In order to pursue the effect close to color printing and do high-definition printing, the line number of the anilox roller has been continuously improved, and the control of pH, viscosity and surface tension (static and dynamic) of water-based inks is very important.
So first understand what pH is:
It was invented by Roman scholars, and was originally named potential hydrogenii. It is expressed in lowercase p and uppercase H in English. PH is used to measure the acidity or alkalinity of ink or other chemical components.
It is represented by 1 to 14, the middle point 7 represents neutrality, such as pure water, and general tap water is between 6.9 and 7.1, so when mixing ink, you must first check the pH value of the water. The solution should be acidic if the solution is lower than 7.0 The smaller the number, the stronger the acidity, and the larger the number, the stronger the alkaline.
Baking powder is a weak alkali, about 8.0, and the pH value of most cleaning liquids for cleaning anilox rollers is about 11.0, which can wet dry ink. It should be noted that the pH readings are 7.0 and 8.0, and the difference between the acidity and alkalinity of the two is 10 times, so the pH value changes slightly, and the result has a great impact.
The choice of alkali is very important. An alkali that is easy to dry, such as ammonia, will make the resin solution dry very quickly and harden. This will make it difficult to re-dissolve the ink and produce a strong odor. Slow-drying alkalis, such as triethanol ammonia, cannot be dried in real time and cause problems. The increase in adjustment during the printing process is about 2% without generating a strong odor.
Now many carton factories have begun to measure the initial viscosity and pH value of the new ink. The ideal pH range of the new ink is 8.3 ~ 9.5, but the higher the pH value of the coated paper is, the higher the number of lines is. Anilox rollers with low ink content must pay attention to the use of increasing pH.
Viscosity affects pH, and pH also affects viscosity. However, the viscosity of water-based ink is not equal to the color density. If the viscosity increases and the pH value starts to decrease, pigments will remain in the printing plate, which will cause the ink holes of the anilox roller to be blocked, and there will be color differences in the printed matter. phenomenon.
Because during the transfer of ink, it will dry on the printing plate due to the volatilization of amine water, and a small amount of ink will be transferred to the corrugated cardboard. This is the effect of the pH value being too low. Can judge.
The addition of water will lower the pH of the water-based ink (because the pH of the water is 7), which will make it difficult for the pigment to re-wet, the ink in the anilox roller will be difficult to transfer to the printing plate, and it will be more difficult for the ink to adhere to the corrugated Cardboard.
The transfer ability of water-based ink is controlled by surface tension, and the ink itself will not flow from this surface to another surface, unless the new surface tension is greater than the leaving surface tension.
If the water-based ink contains too much water to increase the surface tension (water-based ink 34 dyne, water 74 dyne), it will be difficult to adhere from the rubber roller to the anilox roller, and when the printing speed is fast, splashing will occur.
What are the negative effects of adding water to water-based inks to lower the pH?
1.Accelerated drying time, water-based ink will accumulate on the printing plate because it reduces the water amine.
2. Viscosity will increase, the drying speed of water-based ink on anilox rolls, printing plates, and cardboard will become faster, and the resin will also condense. The ink film will be difficult to wet or clean, and the printing plate will become dirty. And pulling hair phenomenon.
3. If the PH value is too low, the ink and ink will be agglomerated, dirty, the packing on the printing plate will be blocked, and the anilox roller mesh will be blocked.
Generally speaking, the pH value of ink is in the range of 8.0-9.5.
However, too high pH value will also reduce viscosity and increase drying time (this is a slow-drying amine water) resulting in smearing and smearing. It is easy to get wet and de-inked when it encounters water, the ink film will become softer, the printing plate will be easier to clean, and it is more suitable for coated paper printing.
What are the printing problems caused when the pH value of ink is too high?
Not suitable for drying, poor water resistance, image stuffing on prints, odor, etc.