Virtual Flexo Plant

Dampening System

Description

In-line die cutting
Dampening Rollers

The dampening system consists of a dampening fountain and roller train. Dampening fountain solution (commonly referred to as "water") is held in the fountain and then delivered to the plate. There are several types of dampening systems used in lithography. The systems differ in how they deliver the fountain solution. One system meters the fountain solution through a series of rollers, while another uses a brush system utilizing bristles. The choice of dampening system will depend mainly upon the type of press and products produced.

Fountain solution composition will also vary, but at a minimum will contain some type of desensitizer, either synthetic or Sudanese gum arabic. It may also contain acids or bases, buffering agents, corrosion inhibitors, fungicides, antifoaming agents, drying stimulator, and wetting agents. The role of the wetting agent is to reduce the surface tension and increase the viscosity of the fountain solution. Common wetting agents are isopropyl alcohol (IPA) or alcohol substitutes like glycol ethers, ethylene glycol, or other surfactants. Fountain solution is typically prepared by adding 1-5 oz. of concentrate per gallon of water. Additional wetting additives could be added as an additional step.

Best Management Practices & Pollution Prevention

One environmental concern with fountain solutions is the volatile organic compound (VOC) content and associated emissions from wetting agents. An option to reduce VOC emissions is to change from an alcohol based wetting agent to an alcohol substitute. This requires many process adjustments to ensure that print quality is not affected. Adjustments include checking roller durometers and maintaining rollers properly. If the process does not allow for changing from IPA to alcohol substitutes, refrigeration of fountain solution to 60F or less will help to prevent evaporation of the alcohol, reducing VOC emissions and the amount of alcohol purchased.

Another option for pollution prevention is to install recirculating and automatic mixing units for fountain solution, to ensure consistent levels of wetting agent are added. Adding filters to an inline recirculating system will also reduce the need to dispose of fountain solution prematurely.

For access to vendors who may supply alternative materials and equipment, see the PNEAC Vendor Directory.

Environmental Regulations

States with ozone nonattainment areas have developed or are in the process of developing regulations concerning the VOC content of fountain solutions, as a result of the Environmental Protection Agency’s 2006 Control Techniques Guidelines for Offset Lithographic Printing and Letterpress Printing. These limits are set based on type of press, refrigeration of dampening solution, and alcohol vs. alcohol substitutes used in the dampening solution.

Health & Safety

One risk with IPA is flammability. Pure IPA has a flash point of 53°F (11.7°C). When IPA is mixed in dampening solution flammability is reduced, but IPA solutions must still be handled with caution. IPA can also act as an irritant when present as vapors in the air. The Occupational Safety and Health Administration (OSHA) has set maximum exposure limits at 400 parts per million (ppm) over an eight-hour timeweighted average or 500 ppm for 15 minutes. Current information indicates that there are no long-term health effects associated with IPA.

Since the flash point of alcohol substitutes is greater than 100°F (37.8°C), flammability is not a major concern, and any adverse health effects depend on the substitute’s chemical composition. Glycol ethers and glycols are generally recognized as safe when handled properly with adequate ventilation and personal protection. OSHA’s permissible skin exposure limit for one glycol ether (known as Butyl Cellosolve® and used as a substitute or extender) is 25 ppm over an eight-hour time-weighted average. However, the National Institute of Occupational Safety and Health recently recommended a 5 ppm limit for Butyl Cellosolve® and butyl acetate. Studies performed on workers in printing have shown that the average exposure is 1–2 ppm because Butyl Cellosolve® is not very volatile.

Additional Information

Fact Sheet

Alcohol Free Printing