Treatment of paper curl in printing

The "curled" paper refers to the wrinkles that occur in the paper perpendicular to the paper feed direction. Looking in the direction of paper feeding, both sides of the paper or finished product curl up. As the speed of modern packaging machinery is getting faster and faster, the demand for products is bound to become higher and higher. Once a printed product is curled, it will cause certain troubles for the packaging assembly line operations. Therefore, whether it is a cigarette factory or a brewer, the flatness requirements of the printed products are very strict.

Analysis of the causes of paper curling, there are two main aspects, one is due to the difference between the positive and negative tension of the thin paper caused, and second, because of the paper surface humidity changes. Thin and thin paper also has a certain thickness. If the single side (or both sides) of the paper is damp, the tension on the front side and the back side is inconsistent, and the stiffness of the printed paper running fiber is generally better than that of the transverse direction. Paper will inevitably curl. Here is an example. In the case of a long-term shutdown or before starting the machine every day, we will find that the paper on the gravure printer is bowed, which is caused by the hygroscopicity of the paper.

The printed product was flat, but the product was curled after the printed product was placed in the cigarette factory packaging plant for a period of time. This is because the relative humidity of cigarette factory packaging and packaging plant is much higher than our printing plant. The vast majority of printed products, because the front surface is covered with ink and varnish, and moisture is difficult to enter the paper from the front, so there is only one choice in this environment, that is, the back of the product absorbs moisture, causing curling. If such a problem is encountered, the cigarette factory will always complain about the curling of the box and the cigarette maker will not be able to produce normally, which will seriously affect the output. At this time, we can try to use a plastic bag to seal the package, and flatten the box, try to level the box, but the effect is not obvious, because the most important point is the temperature and humidity conditions and the printing shop The temperature and humidity conditions are too different.

For the anti-curling problem, two methods are recommended. One is to add anti-curling additives to the printing ink (referring to the solid ground ink and coating oil), and to consult the ink manufacturer; the second is to print the back coating on the back of the paper. The fundamental purpose of the back coating is to counteract the difference in tension between the front and back sides of the paper and to prevent further moisture absorption on the back side of the paper so that the finished product becomes flat. Just want to carry out the back coating in the gravure printing machine, need to carry on the simple transformation to the apparatus, namely increase the transfer roller in the printing unit, change the paper's transmission route, change the paper to the reverse printing.