JPH10213946A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent electrification performance from being lowered by the increase of the resistance value of the magnetic grain of a contact type electrification means occurring because toner is mixed in. SOLUTION: This image forming device is provided with a magnetic brush 30 having the magnetic grain as the contact type electrification means and constituted so that toner left on a photoreceptor after transfer is developed and recovered at the same time by a developing device 4. Then, an image is formed by setting the saturated potential of the photoreceptor 1 electrified by the brush 30 so as to be higher toward a charge polarity side than a voltage impressed on the brush 30 from a power source S1. Even when the resistance value of the magnetic grain single body is increased by stain occurring because toner is fused on the magnetic grain by endurance, the increase of the resistance value as the whole of the brush 30 becomes small. Thus, electrification unevenness occurring because the toner is mixed in the magnetic grain of the brush 30 is eliminated and an excellent image is obtained by preventing defective electrification from occurring.

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 using an electrophotographic process, such as a copying machine, a laser beam printer, and a facsimile.

[0002]

2. Description of the Related Art FIG. 5 is a schematic structural view showing an example of a conventional image forming apparatus. This image forming apparatus is a laser beam printer utilizing an electrophotographic process.

In FIG. 1, A is a laser beam printer as an image forming apparatus, and B is an image reading device (image scanner) mounted on the laser beam printer A.

In the image reading apparatus B, reference numeral 20 denotes a fixed original platen glass. The original G is placed on the upper surface of the original platen glass 20 with the surface to be copied facing downward, and an original (not shown) is placed thereon. Set it over the board. An image reading unit 21 includes a document irradiation lamp 21a, a short focus lens array 21b, a CCD sensor 21c, and the like.
When a copy button (not shown) is pressed, the image reading unit 21 moves forward from the home position on the left side of the original table glass 20 to the right side along the lower surface of the original table glass 20 when the copy button (not shown) is pressed. When it is driven and reaches a predetermined end point of reciprocation, it is driven backward and returned to the initial home position.

In the forward driving process of the image reading unit 21, the downward image surface of the placed and set original G on the original platen glass 20 is sequentially illuminated and scanned from the left side to the right side by the original irradiating lamp 21a. The light reflected on the document surface is converted into a CCD by the short focus lens array 21b.
An image is incident on the sensor 21c.

The CCD sensor 21c comprises a light receiving section, a transfer section, and an output section (not shown). In the light receiving section, an optical signal is converted into a charge signal, and the transfer section sequentially outputs an output signal in synchronization with a clock pulse. The charge signal is converted to a voltage signal at the output unit, amplified, reduced in impedance, and output. The analog signal thus obtained is converted into a digital signal by well-known image processing and output to the laser beam printer A.

On the other hand, in a laser beam printer (image forming apparatus) A, reference numeral 1 denotes a rotating drum type photosensitive member as an image carrier. The photoreceptor 1 is driven to rotate around a central support shaft at a predetermined peripheral speed (process speed) in the direction of arrow a, and receives a uniform charging process by the charging device 2 during the rotation process.

Then, the uniformly charged surface of the photoreceptor 1 is modulated in accordance with an image signal output from the exposure device (laser scanning device) 3 and output from the image reading device B to the laser beam printer A side. By performing the scanning exposure L by the laser beam thus formed, an electrostatic latent image corresponding to the image information of the document G photoelectrically read by the image reading device B is sequentially formed on the photoconductor 1. The electrostatic latent images formed on the photoreceptor 1 are sequentially reversely developed as toner images by the developing device 4. The developing method using the developing device 4 is preferably a two-component contact developing method in which a mixture of toner particles and a magnetic carrier is used as a developer and conveyed by magnetic force to develop the photosensitive member 1 in a contact state. Used for

On the other hand, the transfer material P such as paper stored in the paper feed cassette 5 is fed one by one by the paper feed roller 6,
The paper is fed to the transfer nip portion between the photoconductor 1 and the transfer device 8 at a predetermined timing by the registration roller
The transfer blade 9 transfers the toner image on the photoconductor 1 to the transfer material P. The transfer material P on which the toner image has been transferred is transferred to the fixing device 1 by a transfer belt 10 also serving as a transport belt.
1 and is discharged outside after being fixed as a permanent fixed image.

[0010] Adhered contaminants such as untransferred toner adhering to the photoreceptor 1 after the transfer of the toner image are removed by the cleaner 1.
2 is removed by the cleaning blade 13 and image formation is repeated.

[0011]

In recent years, a so-called cleaner-less system has been put into practical use for the purpose of reducing the size and simplification of the apparatus, or not producing waste toner (transfer residual toner) from the viewpoint of ecology. I have.

In the laser beam printer (image forming apparatus) A, the cleaner 12 for removing the transfer residual toner from the surface of the photoreceptor 1 after the transfer of the toner image to the transfer material P is removed, and the developing device 4 The transfer residual toner is collected by simultaneous cleaning with development.

Simultaneous development cleaning is the potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photoreceptor 1 when the transfer residual toner remaining on the photoreceptor 1 after transfer is developed in the next and subsequent steps. This is a method of recovering by fogging potential difference. According to this method, the transfer residual toner is collected and used in the subsequent steps, so that the transfer residual toner can be eliminated. In addition, there is a great advantage in terms of space, and the size of the apparatus can be greatly reduced.

However, as described above, when the image is formed by removing the cleaner 12 and collecting the transfer residual toner by simultaneous cleaning with the developing device 4, the image is formed on the portion of the transfer material P where the image is formed without the image. There is a problem that a so-called positive ghost occurs in which the previous image remains thin in the rotation cycle of the photoconductor 1. This positive ghost is a phenomenon that occurs because the toner remaining after transfer of the previous image could not be collected in the developing area, and the toner is transferred to a place that is originally a white background.

On the other hand, in a cleaner-less system for simultaneous recovery of development by a contact charging device using magnetic particles such as a magnetic brush as the charging device 2, transfer residual toner remaining on the photoreceptor 1 during the transfer process is peeled off. Many toners are charged to the opposite polarity of the normal charging polarity by discharge or the like, and generally the charging potential is lower than the voltage applied to the magnetic brush. Therefore, the transfer residual toner is collected by the magnetic brush. The collected toner is charged to normal charging polarity by frictional charging with magnetic particles in the magnetic brush, and
Spitted up. The toner discharged in this manner is collected by the developing device 4 due to a fog removal potential difference during development.

However, even in an image forming apparatus using such a contact charging device (magnetic brush), the above-described positive ghost occurs when image formation is repeated. This positive ghost is generated because it is impossible to charge below the transfer residual toner when passing through the contact charging device (magnetic brush), and becomes more conspicuous when the contact charging device (magnetic brush) is contaminated. Therefore, the transfer residual toner is peeled off from the surface of the photoconductor 1 at the time of charging, and is returned to the surface of the photoconductor 1 after the charging.
It is important to collect at

Further, since toner particles having a relatively high electric resistance are generally used, if toner is excessively mixed or adhered to the contact charging device (magnetic brush), the contact charging device (magnetic brush) may be damaged. There has been a problem that charging unevenness and charging performance are reduced due to an increase in resistance and image defects occur.

As described above, in the conventional cleaner-less image forming apparatus in which the transfer residual toner and the like remaining on the photoreceptor are collected by the developing device, charging non-uniformity occurs due to mixing of the transfer residual toner into the contact charging device, and charging is performed. Performance degrades,
Good image formation could not be performed over a long period of time.

Therefore, the present invention provides a cleaner-less image forming apparatus in which a transfer residual toner or the like remaining on a photoreceptor is collected by a developing device. It is an object of the present invention to provide an image forming apparatus capable of preventing the occurrence of an image.

[0020]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an image carrier for carrying an image, and magnetic particles which contact the image carrier and charge the image carrier. , A power supply for applying a voltage to the contact charging means, an exposure means for forming an electrostatic latent image on the image carrier, and a toner image formed by developing the electrostatic latent image Developing means for transferring the toner image to a transfer material at a transfer portion, and developing the residual toner on the image carrier after transferring the toner image to the transfer material by the transfer means. The saturation potential of the image carrier charged by the contact charging unit is higher on the charging polarity side than the voltage applied from the power supply to the contact charging unit. Settings It is characterized by performing the formation.

Further, a predetermined amount of toner particles is mixed in the magnetic particles in the contact charging means in advance.

Further, the magnetic particles and the toner particles in the contact charging means have a volume resistance of 1 × 10 ⁶ or more when the image carrier is charged by the contact charging means.
It is characterized by being in the range of 1 × 10 ⁹ Ω · cm.

Further, the image carrier has a photosensitive layer and a surface layer thereon, wherein the surface layer has a resin and conductive fine particles.

Further, the surface potential of the image carrier due to the rubbing when no voltage is applied to the image carrier due to the rubbing with the contact charging means gradually decreases toward the charging polarity side with the endurance.

(Operation) In the image forming apparatus for simultaneously recovering the transfer residual toner by the above-described developing device during development, as described above, many toners are charged to the opposite polarity to the normal charging polarity during transfer, and generally, Since the charging potential is lower than the voltage applied to the contact charging device such as a magnetic brush, the transfer residual toner is collected by the contact charging device (magnetic brush). However, according to experiments performed by the present inventors, it has been found that the transfer residual toner is recovered by the contact charging device even when the toner is charged higher than the voltage applied to the contact charging device. This means that, even when charging is higher than the applied bias at the end of charging, at the start of charging,
Since it is lower than the applied bias, it is considered that the toner is collected on the upstream side of the charging nip in the photoconductor rotation direction.

However, when the toner is charged higher than the applied bias at the end of charging as in the present invention, the toner collected and charged to the normal charging polarity by frictional charging is:
The toner cannot be discharged to the photoconductor, and the amount of toner mixed into the contact charging device increases. When toner is mixed into the contact charging device to a certain extent, a large amount of toner having frictional charging characteristics on the charging polarity side is mixed in, so that the frictional charging property is reduced to a charging potential lower than the applied bias, and the mixing amount increases beyond that. No longer.

The present invention utilizes this principle,
For magnetic particles alone, using a contact charging device (magnetic brush) having magnetic particles charged higher than the applied bias,
In a state in which toner is mixed to some extent and the charged potential is substantially the same as the applied bias, a single magnetic particle having a low resistance value is used so as to obtain an appropriate resistance value. As described above, by using magnetic particles having a resistance value slightly lower and having an appropriate resistance in a state in which the toner is mixed, due to durability, the toner is contaminated on the magnetic particles by fusion or the like.
Even when the resistance value of the magnetic particles alone increases, the increase in the resistance value of the entire contact charging device becomes small.

This is because when the magnetic particles alone are charged higher than the applied bias, the surface of the magnetic particles has the characteristic of charging the photosensitive member to the charging polarity side with respect to the triboelectric charging polarity. When the toner or the like is fused, the portion of the triboelectric charge polarity shows the opposite characteristic. For this reason, the charging potential is lowered, and the discharge of the toner is promoted. As a result, the amount of mixed toner is reduced. Thus, good image formation can be performed while maintaining good charging performance.

[0029]

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

(First Embodiment) FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. The image forming apparatus of the present embodiment is a laser beam printer using an electrophotographic process, uses a magnetic brush type contact charging device as a charging unit for an image carrier, and is a cleanerless system device. Note that the same members as those of the conventional example shown in FIG. 5 are denoted by the same reference numerals, and redundant description will be omitted.

In FIG. 1, A is a laser beam printer as an image forming apparatus according to the present embodiment, and B is an image reading device (image scanner) mounted on the laser beam printer A. The configuration of the image reading device B is the same as that of the conventional example shown in FIG. 5, and a description thereof will be omitted in the present embodiment.

A laser beam printer (image forming apparatus) A includes a rotating drum type photosensitive member 1 as an image carrier.
The apparatus includes a magnetic brush charging device 30 serving as a contact charging device, an exposure device 3, a developing device 4, a transfer device 8, a fixing device 11, and the like.

As the photoreceptor 1, a commonly used organic photoreceptor or the like can be used. Preferably, a surface layer having a resistance of 10 ⁹ to 10 ¹⁴ Ω · cm is formed on the organic photoreceptor. The use of an element having an amorphous silicon photoreceptor or the like makes it possible to realize charge injection charging, which is effective in preventing ozone generation and reducing power consumption. Further, the chargeability can be improved.

In the present embodiment, the photosensitive member 1 is a negatively charged organic photosensitive member as shown in FIG. 2, and is formed on a drum base 1a made of aluminum having a diameter of 30 mm from first to fifth in order from the bottom.
And a photoreceptor layer 1b composed of the following five layers, and is driven to rotate at a predetermined process speed (for example, 100 mm / sec) in the direction of arrow a.

The lowermost first layer of the photoreceptor layer 1b is a subbing layer, which is a conductive layer having a thickness of 20 μm and provided for smoothing out defects or the like of the drum substrate 1a. The second layer is a positive charge injection preventing layer, which serves to prevent positive charges injected from the drum substrate 1a from canceling out negative charges charged on the surface of the photoreceptor 1, and comprises an amylan resin and methoxymethylated nylon. Is a 1 μm thick medium resistance layer whose resistance is adjusted to about 10 ⁶ Ω · cm. The third layer is a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and generates positive and negative charge pairs upon exposure. The fourth layer is a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor.

Therefore, the negative charges charged on the surface of the photoreceptor 1 cannot move through this layer, and only the positive charges generated in the third layer (charge generation layer) can be transported to the surface of the photoreceptor 1. it can. The fifth layer, which is a surface layer, is a charge injection layer, and is used as a conductive fine particle in a binder of an insulating resin.
This is a coating layer of a material in which O ₂ ultrafine particles are dispersed. Specifically, SnO ₂ ultrafine particles having a particle diameter of about 0.03 μm obtained by doping antimony, which is a light-transmitting conductive filler, to an insulating resin to reduce the resistance (conducting) are dispersed in the resin by 70% by weight. It is a coating layer of the material obtained. The coating solution thus prepared was applied to a thickness of about 3 μm by a suitable coating method such as dipping coating method, spray coating method, roll coat coating method, beam coat coating method, etc. to form a charge injection layer.

The contact charging means is a magnetic brush charging device (hereinafter referred to as a magnetic brush) 30 as shown in FIG.
In this embodiment, the magnetic brush 30 includes a fixed magnet roller 30a having a diameter of 16 mm, a nonmagnetic SUS sleeve 30b rotatably fitted on the magnet roller 30a, and a magnet on the outer peripheral surface of the sleeve 30b. This is a sleeve rotating type of a magnetic brush layer 30c of conductive magnetic particles (magnetic carrier) adhered and held by the magnetic force of the roller 30a.

The magnet roller 30a included in the sleeve 30b has four magnetic poles that generate a magnetic flux density peak of 800 G in the radial direction on the surface of the sleeve 30b, and one magnetic pole is provided on the photosensitive member 1 side. Fix the magnet roller 30a so that it faces
The sleeve 30b is rotatably arranged along the outer circumference of the.
The sleeve 30b is arranged so as to keep a constant interval (0.5 mm in the present embodiment) with respect to the photoconductor 1, and the width of the charging nip portion n between the magnetic brush layer 30 and the photoconductor 1 is set to 6 mm.
mm. Then, a predetermined charging bias voltage (DC voltage in the present embodiment) is applied to the sleeve 30b from the power supply S1.
Is applied to the sleeve 30b at the charging nip portion n with the photoconductor 1 in the direction of arrow b opposite to the rotation direction a of the photoconductor 1, for example, at a rotational speed of 100 mm / sec of the photoconductor 1.
By rotating the photosensitive member 1 at a peripheral speed of 150 mm / sec, the surface of the photosensitive member 1 is rubbed with the magnetic brush layer 30c to which the charging bias is applied, and the surface of the photosensitive member 1b of the photosensitive member 1 has a desired potential. The primary charging process is uniformly performed by an injection charging method. Here, the charging potential is based on the sum of the electric charge injected through the magnetic particles and the electric charge given by the triboelectric charging of the magnetic particles and the surface of the photosensitive member 1. Depending on the case, the charging potential may be higher than the applied voltage.

The conductive magnetic particles constituting the magnetic brush layer 30c were prepared by oxidizing and reducing the ferrite surface to adjust the resistance, whereas the resistance was adjusted by dispersing carbon black in a silicon-based resin. A coating agent coated with 1.0% by weight of a coating agent is used. The core of the conductive magnetic particles has an average particle diameter of 10 to 100 μm, a saturation magnetization of 20 to 250 emu / cm ³ , and a resistance of 10 ² to 10 ¹⁰
Ω · cm is used. Further, considering that there is an insulation defect such as a pinhole in the photoreceptor 1, it is preferable to use one having a resistance of 10 ⁶ Ω · cm or more. Further, it is better to use one having a resistance as small as possible to improve the charging performance, and it is preferable to use one having a resistance of 10 ⁹ Ω · cm or less in order to perform uniform charging. Therefore, in the present embodiment, the average particle size is 25 μm.
m, resistance 5 × 10 ⁶ Ω · cm, saturation magnetization 200 A · m ²
/ Kg. The magnetic particles used in the present embodiment are obtained by coating the core magnetic particles with a coating agent. By selecting a resin of the coating agent, the triboelectric charging characteristics of the photoconductor 1 can be changed.
Also, by changing the amount of dispersion of carbon black, the resistance as magnetic particles can be changed. In the present embodiment, as shown in Table 1, four types of resins A to D are used for the triboelectric charging characteristic, and four types a to d having different resistance values are used by changing the dispersion amount of carbon black for the resistance value. And evaluated (details will be described later).

[0040]

[Table 1] The above-described resistance measurement of the magnetic particles was performed by filling a cylindrical container having a bottom area of 228 mm ² with 2 g of the magnetic particles and then charging 6.6 kg.
/ Cm ^2, and a voltage of 100 V was applied between the upper and lower sides, and the value was defined as a value calculated from the current flowing through the system.

The exposure apparatus 3 includes a rotating polygon mirror 31, fθ
Lens group 32, reflection mirror 33, solid-state laser element 34
When the surface of the photosensitive member 1 is subjected to laser scanning exposure L by the exposure device 3, a light emission signal generator (not shown) based on an image signal input from the image reading device B is provided.
Thereby, the solid-state laser element 34 is lightened (ON / OFF) at a predetermined timing. And the solid-state laser element 3
4 is converted into a substantially parallel light beam by a collimator lens system (not shown), and is further scanned by a rotating polygon mirror 31 rotating at a high speed. Is formed in the form of a spot. By such laser scanning, the photosensitive member 1
An exposure distribution for one scan of the image is formed on the surface,
By scrolling the surface of the photoconductor 1 vertically by a predetermined amount for each scan, an exposure distribution according to the image signal input from the image reading device B is obtained on the surface of the photoconductor 1.

That is, the solid-state laser element 34 which emits ON / OFF light corresponding to an image signal on the uniformly charged surface of the photosensitive member 1
Is scanned by a rotating polygon mirror 31 rotating at a high speed, an electrostatic latent image corresponding to the scanning exposure pattern is sequentially formed on the surface of the photoconductor 1.

FIG. 3 is a schematic structural view showing a developing device 4 which is a two-component contact developing device (two-component magnetic brush developing device) of the present embodiment. In this drawing, reference numeral 41 denotes a developing sleeve that is driven to rotate in the direction of arrow e, 42 denotes a magnet roller fixedly arranged in the developing sleeve 41, and 43 and 44.
Is a stirring screw, and 45 is a developing sleeve 41 for the developer T.
A regulating blade arranged to form a thin layer on the surface of the
46 is a developing container, and 47 is a toner hopper for replenishment.

The developing sleeve 41 is arranged so that a region closest to the photoconductor 1 is at least about 500 μm at least during development, and a thin layer Ta of the developer T formed on the surface of the developing sleeve 41 is It is set so that development can be performed in a state of contact with. The toner t, which is the developer T used in the present embodiment, is obtained by externally adding 1.5% by weight of titanium oxide having an average particle diameter of 20 nm to a negatively charged toner having an average particle diameter of 6 μm manufactured by a pulverization method. The carrier c has a saturation magnetization of 205 emu /
A magnetic carrier having an average particle size of 35 μm in cm ³ was used. A mixture of the toner t and the carrier c at a weight ratio of 8:92 was used as the developer T. Toner in the developer T in this case, the frictional charge amount of about -25 × 10 ^- was ³ c / kg. FIG. 4 is a view showing a device for measuring the triboelectric charge amount of toner. As shown in this figure, a metal cylindrical measurement container 52 having an 800 mesh screen 53 is provided with:
A two-component agent obtained by mixing the toner particles whose magnetic charge amount is to be measured and the magnetic carrier at a weight ratio of 5:95 was mixed with 50-1.
In a polyethylene bottle (not shown) having a capacity of 00 ml and shaken by hand for about 10 to 40 seconds, add about 0.5 to 1.5 g of the two-component agent, and put a hole in the upper opening of the measuring container 52. Have many open lids 54. Measurement container 5 at this time
2 Let W1 (kg) be the total weight.

Then, suction is performed from a suction port 57 of a suction device 51 (at least a portion in contact with the measurement container 52 is an insulator) connected to a lower portion of the measurement container 52, and an air volume adjusting valve 56 is adjusted to reduce the pressure of the vacuum gauge 55. It is 250 mmAq. In this state, suction is sufficiently performed, preferably for 2 minutes, to remove the resin by suction. The potential of the electrometer 59 at this time is set to V (volt).

A condenser 58 has a capacity C (F), and the total weight of the measuring container 52 after suction is W.
Assuming that the toner is 1 (kg), the triboelectric charge amount of the toner is obtained by the following equation (1).

[0047]

(Equation 1) Next, a developing process of visualizing the electrostatic latent image on the surface of the photoconductor 1 by a two-component magnetic brush method using the developing device 4 and a circulation system of the developer T will be described. First, the developing sleeve 41
The developer T pumped up by the N ₂ pole of the magnet roller 42 with the rotation of the magnet roller 42 is regulated by the regulating blade 45 arranged perpendicular to the developing sleeve 41 in the process of being transported from the S ₂ pole to the N ₁ pole. Thus, a thin layer Ta of the developer T is formed on the developing sleeve 41. When the developer T thin layer Ta is formed is conveyed to the S ₁ pole, brush is formed by the magnetic force. Developing the electrostatic latent image by the developer T formed on the spikes, then, N _3-pole, N
The developer T on the developing sleeve 41 is generated by the repulsive magnetic field of the _two poles.
Is returned into the developing container 46.

A direct current (DC) voltage and an alternating current (AC) voltage are applied to the developing sleeve 41 from a power source S2. In the present embodiment, a DC voltage of -480 V and a frequency of 30
An AC voltage having a peak-to-peak voltage of 1500 V is applied at 00 Hz. In general, in the two-component developing method, when an AC voltage is applied, the developing efficiency is increased, and the quality of an image is high, but on the contrary, fogging is likely to occur. For this reason, fogging can be prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photoconductor 1. The potential difference for preventing fogging is called a fogging potential. This potential difference prevents toner from adhering to a non-image area during development and collects untransferred toner.

The transfer device 8 of the present embodiment is a belt transfer device, which suspends an endless transfer belt 10 between a driving roller 61 and a driven roller 62, and is substantially the same as the peripheral speed of the photosensitive member 1 in the direction of arrow f. It is driven to rotate at the peripheral speed. The transfer belt 1 is provided by a transfer charging blade 9 provided inside the transfer belt 10.
0 is brought into contact with the surface of the photoconductor 1. The transfer material P is conveyed to the transfer nip 63 on the upper surface of the ascending belt portion of the transfer belt 10. The tip of the transfer material P is the transfer nip 63
At the time when the transfer charging blade 9
By applying a predetermined transfer bias from 3, the reverse polarity of the toner t is applied from the back surface of the transfer material P, and the toner image on the surface of the photoconductor 1 is sequentially transferred to the upper surface of the transfer material P.

In this embodiment, the transfer belt 10
A film made of a polyimide resin having a film thickness of 75 μm was used. The material of the transfer belt 10 is not limited to a polyimide resin, but may be, for example, a polycarbonate resin, a polyethylene terephthalate resin, a polyvinylidene fluoride resin, a polyethylene naphthalate resin, a polyether ether ketone resin, or a polyether resin. Plastics such as sulfone resins and polyurethane resins, and fluorine-based and silicon-based rubbers can be suitably used. Also, the thickness is not limited to 75 μm, but is 25 to 2000 μm, preferably 50 μm.
Those having a thickness of up to 150 μm are preferably used.

The transfer charging blade 9 has a resistance of 1 × 1
A material having a thickness of 2 mm and a length of 306 mm having a thickness of 0 ⁵ to 1 × 10 ⁷ Ω was used. In the present embodiment, transfer is performed by applying a bias of 15 μA to the transfer charging blade 9 by constant current control.

Next, the operation of the above-described image forming apparatus (laser beam printer) A will be described.

At the time of image formation, the photosensitive member 1 is rotationally driven in the direction of arrow a by driving means (not shown),
With 0, the surface is uniformly charged. At this time, a DC voltage of −650 V is applied to the magnetic brush 30 in the present embodiment. Then, an image exposure L by a laser beam is given to the charged photoconductor 1 by an exposure device (laser scanning device) 3 to form an electrostatic latent image corresponding to input image information. The image is developed as a toner image by the developing device 4. At this time, a DC voltage of -480 V and a peak-to-peak voltage of 1500 at a frequency of 3000 Hz are applied to the developing sleeve 41 of the developing device 4 in this embodiment.
V AC voltage is applied. Then, when the toner image on the photoconductor 1 reaches the transfer nip 63 between the transfer belt 10 and the toner image, the transfer material P such as paper in the cassette 5 is fed by the feed roller 6 at this timing. The toner t is transferred to the back side of the transfer material P by the transfer charging blade 9 to which the transfer bias is applied by the transfer roller 7.
, And a toner image on the photoreceptor 1 is transferred to the surface side. Then, the transfer material P to which the toner image has been transferred is conveyed to the fixing device 11 by the transfer belt 10, and the toner image is fixed as a permanently fixed image on the surface by the fixing device 11, and is discharged.

On the other hand, the transfer residual toner remains on the surface of the photoconductor 1 after the transfer of the toner image. As for the transfer residual toner, there are toners whose charge polarity is inverted due to peeling discharge or the like at the time of transfer and toners whose charge polarity is not inverted. The transfer residual toner in which the two polarities are mixed is collected by the magnetic brush 30,
The magnetic brush 30 is charged to a negative polarity by the influence of frictional charging with the magnetic particles constituting the magnetic brush layer 30 c and the applied voltage, and is discharged onto the photoconductor 1. The discharged negative polarity toner is developed and collected simultaneously by the developing device 4 and reused.

The above-mentioned recovery and discharge of the transfer residual toner in the magnetic brush 30 is caused by the sliding force of the magnetic particles constituting the magnetic brush layer 30c of the magnetic brush 30, the centrifugal force due to the rotation of the sleeve 30b of the magnetic brush 30, and the like. Although there are some, the electric field effect due to the relationship between the applied voltage and the charging potential of the photoconductor 1 is very large. For example, when the charging potential is lower than the applied voltage, the toner charged to the normal reverse polarity among the transfer residual toner is positively collected by the magnetic brush layer 30c of the magnetic brush 30, and forms the magnetic brush layer 30c. The toner is charged to a normal charge polarity by rubbing with the magnetic particles and is discharged onto the photoconductor 1.

In this case, since the mixed toner can be sufficiently discharged, the toner mixing rate in the magnetic brush layer 30c is kept low. However, since the transfer residual toner having a normal charge polarity is difficult to collect when charged in an electric field, a positive ghost in which the history of the previous image remains because the lower part of the toner cannot be charged, for example, when the charge state is deteriorated. There are cases.

On the other hand, when the charging potential is finally higher than the applied voltage, in the initial stage of the charging area (between the applied voltage and the charging potential), the remaining toner after transfer is charged to the normal opposite polarity. The toner is collected on the magnetic brush layer 30c of the magnetic brush 30, and the toner charged to the normal polarity is collected on the magnetic brush layer 30c of the magnetic brush 30 at the rear end of the charged area (applied voltage <charging potential or later). By doing so, the recoverability of the transfer residual toner can be improved.

However, when the charging potential is higher than the applied voltage at the rear end of the charging area, the magnetic brush 30
The toner charged to the normal charging polarity by frictional charging with the magnetic particles constituting the magnetic brush layer 30c cannot be discharged from the magnetic brush layer 30c, and the toner mixing rate increases. And when a certain amount of toner is mixed in,
When a large amount of toner having frictional charging characteristics on the charging polarity side is mixed, the frictional charging property is lowered, and discharge is started under conditions where the charging potential is lower than the applied voltage. A state of equilibrium is reached.

In this embodiment, the magnetic particles constituting the magnetic brush layer 30c of the magnetic brush 30 are as follows.
The evaluation was performed using those having the initial characteristics and durability characteristics shown in Table 1 described above. The magnetic particles used have four different types of resins A to D for triboelectric charging characteristics and different resistance values by changing the dispersion amount of carbon black for resistance values.
Using four types of d, 16 types of magnetic particles were evaluated in combination with each other. When the photoreceptor 1 is rubbed and rotated without applying a bias voltage by the magnetic particles using the resins A to D, A = 30 V, B = 0 V, and C, respectively.
= -30V and D = -80V (charge potential). When charging is performed by applying a voltage of −650 V using these magnetic particles, the potentials saturated after several rotations are A = −620 V and B = −6, respectively.
50V, C = -680V, D = -730V. Further, the resistance value was changed according to the dispersion amount of carbon black.
The four types of magnetic particles a to d are respectively a = 8 × 10 ³ Ω.
Cm, b = 2 × 10 ⁵ Ω · cm, c = 5 × 10 ⁷ Ω ·
cm, d = 6 × 10 ⁹ Ω · cm.

In the column of "mixing-after discharge" in Table 1, the toner is mixed with 1% by weight of the magnetic particles in advance, and 50 blank sheets are passed as the transfer material P, whereby the amount of mixed toner can be reduced. Was put in an equilibrium state, an image was output, and the charging potential and resistance value after the completion of this work were described.

As shown in the evaluation results shown in Table 1, when the triboelectric charging characteristics are the normal charging polarity side and the resistance value of the resin C is low and the resistance values of the resins D are a and b, the leakage is small. A good image could be obtained without generation of ghost or ghost. This can be explained as follows.

First, when the resin of the coating agent is A or B,
Since the charged potential is lower than the applied voltage, the discharge of the mixed toner is sufficiently performed. Even when the discharge of the toner is performed, a large resistance change is not observed. Therefore, an image having only a resistance value c in the range of 1 × 10 ⁶ to 1 × 10 ⁹ Ω · cm exhibiting good charging characteristics without occurrence of leakage and charging ghost was obtained. But 2000
After the endurance of the sheet, the resistance increased due to the influence of the fusion of the toner to the magnetic particles and the like, and ghost occurred.

On the other hand, when the resin of the coating agent is C or D, the charging potential is higher than the applied voltage when the toner is not mixed due to the effect of frictional charging. However, even if the discharge is performed with “applied voltage> charge potential”, the discharge becomes difficult immediately because “applied voltage = charge potential”. For this reason,
Even after the discharge of the toner, the toner remains mixed in a relatively large amount, and the resistance is higher than that of the magnetic particles alone.

For this reason, the resistance values a and b which cannot be used due to the normal leakage can be used, and the resistance value after the toner mixing discharge operation is 1 × 10 ^6.
A resistance value b of the resin C in a range of ~ 1 × 10 ⁹ Ω · cm;
By using a charging member (magnetic particles) having a slightly lower resistance and having an appropriate resistance in a state where the toner is mixed, such as the resistance values a and b of the resin D, the toner is fused on the magnetic particles due to durability. Even when the resistance of the magnetic particles alone increases due to contamination, the increase in the resistance of the magnetic brush 30 as a whole becomes small.

When the magnetic particles alone are charged higher than the applied bias, the surface of the magnetic particles has a characteristic of charging the photosensitive member 1 to the charging polarity side with respect to the triboelectric charging characteristic. When the toner or the like is fused, the portion of the triboelectric charge characteristic shows the opposite characteristic, so that the charging potential is lowered and the discharge of the toner is promoted, and as a result, the amount of mixed toner is reduced. The increase in the resistance value is offset by the reduction in the resistance value due to the reduction in the mixing ratio of the toner, so that good charging performance can be maintained.

As described above, in the present embodiment, in a state where the toner is mixed to some extent and the charged potential is substantially the same as the applied bias, a single magnetic particle having a low resistance value is used so as to obtain an appropriate resistance value. Accordingly, even if the resistance of the magnetic particles alone increases due to contamination such as fusion of the toner onto the magnetic particles due to durability, the increase in resistance of the magnetic brush 30 as a whole becomes small, and the magnetic brush 30 The occurrence of charging unevenness due to toner mixing into the layer 30c is eliminated, and poor charging can be prevented to obtain a good image.

In this embodiment, the magnetic brush 30
The bias voltage applied to the magnetic brush 30 is only the DC voltage. However, in order to further improve the recoverability of the transfer residual toner and the charging uniformity by the magnetic brush 30, an alternating voltage (AC voltage) may be used.
Is desirably superimposed. Specifically, the frequency 200
An alternating voltage of ０００8000 Hz and a peak-to-peak voltage of 200 to 1500 V may be superimposed and applied.

In this embodiment, the magnetic brush 30
Is a fixed non-magnetic sleeve rotating type, but other types such as a type in which a magnet roller rotates, or a type in which a magnet roller itself rotates with a configuration of only a magnet roller (in this case,
This roller surface may be subjected to a conductive treatment).

(Second Embodiment) In the first embodiment described above, the frictional charging characteristics with the photosensitive member 1 depend on the type of resin of the coating agent of the magnetic particles constituting the magnetic brush layer 30c of the magnetic brush 30. However, in the present embodiment, the resin of the coating agent of the magnetic particles constituting the magnetic brush layer 30c of the magnetic brush 30 is fixed, and the surface layer (charge injection layer) of the photoconductor 1 is fixed. The evaluation was performed by changing the triboelectric charging characteristics. Another configuration is the first configuration shown in FIGS.
This is the same as the embodiment.

More specifically, as shown in Table 2, the evaluation was performed by changing the type of insulating resin of the charge injection layer, which is the surface layer of the photoreceptor (photosensitive drum) 1, by changing four types of A to D. .

[0071]

[Table 2] On the other hand, as the resin of the magnetic particles constituting the magnetic brush layer 30c of the charging magnetic brush 30, the resin “B” shown in Table 1 was used as a coating agent, and the resistance was “a” to “a” shown in Table 1.
d ″ were used.

The four types of photosensitive members 1 described above are
When magnetic particles using the resin “B” as a coating agent are rubbed and rotated without applying a bias voltage,
The photosensitive member 1 has characteristics (charge potential) of 40 V, A = 0 V, C = −45 V, and D = −90 V. When charging is performed by applying a voltage of −650 V using these photoconductors 1, the potentials that saturate after several rotations are: a = −610 V, a = −650 V, c = −695 V, d = − respectively. It was 740V.

In the evaluation results shown in Table 2, "mixed-
As for the item "after discharge", as in the first embodiment, 1% by weight of the toner is mixed in advance with the magnetic particles and 50 blank sheets are passed as the transfer material P, so that the mixed toner amount is in an equilibrium state. Then, an image was output, and the charged potential and the resistance value after the completion of the work were described.

As shown in the evaluation results shown in Table 2, similarly to the first embodiment, the resistance value b of the photosensitive member (photosensitive drum) C whose frictional charging characteristic is lower on the normal charging polarity side and the resistance value is lower. The resistance values a and b of the photosensitive member (photosensitive drum) d were good. From this, if the frictional charging characteristic charges the photoconductor 1 to the normal charging polarity side, the same applies regardless of whether the surface of the magnetic particles constituting the magnetic brush layer 30c of the magnetic brush 30 or the surface of the photoconductor 1 is changed. It turned out that an effect was obtained.

When the magnetic particles alone are charged higher than the applied bias, the photosensitive member 1 has such a characteristic that the frictional charging characteristic causes the photosensitive member 1 to be charged to the charging polarity side by rubbing against the surface of the magnetic particles. When the toner or the like is fused to the magnetic particles, the portion is rubbed with the resin, and thus loses the property of frictionally charging to the charging polarity side. Therefore, the discharging potential of the toner is reduced and the discharge of the toner is promoted.
As a result, similarly to the first embodiment, since the amount of mixed toner is reduced, the increase in the resistance value due to the fusion of the toner and the reduction in the resistance value due to the reduction in the mixing ratio of the toner are offset, and the good charging performance is obtained. Maintenance can be realized.

In the first and second embodiments, the relationship between the applied bias and the charging potential is changed by changing the frictional charging characteristics of the magnetic particles constituting the magnetic brush layer of the magnetic brush and the surface of the photoreceptor. In addition, the contact state (contact nip) between the magnetic particles forming the magnetic brush layer of the magnetic brush and the photoconductor is changed, and the sliding state (peripheral speed ratio) is changed. The same result can be obtained by changing the triboelectric charging characteristics by changing the temperature and humidity environment.

As described above, according to the present invention, in the image forming apparatus in which the developing means also serves as a means for collecting untransferred toner, the charging member is a contact charging means using magnetic particles.
In addition, it includes all configurations in which the saturation potential of the photoconductor charged by the charging member is higher on the charging polarity side than the applied voltage. More preferably, in the above-described configuration, an amount corresponding to the toner mixing amount in an equilibrium state where the applied voltage and the charging potential are substantially equal is previously mixed,
In this state, the resistance value of the magnetic particles of the charging member is 1 × 10 ⁶ to
By selecting a magnetic particle having a resistance value slightly lower than an appropriate value for a single magnetic particle so as to be in the range of 1 × 10 ⁹ Ω · cm, a great effect on the improvement of durability can be obtained.

The surface resistance of the photoreceptor is 1 ×.
It is desirable to have a low-resistance layer of 10 ⁹ to 1 × 10 ¹⁴ Ω · cm from the viewpoint of realizing charge injection and preventing ozone generation. However, organic photoconductors other than the above-described photoconductors also have improved durability. Therefore, a sufficient effect can be obtained.

In this embodiment, the developing method is based on the two-component developing method, but other developing methods may be used. Preferably, a one-component contact developing method or a two-component contact developing method in which the developer is developed in contact with the photoreceptor is more effective in enhancing the simultaneous recovery effect during development. Further, the toner particles in the developer may be pulverized toner or the like, and more preferably, when a polymerized toner is used, the one-component contact development method or the two-component contact development method may be used.
In other developing methods such as a one-component non-contact developing method and a two-component non-contact developing method, a sufficient recovery effect of the transfer residual toner can be obtained.

[0080]

As described above, according to the present invention, the saturation potential of the charged image carrier is set to be higher on the charging polarity side than the voltage applied to the contact charging member, and the frictional charging is performed. By adjusting the characteristic to an appropriate resistance value in a state where the toner is mixed, even if the resistance value of the magnetic particles alone increases due to contamination such as fusion of the toner on the magnetic particles due to durability, the resistance of the contact charging means as a whole is increased. As the rise of the charge becomes small, the occurrence of charging unevenness due to toner mixing into the magnetic particles of the contact charging means is eliminated, and poor charging can be prevented to obtain a good image.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a magnetic brush of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram showing a developing device of the image forming apparatus according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing a device for measuring a triboelectric charge amount of toner.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor (image carrier) 3 exposure device (exposure device) 4 developing device (developing device) 8 transfer device (transfer device) 30 magnetic brush (contact charging device) 30a magnet roller 30b sleeve 30c magnetic brush layer (magnetic particles)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03G 15/08 507 G03G 9/10

Claims (10)

[Claims] 1. An image carrier for carrying an image, contact charging means using magnetic particles which contact the image carrier and charge the image carrier, and a power supply for applying a voltage to the contact charging means. ,
Exposure means for forming an electrostatic latent image on the image carrier, developing means for developing the electrostatic latent image to form a toner image, and transfer means for transferring the toner image to a transfer material at a transfer site An image forming apparatus that also serves as a cleaning unit that collects the remaining toner on the image carrier after the transfer of the toner image onto the transfer material by the transfer unit. An image forming apparatus configured to perform image formation by setting the saturation potential of the image carrier to be higher than the voltage applied from the power supply to the contact charging unit on the charging polarity side. 2. The image forming apparatus according to claim 1, wherein a predetermined amount of toner particles is previously mixed into said magnetic particles in said contact charging means. 3. The magnetic particles and the toner particles in the contact charging unit have a volume resistance of 1 × 10 ⁶ to 1 × when the image carrier is charged by the contact charging unit.
The image forming apparatus according to claim 2, wherein the value is in a range of 10 ⁹ Ω · cm. 4. The image forming apparatus according to claim 1, wherein the image carrier has a photosensitive layer and a surface layer thereon, and the surface layer has a resin and conductive fine particles. 5. The image forming apparatus according to claim 1, wherein the surface potential of the image bearing member caused by the rubbing when the voltage is not applied due to the rubbing with the contact charging unit gradually decreases with the endurance. Image forming device. 6. The image forming apparatus according to claim 4, wherein said conductive fine particles are SnO ₂ . 7. The image bearing member has a resistance of 10 ⁹ to 10 ^14.
The image forming apparatus according to claim 1, further comprising a surface layer made of a material of Ω · cm. 8. The image forming apparatus according to claim 1, wherein said image carrier is made of amorphous silicon. 9. The image forming apparatus according to claim 1, wherein the developing method by the developing unit is a contact developing method in which a developer is brought into contact with the image carrier. 10. The image forming apparatus according to claim 1, wherein the developer has toner particles and magnetic particles.