JP2000338708A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device which is capable of restraining the lowering of image density caused when the diameter of toner becomes smaller, preventing the adhesion of a carrier and yielding a higher-definition and higher-quality image and which is excellent in developing efficiency. SOLUTION: In this image forming device, an electrostatic latent image is developed to form a toner image by bringing a magnetic brush consisting of two-component type developer into contact with an image carrier and applying AC voltage to a developer carrier. In this process, a toner having a volume average particle size of 3 to 6 μm is used, the electrostatic capacity per unit area of the image carrier is controlled to be larger than 2.0×106(F/m2), and hard ferromagnetic particles whose volume average particle size D (cm) is within the range of 0.8×10-3<D<3.5×10-3 and which satisfy a condition D×σr>=0.2(emu/cm2) [residual magnetization: σr(emu/cm3)] are used as magnetic particles constituting the developer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image formed on an image carrier corresponding to an image to be recorded, developed by a developer, and transferred to a transfer material such as paper to transfer the recorded image. The present invention relates to an image forming apparatus to be formed.

[0002]

2. Description of the Related Art Conventionally, many ideas have been devised for an image forming apparatus using an electrophotographic system or an electrostatic recording system. The schematic configuration and image forming operation will be briefly described with reference to FIG. When a copy start signal is input to the image forming apparatus shown in FIG.
An image carrier (hereinafter, referred to as a photosensitive drum) 1 is charged by a charging member 3 so as to have a predetermined potential. On the other hand, an image signal for the document G placed on the document table 8 is obtained as follows by the unit 9 integrally configured with the document irradiation lamp, the short focus lens array, and the CCD sensor. First, the document irradiating lamp is set to the document table 8.
Scanning is performed while irradiating the original G placed thereon, and the reflected light of the illumination scanning light on the original surface is imaged by the short focus lens array and is incident on the CCD sensor. The CCD sensor is composed of a light receiving unit, a transfer unit, and an output unit.
In the CCD light receiving unit, the light signal is converted into a charge signal,
The transfer unit sequentially transfers the charge signal to the output unit in synchronization with the clock pulse. The output unit converts the charge signal into a voltage signal, amplifies the voltage signal, reduces the impedance, and outputs the voltage signal. Further, the obtained analog signal is converted into a digital signal by performing well-known image processing and sent to a printer unit. In the printer section, receiving the above image signal, ON, OFF
An electrostatic latent image corresponding to the document image is formed on the surface of the photosensitive drum 1 by the laser exposure unit 2 that emits light. Then, the electrostatic latent image is developed by a developing device 4 containing a so-called two-component developer having toner particles and carrier particles, and a toner image is formed on the photosensitive drum 1. next,
The development process of developing an electrostatic latent image will be described.

FIG. 2 is a schematic view of a developing device 4 for two-component magnetic brush development. In the drawing, reference numeral 41 denotes a developer carrier (hereinafter, referred to as a developing sleeve), and reference numeral 42 denotes a developing sleeve 41.
Magnet rollers 43 and 44 fixedly arranged in
Is a stirring screw, and 45 is a developer
A regulating blade arranged to form a thin layer on the surface, 4
6 is a developing container. At least at the time of development, the developing sleeve 41 is arranged so that the area closest to the photosensitive drum 1 is about 500 μm, and is set so that development can be performed in a state where the developer contacts the photosensitive drum 1. . Further, the developing sleeve 41 rotates in the forward direction with respect to the rotation direction of the photosensitive drum 1 in the developing section in which the developing sleeve and the photosensitive drum are arranged to face each other. And
In the course of transport, the layer thickness of the developer pumped up by the developer is regulated by a regulating blade 45 arranged perpendicular to the developing sleeve 41, and a thin layer is formed on the developing sleeve 41. Here, when the thin-layered developer is conveyed to the main developing electrode, the developing sleeve 41
Since the magnet roller is fixedly disposed inside, the ears are formed by the magnetic force. The electrostatic latent image is developed with the spike-shaped developer, and then N
The developer on the developing sleeve 41 is returned into the developing container 46 by the repulsive magnetic field of the pole and the N pole.

As shown in FIG. 1, the toner image formed on the photosensitive drum 1 is electrostatically transferred by a transfer device 7 onto a transfer material such as paper. Thereafter, the transfer material is electrostatically separated and conveyed to the fixing device 6, where it is thermally fixed to output an image. On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image is subjected to removal of adhered contaminants such as untransferred toner by the cleaner 5 and is repeatedly used for image formation. In the digital image forming apparatus having such a configuration, the recording density has been gradually increasing in recent years for the purpose of higher definition and higher image quality. Accordingly, the particle size of toner particles used for image formation has been reduced year by year, and at present, toner having a particle size of about 8 μm is often used. Further, further reduction in the particle size of the toner is desired in order to cope with higher resolution.

[0005]

However, in the case where toner particles having a volume average particle diameter of 6 μm or less are used by reducing the particle diameter of the toner particles, a decrease in the density occurs, and a satisfactory There is a problem that an image cannot be obtained.

The inventor of the present invention has conducted intensive studies on the above-mentioned factors of the decrease in density. As a result, one of the factors is that the amount of charge per unit weight of toner particles caused by the reduction in particle size is increased. all right. That is, when the amount of charge per unit weight of the toner particles increases, the electrostatic latent image formed on the photosensitive drum formed by the charging process and the image exposing process described above is changed to a developer having such toner particles. It was found that, when the development was performed, the toner was filled with a small amount of toner particles, resulting in a decrease in the amount of applied toner.

[0007] As another factor, generally, when the particle size of the toner is reduced, the surface area per unit weight is increased. Since it is necessary to reduce the weight ratio of the toner particles in the agent, the image density is reduced. On the other hand, if the particle size of the magnetic particles is reduced in accordance with the particle size of the toner so as not to reduce the weight ratio of the toner particles, the phenomenon that the magnetic particles adhere to the non-image area (carrier (Adhesion) may worsen. Further, even if the toner ratio in the developer is the same, the charge amount of the toner increases due to the decrease in the particle diameter of the toner, and the development efficiency decreases due to the decrease in the particle diameter. Further, when the toner ratio decreases,
These phenomena become more pronounced.

Accordingly, it is an object of the present invention to suppress a decrease in image density caused by reducing the particle size of the toner, and achieve higher definition and higher image quality of the formed image without causing carrier adhesion. An object of the present invention is to provide an image forming apparatus which is excellent in developing efficiency.

[0009]

The above objects are achieved by the present invention described below. That is, in the present invention, the image carrier is charged by a charging member, and a dot distribution electrostatic latent image is formed on the image carrier by image exposure means in accordance with a recorded image signal. Is transported to the developing section by a developer carrier opposed to the image carrier, and is formed in the developing section by a magnet arranged inside the developer carrier. In the developing magnetic field,
A magnetic brush made of the developer is brought into contact with the image carrier, and the dot distribution electrostatic latent image is developed by applying an alternating voltage to the developer carrier to form a toner image.
In an image forming apparatus for forming an image by transferring the toner image to a transfer material, a toner having a volume average particle diameter in a range of 3 μm to 6 μm is used as the toner particles, and a unit of the image carrier is used. Capacitance per area C / S
Is controlled so as to be larger than 2.0 × 10 ⁻⁶ (F / m ² ). Further, the magnetic particles constituting the two-component developer have a volume average particle diameter of D (cm) and a residual particle diameter of D (cm). When the magnetization is σ _r (emu / cm ³ ), the volume average particle diameter D
Is 0.8 × 10 ⁻³ (cm) <D <3.5 × 10 ⁻³ (c
m) and D × σ _r ≧ 0.2 (emu
/ Cm ² ), wherein hard ferromagnetic particles satisfying the condition of (c) are used.

The inventor of the present invention has first made an intensive study on the phenomenon of filling an electrostatic latent image with the amount of toner charge, which was a problem of the prior art which occurs when a small particle size toner is used. As the photosensitive drum constituting the forming apparatus, the capacitance C / S per unit area of the photosensitive drum is set to 2.
It has been found that the above phenomena can be effectively prevented by making it larger than 0 × 10 ⁻⁶ (C / m ² ). Further, at the same time, magnetic particles (carrier) constituting the two-component developer
, The volume average particle diameter is D (cm), and the residual magnetization is σ
_r (emu / cm ³ ), 0.8 × 10 ⁻³ (c
m) <D <3.5 × 10 ⁻³ (cm) and D × σ _r ≧
By using hard ferromagnetic particles satisfying the condition of 0.2 (emu / cm ² ), it is possible to reduce the particle size of the magnetic particles, to prevent a decrease in the toner ratio, and to improve the development efficiency. At the same time, it has been found that the occurrence of the carrier adhesion phenomenon can be prevented by the specific remanent magnetization of the magnetic particles having hard ferromagnetism.

Further, as another embodiment of the image forming apparatus of the present invention, a magnetic particle (carrier) constituting a two-component developer is provided.
When magnetic particles exhibiting soft ferromagnetism are used, when the volume average particle diameter is D (cm) and the magnetization under an external magnetic field of 1000 Gauss is σ ₁₀₀₀ (emu / cm ³ ), 1.6 × 10 ⁻³ (cm) <D <3.5 × 10 ⁻³ (c
m) and by using magnetic particles satisfying the condition of D × σ ₁₀₀₀ ≧ 0.5 (emu / cm ² ), it is possible to reduce the particle size of the magnetic particles, prevent a decrease in the toner ratio, and improve the development efficiency. It has been found that, by realizing the improvement and satisfying the relationship of the above expression, the occurrence of the carrier adhesion phenomenon can be prevented.

[0012]

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. <Embodiment 1> The image forming apparatus of this embodiment shown in FIG. 1 will be briefly described. In this embodiment, a negatively charged organic photoreceptor is used as a photosensitive drum, and a photosensitive drum 1 having the following first to fourth four layers provided in order from the bottom on an aluminum drum base having a diameter of 30 mm is used. Was. The first layer is an undercoat layer, and has a thickness of 20 μm provided for smoothing defects or the like of an aluminum substrate (hereinafter referred to as an aluminum substrate).
m of the conductive layer. The second layer is a positive charge injection preventing layer,
Serves to prevent canceling the negative charge positive charge injected from the aluminum substrate is charged to the photosensitive member surface, 10 ⁶ Omega by Amilan resin and methoxy methylated nylon
A medium resistance layer having a thickness of 1 μm and a resistance adjusted to about 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 a positive and negative charge pair 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 photoconductor surface cannot move through the charge transport layer, and only the positive charges generated in the charge generation layer can be transported to the photoconductor surface. In this embodiment,
The thickness of the charge transport layer is set to 8, 10, 13, 16, and 20.
One controlled to five types of μm was used.

The photosensitive drum 1 having the above-described configuration is first uniformly charged on the surface in the same manner as in the conventional example so that the surface potential becomes -600 V. Subsequently, an electrostatic latent image is written on the charged drum by a laser exposure unit 2 as a latent image forming unit as in the conventional example. At this time, the photosensitive drum 1 corresponding to the maximum density
Is attenuated to -100V.

Next, the developing process for visualizing the electrostatic latent image thus formed will be described. Here, in the present embodiment, a two-component contact developing system was used in the developing process. FIG. 3 is a schematic view of the developing device 4 for two-component magnetic brush development used in this embodiment when a hard ferromagnetic carrier is used as the magnetic particles constituting the two-component developer. When a soft ferromagnetic carrier was used as the magnetic particles, the developing device 4 shown in FIG. 2 similar to the conventional example was used. 3 and 4, 41 is a developing sleeve, 42 is a magnet roller fixedly arranged in the developing sleeve 41, 43 and 44 are stirring screws, 45
Reference numeral denotes a blade for regulating the thickness of the developer, which is arranged to form a thin layer of the developer on the surface of the developing sleeve 41. Reference numeral 46 denotes a developing container. Reference numeral 47 in FIG. 4 denotes a peeling unit for peeling the developer integrally formed with the stirring screw 43 from the developing sleeve 41. At least at the time of development, the developing sleeve 41 is arranged so that the area closest to the photosensitive drum 1 is about 500 μm, and is set so that the developer can be developed in contact with the photosensitive drum 1. ing.

Here, a non-magnetic material is used as a material for forming the layer thickness regulating blade 45. In the case of a soft ferromagnetic carrier, a magnetic blade or a non-magnetic blade to which a magnetic plate is adhered is often used for stability of controlling the carrying amount. However, in the case of a hard ferromagnetic carrier, when a magnetic plate is used for the layer thickness regulating blade, the magnetic particles are magnetized, and are attracted to the blade so that the developer cannot pass. Therefore, in this embodiment,
A 1 mm thick SUS blade was used.

In the present embodiment, the following two-component developer obtained by mixing toner particles and magnetic particles (carrier) was used. As the toner particles, eight kinds of toners having different toner particle diameters and varying in volume average particle diameter from about 1 μm to about 8 μm every about 1 μm were prepared and used. The toner particles were prepared using a polymerization method. At this time, the particle size of the toner particles was measured in a range of 0.4 μm to 60 μm using a laser scan type particle size distribution measuring device (manufactured by CIS-100 GALAI) for toner having an average particle size of 1 μm or more. Was measured. Preparation of the measurement sample was performed as follows. First, a toner to be measured is added in a range of 0.5 to 2 mg to a solution in which 0.2 ml of a surfactant (alkylbenzenesulfonate) is added to 100 ml of water, and dispersed in an ultrasonic disperser for 2 minutes. Approximately 80% of water was placed in a cubic cell containing a magnetic stirrer, and one or two drops of the above-described ultrasonically dispersed sample were added thereto using a pipette. Then, the number average particle diameter and the volume average particle diameter were obtained by using these. To the above negatively charged toner, silica and titanium oxide having an average particle diameter of about 20 nm were externally added and used for the purpose of improving fluidity.

On the other hand, as a magnetic carrier constituting a two-component developer together with the toner particles, a carrier having a hysteresis characteristic shown in FIG. 15, that is, a soft ferromagnetic carrier, and a hysteresis characteristic as shown in FIG. The hard ferromagnetic carriers were used. In addition, for the carriers having the respective characteristics, the volume average particle size was 10, 16,
22, 28, 35 and 42 μm, saturation magnetization 65 to 27
8 emu / cm ³ , residual magnetization of 52 to 260 emu / c
Various carriers having m ³ and holding power of about 2000 (Oe) were used. The magnetic carrier used in this example is coated on the surface with a resin, has a specific resistance of 2.0 × 10 ⁻¹² (Ω · cm) in a core state before being coated, and has a magnetic carrier after being coated. With a specific resistance of 2.5 × 10 ⁻¹³ (Ω · cm). In order to prevent carrier adhesion, use a core having a specific resistance of 1 × 10 ⁻¹⁰ (Ω · cm) or more and a specific resistance after coating of 1 × 10 ⁻¹² (Ω · cm) or more. Is preferred. In addition, by setting the resistance to be high as described above, a phenomenon that charge is injected into the photosensitive drum at the time of development to disturb the latent image does not occur.

A hard ferromagnetic carrier having a hysteresis characteristic as shown in FIG. 16 is characterized by having a coercive force and a residual magnetization. Since the hard ferromagnetic carrier has residual magnetization, the magnetization remains even when the external magnetic field is weakened (in a state away from the developing unit), so that the attractive force between the carriers is increased, and the hard ferromagnetic carrier is harder than the soft ferromagnetic carrier. This is advantageous in preventing carrier adhesion (a phenomenon in which a carrier adheres to an image portion and disturbs an image).

Hereinafter, a method for measuring the average particle size, magnetic characteristics, and specific resistance of the magnetic carrier used in this embodiment will be described. First, a method for measuring the carrier particle size will be described. The particle size of the carrier in this example was determined by a scanning electron microscope (100 to 5).
000 times), randomly extract 300 or more carrier particles having a particle size of 0.1 μm or more, measure the carrier diameter with the Feret diameter in the horizontal direction using an image processing analyzer Luzex3 manufactured by Nireco Co., Ltd. The particle size and the volume average particle size were calculated.

The magnetic properties of the carrier were measured using an oscillating magnetic field type automatic magnetic property recording apparatus BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic characteristic value of the carrier powder is obtained by generating an external magnetic field of 1 kOe and determining the intensity of magnetization at that time by the following method. The measurement of the magnetization of the carrier is made in a state packed in a cylindrical plastic container so that it is sufficiently dense, the magnetization moment is measured in this state, the actual weight when the sample is put in is measured,
The magnetization intensity (emu / g) is determined. Then, the true specific gravity of the carrier particles was measured using a dry automatic densimeter Acupic 1330.
(Emu / g) obtained by the above method (manufactured by Shimadzu Corporation) and multiplied by the true specific gravity to obtain the magnetization intensity per unit volume used in the present invention. (Emu / cm ³ ) was determined.

The measurement of the specific resistance of the resin-coated magnetic carrier or its core particle was performed as follows. First, the cells are filled with carrier or core particles.
Next, electrodes were arranged at both ends so as to be in contact with the filled carrier or core particles, a voltage was applied between these electrodes, and a current flowing at that time was measured to obtain a specific resistance. The measurement conditions of the specific resistance used in the present invention are as follows: the contact area S between the filled carrier or core particles and the electrode is about 2.3 cm ² , the thickness d is about 2 mm, the load of the upper electrode is 180 g, and the measured electric field strength is 5 ×. It was set to 10 ⁴ V / m.

A two-component developer was prepared by mixing a toner having the above-mentioned characteristics and a magnetic carrier, and used in this embodiment. When creating a developer,
The toner was prepared by changing the weight ratio of the toner from the relationship between the particle size of the toner and the particle size of the magnetic carrier. As shown in Table 1, the smaller the carrier particle size, the larger the specific surface area.
The weight ratio of the toner was increased. The numbers in Table 1 indicate the weight ratio of the amount of toner in the two-component developer. Further, when the particle size of the toner becomes smaller, in the case of the same particle size ratio, due to factors such as an increase in the amount of charge per unit weight of the toner,
Since toner scattering is less likely to occur, the toner ratio was set slightly higher.

[0023]

[Table 1]

FIG. 4 shows three kinds of environments (L / L: room temperature 15 ° C., humidity 10 °) when the particle size of the magnetic carrier is 42 μm among the two-component developer thus prepared.
%, N / N: room temperature 20 ° C., humidity 60%, H / H: room temperature 30
The absolute value of the amount of charge per unit weight of the toner at 80 ° C. and a humidity of 80% is measured by a method described later and graphed. As can be seen from FIG. 4, the absolute value of the charge amount per unit weight of the toner increases as the particle size of the toner particles decreases. Further, the lower the humidity environment, the higher the absolute value of the charge amount of the toner. In addition, as compared with the results in FIG. 4, the results when the soft ferromagnetic carrier was used were almost the same as those when the hard ferromagnetic carrier was used because the same coating agent was used. However, when the measurement was performed using a hard ferromagnetic carrier, the measurement was performed in a non-magnetized state because the particles were aggregated after magnetization and could not be measured well.

The method for measuring the amount of charge per unit weight of toner will be described below with reference to the drawings. FIG.
FIG. 3 is an explanatory diagram of an apparatus for measuring a triboelectric charge amount of toner.
First, a measurement sample is put in a metal measurement container 102 having a mesh screen 103 for preventing the passage of a magnetic carrier, and a metal lid 104 is placed. As a measurement sample, a two-component agent obtained by mixing a toner carrier and a magnetic carrier whose charge amount per unit weight is to be measured is placed in a polyethylene bottle having a volume of 50 to 100 ml,
Shake by hand for about 10 to 40 seconds, and then
2, add about 0.5 to 1.5 g of the two-component agent. At this time, the entire measurement container 102 is weighed, and the value is referred to as W1
(Kg). Next, the suction device 101 (measurement container 102)
At least in the insulator).
07, and adjust the air volume control valve 106 so that the vacuum gauge 1
05 is set to 250 mmAq. In this state enough,
Preferably, suction is performed for 2 minutes to remove the toner particles by suction. The potential of the electrometer 109 at this time is set to V (volt). Here, reference numeral 108 denotes a capacitor whose capacity is C
(F). Also, the entire measurement container 102 after suction is weighed, and the value is set to W2 (kg). The amount of charge per unit weight of the toner is calculated from these measured values according to the following equation.

[0026]

(Equation 1)

Hereinafter, using the developing device 4 shown in FIG.
The development process using the component-based magnetic brush method and the circulation system of the developer will be described. First, the developing sleeve 41 rotates in a forward direction in the developing region with respect to the rotation direction of the photosensitive drum 1, and the developer pumped up by the rotation is perpendicular to the developing sleeve 41 in the process of being conveyed. The layer thickness is regulated by the regulating blade 45 disposed on the developing sleeve 41, and a thin layer is formed on the developing sleeve 41. Here, when the developer formed in a thin layer is conveyed to the developing main pole in the developing area, a spike is formed by the magnetic force. The electrostatic latent image is developed by the spike-shaped developer, and thereafter, the developer on the developing sleeve 41 is returned into the developing container 46 by the N-pole and N-pole repelling magnetic fields.

Here, in the case of the soft ferromagnetic carrier, the developer can be easily peeled off by the repulsive magnetic field, but in the case of using the hard ferromagnetic carrier, the developer cannot be peeled off only by the repulsive magnetic field. , And stay on the developing sleeve. For this reason, a developer peeling means as shown by 47 in FIG. 3 is required. The peeling means used this time has a shape in which the outer circumference is a scraping blade and the inner circumference is a screw so that the function of peeling the developer from the developing sleeve 41 and the function of transporting the developer in the longitudinal direction are compatible. The one that also doubled was used.

When outputting an image, the developing sleeve 41 is used.
, A DC voltage and an AC voltage are applied from a power supply (not shown). In the present embodiment, for the DC voltage V _DC = −450 V, the AC voltage V _pp = 1500 V and V _f = 3000 Hz.
Was superimposed as a developing bias. 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. On the contrary, there is a risk that fogging is likely to occur. For this reason, fog is generally prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1. The potential difference for preventing fogging is called a fogging potential (V _back ). The potential difference can prevent toner from adhering to a non-image area during development.
In this embodiment, the fog removal potential V _back = 150 V
Is set to

The toner image thus formed is then transferred to a transfer material by a transfer device 7 (see FIG. 1). The transfer device 7 is rotated by suspending an endless belt 71 between a driving roller 72 and a driven roller 73. Further, a transfer charging blade 74 is provided in the transfer device 7. The transfer charging blade 74 is supplied with power from a high-voltage power supply while generating a pressing force in the direction of the photosensitive drum 1 from the inside of the belt 71. The toner image on the photosensitive drum 1 is sequentially transferred to the upper surface of the transfer material by performing charging of a polarity opposite to that of the toner from the back side of the transfer material. After that, the material to be transferred is
The sheet is conveyed to the fixing device 6 and is thermally fixed to output an image.

On the other hand, the transfer residual toner remains on the surface of the photosensitive drum 1 after the transfer of the toner image. Transfer residual toner is
It is scraped off by the cleaning blade of the cleaning means 5 and housed in a cleaning container. here,
Since the phenomenon that the carrier adhesion increases when the volume average particle diameter of the carrier decreases was observed, the carrier adhesion phenomenon was evaluated for the soft ferromagnetic carrier and the hard ferromagnetic carrier. As a method for preparing a two-component developer using each magnetic carrier, a toner having an average particle diameter of about 5 μm is used and mixed with the magnetic carrier so that the weight ratio of the toner is as shown in Table 1 above. Created by In the present embodiment, a plurality of developers thus obtained were used.

As a method of evaluating the carrier adhesion phenomenon, the fogging potential of the above-described applied voltage is changed from 25 V to 450 V in steps of 25 V, the operation is stopped when a white background image is output, the photosensitive drum is observed, and the photosensitive drum is observed. The voltage at which the magnetic carrier could be visually confirmed was defined as the carrier adhesion start voltage, and evaluation was performed using this value. That is, the thus obtained carrier adhesion starting voltage was written in the graph of the volume average particle diameter and the residual magnetization in the case of the hard ferromagnetic carrier in FIG. Also, the graph of the volume average particle diameter in the case of the soft ferromagnetic carrier and the magnetization under an external magnetic field of 1000 Gauss was written in FIG. Further, when the carrier adhered even at a fogging potential of 25 V, a mark "x" was written.

According to the above measurement, the fog removal potential was 150
When a condition in which no ferromagnetic carrier was adhered was found, when a hard ferromagnetic carrier was used, the volume average particle diameter was changed to D (c
m) and residual magnetization σ _r (emu / cm ³ ), D
× σ _r ≧ 0.2 (emu / cm ² ). When a soft ferromagnetic carrier is used, when the volume average particle diameter is D (cm) and the magnetization under an external magnetic field of 1000 Gauss is σ ₁₀₀₀ (emu / cm ³ ), D × σ ₁₀₀₀ ≧
It was found to be 0.5 (emu / cm ² ). FIG.
As can be seen from FIG. 14 and FIG. 14, when the volume average particle size of the hard ferromagnetic carrier is 8 μm or less, and when the volume average particle size of the soft ferromagnetic carrier is 16 μm or less, the fogging potential 15
There was no area that did not adhere at 0V.

FIGS. 5 and 6 show the three kinds of environments shown in FIG. 4 (L / L: room temperature 15 ° C., humidity 10%, N / N: room temperature 20 ° C., humidity 60%, H / H: room temperature 30). Humidity 80 ° C)
In the graph of the amount of charge per unit weight of the toner, the thickness of the charge transport layer of the organic photoreceptor is 8 μm and 20 μm.
In this case, the maximum image density in each case of μm is written. The image density was measured with a 404 reflection densitometer manufactured by X-Rite. Also, the charge amount of the toner plotted with black circles in the figure is a value when the volume average particle diameter of the magnetic carrier is 42 μm. Volume average particle size is 10μm
The value in the case of is slightly
Although there was a difference in the value of the charge amount, the value of the image density in that case was also written in the same graph in order to compare the image densities. The numerical value on the left side of the plot of the graph is the maximum image density when the volume average particle diameter of the magnetic carrier is 42 μm, and the numerical value on the right side is when the volume average particle diameter of the magnetic carrier is 10 μm.

FIGS. 5 and 6 show the results in the case of using a hard ferromagnetic carrier (in the case of using a soft ferromagnetic carrier, there is no area where no carrier adheres at 10 μm). As is clear from the figures, in each case, the concentration was higher when the volume average particle diameter of the magnetic carrier was 10 μm. However, when comparing FIG. 5 with FIG. 6, the difference in concentration with respect to the carrier particle size is as follows.
In the case of m, the charge transport layer in FIG. 5 was smaller than that in the case of 8 μm.

As is clear from FIGS. 5 and 6, when the volume average particle size of the used toner is 7 μm or more, a sufficient image density is obtained under any of the conditions, and the volume average particle size of the toner is In the case of 3 to 6 μm, it was found that a sufficient concentration was obtained when the thickness of the charge transport layer was 8 μm and the volume average particle diameter of the magnetic particles was 10 μm. When the volume average particle diameter of the used toner was 2 μm or less, the maximum image density did not exceed 1.5 in both cases.

Regarding the absolute value of the average 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 conditions. Has a charge amount of 30 × 10 ⁻³ (C / kg) or more,
In the case of 0 × 10 ⁻³ (C / kg) or less, the thickness of the charge transport layer is 8 μm, and the volume average particle size of the magnetic particles is 10 μm.
It was found that a sufficient image density was obtained in the case of μm (see FIG. 5). In other words, when the charge amount per unit weight of the toner is 80 × 10 ⁻³ (C / kg) or more, it can be said that a sufficient image density was not obtained in any case.

Here, when the charge transport layer is 20 μm,
The ratio of the change in image density to the change in carrier particle size is
In order to investigate the reason why the charge transport layer was smaller than that in the case of 8 μm, an electrometer for measuring the surface potential of the photosensitive drum was installed downstream of the developing device in the photosensitive drum rotation direction.
As a result, when the toner particle size is 3 to 8 μm, and when the thickness of the charge transport layer of the photoreceptor is 20 μm, the surface after development has not reached a sufficient value as the image density. The DC voltage _{VDC of the} potential applied to the developing sleeve has reached a level close to -450 V. However, when the toner particle size is 1 μm and 2 μm,
The surface potential reached only about -300 V. On the other hand, the thickness of the charge transport layer of the photoconductor is 8 μm.
In the case of, when the average carrier particle diameter is 42 μm, when the toner ratio is low and the development efficiency is low, the surface potential after development is about −200 to −300 V, and the carrier average having a sufficient image density is obtained. Even when the ratio of toner having a particle diameter of 10 μm was high, the surface potential after development was about −350 to −400.

From the above results, it can be seen that when the thickness of the charge transport layer of the photoreceptor is 20 μm, the contrast is buried by the charge of the toner, and a high image density cannot be obtained. Here, the capacitance C / S (F / m ² ) per unit area of the photoconductor is obtained by calculating the dielectric constant of vacuum as ε _o =
8.85 × 10 ⁻¹² , the relative permittivity of the organic photoreceptor is ε = 3,
Assuming that the thickness of the charge transport layer is d, it can be expressed as ε _o × ε / d. Therefore, the thickness of the charge transport layer is 8, 10, 13, 1
The capacitance per unit area of the photoreceptor at 6, 20 μm is C / S (F / m ² ) = 3.3 × 10 ^{−6, respectively.}
(Film thickness = 8 μm), 2.7 × 10 ⁻⁶ (film thickness = 10 μm)
m), 2.0 × 10 ⁻⁶ (film thickness = 13 μm), 1.7 × 1
0 ^-6 (film thickness = 16 μm), 1.3 × 10 ^-6 (film thickness = 20
μm).

FIG. 8 shows the relationship between C / S (F / m ² ) and the maximum density when an image is output using a hard ferromagnetic carrier having a volume average particle size of 10 μm in an N / N environment. It is shown. FIG. 8 shows that the density is high when C / S (F / m ² ) is greater than 2.0 × 10 ⁻⁶ . In other words, when an organic photoreceptor is used,
It can be said that the image density is increased by satisfying the condition that the thickness of the charge transport layer is 13 μm or less. As described above, when the volume average particle diameter of the carrier is reduced, the toner ratio is prevented from lowering, and the development efficiency is increased, the image density is sufficiently obtained because the capacitance per unit area of the photoconductor is reduced. This is considered to be because the increase in the potential prevented the potential increase due to the charge amount of the toner, and prevented the small amount of toner from filling the electrostatic contrast.

FIG. 10 shows the same result as above when the volume average particle size of the hard ferromagnetic carrier is 42 μm.
However, in this case, if the toner ratio is reduced by setting the toner particle diameter to 6 μm or less, the C / S
Even if (F / m ² ) is increased, the development efficiency itself is low.
It was found that a sufficient image density could not be obtained. FIGS. 11 and 12 show the case where the hard ferromagnetic carrier was used in an N / N environment, the volume average particle diameter was changed, and the weight ratio of the toner was changed as shown in Table 1. Each of the charge transport layers has a thickness of 10 μm (see FIG. 11),
This shows the relationship between the volume average particle diameter and the maximum image density in the case of 20 μm (see FIG. 12). As is clear from the figure, the case where the thickness of the charge transport layer having a small C / S (F / m ² ) is 20 μm or the case where the volume average particle diameter of the carrier is 35 μm
In the case where the toner particle diameter is larger than the above, it was found that a sufficient image density could not be obtained with a toner having a small particle diameter of 6 μm or less.

Here, FIGS. 11 and 12 show the case where the hard ferromagnetic carrier is used. In the case of the soft ferromagnetic carrier, a region where no carrier adheres was obtained.
Image output was performed for each of the carriers of 2, 28, 35, and 42 μm, and almost the same results as in the case of the hard ferromagnetic carrier were obtained. In other words, the necessary conditions differ for carrier adhesion, but for the maximum image density,
It was found that the soft ferromagnetic carrier is determined under the same conditions as the hard ferromagnetic carrier.

D × σ _r ≧ 0.2 (emu / cm ² ) [volume average particle diameter: D in the case of a hard ferromagnetic carrier, which is the condition when the fogging potential is 150 V and no adhesion occurs. (Cm), residual magnetization: σ _r (emu / c
m ³ )] and D × σ ₁₀₀₀ ≧ 0.5 (emu / cm ² ) [volume average particle diameter: D (cm) in the case of a soft ferromagnetic carrier, magnetization under an external magnetic field of 1000 Gauss:
σ ₁₀₀₀ (emu / cm ³ )], and when the volume average particle diameter of the hard ferromagnetic carrier is 8 μm or less, and when the volume average particle diameter of the soft ferromagnetic carrier is 16 μm or less, the fogging potential is 150 V. The following facts can be understood from the fact that there was no area where the toner particles did not exist, and that when the volume average particle diameter of the carrier was larger than 35 μm, a sufficient image density was not obtained with a toner of 6 μm or less. Was. That is, the condition of the magnetic carrier for obtaining a sufficient image density when using a toner of ^{3 to 6} μm is 0.8 × 10 ⁻³ (c
m) <D <3.5 × 10 ⁻³ (cm) and D × σ _r ≧
When a condition of 0.2 (emu / cm ² ) is used and a soft ferromagnetic carrier is used, 1.6 × 10 ⁻³ (cm) <D <3.5
× 10 ⁻³ (cm) and D × σ ₁₀₀₀ ≧ 0.5 (emu
/ Cm ² ).

That is, from the above results, when the average particle size of the toner is larger than 6 μm, a sufficient image density can be obtained without particularly considering the volume average particle size of the photosensitive member and the carrier. In the case where the average particle size is 3 to 6 μm, the capacitance C / S (F / m ² ) per unit area of the photoreceptor under the above conditions is made larger than 2.0 × 10 ⁻⁶ , When a hard ferromagnetic carrier is used as the magnetic carrier used for the developer, 0.8 × 10 ⁻³ (cm)
<D <3.5 × 10 ⁻³ (cm) and D × σ _r ≧ 0.
2 (emu / cm ² ) and using a soft ferromagnetic carrier, 1.6 × 10 ⁻³ (cm) <D <
3.5 × 10 ⁻³ (cm) and D × σ ₁₀₀₀ ≧ 0.5
It can be seen that a sufficient image density is obtained only when the condition of (emu / cm ² ) is satisfied. Further, it was found that when the average particle size of the toner was smaller than 2 μm, a sufficient image density could not be obtained even under the above conditions.

<Embodiment 2> In Embodiment 1, a negatively charged organic photoconductor was used as the photoconductor. However, in this embodiment, a surface layer having amorphous silicon (film thickness = 25 μm) was used.
m) (hereinafter, referred to as an amorphous silicon photoconductor). In the first embodiment, a method (reversal development) of exposing an image portion with a laser using a negatively charged photoconductor and a negatively charged toner is employed. In the present embodiment, a positively charged photoconductor and a negatively charged toner are used. And a method (laser development) of exposing a non-image portion with a laser. Although the main body configuration of the image forming apparatus is the same as that of the first embodiment, the relationship of the applied bias is different from that of the first embodiment because the above-described method is used.

In the image forming apparatus of this embodiment, first, the surface of the amorphous silicon photosensitive drum 1 is uniformly charged so that the surface potential becomes +600 V.
Subsequently, an electrostatic latent image is written on the charged drum by a laser exposure unit 2 as a latent image forming unit as in the conventional example. At this time, the surface potential of the portion corresponding to the non-image portion is attenuated to +100 V, and when it reaches the maximum density, it is basically not exposed (although due to control, there is very weak light emission and attenuation of several tens V). On the other hand, at the time of development, a DC voltage V _DC = + 250 V and an AC voltage V _pp = 1500 V and V _f = 3000 Hz are applied to the developing sleeve, and a toner image is formed on the amorphous silicon photosensitive drum. It is formed.

The relative dielectric constant of the amorphous silicon photoreceptor used in this example was about 10, and the film thickness of the amorphous silicon photoreceptor used in this example was 25 μm. Capacitance C / S per unit area of used amorphous silicon photoreceptor
(F / m ² ) is about 3.5 × 10 ⁻⁶ . FIG. 7 shows three types of environment (L / L: room temperature 15 ° C., humidity 10%, N / N: room temperature 20 ° C., humidity 60%, H
/ H: room temperature 30 ° C., humidity 80%), the graph showing the amount of charge per unit weight of each average particle size toner shows the maximum image density when an amorphous silicon photoconductor having a film thickness of 25 μm is used. It is written. The image density was measured with a 404 reflection densitometer manufactured by X-Rite.

Also in this embodiment, a hard ferromagnetic carrier having a volume average particle size of 42 μm and a volume ferromagnetic carrier having a volume average particle size of 10 μm were used for image output (in the case of a soft ferromagnetic carrier, 10 μm was used). In this case, there was no area where carrier adhesion did not occur). The tendency of carrier adhesion is almost the same as that in Example 1. As a good condition for carrier adhesion, when a hard ferromagnetic carrier is used, D × σ _r ≧ 0.2 (emu / cm ² ) [volume average particle diameter: D (cm), residual magnetization: σ _r (emu / cm ³ )], when a soft ferromagnetic carrier is used, D × σ
₁₀₀₀ ≧ 0.5 (emu / cm ² ) [volume average particle size: D (c
m), magnetization under an external magnetic field of 1000 Gauss: σ ₁₀₀₀ (e
mu / cm ³ )]. Further, when the volume average particle diameter of the hard ferromagnetic carrier is 8 μm or less, and
When the volume average particle diameter of the soft ferromagnetic carrier was 16 μm or less, a result was obtained in which there was no region where the fogging potential was 150 V and there was no adhesion.

As in Example 1, the numerical value on the left side of each plot of the graph in FIG. 7 is the maximum image density when the volume average particle diameter of the magnetic carrier is 42 μm, and the numerical value on the right side is
The case where the volume average particle size of the magnetic carrier is 10 μm, in each case, the volume average particle size of the magnetic carrier is 10 μm.
The concentration was higher in the case of μm. Regarding the maximum image density, the charge transport layer of the organic photoconductor was 8 μm when the amorphous silicon photoconductor of this embodiment was used.
It can be seen that it is higher than that of the case (see FIG. 5).

FIG. 9 shows the C / S (F / m ² ) and the maximum when the developer having a volume average particle diameter of the magnetic carrier of 10 μm was used in the N / N environment of FIG. A graph showing the relationship between the concentrations is obtained by adding the result when the amorphous silicon photoconductor of this embodiment is used.
As shown in FIG. 9, even when the amorphous silicon photoconductor is used as in the present embodiment, the capacitance per unit area C / V is similar to the case of the organic photoconductor.
When (F / m ² ) was plotted on the horizontal axis, it was found that the vehicle was on the line.

From the above, when the amorphous silicon photoconductor is used, the capacitance C / S (F / m ² ) per unit area of the photoconductor is 3. Since 5 × 10 ⁻⁶ and 2.0 × 10 ⁻⁶ have sufficient capacitance, the phenomenon that the electrostatic contrast is buried by the charge of the toner does not occur, and the average of the toner used is It has been found that even when the particle size is as small as 3 to 6 μm, a sufficient image density can be obtained without lowering the toner ratio in the developer when the following requirements are satisfied. That is, when a hard ferromagnetic carrier is used as the magnetic carrier used for the developer, 0.8 × 10
⁻³ (cm) <D <3.5 × 10 ⁻³ (cm) and D ×
When a condition of σ _r ≧ 0.2 (emu / cm ² ) is used and a soft ferromagnetic carrier is used, 1.6 × 10 ⁻³ (cm) <D
<3.5 × 10 ⁻³ (cm) and D × σ ₁₀₀₀ ≧ 0.5
By satisfying the condition of (emu / cm ² ), a sufficient image density can be obtained without lowering the toner ratio in the developer. Further, in the present embodiment, the case where the development is performed by the regular development using the positively charged amorphous silicon photoreceptor has been described, but it has been confirmed that the same effect can be obtained with the negatively charged amorphous silicon photoreceptor.

[0052]

As described above, according to the present invention,
The phenomenon that the image density is reduced when the toner having a small particle diameter having a volume average particle diameter of 3 μm or more and 6 μm or less is used, whereas the electrostatic latent image is filled with a small amount of toner and a large charge amount. , The capacitance C / S per unit area of the photoconductor is set to 2.0 × 10 ⁻⁶ (C / S
m ² ), and when hard ferromagnetic particles are used as the magnetic particles in the two-component developer, 0.8 × 10 ⁻³ (cm) <D <3. 5x
10 ⁻³ (cm) and D × σ _r ≧ 0.2 (emu / c
m ² ), or when using magnetic particles exhibiting soft ferromagnetism, 1.6 × 10 ⁻³ (cm) <D <3.
5 × 10 ⁻³ (cm) and D × σ ₁₀₀₀ ≧ 0.5 (em
u / cm ² ),
An excellent image forming apparatus capable of preventing a decrease in toner ratio, improving development efficiency, preventing carrier adhesion phenomenon, and forming a high quality image by reducing the particle size of the magnetic particles is provided. You.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image forming apparatus according to a conventional example and an embodiment of the present invention.

FIG. 2 is a schematic diagram used for explaining a two-component contact developing device.

FIG. 3 is a schematic diagram used for describing a two-component contact developing device.

FIG. 4 is a graph showing the relationship between the toner average particle diameter and the charge amount of the toner.

FIG. 5 is a diagram showing the maximum image density when the average particle diameter of a carrier is 10 μm and 42 μm when an organic photoreceptor (charge transport layer 8 μm) is used.

FIG. 6 is a view showing the respective maximum image densities when the average particle diameter of a carrier is 10 μm and 42 μm when an organic photoreceptor (charge transport layer 20 μm) is used.

FIG. 7 shows a case where an amorphous silicon photoconductor is used.
FIG. 9 is a diagram showing the maximum image density when the average particle size of the carrier is 10 μm and 42 μm.

FIG. 8 shows the maximum image density when the thickness of the charge transport layer of the organic photoreceptor is changed when the average particle diameter of the carrier is 10 μm.

FIG. 9 is a graph in which the result of the amorphous silicon photoconductor is added to FIG.

FIG. 10 shows the maximum image density when the thickness of the charge transport layer of the organic photoreceptor is changed when the average particle size of the carrier is 42 μm.

FIG. 11 is a diagram showing the relationship between the carrier particle size and the concentration when the thickness of the charge transport layer of the organic photoreceptor is 10 μm.

FIG. 12 is a diagram showing the relationship between carrier particle size and concentration when the charge transport layer thickness of the organic photoreceptor is 20 μm.

FIG. 13 is a diagram showing a relationship among carrier particle diameter, residual magnetization, and carrier adhesion start voltage when a hard ferromagnetic carrier is used.

FIG. 14 is a graph showing the relationship between the carrier particle size, the magnetization under 1000 gauss, and the carrier adhesion onset voltage when a soft ferromagnetic carrier is used.

FIG. 15 is an example of a hysteresis curve of a soft ferromagnetic carrier.

FIG. 16 is an example of a hysteresis curve of a hard ferromagnetic carrier.

FIG. 17 shows a measuring device for measuring the charge amount of toner.

[Explanation of symbols]

 1: photosensitive drum 2: laser exposure means 3: charging device 42, 421: fixed magnet 41: non-magnetic sleeve 4: developing device 5: cleaner 6: fixing device 7: transfer device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/08 507 G03G 15/08 507L

Claims (10)

[Claims] 1. An image bearing member is charged by a charging member, and a dot distribution electrostatic latent image is formed on the image bearing member by image exposure means in accordance with a recorded image signal. The mixed two-component developer is conveyed to the developing section by a developer carrier opposed to the image carrier, and is developed in the developing section by a magnet arranged inside the developer carrier. In a magnetic field, a magnetic brush made of the developer is brought into contact with the image carrier, and the dot distribution electrostatic latent image is developed by applying an alternating voltage to the developer carrier to form a toner image. In an image forming apparatus for forming an image by transferring the toner image to a transfer material, a toner having a volume average particle diameter in a range of 3 μm to 6 μm is used as the toner particles, and a unit of the image carrier is used. Capacitance per area C / ^{There, 2.0 × 10 -6 (F /} m 2)
And the volume average particle diameter of the magnetic particles constituting the two-component developer is D
(Cm) and the residual magnetization is σ _r (emu / cm ³ ), the volume average particle diameter D is 0.8 × 10 ⁻³ (cm) <D
<3.5 × 10 ⁻³ (cm) and D ×
An image forming apparatus using hard ferromagnetic particles satisfying a condition of σ _r ≧ 0.2 (emu / cm ² ). 2. The image forming apparatus according to claim 1, wherein the image carrier is made of an organic photoreceptor, and the charge transport layer constituting the organic photoreceptor has a thickness of 13 μm or less. 3. The image forming apparatus according to claim 1, wherein the image carrier is formed of a photoconductor composed of a surface layer having amorphous silicon. 4. The surface of the magnetic particles in the two-component developer is coated, and the specific resistance before coating is 1 × 10
The image forming apparatus according to any one of claims 1 to 3, wherein the magnetic particles have a resistivity of not less than ^-10 (Ωcm) and a specific resistance of the magnetic particles is not less than 1 x ^10-12 (Ωcm). . 5. The absolute value of the average charge amount per unit weight of toner particles in a two-component developer is 30 × 10 ⁻³ (C /
5. The image forming apparatus according to claim 1, wherein the pressure is not less than 80 × 10 ⁻³ (C / kg). 6. An image carrier is charged by a charging member, and a dot distribution electrostatic latent image is formed on the image carrier by image exposure means in accordance with a recorded image signal. The mixed two-component developer is conveyed to the developing section by a developer carrier opposed to the image carrier, and is developed in the developing section by a magnet arranged inside the developer carrier. In a magnetic field, a magnetic brush made of the developer is brought into contact with the image carrier, and the dot distribution electrostatic latent image is developed by applying an alternating voltage to the developer carrier to form a toner image. In an image forming apparatus for forming an image by transferring the toner image onto a transfer material, a toner having a volume average particle diameter of 3 μm or more and 6 μm or less is used as the toner particles, and the toner particles per unit area of the image carrier are used. When the capacitance C / S is 2 ^{0 × 10 -6 (F / m} 2) is controlled to be larger than, further, as the magnetic particles constituting the two-component developer, the volume average particle diameter D (cm),
The magnetization under an external magnetic field of 1000 Gauss is changed to σ ₁₀₀₀ (emu /
cm ³ ), 1.6 × 10 ⁻³ (cm) <D <
3.5 × 10 ⁻³ (cm) and D × σ ₁₀₀₀ ≧ 0.5
(Emu / cm ² ) An image forming apparatus comprising soft ferromagnetic particles satisfying a condition of (emu / cm ² ). 7. The image forming apparatus according to claim 6, wherein the image carrier is made of an organic photoreceptor, and the charge transport layer constituting the organic photoreceptor has a thickness of 13 μm or less. 8. The image forming apparatus according to claim 6, wherein the image carrier is formed of a photoconductor composed of a surface layer having amorphous silicon. 9. The magnetic particle surface in a two-component developer is coated, and the specific resistance before coating is 1 × 10
^-10 and the (Ω · cm) or more and an image forming apparatus according to any one of claims 6 to 8 specific resistance of the magnetic particles is ^{1 × 10 -12 (Ω · cm} ) or higher . 10. The absolute value of the average charge amount per unit weight of toner particles in a two-component developer is 30 × 10 ⁻³ (C
The image forming apparatus according to any one of claims 6 to 9, wherein the pressure is not less than 80 x ^10-3 (C / kg).