<H1><B><center>What is Emulsification in Offset Printing?</H1></B></center>

Emulsification in offset printing is the mixture of ink and water that will not dissolve into one another. In offset printing, the ink is oil based and the fountain solution is water based. Since oil and water will not dissolve into one another, the result is an emulsion.

Emulsification in an offset printing unit.

How Emulsification Happens in Offset Printing

In the printing unit, water and ink will mix together.  There are basically 5 points of contact where this happens.  See illustration above.  Note that there are water, or fountain solution rollers (blue) and ink rollers (black). Each supply the printing plate (represented as the largest cylinder - white). 

Emulsification happens when the fountain solution enters the ink rollers and mixes.  It enters in 4 or 5 places, depending on the printing unit configuration.  Each point below references the illustration above:

• Point of contact #4. Here is where fountain solution (and thus water) enters the process.  It touches the plate which has water loving properties.  The fountain solution does not intentionally enter the ink train this way, but is a natural process to keep the non-image areas of the plate clean.

• Points of contact #1, #2 and #3. Each point touches the printing plate.  The wet plate is carrying water in the non-image areas.  The ink will mostly repel this water since it is oil based, but not all - especially if the water is too high.  It then enters and mixes with the other rollers.

• Point of contact #5. Many offset printing unit configurations now come with a "bridge roller". This purposefully bridges the water over to the inking system since it is now recognized that this is necessary in the printing process.  It can usually be taken off if so desired.

The Advantages of a Bridge Roller in the Emulsion Process

1. Gives an even emulsion across the entire ink train. This would otherwise not occur if there are large image areas of the plate that are carrying no water.

2. Transfers ink back that has accumulated in the water train.  This happens especially where there is no paper to carry the ink away.  Some printers will run "take-off" bars on the very edges of the paper to help remove it.  But the bridge roller is another way of sending it back to the ink train.

A bridge from the water train helps remove emulsified ink.

The final process of the emulsion on press.

Once the emulsion has entered the inking system and is transferred to the image area, the process continues.  The emulsion (ink, water and pigment) is sent to the blanket, then to the paper.  

Then the emulsified ink dries.  It can happen through evaporation or it can happen in a heated dryer.  Whatever the case, the water is gone and the end result of the emulsion is pigment, water, and other ingredients depending on the offset printing process.

Common uses of the expression "emulsification" on an offset press.

1. When ink is over emulsified. There is always a danger of over-emulsifying ink.  Too much water will do this. The ink vehicle is able to hold water, but only so much.  This is called a water pickup.  There are special instruments designed to test how much an ink can be emulsified before it loses it's printing properties.  See this article for more of an explanation.

2. The the ink fountain is water-logged.  If ink has been emulsifying for a while beyond the minimum amount required for printing, it will travel all the way up to the ink fountain itself.  Once the ink fountain itself has been taking on water, it is no longer worth running.  Take it out and throw it away.

The ink train can become over emulsified 
from water backtracking to it.

 

How to detect emulsification.

By watching the printed sheet, a pressman can tell if density is dropping despite supplying enough ink.  There are many other quality and running problems that take place when this happens.

A new approach to detection of emulsification.

There has been a study done to show that an ink film that splits between two rollers has a certain sound frequency.  This largely depends on the tack value.  However when emulsified, the ink gives off a different frequency.  By getting a reading of the frequency of the running rollers, a press operator can be given live feedback and take appropriate action.

Conclusion

This is what emulsification is for offset printing.  If you would like a more detailed explanation about balancing ink and water to prevent over-emulsification, please see my other article on this topic.