JPH0798548A - Image forming device - Google Patents

Abstract

PURPOSE:To realize stable transfer and stable separation by executing the separation by a bias current consisting of a DC or DC, and AC components and controlling a transfer means by a constant current in a device using a specified photoreceptor drum or a photoreceptor drum whose radius of curvature at a transfer and separation part is set to be within a specified range. CONSTITUTION:The position of a transfer roller 18 is variable with respect to the circumferential surface of the photoreceptor drum 10 and the roller 18 is always made to press-contact with it when a monochromatic image is printed. However, it is held at a position where it is retreated and separated from the drum 10 while a color image is formed and made to press-contact with the circumferential surface of the drum 10 only when the color image is transferred. A separation brush 19 is also made to press-contact and separated with/from the circumferential surface of the drum 10 synchronously with the positional fluctuation of the roller 18. Then, the surface of the roller is cleaned by a blade at the impressed voltage of +3 or 4KVDC. Besides, the bias voltage obtained by superimposing the DC and the AC components is impressed on the brush 19 and a transfer current is controlled by the constant current. Thus, jamming is hardly caused at a separating time in comparison with a constant voltage control system and a high-quality transferred image without image omission or defective transfer is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrostatic copying machine or an electrostatic printer which utilizes an electrostatic transfer or electrostatic separation process, and more particularly an image forming apparatus which uses a contact transfer means such as a transfer roller. It is about. Further, the present invention relates to a color image forming apparatus for forming a color toner image by superimposing at least two monochromatic toner images on an image carrier.

[0002]

2. Description of the Related Art In electrostatic copying machines and electrostatic printers using electrophotography, corona dischargers have been widely used as a charging / transferring device. However, the corona discharger requires a high voltage of 5 to 10 KV and has problems such as generation of ozone due to discharge. Therefore, in recent years, a contact charging method and a transfer roller method aiming at low voltage and ozoneless have been attracting attention as alternative technologies.

The transfer roller method has been put into practical use in recent years because it has the advantages that the amount of ozone generated is smaller than that in the conventional transfer by corona discharge and there is no transfer unevenness due to dirt on the discharge wire. .

Known techniques for controlling the current and voltage in the transfer roller system include Japanese Patent Publication No. 52-33494 and Japanese Patent Application Laid-Open No. 50-19456.
JP-A-52-45344 and JP-A-2-123385.

[0005]

An image carrier such as a photoconductor drum, a photoconductor belt, a dielectric drum or the like has a diameter of 70 mm or less, or a radius of curvature of 35 mm or less at a transfer portion or a separation portion. In that case, so-called curvature separation was possible by the rigidity of the transfer material (recording paper or the like) (stiffness, stiffness of paper or the like) without particularly providing a separating means.

In a color image forming apparatus in which toner images of respective colors are superposed on a photosensitive drum, a toner image for one image has to be formed on an image carrier, and the toner image of one round of the image carrier must be formed. The length must be longer than the image length. Therefore, the diameter of the photoconductor drum is inevitably increased, which makes it difficult to separate the transfer material due to its rigidity. Also,
In such a color image forming apparatus, the superimposed color is
Since a large amount of toner adheres to the photosensitive drum, there is a problem that compatibility between superposed colors and single colors does not exist when transfer is performed by constant voltage control using a transfer roller.

The present invention has been made in order to solve the above problems, and solves the above problems and achieves the following objects to provide stable and good transferability and separability. The resulting image forming apparatus is provided.

(1) To achieve both transfer and separation in an image forming apparatus using a drum-shaped image carrier having a diameter of 70 mm or more, or a belt-shaped image carrier having a curvature radius of 35 mm or more at least at a transfer portion or a separation portion.

(2) The compatibility of transfer and separation is measured in the process of superimposing toner images of respective colors on the image carrier to form a good color image on the transfer material.

(3) To obtain a high-quality transferred image free from uneven transfer and white spots due to separation cissing.

(4) To provide a process that does not generate ozone due to high-voltage discharge or nitride and does not cause deterioration of a photoreceptor or deterioration of image quality due to these.

[0012]

The image forming apparatus of the present invention which achieves the above object is a drum-shaped image bearing member having a diameter of 70 mm or more, or a belt-shaped image bearing member having a radius of curvature of 35 mm or more at least at a transfer portion or a separation portion. Image carrier, charging means for uniformly charging the image carrier, exposure means for forming an electrostatic latent image on the image carrier, developing means for developing the electrostatic latent image to obtain a toner image An image forming apparatus having a transfer means for electrostatically transferring the toner image onto a transfer material and a separating means for separating the transfer material on which the toner image is transferred from the surface of the image carrier, wherein the separating means is a direct current Alternatively, at least a means for electrostatically separating by a bias current composed of a direct current and an alternating current component is provided, and when the transfer material passes through a transfer portion formed between the image carrier and the transfer means, the transfer means is Constant current control The is characterized in that provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the structure and operation of a color printer which is an example of the image forming apparatus of the present invention will be described with reference to FIG.

In this color printer, toner images of respective colors sequentially formed on an image carrier are superposed, and then transferred at one time on a recording paper at a transfer portion to form a color image, and thereafter, an image is separated by a separating means. It is a color image forming apparatus of the type that is peeled from the surface of a carrier.

In the figure, reference numeral 10 is a photosensitive drum which is an image bearing member, and is an OPC photosensitive member (organic photosensitive member) formed by coating on a drum substrate, which is grounded and driven and rotated clockwise in the drawing. 12 is a scorotron charger, which is a photosensitive drum 10
A uniform charge of V _H is applied to the peripheral surface by a corona discharge wire and a corona discharge wire that holds the potential at V _G. Prior to the charging by the scorotron charger 12, exposure is performed by a PCL (pre-charging static eliminator) 11 using a light emitting diode or the like to eliminate the history of the photoconductor until the previous printing, and the peripheral surface of the photoconductor is neutralized. deep.

After the photosensitive drum 10 is uniformly charged, the image exposing means 13 performs image exposure based on the image signal.
The image exposure means 13 is a means for performing a main scan in which an optical path is bent by a reflection mirror 134 through a polygon mirror 131, an fθ lens 132, and a cylindrical lens 133 which rotate using a laser diode (not shown) as a light emitting source. A latent image is formed by (sub scanning). In this embodiment, the character portion is exposed, and the character portion has a lower potential V _L.
To form a reverse latent image.

Around the periphery of the photosensitive drum 10, a developing device 14 (14Y) containing a developer containing toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier is incorporated. , 14M, 14C, 14K), and first, the development of the first color yellow is carried out by the developing sleeve 141 which has a magnet built therein and rotates while holding the developer. The developer consists of a carrier in which ferrite is used as a core and is coated with an insulating resin around it, and a toner whose main component is polyester and pigments according to the color and charge control agents, silica, titanium oxide, etc. are added. The agent is applied to the developing sleeve 141 by the layer forming means in an amount of 100 to 60.
The layer is regulated to a layer thickness (developer) of 0 μm and conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.2 to larger than the layer thickness (developer).
As 1.0mm, D of the AC bias and V _DC of V _AC during this time
The C bias is superimposed and applied. Since V _DC and V _H and the toner are charged with the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion, which has a higher potential than V _{DC, and} has a potential higher than V _DC. attached to a lower V _L portion of visualized (reversal development) is carried out.

After the visualization of the first color is completed, the process proceeds to the magenta image forming process for the second color, and the scorotron charger 12 again.
Uniform charging is performed, and a latent image based on the image data of the second color is formed by the image exposure unit 13. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M ′ and V _M ′. In the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
When the latent image of is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M > V
_It may be an intermediate potential that becomes _L.

An image forming process similar to that for the magenta of the second color is performed for the cyan of the third color and the black of the fourth color, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, one sheet of transfer material (recording paper) P that has been unloaded from the paper feed cassette 15 via the half-moon roller 16 is temporarily stopped, and when the transfer timing is adjusted, the transfer operation is performed by the rotation operation of the paper feed roller 17. Is fed to the area.

In the transfer area, the transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 10 in synchronization with the transfer timing.
The supplied recording paper P is sandwiched and the multicolor image is transferred at once.

Next, the recording paper P is discharged at almost the same time by a separating brush 19 which is brought into a pressure contact state, separated by the peripheral surface of the photosensitive drum 10 and conveyed to a fixing device 20, where a heat roller (upper roller) 201 and a pressure roller ( After the lower roller) 202 is heated and pressed to fuse the toner, the toner is ejected to the outside of the apparatus via the paper ejection roller 21. The transfer roller 18 and the separation brush 19 are retracted and separated from the peripheral surface of the photosensitive drum 10 after the recording paper P has passed, to prepare for the next toner image formation.

On the other hand, the photosensitive drum 10 from which the recording paper P is separated
Removes and cleans the residual toner by pressing the blade 221 of the cleaning device 22, and again receives the charge removal by the PCL 11 and the charge by the charger 12 to start the next image forming process. The blade 221 immediately moves after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 10.

The features of the functions and performances of the respective equipments constituting the image forming section of the above apparatus will be described below.

(Photosensitive member) The photosensitive drum 10 is stably rotated so that the OPC photosensitive member on the peripheral surface is uniformly charged by the scorotron charger 12. During charging, the grid potential is controlled to stabilize the charging potential.
The specifications of the photoconductor and the charging conditions thereof are set as follows as an example. In particular, JP-A-64-17066 and JP-A-2-18
OPCs using Y-type titanyl phthalocyanine or polycrystalline titanyl phthalocyanine described in JP-A No. 3258, JP-A-2-183265 and JP-A No. 3-128973 are preferable.

Photoconductor: OPC, diameter 120 mm, linear velocity 100
mm / sec, negative charging Charging conditions: Charging wire: Platinum wire (clad or alloy) is preferably used. _VH -850V, _VL -50V (image exposure) OPC photoconductor on the peripheral surface of photoconductor drum 10 is a charger.
After being negatively charged by 12, the semiconductor laser unit 135 of the image exposing means 13 is exposed to light to form an electrostatic latent image.

Image data from the formatter which decodes the printer command is sent to the laser diode (LD) modulation circuit, and when the LD of the semiconductor laser unit emits light by the modulated image signal, the beam light is changed by the beam index. The scanning lines are synchronized and projected onto the polygon mirror 131.

The polygon mirror 131 reflects and scans the beam light on its polyhedron. The scanning light is beam-corrected by the fθ lens 132 and the cylindrical lens 133, and then the photoconductor is exposed through the reflecting mirror 134. Main scanning is performed to form an electrostatic image.

The beam system of laser light is narrowed down to an equivalent of 600 DPI by an optical system. Therefore, in order to obtain a high quality image, it is necessary to reduce the particle size of the toner. In this embodiment, toner of 8 μm size is used for each color. But most important to the user is the black text quality,
The black toner is preferably a small particle size toner (7 μm to 11 μm).

As the image exposure optical system, for example, one having the following construction is used.

Polygon mirror: 6 faces, rotation speed 23600rp
m, Air bearing adopted Lens focal length: f = 140mm Dot clock: 20MH _Z beam diameter: Approximately 60 × 80μm (Development) The toner supplied from the toner replenishing box is dropped to the right end of the developing device and rotates in opposite directions. Is stirred and mixed with the carrier by a pair of stirring screws 142,
It is set to a predetermined charge amount (Q / M).

On the other hand, the toner density is detected by the magnetic permeability detection method (L detection method), and the toner supply amount is controlled based on the output frequency to set the toner density value to about 5 to 7%.

The agitated two-component developer is supplied to the supply roller 143.
Is conveyed to the developing sleeve 141 via the layer thickness regulating member 144.
Is transferred to the developing area of the photosensitive drum 10 as a thin layer, and reversal development of the electrostatic latent image is performed under the developing conditions described below.

The development gap: 0.5mm toner transport amount: 20-30 mg / cm ² developing bias _{(AC): 2KV, 8KH Z} (DC): -750V developing sleeve rotation direction: forward image density adjusting the photosensitive drum: Development sleeve rotation speed control or development bias control (a standard printing plate is formed on the photoconductor by a laser beam, the reflection density is measured after development to adjust the image density) Toner density control: L detection method (paper feed) Recording paper P Is stored in the paper feed cassette 15 on the basis of one side. Therefore, the separating claw 151 is provided only on the reference surface side of the recording paper P, and the half-moon roller 16 is also cantilevered to the reference surface side of the recording paper P. It is located on one side.

The paper feeding section has a dedicated motor, and the half-moon roller 16 rotates in the direction of the arrow to move the recording paper P stacked on the push-up plate 152 by the action of the separating claw 151 to the uppermost layer. Carry out only one.

The recording paper P carried out from the paper feed cassette 15 enters the carrying path and makes a U-turn, and the leading end thereof is the registration roller 17
Immediately after passing the sheet, the motor is temporarily stopped by the detection of a paper feed sensor (not shown), and then the motor starts to rotate again at the timing when the transfer timing is adjusted, and the transfer area is maintained at a predetermined angle with respect to the photoconductor surface. To be paper.

On the other hand, manual feeding is performed by rotating the manual feeding tray 153 located on the front surface of the apparatus main body from the position shown by the one-dot chain line in FIG. 1 to the position shown by the solid line.

The manually fed paper is picked up by a pickup roller 154.
Is conveyed by the rotation of, and is fed to the transfer area via the registration roller 17.

Paper to be manually fed is not limited to the general recording paper P of 16 lbs to 24 lbs which is usually used, and 36
Examples include lbs thick paper and OHP transparency sheets. Further, by removing the manual paper feed tray 153 and installing a dedicated feeder as an option, it is possible to feed envelopes.

(Transfer) The transfer roller 18 has a variable position with respect to the peripheral surface of the photoconductor drum 10, and is always placed in a pressure contact state as shown in FIG. 2 at the time of printing a single color image, but during the formation of a color image. It is retracted and kept in a separated position, and is pressed into contact only during transfer. On the other hand, the separation brush 19 also presses and separates from the peripheral surface of the photoconductor drum 10 in synchronism with the position variation of the transfer roller 18.

The apparatus of this embodiment uses a transfer roller 18 in which the applied voltage is +3 to 4 KVDC and the roller surface is cleaned by a blade.
A bias voltage in which DC and AC are superposed is applied to 19 for use.

(Fixing) Fixing device provided in the apparatus of this embodiment
As shown in FIG. 3, reference numeral 20 denotes a so-called heat roller type fixing device composed of a pair of rollers, which is an upper roller 201 having a built-in heater H and rotating in a clockwise direction, and a driven roller which is pressed against the upper roller 201. The recording paper P is heated and conveyed by the nip portion formed between the lower roller 202 and the lower roller 202, and the toner image is fused.

Both the upper and lower rollers 201 and 202 are covered with a heat-resistant tube, and the nip portion is formed in a substantially linear shape by pressure contact, so that wrinkles on the paper surface which are likely to occur when an envelope or the like is conveyed are prevented. To be done.

The temperature of the peripheral surface of the upper roller 201 is controlled by being detected by a temperature sensor 205 such as a thermistor to be kept within a predetermined temperature range, and dirt adhering to the toner by welding is pressed against the cleaning roller 203. Removed and cleaned by. The cleaning roller 203 is replaced with a new one when the number of printed sheets is about 40,000. Also,
If the fixing heater is not used for a certain period of time SLEE
It becomes P mode and energy saving is controlled.

Further, when a transparency sheet used for OHP is used as a transfer material, the periphery of the upper roller 201 is smoothed for the purpose of smoothing the toner image surface to prevent irregular reflection in order to improve the transmittance of the color toner image. Silicon oil is applied to the roller surface by the oil pad 204 on the surface.

Therefore, in the apparatus of this embodiment, the transfer material conveying speed can be switched among three stages of 100 mm / sec, 50 mm / sec and 12.5 mm / sec, and three types of plain paper, envelope and transparency sheet can be selected. It has a mode in which the transfer material of can be used and is used for a wide range of applications.

The set temperature of the upper roller 201 can be lowered to about 180 ° C. by using a toner that melts at a low temperature, and the oil pad 204 is sponge material (porous PTFE coating). By using, the uneven pressure is eliminated and uniform oil application is realized.

(Transfer roller) Next, the above-mentioned transfer roller
The configuration of 18 will be described.

FIG. 4A is a sectional view of a single-layer type transfer roller 18. In the figure, the transfer roller 18 includes a shaft body (core bar) 181 made of a stainless steel rod, and a resin material such as polyurethane rubber, silicone rubber, styrene-butadiene copolymer elastomer, and olefin elastomer on the outer periphery of the shaft body (cell size 10). -100 μm foam type or open-cell type, and a conductive elastic part capable of supplying electric charge, in which the resin material is mixed with an inorganic substance such as carbon black and / or an organic conductive agent as a conductivity-imparting agent.
It is composed of 182 and. As the elastic portion 182, a polyurethane resin rubycell roller (manufactured by Nitto Kogyo Co., Ltd.) was used.

FIG. 4B shows a coating type transfer roller 18
FIG.

This transfer roller 18 comprises polyvinylidene fluoride (PVDF), polyamide 6 (nylon 6), polyamide 66 (nylon 66) and polyethylene terephthalate (on the outer peripheral surface of the elastic portion 182 of the single layer type transfer roller described above. PET), perfluoroacrylate resin (PF
A), surface coating layer portion 183 made of polyester resin or the like
Is provided with a film thickness of 5 to 100 μm. By providing the coating layer portion 183, the surface of the transfer roller 18 can be easily and reliably cleaned, and the maintainability is improved.

FIG. 4C shows a coating type transfer roller 18
It is sectional drawing which shows the other Example.

The transfer roller 18 has a medium resistance layer portion 184 as an outer layer of an elastic portion 182 provided on the outer peripheral surface of the shaft body 181, and the coating layer portion 183 formed on the outer peripheral surface thereof. is there. For the intermediate resistance layer portion 184, a material capable of optimally controlling electric resistance can be selected. This makes the elastic part
182 can have a required elasticity, and the middle resistance layer portion 184 can be a function separation type having a required conductivity imparting property. The electrical resistance is measured by, for example, pressing both ends of the roller shaft against a conductive plate such as Al with a force of 500 g and measuring the resistance value of the conductive plate and the roller shaft in units of Ω to measure the elastic layer and the coating layer. It can be converted from the total layer thickness and the forming nip area to the unit of Ω · cm.

The electric resistance of the transfer roller 18 is 10
It is preferably ² Ω · cm to 10 ¹⁰ Ω · cm.

The rubber hardness of the transfer roller 18 is 60 ° or less as measured by a rubber hardness meter (JIS-K6301 Asuka-C).
(Scale hardness) is preferred.

In the roller transfer by the transfer roller 18, the transfer roller 18 is brought into direct contact with the back surface of the recording paper P, the toner is pressure-contacted, and an electric property having a polarity opposite to that of the toner is applied to the transfer roller 18 to perform the transfer. .

(Separation Means) With respect to the belt photosensitive member and the small diameter drum photosensitive member, the small radius of curvature of the separating portion can be used to separate the recording paper only with the steel property, but the shape of the photosensitive member is restricted. In addition, stable high-speed separation is achieved by using it in combination with AC static elimination separation in high-speed machines and the like. In the AC charge elimination separation, the recording paper is eliminated by AC corona or high-voltage AC immediately after transfer to reduce the electrostatic attraction force of the recording paper to the photoconductor, and it is separated by utilizing the rigidity and dead weight of the paper. is there. However, if the AC charge removal is too strong, transfer defects such as image dropouts tend to occur, and if it is weak, it becomes difficult to separate thin recording papers with weak rigidity. Therefore, it is necessary to set the balance of charge removal in consideration of the recording paper type and environment. There is. Various embodiments of the separating means by high-voltage AC static elimination are shown in FIGS. 5 (A) to 5 (E).

FIGS. 5A and 5B are perspective views of the separating brush 19 in which a metal wire 191 such as a stainless steel wire or an aluminum wire is arranged on the holding member 192 in one or more rows.
(A) shows a dense array type, and (B) shows a sparse array type. The metal wire 191 (filament) has a diameter of 0.01 to 0.1 mm, and the protruding length of the metal wire from the holding member 192 is 3 to 5 mm. In the sparse array type shown in FIG. 5 (B), it is possible to obtain a preferable result as a separating effect when the bundles of the metal wires 191 are arranged at intervals of 2 to 5 mm. Instead of the metal wire 191, it is also possible to use a separation brush using a thread in which a conductivity-imparting agent is added to rayon or the like.

In FIG. 5C, instead of the metal wire 191, a metal needle 193 having a small spherical shape with a tip radius of curvature of 100 μm is implanted in the holding member 192.

In FIG. 5D, the tip of the conductive static elimination tape 194 is formed in a sawtooth shape and is sandwiched by the holding members 192. Examples of the conductive static elimination tape 194 include Teijin Metallian static elimination tape (manufactured by Teijin Ltd.) and Syntron 9212 (Shin
manufactured by tron Fabric).

In FIG. 5 (E), each of the above-mentioned separation brushes is in the shape of a roller, and metal needles, conductive filaments, conductive webs, etc. are projected on the peripheral surface of the cylinder.

(Experimental example) -Exposure light source; Semiconductor laser-Photoconductor; Drum or belt provided with organic photoconductive layer on aluminum substrate, OPC photoreceptor containing Y-type titanyl phthalocyanine-Developer; Toner (yellow) Y, magenta M, cyan C, black BK): particle size of each toner 7.5 μm, charge amount -20 μC / g, toner concentration 7% carrier: particle size 45 μm,
Cu-Zn-Ferrite, St-MMA copolymer coating ・ Photoreceptor drum (10); Diameter 100mm, linear velocity 74mm / sec ・ Transfer roller (18) ； Roller outer diameter 24mm, elastic part (18
2) is a polyurethane-based rubycell roller (Nitto Kogyo Co., Ltd.)
(Manufactured) (measured electrical resistance between shaft 181 and roller outer periphery when 100 V is applied, 5.0 × 10 ⁴ Ω), coating layer part (183) is PVDF (see FIG. 4 (B)) ・ Separation brush (19) ; Stainless steel wire brush (Fig. 5
(Refer to (B)) Projection length of the metal wire (191) from the holding member is 5 mm, spacing between each metal wire bundle is 2 mm, metal wire diameter is 100 μm, non-spark JS type (manufactured by Achilles Co., Ltd.)-Separated from transfer roller (18) Arrangement and operation of the brush (19): The separation brush 19 is arranged in the vicinity of the vertically lower portion of the photoconductor drum 10 and is movable toward the center of the photoconductor drum 10.

The transfer roller 18 is arranged at an interval of about 15 mm on the peripheral surface of the photosensitive drum 10 on the upstream side of the separating brush 19 and is movable in the center direction of the photosensitive drum 10.

The transfer roller 18 and the separation brush 19 are pressed and nipped on the surface of the photosensitive drum 10 only when the recording paper P is passed. That is, when the transfer roller 18 is fed from the nip position to the position 5 mm upstream from the nip position, the leading end of the recording paper P starts the pressure bonding. Then, when the paper is not passed, it is separated from the surface of the photosensitive drum 10.

Surface potential of the photoconductor drum 10 The surface potential of the photoconductor drum 10 is controlled to be −750V at the positions of the developing devices 14Y, 14M, 14C and 14K facing the developing sleeves 141, respectively.

Developing bias The developing bias of each of the developing devices 14Y, 14M, 14C and 14K is set to −650V _DC at 2.4KV _PP , 8KH _Z and AC.

[0069]

[Table 1]

Table 1 above shows the amount of each color toner adhering to the photosensitive drum 10. The following experimental data were obtained under these conditions. In the table, Y is yellow toner, M is magenta toner, and C.
Is a cyan toner, K is a black toner, R (red) is a superimposed color of the above Y toner and M toner, and G is G.
(Green) is the superimposed color of Y toner and C toner, B
(Blue) indicates an overlapping color of M toner and C toner.

[0071]

[Table 2]

Table 2 summarizes the relationship between the transfer current I _t and the separation current I _s from the experimental results using the single-layer type transfer roller 18 without the coating layer shown in FIG. 4A. . According to Table 2, in the embodiment of the present invention that the constant current control to the transfer current I _t to + 20 .mu.A, the separation voltage V _s by the type of recording paper passes through the transfer-separation site will vary, less separation jam, A high-quality transferred image having no transfer defects such as missing images was obtained. On the other hand, as shown in the comparative example, in the conventional constant voltage control method, when the transfer voltage V _t is controlled to be constant, the separation jam increases, the image density becomes low, and the partial white spots due to the image repelling occur. To occur.

[0073] Also, when the set constant current control to the + 30 .mu.A transfer current I _t is improved separation performance and transfer quality. That is, the transfer current I _t + 20 .mu.A, even when set to either + 30 .mu.A, by constant current control, high transfer rate for various recording paper, less occurrence of separation jams, good transfer quality can be obtained I understand.

[0074]

[Table 3]

Table 3 shows the coating layer portion 18 shown in FIG. 4 (B).
3 is data obtained by experimenting the separability using the transfer roller 18 having the number 3. That is, the coating layer portion 183 is PVD having a film thickness of 100 μm.
F, transfer roller 18 has a total resistance of 1 × 10 ⁶ Ω transfer roller 1
With 8, it is applied to the transfer current I _t of + 25 .mu.A to the transfer roller 18. When fed various recording paper, but the separation voltage V _s varies, by constant current control of the transfer current I _t,
High transfer rate, less occurrence of separation jam, and good transfer image quality can be obtained.

FIG. 6 is a characteristic diagram showing the results of a comparative study using black toner on the difference between the constant current control mode (invention) and the constant voltage control mode (prior art) for the transfer current depending on the paper quality of various recording papers. Is.

FIG. 6A shows the results of measuring the black toner (BK) transfer density of various recording papers P ₁ , P ₂ , P ₃ , P ₄ , P ₅ using the constant current source according to the present invention. It is a characteristic diagram.
The recording paper used for the test is 20 Lbs paper for the Xerox copier (P
_1), the same 241Lbs paper (P _2), 110kg for Konica copiers
(P ₃ ), 55 kg paper (P ₄ ) and 55 kg recycled paper (P ₅ )
It is a kind. As shown, if the constant current control transfer current I _t in the range of 7～14Myuei, stamp by characteristic curves substantially coincide with the black toner density of each recording sheet P ₁ to P ₅ are almost constant at The density difference is small regardless of which recording paper is used for copying.

On the other hand, as shown in the characteristic of FIG. 6B, in the prior art in which the transfer voltage V _t is controlled by a constant voltage using a constant voltage power source, the various recording papers P _{1 to} P ₅ are used. The characteristic curves greatly differ, and the variations in the black toner density between the recording sheets are large.

FIG. 7 is a characteristic showing the result of comparative examination of the difference between the constant current control mode (invention) of the transfer current and the constant voltage control mode (prior art) depending on the paper quality of the various recording papers P _{1 to} P _5. It is a figure.

FIG. 7A is a diagram showing the black toner (BK) transfer characteristics of the various recording papers P _{1 to} P ₅ described above using the constant current source according to the present invention. In the figure, each line segment AB indicates a range in which a good transfer image can be obtained. The left side of the point A in the figure has a low density of black toner (BK), and the right side of the point B is a separation site where the image is repelled. The generated transfer image is partially thinned, and the image quality is poor in both the left and right regions other than AB. But if the constant current control transfer current I _t is in the range of 8～14Myuei, even with the recording sheet P ₁ to P ₅ of any good images are obtained.

FIG. 7B shows the result of a comparative example in which various recording papers P _{1 to} P ₅ are transferred and separated by the conventional constant voltage control.
In this comparative example, the areas in which the transferred image is good differ greatly depending on each recording paper, and constant voltage control by the common transfer voltage V _t is impossible.

FIG. 8 is a diagram showing the results of comparative examination of the difference between the constant current control and the constant voltage control mode in the color image forming apparatus using color toner (Y, M, C, K or R, G, B). Is.

[0083] FIG. 8 (A), the constant current control mode according to the present invention, transfer image good region between the line segment A-B is in the range of the common transfer current I _t = 10~15μA the respective color toners Therefore, if a constant current control current is set in this area, a good color transfer image can be obtained.

On the other hand, in the constant voltage control mode according to the prior art, there is no area of the transfer voltage V _t common to the toners of the respective colors, and a well-balanced and good color transfer image cannot be obtained.

As the constant current control device used for the constant current control, for example, Trek Mode manufactured by Trek (USA)
Using a 610-C high-voltage power supply / amplification / control device, constant current control of the transfer current according to the present invention (however, the voltage limit was 6 kV) and constant voltage control in the comparative example (however, the current limit was
50 μA was set) and the above comparison data was prepared.

FIG. 9 is a sectional view of a color printer showing another embodiment of the image forming apparatus to which the invention is applied. In addition, about the code | symbol used in drawing, the same code | symbol is attached | subjected to the part which has the same function as FIG. Further, the points different from the above embodiment will be described. Around the photosensitive belt (image carrier) 103 wound around the driving roller 101 and the driven roller 102 and rotatable, a scorotron charger 12, an image exposure unit (semiconductor laser light scanning device) 13, and a developing device 14Y. , 14M,
14C, 14K, a transfer roller 18, a separation brush 19, and a cleaning device 22 are provided.

[0087] photosensitive belt 103 whose diameter wound over the driving roller 101 70 mm, since the problem similarly transferred and isolation large径感light drum 10 described above occurs, in the same way as described above the transfer current I _t By controlling the constant current of
Under the conditions common to each color toner, the transfer rate is improved, separation jam is prevented, and the transfer image quality is improved.

[0088]

According to the present invention, the radius of curvature of the photosensitive drum having a drum diameter of 70 mm or more, or the transfer / separation portion is 35.
An image forming device using a photosensitive drum of mm or larger, effective for improving the transfer rate, preventing jams in the separation section, and improving the image quality of the transferred image under the conditions common to various recording papers and toners of each color. is there. In particular, it was applied to a color image forming apparatus in which toner images of respective colors are superposed on an image carrier, and compatibility of transfer and separation was achieved and a good color image was obtained.

[Brief description of drawings]

FIG. 1 is a sectional configuration diagram of a color printer as an example of an image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view of a main part of a transfer part.

FIG. 3 is a sectional view of a main part of a fixing device.

FIG. 4 is a cross-sectional view of various transfer rollers.

FIG. 5 is a perspective view of various separating means.

FIG. 6 is a characteristic diagram showing a density comparison of different transfer power control methods when black toner is used depending on the paper quality of various recording papers.

FIG. 7 is a characteristic diagram comparing the differences on the image quality of different transfer power supply control methods depending on the paper quality of various recording papers.

FIG. 8 is an image quality comparison characteristic diagram of different transfer power supply control methods in a color image forming apparatus using color toner.

FIG. 9 is a sectional view showing another embodiment of a color printer to which the invention is applied.

[Explanation of symbols]

10 photoconductor drum (image carrier) 103 photoconductor belt (image carrier) 11 PCL (pre-charging static eliminator) 12 scorotron charger 13 image exposure means 14, 14Y, 14M, 14C, 14K developing device 15 paper feed cassette 18 a transfer roller (transfer unit) 181 shaft 182 elastic portion 183 covering layer portion 19 separated brush (separation means) 20 fixing device 22 cleaning unit I _t transfer current V _t transfer voltage _{P, P 1, P 2,} P 3, P 4 , P ₅ recording paper (transfer material)

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area G03G 21/14

Claims (4)

[Claims] 1. A drum-shaped image carrier having a diameter of 70 mm or more, or a radius of curvature of 35 mm at least at a transfer portion or a separation portion.
The above belt-shaped image carrier, charging means for uniformly charging the image carrier, exposure means for forming an electrostatic latent image on the image carrier, developing the electrostatic latent image to form a toner image. An image forming apparatus comprising: a developing unit for obtaining the toner image, a transferring unit for electrostatically transferring the toner image onto a transfer material, and a separating unit for separating the transfer material on which the toner image is transferred from the surface of an image carrier.
When the separating means has at least means for electrostatically separating by a direct current or a bias current composed of a direct current and an alternating current component, and the transfer material passes through a transfer portion formed between the image carrier and the transfer means. An image forming apparatus characterized in that a power source for controlling the transfer means with a constant current is further provided. 2. The image forming apparatus according to claim 1, wherein the transfer unit is a transfer roller. 3. The image forming apparatus according to claim 1, wherein the separating unit is a conductive brush. 4. The developing means is composed of a plurality of developing devices having different toner colors, and superimposing development of at least two colors is performed on the image carrier, each developing method being a bias composed of a DC component and an AC component. The image forming apparatus according to claim 1, wherein non-contact reversal development is performed by applying a current.