JP2008122427A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus, capable of maintaining image quality by stabilizing the distribution of the charge amount of supplied toner, in a flare developing system excellent in dot reproducibility. <P>SOLUTION: The developing device 20 and the image forming apparatus 21, are characterized in that a two-component developer having magnetic particles and a nonmagnetic toner is supported on a developer carrier 12 incorporating a magnetic field generation means having a plurality of magnetic poles and is transported to a supply area opposite to a toner carrier, the magnetic brush of the developer is formed in the supply area, and a DC voltage is applied to the developer carrier 12, for supplying the toner to the toner carrier 19. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus having the developing device.

Conventionally, there are a large number of development methods including those in practical use. Typical development methods include a two-component development method and a one-component development method.
The two-component development method is very suitable for high-speed development, and is the mainstream method for current medium-speed and high-speed output machines. In order to aim for high image quality, it is necessary to make the state of the developer in contact with the electrostatic latent image very dense. For this reason, the carrier particles are now being reduced in diameter, and carriers of about 30 μm are beginning to be used on a commercial level. However, the demand for higher image quality is increasing, and the required dot size of the pixel itself must be equal to or smaller than the current carrier particle size, which means the reproducibility of isolated dots. Then, it is necessary to further reduce the carrier particles. However, as the carrier diameter is reduced, the permeability of the carrier particles decreases, so that the carrier is easily detached from the developing roller. If the detached carrier particles adhere to the latent image carrier, the carrier adheres. Not only does this cause image defects, but it also causes various side effects such as scratching the latent image carrier starting from the image defects. In order to prevent this carrier detachment, attempts have been made to increase the magnetic permeability of carrier particles from the material surface and to increase the magnetic force of the magnet included in the developing roller. Development is extremely difficult due to this balance. In addition, due to the downsizing of the developing roller, the developing roller is becoming smaller in diameter, and it becomes difficult to design a developing roller having a strong magnetic field configuration that can completely prevent carrier detachment. Yes.
In the first place, the two-component development system is a process of forming a toner image by rubbing the ears of a two-component developer called a magnetic brush against an electrostatic latent image. Unevenness tends to occur in the developability of isolated dots.
Although an image quality can be improved by forming an alternating electric field between the developing roller and the latent image carrier, it is difficult to completely eliminate the fundamental image unevenness such as the unevenness of the ears of the developer.
In order to improve transfer efficiency and cleaning efficiency in the step of transferring the developed toner image to the latent image carrier and the step of cleaning the toner remaining on the latent image carrier after the transfer, the latent image carrier It is necessary to reduce the non-electrostatic adhesion force between the toner and the toner as much as possible. As a method for reducing the non-electrostatic adhesion force between the latent image carrier and the toner, it is known that it is effective to reduce the friction coefficient on the surface of the latent image carrier. Since the spikes of the agent smoothly pass through the developing portion, the development efficiency and the dot reproducibility become very poor.

The one-component developing method is the mainstream method of current low-speed output machines because the mechanism is small and light. In order to form a thin toner layer on the developing roller, a toner regulating member such as a blade or a roller is brought into contact, and at that time, the toner is charged by friction with the developing roller and the toner regulating member. The charged toner layer formed as a thin layer on the developing roller is transported to the developing unit and developed. The developing system here is largely divided into a contact type and a non-contact type. In the former, the developing roller and the latent image carrier are not in contact, and the latter is in contact. In any system, the toner layer thinned on the developing roller is sufficiently pressed, so that the toner responsiveness to the electric field in the developing unit is very poor. Therefore, in general, in order to obtain high image quality, it is mainstream to form a strong alternating electric field between the developing roller and the latent image carrier. However, even if this alternating electric field is formed, an electrostatic latent image is formed. On the other hand, it is difficult to stably develop a certain amount of toner, and it is difficult to uniformly develop high resolution minute dots. In addition, this one-component developing system applies a very large stress to the toner when the toner thin layer is formed on the developing roller, so that the toner circulating in the developing device deteriorates very quickly. As the toner deteriorates, unevenness and the like are likely to occur in the process of forming a toner thin layer on the developing roller, which is generally not suitable as a high-speed or highly durable image forming apparatus.

In order to compensate for the shortcomings of the two-component method and the one-component method, some hybrid devices such as Patent Document 1 have been proposed. Although such a hybrid increases the size and the number of parts of the developing device itself, some problems are overcome. However, in the developing portion, the same problem as that of one component, that is, difficulty in developing a high-resolution minute uniform dot remains.
Therefore, as a method for developing high-resolution minute uniform dots, for example, there is a method disclosed in Patent Document 2. In contrast to the hybrid configuration described above, by installing a wire to which a high frequency bias is applied to the developing unit, toner clouding is performed in the developing unit, thereby realizing high-resolution dot developability. With this method, the configuration of the developing device is complicated, but it is considered that highly stable and high-quality development can be realized.
In order to form the most efficient and stable toner cloud, Patent Document 3 and the publicly known example cited therein propose a method of forming an electric field curtain on a rotating roller. This method can be interpreted as being very good for obtaining small-sized and high-quality development, but in order to obtain an ideal high-quality image, the conditions such as the electric field curtain to be formed and development must be limited. Don't be. In other words, if image formation is performed under conditions that deviate from the appropriate conditions, not only the effect is not obtained, but also poor image quality is provided.
Therefore, as a developing method for forming a toner cloud, there is a method of eliminating the mechanical driving of the toner carrier and electrostatically conveying and developing the toner by an alternating electric field of three or more phases, as in Patent Document 4 and the like. It is disclosed. In order to make the charge amount of the toner supplied to the transport substrate constant, in Patent Document 5, a toner storage area is provided in front of the development area, and a voltage is applied in that area to charge the toner.
However, in the above method, even though the charge of the toner can be locally increased, it is very difficult to make the charge of the toner uniform, and a more uniform charge is desired to obtain high image quality.

Japanese Patent Laid-Open No. 3-100575 JP-A-3-113474 JP-A-3-21967 JP 2002-341656 A JP 2004-205644 A

  Accordingly, the present invention has been made in view of the above-described problems, and a problem thereof is a developing device capable of stabilizing the charge amount distribution of the supplied toner and maintaining high image quality in a flare development method having excellent dot reproducibility. An image forming apparatus is provided.

The features of the present invention, which is a means for solving the above problems, are listed below.
The present invention provides a developing device in which a moving toner carrier surface layer is provided with electrode groups alternately with respect to the moving direction via an insulating portion, and a time-periodic potential difference is formed between the alternating electrode groups. A two-component developer having magnetic particles and non-magnetic toner is carried on a developer carrying member having a built-in magnetic field generating means having a plurality of magnetic poles, and conveyed to a supply area facing the toner carrying member, In the developing device, a magnetic brush of the developer is formed in a supply region, and a DC voltage is applied to the developer carrier to supply toner to the toner carrier. Here, the electrode group is an assembly of electrodes that are alternately installed from both ends.
In the present invention, the distance between the toner carrier and the developer carrier is d (mm), the weight of the magnetic brush per unit area formed on the developer carrier is ρ (mg / mm ² ), and the toner carrier and the developer are developed. When the moving speed ratio of the developer carrier (developer carrier speed / toner carrier speed) is a,
ρ · a / d> 4
The relationship is established.
The present invention is characterized in that the surface of the toner carrying member is coated with a material capable of giving a regular charge to the toner in friction with the toner.
The present invention is characterized in that the surface of the toner carrier is coated with a material having a volume resistivity of 10 ⁹ to 10 ¹² (Ω · cm).
The present invention is characterized in that the toner carrier is in the form of a rotating roller, an electrode is connected to one of the rotating shafts, and an electrode is connected to the other of the rotating shafts.
According to the present invention, an average value of potential at each instant of time-periodic potential applied to the alternating electrode group is a value between an image portion potential and a non-image portion potential formed on the electrostatic latent image carrier. It is characterized by being.
The present invention is an image forming apparatus in which two or more kinds of toner images are superimposed on an electrostatic latent image carrier by using the developing device described above.

  According to the present invention, it is possible to provide a developing device and an image forming apparatus capable of stabilizing the charge amount distribution of the supplied toner and maintaining high image quality in the flare developing method having excellent dot reproducibility by the means for solving the problems. It became.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

FIG. 1 is a view showing a flare developing substrate. Here, flare is a phenomenon in which, for example, toner floats on an electrode by applying an alternating voltage having an inverted phase to two electrode groups arranged alternately. As shown in FIG. 1, an electrode pattern 3 is formed on a glass substrate 4 by vapor deposition of aluminum, and a flare development substrate on which a resin coat 2 having a thickness of about 3 μm and a volume resistivity of about 10 ¹⁰ Ω · cm is applied as a protective layer. On the other hand, toner was supplied by a two-component developer. As the two-component developer, a normal one was used. Specifically, a two-component developer in which a magnetic carrier powder having a particle size of 55 μm and a polyester toner having a particle size of about 7 μm were mixed at a weight ratio of 5 to 7 wt%, The toner is transferred to the supply area to the flare development substrate by the developer carrier 12, and a part of the toner is transferred to the flare development substrate by the bias potential applied in the supply area. Here, the developer carrying member 12 is a non-magnetic material that covers the outer periphery of a fixed magnet roller that is a magnetic field generating means having a plurality of magnetic poles therein, and has an uneven surface.

FIG. 2 shows the toner charge amount distribution in the two-component developer and the toner charge amount distribution supplied onto the flare development substrate when a DC bias is applied and when an AC bias is applied, respectively. Show.
In this embodiment, the toner in the developing device that was actually repeatedly printed was used, and the charge amount of the toner was about −30 μC / g. From FIG. 2, the charge amount distribution of the toner supplied onto the flare developing substrate is different between the DC bias and the AC bias. When an AC bias is applied, since a strong voltage is instantaneously applied, toner having a high charge amount and toner having a high adhesion force are also supplied. On the other hand, when a DC bias is applied, only toner that is easily developed is selectively supplied.

FIG. 3 shows the charge amount of the toner supplied on the flare development substrate and the flare activity on the development substrate. Here, the flare activity is obtained by sensory evaluation of about five stages by observing the state of toner that sticks to the substrate surface and does not move. Specifically, if the toner on the electrostatic transfer board jumps 100% by visual observation, it is “very active”, and if all of the toner is stationary and not even one of them is “completely stationary”, it can fly n%. For example, “very active” is plotted in n% with 100% “completely resting” being 0%.
If the charge amount of the toner on the flare development substrate is too high, the contribution of the mirror image force becomes large, so that the toner becomes difficult to move. That is, there is an optimum charge amount for activating the flare. In the two-component developing device, the charge amount of the toner is changed by repeating mixing, stirring, consumption, and replenishment with the carrier. When the charge amount changes, the flare activity also changes. Therefore, as shown in FIG. 2, the charge amount distribution always supplied by applying a DC bias is made constant.

Even when a DC bias is applied, the supplied charge amount distribution varies depending on the conditions. FIG. 4 shows the result when the developer in the developing device deteriorates under the above supply conditions. The supply conditions at this time are as shown below.
Distance d between toner carrier and developer carrier d: 0.35 mm
Magnetic brush weight on developer carrier ρ: 1 mg / mm ²
Toner carrier and developer carrier speed ratio a: 2
ρ · a / d = 5.7 (> 4)
This condition is within the range defined by the present invention. As shown in FIG. 4, the supplied charge amount distribution is almost in the same range regardless of the deterioration of the developer.
On the other hand, the charge amount distribution outside the specified range is also shown in FIG. The supply conditions are as shown below.
Distance d between toner carrier and developer carrier d: 0.55 mm
Magnetic brush weight on developer carrier ρ: 1 mg / mm ²
Toner carrier and developer carrier speed ratio a: 2
ρ · a / d = 3.6 (<4)
From FIG. 4, under the above conditions, the charge amount distribution of the toner supplied in accordance with the change in the charge amount distribution of the developer also changes. This is because the weakly charged toner cannot be supplied as the adhesion force increases. This is because a lot of toner is present in the vicinity of the flare development substrate in the supply region, so that toner having a charge amount distribution that is not actually suitable for flare development is supplied.

In addition, in order to investigate the influence of the electrical characteristics of the substrate surface, the same flare activity was confirmed by varying the volume resistivity of the surface layer. The material used for the surface layer is a silicone resin, and by changing the amount of carbon fine particles dispersed therein, a protective layer having a volume resistivity of 10 ⁷ to 10 ¹⁴ Ω · cm and a thickness of about 5 μm was formed. .
FIG. 5 is a diagram showing the relationship between volume resistivity and flare activity. From this figure, it is appropriate that the volume resistivity is in the range of 10 ⁹ to 10 ¹² Ω · cm. This is because, when a surface layer having a very high volume resistivity is used, the surface of the toner carrying roller 19 as a toner carrying member remains charged due to friction with the toner that repeatedly flies, and conversely, it is too conductive. If it is high, charge leakage (short circuit) occurs between the electrode groups, so that an efficient bias effect cannot be obtained. The volume resistivity needs to be 10 ⁹ to 10 ¹² Ω · cm as an appropriate resistivity so that charges accumulated on the substrate surface can escape to the electrode group.

Furthermore, in order to investigate the influence of the triboelectric charging characteristics on the substrate surface, the flare activity was observed in the same manner as described above with the surface coat layer being two types of silicone resin and fluorine resin. By minutely dispersing the carbon fine particles, the volume resistivity was set to 10 ¹¹ to 10 ¹² Ω · cm for any coating layer of the silicone resin and the fluorine resin. When the flare activity was observed by applying an alternating bias to the substrate, the flare state was maintained for a long time with the silicone resin, but in the case of the fluorine resin, the flare immediately disappeared and the toner stuck to the substrate. It became. After the observation, the charge amount of the toner on the substrate was measured. In the case of the silicone resin, only a slight decrease was observed compared to the initial value, but in the case of the fluorine resin, the charge of the toner was reduced. It was almost gone. Therefore, when an uncharged toner is rubbed against each surface, a triboelectric charge of normal polarity was obtained in the case of a silicone resin, whereas an almost triboelectric charge was obtained in the case of a fluororesin. In addition to being unable to do so, it had a slightly opposite polarity. Therefore, since the flare phenomenon is a process in which the toner and the substrate surface collide with each other innumerably, the substrate surface material does not take away the charge of the toner, and is preferably a material that can give the toner a regular charge. . This is learned from the triboelectric charging series of materials, and as the substrate surface material, for example, a glass-based material or a material used for a carrier coat of a two-component developer is preferably used.

FIG. 6 shows a representative example of the toner carrier of the present invention. FIG. 6-1a is an overview, and an electrode shaft 6 in which electrode groups from the left front side to the right back in the figure are bundled, and electrode groups installed alternately from the right back side to the left front side with respect to the electrode groups. The bundled electrode shaft 7 can be rotated as a rotation axis. A bias potential can be applied to each of the electrode shafts 6 and 7 by an electrode brush or the like (not shown). The configuration of the toner carrying roller 19 as the toner carrying member will be described below.
As shown in (1) of FIG. 6-1b, a shaft hole is provided in an acrylic resin cylinder, and a stainless steel electrode shaft is press-fitted as shown in (2). Next, a patterned electrode is formed by the steps (1) to (5) in FIG. FIG. 6-2c is a diagram when the surface of the toner carrying roller 19 is viewed in the direction along the rotation axis. In FIG. 6-2c (1), the surface of the roller obtained by FIG. 6-1b is finished smoothly by peripheral turning. In (2), the groove is cut so that the groove pitch is 100 μm and the groove width is 50 μm. In (3), electroless nickel plating is performed, and in (4), the outer periphery is turned to remove unnecessary conductor films. At this point, an electrode is formed in the groove portion. Thereafter, the roller surface was smoothed by coating with a silicone resin, and at the same time, a surface protective layer (thickness: about 5 μm, volume resistivity: about 10 ¹⁰ Ω · cm) was obtained.

FIG. 7 shows an example of a developing device using the toner carrying roller of FIG. 6D, the electrode shaft 6 and the electrode groups 6a and 7a from the electrode shaft 7 and the insulating portion 22 are alternately provided in the moving direction of the toner carrying roller 19. In FIG. The AC voltage applied to the toner carrying roller 19 is applied to the electrode shaft 6 and the electrode shaft 7 shown in FIG. 6-2 (d) in an inverted phase, and a time-periodic potential difference is formed. The AC voltage was realized by applying an average potential having a peak of −400 V and 0 V at a frequency of −200 V and 5 kHz. The AC voltage is good when the peak-to-peak is 200 V to 1000 V and the cycle is 0.5 kHz to 5 kHz. The toner carrying roller 19 is in contact with the ears of the two-component developer 10 by a normal two-component developer. Specifically, it is a two-component developer 10 in which a magnetic carrier powder having a particle size of 55 μm and a polyester toner having a particle size of about 6 μm are mixed at a weight ratio of 5 to 7 wt%.
A voltage of −400 V is applied to the developer carrier 12, and the negatively charged toner is transferred from the developer carrier 12 to the toner by the difference between the potential −400 V of the developer carrier 12 and the average voltage −200 V of the toner carrier roller 19. It is supplied to the carrying roller 19.
The toner supplied to the toner carrying roller 19 is conveyed to a portion facing the latent image carrier 13 while forming a flare on the toner carrying roller 19, and the average potential on the surface of the toner carrying roller 19 and the potential of the latent image carrier 13 are conveyed. As a result, a toner image is formed, and unnecessary toner that has not contributed to development returns to the developer carrier 12 again. Since the flare is formed, the adhesion force of the toner to the toner carrying roller 19 is very low, and the toner returned from the developing unit by the toner carrying roller 19 is a two-component developer following the rotation of the developer carrying body 12. It is easily scraped and habituated by the ears. By repeating this, a substantially constant amount of toner flare is always formed on the toner carrying roller 19.

An embodiment in which an organic photoreceptor having a thickness of 13 μm is used as the latent image carrier 13 and a latent image is formed using a 1200 dpi laser writing system will be described below. A latent image is formed under the conditions that the photosensitive member charging potential is −300V and the writing potential at the solid portion is −50V. At this time, when 6 μm toner having a toner charge amount of about −22 μC / g was used and conditions were set so that there was no background stain, solid filling was possible, and 1 dot of 1200 dpi could be reproduced, toner carrier roller 19 and photoconductor 13 was realized by applying an AC bias having an average potential of −200 V having peaks of −400 V and 0 V at a frequency of 5 kHz, and a potential applied to the toner carrying roller 19 of about 500 μm. If excessive toner is placed on the toner carrying roller 19, the electric field curtain is shielded by the charge of the toner and flare cannot be formed, so the amount of toner per unit area on the toner carrying roller 19 is 0. A DC bias of about 200 V is applied between the developer carrying member 12 and the toner carrying roller 19 so as to be ² mg / cm ² . On the other hand, since the amount of toner required as a solid image on the photosensitive member 13 is 0.4 mg / cm ² , the moving speed of the toner carrying roller 19 is set so that toner depletion does not occur in the developing unit. The moving speed of 13 needs to be twice or more, and is 2.5 times here. The moving directions of the toner carrying roller 19 and the photosensitive member 13 may be the same as shown in FIG. 8 or may be reversed. The moving directions of the developer carrying member 12 and the toner carrying roller 19 are preferably reversed as shown in FIG. 8 in order to obtain a return toner scraping effect. It has been confirmed that the above system can realize high-quality development without smearing excellent in solid filling property and 1200 dpi dot reproducibility under a photosensitive member linear velocity of 300 mm / s.

FIG. 8 shows an example of a color superimposed image forming apparatus on the photoconductor 13 configured by using the developing device of FIG. 7. With such a system, writing for four colors on the same photoconductor 13 is performed. As a result, in principle, there is almost no positional deviation compared to the normal quadruple tandem system. Further, by using the developing device 20 according to the present invention, the toner image once formed on the photosensitive member 13 is not affected at all, so that there are no problems such as scavenging and color mixing, and the image quality is high. The image forming process can be performed stably over a long period of time.

It is the figure which showed the flare developing substrate. FIG. 6 is a diagram illustrating a toner charge amount distribution in a two-component developer and a toner charge amount distribution supplied onto a flare development substrate. FIG. 6 is a diagram illustrating a charge amount of toner supplied on a flare development substrate and flare activity on the development substrate. FIG. 6 is a diagram illustrating a charge amount distribution when a developer in a developing device is deteriorated. It is a figure which shows the relationship between volume resistivity and flare activity. FIG. 3 is a diagram illustrating a representative example of a toner carrier of the present invention. FIG. 3 is a diagram illustrating a representative example of a toner carrier of the present invention. 7 is an example of a developing device using the toner carrying roller of FIG. 6. FIG. 8 is an example of a color overlay image forming apparatus configured using the developing device of FIG. 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Toner layer 2 Resin coat 3 Aluminum vapor deposition electrode 4 Glass substrate 5 Resin roller 6 Electrode axis A
6a Electrode group 7 Electrode axis B
7a Electrode group 8 Resin cylinder 9 Shaft 10 Two-component developer 11 Stirring screw 12 Developer carrier 13 Latent image carrier (photosensitive member)
14 Cleaner 15 Charger 16 Charger 17 Belt OPC
18 Fixing device 19 Toner carrying roller (toner carrying member)
20 Developing Device 21 Image Forming Device 22 Insulating Part

Claims (7)

In the developing device in which an electrode group is alternately provided in the moving toner carrier surface layer via an insulating portion with respect to the moving direction, and a time-periodic potential difference is formed between the alternating electrode group.
The developing device carries a two-component developer having magnetic particles and non-magnetic toner on a developer carrying member having a magnetic field generating means having a plurality of magnetic poles, and transports it to a supply region facing the toner carrying member. A developing device characterized in that a magnetic brush for the developer is formed in the supply region, and a DC voltage is applied to the developer carrier to supply toner to the toner carrier. The developing device according to claim 1,
In the developing device, the distance between the toner carrier and the developer carrier is d (mm), the weight of the magnetic brush per unit area formed on the developer carrier is ρ (mg / mm ² ), and the toner carrier and When the moving speed ratio of the developer carrier (developer carrier speed / toner carrier speed) is a,
ρ · a / d> 4
A developing device characterized in that the relationship is established. The developing device according to claim 1 or 2,
In the developing device, the surface of the toner carrying member is coated with a material capable of giving a regular charge to the toner in friction with the toner. In the developing device according to any one of claims 1 to 3,
In the developing device, the surface of the toner carrier is covered with a material having a volume resistivity of 10 ⁹ to 10 ¹² (Ω · cm). The developing device according to any one of claims 1 to 4,
In the developing device, the toner carrier has a rotating roller shape,
An electrode group is connected to one of the rotating shafts,
A developing device, wherein an electrode group is connected to the other end of the rotating shaft. The developing device according to any one of claims 1 to 5,
In the developing device, the average potential value at each moment of the time-periodic potential applied to the alternating electrode group is between the image portion potential formed on the electrostatic latent image carrier and the non-image portion potential. A developing device characterized in that it is a value. An image forming apparatus uses the developing device according to claim 1 to superimpose two or more types of toner images on an electrostatic latent image carrier. apparatus.

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