The quality of the air in a printing facility will effect the quality of the printing on its products. This is particularly true for sheetfed lithographic printers who spray powder onto printed sheets prior to stacking them. Excess spray powder in the air which settles on unprinted paper or printing equipment can cause poor ink gloss and hickeys. Rollers and blankets need to be cleaned more often with more chemicals. All of these lead to more waste.

A well-functioning heating, ventilating and air conditioning system will provide air within the printing plant which is between 72-74F with a relative humidity between 45-50% all year. This will require heating, cooling, humidification, and dehumidification.

Air needs to be exhausted from the pressroom in order to remove spray powder, paper dust, and to purge solvent odors from printing and cleaning operations. Each pressroom will need its own tailored air handling system. It is also wise to separate the pressroom air handling from the prepress area to provide each with their needs.

If humidity is not properly controlled, printing problems can occur on the dry and wet sides. Problems include:

• Paper feeds erratically into the press
• Paper is distorted, causing registration problems
• Paper waves develop in high humidity
• Paper dimples occur in the center of dry sheets
• Static electricity causes ink adhesion problems

In order to reduce static electricity problems, maintain the relative humidity above 35%. The target of 45-50% is even better.

Source: GATF Sheetfed Operations Quarterly, vol 6, no. 4, 1999, p. 4.