All printers using water-based inks always encounter the problem of ink foaming. This is a costly failure that can result in equipment downtime, leading to discouragement of operators. Ink suppliers are trying their best to propose solutions, but this issue will almost never be completely eradicated.
All printers using water-based inks always encounter the problem of ink foaming. This is a costly failure that can result in equipment downtime, leading to discouragement of operators. Ink suppliers are trying their best to propose solutions, but this issue will almost never be completely eradicated. In order to minimize the occurrence of ink blistering, equipment suppliers have devoted extra attention to the design of ink metering systems. However, the problem of foaming of aqueous inks will continue to exist.
The printer first needs to ask himself: Is ink bubbling really a problem for print buyers? Customers often do not complain about poor print quality due to ink blisters. They may only complain about color consistency, overprinting, edge definition, inability to identify barcodes, or defects in printed matter.
This article describes the results of tests on different ink supplier products, and the waterborne ink blistering and print color inconsistencies of these suppliers under monitoring.
problem
Water-based flexo inks almost always blisters. Although in most cases this phenomenon will not be noticed, the day-to-day ink blistering problem becomes a problem. This phenomenon is unavoidable on any printing device that uses aqueous ink. Foaming of ink is more common on printing equipment equipped with a chambered squeegee system, but this is not relevant to the supplier of the squeegee system. The appearance of bubbles means that there are two ink phases instead of one. Compared to the original ink phase, the foam phase has a different composition within the unit volume.
The flexographic industry has many explanations for ink blistering, and some of the solutions and solutions provided have now been confirmed.
Basic elements
The following are the factors that affect the bubbling of the ink: the ink itself; the system that controls the ink (ink pump, ink tube and metering system); and the operator.
Ink suppliers can change the ink formulation so that the ink does not foam easily.
If the ink bubbles or air is trapped in the ink, the system controlling the ink will increase the foam generation.
The operator took the wrong action and caused the ink bubble to intensify.
When the ink is blistering, only the above-mentioned party is responsible for the fact that it is not a fantasy. Each of these factors has its own responsibility to create a stable condition to minimize the risk of severe bubbling.
The ink is blistering due to the air contained in the ink. When the blistering phenomenon occurs, the density of the ink is greatly reduced. If viscosity cup measurements are used, the viscosity will increase. Foam increases when the operator adds water to lower the viscosity. If the viscosity of the ink is measured when the ink is foamed, it will result in incorrect corrective actions.
Ink suppliers usually recommend adding a defoamer when the ink is foamed, but this only works if the surface of the ink is foamed. If the bubbles in the ink are evenly distributed (micro-bubbles), then in most cases the operator or the ink supplier is at a loss.
It is almost impossible to know how the ink started to foam. This is generally believed to be related to the use of a chambered squeegee system and begins to bubble at the front squeegee. Assuming that the air is carried into the chamber by the anilox roller, it is also believed to be related to the ink pump system and ink flow.
Most materials will be foamed, such as heating the plastic to start the foaming process. As for the bubbles in the liquid, physical knowledge tells us that when a bubble with a radius r is formed in a liquid with an interfacial tension of Y, the vapor pressure it contains is P, then P=2*Y/r.
Heat is used to release water vapor from liquids or solids. In solids, the bubbles are partially trapped, forming a rigid foam; whereas in liquids, the bubbles break up after they have surfaced.
In order to minimize the risk of foaming of aqueous flexo inks, the following measures can be taken:
· Minimize ink agitation caused by the ink circulation system;
· Add unnecessary water as little as possible (operator added water or water left in the inking system after cleaning);
Use non-foaming ink formulations (eg avoid solids in the ink formulation);
Ink suppliers and operators have agreed procedures for maintaining ink quality;
Keep records of what was done during production. Record the time and activity of a single variety of ink production, which will help to take corrective action when foaming.