Water-based or dispersion coatings emerged in the 1980’s and came to dominate the industry in the ‘90s thereafter.
Previously, solvent-based coatings offered superior performance characteristics in the manufacturing of tags, tapes and labels. As the regulatory costs of using solvents grew in the 70’s and 80’s, development of water-based adhesive products intensified. Now water-based solutions meet 80% or more of application needs.
Coatings are often named for the solids being deposited such as acrylic or latex. The formulation may also include performance additives and pigments.
During the application process, water-based adhesives of a particular coating formulation are applied to a substrate then the water is dried off causing the organic solids to form a bond with the substrate. The coating can be applied via roll, air knife, doctor blade, disk or other technique. The drying will typically be air flow or infrared, leaving the coating deposition on the substrate.
Implementation of a Process Sensors Corporation Guardian Web Profiling System or NIR Smart Sensor for water-based adhesive measurement provides instant coating thickness measurement which speeds start up, increases production output, reduces scrap and allows for data archiving by roll or production run for traceability.
Water-based coat weight can be precisely measured with NIR sensors.
The Guardian and Guardian-HD NIR Web Profiling Systems from Process Sensors provide a zoned, cross-direction, web coating profile and machine direction trend measurements. The color-coded web profile visually displays in-spec product as green zones, alerts in yellow and alarms in red. This is often connected to a color-coded stack light alarm with annunciator to alert the operator when the product is out of specification or trending out of specification. Machine direction trends allow troublesome zones to be diagnosed and corrected.
Fixed NIR Smart Sensors from Process Sensors can also be used to monitor and control adhesive coat weight. Fixed sensors are typically mounted in the center of the web or in series on the left, right and center of the web. This arrangement allows for control of the coating process but it does not monitor the entire width of the web. If a steam valve or disk rotation falters and it’s not in scanning window of a fixed transmitter, it will not be detected. Similarly, if dirt or specks of coating attach to the roll in places where the web isn’t being monitored, streaking may result.
Guardian systems and NIR Smart Sensors are usually mounted on the wet end at an angle of 15-20⁰ from perpendicular at a distance of 6-16” from the web. The system is calibrated in engineering units such as GSM (grams per square meter) or mils thickness based on the liquid to solids ratio of the coating.
Alternatively, the systems may be mounted on the dry end and measure the solid deposition. The installation location choice is based on available space and process control scheme. Process Sensors Application Specialists are ready to discuss your best application solutions.
Without an on-line measurement system, the line must be started, a sample collected and sent to the factory laboratory for analysis, then system adjustments can be done. This manual process is then repeated until the line is running efficiently. With an on-line system this process is done in real-time resulting in increased efficiency and cost savings. Throughout the coating process, an NIR sensor immediately identifies out-of-spec product to minimize the over-application of expensive raw materials and reduce scrap.
Data archiving via Ethernet allows production lots to be associated with modifications to unit operations, setups, operators or work shifts, for quality control purposes.
To learn more about how an on-line NIR analyzer can optimize your converting operation, please fill out the contact form below.
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