CA1277083C - Pressure sensitive adhesives and adhesive articles - Google Patents

Abstract

ABSTRACT

Normally tacky, pressure sensitive adhesive compositions comprise one or more polymers containing pendant functional groups attached to a polymer backbone and having the formula:

in which R1 is a divalent organic radical at least 3 atoms in length, and X is organoacyl or cyano, and wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxylic acid ester monomers, (4) alkenyl ether polymers comprising at least about 30 weight percent alkenyl ether monomer units, and (5) combinations thereof.

Such polymers have improved cohesive strength with little or no detriment to adhesive tack or adhesion, and these improvements are realized without the necessity of incorporating crosslinking monomers such as N-methylolamides or other crosslinking agents.
Pressure sensitive adhesive, water-based emulsions, hot melts and solutions containing such polymers and adhesive articles having at least a portion of one surface thereof coated with such adhesives are also provided.

Description

~ 0~3 PRESSURE SENSITIVE ADHESIYES AND ADHSIVE ARTICLES
BACKGROUND r Field of the Invention This invention relates to the field o~
pressure sensitive adhesives and to articles comprising such adhesives.
In~roduction Normally tacky, pressure sensitive adhesives ~PSAs) are used in the ~anufacture af ~ var1ety of articles such as adhesive tapes and other materials which are intended to be easily attachable to another substrate by the application of pressure alone. Many adhesives preferably have a balance of one or more properties such as tackiness at the temperature o~
use, adhesion (peel resistance~, cohesion (shear resistance), elongation, elasticity, color clarity and color stability, and resistance to sunlight and other ultraviolet and degrading radiation sources.

2~ Maintaining the requisite balance of such properties while improving one or more characteristics of such pressure sensitive adhesives is both difficult and unpredictable. Any modification of adhesive co~positions which improves one adhesive property may detrimentally affect one or more other desirable properties. For instance, it is difficult to improve an adhesive's shear strength w;thout reducing one or more other desirable properties.

Homopolymers and ;nterpolymers of a variety o~ monomers are useful as pressure sensitive adhesives when applied to a backing as solutions, dispersions ~;

~'~'7~3~3 (emulslons) ~nd/or hot melts. However, many PSA
applications require shear strength values higher than those that can be provided by otherwise useful polymers. Some appllcations requlre shear strength values of at least about 50 minutes and h19her, ~.e, on the order of 500 to 10,000 minutes (determtned by the shear value test described hereinafter). While there are various ways of improving PSA shear strength, many if not all of these detrimentally affect one or more other desirable properties.
Polymer molecular weight can be increased to improve shear strength, but this route generally reduces tack and adhesion. Polar monomers, such as polymerizable carboxylic acids~ often increase cohesive strength but also may result in low adhesion and tack.
Cross-linking monomers, such as the N-methylol amides, or other crosslinking agents are generally expensive and they may reduce tack and adhesion. Their use also may reduce processability and may impair other properties such as clarity, color stability and UY
stability.

The suitability of pressure sensitive adhesive compositions is also influenced by the ease of manufacture of both the adhesive and of artic1es containing the adhesive and by environmental and personnel safety hazards. For instance, PSAs are often applied to a backing as hot ~elts, polymer solutions or as dispersions of a polymer in an aqueous medium. Such solutions and dispersions must possess properties which facilitate their use in the manufac~ure of PSA-containing articles. Thus, the melt, solution or dispersion9 as well as the polymer per se, must adequately wet the backing to assure adequate adhesive distribution, coverage and bonding to the backing.

f 3 ~ ~7t7a:~3 The chemical composition of the PSA polymer carr~ers (when used) is also signlficant for several reasons. Solvents other than water are beco~ing more and more undesirable due to solvent expense and the cost and hazards involved In controlling solvent vapors. Yet such solvents are often necessary ~or adequate distribution and handling of polymers that cannot be employed effectively in water-based systems.
Thus~ water-based polymer latexes are much preferred in the adhesive manufacturing industry provided that the necessary physical and chemical properties of the finished article can be achieved. However, substitution of water-based latexes or hot melts ~or solvent-based polymers may reduce one or more physical properties.

N-methylol amide functional groups and other crosslinking monomers and agents are known to improve adhesive performance in several respects. However9 such polymers release formaldehyde upon curing or can result in the presence of potentially toxic residues in the finished article. In par~icular, N-methylol amide-containing polymers release formaldehyde when 2~ cured, and they can result in formaldehyde residues in the finished product. Such formaldehyde release and residues are often undesirable since formaldehyde is coming under ever increasing scrutiny in both the workplace and home. It is particularly undesirable in medical an~ personal contact applications, such as adhesive bandages, and the state and federal Occupational Health and Safety Administrations ~OSHA) have set stringent formaldehyde exposure li~its for industrial workers.
~5 Various rheological propert;es of water-base latexes are particularly important with regard to the !

_4 ~ ~ ~ 7 ~;3 suitabil~ty of such latexes for adhesive art~cle manuf~cture. Latex particle s~ze and particle ~ze distr~bution can signlficantly influence l~tex physical prcperties wh~ch affect appl1cat~on o~ the latex to a back~ng. Similarly, latex vtscos~ty can limit latex util~ty in adhesive art~cle manufactllre due to the inf1uence of viscos~ty on adhes~ve distribution, filler loading (of the latex~ and wetting of the adhesive artic1e backing.
Yet further demands are placed on the chemical composition and physical properties of tow temperature pressure sensitive adhesives, i.e., adhesives intended for use at relatively low temperatures. Often, PSAs which haYe adequate cohesive and adhesive strength at low temperatures are so "gummy" at ambient conditions that they complicate both adhesive handling at ambient temperatures and the manufacture of adhesive-containing articles. Such gummy adhesiYes also tend to "creep" and to "bleed-through" labels and other backings.

rhUS 9 it can be seen that the physical and chemical properties desired in adhesive compositions and articles, and in the polymer solutions, dispersions and melts employed in the manufacture of adhesive articles, place various, sometimes conflicting, demands on polymer composition and on the polymer carrier, i.e, solvent or water, if usedO It is desirable to obtain a polymer system~ preferably a water-base or hot melt system, which possesses a balance of properties suitable for the manufacture o~
pressure sensitive adhesives and PSA-containing articles.

~ ~ 77 ~3 SUMMARY OF THE INYENTION

It has now been found ~ha~ pressure sensit~Ye adhesives, and art~cles conta~n~ng pressure sens~tive adhesives, having an improved balance o~ PSA
properties and, in particular, hav~ng improved shear holding value and acceptable adhesive strength and tack, can be obtained by employing, as a component of the adhesive, a polymer having a Tg o~ about 0 C. or less containing pendant functional groups of the formula:

~ R1 - C. - CH2 - X (l) wherein R1 is ~ divalent organic radical at least 3 atoms in length, and X is organoacyl or cyano.
Functional groups contdining different R1 and X
radicals san be contained in the same polymer molecule, or polymers containing different R1 and X
groups can be blended in the same solution or disper-sion. The polymers can be manufactured and applied to backings either as solutions, aqueous dispersions or hot melts, although aqueous dispersions and melts are particularly preferred since they eliminate the costs and hazards associated with solvents other ~han water.
Such pressure sensitive adhesives and adhesive articles have an improved balance of properties. In particular, they possess improved cohesive strength without significant, if any, loss of adhesion or tack. They are relatively clear, colorless materials (unlecs intentionally colored by the addition of colorants), and they possess adequate color stability and resis-tance to sunlight and other ultraviolet sources. Theydo not require the use of crnsslinking agents ( ~
a ~77~ 3 and catalysts, such as N-methylol amide monomers, although they may contain one or more of such materlals. The low Tg polymers which are useful as 5 low temper~ture pressure sens1tive adhesives7 e.g.
adhesives intended ~or use at about 1~ C. or less~
have adequate cohesive and adhes~ve strength at low temperatures yet are not excessively gummy at ambient tempe ra t u res.

DETAILED DESCRIPTION OF THE INVENTION
.

Normally tacky and pressure sensitive adhesive compositions are provided which comprise a polymer containing pendant functional groups of the formula:

Rl e CH2 x ~1) wherein R1 is a divalent organic radical at least 3 atoms in length, and X is organoacyl or cyano, and wherein the remainder of the polymer is selected from (1) conjugated diolefin polymers comprising at least about 50 wei~ht percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 50 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprisin~ at least about 1 weight percent of a monoolefin monomer havin~ up to about 4 carbon atoms and at least about 40 weight.
percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percen~ polymerized olefinically unsaturated carboxylic acid ester monomers 9 ~4) alkenyl ether polymers containing at least about 30 weight percent alkenyl ether monomer units, and ~5) .
~ ~77083 comb~n~tlons thereof. Functlonal groups conta~n1ng dlfferent R1 and X radlcals can be contained ~n the same polymer molecule~ or polymers contaln~ng different R1 and X groups can be blended ~n the same solutlon or dispersion. It ls essential only that the useful poly~ers (1) contain functional groups containing elther two carbonyl ~roups or a carbonyl and a cyano group separated by a single methylene group, as illustrated, and (2) the methylene group is separated from the polymer main chain (backbone) by at least 4 atoms (R1 plus the "interior" carbonyl group).
Thus, R1 is at least 3 atoms in length; i.e., the shortest link between the interior carbonyl group and the polymer backbone is at least 3 atoms long.
Otherwise, the molecular weight, structure and elemental composition of R1 does not negate the effectiveness of the dual keto or keto-cyano functionality of the pendant side chains. Thus, R1 can be of any molecular weight sufficient to allow incorporation of the pendant functional groups into the polymer backbone, for instance, as part of a polymerizable olefinically unsaturated monomer or by substitution onto a preferred polymer by any suitable addition reaction, e.g.:

Ol O
Polymer (C - Cl)n + n~H - O - R2 ~ C - CH2-X) -(HCl )n 01 o ~ Polymer (C - O - R2 - C ~ CH2 - X)n where n is an integer, and -O-R2 is R1 in expression (1~, supra. R1 can contain heteroatoms, such as oxygen, sulfur, phosphorus, and nitrogen, functional groups such as carbonyl, carboxy-ester, thio, and 8 ~ 7'7~)8~

amino substltuents, and can comprise ~romatic, olefinic or alkynyl unsaturation. Typically, Rl w111 be a cycl~c or acyclic divalent organic radical of 3 ~o abou~ 40 atoms ~n length; i.e., having 3 to about 40 atoms in its shortest chain between the polymer backbone and the interior carbonyl group~ For ease of manufacture from readily avallable reactants~ R1 ~s preferably of the formula:
lo 8 - C - Y - R3 - Z - (2~

wherein Y and Z are independently selected from 0, S, and NR7~ and R3 is a divalent organ~c radical at least 1 atom in length, preferably 2 to about 40, and most preferably 2 to about 20 atoms in length. Y and Z are preferably 0, and R7 is H or a monovalen~ organic radical9 pre~erably H or hydrocarbyl radical having up to 6 carbon atoms.
~0 X in expression (1) is - C0 - R~ or -CN, preferably - C0 - R4 where R4 is hydrogen or a monoYalent organic radical preferably having up to 10 atoms other than hydrogen (i.e., up to 10 atoms not counting hydrogen atoms which may be present in the radical). Most pre~erably, R3 is selected from substituted and unsubstituted alkylene, polyoxy-alkylene, polythioalkylene and polyaminoalkylene radicals, typically up to about 40 atoms in length, preferably up to about 20 atoms in length. The substituted and unsubstituted polythio-, polyoxy-, and polyaminoalkylenes can be readily formed by the well known condensation of alkylene oxides9 alkylene amines, glycols, dia~ines, and dithiols. Thus:
/ 0\ R8 n(R8 - CH - CH2) ~O(CH2 ~ ~H2 ~ O)nH

- 9~ 77C~3 where R8 1s H or a monovalent organlc rad1cDl, prefer-ably H or alkyl radlcal~ To 111ustrate, such pendant ~unctional groups (formula 1) can be lntroduced 1nto !, the polymer backbone by copolymer~zation of other monomers (discussed here~nafter) with a polymer1z~ble monomer of the formula:

5 ll R6 - CH = - Rl - C ~ CH2 ~ X (3) where~n X is as defined for ~ormula 1, supra, R6 and R5 are independently selected from hydroxy~ halo, thio, amino, and monovalent organic radicals~ prefer-ably having up to 10 atoms other than hydrogen~ most preferably alkyl radicals having up to 10 carbons atoms. Substitutlng the preferred form of the group Rl illustrated in formula 2 for Rl in formula 1 yields the most preferred functional monomers:

6 y R3 - Z - C - CH2 ( ) where R3, R5, R6, X, Y and Z have the definitions given above. From this expression it can be seen tha~
when R6 is hydrogen, X is - C0 - R~, R4 and R5 are methyl, Y and Z are 0, and R3 is an ethylene radical, the resultin~ monomer is acetoacetoxyethyl methacrylate, - one of the class of monomers described by Smith in U.S. Patent 3,S54,937 This monomer can be prepared by first treating ethylene glycol with methacrylic acid to form hydroxyethyl methacrylate which then is treated with diketene, as described by Smith, to form acetoacetoxyethyl meth-acrylate. A particularly preferred class of functionalmonomers~ due to their relative aYailability, are those )83 disclosed by Smlth, whlch correspond tc ~ormula (4) in which R6 ls hydrogen, Y ~nd Z are oxygen, R5 is hydrogen or an alkyl group havlng up to 12 carbon atoms~ R3 ts an alkylene group containing up to 10 carbon atoms, X is - C0 - R4, and R4 is an alkyl group having up to 8 carbon atoms.

The useful pressure sensitive ~dhesiYe polymers contaln a sufficient amount of one or msre of the described functional monomers to in~rease cohesive strength of the adhesive relative to an otherwise identical pressure sensitive adhesive in the absence of such functional monomers. Detectable enhancement of cohesive strength is found in many polymers at functional monomer concentrations as low as 0.05 weight percent. 6enerally, however, the useful polymers will contain at least about 0.1 and typically at least about 0.~5 weight percent of the functional monomer based on total polymer weight. Much higher functional monomer concentrations can be employe~.
Thus, functional monomer concentrations will usually be between about 0.1 to about 20 weight percent or more, typically about 0.1 to about 10 weight percent.
Surprisingly, very significant increases in cohesive strength can be achieved at functional monomer concentrations below 5 weight percent and even below 2 weight percent. Hence, preferred functional monomer concentrations in many of the useful pressure sensitive adhesives will be within the range of about 0.1 to about 5 weight percent, often within the range of about 0.1 to about 2 weight percent.

Presently preferred polymers which contain the above described functional monomers include (1) ~ 7 0~3 copolymers o~ subst1tuted or unsubstltuted alkenyl aromatic monomers and con~ugated d~olef~ns, (2) olefin ester interpolymers of C2 4 monoolef~ns and C2 8 alkenyl or alkeno~ esters of Cl 12 saturated carboxylic ac~ds, ~3) polymer1zed alkyl ~nd alkanol esters of olefin~cally unsaturated carboxyl~c aclds, ~4) alkenyl ether homopolymers and lnterpo1ymers of C2 10 olefin ethers of C1 1~ alcohols~ and (5) com-binations thereof. In addition to the above describedfunctional monomers, each of these preferred classes of polymers can contain additlona~ monomers such as olefinically unsaturated mono- and polycarboxyl~c;
acids, amides, aldehydes, etc.
1~
Illustrative polymers of esters of olefinically unsaturated carboxyl~c acids are described by Midgley in U.S. Patent No. 4,540,739 ( 1985) .

These polymers comprise, primari1y, one or more polymerized, olefinically unsaturated mono- and/or polycarboxylic acid esters, and optionally may contain other polymerized monomers. Thus, the ester polymers usually contain at least about 40 weight percent, often at least about 60 weight percent, and preferably at least about 80 weight percent polymeri2ed, olefinically unsaturated carboxy~ic acid ester monomers other than the above described functional monomers. Presently preferred ester monomers are esters of olefinically unsaturated mono- and polycarboxylic acids having 4-17 carbon atoms, and hydroxy-, amino-, or thio-substituted or unsu~stituted alcohols, amines, dnd thiols having from 1 to about 30 - 1 2~ 770~3 carbon ~toms, preferably 1 to about 20 carbon atorns, per molecule. Illustrat1vc unsaturated carboxyl1c ac1ds are acryllc, methacryllc, fumaric~ maleic, itaconlc, etc. Illustrative hydroxy-, am~no-, and ~hio-substituted alcohols, amines, and thiols are glycerol, l-hydroxy-5- thiododecane, 2-amino-S~hydro-~yhexane, etc. Presently preferred est~rs, due pr~marily ~o cost and ava~lab11~ty, are hydroxy-substituted and unsubstituted alcohol esters ofacrylic and methacrylic acids such a butyl acrylate, 2-ethylhexyl acrylate, methyl me~hacryla,e, hydroxy-ethyl acrylate, etc.

A varie~y of olefinically unsaturated carboxylic acid ester monomers, as well as a variety of other polymerizable olefinically unsaturated monomers useful for the manufacture of pressure sensitive adhesive polymers, and the interrelationsh~p of these monomers to polymer Tg tglass transition temperature) are dlscussed in the Handbook of Pressure-Sensitive Adhesive Technology, Yan Nostrand-Reinhold Company, New York, 1982 particular1y at pages 298 through 329.

The principal character-istic of pressure sensitive adhesives based on such carboxylic acid ester homo- or interpolymers is the low glass transition temperature (Tg) which can be achieved, in some instances, with carboxylic acid ester homopolymers but is usually obtained by polymer-izing "hard" ester monomers with suitable proportions of "soft" ester monomers to form a polymer having the Tg best suited to the particular application. So called "hard" monomers are those which produce homo-polymers having relatively high Tgs, while "soft"
monomers are those which form homopotymers having .~

- 13~ 1~7'7~33 relatiYely low Tgs. For lnstance, ~crylate monomers are typlcally "softer" than the correspond~ng methacryl~c acid esters. Thus, polyethyl acrylate has a Tg of -22 C. while polyethyl methacrylate has a Tg of 65 C. The ~9 of poly-n-butyl acrylate ls -54 C. as compared to ~ Tg of 20 C. for poly-n-butyl ~ethacrylate.
n-butyl acrylate, 2-ethylhexyl acrylate and n-octyl acrylate are commonly employed "soft" monomers while various methacrylates, including methyl, isopropyl, n-butyl, and t-butyl methacrylate, are typical "hard"
monomers.

The Tg of any homopolymer can be readily determined, and the Tg of an interpolymer of two or more such monomers can be predicted, roughly, from the respective T~s of each of the monomers involved. The most exact method of determining the glass transition temperature of the selected interpolymer of any combination of monomers iS9 of course, measurement of the Tg of that interpolymer per se. The homo- and interpolymers useful in the pressure sensitive adhesives of this invention typically have Tgs of about 0 C. or less, preferably about -10 C. or less.
Polymers having lower Tgs are particularly preferred for use as low temperature pressure sensitive adhesives which generally have T~s on the order of about -40 C. or less. Thus, the useful polymers will generally have Tgs within the range of about _80D to about 0 C., preferably about -60 to about -10 C.
The described functional monomers and olefinically unsaturated carboxylic acid ester monomers can constitute the total composition of this polymer class, or the portion of the polymer molecule not accounted for by those two monomer classes can be ~ ~t7~ 3 any polymeriz~ble, otefinically unsatur~ted monomer or combinat~on of such monomers. IllustratiYe of other poly~er~able monomers are vinyl esters of carboxylic ac~ds, the ac~d moiety of which contains from 1 to about 20 carbon atoms (e.g., vinyl acetate, vinyl propionate, vinyl isononanoate); aromatic or aliphatic, alpha beta-unsaturated hydrocarbons such as ethylene, propylene, styrene, and vlnyl toluene; v1nyl halides such as vinyl chloride and vinylidene chloride; olefinically unsaturated nitriles such as acrylonitrile; and olefinically unsaturated carboxylic acids having up to 10 carbon atoms such as acrylic, methacrylic~ crotonic, itaconic, and fumaric 15 acids, and the like.
The conjugated diolefin polymers typically contain about 0. 5 to about 50 weight percent of one or more vinyl aromatic monomers and about 50 to about 99 weight percent of one or more conjugated diolefins having 4 to about 8 carbon atoms. These copolymers may be either random or block interpolymers. Illus-trative alkenyl aromatic monomers include styrene, alpha-methylstyrene, p-methylstyrene, chlorostyrene, methyl-bromostyrene, etc. Illustrative conjugated diolefin monomers include butadiene~ isoprene, etc.
The alkenyl aromatic monomer is preferably present at a concentration of about 5 to about 70 weight percent, most preferably about 20 to about 50 weight percent, while the conjugated diolefin monomer is typically present at a concentration of about 30 to about 95 weight percent~ most preferably about 50 to about 80 weight percent.

As in the case of the olefinically unsaturated carboxylic acîd ester polymers discwssed above, the conjugated diolefin polymers can contain ~ t7~

various other monomers, in addition to the above descrlbed functional monomers, such as the vinyl esters of carboxylic acids, mono-olefins, olefinically unsaturated nitriles, olefinically unsaturated carboxylic acids~ etc., discussed above with regard ~o the olefinically unsaturated c~rboxylic ac1d ester interpolymers. Furthermore, the conjugated diolefin polymers can contain up to about 40 weight percent~
typically up to about 20 weight percent, of olefinically unsaturated carboxylic acid ester monomer units such as those described above for use in production of the useful carboxylic acid ester interpolymers.

The olefin ester polymers typically contain about 1 to about 40 weight percent of a C2 4 monoolefin monomer, from about 60 to about 99.5 weight percent of a C2 8 alkenyl or alkenol ester of a C1 12 saturated carboxylic acid and about 0.5 to about 10 weight percent of a functional monomer as described above. Preferably, the monoolefin monomer is present in an amount from about 1 to 25 weight percent, most preferably from about 10 to 15 weight percent. Illus-2~ trative mono-olefins are ethylene, propylene and butylene, with ethylene being preferred.

The ester component of the olefin ester polymers is preferably a C2 8 alkenyl or alkenol ester of a C1 12 saturated carboxylic acid. Illustrative C2 8 unsaturated alcohols and diols which can be reacted with C1 12 saturated carboxylic acids to form reactive esters are C2 8 alkenols suoh as propenol, butenol, pentenol, hexenol, heptenol and octenol and their diol homologues. Suitable saturated acids include formic, acetic, propionic, butanoic, valeric, caproic, heptanoic and octenoic acids~

! !

~ 1 6~ 70t33 The most common of the foregoing esters are v~nyl acetate, v~nyl proploniate, and vinyl butanoate.

The alkenyl ether polymers ~ypically conta~n at least about 30 weight percent, preferably at least about 50 weight percent~ polymerized alkenyl ether mono~er units in which the alkenyl group has at least 2 carbon atoms, typically 2 to about 10 carbon atoms, and the alcohol (hydrocarbyl-oxy) group has from 1 to a~out 10 carbon atoms. Illustrative are methylvinyl ether, n-octyl-1- propenyl ether, 2,4-dimethylbutyl-2 -hexenyl ether, vinylphenyl ether, etc.

The polymers encompassed by the four general classes described above can contain minor amounts, e.g. up to 30 weight percent, of one or more additional monomers, and they can be grafted or reacted with other chemical agents to modi~y their che~ical composition. Thus, the polymers of groups ~1) and (3) may contain minor amounts of substituted and unsubstituted monoolefin monomers such as ethylene, isobutylene, chlorobutenes, acrylonitrile, vinyl ethers, alkenyl esters of saturated carboxylic acids, etc. The conjugated diolefin polymers (group 1) may also contain olefinically unsaturated carboxylic acid ester monomers, and the olefinically unsaturate~ acid ester polymers (group 3) may contain conjugated diolefin and/or alkenyl monoaromatic monomers. Similarly, the alkenyl ester polymers of group (2) and the alkenyl ether polymers of group (4) can contain substituted and/or unsubstituted conJugated diolefins, alkenyl aromatics, olefinically unsaturated carboxylic acid esters, etc.

It has been found that minor amounts of olefinically unsaturated mono- and polybasic carboxylic ~17-ac~ds and/or sulfoalkyl esters of such carboxylic acids significantly improve cohesive strength of the PSA polymers. Thus, it is presently preferred that the polymers contain at least about 0.1 weight percent, usually about 0.1 to about 10 weight percent, and preferably about 0.1 to about 5 weight percent of a polymerizable, olefinically unsaturated carboxylic acid having up to about 10 carbon atoms and/or a 1~ sulfoalkyl este~s of such acids~ e.g. sulfoethyl methacrylate, sulfoethyl itaconate~ sulfo~e~hyl malonate, etc.

Although the polymers can contain other "functional" monomers such as N-methylol amides, e.g., N-methylol acrylamide, it has been found that such other functional monomers are not essential to achieving acceptable adhesive properties and that the detriment associated with the presence of such mcnomers, such as formaldehyde release upon curing, loss of tack and adhesion, etc., can be avoided by minimizing the concentration of such N-methylol amides or eliminating them altogether. Thus, the preferred polymers contain less than about 1 percent, preferably less ~han about 0.5 percent, and mos~ preferably no amount of N-methylol amide monomer units.

It also has been found that suitable adhesive properties can be achieved without crosslinking or hardening agents such as aldehyde hardeners (e.g., formaldehyde, mucochloric acid, etc.~, crosslinking catalysts such as the strong base catalysts discussed by Bartman in U.S. Patent 4,408,018, acid catalysts such as phosphoric or ; 35 methane sulfonic acid, complexing agents such as metals and metal compounds and complexes, or reactive monomers (e.g., glycols, polyamides, etc.). Since ~7~ 3 such hardening 3gents ~ncrease the complexlty and expense of polymer manufacture9 they are not requ~red to obtain the necessary pressure sensitive propert~2s with the polymers o~ this invention, and~ in many instances, the lncorporation of such "harden~ng"
agents impairs other desirable PSA properties such as tack and adhesion, the preferred polymers are substantially free of such hardening agents or their residues. Nevertheless, minor amounts of such materials can be present.

Polymer molecular weight can have a significant effect on the balance of pressure sensitive adhesive properties in polymers of a given rnonomer cDmposition, i.e. polymers of identical monomer content. Thus, as discussed in the Handbook of Pressure Sensitive Adhesive Technology, for instance at pages 307-311, shear resistance is roughly proportional to molecular weight up to relatively high molecular weights at which shear resistance drops off dramatically in some polymers. Tack is typically high at very low molecular weights and decreases gradually as molecular weight is increased after a molecular weight value yielding optimum tack is exceeded.
Adhesion typically exhibits discontinuous behavior, increasing with molecular weight up to moderate molecular weight levels and then gradually decreasing as molecular weight is increased further. The polymers useful in the adhesives of this ~nvention typically have number average molecular weights of at least about 10,000, generally within the range of about 10,000 to about 1,000,000 as determined by gel permeation chromatography. Such polymers have relatively hi~h shear values and a favorable balance of other properties including peel value and tack.
Thus, the adhesives typically have shear holding 7~)a3 - 1 g -values of at least about 20 minutes, typically at leas~ about 50 min tes, and, in high shear formulat10ns, as much as 19000 minut~s or more measured at 75 F.
under 500 gram loading as described hereinafter. Peel values are generally at least about 1.5, most o~ten at least about 1.8, and preferably at 1east about 2 pounds per inch width. Yet the hlgh shear and peel values of these pressure sens~tive adhesives are not achieved at the expense of significant, if any, loss o~ tack. Thus, the polymers generally have loop tack values of at least abou~ 0.8. pounds per half inch width, i,e., they exhibit loop tack approximately equivalent to, and sometimes even higher than, the loop tack exhibited by otherwise identical polymers not containing the described functional monomers under otherwise identical conditions (monomer content, molecular weight, etc.) For the purposes of this disclosure, shear strength, peel adhesion, and loop tack are determined as described hereinafter in the illustrative examples unless otherwise specified.

Many of the polymers useful in this invention exhibit sufficient tack for many PSA
applications without added tackifiers, although the conjugated diolefin polymers generally require tackifiers to posses tack sufficient for many applications. Illustrative of polymers which are usuàlly employed with tackifiers are conjugated diolefin polymers and their interpolymers, such as polymers and interpolymers of isoprene, butadiene, etc. in the presence or absence of other monomers, e.g. styrene. On the other hand, the polyalkenyl ether and olefinically unsaturated carboxylic acid ester polymers, and interpolymers of olefins and alkenyl carboxy7ic acid esters usually exhibit t7()~33 sufflc~ent tack~ 1n the absence of tackifiers, to be useful as pr~ssure sensitive adhesiYes. Nevertheless, adhesives based on such polymers also may contain 5 compatible tackifiers to provide increased ~ack ~f des i red .

The adhesives may contain very minor amounts of tackifiers to increase tack on1y slightly, or they may contain up to 150 weight parts or more of tackifier per 100 weight parts of one or more of the described polymers. Suitable tackiFiers include rosins, hydrogenated rosins, esters of such rosins, synthetic hydrocarbon tacki~iers and low molecular weight and low Tg polycarboxylic acid esters. Typical rosins and hydrogenated rosin ester tackifiers have ring and ball softening temperatures of about 25 C.
to about 115 C., while preferred tackifiers have softening temperatures of about 50 C. to about 110 C. Useful hydrocarbon tackifiers may be manufactured from C9 aromatic monomers or from C5 aliphatic monomers and mixtures of such aromatic and aliphatic monomers.
Such monomers are usually derived from the so called Cg and C5 cuts in the fractîonation of crude oil or similar material. Such -synthetic hydrocarbon tackifiers generally have ring and ball softening temperatures of about 10 C. to about 100 C. The polycarboxylic acid ester tackifier resins are polymerized from ore or more monomers such as acrylic acid which is substituted or unsubstituted with alkyl or alkoxyl radicals having one to four carbon atoms or with alkyl or alkanol esters of such acids in which the alkyl or alkanol moiety has from one to about six carbon atoms.

~he useful polymers can be prepared by free radical solution and emulsion polymerizat;on methods ~7~7(3~33 known in the ar~ ~ncludlng batch, cont~nuous andsemicontinuous procedures. For the purposes of this d~sclosure, free rad~cal polymerizat~on methods are 5 ~ntended to include radiation polymerization techniques.
Illustrative free-radical polymerization procedures suitable for preparing aqueous polymer emulsions involve gradually adding the monomer or monomers to be polymerized simultaneously to an aqueous reaction 1~ medium at rates proportionate to the respective percentage of each monomer in the finished polymer and initiating and continuing polymerization with a suitable free radical polymerization catalyst.
Optionally, copolymers can be obtained by adding one or more comonomers disproportionately throughout the polymerization so that the portions of the polymers formed during the initial polymerization stage comprise a monomer composition differing from that formed during intermediate or later stages of the same polymerization. For instance, a styrene-butadiene copolymer can be formed by adding a greater proportion or all of the styrene during the initial polymerization stages with the greater proportion of the butadiene being added later in the polymerization.

Illustrative free-radical catalysts are free radical initiators such as hydrogen peroxide, potassium or ammonium peroxydisulfate, dibenzoyl peroxide, lauroyl peroxide, ditertiarybutyl peroxide, 2,2'-azobis-isobutyronitrile, etc., either alone or together withone or more reducing components such as sodium bisul-fite~ sodium me~abisulfite, glucose, ascorbic acid, erythorbic acid, etc. Ultrav;olet ~UV) and electron beam polymerization methods suitable for initiating free radical polymerization are discussed in the Handbook of Pressure-Sensitive Adhesive Technology, 70~33 partlcularly at pag2s 586-604 and the references c~ted therein. The reaction is continued w1th ag1tat1On at a temperature suff~clent to maintain an adequate reactlon rate unti1 most or all monomers are consumed.
Mono~er addition is usually contlnued unt11 the latex reaches a polymer concentration of ~bout 20 to about 70 wei~ht percent.

Physical stability of the dispersion usually is achieved by providing ln the aqueous reaction medium one or more nonlonic, anionic, and/or amphoteric surfactants including copolymerizable surfactants such as sulfonated alkylphenol polyalkyleneoxy maleate and copolymerizable stabilizers such as sulfoethyl meth-acrylate, alkenyl sulfonates, etc.~ I11ustrative of nonionic surfactants are alkylpolyglycol ethers such as ethoxylation products of lauryl, oleyl, and stearyl alcohols or mixtures of such alcohols as coconut fatty alcohols; alkylphenol p~lyglycol ethers such as ethoxyla-tion products o~ octyl- or nonylphenol, diisopropylphenol, triisopropylphenol, di- or tritertiarybutyl phenol, etc. Illustrative of anionic surfactants are alkali metal or ammonium salts of ~lkyl, aryl, or alkylaryl sulfonates, sulfates, phosphates, phosphonates, etc.
Examples include sodium lauryl sulfate, sodium octyl-phenol glycolether sulfate, sodium dodecylbenzene sulfonate9 sodium lauryldiglycol sulfate, and ammonium tritertiarybutylphenol penta- and octa-glycol sulfates.
Numerous other examples of suitable ionic, nonionic and ~mphoteric surfactants are disclosed in U.5.
Patents 2,600,831, 2,271,622, 2,271,623, 2,275,727, 2,787,604, 2,816,920, and 2,739,891.

Protective colloids may be added to the aqueous polymer dispersions either during or .fter the 7 ~3 reaction per~od. Illustrat~ve protect~ve colloids include gum arablc, starch, alginates, and modified natural substances such as methyl-, ethyl-, hydroxyalkyl-, and carboxymethylcellulose, and synthetic substances such as polyvinyl alcohol, polyvinyl pyrrolidone, and mixtures of two or more o~ such substances. F~llers and/or extenders such as d~spersible clays, and colorants, such as pigments and dyes, can also be added to the aqueous dispersions either during or after polymerization. Those skilled in the art of emulsion polymers will appreciate that protective colloids9 tackifiers, and other additives should be compatible with the polymer emulsion to assure formation of a stable dispersion.
The emulsions typically contain about 20 to about 70 percent polymer as manufactured, while preferred latexes typically have solids contents of about 40 to about 60 weight percent polymer solids.
The dispersed polymer particles can be of any size suitable for the intended use, although particle sizes of at least about 100 nanometers are presently preferred. Most often, the described latexes will have particle sizes within the range of about 100 to about 1000 nanometers as determined on the model N-4 or the "Nanosizer" available from Coulter Electronics, Inc., of Hialeah~ Florida.

Solutions of the useful polymers can be prepared by polymerizing the selected monomers as described above in solvents in which both ~he monomers and the polymers are soluble. Suita~le solvents include aromatic solvents such as xylene and toluene, alkanes such as hexane, and alcohols such as butanol.
Polymerization initiators and reducing components, when employed, should be soluble in the selected 7'70~33 -2q-solvent or mixture of solvents. Illustrative free radical initiators soluble in the noted organic solvents include dibenzoyl peroxide, lauroyl peroxide, and 2,2'-azobislsobutyronitrile. Erythorblc and ascorbic acids are illustrative of reducing components soluble In polar organic solvents.

Hot melt adhesives containing the described polymers can be obtained by procedures and with form-ulations known in the art to be suitable for the form-ulation of pressure sensitive adhesives of such polymers which do not contain the described functional monomers. For instance, the useful polymers can be separated from their solutions by evaporation of the solvent; and they can be separated from water based emulsions by evaporation of water, coagulation with strong acids and/or multivalent metal ions~ e.g.
calcium, aluminum, magnesium, etc, or by subjecting the emulsion to one or more freeze-thaw cycles. The coagulated polymer is then filtered from the aqueous phase and dried prior to compounding~

Typically, the compounded hot melt adhesives will contain about 10 to about 98 weight percent, generally about 15 to about 90 weight percent of one or more of the described polymers in the presence or absence of other polymers, tackifiers, antioxidants, wa~es or oils and optional additives such as colorants and fillers. The higher polymer concentrations wîthin these ranges generally are employed only with polymers which themselves ~re normally tacky~ such as the homo-polymers and copolymers of olefinically unsaturated carboxylic acid esters, ole~in-alkenyl carboxylate copoly~ers~ and alkenyl ether polymers. Other of the useful polymers which are no~ normally tacky, and which therefore require significant amounts of tacki-~770~3 - 2 s ~

fiers, are usually employed dt lower concentrations of about 10 to ~bout 60, generally about 15 to about 50 weight percent; the remainder of the hot melt formu lation comprising t~ckifiers in the presence or absence of other addit~ves9 e.g. ant~ox~dants, wa~es~
oils, fillers, etc. The use of waxes and o11s in the described adhesives usually is undesirable due to the detrimental effects such materials may have on adhesive tack. Howevert small amounts of such materials can be employed, usually to reduce melt viscos~ty. Those skilled in the art of pressure sensitive adhesives will, of course, recognize that the tackifier or tackifiers, when employed, should be compatible with the selected polymer or polymers to ensure homogenity in the final hot melt formulation.

The hot melt adhesives can be compounded by mixing the selected polymer or polymers, antioxidants and optionally fillers in a jacketed mixing kettle, such as a heavy duty mixer of the Baker-Perkins or Day mixer type, equipped with rotors and operated at temperatures of about 200 to about 350 F., the precise temperature employed depending on the melting point of the polymers selected. After complete melting has occurred, the tackifiers are added and mixing is continued. Waxes and/or oils, when employed, are usually added toward the end of the mixing cycle after which mixing is continued until a smooth, homogeneous composition is obtained. The resulting hot melt composition can be drawn off and used im~ediately in hot pots, or it may be shaped or cast into any desired form for a later use.

The pressure sensitive adhesives can be applied to any backing which it is desired to adhere to another surface or article. Illustrative backings ~ 3 ~nclude flexlble and r~g~d, natural ~nd synthet1c ~ater~als such as plast~cs, elastomers. solld metals and foils, ceramlcs (tlles, glass~ etc.), wood, papers and cardboard, leather mater~als, etc. of essent1~11y any for~ ~ncludlng films, solld artfcles, woven and non-woven textile mater~als, etc. Illustrat~ve uses of such articles ~nclude wal1 coverings (paper, ~abr~c, films, etc.), upholstery ite~s, constructlon roo~ing and siding materials, tapes of al1 varieties ~includ~ng those having backings comprised of woven or non-woven ~abrics9 paper9 polymeric films, metal foils~ foams, etc., including doub1e ~aced tapes and so called transfer tapes), packaging, floor and wall tile and other floor and wall cover~ngs, panel~ng, etc.
Suitable backinq and substrate materials can be of essentially any chemical composition and Include metals. ceramics (including all varieties of glass), and natural and synthetic polar and non-polar materials such as polyolefins, e.g. homopolymers and ~nterpolymers of substituted and nonsubstituted olefinically unsaturated hydrocarbons including ethylene, propylene, styrene, butadiene, dicyclopentadiene, etc., and materials which typically contain polar functional groups such as hydroxy, etheral, carbonyl, carboxylic acid (including carboxylic acid salts), carboxylic acid esters (including thio esters), amides, amines, etc. Essentially all natural materials include one or more polar functional groùps. Illustrative are virgin and reclaimed cellulosic fibers such as cotton, paper, wood, coconut fiber, jute, hemp~ etc., and protenaceous materials such as leather, wool, and other animal fur~ IllustratiYe synthetic materials containing polar functional groups are polyesters, polyamides, carboxylated styrene-butadiene polymers, etc., such as Nylon-6, Hylon-66, Nylon-610, "Dacro*n'', "Fortrel"? "Kodel", "Acrilan~9 "Orlon~', "Creslan"p "Verel" and "Dynel". Illustra~ive o~ other use~ul Trademark 1 ~d~7~383 polar materials are synthetic carbon, silicon, and magnes~um sllica~e (e.g., asbestos).

The adhesive compositions may be applied tu the backing by any one of a variety of conventional coating ~echniques such as roll coating, spray coating, curtain coating, etc. They also may be applied to the backing without modification by extrusion coating, coextrusion, hot melt coating, etc., by employing suitable conventional coating devices known for such coating methods. While primers may be employed to pretreat the backinq, they are unnecessary in many applica~ions. Dry coating weight (the weight of dry adhesive applied per unit surface area) can vary substantially depending upon the porosity and irregularity of the backing and of the substrate surface to which the backing is to be adhered, and other factors. For instance~ higher polymer loadings are preferred for adhering porous, irregular ceramic tiles to porous surfaces, while lower adhesive loadings are usually required to manufacture tapes, films, and other articles from relatively non-porous, smooth-surfaced materials such as synthetic polymer films and sheets. When the adhesive is applied to non-porous polymeric or metallic substrates intended for adhesion to non-porous polymeric or metallic surfaces, adhesive loadings of about 5 to about 50 pounds of dry adhesive per 3,000 square feet of treated surface are generally adequate. Adequate adhesion in tapes manufactured from continuous sheet polymeric substrates can usually be achieved with dry coa~ing adhesive weights of about 10 ~o about 20 pounds per 3,000 square feet o~ treated surface, while coating weights of 20 to about 40 pounds per 3,000 square feet are usually employed for paper-backed tapes such as masking tapes.

~77~)83 - 2 ~ -The invention Is further described by the following ~xanlples which are illustrative of specific modes of practic~ny ~he invention and are not intended as limlting the scope of the invention as defined by the appended claims.

TEST STANDARDS
. _ Test samples are prepared by applying to a 1-mil mylar backing a film of adhesive latex, solution or melt which, when cured, forms a 1-mil adhesive layer. Hot melts are applied hot, drawn down to about 1-~il films and cooled. Solution polymers are applied 15 in somewhat thicker layers and oven dried for a peri~d sufficient to evaporate the solvent. Emulsion polymers are also appl ied in layers slightly thicker than 1-mil and are dried at 150 F. for 20 minutes, covered with a release liner and aged 24 hours at 73 F. and 50 percent relative humidity.
Shear strength is determined in accordance with ASTM D3654 78, PSTC-7 and is a measure of the cohesiveness (internal strength) of an adhesive.
~"PSTC" designates the Pressure SensitiYe Tape Council) It is based on the time required for a static loaded tape sample to separate from a standard flat surface in a direction essentially parallel to the surface to whi~ch it has been affixed with a standard pressure.
Each test is conducted on an adhesive coated strip applied to a standard stainless steel panel in a manner such that a one-half ineh by one-half inch portion of the strip is in firm contact ~ith the panel with one end portion of the strip being free. The steel panel, with coated strip attached, is held in a rack such that the panel forms an angle of 178 to 180 with the extended tape free end which is then 7~)~3 tens~oned by appl~cat~on of a force of 500 grams appl~ed ~s ~ hang~ng weight from the free end of the test strip. The elapsed t~me required for each test strip to separate from the test pane1 at 73~ F ~s recorded ~s shear s~rength.

Peel adhesion is determined in accordance with ASTM ~-3330-78, PSTC-1 and ~s a measure of the I0 force required to remove a coated, flexible sheet material fro~ a test panel at a speeific angle and rate of remova1. Unless otherwise specified, the values for peel adhesion reported hereln are force values expressed as pounds per inch width of coated ~est sheet mater~al determ~ned at 73 F. by the following procedure, A one-~nch width of the coated sheet is applied to a horizontal surface of a clean, stainless steel test plate with at least five lineal inches of the coated sheet material in firm contact with the steel plate. A hard rubber roller is used to firmly apply the strip and remove a71 discontlnui~ies and entrapped air. The free end of the coated strip is then doubled back nearly touching itself so that the angle of removal of the strip from the steel plate will be 180. The free end of the test strip (the one pulled) is attached to the adhesion tester scale (an Instron tensile tester or Harvey tensile tester). The test plate is then clamped in the jaws of the tensile tes`ting machine capable of moving the plate away from the scale at a constant rate of 12 inches per minute.
The scale reading in pounds is recorded as the tape is peeled from the steel surface.

Loop tack is a measure of the force required to remove a standard adhesive coated Mylar film loop from a standard ~P5TC) stainless steel plate at 73 F.
after only nominal contact of the test strlp with the Txademark ~ t~3 steel plate ~n the absence of s~gn~ficant pressure. A
one-half by four-~nch strip of one mil Mylar film coat2d with the sa~ple adhesive ls formed into a loop with the adhes~ve side out, and the loop is appl~ed to a stainless steel plate until the tape loop contac~s 0O5 square inch of surface area on the pla~e. The loop is retracted from the plate at a rate of 12 inches per minute, and loop tack is defined as the force observed when the final portion of the adhesive strip separates from the test plate. Specifically, the steel test plate is inserted in the 70wer jaws of an Instron tensile tester while the upper portion of the loop is clamped in ~he upper jaw of the ~ester and is moved downward toward the test plate at a rate of 12 inches per minute~ When the ~est loop has contacted 0.5 square inch of te~t plate area, the direction of travel of the upper jaw of the Instron tester is reversed and set to remove the loop from the plate at a rate of 12 lineal inches per minute.
"Twenty degree hold strength to corrugated board" is a measure of combined peel and shear strength of the adhesive mounted on 1-mil Mylar film when applied under standard force to a corrugated cardboard substrate. Samples of adhesive coated Mylar are applied to a standard corrugated cardboard substrate such that a one and one-half inch length of the adhesive coated film adheres to the corrugated surface of the test substrate with the one and one-half inch edge of the sample tape aligned parallel to the corrugated flutes (ridges) of the substrate. After application of the film to the substrate in this manner, the film portion contacting the substrate is rol1ed down with a standard four and one-half pound rubber-covered roller one time parallel to the one and one-half inch edse cf the test tape at a roller spe~d 77~)83 of 12 ~nches per minute. The sa~ple i5 then mounted in a shear test block set at an angle of 20 to the vertical so that the ~tai1" of the adhesive test strip (the portiDn of the test tape not adhered to the corrugated substrate) is hanging down from the bottom portion of the corrugated board at an angle of 160 to the plane of the corrugated board. A 500 gram weight is then affixed by appropriate clamps to the "tail end" of the test strip so that the weight is hanging at an angle of 160 from the portion of the test strip bonded to the corrugated board. A timer ~s started immediately upon application of the 500 gram weight to the test strip, and hold value is reported as the number of minutes required for the weight to tear the test strip from the corrugated backing at a temperature of 73 F.

A water based emulsion of an acrylate polymer containing 98.5 weight percent butyl acrylate and 1.5 weight percent methacrylic acid can be prepared by free radical polymerization of the premixed monomers in the presence of water, surfactants and catalysts in an agitated reactor. The monomer premixture is ~ormed by blending 862 grams butyl acrylate, 13 grams methacrylic acid, and 0.1 gram of chain transfer agent. The catalyst premixture can be formed by dissolving 4.0 grams of sodium persulfate in 114 grams deionized water, and the reactor is then charged with 690 grams deionized water~ 20 grams of an alkylphenoxy poly(ethyleneoxy) ethanol surfactantD 2.5 grams of a sodium alkyl sulfonate surfactant, and 50 grams of the monomer ~remixture. This reactor charge is then heated to 90 C., 10 ml. of catalyst solution is added, and the resulting mixture is agitated for 10 ~'7~ 0~3 mlnutes. Monomer prem~xture and catalyst solution additions are then commenced. Eight hundred ninety ml. of the monomer premixture is added over a period of 2 hours, and the total catalyst solut~on ~s added over a period of 2.5 hours. Thus, catalyst add~t~on is continued for one-half hour aft~r mono~er addition is discontinued. After catalyst addition is discon-tinued, the reaction phase is maintained at 90 C. for an additional 1 hour, is then cooled to 35~ C. and removed from the reactor. The pH can be adjusted to 7.5 to 8.0 with ammonium hydroxide.

The operation described in Example l can be repeated employing identical reactor feed materials and operating procedures with the exception that the monomer premixture contains 887 grams butylacrylate, 13.7 grams methacrylic acid9 and 18.4 grams of aceto-acetoxyethyl methacrylate (AAEMA) correspondin~ to a finished polymer composition of 96.5 weight percent butylacrylate, 1.5 weight percent methacrylic acid, and 2.0 weight percent AAEMA.

The polymers of Examples 1 and 2 will exhibit am~ient and low temperature peel, tack, and shear values characteristic of low temperature pressure sensitive adhesives. However, the polymer of Example 2, containing 2 weight percent acetoacetoxye~hyl methacrylate, will possess a substantially higher shear value than the polymer of Example 1 and room temperature tack comparable to that of the polymer of Example 1. The adhesive of Example 2 will evidence much less tendency to be gummy and therefore unmanageable, to creep9 or to bleed-through adhesive backings or substrates at ambient temperatures than will the polymer of Example l.

~77()83 To a 2-liter reactor equ~pped w~th heating mantle, mechanical s~irrer, reflux condenser, n~trogen sparge and three laboratory meter~ng pumps are added 140 grams of distilled water9 and the water ls sparged with nitrogen and heated to 75 C. The n1trogen sparge is then removed and a nitrogen atmosphere is maintained over the liquid phase~
A monomer pre-emulsion is formed by blending 426 grams of 2-ethylhexyl acrylate, 162 grams methyl acrylate, 12 grams of acrylic acid~ 9 grams of nonyl-phenoxy poly(ethyleneoxy)ethanol nonionic water-soluble surfactant, and 21 grams of ~ctylphenoxy poly(ethylene-oxy)ethanol nonionic surfactant in l40 grams of distilled water. Five percent of this pre-emulsion is introduced to the reactor with agitation. After stirring for 3 minutes, 0.5 gram of sodium persulphate dissolved in 10 grams of distilled water is added. A~ter a further 3 minutes, 0.5 gram of sodium metabisulfite is added, and the mixture is held at 75~ C., for 20 minutes.
The remainder of the monomer pre-emulsion is then added gradually over a period of 3 hours through one of the metering pumps provided. The catalyst solutions are added through the two remaining metering pumps and concurrently with monomer emulsion addition. One catàlyst solution contains 1.5 grams of sodium persulphate dissolved in 75 grams of distilled water) and the other contains 1.5 grams of sodium metabisulphite dissolved in 75 grams of distilled water. These catalyst solutions are added gradually at a rate such that they are metered into the reactor o~er a period of 3.5 hours. Monomer addition is discontinued 1/2 hour before catalyst addition is discontinued, and polymerization temperature is maintained at 75~ C.

throughout the run. After all of the sodium persulphate and sod~um metabisulphite solutions have been added, the reaction mixture is held for an additional 30 minutes at 75 C. and is then cooled to rosm temperature~
The resulting latex is neutral ized to a pH between 4 and 6.5 with either 7 percent ammonia or 10 percent sodium hydroxide in distilled water. The resulting latex is tested by the procedures described above and is found to have a peel value of 6 pounds and evidences cohesive failure, a loop tack of 1.3 pounds, and a shear value of 100 minutes. Cohesive failure is evidenced by tearing or separation of the adhesive itself, with the separated portions of the adhesive remaining adhered to their respective substrates.
These results are summari~ed in Table 2 which follows Example 5.

The operation described in Example 3 is repeated with the exception that the monomer pre-emulsion contains 426 grams 2-ethylhexyl acrylate, 156 grams methyl acrylate, 12 grams acrylic acid, and 6 grams o~ acetoacetoxyethyl methacrylate ~AAEMA).
Surfactant compositions and operating procedures are as defined in Example 3.

The resulting latex is tested by the procedures described above and has a peel value 3.~ pounds per inch width (evidencing adhesive faiJlure) 9 a loop tack of 1.2 pounds per 1/2 inch width, and a shear value of 186 minu~es. Although this adhesive has a peel strength lower than that obtained in Example 3, its loop tack is essentially equivalent, and its shear strength is substantially higher. These results are summarized in Table 2.

The operation descr~bed 1n Example 3 is again repea~ed with ~he exseption ~hat the monomer pre-emulsion contains 426 grams of 2-ethylhexyl acrylate, 150 grams methyl acrylate, 12 grants acrylic acid, and 12 grams AAEMA. Surfactant compos1tion and concentration and op~rating conditions are otherwise as defined in Example 3.
This product ~s tes~ed by the procedures de-scribed above and has a peel value of 2.6 pounds per inch width (evidencing adhesive failurè), a loop tack of 1.1 pounds per 1~2 inch width and a shear value of 1,866 minutes. These results demonstrate an l8-fold increase in shear value over the adhesive of Examp1e 3 with little or no loss in loop tack.

TA8LE_2 MONOMERS~ ~
Ex.No. 2-EHA MA AA AAEMA PEEL TACK SHEAR
. . .
3 71 27 2 0 6 1.3lOO
4 71 26 2 1 3.2 1.2186 71 25 2 2 2.6 l.l1,866 A latex can be prepared by the procedures described in Example 3 employing a monomer pre-emulsion containing 582 grams (97 weight percent~ butyl acrylate, 18 grams (3 weight percent) acrylic acid, 0.1 weight percent of a sodium salt of sulphated nony1phenoxy poly(ethyleneoxy)ethanol surfactant, and 1.5 weight percent of the octyl phenoxy sur~actant described in Example 3.

~77 The operation descr~bed in Example 6 car be repea~ed with the exception that the msnomer compositiDn in the pre-emulsion contains 576 grams (96 weight percent) butyl acrylate, 18 grams (3 weight percent) acrylic acid, and 6 grams (1 weight percent) AAEMA
with all other compositions and operating conditions remaining the same. The resulting adhesive will have significantly higher shear strength than will the adhesive of Example 6 with little or no loss of tack.

EXAMP~E 8 The operation of Example 6 can be repeated employing a monomer pre-emulsion contai ni ng 582 grams 2-ethylhexyl acrylate and 18 grams acrylic acid corre-sponding to a polymer composition of 97 weight percent 2-ethyl hexylacrylate and 3 weight percent acrylic acid, with surfactant compos~tions and operating conditions otherwise remaining the same.

The operation described in Example 6 can be repeated with the exception that the monomer content of the monomer pre-emulsion corresponds to 576 grams 2-ethylhexyl acrylate, 18 grams acrylic acid and 6 grams AAEMA resulting in a polymer containing 96 weight percent 2-ethylhexyl acrylate, 3 weight percent acrylic acid, and 1 weight percent AAEMA. This polymer will have significantly higher shear than the polymer obtained in Example 8 with little or no loss in tack.

~3 The operation described in Example 6 can be repeated with a monomer pre-emulsion having a monomer content of 291 grams butyl acrylate, 2g1 grams 2-ekhyl~
hexyl acrylate, and 18 grams acryl~c acid corresponding to a polymer compositior of 48.5 we~ght percent butyl-acrylate, 48.5 weight percent 2-ethylhexyl acrylate, and 3 weight percent acrylic acid.

The operation described in Example 6 can be repeated employing otherwise identical compositions and conditions with the exceptinn that the monomer pre-emulsion contains 288 grams butyl acrylate, 288 grams 2-ethylhexyl acrylate, 18 grams acrylic acid~
and 6 grams AAEMA corresponding to a polymer com-position of 48 weight percent butyl acrylate, 48 weight percent 2-ethylhexyl acrylate, 3 weight percent acrylic acid, and 1 weight percent AAEMA. The result-ing polymer will have significantly higher shear than the polymer of Example 10 with little or no loss of tack.

An N-methylolacrylamide-containing polymer can be obtained by the procedure described in Example 6 with the exception that the monomer pre-emulsion contains 288 grams butyl acrylate, 288 grams 2-ethylhexyl acrylate, 18 grams acrylic acid and 6 grams ~-methylolacrylamide with all other operating condi~ions and surfactant composi~ions being the same as described in ~xample 6. The resulting polymer witl 7 ~ 3 con~in 48 ~e19ht percent butyl acrylate, 4~ we1ght percent 2-ethylhexyl 3crylate, 3 weight percent acrylic acid, and 1 weight percent H-methylolacrylamide.
Th~s polymer will have s~gn~cantly h1gher cohes~ve (shear) strength than the polymer descrfbed ~n Example 10 and peel and tack values substantially lower th~n the peel and tack values of the polymer obta1ned in Exa~ple 11.

. .
A styrene--butadiene-acrylic acid polymer can be prepared by adding to a pressure reaceor 67 we~gh~
parts water, 8.3 weight parts Polystep RA 35 S surfactant ~thc sodium salt of a sulfonated nony1phenol polye~hyl-eneoxy maleate available from Stepan Chem~cal Company, Northfield, Illinois), 2.5 weight parts acrylic acid, 0.2 weight parts tetrapo~assium pyrophosphate and 0.83 weight parts sodlum hydroxide with continuous agitation.
2 weight parts dodecyl mercaptan dissolved ~n 30 weight parts styrene is added, and 67.5 weight parts butadiene is then introduced. Reaction is initiated by introduction of 8.3 weight parts of a 4 weight percent solution of potassium persulfate, reactor temperature is brought to 100 F., 0.002 9. sodium ferric ethylenediamine tetracetate i5 added, and polymerization is continued for 1 hour dt 100 to 115 F. Reaction temperature is then incrementally increased over the next 6 hours to 155 F., and polymerization is continued at that temperature for an additional 24 hours. 50 weight parts of the resulting polymer latex (dry weight) is then blended with 50 weight parts (dry weight) of an aqueous emulsion of Burez Stabilized Ester 85, a pentaerythritol ester of dispropor-tionated rosin available from Tenneco Malrose Ltd., Rocklngham ~orks, Avonmouth, Bristot, Engl~nd. The Trademark 7 ~ 83 peel, shear, 700p tack and corrug~ted hold values for this adhesive can be determined by the prosedures discussed above.

The procedure described in Example 13 can be repeated with the exceptlon that 2 weight parts AAEMA
is added to the polymerization mixture along with the butadiene. Reaction conditions, polymer eomposition and tackifier blending are otherwise as described in Example 13. The peel, shear, loop tack and corrugated hold values for the product can be determined by the procedures discussed above, and it will be found to have significantly higher shear and a~ least comparable or higher peel, loop tack and corrugated hold values in comparison to the polymer of Example 13.

The operation described in Example 13 can be repeated using a monomer mixture containing 30 weight parts styrene, 69 weight parts butadiene and 1 weigh~
part itaconic acid, with all other conditions and compositions remaining the same. The resulting latex can be blended with tackifier emulsion as described in Example 13, and strength values can be determined as described above.

The operation described in Example 15 can be repeated with the exception that 1 weight part AAEMA
is added to the monomer mixture along with the butadiene.
When evaluated by the test procedures discussed above, the adhesive of this example will exhibit signi~icantly 7C)8~3 higher shear strength dnd approx~mately comparable or higher peel, loop tack and corrugated hold values in comparison to the adhesive of Example 15.

While part~cular embodiments of the inYention have been descr~bed, it will be understood, of course~
that the invention is not limited to these embodiments, since many obvious modifications can be made, and it is intended to include within this invention any such modifications as will fall within the scope of the appended claims.

Claims (44)

1. A normally tacky and pressure-sensitive adhesive composition comprising a polymer containing at least one polymerizable functional monomer of the formula:
in which R1 is a divalent organic radical of at least 3 atoms in length, R5 and R6 are independently selected from hydrogen, hydroxy, halo, thio, amino or monovalent organic radicals, and X is - CO - R4 or - CN wherein R4 is hydrogen or a monovalent organic radical, wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxylic acid ester monomers;

(4) alkenyl ether polymers comprising at least about 30 weight percent alkenyl ether monomer units, and (5) combinations thereof,

2. The adhesive composition defined in claim 1 wherein said polymer has a Tg of about 0° C.
or less and comprises about 0.1 to about 40 weight percent of said functional monomer.

3. The adhesive composition defined in claim 1 wherein said polymer has a Tg of about 0° C.
or less and said composition comprises at least about 20 weight percent of said conjugated diolefin polymer comprising at least 5 weight percent of said mono-aromatic monomer and at least about 0.1 weight percent of said functional monomer.

4. The composition defined in claim 3 wherein said aromatic monomer comprises styrene, said conjugated diolefin comprises a member selected from the group consisting of butadiene, isoprene and combinations thereof, and said composition further comprises a tackifier.

5. The composition defined in claim 3 wherein said polymer further comprises about 0.2 to abnut 10 weight percent of a member selected from the group consisting of acrylic acid, itaconic acid, and combinations thereof.

6. The composition defined in claim 1 wherein said polymer further comprises a member selected from the group consisting of acrylic acid, itaconic acid, and combinations thereof.

7. The adhesive composition defined in claim 1 wherein said polymer comprises about 0.1 to about 10 weight percent of said functional monomer.

8. The adhesive composition defined in claim 1 wherein said polymer comprises about 0.1 to about 5 weight percent of said functional monomer.

9. The adhesive composition defined in claim 1 having a shear holding value of at least about 500 minutes at 75° F.

10. The adhesive composition defined in claim 6 having a shear holding value of at least about 500 minutes at 75° F. and a loop tack value of at least about 0.8 pound per half inch.

11. The adhesive composition defined in claim 1 wherein said polymer is substantially free of polyvalent metals, compounds and complexes.

12. The adhesive composition defined in claim 1 wherein said polymer is substantially free of crosslinking agents.

13. The adhesive composition defined in claim 12 having a shear holding value of at least 50 minutes at 75° F.

14. The adhesive composition defined in claim 1 wherein R1 is a divalent organic radical 3 to about 40 atoms in length, and X is - CO - R4.

15. The adhesive composition defined in claim 1 wherein said polymer comprises at least about 0.1 weight percent of at least one functional monomer having the formula:
wherein R4, R5, and R6 are as defined in claim 1, R3 is a divalent organic radical, Y and Z are indepen dently selected from the group consisting of 0, S, and NR7, and R7 is H or monovalent organic radical.

16. The adhesive composition defined in claim 13 wherein R4 is hydrogen or alkyl having up to about 8 carbon atoms, R3 is a divalent organic radical at least 2 atoms in length, and said composition comprises at least about 20 weight percent of said conjugated diolefin polymer containing at least 5 weight percent of said monoaromatic monomer.

17. The adhesive composition defined in claim 16 wherein each of Y and Z is 0.

18. The adhesive composition defined in claim 1 wherein said polymer comprises about 0.1 to about 10 weight percent of a member selected from the group consisting of acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, and combinations thereof.

19. The adhesive composition defined in claim 1 wherein said polymer comprises less than about 1 weight percent of an N-methylolamide.

20. The adhesive composition defined in claim 1 wherein said polymer is substantially free of N-methylolamides.

21. The adhesive composition defined in claim 1 wherein said polymer comprises a polymerizable carboxylic acid monomer.

22. The adhesive composition defined in claim 1 wherein said polymer further comprises at least about 0.1 weight percent of a polymerizable acid selected from the group consisting of olefinically unsaturated carboxylic acids having up to about 10 carbon atoms, sulfoalkyl esters of said olefinically unsaturated acids, and combinations thereof.

23. A normally tacky and pressure sensitive adhesive composition comprising a polymer containing pendant functional groups of the formula:

wherein R1 is a divalent organic radical at least 3 atoms in length, and R4 is H or a monovalent organic radical, and wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxylic acid ester monomers, (4) alkenyl ether polymers comprising at leastabout 30 weight percent alkenyl ether monomer units, and (5) combinations thereof

24. The adhesive composition defined in claim 23 wherein said polymer comprises at least about 0.1 weight percent of said pendant functional groups.

25. The adhesive composition defined in claim 24 having a sheer holding value of at least about 1,000 minutes at 75° F.

26. The adhesive composition defined in claim 23 wherein said polymer is substantially free of crosslinking agents and residues thereof.

27. The adhesive composition defined in claim 23 wherein R1 is of the formula:

wherein Y and Z are independently selected from the group consisting of oxygen, sulfur, and NR7, R3 is a divalent organic radical at least about 2 atoms in length, and R7 is H or hydrocarbyl.

28. The adhesive composition defined in claim 27 wherein R3 is selected from the group consisting of substituted and unsubstituted alkylene, alkylene-oxy, alkyleneimine and alkylene-thio radicals

29. The adhesive composition defined in claim 23 wherein R1 is an ethylene radical, R4 is a methyl radical, and said polymer comprises about 0.1 to about 10 weight percent of said functional monomer.

30. The adhesive composition defined in claim 23 wherein said polymer further comprises at least about 0.1 weight percent of a polymerizable, olefinically unsaturated carboxylic acid monomer.

31. A normally tacky and pressure sensitive adhesive composition comprising a polymer which contains at least about 0.1 weight percent pendant functional groups of the formula:

wherein R3 is a divalent organic radical at least 2 atoms in length, and R4 is hydrogen or an organic radical, and wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxylic acid ester monomers, (4) alkenyl ether polymers comprising at least about 30 weight percent alkenyl ether monomer units, and (5) combinations thereof.

32. The adhesive composition defined in claim 31 wherein said polymer comprises at least about 0.1 weight percent of a polymerizable, olefinically unsaturated carboxylic acid monomer.

33. A normally tacky and pressure sensitive adhesive composition comprising a polymer containing pendant functional groups attached to the polymer backbone having the formula:

in which R1 is a divalent organic radical at least 3 atoms in length, and X is - CO - R4 or - CN wherein R4 is hydrogen or a monovalent organic radical, and wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxylic acid ester monomers, (4) alkenyl ether polymers comprising at least about 30 weight percent alkenyl ether monomer units, and (5) combinations thereof.

34. A pressure sensitive adhesive composition comprising a water-based latex comprising a continuous aqueous medium containing dispersed particles of a polymer comprising at least about 0.1 weight percent of at least one polymerizable functional monomer of the formula:

in which R1 is a divalent organic radical of at least 3 atoms in length, R5 and R6 are independently selected from hydrogen, hydroxy, halo, thio, amino or monovalent organic radicals, and X is - CO - R4 or - CN wherein R4 is hydrogen or a monovalent organic radical, and wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxylic acid ester monomers, (4) alkenyl ether polymers comprising at least about 30 weight percent alkenyl ether monomer units, and (5) combinations thereof.

35. An adhesive article coated on at least a portion of one surface thereof with a normally tacky and pressure sensitive adhesive composition comprising a polymer containing at least one polymerizable functional monomer of the formula:

in which R1 is a divalent organic radical at least 3 atoms in length, R5 and R6 are independently selected from hydrogen, hydroxy, halo, thio, amino or monovalent organic radicals, and X is - CO - R4 or - CN wherein R4 is hydrogen or a monovalent organic radical, wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxy1ic acid ester monomers, (4) alkenyl ether polymers comprising at least about 30 weight percent alkenyl ether monomer units, and (5) combinations thereof.

36. The article defined in claim 35 wherein said polymer comprises about 0.1 to about 5 weight percent of said functional monomer.

37. The article defined in claim 35 comprising a flexible backing and having a shear holding value of at least about 50 minutes at 75° F. and a loop tack value of at least about 0.8 pound per half inch.

38. The article defined in claim 35 wherein said polymer is substantially free of polyvalent metals, compounds and complexes.

39. The article defined in claim 35 wherein said polymer is substantially free of crosslinking agents.

40. The article defined in claim 35 wherein R1 is a divalent organic radical 3 to about 40 atoms in length, and X is - CO - R4.

41. The article defined in claim 35 wherein said polymer comprises about 0.1 to about 10 weight percent of a member selected from the group consisting of acetoacetoxyethyl methacrylate, acetoacetoxyethyl acrylate, and combinations thereof; and said adhesive composition comprises at least about 20 weight percent of said conjugated diolefin polymer containing at least about 5 weight percent of said monoaromatic monomer.

42. The article defined in claim 35 wherein said polymer further comprises at least about 0.5 weight percent of a polymerizable acid selected from the group consisting of olefinically unsaturated carboxylic acids having up to about 10 carbon atoms, sulfoalkyl esters of said olefinically unsaturated acids, and combinations thereof.

43. The adhesive article defined in claim comprising (a) said conjugated diolefin polymer comprising at least about 50 weight percent of said conjugated diolefin monomer, at least about 5 weight percent of said alkenyl substituted monoaromatic monomer, about 0.1 to about 10 weight percent of said functional monomer, and a member selected from the group consisting of acrylic acid, itaconic acid, and combinations thereof, and (b) a tackifier.

44. A normally tacky, pressure-sensitive, hot melt adhesive composition comprising a polymer containing at least one polymerizable functional monomer of the formula:

in which R1 is a divalent organic radical of at least 3 atoms in length, R5 and R6 are independently selected from hydrogen, hydroxy, halo, thio, amino or monovalent organic radicals, and X is - CO - R4 or - CN wherein R4 is hydrogen or a monovalent organic radical, wherein said polymer is selected from the group consisting of (1) conjugated diolefin polymers comprising at least about 30 weight percent of one or more conjugated diene monomers having 4 to about 8 carbon atoms and 0 to about 70 weight percent of one or more alkenyl-substituted monoaromatic monomers, (2) olefin ester interpolymers comprising at least about 1 weight percent of a monoolefin monomer having up to about 4 carbon atoms and at least about 40 weight percent of an alkenyl or alkenol ester of a saturated carboxylic acid, (3) olefinically unsaturated carboxylic acid ester polymers comprising at least about 40 weight percent polymerized olefinically unsaturated carboxylic acid ester monomers, (4) alkenyl ether polymers comprising at least about 30 weight percent alkenyl ether monomer units, and (5) combinations thereof.