JPS63278078A - Developing device - Google Patents

Abstract

PURPOSE:To obtain a distinct image free from photographic fog by applying an alternating electric field having such frequency between an image supporting body and a developing roll that a developer having a normal polarity cannot reach the non-image part of the image supporting body but only the developer having the opposite polarity can reach this part. CONSTITUTION:In a developing device where the developer is flown from a developer carrier 16 to an image supporting body 14 and is stuck to its image part to develop an electrostatic latent image, an alternating electric field applying means 26 applies such frequency that the developer having the normal polarity cannot reach the non- image part of the image supporting body 14 but only the developer having the opposite polarity can reach this part. The alternating electric field is given to the space between the developer carrier 16 and the image supporting body 14 to move the developer back and forth. In this case, the alternating electric field having a prescribed frequency is applied so that the developer having the normal polarity cannot reach the non-image part of the image supporting body but only the developer having the opposite polarity can reach this part. The developer having the opposite polarity is not transferred to a transfer paper in the transfer process because it has the same polarity as transfer corona. Thus, a satisfactory image which is completely free from photographic fog is obtained.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) This invention is used, for example, in an electrophotographic apparatus, and is directed to a static image forming apparatus that is used in an electrophotographic apparatus, and which is formed on a latent image carrier such as a dielectric or a photoreceptor. 2. Description of the Related Art A non-contact development type developing method using a developing device for developing an electrostatic latent image is known. For example, U.S. Patent No. 3,232,190 describes an electrophotographic photoreceptor (
A belt (developer carrier) 'f: carrying a thin layer of non-magnetic component developer (hereinafter referred to as toner) on its surface is opposed to the image carrier) with a gap maintained between them. A developing device is disclosed. In this conventional developing device, the toner carried by Bell) K is
It flies toward the electrostatic latent image formed on the surface of the electrophotographic photoreceptor, adheres to the electrostatic latent image, and develops it.

(Problems to be Solved by the Invention) However, strictly speaking, toner particles are not uniform in particle size, and include particles with a large particle size and particles with a small particle size. For this reason, not only can the toner not be uniformly charged, but particles with a predetermined particle diameter or less may be charged with opposite polarity.

If the toner is insufficiently charged or if toner of opposite polarity is mixed, the image density after development may be insufficient or fog may occur, resulting in the inability to obtain a clear image. .

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a developing device that can produce clear images.

[Objective of the Invention (Means for Solving Problems) A developing device according to the present invention is provided facing an image support on which an electrostatic latent image is formed, with a gap therebetween, and supports a developer. comprising a developer carrier, a developer supply means for supplying developer to the developer carrier, and an alternating electric field means for applying an alternating electric field to the gap between the image support and the developer carrier, A developing device that develops an electrostatic latent image by flying developer from a developer carrier toward an image support and attaching the developer to the image area, wherein the alternating electric field means It is characterized by applying a frequency that does not allow the developer of normal polarity to reach the image area, but only allows the developer of opposite polarity to reach the image area.

(Function) According to the developing device according to the present invention, an alternating electric field is applied to the gap between the developer carrier and the image support to cause the developer to reciprocate. In this case, an alternating electric field of a predetermined frequency is applied, and the developer of normal polarity is not allowed to reach the non-image area of the image support, but only the developer of opposite polarity is allowed to reach. However, since the developer of opposite polarity has the same polarity as the transfer corona in the transfer process, it is not transferred to the transfer paper, and as a result, a good image with no fogging is obtained.

(Embodiments) Examples of the present invention will be described in detail below with reference to FIGS. 1 to 5 of the accompanying drawings. Note that this embodiment will be explained using regular development as an example.

As shown in FIG. 1, a developing device 10 according to the present invention includes a holster/arm 12 for storing developer and a developing roller 16 for supplying toner in the hopper 12 toward a photoreceptor 14 in the direction of arrow A. It is rotatably installed. As the developer, a non-magnetic component developer (toner) of electroscopic powder containing a resin and a colorant is used. The circumferential surface of the developing roller 160 is roughened to facilitate frictional charging and conveyance of the developer. A free end portion of an elastic blade 18 extending toward the hopper 14 is pressed against the circumferential surface of the developing roller 16 . Since the free end of the elastic blade 18 extends in the direction opposite to the rotation of the developing roller 16, the wedge-shaped space formed by the surfaces of the elastic blade 18 and the developing roller 16 is reduced. This can prevent the toner T from being embedded. the result,
Since the toner coating action and toner charging action by elastic grade 18 are performed uniformly, a stable toner thin film can be formed. The elastic grade 18 may be made of any elastic material, but it is preferable to use a plate made of stainless steel, phosphor bronze, or the like. The plate thickness is
Approximately 0.1 to 0.41111 is preferable, and the developing roller 1
The developing roller 16 is arranged so as to form an error width with respect to the developing roller 16, and its center is a pressing point against the developing roller 16. in this case,
Approximately 1 to 5 m11 from the free end side of the elastic blade 18
The part 1 point away is the pressing point.

Inside the hopper 12, a supply roller 20 that supplies developer to the developing roller is further provided in contact with the developing roller 16, and is configured to rotate in a direction CK opposite to the rotational direction A of the developing roller 16. The supply roller 20 has a rotating shaft 22 provided with a polyurethane foam roller 24 .

A bias power supply 26 that applies a DC voltage and an AC voltage in a superimposed manner is connected to the developing roll 16. A collection grade 28 is pressed under the developing roller 16 and collects the toner remaining on the developing roller 16 into the hopper 12 . The collection blade 28 is made of a thin plate material such as metal, plastic, or rubber, and collects the toner adhering to the developing roller and prevents the toner T from flowing out from the hopper 12.

On the other hand, the developing roller 16 and the photoreceptor 14 are opposed to each other with a gap d1, and the photoreceptor drum 14 is provided to rotate in the direction of arrow B and is grounded. The gap d is set to about 0.1 to 0.5 fins. The photosensitive drum 14 is manufactured by forming a photosensitive layer on the surface of an aluminum drum.

Next, the operation of this developing device will be explained.

The toner T in the hole 1912 is supplied to the developing row 216 while being agitated by the rotation of the supply roller 160. The developing roller 16 has a toner conveying force due to its rough surface, so it resists the pressing force of the elastic blade 18 and transfers the toner T.
is transported toward the developing area. The elastic blade 18 in this case applies a linear pressure of approximately 10 to 20011/cIIL. In the developing roller 16, the toner T is transferred to the elastic blade 1.
8 to form a thin layer and triboelectrically charge it.

The thickness of one layer of toner is approximately 8 to 80 μm.

The polarity of the toner band 1 varies depending on the polarity of the electrostatic latent image to be developed and the selection of regular development or reverse development, but here, a toner that is charged to a positive polarity is used as the regular charging polarity. The triboelectrically charged toner T is transported to a development area facing the photoreceptor 14.

On the other hand, after an electrostatic latent image (indicated by the symbol "-") is formed on the surface of the photosensitive drum 14Fi, it is rotated along the direction of arrow B and conveyed to the developing area. In the developing area, since a distance d is formed between the photoreceptor 14 and the developing roller 16, in the developing area, the developing roller 16VC
The supported developer flies toward the surface of the photoreceptor 140 and adheres thereto due to electrostatic force.

From the bias power supply 26, the DC voltage is approximately 50 to 300V.
(, Ie silt and the AC voltage provides a superimposed bias voltage with its peak-to-peak value of approximately 1.5 to 3.0 kV (kilogelds). The force due to the DC voltage moves the toner particles from the photoreceptor drum 14 to the developer roller 16. This prevents toner from adhering to non-image areas.As a result, toner fogging is prevented and clear images are obtained, while wasteful consumption of developer is prevented and recording costs are reduced. The AC voltage vibrates and activates the toner particles in the development area, thereby increasing the gradation of the visible image.The frequency of the AC voltage in this case will be described later, but it is possible to The frequency is set at a time when the absolute value of the total sum of the amount of charge of the attached toner is the minimum, that is, approximately 700 Hz to 3 kHz.

The developer image after development is transferred to a sheet of paper; in this case, the sheet of paper is negatively charged with corona, and the positive developer image i is electrostatically attracted and transferred to the sheet of paper.

Here, the relationship between the frequency applied to the gap d and the effect of toner will be explained with reference to FIGS. 4 and 5.

It is generally known that when an alternating current bias is applied, toner particles fly between the developing roller 16 and the photoreceptor 14 and move back and forth depending on the frequency. As shown in FIG. 4, when the frequency is low, in the non-image area, insufficiently charged toner T1 and sufficiently charged toner 2 reach the photoreceptor and adhere there, causing fog. . On the other hand, as shown in FIG. 5, when the frequency is high, in the non-image area, the fully charged toner T2 is drawn back to the developing roller before reaching the photoreceptor. The fog caused by this decreases. However, some of the fine particles contained in the toner have a reverse charge, and this reversely charged toner is pushed toward the photoreceptor 14 by the electric field in the non-image area. Therefore, in the image area, the higher the frequency, the higher the image density becomes, and similarly, the higher the frequency, the more reversely charged toner adheres to the non-image area. This is thought to be because toner of opposite polarity adheres to the developing roller 16 due to mirror image force, and as the frequency increases, the vibration force of this toner overcomes the mirror image force of the toner and becomes more likely to fly out.

- 10,000, frequency at which regular toner does not adhere to non-image areas (1
, 5 kHz or higher, on the other hand, toner of opposite polarity (
Only negative polarity toner) will adhere. However, in this case, when transferring the next developer image, the paper is charged with negative corona, so the regular toner (positive polarity toner) is transferred, but the opposite polarity toner is transferred. It is designed not to be transferred.

Therefore, a good transferred image with no fogging can be obtained. In this way, by setting the frequency of the applied AC bias higher than the point at which the apparent amount of charge becomes 0, even if a relatively large fog appears on the photoreceptor, it can be transferred to the final paper. The image becomes a clear image with no fog at all.

The developing row 216, which has partially passed through the developing area, further rotates, and the toner that did not contribute to development is collected by the collection blade 26t while being carried on its surface and stored in the hopper 14. Here, part of the toner adhering to the developing roller 16 is scraped off by the supply roller 20, and new toner is adhering to the developing roller 16. Therefore, new toner is constantly supplied to the surface of the developing roller 16, and no toner remains on the surface of the developing roller 16 after development, thereby preventing any adverse effects on the next development.

[Test Example 1] After the surface of the photoreceptor drum 14 was uniformly charged by corona charging, the original was imagewise exposed to form an electrostatic latent image. In this case, the potential of the image area (unexposed area) is -67
5V, and the potential of the non-image area (n-tip area) was -70V.

The gap d between the photosensitive drum 14 and the developing roller 16 is 300.
.mu.m, and the thickness of the developer layer was 20 to 30 .mu.m. The single layer of toner formed on the developing roller 16 had a triboelectric charge amount of 6 to 20 μI/11.

Note that this charge amount does not change before and after the latent image, so
It is considered that no development such as charge injection occurs in the development area. That is, the toner used here was 3000
The toner has a high resistance of more than 100 F even under an electric field of V/am and 30,000 V/[.

Based on its particle size and particle size distribution, the toner has a 3a[
Samples A, B, and C were used separately.

sample people Volume average particle size: 14.8 μm.

Particles with a particle size of 4 μm or less: 3.6% or less (cumulative value) Particles with a particle size of 16 μm or less: 95.01 or more (cumulative value) Sample B Volume average particle size: 14.0 μm, particles with a particle size of 4 μm or less: 8 B, 3% or less (cumulative value) Particles with a particle size of 16 μm or less: 98.4% or more (cumulative value) Sample C Volume average particle size: 12.3 μm.

Particles with a particle size of 4 μm or less: 56.95G or less (cumulative value)
Particles with a particle size of 16 μm or less: 96.6% or more (cumulative value)
Note that the above-mentioned distribution of toner particles is a measured value that depends on the number distribution, and is a numerical value measured by a measuring method using He--N Rede analysis and scattering.

The bias power supply 26 is DC voltage -275V.

and AC voltage 2.4 kV C + absolute value of the difference between peaks) And for sample C, the frequency of AC bias when changing the frequency from 200 Is to 4 kHz,
The relationship between toner adhesion t (fogging) in non-image areas is shown by black circles in FIG.

In Figure 2, the horizontal axis is the frequency of the AC bias (kHz), and the vertical axis is the amount of toner adhesion in the non-image area (reflection density C%).
These are shown in the following. As is clear from Figure 2,
When the AC bias becomes about 700 Hz or higher, toner adhesion (fogging) in non-image areas rapidly decreases.
It reaches a minimum at about 1.2 kHz (symbol a in the figure). The minimum value is around 1.2 kHz, and the fogging tends to gradually increase as the frequency increases thereafter. When samples A and B were subjected to similar tests, they showed the same results as sample C, but sample C had the least amount of fog, and the amount of fog tended to increase in the order of sample A and sample B. . That is, it is shown that the more toner particles with small particle diameters are included, the more fogging increases.

In this test example 1, the frequency of the AC bias was set to about 1.5 to
When the frequency was set to 2 kHz or higher, a clear image with almost no fog and excellent gradation could be obtained.

The volume average particle size is 8 to 16 μm, the number distribution of toner with a particle size of 4 μm or less is about 10° to 80 cm, and the number distribution of toner with a particle size of 16 μm or less is 97% or more (all cumulative values)
As long as a toner with a particle size distribution of
A similar result was obtained.

In this case, if a large amount of toner with extremely small particle size or toner with extremely large particle size was included, fogging would increase and sufficient density and resolution could not be obtained.
In the case of a particle size distribution in the range including the above-mentioned temples A, B, and C, a clear image can be obtained. In addition, the elastic blade 180
The linear pressure was approximately 80 g/cm.

[Test Example 2] The potential of the image area (unexposed area) after charging is -600V.

The potential of the non-image area (exposed area) is -70V.

The gap d between the photosensitive drum 14 and the developing roller 16 is 200.
μm.

The bias power supply 26 is DC voltage -200V.

and the alternating current voltage, s kv <+absolute value of the difference between peak and female peak).

Note that other conditions were the same as in Test Example 1.

The reason why the bias voltage in Test Example 2 was changed from that in Test Example 1 was to make the electric field in the gap d substantially equal to that in Test Example 1. The results of this second test example are shown in FIG. 2 by white circles.

As is clear from FIG. 2, the relationship between the amount of fog and the frequency of the AC bias showed the same tendency as in Test Example 1. Furthermore, as is clear from Fig. 2, the frequency that gives the minimum value of fog is 1.7 kHz (symbol b in the figure) in Test Example 2, which is between 1 and 7 kHz (symbol b in the figure). It can be seen that by decreasing IId, the frequency is shifted to the higher frequency side. Note that similar results were obtained for other toner samples A and H.

Here, the relationship between AC bias and fog will be explained with reference to FIG.

When the frequency is lower than about 700 to 1500 Hz, the fogging increases rapidly, and when the frequency is higher than this, the adhesion k decreases, but as mentioned above, as the bias frequency increases, the toner particles move back and forth. This is because when the electric field changes, the direction changes before reaching the photoreceptor, and as a result, it does not reach the non-image area and adhere. Therefore, in this embodiment, the frequency of the AC bias must be greater than 700 to 1500 Hz.

Next, the relationship between the gap d and fog will be explained.

In the above-mentioned high frequency range of AC bias, toner particles cannot reach the photoreceptor due to changes in the electric field during reciprocating motion, so toner will not adhere (therefore, it will not adhere) unless there is a sufficient developing electric field due to the electrostatic latent image. (The amount of toner adhering to the image area will be less.)

If the gap d is large, the time required for the toner to reach the photoreceptor increases, and the amount of toner adhesion decreases.

According to these tests, the AC bias frequency was set to 1.5
By setting the frequency above kHz, fogging could be minimized.

[Test Example 3] Sample C used in Test Example 1 was tested under the same conditions as Test Example 1. Furthermore, as shown in the upper graph of FIG. 3, the density in one image area (density difference with respect to the original) is measured, and as shown in the lower part of the same figure, the charge fkt of the entire toner particles attached to the non-image area is measured. It was measured.

In Figure 3, the horizontal axis shows the frequency, the vertical axis shows the image density in the image area, the middle line shows the toner adhesion cover in the non-image area, and the bottom line shows the toner charge in the non-image area. be.

As is clear from FIG. 3, sufficient density can be obtained in the image area if the frequency is in the region of 400 Hz or higher. On the other hand, as shown in the lower part of FIG. 3, in a region where the frequency exceeds 1 kHz, the amount of charge on the toner particles attached to the non-image area changes from positive to negative. From this, Kabu9 toner in the high frequency range is different from the oppositely charged torch contained in the toner layer.
It can be seen that it is.

That is, as shown by the dashed line in the middle part of FIG. 3, the amount of adhesion of the oppositely charged toner gradually increases with frequency. On the other hand, as shown by the broken line, the adhesion t of positively charged toner rapidly decreases. These combined amounts are drawn as a solid line curve in the middle. That is, the frequency is approximately 1 kHz
(Turning I-in) R) is exceeded, the amount of toner adhering to the non-image area increases. As is clear from the graph at the bottom, this turning point R coincides with the point of change (point 0) in the charging polarity of the toner as a whole.

This invention is not limited to the one embodiment described above, and can be modified in various ways without departing from the gist of the invention.

For example, the present invention can produce the same effect even when used in a color copying device that uses multiple developing devices to develop with toner of multiple colors, instead of using it in a one-color electrophotographic device that uses only one developing device. can be obtained. In this case, in order to avoid the second developing device from coming into contact with the toner image developed by the first developing device, it is desirable to increase the development low in the second developing device and lower the applied frequency. By setting like this, the first and second
The developing characteristics of the developing device can be set almost the same as that of the developing device. Note that, if necessary, the frequency may be increased if the gap d needs to be made smaller. That is, the gap d
The desired development state can be adjusted simply by changing the frequency according to the conditions.

Furthermore, although the above-mentioned embodiments have been described using regular development as an example, it goes without saying that similar effects can be obtained even when reverse development is used.

[Effects of the Invention] According to the present invention, an alternating electric field of a frequency that prevents the developer of the normal polarity from reaching the non-image area of the image support and only allows the developer of the opposite polarity to reach the image support and the developing roller. Since the voltage is applied between the two, clear images without fogging can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an image carrier according to an embodiment of the present invention, FIG. 2 is a graph showing the relationship between AC bias and fog, and FIGS. FIGS. 4 and 5 are graphs showing the relationship between the amount of charge and the amount of charge. FIGS. 4 and 5 are diagrams explaining the movement of toner when an AC bias is applied. ! 0...Developing device, 12...Hopper, 16...Developing roller, 26...AC bias power supply. Applicant's agent Patent attorney Takehiko Suzue F. Figure 1

Claims (2)

[Claims] (1) A developer carrying member that is disposed opposite to the image support member on which the electrostatic latent image is formed, with a gap therebetween, and carries a developer, and a developer supplying means that supplies the developer to the developer carrying member. and an alternating electric field means for applying an alternating electric field to the gap between the image support and the developer carrier, and the device is configured to fly the developer from the developer carrier toward the image support and apply the developer to the image area. A developing device for developing an electrostatic latent image by depositing an electrostatic latent image, wherein the alternating electric field means does not allow a developer of normal polarity to reach a non-image area of an image support, but allows only a developer of opposite polarity to reach a non-image area of the image support. A developing device characterized by applying a frequency. (2) The frequency of the alternating electric field is 2 kHz or more when the gap is 200 μm or less, and 1.5 kHz or more when the gap is greater than 200 μm and 300 μm or less, and the average particle diameter of the developer is 8 μm or more and 16 μm or less. A developing device according to claim 1, characterized in that: