Industrial Properties and Research Status of One-component Epoxy Adhesives

Epoxy resin has excellent adhesion to various metal materials, non-metal materials, thermosetting polymer materials, etc. It has strong adaptability, does not contain volatile solvents, does not require pressure to cure, and has a low curing shrinkage rate. Good environment, widely used in many fields. Epoxy adhesives are usually provided in a two-pack package in which the main agent (epoxy resin component) and the curing agent are separated. When the epoxy resin is blended with a curing agent, the reaction starts immediately and the viscosity rises over time, and it cannot be used until the pot life is reached. However, the use of two-component mixing is inconvenient to use, and has the following disadvantages: (1) increased packaging and storage troubles; (2) accuracy and uniformity of the mixing ratio will affect the bonding when the two-component adhesive is used Strength; (3) Shorter use time after the resin and curing agent are mixed. Different types of curing agents in adhesives have different service life. For example, aliphatic amines last for tens of minutes, tertiary amines or aromatic amines last for several hours, and anhydrides last from one day to several days, and cannot be stored for a long period of time. Failure to use it in time will result in waste. (5) Since the viscosity increases with time, the workability is changed and it cannot be used for automatic bonding. The single-component adhesive avoids the above disadvantages, it can make the bonding process simple and suitable for automation. The curing agent and the epoxy resin are mixed to prepare a single-component adhesive, mainly relying on the chemical structure of the curing agent or adopting some technical means to temporarily freeze the ring-opening activation of the epoxy resin by the curing agent, and then heat and light. , mechanical force or chemical action (such as water decomposition), so that the curing agent activity is excited, so that the epoxy resin quickly solidified. Currently, most of the one-component epoxy resin adhesives sold at home and abroad are latent curing agents or self-curing epoxy resins. The product forms are liquid, paste, powder, and film. The one-component epoxy adhesives with practical value are mainly the following: (1) moisture curing type; (2) microcapsule coating type: the curing agent is encapsulated in microcapsules and not mixed with epoxy resin. Curing reaction occurs. Film forming materials include gelatin, vinyl cellulose, polyvinyl acetal, and the like. The capsule is broken by heating or pressure, and the curing agent and the epoxy resin react. (3) Latent curing agent type: A thermoreactive curing agent that can be activated and reacted at a temperature higher than the specified temperature, including intermediate temperature curing type and high temperature Fast curing type; (4) Cationic photocurable.
1 Research progress of one-component epoxy adhesives

1 1 moisture curing type

This is a room-temperature curing one-component epoxy adhesive, the key to which is the curing agent. The most studied so far are ketimine compounds, which are synthesized from aliphatic polyamines and ketones, and the remaining polyamines in ketimines must be blocked with a monoepoxy compound. Ketimines and epoxy resins release amines by adsorbing moisture from the air or wet adhesive surfaces during curing:

Ketimine-containing resin complexes produce polyamines according to the above formula, can cure at room temperature, but the curing speed is not too fast, the use period is not as long as other latent curing agents, at best, only about 8h, add water or use fat Group polyamines as accelerators can speed up the cure. The cured product has essentially the same properties as the starting polyamine compound. Because it absorbs moisture during curing, it is not suitable for thick adhesive layers. Recently, Japanese patents have used polyether-modified amine compounds and methyl isobutyl ketone to prepare ketimines, which are used as curing agents for one-component epoxy adhesives. The cured product has good toughness, elongation of 150%, and good adhesion to the plaster surface. One-component room-temperature curing epoxy adhesives cause nucleophilic attack on the epoxy ring due to the lone pair of electrons on the ketimine nitrogen atom, resulting in epoxy polymerization and increased relative molecular mass (viscosity, gelation). There is no effective way to inhibit it, resulting in a decrease in the shelf life of the adhesive; in addition, if a ketimine made of an amine having a lower reactivity due to the presence of a methyl group or the like in the primary amine group is used as a latent curing agent, the storage stability is improved. Can be improved, but the curing speed is too slow. To address this issue, Toda Takeda et al. used a steric hindrance group in its vicinity (on the ketone side) to protect the lone pair electrons on the ketimine nitrogen atom prepared with a high activity diamine as a starting material. It is difficult for a lone pair of electrons to undergo a nucleophilic reaction with an epoxy group, thereby improving the storage stability.

Source: Glue Online