JPH0934335A - Image forming device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve electrostatic charging unevenness of the magnetic pole pitch of a magnet roller and eliminate non-image part fogging of a reversal development system as to the image forming device which directly discharges electric charges by bringing a magnetic brush into contact with a charge injec tion layer on the top surface of a photosensitive drum. SOLUTION: The respective valuse of the radius R of the photosensitive drum 1, the moving speed V of the surface, the radius (r) of the magnet roller 201, the half-value ω of the normaldirectional magnetic flux density of the magnetic poles, the rotational frequency (m), the gap (g) between the photosensitive drum 1 and magnet roller 201, and the width (x) of an electrostatic charging nip formed on the photosensitive drum by the magnetic brush are so set that |(360mx/v)+atan(Rsin(360x/2πR)/(r+g+R-Rcos(360x/2πR)))>=ω. Then an optional point on the photosensitive drum is able to comes into contact with an area where the magnetic brush is very thick between the magnetic poles while passing through the electrostatic charging nip, so the contact between the photosensitive drum surface and magnetic brush is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer, and a process cartridge detachably attached to an image forming apparatus main body.

[0002]

2. Description of the Related Art Conventionally, a corona charger has been used as a charging device mounted on an electrophotographic image forming apparatus. In recent years, a contact charging device has been put into practical use instead of this. This aims at low ozone and low electric power, and in particular, a roller charging method using a conductive roller as a charging member is preferable and widely used in terms of charging stability.

In roller charging, a conductive elastic roller is brought into pressure contact with a photoconductor (member to be charged), and a voltage is applied to the photoconductor to charge the photoconductor by discharging. Specifically, the DC charging method, that is, the discharge start voltage (OP
When the charging roller is pressed against the C photoconductor, the required photoconductor surface potential V _d is about 550 V).
A charging method in which charging is performed by applying a charged DC voltage, or an AC charging method, that is, a voltage equivalent to the surface potential V _d of the photoconductor required for the purpose of improving the fluctuation of the potential due to environmental and durability fluctuations. There is a charging method in which charging is performed by applying a voltage obtained by superimposing an AC component having a peak-to-peak voltage that is at least twice the discharge start voltage to the contact charging member. However, even in these charging methods, there remain problems such as generation of a very small amount of ozone, vibration between the charging member and the photoconductor due to the electric field of AC voltage, generation of charging sound, and deterioration of the photoconductor surface due to discharge. Has been done.

Therefore, as a new charging method, a charging method by directly injecting charges into the photosensitive member is disclosed in Japanese Patent Application No. 04-15.
8128, and Japanese Patent Application No. 05-066150. This charging system consists of charging roller, charging brush,
A voltage is applied to a contact conductive member such as a charging magnetic brush to inject charge into a charge injection layer (for example, conductive fine particles dispersed in a high-resistive resin) provided on the surface of the photoconductor to perform contact injection charging. Is the way to do it. In this charging method, since the discharge phenomenon is not used, the voltage required for charging is about the desired surface potential of the photoconductor, and no ozone is generated. It is a charging method that has advantages such as little surface deterioration.

The charging magnetic brush in the above-mentioned charging member is
A sleeve rotating system in which a magnetic brush of conductive magnetic particles is formed on a sleeve-shaped rotating body containing a multi-pole magnet roller, and the sleeve-shaped rotating body is abolished to reduce the cost directly and the magnetic roller is directly magnetized. Forming a brush,
There is a magnet rotating system that rotates a magnet roller.

[0006]

However, when charging is performed by using the above-mentioned charging member of the magnet rotating system, the density of the magnetic brush becomes sparse at the magnetic pole position on the magnet roller, and the magnetic pole pitch is changed. There is a problem in that a charging failure occurs, which causes density unevenness and causes fog in a non-image area in a so-called reversal developing device that forms a toner image on an exposed area.

This is because a strong magnetic field at the magnetic pole position widens the distance between the magnetic brushes by the magnetic particles to create a sparse state, and when the magnetic pole position comes to the contact nip with the photoconductor by the rotation of the magnet roller, the surface of the photoconductor is This is because the contact property of is deteriorated, resulting in poor charging.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus and a process cartridge in which uneven charging of a magnetic pole pitch of a magnet is improved and density unevenness and non-image portion fog are eliminated.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, in which conductive magnetic particles are carried on the surface of a magnet roller to form a magnetic brush, and the conductive magnetic particles are provided on the surface of a photosensitive drum. In the image forming apparatus equipped with a charging device that contacts the charge injection layer formed on the surface of the photosensitive drum, rotates the magnetic brush, and applies a voltage to the magnetic brush to charge the charge injection layer. R (mm), the moving speed of the surface is V (mm / s),
The radius of the magnet roller is r (mm), and the half-value width of the magnetic flux density in the normal direction of the magnetic poles (1 / the maximum magnetic flux density Br _max ).
The angle of magnetic flux density of 2 or more is ω (°), and the rotation speed is m (r
ps), the gap between the photosensitive drum and the magnet roller is g (mm), and the width of the charging nip formed on the photosensitive drum by the magnetic brush is x (mm). Each value is set so that 360mx / v + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] | ≧ ω holds.

Further, magnetic particles are supported on the surface of the magnet roller to form a magnetic brush, and the magnetic particles are brought into contact with the charge injection layer formed on the surface of the photosensitive drum, and the magnetic brush is rotated to cause the magnetic brush to rotate. In an image forming apparatus including a charging device that applies a voltage to charge the charge injection layer, the radius of the photosensitive drum is R (m
m), the moving speed of the surface is V (mm / s), the radius of the magnet roller is r (mm), the number of poles of the magnetic pole is n, the number of rotations is m (rps), and the gap between the photosensitive drum and the magnet roller is G (mm), and the width of the charging nip formed on the photosensitive drum by the magnetic brush is x (mm)
, Such that | 360mx / v + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] ｜ ≧ 360 / n holds The feature is that each value is set.

Further, the process cartridge is formed by integrally incorporating any one of the above-mentioned charging device and at least one of an image carrier, a developing means and a cleaning means into a cartridge container, and is formed with respect to the main body of the image forming apparatus. It is characterized in that it is detachably attached.

[Operation] Based on the above configuration, the radius R (mm) of the photosensitive drum, the surface moving speed V (mm / s), the radius r (mm) of the magnet roller, and the half value width of the magnetic flux density in the normal direction of the magnetic pole. (Angle of magnetic flux density of 1/2 or more of maximum magnetic flux density Br _max ) ω (°), rotation speed m (rps), gap g (mm) between photosensitive drum and magnet roller, formed on photosensitive drum by magnetic brush By setting the width x (mm) of the charging nip and the number n of the magnetic poles to satisfy the above relational expression, the magnetic pole of the magnet roller is positioned at any position on the photosensitive drum. Even if there is such a point, the magnetic brush between the magnetic poles can always come into contact with the very dense area while the point passes through the charging nip, and the contact property between the surface of the photosensitive drum and the magnetic brush is improved. Magnetic pole Improve charge unevenness of pitch, it is possible to eliminate the non-image portion fog in uneven density or reversal development system.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIGS. 1 and 2 are sectional views of an image forming apparatus according to the present embodiment and a main portion thereof. The present embodiment is an image forming apparatus using a so-called reversal development method, which forms a toner image on an exposed portion. In these figures,
1 is a photosensitive drum having a charge injection layer on the surface as a latent image carrier (a conductive organic fine particle is dispersed in a high resistance resin to form a thin layer on the surface of an ordinary organic photoreceptor), and 200 is a photosensitive drum 1. A charging member for charging the toner, 3 is a laser beam that is an exposing unit that writes an electrostatic latent image on the photosensitive drum 1,
Numeral 4 is a developing sleeve which is a developer carrying member arranged in proximity to the toner, and thereby the electrostatic latent image on the photosensitive drum 1 is transferred to the toner 6
To develop. A doctor blade 12 made of urethane rubber or the like is elastically contacted with the developing sleeve 4 to make the toner layer thickness on the surface of the developing sleeve 4 a uniform predetermined value. Reference numeral 5 is a developing sleeve 4 and a developing device containing toner 6, and 7 is a transfer roller for transferring the toner image on the photosensitive drum 1 onto a paper 11 which is a recording medium. Reference numeral 8 is a cleaning blade for cleaning the transfer residual toner on the photosensitive drum 1, and 9 is a waste toner container for storing the scraped transfer residual toner. The paper 11 on which the toner image is transferred is the fixing device 10
Then, the fixing process is performed, the sheet is ejected outside the apparatus, and the printing operation ends.

The charging member 200 is a so-called magnet roller 201 in which a multi-pole magnet is formed in a roll shape around the shaft, and the surface of the magnet roller is coated with a thin layer of a conductive resin. The diameter is about 30 μm and the volume resistivity is 10 ⁶ Ω · cm. The magnetic brush is formed by magnetically adhering the conductive magnetic particles 202. Further, the charging device is configured to include, in addition to the magnetic brush, a driving device (not shown) that rotationally drives the magnetic brush, and a power supply circuit 204 that applies a voltage. The magnet roller has a gap 203 from the surface of the photosensitive drum 1 by the roller 203.
(Mm), magnetic brush nip width x (mm)
It is in contact with. Further, the drive device sets the rotation direction of the photosensitive drum 1 (clockwise direction in the figure) to be positive, and m
It is rotated at (rps).

Since the magnetic brush formed on the surface of the magnet roller 201 has a high magnetic flux density in the normal direction, the density becomes sparse as shown in FIG. 3 at the magnetic pole positions (N pole and S pole). When this portion is brought into contact with the photosensitive drum 1 to perform charging, a portion which cannot sufficiently come into contact with the magnetic brush is formed on the photosensitive drum 1, and the charging member 200 is brought into contact with the photosensitive drum 1 to directly inject the electric charge into the photosensitive drum 1. It will be defective. On the other hand, between the magnetic poles (between the magnetic poles: C), the magnetic brush is very dense, so that the magnetic brush can sufficiently contact with the photosensitive drum 1 and the charging is good. In the area where the magnetic brush is sparse, the distribution half-value width of the magnetic flux density in the direction normal to the magnet roller 201 (angle of ½ or more of the maximum magnetic flux density of the pole: ω
(°)) tends to increase as it increases. When a region where the magnetic brush becomes sparse due to the rotation of the magnet roller 201 periodically arrives at the charging nip, good charging and poor charging are alternately caused (uneven charging of magnetic pole pitch), resulting in density unevenness and non-uniformity in the image portion. The toner will be fogged in the image area. In the above-described image forming apparatus, when comparing the potential difference between the surface potentials of the well-charged portion and the poorly-charged portion (potential difference of uneven charging) with the actual degree of image density unevenness or non-image portion fog, as shown in FIG. It was found that if the potential difference of the charging unevenness was within 30 V, there was no problem in the actual image.

Therefore, the applicant considers that the cause of the uneven charging of the magnetic pole pitch is the moving distance (angle) of the surface of the magnet roller 201 with respect to the surface of the photosensitive drum 1 and the magnetic flux density distribution in the normal direction of the magnet roller 201. Experiments were conducted to obtain conditions for improving pitch charging unevenness.

The moving distance (angle) of the surface of the magnet roller 201 with respect to the surface of the photosensitive drum 1 can be considered as follows. In FIG. 5, assuming that the magnet roller 201 is rotating in the positive direction (clockwise direction in the figure), the closest contact points between the photosensitive drum 1 and the magnet roller 201 at a certain moment (upstream ends of the charging nip: a1, b1). ) Are A and B, respectively. Process speed V (mm / s)
Then, the time t for the point A on the photosensitive drum 1 to pass through the width x (mm) of the charging nip is t = x / V (sec), and at that time, the point B on the magnet roller 201 has an angle θ1 = 360. Rotate by × m × t = 360 × m × xx / V (°) and come to the position of b3. However, the photosensitive drum 1
The upper point A has moved to the downstream end a2 of the charging nip,
The point on the facing magnet roller 201 is b2. The angle between the closest contact b1 of the photosensitive drum 1 and the magnet roller 201 and the point b2 (charging nip angle of the magnet roller 201: θ2 (°)) is
Radius r (mm), gap between magnet roller 201 and photosensitive drum 1 g (mm), radius R of photosensitive drum 1
(Mm), charging nip width x (mm), given by θ2 = atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}]. That is, when viewed from the point A on the photosensitive drum 1, the point A is the angle of the magnet roller 201 on the point A during the charging nip passage time, θ3 = θ1 + θ2 = (360mx / v) + atan [Rsin (360x / 2πR) / It means that it rotates by {r + g + R-Rcos (360x / 2 πR)}].

The half-value width ω (°) of the magnetic flux density in the normal direction of the magnet roller 201 is ½ of the maximum value of the magnetic poles by actually measuring the magnetic flux density in the normal direction every 1 ° in the circumferential direction.
Given from the angle. 6 (a) and 6 (b) respectively show NO. 1 Mag and NO. The magnetic flux density distribution of the normal direction of two 2Mag magnet rollers is shown. FIG. 6 (a),
As shown in the magnetic flux density distribution of (b), NO. The full width at half maximum of 1 Mag is ω1 = 54 °, and NO. The half-value width of 2 Mag is ω2
= 77 °.

The experiment was conducted as follows. NO. 1M
ag and NO. A magnet roller having a radius of 2 Mag (radius r = 7 mm) is arranged in proximity to the photosensitive drum 1 having a radius R = 15 (mm) with a gap g = 500 μm, and conductive magnetic particles 202 are attached to the magnet roller to charge nip width x by a magnetic brush.
(Mm) is formed. A DC voltage of -400 V is applied from the power supply circuit 204 to the magnet roller 201 while rotating the photosensitive drum 1 at the surface moving speed V = 70 (mm / s) and the magnet roller 201 at m (rps) by the driving device. The surface potential of the photosensitive drum 1 after being charged is about −
By applying a voltage of 400 V to the developing sleeve 4 with a DC voltage of −500 V superposed with an AC voltage of peak-to-peak voltage V _PP = 1500 V, the toner 6 negatively charged on the photosensitive drum 1 at a developing contrast of about 100 V. Then, it is transferred to paper 11 and fixed to obtain a printer output result. Since the potential difference between the surface potential of the photosensitive drum 1 and the developing sleeve 4 is reduced due to the charging failure, the density of the output result is high. Since the surface potential of the photosensitive drum 1 and the image density correlate with each other, it is possible to know the potential difference of the charging failure by converting the density of the defective charging portion into the surface potential. With such an experimental method, the charging nip width x (m
m), the rotation speed of the magnet roller 201 m (rps)
Was changed to change the rotation angle θ3 of the magnet roller 201 viewed from the point on the photosensitive drum 1, and the potential difference of the charging failure at that time was measured. When the experiment was conducted under the above conditions, the results shown in FIGS. 7 and 8 were obtained.

FIG. 7 shows NO. When 1Mag is used, FIG.
Is NO. The results are obtained when 2 Mag is used, the horizontal axis represents the rotation angle θ3 of the magnet roller 201 viewed from a point on the photosensitive drum 1, and the vertical axis represents the potential difference of the charging unevenness at that time. NO. In the case of 1 Mag, from the result of FIG. 7, in order to reduce the potential difference of charging unevenness to 30 V or less, the rotation angle θ3 of the magnet roller 201 viewed from the point on the photosensitive drum 1 is set to 50.
I found that it should be above °. In addition, NO. 2M
In the case of ag, similarly from the result of FIG. 8, the rotation angle θ3 of the magnet roller 201 when viewed from a point on the photosensitive drum 1 is set to 7
It turns out that it should be 0 ° or more. The results are shown as half widths ω1 and ω2 of the respective magnet rollers 201.
When compared with (°), ω1 = 54 °> 50 °, ω2 =
77 °> 70 °, and if the rotation angle θ3 of the magnet roller 201 viewed from the photosensitive drum 1 is equal to or greater than the half-value width ω, the potential difference due to poor charging is equal to or less than the potential difference at which practically no problem occurs (from the experimental result, It was found that it could be within 25V).

Therefore, from the above results, θ3 ≧ ω, that is, (360mx / v) + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] ≧ ω is satisfied. By setting the respective parameters in this manner, it is possible to bring the density unevenness and the non-image portion fog due to the charging failure of the magnetic pole pitch to a level at which there is no practical problem. This is because, by satisfying the above conditions, when an arbitrary point on the photosensitive drum 1 is taken, the magnetic brush between the magnetic poles will be located at any position of the magnetic pole of the magnet roller 201 while the point passes through the charging nip. This is probably because it became possible to make contact with a very dense region without fail, and the contactability between the VKA degree 1 surface and the magnetic brush was improved, thus improving the charging failure.

In this embodiment, the magnet roller 20 is used.
Although the description has been made by using the device in which 1 is rotating in the forward direction, the same description can be made when the magnet roller 201 is rotating in the reverse direction, that is, when the rotation speed is m (rps) <0. However, when the rotation speed m (rps) <0, the left side of the conditional expression becomes negative, so an absolute value is taken,
With the left side being positive, the conditional expression is expressed as | (360mx / v) + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] | ≧ ω.

In this embodiment, in an image forming apparatus in which the surface moving speed of the photosensitive drum 1 is 70 (mm / s), the photosensitive drum 1 having a radius of 15 (mm) and the magnetic flux density half the normal direction at the radius (7 mm). NO. The 1 Mag magnet roller 201 is used, the gap between the photosensitive drum 1 and the magnet roller 201 is 0.5 (mm), and the width of the nip formed on the photosensitive drum 1 by the magnetic brush is 4 (mm).
The magnet roller 201 at a rotational speed of 1.5 (r
By rotating in the positive direction at (ps), density unevenness and non-image portion fog due to defective charging of the magnetic pole pitch could be brought to a level at which there is no practical problem.

The applicant of the present invention further conducts experiments to obtain a margin for obtaining a good image even if other conditions such as a developing device and a transfer device change due to environment, durability, etc. The conditions under which the voltage can be 20 V or less were determined.

The experiments are shown in FIGS. 6 (a) and 9 (a),
The number of poles having a magnetic flux density distribution in the normal direction as shown in (b) is 4,
Magnet roller Nos. 6 and 8 with radius r = 7 (mm)
1 Mag, NO. 3 Mag, NO. The same method as described above was performed using 4Mag. The experimental conditions are as follows. Radius R of photosensitive drum 1 = 15 (mm), gap between photosensitive drum 1 and magnet roller 201 g = 500 (μ
m), the surface moving speed of the photosensitive drum 1 V = 70 (mm /
s), the charging nip width x by the magnetic brush is 4, 6 (m
m) and adjust the magnet roller 201 to m (rps)
The above voltages were applied while rotating at to obtain a printer output result. The potential difference between the portion where the surface potential of the photosensitive drum 1 drops due to charging failure and the portion where charging is good is converted from the density difference of the output image to obtain the potential difference due to charging failure.
1, the results as shown in FIG. 12 were obtained. FIG. 10 shows NO. 1
When Mag is used, FIG. When 3Mag is used, FIG. 4 is the result when 4 Mag is used, the horizontal axis is the rotation angle θ3 of the magnet roller 201 viewed from a point on the photosensitive drum 1, and the vertical axis is the potential difference of the charging unevenness at that time. NO. In the case of 1 Mag, it was found from the result of FIG. 10 that the rotation angle θ3 of the magnet roller 201 viewed from the point on the photosensitive drum 1 should be set to 80 ° or more in order to reduce the potential difference of the charging unevenness to 20 V or less. . In addition, NO. 3 Mag, NO. In case of 4 Mag, FIG.
Similarly, from the result of FIG. 12, the rotation angle θ3 of the magnet roller 201 when viewed from the point on the photosensitive drum 1 is set to 55.
It has been found that it is better to set the angle to more than 42 ° and more than 42 °. When this result is compared with the magnetic pole pitch 360 / n (°) of each magnet roller 201, 360/4 = 90 °
> 80 °, 360/6 = 60 °> 55 °, 360/8 =
45 °> 42 °, and the rotation angle θ3 of the magnet roller 201 viewed from the photosensitive drum 1 is set to the magnetic pole pitch 360 / n.
With the above, it was found that the potential difference due to poor charging can be kept within 20V.

Therefore, from the above results, θ3 ≧ 360 / n, that is, | (360mx / v) + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] | ≧ If each parameter is set so as to satisfy 360 / n, density unevenness and non-image-area fog caused by poor charging of the magnetic pole pitch can be reduced to a level that is practically acceptable, even when variations due to the environment and durability are taken into consideration. This is because by satisfying the above conditions, the contact between the magnetic poles and the region where the magnetic brush is very dense becomes more reliable, the contact between the surface of the photosensitive drum and the magnetic brush is improved, and the charging failure is eliminated. it is conceivable that.

As described above, the photosensitive drum 1 having the charge injection layer on the surface thereof is contacted with the magnet roller 201 having a magnetic brush formed of the magnetic particles 202 and rotated, and a voltage is applied to perform charging. In the charging device, the radius R (mm) of the photosensitive drum 1, the surface moving speed V (mm / s), and the radius r (m of the magnet roller 201).
m), the half-width of the magnetic flux density in the normal direction of the magnetic pole (angle of magnetic flux density of 1/2 or more of the maximum magnetic flux density value Br _max ) ω (°),
Between the rotational speed m (rps), the gap g (mm) between the photosensitive drum 1 and the magnet roller 201, and the width x (mm) of the charging nip formed on the photosensitive drum 1 by the magnetic brush, | (360mx / v ) + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] | ≧ ω, and more desirably, the above item and the number of magnetic poles n The relationship between | (360mx / v) + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] ｜ ≧ 360 / n 201
It was possible to improve the charging unevenness of the magnetic pole pitch, and to supply a charging device free from density unevenness and non-image portion fog.

In this embodiment, the surface of the image forming apparatus using a so-called reversal developing method for forming a toner image on the exposed portion has been described, but a so-called regular developing method for forming a toner image on the non-exposed portion. The same effect can be obtained in the image forming apparatus using. The photosensitive drum 1 having a charge injection layer on the surface is not limited to the one used in the present embodiment in which conductive fine particles are dispersed in a high-resistive resin to form a thin layer on the surface of an ordinary organic photoreceptor, and also amorphous silicon. There are some that use a photoconductor. In addition, the magnet roller 20
As for No. 1, in addition to the multi-pole magnet formed in a roll shape around the shaft used in the present embodiment, a resin-integrated product or a roll magnet extruded and passed through the shaft is also available. It can be used. <Embodiment 2> FIG. 13 is a sectional view of Embodiment 2 of the present invention, in which the charging device of Embodiment 1 is applied to a belt photosensitive member.

In the figure, 100 is a belt photosensitive member having a charge injection layer on its surface, and 210 is this belt photosensitive member 10.
A charging device for charging 0. In the present embodiment as well, for the same reason as in the first embodiment, it is possible to improve density unevenness and non-image area fog due to defective charging of the magnetic pole pitch, but unlike the case of the photosensitive drum 1, the surface of the photosensitive member is linear. However, it is necessary to partially change the conditional expression in the first embodiment.

V is the moving speed of the surface of the belt photosensitive member 100.
(Mm / s), the radius of the magnet roller 211 is r (m
m), the full width at half maximum of the magnetic flux density in the normal direction of the magnetic pole is ω (°), the rotation speed is m (rps), the gap between the belt photosensitive member 100 and the magnet roller 211 is g (mm), and the belt photosensitive member 100 is separated by a magnetic brush. If the width of the charging nip formed above is x (mm), the charging nip angle θ2 (°) of the magnet roller 201 in the first embodiment is rewritten as θ2 = atan {x / (r + g)}. Therefore, the rotation angle θ3 of the magnet roller viewed from the photosensitive drum is also rewritten as θ3 = θ1 + θ2 = (360mx / V) + atan {x / (r + g)}. That is, when the belt photosensitive member 100 is used, the conditional expression for improving density unevenness and non-image-area fog due to poor charging of the magnetic pole pitch is | (360mx / V) + atan {x / (r + g)} | ≧ ω Is | (360mx / V) + atan {x / (r + g)} | ≧ 360 / n, where n is the number of magnetic poles, and by using the above relationship, the belt photoreceptor 100 is used. In addition, it was possible to improve density unevenness due to charging unevenness of the magnetic pole pitch of the magnet and fogging in non-image areas.

As described above, the present invention can be applied even when the shape of the body to be charged changes from, for example, a drum shape to a belt shape, and density unevenness and non-image portion fog due to uneven charging of the magnetic pole pitch of the magnet are caused. Can be improved. <Third Embodiment> FIG. 14 shows an example in which the charging member 200 described in the first embodiment is incorporated in a cartridge container to form a process cartridge.

In the figure, 1 is a photosensitive drum, 200 is the above-mentioned charging member, 3 is a laser beam, 4 is a developing sleeve, 5 is a developing device, and 7 is a paper 11 which is a recording medium for recording the toner image on the photosensitive drum 1. Is a transfer roller, 8 is a cleaning blade, and 9 is a waste toner container. In the present embodiment, among these, the photosensitive drum 1, the charging member 200, the developing sleeve 4, the developing device 5, the cleaning blade 8 and the waste toner container 9 are integrated into a cartridge, and the image forming apparatus main body (not shown) is formed. Removably attached to.

As a result, it was possible to supply a process cartridge having a small size, a simple structure, and an inexpensive structure and having the effects of the present invention.

[0034]

As described above, according to the present invention,
Conductive magnetic particles are carried on the surface of the magnet roller to form a magnetic brush, and the conductive magnetic particles are brought into contact with the charge injection layer formed on the surface of the photosensitive drum and the magnetic brush is rotated to apply a voltage to the magnetic brush. In the image forming apparatus including a charging device that charges the charge injection layer, the radius of the photosensitive drum is R (mm), the moving speed of the surface is V (mm / s), and the radius of the magnet roller is r ( mm), half-value width of magnetic flux density in the normal direction of magnetic poles (angle of magnetic flux density of 1/2 or more of magnetic flux density maximum value Br _max ) is ω (°), rotation speed is m (rps), the photosensitive drum and magnet When the gap with the roller is g (mm) and the width of the charging nip formed on the photosensitive drum by the magnetic brush is x (mm), | (360mx / v) + atan [ Rsin (360x / 2πR) / (r + g + R-Rcos (360x / 2πR)}] | ≧ ω, each value is set so that, more preferably, | (360mx / v) +, where n is the number of magnetic poles atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] ｜ ≧ 360 / n When a point is taken, no matter where the magnetic pole of the magnet roller is located, it is always possible to make contact with a region where the magnetic brush between the magnetic poles is very dense while the point passes through the charging nip. Since the contact between the surface and the magnetic brush is improved, it is possible to improve charging unevenness of the magnetic pole pitch of the magnet roller and eliminate density unevenness and non-image portion fog in the reversal development method.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a vertical cross-sectional view showing the configuration around the photosensitive drum in the first embodiment.

FIG. 3 is an enlarged vertical sectional view of a photosensitive drum and a charging member according to the first embodiment.

FIG. 4 is a diagram showing the relationship between the potential difference of charging unevenness, density unevenness, and non-image-area fog in the first embodiment.

FIG. 5 is a diagram illustrating a contact state of a magnetic brush with respect to the photosensitive drum according to the first embodiment.

6A and 6B are views showing magnetic flux density distributions in the normal direction of different magnet rollers.

FIG. 7 is a diagram showing a relationship between a rotation angle of a magnet roller and a potential difference of defective charging according to the first embodiment.

FIG. 8 is a diagram showing a relationship between a rotation angle of a magnet roller and a potential difference of defective charging according to the first embodiment.

9A and 9B are views showing magnetic flux density distributions in the normal direction of different magnet rollers.

FIG. 10 is a diagram showing a relationship between a rotation angle of a magnet roller and a potential difference of defective charging according to the first embodiment.

FIG. 11 is a diagram showing the relationship between the rotation angle of the magnet roller and the potential difference of defective charging according to the first embodiment.

FIG. 12 is a diagram showing a relationship between a rotation angle of a magnet roller and a potential difference of defective charging according to the first embodiment.

FIG. 13 is an enlarged vertical sectional view of a belt photosensitive member and a charging member according to the second embodiment.

FIG. 14 is a vertical sectional view showing a schematic configuration of a process cartridge.

[Explanation of symbols]

1 Photosensitive Drum 3 Exposure Means 4 Developing Sleeve 5 Developing Device 6 Toner 7 Transfer Roller 8 Cleaning Blade 9 Waste Toner Container 10 Fixing Device 11 Transfer Material 200 Charging Member (Magnetic Brush) 201 Magnet Roller 202 Conductive Magnetic Particle R Radius of Photosensitive Drum V Moving speed of photosensitive drum surface g Gap between photosensitive drum and magnet roller m Rotation number of magnet roller r Magnet roller radius x Charging nip width ω Half width of magnetic flux density in normal direction of magnetic pole

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masashi Ojima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masahide Kinoshita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Satoshi Tsurutani 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroki Kisu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Within

Claims (3)

[Claims] 1. A magnetic brush is formed by supporting conductive magnetic particles on the surface of a magnet roller, and the conductive magnetic particles are brought into contact with a charge injection layer formed on the surface of a photosensitive drum and the magnetic brush is rotated to move the magnetic brush. In an image forming apparatus including a charging device that applies a voltage to a brush to charge the charge injection layer, the radius of the photosensitive drum is R (mm), the moving speed of the surface is V (mm / s), and the magnet roller is The radius of r (m
m), the half value width of the magnetic flux density in the normal direction of the magnetic pole (angle of magnetic flux density of 1/2 or more of the maximum magnetic flux density value Br _max ) is ω
(°), the number of rotations was m (rps), the gap between the photosensitive drum and the magnet roller was g (mm), and the width of the charging nip formed on the photosensitive drum by the magnetic brush was x (mm). Sometimes, between these, | (360mx / v) + atan [Rsin (360x / 2πR) / {r + g + R-Rcos (360x / 2πR)}] | ≧ ω holds An image forming apparatus characterized by setting a value. 2. A magnetic brush is formed by supporting magnetic particles on the surface of a magnet roller, the magnetic particles are brought into contact with a charge injection layer formed on the surface of a photosensitive drum, and the magnetic brush is rotated to cause the magnetic brush to rotate. In an image forming apparatus including a charging device that applies a voltage to charge the charge injection layer, a radius of the photosensitive drum is R (mm), a moving speed of the surface is V (mm / s), a radius of the magnet roller. R (m
m), the number of magnetic poles is n, the number of rotations is m (rps), and the gap between the photosensitive drum and the magnet roller is g (m).
m), when the width of the charging nip formed on the photosensitive drum by the magnetic brush is x (mm), | (360mx / v) + atan [Rsin (360x / 2πR) / [r + g + R-Rcos (360x / 2πR)}] | ≧ 360 / n, respective values are set so that the image forming apparatus is characterized. 3. A charging device according to claim 1 or 2, and at least one of an image carrier, a developing means, and a cleaning means are integrally incorporated into a cartridge container to form the image forming apparatus main body. The process cartridge is characterized in that it is detachably mounted.