CA2232713A1 - Process for preparing hot water whitening resistant emulsion pressure sensitive adhesives - Google Patents

Abstract

There is provided clear emulsion acrylic pressure sensitive adhesive polymers which resist water whitening by hot water which are formed by copolymerizing a monomer mixture containing at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms, at least one polar comonomer and at least one partially water soluble comonomer present in an amount of at least about 7 % by weight of total monomers. Polymerization is in the presence of at least one nonionic surfactant containing at least about 8 moles of ethylene oxide per mole nonionic surfactant and at least one anionic surfactant containing up to about 10 moles ethylene oxide per mole anionic surfactant. There is added to the product of polymerization at least one base to produce an emulsion having a pH greater than 7 and containing particles having an volume average particle diameter up to about 165 nm as determined by laser light scattering. An electrolyte is post polymerization added to stabilize opacity of adhesive films cast from the emulsion.

Description

PROCESS FOR PREPARlNG HOT WATER W~ill~ING
RESISTANT EMIJLSION PRESSURE SE~ lV~; AD~;~lV~
S
Field of the Invention The invention PG~ nS to clear film emulsion acrylic pr~i~a~llG sensitive adhesives (PSA) which resist whitPning by the action of hot water.

10 R~ , uu~-d of the I~ tiû.-A high degree of recict~nr-e to water whit~ning, çcreri~lly hot water, by ~lG~a~llG
sc.lalLive adhesives (PSA's) is le~luil~d for some label applir~tion~ For ~ ..plc, bottles labeled with clear film pl~,~a~ll'e sensitive adhesive labels can be subjected to ~ Pu~ I;or cnn-litin,nc where the label is e~ d to remain clear through the process. ~ictorir~lly 15 solvent based adhesives have been used for such ~rm~n~iing applir~tionc ~m~ilo~ nt~l c~nCi~le-~tinnc~ however, favor çlimin~tilDn of solvents. This and higher coating speeds 1e with emulsion pl~ llG sensitive adhesives, favor their use in place of solvent based ~ a~le sensitive adhesives.
Fmlllcion based pl~i~aLIfe sensitive adhesive polymers are made in the presence of 20 s~ rt~ntc and other water soluble electrolytes such as iniliat~la. In ~ 1itinn, coul~no~
such as ~ln~l~ d carboxylic acids are employed to impart or enh~nce adhesive pl~t;llies and tend to be present at the latex-particle interface and remain there during film form~tinn This had lead to cast films which are sensitive to water and which became cloudy simply when a drop of water was placed on the film. Water v~l,il.~.-h-g is almost assured when the 25 water is hot, e.g., 70~C or more to boiliing.
The water recict~nr~ of emulsion acrylic polymer films has long been addressed in the art particularly with respect to paint films. The art has observed that the presence of water soluble electrolytes, surfactants and polyelectrolytes such as sodium polymeth~rrylate cause or enh~nre water sensitivity ("The Applications of Synthetic Resin Fm~ ionc~ H. Warson, 30 Ernest Benn Ltd., Ton~lon~ 1972, incol~,l~led herein by lererence). It is also well known that sllrf~rt~ntc are migratory species that with time move towards and bloom to the surface of films also re-n~lPring them water sensitive.
The art has taught that the use of low levels of surfactant, a re~uctiQn or Plimin~tinn in soluble electrolytes and crosclinking between the emulsion particles can all serve to 35 improve or impart water recict~nre U.S. Patent 5,202,375 to Biale, incol~ol~Led herein by reference, teaches for this ~ul~ose a polymer emulsion that is synthPci7~A with less than about 1% by weight surfactant and with high surface tensions (i.e., greater than 45 dynes/cm) and made in the presence of W O 97/11996 PCT~US96/15S4F

high levels of a crosslinking agent. Although the use of such emnl~i~n polymers as ~ c sensitive adhesives is contc~ lated, no useful PSA ~upclLies are r~o,lcd. Moreover, with such high levels of cro~linking and low levels of surfactant, poor PSA plu~,Lies would be c~ecled in ~ ition ~ignifi~nt stability prûblems during poly."e~izdlion. The col-te~"l.lated use is as a water resistant edge sealer for co",posile boards and plywood. Low swelling of the films by water after long term drying is used to ~Içmol~ P water rÇ~ict~nr~
Eu~u~l Patent Publication 554832 to Lu et al., inco,po,dtcd herein by lc~clcnce,teaches a high solids, moisture resistant prcs;,.lrc sensitive adhesive emlll~ion polymers. The Pmnl~;on polymer is ;~y~ F.~.;7~ in the presence of copoly..~ hle ionic surfact~nt and in 10 the presence of a hydrophobic polymeric t~r~ifier with a number average mûlecular weight ranging from 400 to about 50,000.
There is no mention of water wl.;~e~ of the PSA film in the '375 and '832 patentspçcifir~tion~
U.S. Patent 4,994,538 tû Lee, et al,. incol~u,at~d herein by reference, teaches a 15 silicone acrylate PSA polymer having good water whitPning rÇ~i~t~nce synthP~i7P~I in the ~,~s~.,ce of anionic surfactant, Methyl acrylate and vinyl acetate are optionally present.
U.S. Patent 5,286,843 to Wood, inco~u~dled herein by lcfe.~nce, teaches a process for improving the water whitPning rP~i~t~nce of a PSA by use of ion eYchange to remove water soluble ions. The ~eic!ni7P~ latex is cl~imP~ to provide superior rP~i~t~nrP to water~0 ~I.it~
of the I~ ;..ti~..
It has now been found that water wh;l~n;l~g can be Pli,.,ill~l~l or ~ignific~ntly reduced in clear em--l~ion acrylic plCs~ sensitive adhesive polymers based on alkyl acrylates by ;n. l"~ g in the monomer charge at least one partially water soluble comonomer and at least 25 one polar comonomer and forming the copolymers in the p,e,~ ce of a nonioniC sl~ rt~nt ;--;ng at least about 8 moles (mols) ethylene oxide per mole (mol) and an ionic sllrfa~t~nt cQ~ g less than about 10 moles (mols) ethylene oxide per mole (mol) in which the weight ratio or nonionic to an ionic sl-rf~t~nt is at least about 1 to 1, con~ cfin~
polymPri7~tion under conditions which forrn particles having volume average ~ m-~t~rs up 30 to about 150 nm and in which formed emulsion is neutrali_ed with a base to a pH above 7.
The adhesive products formed pLerc ~bly have an opacity less than about 5%, morecre~dbly less than about 2.5% as measured using the boiling water resi~t~n~ test as described herein. Opacity is measured on a 1~...;n~P of a layer of the pl~,S;~llC se~ls;live adhesive on a biaxially o~ t~d polypropylene film stock l~min~t~ to a 2 mil. polyester 35 release. film after ~,A~:~I.lle of the face stock and adhesive layer to the action of boiling water for ten ~ ~il-~ or ambient te-,-peldture water for 60 min~lte~ Opacity is measured using a s~ ùcolorimeter. Tn-lepPndent of the opacity ch~ teristics of the adhesive film, opacity WO 97/11996 PCT~US96/15545 can be stabilized against change with time by post polyrnen7~tion addition to the formed em~ ion of an inorganic electrolyte.
The adhesive products of the invention provide as part of a label l~ r a "no label look". That is a label does not appear to be on a ~ul~sll~t~

W O 97/11996 PCT~US96/15545 DPt~ l Des~ .lion There is provided, in accordance with the instant invention, clear emulsion acrylic ,ulc-sensitive adhesive polymer compositions which are .,u'u~l 1nl;~11y unaffected by the action of hot water.
The clear emulsion acrylic pLes~u,c-sensitive adhesive polymers are comprised of at least one acrylate ester of an alcohol co~ ;..ing at least 4 carbon atoms, at least one partially water soluble comonomer and at least one polar comonomer. They are forrned in the ~,~e-,ce of a IlliAlule of nonionic and anionic suffact~nt~ provided in a weight ratio of at least 1.5:1 to form utile particles have a volume average particle ~ er (particle si~) up to about lSOnm plGrcldbly about 135 nm as l-l~sulcd by laser light ~c5~ g pl~f~ly using a Nicomp In~LIull-cl.l ~L,ull.eter tModel HN 5-90 c lui~yed with and an auluco,l~llator Model TC-100]. Butylacrylate, 2-ethylhexyl acrylate and IlliAlul~s thereof are the ~rGl~d alkyl acrylate. Methyl ac, ylate, methyl mPth~rrylate and IniA~ul~ thereof are the prefu~lGd partially water soluble comonoll,e.~. Acrylic acid is the prerc.lcd polar comonomer and is most ~rGrGl~ly employed in a~ e with another carboxylic acid, preferably mPth~rylic acid. The formed latex is adjusted to a pH of at least 7. The crellGd pH is from about 7.2 to about 9, more ~rGrGldbly from about 7.8 to about 8.
Post polymPn7~tion addition of a water soluble inol~;dllic electrolyte stabilizes opacity of films forrned from the e.mul~ion.
Films cast from such an Pmnl~ion when dried exhibit outct~n-ling boiling water re~ict~n-e as demon~tr~t~l by low opacity numbers.
As used herein, polymer particles means particles of a polymer cu...~ g a "core"and a "shell" ~ulluul-ding the core. "Intel~ ial space" as used herein means the space bel~n particles.
It is believed in the art that the çmnlcion particles on drying form a film wh~ the s~ ct~nt and other water soluble species, such as electrolytes, remain in the ;I~ ;A1 space b~ween the particles. The il~le~ space provides ch~nnPl~ or p~lhw~ys for the water ll.~ 1ps to diffuse into the polymer film. When water dirruscs into the film, ~Ldcli~re index bclween the polymer particles and the interstitial space become ~ignifi~ntly dirrelenl leading to light sc~ g and coloration of the film. This is believed to cause the phen~".~non known as "water wl.il~.~in~."
It was our initial intent to minimi7P the pr~se.-ce of water sensitive species and to col"p~LLibilize the water sensitive species present with the rest of the polymer and thereby prevent the forrnation of ch~nn~l~ for diffusion of water into the polymer film. "Water sensitive" species include inorganic species such as potassium persulfate and the like and organic species such as surfactants and the like.

WO 97tl1996 PCTAJS96/15545 , Boiling Water l~e~ ~t~n~e Test A boiling water re~i~t~nre test was developed to simulate the effect of p,.~lt u. ;~ n and as a standard to de~~ e c~ndid~t~ ;ldhesive polymer opacity. Opacity is the ratio of the reflP~f~nr,e of a sarnple backed with a white background to that of the sample backed with - 5 a black bacL~;Iou,.d times 100 and reported as percent opacity. In the test, a plG77Ul~, sensitive adhesive is coated to a level of 20-22 g/m2 on a clear 2 mil-biaxially ~J.;f.~
polypl~rlene (BOPP) (Label-Lyte~ 434, Mobil Corp) dried at 200~F in an oven for 10 ~i"~Jt~ s and the p~ ,G-sensitive adhesive, film f~cPstocl~ or b~rl~ing is i.. ~-~,ed in a beaker of boiling water (95+~C) for 10 minutes The ~les,.,lG sensitive adhesive coated f~c~-~tocl~ is then immPAi~tPly l~ d to a clear 2 mil polyester (Mylar~) release film .pl~n~ ZSLK, ~oe~h~t Diafoil) and the opacity of the resl~lt~nt l~ e de~ in~
using a s~ ocolorimeter (Hunter Lab colorquest 45/0). Per~cll~ge opacity is used as a IllCa iUlC for boiling water rP~i~t~nre The lower the number, the greater the boiling water r~ t~nre A l~ P of a 2 mil BOPP with an optically clear adhesive to a 2 mil Mylar not subjected to the action of boiling water gave opacities of around 0.4 - 0.6%. This is the lowest null-bel ~Yl~l~l for such an adhesive l~min~tP An opacity up to about 2.5% was led as good. An opacity above 5% was regarded as poor for applir~tion~ Uiling a non-water wl~ ing p~ sensitive adhesive.
Room Ten.~.at~r~ Water R~~ re l'est A room ~ water (ambient) rP~ict~nre test was also developed. First, the opacity of the 2 mil BOPP film- adhesive layer-1.5 mil polyester release liner was dcl~ ined. The polyester liner was removed and the liner-free adhesive p.~;,u.c sensitive coated BOPP f~restock immersed in deionized ambient ~ p~ ne water for 60 min~ltPs, removed, and re-l~ t~P~ to the release liner and opacity .~ d. The difference in~er~er,~ge opacity before and after immP.~sion was noted. With the good water resistant adhesives, a very small increase in opacity was seen with little or no visual dirrclcnces before and after i.. ~ on in water.
Without being bound by theory, emulsion particles formed in accordance with thisinvention are envisioned to have a "core and shell" type structure with the outer shell being 30 more polar than the core and predominantly the result of the copolymPri7~tion of an alkyl acrylate with the partially water soluble comonomer and the polar comonomer. The water soluble comonomer is believed to copolynnerize in the aqueous phase before being ca~Lu.~d by the growing polymer particles.
On nP~ltr 1i7~tion with a base, the xhell eYr~n~ to form a hyd~ ilic zone ~ rPnt35 to and surrounding the particle core in which hydrophilic spccies inrl~ in~ nonionic and anionic s~ rt~nt~ dissolve or co",pa~ibilize. When the level of water soluble comonomer is too low, the hydrophilic zone is small resulting in PYrhl~ion of the hydrophilic species leading to poor reci~t~nce to water whitening.

CA 022327l3 l998-03-20 W O97/11996 PCT~US96/lS545 The pH of the latex was found to be critical to obt~"ning good opacity and L~
re~ ;..ce to water whitening. We had ekpecl~d to obtain high water reci~t~nce by...~;..I;~;.~;..g the emu1~ion~ at a low pH since carboxyl groups would be less ionized. We uneYrect~l1y found, by contrast, that pH had to be above 7, ~,~Çe,~ly at least about 7.2, to about 9 or more p-efe.dbly from about 7 to about 8. The bases which may be used for n~utr~1i7~tion include weak bases such as ~mmoni~; strong bases, such as sodium hydroxide;
organic amines and the like. The presently ~rer~ d and most effective base is ~mmnnium hydroxide.
High water recict~nc~ is believed to be intl~1ced by the inw~l pola-i~y and size of the hydl~hilic shell outside the em1~1cic-n particle core in which the hydn~philic species can be co...l.;.libi1i7f~
The ~... r;.~ t ~y~L~"~S employed during polymPri7~tic n must be co"ll)dlible with the whole emulsion polymer i.e., the predo,--in~lLly hydrophobic alkyl acrylate core and the hydr~philic copolymer shell surrounding the core and thereby det~,l"ining water whit~ lg lS reSict~nre of the coated film product. The surfactant(s) employed during polymeri7~tion are also i",~,~t in stabilizing the particles during pol~ l;on and in st~ e We have found that with anionic surf~rt~ntc, the level of ethoAylation has to be about 10 moles per mole s11rf~rt~nt or less, l"cÇc,dbly 4 moles (ethylene oxide units per molecule) or less for good water whitPning rçcict~nre When the average moles of ethylene oAide is 20 too high, opacities tend to be high. It was also observed that even when good, the orariti~S
are not reproducible when an anionic surfactant was the only surfactant. That is, ~
film dl~wdo~ns from the same emulsion gave desirably low opacities at times and ...~ie~ hly high opacities at other times.
Other anionic surf~rt~ntc and anionic surfactants with higher levels of ethylene oxide 25 (moles per mole) may be used to stabilize the emulsion particles during pol~ linn or other reasons but do not impart r~cict~nce to water w1-i~e..i11g.
F--ncticn~1 anionic c11rf~rt~ntc include lauryl ether sulfates such as Disponil~ FES-32, Disponiln' FES-993 made by Henkel; salts of s111f~t~1 nonyl and octyl phenoxy poly(ethyleneoxy) ethanols such as AerosollU NPES~58, Aerosol~ NPES-930 made by Cytek Tn-lustries sulfosuc~ s such as Aerosoln' OT-75, Aerosol~ A-SOl made by Cytek Tn-luctrieS; aromatic phosph~te ester surfactants such as Pho~l~f~ PE-SlO made by Rhone Poulenc; copolym~ri7~hle surfactants such as slllfat~d acrylic polyethers such as SAM 211 from PPG Industries and the like. Other anionic surf~rt~ntc useful for pol~n.P~ ;,;.l ion include salts of dodecyl benzene sulfonate, lauryl sulfate and the like may also be used.
It was found that nonionic surfactants which are more co",paLible with the acrylic polymers, and which contain about 8 or more moles ethylene oxide per mole surfactant also tended to co"~libilize in the shell and not be present in the intel~LiLal space.

In order to ensure good stability in polymert7 ttion process and provide particles having good water wl.;l~ (boiling water) rç~i~tztnce7 it was found nPcç~ztry to employ a weight ratio of nr~nionic to anionic surfactants of at least about 1:1, plerG dbly about 1.5 to 1, more preferably from about 1.5:1 to about 6:1, more ~lerG.dbly from about 1.5:1 to about 4:1.
Among the nonionic surfactants thal: can be used are octyl and nonylphenol ethoAylat~s such as the Igepal~ s~ tztnt~ made by Rhone Poulenc; Polystepn' s---fzt---tztnt made by Stepan ChPmi~ztl Co. and the like. CopolymP~ri7~hle nonio~ic sllrfztrtztntc such as SAM 185N
nùnyll)llenoxypoly(ethyleneoxy)-ethylacryl(mPthzt~ry)lates available from Monomer-Polymer Labs and the like may also be used.
The clear çml~ n acrylic pr~,.l-e se.,siLi~re adhesive polymers of the invention are co...~ d of a lJlGdolllillaLG amount of one or more alkyl acrylate esters of an alcohol c~ i--g at least 4 carbon atoms, at least one partially water soluble COIIIOI1O111Gt, and at least one polar comonomer.
The alkyl acrylate esters serve to control glass t~n~iti~)n tGIll~GlaLulG (Tg) of the 15 formed polymer and are generally presen~: in an amount of from about 50 to about 90~ by weight, and l)lGrGlably from about 55 to about 85% by weight of total mono"~
Alkyl acrylate esters of an alcohol which form the bulk of the mono,~ of the core and which contain at least 4 carbon atoms in the alkyl group of the alcohol in~ e, among others, n-butyl acrylate, 2-ethyl hexyl acrylate, hexyl acrylate, decyl acrylate, dodecyl 20 acrylate, isoo~;~ylacrylate and the like. Methacrylates can also be used. N-butyl ac,ylalG, 2-ethyl hexyl acrylate and Illi~Lul~s thereof are pl~se.lLly p-~ Çe.~
A partially water soluble comonomer is l~uiled to ensure adequate boiling water or water wl.it~.-ing r~Cictztnce. It is believed that this comonomer copolymerizes with the polar comonomer and 25 alkyl acrylate ester to form the shell around the çm-llcil n particle core that co...~ .;li7Ps electrolytes and the anionic surfactant. Paltially water soluble comonomers in~.lnrling methyl ae,ylale, ethyl acrylate, methyl mPthztf~rylate, vinyl acetate and the like may used in order to obtzun the desired opacity. Methyl acrylate (5.6% by weight soluble in water ~45~C) and/or methyl mPthz~-~rylate (1.5% by weight soluble in water ~? 45~C) are ~lGrGllcd. The 30 partially water soluble monomer content is above about 7~O preferably from about 8% to about 25% by weight of total monomers. Levels of about 8 to about 20% provides by weight of monomers o~lim.l--- opacity and levels above about 10% are generally not lG lUil~d except to modify adhesive p.ù~G.lies or glass transition le~..pr,~ G.
In addition to partially water soluble comonomer, a highly polar collloncJlll~l is 35 required to be present. The amount of polar comonomer is generally in the range of from about 1 to about 10% by weight of the monomers. The ~lGrGllGd polar colllonolll~ l~ are c~bu~Lylic acids co.~ h-it-g from 3 to about 5 carbon atoms. Acrylic acid and a mixture of acrylic and methztcrylic acids are presently p-er~ d. Among the carboxylic acids, there WO97/11996 PCT~US96/15545 may be mP!ntion~ acrylic acid, mPth~rrylic acid, maleic acid, fumaric, it~ronic acid, and ~e like.
Results to date show that use of a IllixLulc of polar monomers synegictir~lly gives an opacity lower than the same amount of each polar monomer sep~r~tely. It is well known in S the lilf, ,,~le that mPth~crylic acid tends to become buried inside the particle core to a greater extent than acrylic acid during emulsion polym~ri7~tion. Co,l-bin~lLion of polar monomers which tend to partition differently between the polymer particles and the aqueous phase during em~ ,n polymeri7~tion may therefore be effectively used to provide a shell which solubili_es hydrophilic species.
Other polar comonomers cont~inin~ carboxylic and hydroxyl groups can also be used.
FY~mp1~ of such polar co...onol-~e.., could be beta-carboxyethyl a;,ylate, ~llo~-ol..P~ rryloylethyl succin~t~ monometh~rryloylethylphth~l~t~-7 polyethylene(propylene) glycol mono~ry(meth~rry)lates, 2-hydroxyethyl acry(...~ )late, 2-hyd,~lAy~
acry(mloth~ry)lates and the like.
Other modifying monomers for the clear emulsion acrylic polymers include one or more diesters of a dicarboxylic acid wl~er~in each ester group of the diester acid in~Ppenr~ntly co~ in~ from about 8 to about 16, preferably from about 8 to about 12 carbon atoms. FY~mrles of diesters are di-2-ethyl hexyl maleate, di-2- ethyl hexyl ru~ .AIe and IlliALulc;S thereof.
Other comonomers, such as styrene, tertiary butyl styrene and the like, may be used to modify the Tg or other copolymer pr~e.Lies.
Other comonomers in-~lu~iin~ N-vinyl caprolactam, hydroxyethyl(propyl) (meth)acrylate, ~c~to~re~o~yeLllyl (meth)acrylate, and the like, could be used to further ~nh~nre ~-lhtosion to various surfaces and partitioning between the aqueous and particle phases while other comonomers, such as glycidyl m~th~rrylate or allyl glycidyl ether, can also be used to further ~nh~n~'~ high le~pe~ e shear p-UpG ~ies. Multifunctional acrylates can also be used to cause cross linking and improve shear ~ ies.
Ch~omic~l cross-linkers provided in an amount of up to about 1% by weight, can be errGc~ ly used to further increase cohesive strength. These include cl.-u",iu", acetate, ~il~ni~ .. oni~.. c~l~o.. a~G, ~lumim~m acetate and the like. Cross-linking may also be achieved using actinic or electron beam r~ tion.
The copolymers of the instant invention can be stabilized against UV and oxidative degr~d~tion by using UV stabilizers and ~ntiox~ nt~
In ~d~ition, fillers, cûlorants and the like, t~ ifiers~ plasticizers and oils may be added 35 to modify the ~.o~G.lies of the clear acrylic emulsion polymers of this invention.
The monomer p~ ions of the clear acrylic polymer are typically adjusted in such a way that the ~r~s;,u.G sensitive adhesive polymer have a glass transition lempG ~LtUl~ of least 10~C below use lG~ ur~ and preferably be from about 0~C to about -60~C as measured CA 022327l3 l998-03-20 W O 97/11996 PCT~US96/15545 by a dirrer~;;..Lial sc~nninE calorimeter. Use l~;;lllpeldtUlC; iS the ~---y~lalule at which a f~n~stocl~-adhesive 1~...;n~tf is typically applied to a ~.lb~LldLe and is normally 25~C.
In any event, the polymer has to be decignPA to convert well, i.e., to slit, diecut, matrix strip, run on printinE presses and be ~lispenced from l~hellinE ...~ to clear 5 ~ b~ t~5 such as glass bottles.
The clear çm1l1cinn acrylic polymeri of this invention are to provide ~tih.o.cinn and tack at room ~ e, elevated and low t~n~ dLur~s to glass and coated g1ass or other clear s~lrf~ s. What is e~ 1 is that they provide low opacities by the boiling water ~ r,e test or minim~1 changes in opacity by the recict~nce test to room ~ e water.
Poly~ .lion can be carried out in the presence of electrolytes such as Lel~
yyl~hOs~ - to regulate particle size and emulsion viscosity. Electrolytes genPr~11y cause particle si~ to increase with an increase in electrolyte content and this can increase opacity.
Tnrlep~.ule.-t of the use of electrolytes during polymP i7~tinn, it was ~.. l~l~Aly found that on post- polymPri7~tion addition of small levels of an ino.E,~lic electrolyte to the latex stabilizes the latex against increases in opacity with time. This was u~ ~l~ because the relevant lilr.l~ lc; makes clear that water rç~i~t~nce would be adversely ~ffect~ by the ~ 1ition of water sen~ /e species such as electrolytes. However, our results clearly demon~.dle the films col-t~ added illu,~ ic electrolytes even after long term aging .c~ined the initial level of opacity. The amount to electrolyte to be added will range from about 0.025 to about 0.25, I,rer~.dbly from about 0.03 to about 0. l percent by weight of the em--lcion It is yl~se~y " er~ -~ to employ as added electrolyte alkali met~ S~lf~tPS, ~lk~inf~
earth metal s--1f~t~s, alkali metal ~t~es, ~lk~linP earth metal ~cRt~t~os, alkali metal plln~ .s, ~lk~lin~. earth metal pho~ph~t.~s and the l~t;Çel.ed metal is so~ lm-Particle size also controls opacity. Volume average particle ~ e~ ~ up to about 150 nm ~l-~sured using the Nicomp Instrument s~e~ u-~eter were found to have good opacities while çm~ ion~ having a larger volume a~rerage particle rii~mr~tpr had greater opacities than ~~ui-~d for use as a clear pl'eS:~UlC sensitive adhesive.
Conventinn~1 water soluble free radical iniliatc,l~ can be used for polymPri7~ticn 30 They include pot~inm, ammonium and sodium pers~l1f~tPs Other iiLialol~ such as water soluble azo inilia~l~ (such as Wako V-50 made by Wako ~hPmir~1~ USA, Inc), redoxiniliatul~ such as persulfate/bisulfite catalyst systems can also be used. The results in~ tP
that a small amount of strong acid groups rnay be nece~ry in the outer shell of the polymer particles to co--.l)alil)ilize with the strong acid groups of the anionic sllrf~rt~nt Results also in~ tP that with low or no persulfate content, opacities are high. This is contrary to eYpe~t~tion since higher water rÇcict~n~e a.s in~lic~tPIi by the absence of such water sensitive sulfate groups at the surface was regarded as i~.po~L~nt to good water whitPning re~i~t~nce W O 97/11996 PCT~US96/lS545 The emnlcion polymers of the instant invention are framed at a solids level of 45% by weight solids or more preferably from 50% to 60% by weight solids and when cast from emulsion onto a face stock (direct coating) or transferred from a release lever or surface to a face stock (transfer coated) are to provide clear coating at coat weights of about 20 to about 5 22 grams per square meter with low per~el,ldge opacities as per the boiling water rÇ~ict~n test.
Percent opacity of the cast film should be about 5 % or less, ~.erc.dbly 2.5% or less about preferably 1.5% or less as determined in the boiling water rç~i~t~nce test or remain ec~nti~lly unrh~nged in the room ~ p~ re water re~ict~nrP test. Direct coated film 10 l~ in~ generally give lower opacities than transfer coated film lz---;-~ 5 In ~lAitic-n to the Boiling Water Resict~nr~ and Room Tc...lk~ c Water ~çcict~nre Tests, the following tests were also pc.rol",ed.
Room T~ .~ul~ Shear Room Lclll~ldLulc shear was nled~ ut by applying c~mpl~s of adhesive coated film.. ~c.. ;.-g 1.25 cmx 5 cm strips to a 1.25 x 1.25 cm area of the st~inlpcs steel panel. The film is rolled down twice with a 2 kg rubber-clad roller at the rate of 30 cm/min. The panel is then clal,l~ed in a vertical position with 500 g weight ~tt~ch~l to the e~ c end of the strip. The time elapsed before the weight cm pulls the sample from the panel is measured in ...i.-."~s.
20 % Gel The % gel content was ~.,eaa.llt;d by placing an amount of dry adhesive, eg. 75 mg., in a 10 micron polyLcLld~luol~ethylene ~,.~.I.bl~le filter. The edges of the lll~lllbldllc are sealed ts) contain the sarnple and placed in a 20 ml. vial cu.~ g tetrahydrofuran. The vial is lulllblcd for 24 hours, filter taken out and dried at elevated le~ e under vacuum.
25 The filter is weighed and the percent insolubles is calculated by the formula:
% Insolubles = final weight of sample X 100 initial weight of sample ~ot Water Bottle Peel The clear film labels employing the adhesives of this invention are normally applied 30 to glass bottles with ",ini",.l,ll application pre~s~ulc. The adhesive is formulated to wet out rapidly on bottles so as to give a "no label look" within about 24 hours of appli~ti~-n During bottle making, the glass bottles may be treated with ingredients to prevent the bottles from sc~ ~t~ l ,i "g. The adhesive should also adhere to such treated surfaces and .. .~ - good ~hto.~ion char~teri~tics even under severe cQndition~ such as e~ ule to high water 35 te~ x;ldLul~s. This characteristic is determined by what is known as a hot water bottle peel test (HWBP). In this test, a 1" x 8" strip of adhesive coated on BOPP f~cestock at a coat weight of 20-22 grams per square meter is applied to a glass bottle with no applied ~LC~ U1G~
allowed to dwell for 20 minutes and then immersed in a water maintained at 77~C for 0.5 hour. At the end of this period, the bottle is taken out and 90 peel imm.oAi~tPly ,,,easulcd.
Peel is lG~l~d in Newtons per meter (m'm).
The following data is provided to illustrate as regarded as si~nifil~nt ~ow~.,.ls ob~ it~
and ...~ ;ng clear em~ ion acrylic polymers of desired opacity which resist water 5 wl-ilen;ll~ as deLel.,.ined by particle size and/or opacity.
~tt~rh-fYl Table I cont~in~ the mP~nin~ of certain abbreviations in Tables II to Table B.
F
There was fonned a reactor charge co-.~ a solution of 1.14 g of Disponil FES-32 (32% solids, m~nllf~ctllred by Henkel) dissolved in 123 g of ~lfi'~ni~i water. A pre-emulsion feed soap solntion was formed by dissolving 0.34 g of Aerosol OT-75 (75% solids, Cytec), 0.5 g Aerosol A501:(507 Cytek), 2.27 g of Disponil FES-32 and 4.19 g of Polystep F-4 (Stepan Chf mir-~l) in 93 g of dPioni7~ water.
A monomer mix was made up with 222.4 g of 2-ethyl hexyl acrylate, 73 g of n-butyl lSacrylate, 52 of methyl acrylate, 6.3 g of methacrylic acid, 9 g of acrylic acid and 0.037 g of n-dodecyl melcayL~l. The monomer mix was added to the pre-emlll~ion solntion with mixing and was stirred till the viscosity was about 2000 cps (Brookfield, RV,#3 ~a? 12 rpm).
An "Aqueous Feed" solution was pl~cd by dissolving 1 g of pol;.c~ ,.. pçn~lllf~t~
in 106 g of deionized water. A kickoff i~ r solution was formed of 0.75 g of 20 pot~ m pers~ te- in lS g of deionized water.
The reactor charge was introduced to a 1 liter reactor which was flushed with niLl~gcll. The reactor charge was heated to 78~C and the kickoff i~ sol--ti~ n added.
The ll..,.lul~ were held for 10 minutes at 78~C. The pre-em~ n feed was started at the rate of 1.99 g/min. Ten minutes after start of pre-emnl~iQ~ feed, the Aqueous Feed was 25added at the rate of 0.89 g/min. The pre-çm-ll~ior was added over four hours. Aqueous Feed was added over 4 hours. Through out the feeds, the Lel~lpela~ulc inside the reactor was ~1 at about 80~C. After the feeds were compl~t~l, the con~e~ were held at 80~C
for an additional 45 IllinuLes and then cooled. The final pH was 3.1. The latex was nP~ltr~li7pd with a dilute ~mmonillm hydroxide sc Intion to a pH of 7.9. The final latex solids 30were 57.3%, and viscosity was 3150 cps (E~rookfi~ld RV, ~4~20rpm) and particle ~ m~t~r was 112 nm.
The latex was coated directly onto a 2 mil BOPP f~r~sto~lr (Mobil-Labelyte 434),dried in an oven at 70~C for 10 ",inu~s to a dry coat weight of 20-22 grams per square meter and l~min~terl to a 1.5 mil polyester release liner. A sample cut out from this l~,-.;n~
35was used for mP~Ilring boiling water re~i~t~nce the release liner was removed, the adhesive-r;.~ il,lllle :,ed in boiling w;ater and its opacity after eAyo~ule to boiling water -for 10 ...ilu~les in the test was found to be 1.21%.

W O 97/11996 PCTrUS96tl5545 When the cold water test was applied for the products of ~xample 1 in co...p~...con to a normally clear commercial gene;al purpose permanent (GPP) ~ lG sensitive adhesive, the pGl~;GIl~ge opacity of the product of Example 1 increased by 0.31 while the ~er~G.,~ge point increase in opacity of the GPP adhesive was 12 pe.~cll~ge points.
5 Example 2 There was formed a reactor charge co..lAin;llg a solution of 0.65 g of Disponil FES-32, 0.35 g of Polystep G-S, 0.16 g of Aerosol A-501 dissolved in 123 g of deioni2~ water.
A pre-Pmlllcion feed soap soll~tion was formed by dissolving 0.34 g of Aerosol OT-75, 0.34 g of Aerosol A-501, 2.27 g of Disponil FES-32 and 3.88 g of Polystep F-5 in 110 g of 10 deionized water.
A monomer mix was made up with 217.4 g of 2-ethyl hexyl acrylate, 84 g of n-butyl a~lyl~le, 46 of methyl methArrylate, 6.5 g of m~th~-rylic acid, 9.1 g of acrylic acid and 0.248 g of n-dodecyl Illcl~lpl~n. The ",ono",er mix was added to the pre-çrnl-lcic-n s-luti~ n with mixing and was stirred till the viscosity was about 2000 cps (Brookfit-ld, RV,#3 ~ 12 lS rpm).
An "Aqueous Feed" solution was pr~ared by dissolving 1 g of pot~ccillm pers--lf~t~
in 106 g of ~eioni7P~ water. A kickoff i..il;~tor solution was formed of 0.75 g of ~!~;.....
persulate in 15 g of ~If 01li7~i water.
The reactor charge was introduced to a 1 liter reactor which was flushed with 20 llil.u~;~,n. The reactor charge was heated to 78~C and the kickoff i..iliA~or sol~ltion added.
The mixture were held for 10 .~in~lfes at 78~C. The pre-çml~ n feed was started at the rate of 1.99 g/min. Ten ~ eC after start of p~ ~ ulsion feed, the Aqueous Feed was added at the rate of 0.89 g/min over 4 hours. Through out the feeds, the te~ .A~ G inside the reactor was ~Ai~lAill~ at about 80~C. After the feeds were completed, the co..l~u 25 were held at 80~C for an ~A~Iitinn~l 45 .ui~ulPS and then cooled.
The final solids was 51.4%, pH was 3.2 and latex viscosity was 400 cps (Broo'~iel(i, RV, #~20 rpm). The latex was neutralized with a dilute A..~l~.oniu"~ hydroxide solllti~n to a pH of 7.8. The final viscosity was 3350 cps (Brookfield, RV, #4~20rpm) and particle .liA....,t~- was 124 nm.
The latex was coated directly onto a 2 mil BOPP rA~e~"~h (Mobil-Labelyte 434), dried in an oven at 70~C for 10 ~ es to a dry coat weight of 20-22 grams per square meter and 1A...;I-A1P~ to a 1.5 mil polyester release liner. A sample cut out from this l~...;n~l~
was used for ,--e~ g boiling water rçci~tAnce., the release liner was removed, the adhesive-f~r~stnc~ 111;11AI~ immersed in boiling water and its opacity after CA~o~ule to boiling water for 10 "li"u~es in the test was found to be 1.35%.
When the cold water test was applied for the products of Example 1 in CO.I~p~ on to a normally clear commercial general pul~ose permanent (GPP) ~ sensitive adhesive, CA 022327l3 l998-03-20 WO 97/11996 PCT~US96/15545 the pel~;entage opacity point of the product of ~xample 1 increased by 0.31 while the ~er~enlage point increase in opacity of the GPP adhesive was 12 ~erc~ ge points. F~ 3 There was formed a reactor charge cont~ining a solution of 0.9 g of Disponil FES-32 5 (32% solids, m~nl~f~ctured by Henkel) disssolved in 123 g of deioniLed water. A pre-em~ ion feed soap solution was formed by dissolving 0.39 g of Aerosol OT-75 (75% solids, Cytec), 2.61 g of Disponil FES-32 and 3.9 g of Polystep F-4 in 110 g of de;oni7Pd water.
A monomer mix was made up with 240 g of 2-ethyl hexyl acrylate, 55 g of n-butyl acrylate, SS of methyl mPth~rylate, 6.5 g of meth~-~rylic acid, 9.1 g of acrylic acid and 10 0.238 g of n-dodecyl Ill. rea~n. The monomer mix was added to the pre-emulsion sol~ tion with mixing and was stirred till the viscosity was about 2000 cps (Brookfield, RV,#3 ~? 12 rpm).
An "Aqueous Feed 1 " sol~ltic-n was pr~zued by dissolving 0.74 g of of Disponil FES-32, 1.25 g Polystep F-5 and 0.5 g of pot~c~ m persulfate in 70 g of (~pioni7p~ water.
An "Aqueous Feed 2" solutio was pl~cd by mixing 0.50 g of pu~ .. pPrsnlfzltP
in 50 g of deionized water.
A kickoff i.~ l... solution was formled of 0.75 g of potassium persulate in 15 g of ~leioni7~ water.
The reactor charge was introduced to a 1 liter reactor and was flushed with niLIvgen.
20 The reactor charge was heated to 78~C and the kickoff initi~ r solution added. The mixture were held for 10 ...;.~."~s at 78~C. The pre-emulsion feed was started at the rate of 1.99 g/min. Ten ...i..u~ s after start of pre-emnl~icm feed, the Aqueous Feed 1 was added at the rate of 0.6 g/min. The pre-emulsion was added over four hours. Aqueous Feed 1 was added over two hours. After co,l.~lction of ~ iticm of the Aqueous Feed 1, Aqueous Feed 2 was 25 started and added at the rate of 0.42 g/min. for two hours. Through out the feeds, the t~ --e inside the reactor was ...~ P~ at about 80~C. After the feeds were completed, the conl~ were held at 80~C for an additional 45 mimlt~Ps and then cooled.
The final solids was 50.441 %, pH was 2.3 and lates viscosity was 480 cps (Brookfield, RV, #4~?20rpm). The latex was ne~ltr~li7ed with a dilute au~loniuu~ hydroxide solution to a pH of 7 g. The final viscosity was 3100 cps (Brookfield, RV, #4~20rpm) and particle ~ was 114nm.
The latex was coated directly onto a 2 mil BOPP f~çstocL~ (Mobil-Labelyte 434), dried in an oven at 70~C for 10 ..~inu~. s to a dry coat weight of 20-22 grams per square meter and l~ to a 1.5 mil polyester release liner. A sample cut out from this 1~ P
35 was used for measuring boiling water rçci~t lnce, the release liner was removed, the adhesive-f~fPstoc~ 1P immersed in boiling water and its opacity after W~JO:~UIC; to boiling water for 10 ~ rs in the test was found to be 1. 1 %.

WO 97/11996 PCT~US96/15545 When the cold water test was applied for the products of Example 1 in co...~ on to a normally clear commercial general purpose permanent (GPP) ple~ufe sensitive adhesive, the ~er~e.lldge opacity point of the product of Example 1 increased by 0.31 while the ~.lldge point increase in opacity of the GPP adhesive was 12 percentage points.
S Example 4 There was formed a reactor charge CQ~ ;n;l~g a solution of 0.9 g of Disponil FES-32 dissolved in 123 g of ~Pioni7P~ water. A pre-emulsion feed soap soll-tion was formed by dissolving 0.34 g of Aerosol OT-75, and 4.19 g of Polystep F-5 (Stepan C'hPmic~l) in 105 g of dtoinni7~1 water.
A monomer mix was made up with 240 g of 2-ethyl hexyl acrylate, 55 g of n-butyl acrylate, 55 of methyl mPth~crylate~ 6.5 g of meth~rylic acid, 9.2 g of acrylic acid and 0.238 g of n-dodecyl me,wplan. The monomer mix was added to the pre-eml-lQion solution with mixing and was stirred till the viscosity was about 2000 cps (Broolcfi~lcl, RV,#3 ~ 12 rpm).
An "Aqueous Feed 1" solution was prepared by dissolving 1.5 g of Polystep F-5 and 0.5 g of potassium persulfate in 60 g of deioni_ed water.
An "Aqueous Feed 2" solution was ~al~d by mixing 0.5 g of ~i,iu~ r~
in 60 g of deionized water.
A kickoff iniLi~ solution was formed of 0.75 g of pot~ -m persulate in 15 g of 20 d~ioni7P~ water.
The reactor charge was introduced to a 1 liter reactor which was flushed with nillogell. The reactor charge was heated to 78~C and the kickoff iniLiator solution added.
The Illi~lUl~ were held for 10 ...i~ -s at 78~C. The pre-emulsion feed was started at the rate of 1.99 g/min. Ten l~ o3 after start of pre-çmlll~icn feed, the Aqueous Feed 1 was added at the rate of 0.6 g/min. The pre-emulsion was added over four hours. Aqueous Feed 1 was added over two hours. After completion of addition of the Aqueous Feed 1, Aqueous Feed 2 was started and added at the rate of 0.42 g/min for tow hours. Through out the feeds, the le.l.~rdlu.~ inside the reactor was m~int7.in~ at about 80~C. After the feeds were complçted, the conl~; were held at 80~C for an ~ ition~l 45 ~-~ s and then cooled.
The final solids was 50.5~O, pH was 2.52 and lates viscosity was 420 cps (Brool~ield, RV, #4@~20rpm). The latex was nPutr~li7~ with a dilute ammonium hydroxide sollltion to a pH of 7.9. The particle ~ mpter was 137 nm.
The latex was coated directly onto a 2 mil BOPP f~--estock (Mobil-Labelyte 434),dried in an oven at 70~C for 10 minutes to a dry coat weight of 20-22 grams per square meter and l~...i..~i to a 1.~ mil polyester release liner. ~ sample cut out from this l~ A~r was used for measuring boiling water rç~i~t~nce, the release liner was removed, the adhesive-WO 97/11996 PCT~US96/1~545 f~r~st~~ immersed in boiling water and its opacity after e~po~ c to boiling water for 10 ...;.~ s in the test was found to be: 0.8%.
When the cold water test was applied for the products of Fy~mple 1 in co --p~ o~ to a normaUy clear commercial general purpose permanent (GPP) ple.~UlC sensitive adhesive, - S the y~lwll~ge opacity point of the product of Example 1 increased by 0.31 while the ~e.~.,el,~ge point increase in opacity of the GPP adhesive was 12 ~n;el.~ge points.
Example 5 There was formed a reactor charge con~ a solution of 0.855 g of Disponil FES-32 (32% solids, m~mlf~tllred by Henkel) dissolved in 123 g of ~IPio~i7PA water. A pre-Pmlll~i~ n feed soap solution was formed by dissolving 2.7 g of SAM 211 (80% solids, PPG), 0.69 g tçtr~lium pyropho~ph~t~ and 3.37 g of Polystep F-4 (Stepan ChPrnir~l) in 93 g of d~-Ol~i~fd water.
A monolll~,r mix was made up with 287.4 g of 2-ethyl hexyl acrylate, 59 of methyl mPth~rylate, 6.3 g of mrth~rrylic acidl 9 g of acrylic acid and 0.24 g of n-dodecyl 15 ".e~ . The mono~,~ mix was added to the pre-emulsion solution with mixing and was stirred till the viscosity was about 2000 cps (Brookfield, RV,#3 ~? 12 rpm).
An "Aqueous Feed 1 " solution was pl~ed by dissolving 0.3g of SAM 211, 1.24 g of Polystep F-5 and 0.5 g of pot~ m pf ns~lf~tP in 77 g of ~lPioni7pci water.
The "Aqueous Feed 2" solution was prepared by mixing 0.5 g of pot~inm pçrslllf~tr in 53 g of ~1e~ 7~2~ water.
The reactor charge was introduced to a 1 liter reactor which was flushed with n iL~vgen. The reactor charge was heated to 78~C and tne kickoff inilialor scllltion added.
The mixture were held for 10 ...;~ -s at 78~C. The pre-eml-l~inn feed was star~d at the rate of 1.99 g/min. Ten .~.il.~.les after start of pre-eml-lcion feed, the Aqueous Feed 1 was 25 added at the rate of 0.60 g/min. The pre-emlll~ic)n was added over four hours. Aqueous Feed 1 was added over two hours. After completion of the Aquious Feed 1, Aquious Feed 2 was started and added at the rate of 0.42 g/min for two hours. Through out the feeds, the If-..pe~ .e inside the reactor was ...~ at about 80~C. After the feeds werecompleted, the conte.lt:i were held at 80~C for an additional 45 .~;nl~(es and then cooled.
The pH was 2.8 and latex viscosity was 200 cps (Brookfield, RV, #4~20rpm). The latex was nelltr~li7~ with a dilute a""l,oi-iu.l- hydroxide solution to a pH of 7.8. The final latex solids were 49.4%, viscosity was 7300 cps (Brookfield, RV, #4~a?20rpm) and particle l was 136 nm.
The latex was coated directly onto a 2 mil BOPP f~r~tock (Mobil-Labelyte 434), dried in an oven at 70~C for 10 .. i-~ s to a dry coat weight of 20-22 grams per square meter and l~min~t~l to a 1.5 mil polyester release liner. A sample cut out from this l~r~
was used for mr~llrin~ boiling water rçcict~nre, the release liner was removed, the adhesive-f~r~stock l~min~tr. i,l""cl ,ed in boiling water and its opacity after exposure to boiling water for 10 Illh.uL~s in the test was found to be 1.27%.
When the cold water test was applied for the products of Example 1 in co...p~ Oil to a normally clear commercial general p,l~ose permanent (GPP) ple~,~ule sensitive adhesive, the ~c~ccll~Lge opacity point of the product of FYample 1 increased by 0.31 while the .cenlage point increase in opacity of the GPP adhesive was 12 pe,~n~,e points.
F~;..niJl~s 6-27 and Table II
Table II shows the effect of surfactant choice on opacity. The principal s~ rt~nt employed was "Anionic 1." "Anionic 2" c~nt~ined no ethylene oxide units while "Anionic 3" was a ~l~JliCL~ly blend col.l; h-rcl an unknown amount of ethylene oxide units.
The suppl-o.mPnt~l anionics were useful for other cQn~litions such as stabilization of the emlllcinn An opacity of about 2.5% or less may be regarded as "good" while products having an opacity less than S may also be employed. We found that with an anionic sllrf~rt~nt, the level of ethoxylation has to be below about 10 moles per mole for good hot water resict~nre When the moles of ethylene oxide were about 10 or at times when at 10, higher op~riti.-~ were obtained. When a anionic surfactant was the only surfactant system employed, opacities were not lc~l.d~-r-ihl~. (See Fy~mple 6) that is, opacity varied si~nifir~ntly from dld~vdu~ to drawdûwn, where drawdown is the forming of a coated layer to a coat level of 20-22 g/sq. meter. This lead to the use of a non-anionic su- r; ~ t Employing an anionic surfactant of 4 ethylene oxide units and a nonioni~ snrfar-t~nt of 8 or more ethylene oxide units gave very low op~citir~ Without being bound by theory, it is believed that the nonionic surfactants which are co,l,l)atible with the acrylic polymers are present to the lesser degree in the intcl~liLial spaces between particles.
F~ es 2B to 38 and Table m The partly water soluble monomer is believed to be primarily present in the shell of the polymer particle and renders the particle more hydrophilic by pol~, . . .~.;, hlg with the polar comonomer and the alkyl acrylate to provide a transition from a hydrophobic core which is prim~rily an aLtcyl acrylate outward to a polar end group which imparts hydrophilicity. This allows the sllrf~rt~nt~ to disperse within the shell of the polymer particle Pnhz~n~in~ reci~t~nre to water whitening as inl1irat~d by low opacity. The absence of partly water soluble comonomer resulted in too high in opacity (Ex. 24) or signific~ntly inconsistent opacities (Ex. 26 and 30).
F~ml?les 39 tû 43 and Table IV
Table IV shows the effect of particle size on opacity in that a variety of polymers formed having a volume average particle rli~mete~r approaching lSOnm had borderline op~rities~ When particle ~ mlotpr was 198 nm opacity was lln~nceptable. The prerelled upper volume average particle rli~mPtrr is 135 nm.

CA 022327l3 l998-03-20 W O 97/11996 PCTrUS96/15S45 F~ es 44-49 and Table V
Table V shows the effect of initiator on opacity. The results show that when too little persulfate is employed or is absent, opacities are high infli~tin~ the likelihood that perslllf~tP, bPnpfi~ ly provides water sensitive sulfate groups at the surface of the shell of the polymer.
- S This is contrary to ~ ;on since a lack of sulfate groups would have been PYpe~t~ to induce water-recict~n~ by Plimin~tin~ the presence of water sensitive groups in the shell.
FY~ S 50-56 and Table VI
Table VI, inrlepen~nt of surfactant system, shows the general effect of c~l)oAylic acid on opacity. Acrylic acid and ll~iAtUl~S of mell.ac.~lic and acrylic acids gave ~i~nifir~ntly 10 better opacities than m~th~crylic acid alone.
F..~-.l~les 57 to 69 and Table V~l Table VII, shows effect on pH and base on opacity. Below a pH of seven opacitiesare quite high. The best results are obtained for ~mmoni~lm hydroYide at a pH above 7Ø
FY~m~les 70 to 79 and Table V~II
Table VIII shows the effect of use cross linking monomers and chain ~Idnsrel agents on bottle peel and shear.
FY~m~;les 76 to 85 and Table IX
Table IX shows the effect of post polymerization addition of an electrolyte to the emulsion on changes in opacity with timie. The starting point (Ex. 80 and 84) were the 20 em~ ion~ as formed with addition of ammonium hydroxide to a pH of 7.5-8Ø For ~ ples 80 and 84 no electrolyte was post polymerization added and opacity of films drawn from the emUl~ion increase signifi~ntly with days(d) of aging whether at room le~ e~
or 50~C. When an electrolyte was added post polymerization retention of initial opacity was ~ignifi--~nt FY~mple S which had an initial opacity of 1.27 and to which no electrolyte was 25 added after poly.. ,~ l;on had an opacity of 3.03 after G~JO~lG to 50~ C for two days.

W O97/11996 PCT~US96/15545 1 T~bleI
EHA - 2 ethyl hexyl acrylate BA - n-butyl acrylate MeA or MA-methyl acrylate MMA - ~ Lac~y~
MAA - ~.._lLac-ylic acid AA - acrylic acid TSPP - ~ uFl Disponil FES-77 - sodium lauryl ether sulfate - 30 moles ethylene o~cide (Henkel) Disponil FES-993 - sodium lauryl ether sulfate - 10 moles ethylene o~cide (EIenkel) Disponil FES-32 - sodium lauryl ether sulfate - 4 moles ethylene o~cide (EIenkel) Aerosol A-501 - ~JlU~ taly . o~,oc,~, sulr~ (Cytek) Aerosol OT-75 - sodium dioctyl sulf~ (Cytek) NPES-930 - salt of sulfated nonyl~ .. oAy poly(.,ll-yl~.. ~,~y)ethanol- 9 moles Ethylene oxide (Cytek) Rhodafac PE-S10 aromatic ~ û~ t ester - 6 moles ethylene o~ide (Rhone Poulenc) Polystep F4 - ro ~I~JL_.~ol etho~cylate - 10 moles ethylene oxide (Stepan) Polystep F5 - nv..~ltJh_.ol ~lh~ yldt~ - 12 moles ethylene o~cide (Stepan) Polystep F3 - nu yl~Jh~, ol clhu~y' ~ 8 moles ethylene o~cide (Stepan) I~epal C0-850 - nu..yl~ l ' y; ' - 20 moles ethylene oxide (Rhone Poulenc) Igepal C0-887 - n~"ly', ' ~l ' y' ' - 30 moles ethylene oxide (Rhone Poulenc) SAM 211 - surface active ~ - 15 moles ethylene oxide (PPG) HEA - L~l~u~ lLyl acrylate VAc - vinyl acetate HDODA - h ' -l d;a~
n-DDM - n-dodecyl ~..~., , pphm - parts hundred parts parts . .
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~ ~ ~ ~ u~ ~ ~ ~ a~ ~ _ 0 m o ~ v ~ _ _ O _:
Ei~ ~' 0 0 0 0 0 0 ~n 0 a o o o o o o o o o c~
~n ~ o T
~1: 0 0 0 0 0 o o al ,~ ~ ~
~i o ~i 0 _ ~ _ o a~ ~ o ~ a~ o o o o o ~ o - ~ ~ ~

al al 0 1~ 0 r~ r~

~S ~ ~ 0 ~ 0 o al o o ~ a~
m 35 ~ ~ ~ ~ ~ ~ _ a~ _ ~ al a~
_ ~ ~ al al a~ ~ ~ ~ ~ 0 0 x 0 0 o -- c~
al al al al al ~ al al a~

WO 97/11996 PCT~US96/15545 o o o ,c, ~ o o +
~ = = = o O
: + + + + +
N N N N N

~

O ~t ~ N 0~

~ eo co l~ N
~ N ~ ~ ~

N N N N N

~~ E N N N - -~ ~ ~ ~ ~ o O

e N N N N N
e ~
~ - - - - -e ~ ~ N _ _ ~ 2 N ~ N N

_ o o o - ~

X a~

w w ~ ~ l~
~n o ~ o ~ o T~ble V
TSSPP, KPS hit, I~PS fa-d, PH
Ex.EHABA MoA MAA AA pphm pphm pphm Othar hit,pphm P~k~,nm % cp~city %Ged Pnm ' ' Srst-m ~
4661.320.1 14.3 1.742.6 0.19 0.21 0.28 0 129 1.4 7.6 FES32+F4+0T-76+A501 ~' 4761.320.1 14.3 1.742.6 0.19 0.14 0.14 0 2.3 7.6 FES32+F4+0T-76+A601 4861.320.1 14.3 1.742.6 0.19 0.21 0.22 0 198 6.6 71.9 7.2 FES32+F4+0T-76+A501 4961.320.1 14.3 1.742.6 0.19 0.21 0 Wako V-60 8.6 7.2 FES32+F4+0T-76+A501 feed,.06 6022 64 10.3 2.9 1.4 0 0.21 0.28 0 160 >6 66.8 7.4 FES32+0T-76+A601 6122 64 10.3 2.9 1.4 0 0 0 Wako V-60 131 >6 71.7 7.2 FES32+0T-76+A601 nit,.04 Nako V-60 D
ead,.06 w ~

W O 97/11996 PCTrUS96/15545 o o o o o o o + _ _ _ +
~ ~ ~ ~ O o o u~ 0 ~ o~
+ + + + + + +

1~ E ~ ~ ~ ~ ~ ~ ~

0 ~ 0 ~
~ ~ ~ _ o ~,, o o o u~
~ ~ o 0 8 ,o _ 8 ~ ~
T 1~ 1~
~ ~ a~ a~ ~ 0 ~ ~. ~ ~ ~ ~ ~ ~
~ o o o o o o o O ID ~ ~ ~ U~ a~

~C ~ C') 0 0 o ~ ~ ~ ~ ~ ~ - -,~ 0 0 0 0 0 0 0 Ul X o - ~ ~ ~ ~ ~

-u~ o ~ o ~ o Table Vll Ex.N~. EHA BA MAA AA M-A C : pH B~- Op~chy % S ' - -67 21.7 63.6 2.9 1.4 10.3 0 7.3 NH40H <5 FES32+0T-76+A601 68 21.7 63.6 2.9 1.4 10.3 0 7.3 LiOH >6 FES32+0T-76+A601 69 62 20 1.7 2.1 14.3 0 6.4 NH~OH 4.4 FES32+FES993+0T-76+A601+F4 62 20 1.7 2.1 14.3 0 7.2 NH~OH 1.9 FES32+FES993+0T-76+A601+F4 61 62 20 1.7 2.1 14.3 0 7.3CbHllNH2 4.0 FES32+FES993+0T-76+A601+F4 62 62 20 1.7 2.1 14.3 TEA-6.4 FES32+FES993+0T
0 7.89 NH40H-7.82.9 76+A601+F4 ~
63 32 48 2.9 1.43 14 2 HEA,0.2 8.0 NH40H 2.0 FES32+FES993+0T-76+A601 HDODA
64 32 48 2.9 1.43 14 2 HEA,0.2 8.0 PEI 11.7 FES32+FES993+0T-76+A601 ~n HDODA
32 48 2.9 1.4 15.5 0.2 HDODA 3.9 NH40H 27.7 FES993+0T-76+A601+FES32 66 32 48 2.9 1.4 16.6 0.2 HDODA 6.1 NH~OH 6.9 FES993+0T-76+A601+FES32 67 32 48 2.9 1.4 16.6 0.2 HDODA 7.36 NH40H 2.2 FES993+0T-76+A601+FES32 68 32 48 2.9 1.4 16.6 0.2 HDODA 8.2 NH~OH 1.16 FES993+0T-76+A601+FES32 69 32 48 2.9 1.4 16.6 0.2 HDODA 9.1 NHIOH 2.7 FES993+0T-76+A601+FES32 V

m WO 97/11996 PCT~US96/15545 ~ ~ ~ U~
C
~ r~ r-- r~ C r ~ r-- r~ r~
- - - - r' _ _ _ _ 0 U~ 0 -- ~ --+ + + + _ + _ +

~n 1~ o ~ o ~ O
~ ~ r~ ~ ~ O a~
U~ C
C ~o ~o 8 ~ ~ tn ~ ~~
o v v v ~ ~ ~ _ ~ o o o a~ r~ ~ <o o ~ ~ a~ o C~ ~ o _ ~ ~ ~ ~ ~
C
~e 20 -o - 0 ~ ~ ~ ~
r~ o ~ D ~t -- _ _ _ _ ~ r~ r~ _ S ~ ~ ~ ~ ~ ~ ~ ~ O ~
Zj,~ O O O O O O O O O
~, ~ 0 ~ ~ ~ ~ ~ ~ ~ ~ ~

~, et ~ ~ O ~ ID ID ~ ~ ~ ~
~ ~ o ~ ~ r~ r~ r~ 0 r~ 0 ~ o o o o ~ ~ ~ ,~
- - - _ _ U~ ~ ID r~ O O O O O O
ID ~D ID
- - - -t r~ ~ ~ ~ ~ ~
~ ~ ~ ~ ~ ~ ~ ~ 0 ~ D

Z
X O -- ~ ~ ~ ~ ~D r~
ul r~ r~ r~ r~ r~ r~ r~ r~ r~ r~

~ o ~ o ~ o Table IX
AGING TEST

Ex. Post %
Addod IniOial R.T. A13in~, 50 C A~ing, Eloctrolyto Opacitv % Opacitv IDaYs~~ 96 Opacity IDsvs~~
nono 1.08 3.3113d~, 12.59111d~, 37.45147d~81 0.094% TSPP '-3' 1.03~3d), 1.14(1 ld), 2.25(18d), 0.047% TSPP 0.92 3.64144d~; 4.15(54d~
82 0.19%TSPP 0.95 0.79(6d~, 1.16(13d~, 2.35(40d~
83 1.00(6d~, 7.01 (40d~
84 nono 0.72 0.96(9d~- 2.78(22d~- 3.18(27dl 0.05% TSPP 0.95 0.83110d); 1.07(22d); 1.14127di D
86 0.06% Na2SO~ anhØ91 0.77(8d~- 0.97(20d~- 1.03(35d~ o 87 0.03% Na2SO~ anhØ96 0.89(59d~ 0.75(8d~, 0.87(20d~, 1.05(35d~
88 0.04% Na3PO~ 12H20 0.94 0.79(8d~; 0.90(20d~; 0.96(35d~
89 0.067% Sodium Acotato 1.09 0.79(8dl- 0.91 (20d~, 0.89(35d~
0.04%(NH4~2HPO~ 8.16 5.84(8d~, 7.42(20d~, 9.09(35dl 91 0.03% NaCI 1.49 6.21(8d~; 7.16(20d~; 5.65(35di 92 0.025%TSPP~.03%Na250~ 0.96 0.84(58dl 0.70(8d~; 0.83(20d~; 0.87(35d~

Days~ = days aftor coatin~ and dryinl~ of tho pressuro sonsiOvo adhosivo on a BOPP film and forrnotion of a Ismin~to to a rdoaso linor.

Claims (45)

WHAT IS CLAIMED IS:

1. A process for the production of clear emulsion acrylic pressure sensitive adhesives copolymers which resist water whitening, which comprises copolymerizing a mixture of monomer containing at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms, at least one polar comonomer and at least one partially water soluble comonomer present in an amount of at least about 7% by weight of total monomers and dispersed in an aqueous polymerization media in the presence of at least one nonionic surfactant containing at least about 8 moles of ethylene oxide per mole nonionic surfactant and at least one anionic surfactant containing up to about 10 moles ethylene oxide per mole anionic surfactant in a weight ratio of nonionic to anionic surfactant of at least 1 to 1 and, thereafter, adding at least one base to produce an emulsion having a pH of greater than 7, said copolymers forming a clear film when coated on a substrate and dried.

2. A process as claimed in claim 1 in which the pH is from about 7.2 to about 9.

3. A process as claimed in claim 1 in which the pH is from about 7.8 to about 8.

4. A process as claimed in claim 1, 2 or 3 in which the partially water soluble comonomer is present in an amount of from about 8 to about 25% by weight of the total monomers.

5. A process as claimed in claim 1, 2 or 3 in which the partially water soluble comonomer is present in an amount of from about 8 to about 20% by weight of the total monomers.

6. A process as claimed in any one of the previous claims in which the partiallywater soluble comonomer is selected from the group consisting of methyl acrylate, methyl methacrylate and mixtures thereof.

7. A process as claimed in any one of the previous claims in which the polar comonomer is selected from the group consisting of acrylic acid and a mixture of acrylic acid and methacrylic acid.

8. A process as claimed in any one of claims 1 to 7 in which the weight ratio ofnonionic surfactant to anionic surfactant is at least 1.5 to 1.

9. A process as claimed in any one of claims 1 to 7 in which the weight ratio ofnonionic surfactant to anionic surfactant is from 1.5:1 to 6:1.

10. A process as claimed in any one of claims 1 to 7 in which the weight ratio of nonionic surfactant to anionic surfactant is from 1.5:1 to 4:1.

11. A process as claimed in any one of the previous claims in which the anionic surfactant contains about 4 moles of ethylene oxide per mole of anionic surfactant.

12. A process as claimed in any one of the previous claims in which the base is ammonium hydroxide.

13. A process as claimed in any one of the previous claims in which, based on the total weight of monomers, the at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms is present in an amount of from about 50 to about 90% by weight, the polar comonomer is present in an amount of from about 1 to 10% by weight, the partially water soluble comonomer is present in an amount of about 7 to about 20% by weight.

14. A process as claimed in any one of the previous claims, in combination with adding to said emulsion, following polymerization of said monomer mixture, at least one electrolyte provided in an amount sufficient to stabilize opacity of a pressure sensitive adhesive film cast from said formed emulsion.

15. Emulsion acrylic pressure sensitive adhesive copolymers which form clear films which resist water whitening, comprised of copolymerized mixture of monomers containing at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms, at least one polar comonomer and at least one partially water soluble comonomer present in an amount of at least about 7% by weight of the monomers forming the total mixture, said copolymer formed in an aqueous polymerization media in the presence of at least one nonionic surfactant containing at least about 8 moles of ethylene oxide per mole nonionic surfactant and at least one anionic surfactant containing up to about 10 moles ethylene oxide per mole anionic surfactant, at a weight ratio of said nonionic surfactant to said anionic surfactant of at least 1 to 1, in which the product of polymerization is neutralized in emulsion by at least one base to produce an emulsion a pH greater than 7, said copolymers, when formed as a film on a biaxially oriented polypropylene film to a level of 20 to 22 g/m and immersed in water of at least 95°C for 10 minutes and laminated to a 1.5 mil polyester release film, providing an opacity of about 5% or less, as measured with a spectrocolorimeter.

16. Emulsion polymers as claimed in claim 15 in which the emulsion produced is neutralized to a pH of about 7.2 to about 9.

17. Emulsion polymers as claimed in claim 15 in which the the emulsion produced is neutralized to a pH of about 7.8 to about 8.

18. Emulsion polymers as claimed in any one of claims 15 to 17 in which the partially water soluble comonomer is present in an amount of from about 8 to about 25% by weight of the total monomers.

19. Emulsion polymers as claimed in any one of claims 15 to 17 in which the partially water soluble comonomer is present in an amount of from about 8 to about 20% by weight of the total monomers.

20. Emulsion polymers as claimed in any one of claims 15 to 19 in which the partially water soluble comonomer is selected from the group consisting of methyl acrylate, methyl methacrylate and mixtures thereof.

21. Emulsion polymers as claimed in any one of claims 15 to 20 in which the polar comonomer is selected from the group consisting of acrylic acid and a mixture of acrylic acid and methacrylic acid.

22. Emulsion polymers as claimed in any one of claims 15 to 21 in which the alkyl acrylate is selected from the group consisting of 2 ethyl hexyl acrylate, butyl acrylate and mixtures thereof.

23. Emulsion polymers as claimed in any one of claims 15 to 22 in which the baseis ammonium hydroxide.

24. Emulsion polymers as claimed in any one of claims 15-23 in which the weight ratio of nonionic surfactant to anionic surfactant was at least 1.5:1.

25. Emulsion polymers as claimed in any one of claims 15-23 in which the weight ratio of nonionic surfactant to anionic surfactant was from 1.5:1 to 6:1.

26. Emulsion polymers as claimed in any one of claims 15-23 in which the weight ratio of nonionic surfactant to anionic surfactant was 1.5:1 to 4:1

27. Clear emulsion acrylic pressure-sensitive adhesive polymers comprised of a copolymerized monomer mixture, comprising at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms and present in an amount of from about 50 to about 70% by weight, at least one polar comonomer present in an amount of at least 1% by weight of the monomer mixture, and at least of one partially water soluble comonomer present in an amount of at least about 7% by weight of the monomer mixture, dispersed in an aqueous emulsion polymerization media and copolymerized in the presence of at least one nonionic surfactant containing at least about 8 moles of ethylene oxide per mole nonionic surfactant and at least one anionic surfactant containing ethylene oxide in an amount up to about 10 moles per mole anionic surfactant, at a weight ratio of said nonionic surfactant to said anionic surfactant of at least about 1 to 1, neutralized by at least one base to a pH greater than 7, and containing particles having a volume average particle diameter up to about 150 nm as determined by laser light scattering, said particles, when formed as a coating on a biaxially oriented polypropylene film to a level of 20 to 22 g/m2 and immersed in water of at least 95°C for 10 minutes and laminated to a 1.5 mil polyester release film, providing an opacity of about 5% or less, as measured with a spectrocolorimeter.

28. Clear polymers as claimed in claim 27 in which the opacity is less than about 2.5%.

29. Clear polymers as claimed in claim 27 or 28 in which the pH is from about 7.2 to about 9.

30. Clear polymers as claimed in claim 27 or 28 in which the pH is from about 7.8 to about 8.

31. Clear polymers as claimed in any one of claims 27 to 30 in which the base is ammonium hydroxide.

32. Clear polymers as claimed in any one of claims 27 to 31 in combination with adding to said emulsion following polymerization of said mixture of monomers, at least one electrolyte provided in an amount sufficient to stabilize opacity of a pressure-sensitive adhesive film formed from said polymers.

33. In a process for the formation of clear emulsion acrylic polymers useful as pressure-sensitive adhesives by emulsion polymerization of a mixture of monomers containing at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms and adding at least one base to said emulsion to a pH of at least 7 to provide emulsion particles which deposit as clear films from the emulsion, the improvement which comprises adding to the emulsion having the pH of at least 7 following polymerization of said mixture of monomers at least one inorganic electrolyte in an amount sufficient to stabilize the opacity of a film formed from the emulsion.

34. A process as claimed in claim 33 in which the electrolyte is added in an amount of from about 0.025 to about 0.25 percent by weight of the emulsion.

35. A process as claimed in claim 33 in which the inorganic electrolyte is added to the emulsion in an amount of from about 0.03 to about 0.1 percent by weight of the emulsion.

36. A process as claimed in claims 33, 34 or 35 in which the inorganic electrolyte is selected from the group consisting of alkali metal sulfates, alkaline earth metal sulfates, alkali metal acetates, alkaline earth metal acetates, alkali metal phosphates alkaline earth metal phosphates, and mixtures thereof.

37. A process as claimed in claim 36 in which the alkali metal is sodium.

38. A process as claimed in any one of claims 34 to 37 in which the monomer mixture contains at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms, at least one polar comonomer present in an amount of at least about 7% by weight of the monomer mixture, and at least one polar controller, said monomer mixture being polymerized in the presence of at least one nonionic surfactant containing at least 8 moles of ethylene oxide per mole of nonionic surfactants and at least one anionic surfactant containing up to about 10 moles ethylene oxide per mole anionic surfactant, the weight ratio of said nonionic surfactant to anioic surfactant being at least 1 to 1.

39. A process as claimed in claim 38 in which the partially water soluble comonomer is present in an amount of from about 8 to about 25 % by weight of the total monomers.

40. A process as claimed in any one of claims 33 to 39 in which the added base comprises ammonium hydroxide.

41. A process as claimed in any one of claims 33 to 40 in which the emulsion particles have a volume average particle diameter up to about 150 nm, as determined by laser light scattering.

42. A process as claimed in any one of claims 33 to 41 in which the pH is from about 7.2 to about 9.

43. A process as claimed in any one of claims 33 to 41 in which the pH is from about 7.8 to about 8.

44. A process as claimed in any one of claims 38 to 43 in which the partially water soluble comonomer is present in an amount of from about 8 to about 20% by weight of the monomers.

45. A process as claimed in any one of claims 38 to 44 in which the partially water soluble comonomer is selected from the group consisting of methyl acrylate, methyl methacrylate and mixtures thereof.