There are a number of topics that are not sexy in printing. Humidification is one of them. With many parts of the country moving into colder weather, dry air can pose a serious waste and productivity issue.
“Humidity is simply the moisture in the air. The amount of water that a cubic foot of air can hold changes with its temperature, increasing as the temperature of the air increases.”
Humidity is simply the moisture in the air. The amount of water that a cubic foot of air can hold changes with its temperature, increasing as the temperature of the air increases. This is due to the fact that air expands as it warms and contracts as it cools.An optimum relative humidity for most pre-press, paper storage and pressroom environments is 45-50%.
Paper is very sensitive to changes in temperature and humidity. If paper is unloaded from a truck that has been in freezing temperatures and the paper is used immediately for printing (presumably in a heated room), problems will occur.
“Paper is conditioned at the paper mill to certain moisture content and wrapped by a vapor barrier paper to help retain this moisture. As soon as this wrapper is removed, the paper begins to lose moisture to the surrounding air if it is drier, or to take on moisture if it is moister.”
Paper is conditioned at the paper mill to certain moisture content and wrapped by a vapor barrier paper to help retain this moisture. As soon as this wrapper is removed, the paper begins to lose moisture to the surrounding air if it is drier, or to take on moisture if it is moister. As the paper absorbs moisture its cells expand, and conversely shrink when giving off moisture. Paper can change dimension in width and length.
Purchasingshould always order paper stock with enough lead time so that the paper has an opportunity to become acclimated to the temperature and humidity conditions of the printing facility. Paper should be left in its original wrapping and it should remain unopened until it becomes conditioned to the humidity and temperature of the pressroom.The time necessary for the paper to be conditioned properly will range from a few hours up to several days, depending upon the quantity of paper to be used and the differences in the temperature and humidity levels between the pressroom and the environment where the paper had been stored previously.
Static electricity is caused by the movement of materials of high electrical resistance against one another and is generated around us at all times. Typical examples are people walking across carpeted floors, paper going through a printing press or folder.
Only when atmospheric conditions allow static electricity to accumulate does it become a problem. People may receive unpleasant shocks. Paper, films and fabrics are repelled or attracted to each other or to processing machinery. Sparks from static electricity are extremely dangerous in the presence of gases, volatile liquids or other places where volatile chemicals are used or stored. For most environments, maintaining sufficiently high RH levels provide the most effective and economical means of preventing the build-up of static charges.
Three main humidifying methods are available: steam, evaporative pan and water spray. Each has particular advantages and limitations, which determine its suitability for a particular application.
Steam is readymade water vapor that needs only to be mixed with the air. With evaporative pan humidification, air flows across the surface of heated water in the pan and absorbs the water vapor. Both steam and evaporative pan humidification do not affect the temperature of the humidified air. Water spray humidification disperses water as a fine mist into the air stream where it evaporates. As it evaporates it draws heat from the air and cools it.
Prisco offers humidification systems to fit any size printer or environment. Systems can be designed to work in specific locations or cover larger areas. If you will be at Graph Expo, Prisco will have humidification equipment at booth #3207.
Here are some of the benefits you can expect with a controlled humidification system:
•Increased productivity - Maintains optimum humidity levels for production equipment
•Reduces paper-handling problems and improves register
•Increased worker productivity - People work best in 40-60% humidity
•Increased consistency - Uniform humidity year round
•Reduced air contaminants - Up to 35% lower dust levels
•Reduced static electricity - Maintaining humidity above 45% reduces static build up
•Reduced fire hazard - Less dust, static and friction mean fewer potential fires
As I said in the beginning this is not a sexy topic but one that many printers avoid addressing. Look at the potential benefits and determine if it isn’t time to take care of the issue. Help in preparing this article was supplied by Prisco and the Armstrong Humidification Handbook.
