JPH10186883A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of forming an excellent color image by preventing transfer defect even in the case of performing the image formation by laminating discontinuous colors. SOLUTION: In this device, 4 sets of image forming parts 10Y, 10M, 10C and 10BK, provided with respective photoreceptor belt 18Y, 18M, 18C and 18BK, being placed side by side, and respective photoreceptor belt 18Y, 18M, 18C and 18BK is held in contact with a transporting belt 14 on several transferring position. Then, the toner image formed on respective photoreptor belt is successively laminated on transfer paper sheets P transported by the transporting belt 14 and transferred. On the respective transfer position, the change ratio R1 of a gap between the photoreceptor belt 18 and the transporting belt 14 on the upstream side in the traveling direction from the transferring position of the photoreceptor belt 18 (18Y, 18M, 18C and 18BK), and the changing ratio R2 of the gap between the photoreceptor belt 18 and the transporting belt 14 in the traveling direction from the transferring position, is set in the relation of R2>R1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus capable of forming a color image.

[0002]

2. Description of the Related Art In recent years, as an image forming apparatus, a color copying machine or the like capable of forming a color image has been widely used. As an image forming method of such a color copying machine, a method in which developer images having different colors are formed on a plurality of photoconductors and the formed developer images are sequentially transferred to transfer paper, or a single photosensitive 2. Description of the Related Art A method of forming a color image by forming a developer image on a body a plurality of times and transferring the developer image to a transfer sheet for each image formation is known.

For example, in an apparatus for forming a color image using a plurality of photoconductors, four photoconductors arranged side by side are yellow (Y), magenta (M), cyan (C),
After the black (BK) developer images are sequentially formed, the transfer sheet is conveyed through these four photoconductors in a state where the transfer sheet is electrostatically attracted to the conveyance belt. Then, at the transfer position of each photoconductor,
A transfer electric field is formed by a transfer roller, and a developer image on a photoreceptor is sequentially superimposed on a transfer sheet and transferred to form a color image.

[0004]

In the above-described color image forming apparatus, the following problems occur.
For example, when printing a band of seven colors by variously combining yellow (Y), magenta (M), and cyan (C), if the transfer bias condition at the transfer position of each color is optimally set, three of Y, M, and C are set. There is no problem when a black image is formed by transferring color developer images in order and transferring them,
As in the case where a green image is formed by superimposing the Y and C developer images, two discontinuous colors, that is, two discontinuous Y and C photosensitive members sandwiching the M photosensitive member therebetween When an image is formed by superimposing a developer image formed on a body, there arises a problem that transferability deteriorates.

[0005] This is because a developer image is not formed on the photoconductor for M and the potential is high, so that a strong transfer electric field is formed between the white background potential of the photoconductor for M and the transfer roller. When the transfer sheet passes through the photoconductor for M, the strong transfer electric field causes a discharge to occur between the Y developer image already formed on the transfer sheet and the photoconductor for M, and the Y development The potential of the agent image increases. Therefore, when the C developer image is transferred, C
This is because the transfer electric field at the photoconductor is weakened.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus capable of preventing defective transfer and forming a good color image even when forming images by overlapping discontinuous colors. To provide.

[0007]

According to another aspect of the present invention, there is provided an image forming apparatus for forming a developer image on an image carrier that moves in a predetermined direction. A transfer member disposed so as to be in contact with the image carrier at a transfer position, and a transfer unit configured to transfer the developer image on the image carrier onto the transfer member at the transfer position. Wherein at least one of the image carrier and the transfer object is formed in a belt shape, and a rate of change R1 of a gap between the image carrier and the transfer object on the upstream side in the predetermined direction from the transfer position. The rate of change R2 of the gap between the image bearing member and the transfer-receiving member on the downstream side of the transfer position in the predetermined direction is set to satisfy a relationship of R2> R1.

According to a second aspect of the present invention, there is provided an image forming apparatus, comprising: image forming means for forming developer images of different colors on an image carrier moving along a predetermined direction; And a transfer means for transferring the developer image on the image carrier onto the transfer member at the transfer position, wherein the image carrier and the transfer member are provided. At least one of the transfer members is formed in a belt shape, and a rate of change R1 of a gap between the image carrier and the transfer member on the upstream side in the predetermined direction from the transfer position;
The rate of change R2 of the gap between the image bearing member and the transfer-receiving member downstream from the transfer position in the predetermined direction is R
2> R1.

According to a third aspect of the present invention, there is provided an image forming apparatus having a belt-shaped image carrier which is arranged side by side and runs in a predetermined direction, and has a developer image on the image carrier. A plurality of image forming units to be formed and a plurality of image transfer units are provided in contact with the plurality of image carriers at a plurality of predetermined transfer positions respectively corresponding to the image forming units, and transfer paper is passed through the plurality of transfer positions. Transport means for transporting, and, at each of the transfer positions, a plurality of transfer means for transferring a developer image on a corresponding image carrier to the transfer paper; The rate of change R1 of the gap between the image carrier and the transfer sheet on the upstream side of the body in a predetermined direction, and the gap rate between the image carrier and the transfer sheet on the downstream side of the predetermined direction from the transfer position. The ratio R2, is characterized in that it is set to the relationship of R2> R1.

According to a fourth aspect of the present invention, there is provided an image forming apparatus which has a belt-like image carrier which is arranged side by side and which runs in a predetermined direction, and has a developer image on the image carrier. A plurality of image forming means for forming, an intermediate transfer belt running in contact with a plurality of predetermined transfer positions respectively corresponding to the image forming means, and a developer image on an image carrier corresponding to each of the transfer positions A plurality of first transfer means for transferring the developer image onto the intermediate transfer belt; and a second transfer means for transferring the developer image transferred on the intermediate transfer belt to a transfer sheet. The change rate R of the gap between the image carrier and the intermediate transfer belt on the upstream side of the image carrier in a predetermined direction from the transfer position.
1 and the rate of change R2 of the gap between the image carrier and the intermediate transfer belt on the downstream side in the predetermined direction from the transfer position is set to satisfy a relationship of R2> R1.

According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising: a belt-shaped image carrier which runs along a predetermined direction;
Image forming means for forming a plurality of developer images of different colors on the image carrier, and a transfer roller provided in contact with the image carrier at a predetermined transfer position and transporting a transfer sheet to the transfer position And a transfer unit for transferring the developer image on the image carrier to the transfer sheet at the transfer position, wherein the image at a predetermined direction upstream of the image carrier from the transfer position at the transfer position. The relationship R2> R1 is established between the rate of change R1 of the gap between the carrier and the transfer drum and the rate of change R2 of the gap between the image carrier and the transfer drum downstream of the transfer position in the predetermined direction. It is characterized by being set to.

Further, according to the image forming apparatus of the present invention, a belt-shaped image carrier running along a predetermined direction and a plurality of developer images of different colors are formed on the image carrier. Image forming means, an intermediate transfer drum provided in contact with the image carrier at a predetermined transfer position, and a developer image formed on the image carrier at each of the transfer positions. And a second transfer unit for transferring the developer image transferred on the intermediate transfer drum to a transfer sheet. The rate of change R1 of the gap between the image carrier and the intermediate transfer drum on the upstream side of the body in a predetermined direction, and the gap rate between the image carrier and the intermediate transfer drum on the downstream side of the predetermined direction from the transfer position. The rate of change R2 is It is characterized in that it is set to satisfy the relationship of 2> R1.

Further, according to the image forming apparatus of the present invention, a drum-shaped image carrier which rotates along a predetermined direction, and a plurality of developer images of different colors are formed on the image carrier. Image forming means, an intermediate transfer belt provided in contact with the image carrier at a predetermined transfer position and running along a predetermined direction, and a developer image formed on the image carrier at the transfer position First transfer means for transferring the developer image onto the intermediate transfer belt, and second transfer means for transferring the developer image transferred onto the intermediate transfer belt to transfer paper. A rate of change R1 of the gap between the image carrier and the intermediate transfer belt on the upstream side of the image carrier in a predetermined direction from the position; and the image carrier and the intermediate transfer belt on the downstream side of the image carrier in the predetermined direction from the transfer position. Gap between The rate of change R2, is characterized in that it is set to the relationship of R2> R1.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the image forming apparatus of the present invention is applied to a color printer will be described below in detail with reference to the drawings. As shown in FIG. 1, the color printer is configured as a so-called four-photoconductor type color printer having four photoconductors arranged side by side. That is, the color printer uses yellow (Y), magenta (M), cyan (C),
Four sets of image forming units 10Y, 10M, 10 for forming an image for each color component of an image using black (BK) toner
C, 10BK, and these image forming units are arranged in order along a transport belt 12 that transports the transfer paper P. A laser exposure device 14 is disposed above the four sets of image forming units 10Y, 10M, 10C, and 10BK that function as image forming means. Downstream of the image forming unit 10BK, a fixing unit 16 for fixing the toner images formed on the transfer paper by the four image forming units is provided.

Each of the image forming apparatuses 10Y, 10M, 10C,
The 10BKs have the same configuration. Therefore, in order to simplify the explanation, the image forming unit 10 for cyan is used.
The configuration will be described in detail on behalf of C, and the detailed description of the other image forming units 10Y, 10M, and 10BK will be omitted. Note that the same components of the image forming units of the respective colors are denoted by the same reference numerals, and the reference numerals are added with suffixes Y, M, C, and BK to distinguish the image forming units of the respective colors.

The image forming section 10C includes a photosensitive belt 18C functioning as an image carrier, and this photosensitive belt is wound around three pulleys 20 parallel to each other. The photoreceptor belt 18C is formed by laminating an OPC photosensitive layer on a conductive base material such as rubber. Then, by rotating at least one pulley 20 by a driving mechanism (not shown), the photosensitive belt 18C runs clockwise.

Around the photoreceptor belt 18C, a charging charger 22C for charging the photoreceptor belt to -400 to -800V, and an electrostatic latent image formed on the photoreceptor belt 18C by a laser beam 23C from the laser exposure device 12. A developing unit 24C for developing the image with cyan toner to form a toner image, a cleaner 26C for cleaning the surface of the photoreceptor belt 18C after the transfer of the toner image, and the like are provided. The charge polarity of the toner is negative, and the development is reversal development. The laser exposure device 12 receives image data for each color component sent from an external device, and exposes the photoreceptor belt according to the image data.

On the other hand, the transport belt 14 (transfer object) is stretched between a driving pulley 30a and a driven pulley 30b, extends substantially horizontally, and includes four sets of image forming units 1.
0Y, 10C, 10M, and 10BK. Further, the transport belt 14 is provided in each image forming section.
It is arranged so as to run in a state of being in contact with the photosensitive belt 18C at the position of one pulley 20. Drive pulley 3
At 0a, a charging roller 31 rolls in contact with the conveyance belt 14 therebetween, and the charging roller charges the conveyance belt to a predetermined value in order to electrostatically attract the transfer paper P to the conveyance belt.

Further, the image forming section 10C has a transfer roller 32C opposed to the pulley 20 with the photosensitive belt 18C and the transport belt 14 interposed therebetween, and a power supply 34C for applying a transfer bias to the transfer roller. Is connected. The transfer roller 32C functions as a transfer unit and a first transfer unit.

The transfer paper P fed from the paper feeding means (not shown) onto the conveyor belt 14 is electrostatically attracted to the surface of the conveyor belt, and is transferred to the image forming units 10Y, 10C, 10M and 10B.
K is sequentially transported. At this time, the transfer paper P is transferred between the transfer rollers of the image forming units 10Y, 10C, 10M, and 10BK and the photosensitive belt, that is, the transfer units 36Y and 36.
Pass through C, 36M, 36BK.

In the transfer section 36C, for example, as shown in FIG. 2, a transfer bias having a polarity opposite to the charge polarity of the toner is applied between the transfer roller 32C and the photosensitive belt 18C to form a transfer electric field. Is done. Thereby,
The Y, C, M, and BK toner images are sequentially transferred onto the transfer paper P to form a color image. The color image formed on the transfer sheet P is fixed by the fixing device 16 with heat and pressure.

Here, the transfer bias applied in each transfer section is determined by changing the transfer section 36Y on the upstream side from the transfer section 36B on the downstream side.
The value is set so as to gradually increase toward K. In the present embodiment, the first transfer unit 36Y is +1
000V, + 1080V for the second transfer unit 36C, + 1200V for the third transfer unit 36M, and 1350V for the fourth transfer unit 36BK. The appropriate bias value of each transfer unit varies depending on the belt resistance of the transport belt, the transfer roller resistance, and the like.

Each of the transfer rollers 32Y to 32BK is a conductive roller in which carbon is dispersed in an elastic roller made of a urethane foam or the like and the resistance value of which is adjusted to 10 ⁴ Ω · cm to 10 ⁸ Ω · cm. If the resistance of the transfer roller is too low, the electric field formed between the transfer roller bias and the surface potential of the photoreceptor belt causes a leak between the photoreceptor belt and the transfer roller, and the photoreceptor belt or photoreceptor layer Pinholes occur On the other hand, if the resistance of the transfer roller is too high, an effective transfer electric field for transferring the toner is not formed, and good transfer cannot be performed.

[0024] As the conveyor belt 14, polyimide, polyethylene Capo Nate, such as by dispersing the conductivity-imparting member such as carbon or ion conductive material on the resin belt Funn resin window of ¹⁰ 10 ~10 ¹⁴ Ω · cm The one adjusted to the resistance is used. When the belt resistance is low, the electric field between the transfer roller and the surface potential of the photoreceptor belt is strengthened, causing a leak and a pinhole in the photoreceptor belt. On the other hand, if the conveyance belt resistance is high, an effective transfer electric field for transferring the toner is not formed, and good transfer cannot be performed.

In this embodiment, the resistance is 5 × 10 ⁵ Ω · c.
A conductive urethane sponge roller having a diameter of 12 mm and a diameter of 12 mm is used as a transfer roller, and a polyimide belt in which carbon is dispersed is used as a transport belt 14. The transport belt had a thickness of 100 μm and a resistance of 1 × 10 ¹² Ω · cm.

In this case, the transfer bias is switched according to the output of a humidity sensor (not shown),
And the first transfer unit 36Y is 100
0V, 1050V for the second transfer unit 36C, 1100V for the third transfer unit 36M, and 1200 for the fourth transfer unit 36BK.
V is set.

Further, the transfer rate of the toner image in the transfer section varies depending on the change rate of the gap formed between the photosensitive belt and the transfer sheet P at the position of the transfer section. Then, the transfer portion 3 of the photosensitive belt 18C of the second color is used.
The transfer rate of the toner image was examined by variously changing the change rate of the gap in 6C.

Here, as shown in FIG. 3, the rate of change of the gap formed by the photosensitive belt 18C and the transfer paper P at the entrance side of the transfer section 36M for the second color is R1, and the rate of change of the gap is at the exit side of the transfer section 36C. The rate of change of the gap formed by the photoreceptor belt 18C and the transfer paper P was R2. The gap A between the photoreceptor belt 18C and the transfer paper P is 10 at the entrance side and the exit side, respectively.
The distance between the portion that becomes 0 μm and the center of the transfer portion 36C is d.
Assuming that 1, d2, the rate of change R1 = 0.1 / d1, and the rate of change R2 is determined by 0.1 / d2.

Then, as shown in FIG. 4, the rate of change R1,
By changing R2 variously, solid images of seven colors were formed by a combination of Y, M, and C, the toner remaining on the photoreceptor belt 18C was taped with a mending tape, and the optical density of the taped sample was measured. The optical density was measured using a Macbeth densitometer. It should be noted that the smaller the diameter of the pulley 20 around which the photoreceptor belt is wound, the more R2,
The value of R1 increases, and the value of R1 decreases as the winding of the photosensitive belt around the pulley 20 decreases.

FIG. 5 shows the measurement results. In the figure, square measurement points indicate the value of R1, and circle measurement points indicate the value of R2. Also, the measurement of R1 is R2 = 0.
R1 was fixed at R1 and the measurement of R2 was performed at R1 = 0.15.

As can be clearly understood from FIG. 5, the transfer other than the Y + C (green) overlap transfer is good regardless of the values of R1 and R2, but only the Y + C overlap transfer depends on the values of R1 and R2. The transfer residue changes. The smaller the value of R1 and the larger the value of R2, the smaller the remaining transfer and the better the transfer.

FIG. 6 shows the change in the charge amount when the toner on the transfer paper P passes through the white area of the second transfer portion 36M when R1 and R2 are changed. It can be seen that the larger the R1 and the smaller the R2, the greater the charge-up of the Y toner. That is, as shown in FIG. 7, when the transfer sheet P passes through the second transfer section 36M, the Y toner transferred onto the transfer sheet P in the first transfer section 36Y is charged up, and the third transfer section 36Y is charged. The transfer electric field at the portion 36C is weakened.

From the above, by superposing R1 of the photoreceptor belt 18M in the second transfer section 36M as small as possible and making R2 as large as possible, that is, by satisfying the relationship of R2> R1, the overlapping transfer of Y + C is performed. Can be performed well. In FIG. 5, when the case where the density of the transfer residual toner is 0.35 or less is regarded as an acceptable level, R1 is set to be equal to 0.1.
It can be seen that transfer of Y + C can be favorably performed when R2 is 0.27 or less and R2 is 0.27 or more.

In FIG. 6, the initial charge amount is 15 μm.
It is desirable that the charge-up of the C / g toner is 20 μC / g. In consideration of this point, R1 is set to 0.2 or less and R2 is set to 0.3 or more, in addition to the measurement result of FIG. Is desirable.

Therefore, R2> R1, R1 ≦ 0.2,
By satisfying the relationship of R2 ≧ 0.3, it is possible to form a good image without transfer omission even when performing Y + C overlap transfer. For example, the pulley 2 of the image forming unit
0 is 20 mm, R1 is 0.15, R2 is 0.7
By setting it to 1, the above relationship is satisfied, and good superimposition transfer is also possible for Y + C.

FIG. 8 shows a color printer according to a second embodiment of the present invention. According to this color printer, the transport belt 14 in the above embodiment is configured as an intermediate transfer belt 40 (transfer target), and as a first transfer unit of each of the image forming units 10Y, 10M, 10C, and 10BK. Transfer brushes 42Y, 42M, 42C,
42BK is used. The toner images formed on the photoreceptor belt of each image forming unit are sequentially transferred onto the intermediate transfer belt 40, and a color image is formed on the intermediate transfer belt. Then, the color image is formed by the driven roller 30b.
Is transferred to a transfer sheet P passing between the transfer roller 44 serving as a second transfer unit that is in rolling contact with the driven roller, and is thereafter fixed on the transfer sheet P by a fixing device (not shown).

The first to fourth transfer portions 36Y, 36M,
In the case of 36C and 36BK, as in the embodiment shown in FIG. 1, a transfer electric field is formed by transfer brushes 42Y to 842BK to which a positive bias having a polarity opposite to the charged polarity of the toner is applied, and Y, M, C, and BK are formed. Are sequentially transferred onto the intermediate transfer belt 40.

The transfer brush used here is a brush made of rayon fiber in which carbon is dispersed.
The resistance value is adjusted to 10 ⁴ Ω · cm to 10 ⁸ Ω · cm. If the resistance of the transfer brush is too low, the electric field formed by the transfer brush and the surface potential of the photoreceptor belt causes
Leaks occur between the photoreceptor belt and the transfer brush, and pinholes occur in the photoreceptor belt or the photoreceptor layer. On the other hand, if the resistance of the transfer brush is too high, an effective transfer electric field for transferring the toner is not formed, and good transfer cannot be performed.

If the thickness of the fibers of the transfer brush is too large, local unevenness in the electric field occurs, which causes transfer roughness. Also,
If it is too thin, the brush may be cut or the transfer brush may be insufficiently pressed against the intermediate transfer belt 40. Therefore, the thickness of the transfer brush is desirably formed in the range of 1D (denier) to 15D. Further, if the brush flock density is too low, transfer unevenness occurs. Therefore, it is necessary to be 70 bundles F / inch or more.

The intermediate transfer belt 40 is formed by dispersing a conductive material such as carbon or an ionic conductive material on a resin belt such as polyimide, polycarbonate, fluorine resin or the like, and has a resistance of 10 ¹⁰ to 10 ¹⁴ Ω · cm. Is adjusted. If the resistance of the intermediate transfer belt is low, the electric field between the transfer brush and the photoreceptor belt is strengthened, causing a leak and a pinhole in the photoreceptor belt. On the other hand, if the resistance of the intermediate transfer belt is high, an effective transfer electric field for transferring the toner is not formed, and good transfer cannot be performed.

The transfer bias in each transfer section is +800 V for the first transfer section 36Y and +840 V for the second transfer section 36M.
V, the third transfer unit 36C is at + 980V, and the fourth transfer unit 3 is
6BK is set to + 1080V. The intermediate transfer belt 40 has a resistance of 1 × 10 ¹¹ Ω · cm and a thickness of 100 × 10 ¹¹ Ω · cm.
μm, the material is a polycarbonate resin, and the transfer brush has a resistance of 5 × 10 ⁵ Ω.

The other structure is the same as that of the embodiment shown in FIG. 1, and the same portions are denoted by the same reference characters and will not be described in detail. The second configured as described above
In the embodiment, similar to the above-described embodiment,
In the transfer section 36M for the second color, the change rates R1 and R2 of the gaps on the entrance side and the exit side are variously changed, so that Y, M, C
Were formed, and the toner remaining on the photoreceptor belt 18C was taped with a mending tape, and the optical density of the taped sample was measured. The optical density was measured using a Macbeth densitometer. R1 and R2 are the diameter of the pulley 20 of the photoreceptor belt,
Various changes can be made by changing the winding angle of the photoreceptor belt with respect to the pulley.

FIG. 9 shows the measurement results. In the figure, square measurement points indicate the value of R1, and circle measurement points indicate the value of R2. Also, the measurement of R1 is R2 = 0.
The measurement was carried out with R1 fixed at 58, and the measurement of R2 was carried out with R1 fixed at 0.14.

As can be clearly understood from FIG. 9, the transfer other than the Y + C (green) overlap transfer is good regardless of the values of R1 and R2, but only the Y + C overlap transfer depends on the values of R1 and R2. The transfer residue changes. The smaller the value of R1 and the larger the value of R2, the smaller the remaining transfer and the better the transfer.

FIG. 10 shows the change in the charge amount when the toner on the transfer sheet P passes through the white background area of the second transfer portion 36M when R1 and R2 are changed. R1
It can be seen that the larger the value of R2 and the smaller R2, the greater the degree of charge-up of the Y toner. That is, as shown in FIG. 7, when the transfer sheet P passes through the second transfer portion 36M,
The Y toner transferred onto the transfer sheet P in the first transfer unit 36Y is charged up, and the transfer electric field in the third transfer unit 36C is weakened.

From the above, by superposing R1 of the photoreceptor belt 18M in the second transfer portion 36M as small as possible and R2 as large as possible, that is, by satisfying the relationship of R2> R1, the overlap transfer of Y + C is performed. Can be performed well. In FIG. 9, when the density of the untransferred toner is 0.35 or less, which is regarded as an acceptable level, R1 is set to 0.1.
It is understood that the transfer of Y + C can be favorably performed when R2 is 0.22 or less and R2 is 0.28 or more.

In FIG. 10, the initial charge amount is 15
It is desirable that the charge-up of the toner of μC / g is 20 μC / g, and in consideration of this point, R1 is set to 0.2 or less and R2 is set to 0.3 or more in addition to the measurement result of FIG. Is desirable.

Therefore, R2> R1, R1 ≦ 0.2,
By satisfying the relationship of R2 ≧ 0.3, it is possible to form a good image without transfer omission even when performing Y + C overlap transfer. For example, the pulley 2 of the image forming unit
0 is 30 mm, R1 is 0.14, R2 is 0.5
By setting it to 8, the above relationship is satisfied, and good superimposition transfer is also possible for Y + C.

The present invention is applicable not only to the above-described four-photosensitive color printer but also to a multi-rotation, one-copy color printer. According to the third embodiment shown in FIG. 11, the photosensitive belt 5 as an image carrier
0 and a transfer drum 52 are used. The photoreceptor belt 50 has three pulleys 51.
(First transfer means). The photoreceptor belt 50 is charged by the charging charger 53 at −400 to −8.
It is charged to about 00V, and a latent image is formed by a laser optical system (not shown). A rotary developing device 54 is provided in contact with the photoreceptor belt 50, and the developing device is integrally formed with developing devices of four colors of Y, M, C and BK. Then, image exposure and development corresponding to each color are sequentially performed on the photoreceptor belt 50, and the color image formed on the photoreceptor belt is transferred to a transfer sheet P electrostatically held on a transfer drum 52. Are sequentially transferred for each corner color. Image formation is Y,
The processing is performed in the order of M, C, and BK.

The transfer roller 56 is used as the second transfer means. The transfer roller 56 is provided inside the transfer drum 52, and faces the pulley 51 via the transfer drum and the photosensitive belt 50.

Here, R1 between the transfer drum 52 and the photosensitive belt 50 is determined by the diameter of the transfer drum, R2 is the diameter of the pulley 51 around which the photosensitive belt 50 is wound,
It is determined by the winding angle of the photosensitive belt around the pulley 51.

Also in the third embodiment, R1, R2
Is set so as to satisfy the above-described relationship, for example, R1
= 0.12 and R2 = 0.35. As a result, good transfer is performed even in Y + C color superposition,
Good color images can be obtained.

According to the fourth embodiment shown in FIG.
A process structure in which the photosensitive belt 60 and the intermediate transfer drum 62 (transfer object) are combined is used. The photoreceptor belt 60 is wound around four pulleys 61 (first transfer means). The photoreceptor belt 60 includes a charging charger 63.
To about -400 V to -800 V, and an electrostatic latent image corresponding to each color is formed by a laser optical system (not shown).

The electrostatic latent images formed on the photoreceptor belt 60 are developed by developing units 64Y, 64M, 64C, and 6 corresponding to their colors.
It is developed by 4BK. The four color images formed on the photoreceptor belt 60 are sequentially transferred onto the intermediate transfer drum 62 in a superimposed manner. Thereafter, the intermediate transfer drum and the transfer roller 66
The transfer paper P is inserted between the transfer paper P and the second transfer unit, and the color image on the intermediate transfer drum 62 is collectively transferred by the transfer bias applied by the transfer roller.

Here, R1 between the photosensitive belt 60 and the intermediate transfer drum 62 is determined by the diameter of the intermediate transfer drum, and R2 is the diameter of the intermediate transfer drum, the diameter of the pulley 61 of the photosensitive belt 60, and the sensitivity to the pulley. It is determined by the winding angle of the body belt.

Also in the fourth embodiment, R1 and R2
Is set so as to satisfy the above-described relationship, for example, R1
= 0.12 and R2 = 0.44. As a result, good transfer is performed even in Y + C color superposition,
Good color images can be obtained.

According to the fifth embodiment shown in FIG.
A multi-rotation, one-copy process structure is used in which a photosensitive drum functioning as an image carrier and an intermediate transfer belt functioning as a transfer object are combined. Photoconductor drum 70
Is charged to about −400 to −800 V by the charging charger 71, and an electrostatic latent image corresponding to each color is formed on the photosensitive drum 70 by a laser optical system (not shown).

The electrostatic latent image formed on the photosensitive drum 70 is developed according to its color by a rotary developing device 72 integrally having four color developing devices of Y, M, C and BK. Is done. After the four color images are sequentially transferred onto the intermediate transfer belt 74 in a superimposed manner, they are collectively transferred onto the transfer paper P passing between the intermediate transfer belt and the transfer roller 76.

The intermediate transfer belt 74 is wound around three pulleys 73, each of which is formed by a 10 ⁶ Ω · cm conductive rubber roller. The transfer from the photosensitive drum 70 to the intermediate transfer belt 74 is achieved by a transfer electric field formed by the transfer bias applied from the pulley 73 functioning as the first transfer unit and the photosensitive drum potential. The transfer roller 76 as the second transfer means is a commonly used known roller.

Here, R1 between the photosensitive drum 70 and the intermediate transfer belt 74 is determined by the diameter of the photosensitive drum 70, and R2 is the diameter of the photosensitive drum, the diameter of the pulley 73, and the intermediate transfer belt for the pulley 73. 74 is determined by the winding angle.

Also in the fifth embodiment, R1 and R2
Is set so as to satisfy the above-described relationship, for example, R1
= 0.12 and R2 = 0.44. As a result, good transfer is performed even in Y + C color superposition,
Good color images can be obtained.

The present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the present invention. For example, the present invention is not limited to a color printer,
The present invention is also applicable to other image forming apparatuses such as a color copying machine.

[0063]

As described in detail above, according to the present invention, at least one of the image bearing member on which the developer image is formed and the transfer member onto which the developer image is transferred from the image bearing member is belt-mounted. And the rate of change R of the gap on the entrance side and the exit side in the transfer portion between the image bearing member and the transfer member.
By setting R1 and R2 so as to satisfy the relationship of R2> R1, an image forming apparatus capable of preventing poor transfer and forming a good color image even when performing discontinuous color overlapping image formation is provided. be able to.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a four-photoreceptor type color printer according to an embodiment of the present invention.

FIG. 2 is an enlarged schematic view showing a transfer unit of the color printer.

FIG. 3 is a schematic diagram showing a gack change rate R1 on the inlet side and a gap change rate R2 on the outlet side.

FIG. 4 is a schematic view showing a state in which R1 and R2 are variously changed.

FIG. 5 is a graph showing the relationship between R1 and R2 and transfer residue.

FIG. 6 is a graph showing a relationship between R1 and R2 and a toner charge amount.

FIG. 7 is a diagram schematically showing a discharge state in a transfer unit.

FIG. 8 is a view schematically showing a quadruple photoreceptor type color printer according to a second embodiment of the present invention.

FIG. 9 is a graph showing a relationship between R1 and R2 and transfer residue in the color printer according to the second embodiment.

FIG. 10 is a graph showing a relationship between R1, R2 and a toner charge amount in the color printer according to the second embodiment.

FIG. 11 is a diagram schematically showing a color printer according to a third embodiment of the present invention.

FIG. 12 is a diagram schematically showing a color printer according to a fourth embodiment of the present invention.

FIG. 13 is a diagram schematically showing a color printer according to a fifth embodiment of the present invention.

[Explanation of symbols]

 10Y, 10M, 10C, 10BK Image forming unit 12 Laser exposure device 14 Transport belt 18Y, 18M, 18C, 18BK Photoconductor belt 20, 51, 61, 73 Pulley 22Y, 22M, 22C, 22BK Charging charger 24Y, 24M, 24C, 24BK developing device 32Y, 32M, 32C, 32BK transfer roller 50, 60 photosensitive belt 62 intermediate transfer drum 70 photosensitive drum 74 intermediate transfer belt 56, 66, 76 transfer belt P… Transfer paper

Claims (8)

[Claims] An image forming means for forming a developer image on an image carrier which moves along a predetermined direction; a transfer member arranged to be in contact with the image carrier at a transfer position; Transfer means for transferring the developer image on the image carrier onto the transfer body at the transfer position, at least one of the image carrier and the transfer body is formed in a belt shape; A rate of change R1 of the gap between the image carrier and the transfer body on the upstream side in the predetermined direction from the position, and the gap between the image carrier and the transfer body on the downstream side in the predetermined direction from the transfer position. Is the rate of change R2 of R2>
An image forming apparatus characterized by being set in a relationship of R1. 2. An image forming means for forming a plurality of developer images of different colors on an image carrier moving in a predetermined direction, and arranged so as to be in contact with the image carrier at a transfer position. A transfer target, and a transfer unit configured to transfer the developer image on the image carrier onto the transfer target at the transfer position, wherein at least one of the image support and the transfer target has a belt shape. The rate of change R1 of the gap between the image carrier and the transfer object at the upstream side in the predetermined direction from the transfer position; and the image carrier and the transfer object at the downstream side in the predetermined direction from the transfer position. And the rate of change R2 of the gap between R2>
An image forming apparatus characterized by being set in a relationship of R1. 3. A plurality of image forming means arranged side by side, each having a belt-shaped image carrier running in a predetermined direction, and forming a developer image on the image carrier, and A transfer unit that is provided in contact with the plurality of image carriers at a plurality of predetermined transfer positions respectively corresponding to the forming unit, and that transfers transfer paper through the plurality of transfer positions; A plurality of transfer means for transferring a developer image on a corresponding image carrier to the transfer sheet, wherein at each of the transfer positions, the image carrier at a predetermined direction upstream of the image carrier from the transfer position The rate of change R1 of the gap between the image carrier and the transfer sheet and the rate of change R2 of the gap between the image carrier and the transfer sheet downstream from the transfer position in the predetermined direction are set in a relationship of R2> R1. An image forming apparatus characterized in that it is. 4. A plurality of image forming means arranged side by side, each having a belt-shaped image carrier running in a predetermined direction, and forming a developer image on the image carrier; An intermediate transfer belt that travels in contact with a plurality of predetermined transfer positions respectively corresponding to the forming unit; and a plurality of second transfer belts that transfer a developer image on a corresponding image carrier to the intermediate transfer belt at each of the transfer positions. 1 transfer means, and second transfer means for transferring the developer image transferred on the intermediate transfer belt to transfer paper, wherein at each of the transfer positions, a predetermined direction of the image carrier from the transfer position The rate of change R1 of the gap between the image carrier and the intermediate transfer belt on the upstream side, and the rate of change R2 of the gap between the image carrier and the intermediate transfer belt on the downstream side in the predetermined direction from the transfer position are: Is an image forming apparatus, wherein R2> R1 is set. 5. A belt-shaped image carrier running along a predetermined direction; image forming means for forming a plurality of developer images of different colors on the image carrier; Provided in contact with the carrier,
A transfer roller configured to transfer a transfer sheet to the transfer position; and a transfer unit configured to transfer a developer image on the image carrier to the transfer sheet at the transfer position. The rate of change R1 of the gap between the image carrier and the transfer drum on the upstream side of the image carrier in the predetermined direction, and the change rate of the gap between the image carrier and the transfer drum on the downstream side in the predetermined direction from the transfer position. An image forming apparatus, wherein the rate of change R2 is set in a relationship of R2> R1. 6. A belt-shaped image carrier running along a predetermined direction, image forming means for forming a plurality of developer images of different colors on said image carrier, and said image at a predetermined transfer position An intermediate transfer drum provided in contact with a carrier, a first transfer unit configured to transfer a developer image formed on the image carrier onto the intermediate transfer drum at each of the transfer positions; A second transfer means for transferring the developer image transferred onto the transfer drum to transfer paper, wherein the transfer position is an intermediate position between the image carrier and the image carrier at a predetermined direction upstream of the image carrier from the transfer position. A rate of change R1 of the gap between the transfer drum and the rate of change R2 of the gap between the image carrier and the intermediate transfer drum downstream of the transfer position in the predetermined direction is set to have a relationship of R2> R1. Features that are An image forming apparatus. 7. A drum-shaped image carrier which rotates along a predetermined direction; image forming means for forming a plurality of developer images of different colors on the image carrier; An intermediate transfer belt provided in contact with a carrier and traveling along a predetermined direction; and a first transfer for transferring a developer image formed on the image carrier onto the intermediate transfer belt at the transfer position. Means, and a second transfer means for transferring the developer image transferred onto the intermediate transfer belt to transfer paper, wherein at the transfer position, the upstream side of the image carrier in a predetermined direction from the transfer position is provided. The rate of change R1 of the gap between the image carrier and the intermediate transfer belt and the rate of change R2 of the gap between the image carrier and the intermediate transfer belt downstream from the transfer position in the predetermined direction are R2> Set to R1 relationship An image forming apparatus characterized in that it is. 8. The image forming apparatus according to claim 1, wherein R1 is set to 0.2 or less, and R2 is set to 0.3 or more.