The packaging and label industries must be mindful of the material and tools they use because of the delicate materials they work with like paper, cardboard, etc. Hot melt adhesives are widely used by these manufacturers due to their versatility, strength, efficiency, and beneficial outcomes.
What Are Hot Melt Adhesives?
Hot melt adhesives (HMAs), or hot melts, are a 100% thermoplastic polymer and are solid when they are at room temperature but liquefy when they are heated to their softening point. Once the hot melt is softened and liquified, it can be applied and used for numerous packaging applications by binding together the substrate materials.
In its solid state, the hot melt adhesive can come in a variety of forms, including chips, pellets, glue sticks, beads, or blocks. Once they are heated, they can either be sprayed or squeezed through a nozzle onto a surface. They typically have strong initial tack, which permits fast processing while maintaining flexibility and resistance to chemicals and water.
How are they Made?
Thermoplastic refers to the adhesive becoming malleable when heated and then hardening when it cools, turning it into a solid form. Polymer signifies that the hot melt adhesive is made up of many different bonded components. It is important to note that hot melt adhesives do not contain any liquids or water.
Hot Melt Adhesive Components
- Polymers make up the adhesive properties while providing strength and flexibility and allowing the hot melt to sustain a bond between materials.
- Plasticizers modify the adhesive’s viscosity, which makes its application easier.
- Resins allow the adhesive to have a “wet” feel and deliver the initial bond between materials.
Waxes can also be added to hot melt adhesives to manage viscosity, flexibility, and speed, while antioxidants can be added to preclude degradation or biocides to control bacteria growth. The most common kinds of hot melt adhesives include:
- Polyethylene
- Polyurethane
- Metallocene
- EVA hot melt
How to Apply Hot Melt Adhesives
Once the hot melt adhesive has been heated to its softening point and becomes liquid, the liquid is applied to a surface via rolling, spraying, or extruding and briefly exposing it to an “open time” so it can reach its ideal temperature to bind to the initial material surface. After it is exposed to the open time, the surfaces being bound are put together, causing the adhesive to begin cooling, returning it to its solid state, and bonding the two substrates together.
It is important to maintain the correct temperature for application and open time for the optimal bonding of materials. Further guidelines regarding temperature in specific industries include:
- Graphic arts – hot melt adhesives should have adjustable open times and be heated to 350˚ Fahrenheit for application.
- Packaging – organic and cardboard substrate markets should heat hot melt adhesives to 350˚ Fahrenheit with an open time of 4 seconds for optimal bonding and will stay effective in a variety of hot and cold conditions.
- Liquid labeling and pressure sensitive – for label applications, the best adhesion occurs at 40˚- 50˚ Fahrenheit with a dwelling time of 24-48 hours before being handled by consumers.
Hot Melt Adhesive Applications
Numerous industries rely on hot glue adhesives for bonding through their diverse set of applications. The variety of adhesive types means there is a large potential for further industry applications. Key industries that benefit from hot melt adhesives include:
- Packaging – regardless of the industry, hot melt adhesive used to seal cartons and corrugated boxes, stabilizing pallets, and seal wrapping materials provide many benefits and efficiency.
- Furniture and woodworking – hot melt adhesives can be used for furniture assembly, cabinetry, and paneling industries.
- Automotive – the assembly of automotive seating and trim relies on the use of hot melt adhesives.
- Food and beverage – hot melt adhesives are widely used in the food and beverage industry because of their ability to endure extreme temperatures and moisture.
- Bookbinding –hot melt adhesives are widely used in the bookbinding industry to complete the final binding of their products.
Packaging Industry-Specific Applications
HMAs are widely used in the packaging industry because they can be used on several substrates. HMAs can be applied for larger production jobs by using a reservoir tank to input large amounts of adhesive pellets and then drawn from an external tank. For smaller production applications, hot melt adhesive can be applied manually via glue guns or glue sticks.
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- Paper goods – HMAs can be used on everything from paper bags to paper cups for superior bonding applications. EVAs (ethylene vinyl acetate) are also commonly used due to the ease of application, but for products that may reach high temperatures, a specialty formula may be required.
- Case and carton Sealing – one of the major applications for hot melt adhesives is sealing cases and cartons because of the superior adhesion on cardboard and paper substrates. EVAs may require additives if the product will reach cold temperatures nearing – 40˚ Fahrenheit.
- Labeling – HMAs can be widely used for all types of labeling applications due to the variety of HMAs available.
- Plastic containers – hot melt adhesives are also used for plastic containers with enhanced bonding ability by using polyolefin-based adhesives. It is important to note that in order not to distress the substrate, you must use a low enough temperature for the application.
Sustainability
Hot melt adhesives offer easy application, low melting temperatures, and optimal flexibility when compared to other kinds of adhesives and are safe to use on a wide array of substrates, including:
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- Corrugated cardboard
- Paper
- Wood
- Plastic
- Metal
- Fabric
- Glass
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Benefits of Using Hot Melts
Using low-temperature hot melts on delicate materials such as paper can help avoid damaging the substrates during the application process. Low-temperature hot melts refer to the adhesive’s ability to be applied at a much lower temperature than normal hot melts. Typically, synthetic resins are the base of these types of hot melts.
Manufacturers generally choose to use low-temperature hot melts because they are cost-effective by reducing:
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- Cost of materials – low-temperature hot melts typically are less expensive to purchase than regular hot melts.
- Energy consumption – due to the lower temperature required, in turn, the amount of energy required is also lower.
- Operation costs – reduced wear and tear on machinery is a benefit of using low-temperature hot melts because the machinery does not reach such extreme temperatures, reducing frequent maintenance and repairs.
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Benefits of Using Low-Temperature Hot Melts for Packaging
The primary benefit of cost-effectiveness derived from using low-temperature hot melts for the packaging industry is supported by:
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- Operator safety – using lower temperatures reduces the operator’s chances of becoming injured from burns and reduces the amount of odor emitted from the adhesive.
- Reduced energy consumption – reducing energy consumption increases sustainability, causing a reduction in a manufacturer’s carbon footprint.
- Delicate material applications – some materials that require bonding and sealing are delicate and can easily be damaged from high-temperature applications. Reducing the adhesive temperature can ensure no damage is caused to delicate substrates.
- Operation efficiency – minimal maintenance combined with the fast application and curing time of low-temperature hot melts increase operational performance.
- Increases machinery life – extreme temperatures can cause the need for more frequent repairs or maintenance, causing the machine to deteriorate. Using lower temperatures can increase the life of your machinery.
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