4.6.1 Adhesives which harden on cooling

Adhesives which harden on cooling: Hotmelts

General description:

  • One-component adhesives
  • Adhesive based on thermoplastics (can be melted)
  • Hardening on cooling

A wide range of thermoplastic materials are available as hotmelts.
The most important are:

  • Polyolefins
  • EVA
  • Polyesters
  • Polyamides
  • Polyurethanes
  • Thermoplastic natural rubbers (butyl rubbers)
  • Acrylates
  • (Bitumen)
  • (Wax)

Physical properties in the as-supplied state:

  • Solid rods or granulate; viscous to paste-like once melted

Processing

  • Semi-automated or fully automated processing
  • For preferred equipment contact the adhesive manufacturer
  • Processing temperature: room temperature; adhesive application as a melt (temperature over 100°C)
  • Normal contact pressure
  • Adhesive film thickness: 0.2 – 2 mm
  • 1-C processing
  • The adhesive is solid at room temperature; as-supplied state: blocks, rods, granulate, powder, film
  • Application: heat and apply as a melt, or apply as a solid and then heat
  • Very rapid cohesion development (inner strength) on cooling
  • Detachable by heating the adhesive
  • Secure until the bonded joint has reached hand strength
  • Take relevant measures for health and safety at work and environmental protection (General: see Section 7; Details: see safety data sheet)

Typical properties of the hardened adhesives:

  • Free of solvents and monomers (individual building blocks of the polymers)
  • Medium to high strength in the bonded joint
  • Differing flexibility depending on the thermoplastic
  • Temperature for continuous use lies below the softening temperature
  • Can be swollen
  • Tend to undergo creep

Typical processing parameters for selected hotmelts:

Base material Softening range [°C] Processing temperature [°C]
Polyamides 95 – 195 120 – 240
Polyesters 50 – 230 150 – 240
Ethylene vinyl acetate 80 – 200 140 – 200
Polyolefins 85 – 160 120 – 200
Polyurethanes  90 – 200
Natural rubbers 80 – 140 130 – 200
Ethyl vinyl acetate copolymer (EVA)  130 – 200

Points to heed:

  • The substrates must be acclimatised prior to bonding. Important for metallic substrates (high thermal conductivity): risk of shock-induced hardening
  • The processing time depends on the thermal conductivity of the substrate
  • Damage to the substrates by high temperatures must be avoided

If you have questions about the product then see the technical data sheet or contact the adhesive manufacturer