Note: Descriptions are shown in the official language in which they were submitted.
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
1 322064
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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
1 322064
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
1 322064
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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
1 322064
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
1 322064
-- 7 --
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,
1 322064
-- 8 --
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.
1 322064
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.
1 322064
-- 10 --
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
1 322064
11 -
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.
TABLE 1
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
1 322064
_ 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.
TABLE 2
RUN A 5 6 7
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
-
1 322064
- 13 -
EXAMPLE 1
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
1 322064
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.
1 322064
- 16 -
EXAMPLE 2
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.
TABLE 3
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.
1 322064
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.
EXAMPLE 3
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.
1 322064
--18--
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1 322064
- 19 -
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.
EXAMPLE 4
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.
1 322064
--20--
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
- 21 -
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.
