JP2001034067A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain an image of satisfactory density by preventing an electrostatic latent image from being buried in a small number of toner due to the increase of the charge amount of the toner, and preventing the lowering of an developing efficiency, even in the case of using small grain toner having 3 to 6 μm grain size in two-component developer. SOLUTION: As for the developing device 14 for an image forming device, the two-component developer is carried on the developing sleeve 41, and then, a magnetic developer brush is brought into contact with a photoreceptor drum 1 in a developing part so as to develop the electrostatic latent image on the photoreceptor drum 1. An electrostatic capacity C/S per unit area of the photoreceptor drum 1 is controlled to be >2.0×10-6 (F/m2) so as to prevent the electrostatic latent image from being buried in accordance with the charged toner amount due to the increase of the charged amount accompanied with the downsizing of the toner grain, and the lowering of the developing efficiency is prevented by controlling the half width of the developing main pole S1 of the magnet roller 42 in the sleeve 41 to be >=40 deg. so as to increase a contact nip in the developing area and also the napping area of the developer.

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 for developing an electrostatic latent image formed on an image carrier with a developer and recording the visible image on a transfer material such as paper.

[0002]

2. Description of the Related Art Conventionally, many image forming apparatuses using an electrophotographic system or an electrostatic recording system have been proposed. A schematic configuration and operation of the image forming apparatus will be described with reference to FIG.

In the image forming apparatus shown in FIG. 1, when a copy start signal is input, a photosensitive drum 1 of a printer section is charged to a predetermined potential by a charger 3. On the other hand, a unit 9 having a document illumination lamp, a short focus lens array, and a CCD sensor integrally scans a document G placed on a document table 8 of a reader unit while irradiating the document with the document G. The original surface reflected light of the illumination scanning light is imaged by the short focus lens array and is incident on the CCD sensor.

The CCD sensor comprises a light receiving section, a transfer section, and an output section. In the CCD light receiving section, an optical signal is converted to a charge signal, and the transfer section sequentially transfers the signal to an output section in synchronization with a clock pulse, and outputs the signal. The unit converts the charge signal into a voltage signal, amplifies the signal, reduces the impedance, and outputs the signal. The analog signal thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to a printer unit.

[0005] In the printer section, an electrostatic latent image corresponding to the original image is formed on the surface of the photosensitive drum 1 by the laser exposure means 2 which is turned on and off in response to the image signal. Next, the electrostatic latent image on the photosensitive drum 1 is developed by a developing device 4 using a two-component developer in which a toner and a magnetic carrier are mixed, and the latent image is visualized as a toner image.

FIG. 26 shows a two-component magnetic brush developing device used as the developing device 4 in this embodiment. The developing device 4 includes a developing sleeve 41, a magnet roller 42 fixedly arranged in the developing sleeve 41, and stirring screws 43 and 44 in a developing container 46 containing a two-component developer in which a toner and a magnetic carrier are mixed. , A regulating blade 45.

The developing sleeve 41 has an opening closest to the photosensitive drum 1 at an opening facing the photosensitive drum 1.
The photosensitive drum 1 is set so that the developer carried on the developing sleeve 41 can be developed while being in contact with the photosensitive drum 1. The developing sleeve 41 is rotated in the forward direction with respect to the rotation direction of the photosensitive drum 1, and is drawn up onto the developing sleeve 41 by the magnetic force of the magnet roller 42 and is conveyed in a direction perpendicular to the developing sleeve 41. The thickness of the developer is regulated by the regulating blade 45 disposed on the developing sleeve 41, and a thin layer of the developer is formed on the developing sleeve 41.

When the developer formed in the thin layer is conveyed to the developing section, the magnetic force of the developer near the main developing pole of the magnet roller 42 causes ears on the surface of the developing sleeve 41 to form a magnetic brush. Is done. The developer formed on the magnetic brush contacts the surface of the photosensitive drum 1 to develop the electrostatic latent image, and the developer after the development is returned into the developing container 46 by the developing sleeve 41, N, N
It is separated from the developing sleeve 41 by the repulsive magnetic field of the pole,
It is collected in the developing container 46.

The toner image thus formed on the photosensitive drum 1 is electrostatically transferred to a transfer material by the transfer device 7 shown in FIG. Thereafter, the transfer material is electrostatically separated from the photosensitive drum 1 and conveyed to the fixing device 6, where the toner image is thermally fixed and output as a print image. After the transfer of the toner image, the photosensitive drum 1 is used repeatedly for the next image formation after removing contaminants such as transfer residual toner adhered to the surface by the cleaner 5.

[0010]

The recording density of the digital image forming apparatus as described above has been gradually increasing in recent years for the purpose of achieving higher definition and higher image quality. Along with this, the above-mentioned toner has also been reduced in particle size year by year, and at present, toner having a particle size of about 8 μm has been widely used. Therefore, it is desired to use a toner having a smaller particle size.

However, conventionally, when the particle diameter of the toner is reduced and a toner having a volume average particle diameter of 6 μm or less is used, there is a problem that a decrease in density occurs and a good image cannot be obtained. .

Accordingly, an object of the present invention is to provide a toner for developing an electrostatic latent image by increasing the charge amount of the non-magnetic toner as the particle size of the non-magnetic toner used in the developer of the two-component magnetic brush developing device is reduced. An image forming apparatus capable of stably obtaining an image having a sufficient density even when a toner having a small particle diameter of 3 to 6 μm is used by preventing a small amount of toner from being applied or a reduction in development efficiency. To provide.

[0013]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier, and a developing device for developing an electrostatic latent image formed on the surface of the image carrier through charging and exposure, wherein the developing device includes a non-magnetic toner on a developer carrier having a built-in magnet. And a magnetic carrier, carrying a two-component developer, transporting the developer to a developing unit facing the image carrier, and developing the developer in a developing magnetic field formed by a developing main pole of the magnet in the developing unit. Contacting the magnetic brush with the image carrier and applying a developing bias to the developer carrier to develop an electrostatic latent image on the image carrier with a developer formed on the magnetic brush. In the forming apparatus, the volume average particle diameter of the toner is 3 μm or more and 6 μm or less, and the electrostatic capacity per unit area of the image carrier is 2.0 × 10 ⁻⁶ F / m ^2.
The angle between the upstream portion and the downstream portion of the magnetic field in the vertical direction of the main developing pole of the magnet on the surface of the developer carrier at which the magnetic field has a strength of 50% of the peak value is 40 ° or more. An image forming apparatus characterized in that: The main developing pole is 2
With two peaks.

Further, the present invention comprises an image carrier, and a developing device for developing an electrostatic latent image formed on the surface of the image carrier through charging and exposure, wherein the developing device has a built-in magnet. A two-component developer in which a non-magnetic toner and a magnetic carrier are mixed is carried on a developer carrier, and is conveyed to a developing section facing the image carrier, and a developing magnetic field formed by the magnet in the developing section is provided. Then, a magnetic brush of the developer is brought into contact with the image carrier, and a developing bias is applied to the developer carrier. Then, the electrostatic latent on the image carrier is developed by the developer formed on the magnetic brush. In an image forming apparatus for developing an image, the volume average particle diameter of the toner is 3 μm or more and 6 μm or less, and the electrostatic capacity per unit area of the image carrier is 2.0 × 10 ⁻⁶ F / m ² or more. The magnet rotates within the developer carrier And by an image forming apparatus, characterized in that for conveying the developer carried on said developer carrying member in the developing unit. The magnetic carrier is made of a hard ferromagnetic material having residual magnetization.

According to the present invention, the photoconductor of the image carrier is an organic photoconductor, and the thickness of the charge transport layer of the organic photoconductor is 13 μm or less. The photosensitive member of the image carrier is made of amorphous silicon. The average charge amount per unit weight of the toner is 30 × 10 ⁻³ C / kg or more in absolute value,
× 10 ^-3 C / kg or less. The electrostatic latent image is a dot distribution electrostatic latent image formed by laser exposure.

[0016]

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

The inventor of the present invention has studied the cause of the image density reduction described in the conventional example. As a result, the increase in the amount of charge per unit weight of the toner due to the reduction in the particle size has resulted in the electrostatic latent image Was filled with a small amount of toner charge, and as a result, the amount of applied toner was reduced.

Even when the electrostatic latent image is not sufficiently filled with the charge of the toner, the developing efficiency is reduced due to the increase in the charge of the toner and the reduction in the particle diameter, and the amount of the applied toner is reduced. Was also found to be the cause.

On the other hand, the present invention reduces the electrostatic capacity per unit area of the photosensitive member to 2.0 × 10 ^-6
(F / m ² ).

In order to reduce the developing efficiency, one method of the present invention is to set the half width of the developing main pole of the magnet disposed in the developer carrier of the developing device to 40 ° or more, thereby reducing the developing efficiency. The contact nip in the area and the area of the developer rising are increased to improve the development efficiency. In another method of the present invention, by rotating the developer-carrying internal magnet, the developer magnetic brush itself is transported while rotating,
Not only the toner in the vicinity of the image carrier but also all the toner on the developer carrier contribute to the development, thereby improving the development efficiency.

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention.

The image forming apparatus includes a reader unit having a unit 9 for irradiating and scanning a document G on a document table 8 integrally configured with a document illumination lamp, a CCD sensor, and the like;
A charger 3 for charging the surface of the photosensitive drum 1 to a predetermined polarity and potential;
Laser exposure means 2 for forming an electrostatic latent image corresponding to the original image on the surface of the document, developing device 4 for developing the electrostatic latent image using a two-component developer, and applying the toner image obtained by the development to a recording material The printer comprises a transfer device 7 for transferring the image, and a fixing device 6 for thermally fixing the toner image on the recording material.

In this embodiment, as the photosensitive drum 1, the following first to fourth layers are formed on an aluminum drum substrate having a diameter of 30 mm and made of a negatively chargeable organic photosensitive member (OPC photosensitive member). The components provided in order from the bottom were used.

The first layer is a subbing layer, which is formed of a conductive layer having a thickness of 20 μm and provided for smoothing defects of the aluminum drum base. The second layer is a positive charge injection preventing layer, which serves to prevent positive charges injected from the drum substrate from canceling out negative charges charged on the surface of the photosensitive drum, and is formed of an amylan resin and methoxymethylated nylon. In addition, the thickness 1 whose resistance is adjusted to about 10 ⁶ Ωcm
It has a medium resistance layer of μm. The third layer is a charge generation layer and has a thickness of about 0.3 μm in which a diazo pigment is dispersed in a resin.
In the layer m, positive and negative charge pairs are generated by exposure.

The fourth layer is a charge transport layer, and is a p-type semiconductor layer formed by dispersing hydrazone in a polycarbonate resin. Therefore, the negative charges given to the photosensitive drum cannot move through this layer, and only the positive charges generated in the charge generation layer can be transported to the surface of the photosensitive drum.

In this embodiment, five types of photosensitive drums 1 were used in which the thickness of the charge transport layer was controlled to 8, 10, 13, 16, and 20 μm.

To form an image, the surface of the photosensitive drum 1 is uniformly charged to, for example, -600 V by the charger 3 and exposed by the laser exposure means 2 to form an electrostatic latent image on the surface of the photosensitive drum 1. The surface potential of the photosensitive drum is attenuated to -100 V at a portion where the exposed portion has the maximum density, and an electrostatic image is formed. This latent image is developed
Thus, reversal development is performed using a two-component developer containing a negatively charged toner, and the toner is visualized as a toner image.

The toner image formed on the photosensitive drum 1 by development is transferred to a recording material by a transfer device 7.
The transfer device 7 transfers the endless transfer belt 71 to the drive roller 7.
2 and the driven roller 73, and the transfer belt 7
A transfer charging blade 74 is provided inside a portion facing the photosensitive drum 1. The transfer belt 71 is rotated in the direction of the arrow by the drive of the drive roller 72, and carries the recording material fed from the paper feed cassette 75 and
Is transferred to the transfer section opposed to.

The recording material conveyed to the transfer section is pressed against the photosensitive drum 1 by pressing the transfer belt 71 by the transfer charging blade 74, and reverses the toner from the back side by a transfer bias applied to the blade 74 from a transfer power supply (not shown). Upon receiving the polarity charge, the toner image on the photosensitive drum 1 is transferred to the surface of the recording material.

The recording material onto which the toner image has been transferred is separated from the transfer belt 71 and conveyed to the fixing device 6, where the toner image is thermally fixed and then output as a print image. After the transfer of the toner image, the toner remaining on the surface of the photosensitive drum 1 is scraped off by the clean blade of the cleaner 5 to prepare for the next image formation. The scraped toner is stored in the container of the cleaner 5.

FIG. 2 shows a two-component magnetic brush method developing device used as the developing device 4 in this embodiment. Main developing device 4
As in the conventional developing device shown in FIG. 26, as shown in FIG. 2, the developer is basically carried in a developing container 46 containing a two-component developer in which a negative toner and a magnetic carrier are mixed. A developing sleeve 41 which conveys the developer to the developing unit facing the photosensitive drum 1, a magnet roller 42 fixedly arranged in the developing sleeve 41, and a stirring screw 43 for circulating the developer in the developing container 41 and supplying the developer to the developing sleeve 41. And a regulating blade 45 for regulating the developer on the developing sleeve 41 to form a thin layer.

The developing sleeve 41 has an opening closest to the photosensitive drum 1 at an opening facing the photosensitive drum 1.
The photosensitive drum 1 is set so that the developer carried on the developing sleeve 41 can be developed while being in contact with the photosensitive drum 1. The developing sleeve 41 was rotated in a forward direction with respect to the rotation direction of the photosensitive drum 1.

The two-component developer in the developing container 46 is placed on the rotating developing sleeve 41 by the magnetic pole N of the magnet roller 42.
3 and is conveyed to a regulating blade 45 arranged perpendicular to the developing sleeve 41, the thickness of the layer is regulated by the regulating blade 45, and a thin layer of developer is formed on the developing sleeve 41. Is done. The developer formed in this thin layer is conveyed to the developing section with the rotation of the developing sleeve 41, and rises on the surface of the developing sleeve 41 due to its magnetic force near the main developing pole S1 of the magnet roller 42, thereby causing the magnetic force to rise. Formed on the brush.

The developer formed on the magnetic brush comes into contact with the surface of the photosensitive drum 1 to develop an electrostatic latent image.
And is separated from the developing sleeve 41 by the repulsive magnetic field formed by the magnetic poles N2 and N3 of the magnet roller 42 and collected in the developing container 46.

At the time of development, the developing sleeve 41 is supplied with a frequency f from a developing power supply (not shown) to a DC voltage of VDC = −450 V.
= 3000 Hz, peak-to-peak voltage Vpp = 1500
A developing bias on which an AC voltage of V was superimposed was applied.

In general, in the two-component developing method, when an AC voltage is applied, the developing efficiency is increased and the quality of the image is high, but on the contrary, there is a risk that fogging is likely to occur. For this reason, usually, fog is prevented by providing a potential difference between the DC voltage of the developing bias and the surface potential of the photosensitive drum 1. The potential difference for preventing fog is the fog removal potential (Vback), and the potential difference can prevent toner from adhering to the non-image area during development. In this embodiment, the fog removal potential Vback =
150V (| -650-(-450) | = 150).

In the present invention, as the two-component developer, a small particle size toner having a volume average particle diameter of 3 μm or more and 6 μm or less is used as a nonmagnetic toner. This toner was externally added with silica and titanium oxide having an average particle diameter of 20 nm for the purpose of improving fluidity.

The volume average particle diameter of the toner is measured by a laser scan type particle size distribution analyzer (CIS-GALAI).
100), the measurement was performed in the range of 0.4 μm to 60 μm.

The measurement sample was prepared by adding 0.5 to 2 mg of toner to a solution obtained by adding 0.2 ml of a surfactant (alkylbenzene sulfonate) to 100 ml of water, dispersing the mixture with an ultrasonic disperser for 2 minutes, and then magnetizing. About 80% of water was put into a cubic cell containing a stirrer, and one or two drops of a sample ultrasonically dispersed therein were added with a pipette to prepare the mixture.
This was measured with a measuring device, and the number average particle size and volume average particle size were determined.

In this embodiment, without changing the magnetic carrier, eight kinds of two-component developers were prepared in which the volume average particle diameter of the toner was changed from about 1 μm to about 8 μm every about 1 μm.
N / L environment (temperature 15 ° C, humidity 10%),
The toner was left in each of an N / N environment (temperature 20 ° C., humidity 60%) and an H / H environment (temperature 30 ° C., humidity 80%), and the absolute value of the charge per unit weight of the toner was measured. . The toner was prepared by a polymerization method, and silica and titanium oxide having an average particle diameter of 20 nm were externally added for the purpose of improving fluidity. The magnetic carrier used had a volume average particle size of about 40 μm and a saturation magnetization of 140 emu / cm ³ .

FIG. 3 shows the results. As can be seen from FIG. 3, the absolute value of the charge amount per unit weight of the toner increases as the particle size of the toner decreases. The lower the humidity (H / H → N / N → N / L), the higher the absolute value of the charge amount of the toner.

In the present invention, the amount of charge per unit weight of the toner (the amount of triboelectric charge) was measured as follows.

FIG. 4 shows an apparatus for measuring the triboelectric charge amount (triboelectric charge) of the toner. First, the toner whose triboelectric charge amount is to be measured is combined with the carrier at a weight ratio of 5.95 to form a two-component developer, put into a 50-100 ml capacity polyethylene bottle, The developer was shaken by hand for 40 seconds, and then about 0.5 to 1.5 g of this developer was put into a metal measuring instrument 102 having a conductive screen 103 with a bottom of 500 mesh. 104. The weight of the entire measuring instrument 102 in this state is weighed and defined as W1 (kg).

Next, the measuring device 102 is set on the suction device 101 (at least the portion of the suction device 101 that is in contact with the measuring device 102 is an insulator), the sample is sucked from the suction port 107, and the air volume control valve 106 is adjusted. , The pressure of the vacuum gauge 105 is 250 m
mAq. In this state, suction is performed sufficiently, preferably for 2 minutes, to remove the toner by suction. Measurement device 1 at this time
The potential indicated by the electrometer 109 connected to the terminal 02 is read, and this is set to V1 (V). In addition, the entire measurement container 102 after suction is weighed and defined as W2 (kg). Measuring instrument 10
Assuming that the capacitance of the capacitor 108 connected in parallel with the electrometer 109 is C1 (F), the triboelectric charge per unit weight of the toner is expressed by the following formula: triboelectric charge of toner (μC / g) =
It is calculated as C1 × V1 × 10 ⁻³ / (W1−W2).

In the present embodiment, a photosensitive drum 1 having a charge transport layer having a thickness of 8 μm or 20 μm is prepared, and is used in three environments of N / L, N / N and H / H. It was formed and the maximum image density at that time was examined. The magnet roller 42 has a half-width of the vertical magnetic field on the surface of the developing sleeve 41 of the main developing pole S1 (that is, an angle between two points of the magnetic field strength of 50% of the peak value of the vertical magnetic field).
Two types, 2 ° and 52 °, were prepared and used by being enclosed in the developing sleeve 41.

The measurement of the image density was carried out by using X-rite 4
The measurement was performed using a 04 reflection densitometer. FIGS. 5 and 6 show the magnetic patterns on the developing sleeve surface of the magnet roller when the half width of the developing main pole S1 is 22 ° and 52 °, respectively.
Shown in

FIGS. 7 and 8 show the above-mentioned maximum image densities in the graphs of FIGS. 3 and 8, respectively, when the film thickness of the charge transport layer of the photosensitive drum is 8 μm and 20 μm, respectively. 7 and 8
In the maximum image density in each environment, the numerical value on the left is when the half width of the developing main pole S1 is 22 °, and the numerical value on the right is when the half width is 52 °.

As shown in FIGS. 7 and 8, in each case, the density is higher when the half width of the developing main pole is 52 ° than when it is 22 °. However, the difference in the density is larger in FIG. 7 where the charge transport layer thickness of the photosensitive drum 1 is 20 μm.
It is smaller than that of FIG.

In this embodiment, a photosensitive member having a charge transport layer having a thickness of 8 μm or 20 μm is used as the photosensitive drum 1.
As the magnet roller 42, the half width of the developing main pole S1 is 2
2 °, 27 °, 31 °, 35 °, 42 °, 46 °, 52
An image was formed in an N / N environment using the seven types set at °, and the change in the maximum image density at that time due to the half-value width of the developing main electrode S1 was examined. The results are shown in FIGS. 9 and 10, respectively.

FIGS. 9 and 10 also show that the charge transport layer has a thickness of 20 μm.
It can be seen that the variation of the image density with respect to the half-value width of the developing main electrode in the case of m is smaller than that in the case where the charge transport layer is 8 μm. In the case where the charge transport layer is 8 μm, a sufficient density is obtained when the half width of the developing main electrode is 40 ° or more.

The reason why the image density is increased by increasing the half value width of the developing main pole S1 as described above is considered as follows. When the half value width of the developing main pole S1 is increased, the area of the magnetic brush of the developer formed on the developing sleeve 41 in the developing section is widened, and the contact nip of the developer with the photosensitive drum 1 is widened. Is one of the reasons. However, not only this, but also because it is difficult for toner to stay in the upstream of the developing region due to the curvature of the developing sleeve 41 and the photosensitive drum 1. In fact, it has been confirmed that the sweeping phenomenon of the developed image caused by the stay of the toner is reduced as the half width increases, and is improved.

As can be seen from FIGS. 9 and 10, when a toner having a volume average particle diameter of 7 μm or more is used, any of the conditions of the film thickness of the charge transport layer of the photosensitive drum 1 and the half width of the developing main pole S1 is required. However, a sufficient image density is obtained. When the average particle diameter of the toner was 3 to 6 μm, a sufficient image density was obtained under the conditions that the thickness of the charge transport layer was 8 μm and the half width was 40 ° or more. With a toner volume average particle diameter of 2 μm or less, sufficient image density was not obtained under any of the conditions.

When the absolute value of the average charge per unit weight of the toner shown in FIG. 3 is applied to the average particle diameter of the toner, when the average charge amount per unit weight of the toner is 30 × 10 ⁻³ C / kg or less, under any condition. When a sufficient image density is obtained and is 30 × 10 ⁻³ C / kg or more and 80 × 10 ⁻³ C / kg or less, the thickness of the charge transport layer is 8 μm and the half width of the main development electrode is 40 ° or more. Under the above condition, a sufficient image density can be obtained. If the average charge per unit weight of the toner is 80 × 10 ⁻³ C / kg or more, it can be said that a sufficient image density cannot be obtained under any of the conditions.

In the above description, when the charge transport layer of the photosensitive drum is 20 μm, the variation in image density with respect to the half width of the developing main electrode is smaller than that in the case where the charge transport layer is 8 μm. A surface potentiometer (not shown) was installed on the downstream side of the developing device 5 in the rotation direction of the above, and the surface potential of the photosensitive drum after development was measured.

The charge transport layer of the photosensitive drum 1 has a thickness of 20 μm.
In the case of m, when development is performed with a two-component developer having an average particle diameter of the toner of 3 to 6 μm, the surface potential of the photosensitive drum after the development is increased even though the image density does not reach a sufficient value. The DC component of the developing bias applied to the developing sleeve reached a level close to VDC = -450V. When the average particle diameter of the toner of the developer is 1 μm or 2 μm, the surface potential of the photosensitive drum after development reaches only about −300 V.

On the other hand, when the thickness of the charge transport layer of the photosensitive drum 1 is 8 μm, the half width of the developing main electrode S1 is 35 μm.
The surface potential of the photosensitive drum after development is about -200 to -300 V under the condition that the development efficiency is not higher than 0 ° C, and even if the half-value width at which a sufficient density is obtained is 52 °, the surface potential after development is It was about -350 to -400V.

From this result, it can be seen that when the thickness of the charge transport layer of the photosensitive drum is 20 μm, the contrast of the electrostatic latent image is buried by the charge of the toner, and the image density cannot be obtained.

The capacitance C per unit area of the photosensitive drum
/ S (F / m ² ) is the dielectric constant in a vacuum of ε 0 = 8.85 ×
10 ^-12, the dielectric constant of the photosensitive drum epsilon = 3, and the thickness of the charge transport layer is d, so represented by .epsilon.0 × epsilon / d, the film thickness of the charge transport layer 8, 10, 13, In the case of 16, 20 μm, the capacitance C / S (F / m ² ) = 3.3 × 10 ⁻⁶ ,
2.7 × 10 ^-6 , 2.0 × 10 ^-6 , 1.7 × 10 ^-6 ,
1.3 × 10 ⁻⁶ .

FIG. 11 is a graph showing the relationship between static electricity per unit area of the photosensitive drum when an image is formed by using a developing roller with a developing roller and a magnet roller in which the half width of the developing main electrode is set to 52 ° in an N / N environment. 5 is a graph showing the relationship between the capacitance C / S and the maximum image density. From FIG. 11, the capacitance C / S per unit area of the photosensitive drum is 2.0 × 10 ⁻⁶ F /
If it is larger than m ^2, it can be seen that a sufficient image density is obtained.

This is because, by increasing the capacitance per unit area of the photosensitive drum, the rise in the surface potential of the photosensitive drum due to the amount of charge of the toner is suppressed, and the contrast of the latent image is buried with a small amount of toner. Was prevented.

From the above results, the average particle size of the toner was 7 μm.
When the average particle diameter is 3 m or more, a sufficient image density can be obtained without considering the photosensitive drum and the developing sleeve. Capacitance per unit area C / S is 2.0
It can be seen that a sufficient image density is obtained for the first time by setting the half width of the developing main pole of the magnet roller of the developing sleeve to 40 ° or more by setting × 10 ⁻⁶ F / m ² or more. Further, it was found that in the case of the toner having an average particle diameter of 2 μm or less, a sufficient image density could not be obtained even under the conditions of the present invention.

Embodiment 2 This embodiment is different from Embodiment 1 shown in FIG. 1 in that a surface layer of amorphous silicon (amorphous silicon) is used instead of the photosensitive drum 1 made of a negatively chargeable organic photosensitive member. A positively charged photoconductor was used. Other mechanical configurations of the image forming apparatus of this embodiment are basically the same as those of the first embodiment, and therefore, in the following description of this embodiment, FIG.
Invite.

In this embodiment, a positively chargeable amorphous silicon photosensitive member is used as the photosensitive drum 1. In the first embodiment, an electrostatic latent image is formed on the photosensitive drum by a laser exposure section, Toner is adhered to the laser exposure area and the latent image is developed by the reversal development method.
In this embodiment, an electrostatic latent image was formed on a photosensitive drum in a laser non-exposed area, a positively charged toner was adhered to the laser non-exposed area, and the latent image was developed by a regular development method.

The surface of the photosensitive drum 1 is uniformly charged to, for example, +600 V by the charger 3 and the laser exposure means 2
To attenuate the surface potential of the exposed portion of the photosensitive drum to +100 V to form an electrostatic latent image on the photosensitive drum as a non-exposed portion (a portion corresponding to the maximum density is basically not exposed, There is weak light emission due to the control of the exposure means, and there is an attenuation of about several tens of volts).

The latent image is regularly developed by a developing device 4 using a two-component developer, and is visualized as a toner image.
At the time of development, a developing bias in which an AC voltage having a frequency Vf = 3000 Hz and a peak-to-peak voltage Vpp = 1500 V was superimposed on a DC voltage VDC = + 250 V from a developing power source was applied to the developing sleeve 41. After that, as in Example 1,
The toner image is transferred to the recording material by the transfer device 7, fixed by the fixing device 6, and output as a print image.

The relative permittivity of the amorphous silicon photosensitive member of the photosensitive drum 1 used in this embodiment is about 10, and
The thickness of the photoreceptor was 25 μm. From this value, the capacitance C per unit area of the amorphous silicone photoreceptor is calculated.
Calculating / S results in about 3.5 × 10 ⁻⁶ F / m ² .

FIG. 12 shows an N / L environment (temperature 15 ° C., humidity 10%) and an N / N environment (temperature 20
℃, humidity 60%), H / H environment (temperature 30 ℃, humidity 80
3) shows the measurement results of the absolute value of the charge amount per unit weight of the toner in each environment of (%) in each environment when the photosensitive drum 1 having an amorphous silicon photoconductor having a film thickness of 25 μm is used. Is the maximum image density. Similarly, the image density was measured using a 404 reflection densitometer manufactured by X-rite.

As in FIGS. 7 and 8, in FIG. 11, the maximum image density in each environment is such that the half-width of the developing main pole S1 is 22 ° on the left and the half-width is 52 ° on the right.
°. In any case, as in Example 1, the density was higher when the half width of the developing main pole was 52 ° than when it was 22 °. Further, the use of the photosensitive drum with the amorphous photosensitive member is higher than the case where the photosensitive drum having the charge transport layer of the organic photosensitive member with a thickness of 8 μm is used in Example 1.

FIG. 13 is a diagram showing the relationship between the photosensitive drum unit area when an image is formed using the developing sleeve in which the half width of the developing main electrode is set to 52 ° in the N / N environment of FIG. A graph showing the relationship between the capacitance C / S and the maximum image density is shown in the graph of the maximum image density (capacitance C / S = 3.5) when the photosensitive drum of the amorphous silicon photosensitive member of this embodiment is used. × 10 ^-6 F / m ² ).

As shown in FIG. 13, an amorphous silicon photosensitive film as in this embodiment is placed on the line of the maximum image density with respect to the capacitance C / S per unit area in the photosensitive drum of the organic photosensitive member of the first embodiment. It was also found that the rider could ride on the body using the photosensitive drum.

From this, when the amorphous silicon photosensitive member is used, the capacitance C per unit area of the photosensitive member is
/ S (F / m ² ) is 3.5 × 10 ⁻⁶ and 2.0 × 1
0 ^-6 because there is a sufficiently large capacitance than not occur phenomena such as contrast of an electrostatic latent image will be filled by the charge of the toner, the use of toner having an average particle diameter of 3 to 6 [mu] m, As in Example 1, it was found that a sufficient image density could be obtained by setting the half width of the developing main pole of the magnet roller of the developing sleeve to 40 ° or more.

As described above, in the present embodiment, the case where the development is performed by the regular development using the positively charged amorphous silicon photosensitive member has been described. It was also confirmed that the same effect was obtained.

Embodiment 3 In Embodiments 1 and 2, the developing sleeve 41 is a magnet roller having a magnetic force pattern as shown in FIGS. 5 and 6, and the half-width of the developing main pole S1 is changed from 22 ° to 52 °. In this embodiment, a magnet having a magnetic force pattern as shown in FIG. 14 was used in order to further increase the development efficiency.

The magnetic force pattern shown in FIG.
1 has a magnetic force distribution having two peaks such that the magnetic forces in the vertical direction on the surface of the developing sleeve partially overlap each other. The half width of the development main pole S1 is 48 °.

As described above, when the developing main pole S1 has a two-peak configuration, the maximum image density is higher in the case of the same half width than in the case of the normal one peak. This is because, when the developing main pole has two peaks, the transport state of the developer is as shown in FIGS.
Unlike the case where the developing main pole of 0 has a magnetic pattern of one peak, when the magnetic carrier passes between the two peaks, the magnetic brush is conveyed at a high speed with the ears of the magnetic brush standing. This is because the toner is easily released from the magnetic carrier by the high-speed conveyance, and the developing efficiency is improved.

FIG. 15 shows a half of the developing main pole of the magnet roller in the developing sleeve under the N / N environment when the thickness of the charge transport layer of the organic photoreceptor shown in FIG. In the graph showing the relationship between the value width and the maximum image, the maximum image density in the case of using the magnet roller having two peaks at the developing main pole in this embodiment is added.

As can be seen from FIG. 15, as in the present embodiment, when a magnet roller having a developing main pole having two peaks is used for the developing sleeve, the developing main pole is changed regardless of the toner of each particle diameter. A higher density can be obtained than when a one-peak magnet roller is used, and a high development efficiency can be obtained even with a similar half width.

Embodiment 4 In Embodiments 1 to 3 described above, the half width of the developing main pole of the magnet 42 in the developing sleeve 41 is set to 40 to reduce the developing efficiency.
By increasing the angle to at least the angle, the contact nip of the magnetic brush of the developer in the developing area and the area of the magnetic brush rising are increased, thereby improving the developing efficiency.

In this embodiment, the magnetic brush of the developer is rotated by rotating the magnet in the developing sleeve.
The development efficiency was improved by contributing not only the toner near the photoreceptor but also all the toner on the developing sleeve to the development. Similarly, for the phenomenon that the electrostatic latent image is buried by the charge amount of the toner, the capacitance C / S per unit area of the photosensitive drum is set to 2.0 × 10 ⁻⁶ (F / m
² ) Prevented by making it larger.

FIG. 16 is a schematic structural view showing a developing device used in this embodiment. As in the developing device shown in FIG. 2, the developing device 4 includes a developing container 41 containing a two-component developer in which a negative toner and a magnetic carrier are mixed, a developing sleeve 41, and a magnet roller disposed in the developing sleeve 41. 42, stirring screws 43 and 44, and a regulating blade 45.
Are arranged in the opening facing the photosensitive drum 1 at an interval of about 500 μm in a region closest to the photosensitive drum 1 so that the developer on the developing sleeve 41 can be developed in contact with the photosensitive drum 1.

According to this embodiment, the outer diameter of the developing sleeve 41 is 20 mm, and the magnet roller 42 is rotatably disposed inside the developing sleeve 41. The magnet roller 42 has eight magnetic poles having a magnetic force of 800 to 1000 Gauss (G), which are evenly arranged in the circumferential direction. Then, the photosensitive drum 1 is rotated in the direction of the arrow at a peripheral speed of 150 mm / sec, while the magnet roller 42 in the developing sleeve 1 is rotated at 2500 rpm in the reverse direction.
m, the developer on the developing sleeve 41 was conveyed in the direction in which it moves in the same direction at the portion facing the photosensitive drum 1, that is, in the forward direction.

According to the developer conveyance by the reverse rotation of the magnet roller 42, the magnetic brush itself of the developer is conveyed while rotating, and not only the toner near the photosensitive drum 1 but also all the toner on the developing sleeve 41. Can contribute to the development, and the development efficiency can be improved. At this time, in the present embodiment, the developing sleeve 41 was also rotated at a rate of 100 mm / sec in the forward direction in which the portion facing the photosensitive drum 1 moved in the same direction in order to enhance the transportability of the developer on the developing sleeve 41.

In the present embodiment, the same negative particle diameter toner as in Example 1 was used as the negative toner used for the two-component developer, but the magnetic carrier had a volume average particle diameter of 40 μm.
Saturation magnetization is 170 emu / cm ³ and residual magnetization is 140 e
At mu / cm ³ , the holding force as shown in FIG.
A carrier having 0 Oersted (Oe) hysteresis characteristics, that is, a hard ferromagnetic carrier was used. Incidentally, conventionally, carriers having hysteresis characteristics without residual magnetization as shown in FIG. 18, that is, soft ferromagnetic carriers are used.

A hard ferromagnetic carrier as shown in FIG.
It is characterized by having coercive force and residual magnetization,
Since it has residual magnetization, it has a magnetic force even in a state where the external magnetic field is weakened, that is, in a state away from the developing unit, and the magnetic force between the carriers is stronger than that of the soft ferromagnetic carrier. This is advantageous in that a carrier adheres to an image portion and disturbs an image, and a carrier adherence phenomenon is prevented.

When a carrier having remanent magnetization is used to transfer the developer by rotating the magnet roller 42 in the developing sleeve 41 as in this embodiment, as shown in FIG. The formed developer magnetic brush itself is transported while rotating. On the other hand, when the developer is transported while the magnet roller 42 in the developing sleeve 41 is fixed, the formed magnetic brush of the developer is formed in the direction of the line of magnetic force.
As shown in (1), the magnetic brush itself is conveyed while standing in the developing section toward the photosensitive drum 1, and the magnetic brush itself does not rotate.

In this embodiment, a two-component developer on the developing sleeve 41 is conveyed by rotating the magnet roller 42 in the developing sleeve 41, and FIG.
A comparison was made between a conventional developing device in which the two-component developer on the developing sleeve 41 was conveyed by fixing the magnet roller 42 in the developing sleeve 41 and rotating the developing sleeve 41.

A voltage obtained by superimposing a DC voltage of VDC = −450 V, an AC voltage having a peak-to-peak voltage Vpp = 1500 V, and an AC voltage having a frequency f = 3000 Hz was applied to the developing sleeve 41 from a developing power source (not shown).

As the photosensitive drum 1, the charge transport layer has a thickness of 8
N / L, N /
The graphs of FIG. 3 showing the maximum image densities in the three environments of N and H / H are shown in FIGS. 20 and 21, respectively. The image density was measured using a 404 reflection densitometer manufactured by X-rite.

In FIG. 20 and FIG. 21, the maximum image density in each environment is indicated by a value on the left-hand side of the developing method in which the developing sleeve 41 is rotated with respect to the non-rotating magnet roller 42. In the case of the system in which the developer is conveyed to the developing section and developed, the numerical value on the right side is the magnet roller rotating developing system, that is, the magnet roller 42 is used for the non-rotating or rotating developing sleeve 42.
Is rotated, and the developer on the developing sleeve 41 is transported to the developing section and developed.

In each case, the density is higher in the magnet roller rotary developing system. However, the density difference is smaller in FIG. 21 where the charge transport layer of the photosensitive drum 1 is 20 μm than in FIG. 20 where the charge transport layer is 8 μm.

In the magnet roller fixed developing system in which the developer is transported by the rotation of the developing sleeve 41 to perform the development,
As shown in FIG. 19 (B), the spikes of the magnetic brush of the two-component developer are conveyed while standing in the developing section toward the photosensitive drum 1, and the toner in the developer is a small particle size toner. If the toner has a high charge amount, the toner near the developing sleeve 41 cannot contribute to the development. On the other hand, in the magnet roller rotary developing system in which the developer is conveyed by rotating the magnet roller 42 to perform the development, as shown in FIG. 19A, the spikes of the magnetic brush of the two-component developer are rotated. Since the toner is conveyed, the toner in the developer can uniformly contribute to the development, and therefore, the development efficiency is increased, and as shown in FIG. 21, a sufficient image density is obtained.

As can be seen from FIGS. 20 and 21, when a toner having a volume average particle diameter of 7 μm or more is used, a sufficient image density is obtained under any conditions, and the toner has a volume average particle diameter of 3 μm. In the case of の 6 μm, a sufficient image density was obtained under the condition that the thickness of the charge transport layer was 8 μm and the magnet roller was rotated. With a toner volume average particle diameter of 2 μm or less, sufficient image density was not obtained under any of the conditions.

Regarding the absolute value of the amount of charge per unit weight of the toner, if it is 30 × 10 ⁻³ C / kg or less, a sufficient image density can be obtained under any of the conditions.
30 × 10 ⁻³ C / kg or more and 80 × 10 ⁻³ C / k
g, a sufficient image density was obtained only when the thickness of the charge transport layer was 8 μm and the method of rotating the magnet roller was used. In the case of 80 × 10 ⁻³ C / kg or more, it can be said that a sufficient concentration could not be obtained under any of the conditions.

In the above, when the charge transport layer of the photosensitive drum is 20 μm, the variation in the density due to the developing method is smaller than that when the charge transport layer is 8 μm. A surface voltmeter (not shown) was installed on the downstream side of the developing device 5 in the rotation direction of the photosensitive drum 1, and the surface potential of the photosensitive drum after development was measured.

The charge transport layer of the photosensitive drum 1 has a thickness of 20 μm.
In the case of m, when development is performed with a two-component developer having an average particle diameter of the toner of 3 to 6 μm, the surface potential of the photosensitive drum after the development is increased even though the image density does not reach a sufficient value. The DC component of the developing bias applied to the developing sleeve reached a level close to VDC = -450V. However, when the average particle size of the toner of the developer is 1 μm or 2 μm, the surface potential of the photosensitive drum after development reaches only about −300 V.

On the other hand, when the film thickness of the charge transport layer of the photosensitive drum 1 is 8 μm, in the system in which the developer is transported by rotating the developing sleeve 41 to perform the development, the surface potential after the development is −200. The voltage was about -300 V, and the surface potential after development was also about -350 to -400 V in the method of transporting and developing the developer by rotating the magnet roller 42.

From the results, as described above, when the thickness of the charge transport layer of the photosensitive drum is 20 μm, the contrast of the electrostatic latent image is buried by the charge of the toner, and the image density is obtained. You can see that it cannot be done. Capacitance per unit area of photosensitive drum C / S (F / m ² )
Is expressed as ε0 × ε / d, where ε0 = 8.85 × 10 ⁻¹² , the relative dielectric constant of the photosensitive drum is ε = 3, and the thickness of the charge transport layer is d. When the thickness of the charge transport layer is 8, 10, 13, 16, or 20 μm, the capacitance C /
S (F / m ² ) = 3.3 × 10 ⁻⁶ , 2.7 × 10 ⁻⁶ ,
2.0 × 10 ⁻⁶ , 1.7 × 10 ⁻⁶ , and 1.3 × 10 ⁻⁶ .

FIG. 22 shows the relationship between the capacitance C / S per unit area of the photosensitive drum and the maximum image density when an image is formed by development using a magnet roller rotary developing system in an N / N environment. It is a graph shown. FIG.
Is a graph showing the relationship between the capacitance C / S per unit area of the photosensitive drum and the maximum image density when an image is formed by development using a magnet roller fixed development method in an N / N environment. .

22 to 23 that the capacitance C per unit area of the photosensitive drum in the case of the magnet roller rotation type is used.
When / S is larger than 2.0 × 10 ⁻⁶ F / m ^2, it can be seen that a sufficient image density is obtained.

This is because, by increasing the capacitance per unit area of the photosensitive drum, the rise in the surface potential of the photosensitive drum due to the amount of charge of the toner is suppressed, and the contrast of the latent image is buried with a small amount of toner. Was prevented.

From the above results, the average particle size of the toner was 7 μm.
When the average particle diameter is 3 m or more, a sufficient image density can be obtained without considering the photosensitive drum and the developing sleeve. Capacitance per unit area C / S is 2.0
It can be seen that a sufficient image density can be obtained for the first time by adopting a method in which the developing is carried out by rotating the magnet roller of the developing sleeve and transporting the developer at a pressure of 10 ^-6 F / m ² or more. Further, it was found that in the case of the toner having an average particle diameter of 2 μm or less, a sufficient image density could not be obtained even under the conditions of the present invention.

Embodiment 5 In this embodiment, similarly to Embodiment 2, a positively charged photosensitive member having a surface layer of amorphous silicon (amorphous silicon) was used as the photosensitive drum 1 of FIG.

As in the case of the second embodiment, the surface of the photosensitive drum 1 is uniformly charged to, for example, +600 V by the charger 3 and the surface potential of the exposed portion of the photosensitive drum is attenuated to +100 V by exposure by the laser exposure means 2. Then, an electrostatic latent image is formed as a non-exposed portion on the photosensitive drum, and a positive charging toner is attached to the non-exposed portion using a positive charging toner by the developing device 4, and the latent image is formed by a regular development method. Developed.

At the time of development, a DC voltage VDC = + 250 V from the developing power source and a frequency Vf = 3000 are applied to the developing sleeve 41.
Hz, a peak-to-peak voltage Vpp = 1500 V AC was applied with a developing bias superimposed thereon. After that, similarly to the first embodiment, the toner image is transferred to the recording material by the transfer device 7, fixed by the fixing device 6, and output as a print image.

The relative permittivity of the amorphous silicon photosensitive member of the photosensitive drum 1 used in this embodiment is about 10,
The thickness of the photoreceptor was 25 μm. From this value, the capacitance C per unit area of the amorphous silicone photoreceptor is calculated.
Calculating / S results in about 3.5 × 10 ⁻⁶ F / m ² .

FIG. 24 shows N / L as in the case of the second embodiment.
Environment (temperature 15 ° C, humidity 10%), N / N environment (temperature 2
0 ° C, humidity 60%), H / H environment (temperature 30 ° C, humidity 8)
FIG. 3 shows the measurement result of the absolute value of the charge amount per unit weight of the toner in each environment (0%).
Is used to write the maximum image density in each environment.

As in the above, in FIG. 24, the maximum image density in each environment is the case where the left-hand numerical value is the magnet roller fixed developing system and the right-hand numerical value is the case of the magnet roller rotating developing system. In each case, the image density is higher in the case of the magnet roller rotary developing system than in the fourth embodiment. Further, in the case of using the photosensitive drum of the amorphous photosensitive member, the thickness of the charge transport layer was 8 μm in Example 4.
Is higher than when the photosensitive drum of the organic photoreceptor is used.

FIG. 25 shows the capacitance C / S per unit area of the photosensitive drum and the maximum image when the image is formed by the development using the magnet roller rotary developing system under the N / N environment of FIG. In the graph showing the relationship with the concentration,
The maximum image density when the photosensitive drum of the amorphous silicon photosensitive member of this embodiment is used (capacitance C / S = 3.5 ×
10 ⁻⁶ F / m ² ).

As shown in FIG. 25, on the line of the maximum image density with respect to the capacitance C / S per unit area in the photosensitive drum of the organic photosensitive member of the fourth embodiment, the amorphous silicon It was also found that the rider could ride on the body using the photosensitive drum.

From this, when the amorphous silicon photosensitive member is used, the capacitance C per unit area of the photosensitive member is
/ S (F / m ² ) is 3.5 × 10 ⁻⁶ and 2.0 × 1
0 ^-6 because there is a sufficiently large capacitance than not occur phenomena such as contrast of an electrostatic latent image will be filled by the charge of the toner, the use of toner having an average particle diameter of 3 to 6 [mu] m, As in Example 4, it was found that sufficient image density could be obtained by performing development in the developer transport system by rotating the developing sleeve with the magnet roller.

As described above, in this embodiment, the case where the development is performed by the regular development using the positively charged amorphous silicon photosensitive member has been described. However, the case where the reversal development is performed using the negatively charged amorphous silicon photosensitive member is described. It was also confirmed that the same effect was obtained.

[0112]

As described above, according to the present invention,
When the electrostatic latent image formed by charging and exposing the image carrier is developed by contacting the image carrier with a two-component developer magnetic brush carried on the developer carrier of the developing device, the surface of the image carrier is developed. The capacitance per unit area is 2.0 × 10 ⁻⁶ F / m
^{Since it is 2} or more, it is possible to prevent the electrostatic latent image from being buried in potential with a small amount of toner due to the amount of charge of the toner, to increase the amount of toner on the developed latent image, Since the half width of the magnetic field in the vertical direction of the main developing pole of the magnet on the surface of the developer carrier is set to 40 ° or more, the magnetic brush of the developer is formed by widening the contact nip with the image carrier, thereby improving the development efficiency. Can be improved. In the other method of the present invention, since the magnet in the developer carrier is rotated, the developer is transported while rotating the magnetic brush itself, so that not only the toner in the vicinity of the image carrier but also the developing agent is developed. All the toner on the agent carrier can contribute to the development, and similarly, the development efficiency can be improved. As a result,
Even when a toner having a small particle diameter of 6 μm is used, an image having a sufficient density can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a sectional view illustrating a developing device installed in the image forming apparatus of FIG. 1;

FIG. 3 is a graph showing the relationship between the particle size of the toner and the charge amount of the toner.

FIG. 4 is a perspective view showing a measuring device used for measuring the charge amount of the toner.

FIG. 5 is a diagram illustrating a magnetic force pattern in which a half width of a developing main pole of a magnet roller in a developing sleeve of a developing device is 22 °.

FIG. 6 is a diagram illustrating a magnetic force pattern in which a half width of a developing main pole of a magnet roller in a developing sleeve of a developing device is 52 °.

FIG. 7 is a graph showing the relationship between the particle size of the toner and the amount of charge of the toner in FIG. 3; 7 is a graph in which the maximum image density at the time is written.

FIG. 8 is a graph showing the relationship between the particle size of the toner and the charge amount of the toner in FIG. 3 using an organic photoreceptor having a charge transport layer having a film thickness of 20 μm and having a half width of the main developing electrode of 22 ° and 52 °. 7 is a graph in which the maximum image density at the time is written.

FIG. 9 shows an organic photoreceptor having a charge transport layer having a thickness of 8 μm.
9 is a graph showing a change in the maximum image density when the half width of the developing main pole is changed.

FIG. 10 is a graph showing a change in maximum image density when the half-width of the developing main electrode is changed using an organic photoconductor having a charge transport layer having a thickness of 20 μm.

FIG. 11 is a graph showing a change in the maximum image density when the thickness of the charge transport layer of the organic photoreceptor is changed when the half width of the developing main electrode is 52 °.

12 is a graph showing the relationship between the particle size of the toner and the amount of charge of the toner in FIG. 3, in which the maximum image density when the half width of the main developing electrode is 22 ° and 52 ° is written using an amorphous photoreceptor. It is a graph.

13 is a graph in which the result of the amorphous silicon photoconductor is added to the graph showing the change of the maximum image density when the half width of the developing main pole is changed using the organic photoconductor of FIG. 11;

FIG. 14 is a diagram showing two magnetic force patterns in which the peak of the main developing pole of the magnet roller used to increase the developing efficiency in the present invention is two.

FIG. 15 is a graph showing a change in the maximum image density when the half width of the developing main electrode is changed using the organic photoreceptor of FIG. It is.

FIG. 16 is a sectional view showing a developing device used in another embodiment of the image forming apparatus of the present invention.

FIG. 17 is a diagram of a hysteresis curve showing an example of magnetic characteristics of a hard ferromagnetic carrier.

FIG. 18 is a diagram of a hysteresis curve showing an example of magnetic characteristics of a soft magnetic carrier.

FIG. 19 shows a case in which a developing device shown in FIG. 16 rotates a magnet roller in a developing sleeve to perform development by rotating a magnet roller, and a conventional developing device in which a developing sleeve is rotated and developed by rotating a developing sleeve. FIG. 5 is a model diagram showing a state of a magnetic brush of a developer in a developing unit.

20 is a graph showing the relationship between the particle size of the toner and the amount of charge of the toner shown in FIG. 3; FIG. 7 is a graph in which the maximum image density in the case is written.

FIG. 21 is a graph showing the relationship between the particle size of the toner and the amount of charge of the toner shown in FIG. 3 using an organic photoreceptor having a charge transport layer having a thickness of 20 μm; 7 is a graph in which the maximum image density in the case is written.

FIG. 22 is a graph showing a change in the maximum image density when the electrostatic capacity of the photoconductor is changed using the developing device of FIG. 16 for development.

FIG. 23 is a graph showing a change in the maximum image density when the capacitance of the photoconductor is changed using a conventional developing device for development.

24 is a graph showing the relationship between the toner particle size and the toner charge amount in FIG. 3 in which the maximum image density in the case of using the amorphous photosensitive member and the developing method of the developing sleeve rotation method and the magnet roller rotation method is written. It is a graph.

25 is a graph obtained by adding the result of the amorphous silicon photoconductor to the graph showing the change of the maximum image density in the development by the magnet roller rotation developing method using the organic photoconductor of FIG. 22.

FIG. 26 is a cross-sectional view illustrating a conventional developing device.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 laser exposure means 3 charger 4 developing device 41 developing sleeve 42 magnet roller 45 regulating blade

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/08 507 G03G 15/08 507X F term (Reference) 2H005 AA00 BA02 CB02 CB03 CB04 DA01 EA01 EA05 FA02 2H031 AC19 AC20 AC23 AC34 AD01 BA08 BA09 BB01 CA11 CA13 2H068 AA28 AA35 DA00 DA36 FB07 2H077 AB02 AB14 AC02 AD06 AD13 AD18 AD36 BA07 EA01

Claims (8)

[Claims] An image carrier, and a developing device for developing an electrostatic latent image formed on a surface of the image carrier through charging and exposure, wherein the developing device includes a developer carrier having a magnet built therein. A two-component developer in which a non-magnetic toner and a magnetic carrier are mixed is carried thereon, and is conveyed to a developing section facing the image carrier, and a developing magnetic field formed by a developing main pole of the magnet is formed in the developing section. Then, a magnetic brush of the developer is brought into contact with the image carrier, and a developing bias is applied to the developer carrier. Then, the electrostatic latent on the image carrier is developed by the developer formed on the magnetic brush. In the image forming apparatus for developing an image, the volume average particle diameter of the toner is 3 μm or more and 6 μm or less, and the electrostatic capacity per unit area of the image carrier is 2.0 μm.
× 10 ⁻⁶ F / m ² or more, and the peak value of the magnetic field in the vertical direction on the surface of the developer carrier of the main developing pole of the magnet is 50 times.
The angle between the upstream and downstream parts, which results in a magnetic field strength of
An image forming apparatus characterized by being at least 0 °. 2. The image forming apparatus according to claim 1, wherein said main developing pole has two peaks. 3. An image carrier, and a developing device for developing an electrostatic latent image formed on the surface of the image carrier through charging and exposure, wherein the developing device includes a developer carrier having a built-in magnet. A two-component developer in which a non-magnetic toner and a magnetic carrier are mixed is carried thereon, and is conveyed to a developing unit facing the image carrier. In a developing magnetic field formed by the magnet in the developing unit,
A magnetic brush of the developer is brought into contact with the image carrier, and a developer bias is applied to the developer carrier, and a developer formed on the magnetic brush forms an electrostatic latent image on the image carrier. In the image forming apparatus for developing, the volume average particle diameter of the toner is 3 μm or more and 6 μm or less, and the electrostatic capacity per unit area of the image carrier is 2.0 μm or less.
X 10 ^-6 F / m ² or more, wherein the magnet is rotated in the developer carrier to transport the developer carried on the developer carrier to the developing unit. Forming equipment. 4. The image forming apparatus according to claim 3, wherein said magnetic carrier is made of a hard ferromagnetic material having residual magnetization. 5. The image forming apparatus according to claim 1, wherein the photoconductor of the image carrier is an organic photoconductor, and the charge transport layer of the organic photoconductor has a thickness of 13 μm or less. apparatus. 6. The image forming apparatus according to claim 1, wherein the photosensitive member of the image carrier is made of amorphous silicon. 7. An average charge amount per unit weight of the toner is 30 × 10 ⁻³ C / kg or more and 80 × 10 ³ or more in absolute value.
The image forming apparatus according to claim 1, wherein the pressure is ⁻³ C / kg or less. 8. The image forming apparatus according to claim 1, wherein said electrostatic latent image is a dot distribution electrostatic latent image formed by laser exposure.