use in the United States and Europe are based on hot melt compositions. Since these adhesives are applied at elevated temperatures considerable amounts of energy are required to maintain suitable application temperatures. A
primary performance parameter is the adhesive s ability to set a bond rapidly and to maintain this bond after a short application of pressure.
As energy costs continue to rise the need increases to replace hot melts with cold or room temperature setting adhesives. By improving i.e. accelerating the emulsion setting speed it would be possible to substitute or use water based adhesives in place of the more energy intensive hot melt products.
One method of enhancing adhesive performance parameters such as speed of set PVC peel strength water resistance smoothness (less wood grain raising) and other properties would be to increase the emulsion solids content. In other words reducing the continuous phase volume or conversely increasing the level of dispersed phase might have an impact.
The general concept is to drive the solids up by removing water or continuous phase volume of the polyvinyl alcohol based vinyl acetate-ethylene copolymer emulsions.
Theories on polyvinyl alcohol stabilization rest with steric stabilization via acetyl interactions. Therefore to obtain optimum stabilization at a given solids one would predict that increasing polyvinyl alcohol molecular weight would enhance steric factors and thus overall latex stability.

1 322~64 Prtor act regarding vinyl acetate-ethylene copolymer emulsions prepared in the presence of polyvinyl alcohol includes the following:
U.S. 3,661,696 discloses a process for the production of an aqueous emulsion of an ethylene-vinyl acetate copolymer wherein the polymerization is performed in the presence of a preformed seed emulsion and a minor amount, from 1.5 to 6 wt%, of a protective colloid comprising a mixture of fully and partially hydrolyzed polyvinyl acetate. The resulting emulsion can be used as an adhesive. In Example 9 several emulsion compositions were prepared using a low molecular weight polyvinyl alcohol mixture in combtnation with a nonionic surfactant. In U.S. 3,734,819 and 3,769,151 a similar process is disclosed in which the ethylene-vinyl acetate polymer is prepared in the presence also of a small amount of a vinyl sulfonic ac~d comonomer or an unsaturated C3-C6 acid, respectively. Similarly, these patent show emulsion compositions prepared using a seed emulsion, the polyvinyl alcohol mixture and a nontonic surfactant.
U.S. 3,692,723 discloses aqueous dispersions and heat melting adhesives comprising same, which dispersions contain a copolymer of ethylene and vinyl acetate wherein the ethylene content is from 30 to 98 wt%, the copolymer having been prepared by a copolymerizatton process utilizing a particular combination of nonionic emulsifier, antonic emulsifier and protective colloid.
U.S. 3,816,362 discloses a process for preparing a stable aqueous ethylene-vinyl ester copolymer emulsion having an ethylene content of 4 to 20 wt%. Example 1 shows the use of a polyvinyl alcohol, a polyoxyethylene nonylphenyl ether (nonionic surfactant) and sodium dodecyl benzene sulfonate (anionic surfactant).
U.S. 3,827,996 discloses aqueous disperstons of vinyl ester polymers containing as a protective colloid parttally hydrolyzed polyvinyl alcohol having an average vinyl acetate content of S to 7 mole%. The polyvinyl alcohol may consist of a blend of two or more polyvinyl alcohols, each of which has an average vinyl acetate content different from the average of the blend. Several examples show the use of a partially hydroly2ed and a fully hydrolyzed polyvinyl alcohol in combination with a nonionic surfactant in the preparation of vinyl acetate-ethylene copolymer emulsions.
U.S. 4,043,961 discloses adhesive compositions consisting essentially of an aqueous emulsion of vinyl acetate-ethylene copolymer prepared in the presence of protective colloid comprising fully hydrolyzed vinyl alcohol copolymer containing methyl methacrylate. The examples show the use of such vinyl alcohol copolymer in combination with a medium and/or low viscosity partially hydrolyzed polyvinyl alcohol and a nonionic surfactant.
U.S. 4,267,090 and 4,287,329 disclose the preparation of vinyl acetate-ethylene copolymer emulsions in a reaction medium containing a protective colloid and a surface active agent.
U.S. 4,521,561 discloses a vinyl acetate-ethylene copolymer emulsion exhibiting both partially- and fully-hydrolyzed polyvinyl alcohol compatibility prepared in the presence of a polyvinyl alcohol stabilizing system having an 8-10 mole% residual vinyl acetate content. Since the degree of polymerization of the polyvinyl alcohol affects the v~scosity of the emulsion product and is not critical to the invention, polyvinyl alcohols having a degree of polymerization ranging from 200 to 2000 are suitable for use in the invention. In addition to the polyvinyl alcohol stabilizing system, emulsifying agents and protective colloids well known in the polymerization art may also be added in low levels, for example to enhance stability, mentioning polyoxyalkylene condensates.

SUMMARY OF THE INVENTION
The present invent~on provides stable aqueous dispersions of vinyl acetate-ethylene copolymers of high solids, i.e. greater than 60 wt~
solids, which are useful as packaging adhesives and demonstrate surprisingly good speed of set at such high solids level. The aqueous emulsion compr~ses a vinyl acetate-ethylene copolymer which is 60-95 wt%
vinyl acetate and 5-40 wt~ ethylene. The copolymer is dispersed in an aqueous medium and prepared by the emulsion copolymerization of the vinyl acetate and ethylene monomers in the presence of a stabilizing system consisting essentially of (1) a low molecular weight polyvinyl alcohol which is 75-99~ mole% hydrolyzed and has an average degree of polymerization ranging from 100-600 and (2) a surfactant. The resulting copolymer emulsions will comprise about 65 to about 70 wt% solids with a viscosity of less than about 3500 cps, preferably less than about 2500 cps at 65% solids and at 60 rpm and 25C.
The use of a stabilizing system consisting essentially of a low molecular weight polyvinyl alcohol and a surfactant during the emulsion polymerization of vinyl acetate with ethylene provides the following advantages:
Increased polymer solids at viscosities comparable to lower solids emulsions, a lower dibutyl phthalate thickening ratio and lower product surface tensions than vinyl acetate-ethylene copolymer emulsions stabilized solely with polyvinyl alcohol.
By increasing the copolymer solids of the dispersed phase and simultaneously lowering the surface tension of the continuous aqueous lS phase, intraparticle coalescence (bonding) is enhanced or accelerated.
Increased copolymer solids increases particle crowding while lower continuous phase surface tension accelerates the wicking of the continuous phase into porous or semi-porous substrates. Both factors accelerate bond formation and adhesive setting speed.
Organic solvents and/or plasticizers like dibutyl phthalate are added to adhesive copolymer emulsions to obtain a thickening response and accelerate the setting speed as is well known in the art. It is also known that too high a compound viscosity can slow wicking of the water into the substrate and thereby produce an opposite effect, i.e. a slower setting speed. The present invention lowers the response at a given additive level while maintaining or improving the speed of set at increased solids content.
Thus by increasing the solids content of the emulsion adhes~ve while lowering both surface tension and solvent thlckening ratio, intraparticle coalescence and substrate bonding are improved.
In addition, the use of the stabilizing system according to the invention results in a product having improved water resistance as well as significantly reducing the reactor cycle time required to produce such high solids emulsion.
3s The products of this invention result in less grain raislng when used as a laminate adhesive to adhere a vinyl substrate to a cellulosic substrate. Prior to this invention water-based adhesives could not be used as an adhesive to laminate such substrates.

DETAILED DESCRIPTION OF THE INVENTION
The copolymers according to the invention comprise 60-95 wt% vinyl acetate and 5-40 wtX ethylene to provide a Tg ranging from about -30 to 20C, preferably the copolymer contains 75-80 wt% vinyl acetate and 20-25 wt~o ethytene on a monomer basis.
The vinyl acetate-ethylene copolymers may optionally include one or more additional ethylenically unsaturated copolymerizable monomers.
Exemplary of such comonomers, wh~ch may be present at up to 10 wtZ or more, are C3-C10 alkenoic acids, such as acrylic acid, methacryllc acid, crotonic acid and isocrotonic acid and their esters with Cl-C18 alkanols, such as methanol, ethanol, propanol, butanol, and 2-ethylhexanol; vinyl halides such as vinyl chlorides;
alpha,beta-unsaturated C4-C10 alkenedioic acids such as maleic acid, fumaric acid and itaconic acid and thelr monoesters and diesters with the same Cl-Cl8 alkanols; and nitrogen containing monoolefinically unsaturated monomers, particularly nitrlles, 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 2s esters of N-methylol acrylamide, N-methylol methacrylamide and N-methylol allylcarbamate. If such additional ethylenically unsaturated comonomer is used, about 2-5 wt% is preferred.
Contemplated as the functional, or operative equivalents of vinyl acetate in the copolymer emulsions are vinyl esters of Cl-C18 alkanoic acids, such as vinyl formate, vinyl propionate, vinyl laurate and the like.
The stabilizing system for the copolymerization reaction to prepare the copolymer emulsion adhesiYes of the invention consists essentially of 2-4 wt~ of a low molecular welght polyvinyl alcohol and 1-4 wt~ of a surfactant, based on vlnyl acetate monomer. The low molecular welght polyvinyl alcohol whlch is used in the stabilizing system can be 75-99+
mole% hydrolyzed, preferably 85-90 and especially 87-89 mole7. hydrolyzed when used ln conjunction with a fully hydrolyzed polyvlnyl alcohol, and has a degree of polymerizatlon ranging from lOO to 600, preferably, 185-255. Another means for assesslng the degree of polymerization of the polyvlnyl alcohol is its viscoslty as a 4 wt% aqueous solution at 20C.
Su~table polyvinyl alcohols would have a viscoslty ranglng from 2.4 to about 7. Such polyvinyl alcohols can be prepared by synthesis and saponiflcation technlques well known to those skilled ln the art of manufacturlng polyvlnyl alcohol. A preferred polyvinyl alcohol havlng a degree of polymerlzatlon of about 235 ls marketed by Alr Products and Chemlcals, Inc. under the trademark VINOL0 203.
The amount of such polyvlnyl alcohol stabl1~zing component used ln the polymerlzatlon reactlon is about 2-4 wt%, preferably about 3 wt%, lS based on vlnyl acetate monomer ln the polymerlzatlon recipe. The polyv;nyl alcohol ls added to the polymerizatlon reactlon medlum all at once prlor to lnltlation or incrementally dur~ng the course of the polymerlzatlon, provlded a sufficlent amount ~s present lnltlally to provlde emulslon stablllty.
In addltlon to the polyvlnyl alcohol component the stablllzer system accordlng to the lnvention also conta~ns a surfactant at a level of about l-4 wt%, preferably 2-3 wt%, based on vlnyl acetate monomer.
The surfactants contemplated by the lnvention ~nclude any of the known and conventional surfact~nts and emuls~fy~ng agents, prlnclpally 2s the nonlonlc and anlonlc materlals, heretofore employed ln the emulslon copolymerlzatlon of vinyl acetate and ethylene, the nonlonlc polyalkoxylated surfactants belng especlally preferred. Among the nonlonlc surfactants whlch have been found to provlde good results are included the *Igepal surfactants marketeci by GAF and the *Pluronic surfactants marketed by BASF Wyandotte. The Igepal surfactants are members of a series of alkylphenoxy poly(ethy-leneoxy)ethanols which can be represented by the general formula RPhO~(CHzCH20)n 1-CH2CH20H

.,~"~,~
~ *trade mark wherein R represents an alkyl radical and n represents the number of rnoles of ethylene oxide employed. Illustrative are alkylphenoxy poly(ethyleneoxy)ethanols having alkyl groups containing from about 7-18 carbon atoms, inclusive, and having from about 4 to about 100 ethyleneoxy units, such as the octylphenoxy poly(ethyleneoxy)ethanols, nonylphenoxy poly~ethyleneoxy)ethanols and dodecylphenoxy poly(ethyleneoxy)ethanols; a sodium or ammonium salt of a sulfate ester of these alkylphenoxy poly(ethyleneoxy)ethanols; alkyl poly(ethyleneoxy)ethanols; alkyl poly(propyleneoxy)ethanols. The Pluronic surfactants are condensates of ethylene oxide with a hydrophoblc base formed by condensing propylene oxide with propylene glycol, and the like. Suitable nonionic surfactants also include polyoxyalkylene derivatives of hexitol (including sorbitans, sorbides, mannitans and mannides) anhydride, partial long-chain fatty acid esters, such as the polyoxyalkylene derivatives of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate. Other suitable nonionic surfactants which can be employed are alkylene oxide derivatives of long chained fatty alcohols such as octyl, dodecyl, lauryl or cetyl alcohol and polyethoxylated derivatives of acetylenic alcohols which are marketed under the trademark Surfynol by Air Products and Chemicals, Inc.
Various free-radical forming sources can be used in carrying out the polymerization of the monomers, such as peroxide compounds.
Combination-type systems employing both reducing agents and oxidizing agents can also be used, i.e. a redox system. Suitable reducing agents, or activators, include bisulfites, sulfoxylates, or other compounds hav~ng reducing propertles such as ascorbic acid, erythorbic acid and other reducing sugars. The oxidizing agents include hydrogen peroxide, organ~c peroxide such as t-butyl hydroperoxide and the like, persulfates, such as ammonium or potassium persulfate, and the like. Specific redox systems which can be used include hydrogen peroxide and zinc formaldehyde sulfoxylate; hydrogen peroxide and erythorbic acid; hydrogen peroxide, ammonium persulfate or potassium persulfate with sodium metabisulfite, sodium bisulfite, ferrous sulfate, zinc formaldehyde sulfoxylate or sodium formaldehyde sulfoxylate. Other free radical forming systems that are known in the art can also be used to polymerize the monomers.
The oxidizing agent is generally employed in an amount of 0.01-1%, preferably 0.05-0.5%, based on the weight of the vinyl acetate introduced into the polymerization system. The reducing agent is ordinarily added in an aqueous solution in the necessary equivalent amount.
In genera1, suitable vinyl acetate-ethylene copolymer emulsions can be prepared by the copolymerization of the monomers in the presence of the polyvinyl alcohol-surfactant stabilizing system in an aqueous medlum under pressures up to about 100 atm and in the presence of a redox system which is added incrementally, the aqueous system being maintained by a suitable buffering agent at a pH of about 2-6. The process first involves the homogenization in which the vinyl acetate suspended in water is thoroughly agitated in the presence of ethylene under the working pressure to effect solution of the ethylene in the vinyl acetate while the reaction medium is gradually heated to polymerization temperature.
The homogenization period is followed by a polymerization period during which the redo~ system is added incrementally The reaction temperature can be controlled by the rate of redox addition and by the rate of heat dissipation. Generally, lt is advantageous to maintain a mean temperature of about 55C during the polymerization of the monomers and to avoid temperatures much in excess of 80~. While temperatures as low as zero degrees can be used, economically the lower temperature limit is about 30C.
The reaction time will depend upon the variables such as the temperature, the free radical forming source and the desired extent of polymerization. It is generally desirable to continue with the reaction until less than 0.5% of the vinyl acetate remains unreacted. ~hile the reaction time of the polymerization process will vary as mentloned above the use of the stabillzing system according to the invention not only provides a high solids vinyl acetate-ethylene copolymer emulsion but also provides the emulsion in a surprisingly shorter reaction time, i.e. the polymerization reactor cycle time is significantly decreased.

g In carrying out the polymerization, an amount of the vlnyl acetate is initially charged to the polymerization vessel and saturated with ethylene. Most advantageously, at least about 50% of the total vinyl acetate to be polymerized is initially charged and the remainder of the vinyl acetate is added incrementally during the course of the polymerization. The charging of all the vinyl acetate initially is also contemplated with no additional incremental supply.
When reference is made to incremental addition, substantially uniform additions, both with respect to quantity and time, are contemplated. Such additions can be continuous or discontinuous and are also referred to as delay additions.
The quantity of ethylene entering into the copolymer is influenced by pressure the agitation and viscosity of the polymerization medium.
Thus, to increase the ethylene content of the copolymer, high pressures, greater agitation and a low viscosity are employed.
The process of forming the vinyl acetate-ethylene copolymer emulsion generally comprises the preparation of an aqueous solution containing the stabilizing system and, optionally, the pH buffering system. This aqueous solution and the initial or total charge of the vinyl acetate are added to the polymerization vessel and ethylene pressure is applied to the desired value. The pressurized ethylene source can be shut off from the reactor so that the ethylene pressure decays as it is polymerized or it can be kept open to maintain the ethylene pressure throughout the reactton, i.e. make-up ethylene. As previously mentioned, the mixture was thoroughly agitated to dissolve ethylene in the vinyl acetate and in 2s the water phase. Conveniently, the charge is brought to polymerization temperature during this agitation period. The polymerizatlon is then tnitiated by tntroducing initial amounts of the oxidant, the reductant having been added with the initial charge. After polymerization has started, the oxidant and reductant are incrementally added as required to continue polymerization. Any third copolymerizable monomer and the remaining vinyl acetate, if any, may be added as separate delays.

As mentioned, the reaction is generally continued until the residual vinyl acetate content is below about 0.5%. The completed reaction product is then allowed to cool to about room temperature while sealed from the atmosphere. The pH is then suitable adjusted to a value in the range of 4.5 to 7, 4.5 to 5, to insure maximum stability.
A preferred method for producing the vinyl acetate-ethylene copolymer emulsions is a cold initiation process which comprises first forming an aqueous emulsion vinyl acetate and the stabilizing system in the reactor. The reactor is then pressurized with ethylene to an ethylene-equilibrium pressure of about 200-500 psig. The resulting reaction mixture is adjusted to a temperature from about 10-30C.
Polymerization is initiated by the addition of a free radical source at a rate such that the reaction mixture is brought to a temperature of 45-85C, preferably 55-65C, within a period of one hour or less, preferably 30 minutes. The polymerization is continued at this higher temperature range until the vinyl acetate content is below about 0,5 wt%.
Vinyl acetate-ethylene copolymer emulsions can be directly produced having a solids content of about 65-70% and a viscosity of less than about 3500 cps, preferably less than about 2500 cps and most desirably less than about 1500 cps, at 65% solids and at 60 rpm and 25~. It is not necessary to employ seed emulsion polymerization techniques to obtain the emulsions of the invention. ~eed emulsion polymerization may be detrimental to the properties of the adhesive emuls~on product.
Historically, in the preparation of polyvinyl alcohol-stabilized 2s vinyl acetate-ethylene copolymer emulsions 5 wt% polyvinyl alcohol, based on vinyl acetate monomer, was used. In addition, blends of low and medium molecular weight polyvinyl alcohols were used at such levels. In an attempt to increase the solids content of the emulsions in preliminary work leading to the present invention, the amount of polyvinyl alcohol was reduced to the 2.5-4 wt% range while using solely a low molecular weight polyvinyl alcohol, namely VINOLo 205 polyvinyl alcohol having a degree of polymerization of about 550 and a viscosity of 4-6 cps a 4%
aqueous solution. Such change in the stabilizing system raised product solids from the historical 50-55 wtX level to about 60X. Measurement of performance parameters compared to a typical prior art emulsion revealed increases in PVC adhesion and slower setting speed, while most of the remaining measured properties were unchanged (see Table 2). While viscos~ty reduction was obtained by polyvinyl alcohol reduction, the products suffered from poor storage stability.
Attempts to push the solids content to 65% at the 4% polyvinyl alcohol level proved difficult. Processing cycles had to be extended and final viscosities remained high, generally above 3000 cps. Even at the 3% polyvinyl alcohol level product solids did not respond to water removal, that is to say solids did not rise to calculated levels and processing viscosities were high. Generally, when sufficient water was removed to approach 65% solids, product viscosities were too high to be measured. The data in Table 1 demonstrates this.

RUN % SOLIDS TARGET % PVOH X SOLID ACHIEVED VISCOSITY 60 rpm 1 60 4 61.2 4,460 2 65 4 64.8 off-scale 3 60 3 61.8 3,100 4 65 3 62.7 2,870 Thus lowering the polyvinyl alcohol levels 40% below the historical level of 5X based on vinyl acetate monomer and using 100% of low molecular weight stabilizer did not produce satisfactory products at 65%
solidS-To achieve the solids target of 65%, polyvinyl alcohol levels had to be reduced below 3~ and the molecular weight of the polyv~nyl alcohol utllized was also reduced. Emulsions were prepared using lOOX of a low molecular weight polymer having a degree of polymerizat~on about 235 (VINOL~ 203 polyvinyl alcohol) or blends of VINOLo 203 polyvinyl alcohol with VINOL3 205 polyvinyl alcohol. To maintain a minlmum polyvinyl alcohol level of 3X a 60/40 blend of V-203/V-205 polyvinyl alcohols was trialed. Product viscosities generally fell into the 2000 cps range after ad~usting solids to 62.5~. As can be seen ~n Table 2 _ 12 -performance testing of these products showed some improvement in PVC
adhesion but setting speeds were only marginally improved compared to Run 6 using solely Vinol 205 polyvinyl alcohol. Also e~ulsion shelf stability was observed to be poor. After several weeks all three of the products listed in Table 2 show signs of severe sludging on storage.

5 Emulsion A is a prior art vinyl acetate-ethylene copolymer emulsion.

Process Type: Batch Batch 50% Delay 25% Delay*
% PVOH 5.0 3.0 4.0 3.0 % PVOH Grades V-205l V-203/ V-205 V-203/
lS V-523 V-205 V-205 % Solids 55.8 62.4 60.2 62.6 Viscoslty 60 rpm 1,440 1,560 3,940 1,840 Index 2.0 1.3 1.9 1.4 PVC/C Peel 2.9 4.5 S.O ~.1 ClothlCloth Peel Dry 15.5 10.8 13.4 9.6 Wet 1.4 3.4 1.6 3.1 Speed-of-Set, Sec. 9-12 18-21 21-24 18-21 Creep Rate, mmlmin. 0.012 0.039 0.004 0.006 Thickening Ratio S.l 18.3 13.0 20.0 * Cold Initiation -The following is a general procedure for preparlng the vinyl acetate-ethylene copolymer emulslons of the inventlon.
The components of the lnltlal reactor charge and the varlous delay feeds were as follows:
s INITIAL REACTOR CHARGE
1) *Vinol 203a, 10% aqueous soln. 333 gms 2) *Vinol 205a, 10% aqueous soln. 222 gms 3) ~ater (deionized) 437 gms 4) Ferrous ammonlum sulfate 1% aqueous soln.5 mls lo 5) Zlnc formaldehyde sulfoxylate 10% aqueous soln. 10 mls 6) Igepal C0-887b surfactant 52.8 gms 7) Vinyl acetate 1387.5 gms 8) Acetlc acld 3.2 gms 9) Ethylene - Quantity to equillbrate reactor to 550 psi at 25C

~ELAY FEEDS
1) Hydrogen peroxlde 0.6% aqueous soln. 177 mls 2) Hydrogen peroxlde 7.0~. aqueous soln. 58 mls 3) Zlnc formaldehyde sulfoxylate 10% aqueous soln. 48 mls 4) Vlnyl acetate 462.5 mls a Polyvlnyl alcohols marketed by Alr Products and Chemicals Inc. See Table 4.
b Nonylphenoxy poly(ethyleneoxy)ethanol marketed by GAF Corp. 70% aqueous solution of Igepal 2s C0-880 surfactant.

The pH of comblned polyvlnyl alcohol solutlons and the delonlzed water were adjusted to 4 wlth the acetlc acld. Next the surfactant was fully dlssolved ln the pH adjusted polyv~nyl alcohol solutlon to whlch the ferrous ammonlum sulfate solutlon was then added.
A one gallon reactor was fllled wlth the water purged wlth nltrogen and the polyvinyl alcohol solutlon was then added. Wlth the solutlon belng agltated at 200 rpm the vlnyl acetate monomer lnltlal .....
. ~ *trade mark charge was added. The reactor was purged twice with nitrogen (30 psi) followed by one ethylene purge ~30 psi) at 25C. The agitator speed was increased to 900 rpm and the reactor was pressurized to 550 psi with ethylene tsubsurface). The reactor temperature and the ethylene pressure were allowed to equilibrate at 25C and 550 psi, respectively. The ethylene supply was shut off to the reactor.
The 10% aqueous zinc forma1dehyde sulfoxylate was added to the reactor. The reaction was initiated using the 0~6Z aqueous hydrogen peroxide solution at a rate of 0.3 ml/min. After the reactor temperature increased 1C (initiation), the vinyl acetate monomer delay was started at 3-3 ml/min. Once the initial temperature rise started to level off, the reaction temperature was ramped from 25C to 55C after one hour by slowly increasing the rate of addition of the 0.6% hydrogen peroxide solution to achieve 0.8 ml/min addition rate at the one hour mark. The ethylene make-up pressure was then set to 350 psi, the 10% zinc formaldehyde lS sulfoxylate delay addition was commenced at 0.4 ml/min and the 0.6%
hydrogen peroxide solution was automatically controlled to provide a set point 20C ~T (T reaction-T jacket). After 3 hours the agitation was increased to lOOO rpm, the vinyl acetate monomer and zinc formaldehyde sulfoxylate additions were stopped.
When the vinyl acetate free monomer level was less than about 3%, the 0.6% hydrogen peroxide delay was stopped and the 7% hydrogen peroxide delay was begun increasing from 0.5 to l ml/min over a period of 5-lO minutes.
The ethylene make-up was also stopped at this time. ~hen the 7Z hydrogen peroxide delay addition was complete, the free monomer content was measured and when less than 0.7% the reaction medium was cooled to 30C and adjusted to pH 5 with 14~ ammonium hydroxide solution. The reaction mixture was then transferred to a degasser to vent off any excess ethylene pressure.
Colloid 585 was then added to the degassing vessel followed by the following materlals dissolved in deionized water (259):
t-butyl hydroperoxide 2.59 sodium acetate 3.29 sodium citrate 1.69 The above was added at a rate of l ml/min while the contents were agitated in the degasser at 200 rpm and then filtered.

_ 15 -The emulsion product (Run 8) had the following properties in comparison to another prior art vinyl acetate-ethylene copolymer l-mulsion A:

PRODUCT PROPERTIES
A. Colloidal Properties Run 8 Emulsion A
Solid, % 64.4% 55.2 Viscosity 12 rpm 2300 20 rpm 1630 , 60 rpm 1160 2150 Surface Tension, dynes/cm2 44.7 50+
Particle Size(l) DW, microns 0.86 DN, microns 0.39 Polydispersity 2.23 (1) method of measurement - disc centrifuge B. Copolymer Properties Tg, C -7.5 Toluene Insolubles, 7~ 43.4 C. Adhesive Performance Values PVC/Cloth Peel, lbs 3.6 Creep Resistance, mm/min. 0.150 Speed of set, sec 3-6 9-12 Cloth/Cloth, lbs Dry 11.5 ~et 3-4 Thickening Ratio 3.6 6.1 The use of a surfactant in combination with a low molecular weight polyvinyl alcohol as a stabilizing system during the polymerization of vinyl acetate with ethylene affords the following advantages compared to the prior art vinyl acetate-ethylene copolymer emulsion ( A ) prepared in the presence of a stabilizing system compris~ng solely a blend of Vinolo 205 and Vinol~ 523 polyvinyl alcohols:
Increased polymer solids at viscosities comparable to lower solids products, Increased polymer solids yielding lower plasticizer thickening ratio, and Increased polymer solids and lower product surface tensions.

This example demonstrates that the addition of a nonionic surfactant (Igepal C0-880, 2% based on vinyl acetate monomer) to the polyvinyl alcohol stabilizing system in the preparation of a vinyl acetate-ethylene copolymer emulsion recipe affords a higher solids loading wlth no accompanying viscosity or reaction time increases and represents an approximate 18% increase in vinyl acetate monomer conversion/reactor power. The preparation procedure was similar to that of Example 1 except that all the vinyl acetate monomer was batched into the reactor prior to initiation. All runs contained 4.87% total stabilizer. Runs containing no surfactant were stabilized with 4.87% polyvinyl alcohol (65/35 of Vinol~ 205 PVOH/Vinol0 523 PVOH). Co-stabilized runs contained 2.87%
polyvinyl alcohol (65/35 of Vinol0 205 PVOH/Vinol~ 523 PVOH) and 2%
Igepal C0-880 surfactant.

Emulsion A Run 9 Run 10 Run 11 55X Sollds 60% Solldsl60% Solidsl 62% Solids,2 No Surf. No Surf. 2% Surf. 2% Surf.

Solids, % 55 C 60 62 Viscosity, cps 820 A 800 1900 Rxn Time, hrs. 3.1 U 2.4 2.9 Avg. VAM Conv., gms/hr. 550 AT 600 650 Speed of Set, sec. 9-12 E 9 g 1 Target was 60% sollds.
2 Target was 65% solids.

It can be seen from Tab1e 3 that addition of a surfactant to a polyvinyl alcohol stabilizing system permited the preparatlon of a higher solids content emulsion in a shorter reaction time. It should be noted that a solids level of 65% was not attained using the low molecular weight Vinol~ 205 PVOH in combination with a substantial amount of medium molecular weight VinolO 523 PVOH.

This example demonstrates that partially and fully hydrolyzed low molecular weight polyvinyl alcohols afford high solids (65X) emulsions with no adverse processing effects. Runs 12-32 were prepared following the delay process of Example 1. With the exception of the Emulsion A
control and Run 12, all the runs contain 2% Igepal C0-880, based on vinyl acetate monomer. The final emulsions of Runs 12-32 were roughly 65%
solids. Emulsion A was 55% solids.

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The results of Table 4 indicate that the optimum total polyvinyl alcohol level is between 2 and 3%, based on vinyl acetate monomer. Even at these levels, the use of greater than 2% of the low molecular weight Vinol~ 107 and Vinol~ 205 polyvinyl alcohols generally resulted in slightly higher viscosities and slower setting speeds while the addition of as little as 0.6% of the medium molecular weight VinolO 523 polyvinyl alcohol yielded extremely high viscosities. Accordingly, the preferred low molecular weight polyvinyl alcohol for use in the invention is VinolO 203 polyvinyl alcohol which has an even lower molecular weight than that of Vinol~ 107 or VinolO 205 polyvinyl alcohols.
Vinol 203 polyvinyl alcohol afforded superior water resistance.

In this example various anionic and nonionic surfactants were tested as the surfactant component of the stabilizing system of the invention.
With the exception of the Emulsion A control, all the runs were prepared in the presence of 3% polyvinyl alcohol (60/40 of Vinol~ 203 PVOH/Vinol~ 205 PVOH) in addition to the specified surfactant. Final emulsions were roughly 65% (Emulsion A was 55%). The delay emulsion procedure according to Example 1 was followed. See Table 5.

D ~ 1 _ _ N _ N N _ N N
o ~1 0 u~ tr~ N 7 r7 t~7 d ~ t~7 _ u7 0 l~ ~ t 7N O 1-1 N N N Nr7 N N N <`I

~ u7 _t~ ~_ ~7 N _ N N N

1~ C~7 V N _ t! N N N N ~ N
V7 tY

0 N ~ 1 U7 .17 t~ C~ U7 tl~ U7 N O ~L7 r7 v7 N CC) U7 .X ~ r7 r~r7 ~ u7 1_ d r7 r7 ~ r7 r7 r7 r7 r7 u7 r7 r7 ~L7 7 r7 O Vl ~~ N ~r ~ c O C O C t~ V~ 0 ~7 U7 C~7 c ~L7 U7 d' U7 U7 1 ~ ~ C r7 r~ C~ CN g'7 ~ 0 1'/ - ~

~ V7 U7 U7 U7 C ~3 r7 N O N N r7 N O t'- N N r7 N O t.7 ~ o t~l t~l E_ 3~o ~ -9''=' '= -'2 r7 7 ~o t7 ~7 r7 r07 t~7 ~ ~ ~r ~ ~

~ ~ .

1 3~2064 In general, the nonionic surfactants provided 65~ solids content wlth no adverse processing effects, i.e. less than 2000 cps viscosities, 3-4 hour reaction times and increased vinyl acetate monomer conversion efficiency, and maintained or improved the speed of set compared to Emulsion A (55% solids). Similar speed of set results could be obtained for Run 38 if the surfactant level were raised another 1 or 2%. Speed of set improvements are observed for the nonionic polyoxyalkylene derivatives of alkylphenols and propylene glycol containing 30-40 ethylene oxide units.
From the examples lt can be seen that the inventor provides high sollds vinyl acetate-ethylene copolymer emulsions possessing a speed of set of about 12 seconds or less, preferably about 9 seconds or less, and most deslrably about 6 seconds or less. The speed of set values are determined by the standard test in TAPPI s Tests of Adhesives. Monograph 35, page 103 using 50% bond and kraft paper.
Both nonionlc and anionic surfactants, when mixed with low molecular weight partially hydrolyzed (87-89%) polyvlnyl alcohol or mixtures of low molecular weight partially and fully hydrolyzed (96-99%) polyvlnyl alcohols have marked effect on processing viscosity. This effect in turn is reflected in reduced polymerization cycle time due to polymerization rate enhancement and heat transfer.

STATEMENT OF INDUSTRIAL APPLICATION
The invention provides vinyl acetate-ethylene copolymer emulsions of high solids content and relatively low viscosities for use as adhesive compositions in maklng laminates, partlcularly cloth to cloth laminates and vlnyls to celluloslc substrates such as wood chlp partlcle board.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a vinyl acetate-ethylene copolymer emulsion prepared by the aqueous emulsion copolymerization of vinyl acetate and ethylene monomers in the presence of a polyvinyl alcohol and a surfactant, the improvement which comprises a stable vinyl acetate-ethylene copolymer emulsion, the copolymer containing 60-95 wt.% vinyl acetate and 5-40 wt% ethylene, the emulsion being about 65-70% solids, having a viscosity of less than about 3500 cps at 65% solids and prepared by aqueous emulsion copolymeriza-tion in the presence of a stabilizing system consisting essen-tially of 2-4 wt% based on vinyl acetate monomer, of low molecu-lar weight 75-99+ mole% hydrolyzed polyvinyl alcohol which has a 100-600 degree of polymerization and 1-4 wt%, based on vinyl acetate monomer, of a nonionic surfactant which is a polyethyoxy-lated derivative of about 30-40 ethylene oxide units of (a) an alkyl phenol, the alkyl group containing 7-18 carbon atoms, or (b) a hydrophobic base formed by condensing propylene oxide with propylene glycol.

2. The vinyl acetate-ethylene copolymer emulsion of claim 1, in which the viscosity is less than 2500 cps at 65% solids.

3. The vinyl-acetate-ethylene copolymer emulsion of claim 1, in which the viscosity is less than about 1500 cps at 65%
solids.

4. The vinyl acetate-ethylene copolymer emulsion of claim 1, in which the surfactant is an alkylphenoxy poly(ethyleneoxy) ethanol in which the alkyl group is octyl or nonyl.

5. The vinyl acetate-ethylene copolymer emulsion of claim 1, in which the surfactant is a nonylphenoxy poly(ethyleneoxy) ethanol.

6. The vinyl acetate-ethylene copolymer emulsion of claim 5, in which the surfactant contains about 30 ethylene oxide units.

7. The vinyl acetate-ethylene copolymer emulsion of claim 1, in which the low molecular weight polyvinyl alcohol is about 3 wt%, based on vinyl acetate.

8. The vinyl acetate-ethylene copolymer emulsion of claim 7, in which the nonionic surfactant is 2-3 wt%, based on vinyl acetate.

9. The vinyl acetate-ethylene copolymer emulsion of claim 8, in which the surfactant is nonylphenoxy poly(ethyleneoxy) ethanol.

10. The vinyl acetate-ethylene copolymer emulsion of claim 2, in which the polyvinyl alcohol is a mixture of two polyvinyl alcohols having a 100-600 degree of polymerization, one of which has a degree of polymerization in the range of 185-255.

11. The vinyl acetate-ethylene copolymer emulsion of claim 10, in which the surfactant is a nonylphenoxy poly(ethyleneoxy) ethanol.

12. In a vinyl acetate-ethylene copolymer emulsion prepared by the aqueous emulsion copolymerization of vinyl acetate and ethylene monomers in the presence of a polyvinyl alcohol and a surfactant, the improvement which comprises a stable vinyl acetate-ethylene copolymer emulsion of about 65-70% solids having a viscosity of less than about 2500 cps at 65% solids and pre-pared by aqueous emulsion copolymerization in the presence of a stabilizing system consisting essentially of 2-4 wt%, based on vinyl acetate monomer, low molecular weight 75-99+ mole% hydro-lyzed polyvinyl alcohol which has a 100-600 degree of polymeriza-tion and 1-4 wt%, based on vinyl acetate monomer, of a nonionic octyl- or nonylphenoxy poly(ethyleneoxy) ethanol surfactant having about 30-40 ethylene oxide units.

13. The vinyl acetate-ethylene copolymer emulsion of claim 12, in which the polyvinyl alcohol comprises a mixture of polyvinyl alcohols which are 85-90 mole% hydrolyzed and have a 100-600 degree of polymerization, one of the polyvinyl alcohols having a degree of polymerization in the range of 185-255.

14. The vinyl acetate-ethylene copolymer emulsion of claim 12, in which the polyvinyl alcohol has a degree of polymerization in the range of 185-255.

15. The vinyl acetate-ethylene copolymer emulsion of claim 13, in which the viscosity is less than about 1500 cps at 65%
solids.

16. The vinyl acetate-ethylene copolymer emulsion of claim 13, in which the polyvinyl alcohol component is about 3 wt% and the nonionic surfactant component is about 2-3 wt%.

17. The vinyl acetate-ethylene copolymer emulsion of claim 16, in which the viscosity is less than about 1500 cps and the surfactant is nonylphenoxy poly(ethyleneoxy) ethanol.

18. The vinyl acetate-ethylene copolymer emulsion of claim 17, in which the surfactant contains about 30 ethylene oxide units.

19. A stable vinyl acetate-ethylene copolymer emulsion comprising a stable aqueous colloidal dispersion of a copolymer containing 75-80 wt% vinyl acetate and 20-25 wt% ethylene pre-pared by the emulsion copolymerization of vinyl acetate and ethylene monomers in the presence of a stabilizing system consisting essentially of 2-4 wt%, based on a vinyl acetate monomer, low molecular weight 75-99+ mole% hydrolyzed polyvinyl alcohol which has a 100-600 degree of polymerization and 1-4 wt%, based on vinyl acetate monomer, of a nonylphenoxy poly(ethylene-oxy) ethanol having about 30-40 ethylene oxide units, the copoly-mer emulsion being about 65-70% solids and having a viscosity of less than about 1500 cps at 65% solids.

20. The vinyl acetate-ethylene copolymer emulsion of claim 19, in which the polyvinyl alcohol comprises a mixture of polyvinyl alcohols which are 87-89 mole% hydrolyzed and have a 100-600 degree of polymerization, one of the polyvinyl alcohols having a degree of polymerization in the range of 185-255.

21. The vinyl acetate-ethylene copolymer emulsion of claim 20, in which the polyvinyl alcohol has a degree of polymerization in the range of 185-255.

22. The vinyl acetate-ethylene copolymer emulsion of claim 12, in which the polyvinyl alcohol comprises a mixture of a fully hydrolyzed (96-99 mole%) polyvinyl alcohol and a partially hydrolyzed (87-89 mole%) polyvinyl alcohol, the polyvinyl alcohols having a 100-600 degree of polymerization, one of which has a degree of polymerization in the range of 185-255.

23. The vinyl acetate-ethylene copolymer emulsion of claim 22, in which the partially hydrolyzed polyvinyl alcohol has a degree of polymerization in the range of 185-255.

24. The vinyl acetate-ethylene copolymer emulsion of claim 22, in which the emulsion viscosity is less than about 1500 cps and the surfactant is nonylphenoxy poly(ethyleneoxy) ethanol.

25. The vinyl acetate-ethylene copolymer emulsion of Claim 24 in which the surfactant contains about 30 ethylene oxide units.

26. The vinyl acetate-ethylene copolymer emulsion of Claim 23 in which the viscosity is less than about 1500 cps and the surfactant is a nonylphenoxy poly(ethyleneoxy) ethanol.

27. The vinyl acetate-ethylene copolymer emulsion of Claim 26 in which the surfactant contains about 30 ethylene oxide units.