JPH11151828A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of toner dust in an image forming apparatus using a direct image forming method. SOLUTION: Colonna chargers 101Bk, 101C, 101M, 101Y are respectively provided at each downstream side of each of image forming sections 40Bk, 40C, 40M, 40Y. As a result, immediately after each color image is formed by each of the image forming sections 40Bk, 40C, 40M, 40Y, an electric charge is applied to an image-formed surface of a recording member 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, an electric field is applied to a charged toner layer or toner cloud by applying a voltage to a control electrode portion provided around a hole or a slit.
2. Description of the Related Art There is known an image forming apparatus in which a toner at a specific position is selectively fly and moved through a hole or a slit to directly form an image on a recording member such as paper. Further, in such an image forming apparatus, a toner carrier for carrying toner, and
A toner flight control member having the control electrode portion, a plurality of toner images being formed by applying a voltage to the control electrode portion based on image information and adhering the toner passed through the minute opening onto the recording member to form an image; There is also known an image forming apparatus which has an image forming section, and which forms an image by superimposing toner on the recording member sequentially with the plurality of image forming sections to form an overlaid toner image.

[0003]

However, in an image forming apparatus configured to directly form an image on the recording member, if the amount of toner adhering to the recording member is large, the area around the image portion to which toner is originally supposed to adhere Toner tends to be scattered, and an abnormal image called toner dust is easily formed. In particular, in an image forming apparatus that forms a superimposed toner image by a plurality of image forming units, among the images that constitute the superimposed toner image, the image that is formed later becomes the image that is formed second or third time. As a result, the toner dust is easily generated. Then, there is a problem that the toner dust becomes blurred or bleeding of the image and the sharpness of the image is reduced.

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problem of toner dust. As a result, the toner which has once adhered to the recording member has been changed from an image area where the toner has adhered to a non-image area where the toner has not adhered. It has been found that the main cause of the toner dust is that the toner flies around the image area to which the toner should originally adhere due to the electric field formed by the potential difference between the toner and the toner. In a full-color image forming apparatus, since a full-color image is formed by superimposing toners such as magenta, cyan, and yellow on a recording member, the height of the superimposed toner image formed on the recording member is several tens μm or more. There are cases. When a large amount of charged toner is accumulated, the Coulomb repulsion acting between the charges of the toner itself increases, and if the repulsion exceeds the adhesive force between the toners, the toner becomes very unstable. In particular, as schematically shown in FIG.
When a locally high toner image is present on the recording member in a state where there is no image around, the image portion where the toner exists and the non-image portion around the image portion where the toner does not exist are present. Due to the potential difference therebetween, an electric field from the image portion to the non-image portion is formed as shown by the lines of electric force in the drawing. Then, it has been found that the toner constituting the toner image scatters along the electric field on the recording member, resulting in the toner dust. Such toner dust can occur even when the amount of toner adhered to the recording member is large even in a device other than the full-color image forming apparatus.

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing generation of toner dust.

[0006]

In order to achieve the above object, according to the present invention, a toner carrier for carrying a toner, a counter electrode facing the toner carrier, the toner carrier and the toner carrier are provided. An image forming unit having a toner control member disposed between the counter electrode and having a plurality of independent or a series of minute openings and a plurality of control electrodes controlling the passage of toner through each minute opening; Then, in the image forming apparatus for forming an image by adhering toner on the recording member in the image forming unit, the electric charge is applied to the image forming surface of the recording member on which the image is formed by the image forming unit. It is characterized in that a charge applying means is provided.

In this image forming apparatus, the electric charge is applied to the image forming surface of the recording member by the electric charge applying means, so that the image is formed between the image area where toner adheres and the non-image area where toner does not adhere. Reduce the potential difference.
This prevents the toner in the image area from moving to the non-image area along the electric field formed by the potential difference.

According to a second aspect of the present invention, a plurality of sets of the image forming units are provided, and the plurality of sets of the image forming units successively deposit toner on the recording member to form an image. 2. The image forming apparatus according to claim 1, wherein the charge applying unit is arranged so as to apply a charge toward the image forming surface of the recording member each time the image is formed by each image forming unit. Is what you do.

In this image forming apparatus, each time the image forming section forms the image, the charge applying section applies an electric charge toward the image forming surface of the recording member. Thereby, in each image, the potential difference between the image portion where the toner is attached and the non-image portion where the toner is not attached can be reduced. This prevents the toner constituting each image from moving to the non-image portion along the electric field formed by the potential difference.

Here, in the case where a charge having a different polarity from the charge polarity of the toner is applied by the charge applying means to reduce a potential difference between the image portion and the non-image portion, The charge of the toner is eliminated. However, when the toner charge is eliminated, the adhesive force between the toner and the recording member is weakened, and the toner is easily scattered due to vibration or the recording member is not charged. There is a possibility that the electrostatic attraction force to the guide plate or the like is weakened, and the recording member is not conveyed satisfactorily, causing a jam.

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the charge applying means directs a charge having the same polarity as the charge polarity of the toner toward the image forming surface of the recording member. It is characterized in that it is provided.

In this image forming apparatus, the charge applied by the charge applying means toward the image forming surface of the recording member is the same as the charge polarity of the toner.
The toner charge is not removed.

[0013] The invention of claim 4 is the invention of claim 1, 2, or
In the image forming apparatus of the third aspect, the charge applying means is provided so as to be in non-contact with the recording member.

In this image forming apparatus, the charge applying means is provided so as not to be in contact with the recording member, so that the image already formed on the recording member is not disturbed by the charge applying means. To do.

According to a fifth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, further comprising a fixing device for fixing an image to a recording member on which image formation by the image forming unit is completed. At least the image forming surface side of the recording member is made of a material capable of holding the charge from the first charge application by the charge applying unit to the fixing by the fixing device. It is assumed that.

In this image forming apparatus, at least the image forming surface of the recording member can hold the charge from the first charge application by the charge applying means to the fixing by the fixing device. . Here, the second and subsequent charges are applied after the first charge is applied and before the fixing by the fixing device is performed, so that the second and subsequent charges can be held until the fixing is performed. Therefore, it is possible to maintain a state in which the charge is applied by the charge applying unit and the potential difference between the image portion and the non-image portion is reduced until the fixing is performed.

According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, before forming an image to be formed for the first time, the resistivity of at least the surface layer of the recording member is adjusted by the first charge application by the charge application means. And a resistance adjusting means for adjusting the resistivity so as to maintain the electric charge until the fixing is performed by the fixing device.

In the image forming apparatus, the resistivity of at least the surface layer of the recording member is adjusted by the resistivity adjusting means until the electric charge is applied by the charge applying means for the first time and the fixing is performed by the fixing device. The value is adjusted so as to maintain the charge. Thus, at least the image forming surface of the recording member holds the charge from at least the first charge application by the charge applying unit to the fixing by the fixing device. Here, since the second and subsequent charges are performed after the first charge is applied and before the fixing by the fixing device is performed, the second and subsequent charges are also held until the fixing is performed. Therefore, until the fixing is performed, the state in which the potential difference between the image portion and the non-image portion is reduced by the charge application by the charge application means is maintained.

According to a seventh aspect of the present invention, in the image forming apparatus of the sixth aspect, a heating device for heating a recording member is used as the resistivity adjusting means.

In this image forming apparatus, since a heating device for heating the recording member is used as the resistivity adjusting means, the recording member before the adjustment is heated by heating the recording member to a desired temperature or higher within a desired time. Regardless of the value of the resistivity of the member, the resistivity of the recording member can be adjusted to a value equal to or higher than a desired resistivity. Therefore, the adjustment of the resistivity of the recording member can be performed stably and in a short time.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a full-color image forming apparatus will be described below. FIG.
1 is a front view illustrating a schematic configuration of an image forming apparatus according to an embodiment. This image forming apparatus includes four image forming units. Each image forming unit 40Bk, 40C, 40M, 40Y
Are black toner (Bk), cyan toner (C), magenta toner (M), and yellow toner (Y), respectively.
Is used to form a toner image on the recording member 6, and a developing roller 1 as a toner carrying member for carrying toner, and a conductive counter member as a counter electrode member arranged to face the developing roller 1. Roller 2, toner control member 3
Etc. are provided. In addition, a paper feed cassette 42 on which a recording member 6 such as paper before image formation is set, a fixing device 43 including a set of fixing rollers for fixing a toner image formed on the recording member 6, and the like are also provided. In FIG. 1, reference numerals Bk, C, M, and Y corresponding to the respective color toners are attached to the reference numerals of the members constituting each image forming unit.

FIG. 2 is a perspective view showing a schematic configuration of the image forming section. The above four image forming units 40Bk, 40
C, 40M, and 40Y have substantially the same configuration. The developing roller 1, the opposing roller 2 disposed so as to face the developing roller 1, and the developing roller 1 facing the developing roller 1 between the developing roller 1 and the opposing roller 2. The toner control member 3 includes a toner passage hole for controlling the flight of toner to the roller 2 and a control electrode around the hole.

The developing roller 1 is disposed inside a toner hopper 45 for storing toner. The developing roller 1 is provided on the surface of the developing roller 1 when a known electrophotographic image forming apparatus carries toner on a toner carrier. The toner can be carried by a known technique. In this embodiment,
The toner, which is negatively charged by friction between the doctor blade 5 or a toner supply member (not shown) and the developing roller 1, is carried on the developing roller 1 by electrostatic force and regulated by the doctor blade 5 to form a toner layer. Has formed.

The toner control member 3 includes a toner hopper 4
5 so as to close the opening formed in the lower wall. This toner control member 3 is, as shown in FIG.
A plurality of toner passage holes (hereinafter, referred to as “holes”) 31 as a plurality of minute openings are provided between the developing roller 1 and the opposing roller 2 so as to control the toner flying from the developing roller 1 to the opposing roller 2. The inner diameter φ formed around the hole is 0.16
It has a ring-shaped control electrode 32 of 0 mm. This hole 3
1 and the pitch P between the holes 31 in a direction perpendicular to the conveying direction of the recording member 6 (axial direction of the developing roller 1).
h and the like are set according to the resolution of the image recorded on the recording member 6. In this embodiment, the hole 3 having a diameter φh of 0.140 mm is formed in a substrate made of polyimide having a thickness of 0.075 mm so that an image having a resolution of about 300 dpi can be recorded.
1 are formed at intervals such that the pitch Ph is 0.0845 mm. The holes 31 have eight rows (31-1 to 31-31) in a region where the width W of the recording member 6 in the transport direction is about 2 mm.
8) The total number of holes 31 formed is 2300. The ring-shaped control electrodes 32, which are electrically independent from each other, are formed around each hole 31.
Are connected to a power supply circuit for applying a voltage corresponding to image information.

FIG. 4 is an enlarged schematic view of the image forming section. The developing roller 1 carrying the toner 7 is grounded, and causes the toner 7 carried on the developing roller 1 to fly toward the opposing roller 2 between the developing roller 1 and an opposing roller 2 provided opposite thereto. Power supply 8 is connected as a flying electric field forming means for forming a flying electric field. This power supply 8 applies a high DC voltage having a polarity opposite to the average charging polarity of the toner 7 to the opposing roller 2.

The toner control member 3 having the hole 31 and the control electrode 32 is provided between the developing roller 1 and the opposing roller 2. A power supply (hereinafter referred to as “image power supply”) for applying a control voltage generated based on image information to each control electrode 32 is provided between the developing roller 1 and each control electrode 32 of the toner control member 3. 9 is connected. The image power supply 9 applies a pulse-like control voltage that is ON / OFF controlled based on image information to each control electrode 32. ON of this control voltage
The value of the voltage at the time (hereinafter referred to as the image signal voltage) is, for example, +
The value of 325 V, the voltage at the time of OFF (hereinafter, referred to as a non-image signal voltage) is set to, for example, -50 V.

Further, in the illustrated apparatus, the distance Li between the control electrode 32 of the toner control member 3 and the opposing roller 2 is 0.1.
5 mm, the distance Lk between the control electrode 32 and the developing roller 1 is 0.075 mm, and the peripheral speed of the developing roller 1 is 300 mm / s.
ec, the conveying speed of the recording member 6 is, for example, 100 mm / sec.
c.

FIG. 5 is a schematic diagram showing the flying state of the toner. For example, when the negatively charged toner 7 is used, the developing roller 1 is grounded, a high DC voltage of +2.0 kV is applied to the opposing roller 2, and an image signal voltage Vblack of +325 V is applied to the control electrode 32 for 200 μsec. An electric field of about 4 × 10 ⁶ V / m acts on the toner 7 on the surface of the toner. As a result of the action of the electric field, the force applied to the toner 7 by the electric field exceeds the sum of the adhesive force and the image force acting between the toner 7 and the developing roller 1, and the toner 7 moves toward the opposing roller 2. Begins to fly, the toner control member 3
Through the holes 31, and accelerated by an acceleration electric field formed by the voltage applied to the opposing roller 2, and continue to fly.
The recording member 6 stops at the upper recording member 6, and an image is recorded on the recording member 6. In this apparatus, the control electrode 3 corresponding to the non-image portion where the toner on the recording member 6 does not adhere is used.
2, a non-image signal voltage Vwhite of -50 V is applied. Thus, each color image is formed by the image forming unit.

In the image forming apparatus having the above-described configuration, the recording member 6 is fed from the sheet feeding cassette 42 by a sheet feeding roller 42a or the like, and is conveyed to an upper portion in the figure through a guide plate (not shown). The recording member 6 is fed by a pair of registration rollers 48 between the opposing roller 2 at the image forming position and the toner control member 3 installed outside the toner hopper 45. Then, the above four image forming units 40B
Each color image is formed by sequentially and selectively flying toner at k, 40C, 40M, and 40Y, and a full-color superimposed toner image is directly formed. The recording member 6 on which the full-color image has been formed is sent to a fixing device, and the toner image attached on the recording member 6 is fixed.

A full-color image is formed as described above. However, when a full-color image is formed as described above and the amount of adhered toner on the recording member 6 increases, the toner becomes unstable due to the Coulomb repulsion between the toners. And the toner moves along the electric field formed by the potential difference between the image portion and the non-image portion to which the toner adheres, which may cause toner dust. (Hereinafter, margin)

Therefore, the image forming apparatus according to the present embodiment employs a configuration capable of reducing the potential difference between the image portion and the non-image portion. Hereinafter, this configuration and operation will be described in detail. In the image forming apparatus according to the present embodiment, a corona charger 101 is provided as charge applying means for applying charges to the image forming surface of the recording member 6 on which an image is formed by the image forming unit. Specifically, each image forming unit 40B
Each time each color image is formed by k, 40C, 40M, and 40Y, four corona chargers 101Bk, downstream of each image forming unit 40Bk, 40C, 40M, and 40Y are provided so that the charge is applied immediately after each image formation. 101C, 101
M and 101Y are provided.

In the present image forming apparatus, the charge given to the recording member 6 by the corona charger 101 is as follows:
When the toner 7 has the same polarity as that of the toner 7, for example, the toner 7 is negatively charged, the charge is negative. Since the charge repels the charge of the toner in the image portion, it is mainly applied to the non-image portion on the recording member 6. FIG.
FIG. 4 is a diagram showing lines of electric force when a non-image portion on the recording member 6 to which the toner 7 is not adhered is given the same polarity as the toner 7, specifically, a negative charge. Unlike the electric lines of force in the case where the electric charge is not applied as shown in FIG. 11 described above, the electric lines of force are directed upward from the image section, and the electric field from the image section toward the non-image section is weakened. Or it turns out that the direction of an electric field changes. When a charge having the same polarity as that of the toner is applied to the non-image portion in this manner, the potential difference between the image portion and the non-image portion decreases, and the electric field formed by the potential difference weakens, or the direction of the electric field changes. This makes it difficult for the toner in the image portion to move to the non-image portion. Therefore, toner dust can be reduced.

The charge applied to the recording member 6 by the corona charger 101 may have a polarity different from that of the toner 7. In this case, since the toner charge is eliminated, the potential difference between the image portion and the non-image portion is reduced. However, when the charge of the toner is eliminated, the adhesive force between the toner 7 and the recording member 6 is weakened, and the toner is easily scattered due to vibration or the like, or the recording member 6 is not charged. Then, the electrostatic attraction force of the recording member 6 to the guide plate or the like constituting the conveyance path is weakened, and the conveyance of the recording member 6 may not be performed well, and a jam may occur. For this reason, it is desirable that the charge applied to the recording member 6 by the corona charger 101 be of the same polarity as the toner 7.

In the illustrated apparatus, the backup electrodes 102Bk, 102C, 101M, and 10 having a fixed potential are provided at positions opposed to the corona chargers 101Bk, 101C, 101M, and 101Y with the recording member 6 interposed therebetween.
1Y is provided. Thereby, the charge can be sufficiently and relatively uniformly applied to the recording member 6. If such a backup electrode is not provided, the potential of the recording member 6 becomes unstable, and there is a possibility that the charge may not be sufficiently applied.

The charge applying means is desirably provided so as to be in non-contact with the recording member 6 like the corona charger. Thus, the color image formed on the recording member 6 can be prevented from being disturbed by the contact with the charge applying unit. In addition, as the non-contact charge applying means, in addition to the corona charger, a scorotron charger, a device that applies a high voltage to the needle electrode, and generates a discharge between the recording member 6 and a high voltage to the flat electrode. It is also possible to use a device to which the applied wave is applied, a device to irradiate the electromagnetic wave into the air, and adsorb and ionize the ionized ions to the recording member 6 by an electric field. However, when a high voltage is applied to the needle electrode,
It is difficult to uniformly apply a charge using a device that generates a discharge between the recording member 6 and a device that applies a high voltage to a flat plate electrode. In an apparatus using electromagnetic waves, soft X
Since light in the X-ray and X-ray regions is used, shielding is required, and it is difficult to put it to practical use. Therefore, it is desirable to use a corona charger and a scorotron charger which can perform uniform charging and are inexpensive.

In the present image forming apparatus, when a charge is applied to the recording member 6 to be recorded,
If the resistance of the recording member 6 is too low, the applied electric charge escapes instantaneously and the effect is hardly obtained. Accordingly, as the recording member 6, at least the image forming surface is provided with a black corona charger 101 for applying a first charge.
It is desirable to use a material made of a material capable of holding the charge from the time when the charge is applied by Bk to the time when the fixing by the fixing device 43 is performed. As a result, the charge is held from the first charge application to the fixing by the fixing device 43. Here, the second and subsequent charges are applied from the time when the first charge is applied to the time when the fixing is performed by the fixing device. Therefore, the charges after the second time are also held until the fixing is performed. Therefore, until the toner image is fixed, the state where the electric charge is applied by the corona charger 101 and the potential difference between the image portion and the non-image portion becomes small can be maintained, and the generation of toner dust can be suppressed. . FIG.
Means that the sheet surface potential is 5 on resin sheets having different resistivity.
This is a result of applying a charge having a charge amount of 00 V with a corona charger and measuring the potential after 1 msec. The horizontal axis represents the volume resistivity of the sheet, and the vertical axis represents the sheet surface potential after 1 ms. The resin sheet was used as a substitute for paper because resistance control was easier than paper. FIG. 6 shows that when the volume resistivity is 10 ¹⁰ Ωcm or more, almost the initial potential is maintained. From this measurement result, it can be seen that if a recording member having a volume resistivity of 10 ¹⁰ Ωcm or more is used, the applied charge stays on the recording member 6 and the effect of suppressing toner dust is maintained until the fixing by the fixing device 43 is performed. We can see that we can do it. Therefore, at least the surface is 10 ¹⁰
It is preferable to use a material having a volume resistivity of Ωcm or more, or a recording member made of an insulator. As the recording member 6, for example, an OHP sheet other than paper can be used.

When paper is used as the recording member 6, the resistivity of the paper varies depending on the surrounding environment and the characteristics of the paper. Therefore, the image forming apparatus according to the present embodiment employs a configuration in which a resistivity adjusting unit that adjusts the resistivity of the paper is provided so that toner dust can be suppressed even when paper is used as the recording member 6. doing. The resistivity of the paper is
It varies mainly with the water content of the paper. Specifically, the resistivity increases as the water content of the paper decreases. Therefore, if the paper is heated to evaporate the moisture, the resistance of the paper will increase. In the apparatus shown in the figure, a heating device 103 is provided as the resistivity adjusting means for heating the recording member 6 while nipping the recording member 6 between the heating roller 103a and the opposing roller 103b facing the heating roller. When paper is used as the recording member 6, when the paper passes through the heating device 103, water evaporates due to heating, and the water content is reduced. Thereby, the resistivity of the paper can be increased, and the volume resistivity of the paper can be set to a value in the above-described range of the volume resistivity. Therefore, by heating the paper to a desired temperature or higher within a desired time, it is possible to adjust the resistivity of the paper to a desired resistivity or more, regardless of the resistance value of the paper before adjustment. Can be. Therefore, the adjustment of the resistivity of the paper can be performed stably and in a short time. When the volume resistivity of the paper falls within the above-described range of the volume resistivity, it is possible to hold the charge applied for each color image formation until the fixing device 43 performs fixing. Therefore, even if the resistivity of the paper becomes low at the time of high humidity, toner dust can be satisfactorily reduced. The heating device 103
Is provided, for example, a heat generating mechanism is provided in the registration roller pair 48 for conveying the recording member 6, and the registration roller pair 4 is provided.
8 may have a heating function.

FIG. 8 is a schematic configuration diagram of another example of the image forming apparatus. This image forming apparatus differs from the image forming apparatus of FIG. 1 in that a conductive conveying belt 41 is used to convey the recording member 6. In the illustrated apparatus, a nickel belt is used as the transport belt. The conveyor belt 4
Reference numeral 1 is stretched around four support rollers 44, and rotates in the direction of the arrow at a linear velocity of 20 mm / s. As a result, in this apparatus, the recording member 6 is conveyed at a linear velocity of 20 mm / sec.
In this apparatus, the registration roller pair 48 moves the recording member 6 to a position where the recording member 6 is conveyed by the conveyance belt 41.
It works to transport the tip. In this apparatus, since the paper transport belt 41 is conductive, by applying a constant potential to the belt, a backup electrode provided opposite to the corona charger 101 becomes unnecessary. Further, since the leading end of the recording member 6 does not easily float from the transport path, paper jam can be reduced as compared with the image forming apparatus having the configuration of FIG. Instead of providing the heating device 103, a configuration in which a heating mechanism is provided on the transport belt 41 that transports the recording member 6 may be adopted.

[0039]

[Example 1] Next, a more specific example of this embodiment will be described. In the apparatus shown in FIG. 1, the heating device 103 was kept OFF, and the conveying speed of the recording member was set to 100 mm / sec. A PET sheet was used as a recording member. The reason why the PET sheet is used is that since the resistance is large and the resistance is stable, the effect of the charge imparting by the corona charger is easily understood. The polarity of the toner was negatively charged.

For image formation, the image forming section 40 for cyan is used.
C and the image forming unit 40M for magenta, and the image forming unit 40Bk for black and the image forming unit 4 for yellow are used.
0Y is a non-operating state, specifically, a state in which a voltage is applied to the counter electrode and a non-image signal voltage is applied to the control electrode.

A voltage having the same polarity as the toner, that is, a negative voltage is applied to the corona charger 101C for cyan and the corona charger 101M for magenta, whereby a negative charge is applied to the PET sheet. Also, the four backup electrodes 102Bk, 102C, 1
02M and 102Y were all grounded. The corona charger 101Bk for black and the corona charger 101Y for yellow were kept OFF.

In the image forming apparatus configured as described above, the corona charger 101C as the charge applying means,
By changing the bias applied to 101M, the amount of charge applied to the image forming surface of the PET sheet is changed. At this time, the surface potential of the image portion where toner is attached and the non-image portion where toner is not attached are measured. The difference (hereinafter referred to as edge potential difference) is measured, and an output image (line width 10
(A line image in the sub-scanning direction at 0 μm and a line interval of 100 μm) on the image quality was observed. Specifically, 100mm
After the line image was formed by the cyan image forming unit 101C on the PET sheet conveyed at / sec, an electric charge was applied to the PET sheet by the cyan corona charger 101C. Next, after a similar line image was formed on the line image formed by the cyan image forming unit by the magenta image forming unit 101M, a charge was applied to the PET sheet by the magenta corona charger 101M. .
Thereafter, the apparatus is forcibly stopped, and a PET sheet on which a superposed toner image of cyan and magenta is formed is placed on a grounded electrode as shown in FIG. Potential V2 and the edge potential difference ΔV
= V1-V2. Thereafter, the observation area of 1 mm × 1 mm was enlarged and read into a personal computer, and the number of scattered toner was counted. The number of the scattered toner is called a dust toner number. The surface potential was measured using a high-resolution surface potentiometer developed by the present inventors. This surface potentiometer is A
It uses FM and can measure at a resolution of 32 μm without contact.

FIG. 10 shows the relationship between the edge potential difference and the number of dust toners. The horizontal axis represents the edge potential difference, and the vertical axis represents the number of dust toners. By changing the voltage applied to the corona chargers 101C and 101M, the edge potential difference changes. As the edge potential difference increases, that is, PE
It can be seen that the larger the potential difference between the image area and the non-image area on the T sheet, the more toner dust is generated. In other words, the smaller the edge potential difference, the smaller the number of dust toners. When the edge potential difference becomes +200 V, the toner dust becomes substantially zero. However, at this time, the non-image portion surface potential needs to be more negatively charged than the image portion surface potential V1, and it is not practically feasible with a configuration using a corona charger. Therefore, in reality, it can be said that toner dust can be reduced most when the potential of the toner layer and the potential of the non-image portion are substantially the same. Thus, the corona chargers 101C, 101
It has been found that by adjusting the charge on the sheet by M, toner dust can be reduced and image deterioration can be prevented.

Next, instead of the PET sheet as the recording member 6, normal paper, specifically, paper made by Ricoh (trade name:
An experiment was performed in the same manner except that (type 6000) was used. The environmental conditions at this time were a temperature of 24 ° C. and a humidity of 54%. After the image formation, the edge potential difference was measured in the same manner as when a PET sheet was used as the recording member 6. Regardless of the voltage applied to the corona chargers 101C and 101M, the edge potential difference was about -400 V, and the number of dust toners was 300. Pieces / mm ^{2 to} 400 pieces / mm ² . This is presumably because the resistance of the paper is low and the charge provided by the corona chargers 101C and 101M is not retained.

Next, an experiment was conducted in the same manner as above, except that the paper was left on a hot plate (temperature: 180 ° C.) for 10 seconds before the image formation to evaporate the water content of the paper. As a result, almost the same results as the experimental results shown in FIG. 10 were obtained. This is because the paper resistance increases and the corona charger 101
It is considered that the charge given by C and 101M was held on the paper.

[Embodiment 2] Next, the heating device 103 is turned on.
Then, the resistance of the paper was adjusted by heating the paper in close contact with the heating roller 103a and the opposing roller 103b to evaporate the moisture of the paper. When the paper resistance after resistance adjustment was measured with a Mitsubishi Yuka resistance measuring instrument (trade name: Hiresta, probe: HRS), the volume resistance was 10 ¹³ Ωcm or more (applied voltage to probe: 500 V, current after 10 seconds). The resistance value was calculated from the value). Next, in this apparatus, all of the four image forming units 40Bk, 40C, 40M, and 40Y were made operable. Also, four corona chargers 1
01Bk, 101C, 101M, 101Y are all ON
The voltage applied to the black corona charger 101Bk was adjusted so that the charged potential on the paper surface became -300V. Also, the corona charger 101 for cyan described above.
C has a paper surface charging potential of -600 V, and the magenta corona charger 101M has a paper surface charging potential of -900V.
The applied voltage was set to V so that the paper surface charging potential of the above-described corona charger 101Y for yellow became -1200V.

Paper is fed to this device, and the heating device 10
3 and the image forming unit 40 for black
A black image was formed on the paper by Bk, and the potential on the paper was uniformly set to -300 V by the corona charger 101Bk. Next, a cyan image is formed in the image forming unit 40C for cyan, and the potential on the paper is made uniform by −6 by the corona charger 101C.
00V. Similarly, after the magenta (M) image was formed, the on-paper potential was uniformly set at -900 V, and after the yellow (Y) image was formed, the on-paper potential was uniformly set at -1200 V. The paper on which the image formation has been completed is fixed by the fixing device 43.

In the full-color image obtained in this manner, a portion where two toner layers are overlapped (C + M, C + Y,
Not only M + Y), but also in a portion where three layers are overlapped, toner dust peculiar to color superposition was hardly found, and a very clear image was obtained.

Example 3 An image was formed in the same manner as in Example 2 except that the image forming apparatus shown in FIG. 8 was used. As a result, a good overlapping toner image similar to that of Example 2 could be obtained. Further, the paper jam was reduced as compared with the second embodiment, and the system was very stable.

Note that, in the above embodiment, the image forming unit is
Although a full-color image forming apparatus provided with a set has been described, the present invention can be applied without being limited to the number of image forming sections, for example, an image forming apparatus having only one set of image forming sections can be applied. It is.

[0051]

According to the first to seventh aspects of the present invention, there is an excellent effect that generation of toner dust can be suppressed.

Further, according to the inventions of claims 2 to 7, there is an excellent effect that generation of toner dust can be suppressed in each of the images formed by the plurality of image forming units.

Further, according to the present invention, the potential difference between the image portion and the non-image portion can be reduced without causing toner scattering or jam due to the charge removal of the toner. This has an excellent effect that generation of toner dust can be suppressed.

According to the invention of claims 4 to 7, the charge applying means provided so as not to contact the recording member does not disturb the image already formed on the recording member. There is an effect that deterioration of image quality can be prevented.

According to the present invention, the image forming surface of the recording member can hold the charge applied by the charge applying means until the fixing is performed. There is an excellent effect that generation of toner dust can be suppressed before the fixing.

According to the sixth and seventh aspects of the present invention, the image forming surface of the recording member can hold the charge applied by the charge applying means until the fixing is performed. Has an excellent effect that generation of toner dust can be suppressed.

In particular, according to the seventh aspect of the invention, it is possible to stably adjust the resistivity of the recording member in a short time, and to suppress generation of toner dust before the fixing is performed. There is an excellent effect.

[Brief description of the drawings]

FIG. 1 is a front view illustrating a schematic configuration of an image forming apparatus according to an embodiment.

FIG. 2 is a perspective view illustrating a schematic configuration of an image forming unit of the image forming apparatus.

FIG. 3 is an explanatory diagram showing a pattern of a control electrode in a toner control member of the image forming apparatus.

FIG. 4 is an enlarged schematic diagram of an image forming unit of the image forming apparatus.

FIG. 5 is a schematic diagram illustrating a flying state of toner in the image forming unit.

FIG. 6 is an explanatory diagram showing an electric field formed on a recording member to which electric charge is applied.

FIG. 7 is an explanatory diagram showing a result of measuring a potential 1 msec after the charge is applied to the resin sheet.

FIG. 8 is a schematic configuration diagram of another example of the image forming apparatus.

FIG. 9 is an explanatory diagram of a method for measuring a surface potential of a recording member.

FIG. 10 is an explanatory diagram showing a relationship between an edge potential difference and the number of dust toners.

FIG. 11 is a diagram illustrating the cause of toner dust generation.

[Explanation of symbols]

 1 (Y, M, C, BK) Developing roller 2 (Y, M, C, BK) Counter electrode member 3 (Y, M, C, BK) Toner control member 31 Hole 32 Control electrode 6 Recording member 7 Toner 8 Power supply Unit 9 Image power supply 40 (Y, M, C, BK) Image forming unit 41 for each color 41 Conveyor belt 42 Paper feed cassette 43 Fixing device 44 Support roller 45 (Y, M, C, BK) Toner hopper 101 (Y, M, C) , BK) Corona charger 102 (Y, M, C, BK) Backup electrode 103 Heating device

Claims (7)

[Claims] 1. A toner carrier for carrying a toner, a counter electrode facing the toner carrier, and a plurality of independent or series of fine openings disposed between the toner carrier and the counter electrode. And a toner control member having a plurality of control electrode units for controlling the passage of toner through each minute opening.The image forming unit includes a toner control member, and the image forming unit applies toner to the recording member to form an image. An image forming apparatus, comprising: a charge applying unit that applies an electric charge to an image forming surface of a recording member on which the image is formed by the image forming unit. 2. An image forming apparatus according to claim 1, wherein a plurality of sets of the image forming sections are provided, and the plurality of sets of image forming sections sequentially form toner by adhering the toner onto the recording member to form an overlapped toner image. The image forming apparatus according to any one of the preceding claims, wherein the charge applying means is provided so as to apply an electric charge toward the image forming surface of the recording member each time the image is formed by each image forming unit. 3. The image forming apparatus according to claim 1, wherein the charge applying means applies a charge having the same polarity as the charge polarity of the toner toward the image forming surface of the recording member. Characteristic image forming apparatus. 4. An image forming apparatus according to claim 1, wherein said charge applying means is provided so as not to contact said recording member. 5. The image forming apparatus according to claim 1, further comprising a fixing device for fixing an image to a recording member on which image formation by said image forming section is completed. The image forming apparatus is characterized in that the image forming surface is made of a material capable of holding the charge from the first charge application by the charge applying unit to the fixing by the fixing device. . 6. An image forming apparatus according to claim 5, wherein, before forming an image to be formed first, the resistivity of at least the surface layer of the recording member is adjusted after the first charge application by said charge applying means. An image forming apparatus, comprising: a resistivity adjusting unit for adjusting the resistivity so that the electric charge is maintained until the fixing by the fixing device is performed. 7. An image forming apparatus according to claim 6, wherein a heating device for heating a recording member is used as said resistivity adjusting means.