A humidity-resistant wet-stick adhesive is comprised of a vinyl acetate-acrylic acid-2-ethyl hexyl acrylate elastomer, a methacrylic acid-ethyl acrylate copolymer, and an acrylic acid polymer system having an average molecular weight of from about 70,000 to about 90,000, and as the tackifier, at least one alkylaryl polyether alcohol.

BACKGROUND OF THE INVENTION 
Conventional pressure-sensitive adhesives are hydrophobic in nature. As 
such, they adhere poorly to wet or damp surfaces and cannot generally be 
effectively removed by water, even using automated cleaning procedures 
which employ detergents, warm water, and/or mild caustics. 
While water resistance of conventional pressure-sensitive adhesives is an 
obvious advantage to many enduse applications, there are certain 
applications where it is desired to have an adhesive adhere to a wet 
surface. For instance, in the pharmaceutical and beverage industries, it 
is frequently desirable to label bottles and other containers in-line 
immediately after washing and rinsing processes, while the containers are 
still surface-wet. In this application, conventional pressure-sensitive 
adhesives simply will not adhere satisfactorily. 
For many applications it is desirable to use pressure-sensitive adhesives 
for permanent labeling of an object to provide sufficient tamperproofness 
so that labels cannot be removed intact while the label is still needed. 
Examples include price-marking labels which cannot be transferred by a 
customer in retail outlets, and product-identification labels used on 
recyclable containers. While conventional pressure-sensitive adhesives can 
meet the tamperproofness requirements, they are very difficult to remove 
when the function of tamperproofness is no longer required. 
It would be desirable, therefore, to have a pressure-sensitive adhesive 
which is tamperproof under ordinary use conditions but which can be easily 
removed with water in a household and/or commercial cleaning process(es). 
Several attempts have been made to develop water-soluble, 
pressure-sensitive adhesives, but the adhesives heretofore known have 
suffered from deficiencies in performance, which has retarded their 
utility. 
Adhesives based on polyvinyl methyl ether were among the earliest 
water-soluble, pressure-sensitive adhesives. While they had fair adhesive 
properties and could be used for limited applications, several 
deficiencies restricted their utility. They did not, for instance, absorb 
water rapidly enough to adhere to a wet surface. In addition, they were 
insoluble in hot water, and could not be removed by commercial cleaning 
equipment. Also, their holding power under stress prohibited use on 
small-diameter cylindrical objects where the paper facestock used was 
conventional. 
Partial esters such as polyvinylmethyl ether/maleic anhydride with nonionic 
surfactants of the nonyl phenol ethylene oxide adduct type have also been 
used. These adhesives were soluble in both hot and cold water for easy 
removability, but were so extremely humidity-sensitive that they could not 
be used for application to small items or objects because of low adhesion 
at low relative humidity and ready cohesive failure at high relative 
humidity. 
Other water-soluble, pressure-sensitive adhesives have been developed which 
include compounds of polyvinyl pyrrolidone with water-soluble 
plasticizers, copolymers of acrylic acid and alkyl acrylates and others, 
but none has had the desired good pressure-sensitive adhesive properties, 
rapid adhesion to wet surface and easy removability in commercial 
equipment, and retention of the desired properties at high and low 
relative humidities. 
A need therefore exists for an adhesive which has good adhesion to both wet 
and dry surfaces, whether cold or warm, whether polar or non-polar, with 
sufficient permanence to be regarded as tamperproof when combined with 
ordinary label papers; but yet easily removed, when desired, with warm or 
cold water or with detergents and alkalis used in commercial, or even 
domestic, cleaning operations. These objectives, as well as the objective 
of providing adhesives which resist degradation or deterioration under 
conditions of high and low relative humidity, are the subject of the 
instant invention. 
SUMMARY OF THE INVENTION 
It has now been found that pressure-sensitive adhesives of the desired 
properties can be formulated from three basic components. The first 
component is a backbone-resin system formed of a normally solid, 
elastomeric polymer and a normally solid, brittle copolymer. 
The second component of the adhesive composition is a normally solid, 
non-tacky acrylic acid polymer system having an average molecular weight 
of from about 70,000 to about 90,000 and capable of controlled absorption 
of moisture from a surface without loss of pressure-sensitive adhesive 
tack and solubilization of the adhesive formulaiton. It is presently 
preferred that the acrylic acid polymer system comprise a mixture of a 
normally solid, high molecular-weight acrylic acid homopolymer having a 
molecular weight of about 100,000 in combination with a normally solid, 
low molecular-weight acrylic acid homopolymer having a molecular weight of 
about 60,000. In combination, the high molecular-weight acrylic acid 
homopolymer provides controlled moisture absorption synergistically in 
cooperation with the low molecular-weight acrylic acid homopolymer, which 
provides fast water take-up. The normally solid polymeric materials used 
in the two components are all non-pressure-sensitive. To induce tack 
required for pressure-sensitive properties, there is employed at least one 
nonionic surfactant, which is an alkylaryl polyether alcohol, present in 
an amount sufficient to impart tack to the normally non-pressure-sensitive 
polymers, and is preferably a nonyl phenol or octyl phenol adduct of 
ethylene oxide containing from about 8 to about 14 ethylene oxide units in 
the molecule. A blend of surfactants is preferably employed. Surfactants 
with higher concentrations of ethylene oxide units, e.g., about 30 to 
about 50 ethylene oxide units in the molecule, aid component compatibility 
but at some expense to humidity resistance. 
There may be optionally included a catalyst for achieving crosslinking 
between the available acrylic acid units to control cohesive strength, the 
catalyst being water-soluble salts of at least one di- or tri-valent 
metal, preferably organic acid salts of a di- or tri-valent metal. 
The adhesive compositions of the instant invention are applied to a 
substrate forming a label stock as a water base. 
In the presently preferred composition, the elastomeric polymer is an 
interpolymer of vinyl acetate-acrylic acid and 2-ethylhexyl acrylate. 
Although alkali-soluble and formable by emulsion polymerization, such 
polymers are generally non-water-soluble and have no adhesion, but are 
elastomeric. 
The second component is preferably an emulsion copolymer of methacrylic 
acid and ethyl acrylate; which again is non-water-soluble and, although 
pliable, is brittle and not a pressure-sensitive adhesive. The total of 
the backbone copolymers in the dry-base pressure-sensitive composition is 
from about 20 to about 55 percent by weight. The acrylic acid polymer 
system comprises from about 8 to about 35 percent by weight of the total 
composition on a dry basis, and is present in an amount adequate to absorb 
moisture at a controlled rate from a surface without loss of tack or 
degradation of the adhesive. 
The acrylic acid polymer system is presently preferred to be a blend (dry 
basis) of from about 3 to about 15 parts by weight of an acrylic acid 
homopolymer having a molecular weight of about 60,000, and from about 5 to 
about 20 parts by weight based on total dry weight of the composition, of 
an acrylic acid homopolymer having a molecular weight of about 100,000. 
The tackifier system is preferably composed of an octyl phenol adduct of 
ethylene oxide containing from about 12 to about 14 ethylene oxide units 
per molecule and present in an amount of from about 20 to about 40 percent 
by weight of the dry composition, a nonyl phenol adduct of ethylene oxide 
containing from about 9 to about 10 ethylene oxide units per molecule and 
present in an amount of from about 5 to about 15 parts by weight of the 
total composition, and an octyl phenol adduct of ethylene oxide containing 
about 40 ethylene oxide units in the molecule and present in an amount of 
from about 2 to about 10 percent by weight, dry basis. If employed, the 
catalyst is normally present in an amount of up to about 0.25 percent by 
weight. The adhesive composition may include, besides water, defoamers and 
the like. Also included in the adhesive composition are colorants and 
other materials which do not influence the adhesive properties.

DETAILED DESCRIPTION 
There is provided a three-component adhesive system formed of constituents, 
none of which is pressure-sensitive in nature but which in combination 
provides a pressure-sensitive adhesive system which is resistant to 
modification by changes in humidity; can be applied to wet surfaces by 
conventional means with permanence of adhesion; and yet is removable by 
cold and hot water-based cleansing operations. The adhesive comprises a 
non-water-soluble, normally copolymeric backbone system in combination 
with a water-soluble acrylic acid polymer system and a tackifier which is 
a non-ionic alkylaryl polyether surfactant. 
The first component of the system is a water-insoluble, or substantially 
water-insoluble, polymeric system comprised of an elastomeric polymeric 
component and a brittle polymeric component. The elastomeric component 
adds softness to the net composition, while the more brittle copolymeric 
component adds backbone to the adhesive system. 
In the preferred compositions, the elastomeric component is alkali-soluble 
and comprises an interpolymer of vinyl acetate and acrylic acid, alone or 
with one or more additional comonomer(s). The elastomeric component forms 
a tough, elastic film and imparts water resistance, even though it is 
alkali-soluble. The presently preferred elastomeric component is an 
emulsion terpolymer of vinyl acetate, acrylic acid and 2-ethylhexyl 
acrylate. While alkali-soluble, the terpolymer is water-insoluble and is 
not a pressure-sensitive adhesive. 
The second component of the polymer is also water-insoluble and not a 
pressure-sensitive adhesive, and is normally regarded as providing a 
brittle, though pliable, film which imparts cohesive strength. The 
preferred copolymers are emulsion copolymers of methacrylic acid and ethyl 
acrylate, which are not hydrophilic and which also impart water 
resistance. 
The second constituent of the system is the acrylic acid polymer system. By 
"acrylic acid polymer system" as used herein, there is meant one or more 
acrylic acid homopolymer(s) and/or acrylic acid copolymer(s) containing a 
predominant amount of acrylic acid. Where a copolymer is employed, the 
comonomer, if present in any significant amount, must be hydrophilic, for 
hydrophobic properties will hinder the functionality of the acrylic acid 
polymer system in the combination. A minor amount of a hydrophobic 
comonomer is, however, tolerable. Whether provided by a single polymer or 
a mixture of polymers, it is presently required that the acrylic acid 
polymer system have an average molecular weight between about 70,000 and 
about 90,000 and display the properties of moisture absorption without 
adhesive degradation. It is preferred that the acrylic acid polymer system 
be composed of a high molecular-weight acrylic acid homopolymer having a 
molecular weight of about 100,000 and a low molecular-weight acrylic acid 
homopolymer having a molecular weight of about 60,000. The high 
molecular-weight acrylic acid homopolymer is water-soluble and, in the 
adhesive composition, controls the rate at which water is absorbed from a 
substrate. This enables water to be absorbed form a substrate without loss 
of tack. The low molecular-weight acrylic acid homopolymer acts 
synergistically and balances the high molecular-weight acrylic acid 
homopolymer by affording fast water pickup to enable attachment of 
adhesive labels to a moist substrate by conventional label application 
machinery. If used alone, however, water pickup would occur to the extent 
of causing a loss of cohesive strength of the polymer and adhesive 
failure. 
The third component of the system is a liquid plasticizer based on one or 
more nonionic surfactants which are alkylaryl polyether alcohols, 
preferably nonyl phenol adducts of ethylene oxide and/or octyl phenol 
adducts of ethylene oxide. They induce tack to the film-forming components 
of the pressure-sensitive adhesive, which are non-pressure-sensitive in 
nature while, at the same time, imparting humidity resistance. The 
preferred adducts contain from about 8 to about 14 ethylene oxide units 
per molecule. Adducts containing higher ethylene oxide may be employable 
to aid in forming a homogeneous adhesive composition but are more 
hydrophilic. In the preferred composition, there is employed a combination 
of a nonyl phenol adduct of ethylene oxide containing from about 9 to 
about 10 ethylene oxide units per molecule, an octyl phenol adduct of 
ethylene oxide containing from about 12 to about 14 ethylene oxide units 
per molecule, and an octyl phenol adduct of ethylene oxide containing 
about 40 ethylene oxide units per molecule. The latter is the most 
hygroscopic of the tackifier system, and is employed to render the low 
molecular-weight acrylic acid homopolymer of the acrylic acid component 
mutually soluble in the adhesive system. 
In the preferred adhesive compositions of the invention, the adhesive will 
contain from about 20 to about 45 percent by weight, based on the total 
weight of the dry adhesive constituents, of the backbone polymers, of 
which from about 15 to about 40 percent by weight is the elsatomeric 
interpolymer, and from about 5 to about 15 percent by weight is the 
brittle copolymer. The acrylic acid polymer system comprises from about 8 
to about 35 percent by weight, based on the total weight of the dry 
adhesive. When the acrylic acid polymer system employs a mixture of high 
molecular-weight acrylic acid homopolymers and low molecular-weight 
acrylic acid homopolymers, the high molecular-weight acrylic acid 
homopolymer comprises from about 5 to about 20 percent by weight of the 
adhesive, while the low molecular-weight acrylic acid homopolymer 
comprises from about 3 to about 15 percent by weight of the adhesive. 
Tackifier plasticizers comprise from about 25 to about 45 percent by weight 
of the adhesive on a dry basis. It is presently preferred that an octyl 
phenol adduct of ethylene oxide having from about 12 to about 14 ethylene 
oxide units in the molecule be present in an amount of from about 20 to 
about 40 percent by weight of the adhesive; an octyl phenol adduct of 
ethylene oxide having about 40 units of ethylene oxide be present in an 
amount of from about 2 to about 10 percent by weight of the adhesive; and 
a nonyl phenol adduct of ethylene oxide having from about 9 to about 10 
ethylene oxide units be present in an amount of from about 5 to about 15 
percent by weight of the dry adhesive. 
The adhesive is formulated as an aqueous system for application to a face 
material. On a corresponding basis, the elastomeric interpolymer will 
comprise from about 15 to about 30 percent by weight of the wet adhesive 
formulation; the brittle copolymeric component from about 4 to about 20 
percent by weight; the high molecular-weight acrylic acid homopolymer from 
about 5 to about 25 percent by weight; the low molecular-weight acrylic 
acid homopolymer from about 5 to about 25 percent by weight; the octyl 
phenol adduct of ethylene oxide constituent containing from about 12 to 
about 14 ethylene oxide units per molecule present in an amount of from 
about 10 to about 30 percent by weight; the nonyl phenol adduct of 
ethylene oxide containing from about 9 to about 10 ethylene oxide units 
per molecule and present in an amount of from about 2 to about 10 percent 
by weight, and the octyl phenol adduct of ethylene oxide containing 40 
ethylene oxide units per molecule present in an amount of from about 2 to 
about 40 percent by weight. To induce crosslinking within the polymer and 
to improve cohesive strength, there may be employed a catalyst which 
causes crosslinking between the acrylic acid groups. An amount up to about 
0.25 percent by weight of either the wet or dry adhesive composition may 
be employed. The normal catalysts are soluble salts of di- and tri-valent 
metals such as zinc and chromium salts, with a chrome complex of stearic 
acid being presently preferred. Defoamers may be included, normally in an 
amount of up to about 0.1 percent by weight of the total composition, wet 
or dry. Water provides the balance of the wet adhesive composition, and is 
normally added in an amount of from about 20 to about 40 percent by weight 
of the total wet adhesive composition for application to a paper 
substrate. 
The wet adhesive formulation may be applied to one or both components of an 
adhesive label stock by any conventional means to yield, upon evaporation 
of water and lamination, an adhesive stock having excellent 
pressure-sensitive, quick-stick characteristics, the ability to be applied 
to wet or dry surfaces, whether polar or non-polar in nature, hot or cold, 
over a range of temperatures from reduced-humidity conditions to 
elevated-humidity conditions. 
By "wet surface" as used herein there is meant a surface which may range 
from a water-rinsed surface having residual water contained thereon, to 
one which is a cold substrate having water of condensation thereon. 
Adhesives of the instant invention are adaptive to all such conditions and 
impart a quick, permanent adhesive tack to a substrate and while in 
storage, i.e., pre-application to the substrate and after application to 
the substrate, are relatively unaffected by changes in humidity. They are 
particularly of low cost and are readily formulatable for a wide range of 
permanent adhesive compositions for conventional tamperproof application 
to a substrate but where the adhesive can yet be removed by water and/or 
alkali, with or without water-detergent systems, either cold or hot, 
depending on the net composition formulated. What is particularly unique 
about the adhesive systems of the invention is that the tackifying agent 
is normally a surfactant. Although expected to aid in removal of adhesive 
from the substrate, this property plays essentially no part in the 
adhesive formulation, and enhances humidity resistance. The balance of the 
constituents of the adhesive are non-pressure-sensitive in nature, and 
without the presence of the liquid plasticizer/tackifier, would be 
non-functional as pressure-sensitive adhesives in the composition ranges 
described herein. When placed together, however, all constituents are 
compatible, all mutually interact to provide a permanent adhesive and one 
which can be applied to a paper base typical of pressure-sensitive 
adhesive labels and a labelstock without bleed-through of the paperstock 
with, as indicated, excellent resistance to humidity, tamperproofness, and 
yet ready removability when the label has served its utility as a label. 
The presently preferred compositions of the instant invention, in their 
broadest and narrowest and wet and dry formulations, are as follows: 
TABLE 1 
______________________________________ 
BROAD COMPOSITION RANGE 
Weight Percent 
Weight Percent 
Ingredient of Wet Adhesive 
of Dry Adhesive 
______________________________________ 
Covinax 107 UFP.sup.(1) 
15-30 15-40 
Viscon 103.sup.(2) 
4-20 5-15 
Alcosperse 406.sup.(3) 
5-25 5-20 
Alcosperse 404.sup.(3) 
5-25 3-15 
Triton X-102.sup.(4) 
10-30 20-40 
Triton X-405.sup.(4) 
2-10 2-10 
Triton N-101.sup.(4) 
2-10 5-15 
Quilon C.sup.(5) 
0-0.25 0-0.11 
L-418 Defoamer.sup.(6) 
0-0.10 0-0.10 
Water 20-40 -- 
______________________________________ 
TABLE 2 
______________________________________ 
PREFERRED COMPOSITION RANGE 
Weight Percent 
Weight Percent 
Ingredient of Wet Adhesive 
of Dry Adhesive 
______________________________________ 
Covinax 107 UFP.sup.(1) 
17-19 20-22 
Viscon 103.sup.(2) 
16-17 13.5-14.5 
Alcosperse 406.sup.(3) 
12-14 8-9 
Alcosperse 404.sup.(3) 
6-7 4-5 
Triton X-102.sup.(4) 
13-14 30-35 
Triton X-405.sup.(4) 
4-5 8-9 
Triton N-101.sup.(4) 
3.5-4.5 8-9 
Quilon C.sup.(5) 
0-0.15 0-0.11 
L-418 Defoamer.sup.(6) 
0-0.04 0-0.10 
Water Balance -- 
______________________________________ 
.sup.(1) a vinyl acetateacrylic acid2-ethylhexyl acrylate polymer 
manufactured and sold by Franklin Chemical Company 
.sup.(2) a methacrylic acidethyl acrylate copolymer manufactured and sold 
by Armak Pioneer Chemical Division, Akzona, Inc. 
.sup.(3) acrylic acid homopolymers manufactured and sold by Alco Chemical 
Corporation 
.sup.(4) ethylene oxide adducts manufactured and sold by Rohm & Haas 
Company 
.sup.(5) a chrome (III) stearic acid complex manufactured and sold by E. 
I. duPont de Nemours, Inc. 
.sup.(6) Drew Chemical Company 
As stated in part, the adhesive compositions of the present invention have 
very good adhesion to both wet and dry surfaces, whether they are polar or 
non-polar, and develop sufficient permanence to be tamperproof when 
combined with ordinary label papers, but are easily removed when desired 
with hot or cold water or with detergents and alkalis such as are used in 
commercial cleaning operations. They resist both high and low relative 
humidity well enough to hold labels securely on small-diameter objects 
under humidity extremes, and do not require special packaging as do other 
water-soluble pressure-sensitive tape and label products. Moreover, 
compounding is inexpensive from available commercial materials, from an 
aqueous medium which eliminates the hazards of solvent-borne adhesives. 
Since the pressure-sensitive adhesives resist the effects of humidity 
extremes, high relative humidities do not cause liquid components to 
migrate through label papers, so there is no staining, which is a common 
characteristic with other water-soluble adhesives. 
While the specification has been directed to novel adhesive compositions, 
both in their wet-formulation and dry-use states, it is to be understood 
that there may be included as functional ingredients but as diluents, 
insofar as adhesive properties are concerned. Materials such as colorants, 
anti-oxidants, UV stabilizers and the like may be included without 
departing from the properties of the adhesive compositions. 
While the invention, as indicated, is primarily concerned with adhesive 
compositions, there is also contemplated within the scope of the 
invention, facestocks and their obvious sub-components, tapes and labels, 
which comprise as the adhesive portion thereof the humidity-resistant 
wet-stick adhesives of the instant invention. Stock materials are formed 
by applying from the water-base composition, the adhesive formulation, 
preferably to the release liner, but alternately to the face material, or 
both, followed by drying to remove the water, which may normally be 
achieved within two minutes at 90.degree. C., then laminating the face 
material to the release liner to form a pressure-sensitive adhesive stock 
from which tapes and labels may be cut.