JPS63313174A - Image forming method - Google Patents

Abstract

PURPOSE:To enhance the high resolving power and high image quality of a multicolor image by using a carrier layer having a prescribed relation between the intensity of magnetization and an average diameter of grain, which provides a covering layer made of insulating substance on its surface, for two-component developer and executing non contact developing. CONSTITUTION:The carrier provided the covering layer made of insulating substance such as a resin and a ceramics, etc., which has the relation such as 30<=M<=-0.8R+150 (provided that 10<=R<=150) between the average diameter of grain R(mum) and the intensity of magnetization M(emu/cm<3>) is selected for two-component developer. If the diameter of grain of the carrier becomes <10mum or the intensity of magnetization of the carrier becomes <30emu/cm<3>, it is hard to obtain uniform developer layer and it is easy to cause the scatter, etc., of the carrier. When the diameter of grain becomes >150mum or the intensity of magnetization becomes >-0.8R+150emu/cm<3>, the grains become rough and the image quality is deteriorated. Then, by making the diameter of grain and the intensity of magnetization of the carrier within this range, the multicolor image having the high resolving power and high image quality can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming method, and particularly to an image forming method for forming a multicolor image on an image carrier using a two-component developer.

[Background of the invention]

Conventionally, in order to form a multicolor image using an electrophotographic method, as described in, for example, Japanese Patent Application Laid-open Nos. 47-27537 and 59-58452, an image carrier that has been uniformly charged in advance is The process of exposing to color separated light to form an electrostatic latent image, developing the latent image with complementary color toner, and transferring the obtained color toner image onto a transfer material wound around a transfer drum is repeated. A method is used in which a multicolor toner image is formed on the transfer material. That is, for example, color-separated light obtained from a multicolor original through blue (B), green (G), red (R), and ND filters is exposed onto an image carrier to form corresponding electrostatic latent images. and developed with complementary color toner to produce yellow (Y), magenta (M), cyan (C), and black (BK).
Each time a toner image of each color is formed on an image carrier, it is sequentially transferred onto a transfer material on a transfer drum, and the transfer material is fixed after 3 minutes to form a multicolor image. I have to.

The image forming method described above is superior in that more accurate and rich information can be obtained than in the case of black and white images, but "misalignment" easily occurs in the superposition of the toner images of each color, resulting in color turbidity. , and the resolution decreases.

Further, since a transfer drum is required, there is a problem that the apparatus becomes larger.

On the other hand, as methods for developing an electrostatic latent image on an image carrier, there are two methods: one using a single-component developer consisting only of magnetic toner, and the other using a two-component developer containing non-magnetic toner and a magnetic carrier.

When using the above-mentioned -component developer, the amount of magnetic material that can be contained in the magnetic toner is at most 70 wt% or less, and the particle size is small. The adhesion force to the toner is weak, and the toner is easily scattered, and the fluidity and triboelectric charging properties of the developer are insufficient, resulting in poor developability and the inability to obtain clear images with high density. Because it contains magnetic substances,
Color toners become cloudy, making them unsuitable for multicolor image formation.

On the other hand, when using a two-component developer, it contains a magnetic carrier with a relatively large particle size in addition to the non-magnetic toner.
Compared to the above-mentioned -component developers, it has excellent transportability by the developer transporting carrier, developer fluidity, and triboelectric charging properties, and is suitable for multicolor image formation, allowing the use of color toners without brownish turbidity. Excellent in many ways.

When developing an electrostatic latent image using such a two-component developer,
A method is used in which a magnetic brush is formed using a magnetic carrier along the lines of magnetic force of a magnet placed in an image sleeve, and the surface of the image carrier is rubbed with the magnetic brush for development.

However, in the above development method, the toner image once developed moves due to the force received from the magnetic brush, resulting in streaks, thin lines becoming blurred and resolution being reduced, and redundant toner development leading to multi-color image formation. There are problems such as the toner image obtained by development being destroyed by subsequent development.

For example, in JP-A-56-144452, a process of developing an electrostatic latent image on an image bearing member in a non-contact manner using a two-component developer consisting of color toner and a magnetic carrier is repeated, and each color toner image is polymerized. A multicolor image forming method has been proposed in which a multicolor toner image is formed on a 1n image carrier and transferred to a transfer material.

In addition, the above-mentioned publication states that, for example, there is a
A gap of 0 to 500μ is provided, and a DC voltage of 100 to 300μ and a frequency of 100 to 5 are applied to the sleeve that conveys the developer.
There is a description of non-contact development by applying a bias with a superimposed alternating current voltage of 100 to 2000 V at 000 Hz.

According to the multicolor image forming method described in the above publication, since a two-component developer is used and non-contact development is performed, the above-mentioned problems in forming a multicolor image are improved. Improved fluidity, tribo-electrification properties, sweeping lines, image tone, resolution, etc. Furthermore, toner images of each color are formed on the image carrier by superimposing them and transferred to the transfer material at once, eliminating the need for a transfer drum. Therefore, improvements such as the ability to miniaturize the device are expected.

Furthermore, in Japanese Patent Application Laid-Open No. 59-121077, a dot latent image written by exposure to a laser beam is developed in a non-contact manner using a two-component developer containing color toners, and red, red, and red are formed on an image carrier. A multicolor image method has been proposed that obtains three-color images of blue and black. In addition, in the above publication, as specific details, an insulating toner with an average particle size of 13 μm for each color of red, blue, and black, an average particle size of 25 μm for red color, 30 μm for blue color, and 50 μm for black color, resin dispersion, etc. Using a type insulating magnetic carrier,
The gap between the sleeve and the image carrier is 500 to 1000 μm, and the developer layer thickness is smaller than the gap. For example, if the gap between the developer layer and the image carrier is 150 μm, the sleeve is
Non-contact development is performed by rotating a 0RP ring magnet roll at 1500 rpm.

In addition, the development bias conditions are: during red development: DC bias; -100VAC bias; 1000Hz, 900V (P-P) during blue development.
: DC bias; -100VAC bias; 11
00Hz, 1050V (P-P) During black development: DC
Bias; -100VAC bias; 130011
z, 1200V (P-P).

Further, as the resin dispersion carrier, for example, 200 parts by weight of ferrite powder with an average particle size of lμ is dispersed in 100 parts by weight of a styrene-acrylic copolymer resin, and the average particle size is 25 μm.
According to the estimations of the present inventors, the strength of magnetization of such carrier particles is:
It is determined to be 98-99 emu/cm3.

Thus, the above-mentioned publication contains specific descriptions regarding development conditions when forming a multicolor image, particle sizes of toner and carrier in the developer used, and the like.

Further, JP-A-59-154469 proposes a non-contact reversal development method using a two-component developer containing a resin-dispersed carrier and a toner. In the reversal development method, for example, an electrostatic latent image with a dark potential of -600V and a light potential of -150V is formed on the image carrier, and a frequency of 1800H2, 1600V (P
The resin-dispersed carrier (regular band) and toner (
A developer consisting of negative band $) is used.

JP-A-59-121077 and JP-A No. 59-15446
No. 9 and the like use a resin dispersion type in which a magnetic material is dispersed and contained in a resin as a carrier in the developer.

In the case of this resin dispersion type carrier, the magnetic powder in the resin is within 70 wt% at most, so apart from those with particularly strong magnetization such as iron, commonly used alloy types such as magnetite and ferrite are Due to insufficient magnetization strength, when the developer is transported by magnetic attraction by the developer transport carrier, the binding force of the magnetic poles within the developer transport member is weak, resulting in carrier scattering and carrier adhesion to non-image areas.

Furthermore, dispersion type carriers are inherently amorphous and have poor fluidity when forming a developer, and therefore tend to have insufficient triboelectric charging properties.Also, their surfaces have resin parts and magnetic properties that differ from this in their charging properties. There are exposed areas on the body, and the palm-rubbing electrification with the toner is unstable, making it impossible to maintain stable development characteristics especially when performing non-contact development.As a result, for example, fogging may occur or a "solid image" may result. In addition, so-called selective development occurs in which relatively large toner particles are consumed preferentially for development, and when images are repeatedly formed, there are problems such as density reduction.

Furthermore, since the surface of the carrier has parts with different charging properties as described above, some of the carriers may be charged to the same polarity as the toner due to frictional charging between the carriers, causing the carrier to adhere to the image area together with the toner. In particular, when forming a multicolor image, there is a problem in that dark brown carriers mix into the color image, causing color turbidity, making it impossible to obtain an image with clear tones.

For example, in the case of non-contact reversal development using a two-component developer consisting of a resin-dispersed carrier and toner, as disclosed in Japanese Patent Application Laid-Open No. 59-154469, toner is attached to exposed areas by development. However, when reverse development is performed using a developer using a resin-dispersed carrier, carrier may not only adhere to unexposed areas, but also carrier may adhere to exposed areas together with toner.

Figure 6 is a reference diagram of the developing device that performs the reversal development;
The figure is a potential diagram explaining the mechanism of reversal development.

In FIG. 6, l is an image carrier, 2 is a developer layer, 3 is a sleeve that rotates in the direction of the arrow, 4 is a magnet that rotates in the opposite direction to the sleeve (arrow b), and 5 is a oscillating electric field. 6 is a DC bias (developing bias) power source for performing reversal development, 8 is a developer layer thickness regulating member, and 7 is a developer stirring member.

Hereinafter, the state of carrier adhesion to the unexposed and exposed areas when the electrostatic latent image on the image carrier 1 is developed using a developer containing the resin-dispersed carrier in an inversion manner using the developing device shown in FIG. This will be explained using the potential diagram shown in FIG.

In the figure, DA has a dark potential VH in the unexposed region (here V+, t = -700V).

Further, P tl has a bright area potential (2) in a region exposed to coffee lint light such as a laser beam.

(Here, VL = 100V).

Also, vn is the developing bias voltage, here Vn=-600
It is V. The developer on the sleeve has a development bias V
The toner T, which is placed at the potential level B, but is negatively charged due to frictional charging with the carrier in the developer, is attracted by the potential difference between vL and Va (here, V, -VB = +500V) and is drawn to the bright area P.
It comes to adhere to H. However, when a resin-dispersed carrier is used as described above, the carriers are mutually charged by friction and the negative carrier P1 is mixed in with the positive carrier P2, so the positive carrier P2 adheres to the unexposed area. In addition to interfering with the adhesion of color toners during subsequent development, the carrier P also adheres to the bright areas PH together with the toner, causing color turbidity in the multicolor image.

[Problem that the invention seeks to solve]

Various studies have been conducted on the development conditions and properties of the developer in a non-contact development method that uses the two-component developer to form, for example, a multicolor image, and the range and conditions under which development is possible are being sought. However, detailed consideration has not been made at the stage of practical application.
Therefore, at present, problems associated with practical use, particularly problems associated with multicolor image formation, have not been resolved.

As a result of studying the characteristics of developers based on the development conditions necessary for practical use, IJt researchers found that, in particular, the characteristics of two-component developers
We have found that the characteristics of the rear color are the dominant factor when forming multicolor images.

[Means for solving problems]

(Objective of the Invention) The object of the present invention is to have good fluidity, triboelectrification, durability, magnetic properties, etc., and high resolution without fogging, density reduction, ghost image generation, carrier adhesion, etc. An object of the present invention is to provide an image forming method for forming a high-quality multicolor image.

(Structure of the Invention) The above object is a step of developing an electrostatic latent image on an image bearing member in a non-contact manner by applying an oscillating electric field to a developing area and using a two-component developer containing an I-ner and a carrier. In an image forming method in which a plurality of toner images are repeatedly formed on the image carrier in a superimposed manner, and the plurality of toner images are transferred onto a transfer material,
The two-component developer has a magnetization strength M (unit emu/am') measured in a magnetic field of 1000 oersteds and an average particle diameter R (unit μ-) that satisfy the following relational expression, and has an insulating surface. This is achieved by an image forming method in which only toner is attached to the electrostatic latent image on the image carrier during non-contact development in the developing step using a carrier having a coating layer made of a magnetic substance.

30≦M≦-0,8R+ 150 (However, 10≦R≦150) (Detailed Description of the Invention) When developing in a non-contact manner under an oscillating electric field as is known, the image carrier and the developer are transported. The gap with the sleeve is 1000
It is kept extremely narrow, less than μ. That is, if the gap is wide, an excessively high electric field is required to make the toner fly, causing breakdown, discharge, etc., and deteriorating the image quality. Furthermore, it becomes difficult for the toner to fly toward the image carrier, resulting in a decrease in development efficiency.

As a result of numerous experiments conducted by the present inventors, the gap between the image carrier and the sleeve in the developing area is preferably 250 to 250 mm.
The range is 600 μm. Here, if it is less than 250 .mu.-, the image quality is likely to deteriorate due to discharge under a normal oscillating electric field (1 to 3 KV), making it practically impossible to carry out non-contact development.

Moreover, if it exceeds 600 μm, the electric field necessary to develop the aI line cannot be obtained, and sufficient resolution cannot be obtained.

As will be described later, the image forming method of the present invention involves repeatedly developing to form a plurality of color toner images on an image carrier, transferring this to a transfer material at once, and fixing it by heating or the like to form a multicolor image. It consists of a process of forming. Therefore, during repeated development, it is necessary to absolutely avoid damaging the toner image obtained by the preceding development by the subsequent development.

For this reason, it is necessary to maintain an appropriate gap between the spikes of the developer layer and the image carrier, and according to experiments conducted by the present inventors, the gap is approximately 50 to
A gap of about 200μ is required.

If it falls below the 50μ end, the tips of the spikes may come into contact with the image carrier during the development process, causing sweeping marks or damaging the preceding toner image during subsequent development. It may go back to. If it exceeds 200 .mu.-, it becomes difficult for the toner to fly to the image carrier, resulting in a decrease in development efficiency. Therefore, a desirable developer layer has a thickness of 200 to 400 .mu.- in the development area, which is also convenient from a practical standpoint.

That is, if it is less than 200 .mu.m, flight will be hindered and the developing effect will be reduced, and if it is more than 400 .mu.m, contact development will occur and the resolution of the image will be reduced.

On the other hand, when performing non-contact development, the strength of the magnetic field of the developer transport carrier is approximately 1000 Gauss, for example, in Japanese Patent Application Laid-Open No. 60-2424.
No. 69), but according to the study results of the present inventors, it is 500 to 1000 Gauss. If it is less than 5oO Gauss, the force for restraining the developer layer on the sleeve surface is weak, making it difficult to form a uniform developer layer, and causing carrier and toner to fly.

If it exceeds 1000 Gauss, the developer will vibrate under the oscillating electric field, making it difficult for the toner to fly to the image bearing member and reducing the development efficiency.

Furthermore, as mentioned above, since the developer layer conveyed onto the sleeve is an extremely thin layer, most of the toner in the developer layer on the sleeve is consumed each time development is performed, and the toner is used for the next development. Carrier contamination on the sleeve caused by residual carrier from previous development is carried over, resulting in decreased density, uneven density, and
Ghost images are likely to occur.

To avoid this, the image f! It is necessary to increase the replacement efficiency of A7VII M and create a replacement sleeve that does not cause carrier contamination. That is, it is essential that the developer has excellent fluidity, and it is particularly desirable that the above requirements be satisfactorily met when forming multicolor images.

It is necessary to select a developer that has its own specific regulatory properties.

Based on the above-mentioned requirements, the present invention has a coating layer of an insulating material such as resin or ceramic as a carrier in the developer used, and has an average particle diameter l (μ theory and magnetization strength M-emu).
/ cm”; 30≦M≦−〇, 8R+
150 (provided that lO≦R≦150), preferably a spherical one with a core material of ferrite and a ratio of short axis to long axis of 1:1.5 is selected.

Here, if the carrier particle size is less than 10 μm, the binding force of the developer transport carrier to the carrier is weak, a uniform developer layer cannot be formed, carrier scattering etc. are likely to occur, and furthermore, developer Poor fluidity (insufficient triboelectric charging properties, reduced exchange efficiency of the developer layer after development, resulting in a decrease in density and generation of ghost images during the image formation process.Also, 150 μm)
If this value is exceeded, the spikes of the developer layer will become too high, leading to problems such as contact development being likely to occur, particles becoming coarse, and image quality worsening. Furthermore, if the magnetization strength is less than 30 esu/am', the restraining force of the developer by the developer transport carrier becomes weak, making it impossible to obtain a uniform developer, and carrier scattering etc. are likely to occur, and the magnetization strength becomes - If it exceeds 0.8R+150, hard and high spikes of developer are formed and contact development is likely to occur, resulting in a decrease in image quality accompanied by cross-cuts, decreased resolution of fine lines, damage to toner images, etc.

Here, in order to make the present invention easier to understand, the average particle diameter R (μ transport) of the carrier and the magnetization strength M (emu/cm')
The above-mentioned relational expression is shown in a graph in FIG.

In Figure 1, the horizontal axis is the average particle diameter R of the carrier (μ theory)
The vertical axis is the carrier magnetization strength M (e+*u/cm'
), and the hatched area is the range of conditions within which the carrier of the present invention falls.

In addition, Special No. 1m Showa 60131551 states that when performing non-contact development using a two-component developer, the carrier in the developer should have an average particle size of 30μ and a magnetization strength of 20eμ/g (
It is described that a resin-coated spherical ferrite carrier having a low efficiency of 1014 Ω or more is used. Although this carrier falls within the scope of the above relational expression, the developing method is completely different from that of the present invention. In other words, the technique described in the above publication, when forming a toner image on an image bearing member by non-contact development, causes both toner and carrier to fly toward the image bearing member, so that the toner is applied to the image area and the toner is applied to the non-image area. A carrier of opposite polarity is attached. When such a developing method is used in the image forming method of the present invention in which multiple color toner images are superimposed and formed on an image carrier during multiple development, carriers may adhere to non-image areas during the initial development. Therefore, it becomes impossible to form a latent image from the second time onward, and as a result, it becomes impossible to form a multicolor image.

More specifically, an electrostatic latent image obtained by dot exposure on an image carrier with a laser beam modulated by an image signal is reversely developed using the developing method described in the above publication, and toner is applied to the exposed area in the non-exposed area. When a toner image is formed by attaching carrier to the exposed area, the carrier is already attached to the non-exposed area.
The carrier prevents the next beam exposure from being possible.

That is, the above-mentioned technique rejects the method of forming a multicolor image of the present invention, and is in a completely different technical field in terms of drawing technology.

Here, the relational expression between the particle size of the carrier and the strength of magnetization is:
The results were obtained through numerous experiments carried out by the inventors over many years, of which one or two experimental examples are shown below.

(Experiment 1) Figure 2 (a) shows the multicolor image forming apparatus used in this experiment.
FIG. 2(B) shows a laser optical system incorporated into the apparatus, and FIG. 2(C) shows a developing device.

In this experiment, we used the multicolor image forming apparatus shown in FIG. A developability test was conducted by relatively changing h (μ theory) (however, the spike height was changed by changing the magnetization strength of a carrier having a constant particle size).

The image input unit IN includes an illumination light source 11, a color separation device ff112' that separates colors into red and cyan, a mirror 12, a lens 13,
The -dimensional color CCD11 image element 14 is integrated into a unit, and the image input section IN is moved in the direction of arrow X by a drive device (not shown), and the CCD image sensor 14 reads the original.

The image information read by the image input section IN is sent to the image processing section T.
Although the data is color-separated by R and converted into data suitable for red, blue, and black recording, red recording data is used in this experiment.

The laser optical system 16 forms a latent image on the image carrier 1 in the following manner based on the red image data, and this latent image is developed to form a toner image on the image carrier. The surface of the image carrier 1 is uniformly charged by a scorotron charging electrode 21. Subsequently, image exposure light L R according to the red recording data from the laser optical system 16 is irradiated onto the image carrier 1 through the lens. In this way, an electrostatic latent image is formed. This electrostatic latent image is developed by a developing device A. This developing device A has the configuration shown in FIG. 2(C). Components in FIG. 0 that are the same as in FIG. 6 are given the same reference numerals.

9 is a developer tank, 10 is a developer layer scraping member consisting of a sponge roll, a gap between the developer layer and the image carrier, and D is a developer. Note that the magnet body 4 is N.

A fixed magnet body having S12 poles, 8 a developer layer thickness regulating member, and K a developing area. The developer used was composed of the carrier and red toner used in Example 1 below, and had a toner content of 6 wt %.

The red toner image obtained through development is neutralized by an exposure lamp 22 to make it easier to transfer, and then transferred by a transfer pole 23 to a recording paper P fed from a paper feeding device 28 in synchronization with image formation. be done. The recording paper P is separated from the image carrier 1 by the separation pole 24 and fixed by the fixing device 25. On the other hand, the image carrier 1 includes a removal electrode 26 and a cleaning device 112.
Cleaned by 7.

The cleaning device W127 is a cleaning blade 27a.
and a faplash 27c. These are kept out of contact with the image carrier 1 during image formation, and when a multicolor image is formed on the image carrier 1, they come into contact with the image carrier 1 after the transfer and scrape off residual toner after transfer. . After that, cleaning blade 2
7& separates from the image carrier 1, and a little later, the fabrush 27
c leaves the image carrier 1. The fabric brush 27c functions to remove toner remaining on the image carrier 1 when the cleaning blade 27a leaves the image carrier 1. 27b is a roller that collects the toner scraped off by the blade 27a.

The laser optical system 16 is shown in FIG. 2 (B), in which 17 is a semiconductor laser oscillator, 18 is a rotating polygon mirror, and 19 is an f-θ
It's a lens.

According to the above-mentioned development and image forming process, a test was conducted under the development and image forming conditions shown in Table 1 below, changing the carrier head hμ and development gap dμ in 38 ways to evaluate the developability and image quality.

Figure 3 (a) shows the evaluation results of image quality when an image formation test was conducted according to the conditions in Table 1 above.

In the figure, "Δ" indicates carrier adhesion in the non-image area, "O" indicates good developability and image '11, and "x" indicates poor developability.

From Figure 3 (a), the development gap d is 300 to 650 μm.
It can be seen that even if the development gap d changes within this range, as long as the height h of the carrier spikes is within the range of 200 to 400 Jim, the developability is excellent and the image obtained is excellent.

(Actual @ 2) Writing is performed on the image carrier by a laser beam modulated based on the color-separated blue recording signal, and the blue developing device liB
The same test as in Experiment 1 was conducted, except that only the computer was operated.

Furthermore, a test similar to Experiment 1 was conducted except that writing was performed on the image carrier with a laser beam modulated based on the black recording signal and only the black developing device C was operated. Almost the same results were obtained.

(Experiment 3) Using the developing device shown in Fig. 2 (c), using the red developer from Experiment 1, and setting the carrier average particle diameter R (20 to 120 μm theory) as a parameter, the magnetization strength M of the carrier was set to 30 μm. ~150
The height hμ of the spikes on the sleeve when changing within the range of u/am' was measured based on the following measuring method, and the results are shown in Figure 3 (b).

Also, by modifying Fig. 3 (b), the horizontal axis represents the average particle diameter R of the carrier.
, and plotted the magnetization strength M on the vertical axis to create a graph as shown in Figure 3 (c).

In Fig. 3 (C), the area above the straight line Lx is the area where the height of the panicle stand exceeds h = 400 μ- (the area marked with X), and the area below the straight line Lx is the area where the height of the panicle stand is h = =400μ- (region marked O).

As seen from the results of Experiment 1, the region below the height h of the panicle stand, h=400 μm, is a region where a good image can be obtained. Therefore, the straight line Lx represents extremely important characteristics that are critical conditions for the characteristics of the average particle size R and the magnetization strength M of the carrier.

This direct @L x is M = -0,8R+ in the present invention.
It can be expressed by the formula 150, which served as a powerful clue to discovering the present invention.

Measuring method of height h of spikes of developer layer: When a certain amount of the red developer is put into the developer and rotated for 1 minute at a predetermined rotation speed (1BOrpm in this case),
A spike is formed on the sleeve by joining the carrier along the lines of magnetic force.

The selected 20 panicle stands were enlarged and projected by 11l (Nippon Kogaku Profile Projector Model 6C-2).
The height 11 of the spike is calculated from the average value of the heights of the projected images obtained by projecting at 0x magnification.

The above is a detailed explanation of the present invention, and the developer, developing method, image forming method, etc. according to the present invention will be further explained below.

The developer of the present invention has an average particle size R (μ
It contains a carrier having a magnetization strength M (emu/c), but more preferably the average particle size R of the carrier is 20 to 60 μm and the magnetization strength M is 40-60 μm.
10100e/am'.

As the core material of the carrier, iron powder, nickel powder, cobalt powder, magnetite powder, ferrite powder, etc. can be used. Ferrite is used herein as a general term for magnetic oxides containing iron, and is not limited to spinel-type ferrite 1-, which is represented by the chemical formula MO・FFe203 (a divalent metal). Since various magnetic properties can be obtained by changing the , it is suitable for obtaining a carrier suitable for the purpose of the present invention.

In addition, since ferrite is an oxide, its specific gravity is smaller and lighter than metal powders such as iron powder and nickel powder.
Easy to mix and stir with toner, uniform toner concentration and band 1! It is suitable for realizing the quantity. Moreover, since ferrite has a higher electrical resistance (10" to 10'2 Ω-c+s) than iron powder, nickel powder, cobalt powder, etc., the film F!X0 of the resin insulation layer (insulating coating layer) on the surface
．． Even if it is a thin film of about 5 μm, it has the advantage that it can provide an insulating carrier that can be used in a development method in which a high bias electric field is applied to the development gap.

The above resistance value is determined by placing the particles in a container with a cross-sectional area of 0.50 cm and tapping the I.
This value is obtained by applying a load of Kg/cm2 and reading the current value when applying a voltage that generates an electric field of 100OV/cm between the electrode that also serves as the load and the bottom electrode.

In addition, the above average particle diameter is measured using a laser light scattering type particle size distribution measuring device H.
This is the weight average particle size measured using "Microtrack" (Seishin Enterprise Co., Ltd.).

Since the electrical resistance of ferrite alone is about 10'2 Ω-e1m at the highest, under an alternating electric field, there is a risk that charges will be induced up to the leading edge of the carrier.
Therefore, in order to achieve high insulation, it is necessary to coat the surface of the core material with an insulating resin (coating carrier).
It is necessary for stable development in both normal and reverse development.

Examples of the coating resin include styrene-acrylic resin, silicone resin, fluororesin, acrylic resin, polyester resin, epoxy resin, vinyl chloride/vinyl acetate copolymer, and nitrogen-containing resin. In addition to resins, inorganic insulating materials such as glass and ceramics can also be used.

Usually, a resin is used that is soluble in a solvent and can be formed into a film by spray coating, impregnation treatment with a solution, or the like.

The thickness of these coatings is 0.1S-10μ, preferably 0.3 to 3μ, and may be set to a value that provides sufficient insulation and stable characteristics.

The carrier used in the present invention constitutes a toner and a two-component developer. Among these, preferred toners include those using polyester resin or styrene/acrylic resin as a binder.

Polyester resin is obtained by condensation polymerization of alcohol and carboxylic acid, and the alcohols used include, for example, ethylene glycol, diethylene glycol,
Diols such as triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butynediol, 1゜4-bis(hydroxymethyl)cyclohexane and etherified bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, and polyoxypropylenated bisphenol A, and other dihydric alcohol monomers.

Examples of carboxylic acids include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, cepatic acid, and malonic acid. , anhydrides of these acids, dimers of lower alkyl esters and lyluic acid, and other divalent compounds
Mention may be made of acid monomers.

As the polyester resin preferably used in the present invention, it is preferable to use not only a polymer made only of the above difunctional monomers but also a polymer containing a component made of trifunctional or higher polyfunctional monomers. . Examples of trivalent or higher polyhydric alcohol monomers that are such polyfunctional monomers include sorbitol, 1,2,3.6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipenta Erythritol, tripentaerythritol, sucrose,
1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3
．． 5-) hydroxymethylbenzene, and others.

In addition, examples of trivalent or higher polycarboxylic acid monomers include 1,2,4-benzenetricarboxylic acid, l, 3゜5-
Benzenetricarboxylic acid, 1.2.4-cyclohexanetricarboxylic acid, 2,5.7-naphthalenetricarboxylic acid, 1.2.4-butanetricarboxylic acid, 1,2.5-
Hexanetricarboxylic acid, 1,3-dicarboxyl-2
-Methyl-2-methylenecarboxypropane, tetra(
Mention may be made of methane (methylenecarboxyl), 1,2,7.8-octane tetracarboxylic acid, embol trimer acid, and anhydrides of these acids.

It is desirable that the above-mentioned polyfunctional monomer component be contained in a proportion of 20 to 30 mol % in each of the alcohol component or acid component as a structural unit in the polymer.

As the above styrene/acrylic resin, JP-A-50
-134652, which contains the α,β-unsaturated ethylenic monomer as a constituent unit and has a weight average molecular weight (Mw)/and a number average molecular weight (Mn) of 3.5 or more. Can be used.

In order to produce the toner used in the present invention, carbon black, nigrosine dye (C,
1, No. 50415B), Aniline Blue (C, I.

No. 50405), Calco Oil Blue (C, 1,
No, azoec old UE 3), Rhodamine B (C, 1
, No. 45170), Chrome Yellow (C, 1, No.
, 14090>, Ultramarine Blue (C, I.

No. 77103>, DuPont Oil Red (C, 1
, No. 26105), quinoline yellow (C, 1, N
o, 47005), methylene blue chloride (C, 1
, No. 52015), Phthalocyanine Blue (C, 1
, No. 74160), malachite green off-salate (C, 1, No. 42000), lamp black (C
,1,No.

Hu 26B), Rose Bengal (C, 1, No. 454
35) The toner used in the present invention is prepared by adding a mixture of these and the like, and adding a charge control agent, an anti-offset agent, etc. as necessary, mixing in a ball mill, etc., and passing through the steps of mixing, crushing, and classifying. Obtainable.

The particle size of the toner may be 1 to 30 microns, preferably 5 to 25 microns.

Note that it can also be obtained by a manufacturing method other than the above, such as a spray drying method, interfacial polycondensation, suspension polycondensation, or solution polycondensation.

The carrier and toner obtained as described above are mixed so that the toner content in the developer is 3 to 10 wt % to obtain the developer of the present invention.

Such a developer is triboelectrically charged during the stirring and flowing process, and it is preferable that a charge of 10 to 30 μCOW be applied to the toner.The average particle size of the toner is measured using a Coulter Counter manufactured by Coulter Co., Ltd. , weight average particle size.

In the developing method of the present invention, as described above, an elastic press plate is brought into pressure contact with the sleeve of the developer transport carrier to form a thin developer layer of the two-component developer consisting of the carrier and toner to a thickness of 200 to 400 μm. The gap between the image carrier and the sleeve is 1000 μm or less, preferably 250 μm to 6 μm.
00μ-, and the gap 5 between the developer layer and the image carrier
The film is developed in a non-contact manner under an oscillating electric field with a distance of 0 to 200 μm.

In order to form such a single developer layer, the pressing force of the elastic pressing plate is set to 0.5 to 2 g7-m, and the bias for forming the oscillating electric field in the development area is set to a DC component VOc±50 to ± 700■, AC component■A C500V
~5K V (P-P), preferably 1 to 3 (P
-P), frequency fl~10KHz, preferably 3~5K
It is assumed to be Hz.

When the development method is reversal development, the DC component Voc of the bias is set to a voltage close to the potential VH of the unexposed portion of the image carrier.

The diameter of the sleeve is preferably a small diameter of 15 to 30 mm, and the rotation is preferably 100 to 500 rpm, preferably 200 to 500 rpm, in the forward direction (same direction as the surface of the opposing image carrier) or in the opposite direction. It is rotated at 300 rp-, and at a circumferential speed of 1 to 10 times that of the image carrier, preferably 1.5 to 4@.

The magnetic body of the developer transport carrier may be fixed or rotating, and the number of magnetic poles is selected from 4 to 32. In order to form a sleeve, it is recommended to have 8 or more poles, and in the case of fixed magnets, the distance between the magnetic poles in the development area is such that the angle between adjacent magnetic poles with respect to the sleeve axis is 40 degrees or less, and the magnetic poles are arranged closely. Outside the area, the magnetic poles may be eliminated or the number may be reduced.

The strength of the magnetic pole in the development zone is between 300 and 1000 Gauss, preferably between 500 and 800 Gauss.

As the image carrier used in the present invention, binder type C
Any of dS photoreceptors, Se photoreceptors, OPc photoreceptors, amorphous silicon photoreceptors, etc. can be used, but O
A PC photoreceptor is used, and is provided by laminating a carrier generation layer and a carrier transport layer on a drum-shaped metal substrate.

Such an image carrier is normally given a dark potential of VH±500±800v, but it may have a relationship of l VH−V c l <200■ with the DC bias Voc during the reversal development. Preferably, the bright area potential vL obtained by exposing the image carrier to an image such as a laser beam is ±20 to ±
100V, and l Vo between the DC bias VOc
It is preferable to have a relationship of CVL l >300V. The peripheral speed of the image carrier is 30 to 100 mm/see.

As described above, in the present invention, a thin developer layer is formed on the sleeve for development, and the developability and image quality of the obtained image depend on the relative relationship between the image carrier and the sleeve. There is a close relationship with the speed ratio and the amount of toner in the thin developer layer conveyed on the sleeve.

In general, when the linear velocity of the sleeve is Vs4, the linear velocity of the image carrier is Vd, and the amount of toner in the thin developer layer on the sleeve is t, then 1 abundance theory t≧0.4 [Yuzu g/c Theory 2] It is necessary to satisfy the following condition.

Considering development efficiency, 1 ¥, s, l I , , 1 ≧ 0.5
(mg/am”)l vsl/vdl≦8, and from experimental facts it is also preferable that the toner stoichiometry t on the sleeve is 0.2.
~1.0B/am”, preferably 0.3-0.7 wheels gZ
This is C-wheel 2.

The layer thickness regulating member forming the thin developer layer is described in the developing device of FIG. 2 (c) used in Experiment 1,
The configuration near the tip of the layer thickness regulating member is shown in FIG. 4(A).

In the figure, 8 is a layer thickness regulating member made of an elastic pressure contact plate as explained previously, 3 is a sleeve, and 10 is a wedge-shaped region E formed by the 1i1 thickness regulating member 8 and the sleeve 3, which is a gap close to the carrier particle diameter, i is the horizontal length of the tip of the layer thickness regulating member 8, S is the gap between the tip 11 of the layer thickness regulating member 8 and the sleeve 3, and γ is the diameter of the sleeve.

Figure 4 (b) shows the tip 11 of the layer thickness regulating member 8 and the sleeve 3.
3 is a graph showing the relationship between the gap S between the sleeve and the amount of developer attached to the sleeve.

It can be seen from the figure that when the gap exceeds a certain value, the amount of developer on the sleeve is stable against these changes.

In this stable state, the toner necessary for the above-mentioned development can be sufficiently transported.

Other experiments have shown that the layer thickness changes little and that other parameters have little effect on the appearance of this stable state.

Therefore, if the gap at the tip is set to 0.08 or more, it is possible to stably convey toner of a constant consistency even if the mounting accuracy and mechanical accuracy vary. Furthermore, the gap at the tip was set to 0.
Setting the time to 1 ms+ is not preferable because stability increases.

Of course, it is not desirable to make the gap at the tip unnecessarily large, and it has been observed that when the gap is increased to 5+*m or more, the uniformity of the developer layer is disrupted.

As mentioned above, in the non-contact development method that applies an alternating electric field, the shorter the distance between the photoreceptor and the developing sleeve, the better the developing performance and the higher the resolution of the image. , development gap) is desirably set to 1+am or less, preferably in the range of 0.3 to 0.6--.

However, under these conditions, the developer is not in contact with the photoreceptor! This is not possible with a developer using a carrier having a particle size and magnetization used in a two-component developing method using a normal contact method. Very satisfactory results are obtained by using carriers with an insulating coating on their surface.

In the present invention, a multicolor image is formed in the following manner using the two-component developer and developing method described above.

The multicolor image process explained earlier in Experiment 1 based on the multicolor image forming apparatus shown in FIG. A multicolor toner image in which each color toner image is polymerized is formed on the image carrier by repeating image exposure and development with a developer containing the corresponding color toner on the image carrier for each color separation information based on the image carrier. Then, this is transferred onto a transfer material at once, and after transfer, it is heated and fixed using a heated roll or the like to form a multicolor image.

Furthermore, the color separation information is converted into an electrical signal, and based on the recorded signals of multiple colors obtained by image processing, image exposure and corresponding color l/toner are included on the image carrier for each recording signal. The multicolor one-henner image may be formed on the image carrier by a digital method by repeating development with a developer.

The image exposure based on the recording signal is performed by the recording signal.
It is performed using modulated light obtained by modulating ED, a semiconductor laser oscillation device, etc., and the static i obtained on the image carrier by the image light is
! ! The latent image is preferably developed by a reversal development method in which the exposed portion of the image is developed to form an image.

Furthermore, when forming a multicolor image using the digital method, a single image exposure device may rotate the image carrier multiple times to form a multicolor toner image on the S method carrier. An image exposure device may be provided to form a multicolor toner image by one rotation of the image carrier.

Furthermore, as the multicolor image forming process, simply charging,
The Carlson process, which repeats image exposure and development, may also be used.
Furthermore, using an image carrier with an insulating layer provided on the photoconductive layer, NP is produced by repeating secondary charging, image exposure, secondary charging, full-surface exposure, and development.
It may be a formal process.

By using the image forming method as described above, a transfer drum is not required and the size of the apparatus can be reduced.

Further, since toner images of each color are formed on the image carrier in a superimposed manner and transferred at once, there is no transfer deviation during transfer.

Furthermore, since the development method unique to the present invention is used in the process of image formation, fogging, density reduction due to selective phenomena, ghost images, etc. do not occur, and sweep marks and damage to toner images are also avoided. A multicolor image with high resolution and clear tones can be obtained.

That is, in the multicolor image forming process of the present invention in which a multicolor toner image is formed by superimposing each color toner image on an image carrier, and the multicolor toner image is transferred all at once, it is possible to achieve an excellent performance by satisfying the above-mentioned specific development conditions. The formation of a multicolored image is achieved.

〔Example〕

The present invention will be explained below with reference to Examples, but the embodiments of the present invention are not limited thereto.

(Example 1) Developer used in this example: <i> Resin-coated carrier A metal oxide such as Fe, Ni, Cu, Zn, Mn or Mg was appropriately blended to form an average as shown in Table 1. Twenty types of spherical ferrite particles with different particle sizes and magnetization strengths were prepared, and their surfaces were coated with styrene-acrylic resin to a thickness of 1.5 μm using a known spira coater to create 20 types of carriers shown in Table 2. . Furthermore, the strength of magnetization is 100e@u/c
Carrier No.: m3 or more and less than 200 emu/am3, 2.3, 5, 6, 7.8, 9, 10, 11, 12
．． 14, 16, 19.20) are Cu-Zn-Mg-Fe
The magnetization strength of the ferrite (ferrite A) is 101
Less than 00e/cm' (carrier No. 1.4,
Nos. 13, 15, 17, and 18) used Cu-Mn-Zn-Fe-based ferrite (ferrite B).

To measure the particle size, use a laser light scattering particle size measuring device.
Microtrack" (manufactured by Seishin Enterprise Co., Ltd.) was used. In addition, to measure the strength of magnetization, we used a sample vibrating magnetometer rVSM-30.
0" (Toei Kou Isha ICl") for use.

(ii) Resin dispersed carrier styrene-acrylic resin (manufactured by fi! Suikagaku Co., Ltd., Mwl
lo, 000, M w / M n20) 30 parts by weight and magnetite powder B L-100 (manufactured by Titanium Kogyo Co., Ltd.) 60
weight and were mixed using a Henshil mixer.

Further, this mixture was heated to 140°C with three rolls and thoroughly kneaded, then allowed to cool, coarsely pulverized with a hammer mill, finely pulverized with a jet mill, and classified to obtain carrier No. 21.22 in Table 1. obtained a decentralized carrier. Furthermore, a dispersed carrier No. 23 in Table 1 was obtained in the same manner except that 50 parts by weight of magnetite B L-10050 was added.

(iii> Black toner polyester resin rUXK-120PJ (manufactured by Kao Corporation)
10Qfi fi part Polypropylene [Viscol 660PJ (manufactured by Sanyo Chemical Industries, Ltd.)
4 parts by weight of carbon black "Mogul L" (manufactured by Capot Co., Ltd.) 10 parts by weight or more were mixed in a Henshil-containing mixer, kneaded for 11 L with three rolls at a temperature of 140°C, left to cool,
After 1 pulverization, the mixture was finely pulverized in a jet mill and classified to obtain colored particles with an average particle size of 11 μm.

This colored particle 10,000 weight hydrophobic silica R-812 (
A black toner was obtained by adding 0.4 weight parts (manufactured by Hon Aerogi Co., Ltd.) and mixing and dispersing for 30 minutes in a V-type mixer.

(1v) Cyan toner Carbon black in the black toner of (iii) above
Copper phthalocyanine pigment rllel instead of "Mogul L"
iogen Blue D-7080J (B A
A cyan toner having an average particle size of 12 .mu.m was obtained in the same manner except that 3 parts by weight (manufactured by SF Co., Ltd.) was used.

(V) Magenta toner Azo pigment rPer+5ane in place of the carbon black "Mogul L" applied to the black toner in (iii) above.
nLCarsire5 B J (manufactured by Hoechst) was treated in the same manner except that 3 parts by weight was used to obtain an average particle size of 12.
A magenta toner of μm was obtained.

(My) Yellow toner Carbon black in the black toner of (iii) above
Quinophthalone pigment instead of “Mogul L” rPal
The average particle size was 11 μ-
Yellow toner was obtained.

Next, divide each of the 23 types of carriers in Table 2 into four,
The black, cyan, magenta, and yellow toners obtained as described above were divided into 23 parts and combined so that the toner concentration in the developer was 5 wt%, and 23 kinds of 92 test pieces were prepared. A developer was obtained.

Table 2: Copying experiments were carried out using the 92 types of developers described above using the multicolor image forming apparatus shown in Fig. 5 equipped with the developing device shown in Fig. 2 (c), and the image resolution, image density, and fog were evaluated. Observations and measurements were made for the following items: , li% cut, carrier scattering, and carrier adhesion.

The image carrier 1 in FIG. 5 is a negatively charging OPC photoreceptor consisting of a carrier transport layer laminated on a carrier generation layer, and is made by dispersing a bizuzu azo pigment of tl1m below in a polycarbonate resin on an aluminum tube. This photoreceptor is provided with a carrier generation layer, and on the carrier generation layer is provided a carrier transport layer made of a polycarbonate resin and a styryl 44 compound made from Ti below, which rotates in the direction of the arrow.

Bisazo Pigment Nistyryl Compound The developing devices A, B, C, and D used in this example all have almost the same structure as that shown in FIG. The magnetic pole N at the position facing the holding member 10 is removed, and the number of magnetic poles of the magnet body 4 is 11.

In this way, the developer layer after development is more easily scraped off by the developer layer scraping member 10, and the developer layer to be subjected to the next development is newly placed on a renewed sleeve that has no history of previous development. It comes to be composed of a developer.

Therefore, during repeated development, reduction in density, deterioration of image quality, and generation of ghost images due to image selection phenomena are prevented.

Next, Table 3 shows the development conditions which are the main points of multicolor image formation in this example.

Table 3 Next, the configuration and image forming process of the multicolor image forming apparatus shown in FIG. 5 will be explained.

In the figure, 30 is an image carrier consisting of a negatively charged OPC photoreceptor using the bisazo pigment, 31 is an illumination light source, and 31' is a plurality of replaceable color separation filters (blue (I3), green (G), red ( R), neutral (ND) filters), 32 is a reflecting mirror, 33 is a lens, 34 is a one-dimensional CCD image sensor;
2, 33, and 34 are integrated into a unit and constitute an image input section IN.

TR is an image processing unit including an inverter that converts color separation information into complementary colors; 35 is a multicolor original; 36 is a laser optical system; and 36 is a laser beam output from the laser optical system.

41 is a charger for negative charging, 42 is a pre-transfer exposure lamp, 43
is a transfer pole, 44 is a polarization M pole, 45 is a heat roll constant PX device, 4
6 is a pre-cleaning static eliminator, 47 is a cleaning device,
47a is a cleaning blade, 47c is an auxiliary cleaning brush, 47b is a collection roller, and A, B,
C and D are developing devices that accommodate Y, M, C, and BK color toners.

The image input unit IN is moved in the direction of arrow X by a drive device (not shown), and the COD image sensor 34 reads color separation information obtained by color separation using B, G, R, and ND filters. , converted into an electrical signal.

This electrical signal is converted into data suitable for recording in the processing section TR. The laser optical system 36 forms an electrostatic latent image on the image carrier 30 in the following manner based on the above image data. That is, the image carrier 30 has a scorotron charged electrode 4
1, the surface is uniformly negatively charged, and then a light image of the document according to the recorded data is irradiated from the laser optical system 36 onto the image carrier 30 through the lens, thereby forming an electrostatic latent image corresponding to the document. is formed on the image carrier 30.

This electrostatic latent image is first developed by a developing device A containing yellow (Y) toner.

The image carrier 30 on which the toner image of yellow (Y) toner has been formed is uniformly charged again by the scorotron charging electrode 41 by the next rotation of the image carrier, and an optical image of the original according to recorded data of another color component is generated. irradiation. The electrostatic latent image thus formed is developed by a developing device B containing a magenta (M) lner.

As a result, a two-color toner image of yellow (Y) l-toner and magenta (M) toner is formed on the image carrier 30. Subsequently, in the same manner as described above, a toner image made of cyan (C) toner and a toner image made of black (BK) toner are sequentially superimposed by rotation of the image carrier 30, so that four color toners are formed on the image carrier 30. An image is formed. The developing devices A, B, C, and D all have the same configuration as the developing device shown in FIG. 2(c).

The thus obtained multicolor toner image is transferred onto the recording paper P by the transfer electric current @143.

The recording paper P is separated from the image carrier 30 by the separation electrode 44 and undergoes a fixing process in the fixing device 45, thereby forming a fixed image. On the other hand, the image carrier 30 is charge-eliminated by the removing electrode 46, and its surface is cleaned by the cleaning device 47.

The cleaning device 47 in this example includes a cleaning blade 47&, a fabric brush 47c, and a toner collection roller 47.
b.

These are kept in a non-contact state with the image carrier 30 during the image forming process, and when the final multicolor toner image is formed on the image carrier 30, the cleaning blade 47m and The fabrush 47c is the image carrier 3
0 to scrape off the toner remaining on the image carrier after the toner image is transferred.

Thereafter, the cleaning blade 47a leaves the image carrier, and a little later, the fabric brush 47c leaves the image carrier. The fabric brush has a function of removing toner remaining on the image carrier 30 when the cleaning blade leaves the image carrier. 47b collects the toner scraped off by the blade.

The above 23 types, 92 developers (Developers No. 1 to 23)
23 types of image forming tests shown in Table 4 were conducted based on the development conditions and multicolor image forming process, and the resulting images were measured according to the items in Table 4, and the image density was determined by the following measuring method. The other data were evaluated using the "O" or "x" system, and the results are shown in Table 4.

Image formation was performed 100 times in a row for each test.
Tested under 0°C and 11860% environmental conditions.

The image density was measured using a PDA type densitometer (manufactured by Konishiroku Photo Industry Co., Ltd.), and a blue filter was used for yellow images.
A green filter was used for the magenta image, and a red filter was used for the cyan image.

The amount of charge is determined by blow-off charging till fixed ff T B -
Measurement was performed using a Zoo model (manufactured by Toshiba Chemical Co., Ltd.).

According to the fourth person in the margin below, the test results of the present invention are excellent in resolution, image density, fogging, sweeping stitches, carrier scattering, and carrier adhesion, but in the comparison test, there were defects in some of the above evaluation items. I understand that there is something.

〔Effect of the invention〕

As explained above, according to the image forming method of the present invention, the apparatus can be made compact, there is no color blurring due to poor transfer of toner images of each color, and a high-resolution, clear multicolor image with particularly excellent developability can be obtained. Effects such as these are produced.

[Brief explanation of drawings]

FIG. 1 is a graph showing the particle size and magnetization strength range of the carrier included in the present invention, FIG. Figure (I7) is a sectional view of the laser beam system, and Figure 2 (c) is a sectional view of the developing device. Figure 3 (a) is the characteristic diagram obtained in experiment 1, Figure 3 (b)
and (c) are characteristic diagrams obtained in actual @2, Fig. 4 (a) is a partial cross-sectional view showing the configuration of the tip of the layer thickness regulating member, and Fig. 4 (c) is the tip of the layer thickness regulating member. A graph showing the relationship between the gap and the developer layer on the sleeve, and FIG. 5 is a sectional view of a main part of the multicolor image forming apparatus of the embodiment. FIG. 6 is a cross-sectional view of a reference developing device, and FIG. 7 is a potential diagram illustrating carrier adhesion during reversal development with a developer using a resin-dispersed carrier. 1.30... Image carrier (OPC photoreceptor) 2...
Developer layer 3... Sleeve 4... Magnet 5... AC bias 6... DC bias 7... Stirring device 8... Developer layer thickness regulating member 9... Developer layer 10 ...Developer layer scraping member 11.31...Exposure lamps 12', 32'...Color separation filter 12.32...Reflection mirror 14.32...CCD image element IN...Image input Part 16.36...Laser optical system 17...Laser light source 18...Rotating polygon mirror 19...r-θ lenses A, B, C, D...Developer 21.41...Charger 22.42... Pre-transfer exposure lamp 23.43... Transfer pole 24 , 44 , , minute M! a! 24.45...Fuser 26.46...Static eliminator before cleaning 27.47...
・Cleaning device 28.48...Paper feeding device

Claims (1)

[Claims] (1) Repeating the process of applying an oscillating electric field to the development area and developing the electrostatic latent image on the image bearing member in a non-contact manner using a two-component developer containing toner and carrier. In an image forming method in which a plurality of toner images are superimposed to form a plurality of toner images and the plurality of toner images are transferred onto a transfer material, the two-component developer has a magnetization strength M (measured in a magnetic field of 1000 Oe). Non-contact development in the development step is performed using a carrier whose unit emu/cm^3) and average particle diameter R (unit μm) satisfy the following relational expression and which has a coating layer made of an insulating material on its surface. An image forming method characterized in that only toner is attached to the electrostatic latent image on the image carrier. 30≦M≦-0.8R+150 (However, 10≦R≦150)