JP2002287502A - Developing roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing roller having a developing pole uniformly and highly concentratedly filled with magnetic powder at low pressure. SOLUTION: An additive consisting of the component of the magnetic powder different from the lubricating magnetic powder is dispersed in the magnetic powder compressed in a housing groove 49, and the average particle size of the additive is smaller than that of the magnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., and a developing roller of a developing device mounted on the image forming apparatus.

[0002]

2. Description of the Related Art Magnetic brush development using a two-component developer in electrophotography and other image forming methods using powder toner is well known and widely used in image forming apparatuses.

In this magnetic brush development, a magnetic brush is formed by magnetically adsorbing a developer on an outer peripheral surface of a developing roller, and a magnetic brush is formed in a developing area (an area where a developable electric field is secured between the developing roller and the image carrier). An electric field between the image carrier on which the electrostatic latent image is formed and the sleeve to which an electric bias is applied, selectively supplying and attaching toner from the magnetic brush to the latent image surface of the opposite image carrier. Thereby, development is performed.

The developing roller is usually formed as a cylindrical sleeve (developing sleeve), and has a magnet body (magnet roller) inside the sleeve which forms a magnetic field so as to cause the developer to spike on the surface of the sleeve. ing. When the ears are raised, the carrier is raised on the sleeve so as to follow the lines of magnetic force generated by the magnet roller, and the charged toner is attached to the carrier related to the raised ears. The magnet roller has a plurality of magnetic poles, and the magnets forming the respective magnetic poles are formed in a rod shape or the like. In particular, the developing roller is provided with a developing main magnetic pole for starting up a developer in a developing region on the sleeve surface. By moving at least one of the sleeve and the magnet roller, the developer that has raised ears on the sleeve surface moves, and the developer conveyed to the developing area moves along the magnetic force lines generated from the developing main magnetic pole. The chain of the developer contacts the surface of the image carrier so as to bend, and the chain of the contacted developer rubs against the electrostatic latent image based on the relative linear velocity difference with the image carrier. While
Supply toner.

In the conventional magnetic brush developing device, the developing condition for increasing the image density and the developing condition for obtaining a good contrast image are incompatible, and both the high density portion and the low density portion are simultaneously used. Difficult to improve. That is, the developing conditions for increasing the image density include (i)
For example, the developing gap, which is the distance between the image carrier and the developing sleeve, may be reduced, or (ii) the width of the developing area may be increased. On the other hand, developing conditions for obtaining a low-contrast image favorably include (i ′) widening the developing gap or (ii ′) narrowing the developing area width. In other words, both development conditions are opposite and incompatible, and it is generally difficult to satisfy both conditions over the entire density range to obtain a good quality image.

For example, when emphasis is placed on a low-contrast image, a so-called “back-end blank area” in which a blank portion occurs at a cross portion of a solid line, a black solid area, or a rear end section of a half-tone solid image.
An abnormal image called “image” easily occurs. Further, such a phenomenon that a horizontal line of a grid image formed with the same width becomes thinner than a vertical line, and a small point image such as one dot is not developed has occurred.

[0007] The development conditions for increasing the image density and the development conditions for obtaining a low-contrast image, which have been problems in the past, are satisfied at a high point in time, and a high-quality image can be obtained over the entire density range. The applicant of the present application has previously proposed a developing method and a developing device for obtaining the same (Japanese Patent Application 200
0-29637).

[0008]

However, in the developing device proposed by the applicant of the present invention, since the angle between the main poles of the developing roller is narrower than that of the conventional developing roller, it is difficult to use magnet material. High magnetic properties are required.
In addition, the accuracy of the main pole portion is required to be higher than that of the conventional developing roller (± 1 ° for the conventional ± 2 °).

[0009] In order to achieve these requirements, it is difficult to implement the conventional materials, the roller configuration and the manufacturing method. In particular, with respect to the magnet material, sufficient magnetic properties cannot be obtained with a generally used ferrite-based magnet, which is difficult to achieve, and a rare-earth magnet must be used. Further, since rare earth magnets are expensive, as a practical magnet configuration of the roller, it is desirable to use a rare earth magnet only for the developing pole requiring high magnetic properties and use a ferrite magnet for the other poles.

Here, a conventional method for manufacturing a developing roller will be described. Manufacturing method A: As shown in FIG. 1, a method of attaching a sintered magnet 68 to a holder 66 integrated with a cored bar 67. As a merit, the position accuracy of the magnetic poles is good. High and man-hours increase.

Manufacturing method B: As shown in FIG.
This method has the advantage that the cost of the core metal is lower than that of the manufacturing method A, but has the disadvantage that the magnetic pole position accuracy is not high and that the number of steps is increased as in the manufacturing method A.

Manufacturing method C: As shown in FIG. 3, a rare earth magnet 68 is attached to a ferrite magnet molded product 66. The ferrite magnet 66 can be formed by injection molding or extrusion molding. It has an integral shape in the circumferential direction. As an advantage of injection molding, a high magnetic force can be easily obtained, and relatively stable characteristics such as a magnetic pole position can be obtained. However, the equipment is complicated and processing tact is required. As an advantage of the extrusion molding, although the processing tact is short, as a disadvantage, it is difficult to control the characteristics of the molded product.

Manufacturing method D: As shown in FIG. 4, a rare earth magnet 68 is attached to a ferrite magnet molded product 66 via a non-magnetic holder 71. High accuracy can be achieved.

However, as in the case of the above-mentioned production, there remains a problem that the processing accuracy of the molded rare earth magnet is not sufficient, the mechanical strength is not sufficient, and the cost is high. The developing roller has a long width of about 30 cm, and is 30 cm long.
Uniform dimensional accuracy is required over the entire length. Sintered rare earth magnets are limited to a length of 10 cm,
Molding of 0 cm width is not feasible. A compression molded product using an epoxy resin is also difficult to be long, and a size of 30 cm cannot be realized.

Extrusion molding and injection molding can be made long, but the mechanical strength is not sufficient, and there is a problem that the magnet is easily broken at the time of sticking. Generally, in order to achieve a high magnetic force, it is important to increase the filling rate of the magnetic powder in the plastic magnet. Magnet content is 80
Since it is at least wt%, the mechanical strength, particularly the bending strength, is very weak.

In view of this, it has been proposed to directly fill the groove corresponding to the developing pole with the magnet powder and perform compression molding. In this method, as is clear from the graph of FIG. 5, the packing density and the magnetic flux density are in a substantially proportional relationship, and therefore, in order to achieve both high magnetic force and magnetic pole accuracy, the packing density of the magnet powder is increased. .

However, in order to increase the packing density of the magnet powder, the pressure during compression molding must be increased. However, increasing the pressure causes various adverse effects. Filling has been desired.

The present invention has been made in view of the above circumstances, and has as its object to provide a developing roller having a developing pole in which magnetic powder is uniformly and highly filled at a low pressure.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, the present invention provides a cylindrical developing roller comprising a plastic magnet in which a magnetic powder is dispersed in a polymer compound, wherein at least one developing pole of the developing member is provided. In a developing roller in which a groove-shaped storage portion is provided in a corresponding portion, and magnet powder is compression-molded and embedded in the storage portion, the magnetic powder compressed in the storage portion includes lubrication of the magnetic powder. An additive comprising a component different from the magnetic powder to be formed is dispersed, and the average particle size of the additive is smaller than the average particle size of the magnetic powder.

According to another aspect of the present invention, there is provided a cylindrical developing roller made of a plastic magnet in which a magnetic powder is dispersed in a polymer compound. A groove-shaped storage portion is provided in a portion corresponding to the pole, and a holder made of a non-magnetic material having a groove-shaped storage portion is embedded in the storage portion, and the magnetic powder is compressed in the storage portion of the holder. In the molded and embedded developing roller, an additive composed of a component different from the magnetic powder for lubricating the magnetic powder is dispersed in the magnetic powder compressed in the storage portion, and the average particle size of the additive is adjusted. It is characterized in that the diameter is smaller than the average particle diameter of the magnetic powder.

In the present invention, it is effective if the additive dispersed in the magnetic powder comprises PTFE particles. Further, in the present invention, it is effective if the magnetic powder is finely pulverized to have an average particle diameter of 50 μm or less.

Furthermore, in the present invention, it is effective if the surface of the magnetic powder is coated with an ultraviolet curable adhesive and is adhered to the plastic magnet or holder.

[0023]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. First, an image forming unit of an image forming apparatus equipped with a developing device according to the present invention will be described with reference to FIG.

In FIG. 1, a charging device 2 for charging the surface of a photosensitive drum 1, which is an electrostatic latent image carrier, and a laser beam for forming a latent image on a uniformly charged surface. A developing device 4 for forming a toner image by attaching charged toner to a latent image on the drum surface;
A transfer device 5 for transferring the formed toner image on the drum onto the recording paper, a cleaning device 7 for removing the residual toner on the drum, and a static elimination lamp 8 for removing the residual potential on the drum are arranged in this order. Has been established.

In such a configuration, the photosensitive member 1 whose surface is uniformly charged by the charging roller of the charging device 2 is
The exposure 3 forms an electrostatic latent image, and the developing device 4 forms a toner image. The toner image is transferred from the surface of the photosensitive drum 1 to recording paper conveyed from a paper feed tray (not shown) by a transfer device 5 including a transfer belt or the like. The recording paper electrostatically attached to the photosensitive drum at the time of this transfer is separated from the photosensitive drum 1 by a separation claw. The unfixed toner image on the recording paper is fixed on the recording paper by the fixing device 9. On the other hand, the toner remaining on the photosensitive drum without being transferred is removed and collected by the cleaning device 7. The photosensitive drum 1 from which the residual toner has been removed is initialized by the discharge lamp 8, and is used for the next image forming process. Reference numeral 6 denotes a registration roller for sending recording paper from a paper feed tray (not shown) in synchronization with the toner image on the photoconductor 1.

In the developing device 4, a developing roller 41, which is a developing roller, is disposed so as to be close to the photosensitive drum 1, and a developing area where the photosensitive drum and the magnetic brush are in contact is provided at both opposing portions. Are formed. Developing roller 4
Reference numeral 1 denotes a developing sleeve formed by forming a non-magnetic material such as aluminum, brass, stainless steel, or a conductive resin into a cylindrical shape, and is rotated clockwise in the figure by a rotation driving mechanism (not shown). Reference numeral 42 denotes a doctor blade for regulating the height of the developer chain, ie, the amount of the developer on the developing sleeve, reference numeral 43 denotes an inlet seal member, and reference numeral 44.
Reference numeral denotes a screw for pumping the developer in the developing device casing to the developing roller 41 while stirring the developer.

The developing roller 41 is provided with a magnet body (hereinafter, referred to as a magnet roll 46) that forms a magnetic field so as to cause the current agent to spike on the peripheral surface of the developing sleeve 45 in a fixed state. The magnet roll 46 has a main magnetic pole that causes the developer to spike in the development area, a transport pole for transporting the pumped developer to the development area,
And a transport pole for transporting the developer in the area after the development. In the present embodiment, the main magnetic pole is formed by one magnet 48, but a plurality of magnets 48 (two poles or three
The developing pole may be formed by the (pole) magnet block. When the main magnetic pole is formed by one magnet 48, the half width of the main magnetic pole is set to 25 ° or less, and the attenuation rate of the magnetic flux density in the normal direction of the developing magnetic pole is set to 40% or less.
Note that the half width is an angular width of a portion indicating a half value of the highest normal magnetic force (apex) of the magnetic force distribution curve in the normal direction of the developing main magnetic pole. If the maximum normal magnetic force is 120 mT, it is the angular width of the portion indicating a value of 60 mT. Further, the attenuation rate of the magnetic flux density in the normal direction of the developing magnetic pole is a numerical value representing how much the magnetic flux density y in the normal direction at a portion 1 mm away from the surface of the developing roller has decreased with respect to the magnetic flux density x in the normal direction ( xy) ÷ xx
For example, when the magnetic flux density in the normal direction on the surface of the developing roller is 100 mT, and the magnetic flux density in the normal direction at a portion 1 mm away from the surface of the developing roller is 80 mT, the attenuation rate is 20%.
%.

FIG. 2 is an explanatory view of a developing roller according to an embodiment of the present invention. In this embodiment, the magnet 48 has a single main magnetic pole. In FIG. 2, a developing roller 41 is a plastic magnet or a rubber magnet in which a magnet roller 46 is a polymer compound in which magnetic powder is dispersed, and uses Sr ferrite or Ba ferrite as magnetic powder and 6P as a polymer compound.
PA (polyamide) based material such as A or 12PA, E
Ethylene compounds such as EA (ethylene / ethyl copolymer) or EVA (ethylene / vinyl copolymer), CPE
Chlorine-based materials such as (chlorinated polyethylene) and rubber materials such as NBR can be used. A storage groove 49 is formed in the magnet roller 46 as a storage part in which another member can be embedded in a part corresponding to the development pole 48 of the cylindrical development roller. The storage groove 49 is used to lubricate magnetic powder. The magnetic powder in which an additive composed of a component different from the magnetic powder to be dispersed is filled and compression-molded to form a developing electrode 48.

In general, powder compaction tends to become porous due to large or small agglomeration caused by low fluidity, and it is necessary to devise measures such as finer particles and increased pressure. According to this embodiment, since the additive improves the slipperiness between the magnetic powders, the fluidity is high, and no void due to aggregation or the like is generated even at a low pressure. In addition, if the particle size of the additive is sufficiently smaller than the particle size of the magnetic powder, it does not hinder the gap between the magnetic powders and hinders the filling rate of the magnetic powder. Therefore, as a result, a more ideal high-density filling can be performed at a low pressure as compared with a filling state due to aggregation or the like which occurs when only the magnetic powder is used, whereby the developing pole 48 can obtain high magnetic characteristics.

In another embodiment of the present invention, as shown in FIG. 3, a holder 50 made of a non-magnetic material and having a storage groove 51 formed at a position where the developing pole 48 of the magnet roller 46 is disposed. I have. A magnetic powder in which an additive composed of a component different from the magnetic powder to be lubricated with the magnetic powder is filled in a storage groove 51 formed in the holder 50 and compression molded to form a developing pole 48.

According to this configuration, since the magnet is molded in the holder 50, if a strong holder material is used, the pressure can be increased as compared with the case of directly filling the developing roller. Filling becomes possible, and higher magnetic properties can be obtained.

In the above embodiment, PTFE particles are used as an additive dispersed in the magnetic powder. PTFE has a surface energy having any solid with a very large slip properties very small. Therefore, if PTFE particles are used as an additive, higher fluidity of the magnetic powder mixture can be ensured, so that the filling rate can be increased at low pressure and high magnetic properties can be obtained.

The magnetic powder used has an average particle diameter of 50 μm or less. The average particle size greatly contributes to the filling rate when the same pressure is applied, and when the average particle size is 200 to 300 μm when the pressure is 500 kg · cm ² , the average particle size is 3.2 to 3.5 g / c.
m ³ , 5.0 to 5.3 g / c with an average particle size of 50 to 30 μm
m ³ , 5.5 to 5.7 g / c with an average particle size of 10 to 30 μm
smaller and m ³ can be obtained a high filling rate.

Further, rare-earth magnets, particularly rare-earth-iron magnets, are extremely rusty, have poor touch resistance, and have a property of easily falling off. For this reason, as shown in FIGS. 2 and 3, the surface of the developing electrode 48 of the compression-molded rare earth magnet powder is coated with an ultraviolet curable adhesive 52, and the developing electrode 48 and the developing roller are bonded. .

[0035]

As described above, according to the present invention,
Since high-magnetism magnetic powder such as a rare-earth magnet can be directly molded integrally with the developing roller, the number of production steps can be reduced and a low-cost developing roller can be achieved. Furthermore, since the magnetic powder mixture having high fluidity is compression-molded by adding an additive to the groove portion of the developing roller, it is possible to integrally mold a magnet having a very uniform and high filling ratio even at a low pressure. A magnetic developing roller can be obtained.

Further, when magnet powder is formed on a non-magnetic holder, the compression pressure can be increased, the packing density can be further improved, and a magnet having a high magnetic force can be molded, so that the magnet thickness can be reduced. Roller design latitude is expanded. Also,
Since the pole position of the magnet can be adjusted when the magnetic holder is fixed and bonded, a highly accurate pole position can be secured.

Further, since the additive has a very high sliding property to the magnetic powder, the fluidity of the magnetic powder mixture is very high, and the filling rate can be further increased, so that a developing roller having high magnetic properties can be obtained. Can be.

Further, by setting the average particle diameter of the magnet powder to be equal to or less than the set value, the packing density can be increased even at a low compression pressure. Further, since the magnetic powder and the developing roller or the non-magnetic holder can be bonded with the ultraviolet curing adhesive, a highly reliable developing roller can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the vicinity of an image forming unit of an image forming apparatus equipped with a developing device according to the present invention.

FIG. 2 is an explanatory diagram of a developing roller according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a developing roller according to another embodiment of the present invention.

FIG. 4 is an explanatory view of a developing roller according to a conventional manufacturing method.

FIG. 5 is an explanatory view of a developing roller according to another conventional manufacturing method.

FIG. 6 is an explanatory view of a developing roller according to still another conventional manufacturing method.

FIG. 7 is an explanatory view of a developing roller according to still another conventional manufacturing method.

FIG. 8 is a graph showing a relationship between a packing density and a magnetic flux density.

[Explanation of symbols]

 Reference Signs List 41 developing roller 45 developing sleeve 46 magnet roll 48 magnet 49 storage groove 50 holder 51 holder storage groove 52 ultraviolet curing adhesive

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Sumio Kamoi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Noriyuki Kamiya 1-3-6 Nakamagome, Ota-ku, Tokyo Stock In Ricoh Company (72) Inventor Mieko Kakegawa 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Company (reference) 2H031 AC11 AC14 AC18 AC19 AC20 AC30 AD01

Claims (5)

[Claims] 1. A cylindrical developing roller comprising a plastic magnet in which a magnetic powder is dispersed in a polymer compound, and a groove-shaped housing part in a part corresponding to at least one developing pole of the structural member. In the developing roller in which the magnetic powder is compression-molded and embedded in the storage portion, the magnetic powder compressed in the storage portion includes a component different from the magnetic powder that lubricates the magnetic powder. Additives are dispersed,
And a developing roller wherein the average particle size of the additive is smaller than the average particle size of the magnetic powder. 2. A cylindrical developing roller composed of a plastic magnet in which a magnetic powder is dispersed in a polymer compound, and a groove-shaped housing part is provided at a portion corresponding to at least one developing pole of the structural member. Is provided, a holder made of a non-magnetic material having a groove-shaped storage portion formed therein is embedded in the storage portion, and a magnet roller is compression-molded and embedded in the storage portion of the holder. In the magnetic powder compressed in the storage portion, additives composed of components different from the magnetic powder to lubricate the magnetic powder are dispersed,
A developing roller wherein the average particle size of the additive is smaller than the average particle size of the magnetic powder. 3. The developing roller according to claim 1, wherein the additive dispersed in the magnetic powder comprises PTFE particles. 4. The developing roller according to claim 1, wherein the magnetic powder has an average particle diameter of 50 μm.
A developing roller which is finely crushed below. 5. The developing roller according to claim 1, wherein the surface of the magnetic powder is coated with an ultraviolet curable adhesive, and is adhered to the plastic magnet or the holder. A developing roller.