JPH0439070B2 - - Google Patents

Description

[Detailed description of the invention] Industrial applications The present invention relates to an image forming method.

Prior Art First, an image forming method in which development is repeated a plurality of times will be described using a color copying machine shown in FIG. 1 as an example. In the case of color copying machines, the light reflected from the original is separated,
A filter is required to extract light of a single color, and this copying machine is provided with a filter bag 2 containing three types of filters of different colors. For example, first, the reflected light from the original is separated by a green filter, and this transmitted light forms an electrostatic latent image on the photoreceptor drum 1, which is an image carrier, which has already been charged by the charging electrode 9, and is developed. When the developing device 3B containing magenta toner in the device 3 develops the image, a magenta toner image is formed on the photoreceptor drum 1. This toner image is conveyed from a paper feed box 8 and is transferred onto copy paper 7, which is a transfer body, wrapped around a transfer drum 4, by a transfer pole 10. Thereafter, the photosensitive drum 1 is neutralized by the removing electrode 11, residual toner is removed by the cleaning device 5, and then charged again by the charging electrode 9.
Next, image exposure is performed by the light transmitted through the blue filter, and a yellow toner image is formed on the photoreceptor drum 1 by the developing device 3A, which is then transferred onto the copy paper 7 on which the magenta toner image has already been transferred from the previous step. The images are superimposed and transferred. Similarly, after the cyan toner image is transferred to the copy paper 7, the copy paper 7 is separated from the transfer drum 4, fixed by the fixing device 6, and then discharged outside the machine. Although this image forming method is desirable because it can add color information compared to information obtained from only black and white images, it has the following problems.

(1) Each time the development of each color is completed, a transfer drum 4 must be provided to transfer the image onto copy paper, which increases the size of the machine and increases the time required for image formation.

(2) It is necessary to repeat the developing process and the transferring process several times, and it is necessary to guarantee the accuracy of positional deviation.

For these reasons, instead of transferring the toner image to the copy paper 7 for each development, by forming each toner image of all colors on the photoreceptor drum 1 and then transferring it to the copy paper 7 at once, Image forming methods have been proposed that solve the above-mentioned problems. According to this image forming method, a toner image of a different color is again formed in an image area where a toner image has already been formed on the photoreceptor drum 1. This may disturb the toner image formed on the photoreceptor drum 1, or the toner image already formed on the photoreceptor drum 1 may return to the developer conveying body in the developing device, and this may contain toner of a different color from the toner in the previous stage. There is a problem in that it may invade the developing device in the subsequent stage, causing color mixing. For this,
Except for the developing device that initially forms a toner image on the photoreceptor drum 1, the photoreceptor drum 1 and the developer layer of the developer transporting member that develops this electrostatic latent image are not in contact with each other.
The means for superimposing an AC component as a developing bias is
For example, as disclosed in Japanese Patent Application Laid-Open No. 56-144452, there are problems in that, depending on the developing conditions, a sufficient developed density may not be obtained, and image disturbances and color mixing may not be eliminated.

OBJECTS OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an image forming method that has a desirable density and records images without image disturbance or color mixture.

Structure of the Invention That is, the present invention involves repeating a step of forming a latent image on an image carrier and a step of developing the latent image using a developer made of a plurality of components multiple times, and then forming a latent image on the image carrier. In the image forming method for forming an image on the image, in each development step, the amplitude of the AC component of the developing bias is V _AC (V), the frequency of the AC component is f (Hz),
When the gap between the image carrier and the developer conveying body that conveys the developer is d (mm), the following equations (1) and (2) are expressed.
The present invention relates to an image forming method characterized in that the image forming method is operated under conditions that satisfy the formula, and the amplitude V _AC (V) of the alternating current component is sequentially decreased for each development.

0.2≦V _AC /(d・f) (1) Formula {(V _AC /d)−1500}/f≦1.0 (2) Formula Examples Examples of the present invention will be explained in detail below using the drawings. .

First, the process by which the present inventor came to make this invention will be explained. An image forming method in which a process of forming a latent image on an image carrier and a process of developing the latent image are repeated, and a visible toner image is sequentially superimposed on the image carrier. It is necessary to carry out development to an appropriate density without disturbing the toner image already formed on the image carrier.

As a result of the study, in order to satisfy this condition, the gap d (mm) between the image bearing member and the developer conveying member in the developing area is
(hereinafter sometimes simply referred to as gap d), the voltage V _AC (V) and frequency (Hz) of the alternating current component of the developing bias maintain the toner image in the subsequent stage at an appropriate density without disturbing the toner image formed in the previous stage. It became clear that it became a parameter when forming.
Therefore, an experiment was conducted using a developing device 13 as shown in FIG. 2 while changing parameters such as the frequency and voltage of the alternating current component of the developing bias. In the developer reservoir 19 of the developing device 13, there is a developer D composed of toner T and carrier, and as the stirring screw 18 rotates, the toner T rubs against the carrier and is sufficiently charged to either positive or negative polarity. do. Here, when the sleeve 20 and/or the magnetic roll 21 serving as the developer transport body rotate, the developer D is transported along the circumferential surface of the sleeve 20 . In FIG. 2, the magnetic roll 21
indicates that the developer D is being conveyed on the circumferential surface of the sleeve 20 in the direction of arrow B as the sleeve 20 rotates in the direction of arrow A and the sleeve 20 rotates in the direction of arrow B. The thickness of the developer D is regulated by the spike control plate 17, and the developer D forms a uniform layer toward the photoreceptor drum 1, which is an image carrier. When the developer D reaches the development area 24, the toner in the developer D is applied according to the potential of the electrostatic latent image formed on the photoreceptor drum 1 and the electric field generated by the AC and DC voltages as the development bias. An electrostatic force acts on the toner T, and the toner T flies from the sleeve 20 and adheres to the photoreceptor drum 1, thereby forming a toner image. Toner T that was not subjected to development here
The cleaning blade 26 scrapes off the developer D on the circumferential surface of the sleeve 20 . The AC power supply 22 and the DC power supply 23 are power supplies for applying a developing bias to the sleeve 20, and R is a protection resistor. When the developer D is used for development and there is a shortage of toner T in the developer D in the developer reservoir 19, the toner T is replenished from the toner hopper 14 by rotating the replenishment roller 16.

Here, a toner image is formed on the photoreceptor drum 1 in advance, and when the toner image is superimposed on the photoreceptor drum 1 and developed, experiments are conducted by changing the parameters variously. As a result of measuring the disturbance and the image density of the overlapping toner images,
We were able to obtain the results shown in Figures 3 and 4. Note that a two-component developer in which the toner is positively charged was used as the developer.

In Figure 3, the gap d between the photoreceptor drum 1 and the sleeve 20 is 1.0 mm, the developer layer thickness is 0.5 mm, the charging potential of the photoreceptor drum 1 is 600V, the DC component of the developing bias is 500V, and the frequency of the AC component. The graph shows the relationship between the amplitude V _AC of the AC component and the image density of the toner image developed on the exposed portion (potential is 0 V) on the photoreceptor drum 1 when V AC is set to 1 KHz. Amplitude of alternating electric field
E _AC is a value obtained by dividing the amplitude V _AC of the AC component of the developing bias by the gap d. Curves A, B shown in Figure 3,
C has an average charge amount of toner of 30μC/g,
These are the results of using charge control controlled to 20μC/g and 15μC/g. For all three curves A, B, and C, the effect of the AC component appears when the AC electric field amplitude E _AC is 200 V/mm or more, and when it is 2500 V/mm or more, the toner image previously formed on the photoreceptor drum 1 appears. was observed to be partially destroyed.

Figure 4 shows the frequency of the AC component of the developing bias.
2.5 KHz, and shows the change in image density when the amplitude E _AC of the alternating current electric field is changed under the same conditions as in the experiment shown in Fig. 3.

According to this experimental example, the amplitude of the alternating current electric field E _AC
When exceeds 500V/mm, the image density increases,
Although not shown, it was observed that when the voltage exceeded 4 KV/mm, part of the toner image previously formed on the photosensitive drum 1 was destroyed. The shapes of curves A, B, and C in FIGS. 3 and 4 are almost the same, except that the image density increases as the average toner charge amount increases. Generally, the amount of charge of each toner particle is distributed within a certain range around an average value. The above experimental results are believed to be due to the fact that toner particles with a relatively high charge amount within that range are preferentially developed.

Now, when we conducted experiments similar to those shown in Figures 3 and 4 while changing the conditions, we were able to sort out the relationship between the amplitude E _AC of the alternating current electric field and the frequency, and obtained the results shown in Figure 5. In FIG. 5, the area indicated by is an area where uneven development is likely to occur, the area indicated by is an area where the effect of the alternating current component does not appear and the density is insufficient, and the area indicated by is the area where toner has already adhered to the photoreceptor drum 1. from photoconductor drum 1 to sleeve 2
The region where it is easy to return to 0 is a region where the effect of the alternating current component appears and a high density is obtained, and where the toner previously attached to the photoreceptor drum 1 does not return to the sleeve 20, and is a particularly preferable region. be. These areas are divided by straight lines G, H, and I. Among these, H and I each indicate conditions that give equal concentrations. This result shows that in order to develop the next (later) toner image at an appropriate density without destroying the toner image that has already been formed on the photoreceptor drum 1, the amplitude of the alternating current electric field E _AC This shows that there is an appropriate range for that frequency.
The cause is considered to be due to the reasons described below.

In the region where the image density tends to increase with respect to the amplitude E _AC of the AC electric field, for example, in the density curve A of Fig. 3, in the region where the amplitude E _AC of the AC electric field is 0.2 to 1.2 KV/mm, the AC component of the developing bias Therefore, the force acting in the direction exceeding the threshold for flying from the sleeve 20 makes a large contribution to the toner, and as the alternating current component becomes stronger, toner with a smaller charge amount is successively used for development. Therefore, the amplitude of the alternating electric field
As E _AC increases, image density increases.

On the other hand, in the region where the image density is saturated with respect to the amplitude E _AC of the AC electric field, curve A in Figure 3 shows the amplitude of the AC electric field.
For regions where E _AC is 1.2 KV/mm or more, this development can be explained as follows. That is,
In this region, as the amplitude E _AC of the alternating current electric field increases, the toner T vibrates strongly, the clusters of aggregated toner T are destroyed, and only the toner T with a large charge is selectively applied to the photoreceptor drum 1. adhere to. In such a situation, since the amount of toner supplied to the development area in a certain period of time is finite, the image density is considered to be saturated with respect to the amplitude E _AC of the alternating current electric field.
Furthermore, when the amplitude E _AC of the alternating current electric field increases, the charge on the surface of the photoreceptor drum 1 leaks, and a phenomenon occurs in which the toner T becomes difficult to be developed. In reality, it is considered that these factors overlap to keep the image density constant as the amplitude E _AC of the alternating current electric field increases.

Furthermore, the amplitude E _AC of the alternating current electric field is increased to, for example, the amplitude 2.5 KV/
It has been found that when the amount is more than mm, the toner image previously formed on the photoreceptor drum 1 is destroyed as described above, and the larger the alternating current component, the greater the degree of destruction. The reason for this is thought to be that the toner adhering to the photoreceptor drum 1 is pulled back to the sleeve 20 by the alternating current component. When toner images of different colors are superimposed and developed on the photoreceptor drum 1 to form a color image, it is fatal to destroy the toner images that have already been formed.

Based on the above experimental results, the inventor determined that the amplitude of the alternating current component of the developing bias was adjusted to V _AC during each development.
(V), the frequency is (Hz), and the gap between the photosensitive drum 1 and the sleeve 20 is d (mm), then 0.2≦V _AC /(d・f) (1) Formula {(V _AC /d) −1500}/f≦1.0 If development is performed under the conditions that satisfy the above two equations (2), the subsequent development can be performed appropriately without destroying the toner image already formed on the photoreceptor drum 1. They concluded that it could be done with concentration. In order to obtain sufficient image density, it is desirable to satisfy the condition of 0.8≦V _AC /(d·f) (3) and further satisfy the condition of 1.0≦V _AC /(d·f) (4).

Here, when the toner images are superimposed on the photoreceptor drum 1, if the conditions during each development are the same,
During the subsequent development, the same force as during the previous development is applied to the toner that has already adhered to the photoreceptor drum 1 during the previous development, and there is a risk that the toner may separate from the photoreceptor drum 1. A method of setting the amplitude V _AC of the alternating current component of the developing bias in order to prevent this will be explained with reference to FIG. As mentioned above, the regions , , , are divided by straight lines G, H, and I. Among these, G is a straight line indicating the boundary where the toner, which has previously formed an image on the photoreceptor drum, begins to return to the sleeve due to the alternating current electric field. For example, when the frequency of the alternating current electric field is 2KHz, the point J where the amplitude V _AC is 3.5KV/mm is on the straight line G. Also, point K, where the frequency remains 2KHz and the amplitude V _AC is 2KV/mm, is away from straight line G. As is clear from the above description, the further away from the area, the more difficult it is for the toner on the photosensitive drum 1 to return to the sleeve 20. This shows that the smaller the amplitude is, the more effective it is in preventing the phenomenon that the toner leaves the photosensitive drum 1 and returns to the sleeve 20.

Therefore, when superimposing toner images on the photoreceptor drum 1, the amplitude of the alternating current electric field E _{AC is}
If it is made smaller, during subsequent development, toner that has already adhered to the photoreceptor drum 1 may separate from the photoreceptor drum 1, or enter the subsequent development device where toner of another color is stored, resulting in color mixing. It is possible to prevent such situations from occurring.

To gradually reduce the amplitude E _AC of the AC electric field in the gap d between the photosensitive drum 1 and the sleeve 20,
There are means for sequentially lowering the alternating current voltage applied as a developing bias for each development, and means for sequentially widening the gap d for each development. The means for changing the gap d between the photoreceptor drum 1 and the sleeve 20 for each development requires accurate mounting positions of the photoreceptor drum 1 and the sleeve 20, requires precise processing technology, and requires time and effort to adjust. It takes. In comparison, the method of sequentially lowering the AC voltage has the advantage of being easy to implement without the above-mentioned problems.

The frequency of the alternating current component applied as the developing bias is set to 200 Hz or more to prevent uneven development due to the alternating current component, and the developer D is supplied to the photosensitive drum 1 by rotation of the magnetic roll 21 shown in FIG. In this case, in order to eliminate the influence of the beat caused by the alternating current component and the rotation of the magnetic roll 21,
It is desirable to set it to 500Hz or higher.

Furthermore, in order to sequentially develop subsequent toner images on the photoreceptor drum 1 without destroying the toner image formed on the photoreceptor drum 1, the amplitude E _AC of the alternating current electric field is gradually lowered, and the amount of charge is gradually reduced. Using a larger toner, increasing the frequency of the alternating current component applied as a developing bias, and increasing the amount of developer D supplied to the photosensitive drum 1, either alone or in any combination. is preferred.

That is, toner particles with a larger amount of charge are more susceptible to the influence of the electric field. Therefore, if large toner particles adhere to the photosensitive drum 1 during initial development, these toner particles may return to the sleeve 20 during subsequent development. Therefore, as mentioned above, by using toner particles with a small amount of charge in the first stage development,
This prevents the toner particles from returning to the sleeve during subsequent events. This is a method in which the vibration range of toner particles is narrowed by sequentially increasing the frequency to prevent the toner attached to the photoreceptor drum 1 from returning. On the other hand, method takes advantage of the fact that the larger the amount of toner supplied to the development area, the easier the development is, and is a method in which a weaker external force is applied to later stages of development to prevent the toner from returning. The amount of toner supplied can be adjusted by the conveyance speed of the developer D, the thickness of the developer layer on the sleeve 20, the mixing ratio of toner and carrier, the stirring of the developer D, and the like.

As a two-component developer, the developer D used in this image forming method is particularly preferably composed of a magnetic carrier and a non-magnetic toner.

The composition of toner is generally as follows (1) Thermoplastic resin: binder 80-90wt% Examples: polystyrene, styrene acrylic polymer, polyester, polyvinyl butyral, epoxy resin, polyamide resin, polyethylene, ethylene-acetic acid Vinyl copolymers and the like are often used in combination.

(2) Pigment: Colorant 0-15wt% Example: Black: Carbon black Blue: Copper phthalocyanine, sulfonamide dielectric dye Yellow: Benzine derivative Magenta: Polytungstophosphoric acid, Rotamine B
Lakey, Carmine 6B, etc. (3) Charge control agent 0-5wt% Example: Plus: Nigrosine type (electron donor) Minus: Organic complex (electron acceptor) (4) Glidifier example: Colloidal silica, hydrophobic silica Typical examples include silicone varnish, metal soap,
Examples include nonionic surfactants.

(5) Cleaning agent Prevents toner filming on the photoreceptor.

Examples: fatty acid metal salts, oxidized silicon acids with organic groups on the surface, and fluorine-based surfactants.

(6) Filler The purpose is to improve the surface gloss of images and reduce raw material costs.

Examples: calcium carbonate, clay, talc, pigments, etc.

In addition to these materials, a magnetic material may be included to prevent fogging and toner scattering.

As magnetic powder, 0.1 to 1 μm triiron tetroxide, r
- Ferric oxide, chromium dioxide, nickel ferrite, iron alloy powder, etc. have been proposed, but at present, triiron tetroxide is often used and contains 5 to 70 wt% of the toner. The resistance of the toner varies considerably depending on the type and amount of magnetic powder, but in order to obtain sufficient resistance, it is preferable that the amount of magnetic material is 55 wt% or less. In addition, in order to maintain clear colors as a color toner, the amount of magnetic material must be increased to 30wt.
% or less.

Other resins suitable for pressure fixing toners include waxes, polyolefins, ethylene-vinyl acetate copolymers, polyurethanes, rubbers, and other adhesive resins that can be plastically deformed with a force of about 20 kg/cm and adhere to paper. Resin etc. are selected. Capsule toners can also be used.

A toner can be made using the above-mentioned materials by a conventionally known manufacturing method.

In the above configuration, in order to obtain a more preferable image, it is desirable that the average particle size of these toner particles is usually about 50 microns or less in view of the resolution. In this method, there is no theoretical limit to the toner particle size, but from the viewpoint of resolution, toner scattering, and conveyance, it is usually preferable to use a particle size of about 1 to 30 microns.

In addition, in order to improve fine dots and lines or to improve gradation, magnetic carrier particles are particles made of magnetic particles and resin, such as resin dispersion systems of magnetic powder and resin, or resin-coated magnetic particles. , more preferably spherical, the average particle size is preferably 50 μm or less, particularly preferably 30 μm or less,
Particles of 5 μm or less are preferred.

In addition, the problem of the carrier particles being easily injected with charges due to the bias voltage, which hinders good image formation, and the carrier particles tending to adhere to the surface of the image bearing member, and the problem of not applying enough bias voltage can be solved. In order to prevent this from occurring, the carrier should have an insulating resistivity of 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm or more, and more preferably 10 ¹⁴ Ωcm or more, and also have a particle size of the above-mentioned resistivity. Good. This resistivity is determined by placing particles in a container with a cross-sectional area of 0.50 cm ² and tapping them, applying a load of 1 kg/cm ² on the packed particles, and adjusting the amount of carrier to an appropriate amount. At this time, the carrier particles are 1 mm Make sure it is about the same thickness. This value is obtained by reading the current value when applying a voltage that creates an electric field of 1000 V/cm between the load and the bottom electrode.
If this resistivity is low, when a bias voltage is applied to the sleeve 11A, charge is injected into the carrier particles, making it easier for the carrier particles to adhere to the photoreceptor drum 9, or for bias voltage breakdown to occur more easily. I feel relaxed.

A method for manufacturing such a finely divided carrier is to use a magnetic material and a thermoplastic resin as described for toner, and coat the surface of the magnetic material with the resin, or coat the particles with a resin containing fine magnetic particles dispersed therein. It can be obtained by preparing the particles and selecting the particle size using a conventionally known average particle size selection means.
The carrier is shaped into a spherical shape in order to improve the agitation performance of the toner and carrier and the transportability of the developer, as well as to improve the charge control performance of the toner and to prevent agglomeration of toner particles and toner particles and carrier particles. However, for spherical magnetic carrier particles, resin-coated carrier particles should be selected as spherical as possible and coated with resin. It is produced by using fine particles of a magnetic material, forming dispersed resin particles and then subjecting them to a spheroidizing treatment using hot air or hot water, or directly forming spherical dispersed resin particles by a spray drying method.

A specific example using the developing device 13 and the two-component developer described above will be described with reference to FIG.

Embodiment 1 FIG. 6 is a schematic diagram of the main parts of a color image forming apparatus, in which a photosensitive drum 1 uniformly charged by a scorotron charger 30 is irradiated with a rotating multi-faceted drum from a He-Ne laser light source (not shown). Mirror 31, imaging lens 32
An electrostatic latent image is formed by imagewise exposure by the light sent through the . This electrostatic latent image is developed by the first developing device 13A, and a first toner image is formed on the photosensitive drum 1. This toner image is then charged again by the scorotron charger 30 without being transferred to the recording paper, and imagewise exposed in the same manner to form a second electrostatic latent image. and,
This time, a second toner image is formed by the developing device 13B. Similar steps are repeated until a third toner image is formed. That is, the steps of charging (not necessarily required from the second time onwards), exposure, and development are repeated three times. Thereafter, the pre-transfer exposure lamp 33 irradiates the area of the photoreceptor drum 1 on which the toner image has been formed, and the recording paper (its path is marked by a broken line 35) fed from a paper feeder (not shown) by the transfer device 34 This toner image is transferred to the paper (shown by ). The recording paper is heated and fixed by a fixing device 36 including at least one heated roller, and then discharged outside the machine.

On the other hand, after the photosensitive drum 1 has been transferred, the static electricity is removed by the static eliminator 37, which was not used during the toner image formation, and the remaining toner on the surface is removed by the cleaning device 3, which was not used during the toner image formation.
8 is removed.

This color image forming apparatus repeats the above operation every time the operation button is operated.

Each developing device used in this color image forming apparatus has the same configuration as the developing device 13 shown in FIG. contains cyan toner. And the amplitude of the AC component of the developing bias applied during development.
V _AC is 2.0,
1.8, 1.5KV, frequency is commonly set to 2KHz.
These developing biases are applied to the developing device 1 that performs development.
3, and the developing device that does not participate in development is grounded.

In addition, the charge amount of each toner T is 20μC/
g, the charging potential of the photoreceptor drum 1 is 600V, the gap d between the photoreceptor drum 1 and the sleeve 20 is 0.5 mm, the thickness of the developer layer on the circumferential surface of the sleeve 20 is 0.3 mm, and the DC voltage of the developing bias is set at each development stage. 500V was applied to the device.

When a multicolor image was formed using this image forming apparatus under the above conditions, during the subsequent development,
Each toner image with sufficient density was formed without destroying the toner image already formed on the photoreceptor drum 1 or mixing toner of another color into each developing device.

Example 2 In the color image forming apparatus shown in FIG. 6, which is the same as Example 1, the frequency of the AC component of the developing bias applied to the sleeve of each developing device was set to 2.0, 2.2, and 2.5 KHz in the order of development. When a multicolor image was formed under the same conditions as in Example 1 except for the combination of means for preventing the toner from returning due to increasing the height, the toner image already formed on the photoreceptor drum 1 was destroyed during the subsequent development. Toner images of sufficient density were formed without toners of other colors being mixed into each developing device.

Note that the present invention can be further modified based on its technical idea. In the above embodiments, a two-component developer is used as the developer, but a developer containing a third component may also be used.

In the embodiment, only the development of a color image is described, but the present invention can also be applied to developing the same color toner in multiple stages. In this case, a toner image with excellent gradation can be formed on the photoreceptor drum 1 by using one developing device and sequentially decreasing the amplitude of the alternating current component of the developing bias for each development.

In addition, the present invention utilizes not only an electrophotographic recording method but also an electrostatic recording method and a magnetic recording method.
It is possible to apply to non-impact printers.

Effects of the Invention As described above, according to the present invention, the step of forming a latent image on an image carrier and the step of developing the latent image using a developer made of a plurality of components are repeated multiple times, In an image forming method for forming an image on an image carrier, in each development step, the amplitude of the AC component of the developing bias is V _AC (V), the frequency of the AC component is f (Hz), and the image carrier and the developer are When the gap between the developer transporting body and the developer transporting body is d (mm), the following formulas (1) and (2) 0.2≦V _AC /(d/f) (1) Formula {(V _AC /d )−1500}/f≦1.0 By operating under the conditions that satisfy equation (2) and decreasing the amplitude V _AC (V) of the alternating current component sequentially for each development, the former stage is already used during the latter stage of development. The electrostatic force applied to the developer adhering to the image carrier during development can be reduced. Therefore, during the subsequent development, the subsequent development can be performed without disturbing the image formed on the image carrier by the previous development. As a result, even if an image is formed on the image carrier by repeating development multiple times, a clear image without any disturbance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional color image forming apparatus. 2 to 5 show embodiments of the present invention, in which FIG. 2 is a sectional view of a developing device and a photosensitive drum, and FIGS. A diagram showing the concentration change when
FIG. 5 is a diagram showing density characteristics when the amplitude and frequency of an alternating current electric field are changed, and FIG. 6 is a diagram showing essential parts of a color image forming apparatus equipped with a plurality of developing devices. Regarding the symbols used in the drawings, 1
...Photosensitive drum, 13, 13A, 13B, 13
C...Developing device, 14...Toner hopper, 17...
... Ear standing regulation plate, 20 ... Sleeve, 21 ... Magnetic roll, 22 ... DC power supply, 23 ... DC power supply,
D...developer, T...toner.

Claims (1)

[Scope of Claims] 1. A process of forming a latent image on an image carrier and a process of developing the latent image using a developer comprising a plurality of components are repeated multiple times to form an image on the image carrier. In an image forming method that forms _a
The frequency of the AC component is f (Hz), and the gap between the image carrier and the developer conveying body that conveys the developer is d (mm).
An image forming method characterized in that the image forming method is operated under conditions that satisfy the following equations (1) and (2), and the amplitude V _AC (V) of the alternating current component is sequentially reduced for each development. 0.2≦V _AC /(d・f) (1) Equation {(V _AC /d)−1500}/f≦1.0 (2) Equation.