JPH0535048A - Electrifying device and process cartridge or image forming device having electrifying device - Google Patents

Abstract

PURPOSE:To suppress the deformation of a body to be electrified, such as image carrying member, and to eliminate the vibration by the deformation as well as to prevent the electrifying sounds produced therefrom by including an object having >=0.5 sp. gr. in the body to be electrified. CONSTITUTION:A photosensitive drum 1 which is the image carrying member consists of a grounded base body 1a consisting of aluminum and an org. photosensitive layer 1b formed on the outer peripheral surface of this base body 1a and is rotated at a prescribed circumferential speed in an arrow A direction. An electrifying roller 2 consists of a conductive metal core 2a consisting of SUS and a conductive elastic layer 2b consisting of urethane rubber contg. carbon formed on the outer peripheral surface thereof and is driven and rotated by being brought into pressurized contact with the surface of the photosensitive drum 1 by means of a spring not shown in Fig. Water 16 which is a material to be included and is sealed into a thin PVC bag 15 having the outside diameter of the diameter nearly the same as the inside diameter of the photosensitive drum 1 and making contact with the inside surface of the photosensitive drum 1 is included over the entire area of the effective electrification width of the electrifying roller 2 in contact with the photosensitive drum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for contacting an object to be charged such as an electrophotographic photosensitive member (including discharging) and a process cartridge or an image forming apparatus having the charging device. .

BACKGROUND ART Conventionally, a corona discharge device has been generally used as a charging device for charging a charged body such as a photoconductor used in an image forming apparatus such as an electrophotographic apparatus. However, recently, it has advantages such as low power supply voltage and very small amount of ozone generation. Therefore, contact charging by contacting a roller-type or blade-type member with a body to be charged. The device is being adopted.

FIG. 11 is a schematic configuration diagram showing an example of a contact charging device using a roller type charging member, that is, a so-called charging roller.

In FIG. 11, 101 is a member to be charged, which has a predetermined peripheral speed (process speed) in the direction of arrow B.
It is a photosensitive drum as an image bearing member which is rotationally driven by.
This photosensitive drum 101 is a base 1 made of aluminum.
01a and an organic photosensitive layer 101b formed on the outer peripheral surface of the base 101a. Further, 102 is a charging roller as a contact charging device which is brought into contact with the surface of the photosensitive drum 101 and is driven to rotate, and 103 is the charging roller 102.
It is a high voltage power supply for applying a voltage to.

The charging roller 102 is formed by coating the outer peripheral surface of a conductive cored bar 102a of iron, SUS or the like with a conductive elastic layer 102b such as urethane rubber containing carbon. The charging roller 102 is electrically conductive. At both ends in the longitudinal direction of the core metal 102a, spring members (not shown) are pressed against the surface of the photosensitive drum 101.

The charging roller 102 is vibrated by superimposing an AC voltage having a peak-to-peak voltage which is more than twice the charging start voltage on the surface of the photosensitive drum 101 when a DC voltage is applied to the DC voltage by a high voltage power source 103. A voltage is applied to charge the surface of the photosensitive drum 101 to a predetermined potential.

[0007]

However, in the contact charging device as shown in the above-mentioned conventional example, as the peripheral speed of the photosensitive drum is increased, the voltage is applied to the charging roller in order to ensure uniform charging of the surface of the photosensitive drum. It is necessary to increase the frequency of the alternating voltage
When it exceeds Hz, there is a problem that so-called charging noise becomes large due to the vibration of the photosensitive drum and the charging roller.

It has been clarified that this phenomenon occurs by the following mechanism.

That is, when an oscillating voltage is applied to the charging roller, an attractive force acts between the photosensitive drum and the charging roller by an electrostatic force, and the maximum and minimum values of the oscillating voltage attract each other. Becomes larger, the photosensitive drum and the charging roller are elastically deformed and attracted to each other.
At the central value of the oscillating voltage, the mutual attractive force becomes small, and the photosensitive drum and the charging roller tend to separate from each other due to the elastic deformation recovery force of the charging roller. Therefore, the photosensitive drum and the charging roller vibrate at a frequency twice as high as the applied vibration voltage.

Further, the photosensitive drum and the charging roller rotate while moving while rubbing against each other, but an attractive force is exerted by the electrostatic force, and the mutual attractive force between the maximum value portion and the minimum value portion of the oscillating voltage is large. When the charging roller is elastically deformed and attracted to the photosensitive drum, the mutual rotational movements are braked, and the mutual attractive force becomes small at the center value of the oscillating voltage, resulting in elastic deformation of the charging roller. When the photosensitive drum and the charging roller are about to separate from each other, this braking force is relaxed. For this reason, vibration due to stick-slip occurs as if the surface of the glass that was wet was rubbed with a finger. This vibration also occurs at a frequency twice that of the applied oscillating voltage, as in the above.

Although the charging sound is caused by the vibration as described above,
Since this basically occurs at a frequency twice that of the applied AC voltage, for example, when the frequency of the AC voltage is 300 Hz, a sound of 600 Hz is observed. In addition to this, there are also cases where a harmonic component of an integral multiple thereof, or, rarely, a frequency of an applied oscillating voltage and a harmonic component of an integral multiple thereof are also observed.

Such a charging sound is directly emitted as a sound from the contact portion between the photosensitive drum and the charging roller, and the vibration of the photosensitive drum is transmitted to, for example, a process cartridge or an image forming apparatus, and converted into a sound there. It may be done.

[Object of the Invention] The present invention has been made in view of the above problems, and an object thereof is to provide a charging device, a process cartridge and an image forming apparatus which prevent charging noise.

Another object of the present invention is to provide a charging device, a process cartridge and an image forming apparatus in which deformation of a member to be charged such as an image carrier is suppressed and vibration due to the deformation is prevented.

In order to achieve the above object, according to the present invention, a charging member that comes into contact with a member to be charged is provided, and a voltage is applied between the member to be charged and the charging member. In the charging device for charging the charged body, the charged body contains a substance having a specific gravity of 0.5 or more.

According to the present invention, there is provided a process cartridge detachably mountable to an image forming apparatus, wherein a voltage is applied between the image carrier and the image carrier, and a voltage is applied between the image carrier and the image carrier. In a process cartridge having a charging member that charges the image carrier, the image carrier has a specific gravity of 0.
It is characterized by containing 5 or more substances.

Further, according to the present invention, a voltage is applied between the image carrier, the image forming means for forming an image on the image carrier, the image carrier and the image carrier. In the image forming apparatus having a charging member that charges the image carrier, the image carrier contains a substance having a specific gravity of 0.5 or more.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an electrophotographic printer as an example of the image forming apparatus of the present invention.

Reference numeral 1 denotes an electrophotographic photosensitive drum, in which a photosensitive material such as OPC, amorphous Se or amorphous Si is formed on a cylindrical or belt-shaped base made of aluminum or nickel. In this embodiment, it has a cylindrical shape. The charging roller 2 uniformly charges the photosensitive drum 1. Next, the laser scanner 3 performs a raster scanner exposure based on the image signal. The laser scanner 3 scans the blinking of the semiconductor laser with a polygon scanner and irradiates the photosensitive drum with an optical system. As a result, an electrostatic latent image is formed on the photosensitive drum 1. The produced electrostatic latent image is developed by the developing device 4. Development is
Jumping development, two-component development, FEED development, etc. are used. When recording, the laser is turned on and toner is attached to the latent image having the lower potential. Reversal development is used in combination.

The developed toner image is transferred to a transfer material. The transfer material is contained in the cassette 5 and is fed one by one by the paper feed roller 6. When the print signal is sent from the host computer, the paper is fed by the paper feed roller 6, and the toner image is transferred onto the transfer material by the transfer roller 8 by the timing roller 7 in synchronization with the image signal. The transfer roller 8 is an electrically conductive elastic body having a low hardness, and is electrostatically transferred by a bias electric field at a nip portion formed by the photosensitive drum 1 and the transfer roller 8.

The transfer material onto which the toner image has been transferred is fixed by the fixing device 9, sent out of the apparatus by the paper discharge roller 10, and discharged to the paper discharge tray 11. On the other hand, the toner remaining after the transfer is cleaned by the cleaner 12 by the blade.

FIG. 2 is a side view of a process cartridge which can be attached to and detached from the image forming apparatus of FIG. 1. The process cartridge C is a photosensitive drum 1, a charging roller 2 as a charging member,
The developing device 4 and the cleaner 12 are supported. Further, the process cartridge C is provided with a shutter 14 for protecting the photosensitive drum 1. Here, the process cartridge C may include at least the photosensitive drum 1 which is an image carrier and the charging roller 2 which is a charging member.

FIG. 3 is a diagram showing an embodiment of a photosensitive drum as a member to be charged and a charging roller as a contact charging device according to the present invention.

In FIG. 3, reference numeral 1 denotes a photosensitive drum, which is composed of a conductive base 1a made of aluminum having a thickness of 1 mm and connected to the ground, and an organic photosensitive layer 1b formed on the outer peripheral surface of the base 1a. Its outer diameter is 30 mm and the arrow A
Is driven to rotate at a predetermined peripheral speed in the direction.

A charging roller 2 is composed of a conductive cored bar 2a made of SUS and a conductive elastic layer 2b made of urethane rubber containing carbon, which is formed on the outer peripheral surface thereof, and has an outer diameter of 12 mm. Yes, at both ends of the conductive core metal 2a in the longitudinal direction (direction perpendicular to the paper surface of FIG. 3), they are pressed against the surface of the photosensitive drum 1 by spring members (not shown).
Followed rotation.

The charging roller 2 is provided with a high voltage power source 3
By applying a predetermined voltage, the surface of the photosensitive drum 1 is charged to a predetermined potential. The voltage applied to the charging roller 2 is preferably an oscillating voltage obtained by superimposing an AC voltage on a DC voltage. The oscillating voltage mentioned here is a voltage whose voltage value periodically changes with time, and the oscillating voltage has a peak-to-peak voltage that is at least twice the charging start voltage of the surface of the photosensitive drum 1 when only a DC voltage is applied. It is preferable for charging uniformity, and the waveform is not limited to a sine wave, and may be a rectangular wave, a triangular wave, or a pulse wave, but from the viewpoint of charging sound, a sine wave that does not include a harmonic component is preferable. Further, the oscillating voltage may be a pulse waveform formed by turning on and off a DC voltage.

Further, the inside of the photosensitive drum 1 has an outer diameter substantially the same as the inner diameter of the photosensitive drum 1 and is enclosed in a thin bag 15 made of polyvinyl chloride that contacts the inner surface of the photosensitive drum 1. Water 16, which is an inclusion substance, is included over the entire effective charging width of the charging roller 2 that contacts the photosensitive drum 1 (see FIG. 4).

Now, two examples of experimental results concerning the charging noise by the present inventors will be shown.

First, with respect to the relationship between the charging sound and the frequency of the oscillating voltage applied to the charging roller, an experimental result using a so-called conventional photosensitive drum 1 in which nothing is included is shown. As an experimental method, background noise 30d
Laser beam printer "LBP-A" in the anechoic chamber of B (A)
404 "(manufactured by Canon Inc.) with a charging roller-containing process cartridge installed and installed in an idler, and at a position 50 cm from the front of the process cartridge,
An ordinary sound level meter "NL-02" (manufactured by Rion Co., Ltd.) is installed.

In the process cartridge, the photosensitive drum is freely rotated by the idler, and a desired voltage can be applied to the charging roller by an external high voltage power source. Then, the noise level XdB (A) when the photosensitive drum is simply driven to rotate and no voltage is applied to the charging roller, and a predetermined frequency obtained by changing the frequency of the charging roller in contact with the photosensitive drum while rotating the photosensitive drum. The noise level YdB (A) when the oscillating voltage is applied is measured, and the difference Δ = Y−XdB
Calculate (A) as the increase in noise level due to charging noise,
Compare. At this time, the peripheral speed of the photosensitive drum is 50 mm.
/ Sec, the peak-to-peak voltage of the vibration voltage applied to the charging roller was 2000V. The measurement results are shown in FIG. 5. The horizontal axis represents the frequency fHz of the vibration voltage applied to the charging roller,
The vertical axis shows the increase in noise level due to charging noise ΔdB (A)
Has been taken.

According to this, when the frequency f of the oscillating voltage applied to the charging roller is in the range of about 400 to 600 Hz, the noise level increase ΔdB (A) due to the charging sound.
It turns out that is the maximum. According to the study by the present inventors, the increase Δ of the noise level due to the charging noise is 4 dB.
It has been confirmed that the noise level is (A) or less so that there is no practical problem, and from this viewpoint, it is understood that the noise level is environmentally unfavorable in the frequency range.

Then, next, the results of experiments on the relationship between the charging sound and the specific gravity of the substance to be encapsulated contained in the photosensitive drum will be shown. The experiment method is basically the same as the above experiment, in which several types of photosensitive drums containing substances having different specific gravities are sequentially mounted in the process cartridge, and in each case, the noise when simply rotating the photosensitive drums is increased. Level X
dB (A) and the noise level YdB (A) when a predetermined vibration voltage is applied to the charging roller in contact with the photosensitive drum while rotating the photosensitive drum are measured, and the difference Δ
= Y−XdB (A) is calculated and compared as an increase in the noise level due to the charging noise. At this time, the peripheral speed of the photosensitive drum was set to 50 mm / sec, and the frequency of the vibration voltage applied to the charging roller was set to 400 Hz based on the above experimental results. The substances contained inside the photosensitive drum include maltoprene (Made by Inoue MTP, specific gravity 0.03), cork (specific gravity 0.22), ethanol (specific gravity 0.79),
Water (specific gravity 1.00), urethane rubber (specific gravity 1.2)
4) and 6 types of fluororubber (specific gravity 1.85) were used. Here, the porous physical properties such as the above-mentioned maltoprene and cork, and the specific gravity of powder and granules are indicated by the apparent specific gravity determined by the external volume. FIG. 6 shows the measurement results. The horizontal axis shows the specific gravity of the substance contained in the photosensitive drum, and the vertical axis shows the increase ΔdB (A) in the noise level due to the charging noise.

According to this, from the curve extrapolated from the measurement result, the increase Δ of the noise level due to the charging sound is 4 dB (by incorporating the substance having the specific gravity of 0.5 or more inside the photosensitive drum. It can be seen that it is possible to set the value to A) or less, which is a level at which there is no practical problem. In order to make the sound deadening effect more reliable, it is desirable that the increase Δ of the noise level be 3 dB (A) or less. For this purpose, the specific gravity of the substance to be encapsulated is 0.8 or more. Preferably there is.

From the following results, in this embodiment, as described above, the inside of the photosensitive drum 1 has an outer diameter substantially the same as the inner diameter of the photosensitive drum 1 and is in contact with the inner surface of the photosensitive drum 1. The water 5 enclosed in the vinyl chloride thin bag 15 is contained over the entire effective charging width (width in contact with the drum 1 in the longitudinal direction of the charging roller) of the charging roller 2 contacting the photosensitive drum 1. As a method of manufacturing such a photosensitive drum, as in the conventional method, after forming the organic photosensitive layer 1b on the outer peripheral surface of the substrate 1a such as aluminum and drying it, the thin bag 15 in which water 16 is sealed in advance is used. Since it need only be inserted into the photosensitive drum 1, for example, an increase in the heat capacity of the photosensitive drum base 1a leads to extreme deterioration of productivity such as formation of the organic photosensitive layer 1b and a long drying process. There is no such thing. Also, in recent years, from the viewpoint of our living environment and protection of resources, the collection and recycling of waste process cartridges and the like have been attracting attention, but by taking the form as shown in this embodiment, It is possible to remove the substance to be encapsulated from the inside of the photosensitive drum of the process cartridge, insert it again into a new drum, and reuse it, which is suitable for so-called recycling.

In general, a process cartridge or the like having a photosensitive drum mounted thereon may have a storage environment below freezing. Therefore, an antifreeze solution may be mixed with the water so that the specific gravity becomes 0.5 or more. Alternatively, a thin bag that contains water may be made of a rubber material that is capable of slightly expanding and contracting so that it can follow the volume change of the substance to be encapsulated.

Next, another embodiment of the substance to be encapsulated inside the photosensitive drum 1 will be described.

Further, in this embodiment, the photosensitive drum 1
The inside of the photosensitive drum is enclosed in a thin bag 15 made of polyvinyl chloride, which has an outer diameter approximately the same as the inner diameter of the photosensitive drum and is in contact with the inner surface of the photosensitive drum 1, and its packing density (bulk density) is 1.
The slaked lime 17 adjusted to 25 g / cm ³ is included over the entire effective charging width of the charging roller 2 that contacts the photosensitive drum 1 (see FIG. 7).

FIG. 8 shows an experimental result by the present inventors regarding the relationship between the charging sound and the frequency of the oscillating voltage applied to the charging roller, using the photosensitive drum.

The experimental method is the same as the above experiment.

According to this, even if the powder is not solid or liquid as shown in the experimental results of the above-mentioned embodiment, the increase Δ of the noise level due to the charging noise can be suppressed to a level at which there is no practical problem. Is possible. As described above, using a powder or granules as a substance to be contained inside the photosensitive drum instead of a liquid such as water makes it possible to prevent thinning due to freezing even when the process cartridge is stored below freezing. It is possible to eliminate concern about damage to the bag 15.

Still another embodiment of the substance to be encapsulated inside the photosensitive drum 1 will be described.

In the present embodiment, the inside of the photosensitive drum 1 has an outer diameter substantially the same as the inner diameter of the photosensitive drum 1 and a length of 50% of the effective charging width of the charging roller 2 contacting the photosensitive drum 1. Columnar molded polyacetal resin 1
8 (specific gravity 1.42) is, for example, by press fitting the photosensitive drum 1
It is contained in the central portion in the longitudinal direction of the photosensitive drum 1 so as to come into contact with the inner surface of the photosensitive drum 1 (see FIG. 9).

Now, two further experimental results regarding the charging noise by the present inventors will be shown.

First, the experimental results on the relationship between the charging sound, the specific gravity of the substance contained inside the photosensitive drum, and the length will be shown. The experimental method is basically the same as the above-described experiment, and the process cartridge has a plurality of cylindrical modified polyphenylene ether resins (specific gravity 1.06) and polybutylene terephthalate resin (specific gravity 1.31) having different lengths. ), A photosensitive drum containing polyethylene terephthalate resin (specific gravity 1.56) is sequentially mounted, and each time, the noise level XdB (A) when no voltage is applied to the charging roller by simply driving the photosensitive drum to rotate.
And the noise level YdB (A) when a predetermined AC voltage is applied to the charging roller in contact with the photosensitive drum while rotating the photosensitive drum, and the difference Δ = Y−Xd
B (A) is calculated and compared as an increase in the noise level due to the charging sound. At this time, the peripheral speed of the photosensitive drum is 50.
mm / sec, the frequency of the vibration voltage applied to the charging roller was set to 400 Hz based on the above experimental results. The outer diameter of each of the cylindrical resins is approximately the same as the inner diameter of the photosensitive drum, and is configured to contact the inner surface of the photosensitive drum. The measurement results are shown in FIG. 10. The horizontal axis represents the ratio of the length a of the cylindrical resin contained inside the photosensitive drum to the effective charging width b of the charging roller in contact with the photosensitive drum Z = a.
/ B, and the vertical axis represents the increase in noise level due to charging noise Δd
B (A) is taken.

According to this, the product of the specific gravity ρ of the cylindrical resin contained in the photosensitive drum and the ratio Z of the lengths is 0.5.
In other words, in other words, by setting the length a of the cylindrical resin so as to satisfy the following expression, a ≧ 0.5 × d / ρ, the increase in the noise level due to the charging noise is 4 dB. (A) It became possible to make it below, and it was found that there was no problem in practical use. Regarding the position where the cylindrical resin is arranged inside the photosensitive drum, even when it is arranged at the longitudinal end of the photosensitive drum, the same effect as when it is arranged at the center is obtained. It was

Next, Table 1 shows the experimental results on the relationship between the charging sound and the contact state between the substance contained inside the photosensitive drum and the inner surface of the photosensitive drum. In the photosensitive drum shown in this embodiment, a cylindrical polyacetal resin having an outer diameter of 26 mm and a length of 50% of the effective charging width of the charging roller contacting the photosensitive drum is exposed through a supporting member (not shown). By supporting the driving flanges at both ends of the drum, a photosensitive drum that maintains it in a non-contact state with the inner surface of the photosensitive drum, and a so-called conventional photosensitive drum that does not contain anything inside, are prepared. The amount of increase ΔdB (A) in noise level due to the charging noise was measured for each of them by the experimental method shown in the above-mentioned example. At this time,
The frequency of the vibration voltage applied to the charging roller was 400 Hz.

[0048]

[Table 1]

According to this, even if the specific gravity of the substance contained in the photosensitive drum is large, the vibration of the photosensitive drum cannot be suppressed unless it is in contact with the inner surface of the photosensitive drum. It turns out that it is impossible to suppress the generation of charging noise.

From the above results, in the present embodiment, as described above, the effective charging of the charging roller 2 contacting the photosensitive drum 1 with the outer diameter substantially the same as the inner diameter of the photosensitive drum 1 inside the photosensitive drum 1. A cylindrical polyacetal resin 18 (specific gravity 1.42) having a length of 50% of the width is included in the longitudinal center of the photosensitive drum 1 so as to come into contact with the inner surface of the photosensitive drum 1. However, by using a solid substance as the substance to be contained inside the photosensitive drum in this way, even when the process cartridge is stored below freezing, the thin bag is damaged due to freezing as shown in the first embodiment. It goes without saying that such concerns can be eliminated, and productivity and workability during assembly can be significantly improved.

In this embodiment, the polyacetal resin is used. However, in addition to this, for example, resins such as polymethylmethacrylate, fluorine, silicone, polycarbonate, polyphenylene sulfide, and metal such as SUS and brass may be used. Not to mention good things.

As shown in the experimental example of the first embodiment, when an elastic body such as urethane rubber or fluororubber is used as the substance to be encapsulated, its outer diameter is made slightly larger than the inner diameter of the photosensitive drum. This ensures a reliable contact state with the inner surface of the photosensitive drum, which is very effective.

[0053]

As described above, according to the present invention,
When the charged body such as the image carrier contains a substance having a specific gravity of 0.5 or more, the vibration of the charged body can be suppressed and the generation of charging noise can be suppressed to a low level.

[Brief description of drawings]

FIG. 1 is a schematic side view of an image forming apparatus of the present invention.

FIG. 2 is a schematic side view of a process cartridge of the present invention.

FIG. 3 is a schematic side view showing a first embodiment of the charging device of the present invention.

FIG. 4 is a front view showing details of the photosensitive drum in the first embodiment.

FIG. 5 is a graph showing a relationship between charging sound and applied frequency.

FIG. 6 is a graph showing the relationship between the charging sound and the specific gravity of the substance to be encapsulated.

FIG. 7 is a front view showing details of a photosensitive drum according to a second embodiment.

FIG. 8 is a graph showing a relationship between charging sound and applied frequency.

FIG. 9 is a front view showing details of a photosensitive drum in a third embodiment.

FIG. 10 is a graph showing the relationship between the charging sound, the specific gravity of the substance to be encapsulated, and the length.

FIG. 11 is a side view showing a conventional charging device.

[Explanation of symbols]

1 101 is a photosensitive drum 2 102 is a charging roller 3 103 is a high voltage power supply 15 Thin bag for encapsulating substances 16 Water as a substance to be encapsulated 17 Slaked lime as an encapsulated substance 18 Polyacetal resin as encapsulated substance

Continued front page    (72) Inventor Hiroshi Sasame             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation (72) Inventor Manabu Takano             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation

Claims (6)

[Claims] 1. A charging device, comprising: a charging member that is in contact with a member to be charged, wherein a voltage is applied between the member to be charged and the charging member to charge the member to be charged; A charging device characterized by containing a substance having a specific gravity of 0.5 or more. 2. The charging device according to claim 1, wherein at least a part of the substance to be encapsulated or a part of a member including the substance comes into contact with the inner surface of the body to be charged. 3. A process cartridge attachable to and detachable from an image forming apparatus, wherein an image carrier and the image carrier are in contact with each other, and a voltage is applied between the image carrier and the image carrier to charge the image carrier. In the process cartridge having the charging member, the image carrier contains a substance having a specific gravity of 0.5 or more. 4. The process cartridge according to claim 3, wherein at least a part of the substance to be encapsulated or a part of a member including the substance comes into contact with the inner surface of the image bearing body. 5. An image carrier, an image forming means for forming an image on the image carrier, and the image carrier which is in contact with the image carrier and a voltage is applied between the image carrier and the image carrier. An image forming apparatus having an electrifying charging member, wherein the image carrier contains a substance having a specific gravity of 0.5 or more. 6. The image forming apparatus according to claim 5, wherein at least a part of the substance to be encapsulated or a part of a member including the substance comes into contact with the inner surface of the image bearing body.