Applications for anti-stat poly film range from avoiding nuisance static and packaging circuit boards to operating room kits and other mission-critical items.
Polyethylene in its natural state tends to harbor a charge, especially in low humidity ambient conditions.
In some applications, natural static cling helps.
An antistat agent must be added to polyethylene to counteract this natural tendency of polyethylene. The goal of all "anti static" additives is to dissipate accumulated static as rapidly as possible and avoid an arc. For this reason, anti stat performance is measured by the time in milliseconds required to get rid of the charge. The range can be avoiding "nuisance static" to well defined MIL SPEC and ASTM tests. There are several test methods such as MIL B 81705B and its revisions such as MIL PRF–81705C, NFPA 99 12–188.8.131.52, ASTM D 257 and E 1A–541.
Whether tested by static decay, surface resistivity, volume resistivity or DC insulation resistance, the mode of action of all classes of antistats is to attract ambient moisture to the surface. The water molecules then act as a conduit to conduct and dissipate the static charge. MIL SPEC humidity conditions of 12% RH are severe to determine the effectiveness in a very dry environment.
So called "conductive" packaging is an entirely different category.
Obsolete specifications usually call out a percentage of antistatic additive. They are meaningless in context of the type of antistat and usage environment.
There are four basic classes of anti-stats for LDPE film:
1. GMS, or glycerol mono-stearate types generally used for convenience to avoid static cling, dust buildup and general nuisance static. Besides low cost, advantages include GRAS acceptance and usefulness in dry environments. The main disadvantage is greasiness which can impair heat sealing, laminating and printing.
2. Etholxylated amines. Advantages: effective in dry conditions. Disadvantages: limitations from FDA and electronics standpoints, limited shelf life.
3. Ethoxylated amides. Advantages are rapid functionality which is critical for manufacturing foamed extrusions, ability to meet Military ( MIL) Specifications, acceptable for direct food contact and lack of greasiness.
4. Non-amine, non-amide with "dual function" mode of action. Advantages: best performance at low usage levels, suitability for electronics, GRAS, FDA, Kosher acceptable for food contact, good cosmetics, non-corrosive, heat stable. While cost could be considered a disadvantage, less is required to deliver optimum performance.
Old school anti-stats were humidity and temperature dependant. The mode of action relied on "blooming", or forcing the agent to the surface of the film. Newer generations work more on what is referred to as the "reservoir" of the film without as much blooming. The result for either is eventually a greasy surface. This is of course at cross purposes with high speed packaging machines or bag machines.
Taking static out of the film on the unwind station is an effective way to take the static out of the equation. Anti-static fans and " tinsel " with a high loading of copper to conduct the electricity out. My favorite home grown method is to string copper gauze across the unwinding roll and of course, ground it. It is in stock at Grainger's. #45TR03
There is a valid reason your engineer is calling out "amine free" film or bags. The interaction between the components of antistats and the package contents can be ruinous.
Did you know?
Pink pigment does not make plastic anti-static. Decades ago, someone had the idea to tint antistatic polyethylene pink to distinguish it from ordinary polyethylene layflat tubing and sheeting.
Based on our nearly five decades of experience with applications such as the space program from Gemini to the Shuttle, dynamite case liners, electronics packaging, surgical / OR packs and munitions packaging, we can prescribe the right antistat to relieve your static electric pain.