Wax has long been used throughout history for a wide number of applications, from makeup cosmetics and candle-making to cheese wraps and gum manufacturing. It is also used in the earliest converting applications!
Wax is hydrophobic and resists water penetration. Many cultures from Asia, the Middle East and medieval Europe would protect the paper or papyrus writings with a light wax coating from degradation due to humidity. They may not have realized it, but they were performing one of the earliest examples of wax converting applications.
Today, polyethylene and polypropylene waxes are commonly used as moisture barriers for paper cups and plates, corrugated boxes and other applications due to their low cost and high performance.
Wax can be applied via a melting machine with doctor blade or other, or as a water-based carrier solution that is dried, allowing for wax solid deposition. The wax coating serves as a water barrier and may also be infused with mold inhibitors or other additives in the solution phase. Converters can control the flow rate, web speed and other parameters to reach set point.
The MCT series of NIR stand-alone transmitters are usually mounted in the center of the web or in series on the left, right and center of the web. This is of great value to the converter; however, it doesn’t cover the complete web making it difficult to discern if a hot melter zone or doctor blade needs orientation or a roller requires skew or gap adjustment, for example. Similarly, if dirt or specks of coating attach to the roll in places where the web isn’t being monitored, streaking can result.
The Guardian Cross Direction Web Profile System supplies a cross direction zoned web profile and machine direction trend for system operation. The color-coded CD profile visually displays in-spec product as green zones, alerts in yellow and red alarms. This is often connected to a color-coded Stack Light with annunciator to alert the operator when a product is in the alarm condition. Machine Direction Trends allows troublesome zones to be diagnosed and corrected.
The Profile System or fixed-point transmitter is usually mounted on the wet end at an angle of 15–20 degrees off the normal, 6–16 inches from the web. The system is calibrated in engineering units such as GSM or mils thickness based on the fixed liquid solids ratio of the coating.
Wax is a strong NIR absorber, so implementation of NIR technology to measure wax coating thickness can help speed start up, increase production, reduce scrap and allow for data archiving by roll or run. Without an on-line measurement system, the line must be started up, a sample collected for laboratory analysis, the system optimized, and it started up again with another sample collected to confirm the optimization. With an on-line system this process is streamlined resulting in much greater efficiency. The data archiving, whether from fixed or scanning transmitters via Ethernet communications, protects against customer complaints and allows data histories to be associated with modifications to unit operations or work shifts.
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Accurate moisture, coat weight and film thickness profiles for process control in even the most difficult converting applications
Reliable cross direction web profiling for process control in converting applications
Reliable in-process monitoring of multiple constituents for improved process control, increased yield and maximum production efficiency