Flexographic print curling causes and solutions

In flexo printing, there are occasions where the paper is curled to the front, making the appearance of the product uneven, and affecting the customer's use in severe cases.

The reason for this phenomenon is that hot air helps drying during the flexo printing process. When printing is complete, the moisture content of the paper itself is less than the white material before printing. In addition to printed matter, UV coating is generally required. In this way, the front side of the printed matter is protected by a UV layer, which plays a role in the contact with the air, resulting in a small extension. On the other hand, because there is no protective layer on the reverse side, the paper is affected by the humidity of the air, and the paper is surely elongated. Moreover, the paper itself is subject to deformation due to different humidity. The reverse is larger than the front, and the product is curled upward. We might as well do a little experiment: Place the product of the flexo-printed UV coating on a cup with a certain water temperature, and steam upwards to make the paper face wet. We can see that the UV is facing the cup mouth and receives moisture, and the product is almost not deformed; but if the back is toward the cup, the product will be deformed immediately and curled toward the front.

After knowing the reason, we can take measures: on the back of the paper, apply a layer of material with a minimum amount, so that it acts as a protective layer in contact with the air. For example: Arabic gum 3% ~ 5%, this phenomenon is basically resolved.