The initial viscosity of the hot melt adhesive reflects the bonding strength, and the tackiness is more reflected in the stability after bonding. Therefore, what is the relationship between initial viscosity and retention viscosity as a performance indicator for hot melt adhesives at different bonding stages?
Most people who use hot melt adhesives know the initial tack, but the tack isn't well known. Many people think that stickiness equals initial stickiness, and this understanding is incomplete. The viscosity of a hot melt adhesive can be divided into parts that are in the initial tacky performance stage upon and prior to initial contact with the substrate, and the viscosity is more reflected in the tack as the glue reacts with the substrate. It can be seen that the performance from initial tack to tack is an integral and consistent performance progression of the hot melt adhesive. One of the main prerequisites for maintaining good viscosity is that the initial tack must also meet certain adhesion criteria. Otherwise, there is no initial stickiness.
After the thermal initial bonding is completed, the hot melt adhesive is usually combined with the substrate, and can show adhesion and bonding strength, reaching the stage of testing the adhesion. That's not to say it won't be a problem once it's bonded, it also depends on how the external environment affects the bonding layer. Generally speaking, the contact surface of the hot melt adhesive with the external environment on the substrate is very small, but the moisture and particles in the air can still enter the adhesive layer from the gap. If the molecular structure of the substrate and the hot melt adhesive is not fixed enough, the foreign material molecules can take full advantage of it. There are many kinds of invading material molecules, some can react directly with the hot melt adhesive, disperse stable and orderly molecules, and some do not react with the hot melt adhesive, but will fill the remaining space outside the molecular structure, so that the adhesive layer will be lost. The original molecular cohesion, but the adhesive layer without elastic force is easily separated from the substrate by external force. If the adhesive layer can resist the influence of the above external factors, it proves that it has good adhesion.
A good bond is not only tacky at first, but also good at staying tacky. Hot melt adhesives have different viscous properties at different stages of life. Has good initial viscosity, possibly good adhesion. This is a link between a ring and a ring.