In offset printing, a common issue known as "powder on the ink roller" can occur after the press has been running for some time. This phenomenon is characterized by the appearance of fine, powdery particles on the ink rollers, which can lead to ink deposits in unwanted areas or cause deinking on the rollers. As a result, ink transfer becomes inefficient and uneven, affecting print quality.
The root cause of this problem often lies in the interaction between water and ink, two critical components in the offset printing process. The fountain solution, primarily composed of water, and the printing ink must work in harmony for a successful print. However, various factors can disrupt this balance, making ink control one of the most challenging aspects of offset printing. One such issue is the formation of a powdery coating on the ink rollers, which can interfere with proper ink distribution.
Water hardness plays a significant role in this issue. The total hardness of water varies depending on the region, typically ranging from 0–30 ppm for soft water to over 60 ppm for hard water. When using hard water, calcium ions (Ca²âº) can react with the resin in the ink, forming calcium soaps. These soaps are oil-loving (oleophilic), which means they can accumulate on the rubber rollers, causing surface crystallization and poor ink and water transfer. Additionally, when calcium ions interact with acidic components in the fountain solution, compounds like calcium citrate or calcium phosphate may form. These are water-loving (hydrophilic) and can hinder ink transfer, leading to ink separation from the rollers.
To prevent these issues, it's advisable to use soft water with low calcium content when preparing or diluting the fountain solution. Selecting fountain solutions that help reduce calcium buildup can also be effective in minimizing the occurrence of this problem.
Besides water and ink, the substrate used in printing can also contribute to the formation of powdery particles. If the paper surface is not clean or has excessive dust, fibers, or coatings, these materials can be transferred into the ink system during the printing process. For example, if the paper contains a lot of loose particles, they may adhere to the printing plate and eventually settle on the ink rollers, causing the "powder on the ink roller" issue.
Even if the paper appears clean, poor coating quality can lead to fluffing or powdering during the printing process. This can also result in similar problems. To resolve this, you can try reducing the press speed, adjusting ink viscosity, or switching to a higher-quality paper.
In addition to direct contamination from the substrate, chemical reactions between the fountain solution and the ink can also generate calcium precipitates, which can act as an indirect source of powdery particles in the system. Therefore, managing both the water quality and the chemical compatibility between the fountain solution and ink is essential for maintaining smooth and consistent printing operations.
Household Toothbrush,Hangable Laundry Brush,Home Soft Bristle Brush,Hangable Multifunctional Shoe Brush
Huayao Master (Puyang) Automation Equipment Co., Ltd. , https://www.huayaomaster.com