Conductive Coatings and Conductive Lacquers: EDAG for Printed Electronics and ESD
Conductive coatings, also known as conductive lacquers, render surfaces electrically conductive. They enable the production of printed resistors, film heaters, keyboards, and protection against electrostatic discharge. The LOCTITE EDAG series covers these applications. This article explains their structure, applications, and selection.
At a Glance: What Conductive Coatings Can Do
A conductive lacquer creates a conductive path on a non-conductive substrate. This allows circuits, resistors, heating surfaces, and sensors to be printed directly, and static charges to be dissipated in a targeted manner. The quality of a layer's conductivity is described by its sheet resistance, which varies significantly depending on the type.
How a Conductive Lacquer Works
A conductive lacquer consists of a binder and a conductive filler. In the EDAG series, this is usually carbon in the form of graphite or carbon black; for higher conductivity, silver-filled types are also available. The lacquer is printed and dried, during which the filler forms a conductive network. The key parameter is the sheet resistance in ohms per square (Ohm/sq); low values indicate good conductivity.
Typical Applications
| Application | Example |
|---|---|
| Printed Resistors and Circuits | Low-voltage circuits on film |
| Heating Elements | Large-area film heaters |
| Membrane keypads and touch switches | Membrane switches, keypads |
| Flexible Circuits | Printed Conductor Tracks on Polyester or Polyimide |
| Sensor Technology | Conductive sensor surfaces |
| ESD Protection | Dissipation of Static Charge |
Selecting the Appropriate Type
Three criteria determine the selection. The surface resistivity determines the function. Depending on the type, it ranges from approximately 20 Ohm/sq up to the megohm range, and for certain products it can be adjusted by mixing, such as LOCTITE EDAG 6017SS together with EDAG PM-404. The substrate must be suitable; common options include polyester, polyimide, polycarbonate, as well as paper and cardboard. The process also plays a decisive role: the EDAG inks are screen-printable, from manual to roll-to-roll. The data sheet of the respective type is authoritative.
Screen Printing Processing
- Stir the material thoroughly before use, avoiding air entrapment.
- Apply using screen printing; select screen and squeegee according to the data sheet.
- Dry according to specifications, typically 90 to 120 °C; higher temperatures shorten drying time.
- Clean the screen and device with MEK, MIBK, or acetone.
- Do not return removed material to the original container.
Limits and Notes
The EDAG inks are thermoplastic; the continuous service temperature is typically around 100 °C. They are designed as a printed functional layer, not as a decorative lacquer. For EMC shielding of housings or for high-performance inks with high silver content, there are separate coatings; we provide specific advice on this. Preliminary suitability tests are recommended, as specified by the manufacturer.
Typical errors
- A type with unsuitable sheet resistance was selected.
- The substrate cannot withstand the solvent of the lacquer.
- Dried too briefly or at too low a temperature, resulting in unstable resistance values.
- Material not stirred, resulting in an uneven layer.
- Continuous temperature above the type's limit.
We will be happy to clarify which EDAG type suits your surface resistivity, substrate, and process based on the data sheet.
