Coldset and heatset both refer to a process used to dry ink after it has already been applied to the paper. With both coldest and heatset offset printing the paper is run through the printing press in the same way. The difference comes when it is time for the ink to dry.
Coldset offset printing is a process by which the ink dries gradually through evaporation and absorption into the paper.
Coldset printing is most commonly used on uncoated paper stocks like newsprint. Since the ink is not set immediately, there is always a little bit of residue that remains on the paper. This is what you sometimes get on your hands if you have been holding a newspaper. Coldset is one of the more economical forms of printing that allows multiple webs to run concurrently, while using less expensive uncoated paper and energy to produce the product.
Heatset printing is the process by which ink is dried by running the printed paper through an oven immediately after ink is applied by the printing units.
As the paper passes through the oven, the oil based solvents in the ink reach a “flashpoint” or evaporation point. What are leftover are waxes, resins, and pigment. The paper then passes through chilling rollers where the waxes and resins cool down and solidify, or set. This is the process that gives heatset printing its name. This process of printing yields a cleaner more upscale product.
Coated (Glossy) paper such as the paper used in magazines and catalogs always has to go through a heatset process because it does not absorb ink.
Heatset printing has become more popular recently because advertisers are more often turning to supplemental inserts and direct mail campaigns that use glossier paper.
Both coldest and heatset offset printing have a place in web offset printing. Which one you use depends on what type of publication you are printing. WebOffset can help you decide which process is best for your next printing project.