Wet-offset lithography, or wet litho, requires the printing press operator to manage a complex mix of wetting fluids and ink. The water used in wet offset is not just plain water—it’s been optimized by adding several chemicals to make it wet the plate more efficiently. These are typically surfactants, detergents, wetting agents, acids, gums, and alcohols, all to make the water wetter and to stabilize interactions with the plate and ink. It’s still mostly water, but with all these chemicals included it is commonly called fountain solution.
There is an obvious benefit to eliminating fountain solution from the printing process. First, there is the total amount of water that is consumed in the wet-offset process—about one gallon for every 8,000 25" x 40" color press sheets. Depending on where you live, water usage may be a bigger or smaller issue; but no matter where you live, water is a natural resource that is consumed during wet offset printing.
High-speed printing using wet offset generates waste. Fountain solution that is exposed to inks, solvents, and paper debris carries some of the material back to the circulation tank that supplies the fluid to the press. After about a week of production, the fountain solution is contaminated and is generally disposed of as industrial wastewater. So, in addition to not using large quantities of clean water, waterless printing does not generate any industrial wastewater—a double benefit.
Because the printing press does not have be brought to a condition of chemical balance between two fluids, waterless generally starts up and reaches stable color faster than wet offset. This results in lower start-up paper waste for print jobs. Also, the single-fluid waterless process is more stable than wet offset, so color stays more consistent throughout the press run. This reduces running waste, where the press operator may need to discard sheets during the run for color variation.
A Sharper Image
Waterless printing reproduces a better, sharper, and more consistent dot than wet offset. Additionally, waterless prints with lower dot gain than wet offset, allowing higher ink densities to be printed without the color getting muddy. The combination of sharper dots and higher ink density creates higher print contrast. Waterless prints can have more snap or pop than wet offset prints. Finally, due to the higher stability and lower inherent dot gain of waterless, finer screen rulings can be used, allowing higher-resolution, more photo-realistic printing than wet offset.
There are many printing applications where the presence of water creates more than the normal amount of challenges. UV printing, for example, uses inks that do not react well with fountain solution in the press. UV is commonly used in printing on nonabsorbent substrates like plastics. When the substrate does not absorb some of the water during the printing process, the correct balance of ink and water becomes very challenging for the press operator to maintain. Waterless printing is an excellent choice for UV printing because it is easier to run and more stable during the printing process.
Wet-offset lithography is a complex process that requires a chemical interaction to be maintained during the physical act of transferring ink from the press to the paper or substrate. Waterless offset is really a physical process, where the physical properties of the ink and plate interact to allow the correct transfer of ink. Waterless is simply easier to print than offset lithography.
Better for the environment, more efficient press operation, brighter, sharper, more consistent color, more substrate choices—waterless printing is simply a better choice.