Water is a life-giving substance essential for the survival of all biological life on the planet. But as a pervasive and somewhat corrosive substance, water is also a nightmare in many industrial settings and can negatively affect a production process. Exposure to water can degrade a wide array of materials, including metals, concrete, wood, and more.
As a by-product of wood, paper is particularly susceptible to water damage. You don’t necessarily need direct physical contact or immersion in liquid water for paper stocks to become degraded. Even the presence of water vapor in the air can render paper useless for industrial use.
Excessive moisture from high humidity is not the only threat here. Extremely dry air with low levels of humidity can also degrade the quality of paper used in printing plants. Keeping paper stocks safe at a printing operation is a tight-rope walk.
In this blog post, we will explore in detail how variations in relative humidity levels can affect the suitability of the paper for various printing processes. We will also explain how an industrial humidification system can make a marked difference in paper quality.
Understanding Relative Humidity
There are two main measurements of humidity in the air – absolute humidity and relative humidity. Out of the two, relative humidity is more important from a human perspective. When newscasters mention humidity in weather reports, they are talking about relative humidity.
Absolute vs. Relative Humidity
Absolute humidity is a straightforward measurement of moisture or water vapor in any given volume of air. It is expressed in grams per cubic meter. While it is useful in many contexts, the absolute humidity level does not focus on one critical factor that affects humidity – the ambient temperature.
Temperature can drastically alter the physical properties of both air and water. In high temperatures, more water evaporates into water vapor while lower temperatures encourage more water vapor to condense back into water droplets or dew.
Temperature fluctuations also drastically affect the ability of the surrounding air to hold moisture. At higher temperatures, the spaces between air molecules increase, giving it the ability to hold more water vapor. At lower temperatures, the opposite is true.
We can see this clearly in the gap between the absolute humidity of air at different temperature points. Warm air at 86° F can hold up to 30 g (1.05 oz) of water per cubic meter. If we reduce the temperature of the surrounding air to 32° F, it can hold just 5 g (0.17 oz) of water per cubic meter.
Relative humidity expresses the current amount of water vapor in the air in relation to the maximum capacity at the current temperature. It gives a more nuanced picture of atmospheric water levels than absolute humidity. Relative humidity is expressed in percentages.
Think of humidity as a glass filled with water. Absolute humidity only tells us about the actual amount of water in the glass. It ignores the fact that with changes in temperature, the size of the “glass” can change (as the holding capacity of air increases or decreases).
Consider two examples where the absolute humidity is the same:
- 0.17 oz per cubic meter at 32° F – This is also 100% relative humidity at that temperature because the air cannot hold any more water vapor.
- 0.17 oz per cubic meter at 86° F – This translates into just 16.66% of relative humidity because air at higher temperatures can hold a lot more water vapor.
Why Is Relative Humidity More Important?
Relative humidity is more important than absolute humidity because most things are sensitive to changes in temperature. Take humans for example. At higher temperatures, we sweat to cool down our bodies. High levels of humidity prevent the sweat from evaporating and make us feel hotter and more uncomfortable.
This is a substantial reason why we focus more on relative humidity. If it is very high, it can actually make ambient temperatures seem much worse than they are.
Fluctuations in relative humidity levels can also affect the growth rate of other living organisms like mold and bacteria. These are often bad for human health. They can also lead to spoilage of food items, as well as the deterioration of building materials like wood.
High humidity is also bad news for sensitive electronic equipment and many types of raw materials used in industries as diverse as medical, construction, food processing, science, IT, printing, and more. Paper used for printing is particularly vulnerable to extreme fluctuations in relative humidity.
The Impact of Humidity on Commercial Printing
The commercial printing industry is a massive sector with an estimated global value of around $730 billion. The United States accounts for more than 10% of that at $78 billion. Each year, companies spend billions of dollars on temperature and humidity control across printing presses and storage facilities for paper.
The impact of humidity on printing is not restricted to any one area. It can impact facilities in diverse ways, including the following:
- Quality of paper
- Quality of printing
- Worker safety
Negative effects on any one of these aspects can have a critical impact on the profitability and viability of a commercial printing company. Let’s take a closer look at each aspect in the printing industry, starting from the ones that are more vulnerable to humidity damage.
The Impact of Relative Humidity on Printing Paper
Paper is by nature a hygroscopic substance, meaning it readily absorbs or adsorbs water from its surrounding environment, at or close to room temperature. This property of paper comes from its parent material – wood or wood pulp.
By absorbing or releasing water, hygroscopic substances try to maintain an equilibrium with the surrounding atmosphere. Correlating with this, if you keep paper in a relatively stable temperature and humidity setting, it will stay in a pristine condition.
In contrast, if the paper is stored at high or low ambient humidity, it will either become too dry or too moist, both of which can have a negative impact on printing and ultimately, product quality. Consequently, paper is kept in storage in waterproof packaging whenever possible in most printing presses.
Waterproof packaging at a print shop helps mitigate the impact of relative humidity. However, once the packaging is removed, paper can react to changes in humidity in a matter of hours. Depending on the type and quality of paper, it can take anywhere from 4 hours to 24 hours for a ream of paper to reach equilibrium with the surroundings.
Humidity Levels for Various Printing Applications
With most kinds of paper, the absolute humidity is around 5% of its total mass – if a ream weighs 20 lbs, it contains around 1 lb of moisture. Some types of paper can have it as high as 10%, but that is in exceptional cases. Here are some typical recommendations for popular printing applications:
- Offset Grade: This printing requires slightly higher moisture levels of around 5.5% or more to reduce the potential reaction to the fountain solution.
- Digital & Offset: When digital printing is also included, the paper should have slightly less moisture (around 5%) than for pure offset printing.
- Laser Grade: To reduce the reaction to fuser heat, the recommended moisture level in paper is around 4.5% for laser printing.
Negative Effects of Low/High Humidity Levels on Paper
The ideal humidity range for paper is somewhere between 45% to 60%, depending on the type of paper, ambient temperature, and a few other factors. If the relative humidity is above or below this recommended range, the following things can happen:
- Change in Size: Often, when exposed to excessive moisture, the edges of the paper in a ream will absorb more water than the center of the page, resulting in changes in length and width (corrugation).
- Loss of Flatness: Excess moisture can make paper wrinkly, while excessive dryness can cause the edges to curl upwards. Paper curl happens when the sides of the paper release more moisture than the center.
- Other Physical Changes: Due to changes in moisture levels, hygroscopic materials like paper can become excessively stiff, fragile, and prone to damage from tears and creases. These changes can also prevent optimum ink transfer, resulting in poor-quality printing.
All these changes to the dimensions and topology of the paper can have massive consequences during the printing process, resulting in both quality and productivity issues.
The Impact of Relative Humidity on Print Quality
One critical impact of a low humidity level not mentioned in the previous section is static electricity. When the air is excessively dry, there is a higher chance of static electricity build-up in the paper. This can lead to several issues with a printing press.
Modern printing involves a wide range of technologies ranging from offset printing to digital inkjet printing to digital laser printing. All three modes are affected by changes in humidity and static electricity build-up in more or less identical ways.
- Printing Defects: Due to changes in dimensions or flatness, paper sheets may enter the machine inappropriately, resulting in printing defects.
- Misregister: When the paper is not flat, it can also cause a defect called misregister, causing the ink to release in the wrong areas. This will result in blurred images and a general loss of sharpness.
- Ink Mist: High levels of static electricity on the paper surface may cause ink droplets to deviate from the planned paths. They can even clog up the nozzles on printing machines. The outcome is usually print defects, including blurred images and halos.
Offset printing has been followed by newer techniques in the industry like digital printing and laser digital printing. In the grand scheme of things, all forms of printing are affected when humidity levels drop or spike.
Loss of flatness and electrostatic discharges can affect all types of printing machines in the same way. While slow ink drying is a problem for offset and inkjet printing, laser printing is affected by difficulties in toner adhesion and passing through the fuser roller.
General Productivity and Safety Issues
Frequent paper jams can reduce the speed of printing or result in outright machine stoppages. High humidity levels can also affect the sensitive electronics and metal pieces of industrial presses. In extreme situations, it can lead to corrosion and reduced operating life of valuable assets.
On the flip side, low humidity can lead to a buildup of static electricity and cause conveyor jams, paper feed defects, ink striation, and a whole lot of other issues that reduce both the speed and quality of printing processes and drive up operating costs.
These issues can affect the workers in at the print shop, adding to their job burden and stress levels. Apart from that, the humidity can also have a real physical effect on their bodies and minds, sapping energy levels. This is more of an issue in areas with warm temperatures and high humidity levels.
Then there are the major concerns related to industrial fires. Since paper is a highly flammable substance, dryness due to low humidity should always be treated with extreme caution. In some situations, electrostatic discharges can spark fires.
Using an adiabatic humidification system can help offset this danger by keeping paper at optimal moisture content and reducing electrostatic charges build-up in your storage areas.
Regional and Seasonal Variations to Humidity in the Printing Industry
Here in the US, the climate regions can be broadly split into two from a humidity level perspective. Anything West of the 100th meridian has a dry climate and is more susceptible to challenges from low humidity.
To the east, there is a humid continental/subtropical climate, with states like Florida and Louisiana reporting high annual humidity levels north of 70%.
In the West, Southwest, or parts of the Midwest, a low humidity level can lead to challenging winters for the printing industry. During winter, water vapor levels in the ambient air can drop to extremely low levels, particularly in indoor industrial settings. The printers and other machines often generate quite a lot of heat, which can reduce the already depleted moisture levels.
This can bring the indoor humidity levels in a printing press far below the minimum of 45% to 50% required for optimal paper moisture content and smooth printing.
Printing Industry Best Practices for Optimal Humidity Levels
The following are some of the printing industry best practices recommended for facilities:
- Whenever possible, store all printing paper stock in temperature and humidity-controlled storage areas.
- Keep paper covered with waterproof/shrink wrap at all times, and away from outside walls and windows/doors.
- Try to keep the printing area at a constant temperature and relative humidity between 45% to 55% at all times.
- If there is a significant difference in temperature between the wrapped paper storage area and the production area, give the paper at least a few hours to acclimatize and reach equilibrium.
- Use an industrial adiabatic humidification system designed for the printing industry if your facility has lower than recommended relative humidity levels, especially during winters.
MicroCool Industrial Humidification Systems for Printing
MicroCool has over 40 years of experience in providing adiabatic humidification, cooling, and air quality systems for businesses involved in manufacturing, printing, heavy industries, and agriculture.
The pinnacle of over 30 years of development, the IBEX heavy-duty industrial humidifier system comes with the following features that make it ideal for digital printing facilities:
- Advanced Customization: MicroCool design experts work with you closely to create a highly customized humidifying system that is perfectly aligned with your printing facility’s relative humidity needs.
- Zonal Systems: With the optional zoning system, you can strategically distribute fogging nozzles across an indoor facility to deliver a uniform humidity level.
- Precise Controls: Using a convenient LCD control system, you can assign precise humidity levels for different areas like paper storage, printer head area, and paper feed locations.
- High Precision Nozzle: The trademark MicroCool nozzles are designed to deliver water in the form of a fine mist that increases humidity levels without accumulating on hardware as mist. Multiple design variants are available to serve areas with low headroom, large open spaces, and small compact locations.
- Pump Capacity Options: Apart from the heavy-duty IBEX, we also have other families of systems like FOCUS, BIGHORN, and HUMMINGBIRD. These systems have capacities ranging from 148 lbs/hr to 5,500 lbs/hr, ideal for a variety of printing and paper management facilities.
- Water Treatment: To prevent or reduce the chance of mineral/pathogen build-up in a humidifier system, we offer carbon filters, Reverse Osmosis units, and UV light filters across all industrial humidifier solutions.
- Safe and Reliable: All MicroCool products are manufactured in the United States with high-quality components, like powder-coated steel for frames and stainless steel inner fittings and lines. Control panels are built to the UL 508A standard for maximum reliability and safety.
MicroCool is an industry leader in heavy-duty adiabatic humidification and cooling. All our models are constantly updated to the latest standards and come with full digital interfaces for optimal control over humidity levels.
Speak with our resident fog experts today to learn more about MicroCool products and services and how our humidifier for printing plant can meet your digital printing needs. Contact us to set up an appointment today!