Not all two-side stocks are coated alike. Most have better printability and consistency on one side or another, which on press, results in unevenness in color and gloss. This is why one side of a sheet is typically preferred when a job requires high-quality graphics and color. But if both sides require the same high-quality graphics and color, significant press adjustments are required, creating press downtime, inefficient use of labor and wasted press sheets. And in the end, usually one side still presents better quality over the other.
Why the difference?
Why does coating each side of a sheet with two coatings make a difference, as opposed to double-coating the front side and single coating the back? For starters, the thickness of the coating may differ from one side to another. While some paper mills attempt to achieve even thickness on each side, it's a difficult task. To simulate a double-coating, a single coating is applied at greater thickness than the two individual layers on the other side. In contrast, when the coated, two-sided stock (C2S) receives coating from two coaters in a single pass, the mill is better able to achieve consistent coat weight across the sheet. But if an excess amount of coating is applied in one pass (more than six or seven lbs. of coat weight), it's difficult to control the thickness across the full length of the machine. A true double coating is the only guarantee for overall quality assurance.
On press, two problems can arise for printers working with double-sided coat sheets. For instance, if the coatings have two different thicknesses, printers will experience different ink holdout on each side of the sheet. The single- and double-coated sides of the sheets are essentially two very different surfaces; ink can vary dramatically.