JP2623681B2 - Contact charging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a charging device. More specifically, the present invention relates to a contact charging device that performs charging processing (including charge elimination processing, the same applies hereinafter) on a charging target surface by bringing a charging member to which a voltage is applied into contact with the charging target surface.

(Prior Art) For example, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a corona discharge device has been widely used as a means for charging a surface of an image carrier such as a photoreceptor and a dielectric. I have.

The corona discharge device is effective as a means for uniformly charging a surface of a charged body such as an image carrier to a predetermined potential. However, there is also a problem that a high-voltage power source is required and undesired ozone is generated due to corona discharge.

In contrast to such a corona discharge device, a contact charging device that performs charging processing on the surface of the charged object by bringing the charging member to which the voltage is applied into contact with the surface of the charged object as described above can reduce the power supply pressure and generate ozone. Because of its advantages such as small amount, it is attracting attention, for example, as an image carrier such as a photoconductor and a dielectric, and other charging means for a surface of an object to be charged, in place of a corona discharge device in an image forming apparatus. It is being studied for practical use.

For example, the present applicant has previously proposed (Japanese Patent Application Nos. 62-51492 and 6
As described above, in the contact charging device, an oscillating electric field (alternating electric field) having a peak-to-peak voltage that is at least twice the charging start voltage when a DC voltage is applied to the charging member is applied to the charging member and the member to be charged. And the use of a charging member provided with a high-resistance layer on the surface layer to prevent charge leaks due to pinholes and scratches on the surface of the charged object such as a photoreceptor. Etc. can be achieved.

FIG. 5 shows a schematic configuration of an example of a drum-type transfer electrophotographic apparatus using a contact charging device of this type as a charging means. Reference numeral 2 denotes a predetermined direction in the counterclockwise direction indicated by an arrow around the support shaft 2a. It is a photosensitive drum as a member to be charged, which is driven to rotate at a peripheral speed.
Reference numeral 1 denotes a charging member for performing a contact charging process on the photosensitive drum surface. The charging member of the present embodiment is of a roller type and has a conductive metal core.
1c, a low-resistance base layer 1b on the outer periphery thereof, and a high-resistance coating layer 1a on the outer periphery thereof.The high-resistance coating layer 1a is specifically made of a nylon-based resin material such as resin / amilan, cellophane,
The low-resistance base layer 1b such as NBR is made of carbon-dispersed EPDM or the like.

The charging roller 1 is brought into contact with the surface of the photosensitive drum 2 with a predetermined pressing force, and rotates following the rotation of the photosensitive drum 2. Reference numeral 8 denotes an external power supply for applying a DC voltage in which an AC component (oscillation voltage component) is superimposed on the charging roller 1, and the voltage of the power supply is applied to the cored bar 1c via the electric brush 8a.

As the photosensitive drum 2 rotates, the charging roller 1 undergoes a uniform charging process of a predetermined positive or negative potential with the rotation of the charging roller 1, and an image exposure L by an image exposure unit (not shown) is formed on the charged surface.
(Slit exposure of a document image, laser beam scanning exposure, etc.), an electrostatic latent image corresponding to the exposure image pattern is formed on the photosensitive drum surface. The latent image is visualized as a toner image by the developing device 6, and the toner image is synchronized between the photosensitive drum 2 and the transfer device 4 at a transfer portion from a paper feeding portion (not shown) with the rotation of the photosensitive drum 2. The transfer material 5 is sequentially transferred onto the surface of the transfer material 5 fed. The transfer material 5 to which the toner image has been transferred is separated from the surface of the photosensitive drum 2 and is introduced into an image fixing device (not shown). After the transfer of the toner image, the surface of the photosensitive drum 2 is cleaned by the cleaning device 3 to remove the residual toner, and is repeatedly used for image formation.

The contact charging device as described above prevents a large current from flowing through the high-resistance layer 1a of the charging member 1 even if a scratch such as a pinhole or a dent occurs on the surface of the photosensitive drum 2, which is a member to be charged. . Therefore, spark discharge does not occur, and as a result, it is possible to eliminate the charging abnormality caused by the voltage drop of the external power supply 8.

(Problems to be Solved by the Invention) The high-resistance layer 1a of the charging member 1 functions as described above and is an important component, but a nylon-based resin material usually used as the high-resistance layer, cellophane Rubber-based materials, such as NBR and NBR, have considerably large fluctuations in resistance due to fluctuations in the external environment. For example, in a high-temperature and high-humidity environment, a portion where a charging member is in contact with a member to be charged (hereinafter referred to as a nip, 220 ^mm ×
The resistance of 1 ^mm ) was 6.3 × 10 ⁴ Ω, but may fluctuate to 2.5 × 10 ⁷ Ω under low temperature and low humidity.

 As a result, the following problem occurs.

1) High temperature and high humidity (32.5 ° C., 85%) Since the resistance of the high resistance layer 1a of the charging member 1 decreases in a high temperature and high humidity environment, if a pinhole is generated on the member 2 to be charged, the pinhole is directed toward the portion. Large current flows. As a result, the output of the power supply is reduced, and a charging abnormality occurs in that portion.

In other words, in a high-temperature and high-humidity environment, the leak countermeasure effect is lost.

2) Low temperature and low humidity (15 ° C., 10%) In an environment of low temperature and low humidity, a spot-like charging defect called “sand fog” such as sand on a white background occurs in the reversal developing method. The reason is considered as follows.
That is, the AC component of the power supply 8 applied to the charging member 1 is for making the potential on the charged body 2 uniform. Therefore, if the alternating current is small, uniform charging on the member to be charged is hindered and development called "sand fog" occurs.

Table 1 shows the relationship between the “sand fog” and the AC current I _AC (μA).

The circles indicate that no "sand fog" occurs in the output sample.

 The mark Δ occurs in 50% of the output samples.

 The mark "x" indicates that all of them occur.

From this result, it is understood that it is necessary to supply an alternating current of 750 μA or more to the member to be charged 2 so that “sand fog” does not occur at all.

However, in the case where nylon or cellophane, which is generally used as a constituent material of the high-resistance layer 1a of the charging member 1, is used, in order to flow an alternating current of 750 μA or more under low temperature and low humidity, the peak-to-peak voltage V _PP of 2500 V is charged. It has to be applied to the member 1, which has led to dielectric breakdown of the high resistance layer 1a.

FIG. 2 shows the relationship between the peak-to-peak voltage V _PP and the alternating current I _AC . The horizontal axis represents the peak-to-peak voltage V _PP of the AC power supply 8 applied to the charging member 1, and the vertical axis represents the AC current I flowing at that time.
_AC (μA) is shown. a shows the case where a conventional material such as nylon or cellophane is used for the high-resistance layer 1a of the charging member 1. The right part of the range of a is the case of low temperature and low humidity, and the left part is the AC voltage of high temperature and high humidity. -Shows current characteristics.

In it it can be said so from the Figure 2 graph, the conventional charging member of the nylon cellophane the high resistance layer 1a is was required power 8 put out the above peak-to-peak voltage V _PP 2500V.

Also, as the peak-to-peak voltage _VPP increases, the amount of ozone generated also increases. This is shown in FIG. The horizontal axis indicates the peak-to-peak voltage V _PP applied to the charging member 1, and the vertical axis indicates the amount of ozone generated at that time in PPM.

From this graph, it can be seen that when the peak-to-peak voltage V _PP becomes 2300 V or more, the amount of ozone generated also sharply increases.

On the other hand, materials such as nylon, cellophane, and NBR are vulnerable to ozone and deteriorate significantly, so that there has been a problem that the durability of the charging member 1 is not sufficient.

From the above, in this type of contact charging device, there is no change in characteristics such as resistance due to environmental fluctuation as a charging member, or a device having a small fluctuation range, and has ozone resistance and durability durability. What is needed is development. The present invention addresses this need.

(Means for Solving the Problems) The present invention is a contact charging device having the following configuration.

(1) A charging member for charging an object to be charged by contacting the object, comprising: a base layer; a surface layer; and a resistance layer provided between the base layer and the surface layer. A contact charging device having a charging member to which a voltage is applied, wherein the resistance layer includes epichlorohydrin rubber, and the surface layer includes a nylon resin.

(2) The contact charging device according to (1), wherein the charging member has a roller shape.

(3) The contact charging device according to (1), wherein the charging member has a blade shape.

(Operation) The resistance layer of the charging member is provided with epichlorohydrin rubber, so that the resistance fluctuation with respect to the environmental fluctuation is small. That is, epichlorohydrin rubber has a sufficiently high resistance value as a material for the resistance layer, and furthermore, its resistance value does not fluctuate due to environmental fluctuations and has excellent ozone resistance. Therefore, it is possible to prevent leakage from the charging member to the member to be charged in a high-temperature and high-humidity environment, and to prevent uneven charging by sufficiently preventing an oscillating voltage from being applied to the member in a low-temperature and low-humidity environment. It has good ozone resistance and can be used for a long time.

In addition, by providing the surface layer with a nylon-based resin, it is possible to prevent the plasticizer of the rubber from adhering to the member to be charged.

In addition, by providing a resistance layer having epichlorohydrin rubber, which has a small resistance variation with respect to environmental fluctuations, it is possible to make a surface layer having a nylon-based resin having a large resistance variation with respect to environmental fluctuations thinner than the resistance layer. A charging member with less resistance fluctuation can be obtained.

(Example) FIG. 1 shows a roller type charging member 1 in the electrophotographic apparatus shown in FIG. 5, that is, a charging roller 1, in which a base layer 1b, a resistance layer 1a, and a surface layer 1d are sequentially formed around a cored bar 1c. It was made into a layer configuration. Specifically, the core metal 1c is a φ6 mm metal rod, the base layer 1b is a low-resistance layer of carbon-dispersed EPDM having a thickness of 3 mm, the resistance layer 1a is an epichlorohydrin rubber layer having a thickness of 80 μm, and the surface layer 1d is The resin layer is a nylon resin, in this example, a resin layer having a thickness of about 20 μm.

A voltage superimposed on a DC voltage and an oscillating voltage (a voltage whose voltage value changes periodically with time; a sine wave, a rectangular wave, a triangular wave, etc.) was applied from a power supply 8 to the core metal 1c of the charging roller 1. In this embodiment, the DC component from the power source 8 is controlled at a constant voltage of -750 V, and the AC component (oscillating voltage component) is controlled at a constant current of 750 μA to apply a voltage to uniformly charge the photosensitive drum 2 as an object to be charged. Processing was performed, and image formation was performed.

In this embodiment, since epichlorohydrin rubber having extremely excellent environmental stability of electric resistance was used for the high resistance layer 1a of the charging member 1, the peak-to-peak voltage V _PP required for flowing 750 μA was determined.
It became possible to put it in about 1400-2000V. This is shown in FIG. In the range b, the right side shows the peak-to-peak voltage / current characteristics in the case of low temperature and low humidity, and the left side shows the peak-to-peak voltage / current characteristics in the case of high temperature and high humidity. It can be seen that the fluctuation range of the peak-to-peak voltage is much narrower than the range a of the conventional example described above.

As a result, even in a high-temperature and high-humidity environment, if epichlorohydrin rubber is used for the high-resistance layer 1a, the resistance does not decrease. lost.

Furthermore, since the electrical resistance is stable even in a low-temperature and low-humidity environment, the peak-to-peak voltage V _PP must be increased to 2000 V to supply 750 μA.
It is sufficient to apply the pressure to the extent that ozone generation is reduced.

Next, the resistance fluctuation of the high resistance layer in each environment
Table 2 shows a comparison between that for a nylon-based material such as amilan and that for epichlorohydrin rubber.

From this table it can be said that the resistance of epichlorohydrin rubber is more stable to the environment than other materials.

Since epichlorohydrin rubber has excellent ozone resistance, it does not deteriorate even with a small amount of ozone, and the durability as a charging member is improved. Since the permanent compression strain is very good, the durability of the roller-type charging member is good, and since the hardness is low, the elasticity is also good and a nip width suitable for charging can be obtained with relatively small pressure.

In addition, since the applied voltage can be small at low temperature and low humidity, the high resistance layer does not cause dielectric breakdown.

The surface layer 1d includes a nylon resin. In this example, the surface layer 1d includes the resin layer having a thickness of about 20 μm as described above, so that the charging member 1 is stuck even when left in contact with the member 2 for a long time. No more. further,
The plasticizer in the epichlorohydrin rubber layer 1a directly adheres to the member to be charged 2 and does not reduce the resistance of that portion. Further, since the resin layer 1d has a very small thickness of 20 μm, it is not necessary to consider a change in resistance due to an environmental change.

The charging roller 1 as a charging member may be a stationary roller that does not rotate, or may be a roller that is driven to rotate in the reverse direction. Further, instead of the form of a roller, a blade-like member, a block-like member, a rod-like member, or a brush-like member that is brought into contact with the surface of the member to be charged 2 with a predetermined pressing force may be used.

FIG. 4 shows a cross section of a blade type. In this case, the direction in which the surface of the member to be charged abuts may be either the forward direction or the reverse direction of the surface movement direction of the member to be charged.
In the case of this blade shape, since there is no sliding portion of the contact for applying a voltage to the charging member 1 (the mutual contact sliding portion between the members 1c and 8a in FIGS. In addition to the advantage that the electrical noise is not generated as described above, there is an advantage that the space can be saved and the cleaning blade can also be used.

(Effect of the Invention) As described above, the contact charging device of the present invention has the following effects.

That is, since the resistance layer of the charging member includes the epichlorohydrin rubber, the resistance change with respect to the environmental change is small.
That is, epichlorohydrin rubber has a sufficiently high resistance value as a material for the resistance layer, and furthermore, its resistance value does not fluctuate due to environmental fluctuations and has excellent ozone resistance. Accordingly, it is possible to prevent leakage from the charging member to the member to be charged in a high-temperature, high-humidity environment, and to prevent uneven charging due to insufficient vibration voltage being applied to the member in a low-temperature, low-humidity environment. It has good ozone resistance and can be used for a long time.

In addition, by providing the surface layer with a nylon-based resin, it is possible to prevent the plasticizer of the rubber from adhering to the member to be charged.

In addition, by providing a resistance layer having epichlorohydrin rubber, which has a small resistance variation with respect to environmental fluctuations, it is possible to make a surface layer having a nylon-based resin having a large resistance variation with respect to environmental fluctuations thinner than the resistance layer. A charging member with less resistance fluctuation can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view of a roller-type charging member, FIG. 2 is a graph _showing a relationship between a peak-to-peak voltage V _PP and an alternating current IA, FIG. Figure is a cross-sectional view of the charging member has a blade-type, Fig. 5 an example schematic diagram of an electrophotographic apparatus using a contact charging device, FIG. 6 is relationship graph of peak-to-peak voltage V _PP and the amount of ozone generated PPM It is. 1 is a charging member, 1a is a high resistance layer, 1b is a low resistance base layer, 1c is a metal core, 8 is a voltage application power supply, and 2 is a photosensitive drum as a member to be charged.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junji Araya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shunji Nakamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc. (72) Inventor Masanobu Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-56-104346 (JP, A) JP-A-60-150071 ( JP, A) JP-A-58-194061 (JP, A) JP-A-64-66674 (JP, A) JP-A-58-49960 (JP, A) JP-A-1-142569 (JP, A) 1975-13661 (JP, B2)

Claims (3)

(57) [Claims] 1. A charging member for charging an object to be charged by contacting the object, comprising a base layer, a surface layer, and a resistance layer provided between the base layer and the surface layer. A contact charging device having a charging member to which an oscillating voltage is applied, wherein the resistance layer includes epichlorohydrin rubber, and the surface layer includes a nylon resin. 2. The contact charging device according to claim 1, wherein said charging member has a roller shape. 3. The contact charging device according to claim 1, wherein said charging member has a blade shape.