JPH0435074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image forming method in an electrophotographic copying machine electrostatic recording device, and in particular, the present invention relates to an image forming method in an electrophotographic copying machine electrostatic recording device, and in particular, the present invention relates to an image forming method in which the surface of a rotating image forming body is charged to a uniform potential, A latent image area in which low potential spots or potential spots of opposite polarity are distributed is formed on the charged surface by means such as a laser beam scanner or an electrostatic recording head, and the developing sleeve is applied with an alternating current voltage and the same polarity as the uniform potential. By applying a bias voltage superimposed with a DC voltage of The present invention relates to an image forming method that performs development in which toner charged to the same polarity as the potential is caused to fly and adhere to spots in the latent image area.

[Prior art]

As a typical image forming method as described above, an image forming body having a photoconductor layer on the surface is used,
A laser beam scanner performs spot exposure on the uniformly charged surface of the image forming body to form an electrostatic latent image consisting of low potential dots, and toner charged to the same polarity as the image forming body is deposited on the low potential dots. One example is a method of attaching. This method is compared to an image forming method in which toner charged with the opposite polarity is caused to fly from the developer layer of the developing sleeve and adhere to an electrostatic latent image whose image portion potential is higher than the background potential. In order to cause the toner to adhere to the image forming body against the electrical repulsion from the charging of the image forming body and to prevent fogging, the DC component of the bias voltage applied to the developing sleeve is applied to the uniform charging of the image forming body. It is required that the potential be close to the background potential of the latent image, and that the amplitude of the alternating current component be increased. Therefore, if a bias voltage is applied to the developing sleeve while an uncharged area of the image forming body is passing through the developing area, toner may be unnecessarily attached to the image forming body and excess toner may be generated. This may consume a lot of toner, increase the burden on cleaning equipment, etc., and cause toner to scatter, increasing the occurrence of dirt.

In image forming methods in which toner charged with opposite polarity is attached to an electrostatic latent image whose image partial potential is higher, in order to save power and prevent toner from scattering,
USP 3,893,418 and Japanese Patent Application Laid-Open No. 1983-1989 disclose a system in which the application of bias voltage to the developing sleeve is stopped while the uncharged area of the image forming body passes through the developing area.
It is known from Publication No. 14266.

However, in an image forming method in which toner charged to the same polarity as the image forming member is attached to an electrostatic latent image, the bias voltage to the developing sleeve is applied only while the uncharged area of the image forming member passes through the development area. Even if the application is stopped, it is insufficient to prevent toner scattering and wasted costs.

[Purpose of the invention]

The present invention solves the problem that toner scattering and wasted costs cannot be prevented even if the application of the bias voltage is stopped only while the uncharged area of the image forming body passes through the development area. The influence of bias voltage application extends even when passing through an uncharged area, such as when the image forming body floats when the application is stopped, or because the potential changes greatly at the boundary between the charged and uncharged areas of the image forming body. This was done as a result of discovering a method of applying bias voltage that effectively prevents toner scattering and wasted waste. An image in which toner charged to the same polarity as that of the forming member is caused to fly from the developer layer on the developing sleeve and adhere to an electrostatic latent image consisting of a distribution of low potential spots or opposite polarity potential spots on the charging surface of the image forming member. A forming method is provided.

[Structure of the invention]

The present invention charges the surface of a rotating image forming member to a uniform potential, forms a latent image area in which low potential spots or opposite polarity potential spots are distributed on the charged surface, and applies an alternating current voltage to the developing sleeve. By applying a bias voltage in which a uniform potential and a DC voltage of the same polarity are superimposed, the developing sleeve is formed in a layer thickness that does not come into contact with the surface of the image forming body on the developing sleeve in the developing area close to the image forming body. In an image forming method in which toner charged to the same polarity as the uniform potential is caused to fly from an agent layer and adhere to spots in the latent image area for development, after the latent image area of the image forming body passes through the development area. The image forming method is characterized in that the bias voltage is changed so that a maximum voltage of the same polarity as the uniform potential decreases while the charged surface of the uniform potential passes through the image forming method. The above objective is achieved through the configuration.

〔Example〕

The present invention will be explained below using illustrated examples.

FIG. 1 is a schematic configuration diagram showing an example of a recording apparatus that implements the method of the present invention, FIG. 2 is a partial diagram showing an example of a developing device, and FIGS. 3 to 6 are bias voltages applied to the developing sleeve, respectively. Graphs showing examples of the above, and FIGS. 7 to 9 are circuit diagrams showing examples of configurations of bias power supplies that apply the bias voltages shown in FIGS. 3 to 5, respectively.

The recording device shown in FIG. 1 uses a signal processing device 1 to process image data obtained from a signal input from a document image sensor or other equipment, or from data in a data storage unit, so that binary (i.e., black and white)
An image signal composed of converted pixel data (hereinafter referred to as a binary image) is obtained, and the pixel data of this binary image is used to control a laser beam scanner consisting of a laser, an acousto-optic modulator, a lens device, a rotating polygon mirror, etc. The YANA 2 is controlled ON and OFF for each pixel, rotates in the direction of the arrow, and performs image exposure with a laser spot on the surface of the photoconductor layer of the image forming body 3, which is uniformly charged by the charger 4. A toner image is formed by attaching toner charged to the same polarity as that of the image forming member 3 under an electric field using a developing device 5 as shown in detail in FIG. 2 on the exposed portion. Then, the formed toner image is transferred by a transfer device 6 onto a recording paper P that is fed so as to be in contact with the surface of the image forming body 3 in synchronization with the rotation of the image forming body 3, and the toner image is transferred. The recorded paper P′ is transferred to the separator 7
The toner image is separated from the surface of the image forming body 3 by a roller fixing device 8, and then the toner image is fixed by a roller fixing device 8 and discharged from the recording apparatus. On the other hand, the surface of the image forming body 3 to which the toner image has been transferred is neutralized by a static eliminator 9, and then residual toner is removed by a cleaning device 10 to complete one image forming process.

In the developing device 5 shown in FIG. 2, a bias voltage is applied by a bias power supply 11 to a developing sleeve 51 made of a non-magnetic material such as aluminum or stainless steel, and an image forming member 3 whose base portion is grounded
An electric field is generated in the development area A between the two. Inside this developing sleeve 51, there are a plurality of N and S on the surface.
A magnet body 52 having magnetic poles is provided. Then, as the developing sleeve 51 stands still or rotates counterclockwise and the magnet body 52 rotates clockwise or stands still, the developer attracted from the developer reservoir 53 to the surface of the developing sleeve 51 by the magnetic force of the magnet body 52 is transferred to the surface of the developing sleeve 51. One or both rotations result in counterclockwise movement. The developer transported in this manner is directed to the image forming body 3 by the layer thickness regulating blade 54.
The toner is regulated to a layer thickness within a range that does not contact the surface of the image forming member 3, and in the development area A, toner flies from the developer layer due to the action of an electric field and develops the electrostatic latent image on the image forming member 3.
Note that it is preferable that the magnet body 52 rotates in that the influence of unevenness of the developer layer is less likely to appear in the development.

The remaining developer layer that has passed through the developing area A is removed from the surface of the developing sleeve 51 by the cleaning blade 55 and returned to the developer reservoir 53. The developer in the developer reservoir 53 is a so-called two-component developer containing a mixture of toner and carrier, and is agitated by an agitating blade 56 so that the toner is charged to the same polarity as that of the image forming member 1. Since the toner is consumed during development, it is replenished from the toner hopper 57 to the developer reservoir 53 by the toner replenishment roller 58.

In order to develop an electrostatic latent image by causing toner charged to the same polarity as that of the image forming member 3 to fly from the developer layer on the developing sleeve 51 in the developing area A, the developing sleeve 51 is provided with the toner of the image forming member 3. A bias voltage in which a DC voltage and an AC voltage having the same polarity as the background potential are superimposed is applied. The bias power supply 11 applies this bias voltage as shown in FIGS. 3 to 6, thereby preventing toner scattering and wasted costs.

In FIGS. 3 to 6, Ti is the image forming member 3.
Tv is the time period during which the image forming area on which the electrostatic latent image has been formed through image exposure passes through the development area A, and Tv is the non-image charging period when the image forming body 3 is only charged after the image exposure has been completed. The time period during which the area passes through the development area A,
To is the image forming body 3 that has finished being charged by the charger 4.
This shows the time period during which the uncharged area passes through the development area A. FIG. 3 shows that during time period Ti, a bias voltage obtained by superimposing a direct current voltage V _DC , which is slightly lower than the charged potential Vi of the image forming body 3, on an alternating current voltage is applied to the developing sleeve 31, and when time period Tv begins, a bias voltage is applied to the developing sleeve 31. An example is shown in which the bias voltage is converted into a pulsed voltage showing only a potential of opposite polarity to the charging of the image forming body 3 in a rectified form, and then the application is stopped within the time period Tv,
FIG. 4 shows that when entering the time period Tv, the amplitude of the AC component of the bias voltage is attenuated to 0, and then the DC component V _DC is changed from 0 to a level showing the opposite polarity to the charging of the image forming member 3. Fig. 5 shows an example that differs from Fig. 3 in that when the time period Tv is entered, the DC component V _DC of the bias voltage is first set to 0 or a level indicating the opposite polarity to the charging of the image forming body 3. This shows an example that differs from Fig. 3 or 4 in that the amplitude of the AC component is converted to 0 and then the amplitude of the AC component is attenuated to 0. The fifth point is after entering the time zone To.
An example different from the figure is shown.

The example of FIG. 3 can be implemented by using a circuit as shown in FIG. 7 for the bias power supply 11, and the example of FIG. 4 can be implemented by using a circuit as shown in FIG. It can be implemented by a circuit that combines the circuits shown in FIG.
The examples shown in FIGS. 9 and 6 can be implemented by using a circuit that is a combination of the circuit shown in FIG. 9 and the circuit shown in FIG. 8 for the bias power supply 11. That is, in the circuit shown in FIG. 7, by turning on the switch 12 of the rectifier circuit, the bias consisting of the superposition of the DC voltage and AC voltage, which had been applied to the developing sleeve 31, is changed into a pulsed form as shown in FIG. By sliding the short circuit contact 13 of the secondary coil toward the DC power source in the circuit shown in Figure 8, the AC component of the bias voltage can be converted to the bias voltage of Figures 4, 5, or 6. As shown in the diagram, the amplitude can be attenuated to 0, and by sliding the moving contact 14 of the variable resistor from top to bottom or from bottom to top in the circuit shown in FIG. , can be changed as shown in FIG. 6 or FIG. Note that attenuation of the alternating current component is not limited to the above-mentioned example, and it goes without saying that the attenuation of the alternating current component may be performed on the oscillation circuit side. In addition, when changing the DC component to 0, it goes without saying that one reverse potential circuit part of the DC power supply circuit shown in Fig. 9 is not required, or the secondary coil is connected to the DC power supply by a switch. The side may be switched from being connected to a DC power supply to being grounded.

By applying a bias voltage to the developing sleeve 31 as shown in FIGS. 3 to 6, the non-image charged area of the image forming body 3 that is charged to repel toner becomes a developing area. While passing through A, the force of the electric field in the developing area A to cause the toner to fly from the developer layer and adhere to the image forming member 3 is weakened, and as a result, the toner in the non-image charged area of the image forming member 3 is weakened. Since the toner is returned to the developer layer by the repulsive force, toner is prevented from adhering to areas other than the image forming area and being wasted or being scattered. Note that the alternating current component of the electric field has a large effect on causing the toner to fly from the developer layer, so it depends on the time of day.
It is more preferable to use the example shown in Fig. 3 or 4, in which the alternating current component of the bias voltage is first changed when entering the TV, and in the examples shown in Figs. 5 and 6, the alternating current component is quickly attenuated. The illustrated example is preferred. In addition, changing the bias voltage as shown in FIGS. 3 to 6 may be done each time image formation is performed, or when image formation is performed continuously, during image formation during development. Alternatively, the bias voltage may be maintained and changed during the time period Tv in the final image formation.

The alternating current voltage component and direct current voltage component of the bias voltage during development are determined so that a clear and fog-free toner image can be obtained. In order to easily determine such a bias voltage, it is necessary to
The two-component developer preferably uses insulating magnetic carrier particles having a resistivity of 10 ⁸ Ωcm or more, particularly 10 ¹³ Ωcm or more. As such carrier particles, carrier particles having a resin coating formed on the surface of magnetic particles or carrier particles made of resin particles containing magnetic particles dispersed therein are used. In addition, the resistivity of the insulating particles is 0.5
After putting it in a container with a cross-sectional area of cm ² and tapping it to a thickness of about 1 mm, 1 kg/kg was poured onto the packed particles.
Apply a load of ^cm2 , and connect the load to the bottom electrode.
This value is obtained by reading the current value when applying a voltage that produces an electric field of 1000 V/cm. Also,
In order for development to be carried out clearly and with good resolution, the average particle diameter of the toner particles in the two-component developer must be 20 μm or less.
In particular, it is preferably 1 to 10 μm, and the average particle size of the carrier particles is also preferably 5 to 50 μm. The average particle size of these particles is a weight average particle size, and is measured with a Coulter Counter (manufactured by Coulter) or Omnicon Alpha (manufactured by Boshilom). If the average particle size of the toner particles becomes too small, the van der Waals force becomes relatively large as the amount of charge due to friction of a single toner particle becomes small, making it easier to aggregate or difficult to separate and fly. On the other hand, if the average particle diameter becomes too large, the amount of charge for superimposition decreases, making it difficult to control flight and reducing resolution. Also,
If the average particle size of the carrier particles becomes too small,
While the adsorption force due to the magnetic force of the magnet body 52 becomes weaker, the electric Coulomb force becomes stronger due to the Van der Waals force, so that the carrier particles migrate to the surface of the image forming member 3 together with the toner particles. On the other hand, if the average particle size becomes too large, the developer layer formed on the developing sleeve 51 will become coarse, making it difficult to form a thin and uniform developer layer, and also causing problems in the developer layer. The state of adhesion of toner particles is no longer uniform, and breakdown and discharge of the voltage applied to the developing sleeve 51 are likely to occur, making it difficult to control the flight of toner particles.

Furthermore, in order to effectively control toner flight by applying a bias voltage to the developing sleeve 51, it is necessary to increase the gap between the image forming body 3 and the developing sleeve 51 by several times.
It is preferable that the thickness of the developer layer is in the range of 10 to 2000 μm, and therefore the thickness of the developer layer regulated by the layer thickness regulating blade 54 is smaller than this. If the gap in this development zone is made too narrow, the thickness of the developer layer must be made very thin, which makes it impossible to obtain a uniform layer thickness and therefore to supply a stable supply of toner particles to the development zone. Not only is this impossible, but also electric discharge is likely to occur between the developing sleeve 51 and the image forming body 3, damaging the developer and causing toner particles to scatter. On the other hand, if the gap between the developing areas is made too wide, it becomes difficult to control the flying of toner using the oscillating electric field.

Developing is carried out under the preferable conditions described above,
If the bias voltage applied to the developing sleeve 51 during development is changed as shown in FIGS. 3 to 6 to complete image formation, a clear recorded image without fogging can be obtained. Moreover, it is possible to obtain the result that toner consumption and scattering are reduced. Note that the developing sleeve 51 and the magnet body 52
The rotation of the developer may be stopped at any time after the image forming area of the image forming body 3 has passed through the development area A, but it is best to stop the rotation of the developer after the bias voltage in the time period Tv changes. This is preferable because the amount of toner collected in the layer does not increase locally.

Next, more specific embodiments of the present invention will be described.

Example 1 The apparatus shown in FIGS. 1 and 2 was used.

The image forming body 3 has a selenium photoreceptor layer on its surface, rotates in the direction of the arrow at a surface speed of 120 mm/sec, and is charged to 500 V by the charger 4. The laser beam scanner 2 forms an electrostatic latent image in the form of 50V dots. The gap between the image forming body 3 and the developing sleeve 51 in the developing area A is 700 μm, the outer diameter of the developing sleeve 51 is 30 mm, and the rotation speed in the left direction is 65 rpm. in the gap,
Rotates at 700rpm in the direction of the arrow. Developer reservoir 53
The developer consists of an insulating carrier with a resistivity of 10 ¹⁶ , which is made by dispersing magnetic powder in a resin with a weight average particle size of about 30 μm, and a positive carrier with a weight average particle size of 14 μm.
A two-component developer mixed with insulating non-magnetic toner charged at about 20 μC/g was used, and the layer thickness of the developer layer formed on the developing sleeve 51 was regulated to about 500 μm by a layer thickness regulating blade 54. Image forming body 3
Simultaneously with the rotation of the developing sleeve 51, a DC voltage of -150V is applied from the bias power supply 11 to the developing sleeve 51. and,
The bias power supply 11 applies a bias voltage of 2 kV, 2 kHz AC to the developing sleeve 51 in a non-image charging area before the image forming area on which the electrostatic latent image of the image forming body 3 is formed reaches the developing device 5. voltage and
Switch to superimposed voltage of 400V DC voltage. At the same time, the developing sleeve 51 and the magnet body 52 are rotated. While the image forming area passes through the development area A and the non-image charged area passes through the development area A, the bias power supply 11 reduces the AC component of the bias voltage and then changes the DC component to -150V. The rotation of the developing sleeve 51 and the magnet body 52 is stopped when the DC voltage component of the bias voltage is changed to -150V.
Then, the bias power supply 11 sets the bias voltage to 0 when the uncharged area passes through the development area A and the image forming body stops rotating. That is, the bias power supply 11 controls the bias voltage as shown in FIG.

Developed under the above conditions, the resulting toner image was transferred to recording paper P made of plain paper, and the surface temperature was 140°C.
The image was fixed by a roller fixing device 8.

The recorded image thus obtained was extremely clear with high density and no fog. After recording images on 50,000 sheets of recording paper, we were able to obtain recorded images that remained stable from beginning to end, and there was no toner scattering from the gap between the developing device 5 and the image forming body 3. Therefore, the amount of toner collected by the cleaning device 10 was also small.

On the other hand, after the uncharged area of the image forming body 3 passes through the development area A, the bias power supply 1
1 inverts the DC component of the bias voltage and attenuates the AC component to 0, the cleaning device 1
Not only did the amount of toner collected at zero increase significantly, but also the amount of toner scattering from the developing device 5 increased, making it impossible to obtain 10,000 sheets of recording paper.

Note that the AC component of the bias voltage applied to the developing sleeve 51 during development has a frequency of 100 to 10,000.
Hz, preferably 1000~5000Hz, effective amplitude 200~
At 5000V, there is an effective value of 300~ between the image forming body 3 and
A type that produces an electric field strength of 5000 V/mm is preferably used, and the waveform is not limited to a sine wave, but may be a rectangular wave or a triangular wave. In addition, it is preferable to use a two-component developer as the developer.
A one-component developer known from USP 3893418 and Japanese Patent Application Laid-Open No. 18656/1984 may be used.

〔Effect of the invention〕

According to the image forming method of the present invention, a clear toner image without fogging can be formed using toner charged to the same polarity as that of the image forming member, without scattering the toner or wasting the toner.

The present invention is applicable not only to recording devices that use laser beam scanners but also to recording devices that use multi-needle electrodes and the like. Further, the present invention can also be applied to an image forming method using an image forming body having an insulating layer on a photosensitive layer. Further, the present invention provides a color image recording device having a plurality of developing devices and a color image recording device that superimposes toner images on an image forming body (Japanese Patent Application Nos. 58-184381, 58-183152, and 58-187000). )
It can also be applied to

In addition, although the attenuation of the AC bias at the end of development has been described in connection with the example, scattering and consumption of toner can be reduced by applying the AC bias at the start of development in a process reverse to that shown in Figures 3 to 6. Needless to say, it is possible to obtain favorable results.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a recording apparatus that implements the method of the present invention, FIG. 2 is a partial diagram showing an example of a developing device, and FIGS. 3 to 6 are bias voltages applied to the developing sleeve, respectively. FIGS. 7 to 9 are circuit diagrams showing examples of configurations of bias power supplies that apply the bias voltages shown in FIGS. 3 to 6. 2... Laser beam scanner, 3... Image forming body, 4... Charger, 5... Developing device, 51... Developing sleeve, 52... Magnet, 53... Developer reservoir, 54... Layer Thickness regulation blade, A...Development area,
11...Bias power supply, Ti...image forming area passing time period, Tv...non-image charging area passing time period,
To... Time period when passing through an uncharged area.

Claims (1)

[Claims] 1. The surface of the rotating image forming body is charged to a uniform potential, a latent image area in which low potential spots or reverse polarity potential spots are distributed is formed on the charged surface, and an alternating current is applied to the developing sleeve. By applying a bias voltage that is a superimposed voltage and a DC voltage having the same polarity as the uniform potential, the layer thickness is increased so that the developing sleeve does not come into contact with the surface of the image forming body on the developing sleeve in the developing area close to the image forming body. In an image forming method in which toner charged to the same polarity as the uniform potential is caused to fly from a formed developer layer and adhere to spots in the latent image area for development, the latent image area of the image forming body is formed in the developing area. An image forming method characterized in that the bias voltage is changed so that a maximum voltage having the same polarity as the uniform potential decreases while the charged surface having the uniform potential passes through the charged surface. 2. The image forming method according to claim 1, wherein the change in the bias voltage is performed by blocking a voltage portion having the same polarity as the uniform potential by rectification. 3. The image forming method according to claim 1, wherein the change in the bias voltage is performed by attenuating the amplitude of the alternating current voltage. 4. The image forming method according to claim 1, wherein the change in the bias voltage is performed by changing the DC voltage to a low potential or a reverse polarity potential.