Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
  • C09J11/02—Non-macromolecular additives
  • C09J11/04—Non-macromolecular additives inorganic
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J163/00—Adhesives based on epoxy resins; Adhesives based on derivatives of epoxy resins
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2666/00—Composition of polymers characterized by a further compound in the blend, being organic macromolecular compounds, natural resins, waxes or and bituminous materials, non-macromolecular organic substances, inorganic substances or characterized by their function in the composition
  • C08L2666/54—Inorganic substances

Definitions

• This invention relates to adhesives containing an agent to resist corrosion on metal surfaces.
• Corrosion resistant treatments for metals are well known in the art and play an important role in maintaining the bond between a coating, such as paint, or an adhesive to the metal over long periods of time, especially in corrosive environments.
• the most commonly encountered corrosive environments include exposure to salt water from oceans, road treatments for ice containing corrosive chemicals and/or salt, acid rain, and the like.
• 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.
• FPL Etch One well known method of preparing aluminum is referred to as an "FPL Etch" which has been used in the aerospace industry since the early 1950's.
• the FPL etch process includes the steps of optionally degreasing the aluminum part with solvent, degreasing with an alkaline solution at 180°F, immersing the part in an aqueous solution of sulfuric acid and sodium dichromate at 160°F, rinsing, and drying the part at room temperature and elevated temperature.
• Conversion coatings known in the art include phosphate conversion coatings, chromate conversion coatings, and cobalt conversion coatings.
• Other methods of improving corrosion resistance include adding a corrosion inhibitor to adhesives.
• Inhibitors currently used include chromate salts, such as barium chromate, strontium chromate, magnesium chromate, etc. Certain cations, such as zinc and calcium, have been used as corrosion inhibitors in protective coatings such as paints. The cations are typically used in the form of sparingly water soluble salts.
• ShieldexTM anti-corrosion pigment is an ion-exchanged silica said to be useful in paints and coatings.
• the present invention provides a curable, structural epoxy adhesive composition
• a curable, structural epoxy adhesive composition comprising: (a) an epoxy resin having an average epoxide functionality of greater than one;
• 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 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 composition 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.
• the present invention provides epoxy adhesive compositions that are useful as structural adhesives that provide corrosion resistance to the substrate from salt solutions.
• the adhesives are particularly useful for metal substrates such as aluminum and steel and the preferred compositions do not contain undesirable heavy metal elements such as chromium.
• Structural adhesives form strong integral bonds between substrates. Bonds formed with structural adhesives have a room temperature 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 (0.25mm). The upper limit on the structural bond strength would be the cohesive failure of the substrate or yielding of the substrate.
• the adhesive compositions of the present invention form room temperature T-peel bond strengths on a bond line thickness of 0.010 inch (.254 mm) of at least 12 pli, with preferred compositions having bond strengths greater than about 14 pli, and the most preferred compositions having bond strength greater than 17 pli.
• Structural adhesive bonds can also be characterized by a room temperature modulus, as measured by a test known in the industry as the overlap shear test, of at least 3 megaPascals (MPa).
• the upper limit of the overlap shear strength would be the cohesive failure of the substrate, or yielding of the substrate.
• the adhesive compositions of the invention form bonds with overlap shear strengths at room temperature of at least 5 MPa, with preferred compositions forming overlap shear strength bonds of at least 7 mPa, and with the more preferred compositions forming overlap shear strength bonds of at least 10 MPa, and with the most preferred compositions forming overlap shear strength bonds of at least 14 MPa.
• Structural bonds typically have a thickness greater than 2 mils (0.5 mm). In the practice of the invention, bond lines formed are typically greater than 5 mils (0.127 mm).
• Epoxides that are useful in the adhesive composition of the present invention can be any organic compound having at least one epoxy ring that is polymerizable by ring opening. Preferred are organic compounds having an average epoxy functionality greater than one, and preferably at least two.
• the epoxides can be monomeric or polymeric, and aliphatic, cycloaliphatic, heterocyclic, 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 and preferably from about 300 to 1,000.
• 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.,polybutadiene polyepoxy), and polymeric epoxides having pendant epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer), and mixtures thereof.
• terminal epoxy groups e.g., a diglycidyl ether of a polyoxyalkylene glycol
• polymeric epoxides having skeletal epoxy groups e.g.,polybutadiene polyepoxy
• polymeric epoxides having pendant epoxy groups e.g., a glycidyl methacrylate polymer or copolymer
• Useful epoxide containing materials include compounds having the required molecular weight of the general Formula I:
• R' is alkyl, alkyl ether, or aryl, preferably aryl and n is an integer between 2 and 6.
• aromatic glycidyl ethers such as those prepared by reacting a polyhydric phenol with an excess of epichlorohydrin.
• phenols include resorcinol, catechol, hydroquinone, and the polynuclear phenols including p,p'-dihydroxydibenzyl, p,p'-dihydroxydiphenyl, p,p'-dihydroxydiphenyl sulfone, p,p'-dihydroxybenzophenone, 2,2'-dihydroxy- 1,1-dinaphthylmethane, and the 2,2', 2,3', 2,4', 3,3', 3,4', and 4,4' isomers of dihydroxydiphenylmethane, dihydroxydiphenyldimethylmethane, dihydroxydiphenylethylmethylmethane, dihydroxydiphenylmethylpropylmethane, dihydroxydiphenylethylphenylmethane, dihydroxydiphenylpropylphenylmethane, dihydroxydiphenylbutylphenylmethane, dihydroxydiphenyltolyl
• 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), incorporated herein by reference. Epoxides with fiexibilized 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 commercially available epoxides useful in the invention include diglycidyl ethers of bisphenol A (e.g., those available under the trademarks 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 functionality; flame retardant epoxy resins (e.g., DER 580, a brominated bisphenol type epoxy resins available from Dow Chemical Co.); and 1,4- butanediol diglycidyl ethers.
• diglycidyl ethers of bisphenol A e.g., those available under the trademarks Epon 828, Epon 1001, and Epon 1510 from Shell Chemical Co., and DER-331, DER-332, and DER-334 available from
• a base curing agent is used in an amount sufficient to cure the epoxy adhesive composition.
• the amount can vary from an approximate stoichiometric 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.
• the base curing agent will be present in an amount of about 2.5 to 75 parts by weight of the curing agent per 100 parts of epoxide.
• the base curing agent contains at least one nucleophilic or electrophilic group which reacts with the epoxy ring to cross-link the adhesive composition.
• Suitable base curing agents include polyamide resins, aliphatic amines, polyether diamines, aromatic amines, polyamines, polyamidoamines, polyetherdiamines, phenol compounds, and mercaptan resins.
• primary amines include di-(4-aminophenyl)sulfone, di-(4-aminophenyl)-ethers, and 2,2-bis(4-(aminophenyl)propane, ethylene diamine, hexamethylene diamine, isomers of hexamethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, bishexamethylene triamine, N,N'-Bis (3-aminopropyl)- 1,2-ethane diamine, N-(3-Aminopropyl)-l,3-propane diamine N-(2-aminoethyl)- 1,3 propane diamine, isomers of cyclohexane di
• Examples of useful tertiary amines are dimethylaminopropylamine and pyridine.
• useful aromatic amines include di-(4-aminophenyl)sulfone, di-(4-aminophenyl)ether, 2 ,2-bis(4-aminophenyl)propane, 4,4' -diamino diphenylmethane, 3,3'-dimethyl(4,4'-diaminodiphenyl methane, m-phenylene diamine, p-phenylene diamine, m-xylylene diamine, toluene diamine, 4,4'- methylene dianiline benzidine, 4,4'-thiodianiline, 4-methoxy-l,3-phenyldiamine, 2,6-diaminopyridine, and dianisidine.
• polyether diamines examples include 4,9-dioxadodecane-l,12- diamine, 4,7,10-Trioxatridecane-l,12-diamine, bis(3-amino propyl)polytetrahydrofurans of varying molecular weights, and commercially available from Texaco Chemical Co. under the Jeffamine trade name as D230, D400, D2000 and T403.
• Suitable polyamido amines are the reaction products of polyamines and dimer acids. Dimer acids are prepared by dimerizing C lg or C 22 fatty acids from vegetable oils or animal fats. The dimer acids are then reacted further with polyamines by a condensation reaction to produce the polyamido amine oligomers. These oligomer are described by V. Brytus, Modern Paint and Coatings. Vol. 74 No.10, p. 172 (1984). Examples of phenol compounds include phenol, substituted alkyl phenols (nonyl phenol), diphenols such as catechol, and alkyl substituted catechol, resorcinol, hydroquinone.
• mercaptan resins examples include alkyl dimercaptans such as ethane dithiol, nonane dithiol, penta erythritol tetra (3-mercapto propionate), trimethylol propane tri(3-mercapto propionate), glycol dimercapto acetate, thiol terminated polyethers and thiol terminated poly sulphides.
• alkyl dimercaptans such as ethane dithiol, nonane dithiol, penta erythritol tetra (3-mercapto propionate), trimethylol propane tri(3-mercapto propionate), glycol dimercapto acetate, thiol terminated polyethers and thiol terminated poly sulphides.
• boron complexes and in particular, boron complexes with monoethanolamine; imidazoles such as 2-ethyl-4-methyl imidazole; guanidines such as tetramethyl guanidine; substituted ureas such as toluene diisocyante urea; dicyandiamide; and acid anhydrides such as 4- methyltetrahydroxyphthalic acid anhydride, 3-methyltetrehydroxyphthalic acid anhydride, and methylnorbornenephthalic acid anhydride.
• Preferred curatives for one-part adhesive compositions are amines, acid anhydrides, guanidines, dicyandiamide, and mixtures thereof.
• base curing agents are AncamideTMSeries, commercially available from Air products and Chemical Company, and the Scherex Series, commercially available from Schering-Berling.
• Accelerators known in the art can also be added to increase the cure rate of the epoxy adhesive.
• Such accelerators include compounds that can act as a curative when used alone, but when combined with a different class of curatives, will accelerate the curing of the epoxy adhesive composition.
• useful accelerators include phenolic compounds, tertiary amines, dicyandiamides, imidazole, substituted imidazole hexakis imidazole nickel phthalate complex, substituted ureas and calcium trifluoromethylsulfonate.
• accelerators may be used alone or in combination together to accelerate the cure of an epoxy adhesive combination.
• useful combinations include phenolic compounds with tertiary amines, dicyandiamides with imidazole and/or substituted imidazoles, dicyandiamides with substituted ureas, dicyandiamides with hexakis imidazole nickel phthalate complex and calcium trifluoromethyl sulphonate with imidazoles.
• a preferred curing agent/accelerator combination is toluene diisocyanate urea and dicyandiamide.
• the preferred amount of the accelerator is from about 0.5 to 15 percent by weight of the adhesive system.
• the epoxy adhesive composition includes a particulate 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 (Ca 2+ ), zinc (Zn 2+ ), cobalt (CO 2"1” ), lead (Pb 2+ ), strontium (Si 2"1” ), lithium (Li + ), barium (Ba 2+ ), and magnesium (Mg 2+ ).
• Preferred cations include calcium and zinc.
• the additive particles will preferably have an average diameter of about 0.1 to 200 microns. More preferably, the particles have an average diameter of about 1 to 50 microns.
• Suitable additive particles include a calcium ion exchanged amorphous silica gel commercially available from W. R. Grace & Co. under the tradename "Shieldex”.
• the epoxy adhesive composition preferably includes a toughening agent, and in particular, a polymeric toughening agent or a combination of polymeric toughening agents.
• a toughening agent and in particular, a polymeric toughening agent or a combination of polymeric toughening agents.
• Useful toughening agents have an epoxide incompatible component substantially insoluble in the epoxy resin and an epoxide compatible component substantially soluble in epoxy resin.
• the toughening agents which are useful in the present invention include polymeric compounds having both a rubbery phase and a thermoplastic phase, such as graft copolymers having a polymerized diene rubbery core and a polyacrylate or polymethacrylate shell; graft copolymers having a rubbery core with a polyacrylate or polymethacrylate shell; and elastomeric particles polymerized in situ in the epoxide from free-radical polymerizable monomers and a copolymeric stabilizer.
• polymeric compounds having both a rubbery phase and a thermoplastic phase such as graft copolymers having a polymerized diene rubbery core and a polyacrylate or polymethacrylate shell; graft copolymers having a rubbery core with a polyacrylate or polymethacrylate shell; and elastomeric particles polymerized in situ in the epoxide from free-radical polymerizable monomers and a copolymeric stabilizer.
• useful toughening agents include graft copolymers having a polymerized diene rubbery backbone or core which is grafted to a shell of an acrylic acid ester or methacrylic acid ester, monovinyl aromatic hydrocarbon, or a mixture thereof, such as disclosed in U.S. Patent No.3,496,250.
• Preferable rubbery backbones comprise polymerized butadiene or a polymerized mixture of butadiene and styrene.
• Preferable shells comprising polymerized methacrylic acid esters are lower alkyl (C j -C ⁇ substituted methacrylates.
• Preferable monovinyl aromatic hydrocarbons are styrene, alpha-methylstyrene, vinyltoluene, vinylxylene, ethylvinylbenzene, isopropylstyrene, chlorostyrene, dichlorostyrene, and ethylchlorostyrene.
• acrylate core-shell graft copolymers wherein the core or backbone is a polyacrylate polymer having a glass transition temperature (T g ) below about 0°C, such as polybutyl acrylate or polyisooctyl acrylate to which is grafted a polymer (shell) having a T g above 25 °C such as polymethylmethacrylate.
• T g glass transition temperature
• toughening agents useful in the invention are elastomeric particles that have a T below about 25 °C and have been polymerized in situ in the epoxide before mixing with the other components of the composition.
• elastomeric particles commonly referred to as “organosols" are polymerized from free-radical polymerizable monomers and a copolymerizable polymeric stabilizer that is soluble in the epoxide.
• the free- radical polymerizable monomers are ethylenically unsaturated monomers or diisocyanates combined with co-reactive difunctional hydrogen compounds such as diols, diamines, and alkanolamines. Examples of these elastomeric particles are disclosed in U.S. Patent No. 4,525,181.
• Still other toughening agents are rubber modified liquid epoxy resins.
• An example of such a resin is KratonTM RP6565 Rubber available from Shell 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 elastomeric block copolymers.
• Toughening agents can also include liquid epoxies, liquid amines, polyether diamines, polyhydroxyethers, polyvinylacetals, and liquid acrylonitrile butadiene polymers, butadiene/nitrile rubbers, carboxylated butadiene/nitrile rubbers, amine-terminated butadiene/nitrile rubbers, carboxyl-terminated butadiene/nitrile rubbers and the amine or carboxyl terminated adducts of the polymers with epoxy resins.
• Amine-terminated and carboxyl-terminated butadiene-acrylonitrile rubbers are commercially available from B.F. Goodrich under the HYCAR tradename as ATBN and CTBN reactive liquid polymers.
• Combinations 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 invention add strength to the composition after curing without interfering with curing.
• the toughening agent may or may not react with the epoxide.
• reactive diluents may be added to control the flow characteristics of the adhesive composition.
• Suitable diluents have at least one reactive terminal end portion and preferably, a saturated or unsaturated cyclic backbone.
• Preferred reactive terminal ether portions include glycidyl ether and vinyl ether.
• suitable diluents include the diglycidyl ether of resorcinol, diglycidyl ether of cyclohexane dimethanol, diglycidyl ether of neopentyl glycol, triglycidyl ether of trimethylolpropane dipentene, and the divinyl ether of cyclohexanedimethanol.
• epoxide composition can be added to the epoxide composition to enhance properties of the composition before and after curing.
• useful adjuvants include nonreactive diluents; plasticizers such as conventional phosphates and phthalates; flame retardants such as borates, metaborates, aluminum hydroxide, magnesium hydroxide, and bromine compounds; thixotropic agents such as fumed silica to provide flow control; pigments to enhance color tones such as ferric oxide, brick dust, carbon black, and titanium dioxide; fillers such as talc, silica, magnesium, calcium sulfate, beryllium aluminum silicate; clays such as bentonite; glass and ceramic beads and bubbles; compounds imparting X-ray opacity, such as barium metaborate; 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 long as they do not interfere with the curing reaction of the epoxy adhesive composition.
• 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 formulation can be used.
• compositions of the invention or compositions to be used in the methods of the invention are substantially free of conventional 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 the adhesive composition or as a pretreatment of one or both of the surfaces to be bonded before application of the adhesive.
• the epoxy adhesive composition 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 composition, with the two parts being combined prior to use of the composition, desirable shelf-life or pot-life of the composition is obtained. In some applications, it is desirable to select the amounts and the distribution of the ingredients in each part to provide viscosity control and better mixing of the two parts. For example, the fillers can be divided so that each part contains a portion of the fillers used.
• the epoxy compositions of the present invention can be cured by any means which allow sufficient heat to start the curing reaction. The means of curing can include conventional ovens, induction heating, infrared radiation, microwave radiation, immersion into liquid baths, or any combination thereof.
• the curing can be effected at room temperature for about 24 hours.
• the final curing is conducted at a temperature in the range of about 15°C to about 230°C for a time ranging from 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 215 °C.
• the curing time will depend upon the particular process for curing. Induction heating times typically range from about 1-60 seconds while oven curing times can range from about 0.1 to about 2 hours.
• the epoxy adhesive compositions 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.
• metal surfaces include steel, titanium, oily steel, aluminum, and magnesium.
• Plastic surfaces include sheet molding compounds, polyethylene, polycarbonate, polyester, polyurethane, acrylonitrile butadiene styrene, and ureaformaldehyde.
• the epoxy adhesive can be used in assembling parts such as for automobiles, aircraft, refrigeration units, etc.
• This test measures the shear strength that an epoxy adhesive composition 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 overlapping 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.
• the adhesive is mixed with about 1 % glass beads ("MicrobeadTM 1405 Class IV Engineering Grade" measuring between 0.35 to 0.246 mm in 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 and cured according to the conditions detailed in the examples.
• the prepared samples are conditioned for at least two hours at between 21 °C and 23 °C before testing to determine the initial (INIT) strength, and the aged samples are subjected to the aging conditions described below, and conditioned for 2 hours at between 21 °C and 23 °C before testing. Elevated temperature shear tests are run at the temperatures shown in the examples and samples are conditioned at the test temperature for at least 15 minutes, but no more than 30 minutes, before testing.
• the lap shear is determined using a tensile tester according to ASTM Test Method D 1002-72 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 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 approximate area of corrosion is also noted as a percentage of the total area covered by the adhesive. The test results represent the average of at least three independent samples involving a particular epoxy adhesive composition.
• the samples are soaked in 23 °C deionized water for 750 hours.
• the samples are subjected to a 5% salt spray at 35 °C according to ASTM Bl 17-90 and tested after 750 hours.
• the samples are aged at 50°C and 95% RH for 750 hours.
• Lap shear samples are prepared and cured according to the above- described procedure.
• the sampls are then immersed into a 5 % NaCl colution at room temperature (betweeen about 21° and 23°) for 15 minutes.
• the samples are then drip dried at room temperature for 105 minutes and placed in a humidity chamber at 50° C, 90% relative humidity for 22 hours.
• Each immersion in the salt water solution marks the beginning of one cycle.
• the samples are stored in the heated humidity chamber detailed above and these days are not counted in the total number of cycles.
• a one-part epoxy adhesive composition was prepared by mixing 10.73 parts of a methacrylate butadiene styrene terpolymer (ParaloidTMEXL2691 available from Rohm & Haas) with 40.22 parts of a diglycidyl ether of bisphenol A (EponTM828 available from Shell Chemical Co.), and 13.4 parts of a flexible resin (CIBATMXB4122 made by Ciba Geigy), and heating at about 80 °C for about 60 minutes with constant stirring.
• a methacrylate butadiene styrene terpolymer ParaloidTMEXL2691 available from Rohm & Haas
• EponTM828 diglycidyl ether of bisphenol A
• CIBATMXB4122 made by Ciba Geigy
• the mixture was then cooled to about room temperature and the following were added and mixed with a high shear mixer: 2.68 parts of aluminum powder, 4.29 parts fumed silica (Cab-O- SilTMTS-720 silica available from Cabot Corp.), 5.36 parts barium metaborate (BUSAN 11-M2 available from Buckman Laboratories), 16.09 parts alumina tri-hydrate, 2.68 parts of calcium ion-exchanged silica gel (SHIELDEXTMAC5 available from W. R. Grace & Co.), 3.21 parts dicyandiamide (Amicure CG 1200 available from Air Products, Inc.), and 1.34 parts hexakis (imidazole) nickel phthalate.
• a high shear mixer 2.68 parts of aluminum powder, 4.29 parts fumed silica (Cab-O- SilTMTS-720 silica available from Cabot Corp.), 5.36 parts barium metaborate (BUSAN 11-M2 available from Buckman Laboratories), 16.09 parts alumina tri-hydrate
• the dicyandiamide and hexakis(imidazole) nickel phthalate were micronized to a particle size of about 10 micrometers.
• the adhesive composition was degassed, made into lap shear samples with substrate B, and cured for 40 minutes at 170 °C.
• the samples were tested for initial lap shear, and aged lap shear using Shear Test II.
• the samples were aged under the Cyclic Corrosion Exposure Test under stresses of 2 MPa, 5 MPa, and 7 MPa. Test results are shown in Table 1.
• a one-part epoxy adhesive composition was prepared by mixing 41.7 parts EPIKOTETM828 (also sold as EPONTM828), 16.6 parts of a diglyciyl ether of bisphenol F (EPIKOTETM862 available from Shell Chemical Co.), 13.2 parts ParaloidTMEXL 2600 methacrylate butadiene styrene terpolymer (available from Rohm & Haas), and an adduct of diglycigyl ether of bisphenol A and carboxyl- terminated butadiene rubber (EPIREZTM58006 available from Rhone Poulenc) at about 80 °C for about an hour.
• the mixture was cooled to about room temperature and the following were added using a high shear mixer: 2.6 parts AerosilTM200 silica (available from DeGussa), 0.7 parts glycerol, 4 parts micronized dicyandiamide, 4 parts AncamineTM2014 S (available from Air Products and Chemical Co.), 0.7 parts glass beads having a particle size between about 90 - 150 micrometers (available from Glaverbel, of Belgium) and 3.3 parts ShieldexTMAC5.
• the adhesive composition was degassed and tested for lap shear strength and aging on substrate E. The adhesives were cured for 120 minutes at 130°C under a heated platen at a pressure of 100 kiloPascals. Test results are shown in Table 2. Comparative Examples C2 - C3

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• 1994
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