The Secret to Color Difference Control in Paper Bag Printing (Part 2)

In the previous issue, we talked about the first phenomenon (the color of the same batch of products is consistent, but there is a color difference from the sample). Next, let's take a look at the second phenomenon:



2、 The second phenomenon (there is color difference among the same batch of colors, some are consistent with the sample, but some are inconsistent with the sample)



1. Human factors:



Paper bag printing believes that the color of the first few sheets is accurate. In the case where the ink is not yet balanced, it starts to run all the way. During the printing process, the amount of water and ink is constantly adjusted while running, which inevitably causes color differences in the same batch of printed products. This is closely related to the skill level, experience, and personality of the printer, and is caused by insufficient ability to produce color differences in the same batch of products.



2. Moisturizing solution:



Offset printing utilizes the principle of oil-water repulsion for printing. This water refers to the moisturizing solution. Its size directly affects the color of the ink layer. The color of the ink layer is lighter when the water is larger, and darker when the water is smaller. The larger the water, the more severe the emulsification of ink. Emulsified ink has no luster and the color is light. Emulsified ink not only causes severe color difference in printed products, but also produces quality problems such as sticking, non drying, and weak imprints. So in printing, it is necessary to strictly control the size of the wetting liquid on the printing plate and the layout, and do a good job of ink balance. It is required that the smaller the water, the better without getting dirty.



3. Printing speed:



The speed of the vehicle during printing can affect the color depth of the printed material. This is because the speed of the vehicle can affect the balance of the ink. The moisture content on express printing plates and slow printing plates varies. The moisture evaporation of fast printing plates is small, while the moisture evaporation of slow printing plates is large. Due to the change in moisture content, ink imbalance will inevitably cause color changes in the ink. So when printing, it is necessary to pay attention to a constant speed and never drive too fast and too slow at the same time, as this will inevitably result in color differences in the printed products. At the same time, it is necessary to adjust to the most stable vehicle speed based on the condition of the machine. For example, some imported offset printing machines indicate a maximum speed of 16000 sheets per hour, while domestic machines have a maximum speed of 8000 sheets per hour, but these speeds are not stable. Generally speaking, whether it is an imported or domestically produced machine, a stable vehicle speed of 70% of the maximum speed is most ideal, that is, around 11000 frames per hour for imported machines and around 5600 frames per hour for domestically produced machines. Such vehicle speeds can easily control ink balance and reduce color difference.



4. Poor ink roller:



The quality of the rubber roller plays a crucial role in achieving uniform ink color in offset printing technology. Generally, there are three types of rubber rollers: ink roller, ink roller, and ink roller, which have a significant impact on the color intensity of ink. The elasticity, viscosity, roundness, hardness, and surface smoothness of the ink roller largely determine the ink color quality of the printed product. If the elasticity of the ink roller is poor, the viscosity is insufficient, the roller body is eccentric, the colloid is hard, and the colloid is aged, it is easy to cause uneven or unstable ink during the printing process, resulting in inconsistent ink color on the printed sheet. So when printing, it is necessary to ensure the quality of the rubber rollers in order to ensure that the ink applied to the printing plate is basically consistent in each printing cycle. So in daily work, it is necessary to clean the rubber roller to remove the paper dust and impurities stuck on it, ensuring the uniform transfer of ink. At the same time, the contact pressure between the ink rollers and between the ink rollers and the printing plate should also be adjusted, otherwise it will also cause uneven ink transfer and serious color difference. （yinshua96.cn)



5. Equipment maintenance:



Maintaining good performance of the machine is a reliable guarantee for improving the quality of printing ink. If the machine is unstable, such as inconsistent pressure, unstable paper feeding, frequent occurrence of empty or multiple sheets during printing. It will inevitably cause color deviation in printing. So we need to maintain and upkeep the equipment regularly, pay attention to the lubrication of key parts of the machine, prevent the aggravation of wear and tear, and keep the equipment in a stable state. As an offset printing worker, one should do a good job in "three aspects" (managing, using, and repairing) and "four aspects" (knowing how to use, maintain, inspect, and troubleshoot).



There are many reasons for the formation of printing color difference, and there are more methods to control it. This requires us to constantly explore and accumulate in printing operations, develop good habits of taking notes, which is conducive to improving our own abilities. In our spare time, we should read more books about printing theory, have theories to guide us, and avoid many detours. Customers have increasingly high requirements for the quality of printed products, which is not only pressure but also motivation for us. We believe that as long as we can face it with a positive attitude, you will go smoothly on the road to success.