JPH0664394B2 - Development method using two-component developer - Google Patents

Description

The present invention relates to a developing device for developing an electrostatic latent image formed on an image forming body used in an electrophotographic copying machine or the like, and more particularly to a two-component developer. The present invention relates to an improvement of a developing device by a non-contact developing method using the.

[Background of the Invention]

In an electrophotographic system in which an electrostatic latent image on an image forming body is visualized by development to form a final image, a developing method using a one-component type developer and a two-component type composed of a magnetic carrier and a non-magnetic toner are currently used. It is roughly classified into a developing method using a system developer.

However, even in the developing method using a one-component developer, in the developing method using a one-component non-magnetic developer, the force for carrying the developer on the developer carrier depends on the charge of the developer. Only Coulomb force and van der Waals force make it difficult to form a stable and uniform developer layer. Further, in a developing method using a one-component magnetic developer, a magnetic material which is generally black magnetite powder is included in the toner, so that it is difficult to obtain a toner having a vivid color other than black. On the other hand, the developing method using a two-component developer has an advantage that a stable developer layer can be formed and vivid color toner can be used as compared with other developing methods.

Generally, when a latent image on an image forming body (photoreceptor) is developed by a developer held and conveyed on a developer carrier, in order to increase the contrast of the obtained image, the image forming body and the developer carrier are carried. The image quality can be improved by reducing the body distance. In the contact type developing method in which the gap between the image forming body and the developer carrying body is made small, in the contact developing method in which the image forming body and the developer layer are brought into contact with each other to develop, the developer is formed between the image forming body and the developer carrying body. Is compacted, or with that pressure,
In order not to destroy the latent image or the developed image, it is necessary to reduce the amount of the developer held / conveyed on the developer carrier to keep it within an appropriate range. The "developer amount" here is the weight of the developer per unit area held on the surface of the developer carrier.

Even in a non-contact development method in which development is performed while keeping the image forming body and the developer layer in a non-contact state, when the gap between the image forming body and the developer carrying body is reduced, the image forming body and the developer layer are Therefore, it is necessary to reduce the amount of the developer on the developer carrier so as not to come into contact with each other and keep it within an appropriate range.

In the conventional developing method using a two-component developer, for example, development has been performed by a developing device having the following configuration. FIG. 8 is a partial configuration diagram of a conventional developing device.

In the figure, the developing roll is a magnetic pole with an equal magnetic force and an N pole, S
It was composed of a magnetic roll 104 whose poles were alternately magnetized and a non-magnetic cylindrical developer carrier (sleeve) 103. The magnetic roll 104 and the developer carrier 103 are relatively rotatable. A two-component developer containing a carrier, toner and the like is supplied onto the developing roll, and the image forming member 10 is rotated by relative rotation of the magnetic roll 104 and the sleeve 103.
1, for example, it is conveyed to the developing area facing the photosensitive drum.

Conventionally, a layer thickness regulating plate made of metal or resin as shown in FIG. 8 is used in order to obtain a desired amount of developer and a desired developer layer thickness of the developer layer held on the surface of the developer carrier. 105 is disposed in the vicinity of the surface of the developer carrying member 103, and the developer d is moved while being held by the surface of the developer carrying member 103 and slips through the gap between the layer thickness regulating plate 105 and the surface of the developer carrying member 103. It was configured to be carried to the development area.

Among the developers on the developer carrying surface, the magnetic carrier receives a force from the magnetic field of the magnet of the magnetic roll 104 arranged on the opposite side of the developer carrying surface, and the magnetic carrier of the magnet and the magnetism of the carrier cause the magnetic ears to come out. After being formed and rising, the carrier is held on the developer carrying surface. Non-magnetic toner is a developer container
By being stirred in 102, the magnetic carrier is triboelectrically charged, and the non-magnetic toner and the magnetic carrier have charges of opposite polarities and are bound to each other by the Coulomb force. Since the magnetic carrier is held on the developer carrying surface by the magnetic field of the magnet, the non-magnetic toner is also held on the developer carrying surface together with the magnetic carrier, and the magnetic carrier is held on the developer carrying surface. A developer layer made of non-magnetic toner is formed. This developer layer is held and conveyed on the developer carrying surface to develop the latent image on the image forming body 101.

As described above, this developer layer is not compacted in the gap between the image forming body 101 and the developer carrying body 102, or the image forming body 101 and the developer layer which should be kept in non-contact are not in contact with each other. The minimum requirements must be met. Further, the phenomenon of "fogging" in which toner adheres to the surface of the image forming body other than the image portion does not occur.

"Carrier adhesion" in which carriers adhere to the surface of the image forming body
Does not occur.

Toner sufficient to obtain a sufficient image density adheres to the latent image portion.

The toner image has a gradation that is sufficient to reproduce the gradation of the latent image.

The developer layer must satisfy the above conditions.

To meet these conditions, the physical properties of the developer itself and the stirring method thereof, the physical properties of the latent image bearing member, the relative speed of the image forming member and the developer layer, the means for forming a latent image on the latent image bearing member, the image An electrical bias applied between the former and the developer carrier,
The magnetic force of the magnet and the shape of the magnetic field must be within the proper range. Among such conditions, there is the amount of developer on the surface of the developer carrying member and the thickness of the developer layer, and the appropriate range is smaller than the minimum conditions described above.

As described above, using a two-component developer consisting of a carrier and toner, these are magnetically held on the developing sleeve and conveyed to a narrow space in the developing area to develop the electrostatic latent image on the image forming body. In the developing method, a DC and AC voltage bias is applied, the developer layer on the sleeve does not come into contact with the surface of the image forming body, the carrier particle size is a minute particle size of 10 to 50 μm, and the reversal development is performed. There is a developing method which has characteristics such as being used, and has recently been drawing attention. In particular, the developing method described above is an effective method for forming a color image.

[Problems to be solved by the invention]

However, in the conventional developing method as described above,
AC is used to improve the developability when developing in a non-contact state with the image forming body using a carrier with a fine particle size.
Since a bias is applied, there is a drawback that carrier adhesion is likely to occur on the latent image forming surface of the image forming body. Particularly, in the case of reversal development, there is a problem that the potential of the portion corresponding to the background is high, and there is a large variation depending on the characteristics of the image forming body, and carrier adhesion to this portion easily occurs.

[Means for solving problems]

(Object of the Invention) The present invention was obtained as a result of research aimed at reducing the above carrier adhesion.

That is, the present invention is a non-contact development method using a two-component developer containing a magnetic carrier capable of forming a stable developer layer and a non-magnetic toner capable of using a clear color toner,
The purpose of the present invention is to find an AC bias condition in which sufficient toner developability can be obtained and carrier adhesion does not occur. In particular, it is an object of the present invention to provide a means for achieving a developing method for forming a high quality multicolor image by using the non-contact two-component developing method.

(Structure of the Invention) The above-mentioned object is to form a layer on a developer carrying member so as not to contact the image forming member under a magnetic field, and use a two-component developer to apply an AC bias voltage between the developer carrying member and the image forming member. In a developing device that visualizes a latent image on an image forming body under application, a frequency of the AC bias voltage f is set as follows, which is achieved by a developing method using a two-component developer. It

In the formula, qc: charge amount of carrier, mc; mass of carrier qt; charge amount of toner, mt; mass of toner E; applied electric field in developing space l; developing gap Fm, magnetic force, where: However, Vc; carrier volume M; carrier magnetization (emu / g) H; magnetic field strength r; carrier particle size Unit is MKS unit system In the developing method of the present invention, the developer is a particle as described below. It is composed of a toner having a diameter of 50 μm or less, preferably 15 μm or less, and a carrier having a small particle diameter which is not much different from the particle diameter of the toner, and 300 μm or less, preferably 200
A two-component developer having a thickness of μm or less has never been used before, and a thin developer layer is used for non-contact development.

The toner particle size is 1 to 20 μm, and the carrier size is 10
.About.50 .mu.m is preferable, and when these are used, the developability is further improved.

FIG. 1 shows a sectional view of a developing device suitable for carrying out the developing method of the present invention. In the figure, 1 is an image forming body, 2 is a housing, 3 is a sleeve, 4 is a magnetic roll having N and S8 poles, 5 is a thin layer forming member, 6 is a fixing member for the member, 7 is a first stirring member, 8 Is a second stirring member. Reference numerals 9 and 10 denote rotating shafts of the stirring members 7 and 8, 11 is a developer reservoir, 12 is a replenishing toner container, 13 is a toner replenishing roller, 14 is a developing bias power source, and 15 is a developing area, that is, toner on the sleeve is electrostatic. Area that can be transferred onto the image forming body under the influence of a repulsive force, t is a replenishment toner, and d is a developer.

In such a developing device, the developer d in the developer reservoir 13 is sufficiently agitated and mixed by the first stirring member 7 rotating in the direction of the arrow and the second stirring member 8 rotating so as to overlap each other in the opposite direction. By the conveying force of the sleeve 3 rotating in the direction of the arrow and the magnetic roll 4 rotating in the opposite direction, it is attached and conveyed to the surface of the sleeve 3. A layer forming member 5 held by a fixing member 6 extending from the housing 2 is pressed against the surface of the sleeve 3 at a surface close to the end, and regulates the layer thickness of the developer d to be conveyed.
A thin developer layer having a thickness of m to 300 μm, preferably 50 to 200 μm is formed. If the thickness is less than 10 μm, the developing density is lowered, and if it exceeds 250 μm, the carrier and toner are scattered. This developer layer develops the latent image on the image forming body 1 which rotates in the direction of the arrow in the developing area 15 in a non-contact manner at intervals to form a toner image. During this non-contact development, a developing bias containing an AC component is applied from the power source 14 to the sleeve 3, and as a result, only the toner in the developer on the sleeve 3 is selectively transferred to the surface of the latent image and attached. . The layer thickness of the developer is measured as follows. That is, the layer thickness is obtained by comparing the positions of the projected image of the screen of the sleeve and the projected image of the state in which a thin layer is formed on the sleeve using a Nikon profile projector manufactured by Nihon Kogaku Co., Ltd.

The layer forming member 5 is an extremely uniformly formed thin plate made of, for example, a magnetic or non-magnetic metal, a metal compound, plastic, rubber or the like, one end of which is fixed by a fixing member 6 and which is given elasticity. The thickness is 50 to 500 μm.

As described above, the sleeve 3 is elastically slightly pressed at a portion close to the other end of the thin layer forming member having one end fixed, and the pressing causes the carrier and the toner particles at the contact position between the sleeve 3 and the thin plate. Of the developer d, and impurities and carriers in the developer d and / or aggregates of toner are prevented from passing therethrough. Therefore, the developer reaching the developing area 15 is always thin and uniform and stable.

The thickness of the developer reaching the developing area 15 is controlled by changing the pressing force and the contact angle of the thin layer forming member 5 with respect to the sleeve 3.

As described above, it is advantageous that the carrier and toner constituting the developer have a small particle size from the viewpoint of the resolution of image quality and the reproducibility of gradation. For example, when the carrier of the developer layer has a small particle size of 30 μm or less. However, by using a means such as the thin layer forming member 5 described above, it is possible to automatically remove impurities, agglomerates and the like in the developer to form a uniform thin layer. Moreover, even when the carrier has a particle size as small as that of the toner, the mixture of impurities is eliminated and a uniform thin layer can be formed. Since the two stirring members 7 and 8 incorporated in the developing device are configured so that the stirring blades overlap each other without colliding with each other, the stirring in the left-right direction (FIG. 1) is sufficiently performed. At the same time, due to the inclination of the stirring plate, the stirring in the front-back direction (FIG. 1) is sufficiently performed.

Further, the toner T replenished from the hopper 11 via the replenishing roller 12 is also uniformly mixed in the developer d in a short time.

As described above, the developer d, which has been sufficiently stirred and given the desired triboelectrification, is regulated by the thin layer forming member 5 in the process of being attached and conveyed onto the sleeve 3 to form an extremely thin and uniform developer layer. To be done. This developer layer is sleeve 3
Is conveyed in one direction by rotation of the magnetic roll 4
Rotation in the opposite direction causes a magnetic bias having an oscillating component, which causes complicated movement such as rolling on the sleeve 3 to reach the developing area 15 and develop the latent image of the image forming body 1 in a non-contact manner. At this time, the toner is effectively supplied toward the latent image surface. Since the developer layer is extremely thin (10 μm to 250 μm) as described above, non-contact development is possible by narrowing the gap between the image forming body 1 and the sleeve 3, that is, the developing gap to around 200 μm. Becomes When the development gap is narrowed in this way, the development area
Since the electric field of 15 becomes large, there is an advantage that sufficient development is achieved even if the developing bias applied to the sleeve 3 is small, and leak discharge of the developing bias is reduced. Further, the resolution and other image quality of the image obtained by development are generally improved.

The present invention is the result of research in the above-described developing method, focusing on the AC component, particularly the frequency component, in the developing bias.

That is, in the developing method of the present invention, by applying an AC electric field to the sleeve 3, the developer d on the sleeve 3 is vibrated to separate the toner and the carrier, and only the toner is moved along the latent image electric field. , Is to be attached to the image on the image forming body 1.

Therefore, in the separation and movement of the toner and the carrier in the AC electric field, the respective kinetic responses to the electric field are important factors. Then, this response changes the developability.

The present invention solves one of the drawbacks of the developing method of non-contact development using a two-component developer, that is, the problem that carrier adhesion is likely to occur, by utilizing the difference in response between the toner and the carrier with respect to an alternating electric field. To do.

The experimental results will be described below with reference to FIGS. 2 to 4.

FIG. 2 is a graph showing the relationship between AC bias and frequency. Here, a typical example is shown. Table 1 shows the image forming conditions according to this developing method. The DC bias potential of the developing device was set to -500 V, and reversal development was performed. Table 2 shows the prescription of a two-component developer including toner and carrier used for development. Here, a toner having an average particle diameter of 11 μm and a carrier having an average particle diameter of 30 μm was used.

As shown by the curve A in FIG. 2, it is understood that the frequency that gives the lower limit of the proper condition as the condition of carrier adhesion is almost proportional to the square root of the AC bias voltage.

Next, FIG. 3 is a diagram showing the relationship between carrier magnetization and frequency. Here, the AC bias voltage was set to 2 KV _pp . As shown by the curve B in the figure, it is understood that the frequency that gives the upper limit of the proper condition as the condition of carrier adhesion has a correlation with the square root of the magnetization M. That is, it is clear that as the carrier suction force to the sleeve side becomes stronger, the response is lowered even at low frequencies.

Furthermore, FIG. 4 is a diagram showing the relationship between the mass m of the carrier and the frequency. This indicates that the curve C indicating the upper limit of the carrier attachment easy region is inversely proportional to the square root of the mass m of the carrier. Further, it is known that the upper limit of the proper amount of adhered toner is also inversely proportional to the square root of the mass of toner, as described above.

This is because these developments shown in FIGS. 2 to 4 are based on the motion described by the following equation.

m; mass q; charge amount r; particle radius η; grain resistance k; constant term (magnetic force, van der Waals force etc.) From various experiments, it was found that this phenomenon can be explained by the solution of this differential equation. It was

That is, the response to the carrier's electric field police box is The value represented by changes suddenly. Along with this, it can be seen that the carrier adhesion generation limit also changed experimentally.

In the above formula (1), qc: carrier charge amount, mc: carrier mass E: applied electric field in developing space l: developing gap Fm, magnetic force, where: However, Vc; carrier volume M; carrier magnetization (emu / g) H; magnetic field strength r; carrier particle radius The same applies to toner, It is known that the toner adhesion amount greatly changes at the boundary.

In the above formula (2), qt is the charge amount of toner, mt is the mass of toner, and therefore, in the non-contact two-component developing method, when developing using an AC voltage, the AC The frequency of the voltage is calculated from the equations (1) and (2) above. It is necessary to be within the range of.

Here, the charge amounts of the toner and the carrier are generally used. The blow off method was used. For magnetic force, use a Gauss meter I asked. It can also be calculated. The particle size is measured with a Coulter counter. The magnetization of the carrier was measured with a hysteresis curve tracer.

The organic photosensitive layer in Table 1 above is composed of a function-separated photosensitive layer having a carrier generating layer containing a triazo pigment as a lower layer and a carrier transporting layer containing an aromatic amino compound as an upper layer. The developing method is non-contact development. And the reversal development method.

[Examples] The present invention will be specifically described below with reference to Examples.

FIG. 5 shows the structure of the image forming apparatus used. Image input section
IN is the illumination light source 1, mirror 22, lens 23, one-dimensional color
CCD image sensor 24 is integrated into a unit,
The image input unit IN is moved in the direction of arrow X by a driving device (not shown), and the CCD image pickup device 24 reads the original. Image input section I
The document 25 may be moved by fixing N and moving the document table.

The image information read by the image input unit IN is converted into data suitable for recording by the image processing unit TR.

The laser optical system 26 forms a latent image on the image forming body 20 in the following manner based on the above image data, and the latent image is developed to form a toner image on the image forming body 20. The surface of the image forming body 20 is uniformly charged by the scorotron band electrode 27. Subsequently, the image forming body 20 is irradiated with image exposure L according to the recording data from the laser optical system 26 through the lens. In this way, an electrostatic latent image is formed. This electrostatic latent image is developed by the developing device A containing yellow toner. The image forming body 20 on which the toner image is formed is uniformly charged again by the scorotron band electrode 27 and is subjected to image exposure L according to the recording data of another color component. The formed electrostatic latent image is a developing device B containing magenta toner.
To be developed. As a result, a two-color toner image of yellow toner and magenta toner is formed on the image forming body 20. Similarly, cyan toner and black toner are overlaid and developed to form a four-color toner image on the image forming body 20. Each of the developing devices A, B, C, and D containing the respective color toners has the same structure as the developing device of FIG.

The multicolor toner image thus obtained is exposed to the exposure lamp 28
Then, the charge is removed to facilitate transfer, and then transferred to the recording paper P by the transfer pole 29. The recording paper P is separated from the image forming body 20 by the separation pole 30 and fixed by the fixing device 31. on the other hand,
The image forming body 20 is cleaned by the removing electrode 32 and the cleaning device 33.

The cleaning device 33 has a cleaning blade 34 and a fur brush 35. These are kept out of contact with the image forming body 20 during image formation, and when a multicolor image is formed on the image forming body 20, they come into contact with the image forming body 20 and scrape off the transfer residual toner.
Thereafter, the cleaning blade 34 separates from the image forming body 20, and the fur brush 35 separates from the image forming body 20 after a short delay. The fur brush 35 functions to remove the toner remaining on the image forming body 20 when the cleaning blade 34 separates from the image forming body 20. A roller 36 collects the toner scraped by the blade 34.

The laser optical system 26 is shown in FIG. In the figure, 37 is a semiconductor laser oscillator, 38 is a rotating polygon mirror, and 39 is an fθ lens.

Further, in such an image forming apparatus, it is effective to set an image exposure start timing by receiving an optical mark on a photoconductor and reading the mark by an optical sensor or the like in order to align each image. .

In the image forming process in the copying machine shown in FIG. 5, reversal development is performed using the developer having the formulation shown in Table 2, and the image forming conditions shown in Tables 1 and 3 to 5 and the operation timing shown in FIG. To form an image. (In FIG. 7, the high level indicates the operating state.) In the timing chart of FIG. 7, the horizontal axis represents the image forming process and the vertical axis represents each image forming department. Also A, B, C, D
Represents a yellow toner developing device, a magenta toner developing device, a cyan toner developing device, and a black toner developing device.

When a multicolor image was formed under the above conditions, good resolution and good dot-like reproducibility of halftones were obtained. Further, the scattering of toner and carrier could be suppressed to a minimum.

Example 2 The following toner has an average particle size of 3 μm and the carrier has an average particle size of 30 μm. Multicolor images were formed in the same manner as in Example 1 except that the image forming conditions were set as shown in Tables 6 to 9.

When a multicolor image was formed under the above conditions, a copy image having high resolution and good color tone and gradation reproducibility was obtained without scattering of toner and carrier as in the case of Example 1.

〔The invention's effect〕

As is clear from the above description, according to the developing conditions disclosed in the developing method of the present invention, a developing device without carrier adhesion and a large toner adhesion amount can be obtained, and in the color image forming method described in Examples, It has become possible to obtain good color image quality.

Furthermore, even if the type of carrier, such as CL carrier, resin dispersion type carrier, ferrite carrier, etc., changes in mass, magnetization, etc., it is possible to always obtain good image quality by applying the conditional expression according to the present invention. . Similarly, with respect to the toner, by applying the above conditional expression even if the parameter thereof is changed, it is possible to achieve stable formation of a high-quality recorded image.

[Brief description of drawings]

FIG. 1 is a sectional view of a developing device to which a developing method according to the present invention is applied, and FIGS. 2 to 4 are diagrams showing AC bias frequency characteristic curves according to the present invention. FIG. 5 is a sectional view showing the construction of an embodiment of a copying machine equipped with the above developing device, FIG. 6 is a schematic view of the laser optical system of the copying machine, and FIG. 7 is a diagram showing the image forming timing in the embodiment. Is. FIG. 8 is a partial sectional view of a conventional developing device. 1,20,101 …… Image forming body (photoreceptor) 3,103 …… Developer carrier (developing sleeve) 4,104 …… Magnetic roll 5,105 …… Layer thickness regulating plate (ear cutting plate) 14 …… Development bias power supply, 15 …… Development area A, B, C, D ... Development device d ... Developer, t ... Toner ... AC bias frequency l ... Development gap

(72) Shinobu Soma Inventor Shinobu Soma 2970 Ishikawacho, Hachioji City, Tokyo Rokusha Konishi Shin Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A developer layer is formed on a developer carrying member so as not to contact the image forming member under a magnetic field, and an AC bias voltage is applied between the developer carrying member and the image forming member using a two-component developer. In the developing device for visualizing the latent image on the image forming body underneath, the developing method using a two-component developer is characterized in that the frequency f of the AC bias voltage is set as follows.