Main Performance Indicators of Hot Melt Adhesive
Published on Mar. 27, 2020
The determination of the composition and amount of hot melt adhesive mainly depends on whether the performance that meets the requirements of the application can be obtained. At the same time, when using hot-melt adhesives, it is also necessary to fully understand the properties of the adhesive used to determine the appropriate conditions of use.
1. Melt viscosity (or melt index)
This is a performance index that reflects the flow performance of hot melt adhesives. It directly affects the coating, wettability, and permeability of the glue to the adherend, and also has an effect on the drawing of the glue. Therefore, melt viscosity is an important basis for determining the melting and coating process. Melt viscosity is closely related to temperature. It increases with decreasing temperature, so it must be measured at a certain temperature. Generally, the measurement is performed at an average temperature (190 ± 2 ° C) when the hot melt is used.
In order to obtain a good bonding effect, a hot melt adhesive with an appropriate melt viscosity (or melt index) should be selected according to the type of material to be bonded and the shape of the bonding surface.
2. Softening point
The softening point is the temperature at which the no smoke hot melt adhesive begins to flow, and can be used as a rough indicator of the heat resistance, ease of melting and drying time of the hot melt. It depends on the structure and molecular weight of the base polymer. The softening point temperature is higher than the glass transition temperature, but there is no certain relationship between them. Generally, high softening point glue has good heat resistance but has a short drying time. But the glues with different compositions do not necessarily follow this rule.
The softening point is usually measured by the ring and ball method.
High Grade Hot Melt Glue Stick
3. Thermal stability
Thermal stability is the performance of high grade hot melt glue stick against oxidation and thermal decomposition under long-term heating. It is an important indicator of heat resistance of glue. Although anti-oxidants are added to the hot-melt adhesive, they have a certain effect, but if they are used at high temperatures for a long time, even if they are added, they cannot prevent oxidation and thermal decomposition. Therefore, it is necessary to determine the amount of melted glue and the heating and melting time of the glue according to the thermal stability of the glue and to design the capacity of the melted glue tank. The stability of hot melt adhesive mainly depends on the heat resistance of its main components. Thermal stability is generally measured at the temperature of use, the glue does not oxidize, the viscosity changes within 10%, the longest time that can be experienced as a standard. If it can go through 50-70h, the thermal stability is good.
4. drying time
The drying time refers to the time from the time when the glue is applied to the time when it is effectively exposed to the pressure to be bonded. After curing, it has better bonding performance. After this period of time, the bonding performance is greatly reduced, and even Can not be glued, this is an important process performance of hot melt adhesive. The main factors affecting the drying time are the specific heat of the hot melt adhesive, the coating temperature, the amount of glue, the method of coating, the ambient temperature, the type of material being bonded, the preheating temperature of the material being bonded, and the thermal conductivity. In actual use, it should be pressed quickly after the glue is applied, that is, the drying time is minimized to ensure the quality of the glue.