JPH04311987A - Image forming device - Google Patents

Abstract

PURPOSE:To avoid the deterioration and useless consumption of toner, provide image stable even with the elapse of time, and reduce running cost by separating a belt photo-sensitive body from a development means, when image is not formed. CONSTITUTION:A photo-sensitive belt 2 is provided with a separation member 48. A pressure roller 50 is made of such material as not adversely influences the belt 2, even when in contact therewith. The pressure roller 50 is laid at the downstream side of a development position where a development roller 18 is in contact with the belt 3 in the travel direction thereof. Furthermore, a separation mechanism presses and deforms the belt 2 in an F direction, thereby separating the belt 2 from the development roller 18. Namely, the separation member 48 oscillates in a G direction at an ordinary development process. As a result, the member 48 is separated from the belt 2, and consequently the belt 2 is reset to be in slidable contact with the development roller 18 for performing a development process. As aforementioned, the separation member 48 oscillates about an oscillation support point, and presses and deforms the pressure roller 50 pivotally supported on an arm 54, thereby separating the belt 2, when no development process takes place.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method of transferring an electrostatic latent image formed on an electrostatic latent image carrier (hereinafter referred to as a photoreceptor) used in an electrophotographic copying machine, printer, facsimile, etc. to a toner. The present invention relates to an image forming apparatus using a process of visualizing images, and specifically relates to a mechanism for reducing unnecessary toner adhering to a photoreceptor and deterioration of the toner.

0002

[Prior Art] Conventionally, an image forming apparatus uses a process in which an electrostatic latent image formed on an electrophotographic photoreceptor through a charging and photoimage exposure process is visualized on a recording paper through a development, transfer, and fixing process. It has been known.

Conventionally, a two-component developing method in which carrier and toner are mixed is used as a developing method used in such image forming apparatuses, but in this method, the life of the carrier is short, and in order to obtain stable image forming performance, However, it is necessary to maintain the mixture ratio of carrier and toner within a certain range, and not only regular maintenance is required, but the device itself has disadvantages such as being large and complicated.

On the other hand, in order to improve the drawbacks of the two-component developing method, a one-component developing method using only a magnetic or non-magnetic one-component toner as a developer has been devised and put into practical use. Among these, the non-magnetic one-component development method has the characteristics of excellent image resolution and sharpness, as well as the ability to obtain vivid color images because the toner particles do not contain magnetic powder.
A developing method using an elastic developing roller disclosed in Japanese Patent Publication No. 2-143831 and a hollow cylindrical conductive thin film member disclosed in Japanese Unexamined Patent Publication No. 64-65579 by slidingly contacting a photoreceptor. A method is proposed.

[0005]

[Problems to be Solved by the Invention] However, in the non-magnetic one-component developing method, the magnetic attraction force found in magnetic toner cannot be used as the attraction force to support the toner on the surface of a carrier such as a developing roller or a developing sleeve. It relies on the electrostatic mirror image force of the charged toner. This mirror image force is affected by the amount of charge on the toner particles, so if the toner deteriorates due to physical stress and the amount of charge decreases, there is a risk that the toner will scatter outside the developing device. It had the disadvantage that the initial development characteristics could not be maintained.

[0006] Furthermore, with magnetic toner, since a magnetic attraction force acts in the direction of the developing sleeve during development, it is expected that the toner that has physically adhered to the non-image area will be pulled back toward the developing sleeve. However, since non-magnetic toner cannot be expected to have such a magnetic force, it has the disadvantage that so-called scumming is likely to occur and the toner is wasted.

[0007]The present invention is intended to solve these problems, and its purpose is to suppress toner deterioration and wasteful toner consumption, and to provide an image that is stable over time. The purpose is to provide a forming device.

[0008]

[Means for Solving the Problems] The image forming apparatus of the present invention is an image forming apparatus using a belt photoreceptor, and is characterized in that the belt photoreceptor is separated from a developing means during non-development.

[0009]

According to the present invention, the belt photoreceptor is deformed by the spacing member disposed near the developing means to separate it from the surface of the toner carrier of the developing means.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a printer will be described below with reference to the drawings. FIG. 1 is a sectional view of the entire device. FIG. 2 is a sectional view of the main parts of the developing device. The photoreceptor belt 2 has a belt shape with a circumference of 283 mm and a width of 250 mm, and is constructed by applying OPC (organic photoconductor) to a Ni base with a thickness of 35 μm produced by electroforming. Then, it rotates in the direction shown by arrow A in the figure by receiving a driving force from a driving source (not shown). The rotation speed of the photoreceptor belt 2 is 36 m.
m/S. The charging device 4 uniformly charges the surface of the photoreceptor belt 2 to -680V by corona discharge. Thereafter, the laser beam modulated by the image signal is swept by a polygon mirror 6 that rotates at high speed, passes through an imaging lens system 8 and a reflection mirror 10, and exposes the surface of the photoreceptor belt 2 to form an electrostatic latent image. . As a means for this optical image exposure, it is also possible to use an LED array, a liquid crystal shutter array, or the like.

[0011] Normally, the printer device is a negative type or a positive type in which a portion corresponding to the image area is irradiated with light, and in this embodiment, the potential corresponding to the image area is -
It drops to 70v. On the other hand, the potential corresponding to the non-image area is -
It remains at 680v. The latent image thus formed moves to the development position as the photoreceptor belt 2 rotates.

The developing device 12 includes a hopper 16 containing approximately 200 g of one-component non-magnetic toner 14;
an agitator 2 that supplies toner 14 and a developing roller 14 to a developing roller 18 by rotating at a cycle of 15 γ pm within
0, a replenishment roller 22, a doctor blade 24, etc. The supply roller 22 is made of conductive sponge with an outer diameter of φ9 mm and a volume resistance of 106 Ω·cm, and has a length of 170 m.
It rotates in sliding contact with the developing roller 18 in the direction of arrow B in the figure at a circumferential speed of m/s to supply the toner 14 to the surface of the developing roller 18. The developing roller 18 has an outer diameter of 12 mm and has a two-layer structure.
In contrast to the nitrile butadiene rubber (NBR) of the inner layer 56, the outer layer 58 is made of 50 μm thick urethane rubber. Al fine particles 60 are dispersed in the urethane rubber layer, and the volume resistance of the roller as a whole is about 109 Ω·cm.

The doctor blade 24 is made of silicone rubber and comes into contact with the surface of the developing roller 18 which rotates in the direction of arrow C in the figure at a circumferential speed of 170 mm/s to regulate the toner layer thickness. -550v and -400v are applied to the core metals of the replenishing roller 22 and the developing roller 18, respectively, and the toner is approximately -3
Charge to 5μc/g. The charged toner is carried on the developing roller 18 by mirror image force, and is conveyed to the developing position as it rotates. The transported toner 14 is transferred to the photoreceptor belt along the electric field between the developing bias voltage applied to the developing roller 18 and the electrostatic latent image potential formed on the photoreceptor belt 2 by the above-mentioned photoimage exposure. The developing operation is completed by moving to the 2nd side.

FIG. 3 shows the developing characteristics when the developing device of this example is used. The horizontal axis shows the surface potential Vo of the photoreceptor belt 2.
and the developing bias VB, and the vertical axis represents the image density on the recording paper. In this example, developing bias -3
At 50V, an image density of 1.4 or higher was obtained.

The surface of the photosensitive belt 2, which has been visualized by the toner 14 in the above-described process, rotates to a position facing the transfer device 26. On the other hand, the recording paper 30 is fed from the paper feeding device 28 to the transfer position in synchronization with the developed toner image. At this time, a transfer device 26 using corona discharge
is activated, and the back surface of the recording paper 30, the lower side in FIG. 1, is uniformly charged with positive ions. Due to the action of the electric field generated by this uniform charging, the toner 14, which has been negatively charged in advance, is transferred from the surface of the photoreceptor belt 2 to the surface of the recording paper 30.

The recording paper 30, which has been transferred to the rear end in the transfer process, is separated by curvature from the surface of the photoreceptor belt 2 due to the rigidity of the recording paper 30, and the toner particles are fused to the recording paper 30 by the action of heat and pressure. In order to do this, the image is conveyed to a fixing device 36 that includes a heating roller 32 and a pressure roller 34. The recording paper 30 that has been fixed is ejected onto a paper ejection portion 40 formed on the upper surface of the main body of the apparatus in a so-called face-down state with the printed surface facing downward in the drawing by receiving the conveyance force of the paper ejection roller 38.

On the other hand, about 10% of untransferred toner remains on the surface of the photoreceptor belt 2 after the transfer process. Since this untransferred toner becomes an obstacle to the next image forming process, it is physically scraped off by a cleaning blade 42 made of polyurethane rubber. The scraped off untransferred toner is
The toner is collected into the rear waste toner box 44 and disposed of as waste toner. Through this cleaning process, the surface of the photoreceptor belt 2 becomes visually clean, but since a latent image still remains, the surface potential is uniformly lowered by uniformly exposing the photoreceptor belt 2 to light using the static elimination lamp 46, and initialization is performed. After that, proceed to the next charging process.

Next, the spacing member 48 of the photoreceptor belt 2, which is a feature of the present invention, will be explained using FIG. 4. Pressing roller 5
0 has an outer diameter of 5 mm and is made of a material such as a sponge roller or urethane roller that does not have an adverse effect even if it comes into contact with the photoreceptor belt 2. The photoreceptor belt 2 is separated from the photoreceptor belt 2 by a separating mechanism which will be described later.
The photoreceptor belt 2 is pressed and deformed in the direction indicated by the middle arrow F to separate the photoreceptor belt 2 from the developing roller 18 . Further, during a normal developing operation, the spacing member 48 swings in the direction shown by arrow G, separates from the photoreceptor belt 2, and the photoreceptor belt 2 returns to its original position and comes into sliding contact with the developing roller 18 to perform the developing operation.

Development is carried out according to the above explanation, and toner 1
Toner 4 is developed and consumed sequentially from the top of the developing roller 18 to the photoreceptor belt 2 side, but when the ratio of images (characters, figures, etc.) occupying the surface of the recording paper is low, the amount of toner 14 consumed is small. Identical toner particles that are not produced by the developing roller 18
The photoreceptor belt 2 is held on the photoreceptor belt 2 for a long time, and physical abrasion between the doctor blade 24 and the photoreceptor belt 2 is repeated. This stress causes the toner particles to coagulate with each other or to be flattened, resulting in a change in the amount of charge, resulting in the so-called fog phenomenon that adheres to the discharged image area and an increase in toner scattering.

On the other hand, in an image forming apparatus using an electrophotographic method, since the photoreceptor is uniformly irradiated with light by the static elimination lamp 46 before the charging process, The surface potential of the photoreceptor belt 2 is approximately 0V. The image forming process starts from this state, but since the image device according to this embodiment uses a reversal image method, the toner particles 14 are deposited on the portion where the light image has been exposed, that is, on the photoreceptor belt. 2 is developed in areas where the surface potential has decreased. Therefore, the photoreceptor belt 2 of the printer device
When a developing bias is applied in synchronization with the start of the rotation, the entire area D in FIG. 5 is developed, resulting in wasted toner.

As a method for solving this phenomenon, the potential relationship at point E where the amount of development becomes zero in the graph showing the development characteristics shown in FIG.
Since o is approximately 0V, it is necessary to set the developing bias VB to +70V and maintain this state while the area D of the photoreceptor belt 2 passes the developing roller 18. However, since the polarity of the developing bias in the normal developing state is negative, in order to eliminate the toner electrically adhering to the area D, a power source with both positive and negative polarities is prepared as the developing bias power source.
Control such as switching these is required, which causes high costs.

According to the features of the present application, the above two problems, that is, toner deterioration and toner waste can be solved. The timing chart shown in Figure 6 below, as well as Figures 4 and 7
The control method and operation of the spacing member 48 of the photoreceptor belt 2 will be explained in detail with reference to FIG.

The spacing member 48 operates during the following three periods to press and deform the photosensitive belt 2, thereby separating the photosensitive belt 2 from the developing roller 18.

(2) Period from the start of rotation of the photoreceptor belt to just before the beginning of the latent image.

■Period corresponding to the paper interval of continuous printing.

(2) The period from immediately after the trailing edge of the last latent image until the recording paper is ejected and the photosensitive belt stops.

First, period (3) will be explained. The main purpose of period (3) is to reduce the amount of toner that is wasted adhering to the area D mentioned above to zero. In the initial state when the printer main body is stopped, the pressure roller 50 is located in a non-contact state with the surface of the photoreceptor belt 2, and the photoreceptor belt 2 is maintained in a state of sliding contact with the developing roller 18 under the tension of the tension roller 52. has been done. Immediately before print data is input to the printer from an external host computer, etc., and the photoreceptor belt 2 starts rotating for printing, the arm 54 is pulled in the direction of arrow H in FIG. 4 by the acting force of a solenoid (not shown). Accordingly, the pressure roller 50 swings in the direction of arrow F, presses the photoreceptor belt 2, deforms it, and slightly separates it from the developing roller 18. (Period shown in FIG. 6) As a result, the photoreceptor belt 2 is separated from the developing roller 18 and allowed to pass through so as not to develop the area D shown in FIG. 5 where the surface potential is approximately 0V and initial charging is impossible. , to reliably prevent toner from sticking and being wasted.

This separation state is maintained until just before the beginning of the latent image corresponding to the image to be developed reaches the development position. Immediately before the beginning of the latent image reaches the development position, the arm 54 of the spacing member 48 swings back in the direction of arrow G in the figure by turning off the power to the solenoid.
Accordingly, the pressure roller 50 separates from the surface of the photoreceptor belt 2. As the photoreceptor belt 2 returns to its normal state under the tension of the tension roller 52, its surface comes into sliding contact with the developing roller 18 and a predetermined developing operation is started.

FIG. 7 shows the positional relationship between the photosensitive belt 2, the pressing roller 50, and the developing roller 18 in the developing state and FIG. 8 in the separated state. Here, the beginning of the latent image may be the same as the beginning of the fed recording paper, but if the beginning of the image starts from the latter half of the recording paper as in the image shown in FIG. It is also possible to carry out control in which the photoreceptor belt 2 is separated for a time corresponding to area J in FIG.

Next, period (3) will be explained. The purpose of period ■ is to prevent toner from inevitably adhering to non-image areas, and when printing on multiple sheets of recording paper continuously, the For the area corresponding to the non-image area, the photoreceptor belt 2 is moved to the developing roller 1.
8.

FIG. 6 shows a timing chart for printing two consecutive sheets. The printer in this embodiment has a printing speed that is capable of conveying A4 paper in the vertical direction and continuously printing 6 sheets per minute, and in this state, the paper interval is 75
．． It is 6mm.

Next, the operation of the spacing member 48 will be explained. After starting the developing operation described in the above-mentioned period (■), the arm 54 is moved in synchronization with the trailing edge portion of the photoreceptor belt 2 corresponding to the trailing edge position of the first recording sheet passing through the developing position. is swung in the direction of arrow F to separate the photoreceptor belt 2 from the developing roller 18. Thereafter, just before the leading edge portion of the photoreceptor belt 2 corresponding to the leading edge position of the second subsequent recording sheet reaches the developing position where it comes into sliding contact with the developing roller 18, the arm 5
4 in the direction of arrow G, the photoreceptor belt 2 is brought into sliding contact with the developing roller 18, and a predetermined developing operation is started. In this way, by separating the photoreceptor belt 2 from the developing roller 18 in the area corresponding to the paper interval (period shown as 6 and M in the figure), the generation of toner that inevitably adheres to the non-image area is prevented. At the same time, it reduces the time of physical stress that the toner undergoes between the developing roller 18 and the photoreceptor belt 2,
Reduces the risk of toner deterioration.

The above explanation has been about control for separating the photoreceptor belt 2 for a predetermined paper distance equivalent time (75.6 mm in this embodiment), but as shown in FIG. When the image exists in the first half and the image on the subsequent recording paper exists in the second half, the controller controls the separation of the photoreceptor belt 2 during the non-image area equivalent time T2, which is longer than the paper interval equivalent time T1. It is also possible to make a judgment and execute it.

Next, period (3) will be explained. Period ■, like the above-mentioned period ■, aims to prevent the generation of toner that inevitably adheres to the non-image area, and after the last latent image to be printed is developed, the recording paper is The photosensitive belt is separated for a period of time until the paper is completely ejected to the upper part of the printer main body and the drive source stops. In other words, in FIG. 6, the arm 54 is swung in the direction of arrow F in synchronization with the portion of the photoreceptor belt 2 corresponding to the rear end of the second recording sheet passing through the development position. move,
The photoreceptor belt 2 is separated from the developing roller 18. After that, this non-contact state is maintained until the paper is ejected and the photoreceptor belt 2 stops, and then the arm 54 is swung in the direction of arrow G to return the photoreceptor belt 2 to the state in which it comes into sliding contact with the developing roller 18. This stops all operations. (Period indicated by N in FIG. 6) The above explanation has been about the case where the separation operation of the photoreceptor belt 2 is performed from the position corresponding to the rear end of the last recording sheet on the photoreceptor belt 2. As shown in , when the image on the last recording sheet exists in the first half, the final end of the image, that is, the corresponding part on the photoreceptor belt 2 corresponding to point K, is developed without waiting for the rear end of the sheet. It is also possible to perform control to start an operation of separating the photoreceptor belt 2 in synchronization with the passage of the position.

In this way, by separating the photoreceptor belt 2 from the developing roller 18 during the period corresponding to the ejection period of the last paper, the generation of toner that inevitably adheres to the non-image area is prevented, and the toner is removed. The time of physical stress applied between the developing roller 18 and the photoreceptor belt 2 is shortened, and the risk of toner deterioration is reduced.

In the method for controlling the swing of the arm 54 of the spacing member 48 described above, the photosensitive belt 2 is brought into sliding contact with the developing roller 18 when the printer body is in a completely stopped state, but conversely, when the printer body is in a completely stopped state, It is also possible to use a control method in which the arm 54 is held in a separated state and the arm 54 is swung in the direction of the arrow G for the period necessary to develop the latent image to perform the developing operation.

Furthermore, the position where the pressing roller 50 of the spacing member 48 presses against the photoreceptor belt 2 can also be arranged upstream of the developing position, instead of downstream from the developing position as shown in this embodiment. On the other hand, the separating mechanism for the photoreceptor belt 2 is not limited to the relenoid mechanism shown in this embodiment, but may be improved in design, such as by using gears, rack and pinions, or the like.

[0038]

As described above, according to the present invention, in an image forming apparatus using a belt photoreceptor, by separating the belt photoreceptor from the developing means when no image is being formed, the developing roller of the developing means and the photoreceptor can be separated from each other. The toner is subjected to physical stress when it comes into sliding contact with the surface of the body belt, which causes the toner to aggregate and deform, reducing the amount of charge and causing problems such as background fog, toner scattering, and reduced image quality. This can be avoided and print quality that is stable over time can be obtained. Another effect is that the generation of toner that adheres to the area from the initial charging position to the developing position during image formation is prevented, and at the same time, the developing operation for the paper gap and the last paper is completed, and that paper Since the generation of toner that inevitably adheres to non-image areas on the photoreceptor belt during the period before it is discharged is also prevented, toner is not wasted and the life of consumables is extended. It also has the effect of reducing running costs.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the main parts of an image forming apparatus according to the present invention.

FIG. 2 is a sectional view showing the main parts of an image device used in the image forming apparatus according to the present invention.

FIG. 3 is a diagram illustrating development characteristics using the developing device of this example.

FIG. 4 is a diagram illustrating the operation of a separating member that separates the photoreceptor belt from the developing means according to the present invention.

FIG. 5 is a diagram illustrating toner developed in an area from a charging position to a developing position.

FIG. 6 is a timing chart illustrating control of the operation of the spacing member according to the present invention.

[Figure 7] Photoreceptor belt, pressure roller, in developing state,
FIG. 3 is a diagram showing the positional relationship of developing rollers.

[Fig. 8] Photoreceptor belt, pressure roller, in a separated state,
FIG. 3 is a diagram showing the positional relationship of developing rollers.

FIG. 9 is a diagram showing that the image on the recording paper is present in the latter half.

FIG. 10 is a diagram illustrating that when two sheets of paper are continuously printed, the image on the first sheet of recording paper is present in the first half, and the image on the second sheet of recording paper is present in the second half.

FIG. 11 is a diagram showing that the image on the last recording sheet exists in the first half.

[Explanation of symbols]

2 Photoreceptor belt 18 Developing roller 48 Spacing member 50 Press roller

Claims (2)

[Claims] 1. An image forming apparatus using a belt photoreceptor, characterized in that the belt photoreceptor is separated from a developing means during non-development. 2. The image forming apparatus according to claim 1, wherein the separating operation is performed by deforming the belt photoreceptor.