Analysis of Difficulties in Ink Control of Whiteboard Paper Printing

My company (affiliated subsidiary of Jiangsu Yanghe Group) is mainly responsible for printing wine packaging boxes and packing boxes. Its characteristics are: white paper printing, ink thick, large-area multi-color on the ground. How to control the ink consistency of each batch of products is one of the major difficulties.

I. Ink problem

Ink refers to various factors such as printing ink, printing pressure, amount of fountain solution, ink viscosity, etc. When the ink layer is not thick in real time, it usually only pays attention to increase the ink supply. Although this can temporarily solve the problem, it will affect the entire Printability. Combining with the characteristics of our printing products, we have made some attempts in the following aspects, and the effect is also acceptable. First of all, strictly check the machine plate material, can not reproduce the 5% small dot plate can not be on the machine; strictly control the printing time and development time. The printing of the PS plate at night must be properly reduced exposure time, due to high voltage at night, strong light; as much as possible so that each batch of the same product drying PS version of the appearance of the same, and make a detailed record to provide assurance for the post-process .

Second, printing pressure, lining

Because my company uses the white paper produced by Hangzhou Yongtai Group, the texture is relatively loose, and the printed material has a large area in many fields. Therefore, the soft packing is used. The pressure of the printing plate and the rubber roller is adjusted to 0.25mm. The rubber roller and the imprint Roller pressure is adjusted to 0.35mm. Strictly control the amount of fountain solution (the pH is maintained at about 5). Previously, the amount of fountain solution used in the first color group affected the inking effect of the second color group. Why did this happen? Because more than 80% of the substrates are spot color printing, basically the latter three colors are superimposed together (ie, magenta, red, yellow), and the main color is magenta. The thickness of this hue ink layer directly affects the appearance of the product, so it is controlled. Focus on the second color group. In the actual production process, it was found that the first color group (black) has a great influence on the second group. Its main performance is that the first group of ink ink balance control is not good. When the amount of the fountain solution is too large, a very hidden problem occurs. The ink in the second group was not true, and the printed products were dark, hairpins, and blots floating on the surface of the paper, and the back of the paper was dirty. It was thought that the second group was faulty. Changing the printing plate, adjusting the pressure, changing the lining, etc. did not help. In fact, it is mainly due to the imbalance of the ink of the first color group. Because the first color group is mostly texts and lines, in order not to paste version or stickiness, the first color group is often large and large, so that the paper is imprinted. The surface absorbs excess water from the blanket. When the second color group is imprinted, the paper cannot properly absorb the ink from the blanket, resulting in the printing product being not bright, unevenly laminated, non-layered, and sticky behind. dirty. As long as the first color group water control to the minimum, the failure will be solved. The speed of printing will also make the ink color different. In the three-shift operation system, we set a speed of 6000 sheets/hour, which can promote ink consistency to a certain extent.

Large batches of products each color group must change the version, the new version of the ink performance is good, print plain clothes, with the increase in the number of prints, the printing plate gradually wear, ink absorption worse, ink uneven. In order to control this phenomenon, it is stipulated that 60,000 copies of each plate must be replaced with new ones.

Third, regular shutdown, start-up caused by ink error

After printing and printing the first few dozen sheets of printing, the ink is always heavy. The main reason is that the use of small prints on the boot printing, the initial printing of dozens of ink and ink caused by imbalance. We summarize the shutdown for two reasons: First, the printing plate crust, with paper hair, need to stop the exclusion. Secondly, the printed sheets were wiped dirty and shut down. In the first case, the number of shutdowns accounts for a large proportion. The solution we have is: if there are too many inks, the ink should be replaced. When the number of inks is small, the ink fountain screws can be adjusted to increase the number of teeth and increase the amount of ink transferred. The ink sticks in the ink fountain and requires more ink to be kept regularly in the ink fountain. Paper and paste and other debris stuck to the plate, resulting in more dirt on the print, can be properly added in the ink detackifier or ink additives to reduce the viscosity of the ink. It's because of our four-color machine
(Pz4800-01B type) The roller diameter is small. The paper is transferred to the small transfer drum via the impression cylinder. Because the whiteboard paper has a certain degree of stiffness and the inertia during operation, the trailing printing surface hits the small biography at the moment of peeling of the printed sheet. Rolled paper causes dirt. Clean up the sticky ink on the surface of the small transfer roller and stick it with dirty paper. The situation has improved but it cannot be eradicated. Later, through experiments, during the cutting, the direction of the printed fiber was kept consistent with the axial direction of the roller, so that the paper was closely attached to the impression cylinder, the stiffness was relatively reduced, and the impact of the printed sheet on the surface of the small transfer roller was reduced. The dirt disappeared, reducing the number of shutdowns and giving the ink a better control.

These are some of our attempts to print bulk packaging products, peers may wish to try.

(author/Wang Xiangdong)