表面層の樹脂に加えるこれらの導電材の配合量は、表面層の樹脂の体積固有抵抗値が１０６〜１０１４Ωｃｍになるように決めることが好ましい。また、特願昭６２−２３０３３４号公報に示されるように表面層の体積固有抵抗値は表面層に接する下層の体積固有抵抗値より大きいことが好ましい。本発明において「表面層に接する下層」とは、主に導電性弾性層である。具体的には、表面層の体積固有抵抗値が１０６〜１０１４Ωｃｍで、導電性弾性層の体積固有抵抗値が１０１〜１０１１Ωｃｍであることが好ましい。
The amount of these conductive materials added to the resin of the surface layer is preferably determined so that the volume resistivity of the resin of the surface layer is 10 6 to 10 14 Ωcm. Further, as disclosed in Japanese Patent Application No. 62-230334, the volume resistivity of the surface layer is preferably larger than the volume resistivity of the lower layer in contact with the surface layer. In the present invention, the “lower layer in contact with the surface layer” is mainly a conductive elastic layer. Specifically, the volume resistivity value of the surface layer is preferably 10 6 to 10 14 Ωcm, and the volume resistivity value of the conductive elastic layer is preferably 10 1 to 10 11 Ωcm.
表面層に用いる導電材の具体的な含有量としては、ポリウレタン樹脂１００質量部に対して３０〜２００質量部が好ましい。表面層の体積固有抵抗値が導電性弾性層の体積固有抵抗値より小さいと高電圧印加の元で帯電部材の抵抗が低下しやすく、リーク性が不良となる。
As specific content of the electrically conductive material used for a surface layer, 30-200 mass parts is preferable with respect to 100 mass parts of polyurethane resins. If the volume specific resistance value of the surface layer is smaller than the volume specific resistance value of the conductive elastic layer, the resistance of the charging member tends to decrease under application of a high voltage, resulting in poor leakage.
表面層の膜厚を上記範囲とするには、表面層を成形する際に、成形法に応じ、表面層形成用の樹脂塗料の固形分、粘度等を適正な範囲に調整することで制御する。膜厚の測定は、以下の方法により行う。
１）帯電部材の９個所（ローラ形状の場合、両端部から１０ｍｍ位置、と中央部の３位置で、周方向３個所（任意の場所を起点に１２０°刻み））から、ナイフで試料を切り出す。
２）光学顕微鏡で各試料の断面を観察し（４００倍程度）、表面層の膜厚を求める。９点の算術平均をもって表面層膜厚とする。
In order to make the film thickness of the surface layer within the above range, when the surface layer is molded, it is controlled by adjusting the solid content, viscosity, etc. of the resin coating for forming the surface layer to an appropriate range according to the molding method. . The film thickness is measured by the following method.
1) A sample is cut out with a knife from nine places on the charging member (in the case of a roller shape, 10 mm from both ends and three positions in the center and three places in the circumferential direction (incremented 120 ° starting from an arbitrary place)). .
2) The cross section of each sample is observed with an optical microscope (about 400 times), and the film thickness of the surface layer is obtained. The arithmetic average of 9 points is used as the surface layer thickness.
本発明の接触式帯電装置は、帯電部材に本発明の接触式帯電部材を用いることにより、上述のような（１）低電圧から高電圧に渡り帯電部材の抵抗が安定している、即ち、抵抗の電圧依存性が小さい。（２）少量の導電材添加で表面層抵抗を安定して制御できるため、表面層のミクロ的な抵抗ムラが小さいなどの帯電部材自体の効果をもたらすので、帯電部材を用いた帯電装置は、「帯電均一性に優れ、感光体の放電絶縁破壊による画像欠陥等の発生がない」ものを構成することが可能となる。その導電性基体への印加電圧は直流電圧、もしくは交流電圧と直流電圧の重畳電圧などの振動電圧のいずれであってもよく、いずれの場合も本発明の優れた効果を発揮することができる。特に交流電源を廃した直流電圧のみの場合その効果が顕著である。
In the contact charging device of the present invention, by using the contact charging member of the present invention as the charging member, (1) the resistance of the charging member is stable from low voltage to high voltage as described above. The voltage dependency of the resistance is small. (2) Since the surface layer resistance can be stably controlled with the addition of a small amount of a conductive material, the effect of the charging member itself such as micro resistance unevenness of the surface layer is small. Therefore, the charging device using the charging member is It is possible to configure a device that is “excellent in charging uniformity and free from image defects due to discharge dielectric breakdown of the photoreceptor”. The applied voltage to the conductive substrate may be either a DC voltage or an oscillating voltage such as a superimposed voltage of an AC voltage and a DC voltage. In any case, the excellent effect of the present invention can be exhibited. In particular, the effect is remarkable when only the DC voltage is used without the AC power supply.