Printing PP film coating woven fabric technology and common troubleshooting

With the continuous development of China's packaging industry, many low-end packaging products are moving toward high-grade products. A lot of cloth products were changed to woven packaging, such as: seed packaging, rice packaging, fertilizers and other packaging. The woven cloth packaging surface printing, most of them are now changed to print film, so that the entire packaging image is more dazzling, improve the grade. At the same time, many failures in the coating film are also difficult to eliminate, so that the product quality does not meet the requirements. The following analysis and elimination of the common failures of the printing process and coating process.
First, the printing process:
1. The gravure plastic printing machine is required to gravure plate-making steel roll and plate roller to be printed (printed in) into a coil by a printing machine, and then coated with a film-coated woven fabric.
2, printing ink can be divided into two kinds: one is a special compound ink in India and then coated; the other is printed on the surface, such as: table printing pearl film coating compound after printing, this table printing ink easy Bad fastness occurs, some colors are easy to fade, discoloration, and difficult to overlap with multiple inks. After printing the finished product in the printing, the aluminum is processed again. For example, a clear and colorful pattern is obtained after printing aluminum in a transparent series of printing inks, and then a film is coated.
3, different types of ink used, the diluent used is also different. The compound ink thinners are benzenes and lipids; the surface printing ink diluents are benzenes and alcohols. The two diluents cannot be mixed.
Second, coating process:
After the coating machine is mixed and melted and plasticized uniformly, the temperature of the coating machine is generally around 220°C. The temperature is too high and will affect the physical properties. If the temperature is too low, it will also affect the peeling strength. Therefore, it should be based on the equipment for personal use. The optimum temperature is then applied to the woven cloth substrate through a double die, and then rapidly cooled by a cooling steel roll to form a composite film on the surface of the woven cloth to achieve a desired effect.
Coating material selection: one is high density polyethylene (coating grade) one is low density polyethylene (coating grade) and a special PP coating material is used in combination. At present, the coating material used is Ethylene seven A, ethylene seven B more extensive. The application of coating material is preferably controlled at about 15 grams per square meter. The ratio of using polyethylene and PP special materials is generally 4:6. The increase of PP material will make the coating film more brittle.
Third, common faults and exclusion
A. There is no peeling strength after the coating is applied. After the coated laminated product is finished, the product has little strength and the delamination is separated.
Causes and exclusions:
1. Check whether the thin film corona treatment at the sub-level meets the requirements and determine whether the ink reaches the peel strength. In general, printing inks use composite inks, but some composite inks do not achieve peel strength. At present, many ink manufacturers specialize in printing BOPP coated woven fabric inks to solve this problem, which will increase the peel strength.
2. The delamination is to separate from the coating material and the woven fabric. The corona treatment of the woven fabric and the matching ratio of the coating material should be inspected to find out the reason for elimination.
B. Poor peel strength After coating, the peel strength is not satisfactory and the peel strength is uneven.
Causes and exclusions:
1, the composite pressure of a small coating melt and the woven cloth substrate is not closely fit, so that the peel strength decreased. The pressure of the pressure roller needs to be increased so that the gap between the coating material and the woven cloth is closely adhered and the peel strength is improved.
2. Check whether the coating of the coating material is too thin or uneven to cause the peel strength to decrease; the thickness of the coating layer should be increased.
3. The extrusion compounding temperature is slightly lower, and the resin is poorly plasticized. The molten resin flowing out from the die mouth cannot be well compounded with the braided substrate and will cause the peeling strength to decrease.
4. The unqualified coating material quality or the unreasonable proportioning may also cause the peeling strength to decrease. The temperature of each part of the extruder should be adjusted to make the resin plasticized and increase the peeling strength.
C. Non-uniformity of the coating layer after coating The coating layer is thick at some places after the coating is applied. In some places, the coating layer is thin, the packaging is uneven, and the peeling strength is uneven.
Causes and Remedy 1. The temperature of the extruder is not controlled properly, and the thickness of the coating layer is not even due to the uneven temperature of the die. The section temperature of the extruder should be adjusted in a timely manner. The temperature of the die head ensures that the temperature of each part of the extruder is uniform and constant, so that the coating material can be evenly coated.
2. The gap between the die mouth is uneven or foreign matter is locally attached to the die, so that the extrusion coating amount of this part is reduced compared to other parts, and the coating layer is thin. The die gap should be adjusted in a timely manner to eliminate the local adhesion of the die to keep it clean, so that the coating amount is consistent with other parts.
3, composite pressure roller uneven or rubber roller surface aging, hardness is not uniform, the surface is uneven, there are pits, scratches and other phenomena, resulting in unable to maintain a constant value, so that the coating material can not be uniformly coated. To adjust the composite pressure consistent. Determine that the rubber roller can not be replaced in time, to ensure uniform surface hardness of the roller.
D, wrinkles caused by the coating film causes and exclusion methods:
1. When the substrate position is skewed, it will cause wrinkles when coating and compounding. With the accumulation of skew, the degree of wrinkles generated will increase relatively. It is necessary to adjust the position of each substrate on one line, and it must not be deflected to avoid wrinkling.
2. The problem of wrinkling and poor peeling strength can also be caused by severe moisture in the printed substrate. The printed substrate should be properly stored to prevent moisture.
3, improper tension setting and control, so that the tension of each part does not match the mismatch, causing wrinkles phenomenon. The tension setting and control of each part should be consistent and synchronized. Make the unwinding and rewinding adapt and match each other.