Hot melt adhesives are solid and contain no solvents or water and set by the loss of heat which gives them a very fast setting speed.
They are a popular choice in the manufacturing industry because they can bond both similar and dissimilar materials.
Hot melt adhesives comprise:
- Polymers – these give the adhesive strength and flexibility
- Resins – give the immediate hot tap of the adhesives
- Wax – thins the adhesive so that it can be easily applied
- Antioxidants – preserves the adhesive at high temperatures
How Hot Melt Adhesives Work
Hot melt adhesives are applied to a material in the liquid or molten state. When the two materials are brought into contact the adhesive quickly cools down and solidifies.
Hot melt adhesive is set by the loss of heat and the temperature at which they are applied is critical. It must be liquid or molten enough to wet out the substrates and be hot enough for assembly before cooling.
If the adhesive is not hot enough in the molten stage the bond will fail at a later stage. On the other hand if the adhesive is applied at too high a temperature, it will remain molten for too long and may be still soft when it comes out of the compression stage.
Any stress caused on the bond causes immediate failure or produces a weakened bond which can fail at a later stage.
Advantages of Hot Melt Adhesives
Hot melt adhesives have several advantages to water-based adhesives.
Some of these include:
- Long shelf-life
- The curing or drying step is eliminated during the bonding process
- There is no loss of thickness in the material during solidification
- Do not require any specific precautions to be taken for disposal
- Reduction in the use of volatile organic compounds
- Versatile in the array of different materials they can bond with – ceramics, metals, rubbers, plastics, paper, wood and glass.
- Flexibility – Suitable whether the time it takes to form a bond is just a few seconds to longer periods such as using pressure-sensitive adhesives.
- Variety – Hot Melt Adhesives are available in a variety of types which include glue sticks with high melting rates to granular or power hot melt blocks used for bulk melt processors.
Application of Hot Melt Adhesives in Manufacturing
Hot Melt Adhesives are suitable for a number of applications in the manufacturing industry.
Here are a few common applications:
Packaging Industry – Paperboard cartons and corrugated boxes
Hygiene Industry – Disposable diapers
Bookbinding Industry – Spine gluing
Electronics Industry – Wires and affixed parts
Woodworking – Product assembly and lamination
Choosing the Right Hot Melt Adhesive
When selecting a grade of hot melt adhesive, it is important to determine the type of glue required.
Is a high heat-resistant glue required and will the glue line be exposed to direct sunlight or water?
Standard hot melt adhesives such as Ethylene Butyl Acrylates (EBA), acrylic polyamide and polyolefin are not waterproof and applications involving water should be avoided.
Are the materials being bonded similar or do they have different attributes?
For example one is porous and the other one is not.
Hot melt adhesives are not recommended for external use in most instances, however polyurethane adhesives cross-laid offer excellent heat and chemical resistance once they are laid.
Tips for Applying Hot Melt Adhesives
The materials being bonded must be clean, dry and free of dust, oil and grease. The hot melt adhesives must be applied at the correct temperature as the temperature of the materials and surrounding areas can affect performance.
The amount of adhesive applied will greatly affect the bonding – using little will cause the adhesive to cool more quickly, not allowing for sufficient time for the bond to become sufficiently strong.
Using too much adhesive will prevents the bond cooling down before coming out of compression and the materials will come apart
If you are looking for high-grade hot melt adhesives or need assistance on which adhesives are suitable for your industry, CLICK HERE to contact us or call us on 07 3266 8699 for more help or guidance.