Vinyl acetate/ethylene copolymer emulsions useful as carpet adhesives

A vinyl acetate-ethylene copolymer emulsion comprising an aqueous colloidal dispersion of a copolymer containing 65 to 90 wt % vinyl acetate and 10 to 35 wt % ethylene prepared by the emulsion polymerization of the monomers in the presence of a stabilizing system consisting essentially of an 86 to 90 mole % partially hydrolyzed polyvinyl alcohol, a 98 to 99+ mole % fully hydrolyzed polyvinyl alcohol, in a partially hydrolyzed polyvinyl alcohol:fully hydrolyzed polyvinyl alcohol weight ratio from 3:1 to 1:3, and a nonionic polyalkoxylated surfactant. Also disclosed is a carpet backing adhesive composition comprising such a vinyl acetate-ethylene copolymer emulsion, about 0.1 to 3 parts by weight dispersant, about 0.1 to 10 parts by weight thickening agent and between 300 and about 1000 parts by weight filler, all of the components being per 100 parts of the copolymer.

TECHNICAL FIELD 
The invention relates to vinyl acetate-ethylene copolymer emulsions and, 
more particularly, it relates to such copolymer emulsions as a component 
of adhesives for use with rugs and carpets. 
BACKGROUND OF THE INVENTION 
A vinyl acetate-ethylene copolymer emulsion stabilized with polyvinyl 
alcohol has been used by the carpet industry as an adhesive for tufted 
carpet manufacture since about 1970. Such copolymer had a Tg in the range 
of -15.degree. to -18.degree. C. and contained 5% polyvinyl alcohol based 
on vinyl acetate. The polyvinyl alcohol stabilizer system comprised a 
mixture of low viscosity partially hydrolyzed polyvinyl alcohol and medium 
viscosity partially hydrolyzed polyvinyl alcohol. The emulsion was about 
52% solids and had a Brookfield viscosity of 500 cps. The emulsion 
demonstrated adequate performance in the carpet backing application 
although the water resistance was less than desired. 
With the advent of newer, modern methods of carpet backing manufacture, 
including higher calcium carbonate loadings and frothing the adhesive 
compound, the vinyl acetate-ethylene copolymer emulsion was becoming an 
obsolete product. The emulsion could not be compounded to the higher 
calcium carbonate loadings and was not compatible with all grades of 
calcium carbonate nor with styrene-butadiene emulsions. 
U.S. Pat. No. 4,239,563 discloses such vinyl acetate-ethylene copolymer 
emulsions having a Tg between about -35.degree. C. and about -10.degree. 
C. as laminating adhesives for rugs and carpets. The amount of vinyl 
acetate in the copolymer of the emulsion is between about 20 and 70 parts 
by weight and the corresponding amount of ethylene in the copolymer is 
between 30 and about 80 parts by weight. The copolymer emulsions can be 
prepared with or without surfactants. When polyvinyl alcohol is used as a 
protective colloid during the polymerization, it is not necessary to add a 
surfactant. If such a protective colloid is not employed, a surfactant 
such as a nonionic or anionic surfactant can be employed. 
Prior art regarding vinyl acetate-ethylene copolymer emulsions prepared in 
the presence of polyvinyl alcohol includes the following: 
U.S. Pat. No. 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 the polyvinyl alcohol mixture in 
combination with a nonionic surfactant. In U.S. Pat. Nos. 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 acid comonomer or an unsaturated C.sub.3 -C.sub.6 acid, 
respectively. Similarly, these patents show emulsion compositions prepared 
using a seed emulsion, the polyvinyl alcohol mixture and a nonionic 
surfactant. 
U.S. Pat. No. 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 copolymerization process 
utilizing a particular combination of nonionic emulsifier, anionic 
emulsifier and protective colloid. 
U.S. Pat. No. 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. Pat. No. 3,827,996 discloses aqueous dispersions of vinyl ester 
polymers containing as a protective colloid partially hydrolyzed polyvinyl 
alcohol having an average vlnyl acetate content of 5 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 hydrolyzed and a fully hydrolyzed polyvinyl alcohol in 
combination with a nonionic surfactant in the preparation of vinyl 
acetate-ethylene copolymer emulsions. 
U.S. Pat. No. 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. Pat. Nos. 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. Pat. No. 4,521,561 discloses the preparation of vinyl acetate-ethylene 
copolymer emulsions exhibiting both partially- and fully-hydrolyzed 
polyvinyl alcohol compatibility prepared in the presence of a polyvinyl 
alcohol stabilizing system having an 8 to 10 mole % residual vinyl acetate 
content. 
SUMMARY OF THE INVENTION 
The present invention provides an aqueous dispersion of vinyl 
acetate-ethylene copolymers of 40 to 70 wt % solids which are prepared in 
the presence of a low level of both partially and fully hydrolyzed 
polyvinyl alcohols and, in addition, a low level of nonionic surfactant. 
Such vinyl acetate-ethylene copolymer emulsions are very useful as a 
carpet backing adhesive. 
The aqueous emulsion, or colloidal dispersion, comprises a vinyl 
acetate-ethylene copolymer dispersed in an aqueous medium which is 
prepared by the emulsion copolymerization of vinyl acetate and ethylene 
monomers in the presence of about 4 to 8 wt %, based on vinyl acetate 
monomer, of a stabilizing system consisting essentially of a partially 
hydrolyzed polyvinyl alcohol, a fully hydrolyzed polyvinyl alcohol and a 
nonionic polyalkoxylated surfactant. The preferred polyvinyl alcohol 
component of the stabilizing system consists essentially of a fully (at 
least 98 mol %) hydrolyzed polyvinyl alcohol and a partially (86 to 90 mol 
%) hydrolyzed polyvinyl alcohol in a weight ratio of fully hydrolyzed 
polyvinyl alcohol to partially hydrolyze polyvinyl alcohol ranging from 
3:1 to 1:3. The nonionic polyalkoxylated surfactant component of the 
stabilizing system may comprise an oxyalkylated product of an alkyl 
phenol, an aliphatic alcohol, an aliphatic carboxylic acid, or an 
acetylenic glycol or block copolymers of ethylene oxide and propylene 
oxide. 
Another embodiment of the invention is an adhesive polymeric composition 
for adhering fibers or a pile material to a carpet or rug backing 
substrate comprising a vinyl acetate-ethylene copolymer emulsion of the 
invention, about 0.1 to 3 parts by weight dispersant, about 0.1 to 10 
parts by weight thickening agent, and between 300 and about 1000 parts by 
weight filler, all parts by weight are per hundred parts of the copolymer. 
The vinyl acetate-ethylene copolymer emulsions most advantageously can be 
compounded with filler to provide an adhesive composition of high coatings 
solids of about 80% up to about 85% or more. 
Additionally, the emulsions are compatible with most commercially available 
grades of calcium carbonate filler and are also compatible with most 
styrene-butadiene emulsions. 
The emulsions which can be prepared at high emulsion solids of 65 to 70 wt 
% demonstrate good coating viscosity stability and improved water 
resistant properties. 
The adhesive compositions containing the emulsions possess better strength 
(tuft lock and T-peel) at comparable hand compared to the prior art vinyl 
acetate-ethylene copolymer-based rug backing adhesives. 
DETAILED DESCRIPTION OF THE INVENTION 
The copolymers use in the present invention comprise 65 to 90 wt % vinyl 
acetate and 10 to 35 wt % ethylene, on a monomer basis, to provide a Tg 
ranging from about -20.degree. to 10.degree. C., preferably 85 to 90 wt % 
vinyl acetate and 10 to 15 wt % ethylene and may optionally include minor 
amounts, i.e. to about 5 wt %, of one or more other monomers which are 
copolymerizable with vinyl acetate and ethylene. Exemplary of a monomer 
which can be added is maleic acid in an amount to about 1 wt %. Preferably 
the emulsions are greater than about 60% solids and most desirably about 
65% solids or more. 
Contemplated as the functional, or operative, equivalents of vinyl acetate 
in the copolymer emulsions are vinyl esters of C.sub.1 -C.sub.18 alkanoic 
acids, such as vinyl formate, vinyl propionate, vinyl laurate and the 
like. 
The amount of the stabilizing system used in the polymerization reaction is 
about 4 to 8% based on the weight of vinyl acetate monomer. The 
stabilizing system preferably is added to the polymerization reaction 
medium all at once prior to initiation, or may be added incrementally 
during the course of the polymerization, provided a sufficient amount is 
present initially to provide emulsion stability. 
The stabilizing system which is used in the polymerization recipe to 
prepare the carpet adhesive emulsion consists essentially of a mixture of 
a 98 to 99+ mole % hydrolyzed (fully) polyvlnyl alcohol and an 86 to 90 
mole % hydrolyzed (partially) polyvinyl alcohol, preferably 86 to 88 mole 
% hydrolyzed, and a nonionic polyalkoxylated surfactant. The fully and 
partially hydrolyzed polyvinyl alcohols should have a degree of 
polymerization ranging from 100 to 600, although small amounts of 
polyvinyl alcohol having a higher degree of polymerization can also be 
present. 
The amount of the polyvinyl alcohol component of the stabilizing system 
used in the polymerization reaction is about 3 to 5 wt % based on vinyl 
acetate monomer. The relative amount of each type of polyvinyl alcohol 
that is used is in the range of 3:1 to 1:3 wt ratio of fully hydrolyzed 
polyvinyl alcohol to partially hydrolyzed polyvinyl alcohol, desirably at 
a 1:1 wt ratio. 
In addition to the polyvinyl alcohol component the stabilizing system 
according to the invention also contains a nonionic polyoxyalkylene 
condensate surfactant (polyalkoxylated surfactant) in an amount ranging 
from 1 to 3 wt % based on vinyl acetate. 
The polyalkoxylated surfactants have repeating alkylene oxide units 
represented by (alkylene oxide).sub.n. The preferred polyethoxylated and 
polypropoxylated surfactants have at least a portion of their structure 
represented by the following general formula: 
##STR1## 
wherein R is methyl or hydrogen and n represents the number of moles of 
alkylene oxide. Polyethoxylated substances are preferred. 
Among the nonionic surfactants which have been found to provide good 
results are included the Igepal surfactants marketed by GAF Corp., and the 
Pluronic surfactants marketed by BASF Wyandotte. The Igepal surfactants 
are members of a homologous series of alkylphenoxy poly(ethyleneoxy) 
ethanols which can be represented by the general formula: 
EQU R.sup.1 --Ph--O--CH.sub.2 CH.sub.2 O).sub.n-1 CH.sub.2 CH.sub.2 OH 
wherein R.sup.1 represents an alkyl radical, Ph represents a phenylene 
radical and n represents the number of moles of ethylene oxide employed, 
among which are alkylphenoxy poly(ethyleneoxy) ethanols having alkyl 
groups containing from about 7 to about 18 carbon atoms, inclusive, and 
having from about 4 to about 100 ethyleneoxy units, such as the 
heptylphenoxy poly(ethyleneoxy) ethanols, nonylphenoxy poly(ethyleneoxy) 
ethanols and dodecylphenoxy poly(ethyleneoxy) ethanols; alkyl 
poly(ethyleneoxy) ethanols; and alkyl poly(propyleneoxy) ethanols. The 
Pluronic surfactants are condensates of ethylene oxide with a hydrophobic 
base formed by condensing propylene oxide with propylene glycol, and the 
like. 
Suitable nonionic surfactants would also include the Tween surfactants 
marketed by Atlas Chemical which are polyoxyalkylene derivatives of 
hexitol (including sorbitans, sorbides, mannitans and mannides) anhydride 
partial long-chain fatty acid esters, such as 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 ethylene oxide 
derivatives of long chain fatty alcohols such as octyl, dodecyl, lauryl or 
cetyl alcohol and ethylene oxide adducts of acetylenic glycols marketed by 
Air Products and Chemicals, Inc. under the registered trademark 
"Surfynol". 
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, i.e. a redox system, can also be used. Suitable reducing agents 
include bisulfites, sulfoxylates, or other compounds having reducing 
properties such as ascorbic acid, its enantiomer erythorbic acid and other 
reducing sugars. The oxidizing agents include hydrogen peroxide, organic 
peroxides 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, ammonium persulfate or potassium 
persulfate with sodium metabisulfite, sodium bisulfite, ferrous sulfate, 
zinc formaldehyde sulfoxylate or sodium formaldehyde sulfoxylate; and the 
much preferred hydrogen peroxide and ascorbic acid or erythorbic acid 
combination which enhances water resistance and avoids the introduction of 
formaldehyde to the emulsion as results from zinc or sodium formaldehyde 
sulfoxylate. 
The oxidizing agent is generally employed in an amount of 0.01 to 1.0%, 
preferably 0.05 to 0.5% based on the weight of vinyl acetate introduced 
into the polymerization system. The reducing agent is ordinarily added in 
an aqueous solution in the necessary equivalent amount. 
The preferred method for producing the vinyl acetate-ethylene copolymer 
emulsions comprises the following "cold initiation" process: 
(a) forming an aqueous emulsion reaction mixture comprising the stabilizing 
system and the vinyl acetate monomer in a suitable pressure reactor, 
(b) pressurizing the reactor with ethylene to an ethylene-equilibrium 
pressure suitable for providing the copolymer with the desired ethylene 
content, 
(c) initiating the reaction mixture by the addition of a free radical 
source at a temperature from about 10.degree. to 40.degree. C. and 
bringing the reaction mixture to a reaction temperature of from 45.degree. 
to 85.degree. C. within a period of not more than 2 hours with the 
reaction temperature exceeding the initiation temperature by at least 
15.degree. C., and 
(d) continuing polymerization of the reaction mixture until the vinyl 
acetate content as free monomer in the reaction mixture is reduced below 
about 1 wt %. 
The reaction rate and temperature can be controlled by the rate of free 
radical source, e.g. redox system, addition and by the rate of heat 
dissipation. Generally, it is advantageous to maintain a mean temperature 
of about 55.degree. C. during the polymerization of the monomers. 
Typically the polymerization is initiated by introducing initial amounts of 
the oxidant, the reductant having been added with the initial charge. 
After polymerization has started, additional oxidant and reductant are 
incrementally added as required to continue polymerization. Any third 
copolymerizable monomer may be batched or may be added as separate delays 
with the remaining vinyl acetate, if any. 
When reference is made to incremental addition, whether of monomer or redox 
system, substantially uniform continuous or intermittent additions, both 
with respect to quantity and time are contemplated. Such additions are 
also referred to as "delay" additions. 
The reaction time will depend upon 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 monomer remains unreacted. 
More specifically, the polymerization method for preparing the vinyl 
acetate-ethylene copolymers utilizes a "cold initiation" process. The 
first step, as with most other aqueous emulsion processes, lies in the 
formation of an aqueous emulsion of vinyl acetate and other components 
used in the reaction mixture. In this regard, water is first mixed with 
the stabilizing system described above. Other components, for example, 
buffers may be added as needed to form a premix. The premix is then 
charged to the reactor and the vinyl acetate added. Optionally, the vinyl 
acetate can be added to the premix. At least 75% and preferably the entire 
amount of the vinyl acetate monomer is added prior to initiation. Then the 
oxidizing agent of the redox initiator system is added to the reactor. 
The reactor is initially pressurized with ethylene to provide a minimum 
ethylene equilibrium pressure from about 100 to 1000 psig. This pressure 
may generally be less than the operating pressure. Agitation is effected 
during pressurization and typically ethylene is introduced by subsurface 
means through spargers to ensure that ethylene is rapidly transferred to 
the vinyl acetate. 
Prior to initiation the reaction mixture is adjusted to a temperature from 
about 10.degree. to 40.degree. C., preferably about 25.degree. to 
35.degree. C. Pressurization of the reaction mixture with ethylene may be 
prior to or subsequent to this adjustment step. Typically, for commercial 
reactions, this will be from 400 to 750 psig. After the reaction mixture 
is brought to the initiation temperature, and the ethylene is present in 
the vinyl acetate monomer droplets, polymerization of the reaction mixture 
is commenced by the addition of the reducing component of the redox 
system. The low Tg, -20.degree. to 10.degree. C., copolymers can be 
prepared by adding some ethylene during the reaction or toward the end of 
the reaction. The amount of ethylene required at the end will depend upon 
how much ethylene is added in the initial charge and the free space in the 
reactor. 
On initiation, the temperature of the reaction mixture begins to rise and 
on continued addition of reducing agent the temperature will increase 
rapidly. Reducing agent addition is adjusted to reach a reaction 
temperature of about 45.degree. to 85.degree. C., typically 50.degree. to 
60.degree. C., ideally about 55.degree. C., about 2 hours, preferably 
within one hour, and most desirably within thirty minutes, and then it is 
added at a rate to maintain such temperature. The reaction temperature is 
set to be at least 15.degree. C., preferably at least 20.degree. C., above 
the initiation temperature. As a result of the temperature increase the 
ethylene pressure will increase correspondingly. 
Once the reaction temperature rises about 1.degree. C. upon initiation, the 
remaining vinyl acetate monomer, if any, and any comonomers are added in a 
delay mode. Such a delay addition is desirable in view of the difference 
in polymerization rates of many of the various monomers. So it is 
preferable to delay the addition of those monomers having a fast 
polymerization rate into the polymerization medium. 
It is not necessary to use seed emulsion polymerization techniques to 
obtain the emulsions used in the invention. Seed emulsion polymerization 
may be detrimental to the properties of the adhesive emulsion products. 
The carpet backing adhesive compositions containing the copolymer emulsions 
also generally contain thickening agents, dispersants, and fillers which 
are customarily used in the art. Where the adhesive compositions are 
frothed for application, foaming aids and foam stabilizers would be 
included in the composition. 
Conventional thickening agents such as sodium polyacrylates and 
hydroxyethyl cellulose can be employed in an amount between about 0.1 and 
10 parts per hundred parts of copolymer. A dispersant, or deflocculating 
agent, such as tetrasodium pyrophosphate or low molecular weight 
polyacrylates, can be employed in an amount of about 0.1 to 3 parts by 
weight per hundred parts of copolymer. 
In addition, conventional fillers such as hydrosilicates of alumina, 
titanium dioxide, aluminum hydroxide, preferably calcium carbonate, and 
barium sulfate can be employed in an amount between 300, preferably 400, 
and about 1000 parts by weight per hundred parts copolymer. Since the 
copolymer emulsions of the present invention can be loaded to an 
exceptionally high filler level, in excess of 400 parts by weight per 
hundred parts of copolymer, a significant economic advantage can be 
obtained using relatively large amounts of inexpensive filler in the 
copolymer emulsion adhesive compositions. 
Minor amounts of other conventional additives such as stabilizers, pigments 
and defoamers can also be included in the adhesive compositions. 
Conventional application techniques can be employed, i.e. the same 
application techniques employed for styrene-butadiene rubber adhesives. 
The adhesive compositions can be applied to the underside of the pile 
fiber primary substrate composite by means of a kiss-roller, the use of 
which is common in conventional carpet backing processes to coat or 
impregnate the jute fibers of the primary substrate and wipe off the 
excess emulsion. Other suitable methods of application can, of course, be 
used such as spreading with a roll, a doctor blade, spraying, etc. The 
amount of latex applied is normally just sufficient to obtain adequate 
adhesion of the pile fibers to the primary substrate and obtain sufficient 
bundle wrap. Excess emulsion material can be used but is wasteful and 
necessitates longer drying times by infra-red lamps or hot air ovens or a 
combination of both. Conventional coating weights on carpets can be used. 
Typically, the coating weights will vary from about 17 to 37 ounces per 
square yard. The method of applying rug backing compositions to various 
types of carpeting material can vary from company to company. Some 
companies prefer to use a rug backing composition with a working viscosity 
of 8,000 to 15,000 cps. The filler levels will also normally vary from 
company to company. 
The vinyl acetate-ethylene copolymers prepared in accordance with the 
present invention can be applied to carpets made from any of the usual 
fibers, such as nylons, acrylates, polyesters and wool, and can be used 
with all normal backing materials, including jute and polypropylene. The 
vinyl acetate-ethylene copolymer emulsions are advantageously laminating 
adhesives for indoor-outdoor carpeting made from polypropylene. 
Some of the important characteristics of laminating adhesives are 
determined by the T-peel, tuft lock and pill tests. 
T-peel is a value obtained when the secondary backing is pulled away from 
the primary backing and is determined by using a Scott tester or Instron 
tester. Adhesion of the scrim, or secondary backing, through the primary 
substrate is referred to as the "peel strength". This term is used in its 
normal sense in the carpet manufacturing industry to mean the force 
required to peel apart a strip of the two adhered components 3 inches wide 
which have been aged 24 hours. It is measured by gripping one of the 
components in each jaw of the Scott tensile tester and then moving the 
jaws apart at a rate of 3 inches per minute. A value of between 2.5 and 6 
pounds is normally obtained. Normally, the lighter the coating weight the 
lower the T-peel. 
Tuft lock is a determination of the ability of a rug backing composition to 
hold fiber to both the primary and secondary backing. Tuft lock is 
determined by using a Scott tester or Instron tester to pull a single span 
of pile yarn and measuring the force required to pull the fiber away from 
the structure. Normally, values for styrene-butadiene rubber emulsions 
will vary from 4 to 10 pounds of pull. 
Additional information with respect to the manufacture of rugs and carpets 
using backing adhesive compositions can be found in U.S. Pat. No. 
4,239,563 which disclosure is incorporated by reference.