In the formulation system of hot melt adhesives, polyethylene wax is an indispensable core modified component, which directly determines the fluidity, bonding strength, temperature resistance stability and service life of the colloid. Many practitioners know that the dropping melting point of polyethylene wax for hot melt adhesives should not be too high or too low, but they often ignore the differentiated selection logic under different seasonal working conditions. Especially when facing the high temperature environment in summer, a slight mistake will lead to a series of problems such as softening of the adhesive layer, debonding, and slow curing.
In conventional cognition, the dropping melting point of polyethylene wax for hot melt adhesives is usually recommended to be controlled in a reasonable range of 100-120℃, but many experienced downstream customers will explicitly reject products in the 115-120℃ range, which has very practical production logic behind it. Polyethylene wax with too low dropping melting point will directly lower the overall softening point of the hot melt adhesive. In the continuous high temperature environment above 35℃ in summer, the adhesive layer is prone to problems such as softening, deformation, and sharp drop in shear resistance, and even the adhesive particles will agglomerate and stick together during storage. However, high melting point wax with a dropping melting point exceeding 115℃ will have poor compatibility with base resins such as EVA, which not only easily leads to appearance problems such as surface precipitation and fogging, but also greatly shortens the effective open time of the hot melt adhesive. The adhesive will cure quickly before fully wetting the substrate after application, which will instead reduce the actual bonding strength. Therefore, avoiding the high melting point range of 115-120℃ and choosing the medium and low melting point grades of 100-114℃ is a pragmatic choice for many industrial customers after long-term working condition verification.
In addition to the dropping melting point, viscosity is another core indicator for summer selection, and it is not the lower the better. Under conventional working conditions, the viscosity of polyethylene wax for hot melt adhesives at 140℃ is recommended to be controlled in the range of 200-600cps, while in summer, it is recommended to lock the viscosity in a narrower range of 250-500cps. Wax with too low viscosity will make the hot melt adhesive too thin in a high temperature environment, the curing speed will be greatly slowed down, and it cannot be shaped for a long time after application, which is prone to problems such as sliding and misalignment of the bonding surface. Wax with too high viscosity cannot play the role of improving fluidity, and it is prone to wire drawing and glue breaking during application, cannot fully penetrate into the gaps of the substrate, and eventually leads to poor bonding. Different application scenarios can be fine-tuned on this basis: hot melt adhesives for bookbinding can choose grades with slightly lower viscosity to ensure leveling properties, while hot melt adhesives for packaging and automotive interiors can choose grades with medium and high viscosity to improve the cohesion and long-term resistance of the adhesive layer.
Aiming at the special working conditions in summer, polyethylene wax also has several key requirements that are easy to be ignored. First of all, it is thermal stability. It is necessary to select products with narrow molecular weight distribution and narrow melting range to ensure no precipitation and no yellowing during high-temperature sizing and long-term storage, which will not affect the appearance and long-term performance of the hot melt adhesive. Secondly, the crystallization rate should be moderate, and the penetration should not be too high, so as to avoid the slow crystallization of the colloid caused by the high ambient temperature in summer, which will slow down the operation efficiency of the entire production line. Finally, it is necessary to ensure good compatibility with components such as EVA and tackifying resins, so that the hot melt adhesive can still maintain stable cohesion in a high temperature environment, and can still maintain a firm bond for a long time under the complex working conditions of dynamic load and temperature difference change, and will not fail due to debonding.
Choosing the right polyethylene wax adapted to summer working conditions can not only reduce after-sales problems caused by bonding failure, but also reduce the amount of glue used per unit and reduce the frequency of repeated sizing. While ensuring product performance, it helps downstream customers reduce comprehensive production costs, which is also the key detail for hot melt adhesive products to establish competitiveness in the summer market.
