Surface Finishing Tutorial

#202 Antistatic Paints

Category : Special paints

February20, 2015

Disasters and accidents related to static electricity are caused by electrostatic attraction or discharge. Examples of accidents related to electrostatic discharge include: [1] Fire ignited by flammable materials; [2] Electric shock/discomfort to human body; [3] Light exposure to photographic films, etc.; [4] Failure or destruction of electronic devices including IC; [5] Malfunction or fire in chemical equipment, etc.
Unfavorable events by electrostatic attraction include: [1] Attachment of dust, bacteria, or mold onto electronic devices/components and precision machinery components; [2] Clogging of pipes of precision machinery; [3] Irregularity (jamming) of sheets/films, etc.; [4] Entanglement of threads/fibers; [6] Printing failure; [6] Discomfort to human body.

In Japan, these accidents used to occur in the winter time when humidity is low. However, due to the spread of air-conditioning use and the development of precision electronic components, it is now necessary to implement the countermeasures all year round. The areas that require countermeasures against static electricity include indoor locations, floors, electronic devices and components. [Table 1] shows electrical (leakage) resistance based on the hazard and obstacle levels of the work environment.

[Table 1] Work environment and electrical resistance on floor surface

Work environment	Electrical resistance	Location applicable
A dangerous place where an explosion or a fire may occur	10⁸Ω or less	Operating room, storage room for flammable gas or solvent, or process to handle these
A place where electric shock may occur	10¹⁰Ω or less	Powder packaging process, paper rewinding process, etc.
A place where a production bottleneck may arise	10¹¹Ω or less	Computer room, semiconductor handling room, etc.

The following materials are used for the antistatic coatings.

1. Composite	1) Metal: Ag, Cu, Ni; 2) Carbon: conductive carbon; 3) Metal-oxide: tin oxide, antimony-oxide treated TiO2 and Sb-doped tin oxide
2. Surfactant	Quaternary ammonium salt, sulfonate, phosphate, alkylbetaine type, alkylimidazolium type, alkylamine, alkyl ether, glycerin fatty acid ester, polystyrenesulfonate, etc.
3. Deposition	1) Metal: Au-Pd 2) Oxide: indium oxide, tin oxide, cadmium tin oxide, etc.

The combination of carbon conductive paints and coated materials includes the followings: [1] Acrylic coating with ABS resin, PS, or PPO coated materials; [2] Urethane coating with FRP or polyester; [3] Polyolefin coating with PP or FRP; [4] Alkyd coating with metal; [5] Epoxy resin coating with metal, FRP, or cement.

Carbon powders are stable in the heat. Most of them are made with melamine-based materials with room temperature setting or thermosetting properties.

For the clean room specification, acrylic or vinyl materials are used for walls, ceilings, and light-duty floors while urethane or solventless epoxy materials are used for heavy-duty floors.
In addition, highly conductive carbon coatings are applied to plastic cases of electronic equipment as a static protection measure.

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