Common Issues and Solutions with Dingli Hot Melt Adhesives
Problem:
Dingli hot melt adhesives are typically yellowish, clear, and translucent. However, the issues that arise during their use are often subtle and can go unnoticed for a long time. These problems are commonly found in printing companies and small bookbinding operations where the production volume is low and the variety of products is high. As a result, the adhesive in the glue tank is not fully consumed each time, leading to long-term reuse without replacement. In many cases, the adhesive is only replaced once every six months or even less frequently. This repeated heating and reboiling over time causes the adhesive to undergo high-temperature oxidation, leading to the volatilization of ethylene and vinyl acetate. Over time, this creates a rubber-like residue that settles at the bottom of the glue tank. When the temperature exceeds 180°C, the rate of volatilization increases significantly. Although the adhesive may still be in a molten state and sticky, once the glued books cool down, the back of the book becomes brittle and prone to breaking, causing pages to loosen and resulting in major quality issues.Solution:
The accumulation of these issues is a gradual process, not caused by a single boiling event. Therefore, it’s important to regularly monitor the adhesive and perform destructive testing on finished products to ensure the flexibility and tensile strength meet required standards. Additionally, the glue tank should be cleaned frequently—ideally once every 1–2 months—to prevent the buildup of rubbery deposits. This not only helps maintain consistent heating but also reduces energy waste. During cleaning, the top layer of glue can be removed and mixed with new adhesive. However, any rubber-like sediment at the bottom must be completely removed. If necessary, the entire contents of the tank should be discarded, and fresh adhesive should be added.Common Issues and Solutions with Wanli Hot Melt Adhesive
Problem:
Wanli hot melt adhesive has a milky white appearance and lacks transparency. While similar to Dingli adhesive in terms of issues caused by repeated heating, the nature of the problem differs. Prolonged exposure to high temperatures causes the tackifiers and viscosity modifiers in the adhesive to evaporate, reducing its stickiness and forming a rubbery residue. Instead of settling at the bottom, this residue floats within the glue, resembling an incomplete rubber sheet. When the temperature exceeds 180°C, this issue worsens, and the adhesive loses most of its cohesion, making it difficult to bond properly. The rubbery film can get tangled around the rotating rollers, leading to messy glue application and potential damage to the machine.Solution:
To avoid such problems, regular cleaning of the glue tank is essential, along with strict control over the heating temperature. When melting the adhesive, the temperature can be slightly higher initially, but once melted, it should be adjusted to 160–180°C. In colder weather, increase the temperature by about 10°C, and in warmer conditions, reduce it to normal levels. It's also important to verify the actual temperature of the adhesive, as relying solely on the thermometer may not be accurate. Additionally, it's crucial to understand the melting points of different components: the side rubber melts at 80–100°C, while the backing rubber melts at 160–180°C. After melting, the adhesive should be maintained between 100–180°C. Don’t assume a high melting point means a high working temperature. Understanding this distinction ensures proper troubleshooting and timely corrections. In production, failures caused by hot melt adhesives should not be underestimated. With proper handling and attention to detail, these issues can be avoided, leading to high-quality printed materials. (Editor: Pang Junqi)The above content is selected from Issue 11 of “Printing Technology · Digital Graphic Arts†in 2012. For more information, please visit the journal channel.
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