JP2002351151A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device equipped with a developing device used for a single-drum color superimposing method by which an afterimage (ghost) at the consecutive developing is prevented without complicating the developing device, reliably electrified toner is supplied to a developing roll and a plurality of color images are successively formed. SOLUTION: By a single-component non-contact developing method in which an image is developed by applying DC and AC electric field to the space between a photoreceptor and a developing roll after forming, on a magnetic roll, a magnetic brush by employing two-component developer using a high-resistance carrier for electrifying and holding the toner and a low-resistance carrier for recovering the toner remaining on the developing roll as a non-developing part in development and further forming a thin layer of the toner on the developing roll by the magnetic brush, the toner is made to fly to an electrostatic latent image, and the toner remaining on the developing roll is recovered by the magnetic brush. Thus, a compact and practical developing system is provided to solve a problem on a history phenomenon such as the afterimage (ghost) in development, which has been a problem in the conventional technique.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a multifunction machine using an electrophotographic method, and more particularly, to charging a non-magnetic toner using a magnetic carrier. Non-contact development in which a two-component developer is used to hold only charged toner on a developing roll and fly onto an electrostatic latent image on an electrostatic latent image carrier (photoconductor), thereby developing the latent image The present invention relates to an image forming apparatus to be provided to a method.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image carrier (photoreceptor) has been used in which a two-component developer that charges a non-magnetic toner using a magnetic carrier is used, and only the charged toner is held on a developing roll. The non-contact developing method of flying on the electrostatic latent image and developing the latent image has been considered as a means of non-contact one-component development. It has also been studied for a one-drum color superposition method for sequentially forming a plurality of color images on an electrostatic latent image carrier (photoconductor). In this method, it is possible to form a color image with less color misregistration by accurately overlaying toner on an electrostatic latent image carrier (photoconductor), and it is attracting attention as a technique corresponding to higher color image quality.

[0003] US Pat. No. 3,866,574 discloses a prior art relating to such a technique. In US Pat. No. 3,866,574, a donor roll (developing roll) is provided in non-contact with an electrostatic latent image carrier (photoreceptor). It has been proposed that a thin layer is formed with a non-magnetic toner and the toner flies on a latent image on an electrostatic latent image carrier (photoconductor) by an AC electric field. U.S. Pat. No. 3,929,098 discloses a developing device in which a developer is advanced to a donor roll using a magnetic roll, and toner is transferred onto the donor roll to form a toner layer. .

However, in these proposals, although a thin layer can be formed on the donor roll by using a two-component developer, it becomes difficult to separate the toner on the donor roll when the charge of the toner is increased. , A strong alternating electric field is required. Since this electric field disturbs the toner layer on the electrostatic latent image carrier (photoconductor), there is a problem in color superposition and the like. For this reason, Japanese Patent Application Laid-Open No. Hei 3-113474 discloses a method in which an auxiliary electrode composed of a wire is provided between a donor roll and an electrostatic latent image carrier (photoreceptor), and a toner is developed by applying a weak AC electric field to the auxiliary electrode. A so-called powder-cloud development method which does not disturb the image has been proposed.

Further, in this type of technology, if a toner consuming area and a non-consuming area are formed on a developing roll, a variation occurs in a toner adhesion state on the roll and a potential difference of the toner. A phenomenon in which a part of an image appears as an afterimage (ghost) at the next development, that is, a so-called hysteresis phenomenon occurs. However, a complicated mechanism is required to prevent this phenomenon, and it has not been put to practical use in a small electrophotographic process. Was. To prevent this, JP-A-11-231
Japanese Patent Application Publication No. 652 proposes a member for scraping off the undeveloped toner on the developing roll and a device for collecting the scraped toner. Also, Japanese Unexamined Patent Publication No.
No. 5,420,375 proposes a method in which toner on a developing roll is collected by a magnetic roll using a potential difference between copies or between papers, and the charge of the toner is stabilized. Further, as a countermeasure against the hysteresis phenomenon using a magnetic brush, Japanese Patent Application Laid-Open No. 7-128983 proposes to collect and supply the toner on the developing roll by setting a half width region of the magnetic flux density of the magnetic roll to be wide. Has been made.

[0006] In theory, the Journal of the Institute of Electrophotography 19
Vol. 2 (1981) reports from Toshiba Corporation on the formation of a toner layer on a developing roll using a two-component developer, and a patent application is filed in JP-A-59-121077. . As a method for reliably collecting the toner on the developing roll, Japanese Patent Application Laid-Open No. 2000-81788 proposes to use a dedicated collecting roll.

[0007]

However, in the powder cloud developing method described in the above-mentioned Japanese Patent Application Laid-Open No. 3-113474, the wire of the auxiliary electrode is very dirty,
Further, since image deterioration or the like due to vibration occurs, it is not a very common method. Further, JP-A-11-23
1652, JP-A-7-72733 (USP
5,420,375), JP-A-7-128983
JP, JP-A-59-121077, JP-A-200
In the apparatus disclosed in Japanese Patent Application Publication No. 0-81788, the stress of the toner is increased due to the toner scraping device or the application of a special recovery bias, which is a cause of the deterioration of the durability performance of the toner. In addition, during long-term use, the chargeability of the toner changes due to deterioration of the durability performance of the carrier, the charge characteristic of the toner on the developing roll changes greatly, the distribution of charge of the replenishment toner and the collected toner becomes wide, and toner It was causing scattering and fog. Further, there is a troublesome replacement of the deteriorated carrier, and the fact is that it has not been practically used.

Further, in the prior art, since the polarity of the toner is negatively charged, the charged potential difference between the developing portion and the non-developing portion becomes large, particularly in a low-temperature and low-humidity environment. Tended to be. This is because the toner material is generally easily negatively charged, and the potential of the toner layer on the developing roll increases when repeatedly exposed to a high electric field.

A technique for preventing fog is disclosed in Japanese Patent Application Laid-Open No. 6-186811, for example, which discloses a technique in which a photoconductive layer is provided on a transparent conductive support. In an image forming apparatus that forms an image by exposing from a surface, a photosensitive roller is charged by a charging roller, and a developer is composed of a high-resistance carrier, a low-resistance carrier, and an insulating magnetic toner to form a magnetic brush. The carrier injects charge into the photoconductive layer of the photoreceptor, charges the high-resistance carrier to the opposite polarity to the toner to improve toner retention and developability, and reduces charge decay with the insulating magnetic toner. There is disclosed an image forming apparatus in which transfer can be performed with high efficiency, and toner remaining at the time of transfer is charged by a charging roller and collected by a developing device to improve transferability and developability.

However, the method disclosed in Japanese Patent Application Laid-Open No.
In the image forming apparatus disclosed in Japanese Patent Application Laid-Open Publication No. H10-207, an electric charge is injected into a photoconductive layer of a photoconductor using a low-resistance carrier in an image forming apparatus that is exposed from the back side of an electrostatic latent image carrier (photoconductor). The purpose is to reduce the fogging phenomenon, and a complicated mechanism for exposing from the back side is required, and the toner remaining at the time of transfer is charged and collected by a charging roller. It cannot be used for the one-drum color superposition method for sequentially forming a plurality of color images.

Therefore, the present invention prevents the occurrence of an afterimage (ghost) during continuous development without complicating the developing device, and enables the charged toner to be reliably supplied to the developing roll, so that a plurality of color images can be formed. An object of the present invention is to provide an image forming apparatus including a developing device that can be used in a one-drum color superposition method for sequentially forming.

[0012]

In order to solve the above-mentioned problems, according to the present invention, a carrier having a role of charging and holding a toner as a developer and remaining on a developing roll as a non-developing portion during development. Forming a magnetic brush on a magnetic roll with a two-component developer using a carrier having a different function from a carrier having a role of collecting the toner,
After a thin layer of toner is formed on a developing roll with the magnetic brush, a DC or AC electric field is applied to a space between the toner and a photoconductor to develop the toner into an electrostatic latent image by a one-component non-contact developing method. By collecting the toner remaining on the developing roll with the magnetic brush, a compact and highly practical developing system can be constructed, and a hysteresis phenomenon such as a residual image (ghost) of the developing problem, which has been a problem in the prior art. Problem can be solved.

Therefore, in the present invention, as described in the first aspect, a magnetic member formed on a magnetic roll with a two-component developer, facing a photosensitive member in an image forming apparatus for forming an image by an electrophotographic developing method. In an image forming apparatus including a developing device having a developing roll for forming a thin layer with a toner from a brush to develop a latent image on the photoreceptor, the two-component developer includes a toner and a volume resistivity of 10%. ⁹ Ωcm
The high-resistance carrier and the low-resistance carrier having a volume resistivity of 10 ⁸ Ωcm or less are provided, and the ratio of the low-resistance carrier is 50% to 80% of the entire carrier.

As described above, the developer is supplied with a volume resistivity of 10 ⁹
High resistance carrier of Ωcm or more and volume resistivity of 10 ⁸ Ω
cm, and the ratio of the low-resistance carrier is 50% to 80% of the entire carrier, so that the high-resistance carrier in the magnetic brush made of the developer retains toner and is optimal. Since the toner in the non-image area remaining on the developing roll at the time of development can be collected by a low-resistance carrier. It is possible to provide an image forming apparatus having a compact and highly practical developing device which can solve the problem of the phenomenon and can be used for a one-drum color superposition method for sequentially forming a plurality of color images.

The toner is a non-magnetic toner having a positive polarity, and the charge amount of the toner on the developing roll is 5 to 20 μC / g.

By using the non-magnetic toner having the positive polarity as described above, the development due to the enlargement of the difference in the charged potential of the toner between the developing portion and the non-developing portion in a low-temperature and low-humidity environment caused when the negatively charged toner is used. An afterimage (ghost) can be prevented. When a negatively charged toner is used, the toner material generally tends to be negatively charged, and the potential of the toner layer on the developing roll increases when repeatedly exposed to a high electric field. Can also be prevented. In addition, by controlling the charge amount of the toner to 5 to 20 μC / g, toner scattering and fogging are prevented, and the toner is collected without developing history phenomenon on the developing roll by developing with a low electric field. An image forming apparatus having a developing device having excellent performance can be provided.

The low-resistance carrier is characterized in that the low-resistance carrier has an average particle diameter of 40 μm or less and a saturation magnetization of 67 emu / g or more.

By configuring the low-resistance carrier as described above, the surface area of the carrier is increased and the number of contact points with the toner is increased, so that the magnetic brush formed in the nip between the developing roll and the magnetic roll has a peeling property due to an electrode effect. Thus, the electrode effect at the time of toner recovery and the scraping effect by the magnetic brush can be sufficiently exhibited.

The high-resistance carrier has an average particle diameter of 50 μm.
A surface coating is formed on the surface of a ferrite magnetic carrier having a saturation magnetization of 60 to 200 emu / g with a high molecular weight polyethylene having a weight average molecular weight Mw of 50,000 or more, and the coating amount is 1 to 5 Wt in polyethylene amount. %, And the surface is made 1% by conductive particles.
And wherein 0 ^{9 1012} that resisted controlled [Omega] cm.

By forming the high-resistance carrier having a surface coating formed of high-molecular-weight polyethylene,
It has a tough surface performance against problems such as toner adhesion and coat peeling, and prevents the coating agent from peeling off until the mechanical life of the developing device has expired. Thus, it is possible to prevent the toner from scattering due to poor charging and contaminating the image, and to prevent the occurrence of selective development due to the deterioration of the developing performance. By controlling the resistance of the surface to be 10 ⁹ to 10 ¹² Ωcm by the conductive particles, it is possible to prevent image quality deterioration such as carrier development, fogging, and image density reduction.

[0021]

Embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention to them unless otherwise specified. This is just an example.

FIG. 1 is a view for explaining a developing device in an image forming apparatus according to the present invention, and FIG. 2 is a diagram showing a basic structure of a-Si of an electrostatic latent image carrier (photoreceptor) used in the present invention. FIG. 3 is a diagram for explaining an appropriate developing region of a bias voltage applied to a developing device in the image forming apparatus according to the present invention, and FIG. 4 is a diagram showing high-resistance carriers and low-resistance carriers. Afterimage (ghost) generated by content ratio
FIG. 4 is a diagram for explaining the occurrence of the above.

In FIG. 1, reference numeral 1 denotes a magnetic roll for generating a magnetic brush 10 by a carrier 4 contained in a developer by means of a magnet provided therein, and 2 denotes a thin toner layer 6 formed by a toner 5 supplied from the magnetic brush 10. , A developing roll for developing the electrostatic latent image on the electrostatic latent image carrier 3, 4 is a toner carrier, of which 4-1 is a low-resistance carrier, 4-2 is a high-resistance carrier, and 5 is Toner, 6 is a thin toner layer on the developing roll 2, 7 is an electrostatic latent image carrier (photoconductor)
Reference numeral 7a denotes a developing bias power supply for applying a developing bias between the developing roller 3 and the developing roll 2;
_dc1 ) power supply, 7b is an alternating current (AC) bias power supply, 8 is a direct current (DC) bias (V _{dc 2} ) power supply of the magnetic roll 1, and 9 is a regulating blade that regulates the thickness of the magnetic brush 10 on the magnetic roll 1. is there.

In FIG. 2, reference numeral 20 denotes a substrate of the electrostatic latent image carrier (photoconductor) 3, reference numeral 21 denotes a blocking layer, reference numeral 22 denotes a photosensitive layer made of a-Si, and reference numeral 23 denotes a surface protection layer. In the following description, the a-Si electrostatic latent image carrier (photoconductor) 3
Is expressed as “thickness”, the surface of the electrostatic latent image carrier (photoconductor) 3 on the opposite side of the substrate from the surface of the substrate 20 in the electrostatic latent image carrier (photoconductor) 3 Means the distance to Therefore, as shown in FIG. 2, the electrostatic latent image carrier (photoconductor) 3 is composed of the blocking layer 21 and the photosensitive layer 22, and the surface protection layer 2
3, the thickness of the photosensitive layer is a value obtained by adding the thicknesses of the respective layers.

In the developing device of the image forming apparatus according to the present invention configured as described above, the magnetic roll 1 includes the toner 5 and the low-resistance carrier 4 from a developer container (not shown).
1. A two-component developer composed of the high-resistance carrier 4-2 is supplied. The developer forms a magnetic brush 10 to positively charge the toner 5 by stirring, and a regulation blade 9 regulates a layer thickness. Done. Then, the charged toner 5 is transferred to the developing roll 2 by the potential difference between the magnetic roll 1 and the developing roll 2 to form a thin layer 6 of only toner on the developing roll 2. An electrostatic latent image carrier (photosensitive member) is superimposed on a direct current (DC) bias 7a (V _dc1 ) and an alternating current (AC) bias 7b applied to the electrostatic latent image carrier (photoconductor) 3. It flies to the electrostatic latent image formed on the body 3 and is developed. After the development, the thin toner layer 6 remaining on the developing roll 2 is formed by the magnetic brush 10 on the magnetic roll 1 and the toner layer 6 on the developing roll 2.
Only by the brush effect due to the peripheral speed difference of each roll,
The toner can be easily collected and replaced without providing a special device such as a scraping blade.

If the collection and replacement of the toner are not sufficiently performed, as shown in FIG. 4B, the portion corresponding to the previously developed solid image is not sufficiently developed when the next electrostatic latent image carrier is developed. Cannot be performed, and a ghost (afterimage) occurs on the half image. That is, as shown in FIG. 4, if a solid image composed of rectangular black solids and a subsequent halftone image wider than the solid image are arranged so as to be developed continuously, toner collection and replacement can be sufficiently performed. 4B, an afterimage remains in a portion corresponding to the previously developed solid image as shown in FIG.

Further, when the charging failure of the toner occurs, the toner is not sufficiently held on the surface of the carrier, and the image scattering due to the scattering of the toner occurs. Therefore, the density ratio between the density of the portion corresponding to the solid image where the ghost (afterimage) has occurred and the other portion where no afterimage has occurred was determined as the solid image followability. Further, the toner scattering level was evaluated by being ranked in such a way that the larger the number was, the better it was at five levels. FIG. 5 shows the characteristic values, and FIG. 5 (a) shows the change according to the resistance value of the carrier used in the present invention. The horizontal axis is the carrier resistance (Ωcm), and the left side of the vertical axis is the solid image tracking property. The right side shows the toner scattering level (curve 51). FIG. 5B shows the change due to the toner chargeability (toner charge amount). The horizontal axis indicates the toner chargeability (μC).
/ G), and the left of the vertical axis indicates the solid image followability (curve 52).
The right side shows the toner scattering level (53 curve). FIG. 5C and FIG. 5D show the carrier particle size (particle size, μ).
m) and the results of evaluating changes in toner scattering (c) and solid image followability (d) due to the magnetic force (emu / g) of the carrier.

As shown in FIG. 5 (a), in order to prevent toner scattering, it is appropriate that the resistance of the carrier holding the toner is not less than 10 ⁹ Ωcm, at which the carrier almost starts to be saturated. Also,
In order to collect the toner remaining on the developing roll and secure the solid image followability, the carrier resistance for collecting the toner on the developing roll is set to 10 ⁸ Ωcm or less at which the solid image followability starts to be saturated. Is appropriate.

As shown in FIG. 5C, a stable toner scattering level can be obtained by setting the particle size (particle size) of the carrier holding the toner to 40 μm or less. Further, as shown in FIG. 5 (d), the solid image followability begins to saturate when the carrier magnetic force is 67 emu / g or more.
To a sufficient level. Therefore, for the carrier holding the toner, if the resistance value is set to 10 ⁹ Ωcm or more, a sufficient toner scattering level can be obtained, and it is not appropriate that the toner particle size (particle size) is larger than 50 μm. In addition, it can be seen that the carrier for collecting the toner on the developing roll should have a carrier resistance of 10 ⁸ Ωcm or less and a carrier magnetic force of 67 emu / g or more. Further, when the carrier particle size (particle size) is set to 40 μm or less, a very stable toner scattering level can be obtained. Therefore, it has been found that this is an effective means for compensating for a decrease in the toner scattering level in a low-resistance carrier.

The low-resistance carrier 4-1 used in the present invention comprises:
This is for collecting the residual toner remaining on the developing roll 2, and in the present invention, the volume specific resistance is 10 ⁶ Ωc.
m, a ferrite carrier having a saturation magnetization of 70 emu / g and an average particle diameter of 35 μm was used. That is, in order to collect the residual toner from the developing roll, as shown in FIG. 5, a carrier having a low resistance of 10 ⁸ Ωcm or less is used, and a strong electrostatic force is applied to the nip between the developing roll and the magnetic roll. It is necessary to peel off the toner adhering to the surface with a magnetic brush. In order to enhance the peelability of the magnetic brush formed in the nip between the developing roll and the magnetic roll due to the electrode effect, it is effective to set the saturation magnetization of the low-resistance carrier to a high magnetic force of 67 emu / g or more. . When the saturation magnetization of the low-resistance carrier is less than 67 emu / g, the electrode effect at the time of recovery and the scraping effect by the magnetic brush are reduced, and a sufficient effect cannot be obtained. At this time, in order to increase the number of contact points with the toner, it is preferable to use a carrier having a small diameter of 40 μm or less and increase the surface area of the carrier. High-magnetic and low-resistance carriers include magnetite carriers, Mn-based ferrites, and Mn-Mg-based ferrites. These carriers may be used as they are, but they must be surface-treated as long as the resistance is not increased. Is also possible.

The high-resistance carrier 4-2 is used to hold the negatively charged and positively charged toner 5. In the present invention, the ferrite surface is covered with a high molecular weight polyethylene surface polymer and the resistance is increased. It is treated with an adjusting agent so as to have a tough surface performance against problems such as toner adhesion and coat peeling, and to prevent the coating agent from peeling off until the mechanical life of the developing device is over. Generally, in the case of a surface-coated carrier, when the coating agent on the surface is peeled off by 20% or more, the charging performance to the toner is changed. Contamination occurs, and when the concentration is 20 μC / g or more, the developing performance is reduced, and selective development or the like is likely to occur. That is, as shown in FIG. 5B, regarding the chargeability of the toner (the charge amount of the toner), since the solid image follow-up property and the toner scattering level are in a conflicting relationship, in the case of the present invention,
In order to ensure both solid image followability and toner scattering, the chargeability of the toner needs to be 5 to 20 μC / g.

The high-resistance carrier 4-2 is particularly important for imparting charge to the toner 5, and simultaneously with imparting charge to the toner 5, the developing roll 2 is charged when an alternating current (AC) is applied.
It is also effective in suppressing toner scattering from the toner. In other words, the low-resistance carrier 4-1 which emphasizes the recovery is effective in preventing the development residual image (ghost), but it is difficult to impart accurate charging to the toner 5 to maintain the development without fogging. Yes, the toner thin layer 6 scatters from the surface of the developing roll 2 when the device is operated for a long period of time, causing a problem of contaminating the charger and the exposure unit. Therefore, a high-resistance carrier 4-2 having charging performance is used together. Is essential.

The high-resistance carrier 4-2 has an average particle diameter of 50 μm or more and has a saturation magnetization of 60 to 200 em.
A polymerization catalyst is held on the surface of a u / g ferrite magnetic carrier, and ethylene gas is introduced to perform polymerization growth to form a surface coating with a high molecular weight polyethylene having a weight average molecular weight Mw of 50,000 or more. It is preferable to use an electrostatic latent image developing carrier in which the amount of polyethylene is 1 to 5 Wt%, and the surface of which is resistance-controlled to 10 ⁹ to 10 ¹² Ωcm by conductive particles. The resistance value is 10 ⁸ Ω
If it is less than 10 cm, carrier development or fogging may occur, and if it exceeds 10 ¹² Ω · cm, there is a possibility that image quality may be degraded such as a decrease in image density. Note that the resistance value shown here is determined by applying a voltage of 1 to 500 V to the upper and lower electrodes by providing a carrier layer having a thickness of 0.5 cm for an electrode area of 5 cm ² and a load of 1 kg. It is obtained by measuring and converting.

As for such a high-resistance carrier, for example, as proposed by the present applicant in Japanese Patent Application Laid-Open No. 10-142842, a carrier core material having magnetism and a high molecular weight coating the surface of the carrier core material are disclosed. A coating layer made of a polyethylene resin, wherein the coating layer made of a high-molecular-weight polyethylene resin contains, as at least the outermost shell layer thereof, a charge control agent, a resistance control agent, a fluidity control agent, and the like. By setting various external additives on the surface of high molecular weight polyethylene, durability and charge control can be achieved. As the high-resistance carrier, a carrier treated with a high-resistance treatment agent or the like can be used as long as high durability performance is confirmed in addition to the above-described carrier.

The mixing ratio of the high-resistance carrier 4-2 and the low-resistance carrier 4-1 depends on the collection performance of the thin toner layer 6 remaining on the developing roll 2 and the charging of the toner 5 in the entire carrier 4. The ratio of the low-resistance carrier 4-1 is 50% to 8
Suitably, it is about 0%. If it is less than 50%, sufficient recovery of the thin toner layer 6 cannot be performed, resulting in occurrence of an afterimage (ghost). If it is more than 80%, scattering of the toner 5 cannot be prevented.

The mixing ratio of the toner 5 in the present invention is 2 to 40 Wt%, preferably 3 to 30 Wt%, more preferably 4 to 25 Wt% based on the total amount of the carrier 4 and the toner 5. . That is, if the mixing ratio of the toner is less than 2 Wt%, the charge amount of the toner 5 becomes high and a sufficient image density cannot be obtained.
%, A sufficient charge amount cannot be obtained, and the toner scatters from the developing device, thereby contaminating the inside of the image forming apparatus and causing toner fog on the image.

As described above, by combining both carriers at a fixed ratio, it is possible to collect the toner thin layer 6 on the developing roll and to recharge the charged toner 5 to the developing roll 2 again. Become. 5 to 20 μm of toner 5
C / g, toner scattering / fogging is prevented, and development is carried out with a low electric field, so that the development history phenomenon is not left on the development roll 2 and image formation with excellent recoverability of the toner thin layer 6 is achieved. A development method in an apparatus can be provided.

The surface potential (charge potential) of the electrostatic latent image carrier (photoconductor) 3 is 250 V or less, and
By setting the post-exposure potential to 100 V or less, a sufficient image density can be obtained while reducing the potential applied to the developing roll 2. As the electrostatic latent image carrier (photoconductor) 3 used in the image forming apparatus, a positively charged organic photoconductor (OPC) is conventionally known, and the electrostatic latent image carrier (photoconductor) is known.
When this organic photoreceptor (OPC) was used as No. 3, the thickness of the photosensitive layer was 25 μm in order to keep the residual potential at 100 V or less.
It is important to set it to m or more and increase the amount of charge generation material added. In particular, a single-layer organic photoreceptor (OPC)
This is advantageous because a charge generating material is added to the photosensitive layer.

However, the OPC photosensitive member has a problem that the surface of the photosensitive layer is soft and the photosensitive layer is easily scraped by the rubbing of the cleaning blade. Therefore, an a-Si photosensitive member having a photosensitive layer thickness of 25 μm or more has recently been used because the surface thereof is harder than the OPC photosensitive member and has excellent durability and function retention (maintenance-free). ing. However, since the a-Si photoreceptor is formed using a glow discharge decomposition method or the like, if the photosensitive layer is thick as described above, the production time and production cost are increased, which is economically disadvantageous. Accordingly, the present applicant has disclosed in Japanese Patent Application Laid-Open No. Hei 7-175276 that the thickness of the photosensitive layer is set to less than 25 μm.
-Proposing a photoreceptor for Si.

When an a-Si photosensitive member is used as a photosensitive material for the electrostatic latent image carrier (photosensitive member) 3, the surface of the surface has a very low potential after exposure of 10 V or less. When the film thickness is reduced, the saturation charging potential decreases, and the withstand voltage that causes dielectric breakdown decreases. On the other hand, the charge density on the surface of the electrostatic latent image carrier (photoconductor) 3 when the latent image is formed tends to be improved, and the developing performance tends to be improved. This characteristic is particularly remarkable when the a-Si photoreceptor has a dielectric constant as high as about 10 and is 25 μm or less, and more preferably 20 μm or less.

However, if the thickness of the photosensitive layer 22 is less than 10 μm, it becomes difficult to adjust the potential of the electrostatic latent image carrier (photoconductor) 3, so that so-called black spots and fogging are likely to occur.
On the other hand, when the thickness of the photosensitive layer 22 is less than 10 μm, the saturated charging potential tends to decrease, and the required charging potential tends to be insufficient. On the other hand, if the thickness of the photosensitive layer 22 exceeds 25 μm, low-potential development becomes difficult, and ozone is easily generated, or the production time of the photosensitive layer becomes longer, which tends to be economically disadvantageous. Furthermore, since the time required for holes generated in the charge generation layer in the photosensitive layer 22 to move to the surface of the photosensitive layer becomes longer, the electrostatic latent image carrier (photoconductor)
It is difficult to adjust the potential of No. 3 and problems such as occurrence of so-called fog and reduction of image density are likely to occur. Therefore, from the viewpoint of more excellent adjustment of the potential of the electrostatic latent image carrier (photoconductor) 3 and economy, etc.,
The thickness of the photosensitive layer 22 in the electrostatic latent image carrier (photoconductor) 3 is more preferably set to a value in the range of 11 to 25 μm, and even more preferably to a value in the range of 12 to 18 μm.

Further, as a more preferable state of the photosensitive layer 22, the thickness of the surface protective layer 23 is preferably set to a value of 0.3 μm or more and 5 μm or less. That is, when the thickness of the surface protective layer 23 is less than 0.3 μm, the characteristics of the photosensitive layer 22 such as the saturation charging potential, abrasion resistance, and environmental resistance tend to decrease. If the thickness of the layer 23 exceeds 5 μm, it causes deterioration of the image quality, and the manufacturing time becomes longer, which is economically disadvantageous. Therefore, from the viewpoint of better balance between the saturation charging potential of the photosensitive layer 22 and the manufacturing time, it is more preferable to set the thickness of the surface protective layer 23 to a value within the range of 0.3 to 3 μm.

The material constituting the photosensitive layer 22 is not particularly limited as long as it is amorphous silicon (a-Si). Preferred materials include a-Si, a-SiC,
Inorganic materials such as a-SiO and a-SiON can be exemplified. Further, as the surface protective layer 23, a-SiC is particularly preferable as a photosensitive layer material in the present embodiment because it has a particularly high resistance and can obtain more excellent saturated charging potential, abrasion resistance and environmental resistance. is there. In addition, it is preferable to use a specific a-SiC having a specific ratio of Si to C (carbon).
i _(1-X) C _X (0.3 ≦ X ≦ 1.0), and more preferably a-Si _(1-X) C _X (0.5 ≦ X ≦
0.95). The reason is that such a-SiC
Has a particularly high resistance of 10 ¹² to 10 ¹³ Ω · cm, and provides excellent saturated charging potential, abrasion resistance, and environmental resistance (moisture resistance).

Development roll 2 and electrostatic latent image carrier (photoreceptor)
3 is applied to the DC bias power supply 7a (V
_dc1 ), which is determined by the AC bias power supply 7b. In order to efficiently collect the _undeveloped toner by the magnetic roll 1, the potential of the bias 8 ( _Vdc2 ) is preferably 500 V or less. When a voltage of 150 V or more is applied by the DC bias power supply 7a ( _Vdc1 ), the electrostatic force that causes toner to adhere to the developing roll 2 increases, and it becomes difficult to collect the toner with a magnetic brush. In addition, by using an alternating electric field with the AC bias power supply 7b, development on the electrostatic latent image carrier (photoconductor) 3 can be accurately performed, and collection of residual toner on the magnetic roll 1 becomes easy. There are benefits.

FIG. 3 is a view showing the residual development in the developing device of the present invention.
Good development DC bias without image (ghost) and fog
Ass potential 7a (V_dc1) And 8 (V_dc2) Indicates the range
It is a thing. The horizontal axis is the potential difference | V_dc2−V_dc1|
The vertical axis represents the bias potential (V _dc1). And
As shown in FIG. 3, the bias potential (V_dc1) Is 150V
If it is higher than that, a ghost occurs and the potential difference | V_dc2−V
_dc1Ghost occurs even when | becomes less than 100V
You. Therefore, the DC bias potential 7a (V
_dc1) Is 150 V or less, and the magnetic roll 1
DC bias potential 8 (V_dc2) And development roller 2
Current bias potential 7a (V_dc1) And potential difference | V _dc2−
V_dc1If | is in the range of 100V to 350V, high quality
It can be seen that high quality image can be obtained and applied to the developing roll 2.
The alternating current (AC) bias power supply 7b
Voltage (V_pp) Is 500-2000V, frequency is 1
The frequency may be set to be in a range of up to 3 kHz.

Setting the developing bias low in this way suppresses dielectric breakdown of the a-Si thin film of the electrostatic latent image carrier (photoconductor) 3, prevents excessive charging of the toner 5, and reduces the This is effective for suppressing the occurrence of the history phenomenon.
Further, a thin toner layer 6 having a thickness of 10 to 100 μm, preferably 30 to 70 μm is formed on the developing roll 2.
Gap between the photoconductor and the electrostatic latent image carrier (photoconductor) 150
A clear image can be obtained by causing the toner to fly onto the electrostatic latent image carrier (photoconductor) 3 by a DC and AC electric field in this space of 400 μm, preferably 200 to 300 μm.

The gap between the regulating blade 9 and the magnetic roll 2 is 0.3 to 1.5 mm, and the magnetic roll 1 and the developing roll 2
The gap between them is also about 0.3 to 1.5 mm.
By doing so, the thin layer 6 of the toner on the developing roll is formed.
Is set to a thickness of 10 to 100 μm, preferably 30 to 70 μm. This thickness allows the average particle diameter of the toner 5 to be 7 μm.
When m is set, the value corresponds to about 5 to 10 layers of the toner 5. Developing roll 2 and electrostatic latent image carrier (photoconductor)
3 is 150-400 μm, preferably 200-300 μm. If the width is smaller than 150 μm, fogging is caused. If the width is larger than 400 μm, it becomes difficult to cause the toner 5 to fly onto the electrostatic latent image carrier (photoconductor) 3, and a sufficient image density cannot be obtained. In addition, it is a factor that causes selective development.

In the developing device of the image forming apparatus according to the present invention, the electrostatic latent image carrier (photoconductor) 3 is made of a-Si having a layer thickness of 15 μm, the surface potential is set to 230 V, and the developing device is developed. DC bias 7a (V
_dc1 ) is 50 V, an alternating current (AC) bias 7b is a peak _-to- peak voltage (Vpp) of 1.1 kV, a frequency of 3.0 kHz,
DC bias 8 (V _dc2 ) to magnetic roll 1 is 200V
And the low-resistance carrier 4-1 and the high-resistance carrier 4
Table 1 shows examples in which the presence or absence of a ghost was evaluated by changing the ratio of −2 in various ways.

[0049]

[Table 1]

Ghost Evaluation Criteria The image pattern shown in FIG. 4 was printed and judged according to the following criteria. ：: No ghost image can be seen on the half image. Δ: The ghost image is one of the developing rolls 22 on the half image
It should be slightly visible on the lap, not visible at all on the second lap. X: The ghost image is clearly visible on the first round on the half image. The density was measured using a MacbeTh reflection densitometer RD914.
The points were measured and the average value was described.

The evaluation machine was FS-1750 of Kyocera Corporation.
(14 sheets / minute) The developing device was modified and used. The low-resistance carrier in the developer used was Mn-Mg ferrite, the resistance was 1.4 × 10 ⁶ Ωcm, and the average particle size was 35 μm.
m, saturation magnetization is 72 emu / g, high-resistance carrier is Cu
-Zn-based ferrite obtained by subjecting polyethylene to 3% surface treatment, with a resistance of 5.5 × 10 ¹⁰ Ωcm and an average particle size of 6
5 μm, the saturation magnetization was 63 emu / g, and 10% of nonmagnetic positively charged toner was added to the toner. The charge amount of the toner is determined by applying a thin layer of toner formed on the developing roll to an area of about 1 cm ²
Was measured at room temperature by suction using a capacitance meter (QM meter) manufactured by Trek. In the case of the initial image, the value is measured after setting the developing device and printing five sheets.

As shown in FIG. 4, a ghost evaluation criterion is such that a solid image composed of rectangular solid black and a halftone image wider than the solid image are arranged so as to be continuously developed. At that time, it was determined whether or not an afterimage of a solid black solid image appeared. Here, the density of the halftone image is set to 25% of the density of the solid image, but this is because afterimages relatively easily appear. These image patterns are printed, and when the ghost image is not seen at all on the half image as shown in (a), ○ is shown on the half image, and as shown in (b), the ghost image is placed on the half of the development roll 2 as shown in FIG. When the ghost image was slightly visible on the lap and was not visible at all from the second lap, Δ was added, and when the ghost image was clearly seen on the first lap on the half image, x was added. The density was measured with a MacbeTh reflection densitometer RD914.
The points were measured and the average value was described.

As is clear from Table 1, when the ratio of the high-resistance carrier to the low-resistance carrier shown in Comparative Example 1 was 1: 9, the initial image was good even after printing 50,000 sheets, but the development was good. Toner scattering in the container,
In Comparative Examples 2 to 4 in which the ratio was 6: 4 to 8: 2, the toner scattering in the developing device was good, but the initial image was 50,000.
The occurrence of an afterimage is observed even after printing of one sheet. On the other hand, when the ratio of the high resistance carrier to the low resistance carrier shown in Examples 1 to 4 is 2: 8 to 5: 5, the initial image is also 500
After printing of 00 sheets, generation of an afterimage is not seen, and toner scattering in the developing device is not seen.

As described above, by setting the ratio of the low-resistance carrier 4-1 in all the carriers 4 to about 50% to 80%, the thin toner layer 6 remaining on the developing roll 2 is collected and the toner 5 is charged. After the toner thin layer 6 is sufficiently recovered, no ghost (ghost image) is generated.
Can be prevented from scattering. By combining both carriers at a fixed ratio in this way, it is possible to collect the toner thin layer 6 on the developing roll and to recharge the charged toner 5 to the developing roll 2 again. It is possible to provide an image forming apparatus having a developing device that does not leave a development history phenomenon on the roll 2 and is excellent in recovering the thin toner layer 6.

[0055]

As described above, according to the first aspect of the present invention, the developer is made to have a volume resistivity of 10 ^9.
High resistance carrier of Ωcm or more and volume resistivity of 10 ⁸ Ω
cm, and the ratio of the low-resistance carrier is 50% to 80% of the entire carrier, so that the high-resistance carrier in the magnetic brush made of the developer retains toner and is optimal. High charge, and the non-image area toner remaining on the developing roll at the time of development can be recovered by a low-resistance carrier. It is possible to provide an image forming apparatus having a compact and highly practical developing device which can solve the problem of the phenomenon and can be used for a one-drum color superposition method for sequentially forming a plurality of color images.

According to the second aspect of the present invention, by using a non-magnetic toner having a positive polarity,
The development residual image (ghost) due to the enlargement of the difference in the charged potential of the toner between the developing unit and the non-developing unit in a low-temperature and low-humidity environment, which occurs when the negatively charged toner is used, can be prevented. When a negatively charged toner is used, the toner material generally tends to be negatively charged, and the potential of the toner layer on the developing roll increases when repeatedly exposed to a high electric field. Can also be prevented. Further, the charge amount of the toner is 5 to 20 μC /
g to prevent toner scattering and fogging, and develop with a low electric field, leaving no development history phenomenon on the developing roll, and forming an image with a developing device excellent in toner recovery. Equipment can be provided.

According to the third aspect of the present invention, by configuring the low-resistance carrier to have an average particle diameter of 40 μm or less and a saturation magnetization of 67 emu / g or more, the surface area of the carrier is increased and the contact with the toner is increased. And the peeling property of the magnetic brush formed in the nip between the developing roll and the magnetic roll by the electrode effect can be enhanced, and the electrode effect at the time of toner collection and the scraping effect by the magnetic brush can be sufficiently exhibited. .

According to the fourth aspect of the present invention, by forming the high-resistance carrier on the surface of which is formed of a high-molecular-weight polyethylene, it is tough against problems such as toner adhesion and coat peeling. In addition to having surface performance, the coating agent can be prevented from peeling off until the mechanical life of the developing device has expired, there is no change in the charging performance to the toner, and the toner is scattered due to poor charging and the image is contaminated. And the occurrence of selective development due to a decrease in developing performance can be prevented. And by controlling the resistance of the surface to 10 ⁹ to 10 ¹² Ωcm by the conductive particles,
It is possible to prevent the occurrence of carrier development, fog, image quality deterioration such as image density reduction, and the like.

As described above, according to the present invention, low electric field development using a positively chargeable photoreceptor, even when a positively charged toner is repeatedly charged with a small amount of carrier, the surface deterioration of the carrier is small, and the carrier is stable on a developing roll. By forming the charged toner layer, it becomes possible to appropriately develop the electrostatic latent image carrier (photoconductor). In addition, it was necessary to accurately charge the toner with regard to the deterioration of the developing property due to the replacement of the undeveloped toner and the selective development, which were one of the problems of the touchdown developing method and the hybrid developing method. This makes it possible to easily replace the undeveloped toner and the fresh toner on the developing roll, thereby providing a great effect.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a developing device in an image forming apparatus according to the present invention.

FIG. 2 shows a basic layer configuration model of a-Si of an electrostatic latent image carrier (photoconductor) used in the present invention.

FIG. 3 is a diagram for explaining an appropriate developing region of a bias voltage applied to a developing device in the image forming apparatus according to the present invention.

FIG. 4 is a diagram for explaining the occurrence of an afterimage that occurs at a content ratio of a high-resistance carrier and a low-resistance carrier.

FIG. 5 is a graph showing a solid image follow-up property and a toner scattering level according to the characteristics of a carrier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic roll 2 Developing roll 3 Electrostatic latent image carrier 4-1 Low resistance carrier 4-2 High resistance carrier 5 Toner 6 Toner thin layer 7a Direct current (DC) bias power supply 7b Alternating current (AC) bias power supply 8 Direct current (DC) Bias power supply 9 Regulator blade 10 Magnetic brush

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) G03G 15/08 501 G03G 9/10 321 507 351 341 (72) Inventor Shoichi Sakata Noshinaji Matabei, Tamaki-cho, Mie Prefecture 704 19 Kyocera Corporation Mie Plant Tamaki Block F term (reference) 2H005 BA05 BA06 BA18 CA13 CB04 DA03 DA09 EA01 EA02 EA05 EA06 EA07 2H077 AC04 AC12 AC16 AD06 AD13 AD23 AD24 AD31 AD36 AE04 EA14 GA03

Claims (4)

[Claims] An image forming apparatus for forming an image by an electrophotographic developing method is arranged to face a photoreceptor, and a thin layer is formed by a toner from a magnetic brush formed on a magnetic roll with a two-component developer to form the thin layer. In an image forming apparatus provided with a developing device having a developing roll for developing a latent image on a body, the two-component developer includes a toner and a volume resistivity of 10 ⁹ Ω.
cm high resistance carrier and volume resistivity of 10 ⁸ Ωc
m, wherein the ratio of the low-resistance carrier is 50% to 80% of the entire carrier. 2. The toner according to claim 1, wherein the toner is a non-magnetic toner having a positive polarity, and a charge amount of the toner on the developing roll is 5 to 2.
2. The image forming apparatus according to claim 1, wherein the value is 0 μC / g. 3. The low-resistance carrier has an average particle size of 40 μm.
2. The image forming apparatus according to claim 1, wherein the saturation magnetization is 67 emu / g or more. 4. The high-resistance carrier has an average particle diameter of 50.
μm or more, and its saturation magnetization is 60 to 200 emu /
g ferrite magnetic carrier has a weight average molecular weight M
A surface coating is formed with a high molecular weight polyethylene having w of 50,000 or more, and the coating amount is 1 to 5 Wt in terms of polyethylene.
2. The image forming apparatus according to claim 1, wherein the resistance of the surface is controlled to 10 ⁹ to 10 ¹² Ωcm by conductive particles.