CA2175574A1 - Anticorrosion adhesive composition and method - Google Patents

Abstract

An adhesive composition comprising particles of an inorganic oxide of silica or alumina having cations bound thereto, which particles inhibit or prevent corrosion of metal when the cured adhesive composition is in contact therewith. A method of bonding is also described

Description

W09S1126.17 21 7~74 PCT/US9~11273~
Ant~corroslon adhes~Ye compos~t~on and method FJFT n OF TE~ ~VEI`lTION
This invention relates to adhesives containing an agent to resist corrosion S on metal surfaces.
BACKGROUI~D OF T~TF. I~VF.l~lTION
Corrosion resistant treatments for metals are well known in the art and play an important role in l,, the bond between a coating, such as 10 paint, or an adhesive to the metal over long periods of time, especially in corrosive ~I.vil~ The most commonly ~ corrosive CIIV;I~ ' include exposure to salt water from oceans, road treatments for ice containing corrosive chemicals and/or salt, acid rain, and the like.
There are methods of treating metal surfaces before applying paints and 15 adhesives to protect the metal surface from corrosion. The methods generally involve a conversion coating in which a protective oxide is formed on the metal surface, or an etching process to form a protective oxide. The etching process may further include processes of anodizing and/or priming.
One well known method of preparing aluminum is referred to as an 20 "FPL _tch" which has been used in the aerospace industry since the early 1950's. Tbe FPL etch process includes the steps of optionally degreasing the aluminum part with solvent, degreasing with an alkaline solution at 180F, immersing the part in an aqueous solution of sulfuric acid and sodium di~lu~ at 160F, rinsing, and drying the part at room i , and 25 elevated ~I~ ldlUlC. Although the process has been useful, there are .,vil~ ' and health concerns in using chromates and corrosive acids.
Conversion coatings known in the art include phosphate conversion coatings, chromate conversion coatings, and cobalt conversion coatings.
Other methods of improving corrosion resistdnce include adding a 30 corrosion inhibitor to adhesives. Inhibitors currently used include chromate salts, such as barium chro~ate, stro~tium chromate, l~.-g~ ~ . chromate, etc.

WO 95112647 2~ P~ 7 ~ PCTNS91/1273 Certain cations, such as zinc and calcium, have been used as corrosion inhibitors in protective coatings such as paints. The cations are typically usedin the form of spanngly water soluble salts.
Shieldex'U anti-corrosion pigment is an io.. CAC.II~lLlgC~i silica said to be 5 useful in paints and coatings.
SUMMARY OF THE INVENTION
The present invention provides a curable, structural epoxy adhesive c ~ , "~,, (a) an epoxy resin having an average epoxide functionality of greater than one;
(b) a base curing agent in an amount sufficient to cure the epoxy resin through reaction of a, ~ 1 ..l.l.;li- or electrophilic group contained in the base curing agent with the epoxy ring contained in the epoxy resin;
(c) particles comprising an inorganic oxide of silica or alumina having cations bound thereto, the particles being of a type which and present in an amount effective to inhibit or prevent corrosion of metal to which the epoxy adhesive ~ has been applied.
The present invention further provides a method for inhibiting or preventing corrosion of a metal substrate which has been bonded to another substrate, the method comprising including particles ~c~pn~in~ am inorgamic oxide of silica or alumina having cations bound thereto in the adhesive being employed to bond the metal substrate to the other substrate, 25 the particles being of a type which and present in the adhesive cu~ o~ , in an amount effective to inhibit or prevent corrosion of the metal substrate in the area thereof which is in contact with the adhesive DF-~CRIPTION OF TT~F. INVENTION
The present invention provides epoxy adhesive ~ ;r ~ c that are useful as structural adhesives that provide corrosion resistance to the substr2te WO 95/12647 2 1 ~7~; 7~ PCI/I~S94/1273J
from salt solutions. The adhesives are y~ULi~;ulAlly useful for metal substratessuch as aluminum and steel and the preferred v,~ do not contain hl.' heavy metal elements such as chromium.
Structural adhesives form strong integral bonds between substrates.
S Bonds formed with structural adhesives have a room t~ u.c bond strength, as measured by a test well known in the industry, referred to as a T-peel test, of at least 10 pounds per lineal inch (pli) on a bond line thickness of 0.010 inch (0.2~imm). The upper limit on the structural bond strength would be the cohesive failure of the substrate or yielding of the substrate. The adhesive 10 . , -- - of the present invention form room t~ Lu,c; T-peel bond strengths on a bond line thickness of 0.010 inch (.254 mm) of at least 12 pli, with preferred ~ ;"Ac having bond strengths greater than about 14 pli, and the most preferred ~ having bond strength greater than 17 pli.
Structural adhesive bonds can also be ~ I by a room 15 t ~ modulus, as measured by a test known in the industry as the overlap shear test, of at least 3 megaPascals (MtPa). The upper limit of the overlap shear strength would be the cohesive failure of the substrate, or yielding of the substrate. The adhesive of the invention form bonds with overlap shear strengths at room i , c of at least S MPa, with 20 preferred , forming overlap shear strength bonds of at least 7 mPa, and with the more preferred r~ ; forming overlap shear strength bonds of at least 10 MPa, and with the most preferred r~ forming overlap shear strength bonds of at least 14 MPa.
Structural bonds typically have a thickness grcater than 2 mils (0.5 mm).
25 In the practice of the invention, bond lines formed are typically greater than S
mils (0.127 mm).
Epoxides that are useful in the adhesive ~. ~ of the present invention can be any organic compound having at least one epoxy ring that is pol~..._.i~11~ by ring opening. Preferred are organic ~ , having an 30 average epoxy fimAtion~ y greater than one, and preferably at least two. The epoxides can be ~ or polymeric, and aliphatic, ~J~

W095/126~7 2~5~74 `` PCT/US9-1/12734 --uuy~ , aromatic or mixtures thereof. The more preferred epoxides are aromatic and contain more than 1.5 epoxy groups per molecule and most preferably more than 2 epoxy groups per molecule.
The useful materials have a molecular weight of about 150 to 10,000 5 and preferably from about 300 to l,OOû. Useful materials include linear polymeric epoxides having terminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymeric epoxides having skeletal epoxy groups (e.g.,p.~lybu~l;_l._ PUIY~UAY)~ and polymeric epoxides having pendant epoxy groups (e.g., a glycidyl ".~ LI,a. ly polymer or ,u~ulylll~,.), and mixtures 10 thereof.
Useful epoxide containing materials include ~u"lr ' having the required molecular weight of the general Formula I:
R' ~OG~CH-GH~d I

wherein:
R' is alkyl, alkyl ether, or aryl, preferably aryl and n is an integer 20 between 2 and 6. Preferred are aromatic glycidyl ethers such as those prepared by reacting a polyhydric phenol with an excess of epichlorohydrin. Examples of useful phenols include resorcinol, catechol, llyd-~l o, and the pol~..u_l~u phenols including p~p'-d;i~ydluAy-l;b~ yl~ p~p~-dil~ydluAy~ ' yl~
p~p~-dil~ydluAy~ ' yl sulfone, p~p~-dil~ydluAy~ , 2,2'-dihydroxy-25 1,1-' , ' y' , and the 2,2', 2,3', 2,4', 3,3', 3,4', and 4,4' isomers of ~lihyJluAy~ y , ~ llUAy~ ,i; yl~ ,LI-yl llillyllluAy~ Jh~ Llly y~ UAy~ h_.~yll.. _,llyl~lu~yll~. - Lll~ule~
y~lluAy~ h ~lyl~,~llyli' y' '- ', d;l~yllluAy~ Jh-~yllJlu~yl~ ylll~
llilly~llUAy~ yll~u~yl~ llyl~ lihylluAy~ yl~ulyllll~
30 dihJI~uAyJ;~ yl~uly y , dil~yllluA~ yl li~ y~ Aylll~
and dillylluAyd ~II_.~yl~;y~,lu~l~ A~U~C. Also preferred are polyhydric phenolic ~ .

2175~
WO95/12617 ' PCTtUS9~i/12731 ~ ~ ~ yJ~ products as well as polyglycidyl ethers that contain as reactive groups only epoxy groups or hydroxy groups.
Cnmro~ c of the above general Formula 1, but wherein n=l, are useful as optional additives in the c ~ of the instant invention so long 5 as, in the preferred ~ bol~ t, the average epoxy ~ ;ly relative to the total number of epoxy ~ r employed is greater than one.
Useful materials include diglycidyl ethers of bisphenol A and of novolak resins, such as described in "Handbook of Epoxy Resins" by Lee and Nevill, McGraw-HIll Book Co, New York (1967), '--, ' ' herein by reference 10 Epoxides with flPYihiii7PA backbones are also useful. Preferred materials include diglycidyl ethers of bisphenol A and diglycidyl ethers of bisphenol F, and most preferably diglycidyl ethers of bisphenol A, because of the desirable structural adhesive properties that these materials attain upon curing Examples of ;ally available epoxides useful in the invention 15 include diglycidyl ethers of bisphenol A (e g, those available under the tr~iPm~ c Epon 828, Epon 1001, and Epon 1510 from Shell Chemical Co, and DER-331, DER-332, and DER-334 available from Dow Chemical Co );
diglycidyl ethers of bisphenol F (e.g., EpiclonTM830 available from Dai Nippon Ink and Chemicals Inc ); silicone resins containing diglycidyl epoxy 20 r.. 1;.. 1;l~, flame retardant epoxy resins (e g, DER 580, a b.~ ' bisphenol type epoxy resins available from Dow Chemical Co ); and 1,4-butanediol diglycidyl ethers In the practice of the invention, a base curing agent is used in an amount sufficient to cure the epoxy adhesive ,: , The amount can vary from 25 an ~ ' amount based on the type of epoxy resin used to an excess of either the epoxy or the base curative, depending upon the end use of the epoxy adhesive. The amount typically ranges from about 1,5 to 200 parts by weight of curing agent per 100 parts of the total amount of epoxide used Preferably, the base curing agent will be present in an amount of about 30 2,5 to 75 parts by weight of the curing agent per 100 parts of epoxide WO 95/126 17 ~ 1 : ; PCI/US9.1/1273.1 217~5~4 The base curing agent contains at least one ~ ~rhili~ or ~ -ct~rhilir group which reacts with the epoxy ring to cross-link the adhesive ~
Suitable base curing agents include polyamide resins, aliphatic amines, polyether diamines, aromatic amines, pOl,ya~ C:" POI~
5 polyeth~.J;,.~ , phenol c.~ and mercaptan resins. Examples of primary amines include di-(4~ u~ ..yl)sulfone, di-(4-all.inu~ lyl)-ethers, and 2,2-bis(4-(,.~; ~pl "~I)propane, ethylene diamine, I ' yl~ diamine, isomers of l~ .dl~ C diamine, diethylene triamine, triethylene tetramine, L~L-~l~,Lllyl_~., pentamine, ~ triamine, N,N'-Bis (3-~ JlUltJ.Yl)-10 1,2-ethane diamine, N-(3-A r u~J~1)-1,3-propane diamine N-(2-aminoethyl)-1,3 propane diamine, isomers of c.~Iûll~ m~ diamine, 4,4'-methylene k ' , 4,4'-methylene bis[2-1l.~ , ' ' ], isophorone diamine. Examples of useful tertiary amines are di~ ,Ll~yl~lll;l~ulJIu~
and pyridine.
Examples of useful aromatic amines include di-(4-d.. li.. op'.~ l)sulfone, di (~ ~' yl)ether, 2,2-bis(4-d,..illu~ l)propane, 4,4'-diamino lliJ ' y' ~, 3,3'-dimethyl(4,4'-~ 1 methane, m-phenylene diamine, p-phenylene diamine, m-xylylene diamine, toluene diamine, 4,4'-methylene dianiline benzidine, 4,4'-i ' lin~, 4-methoxy-1,3-~ll.,..,yl-lid.l.il~c, 20 2,6-~" rJ.iJ;,I~, and ~
Examples of polyether diamines include 4,9 ,~ 1,12-diamine, 4,7,10-T - 1,12-diamine, bis(3-amino propyl)~l~i ' yJ~uru~S of varying molecular weights, and w.. ~;~lly available from Texaco Chemical Co. under the Jeffamine trade name as D230, 25 D400, D2000 and T403.
Suitable polyamido amines are the reaction products of pcl~ and dimer acids. Dimer acids are prepared by dimerizing Cl8 or C22 fatty acids from vegetable oils or animal fats. The dimer acids are then reacted further with ~1~ by a c. .- -~ ' ;. . reaction to produce the polyamido amine 30 oligomers. These oligomer are described by V. Brytus, Modern Paint and CQatin~s. Vol. 74 No.10, p. 172 (198*.

WO951126.17 i~ 7~ PCTIUS9~/12734 Examples of phenol c~ u~ include phenol, substituted adicyl phenols (nonyl phenol), diphenols sueh as eateehol, ~ind aiicyl substituted catechol, resorcinol, lly ilu~luii~u~
Examples of mereaptan resins include a'iicyl di..._.~ij~.~ such as ethane 5 dithiol, nonane dithiol, renta erythritol tetra (3-mercapto propionate), trimethylol propane tri(3-mercapto propionate), glyeol dimereapto acetate, thiolterminated polyethers and thiol terminated puly~ul~
Also useful are boron rCl~rlr~yr~ and in particuiar, boron eomplexes with "~ " ~ imidazoles such as 2-ethyl-4-methyl imidazole;
10 guanidines such as t~ llyl guanidine; substituted ureas sueh as toluene C~ u~.~ urea; ~' y, l-~ , and aeid anhydrides sueh as 4-yll~idl~ u~Ly~ ic acid anhydride, 3-1~ lL~id~yJIu~y~ la~iic aeid arihydride, and ' ylllu~b~ h ~ acid anhydride. Mixtures of more than one curative may be used. Preferred curatives for one-part adhesive 15 cr~ ~ are amines, acid anhydrides, ell~nillinr~c ' yr l ~ ir~ and mi,ctures t~iereof.
Speeific examples of base curing agents are A "rMSeries, ~ iially available from Air products and Chemica'i Company, and the SchereY Series, cu...lll~.uially available from S.h~i.lg 3~1u~g.
A. ~ nown in the art can a'iso be added to increase the cure rate of the eroxy adhesive. Such 2. ' include , ' that ean act as a curative when used a1ione, but when combined with a different class of euratives, will accelerate the curing of the epoxy adhesive ~
Examples of useful ~ include phenolic . ', tertiary amines, 25 d;~ y " I imidazole, substituted imidazole hexakis imidazole nickel phthadate eomplex, substituted ureas arid edcium ~iinuulull~ lyl~ulr~
These: ' may be used alone or in together to sccelerate the cure of an ej~oxy adhesive . ' Some examples of useful ~- include phenolic , ' with tertiary amines, 30 ~'ii. y, .~ witi'i imidazole and/or substituted ' ' . di~y~
with substituted ureas, ~iiuy~ with hexakis imidazole nickel phthdate W095/12647 217 5 5 7 4 , ` ~ PCT/US9~/1273~ ~
complex and calcium llilluulu~ 1 sulphonate with ' ' A preferred curing agenV~ i.),, is toluene .lii,u~,~ urea and d;c~ ' ' The preferred amount of the accelerator is from about 0.5 to 15 percent by weight of the adhesive system.
Tbe epoxy adhesive OI l~ includes a partieulate ion exchange corrosion inhibiting additive. The additive particles are formed from an inorganic oxide of silica or alumina and have cations chemically bound to them that are useful for corrosion inhibition. The useful cations include calcium (Ca2+), zinc (Zn2+), cobalt (Co2+), lead (Pb2+), strontium (Sr2+), lithium 10 (Li+), barium (Ba2+), and m~nrCi~.m (Mg2+). Preferred cations include calcium and zinc.
The additive partides will preferably have an average diameter of about 0.1 to 200 rnicrons. More preferably, the particles have an average diameter of about 1 to 50 mierons. Suitable additive particles include a calcium ion 15 exchanged amorphous silica gel c~llll,l~l.;ally available from W. R. Grace &
Co. under the tradename "Shieldex".
The epoxy adhesive ~,,...I,, c:l;,,,~ preferably includes a toughening agent, and in partieular, a polymeric toughening agent or a ~ ;. " of polymerie Luu~h~.~.g agents. Useful toughening agents have an epoxide; u ~, ';l.l~
20 component s~lh~t~nt~ ly insoluble in the epoxy resin and an epoxide compatible component 5~hct~nti~11y soluble in epoxy resin.
The toughening agents which are useful in the present invention include polymeric eu~ o~ having both a rubbery phase and a ~ phase, such as graft ~u~ having a pùl~ i~i diene rubbery core and a 25 pOl~ yla~G ûr P~ G shell; graft l,V~ having a rubbery core with a polyacrylate or pol~ Ll~ y- shell; and ~ particles pOIylll~.iL~ in situ in the epoxide from free-radical poly..,~liL~Lle monomers and a ~ulJol~",. lic stabilizer.
Specific examples of useful toughening agents include graft wlJolyl,.
30 having a pul~ I;L~I diene rubbery backbone or core which is grafted to a shell of an acrylic aeid ester or ..~ .11~..,l~1;. aeid ester, monovinyl aromatic WO 951126~7 21 7 ~ 5 7 ~ PCTIUS9~/1273~
llydlu~lJull, or a mixture thereof, such as disclosed in U.S. Patent No.3,496,250. Preferable rubbery backbones comprise pul~ ~ butadiene or a pol~ li~l mixture of butadiene and styrene. Preferable shells comprising pùlyl..v~ lic acid esters are lower alkyl (Cl-C4) S substituted Ir~lllll .y' Preferable monovinyl aromatic llydlu~ulJolls are styrene, alpha~ .lh.~l~L~.clle, villy I , vi~ ylv;~ b~
ia~lu~la~yl~ U~iyl~ , d;~.lllulualyl~ , and ethylchlulua~yl~
Further examples of useful IUU~ ..UI.~6 agents are acrylate core-shell graft culJul~ ,.a wherein the core or backbone is a pul~lyl~k polymer 10 having a glass transition t~ laLul~; (T8) below about 0C, such as polybutyl acrylate or ~ul.~;~ùùu~yl acrylate to which is grafted a polymer (shell) having a Tg above 25C such as pùly ' yl~
Still further examples of luu~ agents useful in the invention are ; ' particles that have a Tg below about 25C and have bcen 15 ,ool~ i~i in situ in the epoxide before mixing with the other ~ r of the r These ~ particles, commonly referred to as "organosols", are ~ol.~ i from free-radical pul~ li~l,le monomers and a ~u~ u~y ' ' polymeric stabilizer that is soluble in the epoxide. The free-radical pul~ monomcrs are ethylenically I ' monomers or 20 J;;au~"~ combined with co-reactive ~--r '- 1 hydrogen ~ . ' such as diols, diamines, and ~ Examples of these ~ particles are disclosed in U.S. Patent No. 4,525,181.
Still other lu. ~' I,, agents are rubber modified liquid epoxy resins.
An example of such a resin is KratonTM r~P656s Rubber available from Shell 25 Chemical Company. The modified epoxy resin is made from 85% by weight EponTM 828 and 15% by weight of a KratonTM rubber. The KratonTM rubbers are known in the industry as Pl~ block culJul~ .la.
Toughening agents can also include liquid epoxies, liquid amines, polyether diamines, polyhydlu~ , pul~v;..~ld~ ls, and liquid ~ly- l~
30 butadiene polymers, l,u~.li.;..e/..il-ile rubbers, ~.cubu~.y' I butadiene/nitrile rubbers, amine-terminated butadiene/nitrile rubbers, carboxyl ~ ~
g wo 951126~7 2 1 7 ~ 5 7 ~ - pCTlUS9~/1273~ --I-u~l;~ 1iuile rubbers and the amine or carboxyl terminated adducts of the polymers with epoxy resins. Amine-terminated and carboxyl t~.111;1._'~i bul~ acrylonitrile rubbers are :U.I~ .I ially available from B.F. Goodrich under the HYCAR tradename as ATBN and CTBN reactive liquid polymers.
5 t'11 11.;, '11111C of toughening agents may also be used to enhance the properties of the cured epoxy adhesive.
The toughening agent is preferably used in an amount equal to about 3 to 35 parts by weight, and more preferably about 5 to 15 parts by weight per 100 parts by weight of the epoxy resin. The toughening agents of the present 10 invention add strength to the ~ul.,~ " after curing without interfering with curing. The toughening agent may or may not react with the epoxide.
In some cases reactive diluents may be added to control the flow ;fS of the adhesive c~ ';-- Suitable diluents have at least one reactive terminal end portion and preferably, a saturated or .... ~,, t .1 cyclic 5 backbone. Preferred reactive terminal ether portions include glycidyl ether and vinyl ether. Examples of suitable diluents include the diglycidyl ether of resorcinol, diglycidyl ether of . y.' ' ~' ' ~1, diglycidyl ether of neopentyl glycol, triglycidyl ether of I ~1~1PIU1J~UIIS dipentene, and the divinyl ether of c~ " ~' Commercially available reactive 20 diluents are "WC-68" from Rhone Poulenc, and RapicurerM CHVE, a divinyl ether of ~ ~. ' ' " ' ' available from Allied-Signal Corp. of r~ .. , NJ.
Various ûther adjuvants can be added to the epoxide ~ ;-,, to enhance properties of the ' . before and after curing.
Included among useful adjuvants are nonreactive diluents; ~)L.,ii.,;4~.
such as ~UI1v~ iO..~I phosphates and phthalates; flame retardants such as borates, '..1 aluminum hydroxide, m~nf-ci~1~ hydroxide, and bromine J ~i~ thixotropic agents such as fumed silica to provide flow control;
pigments to enhance color tones such as ferric oxide, brick du$, carbon black, 30 and titanium dioxide; fillers such as talc, silica, , , calcium sulfate, beryllium aluminum silicate; clays such as bentonite; glass and ceramic beads .
W0951126~7 21 7Ss7~ , PCT/US9t~1273~
and bubbles; ~ c imparting X-ray opacity, such as barium .,.~
and reinforcing materials, such as woven and nonwoven webs of organic and inorganic fibers such as polyester, polyimide, glass fibers, and ceramic fibers.Dispersing agents and wetting agents, such as silanes, can also be added so long5 as they do not interfere with the curing reaction of the epoxy adhesive c~ The adjuvants can be added in an amount effective for the intended purpose; typically, amounts up to about 50 parts of adjuvant per total weight of ~ ' can be used.
Presently preferred ~ Of the invention or c~ to be 10 used in the methods of the invention are ~ c~n~ ly free of W..~,-lLiUII`~II
corrosion inhibitors such as aluminum phosphates and chromate salts. Further, preferred methods of the invention rely on the use of an oxide of silica or alumina having cations bound thereto, and do not involve the use of other corrosion inhibitors such as aluminum phosphates or chromate salts either in the15 adhesive , or as a ~ t of one or both of the surfaces to be bonded before application of the adhesive.
The epoxy adhesive ~ of the present invention may be formulated in a variety of ways, including one-part and two-part adhesive systems. By providing a two-part ~ ; l ;- . with the two parts being 20 combined prior to use of the c~ desirable shelf-life or pot-life of the :1;.... is obt3ined. In some ,~ it is desirable to select the amounts and the ,' ' of the ~gr-~' ' iri each part to provide viscosity control and better mixing of the two parts. For exarnple, the fillers can be divided so that each part contains a portion of the fillers used.
The epoxy L "' of the present invention can be cured by any means which allow sufficient heat to start the curing reaction. The merins of curing can include Cul.~ i ovens, induction heating, infrared radiation, microwave radiation, immersion into liquid baths, or any -,...l. - ';.~1~ thereof.
For two part adhesive the curing can be effected at room 30 i , ~ for about 24 hours. Typicalily, the finai curing is conducted at a ~.lli.~ul~ in the range of about 15C to about 230C for a time ranging from -Il-WO 95/12647 ~17 ~ 5 7 4 : PCTIUS9111273 4 about 1 second to about 2 hours. Curing may be done in several stages, e.g., induction curing for 30 seconds, and oven curing at 215C.
The curing time will depend upon the particular process for curing.
Induction heating times typically range from about 1-60 seconds while oven 5 curing times can range from about 0.1 to about 2 hours.
The epoxy adhesive ' A ' - of the present invention are especially useful for bonding metal to metal and plastic to metal, although it can be used for bonding only plastic surfaces. ~xamples of metal surfaces include steel, titanium, oily steel, aluminum, and ~ Plastic surfaces include sheet 10 molding -r ~, pOl~,~Ll~ c~ poly~l,. , polyester, pol~ cL}.~,~, acrylonitrile butadiene styrene, and IIIC C( ~ ~ ~ yde. The epoxy adhesive can be used in assembling parts such as for ~ c, aircraft"~
units, etc.
The following non-limiting examples serve to further illustrate the 15 present invention in greater detail.
TEST PROCE~DURLS
LAP SHEAR STRENGTH
This test measures the shear strength that an epoxy adhesive cl, 'l"~` ""'~
20 will achieve in a single overlap bond after being fully cured. The lap shear strength is also referred to as the "overlap" shear strength. A test sample is prepared by applying the adhesive to 2.54 cm x 10.16 cm U~
aluminum strips and curing as detailed below. The aluminum strips used in the tests were:
A - 1.6 mm thick 6111 aluminum having a "mill finish", available from Alcoa Aluminum Co.
B - 1.6 mm thick 5754-0 treated aluminum from Alcan.
C - 0.9 mm thick 6111 aluminum treated with Parker MP404 Lube (treatment available from Parker Div. of Henkel Corp.) D - 0.9 mm thick 6111 aluminum treated with Parker MP404 Lube &
Parker PL303 Wash (treatment available from Parker Div. of Henkel Corp.) WO 95/12647 7S~ 7~ PCT/US9~/1273.1 ~ - 1.6 mm thick 2024 T3 clad aluminum with surface prepared with an FPL etch The adhesive is mixed with about 1% glass beads ("Microbeadm 1405 Class IV r,.L;,.r. ;,~ Grade" measuring between 0.35 to 0.246 mm in 5 diameter, available from Cataphote, Inc.) to provide a 0.25 mm thick bond.
The adhesive is then applied, within 30 minutes of mixing, to a 1.27 cm area on one end of one strip of aluminum and a second strip of aluminum is placed so that 1.27 cm of one end overlaps the adhesive and with the uncoated ends of each strip extending in opposing directions. The strips are clamped together 10 and cured according to the conditions detailed in the examples. The prepared samples are cl~ A for at least two hours at between 21C and 23C
before testing to determine the initial (INIT) strength, and the aged samples are subjected to the aging conditions described below, and: " ~ ' for 2 hours at between 21C and 23C before testing. Llevated ~ shear tests are 15 run at the i , ci~ shown in the examples and samples are ~ ..,..ri at the test i ~ for at least 15 minutes, but no more than 30 minutes, before testing.
The lap shear is ~ i using a tensile tester according to ASTM
Test Method D1002-72 under one of two conditions as follows:
Shear Test I - The crosshead speed is run at the speed required to maintain a rate of loading between 800 to 1000 N/minute.
Shear Test II - The crosshead speed is run at 1.27 cm/min.
The lap shear is reported in units of megaPascals (MPa).
The mode of failure is also recorded and noted as adhesive (A), wherein 25 the adhesive pulls away from one of the aluminum strips, cohesive (C), wherein the adhesive splits leaving adhesive on each of the strips, or mixed (M), wherein both modes of failure are observed. If corrosion is visible along the edges of the aluminum strips or in extreme cases when there is an adhesive failure and corrosion is exposed, the a~ v~ area of corrosion is also 30 noted as a percentage of the total area covered by the adhesive.

wo 95/126~7 217 5 5 7 4 PCT/USg~11273 1 ~1 The test results represent the average of at least three samples involving a particular epoxy adhesive AGING TESTS
Samples are prepared and tested as described above for overlap shear except that the samples are aged in one or more of the following aging tests:
1) Water Soak The samples are soaked in 23C deioni2ed water for 750 hours.
2) Salt Spray Test The samples are subjected to a 5% salt spray at 35C according to ASTM B117-90 and tested after .750 hours.
15 3) Elevated T, ~ /Humidity The samples are aged at 50C and 95% RH for 750 hours.

4) Cyclic Corrosion Aging Test Lap shear samples are prepared and cured according to the above-20 described procedure The sampls are then immersed into a 5 % NaCI colutionat room ~.~ u1~ ~betweeen about 21 and 23) for 15 minutes. The samples are then drip dried at room t~ Lu1~i for 105 minutes and placed in a humidity chamber at 50C, 90% relative humidity for 22 hours. Each immersion in the salt water solution marks the beginning of one cycle. On days 25 when the samples are not immersed in water, the samples are stored in the heated humidity chamber detailed above and these days are not counted in the total number of cycles.
If the samples are exposed to the above cyclic corrosion test under stress, six lap shear samples are prepared for each adhesive Cu.l.~,u,;Liu... The 30 samples are loaded into a fixture which uses a ' . u ~ spring to exert a tensile load on the lap shear coupons. The spring is then cu..l~ ,cd in a vise WO 95/126~7 1 7 $ $ 74 PCT/US9~/12734 to the proper ~ to apply a tensile load of 2 MPa, S MPa, or 7 MPa, and the fixture is tightened to maintain the desired load. The samples are then exposed to the cyclic corrosion test conditions detailed above. The samples are checked daily for joint failure. Failure is noted when lap shear joints break S apart. The failed sample is then replaced in the fixture with a solid strip of aluminum of the ~ ,l length and the cyclic corrosion test is continued until the third sample fails. Results are recorded as the number of days to failure (DAYS TO FAILURE). The remaining three samples are then tested for residual lap shear strength (RESIDUAL STRENGTH) according to the Lap 10 Shear Test procedure described above. Results are recorded in MPa.
Examyle I
A one-part epoxy adhesive ~ was prepared by mixing 10.73 parts of a methacrylate butadiene styrene h.l~vlyl~. l (Paraloid~EXL2691 15 available from Rohm & Haas) with 40.22 parts of a diglycidyl ether of bisphenol A (Eponn'82g available from Shell Chemical Co.), and 13.4 parts of a flexible resin (CIBATYXB4122 made by Ciba Geigy), and heating at about 80C for about 60 minutes with constant stirring. The mixture was then cooled to about room ~ r, and the following were added and mixed with a high 20 shear mixer: 2.68 parts of aluminum powder, 4.29 parts fumed silica (Ca~-O-SilD'TS-720 silica available from Cabot Corp.), 5.36 parts barium ~
(BUSAN 1l-M2 available from Buckman ~ ,), 16.09 parts alumina tri-hydrate, 2.68 parts of calcium io.. ~ ~ ' silica gel (SHIELDE~ACS
available from W. R. Grace & Co.), 3.21 parts J;~,y-...l:.", -~. (Amicure CG
25 1200 available from Air Products, Inc.), and 1.34 parts hexakis (imidazole) nickel phthalate. The d;~ y ' ' and hexakis(imidazole) nickel phthalate were micronized to a particle size of about 10 l~ The adhesive rt~mlu~si~ n was degassed, made into lap shear samples with substrate B, and cured for 40 minutes at 170C. The samples were tested for initial lap shear, 30 and aged lap shear using Shear Test II. The samples were aged under the 21~S5~4 WO 9~i/126 ~7 ; ~r ; PC'I'IUS9J/1273 Cyclic Corrosion Exposure Test under stresses of 2 MPa, 5 MPa, and 7 MPa.
Test results are shown in Table 1.

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WO 95/126~7 ~ ; " PCT/US9-111273-1 The data in Table I show that bonds made with the adhesive . ù ~ of the invention last longer under a corrosive environment and stress than bonds made with a state-of-the-art adhésive containing a well known aluminum corrosion inhibition treatment.
C ^ Examvle Cl A ~:u~ llly accepted toughened epoxy adhesive ~.. ,1,.,~:l;.. . having strontium chromate as a corrosion inhibitor was used. The strips were tested under a load of 7 MPa.
A one-part epoxy adhesive CC"'~I~J~ was prepared by mixing 41.7 parts EPD~OTEn'828 (also sold as EPON~828), 16.6 parts of a diglyciyl ether of bisphenol F (EPIKOTEn'862 available from Shell Chemical Co.), 13.2 parts 1~ ' ~L 2600 I..~LI.~Iy' butadiene styrene terpolymer (available from Rohm & Haas), and an adduct of diglycigyl ether of bisphenol A and carboxyl-terminated butadiene rubber (EPIREZn'58006 available from Rhone Poulenc) at about 80C for about an hour. The mixture was cooled to about room t~ lr and the following were added using a high shear mixer: 2.6 parts Aerosiln'200 silica (available from DeGussa), 0.7 parts glycerol, 4 parts micronized d;~ n -l^~ 4 parts Ancamine~2014 S (available from Air Products and Chemical Co.), 0.7 parts glass beads having a particle size between about 90 - 150 IlPl~u~ t~.~ (available from Glaverbel, of Belgium) and 3.3 parts Shieldex~^AC5. The adhesive , was degassed and tested for lap shear strength and aging on substrate ~. The adhesives were cured for 120 minutes at 130C under a heated platen at a pressure of 100 kiloPascals. Test results are shown in Table 2.

WO95/l26l7 1 7~S74 PCT/US9~/1273 Cn~nn ~r;Ve FY~ C C2 - C3 Adhesive ~ ,n ~ were prepared as in Example 2 except that Example C2 had no corrosion inhibitor, and Example C3 had 3.3 parts of strontium chromate which is a state-of-the-art corrosion inhibitor.

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The data in Table 2 show that the use of a calcium ion-exchanged silica gel ~ the p~:lru."~ e of strontium chromate as a corrosion inhibitor without the ~,..v;lu~ t~l hazards of heavy metals.
S FY~m~l~ 3 Part A of a 2-part adhesive . was prepared by mixing 4û
patts of a polyether diamine (sold by Minnesota Mining & r ~ ~ g Co.
as Part A [amine curativq of a Sco~ LwkLDTM22l6 BA Clear Amber epoxy adhesive kit), 6.0 pafts 4,7,10-~ 1,13-diamine (TI~
lû available from BASF), 8.0 parts 2,4,6-tri-dil,.~ Ll,y ' yl phenol (K-54 available from Anchor Corp.), 3.0 parts ~ I ' butadiene rubber (ATBN 1300X16 available from B. F. Goodrich Co.), and heating to a t. ..,~.~lu,~ of about 70C to form a uniform mixture. The mixture was cooled to about room ~111~ , and 20 parts amorphous silicon dioxide (GP-71) and 15 3.0 parts fumed silica (Cab-O-SilTM TS-720) were added with a high shear mixer.
Part B of the 2-part epoxy adhesive , was prepared by mixing together 15 parts of Ill.,Lll.l.lylal~ butadiene styrene IC~I~JUI~YIII~
(I` ' ~XL2691) with 80 parts of a diglycidyl ether of bisphenol A
20 (E~pon'Y828) and 20 parts diglycidyl ether of "~ l (Hdoxy MK 107 made by Rhone Poulenc), and heating at about 80C for about 60 minutes with constant stirring. The mixture was then cooled to about room t~ lll~l~lLI,.I, and the following were added and mixed with a high shear mixer:2.0 parts Ca(SO3CF3)~ (micronized to a nominal particle size of about 10 25 Il-i~lUII~ s), 2.5 parts epoxy silane (Z-6040 available from Dow Coming), 2.0 parts fumed silica (Cab-O-Siln'TS-720), 3.0 parts glass beads having an average diameter of about 0.01 inch [0.25mm] (available from Cataphote, Inc.), 2û parts: .' silicon dioxide (GP-71 available from Harbison-Walker Corp.), and 18 parts glass bubbles (1337/2000 available from Minnesota Mining 30 & r~ ~ ~, Co.), and 5.0 parts of calcium ion-exchanged silica gel (SHIFT DEX~AC5).

W0951126-17 21~74 . PCT/US9~/1273-1 ~
An adhesive ~ was prepared by mixing a 2:1 volume ratio of Part B:Part A. The adhesive was made into lap shear samples as described above on substrates C and D at two cure conditions. Cure 1 indicates that the curing was done with a 6-second induction heating cycle to a b,~ u~c of 5 135C and then oven cured for 20 minutes at 170C. Cure 2 indicates a room ~""~ c (between about 21~C to 23) cure for 20 to 24 hours and a subsequent oven cure for 20 minutes at 170C. The test was conducted using Shear Test 2. Test results are shown in Table 3.

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Example 4 Part A of a two-part epoxy adhesive ~...,.l,..~ l,..,. was prepared by mixing 29 parts polyeeher diamine (TTD) and 5.0 parts of a 2,4,6-tri-d;~ Y1AIII~ yl phenol (DMP 30 available from Rohm & Haas), and 5 applying sufficient heat to form a uniform solution.
Part B of the 2-part epoxy adhesive C~ ,u~ ~i. n was prepared by mixing together 20 parts of ~ .LIl~lyl~ butadiene styrene terpolymer ~ParaloidlYEXL2600) with 100 parts of a diglycidyl ether of bisphenol A
(Epon'U828) and heating at about 80C for about 60 minutes with constant 10 stirring. The mixture was then cooled to about room ~.llp~ldlul~ and the following were added and mixed with a high shear mixer: 4.0 parts fumed silica (Aerosiln' R202 available from DeGussa), 2.5 parts glass beads having a particle size between about 90 - 150 Ill;. ~ (available from Glaverbel), and ~.0 parts of calcium ion ~Aul-~l6c~ silica gel (SHIELDEXD'AC5 available 15 from W. R. Grace & Co.).
A 2-part adhesive was prepared by mixing Part B with Part A (in a 2:1 volume ratio and Part B:Part A) and preparing lap shear samples on substrate E. The adhesive was cured for 24 hours at 23C under 100 IcPa pressure and then oven cured for 60 minutes at 80C. The samples were tested for initial 20 lap shear and aged lap shear strength using Shear Test 1. Data is shown in Table 4.
C~:, v~ Examples C4 - C5 Two-part epoxy adhesive c~ )c~ were prepared as in Example 4 25 except Example C4 had no corrosion inhibitor, and Example C5 had 5 parts of Strontium chromate. Samples were tested as in Example 4 and test results are shown in Table 4.

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o ~ o 6~7 ~ ~5~l ~ PCT/US9.1/1273 l~xample S
Part A of a 2-part adhesive ~ o~iLiu-- was prepared by mixing 40 parts of a polyether diamine (sold by Minnesota Mining & 1` ~ ' ~ as Part A of Scol~HwklD~22l6 BA Clear Amber epoxy adhesive kit), 6.0 5 parts polyether diamine (H221 available from Union Carbide Inc.), 8.0 parts 2,4,6-tri d;ll~c Lll~ 1 phenol (K-54) 3.0 parts-amine terminated butadiene rubber (ATBN 1300X16 available from B. F. Goodrich Co.), and 5 parts imidazole and heating to about 70C with constant stirring to form a uniform mixture. The mixture was cooled to about room t~ Lulc: and 20 10 parts amorphous silicon dioxide (GP-71) and 3.0 parts fumed silica (Cab-O-Siln'TS-720) with a high shear mixer.
Part B of the c~. l-u~ was prepared as in Fxample 3 except that 19.5 parts of glass bubbles were used.
An adhesive ~ was prepared by mixing 2 parts ûf Part B to 15 one part of Part A by volume.

Claims (8)

WHAT IS CLAIMED IS:

1. A curable, structural epoxy adhesive composition comprising:
(a) an epoxy resin having an average epoxide functionality of greater than one;
(b) a base curing agent in an amount sufficient to cure the epoxy resin through reaction of a nucleophilic or electrophilic group contained in the base curing agent with the epoxy ring contained in the epoxy resin;
(c) particles comprising an inorganic oxide of silica or alumina having cations bound thereto, the particles being of a type which and present in an amount effective to inhibit or prevent corrosion of metal to which the epoxy adhesive composition has been applied.

2. A composition according to Claim 1, wherein the cation is selected from the group consisting of Ca2+, Zn2+, Co2+, Pb2+, Sr2+, Li+, Ba2+ and Mg2+.

3. A composition according to Claim 1, wherein the cation is selected from the group consisting of Ca2+ and Zn2+.

4. A composition according to Claim 1, wherein the particles comprise a calcium ion-exchanged amorphous silica gel.

5. A composition according to Claim 1, further comprising a toughening agent having an epoxide compatible component substantially soluble in the epoxy resin and an epoxide incompatible component substantially insoluble in the epoxy resin.

6. A composition according to Claim 1, further comprising an accelerator to increase the cure rate of the epoxy adhesive composition.

7. A method for inhibiting or preventing corrosion of a metal substrate which has been bonded to another substrate, the method comprising including particles comprising an inorganic oxide of silica or alumina having cations bound thereto in the adhesive composition being employed to bond the metal substrate to the other substrate, the particles being of a type which and present in the adhesive , in an amount effective to inhibit or prevent corrosion of the metal substrate in the area thereof which is in contact with the adhesive composition.

8. A method according to Claim 7, wherein the other substrate is also metal.