JPS6048060A - Developing device for electrostatic latent image - Google Patents

Abstract

PURPOSE:To maintain stably a carrier recovering function all the time by connecting respective two bias power sources to a developing sleeve and a carrier recovery plate, and applying the recovery plate with a voltage having the same polarity with carriers, and removing toner repulsively. CONSTITUTION:When the surface of a photosensitive body 1 passes through a development area A, a contact a1 is made to apply a 200V voltage from a bias power source 5 to the developing sleeve 2 and then a -700V voltage from a bias power source 6 to the carrier recovery plate 4, thereby attracting carriers which stick to the surface to the photosensitive body 1 to the plate 4. The no- image part of the photosensitive body 1, on the other hand, is applied with a 700V voltage from a bias power source 6'. Therefore, even if toner sticks to the surface of the recovery plate 4, the voltage having the same polarity that the carriers have is applied from the bias power souce 6' to repulse and remove it electrostically. A control circuit 7 controls the switching periods of switches Sa and Sb to make the surface of the recovery plate 4 invariably clean, maintaining the carrier recovering function stably all the time.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an electrostatic latent image held on the surface of a moving electrostatic latent image carrier by toner and carrier that are each frictionally charged to opposite polarities.
The present invention relates to an electrostatic latent image developing device that performs development using a two-component developer made of a mixture with a rear and rear developer.

Technical background Currently, the electrostatic latent image developing device as described above includes a developing sleeve provided facing the surface of an electrostatic latent image carrier;
Magnetic brush developing devices equipped with a magnetic roller provided inside are often used, and the inventor of the present invention has developed a developing device as shown in FIG. 1 as one of these devices.

This developing device will be described in detail with reference to FIG. 1. This developing device is roughly opposed to the surface of an electrophotographic photosensitive drum (1) which is rotationally driven in the direction of arrow (a). a conductive developing sleeve (2) provided therein; a magnetic roller (3) provided therein; It is composed of a conductive carrier collection plate (4).

Here, the developing sleeve (2) is connected to the arrow (
Since it is rotationally driven in the b) direction and also functions as a developing electrode, a developing bias voltage of (+) 200 V is applied by the first developing bias power supply (5). Note that the setting of the developing bias voltage is such that the electrostatic latent image to be developed, that is, the electrostatic latent image carried on the surface of the photoreceptor drum (1) is the highest (+).
The potential of 650 V and the background part of the electrostatic latent image (+)
50~], 00V.

On the other hand, the magnetic roller (3) is driven to rotate at high speed in the direction of arrow (b) in synchronization with the rotation of the developing sleeve (2).

Therefore, the two-component magnetic developer (
De), that is, a developer (De) consisting of a mixture of toner (TO) and magnetic carrier (Ca) is transferred to a magnetic roller (3).
Due to the magnetic action of the developing sleeve (2), it is attracted to the circumferential surface of the developing sleeve (2) like a magnetic brush and is conveyed along the circumferential surface of the developing sleeve (2) in the direction of the arrow (C) to the developing area (A). and is transported. Here, the development area (A) is the photosensitive drum (
1) and the circumferential surface of the developing sleeve (2) are close to each other, and in this developing area (A), the surface of the photosensitive drum (1) is exposed to the developer (De) that has been transported.
The electrostatic latent image is sequentially developed as a result of this rubbing.

At this time, the developer (D
The toner (TO) in e) is electrostatically attracted to the electrostatic latent image because it already holds a triboelectric charge with a polarity opposite to that of the electrostatic latent image. The magnetic carrier (Ca) is magnetically attracted to the developing sleeve (2) by the magnetic action of the magnetic roller (3), so that it adheres to the photoreceptor drum (1). It will not be done.

However, as a practical matter, due to a kind of electric field effect during development, a small amount of magnetic carrier (Ca) is deposited on the periphery of the electrostatic latent image on the surface of the photoreceptor drum (1) or on the electrostatic latent image. It has been experienced to be placed in the background of the scene.

Such adhesion of magnetic carriers (Ca) is caused by magnetic carriers (Ca) that have relatively high resistance, small particle size, or weak magnetism, such as magnetic fine powder dispersed in resin. This problem is likely to occur when a photosensitive drum (1) is used after the toner image is transferred.
) is collected and reused for development. Regarding a powder image transfer type electrophotographic copying machine that does not adopt a so-called recovered developer reuse system, for example, the absolute amount of magnetic carrier (Ca) in the developer (D'e) contained in the developing device is decrease, and in turn the developer (
It has also been experienced that it is a direct cause of a decrease in the absolute amount of De) itself.

Therefore, regarding the developing device, the photoreceptor drum (1
) to electrostatically collect the magnetic carrier (Ca) attached to the surface of the photoreceptor drum (1
), and a carrier recovery plate (4) is attached opposite to the surface of the carrier recovery plate (4), and a bias voltage of (-) 700 V is applied to this carrier recovery plate (4) by the first bias power supply (6). is being applied.

As a result, a magnetic carrier (Ca) holding a triboelectric charge having the same polarity as the electrostatic latent image is collected between the photoreceptor drum (1) and the carrier collection plate (4). A strong electric field is formed in a direction that electrostatically attracts the plate (4), and due to the action of this electric field and the magnetic action of the magnetic roller (3), it is temporarily attracted to the surface of the photoreceptor drum (1). The attached magnetic carrier (Ca) is transferred to the carrier collection plate (4
) is adsorbed onto the surface t and collected. Here, the magnetic carrier (Ca) collected onto the surface of the carrier collection plate (4) is transferred on the surface as the magnetic roller (3) is rotated and is moved in the direction of arrow (d). It is transported and returned into the developing device.

The above is a description of the developing device developed by the present inventor. According to this developing device, even if magnetic carrier (Ca) is attached to the surface of the photoreceptor tram (1), it will not be removed from the carrier collecting plate (4). ) and returned to the developing device, various problems that may occur due to the adhesion of magnetic carrier (Ca) can be prevented. For this reason, the developing device is considered to be suitable for practical use. However, according to the results of various detailed experiments conducted by the present inventor, when the developing device is operated for a long period of time, the function of collecting magnetic carrier (Ca) by the carrier collecting plate (4) gradually deteriorates. A new situation has arisen in which the carrier recovery plate (4) cannot fully perform its original function, and it has been made clear that improvements are needed in terms of durability in use.

OBJECTS OF THE INVENTION An object of the present invention is to provide a carrier recovery function using a carrier recovery electrode member, which is specifically exemplified as the carrier recovery plate (4), by constantly stabilizing the function.
The purpose is to maintain a sufficient carrier recovery function over a long period of time, thereby improving the above-mentioned problems.

Summary of the Invention The present inventor believes that the toner (TO) adheres and accumulates, and that the toner (TO) that adheres and accumulates holds an electric charge of the same polarity as the frictional charge polarity of the magnetic carrier (Ca). This was done based on consideration.

The present invention itself is as shown in FIG. For example, by applying a bias voltage of (+)700V, the toner (TO) adhering to the surface of the carrier collection plate (4) is electrostatically repelled in the direction of arrow (e) and removed. It is a clever use of

Note that, on the premise that the above-mentioned phenomenon is skillfully utilized, the electrostatic latent image developing device according to the present invention applies to the carrier recovery electrode member a magnetic pressure having the same polarity as the friction charge polarity of the carrier. It is characterized by comprising a power source and a control means for connecting the bias power source and the electrode member when the surface of the electrostatic latent image carrier that is not subjected to the developing action by the developing means passes through a position opposite to the electrode member. That is.

Embodiment One embodiment of the electrostatic latent image developing device according to the present invention will be described with reference to FIGS. 2 and 3. Note that FIG. 2 is an auxiliary drawing for clearly explaining the behavior of toner (TO) in the above embodiment.

The developing device shown in FIG. 3 is shown built into a powder image transfer type electrophotographic copying machine, and is driven to rotate at a circumferential speed of 110π- in the direction of arrow (a) during copying. It is attached at a position facing the surface of the photoreceptor drum (1). As the photoreceptor drum (1) is rotated, an electrostatic latent image to be developed is formed on the surface of the photoreceptor drum (1) by an imaging device (not shown). The highest potential of the latent image is set to (g) 650 cm, and the potential of the background portion of the electrostatic latent image is set to (g) 50 to 100 cm. Note that the potential of the non-image area of the photosensitive drum (1), that is, the area where no electrostatic latent image is formed, is optically erased from 0 to 50 V or less.

By the way, regarding the above-mentioned developing device, the means for imaging the electrostatic latent image carrier consists of a developing sleeve (2) functioning as a developing electrode and a magnetic roller (3), and that the photosensitive drum (1) is Magnetic carrier (Ca) attached to the surface
The basic structure is the same as that of the developing device shown in FIG. 1 in that the carrier recovery electrode member for adsorbing and recovering the carrier consists of a carrier recovery plate (4), and the conditions for each member etc. are set as follows. It is said to be a street.

In addition, the developer (De) has an insulation value of 12μ.
non-magnetic toner (TO) having an average particle size of m and 10”
It is a two-component magnetic developer consisting of a mixture of a magnetic carrier (Ca) having a resistance value of hcm and an average particle size of 20 μm, and the magnetic carrier (Ca) is a mixture of magnetic fine powder dispersed in a resin. It is what it is. Here, the developer (De
) toner density is set to JQwL%, while
The toner (To) and the carrier (Ca) are charged to (→ polarity, (g) polarity, respectively) by frictional charging.

In such a configuration, regarding the developing device shown in FIG. 3, the first and second developing bias power supplies (5),
(5) and the developing sleeve (2), and between the 1st and 2nd bias power supplies (6), (6') and the carrier collection plate (4).
) are provided with changeover switches (Sa) and (Sb) respectively, and these changeover switches (Sa) and (Sb) are provided between the changeover switches (Sa) and (Sb).
), (Sb) is further provided with a control circuit (7) for controlling the switching of the contacts.

Here, the switch (Sa) has two contacts (al), (
az), and under the control of a control circuit (7), a photoreceptor drum (1) carries an electrostatic latent image to be developed.
When the surface of the photoreceptor drum (1) passes through the developing area (A), the contact point (a) is closed, while when the surface of the non-image area of the photoreceptor drum (1) passes through, the contact point (a-z) is closed. Therefore, when an electrostatic latent image is developed, a developing bias voltage of (g) 200 cm is applied to the developing sleeve (2) via the first developing bias voltage (5). The development of the electrostatic latent image is carried out well while toner (TO) adhesion to the background area is prevented.Also, when the surface of the non-image area passes through the development area (A), the developing sleeve ( For 2), 50
Since a developing bias voltage equal to or less than v is applied and the value of this developing bias voltage is approximately equal to the voltage of the non-image area, no developing action occurs on this non-image area. The second developing bias voltage (5') may be omitted depending on the voltage of the non-image area, and in the latter case, the developing sleeve (2) may be grounded.

Similarly, the switch (sb) has two contacts (b+).

(b2) is 4, and under the control of the control circuit (7),
Normally, contact (b+) is closed. On the other hand, when passing through the surface of the photosensitive drum (1) that is not undergoing the development action, that is, the non-image area or the position facing the carrier collection plate (4), the contact is switched and the contact (b2) is closed. It looks like this. For this reason, the carrier recovery plate (4) is normally supplied with (-)7nO through the J-th bias power supply (6).
A bias voltage of V is applied, and carriers ( If Ca) is present, the carrier (Ca) is electrostatically adsorbed to the carrier collection plate (4). It is then returned into the developing device according to the procedure described with respect to the developing device shown in FIG. On the other hand, when the non-image area passes through the position facing the carrier collection plate (4), the contact point (b2) is idle! Ru. As a result, the connection between the first bias power source (6) and the carrier recovery plate (4) is cut off, and the second bias power source (6) and the carrier recovery plate (4) are connected, and the carrier recovery plate (4) is disconnected from the first bias power source (6) and the carrier recovery plate (4). (+)700V via the second bias power supply (61)
A bias voltage of

Here, toner (TO) in the form of powder smoke often tends to adhere to and accumulate on the carrier collection plate (4) during the operation of the developing device. It has been confirmed by the present inventor that Oshinami holds a charge of (g) polarity, and from this, a bias voltage of (g) 700 ■ is applied to the carrier collection plate (4). When the contact (b2) is closed, such toner (TO) is electrostatically repelled in the direction of the arrow (e) in FIG. attached to. Therefore, in the developing device shown in FIG. 3, each time the contact (b2) is closed, the toner (TO) is removed from the carrier collection plate (4).
4) is constantly kept in a cleaned state, and toner α0) is deposited on the surface of the carrier collecting plate (4).
The carrier recovery function will not be impaired.

According to the inventor's confirmation, -A4
Even when copying 50,000 sheets in size, the toner (
It was also clear that TO) was reliably removed and recovered from the surface by the carrier recovery plate (4).

Note that in the developing device, a switch (Sa) is used.

Regarding the switching of (sb), the switching timing of switch (sb) is controlled to be delayed relative to switch (Sa) by the time shown by [ in the formula below. 1) Carrier (Ca
) This is particularly important in order to reliably remove and recover all of the toner (TO) and also to prevent the developed image from being contaminated with toner (TO). This is because the surface portion of the photoreceptor drum (1) carrying the developed electrostatic latent image or the carrier collection plate (
4) When the switch (s
When the contact point b) is switched from ('b+) to (b2), the carrier (Ca) attached to the unpassed area cannot be removed and recovered, and the developed electrostatic latent image is carried. Toner (TO) repelled by the surface of the photoreceptor drum (1)
This is also because it may result in adhesion of

L-A/V...(1) t: Timing slip time (see)! : Distance from the developing area (A) to the opposite end of the carrier collection plate (4) ■ Circumferential speed of the photoreceptor drum (1) (y+++ psec) However, the (bl) of the contact point of the switch (sb) ) to (b
The switching to 2) may be performed with a time lag of more than the above-mentioned time, and the timing at this point may be set arbitrarily.

By the way, regarding the developing device, the developing sleeve (2
) By varying the developing bias voltage applied to the surface of the photoreceptor drum (1), the developing action on the surface of the photoreceptor drum (1) can be controlled. The toner (TO) and carrier (
Ca)'s thin neck is completely prevented. However, such control can also be similarly performed by varying the supply state of the developer (De) to the development area (A).

That is, the same effect can be achieved by cutting off the conveyance of the developer (De) to the development area (A) and cutting off the contact between the photosensitive drum (1) and the developer (De).

For example, the developing action can be made substantially inactive by stopping the rotation of the magnetic roller (3) without stopping the rotation of the developing sleeve (2). In addition, by stopping the rotational drive of Nokkeratro →, etc., the supply of the developer (Dc) itself to the circumferential surface of the developing sleeve (2) is cut off, thereby substantially deactivating the developing action. You can also do that.

Effects of the Invention In the electrostatic latent image developing device according to the present invention, even if toner adheres to the surface of the carrier recovery electrode member, such toner is removed by the connection between the second insulator source and the electrode member. As a result of applying a magnetic pressure having the same polarity as the friction charge polarity of the carrier to the electrode member, the carrier is electrostatically repelled from the surface of the electrode member and removed. Therefore, the carrier recovery function of the electrode member is not damaged due to toner adhering and depositing on the surface of the electrode member, and a stable carrier recovery function can be obtained at all times.

Further, sufficient carrier recovery function is maintained over a long period of time.

In addition, the connection between the second bias power source and the electrode member is limited to when the surface of the electrostatic latent image carrier, which is not being developed by the developing means, passes through a position facing the electrode member. There is no incomplete recovery of the carrier adhering to the surface of the latent image carrier, or the repelled toner does not stain the developed image.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing an example of an electrostatic latent image developing device that has already been developed by the present inventor, and FIG. 2 shows the bias voltage and voltage applied to the developing sleeve and carrier collection plate in the developing device. FIG. 3, which is a diagram for explaining the behavior of the developer when the developer changes, is a diagram showing an embodiment of the electrostatic latent image developing device according to the present invention. De...Two-component magnetic developer TO...Toner Ca...
Magnetic carrier Sa, Sb...Switch switch 1...
Electrophotographic photosensitive drum 2...Developing sleeve 3...
Magnetic roller 4...Carrier collection plate 5...First developing bias power supply 5'...Second developing bias power supply 6.
・First bias power supply 6'・Second bias source 7
...Control circuit applicant Minolta Camera Co., Ltd. Figure 3

Claims (1)

[Scope of Claims] 1. An electrostatic latent image carried on the surface of a moving electrostatic latent image carrier is formed using a two-component system consisting of a mixture of toner and carrier, each of which is tribo-charged to opposite polarities. A means for developing using a developer, and a carrier recovery electrode unit installed opposite to the surface of the electrostatic l&i image carrier in order to adsorb and recover the carrier that is narrowed on the surface of the electrostatic l&i image carrier during development. In order to electrostatically attract carriers to this electrode member, a bias voltage of the same polarity as the friction charge polarity of the carrier collection electrode member is applied to the electrode member. When the second bias voltage iLj passes through a position where the surface of the electrostatic latent image carrier, which has not been subjected to the developing action by the developing means, faces the electrode member, the connection between the first bias power source and the electrode member is cut off. An electrostatic latent image developing device comprising: a control means for connecting a second bias power source and an electrode member; 2. The developing means has a developing bias having the same polarity as the polarity of the electrostatic latent image. A patent claim comprising a developing electrode to which a voltage is applied, and by varying the developing bias voltage applied to the developing electrode, the developing action of the developing means is substantially rendered inactive. The electrostatic latent image developing device according to item 1. 6.1'' carrier or magnetic carrier;
The developing means has a developing sleeve that is rotationally driven in a direction opposite to the developer conveyance direction, and a magnetic roller that is rotationally driven in the same direction as the developing sleeve inside the developing sleeve,
2. The electrostatic latent image developing device according to claim 1, wherein by stopping the rotational drive of the magnetic roller, the developing action by the developing means is substantially rendered inactive.