Curing methods of adhesives are cured by physical methods, such as solvent evaporation, emulsion condensation and melt cooling and chemical methods.
(1) Hot melt adhesive: polymer melt can solidify by cooling after it soaks into the surface.
(2) Solution adhesive: with the volatilization of the solvent and the increasing concentration of the solution, it gradually reaches a certain strength of curing.
(3) emulsion adhesive: as the water in the emulsion gradually penetrates into the porous sticky substance and evaporates, the concentration of the emulsion increases continuously. Finally, due to the effect of surface tension, the polymer colloid particles coagulate. When the ambient temperature is high, the emulsion is condensed into a continuous film, while the ambient temperature is lower than the minimum film forming temperature (MFT), forming a white discontinuous film. Emulsion adhesives are mainly copolymers of polyvinyl acetate and its copolymer and acrylate.
(4) polyfunctional monomers or prepolymers of thermosetting adhesives of thermosetting adhesives are polymerized. With the increase of molecular weight, molecular chain changes and crosslinks are formed at the same time, forming insoluble or melted gelation or basic curing. In a certain range, prolonging curing time is not equivalent to increasing curing temperature, and reducing curing temperature is difficult to compensate with prolonging time. Because there is a certain chemical reaction between the adhesive and the surface of the object to be adhered, it is necessary to have a high enough temperature.
Curing pressure:
It is conducive to the full infiltration of the adhesive on the surface; it is conducive to the elimination of the low molecular volatiles produced by the adhesive curing reaction; it is conducive to the removal of the residual volatile solvents in the adhesive layer; it is conducive to the control of the thickness of the adhesive layer; the adhesive with large viscosity tends to have a thick adhesive layer, and the adjustment of the curing pressure controls the thickness range of the adhesive layer.
It is placed for a period of time after application of glue, which is called pre curing. When the viscosity of the glue liquid increases, apply pressure to ensure the uniformity of the thickness of the glue layer.
Curing temperature:
If the curing temperature is too low, the crosslinking density of the adhesive layer is too low, and the curing reaction is not complete; if the curing temperature is too high, it is easy to cause the loss of the adhesive liquid or the embrittlement of the adhesive layer, resulting in the decrease of the bonding strength. Heating is beneficial to the molecular diffusion between the adhesive and the adhesive, and to the formation of chemical bond.
(1) Oven direct heating method: use air blower to make it evenly heat transfer.
(2) External heating method: quickly transfer heat to the inner part of the adhesive layer, greatly shortening the curing time. Acoustic heating method: it is not suitable for thermosetting rigid adhesive to cure adhesive with viscoelasticity and solventless adhesive solution by heating.
Source: China adhesive net
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