JPH01118879A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent image quality without an image memory and a ghost image by using developer having color powder whose permittivity is specified so that development is performed and collecting the toner of a photosensitive body after a transfer stage simultaneously with the developing stage of a developing device. CONSTITUTION:An electrostatic latent image formed in the exposing stage of an exposing part is developed by using the developer D having the coloring powder (t) whose permittivity shows the value of 3.0-5.0 and also the toner of the photosensitive body 2 after the transfer stage of a transfer device 6 is collected simultaneously with the developing stage of the developing device 5. Therefore, the sticking of opposite polarity coloring powder onto the image carrier 2 caused by injecting a charge at the time of developing, that means, the inverted sticking onto a non-image part, is not caused and the filter effect of the coloring powder (t) invertedly sticked in the exposing stage to the next cycle can be removed since the image density, etc., can be maintained. Thus, the excellent image quality without the image memory and the ghost can be obtained.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to an image forming apparatus that can be applied to, for example, a laser printer, and in particular, to an image forming apparatus that is applicable to a laser printer, etc. The present invention relates to an image forming apparatus that simultaneously performs image forming using the same apparatus.

(Prior Art) As shown in FIG. 11, a conventional image forming apparatus uses a corona charger around a drum-shaped photoreceptor a as an image carrier along the rotational direction of the photoreceptor a.

Laser exposure means C1 developer d, transfer charger e, peeling charger f, blade type cleaning device (cleaner) g,
It has a structure in which static eliminators, etc. are arranged in sequence.

Further, a paper transport path j is formed for transporting paper P as a recording medium through an image transfer portion i between the transfer charger e and the photoreceptor a. k is a pair of aligning rollers provided slightly upstream of the image transfer section i in the paper conveyance path j.

After the photoreceptor a is charged by a charger, an electrostatic latent image is formed on the photoreceptor a by irradiation with a laser exposure means C. Next, this electrostatic latent image is developed and visualized with colored powder (hereinafter referred to as toner) in a developer by facing a developing device d.

Meanwhile, in synchronization with this developer image forming operation, the paper P taken out from the paper feed cassettes m and n and the manual paper feed stand O is fed through a pair of aligning rollers k, and is formed on the photoreceptor a in advance. The developed developer image is transferred onto the paper P by the action of the transfer charger e.

Then, the paper P passes through the paper transport path j and is placed in the fixing device q.
Here, after the developer image is fused and fixed on the paper P, it is discharged to the paper discharge section S via a pair of paper discharge rollers.

Note that after the developer image is transferred onto the paper P, the residual developer remaining on the photoreceptor a is cleaned by a cleaning device g, and then the latent image is erased by a static eliminator to complete one process. The configuration is such that the next image formation is possible.

(Problems to be Solved by the Invention) However, in the past, in order to collect the toner remaining on the photoreceptor a after image transfer into the cleaning device g,
Usually, after 2000 to 3000 sheets have been recorded, the cleaning device g becomes full of toner and becomes unusable.

Note that with some equipment, the cleaning device g is discarded together with the photoreceptor a, but this increases the cost of consumables, and with frequently used equipment such as printers, it is necessary to discard the cleaning device g together with the photoreceptor a. It is not preferred because it becomes impossible.

Therefore, normally, a recovered toner delivery screw (toner auger) t is provided in the cleaning device g to send and collect the toner to a toner recovery box (not shown) provided outside the cleaning device g. .

However, since the collection box occupies space within the device, it is not possible to attach a large one, and it is not preferable that it needs to be replaced after several dozen records. Further, when the collection box is removed, some of the toner may spill and stain the hands, clothes, floor, etc. of the person replacing the toner, which is not preferred. Furthermore, in order to bring the blade U into contact with the surface of the photoreceptor a, the cleaning device g
The photoconductor a is easily scratched, and although it is safe and harmless like the OPC photoconductor, the soft photoconductor a has an extremely shortened lifespan.
In the case of a small-diameter photoreceptor a, the replacement cycle becomes short, which is undesirable, and there is a problem in that it becomes an obstacle to miniaturization of the device.

Therefore, a process is being developed that attempts to solve the above problems by configuring a process in which the cleaning device g is removed, but the following problem has occurred and is a major obstacle to practical application.

In other words, if toner of opposite polarity adheres to the photoreceptor a due to charge injection during development, so-called reverse adhesion to a non-image area, the toner that is not transferred during transfer will be exposed during the next cycle. This is a problem because it functions as a filter in the image memory.

The present invention has been made based on the above-mentioned circumstances, and its object is to provide an image forming apparatus that simultaneously performs a developing process and a cleaning process on an image bearing member using the same device, and which includes the following: It is an object of the present invention to provide an image forming apparatus which can form good images without using colored powder or generating image memory.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides charging means for uniformly charging the photoreceptor around the photoreceptor, and charging means for charging the photoreceptor by the charging means. An exposure section that exposes the photoreceptor to form an electrostatic latent image, and a colored powder that has a dielectric constant of 3.0 to 5.0, and the electrostatic latent image formed by the exposure process of this exposure section. A developing means that performs development using a developer, and a transfer device that transfers an image visualized by the developing step of the developing means onto a transfer material are arranged in sequence, and the toner on the photoreceptor after the transfer step of the transfer device is disposed in sequence. It is designed to be collected at the same time as the developing process of the developing device.

(Function) That is, in the present invention, since the colored powder in the developer contained in the developing means has a dielectric constant of 3.0 to 5.0, Adhesion of colored powder of opposite polarity onto the image carrier due to charge injection does not occur, so-called reverse adhesion to non-image areas, and the image density can be maintained, so no reverse adhesion occurs during the exposure process in the next cycle. The filter effect of colored powder can be removed, thus making it possible to prevent ghost images and the like in the image memory 2.

(Embodiment) Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 10.

FIG. 2 shows the overall structure of an electrophotographic image forming apparatus using a semiconductor laser, and FIG. 1 shows the structure of its main parts.

This image forming apparatus (laser beam printer) is connected to a host system (not shown), which is an external output device such as an electronic computer or word processor, via a transmission controller such as an interface circuit.

When a print start signal is received from the host system, an image recording operation is started, and the image is recorded on paper P as a recording medium and output.

This image forming apparatus has the following configuration.

That is, in the figure, 1 is an apparatus main body, and within this apparatus main body 1, a drum-shaped photoreceptor 2 as an image carrier is arranged. Around the photoreceptor 2, a charging means 3 consisting of a scorotron is arranged along the direction of rotation of the photoreceptor 2. An exposure section 4a of a laser exposure means 4, which will be described later, serves as an electrostatic latent image forming means, and a magnetic brush developing means 5 serves as a device that simultaneously performs a developing process and a cleaning process. Transfer means consisting of a scorotron6. Memory removing means 7 consisting of a brush member are sequentially arranged.

Further, in the lower part of the apparatus main body 1, there is an image transfer section 11 between the photoreceptor 2 and the transfer means 6, which transfers the paper P as a recording medium fed from the paper cassette 9 through the paper feed means 10. A paper transport path 15 is formed which leads to a paper discharge tray 12 provided on the upper surface side of the apparatus main body 1.

Further, a pair of double rollers 16 is arranged on the φ upstream side of the image transfer section 11 of the paper transport path 15, and a fixing device 17 and a pair of paper discharge rollers 18'' are arranged on the downstream side.

The laser exposure means 4 also includes a semiconductor laser oscillator (not shown), a polygon scanner 22 consisting of a polygon mirror 20 and a mirror motor 21, an FE lens 23, a correction lens 24, and a reflector for scanning the scanned laser beam to a predetermined position. It is composed of mirrors 25, 26, etc. Note that 27 in FIG. 2 is a control board constituting a control means for controlling this apparatus.

The photoreceptor 2 uses an organic photoconductor, and as shown in FIG. The structure includes a charge generation layer 31 and a charge transport layer 32 covering the charge generation layer 31.

When a printing start signal is received from the host system, the drum-shaped photoreceptor 2 rotates, and the photoreceptor 2 is charged by the charging means 3. Next, the laser beam l is modulated by receiving the dot image data from the host system.
The photoreceptor 2 is scanned and exposed using a laser exposure means 4 including a polygon mirror scanner 20 to form an electrostatic latent image on the photoreceptor 2 corresponding to the image signal.

This electrostatic latent image on the photoreceptor 2 is developed and visualized by the developing means 5.

Meanwhile, in synchronization with this developer image forming operation, the paper P taken out from the paper feed cassette 9 is fed through the aligning roller pair 16, and the developer image previously formed on the photoreceptor 2 is transferred. The image is transferred onto the paper P by the action of the means 6.

Next, the paper P passes through the conveyance path 15 and is sent to the fixing means 17, where the developer image is melted and fixed on the paper P, and then discharged onto the paper output tray 12 via a pair of paper discharge rollers 18. be done.

Note that after the developer image is transferred onto the paper P, the residual toner remaining on the photoreceptor 2 is diffused and removed by the memory removing means 7 made of a conductive brush, and the next copying operation is possible. It becomes a state.

Further, the developing means 5 has a structure as shown in FIG. - In the figure, numeral 35 is a casing that has a developer storage section 36 containing a two-component developer consisting of colored powder (hereinafter referred to as toner) T and magnetic powder (hereinafter referred to as carrier) C. . A developing roller 37 is provided in the casing 35 facing the photoreceptor 2, and a sliding contact portion of a developer magnetic brush D' with the photoreceptor 2 formed on the surface of the developing roller 37, That is, the development position 38
A doctor 39b for regulating the thickness of the developer magnetic brush D' is provided on the upstream side in the rotational direction of the photoconductor 2.Furthermore, in the developer storage section 36, a first blade 39b is provided.
A second developer stirring body 40°41 is housed.

Further, the developing means 5 is equipped with a toner replenishing device 42, so that the toner t is appropriately replenished into the developer storage portion 36.

Further, the casing 35 has a structure in which the photoreceptor 2 is built-in, and the developing roller 37 passes through the rotation center of the photoreceptor 2 at an angle α (approximately 50
The center is located on the line that corresponds to (°).

The developing roller 37 is composed of a magnetic roll 48 having three magnetic pole portions 45.46° 47, and a non-magnetic sleeve 49 fitted around the magnetic roll 48 and rotating counterclockwise in the figure.

Of the three magnetic pole parts 45, 46° 47 of the developing roller 37,
The magnetic pole portion 46 facing the development position 38 is a north pole, and the other magnetic pole portions 45 and 47 are south poles. In addition, the magnetic pole part 4
5 and the magnetic pole part 46 is 150', the magnetic pole part 4
6 and the magnetic pole part 47 is set to 120'.

By the way, in the present invention, in order to simplify the electrophotographic process, a reversal development method is adopted, and
A method was adopted in which the residual toner t after transfer was removed at the same time as development. At this time, changes in the surface potential of the photoreceptor 2 and the state of toner on the photoreceptor 2 are as shown in FIGS. 4 and 5.

That is, the photoreceptor 2 is shown in FIGS. 4(a) and 5(a).
As shown in the figure, the charging means 3 charges the battery to, for example, -600V. At this time, the toner t on the photoreceptor 2 that was not completely transferred in the previous image forming operation is simultaneously charged, and the photoreceptor 2 below the toner t is also charged. This has been found from experimental results showing that even if the toner t is removed with a urethane blade or the like, the surface potential of the photoreceptor 2 is maintained at about 80 to 90%.

In the apparatus of this embodiment, a scorotron charger is used as the transfer means 3 to equalize the surface potential, so that the potential of the portion of the photoreceptor 2 below the toner t is as described above. Although this potential difference is slightly lower than that of , this potential difference poses no practical problem at all.

Further, as described above, the surface potential of the photoreceptor 2 is attenuated by receiving the scanned laser beam by the laser optical means 4 which is modulated in response to the dot image data from the host system, and the surface potential of the photoreceptor 2 is attenuated by the fourth Figure (b) and Figure 5 (b)
), an electrostatic latent image is formed.

This electrostatic latent image is developed by the developing means 5. At this time, the toner t, which is unnecessary for the image and has adhered to the photoreceptor 2 as a transfer residue, is simultaneously cleaned by the developing means 5. Further, the electrostatic latent image on the photoreceptor 2 is visualized by the toner t supplied by the developing means 5, as shown in FIG. 4(d).

As shown in FIG. 5(d), the toner 6 is transferred onto the paper P by the action of the transfer means 6. A high voltage having the opposite polarity to the negatively charged toner t is applied to the transfer means 6. Corona discharge on paper P
It serves to positively charge the paper P and attract negative toner t to the paper P. After the image is transferred in this way, FIGS. 4(e) and 5(e)
As shown in FIG. 2, the toner t remaining on the photoreceptor 2 is diffused by a memory removing means 7 consisting of a brush.

Next, the principles, principles, conditions, etc. will be explained, including experimental data.

The cleaning and developing process of the present invention (CD
The point of P) is that it is performed by reversal development. This is because the polarity of the toner t and the polarity of the charge are the same.
This is because the polarity of the toner t produced by the charging means 3 will not be reversed.

However, in this DP method, certain process conditions are required in order to obtain good image quality.

FIG. 6 is an explanatory diagram of the terms used herein, and the potential when the photoreceptor 2 is charged by the charging means 3 and reaches the development position without exposure is called the charging potential V. The potential applied to the developing roller 37 of the developing means 5 is the developing bias Vb1.
The difference between the post-exposure potential ver and the development bias vb is defined as a cleaning potential (cleaning potential) Vc IV, )-Vb.

In this embodiment, the photoreceptor 2 used OPC for negative charging, but it was also set to V in consideration of a positive charging type. , Vb, Ver,
Vb-Ver, VO-Vt) are absolute values.

In Figure 7, the measurement data is plotted with the horizontal axis representing the developing bias and the vertical axis representing the photoreceptor charging potential.The cleaning potentials Vc and ff must be at least 100V; Since a large potential difference cannot be maintained, cleaning failures tend to occur in the image memory of the next cycle, and uneven charging, fogging, etc. are likely to occur due to the fluctuation margin of the charging potential.

On the other hand, if the cleaning potential is set to 300 V or more, charges will be injected back into the toner t from the developing roller 37, and injected toner t with a reverse polarity that cannot be transferred will be generated during development, and will be generated as an image memory to be described later. There are also reports of adhesion, etc., which is not desirable.

Therefore, the relationship of 100v x vci x 300v is required in this process.

First, an outline of how the toner t of opposite polarity is generated as an image memory will be explained.

Referring to FIGS. 8 and 9, (a)
In this case, the toner remaining without being transferred in the non-image area, that is, the reverse adhering toner t', adheres in a larger amount than the transfer residual toner t in the image area, but when it is charged, it becomes a negatively charged toner due to the negative corona.

Further, in (b), a dot image for the next cycle is written by laser exposure to form a latent image. Here, as mentioned above, the transfer residual toner t is small in absolute quantity and does not pose a problem because the transfer residual image, which is the dot image of the previous cycle, is diffused by the memory removal means 7, but the reverse adhesion toner t' is not a problem. The memory removal means 7 also remains without being diffused, and during this exposure, the laser beam is filtered more strongly than some of the transferred residual toners, so the photoreceptor potential of some of the transferred residual toners is low and the reverse adhesion toner is A latent image pattern with a high area is formed as shown in (b).

When this latent image progresses to the development shown in (c) in the figure, a portion of the transfer residual toner is developed to a high density, and a portion of the reversely adhered toner is further developed to a low density due to the development potential relationship. Put it away.

At this time, during development, the toner t on the charged potential portion of the photoreceptor 2
is cleaned, but at the same time, toner t is reversely attached to this charged potential area.
' is attached.

These reversely attached toners t' are positive polarity toners into which positive charges are injected from the developing roller 37 based on the potential difference between the charging potential of the photoreceptor 2 and the developing bias voltage.

Therefore, even in the transfer process shown in (d) in the figure, it remains on the photoreceptor 2 without being transferred.

As a result of the above process, if reverse adhesion toner t' is generated, it will be generated as an image memory due to its effect as an optical filter.

In order to eliminate these problems, the following experiment was conducted.

The volume resistivity Rt of the toner t was varied and the reverse adhesion characteristics were studied. Incidentally, the reverse adhesion density is set at a charging potential Vo of the photoreceptor 2 of -500v as a process condition using the mending tape method described later.

Developing bias Vb--300 V was used, and the carrier C in the developer had a maximum magnetization of 80 eiu/g and an average particle diameter of about 1001 m, and the magnetic flux density of the main magnetic pole portion 46 of the developing roller 37 was 1000 Gauss. did. The physical properties of the toner are shown in Table 1.

Table 1 Values in parentheses indicate more preferable values.

The volume resistivity of the toner is 0.1 g of toner is pressurized at 500 degrees, and the area is 1. 33c1j, thickness 0.8~1, approximately OH tablets were molded using a commercially available dielectric loss meter (TR
-C type (manufactured by Ando Electric Co., Ltd.)), and the dielectric constant was calculated from this.

FIG. 10 is a graph in which the horizontal axis represents the dielectric constant of the toner and the vertical axis represents the reverse adhesion reflection density 1-image reflection density.

When the dielectric constant of the toner t becomes 5.0 or more, the reflection density of reverse adhesion increases, and image memory of the previous cycle actually occurs on the image. On the other hand, if it is less than 3.0, it will not be possible to obtain a satisfactory image density. Therefore, from the relationship between image density and reverse adhesion, it can be seen that unless it is within the range of 3.0 to 5.0, it does not match the process in which the cleaning means (cleaner) of this process is removed.

In addition, at this time, the sleeve 4 of the photoreceptor 2 and the developing roller 37
The gap between the doctor 39 and the sleeve 49 (Dc-S) is Q< (Dr
5))-(Dc-3))<0.3, there will be no major change.

Here, as an example of the composition of the toner t used, the resin is styrene-lobyl methacrylate copolymer (
Kochu Kasei: Hymer SBM-73), carbon black (Mitsubishi Kasei: MA-100), water-based colloidal silica (Nippon Ferrosil: R972), a charge control agent, etc.

As an example of changing the resistance, the resistance value was selected depending on the blending ratio of carbon black, crosstalk change in toner t, etc.

Note that the carrier C is Cu-Zn ferrite.

A ferrite carrier such as Mn-Cu-Zn ferrite or Zn ferrite or a magnet carrier, in some cases with an acrylic resin coating, was mainly used.

On the other hand, the simultaneous development and cleaning method is affected by the characteristics of the toner t. Here, in order to investigate the characteristics of toner t, the following experiment was conducted.

First, the photoreceptor 2 to which toner t is not attached is charged,
Exposure is performed to form an electrostatic latent image, which is then subjected to reversal development to form an image.

At this time, the toner image on the photoconductor 2 is covered with mending tape (
(manufactured by 3M Company) and pasted it on white paper to measure the reflection density, which is defined as Dd.

Next, an image is formed on the photoreceptor 2 in the same manner as described above, and without being transferred, the photostatic charge is removed and the image is recharged. And without exposure,
After passing through the developing means 5, take the toner image with a mending tape (3M company!!) and measure the density on white paper.The density at this time is designated as DcJ.Then, the cleaning efficiency ξ is ξ-1 −DC)/Dd.

Usually, the case where there is a large amount of untransferred toner t occurs when the image density is high, and the transfer density is approximately 1.6.

The transfer efficiency is about 75 to 90%. here,
When the transfer efficiency is set to the lower value of 75%, the density of untransferred toner remaining on the photoconductor 2 (mending tape method) is expressed by the following formula: Dp / (Dd + Dp ) - η 1, 6/ (Dd + 1.6) -0,75
(Dp: transfer density, Dd: remaining transfer density, η: transfer efficiency), it is approximately 0.53. If this amount is on the photoreceptor 2, it will become a memory if not cleaned, but if Dc, +7 can be reduced to 0.1 by cleaning at the same time as development on the photoreceptor 2, there will be no problem at all on the transferred image. It won't happen.

Here, the formula for cleaning efficiency ξ is Dc menau, 1°Dd-0,
53 is substituted, it becomes ξ-1-, Da/Dd 1-0.110.53÷0.81, and it can be seen that cleaning efficiency of approximately 80% or more is sufficient.

In addition, the transfer residual toner is removed by a conductive brush (approximately 103Ω・α) as the memory removal means 7 installed before recharging.
Therefore, cleaning can be carried out at the same time as development without any problem.

In addition, in this process, as described above with reference to FIG.
A functionally separated organic photoconductor constituted by a charge transport layer 32 coated on the surface of the photoconductor 1 is used.

This is because the charge transport layer 32 is transparent and is located above the charge generation layer 31, so when the photoreceptor 2 is exposed to light, it has the advantage that underexposure is easily reduced by diffracted light or reflected and scattered light. Furthermore, due to problems in the production of toner t, positive polarity toner easily absorbs moisture in a humid environment and its volume resistivity changes, making it more likely that the above-mentioned reverse adhesion will occur.

Therefore, it is necessary to use a negatively charged toner with excellent stability, and when performing reversal development, a negatively charged corona is required, so it is necessary to use the above-mentioned organic photoconductor.

It goes without saying that the present invention can be modified in various ways without departing from the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, the colored powder remaining on the image carrier is removed by electrical suction at the same time as the development is performed by the developing means. There is no need for a collection box, making it possible to reduce the size, weight, and cost, and there is no risk of dirt.
Furthermore, since the cleaning blade does not come into contact with the image carrier,
The life of the image carrier can also be extended. In addition, the dielectric constant of the colored powder in the developer contained in the developing means is 3.0 to 5.
．． Since we use a powder with a value of 0, the adhesion of colored powder of opposite polarity to the image carrier, which is caused by charge injection during development, and so-called reverse adhesion to non-image areas does not occur, and the image density etc. The filter effect caused by reversely deposited colored powder can be removed during the exposure process for the next cycle.
The effect is that good image quality without image memory, ghost images, etc. can be obtained.

[Brief explanation of the drawing]

1 to 10 show an embodiment of the present invention, in which FIG. 1 is a diagram schematically showing the configuration of the main parts, FIG. 2 is a vertical sectional side view schematically showing the overall configuration, and FIG. Figure 3 is a diagram showing the structure of the photoreceptor, Figure 4 is an explanatory diagram showing the image forming process, Figure 5 is an explanatory diagram showing changes in the surface potential of the photoreceptor during the image forming process, and Figure 6 is an explanatory diagram showing various types of Diagram showing potential, 7th
The figure shows the relationship between the photoconductor charging potential and the developing bias. Figure 8 is an explanatory diagram showing the image forming process when reverse-adhering toner occurs. Figure 9 shows the image-forming process when reverse-adhering toner occurs. FIG. 10 is a diagram showing reverse adhesion characteristics and image characteristics when the dielectric constant of toner is changed. FIG. 11 is a schematic configuration diagram showing a conventional example. It is. 2... Image carrier (photoreceptor), 3... Charging means, 4...
...Laser exposure means, 5.Development means, 6.Transfer means, 7.Memory removal means, P.Paper, D.
...Developer, T...Colored powder (toner), C...Magnetic powder (carrier). Applicant's representative Patent attorney Takehiko Suzue Present bias (-V) Figure 7 Figure 4 Figure 5 Figure 6 Mouth (a) ((Q (e) Figure 8 Figure 9

Claims (3)

[Claims] (1) A charging means for uniformly charging the photoreceptor around the photoreceptor, an exposure section for exposing the photoreceptor charged by the charging means to form an electrostatic latent image, and exposure of the exposure section. A developing means for developing an electrostatic latent image formed by the process using a developer having a colored powder having a dielectric constant of 3.0 to 5.0, and an image visualized by the developing process of this developing means. An image forming apparatus characterized in that a transfer device for transferring the image to a transfer material is sequentially arranged, and the toner on the photoreceptor after the transfer process of the transfer device is collected at the same time as the development process of the development device. (2) The image forming apparatus according to claim 1, wherein the developing step is reversal development. (3) The image forming apparatus according to claim 1, wherein the developer is a two-component developer consisting of colored powder and magnetic powder.