Causes and Countermeasures of paper "curl"
paper curl refers to the folding of paper in the direction perpendicular to the paper feeding direction. Look along the paper direction, and both sides of the paper or finished product curl up. Due to the faster and faster running speed of modern packaging machinery, the requirements for the production of tensile testing machines that need to use constant speed motion are also higher and higher. Once the printed products are curled, it will bring some trouble to the packaging assembly line. Therefore, both cigarette factories and breweries have strict requirements on the flatness of printing products
there are two main reasons for the curling of paper, one is caused by the difference in the tension between the front and back sides of thin paper, and the other is caused by the change in humidity on the surface of paper. No matter how thin the thin paper is, it also has a certain thickness. If one side (or both sides) of the paper is damped and the tension between the front and back sides is inconsistent, and the printing runs on the paper, "Wang Xianhong added, the stiffness of the fiber direction is generally better than that of the horizontal direction, then under the joint action of the two, the paper will inevitably curl. Here is an example. In the long-term shutdown state or before starting up every day, we will find that the paper on the gravure machine presents a bow bending state, which is caused by the moisture absorption of the paper
the printed product is flat, but after the printed product is placed in the packaging workshop of the tobacco factory for a period of time, the product curls. This is because the relative humidity of the cigarette factory's crimping and packaging workshop is much higher than that of our printing workshop. Most printing products have been covered with ink and varnish on the front, so it is difficult for moisture to enter the paper from the front. Therefore, in this environment, there is only one option, that is, the back of the product is hygroscopic, causing curling. If such a problem is encountered, cigarette factories will always complain that the cigarette bag cover is curly, and the cigarette machine cannot produce normally, which has seriously affected the output. At this time, you can try to seal and pack with plastic bags, and flatten the box cover. A total of 5415 meters of DN500 welded pipes are installed in the project, trying to flatten the box cover, but the effect is not obvious, because the most important point is that the temperature and humidity conditions in the cigarette factory's crimping workshop are too different from those in the printing workshop
for anti curl problem, two methods are recommended. One is to add anti curl additives to printing inks (referring to large field base ink and glazing oil). You can consult the ink manufacturer; The second is to print and paint on the back of the paper. The fundamental purpose of back coating is to offset the tension difference between the front and back sides of the paper and prevent further moisture absorption on the back of the paper, so that the finished product becomes flat. Just want to carry out back coating in the gravure press, "the electric vehicle expert added:" the performance of the materials used around the battery requires a simple transformation of the equipment, that is, adding a paper transfer roller in the printing unit, changing the paper transfer route of the paper, and changing the paper to back printing