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Importance of Humidity Control in a Bindery

Posted 04/05/2019 by Gregg Howard, Technical Manager, Graphic Arts

Humidity—simply defined as the amount of water vapor, or moisture, in the air—can vary widely throughout the year. Levels typically run higher during the warmer months and much lower during the colder months. With winter firmly upon us, it’s important to understand the different ways these lower levels can impact bindery processes.

Humidity control is critical to product quality and process efficiency. Improved print quality, elimination of paper distortion, static prevention, and consistent adhesive application are all byproducts of effectively controlling humidity levels in your bindery. If you don’t maintain a proper level, issues can quickly arise, disrupting your entire process.

Improved Print Quality

Fibers in paper pick up moisture from the surrounding environment, which can change the physical structure of the paper—causing distortion, warping, or curling—and impact print quality. Paper stocks can shrink or tighten in low-humidity environments, leading to inconsistent or repeating imaging during the printing process. Because inks dry faster in the absence of moisture, too little humidity can also cause inks to appear faded or discolored. Storing paper in the proper conditions will help prevent most of these issues. A widely accepted environmental range for storage is typically 62-72 degrees F air temperature, with a 45-60 percent humidity level.

Static Control

In the cold, dry winter months, reduced humidity levels make air more of an insulator than a conductor. Since paper is considered an insulating substrate, a static charge can build to high levels. This increase can negatively impact both the printing and binding processes, as pages are more likely to stick together, leading to more paper jams and other process malfunctions that cause unwanted and costly downtime. Dust is also more likely to collect on a static-charged surface and, if this buildup goes unnoticed, it can cause major printing issues and compromise adhesive application and overall performance.

PUR Application

Maintaining consistent humidity is especially important when using polyurethane reactive adhesives (PUR). These adhesives react with moisture to form a very strong bond after application. The process of building up strength to form that bond is called the “curing” process. With little moisture to pull from the air, a PUR will take much longer to properly cure, which can delay getting product out the door. And, if you’re like most binderies, you don’t have that luxury.

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To counter this issue, some binderies have added ceiling misters to provide additional humidification during the winter months, enabling the adhesive to cure at a faster rate.

Ultimately, maintaining a consistent and proper humidity level is vital to any print finishing operation. It’s important to monitor humidity levels so you can identify and quickly alleviate issues that arise. This will ensure your bindery runs smooth and hassle-free during this seasonal transition. H.B. Fuller recommends using a climate control system to regulate and stabilize your bindery environment. Also, consider investing in a portable hygrometer, which measures the amount of moisture in the air; it’s an easy and effective way of quickly determining humidity levels in a bindery.

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