Patent ID: 11934110
Assignee: NOK CORPORATION
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. A developing roll used in an electrophotographic image forming apparatus, the developing roll comprising:
a core member made of a metal;
an elastic layer made of a rubber disposed around the core member; and
a surface layer disposed around the elastic layer,
wherein a value X defines an index of a compressive strength of the surface layer and is equal to or greater than 65.6 N/mm3, and a value Y is equal to or greater than 229 μm, wherein the value X is calculated from the following equation:

X=P1/(D1×A)−P2/(D2×A),

where
P1 is a load required to displace the developing roll by a depth of 100 μm in a radial direction when a truncated cone-shaped metal probe having a distal end of which a diameter is 40 μm is pressed against the developing roll,
D1 is a displacement of the developing roll caused by the probe under the load P1,
A is an area of the distal end of the probe,
P2 is a load required to displace a material roll by a depth of 100 μm in a radial direction when the probe is pressed against the material roll that includes the core member and the elastic layer and does not include the surface layer,
D2 is a displacement of the material roll caused by the probe under the load P2,

the value Y is a displacement of the developing roll caused by the probe when the probe, which is pressed against the developing roll and is displaced in a radial direction of the developing roll, pierces the surface layer.