What are the different adhesive curing methods?
Time：2012-10-25 12:48:41 Hits：2395
In order to facilitate the infiltration of adhesive on the surface of the adherend prior to bonding adhesive to be made of liquid or make it into a liquid, it has only become solid strength after bonding. Process referred to as curing of the adhesive by the appropriate method of the subbing layer by the liquid into a solid. Different adhesives are often using different curing methods
Hot melt adhesive curing
After heating the molten thermoplastic polymer material to obtain fluidity, many polymer melt can be used as an adhesive. After the polymer melt in the infiltration of the surface of an adherend by cooling can be cured, the adhesives of this type are called hot melt adhesive.
The curing of the hot melt adhesive is a simple process of heat transfer, and the gumming adhesive is heated and melted, the cooling can be cured. The curing process are greatly affected by ambient temperature, the ambient temperature is low, fast curing. To make hot melt adhesive liquid can wet is sticky material, the use must be strictly controlled melting temperature and the dry set time for sticky materials with crystalline hot melt adhesive, especially should pay attention to, otherwise due to the cooling too sticky material crystallization not allow sub complete and reduces the bonding strength.
Solution type adhesive curing
The thermoplastic polymeric substance may be dissolved in a suitable solvent in a polymer solution was obtained in the flowability, in the polymer solution and infiltration after the adherend surface evaporate the solvent will produce - given the adhesion. Many polymer solution can be used as the adhesive used, adhesive agent is the most commonly encountered governance solution Solution patch bicycle inner tube with a rubber solution, many of the adhesive is a solution type.
The essence of the solution glue strong curing process with the volatile solvent. The solution concentration is increasing, and to finally reach a certain intensity. The curing speed of the solutions to gel decided at the evaporation rate of the solvent, but also by the ambient temperature, humidity, and the degree of denseness of the adherend and water content, the size of the contact surface, and other factors. Preparation of the solution of glue should be sample specific solvent to change the composition of the mixed solvent to adjust the curing speed. Optional easy solvent held hair is likely to affect the crystallization speed and degree of the crystalline material, or even cause the subbing layer crusts and reduce the adhesive strength, in addition to the rapid evaporation of the adhesive to cool the condensate water on the adhesive strength is also a disadvantage. Optional solvent evaporation is too slow, the curing time is long, low efficiency, may also cause the layer solvent retention on the adhesive adversely. Solution glue should pay strict attention to the phenomenon of fire and poisoning.
Emulsion adhesive curing
Water emulsion-type adhesive is a dispersion of the polymer gel in the water is small as a relatively stable system. When the water in the emulsion is gradually penetrated into the adherend and evaporation, the concentration will be gradually increased, thereby curing due to the effect of surface tension so that the micelle aggregation. Can not form a continuous film when the environmental temperature on the emulsion aggregation of a great impact, when the temperature is high enough emulsion can be condensed into a continuous film, the temperature is too low or lower than the minimum film-forming temperature (the temperature is generally slightly lower than the glass transition temperature point) The film was white, strength roots Poor. Different minimum film forming temperature of the polymer emulsion is different, therefore, when using the class adhesive must make the ambient temperature is higher than the minimum film-forming temperature, otherwise the adhesive effect is not good.
Plasticized paste-type adhesive curing
The plastisol is an unstable dispersion system of the polymer compound in the plasticizer, the curing is essentially the process of the polymer compound was dissolved in the plasticizer. This paste downstream stability at room temperature. When heated (generally at 150 to 209 ° C) for the polymer compound of the plasticizer can rapidly miscible completely gelled, increase temperatures favor the movement of the polymer chains, and is conducive to the formation of a uniform and dense adhesive layer. However, the high temperature will cause the polymer decomposition.
The curing of the adhesive of the reaction type adhesive
Reactive adhesives small active group, and assimilation agent, initiator, viscous material is polymerized under the role of the agent, and other physical conditions of the chemical reaction such as a crosslinking curing. Mediated formula according to curing reaction type adhesives can be divided into the type of curing agent, and the catalyst curing type initiator curing type and other types. The photosensitive curing, radiation assimilation Curing mechanism generally belong to more than one type.
An epoxy resin, urethane-based adhesive is cured with a stoichiometric amount of curing agent; second generation acrylic structural adhesive, unsaturated polyesters, such as plastic commonly used in the curing initiator; phenolic, urea-formaldehyde resin available acidic catalyst catalytic curing. The automatic acceleration phenomenon, some reactive adhesives assimilation when the design formula or use glue Leopard viscosity particular attention should be generated defects because the sharp exothermic makes gelation layer, destruction of the sticky material leaving bonding fail.
Glue preliminary cured, the adhesive layer is generally available adhesive strength over an extended period after the initial curing adhesive strength will continue to improve. Molecular motion becomes difficult after initial curing of such adhesives is appropriate to extend the initial cured curing time or curing curing temperature to promote the smooth progress of an appropriate increase in adhesive strength is extremely favorable.
For certain specific types of plastic, the curing temperature setting is not lower, the result of lowering the temperature of curing can not be completely, resulting in decreased adhesive strength, and this deterioration is difficult to extend the curing time to compensate. Preferably used for setting the glue is cured at a higher temperature, the curing temperature program, and to avoid glue overflow, and the insoluble component separation, and can reduce the internal stress of the adhesive layer. For plastic types of volatile low molecular weight substance generated in the curing process, curing is often required to apply a certain pressure, if the small molecules, is not generated in the curing process is only subjected to the contact pressure in order to prevent the adhesive surface on the line dislocation.
Gum Activity agent with a curing agent, a curing agent with associated generally stoichiometric excess, the added amount is insufficient is difficult to cure fully, a curing agent is generally a slight excess. Using the larger molecular weight of the curing agent, the member can be slightly larger amount ranging. For example, with a 650-polyamide curing epoxy used in an amount of 30 ~ l100 parts by mass. Curing the adhesive with the initiator agent, is increased within a certain range the amount of initiator can increase the curing speed of the adhesive performance is not affected. Insufficient amount of the reaction premature termination can not be completely cured; reduce excessive degree of polymerization lower adhesive strength. In order to avoid the gelling phenomenon of the adverse effects of the adhesive, can use composite initiator: the upcoming low activity of the high activity of the initiator with the use. The initiator is added and then appropriate to add some special reducing substances (called accelerators) can greatly reduce the reaction energy to increase the reaction rate. Can even be made of a room temperature fast curing fatty species, which wish is a redox initiator system, the initiator efficiency due to a reducing agent to promote the decomposition of initiator while reduced, therefore, the redox initiator system, should increase the amount of initiator. Catalyst only change the speed of response, and without catalytic Lee catalyst curing adhesives reaction extremely slow (referring to room temperature) can be stored for a long catalyst causes the excessive use of adhesive layer performance degradation. When a small amount of catalyst is an appropriate increase in the curing temperature is possible.
