What is the diluent of adhesive?
Diluents are applied to reduce the adhesive viscosity and improve permeability. Some diluents can reduce the activity of adhesive to prolong the use life. It is common to adjust viscosity of adhesive through using diluents. Diluents are divided into reactive diluents and inactive diluents.
(1) Inactive diluents do not have reactive group. Most inactive diluents are inert solvent, such as ethanol,acetoneand toluene.(2) During the dilution process, diluent coexists with resin to reduce viscosity without any reaction. Besides dilution, it has influence in mechanical property, heat distortion temperature, medium resistance and aging resistance. If the solvent evaporation speed is fast, the adhesive layer is easy to form film with most bubbles to impede other adhesive squeezing out. If the solvent evaporation speed is slow, the adhesive layer will remain solvent which may affect bonding strength. So it is wise to mix many solvents with different boiling points. It is widely used rubber adhesive, phenolic adhesive, polyester adhesive and epoxy adhesive.
(2) Reactive diluent is a kind of diluent with activated group. It will react with adhesives to improve the flexibility and toughness during the dilution process. For example, epoxy adhesives can be toughened by glycerol epoxy resin, or propylene oxide tert-butyl ether. Reactive diluent is widely used in epoxy adhesive.