JPH058825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device that develops a latent image using a non-magnetic developer.

Conventionally, various devices have been proposed and put into practical use as dry one-component developing devices. However, in any of the development methods, it is extremely difficult to form a thin layer of dry one-component developer, and for this reason, a developing device has been constructed by forming a relatively thick layer. However,
At present, there is a need to improve the clarity and resolution of developed images, and it is essential to develop a method for forming a thin layer of a dry one-component developer and an apparatus therefor.

As a conventionally known method for forming a thin layer of a dry type one-component developer, Japanese Patent Application Laid-Open No. 43037/1983 has been proposed and has been put to practical use. However, this concerned the formation of a thin layer of magnetic developer. In order to make magnetic developers magnetic, a magnetic material must be added to the toner. Since it is internally added, there are problems such as poor color reproduction during color reproduction.

For this reason, as a method for forming a thin layer of non-magnetic developer,
Two methods have been proposed: using a cylindrical brush made of soft beaver hair to apply the developer, and applying the developer to a developing roller whose surface is made of fibers such as velvet using a doctor blade. ing. However, when an elastic blade is used as a doctor blade for the above-mentioned fiber brush, it is possible to regulate the amount of developer, but uniform application is not achieved, and the fibers of the brush are simply rubbed by the fiber brush on the developing roller. Since no triboelectric charge is imparted to the developer present in between, there is a problem in that ghosts and the like are likely to occur.

In response, the present applicant has developed a new developing device that forms a non-magnetic developer as a uniform thin layer on the surface of a developing agent holding member and applies sufficient frictional electrification. a developer holding member for rotatably conveying the nonmagnetic developer to the latent image carrier; a regulating member disposed on the opposite side of the regulating member via the holding member, and a magnetic pole forming a magnetic brush made of magnetic particles on the upstream side of the regulating member on the developer outlet side of the container. magnetic field generating means, the particle size of the magnetic particles is 30μ to 100μ, the concentration of the non-magnetic developer is 25 to 70% by weight,
A thin layer of non-magnetic phenomenon agent is formed on the surface of the developer holding member, and this is made to face the latent image carrier with a gap of about 300μ, and a frequency of 1000 to 1000 is applied between the latent image carrier and the surface of the developer holding member. 2000Hz, peak-to-peak voltage 1000~
We proposed a method of developing by applying an alternating voltage of 2000V.

FIG. 1 shows a sectional view of a developing device for explaining the developing principle of such a developing method. In the figure, reference numeral 1 denotes an electrophotographic photosensitive drum as a latent image carrier, which holds a latent image formed by a latent image forming means (not shown) and rotates in the direction of arrow a to pass through a developing position shown in the drawing. A non-magnetic sleeve 2, which is a developer holding member that holds developer, faces the photosensitive drum 1 with a predetermined gap maintained therebetween, and this sleeve 2 rotates in the direction of arrow b. A non-magnetic container 3 made of resin or aluminum, which stores a mixture 4 of non-magnetic developer and magnetic particles, is located above the sleeve 2, and a developer regulating member is located downstream of the container 3 in the rotational direction of the sleeve. A magnetic blade 5 is screwed.

On the other hand, the sleeve 2 for this magnetic plate 5
On the opposite side are magnetic poles 61 to 6 as magnetic field generating means.
6 is provided. The mounting position of this magnet is determined by the relationship between the position of the magnetic pole and the magnetic blade 5, and in reality, the magnetic pole is provided slightly upstream of the position of the magnetic blade 5 in the direction of movement of the sleeve. By doing so, the magnetic particles are prevented from flowing out and the developer is uniformly applied by the action of the formed magnetic field.

In the above configuration, the magnetic particles in the container 3 form a magnetic brush 7 due to the magnetic field generated between the N ₁ pole 61 of the magnet 6 and the magnetic blade 5 . Then, as the sleeve 2 rotates, the magnetic particles and the non-magnetic developer are stirred and mixed while the magnetic brush 7 is held. In this state, on the magnetic blade side of the container 3, due to the presence of the blade 5, the mixture of developer and non-magnetic particles is prevented from moving by the blade, rises, and circulates in the direction of arrow c.

Non-magnetic developer is triboelectrically charged by mixing with magnetic particles. The charged developer is transferred to the magnetic blade 5
The magnetic brush 7 formed near the sleeve 2 is uniformly and thinly applied to the surface of the sleeve 2 by reflection force, and reaches a position facing the photoreceptor drum. At this opposing position, the layer thickness of the non-magnetic developer is thinner than the gap between the sleeve and the drum, and a bias voltage of alternating current or direct current superimposed on alternating current is applied between the sleeve and the drum from a bias power supply 8. It is preferable to carry out development by the development method described in Japanese Patent No. 32375.

By the way, the magnetic particles constituting the magnetic brush 7 are set so that the binding force due to the magnetic field of the magnet 6 is greater than the conveying force caused by the electrostatic adhesion force and frictional force between the sleeve and the magnetic particles. , does not flow onto the sleeve 2. If there is non-magnetic developer within the area of the magnetic brush 7, the ratio of the magnetic particles of the magnetic brush 7 to this developer remains approximately constant as the sleeve 2 rotates. Thereby, even if the developer on the sleeve is consumed during development, the developer is automatically supplied to the area of the magnetic brush 7. Therefore,
A constant amount of developer can always be supplied and coated onto the sleeve 2.

In addition, in the above explanation of the principle, a magnetic blade is used as the regulating member, but the non-magnetic blade or the wall of non-magnetic material such as resin or aluminum that constitutes the container can be
It can also be used as this regulating member. However, in this case, to prevent the outflow of magnetic particles,
It is necessary to make the gap between the sleeve and the regulating member even smaller than when using a magnetic blade. Further, when a magnetic blade is used, it is preferable because a magnetic brush can be stably formed at the developer outlet by the magnetic field between the blade and the magnetic pole, and the magnetic particles can be restrained and circulated.

The role of the magnetic particles is to disperse the non-magnetic toner and transport the non-magnetic toner while being adsorbed onto the sleeve. The developer used is the toner concentration used in normal two-component magnetic brush development (for example, 2 to 12 wt%).
A two-component developer containing 30 to 70 wt% toner is used, which is several times the amount of toner.

The two-component developer attracted by the magnet is conveyed to the magnetic blade 5 by rotation of the sleeve.
During this conveyance process, the two-component developer consisting of non-magnetic toner and magnetic particles is transferred to the sleeve 2 by magnetic force.
Since the non-magnetic toner is attracted to the surface of the developing sleeve 2 and rubbed against the sleeve, the non-magnetic toner is also attracted to the surface of the developing sleeve 2 by electrostatic force. In the magnetic blade 5 section, the magnetic particles stay in the brush-like shape due to the magnetic field in the gap between the magnetic pole 61 and the magnetic blade 5, and as a result, the magnetic particles sent later are scraped off from the surface of the sleeve 2. Ru.

On the other hand, the non-magnetic toner adhering to the surface of the sleeve 2 passes through the blade 5 without being affected by this magnetic field, and a thin layer of non-magnetic toner is formed on the surface of the sleeve 2. is supplied to the nearby developing section. In order to prevent magnetic particles from leaking out from the blade 5 portion, the cut magnetic pole 61 is slightly inclined (θ ₁ in the figure) toward the developing container 3 side. By tilting the magnetic pole 61 toward the developing container side in this way, magnetic flux leakage from the magnetic blade 5 to the developing section side is prevented, and since the magnetic flux is limited only to the inside of the developing container 3, the magnetic particles are transferred from the blade 5 section to the developing section. It will almost never be taken out of the container.

By the way, when an image is formed using the developing device shown in FIG. 1, spark discharge sometimes occurs between the drum 1 and the sleeve 2 immediately after the sleeve rotates. This is because some of the magnetic particles that were magnetically trapped at the tip of the magnetic blade at the beginning of the rotation of the sleeve cannot withstand the impact applied to the tip of the blade immediately after rotation, and are not restrained by the tip of the blade and are trapped on the sleeve surface. It is pulled by the frictional force and passes through the blade section and reaches the developing section, resulting in the _Vpp applied to the narrow gap between the drum and the sleeve =
Spark discharge occurs through magnetic particles in an alternating electric field of 1300 to 2000V.

This phenomenon appears more often on the first copy after a large number of copies have been made in succession. This is because as a large number of copies are continued, the number of loosely restrained magnetic particles that tend to leak out from the blade increases before the magnetic blade. In such cases, pinhole-like damage is often caused on the surface of the photosensitive drum due to spark discharge. These phenomena become noticeable at the start of rotation of a high-speed machine in which the sleeve circumferential speed is high. This is also noticeable when the sleeve starts to rotate after the machine has been moved to another location with some rattling.

In such a developing device, as explained in the above-mentioned principle of toner coating, the blocking force of the blade and the conveying force on the sleeve surface are balanced to coat only toner. Therefore, when the sleeve starts to rotate or is subjected to vibration impact force due to movement, the balance is lost and the amount of magnetic particles that are likely to leak into the blade increases, resulting in the above-mentioned drawbacks.

The present invention aims to prevent the above-mentioned drawbacks,
In particular, in a developing device that obtains a coating of non-magnetic toner while restraining magnetic particles using a magnetic blade, this developing device specifies the timing of application of a developing bias.

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows a time chart showing the timing of bias application. In FIG. 2, the photosensitive drum starts rotating in synchronization with the copy button signal _T1 . Further, the developing sleeve starts rotating in synchronization with the photosensitive drum.

At this time, the impact of the start of rotation is transmitted to the developer restrained at the tip of the magnetic blade, and a minute amount of magnetic particles leak out from the blade section, are attracted to the sleeve surface, and are transported to the developing section. be.
Now, assuming that the outer diameter of the sleeve is γ, the circumferential speed is ν _s , and the angle from the blade to the developing section is θ ₂ , the time ΔT for the magnetic particles to reach the developing section is ΔT=2πγθ/360ν _s . Therefore, it is necessary to set conditions such that the developing bias is applied with a delay of at least ΔT after the sleeve starts rotating.

In the case of the developing device configuration shown in Figure 1, ΔT is the time it takes for the sleeve to rotate approximately 1/4, but when designing an actual machine, T ₂ It is better to set the bias to be applied at
Spark discharge caused by magnetic particles that leak out after a time delay can also be prevented, making it more effective.

The photosensitive drum stops after copying a predetermined number of sheets, and at the same time, the rotation of the developing device also stops (T ₅ ). The bias can be stopped at any point before or after the developing device is stopped after the final copy is developed.

FIG. 3 is a timing chart of another embodiment of the present invention, showing the timing when the developer is driven via a clutch. This method of intermittent rotation to develop only a specific portion of the photoreceptor drum where a latent image is formed is effective in preventing fatigue of the developer due to unnecessary rotational load.
This is a good configuration that allows beautiful images to be maintained over a large number of copies.

In this case, the developing bias is applied at T ₄ at least ΔT after the start of rotation of the sleeve (T ₃ ), preferably 2×ΔT, as explained in the example of FIG. In reality, since the drum is being developed at the timing of bias application, the developing device must be driven via the clutch approximately 2×ΔT before the latent image portion on the drum reaches the developing section. The timing (T ₆ ) for turning off the bias can be selected at any time after the latent image area has been developed, almost the same as in the example shown in FIG.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the developing device, FIG. 2 is a timing chart of an embodiment of the present invention, and FIG. 3 is a timing chart of another embodiment of the invention. In the figure, 1 is a photosensitive drum, 2 is a sleeve,
3 is a container, 4 is a developer mixture, 5 is a magnetic blade, 6 is a magnet, 7 is a magnetic brush, and 8 is a bias power source.

Claims (1)

[Claims] 1. A container for storing a non-magnetic developer and magnetic particles, a rotating developer holding member for holding a non-magnetic developer layer and transporting it to a latent image carrier, and at an outlet of the non-magnetic developer from the container, a regulating member facing the surface of the developer holding member with a gap therebetween; and a magnetic pole fixedly disposed inside the developer holding member at a position on the upstream side with respect to the rotational direction of the developer holding member. The magnetic particles are restrained in the container by the magnetic pole and the regulating member, and the non-magnetic developer layer is carried out from the outlet, and the developer holding member and the latent image carrier face each other in a developing section. In a developing device that develops a latent image by applying an alternating electric field, the alternating electric field is opposed to the regulating member of the developer holding member at the time of starting rotation after the developer holding member starts rotating. A developing device characterized in that the voltage is applied to the developing section after the time required for the part to pass through the developing section has elapsed.