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For achieving optimum flexo printing quality, there are major steps that should be followed.

PH CONTROL: 

Proper pH is critical to achieving sharp and defined printing image. Ph that is not properly adjusting from color to color on the printing machine will cause a number of printing defects. pH is acidity, neutrality or alkalinity of a liquid ranging from 1 to 14 on a pH meter. Below 7 is acid and above 7 is alkaline and 7 is neutral. Flexographic ink should be on the alkaline side of the scale, so pH should never be below 8 or higher than 9.5 in flexo ink pH reading should be taken and adjustment made when viscosity readings and adjustment are made. pH adjuster, supplied by the same ink supplier. The challenge is in keeping pH up, not down, and to achieve the stepping of pH, it is important to use measuring cup amounts for this purpose, hot humid condition and evaporation accelerate downward movement in pH.

VISCOSITY CONTROL: 

Ink viscosity determines the rate of flow and is measured in seconds by using a No.2 Zahn cup, the device that allows liquid to through an opening at the bottom of the cup, and which is the adopted instrument of the corrugated board industry. The proper viscosity is that which achieve suitable coverage and color density matching a costumer color sample.

Two vehicles are used to reduce the viscosity, water, and extender varnish. As with pH adjuster, a measuring cup of either water to extender varnish should be used to avoid reducing viscosity to a point where desire coverage and density are no longer achieved. Often it is better to use extender varnish that has the same properties as ink, except pigment. This vehicle will have less effect in reducing the solid content of the ink.

In the next article, we will talk about setting impression and cleaning printing plate.