JPH08114986A - Developing device and color image forming device using the same - Google Patents

Abstract

PURPOSE: To secure a required amt. of developer without carrier scattering even when small-particle size toner is used for securing high image quality, to effectively avoid the occurrence of brush mark pattern, and also to prevent irregularities in a magnetic black toner image and the color mixing on a color developing means in a color image forming device. CONSTITUTION: As for a non-contact two-component developing device in which developing magnetic poles 3a are set in plural-column state on a developing carrier 1 corresponding to an effective developing area Y; the magnetic carrier C in developer G is the one obtained by mixing and dispersing magnetic powder in a resin binder, then pulverizing and classifying the magnetic powder. As for the color image forming device in which plural color toner images are formed on a latent image carrier 4 then transferred to a recording medium 5 altogether; magnetic one-component black toner is used as a developing means 6 for a black color, and the non-contact two-component developing device is used as the color developing means 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer using an electrophotographic system, and more particularly, a plurality of rows of developing magnetic poles arranged in a narrow pitch interval in an effective developing area. And a color image forming apparatus using the same.

[0002]

2. Description of the Related Art As a conventional color image forming apparatus, for example, a plurality of color toner images are sequentially superposed on a latent image carrier such as a photosensitive drum, and then the color toner images are collectively transferred onto a recording sheet. The ones that have been made are already known. In this type of color image forming apparatus, there is an advantage that the apparatus can be inexpensive and downsized because a transfer drum that holds the recording paper and copies the toner image on the latent image carrier for each color is not used. In this case, since the toner image previously developed on the latent image carrier should not be disturbed in the subsequent developing process, a non-contact developing system is often adopted as the normal developing device.

As the non-contact developing system of this type, a one-component developing system in which only a toner is magnetically or electrostatically carried on a developing roll for development, and a two-component developing system in which a developing roll comprises toner and a magnetic carrier are used. There is a two-component developing method in which an agent is magnetically carried and development is performed, but the present applicants have studied a non-contact type two-component developing method that is generally superior in terms of image quality and maintainability. With respect to this type of non-contact type two-component developing system, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 56-144452 (Japanese Patent Publication No. 2-4903) has been proposed. This is because the developing magnetic pole is fixed inside the developing roll so as to face the effective developing area (the area where the toner effectively acts on the latent image carrier to develop the latent image on the latent image carrier) and only the sleeve is fixed. A method of rotating and a method of forming the magnetic brush of the developer as a soft brush by making the developing magnetic pole repulsive to the same polarity have been proposed, but the action of a strong electric field is required to obtain a sufficient amount of development in non-contact development. Therefore, it is necessary to dispose the sleeve serving as an electrode as close to the latent image carrier as possible while applying an oscillating electric field (alternating electric field).

[0004]

However, in the system described in the above publication, one magnetic pole exists in the effective developing region, or if the magnetic pole is a repulsive magnetic pole of the same polarity, a magnetic field of 2 in the direction perpendicular to the sleeve surface is generated. In the effective developing area, there is one magnetic pole composed of one maximum value and one minimum value existing between the two maximum values.
The spikes of the developer have risen to a high level,
If it is attempted to keep the developer in non-contact with the latent image carrier, it will be difficult to satisfy both the securing of the developer conveyance amount necessary for development and the setting of a narrow gap between the latent image carrier and the sleeve. A technical problem arises.

As a solution to such a technical problem (problem that rises sharply), for example, a pair of magnetic poles having different polarities are fixed at positions sandwiching an effective developing area inside a developing roll, and only a sleeve is used. A method of rotating has been proposed (for example, JP-A-60-176069 (Japanese Patent Publication No. 4-3).
6383))). In such a system, the spikes of the developer are laid down in the effective developing area, so the developer transport amount required for development is kept while the developer is not in contact with the latent image carrier. It is possible to satisfy both of the above requirement and the setting of a narrow gap between the latent image carrier and the sleeve. However, in such a method, since the ears of the developer layer are in a resting state, the toner in the lower layer portion of the developer layer is hard to be developed, and even if the developer transport amount is increased, the developability is eventually lowered. There is a problem that it does not rise so much.

On the other hand, in the developing device disclosed in Japanese Examined Patent Publication No. 1-291268, the pitch between the magnetic poles of the developing rolls is made small to secure the developer carrying amount necessary for the development, the latent image carrier and the sleeve. A method has been proposed which is compatible with setting a narrow gap between them. That is, in this type of developing device, since the developing magnetic poles in a plurality of rows are arranged in the effective developing area,
There are many locations where the developer layer spikes in the effective developing area, and the surface area of the developer in the effective developing area is significantly increased. On the other hand, since the pitch between the magnetic poles is small, the amount of spikes of the above developer is large. Is not so large that the developer is kept in a good thin layer state. Therefore, this type can improve the developability while keeping the developer in a thin layer state, and can be said to be suitable for the non-contact two-component developing method.

According to the results of the tests carried out by the applicants, the average particle size (weight average) of the styrene / acrylic toner or the polyester toner having an average particle size (weight average) of 13 μm and 11.5 μm is about 10 μm. Combine with a carrier such as iron powder, ferrite powder, nickel powder of 40-60 μm
When non-contact two-component alternating electric field development was carried out in a structure in which two rows of spikes at 5 mm intervals existed in the 0 mm width effective development area or four rows of spikes at 3 mm intervals existed, the developer was latent While maintaining non-contact with the image carrier, it is possible to secure both the developer transport amount necessary for development and the setting of a narrow gap between the latent image carrier and the sleeve. A high development amount could be obtained.

After that, the inventors of the present invention aimed at achieving higher image quality, and used the average particle diameter (weight average) 13 used until then.
When the improvement activities were promoted by using 9 μm toner and 7 μm toner, which are finer than μm toner and 11.5 μm toner,
Although the toner particle size has become smaller and the reproducibility of the digital screen latent image has improved remarkably, the "sweep pattern" on the image, which was not noticeable until then, has become a problem. It is considered that this "sweep pattern" is caused by the fact that the ears of developer standing on each magnetic pole on the developing roll are high and lined up in an orderly manner.

As one of the solutions to this problem,
There is a method of narrowing the pitch between magnetic poles corresponding to the effective developing area to increase the number of rows of developer spikes present in the effective developing area. However, when the pitch between the magnetic poles was narrowed, there was a problem in that it was difficult to “control carrier scattering and secure the development amount”.

The reason for this is that if the gap between the magnetic poles is narrowed, even if the vertical component magnetic flux density of each magnetic pole is the same on the surface of the magnet roll inside the developing roll, the vertical component magnetic flux density on the sleeve becomes weak, and the sleeve Since the ratio of the upper horizontal component magnetic flux density is high, the height of the highest spikes is lowered and the uniformity of spikes is improved, while the magnetic binding force to the carrier away from the sleeve is weakened, This is because the amount of developer that can be held decreases.

Regarding the uniformity of the ears, Japanese Patent Laid-Open No. 63-
In Japanese Patent No. 278082, a method is proposed in which the magnetic poles are spaced at a distance on the surface of the sleeve of 2 mm or less, preferably 1 mm or less, but it is unclear how the problems of carrier scattering and securing the required developer transport amount have been solved. .

Further, comparing the particle size distribution of the toner in the developer on the developing sleeve with the particle size distribution of the toner developed on the latent image, the non-contact two-component developing system is better than the contact two-component developing system. Regardless of DC electric field or alternating electric field,
It is much more difficult to develop a toner having a small particle size. From this fact as well, when the toner having a small particle size is applied to the non-contact two-component developing method, carrier scattering is suppressed and the developing amount is secured. It turns out that things are very difficult.

As described above, in the non-contact two-component alternating electric field development method, when a small particle size toner is used to achieve high image quality, a plurality of rows of developer spikes are present in the effective development area for development. However, the conventional developing device has a technical problem that it is difficult to satisfy all of the three requirements of suppressing the sweep pattern, suppressing carrier scattering, and securing the developing amount.

Also, in general, particularly in small and medium speed monochrome copying machines and printers, the method of using magnetic one-component toner for black development is widely adopted and popularized in terms of downsizing, cost reduction and easy maintenance. are doing. Therefore, assuming a copying machine or a printer that mainly develops black and adds a color developing function thereto, magnetic one-component toner is used for black development and the non-contact two-component development is used for color toner development. With the device
A method of forming a composite image of black and color by superposing a plurality of colors of toner including black toner on the latent image carrier is desirable in view of downsizing of the entire apparatus, cost reduction, and ease of maintenance. Can be said to be a thing.

However, when the magnetic one-component toner is actually developed on the latent image carrier first and then the color toner is developed using the non-contact two-component developing device, the development of the non-contact two-component developing device is performed. Due to the magnetic field generated from the roll, the magnetic one-component black toner developed on the latent image carrier is attracted to the developing roll side, and the black toner image on the latent image carrier is disturbed, and at the same time, the black toner in the color toner developing device. However, there is a technical problem that the mixed colors cause color mixing. On the other hand, when developing the magnetic one-component toner last, the applied AC bias voltage required for the magnetic one-component toner development itself is relatively high, so the color toner image developed on the latent image carrier is developed by the magnetic one-component toner development. There is a technical problem of disturbing the AC bias voltage of.

A structure in which a magnetic one-component developing device and a non-magnetic two-component developing device are arranged on the same latent image carrier is described in, for example, Japanese Patent Application Laid-Open No. 61-203478.
In this description, a system in which either one of the magnetic one-component developing device and the non-magnetic two-component developing device is selected is explained, and it is not a so-called multiple developing system on the same latent image carrier.

The present invention has been made in order to solve the above technical problems. Even if a small particle size toner aiming at high image quality is used, the developing amount can be secured without carrier scattering and the sweeping can be performed. A first object of the present invention is to provide a developing device of a non-contact two-component alternating electric field developing system having no pattern.

In the present invention, a magnetic one-component developing device is used for black development, and a non-contact two-component developing device is used for color toner development to develop magnetic black toner on the same latent image carrier, Subsequently, a magnetic one-component black toner developed on the latent image carrier is brought into non-contact with the provision of a color image forming apparatus of the type in which a plurality of color toner images other than black are developed and transferred onto a recording medium at a time. Adsorption by the developer carrier of the two-component color developing device disturbs the magnetic one-component black toner image on the latent image carrier, or the magnetic one-component black toner mixes in the two-component color developing device to cause color mixing trouble. A second object is to provide a color image forming apparatus that does not generate

[0019]

According to the present invention for achieving the first object, as shown in FIG. 1A, a surface is covered with a non-magnetic member 2 and a magnet member 3 is installed inside. The developer carrying member 1 is provided, the developer carrying member 1 is arranged so as to face the latent image carrying member 4, and the magnet members 3 corresponding to the effective developing regions Y facing the latent image carrying member 4 have different polarities. A plurality of rows of developing magnetic poles 3a arranged alternately are arranged to form the developer carrier 1
A two-component developer G composed of a non-magnetic toner T and a magnetic carrier C is carried on the latent image carrier 4 in a non-contact state, and a direct current component is present between the latent image carrier 4 and the developer carrier 1. In the developing device that develops the electrostatic latent image Z on the latent image carrier 4 by applying the alternating electric field EAC superposed with
The magnetic carrier C is a carrier obtained by mixing and dispersing magnetic powder in a resin binder, then pulverizing and classifying.

With such technical means, the developing device according to the present invention can be applied not only to a color image forming device but also to a single color image forming device. Further, as the developer carrying body 1 to which the present invention is applied, a magnet member 3 may be fixedly installed in a rotatable non-magnetic sleeve (corresponding to a non-magnetic member) 2, or it may be rotatable. The non-magnetic sleeve 2 is made by fixing the magnet member 3 to the non-magnetic sleeve 2 side.
And the magnet member 3 may be integrally rotated, or the non-magnetic sleeve 2 may be fixed and the inner magnet member 3 may be rotated, or the rotatable magnet member 3 may be rotated. A nonmagnetic coating film (corresponding to a nonmagnetic member) 2 on the surface of 3 may be appropriately selected. Further, the magnet member 3 is not limited to a roll shape as long as it has a magnetic pole including at least a plurality of rows of developing magnetic poles 3a, and may have any shape including a sheet shape.

Further, the above-mentioned effective developing area Y means an area where the toner effectively acts on the latent image carrier 4 to develop the latent image on the latent image carrier 4, as defined above. However, specifically, in the two-component alternating electric field developing system type, the same alternating electric field as the alternating electric field EAC applied at the time of development is applied with the developer carrier 1 and the latent image carrier 4 stopped. It means a region where the toner flies to the latent image carrier 4 side.

Further, the developer G used in the present invention
As for the magnetic characteristics of the magnetic carrier C, the practical magnetization at 1000 Oersted is 20 emu / g or more and 60 emu or more.
/ G or less, and the average particle size (weight average) of the magnetic carrier C is 20 μm or more and 7 or more.
It is preferably 0 μm or less. On the other hand, the average particle diameter (weight average) of the toner T of the developer G is preferably 9 μm or less.

Further, regarding the developer carrying member 1, in the effective developing region Y, the center interval of the developing magnetic poles 3a on the surface of the developer carrying member 1 is L (unit: mm), and each developing magnetic pole 3 is
When the peak value of the magnetic flux density in the radial direction on the surface of the developer carrying member 1 of a is B (unit: Gauss), 2 ≦ L ≦ 5, 20
It is preferable to satisfy all of 0 ≦ B ≦ 600 and B × (B / L) ≧ 20000.

An example of the basic manufacturing method of the magnetic carrier C used in the present invention will be described. As a raw material, 25% by weight of a styrene-acrylic copolymer, 70% by weight of magnetite, and 8 for charging the polyester toner to a negative polarity
-Uses nylon. In addition to these raw materials, a styrene-n-butyl methacrylate copolymer or the like may be used as a resin, and a basic carbon black (for example, manufactured by Cabot Co.) as a material for negatively charging the polyester toner. REGAL330R, pH = 8.
5) may be used. To charge the toner to the positive polarity, polyvinylidene fluoride (eg, trade name: KYNA
R), acidic carbon black (eg Cabot M
ONARCH, pH = 2.5), etc., and can be selected according to the latent image carrier used in the image forming apparatus and the image forming process. After kneading (mixing, dispersing) these, crushing,
The desired carrier can be obtained by classification.

In the present invention which achieves the second object, as shown in FIG. 1B, at least the black toner image TB and the color toner image TC other than black are formed at least in the order of formation of the black toner image TB. After being formed on the latent image carrier 4 by an image forming process that does not cause
In the color image forming apparatus in which B and TC are collectively transferred to the recording medium 5, a one-component developing system using magnetic black toner is used as the black developing means 6, and a developing means for colors other than black is used. 7, a non-contact two-component developing method that achieves the first object, that is, a surface is covered with a non-magnetic member 2 and a magnet member 3 is installed inside, as shown in FIG. 1 (a). And a magnet member 3 corresponding to the effective developing region Y facing the latent image carrier 4 and having different polarities. A plurality of rows of developing magnetic poles 3a arranged alternately, and a two-component developer G composed of a non-magnetic toner T and a magnetic carrier C on the developer carrier 1.
Is carried in a non-contact state with the latent image carrier 4 and an alternating electric field EAC in which a direct current component is superposed is applied between the latent image carrier 4 and the developer carrier 1 to act on the latent image carrier 4. Which develops the electrostatic latent image Z of the magnetic carrier C, the magnetic carrier C mixes and disperses magnetic powder in a resin binder, and then pulverizes the magnetic powder.
It is characterized by using a classified carrier.

In such a color image forming apparatus,
With respect to the color developing means 7, a plurality of ears of the developer G standing upright on the developer carrying member 1 corresponding to the developing magnetic poles 3a having different polarities are arranged in the effective developing area Y at intervals of 4 mm or less. It is preferable that there are lines, and that the radial magnetic flux density of each developing magnetic pole 3a on the developer carrying member 1 on the surface of the developer carrying member 1 is 330 gauss or more.

In the color image forming apparatus, the black developing means 6 is made of magnetic black toner.
The magnitude of magnetization measured in a K Oersted magnetic field is σ
(Unit: emu / g), the average particle size is r (unit: m)
Then, it is preferable that the relationship of σ × r ³ <3.5 × 10 ⁻¹⁴ holds.

[0028]

In the technical means as described above, first, the operation of the non-contact two-component developing device shown in FIG. 1 (a) will be described. That is, in the developing device of FIG. 1A, a magnetic carrier C is used in which magnetic powder is mixed and dispersed in a resin binder, and then pulverized and classified. Here, the magnetic carrier C of the present invention and the conventionally used metal-based carrier (comparative example) will be compared with respect to the sweep pattern on the image. At this time, when the magnetization per carrier, the particle size, and the total volume of the carriers existing on the developer carrying member 1 are aligned and compared, in the comparative example, the standing upright on each developing magnetic pole 3a on the developer carrying member 1. The spikes of the developing agent G to be formed are arranged in a high order, whereas in the magnetic carrier C of the present invention, the spikes of the developing agent G standing on each developing magnetic pole 3a on the developer carrying member 1 are not so high. The stacked shapes will also be random.
To supplement this point, metallic carriers (comparative example)
Then, even if it is a mixed system such as ferrite, the material is well dispersed, and the deviation of the magnetization inside the carrier is very small. Therefore, the spikes of the developer are high and lined up in an orderly manner. On the other hand, in the carrier C (invention) in which the magnetic powder is mixed / dispersed in the resin binder, pulverized and classified, the dispersion of the magnetic powder is inevitably biased, and the magnetization inside the carrier is also biased. For this reason, the spikes of the developer do not rise so much and the shape is also indefinite, so the stacked shape becomes random. As a result, in the comparative example, a clear sweep pattern appeared on the image at a certain interval, but in the present invention, it becomes almost inconspicuous. Therefore, even if the pitch between the developing magnetic poles 3a is set to a range of 2 to 5 mm where it is easy to achieve both the development amount securing and the carrier scattering suppression without drastically reducing the pitch to 2 mm or less, the sweep pattern does not appear on the image. Effectively avoided.

Further, as an intermediate existence of both (invention and comparative example), there is a carrier in which magnetic powder is mixed and dispersed in a resin binder and then sprayed in a solution state to be solidified. The magnetic powder is better dispersed than the carrier (invention) in which magnetic powder is mixed / dispersed, pulverized and classified, and the shape is close to spherical because it solidifies due to surface tension when sprayed. The effect that the spikes become random is slightly reduced. In addition, the magnetic powder-dispersed resin carrier produced by the polymerization method has the same spherical shape, so that the magnetic powder is mixed and dispersed in the resin binder and then sprayed in a solution state to be solidified. Only the degree of effect can be obtained.

Next, the operation of the color image forming apparatus of FIG. 1B will be described. At least the black toner image T
In the image forming process where the formation order of B is not the last,
After the magnetic black toner image TB and the non-magnetic color toner image TC other than black are formed on the latent image carrier 4, the toner images TB and TC of the respective colors are collectively transferred to the recording medium 5. At this time, as the magnetic carrier C of the developer G of the color developing means 7, a carrier obtained by mixing and dispersing magnetic powder in a resin binder, and then crushing and classifying is used. By adjusting both the magnetic flux density on the developer carrier 1 and the distance between the developing magnetic poles 3a to be small, the developer G on the developer carrier is brought into non-contact with the latent image carrier 4. It is possible to reduce the layer thickness, to secure the development amount, suppress carrier scattering, and avoid sweep pattern. Therefore, not only the developability by the color developing means 7 is kept good, but also the strength of the magnetic field generated from the inside of the developer carrying body 1 of the color developing means 7 on the surface of the latent image carrying body 4. Since it becomes extremely small, even if the one-component developing system using magnetic black toner is used as the black developing means 6, the one-component magnetic black toner developed on the surface of the latent image carrier 4 is used as the color developing means. When passing through 7, the developer carrier 1 is not magnetically adsorbed.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the accompanying drawings. Example 1 (First Example of Developing Device) FIG. 2 shows Example 1 of the developing device to which the present invention is applied.
In the figure, the developing device 20 has a developing roller 23 at a position facing the developing opening 22 of the developing housing 21.
The developing roll 23 is arranged so as to face the latent image carrier 11 such as a photosensitive drum in a non-contact state.

In this embodiment, the developing roll 23 is
Is composed of a non-magnetic hollow cylindrical, rigid, hard and conductive sleeve 24 and a magnet roll 25 having a plurality of magnetic poles, and only the sleeve 24 rotates. The sleeve 24 is rotating in the direction of the arrow, and the developer G scraped up by the paddle 26 is thinned by the layer thickness regulating plate 27 and conveyed to the effective developing area Y.

The developer G used in this example is a magnetic carrier prepared by mixing and dispersing magnetic powder in a resin binder so as to obtain a practical magnetization of 40 emu / g with a weight average particle diameter of 40 μm and pulverizing and classifying it. A polyester color toner having an average particle diameter of 7 μm was mixed and stirred, and the toner charge ratio in the developer was adjusted to about 10% by weight and the toner charge amount was adjusted to 12 to 25 μC / g at a relative humidity of 30% to 85%. is there.

The outer diameter of the sleeve 24 is 25 mm.
And the surface roughness is Rz = 20 μm. The distance between the latent image carrier 11 and the sleeve 24 is set to 500 μm, and in this state, when an alternating electric field in which a DC component is superimposed is applied between the latent image carrier 11 and the sleeve 24. The effective developing area Y is set to have a width of 10 mm. Needless to say, the width of the effective developing region Y is affected by the electric field condition, but generally, the larger the electric field of the direct current component and the larger the electric field of the alternating current component are, the wider the width is. Regarding the influence of the frequency on the developer G to be used, it is 1 to 3 in the range up to 10 and several kHz.
There is a place where the width of the effective developing region Y is widest around kHz. In the present embodiment, considering that the toner image previously developed on the latent image carrier 11 is not disturbed, the dark potential of the latent image carrier 11 is -600V to -900V, the light potential is -50V to -200V, It is desirable that the difference between the dark potential and the DC component of the bias applied to the sleeve 24 is 50 to 150 V, the peak value of the AC component of the bias is 1.5 kV, and the development is performed in the frequency range of 4 to 10 kHz. The effective developing area Y when optimized has a width of about 10 mm as described above.

Furthermore, the height of the spikes of the developer G thinned by the layer thickness regulating plate 27 is 350 in the effective developing area m.
μm.

Further, the magnet roll 25 is obtained by winding a sheet-shaped multi-pole rubber magnet 252 around a core member 251 fixed in the rotary sleeve 24. The rubber magnet 252 includes the effective developing area Y and extends about 3 mm on the surface of the sleeve 24 over a range from the magnetic pole facing the layer thickness regulating plate 27 to the opposite side by about 180 °.
A pair of repulsive magnetic poles for peeling the developer over a portion in which the N poles and the S poles are alternately magnetized so as to have a pitch interval and a magnetic flux density of 40 mT (400 gauss) and the other half area (this embodiment). (The S pole) is magnetized. still,
A cylindrical ferrite magnet may be used instead of the multipolar rubber magnet 252.

In this embodiment, the inventors of the present invention can obtain a very excellent developability, can obtain a developed image without carrier scattering and have no sweep pattern, and can design an image with a margin. It was In addition, in this embodiment, the developing roll 2
There is nothing to contact except the developer G of No. 3, and the developing roll 2
Since there is no fear of wear of No. 3, it is suitable for a long life such as a high speed image forming apparatus.

Example 2 (Second Example of Developing Device) FIG. 3 shows Example 2 of the developing device to which the present invention is applied.
The same components as those of the first embodiment are designated by the same reference numerals as those of the first embodiment, and the detailed description thereof is omitted here.
In this embodiment, the developing roll 23 has a non-magnetic hollow cylindrical shape and a rigid and conductive sleeve 24.
And a magnet roll 31 having a plurality of magnetic poles, and the sleeve 24 and the magnet roll 31 are configured to rotate in mutually opposite directions as indicated by arrows in the figure.

The magnet roll 31 is formed by winding a sheet-shaped multi-pole rubber magnet 312 around a core member 311 which rotates in the opposite direction to the rotary sleeve 24 in the rotary sleeve 24. The rubber magnet 312 is
Approximately 3 mm pitch interval and 40 mT on the surface of the sleeve 24
The N pole and the S pole are alternately magnetized over the entire circumference of the core 311 so that the magnetic flux density is (400 gauss). still,
Also in this embodiment, the multi-pole rubber magnet 31 is used.
Instead of 2, a cylindrical ferrite magnet may be used.

Further, in this embodiment, the developing roll 2 is used.
A scraper 32 that elastically contacts the sleeve 24 is provided near the paddle 26 in the lower part of 3, and the collected developer G that has finished development
Is separated from the developing roll 23 by the scraper 32,
The paddle 26 is fed into a developer (not shown) for mixing and stirring.

The developer used in this embodiment, the sleeve 2
4, outer diameter, surface roughness, height of spike of developer G, distance between latent image carrier 11 and sleeve 24, width of effective developing area Y, dark potential / bright potential of alternating electrostatic latent image, and alternating The electric field conditions are set in the same manner as in Example 1.

Therefore, also in this embodiment, the first embodiment
Similarly to the above, the inventors of the present invention obtained a very excellent developability, and were able to design a high image quality with a margin without carrier scattering and sweep patterns. In particular, in this embodiment, the scraper 32
Is not in contact with the sleeve 24, the life of the developing roller 23 is not as long as that of the first embodiment, and although the driving method is complicated, the developing efficiency is further improved by the rotation of the magnet roller 31 inside, and the image quality is designed. Therefore, it is suitable for an image forming apparatus aiming for high image quality.

Example 3 (Third Example of Developing Device) FIG. 4 shows Example 3 of the developing device to which the present invention is applied. The same components as in the second embodiment will be described in the second embodiment.
The same reference numerals are given and detailed description thereof is omitted here. In the figure, the developing roll 23 includes a rotatable magnet roll 31 (core material 311 and multi-pole rubber magnet 31).
2) is provided with a conductive non-magnetic coating layer 33 on the surface thereof, and the developing roller 23 has an outer diameter of 25 mm and a surface roughness Rz = 4 μm. The developer used in this embodiment, the height of the spikes of the developer G, the distance between the latent image carrier 11 and the developing roll 23, the width of the effective developing region Y, the dark potential / brightness of the electrostatic latent image. Both the electric potential and the alternating electric field conditions are set as in the second embodiment.

Therefore, also in this embodiment, the inventors of the present invention were able to obtain a very excellent developing property and design the image quality with a margin without carrier scattering or sweep patterns.
In particular, in this embodiment, since the conductive coating layer 33 on the surface of the developing roll 23 does not have the rigidity as much as the surface of the second embodiment, the life is shortened. Double structure (sleeve 24, magnet rolls 25, 31)
Therefore, since the structure of the developing roll 23 is simple, and since the magnet roll 31 is located immediately below the conductive coating layer 33, the strength of the magnetic field on the surface of the developing roll 23 can be easily increased. Since the magnet roll 31 can be made relatively thin, the diameter of the developing roll 23 and the developing device can be made small. Therefore, it is suitable for an inexpensive image forming apparatus of a cartridge system in which the developer is exchanged for each developing device. ing.

Example 4 (Fourth Example of Developing Device) FIG. 5 shows Example 4 of the developing device to which the present invention is applied. The same components as in the second embodiment will be described in the second embodiment.
The same reference numerals are given and detailed description thereof is omitted here. In the figure, the developing roll 23 has a non-magnetic hollow cylindrical shape and has a rigid and hard conductive sleeve 24, and a sheet-shaped multi-pole rubber magnet 34 is fixed to the back surface of the sleeve 24. The sleeve 24 and the rubber magnet 34 are integrally rotated. The rubber magnet 34 is used in the first embodiment.
Similar to No. 2, the N pole and the S pole are alternately magnetized over the entire circumference on the sleeve 24 so that the magnetic flux density is 40 mT (400 Gauss) at a pitch interval of about 3 mm. Also in this embodiment, a cylindrical ferrite magnet may be used instead of the rubber magnet 34.

The developer and sleeve 2 used in this embodiment are
4, outer diameter, surface roughness, height of spike of developer G, distance between latent image carrier 11 and sleeve 24, width of effective developing area Y, dark potential / bright potential of alternating electrostatic latent image, and alternating The electric field conditions are set in the same manner as in Example 1.

Therefore, also in this embodiment, the inventors of the present invention could obtain a very excellent developing property and could design the image quality with a margin without carrier scattering or sweep pattern. Particularly, in this embodiment, unlike the first and second embodiments, the developing roll 23 does not have a double structure, so that the developing roll 2
3 is simple, and since the sleeve 24 and the rubber magnet 34 are in close contact and integrated, the strength of the magnetic field on the surface of the sleeve 24 can be easily increased, and the rubber magnet 34 is relatively thin. Development roll 2
Because of the two reasons that it can reduce the diameter and the developing device,
Not only is it suitable for an inexpensive image forming apparatus, but it is more advantageous than the third embodiment in terms of the life of the developing roller 23.

In fact, the inventors of the present invention have prototyped a developing roll having an outer diameter of the sleeve 24 of 20 mm, an interval between the S pole and the N pole on the surface of the sleeve 24 of about 2 mm, and a magnetic flux density of 400 gauss. Good results similar to those of the developing roller having the outer diameter of the sleeve 24 of 25 mm could be obtained.

Characteristic Parameters of Developing Devices of Examples 1 to 4 Next, characteristic parameters common to the developing devices of Examples 1 to 4 will be described. First, regarding the magnetizing intervals of the S poles and the N poles that are alternately arranged in the magnet rolls 25 and 31 and the rubber magnet 34, in general, in the comparison when the vertical component magnetic flux density peak values on the surface of the developing roll 23 are similar, When the magnetizing interval is narrowed, the height of the spikes of the developer is lowered, and the developing roll 23 and the latent image carrier 11 are
Since it is possible to narrow the distance between the two, it is advantageous for the non-contact two-component alternating electric field developing method in that it receives a strong electric field. However, in the developer currently in practical use, if the magnetizing interval is made too narrow, the strength of the magnetic field at a position slightly distant from the surface of the developing roll 23 becomes insufficient, causing carrier scattering. Therefore, if it is attempted to prevent carrier scattering, a sufficient transport amount cannot be secured and the image density becomes insufficient. From this point of view, if the magnetizing distance is the magnetic pole center distance L on the surface of the developing roller 23, the magnetizing distance of 1 mm or less is not practical for the developing roller 23 having the double structure as in the first and second embodiments. In the configurations of Examples 3 and 4, the magnetization interval of 0.5 mm or less is not practical. With respect to the developer used in the above-described examples, the magnetization interval of 2 mm or more is desirable in Examples 1 and 2, and the magnetization interval of 1 mm or more is desirable in Examples 3 and 4.

Further, as the magnetizing interval becomes wider, the height of the spikes of the developer becomes higher, and the developing roll 23 and the latent image carrier 11 are made.
Since the space between and cannot be narrowed, it is disadvantageous in receiving a strong electric field. However, since the developer conveyance amount can be increased, a magnetizing interval of about 10 mm is practical. However, the example of the magnetizing interval of 10 mm is a case in which the latent image carrier 11 is a belt type and can be implemented in a large-sized image forming apparatus having a developing roller 23 diameter of 50 mm or more. It is necessary to rotate the developing roll 23 at a considerably high speed. For example, in a small drum type image forming apparatus having a developing roller diameter of 30 mm or less and a latent image carrier 11 having a diameter of 200 mm or less, the magnetization interval is 5
mm or less is desirable.

Next, regarding the magnetic characteristics of the developing roll,
On the surface of the developing roll 23, if the maximum value of the magnetic flux density in the vertical direction from each magnetic pole is less than 20 mT (200 gauss), carrier scattering occurs, and if it exceeds 100 mT (1000 gauss), the spike of the developer is too high. However, the space between the developing roller 23 and the latent image carrier 11 cannot be reduced, which is not practical. Further, if it exceeds 60 mT (600 gauss), it is necessary to increase the peripheral speed of the developing roll 23 in order to suppress the sweep pattern, and for a small-diameter roll having a diameter of less than 30 mm, practical rotation of ordinary machine parts is possible. No longer a number. Also, from the viewpoint of centrifugal force, carrier scattering worsens,
Both the sweep pattern and carrier scattering cannot be suppressed. Therefore, the practical range is 20 mT (200 gauss) or more and 60 mT (600 gauss) or less.

Furthermore, it is known that carrier scattering occurs when the force received from the centrifugal force and the electric field becomes stronger than the magnetic restraining force acting on the carrier. According to the present inventors, the effective developing area Y
With the developing roll 23 used in Examples 1 and 2 in which both the pitch and the magnetic flux density are uniformly magnetized, or a developing roll conforming to the former even if the peak magnetic flux density of the pitch and the magnetic pole is not uniform, Is L (unit: mm), and the peak value of the magnetic flux density in the vertical direction (radial direction) on the surface of the developing roll 23 of each magnetic pole is B (unit: Gau).
ss), as shown in FIG. 6, suitable conditions in this embodiment (conditions that do not include the carrier scattering generation region, the sweep pattern generation region, and each region of the roll diameter of 30 mm or less that is inappropriate) In the above, it was found that if B × (B / L) ≧ 20000 is satisfied, carrier scattering can be prevented without performing a strict magnetic force calculation. Here, the above formula “B ×
(B / L) ≧ 20000 ”, the magnetic force applied to a certain magnetization is generally the product of“ magnetization ”,“ the magnetic flux density where the magnetization exists ”and“ the magnetic flux density change where the magnetization exists ”. The vector display or the absolute value display is performed after calculating for each coordinate component, but the above formula is simply the above formula, in which the magnetic force is constant and the magnetic force is constant only for the radial direction magnetic flux density for the coordinate component in the L direction. Is a relative comparison. In addition, from the condition of using a developing roll having a diameter of 18 mm / 400 rpm and a carrier having a true specific gravity of 5, a disadvantageous condition from the viewpoint of centrifugal force (for example, a heavy carrier of iron powder is held by a small diameter roll and conveyed to the developing area). If the roll is rotated at a high speed to obtain a required amount of developer per unit time, it is assumed that carrier scattering will occur violently), and the above relational expression does not hold even under the conditions appropriate in this embodiment.

Regarding the characteristics of the carrier of the developer, the practical magnetization at 1000 Oersted is 20 em.
If it is less than u / g, carrier adhesion to the latent image carrier 11 is likely to occur, and if it exceeds 60 emu / g, the developing roll 2
On the top of Fig. 3, repulsion due to the magnetic force between the carriers occurs and the intervals between the individual chains are widened, making the sweep pattern more noticeable. Therefore, the practical magnetization is 20 emu / g or more and 60 emu.
/ G or less is desirable. Also, the average particle size (weight average particle size)
For the carrier of less than 20 μm, the carrier is easily attached to the latent image bearing member 11 due to the relationship between the magnetic force acting on one carrier and the electrostatic force. Also decreases, so the image density becomes insufficient. Therefore, the average particle diameter (weight average particle diameter) is preferably 20 μm or more and 70 μm or less.

Further, regarding various characteristics of the toner of the developer, when the average particle diameter (weight average particle diameter) is less than 3 μm, the developing property is seriously deteriorated, and the toner average particle diameter of 5 μm or more is practically used. Is desirable. On the other hand, when the average particle diameter of the toner exceeds 15 μm, the sharpness of fine lines of the image and the graininess in the low density region become poor. Further, in forming an image using the developing device according to the present embodiment, laser exposure is performed by pulse width modulation of 256 gradations of 63.5 μm per pixel to form an electrostatic latent image with a sharp thin line image. When the toner for developing the toner is made finer to improve fine line sharpness and graininess in a low density region, it is desirable that the average particle diameter is 9 μm or less.

Further, regarding the triboelectric charging with the carrier, it is necessary to set the charge amount of the toner within the range of 5 to 50 μc / g. When it is less than 5 μc / g, not only the electrostatic bond between the toner and the carrier is weakened to cause toner scattering, but also the response to the developing electric field is slowed down, resulting in poor reproducibility of fine lines and low density. Further, when the charge amount of the toner becomes high, the latent image on the latent image carrier is electrostatically saturated with a small amount of toner, and a very high voltage latent image is required to secure the image density. As a means for securing the image density, there is a method of increasing the coloring power of the toner, but in this embodiment, the optimization of the coloring material dispersion has already been completed, and the amount of the coloring material is doubled at this stage. Even if it is raised, the amount of coloring does not simply double. Therefore, if it exceeds 50 μc / g, the initial charging potential becomes 100
It becomes difficult to use a conventional latent image carrier which is used at 0 V (absolute value) or less.

Regarding the surface roughness of the developing roll 23, in the apparatus described in Examples 1 to 4, if the surface roughness is too small, the developer is apt to slip when passing through the layer regulating member 27, and The toner amount in G makes it easy for the amount of conveyance to change, and as a result, the stability of image density deteriorates. If the surface roughness is too large, the developing roll 2
It becomes difficult to manage the shake of No. 3, and uneven image density according to the rotation cycle of the developing roll 23 is likely to occur. For example, when a magnetic carrier having the smallest average particle size of 20 μm is used, and if the surface roughness is Rz = 2 μm (10% of the average particle size of the magnetic carrier) or more, it passes through the layer regulating member 27. The slip at the time can be suppressed practically. The largest average particle size of the magnetic carriers is 70 μm.
It was found that, when the surface roughness Rz was 50 μm (70% of the average particle diameter of the magnetic carrier), the image density unevenness was generated, and it was not practical. That is, the surface roughness Rz is preferably at least 2 μm or more and 50 μm or less.

Example 5 (First Example of Color Image Forming Apparatus) Next, an example of a color image forming apparatus using a developing device to which the present invention is applied will be described. In FIG. 7, reference numeral 51 is a latent image carrier such as a cylindrical photosensitive drum, and 5
Reference numeral 2 is a charger for charging the latent image carrier 51, 53 is a built-in semiconductor laser, polygon mirror 531 and the like (not shown), and the latent image carrier 51 is charged with a light beam corresponding to each color component image data. A laser writing unit for writing an electrostatic latent image,
Reference numerals 54 to 57 denote developing devices for black, yellow, magenta, and cyan, and 58 charges or charges each toner image and the latent image carrier 51 to an optimum state for transfer after a toner image for each color component is formed. A pre-transfer charger that removes electricity, a transfer charger that collectively transfers toner images of respective color components to a recording paper 61 carried along a paper guide 60, and a recording paper 61 that adheres to the latent image carrier 51 after transfer. A peeling charger for peeling, 63 is a cleaning device for removing the residual toner on the latent image carrier 51, 64 is a destaticizing exposure device for removing the residual charge on the latent image carrier 51, and 65 is the recording paper 62 after transfer. A conveyance belt for conveying to a fixing device (not shown).

In this embodiment, the black developing device 54 uses the magnetic one-component black toner for the developing roll 5.
41, and the toner is thinned by the layer thickness regulating plate 542 and an electric charge necessary for development is given. Thereafter, an AC bias in which a direct current is weighted is applied to the opposing portion of the latent image carrier 51, so that The toner is jump-developed onto the image carrier 51. The magnetic one-component toner used in this example has an average particle size of 9 μm produced by kneading magnetic powder in a resin binder, and has a large magnetization value measured in a magnetic field of 5K Oersted (KA / m). Saga 34
A magnetic toner having an emu / g (Am ² / Kg) was used.

Each of the yellow, magenta, and cyan developing devices 55 to 57 employs a non-contact two-component alternating electric field developing system to which the present invention is applied.
For example, in addition to basically including the configuration shown in Embodiment 1, the toner image on the latent image carrier 51 developed in the previous step is disturbed, or the existing toner image on the latent image carrier 51 is transferred to each of the developing devices 55 to 55. To prevent reverse transfer to the 57 side,
The air gap and alternating electric field conditions are optimized.

The latent image carrier 51 is made of an organic photoconductor that is negatively charged, and the surface potential of the latent image carrier 51 after being uniformly charged by the charger 52 is substantially constant in each cycle. -7
The surface potential of the latent image carrier 51 in the exposed portion was set to 00V at about −200V in each cycle.
Further, the latent image carrier 51 rotates at a speed of 120 mm / sec, the developing roll surface speed of the non-contact two-component developing devices 55, 56 and 57 is 240 mm / sec, and the developing roll of the magnetic one-component developing device 54. Surface speed of 180mm /
It was set to sec.

Next, the image forming process of the color image forming apparatus according to this embodiment will be described. First, as the first cycle, the latent image carrier 51 is charged by the charger 52, and a latent image corresponding to black is formed at a predetermined position on the latent image carrier 51 by the laser light 532 from the laser writing unit 53. The latent image is developed by the black developing device 51. At this time, the laser light is adapted to write the image portion, and the latent image carrier 51 charged by the charger 52.
The toner having the same electric charge as the surface potential polarity is developed on the laser light irradiation portion of the latent image carrier 51.

Next, in the second cycle, the latent image carrier 51 is recharged by the charger 52, and the latent (black)
In the process, the portion of the latent image carrier 51 whose potential has been lowered by the irradiation of the laser beam 532 is restored to the original potential again. Thereafter, the laser beam 532 from the laser writing unit 53 irradiates an image corresponding to a yellow color to a predetermined position of the latent image carrier 51 again, and the yellow developing device 55 charges the latent image carrier charged by the charger 52. The laser light irradiation portion of the latent image carrier 51 is developed with yellow toner having the same electric charge polarity as the surface potential polarity of the body 51.

Thereafter, similarly, as the third cycle, recharging by the charger 52, irradiation of the magenta image by the laser beam 532 from the laser writing unit 53, development of the magenta image by the magenta developing device 56, and the fourth cycle. As a cycle, each step of recharging by the charger 52, irradiation of a cyan image by the laser beam 532 from the laser writing unit 53, and development of a cyan image by the cyan developing device 57 is performed.

At the time when the cyan image developing process by the cyan developing device 57 is completed, black, yellow, magenta, and cyan toner images corresponding to the irradiation image are present on the latent image carrier 51. These toner image and latent image carrier 51
Is irradiated by the pre-transfer charger 58 as necessary, and is charged or discharged to a state suitable for transfer, and then transferred to the transfer charger 5.
The recording paper 6 coming in from the paper guide 60 by 9
The toner images of black, yellow, magenta, and cyan on the latent image carrier 51 are transferred onto the image carrier 1 in one step. After the transfer is completed, the recording paper 61 is de-charged by the peeling charger 62, peeled off from the latent image carrier 51, and conveyed by a conveyor belt 65 to a fixing device (not shown) for a fixing step.

On the other hand, after the transfer process is completed, the residual toner on the latent image carrier 51 is cleaned by the cleaning device 63, subsequently exposed by the neutralization exposure device 64, and again enters the charging process by the charging device 52. Repeat all steps to output multiple continuous prints. The cleaning device 63 is configured such that all or part of the cleaning device 63 can be retracted, and is in a non-contact state with the latent image carrier 51 during the formation of the toner images of the four colors.
The toner on the latent image carrier 51 is not disturbed.

Next, various experiments were conducted on the color image forming apparatus according to this embodiment. In such a color image forming apparatus, the magnetic one-component toner developed on the latent image carrier 51 by the black developing device 54 is transferred between the non-contact two-component developing devices 55, 56 and 57 and the latent image carrier 51. When passing through the gap, the magnetic one-minute toner developed on the latent image carrier 51 is transferred to the non-contact two-component developing devices 55, 56,
In order to prevent the non-contact two-component developing devices 55, 56, 57 from being magnetically attracted to the non-contact two-component developing devices 55, 56, 57 side by the magnetic field generated from the developing roll in 57, the non-contact two-component developing device 55,
It is necessary that the magnitude of the magnetic field generated by 56, 57 is extremely small near the latent image carrier 51.

Further, the non-contact two-component developing devices 55, 56,
The carrier in the two-component developer on the developing roll 23 of No. 57 has a Cloning force represented by the product of the electric field formed by the potential difference between the surface potential of the latent image carrier 51 and the developing roll 23 and the charge of the carrier. Therefore, in order to prevent the latent image carrier 51 from being easily attracted, the magnitude of the magnetic field generated by the non-contact two-component developing devices 55, 56, 57 must be sufficiently large on the developing roll 23. .

Therefore, the non-contact two-component developing devices 55, 5
The carrier in the two-component developer on the developing rolls Nos. 6 and 57 is prevented from adhering to the latent image carrier 51, and the magnetic one-component toner developed on the latent image carrier 51 is not contacted. In order to prevent the non-contact two-component developing devices 55, 56, 57 from being magnetically attracted to the non-contact two-component developing devices 55, 56, 57 by the magnetic field generated from the developing roll 23 in the two-component developing devices 55, 56, 57, the non-contact two-component developing device is used. It is required that the magnetic field generated from the magnet roll inside the developing roll 23 of each of the devices 55, 56 and 57 is sufficiently large on the developing roll 23 and sufficiently small near the latent image carrier 51. That is, the attenuation of the magnitude of the magnetic field must be large in the range of the distance from the developing roller 23 to the latent image carrier 51.

As a method for practically controlling the attenuation rate of this magnetic field, several prototypes having different distances between magnetic poles in the effective developing region were prototyped, and the distances between magnetic poles on the sleeve surface and on the sleeve surface were measured. When the attenuation rate of the magnetic flux density peak value, that is, {1- (magnetic flux density on latent image carrier 51 / magnetic flux density on sleeve surface)} × 100 is taken, the result is as shown in FIG.

Next, the five types of developing rolls 23 shown in Table 1 are actually sequentially mounted on the non-contact two-component developing device 55 of the color image forming apparatus shown in FIG. 7, and (1) latent image carrier is actually mounted. 5
Whether the magnetic one-component toner developed on No. 1 is magnetically attracted to the non-contact two-component developing device 55 side by the magnetic field generated from the developing roll 23 of the non-contact two-component developing device 55, (2) non- The latent image carrier 5 of the carrier in the two-component developer on the developing roll 23 of the contact two-component developing device 55.
When an experiment was conducted to determine whether or not adhesion to 1 occurred, the results shown in Table 1 were obtained.

[0071]

[Table 1]

From this result, in order to prevent the magnetic one-component toner from being attracted onto the latent image carrier 51, the latent image carrier 5 is used.
It is necessary to suppress the magnetic flux density on the surface of the developing roller 23 to about 250 Gauss or less. In order to prevent the carrier from adhering to the latent image carrier 51, the magnetic flux density on the sleeve surface of the developing roller 23 should be at least 330 Gauss. It was verified that the above needs to be done.

Further, in FIG. 9, a region in which the magnetic flux density on the sleeve of the developing roll 23 and the magnetic flux density on the surface of the latent image carrier 51 are allowed is shown by hatching. In one developing roll 23, the relationship between the magnetic flux density on the sleeve and the magnetic flux density on the surface of the latent image carrier 51 is determined by the attenuation rate of the magnetic flux shown in FIG. 8, and this attenuation rate is related to the distance between the magnetic poles on the sleeve. Therefore, the straight line shown in FIG. 9 can be drawn by taking the relationship between the magnetic flux density on the sleeve and the magnetic flux density on the surface of the latent image carrier 51 with the distance between the magnetic poles on the sleeve as a parameter.

In FIG. 9, the distance between the magnetic poles on the sleeve is 5 m.
By setting m or less, the magnetic flux density on the latent image carrier 51 is suppressed to about 250 Gauss or less to prevent the adsorption of the magnetic one-component toner on the latent image carrier 51, and the latent image carrier 51 on the carrier is It is shown that the magnetic flux density on the surface of the sleeve can be set to about 330 gauss or more in order to prevent the adherence to the sleeve. However, when the distance between the magnetic poles on the sleeve is set to 5 mm, the allowable width of the magnetic flux density on the sleeve is only about 40 gauss, which is not practical. Therefore, it is actually 4 mm or less, preferably about 3 mm.

As the developing roll 23 used in the above experiment, a cylindrical iron core (core material) wound in advance with a plate-shaped rubber magnet and fixedly bonded, and a cylindrical ferrite magnet were magnetized. I used one. In both types, actually, when the distance between the magnetic poles is reduced, the magnetic field on the magnetic poles that are saturated and magnetized decreases. Actually thickness 0.5mm
As shown in FIG. 2, the magnet roll 25
The experiment was conducted by setting the gap between the sleeve 24 and the sleeve 24 to 0.3 mm. However, when the distance between the magnetic poles on the sleeve surface was 3 mm, the magnetic flux density on the sleeve surface was 400 gauss, and the magnetic pole on the sleeve surface. When the distance was set to 2 mm, the magnetic flux density on the sleeve surface was limited to about 250 gauss. Even if the distance between the magnetic poles on the sleeve surface is set to 2 mm, it is possible to increase the magnetic flux density on the sleeve by using a magnetic material having a high magnetic force, but the price becomes too high and the device becomes widespread. Then there is a problem.

In the developing device 54 of the color image forming apparatus according to this experiment, the average grain size was 9 μm, and the magnitude of magnetization measured in a magnetic field of 5K Oersted (KA / m) was 34.
A magnetic one-component black toner of emu / g (Am2 / kg) is used in the developing devices 55, 56, and 57, and the distance between the magnetic poles on the sleeve surface is 2.8 mm and the magnetic flux density on the sleeve surface is 380 gauss. The magnetic powder was mixed and dispersed in a resin binder so as to have a practical average magnetization of 40 emu / g and a weight average particle diameter of 40 μm as a developer, using the developing device of Example 1 equipped with a ferrite magnet roll, and then pulverized and classified. Using a developer in which polyester yellow, magenta, and cyan toners each having a weight average particle diameter of 7 μm are mixed and stirred as a magnetic carrier, and an image formation by multicolor overdevelopment was tried in the above-mentioned step, a magnetic single component was obtained. Distortion of the black toner image and mixing of the magnetic one-component black toner into the non-contact two-component developing devices 55, 56 and 57 do not occur at all, and good full color An image was obtained.

In this embodiment, the magnetic one-component toner is manufactured by mixing powder in a resin binder, has an average particle size of 9 μm, and has a particle size of 5K oersted (KA).
/ M), the magnitude of magnetization measured in a magnetic field of 34 emu /
A magnetic toner of g (Am ² / Kg) was used. However, as a condition that the magnetic one-minute toner on the latent image carrier 51 is not adsorbed by the developing roll 23 of the non-contact two-component developing devices 55 to 57, the magnetization size and the particle size of the magnetic one-component toner are also major factors. Become. Generally, the magnitude of magnetization is σe
When mu / g (Am ² / Kg) and the particle size are rm, the magnitude of the magnetic force acting on one toner in the magnetic field is σ × r
Proportional to ³ . For example, the average particle size of the magnetic one-component toner is 9
When the thickness is changed from μm to 12 μm, the magnetic force acting on the magnetic one-component toner becomes 2.4 times. At this time, in order to establish the allowable range shown in FIG. 9, it is necessary to reduce the amount of internally added magnetite magnetic powder and control σ to 1 / 2.4. The magnitude of magnetization actually measured in a magnetic field of 5K oersted (KA / m) is 34 emu / g (Am ² / Kg)
The toner having average particle diameters of 10 μm and 12 μm is used, and the developing devices 55 to 57 have a magnetic pole distance on the sleeve surface of 2.8 mm and a magnetic flux density of 380 on the sleeve surface.
Using the non-contact two-component developing apparatus of Example 1 equipped with a Gaussian cylindrical ferrite magnet roll, an image formation by multi-color over-development was tried in the above-mentioned steps, and the average particle size was 1
With the magnetic one-component toner of 0 μm, the magnetic one-component toner on the latent image carrier 51 was not adsorbed by the developing roll 23 of the non-contact two-component developing devices 55 to 57, but the average particle diameter of the magnetic one-component toner was 12 μm. The adsorption phenomenon occurred in the one-component toner. From this, in order to establish the allowable range shown in FIG. 9, the magnitude of magnetization measured in a magnetic field of 5K Oersted (KA / m) is σemu / g (Am ² / K).
g), when the average particle size is rm, σ × r ³ <3.5 ×
It can be seen that it is necessary to have the values of σ and r in the range of 10 ⁻¹⁴ .

In the color image forming apparatus according to this embodiment, the same experiment as described above was carried out by using the developing devices 55 to 57 in any of the embodiments 2 to 4, and a magnetic one-component black toner image was obtained. And the magnetic one-component black toner was not mixed into the non-contact two-component developing devices 55, 56 and 57, and a good full-color image was obtained.

Example 6 (Second Example of Color Image Forming Apparatus) FIG. 10 shows another example of the color image forming apparatus to which the present invention is applied. The same components as those in the fifth embodiment are designated by the same reference numerals as those in the fifth embodiment, and detailed description thereof will be omitted here. In the color image forming apparatus according to this embodiment, the laser writing unit 53 forms the first latent image by the first exposure 533 corresponding to the black image, and the second exposure 534 by the second exposure 534 corresponding to the red image, for example. To form the latent image of. In this embodiment, the black developing device 54 is provided around the latent image carrier 51.
And developing device 5 for colors other than black, for example red
5 is installed, magnetic one-component toner is used as the black developing device 54, and the red developing device 55 is used.
A non-contact two-component developing system was used.

Red developing device 55 used in this embodiment
Is a developing roller 23 having a magnetic pole distance on the sleeve surface of 2.8 mm and a magnetic flux density on the sleeve surface of the cylindrical ferrite magnet roll of 380 gauss. Magnetic powder was mixed, dispersed, pulverized and classified in a resin binder so that the practical magnetization was 40 eum / g with an average particle diameter of 40 μm, and a styrene acrylic red toner with a weight average particle diameter of 12 μm was mixed and stirred. The mixing ratio of the toner in the developer is about 10% by weight, the toner charging polarity is positive at a relative humidity of 30% to 85%, and the charging utilization is 12 to 25 μc /
What was adjusted to g was used.

The negatively charged magnetic one-component black toner of the black developing device 54 is manufactured by mixing magnetic powder in a resin binder and has an average particle size of 9
μm, and the magnitude of magnetization measured in a magnetic field of 5K Oersted (KA / m) is 34 emu / g (Am ² / Kg)
Therefore, a magnetic toner that is negatively charged was used.

Next, the image forming process of the color image forming apparatus according to this embodiment will be described. In this embodiment, the latent image carrier 51 is uniformly negatively charged by the charger 52, and the first latent image corresponding to the black image is formed on the latent image carrier 51 by the first exposure 533. , This first
The latent image of (1) is reversely developed by the developing device 54 with the magnetic one-component black toner charged with negative polarity. Next, for example, a second latent image corresponding to a red image is formed on the latent image carrier 51 by the second exposure 534, and the second latent image is positively charged by the non-contact two-component developing device 55. Regular development with non-magnetic red toner. The polarities of the magnetic one-component black toner and the non-magnetic red toner developed on the latent image carrier 51 are made uniform by the transfer pretreatment charger 58,
It is transferred onto the recording paper 61 at once by the transfer charger 59.

In such a color image forming process,
Disturbance of the magnetic one-component black toner image and mixing of the magnetic one-component black toner into the non-contact two-component developing device 55 did not occur at all, and a good two-color image was obtained.

[0084]

As described above, according to the developing device of the present invention, the resin binder is used as the magnetic carrier of the developer in contrast to the non-contact two-component developing method in which the developing magnetic poles in a plurality of rows are arranged in the effective developing area. The magnetic powder is mixed and dispersed in it, and then crushed and classified.The height of the spike of the developer standing on each developing magnetic pole is controlled to be low, so the developing magnetic pole pitch is set to the developing amount. Even if the range is set so that both securing and suppressing carrier scattering can be easily achieved, it is possible to effectively avoid the occurrence of the sweep pattern on the image.

In particular, in the present invention, by optimizing the magnetization characteristics of the magnetic carrier, and further by optimizing the magnetic force distribution of the developer carrying member, it is possible to secure the development amount, suppress carrier scattering, and avoid sweep patterns. Can be easily realized.

Further, according to the color image forming apparatus of the present invention, after the magnetic black toner image and the non-magnetic color toner image other than black are formed on the latent image carrier, the toner images of respective colors are collectively transferred to the recording medium. In this type, as the color developing means, a plurality of rows of developing magnetic poles are arranged in the effective developing area, magnetic powder is mixed and dispersed in a resin binder as a magnetic carrier of the developer, and then crushed and classified. Since the height of the spike of the developer rising on each developing magnetic pole is regulated to a low level, both the magnetic flux density on the developer carrier and the distance between the developing magnetic poles should be adjusted to be small in the effective developing area. By this, the developer on the developer carrier can be thinned so that the developer is not in contact with the latent image carrier, and the amount of development can be secured, carrier scattering can be suppressed, and sweep pattern can be easily avoided. Door can be.

For this reason, the developability by the color developing means can be kept good, and the strength of the magnetic field generated from the inside of the developer carrier of the color developing means is made extremely small on the surface of the latent image carrier. Therefore, it is possible to effectively avoid the situation where the one-component magnetic black toner developed on the surface of the latent image carrier is magnetically adsorbed to the developer carrier when passing through the color developing means. It is possible to effectively avoid the disturbance of the magnetic one-component black toner image on the latent image carrier and the color mixture due to the mixing of the black toner into the color developing means.

Furthermore, in the above color image forming apparatus,
By optimizing the magnetization characteristics of the magnetic black toner, it is possible to more reliably avoid the disturbance of the magnetic one-component black toner image on the latent image carrier and the color mixture due to the mixing of the black toner into the color developing means. You can

[Brief description of drawings]

FIG. 1A is an explanatory diagram showing a configuration of a developing device according to the present invention, and FIG. 1B is an explanatory diagram showing a configuration of a color image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram illustrating details of the developing device according to the first embodiment.

FIG. 3 is an explanatory diagram illustrating details of a developing device according to a second embodiment.

FIG. 4 is an explanatory diagram illustrating details of a developing device according to a third embodiment.

FIG. 5 is an explanatory diagram illustrating details of a developing device according to a fourth embodiment.

FIG. 6 is a graph showing the relationship between the magnetic pole pitch L on the surface of the developing roll and the magnetic flux density B in the vertical direction on the surface of the developing roll, and the usable area in Examples 1 and 2.

FIG. 7 is an explanatory diagram illustrating details of a color image forming apparatus according to a fifth embodiment.

FIG. 8 is a graph showing the relationship between the developing magnetic pole spacing and the magnetic force attenuation rate of the non-contact two-component developing device in Example 5.

FIG. 9 is a graph diagram for deriving a required magnetic pole spacing on the sleeve surface of the developing roll of the non-contact two-component developing device in Embodiment 5.

FIG. 10 is an explanatory diagram illustrating details of a color image forming apparatus according to a sixth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Developer carrying body, 2 ... Non-magnetic member, 3 ... Magnet member, 3
a ... development magnetic pole, 4 ... latent image carrier, 5 ... recording medium, 6 ... black developing means, 7 ... color developing means, G ... two-component developer, C ... magnetic carrier, T ... toner, Z ... static Electrostatic latent image, EAC ... alternating electric field, TB ... Black toner image, TC ... Color toner image

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 15/01 113 Z 15/08 507 X

Claims (5)

[Claims] 1. The inside whose surface is covered with a non-magnetic member (2)
Has a developer carrying member (1) on which a magnet member (3) is installed, and the developer carrying member (1) is disposed so as to face the latent image carrying member (4), and at the same time, the latent image carrying member (4). A plurality of rows of developing magnetic poles (3a) having different polarities alternately arranged on the magnet member (3) corresponding to the effective developing area (Y) facing each other, and nonmagnetic on the developer carrier (1). The two-component developer (G) composed of the toner (T) and the magnetic carrier (C) is carried in a non-contact state with the latent image carrier (4), and the latent image carrier (4) and the developer carrier (1) are also supported. ) And an alternating electric field (EAC) in which a DC component is superposed on the latent image carrier (4)
In the developing device adapted to develop the electrostatic latent image (Z), the magnetic carrier (C) is a carrier obtained by mixing and dispersing magnetic powder in a resin binder, and then crushing and classifying the magnetic powder. Characteristic developing device. 2. The magnetic carrier according to claim 1, wherein the magnetic carrier (C) has a practical magnetization at 1000 Oersted of 20 emu / g or more and 60 emu / g or more.
A developing device characterized by the following. 3. The developer carrier (1) according to claim 1, wherein the developing magnetic pole (3a) center interval on the surface of the developer carrier (1) is L in the effective developing region (Y).
(Unit: mm), and the peak value of the radial magnetic flux density on the surface of the developer carrying member (1) of each developing magnetic pole (3) is B (unit:
Gauss), 2 ≦ L ≦ 5, 200 ≦ B ≦ 60
0, B × (B / L) ≧ 20,000, all of the developing devices. 4. A black toner image (TB) and a color toner image (TC) other than black are formed on a latent image carrier (4) by an image forming process in which the formation order of at least the black toner image (TB) is not the last. After that, in the color image forming apparatus in which each color toner image (TB, TC) is collectively transferred to the recording medium (5), the black developing means (6) is of a one-component developing system using magnetic black toner. On the other hand, the developing means (7) for colors other than black has the developer carrying member (1) whose surface is covered with the non-magnetic member (2) and in which the magnet member (3) is installed. The developer carrying member (1) is arranged opposite to the latent image carrying member (4), and the magnet member (3) corresponding to the effective developing area (Y) facing the latent image carrying member (4) is different. Multiple lines of developing magnetic poles with alternating polarities ( Arranging a), the developer carrying member (1)
A two-component developer (G) composed of a non-magnetic toner (T) and a magnetic carrier (C) is carried on the latent image carrier (4) in a non-contact state, and the latent image carrier (4) and the developer are also supported. An alternating electric field (EA) in which a DC component is superposed between the carrier (1)
C), and the electrostatic latent image (Z) on the latent image carrier (4)
In which magnetic powder is mixed and dispersed in the resin binder by the magnetic carrier (C), and then pulverized,
A color image forming apparatus, which is a classified carrier. 5. The color image forming apparatus according to claim 4, wherein the black developing means (6) has a magnetization magnitude σ (unit: emu / g) measured in a magnetic field of 5K Oersted of magnetic black toner. , Its average particle size is r (unit:
m), the relationship of σ × r ³ <3.5 × 10 ⁻¹⁴ is established.