JPH10186860A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress production of image defects such as fog and white voids and to obtain a high quality image. SOLUTION: By this method, a magnetic brush of a developer comprising a mixture of an insulating toner and magnetic particles is formed on the surface of a developer carrying body. The obtd. magnetic brush us brought into contact or nearly contact with an electrostatic latent image holding body on which an electrostatic latent image is formed by laser beams according to digital signals, while a bias voltage including an AC component is applied between the electrostatic latent image holding body and a developer carrying body to deposit the insulating toner on the electrostatic latent image to visualize the image. In this image forming method, the insulating toner has 5 to 10μm average volume average particle size and contains a binder resin having 1 to 25wt.% tetrahydrofuran-insoluble content, and a coloring agent. The magnetic particles used satisfy the relation of r<=-12×log(ρ)+216(r<=100), wherein r (μm) is the diameter of the laser beam and ρ (Ωcm) is the electric resistivity of the particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method for visualizing a latent image formed by an electrophotographic method or an electrostatic recording method using a two-component developer containing an insulating toner and magnetic particles. .

[0002]

2. Description of the Related Art Conventionally, as a developing method using a two-component developer, there has been known a method in which a developer carrier is used and toner is attached to an electrostatic latent image on an electrostatic latent image holding member which is in close proximity to the developer carrier. Have been. The outline of this method is as follows. In other words, a developer in which insulating toner and magnetic particles are mixed is supplied to the surface of the developer carrier, and the magnetic particles are applied to the surface of the developer carrier by the magnetic force of a magnet that is fixed and built in the developer carrier. A magnetic brush having a spike shape is formed, while an electrostatic latent image is formed on the surface of the electrostatic latent image holding body by irradiating light based on an image signal due to a difference in charged potential. Next, a magnetic brush is brought into contact with or close to the surface of the electrostatic latent image holding member, and a bias voltage is applied between the developer holding member and the electrostatic latent image holding member, thereby isolating the insulating toner. The electrostatic latent image is visualized by attaching to the electrostatic latent image.

It is known that the insulating toner used in the above-mentioned developing method generally has a high average quality, a high character reproducibility, and a granularity that gives a sense of smoothness of characters to the eyes when the average particle size is reduced. ing. For this reason, toners used in recent years tend to be reduced in diameter. However, when only small-diameter toner particles are used and only a DC component is applied as a bias voltage, it is difficult to obtain a required image density. for that reason,
As a method of increasing the image density, a method of increasing the rotation speed of the developer carrier, or reducing the gap between the developer carrier and the electrostatic latent image holder is known. However, the former has a problem that the toner smoke and the developer are easily spilled, and the latter requires the developer layer on the developer carrier to be thinner, and a gap for regulating the developer layer thickness. In order to reduce the size of the image, there is a disadvantage that a clog of the developer or other foreign matter, for example, a foreign matter is clogged with thread waste or the like, and a streak-like portion that is not developed is easily generated on an image.

For this reason, in order to obtain a sufficient image density, a bias voltage containing an AC component is applied between the developer carrier and the electrostatic latent image carrier, and the electrostatic latent image carrier is Due to the oscillating electric field formed at the close position (development area),
A method of attaching charged toner to an electrostatic latent image is becoming mainstream.

Conventionally, an image forming method in which a two-component developer is used and an AC voltage and a DC voltage are superimposed and applied as a bias voltage between a developer carrier and a latent image holder (Japanese Patent Application Laid-Open No. Sho 62-62). 289858) is known to have the advantage of increasing the image density by adhering more toner to the developer carrier as compared with the case where only a DC voltage is applied. The frequency of the AC component of the bias voltage is such that a sufficient image density can be obtained and the range is suitable for forming high-quality images.
As disclosed in Japanese Patent No. 2758, usually 200 to 3
The frequency is set within the range of 000 Hz.

When the magnetic particles in the developer used in the above-described developing method have a low electric resistivity (volume resistance) value, a discharge occurs under a developing bias, a charge is injected into the magnetic particles, and a gradation is generated. Since a phenomenon such as deterioration in reproducibility may occur, the electric resistivity of the magnetic particles is usually 10 ¹² Ω · cm.
These are set as described above (JP-A-61-73975, JP-A-62-289858, JP-A-63-1230).
69, JP-A-2-29762, etc.).

[0007]

Generally, in order to obtain a high-quality image faithful to a document, it is necessary to develop not only a sufficient image density but also a faithful reproduction of a latent image. However, with the conventional image forming method using a two-component developer using an AC bias voltage, it is difficult to obtain an image having excellent so-called graininess. The bias was not used because the density of the solid image portion was insufficient.

Further, when a small-diameter toner is used in the above-described image forming method, that is, when the average particle size of the toner particles is 10 μm or less, the frequency of the AC component of the bias voltage is set to 200 to 3000 Hz. If the range is set, the non-image portion on the image will be fogged by the toner, and the image quality will not be effectively improved, but rather will be lowered.

In order to solve these problems, it is conceivable to set the frequency of the AC component to be as high as about 4000 to 8000 Hz.
Although improvement in prevention of fogging and improvement in graininess can be seen, there is a disadvantage that image abnormalities are likely to occur as shown in FIG. This image abnormality means that when an image having a high density portion 30 and a halftone portion 31 which is in contact with the downstream side of the development process of the high density portion is developed, a portion 32 of the low density portion which contacts the high density portion becomes blank. Is not developed.
This image abnormality appears more remarkably when a line screen is used to irradiate the electrostatic latent image holding member with light.
Therefore, in image formation using a small-diameter toner having an average particle diameter of 10 μm or less, it is difficult to obtain a high-quality image with good graininess without the above-mentioned white spots and fogging phenomenon.

[0010] The present invention has been made in view of the above-mentioned circumstances in the prior art. That is, an object of the present invention is to provide a high-quality image excellent in character reproducibility and graininess while suppressing the occurrence of image abnormalities such as stains and white spots in a non-image portion, which is referred to as fogging, for a long time. An object of the present invention is to provide an obtained image forming method.

[0011]

According to the image forming method of the present invention, a magnetic brush of a developer in which an insulating toner and magnetic particles are mixed is formed on the surface of a developer carrier, and the obtained magnetic brush is The electrostatic latent image is brought into contact with or close to the electrostatic latent image holder formed on the surface by laser beam irradiation based on a digital signal, and an alternating current component is applied between the electrostatic latent image holder and the developer carrier. By applying a bias voltage including the toner, the insulating toner is adhered to the electrostatic latent image for visualization, and the volume average particle diameter of the insulating toner is in the range of 5 to 10 μm, and the amount of tetrahydrofuran-insoluble Contains 1 to 25% by weight of a binder resin and a colorant. The magnetic particles have an electric resistivity ρ (Ω · cm) of a diameter r (μm) of the laser beam.
And the frequency f of the AC component in the bias voltage is in the range of 3,000 to 16,000 Hz, and the vibration amplitude of the AC frequency ( Peak-to-peak voltage) is 1 to 2.2 kV
It is characterized in that the voltage is applied so as to fall within the range. r ≦ −12 × log (ρ) +216 (r ≦ 100) (1) The volume average particle diameter of the toner is obtained by obtaining a particle size distribution using a Coulter Counter Model-TAII type (manufactured by Coulter Corporation). It means the median value (volume% average value).

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The insulating toner used in the developer of the present invention contains at least a binder resin and a colorant. The binder resin has a tetrahydrofuran (THF) insoluble content of 1%.
A resin containing a polyester in the range of ２５25% by weight is used, and any composite resin containing the polyester can be used, but it is preferable to use the polyester resin alone. This polyester resin is obtained by a polymerization reaction of a polyvalent hydroxy compound and a reactive acid derivative such as a polyvalent carboxylic acid, a lower alkyl ester thereof, an acid anhydride or an acid halide. In the present invention, the insulating toner has a THF-insoluble content of 1% by weight.
If the binder resin is less than the above, sufficient offset resistance cannot be obtained. On the other hand, if the binder resin having a THF-insoluble content exceeding 25% by weight is used, the fixability is impaired. TH of this binder resin
The F-insoluble portion means a filter paper impervious portion when a sample is dissolved in THF.

As the colorant, any known colorant can be used, for example, carbon black, aniline blue, calcoil blue, chrome yellow, ultramarine blue, Dupont oil red, quinoline yellow , Methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, C.I. I. Pigment Red 48: 1, C.I. I. Pigment Red 57: 1, C.I. I. Pigment Red 122, C.I.
I. Pigment Yellow 12, C.I. I. Pigment
Yellow 17, C.I. I. Pigment Yellow 97,
C. I. Pigment Yellow 170, C.I. I. Pigment Blue 15: 1, C.I. I. Pigment Blue 1
5: 3 and the like are typical examples. The content of the coloring agent is preferably in the range of 1 to 20% by weight based on 100 parts by weight of the binder resin. 1 colorant content
When the amount is less than 20% by weight, the coloring power is weakened. The range of 2 to 8% by weight is preferable for preventing charge injection fog.

In addition, various substances can be added to the insulating toner of the developer used in the present invention for the purpose of charge control, electric resistance control and the like, if necessary. For example, fluorinated surfactants, salicylic acid, chromium dyes such as chromium complexes, maleic acid, charge control resins such as polymers containing amino group-containing vinyl monomers as monomer components, quaternary ammonium salts, nigrosine, etc. Azine-based dyes can be added. Further, a release agent may be added to improve the offset resistance, for example, low-molecular-weight polyethylene, polyolefin represented by low-molecular-weight polypropylene or paraffin wax, candelilla wax, carnauba wax, montan wax, etc. Natural wax and derivatives thereof are appropriately used. In the present invention, the insulating toner having the above-mentioned components has a volume average particle diameter in the range of 5 to 10 μm.

On the other hand, the magnetic particles used in the developer of the present invention preferably have a resin coating layer in which fine resin particles are dispersed on a core material. Examples of the core material of the magnetic particles include iron, steel, nickel, magnetic metals such as cobalt, ferrite, magnetic oxides such as magnetite, glass beads, and the like.
Desirably, it is a magnetic carrier. The average particle size of the core material is usually 10 to 500 μm, preferably 30 to 100 μm.
m range is used.

As the resin fine particles in the resin coating layer of the magnetic particles, any fine particles of a thermoplastic resin or a thermosetting resin can be used, and fine particles of a nitrogen-containing resin are preferable. It is more preferable to use resin fine particles. The method for producing these resin fine particles is a method in which a polymerizable monomer or oligomer is dispersed in a poor solvent, emulsion polymerization or suspension polymerization is performed, and then a method of granulating by surface tension while performing a cross-linking reaction, a low molecular weight method After mixing and reacting the components and the crosslinking agent by melt kneading or the like,
A method of pulverizing to a predetermined particle size by wind force and mechanical force can be used. The average particle size of the resin fine particles is 0.1 to 2
It is preferably in the range of μm, more preferably 0.2 to
1 μm. If the average particle size is smaller than 0.1 μm, the dispersion in the resin coating layer is very poor. On the other hand, if the average particle size is larger than 2 μm, it tends to fall off from the resin coating layer and the original function may not be maintained.

In the resin coating layer according to the present invention, the resin fine particles are uniformly dispersed in the thickness direction, that is, both in the direction parallel to the carrier surface and in the tangential direction. (Resin) is also preferably uniformly dispersed. If the resin coating layer is formed, even if the surface of the resin coating layer is worn for a long time and used, the resin coating layer can maintain the same surface composition as at the beginning, so that the toner can maintain a good charging ability. It is possible to do.

Examples of the matrix resin used for the resin coating layer include polystyrene, polyethylene, polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, polytetrafluoroethylene, polyhexafluoropropylene, and the like. Copolymers of vinylidene and acrylic monomers, copolymers of vinylidene fluoride and vinyl fluoride, and fluorine-containing terpolymers of tetrafluoroethylene, vinylidene fluoride and non-fluorinated monomers. These may be used alone or in combination of two or more.

As a method for forming a resin coating layer containing melamine resin particles and a styrene-acrylic resin, a fluorine-containing resin or a silicone resin as a matrix resin on the surface of the core material of the magnetic particles, for example, A dipping method in which the powder is immersed in the layer forming solution, a spray method in which the layer forming solution is sprayed on the surface of the core material, a fluidized bed method in which the layer material is sprayed while the core material is suspended by flowing air, There is a kneader coater method in which a core material and a layer forming solution are mixed in a kneader coater to remove a solvent. In the present invention, it is preferable to use a kneader coater method.
The solvent used in the coating solution for forming the resin coating layer is not particularly limited as long as it dissolves the matrix resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene, acetone, and methyl ethyl ketone. Ketones and ethers such as tetrahydrofuran and dioxane. The average film thickness of the resin coating layer of the magnetic particles is usually 0.1 to 10 μm, preferably 0.2 to 3 μm.
m.

Further, since the magnetic particles are insulated along with the resin coating and hardly function as a developing electrode as a carrier at the time of development as a carrier, the reproducibility of solids is particularly caused by the occurrence of an edge effect in a black solid portion. Deteriorates. Therefore, a conductive material may be dispersed in the resin coating for the purpose of improving the reproducibility of the solid. Metals such as gold, silver or copper, carbon black, titanium oxide, zinc oxide and semiconductive oxide, zinc oxide, barium sulfate, aluminum borate, potassium titanate, etc. And the like. The surface of the inorganic fine powder is coated with tin oxide, carbon black, metal, and the like. Preferably, carbon black is preferable from the viewpoint of good conductivity, production stability, low cost, and the like. The carbon black is not particularly limited, and any known carbon black may be used.
It is more preferable to use carbon black having good production stability in the range of 250 ml / 100 g.

According to the image forming method of the present invention, a magnetic brush made of a developer obtained by mixing the above-mentioned insulating toner and magnetic particles is formed on the surface of a developer carrier, and a digital signal is formed by using the magnetic brush. The electrostatic latent image formed on the electrostatic latent image holding body is developed by irradiating a laser beam controlled by the above, and is visualized. At that time, the magnetic brush is used as the electrostatic latent image holding body. A bias voltage including an AC component is applied between the electrostatic latent image holding member and the developer carrying member while the electrostatic latent image holding member is brought into contact with or close to the electrostatic latent image holding member.

According to the present invention, the electric resistivity ρ (Ω · cm) of the magnetic particles used in the developer of the image forming method is determined by the diameter r (μ) of the width of the laser beam irradiated at the time of image formation.
m) must satisfy the relationship of the following equation (1). r ≦ −12 × log (ρ) +216 (r ≦ 100) (1) The electric resistivity ρ (Ω · cm) of the magnetic particles is 2
This is a resistance value when magnetic particles are placed in a cell having a fixed volume sandwiched between two electrodes and an applied voltage between the electrodes is set to 1 (V / μm). The laser beam has a diameter r (μ
m) is defined as follows. That is, as shown in FIG. 5, the energy density of the beam decreases as it moves away from the center of the beam in the radial direction, and the energy density becomes 1 / e ² = 13.5% of the maximum value (center of the beam). This is the diameter at a given position, which is indicated as r in FIG.

The frequency f of the AC component of the bias voltage applied between the developer carrying member and the latent image holding member is in the range of the following equation. 3,000 ≦ f ≦ 16,000 (Hz) Further, the vibration amplitude (peak-to-peak voltage) of the AC frequency is in the following range. 1 kV ≦ peak-to-peak voltage ≦ 2.2 kV The above-mentioned peak-to-peak voltage of the AC frequency means the vibration amplitude of the AC frequency, and its peripheral waveform is selected from a rectangular wave, a sine wave, a triangular wave, a sawtooth wave, or the like. And any wave shape is effective. The frequency f of the AC component is in the range where the above-mentioned 3,000 to 16,000 Hz is used, because when the frequency is lowered, the granularity is reduced. The peak-to-peak voltage of the AC frequency is 1k
When the voltage is higher than V, the toner is easily peeled off from the magnetic particles. Further, as the voltage increases, the electric field followability of the toner increases and the granularity is improved.
V is the range used.

According to the present invention, in forming an image using the above-described developer, a toner used for developing an electrostatic latent image generates a reverse electric field due to residual charges remaining on magnetic particles.
Once the toner used for development is returned to the developer carrier and reused, white spots occur. In addition, the larger the potential difference between the high-density part and the low-density part, the stronger the reverse electric field is generated, and white spots occur frequently. When the diameter of the laser beam used to form the electrostatic latent image is reduced, the potential difference between the high density area and the low density area is reduced. It was found that white spots were less likely to occur. Thus, the lower the resistivity of the magnetic particles and the smaller the diameter of the laser beam, the smaller the occurrence of white spots, and the resistivity ρ of the magnetic particles
(Ω · cm) and the diameter r (μm) of the laser beam, the relationship shown in the above equation (1), r ≦ −12 × log (ρ)
+216 (r ≦ 100), and the frequency f of the AC component in the applied bias voltage is set to 3,000 to
By setting the frequency in the range of 16,000 Hz and the vibration amplitude (peak-to-peak voltage) of the AC frequency in the range of 1 to 2.2 kV, the occurrence of white spots and the fogging phenomenon are substantially eliminated.

Further, the image forming method according to the present invention comprises
Since a two-component developer using a toner having a small particle diameter of 10 μm and an AC frequency are adopted for the developing device, the toner is disposed in a narrow gap region between the magnetic particles and the electrostatic latent image holding member (photoconductor) in the developing section. Is effectively separated from the carrier, and the toner adheres and develops to the latent image on the photoreceptor by following the change in the spatial electric field. If the toner particle size is 11 μm or more, the inertia force due to the weight of the toner is large, so that the followability in a high-frequency electric field is reduced, and the fidelity to a latent image, that is, the granularity is deteriorated. 5-1
By using a toner having a thickness of 0 μm, the ability of the toner to follow the electric field is enhanced, and it becomes possible to develop the latent image faithfully.

[0026]

FIG. 1 is a schematic diagram showing an example of an image forming apparatus used for image formation according to the present invention. In FIG. 1, a photosensitive member (electrostatic latent image holding member) 1 rotates in a direction of an arrow a, and the surface of the photosensitive member 1 is charged by a charger 6 and irradiated with a laser beam 7 to charge the electrostatic latent image. An image is formed, the obtained electrostatic latent image is developed and visualized by the two-component magnetic brush developing device 2, the obtained toner image is transferred to a transfer member on the transfer device 8, and then the blade cleaning device 9 The cycle of cleaning is repeated. On the other hand, the transferred toner image is fixed on a transfer body by a fixing device (not shown). In addition, 10 is a potential stabilizer. FIG. 2 is a schematic configuration diagram showing an enlarged part of the two-component magnetic brush developing device 2 of the image forming apparatus shown in FIG. In FIG. 2, a developing roll (developer carrier) 3 is provided with a developing sleeve 3 a that rotates around a fixed magnet, and an AC bias voltage is applied to the developing sleeve 3 a by a voltage applying device 4. Is set to In FIG. 2, the arrow b indicates the rotation direction of the developing roll.

Hereinafter, a preferred embodiment of the present invention will be illustratively described with reference to FIGS. The dimensions, characteristics and other parameters of the arrangement described in this example do not limit the invention in any way. First, the photoconductor 1 is rotated at a constant rotation speed in the direction shown by the arrow a, and is charged to -600 V during uniform charging. Developing sleeve 3
a is a cylindrical type having a diameter of 15 to 25 mm and is non-magnetic conductive, and the rotation direction and the rotation speed can be arbitrarily set. This developing sleeve contains a fixed magnet with seven poles, and the set angle can be changed. The magnetic force of the developing pole of the magnetic roll is set so that a magnetic field of 120 mT is formed on the surface of the developing sleeve. The regulating blade 11, which forms the layer thickness of the developer layer on the surface of the developing sleeve, includes an inner plate 11a of a magnetic material, and the distance between the regulating blade and the developing sleeve is 0.7 to 0.9 mm.
The distance between the photoconductor and the developing sleeve is 0.5 mm
Set to. In addition, the surface of the developing sleeve was set so that a voltage applying device 4 could apply a bias voltage in which an arbitrary DC voltage and an arbitrary AC voltage were superimposed.

The developer 5 is a two-component developer, and its toner has a volume average particle diameter of 12 μm, 10.5 μm and 10.5 μm, respectively.
μm, 9 μm, and 7 μm, four kinds of black non-magnetic toners (binder resin: polyester) were used, and their charge amounts were −2.
The amount was 0 μC / g (blow-off method). The carrier used was a ferrite having an average particle size of 50 μm. The toner density of these developers is such that the amount of toner required on the paper to obtain a solid density is 0.7 mg / cm ^2.
Is adjusted so that the toner density at this time is 3
９9% by weight. The position of the magnet contributing to development in the magnet in the developing sleeve was arranged within ± 5 ° with respect to the closest position to the photoconductor. The moving speed of the photoconductor was 300 mm / sec, and the developing sleeve was rotated at 480 mm / sec in the same direction as the photoconductor. Further, an experiment was performed with the DC component of the voltage application device set to -450 V, the amplitude value of the AC component set to 1.5 kV (PP), and the frequency set to 2 to 8 kHz.

With respect to the halftone graininess at the same density of 0.4 to 0.6 of the copied image obtained under the above operating conditions, the frequency satisfying the optimum graininess is such that the volume average particle diameter of the toner is 10.5 μm. And about 4 kHz when a toner of 9 μm was used, and 6 kHz when a toner having a volume average particle diameter of 7 μm was used. This means that the smaller the volume average particle diameter of the toner, the more remarkable the effect of the frequency appears, indicating good granularity. From this result, the volume average particle diameter of the toner is
It has been found that the thickness is preferably 10 μm or less, and more preferably 9 μm or less.

Next, using the developing device shown in FIG. 2, using a developer comprising a toner having a volume average particle diameter of 9 μm and a carrier having an average particle diameter of 50 μm, the frequency of the AC component is 0 to 20.
At kHz and its amplitude value of 0 to 1.8 kV, the halftone granularity and the fog of the image background were measured at the same concentration of toner by weight. In the prior art, a decrease in density due to high frequency was observed, but in this experimental example of the present invention, no decrease in density occurred until the frequency was increased to 16 kHz. In addition, the graininess was also 4 as in the above experiment.
The optimum was obtained at kHz. Further, it was found that fogging of the image background portion occurred at a frequency of less than 3 kHz, and that the frequency required for the graininess was 3 kHz or more. Although the voltage waveform of the AC bias used in this experimental example was a rectangular wave, other sine waves, triangular waves, or sawtooth waves provided similar effects. Further, although the contact development method is used in this experimental example, the same effect can be obtained by non-contact jumping development. Further, when the change in granularity was confirmed with respect to the frequency when the vibration amplitude of the AC frequency was 0.9 kV and 1.8 kV, the vibration amplitude was 1.8 kV.
It was found that the graininess was improved when the temperature was increased. Further, it was found that the relationship between the vibration amplitude and the image density required a voltage of 1 kV or more in order to obtain a good image density, although the frequency waveform was somewhat dependent on the waveform.

Further, as another embodiment of the present invention, FIG.
This will be specifically described with reference to FIG. Around the photoconductor 1, a charger (scorotron charger) 6 for uniformly charging the photoconductor upstream of the position where the two-component magnetic brush developing device 2 is provided in the rotation direction, and a laser based on a digital image signal A writing device (not shown) for irradiating the beam 7 to form an electrostatic latent image is provided, and a line screen is used for irradiating light by the image signal.
A transfer device that transfers the developed toner image to a sheet at a position facing the transfer device 8 is provided downstream of the photoconductor 1 in the rotation direction. Further downstream, a cleaning device is provided for removing toner remaining on the photoconductor after transfer. On the other hand, a paper feeder for transporting the paper unloaded from the transfer unit is provided on the paper transport path, and a fixing device for fixing the transferred toner image to the paper is provided downstream thereof. . Further, the writing device irradiates a laser beam based on a digital signal, uses a laser diode as a light source, and uses a laser beam having a wavelength of 780 nm. By the irradiation of the laser beam, the potential of the image portion exposed entirely is -10.
It is set to be 0V.

In the two-component magnetic brush developing device 2 shown in FIG. 2, a cylindrical developing roll 3 for transporting the developer by adsorbing the developer on the surface and rotating the housing is provided in a housing containing the developer 5. A regulating auger 11 for regulating the amount of the developer adhering to the surface thereof, and a screw auger for rotating the agitator, which is located upstream of the regulating blade 11 and agitates and transports the developer to supply the developer to the developing roll.

The developing roll 3 incorporates a magnet roll fixed so as not to rotate, and has a developing sleeve rotatably supported around the magnet roll. The developing sleeve is arranged so as to face the photoconductor at a distance of 0.5 mm, and a portion where the surfaces are close to each other is a developing area. Further, the magnet roll disposed inside has a plurality of magnetic poles, and forms a magnetic brush of magnetic particles on the surface of the developing sleeve by a magnetic field formed between adjacent magnetic poles, and the developer is rotated by rotation of the sleeve. It can be transported. The rotational speed of the developing sleeve is set so that the peripheral speed ratio between the photosensitive member and the developing sleeve is approximately 1: 1.6.

A DC voltage and an AC voltage are applied to the developing roll 3 as a developing bias voltage from a DC power supply and an AC power supply, and the electric charge is generated by an electric field formed at a position (developing area) close to the photoreceptor 1. Is set such that the toner having the following formula is adhered to the electrostatic latent image. The applied voltage is such that the DC component is a negative voltage and the voltage of the image area of the entire surface of the photoconductor is -100 V, while the development contrast (the potential difference between the DC component voltage and the entire surface exposure potential of the photoconductor) is 3
So that it becomes about 50 V, that is, the DC component is -450 V
And

In the case of the photoreceptor of this embodiment, when the developing contrast is set to 450 V or more, the gradation deteriorates. Therefore, 450 V is used as a value at which good gradation can be obtained. The AC component of the applied voltage has a peak value and a peak value of 1.5 kV, a frequency of 4 kHz, and a rectangular waveform. One end of the developer regulating blade 11 is fixedly supported, and the other end is attached so as to protrude in the vicinity of the surface of the developing roll 3 so that the developer adsorbed on the surface of the developing roll is kept constant. The amount is regulated.

Using the above-described image forming apparatus, an image was formed in the following steps. The photoreceptor 1 is uniformly charged by a charger 6 and is irradiated with a laser beam 7 from a writing device to form an electrostatic latent image. Next, the surface of the photoconductor on which the electrostatic latent image is formed by the rotation of the photoconductor moves to a development area facing the development device and is developed. Next, the developed toner image is moved by the rotation of the photoconductor, and is transferred onto a sheet by the transfer unit 8. The electrostatic latent image holding body after the transfer is cleaned by the cleaning device, and charged again by the charger. The formed toner image is conveyed to a fixing device, and is heated and pressed to be fixed on a sheet.

In the above image formation, the diameter of the laser beam of the writing device and the resistivity of the magnetic particles are changed,
An electrostatic latent image was formed and developed. As the developer, a mixture of a toner having an average particle diameter of 9 μm and magnetic particles (ferrite carrier) having an average particle diameter of 50 μm was used so that the toner concentration became 6% by weight. These results are shown in FIG.

FIG. 3 shows the laser beam diameters of 40 μm, 50 μm, 64 μm, 80 μm and 95 μm, respectively.
m, the electrostatic latent image is formed and developed by changing the resistivity of the magnetic particles of the developer in the range of 10 ⁷ to 10 ¹⁵ Ω · cm for each of them, and the occurrence of white spots is reduced. It shows the result of the observation. In FIG. 3, the state of occurrence of white spots is evaluated by being divided into the following three grades. Grade 1: No white spots occurred (indicated by a circle in the figure) Grade 2: White spots occurred but in an allowable range (indicated by a triangle in the figure) Grade 3: White spots frequently occurred and were out of the allowable range (x in the figure) As shown in FIG. 3, the resistivity ρ (Ω · c) of the magnetic particles
The lower the value of m), the larger the diameter r (μm) of the laser beam
Is smaller, white spots tend to be less likely to occur. FIG.
The broken line shown therein is r = −12 × log (ρ) +
216 [Equation (1)], and the occurrence of white spots is within the allowable range when the resistivity of the magnetic particles and the diameter of the laser beam are smaller than most of the broken lines. Further, in this embodiment, contact development is used, but non-contact jumping development is similarly effective.

[0039]

According to the image forming method of the present invention, by adopting the above-mentioned structure, high image density, no white spots, and
A high-quality image having good graininess without fogging can be obtained. In particular, by using a small particle size toner having an average particle size of 10 μm or less for the insulating toner used for the two-component developer, image defects such as white spots do not occur for a long time,
Further, it is possible to prevent the occurrence of a fogging phenomenon such as contamination of a non-image portion, and to obtain a high-quality image excellent in character reproducibility and granularity. Further, by increasing the frequency of the AC component of the developing bias voltage, the occurrence of the fogging phenomenon can be prevented, and a high-quality image with improved graininess can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an example of a developing device in the image forming apparatus of the present invention.

FIG. 3 is a graph showing the relationship between the electrical resistivity ρ of magnetic particles obtained in the image formation of the present invention and the diameter r of a laser beam.

FIG. 4 is a diagram showing an example of an image for explaining a problem in a conventional image forming method.

FIG. 5 is a diagram showing a definition of a diameter r of a laser beam used in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Two-component magnetic brush developing device, 3 ... Developing roll, 3a ... Developing sleeve, 4 ... Voltage application device, 5 ... Developer, 6 ... Charging device, 7 ... Laser beam, 8 ... Transfer device,
9 cleaning device, 10 potential stabilizer, 11 regulating blade, 11a inner plate.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G03G 9/113 G03G 9/08 331 15/06 101 9/10 15/09 361 (72) Inventor Kozo Ota Takematsu, Minamiashigara-shi, Kanagawa 1600 Fuji Xerox Co., Ltd. (72) Inventor Shinpei Takagi 1600 Takematsu, Minami Ashigara City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (9)

[Claims] 1. A developer magnetic brush in which an insulating toner and magnetic particles are mixed is formed on a surface of a developer carrier, and the obtained magnetic brush is irradiated with a laser beam based on a digital signal to form an electrostatic latent brush. The image is brought into contact with or close to the electrostatic latent image holding member formed on the surface, and a bias voltage including an AC component is applied between the electrostatic latent image holding member and the developer holding member, thereby forming the electrostatic latent image holding member. In the image forming method for visualizing an image by attaching an insulating toner to a latent image, a binder resin having a volume average particle size of 5 to 10 μm and a tetrahydrofuran insoluble content of 1 to 25% by weight is used as the insulating toner. And a magnetic particle having an electrical resistivity ρ (Ω · cm) satisfying the following formula (1) between the laser beam and the diameter r (μm) of the laser beam. Using With further frequency f of the AC component in the bias voltage 3,000～16,0
An image forming method, wherein the application is performed so that the vibration amplitude (peak-to-peak voltage) of the AC frequency is in the range of 1 to 2.2 kV. r ≦ −12 × log (ρ) +216 (r ≦ 100) (1) 2. The image forming method according to claim 1, wherein the developer carrier has a built-in fixed magnetic pole. 3. The image forming method according to claim 1, wherein the magnetic particles are obtained by providing a resin coating layer on core particles. 4. The image forming method according to claim 3, wherein the resin coating layer is formed by dispersing resin fine particles and a conductive material. 5. The resin fine particles have an average particle size of 0.1 to 2 μm.
The image forming method according to claim 4, wherein: 6. The image forming method according to claim 4, wherein the resin fine particles are nitrogen-containing resin fine particles. 7. The image forming method according to claim 4, wherein the conductive material is carbon black. 8. The magnetic particles having an average particle size of 25 to 100 μm
The image forming method according to claim 1, wherein: 9. The image forming method according to claim 1, wherein the binder resin of the toner contains a linear polyester.