JPH0527551A - Contact electrifying blade - Google Patents

Abstract

PURPOSE:To maintain stable electrifying treatability over a long period of time by forming the electrifying blade of a conductive member essentially consisting of epichlorhydrin rubber and specifying the rubber hardness. CONSTITUTION:Four processing apparatus; a drum 1, the electrifying blade 2, a developing device 5, and a cleaning device 8, are built into a common housing 9 by having prescribed positional relations with each other and are constituted as a cartridge 11 which is integrally and freely attachable and detachable to and from an image forming device body. The image forming device body side and the process cartridge 11 side are mechanically and electrically coupled by mounting the process cartridge 11 into the image forming body, by which the cartridge can be operated as the image forming device. The electrifying blade 2 is the blade-shaped conductive material formed by properly dispersing a carbon black as conductive powder into the epichlorhydrin rubber to adjust its volumetric resistivity to a prescribed value and has 55 to 80 deg. rubber hardness (JISA).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member of a contact charging device for charging (including removing electricity) by bringing a charging member (conductive member) to which a voltage is applied into contact with a member to be charged. More specifically, it relates to a blade type charging member (charging blade).

[0002]

2. Description of the Related Art For example, a non-contact type corotron or scorotron is used as a means for charging the surface of an image bearing member such as a photoconductor or a dielectric as an object to be charged in an image forming apparatus such as a copying machine or a printer. The corona discharger is widely used.

However, the corona discharger requires an expensive high-voltage power source, requires a space such as itself and a shield space for the high-voltage power source, and corona products such as ozone are often generated, which is an additional measure. There is a problem in that means and mechanisms are required, which are factors that increase the size and cost of the device.

Therefore, in recent years, a contact charging system has been adopted instead of the corona discharger, which has many problems. The contact charging is performed by contacting a conductive member as a contact charging member to which a voltage (for example, a DC voltage of about 1 to 2 KV or a superimposed voltage of a DC voltage and an AC voltage) is applied by a power source to the surface of the image bearing member as a member to be charged. In this way, the surface of the image bearing member is charged to a predetermined potential, and a roller charging type using a roller body as a charging member (Japanese Patent Laid-Open No. 56-91253) and a blade charging type using a blade body (Japanese Patent Laid-Open No. Sho. 56-19434
No. 9 and No. 60-147756), a charging / cleaning combined type (Japanese Patent Laid-Open No. 56-165166) and the like have been devised.

The present invention particularly relates to a charging blade of the blade charging type.

[0006]

In the blade charging type, as a charging blade, generally, EPDM or the like is used as a base material and conductive powder such as carbon black or titanium oxide is mixed for resistance adjustment. 50 °
A conductive elastic blade of about 90 ° is used.

This charging blade is applied to a surface of an image carrier, which is a member to be charged, in a counter direction or a forward direction with respect to a surface moving direction of the surface of the image carrier with a pressing force of a linear pressure of about 20 g / cm. The blade is disposed so as to abut against the rubber elasticity of the blade, and a bias voltage is applied to the blade from a power source to perform contact charging of the surface of the image carrier.

It has been known from an experiment that the contact pressure of the charging blade with respect to the surface of the image bearing member as the member to be charged should be a linear pressure of at least 5 g / cm.
At a contact pressure of about cm or less, the contact of the charging blade with the surface of the image carrier becomes unstable, and charging failure may occur. On the other hand, if the contact pressure is too high, the surface of the image carrier will be excessively scraped by the charging blade, or the driving load for rotating or rotating the image carrier or running or moving the image carrier will be too large. Conventionally, the contact pressure of the blade with respect to the image carrier is generally set at about 20 g / cm in the initial stage as described above.

With respect to the hardness of the charging blade, in the case of a low hardness blade, the charging area is increased and the charging ability is improved. In the case of a high hardness blade, the permanent deformation rate of the blade is very small, and the contact with the image carrier can be stabilized for a long period of time.

However, in a low-hardness blade, the permanent deformation rate of the blade is so large that the contact pressure of the blade disposed in contact with the image bearing member decreases with time, causing contact instability. Poor charging may occur.

Further, in order to obtain a rubber having a low hardness, oil is generally impregnated, and the lower the hardness, the more the oil is impregnated. In addition, the rubber for the charging blade has a large amount of conductive powder mixed with the base rubber for controlling the resistance value and is hard. Therefore, further oil content must be impregnated in order to improve the toughness of the rubber.

Therefore, in a charging blade using a rubber having a low hardness, when the blade is left in pressure contact with the image carrier for a long period of time, the oil content leaches out from the rubber to stain the surface of the image carrier and to improve the image quality. In some cases, the contact portion of the surface of the image carrier adheres to the surface of the image carrier.

On the other hand, in a charging blade using a rubber having a high hardness, due to a decrease in rubber flexibility, it becomes impossible to absorb the unevenness of the surface of the image bearing member, or the blade is likely to bounce when stick-slip. It may cause a defect.

Further, conventionally, in rubber materials such as EPDM and urethane, the resistance value of the rubber itself is relatively high, so that the amount of conductive powder or the like must be increased in order to use it as a material for the charging member. However, when the amount of the conductive powder added is increased, the elastic force of the rubber itself is lowered, which causes problems such as an increase in permanent deformation strain and poor contact stability. Therefore, if a small amount of conductive powder having a lower resistance is used in order to reduce the added amount of the conductive powder, the variation in the resistance value becomes large due to a delicate difference such as molding conditions.

The present invention has been proposed in view of the above,
Contact charging blades that combine the advantages of low hardness blades and high hardness blades, that is, oil from rubber while holding the minimum pressure necessary for stable contact with the charged object by suppressing the permanent deformation rate of the blade. Prevents stains on the surface of the body to be charged due to leaching (prevents image defects due to stains on the surface of the image carrier due to oil leaching in image forming devices), and has the flexibility to absorb irregularities on the surface of the body to be charged. It is an object of the present invention to provide a charging blade which has a stable charging processability over a long period of time.

[0016]

SUMMARY OF THE INVENTION The present invention is a contact charging blade for applying a voltage to an object to be charged so as to charge the object to be charged. The blade is a conductive material containing epichlorohydrin rubber as a main component. Rubber material (JIS
A) is 55 ° -80 °, which is a contact charging blade.

[0017]

[Function] Since epichlorohydrin rubber has a low resistance value, the amount of conductive powder that must be added to obtain the same resistance value is small, and it is possible to minimize adverse effects on rubber physical properties. Becomes Therefore, it is possible to control the resistance value without significantly impairing the physical properties of rubber, and the charging blade is made of a conductive member containing epichlorohydrin rubber as a main component, and the rubber hardness is 55 ° to 80 °. Prevents stains on the surface of the body to be charged due to oil leaching from the rubber while suppressing the deformation rate and maintaining the minimum required pressure for stable contact with the body to be charged, and also absorbs irregularities on the surface of the body to be charged. It has flexibility and can maintain stable chargeability over a long period of time.

[0018]

【Example】

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus using a blade type contact charging device using a charging blade according to the present invention as a charging process means of an image carrier. The image forming apparatus of this example is a copying machine or a laser beam printer using an electrophotographic process.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a drum) as an image bearing member (charged member). The drum 1 is rotationally driven in the clockwise direction indicated by arrow a at a predetermined peripheral speed (process speed).

Numeral 2 is a charging blade disposed in contact with the surface of the drum 1 in order to uniformly charge the surface of the rotating drum to a predetermined polarity and potential. The charging blade 2 will be described in detail in the next section (2).

The surface of the rotary drum 1 which has been uniformly charged by the charging blade 2 is subjected to image exposure 12 (image forming exposure of a document image, laser beam scanning exposure, etc.) corresponding to desired image information by an exposing means (not shown). As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating drum 1.

The formed electrostatic latent image is visualized as a toner image by the developing device 5. The developing device 5 of this example includes a developing sleeve 3 that rotates in the direction of arrow b to convey toner, and an elastic blade for regulating the toner coat thickness on the sleeve 3.

The carried toner image on the surface of the rotating drum 1 is then transferred to the drum 1 and the transfer roller 1 at the position of the transfer roller 10.
It is sequentially transferred to the surface of the transfer material (recording material) P fed in synchronism with the rotation of the drum 1 from the paper feeding means (not shown).

The transfer material P that has received the toner image transfer is the drum 1
The toner image is fixed by being separated from the surface and conveyed to a fixing unit (not shown).

After the transfer of the toner image onto the transfer material P, the surface of the rotary drum 1 is cleaned by a cleaning blade 6 of a cleaning device 8 to scrape off adhered contaminants such as transfer residual toner, and is repeatedly used for image formation. It Reference numeral 7 is a squi sheet for collecting the transfer residual toner scraped off.

In the image forming apparatus of this example, the four process devices of the drum 1, the charging blade 2, the developing device 5 and the cleaning device 8 are assembled in a common housing 9 with a predetermined positional relationship with each other. It is configured as a cartridge 11 that can be collectively attached to and detached from the main body of the forming apparatus.

By mounting the process cartridge 11 in the main body of the image forming apparatus, the main body of the image forming apparatus and the side of the process cartridge 11 are mechanically and electrically coupled to each other to be operable as the image forming apparatus.

(2) Charging Blade 2 The charging blade 2 is a blade-shaped conductive member having a volume resistivity of 1 × 10 ⁶ Ω · cm by appropriately dispersing carbon black as a conductive powder in epichlorohydrin rubber.

The charging blade 2 has its rear end side electrically connected to the conductive support member 21 to be attached and supported,
The support member 21 is disposed by fixing the support member 21 to the inner surface of the housing 9 of the process cartridge 11 by bringing the front end side toward the counter direction with respect to the rotation of the drum 1 and bringing the front end portion into contact with the surface of the drum 1.

The angle θ formed by the contact point 0 and the charging blade 2 at the contact point of the charging blade 2 with respect to the drum 1 is set to about 20 ° from the point of chargeability, and the contact pressure of the charging blade 2 with respect to the drum 1 is 20 g. The initial setting was / cm (line pressure). The blade free length L between the tip of the charging blade 2 and the tip of the supporting member 21 was set to 7 mm.

A predetermined voltage is applied to the charging blade 2 from the power supply device S on the image forming apparatus main body side through the conductive supporting member 21, so that the surface of the rotary drum 1 is charged to the predetermined polarity by the charging blade 2. The electric potential is uniformly charged.

In this example, an oscillating voltage obtained by superimposing an AC voltage and a DC voltage is applied. The oscillating voltage is a voltage whose voltage value periodically changes with time. More specifically, the charging blade 2 is preferably applied with a voltage obtained by superimposing an AC voltage and a DC voltage having a peak-to-peak voltage that is at least twice the charging start voltage of the drum 1. The waveform of the oscillating voltage is not limited to the sine wave, and may be a rectangular wave, a triangular wave, or a pulse wave.
The AC voltage includes a rectangular wave voltage formed by periodically turning the DC power supply on and off.

In the present embodiment, the contact pressure of the charging blade 2 with respect to the drum 1 is set to 20 g / cm in the initial stage as described above, but the rubber of the charging blade 2 exhibits creep characteristics and permanently deforms over time. Therefore, the contact pressure gradually decreases from the above initial setting. Process cartridge 11 of the cartridge detachable image forming apparatus as in this embodiment
Since the guarantee period is generally 2 years, the contact pressure of about 5 g / cm, which is the minimum required contact pressure, is maintained even after 2 years, and the charging failure due to insufficient contact pressure does not occur. Must be.

Experiment 1 According to the experiments conducted by the present inventors, the charging blades 2 made of the above-mentioned materials and used in the present example and having various hardnesses were set to an initial contact pressure of 20 g / cm and an environment of 45 ° C. The relationship between the rubber hardness and the permanent deformation rate of the blade after left under pressure for 5 days (this is equivalent to 2 years under an environment of 23 ° C. as a normal environment) is as shown in the graph of FIG. is there.

The term "permanent deformation rate" used herein means, for example, 45 ° C./5 with the tip portion of the blade 2 being pressed and deformed by 1 mm.
After leaving for a day, the pressure contact is released, the deformed amount of the blade 2 is set within 1 minute after the release, and the permanent deformation rate is 10% if the deformed amount does not return to 0.1 mm, similarly.
It is assumed that the permanent deformation rate is 50% if it is not deformed by 5 mm and the permanent deformation rate is 100% if it is not deformed by 1 mm. That is, the permanent deformation rate of the blade 2 is smaller as the rubber hardness is higher and larger as the rubber hardness is lower than the graph of FIG.

As described above, the minimum pressure required for stabilizing the contact of the blade is 5 g / cm. Therefore, as in the conventional case, the initial setting of 20 g / cm is left at 45 ° C. for 5 days. In order to maintain the contact pressure of 5 g / cm, the permanent deformation rate must be kept within 75%.

Therefore, in terms of the permanent deformation rate for securing the contact pressure, the rubber hardness must be 55 ° or more.

Experiment 2 Further, as described above, in order to reduce the rubber hardness, the oil content was increased and the molding was conducted.
In the case of materials with low rubber hardness, oil content oozes out when left in pressure contact under high temperature and high humidity, and rubber containing conductive powder to reduce resistance is particularly difficult to knead and more The oil is easily impregnated because it is impregnated with oil. Table 1 shows the results of the relationship between rubber hardness and oil exudation.

Table 1 Rubber hardness VS oil bleeding (measurement condition 35 °, 90% left for 1 week)

[0040]

[Table 1] ◯: Good image quality (no oil bleeding out) ×: Poor image quality (oil bleeding out) As conditions for this experiment 2, the contact condition of the charging blade 2 with the drum 1 was the same as described above, and the charging blade 2 was a drum. The whole process cartridge 11 kept in pressure contact with 1 was left for 1 week in an environment of a temperature of 35 ° and a humidity of 90%, and thereafter, image formation was performed to evaluate the image quality.

As a result, when the rubber hardness is 50 °, the drum 1
Oil oozes out on the top and image quality is poor, but the hardness is 55.
Above 0 °, good image quality was obtained without oil bleeding. Again, it is understood that the rubber hardness must be 55 ° or more in terms of oil bleeding.

Experiment 3 At the temperature of 15 ° C. and the humidity of 10%, which is considered to be a severe condition in which the charging property is easily deteriorated because the charging blade 2 becomes less responsive to the increase in the resistance of the rubber and the vibration. At low temperature and low humidity, the charging blade 2 as described above
Table 2 shows the results of image quality evaluation using the process cartridge 11 in which the above-mentioned settings and configurations were performed.

Table 2 Rubber hardness VS chargeability (measurement environment 15 ° C, 10%)

[0044]

[Table 2] ◯: Good charging property (no charging failure) Δ: Occasionally, charging failure occurred.

X: Mostly, the charging is defective.

Poor charging occurs in almost the entire area of the image.

In Experiment 3, the charging blade 2 was evaluated for the charging property based on the image quality obtained by superimposing an AC voltage of 1.4 KV to 2.4 KV on the charging blade 2 at -700 V. The rubber hardness was swung by 8 points from 55 ° to 83 °.

The reason why the experiment is carried out at an AC voltage of 1.4 KV or higher is that if the voltage is lower than this, the effect of leveling the potential on the drum 1 by the AC voltage becomes small and the image becomes rough. Also, considering the fluctuation of individual components in each transformer, it is desirable to have a margin of ± 10% with respect to the set voltage.

Considering the results of the above Experiment 3 in consideration of the above, the rubber hardness can be allowed only from 50 ° to 80 °.

The reason why the charging failure occurs when the AC voltage is large is that the charging blade 2 which originally stick-slip is promoted by a larger AC voltage, so that the contact state becomes unstable, and the rubber is further damaged. This is because the followability to the rotation of the drum surface is deteriorated due to the increased hardness, and the allowable range of the charging property is narrowed.

From the results of the three experiments 1 to 3 above, the rubber hardnesses that can pass each test are 55 ° to 80 °.
It can be seen that is suitable for obtaining stable image quality in the long term.

As described above, all the blades of each hardness used here adjust the mixing amount of the conductive powder to keep the resistance of the rubber constant and change the hardness.

In the present example, the rubber was made conductive by adding conductive powder of only epichlorohydrin rubber. The reason is that the resistance value of epichlorohydrin rubber itself is relatively lower than that of other rubbers. Since the resistance value of the rubber itself is low, the amount of conductive powder that must be added to obtain the same resistance value is small, and the adverse effect on the physical properties of the rubber can be minimized.

Since epichlorohydrin rubber itself is slightly inferior in permanent deformation, it is effective to improve the permanent deformation by mixing a rubber such as urethane rubber or EDPM.

In FIG. 3, a conductive powder such as titanium oxide is dispersed in urethane resin on the contact surface of the charging blade 2 with the drum 1, and the surface has a resistivity of 1 × 10 ⁹ Ω / □ and a thickness of about 30 μm. The resistance layer 2a of FIG. The blade main body 2 as the base layer is made of the same material as the charging blade 2.

The surface of the drum 1 of the above-mentioned resistance layer 2a may be damaged as a low breakdown voltage defective portion due to some factors,
Even when a pinhole occurs, it has a function of preventing scratches and charge concentration at the pinhole portion, so that stable chargeability can always be obtained.

In this case as well, the characteristics of the blade are the same as described above, and even if there is a thin resistance layer 2a coated or adhered only on the tip of the blade 2, the relationship between the permanent deformation rate and the charging property and the rubber hardness is as follows. Similar results were obtained, and the above characteristics depend on the rubber hardness of the epichlorohydrin rubber as the base layer.

[0058]

As described above, the contact charging blade of the present invention is capable of controlling the resistance value without significantly impairing the physical properties of rubber, and suppresses the permanent deformation rate of the blade to stabilize the contact with the body to be charged. While keeping the minimum required pressure, prevent the surface of the body to be charged from being soiled due to oil seeping out from the rubber (in the image forming apparatus, preventing image defects due to stains on the surface of the image carrier due to oil seeping out), and the surface of the body to be charged. It has the flexibility to absorb even the unevenness of, and can maintain stable chargeability for a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus in which a blade type contact charging device using a charging blade according to the present invention is used as an image carrier charging unit.

[Fig. 2] Relationship graph between rubber hardness and permanent deformation rate

FIG. 3 is a view showing an example in which a resistance layer is provided on a contact surface of a charging blade against a drum.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (charged body) as an image carrier 2 Charging blade 5 Developing device 8 Cleaning device 10 Transfer roller 11 Process cartridge P Transfer material S Power supply device

Claims (1)

Claim: What is claimed is: 1. A contact charging blade for applying a voltage to contact a charged body to charge the charged body, the blade being a conductive member containing epichlorohydrin rubber as a main component. The contact charging blade has a rubber hardness (JIS A) of 55 ° to 80 °.