Viscoelastic Properties Of Adhesive Research Articles

Volume change and viscoelastic properties of UV-curable adhesives for precise positioning during curing process and their formulation

ABSTRACT Optical components are often adjusted to maintain their alignment along the optical axis. They are fixed at their optimal positions particularly using ultraviolet (UV) ray-curable adhesives. To achieve a micron-level positional accuracy, it is necessary to understand adhesive shrinkage while curing and the resulting deformation of the adhesive joint. However, it is challenging to perform a quantitative evaluation of the cure shrinkage and mechanical properties of adhesives given the process complexity and strong dependence on curing conditions. Therefore, this study clarified the effects of various curing conditions on the curing extent of an adhesive under UV curing for positioning and heat curing as a post-curing process. The cure shrinkage, coefficient of thermal expansion, and viscoelastic properties of the adhesive were also measured. Each material property could be defined as a function of the curing extent to predict the changes in the properties under different curing conditions. The adhesive curing process was divided into three stages: adhesive gelation under UV irradiation, fast reaction stage under heating, and slow reaction stage under heating. The adhesive state changed from viscous to viscoelastic to elastic as it cured, and this process proceeded in the aforementioned three stages. Three different formulae were fitted corresponding to each stage, with good agreement with the experimental measurements.

A new class of pressure-sensitive adhesives based on interpolymer and polymer-oligomer complexes

On the basis of previous concepts concerning the molecular nature of pressure-sensitive adhesion, a simple method of preparing new adhesives with the desired mechanical and adhesive behavior and water-absorbability via mixing of nonadhesive polymers has been developed. Pressure-sensitive adhesion is related to the combination of a high energy of cohesion and a large free volume, which leads to a high molecular mobility. This method is based on the formation of interpolymer or polymer-oligomer complexes during mixing of macromolecules capable of hydrogen, electrostatic, or ionic bonding. In interpolymer complexes, a high cohesion results from the formation of bonds between macromolecules carrying complementary groups in main chains, whereas free volume is related to defectiveness of the resulting network and formation of loops. In complexes formed by a high-molecular-mass polymer and an oligomer carrying complementary reactive groups at ends of short chains, a high energy of cohesion is related to their interaction with mainchain functional groups of the polymer, whereas a relatively large free volume is associated with the length and flexibility of intermacromolecular crosslinks via oligomer chains. The adhesive and viscoelastic properties of adhesives and their water absorbability are regulated by changes in the composition of mixtures of a film-forming polymer with a polymer or oligomer crosslinker and a plasticizer. In this case, an increase in cohesive strength is achieved owing to an increase in the crosslinker concentration, while the enhancement of free volume is ensured by the increasing plasticizer content in the blend. Adhesive materials capable of adherence to wet substrates, hydroactivated adhesives, and adhesion moisture sorbents have been prepared for the first time.

接着剤の粘弾性と接着強さ

接着剤の粘弾性と接着強さ