JPS5933000Y2 - developing device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a developing device in an electronic copying machine, an electrostatic recording device, etc.

An electronic copying machine that forms an electrostatic latent image on an image carrier (for example, a photoreceptor with a photoconductive surface), converts this latent image into a toner image using a developer, and transfers the thus formed toner image to a transfer sheet. Alternatively, in an electrostatic recording device, the above-mentioned developer is a type of developer with a relatively high resistance value, that is, 108g-(
1) As mentioned above, if a medium to high resistance toner, preferably 1013g-0m or more, is used, the toner image is transferred to the transfer sheet better than when a low resistance toner is used. Are known.

In this case, when a low-resistance toner is used, the toner particles are attracted to the electrostatic latent image only by the static electricity induced in the toner particles when the toner particles approach the electrostatic latent image, and development can be performed by this. However, when the above-mentioned high to medium resistance toner is used, it becomes difficult to perform good development only by electrostatic induction.

Therefore, when using a high to medium resistance toner, a method has already been proposed in which the particles of this toner are forcibly charged to make it easier to attract the toner to the electrostatic latent image. -117432).

This method applies a voltage or corona discharge of opposite polarity to the electrostatic latent image to the toner particles, and causes the applied toner to adhere to the electrostatic latent image.This method certainly increases the development efficiency. , a clear toner image can be obtained.

However, experiments conducted by the present inventor revealed that this method has the following serious drawbacks.

In other words, in this method, immediately after the start of charge injection into toner particles, the toner image formed by this toner has an abnormally high density compared to subsequent toner images, and the toner image becomes uniform throughout. It has the disadvantage of not being able to maintain its concentration.

The present invention aims to provide a developing device that can eliminate or alleviate the above-mentioned conventional drawbacks, and an embodiment in which the present invention is applied to a developing device of an electronic copying machine will be described in detail below with reference to the drawings.

In FIG. 1, an image carrier configured as a photosensitive drum 1 is rotatably supported on the machine frame of a copying machine, and a latent image forming means (not shown) is provided around the drum 1. A charger that charges the surface of the drum and an exposure device that exposes the charged surface of the drum are provided.

The developer device 2 has a toner carrier configured as a rotatable sleeve 3, which extends close to and parallel to the drum 1.

A magnet 4 is fixed inside the sleeve 3.

5 is a tank for the toner 6, and a hopper 7 for supplying toner to the tank 5 is attached to the upper part of the tank 5.

Toner 6 has a resistance of 108 Ω·cm or more, preferably 10
A medium to high resistance magnetic toner having a resistance value of 13 Ω·cm or more is used.

Reference numeral 8 denotes a charge injection electrode for injecting charge into the toner 6, and this electrode is in contact with the toner 6 and is fixed to the hopper 7.

When the copying operation is started, the drum 1 is driven to rotate counterclockwise as shown by the arrow. At this time, the surface of the drum 1 is charged with a charger and then exposed with light using an exposure device, so that the surface of the drum 1 is exposed to light. An electrostatic latent image is formed on a document (not shown).

On the other hand, in the developing device, the sleeve 3 is rotated counterclockwise, and due to this rotation and the cooperative action of the magnet 4, the toner 6 is conveyed on the sleeve 3 in the direction shown by arrow A.

The toner 6 thus transported circulates in layers on the surface of the sleeve 3.

Thus, the sleeve 3 and the magnet 4 constitute the toner conveying means in this example.

In this case, the toner 6 on the sleeve 3 forms spikes in the area of each magnetic pole of the magnet 4 due to the action of the magnetic force, and the toner passes through the development area B, that is, the area where the drum 1 and the sleeve 3 are closest to each other. When, by the main pole 9 of the magnet 4,
Ears 6a that directly contribute to development are formed.

The electrostatic latent image formed on the surface of the drum 1 is in the development area B.
When this happens, static electricity with a polarity opposite to that of the latent image is induced in the toner particles constituting the toner spikes 6a formed here, and at this time, the toner particles are charged with the latent image by the electrode 8. Since the toner particles are charged with opposite polarity, the toner particles are electrostatically attracted to the latent image, and the latent image is visualized (toner image).

In this way, the toner particles are forcibly charged with a charge having a polarity opposite to that of the latent image, so that the toner particles are efficiently attached to the latent image despite the high electrical resistance value of the toner.

Development is carried out as shown in the upper row, but in this case, as mentioned above, in this type of conventional apparatus, the density of the toner image developed immediately after the charge is injected into the toner is abnormally high. was there.

2a illustrates this state, P indicates the moving direction of the drum 1, and 6b indicates the toner image formed on the surface of the drum 1. In FIG.

And T indicates the time point at which charge injection starts.

As can be seen from this figure, the toner image 6b' formed immediately after the start of charge injection is different from the toner image 6b formed after that.
The concentration is abnormally higher than that of ``.

The reason why such defects have conventionally occurred can be considered as follows.

That is, conventionally, the charge injection electrode and the development area are electrically connected to each other via toner.

In other words, this toner can be regarded as an equivalent circuit including resistance and capacitance, and it can be said that the toner exists in a state where the influence of the resistance and capacitance cannot be ignored.

For this reason, the shock wave generated at the moment a voltage is applied to the charge injection electrode causes a remarkable electrostatic induction phenomenon in a fairly wide area before and after this electrode, and the electrostatic latent image is developed by the toner affected by the shock wave. The toner image has a very high density, and therefore it can be considered that only the toner image formed immediately after charge injection has an abnormally high density.

Starting from the above-mentioned novel recognition, the present invention aims to effectively cut off the electrical connection between the toner existing in the development area and the toner existing in the charge injection area, thereby eliminating or reducing the conventional drawbacks. There is something to do.

In the embodiment shown in FIG. 1, this electrical interrupting means is constituted by a magnet 4.

That is, at two cutoff positions C and D where the charge injection electrode 8 and the development area B can be cut off, the magnet 4 is provided with magnetic poles of the same polarity (the first
At the cutoff position C in the figure, N members are placed close to each other, and at the second cutoff position, S members are placed close to each other.

With this configuration, the toner 6C that passes between the respective homopolar magnetic poles E at the blocking position as shown in FIG. 3 moves at a very high speed.

In other words, the toner 6C is lifted off the surface of the sleeve 3 by the repulsive magnetic field generated by the two same magnetic poles, and the toner 6C is in a very rough state compared to other toner parts. be.

Therefore, electrical connection is effectively cut off at this toner portion 6C.

In this way, charge injection into the toner does not directly affect the development area, and the above-mentioned inconvenience that occurs immediately after the start of charge injection can be eliminated.

Note that even if electrically interrupted in this way, the toner particles charged by the electrode 8 reach the development area while maintaining their charge, so the advantages of charge injection are not impaired.

In the embodiment shown in FIG. 1, the electric interrupting means is constructed by bringing a pair of magnetic poles of the same polarity close to each other, but this means is essentially intended to prevent or reduce the flow of current from the charge injection electrode to the developing area. Therefore, the configuration is not limited to the configuration shown in FIG. 1, but can be configured in various forms as long as this purpose can be achieved.

For example, as shown in FIG. 4, two magnetic poles N of the same polarity,
A blocking means can also be constructed by providing an auxiliary pole S of a different polarity between the two terminals N and N.

However, in the embodiment shown in FIG. 4, the magnetic force of the auxiliary pole S is strong enough not to cancel out the repulsive magnetic field effect caused by the same magnetic poles N and N, preferably equal to or less than the strength of the same magnetic poles N and H. It is set to about.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the configuration of the above embodiments, and can be applied to various types of developing devices.

For example, the charge injection means is not limited to the electrode 8 shown in FIG.
A corona discharger 8a as shown in FIG. 5 can be used, or a device using two electrodes 8b and 8C as shown in FIG. 6, which has already been proposed by the present inventor, can also be used.

In addition, in the example shown in Fig. 1, a pair of magnetic poles N, N: S, S are provided at the two cutoff positions C and D, but a pair of magnetic poles N, N:
Alternatively, the intended purpose of the present invention can be achieved by simply providing S and S at one blocking position.

Furthermore, the present invention can also be applied to a developing device in an electrostatic recording device.

Finally, I would like to make an additional comment about the experiment conducted by the inventor.

The gap between the electrode 8 and the sleeve 1 is l, Qmm, and the sleeve 3
The gap between and drum 1 is 1.2 mm, and the linear speed of the drum is 100.
mm/sec, the linear speed of the sleeve is 300 mm/see,
The strength of the magnetic force on the sleeve surface generated by the main magnet 9 of the magnet 3 was set to 1200 Gauss to 1500 Gauss, and development was performed using the apparatus shown in Fig. 1 using a one-component magnetic toner of 1014 g-0 m or more. As a result, a toner image of uniform density as shown in FIG. 2B was obtained (in FIG. 2B, the same parts as in FIG. 2A are given the same reference numerals).

When developing under the same conditions without using a blocking means, the second
The above-mentioned toner image as shown by a in the figure was obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 a and b are explanatory diagrams showing the state of toner image formation, and FIG. 3 is a portion of FIG. Enlarged explanatory diagram,
FIG. 4 is an explanatory view showing another embodiment of the blocking means, and FIGS. 5 and 6 are sectional views showing other embodiments of the charge injection means. 1... Image carrier, 2... Development device,
4...Magnet, 6゜6C...Toner, 8
, 8 a , 8 b , 8 C...charge injection means, B... development area.

Claims (2)

[Scope of utility model registration request] (1) A developing device that visualizes an electrostatic latent image on the surface of an image carrier using a medium to high resistance toner of 10'Ω or more, and applying a voltage or a voltage of opposite polarity to the electrostatic latent image to the toner particles. The developing device includes a charge injection means for applying a corona discharge, and a conveyance means for conveying the toner to which the charge is applied to a developing area, and the toner particles are transferred to the electrostatic latent image in the developing area. wherein at least a pair of magnetic poles of the same polarity located close to each other are located between the development area and the area of the charge injection means, and the toner existing in the development area and the toner existing in the area of the charge injection means The developing device is characterized in that it is provided with a cutoff means for effectively cutting off electrical connection with the developing device. (2) The developing device according to claim 1, wherein a magnetic pole of a different polarity is arranged between the pair of same-polarity magnetic poles.