Coating and Impregnation

Coating and Impregnation

LAY-ON-AIR®-DRYER

For over six decades, VITS has specialized in engineering VITS-flotation dryers to meet diverse customer requirements and industrial needs. With a solid reputation for drying web materials, VITS has made significant advancements in this core competency. Our patented air cushion nozzle LAY-ON-AIR® ensures contactless transport of web materials with widths extending up to 5 meters. Additionally, VITS provides highly efficient vertical radiation dryers. Our drying systems boast several key features:

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• Modular design for easy transportation, quick on-site installation, and retrofitting in existing plants
• Symmetrical air circulation for uniform drying
• High-grade insulation to reduce heat radiation losses, thus saving energy and keeping the production hall cooler
• Compatibility with all current heating methods such as natural gas, thermal oil, steam, or hot water
• Effective and quick direct heating facilitated by natural gas
• A broad selection of nozzles for a wide range of purposes
• New door designs enabling efficient lining and better heat insulation

We excel in both convection and radiation drying technologies. The custom process design for the required temperature and airflows within the dryer sections is based on VITS-specialists' extensive theoretical and practical experience. The calculated drying simulations during the design phase provide practical insights into the effectiveness of the chosen temperature and air current rates. Graphic drying curves illustrate product behavior within the dryer.

Modern dryer engineering incorporates all necessary technical standards and safety aspects. Depending on the process, the latest ATEX safety measures for explosion protection are implemented. For cases anticipating high solvent concentrations due to the evaporation of explosive gases during production, danger areas of the equipment are determined in advance, analyzed, and technically safeguarded appropriately.

In our commitment to environmental responsibility, we collaborate with our partners, Wessel-Umwelttechnik and Airprotech, for exhaust air cleaning solutions. Airprotech specializes in effective afterburning of polluted exhaust gases during impregnation through their RTO systems, while Wessel offers highly-efficient heat recovery solutions. Up to 70% of the generated heat energy can be recycled back into the drying process, reducing costs and environmental impact.

We are happy to answer your queries regarding our dryers. If you have any questions or need further information, please don't hesitate to contact us. We look forward to hearing from you!

An Overview of Roll Coating | New Era Converting

The following is the second installment in a series of four blogs that elaborate on a white paper written by Bob Pasquale of New Era Converting Machinery. The white paper is titled "An Overview of Roll Coating Methods, Capabilities, and Limitations."

Part 1 provided an overview and introduction to the blog series. Part 2 will delve into Kiss Coaters and Squeeze Roll Coaters. Part 3 will examine Gravure Coating, Offset Gravure Coating, and Reverse Roll Coaters. Part 4 will conclude the series, covering Transfer Roll Coaters and Other Roll Coaters, followed by a brief conclusion.

KISS COATER

Kiss coating involves applying a coating to a web that "kisses" the surface of a coating roll. The apparatus is typically simple in design, featuring a single coating roll mounted such that its bottom is submersed in a pan holding the coating (Figure 1). As the roll rotates, it picks up the coating from the pan and transfers it to the web contacting the roll's top surface. The web usually has minimal wrap on the roll's surface, typically between 5° and 20°. The roll is driven and may rotate in the same direction as the web, splitting the coating between the roll and the web, or in the opposite direction, fully transferring the coating to the web. Entry and exit idler rolls contour the web around the coating roll. The coating pan is usually vertically adjustable.

Various factors influence the amount of coating transferred to the web, including the coating adhering to the roll's surface, roll speed, web speed, web tension, web wrap angle, and web surface characteristics. Table 1 below lists the typical operating speeds, coating application rates, and coating viscosity for a kiss coater.

Due to numerous factors affecting coating accuracy, kiss coaters are commonly used alongside other methods to meter the applied coating. This can be achieved either before the coating is applied to the web, typically by metering the coating on the kiss roll with a roll or knife, or after the coating has been applied to the web, by passing the coated side of the web over a mayer rod, in front of an air knife, or between a set of metering rolls (Photo 1).

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The kiss coater is relatively inexpensive, easy to maintain and operate. It also facilitates quick changeovers between coatings, especially if designed with interchangeable pans. Although it has a limited range of coating laydown, changing coating weights within that range is straightforward. However, due to several conditions affecting laydown rate, it lacks high repeatability and has a limited viscosity range and maximum speed.

SQUEEZE ROLL COATER

This coater type features two rolls that meet at a controlled pressure. Typically, one roll has a steel surface (often chrome-plated), and the other has a rubber surface. The web usually passes between the rolls in a straight line, with coating applied at the nip formed between the rolls. Often, the rolls are configured vertically, with the bottom roll made of steel and sitting in a pan containing the coating, similar to the kiss coater (Figure 2). As the bottom roll rotates, it delivers coating to the nip, transferring some of it to the web. Rolls may also be configured horizontally, with the web traveling between them from top to bottom and the coating held in a puddle between the rolls.

The amount of coating transferred to the web depends on several factors, including the web material, coating viscosity, and web surface, and can be controlled by adjusting the steel roll's speed relative to the web speed and the pressure between the rolls.

Table 2 below shows the typical operating speeds, coating application rates, and coating viscosity for a two-roll squeeze coater.

A variation of this coater uses two precision steel rolls to form the nip (Photo 2). Here, the transferred coating amount is controlled by the gap between the rolls as the web passes through. In this setup, the coating thickness and viscosity can be much higher than those indicated in Table 2.

The squeeze coater is also relatively inexpensive, easy to maintain and operate, and offers a good speed range. It also supports quick changeovers between coatings, especially if designed with interchangeable pans. Though it has a limited coating laydown range, changing coating weights within that range is easy. Despite several factors affecting the application rate, it can be easily controlled. However, it is limited in its viscosity range.

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*That concludes part 2 of our 4-part blog series, "An overview of Roll Coating Methods, Capabilities, and Limitations." To go back and read part 1, click here, or to move ahead and read part 3, click here. Click here for the 4th and final part!*

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