JP2769917B2 - Magnetic developer, image forming method and apparatus unit - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic toner containing a spherical magnetic substance, a magnetic developer having at least hydrophobic silica fine powder, and image formation using the magnetic developer. Method and apparatus unit.

In the electrophotographic image forming method, the magnetic developer, the image forming method, and the apparatus unit of the present invention may be configured such that a latent image is represented by a unit pixel, and the unit pixel is an on-off binary or finite floor. It can be preferably used to visualize a digital latent image expressed by a tone using a reversal development method.

[Prior Art] In an electrophotographic system, a method of exposing a document image and exposing the reflected light to a latent image carrier to obtain a latent image is generally performed. In this method, since the reflected light of the original is directly converted into an image signal, the electric potential of the electric latent image continuously changes (hereinafter referred to as an analog latent image).

On the other hand, recently, the original reflected light is converted into an electric signal,
A method of processing the signal and performing exposure based on the signal has been commercialized. In this system, enlargement and reduction at a high magnification can be easily performed as compared with the analog latent image system, and an image signal can be taken into a computer and output together with other information. Although there are various uses as described above, if the image signal is handled as analog, the signal amount becomes enormous, so the image processing must be divided into pixels (hereinafter referred to as dots) and digital processing to determine the exposure amount for each pixel is necessary. Becomes

When a latent image is digitized, compared to an analog latent image,
A developer that can accurately develop each dot is required.

In the case of developing a digital latent image, the deviation of the surface potential of the latent image during the formation of the latent image is larger than that of the analog latent image, and the potential difference between the developer transport unit and a latent image carrier such as a photosensitive drum is smaller. Development also needs to be performed on the latent image portion.

In an image in which an image / non-image is repeated for each dot, the developability of the developer is particularly important. Therefore, when a developer developed as a developer for an analog latent image is used in a digital latent image system, in particular, in the print pattern in which the image / non-image is repeated for each dot, the development for each dot is insufficient, A phenomenon such that the dots become smaller or the dots are not developed at all occurs, and as a whole, the image density tends to be faint or the characters are faint. This development tends to be remarkable in a developer having a magnetic toner containing a magnetic material whose developer charge amount tends to be small (hereinafter referred to as a magnetic developer).

This is considered to be because the magnetic developer has a portion where the magnetic substance comes out on the surface of the magnetic toner particles, and the surface that can contribute to charging is reduced. Since the amount of exposure of the magnetic material on the toner particle surface changes depending on the amount of the magnetic material contained in one magnetic toner, the distribution of the charge amount of the developer becomes wider than that of other developers. Accordingly, when a magnetic developer is used in a digital latent image system, blurring of characters due to accumulation of magnetic toner particles having a low triboelectric charge in a developing device is likely to occur, and improvement thereof is desired.

Further, in recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, the uses thereof have been diversified, and the demands for image quality have become strict. 2. Description of the Related Art Generally, in copying an image such as a document, it is required to reproduce very finely and faithfully without crushing or breaking even fine characters. In particular, when the latent image on the photoreceptor of the image forming apparatus is a line image having a size of 100 μm or less, a conventional developer generally has poor fine line reproducibility, and the line image is not yet sufficiently sharp. 2. Description of the Related Art Recently, in an image forming apparatus such as an electrophotographic printer using a digital image signal, a latent image is formed by collecting a fixed number of dots, and a solid portion, a halftone portion, and a light portion have different dot densities. It is expressed by things. However, in the toner image, in a state where the toner particles do not exactly adhere to the dots and the toner particles protrude from the dots,
There is a problem that the gradation property corresponding to the dot density ratio between the black part and the white part of the digital latent image cannot be obtained. Further, when the resolution is improved by reducing the dot size in order to improve the image quality, the reproducibility of a latent image formed from minute dots becomes more difficult, and the resolution and gradation are poor. Images tend to be poor.

Initially, the image quality is good, but the image quality may deteriorate while printing is continued. This phenomenon occurs as you continue to print out
It is considered that only toner particles which are easily developed are consumed first, and toner particles having poor developability accumulate and remain in the developing machine.

Heretofore, some developers have been proposed for the purpose of improving image quality. JP-A-51-3244 proposes a non-magnetic toner intended to improve image quality by regulating the particle size distribution. In the toner, 8 to
The main component is a toner having a particle size of 12 μm, which is relatively coarse. According to the study of the present inventors, it is difficult to achieve “density” on a latent image with a particle size of 30 μm.
The characteristic that the particle size distribution is not more than 5% by number is not more than 20% and the particle size distribution is broad, which tends to lower the uniformity. In order to form a clear image using such a coarse toner particle and a toner having a broad particle size distribution, it is necessary to fill the gap between the toner particles by thickly overlapping the toner particles. It is necessary to increase the image density, and there is also a problem that the toner consumption increases in order to obtain a predetermined image density.

Japanese Patent Application Laid-Open No. 54-72054 proposes a non-magnetic toner having a sharper distribution than the former. However, the size of particles having an intermediate weight is as coarse as 8.5 to 11.0 μm, and a high-resolution toner is proposed. As such, there is still room for improvement.

In Japanese Patent Application Laid-Open No. 58-1229437, the average particle size is 6 to 10 μm.
Non-magnetic toners have been proposed in which the largest number of particles is 5 to 8 μm, but the number of particles of 5 μm or less is as small as 15% by number or less, and an image lacking sharpness tends to be formed.

According to the study of the present inventors, it has been found that toner particles having a size of 5 μm or less clearly reproduce the outline of a latent image and have a main function of “glue” of dense toner over the entire latent image. Was. In particular, in the electrostatic latent image on the photoreceptor, due to the concentration of lines of electric force, the contour edge portion has a higher electric field strength than the inside, and the sharpness of the image quality is determined by the quality of the toner particles collected in this portion. According to the study of the present inventors, it has been found that the amount of particles of 5 μm or less is effective in solving the problem of sharpness of image quality.

U.S. Pat. No. 4,299,900 proposes a jumping development method using a developer having 10 to 50% by weight of a magnetic toner of 20 to 35 .mu.m. The toner particle size suitable for frictionally charging the magnetic toner, uniformly and thinly applying the toner layer on the sleeve, and improving the environmental resistance of the developer has been devised. However, there is a need for improvements that can meet more stringent requirements such as fine line reproducibility, resolution, and compatibility with the reversal development system.

On the other hand, as a developing device using one-component magnetic toner,
For example, there is an apparatus proposed in JP-A-57-66455. The apparatus uses a toner carrier having a surface having a roughened surface with specific irregularities by sandblasting with irregular shaped particles as a toner carrier, so that the surface of the toner carrier has no uniform unevenness. A developing device capable of always maintaining a good toner coated state for a long period of time. The surface has an aspect in which countless fine cuts or projections are formed in random directions over the entire area.

However, in a developing device using a toner carrier having such a specific surface state, when the toner having a small particle diameter as described above is used, the toner or a component in the toner easily adheres to the surface. When contamination occurs on the body surface, and as a result, the contamination progresses due to lowering of the density of the initial image and furthermore, durability of the image tends to occur in the rotation cycle of the toner carrier. This is caused by the fact that the components in the toner adhere to the slopes and the concave portions of the convex portions on the surface of the toner carrier at each cycle of rotation, so that poor charging of the magnetic toner particles occurs and the charge amount of the toner layer decreases. Things.

Generally, components in a magnetic toner include a binder resin, a magnetic substance,
It is formed from materials such as a charge control agent and a release agent. Materials are designed so as to prevent contamination on the surface of the toner carrier. However, at present, selection of materials is extremely restricted.

Various proposals have been made as a method for preventing or reducing the contamination of the magnetic toner carrier. For example, Japanese Patent Application Laid-Open Nos. Sho 57-66443 and Sho 58-178380 disclose a toner carrier having a resin film having good releasability formed on the surface of the toner carrier. However, these can prevent contamination of the surface of the toner carrier, but when the toner having a small particle diameter as described above is used, the charge of the toner becomes too high, and the toner adheres strongly to the sleeve surface. However, it is difficult to develop the image, so that the image density tends to decrease.

As described above, it is desired to stably supply a toner image in which a fine latent image is faithfully reproduced.

[Problems to be Solved by the Invention] An object of the present invention is to provide a magnetic developer which has solved the above-mentioned problems.

It is a further object of the present invention to provide a magnetic developer having high image density, excellent fine line reproducibility, and excellent gradation.

A further object of the present invention is to provide a magnetic developer which does not change its performance even when used for a long time.

It is a further object of the present invention to provide a magnetic developer whose performance does not change with environmental changes.

A further object of the present invention is to provide a magnetic developer having excellent transferability.

Another object of the present invention is to provide a magnetic developer capable of obtaining a high image density with a small consumption.

An object of the present invention is to provide a magnetic developer having a large triboelectric charge.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic developer which has good fine line reproducibility and resolution and is preferably used for developing a digital latent image.

Further, an object of the present invention is to provide a toner which is excellent in resolution, gradation and fine line reproducibility even in an image forming apparatus which forms a latent image by a digital image signal and develops the latent image by a reversal development method. It is intended to provide a magnetic developer capable of forming an image.

An object of the present invention is to provide a magnetic developer that is less likely to damage the surface of a photoreceptor.

It is a further object of the present invention to provide a magnetic developer which does not easily fuse to the surface of a latent image carrier such as an organic photoconductor drum.

An object of the present invention is to uniformly coat a magnetic developer on a carrier thereof in the developing method as described above, and to prevent contamination of the surface of the developer carrier by a magnetic developer and / or components during magnetic development. It is an object of the present invention to provide an image forming method and an image forming apparatus unit capable of maintaining prevention or reduction for a long time.

It is a further object of the present invention to provide an image forming method and apparatus unit capable of obtaining a clear, high-quality toner image with high image density, excellent fine line reproducibility, and no fog for a long period of time.

Still another object of the present invention is to provide an image forming method and an image forming apparatus unit whose performance does not change due to environmental fluctuations.

[Means and Actions for Solving the Problems] The present invention relates to a magnetic developer containing an insulating magnetic toner having at least a binder resin and a magnetic material, and hydrophobic silica fine powder. 0.6 to 1.6 parts by weight of hydrophobic silica fine powder is mixed per part by weight, and the magnetic developer has a BET specific surface area of 1.8 to 3.5 m ² / g, and −2.
It has a triboelectric charging property of 0 to -35 μc / g, and has a loose apparent density.
0.40 to 0.52 g / cm ³ , a true density of 1.45 to 1.8 g / cm ³ , the magnetic material is a spherical magnetic material having an average particle size of 0.1 to 0.35 μm, and the insulating magnetic toner is 70 to 120 per 100 parts by weight of resin
The insulating magnetic toner contains 17 to 60% by number of magnetic toner particles having a volume average particle diameter of 4.5 μm or more and less than 6 μm and a particle diameter of 5 μm or less. 5 to 50% by number of magnetic toner particles having a particle size of
The magnetic toner particles having a particle diameter of 8 μm or more are contained at 5.0% by volume or more, and a group of magnetic toner particles having a particle diameter of 5 μm or less is represented by the following formula: N / V = −0.05N + k [where N is a magnetic particle having a particle diameter of 5 μm or less. V represents the volume percentage of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. Here, N indicates a positive number of 17 to 60. ] It has a particle size distribution satisfying the following.

Further, according to the present invention, an electrostatic image holding member for holding an electrostatic charge image and a developer holding member for holding a magnetic developer on the surface are arranged at a constant interval in a developing section, and the developer holding member Has a surface covered with a phenolic resin film containing conductive carbon and graphite, and the magnetic developer contains an insulating magnetic toner having at least a binder resin and a magnetic material, and a hydrophobic silica fine powder. A developer, 0.6 to 1.6 parts by weight of hydrophobic silica fine powder is mixed per 100 parts by weight of the insulating magnetic toner, and the magnetic developer has a BET specific surface area of 1.8 to 3.5 m ² / g, −2
It has a triboelectric charging property of 0 to -35 μc / g, and has a loose apparent density.
0.40 to 0.52 g / cm ³ , a true density of 1.45 to 1.8 g / cm ³ , the magnetic material is a spherical magnetic material having an average particle size of 0.1 to 0.35 μm, and the insulating magnetic toner is 70 to 120 per 100 parts by weight of resin
The insulating magnetic toner contains 17 to 60% by number of magnetic toner particles having a volume average particle diameter of 4.5 μm or more and less than 6 μm and a particle diameter of 5 μm or less. 5 to 50% by number of magnetic toner particles having a particle size of
The magnetic toner particles having a particle diameter of 8 μm or more are contained at 5.0% by volume or more, and a group of magnetic toner particles having a particle diameter of 5 μm or less is represented by the following formula: N / V = −0.05N + k [where N is a magnetic particle having a particle diameter of 5 μm or less. V represents the volume percentage of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. Here, N indicates a positive number of 17 to 60. Wherein the magnetic developer is conveyed to the developing unit with the magnetic developer being regulated to a thickness smaller than the gap on the developer carrier, and an alternating electric field is applied to the developer carrier in the developing unit. And an image forming method, wherein the image forming method is performed while developing.

Further, the present invention provides an apparatus unit detachably mounted on an image forming apparatus main body, the apparatus unit comprising: an electrostatic latent image holder for holding an electrostatic latent image; At least a developing device having a magnetic developer for performing the operation, the electrostatic latent image holding member and the developing device are integrally connected, and the developing device includes the magnetic developer. At least a developer contained therein, and a developer carrier for carrying the magnetic developer contained in the developer for developing the electrostatic latent image and transporting the developer to a developing unit. The electrostatic latent image holding member and the developer carrier are arranged at a fixed interval in a developing section, and the developer carrier is a phenol containing conductive carbon and graphite. The magnetic developer has a surface covered with a resin film, and the magnetic developer is a binder resin. Is a magnetic developer containing an insulating magnetic toner having at least a magnetic material and a hydrophobic silica fine powder, wherein 0.6 to 1.6 parts by weight of a hydrophobic silica fine powder is mixed per 100 parts by weight of the insulating magnetic toner. The magnetic developer has a BET specific surface area of 1.8 to 3.5 m ² / g, and −2.
It has a triboelectric charging property of 0 to -35 μc / g, and has a loose apparent density.
0.40 to 0.52 g / cm ³ , a true density of 1.45 to 1.8 g / cm ³ , the magnetic material is a spherical magnetic material having an average particle size of 0.1 to 0.35 μm, and the insulating magnetic toner is 70 to 120 per 100 parts by weight of resin
The insulating magnetic toner contains 17 to 60% by number of magnetic toner particles having a volume average particle diameter of 4.5 μm or more and less than 6 μm and a particle diameter of 5 μm or less. 5 to 50% by number of magnetic toner particles having a particle size of
The magnetic toner particles having a particle diameter of 8 μm or more are contained at 5.0% by volume or more, and a group of magnetic toner particles having a particle diameter of 5 μm or less is represented by the following formula: N / V = −0.05N + k [where N is a magnetic particle having a particle diameter of 5 μm or less. V represents the volume percentage of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. Here, N indicates a positive number of 17 to 60. ] It has the particle size distribution which satisfies the following.

Each component constituting the magnetic developer of the present invention will be described below.

Dispersing the magnetic material more uniformly in the binder resin can be cited as one solution for narrowing the charge distribution of the magnetic developer.

As a method of uniformly distributing, a method is known in which a magnetic material is subjected to a surface treatment with a treating agent such as a titanium coupling agent to modify the surface of the magnetic material to be lipophilic. However, the treatment agent is expensive, and the surface treatment process is complicated, so that the cost is high, which is not preferable.

As a result of the study by the present inventors, it has been confirmed that the spherical magnetic material is more promoted in dispersibility in resin than the conventional cubic magnetic material.

In the present invention, a spherical magnetic body refers to a magnetic body containing 50% by number or more of magnetic particles whose magnetic particle expression is formed on a curved surface. Even when a spherical magnetic material contains a normal cubic magnetic material or the like in which the magnetic particle surface is formed from a flat surface and the edges are squared, the content must be 50% by number or less. It is.

Furthermore, the spherical magnetic material has a primary average particle size of 0.1 to 0.35 μm.
Those having the following are preferably used. In the present invention,
The average particle size of the spherical magnetic material can be determined by taking a sample as an enlarged photograph with a scanning electron microscope, measuring the major axis value of 100 to 200 particles at random, and calculating the average value. Preferably, spherical magnetic material used in the magnetic toner according to the present invention is 1.2 to 2.5 g / cm ^3, more preferably 1.5 to 2.
Has a packed bulk density of 0 g / cm ^3, and 5~30ml / 100g,
Preferably 10-25ml / 100g, more preferably 12-17ml /
Has a linseed oil absorption of 100 g.

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

In the present invention, the linseed oil absorption of the magnetic material is JIS K51
It refers to the value measured according to the method described in 01-1978 (Pigment sample method).

The conventional magnetic material consisting of cubic magnetite particles
Packed bulk density of less than 0.6 g / cm ^3, typically 0.3 to 0.5
g / cm ³ range.

Conventional magnetic body made of magnetite particles spherical, the packed bulk density of less than 1.0 g / cm ^3, typically 0.7～0.9G /
It is in the range of cm ^3.

Packed bulk density less than 0.6 g / cm ^3, cubic magnetic toner used in the future magnetic body composed of magnetite particles crystallization, the dispersion uniformity of the magnetic particles between toner particles or the toner particles are still insufficient When the digital latent image is developed, the toner image may be blurred. When a digital latent image of an original image having a checker pattern shown in FIG. 10 is developed with a conventional magnetic toner containing a magnetic substance showing a cubic system, a black image portion tends to be partially missing, and There are still points to be improved in the developing characteristics as described above. When a magnetic material composed of cubic magnetite particles is crushed to break up aggregates of magnetite particles, the solidified apparent density of the processed magnetic material increases and the magnetic toner containing the processed magnetic material Although the developing property is improved as compared with the magnetic toner containing the untreated magnetic substance, it is still insufficient. Furthermore, powder having a flat portion in a particle such as a cubic crystal has a high adhesion compared to a curved surface in order to separate the adhesion in the plane of the particles during the disintegration process, and to separate the adhesion. Requires energy. Cubic magnetic particles have sharp edges, and the tips are easily broken by stress. Therefore, when crushing the agglomeration of the cubic magnetic material, a considerable amount of milled fine powder is generated, and the properties (such as BET specific surface area) of the magnetic material after the treatment change.

The magnetic material composed of spherical magnetite particles that have not been crushed has improved dispersibility in the binder resin as compared with the cubic magnetic material. Uncrushed spherical magnetic material is
By the crushing treatment, the apparent density is increased, and the dispersibility in the resin is further improved.

In the present invention, it is preferable to use a spherical magnetic material having a packed bulk density of 1.2 to 2.5 g / cm ^3, said value of the packed bulk density, cubic magnetic material of normal untreated,
The cubic magnetic material subjected to the crushing treatment and the untreated spherical magnetic value are large enough to be unsatisfactory. The specific spherical magnetic material preferably used in the present invention is a spherical magnetic material having a compacted apparent density of 0.7 g / cm ³ or more to less than 1.0 g / cm ³ and a linseed oil absorption of 10 to 35 ml / g. It can be prepared by processing. As a means used for crushing the spherical magnetic material, a mechanical crusher having a high-speed rotor for crushing powder, and for dispersing or crushing powder. A pressure dispersing machine having a weight roller is exemplified.

When using a mechanical pulverizer to disintegrate the aggregates of magnetic particles, the impact force of the rotor is likely to be excessively applied to the primary particles of the magnetic particles, and the primary particles themselves are destroyed. Fine particles are easily generated. Therefore, when a magnetic material crushed by a mechanical pulverizer is used as a raw material for the toner, the frictional charging characteristics of the toner deteriorate due to the presence of the fine magnetic particles. Therefore, a decrease in the toner image density due to a decrease in the triboelectric charge amount of the toner is likely to occur.

On the other hand, a pressure disperser having a load roller such as a fred mill is preferable in terms of the efficiency of the crushing treatment of the aggregates of the spherical magnetic particles and the suppression of the generation of the fine magnetic particles.

It can be understood that the solid apparent density and the oil absorption of the magnetic material indirectly indicate the shape of the magnetic particles, the surface state of the magnetic material, and the abundance of the aggregates of the magnetic particles. When packed bulk density of the magnetic material is less than 1.2 g / cm ^3, either magnetic particles in the form of cubic in the magnetic body is abundant or in agglomerates of magnetic particles are present many This indicates that the disintegration of the magnetic material is substantially insufficient. Therefore, when a magnetic material having a hardened apparent density of less than 1.2 g / cm ³ is used, it is difficult for the magnetic material to be uniformly dispersed in the binder resin. And the surface of the photoreceptor is easily damaged by toner particles.

If packed bulk density of the magnetic material exceeds 2.5 g / cm ^3, and crushed aggregate of the magnetic particles is excessively performed, pressurized sticking of magnetic particles each other occurs by pressure, the pellets of the magnetic material is produced As a result, non-uniform magnetic toner particles tend to form.

Even when the value of the oil absorption of the magnetic material deviates from the upper limit and the lower limit, the same phenomenon as in the case of the solid apparent density is likely to occur.

According to the study of the present inventors, in the case of a cubic magnetic material,
The value of the BET specific surface area after the disintegration treatment of the aggregate of magnetic particles is
It has been found that the BET specific surface area increases by 10% or more compared to the value of the BET specific surface area before the treatment. This is understood that a large amount of fine magnetic particles was generated by the crushing process. On the other hand, in the case of a spherical magnetic material, it has been found that the value of the BET specific surface area after the treatment is substantially equal to the value of the BET specific surface area before the treatment or is reduced by several percent. Therefore,
Regarding the shape of the magnetic particles, it is possible to determine whether the shape of the magnetic particles is cubic or spherical by observing the change in the BET specific surface area of the magnetic material after the treatment before the crushing treatment. is there. Specifically, the value of the BET specific surface area of the magnetic material at the time when the compacted apparent density of the magnetic material is increased by about 30% by the crushing process is substantially equal to or smaller than the value of the BET specific surface area before the treatment. When it is decreasing, the shape of the magnetic body can be considered to be spherical. In the present invention, the primary particle size of the magnetic material according to the electron micrograph is 0.1 to
0.35μ range and nitrogen gas adsorption method
A magnetic substance having a BET specific surface area of 6.0 to 8.0 m ² / g is particularly preferable.

Furthermore, the spherical magnetic material according to the present invention has a saturation magnetization (σ _s ) of 60 to 90 emu / g, a residual magnetization (σ _r ) of 3 to 9 emu / g, and 40 to 80 (preferably 50 to 50) under a magnetic field of 10,000 Oersted. 70) oersted coercivity of (H _c) and / or the value of sigma _r / sigma _s that has a 0.04 to 0.10, the presence of a magnetic field transportability and digital latent image of the magnetic toner on the sleeve This is preferred in the developing method of developing with It is extremely difficult to make the coercive force of the magnetic material 40 to 80 Oe with a conventional cubic magnetic material, and it can be understood that the shape of the magnetic material is indirectly defined.

The magnetic properties of the magnetic material, for example, manufactured by Toei Industry Co., Ltd.
It refers to the value measured by VSMP-1.

The magnetic toner used in the present invention has a triboelectric charge and is therefore substantially electrically insulating. Specifically, 3.0Kg / cm ²
It is preferable that a resistance value when a voltage of 100 V is applied under pressure of 10 V is 10 ¹⁴ Ω · cm or more. Spherical magnetic body according to the present invention, 70 to 1 part by weight of the binder resin
20 parts by weight (preferably 80 to 110 parts by weight) are contained. If the amount is less than 70 parts by weight, the transportability of the magnetic developer on a developer carrier such as a sleeve tends to be insufficient. When the amount exceeds 120 parts by weight, the insulating property and the heat fixing property of the magnetic toner tend to decrease.

The spherical magnetic material used in the present invention is preferably produced by a wet method using ferrous sulfate as a raw material, and is formed from magnetite or ferrite containing 0.1 to 10% by weight of a divalent metal compound such as manganese or zinc. Preferably, it is formed.

In the magnetic developer of the present invention, an insulating magnetic toner having a specific particle size distribution as described above is used. This insulating magnetic toner is particularly excellent in the resolution of a digital latent image due to the synergistic effect of the spherical magnetic substance contained in the toner and the externally added hydrophobic silica fine powder, and is also excellent in image density. ing.

The reason why such an effect is obtained in the magnetic toner used in the present invention is not necessarily clear, but is presumed as follows.

One feature of the magnetic toner used in the present invention is that 17 to 60% by number of magnetic toner particles having a particle diameter of 5 μm or less. Conventionally, in a magnetic toner, magnetic toner particles having a particle size of 5 μm or less are difficult to control the charge amount, impair the fluidity of the magnetic toner, and scatter the toner to contaminate the machine. It was thought that it was necessary to actively reduce it.

However, studies by the present inventors have revealed that magnetic toner particles having a size of 5 μm or less are essential components for forming a high-quality image.

For example, using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm, the surface potential on the photoreceptor is changed, and from a large development potential contrast in which a large number of toner particles are easily developed, to a halftone, and further, a very small amount. A latent image with a changed surface potential on the photoreceptor is developed to a small development potential contrast where only toner particles are developed, and the developed toner particles on the photoreceptor are collected, and the particle size distribution of the toner is measured to be 8 μm or less. It was found that there were many magnetic toner particles, especially 5 μm or less. When the magnetic toner particles having a particle size of 5 μm or less, which are most suitable for development, are supplied smoothly to the development of the latent image on the photoreceptor, the image is faithful to the latent image, and does not protrude from the latent image, and has excellent reproducibility. Can be obtained. This development was the same in the case of reversal development of a digital latent image.

In the magnetic toner used in the present invention, 6.35 to 10.08
One feature is that particles in the range of μm are 5 to 50% by number. This is related to the need for the presence of magnetic toner particles having a particle size of 5 μm or less, as described above. The magnetic toner particles having a particle size of 5 μm or less strictly cover the latent image and have an ability to faithfully reproduce the latent image. However, in the latent image itself, the electric field strength at the peripheral edge portion is higher than that at the central portion, and therefore, the toner particles may be thinner inside the latent image than at the edge, and the image density may appear to be light. In particular, 5 μm
The following magnetic toner particles have a strong tendency. However, the present inventors have found that this problem can be solved and made clearer by containing 5 to 50% by number of toner particles in the range of 6.35 to 10.08 μm. 6.
It is considered that toner particles having a particle size in the range of 35 to 10.08 μm have an excessively controlled charge amount with respect to magnetic toner particles having a particle size of 5 μm or less. Supplied to the small inner side, a uniform developed image is formed by compensating for the small amount of toner particles on the inner side with respect to the edge portion, and as a result, a sharp image with high resolution and excellent gradation is obtained at a high density. Is provided.

Further, for particles having a particle size of 5 μm or less, N / V = −0.05 N + k between the number% (N) and the volume% (V).
(However, one of the characteristics is that the magnetic toner of the present invention satisfies the relationship of 4.6 ≦ k ≦ 6.7; 17 ≦ N ≦ 60).
FIG. 11 shows this range. Along with other features, the magnetic developer containing the magnetic toner according to the present invention having a particle size distribution satisfying this range is excellent in digital latent images formed from minute spots. It can form developability.

The present inventors have studied the state of the particle size distribution of 5 μm or less, and have found that the state of the fine powder that is most suitable for achieving the object as shown by the above formula is present. The fact that N / V is large for a certain value of N indicates that particles up to 5 μm or less are widely included, and the fact that N / V is small means that the particle abundance near 5 μm is high, It is understood that this indicates that there are few particles with a particle size smaller than that, and N / V
Is in the range of 1.6 to 5.85, N is in the range of 17 to 60, and the above relational expression is further satisfied, whereby good fine line reproducibility and high resolution are achieved.

For magnetic toner particles having a particle size of 10.08 μm or more,
It is preferable that the content is not more than 5.0% by volume and is as small as possible.

The magnetic developer of the present invention solves the conventional problems, and can withstand recent severe demands for high image quality.

 The configuration of the present invention will be described in more detail.

Magnetic toner particles having a particle size of 5 μm or less have a total particle number of 17 to
The number is preferably 60% by number, preferably 25% to 60% by number, and more preferably 30% to 60% by number. When the number of magnetic toner particles having a particle diameter of 5 μm or less is less than 17% by number, the amount of magnetic toner particles effective for high image quality is small. In particular, as the toner is used by continuing printout, the effective magnetic toner particle component is reduced. As a result, the particle size distribution of the magnetic toner as shown in the present invention changes, and the image quality gradually decreases. If it exceeds 60% by number, the magnetic toner particles are likely to aggregate with each other, resulting in a toner mass larger than the original particle size, resulting in rough image quality, reduced resolution, or an edge portion of the latent image. The density difference from the inside becomes large, and the image tends to be slightly hollow.

The particle size in the range of 6.35 to 10.08 μm is preferably 5 to 50% by number or less, and more preferably 8 to 40% by number. If the content is more than 50% by number, the image quality is deteriorated, and the development is performed more than necessary (that is, the toner is excessively applied), the reproducibility of fine lines is reduced, and the toner consumption is increased. On the other hand, if it is less than 5% by number, it becomes difficult to obtain a high image density. 5
the number% (N%) of magnetic toner particles having a particle size of μm or less,
There is a relationship of N / V = −0.05N + k between the volume% (V%), and indicates a positive number in the range of 4.6 ≦ k ≦ 6.7. Preferably 4.6
≤ k ≤ 6.2, more preferably 4.6 ≤ k ≤ 5.7. As indicated above, 17 ≦ N ≦ 60, preferably 25 ≦ N ≦ 60,
More preferably, 30 ≦ N ≦ 60.

When k <4.6, the number of magnetic toner particles having a particle diameter smaller than 5.0 μm is small, and the image density, resolution, and sharpness are poor. The appropriate presence of fine magnetic toner particles, which was conventionally considered unnecessary, contributes to the closest packing of the toner in development and contributes to the formation of a uniform image without roughness. In particular, by uniformly filling the fine lines and the contours of the image, the sharpness is further enhanced visually.

If k <4.6, these properties are inferior due to the lack of particles of this particle size distribution.

From another aspect, in production, it is necessary to cut a large amount of fine powder by classification or the like to satisfy the condition of k <4.6, which is disadvantageous in terms of yield and toner cost.
When k> 6.7, the image density tends to decrease during repeated printout due to the presence of unnecessarily fine powder. This phenomenon occurs because excessive fine magnetic toner particles having an unnecessarily high charge are electrostatically deposited on the developing sleeve, which hinders the normal carrying of the magnetic toner on the developing sleeve and the charge application. It is thought to occur.

The content of the magnetic toner particles having a particle size of 10.08 μm or more is preferably 5.0% by volume or less, more preferably 3.0% by volume or less. If it is more than 5.0% by volume, it will hinder the reproduction of fine lines.

The volume average diameter of the magnetic toner is 4.5 μm or more and less than 6 μm, and this value cannot be considered separately from the above-mentioned respective constituent elements.

If the volume average particle size is less than 4.5 μm, the adhesion of toner particles to the surface of the photoreceptor increases, and cleaning failure is likely to occur.

Although the particle size distribution of the toner can be measured by various methods, in the present invention, the measurement was performed using a Coulter counter.

A Coulter Counter TA-II type (manufactured by Coulter) was used as a measuring device, and an interface (manufactured by Nikkaki) for outputting the number distribution and volume distribution and a CX-1 personal computer (manufactured by Canon) were connected. Prepare a 1% aqueous NaCl solution using graded sodium chloride. As a measuring method, a surfactant, preferably an alkylbenzene sulfonate, is used as a dispersant in 100 to 150 ml of the electrolytic aqueous solution.
Add 0.1 to 5 ml, and add 2 to 20 mg of the measurement sample (about 30,000 to about 300,000 particles). The electrolyte in which the sample was suspended was subjected to dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the aperture was measured by the Coulter Counter TA-II as an aperture.
Using a 100μ aperture, 2 to 40μ based on the number
Was measured, and the value according to the present invention was determined therefrom.

The true density of the developer having the magnetic toner (substantially the true density of the magnetic toner) used in the present invention is 1.45 to 1.8 g.
a / cm ^3. Preferably from 1.55~1.75g / cm ^3. Within this range, the magnetic developer of the present invention containing the magnetic toner having the specific particle size distribution of the present invention can exhibit effects in terms of high image quality and durability stability in a reversal development system in the presence of a magnetic field. When the true density of the magnetic developer is less than 1.45, the magnetic toner particles themselves are too light in weight, so that in reversal development, fogging and fine line breakage due to excessive toner particle adhesion, jumping, and deterioration in resolution tend to occur. If the true density of the magnetic developer is greater than 1.8, the image density will be low, and the image will be lacking in sharpness such as breaks in thin lines,
Since the magnetic force is relatively large, the spikes of the toner are likely to be long or branched, and in this case, when the digital latent image is developed, the image quality is disturbed, and the image tends to be rough.

The measurement of the true density of the magnetic toner and the developer can be performed by several methods. In the present application, the following method is adopted as an accurate and simple method for measuring fine powder.

A stainless steel cylinder with an inner diameter of 10 mm and a length of about 5 cm, a disk (A) with an outer diameter of about 10 mm and a height of 5 mm that can be inserted tightly into it, and a piston (B) with an outer diameter of about 10 mm and a length of about 8 cm (B) prepare. The disk (A) is placed at the bottom of the cylinder, then about 1 g of the measurement sample is placed, and the piston (B) is gently pushed. A 400 kg / cm ² force is applied to this with a hydraulic press,
Take out what was compressed for 5 minutes. The weight of the compressed sample is weighed (wg), the diameter (Dcm) and the height (Lcm) of the compressed sample are measured with a micrometer, and the true density is calculated by the following equation.

In order to obtain better developing characteristics, the magnetic toner used in the present invention has a residual magnetization σ _{r of 1} to 5 emu / g, preferably 2 to 4.5 emu / g, and a saturation magnetization _s of 15 to 50 emu / g. , preferably 20~40emu / g, coercive force H _c is 20 to 100 Oe, more preferably more preferably 40 to 100 Oe preferably satisfies the magnetic properties of 40 to 70 oersteds.

The measurement of the magnetic properties is performed with a measurement magnetic field of 1000 Oersted.

As a binder resin used for the magnetic toner used in the present invention, when a heating and pressing roller fixing device having a device for applying oil is used, the following binder resins for toner can be used.

For example, polystyrene; poly-p-chlorostyrene,
A styrene-substituted homopolymer such as polyvinyltoluene; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer,
Styrene-methacrylate copolymer, styrene-
α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer Styrene copolymers such as styrene-isopropylene copolymer, styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenolic resin, natural modified phenolic resin, natural resin modified maleic acid resin, acrylic resin, methacrylic resin, Polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumarone indene resin, petroleum resin and the like can be used.

In the heat and pressure roller fixing method in which almost no oil is applied, it is important to transfer a part of the toner image on the toner image support member to the roller (so-called offset phenomenon) and to adhere the toner to the toner image support member. Problem. Since a toner that fixes with less heat energy tends to block or cake during storage or in a developing device, these problems must also be considered. The physical properties of the binder resin in the toner are most greatly involved in these phenomena. However, according to the study of the present inventors, when the content of the magnetic substance in the toner is reduced, the toner image supporting member is fixed at the time of fixing. The adhesion of the toner to the toner is improved, but offset tends to occur, and blocking or caking tends to occur. Therefore, in the present invention, when using the heating / pressing roller fixing method in which almost no oil is applied, the selection of the binder resin is more important. Preferred binders include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of the comonomer for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylic. Monocarboxylic acids having a double bond such as acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, and acrylamide or their substituted products; maleic acid, butyl maleate, methyl maleate , Dicarboxylic acid having a double bond such as dimethyl maleate and a substituted product thereof; vinyl esters such as vinyl chloride, vinyl acetate and vinyl benzoate; and ethylene-based monomers such as ethylene, propylene and butylene. Fin like; vinyl methyl ketone,
Vinyl monomers such as vinyl ketones such as vinyl hexyl ketone; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; are used alone or in combination of two or more.

As the crosslinking agent, a compound having two or more polymerizable double bonds is mainly used. For example, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; carboxylic acid esters having two double bonds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate and 1,3-butanediol dimethacrylate; divinylaniline; Divinyl compounds such as divinyl ether, divinyl sulfide and divinyl sulfone; and compounds having three or more vinyl groups. These are used alone or as a mixture.

The crosslinking agent is preferably used in an amount of 0.1 to 5 parts by weight, more preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the monomer.

When the pressure fixing method is used, a binder resin for pressure fixing toner can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, ionomer resin, styrene-
Butadiene copolymer, styrene-isoprene copolymer,
There are linear saturated polyester, paraffin and the like.

In the magnetic toner used in the present invention, a charge control agent is blended with toner particles (internal addition) or mixed with toner particles (external addition).
It is preferable to use them. The charge control agent makes it possible to control the optimal charge amount according to the development system. In particular, in the present invention, it is possible to further stabilize the balance between the particle size distribution and the charge, and by using the charge control agent It is possible to further clarify the function separation and the complementarity for higher image quality for each particle size range as described above.

As the negative charge controlling agent that can be used in the present invention, for example, metal complexes or salts of monoazo dyes; metal complexes or salts of salicylic acid, alkylsalicylic acid, dialkylsalicylic acid or naphthoic acid are preferably used.

The above-mentioned charge control agent (having no action as a binder resin) is preferably used in the form of fine particles. In this case, the number average particle size of the charge control agent is specifically preferably 4 μm or less (more preferably 3 μm or less).

When internally added to the toner, such a charge control agent is used in an amount of 0.1 to 10 parts by weight (more preferably 0.1 to 5 parts by weight) based on 100 parts by weight of the binder resin.
Parts by weight).

The magnetic developer of the present invention has a hydrophobic silica fine powder. A magnetic toner having a particle size distribution as a feature of the present invention has a larger specific surface area than conventional toners. When magnetic toner particles are brought into contact with the surface of a cylindrical conductive sleeve having a magnetic field generating means inside due to triboelectric charging, the number of times of contact between the surface of the toner particles and the sleeve increases compared to conventional magnetic toner, and the toner Particle wear and contamination of the sleeve surface are likely to occur. When the magnetic toner used in the present invention is combined with silica fine powder, wear is significantly reduced because the silica fine powder is interposed between the toner particles and the sleeve surface. As a result, the life of the magnetic toner and the sleeve can be prolonged, and a stable chargeability can be maintained, and a developer having a magnetic toner that is more excellent for long-term use can be obtained. Further, magnetic toner particles having a particle diameter of 5 μm or less, which play a major role in the present invention, exhibit more effects in the presence of silica fine powder,
High quality images can be stably provided.

As the silica fine powder, both silica fine powder produced by a dry method and a wet method can be used, but from the viewpoint of filming resistance and durability, it is preferable to use a silica fine powder obtained by a dry method.

The dry method referred to here is a method for producing silica fine powder generated by vapor phase oxidation of a silicon halide. For example, in a method utilizing the thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen-hydrogen, the basic reaction formula is as follows.

SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl In this manufacturing process, a composite fine powder of silica and another metal oxide is obtained by using another metal halide such as aluminum chloride or titanium chloride together with a silicon halide. Things are also possible. In the present invention, they are also included.

Examples of commercially available fine silica powder produced by vapor phase oxidation of a silicon halide used in the present invention include, for example, those commercially available under the following trade names.

AEROSIL 130 (Nippon Aerosil) 200 300 380 OX50 TT600 MOX80 MOX170 COK84 Ca-O-SiL M-5 (CABOTO Co.) MS-7 MS-75 MS-5 EH-5 Wacker HDK N 20 V15 (WACKER-CHEMIE) GMBH) N20E T30 T40 D-C Fine Silica (Dow Corning Co.) Fransol (Fransil) On the other hand, as a method for producing the silica fine powder used in the present invention by a wet method, various conventionally known methods are used. Applicable. For example, there is decomposition of sodium silicate by acid,
The reaction formula is shown below.

Na ₂ O ・ XSiO ₂ + HCl + H ₂ O → SiO ₂・ nH ₂ O + NaCl In addition, decomposition of sodium silicate with ammonium salts or alkali salts, formation of alkaline earth metal silicate from sodium silicate and decomposition with acid Silicate, a method in which a sodium silicate solution is converted into silicate using an ion exchange resin, a method in which natural silicate or silicate is used, and the like.

Examples of the silica fine powder include anhydrous silicon dioxide (silica) and silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate.

Among the above silica fine powders, those having a specific surface area of 70 to 300 m ² / g by nitrogen adsorption measured by the BET method give good results. 100 parts by weight of magnetic toner, preferably 0.7
It is good to use ~ 1.4 parts by weight.

As the hydrophobic silica fine powder, negatively chargeable hydrophobic silica fine powder is preferable in order to stabilize the negative chargeability of the toner.

It is preferable that the hydrophobic silica fine powder used in the present invention has a triboelectric charge amount of −100 μc / g to −300 μc / g. When the triboelectric charge is less than -100 μc / g, the triboelectric charge of the developer itself is reduced, and the humidity characteristics are reduced. If the amount exceeds -300 μc / g, the developer carrier memory is promoted, and the silica itself is easily deteriorated, which is susceptible to the influence, and the durability is impaired. Those with a BET specific surface area of less than 300 m ² / g have little effect on the addition to the developer, and those with a BET specific surface area of more than 70 m ² / g have a high probability of being present as free matter, and have uneven distribution of silica (non-uniform silica dispersion in toner) ) And black spots due to aggregates.

The tribo value of the negatively charged silica fine powder is measured by the following method. Carrier iron powder not coated with resin, having 0.2g of silica fine powder and main particle size of 200 to 300 mesh, which was left overnight in an environment of 23.5 ° C and 60% RH (EFV200 manufactured by Nippon Iron Powder Co., Ltd. Weighs 9.8 g under the above environment, and shakes it sufficiently (hold it up and down approximately 50 times for about 20 seconds in a wide-mouth bottle with a polyethylene lid having a volume of about 50 c.c.). ) Mix.

Next, as shown in Fig. 7, a 400 mesh screen 3
About 0.5 g of the mixture is placed in a metal measuring container 32 having a metal cover 3 and a metal lid 34 is provided. At this time, the weight of the entire measurement container 32 is weighed and set as W ₁ (g). Next, in the suction device 31 (at least a portion in contact with the measuring container 32 is an insulator), the pressure of the vacuum gauge 35 is adjusted to 250 mmH by adjusting the air volume control valve 36 by suctioning from the suction port 37.
g. In this state, suction is sufficiently performed to remove silica by suction. At this time, the potential of the electrometer 39 is set to V (volt). Here, 38 is a capacitor, whose capacity is C (μF). The weight of the entire measuring instrument after suction is weighed and is defined as W ₂ (g). The triboelectric charge (μc / g) of this silica is calculated as shown below.

As the silica fine powder used in the present invention, both a so-called dry method produced by vapor phase oxidation of a silicon halide and a so-called wet silica produced from water glass or the like and dry silica called fumed silica can be used. It is. There are few silanol groups on the surface and inside,
Dry silica without production residue is preferred.

The hydrophobizing treatment is applied by chemically treating with an organic silicon compound or the like which reacts or physically adsorbs with the silica fine powder. As a preferred method, after the dry silica fine powder produced by the vapor phase oxidation of the silicon halide compound is treated with a silane coupling agent, or simultaneously with the treatment with the silane coupling agent, an organic silicon compound such as silicone oil or silicone varnish is used. To process.

Examples of the silane coupling agent used in the hydrophobizing treatment include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, and allylphenyldichlorosilane. , Benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, trilorganosilyl acrylate, vinyldimethylacetoxysilane, Dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltet Lamethyldisiloxane, 1,3
-Diphenyltetramethyldisiloxane.

Examples of the organosilicon compound include silicone oil.

Preferred silane coupling agents include hexamethyldisilazane (HMDS).

As a preferred silicone oil, one having a viscosity at 25 ° C. of 50 to 1,000 centistokes is preferably used. For example, dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorophenyl silicone oil, fluorine modified silicone oil and the like are preferable. For the purposes of the present invention, -OH group, COOH group, a silicone oil containing a large amount of such polar group -NH ₂ group is not preferable.

The silane coupling agent is preferably treated with 1 to 50 parts by weight, more preferably 5 to 40 parts by weight, based on 100 parts by weight of the silica fine powder.

The treatment amount of the silicone oil or silicone varnish in the present invention is preferably 1 to 35 parts by weight, more preferably 2 to 30 parts by weight, per 100 parts by weight of the silica fine powder. The reason for limiting the above treatment amount is that if the silicone oil treatment amount is too small, the same result as the silane coupling agent treatment alone will not result, and the moisture resistance will not be improved and the silica fine powder will absorb moisture under high humidity and high quality Copy images cannot be obtained. If the amount of the processed silicone oil is too large, the above-mentioned aggregates of the silica fine powder are likely to be formed, and free silicone oil is formed, so that when applied to a developer, the flowability cannot be improved. Tends to occur.

The method of silicone oil treatment may be, for example, a method in which silica fine powder treated with a silane coupling agent and silicone oil are directly mixed using a mixer of a Henschel mixer, or a method of injecting silicone oil into base silica. Is also good. Alternatively, it may be prepared by dissolving or dispersing a silicone oil in an appropriate solvent, mixing with a base silica fine powder, and removing the solvent.

The degree of hydrophobicity of the silica fine powder in the present invention uses a value measured by the following method. Other measurement methods can be applied with reference to the measurement method of the present invention.

100 ml of ion-exchanged water and 0.1 g of a sample are placed in a sealed stopper 200 ml separatory funnel, and shaken at 90 rpm for 10 minutes with a shaker (Tavla shaker mixer T2C type). After shaking, the mixture was allowed to stand for 10 minutes.After the silica powder layer and the aqueous layer were separated, 20-30 ml of the lower aqueous layer was sampled, placed in a 10 mm cell, and charged with a blank ion containing no silica fine powder at a wavelength of 500 nm. The transmittance is measured based on the exchanged water, and the value of the transmittance is used as the hydrophobicity of silica.

The hydrophobicity of the hydrophobic silica fine powder in the present invention is 90
% Or more (more preferably 93% or more). If the degree of hydrophobicity is less than 90%, it is difficult to obtain a high-quality image due to moisture adsorption of the silica fine powder under high humidity.

These hydrophobic silica fine powders are effective when the amount is 0.6 to 1.6 parts by weight with respect to 100 parts by weight of the insulating magnetic toner, and particularly preferably 0.7 to 1.4 parts by weight when added. It is possible to provide a developer having a chargeability and a chargeability.

The magnetic developer of the present invention having at least a hydrophobic silica fine powder and an insulating magnetic toner is obtained by a nitrogen gas adsorption method.
BET specific surface area 1.8~3.5m ² / g (preferably, 1.9~3.0m ² /
g), having a triboelectric charging property of -20 to -30 μc / g, an apparent density of 0.4 to 0.52 g / cm ³ , and a density of 1.45 to 1.8 g / cm ³ .

If the triboelectric charge is less than −20 μc / g, a sufficient charge for development cannot be obtained on the developer carrying member, and the image density tends to be reduced from the beginning. When −35 μc / g or more, the amount of charge of the developer in the vicinity of the surface of the developer on the developer carrier is increased by repeating image formation, which hinders proper charging of the developer on the carrier. The so-called charge-up phenomenon occurs,
The image density gradually decreases. This image is likely to occur when developing a digital latent image that is a development of a dot latent image,
Further, it is remarkable in a low potential contrast reversal developing method using an OPC photosensitive member.

When the BET specific surface area of the developer of the present invention by the nitrogen gas adsorption method is less than 1.8 m ² / g, it takes time to obtain a sufficient charge amount for development on the developer carrying member, and the initial concentration is thin and fog is reduced. There are many images.

If the BET specific surface area is larger than 3.5 m ² / g, the reflection power with the sleeve becomes large and the development rate is reduced, and as a result, the image density is reduced.

In the measurement of the BET specific surface area in the present invention, QUANTACHROM
It is determined by the BET one-point method using the specific surface area meter Auto Soap 1 manufactured by Company E.

True density of the developer of the present invention is 1.45~1.8g / cm ^3, 1.
If it is less than 45, fogging is apt to occur in a method of developing by applying an AC bias in a magnetic field, and the line width becomes large and the resolution is deteriorated. If the true density is larger than 1.8, line blurring tends to occur, and the image density also decreases.

The loose apparent density of the developer of the present invention is 0.4 to 0.52 (preferably 0.45 to 0.5), which is smaller than the true density.
It is characteristic that the loose apparent density is small. The porosity calculated from the true density and the loose apparent density is preferably 62 to 75%.

 The porosity (εa) is calculated by the following equation.

The apparent bulk density is preferably in the range of 0.8 to 1.0, and the porosity (εp) at this time is preferably 40 to 50%.

If the porosity (εa) of the loose apparent density is less than 62%, the toner is not sufficiently loosened by stirring inside the developing device, and if it is more than 75%, toner scattering and toner leakage are likely to occur. If the porosity (εp) of the solidified apparent density is less than 40%, the developer tends to be jammed inside the developing device, the developer is not smoothly supplied to the developer carrying member, and white spots are likely to occur.

If the porosity (εp) is larger than 50%, a larger developing device capacity is required to contain the same amount of developer, which hinders downsizing of the printer.

The loose apparent density of the magnetic developer of the present invention is measured using a powder tester manufactured by Hosokawa Micron Co., Ltd. The solid apparent density is measured in the same manner as the method of measuring the solid apparent density of the magnetic material in the future.

The magnetic toner of the present invention may optionally contain additives. Dyes conventionally known as colorants,
Pigments can be used, and usually 0.5 to 20 parts by weight per 100 parts by weight of the binder resin may be used. Other external additives in the magnetic developer of the present invention include, for example, a lubricant such as zinc stearate; an abrasive such as cerium oxide and silicon carbide;
Fluidity-imparting agents such as aluminum oxide or anti-caking agents; conductivity-imparting agents such as carbon black and tin oxide.

For the purpose of improving the releasability of the hot roll fixing agent, waxy substances such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, paraffin wax, etc. are 0.5 to 5 wt.
% Is also one of the preferred embodiments of the present invention.

To prepare the magnetic toner for electrostatic image development according to the present invention, a magnetic powder and a vinyl-based or non-vinyl-based thermoplastic resin, a pigment or a dye as a colorant as required, a charge control agent, and other additives Are mixed sufficiently by a mixer such as a ball mill, and then melted, kneaded or kneaded using a heat kneader such as a heating roll, kneader or extruder to make the resins compatible with each other. Is dispersed or dissolved, and after cooling and solidification, pulverization and strict classification are performed to obtain an insulating magnetic toner according to the present invention.

Further, the magnetic developer of the present invention can be prepared by mixing an insulating magnetic toner having a predetermined particle size and a particle size distribution with a predetermined amount of a hydrophobic silica fine powder.

The amount of triboelectric charging of the magnetic toner used in the present invention and the magnetic developer of the present invention is performed in substantially the same manner as in the case of the silica fine powder described above, but the amount ratio is different and the magnetic developer or the magnetic toner 2.
0 g and 9.0 g of carrier iron powder are precisely weighed and measured in the same manner.

An image forming method to which the magnetic developer of the present invention can be preferably applied will be described with reference to FIGS.

A developing device having a developing sleeve 4 which charges the surface of the photoreceptor to a negative polarity with a primary charger 2 and forms a digital latent image by image scanning by exposure 5 with a laser beam and includes a magnetic blade 11a and a magnet 14; The magnetism is reversal-developed with 9 one-component magnetic developer 10. In the developing section, between the conductive base 16 of the photosensitive drum 1 and the developing sleeve 4, an alternating bias, a pulse bias and / or a DC bias are applied by the bias applying means 12. When the transfer paper P is conveyed and arrives at the transfer section, the transfer charger 3 charges the transfer paper P with a positive polarity from the back surface (opposite side to the photosensitive drum side), so that the negatively charged image on the photosensitive drum surface is developed. The agent is electrostatically transferred onto the transfer paper P. The transfer paper P separated from the photosensitive drum 1 has the toner image fixed on the transfer paper P by the heating and pressing roller fixing device 7.

The one-component developer remaining on the photosensitive drum after the transfer process is removed by a cleaning device 8 having a cleaning blade. After the cleaning, the photosensitive drum 1 is neutralized by the erase exposure 6, and the process starting from the charging process by the primary charger 2 is repeated again.

The electrostatic image carrier (photosensitive drum) has a photosensitive layer 15 and a conductive substrate 16, and moves in the direction of the arrow. The developing sleeve 4 of a non-magnetic cylinder, which is a developer carrying member, rotates in the developing section so as to advance in the same direction as the surface of the electrostatic image holding member. Inside the non-magnetic cylinder 4, a multi-pole permanent magnet (magnet roll) 14 as a magnetic field generating means is arranged so as not to rotate. The one-component insulating magnetic developer 10 in the developing device 9 is applied on a non-magnetic cylindrical surface, and the toner particles are given a negative triboelectric charge by friction between the surface of the sleeve 4 and the toner particles. Further, the thickness of the developer layer is reduced (from 30 μm to 50 μm) by disposing the iron magnetic doctor blade 11 a close to the cylindrical surface (interval: 50 μm to 500 μm) and opposed to one magnetic pole position of the multipole permanent magnet. (300 μm) and uniformly regulated, and a developer layer thinner than the gap between the electrostatic image holding member 1 and the developing carrier 4 in the developing portion is formed so as to be in non-contact. By adjusting the rotation speed of the cylinder 4, the surface speed of the sleeve is made substantially equal to or close to the speed of the electrostatic image holding surface. The opposed magnetic poles may be formed by using permanent magnets instead of iron as the magnetic doctor blade 11a. In the developing section, the developer carrier 4
An AC bias or a pulse bias may be applied by the bias unit 12 between the power supply and the electrostatic image holding surface. The AC bias may be such that f is 200 to 4,000 Hz and Vpp is 500 to 3,000 V.

At the time of transfer of the developer in the developing portion, the developer is transferred to the electrostatic image side due to the electrostatic force of the electrostatic image holding surface and the action of an AC bias or a pulse bias.

Instead of the doctor blade 11a, an elastic blade made of an elastic material such as silicone rubber may be used to regulate the layer thickness of the developer layer by pressing and apply the developer on the developer carrier.

In the image forming method and the image forming apparatus of the present invention,
As the developer carrying member, those covered with a phenol resin containing conductive carbon and graphite are preferably used.

As an electrophotographic apparatus capable of performing the image forming method of the present invention, a plurality of components such as an electrostatic latent image carrier such as the above-described photosensitive drum, a developing device, and a cleaning unit are integrally combined as a device unit. The unit may be configured to be detachable from the apparatus main body.
For example, a unit is formed by integrally supporting at least one of the charging unit, the developing device, and the cleaning unit together with the photosensitive drum, and the unit is detachably attached to the apparatus main body. It may be configured to be detachable. At this time, the above-described device unit may be provided with a charging unit and / or a developing device.

According to such a configuration, since the surface of the developer carrying member is covered with the phenol resin film containing conductive carbon and graphite, the toner component does not easily adhere to the surface, thereby preventing or reducing contamination for a long time. In addition, a stable developer coating layer is always formed in order to appropriately suppress the charge amount of the developer, and a high-density and clear image can be obtained for a long period of time.

Hereinafter, the developer carrier is referred to as a “sleeve”, the layer thickness regulating member is referred to as a “blade”, and the latent image holder is referred to as a “drum”.

In the present invention, the sleeve is formed by coating the peripheral surface of a cylindrical base made of nonmagnetic stainless steel or aluminum with a phenol resin containing conductive carbon and granite. The reason for using a phenolic resin in the present configuration is that the toner component is relatively hard to adhere and is located at a position distant from the developer on the triboelectric series, so that the charge of the developer is too high or too low. This is because they have appropriate charging performance. A phenol resin is a thermosetting resin, and is a resin that is highly cured among general thermosetting resins. Because the phenol resin forms a dense three-dimensional crosslinked structure by a thermosetting reaction, it forms a very hard coating film and can obtain excellent durability not found in other resins. Therefore, even when the sleeve coating film is formed, the coating film is not scratched or peeled off, and stable image quality can always be provided. Examples of the phenol resin include a pure phenol resin composed of phenol and formaldehyde, and a modified phenol resin obtained by combining an ester gum and a pure phenol resin, and any of them can be used in the present invention.

The coating film of the sleeve of the present invention contains conductive carbon and graphite. The conductive carbon and graphite form irregularities on the sleeve surface moderately, and the charges remaining on the sleeve coating are leaked moderately to the sleeve base, so that a stable developer coating layer can always be obtained. Metals such as gold, silver, copper, lead, and tin, and metal oxides such as tin oxide, indium oxide, ammothin oxide, and tungsten oxide were examined, but all showed better characteristics than conductive carbon and graphite. Did not.
The best properties were obtained when conductive carbon and graphite were used in combination. As the conductive carbon used in the present invention, oil furnace, acetylene black,
It is preferable that the resistance value such as Ketzen Black is 120 kg / cm ² and 0.5Ω · cm or less when pressurized. The graphite used in the present invention is a gray or black glossy, lubricious crystalline mineral, and any of natural products and artificial products can be used.

Conductive carbon in the coating of the sleeve according to the present invention,
Other additives may be added in addition to graphite.
For example, a material that acts as a surface roughening agent for adjusting the roughness of the coating film surface, or a charge control agent that controls the amount of charge of the developer is used.

The conductive carbon and graphite are preferably used in a mixing ratio of graphite / carbon = 1/100 to 100/1, preferably 1/10 to 100/1, and the ratio of the mixture to the phenol resin is from 1/3 to 1/3. It is preferable to use in the range of 2/1. By using the ratio of conductive carbon and graphite and the ratio of conductive carbon and graphite mixture and phenolic resin within the above range, the sleeve surface has moderate irregularities, and extremely low contamination with toner components having moderate resistance has high durability. , A stable developer coating layer can be always obtained, and stable image density and image quality can be obtained for a long period of time.

As the blade used in the present invention, any of a metal blade disposed at a certain gap from the sleeve and an elastic blade which abuts on the sleeve surface with an elastic force can be used, but an elastic blade is preferably used in the present invention. Can be

As the elastic blade, a rubber elastic body such as silicon rubber and NBR; a synthetic resin elastic body such as polyethylene terephthalate; and a metal elastic body such as stainless steel and steel can be used. The base on the upper side is fixedly held to the developer container side, and the lower side is bent in the forward or reverse direction of the developing sleeve against the elasticity of the blade, and the inner side of the blade (reverse direction) In this case, the outer surface is brought into contact with the sleeve surface with a moderate elastic pressure. Examples of the image forming apparatus are schematically shown in FIG. 3, FIG. 4, FIG. 5, and FIG. According to such an apparatus, a thin and dense developer layer can be obtained more stably with respect to environmental changes. Although the reason is not always clear, the developer particles are forcibly rubbed against the sleeve surface by the elastic blade as compared with a device in which a commonly used metal blade is attached with a certain gap from the sleeve. It is presumed that the charging is always performed in the same state regardless of the change in the behavior due to the environmental change.

The image forming method and the image forming apparatus of the present invention will be described with reference to FIGS. The photoreceptor surface 15 is charged to a negative polarity by the primary charger 2 and is image-scanned by exposure with the laser beam 5 to form a digital latent image. The surface containing the elastic blade 11b and the magnet 14 is made of conductive carbon and The latent image is developed with a one-component magnetic developer 10 having a developing sleeve 4 covered with a phenol resin film containing graphite. In the developing section, an alternating electric field and / or a DC bias is applied between the conductive base 16 of the photosensitive drum 1 and the developing sleeve 4 by the bias applying means 12. When the transfer paper P is conveyed and arrives at the transfer portion, the transfer charger 3 charges the transfer paper P with a positive polarity from the back surface (opposite side of the photosensitive drum side) of the transfer paper, thereby loading the negatively charged developer on the surface of the photosensitive drum. The image is electrostatically transferred onto the transfer paper. The toner image on the transfer paper P is fixed on the transfer paper separated from the photosensitive drum 1 by the heating and pressing roller fixing device 7.

The one-component developer remaining on the photosensitive drum after the transfer process is removed by a cleaning device 8 having a cleaning blade. After the cleaning, the photosensitive drum 1 is neutralized by the erase exposure 6, and the process starting from the charging process by the primary charger 2 is repeated again.

The electrostatic image carrier (photosensitive drum) has a photosensitive layer 15 and a conductive substrate 16, and moves in the direction of the arrow. The developing sleeve 4 of a non-magnetic cylinder, which is a developer carrying member, rotates in the developing section so as to advance in the same direction as the surface of the electrostatic image holding member. Inside the non-magnetic cylinder 4, a multi-pole permanent magnet (magnet roll) 14 as a magnetic field generating means is arranged so as not to rotate. The one-component insulative developer in the developing unit 9 is thinly applied on the surface of the developing sleeve by the elastic blade 11b, and the friction causes the toner particles to be charged.

In the developing section, an alternating electric field is applied between the developer carrier 4 and the electrostatic image holding surface. This AC bias is f 200 ~ 4,0
00Hz and Vpp should be 500-3,000V.

Upon the transfer of the toner particles in the developing portion, the toner particles are transferred to the electrostatic image side by the action of the electrostatic and AC bias on the electrostatic image holding surface. It is preferable that a stirring device 13 in the developing device is provided in the developing device.
By positively sending the developer to the vicinity of the developing sleeve, it is effective to form a uniform developer layer just before the developer runs out.

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples.

 These are not limited only to the present invention.

 All parts in the following formulations are parts by weight.

Example 1 Were dispersed by a sand mill, and a surface coating film having a thickness of 6 μm was formed on the peripheral surface of the aluminum cylinder having a diameter of 20φ by a spray method. The sleeve coated with this surface is called sleeve A
6 was provided with a rubber elastic blade (blade A) in contact with the developing device.

On the other hand, a negatively chargeable insulating magnetic toner was prepared as follows.

A spherical magnetic material having a solid apparent density of 1.0 g / cm ³ , linseed oil absorption of 25 ml / 100 g, and a BET specific surface area of 7 m ² / g (average particle size of 0.22
μ) was crushed using a fred mill in order to crush the aggregates of the magnetic particles, and the compacted apparent density was 1.7 g / cm ³ , the linseed oil absorption was 17 ml / 100 g, and the BET specific surface area was 7 m ² / g Was prepared. The prepared spherical magnetic material has a saturation magnetization (σ _s ) of 85 emu / g and a residual magnetization (σ _r ) of 5 emu / g.
Σ _r / σ _s was 0.06, and the coercive force (H _c ) was 56 Oe (e).

The above mixture is melt-kneaded with a biaxial extruder heated to 130 ° C., the cooled kneaded material is roughly pulverized with a hammer mill, the coarsely pulverized material is finely pulverized with a jet mill, and the obtained finely pulverized powder is fixed wall. Classified powder was produced by classifying with an air classifier. In addition, the obtained classified powder is multi-divided using the Coanda effect (Nippon Mining Co., Ltd. elbow jet classifier)
The fine powder and coarse powder were simultaneously strictly classified and removed to obtain a black fine powder (magnetic toner) having a volume average particle diameter of 5.0 μm. The obtained black fine powder had a value of −18 μc / g as measured by triboelectric charge after being mixed with the iron powder carrier. Further, the obtained magnetic toner as a black magnetic fine powder had a residual magnetization (σ _r ) of 2.7 emu / g, a saturation magnetization σ _{s of} 39 emu / g, and a coercive force (H _c ) of 52 Oe.

Table 1 below shows data obtained by measuring the obtained negatively charged magnetic toner using a Coulter Counter TA II having an aperture of 100 μ as described above.

100 parts of the magnetic toner and 1.2 parts of -240 μc / g negatively charged hydrophobic silica hydrophobicized with dimethylchlorosilane and silicone oil are mixed with a Henschel mixer, and after mixing, a 100-mesh (tiler mesh) film is formed. To obtain a developer. Triboelectrification amount of the developer is -30.3μc / g, loose apparent density 0.48 g / cm ^3, the packed bulk density of 0.93 g / cm ^3, the true density is 1.72 g / cm ^3, loose apparent density and true The porosity (εa) calculated from the density is 72%
Met.

4 laser beam printers LBP-8AJ1 made by Canon with a cartridge modified by incorporating the above-mentioned developing device.
Modified to a speed of (A4 length), a primary charge of -700 V was performed on the surface of the stacked organic photoconductor (OPC) photosensitive drum, and a digital latent image was formed with the potential at the laser light exposure section at -100 V. A DC bias of -500 V and an AC bias (1800 Hz, peak-to-peak 1600 V) were applied, and 1,000 images were printed in a continuous mode at room temperature and normal humidity (25 ° C., 60% RH) by reversal development. The results are shown in Table 3. In Table 3, Dmax is the density of a solid black square having a side of 5 mm, and the fine dot reproducibility is the reproduction of an image developed by developing a checker pattern with a side of X = 80 μm or X = 50 μm as shown in FIG. The properties were observed and evaluated using an optical microscope (100 times), focusing on the sharpness of the image and the gap to the non-image area.

 The evaluation criteria are as follows.

○… 2 defects or less ○ △… 3-5 defects △… 6-10 defects ×… 10 defects or more As can be seen from Table 3, 1,000 images with high density and excellent in fine dot reproducibility Until it is stable, and
The amount of toner coat on the sleeve after 1,000 sheets of images were printed was about 1.2 mg / cm ^{2 in} each environment, which was almost unchanged from the initial stage.

Tables 1 and 2 show the particle size distribution of the toner and the physical properties of the developer used in the following Examples and Comparative Examples, and Table 3 shows the evaluation results.

The classifying process by the multi-segment classifier and the classifier used in this embodiment will be described with reference to FIGS. 8 and 9. 8 and 9, the multi-segment classifier 40 has a side wall having a shape indicated by 52 and 54, a lower wall has a shape indicated by 55, and a side wall 53 and a lower wall 55 respectively. It is provided with knife edge type classification edges 47 and 48, and the classification zone is divided into three by the classification edges 47 and 48. A raw material supply nozzle 46 that opens to the classification chamber is provided below the side wall 52, and a Coanda block 56 that is bent downward in the direction of extension of the tangent at the bottom of the nozzle to draw a long elliptical arc is provided. Classification room upper wall
57 is a knife-edge type inlet edge in the lower part of the classification chamber 49
In addition to the above, the air intake pipe that opens to the classification chamber
44, 45 are provided. The inlet pipes 44, 45 are provided with first and second gas introduction adjusting means 50, 51 such as dampers, and static pressure gauges 58, 59, respectively. Discharge pipes 41, 42, and 43 having discharge ports that open into the room are provided on the bottom of the classifying chamber corresponding to the respective dividing areas. The classified powder is introduced into the classification region from the supply nozzle 46 under reduced pressure, and moves along the curved line 60 by the action of the Coanda effect of the Coanda block 56 due to the Coanda effect and the action of the high-speed air flowing in at that time. The powder was classified into a black fine powder 42 and an ultra fine powder 43 having a predetermined volume average particle size and a particle size distribution.

Example 2 Evaluation was made in the same manner as in Example 1 except that the amount of the hydrophobic silica used in Example 1 was changed to 1.6 times, and the same good results as in Example 1 were obtained. Table 3 shows the results.

Example 3 A volume average diameter of 5.8 μm produced in the same manner as in Example 1,
A developer was prepared and evaluated in the same manner as in Example 1 except that toner B having a particle size distribution as shown in Table 2 was used. As a result, the same good results as in Example 1 were obtained. Table 3 shows the results.

Comparative Example 1 Instead of the spherical magnetic material used in Example 1, the apparent density was 0.4 g / cm ³ , the linseed oil absorption was 34 ml / 100 g, and the BET specific surface area was 7
A developer prepared in the same manner as in Example 1 except that a toner having a particle size distribution of C in the table using a non-crushed magnetic material mainly composed of cubic magnetic particles having m ² / g was used. As a result, the image density was slightly low as shown in Table 3.

Comparative Example 2 Evaluation was performed in the same manner as in Example 1 except that a developer prepared using untreated silica was used instead of the hydrophobic silica used in Example 1, and the image density was as shown in Table 3. But low fog. Also, the reproducibility of minute dots was poor.

Comparative Example 3 A toner was prepared in the same manner as in Example 1 except that the amount of the spherical magnetic material in Example 1 was changed to 60 parts, and a toner D having a volume average particle diameter of 11.4 μm and a particle size distribution as shown in Table 2 was used. When a developer was prepared and evaluated in the same manner as in Example 1, the reproducibility of fine dots was poor, and there were many dots. Table 3 shows the results.

Example 4 The procedure of Example 1 was repeated, except that a developer prepared using a magnetic toner having a volume average particle diameter of 5.5 μm having a particle size distribution of E in Table 2 was used.

Table 2 shows the physical properties of the developer, and Table 3 shows the results of a printer image test.

In addition, FIG. 12 (○), FIG. 13 (△), and FIG. 14 (×) show the evaluation criteria for the evaluation under a 50-fold visual field with a microscope.

 Table 7 shows the results.

Example 5 A spherical magnetic material having a solid apparent density of 0.8 g / cm ³ , a linseed oil absorption of 20 ml / 100 g, and a BET specific surface area of 6 m ² / g (average particle size of 0.29
μm) was crushed to prepare a spherical magnetic material (average particle size 0.27 μm) having a hardened apparent density of 1.85 g / cm ³ , a linseed oil absorption of 14 ml / 100 g, and a BET specific surface area of 5.9 m ² / g.

A developer was prepared and evaluated in the same manner as in Example 1 except that 90 parts of the spherical magnetic material was used and a magnetic toner having a volume average particle diameter of 5.7 μm having a particle size distribution of F in Table 1 was used. Table 2 shows the physical properties of the magnetic developer, and Table 3 shows the results of the printer test.

Example 6 Except for using an uncrushed spherical magnetic material having a solid apparent density of 0.9 g / cm ³ , a linseed oil absorption of 25 ml / 100 g, and a BET specific surface area of 7 m ² / g as a magnetic material of a toner, Example 1
In the same manner as in Example 1, a magnetic toner and a developer having the particle size distribution of G in the table were prepared, and an image output test was performed in the same manner as in Example 1.

Table 3 shows the results of a printer test in which the physical properties of the magnetic developer are shown in Table 2.

Comparative Example 4 A developer was prepared and evaluated in the same manner as in Example 1 except that the amount of the spherical magnetite was changed to 60 parts and a magnetic toner having a particle size distribution of H in the table was used, and evaluation was performed. .

Table 2 shows the physical properties of the magnetic developer, and Table 3 shows the results of the printer test.

Comparative Example 5 The same procedure as in Example 1 was carried out except that the magnetic toner having an average particle size of 4.0 μm having the particle size distribution shown in Table I and the amount of hydrophobic silica was changed to 2.0 parts. The inside of the aircraft due to the scattering of air was noticeable.

Table 2 shows the physical properties of the magnetic developer, and Table 3 shows the results of the printer test.

[Effect of the Invention] The magnetic developer of the present invention having the above-mentioned particle size distribution and having an insulating magnetic toner containing a predetermined amount of a spherical magnetic substance and a hydrophobic silica fine powder is a latent image formed on a photoreceptor. Up to the fine line, the performance of faithfully reproducing is improved, the reproduction of halftone dots and dot latent images such as digital is excellent, and the gradation and resolution are excellent. Furthermore, it is possible to maintain high image quality even when printout is continued, and to perform good development even with high-density images with less developer consumption than conventional one-component magnetic developers. This has advantages in economy, economy, and downsizing of the printer body.

In particular, the magnetic developer of the present invention develops a digital electrostatic latent image of a minute spot formed on a negatively charged organic photoconductor by a reversal development method, and transfers a toner image by plain paper or OHP by electrostatic transfer. It is preferably used in an image forming method of transferring and fixing to a transfer material such as a plastic sheet for use.

[Brief description of the drawings]

FIGS. 1, 3, and 5 are schematic explanatory views of an image forming apparatus to which the magnetic developer of the present invention can be preferably applied. FIGS. 2, 4, and 6 are FIGS. FIG. 6 is an enlarged view of each of the developing units of the apparatus shown in FIGS. 3 and 5. FIG. 7 is a schematic view of an apparatus for measuring the charge amount of hydrophobic silica or developer used in the present invention. FIGS. 8 and 9 are schematic illustrations of a multi-segment classifier used for classifying magnetic toner in the embodiment. FIG. 10 is a partial view showing an image pattern used in a dot reproducibility test in Examples and Comparative Examples. FIG. 11 is a view showing the range of the content ratio of particles of 5 μm or less in the total toner particles of the magnetic toner used in the present invention. FIG. 12, FIG. 13 and FIG. 14 are diagrams showing the ranks ○, Δ, and × of the dash.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Yusa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kiyoko Tsuchiya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (58) Investigated field (Int.Cl. ⁶ , DB name) G03G 9/083 G03G 9/08 G03G 15/08 507 G03G 15/00 550

Claims (3)

(57) [Claims] 1. A magnetic developer containing an insulating magnetic toner having at least a binder resin and a magnetic material and hydrophobic silica fine powder, wherein 0.6 to 1.6 parts by weight per 100 parts by weight of the insulating magnetic toner is provided. Hydrophobic silica fine powder is mixed, and the magnetic developer has a BET specific surface area of 1.8 to 3.5 m ² / g and -20
~ -35μc / g triboelectricity, loose apparent density
0.40 to 0.52 g / cm ³ , a true density of 1.45 to 1.8 g / cm ³ , the magnetic material is a spherical magnetic material having an average particle size of 0.1 to 0.35 μm, and the insulating magnetic toner is The insulating magnetic toner has a volume average particle diameter of 4.5 μm or more and less than 6 μm and a magnetic toner particle having a particle diameter of 5 μm or less, which contains 70 to 120 parts by weight of the spherical magnetic material per 100 parts by weight of the resin coating. The magnetic toner particles having a particle size of 6.35 to 10.08 μm are contained in an amount of 5 to 50% by number, and the magnetic toner particles having a particle size of 6.35 to 10.08 μm are contained therein.
The magnetic toner particles having a particle diameter of 5 μm or more are contained in a magnetic toner particle group having a particle diameter of 5 μm or less. V represents the volume percentage of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. Here, N indicates a positive number of 17 to 60. ] A magnetic developer characterized by having a particle size distribution satisfying the following. 2. An electrostatic image holding member for holding an electrostatic charge image and a developer holding member for holding a magnetic developer on the surface are arranged at a predetermined interval in a developing section, and the developer holding member is A magnetic developing agent having a surface covered with a phenolic resin film containing conductive carbon and graphite, wherein the magnetic developer contains an insulating magnetic toner having at least a binder resin and a magnetic substance, and hydrophobic silica fine powder; 0.6 to 1.6 parts by weight of hydrophobic silica fine powder is mixed per 100 parts by weight of the insulating magnetic toner, and the magnetic developer has a BET specific surface area of 1.8 to 3.5 m ² / g. 20
~ -35μc / g triboelectricity, loose apparent density
0.40 to 0.52 g / cm ³ , a true density of 1.45 to 1.8 g / cm ³ , the magnetic material is a spherical magnetic material having an average particle size of 0.1 to 0.35 μm, and the insulating magnetic toner is The insulating magnetic toner has a volume average particle diameter of 4.5 μm or more and less than 6 μm and a magnetic toner particle having a particle diameter of 5 μm or less, which contains 70 to 120 parts by weight of the spherical magnetic material per 100 parts by weight of the resin coating. The magnetic toner particles having a particle size of 6.35 to 10.08 μm are contained in an amount of 5 to 50% by number, and the magnetic toner particles having a particle size of 6.35 to 10.08 μm are contained therein.
The magnetic toner particles having a particle diameter of 5 μm or more are contained in a magnetic toner particle group having a particle diameter of 5 μm or less. V represents the volume percentage of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. Here, N indicates a positive number of 17 to 60. Wherein the magnetic developer is conveyed to the developing unit with the magnetic developer being regulated to a thickness smaller than the gap on the developer carrier, and an alternating electric field is applied to the developer carrier in the developing unit. An image forming method, wherein the image is developed while being applied. 3. An apparatus unit detachably mounted on a main body of an image forming apparatus, the apparatus unit comprising: an electrostatic latent image holding member for holding an electrostatic latent image; and a developing unit for developing the electrostatic latent image. At least a developing device having a magnetic developer, the electrostatic latent image holding member and the developing device are integrally connected, and the developing device accommodates the magnetic developer. Developing device,
And a developer carrier for carrying the magnetic developer housed in the developing device for developing the electrostatic latent image and transporting the developer to a developing unit. The latent image holding member and the developer carrying member are arranged at a fixed interval in the developing section, and the surface of the developer carrying member covered with a phenol resin film containing conductive carbon and graphite is provided. The magnetic developer is a magnetic developer containing an insulating magnetic toner having at least a binder resin and a magnetic material, and hydrophobic silica fine powder, and is 0.6 to 1.6 parts by weight per 100 parts by weight of the insulating magnetic toner. Part of hydrophobic silica fine powder is mixed, the magnetic developer has a BET specific surface area of 1.8 to 3.5 m ² / g, and −20.
~ -35μc / g triboelectricity, loose apparent density
0.40 to 0.52 g / cm ³ , a true density of 1.45 to 1.8 g / cm ³ , the magnetic material is a spherical magnetic material having an average particle size of 0.1 to 0.35 μm, and the insulating magnetic toner is The insulating magnetic toner has a volume average particle diameter of 4.5 μm or more and less than 6 μm and a magnetic toner particle having a particle diameter of 5 μm or less, which contains 70 to 120 parts by weight of the spherical magnetic material per 100 parts by weight of the resin coating. The magnetic toner particles having a particle size of 6.35 to 10.08 μm are contained in an amount of 5 to 50% by number, and the magnetic toner particles having a particle size of 6.35 to 10.08 μm are contained therein.
The magnetic toner particles having a particle diameter of 5 μm or more are contained in a magnetic toner particle group having a particle diameter of 5 μm or less. V represents the volume percentage of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. Here, N indicates a positive number of 17 to 60. ] The apparatus unit characterized by having a particle size distribution satisfying the following.