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The packaging industry is rapidly changing with fluctuations in demand from various industries. However, nearly 80 years after the invention of the first adhesive product designed to address temperature and humidity challenges, a fact still exists – all types of industries rely on hot melt adhesives. At the time of its invention, this multifunctional adhesive solved multiple problems caused by traditional adhesives. It quickly became the preferred adhesive for industries such as construction, manufacturing, furniture, automotive, packaging, and bookbinding.
Hot melt adhesive comes in various forms, including glue sticks, granules, blocks, etc. Over time, hot melt adhesives have become more versatile than ever before and continue to have several advantages over other adhesives.
The advantages of hot melt adhesive bonding include:
1. Rapid curing
2. Long term adhesion
3. Can be adhered to almost any substrate
4. Resistance to temperature changes and humidity
5. Simple and universal application methods
6. Easy and automated dispensing process
7. Long shelf life
8. Minimal waste
9. Relatively cheaper compared to other adhesive options
SuccessBondingThe Importance
Although each of the above advantages plays a crucial role in deciding to use hot melt adhesives, it is important to note that these advantages only exist when successfully bonded during application. It is crucial to ensure the use of the correct factors to promote ideal adhesion between the substrate and adhesive. To understand why these factors are so important, the properties of the heat dissipating adhesive must first be considered.
Hot melt adhesives are mainly composed of polymers, resins, and wax or oil, and are a type of thermoplastic with ductility at or above the melting point of the polymer. Once it becomes a liquid, the adhesive will penetrate any pores in the substrate it is applied to; Then, apply the second substrate onto the adhesive. As the adhesive cools and fills the pores and cavities of both substrates, it hardens and adheres to each substrate, providing a strong bond between the two.
Factors affecting adhesive strength
Hot melt adhesives are manufactured in multiple formulations, each specifically designed to provide unique viscosity, melting point, and adhesive strength, making them an ideal choice for specific applications. Based on the required adhesive strength, ideal curing time, preferred viscosity, and type of substrate to be used, manufacturers can modify certain adhesive properties to make them suitable for almost any application.
Hot melt adhesive bonding factors that affect bonding include:
1. Types of polymers
The type of polymer used mainly affects the melting point of the adhesive and can also affect the strength of the final bond. In addition, different polymers can increase flexibility, increase or decrease adhesion, and increase chemical resistance. Finally, the selected polymer will also affect the final application process.
2. Adhesive temperature
The temperature of the hot melt adhesive used will affect the bonding strength and appearance of the final product. Within the ideal temperature range, the adhesive turns into a liquid and can fully penetrate into the pores of the substrate. Outside the ideal range, the adhesive may remain too hard to bond with the substrate, have inappropriate surface tension, fail to wet the surface, or carbonize in the pot and become less effective.
3. Environmental temperature
Although adhesive temperature is the primary concern in mechanical applications, environmental temperature can affect bonding. If the substrate or surrounding air temperature is too cold, the adhesive may solidify too quickly, thereby hindering bonding. If the temperature is too high, the solidification time may be longer than the ideal time for your production process.
4. Quantity of adhesive products
The larger surface area of adhesive products allows more hot melt adhesive to penetrate into the pores of the substrate and provide a strong bond. The required product quantity depends on the adhesive strength, the substrate used, and the properties of the specific application.
5. Porosity of the substrate
The surface characteristics of the substrate used will affect the adhesive strength. Absorbent or rough materials may consume excessive adhesive, while glossy or non porous materials may not be able to bond properly between the substrate and adhesive.
6. Pressure
Applying pressure to the substrate and hot melt adhesive can increase the available surface area for bonding. In addition, it can help the adhesive move into the pores of the substrate and further strengthen the adhesion.
7. Opening hours and curing time
The opening time and curing time are defined as the amount of time between adhesive application and substrate placement, as well as between substrate application and bonding completion, respectively. Ensuring appropriate opening time and solidification time can ensure that viscosity, temperature, and other factors are ideal choices for successful bonding.
Successful Hot Melt AdhesiveBondingSteps
After carefully considering all the above characteristics, choose the hot melt adhesive that is most suitable for your application. Then, follow these steps to ensure successful bonding:
1. Temperature control of bonding
Ensure that the hot melt temperature is within the ideal range to promote proper melting, prevent carbonization, and provide appropriate surface tension and wettability. In addition, ensure that the ambient temperature is within the specified range to keep the adhesive liquid for the desired time.
2. Ensure that the substrate and hot melt adhesive are free from contamination
Dusty or greasy substrates can cause poor adhesion. Similarly, contaminants in hot melt adhesives can damage the performance and appearance of the adhesive.
3. Apply an appropriate amount of adhesive
Depending on the final application, successful bonding may require varying amounts of adhesive. Apply hot melt adhesive to achieve the required surface area.
4. Pay attention to the opening and curing time
Different hot melt adhesives have different ideal opening and curing times. Make sure you pay strict attention to each one to ensure ideal adhesion.
5. Apply pressure
If necessary for the type and application of hot melt adhesive, apply pressure to the substrate to ensure sufficient adhesion.
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