1. It is a solid at room temperature; 2. Thermoplastic polyurethane prepolymer with a solid content of 2.100% solid content; 3. Coated in a melted state after heating, and then react with water vapor in the air and gradually solidify and bond.
General characteristics of PUR hot melt adhesive
Viscosity
Thermal stability
Opening hours
Curing time
Opening hours
The opening time varies according to the hot melt adhesive from the time when the hot melt adhesive is applied to the first substrate until it becomes solid and cannot immerse the surface of the second substrate. The opening time varies according to the hot melt adhesive formula, and the opening time varies with the operating conditions.
Such as operating temperature, coating quantity, substrate temperature
Curing time
The time taken to produce sufficient bond strength by coating the first substrate and contacting the second substrate
PUR curing evolution process
After PUR hot melt adhesive is applied, physical solidification produces initial adhesion - like traditional hot melt adhesive
After the opening time (a), the hot melt glue is solidified to state (b) in seconds to minutes, and the initial strength (e) is obtained.
The hot melt adhesive that has just been coated has an initial viscosity (d), and materials with high rebound force require PUR to have a higher initial viscosity.
Normally, 80% of the final bond strength will be obtained after 24hrs.
The final bond strength is obtained after 3 to 5 days
In some applications, defective products can be reworked before the film is completely cured.
Principle of PUR curing reaction
Polyurethane reactive hot melt adhesive
Prepolymers terminated with isocyanate groups
The presence of n/m=2, n/m>2 prepolymer and free NCO monomer
Different molecular weights and molecular structures determine the state of the product: liquid, semi-solid (very viscous liquid), solid
Typical glue coating method for PUR hot melt adhesive
The main factors affecting the performance and effect of PUR bonding
Base material : surface energy; surface profile; surface pollution
Use environment: chemical solvent; humidity; temperature; pressure; time; additives
Reasons for failure of bonding
PUR does not match
the substrate surface flatness is not enough
for the substrate surface pollution
, low humidity, difficult to penetrate
additive migration and
maintenance time, bonding time
, pressure and
bonding environment
The effect of temperature
Low temperature: OT becomes shorter, false sticky, glue becomes brittle
High temperature: the glue layer becomes softer, initial stickiness becomes lower, OT becomes longer, bubble, peel strength becomes smaller
The impact of pollution
The presence of grease, dust, stone powder, fiber, etc. hinders the bond between the glue and the substrate, affects the adhesiveness of the glue, and reduces the effective contact area.
The impact of stress
Promote full contact between glue and substrate
Surface cleaning treatment
Fingerprint, water vapor (isopropanol)
Oils (n-heptane or butanone)
Release agent (consult the manufacturer)
Surface energy is less than 36 (plasma or corona)
For plastic/metal substrate bonding, it is very important to perform proper cleaning of the substrate!
Advantages of PUR
High quality and high efficiency
No solvents and water, good surface effect, initial viscosity, fast speed
Environmental friendly
Solvent-free F****, 4VOC
Suitable for a variety of materials
Wood, metal, plastic, inorganic and other substrates composite PVC, film, fabric, CPL, veneer, metal
Operation window width
Low temperature in winter and high temperature in summer, different materials and different machine speeds
Excellent final performance
High temperature resistance, water resistance, solvent resistance, weather resistance 100% solid content
Low unit cost
Glue coating volume saves competition among brands, and end customer revenue
