JP2000338741A - Image forming device - Google Patents

Abstract

(57) [Summary] An image forming apparatus using an intermediate transfer member is provided.
An object of the present invention is to improve the throughput of cardboard and OHT while reducing the size of the apparatus body. An image forming apparatus includes a plain paper mode: 120 mm / sec as a secondary transfer / fixing speed and an image interval.
50 mm; cardboard mode: 60 mm / sec, 25 mm; OH
T mode: 40 mm / sec, 25 mm. Since the length of the non-image forming side between the final color image forming portion Pk and the secondary transfer portion of the intermediate transfer belt 6 is only 470 mm, LT
If the interval between R size images is 50 mm, two images Q cannot be carried on the non-image forming side. In thick paper mode,
Since the image forming process speed and the secondary transfer / fixing speed are different,
The image interval is changed from 50 mm to 25 mm so that two images can be held. In the plain paper mode, the image forming process speed and 2
Since the next transfer / fixing speed is the same, the image interval is 50 mm
There is no problem even if an image is formed by using.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile or the like, and more particularly to a color image by superposing a plurality of color toner images on an endless intermediate transfer belt. The present invention relates to an image forming apparatus for obtaining

[0002]

2. Description of the Related Art As a color image forming apparatus, for example, four image forming units are arranged along an endless transfer material conveying belt, and a toner image formed on a photosensitive drum of each image forming unit is conveyed by the conveying belt. There is known a four-drum type (in-line color type) apparatus which superimposes on a transfer material to be subjected to multiple transfer and obtains a full-color image of four colors on the transfer material.

FIG. 5 is a schematic sectional view showing a high-speed in-line color printer of a four-drum multiple transfer system.

As shown in FIG. 5, the printer includes an endless transfer material transport belt 36 which is suspended in a direction indicated by an arrow in FIG. 5 and is suspended between a driving roller 37a and a driven roller 37b. Above, four image forming units Py, Pm, Pc, and Pk are arranged side by side.

Each of the image forming units Py to Pk has basically the same configuration, and includes a photosensitive drum 31 as an image carrier,
A charging roller 32 for uniformly contacting and charging the surface thereof; a laser exposure device 33 for exposing the surface to form an electrostatic latent image; and a developing device 3 for developing the latent image with a developer and visualizing the latent image as a toner image.
4, and a transfer electrode 4 for transferring the toner image to the transfer material P
0, and a cleaner 35 for cleaning the transfer residual toner remaining on the photosensitive drum surface after the transfer of the toner image.
Etc. are provided. The developing units 34 of the image forming units Py, Pm, Pc, and Pk contain yellow (Y), magenta (M), cyan (C), and black (K) developers, respectively.

[0006] The transfer material P is transported from the right side in the drawing to the conveyor belt 3.
6 and the image forming unit Py by the transport belt 36.
To Pk are sequentially conveyed to the transfer units facing the photosensitive drums 31. In the transfer section, a flexible transfer electrode 40 is disposed on the back side of the transport belt 36, and this electrode 40 is in contact with a downstream position in the transfer nip.

In the first image forming section Py, the photosensitive drum 31
A yellow toner image is formed thereon, and the yellow toner image is transferred onto the transfer material P by the action of the transfer electrode 40. Similarly, in the image forming units Pm, Pc, and Pk, a magenta toner image, a cyan toner image, and a black toner image are formed and transferred onto the transfer material P in a superimposed manner.
A color image in which four color toner images of cyan, yellow, and black are superimposed is formed. Thereafter, the transfer material P is separated from the transport belt 36 and sent to a fixing device (not shown), where the four color toners are heated and pressed to melt and fix the transfer material P to obtain a color print image.

An image forming apparatus such as an in-line color type copying machine or printer temporarily transfers toner images of respective colors sequentially formed on one photosensitive drum to an intermediate transfer drum (primary transfer), and thereafter, There is an advantage that high-speed printing is possible as compared with an intermediate transfer type in which a toner image of four colors is collectively transferred to a transfer material (secondary transfer) to obtain a color image on the transfer material.

However, the speed of the image forming process such as charging, exposure, development and transfer can be relatively easily increased. However, there is a problem that the supply of heat in the fixing process of the toner image cannot keep up. The process speed of the forming apparatus is often determined by the fixing ability. That is, in an in-line type printer or a copying machine, an image having a large amount of applied toner enters the fixing process at the process speed of a normal monochrome printer (B / W printer), so that it is difficult to secure the fixing property.

In particular, when printing on OHT or thick paper, if the fixing speed is the same as that during normal printing, light transmittance is insufficient or fixing is poor. Recently, OHT and cardboard (basis weight 105g
/ Cm ² ), high-definition color printing on rough paper and glossy paper is increasing as a market requirement, and toner fixing is an important issue.

Therefore, in the in-line type apparatus, the fixing speed is reduced, and the amount of heat applied per unit area is increased several times as much as that of plain paper to secure the fixing property. However, if the transfer material is allowed to stay between the fixing device after the transfer of the four colors, the transfer length of the transfer material to the fixing device becomes longer. In all steps of charging, exposure, development and transfer, the image forming process speed must be reduced.

However, it is not technically easy to change the above-described image forming process conditions because the parameters of each step are required to be at least twice or more, and the high pressure control becomes complicated. Therefore, the in-line type apparatus has a disadvantage that the compatibility (media flexibility) with the transfer material is poor.

[0013]

Therefore, in an in-line type image forming apparatus, a belt-like intermediate transfer member (intermediate transfer belt) is incorporated in order to provide good compatibility with various transfer materials, and a normal process is performed. Forming a full-color image on the intermediate transfer belt at a speed
There is an apparatus which takes measures to reduce the process speed after the next transfer and to secure the fixing property.

In this apparatus, since the process speed after the secondary transfer is reduced, before starting the secondary transfer of the image,
The image formation of the four colors must be completed on the intermediate transfer belt, and the non-image that does not contact the photosensitive drum between the image forming unit and the secondary transfer unit at the most downstream in the circumferential direction of the intermediate transfer belt It is necessary that the entire full-color image of four colors is completely carried in the formation area.

However, in order to reduce the size of the apparatus, it is necessary to shorten the intermediate transfer belt, and it is necessary to secure a non-image forming area (non-image forming side) capable of carrying the entire image on the intermediate transfer belt. It becomes difficult.

Therefore, conventionally, it is difficult to achieve both good compatibility with the transfer material and fixability, and it is not possible to improve the throughput of thick paper, OHT, etc. while reducing the size of the image forming apparatus main body. Was.

SUMMARY OF THE INVENTION An object of the present invention is to provide an intermediate transfer system which can achieve both good compatibility with a transfer material and fixability, and which can reduce the size of the apparatus body and improve the throughput of thick paper and OHT. Is to provide an in-line type image forming apparatus.

[0018]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
The toner images formed on the plurality of first image carriers arranged along the rotation direction of the intermediate transfer body are sequentially transferred onto the intermediate transfer body at a primary transfer section in each of the plurality of image carriers. In an image forming apparatus, a superimposed primary transfer is performed, and then a multicolor image formed by superimposing the toner images is collectively and secondarily transferred to a transfer material in a secondary transfer unit and then fixed in a fixing unit. The image forming apparatus has a plurality of image forming speeds and a plurality of image forming intervals.

According to the present invention, in the case where the multicolor image is continuously formed by using a transfer material of a type whose image forming speed is lower than usual as the transfer material, the intermediate of the plurality of image carriers is used. In a region between the primary transfer portion and the secondary transfer portion of the image carrier at the most downstream direction in the rotation direction of the transfer member, the interval between the multicolor images carried on the intermediate transfer member is reduced by reducing the interval. Increasing the number of multicolor images carried on the intermediate transfer member in the area.

Further, according to the present invention, the image forming apparatus has a detecting means for detecting a type of the transfer material supplied to the secondary transfer portion, and detects a plurality of types of transfer materials having different image forming speeds. When the multi-color image is formed continuously, the detecting unit detects the type of the transfer material whose image forming speed is lower than usual, and rotates the intermediate transfer member of the plurality of image carriers. In the region between the primary transfer portion and the secondary transfer portion of the image carrier at the most downstream in the moving direction, the multicolor for the slower type transfer material among the multicolor images carried on the intermediate transfer member The speed at which the multicolor image for the next transfer material is carried at a wide interval with respect to the image, and the secondary transfer and fixing of the multicolor image for the slow type transfer material are reduced from the normal image forming speed. And then the secondary of the multicolor image for the next transfer material Shooting and fixing can be performed with increased speed to the normal image forming speed.

[0021]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic sectional view showing an image forming apparatus according to Embodiment 1 of the present invention. The present image forming apparatus includes four image forming units each having a photosensitive drum 1 as a first image carrier, and transfers a toner image formed on the photosensitive drum 1 of each of the image forming units Py to Pk to a second image forming unit. The intermediate transfer belt is superimposed on the intermediate transfer belt 6 serving as an image carrier and subjected to multiple transfer, and then transferred to the transfer material P conveyed to the intermediate transfer belt 6 to obtain a full-color image of four colors on the transfer material. This is a 4-drum type (in-line color type) device.

The intermediate transfer belt 6 is suspended by a driving roller 6a, a tension roller 6b, and a secondary transfer opposing roller 6c, and is rotated in the direction of the arrow in the figure. The four image forming units Py, Pm, Pc, and Pk are arranged side by side along the upper track of the intermediate transfer belt 6.

Each of the image forming units Py to Pk has basically the same configuration, and the photosensitive drums 1 and 2 of the first image carrier are connected to each other.
A secondary charging roller 2, a laser exposure unit 3, a developing unit 4, a flexible transfer electrode 7, a cleaner 5, and the like are provided. The developing units 4 of the image forming units Py, Pm, Pc, and Pk have yellow (Y), magenta (M), cyan (C),
A black (K) developer is stored.

In the first image forming section Py, the photosensitive drum 1
In the rotation process, the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the primary charging roller 2, and then the exposure unit 3 (color separation / imaging exposure optical system for a color document image, image information The surface is exposed by a scanning exposure system using a laser scan that outputs a laser beam modulated in accordance with a time-series electric digital pixel signal, and a first color component image (yellow color image) of a color image is formed on the surface of the photosensitive drum 1. A corresponding electrostatic latent image is formed. Next, the electrostatic latent image is developed by a developing device 4 using a yellow developer, and is visualized as a yellow toner image.

The yellow toner image formed on the photosensitive drum 1 enters a primary transfer nip facing the intermediate transfer belt 6. The flexible transfer electrode 7 is disposed on the back side of the intermediate transfer belt 6 in the primary transfer nip portion, and is in contact with a downstream position in the transfer nip portion. By applying a primary transfer bias to the transfer electrode 7 from the primary transfer power source 7a, the yellow toner image on the photosensitive drum 1 is
The primary transfer is performed on the intermediate transfer belt 6. Each image forming unit P
In order to be able to independently apply a primary transfer bias to the flexible electrodes 7 of y, Pm, Pc, and Pk, primary transfer power supplies are provided independently like power supplies 7a, 7b, 7c, and 7d. I have.

In the same manner as described above, the second, third, and fourth image forming units Pm, Pc, and Pk form a magenta toner image, a cyan toner image, and a black toner image on the intermediate transfer belt 6, respectively. A color image is formed by superimposing and transferring the toner images of four colors of magenta, cyan, yellow, and black on the intermediate transfer belt 6.

Secondary transfer opposing roller 6 of intermediate transfer belt 6
At the point c, a secondary transfer roller 8 is installed on the outer surface side of the intermediate transfer belt 6 to form a secondary transfer unit. The four full-color images formed on the intermediate transfer belt 6 are collectively secondary-transferred onto the transfer material P supplied to the intermediate transfer belt 6 by the transfer roller 8, and then the transfer material P on which the secondary transfer has been completed. Is sent to a fixing unit (not shown), where the four color toners are heated and pressed to fuse and fix the toner on the transfer material P, thereby obtaining a color print image.

After the secondary transfer, the intermediate transfer belt 6 removes the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 6 from the belt cleaner 9.
, And prepares for the next image formation. After the above-described primary transfer, the photosensitive drum 1 of each image forming section is cleaned and removed by a drum cleaner 4 of the primary transfer residual toner remaining on the surface thereof, and prepares for the next image formation.

The intermediate transfer belt 6 is not preferably made of a stretchable material in order to improve registration (color superposition) in each of the image forming portions Py to Pk. Or a composite belt of resin and rubber. In this embodiment,
The resistance of the intermediate transfer belt 6 is reduced to 1 by carbon dispersion.
A resin belt made of polycarbonate (PC) adjusted to the order of 0 ¹⁴ Ω was used. Its thickness is 300 μm, its length in the width direction (longitudinal direction of the photosensitive drum 1) is 320 mm, and its circumferential length is 1000 mm.

As the flexible electrode 7, a carbon-dispersed high-density polyethylene resin having sufficient flexibility and abrasion resistance and capable of controlling low resistance was used. The resistance is 10 ⁴ Ω or less, the thickness is 500 μm, and the length in the width direction (longitudinal direction of the photosensitive drum 1) is 315 mm, so that electrical leakage with the photosensitive drum 1 is avoided.

The image forming conditions in this embodiment are briefly described as follows.

Latent image condition Dark portion potential (non-image portion potential due to primary charging) Vd: -55
0 V Bright part potential (image part potential by laser exposure) Vl: -15
0V Development condition Development method: Non-magnetic one-component jumping development Development bias: DC + AC. DC voltage Vdc = -400
V, AC voltage Amplitude Vpp = 1800 V, Frequency = 2400 Hz Process speed: 120 mm / sec Primary transfer bias: First color = + 800 V, Second color = + 1
000V, 3rd color = + 1200V, 4th color = +1400
V The throughput of plain paper printing under the above conditions is LT
24 in R (Letter) size side (216 mm) feed
ppm and the image spacing is 50 mm.

The feature of the present invention is that while the size of the main body of the image forming apparatus is reduced, when the thick paper or the OHT is selected by a command signal from the root member of the image forming apparatus, the thick paper or the OHT is selected.
It is to improve the throughput of T (as a transparent resin film) and the like. When forming a full-color image by passing OHT or thick paper, it is necessary to apply a larger amount of heat in fixing than in plain paper, and this can be achieved by making the fixing speed slower than normal image formation. General.

In the present invention, in order to realize the above without changing the process conditions for forming an image on the photosensitive drum 1 and the primary transfer conditions, a full-color image can be carried on a non-image forming area of the intermediate transfer belt 6. Thereafter, the process speed of secondary transfer and fixing is reduced, so that only the secondary transfer bias needs to be changed.

FIG. 2 shows an intermediate transfer belt 1 according to the present invention.
It is the schematic which shows the division | segmentation in a circumference.

As shown in FIG. 2, an area of the intermediate transfer belt 6 which is not in contact with the photosensitive drum in the circumferential direction between the fourth image forming unit Pk and the secondary transfer unit at the most downstream position is the intermediate transfer belt 6.
This is a non-image forming area (non-image forming side) in which the formation of four color images has already been completed and the entire full-color image is completely carried. A region from the secondary transfer portion of the intermediate transfer belt 6 to the image formation portion Pk at the most downstream through the first image formation portion Py at the most upstream comes into contact with the photosensitive drum 1 of the image formation portions Py to Pk, and the intermediate transfer is performed. The area where the four-color image is formed on the belt 6 and the belt cleaning area at the preceding stage are referred to as an image forming area (image forming side) including the cleaning area for convenience.

The following describes how an image is carried on the non-image forming side of the intermediate transfer belt. As described above, the present image forming apparatus achieves a throughput of 24 ppm at a distance between images (paper interval) of 50 mm when printing on LTR-size plain paper. When printing on A4 size plain paper,
The distance between the images is 56 mm. The length of the non-image forming side of the intermediate transfer belt shown in FIG. 2 is 470 mm. This length is longer than 432 mm in the Leger size. However, when two LTR size images are arranged, the distance between the images is 50 mm, so that 216 + 50 + 216 = 4 in total.
82 mm, so that two images cannot be carried on the non-image forming side.

A feature of the present invention is that the image interval is reduced during OHT or thick paper printing, the number of images carried on the non-image forming saddle is increased, and the throughput is increased.

In addition to the printing speed of plain paper, the present image forming apparatus uses a half speed of a thick paper and a third speed of an OHT.
And a total of three secondary transfer / fixing speeds. Also, the paper feed is driven by a dedicated motor (not shown).
It can be controlled independently of the next transfer / fixing speed.

The reason why the image interval cannot be the same as that of the thick paper / OHT in the case of plain paper will be described below. The registration roller is a means for temporarily stopping the transfer material at the spot, synchronizing the image on the intermediate transfer belt with the transfer material, and sending the transfer material to the secondary transfer unit. In the case of plain paper having a process speed of 1/1 speed, the transfer material is temporarily stopped for synchronization, and then fed to the secondary transfer unit. At this time, the paper feeding speed for feeding paper to the registration roller position and the secondary transfer speed are substantially the same. Since this is a normal sheet interval, it is necessary to adjust the distance between images to this length. However, in the case of thick paper / OHT, the time required for the transfer material to reach the registration roller is the same as in the case of 1/1 speed.
Since the secondary transfer speed is 1/2 speed or 1/3 speed,
Even if the image interval is short, synchronization can be achieved without delay for the next image. Therefore, the difference in the secondary transfer speed causes the difference in the image interval.

Table 1 shows that the secondary transfer /
The fixing speed and the distance between images at that time (distance between images) are shown. In the present invention, plain paper has a basis weight of 60 to 105 g /
m ² of paper, cardboard basis weight 106~200g / m ^2, OHT is defined as 4~5mil (1mil = 25μm).
All the transfer materials shown in Table 1 are LTR size.

[0043]

[Table 1] As shown in Table 1, in the present invention, the secondary transfer / fixing speed is 120 mm / sec in the plain paper mode, 60 mm / sec in the thick paper mode, and 40 mm / sec in the OHT mode.
The image interval at that time is 50 mm for plain paper, thick paper, OH
T is 25 mm.

The reason for setting the secondary transfer / fixing speed as described above is determined from the fixing property. 105g in plain paper mode
It is needless to say that the fixing temperature is set so as to satisfy the fixing property of a paper type of / m ² or less. 1 in cardboard mode
Exceed 05g / m ^2, in the paper of up to 200 g / m ^2,
The fixing temperature and the fixing speed are determined so that the high-temperature offset of the toner does not occur and the fixing property is satisfied. Also O
In the HT mode, similarly to the thick paper mode, the fixing temperature and the fixing speed are determined so as not to cause a high-temperature offset of the toner and to give the OHT an optimal amount of heat for obtaining high transparency.

FIG. 3A shows the image interval in the plain paper mode.
FIG. 3B shows the image interval in the thick paper mode. FIG. 3 (a)
In the plain paper mode, the interval between the two images Q is set to 50 mm as described above, and the image Q is completely carried on the non-image forming side of the intermediate transfer belt 6 and will reach the secondary transfer portion. And The rear end of the second image Q remains on the image forming side of the intermediate transfer belt 6, and the primary transfer in the image forming section Pk of the final color is performed. In the plain paper mode, since the image forming process speed and the secondary transfer / fixing speed are the same, the secondary transfer of the first image Q and the primary transfer of the second image Q are simultaneously performed. There is no problem.

In the thick paper mode shown in FIG. 3B, since the image forming process speed and the secondary transfer / fixing speed are different, before the image Q on the non-image forming side of the intermediate transfer belt 6 enters the secondary transfer portion. , The image forming portion Pk of the final color of the next second image Q
Is completed, the second image Q needs to be completely carried on the non-image forming side.

As described above, in the present image forming apparatus, since the length of the non-image forming side of the intermediate transfer belt 6 is only 470 mm, when the image interval of the LTR size is set to 50 mm, the image Q is formed on the non-image forming side. Two cannot be supported. Therefore, the image interval is changed from 50 mm to 25 mm,
The primary transfer step of the final color of the second image can be completed before the secondary transfer step.

As described above, when the primary transfer of the final color of the second image Q is completed at the image forming process speed in the plain paper mode in the thick paper mode, the intermediate transfer belt 6, the secondary transfer roller 8, The rotation speed of the roller of the fixing device (not shown) is reduced from the speed in the plain paper mode to half thereof,
The next transfer and fixing steps are performed.

In this embodiment, the sequence of three or more OHTs has not been described in detail. However, when three or more OHTs are to be continuously printed, the same sequence is performed for the first and second OHTs. For the third and subsequent sheets, 1, 2
When the printing of the second OHT is completed, the process speed for forming an image on the photosensitive drum 1 is temporarily returned to 1/1 speed to form an image, and the above sequence is repeated.

As described above, conventionally, only one image having the LTR size can be carried on the non-image forming side of the intermediate transfer belt 6. Therefore, the fixing throughput in the thick paper mode can be increased to 8 ppm, which was 4 ppm in the related art.

Similarly, in the case of OHT, according to the present embodiment, the interval between images is narrowed to 25 mm, so that the throughput can be increased from the conventional 4 ppm to 8 ppm. Further, since the throughput in the thick paper or OHT mode can be improved without increasing the size of the non-image forming side of the intermediate transfer belt 6, the size of the image forming apparatus can be reduced.

Embodiment 2 FIG. 4 is a schematic sectional view showing an image forming apparatus according to still another embodiment of the present invention.

The image forming apparatus of this embodiment has an OHT detection sensor 15 in the paper feed cassette 14 and
It is configured as an in-line type color image forming apparatus having a T detection function. Other mechanical configurations of the present embodiment are basically the same as those of the image forming apparatus of the first embodiment shown in FIG. 1, and the same reference numerals as those shown in FIG. 1 denote the same members in FIG.

The transfer material P in the cassette 14 is taken out by driving the pickup roller 12 based on a paper feed signal, and the taken out transfer material P is conveyed to the registration roller 10 via the paper conveyance path 11 by the paper feed roller 13. Is done. The registration roller 10 sends the transfer material P to the secondary transfer portion in synchronization with the image on the intermediate transfer belt 6, and performs the secondary transfer of the four color toner images from the intermediate transfer belt 6 to the transfer material P. Let

The above-mentioned OHT detection sensor 15 is installed in the cassette 14 on the assumption that the OHT is set together with plain paper as the transfer material P in the cassette 14. In the present embodiment, the OHT detection sensor 15 is of a light reflection type, which detects a transparent OHT by distinguishing it by a difference in light reflectance with plain paper.

According to the present embodiment, the sensor 15 is provided at a rear portion in the cassette 14. This is for the following reason.

In this embodiment, as in the first embodiment, L
When forming an image on plain paper of TR size, the image interval 50
mm. OHT is supplied from the cassette 14 as the transfer material P mixed with plain paper. The image already exists before the secondary transfer unit. In the case of continuous printing, the next image is formed at an image interval of 50 mm on the image forming side of the intermediate transfer belt 6, and the image forming process cannot be changed.

Then, if avoidance measures are taken, OHT
Is stopped at the registration position, the image formation on the intermediate transfer belt 6 is terminated without changing the process speed, and the intermediate transfer belt 6 is caused to make one revolution. Then, when the OHT image reaches the secondary transfer unit, the process speed may be changed to the OHT mode secondary transfer / fixing speed for the first time.

However, in this case, it takes a very long time until the secondary transfer and fixing of the OHT image, and the transferability of the next image is slightly different because of the extra idle rotation. There is a possibility that a difference in color will appear in the next image.

As in the present embodiment, the OHT detection sensor 15
If the transfer material P fed from the cassette 14 is OHT,
An image to be transferred to the OHT on the image forming side of the intermediate transfer belt 6 can be known at an early stage in the stage of development and primary transfer of the first color, and the image interval in the formation of the next image is changed. be able to.

In this embodiment, the image interval of the next image with respect to the image to be transferred to the OHT is widened, and specifically, 1000 mm which is the same as the circumference of the intermediate transfer belt 6.
To Then, after the secondary transfer / fixing is completed by reducing the speed in the OHT mode, the process speed is returned to the normal speed for plain paper, and the operation below the primary charging of the photosensitive drum 1 for the next image is performed. The process was shifted to the image process, and continuous printing was continued. This makes it possible to cope with the mixture of OHT and plain paper without providing idle rotation or the like for speed adjustment, and to perform printing in the shortest time.

In the above description, the transfer material for forming an image is OHT,
Next, the case of plain paper is shown.
There are two types of transfer material detected by the HT detection sensor 15, plain paper and OHT. Even when OHT detection is continuous, it is needless to say that OHT printing can be performed in the shortest time only by changing the image interval. .

That is, when the OHT is detected again after the OHT, the image forming condition on the photosensitive drum 1 is set to 1 / the normal value.
The speed is changed from 1st speed to 1/3 speed, and the image interval is 25 mm. The high pressure condition changed by the image forming condition is such that the circumference of the roller bias is a number and the circumference of the developing bias is a number.

As described above, when the OHT is detected again after the OHT, the image forming speed is set to 1/3 speed and the image interval is set to 2 times.
By setting it to 5 mm, the throughput can be improved.

Further, the same effect can be obtained by installing the OHT detecting means not only in the cassette but also in a manual tray or the like. In addition, a thick paper detecting means may be provided. In this case, the thick paper and plain paper can be printed out in the shortest time in the same manner as in the above-described automatic OHT mode.

As described above, in this embodiment, the OHT
In the image forming apparatus using an intermediate transfer belt, such as an inline color printer or a copying machine, even if the mode of changing the type of the transfer material changes, only the image interval (paper interval) is changed. OHT printing can be performed in the shortest time. Further, since the OHT mode is automatically detected upon detecting the OHT, the machine can be used as a network printer excellent in user-friendliness.

[0067]

As described above, according to the present invention,
The toner images formed on the plurality of first image carriers are sequentially superimposed on the intermediate transfer member and primary-transferred, and then the multicolor image is secondarily transferred and fixed to a transfer material, and the color image is transferred to the transfer material. Since the in-line type image forming apparatus for obtaining an image is provided with a plurality of image forming speeds and a plurality of image forming intervals, a continuous image is formed by using a type of OHT or cardboard whose image forming speed is lower than usual as a transfer material. Also in the case of forming, the interval between images is reduced in the non-image forming area of the intermediate transfer member between the primary transfer portion and the secondary transfer portion of the most downstream image forming portion of the plurality of image carriers. Accordingly, the number of images can be increased and the number of images can be increased, and the productivity of images can be improved. In addition, since it is not necessary to increase the length of the non-image area of the intermediate transfer body, the size of the image forming apparatus can be reduced.

OHT with an image forming speed lower than usual
A transfer sensor for detecting the transfer material such as OHT is installed to confirm that the transfer material such as OHT is used for image formation. The image to be transferred to the transfer material such as OHT on the image forming side of the intermediate transfer body is the first color. When the detection is performed at an early point in the image formation, the image formation is performed with a wide image interval for the next image, so that even when the OHT or the like and the plain paper are mixed as the transfer material, the OHT is performed. For example, an image transferred to a transfer material such as the above can be dealt with without the need for idle rotation of the intermediate transfer body carrying the image, and it is possible to perform secondary transfer, fixation, and output in the shortest time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing division of an image forming area and a non-image forming area in one circumference of an intermediate transfer belt of the image forming apparatus of FIG. 1;

FIG. 3 is an explanatory diagram showing a difference in an interval between images formed on an intermediate transfer belt in a plain paper mode and a thick paper mode in Embodiment 1.

FIG. 4 is a cross-sectional view illustrating an image forming apparatus according to a second embodiment of the present invention.

FIG. 5 is a schematic sectional view showing a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 6 Intermediate transfer belt 7 Primary transfer electrode 8 Secondary transfer roller 14 Paper cassette 15 OHT detection sensor P Transfer material Py First image forming unit Pk Fourth image forming unit

Claims (3)

[Claims] 1. A toner image formed on a plurality of first image carriers disposed along a rotation direction of an intermediate transfer member, and the toner images formed on a plurality of first image carriers are transferred by a primary transfer unit in each of the plurality of image carriers to the intermediate transfer unit. The toner image is superimposed on the transfer body and primary-transferred, and then the multicolor image formed by superimposing the toner images is collectively secondary-transferred to the transfer material in the secondary transfer unit, and then fixed in the fixing unit. In the image forming apparatus, the image forming apparatus has a plurality of image forming speeds and a plurality of image forming intervals. 2. When the multicolor image is continuously formed by using a transfer material of a type whose image forming speed is lower than usual as the transfer material, the rotation of the intermediate transfer member of the plurality of image carriers is performed. From the primary transfer portion of the image carrier at the most downstream
In a region between the next transfer portions, the number of multicolor images carried on the intermediate transfer member in the region is increased by narrowing the interval between the multicolor images carried on the intermediate transfer member. 1 image forming apparatus. 3. The image forming apparatus according to claim 1, further comprising a detecting unit configured to detect a type of the transfer material supplied to the secondary transfer unit. In the case of continuously forming a color image, when the detecting unit detects a type of transfer material whose image forming speed is lower than usual,
Of the plurality of image carriers, in the region between the primary transfer portion and the secondary transfer portion of the most downstream image carrier in the rotation direction of the intermediate transfer member, a plurality of image carriers carried on the intermediate transfer member are arranged. For the multi-color image for the slow type transfer material of the color image,
The multicolor image for the next transfer material is carried with a wide interval,
Then, the secondary transfer and fixing of the multicolor image for the transfer material of the slower type are performed at a speed reduced from the normal image forming speed, and then the secondary transfer and fixing of the multicolor image for the next transfer material are performed. 2. The image forming apparatus according to claim 1, wherein the image forming is performed at a normal image forming speed.