In a recent blog, we looked at troubleshooting common hot melt adhesive and equipment problems, such as charring and stringing. Now let’s take a closer look at the issue of pop-opens and Bostik’s solution.
What are Pop-Opens?
Pop-opens occur when a case or carton is not properly sealed after compression, and the box flaps quite literally “pop open” after leaving the compression chamber.
Due to a combination of increasing production line speeds, low machine compression and the use of higher-recyclable content board stocks, the frequency of pop-opens is increasing in the market. This can significantly slow down productivity and add additional, unexpected costs.
What Specifically Causes Pop-Opens After Compression?
There are several causes of pop-opens:
- Adhesive setting too fast and doesn’t wet out onto the secondary flap: This can be caused by a lower than recommended application temperature or too long of a process open time. In this case, all of the adhesive remains on the primary flap, and there is no adhesive residue on the secondary flap.
- Adhesive setting too slow and cohesively fails: This can occur when the line is going too fast and not enough time is allowed for compression, or the adhesive is applied too hot. In this case, there is adhesive residue on both the primary and secondary flaps and possibly some strings between the flaps.
- Flaps shifting under compression or inadequate compression causing the adhesive to be either sheared or not brought in contact with the secondary flap: The mode of failure will be similar to a slow-setting adhesive.
- Adhesive not penetrating the coating resulting in no fiber tear: In this case, the cooled adhesive can be cleanly back peeled from the primary flap.
How Can the Likelihood of Pop-Opens be Reduced?
Bostik recommends the following methods to reduce the likelihood of pop-opens:
- Increase air pressure and/or adhesive temperatureif the adhesive is setting too slow.
- Lower temperature and/or apply less glue if the adhesive is setting too fast.
- Adjust compression to maintain firm, even pressure
- Apply adhesive hotter with longer compression to try to penetrate coated substrates or change adhesive if compression time cannot be extended.
A Smart Adhesive Solution
Bostik worked directly with a customer that was experiencing an issue with pop-opens. This customer needed to find a solution that offered the green strength required to resist pop-opens in short open time and with demanding applications.
After identifying the customer’s current adhesive shortcomings, Bostik developed a robust solution with Thermogrip® H9529B.
H9529B is a premium product that is one of the fastest setting metallocene-based adhesives in the market. Its low viscosity allows for high machine throughput and excellent wet out on corrugate and highly recycled content board stock.
This combination provides excellent green strength and good fiber tear due to the adhesive’s fast build of internal cohesive strength. As a result, H9529B is able to quickly lock in strong mechanical bonds even in low compression applications and avoid pop-opens.
For more information on Bostik’s ability to reduce pop-opens in short open-time applications, call 800-7-BOSTIK.