As part of our commitment to quality and customer service, I have communicated with our technical team for a preliminary analysis. The bubble phenomenon is a rather complex issue that usually occurs during printing or post-processing stages, especially during the pressing process. Below, I will list the possible causes in more detail so that we can better determine the root cause in your specific situation.
1. Lamination process conditions
The bubble phenomenon typically occurs during the heat lamination process. The main influencing factors include:
Excessive lamination temperature
If the temperature of the heating roller is too high, the moisture inside the paper fibers or in the adhesive layer will rapidly convert into steam. The expanded gas will create pressure between the paper and the film, resulting in small bubbles or larger bulges. This is particularly common when using thicker paper or when the paper has a higher internal moisture content.
Insufficient lamination pressure
Even if the temperature is set correctly, if the pressure is too low, the film may not be firmly attached to the paper surface. When the adhesive cools, due to incomplete contact, air or steam will form bubbles.
Uneven adhesive coating
If the adhesive is applied unevenly on the film, certain areas may have insufficient adhesion, resulting in weak points that may cause bubble formation during or after lamination.
2. Paper moisture content and storage conditions
Paper is a hygroscopic material, meaning it absorbs or releases moisture depending on the environment it is in.
High moisture content
If the paper's moisture content exceeds the ideal range (typically 4% - 6%), the heat during the lamination process will cause the moisture to expand rapidly. This is particularly concerning as the paper may have been stored in a humid environment or the packaging has been opened for an extended period.
Water imbalance
Even if the paper has been properly controlled for moisture at the factory, sudden changes in temperature or humidity during storage or transportation may alter its moisture content. Subsequently, when subjected to lamination treatment, moisture will migrate, leading to the bubble phenomenon.
3. Ink drying and interaction with substrate
Unfully dried ink layer
If the ink layer is not fully dried before lamination, the remaining solvents or moisture in the ink layer will evaporate when heated, creating bubbles between the ink layer and the laminated film. This is more common when the ink layer is thick or when using unfully cured UV ink.
Ink compatibility with adhesive
In some cases, certain ink formulations may not be compatible chemically with the adhesive used for lamination. This incompatibility can lead to weakened adhesion and may cause bubble formation when heated.
4. Paper surface characteristics
Surface porosity and flatness
Paper with high porosity or uneven surface flatness may not absorb the adhesive evenly, reducing the bonding strength. While Longhong paper has ensured consistency in surface characteristics during production, changes during the printing or coating process may still affect the bonding performance.
Coating sensitivity
For coated paper, if the coating layer is not fully cured or has excessive water absorption, it may affect the adhesive bonding effect. Additionally, in a high-temperature environment, it may also cause bubble formation.
5. Post-lamination processing and environmental factors
Even after the lamination process is completed, environmental factors can still have an impact:
Rapid temperature change
If the laminated board is quickly moved from a warm lamination environment to a cooler area, the air or moisture within it will contract and expand over time, potentially causing the laminated layers to separate or form bubbles.
Insufficient cooling time
After lamination, adequate cooling and curing time is crucial. If the sheets are stacked or cut too early, the adhesive bonding may not have fully formed yet, making the material more prone to blistering.
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