JP2003029454A - Magnetic toner and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide magnetic toner where sufficient image formation can be carried out by a non-magnetic one component developing method. SOLUTION: In the method, magnetic powder, binder resin and wax are provided and surface processing is carried out on the magnetic toner by using a composite additive consisting of 2 types of additives with different primary particle diameters. The magnetic toner can be applied for the non-magnetic one component image forming method. This method can be applied effectively for formation of a MICR image where printing of magnetic characters is carried out. Moreover, the benefits of a non-magnetic one component developing system, which are high speed and small size of the device, are also taken advantage of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner used in an image forming method of a non-magnetic one-component developing system in an electrophotographic method, an electrostatic printing method, an electrostatic recording method or the like, and more particularly to a magnetic ink symbol identification (Magnetic Ink). Ch
actor Recognition, below "MI
It is a magnetic toner suitable for forming magnetic characters to be read by a system.

[0002]

2. Description of the Related Art Image forming methods such as electrophotography and electrostatic recording have been applied to office automation equipment such as copying machines, printers and facsimiles. For example, an electrophotographic method is used in which an electrostatic latent image on the surface of a photoconductor is converted into a toner image by a developer, the toner image is transferred to a medium such as paper, and the medium on which the toner image is transferred is passed through a heating roller to be fixed. The known image forming method is well known.

Developers include two-component developers composed of toner and carrier, and one-component developers composed of toner without carrier. The one-component developer is
The toner has a structure in which a colorant is dispersed in a binder resin. Such toner includes magnetic toner and non-magnetic toner. The magnetic toner is composed by further mixing magnetic powder such as black magnetite in a binder resin as a main component, and is suitable for forming a monochrome image.

The black color of magnetite interferes with the colorization of an image, so that the demand for a non-magnetic one-component developer comprising a non-magnetic toner is increasing. Furthermore, in recent years,
In addition to the above colorization, there is a strong demand for speeding up of image formation, and it is said that a non-magnetic one-component developer is suitable for such speeding up.

In a developing system using such a non-magnetic one-component developer, the non-magnetic toner is charged during image formation so that the electrostatic latent image formed on the surface of the photoconductor becomes a toner image. The charging is generally performed by passing the non-magnetic toner conveyed to the developing roll between the tip of the elastic blade whose tip is pressed against the surface of the developing roll and the surface of the developing roll to frictionally charge the toner.

On the other hand, in recent years, along with the widespread use of image forming apparatuses such as electrophotographic copying machines, the applications thereof have been diversified, and a character printer used for MICR system has been devised as an application field of electrophotographic printers. Has been done.

This MICR system is designed mainly for printing information such as check banks, bills, etc. using a magnetic ink, such as a bank, amount and account number, and for efficiently sorting and classifying at a clearing house using a magnetic reader. It was done. In the past, offset printing using magnetic ink was the mainstream, but small MICRs have become smaller as business transactions such as personal checks and bills have become more active.
There is an increasing demand for character printing machines (hereinafter referred to as "MICR encoders").

The mainstream of such MICR encoders are impact printers to which the thermal copying method is applied, but in this case, most of them are single-function machines that print only MICR characters and cannot be used for general document preparation. . Therefore, it is possible to print general documents and / or graphics, and also to print the above MICR characters.
Moreover, the advent of a versatile electrophotographic printer exhibiting a good MICR recognition rate is desired.

[0009]

Since MICR printing uses a toner containing magnetic powder, a magnetic one-component developing method using a magnetic one-component developer, or a magnetic two-component mixture of a magnetic toner and a magnetic carrier is used. It is carried out by a magnetic two-component developing method using a developer. Printing is performed by a developing method using so-called magnetic toner.

However, the magnetic one-component developing method or magnetic two-component developing method using magnetic toner is a non-magnetic one-component developing method using non-magnetic toner, or a non-magnetic toner prepared by mixing non-magnetic toner and non-magnetic carrier. Compared with the magnetic two-component developing method, the amount of charge is low and the charging speed is slow, so high-speed development is difficult.

On the other hand, the two-component developing system requires a mechanism for mixing carrier and toner in the apparatus, as compared with the one-component developing method, and therefore the apparatus cannot be downsized accordingly. In recent years, there is a strong demand for small size and high speed.

Further, the magnetic developing system using the magnetic toner has a larger specific gravity and consumes a larger amount of toner than the non-magnetic developing system using the non-magnetic toner.

Therefore, it is preferable that printing can be performed by a non-magnetic developing method using magnetic toner. In particular, if the magnetic toner can be used in the non-magnetic one-component developing method, it is preferable because the apparatus can be downsized and the speed can be increased.

However, MI for conventional magnetic one-component developer
If the CR toner is used in a non-magnetic one-component developing system capable of high-speed development, a sufficient amount of image density cannot be obtained because of a low charge amount, and fog increases. Further, in the non-magnetic one-component developing method, since toner is pressed against the developing roll and the elastic blade to perform triboelectrification, the conventional magnetic toner is inferior in durability and the magnetic toner adheres to the blade. There has occurred.

An object of the present invention is to provide a magnetic toner which can be applied to a non-magnetic one-component developing system to form MICR magnetic characters.

[0016]

The magnetic toner of the present invention comprises:
A toner used in a one-component developing system, which contains magnetic powder, a binder resin, and wax, and is used in an image forming method based on a non-magnetic one-component developing system. The surface of the magnetic toner is characterized by containing a plurality of types of external additives having different primary particles having a difference in volume average particle diameter of 5 to 50 nm.

The magnetic powder preferably has a residual magnetization of 24 to 40 emu / g after application of 10 k Oersted, and the content of the magnetic powder in the magnetic toner of the present invention is preferably less than 35% by weight. . The magnetic toner preferably has a residual magnetization of 7 to 20 emu / g.

Another aspect of the present invention is an image forming method for use in a non-magnetic one-component developing system for developing an electrostatic latent image formed on a surface of a photoconductor with a magnetic toner, wherein the magnetic toner is any one of the above. The magnetic toner described in (1) is used. The non-magnetic one-component developing system is at least a photoconductor, a charger that charges the surface of the photoconductor, an exposure device that forms an electrostatic latent image on the photoconductor surface, a transfer device that transfers the toner image on the photoconductor surface to a transfer material, The developing system includes a developing roll facing the photoconductor (however, it does not have a permanent magnet therein), an elastic blade in pressure contact with the developing roll, and a toner hopper for supplying toner to the developing roll.

In each of the above inventions, the residual magnetization of the magnetic powder is 24
If it is less than emu / g, the ratio of the magnetic powder added to obtain the required residual magnetization of the toner becomes too large, and the chargeability of the toner becomes poor and the developability deteriorates. If it exceeds 40 emu / g, toner agglomeration tends to occur. Therefore, 24-40
It is preferably emu / g. More preferably 2
It is in the range of 7 to 38 emu / g.

The residual magnetization of the magnetic toner is 7 to 20 emu /
g is preferable, and when it is less than 7 emu / g, the recognition rate (magnetic strength) is lowered, and when it is more than 20 emu / g, aggregation of the toner is likely to occur.

The magnetic powder contained in the magnetic toner is determined so that the residual magnetization of the magnetic toner is within an appropriate range, but it is preferably less than 35% by weight.

The amount of triboelectric charge is -10 to-for negative charge.
The range of 70 μc / g, and the range of +5 to +50 μc / g for positive charging is preferable.

The binder resin is styrene-acrylic type,
It is only necessary to select a resin having characteristics suitable for the fixing system, such as polyester, epoxy, and phenoxy resin. The fixing method suitable for the present invention is heat roll fixing, flash fixing,
Oven fixing.

The magnetic powder is magnetite, Ba ferrite,
A material having a relatively large coercive force or residual magnetization such as Sr ferrite is preferable. A combination of two or more may be used. The shape of the magnetic powder depends on the crystals, but the granular shape is less likely to be exposed on the toner surface than the acicular shape, and therefore, the leakage of charging is less likely to occur, and thus the charging holding ability is excellent and stability is preferable.
The size of the magnetic powder is preferably 1.0 μm or less.

In order to improve the affinity with the binder resin and improve the dispersibility in the toner, it is preferable to hydrophobize the surface of the magnetic powder with a titanate coupling agent or a silane coupling agent. If the ratio of the magnetic powder is large, the charging property and the developing property of the toner are deteriorated. Therefore, the content of the magnetic powder in the toner should be an amount capable of giving the remanent magnetization necessary for magnetic reading, and this is insufficient. It is preferable to supplement the color tone and blackness of the toner with a colorant such as carbon black or dye / pigment.

Wax is added to improve the surface smoothness of the printed surface. Low molecular weight polyethylene, polypropylene, ethylene-propylene copolymer, modified polyethylene, modified polypropylene, Fischer-Tropsch wax, Sazol wax, montanic acid wax, galvana wax and the like can be used. The addition amount is preferably about 1 to 6%. The wax is preferably uniformly dispersed in the toner, and can be dispersed in the binder resin in advance.

The charge control agent is selected according to the polarity of the toner. Chromium azo complex, iron azo complex, salicylic acid metal complex, calixarene and the like are preferable for the negative chargeability, and nigrosine dye and phenylmethane dye are preferable for the positive chargeability.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to Examples. In the examples described below, an image forming apparatus for a non-magnetic one-component developing system having the following structure was used.

The basic structure of the image forming apparatus used in the embodiment is a negatively chargeable OPC photosensitive member formed in a drum shape, and a charging device, an exposing device, a developing roll, and a transfer charging device on the peripheral surface thereof. , And a cleaner are arranged to face each other in order. The developing roll has a conductive shaft connected to a bias voltage source and a conductive elastic layer, and is capable of developing by a contact developing system in a developing area arranged facing the OPC photosensitive member. The developing roller is not provided with magnetic field generating means such as a permanent magnet.

In the above structure, the OPC photosensitive member does not have to have a drum shape, and may have, for example, a conventionally known belt shape. Further, the magnetic toner of the present invention can be applied to a non-magnetic one-component developing system by a non-contact developing system.

The surface of the OPC photosensitive member is uniformly charged by a charger while rotating at a constant peripheral speed. As such a charger, a scotron for corona discharge may be used. In addition to corona discharge, roller charging, brush charging, or magnetic brush charging may be used.

The charged surface of the OPC photosensitive member is further exposed to an optical image by an exposing device to form an electrostatic latent image on the surface of the OPC photosensitive member. The electrostatic latent image is carried on the surface of the rotating OPC photosensitive member, and is conveyed to the developing area where the developing rolls are opposed to each other. The electrostatic latent image is visualized as a toner image by the magnetic toner of the present invention, which is electrostatically carried on the surface of the developing roll connected to the bias voltage source and conveyed to the developing area.

The magnetic toner used in such a non-magnetic one-component developing system is agitated by an agitator in the toner hopper and is first carried on the surface of a rotating replenishing roller, and then the developing roller is rotated with an adjacent potential difference. It is transferred and carried on the surface of the roll. The magnetic toner carried on the surface of the developing roll is conveyed to the side of the elastic blade pressed against the peripheral surface of the developing roll with a predetermined pressure, and is charged when passing under the elastic blade.

The magnetic toner having a predetermined layer thickness that has been charged while passing through the elastic blade is pressed against the surface side of the OPC photosensitive member with a predetermined linear pressure to electrostatically attract the magnetic toner to the electrostatic latent image. Contact development is performed.

Either one of the OPC photosensitive member and the developing roll is structured to have an elastic surface so that the magnetic toner is appropriately brought into pressure contact with the electrostatic latent image during the contact development. For example, at least the surface portion of the developing roll is formed of an elastic material such as urethane or EPDM,
It is sufficient to obtain an elastic surface.

The toner image thus formed on the surface of the OPC photosensitive member is further conveyed to the transfer area where the transfer charger is disposed oppositely. In the transfer area, a material to be transferred such as paper is sent between the transfer charging device and the toner image so that the transfer of the toner image is performed on the back surface of the transfer material from the transfer charging device. The toner image is transferred onto the transfer target material by applying a charge having a polarity opposite to the polarity.

A corona discharge roller or roller for corona discharge may be used as the transfer charger. After that, the transfer material to which the toner image has been transferred is sent to a heat roll portion in which a heating roll and a pressure roll are opposed to each other at a predetermined interval, and the toner image is subjected to pressure heat treatment when passing between the heat roll portions. Heat-roll fixing is performed on the material to be transferred. The toner image may be fixed by pressure fixing or oven fixing.

On the other hand, on the surface of the OPC photosensitive member after the transfer of the toner image, the residual developer is removed by a cleaner. In this embodiment, a conventional blade is used as the cleaner so that the magnetic toner remaining on the surface of the OPC photosensitive member without being transferred can be scraped off. Of course, the present invention can be applied to a configuration without such a cleaner.

Image formation was performed under the following conditions using the above image forming apparatus. As the OPC photosensitive member, a drum-shaped OPC photosensitive member with a diameter of 24 mm is used, and the process speed (V
(P: also referred to as peripheral speed) was rotated at 120 mm / sec, and the surface potential (V0) was set to -480 V with a scotron. The residual potential (VL) of the surface of the OPC photosensitive member after the light image exposure was -30V.

The developing roll has a diameter (φ) of 15 mm,
A urethane rubber roll containing a conductive agent and a foaming agent having a volume resistance (R) of 250 Ω · cm was used. A peripheral speed of 130 mm, which is slightly faster than the OPC photosensitive member
Contact development was carried out by bringing the OPC photosensitive member into pressure contact with the toner layer via a toner layer at a pressure (linear pressure) of 10 g / cm while rotating at a rotation speed of / sec.

The thickness of the magnetic toner layer is 0.03 when a stainless steel blade is used as the elastic blade.
It is regulated to be mm.

Further, for the transfer and fixing of the toner image, a corotron was used as a transfer charger, plain paper was used as the material to be transferred, and heat roll fixing was performed at a fixing temperature of 180 ° C. and a linear pressure of 1 Kg / cm. . In the cleaner, the residual toner was removed by bringing a urethane blade into contact with the surface of the OPC photosensitive member after transfer at a linear pressure of 5 g / cm.

Next, the magnetic toner of the present invention used in an apparatus used in an image forming method based on the non-magnetic one-component developing system having the above-mentioned structure will be described.

[0044]

EXAMPLES Example 1 The magnetic toner of Example 1 has the following constitution. Polyester resin (Tg: 64 ° C, Tm: 136 ° C) 69 parts by weight Polypropylene (NP105) 4 parts by weight Polyethylene (220MP) 1 part by weight Charge control agent (TRH) 1 part by weight Magnetic powder (MAT740) 25 parts by weight With the above configuration The magnetic powder was surface-treated with a silane coupling agent (Toray Dow Corning Silicone, SH6040).

The above components were mixed by a Henschel mixer and kneaded at a set temperature of 120 ° C. by a biaxial extrusion kneader equipped with a cooling device. Then, it was cooled and crushed with a drum breaker, and further subjected to a Rotoflex coarse crusher. The fine pulverization was pulverized with a rotor stator type pulverizer T250 type, and the lower limit classification was performed with Microflex to obtain particles having a volume average particle size of 10 μm and a distribution of 5 to 15 μm.

As external additives to the particles, HMDS-treated silica having a primary particle diameter of 10 nm (external additive A): 0.5% by weight, and HMDS-treated silica having a primary particle diameter of 30 nm (external additive) The magnetic toner of Example 1 was prepared by mixing 0.5% by weight of the agent B) with a Henschel mixer. The saturation magnetization σs (10 kOe) of the obtained magnetic toner is 20.5.
(Emu / g), the residual magnetization σr is 13.5 (emu / g)
g). The amount of charge by blow-off TB200 is-
It was 48.5 μc / g.

MICR printing was performed under the following conditions by using the magnetic toner having such a structure and the image forming apparatus having the above structure, and the results are shown in the table.

[0048]

[Table 1]

The values of the saturation magnetization and the residual magnetization shown in Table 1 were obtained by packing the toner in capsules and using a vibration type magnetic measuring device (VSM). The image density is a reflection densitometer (Macbeth R
The image density according to D914) is 1.35 or more, preferably 1.40 or more. The fog value was expressed as the difference (dH) in the whiteness of the hunter between the white paper before printing and the white background after printing.
The smaller this value is, the less the fog on the white background, and it is preferably 0.5 or less.

In order to correctly recognize the MICR font printed by the magnetic reader, the MICR font has an appropriate magnetic reading strength (Magnetic Strength, Signal Strength).
It is also necessary to have). The magnetic strength standard is set by each country, but is generally 100-200.
%. In this example, the lower limit of the magnetic strength was 110%.

Example 2 The magnetic toner of Example 2 is
It has the following configuration. Polyester resin (Tg: 67 ° C., Tm: 140 ° C.) 75 parts by weight Polypropylene: Viscol 550P 2 parts by weight Polyethylene: Umex 110TS 2 parts by weight Charge control agent (T95) 1 part by weight Magnetic powder (KBN400) 20 parts by weight With the above configuration The magnetic powder was surface-treated with a titanate coupling agent (Plainact TTS manufactured by Ajinomoto Co., Inc.).

The above components were mixed by a Henschel mixer and kneaded at a set temperature of 140 ° C. by a biaxial extrusion kneader equipped with a cooling device. Then, it was cooled and crushed with a drum breaker, and further subjected to a Rotoflex coarse crusher. The fine pulverization was pulverized with a rotor stator type pulverizer T250 type, and the lower limit classification was performed with Microflex to obtain particles having a volume average particle size of 11 μm and a distribution of 5 to 15 μm.

External additives A: 0.
A magnetic toner of Example 2 was prepared by mixing 5% by weight and 0.3% by weight of titanium oxide having a primary particle diameter of 30 nm (STT30A external additive C manufactured by Titanium Industry Co., Ltd.): 0.3% by weight. The saturation magnetization σs (10 kO
e) is 17.2 (emu / g) and the residual magnetization σr is 13.
It was 0 (emu / g).

The charge amount by the blow-off TB200 is -4.
It was 2.3 μc / g. Using the magnetic toner having such a configuration, the image forming apparatus having the configuration described above is used, and
MICR printing was performed under the same printing conditions as above. The results are shown in the table.

(Example 3) The magnetic toner of Example 3 is
It has the following configuration. Styrene-acrylic resin (styrene n-BA Tg: 62 ° C., Tm: 134 ° C.) 75 parts by weight Polypropylene: Viscol 550P 3 parts by weight Polyethylene wax (Mitsui High Wax 220MP) 1 part by weight Charge control agent (T2N) 1 part by weight Magnetic Powder (KBN400) 10 parts by weight (KBI20VH) 15 parts by weight The above components were mixed by a Henschel mixer, and kneaded at a set temperature of 120 ° C. by a twin-screw extrusion kneader equipped with a cooling device. After that, cool and crush with a drum breaker,
Further, it was subjected to a Rotoflex coarse crusher. Fine pulverization is pulverized with a rotor stator type pulverizer T250 type, and the lower limit classification is performed with Microflex, and the volume average particle size is 10μ.
Particles with m and 5 to 15 μm distribution were obtained.

As external additives to the particles, HMDS-treated silica having a primary particle diameter of 7 nm (external additive D): 0.4% by weight, and primary particles having a surface treatment with silicone oil 30
0.4% by weight of silica (external additive E) of nm was mixed by a Henschel mixer to prepare a magnetic toner of Example 3.

The saturation magnetization σs (10
kOe) is 21.1 (emu / g) and the residual magnetization σr is 1
It was 2.2 (emu / g). Blow off TB200
The amount of electrification was −38.5 μc / g. Using the magnetic toner having such a structure, MICR printing was performed under the same printing conditions as in Example 1 by the image forming apparatus having the above structure. The results are shown in the table.

Next, in order to evaluate the magnetic toners of the present invention described in Examples 1 to 3, magnetic toners having the following structures were prepared as comparative examples, and printing similar to those in Examples 1 to 3 was performed. MICR printing was performed under the conditions, and the results are shown in the table.

(Comparative Example 1) Only the composition of the magnetic powder of the magnetic toner of Example 2 was changed, and the other structures were the same. As the magnetic powder, 35 parts by weight of KBN20VH alone was used to prepare a magnetic toner containing an excessive amount of magnetic powder. The results of printing using the magnetic toner having such a structure are shown in the table. When the amount of magnetic powder is large, the amount of charge is small and the image density of the non-magnetic toner is low.

Comparative Example 2 Magnetic powder KBN400 of the magnetic toner of Example 2 was halved to 10 parts by weight to form a magnetic toner having an insufficient content of magnetic powder. The results of printing using the magnetic toner having such a structure are shown in the table. If the amount of magnetic powder is too small, the magnetic strength of the characters decreases and the reader cannot accurately identify the characters.

Comparative Example 3 In the magnetic toner of Example 1, only 0.7% by weight of the external additive A was used as the external additive. The other configurations are the same as those of the magnetic toner of Example 1. That is, a magnetic toner was formed using only an external additive having a small particle size as an external additive. The printing results using the magnetic toner are shown in the table.

Comparative Example 4 In the magnetic toner of Example 1, only 0.5% by weight of the external additive B was used as the external additive. The other configurations are the same as those of the magnetic toner of Example 1. That is, the magnetic toner was prepared using only the external additive having a large particle size. The printing results using the magnetic toner are shown in the table. From Table 1 above, it can be seen that the magnetic strength is better when all the magnetic toners of Examples 1 to 3 are used than in Comparative Example, except for Comparative Example 3.

Comparative Example 5 In the magnetic toner of Example 1, 0.5% by weight of the external additive B and 0.5% by weight of the external additive C were used as the external additives. Other than that, the first embodiment is used.
The same as the magnetic toner of That is, the magnetic toner was prepared by using two kinds of external additives having different materials but substantially the same volume average particle diameters. The printing results using the magnetic toner are shown in the table.

The image densities of Examples 1 to 3 were all 1.39 or more, and it was found that a sufficient image density was obtained. On the other hand, in Comparative Examples 1, 4, and 5, it was confirmed that sufficient image density could not be obtained.

The fog was 0.3 or less in all the examples, and it was confirmed that the fog was sufficiently suppressed.

Regarding the durability test (sticking), except for the case of Comparative Example 3, good results similar to those of Examples and Comparative Examples were obtained.

From the results of the above examples and comparative examples, the following was verified. That is, from the results of Examples and Comparative Examples 1 and 2, in the magnetic toner used in the non-magnetic one-component developing system, the magnetic powder content affects the magnetic strength, and the content is within a certain range. It can be seen that it is effective to keep the magnetic strength within an appropriate range. That is, it is understood that the range of at least 25 parts by weight and less than 35 parts by weight is preferable for maintaining the magnetic strength of 115 or more.

On the other hand, from the results of Examples and Comparative Examples 3 to 5, the influence of the external additive on the developability of the magnetic toner can be confirmed. When only the external additive A having a small particle size is used, the magnetic strength is good, but the toner is apt to adhere to the sleeve surface. On the other hand, when only the external additive having a large particle size is used, the durability is good, but the charge amount is small due to insufficient fluidity of the toner, and therefore the image density is low. As a result, the magnetic strength of the character is reduced. From these results, it is presumed that the combined use of the external additives having different particle diameters maintains the balance between durability and magnetic strength and improves both.

From the above results, the magnetic toner having the constitution of the present invention, when applied to the image forming method based on the non-magnetic one-component developing system, has good magnetic strength, proper image density and no fog. It was confirmed that magnetic characters could be formed.

Therefore, by using the magnetic toner of the present invention, the model to which the non-magnetic one-component developing system is applied can be
It can be configured as a CR printer, and can be made smaller and faster than ever before.

[0071]

According to the present invention, in an image forming method based on a non-magnetic one-component developing system, a magnetic toner can be used to form an excellent image.

In the present invention, since the magnetic toner can be applied to the non-magnetic one-component image forming method, it can be effectively used for forming an MICR image for printing magnetic characters. At the same time, it is possible to enjoy the advantages of the non-magnetic one-component developing system such as high speed and downsizing of the apparatus.

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Claims (6)

[Claims] 1. A magnetic toner containing a magnetic powder, a binder resin, and a wax, which is used in an image forming method based on a non-magnetic one-component developing system. 2. The magnetic toner according to claim 1, wherein the magnetic toner has a volume average particle size difference of 5 to 50 n.
A magnetic toner containing a plurality of types of external additives having different primary particle diameters of m. 3. The magnetic toner according to claim 1, wherein the magnetic powder has a residual magnetization of 24 to 40 emu / g. 4. The magnetic toner according to claim 1, wherein the content of the magnetic powder is less than 35% by weight. 5. The magnetic toner according to claim 1, wherein the magnetic toner has a residual magnetization of 7 to 20 emu /
Magnetic toner characterized by being g. 6. An image forming method using the magnetic toner according to claim 1 to form an image by an image forming method based on a non-magnetic one-component developing system.