Applications of Hot Melt Adhesive Technology
This can be reduced by using a reactive adhesive that after solidifying undergoes further curing e.g., by moisture (e.g., reactive urethanes and silicones), or is cured by ultraviolet radiation. Some HMAs may not be resistant to chemical attacks and weathering. HMAs do not lose thickness during solidifying; solvent-based adhesives may lose up to 50-70% of layer thickness during drying.
In industrial use, hot melt adhesives provide several advantages over solvent-based adhesives. Volatile organic compounds are reduced or eliminated, and the drying or curing step is eliminated. Hot melt adhesives have long shelf life and usually can be disposed of without special precautions. Some of the disadvantages involve thermal load of the substrate, limiting use to substrates not sensitive to higher temperatures, and loss of bond strength at higher temperatures, up to complete melting of the adhesive. Here are the different applications of hot melt technology:
1. Packaging - In packaging, the adhesive should not be that strong because it will be removed upon getting the product out of the package. You do not want to have the product sealed forever inside the box (or whatever container is used). However, the adhesive should be strong enough to keep the product inside the package in a perfectly safe and dry condition (especially if it is food).
There are specially designed industrial hot melt equipment for packaging. These equipments can be used for carton sealing, bag sealing, case sealing, tamper-proof closures, box making, tray making, etc.
2. Nonwovens - The use of nonwoven fabrics in clothing and other furnishings are widely embraced because of their strength and resilience. The hot melt technology has a part in achieving those properties of nonwoven fabrics.
Nonwovens are fabrics that are not knitted or woven. The fibers used in nonwoven fabrics are bonded with the application of heat and pressure. There are special resins, called binders, which are used in holding the fibers together.
The most common fibers used in making nonwovens are cotton, rayon, polyester, wool, acetate and acrylic.
Some binders used in nonwovens are acrylic, vinyl acrylic, vinyl acetate and styrenated acrylics.
3. Appliance assembly - Hot melt technology is starting to get the attention of appliance manufacturers because of its low cost without the strength getting compromised.
Specialized industrial equipment dispenses molten thermoplastic resins that are used as adhesives in assembling an appliance. The strength of the adhesive will be achieved upon the cooling of the pliable resin. This is a great time saver for manufacturers because it reduces the clamping time.
4. School projects, arts and crafts - This is the most basic application of this technology is the traditional consumer glue gun. It is the simplest adhesive dispenser that is readily available in households and schools.
The traditional hot melt adhesive used is the glue stick which may be cleared or colored. There are also novelty glue sticks like glittered sticks and glow-in-the-dark that are made specifically for artworks.
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