JPH0711717B2 - Magnetic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a developing method having a step of causing an electrostatic latent image formed by an electrophotographic method, an electrostatic printing method or the like to develop using a magnetic toner. The present invention relates to a magnetic toner used.

[Prior Art] As a conventional example, USP3,866,574 and US are representative.
There are P3,890,929 and USP3,893,418.

It has been proposed to provide a gap between a latent image carrier and a toner carrier (toner), and apply an asymmetric AC pulse bias to them to control the flight of high-resistance one-component toner. A schematic diagram of the waveform at that time is shown in FIG. In terms of content, the gap between the latent image carrier and the toner carrier is 50 μm to 500 μm.
m (preferably 50 to 180 μm), frequency 1.5K to 10KHz
(Preferably 4 to 8 KHz), development time is 10 μsec T _A 200
μsec (preferably 30 μsec T _A 200 μsec), peeling time is 100 μsec T _D 500 μsec (preferably 100 μsec)
T _D 180 μsec), development voltage V _A −150 V, stripping voltage V _D 400 V, and V _D −V _A 800 V (preferably −150 V V _A
-200V and 400VV _D 450V) etc. By this method, flying toner particles are prevented from adhering to the non-image area, and gradation and line reproducibility are improved. FIG. 2 shows the above schematic diagram.

Further, as a latent image developing method using a high resistance-component developer (volume resistance 10 ¹⁰ Ωcm or more), an impression developing method (USP3405682 specification), a jumping developing method (JP-A-55-18656-18659 etc.) ) Is known, and in particular, the jumping developing method uses an AC bias voltage applied between the toner carrier and the latent image carrier in the developing area, which is the closest area between the toner carrier and the latent image carrier. The toner reciprocates between the development carrier and the latent image carrier, and finally selectively moves and adheres to the surface of the latent image carrier according to the latent image pattern.
To be visualized. These duty ratios are 50%, and the developing side time and the reverse developing side time are the same (see FIG. 3).

However, in some patents relating to the jumping developing method, the duty ratio of the AC bias voltage applied between the toner carrier and the latent image carrier is controlled according to the remaining amount of the developer in order to adjust the image density. . (Japanese Patent Laid-Open No. 60-73647, etc.) A developing method in which the absolute value of the alternating bias voltage is kept low and the developing side voltage is made small in order to prevent toner from adhering to the non-image area, as in the conventional example, is sufficient. It may not be possible to obtain high image density.

Regarding the above-mentioned conventional example, in the case of this developing method, since the developing side bias voltage is large, the developability of the solid latent image (high potential area) is high, while the reverse developing side bias of the low potential area is large, so the development is performed. The toner tends to be stripped off excessively to form an image with no gradation.

Also, the allowable range for setting the voltage (DC component and AC (V _PP & frequency)) is narrow. That is, adjust the voltage (decrease DC or
If you try to increase the density by increasing the AC content, etc.), the background stain (white background fog) will occur. Increasing the AC frequency is effective for white background fog, but the reproducibility of characters and lines is poor (thin).

As a means for improving the above two developing methods, when a developing bias is applied, the developing electric field is increased and the developing time is set to a short time so that the image density is high and the gradation is good, and the white background fog is obtained. You will be able to get images without.

However, when repeatedly used in the image forming method using such a developing method, the image quality may be deteriorated due to a decrease in image density, an increase in fog on a white background, or a deterioration in resolution and line reproducibility. there were.

At this time, the particle size distribution of the toner in the developing unit was measured, and it was found that the particle size distribution changed compared to the initial stage, and the deterioration of the image quality was due to the selective development of the toner.

Further, generally, in the one-component developing method, when image formation is repeated, toner having a small particle diameter adheres to the surface of the toner carrier due to the mirroring force due to the high charge amount, and friction of other toner particles occurs. In some cases, the charging may be hindered, the toner particles that do not have a sufficient amount of charge may increase, and the density may decrease. Such a phenomenon is particularly likely to occur under low humidity.

Such a phenomenon is promoted when the toner on the toner carrier is not consumed (for example, the white background portion of the image), and the image density is reduced. On the other hand, when the toner is consumed from such a state (for example, the black portion of the image), this phenomenon is alleviated, and the density gradually recovers.

Therefore, when an image is formed from a state where the toner carrier has a consumed portion (image portion) and an unconsumed portion (non-image portion), a difference in density on the image (that is, high density in the consumed portion, unconsumed portion) At low concentrations).

Hereinafter, such a phenomenon will be referred to as a carrier memory. Considering the mechanism of formation of the carrier memory, the toner carrier memory is eliminated by toner consumption. That is, the toner is reduced with each revolution of the toner carrier. Therefore, when this phenomenon is light, the memory on the image disappears once, but when it is heavy, it may appear many times repeatedly.

Therefore, in order to obtain good durability, environmental characteristics and excellent image quality in the magnetic toner used in the present invention, the particle size distribution of the magnetic toner and the triboelectric charge amount on the toner carrier are important. Was found to be a factor.

[Problems to be Solved by the Invention] An object of the present invention is to provide a magnetic toner used in a developing method using an asymmetric developing bias, which solves the above-mentioned problems.

Another object is to provide a magnetic toner which has excellent durability, has a high image density even after continuous use for a long period of time, and stably gives an image free from fog on a white background.

Still another object is to provide a magnetic toner that provides images with excellent gradation and excellent resolving power and fine line reproducibility.

Still another object is to provide a magnetic toner that stably provides an image having a high image density even under low humidity.

[Means and Actions for Solving the Problems] In the present invention, a latent image holding member that holds an electrostatic charge image and a toner bearing member that holds a magnetic toner on the surface thereof are arranged in a developing unit with a certain gap. , The magnetic toner is regulated on the toner carrier to a thickness thinner than the gap, and conveyed to the developing section,
In the developing section, a DC bias and an asymmetric AC bias are applied between the toner carrier and the latent image carrier to form an alternating bias electric field, and the alternating bias electric field has a developing side voltage component and a reverse developing side voltage component. And a binder resin used in a developing method in which the voltage component on the developing side is equal to or larger than the voltage component on the reverse developing side, and the application time of the voltage component on the developing side is shorter than the application time of the voltage component on the reverse developing side, A magnetic toner having at least magnetic powder, wherein the magnetic toner is 5
Magnetic toner particles having a particle size of less than or equal to 12 μm are included, magnetic toner particles having a particle diameter of 8 to 12.7 μm are included in an amount of less than or equal to 33%, and magnetic toner particles having a particle size of greater than or equal to 16 μm are included. The content of the magnetic toner is 2 vol% or less, the volume average particle diameter of the magnetic toner is 4 to 10 μm, and the triboelectric charge amount of the magnetic toner particles on the toner carrier and the volume average particle diameter of the magnetic toner are represented by the following general formula (1). ) Is satisfied, it relates to a magnetic toner.

The present invention has achieved this object by providing an image forming method capable of having a triboelectric charge amount on the toner holding member which is suitable not only for the magnitude of the alternating bias electric field but also for the application time t and the developing bias to be controlled. An alternating bias that increases the developing-side bias electric field without changing the frequency of the alternating bias, shortens the application time of the developing-side bias electric field, and accordingly keeps the reverse developing-side bias electric field low, and lengthens the application time. The method of controlling the duty ratio of is used.

In the present invention, the developing-side bias component is a component having a polarity opposite to that of the latent image potential of the latent image carrier with respect to the potential of the toner carrier, and a component having the same polarity as the polarity of the toner. On the other hand, the reverse developing side bias component is a component having the same polarity as the latent image potential of the latent image holding member with respect to the potential of the toner carrier, and a component having a polarity opposite to the polarity of the toner.

For example, in the asymmetrical AC bias shown in FIG. 4, negative polarity toner is used for positive polarity latent image potential, and the potential of the toner carrier is used as a reference (the potential of the toner carrier is zero). The portion is the developing side bias component, and the portion b is the reverse developing side bias component. The magnitudes of the developing-side bias component and the reverse-developing-side bias component are indicated by absolute values of V _a and V _b , respectively.

Further, in the present invention, the duty ratio in the alternating bias electric field is defined by the following formula.

Wherein, t _a polar component in the direction of shifting to the toner latent image holder side in one period of the alternating bias electric field polarity is periodically changed in the positive and negative alternating (constituting the developing side bias component a) shows the application time, t _b indicates the application time of the polar component in a direction separating the toner from the latent image holding side (constituting the reverse development-side bias component b). The present inventors conducted a study using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm in order to see the relationship between the toner particle size and the developability in the developing bias. This is because when a constant developing-side voltage (about 1000 V) is applied between the toner carrier and the latent image carrier (about 250 μm) in pulses, toner begins to adhere to the latent image carrier (image after transfer and fixing). So that the image density becomes 1.0 or more.) The pulse width and the particle size distribution of the toner are checked. That is, the latent potential of the latent image carrier is kept constant, the pulse width is changed to develop the latent image, the developed toner particles on the latent image carrier are collected, and the toner particle size distribution is measured. 8 μm
It was found that there are many magnetic toner particles below and more magnetic toner particles of 5 μm or less. Further, it was also found that the magnetic toner particles of 5 μm or less increased as the pulse width was further reduced.

That is, it can be seen that the smaller the particle size of the toner, the sooner the toner reaches the latent image carrier.

Therefore, when the developing side bias is applied, the developing electric field is increased,
Then, by setting the time to a short time, it is possible to selectively develop the toner particles having a small particle diameter.

Further, when the reverse developing side bias is applied, the stripping electric field is set low and for a long time, so that large toner particles that could not reach the latent image holding member during the developing side bias or toner particles having a low charge amount (moving speed is slow). Is firmly returned to the toner carrier over time. At this time, the toner particles having a small particle size in the image area on the latent image carrier are
Due to strong mirroring power and low stripping electric field,
Although it is scarcely peeled off, toner particles (fogged toner particles) having a small amount of electrostatic charge and attached to the non-image portion due to scattering or the like have a weak mirroring force, and are therefore pulled back onto the toner carrier by the peeling electric field.

As described above, by the developing method using the developing bias, which is a feature of the present invention, gradation can be obtained, and an image having a high image density and free of white background fog can be obtained.

However, in such a developing method, when a large amount of toner particles having a large particle diameter is contained in the magnetic toner, these particles tend to be toner particles having a small charge amount and remain without being developed, and the toner carrier is The upper magnetic toner becomes huge, and causes deterioration of image quality.

On the other hand, if the charge amount of the magnetic toner is too small, the above-mentioned development is promoted, and even if there are few large particles, the image quality is deteriorated.

On the other hand, if the charge amount of the magnetic toner is too large, small particles will remain on the toner carrier, resulting in a change in particle size distribution and deterioration of image quality.

On the other hand, using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm, this time the surface potential on the photoconductor is changed,
From a large development potential contrast where a large number of toner particles are easily developed to a halftone, to a small development potential contrast where only a few toner particles are developed, develop a latent image with the surface potential changed on the photoconductor,
When the developed toner particles on the photoconductor were collected and the toner particle size distribution was measured, it was found that there were many magnetic toner particles having a particle size of 8 μm or less, and particularly 5 μm or less. That is, when the magnetic toner particles having a particle diameter of 5 μm or less, which is most suitable for development, are smoothly supplied to the development of the latent image on the photoconductor, they are faithful to the latent image and do not protrude from the latent image and are truly reproducible. It gives excellent images.

On the other hand, regarding the particle size, in the magnetic toner of the present invention,
One feature is that the magnetic toner particles having a particle diameter of m or less are 12% by number or more. Conventionally, it is 5 for magnetic toner.
The magnetic toner particles having a particle size of μm or less were difficult to control the charge amount and were easily overcharged. For this reason, the toner particles of 5 μm or less have a strong mirroring force on the developing sleeve or the like, and stick to the surface of the sleeve to hinder the triboelectric charging of other particles.
It has been considered necessary to actively reduce toner particles that are not properly charged, which may cause roughness and decrease in density.

However, according to the study by the present inventors, it was found that magnetic toner particles having a particle size of 5 μm or less are an essential component for forming a high quality image.

In the developing method of the present invention, toner particles having a particle size of 5 μm or less are efficiently ejected, so that sticking to the sleeve surface can be prevented.

One feature of the magnetic toner of the present invention is that the number of particles in the range of 8 to 12.7 μm is 33% by number or less. This is related to the necessity of the presence of magnetic toner particles having a particle size of 5 μm or less, as described above, and the magnetic toner particles having a particle size of 5 μm or less have the ability to exactly cover the latent image and faithfully reproduce it. However, in the latent image itself, the electric field strength of the peripheral edge portion is higher than that of the central portion, so that the inside of the latent image has thinner toner particles than the edge portion,
The image density may appear light. In particular, the magnetic toner particles of 5 μm or less have a strong tendency. However, the present inventors have solved this problem by including toner particles in the range of 8 to 12.7 μm at 33 number% or less,
We have found that it can be made even clearer. That is, 8 to 1
It is considered that the toner particles having a particle size range of 2.7 μm have an appropriately controlled charge amount with respect to the magnetic toner particles having a particle size of 5 μm or less, but the inside of the electric field strength is smaller than the edge portion of the latent image. Is supplied to the edge portion to compensate for the small amount of toner particles on the inner side of the edge portion to form a uniform developed image, resulting in a sharp image with excellent resolution and gradation at high density. It is what is done.

12-60% by number for particles with a particle size of 5 μm or less
When the volume average particle size is 7 to 10 μm, N / V = −0.04N + k (however, 4.5 ≦ k ≦ 6.5; 12 ≦ N) between the number% (N) and the volume% (V). It is also preferable that the magnetic toner of the present invention satisfies the relationship of ≦ 60). The magnetic toner of the present invention having a particle size distribution satisfying this range can achieve more excellent developability.

The present inventors, while studying the state of the particle size distribution of 5 μm or less, found that there is a state of presence of fine powder that is most suitable for achieving the purpose as shown by the above formula. Ie 12
For a certain N value of ≦ N ≦ 60, a large N / V means that particles having a particle size of 5 μm or less are widely included, and a small N / V means particles having a particle size of around 5 μm. It is understood that the abundance ratio of N is in the range of 12 to 60, and that the number of particles having a particle size smaller than that is small.
When the N / V value is within the range of 2.1 to 5.82 and the above relational expression is further satisfied, good fine line reproducibility and high resolution are achieved.

For magnetic toner particles having a particle size of 16 μm or more,
It is preferably 2.0% by volume or less and as small as possible.

The constitution of the toner of the present invention will be described in detail.

It is preferable that the magnetic toner particles having a particle diameter of 5 μm or less account for 12% by number or more of the total number of particles, preferably 12-60% by number, and more preferably 17-50% by number. When the number of magnetic toner particles having a particle size of 5 μm or less is 12% by number or less, there are few magnetic toner particles effective for high image quality. Particularly, as the toner is used by continuing copying or printing, the effective magnetic toner particles are effective. The components are decreased, the bias of the particle size distribution of the magnetic toner shown in the present invention is deteriorated, and the image quality is gradually deteriorated. Further, when it is 60% by number or more, the magnetic toner particles are likely to aggregate with each other, resulting in a toner lump having a particle size larger than the original particle size, resulting in a rough image quality, a reduction in resolution, or a latent image edge. In some cases, the difference in density between the inner part and the inner part becomes large, and the image may appear to be hollow.

According to the study by the present inventors, it has been found that the magnetic toner particles of 5 μm or less are essential components for stabilizing the volume average particle diameter of the magnetic toner on the sleeve during image formation and durability.

Since the magnetic toner particles with a particle size of 5 μm or less, which is most suitable for development, are consumed when performing image development durability, and if this amount is small, the volume average particle size on the sleeve gradually increases, and M / S increases and tends to make uniformization of the sleeve coat difficult.

Further, the particles in the range of 8 to 12.7 μm are preferably 33% by number or less, and more preferably 1 to 33% by number. 33 pieces%
When the amount is larger, the image quality is deteriorated, and more development than necessary is required.
That is, the toner is excessively overloaded, resulting in an increase in toner consumption. On the other hand, if it is 1% by number or less, it may be difficult to obtain a high image density. Further, the magnetic toner particle group having a particle size of 5 μm or less has a number% (N%) and a volume% (V
%), There is a relationship of N / V = −0.04N + k, and 4.5 ≦
Indicates a positive number in the range of k ≦ 6.5. Preferably 4.5 ≦ k ≦ 6.0
Is. As shown above, 12 ≦ N ≦ 60, and the volume average particle size at this time is 7 to 10 μm.

When k <4.5, the number of magnetic toner particles having a particle size smaller than 5.0 μm is small, and the image density, resolution and sharpness tend to be poor. The appropriate presence of fine magnetic toner particles, which has been conventionally considered unnecessary, contributes to the closest packing of toner in development and formation of a uniform image without roughness. In particular, by evenly filling the fine lines and the contour portion of the image, the sharpness is visually enhanced. That is, when k <4.5, these properties tend to be inferior due to the lack of the particle size distribution component.

From another point of view, also in terms of production, the conditions such as classification become stricter in order to satisfy the condition of k <4.5, which is also disadvantageous in terms of yield and toner cost. When k> 6.5, the presence of fine particles more than necessary causes the particle size distribution to be unbalanced during repeated copying, resulting in an increase in the toner cohesion and inefficient triboelectric charging, which results in poor cleaning. Fog on a white background may occur.

In addition, magnetic toner particles having a particle size of 16 μm or more are 2.0% by volume.
The amount is preferably below, more preferably 1.0% by volume or less, and further preferably 0.5% by volume or less. 2.0
When the content is more than the volume%, not only does it hinder the reproduction of fine lines, but also rough toner particles of 16 μm or more are prominently present on the thin layer surface of the toner particles developed on the photoconductor during transfer, so that the toner layer The delicate contact state between the photosensitive member and the transfer paper via the irregularity causes irregular transfer conditions, which causes a defective transfer image.

Further, in the developing method of the present invention, toner particles having a particle size of 16 μm or more cannot fly onto the latent image holding member unless they have a sufficient charge amount, and a large amount thereof remains on the toner carrying member, causing a change in particle size distribution and other In many cases, the frictional electrification of toner particles is hindered, the developing ability is lowered, and the image quality is deteriorated.

The volume average particle diameter of the magnetic toner of the present invention is 4 to 10 μm, preferably 4 to 9 μm, and this value cannot be considered in addition to the above-mentioned constituent elements. If the volume average particle diameter is 4 μm or less, the problem that the toner amount on the transfer paper is small and the image density is low is likely to occur in applications such as graphic images having a high image area ratio. It is considered that this is due to the same reason as the reason why the internal density is lowered with respect to the edge portion in the latent image described above. If the volume average particle diameter is 10 μm or more, the resolution is not good, and at the beginning of copying, if it is used continuously, the particle size distribution is changed and the image quality is likely to deteriorate.

The magnetic toner of the present invention having a specific particle size distribution can faithfully reproduce even a fine line of a latent image formed on a photoconductor, and reproduces a dot latent image such as a halftone dot and a digital image. It also provides an image excellent in gradation and resolution. In addition, high image quality can be maintained even when copying or printing is continued, and even in the case of high-density images, good development can be performed with less toner consumption than conventional magnetic toner, which is economical. Also, it has an advantage in downsizing of the copying machine or the printer body.

In the developing method applied to the magnetic toner of the present invention, the above effects can be more effectively exhibited.

The toner particle size distribution can be measured by various methods,
In the present invention, a Coulter counter is used.

That is, Coulter Counter TA-
Using a type II (manufactured by Coulter), an interface (manufactured by Nikkaki) that outputs a number distribution and a volume distribution and a CX-1 personal computer (manufactured by Canon) are connected, and the electrolyte is approximately 1 using primary sodium chloride. % NaCl aqueous solution is prepared. For example, ISOTON-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, a surfactant as a dispersant in the electrolytic aqueous solution 100 to 150 ml,
Preferably, 0.1 to 5 ml of alkylbenzene sulfonate is added, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is dispersed by an ultrasonic disperser for about 1 to 3 minutes,
According to the Coulter Counter TA-II type, a 100 μ aperture is used as an aperture and the number is 2 based on the number.
The particle size distribution of the ~ 40μ particles was measured and the value according to the invention was then determined.

The apparatus that has undergone the developing step in the present invention is given as a specific example, and this is shown in FIG. 1 to describe the constitution of the present invention in more detail, but this does not limit the present invention in any way.

In FIG. 5, reference numeral 1 is a rotary drum type latent image holding member (so-called photoconductor) in the transfer type electrophotographic method (rotating drum type insulator in the transfer type electrostatic recording method, electrofax). Latent image carrier such as photosensitive paper in the method and electrostatic recording paper in the direct electrostatic recording method, an electrostatic latent image is formed on the surface by a latent image forming process device or the same process mechanism not shown in the figure. , Are moving in the direction of the arrow.

Reference numeral 2 is the whole number of the developing device, 21 is a hopper containing toner, 22 is a rotating cylinder (hereinafter referred to as sleeve) as a toner carrier (developer layer supporting member), and a magnetism generating means 23 such as a magnetic roller is provided therein. Built in.

In the drawing, the sleeve 22 has a substantially right half circumferential surface exposed in the hopper 21 and a substantially left half circumferential surface exposed to the outside of the hopper for bearing support.
A doctor blade 24, which is driven to rotate in the direction of the arrow, is a toner applying member disposed on the upper surface of the sleeve 22 with its lower side edge portion being close to the upper surface, and 27 is a stirring member for the toner in the hopper.

The axis of the sleeve 22 is substantially parallel to the generatrix of the latent image carrier 1, and the sleeve 22 closely opposes the surface of the latent image carrier 1 with a small gap α.

The surface moving speeds (peripheral speeds) of the latent image carrier 1 and the sleeve 22 are substantially the same, or the peripheral speed of the sleeve 22 is slightly higher. An alternating bias voltage applying means S ₀ is provided between the latent image carrier 1 and the sleeve 22.
By the DC bias voltage applying means S ₁ , the DC voltage and the AC voltage are applied by weight.

Thus, the substantially right half peripheral surface of the sleeve 22 is constantly in contact with the toner pool in the hopper 21, and the toner in the vicinity of the sleeve surface acts as a magnetic adhesion layer on the sleeve surface by the magnetic force of the magnetism generating means 23 in the sleeve and also as an electrostatic charge. It is attached and held by force. When the sleeve 22 is rotationally driven, the adhered toner layer on the sleeve surface is layered as a thin toner layer T ₁ having a substantially uniform thickness in each part while passing through the position of the doctor blade 24. The toner is charged mainly by frictional contact between the sleeve surface accompanying the rotation of the sleeve 22 and the toner in the toner pool in the vicinity thereof, and the toner thin layer surface of the sleeve 22 is one surface of the latent image holding member as the sleeve rotates. It rotates to the side and passes through the developing area A which is the closest portion of the latent image carrier 1 and the sleeve 22. In the course of this passage, the toner in the toner thin layer on the sleeve 22 surface flies by the direct current and the alternating electric field due to the direct current and the alternating voltage applied between the latent image carrier 1 and the sleeve 22 and the surface of the latent image carrier 1 in the developing area A. And the surface of the sleeve 22 reciprocate. Finally, the toner on the sleeve 22 side selectively moves and adheres to the surface of the latent image holding member 1 according to the potential pattern of the latent image, and toner images T ₂ are sequentially formed.

The sleeve surface on which the toner is selectively consumed after passing through the developing area A is re-rotated to the hopper 21 and the toner reservoir to be re-supplied with the toner, and the developing area A is always supplied with the thin toner of the sleeve 22. The surface of the layer T ₁ is rotated and the copying process is repeated.

By the way, as one of the problems in the case where such a developing method (one-component non-contact developing method) is adopted, there is a case where the developing property lowering phenomenon occurs due to an increase in the adhesive force of toner near the sleeve surface. In other words, the rotation of the sleeve 22 causes the toner and the sleeve to be constantly in contact with each other, and the electrostatic charge (Coulomb force) with the sleeve is increased by gradually increasing the charge amount of the toner, and the flight force of the toner to the latent image holding member 1 is increased. Is weakened, stays in the vicinity of the sleeve, inhibits triboelectrification of other toner, and deteriorates developability. This occurs due to low humidity and repeated copying processes. Similarly, the carrier memory described above also arises from the mechanism.

Now, the force for causing the toner to fly from the sleeve to the latent image holding member 1 must give an acceleration a so that it can reach the latent image surface sufficiently by the AC bias electric field. Toner weight is m
The force f is given by = m. Roughly, if the charge of the toner is q, the distance from the sleeve is d, and the alternating bias electric field is The reaching force of the toner to the latent image surface is determined by the balance between the electrostatic attraction force with the sleeve and the electric field force.

Here, in order to fly the toner of 5 μm or less that tends to collect near the sleeve, the electric field may be increased. However, simply increasing the developing-side bias voltage causes the toner particles to fly to the latent image side regardless of the latent image pattern, and toner particles having a particle size of 5 μm or less have a strong tendency to cause fog on a white background.
Further, white background fogging can be prevented by increasing the reverse development bias voltage, but when a large alternating bias electric field is applied between the latent image carrier 1 and the sleeve 22, discharge is directly generated between the latent image carrier 1 and the sleeve 22, It significantly disturbs the image quality.

Further, as the reverse developing bias voltage is increased, not only the non-latent image portion but also the toner developed in the latent image pattern is stripped off, and the mirror image power on the latent image holding member is relatively weak.
The toner particles of 12.7 μm are removed, the visible image pattern is disturbed, the toner sticking in the latent image portion is deteriorated, the gradation and the line reproducibility are deteriorated, and the intermediate dropout is likely to occur.

From the above results, it is necessary to cause the toner in the vicinity of the sleeve to fly and reciprocate while the alternating bias electric field is not increased so much and the reverse developing bias voltage is kept low.

Therefore, in the present invention, a magnetic toner having a particle size distribution that can have a triboelectrification amount on the toner carrier suitable for the developing method that controls not only the magnitude of the alternating bias electric field but also the application time is provided. Achieved the purpose. That is,
The developing-side bias electric field is increased without changing the frequency of the alternating bias, and the application time of the developing-side bias electric field is shortened, and accordingly, the reverse developing-side bias electric field is suppressed to a low level.
A method of controlling the duty ratio of the alternating bias voltage, in which the application time is lengthened, was used.

Here, the “duty ratio of the AC bias electric field” is defined by the following equation.

a: Application time of the electric field component of the polarity in the direction in which the toner is moved to the latent image holding member side in one cycle of the AC bias in which the electric field polarity alternately changes positively and negatively. At this time, the DC bias electric field is removed.

b: Conversely, the application time of the electric field component of the polarity in the direction of separating the toner from the latent image carrier side.This method is an essential component for improving the image quality on the sleeve by sufficiently strengthening the developing side bias electric field. This coincided with effective reciprocating flight of certain toner particles of 5 μm or less, and it was possible to prevent the toner particles from adhering to the sleeve surface. That is, it becomes difficult to reduce the image density and the carrier memory.

Further, even if the reverse developing side bias electric field is suppressed low, on the contrary, by applying for a sufficiently long time, a force for separating the excess toner adhering to other than the latent image pattern from the latent image holding body 1 is obtained, and white background fog is generated. It can be prevented.

At this time, the bias electric field on the reverse developing side is kept low, so that toner particles of 8 to 12.7 μm, which is an essential component for toner adhesion, are not stripped off. As an example, FIG. 6 shows the waveform of the alternating bias voltage used in the present invention.

That is, even if the reverse developing side bias electric field is weak, the effective value of the force of separating from the latent image holding member becomes the same by lengthening the time. In addition, since the toner image developed in the latent image pattern is not disturbed, it is possible to obtain good image quality with gradation.

By the way, within the range of the general formula (1), preferably within the range of the general formula (2), if the magnetic toner is similarly charged on the toner carrier, good developability can be obtained, and the development used in the present invention can be achieved. An image with excellent image quality can be obtained according to the law. However, at this time, the magnetic toner particles of 16 μm or more may be insufficiently charged and may not be used for development, which may cause a change in particle size distribution.

4 (μc / g) + 0.5 (μc / g) R ≤ Q (μc / g) ≤ 18 (μc / g) + 0.5 (μc / g) R ... (2) When Q <2 + 0.5R The magnetic toner particles of 8 to 12.7 μm are peeled off from the latent image holding member by the reverse developing bias, and the toner sticking is deteriorated, so that the intermediate gap and the line disturbance are likely to occur. Further, since the flying of toner particles is reduced, it is difficult to obtain a sufficient image density, and poor image quality is likely to be obtained.

On the other hand, in the case of Q> 20 + 0.5R, the magnetic toner particles of 5 μm or less are less likely to fly due to the developing bias in the present invention, and the high image quality, which is the effect of the magnetic toner of 5 μm or less, cannot be realized. In addition, the toner easily accumulates on the toner carrier, which hinders triboelectric charging of other toner particles, resulting in deterioration of the developing ability, resulting in a decrease in image density, memory of the carrier, rubbing, and fog on a white background.

Here, when the toner particles of 16 μm or more exceed 2% by volume, it is conceivable to increase the charge amount of the toner in order to prevent selective development.

In this case, since the number of particles having a large particle size increases, it goes without saying that the high image quality aimed at by the present invention cannot be achieved.
Lines, characters will be crushed, and scattering will occur due to excessive glue.

Further, it becomes difficult to prevent the toner particles having a particle size of 5 μm or less from being fixed on the toner carrier, and the developing bias of the present invention may cause an image density lowering carrier memory.

According to the present invention, the developing side bias electric field of the alternating bias electric field is strong and the toner in the vicinity of the sleeve can fly, so that the toner having a large electric charge in the vicinity of the sleeve is developed into a stronger latent image pattern. Therefore, it can be strongly adhered to a weak latent image pattern by the electrostatic force of toner having a high charge amount, and can be developed with good resolution having an edge effect in terms of image, and is an effective component for realizing high image quality. Magnetic toner particles having a particle size of 5 μm or less can be effectively used, and remarkably excellent image quality can be obtained.

In the developing method used in the present invention, the gap between the sleeve 22 and the latent image holding member 1 is 0.3 mm in the embodiment, but 0.1 mm to 0.5 mm is sufficient for the developing method according to the present invention. It can be developed.

As compared with the conventional developing method, the developing side bias becomes larger, so that the result can be developed even if the gap between the sleeve 22 and the latent image carrier 1 is large.

If the absolute value of the alternating bias voltage is 1.0 kV or more, a satisfactory image can be obtained. Further, considering the leak to the latent image carrier, the absolute value of the alternating bias voltage is preferably 1.0 kV or more and 2.0 kV or less. However, it is no wonder that this leak also fluctuates due to the gap between the sleeve 22 and the latent image carrier 1.

Next, the alternating bias frequency is preferably 1.0 kHz to 5.0 kHz. When the frequency is 1.0 kHz or less, the gradation is improved, but it is difficult to eliminate the white background fog. In the low frequency region where the number of reciprocating motions of the toner is small, the pressing force of the toner against the latent image holding member by the developing-side bias electric field becomes too strong even in the non-image part, and the toner peeling force by the reverse developing-side bias electric field also causes It is considered that this is because the toner attached to the non-image area cannot be completely removed. When the frequency is 5.0 kHz or higher, a bias electric field on the reverse developing side is applied before the toner sufficiently contacts the latent image holding member, resulting in a marked decrease in developability. That is, the toner itself cannot respond to the high frequency electric field.

Particularly, according to the present invention, the frequency of the alternating bias electric field is 1.5 kHz.
Showed optimum image quality at 3 kHz.

Finally, the duty ratio satisfying the alternating bias electric field waveform of the present invention may be less than about 50%, but considering the image quality, the duty ratio of 10% is preferably 40%. When the duty ratio exceeds 40%, the above-mentioned drawbacks become noticeable,
The effect of the present invention on higher image quality is weakened. If the duty ratio is less than 10%, the alternating bias electric field response of the toner itself, which has been described above, deteriorates and the developability deteriorates. Particularly, the optimum value of the duty ratio is 15% ≦ duty ratio ≦ 35%.

Further, as the alternating bias waveform, a rectangular wave, a sine wave, a sawtooth wave, a triangular wave, or the like can be applied.

Examples of the binder resin used in the magnetic toner of the present invention include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene and p-.
Phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, p Styrene and its derivatives such as -n-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; Unsaturated polyenes such as butadiene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl bromide; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate; methyl methacrylate, methacrylic acid Ethyl, propyl methacrylate, n-butyl methacrylate, methacrylic acid Isobutyl, methacrylic acid n
-Octyl, dodecyl methacrylate, methacrylic acid-2
-Methacrylic acid esters such as ethylhexyl, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, Acrylic esters such as n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl ether Doll, N- vinyl compounds such as N- vinyl pyrrolidone; vinyl naphthalenes; acrylonitrile, methacrylonitrile, acrylic acid or methacrylic acid derivatives such as acrylamide, acrylic acid,
Vinyl compound derivatives having a carboxyl group such as methacrylic acid, maleic acid, and fumaric acid; half esters such as maleic acid half ester and fumaric acid half ester; maleic anhydride, maleic acid ester, fumaric acid ester derivative; Homopolymers and copolymers containing a monomer component composed of a system compound; polyester, polyurethane, epoxy resin, polyvinyl butyral, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic system Petroleum resin, haloparaffin, paraffin wax, etc. may be used alone or in combination.

Of these, a styrene resin, an acrylic resin, and a polyester resin are particularly preferably used as the binder resin in consideration of the developing characteristics.

The binder resin as described above is more preferably a polymer cross-linked with a cross-linking agent as exemplified below, in consideration of offset resistance as a toner.

Aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, etc .; Diacrylate compounds linked by an alkyl chain such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-
Butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, and acrylates of the above compounds replaced by methacrylate; alkyl chains containing ether linkages Tethered diacrylate compounds, such as diethylene glycol diacrylate, triethylene glycol diacrylate,
Tetraethylene glycol diacrylate, polyethylene glycol # 400 diacrylate, polyethylene glycol # 600 diacrylate, dipropylene glycol diacrylate, and any of the above compounds in which the acrylate is replaced by methacrylate; a chain containing an aromatic group and an ether bond Bonded diacrylate compounds, for example, polyoxyethylene (2) -2,2-bis (4-hydroxyphenyl) propane diacrylate, polyoxyethylene (4) -2,2-bis (4-hydroxyphenyl) Propane diacrylate, and those in which the acrylates of the above compounds are replaced by methacrylates; and further, polyethylene ethacrylate type diacrylate compounds, for example,
Product name MANDA (Nippon Kayaku) is listed. As a polyfunctional crosslinking agent, pentaerythritol triacrylate,
Trimethylol ethane triacrylate, trimethylol propane triacrylate, tetramethylol methane tetraacrylate, oligoester acrylates, and those in which the acrylates of the above compounds are replaced by methacrylates; triallyl cyanurate, triallyl trimellitate; To be

These crosslinking agents are based on 100 parts of other monomer components,
It is preferable to use about 0.01 to 5 parts (more preferably about 0.03 to 3 parts).

Among these cross-linking agents, those which are preferably used in the resin for toner from the viewpoint of fixing property and anti-offset property, are linked by a chain containing an aromatic divinyl compound (particularly divinylbenzene), an aromatic group and an ether bond. Diacrylate compounds may be mentioned, and it is particularly desirable that at least one of them is contained in the binder resin.

Further, as the binder resin for the toner which is particularly subjected to the pressure fixing method, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, higher fatty acid, polyamide resin, It is preferable to use a polyester resin or the like alone or in combination.

The magnetic material contained in the magnetic toner of the present invention includes magnetite, maghematite, iron oxide such as ferrite, and iron oxide containing other metal oxides; metals such as Fe, Co, Ni, or these metals. And Al, Co, Cu, Pb, Mg, Ni, Sn, Zn,
Alloys with metals such as Sb, Be, Bi, Cd, Ca, Mn, Se, Ti, W, V,
And mixtures thereof.

These ferromagnetic materials have an average particle size of 0.1 to 2 μm,
Coercive force 20 to 150e Saturation magnetization 5
0-200emu / g (preferably 50-100emu / g), remanent magnetization 2
-20emu / g is preferable.

The magnetic toner of the present invention is preferably used by internally or externally adding a charge control agent to the toner so that a triboelectric charge amount suitable for the developing method can be obtained. As the positive charge control agent used in the present invention, known ones can be used. Examples thereof include nigrosine and its fatty acids, modified products thereof with fatty acid metal salts, quaternary ammonium salts, diorganotin oxide, diorganotin borate and the like alone or in combination with 2 It can be used in combination of two or more species. Among these, nigrosine type and quaternary ammonium salts are particularly preferably used.

Also, the general formula A homopolymer of a monomer represented by or a copolymer with a polymerizable monomer such as styrene, acrylic acid ester, and methacrylic acid ester as described above can be used as a positive charge control agent. It also functions as (a part or all of) the resin.

On the other hand, as the negatively charged property control agent used in the present invention, known compounds can be used, for example, a carboxylic acid derivative and a metal salt thereof,
The alkoxylates, organometallic complexes, chelate compounds and the like can be used alone or in combination of two or more. Among these, acetylacetone metal complex, salicylic acid metal complex, naphthoic acid metal complex, and monoazo metal complex are particularly preferably used.

In the toner of the present invention, any suitable pigment or dye can be used as a colorant, if necessary.

Further, the toner of the present invention may be mixed with an additive, if necessary. Examples of such additives include Teflon,
Lubricants such as polyvinylidene fluoride and fatty acid metal salts; Abrasives such as cerium oxide, strontium titanate, and silicon carbide; colloidal silica, alumina, or silicone oil, various modified silicone oils, silane coupling agents, silanes having functional groups. Flowability-imparting agents such as silica and alumina treated with coupling agents, anti-caking agents; conductivity-imparting agents such as carbon black and tin oxide;
Alternatively, there are fixing aids such as low molecular weight polyethylene. Also, for the purpose of improving the releasability at the time of fixing with a heat roll,
Wax-like substances such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, and sazol wax are added to the toner of the present invention in an amount of 0.
It is also possible to add about 5 to 5% by weight.

In the production of the toner according to the present invention, the toner constituent materials as described above are thoroughly mixed by a ball mill or other mixing machine, then well kneaded by using a heat kneader such as a heat roll kneader or an extruder, and after cooling and solidification. The method of obtaining the toner by mechanical pulverization and classification is preferable, and the method of obtaining the toner by spray-drying after dispersing the constituent materials in the binder resin solution; or the binder resin should be constituted. Polymerization method toner production method in which a predetermined material is mixed with a monomer to form an emulsion suspension, and then the mixture is polymerized to obtain a toner;
Alternatively, in a so-called microcapsule toner composed of a core material and a shell material, a method such as a method of incorporating a predetermined material into the core material or the shell material or both of them can be applied.

In the present invention, the charge amount of the toner layer on the carrier is determined by using the so-called suction type Faraday cage method. In this suction type Faraday cage method, the outer cylinder is pressed against the toner carrier to suck all the toner on a certain area on the carrier, and the toner is collected by the filter of the inner cylinder and the toner carrier increases from the weight increase of the filter. The weight of the top toner layer can be calculated. At the same time, this is a method in which the amount of charge on the toner carrier can be obtained by measuring the amount of charge accumulated in the inner cylinder that is electrostatically shielded from the outside.

In the present invention, the fine line reproducibility was measured by the following method. That is, an image obtained by copying an original document of a fine line with a width of 100 μm accurately under appropriate copying conditions is used as a measurement sample, and using a Luzex 450 particle analyzer as a measuring device, a line width is displayed by an indicator from an enlarged monitor image. Measure. At this time, since the measurement position of the line width has unevenness in the width direction of the thin line image of the toner, the average line width of the unevenness is used as the measurement point. From this, the fine line reproducibility value (%) is calculated by the following formula.

In the present invention, the resolution is measured by the following method. That is, it is a pattern consisting of 5 thin lines with the same line width and spacing, and 2.8,3.2,3.6,4.0,4.5,5.0,
5.6,6.3,7.1,8.0 Make an original image that is drawn like this. An image obtained by copying an original document containing these 10 types of line images under appropriate copying conditions is observed with a magnifying glass, and the number of images in which fine lines are clearly separated (the number of lines)
/ mm) as the value of resolution. The larger this number is, the higher the resolution is.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. All parts in the following formulations are parts by weight.

Further, FIG. 9 shows the relationship between the volume average particle diameter of the magnetic toner of the present invention and the charge amount on the toner carrier.

Example 1 The following magnetic toner copying test was conducted using an image forming apparatus having a developing device equipped with the selenium photosensitive drum described above.

The waveform of the alternating bias voltage used in this embodiment is shown in FIG. (Duty ratio 20%) After thoroughly mixing the above materials with a blender, they were kneaded with a twin-screw kneading extruder set at 150 ° C. The obtained kneaded product was cooled, coarsely pulverized by a cutter mill, then finely pulverized by a fine pulverizer using a jet stream, and the finely pulverized powder obtained was classified by a fixed wall type air classifier. A classified powder was produced. Furthermore, the obtained finely divided powder is rigorously classified with a multi-division classifier (Elbowjet classifier manufactured by Nittetsu Mining Co., Ltd.) using the Coanda effect to simultaneously remove black fine powder (magnetic toner). Obtained. The particle size distribution of this magnetic toner is shown in Table 1.

0.6 part of hydrophobic dry silica (BET specific surface area 300 m ^{2 /} g) was added to 100 parts of the obtained black fine powder magnetic toner, and mixed with a Henschel mixer.

The result of copying 10,000 sheets of this magnetic toner by the above-mentioned image forming apparatus and the volume average particle size on the toner carrier are shown in Table 2, and the charge amount of the toner on the toner carrier measured during the test is also shown. .

As is clear from Table 2, excellent resolution and fine line reproducibility,
An image with high image density without white background fogging was stably obtained, and no carrier memory was generated. Also 15 ℃, 10% RH
Similar good results were obtained below.

Examples 2 and 3 Instead of the magnetic toner used in Example 1, a particle size distribution as shown in Table 1 is obtained by changing the addition amount of a magnetic substance, a charge control agent, silica and controlling the fine pulverization classification conditions. A copy test was conducted in the same manner as in Example 1 except that toner was used. The results are shown in Table 2, and a stable and clear image was always obtained. Similar results were obtained in a copy test at 15 ° C and 10% RH.

Example 4 Table 1 shows the particle size distribution of the magnetic toner obtained using the above materials in the same manner as in Example 1.

Table 2 shows the results of the same copying test as in Example 1 using this toner. However, as the developing bias power source, the alternating bias voltage waveform (duty ratio shown in FIG.
30%) was used.

As can be seen from this table, an image with excellent image quality was obtained,
Similar results were obtained under 15 ° C and 10% RH.

Examples 5 and 6 In place of the magnetic toner used in Example 4, a particle size distribution as shown in Table 1 is obtained by changing the addition amount of a magnetic substance, a charge control agent, silica and controlling the fine pulverization classification conditions. A copy test was conducted in the same manner as in Example 4 except that toner was used. The results are shown in Table 2. A stable high-quality image was obtained, but in Example 5, a light carrier memory for one round of the toner carrier was found. Also
Similar results were obtained in a copy test under 15 ° C and 10% RH.

Example 7 An alternating bias voltage waveform is shown in FIG. 8 (duty ratio 35
%). The same copying test as in Example 1 was conducted except that the developing bias power source was used. The results are shown in Table 2.

In this case as well, good results were obtained as in Example 1.

Comparative Example 1 An alternating bias voltage waveform is shown in FIG. 3 (duty ratio 50
%). The same copying test as in Example 1 was conducted except that the developing bias power source was used. The results are shown in Table 2. As compared with Example 1, the gradation was inferior, the resolving power and the line reproducibility were slightly inferior, and a little white background fog was observed. A memory on the toner carrier was also found.

Comparative Example 2 A copying test was conducted in the same manner as in Example 1 except that a toner having a particle size distribution as shown in Table 1 was used by controlling the crushing and classification conditions from the coarsely crushed product obtained in Example 1. . The results are shown in Table 2. A good image was obtained in the initial stage, but when the copying was repeated, the image gradually became dull, and the resolution and fine line reproducibility became poor.

Comparative Example 3 Table 1 shows the particle size distribution of the magnetic toner obtained using the above materials in the same manner as in Example 1. Table 2 shows the results of the copy test conducted in the same manner as in Example 1.

The image density was low due to the voids, and the line thickness was not stable.

Comparative Example 4 Table 1 shows the particle size distribution of the magnetic toner obtained using the above materials in the same manner as in Example 1.

Table 2 shows the results of a copying test conducted in the same manner as in Example 1 using this toner.

A good image was obtained in the initial stage, but when the copying was repeated, the density decreased, and the carrier memory also occurred. 15 ℃, 10% R
In the copy test under H, this tendency became remarkable.

[Advantages of the Invention] Since the present invention is a magnetic toner having a specific particle size distribution and a triboelectric charge amount, it exerts the following excellent effects when applied to a developing method using an asymmetric developing bias.

(1) A magnetic toner that is excellent in durability, has a high image density, and gives an image without fog on a white background.

(2) A magnetic toner that is rich in gradation, excellent in resolving power and fine line reproducibility and gives a high quality image.

(3) A magnetic toner that does not cause a reduction in image density even under low humidity.

[Brief description of drawings]

FIG. 1 shows a schematic diagram of an alternating bias voltage waveform, FIG. 2 shows a schematic diagram of flying adhesion of toner, FIG. 3 shows a schematic diagram of alternating bias voltage waveform, and FIG. 4 shows explanation of bias components. FIG. 5 shows a schematic explanatory view of the developing device,
6 to 8 are schematic diagrams of alternating bias voltage waveforms, and FIG. 9 is a graph in which the volume average particle diameter of the magnetic toner and the target amount (μc / g) on the toner carrier are plotted. FIG. T ... toner, T ₁ ... thin toner layer T ₂ ... toner image, A ... developing regions alpha ... latent image bearing member and the toner carrying member gap S ₀ ... alternating bias applying means S ₁ ... DC-bias applying means 1 ... latent Holder, 21 ... Hopper 22 ... Toner carrier, 23 ... Magnetic roller 24 ... Doctor blade

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Kuniko Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masayoshi Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Incorporated (56) Reference JP-A-57-38440 (JP, A) JP-A 1-219761 (JP, A) JP-A 1-219762 (JP, A) JP-A 1-219847 (JP, A) A)

Claims (1)

[Claims] 1. A latent image carrier that holds an electrostatic charge image and a toner carrier that carries magnetic toner on its surface are arranged in the developing section with a certain gap, and the magnetic toner is placed on the toner carrier. The toner is regulated to have a thickness smaller than the gap and is conveyed to the developing unit. In the developing unit, a DC bias and an asymmetric AC bias are applied between the toner carrier and the latent image carrier to form an alternating bias electric field. The bias electric field has a voltage component on the developing side and a voltage component on the reverse developing side, makes the voltage component on the developing side equal to or larger than the voltage component on the developing side, and sets the application time of the voltage component on the developing side to the voltage on the developing side. A magnetic toner containing at least a binder resin and magnetic powder used in a developing method for shortening the application time of components, wherein the magnetic toner contains 12% by number or more of magnetic toner particles having a particle size of 5 μm or less, ~ 12 Magnetic toner particles having a particle size of 0.7 μm are contained in an amount of 33% by number or less and 16 μm
The magnetic toner particles having the above particle diameter are contained in an amount of 2% by volume or less, the volume average particle diameter of the magnetic toner is 4 to 10 μm, and the frictional charge amount of the magnetic toner particles on the toner carrier and the magnetic toner particles A magnetic toner having a volume average particle size satisfying the following general formula (1).