JPH09218592A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device small in size, low in power consumption and capable of forming an image of regular paper and a multicolor image for OHP excellent in light transmissivity. SOLUTION: This device is provided with a mode changeover switch 33 capable of signal outputting a mode for monochromatic printing/color printing, and the regular paper/the OHP paper sheet. The device is provided with a drive controlling circuit 21, for rotary controlling a driving rotary roller 23 and four sets of photoreceptor drums 20a to 20d so that the respective transporting speed becomes 1/3 of the transporting speed of the regular paper at the time of forming the multicolor image on the OHP paper sheet. On the paper sheet attract-transported by a transporting belt 22, the respective toner image of magenta, cyan, yellow and black of the photoreceptor drum 20a on the most upstream to the photoreceptor drum 20d on the most downstream is successively transferred. The transfer electric current controlling circuit 32 is allowed on control so as to successively increase the transfer electric current from the transfer blush 26a on the upstream to the transfer blush 26d on the downstream side in the case of the OHP paper sheet mode, and to control so that the transfer electric current of the transfer blush 26d of the last stage becomes same as the transfer electric current in the case of the regular paper.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to plain paper and OHP.
The present invention relates to an image forming apparatus that forms a clear multicolor image on paper.

[0002]

2. Description of the Related Art Conventionally, various multicolor electrophotographic image forming apparatuses have been proposed. This type of color image forming apparatus is roughly classified into a single drum type and a multi-stage drum type (tandem type). Single drum type is for one page of paper,
Y (yellow: yellow) toner, which is the three primary colors of subtractive color mixing,
A total of four types of toner, M (magenta: red dye) toner, C (cyan: blue with green tint) toner, and Bk (black: black) toner dedicated to printing characters, etc., are superimposed on the paper. In order to transfer the image, the image forming process is individually performed for each color toner using one photosensitive drum and a plurality of developing devices. Therefore, in terms of using a single drum, there is an advantage that the entire apparatus can be downsized, while the paper 1
There is also a drawback that the printing process takes a long time in that the printing process is repeated four times for the page.

On the other hand, the tandem type has four steps in one step.
Since different types of toner are sequentially transferred and superposed on the paper, the processing speed is almost four times that of the single drum type. Therefore, in recent years, the tandem system has attracted attention. The tandem system uses a belt-conveying system because it sequentially superimposes color images on paper. Various types of belts are used to convey the paper, but if a semi-conductive belt is used, it is difficult for the semi-conductive belt itself to be charged, and therefore the transfer current that transfers the image to the paper has a negative effect. It can be said that the ratio of receiving it is small and the ratio is preferable.

FIG. 8 is a side sectional view schematically showing an example of a tandem type color image forming apparatus. In this color image forming apparatus 1, a paper cassette 2 is detachably mounted on the lower right side surface of the main body of the apparatus. The paper 3 in the paper cassette 2 is taken out one by one by the paper feed roller 4, and is fed to the image forming / transfer portion by the pair of standby rolls 5. In the image forming / transferring section, a belt 6 for conveying the sheet 3 is stretched flat in the sheet conveying direction (from right to left in the figure) by a plurality of rotating rollers, and four photosensitive belts are arranged facing the belt conveying surface. The body drum 7 is arranged and configured. Each of the photoconductor drums 7 sequentially surrounds the vicinity of its peripheral surface, and is provided with an initialization charging device 8 and a developing roller 9-1 arranged in a developing device 9.
Transfer charger 1 arranged with the transport surface of the transport belt 6 interposed therebetween.
1 and a cleaner 12 are arranged. A predetermined gap is provided between the initialization charging device 8 and the developing device 9, and digital exposure radiation is performed from the laser head 13 to the peripheral surface of the photoconductor drum 7 through this gap. Laser head 13
Includes a light source, a rotating mirror 13-1, a focusing lens 13-2, a reflecting mirror 13-3, an irradiation port 13-4, and the like.

In this color image forming apparatus, the paper 3 taken out from the cassette 2 by the paper feed roller 4 and fed is
The standby roll pair 5 temporarily stops, and feeding is started in synchronization with the timing of printing (image formation). The sheet 3 is conveyed by a belt 6 that circulates in the counterclockwise direction in the figure, and the photosensitive drum 7 and the transfer charger 11 face each other 4
It passes through the transfer section at one place together with the conveyor belt 6.

On the other hand, the photoconductor drum 7 includes an initialization charger 8
A uniform charge is applied to the peripheral surface by the applied voltage of, and an electrostatic latent image is formed on the charged peripheral surface by exposure by the exposure head 13. The developing roller 9-1 of the developing device 9 transfers the toner to the low potential portion of this electrostatic latent image (in the case of reversal development) to form (develop) a toner image. The toner image developed on the peripheral surface of the photosensitive drum 7 is conveyed to the transfer portion as the photosensitive drum 7 rotates.

The transfer charger 11 corona-discharges and injects an electric charge onto the sheet 3 carried and conveyed by the conveyor belt 6 and passing through the respective transfer portions. The color toner images on the photosensitive drums 7 are sequentially transferred by being attracted by the electric charges. The toner image is transferred onto the paper surface of the paper 3, and the toner image is thermally fixed on the paper surface by a fixing unit 14 composed of a pressure roller and a heat roller. Is discharged toward.

By the way, such full-color images are often used for so-called presentations in offices, lecture halls, various waiting places, and the like. In this case, a projection device is used as a device that can be viewed by a large number of people at the same time. However, when an image is formed on an OHP sheet which is the original, the image is required to have good light transmittance.

When the transparency of the toner after image formation is required as described above, in order to obtain the transparency of the solidified toner portion after fixing, the solidified toner portion does not have turbidity inside and the surface thereof is not turbid. Must be smooth and free of diffuse reflection. To this end, the toner is sufficiently melted in the fixing unit, so that there is no unmelted component of the toner, that is, turbidity due to the unmelted component does not occur in the solidified toner portion after fixing, In the method, irregularities must be prevented from being generated on the surface of the solidified toner portion after fixing due to incomplete melting to cause loss of smoothness.

As described above, in order to sufficiently melt the toner, it is necessary to give sufficient heat energy to the toner. Even so, it is not possible to raise the temperature of the fixing section unnecessarily. If the temperature of the fixing unit is too high, the life of the fixing unit itself will be shortened, and the internal devices around the fixing unit will be adversely affected. Further, a large cooling fan is required, and accordingly, a large driving power source is required, which causes a problem that the entire device becomes large and the product price increases. Therefore, instead of increasing the temperature of the fixing unit, a fixing process time is set longer, that is, the processing speed (paper conveyance speed) is slowed to allow heat to sufficiently penetrate into the toner. ing.

By the way, it is not always decided that printing (image formation) is performed by multicolor printing (full color printing).
In general, the frequency of monochrome printing (monochrome printing) is quite high. This also applies to the above-mentioned OHP image. Therefore, in order to cope with such usage, various tandem type color image recording apparatuses have been proposed which are capable of switching between color printing and monochrome printing. Also, as described above, in order to obtain better light transmission of a color image, the plain paper mode and the OHP
It is proposed to change the processing speed of image formation depending on the mode.

[0012]

However, when OHP paper is used in the full-color printing mode, OHP paper generally has a high electrical resistance, so that a transfer result similar to that of plain paper may be applied. There was a problem that I could not get it. Therefore, as described above, OHP
When the paper conveyance speed is slower in the case of paper than in the case of plain paper, the transfer condition is further changed, so that the problem of transfer current becomes more serious. In order to solve this problem, even when a transfer current different from that of plain paper is set in the case of OHP paper, the OHP paper is electrically connected as described above as it undergoes a plurality of transfer steps for overlapping each color. Due to the high resistance, the charge amount due to transfer increases, and due to this gradually increasing charge amount, if the same transfer current is set and applied at the transfer portion for each color, transfer failure will occur. There was also.

Conventionally, there has been an idea of increasing the transfer current in the tandem type color image forming apparatus using an insulative transfer belt as it goes downstream in the paper transfer direction. However, if it is simply increased, the current value at the most downstream will be increased. Significantly higher, other problems such as larger power supply, increased ozone generated by corona discharge, etc.

In view of such conventional circumstances, in order to improve the light transmittance of the formed image on the OHP paper, a good transfer result can be obtained even if the processing speed is different from that of the plain paper, and the power source is enlarged. In addition, there has been a demand for development of an apparatus capable of obtaining a clear multicolor image with good black printing.

An object of the present invention is not only to form an image on plain paper, but also to form a clear multicolor image with light transparency for OHP, and to use black toner in the black portion in the full color printing mode. An object of the present invention is to provide an image forming apparatus that is small and consumes less power.

[0016]

The construction of the image forming apparatus according to the present invention will be described below. First, in the invention according to claim 1, the step of forming a toner image of a predetermined color on the image carrier is carried out for each color, and the toner images of a plurality of colors are provided inside the transfer material conveying member that circulates. It is applied to an image forming apparatus that forms a multicolor image by sequentially superposing and transferring onto a transfer material carried and conveyed on the outer surface of the transfer material conveying member by a transfer means to which a transfer current is supplied.

The image forming apparatus of the present invention comprises a drive means for driving the surface of the image carrier and the outer surface of the transfer material conveying member so as to move at the contact position in the same direction and at substantially the same speed. The drive speed by the drive control means for controlling the drive means to drive the drive means so that the predetermined speed becomes the first speed and the second speed slower than the first speed, and the drive speed by the drive control means according to the type of the transfer material. Depending on the mode setting means for setting the first and second speeds and the setting of the second speed by the mode setting means, the transfer current of the transfer means is less than or equal to the transfer current at the time of setting the first speed. And a transfer current control means for controlling the above.

Next, a second aspect of the present invention drives the plurality of image carriers arranged in parallel and the surface of at least one of the plurality of image carriers to circulate at a predetermined speed. Image carrier driving means, a plurality of toner image forming means for individually forming a toner image of a predetermined color on the surface of the plurality of image carriers, and a transfer material adsorbed on the outer surface to circulate and move to carry the plurality of image carriers. A transfer material transport belt that transports the transfer material to contact the surface of at least one image carrier of the body, and a belt drive that drives the outer surface of the transfer material transport belt to move at substantially the same speed as the predetermined speed. And a means for transferring the toner image to the transfer material in contact with the image carrier, which is disposed inside the transfer material transport belt so as to form a transfer portion corresponding to the plurality of image carriers. A transfer means to which a transfer current is supplied, and Drive control means for controlling the image carrier drive means and the belt drive means to drive the predetermined speed to the first speed and the second speed slower than the first speed, and the above-mentioned drive means depending on the type of the transfer material. Mode setting means for setting the drive speed by the drive control means to the first speed and the second speed, the plurality of image carriers are driven, and the transfer material contacts all of the surfaces of the plurality of image carriers. An image forming apparatus capable of forming a multicolor image on a transfer material while being conveyed by a transfer material conveying belt, in which transfer by the transfer means is performed according to the setting of the second speed by the mode setting means. It is configured to include a transfer current control unit that controls the current to be equal to or lower than the transfer current when the first speed is set.

The transfer current control means may be, for example, the third aspect.
As described, the first speed by the mode setting means
When setting the degree, the transfer current of the transfer means when transferring each color
To the same current value,
When setting the speed of 2, superimpose the transfer current of the transfer means.
It should be controlled to increase as the number of transfers increases.
It is composed of Moreover, for example, as described in claim 4,
When setting the second speed by the mode setting means
The transfer current of the last transfer means of the overlapping transfer is
Make sure to control the transfer current value to be approximately the same as the above when setting the speed.
It is composed of In addition, the mode setting means is, for example,
When the type of transfer material is a normal sheet as described in Requirement 5
The drive speed by the drive control means is set to the first speed
However, in the case of a transparent resin sheet, the drive control means
Is configured to control the dynamic speed to the second speed.
You. Further, for example, as described in claim 6, the second speed is set.
The speed is set to about 1/3 of the first speed.
Is done. Further, the transfer means is, for example, as described in claim 7.
The transfer material in contact with the image carrier as described above.
Contact the inner surface of the transfer material transport member to press it toward the body
It is composed of a contact type transfer device. In addition, transfer material transfer
The member is, for example, as described in claim 8, 10 ^Ten-10¹⁴
It is composed of a semiconductive material having a resistivity of Ωcm.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. Incidentally, in the present embodiment,
The above-mentioned image carrier is composed of, for example, a photosensitive drum,
The image carrier driving means is, for example, a stepping motor or another motor (not shown), and the toner image forming means is, for example, an exposure head or an image forming unit.
The transfer material is made of plain paper or OHP paper, the transfer material conveying member is made of, for example, a paper winding semi-conductive drum or a paper conveying belt, and the driving means is made of, for example, a stepping motor or other motor not shown. The belt driving means includes, for example, a driving rotation roller, a driven rotation roller, and the like, the transfer means includes, for example, a transfer brush or a transfer roll, and the transfer current control means, the drive control means, and the mode setting means, respectively. It is composed of a control circuit, a switch circuit, etc. incorporated in the electronic parts mounted on the circuit board shown in the figure.

FIG. 1 is a sectional view schematically showing the structure of the main part (image forming / transferring part) of the image forming apparatus in one embodiment. This image forming apparatus has a full-color printing mode and a monochrome printing mode, and further has a plain paper mode and an OHP paper mode in each mode. This figure shows image formation in full-color print mode.
The state of the transfer portion is shown. As shown in the figure, the image forming / transferring unit includes four photoconductor drums 20 (20a, 20b, 20c,
20d). These photosensitive drums 20 are
Anthracene, which covers the surface of the metal roller uniformly,
An organic photoconductor (OPC) such as phthalocyanine or an inorganic photoconductor such as Se or a-Si is deposited to form a photosensitive layer on the surface, and the metal roller portion is grounded to the main body of the apparatus. ing. Each of the photoconductor drums 20 carries on its peripheral surface a toner image of a predetermined color developed according to the electrostatic latent image, and rotates. The photoconductor drum 20 includes a drive control circuit 2 mounted on a circuit board (not shown) via drive systems 21-1 and 21-2 schematically shown by a chain line in the figure.
It is driven under the control of 1 and rotates clockwise in the figure.

A flat loop-shaped sheet conveying belt 22 is arranged facing the photoconductor drums 20 and horizontally in the direction in which the photoconductor drums 20 are arranged in parallel. The paper transport belt 22 has a thickness that gives a volume resistivity of 10 ¹¹ to 10 ¹⁴ Ω · cm by adding carbon black to a fluororesin (tetrafluoroethylene copolymer (ETFE)) to adjust the resistance. It is composed of a film-shaped member of 150 μm. The sheet conveying belt 22 has its flat ends wrapped around the driving rotation roller 23 and the driven rotation roller 24, and is held from the inside of the loop.

Drive rotation roller 23 and driven rotation roller 2
Numeral 4 is rotatably fixed to a frame of an apparatus main body (image forming apparatus) described later. Drive rotation roller 2
3 is driven by the control of the above-mentioned drive control circuit 21 via a drive system 21-3 schematically shown by the one-dot chain line in the figure, and rotates in the counterclockwise direction in the figure. The driven rotation roller 24 is driven by the drive rotation roller 23 and also rotates in the counterclockwise direction. The driven rotation roller 24 includes a suction roller 25.
Are in pressure contact with each other via the paper transport belt 22. A power source (not shown) that outputs a positive polarity voltage is connected to the suction roller 25, and the suction roller 25 gives an electric charge to the sheet carried in the sheet and electrostatically transfers the sheet to the sheet conveyance belt 22. Adsorb.

The above-mentioned sheet conveying belt 22 is driven by a driving rotating roller 23 and a driven rotating roller 24, and circulates from the upstream side to the downstream side in the sheet conveying direction indicated by arrow A in the figure. The sheet conveying belt 22 electrostatically adsorbs and conveys a sheet such as a plain sheet or an OHP sheet on the outer peripheral surface of the upper circulation portion, and at least one photoconductor drum 20d or this photoconductor 20d and another photoconductor drum 20a, 20b and 20
Touch the paper to c. If the volume resistivity of the paper transport belt 22 is lower than 10 ¹¹ Ω · cm, it becomes difficult for the paper to be electrostatically attracted to the paper transport belt 22. It is considered that this is because the electric charge remains on the back surface of the paper transport belt 22 and is not exhausted.

Abutting on the inside of the sheet conveying belt 22,
Four photosensitive drums 20a, 20b, 20c and 22d
Corresponding to the transfer brush 26 (26a, 26b, 26c,
26d) are juxtaposed. These transfer brushes 26 are configured by forming a woven fabric in a pile shape using conductive rayon, nylon, acrylic, or the like as a fiber material into a brush shape and attaching it to a metal or plastic base. These transfer brushes 26 face the photoconductor drum 20 and are arranged so as to sandwich the paper conveyance belt 22 with these photoconductor drums 20 to form a transfer portion. The transfer brush 26 applies a positive charge to the sheet conveyed by the sheet conveying belt 22 to the transfer portion via the sheet conveying belt 22. Due to the electric field of the applied charges, the negative toner image on the photoconductor drum 20 is transferred onto the sheet in contact with the photoconductor drum 20.

As described above, the paper transfer belt 22 is provided with a semiconductive resistance, and the transfer charger is transferred to the transfer belt 22.
By configuring as the contact-type transfer brush 26,
Even if the resistance between the base of the transfer brush 26 and the ground decreases at high humidity, the transfer load resistance becomes less than that, so that the transfer current flows in the direction of the paper, and even in such a case, the transfer electric field is sufficient. You can get it. That is, this image forming apparatus can be used in all environments from a dry state to a high humidity state. If the transfer charger is a contact type, it may be a roller member instead of a brush member like the transfer brush 26.

The tension roller 27 is arranged near the drive rotation roller 23 so as to come into contact with the inner peripheral surface of the lower circulation portion of the paper transport belt 22. This tension roller 27 is
It is rotatably disposed at the tip of a rotation member (not shown) that is rotatably supported by the frame of the apparatus body, and is also biased downward by a biasing member (not shown). As a result, the tension roller 27 always urges the lower circulation portion of the paper transport belt 22 to be pulled downward, and absorbs the bending of the paper transport belt 22 irrespective of the state change accompanying the switching of the print mode described later. The entire sheet conveyance belt 22 is stretched between the driven rotation roller 24 and the drive rotation roller 23 with a predetermined tension.

A rotating arm 28 is disposed between the upper and lower circulating portions of the paper transport belt 22 and extends parallel to the transport direction. The rotating arm 28 has a fixed support roller 29 at its downstream end and a movable support roller 31 at its upstream end. Rotating arm 28
With a cam (not shown) that comes into contact with the lower portion and slides, the upstream end of the fixed support roller 29 pivots up and down. That is, the movable support roller 31 moves vertically.

The fixed support roller 29 is the photosensitive drum 20.
d and the transfer brush 26d, which is the most downstream transfer unit, and the transfer unit, which is immediately upstream of the transfer unit, which is composed of the photoconductor drum 20c and the transfer brush 26c, are provided near the intermediate downstream side, and are rotatably fixed to the frame of the apparatus main body. The paper transport belt 22 is in contact with the inner peripheral surface of the paper transport belt 22 to support it from below, and the paper transport belt 22 is always in contact with the most downstream photosensitive drum 20d.

The movable supporting roller 31 supported on the free end of the rotating arm 28 is a driven rotating roller 24 for supporting the upstream end of the paper transport belt 22, the most upstream photosensitive drum 20a and the transfer brush. It is located in the middle of the transfer portion composed of 26a. As shown in FIG. 1, the movable support roller 31 contacts the inner peripheral surface of the paper transport belt 22 to support the paper transport belt 22 from below when the rotary arm 28 is rotated upward. As a result, each photosensitive drum 2
The sheet conveying belt 22 is brought into contact with all of 0a, 20b, 20c and 20d.

Each of the above-mentioned transfer brushes 26 outputs the output of the transfer power source connected thereto from the transfer current control circuit 32 mounted on the circuit board (not shown) to the control signal line 32-.
1, 32-2, 32-3 and 32-4 are controlled and regulated. And the transfer brush 26d at the most downstream is
It is fixed to the frame of the apparatus main body and is in contact with the paper transport belt 22. On the other hand, the other transfer brushes 26a to 26c
Is fixed to the rotating arm 28, and contacts the paper transport belt 22 when the rotating arm 28 is rotating upward as shown in FIG. With this, from upstream to downstream,
Transfer portions are formed respectively corresponding to the four photoconductor drums 20, and a full-color printing mode of four colors is set.

The drive control circuit 21 and the transfer current control circuit 32 described above are connected to a mode changeover switch 33 arranged at an appropriate position. The mode changeover switch 33 has a function of changing over the full-color printing mode, the monochrome printing mode, and the plain paper mode and the OHP paper mode in the respective modes. Mode switch 3
3 notifies these modes to the drive control circuit 21 and the transfer current control circuit 32, respectively.

When the above-mentioned mode is the full-color printing mode, the drive control circuit 21 rotationally drives the driving rotary roller 23 and also rotationally drives all the four photosensitive drums 20. Further, in the plain paper print mode, the rotary drive is performed at a normal speed, and in the OHP paper print mode, the rotary drive is ⅓ slower than that of the plain paper. Then, the transfer current control circuit 32 controls the transfer power supply so as to output the transfer bias current to all the four transfer brushes 26, and outputs the output to plain paper or O paper.
The transfer brush 26 is changed according to the print mode of HP paper and is changed for each transfer brush 26. This will be described later in detail.

Next, the monochrome print mode for printing only black will be described below. FIG. 2 shows the state of the image forming / transferring section in the monochrome print mode. In the figure, the drive control circuit 21, the drive systems 21-1 to 21-3, the transfer current control circuit 32, the control signal lines 32-1 to 32-4, and the mode changeover switch 33 described above are omitted. doing.

As shown in the figure, in the monochrome printing mode, the rotating arm 28 rotates downward. As a result, the movable support roller 31 moves downward and separates from the paper transport belt 22. The paper transport belt 22 is a drive rotation roller 2
3 and the fixed support roller 29 are supported as before, and the contact state with the photosensitive drum 20d is maintained. On the other hand, between the fixed support roller 29 and the driven rotation roller 24, the movable support roller 31 is supported and released, so that the sheet conveying belt 2
2 is inclined obliquely downwardly on the upstream side together with the transfer brushes 26a, 26b and 26c, and is separated from the three photoconductor drums 20a, 20b and 20c for forming an image of color toner. By the rotation of the rotation arm 28, a monochrome printing mode in which only a black toner image is formed by the transfer portion including only the most downstream photosensitive drum 20d and the transfer brush 26d is set.

In the monochrome print mode, the drive control circuit 21 drives the drive rotation roller 23 to rotate, and drives the photosensitive drum 20d only. Further, in the plain paper print mode, the rotary drive is performed at a normal speed, and in the OHP paper print mode, the rotary drive is ⅓ slower than that of the plain paper. And
The transfer current control circuit 32 controls the transfer power supply so that the transfer current is output only to the transfer brush 26d, and the output is set to a low voltage in the plain paper mode and a high voltage in the OH paper mode. Change to.

FIG. 3 is a side sectional view showing the overall structure of the image forming apparatus. As shown in the figure, the image forming apparatus 40 includes an opening / closing tray 41 on the front surface (right side of the drawing) of the apparatus body.
And a paper cassette 42 is detachably provided at the bottom. Further, a paper discharge tray 44 is formed on the upper surface of the upper lid 43, and image-formed paper discharged from the upper paper discharge port 45 is stacked on the paper discharge tray 44. Although not visible in the figure, a power switch, a liquid crystal display device, a plurality of input keys and the like are arranged on the front side of the upper lid 43.

Inside the main body of the apparatus, approximately at the center, the above-described paper transport belt 22, four photosensitive drums 20 (20a,
20b, 20c, 20d), and an image forming / transfer portion formed by a transfer brush 26 (26a, 26b, 26c, 26d) that faces each photoconductor drum 20 and is in sliding contact with the back surface of the paper transport belt 22. ing. It should be noted that in the figure, in addition to the above-described paper transport belt 22, the photoconductor drum 20, the transfer brush 26, the drive rotation roller 2 shown in FIGS.
3, the driven rotation roller 24, the suction roller 25, the tension roller 27, and the movable support roller 31, the rotation arm 28, the drive control circuit 21, and the drive systems 21-1 to 21-.
3, transfer current control circuit 32, control signal lines 32-1 to 32
-4, the mode selector switch 33, etc. are omitted in the drawing.

A standby roll pair 46 and a sheet detection sensor 47 are disposed on the upstream side (right side in the figure) of the sheet transport belt 22 in the sheet transport direction, and the upstream side thereof branches laterally (front of the apparatus) and downward. Then, in the lateral direction, the paper feed roller 48 and the separating member 4 are provided.
9 and the opening / closing tray 41 described above are arranged. Further, a transport path 51 formed of two guide plates is provided below.
Is arranged, and the above-mentioned paper cassette 42 accommodates a large number of papers P and is positioned upstream (downward) thereof. A paper feed roller 52 is arranged above the paper feed end of the paper cassette 42.

Further, a separation claw 53, a fixing device 54, a paper discharge roller 55, and a switching lever 56 are provided downstream of the paper transport belt 22 in the paper transport direction (to the left in the drawing). Fixing device 5
Reference numeral 4 is composed of a pressure contact roller, a heat generating roller, a peripheral surface cleaner, an oil applying roller, a thermistor, etc., which are assembled in a heat insulating casing, and heat-fixes the toner image transferred onto the paper on the paper. The switching lever 56 guides the sheet to the upper discharge path 57 when it is in the lower position as shown in the figure, and when it is rotated upward, the rear sheet discharge port 58 that opens the sheet on the rear surface of the apparatus. Guide you to. The downstream side (upper side) of the above-described discharge path 57 communicates with the upper discharge port 45 via the discharge roll pair 59.

A cleaner bottle 61 is removably disposed between the paper transport belt 22 and the paper cassette 52. A blade scraper 62 is attached to the upper portion of the cleaner bottle 61, and the tip of the blade scraper 62 is in contact with the surface of the lower circulation portion of the paper transport belt 22. The blade scraper 62 scrapes off the toner remaining on the surface of the paper carrying belt 22 to clean the paper carrying belt 22, and stores the scraped unnecessary toner in the cleaner bottle 61.

The write head 63 disposed on the back surface of the upper lid 43 is located directly above each of the photosensitive drums 20.
(63a, 63b, 63c, 63d) are inserted and arranged by closing the upper lid 43. The upper lid 43 opens and closes around a support shaft 64 at the rear of the device body 40. Each of the above photoconductor drums 20 (20a, 20b, 20c, 20d)
Are image forming units 65 (65a, 65b, 65
c, 65d).

FIG. 4A is an external perspective view of the image forming unit 65, and FIG. 4B is a side sectional view of the internal structure of the image forming unit 65, the writing head 63, the sheet conveying belt 22, the transfer brush 26 described above. And so on. The transfer brush 26 includes
Transfer power source 26- that outputs a positive transfer bias current
1 and a resistance element 26-2 in parallel therewith are connected.
The transfer bias current flowing through the transfer brush 26 varies depending on the feed speed of the paper transport belt 22 and the type of paper, but it has been experimentally found that several μA to several tens of μA is usually sufficient.

The image forming unit 65 (the image forming units 65a, 65b, 65c, 65d in FIG. 3) is different only in the color of the toner contained therein.
It has the same structure as shown in (b). The image forming units 65 are attached and detached by opening the upper lid 43 of the apparatus body.

The image forming unit 65 comprises a cleaner 66, an initialization charging device 67, and a developing device 68 with the photosensitive drum 20 as the center, as shown in FIG. The developing device 68 forms a container, a developing roller 71 is rotatably held in a lower opening of the container, and a toner 72 is stored inside. The developing device 68 of the image forming unit 65d located at the transfer portion closest to the drive rotation roller 23 shown in FIG. 3 stores Bk (black: black) toner dedicated to characters and the like. Then, another image forming unit 65
The toners a, 65b, and 65c respectively contain three subtractive primary colors, M (magenta: red dye), C (cyan: greenish blue), and Y (yellow: yellow).

A toner stirring member 73 is disposed below the inside of the developing device 68, and this toner stirring member 73 rotates as shown by the chain double-dashed line in the figure to stir the toner 72 while lowering the supply roller. The toner 72 is sent to 74. The supply roller 74 is made of a sponge member,
The toner 72 is pressed against the developing roller 71, and the toner 72 sent from the stirring member 73 is rubbed and supplied to the peripheral surface of the developing roller 71. A blade-shaped doctor blade 75 is in contact with the circumferential surface of the developing roller 71 in the rotation direction. The doctor blade 75 gives a frictional charge to the toner 72 to assist the adhesion to the developing roller 71 and regulates the adhered toner layer to a constant thickness. These image forming units 6
Each of the above-mentioned devices incorporated in 5 includes gears or electrodes (not shown), and the gears are engaged with each other inside the unit. When the image forming unit 65 is attached to the apparatus main body as shown in FIG. 3, the support shaft 20-1 of the photosensitive drum 20 and the support shaft 71 of the developing roller 71 shown in FIG.
-1, and each of the above-mentioned electrodes and the like are driven by being engaged with the drive mechanism and the power supply electrode of the apparatus main body.

Between the initialization charger 67 and the developing roller 71, the writing head 63 disposed on the upper lid 43 shown in FIG. 3 is provided with the closing of the upper lid 43 as shown in FIG. Draw an arcuate locus as indicated by the arrow D, and its tip will fit into the slot 65-1 on the upper surface of the lower casing of the image forming unit 65 shown in FIG. It is positioned at the forming position. When the upper lid 43 is opened and the writing head 63 is pulled up, the image forming units 65 can be individually taken out of the machine in the diagonally upper right direction. In this way, when the image forming unit 65 is taken out, the protective lid 69 rotates counterclockwise to cover and protect the exposed lower surface of the photosensitive drum 20.

Next, the operation of the image forming apparatus 40 having the above structure will be described with reference to FIGS. 1 to 4 again.
First, the processing operation in the full-color printing mode will be described. When the apparatus main body 40 is powered on (see FIG. 3) and the number of sheets to be used, the print mode, and other designations are input by a key or as a signal from a connected host device, a cam is driven by a drive mechanism (not shown). When driven, the rotating arm 28 (see FIG. 1) is rotated upward, whereby the movable support roller 31 is moved upward, and the paper transport belt 22 is moved to all four photosensitive drums 20 (20a, 20a,
20b, 20c, 20d).

Subsequently, the paper feed roller 52 (see FIG. 1) conveys the paper P, which is placed and accommodated in the paper cassette 42, to the conveyance path 51.
And feeds to the pair of standby rolls 46 via. Alternatively, the paper feed roller 58 feeds the paper placed on the open / close tray 51 to the standby roll pair 46. The sheet detection sensor 47 detects the fed sheet P. The pair of standby rolls 46 stops rotating, and the leading edge of the sheet P is brought into contact with the nip portion to stand by.

The drive rotation roller 23 starts rotating in the counterclockwise direction, and the driven rotation roller 24 is driven to start rotating in the counterclockwise direction as well. As a result, the entire sheet conveying belt 22 circulates in the direction in which the upper circulation portion contacts the four photoconductor drums 20 and moves from right to left as indicated by arrow A in the figure.

At the same time, the image forming units 65a, 65
5b, 65c, and 65d (see FIGS. 3 and 4) are sequentially driven at the print timing, and the photosensitive drums 20a, 20b, 20c, and 20d are sequentially driven to rotate in the clockwise direction in accordance with the driving. . Then, the write heads 63 corresponding to the respective image forming units 65 are sequentially driven. By this driving, the initialization charging brush 67 (see FIG. 4B) applies uniform electric charge to the peripheral surface of the photoconductor drum 20, and the writing head 63 causes the write head 63 to move to the photoconductor drum 2.
The photosensitive drum 2 is exposed to the 0th circumferential surface according to an image signal.
An electrostatic latent image is formed on the zero circumference surface. The developing roller 71 transfers the toner 72 to the low potential portion of the electrostatic latent image to form a toner image (reverse development) on the peripheral surface of the photosensitive drum 20.

At the timing when the leading edge of the toner image on the peripheral surface of the uppermost photosensitive drum 20a is rotatably conveyed to the point (transfer section) facing the sheet conveying belt 22, the printing of the sheet P is started at the point. The pair of standby rolls 46 starts to rotate and feeds the paper P to the paper carry-in unit of the image forming unit so that the positions match.

The driven rotary roller 24 and the suction roller 25 are
The fed paper P is nipped and carried together with the paper carrying belt 22. The suction roller 25 applies a suction bias voltage supplied from a power source (not shown) to the paper P. As a result, the paper P is attracted to the paper carrying belt 22 and carried, and then carried to the first transfer portion formed by the photoconductor drum 20a and the transfer brush 26a.

The transfer brush 26a (see FIG. 1) applies the transfer current output from the transfer bias power source 26-1 (see FIG. 4B) to the paper P via the paper transport belt 22. This transfer current causes M on the photoconductor drum 20a.
The (magenta) toner image is transferred to the paper P. Then, the sheet conveying belt 22 is charged with a positive polarity by the application of the transfer current from the transfer brush 26a, and the sheet P is charged with a negative polarity by the pressure contact between the transferred toner image and the photosensitive drum 20a. As a result, the adsorptivity of the paper P to the paper transport belt 22 is continuously maintained, and the paper P is
The sheets are sequentially conveyed in the downstream direction of the sheet conveying belt 22.

Then, the C (cyan) toner image is transferred at the second transfer portion from the upstream side formed by the photosensitive drum 20b and the transfer brush 26b, and further formed by the photosensitive drum 20c and the transfer brush 26c. The Y (yellow) toner image is transferred at the third transfer portion from the upstream side. Then, the photosensitive drum 20d and the transfer brush 26
The Bk (black) toner image is transferred at the most downstream transfer portion formed by d, and the toner images of four colors are sequentially overlaid.

The sheet P to which the four color toner images have been transferred in this manner is conveyed to the end of the conveying path (the downstream end of the sheet conveying belt 22) where the separation claw 53 (see FIG. 3) is arranged. To be done. The sheet P is carried into the fixing device 54 while being separated from the sheet conveyance belt 22 by the separation claw 53 which is arranged with its front end lightly abutting the surface of the sheet conveyance belt 22. The fixing device 54 thermally fixes the toner image on the sheet P. After the image is fixed, the paper P is ejected out of the apparatus by the paper ejection roller 55 from the rear paper ejection port 58 with the toner image upward or from the upper paper ejection port 55 with the toner image downward.

Next, the processing operation in the monochrome print mode will be described. For example, when black printing is designated after the full-color printing, as shown in FIG. 2, the turning arm 28 turns downward, which causes the movable support roller 3 to move.
1 moves downward and separates from the paper transport belt 22.
As a result, the paper transport belt 22 is provided between the drive rotation roller 23 and the fixed support roller 29 on the one hand.
The contact state with d is maintained, and on the other hand, the fixed support roller 29
Between the driven rotating roller 24 and the driven rotating roller 24
Separate from contact with (20a, 20b, 20c). As a result, only the black toner transfer portion formed by the most downstream photosensitive drum 20d and the transfer brush 26d is operably formed, and the monochrome print mode is set.

Next, the paper P is fed by the paper feed roller 52 or the paper feed roller 48, the paper is detected by the paper detection sensor 47, the paper P is waited by the standby roll pair 46, and the drive rotation roller 23 and the driven rotation roller 24 are used. The circulating movement of the paper transport belt 22 is the same as in the case of the full-color printing described above.

Then, together with this, the image forming unit 6
5d is driven, and the other image forming units 65a and 65b
And 65c dormant. Rotational drive of the photoconductor drum 20d corresponding to the image forming unit 65d, charge application to the photoconductor drum 20d by the initialization charging brush 26d, formation of an electrostatic latent image on the peripheral surface of the photoconductor drum 20d by the writing head 63d, and The toner image formation of the electrostatic latent image by the developing roller 71 is substantially the same as the case of the full-color printing described above.

At the timing when the front end of the black toner image on the peripheral surface of the photosensitive drum 20d is rotatably conveyed to the point of opposition to the sheet conveyance belt 22, the print start position of the sheet P coincides with the point of opposition. The pair of standby rolls 46 starts rotating to feed the paper P to the paper carry-in section formed by the suction roller 25 and the driven rotary roller 24.

Subsequent application of an attraction bias voltage by the attraction roller 25, attraction / transportation by the sheet transport belt 22, application of a transfer current by the transfer brush 26d and transfer of the black toner image onto the paper surface, and the subsequent transport path. Separation of the sheet by the separation claw 53 at the end, thermal fixing of the toner image by the fixing device 54, rear sheet discharge port 58 by the sheet discharge roller 55.
Alternatively, the ejection of the paper P from the upper paper ejection port 55 is substantially the same as in the case of the full-color printing described above.

Next, the relationship between the sheet conveying speed and the transfer current, which is different for each sheet mode, will be described. still,
Since the paper conveyance speed and the transfer current in the monochrome print mode also conform to the paper conveyance speed and the transfer current in the full color print mode, the case of the full color print mode will be described below.

5 (a) and 5 (b) are transfer characteristic diagrams showing the relationship between the sheet conveying speed and the optimum transfer current in the full-color printing mode, and are shown by straight lines rising to the right. Figures (a), (b)
Shows the process speed (processing speed, that is, the paper transport speed) in mm / s (millimeter / second) on the horizontal axis, and the optimum transfer current value corresponding to the paper transport speed on the vertical axis is μA (micrometer). Ampere). Further, (a) of the figure shows the case of plain paper (plain paper mode), and (b) of the figure shows the case of OHP paper (OHP paper mode).

Further, FIG. 6 shows a transmission characteristic diagram showing the relationship between the sheet conveying speed and the light transmission of the fixed image in the full-color printing mode, with a downward-sloping curve. Also in this case, the horizontal axis indicates the process speed (paper transport speed) in mm / s.
It shows with. The vertical axis shows the light transmittance corresponding to the sheet conveying speed.

Generally, in the case of plain paper, the visibility of the fixed image depends on the reflected light, so that the light transmittance is not required. Therefore, in the fixing unit, heat energy sufficient to fix the transferred color toners to the paper surface may be applied to the paper. From this, the paper conveyance speed is 53 mm / s with respect to the normal heat generation amount which is appropriate for the fixing unit.
It has been confirmed in the present embodiment that the toners overlaid with the four colors are well fixed even if the speed is increased up to. Of course, if the paper transport speed is slower than this, the fixing will be better. However, considering the work efficiency of image formation, it can be said that there is no advantage in the case of plain paper to increase the fixing property by slowing down the conveying speed. Therefore, the above-mentioned sheet conveyance speed of 53 mm / s can be considered as the reference speed of plain paper.

On the other hand, in the case of OHP paper, the visibility of the fixed image depends on the transmitted light, so that the light transmittance is required. Therefore, each color toner transferred at the fixing unit is
It is necessary to melt and fix the toner image so that the solidified toner image does not have turbidity and the surface of the toner image is smooth. In order to melt well, it is necessary to give sufficient heat energy. Then, the thermal energy is inversely proportional to the paper transport speed. FIG. 6 shows the relationship between the sheet conveying speed and the image light transmittance. As a result of this experiment, it was found that, with respect to the normal amount of heat generated by the fixing section, the transparency cannot be obtained at the above-described reference transport speed of 53 mm / s (range indicated by X in the figure). ). In addition, the speed of 1/2 (26.5 mm /
It was found that when it was conveyed after being delayed to s), some permeability was obtained, but it was insufficient (range indicated by Δ in the figure).
Then, the transport speed is further reduced to 1 of the standard speed of plain paper.
It was found that sufficient transparency can be obtained by transporting at ⅓, which is 17.7 mm / s (range indicated by ◯ in the figure). In practice, the transparency is obtained from about 20 mm / s. Below, the slower the transparency, the better the transparency.
However, considering the variation in the equipment and paper quality, a margin of a certain amount, 17.7 mm / s (speed of 1/3 of the standard speed of plain paper), which is a little slower than the above 20 mm / s, is applied to OHP paper. It can be said that it is preferable to use the standard transport speed.

The transfer characteristic diagrams of FIGS. 5 (a) and 5 (b) described above are obtained by measuring the quality of the transfer of the toner image by changing the paper transfer speed variously. Speed 1
7.7 mm / s, 53 mm / s, and an intermediate transfer speed of 26.5 mm / s for reference, and the optimum transfer current value corresponding to the transfer speed are shown. Since the required optimum transfer current is proportional to the sheet conveyance speed, the transfer characteristic is linear.

It can be seen from FIG. 9A that, in the case of plain paper, the optimum value of the transfer current at the above-mentioned proper reference transport speed of 53 mm / s is about 10 μA. In addition, since the chargeability of plain paper is extremely low, the same transfer current can be applied to each of the four transfer parts to transfer the toner image. Therefore, the transfer characteristic of each transfer part is one straight line. It is represented by.

On the other hand, in the case of OHP paper, since the charging property is high, it is necessary to apply a higher transfer current to each transfer section toward the downstream side in order to obtain an appropriate transfer state. In the same figure (b), from the bottom to the top, the transfer characteristics of the most upstream (1st, magenta) transfer section, the transfer characteristics of the next (2nd, cyan) transfer section, and the next (3rd, yellow) The transfer characteristics of the transfer portion and the transfer characteristics of the most downstream (4th, black) transfer portion are shown.

In the present embodiment, as described above, the reference transport speed of OHP paper is set to 17.7 mm / s, which is 1/3 the speed of plain paper. Then, as shown in the characteristic diagram of FIG. 5 (b), the optimum transfer current corresponding to the transport speed of 17.7 mm / s in the final stage (downstream) transfer portion of the black toner is set to the above-mentioned plain paper. Optimal transfer current value 10 μA corresponding to the standard transfer speed of 53 mm / s
And the transfer current on the upstream side is set to be gradually decreased. In other words, the transfer current gradually increases from upstream to downstream, and the O
It can handle HP paper, and the maximum transfer current is 10 μA regardless of the difference between plain paper and OHP paper.
I am trying to be.

In the operation of the above-described image forming apparatus 40, the sheet conveying speed by the conveying belt 22 and the transfer brush 2
The application of the transfer current by 6 is controlled as described above.
Although the tandem type image forming apparatus has been described in the above embodiment, the relationship between the sheet conveying speed relating to the fixing property and the transfer current relating to the sheet conveying speed is limited to the tandem type image forming apparatus. However, the present invention can also be applied to a single drum type image forming apparatus.

For example, FIG. 7 schematically shows a main part of a single-color drum type full-color image forming apparatus. The image forming apparatus shown in FIG. 4 includes four developing units 82 a, 82 b, 82 c and 82 along the peripheral surface of a single photosensitive drum 81.
A sheet winding semi-conductive drum 83 is disposed in which d is disposed and which faces the photoconductor drum 81 and forms a transfer portion. Inside the cylinder of the paper winding semi-conductive drum 83, a charging brush 84 for applying a transfer current to the transfer portion is provided.
Are arranged in sliding contact with the inner surface. Incidentally, in the vicinity of the peripheral surface of the photoconductor drum 81, an initialization charger, a writing head, a cleaner and the like (not shown) are arranged.

The paper winding semi-conductive drum 83 is an OHP paper P which is carried in from the right side as shown by an arrow E in the figure.
1 is wrapped around in a counterclockwise direction as indicated by arrow F in the figure. The paper winding semi-conductive drum 83 is OH
For P paper, it rotates at 1/3 the speed of plain paper. The photoconductor drum 81 rotates at a peripheral surface speed that is the same as the peripheral surface speed of the paper winding semi-conductive drum 83 in the clockwise direction as shown by an arrow G in the drawing, and first, the M (magenta) of the developing device 82a. A toner image is formed, and the transfer brush 84 transfers the toner image onto the sheet P1. Next, the paper winding semi-conductive drum 83 makes one revolution again, and in response thereto, the photosensitive drum 81 forms a C (cyan) toner image of the developing device 82b, and the transfer brush 84 transfers it to the OHP paper P.
Transfer to 1 and stack. At this time, the transfer brush 84 is
A stronger transfer current is passed than when M (magenta).

Further again, the paper winding semiconductive drum 8 is wound.
3, the photosensitive drum 81 forms a Y (yellow) toner image of the developing device 82c in response to this, and the transfer brush 84 transfers and superimposes it on the OHP sheet P1. At this time, the transfer brush 84 supplies a transfer current stronger than that in the case of C (cyan). Finally, the paper winding semi-conductive drum 83 makes one revolution again, and in response thereto, the photosensitive drum 81 forms a Bk (black) toner image of the developing device 82d, which is transferred onto the OHP paper P1 by the transfer brush 84. Transfer and stack. At this time, the transfer brush 84 sends a transfer current stronger than that in the case of Y (yellow). The value of the transfer current that flows at the end is approximately the same as the value of the transfer current when forming an image as described above while rotating at high speed using plain paper. After the transfer (overcoating) of the four color toner images is completed, the winding of the OHP sheet P1 is released, and the OHP sheet P1 is arranged on the left side as shown by an arrow H in the figure. The transferred toner image is conveyed to the fixing unit and heat-fixed.

[0075]

As described above, according to the present invention,
In the case of OHP paper, the carrying speed is controlled to 1/3 of the carrying speed of plain paper, so that the fixing heat penetrates the toner well, and a smooth toner image on the surface without turbidity inside can be fixed.
Therefore, a high-quality full-color image with high light transmittance can be formed.

Further, in the case of OHP paper, the transfer currents of the four transfer sections are sequentially increased from the upstream side to the downstream side, and the transfer current of the final step is controlled to be the same value as the transfer current in the case of plain paper. Therefore, even in the case of OHP paper, the transfer current more than that in the case of plain paper is unnecessary, and as a result,
It is possible to use a small contact type transfer device that operates with a small transfer current. Therefore, it is possible to suppress the generation of unhealthy ozone, reduce power consumption, and contribute to downsizing of the entire apparatus.

Further, even in the case of OHP paper, since four colors of M (magenta), C (cyan), Y (yellow) and Bk (black) can be printed, black toner is applied to the full-color black image portion. Can be used and therefore
It is possible to obtain an image with clear black and good quality, and it is not necessary to superimpose three color toners on the black portion to produce black, so that it is possible to suppress the consumption of expensive color toner, which is economical.

[Brief description of drawings]

FIG. 1 is a side view of a main part (image forming unit) of an image forming apparatus according to an embodiment, showing a state in which an image is formed in a full color print mode.

FIG. 2 is a diagram illustrating a state of an image forming unit in a monochrome print mode.

FIG. 3 is a side sectional view showing the overall configuration of the image forming apparatus.

FIG. 4A is an external perspective view of the image forming unit, and FIG. 4B is a side sectional view of the internal structure of the image forming unit together with a writing head, a sheet conveying belt, a transfer brush, and the like.

5A and 5B are transfer characteristic diagrams showing a relationship between a sheet conveying speed and an optimum transfer current in a full color print mode, FIG. 5A showing a case of plain paper (plain paper mode), and FIG. 5B showing an OHP paper (OHP). FIG. 6 is a diagram showing a case of a paper mode).

FIG. 6 is a characteristic diagram showing a relationship between a sheet conveying speed of a color image fixed on an OHP sheet and light transmittance.

FIG. 7 is a diagram schematically showing a main part of a single-color drum full-color image forming apparatus as another embodiment.

FIG. 8 is a side sectional view schematically showing an example of a conventional tandem type color image forming apparatus.

[Explanation of symbols]

1 Color Image Forming Device 2 Paper Cassette 3 Paper 4 Feeding Roller 5 Standby Roll Pair 6 Conveyor Belt 7 Photosensitive Drum 8 Initializing Charger 9 Developer 9-1 Developing Roller 11 Transfer Charger 12 Cleaner 13 Laser Head 13-1 Rotating mirror 13-2 Focusing lens 13-3 Reflecting mirror 13-4 Irradiation port 14 Fixing section 15 Paper ejection roller 16 Paper ejection port 20 (20a, 20b, 20c, 20d) Photoreceptor drum 20-1 Support shaft 21 Drive control circuit 21-1, 21-2, 21-3 Drive system 22 Paper transport belt 23 Drive rotation roller 24 Driven rotation roller 25 Adsorption roller 26 (26a, 26b, 26c, 26d) Transfer brush 27 Tension roller 28 Rotation arm 29 Fixed support Roller 31 Movable support roller 32 Transfer current control circuit 32-1, 32-2, 32-3, 32- Control signal line 33 Mode selector switch 40 Image forming device 41 Open / close tray 42 Paper cassette 43 Upper lid 44 Paper ejection tray 45 Upper paper ejection port 46 Standby roll pair 47 Paper detection sensor 48 Paper feed roller 49 Separation member 51 Conveyance path 52 Paper feed roller 53 Separation Claw 54 Fixing Device 55 Ejection Roller 56 Switch Lever 57 Ejection Path 58 Rear Ejection Port 59 Ejection Roll Pair 61 Cleaner Bottle 62 Blade Scraper 63 (63a, 63b, 63c, 63d) Writing Head 64 Spindle 65 (65a) , 65b, 65c, 65d) Image forming unit 65-1 Groove hole 66 Cleaner 67 Initializing charger 68 Developer 69 Protective lid 71 Developing roller 71-1 Support shaft 72 Toner 73 Toner stirring member 74 Supply roller 75 Doctor blade 81 Photosensitive Body drum 82a, 8 b, 82c, 82d developing device 83 paper wrapped semiconductive drum 84 charged brush

Claims (8)

[Claims] 1. A process of forming a toner image of a predetermined color on an image carrier is carried out for each color, and the toner images of a plurality of colors are provided inside a transfer material conveying member that circulates and a transfer current is supplied. An image forming apparatus for forming a multicolor image by sequentially superposing and transferring the image on a transfer material carried and transferred to the outer surface of the transfer material carrying member by the transferring means, the surface of the image carrier and the outer surface of the transfer material carrying member. Drive means for moving the and in the contact position at a predetermined speed of substantially the same speed in the same direction, and the drive means for setting the predetermined speed to a first speed and a second speed slower than the first speed. Drive control means for controlling to drive, mode setting means for setting the drive speed by the drive control means to the first and second speeds according to the type of transfer material, and the second for the mode setting means. According to the speed setting An image forming apparatus comprising: a transfer current control means for controlling the transfer current of the transfer means in the following transfer current setting of the first speed, the. 2. A plurality of image carriers arranged side by side, image carrier driving means for driving the surface of at least one of the plurality of image carriers to circulate at a predetermined speed, and A plurality of toner image forming means for individually forming toner images of a predetermined color on the surfaces of the plurality of image carriers, and a transfer material adsorbed on the outer surface to circulate and move so as to carry at least one of the plurality of image carriers. A transfer material transport belt that transports the transfer material to contact the body surface, a belt driving unit that drives the outer surface of the transfer material transport belt to move at substantially the same speed as the predetermined speed, and the transfer material transport belt. A transfer unit that is provided inside the printer so as to correspond to the plurality of image carriers to form a transfer unit and is supplied with a transfer current for transferring the toner image to a transfer material that is in contact with the image carrier. And the predetermined speed is the first speed Drive speed control means for controlling the image carrier drive means and the belt drive means to drive the image carrier drive means and the belt drive means at a second speed which is slower than the drive speed, and a drive speed by the drive control means according to the type of the transfer material. And a mode setting means for setting the first speed and the second speed to each other, wherein the transfer material is conveyed so that the plurality of image carriers are driven and the transfer material contacts all the surfaces of the plurality of image carriers. An image forming apparatus capable of forming a multicolor image on a transfer material while being conveyed by a belt, wherein a transfer current of the transfer means is set to the first speed according to a setting of the second speed by the mode setting means. An image forming apparatus comprising: a transfer current control unit that controls the transfer current to be equal to or lower than a transfer current when the speed is set. 3. The transfer current control means sets the transfer current of the transfer means to the same current value at the time of transfer for each color when the mode setting means sets the first speed, and the mode setting means sets the transfer current to the same value. 3. When the second speed is set, the transfer current of the transfer means is controlled so as to increase with an increase in the number of overlapping transfers.
The image forming apparatus as described in the above. 4. The transfer current control means sets the transfer current of the last transfer means of the overlap transfer when the second speed is set by the mode setting means to the transfer current when the first speed is set. The image forming apparatus according to claim 3, wherein the value is controlled to be substantially the same as the value. 5. The mode setting means sets the drive speed by the drive control means to the first speed when the type of transfer material is a normal sheet, and sets the drive speed by the drive control means when the type is a transparent resin sheet. The image forming apparatus according to claim 1, wherein the image forming apparatus is set and controlled to the second speed. 6. The image according to claim 1, wherein the mode setting means controls to set the second speed to approximately 1/3 of the first speed. Forming equipment. 7. The transfer means is a contact type transfer device which comes into contact with the inner surface of the transfer material conveying member so as to press the transfer material in contact with the image carrier toward the image carrier. The image forming apparatus according to claim 1, 2, 3, 4, 5, or 6. 8. The transfer material conveying member is 10 ¹⁰ to 10 ¹⁴ Ω.
8. The image forming apparatus according to claim 1, wherein the image forming apparatus is made of a semiconductive material having a resistivity of cm.