JPS63229471A - Developing device - Google Patents

Abstract

PURPOSE:To increase an image density while minimizing fogging by executing development while impressing the frequency at which the absolute value of the sum of the electric charge quantity over the entire part of the developer adhering to a non-image region to said region is minimized. CONSTITUTION:An alternate electric field means is provided and the frequency at which the absolute value of the total sum of the electric charge of the developer adhering to the non-image region is minimized is impressed to said region. More specifically, the alternate electric fields are applied between an developer carrying body 16 and an image support 14 to move the developer T back and forth between the developer carrying body 16 and the image support 14. Only the developer T charged sufficiently to a normal polarity flies from the body 16 and contributes selectively to the development when the frequency of the alternate electric fields increases in this case. However, the deposition of the developer T charged to the polarity reverse from the polarity of the normal polarity increases in the non-image region when the frequency increases higher than the prescribed value; therefore, the frequency at which the absolute value of the sum of the electric charge over the entire part of the developer T adhering to the non-image region is minimized is impressed to said part, by which the sufficiently triboelectrostatically charged developer T of the normal polarity can be contributed to the development; in addition, the adhesion of the developer T charged to the reverse polarity is minimized.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention is used, for example, in an electrophotographic device, and is applied to a latent image carrier formed on a latent image carrier such as an electric shield or a photoreceptor. Shizuka 1! The present invention relates to a developing device that develops a latent image.

As this type of developing device, a non-contact developing type developing method using a non-magnetic component developer is known. For example, in U.S. Patent No. 3.232.190, a belt carrying a thin layer of non-magnetic component developer (hereinafter referred to as toner) on the surface of an electrophotographic photoreceptor (image carrier) is disclosed. (
A developing device is disclosed in which developer carriers (developer carriers) are opposed to each other with a gap maintained between them. In this conventional developing device, the toner carried on the belt flies toward the electrostatic latent image formed on the surface of the electrophotographic photoreceptor due to electrostatic force, adheres to the electrostatic latent image, and destroys the electrostatic latent image. It is being developed.

(Problem to be solved by the invention) However, strictly speaking, the particle size of toner is not uniform;
Particles with large particle diameters and particles with small particle diameters coexist. For this reason, the scale may not be able to charge the toner uniformly, or particles with a predetermined particle size or less may be charged to the 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 fogging may occur, making it impossible to obtain a clear image. There is a point.

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.

[Structure of the Invention] (Means for Solving the Problems) A developing device according to the present invention is provided opposite to an image support member on which a latent image is formed, with a gap therebetween, and supports a developer. A developer carrying member, a developer supply means for supplying 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 carrying member, is caused to fly from the developer carrier toward the image support.
A developing device for developing an image, the alternating electric field means comprising:
It is characterized in that a frequency is applied at which the absolute value of the total sum of charges of the developer adhering to the non-image area is minimized.

(Function) According to the developing device according to the present invention, an alternating electric field is applied between the developer carrier and the image support to cause the developer to reciprocate between the developer carrier and the image support. In this case, when the frequency of the alternating electric field becomes high, only the sufficiently charged developer flies away from the developer carrier and selectively contributes to development. However, in the non-image area, as the frequency increases beyond a predetermined value, the amount of developer charged with a polarity opposite to the normal polarity increases. Therefore, by applying frequency #9 that minimizes the absolute value of the sum of the charges of all the developer attached to the non-image area, the developer of the normal polarity that is sufficiently triboelectrically charged is selectively developed. At the same time, it minimizes the adhesion of oppositely charged developer.

(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 hopper 12 for storing developer, and a hopper 12 for storing developer.

A developing roller 16 that supplies toner within /f12 toward the photoreceptor 14 is rotatably provided in the direction of arrow A.

As the developer, a non-magnetic component developer (toner) of electroscopic powder containing a resin and a colorant is used. The peripheral surface of the developing roller 16 is roughened to facilitate frictional charging and conveyance of the developer. A free end of an elastic blade I8 extending toward the roller 414 is pressed against the circumferential surface of the developing roller 16. elastic blade 1
8 has its free end extending in the direction opposite to the rotation of the developing roller 16, so that the elastic blade 18 and the developing roller 16
The wedge-shaped space formed by the surfaces of the toner T is reduced, and it is possible to prevent the toner T from being embedded in this space. As a result, the toner coating action and toner charging action by the elastic blade 18 are performed uniformly, so that a stable toner N film can be formed. The elastic grade 18 may be any elastic material, but it is preferable to use a grade of stainless steel, phosphor bronze, or the like. The thickness of the plate is preferably about 0.1 to 0.4 m, and the plate is arranged so as to form a nip width with respect to the developing row 5p16, and the center thereof becomes a pressing point against the developing row 216. In this case, approximately 1 inch from the free end side of the elastic blade 18
A portion 5 to 5 meters away becomes a pressing point.

Hoy no! A supply roller 20 that supplies developer to the developing roller 12 is further provided in contact with the developing roller 16 and is configured to rotate in a direction C opposite to the rotational direction A of the developing roller 216. . supply laonia 2
0 has a polyurethane foam row 224 on the rotating shaft 22.
is provided.

A bias source 26 is connected to the developing roll 16 to apply a DC voltage and an AC voltage in a superimposed manner. 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, glass, glue, or rubber, and collects the toner adhered to the developing roller and prevents the toner TO from flowing out from the hopper 912.

On the other hand, the developing row 216 and the photoreceptor 14 are opposed to each other with an interval d, and the photoreceptor drum I4 is provided to rotate rather than rotate in the direction of arrow B, and is grounded. The interval d is set to approximately 0.1 to 0.5 degrees. 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 container 12 is supplied to the developing roller 16 while being agitated by the rotation of the supply roller 16 . The developing row 216 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 grade J8 is in this case compressed with a line pressure of approximately 10 to 200/-7 cm. In the developing row 216, the toner T has an elasticity grade of 18.
It is pressed and formed into a thin layer, and is triboelectrically charged. The thickness of one layer of toner is approximately 8 to 80 μm. The charging polarity of the toner varies depending on the polarity of the electrostatic latent image to be developed and the selection of regular development or Fi reversal development, but in this case, a toner that is charged to a positive polarity is used as the regular charging polarity. For triboelectrically charged toner, the photoreceptor 14
is transported to the developing area facing the.

On the other hand, after an electrostatic latent image (indicated by the symbol "-") is formed on the surface of the photosensitive drum 14, the photosensitive drum 14 is rotated along the direction of arrow B and conveyed to the developing area. Since a gap d is formed between the photoreceptor 14 and the developing row 216 in the developing area, the developer carried on the developing row 216 flies toward the surface of the photoreceptor 14 in the developing area. death,
Adheres by electrostatic force.

From the bias power supply 26, the DC voltage is approximately 50 to 300
V (volt), the negative peak value of AC voltage is approximately 1
．． 5 to 3. Apply a bias voltage superimposed on OkV (kilovolts). The force caused by the DC voltage acts to move the toner particles from the photoreceptor drum 14 to the developing roller 16, thereby preventing toner from adhering to the non-image area. As a result, toner fogging can be prevented, clear images can be obtained, trapping and wasteful developer consumption can be prevented, and recording costs can be reduced. The alternating current 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
The frequency is set at a time when the absolute value of the total sum of the toner charge amounts is the minimum, that is, approximately 700 Hz to 3 kHz.

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 140 and reciprocate depending on the frequency. As shown in FIG. 4, when the frequency is low, in the non-image area, the insufficiently charged toner T1 and the sufficiently charged toner T2 reach the photoreceptor and adhere there, causing fog.

On the other hand, as shown in FIG. 5, when the frequency is high, T2! -1: Since the toner is drawn back to the developing row 2 before reaching the photoreceptor, the fogging caused by the toner 2 is reduced even if the toner is sufficiently charged. 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 image density is higher as the frequency becomes higher (11), and similarly, the amount of reversely charged toner that adheres to the non-image area increases as the frequency increases. This is due to the fact that the reverse toner is applied to the developing roller 16 by mirror image force.
It is thought that this is because the vibrational force of this toner overcomes the mirror image force of the toner and becomes easier to fly out as the frequency increases. In other words, the amount of charge of the entire toner that should adhere to the non-image area (apparent charge ff1) is set to a value close to O. Note that the frequency varies depending on the gap d between the developing row 216 and the photoreceptor 14, but in this embodiment, when the gap d is about 200 to 300 μm, the frequency is about 1 to 2.
kHz is preferred.

The developed visible image is then transferred to paper. - On the other hand, the developing roller 16 that has passed through the developing area rotates further, and the toner that did not contribute to the development is collected on the surface of the developing roller 16 and collected by a collection blade 26, and is stored in the hopper 14. here,
A portion of the toner adhering to the developing roller 216 is scraped off by the supply roller 2Q, and new toner is adhered to the developing roller 216. Therefore, new toner is always supplied to the surface of the developing roller 16, and new toner is constantly supplied to the surface of the developing roller 216 after development. Also, no toner remains, which will not adversely affect 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 (exposed 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 frictional charge amount of 6 to 20 μg/g.

Note that this charge amount does not change before and after the latent image, so
It is considered that no phenomenon such as charge injection occurs in the development area. That is, the toner used here was 3000
1 even under an electric field of V/an and 30,000 ■i
It is a toner with a high resistance of 014- or higher.

The toner was divided into three types, Sample A and BSC, based on its particle size and particle size distribution.

Sample A Volume average particle size: 14.8 μm, particle size of 4 μm or less particles near 3.6% or less (cumulative 1[)
Particles with a particle size of 16 μm or less: 95.0% or more (cumulative value)
Sample B Volume average particle size: 14.0 μm, Particles with a particle size of 4 μm or less: 88.3% 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: 56.9% or less (cumulative value) Particles with a particle size of 16 μm or less: 96.6% or more (cumulative value) The above-mentioned distribution of toner particles is a measured value based on number distribution. This is a numerical value measured by a measurement method using He-N Rede analysis and scattering.

The bias power supply 26 has a DC voltage of -275V, an AC voltage of 2.4kV (absolute value of the difference between + peak and -peak), and a frequency of 20V for the sample CK.
The frequency of AC bias when changing from 0 Hz to 4 kHz, and toner adhesion in non-image areas! :The relationship with il (fogging) is shown as the second factor by a black circle.

In Figure 2, the horizontal axis shows the AC bias frequency (kHz),
The vertical axis represents the amount of toner adhesion in the non-image area as reflected density (%).
) are shown respectively. As is clear from Figure 2,
When the alternating current bias becomes about 700 Hz or more, the toner adhesion t (fogging) in the non-image area decreases rapidly, and becomes smaller at about 1.2 kHz (symbol a in the figure). Then, around 1.2 kHz is set as a small value, and thereafter, as the frequency rises, there is a tendency for the fog to gradually increase. In addition, 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 current bias was set to about 1 to 2.
When set to kHz, a clear image with almost no fog and excellent gradation could be obtained.

A toner having a volume average particle diameter of 8 to 16 μm, a toner number distribution of about 10 to 80% with a particle diameter of 4 μm or less, and a particle size distribution of 97% or more of toner with a particle diameter of 16 μm or less (all cumulative values). As long as it was used, the same results as in Test Example 1 were 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 increased9 and sufficient density and resolution could not be obtained.
In the case of a particle size distribution in the range including the above-mentioned samples A, B, and C'i, a clear image can be obtained. In addition, the elastic blade 18
The linear pressure was about 80 VCrn.

[Test Example 2] The potential of the image area (unexposed area) after charging was -600V, and the potential of the non-image area (exposed area) was #1-70V.

The gap d between the photosensitive drum 14 and the developing roller 16 is 200.
The bias power supply 26 had a DC reverse voltage of -200V and an AC voltage of 1.6 kV (absolute value of the difference between +8 and -(the and the difference)).

Note that other conditions were the same as in Test Example 1. Test example 2
The reason why the bias voltage was changed from that in Test Example 1 is 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, and by reducing the gap d, it is possible to move to a higher frequency side. You can see that there is a shift. Note that similar results were obtained for other toner samples A and B.

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 coverage increases rapidly, and the amount of adhesion decreases when it gets higher than this.As mentioned above, as the bias frequency increases, when the toner particles move back and forth, the change in the electric field causes the photoreceptor to This is because the particles change direction before reaching the non-image area and do not adhere to the non-image area. Therefore, in this embodiment, the frequency of the AC bias must be greater than or equal to 700 to 1500 Hz.

Next, the relationship between distance [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 unless there is a sufficient developing electric field due to the electrostatic latent image, toner will not adhere (therefore, , the amount of toner adhering to the non-image area is reduced.

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 700
By setting between Hz and 3.0 kHz,
When the gap d is set in the range of 100 to 500 μm,
I was able to minimize the number of turnips.

[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 graph in the upper part of Figure 3, the density in the image area (ratio of density to the original) is measured, and as shown in the lower part of the figure, the amount of charge of the entire toner particles attached to the non-image area is measured. was measured.

In Figure 3, the horizontal axis represents the frequency, the vertical axis represents the image density in the image area, and the middle represents the toner deposition M in the non-image area.
The toner charge in the non-image area is lined up and compared in the lower row and in the lower row.

As is clear from FIG. 3, if the frequency is in the region of 400 Hz or more, sufficient density can be obtained in the image area. 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 of the entire toner in the non-image area changes from positive to negative. From this, it can be seen that the fogged toner in the high frequency range is an oppositely charged toner contained in the toner layer.

Second, as shown by the dashed line in the middle part of FIG. 3, the amount of oppositely charged toner adhering to the non-image area gradually increases with frequency. On the other hand, as shown by the broken line, the amount of positively charged toner deposited suddenly decreases.

These combined amounts are drawn as a solid line curve in the middle. That is, when the frequency exceeds about 1 kHz (turning point R), the amount of toner adhering to the non-image area increases. As is clear from the graph at the bottom of this Turning-India R, the band as a whole toner! It coincides with the polarity change point (0 point). In other words, the fogging can be minimized as the absolute value of the total sum of the charges of the toner to be attached to the non-image area is smaller.

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 does not have to be used in a single-color electrophotographic device that uses only one developing device, but can also be used in a color copying device that uses multiple developing devices to develop with toners of multiple colors. can be obtained. In this case, in order to avoid contact of the second developing device with the toner image developed by the first developing device, the entire first developing device 14d between the developing roller and the photoreceptor in the second developing device is It is desirable to make it larger than the developing device and to apply a lower frequency. By setting in this way, the developing characteristics of the first and second developing devices can be set to be substantially the same.

Note that, if necessary, the frequency may be increased if the gap d needs to be made smaller. In other words, can the desired development state be achieved simply by changing the frequency according to the gap d? Section A can be done.

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 this invention, since development is carried out by applying a frequency that minimizes the absolute value of the sum of the charges of all the developer attached to the non-image area, it is possible to Image density can be increased. Therefore, clear images can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a developing device according to an embodiment of the present invention, FIG. 2 is a graph showing the relationship between AC bias and fog, and FIG. 3 is a graph showing the relationship between AC bias frequency and fog 9 and toner. Graphs showing the relationship with the band'yi amount, and FIGS. 4 and 5 are diagrams illustrating the movement of toner when an AC bias is applied. 10...Developing device, 12...Hopper, 16...Developing roller, 26...AC bias power supply.

Claims (1)

[Claims] A developer carrying member that is disposed to face the image supporting member on which the electrostatic latent image is formed with a gap therebetween and carries a developer; a developer supply means that supplies the developer to the developer carrying member; An alternating electric field means for applying an alternating electric field to the gap between the support and the developer carrier, and the developer is made to fly from the developer carrier toward the image support to develop an electrostatic latent image. 2. A developing device, wherein the alternating electric field means applies a frequency that minimizes the absolute value of the sum of charges of the developer attached to the non-image area.