Common faults and troubleshooting of coating machine

In recent years, the coating machine process has been gradually popularized in the production process of flexible packaging. Although the process is relatively simple and stable, some common problems are still highlighted in the application process. This paper summarizes the common faults of several types of machines, and gives the causes and solutions for the reference of the industry.
Insufficient curing
Cause analysis: the two-component adhesive is not evenly mixed; The mixing ratio of two-component adhesive is incorrect, for example, the - OH component is too small; The curing time is not good or the curing temperature is low; The adhesive has metamorphosed.
Solution: improve the mixing uniformity of two-component adhesive, check whether the relevant mixing settings work normally, such as check the static mixing pipe, and replace it immediately if any problem is found; Check the mixing ratio of two-component adhesive and adjust it to the correct mixing ratio according to the instructions; Properly extend the curing time and improve the curing temperature; If the adhesive has degenerated, it should be replaced immediately.
Longitudinal or transverse wrinkles on composite membrane
Cause analysis: The primary reason for the occurrence of transverse wrinkles is the tension mismatch between the two composite substrates; The winding pressure is unstable, the winding pressure on both sides of the composite substrate is unbalanced, the lateral tightness of itself is severely inconsistent, and the joint is not flat. The main reason for the onset of longitudinal wrinkles is that the winding tension is too large; The winding pressure on both sides of the composite substrate is not balanced, and the joint is not flat.
Solution: adjust the winding tension of the channel and the second unwinding unit; Replace the composite substrate with better quality; Carefully bond the new and old material belt; Adjust the winding tension and balance the winding pressure on both sides.
Core wrinkle (inner wrinkle)
Core wrinkling (inner wrinkling) refers to wrinkling in the area near the core tube inside the composite roll. In machine production, the occurrence probability and formation impact of core wrinkles are greater than that of dry compound production. The primary cause of core wrinkle attack is the low initial adhesion of adhesive, and other influencing factors are as follows.
(1) Diameter and quality of core tube. Generally, the diameter of core tube we use is 3 inches and 6 inches. Generally, the larger the diameter of core tube, the less the probability of core wrinkle. In addition, the core tube is not round, the surface is not flat or there are other quality defects that will also directly affect the number of core wrinkles.
(2) Material head and tape condition. In single-station coater 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 wrinkle.
(3) Tension matching of two composite substrates. If the tension of the two composite substrates is not well matched, bubbles, wrinkles and other phenomena will occur, and then core wrinkles will occur.
(4) , winding tension, taper or pressure of pressure roller, etc. If the winding tension is too large, the part of the coil close to the core tube will be pulled out of the transverse fold.
Solution: replace the core tube with better quality or suitable diameter; Properly adjust the winding tension, taper and pressure of pressure roller.
Small coater. jpg
White spot
Cause analysis: the gluing amount is too small or part of the gluing amount is insufficient (for example, the height difference between the printed image and text is large); The surface of the coating roller is not clean or there are pits and deformations; There are impurities 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 the amount of glue to improve the uniformity of glue application; Wipe the coating roller surface to ensure cleanliness; If the coating roller is deformed, it needs to be replaced; Remove the impurities in the glue solution or replace the adhesive, and clean the glue mixing appliance; Adjust the winding tension and taper, and properly increase the composite pressure.
Bubble
Cause analysis: the barrier properties of the two composite substrates are good (such as PET/VMPET, PET/AL, etc.), resulting in the abnormal discharge of gases occurring during the curing reaction process; The relative humidity of the composite workshop is too 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 glue applied should be different for different composite substrates. In addition, it is also closely related to the type of adhesive, so it is necessary to select the appropriate adhesive; Increase the winding tension and winding pressure; Extended curing time; Reduce the relative humidity (try to keep it below 70%); Replace the adhesive.
Lack of peel strength
Cause analysis: the type of adhesive is not suitable, for example, solvent free adhesive for light packaging is selected for cooking packaging; There is a problem with the mixing ratio of two-component adhesive, such as less - OH component; The surface condition of the composite substrate is poor, such as the surface tension is lower than the application requirements; Excessive handling of ink or aluminum coating; Lack of glue application; Insufficient curing, etc.
Solution: replace the adhesive type according to the type of composite product; Test and adjust the mixing ratio of two-component adhesive; Reprocess the surface of the composite substrate or replace it with a new composite substrate; Add glue amount.
Friction coefficient addition
In general, the addition of friction coefficient often appears in PE composite structure.
Cause analysis: curing temperature is too high; Too much glue; Excessive winding tension or winding pressure.
Solution: properly reduce the curing temperature; Reduce the amount of glue; Adjust the winding tension (or taper) or winding pressure. If none of the above methods can effectively solve the problem, the content of lubricant in the film can be properly added.
Uneven winding of coating machine (roll shifting)
Cause analysis: the overall gluing amount is too large; The gap between the metering roll and the handling steel roll is inconsistent at both ends, resulting in a large difference in the amount of glue on both sides; The flatness of composite substrate is poor or the tightness of both sides is inconsistent; The winding tension or winding pressure of the composite substrate is too small, or the winding pressure on both sides is unbalanced.
Solution: reduce the amount of glue; Adjust the gap between the two rollers; Replace the composite substrate with good quality; Adjust the winding tension (or taper) or winding pressure.
Ink whiteness decreases
The problem of ink whiteness decline often occurs in the white ink area, especially after the aluminized film is compounded, the ink whiteness will decline slightly.
Cause analysis: the winding tension or winding pressure is too high, and the winding is too tight; Normal visual phenomenon due to small film thickness (only 1/2~1/3 of the thickness of ordinary dry composite film).
Solution: properly reduce the winding tension or winding pressure; Add proper amount of glue; Change the composition of the ink (such as increasing the proportion of titanium dioxide, etc.) to improve the whiteness of the ink.
Ink and adhesive are mixed
Cause analysis: adhesive and ink react; The solvent residue in the ink layer is too high.
Solution: consult the ink supplier and select the ink suitable for solvent-free adhesive; Reduce the solvent residue in the printing process.
Excessive handling of ink or aluminum coating
Cause analysis: The main reason for excessive handling of ink is that the curing temperature is too high and the curing speed is too fast, resulting in sharp shrinkage and deformation of the adhesive film; The matching of ink and adhesive is not good, or the adhesion of ink on the surface of composite substrate is low. The main reason for excessive handling of aluminum coating is that the bonding fastness of aluminum coating on the surface of composite substrate is low.
Solution: properly reduce the curing temperature and slow down the curing speed; Replace the appropriate ink or solvent to improve the adhesion of the ink on the surface of the composite substrate; Replace the aluminum coating with better quality, such as the use of enhanced aluminum coating; Adjust the mixing ratio of two-component adhesive; Adhere to the cleanness of coating machine equipment.