JPH11327326A - Transferring device for electrophotographic printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transferring device for electrophotographic print capable of substantially making an electric field laid on a nip part uniform, and obtaining a composite image with an excellent transfer accuracy. SOLUTION: Relating to this transferring device for the electro-photography the toner image 104 developed by the electrophotographic process is transferred from web 102 to a paper sheet 110 by the press contact force and the electric field. In such a case, a transfer auxiliary roller for holding the paper sheet 110 in between with a transferring roller 120 through the web 102 is formed of a insulating material, and the transferring roller is formed of an ion conductive material having 10 to 40 degree Ascker C hardness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer apparatus for electrophotographic printing on a recording medium of a hard copy output device such as a printer and a copying machine using an electrophotographic recording process using multicolored toner inks. Things.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram schematically showing a conventional electrophotographic printer device disclosed in Japanese Patent Publication No. 6-105377. In FIG. 5, reference numeral 20 denotes a transfer belt formed of a conductive material (for example, polyimide or polycarbonate in which carbon is dispersed). The transfer belt 20 is wound around three rollers 21, 22, and 23. It is driven in the direction of arrow 28. Belt-shaped photoreceptor 30 wrapped around rollers 38 and driven in the direction of arrow 29
The image developed above is transferred to the individual image transfer station 3
At 1, the image is transferred to the transfer belt 20. The composite toner image is transferred to an image receptor embodied on paper 35 at composite image transfer station 32. The plate electrodes 36 and 37 are in contact with the inside of the transfer belt 20. The photoreceptor belt 30 rotates around a roller 38 at the transfer station 31. The voltage source 47 is connected to a brush 49, and the brush 49 comes into contact with the surface of a transfer roller 45 formed of a conductive material (for example, urethane rubber or silicon rubber in which carbon is dispersed). The transfer roller 45 is maintained at a negative potential. The transfer roller 45 is moved so as to sandwich the paper 35 with the transfer belt 20 during the transfer of the composite image.
Moved away from zero.

Next, the operation will be described. An image of the first color (yellow) is developed on the photoreceptor 30 by exposure means and developing means (not shown). In this state, the image is transferred to the transfer belt 20 at the image transfer station 31 by rotating the photoreceptor 30 in the direction of the arrow 29. Then, the image of the second color (cyan) is developed on the photoreceptor 30 in the same manner as described above, and this image is transferred to a predetermined position (a position overlapping with the first color) of the transfer belt 20 at the image transfer station 31. I do. Further, a third color (magenta) image is developed on the photoreceptor 30, and this image is transferred to a predetermined position (a position overlapping the first and second colors) of the transfer belt 20 by the image transfer station 31.

After the three color images have been transferred onto the transfer belt 20, a sheet 35 is supplied to the composite image transfer station 32 by a sheet supply means (not shown). At the same time, the transfer roller 45 moves upward in FIG. 5, and presses the transfer belt 20 and the paper 35 with the transfer roller 45 and the transfer auxiliary roller 58 formed of an insulating material (for example, urethane rubber or silicon rubber). Then, the composite image formed on the transfer belt 20 is transferred to the paper 35. At this time, the transfer belt 2
An electric field is applied between the toner and the paper 35 so that the toner that has been positively charged and transferred on the sheet 0 can be reliably transferred to the paper 35. That is, it is configured by the grounded plate electrode 36, the transfer belt 20, the transfer roller 45, the brush 49, and the voltage source 47.

In the conventional electrophotographic printing apparatus, the transfer roller 45 and the transfer auxiliary roller 58 form a nip at the composite image transfer station 32 so that the composite image can be transferred to the paper 35 satisfactorily. A uniform electric field needs to be applied between the belt 20 and the transfer roller 45. However, as described above, the transfer roller 4
5 is formed by dispersing carbon in urethane rubber or silicone rubber, so that the slight unevenness of the dispersion of carbon causes the electric field applied to the nip portion to be uneven, thereby deteriorating the transfer accuracy of the composite image. there were.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and provides an electrophotographic printing transfer apparatus in which an electric field applied to a nip portion is substantially uniform and a transfer accuracy of a composite image is high. The purpose is to:

[0007]

According to the present invention, there is provided a transfer apparatus for electrophotographic printing, comprising: an image carrier for carrying a toner image developed by an electrophotographic process;
A transfer roller formed of an ion conductive material having a temperature of 0 to 40 degrees and holding the printing medium with the image bearing means to transfer the toner image to the printing medium at the transfer station; And an electric field generating circuit for generating an electric field for transferring the toner image carried by the image carrying means to the printing medium. The transfer roller preferably has an Asker C hardness of 25 degrees, and the transfer roller is made of ethylene oxide, NaCl, and NaBr, which exhibit a high dielectric property on urethane rubber.
And one chosen from the herd consisting of AlCl ₃ 8: 1
Is desirable.

The image bearing means includes a web formed of a conductive material and carrying a toner image, and a transfer auxiliary roller formed of an insulating material and holding a printing medium between the transfer roller and the web via the web. The electric field generating means is provided at a position distant from the transfer station on the downstream side, and has a grounding means for contacting the web and a voltage source for applying a negative voltage to the transfer roller. Furthermore, in a transfer process environment, the electrical resistance of the web between the transfer station and the grounding means is at least 10 times the resistance of the transfer roller.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a sectional view of a main part of an electrophotographic printing transfer apparatus according to Embodiment 1 of the present invention. In FIG. 1, an electrophotographic printing transfer device 10 is shown.
Reference numeral 0 denotes a belt-shaped web 102 (image carrying means), and a ground roller 10 which rotates while electrically contacting the web 102.
6 (grounding means), transfer assist roller 120, transfer roller 1
30, a voltage source 136 and the like. Web 102
Is formed of a conductive material having a surface resistance of 10 ⁷ Ω / □ to 10 ⁹ Ω / □ (for example, polyimide or polycarbonate in which a carbon filler is dispersed), and forms a toner image (composite image) not shown. It carries the toner image 104 formed by the device. Transfer station 112
The resistance value of the web 102 from the roller to the ground roller 106 is 1
To 0 ⁷ Ω~10 ⁸ Ω a position, to place the ground roller 106. Although the case where the grounding roller 106 is used as the grounding means has been described, a grounding plate similar to the conventional example may be used.
6 is preferably used. Further, since the ground roller 106 is provided on the downstream side in the moving direction of the web 102, that is, on the downstream side of the transfer station 112,
2 Since the electric field between the upstream web 102 and the transfer roller 130 is very weak,
The amount of the toner 104 scattered on the paper 110 before the medium 10 (printing medium) enters is very small, and it is possible to perform transfer with high printing accuracy.

The transfer assisting roller 120 has a resistance of about 1013Ω by JIS A hardness of 30 to 60 degrees (preferably 45 degrees), and is fixed to the rotating shaft 122 at the center thereof. It follows and rotates in the direction of arrow E. A negative voltage is applied to the transfer roller 130 by a voltage source 136, and a resistance value of 104Ω to 106Ω is formed by an ion conductive material having an Asker C hardness of 10 to 40 degrees (preferably 25 degrees). 132, paper 110 (recording medium)
Is rotated in the direction of arrow D following the movement in the direction of arrow A. The transfer roller 130 is configured to be movable in the directions of arrows B and C. When the transfer roller 130 is below the solid line in FIG.
Reference numeral 30 contacts the blade 134 to remove toner and the like attached to the transfer roller 130. On the other hand, when the transfer roller 130 is at an upper position (a position indicated by a broken line), that is, during transfer, the sheet 110 is pressed against the web 102 to
2 is transferred to the paper 110. Here, the Asker C hardness is a hardness that is recently used for measuring the hardness of a very soft material, and is, for example, a hardness represented by an Asker rubber hardness meter manufactured by Kobunshi Keiki Co., Ltd.
An Asker hardness of 25 degrees is approximately equivalent to JIS A 4 to 5 degrees. In addition, the ion conductive material is a polymer material,
An ionic compound such as an antistatic agent and a metal salt is added to make it conductive, and the ionic compound is chemically dispersed (bonded) to the polymer and the material, so the carbon filler is physically dispersed. It is a material having a much better uniformity of conductivity than the electron conductive material. Transfer roller 130
When the hardness is less than 10 degrees in Asker hardness, the length of the nip portion 114 contributing to the transfer becomes unnecessarily long, and the pressing force becomes non-uniform. In some cases, the length of the nip portion 114 cannot be obtained, and image loss may occur. When the Asker hardness is 25 degrees, the length of the nip portion 114 has a particularly appropriate value, and a sufficient length of the nip portion 114 for transfer is obtained.
Desirable pressing force and electric field can be applied between 0 and the toner 114, and highly accurate transfer can be performed.

FIG. 2 is an enlarged sectional view showing the vicinity of the transfer station 112 of FIG. 1 during transfer. In FIG. 2, reference numeral 114 denotes a nip portion where the paper 110 is sandwiched between the transfer assist roller 120 and the transfer roller 130, and a pressing force acts between the transfer assist roller 120 and the transfer roller 130. The pressing force is defined by a straight line connecting points 120A and 120B, which are both ends of a range where the transfer assisting roller 120 contacts the web 102,
The pressing force is such that the straight line connecting the points 130A and 130B, which are both ends of the range where the transfer roller 130 contacts the sheet 110, is substantially parallel. 104A-1
04F is a toner for forming the toner image 104. Further, since the hardness of the transfer auxiliary roller 120 is higher than the hardness of the transfer roller 130, as shown in FIG.
Then, the transfer roller 130 is more greatly deformed. There is an effect that a nip having an appropriate width is formed and transfer is improved. That is, if both the transfer roller 130 and the transfer auxiliary roller 120 have a high hardness, the toner 104
Is applied too much, and the toner 104 is crushed and adhered to the web 102 to cause transfer failure.

In the first embodiment, the image carrying means is formed by the web 102 and the transfer auxiliary roller 120,
The electric field generating circuit includes a ground roller 106, a ground 108, a web 102, a toner image 104, a paper 110, and a transfer roller 13.
0, voltage source 136, and ground 138.

Next, the operation will be described. The toner image 104 is carried on the web 102 in the same manner as in the above-described conventional example shown in FIG. That is, when a printing command is issued by a control unit (not shown), a toner image is formed on a photosensitive belt (not shown) by an exposure unit and a developing unit (not shown).
At the transfer station (not shown), the toner image
The image is transferred to the web 102 and the web 102
4 is carried. In the case of a color image, the web 102 carries a composite image of three colors (yellow, magenta, cyan) or four colors (yellow, magenta, cyan, black). During this time, the transfer roller 130 is located below the solid line in FIG.

Next, the control unit (not shown) controls the paper 11
When a transfer instruction to “0” is issued, the paper 110 is supplied to the transfer station 112 at a predetermined timing so that the toner image 104 is transferred to a predetermined position on the paper 110.
Note that the position of the toner image 104 on the web 102 is detected by a sensor (not shown) (or may be detected by the drive timing of a driving unit (not shown) of the web 102). Paper 110 is nip 114
, The transfer auxiliary roller 120 and the transfer roller 1
30 and the electric field E, the toner 104B, 1
04C and 104D are transferred to the sheet 110. That is,
The toner 104A is the toner transferred to the sheet 110, and the toners 104E and 104F are the toner before being transferred to the sheet 110.

As described above, since the transfer roller 130 is formed of an ionic conductive material having an Asker hardness of 25 degrees, the transfer roller 130 is sufficiently soft and has a uniform conductivity and a uniform conductive material (carbon is dispersed in a filler). (There is no local bias in conductivity as in the case of the material), and a sufficient pressing force and electric field can be applied between the sheet 110 and the toner 114 by obtaining a sufficient nip 114 length for transfer. , High-accuracy transfer can be performed. Furthermore, since the transfer is performed by combining the transfer roller 130 formed of an ion conductive material having an Asker hardness of 25 degrees with the image carrying means including the transfer assisting roller 122 and the web 102, image transfer due to overpressurization can be prevented. A clear image without transfer density unevenness due to bias of electric conductivity can be obtained.

Embodiment 2 Hereinafter, another embodiment of the present invention will be described. FIG. 3 is a diagram showing a relationship between the electric conductivity ρ and the temperature T of the ionic conductive material. The vertical axis represents the logarithm of the electric conductivity ρ (Ω · m), and the horizontal axis represents the temperature T (K). FIG.
As shown in FIG. 7, it can be seen that the electrical conductivity of the ionic conductive material changes depending on the temperature. Although this characteristic differs depending on the polymer material used and the ionic compound to be added, the characteristic qualitatively obtained as shown in FIG. 3 was obtained. For example, ethylene oxide and N
aCl (or NaBr, AlCl ₃ ) at a ratio of 8: 1 was added to a material having an outer diameter of φ22, an inner diameter of φ12, and a width of 320 m.
m when the shape of the transfer roller 130 is 283
(K) 10 ^8.5 (Ω), temperature 300 (K) 10
^7.0 (Ω). That is, it was found that when the temperature changes by 11 degrees, the electrical resistance value of the transfer roller 130 changes by one digit.

The transfer roller 130 and the web 10
It is necessary that a constant electric field acts regardless of the environment in order to maintain high transfer accuracy. Hereinafter, the electrical characteristics will be discussed. FIG. 4 is an electrical equivalent circuit of the electric field generating circuit shown in FIGS. In FIG. 4, R10
2 is a resistance value of the web 102 from the transfer station 112 to the ground roller 106, and the resistance value is 10 ⁷ Ω.
It is a ~10 ⁸ Ω. The resistance value R102 needs to be in this range from the viewpoint of transfer accuracy. For example, the resistance value R1 is the transfer current is increased in the following 10 ⁷ Omega, there is a problem causing transfer unevenness concentrated local current is 10 ⁸
Above Ω, there is a problem that the time constant of Expression 1 described below increases, the charge Q decreases, and the electric field E decreases. C is a capacitor formed by the paper 110 and the toner 104, R130 is a resistance value of the transfer roller 130, and a voltage source 136 is a DC voltage of about 1000V (V136). Since the resistance value R130 changes depending on the temperature as described above, the transfer roller 1 is not affected by the temperature change.
A configuration in which a constant electric field acts between the web 30 and the web 102 will be described.

Assuming that the capacitance of the capacitor C110 is C, the stored charge is Q, the transit time of the nip 114 is t, and the current flowing through the circuit is I, the charge Q is expressed by the following equation (1). Q = C × V × {1-exp (−t / R / C)} (Equation 1) where V = V136−I × R (Equation 2) R = R102 + R130 (Equation 3)

As described above, the resistance value R102 is 10 ⁷
Since it is necessary to be Ω to 10 ⁸ Ω, it is sufficient to satisfy this condition and to make the electric charge Q of Expression 1 hardly fluctuate due to a change in temperature. That is, the resistance value R130
Should be sufficiently smaller than the resistance value R102. Preferably, the resistance value R130 is always constant under the use conditions of the transfer device.
Is formed to be less than or equal to one-tenth of the resistance value R102. That is, the resistance value R102 hardly changes with respect to the temperature, while the resistance value R130 at the lowest temperature at which the transfer device can be used becomes the maximum (see FIG. 3). 10 ⁶ Ω to 1
May be formed transfer roller 130 such that 0 ⁷ Omega. That is, the transfer roller 130 having a resistance value R130 of 10 ⁶ Ω to 10 ⁷ Ω or less may be used.

Since the configuration is as described above, the first embodiment
In addition to the effect described above, a substantially constant electric field acts between the transfer roller 130 and the web 102 regardless of the environment (with respect to a change in temperature), and high-accuracy transfer can be performed. In addition, since the transfer roller 130 may be formed of the ionic conductive material so as to have the above-described desired resistance value, that is, since a compensation circuit / control circuit for a temperature change is unnecessary, the apparatus can be made compact, electrically and mechanically. The structure can be configured so that failures are less likely to occur, and maintenance becomes easy. Since the resistance of the transfer roller formed by dispersing the carbon filler in the polymer in the related art hardly changes with temperature, the resistance of the transfer auxiliary roller is 10 ^7.
And Ω~10 ⁸ Ω was substantially the same value.

In the above description, the resistance value R130 is always one-tenth of the resistance value R102 under the use conditions of the transfer device.
Although an example in which the transfer roller 130 is formed as described below has been described, a temperature sensor and a temperature compensation circuit are provided,
The voltage of the voltage source 136 is transferred to the transfer roller 1 according to the temperature.
It may be configured such that an almost constant electric field acts between the web 30 and the web 102. In this case, a temperature sensor and a temperature compensation circuit are required, and the configuration is slightly more complicated than the above configuration.

In the first and second embodiments, a color printing apparatus for forming a toner image 104 as a composite (color) image on the web 102 and transferring the toner image 104 to the paper 110 has been described. May be formed on the web 102 and transferred to the same paper 110 for each color. The printing apparatus may be a monochrome printing apparatus that forms a single-color image on the web 102 and transfers the single-color image to the paper 110. In addition, while a composite image is formed at a transfer station (not shown), that is, a double transfer system has been described, a composite image may be formed by directly exposing and developing on the web 102. Further, the image carrying means is constituted by the web 102, the transfer assisting roller 120 and the like, but may be of a drum type.

[0023]

As described above, the present invention is formed by an image carrying means for carrying a toner image developed by an electrophotographic process and an ion conductive material having an Asker C hardness of 10 to 40 degrees. A transfer roller for sandwiching the printing medium with the image carrying means and transferring the toner image to the printing medium, and when the image bearing means is sandwiched, the toner image carried on the image bearing means is covered with the toner image. Since an electric field generating circuit for generating an electric field to be transferred to a printing medium is provided, a substantially uniform electric field acts on the transfer station, so that highly accurate transfer can be performed. In addition, a clear image without transfer density unevenness due to bias of electric conductivity can be obtained.

The image carrying means has a web formed of a conductive material and carrying a toner image, and a transfer assisting roller formed of an insulating material and holding a printing medium between the transfer roller and the web via the web. The electric field generating means is provided at a position distant from the transfer station on the downstream side, and has a grounding means for contacting the web and a voltage source for applying a negative voltage to the transfer roller. This has the effect of suppressing the generation of an electric field, suppressing toner scattering on the upstream side, and preventing image bleeding.

Further, in a transfer process environment, the electrical resistance of the web between the transfer station and the grounding means is at least 10 times the resistance of the transfer roller, so that the structure is simple and independent of environmental changes. An almost uniform electric field acts on the transfer station, so that transfer with higher precision can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an electrophotographic printing transfer apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing the vicinity of a transfer station in FIG. 1 during transfer.

FIG. 3 is a diagram showing a relationship between electric conductivity ρ and temperature T of an ionic conductive material according to Embodiment 2 of the present invention.

FIG. 4 is an electrical equivalent circuit of the electric field generating circuit shown in FIGS. 1 and 2.

FIG. 5 is a configuration diagram schematically showing a conventional electrophotographic printer.

[Explanation of symbols]

103 web, 104 toner image, 106 ground roller, 110 paper, 112 transfer station,
114 nip portion, 120 transfer assist roller, 13
0 Transfer roller, 136 voltage source.

Claims (6)

[Claims] 1. An image carrying means for carrying a toner image developed by an electrophotographic process, and an ion conductive material having an Asker C hardness of 10 to 40 degrees, and cooperating with said image carrying means at a transfer station. A transfer roller for holding the printing medium and transferring the toner image to the printing medium; and transferring the toner image carried by the image holding means to the printing medium when the image holding means is sandwiched. And an electric field generation circuit for generating such an electric field. 2. The transfer roller has an Asker C hardness of 2
2. The transfer device for electrophotographic printing according to claim 1, wherein the angle is 5 degrees. 3. The transfer roller according to claim 1, wherein the urethane rubber material is made of ethylene oxide, NaCl, Na
_3. A material to which one selected from the group consisting of Br and AlCl ₃ is added.
The transfer device for electrophotographic printing according to the above. 4. The transfer roller according to claim 1, wherein the urethane rubber material is made of ethylene oxide, NaCl, Na
_{3. The} transfer device for electrophotographic printing according to claim 1, wherein the material is a material obtained by adding one selected from the group consisting of Br and AlCl _{3 at} a ratio of 8: 1. 5. The image carrying means includes a transfer supporting roller formed of a conductive material and carrying a toner image, and a transfer auxiliary roller formed of an insulating material and sandwiching a printing medium with the transfer roller via the web. The electric field generating means is provided at a position distant from the transfer station on the downstream side, and has a grounding means for contacting the web, and a voltage source for applying a negative voltage to the transfer roller. 5. The transfer device for electrophotographic printing according to any one of 1 to 4. 6. The electrophotography according to claim 5, wherein the electrical resistance of the web between the transfer station and the grounding means is at least 10 times the resistance of the transfer roller in a transfer process environment. Transfer device.