Moisture stable polyurethane biasable transfer members

A method of controlling the resistivity of a member for electrically cooperating with a conductive support surface to attract charged toner particles from the surface towards the member comprising coating a conductive substrate capable of supporting a uniform bias potential thereon with at least one layer of a resilient elastomeric polyurethane, said coating being in electrical contact with the conductive substrate and formed by reacting:

• (a) a polyisocyanate prepolymer comprising the reaction product of:
• (i) a saturated aliphatic polyisocyanate, a saturated cycloaliphatic polyisocyanate or an aromatic polyisocyanate;
• and
• (ii) a polyol free of aliphatic unsaturation;
• and (b) a hardening mixture comprising:
• (i) a polyol of (a) (ii) or a diamine free of aliphatic unsaturation, or a mixture thereof;
• and,
• (ii) as a conductivity control agent for controlling the resistivity of the elastomeric polyurethane, from 0.001 to 5.0 weight percent, based on the total weight of (b), of a complex of ethylene glycol or an oligoethylene glycol selected from the group consisting of di-, tri- and tetraethylene glycol with an ionizable ferric halide salt selected from the group consisting of ferric fluoride, ferric chloride and ferric bromide,
• whereby the elastomeric polyurethane having an altered resistivity is capable of transmitting a bias potential from the substrate to the outer periphery thereof.

A method of preventing changes in the resistivity of members for electrically cooperating with a conductive support surface to attract charged toner particles from the surface towards the members caused by changes in relative humidity comprising applying at least one coating of a resilient elastomeric polyurethane formed by reacting:

• (a) a polyisocyanate prepolymer comprising the reaction product of:
• (i) a saturated aliphatic polyisocyanate, a saturated cycloaliphatic, polyisocyanate or an aromatic polyisocyanate;
• and
• (ii) a polyol free of aliphatic unsaturation;
• and (b) a hardening mixture comprising:
• (i) a polyol of (a) (ii) or a diamine free of aliphatic unsaturation, or a mixture thereof;
• and,
• (ii) as a conductivity control agent for controlling the resistivity of the elastomeric polyurethane, from 0.001 to 5.0 weight percent, based on the total weight of (b), of a complex of ethylene glycol or an oligoethylene glycol selected from the group consisting of di-, tri- and tetraethylene glycol with an ionizable ferric halide salt selected from the group consisting of ferric fluoride, ferric chloride and ferric bromide,
• to a cylindrical core of electrically conductive material for electrically cooperating with the conductive support surface when brought into contact therewith whereby the elastomer is capable of transmitting a bias potential from the core of electrically conductive material to the outer periphery thereof and significant reductions in the sensitivity of the resistivity to changes in relative humidity occur.