In the actual scenario of hot melt adhesive formulation optimization, many practitioners will form the cognition that "using wax with a melting point of 130℃ can shorten the curing time". The core logic of this idea is to increase the crystallization rate of the system through high melting point wax, so as to accelerate the setting speed of the colloid. However, combined with the industrial product characteristics of current mainstream polyolefin waxes, this selection idea has objective boundaries for actual implementation.
At present, the industrially mass-produced products of conventional non-oxidized polyethylene wax have a dropping melting point generally stably below 120℃. Limited by molecular structure and polymerization process, it is difficult for pure non-oxidized PE wax to stably increase the melting point to 130℃ without changing its basic properties. Ordinary PE wax that forcibly breaks through this melting point range will often have a problem that the compatibility with core components in hot melt adhesives such as EVA and tackifying resin is greatly reduced, which in turn easily causes secondary problems such as precipitation of the adhesive layer and reduced adhesion.
Oxidized wax, which is often used to increase the melting point, has some grades with a melting point close to 130℃. However, after oxidation modification, the molecular polarity of such products is significantly improved, and the melt viscosity will be much higher than that of non-oxidized wax with the same melting point. After adding it to the hot melt adhesive system, it will directly increase the overall melt viscosity, which not only fails to achieve the expected rapid curing effect, but also leads to problems such as poor fluidity during glue application and insufficient wettability to the substrate, which is completely unable to adapt to the production and use requirements of most conventional hot melt adhesives.
At present, the mature commercial products that can achieve the characteristics of "high melting point + low viscosity" are represented by special polypropylene wax for hot melt adhesives. The softening point of such products can stably cover the range of 147-160℃, while maintaining extremely low melt viscosity. It will not have the disadvantage of excessively high viscosity of oxidized wax, and can greatly increase the crystallization rate of the hot melt adhesive system by virtue of higher crystallinity, and finally achieve the goal of shortening the curing time. This category is not in the theoretical stage. At present, a large number of international and domestic manufacturers have achieved stable mass production, but it has not been fully popularized among domestic small and medium-sized hot melt adhesive producers.
For formulation systems that do not consider replacing the wax category for the time being, there is no need to forcibly pursue the single melting point index of 130℃. By adjusting the addition ratio of the existing non-oxidized PE wax in the 120℃ range and matching a small amount of microcrystalline wax to optimize the crystallization behavior of the system, the curing time can be reasonably optimized within the existing process framework.
