JPH06348100A - Method for forming multicolor image - Google Patents

Abstract

PURPOSE:To prevent color mixture from occurring and to improve the reproducibility of a character by making the grain size of the non-magnetic color toner of a second color larger than that of the non-magnetic color toner of a first color as for a multicolor image forming method in full color. CONSTITUTION:An image carrier 30 is scanned by a beam modulated by a first chrominance signal and a latent image is formed. The latent image is developed by the developing device 36Y of yellowcolor toner and a toner image is formed on the surface of a drum. Next, write-in is executed on the surface of the drum by a second chrominance signal and the latent image is formed. The latent image is developed by a developing device 36M loading the toner of a magenta color as the second color. At this time, when the difference of the grain size between the first-color non-magnetic toner to be mixed and the second-color mixing non-magnetic toner is set to be 1.2mum, the color mixture is prevented from occurring even in a sufficiently wide AC developing bias area though a gap between a rotary sleeve for developing is set to be 0.1mm that the color mixture easily occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multicolor image by electrophotography, and more specifically, it is a multicolor image forming method in which a plurality of toner images are superposed on an image carrier and transferred onto a transfer material. The present invention relates to a color image forming method.

[0002]

2. Description of the Related Art Image formation by the above-mentioned electrophotographic method involves charging, image exposure, and image formation on an image carrier having a photoconductive layer on a conductive substrate.
This is realized by performing development twice as one cycle. For example, JP-A-60-76766. Alternatively, a method in which primary charging, secondary charging simultaneous image exposure, uniform exposure, and development are performed twice or more in one cycle by using an image carrier having a transparent insulating layer provided outside a photoconductive layer, or , A method in which primary charging, secondary charging, image exposure, and development are performed twice or more in one cycle, for example, JP-A-60-75850. and so on. All of these methods enable multicolor development and image composition on the image carrier, and since these superposed images can be transferred to a transfer material in a single transfer process, they are simple in structure. The device can obtain a color image and a composite image.

As a developing method for this purpose, for example, a developer comprising a mixture of a non-magnetic toner and a magnetic carrier is used under the conditions described in JP-A-59-181362 or JP-A-62-52565. Need to be done in. This developing method is a kind of magnetic brush developing method, and is characterized in that the magnetic brush is not brought into contact with the image carrier and only the toner is caused to fly to the latent image surface of the image carrier by an AC bias.

As an example of the above-mentioned image forming apparatus, there is one in which the latent image forming means forms a latent image for each color, and each latent image is developed by a developing device using toner of a corresponding color.

In such a multicolor image forming apparatus, an electrostatic latent image is formed by irradiating a light beam such as a laser on an image carrier (hereinafter also referred to as a photoconductor) having a photoconductive substance on a conductive substrate. Is typical. In such an apparatus, a multicolor image is formed by the multicolor image forming apparatus shown in the configuration diagram of FIG.

FIG. 2 shows changes in the surface potential of the image bearing member. PH is the exposed portion of the image bearing member, DA is the unexposed portion of the image bearing member, and T ₁ is the image in the first development. Toner adhered on the carrier, T ₂ is toner adhered on the image carrier in the second development, and DUP is an increase in potential caused by toner T ₁ adhered to the exposed portion PH in the first development. Indicates. For explanation, the polarity of the latent image is positive.

The image carrier A is uniformly charged by a charger to have a constant positive surface potential E.

First image exposure is performed by using an exposure source such as a B laser, a cathode ray tube, and an LED, and the potential of the exposed portion PH decreases according to the amount of light.

C The electrostatic latent image formed in this manner is developed by a developing device to which a positive bias that is approximately equal to the surface potential E of the unexposed portion is applied. As a result, the positively charged toner T ₁ adheres to the exposed portion PH having a relatively low potential, and a first toner image is formed. In the area where the toner image is formed, the potential is DU because the positively charged toner T ₁ is attached.
Although it increases by P, it does not normally have the same potential as the unexposed area DA.

D Next, the surface of the image carrier on which the first toner image is formed is charged a second time by the charger, and as a result, the uniform surface potential E is obtained regardless of the presence or absence of the toner T _1.
Becomes

E A second image exposure is performed on the surface of the image carrier to form an electrostatic latent image.

F A positively charged toner T ₂ of a color different from that of the toner T ₁ is developed in the same manner as the above C, and a second toner image is obtained.

The same process is repeated a required number of times to obtain a multicolor toner image on the image carrier. Transfer this to a transfer material,
Further, by heating or pressurizing this to fix it, a multicolor recorded image can be obtained. In this case, the toner and charges remaining on the surface of the image carrier are cleaned and used for the next multicolor image formation.

In addition to the above-described multicolor image forming method, means for increasing the toner particle size in accordance with the order of development is disclosed.

For example, JP-A-58-82263 discloses a means for forming an image by changing the latent image potential of each color and the DC developing bias. Further, it is a developing system of one-component jumping for an image with color toners of only two colors. Further, Japanese Patent Application Laid-Open No. 63-294579 also discloses a method of developing two colors by using a two-component magnetic brush in contact with the image carrier.

[0016]

As described above, in the conventional multicolor image forming method, when a multicolor image is formed by sequentially superposing toners on the surface of the image carrier as described above, for example, a good image is obtained. When the AC bias frequency at the time of development is lowered to 5 KHz or less to form the image, the character reproducibility and the fine line reproducibility are greatly improved. However, when the above-described process of forming a multicolor image by superposition is used, the toner layer previously developed on the surface of the image carrier is increased in color mixture to the non-image portion when the next development is performed, There is a drawback that the image quality deteriorates. In particular, when developing with a toner having a small particle size of 8.5 μm or less, the above-mentioned color mixing remarkably occurs. At that time, even if the parameters of the developing electric field, that is, the frequency, the margin potential of fogging (initial charging potential-DC developing bias potential), etc. are adjusted in the region where the character reproducibility and the developability are good, color mixing occurs, and the result is good. There is a drawback that a multicolor image cannot be obtained. As a means for preventing such a defect, a means for successively increasing the toner particle size in accordance with the order of development has been disclosed as described above, but it is a means for forming an image in a single color of two colors or less.

The present invention has been particularly conceived in order to improve the above-mentioned drawbacks, and is a method for forming a multicolor image in full color, which is effective for preventing color mixture when toners are successively superposed on the surface of an image carrier to form a multicolor image. It is intended to provide a good full-color image by various means.

[0018]

In order to achieve the above object, a multicolor image forming method according to the present invention is the method according to claim 1, wherein a rotatable image carrier is rotated a plurality of times to develop a plurality of developing images. An image forming method in which a DC and AC bias voltages are applied to the image carrier using a device to develop color toners of different colors, and the color toners are superposed to form a multicolor image. In the plurality of developing devices, each of the plurality of developing devices has a magnetic carrier and a developer made of a non-magnetic toner of a different color, and when the non-magnetic toner of the developer is used to develop on the image carrier, The particle size of the non-magnetic toner is increased according to claim 2, wherein the frequency of the AC bias voltage between the image carrier and the developing device is 100 Hz to 20 KHz, and the peak-to-peak voltage is 0.3 to 3.5 KV.
And further, the distance between the image carrier and the developing sleeve of the developing device is set to 0.1 to 0.6 mm, and the non-magnetic toner of each different color is the developing toner. The difference in the average non-magnetic toner particle size in the steps of performing the development in order was achieved by setting the average non-magnetic toner particle size to 1 μm or more and the maximum non-magnetic toner particle size in all the developing steps to 20 μm or less.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a main structure of a multicolor image forming apparatus of the present invention. A is an image reading system, B is a laser writing system unit, C is an image forming section, and D is a sheet feeding section. Yes,
A color image is formed by the following process.

In the reading system A, 11 is a document table, and the document stored in the document table 11 is illuminated by a halogen lamp 13 attached to a carriage 12 that slides in the horizontal direction. Mirrors 16 and 17 are attached to the movable mirror unit 15, and the same slides in the horizontal direction, and in combination with the mirror 14 attached to the carriage 12, the optical image of the original is led to the lens reading unit 20. To do.

The carriage 12 and the movable mirror unit 15 are driven by wires (not shown) connected to a stepping motor, and are slid in the same direction at speeds of V and 1/2 V, respectively. is there.

The lens reading unit 20 includes a lens barrel 21 and a lens barrel C.
Composed of CD23.

The light image of the original document transmitted by the mirrors 14, 16 and 17 is focused by the lens barrel 21 and focused on the light receiving surface of the CCD 23 provided on the reading substrate 24.

Therefore, when exposing the surface of one document, the above-described scanning by the carriage 12 and the movable mirror unit 15 is performed four times, and each image signal output from the CCD 23 is processed by the signal processing section. .
In the signal processing unit, shedding correction, gradation correction,
Dither processing is performed, and color separation filter (not shown)
A color signal color-separated in accordance with the above is output and input to the laser writing system unit B which is an exposure unit.

In the laser writing system unit B, a laser beam generated by a semiconductor laser (not shown) is rotationally scanned by a polygon mirror 32 rotated by a drive motor 31, and an optical path is bent by an Fθ lens 33 and a mirror 34. Then, a bright line is formed by being projected on the peripheral surface of the image carrier 30 to which electric charges have been applied in advance by the charger 35 as a charging means.

On the other hand, when the scanning is started, the beam is detected by the index sensor, the modulation of the beam by the image signal passing through the first color signal, for example, the blue color separation filter is started, and the modulated beam is the image. The peripheral surface of the carrier 30 is scanned. Therefore, a latent image is formed on the peripheral surface of the image carrier 30 by the main scanning by the laser beam and the sub-scanning by the rotation of the image carrier 30. This latent image is developed by the developing device 36Y loaded with yellow toner in the developing means, and a toner image is formed on the drum surface. The obtained toner image passes under the cleaning device 39, which is a cleaning means separated from the peripheral surface of the image carrier 30 while being held on the drum surface, and enters the next copy cycle.

That is, the image carrier 30 has the charger 35.
Is charged again, and then the second color signal output from the signal processing unit, for example, an image signal passing through a green color separation filter (not shown) is input to the writing system unit B,
Writing on the drum surface is performed in the same manner as in the case of the image signal described above to form a latent image. The latent image is developed by the developing device 36M loaded with magenta toner as the second color.

The magenta yellow toner image is formed in the presence of the previously formed yellow toner image.

Similarly, 36C and 36BK are developing units having cyan toner and black toner, respectively, and a red filter (not shown) and a neutral filter (not shown) on the drum surface based on a control signal generated by a signal processing unit. (Not shown), cyan toner images and black toner images are formed. AC and DC biases are applied to the sleeves of the developing devices 36Y to 36BK, non-contact development is performed by a two-component developer that is a developing device, and the image carrier is grounded.
The toner image 30 is developed without destroying the previously formed toner image.

The color image thus formed on the peripheral surface of the image carrier 30 is sent from the paper feed section D by the paper feed belt 41 and the paper feed roller 42 at the transfer pole 40 provided as the transfer means. The image is transferred onto a recording sheet that is a recording medium. The recording paper on which the toner image has been transferred is separated from the drum surface by the separation electrode 43, and is carried into the fixing device 45 via the conveyor belt 44 to fix the image.

On the other hand, the plate 39A of the cleaning device 39 is attached to the image carrier 30 in which the recording paper is separated from the drum peripheral surface.
Removes the residual toner after contact with the toner. After the completion of the removal, the toner is separated from the peripheral surface of the drum again, and a new color image forming process is started. The above is the configuration of the multicolor image forming apparatus that forms a full-color image using the multicolor image forming method of the present invention.

As shown in FIG. 11, the developing units 36Y, 36M, 36C and 36BK have a housing 361, and a developing sleeve 363 is provided in a developing opening 362 formed in the housing 361. A fixed magnet 364 having alternating S poles is incorporated in the developing rotary sleeve 363. 365 and 366 are stirring members provided in the housing 361, and
A two-component developer D ₁ (hereinafter simply referred to as a developer) composed of a non-magnetic toner and a magnetic carrier contained in 61 is stirred,
The mixing ratio of carrier and toner is always averaged. 36
7 is a supply roller for supplying the developer D ₁ to the developing rotary sleeve 363, 368 is a regulating member for forming the supplied developer D ₁ on the surface of the developing rotary sleeve 363 in a thin layer, On the other hand, on the surface of the image bearing member 30, a developing rotary sleeve 36
In step 3, the developer D ₁ is attracted to the developing portion by the fixed magnet 364 and conveyed, and after the developer D ₁ is returned to the housing 361 again after development, the non-magnetic toner is insufficient in the magnetic carrier of the developer D _1. The tip of the scraper 368 for scraping off the developer D ₁ adsorbed by the fixed magnet 364 from the surface of the developing rotary sleeve 363 is abutted against the surface of the developing rotary sleeve 363, and the scraped developer D ₁ is Agitation is performed by the agitation members 365 and 366 to supply an appropriate amount of toner into the carrier.

The two stirring members 365 and 366 are screw-shaped and rotate in the direction of the arrow in the figure to stir and convey the developer. The stirring member 365 is shaped so as to be conveyed toward the front side of the paper and the stirring member 366 is conveyed toward the back side of the paper. A wall 3611 is provided to prevent the developer D ₁ from staying in the intermediate portion between the two, so that the developer D ₁ is exchanged in the left-right direction of the paper in this region.

The toner supply to the developing device 36 is performed from the front side of FIG. 11, and is roughly circulated to the back side of the paper surface by the stirring member 366 and to the front side of the paper surface by the stirring member 365, and the nonmagnetic material used in the present invention is used. The toner and the magnetic carrier are uniformly mixed. However, the position of toner replenishment is not particularly limited to this, and for example, a method of uniformly replenishing the sleeve shaft from the right side of FIG. 11 may be used.

Reference numeral 340 is a bias power source for applying a bias voltage to the developing rotary sleeve 363.

The developing units 36Y, 36 having the above-described structure
Full color development is performed using M, 36C and 36BK.

The resin used in the non-magnetic toner according to the present invention in the developer D ₁ is styrene resin, vinyl resin, ethyl resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, A polyester resin or the like can be used, and a colorant such as carbon, a fixability improver, and a charge control, if necessary, can be added thereto, and the toner particles can be produced by the same method as a conventionally known toner particle production method.

Further, the toner particles are spray-dried,
Alternatively, when the developer is spheroidized by the spheroidizing treatment after granulation, the developer has improved fluidity and is less likely to aggregate, and uniform mixing with the carrier, transportability and charging property are also improved.

As the colorant, dyes and pigments are generally used, but pigments having high weather fastness are widely used.
Examples of the pigment include black pigments such as carbon black and graft-treated carbon black, and examples of color pigments such as cyan or green pigment include C.I. I. Pigment Blue-1
5, C.I. I. Pigment Blue-15: 2, C.I. I. Pigment Blue-15: 3, C.I. I. Pigment Blue-1
6, C.I. I. Pigment Blue-60, C.I. I. Pigment Green 7 and the like.

Examples of magenta or red pigments include C.I. I.
Pigment Red 2, C.I. I. Pigment Red 3,
C. I. Pigment Red 5, C.I. I. Pigment Red 6, C.I. I. Pigment Red 7, C.I. I. Pigment Red 15, C.I. I. Pigment Red 16, C.I. I. Pigment Red 48: 1, C.I. I. Pigment Red 53:
1, C.I. I. Pigment Red 57: 1, C.I. I. Pigment Red 122, C.I. I. Pigment Red 123, C.I.
I. Pigment Red 139, C.I. I. Pigment Red 1
44, C.I. I. Pigment Red 149, C.I. I. Pigment Red 166, C.I. I. Pigment Red 177, C.I. I.
Pigment Red 178, C.I. I. Pigment Red 222 and the like.

Examples of yellow or orange pigments include C.I.
I. Pigment Yellow 12, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 14, C.I. I. Pigment Yellow 15, C.I. I. Pigment Yellow 17, C.I.
I. Pigment Yellow 93, C.I. I. Pigment Yellow 94, C.I. I. Pigment Yellow 138, C.I. I. Pigment Orange 31, C.I. I. Pigment Orange 43 and the like.

These organic and inorganic pigments can be adjusted to a desired color tone by selecting one or a plurality of them in combination as required.
The amount of pigment added is selected from about 2 to about 20 parts, preferably about 3 to 15 parts, relative to the resin.

Next, when the average particle size of the magnetic carrier is large,
The state of the developer layer formed on the developing sleeve becomes rough, and even if vibration is applied by an oscillating electric field, unevenness in the toner image easily appears, and the toner concentration in the developer layer becomes low, making high-density development difficult. Become. Further, when the average particle size of the carrier is small, if the carrier particles are too fine, they tend to adhere to the surface of the photoconductor and scatter together with the toner particles. These developments are largely related to the strength of the magnetic field acting on the carrier particles as a developing condition and the corresponding strengthening of the carrier particles.

The magnetic carrier particles may be composed of only a magnetic material, or the magnetic material particles may be coated with a resin.

As a result of various examinations as above, the magnetic carrier of the two-component developer according to the present invention has an average particle size of 30 to 80 μm and a magnetic field of
It is a proper condition that the magnetic susceptibility is 500 to 50 emu / g at 500 oersteds.

The magnetic substance used for the above magnetic carrier includes metals such as iron, chromium, nickel, cobalt, etc., or their compounds and alloys, such as ferric tetroxide, γ-ferric oxide, and dioxide. Examples of the particles include ferromagnetic or paramagnetic materials such as chromium, manganese oxide, ferrite, and manganese-copper alloy.

By forming the carrier particles from a resin or the like and preferably having a spherical shape, the developer layer formed on the developing sleeve becomes uniform and a high bias voltage is applied to the developing sleeve. Gives the effect of being able to apply. That is, if the carrier particles are made into particles by a resin or the like, (1) generally, the directional property of being easily magnetized and adsorbed in the long axis direction disappears, the developer layer is uniformly formed, and the basin region with locally low resistance is formed. (2) The carrier particles have a higher resistance, and the edge portions as seen in the conventional carrier particles are eliminated so that the concentration of the electric field on the edge portions does not occur. As a result, even if a high bias voltage is applied to the developing sleeve, the electrostatic latent image is disturbed by the discharge to the photoconductor,
The effect of preventing the breakdown of the bias voltage is given. The ability to apply this high bias voltage can sufficiently bring out the effect of the high bias voltage in the development under the vibration electric field in the present invention.

Further, the resistivity of the carrier particles is 10 ⁸ Ωcm.
Above all, it is particularly preferable that the insulating magnetic particles are formed so as to have a resistance of 10 ¹³ Ωcm or more. This resistivity is 0.50 for particles
After tapping in a container with a cross-sectional area of cm ² ,
It is a current value when a load of 1 kg / cm ² is applied on the packed particles and a voltage that generates an electric field of 1000 V / cm is applied between the load and the bottom electrode. If this resistivity is low, the developing sleeve When a bias voltage is applied to the carrier particles 2, charges are injected into the carrier particles to attach the carrier particles to the photoconductor,
Alternatively, the breakdown of the bias voltage is likely to occur.

That is, the preferred magnetic carrier for the present invention is
Spherical particles with an average particle size of 30-80 μm, 20-50 emu / g in a magnetic field of 500 oersteds, and a resistivity of 10 ⁸ Ωcm or more,
Further, it is preferably 10 ¹³ Ωcm or more.

In the developing mode of the present invention, a developer in which the above-described toner and magnetic carrier are mixed in the same proportion as in the conventional two-component developer is preferably used.

If necessary, the developer may be mixed with a fluidizing agent for improving fluidity and slippage of particles, a cleaning agent useful for cleaning the surface of the photoreceptor, a fixability improving agent, a charge control agent and the like. As the fluidizing agent, colloidal silica, silicone varnish, metal soap, nonionic surface active agent or the like can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicone, fluorine or other surface active agent can be used. You can

Known fixability improvers are used. Generally, a polyolefin type is used.
For example, low molecular weight polyethylene, low molecular weight polypropylene, oxidized polyethylene and polypropylene,
Acid-modified polyethylene, polypropylene and the like are used. These can be introduced into the polymer particles by a conventional method, after being melted, dispersed in water and added in the form of emulsion during emulsion polymerization or seed emulsion polymerization. It is preferable to add it during seed emulsion polymerization so that it can be made to exist as polyolefin fine particles on the particle surface, which is preferable from the viewpoint of improving fixability.

Further, a polyethylene wax emulsion marketed under the trade name "HYTEC" (manufactured by Toho Chemical Industry) can be used for the same purpose.

A charge control agent having a known structure is also used.

As the charge control agent, a nigrosine-based electron-donating dye, a metal salt of naphthenic acid or a higher fatty acid, an alkoxylated amine, a quaternary ammonium salt, an alkylamide, a metal complex, a pigment, or a fluorine treatment is used as a charge control agent. An electron-accepting organic complex such as an activator, which is negatively charged
Examples thereof include chlorinated paraffin, chlorinated polyester, and sulfonylamide of copper phthalocyanine.

[0056] In multicolor image forming apparatus configured as above, first, as a range of development conditions for performing good development in the present invention, the frequency f a 50Hz～30KH _Z by the oscillating electric field of the AC developing bias at the time of reversal development (Short form), the peak-to-peak voltage V _PP is 0.1 to 4.0 KV, Dsd between the image carrier 30 and the developing rotary sleeve 363 is changed from 0.1 to 0.7 mm,
DC developing bias is Vdc-750V, non-image area potential VH
Is −850 V, the image portion potential VL is −50 V, and the linear velocity VS of the image carrier 30 is 140 mm / sec. For developer D ₁ , the magnetic carrier diameter is 43.8 μm and the non-magnetic toner particle diameter is 7.9 to 25.
2 μm, so that the toner developability is sufficiently adhered to the surface of the image carrier 30 more than one layer of the toner layer,
The toner concentration was adjusted within the range of 6 to 10% by weight. Next, when the character reproduction and resolution in the image are evaluated, the image formed by the black toner is used. Also, when evaluating the color mixture state in a multicolor image, a yellow toner is solidly developed for the first color, this is used as a color-mixed toner, and then a black toner is developed for the second color under non-image area electric field conditions. Used as.

FIG. 3 shows an image carrier using the developing device 36.
This is data showing a region where pitch unevenness occurs on an image in the AC developing bias (frequency and peak-to-peak voltage) condition when developing 30 latent image portions. The black toner particle size dt used in the data shown in FIG. 3 is 8.1 μm, and if the frequency of the AC developing bias is too low, uneven pitch occurs in the image. The lower limit is 10 as shown
It was 0 Hz, and no dependency on the peak-to-peak voltage or the development gap was observed.

Next, FIG. 4 shows data obtained by conducting an experiment on a region having a good character reproducibility under the AC developing bias condition as described above. In this data, the black toner particle size dt is 8.1 μm, and in this experiment, the developability is improved as the distance between the image carrier 30 and the developing rotary sleeve 363, that is, the smaller Dsd and the lower the frequency. . The Dsd is 0.7
If the frequency becomes too high, the characters will start to blur, and the good area for character reproduction will become narrow. Therefore, the upper limit of Dsd is 0.6 mm and the upper limit of frequency is 20 KH _Z
Is.

As described above, the Dsd interval and the frequency of the AC bias are important for improving the resolution of the image, and the toner particle size is an important factor for determining the character reproducibility. The smaller the toner particle size, the higher the resolution, and the better the character reproducibility. Table 1 shows the data obtained by examining the relationship between the toner particle size and the resolution.

[0060]

[Table 1]

The above table shows 8.0 line pairs / m as a manuscript.
m and a duty ratio of 50/50 were written by a laser exposure device, and an image was formed on a recording paper by using each toner particle size. By visually observing the line image formed by the image formation,
The evaluation of the resolution was divided into criteria of the best 5, good 4, normal acceptable level 3, bad 2, poor 1 and judged. The developing bias set at this time was set by changing V _{PP of the} AC developing bias to form a solid image for each toner particle size, and checking V _PP for 1 to 1.5 layer development for each toner particle size. .
Other conditions, frequency 2KH _Z, Dsd 0.3mm, the direct current developing bias -750 V, set in the non-image portion potential -850 V. As a result, an image having good resolution could be obtained when the toner particle size was 20 μm or less. Therefore, it was found that the upper limit of the toner particle size is 20 μm.

FIG. 5 shows a good upper limit value in which lightning strikes the image carrier 30 using black toner having a particle size of 8.1 μm. The AC bias frequency and V _PP are varied to obtain Dsd.
This is an investigation of a good image shape range when is used as a parameter. From this investigation, it can be seen that if Dsd is wide, lightning strikes are hard to occur, and a good image forming range is wide. According to FIG. 4, Dsd has a maximum value of 0.6 mm, and therefore the upper limit value of V _PP is 4 KV.

FIG. 6 shows data obtained by investigating a range in which a good developability in which one or more toner layers are developed in a solid image using a black toner having a particle diameter of 8.1 μm is obtained. Dsd is above
When the value is set to a value smaller than 0.6 mm, the electric field becomes strong and the range of good developability becomes wide. However, if Dsd is narrower than 0.1 mm, a part of the developer D ₁ on the developing rotary sleeve 363 comes into contact with the surface of the image carrier 30. Therefore, Dsd cannot be set smaller than 0.1 mm. Therefore, Dsd is 0.1
When it is set to mm, the lower limit of V _{PP in a} good range in which the amount of non-magnetic toner attached can be more than one layer is 0.3 KV or more.

FIG. 7 shows a range of good development conditions in which a color mixture of Dsd is 0.3 mm and no color mixture occurs. Here, color mixture means that the surface of the image bearing member is exposed and developed to form a toner image, and then the image surface is formed. On the other hand, unnecessary toner adheres to the surface that has not been subjected to the next exposure. In addition, the charge amount dependency of the non-magnetic toner that mixes colors is shown. The toner particle sizes of the first color mixed non-magnetic toner and the second color mixed non-magnetic toner are the same, and the two color mixed non-magnetic toners are charged. The amount was changed and the range where color mixing did not occur was investigated. First, if the charge amount of the second-color non-magnetic toner of the second color is reduced, the color mixture amount is slightly reduced, but the color mixture preventing effect is small and is not so improved. In this case, yellow (particle size 7.9 μm, charge amount 27.1 μc / g) was used as the first color (color-mixed non-magnetic toner), and 2
Black (particle size 8.1μ) as the color (mixed color non-magnetic toner)
The experiment was conducted using a charge amount of 19.2 to 35.2 μc / g).

FIG. 8, FIG. 9 and FIG. 10 show a favorable AC developing bias range when the second color non-magnetic toner is successively increased.

First, in FIG. 8, Dsd 0.6 mm, 0.3 mm, 0.
In case of 1 mm, the difference in particle size between the mixed color toner and the mixed color toner is 0.2μ
Dsd for m (7.9 μm for the first color and 8.1 μm for the second color)
Even when it is widened to 0.6 mm and advantageous for color mixing prevention, the AC developing bias region where color mixing does not occur is very narrow. Next, in FIG. 9, the particle size difference between the mixed color toner and the mixed color toner is 0.
Dsd when set to 6 μm (7.9 μm for the first color and 8.5 μm for the second color)
At 0.6 mm, 0.3 mm, and 0.1 mm, the good area where color mixing is not widened, but the range of color mixing prevention is still narrow and insufficient.

In FIG. 10, when the particle size difference between the mixed color toner and the mixed color toner is set to 1.2 μm (the first color is 7.9 μm, the second color is 9.1 μm), AC development is sufficiently wide even if Dsd 0.1 mm is set so that color mixture easily occurs for the first time. It became possible to completely prevent color mixture in the bias region. Therefore, as shown in FIG. 10, color mixing can be completely prevented by setting the particle size difference between the color-mixed toner and the color-mixed toner to be 1 μm or more.

[0068]

As described above, the present invention develops non-magnetic color toners of different colors by applying a direct and AC bias voltage to the image carrier without using the developing device. When the non-magnetic color toners are overlapped to form a multi-color image, the particle size of the second non-magnetic color toner is made larger than that of the first non-magnetic color toner to prevent color mixture and good character reproducibility. By using a large developing electric field region, a high-quality full-color image can be obtained.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a multicolor image forming apparatus using a developing device of the present invention.

FIG. 2 is a flowchart showing changes in surface potential of an image carrier and development of toner.

FIG. 3 is a characteristic diagram showing a relationship between AC bias frequency and Dsd at V _PP .

FIG. 4 is a characteristic diagram showing a relationship between an AC bias frequency and V _PP and Dsd of non-magnetic toner.

FIG. 5 is another characteristic diagram showing the relationship between the AC bias frequency and V _PP and Dsd of the non-magnetic toner.

FIG. 6 is another characteristic diagram showing the relationship between the AC bias frequency and V _PP and Dsd of the non-magnetic toner.

FIG. 7 AC bias frequency and V _PP , development conditions and Dsd
The characteristic view showing the relationship with.

FIG. 8 AC bias frequency and V _PP , development conditions and Dsd
FIG. 6 is another characteristic diagram showing a relationship with.

FIG. 9 AC bias frequency and V _PP , development conditions and Dsd
FIG. 6 is another characteristic diagram showing a relationship with.

FIG. 10 AC bias frequency and V _PP , development conditions and Dsd
FIG. 6 is another characteristic diagram showing a relationship with.

FIG. 11 is a sectional view of a developing device used in the present invention.

[Explanation of symbols]

 A image reading system B laser writing system unit C image forming unit D paper feeding unit 11 document table 20 lens reading unit 21 lens barrel 23 CCD 30 image carrier 36 developing device 363 sleeve 369 DC / AC developing bias 365, 366 stirring member

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G03G 15/09 Z

Claims (4)

[Claims] 1. A rotatable image carrier is rotated a plurality of times to apply non-contact and DC and AC bias voltages to the image carrier using a plurality of developing devices.
In an image forming method of developing color toners of different colors and superposing the color toners to form a multi-color image, a magnetic carrier and a developer of non-magnetic toners of different colors are provided in the plurality of developing devices. A method for forming a multicolor image, which comprises increasing the particle size of the non-magnetic toner according to the order of development when the image carrier is developed with the non-magnetic toner of the developer. 2. The frequency of the AC bias voltage between the image carrier and the developing device is 100 Hz to 20 KHz, and the peak-to-peak voltage is
The multicolor image forming method according to claim 1, wherein the multicolor image forming method is set to 0.3 to 3.5 KV. 3. The distance between the image carrier and the developing sleeve of the developing device is 0.1 to 0.6 mm.
The multicolor image forming method described. 4. The non-magnetic toners of different colors have a difference in average non-magnetic toner particle size of 1 μm or more in the step of developing according to the order of development, and the maximum average particle size of non-magnetic toner in all developing steps. The multicolor image forming method according to claim 1, wherein the diameter is 20 μm or less.