PFFC - November 2008 - (Page 34)

WEB COATING products. In addition, the fundamental mechanisms of the key coating process subsystems continually have been developed and have resulted in the identification of additional process variables to be measured. Use of this new technology will improve process performance and economics significantly. The majority of the necessary process measurements can be made with conventional, commercially available instrumentation, such as thermometers and infrared (IR) thermometers for temperature, velometers for air velocity, speed sensors for line speed, footage counters, viscometers, coating weight measurement devices, etc. However, some characterizations still are subjective, such as substrate roll condition, substrate planarity, and coater roll surface quality. As a result, visual analysis is still a very important characterization method. The figure to the right shows the major subsystems that need to be characterized. Raw Materials �� Optional Components u IR Dryer u UV Cure u Lamination �� Raw material measurements are needed to ensure all compounds have the desired purity and they are the correct compounds. Product performance can be very sensitive to the quality of the coating solution and the substrate. Several instruments can be used to characterize raw materials’ chemical and thermal properties. The most versatile methods for purity and composition are IR and ultraviolet (UV) spectroscopy, atomic absorption, gas chromatography, and scanning electron microscopy (SEM) with energy-dispersive X-ray analysis. Thermal analysis techniques can be used to determine transition temperatures and purity levels. The exact tests and specification will depend on your product needs. If the vendors are ISO certified, then their test results can be used. However, some key properties occasionally should be taken to verify vendor results. The properties of the substrate are critical to ensure good coating quality and product performance. The substrate needs to be uniformly wetted and free of contamination to give a uniform wet coating. Also, the coating solution must adhere to the substrate. A defective substrate will cause yield loss and cannot be corrected by any of the process in the web coating line. Following are the key substrate properties that need to be measured: u Uniform thickness in machine direction �� doctoring process in which the distance from blade to substrate determines final coating weight; u Planarity of the substrate—it should have good planarity and not curl, otherwise it may get damaged in the coating applicator or in the dryer; u Quality of uncoated substrate roll— it should have straight sides and no telescoping; u Contamination level in the substrate; u Transition temperatures—Tg (glass transition temperature), Tm (melting temperature), and Td (temperature difference); u Location in master roll if substrate is slit before coating; u Surface wettability and adhesion; u Identification of the side to be coated; u Surface roughness. u The correct raw materials added in the proper level and at the right addition points; u Batch size; u Mixing time and temperature profile; u Agitator speed; u Solution/dispersion properties—percent solids, pH, particle size, purity; u Viscosity, surface tension, and contact angle; u Special performance properties; u Correct filter type and size— monitoring filter pressure to ensure filter is functional; u Storage conditions of solution if not coated immediately after preparation; u Cleanliness of kettles and transfer lines. Solution Delivery (MD) and transverse direction (TD), which is particularly important in a Typically, a separate feed system is used to supply a uniform coating solution to Solution Preparation and Characterization the coating applicator. Key variables for The coating solution properties need this process are as follows: to be measured to ensure there will be excellent coating quality and no coating u Pump speed and flow rates to applicator; defects. These are the important proper- u Recycle flow rate and line location; ties to characterize in the mixing process: u Consumption rates; WWW.PFFC-ONLINE.COM 34 | NOVEMBER 2008 http://WWW.PFFC-ONLINE.COM

Table of Contents Feed for the Digital Edition of PFFC - November 2008

PFFC - November 2008 Contents First Glance Calendar of Events From the Editor Web Lines Process Management News Clips Narrow Web & Label Reporter Narrow Web & Label: What’s New Products TLMI Awards Card Making Web Coating Ink Dispensing Lab/Pilot/Technical Facilities Directory Testing & Measuring Products What’s New Products Services Directory Classified Marketplace Advertisers Index Experience Speaks

PFFC - November 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.