Key Technical Parameters
Understanding the technical specifications on a hot melt adhesive data sheet is essential for selecting the right product and optimizing your process. Here are the most important parameters explained:
Viscosity (mPa·s or cP)
Viscosity measures the adhesive's resistance to flow at the application temperature. Lower viscosity (1,000-5,000 mPa·s) means the adhesive flows easily, suitable for spray applications and thin coatings. Higher viscosity (10,000-50,000 mPa·s) means thicker application, suitable for edge banding and gap-filling. Viscosity is measured at the application temperature using a Brookfield viscometer per ASTM D3236.
Softening Point (°C)
The softening point (measured by Ring & Ball method per ASTM E28) indicates the temperature at which the adhesive begins to soften. This gives a general indication of the adhesive's heat resistance. A higher softening point generally means better heat resistance, but the actual application temperature should be 50-80°C above the softening point for proper flow.
Open Time (seconds)
Open time is the duration after application during which the adhesive remains tacky enough to form a bond. Short open times (3-8 seconds) are needed for high-speed automated lines. Longer open times (15-60 seconds) allow for manual positioning and adjustment. Open time depends on application temperature, ambient temperature, adhesive mass, and substrate porosity.
Set Time (seconds)
Set time is how quickly the adhesive reaches handling strength after application. Fast set times (3-5 seconds) enable high-speed production. Set time is influenced by the same factors as open time, plus the thermal conductivity of the substrates.
Peel Strength (N/25mm)
Peel strength measures the force required to peel apart two bonded substrates. Higher peel strength indicates a stronger bond. Typical values range from 2-5 N/25mm for packaging applications to 10-30 N/25mm for structural bonds. Test method: FINAT or PSTC-1.
Shear Strength (MPa or psi)
Shear strength measures the adhesive's resistance to sliding forces. This is critical for structural applications where the bond must support weight or resist lateral forces. Typical values range from 1-5 MPa for standard applications to >10 MPa for structural adhesives.
How to Use This Information
When selecting an adhesive, start with the parameters that are non-negotiable for your application (e.g., viscosity range for your equipment, regulatory compliance for food contact). Then optimize for production speed (open time, set time) and bond strength requirements. Always validate with real-world testing under your production conditions.