Spray-Coating of Dow Corning CI-2001 White Reflective Coating Application Bulletin Dow Corning Material Description Dow Corning CI-2001 White Reflective Coating is a highly reflective optical coating that delivers good resistance to environmental aging and enhances LED light output and efficiency. It is a room-temperature-vulcanizing (RTV), solventborne, elastoplastic resin. Key features of this advanced material include: Performance targeting high (96%) reflectance at 5-mil coating thickness and 94% reflectance at 3-mil coating thickness One-component formulation offers simple room-temperature cure that can be accelerated with heat for higher productivity Applies easily by spraying, dipping, brushing or flowing After cure, forms a tough, resilient coating with a nontacky surface Reliable, long-lasting performance between -45 and 200 C (-49 and 392 F) Less than 50 g/l of nonexempt VOC content Adjustable viscosity using VOC-exempt, SNAP-approved, low-odor, lowtoxicity (200 ppm IHG) Dow Corning OS-20 Fluid and other silicone diluents Good electrical properties over a wide temperature range Recognized under UL flammability rating UL-V0 Uses Dow Corning CI-2001 White Reflective Coating is used as a bright-white reflective coating to enhance light output and efficiency for light reflectors, mixing chambers, backlight units, light engine units, printed circuit boards and aluminum surfaces used in assembly of LED lamps and luminaires.
Dilution Dow Corning CI-2001 White Reflective Coating can be diluted as needed for use in specified coating methods. An ozone-safe (OS) diluent, such as Dow Corning OS-20 Fluid, may be one of the best options to lower the coating s viscosity. The following graph shows the correlation between Dow Corning CI-2001 White Reflective Coating s relative viscosity and the amount of Dow Corning OS-20 Fluid added. Example: A 5% ratio of Dow Corning OS-20 Fluid drops the viscosity of Dow Corning CI-2001 White Reflective Coating by approximately 60%. Dow Corning CI-2001 White Reflective Coating relative viscosity 100% 0% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0% 5% 10% 15% 20% 25% Dow Corning OS-20 Fluid added Cure Dow Corning CI-2001 White Reflective Coating cures upon contact with ambient moisture. Cure time depends on the method of application, film thickness, temperature and humidity. Generally, films less than 5 mils in thickness will be tack-free in under 20 minutes at 25 C (77 F) and greater than 30% relative humidity. Under these conditions, final cure will typically be achieved in 48 hours. Tack-free and cure times can be shortened significantly by introducing heat up to 60 C (140 F) and 70% relative humidity. Cracks may occur if the coating is exposed to cold temperatures or thermal cycling before adequate cure has developed. A typical cure schedule for a 3-mil coating is 10 minutes at room temperature followed by 10 minutes at 60 C (140 F). If the coating bubbles, allow additional time at room temperature for the solvent to evaporate prior to oven cure. Adhesion Dow Corning CI-2001 White Reflective Coating adheres to most electronic substrates in one to seven days, depending on processing conditions. Mild heating shortens the time to build adhesion and, in some cases, can improve full adhesion on difficult substrates. The coating achieves ISO Class: 0 and ASTM Class: 5B adhesion on aluminum, steel, FR4, polymethyl methacrylate and polycarbonate substrates. Pot Life The pot life of Dow Corning CI-2001 White Reflective Coating depends on the conditions under which it is processed. Dry nitrogen or other dry blanketing can extend pot life. Dilution using reactive solvents, such as alcohol or solvents containing water, will reduce shelf and pot life.
Application Methods and Equipment Options Application methods Dow Corning CI-2001 White Reflective Coating is compatible with multiple application methods, including spray, brush, flow and automated pattern-coating. Production volume, complexity, selectivity, budget, space and ease of use are among the factors that help determine which method is most productive and cost-effective. Manual spray-coating is one of the most common processing options for evenly coating substrates. While simple to use, this method also can lead to a highly variable application plagued by operational discrepancies, undesired results and waste. However, a proper understanding of manual spraying will result in reliable processing with very repeatable results and optimal efficiency. Manual spray-coating normally is used when low investment in equipment is required or when coating different boards in progression or simultaneously. The equipment usually costs less than $1,000 USD and is easy to acquire, set up, process, clean up and store. Manual spray-coating is most effective on substrates with low masking or other specifications. After initial set-up, operating and maintenance costs and time requirements are low, making this processing option ideal for low to mid-size production runs. Getting the most productivity from manual spray-coating also involves considerations such as equipment selection, available materials, application methods and maintenance practices. Equipment Options for spray-coating include manual (hand-spray) tools or automated for application. Automated spraying is desirable for flat substrates like LED boards, and it can do very precise coating. However, it requires a larger initial investment and can be limited by the shape of the target sample. Handheld spray guns are the more popular option for steady high-volume production, but they may require extra equipment and a wider work area. High-volume manual spraying also can result in high material waste and higher variation, and it may require additional masking prior to spraying. It also requires safeguards such as exhaust systems to control unwanted small particles and VOC emissions. There are multiple options for manual spray-coating as well as several types of spray guns. These include air, airless and air-assisted airless guns; conventional or high-volume low-pressure (HVLP); and one-, two- or three-step trigger mechanisms. Multiple brands are available. Most of the necessary equipment can be purchased online or from hardware stores. No prior expertise or specialized tooling is required for equipment assembly. A complete setup will consist of a compressor or access to a pressurized air line (commonly available in many electronics-manufacturing settings); a water trap, dryer and air regulator; and the spray gun itself. After use, the gun should be disassembled for cleanup or maintenance, which also is a simple process. Spray guns operate by a simple process: The liquid material and air are fed to the gun from different passages and then mixed at the cap in a controlled pattern. The amount of material discharged from the spray gun depends upon the material s viscosity and fluid pressure as well as the size of the fluid orifice opening provided when the needle is unseated from the tip. Fluid tips are available in a variety of sizes to properly handle various types of materials, flow rates and viscosity.
Application Procedure linear paths across the sample with a flexible wrist. Hold the gun at least 6 inches away from the edge of the sample Dry coating thicknesses of 3 to 5 mils will achieve desired to be coated. As the gun reaches approximately 1 inch reflectance. Following are guidelines for coating viscosity from the sample s edge, further depressing the trigger will at approximately 500 cp: begin the application process, and the operator should Air cap: 58 Fluid pressure: 10-20 psig continue the movement across the sample at a steady Fluid tip: AV-2115-FX 15-FX Supply pressure: 40 psig dry air speed. Approximately 1 inch after reaching the end of the Fluid needle: JGA-402-FX Coating distance: 9-12 inches target, the trigger pressure should be reduced until only air is expelled from the gun, while maintaining the speed Notes on application of the gun movement for at least 5 more inches. This last step should keep the gun clean from accumulated coating. The above information is based on lab testing only. To ensure uniform line-of-sight coating coverage, rotating Accessories of the spray-coating system, such as the the target on a turntable at 90-degree intervals between fluid tip and needle, also are referred by DeVilbiss. coats is recommended. It is important to flush the fluid delivery system with an inserting fluid, such as Dow Corning OS-20 Fluid, Before coating the sample, first test the spray pattern on prior to the introduction of the coating. paper to determine the best distance and speed combination. Using the spray adjustment skews will Failure to adequately remove moisture from the achieve the best coverage and finish. Masking off process lines will result in gel formation in the coating. connectors and other areas is critical. Extensive shutdowns should have no effect, as long as the fluid system is sealed and free of air or As a rule of thumb, prior to application, operators also moisture. In addition, air pressure should be turned should test the spray application at a distance of 9 to off during shutdown. 12 inches between the gun tip and target at a speed of approximately 12 inches per second. It is important to When using a spray gun, the air cap, fluid tip, needle and keep the gun moving at a consistent distance from the baffle should be selected as a complete unit, since they all sample. Novice users often arc the movement of the work together to determine the quality of the spray pattern gun by keeping their wrist locked in a fixed position, and finish. These four items are usually referred to as which tends to cause an uneven coating that is thicker the nozzle combination. The gun supplier may suggest the in the middle and thinner on the edges and can prevent best combination for the viscosity of the selected product. the coating from being correctly dispensed close to tall Typical HVLP or low-volume, medium-pressure (LVMP) components. Arcing can be prevented by relaxing the systems, for example, would use a 0.055 t o 0.070 or ifice upper body and keeping the wrist flexible, while steadily size, depending on the application speed required. If moving the spray gun across the sample. using a DeVilbiss gun, a good starting point is an FX tip, a 0.0425 needle and a 58 cap; for a Binks gun, start with For a steady spray-coating process, even for a 100% cap 66SD, fluid tip 66SS and a 565 needle. solid coating, a spray booth equipped with extraction equipment is necessary. This can prevent the spray- Before beginning the coating process, the operator should coating from reaching other areas and, for solvent-based spray a horizontal test pattern with the air cap in vertical coatings, should prevent the solvent from contaminating position, then hold the trigger open until material begins the production floor. Spray booths may be acquired or to run. If the material is not evenly distributed, adjust the self-assembled at a relatively low cost. The use of a pattern width. For air guns, optimum fluid pressures are 8 rotating turntable can be helpful in ensuring even and to 20 psi. Pressures greater than this generally indicate the uniform coverage by rotating the spray direction between need for a larger fluid tip. coats at least four times at 90-degree intervals. If possible, a two-step (also called double-action trigger) spray gun is recommended. Slight pressure on the trigger provides air through the gun, while additional pressure releases both coating and air. To apply, spray straight To reach difficult spots blocked by tall components and components that are aligned on the sample shadow, positioning samples so they are perpendicular to the spray gun movement is recommended.
Maintenance To keep the spray gun operating at optimal capacity, remove the air cap and clean it with solvent after every use. To remove silicone coatings, an ozone-safe (OS) fluid may be the best option. Dow Corning OS-10 Fluid or Dow Corning OS-20 Fluid will remove the silicone residue faster and will evaporate more quickly than Dow Corning OS-30 Fluid. A bristle brush can help clean the sprayer components. Never use metal objects for cleaning. It may be necessary to soak the individual parts in a solvent, but use caution with seals and O-rings, as these have a tendency to swell. Learn More Dow Corning has sales offices and manufacturing sites, as well as science and technology laboratories, around the globe. For more information, please email electronics@dowcorning.com or visit dowcorning.com/contactus. If the spray gun is flushed well, it may not be necessary to disassemble it for cleaning. Remove the cup from the gun if a pressure pot is not used. Empty any excess material and wipe it out with a cloth. Fill the cup with solvent, reassemble the gun and spray the solvent into a container. Next, remove the cap, fluid tip and fluid needle and clean them with solvent. Then, remove the cup, wipe it out and reassemble the gun. Spray air through the system for a few seconds to dry and clean the gun. For companies that understand these factors, manual spraycoating can be a productive and highly cost-effective solution for applying protective coatings to samples.
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