Charge decay

Although it has been generally demonstrated (15,77,86—89) that antistaticaHy treated fabrics exhibit increased surface conductivities, many examples have been found where static behavior is not always related to the conductivity of the fabric (90) or the material. One of the main reasons for this is the fact that static charges decay not only by conduction but also by radiation. 

An alternate test for antistatic performance is the charge-decay test, in which the time of charge-decay is measured after 5 kV have been applied to the specimen (FederalTest Method lOlC, Method 4046.1). For many purposes, a charge-decay time of 0.5 s to 500 W, measured at the RH in end use, indicates good antistatic performance. 

The electrical surface resistivity and charge-decay time of most materials vaiy substantially with the relative humidity. It is important that materials be tested at the lowest RH expected in use. Items that are antistatic at 50 percent RH may not be antistatic at 20 percent RH. 

Ohmic charge decay processes obey a first order rate law from which the charge Q remaining at any time t can be expressed in terms of the initial charge Qq and relaxation time constant r. Using Eqs. (2-3.4) through (2-3.5) the time constant r can alternatively be expressed as... 

Nonohmic behavior is pronounced for nonconductive liquids in plastic tanks, whose dielectric walls further complicate the charge decay rate [206]. 

Table (a) shows experimental data [24] for the initial charge density exiting a fuel filter Qq plus the charge density Q remaining 30 s downstream. At low conductivity the charge decays much faster than predicted by an exponential relaxation law [Eq. (2-3.7)] and instead follows a hyperbolic relaxation law [24] given by... 

Carter, P. A., Rowley, G., Fletcher, E. I, and Sylianopoulos, V. (1998), Measurement of electrostatic charge decay in pharmaceutical powdersand polymer materials used in dry powder inhaler devices, Drug Dev. Ind. Pharm., 24,1083-1088. 

Charge decay rates -use m kinetic measurements [KINETIC MEASUREMENTS] (Vol 14) -of polymers [ANTISTATIC AGENTS] (Vol 3)... 

We introduced a printout system, to demonstrate that the plates had been imaged, by incorporating a leuco dye in the formulation and discovered that there was improved back transfer and charge decay control. 

Photohardenable electrostatic master having improved backtransfer and charge decay. Blanchet-Fincher, Graciela B. Fincher, Curtis R., Jr. Cheung, Lawrence K. F Dessauer, Rolf Looney, Catharine E. (DuPont de Nemours, E. 

These additives perform by migrating to the surface of the film, reducing the surface resistivity, and enabling a more rapid dissipation of static electrical charges. Many of them work best in conditions of high humidity, presumably through the absorption of moisture and a consequent increase in conductivity at the surface. The efficiency of such an additive may be measured by the rapidity with which static charges decay. 

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