Most hot melt users anticipate achieving a high heat resistance with a “high softening point” hot melt adhesive. Softening point, like the viscosity measurement, is simply an indicator used to evaluate if adhesives are consistent between batches or lots.
Softening point is not heat resistance and customers must carefully evaluate their adhesive where temperature resistance is required.
Softening point is the temperature at which a material softens sufficiently to allow significant flow under a small stress. Most hot melt adhesives are measured by a Ring and Ball apparatus according to the ASTM D-2398 Test Method. Softening point is heating rate dependent. If the heating unit cannot provide a consistent heating rate, the determined softening point may be varied. The faster the heating rate - the higher the softening point observed.
For example, any APO-based hot melt adhesives may present very high softening points and yet they actually do not resist flowing in the real world applications. This is because most APO-based adhesives do not have sufficient cohesion to resist both inter and intra-molecular flow upon heating.
To evaluate the heat resistance, one must perform the following tests: shear adhesion fail temperature (SAFT), peel adhesion fail temperature (PAFT), or holding power (shear) at a fixed high temperature.
For more information call or email Pierce Covert,
Glue Machinery Corporation
1(888)202-2468 info@gluemachinery.com
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