Common faults and troubleshooting methods of coating machines

Insufficient curing
Reason analysis: Uneven mixing of two component adhesives; Incorrect mixing ratio of two component adhesive, such as insufficient - OH component; Insufficient curing time or low curing temperature; The adhesive has metamorphosed.
Solution: Improve the mixing uniformity of the two component adhesive, check if the relevant mixing settings are working properly, such as checking the static mixing tube. If any problems are found, they should be replaced immediately; Check the mixing ratio of the two component adhesive and adjust it to the correct mixing ratio according to the instructions; Properly extend the curing time and increase the curing temperature; If the adhesive has deteriorated, it should be replaced immediately.
Longitudinal or transverse wrinkles on the composite membrane
Reason analysis: The primary cause of lateral wrinkles is the mismatch in tension between the two composite substrates; Unstable winding pressure, imbalanced winding pressure on both sides of the composite substrate, severe and inconsistent lateral tightness, and uneven joints. The primary cause of longitudinal wrinkles is excessive retraction tension; The winding pressure on both sides of the composite substrate is unbalanced, and the joint is uneven.
Solution: Adjust the winding tension of the channel and the second unwinding unit; Replace with better quality composite substrates; Carefully bond new and old material strips; Adjust the tension of the winding and balance the winding pressure on both sides.
Core wrinkle (inner wrinkle)
Core wrinkling (inner wrinkling) refers to the wrinkling of the area near the core tube inside the composite material roll. In machine production, the probability and formation impact of core wrinkles are higher than in dry composite production. The primary cause of core wrinkling is the low initial adhesion of the adhesive, and other influencing factors are as follows.
(1) The diameter and mass of the core tube. Generally, the diameter of the core tube we use is 3 inches and 6 inches. In general, the larger the diameter of the core tube, the less likely it is to experience core wrinkling. In addition, non circular core tubes, uneven surface, or other quality defects can directly affect the number of core wrinkles.
(2) Material head and tape condition. In single station coating machine equipment, we often use manual operation to bond new and old material tapes, and whether the joints and tapes are flat will directly affect the occurrence of core wrinkling problems.
(3) The tension matching between the two composite substrates. If the tension matching between the two composite substrates is not good, bubbles, wrinkles, and other phenomena will occur, leading to core wrinkles.
(4) Large or small winding tension, taper, or roller pressure, etc. If the winding tension is too high, it will cause the part of the material near the core tube to be pulled out with horizontal wrinkles.
Solution: Replace the core tube with a better quality or suitable diameter; Properly adjust the winding tension, taper, and roller pressure.
White dot
Reason analysis: The amount of glue applied is too small or some of the glue applied is insufficient (such as in areas where there is a significant height difference between printed images and text); The surface of the coating roller is not clean or has dents or deformations; Impurities exist in the glue solution; The winding tension is too small (or the taper is too large) or the composite pressure is too small.
Solution: Properly add adhesive amount to improve the uniformity of adhesive application; Wipe the surface of the coating roller to ensure cleanliness; If the coating roller has deformed, it needs to be replaced; Remove impurities from the adhesive solution or replace the adhesive, and clean the mixing equipment; Adjust the winding tension and taper, and appropriately increase the composite pressure.
Bubble
Reason analysis: The two composite substrates have good barrier properties (such as PET/VMPET, PET/AL, etc.), resulting in the inability to discharge gases that occur during the curing reaction process normally; The relative humidity of the composite workshop is relatively high; The winding tension is too small (or the taper is too large) or the winding pressure is too small; The adhesive has metamorphosed.
Solution: The amount of adhesive applied should vary depending on the composite substrate, and it is also closely related to the type of adhesive, so it is important to choose a suitable adhesive; Increase the winding tension and pressure; Extension curing time; Reduce relative humidity (try to maintain it below 70%); Replace the adhesive.
Lack of peel strength
Reason analysis: The type of adhesive is not suitable, such as the use of lightweight solvent-free adhesive for cooking packaging; There is an issue with the mixing ratio of the two component adhesive, such as insufficient - OH component; The surface condition of the composite substrate is poor, such as lower surface tension than the application requirements; Excessive handling of ink or aluminum coating; Lack of glue application; Insufficient curing, etc.
Solution: Replace the adhesive type based on the type of composite product; Detect and adjust the mixing ratio of two component adhesive; Reprocess or replace the surface of the composite substrate with a new one; Add adhesive amount.
Friction coefficient addition
In general, the addition of friction coefficient is often present in PE composite structures.
Reason analysis: The curing temperature is too high; Excessive glue application; Excessive winding tension or pressure.
Solution: Properly reduce the curing temperature; Reduce the amount of glue applied; Adjust the winding tension (or taper) or winding pressure. If none of the above methods can effectively solve the problem, the content of the lubricant in the film can be appropriately added.
Uneven winding of the coating machine (curling)
Reason analysis: The overall adhesive amount is too large; The gap between the measuring roller and the handling steel roller is inconsistent at both ends, resulting in a significant difference in the amount of glue applied on both sides; The flatness of the composite substrate is poor or the tightness on both sides is inconsistent; The winding tension or pressure of the composite substrate is too low, or the winding pressure on both sides is unbalanced.
Solution: Reduce the amount of glue applied; Adjust the gap between the two rollers; Replace high-quality composite substrates; Adjust the winding tension (or taper) or winding pressure.
Ink whiteness decrease
The problem of decreased ink whiteness often occurs in the white ink area, especially after the aluminum coating composite, the ink whiteness will slightly decrease.
Reason analysis: The winding tension or pressure is too high, and the winding is too tight; A normal visual phenomenon caused by the small thickness of the adhesive film (only 1/2 to 1/3 of the thickness of ordinary dry composite film).
Solution: Properly reduce the winding tension or pressure; Add the appropriate amount of adhesive; Change the ink composition (such as improving the share of titanium dioxide), and improve the whiteness of the ink.
Ink and adhesive become miscible
Reason analysis: The adhesive and ink have a reaction; The residual solvent in the ink layer is too high.
Solution: Consult the ink supplier and select ink suitable for solvent free adhesives; Reduce the solvent residue in the printing process.
Excessive handling of ink or aluminum coating
Reason analysis: The primary reason for excessive ink handling is that the curing temperature is too high and the curing speed is too fast, causing rapid shrinkage and deformation of the adhesive film; The matching between ink and adhesive is not good, or the adhesion of ink on the surface of the composite substrate is low. The primary reason for excessive handling of the aluminum coating is that the bonding fastness of the aluminum coating on the surface of the composite substrate is low.
Solution: Properly reduce the curing temperature and slow down the curing speed; Replace with suitable ink or solvent to improve the adhesion of the ink on the surface of the composite substrate; Replace high-quality aluminum coating, such as using enhanced aluminum coating; Adjust the mixing ratio of the two component adhesive; Adhere to the cleanliness of the coating machine equipment.