JP2003162126A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tandem type multicolor image forming device that restricts a so-called step-up phenomenon and prevents scatter of toner images superimposed one on another on an intermediate transfer belt. <P>SOLUTION: In the tandem type image forming device that uses electrophotography and forms a multicolor image by overlaying images of separate colors, formed by corresponding image carriers and developing units, onto the intermediate transfer body sequentially while the intermediate transfer body makes one rotation, an electrifying member is provided for electrifying the intermediate transfer body surface prior to a process for transferring the image of the first color onto the intermediate transfer body. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and in particular, a toner image formed by a plurality of image bearing members and a developing unit is sequentially superposed using an endless belt-shaped intermediate transfer member. The present invention relates to an image forming apparatus that forms a color image.

[0002]

2. Description of the Related Art In recent years, full-color image forming apparatuses using an electrophotographic process have been widely used. One of the commercially available products is sequentially superposed with each image produced by a plurality of image carriers and a developing unit at the stage where the intermediate transfer member, which is an intermediate transfer member, makes one rotation to form a multicolor image. There is a tandem type image forming apparatus. In the tandem type electrophotographic apparatus, as shown in FIG. 10, a direct transfer system in which an image on each photoconductor (image carrier) 1 is sequentially transferred to a sheet s conveyed by a sheet conveying belt 3 by a transfer device 2. And the image on each photoconductor (image carrier) 1 is sequentially transferred to the intermediate transfer member 4 by the primary transfer device 2 as shown in FIG. There is an indirect transfer system in which the secondary transfer device 5 collectively transfers to the sheet s. Comparing the direct transfer type and the indirect transfer type, in the former, the paper feeding device 6 is arranged on the upstream side of the tandem type image forming apparatus T in which the photoconductors 1 are arranged, and the fixing device 7 is arranged on the downstream side. It has to be made, and there is a drawback that it becomes large. On the other hand, in the latter, since the secondary transfer position can be set relatively freely, the sheet feeding device 6 and the fixing device 7 can be arranged so as to overlap with the tandem-type image forming apparatus T, and downsizing can be achieved. There is an advantage that becomes possible. Also,
In the former case, the fixing device 7 is arranged close to the tandem-type image forming apparatus T so as not to increase in size, and therefore the fixing device 7 cannot be arranged with a sufficient margin to allow the sheet s to bend. There is a drawback that the fixing device 7 affects the image formation on the trailing edge side depending on the impact when the leading edge of the sheet s enters the fixing device 7 or the difference in the sheet conveying speed when passing through the fixing device 7. In contrast, the latter is
Since the fixing device 7 can be arranged with a sufficient margin that allows the sheet s to bend, it is possible to prevent the fixing device 7 from affecting the image formation.

Under these circumstances, recently, the tandem type electrophotographic apparatus, particularly the indirect transfer type, has been attracting attention. In this type of color electrophotographic apparatus, as shown in FIG. 9, the transfer residual toner remaining on the photoconductor 1 after the primary transfer is removed by the photoconductor cleaning device 8 to clean the surface of the photoconductor 1. In preparation for image formation again. Also, the transfer residual toner remaining on the intermediate transfer body 4 after the secondary transfer is removed by the intermediate transfer body cleaning device 9 to clean the surface of the intermediate transfer body 4 to prepare for the image transfer again.

[0004]

However, in the above-mentioned tandem type image forming apparatus of the indirect transfer type, when color superimposition is performed, a current for transferring the first color to the intermediate transfer body is used to transfer a plurality of colors. -A voltage is applied, but in the case of multicolor superposition, the potential may remain on the intermediate transfer member in the transfer of the first color, and more current and voltage may be required when transferring the next color. . This is a phenomenon generally called transfer step-up. This phenomenon occurs in the intermediate transfer belt, which is an intermediate transfer member having a resistivity of 10 ¹¹ Ω · cm or more, which makes it difficult to self-discharge the potential. In the case of an intermediate transfer belt composed of multiple layers, it is affected by the surface resistance of the surface layer as well as the overall resistance. As a result of this step-up phenomenon, for example, in the case of multicolor printing of general electrophotography, although it is often composed of four colors, the potential of the intermediate transfer belt after transferring the final color is 2 KV in absolute value. Cases in which the amount is exceeded are also observed. On the other hand, the surface resistance and volume resistance of the intermediate transfer belt are often set higher due to dot reproducibility and the like, which inevitably causes an increase in the potential of the intermediate transfer body.

The problem here is that the potential of the intermediate transfer belt in each color, especially the final color, rises due to the above-mentioned potential rise, and the toner image superposed on the intermediate transfer belt scatters due to the repulsive force with the charge. did. The occurrence rate of these toner scattering increases as the amount of toner per unit area of toner increases, and in addition to the potential shown above,
Occurrence occurs when the balance between toner agglomeration and repulsion is lost, such as when the image surface has a curvature and the toner agglomeration force is weakened, such as the circumferential portion along the roller that stretches the intermediate transfer belt, making it easier to fly. Has come to be understood. These problems have become problems in image forming apparatuses that use an intermediate transfer member and when images are superimposed. As a solution to these problems, it is possible to control the potential with the resistance of the intermediate transfer belt, but since variations occur due to changes in the resistance environment and the number of times of color overlapping, variations occur, The current situation is that optimum conditions cannot be obtained under all conditions. The present invention has been made in view of the above problems, and it is an object of the present invention to provide a tandem type multicolor image forming apparatus in which the occurrence of the step-up phenomenon is suppressed and the toner images superimposed on the intermediate transfer belt do not scatter. To aim.

[0006]

The above objects of the present invention can be achieved by the following means. That is, according to the present invention,
First, in claim 1, an image forming apparatus utilizing electrophotography is provided, in which an image of each color produced by a plurality of image carriers and a developing unit is transferred onto an intermediate transfer member by the intermediate transfer member. In a tandem-type image forming apparatus that sequentially superimposes a multicolor image at the stage of rotation, a charging member that charges the surface of the intermediate transfer member is provided before the step of transferring the image of the first color onto the intermediate transfer member. An image forming apparatus including the above is provided. Secondly, in the second aspect, there is provided the image forming apparatus according to the first aspect, wherein the current or voltage applied to the charging member has a polarity opposite to the charging polarity of the toner. . Thirdly, a third aspect of the present invention provides the image forming apparatus according to the first aspect, wherein a current or a voltage applied to the charging member can be changed. Fourthly, in the image forming apparatus of the first aspect, the current or the voltage applied to the charging member is controlled so that the absolute value level becomes larger or equal as the number of times of color superposition increases. An image forming apparatus is provided. Fifth, a fifth aspect of the present invention provides the image forming apparatus according to the first aspect, wherein the current or voltage applied to the charging member can be changed according to the environment.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a tandem type indirect transfer type color copying machine showing an embodiment of the present invention. In the figure, reference numeral 100 is a copying machine main body, 200 is a paper feeding table on which the copying machine is placed, 300 is a scanner mounted on the copying machine main body 100, and 400 is an automatic document feeder (ADF) further mounted thereon. An endless belt-shaped intermediate transfer member 10 is provided at the center of the copying machine main body 100.
The intermediate transfer member 10 has a base layer 11 as shown in FIG.
Is made of a material that does not easily spread, such as fluororesin or canvas, and the elastic layer 12 is provided thereon. The elastic layer 12 is made of, for example, fluororubber or acrylonitrile-butadiene copolymer rubber. The surface of the elastic layer 12 is coated with, for example, a fluororesin to form a coating layer 1 having good smoothness.
It is covered with 3. Then, as shown in FIG. 1, in the illustrated example, the three support rollers 14, 15, 16 are wound around and can be rotated and conveyed clockwise in the drawing. In this illustrated example, an intermediate transfer member cleaning device 17 that removes residual toner remaining on the intermediate transfer member 10 after image transfer is provided on the left side of the second support roller 15 of the three. Further, on the intermediate transfer body 10 stretched between the first support roller 14 and the second support roller 15 of the three, along the carrying direction,
A tandem image forming apparatus 20 is configured by horizontally arranging four image forming units 18 of black, cyan, magenta, and yellow. An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.
On the other hand, the tandem image forming apparatus 2 with the intermediate transfer body 10 interposed therebetween.
A secondary transfer device 22 is provided on the side opposite to 0. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23 and pressed against the third support roller 16 via the intermediate transfer body 10. The image on the intermediate transfer body 10 is transferred to a sheet.

Next to the secondary transfer device 22, there is provided a fixing device 25 for fixing the transferred image on the sheet. Fixing device 25
Is a fixing belt 26, which is an endless belt, and a pressure roller 27.
Press to configure. The secondary transfer device 22 described above is also provided with a sheet carrying function for carrying the sheet after the image transfer to the fixing device 25. Of course, a non-contact charger may be arranged as the secondary transfer device 22,
In such a case, it is difficult to provide this sheet conveying function together. In the illustrated example, a sheet reversing device 28 for reversing the sheet so as to record images on both sides of the sheet in parallel with the above-described tandem image forming apparatus 20 under the secondary transfer device 22 and the fixing device 25. Equipped with.

Now, when making a copy using this color copying machine, the document table 30 of the automatic document feeder 400 is used.
Place the original on top. Alternatively, the automatic document feeder 40
0 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. When a start switch (not shown) is pressed, when the original is set in the automatic document feeder 400, the original is conveyed and moved onto the contact glass 32, and then the original is set on the other contact glass 32. At this time, the scanner 300 is immediately driven to travel the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source, and the light reflected from the document surface is further reflected and directed toward the second traveling body 34, reflected by the mirror of the second traveling body 34, and passed through the imaging lens 35. It is put in the reading sensor 36 to read the contents of the document. When a start switch (not shown) is pressed, one of the support rollers 14, 15 and 16 is rotationally driven by a drive motor (not shown) and the other two support rollers are driven to rotate, and the intermediate transfer member 10 is rotatively conveyed. To do. At the same time, the individual image forming means 18 rotates the photoconductor 40 to form a black, yellow, magenta, and cyan single-color image on each photoconductor 40.
Then, as the intermediate transfer body 10 is conveyed, the single color images are sequentially transferred to form a composite color image on the intermediate transfer body 10. On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, a sheet is fed from one of the paper feed cassettes 44 provided in the paper bank 43 in multiple stages, and the separation roller 45 is provided. Then, the sheets are separated one by one into the sheet feeding path 46, conveyed by the conveying rollers 47, guided to the sheet feeding path 48 in the copying machine main body 100, and abutted against the registration rollers 49 to be stopped. Alternatively, the paper feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, and the separation roller 52 separates the sheets one by one to manually feed the paper.
Then, it is put in 3 and similarly hits the registration roller 49 to stop. Then, the registration roller 49 is rotated in time with the composite color image on the intermediate transfer body 10, the sheet is fed between the intermediate transfer body 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. Record a color image on the sheet.

The sheet after the image transfer is the secondary transfer device 22.
The transfer claw 5 is fed by the fixing device 25 to the fixing device 25, and the fixing device 25 applies heat and pressure to fix the transferred image.
5 and the discharge roller 56 to discharge, and the discharge tray 5
Stack on 7. Alternatively, the sheet is switched by the switching claw 55 and placed in the sheet reversing device 28, reversed there and guided to the transfer position again, and after the image is recorded on the back surface, the sheet is discharged onto the sheet discharge tray 57 by the discharge roller 56. On the other hand, the intermediate transfer body 10 after the image transfer is processed by the intermediate transfer body cleaning device 17
Then, the residual toner remaining on the intermediate transfer body 10 after the image transfer is removed, and the tandem image forming apparatus 20 prepares for another image formation. Here, a conductive rubber roller is used as the registration roller 49, and a bias is applied. Diameter φ18
Then, the surface is made of a conductive NBR rubber having a thickness of 1 mm. The electric resistance is about 10E9Ωcm in volume resistance of the rubber material,
The applied voltage is -850V on the toner transfer side (front side).
A voltage of the order of magnitude is applied. A voltage of about +200 V is applied to the back side of the paper, but it may be grounded if there is little need to consider the transfer of paper dust on the back side. Although a DC bias is applied as the applied voltage, this may be an AC voltage having a DC offset component. The AC superposed DC bias can charge the paper surface more uniformly. The surface of the paper after passing through the registration roller 49 is slightly charged to the negative side. Therefore, in the transfer from the intermediate transfer body 10 to the sheet, the transfer condition may change as compared with the case where the voltage is not applied to the registration roller 49, so it is necessary to be careful.

Now, the tandem type image forming apparatus 2 described above.
0, the individual image forming means 18, in detail, for example, as shown in FIG. 3, has a charging device 60, a developing device 61, a primary transfer device 62, and a charging device 60 around a drum-shaped photosensitive member 40.
A photoconductor cleaning device 63, a charge removing device 64, etc. are provided. In the illustrated example, the photosensitive member 40 has a drum shape in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to an element tube made of aluminum or the like, but may have an endless belt shape. Although not shown, at least the photoconductor 40 is provided, and a process cartridge is formed by all or a part of the portion forming the image forming unit 18, and the process cartridge can be collectively attached to and detached from the copying machine main body 100 to improve maintainability. You may do it. Of the parts forming the image forming unit 18, the charging device 60 is formed in a roller shape in the illustrated example, and contacts the photoconductor 40 to apply a voltage to charge the photoconductor 40. The developing device 61 may use a one-component developer, but in the illustrated example, a two-component developer including a magnetic carrier and a non-magnetic toner is used. Then, the two-component developer is conveyed while being stirred, and the developing sleeve 6
5 and a developing section 67 that transfers the toner of the two-component developer that adheres to the developing sleeve 65 to the photoconductor 40, and the stirring section 66 is lower than the developing section 67. And The stirring unit 66 is provided with two parallel screws 68. The space between the two screws 68 is divided by a partition plate 69 except for both ends (see FIG. 6). Further, a toner concentration sensor 71 is attached to the developing case 70.

On the other hand, the developing unit 67 includes a developing case 70.
The developing sleeve 65 is opposed to the photoconductor 40 through the opening.
A magnet is provided inside the developing sleeve 65.
72 is fixedly provided. In addition, the developing sleeve 65
The doctor blade 73 is provided with the tip approaching. In the example shown
Is the closest distance between the doctor blade 73 and the developing sleeve 65.
The interval between the parts is set to 500 μm. That
Then, while stirring the two-component developer with the two screws 68,
The material is circulated and supplied to the developing sleeve 65. Development three
The developer supplied to the brush 65 is collected by the magnet 72.
Raise and hold, and form a magnetic brush on the developing sleeve 65.
To achieve. The magnetic brush rotates with the developing sleeve 65.
In addition, the doctor blade 73 is used to cut the appropriate amount of spikes.
It The developer that has been cut off is returned to the stirring unit 66.
On the other hand, of the developer on the developing sleeve 65, the toner is currently
Photosensitive by the developing bias voltage applied to the image sleeve 65
Transfers to the body 40 and visualizes the electrostatic latent image on the photoreceptor 40
Turn into. Development remaining on the development sleeve 65 after visualization
The developing agent is used in the developing three when there is no magnetic force of the magnet 72.
It leaves the bush 65 and returns to the stirring unit 66. By repeating this
When the toner density in the agitator 66 becomes low,
The toner concentration sensor 71 detects and supplies toner to the stirring unit 66.
To do. Incidentally, in the illustrated example, the linear velocity of the photoconductor 40 is set to 20.
0 mm / s, the linear velocity of the developing sleeve 65 is 240 mm / s
I am trying. The diameter of the photoconductor 40 is 50 mm, and the development three
The developing process is performed with the diameter of the bump 65 set to 18 mm.
The toner charge amount on the developing sleeve 65 is -10 to -30.
It is in the range of μC / g. Photoconductor 40 and developing sleeve 65
Development gap G, which is the gap between_PIs 0.8mm of the conventional one
It can be set in the range of 0.4 mm, and by reducing the value
It is possible to improve the development efficiency. Of the photoconductor 40
The thickness is 30 μm and the beam spot diameter of the optical system is 50 μm.
× 60 μm, and the light amount is 0.47 mW. Also feeling
Charge (before exposure) potential V of the photoconductor 40 ₀-700V, exposure
After-potential V_LIs -120V and the developing bias voltage is -4.
70 V, that is, development potential of 350 V
This is what is done.

Next, the primary transfer device 62 has a roller shape and is provided by pressing the intermediate transfer member 10 against the photosensitive member 40. Alternatively, it is not limited to the roller shape, and may be a non-contact corona charger or the like. Photoconductor cleaning device 63
Is provided with a cleaning blade 75 made of, for example, polyurethane rubber by pressing its tip against the photoconductor 40, and is provided with a conductive fur brush 76 rotatably in the arrow direction by contacting the photoconductor 40 with its outer periphery. Further, a metal electric field roller 77 that applies a bias to the fur brush 76 is rotatably provided in the direction of the arrow, and the tip of the scraper 78 is pressed against the electric field roller 77. Further, a recovery screw 79 for recovering the removed toner is provided. The fur brush 76 that rotates in the counter direction with respect to the photoconductor 40
Then, the residual toner on the photoconductor 40 is removed. The toner attached to the fur brush 76 is removed by contacting the fur brush 76 and applying a bias by the electric field roller 77 rotating in the counter direction. The electric field roller 77 is cleaned by a scraper 78. Photoconductor cleaning device 6
The toner collected in 3 is moved to one side of the photoconductor cleaning device 63 by the recovery screw 79, and returned to the developing device 61 by the toner recycling device 80 described later for reuse. The static eliminator 64 is, for example, a lamp and irradiates light to initialize the surface potential of the photoconductor 40. Then, as the photoconductor 40 rotates, first the charging device 60 causes the photoconductor 40 to rotate.
The surface of the device is uniformly charged, and then the above-mentioned exposure device 21 causes a laser or LED to be read according to the content read by the scanner 300.
The electrostatic latent image is formed on the photoconductor 40 by irradiating the writing light L such as the above. After that, toner is attached by the developing device 61 to make the electrostatic latent image visible, and the visible image is transferred onto the intermediate transfer body 10 by the primary transfer device 62. The surface of the photoconductor 40 after the image transfer is cleaned by the photoconductor cleaning device 63 to remove residual toner, and the charge is removed by the charge removing device 64 to prepare for another image formation.

FIG. 4 is an enlarged view of a main part of the color copying machine shown in FIG. In the figure, the tandem image forming apparatus 2
No. 0 image forming unit 18, each photoconductor 40 of the image forming unit 18, each developing device 61, each photoconductor cleaning device 63, and each primary provided to face the photoconductor 40 of each image forming unit 18. After each code of the transfer device 62,
BK for black and Y for yellow
Is shown with magenta, M is shown with cyan, and C is shown with cyan. Although not shown in FIGS. 1 and 3, reference numeral 74 in FIG. 4 is a conductive roller provided between the respective primary transfer devices 62 in contact with the base layer 11 side of the intermediate transfer body 10. This conductive roller 74 prevents the bias applied by each primary transfer device 62 at the time of transfer from flowing into each adjacent image forming means 18 via the base layer 11 of medium resistance.

Next, FIGS. 5 and 6 show a toner recycling device 80. As shown in FIG. 5, the recovery screw 79 of the photoconductor cleaning device 63 is provided with a roller portion 82 having a pin 81 at one end. Then, one side of the belt-shaped collected toner conveying member 83 of the toner recycling device 80 is hooked on the roller portion 82, and the pin 81 is inserted into the elongated hole 84 of the collected toner conveying member 83. Blades 85 are provided on the outer periphery of the collected toner conveying member 83 at regular intervals, and the other side is hooked on the roller portion 87 of the rotating shaft 86. The collected toner conveying member 83, together with the rotating shaft 86,
It is placed in the transport path case 88 shown in FIG. The transport path case 88 is formed integrally with the cartridge case 89, and one of the above-described two screws 68 of the developing device 61 is inserted into the end portion on the developing device 61 side thereof. Then, the driving force is transmitted from the outside to rotate the recovery screw 79, the recovered toner transfer member 83 is rotationally transferred, and the toner recovered by the photoconductor cleaning device 63 is transferred to the transfer path case 88.
It is conveyed to the developing device 61 through the inside and is put into the developing device 61 by the rotation of the screw 68. After that, as described above, the two screws 68 carry and circulate while stirring with the developer already in the developing device 61, supply it to the developing sleeve 65 and cut off the ears with the doctor blade 73, and then the photoconductor 40 To develop the latent image on the photoconductor 40.

The toner has a charging property by mixing a charge control agent (CCA) and a colorant in a resin such as polyester, polyol and styrene acrylic, and externally adding a substance such as silica and titanium oxide around the mixture. , Increasing liquidity. The particle size of the additive is usually in the range of 0.01 to 1.5 [μm]. Examples of colorants include carbon black, phthalocyanine blue, quinacridone, carmine and the like.
The charging polarity is negative in the illustrated example. As the toner, it is possible to use a toner obtained by externally adding an additive of the above type to a mother toner in which wax or the like is dispersed and mixed. In the above description, the toner is manufactured by the pulverization method, but a toner manufactured by the polymerization method or the like can also be used. Generally, a toner produced by a polymerization method or a heating method has a shape factor of 9
It is possible to form it to 0% or more, and the coverage of the additive due to the shape becomes extremely high. Where the shape factor is
Originally, the degree of sphericity is defined as "surface area of sphere of the same volume as particle / surface area of actual particle * 100%", but since it becomes considerably difficult to measure, it is calculated as circularity. The definition is “circumferential length of a circle having the same projected area as the particle / projected contour length of the actual particle * 100%”. Then, the closer the projected circle is to the perfect circle, the closer it is to 100%.

The volume average particle diameter of the toner is in the range of 3-12.
μm is preferred. In the illustrated example, it is set to 6 μm and 1200
It is possible to sufficiently deal with high-resolution images of dpi or higher. The magnetic particles contain a magnetic material such as ferrite with metal or resin as a core, and the surface layer is coated with silicon resin or the like. The particle size is preferably in the range of 20 to 50 μm. Also, the resistance is a dynamic resistance of 1
The optimum range is from 0 ⁴ to 10 ⁶ Ω. However, the measurement method was carried on a roller (φ20; 600 RPM) containing a magnet, and an electrode having an area of 65 mm in width and 1 mm in length was brought into contact with a gap of 0.9 mm. Is a measured value when an applied voltage of 400 V to several V for an iron powder carrier is applied. The developing sleeve 65 has a non-magnetic rotatable sleeve-like shape, and has a plurality of magnets 72 arranged therein. Since the magnet 72 is fixed, a magnetic force can be applied when the developer passes through a predetermined place. In the illustrated example, the developing sleeve 65 has a diameter of φ18, and the surface is subjected to sandblasting or a process of forming a plurality of grooves having a depth of 1 to several mm for 10 to 30 mm.
It is rough so as to be in the range of μmRZ. Magnet 7
2 is from the doctor blade 73 to the developing sleeve 65.
It has five magnetic poles of N ₁ , S ₁ , N ₂ , S ₂ and S ₃ in the rotation direction. Formed by magnet 72 (toner + magnetic particles)
Is carried as a developer on the developing sleeve 65, and the toner is mixed with magnetic particles to obtain a specified charge amount. In the illustrated example, the range of −10 to −30 [μC / g] is preferable. The developing sleeve 65 is arranged facing the photoconductor 40 in the area on the S ₁ side of the magnet 72 in which a magnetic brush of developer is formed.

By the way, in the illustrated example, as shown in FIG.
And as a cleaning member in the cleaning device 17.
Two fur brushes 90, 91 are provided. Fur brush
90 and 91 are φ20 mm, acrylic carbon, 6.2
5D / F, 100,000 pieces / inch ², E + 7Ω
Contacting the intermediate transfer body 10 in the counter direction
Provided to rotate. And each fur bra
The terminals 90 and 91 have different polarities from a power source (not shown).
Apply a bias. Such fur brush 90,9
1, the metal rollers 92 and 93 are brought into contact with each other,
It is provided so as to rotate in the direction. And in this example, the middle
The power source 9 is applied to the metal roller 92 on the upstream side in the rotation direction of the transfer body 10.
(−) Voltage is applied from 4 to the metal roller 93 on the downstream side.
A (+) voltage is applied from the power supply 95. Those metal rho
The blades 96 and 97 have tips on the blades 92 and 93, respectively.
Press against. Then, in the direction of the arrow of the intermediate transfer member 10,
With the rotation, the fur brush 90 on the upstream side is used first
For example, a bias of (-) is applied to the surface of the intermediate transfer member 10.
Clean the surface. If the metal roller 92 is -7
When 00V is applied, the fur brush 90 becomes -400V.
The (+) toner on the intermediate transfer member 10 to the fur brush 9
Transfers to the 0 side. The removed toner is further charged by the potential difference.
Transfer from fur brush 90 to metal roller 92
It is scraped off with a do 96.

Now, the fur brush 90 is used to form the intermediate transfer member 10.
Although the upper toner is removed, a large amount of toner still remains on the intermediate transfer body 10. Those toners are (-) by the (-) bias applied to the fur brush 90.
Be charged to. It is considered that this is charged by charge injection or discharge. However, the toner can be removed by subsequently applying the (+) bias with the fur brush 91 on the downstream side to perform cleaning. The removed toner transfers from the fur brush 91 to the metal roller 93 due to the potential difference and is scraped off by the blade 97. The toner scraped off by the blades 96 and 97 is collected in a tank (not shown). You may make it return to the developing device 61 using a toner recycling device. After cleaning with the fur brush 91, most of the toner is removed.
There is still some toner left on top. These toners are (+) charged by the (+) bias applied to the fur brush 91. However, even when the toner cannot be removed by the two fur brushes 90 and 91 and the toner remains on the intermediate transfer body 10, the photoconductor 4 is moved at the black primary transfer position.
Reverse transfer to 0BK side Photoconductor cleaning device 63BK
Can be collected at.

Next, the intermediate transfer member (corresponding to the intermediate transfer belt in the above embodiment) used in the present invention will be described.
Conventionally, fluororesins, polycarbonate resins, polyimide resins, etc. have been used for the belts used for the intermediate transfer belt, but in recent years, all layers of the belt and elastic belts using a part of the belt as an elastic member have been used. Has been done.
This is because the transfer of a color image using a resin belt has the following problems. Color images are usually formed with four color toners. One to four toner layers are formed on one color image. The toner layer receives pressure by passing through the primary transfer (transfer from the photoconductor to the intermediate transfer belt) and the secondary transfer (transfer from the intermediate transfer belt to the sheet), and the cohesive force between the toners becomes high. If the cohesive force between the toners becomes high, the phenomenon of hollow characters or missing edges of solid images is likely to occur. Since the resin belt has a high hardness and is not deformed according to the toner layer, the toner layer is likely to be compressed and the hollow character of the character is likely to occur. Also,
Recently, there is an increasing demand for forming full-color images on various types of paper, for example, Japanese paper, or by intentionally forming unevenness on the paper or forming an image on the paper. However, paper with poor smoothness is likely to cause voids with the toner during transfer, which easily causes transfer omission. If the transfer pressure of the secondary transfer portion is increased in order to improve the adhesiveness, the condensing force of the toner layer is increased, and the hollow character as described above occurs. On the other hand, the elastic belt has a lower hardness than the resin belt,
At the transfer part, the toner layer is deformed corresponding to the paper with poor smoothness. In other words, the elastic belt is deformed following local unevenness, so that good adhesiveness can be obtained without excessively increasing the transfer pressure to the toner layer, and there is no void in characters, and the paper has poor flatness. It is possible to obtain a transferred image with excellent uniformity.

The resin of the elastic belt is polycarbonate, fluorine resin (ETFE, PVDF), polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate. Copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene- Octyl acrylate copolymer and styrene-phenyl acrylate copolymer), styrene-methacrylic acid ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-phenyl methacrylate) Copolymer, etc.), styrene-α-qua Styrene resins such as methyl chloroacrylate copolymer, styrene-acrylonitrile-acrylic acid ester copolymer (styrene or styrene-substituted homopolymer or copolymer), methyl methacrylate resin, butyl methacrylate resin, acrylic Ethyl acid resin, butyl acrylate resin, modified acrylic resin (silicone modified acrylic resin, vinyl chloride resin modified acrylic resin, acrylic urethane resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer, vinyl chloride-vinyl acetate copolymer Polymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene,
Polybutadiene, polyvinylidene chloride, ionomer resin, polyurethane resin, silicone resin, ketone resin,
One or more selected from the group consisting of ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral resin, polyamide resin, modified polyphenylene oxide resin and the like can be used.
However, the material is not limited to the above materials.

As elastic rubber and elastomer, butyl rubber, fluorine rubber, acrylic rubber, EPDM, NB
R, acrylonitrile-butadiene-styrene rubber Natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, ethylene-propylene rubber, ethylene-
Propylene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, recone rubber, fluororubber,
Polysulfide rubber, polynorbornene rubber, hydrogenated nitrile rubber, thermoplastic elastomer (for example, polystyrene type, polyolefin type, polyvinyl chloride type, polyurethane type,
One type or two or more types selected from the group consisting of polyamide type, polyurea, polyester type and fluororesin type) can be used. However, the material is not limited to the above materials.

There is no particular limitation 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 oxide (ATO), indium oxide-tin oxide composite oxide. The conductive metal oxide such as a material (ITO) and the conductive metal oxide may be coated with insulating fine particles such as barium sulfate, magnesium silicate, and calcium carbonate. The conductive agent is not limited to the above. There is no limitation on the surface layer material, but it is required to reduce the adhesion of the toner to the surface of the transfer belt to improve the secondary transfer property. For example, one or more kinds of polyurethane, polyester, epoxy resin, etc. are used to reduce surface energy and improve lubricity, for example, powder of fluororesin, fluorine compound, fluorocarbon, titanium dioxide, silicon carbide, etc. It is possible to disperse and use one kind or two or more kinds of particles or particles having different particle diameters. It is also possible to use a material such as a fluorine-based rubber material having a fluorine-rich layer formed on the surface by heat treatment to reduce the surface energy. The method for manufacturing the belt is not limited. That is, a centrifugal molding method in which a material is poured into a rotating cylindrical mold to form a belt, a spray coating method in which a thin film on the surface layer is formed, a dipping method in which a cylindrical mold is immersed in a solution of a material and pulled up, an inner mold. There is a casting method of injecting into the outer mold, a method of winding a compound around a cylindrical mold, and a method of vulcanizing and polishing, but not limited to these, and a belt is manufactured by combining a plurality of manufacturing methods. be able to.

A method of manufacturing the elastic belt used in this embodiment will be described. 18 parts by weight of carbon black, 3 parts by weight of dispersant, and 4 parts of toluene based on 100 parts by weight of PVDF
A cylindrical mold was dipped in a dispersion liquid in which 100 parts by weight was uniformly dispersed, gently pulled up at 10 mm / sec and dried at room temperature to form a uniform PVDF film of 75 μm. 75μ
The mold on which the m film was formed was repeated, and the cylindrical mold was dipped in the solution under the above conditions, gently pulled up at 10 mm / sec, and dried at room temperature to form a PVDF belt of 150 μm.
To this, 100 parts by weight of polyurethane prepolymer, 3 parts by weight of curing agent (isocyanate), carbon black 20
The cylindrical mold on which 150 μm PVDF was formed was dipped in a dispersion liquid in which 1 part by weight, 3 parts by weight of a dispersant, and 50 parts by weight of MEK were uniformly dispersed, and was pulled up at 30 mm / sec and naturally dried. Repeat after drying and aim at 150
A μm urethane polymer layer was formed. Further, 100 parts by weight of the polyurethane prepolymer, 3 parts by weight of the curing agent (isocyanate), 50 parts by weight of the PTFE fine powder powder, 4 parts by weight of the dispersant, and 500 parts by weight of MEK were uniformly dispersed for the surface layer. The cylindrical mold on which the 150 μm urethane prepolymer was formed was dipped and pulled up at 30 mm / sec for natural drying. After drying, the process was repeated to form a urethane polymer surface layer in which 5 μm of PTFE was uniformly dispersed. After drying at room temperature, crosslinking is carried out at 130 ° C. for 2 hours, and resin layer: 150 μm, elastic layer: 150 μm, surface layer;
A transfer belt having a three-layer structure of 5 μm was obtained.

As a method of preventing the expansion of the elastic belt,
As described above, there are a method of forming a rubber layer on a core resin layer having a small elongation, a method of adding a material for preventing elongation to the core layer, and the like, but the manufacturing method is not limited to these. The material forming the core layer for preventing elongation is, for example, cotton, silk,
Natural fiber such as polyester fiber, nylon fiber, acrylic fiber, polyolefin fiber, polyvinyl alcohol fiber, polyvinyl chloride fiber, polyvinylidene chloride fiber, polyurethane fiber, polyacetal fiber, polyfluoroethylene fiber, synthetic fiber such as phenol fiber, carbon Fibers, glass fibers, inorganic fibers such as boron fibers, and metal fibers such as iron fibers and copper fibers may be used in a woven or thread form by using one or more selected from the group consisting of metal fibers. Of course, the material is not limited to the above. The yarn may be any twisted yarn, such as a twisted yarn of one or a plurality of filaments, a single twisted yarn, a plied yarn, and a twin yarn. Further, for example, fibers of a material selected from the above material group may be mixed and spun. Of course, the thread may be used after being subjected to an appropriate conductive treatment. On the other hand, as the woven fabric, any woven fabric such as a knitted fabric can be used, and of course, a mixed woven fabric can also be used and naturally a conductive treatment can also be applied. The manufacturing method for providing the core layer is also not particularly limited, for example, a woven fabric woven in a tubular shape is covered on a mold or the like,
A method of providing a coating layer on it, a method of immersing a tubular woven cloth in liquid rubber or the like to provide a coating layer on one side or both sides of the core layer, and a thread in a mold or the like spiraled at an arbitrary pitch It is possible to cite a method of wrapping it around, and providing a coating layer on it.

The thickness of the elastic layer depends on the hardness of the elastic layer, but if it is too thick, the expansion and contraction of the surface will increase and cracks will easily occur in the surface layer. It is not preferable that the thickness of the elastic layer is too thick (approximately 1 mm or more) because the amount of expansion and contraction becomes large and the image has a large amount of expansion and contraction. The proper range of the hardness of the elastic layer is 10≤HS≤65 ° (JIS-A). Is. It is necessary to adjust the optimum hardness depending on the layer thickness of the belt. Hardness 1
Those below 0 ° JIS-A are very difficult to be molded with high dimensional accuracy. This is because it is susceptible to shrinkage and expansion during molding. Further, in the case of softening, it is a general method to add an oil component to the base material, but there is a drawback that the oil component exudes when continuously operated in a pressurized state. It was found that this contaminates the photoconductor that comes into contact with the surface of the intermediate transfer member and causes lateral stripe unevenness. Generally, a surface layer is provided to improve releasability, but in order to provide a complete exudation prevention effect, the surface layer has high required quality such as durability quality, so it is necessary to select materials and secure characteristics. It will be difficult. On the other hand, if the hardness is 65 ° JIS-A or higher, molding can be performed accurately due to the increased hardness, and the oil content is not included or can be suppressed to a low level. Although it is possible, the effect of improving the transferability such as missing characters is not obtained, and it becomes difficult to stretch the roller.
Here, the volume resistance of the intermediate transfer belt is generally 10 ⁹ Ω.
・ Use the one with cm or more. A belt of 10 ¹² Ω · cm or more may be used to prevent transfer dust and the like.

Next, an example in which the charging member of the present invention is used is shown in FIG. In FIG. 8, the charging member 104 is a charging roller. These charging rollers 104 may directly contact the intermediate transfer belt 10. Further, a proximity method in which a minute space is separated may be used. Alternatively, a corotron / scorotron method using a metal wire may be used. Also, a charging brush may be used. It is also conceivable to use a charging blade, a charging film or the like.
These can be selected freely, but from the viewpoint of reducing the load on the transfer belt drive, the contact type is preferably a rotating body but is preferably a non-contact type corotron type. The charging method is not limited to these means. By such a charging member, charges are accumulated on the surface of the intermediate transfer belt 10. This polarity is set to the opposite polarity to the toner. In the above embodiment, the toner polarity is negative. In this case, the electric potential supplied to the charging member has a positive polarity. Next, when the surface layer of the intermediate transfer belt 10 has a positive polarity and reaches the transfer point of the first color, the toner is transferred to the transfer belt side due to the positive charge of the surface layer. However, since sufficient transfer capability cannot be obtained with only these charges, a positive voltage / current is applied from the transfer member (62) inside the transfer belt to perform transfer. In this case, it is clearly different between the case where the charge is applied before the transfer and the case where the charge is not applied. In the case where the charge is applied, the same transfer performance can be obtained when the voltage / current application to the transfer member (62) is about half. Confirmed experimentally. Incidentally, the volume resistivity of the transfer belt used in these experiments is 10 ¹² to 10 ¹³ Ω · cm. By suppressing the transfer current applied to the transfer member,
It is possible to reduce the absolute value of the surface potential of the intermediate transfer belt after passing through the transfer point. This is because peeling discharge generally occurs in the area where the transfer belt and the photoconductor are separated from each other in a manner proportional to the voltage and current applied to the transfer member, and in this case, the negative potential remains on the intermediate transfer belt. Is. It is also possible that the charges added before transfer cancel each other out and push down the total amount. Further, this residual potential tends to gradually increase in absolute value as it passes through each color. According to the experiment, it was observed that the absolute value potential of about 100 V to 300 V rises in a portion where the toner is not transferred each time the toner passes through each color. It was also confirmed in another experiment that the higher the resistance of the intermediate transfer belt, the higher this potential rise.

According to the present experimental example, each color of
About -100V to -300V each during transfer
The inter-transfer belt surface potential was lowered. First time again
The current applied to the charging member (104 in FIG. 8) is 30μ
A, the volume resistance of the charging member is 10 ⁹-10¹²Ω ・ cm and setting
The surface potential of the intermediate belt is about + 300V
Was observed to be charged. In this case, the initial potential is
Since it was lath, the intermediate transfer belt was
The current shifts to the eggplant side and eventually the potential becomes negative
Under the conditions, the absolute value of the surface potential of the intermediate transfer belt after the final color transfer is
The value becomes smaller. By the way, a current of −30 is applied to the initial charging member.
When it is set to μA, the surface potential of the intermediate transfer belt 10 is −20.
Of the intermediate transfer belt 10 after the final color transfer by charging to about 0V
The electric potential shifts more negatively, and the absolute value of the electric potential becomes more
It gets bigger. In other words, the difference in the initial charging potential is
There is also a potential difference on the intermediate transfer belt after the end of overlapping.
Appears. However, for example, if the initial potential difference remains the same,
Not the final potential difference, but the difference decreases experimentally
In the direction. However, under the conditions shown above, the charging member
To set the potential of the intermediate transfer belt surface before transfer to the plus side.
By doing so, color overlapping can be achieved compared to when there is no charging member.
The absolute value of the surface potential at the time of completion is suppressed by about 200V.
It becomes possible to obtain. Intermediate transfer which is a problem this time
For the toner scattering due to the rise of the belt potential,
Can be improved by suppressing the potential rise from
It From these results, the polarity applied to the charging member is
It is desirable to have a polarity opposite to that of the toner.

Further, these potential suppression amounts can be controlled by the current and voltage applied to the charging member, and by making this control variable, it is possible to set them according to the respective conditions. Become. When controlling the current / voltage applied to the charging member, the control may be changed by user input. It is also possible to collect some kind of information by a sensor in the device and automatically change the value based on the result. With these controls,
It is possible to provide the optimum potential for each condition, and it is possible to prevent the transfer toner from scattering. For example, as shown above, the increase in potential increases as an absolute value as the number of times each color is overlapped increases. Further, these devices are often provided with a single black color mode, and in this case, the photoconductors of other colors are not brought into contact with the intermediate transfer belt. Therefore, the fluctuation of the potential is actually only one black color. In that case, the increase in the potential of the intermediate transfer belt is not so large in many cases, and it is not a problem in many cases. In this case, there is no need to dare to perform pre-transfer charging. Therefore, in the black one color mode, the current / voltage applied to the charging member may be zero. That is, it is possible to provide a device capable of obtaining the same effect with a small amount of energy by making the same or smaller than when the number of times of superposition is large.

It is also possible to change the control value depending on the environment. Generally, the resistance value of the belt changes depending on the environment. Specifically, the resistance value tends to increase in a low temperature and low humidity environment. Further, in a high humidity environment, the amount of water molecules attached to the surface layer is large and the apparent resistance tends to decrease. If only a constant current and voltage can be applied, the appearance of potential changes greatly due to the difference in surface resistance under low temperature and low humidity and high temperature and high humidity, and the difference widens under each condition. In this state, the problem may be improved under certain conditions, but on the other hand, a problem such as no improvement effect may be observed.
In the first place, peeling discharge charges after transfer are self-discharged in a high-humidity environment, so it is unlikely that the absolute value of the potential will rise.
In some cases, the need for a charging member is small. With respect to these problems, by changing the current / voltage application to the charging member according to the environmental conditions, the most suitable charge can be given under each condition, and the problem under each condition can be improved.

[0031]

As described above, according to the image forming apparatus of the first aspect, in the tandem type multicolor image forming apparatus using the intermediate transfer member, the step of transferring the image of the first color onto the intermediate transfer member is performed. Since the charging member for charging the surface of the intermediate transfer member is provided in advance, the voltage (or current) applied to the transfer member disposed inside the intermediate transfer member can be suppressed, whereby the intermediate transfer member can be suppressed. The increase in the electric potential is suppressed, and the increase in the electric potential is small even if the number of overlapping of each color is increased. Therefore, it is possible to prevent the toner image from scattering due to the increase in the electric potential of the intermediate transfer member. According to the image forming apparatus of claim 2, since the current or voltage applied to the charging member has a polarity opposite to the charging polarity of the toner, the absolute value of the surface potential of the intermediate transfer body after the final color transfer is reduced. Therefore, toner scattering can be efficiently prevented. According to the image forming apparatus of claim 3, since the current or voltage applied to the charging member is controllable, the above-mentioned potential suppression amount can also be controlled by the current or voltage applied to the charging member. The setting can be performed according to the condition (1), and the toner scattering can be efficiently prevented. According to the image forming apparatus of claim 4, the current or voltage applied to the charging member is larger in absolute value level as the number of times of color overlapping is larger,
Or, since the control is performed so as to be equal, even if the increase in the potential of the intermediate transfer member increases due to the increase in the number of overlapping of each color, the current or voltage applied to the charging member can be increased accordingly, so that the intermediate transfer member The increase in the electric potential is suppressed, and the toner scattering can be efficiently prevented.
According to the image forming apparatus of claim 5, since the current or voltage applied to the charging member can be changed according to the environment, even if the resistance value of the intermediate transfer member or the amount of adsorbed water changes depending on the environment. The most suitable charge can be applied to the intermediate transfer member under each condition, the problem under each condition can be improved, and the toner scattering can be efficiently prevented.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a multicolor image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a schematic sectional view of an intermediate transfer member showing an embodiment of the present invention.

3 is a partial configuration diagram for explaining the multicolor image forming apparatus of FIG.

4 is a partially enlarged view of the multicolor image forming apparatus of FIG.

5 is a perspective view for explaining a part of the configuration of the multicolor image forming apparatus in FIG.

FIG. 6 is a perspective view for explaining a part of the configuration of the multicolor image forming apparatus in FIG.

FIG. 7 is a partial configuration diagram of a multicolor image forming apparatus showing an embodiment of the present invention.

FIG. 8 is a partial configuration diagram of a multicolor image forming apparatus showing another embodiment of the present invention.

FIG. 9 is a partial configuration diagram of a conventional indirect transfer tandem type multicolor image forming apparatus.

FIG. 10 is a partial configuration diagram of a conventional direct transfer tandem type multicolor image forming apparatus.

[Explanation of symbols]

1,40 Photoreceptor (or image carrier) 2,62 Primary transfer device (or transfer member) 3 Sheet conveyor belt 4, 10 Intermediate transfer body 5,22 Secondary transfer device 9, 17 Intermediate transfer member cleaning device 18 Image forming means 20 Tandem image forming device 102, 104 charging member

Continued front page    F term (reference) 2H030 AA00 AB02 AD02 BB42 BB46                       BB52                 2H200 FA01 FA08 FA18 GA23 GA33                       GA34 GA36 GA45 GA47 GA49                       GA53 GA56 GA66 GB12 GB13                       HB12 JC03 JC12 JC13 JC15                       JC16 JC17 JC18 JC19 LC03                       LC04 MA02 MA03 MA12 MA13                       MA14 MA20 MB04 MC01 NA02                       NA08 NA09 PA02 PB02 PB03                       PB05 PB28

Claims (5)

[Claims] 1. An image forming apparatus using electrophotography, wherein an image of each color produced by a plurality of image carriers and a developing unit is rotated once on the intermediate transfer member. In a tandem type image forming apparatus that sequentially superimposes a multicolor image by using a charging member that charges the surface of the intermediate transfer member before the step of transferring the image of the first color onto the intermediate transfer member. A characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the current or voltage applied to the charging member has a polarity opposite to the charging polarity of the toner. 3. The image forming apparatus according to claim 1, wherein the current or voltage applied to the charging member is changeable. 4. The image forming apparatus according to claim 1, wherein the current or voltage applied to the charging member is controlled to become larger or equal in absolute value level as the number of times of color superposition increases. . 5. The image forming apparatus according to claim 1, wherein the current or voltage applied to the charging member can be changed according to the environment.