JPH04274445A - Magnetic developer and image forming method - Google Patents

Abstract

PURPOSE:To prevent the electrification unevenness from occurring even in the case of printing a large number of sheets in an image forming method in which contact electrostatic charging is utilized by making developer contain insulating toner containing binding resin and specified magnetic substance. CONSTITUTION:A photosensitive drum 1 obtained by forming an organic photoconductor 1b being a photosensitive layer on the outer peripheral surface of a drum base substance 1a made of aluminum rotates at a specified speed. An electrostatic charging roller 2 obtained by providing a conductive rubber layer 2b on a metallic core bar 2a and further a surface layer 2c being a releasing coating film on the peripheral surface of the layer 2b is brought into contact with the photosensitive drum 1 with specified pressure. A power source part E supplies DC voltage or specified voltage obtained by superposing AC voltage on DC voltage to the core bar 2a of the roller 2. The magnetic developer contains the insulating toner containing at least the binding resin and the magnetic substance. Then, the magnetic substance is obtained by adding at least one substance selected from a polymer, a condensation product, a fatty acid and the derivative of fatty acid to its surface and has a spherical shape or a shape without a pointed corner part.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention is applicable to electrophotography, electrostatic recording,
The present invention relates to a developer and an image forming method for visualizing electrostatic charge images such as electrostatic printing.

More specifically, the present invention relates to a developer and an image forming method used in electrophotography, which includes a charging step in which a charging member to which a voltage is applied from the outside is brought into contact with a member to be charged.

0003

2. Description of the Related Art Corona dischargers are conventionally known as charging means in electrophotographic devices and the like. However, corona dischargers have problems such as the need to apply high voltage and the generation of a large amount of ozone.

Therefore, recently, consideration has been given to using contact charging means without using a corona discharger. Specifically, a voltage is applied to a conductive roller, which is a charging member, and the roller is brought into contact with a photoreceptor, which is an object to be charged, so that the surface of the photoreceptor is charged to a predetermined potential. If such contact charging means is used, the voltage can be lowered compared to a corona discharger, and the amount of ozone generated can also be reduced.

For example, in Japanese Patent Publication No. 50-13661, it is possible to apply a low voltage when charging photosensitive paper by using a roller whose core metal is coated with a dielectric material made of nylon or polyurethane rubber.

However, in the conventional example described above, when the core metal is coated with nylon, it does not have the elasticity of rubber or the like, so it is not possible to maintain sufficient contact with the object to be charged, resulting in charging failure. On the other hand, if the core metal is coated with polyurethane rubber, the softening agent impregnated into the rubber material will seep out, and if a photoreceptor is used as the object to be charged, the charging member will stick to the photoreceptor at the contact area when the photoreceptor stops. However, there is a problem in that the area is blurred or the image is blurred. In addition, if the softener in the rubber material of the charging member seeps out and adheres to the surface of the photoreceptor, the resistance of the photoreceptor becomes low and image deletion occurs, making it unusable in severe cases or toner remaining on the surface of the photoreceptor. may adhere to the surface of the charging member, causing a filming phenomenon. When a large amount of toner adheres to the surface of the charging member, the surface of the charging member becomes insulated, the charging ability of the charging member is lost, and the surface of the photoreceptor becomes non-uniformly charged, which affects the image.

[0007] This is because the charging member presses the photoreceptor surface more strongly, which makes it more likely that the residual developer will stick to the charging member or the surface of the charged object, and that it will also be more likely to be scratched or scraped.

[0008] In the contact charging device according to the present invention, a DC voltage or a DC voltage superimposed with an AC voltage is applied to the charging member. In particular, the abnormal charging and flying motion of the residual developer, which is small in particle size and light in weight, is repeated, and as a result, the residual developer is electrostatically attracted to and embedded in the charging member and the surface of the photoreceptor drum. This is very different from the case of using non-contact charging means using a conventional corona discharger.

On the other hand, in recent years, small and inexpensive copying machines and laser printers for personal use have appeared, and in order to be maintenance-free, these small machines have integrated the photoreceptor, developer, cleaning device, etc. It is desirable to use a magnetic one-component developer because a conventional cartridge system is used and the structure of the developing device can be simplified.

In order to form a visible image of good quality in a method using such a magnetic one-component developer,
It is necessary for the developer to have high fluidity and uniform chargeability, and for this purpose, inorganic fine powder has conventionally been added and mixed into toner powder. but,
In the case of hydrophilic inorganic fine powder, the developer to which it is added may aggregate due to moisture in the air, resulting in a decrease in fluidity, or in extreme cases, the charging performance of the developer may be reduced due to moisture absorption by the inorganic fine powder. Put it away. Therefore, among inorganic fine powders, it is recommended to use silica fine powders that have been subjected to hydrophobization treatment.
This method has been proposed in JP-A No. 5782, JP-A-48-47345, JP-A-48-47346, and the like. Specifically, for example, fine silica powder is used which is made hydrophobic by reacting fine silica powder with an organosilicon compound such as dimethyldichlorosilane and replacing the silanol groups on the surface of the fine silica powder with organic groups.

[0011] However, such a developer externally added with inorganic fine powder is particularly susceptible to damage to the pressure contact member and the photoreceptor during an image forming process in which pressure is applied to the photoreceptor due to contact charging or the like. Toner adhesion, filming, etc. are likely to occur due to toner adhesion, and in severe cases, image defects may occur.

0012

SUMMARY OF THE INVENTION An object of the present invention is to provide a developer that does not cause toner fusion on a photoreceptor.

Another object of the present invention is to provide a developer with high image density and no filming.

Another object of the present invention is to provide a developer that is free from charging unevenness even when a large number of printouts are performed in an image forming method having a contact charging step.

Another object of the present invention is to provide an image forming method comprising a contact charging step and a developing step of developing the developer of the present invention.

[0016]

Means for Solving the Problems and Effects The present invention provides a magnetic developer containing an insulating magnetic toner having at least a binder resin and a magnetic material, wherein the magnetic material has a polymer, condensate, or A magnetic development material characterized by being treated by adding at least one substance selected from fatty acids or fatty acid derivatives and having a spherical shape or a shape substantially free of sharp corners. The present invention also relates to an image forming method comprising a charging step of bringing a charging member into contact with an object to be charged and applying a voltage from the outside to perform charging, and a developing step of using the magnetic developer.

The reason why the magnetic toner using the specific magnetic material of the present invention is effective in fusing the toner to the surface of the photoreceptor is considered to be as follows.

Toner fusion on the photoreceptor surface is caused when the photoreceptor surface is rubbed by a contact charging member to which developer that has slipped from the cleaning blade is attached in an image forming apparatus having a contact charging device. This is because the small-particle, light-weight developer remaining on the surface of the photoreceptor is pressed against the surface of the photoreceptor by the contact charging member due to the scratches, causing fixation and embedding. The surface-treated spherical magnetic material used in the present invention has lubricating properties, and the lubricity of the magnetic material present on the surface of the toner acts even after the toner is formed, so that the contact charging member and the photoconductor Since it acts as a lubricant between the photoreceptors, it prevents fusion without damaging the surface of the photoreceptor.

[0019] A magnetic material having a spherical shape or a shape substantially free of sharp corners and which is treated by adding a polymer, a condensate, a fatty acid or a fatty acid derivative to the surface used in the magnetic developer according to the present invention. For example, in the crushing process, polymers such as polyvinyl fluoride and polyvinylidene fluoride, condensates such as dimethyl silicone oil, fluorine-modified silicone oil, and silicone anise, and fatty acids such as lauric acid and
It can be obtained by adding palmitic acid, stearic acid, oleic acid, etc. or a derivative thereof and treating the surface, but is not limited to the above.

Methods of treating the surface of a magnetic material with various substances have been proposed for the purpose of increasing the compatibility of the magnetic material with organic materials in order to improve the dispersion of the magnetic material in the binder resin. . For example, JP-A-53-137148 discloses fatty acids and derivatives thereof, and JP-A-53-81125 discloses polymeric materials. These materials are excellent in improving compatibility.

[0021] On the other hand, the present inventors have
In Publication No. 8, as a means of dispersing the magnetic material more uniformly in the binder resin, the spherical magnetic material promotes dispersibility in the resin more than the conventional cubic magnetic material, and it is possible to reproduce fine lines. It is proposed that this method is suitable for toner with fine particle size, which has excellent properties and resolution.

[0022] Therefore, by using a magnetic material which has a spherical shape or a shape substantially free of sharp corners and which has been treated by adding a polymer, condensate, fatty acid or derivative thereof to the surface,
It is possible to provide a magnetic developer with high image quality and without toner fusing in an image forming apparatus having a contact charging device.

[0023] The spherical magnetic material used in the present invention is composed of 50% or more of magnetic particles having a true spherical shape with a curved surface or having substantially no sharp corners. (Preferably 70% or more by number, more preferably,
80% or more).

Furthermore, the spherical magnetic material used preferably has an average particle diameter of 0.1 to 0.3 μm.

In the present invention, the average particle size of the spherical magnetic material is
It is determined by taking an enlarged photograph of the sample using a scanning electron microscope, randomly measuring the long diameter of 100 to 200 particles, and calculating the average value.

[0026] If the particle size of the magnetic material is less than 0.1 μm, the cohesive force will be large and it will be difficult to unravel, resulting in poor dispersibility and problems such as durability and image stability.

Furthermore, if the diameter is larger than 0.3 μm, the magnetic material will not be uniformly contained in the toner particles, and toner particles with particularly fine particle diameters will be more likely to be non-uniform, resulting in poor image quality, especially halftones, in a low-temperature, low-humidity environment. It is difficult to maintain stable fine line reproducibility over a long period of time.

The spherical magnetic body according to the present invention preferably has 1
．． 2 to 2.5 g/cm3, more preferably 1.5 to 2
．． It has a consolidated apparent density of 0 g/cm3.

In the present invention, the solidified apparent density of the magnetic material is determined using a powder tester manufactured by Hosokawa Micron Co., Ltd. and the container attached to the powder tester, according to the procedure in the instruction manual of the powder tester. Refers to the measured value.

The value of the solidified apparent density is so large that ordinary untreated cubic magnetic materials and untreated spherical magnetic materials cannot be satisfied. The specific spherical magnetic material preferably used in the present invention is 0.7 g/cm3 or more to 1.0 g/cm3 or more.
It can be prepared by crushing a spherical magnetic material having a solidified apparent density of less than g/cm3.

The means used to crush the spherical magnetic material include a mechanical crusher equipped with a high-speed rotor for crushing the powder, and a mechanical crusher for dispersing or crushing the powder. An example is a pressure dispersion machine equipped with a load roller for this purpose.

[0032] When a mechanical crusher is used to crush aggregates of magnetic particles, the impact force by the rotor is likely to be excessively applied to the primary particles of the magnetic particles, causing the primary particles themselves to be destroyed. This tends to generate fine powder of magnetic particles. Therefore, when a magnetic material that has been crushed by a mechanical crusher is used as a raw material for a toner, the triboelectric charging characteristics of the toner deteriorate due to the presence of fine powder of magnetic particles. Therefore, a decrease in toner image density is likely to occur due to a decrease in the amount of triboelectric charge of the toner.

On the other hand, a pressure dispersing machine equipped with a weighted roller such as a fred mill is preferable in view of the efficiency of disintegrating aggregates of spherical magnetic particles and the suppression of the production of fine powder magnetic particles.

The solidified apparent density of the magnetic material can be understood to indirectly indicate the shape of the magnetic particles, the surface condition of the magnetic material, and the amount of aggregates of magnetic particles present. If the solidified apparent density of the magnetic material is less than 1.2 g/cm3,
A large amount of cubic magnetic particles exist in the magnetic material, or a large number of aggregates of magnetic particles exist,
This indicates that the crushing treatment of the magnetic material is substantially insufficient. Therefore, the solidified apparent density is 1.2g/cm3
If a magnetic material of less than is likely to occur.

[0035] The solidified apparent density of the magnetic material is 2.5 g/cm
If it exceeds 3, the aggregates of magnetic particles will be broken up excessively, and the magnetic particles will stick to each other due to pressure, producing pellets of magnetic material, and as a result, non-uniform magnetic toner particles will be formed. There is a tendency to generate.

The spherical magnetic body according to the present invention has a binder resin 10
50 to 120 parts by weight (preferably 70 parts by weight)
~110 parts by weight). If it is less than 50 parts by weight, the conveyance of the magnetic toner on a developer carrier such as a sleeve will be insufficient. If it exceeds 120 parts by weight, the insulation properties and heat fixing properties of the magnetic toner will deteriorate.

As the binder resin for the magnetic toner according to the present invention, monopolymers of styrene and its substituted products such as polystyrene and polyvinyltoluene; styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-
Vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl acrylate copolymer Polymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-dimethylaminoethyl methacrylate copolymer, styrene-vinyl methyl ether copolymer, Styrene-vinylethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer, etc. Styrenic copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or alicyclic hydrocarbon resin , aromatic petroleum resin, paraffin wax, carnauba wax, etc. can be used alone or in combination.

The magnetic toner of the present invention preferably has a negative charge and may contain a charge control agent if necessary, such as a metal complex salt of a monoazo dye, a metal complex salt of salicylic acid, alkyl salicylic acid, dialkyl salicylic acid, or naphthoic acid. negative charge control agent is used.

Among the inorganic fine powders used in the present invention, particularly preferred are dry silica produced by vapor phase oxidation of a silicon halide compound or fumed silica, and water glass. Both so-called wet silica can be used, but there are few silanol groups on the surface and inside the silica fine powder, and
Dry silica free of production residues such as a2O, SO32-, etc. is preferable.

In addition, in the case of dry silica, a composite fine powder of silica and other metal oxides can be obtained by using other metal halide compounds such as aluminum chloride or titanium chloride together with silicon halide compounds in the manufacturing process. Possible and inclusive.

[0041] The particle size is 0.0 as the average primary particle size.
It is desirable that the particle size is within the range of 0.01 to 2 μm, and particularly preferably, it is good to use silica fine powder within the range of 0.002 to 0.2 μm.

[0042] For the hydrophobization treatment, conventionally known hydrophobization treatment agents and methods are used.

[0043] The degree of hydrophobicity of the inorganic fine powder in the present invention is as follows:
Use the values measured by the following method. Of course, other measurement methods can also be applied while referring to the measurement method of the present invention.

Pour 100 ml of ion-exchanged water and 0.1 g of sample into a 200 ml sealed separatory funnel, and shake at 90 rpm with a shaker (Turbula shaker mixer T2C type).
Shake for 10 minutes under the following conditions. After shaking and allowing to stand for 10 minutes to separate the inorganic powder layer and water layer, the lower water layer was
Collect 30 ml, put it in a 10 mm cell, and measure the transmittance at a wavelength of 500 nm using blank ion-exchanged water that does not contain silica fine powder as a reference, and use the transmittance value as the degree of hydrophobicity of the inorganic fine powder. It is.

The degree of hydrophobicity of the hydrophobic inorganic fine powder in the present invention is 60% or more (more preferably 90% or more). If the degree of hydrophobicity is less than 60%, it is difficult to obtain a high-quality image due to moisture adsorption of the inorganic fine powder under high humidity.

The amount of these hydrophobic inorganic fine powders to be applied is 0.1 to 1.6 parts by weight per 100 parts by weight of the magnetic toner.
The effect is exhibited when the weight part is particularly preferably 0.6
It is possible to provide a developer that exhibits excellent performance when 1.4 parts by weight is added.

The magnetic developer of the present invention may further contain other additives, such as lubricants such as Teflon and zinc stearate, or fixing aids (such as low molecular weight polyethylene), as long as they do not have a substantial adverse effect. A metal oxide such as tin oxide may be added as a conductivity imparting agent.

[0048] In producing the toner of the present invention, the constituent materials are thoroughly kneaded using a heat kneader such as a hot roll, kneader, or extruder, and then obtained by mechanical pulverization and classification, or by mixing the constituent materials in a binder resin solution. Toner production by a method in which materials are dispersed and then spray-dried, or a polymerization method in which toner is obtained by mixing specified materials with the monomers that constitute the binder resin to form an emulsified suspension and then polymerizing the resulting toner. Each method can be applied.

The contact charging process of the present invention applicable to the magnetic developer and image forming method of the present invention will be specifically explained below.

FIG. 1 is a schematic diagram of a contact charging device showing an embodiment of the present invention. Reference numeral 1 designates a photoconductor drum which is an object to be charged, and is composed of an aluminum drum base 1a and an organic photoconductor (OPC) layer 1b formed on the outer peripheral surface of the drum base 1a. Rotate. In this embodiment, the photosensitive drum 1 has an outer diameter of 30 mmφ. A charging roller 2 is a charging member that is brought into contact with the photosensitive drum 1 with a predetermined pressure, and a metal core 2a is provided with a conductive rubber layer 2b, and a surface layer 2c that is a releasable film is provided on the circumferential surface of the roller. has been established. The surface layer in this example is a releasable film, and it is preferable to provide a releasable film in view of matching with the developer and image forming method of the present invention. However, if the resistance of the release film is too high, the photoreceptor drum 1 will not be charged, and if the resistance is too small, too much voltage will be applied to the photoreceptor drum 1, causing damage to the drum and the formation of pinholes. Resistance, i.e. volume resistivity 109-101
4Ωm is good, and the thickness of the releasable film at this time is 3.0μm.
Preferably within Further, the lower limit of the thickness of the coating is considered to be about 5 μm as long as the coating does not peel or crease.

In this embodiment, the outer diameter of the charging roller 2 is 12
mmφ, the conductive rubber layer 2b is EPDM, and the surface layer 2c
A nylon resin with a thickness of 10 μm was used. The hardness of the charging roller 2 was 54.5° (ASKER-C). E is a power supply unit that applies voltage to the charging roller 2, and supplies a predetermined voltage to the core metal 2a of the charging roller 2. In FIG. 1, E indicates a DC voltage, but it is preferable to use an AC voltage superimposed on a DC voltage.

Preferred process conditions in this case are shown below. Contact pressure 5-500g/cm AC voltage
0.5~5KVpp AC frequency 50
~3000Hz DC voltage -200~-90
0V FIG. 2 is a schematic diagram of a contact charging member showing another embodiment of the present invention. Components common to those in the device shown in FIG. 1 are given the same reference numerals and will not be described again.

The contact charging member 2' of this embodiment is a blade-shaped member brought into contact with the photosensitive drum 1 in the forward direction with a predetermined pressure, and this blade 2' is connected to a metal support member 2' to which a voltage is supplied. A conductive rubber 2'b is supported on a, and a surface layer 2'c serving as a releasable film is provided at the portion in contact with the photoreceptor drum 1. The surface layer 2'c has a thickness of 1
Nylon of 0 μm was used. According to this embodiment, there is no problem such as adhesion between the blade and the photoreceptor drum, and the same effects as in the previous embodiment can be obtained.

[0054] In the above-described embodiments, a roller-shaped or blade-shaped charging member is used, but the present invention is not limited to this, and the present invention can be practiced with other shapes as well.

Further, in this embodiment, the charging member is composed of a conductive rubber layer and a release film, but the charging member is not limited thereto, and there is a structure between the conductive rubber layer and the surface layer of the release film to prevent leakage to the photoreceptor. Therefore, it is recommended to form a high-resistance layer, such as a hydrin rubber layer with small environmental fluctuations.

[0056] In place of the nylon resin, PVDF (polyvinylidene fluoride), PVDC (
Polyvinylidene chloride) may also be used. As the photoreceptor, amorphous silicon, selenium, ZnO, etc. can also be used. In particular, when amorphous silicon is used for the photoreceptor, compared to when other materials are used, if even a small amount of the softener in the conductive rubber layer adheres to the photoreceptor, image fading will become severe. The effect of applying an insulating film is significant.

In addition, in the cleaning process according to the present invention, the photosensitive drum after the toner image has been transferred is generally cleaned by wiping off the remaining transferred toner and other contaminants with a cleaning member such as a cleaner blade or roller. It is planarized and subjected to image formation repeatedly.

[0058] Further, it is also possible to carry out such a cleaning step simultaneously during a charging step, a developing step, or a transfer step related to electrophotography.

The present invention is particularly effective for image forming apparatuses in which the surface of the latent image carrier is made of an organic compound. When an organic compound forms the surface layer, it has good adhesion with the binder resin contained in the toner, and especially when the same material is used, a chemical bond occurs at the contact point, causing toner melting. This is to encourage people to wear clothes.

Surface materials of the latent image carrier used in the present invention include silicone resin, vinylidene chloride, ethylene-vinyl chloride, styrene-acrylonitrile, styrene-methyl methacrylate, styrene, polyethylene terephthalate,
Examples include polycarbonate, but the material is not limited thereto, and other monomers or copolymerization or blending of exemplified resins can also be used.

The present invention is particularly effective for image forming apparatuses in which the diameter of the latent image carrier is 50 mm or less. This is because in the case of a small diameter drum, even if the linear pressure is the same, the curvature is large, so pressure concentration tends to occur at the contact area.

It is thought that the same phenomenon occurs with belt photoreceptors, and it is also effective for image forming apparatuses in which the radius of curvature at the transfer section is 25 mm or less.

[0063]

[Examples] The basic structure and features of the present invention have been described above, and the method of the present invention will be specifically explained below based on Examples. However, this does not limit the embodiments of the present invention in any way.

Example 1 Styrene-butyl acrylate-divinylbenzene copolymer (copolymerization ratio 80/19.5/0.5,
Weight average molecular weight 320,000)
100 parts by weight Added 2 wt% of polyvinyl fluoride in the crushing process
Treated, particle size is 0.22μm, hardened apparent density is
1.59 g/cm3 spherical magnetite particles a
80 parts by weight low molecular weight polypropylene
4 parts by weight
Chromium complex of monoazo dye
4
Part by Weight The above mixture was melt-kneaded in a twin-screw kneading extruder heated to 140°C, the cooled kneaded product was coarsely pulverized in a hammer mill, and the coarsely pulverized product was pulverized in a jet mill. Ultrafine powder and coarse powder were classified and removed using a multi-division classifier to obtain a magnetic toner having a weight average particle size of 7.5 μm.

[0065] Hydrophobic silica fine powder was added to the above magnetic toner.
．． 8 wt % was added and mixed in a Henschel mixer to obtain a magnetic developer.

Next, this magnetic developer was applied with a DC voltage and an AC voltage (500Hz, 2000Vpp) using an image forming apparatus (a modified Canon laser beam printer LBP-8II) having a contact charging device as shown in FIG. A live-action test was conducted at high temperature and high humidity (32.5°C, 85% RH) in which a toner image was continuously formed using a reversal development method at a printing speed of 16 sheets (A4)/min by applying electricity to a charging device, and the printout image was was evaluated. At the same time, the charging member (roller type) and the surface of the photoreceptor drum were observed.

Example 2 As a magnetic material, 1 wt% polyvinylidene fluoride was added in the crushing process, and the average particle size was 0.23 μm.
A magnetic developer was obtained in the same manner as in Example 1, except that spherical magnetite particles b having a solidified apparent density of 1.81 g/cm 3 were used.

[0068] This was evaluated in the same manner as in Example 1.

Example 3 A magnetic material with an average particle size of 0.20 was treated by adding 2 wt % of dimethyl silicone oil in the crushing process.
A magnetic developer was obtained in the same manner as in Example 1, except that spherical magnetite particles c having a solidified apparent density of 1.92 g/cm3 were used.

[0070] This was evaluated in the same manner as in Example 1.

Example 4 The magnetic material was treated by adding 2 wt % of fluorine-modified silicone oil (containing trifluoroalkyl group) in the crushing process, and had an average particle size of 0.23 μm and a solidified apparent density of 1. A magnetic developer was obtained in the same manner as in Example 1, except that 85 g/cm3 of spherical magnetite particles d were used.

[0072] This was evaluated in the same manner as in Example 1.

Example 5 As a magnetic substance, 1 isopalmitic acid was added in the crushing process.
A magnetic developer was obtained in the same manner as in Example 1, except that spherical magnetite particles e having an average particle size of 0.21 μm and a solidified apparent density of 1.68 g/cm 3 were used.

[0074] This was evaluated in the same manner as in Example 1.

Example 6 As a magnetic substance, 0.5 stearic acid was added in the crushing process.
A magnetic developer was obtained in the same manner as in Example 1, except that spherical magnetite particles f having an average particle size of 0.20 μm and a solidified apparent density of 1.99 g/cm 3 were used in the same manner as in Example 1.

[0076] This was evaluated in the same manner as in Example 1.

Example 7 As a magnetic material, 2 wt% of oleic acid was added in the crushing process.
Added and treated spherical magnetite particles g having an average particle diameter of 0.22 μm and a solidified apparent density of 1.84 g/cm3
A magnetic developer was obtained in the same manner as in Example 1 except that .

[0078] This was evaluated in the same manner as in Example 1.

Example 8 As a magnetic material, 1 wt % of palmitic acid methyl ester was added in the crushing process, and the average particle size was 0.1.
A magnetic developer was obtained in the same manner as in Example 1 except that spherical magnetite particles h having a diameter of 9 μm and a solidified apparent density of 1.95 g/cm 3 were used.

[0080] This was evaluated in the same manner as in Example 1.

Comparative Example 1 As the magnetic material, untreated spherical magnetite particles i with an average particle size of 0.20 μm and a solidified apparent density of 1.38 g/cm 3 were used, and hydrophobic silica fine powder was used. 0
A magnetic developer was obtained in the same manner as in Example 1 except that wt% was added.

[0082] This was evaluated in the same manner as in Example 1.

Comparative Example 2 A magnetic material was used in the same manner as in Example 1, except that untreated cubic magnetite particles j were used as the magnetic material, with an average particle diameter of 0.18 μm and a solidified apparent density of 1.18 g/cm3. A developer was obtained. This was evaluated in the same manner as in Example 1. Table 1 shows the evaluation results. The evaluation criteria are shown below. Drum fusion ○ ... No fusion at all ○ △ ... 1 to 3 points of fusion on A4 solid black △ ... 4 to 10 points of fusion on A4 solid black × ... A4
More than 11 points fused in solid black

[0084]

[Table 1]

[0085]

According to the present invention, by using a magnetic toner having a specific magnetic substance as a magnetic developer, the magnetic toner has lubricating properties, and when the charging member is brought into contact with the charged object, a voltage is applied from the outside. In an image forming method having a charging step in which charging is performed by applying electrification, it is possible to prevent toner from adhering to the surface of a photoreceptor and to obtain high-quality images without toner contamination.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing a charging roller of the present invention.

FIG. 2 is an explanatory diagram schematically showing a blade that is another embodiment of the present invention. 1 Photosensitive drum 2, 2' Charging member E Power supply

Claims (2)

[Claims] 1. A magnetic developer containing an insulating magnetic toner having at least a binder resin and a magnetic material, wherein the magnetic material has at least a substance selected from a polymer, a condensate, a fatty acid, or a fatty acid derivative on its surface. 1. A magnetic developer characterized in that it is a magnetic material which has been processed by adding one or more of the following: a magnetic material having a spherical shape or a shape substantially free of sharp corners. 2. An image characterized by comprising a charging step of bringing a charging member into contact with a charged object and applying a voltage from the outside to perform charging, and a developing step of using the magnetic developer according to claim 1. Formation method.