Overlaid image forming apparatus with coordinated transfer bias and attraction bias voltage sources

A superposed image forming apparatus wherein different toner images are superposedly transferred onto a transfer material, comprising:

• an image bearing member;
• means for forming a toner image on said image bearing member;
• a transfer material carrying member, disposed opposed to said image bearing member, for carrying a transfer material in synchronism with the toner image on said image bearing member;
• transfer material supplying means for supplying the transfer material to said transfer material carrying member;
• a transfer bias voltage source for applying to said transfer material carrying member a bias voltage for image transfer from said image bearing member to the transfer material;
• an attraction member for urging the transfer material to said transfer material carrying member to hold the transfer material on said transfer material carrying member;
• an attraction bias voltage source for applying a bias voltage to said attraction member;
• wherein the voltage applied to said transfer material carrying member is changed in association with on-and-off of the voltage application to said attraction member so as to maintain a constant surface potential of said transfer material carrying member.

A color image forming apparatus for forming a color image wherein different color toner images are superposedly transferred onto a transfer material, comprising:

• an image bearing member;
• means for forming a toner image on said image bearing member;
• a transfer material carrying member, disposed opposed to said image bearing member, for carrying a transfer material in synchronism with the toner image on said image bearing member;
• transfer material supplying means for supplying the transfer material to said transfer material carrying member;
• a transfer bias voltage source for applying to said transfer material carrying member a bias voltage for image transfer from said image bearing member to the transfer material;
• an attraction member for urging the transfer material to said transfer material carrying member to hold the transfer material on said transfer material carrying member;
• an attraction bias voltage source for applying a bias voltage to said attraction member;
• wherein said transfer material carrying member includes a conductive base member and an electrostatic attraction surface layer;
• wherein a polarity of the voltage applied to said attraction member is changed to the same polarity as that of the voltage applied to said transfer material carrying member when the transfer bias voltage is applied to said transfer material carrying member so as to maintain substantially constant surface potential of said transfer material carrying member.

A color image forming apparatus for forming a color image wherein different color toner images are superposedly transferred onto a transfer material, comprising:

• an image bearing member in the form of an electrophotographic photosensitive member;
• means for forming a toner image on said image bearing member;
• a transfer material carrying member, disposed opposed to said image bearing member, for carrying a transfer material in synchronism with the toner image on said image bearing member;
• transfer material supplying means for supplying the transfer material to said transfer material carrying member;
• a transfer bias voltage source for applying to said transfer material carrying member a bias voltage for image transfer from said image bearing member to the transfer material;
• an attraction member for urging the transfer material to said transfer material carrying member to hold the transfer material on said transfer material carrying member;
• an attraction bias voltage source for applying a bias voltage to said attraction member;
• wherein said transfer material carrying member includes a conductive base member and an electrostatic attraction surface layer;
• wherein the voltage to said attraction member is supplied from said attraction bias voltage source when the voltage is applied to said transfer material carrying member so as to maintain substantially constant surface potential of said transfer material carrying member.

An image forming apparatus, comprising:

• an image bearing member;
• means for forming a toner image on said image bearing member;
• transfer material carrying means for carrying a transfer material thereon to transfer the toner image from said image bearing member on to the transfer material at a transfer position, said transfer material carrying means comprising a surface dielectric material layer and a conductive layer inside thereof;
• a first voltage source for supplying electric power to the conductive layer;
• electrostatic attraction means for electrostatically attracting the transfer material onto said transfer material carrying means;
• a second voltage source for supplying electric power to said attraction means;
• wherein a potential difference between said conductive layer and said attraction means during an attracting operation is constant irrespective of operation or non-operation of said first voltage source.

An image forming apparatus comprising:

• an image bearing member;
• means for forming a toner image on said image bearing member;
• transfer material carrying means for carrying a transfer material thereon to transfer the toner image from said image bearing member onto the transfer material at a transfer position, said transfer material carrying means comprising a surface dielectric material layer and a conductive layer inside thereof;
• a first voltage source for supplying electric power to the conductive layer;
• electrostatic attraction means for electrostatically attracting the transfer material onto said transfer material carrying means;
• and
• a second voltage source for supplying electric power to said attraction means;
• wherein an output of said second voltage source is switched on and off during attracting operation in synchronism with a switching on and off of an output of said first voltage source.

An image bearing member comprising;

• means for forming a toner image on said image bearing member;
• transfer material carrying means for carrying a transfer material thereon to transfer the toner image from said image bearing member to the transfer material at a transfer position, said transfer material carrying means comprising a surface dielectric material layer and a conductive layer inside thereof;
• a first voltage source for supplying electric power to the conductive layer;
• electrostatic attraction means for electrostatically attracting the transfer material onto said transfer material carrying means;
• and
• a second voltage source for supplying electric power to said attraction means;
• wherein the output of said first voltage source is changed when a time period from attraction of a leading edge of the transfer material on said transfer material carrying means by said attraction means to switching of the first voltage source from a non-operative state to an operative state, elapses after arrival of the leading edge at the transfer position.