JP2002304059A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely restrain the deterioration of the quality of carrier in two- component developer and to stably form a high-quality image over a long term even if the two-component developer is mechanically stressed because the two- component developer comes into contact with the surface of an image carrying rotary body whose wear resistance is improved, in an image forming device where the image carrying rotary body and a two-component developing device performing contact development with the two-component developer are combined and used. SOLUTION: This apparatus is constituted so that a flux density pattern M formed for a photoreceptor drum 11 in the developing area E of a developing roll 41 in the two-component developing device may be a pattern having the same polarity and two peaks Q1 and Q2.

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 printer, a copying machine, a facsimile, a multifunction machine, etc., which utilizes a two-component developing system. The present invention relates to an image forming apparatus using, as an image carrier, an image carrier rotator containing at least a surface-wear portion containing wear-resistant fine particles.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, an electrostatic recording system, or the like, a drum or belt on which a photosensitive layer made of an organic photosensitive material is formed is used as an image bearing rotary member on which an electrostatic latent image is formed. Many forms are used. The photosensitive layer composed of the organic photosensitive material generally has a function divided into a charge generation layer and a charge transport layer.

[0003] By the way, such an image bearing rotary member having a photosensitive layer formed of an organic photosensitive material has its surface contacted with a contact-type charging device or a contact-type transfer device or a blade-type cleaning device during image formation or the like. Therefore, the surface of the photosensitive layer is worn. As the wear progresses, image quality deterioration and image defects such as deterioration in gradation reproduction characteristics occur, and therefore, the image bearing rotating body must be replaced at an appropriate time.

As means for reducing the abrasion of the image bearing rotating body, an organic photosensitive layer having a coating layer in which hydrophobic silica is dispersed or a metal or metal oxide having an average particle diameter of 0.3 mm or less is used. A photoreceptor having a protective layer containing fine particles and a photoreceptor having a protective layer containing an inorganic filler have been proposed. All of these are intended to improve the wear resistance of the photoconductor by adding fine particles of high hardness to the surface layer of the photoconductor, thereby realizing a longer replacement period of the photoconductor.

However, in such a photoreceptor having improved abrasion resistance, for example, a two-component developer composed of a toner and a carrier is brought into contact with the surface of the photoreceptor in a development region close to and facing the photoreceptor. When applied to a contact development type image forming apparatus that develops in a state, there is a new problem that the hardness of the surface of the photoreceptor is damaged and an excessive stress is applied to the two-component developer.

In order to solve this problem, there has been proposed a technique of using a magnetic carrier in which the surface of magnetic particles is coated with a polyolefin resin as a carrier in a two-component developer (Japanese Patent Laid-Open No. 9-68826). No.).

[0007]

However, even when a two-component developer having such a magnetic carrier is used in combination with the above-described photoreceptor having improved abrasion resistance, the carrier remains on the photoreceptor surface. Cannot sufficiently absorb and relieve the stress caused by contact with
The quality of the carrier deteriorates due to the wearing or peeling of the coated resin layer, and the toner cannot be charged to a required charge amount by frictional charging with the carrier, thereby deteriorating the image quality. There is. This is because the mechanical strength of the polyolefin resin coated on the magnetic particles of the carrier is lower (softer) than the styrene acrylic resin, silicone resin, and the like, which have been widely used as the resin for coating the carrier.
It is considered that depending on the packing density (filling density) of the developer in the developing region, the mechanical stress caused by contact with the surface of the photoreceptor cannot be sufficiently absorbed and alleviated.

The present invention has been made in view of such circumstances, and an image-bearing rotating body having improved abrasion resistance by containing abrasion-resistant fine particles in at least a surface layer thereof, and a two-component rotating body. When used in combination with a two-component developing device that performs development with a developer, even if the two-component developer may receive mechanical stress due to contact with the surface of the image-bearing rotating body, the two-component developer may be used. It is an object of the present invention to provide an image forming apparatus capable of reliably suppressing deterioration of the quality of a carrier in a developer and stably forming a high-quality image for a long period of time.

[0009]

According to the image forming apparatus of the present invention, which can achieve the above object, an electrostatic latent image is formed on the surface by a potential difference, and at least the surface layer contains abrasion-resistant fine particles. Carrying rotator, and holding and transporting a two-component developer composed of a toner and a resin-coated magnetic carrier for developing the electrostatic latent image in a developing area opposed to the image carrying rotator. An image forming apparatus including a two-component developing device having a developer holding rotator having a magnet fixedly installed, wherein the image forming rotator is formed in the developing region of the developer holding rotator in the two-component developing device toward the image bearing rotator. The magnetic flux density pattern to be formed is a pattern having the same polarity and having two peaks.

Here, the image bearing rotary member is a photosensitive member or a dielectric member in the form of a drum or a belt. In the case of a photoreceptor, it is mainly composed of an organic photosensitive material. The abrasion-resistant fine particles can be directly contained in the material for forming the photosensitive layer and the dielectric layer of the image-bearing rotating body, and a surface protective layer is separately formed on the photosensitive layer and the dielectric layer to form a surface. You may comprise so that it may be contained in a protective layer. The abrasion-resistant fine particles may be any of organic fine particles and inorganic fine particles as long as they can impart abrasion resistance to the surface of the image bearing rotary member. More specifically, fluorine-containing resin powder, metal Oxide powder and the like.

The developer holding rotating body of the two-component developing device is usually composed of a cylindrical developing sleeve and a magnet (magnet) roll fixed and installed inside the space of the sleeve. However, the present invention is not particularly limited to this. The developer holding rotator is used by applying a developing bias. Further, as a developing method of the developing device, a contact developing method such as a magnetic brush developing method is applied.

In order for the magnetic flux density pattern in the developing region of the developer holding rotator to be a pattern having the same polarity and two peaks, for example, the central portion of the magnet portion composed of the magnetic poles for development is used. A concave cut groove is formed over the entire area of the developer holding rotating body in the axial direction, or another member (a non-magnetic metal member, a synthetic resin member, or the like) is fitted into the cut groove. A concave shape pattern is formed between two peaks in this magnetic flux density pattern. When the concave state at this time is expressed by, for example, magnetic flux density, the magnetic flux density of the peak is 1 to 30 m.
It is preferable to set the magnetic flux density to be smaller than T. Further, the separate member to be fitted in the cut groove is preferably a metal member from the viewpoint that the degree of depression between the peaks of the magnetic flux density pattern can be increased.

Further, the resin-coated magnetic carrier of the two-component developer used in the image forming apparatus uses a synthetic resin having a Rockwell hardness of 50 or more on a scale H _RR as the coating resin. Is preferred. The measurement of the Rockwell hardness is performed according to a measurement method standardized in JIS K7202. Coating resin with such Rockwell hardness (on the surface of magnetic particles)
The coated magnetic carrier, even in contact with the surface of the image-bearing rotating body containing the abrasion-resistant fine particles in the developing step, is subjected to mechanical stress, even if the coating resin is more difficult to wear or peel off, Carrier quality can be maintained for a longer period of time.

Further, the toner of the two-component developer used in this image forming apparatus may be a pulverized toner or the like having an irregular shape, but preferably has a shape factor (SF) represented by the following formula of 130. The following spherical toner is used. SF = (M ² / (A ×) × (π / 4) × 100 [where M is the maximum length of the toner particle diameter and A is the projected area of the toner]] When such a spherical toner is used, Since the contact area when adhering to the carrier is reduced, the adhesive force with the carrier is weakened and a suitable fluidity can be obtained. The impact generated when the carrier comes into contact with the surface is alleviated to reduce the wear on the surface, and the wear and peeling of the coating resin layer of the carrier are reduced.

[0015]

[First Embodiment] FIGS. 1 and 2 show an image forming apparatus according to a first embodiment of the present invention, and FIG. 1 is a schematic diagram showing the overall configuration thereof. FIG. 2 is a schematic diagram showing a part thereof in an enlarged manner.

In this image forming apparatus, four color toners of yellow (Y), magenta (M), cyan (C) and black (K) are individually formed by four image forming units 10Y, 10M, 10C and 10K. The image is transferred to the intermediate transfer belt 20.
Is a color image forming apparatus capable of forming a so-called full-color image by performing primary transfer so as to be superimposed on the surface of the recording paper P and then performing secondary transfer from the intermediate transfer belt 20 to recording paper P. The image forming apparatus can also form a monochromatic image such as a black and white image by operating only some of the four image forming units 10, for example, the black image forming unit 10K.

First, all of the image forming units 10
Each of the four color toner images is formed by an electrophotographic process, and is arranged at a position below the intermediate transfer belt 20 with a predetermined interval in the horizontal direction. Each of the image forming units 10 basically includes a photosensitive drum 11 driven to rotate in a direction indicated by an arrow at a predetermined speed, a charger 12 for uniformly charging the surface of the photosensitive drum 11, Rear photosensitive drum 11
A latent image forming apparatus (not shown) that forms an electrostatic latent image by exposing light (H) corresponding to image information input from a document reading device, an externally connected device, etc. Developing devices 14Y, 14Y,
4M, 14C, and 14K, a primary transfer unit 15 that electrostatically transfers a toner image formed by the development to the intermediate transfer belt 20, and before a primary transfer between the primary transfer unit 15 and the developing device 14. A pre-transfer processor 16 for adjusting the charged potential state of the toner image, a blade-type drum cleaning device 17 for cleaning the surface of the photosensitive drum 11, and a static eliminator 18 for neutralizing the cleaned surface of the photosensitive drum 11. Is similarly provided.

The intermediate transfer belt 20 is an endless two-layered structure in which a surface layer such as silicone rubber is laminated on a belt base material such as a polyimide film in which a volume resistivity is adjusted by containing a conductive material or the like. A belt, at least a drive roll 21 and a backup roll 22 of a secondary transfer unit
And is disposed between the drive roll 21 and the backup roll 22 so as to be in contact with the photosensitive drum 11 of each of the image forming units 10, and is rotated in the direction of arrow B by the rotational power of the drive roll 21. It is designed to run.

A secondary transfer unit 25 is disposed at a position on the outer peripheral surface of the intermediate transfer belt 20 opposite to the backup roll 22. Further, a blade-type belt cleaning device 26 that cleans the surface of the intermediate transfer belt 20 is disposed at a position on the outer peripheral surface of the intermediate transfer belt 20 that faces the drive roll 21. Further, between the intermediate transfer belt 20 and the secondary transfer device 25, the recording paper P is fed one by one from a paper feeding device (not shown) at a predetermined timing (arrows in the drawing). The dashed-dotted line indicates the path of the recording paper).

As shown in FIGS. 2 and 3, the photosensitive drum 11 has a cylindrical drum base 1 having conductivity.
1a and an organic photosensitive layer 11b laminated on the outer peripheral surface of the drum base 11a. Organic photosensitive layer 1
1b is, as shown in FIG. 3a, in order from the lower layer side.
It has a three-layer structure of an undercoat layer 11c, a charge generation layer 11d and a charge transport layer 11e, or a surface protective layer 1 on the charge transport layer 11e as illustrated in FIG.
1f has a four-layer structure in which lamination is further formed. The undercoat layer 11c is formed to prevent moire due to exposure during latent image formation, and is formed of a resin layer subjected to a conductivity imparting process. The charge generation layer 11d is a layer for generating positive and negative charges by exposure when forming a latent image. The charge transport layer 11e is a semiconductor layer that transfers charges generated in the charge generation layer.

In the photosensitive drum 11,
The abrasion-resistant fine particles 18 are contained in the charge transport layer 11e of the organic photosensitive layer 11b having a three-layer structure, or
It is contained in the surface protective layer 11f in the organic photosensitive layer 11b having a layer structure. As the wear-resistant fine particles 18, for example, a fluorine-containing resin powder or a metal oxide powder is used.

Examples of the fluorine-containing resin powder include polytetrafluoroethylene, polychlorotrifluoroethylene,
Fine particles such as polyvinylidene fluoride, polydichlorodifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer Powder. These fluorine-containing resin powders have a powder particle size of 0.01 to 1
Those having a range of 0 μm are preferably used. The amount of the fluorine-containing resin powder is preferably in the range of 1 to 80 parts by weight based on 100 parts by weight of the binder resin constituting the charge transport layer 11e. If the compounding amount is less than 1 part by weight, the surface lubricity of the charge transport layer 11e is deteriorated, and uneven wear and generation of abnormal noise (squeal) due to sliding contact of the cleaning blade are likely to occur. Conversely, when the amount is more than 80 parts by weight, the light sensitivity is lowered.

As the metal oxide powder, tin oxide,
Examples include antimony oxide, zinc oxide, titanium oxide, bismuth oxide, indium oxide, mixtures thereof, and composite oxides. These metal oxide powders are 10 ⁶ to
Preferably, it has a conductivity in the range of 1.5 × 10 ⁸ Ω · cm and a powder particle size in the range of 0.01 to 0.3 μm. The amount of the metal oxide powder is preferably in the range of 20 to 180 parts by weight based on 100 parts by weight of the binder resin constituting the charge transport layer 11e. When the amount is less than 20 parts by weight, the residual potential of the charge transport layer 11e increases under low-temperature and low-humidity conditions, resulting in a low-density image. Conversely, if the amount is more than 180 parts by weight, white spots and image bleeding will occur in a high-temperature and high-humidity environment.

When such abrasion-resistant fine particles 18 are contained in the surface protective layer 11f, the surface protective layer 11f
It is preferable that a suitable amount of a material (charge transporting substance) constituting the charge transporting layer 11e is contained. With this configuration,
The charge is transported uniformly, and the charge distribution according to the image content can be formed stably. Also, if necessary,
The wear-resistant fine particles 18 may be contained in the charge transport layer 11e in addition to the surface protective layer 11f.

As shown in FIG. 2, the two-component developing device 14 includes a two-component developer G accommodated in the housing 40 in a container-like housing 40 having an open end facing the photosensitive drum 11. And a developer agitating / transporting member 44a, 4 for agitating and circulating and transporting the two-component developer G accommodated in the housing 40 while transporting the developer to a developing area E facing the photosensitive drum 11.
4b, and the two-component developer G stirred and transported
The developer supply member 45 for supplying the toner to the first member 1 is provided to be driven to rotate. In the developing device 14,
A layer regulating member 46 for regulating the layer thickness of the two-component developer G held by the developing roll 41 is attached to the opening of the housing 40, and the developing roll 41 in the housing 40 and the developer agitating in the rear are attached. At a position between the members 44b, there is provided a peeling developer collecting inclined plate 47 for sliding the developer peeled off from the developing roll 41 after developing and collecting the developer toward the developer stirring member 44b. Reference numeral 40a in the figure
Is a partition that partitions between the two developer stirring and conveying members 44a and 44b and forms a developer circulation path on both sides thereof.

The developing roll 41 in the developing device 14
Uses a non-magnetic developing sleeve 42 having a cylindrical shape and a magnet roll 43 fixed and installed in the internal space of the developing sleeve 42. The developing sleeve 41 has been subjected to a surface roughening treatment (for example, sandblasting) so that the surface roughness Rz of the outer peripheral surface in the initial stage is 20 to 30 μm. The developing sleeve 41 is arranged with a predetermined gap from the photosensitive drum 11, and a developing bias voltage including an AC component is applied from a bias power source (not shown). The magnet roll 42 has a function of capturing the developer from the developer supply member 45 to the developing sleeve 42, and a layer thickness regulating member 46.
And a plurality of magnetic poles S, so as to exhibit a function of forming a uniform layer thickness of the developer, a function of forming a developing brush in the developing area, a function of peeling the developer after development from the developing sleeve 42, and the like. N is appropriately arranged.

In particular, in the developing roll 41, as illustrated in FIG.
The magnetic flux density pattern (M) formed toward the target is a pattern having two peaks (Q1, Q2) of the same polarity (S pole in this example). In order to form such a magnetic flux density pattern (M), a concave cut groove 48 is formed in the center of the developing magnetic pole S of the magnet roll 43 over the entire area in the roll rotation axis direction as shown in FIG. I have. The cut groove 48 has a groove width (length in the roll circumferential direction) of 0.5 to 3 mm and a groove depth of 0.5 to 2 m.
It may be formed so as to be within the range of m. Further, the magnetic flux density pattern M having such two peaks Q1 and Q2
Thus, a pattern in which a concave pattern portion exists between the peaks is obtained. From the viewpoint of increasing the degree of depression in such a magnetic flux density pattern M, the cut groove 48
It is preferable to fit a non-magnetic metal member or the like inside. And, by such a magnetic flux density pattern M, the developing region E
Accordingly, the magnetic brush formed on the developing sleeve 42 is also formed substantially along the magnetic flux density pattern M, and comes into contact with the surface of the opposing photosensitive drum 11.

Further, as the developer stirring and conveying member 44 in the developing device 14, an auger having a helical blade formed on a rotating shaft is usually used. The agitator may be wound around the device. The number of the developer stirring and conveying members 44 is not particularly limited, and may be, for example, one. The developer supply member 45 is a paddle having a plurality of blades attached to a rotating shaft, an elastic roll having a resin foam layer formed thereon, or the like. Further, the developer supply member 45 is not limited to the case where the developer supply member 45 is provided with an interval with respect to the development roll 41, and may be set so as to be in contact with the development roll 41. As the layer regulating member 46, an elastic blade or an elastic roll is used. A new two-component developer (mainly toner) is supplied from a developer replenishing device (not shown) to the portion of the housing 40 where the developer stirring / conveying member 44 is disposed, in accordance with the amount of consumed toner and the like. Is to be done.

The two-component developer G used in the developing device 14 is composed of a toner (particles) of a predetermined color and a resin-coated magnetic carrier (particles) in which magnetic particles are coated (coated) with a coating resin. Things.

The toner is basically composed of a binder resin and a colorant, and contains other additives as necessary. The toner has a volume average particle size of 1 to 20 μm, preferably 4 to 10 μm. The binder resin and the colorant constituting the toner are not particularly limited, and conventionally known resins and colorants can be used. Additives used as needed include charge control agents, release agents such as wax,
Examples include magnetic powders and additive dispersing aids.

The toner may be a pulverized toner manufactured by a pulverizing method, but here, a spherical toner having a shape factor (SF) of 130 or less as described above is used. As a method of manufacturing such a spherical toner,
A method of producing a pulverized toner obtained by a pulverization method by spheroidization, or a polymerization method such as a suspension polymerization method or an emulsion polymerization method is applied.

On the other hand, as the magnetic particles in the magnetic carrier, ferromagnetic metals such as iron, ferrite, magnetite, nickel and cobalt, or alloys or compounds containing these metals can be used. The magnetic particles may be obtained by subjecting the particle surface to an oxidation or reduction treatment, if necessary.

Further, the coating resin in the magnetic carrier is preferably Rockwell hardness (Scale H _R R) is used more than 50 synthetic resin. Examples of the synthetic resin satisfying this hardness condition include polypropylene, polyisobutylene, polymethyl methacrylate and the like.
The measurement of the Rockwell hardness is in accordance with the measurement method of the JIS standard as described above. After a steel ball is brought into contact with a test piece, a reference load of 10 kg is applied thereto, and the pointer of the tester is set to 0 point. Then, after applying a predetermined test load for the test piece for 15 seconds, the load is returned to the reference load again, and the depth of the permanent recess formed on the surface of the test piece after 15 seconds is read. It is to make it hard. In addition,
The coating resin includes a conductive material for adjusting the volume resistivity, specifically, metal fine particles such as iron, aluminum, and nickel, and carbon black, conductive titania, silicon carbide, tin oxide, and magnetite. Fine particles can be used.

Next, the operation of the image forming apparatus will be described.

In this image forming apparatus, first, in each image forming unit 10, the photosensitive drum 1 rotating in the direction of an arrow
After the surface of the photosensitive drum 1 is uniformly charged to, for example, a negative polarity by the charger 12, the charged surface is scanned and exposed to light H (laser beam or the like) corresponding to a color-separated image signal from the latent image forming apparatus. By doing so, an electrostatic latent image is written. Subsequently, the electrostatic latent image is developed into a toner image by magnetic brush contact development by the two-component developing device 14, and is sequentially formed on the surface of the intermediate transfer belt 20 passing between the photosensitive drum 11 and the primary transfer device 15. The primary transfer is performed. The surface of the photosensitive drum 11 after the primary transfer is cleaned by the drum cleaning device 16.
The remaining toner and the like are removed by the blades and the cleaning is performed.

Next, the toner image (multiple) transferred onto the intermediate transfer belt 20 is conveyed to a position facing the secondary transfer unit 25 as the belt 20 rotates. Then, the toner image on the intermediate transfer belt 20 is collectively and secondarily transferred to a predetermined recording sheet P conveyed between the intermediate transfer belt 20 and the secondary transfer device 25. The surface of the intermediate transfer belt 20 after the secondary transfer is cleaned by removing residual toner and the like by a blade of a belt cleaning device 26. Recording paper P on which toner image has been secondarily transferred
Is sent to a fixing device (not shown) to fix the toner image. Image formation is performed as described above.

In the developing step of this image forming operation, first, the two-component developer G accommodated and supplied in the housing 40 of the two-component developing device 14 is developed while being stirred by the developer stirring and conveying member 44. While being conveyed so as to pass through the developer supply member 45, the developer supply member 45
Is supplied to the developing roll 41. By this stirring, the toner of the two-component developer G is frictionally charged between the toner and the carrier so as to have a predetermined charge amount. The two-component developer G supplied to the developing roll 41 is attracted and held on the surface of the developing sleeve 42 by the magnetic force of a predetermined magnet (magnetic pole) of the magnet roll 43, and is transported with the rotation of the developing sleeve 42. Is done.

Subsequently, when the two-component developer G thus held on the developing sleeve 42 passes through the layer regulating member 46, an excessive developer portion is scraped off from the developing sleeve 41 to a predetermined amount. After being regulated to the layer thickness of the photosensitive drum 11, the photosensitive drum 11 is transported to the developing area E which is in close proximity to the photosensitive drum 11. The two-component developer G transported to the development area E is
3 while passing through the surface of the photosensitive drum 11 while forming a magnetic brush along the line of magnetic force of the developing magnet, and at the same time, between the developing roll 41 and the photosensitive drum 11 by the developing bias voltage applied to the developing sleeve 41. Due to the formed alternating electric field, it flies back and forth in the gap between them.
As a result, the toner of the two-component developer G is electrostatically attached only to the portion of the photosensitive drum 11 where the electrostatic latent image is formed, so that development is performed.

When the contact development is being performed in the development area E, the magnetic brush of the two-component developer G formed on the development sleeve 42 is used for the development magnet of the magnet roll 43 as described above. It is formed along a magnetic flux density pattern M formed by lines of magnetic force. As a result, the packing density of the two-component developer G in the developing region E becomes “dense” at the two peak portions Q1 and Q2 of the magnetic flux density pattern M, but the two peak portions Q1 and Q2
2 (approximately at the center of the developing region E), the two-component developer G on the developing sleeve 42 is relatively “sparse”.
Of the magnetic flux density pattern M is reduced between the peaks of the magnetic flux density pattern M due to the contact with the surface of the photosensitive drum 11 in the developing region E. As a result, the two-component developer G
The carrier can sufficiently absorb and alleviate mechanical stress caused by contact with the surface of the photosensitive drum 11 at the time of contact development, and abrasion and peeling of the coating resin layer hardly occur. Further, the photosensitive drum 11 in the developing region E of the carrier
By reducing the degree of contact with the surface, wear of the surface of the photosensitive drum 11 is also reduced.

Therefore, in the contact development, the quality of the carrier in the two-component developer is easily maintained, and therefore, the charge amount of the toner is hardly reduced, so that the normal development can be performed. The image quality of the developed toner image is also maintained. Further, since the coating resin of the carrier in the two-component developer has a Rockwell hardness of H _R R50 or more, the mechanical strength is relatively strong, so that the coating resin layer is hardly abraded or peeled off, and the carrier Quality can be maintained over a long period of time. Furthermore, by using a spherical toner as the toner in the two-component developer,
The adhesive force with the carrier is weakened, so that an appropriate fluidity can be obtained.
The impact generated when contacting the surface of the drum 1 is reduced, so that the wear on the drum surface is reduced, and the wear and peeling of the coating resin layer of the carrier are further reduced.

The two-component developer G after passing through the developing region E in this way is magnetically separated from the developing sleeve 41 when passing through the separating magnet portion of the magnet roll 43, and most of the two-component developer G is removed. The developer is slid on the developer collecting inclined plate 47 and collected at the portion where the developer stirring member 44 is present (see the dotted line in FIG. 2), and is again provided to the next developing step.

Hereinafter, an image forming test performed by using such an image forming apparatus will be described.

The conditions of the image forming apparatus used in this test are as follows.

<Conditions of the photosensitive drum>
As No. 1, one having an organic photosensitive layer 11b having a three-layer structure as illustrated in FIG. 3A was used. This photosensitive drum was manufactured as follows. It is to be noted that all “parts” described in the text hereinafter mean “parts by weight”.

First, n obtained by dissolving 4 parts of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd .: Eslec BM-S)
30 parts of an organic zirconium compound (acetylacetone zirconium butyrate) and 3 parts of an organic silane compound (γ-aminopropyltrimethoxysilane) are added to 170 parts of butyl alcohol, mixed and stirred to form an undercoat layer (11c). A coating solution was obtained. This coating solution is
After coating on a 30 mmφ aluminum roll base (11a) whose surface has been roughened by a honing treatment and air-drying for 5 minutes at room temperature, the base is heated to 50 ° C. for 10 minutes, and then heated to 50 ° C. It was placed in a constant temperature / humidity bath at 85% RH (dew point: 47 ° C.), and was subjected to a humidification and curing acceleration treatment for 20 minutes. Then, it was dried in a hot air dryer at 170 ° C. for 10 minutes.

Subsequently, a mixture of 15 parts of gallium chloride phthalocyanine, 10 parts of vinyl chloride-vinyl acetate copolymer resin (VMCH manufactured by Nippon Unicar Co., Ltd.) and 300 parts of n-butyl alcohol was used as a charge generating material in a sand mill. Dispersed for 4 hours. The resulting dispersion was dip-coated on the undercoat layer (11c) and dried to form a 0.2 μm-thick charge generation layer (11d).

Next, N, N'-diphenyl-N, N '
4 parts of -bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine and 6 parts of bisphenol Z polycarbonate resin (molecular weight 40,000) were dissolved by adding 80 parts of chlorobenzene. . Further, 5 parts of a polytetrafluoroethylene (PTFE) fine powder having a volume average particle diameter of 3 μm, which is a wear-resistant fine particle (18), was added,
A coating solution for forming the charge transport layer (11e) was obtained. The obtained solution was applied on the charge generation layer (11d) and dried to form a charge transport layer (11e) having a thickness of 27 μm.

<Conditions of Developing Apparatus> Next, as the developing apparatus 14, one having the following conditions was used.

The surface of the developing roll 41 is subjected to sand blasting and etching to reduce the surface roughness to Rz.
A combination of an aluminum sleeve 42 having an outer diameter of 18 mm, which is 20 μm, and a magnet roll 43 having the following magnetic force configuration with a magnetic pole arrangement capable of obtaining a magnetic flux density pattern M shown in FIG. 5 was used. The peak of the magnetic flux density in the developing area E: 85 mT The angle α between the magnetic flux density peaks Q1 and Q2 in the developing area E: 27 ° The peak of the magnetic flux density in the developing area E: -1
5mT

<Conditions as Image Forming Apparatus> The developing device 14 was installed and used on the photosensitive drum 11 under the following conditions. -Minimum gap between photosensitive drum 11 and developing roll 41: 35
0 μm ・ Rotation speed of photosensitive drum 11: 100 mm / sec ・ Charging (background) potential of photosensitive drum 11: -600 V ・ Latent image potential of photosensitive drum 11: -200 V to -500 V ・ Developing bias voltage: -450 V ・ Developing sleeve Rotation speed of 42: 200 mm / sec. Amount of developer transported in development area E: 400 g / m ^2.

<Conditions of Two-Component Developer> Next, as a two-component developer G, a volume average particle diameter of 5.5 produced as follows.
A toner (developer) consisting of a μm spherical toner and a plurality of kinds of magnetic coated carriers having a volume average particle diameter of 35 μm produced as described below was used.

[Production of Spherical Toner] First, production of a spherical toner will be described. First, the following materials were weighed into a flask, and then kept at 85 ° C. while stirring. The material in the flask became cloudy in about 3 hours and completely solidified in 5 hours. Thereafter, the temperature was maintained at 85 ° C. for a total of 8 hours to complete the reaction, thereby producing a urethane compound. The urethane compound in the flask was taken out and pulverized by a sample mill into powder. Hexamethylene diisocyanate: 208 g n-octyl alcohol: 323 g The obtained urethane compound has a molecular weight of 428 and a melting point of 10.
8.2 ° C. (peak value in differential calorimeter).

Also, the following materials were mixed and dissolved,
6 g of nonionic surfactant, 10 anionic surfactant
g was added to a solution dissolved in 550 g of ion-exchanged water, dispersed and emulsified in a flask, and slowly mixed for 10 minutes.
Then, 0 g was charged and the atmosphere was replaced with nitrogen. Thereafter, the contents were heated to 70 ° C. in an oil bath while stirring the flask, and emulsion polymerization was continued for 5 hours. Styrene: 340 g n-Butyl acrylate: 60 g Acrylic acid: 6 g Dodecanethiol: 8 g Carbon tetrabromide: 4 g This gives a center particle diameter of 180 nm, a glass transition point of 59 ° C.,
A resin dispersion of an anionic resin having an Mw of 28,000 was obtained.

Further, the following components were mixed and dissolved and dispersed to obtain a cyan pigment dispersion having a center particle diameter of 150 nm. Cyan pigment: 50 g Nonionic surfactant: 5 g Ion-exchanged water: 200 g

Further, the following components were heated and dispersed at 95 ° C. to obtain a release agent dispersion having a center particle diameter of 200 nm. Urethane compound: 0 g Cationic surfactant: 5 g Deionized water: 200 g

The above components and the following materials were placed in a flask at the following ratios, mixed and dispersed, and then heated to 48 ° C. while stirring the flask in a heating oil bath. After holding at 48 ° C. for 30 minutes, observation with an optical microscope confirmed that aggregated particles having a particle size of about 4.8 μm had been formed. Resin dispersion: 200 g Pigment dispersion: 30 g Release agent dispersion: 20 g Cationic surfactant: 1.5 g

60 g of the resin dispersion was gently added to this dispersion, and the temperature of the heating oil bath was increased by 50 g.
C. for 1 hour. Observation with an optical microscope confirmed that aggregated particles having a particle size of about 5.4 μm had been formed. Thereafter, after adding 3 g of a surfactant to this dispersion, the flask was sealed, heated to 105 ° C. while stirring with a magnetic seal, and maintained for 3 hours. After cooling, the mixture was filtered and sufficiently washed with ion-exchanged water to obtain toner particles.

The average particle size of the obtained toner particles was measured by a Coulter counter (particle size analyzer).
It was confirmed to be 5 μm. Further, 0.8% by weight of silica was added to the surface of the toner particles and mixed to obtain a toner.

[Preparation of Carrier] Next, the production of the carrier will be described. First, as a carrier, ferrite particles having a volume resistivity of 10 ⁸ to 10 ⁹ Ω · cm are used as a core material, and the respective surfaces are coated with respective coating resins to which conductive fine particles are added (carriers A to A).
D) was prepared.

As for the ferrite particles, Cu—Zn ferrite (manufactured by Powder Tech, average particle size 50 μm) 1
000 parts and 7 parts of γ-aminotriethoxysilane (KBE903, manufactured by Shin-Etsu Chemical Co., Ltd.) were dispersed in 500 parts of methanol and mixed at room temperature for 5 minutes in a small 5-liter kneader equipped with a heater. Was heated to 120 ° C. and heated under reduced pressure for 40 minutes, and then the heater was turned off.
Cool for 50 minutes with stirring. Thereafter, the particles were sieved with a 105 μm sieve to obtain treated core particles, which were used as ferrite particles.

To 1000 parts of the above ferrite particles, 15 parts of polyethylene (molecular weight: 20,000) was added, mixed in a small 5 L kneader equipped with a heater at room temperature for 5 minutes, and then the temperature of the heating medium was increased to 140 ° C. for 40 minutes. Heat and stir, then turn off the heater and stir for 5
Cool for 0 minutes. Thereafter, the mixture was sieved with a 105 μm sieve to obtain Carrier A.

Further, 1000 parts of the above ferrite particles,
20 parts of polypropylene (molecular weight 30,000) are dispersed in 800 parts of toluene, mixed in a 5 L small kneader equipped with a heater at room temperature for 5 minutes, and then heated under reduced pressure at a heating medium temperature of 140 ° C. for 40 minutes, Thereafter, the heater was turned off, and the mixture was cooled for 50 minutes with stirring. Thereafter, the mixture was sieved with a 105 μm sieve to obtain Carrier B.

Further, 1000 parts of the above ferrite particles,
25 parts of polyisobutylene (molecular weight: 50,000) were dispersed in 500 parts of toluene, mixed in a 5 L small kneader equipped with a heater at room temperature for 5 minutes, and then heated at 140 ° C. and heated under reduced pressure for 40 minutes. Thereafter, the heater was turned off, and the mixture was cooled for 50 minutes with stirring. Thereafter, the mixture was sieved with a 105 μm sieve to obtain Carrier C.

Further, 30 parts of polymethyl methacrylate (molecular weight: 70,000) was added to 1000 parts of the ferrite particles, mixed in a small 5 L kneader equipped with a heater at room temperature for 5 minutes, and then the temperature of the heating medium was increased to 140 ° C. Then, the mixture was heated and stirred for 40 minutes. Thereafter, the heater was turned off, and the mixture was cooled for 50 minutes with stirring. Then 105
The carrier D was obtained by sieving with a sieve of μm.

Further, as the two-component developer G, a pulverized toner having an average particle diameter of 6.1 μm manufactured as described below, and a magnetic coat carrier (A to A) having a volume average particle diameter of 35 μm described above were used.
D) (developer).

[Preparation of Pulverized Toner] The following materials were weighed into a flask, and kept at 85 ° C. with stirring. The material in the flask became turbid in about 3 hours and completely solidified in 4 hours. Thereafter, the temperature was maintained at 85 ° C. for a total of 6 hours to complete the reaction. The urethane compound in the flask was taken out and pulverized by a sample mill into powder. Hexamethylene diisocyanate: 208 g n-propyl alcohol: 148 g

The obtained urethane compound had a molecular weight of 28.
8, melting point 99.1 ° C (peak value in differential scanning calorimeter).

The urethane compound and the following materials were weighed in the following proportions, premixed, kneaded with a Banbury mixer (manufactured by Kobe Steel), coarsely crushed, crushed with a jet mill, and crushed with a small elbow jet. To obtain a base toner having an average particle size of 6.1 μm. Polyester resin: 90 parts by weight Cyan pigment: 5 parts by weight Urethane compound: 5 parts by weight Further, 0.8% by weight of silica was added to and mixed with the surface of the base toner particles to obtain a dispersed toner.

<Conditions of Comparative Example> On the other hand, for comparison, a magnetic flux density pattern as shown in FIG. 6 (particularly, a magnetic flux density pattern in the developing region E has one peak Q3) as the developing roll 41 of the developing device 14. Only pattern K)
The same test was carried out using the developing device 14 and the image forming apparatus, except that the magnet roll 43 having the following conditions was used. Further, as the two-component developer, the above-described developers employing spherical toner were used. The peak of the magnetic flux density in the developing region E: 120 mT The amount of the developer transported in the developing region E: 350 g / m ²

[Measurement of Rockwell Hardness of Carrier Coating Resin] In this test, first, the Rockwell hardness of each coating resin of the carriers A to D was measured. In this measurement, each coating resin was molded into a cube having a side of 20 mm and used as a test piece.
The measurement was performed according to the S standard measurement method. Table 1 shows the measurement results at this time.

[0071]

[Table 1]

In this test, after forming 10,000 test images using the image forming apparatuses of the examples and the comparative examples prepared as described above, the film thickness variation of the organic photosensitive layer 11b of the photosensitive drum 11 ( Abrasion amount), change amount of toner charge amount, peeling state of carrier coating resin layer (coat layer),
The image quality (image density at 100% image density, tone reproducibility, fine line reproducibility, graininess and background fog) was measured and observed, and the results are shown in Table 2.
The image quality was evaluated according to the following criteria. ◎: very good, ：: good, Δ: bad, ×: very bad.

[0073]

[Table 2]

From the results shown in Table 2, the developing device 14
The magnetic flux density pattern in the developing area E of the developing roll 41
By adopting the pattern having the two peaks,
Compared to the comparative example using the component developer (~)
Amount of decrease in toner charge, including wear of photosensitive layer, coating
The peeling of the resin for use and the image quality characteristics are both significantly improved
You can see that Also, as a carrier for two-component developer
Rockwell altitude is H _RCoated with coating resin of R50 or more
When using carriers (B to D),
There is almost no peeling of grease, and the amount of decrease in toner charge is small.
It turns out that it is gone. In addition, spherical as a two-component developer
When using a developer (~) that uses toner
Is the amount of toner charge reduction, including the amount of wear on the photosensitive layer,
Better results for the above image quality
Understand.

[0075]

As described above, according to the present invention,
When a combination of an image-bearing rotating body with improved abrasion resistance and a two-component developing device that performs contact development with a two-component developer is used, the two-component developer contacts the surface of the image-bearing rotating body. Therefore, even if mechanical stress is applied, the deterioration of the quality of the carrier in the two-component developer can be reliably suppressed, and a high-quality image can be stably formed over a long period of time. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a main part of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic diagram illustrating one image forming unit in the image forming apparatus of FIG. 1;

FIGS. 3A and 3B show typical examples of a photosensitive drum, and FIG. 3A is a cross-sectional view of a main part showing an example in which an organic photosensitive layer having a three-layer structure is formed;
(B) is a sectional view of an essential part showing an example in which an organic photosensitive layer having a four-layer structure is formed.

FIG. 4 is an explanatory diagram illustrating a relationship between a magnetic flux density pattern of a developing roll of a developing device and a photosensitive drum in the image forming apparatus of FIG. 1;

FIG. 5 is a diagram showing a magnetic flux density pattern of a developing roll used in an example of an image forming test.

FIG. 6 is a diagram showing a magnetic flux density pattern of a developing roll used in a comparative example of an image forming test.

[Explanation of symbols]

11: photosensitive drum (rotating body for image bearing), 14: two-component developing device, 41: developing roll (rotating body for holding developer), 43:
Magnet roll, G: two-component developer, E: development area,
M: magnetic flux density pattern in the development area, Q1, Q2 ...
peak.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H005 AA15 BA06 CA02 CA13 EA10 2H031 AC20 AD01 AD15 BA05 BA09 FA01 2H077 AD06 AE06 EA03 GA03 GA12

Claims (3)

[Claims] An electrostatic latent image is formed on a surface by an electric potential difference, and an image-bearing rotating body having at least a surface layer portion containing abrasion-resistant fine particles, and the electrostatic latent image is provided on a developing region opposed to the image-bearing rotating body. A two-component developing device having a developer holding rotating body in which a magnet of a predetermined polarity is fixedly installed in an internal space for holding and transporting a two-component developer composed of a toner for developing a latent image and a resin-coated magnetic carrier. In the image forming apparatus, the magnetic flux density pattern formed toward the image bearing rotary member in the developing region of the developer holding rotary member in the two-component developing device is a pattern having two peaks of the same polarity. An image forming apparatus comprising: The image forming apparatus according to claim 1, a resin-coated magnetic carrier of the two-component developer, a resin coating Rockwell hardness using synthetic resin is H _R R50 or as a coating resin An image forming apparatus comprising a magnetic carrier. 3. The image forming apparatus according to claim 1, wherein the toner of the two-component developer is a spherical toner having a shape factor (SF) represented by the following equation of 130 or less. Image forming apparatus. SF = (M ² / (A ×) × (π / 4) × 100 [where M is the maximum length of the toner particle size, and A is the projected area of the toner]