In flexographic printing, sometimes the paper is curled toward the front, which makes the appearance of the product uneven and affects the customer's use in severe cases.
The reason for this phenomenon is that hot air is helping to dry during the flexo printing process. When the printing is completed, the moisture content of the paper itself is less than the white material before printing. Coupled with the printed matter, generally UV glazing. In this way, the front of the printed matter is protected by a UV layer, which plays a role of separation during contact with air, and the extension may be very small. Since the reverse side does not have a protective layer, the paper must be extended due to the influence of air humidity, and the deformation of the paper itself due to different humidity is that the reverse side is larger than the front side, causing the product to curl upwards. We might as well do a small experiment: put the flexo-printed UV-glazed product on a cup with a certain water temperature, and the water vapor will make the paper surface damp. We can see that the UV is facing the cup mouth and accepts moisture, and the product has almost no deformation; but if the back is facing the cup mouth, the product immediately deforms and curls toward the front.
Countermeasure: Apply a minimum amount of material on the back of the paper to make it act as a protective layer in contact with air. For example: gum arabic 3% to 5%, this phenomenon is basically solved.
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