JPH04162048A - Magnetic developer and image forming method - Google Patents

Abstract

PURPOSE:To obtain a magnetic developer excellent in fine line reproducibility and gradient by containing insulating magnetic toner and hydrophobic silica fine powder at least a specified property of bonding resin and magnetic body. CONSTITUTION:In a magnetic developer, a hydrophobic silica fine powder body of 0.6 to 1.6 pts.wt. is mixed in an insulating magnetic toner of 100 pts.wt. It has a BET specific area of 1.8 to 3.5m<2>/g a frictional electrification characteristic of -20 to -35muc/g, a looseness apparent density of 0.40 to 0.52g/m<3>, and a true specific gravity of 1.45 to 1.8g/m<3>. A magnetic body is a spherical magnetic body of 0.1 to 0.35mum in average particle diameter containing more then 50% of spherical magnetic particles in which magnetic particle surface is formed substantially by curved surface, the insulating magnetic toner contains the spherical magnetic body of 70 to 120 parts by weight to bonding resin of 100 pts.wt., and the insulating magnetic toner has an average volumetric particle diameter of 4.5 to 6mum. A latent image is developed reversely by the one component-line magnetic developer 10 in a developing equipment 9 provided with a developing sleeve 4. Namely, alternately bias, pulse bias, and/or DC bias is applied to a clearance between a conductive base body 16 of a photosensitive drum 1 and the developing sleeve 4 by a bias application means 12.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a magnetic developer having at least a magnetic toner containing a spherical magnetic substance and a hydrophobic silica fine powder, and an image forming method using the magnetic toner. Regarding.

The magnetic developer and image forming method of the present invention are an electrophotographic image forming method in which a latent image is expressed by a unit pixel, and each unit pixel is expressed by a binary value of on-off or a finite gradation. , can be preferably used to visualize a digital latent image using a reversal development method.

[Prior Art] In an electrophotographic system, a method is generally used in which a document image is exposed to light and a latent image carrier is exposed to the reflected light to obtain a latent image. In this method, the reflected light from the original is directly used as an image signal, so the potential of the electrical latent image changes continuously (hereinafter referred to as an analog latent image).

In contrast, recently, a method has been commercialized in which the reflected light of the original is converted into an electrical signal, the signal is processed, and then exposure is performed based on the signal. This method allows for easier magnification and reduction at higher magnifications than the analog latent image method, and allows the image signal to be taken into a computer and output together with other information.

Although it has a variety of uses as described above, if the image signal is handled as analog, the amount of signal will be enormous, so digital processing is required to divide the image into pixel units (hereinafter referred to as dots) and determine the exposure amount for each pixel. 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, compared to an analog latent image, the deviation of the surface potential of the latent image during the formation of the latent image is large, and the potential difference between the developer conveying section and the latent image carrier such as a photosensitive drum is small. It is also necessary to develop the latent image area.

Image/non-image is repeated for each dot.

The developability of the developer is especially important for images.

Therefore, if a developer developed as an analog latent image developer is used in a digital latent image system, especially the above-mentioned image
In a printing pattern where a non-image is repeated for each dot, the development of each dot is insufficient, resulting in the dots becoming smaller or not being developed at all, resulting in the overall image density becoming lighter and the characters becoming darker. It has a tendency to fade. This phenomenon tends to be noticeable in a developer containing a magnetic toner containing a magnetic material (hereinafter referred to as magnetic developer), which tends to have a small amount of developer charge.

This is thought to be because in the magnetic developer, there are portions where the magnetic material is exposed on the surface of the magnetic toner particles, and the surface area that can contribute to charging is reduced. Since the amount of exposure on the surface of magnetic toner particles changes depending on the amount of magnetic material contained in each magnetic toner, the distribution of MFt amount of the developer is wider than that of other developers. When used in a digital latent image system, characters tend to become blurred due to accumulation of magnetic toner particles with a low amount of triboelectric charge in the developing device, and an improvement is desired.

Furthermore, in recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, their uses have become more diverse and the demands on their image quality have become stricter. When copying images such as ordinary documents, it is required to reproduce extremely finely and faithfully, even down to the minute characters, without being crushed or cut off. In particular, in the case of a latent image on a photoreceptor of an image forming device or a line image of 100 μm or less, conventional developers generally have poor fine line reproducibility and the sharpness of the line image is still insufficient.Recently, digital In an image forming device such as an electrophotographic printer that uses a fixed image signal, a latent image is formed by a collection of dots in a fixed unit, and solid areas, halftone areas, and light areas are formed by changing the dot density. It is expressed as ``Fu''. However, in a toner image, if the toner particles do not adhere to the dots faithfully and the toner particles protrude from the dots, the gradation that corresponds to the ratio of dot density between black and white areas of the digital latent image cannot be obtained. There is a problem. Furthermore, when improving resolution by reducing dot size in order to improve image quality, it becomes more difficult to reproduce latent images formed from minute dots, resulting in poor resolution and gradation, and poor sharpness. This tends to result in images lacking in detail.

Initially, the image quality is good, but as printing continues, the image quality may deteriorate. This phenomenon is thought to occur because as printouts continue, only toner particles that are easy to develop are consumed first, and toner particles with poor developability accumulate and remain in the developing machine.

Up to now, several developers have been proposed for the purpose of improving image quality. Japanese Patent Publication No. 51-3244
The publication proposes a non-magnetic toner intended to improve image quality by regulating particle size distribution. In the toner,
The toner mainly has a particle size of 8 to 12 μm, which is relatively coarse, and according to the studies of the present inventors, it is difficult to uniformly “glue” the latent image with this particle size, and toner with a particle size of 5 μm or less is 30% by number or less, and 20 μm or more is 5% by number or less, which means that the particle size distribution is broad, which also tends to reduce uniformity. In order to form clear images using such coarse toner particles and a toner with a broad particle size distribution, it is necessary to layer the toner particles thickly to fill the gaps between the toner particles and reduce the apparent appearance. It is necessary to increase the image density, and there is also the problem that toner consumption increases in order to achieve a predetermined image density.

JP-A-54-72054 proposes a non-magnetic toner having a sharper distribution than the former, but the medium weight particles have a rough size of 8.5 to 11.0 μm;
As a high-resolution toner, there is still room for improvement.

In JP-A No. 58-129437, the average particle size is
A non-magnetic toner has been proposed in which the particle size is 10 μm and the maximum number of particles is 5 to 8 μm, but the number of particles of 5 μm or less is as small as 15% or less, and images that lack sharpness tend to be formed.

According to studies conducted by the present inventors, it has been found that toner particles of 5 μm or less have the main function of clearly reproducing the outline of a latent image and of densely “gluing” the toner to the entire latent image. Ta. In particular, in an electrostatic latent image on a photoreceptor, lines of electric force are concentrated, so the electric field strength is higher at the edge portion than inside the image, and the sharpness of the image quality is determined by the quality of toner particles collected at this portion. According to studies conducted by 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.

In U.S. Pat. No. 4,299,900, 20 to 35
A jumping development method using a developer containing 10 to 50% by weight of .mu.m magnetic toner has been proposed. The magnetic toner is triboelectrically applied to apply a thin toner layer uniformly on the sleeve, and in order to further improve the environmental resistance of the developer, the particle size of the toner is designed to be suitable. However, there is a need for improvements that can meet even stricter requirements such as fine line reproducibility, resolution, and compatibility with reversal development systems.

On the other hand, as a developing device using -component magnetic toner, there is, for example, a device proposed in Japanese Patent Laid-Open No. 57-66455. This device uses a toner carrier whose surface is sandblasted with amorphous particles to form a roughened surface with a specific unevenness, so that the surface of the toner carrier is uniform and even. This is a developing device that can always maintain a good toner coating state over a long period of time. Its surface has numerous fine incisions or protrusions arranged in random directions over the entire area.

However, in a developing device using a toner carrier having such a specific surface condition, when toner with a small particle size as described above is used, the toner or components in the toner tend to adhere to the surface, and therefore, the toner carrier If contamination occurs on the body surface, resulting in a decrease in the density of the initial image, and if the contamination progresses over time, there is a tendency for the image to fall off during the rotation period of the toner carrier. This is because components in the toner adhere to the slopes of convex parts and concave parts on the surface of the toner carrier during each rotation, resulting in insufficient charging of the magnetic toner particles and a decrease in the amount of charge in the toner layer. It is something that occurs.

Generally, the components in a magnetic toner include a binder resin, a magnetic material, a charge control agent, and more! It is formed from materials such as type I agents. Although materials are designed to prevent contamination of the surface of the toner carrier, the selection of materials is currently extremely limited.

Various proposals have been made as methods for preventing or reducing contamination of magnetic toner carriers. For example, JP-A-57-66443 and JP-A-58-178380.
A toner carrier in which a resin film with good releasability is formed on the surface of a toner carrier has been proposed as in Japanese Patent Application No. However, although these can prevent contamination of the toner carrier surface, when using toner with a small particle size as mentioned above, the charge of the toner becomes too high than necessary, and it adheres strongly electrostatically to the sleeve surface. However, since it becomes difficult to develop, image density tends to decrease.

As described above, it has been desired to stably supply a toner image that faithfully reproduces a minute latent image.

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

A further object of the present invention is to provide a magnetic developer with high image density, excellent fine line reproducibility, and m-tonality.

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

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

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

A further object of the present invention is to provide a magnetic developer that can provide high image density with low consumption.

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

An object of the present invention is to provide a magnetic developer that has good fine line reproducibility and resolution and is suitable for use in developing digital latent images.

Furthermore, an object of the present invention is to use a toner that has excellent resolution, gradation, and fine line reproducibility even in an image forming apparatus that forms a latent image using a digital image signal and develops the latent image using a reversal development method. A magnetic developer capable of forming images is provided.

An object of the present invention is to provide a magnetic developer that does not easily damage the surface of a photoreceptor.

A further object of the present invention is to provide a magnetic developer that is difficult to 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 toner carrier with magnetic toner in the above-described development method, and to prevent or reduce contamination of the surface of the toner carrier by the magnetic toner and/or components in the magnetic toner. An object of the present invention is to provide an image forming method and an image forming apparatus that can maintain the same performance over a long period of time.

A further object of the present invention is to provide an image forming method and an image forming apparatus that can provide high-quality toner images with high image density, excellent fine line reproducibility, and no fog over a long period of time.

A further object of the present invention is to provide an image forming method and an image forming apparatus whose performance does not change due to environmental changes.

[Means and effects for solving the problems] The present invention is a magnetic developer containing an insulating magnetic toner having at least a binder resin and a magnetic material, and a hydrophobic silica fine powder, the insulating magnetic toner containing 100 parts by weight. 0.6 to 16 parts by weight of hydrophobic silica fine powder is mixed in, and the magnetic developer has a BET specific surface area of 1.8 to 3.5 m2/g.
It has a triboelectric charging property of -20 to -35 μc/g, an apparent loose density of 0.40 to 0.52 g/am', and a true specific gravity of 1.45 to 1.8 g/am'. The magnetic material has an average particle size of 0 and contains 50% or more by number of spherical magnetic particles whose magnetic particle surfaces are substantially curved.
．． It is a spherical magnetic body with a diameter of 1 to 0.35 μm, and the insulating magnetic toner has a particle size of 70 to 100 parts by weight per 100 parts by weight of the binder resin.
The insulating magnetic toner contains 120 parts by weight of spherical magnetic material and has a volume average particle size of 4.5 μm or more and less than 6 μm,
17 to 60 magnetic toner particles having a particle size of 5 μm or less
% by number and 5 to 50% by number of magnetic toner particles having a particle size of 6.35 to 10.08 μm; 10.
Magnetic toner particles having a particle size of 0.8 μm or more are contained in an amount of 5.0% by volume or less, and magnetic toner particles having a particle size of 5 μm or less are represented by the following formula % [where N is magnetic toner particles having a particle size of 5 μm or less]. (2) represents the volume % of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number from 4.6 to 6.7. However, N represents a positive number from 17 to 60. ] The present invention relates to a magnetic developer characterized by having a particle size distribution that satisfies the following.

Further, in the present invention, an electrostatic image carrier that holds an electrostatic image and a toner carrier that carries magnetic toner on the surface are arranged with a certain gap in a developing section, and the toner carrier is conductive. The magnetic toner has a surface covered with a phenolic resin film containing carbon and graphite, and the magnetic toner is an insulating magnetic toner containing at least a binder resin and a magnetic material, and the magnetic material has a substantially curved surface. It is a spherical magnetic body containing 50% or more of spherical magnetic particles formed, and the charge amount of the magnetic toner is -20
-35 μc/g, a volume average particle size of 4.5 μm or more and less than 6 μm, and 17 to 60 number % of magnetic toner particles having a particle size of 5 μm or less, 6.35 to 10
．． The magnetic toner particles having a particle size of 0.08 μm are contained in an amount of 5 to 50% by number, the magnetic toner particles having a particle size of 10.08 μm or more are contained in an amount of 5.0% by volume or less, and the magnetic toner particles having a particle size of 5 μm or less are as follows. In formula 1, N represents the number % of magnetic toner particles having a particle size of 5 μm or less, ■ represents the volume % of magnetic toner particles having a particle size of 5 μm or less, and k is 4.6 to 6.7. indicates a positive number. However, N represents a positive number from 17 to 60. ], the magnetic toner is regulated to a thickness thinner than the gap on a toner carrier and conveyed to a developing section, and the image is developed by applying an alternating electric field to the magnetic toner in the developing section. Regarding the forming method.

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

One solution to narrowing the charge distribution of the magnetic developer is to more uniformly disperse the magnetic material in the binder resin.

As a method for uniformly dispersing the magnetic material, a method is known in which the surface of the magnetic material is modified to be lipophilic by surface treatment with a treatment agent such as a titanium coupling agent. However, the treatment agent is expensive and the surface treatment process is complicated, which increases the cost, which is undesirable.

As a result of studies conducted by the present inventors, it was confirmed that the spherical magnetic material promotes more dispersibility in resin than the conventional cubic magnetic material.

The spherical magnetic body used in the present invention contains 50% by number or more (preferably 70% by number or more, more preferably 80% by number) of magnetic particles whose surfaces are curved. Even if the spherical magnetic material contains a normal cubic magnetic material having a flat magnetic particle surface and angular edges, the content thereof is less than 50% by number, preferably 20. % or less.

Furthermore, the spherical magnetic material has a -order average particle size of 01 to 0.35μ
Those having m are preferably used. In the present invention, the average particle diameter of the spherical magnetic material is determined by taking an enlarged photograph of the sample using a scanning electron microscope, randomly measuring the long diameter values of 100 to 200 particles, and calculating the average value. . Preferably, the spherical magnetic material used in the magnetic toner according to the present invention has an apparent density of 12 to 2.5 g/cm, more preferably 1.5 to 2.0 g/cm, and It has a linseed oil absorption of ~30 mfl/100 g, preferably 10-25 mJ2/100 g, more preferably 12-17 mfl/100 g.

In the present invention, the apparent solidified density (back bulk density) of the magnetic material is determined using a powder tester manufactured by Micron Co., Ltd. and a container attached to the powder tester, and instructions for handling the powder tester are used. The value measured according to the procedures in the manual.

In the present invention, the linseed oil absorption amount of the magnetic material is determined according to JIS
It refers to the value measured according to the method described in K 5101-1978 (pigment test method).

Conventional magnetic materials consisting of cubic magnetite particles have a hardened apparent density of less than 0.6 g/am', usually 0.
, in the range of 3 to 0.5 g/Cm'.

Conventional magnetic materials made of spherical magnetite particles are hardened and have an apparent density of 1. og/cm', usually 0
, ranging from 7 to 0.9 g/cm'.

Magnetic toners using conventional magnetic materials consisting of cubic magnetite particles with an apparent hardening density of less than 0.6 g/cm3 still have insufficient uniformity of dispersion of magnetic particles in toner particles or between toner particles. Therefore, when the digital latent image is developed, the toner image may become blurred. 1st
When the digital latent image of the original image showing the checker pattern shown in Figure 0 is developed with a conventional magnetic toner containing a magnetic material exhibiting a cubic crystal, there is a tendency for the black image area to be partially missing, resulting in poor resolution. There are still points to be improved in the development characteristics.

When a magnetic material consisting of magnetite particles exhibiting a cubic crystal structure is subjected to crushing treatment to break up aggregates of magnetite particles, the treated magnetic material appears hardened and has a very low density. Although the magnetic toner contained therein has improved development characteristics compared to a magnetic toner containing an untreated magnetic material, it is still insufficient. Furthermore, powders with flat parts in their particles, such as cubic crystals, may be crushed during crushing.
Particles adhere to each other on a flat surface, and breaking the adhesion requires higher energy than in the case of a curved surface. Cubic magnetic particles have sharp edges, and the tips are easily destroyed by stress. Therefore, when agglomerated cubic magnetic material is subjected to crushing treatment, a considerable amount of ground fine powder is generated, and the originally desired properties (BET specific surface area, etc.) of the magnetic material after treatment change.

A magnetic material made of spherical magnetite particles that has not been subjected to crushing treatment has improved dispersibility in a binder resin compared to a cubic magnetic material. By crushing the uncrushed spherical magnetic material, it hardens and has a higher apparent density.
Dispersibility in resin is further improved.

In the present invention, 1, 2 to 2, 5 g/
It is preferable to use a spherical magnetic material with a density of c m 3, and the value of the density of the solidified appearance is the same as that of ordinary untreated cubic magnetic material, crushed cubic The crystalline magnetic material and untreated spherical magnetism values are unsatisfactorily large. The specific spherical magnetic material preferably used in the present invention has a weight of 0.7 g/cm 3 or more to 1.0 g/cm 3 or more. O
Hardened apparent density less than g/cm' and 10-35 mft
It can be prepared by crushing a spherical magnetic body having a linseed oil absorption amount of , /g. A mechanical crusher equipped with a high-speed rotor for crushing the powder and a load for dispersing or crushing the powder are used as means for crushing the spherical magnetic material. A pressure disperser equipped with rollers is exemplified.

When crushing aggregates of magnetic particles using a mechanical crusher, the rotor tends to apply excessive impact force to the primary particles of the magnetic particles, destroying the primary particles themselves and causing the magnetic Fine particles are likely to be generated. Therefore, when a magnetic material that has been crushed using a mechanical crusher is used as a raw material for a toner, the triboelectric charging characteristics of the toner deteriorate due to the presence of fine powder of magnetic particles. Therefore, a decrease in toner image density is likely to occur due to a decrease in the amount of friction %F$E of the toner.

On the other hand, a pressurized dispersion machine equipped with a weighted roller such as a fret mill is preferable from the viewpoint of efficiency in disintegrating aggregates of spherical magnetic particles and suppression of generation of fine powder magnetic particles.

The tap density and oil absorption amount of the magnetic material can be understood to indirectly indicate the shape of the magnetic particles, the surface condition of the magnetic material, and the amount of magnetic particle aggregates present. If the apparent hardening density of the magnetic material is less than 1.2 g/cm3, there may be a large amount of cubic magnetic particles in the magnetic material, or there may be a large number of aggregates of magnetic particles. This indicates that the crushing treatment of the magnetic material is substantially insufficient. Therefore, if a magnetic material with a density of less than 1.2 g/cm3 is used, it will be difficult for the magnetic material to be uniformly dispersed in the binder resin, resulting in uneven toner image dispersion and toner The resolution of the photoreceptor is likely to decrease and the surface of the photoreceptor may be damaged by toner particles.

If the tap density of the magnetic material exceeds 2.5 g/cm3,
Excessive disintegration of magnetic particle aggregates causes magnetic particles to stick to each other due to pressure, producing magnetic pellets, and as a result, tends to produce non-uniform magnetic toner particles. .

Even if the oil absorption value of the magnetic material deviates from the upper and lower limits,
The appearance of hardness tends to occur in a similar way to the case of density.

According to the research conducted by 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 magnetic particle aggregates is as follows:
It has been found that the BET specific surface area increases by 10% or more compared to the value before treatment. This is understood to mean that a large amount of fine powder of magnetic particles is produced 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 treatment is substantially the same as the value of the BET specific surface area before treatment, or is decreased by several percent. Therefore, 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 before and after crushing treatment. It is possible. Specifically, the value of the BET specific surface area of the magnetic material at the time when the magnetic material is solidified and its apparent density is increased by approximately 30% by the crushing treatment is the BET before treatment.
The shape of the magnetic body can be considered to be spherical if it is substantially the same or decreased compared to the value of the specific surface area. In the present invention, the primary particle size of the magnetic material according to an electron micrograph is in the range of 01 to 0.35μ, and the BET specific surface area according to the nitrogen gas adsorption method is 60 to 8.0.
In the case of a magnetic material with m2/g, it is particularly preferable.

Furthermore, the spherical magnetic body according to the present invention has a magnetic field of 60 to 90
Saturation magnetization of emu/g ((7s), 3~9 emu
/ g residual magnetization (or), 40 to 80 (preferably 50 to 70) Oersted coercive force (Hc) and/or or / Q E value of 0.04 to 0.10. , is preferable in the conveyance of magnetic toner on a sleeve and in the developing method of developing a digital latent image in the presence of a magnetic field. It is extremely difficult to achieve a coercive force of 40 to 80 oersteds in a conventional cubic system magnetic material, and it can be understood that the shape of the magnetic material is indirectly defined.

The magnetic properties of the magnetic material are, for example, V manufactured by Toei Kogyo Co., Ltd.
This refers to the value measured by SMP-1.

The magnetic toner according to the present invention has a triboelectric charge and is therefore substantially electrically insulating. Specifically, 3.0Kg/c
It is preferable that the resistance value after applying a voltage of 100 V under a pressure of m' is 10 14 Ω·Cm or more. The spherical magnetic body according to the present invention is 70 to 120 parts by weight (preferably 80 to 1 parts by weight) of 100 parts by weight of the binder resin.
10 parts by weight). If it is less than 70 parts by weight, the conveyance of the magnetic toner on a developer carrier such as a sleeve is likely to be insufficient. If it exceeds 120 parts by weight, the insulation properties and heat fixing properties of the magnetic toner tend to deteriorate.

The spherical magnetic body according to the present invention is preferably produced by a wet method using ferrous sulfate as a raw material, and is preferably produced by a magnetite or Preferably, it is made of ferrite.

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 has particularly excellent resolution of digital latent images due to the synergistic effect of the spherical magnetic material contained in the toner and the externally added hydrophobic silica fine powder, and also has excellent image density. ing.

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

One of the characteristics of the magnetic toner of the present invention is that magnetic toner particles having a particle size of 5 μm or less account for 17 to 60% by number. Conventionally, in magnetic toner, magnetic toner particles of 5 μm or less are difficult to control the amount of charge, impair the fluidity of the magnetic toner, and are a component that scatters the toner and contaminates the machine, further causing image fogging. As a component, it was thought necessary to actively reduce it.

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

For example, changing the surface potential on the photoreceptor using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm,
Developing a latent image by varying the surface potential on the photosensitive layer, from a large development potential contrast in which a large number of toner particles are easily developed, to a halftone, to a small development potential contrast in which only a few toner particles are developed,
When the developed toner particles on the photoreceptor were collected and the particle size distribution of the toner was measured, it was found that most of the magnetic toner particles were 8 μm or less, and in particular, many were 5 μm or less. When magnetic toner particles with a particle size of 5 μm or less, which is suitable for development, are smoothly supplied to develop the latent image on the photoreceptor, an image that is faithful to the latent image, does not protrude from the latent image, and has excellent reproducibility. It is something that can be changed. This development is
The same was true for reversal development of digital latent images.

In the magnetic toner according to the present invention, 6.35 to 10.
One of the characteristics is that the number of particles in the range of 0.08 μm is 5 to 50%. As mentioned above, this is related to the necessity of the presence of magnetic toner particles with a particle size of 5 μm or less.
Magnetic toner particles with a particle size of μm or less have the ability to strictly cover the latent image and reproduce it faithfully, but in the latent image itself,
The electric field strength at the surrounding edge portions is higher than that at the central portion, so that the toner particles adhere more sluggishly inside the latent image than at the edge portions, and the image density may appear to be thinner. especially,
This tendency is strong for magnetic toner particles of 5 μm or less. However, the inventors of the present invention have found that this problem can be solved and the image can be made even clearer by containing toner particles in the range of 6.35 to 10.08 μm in an amount of 5% to 50% by number. This is thought to be because toner particles in the particle size range of 6.35 to 10.08 μm have a suitably controlled charge amount compared to magnetic toner particles with a particle size of 5 μm or less; The toner is supplied to the inside where the electric field strength is low, and it compensates for the lack of adhesion of toner particles on the inside to the edge areas, forming a uniformly developed image, resulting in a high density and excellent resolution and gradation. A sharp image is provided.

Furthermore, for particles with a particle size of 5 μm or less, the number %
(N) and volume % (V), N/V=-0,05N
＋k
) is also one of the characteristics of the magnetic toner of the present invention. This range is shown in FIG. 11, and the magnetic developer containing the magnetic toner according to the present invention having a particle size distribution that satisfies this range is excellent for digital latent images formed from minute spots. Developability can be achieved.

The present inventors, while studying the state of particle size distribution of 5 μm or less, found that there is a state of existence of fine powder most suitable for achieving the purpose as shown in the above formula. A large N/V for a given N value indicates that particles of 5 μm or less are widely included, and a small N/V means that the abundance of particles around 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 value is within the range of 16 to 5.85, and N is 1
When it is in the range of 7 to 60 and further satisfies the above relational expression, good fine line reproducibility and high resolution can be achieved.

As for magnetic toner particles having a particle size of 10.08 μm or more, it is preferable that the amount is 5.0% by volume or less, and is as small as possible.

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

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

Magnetic toner particles with a particle size of 5 μm or less account for 17 to 17 of the total number of particles.
The content is preferably 60% by number, preferably 25 to 60% by number, and even more preferably 30 to 60% by number. If the number of magnetic toner particles with a particle size of 5 μm or less is less than 17%, there will be less magnetic toner particles effective for high image quality, and in particular, as the toner is used for continuous printouts, the effective magnetic toner particle component will decrease. decrease,
The particle size distribution of the magnetic toner shown in the present invention changes,
Image quality gradually decreases. If it exceeds 60% by number, magnetic toner particles tend to aggregate with each other, resulting in toner agglomerates larger than the original particle size, resulting in poor image quality.
This lowers the resolution or increases the difference in density between the edges and the inside of the latent image, resulting in a hollow image.

5 to 50 number % of particles in the range of 635 to 10.08 μm
It is good that it is below, preferably 8 to 40% by number. If the number is more than 50%, the image quality deteriorates, more development than necessary (that is, too much toner is applied), fine line reproducibility deteriorates, and toner consumption increases.

On the other hand, if it is less than 5% by number, it becomes difficult to obtain high image density. Number of magnetic toner particles with a particle size of 5 μm or less (%)
(N%), volume% (V%), N/V=-0,05
There is a relationship of N+, which indicates a positive number in the range of 4.6≦ and ≦6.7. Preferably 4.6≦≦6.2, more preferably 4.6≦≦5.7. As shown earlier,
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 size smaller than 5.0 μm is small, resulting in poor image density, resolution, and sharpness. The presence of an appropriate amount of fine magnetic toner particles, which were conventionally thought to be unnecessary, contributes to achieving close packing of toner during development and forming a uniform image without roughness. In particular, by uniformly filling in thin lines and image contours, visual sharpness is further enhanced.

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

From another point of view, in terms of production, it is necessary to cut a large amount of fine powder by classification or the like in order to satisfy the condition of k<4.6, which is disadvantageous in terms of yield and toner cost.

When k is >6.7, the image density tends to decrease as printouts are repeated due to the presence of more fine powder than necessary. This phenomenon occurs when excessive fine magnetic toner particles with more charge than necessary adhere electrostatically to the developing sleeve, which prevents the normal magnetic toner from being carried and charged on the developing sleeve. It is thought that this will occur.

The amount of magnetic toner particles having a particle size of 10.08 μm or more is preferably 50% by volume or less, and more preferably 3.0% by volume or less. If the amount is more than 5.0% by volume, reproduction of fine lines will be hindered.

The volume average diameter of the magnetic toner is 4.5 .mu.m or more and less than 6 .mu.m, and this value cannot be considered in isolation from the components discussed above.

If the volume average particle diameter is less than 4.5 μm, the adhesion of the toner particles to the surface of the photoreceptor increases, which tends to cause poor cleaning.

(Left below) The particle size distribution of toner can be measured using various methods.
In the present invention, a Coulter counter was used.

The measuring device is Coulter counter TA-11 type (
(Manufactured by Coulter Inc.) was used to connect an interface that outputs number distribution and volume distribution (manufactured by Nikkaki) and a CX-1 personal computer (manufactured by Canon), and the electrolyte was a 1% NaCβ aqueous solution using primary sodium chloride. Prepare. As a measurement method, the electrolytic aqueous solution 100 to 150 mJ2
A surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant at 0.1 to 5 mA, and 2 to 20 mg of the measurement sample (approximately 30,000 to approximately 300,000 particles) is added thereto. The electrolytic solution in which the sample was suspended was heated with an ultrasonic disperser to approximately 1
Perform the dispersion treatment for ~3 minutes, and then
The particle size distribution of particles of 2 to 40 .mu. on a number basis was measured using a 100 .mu. aperture using a type A-II, and the values according to the invention were determined therefrom.

The true density of the developer containing the magnetic toner according to the present invention (substantially the true density of the magnetic toner) is 1.45 to 1.8.
g/cm3. Preferably 155-1.75g/c
It is m3. Within this range, the magnetic toner of the present invention having a specific particle size distribution exhibits effects in terms of high image quality and durability stability in a reversal development system in the presence of a magnetic field. If the true density of the magnetic toner is less than 1.45,
The weight of the magnetic toner particles themselves is too light, which tends to cause fogging in reversal development, crushing of thin lines due to too much toner particles, scattering, and deterioration of resolution. If the true density of the magnetic toner is higher than 1.8, the image density will be low and the image will lack sharpness, such as broken thin lines, and the magnetic force will also be relatively large, so the toner spikes will become long or branched. In this case, when the digital latent image is developed, the image quality is likely to be disturbed, resulting in a rough image.

The magnetic toner and developer true densities can be measured using several methods, but in this application, when measuring fine powder, the following method was adopted as an accurate and simple method.

A stainless steel cylinder with an inner diameter of 10 mm and a length of about 5 cm, and an outer diameter of about 10 mm and a height of 5 cm that can be inserted tightly into the cylinder.
Prepare a mm disk (A) and a piston (B) with an outer diameter of about 10 mm and a length of about 8 cm. At the bottom of the cylinder is a disk (A
), then about 1 g of the sample to be measured, and gently push in the piston (B). This is done by a hydraulic press.
A force of 0.00 kg/cm2 was applied and compression was performed for 5 minutes. Weigh the compressed sample (wg), measure the diameter (Dcm) and height (L) of the compressed sample using a micrometer.
Lcm) is measured, and the true density is calculated using the following formula.

In order to obtain even better development characteristics, the magnetic toner of the present invention has a residual magnetization of 1 to 5 emu/g, preferably 2 emu/g.
~4.5 emu/g, saturation magnetization o5 or 15~50
emu/g, preferably 20-40 em
u/g and a coercive force Hc of 20 to 100 oersteds, more preferably 40 to 100 oersteds, and even more preferably 40 to 70 oersteds.

The magnetic properties are measured with a measuring magnetic field of 1000 oersted.

As the binder resin used in the magnetic toner according to the present invention, the following toner binder resins can be used when a heated pressure roller fixing device having an oil applying device is used.

For example, polystyrene: a monopolymer of substituted styrene such as poly-p-chlorostyrene and polyvinyltoluene;
Styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic ester copolymer, styrene-methacrylic ester copolymer, styrene-α-
Methyl chlormethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinylethyl ether copolymer,
Styrenic copolymers such as styrene-vinylmethylketone copolymer, styrene-butadiene copolymer, styrene-isopropylene copolymer, styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenolic resin, naturally modified phenol 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, coumaron indene resin, Petroleum-based resins can be used.

In the heating and pressure roller fixing method, which does not apply much oil, the phenomenon in which a part of the toner image on the toner image support member is transferred to the roller (so-called offset phenomenon) and the adhesion of the toner to the toner image support member are important. This is a serious problem. Toners that are fixed with less thermal energy tend to be prone to blocking or caking during storage or in a developing device, so these problems must also be taken into consideration. The physical properties of the binder resin in the toner are most responsible for these phenomena, but research by the present inventors has shown that when the content of magnetic material in the toner is reduced, the toner image supporting member Although the adhesion of the toner to the toner is improved, offset is more likely to occur, and blocking or caking is also more likely to occur. Therefore, when using the heated pressure roller fixing method in which little oil is applied in the present invention, the selection of the binder resin is more important. Preferred binding materials include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of comonomers for the styrene monomer in the styrenic copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, and 2-ethylhexynopea phenyl acrylate. , methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrinitrile, acrylamide, or a substitute thereof; maleic acid, butyl maleate, maleic acid. Sicarphonic acid and its substituted products having a double bond such as methyl acid and dimethyl maleate; vinyl esters such as vinyl chloride, vinyl acetate, and vinyl benzoate; ethylene-based olefins such as ethylene, propylene, and butylene; Vinyl ketone order like vinyl methyl ketone, vinyl hexyl ketone; vinyl ether neck like vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether: vinyl like!
# Quantity? LL alone or two or more are used.
``As the crosslinking agent, a compound having two or more polymerizable double bonds is mainly used. Examples include aromatic divinyl compounds such as divinylhensen and divinylnaphthalene; carbonic acid esters with two double bonds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, and 1,3-butanediol dimethacrylate; divinyl Examples include divinyl compounds such as aniline, divinyl ether, divinyl sulfite, and divinyl sulfone, and compounds having three or more vinyl groups. These may be used alone or as a mixture.

The crosslinking agent may be used in an amount of 0.1 to 5 parts by weight, more preferably 0.1 to 2 parts by weight, per 100 parts by weight.

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

In the magnetic toner of the present invention, it is preferable that a charge control agent be added to the toner particles (internally added) or mixed with the toner particles (externally added). By using a charge control agent, it is possible to optimally control the amount of charge depending on the developing system. In particular, in the present invention, it is possible to further stabilize the balance between particle size distribution and charge, and by using a charge control agent. As mentioned above, it is possible to clarify the functional separation and mutual complementarity for high image quality in each particle size range.

Negative charge control agents that can be used in the present invention include:
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 (one that does not function as a binder resin) is preferably used in the form of fine particles. In this case, the number average particle size of this charge control agent is specifically 4
The thickness is preferably .mu.m or less (more preferably 3 .mu.m or less).

When internally added to the toner, such a charge control agent is added in an amount of 0.1 to 10 parts by weight (or even 0.1 to 10 parts by weight) per 100 parts by weight of the binder resin.
．． It is preferable to use 1 to 5 parts by weight).

The magnetic developer of the present invention contains hydrophobic silica fine powder. 6B having a particle size distribution characteristic of the present invention
The specific surface area of a synthetic toner is larger than that of a conventional toner. When magnetic toner particles are brought into contact with the surface of a cylindrical conductive sleeve that has a magnetic field generating means inside for triboelectric charging, the number of times the toner particle surface contacts the sleeve increases compared to conventional magnetic toner. , abrasion of toner particles and contamination of the sleeve surface are more likely to occur. When the magnetic toner according to the present invention is combined with fine silica powder, wear is significantly reduced due to the presence of fine silica powder between the toner particles and the sleeve surface. As a result, the life of the magnetic toner and the sleeve can be extended, and stable f-electricity can also be maintained, making it possible to obtain a developer having a magnetic toner that is more excellent even in long-term use. Furthermore, the magnetic toner particles having a particle size of 5 μm or less, which play a major role in the present invention, are more effective due to the presence of fine silica powder, and can stably provide high-quality images.

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 produced by a dry method.

The dry method mentioned here is a method for producing fine silica powder produced by vapor phase oxidation of a silicon halide compound. For example, this method utilizes the thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen and hydrogen, and the basic reaction formula is as follows.

S i Cf14+2H2+02-3 i02 +4H
CJ2 In this manufacturing process, for example, aluminum chloride b
Alternatively, it is also possible to obtain a composite fine powder of silica and other metal oxides by using another metal halide compound such as titanium chloride together with a silicon halide compound. In the present invention, these are also included.

Commercially available fine silica powder produced by vapor phase oxidation of a silicon halogen compound used in the present invention includes, for example, those commercially available under the following trade names.

AEROSIL 130 (Japan Aerosil Co., Ltd.) 200X50 TT60 0 OX80 M OX i 7' O 0K84 Ca-0-S i L
M-5 (CABOTOCo, Inc.) MS
-7MS-5 H-5 Wacker) IDK N 20V
15 (WACKER-CHEMIE GMB) 1 company)
N20ED -CFine 5ilica (Dow Corning Co., Inc.) Fransol (Fransil Inc.) On the other hand, various conventionally known methods can be applied to produce the silica fine powder used in the present invention by a wet method.

For example, sodium silicate is decomposed with an acid, and the reaction formula is shown below.

Na20 ・XS io2+HCj2+H20→S i
02 ・nH2O+NaCjljOther methods include decomposition of sodium silicate with ammonia salts or alkali salts, generation of alkaline earth metal silicate from sodium silicate and then decomposition with acid to produce silicic acid, and ionization of sodium silicate solution. There are methods such as using exchange resin to produce silicic acid, and using natural silicic acid or silicate.

The silica fine powder mentioned here includes anhydrous silicon dioxide (silica), and other silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate.

Among the above-mentioned fine silica powders, those having a specific surface area due to nitrogen adsorption measured by the BET method within the range of 70 to 300 m'/g give good results. 06 to 16 parts by weight of fine silica powder per 100 parts by weight of magnetic toner, preferably 0.7 parts by weight
It is preferable to use ~1.4 parts by weight.

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

The hydrophobic silica fine powder used in the present invention has a tribocharge amount of -
Those having a density of 100 μc/g to −300 μc/g are preferably used. Tribocharge amount -100μc/
If it is less than g, the amount of triboelectric charge of the developer itself decreases, and the humidity characteristics deteriorate. If it exceeds -300 .mu.c/g, the memory of the developer carrier will be accelerated, and the silica itself will be more susceptible to deterioration, which will impede its durability. BET specific surface area 300m2/g
Finer particles have less effect when added to the developer, and 70m
Rougher particles than '/g have a very high probability of being present as free substances, and are likely to cause black spots due to silica uneven distribution (non-uniformity of silica dispersion in the toner) and aggregates.

The tribo value of negatively charged silica fine powder is measured by the following method. 0.2 g of fine silica powder left overnight in an environment of 23.5°C and 60% RH and a carrier iron powder (if durable, Japanese iron powder) with a main particle size of 200 to 300 mesh and not coated with resin. EFV200/300) 9.8
g under the above-mentioned environment, and thoroughly mixed in a wide-mouth polyethylene bottle with a lid having a capacity of approximately 50 c.

Next, as shown in FIG. 7, 0.5 g of the mixture is placed in a metal measuring container 32 with a 400 mesh screen 33 at the bottom and a metal lid 34 is placed.

The weight of the entire measurement container 32 at this time is measured and is defined as Wl (g). Next, in the suction device 31 (at least the part in contact with the measurement container 32 is an insulator), suction is performed from the suction port 37 and the air volume control valve 36 is adjusted to adjust the pressure of the vacuum gauge 35 to 250 m
Let it be mHg. In this state, suction is applied sufficiently to remove the silica. The potential of the electrometer 39 at this time is ■ (volt)
shall be. Here, 38 is a capacitor whose capacitance is C(μ
F). Calculate the weight of the entire measuring container after suction.
(g). Tribocharge amount of this silica (μc/g)
is calculated as shown below.

As the silica fine powder used in the present invention, both so-called dry silica produced by vapor phase oxidation of a silicon halide compound, or dry silica called fumed silica, and so-called wet silica produced from water glass etc. can be used. . Dry silica with fewer silanol groups on the surface and inside and free of production residues is preferred.

The hydrophobization treatment is applied by chemical treatment with an organosilicon compound or the like that reacts with fine silica powder or physically handles it. A preferred method is to treat dry silica fine powder produced by vapor phase oxidation of a silicon halide compound with a silane coupling agent, or at the same time with a silane coupling agent, with silicone oil or an organosilicon compound such as silicone oil. Process.

Examples of silane coupling agents used for hydrophobization include hexamethyldisilazane, trimethylsilane,
trimethylchlorosilane, trimethylethoxysilane,
Dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allyl phenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane Silane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyljethoxysilane, hexamethyldisiloxane, 1.3-divinyltetramethyldisiloxane, 1. 3
-diphenyltetramethyldisiloxane.

Examples of organosilicon compounds include silicone oil.

A preferred silane coupling agent includes hexamethyldisilazane (HMDS).

As a preferable silicone oil, one having a viscosity of 50 to 1,00 centistokes at 25° C. is preferably used. For example, dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorphenyl silicone oil,
Fluorine-modified silicone oil and the like are preferred. For the purpose of the present invention, silicone oils containing a large amount of polar groups such as -OH groups, COOH groups, and -NH2 groups are not preferred.

The silane coupling agent is preferably used in an amount of 1 to 50 parts by weight, more preferably 5 to 40 parts by weight, per 100 parts by weight of the fine silica powder.

The amount of silicone oil or silicone varnish used 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 fine silica powder. The reason for limiting the above treatment amount is that if the amount of silicone oil treated is too small, the result will be the same as that of silane coupling agent treatment alone, and the moisture resistance will not improve and the silica fine powder will absorb moisture under high humidity, resulting in a high quality product. Copy images cannot be obtained. If the amount of silicone oil processed is too large, the above-mentioned silica fine powder agglomerates are likely to form, and free silicone oil is formed, so when applied to a developer, it is impossible to improve fluidity. is easy to grow.

The silicone oil treatment method may be, for example, by directly mixing silica fine powder treated with a silane coupling agent and silicone oil using a Henschel mixer mixer, or by injecting silicone oil onto the base silica. It's also good. Alternatively, it may be prepared by melting or dispersing silicone oil in a suitable solvent, mixing it with the base silica fine powder, and removing the solvent.

The degree of hydrophobicity of fine silica powder in the present invention uses a value measured by the following method. Although referring to the measuring method of the present invention, other measuring methods can also be used.

10 ml of ion-exchanged water in a sealed 200 ml separatory funnel
Add 0mu and 0.1g of sample and shake at 90rpm with a shaker (Turbula shaker mixer TZC type).
Shake for 0 minutes. After shaking, let it stand for 10 minutes to separate the silica powder layer and water layer, and then remove the lower water layer by 20-30mf.
1 sample, put it in a 10 mm cell, and measure the transmittance at a wavelength of 500 nm using blank ion-exchanged water that does not contain silica fine powder as a reference, and the transmittance value is taken as the degree of hydrophobicity of silica. .

The degree of 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 high-quality images due to water adsorption by the silica fine powder at high temperatures.

The typical amount of these hydrophobic silica fine powders is 0.6 to 1.6 parts by weight per 100 parts by weight of the insulating magnetic toner, and is particularly effective when added in 0.7 to 14 parts by weight. It is possible to provide a developer that exhibits chargeability with excellent stability when the developer is charged.

The magnetic developer of the present invention, which includes at least hydrophobic silica fine powder and insulating magnetic toner, has B
ET specific surface area 1.8 to 3.5 m2/g (preferably 1
．． 9-3. om2/g) and -20 to -35 μc/
It has a triboelectric charging property of g, and has an apparent density of 0, 4 to 0.
, with a true specific gravity of 1.45
~1.8g/cm3.

If the triboelectric charge amount is less than 120 μc/g, a sufficient charge amount for development cannot be obtained on the developer carrier, and the image density tends to be low from the beginning. If it is larger than -35 μC/g, the amount of charge of the developer near the surface of the developer carrier becomes too large due to repeated image formation, which inhibits proper charging of the developer on the carrier. , a so-called charge-up phenomenon occurs, resulting in a gradual decrease in image density. This development tends to occur when developing a digital latent image, which is the development of a dot latent image, and is particularly noticeable in a low potential contrast reversal development method using an OPC photoreceptor.

If the BET specific surface area of the developer of the present invention determined by the nitrogen gas adsorption method is less than 1.8 m2/g, it will take time to obtain sufficient 1E current for development on the developer carrier, resulting in a low initial density and a risk of fogging. There will be many images.

When the BET specific surface area is larger than 3.5 m27 g, the mirroring force with the sleeve becomes large, resulting in a decrease in development rate and, as a result, a decrease in image density.

To measure the BET specific surface area in the present invention, QUANT
It is determined by the BET 1 point method using a specific surface area meter Autosorb 1 manufactured by ACHROME.

The true specific gravity of the developer of the present invention is 1.45 to 1.8 g/c
m3, and if it is less than 1.45, fog is likely to occur in a developing method in which an alternating current bias is applied in a magnetic field.
Also, the line width becomes thicker and the resolution deteriorates. true specific gravity is 1
, 8, lines tend to fade and the image density decreases.

The apparent density of the developer of the present invention is 0.4-052 (
It is preferably 0.45 to 0.5), and is characterized in that the density of the loose appearance is small compared to the true specific gravity. The porosity calculated from the true specific gravity and loose apparent density is 62
It is preferably 75%.

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

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

When the density porosity (εa) of the apparent looseness is less than 62%, the toner is not sufficiently combed by stirring inside the developing device, and when it is more than 75%, toner scattering and toner leakage are likely to occur. If the density porosity (εp) of the solidified appearance is less than 40%, developer clogging is likely to occur inside the developing device, the developer is not smoothly supplied to the developer carrier, and white spots are likely to occur.

If the porosity (εp) is greater than 50%, a larger capacity of the developer is required to contain the same amount of developer, which becomes an obstacle to downsizing the printer.

The loose apparent density of the magnetic developer of the present invention is measured using a powder tester manufactured by Hoisen Micron Co., Ltd., and the hardened apparent density is determined by the method used to measure the hardened apparent density of magnetic materials. Do it in the same way.

The magnetic toner of the present invention may contain additives, if necessary. As the colorant, conventionally known dyes and pigments can be used, and usually 0.5 to 20 parts by weight may be used per 100 parts by weight of the binder resin. Other external additives in the magnetic developer of the present invention include, for example, lubricants such as zinc stearate; abrasives such as cerium oxide and silicon carbide; flow agents such as aluminum oxide; or anti-caking agents: carbon black; There are conductivity imparting agents such as tin oxide.

Low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, Sasol wax,
05-5wt of waxy substances such as paraffin wax
% to the magnetic toner is also one of the preferred embodiments of the present invention.

To prepare the magnetic toner for developing electrostatic images according to the present invention, a magnetic powder and a vinyl or non-vinyl thermoplastic resin,
If necessary, pigments or dyes as colorants, charge control agents, other additives, etc. are thoroughly mixed using a mixer such as a ball mill, and then a heat kneader such as a heated roll, kneader, or extruder is used. The insulating magnetic toner according to the present invention is produced by dispersing or dissolving pigments or dyes in the resins which are made to be compatible with each other by melting, kneading or kneading, and after cooling and solidifying, pulverization and strict classification are performed. You can get it.

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

The amount of triboelectric charging of the magnetic toner and magnetic developer of the present invention is determined in almost the same manner as in the case of the silica fine powder described above, but the ratio of amounts is different: 2.0 g of magnetic developer or magnetic toner and 9.0 g of carrier iron powder. Weigh accurately and measure in the same way.

An image forming method to which the magnetic developer of the present invention can be preferably applied will be described with reference to FIGS. 1 and 2.

The surface of the photoreceptor is negatively charged by the primary charger 2, and a digital latent image is formed by image scanning by exposure 5 with laser light, and the magnetic plate 11, a and the magnet 1 are
The latent image is reversely developed using a one-component magnetic developer 10 of a developing device 9 equipped with a developing sleeve 4 containing a developer. In the developing section, an alternating bias, a pulse bias and/or a DC bias is applied between the conductive substrate 16 of the photosensitive tram 1 and the developing sleeve 4 by a bias applying means 12. Transfer paper P is transported and transferred when it comes to the transfer section;
ll! : The negatively charged toner image on the surface of the photosensitive drum is electrostatically transferred onto the transfer paper P by positively charging the transfer paper P from the back side (the opposite side to the photosensitive drum side) using the electric device 3. The toner image on the transfer paper P separated from the photosensitive drum 1 is fixed by a heating and pressure roller fixing device 7 .

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

The electrostatic image holder (photosensitive drum) has a photosensitive layer 15 and a conductive substrate 16, and moves in the direction of the arrow. A non-magnetic cylindrical developing sleeve 4 serving as a developer carrier rotates in the developing section so as to move in the same direction as the surface of the electrostatic image holder. Non-magnetic cylinder 4
Inside, a multipolar permanent magnet (magnet roll) 14, which is a magnetic field generating means, is arranged so as not to rotate. The one-component insulating magnetic developer 0 in the developing device 9 is coated on the non-magnetic cylindrical surface, and the toner particles are given a negative tripo charge by friction between the surface of the sleeve 4 and the toner particles. Furthermore, iron magnetic doctor blade 1+a
close to the cylindrical surface (interval 50 μm to 500 μm),
The thickness of the developer layer can be reduced (30 μm to 300 μm) by arranging it opposite to one magnetic pole position of a multipolar permanent magnet.
) and uniformly regulating the electrostatic image carrier 1 in the developing section.
A developer layer is formed to be thinner than the gap between the developer support member 4 and the developer carrier 4 so that they are not in contact with each other. By adjusting the rotational speed of the cylinder 4, the sleeve surface speed is made to be substantially equal to, or close to, the speed of the electrostatic image holding surface. Instead of iron, a permanent magnet may be used as the magnetic doctor blade 11a to form opposing magnetic poles. In the developing section, an alternating current bias or a pulse bias may be applied by the bias means 12 between the developer carrier 4 and the electrostatic image holding surface. This AC bias f is 200-4.000
Hz, VpP is 5oO~3. It is fine if it is ooO■.

When the toner particles are transferred in the developing area, the toner particles are transferred to the electrostatic image side by the action of the electrostatic force of the electrostatic image holding surface and the alternating current bias or pulse bias.

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

In the image forming method and image forming apparatus of the present invention, a toner carrier coated with a phenolic resin containing conductive carbon and graphite is preferably used as the toner carrier.

As an electrophotographic apparatus capable of carrying out the image forming method of the present invention, an electrostatic latent image carrier such as the above-mentioned photosensitive drum, a developing device,
A plurality of components such as the cleaning means may be integrally combined as an apparatus unit, and this unit may be configured to be detachable from the apparatus main body. for example,%! : At least one of the electric means, the developing device, and the cleaning means is integrally supported with the photosensitive drum to form a single unit that can be attached to and detached from the apparatus main body, and using guide means such as rails of the apparatus main body. It may also be configured to be detachable. At this time, the above-mentioned device unit may include a charging means and/or a developing device.

According to this configuration, since the surface of the toner carrier is covered with a phenolic resin film containing conductive carbon and graphite, toner components are difficult to adhere to the surface.
can prevent or reduce pollution over the long term,
In addition, since the amount of charge on the toner is appropriately controlled, a stable toner coating layer is always formed, and high-density, clear images can be obtained over a long period of time.

Hereinafter, the )/ner carrier will be referred to as a "sleeve", the layer thickness regulating member as a "plate", and the latent image retainer as a "tram".

In the present invention, the sleeve is a cylindrical base made of non-magnetic stainless steel, aluminum, etc., whose peripheral surface is coated with a phenolic resin containing conductive carbon and graphite. The reason why phenolic resin is used in this configuration is that it is relatively difficult for toner components to adhere to it, and because it is located at an appropriate distance from the toner on the triboelectrification series, the toner's charge does not become too high or too low. This is because it has appropriate charging performance. Phenol resin is a thermosetting resin, and is one of the most hardening resins among the thermosetting resins used in boat fishing. This is because phenolic resin forms a dense three-dimensional crosslinked structure through a thermosetting reaction, which allows it to form an extremely hard coating and achieve excellent durability not found in other resins. Therefore, even when a sleeve coating film is formed, there is no scratching or peeling of the coating film, and stable image quality can always be provided. Phenol resin includes pure phenol resin made of phenol and formaldehyde,
There are modified phenolic resins that are a combination of ester gums and pure phenolic resins, and any of them can be used in the present invention.

The coating film of the sleeve of the present invention contains conductive carphone and graphite. The conductive carbon and graphite form appropriate irregularities on the sleeve surface, and the charge remaining on the sleeve coating is appropriately leaked to the sleeve base, so that a stable magnetic toner coating layer is always obtained. Metals such as gold, silver, copper, lead, and tin, tin oxide,
Metal oxides such as indium oxide, antimony oxide, and tungsten oxide were investigated, but none of them showed good properties compared to conductive carbon and graphite. The best properties were shown when conductive carbon and graphite were used in combination. The conductive carbon used in the present invention has a resistance value of 120 kg/cm such as oil furnace, acetylene black, and keratzen black.
2, preferably 0.5 Ω·cm or less when pressurized. The graphite used in the present invention is a gray to black crystalline mineral with luster and slipperiness, and both natural and artificial products can be used.

In addition to conductive carbon and graphite, other additives may be added to the coating film of the sleeve according to the present invention. For example, they act as a surface roughening agent to adjust the roughness of the surface of a coating film, or as a charge control agent to control the amount of charge on a toner.

The conductive carbon and graphite are graphite/
Carbon = 1150 to 100/1, preferably 1/1
It is preferable to use it at a mixing ratio of 0 to 100/1, and it is preferable to use the ratio of the mixture to the phenol resin in the range of 1/3 to 2/1. By using the ratio of conductive carbon and graphite and the ratio of a mixture of conductive carbon and graphite to phenol resin within the above ranges, the sleeve surface has an appropriate level of unevenness, resulting in high durability with extremely little contamination from toner components with appropriate resistance. A stable toner coating layer is always obtained, and stable image density and image quality can be obtained over a long period of time.

The blade used in the present invention can be either a metal blade placed at a certain distance from the sleeve or an elastic blade that contacts the sleeve surface with elastic force, or an elastic blade is preferably used in the present invention. It will be done.

As the elastic plate, rubber elastic bodies such as silicone rubber and NBR; synthetic resin elastic bodies such as polyethylene terephthalate; and metal elastic bodies such as stainless steel and steel can be used. The base, which is the upper side, is fixedly held on 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 plate. (in some cases, the outer surface side) is brought into contact with the sleeve surface with appropriate elastic pressure. The third example of the image forming device is
It is schematically shown in FIGS. 4, 5 and 6. According to such an apparatus, a thin and dense toner layer can be obtained more stably even against environmental fluctuations. The reason for this is not necessarily clear, but the toner particles are forcibly rubbed against the sleeve surface by the elastic blade, compared to the normally used device in which a metal blade is attached to the sleeve with a certain gap. This is presumably because charging is always performed in the same state regardless of changes in behavior due to environmental changes.

The image forming method and image forming apparatus of the present invention will be explained with reference to FIGS. 3 and S4. - The surface of the photoreceptor 15 is negatively charged with the electric device 2, image scanned by exposure with the laser beam 5 to form a digital latent image, and the surface containing the elastic blade Ilb and the magnet 14 is covered with conductive carbon. The latent image is developed with a one-component magnetic toner 10 of a developing device equipped with a developing sleeve 4 covered with a phenolic 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 a bias applying means 12 . When the transfer paper P is conveyed and reaches the transfer section, the transfer charger 3 charges the transfer paper with positive polarity from the back side (the opposite side to the photosensitive drum side), thereby forming a negatively charged toner image on the surface of the photosensitive drum. is electrostatically transferred onto the transfer paper. The toner image on the transfer paper P separated from the photosensitive drum 1 is fixed by a heating and pressure roller fixing device 7.

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

The electrostatic image carrier (photosensitive tram) has a photosensitive layer 15 and a conductive substrate 16, and is rotated in the direction of the arrow. A non-magnetic cylindrical developing sleeve 4 serving as a developer carrier rotates in the developing section so as to move in the same direction as the surface of the electrostatic image holder. Non-magnetic cylinder 4
Inside, a multipolar permanent magnet (magnet roll) 14, which is a magnetic field generating means, is arranged so as not to rotate. The one-component insulating developer in the developing device 9 is transported by an elastic blade 11.
The toner particles are applied thinly onto the surface of the developing sleeve by the toner particles b, and the toner particles are given an electric charge by the friction.

In the developing section, an alternating electric field is applied between the developer carrier 4 and the electrostatic image holding surface. This AC bias has f of 200 to 4
,000Hz and Vpp may be 5oo to 3.0OOV.

When the toner particles are transferred in the developing area, the toner particles are transferred to the electrostatic image side by the action of the electrostatic and alternating current bias on the electrostatic image holding surface. It is preferable that the toner container is provided with a toner container stirring means 13, which is effective in actively sending the toner 10 in the toner container 9 to the vicinity of the developing sleeve to form a uniform toner layer until the toner is about to run out. It is.

(Margin below) [Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

These are not limited to the present invention.

All parts in the following formulations are parts by weight.

Example 1 was mixed, dispersed with a sand mill, and dispersed with a spray method.
A surface coating film with a film thickness of 6 μm was formed on the peripheral surface of an aluminum cylinder for a φ sleeve. A developing device as shown in FIG. 6 was prepared, in which the sleeve whose surface was coated was referred to as sleeve A, and an elastic blade made of rubber (blade A) was provided in contact with the sleeve.

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

Tap density 1.0g/cm3. Linseed oil absorption capacity 25ml
/100g and a BET specific surface area of 7m2/g (average particle size 022μ) was crushed using a fret mill to crush magnetic particle aggregates, and the solidified apparent (tap) density 1.7g/cm', linseed oil absorption 1
A spherical magnetic body having a BET specific surface area of 7 m27 g and 7 mu/100 g was prepared. The prepared spherical magnetic material has a saturation magnetization (Of) of 85 e mu / g, a remanent magnetization (O4) of s e mu / g, or
/σ1 was 0.06, and the coercive force (HC) was 56 oersted (6e).

The above mixture is melt-kneaded with a twin-screw extruder heated to 130°C, the slow-moving kneaded material is coarsely pulverized with a hammer mill, the coarsely pulverized material is pulverized with a jet mill, and the resulting finely pulverized powder is fixed. Classified powder was produced by classification using a wall-type wind classifier. Furthermore, the obtained classified powder is processed using a multi-division classification device (elbow classifier manufactured by Nippon Steel Mining Co., Ltd.) that utilizes the Coanda effect.
The ultrafine powder and the coarse powder were simultaneously strictly classified and removed to obtain a black fine powder (Mi magnetic toner) with a volume average particle diameter of 5.0 μm.

The resulting black fine powder had a tripocharge value of -18 μC/g after being mixed with an iron powder carrier. Furthermore, the magnetic toner, which is the obtained black magnetic fine powder, has a residual magnetization (ar) of 2.7 amu/g, a saturation magnetization σ,
It had a coercive force (Hc) of 39 emu/g and a coercive force (Hc) of 52 oersted.

The obtained negatively charged magnetic toner was transferred to a Coulter counter T A II equipped with a 100μ aperture as described above.
The data measured using the mold is shown in Table 1 below.

100 parts of the magnetic toner and 240 μc/100 parts of the magnetic toner which had been hydrophobized with dimethylchlorosilane and silicone oil.
The mixture was mixed with 1 or 2 parts of negative f-electrophobic hydrophobic silica in a Henschel mixer, and after mixing, the mixture was passed through a 100 mesh (Tiller mesh) sieve to obtain a developer (2). The amount of triboelectric charge of the developer (■) is -30.3 μc/g, and the apparent loose density is 0.48 g/cm3. The apparent density of solidified material is 0.90g.
/cm3, true density is 1.72g/cm3. The apparent looseness is calculated from the density and true density, and the porosity (6a) is 7.
It was 2%.

A Canon laser beam printer LBP-8AJ1 with a cartridge modified by incorporating the above-mentioned developing device was used.
The speed was modified to 1 sheet per minute (A4 vertical), and the surface of the laminated organic photoconductor (OPC) photosensitive drum was primary charged to 1700 μm, and the potential at the exposed area of the laser beam was increased to 11 μm.
00 ■ to form a digital latent image, DC bias -5
00■, AC bias (1800 Hz, peak to beak 1600 V) was applied and reverse development was performed at room temperature and humidity (
1,00 in continuous mode at 25°C, 60% RH)
0 images were printed. The results are shown in Table 3. Dmax in Table 3 is the density of a black square with a side of 5 mm,
Microdot reproducibility is the reproducibility of a developed image of a checker pattern with a square side of x = 80 μm or x = 50 μm, as shown in Figure 10, using an optical microscope (100x magnification) to evaluate the sharpness and non-sharpness of the image. The results were observed and evaluated by focusing on the scattering in the image area.

The evaluation criteria are as follows.

○ ... 2 or less defects ○ △ ... 3 to 5 defects △ ... 6 to 10 defects Images with excellent quality can be stably obtained up to 1,000 sheets, and the amount of toner coated on the sleeve after printing 1,000 sheets is about 1.2 mg/cm' in each environment, which is different from the initial amount. There was almost no change.

The particle size distribution of the toner and the physical properties of the developer used in the following Examples and Comparative Examples are summarized in Table 11 and Table 2, and the evaluation results are summarized in Table 3.

The multi-division classifier used in this example and the classification process using the classifier will be explained with reference to FIGS. 8 and 9. In FIGS. 8 and 9, the multi-segment classifier 40 has a side wall having a shape indicated by 52.54, a lower wall having a shape indicated by 55, and a side wall 53 and a lower wall 55, respectively. Knife-type classification edges 47 and 48 are provided, and the classification zone is divided into three by the classification edges 47 and 48. A raw material supply nozzle 46 opening into the classification chamber is provided below the side wall 52, and a Coanda block 56 is provided which is bent downward in the direction of extension of the bottom tangent of the nozzle to draw an elongated arc. The upper wall 57 of the classification chamber is provided with a knife-shaped edge 49 toward the bottom of the classification chamber, and furthermore, a tube 44, 45 opening into the classification chamber is provided at the top of the classification chamber. Also, the popular tube 44.45 has Dampa no Kiyogi No. 1. Second
Gas introduction adjustment means 50.51 and static pressure gauges 58.59 are provided. At the bottom of the classification chamber are discharge pipes 41, 42, each having a soil discharge port opening into the chamber, corresponding to each fractionation area.
43 is provided. The classified powder is introduced into the classification area from the supply nozzle 46 under reduced pressure, and moves in a curved line 60 due to the Coanda effect of the Coanda block 56 and the action of the high-speed air flowing in at that time, and the coarse powder 41, It was classified into black fine powder 42 and ultrafine powder 43 having a predetermined volume average particle size and particle size distribution.

Example 2 Evaluation was carried out in the same manner as in Example 1 except for using developer ■ in which the amount of hydrophobic silica in Example 1 was changed to 1.6 parts, and the same good results as in Example 1 were obtained. It was done. The results are shown in Table 3.

Example 3 Volume average diameter 5.8 μm produced in the same manner as Example 1,
Developer (2) was prepared and evaluated in the same manner as in Example 1 except that Toner B having the particle size distribution shown in Table 2 was used, and good results similar to those in Example 1 were obtained. The results are shown in Table 3.

Comparative Example 1 Instead of the spherical magnetic material used in Example 1, a tap density of 0.
4. g/cm3. Linseed oil absorption 34mj2/100
Produced in the same manner as in Example 1, except that a toner having a particle size distribution of C in the table was prepared using a crushed magnetic material mainly composed of cubic magnetic particles having a BET specific surface area of 7 m2/g and a BET specific surface area of 7 m2/g. When an evaluation was performed using the developer (2), the image density was slightly low as shown in Table 3.

Comparative Example 2 Example 1 except that developer ■ prepared using untreated silica was used instead of the hydrophobic silica used in Example 2.
When evaluated in the same manner as above, as shown in Table 3, the image density was low and there was a lot of fog. Furthermore, the reproducibility of minute dots was also poor.

Comparative Example 3 Toner D was produced in the same manner as in Example 1 except that the amount of spherical magnetic material in Example 1 was changed to 60 parts, and had a volume average particle diameter of 11.4 μm and a particle size distribution as shown in Table 2. When developer (2) was prepared and evaluated in the same manner as in Example 1, the reproducibility of minute dots was poor and there was a lot of scattering. The results are shown in Table 3.

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

The physical properties of the developer (1) are shown in Table 2, and the results of the printer image reproduction test are shown in Table 3.

In addition, Tobichiri shows the evaluation criteria evaluated under a 50x field of view using a microscope in Figure 12 (○), Figure 13 (△), and Figure 14 (
×) is shown.

The results are shown in Table 7.

Example 5 Tap density 0.8g/cm3.7 Manu oil absorption amount 20mA
/100g and a BET specific surface area of 6m2/g, a spherical magnetic material with an average particle size o of 29μm is crushed to obtain a tap density of 1.85g/am3. Linseed oil absorption 14mfL/1
A spherical magnetic material (average particle size 0.27 μm) having a BET specific surface area of 5.9 m 2 /g and a BET specific surface area of 5.9 m 2 /g was prepared.

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

Example 6 Tap density 0.9 g/cm3. Linseed oil absorption capacity 25 m
fl/1. OOg and BET specific surface area 7m2/g
A magnetic toner and developer (2) having a particle size distribution of G in the table were prepared in the same manner as in Example 1, except that an uncrushed spherical magnetic material having a An image reproduction test was conducted in the same manner as in Example 1.

The physical properties of the magnetic developer (1) are shown in Table 2, and the results of the printer test are shown in Table 3.

Comparative Example 4 A developer [phase] was prepared and evaluated in the same manner as in Example 1 except that the amount of spherical magnetite was 60 parts and the magnetic toner had a particle size distribution of H in the table. was noticeable.

The physical properties of the magnetic developer [phase] are shown in Table 2, and the results of the printer test are shown in Table 3.

Comparative Example 5 The same procedure as in Example 1 was carried out except that a magnetic toner with an average particle diameter of 4.0 μm and a particle size distribution of I in Table I was used, and the amount of hydrophobic silica was changed to 2.0 parts, but 1000 images were printed. There was noticeable dirt inside the machine due to scattering of post-developer.

The physical properties of the magnetic developer 0 are shown in Table 2, and the results of the printer test are shown in Table 3.

(The following is a blank space) [Effects of the invention] The magnetic developer of the present invention, which has the above particle size distribution and includes an insulating magnetic toner containing a predetermined amount of spherical magnetic material and a hydrophobic silica fine powder, can be formed on a photoreceptor. The ability to faithfully reproduce even the fine lines of latent images has been improved, it is excellent in reproducing halftone dots and digital dot latent images, and has excellent gradation and resolution. Furthermore, it maintains high image quality even when printing is continued, and even in the case of high-density images, it is possible to perform good development with less developer consumption than conventional one-component magnetic developers. This has advantages in terms of economy and miniaturization of the printer body.

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

4. Simple gji0den1 "8%%" Figures 1, 3, and 5 are schematic explanatory diagrams of an image forming apparatus that can preferably use the magnetic developer of the present invention, and Figures 2, 4 and 6 are enlarged views of the developing section of the apparatus shown in FIGS. 1, 3, and 5, respectively.

Figure 7 shows the %F of hydrophobic silica or developer according to the present invention.
1 is a schematic diagram of a coulometric measuring device.

FIGS. 8 and 9 are schematic illustrations of a multi-division classifier used for classifying magnetic toner in the embodiment.

FIG. 10 is a partial diagram showing an image pattern used in the dot reproducibility test in Examples and Comparative Examples.

FIG. 11 is a diagram showing the range of the content ratio of particles of 5 μm or less in all toner particles of the magnetic toner according to the present invention.

Figures 12, 13, and 14 are of the highest rank ○
, Δ, and ×.

Claims (1)

[Scope of 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 parts by weight per 100 parts by weight of the insulating magnetic toner. ~1.6 parts by weight of hydrophobic silica fine powder is mixed, and the magnetic developer has a BET specific surface area of 1.8~3.5 m^2/
g, has triboelectric properties of -20 to -35 μc/g, and has a loose apparent density of 0.40 to 0.52 g/cm^3
and has a true specific gravity of 1.45 to 1.8 g/cm^3, and the magnetic material has an average particle size of 50% or more by number of spherical magnetic particles whose magnetic particle surfaces are substantially curved. Particle size 0
．． It is a spherical magnetic body with a diameter of 1 to 0.35 μm, and the insulating magnetic toner has a particle size of 70 to 100 parts by weight per 100 parts by weight of the binder resin.
The insulating magnetic toner contains 120 parts by weight of spherical magnetic material and has a volume average particle size of 4.5 μm or more and less than 6 μm,
17 to 60 magnetic toner particles having a particle size of 5 μm or less
% by number and 5 to 50% by number of magnetic toner particles having a particle size of 6.35 to 10.08 μm; 10.
Magnetic toner particles having a particle size of 0.08 μm or more are contained at 5.0% by volume or less, and the group of magnetic toner particles of 5 μm or less is represented by the following formula N/V=-0.05N+k [where N is a particle size of 5 μm or less]. V represents the volume % of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number from 4.6 to 6.7. However, N represents a positive number from 17 to 60. ] A magnetic developer characterized by having a particle size distribution satisfying the following. (2) An electrostatic image carrier that holds an electrostatic charge image and a toner carrier that carries magnetic toner on the surface are arranged with a certain gap in the developing section, and the toner carrier is made of conductive carbon or graphite. The magnetic toner is an insulating magnetic toner containing at least a binder resin and a magnetic material, and the magnetic material has a surface substantially curved. The magnetic toner is a spherical magnetic material containing 50% or more of spherical magnetic particles, and the amount of charge of the magnetic toner is -20
-35 μc/g, a volume average particle size of 4.5 μm or more and less than 6 μm, and 17 to 60 number % of magnetic toner particles having a particle size of 5 μm or less, and 6.35 to 10.08 μm. Magnetic toner particles having a particle size of 5 to 5
Magnetic toner particles containing 0% by number and having a particle size of 10.08 μm or more are contained in an amount of 5.0% by volume or less and 5 μm
The following magnetic toner particle group is expressed by the following formula N/V=-0.05N+k [where N represents the number % of magnetic toner particles having a particle size of 5 μm or less, and V represents the magnetic toner particle having a particle size of 5 μm or less. It shows the volume % of particles, and k shows a positive number from 4.6 to 6.7. However, N represents a positive number from 17 to 60. ] The magnetic toner has a particle size distribution that satisfies the following, and the magnetic toner is regulated to a thickness thinner than the gap on the toner carrier and transported to a developing section, and the magnetic toner is developed while being applied with an alternating electric field in the developing section. An image forming method characterized by: