During the production and use processes, it is sometimes found that the hot-melt adhesive is clearly white but turns yellow after melting. Is it caused by the hot-melt adhesive itself or are there some problems during the melting process? Comprehensive analysis shows that there are usually four possible reasons for white hot-melt adhesive turning yellow after heating.
1. Poor storage conditions of the hot-melt adhesive lead to deteriorated glue.
Hot-melt adhesive is affected by seasonal changes and is not suitable for long-term storage and use. Although the shelf life of hot-melt adhesive is generally about 12 months, we generally recommend that customers follow the principle of "first in, first out" and use it as soon as possible. Because hot-melt adhesive will inevitably be affected by the external environment during storage. If the time is short, the impact will be relatively small. However, in the case of a long time and harsh environment, it may affect the product performance.
2. Heating the hot-melt adhesive for a long time leads to the destruction of the glue performance.
In the case of a small amount of glue used, if there is unused glue left, users usually keep the glue for the next use, but this way of using the glue is wrong! Repeated heating of hot-melt adhesive will accelerate the aging of the glue and affect the bonding performance. If the glue in the boiler cannot be used up after repeated use, it is recommended to clean it up and clean the melting boiler so that the newly added hot-melt adhesive will not be affected by the deteriorated hot-melt adhesive.
3. There are too many impurities in the melted glue in the boiler and they are mixed into the glue.
After being heated multiple times at a high temperature above 100 degrees Celsius, the remaining glue will gradually turn into black carbides. If these carbides are not cleaned up in time, they will remain as impurities in the boiler and be mixed with the newly heated hot-melt adhesive each time. Once these black impurities are mixed in, they will cause color changes, such as yellow or gray.
4. Mixing other substances during the melting process leads to color changes.
Do not mix other chemical substances during the use of hot-melt adhesive. Sometimes the production environment is complex and other chemical substances may float in the air. After opening the boiler and putting in the hot-melt adhesive, the floating substances in the air will also enter the boiler. The hot-melt adhesive melts and mixes with these foreign substances. When used together, it may cause physical changes in the glue, including color changes. In addition, the components in the formulations of hot-melt adhesives from different manufacturers can also vary. If you have just changed to use hot-melt adhesive of other brands, it is recommended to clean the boiler before melting the glue to avoid reactions of different performances under the heating state.
It is abnormal for the used hot-melt adhesive to suddenly turn yellow. Carefully check every detail during use to avoid wasting the melted hot-melt adhesive.