Cure When an adhesive cures, it is converted from a liquidIto a solid state. The curing process may be accomplished bycooling, loss of solvents, or internal chemical reaction.Curing generally implies some type of physical or chemicalchange in the adhesive, while hardening or melting isreversible.Green strength The green strength is a measure of the abilityof the adhesive to support a load during the green time.Green time (open time) Green time is the time betweenapplication and solidification of the adhesive. During thegreen time, it is still possible to position parts. Fixturing time(the amount of time before bonded parts can be handled) isoften somewhat longer than green time
◼ Cure When an adhesive cures, it is converted from a liquid to a solid state. The curing process may be accomplished by cooling, loss of solvents, or internal chemical reaction. Curing generally implies some type of physical or chemical change in the adhesive, while hardening or melting is reversible. ◼ Green strength The green strength is a measure of the ability of the adhesive to support a load during the green time. ◼ Green time (open time) Green time is the time between application and solidification of the adhesive. During the green time, it is still possible to position parts. Fixturing time (the amount of time before bonded parts can be handled) is often somewhat longer than green time
Kickover Kickover is the sudden increase in viscositywhich accompanies the curing of an adhesive. Oncean adhesive “kicks over", it is almost in its solid stateand can no longer be easily spread.Pot life 混胶时间 The pot life of an adhesive is thelength of time it remains usable for mixing.Pot life isusually an important factor only with adhesives whichgalmostare mixed together and begin curingimmediatelyRheology Rheology is the ability of a material to flowand deform. Adhesives with good rheology flow easilyand break cleanly at the end of a bead
◼ Kickover Kickover is the sudden increase in viscosity which accompanies the curing of an adhesive. Once an adhesive “kicks over” , it is almost in its solid state and can no longer be easily spread. ◼ Pot life 混胶时间 The pot life of an adhesive is the length of time it remains usable for mixing . Pot life is usually an important factor only with adhesives which are mixed together and begin curing almost immediately. ◼ Rheology Rheology is the ability of a material to flow and deform. Adhesives with good rheology flow easily and break cleanly at the end of a bead
Shelf lifeShelf life is the usable storage time of ainaterial. Most adhesives have a shelf life of 6 to 12inonths. The shelf life of an adhesive may be increasedby refrigeration, and is usually shortened by exposureto heat.ViscosityViscosity is the resistance to flow or degree ofthickening of a fluid. Some adhesives flow very easily,whereas other types of adhesives are so thick theyhardly flow at all. Water and thick putties representthe extremes of viscosity.WettingWetting is intimate contact of a liquid and asurface. Good wetting is only possible if there is goodattraction between the surface and the liquid. Properwetting of a mating surface is essential for goodbonding
◼ Shelf life Shelf life is the usable storage time of a material. Most adhesives have a shelf life of 6 to 12 months. The shelf life of an adhesive may be increased by refrigeration, and is usually shortened by exposure to heat. ◼ ViscosityViscosity is the resistance to flow or degree of thickening of a fluid. Some adhesives flow very easily, whereas other types of adhesives are so thick they hardly flow at all. Water and thick putties represent the extremes of viscosity. ◼ WettingWetting is intimate contact of a liquid and a surface. Good wetting is only possible if there is good attraction between the surface and the liquid. Proper wetting of a mating surface is essential for good bonding
5.1.4Basic propertiesBasically an adhesive must do two things:It must wet the surfaces, that is it must spread and makea contact angle approaching zero. Intimate contact isrequired between the molecules of the adhesive and theatoms and molecules in the surface. When applied theadhesive will be a liquid of relatively low viscosity.The adhesive must then harden to a cohesively strongsolid. This can be by chemical reaction, loss of solvent orwater, or by cooling in the case of hot melt adhesives.There is an exception to this, and that is pressure-sensitive adhesives which remain permanently stickyThese are the adhesives used in sticky tapes and labels
5.1.4 Basic properties ◼ Basically an adhesive must do two things: ◼ It must wet the surfaces, that is it must spread and make a contact angle approaching zero. Intimate contact is required between the molecules of the adhesive and the atoms and molecules in the surface. When applied the adhesive will be a liquid of relatively low viscosity. ◼ The adhesive must then harden to a cohesively strong solid. This can be by chemical reaction, loss of solvent or water, or by cooling in the case of hot melt adhesives. There is an exception to this, and that is pressuresensitive adhesives which remain permanently sticky. These are the adhesives used in sticky tapes and labels
YM