JP2002311676A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device where chattering occurring at a secondary transfer nip can be prevented and the image magnification of a toner image on transfer material can become a desired one when a multiple transfer of the toner image from a photoreceptor drum to a rubber secondary transfer belt is carried out and the color image is obtained by carrying out an en bloc transfer to the transfer material. SOLUTION: In the device, the toner image formed in the sub scanning direction on the photoreceptor drum 1 is reduced by making the rotational speed of the photoreceptor drum 1 fast and then transferring to a secondary transfer belt 9. Then, the magnification of the transfer image on the transfer material becomes the desired one by driving so that the carrying speed of the transfer material P carried to a secondary transfer nip N2 and the surface speed of the secondary transfer belt 9 are approximately equal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly, to an image forming apparatus using a second image carrier for collectively transferring toner images.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus,
Various methods such as an electrophotographic method, a thermal transfer method, and an ink jet method are known. Among these, the electrophotographic method is different from the other methods in terms of image forming speed, image quality, quietness, and the like. Is excellent.

[0003] Among image forming apparatuses adopting the electrophotographic system, there are various other systems. For example, a multi-developing system in which a color image (toner images of a plurality of colors) is superimposed on a photoreceptor surface and then collectively transferred to a transfer material to form an image, a multi-transfer system in which development-transfer cycles are repeated, and There is an intermediate transfer method in which toner images of respective colors are sequentially and primarily transferred onto a transfer member and then collectively transferred onto a transfer material. Among them, the intermediate transfer method has the advantages that there is no risk of color mixing and that various transfer materials having different qualities and thicknesses can be used.

An image forming apparatus of the intermediate transfer system will be described below with reference to a four-color full-color laser beam printer shown in FIG. 1 showing an embodiment of the present invention.

As shown in FIG. 1, a charger 2 and a laser beam are irradiated on the peripheral surface of a photosensitive drum 1, which is an image carrier, in order along a rotation direction (direction of arrow R1). A device 3, a developing device (5, 6, 7, 8), an intermediate transfer belt 9 (hereinafter, ITB 9), and a photosensitive drum cleaner 19 are arranged.

In the figure, the surface speed is 117 mm in the direction of arrow R1.
/ Diameter 46.7 mm
Is charged to the negative polarity by the charger 2.

The photosensitive drum 1 charged by the charger 2
The surface potential (hereinafter, charging potential) is usually from -450 V
-800V. The charger 2 has a charger power supply 1.
7, a charging bias in which a DC voltage is superimposed on the alternating voltage is applied. By using a charging bias in which a DC voltage is superimposed on an alternating voltage, charging can be performed efficiently.

An electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by exposure L of the exposure means 3 according to image information sent from a controller (not shown). Here, the exposure unit 3 includes a light source 3a such as a laser, a six-sided polygon mirror 3b for performing raster scan, a lens 3c for image formation, a return mirror 3d, and the like. The resolution of this image forming apparatus is 600 dpi, and the surface speed is 1
The polygon mirror 3b rotates at 461 revolutions / sec with respect to the photosensitive drum 1 rotating at 17 mm / sec.

A black toner charged to a negative polarity by the first-color black developing unit 5 mounted on the rotary 22 adheres to the electrostatic latent image and is developed as a toner image.

Thereafter, the ITB 9 is supported by a plurality of support shafts (secondary transfer opposing roller 12, drive roller 15, tension roller 16).

Here, ITB9 has a thickness of, for example,
An endless resin belt of about 0.1 mm to 0.3 mm
Adjust the volume resistivity to about 1010 to 1016 Ωcm
Can be used. In this case, the resin belt
As the material, for example, PVdF (polyvinylidene fluoride)
), Nylon, PET (polyethylene terephthalate)
G), polycarbonate and other resin films (if necessary
The resistance has been adjusted. ) Etc. can be used.
Further, the resin belt is made of carbon ZnO, SiO _Two,
TiO_Two, Volume resistivity by other conductive filler
10⁷-10¹¹It may be adjusted to about Ω · cm.
You. Like the latter, ITB9 can be realized by lowering resistance to medium resistance.
An image defect due to accumulation of electric charges can be prevented.

As another example, when a rubber belt made of an elastic material (chloroprene rubber, EPDM, NBR, urethane rubber, etc.) having a thickness of about 0.5 mm to 2.0 mm is used in order to improve durability. There is also. In this case, similarly, if necessary, the volume resistivity is adjusted to about 10 ⁷ to 10 ¹¹ Ω · cm with the above-described conductive filler or the like,
An image defect due to charge accumulation in the ITB 9 can be prevented.

The ITB 9 rotates in the direction of the arrow R3 in the figure with the rotation of the drive roller 15 (the direction of the arrow R2 in the figure). When a positive primary transfer bias is applied from the primary transfer power supply 20 to the primary transfer roller 10 having a diameter of 12 mm which is driven to rotate (in the direction of arrow R5 in the figure) by the ITB 9, the toner image on the photosensitive drum 1 becomes primary. Transfer nip N
1 is primarily transferred. Also, the primary transfer roller 10
A resistance adjuster such as carbon is added to EPDM, urethane rubber, CR, NBR, etc., and the volume resistivity is 10 ⁵ Ω.
-It is common to use a material adjusted to cm or less.

The primary transfer residual toner on the surface of the photosensitive drum 1 after the primary transfer is removed by a cleaner 19 having an elastic blade 191.

The above-described series of image forming processes of charging, exposure, development, primary transfer, cleaning, and charge elimination are performed by the second color magenta, the third color cyan, and the fourth color yellow accommodated in the developing units 6, 7, and 8, respectively. Are repeated for the toner of No. 4, and the toner images of four colors are superimposed on the ITB 9.

Incidentally, the surface of the ITB 9 is gradually charged up to a negative polarity every primary transfer. Also, the first color,
As the primary transfer with the second color proceeds, it becomes necessary to superimpose the toner on a place where the toner is already on the ITB 9. Therefore, in order to perform the primary transfer efficiently, it is necessary to gradually increase the primary transfer bias for each color.

In the conventional example shown here, the first color is +
100V, the second color is + 500V, the third color is + 600V,
For the fourth color, a primary transfer bias of +700 V was used.

Then, φ2 rotating in the direction of arrow R4 in FIG.
When a secondary transfer bias is applied to the 0 mm secondary transfer roller 11 from the secondary transfer bias power supply 21, the toner image on the ITB 9 is transferred to the secondary transfer roller 11 via the secondary transfer nip N 2 on the secondary transfer facing roller 12. The secondary transfer is collectively performed on the surface of the transfer material P.

The transfer material P carrying the unfixed toner images of four colors on the surface is conveyed to a fixing device (not shown), where the toner image on the surface is fixed to complete the image formation.

On the other hand, the ITB 9 after the above-described secondary transfer has been completed
After the secondary transfer residual toner remaining on the ITB 9 without being transferred to the transfer material P by the cleaner 13 is removed,
If necessary, the charge is removed by a charge remover (discharge means) 14. As the static eliminator 14, AC corona charging is often used. In addition, ITB9 is used to improve the static elimination efficiency.
In general, an electrode is provided inside the inside.

[0021]

However, in the above-mentioned conventional image forming apparatus, the rubber belt is used for the ITB9.
Is used in the secondary transfer nip N2.
Chatter occurred between B9 and the transfer material P, resulting in a problem of non-uniform images. According to the study of the present inventor, this chatter causes the transfer material P to hinder the rotation of the ITB 9 because the speed of the transfer material P is lower than the surface speed of the ITB 9 in the secondary transfer nip N2. Was the cause.

Therefore, in order to solve this problem, the speed of the transfer material P is adjusted by the ITB 9 in the secondary transfer nip N2.
When the speed was set to be equal to the speed of the surface, the image magnification of the image on the transfer material P became larger than the desired magnification.

That is, as shown in FIG.
Reference numeral 9 denotes a surface extending on a support shaft such as the secondary transfer nip N2. Then, the toner image carried on the ITB 9 also corresponds to the elongation of the surface of the ITB 9, and as a whole, as shown in FIG. 3B, as compared with the image of the desired magnification shown in FIG. Image. Considering from this, in the above-mentioned chatter occurrence state, in the secondary transfer portion,
It is considered that the image once stretched on the surface of the ITB 9 due to the curvature is contracted again by the transfer material having a low speed, and apparently no image expansion has occurred.

The present invention has been made in order to solve the above-mentioned problems. Even in an image forming apparatus using a rubber belt as an ITB, the speed of the transfer material P is optimized to the speed at which chatter is prevented from occurring. Even in such a case, the purpose is to set the image magnification of the toner image on the transfer material P to a desired magnification.

[0025]

According to a first aspect of the present invention, there is provided an exposure apparatus for irradiating a first image carrier with scanning light to form an electrostatic latent image thereon, and A second image carrier to which a toner image formed on the image carrier is repeatedly transferred, wherein the second image carrier has at least an elastic layer, and is multiplex-transferred to the second image carrier. The formed toner image is collectively transferred onto a transfer material on a support shaft that supports the second image carrier from the inner surface. The image magnification of the electrostatic latent image is set to be smaller than the image magnification of the toner image in the traveling direction on the transfer material.

According to a second aspect, in the first aspect,
The moving speed of the transfer material is set to be higher than the speed of the surface of the second image carrier in the secondary transfer nip.

According to a third aspect, in the second aspect,
When the moving speed Vp of the transfer material and the speed Vt2 of the surface of the second image carrier at the secondary transfer nip are set to 1.0 <V
It is characterized in that p / Vt2 ≦ 1.05 holds.

According to a fourth aspect of the present invention, in any one of the above aspects, the speed of the surface of the second image carrier in the primary transfer nip is set to be higher than the speed of the surface of the first image carrier. It is characterized by doing.

According to a fifth aspect of the present invention, in the fourth aspect, when the speed Vt1 of the surface of the second image carrier in the primary transfer nip and the speed Va of the surface of the first image carrier are 1.0 <1.0. Vt1 / Va ≦ 1.05 holds.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. FIG. 1 also shows the second,
Image forming apparatuses according to the third and fourth embodiments are also shown.

Referring to FIG.
Using a 7 mm rubber belt, the secondary transfer facing roller 12
Has a diameter of 27.5 mm. The resolution of the image forming apparatus shown in the present embodiment is 600 dpi, and the six-sided polygon mirror 3b rotates at 461 revolutions / sec, which is the same as the conventional example. Further, the surface speed Va1 of the photosensitive drum 1 is lower than the surface speed Va of the photosensitive drum 1 shown in the conventional example.
114.1 mm / sec. The speed of the transfer material P is substantially equal to the surface speed of the ITB 9 in the secondary transfer nip N2. Further, in the primary transfer nip N1,
The surface speed of the ITB 9 is the surface speed Va1 of the photosensitive drum 1.
It was set to be approximately equivalent to

In this embodiment, the secondary transfer nip N2
And the surface speed Va (=) at which an electrostatic latent image having a resolution of 600 dpi is formed on the surface of the photosensitive drum 1 under the conditions of the polygon mirror 3b described above.
117.0 mm / sec), the surface speed of the photosensitive drum 1 was reduced.

As a result, the electrostatic latent image formed on the photosensitive drum 1 contracts in the rotation direction of the photosensitive drum 1, thereby correcting the expansion of the toner image in the secondary transfer nip N2. Therefore, even when the transfer material P is substantially equal to the surface speed of the ITB 9 in the secondary transfer nip N2, the image magnification on the transfer material P is a desired value.

Hereinafter, the IT in the secondary transfer nip N2 will be described.
Photosensitive drum 1 for elongating the surface of B9 and correcting the elongation
The relationship between the surface speed Va1 and the surface speed Va1 will be described in detail.

FIG. 4 shows the ITB near the secondary transfer nip N2.
9 is shown. In the figure, in a portion E where the ITB 9 is wound around the secondary transfer opposing roller 12, the front side extends and the rear side shrinks around a neutral line which is the center position of the ITB 9 in the thickness direction. Assuming now that the distance X from the center of the secondary transfer opposing roller 12 to the surface of the ITB 9 and the distance Y from the center of the secondary transfer opposing roller to the neutral line of the ITB 9, the elongation rate K of the ITB 9 surface in the secondary transfer nip N 2 is , K = X / Y (however, the elongation percentage of the part where the ITB 9 is not wound around the secondary transfer opposing roller 12 is 1.0).

The surface speed Va1 of the photosensitive drum 1 for correcting the expansion (enlargement of the image magnification) and reducing the electrostatic latent image on the photosensitive drum 1 (reduction of the image magnification) is determined based on the photosensitive drum before correction. When the speed of one surface is Va, Va1 = Va / K.

In the present embodiment, X: 14.45 mm,
Y: 14.1 mm, Va: 117 mm / sec. Then, the elongation rate K of the surface of the ITB 9 in the secondary transfer nip N2 is K = 14.45 / 14.1 = 1.025. Therefore, Va1 = 117.0 / 1.025 = 1114.1 mm / sec. In this embodiment, the toner image on the transfer material P is
A desired image magnification is obtained.

In the present embodiment, the thickness of the rubber belt used as the ITB 9 is 0.7 mm.
If it is 0.5 mm to 2.0 mm, it can be used similarly. However, according to the study of the present inventors,
If it is less than 0.5 mm, sufficient durability cannot be ensured due to wear. On the other hand, if it exceeds 2.0 mm, the rubber belt will not bend properly at the support shaft, and the running will not be stable.

It is also possible to incorporate a thread or a woven fabric core made of cotton, polyester, or the like as a reinforcing member into the rubber belt to reduce stress relaxation. In this case, the secondary transfer nip N2 The neutral line in the surface elongation at becomes the center position of the core.

(Second Embodiment) The schematic configuration of an image forming apparatus according to a second embodiment of the present invention is the same as that of FIG.

Also in this embodiment, a rubber belt having a thickness of 0.7 mm is used as the ITB 9, and the diameter of the secondary transfer opposed roller 12 is φ27.5 mm. The surface speed of the photosensitive drum 1 is 117 mm / sec, which is the same as the conventional example. The resolution of the image forming apparatus described in this embodiment is 600
The polygon mirror 3b of 6 dpi has a rotation speed of 473 revolutions / second, which is faster than the rotation speed of the polygon mirror 3b used in the conventional example. An image clock, which is a transfer speed of image information sent from a controller (not shown) to the exposure device 3, is adjusted in accordance with a change in the rotation speed of the polygon mirror 3 b, and the photosensitive drum of the electrostatic latent image on the photosensitive drum 1 is adjusted. The image magnification in the direction perpendicular to the running direction of No. 1 was set to a desired value. Thereby, similar to the first embodiment,
The image on the photosensitive drum 1 contracts in the running direction (sub-scanning direction).

The speed of the transfer material P is substantially equal to the surface speed of the ITB 9 in the secondary transfer nip N2. The surface speed of the ITB 9 in the primary transfer nip N1 is substantially equal to the surface speed Va1 of the photosensitive drum 1.

In the present embodiment, the secondary transfer nip N2
When the surface speed of the photosensitive drum 1 is 117 mm / sec, which is the same as that of the conventional example, and the resolution is 600 dpi, a six-sided polygon mirror 3b for forming an electrostatic latent image having a resolution of 600 dpi on the surface of the photosensitive drum 1 is formed. The rotation speed of the polygon mirror 3b was increased with respect to the rotation speed.

Thus, similar to the first embodiment,
The electrostatic latent image formed on the photosensitive drum 1
It contracts in the rotational direction, and corrects the elongation of the toner image in the secondary transfer nip N2. Therefore, even when the transfer material P is substantially equal to the surface speed of the ITB 9 in the secondary transfer nip N2, the desired image magnification on the transfer material P is obtained.

Hereinafter, the IT in the secondary transfer nip N2 will be described.
The relationship between the elongation of the B9 surface and the rotational speed Ra1 of the polygon mirror 3b for correcting the elongation will be described in detail.

Also in this embodiment, as described in the first embodiment, the ITB is used in the secondary transfer nip N2.
The surface extends from the 9 neutral line. In FIG. 4, if the distance X from the center of the secondary transfer facing roller 12 to the surface of the ITB 9 and the distance Y from the center of the secondary transfer facing roller to the neutral line of the ITB 9 are the same, the secondary transfer nip N2 is similarly obtained.
The elongation percentage K of the ITB 9 surface at the time is: K = X / Y

Then, this elongation is corrected and the photosensitive drum 1
The rotational speed of the polygon mirror 3b for reducing the electrostatic latent image is Ra1, and when the rotational speed of the polygon mirror 3b before correction is Ra, Ra1 = Ra × K.

In the present embodiment, X: 14.45 mm,
Y: 14.1 mm, Ra: 461 revolutions / sec. Then, the elongation rate K of the ITB 9 surface in the secondary transfer nip N2 is K = 14.45 / 14.1 = 1.025 as in the first embodiment. Therefore, Ra1 = 461 × 1.025 = 473 rotations / sec. Also in the present embodiment, the desired image magnification of the toner image on the transfer material P can be obtained. By the way, ITB9
As in the first embodiment, a rubber belt having a thickness of 0.5 mm to 2.0 mm can be used. Further, a core body can be included as a reinforcing member.

(Third Embodiment) A schematic configuration showing an image forming apparatus according to a third embodiment of the present invention is the same as that of FIG.

Also in this embodiment, a rubber belt having a thickness of 0.7 mm is used as the ITB 9, and the diameter of the secondary transfer opposed roller 12 is φ27.5 mm.

In the present embodiment, in the secondary transfer nip N2, the speed of the transfer material P is set to be 0.5% faster than the surface speed Vt2 of the ITB 9 in the secondary transfer nip N2. Improving efficiency.

Here, the surface speed of the photosensitive drum 1 is 117 mm / sec, which is the same as the conventional example. The resolution of the image forming apparatus shown in the present embodiment is 600 dpi, and the polygon mirror 3b having six surfaces rotates at 475 rotations / sec, which is higher in the number of rotations than in the second embodiment. The magnification of the electrostatic latent image on the photosensitive drum 1 in the direction perpendicular to the running direction of the photosensitive drum 1 was adjusted to a desired value by adjusting the rotation speed of the polygon mirror 3b in accordance with the change in the rotation speed.

Thus, the toner image elongation due to the elongation of the surface of the ITB 9 in the secondary transfer nip N2 and
The image elongation caused by the fact that the speed Vp of the transfer material P in the secondary transfer nip N2 is faster than the ITB9 surface speed Vt2 in the secondary transfer nip N2 is corrected. The surface speed of the ITB 9 in the primary transfer nip N1 is substantially the same as the surface speed Va1 of the photosensitive drum 1.

Hereinafter, when the speed of the transfer material P is higher than the surface speed of the ITB 9 in the secondary transfer nip N2, the polygon mirror 3b for setting the image magnification of the toner image on the transfer material P to a desired value. The rotation speed Ra2 will be described in detail.

Now, as in the first and second embodiments, the surface of the ITB 9 extends at the secondary transfer nip N2. The elongation K at this time is represented by K = X / Y.

When the speed Vp of the transfer material P is higher than the surface speed Vt2 of the ITB 9 in the secondary transfer nip N2, the toner image on the transfer material P further depends on the speed difference between Vp and Vt2. Extends in the direction of travel. The elongation percentage K2 at this time is represented by K2 = Vt2 / Vp.

Then, the IT at the secondary transfer nip N2
The rotational speed Ra2 of the polygon mirror 3b for correcting the elongation of the B9 surface and the elongation of the toner image due to the speed difference between Vp and Vt2, and for reducing the electrostatic latent image on the photosensitive drum 1 is as follows.
When the rotational speed of the polygon mirror 3b before correction is Ra, Ra2 = Ra × K × K2.

In the present embodiment, X: 14.45 mm,
Y: 14.1 mm, Ra: 461 revolutions / second, K2: 1.
005.

Then, the IT in the secondary transfer nip N2
The elongation percentage K of the B9 surface is K = 14.45 / 14.1 = 1.025 as in the first and second embodiments.

Ra2 = 461 × 1.025 × 1.005
= 475 rotations / sec. Even when the speed of the transfer material P is higher than the surface speed of the ITB 9 in the secondary transfer nip N2 as in the present embodiment, the toner image on the transfer material The image magnification is obtained.

In the present embodiment, in the secondary transfer nip N2, the speed Vp of the transfer material P is set to be smaller than the surface speed Vt2 of the ITB 9 in the secondary transfer nip N2.
Although the setting is made 0.5% faster, the same effect can be obtained if it exceeds 0% and is 5% or less. According to the study of the present inventors, 5
%, The rotation of the ITB 9 became unstable due to the impact of the contact of the transfer material P with the ITB 9, and the image quality deteriorated.

In the present embodiment, a method of increasing the rotation speed of the polygon mirror 3b is used to reduce the image on the photosensitive drum 1, but a means for increasing the speed of the photosensitive drum 1 may be used. is there.

(Fourth Embodiment) The schematic structure of an image forming apparatus according to a fourth embodiment of the present invention is the same as that of FIG.

Also in the present embodiment, a rubber belt having a thickness of 0.7 mm is used as the ITB 9, and the diameter of the secondary transfer opposed roller 12 is φ27.5 mm.

Also in the present embodiment, in the secondary transfer nip N2, the speed of the transfer material P is reduced by the secondary transfer nip N2.
Was set to be 0.5% faster than the surface speed Vt2 of ITB9. Further, the ITB in the primary transfer nip N1
By setting the speed Vt1 of the nine surfaces 0.6% faster than the surface speed Va of the photosensitive drum 1, the transfer efficiency in the primary transfer and the secondary transfer is improved.

Here, the surface speed Va of the photosensitive drum 1 is
It is 117 mm / sec which is the same as the conventional example. The resolution of the image forming apparatus shown in this embodiment is 600 dpi, and the six-sided polygon mirror 3b rotates at 478 rotations / sec, which has a higher rotation speed than in the third embodiment, and further has an image clock. Is adjusted in accordance with the change in the rotation speed of the polygon mirror 3b, and the photosensitive drum 1 of the electrostatic latent image on the photosensitive drum 1 is adjusted.
The image magnification in the direction (sub-scanning direction) perpendicular to the running direction of the image was set to a desired value.

Thus, the elongation of the toner image due to the elongation of the ITB 9 surface in the secondary transfer nip N 2 and the elongation caused by the speed Vp of the transfer material P being higher than the ITB 9 surface speed Vt 2 in the secondary transfer nip N 2, , Surface speed Vt1 of ITB 9 in primary transfer nip N1
Compensates for elongation caused by being faster than the surface speed Va of the photosensitive drum 1.

Hereinafter, the IT in the primary transfer nip N1 will be described.
The surface speed Vt1 of B9 is the surface speed Va of the photosensitive drum 1
And when the speed of the transfer material P is higher than the surface speed of the ITB 9 in the secondary transfer nip N2, the rotation of the polygon mirror 3b to make the image magnification of the toner image on the transfer material P desired. The number Ra3 will be described in detail.

As in the present embodiment, the ITB 9 in the primary transfer nip N1 is smaller than the surface speed Va of the photosensitive drum 1.
When the surface speed Vt1 is high, the toner image on the photosensitive drum 1 is primarily transferred onto the ITB 9 and extends in the traveling direction of the ITB 9. The elongation K1 at this time is represented by K1 = Vt1 / Va.

As in the first, second and third embodiments, the surface of the ITB 9 extends at the secondary transfer nip N2. The elongation K at this time is represented by K = X / Y.

Further, in the same manner as in the third embodiment, the speed Vp of the transfer material P is controlled by the ITB in the secondary transfer nip N2.
9 is higher than the surface speed Vt2 of I.
The toner image on TB9 is stretched, and the stretch rate K2 is represented by K2 = Vt2 / Vp.

As described above, the expansion of the toner image in the three steps is corrected, and the electrostatic latent image on the photosensitive drum 1 is reduced.
When the rotation speed of the polygon mirror 3b before correction is Ra, the rotation speed Ra3 of the polygon mirror 3b is as follows: Ra3 = Ra × K1 × K × K2.

In the present embodiment, X: 14.45 mm,
Y: 14.1 mm, Ra: 461 rotations / sec, K1: 1.
006, K2: 1.005.

Then, the IT in the secondary transfer nip N2
The elongation rate K of the B9 surface is K = 14.45 / 14.1 = 1.025 as in the first and second embodiments. Therefore, Ra2 = 461 × 1.006 × 1.025 × 1.005
= 478 revolutions / second, and even when the speed of the transfer material P is higher than the surface speed of the ITB 9 in the secondary transfer nip N2 as in the present embodiment, the toner image on the transfer material The image magnification is obtained.

In the present embodiment, the speed Vt1 of the ITB 9 in the primary transfer nip N1 is set to be 0.6% faster than the surface speed Va of the photosensitive drum 1.
%, The same effect can be considered if it is 5% or less.
According to the study of the present inventor, when the ratio exceeds 5%, it is impossible to ignore so-called color shift, in which the toner images of the respective colors do not overlap correctly in the primary transfer.

In this embodiment, the method of increasing the rotation speed of the polygon mirror 3b is used to reduce the image on the photosensitive drum 1, but a means for increasing the speed of the photosensitive drum 1 may be used. is there.

[0077]

According to the present invention, as the second image carrier,
For example, when an endless rubber belt is used, the electrostatic latent image on the photosensitive drum as the first image carrier is contracted in accordance with the elongation of the rubber belt surface in the secondary transfer nip, so that chatter in the secondary transfer nip is reduced. It has become possible to set the image magnification of the toner image on the transfer material to a desired magnification while preventing the occurrence.

Further, even in the case where the speed of the transfer material in the secondary transfer nip is set to be higher than the surface speed of the rubber belt in the secondary transfer nip, the electrostatic latent image on the photosensitive drum is contracted to reduce the secondary transfer nip. It is possible to set the image magnification of the toner image on the transfer material to a desired magnification while preventing the occurrence of chatter in the above.

Further, the rubber belt is used as the second image carrier, and the speed of the transfer material at the secondary transfer nip is set to be higher than the surface speed at the secondary transfer nip of the rubber belt. Even when the surface speed is higher than the surface speed of the photosensitive drum, by reducing the electrostatic latent image on the photosensitive drum, the occurrence of chatter at the secondary transfer nip is prevented, and the image magnification of the toner image on the transfer material is increased. It has become possible to set a desired magnification.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an image forming apparatus showing a conventional example of the present invention and first to fourth embodiments.

FIG. 2 is a view for explaining expansion of an image on an intermediate belt in a secondary transfer nip portion.

FIG. 3 is a diagram showing an extended state of a diagram formed in the description of FIG. 2;

FIG. 4 is a diagram showing an embodiment of the present invention in detail.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 3 exposure device 3 b polygon mirror 9 ITB 12 secondary transfer facing roller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA16 DA17 DA20 EA20 EB06 EC01 EC18 ED02 ED16 ED24 EE03 EF09 EG06 2H030 AD17 BB02 BB24 BB42 BB44 BB53 BB71 2H200 FA04 FA19 FA20 GA23 GA29 GA34 GA47 HA02B28 J02B03 JC09 JC15 JC16 JC19 LA40 MA03 MA04 MA14 MA20 MB04 PA11

Claims (8)

[Claims] An exposure device configured to irradiate a scanning light onto the first image carrier to form an electrostatic latent image, and a second image to which a toner image formed on the first image carrier is repeatedly transferred. The second image carrier has at least an elastic layer, and the toner images multiplex-transferred to the second image carrier are supported by the second image carrier from the inner surface. In the image forming apparatus, the image magnification of the electrostatic latent image in the traveling direction on the first image carrier is changed to the image of the toner image in the traveling direction on the transfer material. An image forming apparatus, wherein the setting is made to be smaller than the magnification. 2. The moving speed of the transfer material is a speed of the surface of the second image carrier when the toner images carried on the second image carrier are collectively transferred onto the transfer material. 2. The image forming apparatus according to claim 1, wherein the setting is made to be faster than that. 3. The moving speed of the transfer material is Vp, and the speed of the surface of the second image carrier when the toner images carried on the second image carrier are collectively transferred onto the transfer material. 3. The image forming apparatus according to claim 2, wherein when Vt2, 1.0 <Vp / Vt2 ≦ 1.05. 4. When transferring a toner image carried on the first image carrier onto the second image carrier,
4. The image forming apparatus according to claim 1, wherein the speed of the surface of the second image carrier is set to be higher than the speed of the surface of the first image carrier. 5. A method for transferring a toner image carried on the first image carrier onto the second image carrier.
The speed of the surface of the second image carrier is Vt1, and the speed of the surface of the first image carrier is Va, wherein 1.0 <Vt1 / Va ≦ 1.05. 5. The image forming apparatus according to 4. 6. The thickness of the second image carrier is 0.5 m
2. The range of m to 2.0 mm.
6. The image forming apparatus according to any one of claims 1 to 5, 7. The image forming apparatus according to claim 1, wherein the second image carrier includes a core. 8. The image forming apparatus according to claim 1, wherein said second image bearing member is an endless rubber belt.