JP2000321840A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry even a rigid transfer material without generation of a deviation, without being slanted or jamming and to carry out a monochrome output. SOLUTION: In this device A, a color recording mode carrying out color recording by having the carried transfer material come into contact with all of a multiple number of photoreceptor drums 1 (1a to 1d), a first monochrome mode carrying out monochrome recording by having the carried transfer material come into contact with a specified one of the multiple number of photoreceptor drums 1 and a second monochrome mode where the monochrome recording is carried out by having the carried transfer material come into contact with all of the multiple number of photoreceptor drums 1 are provided. Then, either the first monochrome mode or the second monochrome mode is selected according to the type of the transfer material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a color image or a monochrome image using an electrophotographic system.

[0002]

2. Description of the Related Art In recent years, with the spread of electrophotographic color image forming apparatuses, there has been an increasing demand for high-speed color output in addition to the demand for recording quality of color images. To meet this demand, several proposals have been made for image forming systems. Among them, Bk (black) toner, C (cyan) toner, and M (tandem) toner are known.
The respective images of the (magenta) toner and the Y (yellow) toner are formed on a drum-shaped image carrier, and are sequentially transferred to a transfer material conveyed by an electrostatic conveyance belt by respective transfer means, and finally fixed. Color image forming system.

A conventional tandem type color image forming apparatus is
For example, it is described in JP-A-09-288396. FIG. 5 is a side sectional view showing an example of a tandem type color image forming apparatus. In this color image forming apparatus, a transfer material cassette 50 is mounted at a lower portion on the right side of the main body. The transfer material set in the transfer material cassette 50 is taken out one by one by a paper feed roller 51 and fed to the image forming unit by a pair of transport rollers 52 and 53. In the image forming section, an electrostatic transport belt 54 for transporting the transfer material is stretched flat by a plurality of rotating rollers in the transfer material transport direction (from right to left in FIG. 5). By applying a bias to the attraction roller 55 on the upper surface of the electrotransport belt 54, the transfer material is electrostatically adsorbed to the electrostatic transport belt 54. Further, four photosensitive drums 56 as image bearing members in the form of drums are linearly disposed facing the belt conveying surface to constitute an image forming section. Each of the photosensitive drums 56 sequentially surrounds the vicinity of the peripheral surface thereof, and includes a charger 57, a developing unit 58, and an electrostatic transport belt 54.
The transfer member 59 is disposed with the transfer surface of the transfer member 59 interposed therebetween. In the housing of each developing unit 58 described above, the downstream side in the transfer material transport direction (FIG.
From the left), Bk (black) toner, C (cyan) toner, M (magenta) toner, and Y (yellow) toner, respectively. Further, a predetermined gap is provided between the charger 57 and the developing unit 58, and the exposure unit 60 irradiates the peripheral surface of the photosensitive drum 56 with light through the gap.

In this color image forming apparatus, when the electrostatic transport belt 54 circulates in the counterclockwise direction in the figure to transport the transfer material, each charging device 57 causes the corresponding photosensitive drum 56 to correspond thereto.
Is uniformly charged with a predetermined charge, and the exposing means 60 exposes the charged peripheral surface of the photosensitive drum 56 according to image information to form an electrostatic latent image, and a developing device 58 Transfer the toner to the low potential portion of the electrostatic latent image to form a toner image (develop).

Formed (developed) on the peripheral surface of each photosensitive drum 56
The transferred toner images are attracted to the charges generated on the transferred transfer material by a transfer electric field formed by the transfer member 59 corresponding thereto, and are transferred to the transfer material surface. The transfer material onto which the toner image has been transferred is heat-fixed to the paper surface by a fixing unit 61 including a pressure roller and a heat roller, and is discharged outside the apparatus by a pair of discharge rollers 62.

Next, an image forming mode of the apparatus will be described. Image formation is not always determined to be performed in multicolor printing, that is, full-color printing, and the frequency of performing black-only printing, that is, monochrome printing, is quite high. In order to cope with such usage, a tandem-type color image forming apparatus capable of switching between full-color printing and monochrome printing has been proposed.

FIG. 6A shows the time of full-color printing, and FIG. 6B shows the time of monochrome printing. This configuration includes a support roller that contacts the inside of the electrostatic conveyance belt 54 and is provided upstream of the black image forming unit.
With the fulcrum 63 as the fulcrum, the transfer section of a color other than black is integrally rotated and retracted together with the electrostatic transport belt 54, so that the entrance path from the suction roller 55 and the black image forming section 64 to the fixing section 61 is reduced. It is characterized in that stable conveyance performance is obtained in both full-color printing and monochrome printing without being changed.

[0008]

SUMMARY OF THE INVENTION In the above apparatus,
When a black monochrome output is performed, the yellow, magenta, and cyan photosensitive drums are separated from the electrostatic transport belt 54 as shown in FIG. 6B. However, when performing monochrome output on a transfer material such as an envelope or cardboard that has a strong stiffness, sufficient electrostatic attraction force cannot be obtained, and the leading edge displacement due to the displacement of the leading edge of the envelope before reaching the black photosensitive drum. Problems such as jams and jams are likely to occur. Particularly, in a high-humidity environment, the resistance between the electrostatic transport belt 54 and the transfer material is reduced due to moisture absorption, and the charge between the transfer material and the electrostatic transport belt 54 is easily released, and the transfer material attracting force is reduced.

To solve the above problem, it is conceivable to increase the resistance value of the electrostatic transport belt 54 to increase the attraction force between the transfer material and the electrostatic transport belt 54. However, by increasing the resistance value, the electrostatic transport belt 54 is charged up, and the transferability is deteriorated. Also, when the image-transferred transfer material is separated from the electrostatic transport belt 54, the transfer material or the electrostatic transport A special device for forcibly removing electricity from the belt 54 is required, which causes a problem that the size of the device is increased and the price is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a transfer material which is not affected by a low-humidity and high-humidity environment and has high stiffness without increasing the size of the apparatus or increasing the price. It is an object of the present invention to provide an image forming apparatus capable of performing conveyance without causing a shift, a skew, and a jam, and performing monochrome output.

[0011]

In order to achieve the above object, a typical configuration according to the present invention comprises an image carrier for carrying a plurality of color toner images, a transfer material carrier for carrying a transfer material, and In an image forming apparatus that can transfer the toner images of the plurality of colors on the plurality of image carriers sequentially onto a transfer material carried on the transfer material carrier, A color recording mode for performing color recording by contacting all of the image carriers, and a first monochrome mode for performing monochrome recording by contacting a transfer material to be conveyed with a predetermined one of the plurality of image carriers, A second monochrome mode in which a transfer material to be conveyed is brought into contact with all of the plurality of image carriers to perform monochrome recording, and the first monochrome mode and the second monochrome mode are selected according to the type of the transfer material. Characterized by

In the above-described configuration, when performing monochrome recording by transferring a transfer material that is strongly stiff and easily floats from the transfer material carrier, the second monochrome mode is selected so that each image carrier can be used. By transporting the transfer material while pressing it, the transfer material can be transported stably without causing a head position shift, skew, jam, and the like, and monochrome recording can be performed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a multicolor image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment] FIGS. 1 and 2 show an image forming apparatus according to a first embodiment. FIG. 1 shows a four-color full-color laser beam printer as an embodiment of a color image forming apparatus. It is a longitudinal sectional explanatory view showing the configuration,
FIG. 2 is a state explanatory diagram when performing image recording.

{Overall Configuration of Image Forming Apparatus} First, the overall configuration of a color image forming apparatus will be described with reference to FIG. The color image forming apparatus A shown in FIG. 1 includes four photosensitive drums 1 (1
a, 1b, 1c, 1d). The photosensitive drum 1 is driven to rotate clockwise in FIG. 1 by a driving unit (not shown). Around the photosensitive drum 1,
A charging device 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1 in order according to the rotation direction, irradiates a laser beam based on image information to form an electrostatic latent image on the photosensitive drum 1 The scanner unit 3 (3a, 3b,
3c, 3d), a developing device 4 (4a, 4b, 4c, 4) for attaching toner to the electrostatic latent image and developing it as a toner image
d), an electrostatic transfer device 5 for transferring the toner image on the photosensitive drum 1 to a transfer material, and a cleaning device 6 (6) for removing the transferred toner remaining on the surface of the photosensitive drum 1 after the transfer.
a, 6b, 6c, 6d) and the like.

Here, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 for removing toner are integrally formed as a cartridge, and the process cartridge 7 (7
a, 7b, 7c, 7d), and is detachable from the color image forming apparatus A.

Next, the configuration of each section will be described sequentially.
The photoconductor drum 1 is formed by applying an organic photoconductor layer (OPC photoconductor) to the outer peripheral surface of an aluminum cylinder having a diameter of, for example, 30 mm. The photosensitive drum 1 is rotatably supported at both ends by a support member, and is driven to rotate clockwise in the figure by transmitting a driving force from a driving motor (not shown) to one end. Is done.

Each charging device 2 is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photosensitive drum 1, and a charging bias voltage is applied to the roller by a power supply (not shown). Thus, the surface of the photosensitive drum 1 is uniformly charged.

The scanner section 3 is disposed substantially in the vertical direction of the photosensitive drum 1, and a polygon mirror 9 (9a) in which image light corresponding to an image signal is rotated at high speed by a scanner motor (not shown) by a laser diode (not shown). ,
9b, 9c, 9d). The image light reflected by the polygon mirror is applied to the imaging lens 10 (10a, 10b, 10c, 10c).
Through d), the surface of the charged photosensitive drum 1 is selectively exposed to form an electrostatic latent image.

The developing devices 4 (4a, 4b, 4c, 4d) are arranged in order from the upstream side (right side in FIG. 1) of the transfer material in the direction of conveyance of the transfer material, from the developing devices containing the toners of yellow, cyan, magenta, and black, respectively. Be composed. At the time of developing the electrostatic latent image on the photosensitive drum 1, the toner in the container of the corresponding developing unit is fed by the feed mechanism by the application rollers 4a1, 4b1,.
4c1, 4d1, and the developing rollers 4a2, 4
A thin layer of toner is applied to the outer periphery of 4b2, 4c2 and 4d2, and a charge is applied to the toner (frictional charging). By applying a developing bias between the developing roller and the photosensitive drum 1 on which the electrostatic latent image is formed, toner is attached to the electrostatic latent image and developed as a toner image.

After the toner developed on the photosensitive drum 1 by the developing device 4 is transferred to the transfer material S, the cleaning device 6 removes so-called untransferred toner remaining on the surface of the photosensitive drum 1 without being transferred. Things.

All the photosensitive drums 1a, 1b, 1c,
An electrostatic transport belt 11 is disposed as a belt member that circulates and moves so as to face and contact 1d. The electrostatic transport belt 11 is formed of a film-like member having a volume resistivity of 10 ¹² Ω · cm or less and a thickness of about 150 μm.

Here, the volume resistivity was measured using a measuring probe conforming to JIS method K6911, using a high resistance meter R manufactured by ADVANTEST.
The value obtained by applying 100 V at 8340.

The electrostatic transport belt 11 is supported by rollers on four axes in the vertical direction, and circulates so that the transfer material is electrostatically attracted to the outer peripheral surface on the upper side in the figure and the transfer material is brought into contact with the photosensitive drum 1. Moving. The suction roller 8 is in contact with the upstream side (the right side in FIG. 1) of the electrostatic transport belt 11 in the transfer material transport direction. When the transfer material is conveyed, a bias voltage is applied to the suction roller 8 to form an electric field between the transfer roller and the grounded roller 14a, thereby causing dielectric polarization between the electrostatic conveyance belt 11 and the transfer material. Thus, an electrostatic attraction force can be generated between them. Note that the same effect can be obtained by applying a bias to the roller 14a and setting the roller 8 to face the roller 14a.

As a result, the transfer material is transported to the transfer position by the electrostatic transport belt 11, and the toner images on the photosensitive drum 1 are sequentially transferred.

A transfer roller 12 (12a, 12b, 12b, 12b, 12c) is abutted against the inside (back side) of the electrostatic transfer belt 11 and corresponds to the four photosensitive drums 1a, 1b, 1c, 1d.
12c, 12d) are juxtaposed. The transfer roller 12 is connected to a transfer bias power supply (not shown). These transfer rollers 12 face the photosensitive drum 1 and form a transfer section. A positive charge is applied to the transfer material from the transfer roller 12 via the electrostatic transport belt 11, and an electric field generated by the charge causes the transfer material in contact with the photosensitive drum 1 to charge the negative material on the photosensitive drum 1. Is transferred.

The electrostatic transport belt 11 according to the present embodiment is a belt having a circumference of about 700 mm and a thickness of 150 μm.
The roller is wound around four rollers, that is, driven rollers 14a and 14b and a tension roller 15, and rotates counterclockwise in FIG. Thus, the toner image on the photosensitive drum is transferred while the transfer material S is conveyed from the driven roller 14a side to the drive roller 13 side by the circulating movement of the electrostatic conveyance belt 11 described above.

The feeding unit 16 feeds the transfer material S to the image forming unit. A plurality of transfer materials S are stored in a feeding cassette 17. At the time of image formation, the feed roller 18 (half-moon roller) and the registration roller pair 19 are driven and rotated in accordance with the image forming operation to separate and feed the transfer materials S in the feed cassette 17 one by one. The tip is a registration roller pair
After stopping once at 19 and forming a loop, the rotation of the electrostatic transport belt 11 and the image writing position are synchronized,
The sheet is re-fed to the electrostatic transfer belt 11 by the registration roller pair 19.

The fixing unit 20 fixes a plurality of toner images transferred to the transfer material S. The fixing unit 20 is driven by a heating and rotating heating roller 21 to apply heat and pressure to the transfer material S by pressing against the heating roller 21. And a pressure roller 22.

That is, the transfer material S onto which the toner image on the photosensitive drum 1 has been transferred is conveyed by the pair of fixing rollers when passing through the fixing unit 20, and heat and pressure are applied by the pair of fixing rollers 21 and 22. You. Thereby, the toner images of a plurality of colors are fixed on the surface of the transfer material S.

The yellow, magenta, and cyan process cartridges 7a, 7b, and 7c are moved upward from a state in which the photosensitive drums 1a, 1b, and 1c are in contact with the electrostatic transport belt 11 by an elevating mechanism (not shown). It is configured to be movable to a position separated from the electric transport belt 11. Then, the elevating mechanism operates according to the selected recording mode.

{Recording Mode} Next, an image forming operation of the image forming apparatus having the above-described configuration will be described. In this embodiment, the image forming mode includes a color recording mode for performing color recording, and a monochrome mode for performing monochrome recording of only one color. The monochrome mode includes a first monochrome mode according to the type of the transfer material. Mode and the second monochrome mode.

(Color Recording Mode) In the color recording mode, all the photosensitive drums 1a, 1b, 1c and 1d are brought into contact with the electrostatic transport belt 11 as shown in FIG. The image is recorded. That is, the transfer material S is separated and fed one by one from the feeding unit 16, and the registration roller pair
When it hits 19, it stops and forms a loop.

The photosensitive drum 1 is rotated clockwise in the figure in synchronization with the rotation of the electrostatic transport belt 11, and the registration roller pair is rotated.
The transfer material S waiting at 19 is transferred to the uppermost photosensitive drum 1a.
At the timing when the leading end of the toner image on the peripheral surface is rotated to a point facing the electrostatic transport belt 11, the electrostatic transport belt 11 is moved so that the recording start position of the transfer material S coincides with the point.
Re-feed. Then, the surface of each photosensitive drum 1 is uniformly charged by the charging device 2 and the peripheral surface of the photosensitive drum is exposed by the exposing means 3 in accordance with an image signal to form an electrostatic latent image on the peripheral surface of the photosensitive drum. To form The developing roller 4a2 applies a voltage of the same polarity and substantially the same potential as the charging polarity of the photosensitive drum 1 so that the yellow toner adheres to the electrostatic latent image on the photosensitive drum 1, and applies the yellow toner to the electrostatic latent image. Attach and develop.

By applying a bias to the roller 8, an electric field is formed between the roller 8 and the grounded roller 14 a, and dielectric polarization is generated between the electrostatic transport belt 11 and the transfer material S, so that the transfer material S becomes static. The transfer material S is transported while being electrostatically attracted to the electric transport belt 11. After that, since electrostatic attraction occurs due to the electric field of the transfer section between the electrostatic transport belt 11 and the transfer material S, the transfer material S is sequentially transported along the electrostatic transport belt 11 to the next transfer section. You.

While being conveyed in this manner, the transfer material S
By applying a voltage from each of the transfer rollers 12a, 12b, 12c, and 12d, the toner image on each photosensitive drum 1 is sequentially transferred in the order of yellow, magenta, cyan, and black.

The transfer material S to which the four color toner images have been transferred is
The transfer material S is separated from the electrostatic transport belt 11 by the drive roller 13 and reaches the fixing device 20. After the toner image is thermally fixed on the transfer material S, the transfer material S is discharged to a discharge unit 25 by discharge roller pairs 23 and 24.

Next, a monochrome mode in which monochrome recording is performed (here, an example of an image forming process of one color black) will be described.

(First Monochrome Mode) If the transfer material S is a material such as plain paper or a thin sheet that is easily electrostatically attracted to the electrostatic transport belt 11, the first monochrome mode is selected for printing.

In the first monochrome mode, as shown in FIG. 2A, the elevating mechanism operates to raise the yellow, magenta, and cyan process cartridges 7a, 7b, and 7c, and the photosensitive drums 1a and 1b. , 1c is the electrostatic transport belt 11
, And the other photosensitive drums 1a, 1b, 1c, except for the photosensitive drum 1d, are at the transfer impossible position with respect to the electrostatic transport belt 11.

As described above, the electrostatic transport belt 11 maintains the state of contact with the photosensitive drum 1d between the driving roller 13 and the driven roller 14a in exactly the same state as in full color recording.

Subsequently, the transfer material S is fed by the feed roller 18,
The standby of the transfer material S by the registration roller pair 19 and the circulating movement of the electrostatic transport belt 11 by the driven roller 14a and the driving roller 13 are the same as those in the above-described color recording mode.

At the same time, the process cartridge 7d is driven, and the other process cartridges 7a, 7
b and 7c pause. The rotation drive of the photosensitive drum 1d corresponding to the process cartridge 7d, the application of charge to the photosensitive drum 1d by the charging device 2d, the formation of an electrostatic latent image on the peripheral surface of the photosensitive drum by the scanner unit 3d, and the developing device 4
The toner image formation of the electrostatic latent image by d is the same as in the above-described color recording mode.

When the leading end of the black toner image on the peripheral surface of the photosensitive drum 1d is rotated and conveyed to a point facing the electrostatic transport belt 11, the transfer material S
Registration rollers 19 so that the recording start positions of
Starts rotating and feeds the transfer material S to the transfer material carry-in port of the image forming unit.

Also in this case, the roller 8 and the driven roller 14a
Transports the transfer material S while nipping the fed transfer material S together with the electrostatic transport belt 11.

Subsequently, the transfer material S is transported by the electrostatic transport belt 11, the black toner image is transferred to the transfer material S by the transfer roller 12d, and the transfer material S is transferred from the electrostatic transport belt 11 by curvature separation. The separation and heat fixing of the toner image by the fixing unit 20 and the discharge of the transfer material S to the discharge unit 25 by the discharge roller pairs 23 and 24 are the same as those in the above-described color recording mode.

(Second Monochrome Mode) When monochrome transfer is performed, if the transfer material S cannot obtain a sufficient electrostatic attraction force from the electrostatic transport belt 11, such as an envelope or a thick sheet, the above-described case is used. When recording is performed in the first monochrome mode, there is a possibility that the leading edge of the transfer material or a jam occurs before the transfer material S reaches the photosensitive drum 1d. Therefore, when performing monochrome recording on an envelope or the like, the second monochrome mode is selected to perform recording.

In the second monochrome mode, as in the case of the color recording mode, all the photosensitive drums 1a, 1b, 1c, 1d are arranged so as to contact the electrostatic transport belt 11, as shown in FIG. Then, monochrome recording is performed in this state.
The transfer material transfer and image forming process are the same as those in the above-described color recording mode.

In the second monochrome mode, yellow, magenta and cyan photosensitive drums 1a, 1b,
1c is rotated without contacting the transfer material S to be conveyed without transferring the toner, so that they function as a conveyance roller. Accordingly, the transfer material S is stably conveyed to the black photosensitive drum 1d without being lifted from the electrostatic conveyance belt 11 or causing a head shift, and black monochrome recording is performed by the drum 1d. At this time, a voltage may be applied to the transfer rollers 12a to 12c to prevent the transfer material from shifting.

(Selection of Recording Mode) In this embodiment, which recording mode is selected at the time of recording, as shown in FIG. 3, the type of transfer material is determined by a signal from a printer driver. It is supposed to. In the case of color printing, control is performed so as to select a color printing mode regardless of the type of transfer material. Also, in the case of monochrome recording, the first monochrome mode is selected for a transfer material on which the electrostatic transport belt 11 is easily electrostatically attracted, and the second monochrome mode is selected for a transfer material that is difficult to be electrostatically attracted. Controlled. As described above, in the present embodiment, the type of the transfer material is not detected by the mechanical mechanism of the apparatus, but is determined by the signal from the printer driver.

Here, the transfer material which is difficult to be electrostatically attracted is, for example, a transfer material having a basis weight of 150 g / m ² or more, a transfer material having a fold such as an envelope, and forming an air gap. Material. When this is exemplified by the volume resistivity, for example, the volume resistivity of the transfer material is less than 10 ⁷ Ω · cm. In this case, the volume resistivity was measured with a high resistance meter R8340 manufactured by ADVANTEST using a measurement probe conforming to JIS method K6911.
This is an actually measured value obtained by applying 100V.

A transfer material which is easily electrostatically attracted is, for example,
It is a transfer material with a basis weight of less than 150 g / m ² , relatively weak stiffness, and a plain paper without folds and the like, in which an air gap is hardly formed. When this is exemplified by volume resistivity, for example, the volume resistivity of the transfer material indicates a value exceeding the order of 10 ⁷ Ω · cm. In this case, the volume resistivity is JIS method K69.
This is an actually measured value obtained by applying a voltage of 100 V with a high resistance meter R8340 manufactured by ADVANTEST using a measurement probe conforming to No. 11.

As described above, when performing monochrome recording, the recording is performed in the first monochrome mode or the second monochrome mode according to the type of the transfer material, so that regardless of the type of the transfer material such as plain paper or an envelope. It is possible to perform monochrome recording without causing a jam or the like.

Further, since the attitude of the electrostatic transport belt 11 with respect to the transfer unit for performing monochrome recording is always constant, the transfer timing in the transfer unit for recording black toner, the transfer roller and the transfer roller for both full-color recording and monochrome recording. It is not necessary to change the voltage control and the like of 12d, and in any case, the processing can be performed by the same control method. Also,
Since the transfer material carrying-in port of the image forming unit with respect to the transfer material feeding unit such as the transfer material cassette and the registration roller pair is always constant, the position of the transfer material cassette and the registration roller pair can be used for both full-color printing and monochrome printing. The position does not need to be changed up and down in accordance with the position of the transfer material carry-in port as in the related art, and the entire structure can be configured with a simple mechanism. Also. Since the attitude of the transfer material S discharged from the image forming unit is always constant, the guide guide to be conveyed to the fixing device is changed in accordance with the discharge attitude of the transfer material in both full-color printing and monochrome printing. This eliminates the need for this, and this also makes it possible to constitute a simple mechanism as a whole.

[Second Embodiment] In the above-described first embodiment, an example in which the transfer material is transported in the horizontal direction has been described. However, the component in the transport direction of the transfer material by the electrostatic transport belt includes the gravity direction component. The present invention can also be applied to an image forming apparatus in which For example, as shown in FIG. 4, in an image forming apparatus in which a path for transferring the transfer material S by the electrostatic transfer belt 11 is formed in a vertical direction, the suction force is required more than the weight of the transfer material. ,
Even in this case, when the present invention is applied, the transfer material can be stably conveyed regardless of the type of the transfer material, and good color recording or monochrome recording can be performed.

The image forming apparatus shown in FIG. 4 has the same structure as that of the first embodiment except that the transfer material is transported in the vertical direction, and the same members are denoted by the same reference numerals.

In the above-described embodiment, an example in which four photosensitive drums are provided is shown. However, the number of photosensitive drums is not limited to four, and at least a plurality of photosensitive drums including photosensitive drums used in a monochrome color mode are provided. What is necessary is just to have a body drum.

[0058]

The present invention is constructed as described above.
When performing monochrome recording by transporting a transfer material that is strongly stiff from the transfer material carrier, select the second monochrome mode, and transfer while pressing the transfer material with each image carrier. The material is transported stably without causing the head position shift, skew, jam, etc. of the material,
It is possible to perform monochrome recording.

[Brief description of the drawings]

FIG. 1 is an explanatory longitudinal sectional view showing an overall configuration of a four-color full-color laser beam printer which is one mode of a color image forming apparatus.

2A is an explanatory diagram at the time of recording in a first monochrome mode, and FIG. 2B is an explanatory diagram at the time of a second monochrome mode or a color recording mode.

FIG. 3 is an explanatory diagram of a configuration for determining a recording mode based on a signal from a printer driver.

FIG. 4 is an explanatory diagram of an apparatus in which a transfer path of a transfer material is set in a vertical direction.

FIG. 5 is an explanatory diagram of a tandem type color image forming apparatus according to a conventional example.

FIG. 6 is an explanatory diagram at the time of color printing and monochrome printing according to a conventional example.

[Explanation of symbols]

 A: Color image forming apparatus S: Transfer material 1: Photoconductor drum 2: Charging device 3: Scanner unit 4: Developing device 5: Electrostatic transfer device 6: Cleaning device 7: Process cartridge 8: Suction roller 9: Polygon mirror 10 ... imaging lens 11 ... electrostatic transport belt 12 ... transfer roller 13 ... drive roller 14a, 14b ... driven roller 15 ... tension roller 16 ... feeding section 17 ... feeding cassette 18 ... feeding roller 19 ... registration roller pair 20 … Fixing section 21… Heating roller 22… Pressure roller 23,24… Discharge roller pair 25… Discharge section

Claims (3)

[Claims] An image carrier that carries a plurality of color toner images; and a transfer material carrier that carries a transfer material, wherein the plurality of color toner images on the plurality of image carriers are transferred. In an image forming apparatus capable of sequentially transferring a transfer material superimposed on a transfer material carried on a material carrier, a color recording mode in which a transfer material to be conveyed is brought into contact with all of the plurality of image carriers to perform color recording; The material is a predetermined one of the plurality of image carriers.
And a second monochrome mode in which a transfer material to be conveyed is brought into contact with all of the plurality of image carriers to perform monochrome recording. An image forming apparatus for selecting one of the first monochrome mode and the second monochrome mode according to 2. The image forming apparatus according to claim 1, wherein the transfer material carrier conveys the transfer material by electrostatically attracting the transfer material. 3. The image forming apparatus according to claim 1, wherein the type of the transfer material is determined based on a signal from a printer driver, and the first monochrome mode and the second monochrome mode are selected.