JPH117150A - Image forming method and negative electrification type non-magnetic toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high-definition image by using a negative electrification type OPC(organic) photoreceptor and negative electrification type non-magnetic toner for non-contact reversal development. SOLUTION: By optical image exposure, an electrostatic latent image is formed on the surface of the negative electrification type OPC photoreceptor 10 and carried to a developing area. Meanwhile, the negative electrification type non-magnetic toner (non-magnetic one-component developer) whose ratio of volume average particle size (d75 /d25 ) shows a value 1.21 to 1.35 is carried on the surface of a rotating developing roll 40 with layer thickness thinner than a developing gap (g) and fed to a developing area. By impressing DC bias and AC bias on the roll 40, the non-magnetic toner is made to fly to the electrostatic latent image so as to form a toner image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method for visualizing an electrostatic latent image formed on a surface of a negatively chargeable OPC photoreceptor (negatively chargeable organic photoreceptor) by reversal development using a non-contact development method and an image forming method therefor. The present invention relates to a negatively charged non-magnetic toner used.

[0002]

2. Description of the Related Art An electrophotographic image forming method for forming an electrostatic latent image by exposing a uniformly charged photoreceptor surface to a light image to form an electrostatic latent image, and visualizing the electrostatic latent image as a toner image with a developer is known. , Copier, printer, facsimile, etc.
Used for A equipment.

As a dry developer used in such an electrophotographic image forming method, a one-component developer and a two-component developer are known. The two-component developer is composed of a toner and a carrier. The two-component developer applies an electrostatic charge to the toner by frictional charging with the carrier, and electrostatically attaches the toner to an electrostatic latent image formed on the surface of the photoreceptor to form a toner image. Is a developer used in a developing method for forming a toner image.

In an image forming method using a two-component developer, charging of toner is favorably performed by friction with a carrier, so that image density and the like are stable.

However, since the image quality is greatly affected by the mixing ratio of the toner and the carrier, the mixing ratio of the toner and the carrier must always be kept within a certain range. Therefore, it is necessary to provide a toner density control unit or a supply unit for supplying replenishing toner in the image forming apparatus, which makes it difficult to reduce the size of the image forming apparatus.

Further, in the case of a two-component developer, spent toner adheres to the surface of the carrier due to long-term use, and charging cannot be performed satisfactorily on the toner. Was needed.

[0007] In order to solve such a problem, an image forming method using a one-component developer has been proposed. One-component developers include those using magnetic toner and those using non-magnetic toner.

In a one-component developer using a magnetic toner,
Since the toner is carried on the developing roll by the magnetic force, transportability of the developer to the developing area is relatively relatively secured, and stable image quality can be obtained as in the case of the two-component developer.

However, in the above-described one-component magnetic developer composed of a magnetic toner, magnetite is usually used as a magnetic powder, so that there is no problem in forming a monochrome image. However, in forming a color image, the black color of magnetite is an obstacle and cannot be used. Attempts to conceal black color by coating magnetite have been proposed, but are difficult to adopt in terms of cost.

Therefore, use of a non-magnetic one-component developer composed of a non-magnetic toner has been proposed.

[0011] Development methods using such a non-magnetic one-component developer include contact development and non-contact development.

Contact development is a method in which a developer carried on the surface of a developing roll is directly brought into contact with an electrostatic latent image on the surface of a photoreceptor to perform development. On the other hand, in non-contact development, the electrostatic latent image formed on the surface of the photoconductor is conveyed to a developing area in which a gap between the photoconductor and the developing roll is held at a constant developing gap, and the electrostatic latent image is On the surface of the developing roll, a developer layer regulated to a layer thickness smaller than the developing gap interval is carried and conveyed, and the toner in the developer is caused to fly to the electrostatic latent image side to form a toner image of an electrostatic latent image. How to

In the contact development, the image density is sufficiently ensured because the developer directly contacts the electrostatic latent image as described above.
However, since the developer inevitably comes into contact with the non-image portion, there is a disadvantage that unnecessary toner adhesion occurs in the non-image portion. In particular, toner adhesion to a non-image portion is a major obstacle in terms of color reproducibility of an image in a color image forming method in which single color development is repeated.

Therefore, in the color image forming method, non-contact development which can easily avoid unnecessary adhesion of a developer to a non-image portion is replaced with contact development in which a one-component non-magnetic toner is brought into direct contact with an electrostatic latent image. Attention has been paid.

[0015]

However, it has been pointed out that non-contact development using a one-component developer composed of a non-magnetic toner does not provide a fine-textured image, that is, a so-called high-definition image. I have.

On the other hand, recently, in addition to a copying machine, an electrophotographic image forming method has been frequently used in an output section of a printer using plain paper. Therefore, considering high-speed output and downsizing of the device, as well as colorization of images, good image forming technology by non-contact development using a non-magnetic one-component developer that does not require carrier replacement is indispensable. is there.

In particular, since input units such as printers have recently been equipped with high-resolution scanners, printer output units have been required to further improve image definition. I have.

It is an object of the present invention to form a high-definition image by using a negatively chargeable OPC photosensitive member and a negatively chargeable non-magnetic one-component developer in a non-contact development system. .

It is an object of the present invention to provide a negatively charged non-magnetic one-component developer capable of forming a high-definition image in non-contact development using a negatively charged OPC photosensitive member.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0021]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, in the image forming method of the present invention, the negatively chargeable OPC whose surface is negatively charged by corona discharge or the like.
An electrostatic latent image is formed on the surface of the photoreceptor by light image exposure, and while the electrostatic latent image is carried on the surface of the negatively chargeable OPC photoreceptor, the developing roll is moved through a developing gap at a predetermined interval. The sheet is conveyed to a developing area opposed to the surface of the chargeable OPC photosensitive member.

As the negatively chargeable OPC photosensitive member, a laminated type OPC photosensitive member generally used for negative charge may be used. A single-layer OPC photoconductor can be used as long as it is negatively chargeable. Further, the shape of the negatively chargeable OPC photosensitive member may be a drum shape or a belt shape.

On the other hand, on the surface of the developing roll, a thin layer of a negatively charged non-magnetic toner of a one-component developer regulated to a constant layer thickness smaller than the developing gap by a blade or the like is electrostatically carried, It is transported to the developing area.

In the developing area, a DC bias and an AC bias are applied to the developing roller carrying the negatively charged non-magnetic toner to apply the developing roller to the electrostatic latent image on the surface of the negatively charging OPC photosensitive member. The electrostatic latent image is visualized by electrically flying the negatively charged non-magnetic toner on the surface. In this way, reversal development by non-contact so-called jumping development is performed.

When the DC bias is applied, the surface potential (V ₀ ) of the surface of the negatively chargeable OPC photosensitive member is 0.7 to 0.9.
What is necessary is just to apply in twice the range. The AC bias may have a frequency of 1 KHz or less and a peak-to-peak value (V _pp ) in the range of 500 to 2 KV.

The layer thickness of the non-magnetic one-component developer is regulated as follows.
The layer thickness may be regulated by using an insulating roll other than the blade.

The developing roll is rotated at a speed equal to or higher than that of the OPC photosensitive member having, for example, an electrostatic latent image on its surface (the rotating direction may be the same or the opposite direction). The flying of the negatively charged non-magnetic toner may be performed.

Thereafter, the electrostatic latent image visualized in this way, that is, the toner image may be transferred to plain paper or the like and then fixed by a method such as heat roll fixing.

On the other hand, the negatively charged non-magnetic toner used in the image forming method having the above-mentioned structure comprises a binder resin, a colorant, a charge control agent (optional component) and a release agent (optional component). Further, a fluidization improver, a lubricant, an abrasive, and the like may be appropriately externally added.

Examples of the binder resin include known styrene resins such as polystyrene, styrene / butadiene copolymer, styrene / acrylate copolymer, styrene / methacrylate copolymer, epoxy resins and polyester resins. The resin for toner can be used alone or in a mixed state.

As the coloring agent, for example, known pigments or dyes such as carbon black, chrome yellow, Hansa yellow, benzine yellow, rose bengara, aniline red, phthalocyanine blue, aniline blue, nigrosine dye, and aniline black are used. be able to.

As the charge control agent, for example, a metal-containing (C
r) An azo dye or the like can be used.

As the release agent, for example, polypropylene, polyethylene, paraffin wax, carnauba wax, amide wax and the like can be used.

As the fluidization improver used as an external additive, for example, a negatively charged metal oxide such as aluminum oxide (alumina) or titanium oxide may be used. May also be used as an auxiliary agent.

Further, as a lubricant, for example, a metal salt of a fatty acid such as a metal salt of stearic acid can be externally added. As the abrasive, for example, cerium oxide or the like can be externally added.

In the structure of the present invention, the triboelectric charge of the negatively charged non-magnetic toner is set to -10 to -80 .mu.c / g. However, if the amount is higher than -10 .mu.c / g, the image density decreases.
If it is less than -80 μc / g, fog becomes large and image quality is inferior. More preferably, the triboelectric charge amount should be in the range of -10 to -25 µc / g.

The volume average particle size of the negatively charged non-magnetic toner is as follows:
7 to 10 μm is preferred. If it is less than 7 μm, the image density is improved, but the toner adheres to the background portion of the non-image portion, so that the stain is easily generated. Further, fusion of the developing roll and the blade for regulating the layer thickness of the toner is also likely to occur. On the other hand, if it is larger than 10 μm, sufficient image density cannot be obtained in characters and thin lines, and the resolution and the like will be poor.

In particular, d ₇₅ / d ₂₅ (volume average particle size ratio) ≦
Within the range of 1.35, a particularly remarkable high definition image is obtained. If the ratio d ₇₅ / d ₂₅ (volume average particle size ratio) exceeds 1.35, a high definition image cannot be obtained. This is because when the volume average particle diameter ratio is out of the range, the degree of irregularity of the particle diameter of the negatively charged non-magnetic toner becomes large, the negatively charged toner having a relatively large particle diameter is consumed first, and This is presumably because a negatively charged toner having a particle size is subsequently used and fog or the like is likely to occur.

When d ₇₅ / d ₂₅ is less than 1.21,
The toner yield decreases and is not practical.

[0041]

Embodiments of the present invention will be described below in detail.

First, the negatively charged non-magnetic toner of a one-component developer used in the image forming method according to the present invention will be described.

The negatively charged non-magnetic toner used in the present embodiment is composed of a binder resin, a colorant, and a charge control agent, and has a volume average particle diameter ratio within a predetermined range. Configuration.

In the production of such a negatively charged non-magnetic toner, first, a bisphenol A type polyester polymer (weight average molecular weight: 67,000, number average molecular weight:
270) 93 parts by weight, 4 parts by weight of copper phthalocyanine as a colorant, 2 parts by weight of polypropylene (TP32, manufactured by Sanyo Chemical Co., Ltd.) as a release agent, and 1 charge control agent (Bontron E-84, manufactured by Orient Chemical Co., Ltd.) And dry mixing with a ball mill. Thereafter, the mixture is heated and kneaded by a kneader, solidified by cooling, pulverized by a jet mill, and further classified. The toner particles after classification, hydrophobic silica (Nippon Aerosil Co., Ltd., RX-300) the externally added, the final volume average particle size d ₅₀ of 7～10Myuemu, volume average particle diameter ratio (d ₇₅ /
d ₂₅ ) was formed to be not less than 1.21 μm and not more than 1.35 μm.

The amount of triboelectric charge of the toner is measured using a blow-off triboelectric charge meter (TB-200 manufactured by Toshiba Chemical Corporation).
) And a standard ferrite carrier (Hitachi Metal KBN-100) was prepared so that the concentration of the negatively charged nonmagnetic toner was 5% by weight.

The particle diameter of the toner was measured using a call counter model T-II (manufactured by Call Counter).

Next, an image forming method according to the present invention in which non-contact and reversal development is performed using the one-component developer composed of the above-mentioned negatively charged non-magnetic toner will be described.

In the present embodiment, the image forming method comprises:
This was performed using an image forming apparatus whose main part is shown in FIG. Such an image forming apparatus is an image forming apparatus capable of performing reversal development used in a printer or the like. As shown in FIG. 1, a charger 20 is provided on a peripheral surface of a negatively chargeable OPC photoconductor 10 formed in a drum shape. The exposing device 30, the developing roll 40, the transfer charger 50, and the cleaner 60 have a configuration in which the developing roll 40 is arranged opposite to the negative charging OPC photosensitive member 10 with a developing gap g. Non-contact and reversal development can be performed in the development area.

In this embodiment, the case where the negatively chargeable OPC photosensitive member 10 is formed in a drum shape as shown in FIG. 1 will be described. You may. For example, the belt may be configured in a conventionally known belt shape. In that case, devices such as the charger 20 and the exposure device 30 may be arranged according to a conventional configuration.

The surface of the negatively chargeable OPC photosensitive member 10 is uniformly negatively charged by the charger 20 while rotating at a constant peripheral speed. As the charger 20, a scotron for corona discharge was used. In addition to corona discharge, roller charging,
Brush charging or magnetic brush charging may be used.

The surface of the negatively chargeable OPC photosensitive member 10 whose surface is negatively charged in this manner is further exposed to the exposure unit 3
0 to expose the negatively chargeable OPC photoconductor 10
A negative electrostatic latent image is formed on the surface of the substrate. For light image exposure for forming an electrostatic latent image, a printer light source such as a semiconductor laser or an LED light source which has been conventionally used was used.

The thus-formed electrostatic latent image is held on the surface of the rotating negatively-chargeable OPC photoreceptor 10 while the developing roll 40 is held at a predetermined developing gap g.
And transported to a developing area arranged opposite to the developing area. The electrostatic latent image is visualized and developed as a toner image by the negatively-charged non-magnetic toner of the one-component developer having the above-mentioned structure, which is electrostatically carried on the surface of the developing roll 40 and conveyed to the developing area. .

As shown in FIG. 1, the negatively charged non-magnetic toner used in the development is agitated by a stirrer 42 in a toner hopper 41 and rubs against each other to be negatively charged.
The negatively charged non-magnetic toner charged negatively is electrostatically adsorbed and carried on the surface of the rotating developing roll 40.
As shown in FIG. 1, the negatively charged non-magnetic toner carried on the surface of the developing roll 40 is conveyed to the side of the toner layer thickness regulating blade 70 pressed against the peripheral surface of the developing roll 40 at a predetermined pressure. When passing through the lower side of the blade 70, it is formed into a thin layer having a predetermined thickness and is conveyed to the developing area. The blade 70 may be formed of a conventionally known phosphor bronze or the like.

The negatively charged non-magnetic toner having a predetermined layer thickness carried and conveyed on the surface of the developing roll 40 in this manner flies from the surface of the developing roll 40 to the surface of the negatively chargeable OPC photosensitive member 10. By doing so, non-contact development is performed by attracting the latent image to the electrostatic latent image. At the time of flight, a DC bias and an AC bias are applied to the developing roll 40 formed on the metal pipe so that the negatively charged non-magnetic toner easily flies, so that the toner image is surely formed. Has become.

Thus, the negatively chargeable OPC photosensitive member 10
The toner image formed on the surface of the transfer charger 5 is further transferred.
0 is conveyed to the transfer area arranged opposite to the transfer area. In the transfer area, a transfer material 51 such as paper is sent between the transfer charger 50 and the toner image so as to match the conveyance of the toner image, and is transferred from the transfer charger 50 to the back surface of the transfer material 51. Charging with a polarity opposite to the charging polarity of the toner image (positive charging in this case) is performed, and the toner image is transferred onto the transfer material 51.

As the transfer charger 50, a corotron for corona discharge may be used.

Thereafter, the material 5 to which the toner image has been transferred
1 is a case in which a heat roll and a pressure roll are sent to a heat roll section 52 in which two heat rolls and a pressure roll are arranged opposite to each other. Be established. The fixing of the toner image may be performed by conventional pressure fixing or oven fixing in addition to the heat roll fixing.

On the other hand, after the transfer of the toner image, the negatively chargeable O
The remaining developer is removed from the surface of the PC photoreceptor 10 by the cleaner 60. In the present embodiment, a conventional urethane blade is used as the cleaner 60, and the negatively chargeable non-magnetic toner remaining without being transferred to the surface of the negatively chargeable OPC photoconductor 10 can be scraped off. I have.

Next, a non-magnetic one-component developer composed of a negatively-charged non-magnetic toner having the above configuration is applied to the above-described image forming method, and an image actually obtained by non-contact / reversal development is evaluated. The effectiveness of the present invention was verified.

An actual image evaluation was performed using the non-magnetic one-component developer composed of the toner having the above configuration.

The image was formed under the following conditions.

The negatively chargeable OPC photosensitive member 10 is a drum-shaped OPC photosensitive member having a diameter (φ) of 30 mm and a process speed (V _P : also referred to as a peripheral speed) of 60 mm / sec.
And its surface potential (V ₀ ) is
It was set to 550V.

The residual potential ( _VL ) of the surface of the negatively chargeable OPC photoreceptor 10 after light image exposure was -50 V.

On the other hand, in the present embodiment, the developing roll 40 has a diameter (φ) of 20 mm and is made of aluminum alloy A.
6064 pipes are used. Further, the surface of the metal pipe of the developing roll 40 has irregular particles (# 50).
Blasting with an alundum particle of 0) and surface roughness (R _Z : + point average roughness according to JIS B 0601)
Was set to 5 μm. Thus, the carrying property of the negatively charged non-magnetic toner on the surface of the developing roll 40 is improved. The developing roll 40 has a negative charging property OP.
The photosensitive drum was rotated at a peripheral speed of 40 mm / sec, which was slightly slower than that of the C photosensitive member 10.

In this embodiment, a DC bias voltage of -500 V, which is slightly lower than the surface potential V ₀ of the negatively chargeable OPC photosensitive member 10, is applied to the developing roll 40 in order to perform reversal development. At the same time, V
_PP applies an AC bias of 800V.

The layer thickness of the negatively charged non-magnetic toner is regulated so that the phosphor bronze blade is brought into contact with the surface of the negatively charged OPC photoreceptor 10 at a linear pressure of 300 g / cm to be 0.1 mm. Have been. The development gap g is 0.2 mm
Is set to

Further, for the transfer and fixing of the toner image, a corotron is used as the transfer charger 50, plain paper is used as a material to be transferred, a fixing temperature is 160 ° C., and a linear pressure is 1 kg / c.
The fixing was performed by heat roll fixing at a fixing pressure of m.

In the cleaner 60, the residual toner was removed by bringing a urethane blade into contact with the surface of the negatively chargeable OPC photosensitive member 10 after the transfer at a predetermined linear pressure.

Table 1 summarizes image data obtained by the image forming method performed under the above conditions.

The image data in the table shows the image quality when the values of the volume average particle diameter d ₅₀ and the volume average particle diameter ratio d ₇₅ / d ₂₅ of the negatively charged non-magnetic toner are variously changed. .

The image quality includes image density (ID), fog,
From the four viewpoints of line reproducibility and resolution, both the initial image and the image after printing 10,000 sheets were evaluated.
It is to be noted that the ID is preferably 1.3 or more, and the fog is preferably 0.5 or less.

In Table 1, the volume average particle size ratio (d ₇₅ /
The image quality when d ₂₅ ) exceeds 1.35 is compared with the image quality when the volume average particle diameter ratio (d ₇₅ / d ₂₅ ) is 1.21 or more and 1.35 or less. .

When the image data of Examples 1, 3, and 5 in Table 1 are compared with the image data of Examples 2, 4, and 6, the volume average particle diameter d
Assuming that ₅₀ is 7.0, 8.0 and 9.0 μm and the value of the volume average particle size ratio (d ₇₅ / d ₂₅ ) is larger than 1.35, Example 5
It can be seen that the image density (ID) decreases and fog increases, except after printing of 10,000 sheets.

When the high definition of the image quality is evaluated from the viewpoint of the line reproducibility and the resolution, it is found that a high definition image cannot be obtained except for the initial image of Example 1.

Note that the line reproducibility is a value indicating how much a thin line having a predetermined line width can be reproduced. The value of the line reproducibility in Table 1 is such that a thin line having a line width of 75 μm is printed by the image forming method described in the above embodiment, and the reproduced line width (μm) is 75 μm.
(The smaller the value, the better the definition). The value of the line reproducibility is obtained from the following equation (1).

(Line width (μm) on which a 75 μm line is printed) ÷ 75 (1) The resolution in the table is a value indicating how many fine lines can be clearly recognized in a 1 mm width. 10 lines / mm or more, △
Was evaluated as 6 to 8 wires / mm, and x was evaluated as 5 wires / mm or less.

Further, the values of the volume average particle diameters d ₅₀ , d ₇₅ and d ₂₅ are such that when the toner particles are integrated from the smaller one, the volume fractions with respect to all the toner particles are 50% and 75%, respectively.
% And 25% represent the diameter of the toner particles.

[0078]

[Table 1]

Further, assuming that the volume average particle size d ₅₀ is 7 to 9 μm, the value of the volume average particle size ratio (d ₇₅ / d ₂₅ ) is 1.21.
When the ratio is less than 1.10, 1.20, or 1.21, the toner yield is reduced by 5 to 20% as compared with the case where the ratio is not less than 1.21.

The results shown in Table 1 indicate that non-contact development using a one-component developer using a negatively chargeable OPC photoreceptor results in −1
0 ≦ triboelectric charge (TEC) ≦ −80 (μc / g), 7 ≦
Use of a negatively charged non-magnetic toner of a one-component developer having a volume average particle diameter (d ₅₀ ) ≦ 10 (μm) and a relation of 1.21 ≦ volume average particle diameter (d ₇₅ / d ₂₅ ) ≦ 1.35 Indicates that it is effective for forming a high-definition image.

As described above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say, there is.

[0082]

Advantageous effects obtained by typical ones of the inventions disclosed in the present application will be briefly described.
It is as follows.

(1). In the configuration of the present invention, the volume average particle diameter ratio of the one-component negatively charged non-magnetic toner is 1.21 or more,
By regulating the content in a range of 1.35 or less, a one-component developer using the negatively charged non-magnetic toner and a negatively charged OPC
In image formation by a non-contact development method using a photoreceptor, a high-definition image with improved reproducibility of fine lines can be obtained unlike the related art.

(2). In the configuration of the present invention, the volume average particle diameter ratio of the one-component negatively charged non-magnetic toner is 1.21 or more,
By regulating the content in a range of 1.35 or less, a one-component developer using the negatively charged non-magnetic toner and a negatively charged OPC
In image formation by a non-contact development method using a photoreceptor, a high-definition image with improved resolution can be obtained unlike the related art.

(3). In the configuration of the present invention, the volume average particle diameter ratio of the one-component negatively charged non-magnetic toner is 1.21 or more,
Since it is regulated within the range of 1.35 or less, by applying a non-contact developing method using this negatively charged non-magnetic toner and a negatively charged OPC photoconductor to a color image forming method, In contrast, it is possible to obtain a high-definition color image with improved line reproducibility and resolution in which unnecessary toner does not adhere to a non-image portion.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a main part of an image forming apparatus used in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Negative charging OPC photosensitive member 20 Charger 30 Exposure device 40 Developing roll 41 Toner hopper 42 Stirrer 50 Transfer charger 51 Transfer material 52 Heat roller part 60 Cleaner 70 Blade

Claims (2)

[Claims] 1. A developing region in which a negatively chargeable OPC photoconductor and a developing roll are opposed to each other with a developing gap.
The electrostatic latent image formed on the surface of the negatively chargeable OPC photoreceptor is transported while being carried on the surface of the negatively chargeable OPC photoreceptor, and a one-component negatively chargeable non-magnetic layer having a layer thickness smaller than the developing gap. A thin layer of toner is carried on the surface of the developing roll and conveyed to the developing area. While applying a DC bias and an AC bias to the developing roll, the negatively charged O
An image forming method in which the negatively charged non-magnetic toner is caused to fly on a surface of a PC photoreceptor and the electrostatic latent image is subjected to non-contact / reversal development, wherein the frictionally charged amount of the negatively charged non-magnetic toner is -10. ~ -8
At 0 μc / g, the volume average particle diameter d ₅₀ (d ₅₀ represents the diameter of the toner particles when the volume fraction with respect to all the toner particles is 50% when the toner particles are integrated from the smaller one). 7 to 10 μm, and the volume average particle diameter ratio d ₇₅ / d ₂₅ (d ₇₅ , d ₂₅ is the volume fraction with respect to all the toner particles when the toner particles are integrated from the smaller one,
It represents the diameter of the toner particles when they are 75% and 25%, respectively. ) Is in the range of not less than 1.21 and not more than 1.35. 2. A developing area in which a negatively chargeable OPC photosensitive member and a developing roll are opposed to each other with a developing gap provided therebetween.
The electrostatic latent image formed on the surface of the negatively chargeable OPC photoreceptor is transported while being carried on the surface of the negatively chargeable OPC photoreceptor. A thin layer of magnetic toner is carried on the surface of the developing roll and transported to the developing area. While applying a DC bias and an AC bias to the developing roll, the negatively chargeable O
A negatively-charged non-magnetic toner used in an image forming method in which the negatively-charged non-magnetic toner is caused to fly on the electrostatic latent image on the surface of a PC photoreceptor to perform non-contact and reversal development of the electrostatic latent image. When the triboelectric charge amount is −10 to −80 μc / g and the volume average particle diameter d ₅₀ (d ₅₀ is 50% by volume with respect to all toner particles when toner particles are integrated from the smaller one) Is 7 to 10 μm, and the volume average particle size ratio d ₇₅ / d ₂₅ d (d ₇₅ , d ₂₅
Represents the diameter of the toner particles when the volume fraction with respect to all the toner particles is 75% and 25%, respectively, when the toner particles are integrated from the smaller one. ) Is greater than 1.21 and 1.
35. A negatively charged non-magnetic toner, which is in the range of 35 or less.