Report on anti-static polypropylene and other melt-down fabrics used for mask fabrications.
Identifies the chemistry, process, and materials used to achieve anti-static properties.
Addresses the need for continuous discharge of static electricity to prevent explosion-type discharges that can harm electronics, cause fire hazards, and bodily harm.
Introduction To Anti-Static, Conductive And Insulating Materials
Materials are either conductive or insulating; conductive materials allow continuous and rapid passing of electrons, while insulators block flow and cause charge build-up.
Static electricity build-up is primarily caused by tribological friction of materials in contact, such as a dry air stream and a polypropylene surface.
Conductivity or insulation depends on parameters including free electronic cloud (as in metals), continuous or interrupted micro-level structures (most plastics are fiber-like networks with interruptions), and presence of holes for electron transfer.
Anti-static properties are classified as anti-static, conductive, and dissipative anti-static, with resistivity varying over a wide range (more than 10^17 ohm/sq).
Plastic and polymeric surfaces have resistivities higher than 10^12 ohm/sq.
When ESD protection and EMI/RFI shielding are required, conductive agents are the preferred solution.
When thermal management is also required, conductive agents are the preferred solution.
When a controlled dissipation of charges is desired, dissipating anti-statics are preferred.
Anti-statics are chosen when normal build-up of static charges is expected and the actual rate of discharge is not of highest importance.
For face masks, depending on the specific environments of use (general masks, hard protective masks in manufacturing, etc.) and the intended life cycle, all solutions can be feasible.
Temporary Versus Permanent Anti-Static Performance
Temporary solutions lead to short-term anti-static behavior and are used in low-cost objects such as one-use disposable masks, cups, and similar products.
Cost of temporary solutions is very low, with overall product increase less than 2% in most cases.
Compositions used are kept in the 0.1–1.5% w/w range.
Temporary solutions depend on well-known traditional surfactants that orient themselves with one end towards the inside of the surface and the other towards outside, where water is found.
Surfactants have a hydrophilic part and a hydrophobic part; the hydrophilic part attracts moisture and develops a conductive surface due to ions present in water.
Advantages of temporary solutions: very cheap, can be applied everywhere without significant cost increases; agents for PP, PE, and alike are well known; low concentrations required (0.1–1.5% w/w); can be mixed in the melt or applied on the surface.
Disadvantages of temporary solutions: temporary with common duration/life cycle of 15–60 days; can be washed off often during rubbing, cleaning, scratching; depend on the relative humidity of nearby air; offers an anti-static surface, not an anti-static material.
Typical agents used in the blend for temporary anti-static behavior include: aliphatic amines, aliphatic acid, aliphatic esters, aliphatic amides, phosphate esters, ethoxylated amines, polyols, quaternary ammonium salts, esters of PEG, and non-ionic surfactants (such as Tween).
Non-ionic surfactants usually require less than 1% w/w in the PP mass, ensuring stability of mechanical, thermal, and optical properties of the anti-static enhanced PP.
In general, long chain aliphatic compounds with both polar and organic functional groups that can be oriented with their hydrophilic (polar) group towards the atmospheric air and their non-polar (hydrophobic) group towards the polymeric surface (PP, PE, etc.) are used.
The anti-static agent is homogeneously dispersed in the main mass of the extruded material; actual anti-static performance at the time of manufacture is quite low and may take from a few minutes to some days to peak, as the anti-static needs to diffuse to the surface.
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