JPS6231346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic developing device, and particularly to an improvement in a developing roller that contacts the circumferential surface of a photosensitive drum and rotates as the drum rotates.

In an electrophotographic process, an electrostatic latent image formed on a photoreceptor drum is visualized using a colored developer (toner). This process of visualizing the latent image is called development, and the electrophotographic developing apparatus used for this is generally shown in FIGS. 1 and 2.

The electrophotographic developing device shown in both figures uses a one-component type developer, but the electrophotographic developing device itself is in contact with the circumferential surface of the photosensitive drum 1,
A developing roller 2 that rotates as the developing roller 2 rotates, and a charging blade 5 that is in line contact with the developing roller 2 in the longitudinal direction (due to pressure applied by a pressure spring 3) and to which a bias voltage is applied from a power source 4. It mainly consists of In such a developing device, the toner 6 is first charged by the charging blade 5 and attached to and held on the circumferential surface of the developing roller 2, and then the toner 6 held on the developing roller 2 rolls into contact with the developing roller 2. The latent image on the photoreceptor drum 1 is visualized.

By the way, the toner 6 is not held over the entire circumferential surface of the developing roller 2. That is, as shown in FIG.
It does not adhere to B. This is to make the thickness of the six toner layers on the developing roller 2 uniform.

However, despite such considerations, it is extremely difficult to maintain a uniform layer thickness of the toner 6 on the developing roller 2. The layer thickness of the toner 6 on the developing roller 2 changes due to a shortage of toner 6 or a change in the pressure of the pressure spring 3. FIG. 3 is a diagram illustrating changes in the layer thickness of the toner 6. As shown in FIG. a shows a normal case; in this case, the layer thickness of the toner 6 is uniform and thick, so even though the charging blade 5 is pressurized by the pressure spring 3, the toner-free portion 2B of the developing roller 2 difficult to come into contact with. On the other hand, b indicates the case where the layer thickness of the toner 6 becomes thin due to toner shortage, and c indicates the case where excessive pressure is applied to one end of the charging blade 5 due to a change in the pressure of the pressure spring 3. In this case, the developing roller 2 and the charging blade 5 come into contact with each other at the toner-free portion 2B.

However, in the conventional developing roller 2, both the toner-adhered portion 2A and the toner-non-adhered portion 2B are made of the same material over the entire area, and the volume resistivity and hardness are completely the same over the entire area of the roller 2. Uniform, for example, with a volume resistivity of 10 ⁵
The hardness was 45±5HS (Shor hardness), both relatively low.

As a result, the conventional electrophotographic developing apparatus has a problem in that the bias voltage applied to the charging blade 5 leaks, resulting in the following inconveniences. One is that the toner 6 cannot be charged with a predetermined amount of charge, and the other is that an excessive current flows through the developing roller 2, causing the roller 2 to generate heat. If the latter fever occurs,
Problems arise in which the developing roller 2 itself changes in quality due to heat, or the toner 6 aggregates and fuses on the roller 2. In particular, when the toner 6 fuses to the tip of the charging blade 5, the developing roller 2 itself deteriorates. A serious problem arises in that the six layers of toner on the roller 2 are disturbed.

The present invention has been made in consideration of the above points, and its main purpose is to prevent the occurrence of excessive current flowing through both ends of the developing roller.

In this invention, the generation of excessive current is prevented by making the volume resistivity of the toner-free portion 2B of the developing roller 2 higher than that of the toner-adherent portion 2A, and the toner-free portion 2B is
The hardness of the toner adhering portion 2A is made higher than that of the toner adhering portion 2A, thereby preventing changes in the layer thickness of the toner 6.

Hereinafter, the electrophotographic developing device of the present invention will be described in more detail with reference to the accompanying drawings (FIG. 4). Also in this invention, the other parts except the developing roller 2 are the same as those of the above-mentioned conventional apparatus, so the explanation thereof will be omitted.

FIG. 4 is a characteristic diagram showing the relationship between the voltage applied to the charging blade 5 and the current when the developing roller is changed. In FIG. 4, curve a: When a voltage is applied to a silicone rubber developing roller 2 with a volume resistivity of 10 ⁵ Ω·cm without toner 6,
Curve b: When toner 6 is attached in the state of a,
Curve c: When a voltage is applied to the developing roller 2 made of silicone rubber with a volume resistivity of 10 ⁷ Ω·cm without toner 6, and curve d: Volume resistivity of 10 ⁸
The current characteristics are shown when a voltage is applied to the developing roller 2 of Ω·cm without the toner 6.

From these, in order to effectively prevent the generation of excessive current, it is necessary to select a value for the volume resistivity of the toner-free portion 2B of the developing roller 2 that allows at least a smaller current to flow than the current at point b. One thing is understood.

Therefore, in this invention, as the developing roller 2,
The volume resistivity value of the toner non-adhesive area 2B is 10 ⁷
Ω・cm or more, that of toner adhesion area 2A is 10 ⁵
Use one with a diameter of Ω・cm or less. In this case, various materials can be selected for the developing roller 2 as long as they have the above characteristics, but silicone rubber is most suitable from the viewpoint of durability. Note that the surface roughness of the developing roller 2 is desirably 5 μm or less.

Next, regarding the hardness of the developing roller 2,
In short, in this invention, the hardness of the toner-free portions 2B located at both ends of the developing roller 2 is made higher than that of the toner-adhered portions 2A sandwiched therebetween, thereby making the hardness of both portions 2A and 2B the same. The amount of dent in the toner non-adhesive portion 2B may be made smaller than in the case. Therefore, when specifying the rubber hardness, normally ±5HS can be considered as an error, so for example, if the toner-attached area 2A is 50HS.
(Shore hardness), the toner non-adhesive portion 2B may be made of silicone rubber of 60HS or higher or other materials.

As described above, in the electrophotographic developing device of the present invention, the volume resistivity and hardness of the end portions 2B of the developing roller 2 to which the developer (toner 6) does not adhere are compared to those of the intermediate portion 2A to which the toner 6 adheres. This prevents the occurrence of excessive current due to leakage, and also prevents the roller from being dented even if excessive pressure is applied to one end of the charging blade 5, thereby reducing the thickness of the toner layer. It has the excellent effect of keeping the temperature uniform at all times.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of this type of electrophotographic developing device, Fig. 2 is a perspective view of the same developing device, and Figs. 3 a to c.
4 is a diagram for explaining problems in the developing device, and FIG. 4 is a current characteristic diagram that is the basis of this invention. DESCRIPTION OF SYMBOLS 1... Photosensitive drum, 2... Developing roller, 2A... Toner adhering part, 2B... Toner non-adhering part, 3... Pressure spring, 4... Power source, 5... Charging blade, 6
…toner.

Claims (1)

[Claims] 1. A developing roller that is in contact with the circumferential surface of the photosensitive drum and rotates as the drum rotates; A one-component developer is charged by a charging blade that is in contact with the pressure line and to which a bias voltage is applied, and is adhered to and held on the circumferential surface of the developing roller. In an electrophotographic developing device that visualizes an electrostatic latent image on a drum, the width of the charging blade is made larger than the width of the developing roller to which the developer adheres;
An electrophotographic developing device characterized in that the volume resistivity and hardness of both end portions of the developing roller to which the developer does not adhere are higher than those of the intermediate portion to which the developer adheres. 2 In the product described in item 1 above, the volume resistivity value of both end portions of the developing roller to which the developer does not adhere is 10 ⁷ Ωcm or more, and that of the other portions is 10 ⁵
An electrophotographic developing device characterized in that the hardness is Ωcm or less, and the hardness of both end portions to which the developer does not adhere is a Shore hardness of 60 or more, and that of the other portions is a Shore hardness of 50 or less.