JPH07209970A - Image forming method - Google Patents

Abstract

PURPOSE:To provide an image forming method having desirable image density and capable of obtaining high quality removing image irregularity or color mixing in an image forming device for forming a visual image on the surface of an image carrier by repeating respective processes such as electrostatic charging, latent image formation and developement plural times. CONSTITUTION:In the image forming device for forming a visual image on the surface of an image carrier 1 by repeating a charging processing, a process for forming a latent image on the carrier 1 and a process for supplying a two- component developer to a developer carrier 20 and inversely developing a latent image on the carrier 1 by toner with the same polarity as charging polarity plural times, an electric field including an AC component is generated between both the carriers 1, 20, the frequency of the AC component is successively increased in each development and each development is executed so as to satisfy the conditions of {VAC/d-1500}/f<=1.0 and 0.2<=VAC/(d.f) provided that VAC is the amplitude (V) of the AC component, (f) is the frequency (Hz) of the AC component and (d) is a gap (mm) between both the carriers 1, 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method.

[0002]

2. Description of the Related Art First, an image forming method in which development is repeated a plurality of times will be described using the color copying machine shown in FIG. 1 as an example.

In the case of a color copying machine, a filter is required to decompose the reflected light from the original and take out the light of a single color, and this copying machine has a filter back 2 containing three kinds of filters of different colors. Is provided. For example, first, the reflected light from the original is decomposed with a green filter, and an electrostatic latent image is formed on the photosensitive drum 1 which is an image carrier already charged by the band electrode 9 by this passing light.
When development is performed by the developing device 3B in the developing device 3 in which magenta toner is stored, a magenta toner image is formed on the photosensitive drum 1. This toner image is conveyed from the paper feed box 8 and is transferred by the transfer pole 10 onto the copy paper 7 which is a transfer body wound around the transfer drum 4. Photoconductor drum 1
After that, the charge is removed by the removing electrode 11, the residual toner is removed by the cleaning device 5, and the charging is performed again by the charging electrode 9. This time, image exposure is performed by the light transmitted through the blue filter, and a yellow toner image is formed on the photoconductor drum 1 by the developing device 3A. This is already transferred to the copy paper 7 by superimposing the magenta toner image on the copying paper 7. After this, the copy paper 7 is separated from the transfer drum 4,
After being fixed by the fixing device 6, the paper is ejected to the outside of the machine.

[0004]

This image forming method is desirable because it can add color information as compared with information obtained from a black and white image, but has the following problems.

(1) The transfer drum 4 must be provided in order to transfer the image onto a copy sheet each time the development of each color is completed, so that the machine becomes large and the time required for image formation becomes long.

(2) The developing process and the transferring process must be repeated several times, and it is necessary to guarantee the positional deviation accuracy.

For these reasons, the toner image is not transferred onto the copy paper 7 for each development, but each toner image of all colors is formed on the photosensitive drum 1 and then transferred onto the copy paper 7 at once. Therefore, an image forming method for solving the above-mentioned problems has been proposed. According to this image forming method,
A toner image of another color is formed again in the image area where the toner image has already been formed on the photosensitive drum 1, but the toner formed on the photosensitive drum 1 in the previous stage is disturbed during the development in the subsequent stage. Alternatively, the toner that has already formed an image on the photosensitive drum 1 returns to the developer transport body in the developing device, and this enters the developing device in the subsequent stage that stores toner of a color different from the toner in the preceding stage. However, there is a problem that color mixing occurs. Therefore, except for the developing device that first forms a toner image on the photoconductor drum 1, the photoconductor drum 1 and the developer layer of the developer carrier that develops the electrostatic latent image are not in contact with each other, and the developing bias is applied. As means for superimposing the AC component as, for example, is shown in JP-A-56-144452,
For the development conditions, it is not possible to obtain sufficient image density,
There is a problem that image distortion and color mixing cannot be eliminated.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an image forming method for recording with desired density and without image distortion or color mixture. It is an object.

That is, in the image forming method of the present invention, the charging step, the step of forming a latent image on the image carrier, the two-component developer on the developer carrying body are supplied to the image carrier and the latent image is formed. An image forming apparatus for forming a visible image on the image carrier by repeating a step of reversing and developing an image with a toner having the same polarity as the charge polarity, the image carrier and the developer transport body. An electric field containing an alternating current component is generated between and, and the frequency of the alternating current component is sequentially increased for each development,
And each development _{{V AC /d-1500}/f≦1.0 0.2 ≦ V AC} / (d · f) V AC: amplitude of the AC component (V) f: AC component of the frequency (Hz) d: an image bearing member It is characterized in that it is performed so as to satisfy the condition of the gap (mm) between the developer carrier and the developer carrier.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, the process by which the present inventor arrived at the present invention will be described. The image forming method in which the step of forming a latent image on the image bearing member and the step of developing the latent image are repeated to sequentially superimpose toner images that are visible images on the image bearing member is First, it is necessary to perform development at an appropriate density without disturbing the toner image already formed on the image carrier. As a result of examination, in order to satisfy this condition, the gap d (mm) between the image carrier and the developer carrier in the developing area.
(Hereinafter, it may be simply referred to as a gap d), the amplitude V _AC (V) of the _AC component of the developing bias and the frequency f (Hz) do not disturb the toner image formed in the preceding stage, and the toner image in the succeeding stage has an appropriate density. It became clear that it is a parameter when forming with.

Therefore, an experiment was conducted with a developing device as shown in FIG. 2 while changing the frequency and voltage parameters of the AC 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 a carrier, and the toner T rubs against the carrier by the rotation of the stirring screw 18 to have a positive or negative polarity. Fully charged. Here, when the sleeve 20 and / or the magnetic roll 21 as the developer transport body rotates, the developer D is transported on the peripheral surface of the sleeve 20. In FIG. 2, the magnetic roll 21 rotates in the direction of arrow A and the sleeve 20 rotates in the direction of arrow B, whereby the developer D is conveyed in the direction of arrow B on the circumferential surface of the sleeve 20. The thickness of the developer D is regulated by the spike regulation plate 17, and the developer D becomes a uniform layer and moves toward the photosensitive drum 1 which is an image carrier. When the developer D reaches the developing area 24, the toner in the developer D is statically absorbed according to the electric potential of the electrostatic latent image formed on the photosensitive drum 1 and the electric field generated by the AC and DC voltages as the developing bias. Power works,
A toner image is formed by the toner flying from the sleeve 20 and adhering to the surface of the photosensitive drum 1. The cleaning blade 26 scrapes off the developer D on the peripheral surface of the sleeve 20 containing the toner that has not been developed. 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 protective resistance. When the developer D is used for development and the toner in the developer D in the developer pool 19 is insufficient, the replenishing roller 16 rotates to replenish the toner T from the toner hopper 14.

The inventor of the present invention previously formed a toner image on the photosensitive drum 1 by using the developing device described above, and developed the toner image by superposing it on the toner image. At this time, an experiment was carried out by changing the above parameters variously, and the disturbance of the toner image formed in advance and the image density of the superimposed toner image were measured, and the results shown in FIGS. 3 and 4 were obtained. I was able to do it. A two-component developer in which the toner is positively charged was used as the developer.

In FIG. 3, the gap d between the photosensitive drum 1 and the sleeve 20 is 1.0 (mm), the developer layer thickness is 0.5 (mm), and the photosensitive drum 1 is
Charging potential of 600 (V), developing bias DC component is 500
(V), the AC component frequency 1 (KH _z) of the AC component of when setting the amplitude V _AC and the exposure portion on the photosensitive drum 1 of the toner image (the value of 0 (V)) is developed into The relationship with the image density is shown. The amplitude E _{AC of the} AC electric field is the amplitude of the AC component of the developing bias (that is, 1/2 times the peak-to-peak value) V _AC and the gap d.
It is the value divided by. Curves A, B, and C shown in FIG. 3 have toner average charge amounts of 30 (μc / g), 20 (μc / g), and 15 (μc / g), respectively.
It is the result obtained when the one whose charge is controlled to (μc / g) is used. In all three curves A, B, and C, the effect of the AC component appears when the amplitude E _{AC of the} AC electric field is 200 (V / mm) or more, and when it is 2500 (V / mm) or more, it is preliminarily set on the photosensitive drum 1. It was observed that the formed toner image was partially destroyed.

[0016] Figure 4, the frequency of the AC component of the developing bias and 2.5KH _Z, indicates an image density change when changing the amplitude E _AC of the alternating electric field under the same conditions as the experiment of FIG. According to this embodiment, the amplitude E _{AC of the} alternating electric field is 50
If it exceeds 0 (V / mm), the image density becomes large, and if it is not shown (4) (kV / mm) or more, a part of the toner image previously formed on the photosensitive drum 1 is destroyed. Was observed.

In FIGS. 3 and 4, the shapes of the curves A, B, and C are almost the same except that the image density increases as the average toner charge amount increases. It is considered that this is because the toner particles having a high charge amount and having a distribution around the average value are preferentially developed.

When experiments similar to those shown in FIGS. 3 and 4 were conducted under different conditions, the amplitude E _{AC of the AC} electric field and the frequency f
It was possible to sort out the relationship, and the results shown in FIG. 5 were obtained. The area indicated by in FIG. 5 is an area where development unevenness is likely to occur, the area indicated by is an area where the effect of the AC component does not appear and the density is insufficient, and the area indicated by is the photosensitive drum 1 in advance.
The toner attached to the photosensitive drum 1 is transferred to the sleeve 20.
The area where the toner easily returns to the area is an area where the effect of the AC component appears, a high density is obtained, and the toner adhered to the photosensitive drum 1 in advance does not return to the sleeve 20, and is a particularly preferable area. is there. These areas are straight lines G, H,
It is divided by I. Of these, H and I respectively indicate the conditions for giving a special concentration. This result shows that in order to develop the next (post-stage) toner image at an appropriate density without destroying the toner image that was previously formed on the photosensitive drum 1 (pre-stage), the amplitude of the AC electric field E _AC And its frequency f, there is an appropriate region, and it is considered that the cause is due to the reason 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, the region where the AC electric field amplitude E _AC is 0.2 to 1.2 (kV / mm) Because of the AC component of the developing bias, the toner is greatly contributed by the force acting in the direction of exceeding the threshold value for flying from the sleeve 20, and the toner having a smaller charge amount is successively developed as the AC component becomes stronger. become. Therefore, the image density increases as the amplitude E _{AC of the} alternating electric field increases.

[0020] On the other hand, a region where the image density is saturated with respect to the amplitude E _AC of the alternating electric field, the in curve A AC electric field of Figure 3 the amplitude E _AC
With respect to the area of 1, 2 (kV / mm) or more, this development can be explained as follows. That is, in this region, the toner vibrates strongly as the amplitude E _{AC of the} AC electric field increases, and the agglomerated toner clusters are destroyed,
Only the toner with a large charge is selectively used as the photosensitive drum 1.
Adhere to. In such a situation, since the amount of toner supplied to the developing area in a fixed time is finite, the image density is considered to be saturated with respect to the amplitude E _{AC of the} AC electric field. Further, when the amplitude E _{AC of the} AC electric field becomes large, the electric charge on the surface of the photosensitive drum 1 leaks, and the phenomenon that the toner becomes difficult to develop also occurs. In fact, it is considered that these factors are overlapped and the image density is constant as the amplitude E _AC of the _AC electric field increases.

Further, the amplitude E _AC of the _AC electric field is increased,
For example, under the condition that curve A in Fig. 3 is obtained, the amplitude is 2.5 (kV · mm).
As described above, it was found that the toner image previously formed on the photosensitive drum 1 was destroyed as described above, and the greater the AC component, the greater the degree of destruction. It is considered that this is because the toner adhering to the photosensitive drum 1 is pulled back to the sleeve 20 by the AC component. When toner images of different colors are superimposed and developed on the photosensitive drum 1 for color image formation, it is fatal to destroy the toner images that have already been formed.

Based on the above experimental results, the present inventor has determined that the amplitude of the AC component of the developing bias is V _AC (V),
When the frequency f (Hz), the gap between the photosensitive drum 1 and the sleeve 20 and d (mm), a condition that satisfies _{0.2 ≦ V AC / (d ·} f) {V AC /d-1500}/f≦1.0 If the development is carried out by
It was concluded that the subsequent development can be performed at an appropriate density without destroying the toner image formed above. In order to obtain a sufficient image density, it is preferable that the condition of 0.8 ≦ V _AC / (d · f) is satisfied and 1.0 ≦ V _AC / (d · f) is satisfied.

Here, how to set the frequency f of the AC component applied as the developing bias will be described with reference to FIG. As described above, the areas of ,,, are divided by the straight lines G, H, and I. Of these, G is a straight line indicating the boundary where the toner, which previously forms an image on the photosensitive drum 1, begins to return to the sleeve 20 due to the AC electric field, and increases as the frequency f increases. For example, the amplitude E _AC of the alternating electric field is 2.5 (kV · mm) point frequency f is 1 kH _Z in J
Is on the straight line G. The amplitude E _{AC of the} AC electric field is 2.
The point K at 5 (kV · mm) and the frequency f of 3 KH _Z is separated from the straight line G. As deduced from the above description, the further away from the area, the more difficult the toner on the photosensitive drum 1 is to return to the sleeve 20.

This shows that when the frequency is high, it is more effective in separating the toner from the photosensitive drum 1 and preventing the toner from returning to the sleeve 20 when the frequency is higher.

By the way, when the frequency becomes high, the amplitude range of the toner particles is narrowed and the amount of toner adhered to the photosensitive drum 1 is reduced, but the same amount of toner of each color is adhered to the photosensitive drum 1 during each development. Not necessarily necessary. The color correction of the color image can be performed by adjusting other developing conditions, such as the DC component of the developing bias, the latent image potential, and the toner supply amount.

From the above, if the frequency f of the AC component of the developing bias is sequentially increased each time the developing is performed, the toner particles already developed in the preceding stage and adhering to the photosensitive drum 1 will return to the sleeve 20. Therefore, it was concluded that the subsequent development can be carried out. By doing so, the subsequent development can be performed without disturbing the already formed toner image or causing the problem of color mixing.

The frequency of the AC component applied as the developing bias is set to 20 in order to prevent uneven development due to the AC component.
When the developer D is set to 0 (Hz) or more and is supplied to the photosensitive drum 1 by the rotation of the magnetic roll 21 shown in FIG. 2, in order to eliminate the influence of the AC component and the beat generated by the rotation of the magnetic roll 21, It is desirable to set it to 500 (Hz) or more.

Further, in order to successively develop the subsequent toner images on the photosensitive drum 1 without destroying the toner image formed on the photosensitive drum 1, the frequencies are sequentially increased and (1) Use toner with a large amount of charge.

(2) The amplitude of the electric field due to the AC component of the developing bias is gradually reduced.

(3) The amount of the developer supplied to the developing area is gradually increased.

It is preferable to use the above methods alone or in any combination.

That is, the toner particles having a larger charge amount are more likely to be affected by the electric field. Therefore, if toner particles having a large charge amount are attached to the photosensitive drum 1 in the initial development, the toner particles may return to the sleeve 20 in the subsequent development. Therefore, the above-mentioned (1) is to prevent the toner particles from returning to the sleeve 20 during the subsequent development by using the toner particles having a small charge amount for the initial development. The method (2) is a method of preventing the toner particles already adhering to the photoconductor drum 1 from returning by decreasing the amplitude E _AC of the _AC electric field sequentially toward the subsequent development. As a concrete method, there is a method of gradually lowering the voltage of the AC component in the subsequent development, and a method of widening the gap d between the photosensitive drum 1 and the sleeve 20 in the subsequent development. . On the other hand, (3) utilizes the fact that the larger the amount of toner supplied to the developing area is, the easier the development is, and is a method of preventing the toner from returning by applying a weaker external force to the latter development. The amount of toner supplied is determined by the conveyance speed of the developer D, the thickness of the developer layer on the sleeve 20, the mixing ratio of the toner and the carrier,
It can be adjusted by stirring the developer D or the like. By adjusting the DC voltage of the developing bias for each development together with these methods, it is possible to maintain an appropriate image density or color balance.

A specific embodiment of the above-described structure will be described with reference to FIG.

Embodiment 1 FIG. 6 is a schematic view of a main part of a color image forming apparatus, in which a photosensitive drum 1 uniformly charged by a scorotron charger 30.
Is a He-Ne laser light source (not shown), a rotary polygon mirror 31,
The image is exposed by the light sent through the imaging lens 32 to form an electrostatic latent image. This electrostatic latent image is developed by the first developing device 13A, and a first toner image is formed on the photosensitive drum 1. Then, this toner image is charged again by the scorotron charger 30 without being transferred to the recording paper, and is similarly imagewise exposed to form a second electrostatic latent image. Then, the second toner image is formed by the developing device 13B this time. The same process is repeated until the third toner image is formed. That is, the steps of charging (not necessarily required from the second time) → exposure → developing are repeated three times. Then, the pre-transfer exposure lamp 33 irradiates the area of the photosensitive drum 1 where the toner image is formed, and the transfer device
This toner image is transferred onto a recording paper (the path of which is indicated by a broken line 35) sent from a paper feeding device (not shown) by 34. The recording paper is heat-fixed by a fixing device 36 composed of at least one heated roller, and discharged to the outside of the machine.

On the other hand, the photosensitive drum 1 after the transfer is
After the charge is removed by the charge remover 37 that is not used during the toner image formation, the toner remaining on the surface is removed by the cleaning device 38 that is released during the toner image formation. The color image forming apparatus repeats the above operation each time the operation button is operated.

Each developing device used in this color image forming apparatus has the same structure as the developing device 13 shown in FIG. 2, with the developing device 13A being yellow, the developing device 13B being magenta, and the developing device being the developing device 13B. Cyan toner is stored in 13C. The amplitude V _AC of the AC component of the developing bias applied during development is 1 kV for each developing device, and the frequency f is 1.2 (KH _Z ), 1.5 (KH _Z ), and 2.0 (KH _Z ) in the order of development. Set. These developing biases are applied only to the developing device that performs the development, and the developing device that is not involved in the development is grounded. Further, the charge amount of each toner is 20 (μ / g), the charge potential of the photosensitive drum 1 is 600 (V), the gap d between the photosensitive drum 1 and the sleeve 20 is 0.5 (mm) on the peripheral surface of the sleeve 20. The developer layer thickness is 0.3 (mm), and the developing bias DC voltage is applied to each developing device 500 (V).

When a multicolor image is formed by the above-mentioned structure, the toner image already formed on the photosensitive drum 1 is destroyed at the time of the subsequent development, and the toners of other colors are stored in the developing devices. A visible image with sufficient density was obtained without contamination.

Embodiment 2 In the same color image forming apparatus as in Embodiment 1 shown in FIG. 6, the charging potential of the photosensitive drum 1 is 500 (V), 6 for each development.
Change to 00 (V) and 700 (V), and change the DC voltage of the developing bias to 400 (V), 500 (V), and 600 (V) to maintain the density balance of the toner images of each color. When a multicolor image is formed under the same conditions as in Example 1, the toner image already formed on the photosensitive drum 1 may be destroyed during the subsequent development, or toner of other colors may be mixed in each developing device. Without
A visible image with sufficient density was obtained.

The present invention can be further modified based on its technical idea. In the embodiment, the case where the two-component developer is used as the developer has been described, but the same effect as the above can be obtained even when the one-component developer is used. Further, the present invention can be applied not only when forming a color image, but also when forming an image of a single color.
In this case, it is possible to form a toner image with gradation by using one developing device and sequentially increasing the frequency of the AC component of the development balance for each development.

The present invention can be applied to a non-impact printer using not only the electrophotographic recording system but also the electrostatic recording system and the magnetic recording system.

[0041]

According to the present invention, the frequency of the AC component of the developing bias applied between the image bearing member and the developer transporting member is sequentially increased for each development, so that when the subsequent developing process is performed, The electrostatic force applied to the developer adhering to the image bearing member can be reduced by the development described above. Therefore, in the latter stage development, the latter stage development can be performed without disturbing the image formed on the image carrier by the former stage development. As a result, even if an image is formed by repeating development on the image carrier a plurality of times, a clear image without disturbance can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a color image forming apparatus according to a conventional example.

FIG. 2 is a sectional view of a developing device and a photoconductor drum showing an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a change in concentration when the amplitude of an alternating electric field is changed.

FIG. 4 is a characteristic diagram showing a change in concentration when the amplitude of an alternating electric field is changed.

FIG. 5 is a characteristic diagram showing concentration characteristics when the amplitude and frequency of an alternating electric field are changed.

FIG. 6 is a configuration diagram showing a main part of a color image forming apparatus including a plurality of developing devices.

[Explanation of symbols]

 1 Photoreceptor Drums 13, 13A, 13B, 13C Developing Device 14 Toner Hopper 17 Booting Limit Plate 20 Sleeve 21 Magnetic Roll 22 AC Power Supply 23 DC Power Supply D Developer T Toner

Claims (1)

[Claims] 1. A charging step, a step of forming a latent image on an image carrier, a two-component developer is supplied to the image carrier with a developer carrier, and the latent image has the same polarity as the charging polarity. An image forming apparatus for forming a visible image on the image carrier by repeating the step of reversal development with toner a plurality of times in this order, including an AC component between the image carrier and the developer transport body. together give rise to an electric field, the frequency of the AC component, sequentially increased for each developer, and each development _{{V AC /d-1500}/f≦1.0 0.2 ≦ V AC} / (d · f) V AC: AC Amplitude (V) of component f: Frequency (Hz) of AC component d: Image forming method characterized in that the process is performed so as to satisfy the condition of the gap (mm) between the image carrier and the developer carrier.