Troubleshooting Hot Melt Pop Opens

Rows of brightly colored packages line the shelves of markets around the world. When consumers are browsing the shelves for any product, the appearance is the first sign of quality.  If the label is askew or the box flap is not tightly sealed, the consumer will pass. Hot melt adhesive pop opens – a common packaging challenge – occur when a case or carton is not properly sealed after compression. In some cases, hot melt pop opens can occur on the production line.  They can also occur during transit and delivery to retailers.  In the highly competitive food and beverage market, pop opens can impact production efficiency or brand reputation.

Working With Hot Melt Adhesives to Minimize Pop Opens in Consumer Packaging

During the packaging process, pop opens can occur for many reasons. Application settings, processing conditions, and ambient temperature can cause bond failure. Poor compression, higher line speeds, and the trend towards using recycled board stocks can increase the frequency of pop opens. To resolve and eventually prevent pop opens, it is essential to first understand the differences between various types of pop opens. Identifying the signs of a specific pop open aids in the resolution. Our short videos demonstrate the different kinds of pop opens.

Addressing Hot Melt Adhesive Preset Issues

Hot melt preset occurs when the adhesive bead sets before the materials are compressed to create the bond in case and carton sealing. This production line issue can result in a packaging pop open. There are several causes for pre-set issues:

• Incorrect adhesive application temperature
• Unsuitable amount of adhesive applied to the substrate
• Improper substrate temperature causing the adhesive to set up quickly

In many cases, there are simple fixes to correct these issues and keep the packaging line operating efficiently. The first step is to check the application temperature. All adhesives are designed with specific operating temperature ranges. If the temperature is set at the correct range, the next option is to check the tank pressure. The tank pressure can impact the amount of adhesive applied to the substrate. If the tank pressure is too low, there may not be enough force to fire the bead onto the package.

If both the adhesive temperature and tank pressure are within the recommended operating ranges, another option is to preheat or condition the substrate prior to applying the adhesive. If none of these options resolve the preset issues, contact Henkel to assist with troubleshooting the issue on your packaging line.

Resolving Poor Compression Issues with Hot Melt Adhesive

Poor compression can be another cause of hot melt adhesive pop opens. There can often be issues with either the pressure applied to seal two substrates together or the quantity and manner of the adhesive application. Some common indications of poor compression include:

• Uneven bead width
• Inconsistent fiber tear
• Stringing between substrates
• Inconsistent adhesive transfer to the second substrate

Resolving poor compression issues is more challenging because there are more areas to investigate. The first area to investigate the adhesive application. If the adhesive application is inconsistent – either too much or too little adhesive – it can impact the compression. Incorrect amounts of adhesive could be indicative of incorrect application temperature, a clogged nozzle, the wrong nozzle size, or tank pressure. All areas should be checked and corrected if any are found to be outside recommended operating parameters.

Adhesive is not the only area to investigate. Once these areas are checked, it is possible there is an issue with the compression pressure, substrate, or compression time. Operators should determine if something has changed with the type of substrate which could impact the bond. It is possible the substrate could be shifting, or the pressure setting is incorrect. In both cases, consider adjusting the machine settings. If none of these options resolve the poor compression issues, contact Henkel to assist with troubleshooting the issue on your packaging line.

Preventing Hot Melt Adhesive Pop Opens from Cold Failure

Hot melt adhesives can react differently when ambient temperatures are cooler. Whether because the package needs to be refrigerated or the production floor is cold, these temperature variations can cause pop opens from cold crack, also known as cold failure. Colder temperatures can rapidly decrease the adhesive set time and create issues with the package seal. Some common indicators of cold failure include:

• Presence of adhesive on both sides of the substrate
• Compressed adhesive bead
• Atypical/slight fiber tear
• Presence of fracture lines in the adhesive

Pop opens from cold failure can occur when heavy packages are moved around or dropped, especially if the adhesive is not formulated for cold resistance. The primary indicator is fracture lines along the adhesive. Resolving cold failure is entirely about the adhesive chemistry. If the package is expected to be in cold storage during shipment and sale, it is best to use a freezer-grade adhesive. These adhesives, like TECHNOMELT^®, are designed to perform well in environments 4^oC (40^oF) and colder. These cold temperature adhesives are more flexible and can withstand the extreme temperatures. Contact Henkel to learn more about adhesives designed for cold temperatures and to troubleshoot cold failure issues on your packaging line.

Avoiding Hot Melt Adhesive Pop Opens from Heat Failure

Extreme temperatures can influence the adhesive bond. Pop opens can occur when the ambient temperature in a facility or the contents of the package are too warm. Higher temperatures can prolong the adhesive set time and create issues with the substrate bond. Some common indicators of heat failure include:

• Inconsistent adhesive bead compression
• Presence of adhesive on both sides of the substrate
• Appearance of bubbles in the adhesive
• Adhesive stringing between the two substrates
• Present of an oily residue on the substrate surfaces

Resolving heat failure can achieve with two methods. The first is relatively simple – apply more adhesive. The increased amount of adhesive takes longer to cool and is not impacted by the elevated ambient temperatures. The second option is to use an adhesive with higher heat resistance. Some adhesive chemistries are naturally more resistant to high heat environments and packaging. If neither of these options resolve the heat failure issues, contact Henkel to assist with troubleshooting the issue on your packaging line.

Hot Melt Adhesive Sealing Best Practices

Henkel’s technical experts can help identify and resolve hot melt pop opens. These are the top questions to resolve hot melt pop opens.

• Timing: When do the pop opens occur?
• Location: Is there glue on both sides of the case or carton?
• Compression: Is the bond rounded or fully flattened?
• Fiber Tear: Is there partial or missing fiber tear?
• Ambient Temperature: Does the package experience high heat or freezing temperatures?
• Production: Has anything recently changed with your process, equipment, or packaging?

Identifying your pop open is the first step to eliminating adhesive bond failure and reducing downtime. Henkel offers its new Digital Training Platform to help your production line quickly address packaging issues via general adhesive knowledge as well as standardized best practices and troubleshooting.