CHO-SHIELD 2001 is a light brown coating that contains soluble chromate
Parker Chomerics’ CHO-SHIELD® 2000 Series electrically conductive coatings provide a corrosion resistant conductive surface coating on aluminum or composite substrates. By reducing moisture penetration, CHO-SHIELD 2000 Series coatings offer corrosion protection for enclosure flanges which mate with particular EMI shielding gaskets. These tough, urethane coatings offer a highly conductive interface which improves overall EMI shielding performance. When used as a coating on a composite or other non-conductive surface, they provide the conductivity necessary to achieve excellent shielding effectiveness while maintaining their electrical and mechanical stability in hostile environments. CHO-SHIELD 2000-series coatings are three part, copper-filled urethane coating systems which have been formulated with special additives and stabilizers to maintain their electrical stability, even at elevated temperatures, which prevent aluminum surfaces from corroding in high humidity and/or marine environments.
Design Considerations:Flange design and surface preparation have significant impact on the corrosion resistance offered by the CHO-SHIELD 2000-series of coatings. All three coatings best adhere to MILDTL- 5541, Type 1, Class 3 treated aluminum and most plastics and composites. Chomerics provides CHO-SHIELD 1091 primer for enhancing the adhesion of CHO-SHIELD 2000-series coatings on all substrates. Chomerics’ Applications Department will also provide assistance with your design and material requirements. CORROSION RESISTANT FLANGE DESIGN WITH CHO-SEAL® 1298 CONDUCTIVE ELASTOMER, EMI SHIELDING GASKETS The combination of the CHO-SHIELD 2000 series of conductive flange coatings and CHOSEAL 1298 conductive elastomer gaskets can form a virtual corrosion resistant EMI sealing system for passivated aluminum enclosures. CHO-SEAL 1298 is a fluorosilicone elastomer filled with silver plated aluminum filler. Figure 1 shows this application for an aluminum enclosure. First, the aluminum flange is typically treated with a MIL-DTL-5541, Type I, Class 3, hexavalent chromate treatment, or alternatively with Type II, Class 3, trivalent, chromate corrosion treatment. After first applying the CHOSHIELD 1091 primer to ensure adhesion, the CHO-SEAL 2000 series coating is applied according to the instructions contained in this document to mask the flange area for the EMI gasket landing area. The CHO-SHIELD 2000 coating is then masked while the non-conductive topcoat is applied to the aluminum enclosure. However, note that the topcoat must be overlapped onto the CHO-SHIELD coating as shown in Figure 1 to ensure that the CHOSHIELD coating and aluminum interface is not exposed to moisture that could intrude under the coating. Note also in that when choosing a topcoat, that that the maximum temperature for the CHO-SHIELD 2000 coatings is 185°F (85ºC).
Features and Benefits
- Urethane binder provides exceptional physical properties such as hardness and adhesion.
- Excellent chemical resistance, including jet fuel (JP8), hydraulic fluids and motor oil.
- High abrasion resistance even after jet fuel immersion.
- Excellent coating hardness and scratch resistance.
- Significantly more cost effective than silver-filled epoxies.
- No degradation of shielding effectiveness after 500 hours of salt fog.
- Pre-measured kits allow easy mixing of components in one container.
ApplicationSurface preparation has a significant impact on the corrosion resistance offered by the CHO-SHIELD 2000-series of coatings. CHOSHIELD 1091 primer should be used to ensure good adhesion of CHO-SHIELD 2000-series coatings on all substrates. CHO-SHIELD 1091 primer is a one-component, air-drying system, which cures at ambient temperatures.
Recommended Surface Preparation
- Clean the substrate: The substrate surface should be clean, dry and free of oils, release agents, dirt and lint. Clean surfaces to be painted with methyl ethyl ketone (MEK) for aluminum or isopropyl alcohol/ethanol for solvent sensitive substrates. Let the substrate air dry for 15 minutes.
- Apply CHO-SHIELD 1091 primer: Wet a lint-free cotton cloth with CHOSHIELD 1091 primer. Apply primer to the surface in horizontal and vertical strokes. Keep the surface wet at all times. After the entire surface has been coated, air-dry at room temperature for 1 hour or at 190°F (88°C) for 30 minutes.Note: If primed surfaces are not coated within 4 hours of the primer application, repeat the cleaning and primer application procedures before coating. To eliminate the risk of an increase in surface resistance, only a light coating of the primer is recommended, typically less than one mil thick when cured.CHO-SHIELD 1091 is provided with selected kits of CHO-SHIELD 2003. It is not provided with any kits of CHO-SHIELD 2001 or 2002 and must be purchased separately.
- Mix the material: Mix the CHO-SHIELD 2000 series coating according to the weight mix ration in the Properties tab. Combine Part A and Part C. Weigh the components if the entire kit is not to be used. Shake on a paint shaker for 3 minutes. Check the homogeneity of the mixture by feeling the sides and bottom of the container with a spatula to assure all the filler and resin are well dispersed.Note: If the coating mixture is not homogeneous, shake for an additional 3 minutes and check for non-dispersed material. DO NOT screen or filter the mixed coating. Add the Part B. Shake or mix for an additional 3 minutes.
Wet Coating Painting System OptionsUse a pressure pot (20 psi (138 kPa) typical) with large diameter, paddle-type agitator at low mixing speed to keep the metal fillers in uniform suspension. Conventional spray equipment such as HVLP (High Volume, Low Pressure) or LVMP ( Low Volume Medium Pressure) all work well with CHO-SHIELD 2000 series coatings. Binks SD-2 with propeller agitator pressure pots may be used for spray application with approximately 20-50 psi (138-345 kPa) atomizing air. Use lowest pressure possible. Re-circulation of the paint from the mixing pot through the spray gun and back via a pump delivery system is recommended for greater filler uniformity. For large volume applications, a robotic spray system with an HVLP spray gun should be used to minimize material loss due to overspray and maximize paint transfer efficiency. Siphon or gravity feed equipment can be used for small or prototype runs.
Spray Gun and Pressure Painting System OptionUse a standard air gun with approximately 20-50 psi (138-345 kPa) atomizing air. A fluid nozzle with an orifice diameter of 0.040 to 0.070 inch (1.016 to 1.778 mm) is recommended. To obtain maximum adhesion and conductivity, dry spraying should be avoided. Adjust the spray pressure to achieve a proper wet film.
Nominal Dry Film ThicknessA nominal dry film thickness of between 0.003 inches (0.076 mm, 3 mils) and 0.005 inches (0.127 mm, 5 mils) is recommended to obtain typical shielding effectiveness from 80 MHz to 10 GHz and corrosion protection published by Chomerics. Curing Conditions The CHO-SHIELD 2000 Series coatings may be cured using one of the following cure schedules:
- Cure cycle 1 - 2 hours at room temperature followed by 0.5 hour at 250°F (121°C)
- Cure cycle 2 - 2 hours at room temperature followed by 2 hours at 130°F (60°C)
- Cure cycle 3 - Room temperature for 7 days
Clean-upThe spray system, including spray gun, mixing pot, and containers can be cleaned with MEK or Acetone (VOC exempt solvent). Masks can be powerwashed with Challenge 485S barrier coat.
Storage and HandlingCHO-SHIELD 2000 Series coatings should be stored at 50ºF to 86ºF (10ºC to 30ºC) and have a 9 month shelf life from the date of manufacturing in the original sealed container. CHOSHIELD 2000 Series coatings are flammable liquids. Please consult the material safety data sheet for proper shipping and handling procedures before use.
|Product||Weight (grams)||Packaging||Chomerics Part No.||Primer Included|
|CHO-SHIELD 2001*||250||3 component, 1/2 pint aluminum can kit||52-00-2001-0000||No|
|250||3 component, 1/2 pint aluminum can "touch-up" kit||52-00-2001-1000||No|
|700||3 component, 1 pint aluminum can kit||52-01-2001-0000||No|
|1378||3 component, 1 quart aluminum can kit||52-04-2001-0000||No|