Patent ID: 7262548

Claim:
An image forming apparatus comprising a rear plate having plural electron emitting devices and wirings for applying a voltage to the electron emitting devices, a face plate opposed to the rear plate and having a light emitting member capable of light emission by an irradiation with an electron beam emitted from the electron emitting devices and an anode electrode, a frame member provided between peripheral portions of the rear plate and the face plate and constituting a vacuum container together with the rear plate and the face plate, and a spacer positioned in contact with the rear plate and the face plate and set at a potential defined by a current field, wherein Ψ 0 ×Ψ 2 in a following general equation (1) has a positive value not exceeding 0.05: Δ ⁢ ⁢ x P ⁢ ⁢ y = Ψ 0 × Ψ 2 ⁡ ( e ⁢ ⁢ E ⁢ ⁢ a k ⁢ ⁢ T 2 ⁢ h P ⁢ ⁢ y ) ⁢ Δ ⁢ ⁢ T 1 ( 1 ) wherein: Δx: displacement [m] of an incident position of an electron beam in the vicinity of spacer; Py: pitch [m] of electron emitting devices in a direction perpendicular to a spacer surface; e: unit charge [C]; Ea: activation energy [eV] of a resistance of a spacer; h: height of a spacer [m]; k: Boltzmann constant [J/K]; T: average external surface temperature [K] of face plate and rear plate; Ψ 0 : heat resistance division ratio of spacer represented by a following general equation (2): Ψ 0 =Rh sp /( Rh cfp +Rh sp +Rh crp ) (2) Rh cfp : heat resistance between spacer and face plate [m 2 K/W]; Rh sp : heat resistance of spacer [m 2 K/W]; Rh crp : heat resistance between spacer and rear plate [m 2 K/W]; Ψ 2 : spacer sensitivity represented by a following general equation (3): Ψ 2 =γ/20 (3) γ: spacer field influence coefficient represented by h/x 0 ; x 0 : influence range of spacer electric field [m].