JP2006184475A - Recording medium conveying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably forming an image of high picture quality image while suppressing a hollow in an image due to carrier deposition on a latent image carrying body or irregularity in an image due to changes in a developer amount on a developer carrying body even when the particle size of a carrier is decreased or the gap between the latent image carrying body and the developer carrying body is narrowed for obtaining high picture quality. <P>SOLUTION: The carrier used comprises a magnetic carrier having 20 to 60 [μm] average particle size and showing ≥66×10<SP>-7</SP>×4π [(Wb m)/kg] saturation magnetization in a magnetic field of 1×10<SP>6</SP>/4π [A/m]. A developer regulating member 9 is made of a material having rigidity and magnetism. The developer carrying body 7 used has grooves extended along a width direction perpendicular to the circumference direction, the grooves formed at a plurality of different positions in the circumference direction of the surface. The normal magnetic flux density by a magnetic pole of a magnet on the surface of the developer carrying body 7 at a position where the developer regulating member 9 opposes is controlled to 45 [mT] to 70 [mT]. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a fax machine, and more particularly to an image forming apparatus that employs a developing method using a two-component developer obtained by stirring and mixing toner and a carrier. is there.

  In general, in image forming methods such as electrophotography and electrostatic photography, a developer is used to develop an electrostatic latent image formed on a latent image carrier. As this developer, there is a method of using a two-component developer obtained by stirring and mixing a toner and a carrier. This method has better toner charging stability than a method using a one-component developer containing no carrier, and a stable and good image can be obtained. Usually, the two-component developer is carried on a developer carrying member by a magnetic force and conveyed to a portion facing the latent image carrying member for development.

  With the recent demand for miniaturization of machines, it is necessary to reduce the diameter of, for example, a photosensitive drum as a latent image carrier and a developing sleeve as a developer carrier. When the diameters of the drum and the sleeve are small, the magnetic binding force against the carrier of the tip of the magnetic brush at the developing nip exit becomes small. As a result, the smaller the drum diameter and sleeve diameter, the worse the carrier adhesion. Further, with the recent increase in image quality, the toner particle size tends to be further reduced. Accordingly, the carrier needs to have a small particle size. When the carrier diameter is reduced, the magnetization is reduced and the carrier adhesion is deteriorated. As the carrier adhesion deteriorates, deterioration of the drum, drum cleaning blade, intermediate transfer member, and the like is promoted, and white spots on the image are deteriorated.

  As a method for preventing carrier adhesion, a developing pole for generating a magnetic field in a developing area where the developing sleeve and the photosensitive drum face each other, and a developer conveying direction on the developing sleeve from the downstream side in the developer conveying direction from the developing pole. There is a method of increasing the magnetic force between the development downstream pole adjacent to the development pole. There are also methods such as lowering the resistance of the carrier, narrowing the distance between the drum and the sleeve (hereinafter referred to as PG), and increasing the magnetization of the carrier. The method of increasing the magnetic force between the developing pole and the developing downstream pole is that the magnetic brush is moved away from the developing pole and moved to the developing downstream pole. Reduces carrier adhesion to the surface. The method of reducing the resistance of the carrier is to reduce the resistance so that the counter charge remaining on the carrier after solid development is easily dissipated from the carrier, and the carrier adheres to the edge due to the counter charge (hereinafter referred to as edge carrier). (Referred to as adhesion). The PG narrowing method reduces carrier adhesion by increasing the electric field strength by narrowing the PG. It has been found that this PG narrowing is advantageous for improving the image quality of images.

In addition, about the granular carrier used for a two-component type development system, it is usually performed by coating with an appropriate resin material to provide a hard and high-strength coating layer. This prevents toner filming on the carrier surface, forms a uniform carrier surface, prevents surface oxidation, prevents moisture sensitivity, extends the life of the developer, protects the photoconductor from scratches or abrasion, and charge polarity. The purpose is to control the amount of charge or to adjust the charge amount. Patent Document 1 also discloses a material coated with a specific resin material. Patent Documents 2 to 8 disclose those in which various additives are added to the coating layer. Patent Document 9 discloses one in which an additive is attached to the carrier surface. Patent Document 10 discloses one that uses conductive particles larger than the coat film thickness in the coat film. Patent Document 11 discloses that a benzoguanamine-n-butyl alcohol-formaldehyde copolymer is used as a main component for a carrier coating material. Patent Document 12 discloses the use of a cross-linked product of melamine resin and acrylic resin as a carrier coating material.
However, the durability is still insufficient, causing phenomena such as spent toner on the surface of the carrier, resulting in instability of the charge amount, and reduction in resistance due to scraping of the coating resin. A good image can be obtained in the initial stage, but as the number of copies increases, the amount of the developer drawn up decreases with this phenomenon, and the image quality of the copied image decreases. There is still a need for improvement.

With regard to such an improvement, Patent Document 13 describes matters that are partially in common with matters described in the means for solving the problems described below. That is, in Patent Document 13, in a carrier having a coating film having at least a binder resin and particles, the particle diameter (D) and the binder resin film thickness (h) are 1 <[D / h] <5. There has been proposed an electrophotographic carrier characterized in that it is. However, it is not described for magnetization. Patent Document 14 describes that a developer conveying force is increased by forming a groove in the developing sleeve. However, there is no description about highly magnetized carriers.
JP 58-108548 A JP 54-1555048 A JP 57-40267 A JP 58-108549 A JP 59-166968 A Japanese Patent Publication No. 1-19584 Japanese Examined Patent Publication No. 3-628 JP-A-6-202381 JP-A-5-273789 JP-A-9-160304 JP-A-8-6307 Japanese Patent No. 2683624 JP 2001-188388 A JP 2001-134069 A

  The method of reducing the resistance of the carrier and the method of narrowing the PG for preventing the carrier adhesion have the following problems. In the method of reducing the resistance of the carrier, when the developing bias is AC (alternating current), the resistance is low, so that the charge leaks, and an abnormal image is generated due to the leak. The PG narrowing method increases the initial developer pumping amount in order to prevent problems such as ear marks and background stains due to a decrease in the pumping amount of the developer due to deterioration of the developer and the developing sleeve surface over time. It needs to be set to the eyes. If this is set to a high level, the amount of pumping will be too large and packing in the development area will become large, causing agent overflow, development roller lock, development sleeve sticking, and the like. Further, due to a decrease in the toner charging ability of the carrier due to toner fusion to the carrier surface, background contamination, toner scattering, and the like are deteriorated. As described above, this PG narrowing method is advantageous for improving the image quality of an image. Therefore, unlike the above, if it becomes possible to secure a stable developer pumping amount over time without setting the initial developer pumping amount excessively high, the image quality will be improved and the carrier small particle size will be increased. In order to prevent carrier adhesion due to the increase in the size, this PG narrowing method is to be adopted.

  The present invention has been made in view of the above background, and in the case of reducing the particle size of the carrier or reducing the distance between the latent image carrier and the developer carrier for high image quality. An image forming apparatus capable of stably forming a high-quality image by suppressing white spots on the image due to carrier adhesion to the latent image carrier and unevenness on the image due to a change in the developer amount on the developer carrier. The purpose is to provide.

In order to achieve the above object, the invention of claim 1 includes a latent image carrier on which an electrostatic latent image is formed on the surface, and development in which the circumferential surface faces the latent image carrier and is supported so as to be able to go around. A developer carrying member and a two-component developer composed of toner and a magnetic carrier is carried on the developer carrying member, and the amount of the developer carried by the developer regulating member is regulated to be opposed to the latent image carrying member. An image forming apparatus comprising: a developing device that transports and visualizes the electrostatic latent image on the latent image carrier with toner by applying a developing electric field between the latent image carrier and the developer carrier The magnetic carrier has a weight average particle size of 20 [μm] or more and 60 [μm] or less, and the saturation magnetization of the magnetic carrier in a magnetic field of 1 × 10 ⁶ / 4π [A / m] is 66 × 10 ⁻⁷ × 4π. [Wb · m / kg] or more, and the developer amount regulating member is made of a rigid and magnetic material. The developer carrying member is characterized in that a groove extending along the width direction perpendicular to the circumferential direction and is formed respectively on a plurality of different locations in the circumferential direction of the surface.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the volume average particle size of the toner is 3 [μm] or more and 8 [μm] or less, and the average particle size of the inorganic fine particles added to the toner is 30. [Nm] or more and 160 [nm] or less.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, an interval between the latent image carrier and the developer carrier is 0.2 [mm] or more and 0.4 [mm] or less. It is characterized by.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the carrier has a coat film having at least a binder resin and particles, and the particle diameter (D) and the binder The resin film thickness (h) satisfies the relationship of 1 <[D / h] <10.

5. The image forming apparatus according to claim 1, wherein a two-component developer including a toner and a magnetic carrier for holding the toner is in a magnetic brush state in a developing area to develop an electrostatic latent image on the image carrier. .
Since the weight average particle size of the magnetic carrier in the two-component developer is a small particle size of 60 [μm] or less, it is possible to prevent graininess of the ear marks and halftone image due to the magnetic carrier, that is, deterioration of graininess. It becomes possible to improve the image quality. Further, since the lower limit of the weight average particle diameter is 20 [μm], the fluidity and stress on the developer are not deteriorated too much. Further, the saturation magnetization in a magnetic field of 1 × 10 ⁶ / 4π [A / m] (1 k [Oe]) is increased to 66 × 10 ⁻⁷ × 4π [Wb · m / kg] (66 [emu / g]) or more. Therefore, the magnetic binding force of the magnetic brush by the magnetic field generating means is strong, and it is difficult for the carrier to be separated from the tip of the magnetic brush. This suppresses carrier adhesion to the image carrier, which is likely to occur when using the magnetic carrier having a small particle diameter.
Further, since the developer amount regulating member is made of a material having rigidity and magnetism, the charging start-up property is good.
If such a developer amount regulating member is used and the saturation magnetization of the magnetic carrier is set to be high, the developer pumping amount unevenness occurs on the developer carrier, and the image unevenness appears on the image. The problem of being easy has occurred. Therefore, a plurality of grooves were formed on the surface of the developer carrying member. This groove increases the developer conveying force, suppresses the developer from slipping on the developer carrying member, and prevents uneven developer pumping.
Further, since the normal direction magnetic flux density by the magnetic pole of the magnet at the surface portion of the development carrier facing the developer amount restriction member is 45 mT or more, the developer amount restriction member and the latent amount The distance from the surface of the image carrier (hereinafter referred to as a doctor gap) can be set wide enough to prevent foreign matter or toner from being caught. As a result, it is possible to prevent the occurrence of streaks on the image due to foreign matter, toner, etc. Supplementally, the smaller the magnetic flux density, the smaller the developer holding force due to the magnetic force of the developer amount regulating member made of a magnetic material, and the doctor gap passage restriction on the developer conveyed as the developer carrying surface moves. The power is small. For this reason, it is necessary to set the doctor gap narrowly and regulate the passage amount. If it is too narrow, the foreign matter or the like may be caught. If the magnetic flux density is set, the doctor gap can be set wider. On the other hand, if the magnetic density is too large, the developer holding force of the developer amount regulating member is too large, and a large amount of developer held by the developer amount regulating member causes the developer transported as the developer carrier surface moves. On the other hand, excessive stress is applied to increase the deterioration of the developer such as toner spent. Therefore, the magnetic flux density is set to 70 [mT] or less. This suppresses early deterioration of the developer.

According to the present invention, unevenness in the amount of pumping that occurs when a highly magnetized carrier and a magnetic doctor are used at the same time can prevent image unevenness due to carrier adhesion and unevenness in pumping by using a sleeve having a high conveying force. Therefore, even when the carrier particle size is reduced or the distance between the latent image carrier and the developer carrier is reduced to improve the image quality, the carrier adheres to the latent image carrier. Therefore, it is possible to suppress white spots on the image due to the above and unevenness on the image due to a change in the developer amount on the developer carrying member, and to stably form a high-quality image.
Furthermore, by setting the normal direction magnetic flux density by the magnetic pole of the magnet at the surface portion of the development carrier opposite to the developer amount regulating member to 45 [mT] or more and 70 [mT] or less, foreign matter or the like Therefore, it is possible to set a doctor gap so as not to cause streaks on the image due to the pinching of the toner, and to suppress early deterioration of the developer due to excessive developer retention of the developer amount regulating member.

Hereinafter, an embodiment in which the present invention is applied to an image forming apparatus such as a copying machine, a facsimile, or a printer will be described.
In the image forming apparatus according to the present exemplary embodiment, a charging device, an exposure device, a developing device, a transfer device, and a cleaning device are sequentially arranged around a photoconductor as an image carrier. In addition, a paper feeding / conveying device that feeds the transfer paper from the paper feeding tray and a fixing device that fixes the toner onto the transfer paper after the transfer paper on which the toner image has been transferred are separated from the photoreceptor. In the image forming apparatus configured as described above, the surface of the rotating photoconductor is uniformly charged by the charging device and then irradiated with the laser beam of the exposure device based on the image information to form a latent image on the photoconductor. Form. A toner image is formed by attaching toner charged by a developing device to the electrostatic latent image formed on the photoreceptor. On the other hand, the transfer paper is fed from a paper feed tray by a paper feed / conveyance device, and then conveyed to a transfer portion where the photoconductor and the transfer device face each other. The transfer device applies a charge having a polarity opposite to that of the toner image on the photoconductor to the transfer paper, thereby transferring the toner image formed on the photoconductor to the transfer paper. Next, the transfer paper is separated from the photoconductor, sent to a fixing device, and an image is obtained by fixing the toner to the transfer paper.

  FIG. 1 is a schematic configuration diagram of a developing device of an image forming apparatus according to the present embodiment. The developing device employed in the image forming apparatus will be described in detail with reference to FIG. The developing device 1 is disposed on the side of the photoconductor 8 and is a non-magnetic developer as a developer carrier that carries a two-component developer (hereinafter referred to as “developer”) containing toner and a magnetic carrier on the surface. A developing sleeve 7 is provided. The developing sleeve 7 is attached so as to be partially exposed from an opening formed on the photosensitive member 1 side of the developing casing, and is rotated in the direction of arrow b in the drawing by a driving device (not shown). In addition, a magnet roller (not shown) composed of a fixed magnet group as a magnetic field generating means is fixedly arranged inside the developing sleeve 7. Further, the developing device 1 includes a doctor 9 as a developer regulating member that regulates the amount of developer carried on the developing sleeve 7. A developer accommodating portion 4 for accommodating the developer is formed on the upstream side in the rotation direction of the developing sleeve 7 with respect to the doctor 9, and the first and second components for stirring and mixing the developer in the developer accommodating portion 4 are formed. Stir screws 5 and 6 are provided. Further, a toner replenishing port 23 disposed above the developer accommodating portion 4, a toner hopper 2 filled with toner to be replenished to the developer accommodating portion 4, and a toner feeding device that connects the toner replenishing port 23 and the toner hopper 2. 3 is provided.

  In the developing device 1 configured as described above, the first and second stirring screws 5 and 6 are rotated to stir the developer in the developer container 4, and the toner and the magnetic carrier rub against each other in opposite polarities. Charged. This developer is supplied to the peripheral surface of the developing sleeve 7 that is rotationally driven in the direction of arrow b, and the supplied developer is carried on the peripheral surface of the developing sleeve 7, and the rotation direction of the developing sleeve 7 (arrow) (b direction). Next, the amount of the conveyed developer is regulated by the doctor 9, and the regulated developer is conveyed to a development area where the photoconductor 8 and the development sleeve 7 face each other. In this developing area, the toner in the developer is electrostatically transferred to the electrostatic latent image on the surface of the photoconductor 8, and the electrostatic latent image is visualized as a toner image.

In the developing apparatus 1, the carrier has a weight average particle diameter of 20 [μm] or more and 60 [μm] or less, and 1 × 10 ⁶ / 4π [A / m] (1 [kOe]). ) A saturation magnetization of 66 × 10 ⁻⁷ × 4π [Wb · m / kg] or more (66 [emu / g] or more) is used in a magnetic field. If it is less than 66 × 10 ⁻⁷ × 4π [Wb · m / kg], the saturation magnetization is low, so that the transportability is lowered and the carrier adheres to the photoreceptor 100 more. Further, it is preferable to use a material having a saturation magnetization of 100 × 10 ⁻⁷ × 4π [Wb · m / kg] or less in a magnetic field of 1 × 10 ⁶ / 4π [A / m] (1 [kOe]). If it exceeds 100 × 10 ⁻⁷ × 4π [Wb · m / kg], the strength of saturation magnetization is high, so the magnetic brush becomes strong, the scavenging effect is strong, and scavenging marks are generated in the halftone area, resulting in image quality. It is because there is a possibility of lowering. The doctor 9 is made of a rigid and magnetic material. As the developing sleeve 7, one in which grooves extending along the width direction orthogonal to the circumferential direction are respectively formed at a plurality of different locations in the circumferential direction of the surface is used. Furthermore, a magnet is used in which the normal direction magnetic flux density by the magnetic pole of the magnet in the sleeve at the surface of the developing sleeve 7 facing the doctor 9 is in the range of 45 [mT] to 70 [mT]. Yes.

  In the present embodiment, the carrier has a small particle size for high image quality. Carrier adhesion deteriorates as the particle size of the carrier decreases, so the magnetization of the carrier is increased to prevent this. A magnetic doctor 9 having rigidity and magnetism was used to improve the charging start-up property. Since the magnetic doctor and the carrier having a large magnetization are combined, the developer holding force in the doctor 9 is increased. In this case, when the conveying force of the developing sleeve 7 is small, the developer slips on the sleeve, the developer amount on the developing sleeve (hereinafter referred to as the pumping amount) is uneven, and a uneven image is generated.

Therefore, a groove is formed on the surface of the developing sleeve 7 to increase the developer conveying force. As a method for increasing the conveying force on the surface of the developing sleeve, it is considered to increase the surface roughness of the sleeve by sandblasting or the like. However, since the sleeve surface is worn over time and the conveying force is likely to decrease, groove formation that can obtain a stable conveying force over time is adopted.
The method for measuring the saturation magnetization of the carrier is as follows. As a measuring device, a BHU-60 type magnetization measuring device (manufactured by Riken Measurement) is used. About 1.0 [g] of the measurement sample is weighed and packed in a cell having an inner diameter of 7 [mm] φ and a height of 10 [mm], and set in the apparatus. Then added the applied magnetic field is gradually ^{1 × 10 6 / 4π [A} / m] (1k [Oe]) to alter obtains the magnetization in ^{1 × 10 6 / 4π [A} / m] (1k [Oe]).

As described above, in this embodiment, the magnetic carrier has a weight average particle diameter of 20 [μm] or more and 60 [μm] or less, and a saturation magnetization of 66 in a 1 × 10 ⁶ / 4π [A / m] magnetic field. A developer amount regulating member of × 10 ⁻⁷ × 4π [Wb · m / kg] or more was used and made of a magnetic and rigid material, and a plurality of grooves were provided on the developer sleeve. As a result, image unevenness due to carrier adhesion and pumping unevenness can be prevented at the same time, so that the particle size of the carrier is reduced and the distance between the latent image carrier and the developer carrier is narrowed for higher image quality. In this case, it is possible to stably form high-quality images by suppressing white spots on the image due to carrier adhesion to the latent image carrier and unevenness on the image due to changes in the developer amount on the developer carrier. it can.

  In the developing device 1, a toner having a volume average particle size of 3 [μm] or more and 8 [μm] or less is used. Further, inorganic fine particles are added as an additive to the toner. The average particle size of the inorganic fine particles is preferably 30 [nm] or more and 160 [nm] or less. Any conventionally known resin can be used as the binder resin for the toner. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene substitution product) such as styrene-acrylonitrile-acrylic acid ester copolymer, polyester resin, epoxy resin, and the like can be given. Moreover, although single use is also possible, you may use 2 or more types together. The method for producing these resins is not particularly limited, and any of bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization can be used. For oilless fixing, oxidized rice wax, low molecular weight polypropylene wax, carnauba wax or the like can be used as a release agent. You may contain a charge control agent as needed.

In the present embodiment, the toner has a small particle size for high image quality. Here, an experimental example regarding the volume average particle diameter of the toner and the fluidity of the developer will be described with reference to FIG. In the figure, the flow rate [s] of the developer is plotted against the weight concentration [wt%] of the toner in the developer using toners having various volume average particle diameters. The fluidity was determined by the method for measuring the fluidity of metal powder in JIS Z2502. More specifically, the developer 50 [g] was set in a funnel having a diameter of 5 [mm], the weight was dropped from this hole, and the time from the outflow to the end was obtained. Accordingly, as the value of the fluidity becomes smaller, the fluidity becomes better.
As can be seen from FIG. 2, the fluidity [s] increases as the weight concentration value of the toner increases, and the fluidity of the developer deteriorates. It can also be seen that, when the toner weight concentration is constant, the fluidity increases as the volume average particle diameter of the toner decreases, and the fluidity of the developer deteriorates.
Therefore, when reducing the particle size of the toner for the purpose of improving the image quality, there arises a problem that unevenness in the amount of the developer drawn up is likely to occur compared to a toner having a larger particle size.

  Another problem associated with the reduction in the toner particle size is that the cleaning removal performance of the toner remaining on the photoreceptor deteriorates. As an example, consider a case where a cleaning blade method is employed as a cleaning device that removes toner remaining on the photoreceptor. When the toner has a small particle size, the toner passing through the cleaning blade (passing through) increases as compared with a toner having a larger particle size. As a result, the cleaning removal performance for the toner is deteriorated. Further, the amount of wear of the cleaning blade increases, and the life of the cleaning blade (cleaning member) is shortened.

As a technique for avoiding these problems of poor cleaning and shortening the life of the cleaning member, it is effective to add inorganic fine particles as an additive to the toner.
However, when inorganic fine particles are added to the toner, a new problem has arisen in that the amount of developer drawn up decreases with time. An experimental example for explaining this will be described with reference to FIG. In this figure, the developer pumping amount [mg / cm ² ] is plotted against the number of image formation [K] for the sample in which inorganic fine particles are added to the toner and the sample without addition.
From FIG. 3, it can be seen that the toner to which inorganic fine particles are not added hardly changes in the pumping amount, whereas the toner to which inorganic fine particles are added decreases the pumping amount of the developer with time.

  Therefore, in this embodiment, as described above, a groove is formed on the surface of the developing sleeve 7 to increase the developer conveying force. As a result, unevenness in the pumping amount of the developer due to the reduction in the particle size of the toner can be prevented, and changes in the pumping amount of the developer over time due to the addition of inorganic fine particles can be suppressed.

  In this embodiment, a toner having a volume average particle diameter of 3 [μm] or more and 8 [μm] or less is used as the toner, and the average particle diameter of inorganic fine particles added to the toner is 30 [nm] or more and 160 [nm]. The following were used. As described above, a plurality of grooves were provided on the developing sleeve. As a result, as described above, it is possible to prevent uneven developer pumping that tends to occur when using a toner having a small particle diameter, to prevent poor cleaning and to shorten the life of the cleaning member, and to achieve high image quality. Can do. In addition, it is possible to prevent changes in the amount of developer pumped over time.

  The developing device 1 is desirably used with a PG in the range of 0.2 to 0.4 [mm]. By narrowing the PG to 0.4 [mm] or less, it was possible to improve image quality such as graininess and missing characters. Character edge missing, solid / line adhesion amount ratio (ratio of toner adhesion amount to solid patch portion and line portion adhesion amount, closer to 1 is better) and the like are worse as the edge effect is larger. It is known that the edge effect can be reduced by reducing the distance between the developing sleeve and the photosensitive member (hereinafter referred to as PG). By reducing PG, the electric field strength can be increased, dot reproducibility is improved, and graininess is also improved. If the width is less than 0.2 mm, the developer is packed in the development area, and there is a problem such as toner sticking to the development sleeve, and a problem such as the development sleeve and the photoconductor flare. Because it occurs. When the developing sleeve without a groove having a small conveying force is used in a narrowness of 0.4 [mm] or less, the pumping amount unevenness becomes relatively large and image unevenness is likely to occur. Such a problem is avoided by using the developing sleeve 7 having a relatively high conveying force of the developer having a groove.

Further, the developing device 1 has a coating film which is the carrier and has at least a binder resin and particles, and the particle diameter (D) and the binder resin film thickness (h) are 1 <[D / H] <10, preferably 1 <[D / h] <5. In such a carrier, since the particles are more convex than the coating film, a strong impact is applied to the binder resin due to friction with the toner or friction between the carriers by agitation for frictionally charging the developer. The accompanying contact can be mitigated. As a result, it is possible to prevent the toner spent on the carrier and to prevent the binder resin film from being charged. Therefore, the carrier surface shape change with time is small, and the durability can be greatly improved. That is, the life of the developer can be extended. Since the change in the surface shape with time is small, the change in the pumping amount (developer amount per unit area passing through the doctor blade) with time is small, and the developer can be stably supplied onto the developing sleeve 7. Thereby, a stable image can be supplied. When [D / h] is 1 or less, the particles are buried in the binder resin, which is not preferable because the effect is remarkably lowered. When [D / h] is 10 or more, the contact area between the particles and the binder resin is small, so that a sufficient restraining force cannot be obtained and the particles are easily detached. Further, Patent Document 9 cited in the above prior art discloses a carrier in which conductive particles larger than the coating resin film thickness are contained in the coating film. This known carrier is conductive because the particles are used as a conductive path so as not to increase the resistance of the carrier. In the present embodiment, the particles are not used as a resistance adjusting material in this way, but as a protective material for the coating film resin and a surface shape adjusting material. Accordingly, a material having a volume resistivity in the range of 10 ⁹ to 10 ¹⁴ [Ωcm], preferably in a range of 10 ¹² to 10 ¹³ [Ωcm] is used. Further, the carrier core material is 20 [μm] (average particle diameter) or more from the viewpoint of preventing carrier adhesion (scattering) to the photoreceptor 1, and from the viewpoint of preventing image quality deterioration such as prevention of carrier streaks. The thing within the range of 100 [micrometers] or less is used. Specific materials that are known as two-component carriers for electrophotography, such as ferrite, magnetite, iron, nickel, etc., may be appropriately selected according to the use and purpose of use of the carrier.

〔Example〕
Next, the effects of the present invention will be specifically described with reference to examples and comparative examples. However, it goes without saying that the present invention is not limited to these examples.
The machine fixing conditions of the full-color printer used in the examples and comparative examples are as follows.
<Example machine conditions>
Photoconductor linear speed 350 (mm / sec)
Development sleeve linear velocity 700 (mm / sec)
Photoconductor diameter 60 (mm)
Pumping amount 50 (mg / cm2)
Sleeve diameter Φ25 (mm)
Main pole angle 6 °
Main pole magnetic flux density (P1) 120 (mT)
Main pole downstream pole magnetic flux density (P2) 110 (mT)
Charging potential VD -600 (V)
Post-exposure potential VL-60 (V)
Development bias Vb -430 (V)
The main pole magnetic flux density and the main pole downstream pole magnetic flux density (P2) are magnetic flux densities in the normal direction on the surface of the developing sleeve.
Further, a magnet was used in which the normal direction magnetic flux density by the magnetic pole of the magnet in the sleeve at the surface of the developing sleeve 7 facing the doctor 9 is in the range of 45 [mT] to 70 [mT]. . Experiments when the magnets are variously changed will be described in detail later.

Moreover, the magnetic flux density was measured by a sleeve abutting method using a magnetic force distribution measuring device (excel system product 3D magnetic measuring device) and a gauss meter (manufactured by ADS). .
The developing sleeve is V-grooved. The developer amount regulating member is a rigid and magnetic material. The developer amount regulating member is not limited to a metal material such as iron or stainless steel, but may be composed of a resin material containing magnetic particles such as ferrite or magnetite. Further, the developer amount regulating member itself is not made of a magnetic material, and another member such as a metal plate made of a magnetic material is directly or indirectly fixed to the developer amount regulating member. Similar effects can be obtained.

<Example carrier>
Acrylic resin solution (solid content 50 wt%) 56.0 parts guanamine solution (solid content 77 wt%) 15.6 parts alumina particles [0.3 [μm], specific resistance 10 ¹⁴ (Ω ·) 160.0 parts toluene 900 parts butyl cellosolve 900 parts are dispersed with a homomixer for 10 minutes to prepare a coating film forming solution, and a sintered ferrite powder having a predetermined average particle diameter is used as a core material so that the film thickness is 0.15 [μm]. It was applied and dried with a Spira coater (Okada Seiko Co., Ltd.). The obtained carrier was baked by standing in an electric furnace at 150 ° C. for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 [μm] to obtain a carrier.
Note that the ratio D / h of the particle diameter D = 0.3 [μm] of the particles contained in the coating film of the magnetic carrier of Example and the binder resin film thickness h = 0.15 [μm] is 2.

<Comparative carrier>
Acrylic resin solution (solid content 50% by weight) 56.0 parts Guanamin solution (solid content 77% by weight) 15.6 parts Toluene 900 parts Butyl cellosolve 900 parts are dispersed with a homomixer for 10 minutes to prepare a coating film forming solution. Then, a fired ferrite powder having a predetermined average particle diameter was used as a core material, which was applied by a Spira coater (manufactured by Okada Seiko Co., Ltd.) so as to have a film thickness of 0.15 [μm] and dried. The obtained carrier was baked in an electric furnace at 150 [° C.] for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve having an opening of 100 [μm] to obtain a carrier. The measurement of the binder resin film thickness was performed by observing the cross section of the carrier with a transmission electron microscope so that the coating film covering the carrier surface could be observed.
Note that the coating film of the comparative carrier does not contain particles. Therefore, the ratio D / h of the particle diameter D of the particles contained in the coating film shown in the example magnetic carrier and the binder resin film thickness h cannot be applied to the comparative example carrier.

表１より、本実施例は、比較例に対して、小粒径キャリアを使用した場合でも、感光体へのキャリア付着、汲み上げ量ムラによる画像濃度ムラもなく、文字周辺抜け、粒状性なども優れており、高画質、かつ、安定した画像形成装置を提供できることがわかる。 In the above machine, the carrier adhesion, the image density unevenness, the graininess, and the character peripheral missing were evaluated under the conditions shown in Table 1. The results are also shown in Table 1. In the table, ◎ indicates very good, ○ indicates good, Δ indicates bad, and × indicates very poor.

As shown in Table 1, the present embodiment has no image density unevenness due to carrier adhesion to the photosensitive member, uneven pumping amount even when a small particle size carrier is used as compared with the comparative example, and there is no character peripheral missing, graininess, etc. It can be seen that an image forming apparatus that is excellent, has high image quality, and is stable can be provided.

表２より、小粒径トナーを使用した場合において、トナーへの無機微粒子の添加、現像スリーブに複数の溝を設けることにより現像剤の汲み上げ量の経時的低下を抑制し、クリーニングブレードの経時的磨耗を抑制できることがわかる。 In addition, the amount of pumping and the abrasion of the cleaning blade were evaluated based on the toner volume average particle size and the presence or absence of inorganic fine particles added to the toner and the presence or absence of grooves on the sleeve surface. Other conditions are the same as in Example 1 in Table 1 above. The results are shown in Table 2. In the table, ◎ indicates very good, ○ indicates good, Δ indicates bad, and × indicates very bad.

Table 2 shows that when a small particle size toner is used, the addition of inorganic fine particles to the toner and the provision of a plurality of grooves in the developing sleeve suppress the decrease in the pumping amount of the developer over time, and the cleaning blade over time. It can be seen that wear can be suppressed.

  Further, as shown in FIG. 4, a carrier having a coating film having at least a binder resin and particles in which the particle diameter (D) and the binder resin film thickness (h) are 1 <[D / h] <10 is used. In this case, it can be seen that the decrease in the charge amount accompanying the toner fusion to the carrier surface is reduced, and the lifetime of the developer can be increased. That is, FIG. 4 shows the change in the charge amount during running for each of the cases where the carrier C1 where 1 <[D / h] <10 and the comparative example carrier C2 used in this embodiment are used. It is the result shown by the ratio when the quantity is 1. The decrease in the charge amount is caused by toner spent on the carrier during running. If the charge amount is 0.8 or less of the initial charge amount, that is, if the decrease rate exceeds 20%, an image problem occurs. As shown in FIG. 4, in the carrier C1 where 1 <[D / h] <10, the charge amount exceeded the initial 0.8 even when the running number was 100K. On the other hand, in the carrier C2, the charge amount became 0.8 or less at the beginning before the running number reached 100K. As a result, the carrier of this example having a coating film having at least a binder resin and particles, in which the particle diameter (D) and the binder resin film thickness (h) are 1 <[D / h] <10, The resulting decrease in charge amount can be suppressed. The upper limit of the value of D / h is more preferably 5 from the viewpoint of avoiding particle detachment.

Next, a magnet whose normal magnetic flux density by the magnetic pole of the magnet in the sleeve at the surface of the developing sleeve 7 facing the doctor 9 is in the range of 45 [mT] to 70 [mT] is used. If so, a comparative experiment with the other case will be described. In this experiment, the carrier of the example was used under the mechanical conditions of the example, and the volume average particle size was 5.5 [nm] as the toner. To this toner, an external additive of 1.5% by weight of silica, which is inorganic fine particles, and 0.75% by weight of titanium oxide was added. The particle size of silica is 100 [nm].
In the above machine, 60K running evaluation was performed, and the presence or absence of a streak image and the toner spent on the carrier were evaluated. The results are shown in Table 3. In the table, ◎ indicates very good, ○ indicates OK (no streaking, transmittance: 90% or more), and x indicates NG (streaking, transmittance: 90% or less). From Table 3, by setting the magnetic flux density of the doctor-facing magnetic pole to 45 to 70 mT, it is possible to achieve both foreign matter on the doctor, that is, developer deterioration. As can be seen from Table 3, it is a doctor gap of 0.35 mm or more that foreign matter or the like is not easily caught in the doctor gap.
The spent was evaluated by adding 10 g of a solvent (MEK) to 1 g of the carrier from which the toner was removed from the developer, shaking 80 times, and then using a turbidimeter (poic simple type integrating sphere turbidimeter SEP-PT type). The transmittance of the solvent is measured, and the smaller the value, the worse the spent of toner. A transmittance of 90% was taken as an OK line.

  FIGS. 5A and 5B are explanatory views of the developer holding force due to the magnetic force of the doctor 9. (A) is a relatively weak case, and (b) is a relatively strong case. The amount of the carrier 10b held in (b) is larger than that of the carrier 10a held in (a). Not only on the surface of the doctor 9 itself but also on this held carrier, it exerts a regulating force against passage of the doctor gap. As the amount increases as shown in (b), the stress on the passing developer by the held carrier also increases. P1 is a magnet that constitutes a main pole that generates a magnetic field in the developing area with respect to the photoconductor 8, and P4 is a magnet facing the doctor 9. P2 to P3 and P5 are transfer magnets and the like.

1 is a schematic configuration diagram of a developing device used in an image forming apparatus according to an embodiment. The figure which plotted fluidity [s] versus toner weight concentration [%]. The figure which showed the time-dependent change of the developer pumping amount by the presence or absence of inorganic fine particle addition. The graph which showed the change of the charge amount at the time of running about each of Example carrier C1 and Comparative example carrier C2. (A) And (b) is explanatory drawing of the developer retention strength by the magnetic force of the doctor 9. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing apparatus 2 Toner hopper 3 Toner flow apparatus 4 Developer accommodating part 5 1st stirring screw 6 2nd stirring screw 7 Developing sleeve 8 Photoconductor 9 Doctor

Claims (4)

A latent image carrier on which an electrostatic latent image is formed; and
A two-component developer composed of toner and a magnetic carrier is carried on a developer carrier that is opposed to the latent image carrier, has a magnet inside, and is supported so that the peripheral surface thereof can circulate. The amount of developer carried by the substrate is regulated and transported to a portion facing the latent image carrier, and a developing electric field is applied between the latent image carrier and the developer carrier to cause electrostatic charge on the latent image carrier. In an image forming apparatus including a developing device that visualizes a latent image with toner,
The magnetic carrier has a weight average particle diameter of 20 [μm] or more and 60 [μm] or less,
The saturation magnetization of the magnetic carrier in a 1 × 10 ⁶ / 4π [A / m] magnetic field is 66 × 10 ⁻⁷ × 4π [Wb · m / kg] or more,
The developer amount regulating member is made of a material having rigidity and magnetism,
The developer carrier is formed with grooves extending along a width direction orthogonal to the circumferential direction, respectively, at a plurality of different locations in the circumferential direction of the surface,
An image forming apparatus having a normal magnetic flux density of 45 [mT] or more and 70 [mT] or less by a magnetic pole of the magnet at a surface portion of the development carrier facing the developer amount regulating member . The image forming apparatus according to claim 1.
The volume average particle diameter of the toner is 3 [μm] or more and 8 [μm] or less,
An image forming apparatus, wherein an average particle diameter of inorganic fine particles added to the toner is 30 [nm] or more and 160 [nm] or less. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein a distance between the latent image carrier and the developer carrier is 0.2 [mm] or more and 0.4 [mm] or less. The image forming apparatus according to claim 1, 2 or 3.
The carrier has a coating film having at least a binder resin and particles, and the particle diameter (D) and the binder resin film thickness (h) satisfy a relationship of 1 <[D / h] <10. An image forming apparatus.

Images