Activator composition in pressure sensitive adhesive

Adhesive compositions based on cyanoacrylate vinegar are well known and have a wide range of uses due to their rapid curing rate, excellent long-term bonding strength, and application to a wide variety of substrates. Generally, they harden after only a few seconds, after which the attached parts exhibit at least some initial strength.

It is well known that some cyanoacrylate vinegar (CA) binders are generally hardened by anionic polymerization. If the adhesive is routinely coated with a relatively thick layer or a relatively large amount of adhesive so that relatively large drops of adhesive protruded between the connecting parts, rapid hardening of the entire adhesive is almost impossible, that is, the curing of the entire gap or the curing of the whole volume (CTV) is not satisfactory.

For some substrates, especially those with acidic surfaces such as wood or paper, polymerization may be delayed, often to an uncontrollable extent. In addition, unless the adhesive has been gelated or given thixotropy with appropriate additives, the wood or paper matrix, due to its pores, is prone to draw the adhesive out of the joint crevices by capillary action before the adhesive hardens in the crevices.

Therefore, there have been attempts to use certain additives to accelerate the polymerization of such CA adhesives. However, the storage stability of such formulations is generally compromised by the use of alkaline or nucleophilic substances that would normally significantly accelerate the polymerization of cyanoacrylate vinegar adhesives. Therefore, the direct addition of accelerators to adhesive formulations allows only very limited amounts. This accelerator is added a short time before the adhesive is coated, resulting in a de facto two-component system.

However, the disadvantage of this method is that its service life is limited after the activator is mixed. In addition, due to the small activation dose required, it is difficult to achieve the required accurate measurement and uniform mixing. Moreover, using this two-component system is cumbersome for the user, and sometimes only slightly improves the desired results

The activator may also be used in the form of a dilute solution that is pre-coated on the substrate or part to be bonded and/or coated on the adhesive after the substrate has been attached while the adhesive on it is still liquid. The solvent used for diluting solutions of this activator is generally a low-boiling organic solvent, which tends to evaporate, leaving the activator on the substrate/component or adhesive.