By Giancarlo Caimmi, Ph.D., commercial director, Nordmeccanica Group, and Chris Vierra, principal product line manager, Nordson Measurement & Control Solutions

In industries such as flexible packaging, pharmaceuticals, batteries, solar panels and electronics, the converting industry has undergone significant growth, driven by technology advances and substrate advantages. Laminators and coaters have improved, making processes faster and easier to manage while also improving the safety of the equipment. The growing performance of the equipment has necessitated a parallel growth in the technologies that support process handling by offering reliable monitoring of process variables.

The converting industry for flexible substrates has gone through significant growth during the past 30 years, driven by the numerous advantages these substrates offer. These include low energy consumption during processes, reduced transport costs and technological benefits compared to alternative methods. In the conversion process, the availability of high-performance adhesives for lamination and functional coatings, which enhance the mechanical and chemical properties of laminated compounds, offered another important incentive to the growth of market share. All of the above, combined with other factors such as low conversion costs, low emissions and low environmental impact, further have solidified the dominance of converted flexible substrates in various markets. Industries such as flexible packaging, pharmaceuticals, batteries, solar panels and electronics utilize these products in large quantities. The growth of technology went hand-in-hand with the evolution and innovation recorded in the machinery industry serving flexible substrates converting.

Extruders for flexible substrates, printing presses, laminators, coaters, metallizers, slitters and bag-makers evolved in all aspects. Improvements included increased productivity, output quality, safety, reliability, user-friendliness, reduced emissions, energy consumption savings and reduced scrap. It is a matter of evolution.

Laminators and coaters have been no exception. To the contrary, the importance of that hardware within the converting process motivated a fast and constant evolution. New coatings and laminating techniques have emerged, making processes faster and easier to manage while also improving the safety of equipment. The number of patents filed is countless, to the point that the hardware design, in consideration of the evolution, required close collaboration between all members of the value chain. No more an ivory tower innovation, these advances are the fruit of collaborations that perfect machine design in tandem with the evolution of other connected technologies. Among the many aspects of innovation and evolution in machine design, this article will focus on process management in coating and lamination.

Coating equipment evolves

The growing performance of the equipment has necessitated a parallel growth in the technologies that support process handling by offering reliable monitoring of process variables.

Both the coating and the lamination industries involve the deposition of a chemical compound in a fluid state onto a substrate. The large variety of applications required the development of numerous technologies for the deposition of coated compounds in compliance with the rheological requirements of various chemical products. In simpler terms, several coating heads have been introduced and developed, each one designed for a specific application. Examples of this include rotogravure, flexo, offset gravure, post-metered, five-roller systems and slot-die, among others.

All of the mentioned technologies aim to deposit a specific amount of a coated compound, introducing the concept of coating weight. Coating weight represents the amount of product layered on a substrate expressed per unit of surface area. In imperial measurements, it is represented as pounds per ream, while in metric measurements, it is expressed as grams per sq meter, or gsm.

Sensor monitoring for converting

While coating technology has been evolving uninterruptedly, providing better accuracy, better reliability and better operator experience, the monitoring technology of the coating weight also needed to evolve to keep pace. This is a challenging task due to the nature of the substances being monitored, which can exist in various chemical and physical states, not to mention the very fine thickness of the coated compound in most converting applications. Over the decades, the technology of sensors and monitoring devices consequently has evolved in parallel with the converting industry. The evolution of that segment of the industry required consistent investment and the involvement of large corporations. As a result, sensors and monitoring devices have transformed from large, expensive units into today’s compact and affordable technology.

In the 1960s, a company in the UK, part of an American corporation (and where one of the authors of this article currently works), developed an innovative approach to sensor technology for the converting industry. Many readers may be familiar with a laboratory instrument that is used to measure the concentration of specific molecules within chemical compounds. For decades, infrared- (IR) based instrumentation has been widely used in laboratories around the world to quantify the presence of certain molecules dispersed in the chemical compounds.

One significant advancement was the application of infrared technology to monitor coating weight and other variables during the coating-laminating process. Since the 1960s, IR-based devices have sold in tens of thousands for onboard process-related measurements.

Infrared technology

The principle behind IR technology is that matter interacts with infrared radiation, allowing the instrument to identify chemical substances or functional groups. When calibrated to a specific wavelength, the instrument becomes sensitive to a particular chemical target, enabling accurate measurement of the quantity of that specific target per unit of volume.

Within a chemical formulation, a specific molecule is present in exact quantity per unit of volume of the compound. By measuring the amount of this molecule, given the fixed ratio within the compound, one can calculate the total quantity of the compound, expressed in units of volume.

Now consider the specific case of a converting process when a web of a given width is running through the line. To determine the coating weight, the volume (mass) of the compound measured by an instrument needs to be related to the total surface area that the compound is coated on. The surface area is the combination of web width and the length of the material produced, both of which are known variables. Once the instrument measures the volume of the coated compound, the coating weight can be calculated, which is the volume per unit of surface area.

Monitoring NCOs

Since the early days, the practical applications of IR sensors to monitor production processes have been numerous – truly in the tens of thousands. In the case of the converting industry, the focus has been on monitoring the amount of isocyanate molecules (NCO) within a coated compound. NCO is found in many chemical formulations for adhesives and coatings, making it an ideal choice for measurement.

The ability to detect, with great accuracy, isocyanate content within a chemical formulation gave the possibility to precisely measure the coating weight, both in the laboratory and on the production floor. As a result, commercial products have been developed and made available to the industry.

Solventless adhesives are chemically cured by mixing two components. The isocyanate molecule is part of the formulation of one of these components. With all variables known (including the NCO content in the first component and the mixing ratio), it becomes possible to monitor effectively the coating weight.

Nevertheless, since the beginning, it was understood that many variables influence the outcome of sensor readings. The variation in NCO count is not solely connected to changes in coating weight. For instance, variations in the mixing ratio, often due to issues with the mixer dispenser, can alter the NCO readings. As a result, this may cause the instrument to provide a false evaluation of the coating weight. Additionally, the polymerization of solventless adhesive – transitioning from a fluid state to a solid – affects the NCO count. A freshly mixed adhesive shows a higher NCO count when compared to an adhesive that has been coated just minutes after mixing.

So, if the instrument reports an inconsistent count of NCO, it is impossible to determine the cause without further investigation. While the sensor can serve as a useful alert for inconsistencies, it is not a diagnostic instrument for identifying underlying issues. This situation can lead some commercial companies to market these devices as the ultimate solution for process monitoring when, in reality, they serve only as general alert systems that require further analysis.

In fact, the innovation recently presented was driven by a commitment to provide the industry with an effective process monitoring and process handling device (see Figure 1). To achieve this, two companies combined their expertise: one specializing in IR instrumentation and the other in coating and lamination technologies. If the reading of the instrument is reliable, it is possible to use it not only to adjust the coating weight in response to variations, but, more prominently, to precisely set up the coating weight at the beginning of a lamination job, all in full automation.

Sensor development

Here is the format used by the two companies involved in the innovation: The instrument, mounted on the machine, delivers reliable readings, with output data transmitted to the onboard PC of the coater or laminator, controlled by the OEM (see Figure 2). The PC uses incoming data to determine the necessary adjustments. All setting variations on the equipment are calculated and implemented exclusively through algorithms developed by the OEM. This ensures that no third parties can interfere with machine functions, thus maintaining compliance with OEM safety protocols and mitigating risks of potential incidents, liability issues and voided warranties.

The sensor has been developed using technology that allows it to measure not only isocyanates (NCO) but also to continuously and simultaneously measure two other functional chemical groups: hydroxyls (OH) and hydrocarbons (CH). These chemical groups can be measured individually or in combination to enhance measurement capabilities and precision.

As mentioned above, the NCO count can be influenced by the degree of cure and the performance of the mixing dispenser. Therefore, this measurement should be regarded as “inferred,” and certain precautions should be taken. Accurate mixing is crucial, especially in the case of solventless adhesives, as it directly affects the reliability of NCO measurements when determining adhesive weight. To address this, the mixer manufactured by the laminator OEM is integrated with online measurement into a single user interface that also includes coating weight control.

When combined with NCO, OH can provide insights into mixing ratios for specific substrates. This capability gives laminators a better understanding of the mixing process, helping to avoid errors in lamination. Moreover, CH measurements offer superior precision for adhesive weight on reflective substrates, reducing reliance on the “inferred” measurements associated with NCO. Lastly, modern coating and laminating lines increasingly are flexible regarding the types of coatings they can apply. They can switch between PU-based adhesives and barrier or functional coatings simply by changing the coating trolley. In this setup, OH measurements allow for the monitoring and control of functional barrier coatings on the same line with the same measurement device, which adds simplicity, efficiency and economic benefits.

One significant advantage of this technology is that it allows for a one-time calibration of each adhesive in terms of adhesive weight and mixing ratio throughout the sensor’s lifespan. This process saves time and enhances machine efficiency when starting new production runs. Additionally, calibration performed on Machine A can be easily replicated on Machine B within the same production site, leading to further savings in both time and materials for each installation.

The continuous monitoring capability of this technology facilitates precise weight control on the machine, enabling production to start immediately after setup. This results in considerable improvements in coating weight consistency and material savings, both in terms of adhesive usage and reducing out-of-spec materials, that can cause significant economic losses for converters.

Combining accurate and repeatable measurements with stringent machine controls will yield excellent performance in both machine operation and overall production, driving ongoing economic savings during use and ensuring a swift return on investment for new equipment.

Conclusion

In conclusion, the claim is that a process monitoring system finally has evolved reliably into a process managing system – a process that is not limited to solventless lamination but may cover water- and solvent-based adhesives, as well as functional coatings, from job setup to process handling in coating and laminating jobs for most applications. The process monitoring system is exclusive for installations on coaters and laminators manufactured by the company the author is working for. Since the unveiling of the innovation at drupa 2024 (see Figure 3), the system has been sold both as installed at the factory on new machinery and as a retrofit on existing installations. Results, in all cases, have exceeded customer expectations both in reliability and accuracy. Improvements in uptime and reduction in process scrap have been confirmed by users that reported a faster than expected ROI.

In the converting industry, this innovation is a significant step in the direction of simplifying process handling for operators. A large share of the operator responsibility is moved onto a system that takes care not only to assure consistency in quality for the most important variables in a coating and laminating job, but also achieves significant advantages in productivity and cost reduction. 

Giancarlo Caimmi, commercial director for Nordmeccanica USA Group (Hauppauge, NY), holds a Ph.D., in Mechanical Engineering from University Federico Secondo (Italy). He has almost 40 years of experience in the converting-machinery manufacturing field. Giancarlo can be reached at 631-242-9898, email: caimmi@nordmeccanica.com, www.nordmeccanica.com.