JP2010210915A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which achieves high image quality without difference in image quality between front and rear surfaces of a paper by disposing image forming units corresponding to both surfaces of the paper and printing both surfaces by one-time paper passing not to decrease a printing speed and employing the same transfer system for both surfaces. <P>SOLUTION: An operation start timing of a polarity conversion means 47 is synchronized with an operation start timing of a transfer roller 32 of a yellow image forming unit 82Y, and the polarity conversion means 47 is turned off after the time resulting from adding the time required for arrival of an image on the second image carrier belt 31 at the polarity conversion means 47 and the time required for passage of an image having a maximum image size at the polarity conversion means 47. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of providing high-quality double-sided printing by simultaneously transferring front and back image forming surfaces.

Conventionally, as a method for recording images on both the front and back sides of a transfer paper, a method is generally used in which the transfer paper once passed through the fixing device is reversed and the toner is transferred to another side of the transfer paper and fixed again. Yes.
However, in this method, the transfer paper is changed in the transport direction, and once the transfer paper is heated and pressurized through the fixing device, the transfer paper is curled. Have.
As a method for solving such a problem, for example, there is one disclosed in Patent Document 1. In this method, after toner images are formed on both sides of the transfer paper, fixing is performed once.
Specifically, the first image formed on the photoconductor is transferred to the transfer belt by the first transfer unit, and then the second image formed on the photoconductor is transferred to one side of the transfer paper by the first transfer unit. Transcript to. Thereafter, the first image on the transfer belt is transferred to the other surface of the transfer paper by the second transfer means, whereby the image is transferred and fixed on both sides of the transfer paper.

However, in the method of Patent Document 1, it is necessary to carry the image once on the transfer belt, which not only deteriorates printing productivity but also increases the number of times of transfer, and thus has a drawback of causing image deterioration. In addition, since the front and back transfer systems are different, there is a disadvantage that image quality difference occurs.
The present invention has been made in view of the above-described points. The image forming unit corresponding to both sides of a sheet is arranged and double-sided printing is performed by a single sheet passing without reducing the printing speed. It is an object of the present invention to provide a high-quality image forming apparatus in which there is no difference in image quality between the front and the back by making the same transfer system.

  In order to achieve the above object, the invention described in claim 1 includes a first image carrying unit for carrying a first image formed by the first image forming unit on a first image carrying belt, and a second image forming unit. A second image carrying unit for carrying a second image to be formed on a second image carrying belt; and a transfer for transferring the first image and the second image carried by the first and second image carrying units to a recording medium. The recording medium is supplied and conveyed between a first transfer station constituted by a transfer means and the first image carrying belt, and a second transfer station constituted by the transfer means and the second image carrying belt. A recording medium conveying path including a conveying means, a fixing device for fixing the image transferred on both surfaces of the recording medium, and a polarity converting means for converting the polarity of the toner, on the first image carrying belt. Tona Alternatively, in the image forming apparatus, one of the toners on the second image carrying belt is converted into the polarity of the toner by the polarity conversion unit, and then the toner of the opposite sign is simultaneously transferred to the front and back of the recording medium. The operation start timing of the conversion means is synchronized with the operation start timing of the transfer roller of the image forming unit, and the time when the image on the image carrying belt reaches the polarity conversion means and the maximum image size passes through the polarity conversion means. In the image forming apparatus, the polarity conversion unit is turned off in a time period including the time period for performing the above operation.

When the operation of the polarity conversion means starts with the image carrying belt stopped, the image carrying belt is attracted to the counter electrode, and the start of the image carrying belt on the polarity converting side is delayed and the front and back image leading edge positions are shifted. . Further, if the polarity conversion unit is operated more than necessary (giving extra charge to the image carrying belt), the area of the image carrying belt that repeats charge and discharge increases, which adversely affects the life of the image carrying belt. give.
Therefore, in the present invention, the operation timing of the polarity conversion unit is matched with the operation start timing of the transfer roller on which image formation on the image bearing belt is started, and the off timing is set to the time when the image passes the polarity conversion unit. I tried to do it.
As a result, the influence on the image bearing belt can be reduced, and the polarity conversion means is operated after the image bearing belt is rotated, so that the adsorption of the belt is eliminated, and the above problems can be solved, and the high-quality double-sided image forming apparatus Can be realized.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the counter electrode facing the polarity conversion unit is in contact with the image carrying belt.
By reliably bringing the image bearing belt and the counter electrode into contact with each other, the electric field works effectively and the polarity of the toner can be reliably converted.
A third aspect of the present invention is the image forming apparatus according to the second aspect, further comprising an applying member that forcibly contacts the counter electrode with the image bearing belt.
For example, a spring or the like is provided on the counter electrode, and the counter electrode is positively pressed against the image carrying belt to ensure contact between the image carrying belt and the counter electrode, thereby effectively working the electric field and ensuring the polarity of the toner. Can be converted to
According to a fourth aspect of the present invention, in the image forming method according to the second or third aspect, the counter electrode has a flat plate shape and has a shape equal to or larger than a width of the opening of the polarity converting means. Device.
By making the width of the counter electrode large, the electric field works effectively and the polarity of the toner can be reliably converted.

A fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein the polarity conversion means performs the polarity conversion in a non-contact manner.
By converting the polarity of the unfixed image on the belt in a non-contact manner, the image is not disturbed.
A sixth aspect of the present invention is the image forming apparatus according to any one of the first to fifth aspects, wherein the polarity converting means is a corona discharger.
By using a corona discharger as the polarity conversion means, polarity conversion can be performed in a non-contact manner, so that an image forming apparatus that does not disturb the image can be realized.
The invention according to claim 7 is characterized in that the first image carrying belt and the second image carrying belt have polyimide as a base and an elastic layer is provided on the base. Device.
By using elastic belts for the first and second image bearing belts, it is possible to realize a high-quality double-sided image forming apparatus even on paper whose surface is rough and the surface of the paper is rough.

The invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 7, wherein the toner used has an average circularity of 0.90 to 0.99.
The invention according to claim 9 is characterized in that the toner has a shape factor SF-1 of 120 to 180 and a shape factor SF-2 of 120 to 190. The image forming apparatus described in the above.
According to a tenth aspect of the present invention, the ratio of the volume average particle diameter of the toner used to the number average particle diameter of the toner is 1.05 to 1.30. The image forming apparatus according to claim 1.

According to the present invention, the operation timing of the polarity conversion means is matched with the operation start timing of the transfer roller on which image formation on the image bearing belt is started, and the off timing is set to the time when the image passes the polarity conversion means. I tried to do it.
As a result, the influence on the image carrying belt can be reduced, and the polarity conversion means is operated after the image carrying belt is rotated, so that the belt is not attracted and a high quality image forming apparatus with no difference in image quality between the front and back is realized. can do.

1 is a schematic central sectional view showing an internal configuration of an image forming apparatus to which the present invention is applied. FIG. 2 is a simplified diagram showing an arrangement of image carrier belts in FIG. 1. It is an enlarged view which shows one main part for image formation. It is an enlarged view showing the other main part for image formation. It is the figure which showed the operation timing of the polarity conversion means. It is a simplified diagram showing a configuration of a counter electrode. It is explanatory drawing which showed the maximum length of the ellipse figure formed by projecting a spherical substance on a two-dimensional plane. It is explanatory drawing which showed the perimeter of the figure formed by projecting a substance on a two-dimensional plane.

Hereinafter, embodiments according to the present invention will be described in detail.
1 is a schematic central sectional view showing the internal configuration of an image forming apparatus to which the present invention is applied, FIG. 2 is a simplified diagram showing the arrangement of image carrier belts in FIG. 1, and FIG. FIG. 4 is an enlarged view showing the other main part for image formation, FIG. 5 is a diagram showing the operation timing of the polarity conversion means, and FIG. 6 is a simplified diagram showing the configuration of the counter electrode. FIG.
In the image forming apparatus main body 100 shown in FIG. 1, a first image carrier unit 20 including a first image carrier belt 21 that moves endlessly in the direction of the arrow is provided on the upper portion with the recording material conveyance path 43 </ b> A as a boundary. A second image carrier unit 30 having a second image carrier belt 31 that moves endlessly in the direction of the arrow is disposed at the bottom.

Four first image forming units 80 </ b> Y, 80 </ b> C, 80 </ b> M, and 80 </ b> K are provided on the upper tension surface of the first image carrying belt 21. On the other hand, four second image forming units 81Y, 81C, 81M, 81K are arranged on the inclined tension surface of the second image carrier belt 31. Note that Y, C, M, and K along the numbers of the first and second image forming units 80 and 81 correspond to the colors of the toner to be handled. Y is yellow, C is cyan, and M is Magenta and K mean black.
Y, C, M, and K are provided in the same meaning with respect to the photoreceptor 1 provided in the first and second image forming units 80 and 81 and rotating together with the first image carrying belt 21 and the second image carrying belt 31. It is along.
The photoreceptors 1Y to 1K are arranged at the same interval, and at least at the time of image formation, are in contact with a part of the stretched portion between the image bearing belts 21 and 31, respectively. This contacting surface is called an image receiving surface, and the mutual positional relationship is as shown in FIG.

Although the toner colors to be handled are different, the configurations of the first image forming units 80Y, 80C, 80M, and 80K are the same. Therefore, the configuration of the first image forming unit 80 will be described with reference to FIG.
In FIG. 3, during the operation of the image forming apparatus 100, charging means is provided around a cylindrical photosensitive member 1 that is rotatably supported by a drive source (not shown) so as to rotate in the direction of the arrow in accordance with an electrophotographic process. Image forming members such as the scorotron charger 3, the exposure device 4, the developing device 5, the cleaning device 2, and the light static elimination device Q, the potential sensor S1, and the image sensor S2 are disposed.
The photoreceptor 1 is obtained by forming an organic photosensitive layer (OPC), which is a photoconductive substance, on an aluminum cylinder surface having a diameter of about 30 to 120 mm, for example. A photoconductor on which an amorphous silicon (a-Si) layer is formed can also be used. A belt-like photoreceptor can also be employed.
The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, and a recovery member 2c, and removes and recovers foreign matters such as toner remaining on the surface of the photoreceptor.
The exposure device 4 scans the light corresponding to the image data for each color on the surface of each photoreceptor 1 that has been uniformly charged by the charging means, and forms an electrostatic latent image. The exposure apparatus 4 shown in the drawing is an exposure apparatus that includes an LED (light emitting diode) array and an imaging element as light emitting elements, but uses a laser light source, a polygon mirror, etc., and a beam modulated according to image data to be formed. A laser scanning exposure apparatus using light can also be employed.
As the charging means, in addition to the charger 3, a type that is brought into contact with the surface of the photoreceptor 1, for example, a charging roller can be employed.

The development in the present embodiment is a development system that employs a two-component developer composed of toner and carrier. The electrostatic latent image for each color formed on the surface of each photosensitive member 1 by a laser beam with respect to the negatively charged photosensitive member 1 is developed with toner of a predetermined color having the same polarity (negative polarity) as the charged polarity of the photosensitive member. Then, so-called reversal development, which becomes a visible image, is performed.
When the yellow (Y), cyan (C), magenta (M), and black (K) toners are consumed by the developing devices that handle the respective colors, they are detected by the magnetically permeable toner detecting means 5e. The toner of each color is supplied to each developing device 5 by a supply unit (not shown) from a toner cartridge 86 provided in a toner cartridge housing portion 85 inside the image forming apparatus 100 shown. As this supply means, a system using a known MONO pump can be adopted. According to this method, there are few restrictions on the installation location of the toner cartridge, which is advantageous for space allocation in the image forming apparatus. Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device 5, and the developing device 5 can be downsized.

The developing device 5 is provided with screws 5c and 5d for stirring and conveying the toner and the carrier. When the developing device 5 is mounted on the image forming apparatus 100, one end of the toner replenishing means is connected to a part of the screw 5d. The toner is supplied to the developing roller 5a rotating in the direction of the arrow by the screw 5c, but the thickness of the toner layer on the surface of the developing roller 5a is regulated to a predetermined thickness by the blade 5b.
The developing roller 5a is a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device 5 so as to be rotatable and a distance from the photosensitive member is properly secured, and a predetermined line of magnetic force is formed inside. Has a magnet.
The toner used has an average circularity of 0.90 to 0.99, a shape factor SF-1 of 120 to 180, a shape factor SF-2 of 120 to 190, and Dv / Dn of 1.05 to 1.3. [Dv is a volume average particle diameter (μm), and Dn is a number average particle diameter (μm)].
The carrier has a volume average particle size of about 25 to 60 μm.
Details of the toner used in this embodiment will be described later.

The second image forming units 81Y to 81K used in the second image carrier unit 30 will also be described as the second image forming unit 81 as a representative with reference to FIG.
The second image forming unit 81 shown in FIG. 4 has the same constituent members as the first image forming unit 80, but the rotation of the photoreceptor 1 is different from that of the first image forming unit 80 shown in FIG. The direction is different. However, they are mutually shaped with respect to the y-axis passing through the rotation axis 1a of the photosensitive member 1 indicated by an arrow in the drawing. This shape is an important matter although it is related to the arrangement of image forming members provided around the photoreceptor 1. In other words, the first image forming units 80Y to 80K can be obtained by considering the connecting method with the image forming apparatus 100, such as the connecting portion with the driving unit, the electrical connecting portion, the toner supplying portion, and the toner discharging portion. The second image forming units 81Y to 81K can be compatible with each other.
Therefore, it is not necessary to manufacture the developing device, the cleaning device, and the components individually for the first image forming unit 80 and the second image forming unit 81, and the efficiency in the component manufacturing and component management is high. Cost reduction.
As a first condition that can be used in the first image carrier unit 20 and the second image carrier unit 30 in the form of an axis object with the first and second image forming units 80 and 81 as the center of the y axis, photosensitive is used. The peripheral surface on which the image forming member is not provided around the body 1 is secured, that is, a wide range in which the image bearing belt can come into contact is secured. It can be mentioned that the arrangement angle of the first image carrying belt 21 and the second image carrying belt 31 is appropriate.

The above first condition and second condition will be described with reference to FIGS.
3 or 4, the image bearing belt 21 or 31 can be installed between the arrows A1 and A2. That is, the A1 side indicates that the developing device 5 can be installed, and the A2 side indicates that the image carrying belt can be installed in a range where the belt does not contact the cleaning device 2.
The inclusion of the second image carrier belt 31 in FIG. 3 indicates an image carrier belt on which the target image forming unit can be arranged with respect to the y axis including the rotation shaft 1 a of the photoreceptor 1.
If the image forming unit 80 is turned upside down with respect to an axis orthogonal to the y axis and used as the image forming unit 81, there is an influence of earth gravity, and at least in the developing device 5, the toner is agitated and the developing roller 5a is moved. The toner replenishment conditions are different and must be optimized, and it is impossible to share parts.

As shown in FIG. 2, the positional relationship between the image receiving surface of the first image carrying belt 21 and the image receiving surface of the second image carrying belt 31 is such that the angle α exceeds 180 degrees and is 270 degrees, preferably 210 degrees to 255 degrees. In this case, as the image forming unit, the first image carrier belt 21 can be configured as shown in FIG. 3, and the second image carrier belt 31 can be used as the image formation unit. That is, it is possible to avoid an image forming unit that makes it impossible to share parts as described above.
Further, as shown in FIG. 2, since the recording material conveyance path 43A can be ensured almost horizontally and linearly above the second image forming unit 81, the conveyance and reliability of the recording material are excellent, and the entire image forming apparatus. The unity becomes good.

In particular, the first image carrier belt 21 is stretched horizontally and flatly, and the second image carrier belt 31 is elongated in the longitudinal direction and inclined, so that the recording material conveyance path 43A is the boundary. The space in the height direction of the second image carrier belt 31 is increased below, but a paper feeder having a height substantially the same as the height occupied by the second image carrier belt 31 can be installed side by side.
As a result, a paper feeder that can store a large amount of paper can be installed, and the paper feed surface on the upper surface of the paper feeder and the transport path of the recording medium can be made almost the same height, ensuring paper feed and transport reliability. it can.
As described above, in the image forming apparatus according to the present embodiment, the image forming units 80 and 81 share the arrangement of the image forming apparatus around the photosensitive member and the arrangement of the image bearing belt, that is, the realization of the second condition. It has many points and is very advantageous in terms of manufacturing.
A first image carrier belt 21 as an image carrier that is supported by a plurality of rollers 23, 24, 25, 26 (two), 27, 28, 29 and travels in the direction of the arrow is a first image forming unit 80Y. It is provided below the photoreceptors 1Y, 1C, 1M, and 1K at -80K. The image carrying belt 21 is endless and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact.

In addition, a primary transfer roller 22 is provided on the inner peripheral portion of the first image carrying belt 21 so as to face each of the photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 20 </ b> A is provided on the outer periphery of the first image carrying belt 21 at a position facing the roller 23. The cleaning device 20 </ b> A wipes off unnecessary toner remaining on the surface of the image bearing belt 21 and foreign matters such as paper dust.
The members related to the image carrier belt 21 are integrally configured as the first image carrier unit 20 and can be attached to and detached from the image forming apparatus 100.

A second image carrier belt 31 as an image carrier that is supported by a plurality of rollers 33, 34, 35, 36 (two), 37, 38 and runs in the direction of the arrow is a second image forming unit 81 </ b> Y to 81 </ b> K. In contact with the photoreceptors 1Y, 1C, 1M, and 1K.
The second image carrying belt 31 is endless and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact.
A primary transfer roller 32 is provided on the inner peripheral portion of the second image carrying belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 30 </ b> A is provided on the outer periphery of the second image carrying belt 31 at a position facing the roller 33. The cleaning device 30 </ b> A wipes off unnecessary toner remaining on the surface of the second image carrying belt 31 and foreign matters such as paper dust.
The members related to the second image carrier belt 31 are integrally configured as the second image carrier unit 30 and can be attached to and detached from the image forming apparatus 100.

[Configuration and material of image bearing belt]
Next, the configuration and material of the image bearing belt will be described.
The first and second image bearing belts 21 and 31 are, for example, resin films having a base thickness of 50 to 100 μm, for example, belts having polyimide and a rubber elastic layer having a thickness of 50 to 500 μm provided on the base. 1 has a resistance value capable of electrostatically transferring the toner image carried by 1 to the belt surface by a bias applied to the primary transfer rollers 22 and 32.
The volume resistance value is a resistance adjusted to about 10 ⁶ to 10 ¹² Ωcm.
Polyimide is a material with excellent mechanical strength, and has been particularly noticed as a material with little expansion and contraction. The inventor has adopted it as a substrate for an image carrier belt. Since the image forming apparatus forms a color image by superimposing Y, M, C, and K as described above, the expansion and contraction of the image carrier belt affects the color misalignment of the image, the image expansion, and the like. become.
The reason for providing the rubber elastic layer is to improve the paper type compatibility characteristic, and in particular, to improve the image quality for paper having poor surface properties.

In general, the concave portion of the paper causes poor transfer because there is no contact between the toner (belt) and the paper. However, by providing an elastic layer, the belt follows the concave and convex portions of the paper. .
Elastic rubbers and elastomers include butyl rubber, fluorine rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-propylene ter Polymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, silicone rubber, fluorine rubber, polysulfide rubber, polynorbornene rubber, hydrogenated nitrile Selected from the group consisting of rubber, thermoplastic elastomers (eg polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyamide, polyurea, polyester, fluororesin) It is possible to use one kind or two or more kinds that. However, it is a matter of course that the material is not limited to the above materials.

The thickness of the elastic layer depends on the hardness of the elastic layer, but if it is too thick, the surface expands and contracts and cracks are likely to occur in the surface layer. Further, since the amount of expansion / contraction increases, it is not preferable that the image is too thick due to the expansion / contraction of the image (approximately 500 μm or more).
The appropriate range of hardness is 10 ≦ HS ≦ 60 ° (JIS-A). The optimum hardness varies depending on the belt layer thickness. Those having a hardness of less than 10 ° JIS-A are very difficult to mold with high dimensional accuracy. This is due to the fact that it is susceptible to shrinkage and expansion during molding.
When softening, it is a general method to contain an oil component in the base material, but it has a drawback that it begins to bleed when it is continuously operated under pressure.

As a result, it has been found that the photosensitive member in contact with the surface of the intermediate transfer member is contaminated to cause horizontal band-like unevenness. On the other hand, those having a hardness of 60 ° JIS-A or higher can be molded with high accuracy, and the oil content can be reduced or reduced, so that the contamination on the photoreceptor is reduced. Although it is possible, the effect of the elastic body cannot be obtained.
There are no particular restrictions on the conductive agent for adjusting the resistance value. For example, carbon black, graphite, metal powder such as aluminum and nickel, tin oxide, titanium oxide, antimony oxide, indium oxide, potassium titanate, antimony oxide-tin oxide composite Conductive metal oxides such as oxides (ATO) and indium oxide-tin oxide composite oxides (ITO), and conductive metal oxides are coated with insulating fine particles such as barium sulfate, magnesium silicate and calcium carbonate But you can. Of course, the conductive agent is not limited thereto.
Belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt.

[Configuration of primary transfer roller]
Next, the configuration of the primary transfer roller will be described.
As one embodiment, the primary transfer rollers 22 and 32 are obtained by coating the surface of a metal roller serving as a core metal with a conductive rubber material, and a bias is applied to the core metal portion from a power source (not shown). In the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to a volume resistance of about 10 ⁵ Ωcm.
Monochrome recording using only black toner is also possible. In such a case, there are photosensitive members that are not used. Therefore, not only the unused photoreceptors 1Y, 1C, 1M or the developing device 5 are not operated, but also a mechanism for keeping these unused photoreceptors and the image carrier belt 21 or 31 in a non-contact state is provided.

In this embodiment, an internal frame (not shown) that supports the roller 26 and the primary transfer roller 22 is provided, is supported so as to be rotatable around a certain point, and is rotated in a direction away from the photosensitive member. Thus, only the photosensitive member 1K comes into contact with the image carrier belt 21 or 31, and an image forming process is executed to create a monochrome image using black toner. This is advantageous in terms of improving the life of the photoreceptor.
Further, a first secondary transfer roller 28 is provided on the inner periphery of the first image carrying belt 21. The first secondary transfer roller 28 is made of a metal roller that is a core metal and is coated with a conductive rubber. A bias is applied to the core metal part from a power source (not shown).

Carbon is dispersed in the rubber, and the volume resistance is adjusted to about 10 ⁷ Ωcm. By applying a bias to the first secondary transfer roller 28 while passing a recording medium (hereinafter referred to as paper P) between the first image carrying belt 21 and the second image carrying belt 31, the first image carrying belt 21 is An image of the toner to be carried is transferred to the surface of the paper P.
A second secondary transfer roller 34 is provided on the inner periphery of the second image bearing belt 31.
A metal roller is used as the second secondary transfer roller 34, and a first secondary transfer roller is used while a recording medium (hereinafter referred to as paper P) is passed between the first image carrying belt 21 and the second image carrying belt 31. The image of the toner carried by the second image carrying belt 31 is transferred to the back surface of the paper P by applying the bias 28.

The toner used has a negative polarity, and the toner on the first image bearing belt 21 is repulsively transferred onto the paper P by applying a negative bias to the first secondary transfer roller 28. At this time, the toner of the second image carrying belt 31 is used to carry the second image formed by the second image forming units (81Y, 81C, 81M, 81K) on the second image carrying belt 31 and then before the transfer unit. Further, since the polarity is converted from the negative pole to the positive pole by the polarity converting means 47, the toner on the second image bearing belt 31 is sucked and transferred onto the sheet by the bias of the first secondary transfer roller.
For polarity conversion, after the second image formed by the second image forming unit (81Y, 81C, 81M, 81K) is carried on the second image carrying belt 31, positive polarity ions are applied to the polarity conversion means (charger) 47. It is achieved by getting off.
As the counter electrode 48 of the polarity conversion means 47, a general flat electrode is used in this apparatus.

However, in this case, the second image bearing belt 31 is attracted to the counter electrode 48 by the discharge of the polarity converting means 47, and the image formation on the back surface is delayed, and the image positions on the front surface and the back surface are shifted.
Further, when the counter electrode was not in contact with the second image carrier belt 31, the counter electrode 48 was not formed, and the polarity could not be changed, resulting in a transfer failure.
Therefore, in the present embodiment, as a countermeasure, the inventor drives the second image carrier belt 31 first, and operates the polarity conversion means 47 after rotating. By doing so, the adsorption to the counter electrode 48 is eliminated, and a high-quality double-sided image forming apparatus can be achieved by sufficiently bringing the counter electrode 48 into contact with the second image carrying belt 31.
As a method, as shown in FIG. 5, the operation start timing of the polarity conversion unit 47 is matched with the operation start timing of the transfer roller 32 of the yellow image forming unit 82Y, and the image on the second image carrier belt 31 is converted into the polarity conversion unit. This is done by turning off the polarity conversion means 47 for the time that reaches the time 47 and the time that the maximum image size passes through the polarity conversion means 47.
As shown in FIG. 6, the counter electrode 48 disposed opposite to the polarity conversion unit 47 uses a metal flat plate, the width of which is wider than the opening of the polarity conversion unit 47, and the second image carrier belt 31. The contact is forced by a spring (applying member) 49.

As shown in FIG. 1, a paper feeding device 40 that accommodates paper is provided on the right side of the image forming apparatus 100. Paper feed device (tray) 40a storing a large amount of paper in a plurality of stages, for example, the upper stage, and three stages of paper feed cassettes 40b, 40c, 40d below each can be pulled out to the right side (operation surface side) perpendicular to the paper surface. It is arranged. Of the sheets P stored in the sheet feed tray 40a and the sheet cassettes 40b, 40c, and 40d, the uppermost sheet is selectively fed and separated by the corresponding sheet feeding / separating means 41A to 41D. Only one sheet is reliably sent to the recording medium conveyance paths 43B and 43A by the plurality of conveyance roller pairs 42B.
A pair of registration rollers 45 are provided in the recording medium conveyance path 43A in order to take a feeding timing for feeding the paper P to the secondary transfer position.
Further, a jogger 44 for making the position perpendicular to the sheet conveyance direction a normal position is provided in the recording medium conveyance path 43A.
The jogger 44 includes guide members that move from both sides toward the edge of the paper in the paper conveyance direction, and the guides press the paper from both sides of the running paper for a moment to align the paper at a predetermined position. .
The paper P is conveyed from the registration roller pair 45 toward the transfer area.
The recording medium conveyance path 43C having the conveyance roller pair 42C can be supplied with paper from another sheet feeding device 300 that can be installed upstream in the conveyance direction.

The upper sheet feed surface of the sheet feed tray 40a is arranged so that the uppermost sheet in the sheet feed tray 40a is fed and then conveyed substantially horizontally without being bent. Therefore, even thick paper and highly rigid paperboard can be reliably fed. In addition, it is convenient to adopt an air paper feed made up of a vacuum mechanism so that the paper feed tray 40a can reliably feed papers having various characteristics. Although not shown, a sensor for detecting a sheet is provided at a key point of the recording material conveyance path, and serves as a trigger for various signals based on the presence of the sheet.
Recording for transporting the sheet that has passed through the second transfer station on the extension of the recording medium conveyance path 43A to the fixing nip of the fixing device 60 provided downstream in the conveyance direction of the recording medium while maintaining a flat state. Body transport means 50 is provided.
The recording medium transporting unit 50 has rollers 52, 53, 54, 55, and 56 that support the transport belt 51 that moves endlessly in the direction of the arrow. The cleaning device 50A faces the roller 55 on the outside of the transport belt 51. Further, an adsorption charger 57 for adsorbing the recording medium P facing the roller 56 and a charge eliminating / separating charger 58 facing the roller 54 are provided. The traveling speed of the belt 51 is matched with the traveling speed of the recording medium in the fixing device.
A fixing device 60 having a heating unit is provided on the downstream side of the recording material transport unit 50 in the paper transport direction.
As the fixing device 60, a type having a heater inside the roller, a belt fixing device for running a heated belt, a fixing device using induction heating as a heating method, or the like can be used. In order to make the color and glossiness of the images on both sides of the paper the same, the material, hardness, surface properties, etc. of the fixing roller and fixing belt are made equal.

Further, the fixing conditions are controlled by full-color and monochrome images, single-sided or double-sided, and are controlled by a control unit (not shown) so as to obtain an optimal fixing condition according to the type of paper.
A cooling roller pair 70 having a cooling function is provided in the conveyance path after fixing in order to cool the sheet after fixing and stabilize the unstable toner state at an early stage. A heat pipe structure roller having a heat radiating portion can be employed.
The cooled sheet is discharged and stacked by a discharge roller pair 71 on a discharge stack unit (not shown) provided on the left side of the image forming apparatus 100. The discharge stacking unit employs a mechanism in which a receiving member moves up and down according to a stack level by an elevator mechanism (not shown) so that a large amount of sheets can be stacked.
Note that it is also possible to transport the sheet toward another post-processing apparatus through the sheet discharge stack unit. Another post-processing apparatus is an apparatus for bookbinding such as punching, cutting, folding, and binding.
Further, a reversing mechanism for reversing the paper may be disposed after the cooling roller pair 70. The reversing device includes a gate guide, a conveyance roller, a guide, and the like, and is used when page alignment after discharge is required.
The toner cartridges 86Y, 86C, 86M, and 86K for each color in which unused toner is stored are detachably stored in the space 85. A toner conveying means (not shown) supplies toner to each developing device as necessary.

In the configuration of the present embodiment, the toner cartridge is common to the image forming units 80 and 81 arranged vertically, but can be separated. The toner cartridge 86K for black toner, which is highly consumed, can be set to have a particularly large capacity. This storage space 85 is on the back side when viewed from the operation direction on the upper surface of the image forming apparatus, and a plane portion is secured on the front side of the upper surface of the image forming apparatus, so that it can be used as a work table.
The operation provided on the upper surface of the image forming apparatus 100, the display unit 90 is provided with a keyboard or the like, and conditions for image formation can be input, the state of the apparatus is displayed on the display unit, and the operator and Information exchange with the image forming apparatus is facilitated.
The waste toner storage portion 87 provided in the image forming apparatus 100 is connected to the image forming unit cleaning device 2, the image carrier belt cleaning devices 20A and 30A, and the conveying belt 51 cleaning device 50A, and is collectively discarded. Collect and store foreign materials such as toner and paper dust. Since the cleaning devices (2, 20A, 20B, and 50A) do not include a large-capacity waste toner storage unit, each cleaning device can be reduced in size, and the waste toner disposal operability is good. A full sensor (not shown) is used to issue a warning such as toner disposal in the waste toner storage unit 87 or container replacement.

Further, in the electrical / control device 95 provided inside the image forming apparatus 100, various power supplies, control boards, and the like are protected and housed in a sheet metal frame.
The inside of the image forming apparatus becomes hot due to heat from the fixing device 60 or heat generated from the electrical device. However, as a countermeasure against this, a fan F is provided to prevent deterioration of the function due to heat of the internal members. The fan F is coupled to the heat radiating portion of the cooling roller pair 70 to ensure the cooling effect of the cooling roller pair 70.
Reference numeral 200 denotes a document reading device, and 300 denotes a paper feeding device that can be additionally installed. Note that this image forming apparatus achieves simultaneous duplex printing with the first image forming unit and the second image forming unit, but it is normal when either side of the unit fails or troubles such as running out of toner occur. By using the unit on the side, it is not necessary to rest the apparatus, and single-sided printing is possible.

[Single-sided recording operation]
Next, an operation during single-sided recording in which a full-color image is formed on one side of the paper P in the above configuration will be described.
There are basically two types of single-sided recording methods that can be selected. One of the two types is a method of directly transferring an image carried on the first image carrying belt 21 to one side of the paper, and the other method is an image carried on the second image carrying belt 31. Is directly transferred onto one side of the paper.
In the present embodiment, when the image carried on the first image carrier belt 21 is directly transferred to one side of the paper from the configuration of the image forming apparatus 100, the image is placed on the upper surface of the paper and the second image carrier belt 31. When the image carried on the sheet is directly transferred to one side of the paper, the image is formed on the lower surface of the paper. In the case where the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on a paper discharge stack unit (not shown). An explanation will be given of a method in which an image is carried on the first image carrying belt 21 and then transferred to a sheet so that the pages are arranged in order from the image data of the last page.

When the image forming apparatus 100 is operated, the photoreceptors 1Y, 1C, 1M, and 1K in the first image carrying belt 21 and the first image forming units 80Y to 80K rotate. At the same time, the second image carrier belt 31 rotates, but the photoreceptors 1Y, 1C, 1M, and 1K in the second image forming units 81Y to 81K are separated from the second image carrier belt 31 and are not rotated. To be.
First, image formation by the image forming unit 80Y is started.
By the operation of the exposure device 4 composed of an LED (light emitting diode) array and an imaging element shown in FIG. 3, light corresponding to image data for yellow emitted from the LED is uniformly charged by the charging device 3. An electrostatic latent image is formed by irradiating the surface.
This electrostatic latent image is developed with yellow toner by the developing roller 5a, becomes a visible image, and is electrostatically applied on the first image carrying belt 21 that moves in synchronization with the photoreceptor 1Y by the transfer action of the primary transfer roller 22. Primary transfer. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photosensitive members 1C, 1M, and 1K.
As a result, yellow, cyan, magenta, and black toner images are carried on the first image carrying belt 21 as sequentially overlapping full-color toner images, and are moved in the direction of the arrow together with the first image carrying belt 21. .

When the toner image is carried on the second image carrier belt 31, the polarity of the toner image on the second image carrier belt 31 is converted by the polarity conversion means.
At the same time, the paper P used for recording is fed out from the paper feed tray 40a or the paper feed cassettes 40b to 40d in the paper feed device 40 by one of the paper feed / separation means 41A to 41D for feeding the paper P. The pair 42B and 42C are conveyed to the recording material conveyance path 43C. Before the leading edge of the paper is picked up by the registration roller pair 45, the jogger 44 operates to push both sides of the paper from both lateral directions with respect to the paper conveyance direction, and the lateral alignment of the paper is not performed. I can be taken. The registration roller pair 45 is stationary, and the leading edge of the sheet is stationary while entering the nip of the registration roller pair 45, but the timing is set so that the position with the image on the first image carrier belt 21 is normal. Then, the registration roller pair 45 is rotated to convey the sheet to the transfer area.
The full-color toner image on the first image carrying belt 21 is transferred to the upper surface of the paper P conveyed in synchronization with the first image carrying belt 21 by receiving a transfer action by the secondary transfer roller 28. The bias applied to the secondary transfer roller 28 has a negative polarity that is the same polarity as the charging polarity of the toner.
Thereafter, the surface of the first image carrying belt 21 is cleaned by the belt cleaning device 20A. Further, foreign matters such as toner remaining on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 80Y to 80K that have finished the primary transfer are removed by the cleaning brush 2a and the cleaning blade 2b of the cleaning device 2. It is removed from the surface of each photoconductor.

The surface of each photoconductor is subjected to a discharging operation of residual potential by the discharging device Q to prepare for the next image formation / transfer process. The removed foreign matter such as toner is sent to the collecting unit 87 by the collecting unit 2c. Sensors S1 and S2 detect whether the surface potential after exposure on the surface of the photoconductor and the density of the toner adhering to the surface of the photoconductor after the development process are appropriate, and appropriately set the image forming conditions. Information is sent to a control means (not shown) for setting and control.
The paper P onto which the toner image that has been superposed and carried on the image carrying belt 21 is transferred is transferred toward the fixing device 60 by the carrying belt 51 of the carrying device 50. The surface of the transfer belt 51 is charged in advance by a sheet suction charger 57 so that the sheet P can be reliably transferred together with the transport belt 51. The neutralization / separation charger 58 operates so that the paper P is separated from the transport belt 51 and is reliably sent to the fixing device 60.
The toners of the respective colors superimposed on the paper P are subjected to the fixing action by the heat of the fixing device 60, and are melted and mixed to completely form a color image. Since toner is contained only on one side (upper surface) of the paper, less heat energy is required for fixing compared to double-sided recording having toner on both sides. A control means (not shown) optimally controls the power used by the fixing device according to the image. Until the fixed toner is completely fixed on the paper, it is rubbed by a guide member or the like on the conveyance path, and an image is lost or distorted. In order to prevent this problem, the cooling roller pair 70, which is a cooling means, operates to cool the toner and the paper. Thereafter, the paper is discharged by the paper discharge roller 71 onto the paper discharge stack portion with the image surface facing upward.

In the paper discharge stack unit, the image forming order is programmed so that the recorded matter of young pages is stacked so as to be sequentially stacked on top of each other, so the page order is aligned. Since the discharge stacking unit descends as the number of discharged sheets increases, the sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of stacking the recorded paper directly on the paper discharge stack unit, it is possible to carry out a punching process or to transport it to a post-processing device such as a sorter, a collator, a binding device or a folding device.
In another method of forming an image on one side of the paper P, image formation is performed in order from the image data of young pages in order not to form images in the first image forming units 80Y to 80K. However, since it is basically the same as the one-side recording process described above, details are omitted.
If any one of the first image forming units 80Y to 80K fails or the toner runs out during the image formation by the method carried on the first image carrying belt 21, the second image carrying belt 31 is used. The image recording can be performed without stopping the machine.

[Operation during double-sided recording]
Next, the operation at the time of double-sided recording in which images are formed on both sides of the paper P will be described.
When a start signal is input to the image forming apparatus, the first image carrying belt 21 displays an image for each color sequentially formed by the first image forming units 80Y, 80C, 80M, and 80K described in the single-sided recording operation. The image for each color sequentially formed by the second image forming units 81Y, 81C, 81M, 81K is applied to the second image carrier belt 31 substantially in parallel with the step of carrying out the primary transfer sequentially and carrying it as the first image. A step of sequentially performing primary transfer and carrying as a second image is performed.
With the configuration shown in FIG. 1, in order for the first image and the second image to coincide with each other at the leading edge in the sheet transport direction, the second image is formed after the start of the first image formation. Is started. Further, since the sheet is stopped and retransmitted by the registration roller pair 45, the sheet is fed in consideration of the time and aligned by the jogger 44.
The registration roller pair 45 transports the sheet to a first transfer station constituted by the transfer roller 28 as the first secondary transfer unit and the first image carrying belt 21 at a timing. A transfer current having a negative polarity is applied to the transfer roller 28, and a full-color second image carried in advance on one side (upper surface in the drawing) of the paper P from the first image carrying belt and on the second image carrying belt 31. Is converted into a positive pole by the polarity conversion charger 47, and the image is collectively transferred to one side (lower surface) of the sheet.

The paper P on which the full color toner images are transferred on both sides in this way is transported to the fixing device 60 by the transport belt 51. An alternating current is applied to the charge removal / separation charger 58, and the sheet is separated from the belt 51 and transferred to the fixing device 60. The toner images on both sides of the sheet are melted and mixed in response to a fixing process by heat of the fixing device 60. The sheet subsequently passes through the pair of cooling rollers and is discharged onto the discharge stack unit by the discharge roller 71.
When double-sided recording is performed on multiple pages of paper, if the image forming order is controlled so that the image of the young page becomes the bottom surface and is stacked on the paper output stack, the recorded material is removed from it and the top and bottom surfaces are reversed. 1 page in order from the top, 2 pages on the back, 3 pages on the second sheet, 4 pages on the back, and the page order is aligned. Such control of image forming sequence and control such as increasing the power input to the fixing device compared to the one-side recording are executed by a control means (not shown).
As for the single-sided recording and the double-sided recording operation, an example in which full-color recording is executed has been described, but monochrome recording using only black toner is also possible.

Here, the toner used in the present embodiment will be described in detail.
[Circularity and circularity distribution]
It is important that the toner used in the present exemplary embodiment has a specific shape and distribution of the shape, and the toner having an irregular shape having an average circularity of less than 0.90 and far from a spherical shape is satisfactory. High-quality images with no transferability or dust are not obtained.
As a method for measuring the shape, an optical detection band method is suitable in which a suspension containing particles is passed through an imaging unit detection band on a flat plate, and a particle image is optically detected and analyzed by a CCD camera. is there. Toner having an average circularity of 0.90 to 0.99, which is a value obtained by dividing the perimeter of an equivalent circle having the same projected area obtained by this method by the perimeter of the actual particle, has high reproducibility with an appropriate density reproducibility. It was found to be effective in forming a clear image.
More preferably, particles having an average circularity of 0.93 to 0.97 and a circularity of less than 0.94 are 10% or less.

When the average circularity exceeds 0.99, in a system that employs blade cleaning or the like, poor cleaning occurs on the photosensitive member and the transfer belt, causing stains on the image. For example, when outputting an image with a low image area ratio, there is little transfer residual toner and there is no problem with poor cleaning. However, when outputting an image with a high image area ratio such as a color photographic image, If an untransferred image remains on the photoreceptor due to a defect or the like, a cleaning defect is likely to occur.
If the above-mentioned cleaning failures occur frequently, further, the charging roller that contacts and charges the photoreceptor is contaminated, and the original charging ability cannot be exhibited.

[Measurement method of circularity]
The average circularity can be measured by a flow type particle image analyzer FPIA-2100 (manufactured by Toa Medical Electronics Co., Ltd.). As a specific measuring method, 0.1 to 0.5 ml of a surfactant, preferably alkylbenzene sulfonate is added as a dispersant to 100 to 150 ml of water from which impure solids have been removed in advance, and further measurement is performed. Add about 0.1-0.5g of sample. The suspension in which the sample is dispersed is obtained by performing dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser and measuring the shape and distribution of the toner with the above apparatus at a dispersion concentration of 3000 to 10,000 / μl. .

[Shape factors SF-1, SF-2]
As shown in FIG. 7, the shape factor SF-1 here is a value indicating the ratio of the roundness of the shape of the spherical substance, and is the maximum of the elliptical figure formed by projecting the spherical substance on a two-dimensional plane. It is represented by a value obtained by dividing the square of the length MXLNG by the graphic area AREA and multiplying by 100π / 4.
That is, the shape factor SF-1 is expressed by the following equation:
SF-1 = {(MXLNG) ² / AREA} × (100π / 4)
Is defined by
When the value of SF-1 is 100, the shape of the substance becomes a true sphere, and as the value of SF-1 increases, the shape of the substance becomes indefinite.
Further, as shown in FIG. 8, the shape factor SF-2 is a numerical value indicating the ratio of the unevenness of the shape of the substance. It is expressed as a value when divided by AREA and multiplied by 100 / 4π.
That is, the shape factor SF-2 is expressed by the following equation:
SF-2 = {(PERI) ² / AREA} × (100 / 4π)
Is defined by
When the value of SF-2 is 100, there is no unevenness on the surface of the substance, and as the value of SF-2 increases, the unevenness on the surface of the substance becomes more prominent.

In this embodiment, a toner image is sampled 100 times randomly using an FE-SEM (S-800) manufactured by Hitachi, and the image information is introduced into an image analysis apparatus (LUSEX 3) manufactured by Nireco. Then, the analysis was performed and the above formula was calculated.
It has been clarified by the present inventors that the transfer efficiency increases when the toner shape approaches the spherical shape as much as possible (both SF-1 and SF-2 approach 100). This is because there is only a point contact between the toner particles and the thing (toner particles, image carrier, etc.) in contact with the toner particles due to the shape effect, so that the toner fluidity is increased or the toner is adsorbed on the image carrier, etc. This is thought to be because the force (mirror power) is weakened and is easily affected by the transfer electric field.
On the other hand, when the shape of the toner approaches a spherical shape, it is disadvantageous for mechanical cleaning (such as blade cleaning). As described above, this is because the toner fluidity is increased and the adsorbing force (mirroring force) on the image carrier is weakened so that the toner can easily pass through the slight gap between the cleaning member and the image carrier. End up. Therefore, from the viewpoint of cleaning properties, the shape of the toner is somewhat irregular (in the direction in which the value of SF-1 is greater than 100) or uneven (in the direction in which the value of SF-2 is greater than 100). It is more preferable.

[Dv / Dn (ratio of volume average particle diameter / number average particle diameter)]
The volume average particle diameter (Dv) of the toner is 4 to 8 μm, and the ratio (Dv / Dn) to the number average particle diameter (Dn) is 1.05 to 1.30, preferably 1.10 to 1.25. According to a certain dry toner, the toner particle size distribution becomes narrow, and the following merits occur.
A stable image can be formed at all times because a phenomenon such as selective development on the toner particle size surface (toner particles having a (suitable) toner particle size corresponding to the image pattern are selectively developed) hardly occurs. Can do.
When a toner recycling system is installed, small-sized toner particles that are difficult to transfer are recycled in a large quantity. However, since the toner particle size distribution is originally narrow, it is difficult to receive the above-described action. Can always form a stable image.

In the two-component developer, even if the toner balance for a long time is performed, the fluctuation of the toner particle diameter in the developer is reduced, and good and stable developability can be obtained even in the long-term stirring in the developing device.
Even when used as a one-component developer, even if the balance of the toner is performed, fluctuations in the particle diameter of the toner are reduced, the filming of the toner on the developing roller, and a blade for thinning the toner The toner was not fused to a member such as the above, and good and stable developability and an image were obtained even in the long-term use (stirring) of the developing device.
In general, it is said that the smaller the particle size of the toner, the more advantageous it is to obtain a high-resolution and high-quality image, but it is disadvantageous for transferability and cleaning properties. is there.
Further, when the volume average particle size is smaller than that of the present embodiment, in the case of a two-component developer, the toner is fused to the surface of the carrier during a long period of stirring in the developing device, and the charging ability of the carrier is reduced, When used as an agent, toner filming on the developing roller and toner fusion to a member such as a blade for thinning the toner are likely to occur.
In addition, these phenomena are the same for the toner having a fine powder content higher than that of the present embodiment.

Conversely, when the toner particle size is larger than that of the present embodiment, it becomes difficult to obtain a high-resolution and high-quality image, and when the balance of the toner in the developer is performed, In many cases, the variation of the particle size becomes large.
It was also clarified that the same applies when the volume average particle diameter / number average particle diameter is larger than 1.30.
Further, when the volume average particle diameter / number average particle diameter is smaller than 1.05, there is a preferable aspect from the viewpoint of stabilizing the behavior of the toner and uniforming the charge amount, but the thin line portion is developed with small size particles. On the other hand, it is difficult to separate the functions depending on the toner particle diameter, such as developing a solid image mainly on large-size particles, which is not preferable.

[Measurement method for toner particle size]
Examples of the measuring device for the particle size distribution of toner particles by the Coulter counter method include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). The measurement method is described below.
First, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an aqueous electrolytic solution.
Here, the electrolytic solution is a solution prepared by preparing a 1% NaCl aqueous solution using primary sodium chloride. For example, ISOTON-II (manufactured by Coulter) can be used.
Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the measurement device is used to measure the volume and number of toner particles or toner using a 100 μm aperture as an aperture. Volume distribution and number distribution are calculated.
From the obtained distribution, the volume average particle diameter (Dv) and the number average particle diameter (Dn) of the toner can be obtained.
As channels, 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6 .35 to less than 8.00 μm; 8.00 to less than 10.08 μm; 10.08 to less than 12.70 μm; 12.70 to less than 16.00 μm; 16.00 to less than 20.20 μm; Uses 13 channels of less than 40 μm; 25.40 to less than 32.00 μm; 32.00 to less than 40.30 μm, and targets particles having a particle size of 2.00 μm to less than 40.30 μm.

JP-A-1-209470

  DESCRIPTION OF SYMBOLS 1 (Y, C, M, K) ... Photoconductor, 2 ... Cleaning device, 2a ... Cleaning blade, 2b ... Cleaning brush, 2c ... Waste toner collection | recovery means, 3 ... Charging means (scorotron charger), 4 ... Exposure apparatus DESCRIPTION OF SYMBOLS 5 ... Developing device, 5a ... Developing roller, 5b ... Restricting blade, 5c, 5d ... Stirring means, 5e ... Toner sensor, 20 ... First image carrier unit, 20a ... Cleaning device for first image carrier belt, 21 ... First image bearing belt, 22... Primary transfer roller, 23. Belt support roller (backing of cleaning device), 24 drive roller, 26 image receiving surface maintenance roller, 27 tension roller, 28 transfer roller, 29. Bending roller, 30 ... second image carrier unit, 30a ... second image carrier belt cleaning device, 31 ... second image carrier belt, 32 ... second image carrier unit Primary transfer roller, 33 ... cleaning backing roller, 34 ... transfer counter roller, 36 ... image receiving surface maintaining roller, 37 ... tension roller, 40 ... paper feeding device, 40a ... upper paper feeding device (tray), 40b to 40d: paper feeding cassette, 41A to 41D: paper feeding / separating means, 42A to 42C ... conveying roller pair, 43A to 43C ... recording material conveying path, 44 ... jogger, 45 ... registration roller pair, 46 ... main body side plate, 47: Polarity changing means (charger), 48 ... Counter electrode, 49 ... Spring (applying member), 50 ... Recording member transporting means, 50a ... Conveying belt cleaning device, 51 ... Conveying belt, 52 ... Accepting roller, 54 ... Separation / charger facing roller, 55 ... cleaning backing roller, 57 ... suction charger, 58 ... static elimination / separation charger, 60 ... fixing device , 70 ... Cooling roller pair, 71 ... Paper discharge roller pair, 80 (Y, C, M, K) ... First image forming unit, 81 (Y, C, M, K) ... Second image forming unit, 84 ... Toner cartridge storage unit, 85 (Y, C, M, K) ... toner cartridge, 87 ... waste toner collection unit, 90 ... operation / display unit (unit), 95 ... electrical / control device, 100 ... image forming apparatus, 200 ... Image reading device, 300 ... Feeding device, F ... Fan, Y ... Yellow, C ... Cyan, M ... Magenta, K ... Black, Q ... Static elimination device

Claims (10)

A first image carrying unit that carries the first image formed by the first image forming unit on the first image carrying belt, and a second image that carries the second image formed by the second image forming unit on the second image carrying belt. A two-image carrying unit; transfer means for transferring the first image and the second image carried by the first and second image carrying units to a recording medium; the transfer means; and the first image carrying belt. A recording medium transport path including a first transfer station and a transfer means configured to supply and transport the recording medium between a second transfer station constituted by the transfer means and the second image bearing belt, and both surfaces of the recording medium. A fixing device for fixing the image transferred to the toner, and a polarity conversion means for converting the polarity of the toner, and either the toner on the first image bearing belt or the toner on the second image bearing belt Wherein after converting the polarity of the toner in a polar conversion unit, an image forming apparatus to be transferred to front and back of the recording medium the toner of the opposite sign simultaneously,
The operation start timing of the polarity conversion means is synchronized with the operation start timing of the transfer roller of the image forming unit, and the time when the image on the image carrying belt reaches the polarity conversion means, and the polarity conversion means is set to the maximum image size. The image forming apparatus is characterized in that the polarity converting means is turned off in a time period including the time required for passing through.   The image forming apparatus according to claim 1, wherein a counter electrode facing the polarity conversion unit is in contact with the image carrying belt.   The image forming apparatus according to claim 2, further comprising an applying member that forcibly contacts the counter electrode with the image bearing belt.   4. The image forming apparatus according to claim 2, wherein the counter electrode has a flat plate shape and has a shape equal to or greater than a width of the opening of the polarity conversion unit.   The image forming apparatus according to claim 1, wherein the polarity conversion unit performs the polarity conversion in a non-contact manner.   6. The image forming apparatus according to claim 1, wherein the polarity conversion unit is a corona discharger.   2. The image forming apparatus according to claim 1, wherein the first image carrying belt and the second image carrying belt have polyimide as a base, and an elastic layer is provided on the base.   The image forming apparatus according to claim 1, wherein the toner used has an average circularity of 0.90 to 0.99.   9. The image forming apparatus according to claim 1, wherein the toner has a shape factor SF-1 of 120 to 180 and a shape factor SF-2 of 120 to 190.   The image according to any one of claims 1 to 9, wherein the ratio of the volume average particle diameter of the toner to be used and the number average particle diameter of the toner is 1.05 to 1.30. Forming equipment.

Images