JPH0462390B2 - - Google Patents

Description

Detailed Description of the Invention <Technical Field> The present invention relates to development of an electrostatic latent image formed on a photoreceptor into a visible image in an electrophotographic copying machine, and particularly relates to development using a magnetic one-component toner. The present invention relates to a developing device that performs development using a developer made of.

<Prior art> The developing device of an electrophotographic copying machine uses a two-component developer consisting of a colored pigment toner and a magnetic carrier such as iron powder, and transfers the toner to a photoreceptor by frictional charging between the toner and the carrier. The electrostatic latent image is charged to the opposite polarity to the electrostatic latent image, and the toner is attached to the electrostatic latent image.The other is a one-component developer in which the toner itself has magnetic properties. There is a method in which toner is electrostatically attracted to an electrostatic latent image by applying dielectric polarization or the like using the electric field of the image. A magnetic brush development method is widely used as a developing means for conveying the two-component or one-component developer to the development area of the photoreceptor on which the electrostatic latent image is formed and attaching toner. . This development method has advantages over the cascade development method, such as a simpler and more compact structure.The magnetic brush development method uses a cylindrical sleeve made of non-magnetic material,
A developing roller consisting of a magnet roller and a magnet roller rotatably provided inside the sleeve is generally used, and the relative rotation of the two causes the carrier or magnetic toner to be attracted onto the sleeve by magnetic force. The developer is transported to the development area.

The developing device having the above-mentioned structure uses a two-component developer, and requires means separate from the developing roller for stirring the developer in order to triboelectrically charge the toner. However, those using a one-component type developer do not need to provide stirring means for frictionally charging the toner, and can be more compact than two-component type developing devices.

By the way, various developing methods using a one-component developer (hereinafter referred to as toner) are known, and developing devices that have realized this developing method include those using conductive magnetic toner and those using insulating magnetic toner. It is well known to use However, conductive magnetic toner has the disadvantage that transfer efficiency is low when electrostatic transfer using corona discharge or the like is performed, and therefore insulating magnetic toner is often used. As the above-mentioned developing device, for example, Japanese Patent Application Laid-Open No. 50-45639,
It is described in detail in JP-A-53-31136, JP-A-52-92140, etc.

The above method uses a developer whose main component is ferromagnetic and insulating toner, and during development, a desired charge is applied to the toner by the frictional charging effect with the surface of the toner support member. I'm going.

In addition, the second method uses insulating magnetic toner to move the toner at high speed (10 cm/sec or more) and at the same time gives a rapid and turbulent physical mixing action to the toner. After obtaining a sufficient charge of polarity opposite to that of the electrostatic latent image, a bias voltage is further applied between the photoreceptor and the sleeve to perform development.

Furthermore, the second method uses uncharged toner with an electrical resistance of 10 ¹² [Ωcm] or more, and in the developing section, the direction of movement of the sleeve and the direction of the surface of the latent image carrier are the same, and the speed of movement of the sleeve surface is equal to that of the latent image carrier. Development is performed at a speed faster than the moving speed of the image carrier.

According to the above development method, since the sleeve is grounded or electrically connected to the photoreceptor by a bias voltage, an electric field is established from the electrostatic latent image to the sleeve. . Therefore, although it is related to the strength of the electric field, toner is easily attracted to non-image areas as well. Furthermore, in the above method, since the toner is charged by frictional electrification, the attraction of the toner to the non-image area becomes significant. This has the disadvantage that so-called "fogging" occurs. In the other method, the development time is affected and the above-mentioned "fogging" becomes noticeable. According to this method, although a bias voltage is applied, it is not completely eliminated. Furthermore, if the electrical resistance of the toner exceeds 10 ¹⁵ [Ωcm], the occurrence of fog becomes more noticeable.

<Object of the Invention> The present invention provides a developing device that is less likely to cause the "fogging" phenomenon in which toner adheres not only to image areas but also to non-image areas, and that can perform stable and good development. .

<Example> Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1 is a sectional view showing a specific example of a developing device according to the present invention. In the figure, 1 is a cylindrical sleeve made of a non-magnetic material, and 2 is a magnet roller which is rotatably provided within the sleeve and whose outer circumferential magnetic poles are sequentially magnetized with different magnetic poles, and these constitute a developing roller. Reference numeral 3 denotes a one-component magnetic toner held on the sleeve 1 by the magnetic force of the magnet roller 2; 4, the sleeve 1 is rotated in the direction of the arrow;
and a drum-shaped photoreceptor on which an electrostatic latent image is formed, with a layer of toner 3 interposed therebetween. Toner 3 above
is housed in a replenishing hopper 5, flows through an inclined plate 8 having an inclined surface of an angle R provided in an opening 7 at the bottom of the hopper 5, and is moved onto the sleeve 1 by the magnetic force of the magnet roller 2. are supplied sequentially.

On the other hand, a distance B is provided between the developing area facing the photosensitive drum 4 and the hopper 5 from the sleeve 1 in order to regulate the amount of spikes (holding amount) of the toner 3 supplied onto the sleeve 1. A regulating plate 6 is arranged. The regulating plate 6 controls the amount of toner 3 magnetically attracted onto the sleeve 1 in order to always convey a constant amount of toner to a developing area where the toner 3 contacts the surface of the photoreceptor drum 4 . Therefore,
A constant amount of toner 3 is always held on the sleeve 1, and the toner layer thickness A remains constant while the magnet roller 2 is rotating.

Here, if the developing cap D, which is the distance between the sleeve 1 and the photoconductor 4 facing the sleeve 1, is provided in the relationship A≈D with the toner layer thickness A on the sleeve 1, the toner 3 will be transferred to the development area facing the photoconductor 4. becomes very short. Therefore, since sufficient development time is not available, it becomes difficult to develop. Therefore, the present invention makes the development gap D as narrow as possible and maintains the toner layer thickness A on the sleeve and A≈D. The development gap D is preferably set to 0.1 to 0.5 mm, more preferably 0.4 mm or less. However, 0.5mm
If it exceeds this, a problem will occur, which will be described later.

In the above configuration, the sleeve 1, the hopper 5
All of the conductive parts such as the regulation plate 6 and the like that come into contact with the toner transport path are not grounded. In other words,
The sleeve 1, hopper 5, regulation plate 6, etc. are as follows:
Electrically insulated from the main body of the device. however,
Since an electrostatic latent image is formed on the photoreceptor 4, a conductive layer portion thereof is grounded to the main body of the apparatus.

Therefore, from the electrostatic latent image on the photoreceptor 4, no electric field is established for the sleeve 1. In this case, in the image area of the electrostatic latent image, due to the edge effect as in the known cascade development method, white spots or a decrease in image density occur in the center of the solid black area.

However, according to the present invention, the developing gap D is 0.1
Since it is extremely narrow at ~0.5 mm and the toner layer thickness A is similarly thin, the electric lines of force emitted from the electrostatic latent image on the photoreceptor 4 are transmitted to the upper layer of the toner 3, that is, in the vicinity of the area in contact with the photoreceptor 4. of toner particles. Therefore, an electric field is not generated for the sleeve 1 at local locations where the photoreceptor 4 and toner 3 contact each other in the developing area, but in the image area, local toner particles near the photoreceptor 4 that contribute to development are not generated. An electric field acts thereon, and electric lines of force emitted from the image area are dispersed at the interface between the toner particles near the image area and the non-image area. Therefore, no local electric field was applied to the non-image area, and a good toner image with uniform contrast and no fog in the non-image area, no solid black, and no edge effect was obtained. Furthermore, there was no electrostatic adhesion of the toner 3 to the sleeve 1, the regulating plate 6, and the hopper 5, and there was no aggregation of the toner 3, and the conveyance performance was also good.

In order to further enhance the effects of the present invention described above, it is better to set the conveyance speed of the toner 3 on the sleeve 1, the toner layer thickness A, and the development gap as follows. First, to convey the toner, as shown in FIG. 1, the rotation direction of the sleeve 1 is in the direction of arrow a.
The magnet roller 2 is rotated in the same direction as the sleeve 1 in the direction of arrow b to guide the toner 3 to the developing area. In this case, the rotational speed of the sleeve 1 (v _s ) and the rotational speed of the magnet roller 2 (v _n ) should be adjusted appropriately so that the moving speed of the toner on the sleeve 1 in the development area is as low as possible. Set.

Next, the toner layer thickness A will be explained. Now, if the toner layer thickness A becomes thicker, the lower part of the toner 3 in contact with the sleeve 1 will move in the direction of arrow a due to the rotation of the sleeve 1, and the surface part not in contact with the sleeve 1 will be moved by the magnetic roller. 2 moves in the opposite direction to the direction of arrow b, and the toner 3 on the sleeve 1 moves separately in the lower and upper layers. In this way, since the two toner layers formed have opposite toner conveying directions, the toner particles are subject to considerable pressure and tend to aggregate, which impedes the conveyance of the toner 3. Furthermore, since it is difficult to reduce the moving speed of the toner 3 on the sleeve 1 to zero as much as possible in the development area, the toner layer thickness A must be made thin to make it difficult to form two layers of toner 3. Must be.

On the other hand, regarding the number of rotations (v _s ) of the sleeve 1 and the number of rotations (v _n ) of the magnet roller 2, for example, Japanese Patent Application Laid-Open No. 126266/1983 and Journal of the Japanese Society of Applied Magnetics
A general formula for calculating toner movement speed is presented in V0L4 "Magnet Application in Electronic Copying Machines".
However, the characteristics of the toner, such as magnetic characteristics (residual magnetic flux density, coercive force), particle size distribution, particle shape and surface condition (friction coefficient), electrical characteristics (electrical resistance, triboelectrification characteristics), etc., and the surface roughness of the sleeve 1 etc., the values calculated from the general formula and the actual measurements did not necessarily match. Therefore, the inventors also referred to the general formula and determined by actual measurements that the number of rotations of the sleeve 1 (v _s ) and the number of rotations of the magnetic roller 2 ( v _n ) was calculated.

As described above, by narrowing the development gap D (distance between the sleeve 1 and the photoreceptor) and reducing the moving speed of the toner 3 on the sleeve 1 to zero as much as possible in the development area, the toner 3 is transferred to the photoreceptor. The time of contact with toner particles 4, that is, the development time, becomes longer, and the electric field acting on the toner particles also becomes stronger.
is attracted to the photoreceptor 4 side and forms a toner image. In this case, the toner 3 is mixed with the toner particles of the sleeve 1.
Electric charge is obtained by friction with the
Because there is no rapid and turbulent movement as in the publication,
It was verified that the amount did not contribute to development.

Regarding the electrical resistance of the toner 3, FIG. 2 is a cross-sectional view when the electrical resistance was measured by bringing the developing roller into contact with an electrode plate. The symbols are almost the same as those in FIG. 1, and the symbol 9 is an electrode plate, 10 is a high resistance meter including a DC power supply (4329A manufactured by Yokogawa Hardware Pack Card), and the gap G between the electrode plate 9 and sleeve 1 is a toner layer. equal to the thickness. The sleeve 1 and the magnet roller 2 rotate in the same direction, and their respective rotational speeds (v _s ) and (v _n ) are the same as those on the sleeve 1 in the area where the electrode plate 9 and the toner layer 3 contact, as in FIG. The moving speed of the toner 3 is set to be as low as possible. In this state, a DC voltage is applied between the electrode plate 9 and the sleeve 1, and the resistance value is read.

Next, one embodiment of the invention will be described.

The material of the sleeve 1 is SUS304 and the material of the hopper 5 is Al, and these are used in an electrically floating state without being grounded to the main body of the device. The developing roller is placed on the photoreceptor 4 with a developing gap D0.3mm in between.
The toner layer thickness A on the sleeve 1 is
The distance B between the regulating plate 6 and the sleeve 1 was maintained at 0.2 mm so that A≈D. The magnet roller 2 in the sleeve 1 is a 600 Gauss 16-pole one, and the sleeve rotation speed (v _s ) = 30 rpm and the magnet roller rotation speed (v _n ) = 700 rpm are rotated in the same direction. In this region, the speed of movement of the toner on the sleeve 1 has become as close to zero as possible. At this time, the toner is supplied after it has been used for development, but both the sleeve 1 and the magnet roller 2 are rotating, and a balance is maintained in the development area, so if the balance is lost, it can be easily handled. Toner is supplied from the hopper by the force of returning to its original state (rotation of the sleeve and magnet roller).

On the other hand, the photoreceptor 4 is constructed using an organic photoconductor, and the potential of the electrostatic latent image is set to about -500 [V], and the toner 3 is a polystyrene resin containing 40% by weight of magtite as magnetic powder. Using the device shown in Figure 2, a DC voltage of 100 to 1000 V was applied, and the gap G between the electrode plate 9 and the sleeve was set to 0.3 mm, which was equal to the toner layer thickness, and the sleeve rotation speed (v _s ) = 30 rpm. When measured at rotational speed (v _n ) = 700 rpm, the electrical resistance remained constant regardless of changes in the applied voltage, and the sleeve rotational speed (v _s ) and magnet roller rotation speed (v _n ) were The electrical resistance did not change even when the rotational speed of (v _s ) (v _n ) was increased by about 3 times while maintaining the state in which the moving speed of the toner on sleeve 1 was as low as possible in the area where it came into contact with sleeve 9. .

Therefore, it has been found that the electrical resistance of toner does not depend on the electric field and does not depend on the conveyance speed. In another method, the toner was formed into tablets and the electrical resistance was measured, and it was found to be more than 10 ¹⁵ [Ωcm].

Development was carried out using the above toner. As a result of development, a stable and good toner image with almost no fog was formed, and a clear image was obtained on plain paper by corona transfer.

<Effects of the Invention> According to the developing device of the present invention, the developing gap is narrowed, the toner layer thickness is also made thinner, and any electrically conductive parts that come into contact with toner during the toner transport path are not grounded and electrically connected to the main body of the device. It is insulated to enable clear, fog-free development. Here, by reducing the moving speed of the toner on the sleeve in the development area to zero as much as possible, more stable and good development can be expected without forming toner pools.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a specific example of the developing device of the present invention, and FIG. 2 is a sectional view showing a specific example in which the electrical resistance of the toner used in the present invention was measured. 1...Sleeve, 2...Magnetic roller, 3
...Toner, 4...Photoreceptor, 5...Hopper, 6
...Regulation plate, A...Toner layer thickness, D...Distance between photoreceptor and sleeve, (v _n )... Rotational speed of magnet roller, (v _s )... Rotational speed of sleeve.

Claims (1)

[Scope of Claims] 1. A one-component developer containing a magnetic material in a resin is used to form an electrostatic latent image using a developing roller having a rotatable magnet roller inside a sleeve made of a non-magnetic material. In a developing device that performs development by conveying a formed photoreceptor to a developing area facing it, a sleeve is disposed close to the photoreceptor in order to narrow the development gap between the photoreceptor and the sleeve, and the sleeve is placed close to the photoreceptor. A developing device characterized in that a conductive portion that comes into contact with developer in a developer transport path other than the developer is electrically insulated from the device main body. 2. The sleeve and magnet roller are rotated in the same direction, and the rotational speeds of the sleeve and magnet roller are set so that the moving speed of the developer on the sleeve in the development area is as low as possible. A developing device according to claim 1, characterized in that: