1、Advanced MaterialsAdhesivesAraldite STRUCTURAL ADHESIVESIts All In the ChemistryAdvanced MaterialsAdhesives ChemistryVariations in chemical formulations produce distinct differences between:Epoxy adhesives Polyurethane adhesives Methacrylate adhesivesAll are thermoset plastics,when heated:They do no
2、t melt They do not revert back to their pre-reacted forms.Advanced MaterialsAdhesives ChemistryALL two-part epoxies,polyurethanes and methacrylates require accurate measuring of resin and hardener to produce a durable joint:Use correct mix ratio Weigh precise amounts of resin and hardener For cartri
3、dges,dispense precisely to attain a 1:1 or 2:1 ratio Advanced MaterialsAdhesives ChemistryALL two-part epoxies,polyurethanes and methacrylates require thorough mixing of resin and hardener to attain full physical properties:Use a square-bottom mixing stick Use containers with flat bottoms,straight s
4、idewalls Use paper for epoxy,plastic for polyurethane Mix to achieve uniform color with no streaks Stir gently to avoid air entrapmentAdvanced MaterialsAdhesives ChemistryWhen using ALL epoxies,polyurethanesand methacrylates:Apply adhesive to substrates immediately after mixingApply a sufficient amo
5、unt of adhesive to completely fill the joint(the first time)Join substrates and clamp as soon as possibleAdvanced MaterialsAdhesives ChemistryEpoxy adhesives include two-and one-component systems:Two components=“A”resin+“B”hardener -Epoxy resins have minimal odor -Amine hardeners have ammonia-like o
6、dor -Reacting(mix)ratio-A:B-is determined by the reactive sites of the components Advanced MaterialsAdhesives ChemistryEpoxy adhesives include two-and one-component systems:One component=contains“A”+“B”-Epoxy resins are similar to two-component resins -Hardeners are“chemically hindered”from reacting
7、 until heat is applied(250F/121C)-Cured properties are similar to two-component systemsAdvanced MaterialsAdhesives ChemistryEpoxy adhesives characteristics include:100%solids(contain no solvents)Exothermicgive off heat when reacting/curing Do not release volatiles during cure Reaction/cure speed can
8、 be accelerated with heat Cure speed is slower at room-temperature(or cooler)Components react only with each other Viscosities range from thin liquids to thick pastes Easy to applyAdvanced MaterialsAdhesives ChemistryCured epoxies feature numerous benefits:High strength,rigid bonds Good electrical i
9、nsulating characteristics Excellent solvent and chemical resistance Bond metals,metal/metal combinations,thermoset plastics Advanced MaterialsAdhesives Chemistry Araldite polyurethanes are two-component systems:“A”isocyanate resins+“B”polyol hardeners Contain 100%solids Resins react with moisture yi
10、elding undesirable hard foam Reactions are non-reversible(even with heat)Secondary(desired)reactions are with hardeners Polyol hardeners readily absorb moisture Precise ratio control is critical;systems may cure but will remain sticky/tacky Have a broad range of work lives and viscosities from liqui
11、ds to pastes Advanced MaterialsAdhesives Chemistry Cured polyurethanes offer benefits including:Good flexibility even at low temperature Good adhesion to thermoplastic substrates and dissimilar materials High impact resistance Good electrical insulating characteristics Broad range of hardness(Shore
12、10A to Shore 70D)Advanced MaterialsAdhesives Chemistry Polyurethane limitations:Service temperatures are 250F/121C Reactants must be kept dry May require surface preparation to remove dust,oils,mold releases and other contaminantsAdvanced MaterialsAdhesives Chemistry Araldite methacrylate adhesives
13、are high-strength,two-component systems that can be applied via:Automated meter/mix dispensing Conventional mixing No mixingin which a fast drying lacquer can be applied up to 30 days before the adhesive is added to harden and bond the assembly Advanced MaterialsAdhesives ChemistryAraldite methacryl
14、ates feature outstandingperformance characteristics:Gap filling up to 0.3 in./8mm thick Good resistance to fatigue,chemicals,humidity and heat Suitable for bonding greasy/oily surfaces Ideal for use on metals,thermoplastics,thermoset composites and dissimilar materials Good lap shear and tensile str
15、engthAdvanced MaterialsAdhesives Chemistry Methacrylate adhesives feature benefits including:Fast cure Produce tough bonds Epoxy-like strength Join thermoplastics,thermoset composites,metals,ceramics and glass Require minimal surface preparation Advanced MaterialsAdhesives ChemistryAraldite methacrylates feature thedisadvantage of:Detectable odor -Detection level 0.5 ppm -High discomfort level 25 ppm -TLV 50 ppmThe odor serves as its own warningmechanism.Despite this disadvantage,the adhesivesare widely used in the automotive andother industries for their numerous benefits.
