CA2203400A1 - Stable, low cure-temperature semi-structural pressure sensitive adhesive - Google Patents

Abstract

A curable pressure sensitive adhesive having long shelf stability comprising: (1) at least one free radically polymerized polymer; (2) at least one cationically-polymerizable monomer; (3) a photo-activatable catalyst system for the cationically-polymerizable monomer comprising either at least one organometallic complex salt or at least one onium salt; and (4) optionally, a monohydric or polyhydric alcohol, wherein there is essentially no conversion of the cationically-polymerizable monomer of the curable pressure sensitive adhesive when stored in a manner to exclude actinic radiation, and methods of making the same.

Description

. CA 02203400 l997-04-22 W O96/14349 PCTrUS9S/13204 Stable, Low Cur~Temperature Semi-Structural Pressure Sensitive Adhesive Background of the Invention 1. Field of the Invention This invention relates to curable pressure-sensitive adhesives comprising (meth)acrylic polymers and epoxy pre-polymers, whel ein the pressure-sensitive adhesives have extended shelf lives and exhibit ~Ycell~nt bond strengths when cured and the cured plC;Ssulc sensitive adhesives are particularly useful as structural or semi-structural adhesives.

2. Description of the Related Art F.limin~tion of solvents from polymeric articles and co~ting~ and from the processes by which they are produced is the subject of intense, ongoing efforts throughout the world. These efforts have incl~lded the development of high- and 100%-solids formulations polymerized by thermal, photo and energy-ray means to produce a wide variety of polymeric products. Such formulations include polyrners prepared from acrylic, urethane, and epoxy precursors, and mixtures thereof.
However, many of these processes have significant drawbacks, either related to processin~ or related to pel rol lllance characteristics of the polyrneric products.
A number of polyrnerizable systems comprising mixtures of acrylate monomers and urethane precursors or acrylate monomers and epoxy monomers have been described in the art. See, for e,~alll"le, U.S. Patent Nos. 5,086,088 and 5,262,232, EPA 476,822 and WO 91/16387. The processes for these systems have a number of disadvantages. For ~Y~mple, acrylate monomers by themselves are generally polymerized in solution. While solution polyll.cli~ion is useful to control the characteristic polymerization exotherm of the acrylate monomers, there remains the necessity of disposing of organic solvents used in such a process.

W O 96/14349 PCTrUS95/13204 Alternatively, acrylate ...ono~ can be poly.ne.i~ed in bulk with photo or e-beamradiation p-ocesses, which typically require an inert ~tmosphere However, once mixed acrylate-epoxy polymerizable mixtures are exposed to radiation, that is, the radi~tion ~ec~s~ to initiate pol~..,..izalion ofthe acrylate cGlllpGl~l.n, the epoxy cG,.".onenl is invariably cor"~,ro"lised The epoxy colllpon~ can begin to cure, albeit slowly, even though the epoxy initiators have not been fully initiste~l Such a gradual curing process reduces the shelf life of the epoxy co",?onent. This is generally not a serious limitation unless there is a desire to ~ A;~ a distinct period oftime b~ en the cure ofthe acrylate co"-t)one.-and the epoxy co",ponenl.
Many dual-cure sy~lcms have been des_-ibed For e~,.p'e, there are systems having mllltiple cG-"poncnls, each with the app,(p,iate catalysts that are cured at essenti~lly the same wa~el~ylh Additionally, there are systems that aremultiple component, again with the app, op~ iale catalysts that are cured at di~l e.
wavel~ngths Many of these systems have been described in the art, for example, see U.S. Patent Nos 5,252,694, 5,262,232, 4,156,035, 4,277,978, 4,428,807, 4,717,605, 4,657,779, 4,694,029, 4,707,432, 4,950,696, 4,985,340, and 4,849,320 In many cases, photoinitiation of acrylate and epoxy monomers is carried out using di~. e.,l wavelengthc of radiation, in order to separate, in time, the cure of the two systems. Typically, such dual-cure methods are only moderately successfi~l in sepal~ti,-g the two cures (i.e., irra~ tin~ wavelengths overlap) so that the systems have limited shelf life following the initial irradiation step A dual-co",polunt system in which the acrylate polyrner is p, epart;d in a solvent that is subsequently ~ll ipped, followed by admixture with an epoxide precursor that can be pol~"~e~i~ed under W light irradiation is an alternative method of prepàling dual con,poncnt compositions However, this process produces a "release on dem~nd" adhesive that is readily detackified by exposure to actinic radiation See, for example, U.S. Patent No. 4,286,047.
Reactive extrusion is another method for therrnally polymerizing acrylic monomers in bulk using a wiped-film extruder See, for example, U.S Patent No 4,619,979 However, this method is inapplicable for acrylate monomers that cross-link or form gels during polyl.~e. ;~lion. As a result, acrylic polymers made by this method tend to show limited utility as high-strength adhesives. Addition of cationically-poly,l,e.i~ble monomers (e.g., epoxies) during or after acrylate poly".. .iz~lion, and pol~.ll~.i~ion thereof, to prepare dual-coll.pon~nl adhesives 5 has not been dealt with.
What is not .J;sclQsed in the art is a coll.poailion e ,~hll,iling the desirablep. upe~ lies of both a con~e.l~ional pl~,ssure-3ellsili~e adhesive (e.g., a polyacrylate) and a the...~os_ll;ng resin (e.g., an epoxy resin), having a ci~ificqntly longer shelf life a~er the PSA portion has been fully cured than such compositions as are 10 ~ el~lly known.

of the Disclosure The present invention desclil es a curable pr~,sa~re sensitive adhesive that upon curing provides a semi-structural or structural adhesive, Wll~ .;n the pressure sensitive adhesive conlt,lises:
(1) at least one polymer oblained from pol~l"e~ ion of at least one free-radically pol-yl~,c.i~ble monomer;
(2) at least one c~tionic~lly-polylll~i~ble mono",e~, (3) a photo-activatable catalyst system for the cationically-polyl..c.i~able monomer CGIIIplia;l~g either at least one organo,lletallic complex salt or at least one onium salt; and (4) optionally, a monohydric or polyhydric alcohol, wLere;n there is ess~ y no conversion of the cationically-poly"le. i~ble monomer of the curable pressure sensitive adhesive for at least 10 days, at 20C, -50% RH, when stored in a manner to exclude actinic radiation which is capable ofactivating the catalyst system.
In a second aspect of the invention, a method of pr~)a~ g a curable pressure sensitive adhesive is provided, comprising the steps of: -(1) prepa~ing a pol~l"e,;Lable composition COIll~liSii~g a mixture of (a) at least one free-radically polyrnerizable IllonGmer, (b) at least one thermal free-radical initiator, (c) at least one cationically-polymerizable monomer, W O96tl4349 PCT~US95/13204 (d) a photo-activatable catalyst system for the c~tionic~lly-polymerizable monomer con.p, i~ing at least one organometallic complex salt or at least one onium salt, and (e) optionally, a monohydric or polyhydric alcohol; and (2) applying sufficient thermal energy to the mixture to effect ç~cPnti~lly complete pol~".e.i~lion ofthe thermally free-radically poly~l.c,i~ble n~GnG".e-.While any thermally-;..;l;s~ed free radical polyl"e.iz~lion process is useful inthe practice of step 2 of the present invention, reactive extrusion and thermal pol~,l,e.;~alion in the presence of a heat tla"~r~;r merlillm are particularly useful 10 processes. Adv~ntageQusly, the photo-activatable cationic catalyst is not ~ected under the Op~.a~illg pa,a,l,et .~ ofthermal energy application. This provides a stable pressure sensitive adhesive that upon application to a substrate can be subsequently irradiated in si~u to provide a semi-structural or structural adhesive.
In the present invention, a controlled thermal polyme,i~tion process for 15 the production of adhesives and adhesive-coated tapes with acceptable productprope. Iies can be achieved by using a thermal polymerization step conducted in conjunction with a thermal buffer comprising a heat transfer process that features a relatively high heat l. ah~r~r coefficient such as forced convection using flowing water. Preferably, the adhesives are acrylic-based, which exhibit particularly 20 troublesome, and at times, process rate limiting polymerization exotherms.
ACCGId;l~81Y, the inventive process for the production of adhesives co",p~ises allowing a carrier web coated with a free-radically poly~..e.i~ble co,nposilion to remain in a thermal buffer for a time sufficient to effect conversion of the coating to an adhesive while controlling the reaction exotherrn to maintain a reaction te",pe. alllre within 20C of the te"",~ . alllre of the thermal buffer. The thermal buffer is characterized as a system for heat transfer wherein the heat transfer coefficient is at least 25W/(m2 K). Depending on the particular polyrnerizable mixture, it may be advantageous to exclude oxygen from the poly",e~ ion zone.
The coating on the carrier web can be a subst~nti~lly solvent-free thermally polyrnerizable mixture, wherein the polymerizable mixture comprises at least onefree-radically polymerizable monomer, at least one therrnal initiator and optionally W O 96/14349 PCTrUS95/13204 s at least one cross-linker, at least one cdlic--lc~lly polymerizable mono~,.cr and photo-activatable cationic catalyst system. Preferably, the free-radically polymerizable monG...~.~ are predo.~ nlly acrylic-based monomers.
In another embodiment of the present invention, a polymerizable 5 composition is coated t-l~. een a first and second carrier web to form a sandwich, and then processed as above. Advqntq~geously, there is no need to el;~ te oxygen from the pol~."e-~lion zone.
A particularly useful feature of this invention is an adhesive system that has the cG,.,b;"ed pro?cl lies of a pressure sensitive adhesive (for easy application) and 10 a the~ os~ ; resin (for a strong, pc,...anenl semi-structural or structural bond).
Further, the adhesive system ofthe present invention c ~ bilc a s~ fi~qntly longer shelf life after the pressure sensitive portion (the free radically pol~...e.~ble monG...e. ~) has been fully cured than similar compositions that are currently known in the art. Another advantage of the present invention, is the adhesive systems are 15 prepared as 100% reactive coating compositions, substqnti~lly çl;.~ ;ng industrial solvent waste, while also redl~cing energy consumption.
The inventive method provides a significqrlt advantage over the art in that initial poly",~ alion of the free-radically poly."~. izable n,onome- (s) is accomplished in an manner that does not affect polymerization of the cationically-20 polymerizable monomer(s), nor does it activate the cationic pol~...e.i~lion catalyst(i.e., the Glgano.--~lallic co...pl- ,~ salt or onium salt), which is thermally stable and photoche....cally labile. This ability to separate the two cures allows the adhesive systems of the invention to have very long shelf lives in the PSA state before application and use.
The pressure sensitive adhesive can be converted into a structural or semi-structural adhesive by: (a) applying s~-ffi~ient irradiation to the curable PSA to activate the photoactivatable catalyst system, and (b) providing sufficient timeand/or thermal energy to effect essenti~lly complete polymerization of the cationically poly---c.izable mono...er.
An additional advantage ofthe present invention is provided by the lower thermal curing temperatures of the cationically cured polymerizable monomer(s) as opposed to the thermal cure tc."peralures required for cationically-cured W O96/14349 PCT~US95/13204 monomer(s) of known systems. Typically, te.,.?el alllres required to cure cationically-cured ,llono.,lc. ~ such as epoxies can be so high as to preclude the use of certain low-melting or te."?c~ alurc-3e~ ive bac~inec or substrates. In contrast, photo-activatable catalyst systems used in the present invention are such that 5 cationic cure to form structural or semi-structural adhesives can occur at lower, unharmful tempe.dl,~res.
Further, the plefe.l~,d present method of controlling the acrylate poly",e~i~lion exotherm in a heat e~cl~ ge medium allows complete te."i)eral.-recontrol over the p-e~ c sensitive adhesive prepa. alion step. Subsequent 10 photo-activation and curing ofthe lhc~ osel~ ; resin component, that is, the epoxy colllpone.ll ofthe adhesive system inc~ses bond sl,englh to semi-structural level, which cannot be achieved by traditional pressure sensitive adhesives.
Yet another advantage of the invention is achieved due to the ability to control room-te~llpclal~re latency ofthe photopol~,l,e,i~lion catalyst used in 15 curing the th.,oset~ g resin. Thus, reasonable worki"g times after photolysis of the co-l,posilion can be realized (on the order of tens of minutes), allowing for positioning (and repositioning) of the substrates to be adhered before a permanent bond is obtained. The low cure telllpe.al-lre ofthe thermosetting resin makes the adhesive of the present invention especially suitable for those applications where higher tclllpclal~res cannot be tolerated, due to equipment limitations or to the use ofthermally sensitive s~b~Llales (e.g., lLclllloplastics).
In yet a further aspect of the present invention, curable pressure sensitive adhesives can be prepared accGI di"g to the method COlllpl iSillg the steps:
(1) prepali,.g a first polymerizable composition comprising a mixture of (a) at least one free-radically polymerizable monomer, (b) at least one free-radical initiator, (2) applying sufficient energy to the mixture to effect esse~ lly complete polyllle. iLalion of the free-radically polymerizable monomer;
(3) mixing into the polylllcli cd composition, a second polymerizable composition collll,lising a mixture of:
(a) at least one cationically-polymerizable monomer, W O96/14349 PCTrUS95/13204 (b) a photo-activatable catalyst system for the cationically-polymerizable ~llonolllcr corll~ ;ng at least one G.~ano...~l~llic complex salt or at least one onium salt, and (c) optionally, a l.,onoh~dl ic or polyhydric alcohol.
5Alternatively, the cationically-pol~ .i~ble monolller can be added to the first poly,ll~.i~ble composition, ~Lc~,.n the photo-activatable catalyst system for the cationically-pol~ll,.,. iLable ~-~onoll,er is added after the first polymerizable composition has been pol~,..c~ i ~;d.
The free-radically pol~",~,.iLed polymer may be p,e~,al~;d in any of a number means known in the art, such as photo-pol~",~ ion or thermal-poly",e.i~lion, either of which can be carried out in the bulk (100% solids) or in solution. If carried out in solution the solvent must be removed prior to melt blending.
Preferably the free-radically pol~,.,e. ized polymer is prepared by photo-pol~l.le~i,alion in the bulk with the cationically-pol~llle.iLablc monomer present.
Adv~,tageQusly, in contrast to known energy-curable epoxy-acrylate compositions, such as those desclibed in U.S. Patent No. 5,252,694 (col. 7, line 57 thru col. 8, line 56), thermally decollll)osable esters are not required as accelerators/additives in the present forrnulations.
As used in this application:
"acrylate syrup" means a composition comprising a partially polyl-le,ized mixture of (meth)acrylates only or a partially pol~"l.,. iGC~ mixture of (meth)acrylates and unpol~llle~i~e~ epoxy monomers;
"(meth)acrylate-con~ " means materials that are essenti~lly free of (meth)acrylic acid, but contain a (meth)acrylate mono,ller, a mixture of (meth)acrylate n~onGIllers, or a (meth)acrylate-epoxy mixture, further the terms"(meth)acrylate" and "(meth)aclylic" include both acrylate and methacrylate and acrylic and methacrylic, re..~,e~ ely;
"thern.~al buffer" means a system that brings a material in contact with the buffer, such as the coated web, toward the te.l,pel al~lre of the buffer and tends to 30 ",~ the material within the buffer at a relatively consLar,l tel"pe~lule;
"heat transfer coefficient of the thermal buffer" means the effective heat transfer coefficient for the process of heat l.~nsrer that occurs within the buffer W O96/14349 PCTrUS95113204 from the coated carrier web to the thermal buffer This heat l~l;,Ç~r coPffiri~ntcan be either a convective heat ll ~r.s~r coefficient, for example when a water bath is used for the thennal buffer, or a conductive heat l,~.Sre. coefficient, for e,.~nl~le when a heated metal surface is used for the thermal buffer.
b;rlc?:tive monomer" means a ~ nQ~, cr that conldills at least two free radically polyl..e.i~able groups or t~,vo cationically poly,-,c, i~able groups and does not contain both types of groups;
"bifunctional ."ono,.-er" means a ,-ono,-,e. that cG..Ia;.~s at least one free radically polyll,e. ~b'e group and at least one cationically pol~..,e.i~ble group;
"group" or ~/monomer" or "anion" or "ligand" means cl~c~ll.cdl species that allows for s~bstit~ltion or that may be ~ ed by conventional s~bs~ JPntc that do not interfere with the desired product, for ey~nlpl-p~ substit-lent~ can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, 1), cyano, nitro, etc.;

Description of the Preferred Embodiment(s) Cationically-poly.. c.i2able .. ono,.. c~ useful in the invention include but are not limited to epoxy-CGnl~inil~g materials, alkyl vinyl ethers, cyclic ethers, styrene, divinyl ben7Pnç vinyl toluene, N-vinyl c~l..younds, cyanate esters, l-alkenes (alpha olefins), lactams and cyclic acetals Cyclic ethers that can be polymerized in accordance with this invention 20 include those des-,- ;l ed in Frisch and Reegan Ring-Opening Poly~ , izulions Vol .
2 (1969) Suitable 1,2-cyclic ethers include l..onG..,c.ic and polymeric types ofepoxides Particularly suitable are the aliphatic, cycloaliphatic, and glycidyl ether type 1,2 epoxides A wide variety of co.~""e~cial epoxy resins are available and listed in Lee and Neville Handbook of Epoxy Resins I 1967) and P. Bruins Epoxy Resin Technology (1968) Re~.,. sel.la~i~e of 1,3- and 1,4-cyclic ethers that can be polyrnerized in accordance with this invention are oxetane, 3,3-bis(chloromethyl)oxetane, and tetrahydrofuran Additional cationically-pol~",e.i~ble monomers are described in U.S.
Patent No 5,252,694 at col 4, line 30 thru col 5, line 34, the description of which is incorporated herein by lefelence P~efe.l~d monomers ofthis class include EPONTM828, and EPONTMlOOlF and the ERL series of cycloaliphatic epoxy ~l~ono~e, ~ such as ERL-4221TM or ERL-4206TM; most p~efe" ~d ",ono".e. s are theERL series because of their lower cure telllp~- alllres Free-radically polymerizable ~,lL~lenically-unsaturated monomers useful in the invention include but are not limited to (meth)acrylates and vinyl ester 5 functio~ ed materials. Of particular use are (meth)acrylates. The starting material can either be ",ono".e~s or oligomers such be des_,ibed in U.S Patent No 5,252,694 at col. 5, lines 35-68 Alternatively, useful ...ono..~ cG"""ises at least one free-radically poly",.,.;~ble fun.,lionality. Exarnples of such ",ono",~.s include sperifir~lly, but 10 not exclusively, the following classes:
Class A - acrylic acid esters of an alkyl alcohol (pr~-fe~ably a non-tertiary alcohol), the alcohol cGn~ g from 1 to 14 (~.,e~,ably from 4 to 14) carbon atoms and inrludç for eAa,..ple, methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, hexyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isobo""~l acrylate, phenoxyethyl acrylate, decyl acrylate, and dodecylacrylate;
Class B - methacrylic acid esters of an alkyl alcohol (p. ~fe, ably a non-tertiary alcohol), the alcohol cGnl~ g from 1 to 14 (preferably from 4 to 14) carbon atoms and inrl~ldç, for e Aa",ple, methyl meth~çrylate, ethyl methacrylate, n-propyl meth~crylate, n-butyl meth-~rylate~ isobutyl methacrylate and t-butyl meth~crylate;
Class C - (meth)acrylic acid ."onoe;,lers of polyl,~droAy alkyl alcohols such as 1,2-eth~net~iol, 1,2-propanediol, 1,3-propane diol, the various butyl diols, the various h. .~ne~;ols~ glycerol, such that the resulting esters are ~efe"ed to ashydroxyalkyl (meth)acrylates;
Class D - m~lltifiJnctional (meth)acrylate esters, such as 1,4-butanediol diacrylate, 1,6-heY~netliol diacrylate, glycerol diacrylate, glycerol triacrylate, and neope"~yl glycol diacrylate although these mono",e.s are generally not ple~lled for reactive extrusion or melt bl~ `g Class ~ - macromeric (meth)acrylates, such as (meth)acrylate-termin~ted styrene oligomers and (meth)acrylate-termin~ted polyethers, such as are described W O96/14349 PCT~US95113204 1~
in PCT Patent Application WO 84/03837 and European Patent Application EP
140941;
Class F - (meth)acrylic acids and their salts with alkali metals, inclutling, for example, lithium, sodium, and pot~ssi~rn, and their salts with alk~line earth 5 metals, inrl~lding, for e~"pl~ g,.~ .., c~lr~ strontium, and barium.
~ lthol.gJ cure te...p.,.al~lres ofthe cationically polymerizable ",ono",~
can be affected, it is within the scope of the present invention to also use a seventh class of free radically ",onol"e.s, namely "Class G" monomers. Class G monomers include nitrogen-bearing ",ono",e.~ selected from the group con~;cl;~g of 10 (meth)acrylonitrile, (meth)ac.~l~"id~, N-substit--ted (meth)acryl~rnidç~, N,N-dicubstituted (meth)acrylamides, the latter of which may include substituent~ of 5-and 6-...~---be~cd heterocyclic rings CGIll~l;S;ng one or more heteroatoms, and methyl-substituted maleonitrile, and N-vinyl l~ct~nl5, such as N-vinyl pyrrolidinone and N-vinyl caprolactam.
Two other criteria for the free-radical monomers are prel~"ed, but not required: (a) these l"ono",e,~ should be miscible with the epoxy monomer(s) and (b) the free-radical ..,ono,..e.~ are prefe,~bly chosen such that their copolymers have co",pG~ile Tgs in the range of 30C or less, as calculated by, e.g., the Fox equation, Bull. Am. Phys. Soc., 1, 123 (1956).
Bifunctional monomers may also be used and examples that are useful in this invention possess at least one free radical and one cationically reactive functionality per ",onG",er. Ex~ples of such ",ono",~ include, but are not limited to glycidyl (meth)acrylate, hyd,~)x~,Lhyl (meth)acrylate, hydroxypropyl methacrylate and hydroxybutyl acrylate.
Suitable organometallic co~"~,leA salts include those described in U.S.
Patent No. 5,059,701 and such description is incorporated herein by reference. In addition to those des.;,;bed in U.S. Patent No. 5,059,701, the organometallic complex salts desc-ibed in EPO No. 109,851 are also useful in the present invention. Useful orgal-o",etallic complex salts used in the present invention have the following formula:
[(L )(L )MP] Yn ~Le.~.n MP represe,lls a metal selected from the group conci~ting of: Cr, Mo, W, Mn, Re, Fe, and Co;
Ll repl ~,3~ s 1 or 2 ligands contributing pi ele~ ll ons that can be the same or di~.ent ligand sPIected from the group of: s~.bstituted and n.cubstitutecl eta3-allyl, eta5-cycloppn~ipnyl~ and eta7-cyclohe~)tall;cnyl, and eta6-a~olnalic compounds scle~led from eta6-benzene and ~ ed eta6-be.~ene compounds and cGIll?o~lnds having 2 to 4 fused rings, each capable of contributing 3 to 8 pi ele~ l,ons to the valence shell of MP;
L2 I.,ples_nts none, or 1 to 3 ligands contributing an even .I~ bcr of .ci~- ele~,lt(,ns that can be the same or di~rt n~ Iigand s~lected from the group of: carbon monoxide, nitrosoni~"" lliyh.~lyl phosphine, triphenyl stibine and derivatives of phosphorus, arsenic and anli",ony, with the proviso that the total electronic charge contributed to MP results in a net residual positive charge of q to the complex;
- q is an integer having a value of 1 or 2, the residual charge of the complex cation;
Y is a halogen-cG~ ;n;--~ COIIIPIeA anion sPlected from BF4-, AsF6-, PF6-, SbF50H, SbF6, and CF3S03; and n is an integer having a value of 1 or 2, the number of complex anions required to neutralize the charge q on the coMpl~". cation.
Plt;r~lled Gl~anG...el~llic initiators are the cyclopentadienyl iron arenes 25 (CpFeArenes), and pr~fe,ably, SbF6 is the counterion. CpFe(arenes) are prefe,.~d because they are very therrnally stable yet are excellent photoinitiation catalysts.
Useful cationic photoinitiators comprising onium salts have been described as having the structure AX wherein:
A is an organic cation selected from diazonium, iodonium, and sulfonium 30 cations, more preferably A is sPlect~Pd from diphenyliodonium, triphenylsulfonium and phenylthiophenyl diphenylsulfonium; and W O96/14349 PCTrUS95/13204 X is an anion~ the cou-~lt;.ion ofthe onium salts incll~in~ those in which X
is organic sulfonate, or halo~en~ted metal or metalloid.
Particularly useful onium salts includç, but are not limited to, aryl ~i- Dr -~tn salts, diaryl iodonium salts, and triaryl sulro,liu... salts. ~d~litiorlql ~ .. ?leS ofthe onium salts are de3_.;l,ed in U.S. Patent Number 5,086,086, col. 4, lines 29-61, and such de~. i~lion is incol~Jo.aled herein by l efel ence.
Cation;c phot~ ors that are also useful include aromatic iodonium cG...ple,. salts and aromatic sulfor~ m co-,.p1eY salts. The aromatic iodonium complex salts have the formula:

Ar~ ' ~
(~)n/I X
Ar2 ~ I
wherein Ar~ and Ar2 are aro--.alic groups having 4 to 20 carbon atoms and are sçlected from the group consisting of phenyl, thienyl, furanyl and pyrasolylgroups;
Z is selected from the group consisting of oxygen, sulfur, ~=O ; ~=O ; O=S=O ; R=N
where R is aryl (having 6 to 20 carbon atoms, such as phenyl) or acyl (having 2 to 20 carbon atoms, such acetyl, benzoyl, etc.), a carbon-to-carbon bond, or R~ R2 where R~ and R2 are indeper.dçntly selected from hydrogen, alkyl radicals of 1 to 4 carbon atoms, and alkenyl radicals of 2 to 4 carbon atoms;
n is zero or l; and ~ is a halogen-coln~ g co...pleY anion selected from tetrafluoroborate, heY~flllorophosph~te, h~Y~fluo~atsenate, and heY~fluQroa"tinG~ate.
Aromatic sulfonium complex salt photoinitiators are desc~il,ed by the formula:

W O96/14349 PCT~US95/13204 n\ X
'~1 S- R5 R3, R4 and Rs can be the same or di~l.,nt, provided that at least one of such groups is aro,..alic and such groups can be selected from the aromatic groups having 4 to 20 carbon atoms (for example, subsituted and ur~cubstih~ted phenyl, thienyl, furanyl) and alkyl radicals having 1 to 20 carbon atoms. The term "alkyl"
as used here is meant to include subtituted and llnq~bstituted alkyl radicals.
Preferably, RJ, R~, and Rs are each aromatic groups; and Z, n and ~ are as defined above.
Of the aromatic sulfonium corl.ple.~ salts that are suitable for use in the present invention, the p~. f~;l I ed salts are triaryl-substituted salts such as~1 iphenylsulfonium hey~fluorophosphqte and triphenylsulfonium hPx~fl~lQroall~inomate. The triaryl substituted salts are prer~lled because they are more thermally stable than the mono- and diaryl substituted salts.
I S Thermal free radical initiators useful in the present invention include, but are not limited to azo, peroxide, persul&te, and redox inili~lols.
Suitable azo initiators include, but are not limited to 2,2'-azobis(4-methoxy-2,4-dimethlvalelo~ lile) (VAZOTM 33), . 2,2'-azobis(amidinoprGpane) dihydrochloride (VAZOTM 50); 2,2'-azobis(2,4-dimethylvaleronitrile) (VAZO rM
52); 2,2'-azobis(isobutrynitrile) (VAZ) TM 64); 2,2'-azobis-2-methylbutyronitrile (VAZOTM 67); 1,1'-azobis(1-cycloh~Y~ec~rlecarbonitrile) (VAZOTM 88), all of which are available from DuPont Chemicals and 2,2'-azobis(methyl isobutyrate) (V-601) available from Wako Ch~m;c~ls Suitable peroxide initiators include, but are not limited to, benzoyl peroxide, acetyl peroxide, lauroyl peroxide, decanoyl peroxide, dicetyl peroxydicarbonate, di(4-t-butylc,vclohexyl) peroxydicarbonate (PERKADOXTM
16S, available from AKZO Chemicals), di(2-ethylhexyl) peroxydicarbonate, t-butylperoxypivalate (LupersolTM l l, available from Atochem), W O96/14349 PCT~US95/13204 t-bu~yllJcro~r-2-ethylh. Y~noate (TrigonoxT~( 21-C50, available from Akzo Chemicals, Inc.), and dicumyl peroxide.
Suitable persulfate initiators include~ but are not limited to, potassium persulfate, sodium persulfate, and ammonium persulfate Suitable redox (oxidation-reduction) hl;lialGla include, but are not limited to, co...bi~ ;ons of the above persulfate i, ilia~o. a with reduçing agents such as sodium ,ll~labia~lfite and sodium biclllfite; a~alenls based on organic peroxides and tertiary amines, for e ~...plf, benzoyl peroxide plus dimethylaniline; and systems based on organic l.~rd.upe~o,~ides and transition metals, for example, cumene 10 hy~l-uper~ide plus cobalt narh~h~n~te.
Other ;,uLia~G~à includ~, but are not limited to pinacols, such as tetraphenyl 1,1,2,2 e~ nc~iol.
~ l~f~ d thermal free-radical initiators are selected from the group consisting of peroxides and azo compounds that do not contain nitriles or basic groups Most pr~f~"ed initiators are V-601, LupersolTM 11 and PerkadoxTM 16S, and mixtures thereof, because oftheir p.~ft..t;d deco...pos;lion te...?c-all~re is in the range of about 45 to 95C. Additionally, they are generally inert toward cationic poly...cli~lion initiators The initiator is present in a catalytically-effective amount and such amounts 20 are typically in the range of about 0.01 parts to 5 parts, and more pl~ fe.ably in the range from about 0.025 to 2 parts by weight, based upon 100 total parts by weight of l.-onomer or ,l.onG..l~ iAlure If a mixture of initiators is used, the total amount of the mixture of initiators would be as if a single initiator was used Photoinitiators that are useful for partially poly...e,i,h~g alkyl acrylate 25 mono...c. without crosslin~in~ to prepare syrups, include the benzoin ethers, such as benzoin methyl ether or benzoin isopropyl ether, substituted benzoin ethers, such as anisoin methyl ether, substituted acetophenones, such as 2,2-diethoxyacetophenone and 2,2-dimethoxy-2-phenylacetophenone, substituted alpha-ketols, such as 2-methyl-2-hydru~rpropiophenone, aromatic sulfonyl 30 chlorides, such as 2-naphthalene-sulfonyl chloride, and photoactive oximes, such as l-phenyl-1,2-propanedione-2(0-ethoxycarbonyl)oxime They may be used in W O96/14349 PCTrUS95/13204 amounts, which as dissolved provide about 0.001 to 0.5 percent by weight of the alkyl acrylate monG~llcr~ preferably at least 0.01 percent.
Optionally, monohydroxy- and polyhydroxy-alcohols may be added to the curable co",pos;lions of the invention, as chain-eYt~n.l~rs for the epoxy resin.Suitable exarnples of alcohols include but are not limited to meth~nol, ethanol,1-propanol, 2-propanol, 1-butanol, 1-pentAnol, 1-hexanol, l-heptanol, 1-octanol,pentaerythritol, 1,2-plopAn&~:QI ethyleneglycol, 1,4-b~ nçdiol, 1,5-pe.~1~nediol, 1,6-h~ ~ne~iol, 1,4-cycloh~le d;~ h~r~ol~ 1,4-cycloh. ~ne~iol and glycerol.
Pl.;re.~bly, ~",?oul~ds col~lA;/~ g hydroxyl groups, particularly co",poullds cor.lA;~ g from about 2 to 50 hydroxyl groups and above all, compounds having a weight average ~l'olec'~lAr weight of from about 50 to 25,000, preferably from about 50 to 2,000, for e~a",FI~, polyesters, polyethers, polythioethers, polyacetals, pol~ca,l,onales, poly(meth)acrylates, and polyester amides, contAining at least 2, generally from about 2 to 8, but preferably from about 2 to 4 hydroxyl groups, or even hydroxyl-col-lAini,~g prepolymers of these compounds, are representatives compounds useful in accGr.lance with the present invention and are desc, ibed, for example, in SAl~nders, HighPolymers, VoL XVI, "PolyulethA~es Chemistry and Technology," Vol. I, pages 32-42, 44-54 and Vol. II, pages S-6, 198-99 (1962, 1964), and in Kuns~s~off-Handbuch, Vol. VII, pages 45-71 (1966). It is, of course, permissible to use mixtures of the above-mentioned compounds con~Aining at leasttwo hydroxyl groups and having a molecl~l~r weight of from about 50 to 50,000 for ~ .,.ple, mixtures of polyethers and polyesters.
In some cases, it is particularly advAntAgeQus to co",bine low- melting and high-melting polyhydroxyl co~ g compounds with one another (German Offenlegungssc}uifl No. 2,706,297).
Low molecular weight compounds co~ ning at least two reactive hydroxyl gropups (molecular weight from about 50 to 400) suitable for use in accordance with the present invention are compounds preferably conlainJng hydroxyl groups and generally cGl,ldining from about 2 to 8, preferably from about 2 to 4 reactive hydroxyl groups. It is also possible to use mixtures of different compounds containing at least two hydroxyl groups and having a molecular weight in the r_nge of from about 50 to 400. Examples of such compounds are ethylene W O96/14349 PCTrUS95/13204 glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-butylene glycol, 1,5-pe"lanediol, 1,6-h~ eAiol~ 1,8-oct~nediol~ neopcnlyl glycol, 1,4-cyclohexanedimethanol, 1,4-c~lohf ~e~iiol~ ll;nlelh~lolplopanc, 1,4-bis- h~druAy,n~lhyl cyclohexane, 2-methyl-1,3-1)ropq.~cdiQl di~ ,mob~tçne~liol (U.S. Patent No.
3,723,392), glycerol, l~i"~clhyloll"op&ne~ 1,2,6-k- ~;.n~ I.iol, I~;".cll"rloleth~ne, pentaerythritol, quinitol, m~nn;tol, sorbitol, diethylene glycol, triethylene glycol, tetraethylene glycol, higher polyethylene glycols, dipropylene glycol, higher polypropylene glycols, dibutylene glycol, higher polybutylene glycols, 4,4'-dil.~droA~ diphenyl p. ol)ane and dihydroxy methyl hydroquinone.
Other polyols suitable for the purposes of the present invention are the mixtures of hydroxy aldehydes and hydroxy ketones ("formose") or the polyhydric alcohols obtah~ed th~.. fiulll by reduction ("formitol") which are formed in theautocondenc~tion of formaldehyde hydrate in the p, ~sence of metal compounds as catalysts and compounds capable of enediol formation as co-catalysts (German Ol~nle~,-ng.c~cl"inNos. 2,639,084, 2,714,084, 2,714,104, 2,721,186, 2,738,1S4 and 2,738,512).
It is contemplated that polyfunctional alcohols such as ca-l,owaxes poly(ethylene glycol), poly(ethylene glycol methyl ether), poly(ethylene glycol)tetrahydrofurfuryl ether, poly(propylene glycol) may also be used in the compositions of the present invention.
It is also within the scope of this invention to add optional adjuvants provided they are not dcLlil"e.lt~l to the cationic cure and include, for example, lhixo~opic agents; pl~tici7~rs; tou~h~ning agents such as those taught in U.S.
Patent No. 4,846,905; pigments; fillers; abrasive granules, stabilizers, light stabilizers, antioxidants, flow agents, bodying agents, flatting agents, colorants, binders, blowing agents, fungicidç~, bactericides, surf~ct~nts; glass and ceramic beads; and rei"rorci"g materials, such as woven and nonwoven webs of organic and inorganic fibers, such as polyester, polyimide, glass fibers and ceramic fibers;
and other additives as known to those skilled in the art can be added to the compositions ofthis invention. These can be added in an amount effective for their intended purpose; typically, amounts up to about 25 parts of adjuvant per total weight of formulation can be used. The additives can modify the properties of the W O96/14349 PCTrUS9S/13204 basic co..,i)osit;on to obtain a desired effect. Furthermore, the additives can be reactive co.-.ponents such as materials con~ .;ng reactive hydroxyl functionality.
Alternatively, the additives can be also s ,bslan~ ly unreactive, such as fillers, inCIuriing both i.,o. anic and organic fillers.
Optionally, it is within the scope of this invention to include photGsen~ or photoacc~l~ ators in the radiation ser.silive co...pGs;lions. Use of photosenc;l;~ ~ or photoaccelc ators alters the wavelel.~L}I sensitivity of radiation-sensitive compositiQns employing the latent catalysts of this invention.
This is particularly adv~ntageQus when the latent catalyst does not strongly absorb 10 the inrident radiation. Use of a photosPI.~ ~; er or photoaccçlerator increases the radiation sensitivity allowing shorter exposure times and/or use of less powerful sources of radiation. Any photose~.c~ r or photoaccelerator may be useful if itstriplet energy is at least 45 kilocalories per mole. Examples of such photose..si~ are given in Table 2-1 of the reference, S. L. Murov, Handbook of Photochemistry, Marcel Dekker Inc., N.Y., 27-35 (1973), and include pyrene, fluoranthrene, xanthone, thiox~nthone, benLophenone, acetophcnone, benzil, benzoin and ethers of benzoin, chrysene, p-terphenyl, acenaphthene, naphthqlen~,phenarllhr~ne, biphenyl, substit-lted derivatives of the prece~ing compounds, and the like. When present, the amount of photosensitizer or photoaccelerator used in the practice of the present invention is generally in the range of 0.01 to 10 parts, and prere. ably 0.1 to 1.0 parts, by weight of photose ~S;~ or photoaccelerator per part of or~no~ llic salt or onium sa~t.
Glass microbubbles having an average diameter of 10 to 200 ...icro---cLers can be blended with pol~...e.i~ble compositions ofthis invention as taught in U.S.
Patent No. 4,223,067. If the microbubbles comprise 20 to 65 volume percent of the pressure-sensitive adhesive, the polymerized product will have a foam-like appearance and be suitable for uses to which foam-backed p-es~ure-sensitive adhesive tapes are useful.
Electrically conducting particles, as taught in U.S. Patent No. 4,606,962 can be blended with the polymerizable compositions of this invention. The conducting particles, such as solid metal particles, carbon black, metal-coated particles, or metal flakes, added to the polymerizable compositions of this invention WO 96/14349 PCT/US9~/13204 can provide electrical conduction b,et~.een semiconductor chips and circuit traces.
Advantageously, such a contlucting adhesive layer ~h~ utes solder and provides better ...ecl-~nic~ n~,lh ~wlhe.ll~lt;, more con"e~,lions per area (pitch) can be realized using a conducting adhesive. The el;... ~zt;Qn of solder is enviro.~n~nt~lly 5 safer, in that h~ dous solvents and lead from solder are r~ ted In addition, thermally conductive particles, such as metal oxide particles, can be blended with the pol~",~. i~ble compositions of the present invention.
Other materials that can be blended with the pol~ el iLdble compositions of this invention include t~;e~ ;~F~ ;t~olcing agents, and other modifiers, some of10 which may copol~,..c~iL~ with the free radically or cationically poly..leli~ble l"ol-oo,~ .~ or pholopoly,lle.i~ ;~.d~pentl~ntly. However, the addition of any such material adds complexity and hence 1 l.ence to an otherwise simple, straighlro,w~d, economical process and is not p-erellt;d except to achieve specific results.
l 5 While it is p~ d that solvents are not used in p, c;?a~ ing the polymerizable cGl~posilions of the present invention, solvents, preferably organic, can be used to assist in ~ Solution of the catalyst system in the free radically and cationically poly",e~i~ble monomers. It may be adv~nt~eous to prepare a concentrated solution ofthe or~ano~ct~llic complex salt or the onium salt in a 20 solvent to simplify the prepal alion of the pol~ . i~ble composition.
Rep,ese.ll~li.re solvents include a~etone, methyl-ethyl-ketone, cyclopentanone, methyl cellosolve acetate, methylene chloride, nillo...~h~ne, methyl rc,l",ate, gamma-butyrolactone, propylene ca.~ona~e, and 1,2-~imethoxyethane (glyme).
Irradiation sources that provide light in the region from 200 to 800 nm are effective in the practice ofthis invention. A plefelled region is between 250 to 700 nm. Suitable sources of radiation include mercury vapor discharge lamps, carbon arcs, quartz halogen lamps, ~n~ ten lamps, xenon lamps, fluorescent lamps, lasers, sunlight, etc. The required amount of exposure to effect polymerization is dependent upon such factors as the identity and conc~"l, alions of the photo-activatable catalyst system, the particular free radically and cationically polymerizable monomers, the thir~ness of the cA~,osed material, type of substrate, intensity of the radiation source and amount of heat associated with the radiation.

Pl~fe..-,d composition ofthe invention co,.,~,i3es monomer ratios of 10-70, ple~lably 20-50% epoxy monomer(s) and 30-90%, preferably 50-80% acrylate monomer(s).

Partially Pre-polymeriza~ion Syrups The curable adhesive COI,lpGS lion can be p-el~ et using a free radically polymerizable syrup (also refe.. ~d to as "syrup"), that is partially poly-,l~,.ized free radical monGI~e.~ ( 1 % to 30 % conversion), or a Illi~-lUrt of partially polylllcli ed free radical ",onGr"~ and su~ y unpolylllc,;~ed epoxy ",ono",~.~, and optional adjuvants.
Method 1 A first step in the pl ep~ ~tion of a syrup is to mix free radically pol~lllcl i~ble Illono,l-cl ~ with a catalytically e~ e amount of a free radicalinitiator, pr~,fc;,dbly a free radical photoinitiator. Preferably, the free radical photoinitiator is not a cros~linl in~ agent and is generally present in an amount within the range of 0.001 to 5.0% by weight of the polymerizable composition, preferably in the range of 0.01 to 1.0% by weight ofthe pol~",e.,zable composition.
A second step, that is sim~lt~rleQus and concurrent with step (3) is to purge the system (the polymerizable cG",pos;lion, as well as the reaction environment), for example by bubbling an inert gas, such as N2, Ar, or He through the polymerizable composition to remove any residual oxygen.
A third step is to apply energy to the free-radically polymerizable composition to allow it to poly,,,c;,i~e such that the viscosity is increased to within a range of 0.3 to 20.0 Pascal secor.~s at a",b~ t telllpelalllre. Preferably, the viscosity a~er this step is in the range of SOO.to 4000 cps (0.5 to 4.0 Pa-sec). The increased viscosity provides a syrup that is more suitable as a coating composition for production of the articles of the invention. The polymerizable composition may be polymerized using any well-known free-radical poly.,.e.i~tion technique and quenched with air to attain the desired viscosity. Preferably, the free radical initiator is a photoinitiator, and the partial poly,.,c. i~alion may be stopped at any point by eli,..,nating the irradiation source.

oc7 o A fourth step is to mix the cationically polymerizable monomers and optional alcohol-co..~ g material into the sy~up A fifth step is to mix at least one organG-.,-t~ c complex or onium salt and at least one ~dAition~l free-radical initiator, into the syrup of step three. The 5 ~Aitionql free radical i. ilialor can be the same as the initiator of step 1 or di~I~re..l Optionat bireactive free radically pol~ .i~ble monomer, bifi-nctionql monomer, adjuvants may be added to the syrup at this time.
A sixth step is to degas the curable compositions under vacuum to remove bubbles, volatile solvents, dissolved air, oxygen, and the like Although it is 10 preferable to do this step just prior to coeting it may be carried out at any time from a few hours to several weeks prior to coqti~ To insure stability of the deg~csed curable co.nposilions, it is prere.~ble to keep them from unwanted exposure to light.
Method 2 A first step in this alternative p. eparalion for a syrup is to mix the pol~...e.i~able .,ono..le.~, (cationically and free radically polymerizable monomers) with a catalytically effective amount of at least one free radical initiator.
Preferably, the free radical initiator is not a crosslinl~ing agent and is generally present in an amount within the range of 0 001 to 5 0% by weight of the poly.,.~ able co.. posilion, preferably in the range of 0 01 to 1 0% by weight of the polymerizable composition.
A second step, that is sim~llt~neolls and concurrent with step (3) is to purge the system (the pol~"le.i~ble composition, as well as the reaction envi,o,-n-en~), for example by bubbling an inert gas, such as N2, Ar, or He, through the 25 polymerizable composition to remove any residual oxygen.
A third step is to apply energy to the polyrnerizable composition to allow the free radically polymerizable monomers to polymerize such that the viscosity is increased to within a range of 0.3 to 20 0 Pascal seconds (Pa-sec) at arnbient te...pel al~lre. Preferably, the viscosity after this step is in the range of 0 5 to 2 0 30 Pa-sec The increased viscos;ly provides a syrup that is more suitable as a coating composition for production of the articles of the invention. The polymerizable o2 ~
composition may be poly,.,e. i~ed using any well-known free-radically poly",e,i~lion technique and quçnched with air to attain the desired viscosity.
A fourth step is to mix at least one complex or onium salt, and at least one ~-lition91 free radicatly polymer, any optional bireactive free radically 5 polye. iza~le ",ono".er, bifi~nc$iorlql ",ono",er, adjuvants into the syrup of step two.
A fifth step is to degas the curable co""~osilions under vacuum to remove bubbles, dissolved air, volatile solvents, oxygen, and the like. Although it is preferable to do this step just prior to co~tir~ it may be carried out at any time from a few hours to several weeks prior to coating To insure stability of the ~eg~csed curable cGlllpcs;~ion~, it is p~efe~le to keep them from unwanted exposure to light.
Once the curable adhesive compositions have been p, ~pa. ed using either Method 1 or Method 2, the co",?os;lions can be coated onto a carrier web and poly",~ ed to produce a curable pressule sensitive adhesive having an enlh~nced shelf life such that the pressure sensitive adhesive p~opel lies are retained for a time period longer than similar art known epoxy-acrylate curable adhesives.
Thermal rroc~ ,.g Thermally initi~ted free radical pol~"~eli~lions ofthe invention are carried out using a single heating zone in the poly",~.i~lion zone or multiple heating zones in the pol~lllel;~lion zone. The curable adhesive composition, can be coated via a coating station onto at least one major surface of a carrier web. In many situations, it may be desirable to coat between a bottom carrier web and anupper carrier web.
Once coated, the curable adhesive composition is processed through at least one pol~"~el i~alion zone wherein the curable adhesive composition is thermally poly",e.izcd by heating the same within a thermal buffer having a heattransfer process characterized by a heat transfer coefficient of at least 25 W/(m2 K) to a te",pc. atllre sufficient to initiate thermal poly",e, i~tion for a period a time sufficient to effect about 5-100% conversion ofthe free-radically polymerizable monomeric mixture or prepoly",e,i~ed syrup to polymer. When the process is carried out in one heating zone, it is prefe, l ~ d that the time and tt"~?e, al~lre be W O96/14349 PCTrUS95/13204 such that at least 90% of the free radically polymerizable monomeric mixture or prepol~...c.iLed syrup is converted to polymer. Furthermore, it is adv~nt~geous that the heat ll ansl;~. coefficient for the heat l- ansîer process within the thermal buffer be relatively high, prc~.ably 100 W/(m2 K) and most prefc.ably at least 500 5 W/(m2 K) Thermal control of the polyl,-e. i~ation process of the current invention can be stated as follows. As the polylll~ alion occurs throughout the cross-section of the pol~l,.e.;Lalion mixture, the energy balance on a small unit volume of polymerizable mixture cG..~ c conlpon~,.lls relating to the internal heat genclalion 10 created by the pol~...c.i~lion reaction and on the heat llal.srel by conduction into and out ofthe small unit volume from the :~llllOUmling units volumes. The rate of heat flow out of a unit volume must be fast enough to prevent an excessive te~llpp-~alure rise within the unit volume caused by the reaction exotherm.
If more than one heating zone is used, the first heating zone of the 15 poly...e. i~alion zone can effect as little as 5% conversion of the free radically polymerizable ..ono...e. ic mixhtre. Preferably, the multi-stage process (that is, use of more than one heating zone or the co.~ -alion of a pre-heating zone and at least one heating zone) is conducted continuously, that is, in-line without interruption of the poly-..e.i2alion process. The coated mixture is heated to a first 20 te~llpc~alllre and l~a;nt~ ed for a first time period and then immediately moved into a second heating zone with no interruption of the process b~l~. een the heating zones. There may also be a p~ ~ ke~ g zone wherein the coated mixture is heated to a point just before co.. Pnc~ .. , .~ of polymerization of the free radically poly..,c-i able morw".c-ic component(s). When using more than one heating zone, 25 the te..li)el ~lure of the second heating zone is generally greater than that of the first heating zone.
It is within the scope of the present invention to use more than two heating zones. When each zone subsequent to the first heating zone is used to initiate thermal initiators, the tc;",~c. alure of each subsequent zone is higher than the 30 previous zone.
When a single coated carrier web is used to prepare PSAs of the invention, pol~...c~i~lion is preferably carried out such that oxygen is eccçnti~lly excluded W O 96/14349 PCTrUS95/13204 from the pol~ iGn zone. However, when the free-radically polyllle.i~ble monomeric mixture or partially prepolymerized free radically poly.lleli~ble monoll" .ic mixture is coated be~ ,en two carrier webs, it is generally not necescz- y to eYclude oxygen from the polyrnerization zone.
The heat llar.~r~. process within the thermal buffer can include but is not limited to forced or hll?;nged air, helium, or hydrogen; heat llar,sf~r via conduction, such as a metal platen, or heated metal rolls; or via convective ~1 ansl~r to liquids, such as water, perfluorinated liquids, glycerin, or propylene glycol. Heat ~I drlsL r processes that are characterized by having heat ll ~n~re~ coçffi~ientc of at least 25 W/(m2 K) are conQ;dered to be within the scope ofthe present invention.Additionally, it is also within the scope of the present invention to add salts or low molecular weight organic corllpounds to a fluid heat llansrer medit~m to alter the characteristics of the thermal buffer, such as providing for reduced oxygen content, solubility of monomers and the like. It should be noted that it is not neceSsqrywithin the thermal buffer to surround the coated construction with the heat transfer medium; contact on one side ofthe carrier web or poly",e.izalion mixture may be suffici~nt Furthc~",o,t;, physical prol)c. Iies, such as boiling point of the heat l~nsr. ~ fluid should be taken into consideration when designing a thermal buffer, along with initiator type and concenllation~ processing temperature and the like.
Curable adhesive tapes of the present invention, such as ll ~hS~I, microstructured, foamed, and/or opaque tapes can be preparcd as stacked layers and/or in ml~ltiple layers, ~I.c~;n more than one layer of polymerizable compositions is coated between more than one solid sheet material, then passed into at least one heating zone to effect polyl-,e. i~tion of all layers. This is an advantage over photopoly",.,. i~able systems, wherein the poly"~e, i~;"g radiation may have difficulty reaching into all layers of the construction equally. An additional advantage is that two or more di~re-enl liner materials may be used simultaneously in order to improve the efficiency and throughput of tape production facilities. As will be appreciated by those skilled in the art, such liner material can have a low adhesion surface(s) and can be removed after polymerization is complete or one such surface can be a tape backing material that remains pe,...znf~-~ly affixed to the curable adhesive product.

~y It is also contemplated that multiple coating st~tionc can be positioned serially or in parallel up stream from the po~ i~tion zone. This can be accomp!ished with or without the use of multiple upper carrier webs.
A stacked tape configuration is also within the scope of the present 5 invention. For eY~rnrle a four stack layered tape having a bottom liner and three liners sepalaling four coated layers of pol~l"c.izable composition of the invention can be constructed using mllitiFle coating station. Optionally, a top-most (e.g., fifth) layer is within the scope of the invention when, for example, it is desired to exclude oxygen from the top-most coated layer. Furthermore, it should be 10 app, ~"a~ed that a four-layer configuration is merely a single contçmpl~ted confi~u, ~tion. For example, the number of layers should not be construed to be limited to four and could be two or more, the liners used could be di~. ~.lt materials, the curable syrup could be di~r~n~ for each layer, or even multilayered between each liner.
A multi-layered tape configuration is also within the scope of the present invention, wh~rein two or more layers could be coated one atop the other upon a single liner. Optionally, such a multilayer may be part of a stacked configuration, as previously desc,il,ed.
The cured coated constructions can be post-treated or post-conditioned, 20 that is, further treated after poly",e,i~lion of the free-radically poly",e. ~ble component(s), but before the cationically cured cG",pone"l is cured. Such ~,e~..e~le can be useful, for e~alllple to ...; .;~ e monomer residuals, increase shear strength, corona-treat the coating~ and provide cross-linking. Post ~It.~
techniques typically involve an energy source such as microwave, e-beam, IR, electrom~netic radiation, radiant heat, forced.air, impinged air, metal platens, and heated metal rolls. It will be appreciated that any post-treatment or conditioning process typically used by those skilled in the art for treating tapes, films and the like can be used in co,.,bi"alion with the present invention.
Thermally initi~ted free-radical poly",~ ions of the invention may also be carried out in an extruder. See, for exarnple, U.S. Patent No. 4,619,979, thecontents of which are incorporated herein by reference, for a detailed description of free-radical pol~",~,.i~lions in an extruder.

~5 Extruder pol~l"c.;~AI;on.s also known as "reactive extrusions," are similar to bulk pol~",e~i~lions but overcome the dla~backs of poor mixing and poor heat ll ar~srer in the viscous reaction mass, and of loss of control over molecular weight distribution in the res..lt~nt polymer. An extruder is characterized as being a wiped 5 surface reactor colll~l;s;ng a shell or vessel which cGI~ c at least one rotor having a wiping portion located close to the inside surface of the shell and a root portion which is spaced ~ A ~ 11y further from the shell than the wiping portion. As therotor is rotated, the wiping portion passes close enough to the inside surface of the shell to clean the surface and form a seal when the reactor cor,l~ns l~lonGIller10 and/or polymer but not so close as to cause pe.ll,anent defo~ alion of either the rotor or shell. It is ~eceCc-~ y that the root surface of the rotor also be wiped or cleaned continuously during OpC~alion ofthe reactor.
Interrneshing twin screw extruders may be used as wiped surface reactors.
Although corolat;ng twin screw extruders may be used, counter-rotating twin 15 screw extruders are prefe- - d. The counter-rolating extruder acts as a positive displ~sPmP.nt pump conveying the reacting stream, and it also behaves like a series of small mixing zones or continuollc stirred tank reactors. The counter-rotatingtwin screw extruder also gives good control over the reaction telllpe~alure~ thus giving the required control over polymer molecular weight and molecular weight 20 distribution.
Poly...e.;~lion in an extruder can be easily carried out in an oxygen-free manner, since the extruder itself is sealed, and all re2 ct~nt.c can easily be purged of oxygen and stored in an inert atmosphere prior to being pumped into the extruder.
Thus, poly-..e.i~alion is carried out in an atmosphere sufficiently free of oxygen so 25 that no serious inhibition of free-radical poly..,e~ ion occurs.
When the monomeric mixture is converted to polymer and is conveyed to the end of the extruder, it can be conveniently extruded or coated directly onto a suitable substrate (e.g, a tape backing or a liner), since there is no solvent or reaction me~ lm to be evaporated. When the reaction mixture exits the extruder 30 and is exposed to air, pol~,.,e.;~ation ceases. The coated PSA ofthe invention thus obtained can be stored for an extended period before its final use.

W O 96tl4349 PCTrUS95/13204 ~ ~, In use, the counter-rotaling twin screw extruder is divided into a number of sections having controllable configurations of both the extruder screws and the barrel Thus, extruder screws may be composed of a number of separate sectiollc which may fit onto a ccJ~Iu~on drive shaft by means of a keyway and which may be5 dic~ bled and l~.anged in various orders and orienl~l;ons For eAa~..ple, the screw may have one pitch in the inlet section, another pitch in the middle of the screw length and yet another pitch toward the exit end of the extruder. Or, while most sections of the screw may be oriented to convey the reaction mass towards the extruder exit, some sections may be r~ ,ed to increase dwell time and mixing10 Finally, barrel sections may be configured as either heating or cooling sections.
Pcesidence time and time distribution needed to complete the reaction generally in a wiped surface reactor is controlled by the geon.et~y, the ~otational direction, and the rotational speed of the extruder screws Typical residence times for production of PSAs of the present invention are in the range of S min-ltes to 15 1 5 minutes In practice, a ...ono...c. mixture or prepolymer as described in Method One or Method Two, above, is prepar~d in a premix tank or holding tank where it is deg~csed and covered with a blanket of inert gas such as nitrogen From the holding tank, it may optionally be pumped to a static mixer, where it may optionally be preheated to a te~llpe~all~re in the range of 35C to 55C, then introduced into the inlet of the wiped surface reactor at a pressure sufficient to process stability After an approp, ;ate residence time, the resulting polymeric material is withdrawn from the reactor and directed to a coater or otherwise packaged In another aspect of this invention a mixture of free-radically polymerized polymer, cationically-polymerizable monomer and catalyst system may be melt blended A melt blend is formed by heating the mixture to at least the softening point ofthe free-radically polyl~.c.iLed polymer, typically between about 100C and 150C, with ..,echanical agitation to produce a homogeneous mixture During the 30 process of melt-blending, the free-radically polymerized polymer, cationically-polymerizable monomer and catalyst system are mixed, such as in the mixing barrel of a single screw or twin-screw extruding apparatus wherein the mixture is heated during mixing in the Pbsence of actinic radiation that would activate the catalyst.
See, for example, "Polymer Extrusion" by Chris Rauwendaal, ed. Hanser Publish.,-~, 1986, pages 322-330, for a det~iled des~ ion of mixing in screw extruders.
Free-radically pol~ .iLcd polymer, cationically-polymerizable ",ono"ler and catalyst system are cG~ ined in a melt mixing apparatus where they are heated and melt blended to form a homogeneous mixture. A~er an app.op,;ate residence time, the res~llting polymeric material is withdrawn from the melt mixer and direcled to a coater or otherwise pa-~ed and cooled.
Free-radically pol~.,-e,iL~ polymers may be pr~parcd in any of a number means known in the art, such as photo-pol~",~"~alion or thermal-pol~",e,i~lion, either of which can be carried out in the bulk (100% solids) or in solution. If poly",c. i~lion is carried out in solution, the solvent must be removed prior to melt blending. ~ bly the (meth)acrylate polymer is yrepared by photo-polymerization in the bulk with the cationically-polymerizable monomer present.
Curable pressure sensitive adhesive compositions of the present invention are useful for coatin~c foams, shaped articles, adhesives, filled or reinforced composites, abrasives, caulking and sealing compounds, casting and molding compounds, potting and enc~psul~ted compounds, i".pregnating and coating compounds, and other applications which are known to those skilled in the art.
The present process may be used to m~nuf~cture many dif~erent types of tapes. Various flexible b~ckinge and liners (also referred to as "substrates") may be used, including films (t,ans~arenl and no"l,arls~aren~), cloths, papers, non-woven fibrous constructions, metal foils, aligned fil~mente, and the like. The bac~ing.e and liners are chosen to be co",pa~ible with the processing parameters of the present invention. For example, an u~ltreated paper liner may not be the backing or liner of choice when using a fluid heat e,.change rne~iurn such as water.
The poly".e.,z~ble mixture or prepolyrnerized syrup can be coated onto any suitable substrate, using coating techniques known to those skilled in the art.
Furthermore, the poly~nerizable mixture can be coated onto a moving substrate that does not become a part of the finished article, so as to produce a free-standing film W O96/14349 PCTrUS95/13204 or sheeting The compositions are typically coated to a dry thic~ness that rangesbetween 0.025 to 5.0 mm.
Af~er the curable pres;.ure sensitive adhesive co.--posilions have been fabricated into an article, such as, tape, or l,~..s~r film, the articles should be 5 stored in the ?bSel-Ge of actinic ra~ tion which is capable of activating the catalyst system.
To convert the curable pre;,~ule sensitive adhesive into a structural or semi-structural adhesive, the curable pre~;.ul .; sensitive adhesive is irr~ ted Irradiation sources that provide light in the region from 200 to 800 nrn are effective in the practice ofthis invention. A pr.,f,.~,d region is b~l-.2e-l 250 to 700 nm. Suitable sources of radi~tiorl include l~C.~.u~ vapor dis.lla~ lamps, carbon arcs, t..~ten lamps, xenon lamps, fluorescenl lamps, lasers, slmlieht etc. The re~uirct amountof exposure to effect po~ tl iLa~ion is dependent upon such factors as the identity and concentrations of the photoinhi~ted catalyst system, the particular free-15 radically and c~tiDrrC~lly pol~,..c,i~able monomers, the thickness ofthe exposed material, type of substrate, intensity of the radiation source and amount of heat associated with the radiation.
Optionally, the photoactivated adhesive (that is, the structural or semi-structural adhesive) can be heat treated to complete conversion. Suitable 20 sources of heat to cure the thermosetting (epoxy) compositions of the invention include induction heating coils, ovens, hot plates, heat guns, IR sources insludinE
lasers"..ictu~a./e sources, etc.
Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in 25 these examples, as well as other conditions and details, should not be construed to unduly limit this invention. All materials are co...n.e. cially available, for example from Aldrich Chemical Company or known to those skilled in the art unless other~vise stated or app~.,..~.

2q Glossary 350BL bulbs fluo~cscG.ll bulbs available from Sylvania Corp. under the trade decign~tion F15T8/350BL
CpFeXyl SbF6 (eta6-xylenes(mixed isomers))(eta'-cyclopentadienyl)iron(l+) hex~fluQro~ ;...or,ale EPON 1001F diglycidyl ether of ~is~,henol A (epoxy equivalent weight = 525-550 g/eq) (available from Shell Chemical Co.) EPON 828 diglycidyl ether of bi~,h~nol A (epoxy equivalent weight = 185-192 g/eq) (available from Shell Chemical Co.) ERL-4206 vinyl cyrl~heYPne dioxide (available as BAKELITE ERL~206 from Union Carbide Corp.) ERL~221 3,~ cpoA~cyclohexylmethyl-3,1 epoA~c~clohexane carboxylate (available as BAKELITE ERL 4221 from Union Carbide Corp.) ESACURE KB-1 2,2-~ l.oAy-2-phenyl acetophenone (available from Sartomer Chem: -~lc) IBA isobutyl acrylate nBA n-butyl acrylate PERKADOX 16 di(4-t-butylcycloheAyl)peroxydica.l,onate (available from Akzo Ch~mir~lc Inc.) POEA phenoAy ethyl acrylate Super Actinic bulbs fluor~isce.ll bulbs available from Philips T.ighting under the trade decign~tion TLD15W/03 tBOX di-t-butyl oxalate (available from Aldrich Chemical Company) THFA tetra hyd,oru.ru,yl acrylate UVI-6974 50% mixed triarylsulfonium hexafluoroa,llhllonate salts inpropylene ca,l,onate (available as CYRACURE UVI-6974 from Union Carbide Corp.) V-601 dimethyl 2,2'-azobisisobutyrate (available from Wako Chemical Co.) Examples Test Methods Dif~erential Scanning Calorimetry (DSC):
S Dirrercnlial Sranning Calo,i",et,y was used to measure the exothermic heat of reaction aoule/gram (J/g)) associated with the cure of the cationically pol~,.,c. i~Lble monomer. The exotherm profile, that is, peak te.llpc:l d~LIre, onset temperature, etc., of the exotherm provided infol lnation on conditions that were needed to cure the material. DSC samples were typically 6 to 12 milligrams and were run in sealed pans on a Seiko Instruments DSC 220C at a heating rate of 10C/min. The onset tempelat~lre (To~ ) is the point of intersection between thetangents drawn to the curve along the b~sPline, and after the onset of the exotherm at the point of maximum change in slope. The integrated energy under the W O96/14349 PCTrUS95/13204 exothermic peak is related to the extent of cure. For a stable composition, more of that exotherm should remain with time indic~ting the composition is not curing prematurely. For an ~ Cl ~le co.l.pGs;lion, the exotherm energy will de~ - . ase more rapidly with time inAir~tin~ that the cG...pos;lion has undergone some degree of5 cure prematurely.
Photo Differennal Scanning Colorimetry (PDSO
Photo Di~er.lial Sc~nnirlg Calo.i-..~l.y was used to measure the exothermic heat of reaction (Joule/gram (J/g)) associated with the cure of the cationically polymerizable ."ono",er upon eYros~re to light. PDSC samples were 10 typically 6-12 ~ ,~..s and were run in open pans on a Seiko Insllu...e.ltj PDC121 at a heating rate of 10C/minute after a photolysis step using a 200 wattmercury-xenon lamp. The analysis of the exotherm profile was con~ucted in the same manner as desc- ibed under the DSC desc- iption.
Overlap Shear Strength Sarnples were preparcd by cutting 12.7 mm x 25.4 mm spe~ enc from the adhesive film. The silicone release liner was removed from one side of the ~I,eci-..en and the exposed adhesive was applied to one end of an ~ mimlm test coupon measuring 1.7 mm x 25.4 mm x 50.8 mm. The silicone release liner was removed from the other side of the speci--,en and another identical ~lumimlm 20 coupon was placed over the adhesive such that there was a 12.7 mrn overlap of the coupons and with the l~nco~ted ends ofthe coupons aligned in opposite directionsfrom each other. The coupons were clamped together and thermally cured. The pr~pal~ d sa-"ples were cooled for at least 1 hour at about 22C before testing.The lap shear was dete....i-.ed using an Instron Model 1122 tensile tester according to ASTM Test Method D1002-72 with a crosshead speed of 5 cm/min. The lap shear strength is reported in Megapascals (~a).
180 Peel Adhesion Peel adhesion samples were ple~)ared by applying a 12.7 mm wide strip of the PSA tape to a desired panel (either 1.7 mm thick 50mm x 125 mm ~lllmimlm or standard 2S mm x 75 mm glass mi~,oscope slide). The average peel adhesion value was determined by doubling one end of the adhesive strip back over itself at W O96/14349 PCTrUS95/13204 180, and measuring the force required to peel the tape from the substrate at a rate of 30.5 cm/minute using an Instron Model 1122 tensile tester. The 180 peel adhesion values were reported in Newton/ce.,lin,~ lers (N/cm). Further details of this test are shown in "Test Methods for Pressure Sensitive Tapes", available from the Specifir~tions and Technical Cc.. ;l ~ee of the Pressure Sensitive Tape Council, 5700 Old Orchard Road, First Floor, Skokie, IL 60077, under the test d~cig~ ;on PSTC-1.

E~ample 1: Reactive Extrusion of poly(acrylate) A nu~lul~ of 60 parts 75:25 ratio of phenc.~lh~l acrylate:isobo."~l acrylate, 40 parts 75:2S ratio of EPONTM 828:EPON~M 1001F, 3.8 parts 1:1 ratio of cyclohexane ~ h~nol:1,6-h~-AneJ;ol 1.2 parts Wako V-601TM (25 weight percent in propylene carbonate) and 1.6 parts CpFeXyl SbF6 (25 weight percent inpropylene carbonate) was metered into the throat of an 18 mm counter-rotating twin screw extruder by means of a peristaltic pump. The mixture was conveyed 15 down the length of the extruder, operated at a screw speed of 50 rpm, through 8 heated zones (72, 81, 92, 96, 105, 110, 11S, and 120C, res~,e~ ely), exiting the extruder at 120C as a relatively low viscosity, foamy viscoelastic mass. DSC
analysis ofthe material, cooled to room te.l.~,elal, re, indicated a peak exotherm te,..pe.~ure of 229.9C and a cure exotherm of 74.6 J/g. PhotoDSC analysis 20 showed a peak exotherm te...pe.~ re shift to 105.2C and an increase in cure exotherm to 173 J/g after a two-minute photolysis step. A~er 429 days of storagein the dark at room tel"~,c. a~lre, photoDSC of the sample gave a peak exotherm te...perature of 110.3C and a cure exotherm of 171 J/g. This example shows thatthe PSA plepal ed by reactive extrusion has a very long shelf life, with essentially 25 no ad~,anc~...ent of the epoxy resin over a 14-month period.
Adhesive tapes were prep~red by pressing this polymeric material to a thic~ness of 0.200 mm between a 0.036 mm poly(ethylene terephsh~l~te) film and 0.100 mm silicone-coated poly(ethylene terephth~l~te) film using a heated platenpress at a te."pc. a~ure of 170C. A~er cooling to room temperature these tapes 30 were tested for 180 peel adhesion to glass and aluminum substrates with and without curing. Curing was carried out by exposing the previously prepared panels W O96/14349 PCTrUS9S/13204 to irrr~ tion under Super Actinic~ bulbs for 5 minl)tes and then heating in an oven at 100C for 10 min~tes. The res~lfing peel values are sn.. ~.,zed below Average ~eel A(l~- D~ (N/cm width) Sample Glass Aluminum Before cure 0 97 10.3 After cure b?~cl~in~ failure * backing failure 5 ~ The 0.36 mm poly(ethylene te.e~h1h~l~te) film be^l~in~ was dete.l.ut~ed to have a break sl~ ,lL of 31.3 N/cm width, inflic~ting that a peel adhesion greater than this value had de~lelop~d as the result of curing Example 2: Shelf-life of a Coated Sample Prepared by Thermal Polymenzation A -fi~.lu.e of 30 parts phenoxyethyl acrylate, 30 parts isobornyl acrylate, 40 parts ERL~221TM epoxy l"ono.,-c- and 0.01 parts KB-I photoinitiator was prepared and purged with nitrogen and irradiated with 350BL fluo. esc- nl bulbs with stirring until the viscosity of the mixture was suitable for coating (about 1055 kPa).
A mixture of 100 parts of the above syrup, 0 4 parts ground CpFeXyl SbF6, 0 8 parts methyl ethyl ketone, 0.1 parts ~.f~ .~nef~;ol diacrylate, 0.1 parts V601 initiator, 0.075 parts PERKADOX~M 16 initiator and 4 0 parts 1: 1 mixture of 1,4-cyclohexane dimeth~nol:l~6-hexane diol was de~sed and knife-coated at 0 125 mm thic~n-~cc between two 0 050 mm silicone-coated white 20 poly(ethyler.~,t~rephth~l~te) films under subdued lighting The sandwich construction was placed on an ~IIlmimlm plate heated to 90C for 15 minl1tes~ then cooled to room tel~lpe~al~lre~ DSC analysis ofthe acrylate-cured film, in the absence of a photopol~,...e. ~tion step, showed an exotherm onset t~...?e,al~lre of 210.4C, a peak exotherm tt:-"p~ Lre of 226 8C and a cure exotherrn of 45 2 2S J/g PhotoDSC ofthe sample showed an exothenn onset te".pe.al~lre of 77 9C, apeak exotherm at 94.6C and a cure exotherrn of 204 7 J/g after a five-minute photolysis step The cure exotherm energy was monitored as a function of time in subdued lighting at room tcl~lpclal~lre to deterrnine the shelf-stability ofthe sa~--pl~s The measured cure exothenn energy after a photolysis step is ~ 1.5~ ized be!ow.

Table 1 Days at Room Cure Energy Appearance Temperature (J/~) 0 204.7 ll~nsl,ale.,l, tacky PSA
29 188.7 llans~,are.~l, taclyPSA
44 18S.9 llans~are~ tacky PSA
89 174.1 I,~nsyarc.. .l, tackyPSA
139 171.1 l,ans~,~e.lt, tackyPSA
217 195.3 ~lansl.are.~, tacky PSA
258 193.9 l,~s~ t, tackyPSA
332 202.1 l,~hs~ .,l, tackyPSA
391 186.3 ll~ ,a..... nl, tacky PSA
398 213.3 tl~.a,e"l, tacky PSA
422 187.9 transparent, tacky PSA
This e,.~llple shows that no ad~ ceme..l of the epoxy monomer has taken place after more than 14 months of storage at room te.l")er~ re, and that the PSA
has ~XcellPnt shelf life aPter thermal pOl~lllCi i~tion.

Examples ~6 and lC to 4C: Photo-polmeruation of the Acrylate vs.
10 Thermal-polymerization A co~t~ble acrylate syrup was made that conlained 60 parts by weight of nBA and 40 parts by weight of T~A. 0.04 parts by weight of KB-l photoinitiator were added to the acrylate mixture, the mixture was purged with bubbling nitrogen, and the acrylate l,lonon,e.s were taken to appr~Ai"lately 10%
polyrnerization conversion by irradiation with 350BL fluorescent bulbs. 60 partsby weight of this syrup was mixed with 40 parts by weight of an epoxy mixture that consisted of 80 parts by weight of Epon 828 and 20 parts by weight of Epon lOOlF. Eight di~.en~ formulations were prepared from this epoxy/acrylate mixture concisting ofthe cG,I-ponc..ls and quantities s~,m...a,ized in the Table 2 20 (all quantities are parts by weight).

W O 96/14349 PCTrUS95/13204 3 ~) Table 2 Component C1 C2 C3 C4 3 4 S 6 EpoxytAcrylate 100 100 100 100 100 100 100 100 Mixnlre CYC1Q~ 4.0 -- 4.0 -- 4.0 -- 4.0 ?
t-BOX -- -- 0.4 0.4 -- -- 0.4 0.4 KB-I 0.6 0.6 0.6 0.6 CPFeXYISbF6 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 V~01 -- -- -- -- 0.1 0.1 0.1 0.1 r~.hdUA P-16 - - - - 0.15 0.15 0.15 0.15 Prior to co~ting each of the forrn~lqtiQ~e was de-aerated in a vacuum ch~n-ber, then knife coated at 0.75 mm th;~l ness between two 0.100 mm 5 ~ a~ tpolyelh~l~nete.ephlh~lqtereleaseliners. SamplesCl throughC4were irradiated for 13 minlltes with 350BL fluor~sce.ll bulbs at a light dosage of 1960 mJ/cm2. These films were llan~,artll~, tacky, self-supporting pres~,J,e sensitive adhesives. Samples 3 through 5 were i.,u,,e.:;ed in 83C water for 15 mimltes followed by 10 minutes in a 100C oven. These films were also lr~spalen~, tacky,10 self-sup?ol ling pressure sensitive adhesives.
Samples of these adhesives were used to bond 50.8 mm x 25.4 rnm x 1.7 mm ~ mimlm panels. Prior to bonding the panels were wiped clean with iSOpl opanol. Samples 3 through 5 were irradiated for 5 minutes under Super ActinicTM bulbs prior to pr- pal ;ng the bond. An overlap joint of app, o~lllately 1.2 15 cm in length was formed and the bonded strips were placed in an air circul~tinE
oven at 100C for 30 mim)tes The overlap shear bond ~ ir,~;lh was measured using an Instron Tensile Tester, model #1122. The jaw sepa~ a~ion rate was 5 cm/min. The results are sunlll,al;~ed in Table 3.

W O 96/14349 PCTrUS95/13204 Table 3 Overlap Shear BondBond Failure SampleStrength (MPa) Mode C 1 4.48 Adhesive C2 6.72 Adhesive C3 6.53 Adhesive C4 7.52 Adhesive 3 1.01 Adhesive 4 1.73 Adhesive 7.16 Adhesive 6 5.43 Adhesive Sa-~E les 3 and 4 were found not to be fi~lly cured. Additional overlap shear panels were l)r~ ?arcd in the same manner as des_,il.c~ above with the exceptionthat the bondet strips were placed in an air circ~l1qting oven at 120C for 30 minllteS The overlap shear loond strength of these sa.l,ples was measured as described above and the results are t~b~ ted below.

Sample Overlap Shear Bond Bond Failure Strength (MPa) Mode 3 3.30 adhesive 4 5.63 adhesive The room tc.. " c.al~lre shelf-stability ofthese san,~les was monitored by det~ ,n;ng the epoxy cure exotherm energy using a Seiko DSC as a filnction of time at room tc.,.p~ re. Samples 3 through 6 were irradiated for 5 mimltes under Super Actinic~ bulbs prior to analyzing in the DSC. Samples C1 through C4 were analyzed without the photolysis step.

Table 4 Sample 2 days at RT 15 days at RT 33 days at RT
Cl 153.1J/g (tacky) 77.2J/g(lowtack) 21.2J/g (no tack) C2 137.3 J/g (tacky) 47.0 JlB (low tack) 21.0 J/g (no tack) C3 149.2 J/g (tacky) 76.6 J/g (low tack) 30.4 J/g (no tack) C4 139.7J/g (tacky) 60.0J/g(lowtack) 18.5 J/g (no tack) 3 142.0J/g (tacky) 152.5J/g (tacky) 158.9J/g (tacky) 4 148.7J/g (tacky) 146.4J/g (tacky) 150.1Jlg (tacky) 5 159.8J/g (tacky) 159.8J/g (tacky) 166.0J/g (tacky) 6 147.SJ/g (tacky) 157.7J/g (tacky) 156.6J/g (tacky) W O96/14349 PCTrUS95/13204 After 33 days of storage at room t.. .,",~. al~re s~ ..ples C 1 through C4, those that were photo-polymerized, were cured to a significant extent and no longer remain tac.~y or function as pressure sensitive adhesives. Samples 3 through 6, those that were therrnally polyme.iLed, exhibited no signs of cure ad~nce---e-.l 5 and r~ Pd tacky and continued to function as pressure sensitive adhesives.

E~ample 7: Room Temperature L~teng After Photoactivation A IlliAIUI e of 30 parts phenoxyethyl acrylate, 30 parts isobomyl acrylate, 40 parts ERL~206 epoxy l~lono"ler and 0.02 parts KB-I photoinitiator was pl ~ d and purged with n,l~ogcn and irradiated with 350BL fluo,~sc~.,l bulbs with stirring 10 until the ViSCGSIly of the mixture was s_;t_ble for coating (about 700 kPa).
A IIPiAIU~ of 100 parts ofthe above syrup, 0.4 parts ground CpFeXyl SbF6, 0.8 parts methyl ethyl ketone, 0.4 parts h~nediol dia~,ylate, 0. 1 parts V-601 initiator, and 0.15 parts Perkadox 16 initiator was deg~csed and knife-coated at 0.
125 mm thirL . ess bel~ce.l two 0. 100 mm silicone-coated PET films under 15 subdued lighting The sandwich construction was placed in 85C water for 15 rrin~ltes followed by 98C water for 10 minl-tec then cooled to room telllpelalule~
The film was a L~or,s~arc.,l, tacky, self s~ppo, ling pressure sensitive adhesive.
DSC analysis of the film a~er 5 rni~ es of irradiation with Super Actinic~ bulbsshowed a peak exotherrn at 72.2C and a cure exotherm of 297.1 J/g. The rate of 20 cure of this film at an isoll,~ . ",al t~llpclal~lre of 60C was dete""ined by irradiating the film for 2 minllteS with Super ActinicTM bulbs with the top liner removed, after which the liner was replaced and the sample i.-,l,.~.~ed in a silicone oil bath heated to 60C for a predett;. ."i,.ed length of time (see Table 5). DSC
analysis was pe. rO, Illed on the sample after removing it from the silicone oil to 25 determine the extent of cure.

Table S
Minutes ~t Cure Energy (J/g)Residual Cure (%) 0 297.1 100.0 2 91.6 30.8 28.7 9.7 16.5 5.6 0.0 0.0 The rate of cure of this film at room te.~ e.~lu~ e was det~_. ,,uned by irrP~isti~ the film for 2 n~ s with Super ActiniclM bulbs with the top liner 5 removed, after which the liner was r~F'aced and the sarnple stored in the dark at room tc.."J.,.alur~ (-22C). DSC analysis was p~ .îol",ed on the sample a~er various lengths of time to determine the extent of cure.
Table 6 Minutes at Room Cure Energy Residual Cure Temperature (22C) (J/g) (%) 0 297.1 100.0 237.8 80.0 111.9 37.7 180 80.9 27.2 540 50.1 16.9 4680 36.9 12.4 These results show that latency of cure at room te~llpe~al~lres can be achieved after an irradiation step in these materials to allow for positioning and repositioning.

Esamples ~9: Comparison of Cationic Organometallic and Onium Photo Initiators after Thermal Pol~merization A ~ lure of 45 parts phenoxyethyl acrylate, 15 parts isobornyl acrylate, 30 parts EPON 828, 10 parts EPON 1001F and 0.04 parts KB-1 photoinitiator was prepared and purged with n;L,ogen and irradiated with 350BL fluorescel,l bulbs with stirring until the viscosil~ ofthe mixture was suitable for coating (about 700 kPa).
A mixture of 100 parts of the above syrup, 3.8 parts 1: 1 mixture of 1,4-cyclohexane ~ .Anol 1,6 hexanediol, 0.3 parts V-601 initiator, 0.1 parts PERKADOX 16 initiator, and the cationic photocatalyst listed in Table 7 was W O96/14349 PCTrUS95/13204 3 ~
deg~cced and knife-coated at 0.200 mm ~ c~ess b~l~.cen a 0.036 rnm poly(ethylene tereph~h~l~te) film and 0.100 mm silicone-coated poly(ethylene ter~phlh~lqte) film under sllbd~led lighting The sandwich construction was placed in 85C water for 15 mir.l~tes followed by 98C water for 10 min~tec then cooled5 to room te.,.p~.alllre.
These tapes were tested for 180 peel adhesion to glass and ~1- - "~
substrates with and ~nthout curing. Curing of the Example 8 material was carriedout by e~ os;ng the panels to ~ ;on under Super ActinicTM bulbs for 5 minlltes and then heating in an oven at 100C for 10 .~ çs Curing ofthe Example 9 10 material was carried out by e.~Gs;ng the panels to irradiation under 350BL bulbs for 5 mirutes with no heating step. The resulting peel values are a~ ~e~ in Table 7.
Table 7 Average Peel Adhesion (N/cm width) Esample Cst~lyst GlassAluminum 8 0.4 parts Before cure 0.06 4.4 CpFeXylSbF6 A~er cure 86.4 6.6 9 3.0 parts Before cure 0.09 3.0 UVI-6974 After cure 2.1 6.6 These results showed both the c~tiorlic organomet~ c and onium photo-activatable catalysts cant be used to prepare curable PSAs using thermal pol~-,-e. ~lion of the acrylate CO.I,pOACnt. Both of these curable PSAs de...or. ~lla~ed an inc.tase in bond ~llenglll after cure ofthe epoxy.

Esamples 1~11: Comparison of COM and Onium in Melt Blended Curable 20 PSAs Misture 1: A mixture of 45 parts phenoxyethyl acrylate, 15 parts isobornyl acrylate, 30 parts EPON 828, 10 parts EPON 1001F and 0.04 parts KB-1 photoinitiator was prepared and purged with nitrogen and irradiated with 350BLfluortsce.-~ bulbs with stirring until the viscosity of the mixture was suitable for 25 coating (about 700 kPa).
Misture 2: A mixture of 100 parts ofthe above syrup, 3.8 parts 1:1 mixture of 1,4-cycloheY~rle ~imeth~nol l~6 hexane diol, 0.2 parts KB-l W O96/14349 PCTrUS95/13204 ~q photoinitistQr was deg~csed and coated at 0.75 mm thic~npss bet~. cen two 0.100 mm silicone-coated poly(ethylene te. e~ ql~te) films. This dual-liner construction was irradiated for 15 m;nlltçs using 350BL fluoresce~l bulbs at a light dosage of 2260 mJ/cmZ. The pol~",e.iLed mixture was used in Exq-mples 10 and 11. The S liners, used to pol~",~ e the mixture were removed prior to further processin~ with the photo-activatable catalyst of the pressure sensitive adhesive.
In Example 10, a molten mixture of the polyacrylate-epoxy material with cationic photocatalyst was p.~,?ared by cGr.~hi~ g 100 parts ofthe polyl,.~ ed Mixture 2 (the liners having been previously removed before co...b;nalion) with 3.0 10 parts UVI-6974 cstiQn;c photo-;, iliator with stirring in an ~luminum conlainer heatedto 150C.
Pl.,s~ure sensitive adhesive tapes were plep~ed by pres~ing this polymeric material to a thir~n~Pss of 0.250 mm betweell a 0.036 mm poly(ethylene terephthql-q-te) film and 0.100 mm silicone-coated poly(ethylene terephth31~qte) film 15 using a heated platen press at a te.npc.al-lre of 120C. A~er cooling to roomt~..")c.al~lre these tapes were tested for 180 peel adhesion to glass substratebefore and after curing the epoxy co"lpol-~.,l of the pressure sensitive adhesive.
Curing was carried out by exposing the previously prepared panels to irradiationunder 350BL bulbs for 5 min~ltes without a heating step. The resulting peel values are su~................................................ z~i2cd in Table 8 below.In FY~ Ie11~ a molten IlliAIurc ofthe polyacrylate-epoxy material with cationic pholocalalyst was prcp~cd by colllbinillg 100 parts of the poly..,~. ized Mixture 2 with 1.0 parts CpFeXylSbF6 cationic photo-initiator, predissolved at 25 wt-% in propylene c~ul,onate, with stirring in an aluminum container heated to 1 50C.
Pressure sensitive adhesive tapes were prepared by pressing this polymeric material to a thic-~nPcc of 0.250 mm between a 0.036 mm poly(ethylene terephth~l~te) film and 0.100 mm silicone-coated poly(ethylene terephth~l~te) film using a heated platen press at a t~ pclal~lre of 120C. After cooling to room temperature these tapes were tested for 180 peel adhesion to glass substrate before and a~er curing the epoxy co.."~onenl of the pressure sensitive adhesive.Curing was carried out by exposing the panels to irradiation under Super Actinic Y~
bulbs for 5 minvtes followed by heating in a 100C oven for 10 minutes The reslllting peel values are s~ d~ed in Table 8 below.
Table 8 Example Average Peel Adhesion to Glass (N/cm width) Before cure 0.4 After cure 10.5 11 Before cure 0.2 After cure 10.9 These results how that both the c~ionic or~ano.. ,l~llic and onium photo-activatable catalysts could be used to prepare curable PSAs using melt-blending techniques. Both ofthese curable PSAs de~..ofi~l.ated an in~"ease in bond ~ n~,l}
after cure of the epoxy.
Various modifications and all~;. alions of this invention will become 10 appart.,l to those skilled in the art without depa, lhlg from the scope and principles of this invention, and it should be understood that this invention is not be unduly limited to the illustrative embod;...~ .ls set forth hereinabove. All pub!ic~tionc and patents are h~CGI ~JOI aled herein by r~ fe. ~nce to the sarne extent as if each individual publication or patent was specifically and individually inrlic~ted to be incorporated 15 by Icrerence.

Claims (12)

Claims

1. A curable pressure sensitive adhesive comprising:
(1) at least one free radically polymerized polymer;
(2) at least one cationically-polymerizabel monomer, (3) a photo-activatable catalyst system for the cationically-polymerizable monomer comprising either at least one organometallic complex salt or at least one onium salt; and (4) optionally, a monohydric or polyhydric alcohol, wherein there is essentially no conversion of the cationically-polymerizable monomer of the curable pressure sensitive adhesive for at least 10 days at 20°C, 50% RH, when stored in a manner to exclude actinic radiation.

2. A semi-structural or structural adhesive comprising the pressure sensitive adhesive according to claim 1, wherein the cationically polymerizable monomer has been cured.

3. A method of preparing a curable pressure sensitive adhesive comprising the steps of:
(1) preparing a polymerizable composition comprising a mixture of (a) at least one free-radically polymerizable monomer, (b) at least one thermal free-radical initiator, (c) at least one cationically-polymerizable monomer, (d) a photoactivatable catalyst system for the cationically-polymerizable monomer comprising at least one organometallic complex salt or at least one onium salt, and (e) optionally, a monohydric or polyhydric alcohol; and (2) applying sufficient thermal energy to the mixture to effect essentially complete polymerization of the free-radically polymerizable monomer.

4. The method according to claim 3, further comprising the steps of:
(a) applying sufficient irradiation to the curable PSA to activate the photoactivatable catalyst system, and (b) providing sufficient time and/or thermal energy to effect essentially complete polymerization of the cationically polymerizable monomer.

5. A method for preparing a curable pressure sensitive adhesive comprising the steps:
(1) preparing a first polymerizable composition comprising a mixture of (a) at least one free-radically polymerizable monomer, (b) at least one free-radical initiator, (c) at least one cationically-polymerizable monomer, and (d) optionally, a monohydric or polyhydric alcohol;
(2) applying sufficient energy to the mixture to effect essentially complete polymerization of the free-radically polymerizable monomer;
(3) mixing into the polymerized composition, (a) a photoinitiated catalyst system for the cationically-polymerizable monomer comprising at least one organometallic complex salt or at least one onium salt, and (b) optionally, a monohydric or polyhydric alcohol.

6. The method according to claim 5, further comprising the steps of:
(a) applying sufficient irradiation to the curable PSA to activate the photoactivatable catalyst system, and (b) providing sufficient time and/or thermal energy to effect essentially complete polymerization of the cationically polymerizable monomer.

7. A method for preparing a curable pressure sensitive adhesive comprising the steps:
(1) preparing a first polymerizable composition comprising a mixture of (a) at least one free-radically polymerizable monomer, and (b) at least one free-radical initiator, and (2) applying sufficient energy to the mixture to effect essentially complete polymerization of the free-radically polymerizable monomer;
(3) mixing into the polymerized composition, a second polymerizable composition comprising a mixture of:
(a) at least one cationically-polymerizable monomer, (b) a photoinitiated catalyst system for the cationically-polymerizable comprising at least one organometallic complex salt or at least one onium salt, and (c) optionally, a monohydric or polyhydric alcohol.

8. The method according to claim 7, further comprising the steps of:
(a) applying sufficient irradiation to the curable PSA to activate the photoactivatable catalyst system, and (b) providing sufficient time and/or thermal energy to effect essentially complete polymerization of the cationically polymerizable monomer.

9. A pressure sensitive adhesive prepared according to the methods of claims 3, 5 or 7.

10. The pressure sensitive adhesive according to claim 9, further including electrically or thermally conductive particles.

11. A structural or semi-structural adhesive prepared according to the methods of claims 4, 6, or 8.

12. The structural or semi-structural adhesive prepared according to claim 11, further including electrically or thermally conductive particles.