Mistakes with hot melt glue are common, and proper measures will provide the most reliable bond without unnecessary issues. The following are the top 10 mistakes to avoid while using hot melt glue and tips on their resolution.
1. Using the wrong type of glue:
Hot Melt Glues are available in a variety of formulations tailored for different materials and applications. For example, certain hot melt glues are specifically designed for plain and offset substrates. Using these on coated or laminated paper materials can be a common error, particularly in applications such as paper packaging, bookbinding and graphics, leading to de-bonding and product failures.
2. Applying glue at the wrong temperature:
The flow of hot melt adhesives is essential for their performance and machinability. They are designed to melt (soften) when the temperature exceeds their softening point and to flow properly within a specific temperature range. Incorrect temperature settings are a common mistake in edge-banding applications, where the working temperature vastly varies from 120 to 220°C, depending on the type of machines.
3. Not Considering Open and Set Time
Hot melt adhesives have an "open time" where the glue remains workable for a certain period after application. Outside of that period, the bond may be weak or nonexistent. Understand the open and set times of the glue to align with your machine's speed, whether it is automatic or manual operation, to achieve maximum bond strength.
4. Not Considering Summer and Winter time:
During the summer, hot melt adhesives cool down relatively slowly. Conversely, in the winter, they solidify much more quickly, dropping below their softening point. Therefore, it's advised to raise the temperature setting (of the glue pot) by 10°C in winter. Failing to do so may result in weak bonding because the adhesive cools down before being applied to the substrate.
5. Not Considering Temperature Tolerance:
Hot melt adhesives (such as EVA and PO) have temperature constraints. As thermoplastic materials, traditional adhesives will soften above 80°C which can weaken the bond. This poses a problem if finished products are exposed to direct sunlight for extended periods or harsh weather conditions in outdoor applications. Selecting adhesive solutions that offer higher temperature resistance (up to 120°C) is essential.
6. Overfilling of the glue tank:
While it may seem like an excellent idea not to have to refill the hot melt glue tank so often. Overfilling while consuming slowly causes excessive heating, adhesive charring, smoke, odors, and contamination of equipment and nozzles. Fill the tank only up to 75% of its capacity.
7. Wrong pressure settings:
Using hot melt glue systems that depend upon air pressure for application can be prone to several problems if their pressures are set improperly. Too little pressure and the adhesive comes out thin and weak. Too much, and it overflows messy and stringing. Incorrect pressure settings are a common mistake for spray-application, i.e. in mattress and packaging (i.e. carton and case closure) manufacturing.
9. Applying Too Much or Too Little Glue:
Excessive adhesive can lead to a messy, stringy bond-line, impact product finishes, and increase unit costs. Conversely, insufficient adhesive may fail to adequately cover and form a proper bond initially or may de-bond over the product's lifespan.
10. Using the incorrect Glue Applicator:
Correct glue roller and nozzle sizes are essential for effective flow and pattern control. An improperly sized nozzle, whether too small or too large, can compromise bond quality. Pretextures should be applied using appropriately sized rollers and nozzles to ensure optimal glue coverage.
Additionally, ensure that your adhesives are stored in cool and dry locations, avoiding direct sunlight and extreme conditions. Having an excessive inventory and storing it for too long can impair performance. Therefore, it's important to rotate the stock and not keep glue beyond its 24-month shelf life.
Conclusion:
Above all, hot melt glue has proved to be versatile and practical. Set up for success with the best practices to get the most out of your hot melt adhesive. It is while maintaining operations efficient, clean, and safe. Follow closely to the manufacturer's guidelines for hot melt adhesive troubleshooting. Always perform individual adhesive testing for your specific application and production process before mass production.
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Published by TIANJIN SHENG-WANG ELECTRONIC CHEMICAL PLANT
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