test
Three ink suppliers were invited to provide two inks: black ink and green ink, respectively, for testing. The ink formulation must have time stability and minimal foaming. Before the ink was put into the ink fountain, its density was measured and recorded. Recorded during the test are:
Printing color (using spectrophotometer);
Paper color (using spectrophotometer);
Ink density.
After more than 5 hours after the end of each measurement, the ink density was again measured and recorded. The printing speed is 4000 sheets/hour.
The ink density measurement uses a 50 ml Eppendorf Multipet pipette. The pipette is filled with ink and placed on a balance with a measurement accuracy of 0.01g; 50ml of ink is put back into the ink tank and the pipette is put back on the balance; the balance reading is divided by 50, A density value in g/ml (equal to Kg/dm3) is obtained.
Test Results
After the ink in the ink system has been circulated for a short time, the viscosity of the ink has decreased. Of the three inks, the black ink produced by the second ink supplier may be the least affected (see Figure 1).
The second ink supplier adjusted the method is to add a very small amount of defoamer to the green ink 30 minutes after the start of the test, it will be effective in the 35th minute, but the effect will disappear at the end of the test.
The density of the black ink drops less than the green ink density. Compared to the density measured before the test, the ink regained its similar density 5 hours after the end of the test.
The changes in the ink and paper colors of the three ink suppliers during the test are shown in Figure 2. The three suppliers' ink color changes are at an acceptable level.
The second supplier's change in the color of the green ink follows the pace of the paper. Two types of paper were used in the test, the first supplier printed on Type A paper (except for the first sheet), and the third supplier printed on Type B paper. The second supplier chose two types of paper.
It can be inferred from the density measurement that there is blistering in the ink, but this will not affect the printing color, and the bubbling ink will not have any problems.
The test sequence was to use the same ink within 4 hours and add 1 cubic dm of fresh ink every 30 minutes. During this period, the color of the print was stable and the degree of blistering did not exceed the test process.
in conclusion
All three suppliers used in this test had blisters in the ink. Bubbling of the ink does not cause significant color changes within 1 hour. The ink started to foam immediately after the inking system was started, and there was no significant change in blistering during the test. The second supplier's test results showed that the anti-foaming agent can reduce the bubbles, but this is a temporary phenomenon.
The ink density readings recorded more than 5 hours after the end of the test showed that the ink was no longer blistering, the density did not change significantly, and the ink viscosity was not affected.
Suggest
• Adding fresh ink at regular intervals (for example, every 30 minutes), ink suppliers must complete ink formulations as much as possible for this purpose.
• The viscosity of the ink is measured before it is put into the ink system, but if the ink is blistering during printing, the measurement of the viscosity cannot provide useful help for corrective action.
• Avoid high solids content in ink formulations, especially when using chambered squeegee systems.
• Make sure there is enough ink flow through the system.
• Ink systems (tubes, tubes, ink pumps, and chambers) should not have sharp corners.
Good interactions between operators, ink suppliers, and ink metering system designers, setting positive, measurable, achievable goals, that is, maintaining consistent colors, will help overcome problems caused by foaming inks. Of course, this does not change the nature of the ink that is inherently or easily foamed.