5 Key Advancements in Conductive Paint Technology

By Neil Browes, Roy Bjorlin, Gary Shawhan Spraylat Corporation

 

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Introduction

Conductive coatings continue to be a useful problem solving tool for product designers and EMC engineers trying to achieve regulatory compliance. Conductive paint technology has grown steadily in market acceptance since the late 's, when the first viable copper paint product was introduced by Spraylat.

Since this time, 4-5 generations of conductive paint products have been introduced to the market - each product offering incremental improvements in coating performance while steadily improving the application process window. These advancements in paint technology have been driven, in part, by the increasing demands for EMC materials that can provide increased performance and coating quality at a lower application cost. They are also increasingly influenced by the transition from regional to global markets. Market globalization, in fact, has altered the OEM criteria for material selection. The necessity of knowing that a comparable result (from a given technology) is accessible at several alternative global sites has become a must to many manufacturers.

Conductive paint technology has become unique among other conductive coating technologies in its ability to address cost, performance and global infrastructure issues successfully. The following "5 Key Advancements" in conductive paints provide a glimpse at these important transitions that are incorporated into the new SOS Series of conductive paint products from Spraylat.

Advantage#1: Reduced Coating Thickness

There has been a remarkable transition in the ability of conductive paints to deliver a quality result while using less and less material on the part. Compared to even 3 or 4 years ago, the latest generation of conductive paints can be applied at thicknesses that are 2-4 times less compared to their predecessors.

Dry Film Thickness Ranges for Current Generation Paint Products

As shown in the following illustration, the reduction in recommended applied coating thickness (with SOS technology) to achieve reliable coating performance has been substantial. This is especially true in the case of copper paints where the improvement has been 2 or 4 times.

SOS Copper Paint ohms-per-square

SOS Silver Paint Ohms-per-square

Advantage # 2: Improved Electrical Properties

The conductivity of today's conductive paint technology is far superior to earlier paint products. This improved performance is also readily achieved at the lower thicknesses noted above. As a consequence, the ability of today's conductive paints to address electrical performance specification requirements, with a wider process window, has definitely increased. This feature has added flexibility to conductive paints in their ability to satisfy a broader range of product applications in a cost-effective way.

Ohms-per-square resistivity values are used to identify the conductivity of a given coating at a certain location on a given part. Often used as a quality control test, ohms-per-square test results provide a good basis for the comparison of earlier generation conductive paint products and the latest conductive paint technology.

Ohms-per-Square Test Results Latest Generation Paints

Ohms per Square Test Values

SOS copper paint technology has improved 3-4 times in its resistivity values as compared to the earlier generation products. When first introduced, these coatings produced ohms-per-square resistivity values of 90-100 milliohms/square. Mid-generation copper coatings provided resistivities of 50-60 milliohms/square. Recent advancements have taken this down to 15-20 milliohms/square. Most significant this improvement in conductivity is achieved at a 2-4 times reduction in coating thickness.

SOS silver paints have also improved in their electrical conductivity, producing very low resistivity values, even at extremely low coating thicknesses. The engineering involved in the formulation of these newer products provides for greater intimacy of the conductive media within the coating, even when very thin films are applied. Thus SOS silver paint coatings also provide improved resistivity values.

The increased electrical conductivity of these newer conductive paint products is also reflected in their improved point-to-point electrical performance. Today, conductive paints can provide comparable performance to selective plating, even on parts with more complex geometry. As a consequence, the ability of conductive paint coatings to achieve low point-to-point values across highly featured parts has been significantly improved. The following part is one example of a complex part where conductive paint is able to provide adequate point-to-point resistivity (vs. a 1ohm point-to-point specification) from corner-to-corner. Earlier generation conductive paint products could not have met this requirement.

 

 

One additional advantage for conductive paints is the benefit of being able to customize the amount of material delivered to different featured areas on the part. This means that critical locations, such as ground connections, can selectively incorporate more material for performance reasons.

The shielding effectiveness of these latest conductive paint products from Spraylat is excellent and comparable or superior to alternative conductive coating technologies. Typical results, according to the ASTM D-89 Co-Axial Transmission Line test method, are shown in the table below. This test method is designed to test electrically thin materials like conductive coatings at frequencies between 30MHz and 1.5GHz.

ASTM D-89 Shielding Effectiveness Test Results, dB

 

It is important to note (from the preceding table) the excellent shielding effectiveness achieved at "very low" dry film thicknesses. Copper coatings, based on SOS technology, provide more than 70db of shielding at only 10 microns film thickness. The new silver-based coatings provide 70 dB of shielding at only 2.5 microns underscoring their versatility as an EMI shielding solution.

Shielding effectiveness testing has also been performed on these conductive paint products at higher frequencies according to the MIL-STD 285 test method. This testing is performed using a shielded room with results reported at selected frequencies up to 10GHz. As shown in the following chart, conductive paints provide a consistently high degree of shielding effectiveness at all frequencies tested.

MIL STD 285 Shielding Effectiveness Test Results

Advantage # 3: Coating Adhesion/Cohesion and Film Durability

Conductive paints have always achieved good adhesion to a wide range of plastics. Over years of product development, however, paint adhesion has made some additional improvement while the solvents used in product formulation have become more substrate compatible. This latest generation of SOS solvent paint products is alcohol-based and offers low VOC's for improved environmental friendliness. When polycarbonate-based resins are involved and/or thin-wall moldings are being used for the enclosure manufacture, aggressive solvents contained in the paint can result in substrate crazing or cracking. The following illustration shows the advantages of these new products (right) as compared to an earlier generation conductive paint product employing MEK as the solvent (below).

ATTACK (l/handside) compared to SOS PAINT -No Attack (r/handside)

 

The common plastics processed with today's conductive paints include the resins shown in the following table. Special processes or products may be available for certain other resins or grades of plastics to achieve good adhesion for that particular material. These special processes or products are normally best discussed and validated individually with the material supplier.

Common Painted Plastics:

ABS ABS/PC or PC/ABS Blends PC (Polycarbonate) PS (Polystyrene) PPO (Polyphenylene Oxide) PEI (Polyetherimide) Nylon

 

Film cohesion, or "particle pick-off" was a traditional criticism of conductive paint coatings in the past. The latest paint products, however, has rewritten the rules regarding paint film integrity. Today, there is essentially no film cohesion issue associated with these newer products. Examining the tape test result, the comparison of the newer paint coating to earlier ones is clear. In addition, as shown the next illustration, these new coatings can consistently pass the ASTM D-95a Cross-Hatch Adhesion Test. This was not the case with earlier product formulations.

TAPE TEST

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Cross Hatch Adhesion Test

Another area of major improvement in paint coating properties has been film durability. In general, there has always been a desire to achieve a high level of coating integrity, accommodating various assembly and disassembly procedures without affecting the properties of the conductive film. In this regard, the present generation of conductive paints offers several orders of magnitude improvement in coating durability. The following graph shows the relative improvement in coating properties according to the RCA Abrader test method. Results for both of the SOS conductive paint coatings exceeded 500 cycles by a significant number of cycles. Earlier generation copper paints typically produced values below 25 cycles. Silver paint coatings, which had been traditionally soft and abradable, would only provide about 10 abrasion cycles before failure.

 

RCA Abrader Test

COPPER=RED.........SILVER=GREY

Advantage # 4: Increased Productivity

Productivity is an essential element in determining the overall cost for using any process. Spraylat's SOS Series products have made some important strides forward in improving their productivity and, as a consequence, reducing their use cost. In a spray application the issue of transfer efficiency (paint delivered onto the part expressed as a % of the paint used) is always a basic element of cost concern.

Transfer efficiency is affected by several key variables including the part complexity, the type of equipment used (hand vs. robotic spray), gun settings, spray technique or programming in the case of robotics and volume throughput.

The overall productivity achievable from a given coating process is driven by the ability of the technology to adapt to these variables. This is often referred to as the process window for the product or technology. The latest generation of conductive paint products has established a much wider process window within which applicators can achieve a cost-effective result. The key features of these products that have established a wider process window include:

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Product Details

Quality and Fabric Characteristics

• Coating Metal &#; Silver
• Base Material &#; nylon
• Surface resistance of &#;0.05 Ω/sq

• Average attenuation of &#;60dB in 10MHz &#; 3GHz

• Fabric weight of 80±10 g/m²

Features and Benefits

• Highly electrically conductive

• Stretchable
• Washable

• Anti-microbial 

• Low weight and high durability

• RF/EMI/EMF/LF Blocking

• Super Earthing/Grounding Fabric

• Anti-electrostatic/ESD

• Radiation/Radiowave/Microwave shielding 

• Very easy to cut and sew

Superior Durability and Performance

Unlike ordinary metalized fabrics, the coating processes, used to deposit metals in our fabrics, deliver an impervious bond that can&#;t be broken. Proprietary metalizing technology actually bonds the metal to the fabric at the molecular level, essentially melding the fabric to the metal. The resulting bond delivers unparalleled durability even under conditions that require constant flexing, bending, stretching or abrading. No other metalized fabric is more durable and because of superior bonding technology, our conductive fabrics deliver proven, consistent and reliable electrical conductivity and electromagnetic reflectivity performance even in the most challenging environments.

General Description

Stretchable & washable silver conductive fabric blocking RFID/RF. Reduce EMF/EMI Protection. Conductive fabric protects from Radiation/HF Signal/WiFi. Preserves the working integrity of electronic devices in the event of EMP or CME. 

Safety & Documentation

Safety: Non-toxic, tasteless and odorless.  You can treat it as normal trash for waste disposal.

Specification

Silver Conductive Fabric, stretchable & washable

CF-Ag-010-SW1

ItemUnit 

Spec

 

Test StandardWidthmmGB/T-Thicknessmm0.10±0.02FZ/T-Weightg/m280±10GB/T-Surface ResistanceΩ/sq&#;0.05ASTM F390Shielding EffectivenessdB60, 10MHz&#;3GHzCoating MetalSilverBase MaterialsNylon

 

Available sizes: width 59.06&#; inch (150 cm) x length  39.37&#; inch (100 cm), 59.06&#; (150 cm) x 78.74&#; (200 cm), and 59.06&#; (150 cm) x 157.48&#; (400 cm). For customized lengths of silver conductive fabrics, contact Nano3D Systems.

Additional Information

Usage for EMI/RFI shielding gaskets, shielded enclosures, architectural shielding, containers, bags, curtains, tents, covers, anti-static clothes, e-textile etc. Can be used as an insert in the wallet or handbag to protect your credit cards from data theft. Can be also used to shield rooms & booths, as car security keyfob bag et al. Effective shielding from cell towers, wireless routers, microwave signals, smart meters, security systems, radars, etc. Blocks portable encryption scanners. EMI/EMF blocking and EMP protection of electronics. High-shielding conductive fabric for blocking RF signals such as cell phones, bluetooth, WiFi, GPS et al.  

Our conductive fabrics offer the highest standard of performance in shielding and conductivity. Starting with tough, light, tightly woven fabrics found in applications such as ship sails and military parachutes, the proprietary metalizing process is used to apply a thin layer of metal to each fiber. The result is a textile product with the feel, durability, and flexibility of a typical woven fabric and the conductivity and shielding performance of a metal foil.

Market Served

• Aerospace/Military
  • EMI and reflective shielding and tapes, towed arrays
• Medical Equipment and Components
  • Flexible fixed and disposable sensors, defibrillators, shielding gaskets, wound dressings
• Telecommunications
  • Flexible reflective components for portable satellites, shielded gasket components, radar flags, towed arrays
• Commercial and Consumer Electronics
  • Personal security for electronic devices, personal EMI shielding
• Architectural Shielding
  • Medical (MRI, Nuclear Radiology), data center shielded wallpaper
• Mobile Forensics
  • Smartphone, laptop and tablet shielded bags and pouches
  • Shielded tents and enclosures
• Apparel
  • Shielded gloves, outerwear, socks, sleepwear and intimate apparel, sportswear, outdoor wear, hunting apparel

Customer Testimonials

Paul H.

We are happy with the performance of your stretchable & washable silver fabric for using in our products. Very good washing test results. Fabrics stay conductive. Thank you!

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Contact us to discuss your requirements of China EMF Shielding Cloth Supplier. Our experienced sales team can help you identify the options that best suit your needs.