How to Prevent Foaming of Water-based Inks During High-speed Printing?
Date: Jun 25 2025 From: Star Color Views:
Water-based inks are widely used in flexographic and gravure printing. They not only have extremely low volatile organic compounds (VOCs) emissions but also effectively reduce fire hazards, meeting the needs of sustainable development.
During high-speed printing, ink foaming poses a significant obstacle to efficient production and high-quality printing. The intense mechanical movement of ink in high-speed printing equipment leads to foam generation, which not only affects printing effects but also reduces production efficiency and increases costs. Therefore, in-depth exploration of the causes of foaming in water-based inks and the formulation of effective prevention strategies are crucial for industry development.
Causes of Foaming in Water-based Inks
Mechanical Factors
In high-speed printing equipment, the frequent contact and separation of high-speed rotating printing rollers with the ink, as well as the rapid spreading and scraping of ink on the roller surface, introduce a large amount of air. In flexographic printers, anilox rollers rotate at hundreds of revolutions per minute, and the rapid transfer of ink between the cells and the substrate easily causes air to mix in, forming foam nuclei.
Chemical Factors
Water-based inks typically contain various surfactants and wetting agents to achieve good wetting, dispersion, and leveling properties. These substances significantly reduce the surface tension of the ink, making it easier to spread on the substrate. However, the low surface tension also allows air to form bubbles more easily in the ink.
Take alkylphenol ethoxylate surfactants as an example: while reducing surface tension, they form a relatively strong liquid film on the bubble surface, hindering bubble coalescence and collapse, thus leading to foam accumulation.
Equipment System Factors
The design and operation status of the ink circulation system significantly impact foam generation. In the ink return pipeline, sudden changes in pipe diameter, excessive bends, or too fast return speed can cause severe turbulence in the ink, promoting air entrainment. For instance, some old printing equipment lacks flow guides or baffles in the ink tank, causing ink to directly impact the tank bottom during return, forming substantial foam.
Environmental and Parameter Factors
Temperature and pH value greatly affect the foam stability of water-based inks. When temperature rises, the ink's surface tension decreases, and the strength of the bubble film weakens, making originally stable foam more prone to rupture. Meanwhile, high temperatures accelerate solvent volatilization in the ink, changing its viscosity and making it easier for air to be 卷入 (entrained) to form new bubbles.
In terms of pH value, components like resins in water-based inks are sensitive to pH. When the pH value is too low, resins coagulate, leading to instability in the ink system and increased foaming.
Negative Impacts of Foam on Printing Quality
Printing Defects
The presence of foam causes defects such as pinholes and spots on the printed surface, affecting the integrity and aesthetics of the pattern. During printing, foam also leads to uneven ink distribution, resulting in local color lightness, namely "color mottling" or "bleeding," which severely reduces the visual effect of printed products.
Ink Transfer Issues
In gravure printing, bubbles occupy the space of the cells, insufficiently filling the cells with ink, thus causing insufficient ink volume and blurred patterns during printing. In flexographic printing, foam affects the transfer efficiency of ink between the plate and the substrate, causing inconsistent color depth in printed products, which fails to meet printing quality standards.
Reduced Productivity and Increased Costs
Excessive foam leads to frequent shutdowns of printing equipment for cleaning. To prevent foam overflow from contaminating equipment and printed products, operators need to regularly stop the machine to handle the foam in the ink tank, which not only prolongs the production cycle but also increases labor costs.
Practical Solutions to Prevent Foaming
Optimizing Ink Formulations
- Using low-foam surfactants: Select surfactants with special molecular structures, such as block polyether surfactants, which can effectively inhibit foam generation while reducing surface tension.
- Balancing surface tension and viscosity: Adjust the ink formulation to achieve the optimal balance between surface tension and viscosity. Appropriately increasing ink viscosity can accelerate the drainage rate of the bubble film, promoting bubble rupture. In practical production, rheology modifiers can be added to adjust the viscosity and thixotropy of the ink while optimizing the overall performance of the ink in combination with surfactants.
Selecting Suitable Defoamers
- Comparison of defoamer types: Common defoamers mainly include silicone-based and mineral oil-based types. Silicone-based defoamers have high defoaming efficiency, rapidly reducing the surface tension of foam to make it burst quickly. Mineral oil-based defoamers are relatively mild, have good compatibility, and are less likely to cause side effects, but their defoaming efficiency may be slightly lower than silicone-based ones.
- Dosage and compatibility testing: The dosage of defoamers must be determined through strict experimental testing. Too low a dosage fails to achieve the ideal defoaming effect, while too high a dosage may affect other properties of the ink, such as gloss and drying speed. Before adding defoamers, compatibility tests must be conducted to ensure that the defoamer does not chemically react with components like resins and additives in the ink, avoiding negative impacts on ink stability and printability.
- Addition timing and method: The timing and method of adding defoamers also affect their effectiveness. Premixing addition involves fully blending the defoamer with the ink in advance, suitable for scenarios requiring high defoaming effects and batch ink production.
Maintaining Ideal Operating Conditions
- Controlling ink temperature: The ideal working temperature for water-based inks is between 20 - 25°C. Install temperature sensors to monitor ink temperature in real time and equip cooling or heating devices to automatically adjust according to temperature changes, ensuring stable ink temperature.
- Regularly monitoring pH value: Regularly detect the pH value of the ink to ensure it stays within the appropriate range. For most water-based inks, the pH value is typically maintained between 8 - 9.5. When the pH value deviates from the normal range, promptly add pH regulators for adjustment.
- Setting appropriate stirring speed: Reasonably adjust the ink stirring speed to avoid introducing excessive air due to too fast stirring. During the ink standing defoaming stage, stop stirring to allow the foam to break naturally, improving defoaming efficiency.
Conclusion
Although the foaming problem of water-based inks during high-speed printing is complex, effective control of foam can be achieved through scientifically rational ink formulation design, selection of suitable defoamers, optimization of printing equipment configuration, and maintenance of ideal operating conditions.
StarColor's water-based ink system serves as a successful model. It uses advanced low-foam technology to comprehensively optimize ink formulations and production processes, maintaining good stability in high-speed printing environments, effectively reducing foam generation, and providing customers with high-quality and efficient printing solutions.
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