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During the use of hot melt adhesive, many customers have reported that the glue does not stick. Therefore, most users will encounter various troubles in the production process because they do not have a deep understanding of hot melt adhesive. Below is a detailed introduction on how to improve the bonding strength of hot melt adhesive.
1. Improve hot glueGlueSurface roughness
When the adhesive infiltrates the surface of the adhesive material well, surface roughness is beneficial for increasing the degree of infiltration of the adhesive liquid on the surface, increasing the density of contact points between the adhesive and the adhesive material, and thus improving the bonding strength of the hot melt adhesive.
2.HeatMeltingAdhesiveSurface Treatment
Due to the “weak boundary layer” formed by the oxide layer of the adhesive, such as rust, chrome plating, phosphating, release agent, etc., the surface treatment of the adhesive will affect the bonding strength of the hot melt adhesive.
3. PreventingHeatMeltingAdhesivePenetration
Under the influence of environmental atmosphere, adhesive joints often infiltrate some other low molecules. For example, when the joint is in a humid environment or underwater, water molecules will penetrate the adhesive layer;
In organic solvents, solvent molecules will penetrate into the polymer gel layer. The penetration of low molecules first deforms the hot melt adhesive layer, and then enters the interface between the adhesive layer and the adhered material, reducing the strength of the adhesive layer and thus breaking the bond.
4. PreventingHeatMeltingAdhesiveMigration
In bonding materials containing plasticizers, these small molecules are easily migrated from the polymer surface or interface due to poor compatibility with polymer macromolecules. If the migrated small molecules aggregate at the interface, it will hinder the adhesion between the hot melt adhesive and the adhered material, leading to adhesive failure.
5、 IncreaseHeatMeltGluePressure
When bonding, apply pressure to the bonding surface to make it easier for the adhesive to fill the pits on the surface of the object being bonded, and even flow into deep holes and capillaries, reducing bonding defects. For hot melt adhesives with low viscosity, excessive flow may occur under pressure, resulting in a lack of adhesive.
Therefore, pressure should be applied when the viscosity is high, which also promotes the escape of gas from the surface of the adhered material and reduces the pores in the bonding area.
6.HotMeltingAdhesiveLayer Thickness
Thicker adhesive layers are prone to producing bubbles, defects, and early damage, so the adhesive layer should be made as thin as possible to achieve higher bonding strength. In addition, the thermal expansion of the thick adhesive layer after heating can also cause significant thermal stress in the interface area, making it more prone to joint damage.
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