JPH07210007A - Image forming device - Google Patents

Abstract

PURPOSE:To make the improvement of transfer efficiency compatible with the prevention of jamming at a separation part and to obtain a high-quality transfer image without transfer irregularities or separation repelling in an image forming device using a photoreceptive drum whose drum diameter is >=70mm or a photoreceptive drum whose radius of curvature at a transfer and separation part is >=35mm. CONSTITUTION:The image forming device is constituted so that a toner image is formed by developing an electrostatic latent image formed on an image carrier by the electrostatic charge toner of a developing means and electrostatically transferred on a transfer material supplied from a paper supply part and passed through the image carrier and a transfer means 18. Besides, it is constituted so that the transfer material is separated from the image carrier by a separation means. Then, the transfer means 18 is constituted so that plural elastic electrical conductive wires 181 are arrayed in a direction orthogonally crossed to the carrying direction of the transfer material and bent in U-shaped. Besides, both ends of the wires 181 are fixed to a holding member 182 so that the bent top parts thereof are made to press-contact with the surf ace of the image carrier.

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 utilizing an electrostatic transfer process such as an electrostatic copying machine and an electrostatic printer, and more particularly to an image forming apparatus utilizing a contact transfer means such as a transfer roller. . 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 circumference of the image carrier is long. 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. Further, in such a color image forming apparatus, since a large amount of toner adheres to the photosensitive drum for the superposed color, a large amount of transfer current is required, and separation becomes more difficult. The present invention has been made to solve such a problem, and solves the above problems and achieves the following objects, and an image in which stable and good transferability and separability are obtained. A 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) To form a good color image on a transfer material by measuring the compatibility between transfer and separation in the process of superposing toner images of respective colors on an image carrier.

(3) To obtain a high-quality transferred image without uneven transfer or white spots due to separation cissing.

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

[0011]

The above object of the present invention is to develop an electrostatic latent image formed on an image bearing member with a charged toner of a developing unit to form a toner image in the present invention. In the image forming apparatus, in which the image carrier is fed from a paper feeding unit and electrostatically transferred to a transfer material passing between the image carrier and the transfer means, and the transfer material is separated from the image carrier by a separating means. A plurality of conductive wires having elasticity are arranged in a direction perpendicular to the transfer material conveying direction, the conductive wires are curved in a U-shape, and both ends thereof are fixed to a holding member. This is achieved by an image forming apparatus characterized in that the curved top of the above can be pressed against the surface of the image carrier.

Further, in the image forming apparatus of the present invention, the transfer means is formed by bending an elastic conductive net into a U-shape and fixing both ends thereof to holding members, and transferring the curved top portion of the conductive net. It is characterized in that it is arranged in a direction orthogonal to the material conveying direction, and that the curved top portion can be pressed against the surface of the image carrier.

[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.

At the peripheral edge of the photosensitive drum 10, a developing device 14 (14Y) in which a developer composed of toner such as yellow (Y), magenta (M), cyan (C), black (K) and a carrier is built in, respectively. , 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 a layer forming means in an amount of
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.

Photosensitizer: OPC, diameter 100 mm, linear velocity 74 m
m / sec, negative charging Charging conditions: Charging wire: Platinum wire (clad or alloy) is preferably used. _VH : -750V, _VL : -50
V (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 diameter of the laser light is narrowed 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 employs lens focal length: f = 140 mm Dot Clock: 20MH _Z bi chromatography beam diameter: about 60 × 80 [mu] m The toner supplied from the (developed) toner replenishment box is dropped on the right end portion of the developing unit, opposite direction Is stirred and mixed with the carrier by a pair of stirring screws 142 rotating in
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 current image between clearance: 0.5mm preparative Na over conveyance amount: 20-30 mg / cm ² developing bias _{(AC): 2.4KV PP, 8KH} Z (DC): -650V developing sleeve rotation direction: the photosensitive drum On the other hand, normal image density adjustment: development sleeve rotation speed control or development bias control (a standard printing plate is formed on the photoconductor by a laser beam and the reflection density is measured after development to adjust the image density). Control: L detection method (paper feed) The 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 provided. The recording paper P has a cantilever structure and is located on the reference surface side of the recording paper P in a biased manner.

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 / Separation) Transfer means 18 is a photosensitive drum
The position of 10 with respect to the peripheral surface is variable, and when printing a single color image, it is always placed in a pressure contact state as shown in FIG.
During the formation of the color image, it is retracted and kept in a separated position, and is pressed into contact only during transfer. On the other hand, the separating means 19 also press-contacts and separates from the peripheral surface of the photoconductor drum 10 substantially in synchronization with the position change of the transfer means 18.

In the apparatus of this embodiment, the transfer means 18 with an applied voltage of +3 to 4 KVDC is used, and the separating means 19 is applied with a bias voltage in which DC and AC are superposed.

(Fixing) Fixing device provided in the apparatus of this embodiment
Reference numeral 20 denotes a so-called heat roller type fixing device composed of a pair of rollers, which is composed of an upper roller 201 which has a built-in heater and which is driven and rotated clockwise, and a lower roller 202 which is driven to rotate by being pressed against the upper roller 201. The recording paper P is heated and conveyed by the nip portion formed between them to fuse the toner image.

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 Means) Next, the structure of the above-mentioned transfer means 18 will be described.

FIG. 3 is a sectional view of the transfer means 18, and FIG. 4 is a perspective view of each embodiment of the transfer means 18. FIG. 3A shows a transfer means.
18 is a cross-sectional view showing a state where 18 is separated from the surface of the image carrier 10. FIG.

A plurality of thin conductive wires 18 having elasticity
Both ends of 1 are planted in parallel with each other in the conductive holding members 182A and 182B at equal intervals, and each conductive wire 181 has an inverted U-shape protruding upward. The envelope of the inverted U-shaped apex of each conductive wire 181 is straight so as to be orthogonal to the transport direction A of the recording paper P. Reference numeral 183 is an insulating support member.

The conductive wire 181 used in Experimental Example 1 had a diameter of 100 μm of Achilles non-spark JS type (manufactured by Achilles Co., Ltd.) and was planted on the holding members 182A and 182B at a pitch (p) of 5 mm. . The radius R of the U-shape is 12
mm and height H were 12 mm. In the transfer means 18 of Experimental Example 2, a copper wire having a diameter of 50 μm was formed in a mesh shape with an interval of 2 mm, and was installed in the inverted U shape. Transferring means 18 of Experimental Example 3
Then, carbon fibers having a diameter of 100 μm were installed at a pitch (p) of 0.8 mm.

FIG. 3B is a cross-sectional view showing a transfer state in which the transfer means 18 is moved and pressed against the image carrier 10 via the recording paper P during transfer. In this pressure contact state, the plurality of conductive wires 181 elastically deforms the recording paper P to the image carrier 10.
The toner image can be transferred uniformly by bringing the toner image into close contact with the surface. The appropriate range of this pressure contact force varies depending on the elasticity of the wire 181, but is 5 per length of the wire 181 in the longitudinal direction.
8-100 / cm is preferable. The nip width formed at that time is preferably 0.5 to 20 mm.

In FIG. 4A, both ends of a plurality of conductive wires 181 are planted between holding members 182A and 182B, respectively.
The exposed middle part is installed in a curved shape.

In FIG. 4B, the plurality of curved conductive wires 181 are transversely connected to each other by a plurality of other conductive wires 184 in a direction orthogonal to the conveying direction of the recording paper P. Thus, the conductive wire 181 is prevented from falling. It should be noted that the conductive wires 184 connected in the transverse shape may be arranged in an inclined arrangement instead of the illustrated horizontal arrangement to prevent the recording paper P from being caught.

FIG. 4C shows another embodiment of the transfer means 18, which is formed by intersecting a plurality of conductive wires 185 in a mesh shape. The above conductive wire
It is also possible to manufacture the 185 by forming a net-like shape by fitting a large number of small holes in a single conductive thin plate having elasticity.

(Separating Means) With respect to the belt photosensitive member and the small-diameter photosensitive member, the small radius of curvature of the separating portion can be used to separate the recording paper only by 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 made into a roller shape, and metal needles, conductive filaments, conductive webs, etc. are projected on the peripheral surface of the cylinder.

(Experimental Example) Exposed light source; Semiconductor laser; Photosensitizer; Drum or belt provided with organic photoconductive layer on aluminum substrate; OPC photoreceptor containing Y-type titanyl phthalocyanine; Toner (Yellow Y, Magenta M, Cyan C, Black K): 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-MM
Copolymer A-Photosensitive drum (10); Diameter 100 mm, linear velocity 74 mm / sec-Transfer means (18); Example 1; Achillesnon Spark JS type, diameter 100 μm Example 2; Copper wire, diameter 50 μm Example 3: Carbon fiber, diameter 100 μm ・ Separation brush (19); Stainless steel wire brush (Fig. 5)
(See (B)) Projection length of metal wire (191) from holding member 5 mm, spacing between metal wire bundles 2 mm, metal wire diameter 100 μm, non-spark JS type (manufactured by Achilles Co., Ltd.)-Separated from transfer means (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 means 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 means 18 and the separation brush 19 are in pressure contact with the surface of the photosensitive drum 10 only when the recording paper P is passed. That is, when the transfer means 18 is fed from the nip position to the position 5 mm upstream from the nip position, the leading edge of the recording paper P starts 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 obtained by superposing 2.4KV _PP and 8KH _Z AC on -650V _DC , respectively.

[0068]

[Table 1]

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

[0070]

[Table 2]

Table 2 shows the results of the print tests using the experimental examples of the various transfer means 18 and the conventional transfer brush.

In the experimental example (1), as the conductive wire 181, an Achilles non-spark JS type (manufactured by Achilles Co., Ltd.),
As shown in FIG. 4 (A), a diameter of 100 μm was planted at a pitch of 5 mm, and this was installed in a curved shape. In the experimental example (2), as the conductive wire 181, a copper wire having a diameter of 50 μm is formed in a mesh shape with a pitch of 2 mm as shown in FIG. 4 (C), and is laid in a curved shape. Experimental example (3)
Is a carbon wire having a diameter of 100 μm is used as the conductive wire 181, and the carbon fiber is laid at a pitch of 0.8 mm in a curved shape shown in FIG. 4 (A). These experimental examples (1),
In both (2) and (3), the curved top portion of the conductive wire 181 is elastically pressed against the image carrier 10 with the recording paper P sandwiched therebetween, and the durability is small with the aging, so that Table 2 As shown in, the high transfer rate is always obtained both at the start of printing and after printing 100,000 sheets, and good transfer image quality is obtained.

On the other hand, a conventional conductive wire is shown in FIG.
The transfer means of the comparative example planted in an upright state as shown in (A) causes transfer cissing at the start of printing, and when the 100,000 sheets are printed, the conductive wire is significantly frayed or broken,
In either case, the transfer rate is remarkably reduced, and the transfer image quality is impaired.

FIG. 6 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, transfer means 18, separation brush 19, and cleaning device 22 are provided.

Since the photosensitive belt 103 around the driving roller 101 having a diameter of 70 mm or more has a problem in transfer / separation like the large-diameter photosensitive drum 10 described above, the structure of the transfer means is the same as that described above. By setting the material and size range of the conductive wire, it is possible to improve the transfer rate, the toner concentration of the transferred image, and the transferred image quality.

[0076]

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.
This is effective for improving the transfer rate by stabilizing the transfer current, improving the toner density of the transferred image, and improving the image quality of the transferred image in an image forming apparatus using a photosensitive drum of mm or more. 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 separation unit.

FIG. 3 is a sectional view of a transfer unit.

FIG. 4 is a perspective view of various transfer means.

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

FIG. 6 is a sectional view showing another embodiment of the 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 transfer means 181,184,185 conductive wire 182 holding member 183 supporting members 19 separating means (separator brush) 20 fixing device 22 cleaning unit I _t transfer current I _s separation current P recording paper (transfer material)

Claims (6)

[Claims] 1. An electrostatic latent image formed on an image bearing member is developed with a charged toner of a developing means to form a toner image,
Image formation in which the toner image is electrostatically transferred to a transfer material which is sent from a paper feeding unit and passes between the image carrier and a transfer unit, and the transfer member is separated from the image carrier by a separating unit. In the apparatus, the transfer means comprises a plurality of conductive wires having elasticity arranged in a direction orthogonal to the transfer material conveying direction, the conductive wires are curved in a U shape, and both ends thereof are fixed to a holding member. An image forming apparatus, wherein a curved top portion of the conductive wire can be pressed against the surface of the image carrier. 2. An electrostatic latent image formed on an image carrier is developed with a charged toner of a developing means to form a toner image,
Image formation in which the toner image is electrostatically transferred to a transfer material which is sent from a paper feeding unit and passes between the image carrier and a transfer unit, and the transfer member is separated from the image carrier by a separating unit. In the apparatus, the transfer means is formed by bending an elastic conductive net into a U-shape and fixing both ends thereof to a holding member, and arranging curved tops of the conductive net in a direction orthogonal to a transfer material conveying direction. An image forming apparatus, wherein the curved top portion can be pressed against the surface of the image carrier. 3. The image carrier is a drum-shaped image carrier having a diameter of 70 mm or more, or a radius of curvature of at least a transfer portion of 35.
The image forming apparatus according to claim 1 or 2, wherein the image forming body is a belt-shaped image carrier having a size of at least mm. 4. The superimposed toner images of a plurality of colors are formed on the image carrier by the plurality of developing units, and the superimposed toner images are formed on a transfer material by the transfer unit. The image forming apparatus according to claim 1. 5. A bias for superimposing an alternating current component on a direct current component in a developing region where the developing device faces the image bearing member carrying the electrostatic latent image and the developing device carrying a two-component developer. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a non-contact two-component reversal developing means using an electric field. 6. The image forming apparatus according to claim 1, further comprising a separating unit provided on a downstream side of the transfer unit for conveying the transfer material, the separating unit including a separating brush.