JP2000206802A - Image forming device - Google Patents

Abstract

(57) Abstract: A separation claw is inserted between a transfer material onto which an image has been transferred and a transfer material carrier, and a separation bias is applied to a separation and static elimination means to remove electricity from the transfer material and the transfer material carrier. When separating the transfer material, the transfer material can be separated by preventing the separation claw marks on the image and the transfer omission. [Solution] Multiple transfer is performed on the transfer material on the transfer drum, and the final color The leading end of the transfer material onto which the black toner image (K) has been transferred reaches the separation unit 0.5 seconds earlier than the time S1, and the separation bias (AC + DC) AC is applied to the separation neutralizer.
Turn ON only the components, remove electricity from the separation claw, and then
Seconds later, that is, when the leading end of the transfer material reaches the separation section,
The DC component of the separation bias is turned on, and the original separation bias is applied. While the transfer material passes through the separation section, the application of the separation bias is continued, and when the transfer material passes, the separation bias is turned off.
I do.

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 for forming an image by an electrophotographic method or an electrostatic recording method, which is used in a copying machine, a printer, a facsimile, and the like, and in particular, a transfer carried on a transfer material carrier. The present invention relates to an improvement in a technique for separating a transfer material from a transfer material carrier after an image is transferred to the material.

[0002]

2. Description of the Related Art As shown in FIG. 2, there is known an electrophotographic image forming apparatus having a transfer drum 5a as a transfer material carrier, and a drum-shaped electrophotographic image carrier as an image carrier. A toner image is formed on a photosensitive drum 1, which is a photosensitive member, and the toner image is transferred to a transfer material such as paper carried on a transfer drum 5a.

In the case of a color image, for example, magenta, cyan, yellow, and black toner images are sequentially formed on the photosensitive drum 1, and each time a toner image of each color is obtained, the toner image is transferred onto the transfer drum 5a. The transfer is performed in a superimposed manner on the transfer material carried on the sheet.

The transfer material after the transfer is transferred to a transfer drum 5a.
Then, the toner image is melted and fixed on the transfer material by heating and pressurizing in the fixing device 9, so that a monochrome image (usually a black and white image) or a color image is obtained on the transfer material.

In the transfer drum 5a, a transfer sheet 5f as a transfer material holding member is wound in a cylindrical shape on a frame body in which a pair of rings are connected by a connection member 5j.
The front and rear ends of f are attached to the connecting member 5j. The transfer sheet 5f is for electrostatically adsorbing and supporting the transfer material, and is made of a dielectric film such as a polycarbonate resin (PC) having a thickness of 150 μm and a volume resistivity of 10 ¹⁵ Ωcm or more. Prior to image formation, the transfer sheet 5f
By applying AC biases of opposite phases to the internal and external static eliminators 5d and 5e, static elimination is performed to almost 0V.

The transfer material is supplied from the direction of arrow B to the transfer drum 5a from which the transfer sheet 5f has been neutralized by a supply means (not shown). In the vicinity of the transfer material supply destination of the transfer drum 5a, a suction roller 5g is provided on the outer side so as to be able to freely contact and separate, and a suction charging brush 5c is installed on the inner side. In accordance with the supply of the transfer material, the suction roller 5g is brought into close contact with the transfer sheet 5f by a drive source (not shown), and is brought into contact with the transfer sheet 5f by applying a suction high voltage to the suction charging brush 5c by a positive high voltage power supply (not shown). A suction current (charge) is injected from the suction charging brush 5c into the transfer sheet 5f. Since the suction roller 5g is electrically grounded, a current (charge) having a direction opposite to the current (charge) injected from the suction charging brush 5c is induced (induced), and as a result, the transfer material is transferred. Is electrostatically attracted to the surface of the transfer sheet 5f.

The transfer material adsorbed on the transfer sheet 5f is
As the transfer drum 5a rotates in the direction of arrow C, the transfer drum 5a is conveyed to the transfer section where the photosensitive drum 1 is in contact. The transfer sheet 5 is provided inside the transfer drum 5a of the transfer section.
A transfer charging brush 5b that contacts f. Similarly, a transfer charging brush 5b is driven by a positive high-voltage power supply (not shown).
A transfer high voltage is applied to the transfer charging brush 5b.
, A transfer current (charge) is injected, and the toner image (negative charge) formed on the photosensitive drum 1 is transferred to the surface of the transfer material. In the case of a color image, the transfer material is conveyed to the transfer unit a desired number of times by the rotation of the transfer drum 5a, and this transfer operation is repeated a desired number of times to perform multiple transfer.

As shown in FIG. 4, when the transfer material P has approached the push-up roller 8b after a predetermined number of transfers, the push-up roller 8b is driven by a driving means (not shown) to peel off the transfer sheet 5f. It is pushed up to the separation claw 8a side which is a member. The separation claw 8a is driven by a driving unit (not shown) substantially in synchronization with the pushing up, and the separation claw 8a is pushed down in the direction of the transfer sheet 5f. A roller 8c is provided at the tip of the separation claw 8a, and the roller 8c
By contacting the transfer sheet 5f, the tip of the separation claw 8a is prevented from contacting the transfer sheet 5f and being damaged.

As shown in FIG. 4, the transfer sheet 5f is deformed so as to have a partially increased curvature by pushing up the transfer sheet 5f by the push-up roller 8b and pushing it down by the separation claw 8a. Is transfer material 5
separated from f. The transfer material P having the leading end separated therefrom travels on the separation claw 8a as the transfer drum 5a rotates, and the portion following the transfer material P is sequentially separated from the transfer sheet 5f. The separation claw 8a is formed of a conductive resin having a relatively high resistance, and its resistance is 1
It is 10 ⁸ Ω / cm. The separation claw 8a is grounded.

As shown in FIG. 4, a separation neutralizer 5h is provided outside the transfer drum 5a near the transfer material separation section. During the separating operation of the transfer material P, a positive DC voltage is added to the AC voltage as a separating bias during the separating operation of the transfer material P.
A corona discharge is performed by applying a high voltage on which voltage is superimposed to assist the separation of the transfer material P by the push-up roller 8b and the like, and the ions generated by the peeling discharge accompanying the separation of the transfer material P and the transfer sheet 5f are medium. This prevents image disturbance due to discharge unevenness or the like.

When the above-described series of transfer and separation operations is completed, the transfer sheet cleaner 16 shown in FIG. 2 is rotated by a drive motor (not shown), and is brought into contact with the transfer sheet 5f by drive means (not shown). By the action of the backup brush 17 facing the cleaner 16 via the transfer sheet 5f, the transfer residual toner on the transfer sheet 5f is cleaned. The internal and external static eliminators 5d and 5e operate before and after the above-described series of operations of adsorption, transfer, and separation,
The transfer sheet 5f is electrically initialized.

[0012]

However, the conventional image forming apparatus has the following problems.

That is, as described above, when the transfer material P is separated from the transfer sheet 5f, an AC voltage + DC voltage is applied to the separation static eliminator 5h to prevent image disturbance due to peeling discharge or the like. The application of the AC voltage is for preventing separation discharge when the transfer sheet 5f and the transfer material P are separated from each other.
The application of the DC voltage is to prevent the transfer material P and the toner image thereon from being discharged by the application of the AC voltage. If the electrostatic attraction force between the two is reduced, the image is disturbed.

[0014] However, the effect of the separation and charge elimination is as follows.
f, the transfer material P, the toner image, and the separation claw 8a. As an example, the separation claw 8a and the transfer material P at the time of separation will be described with reference to the potential diagram of FIG.

As described above, the separation claw 8a is in an electrically grounded state, but has a resistance of 10 ⁸ Ω. Therefore, as shown in FIG. Under the influence of the corona discharge of the charge elimination, the charge is made to converge to the DC output value of the separation bias.

On the other hand, since the transfer material P on the transfer sheet 5f is pushed up to a certain potential as shown in FIG. 6A by repeated charging by multiple transfer, it is shown in FIG. 6B. So that it cancels and separates claw 8
A separation DC is applied in order to make the charge potential substantially equal to the charge potential a and to prevent the occurrence of image defects due to excessive charge removal of the toner.

However, when the image formation is continuously performed, before the charge applied to the separation claw 8a and biased to the DC side attenuates, the charge is further accumulated by the next separation of the transfer material. The potential of the separation claw 8a increases,
This causes a so-called charge-up.

As a result, the potential difference between the separation claw 8a and the transfer material to be separated increases, and the potential difference causes a charge transfer between the separation claw 8a and the transfer material. The toner on the image surface corresponding to
Separation claw marks are generated.

In order to prevent charge-up of the separation claw 8a, the separation claw 8a has a low resistance (for example, 1 cm).
If it is 10 ⁴ Ω or less, since it is in the grounded state, it is hardly charged even if it receives a separation corona, and the potential difference between the transfer material and the multi-transferred material is not reduced. Further, when a transfer material having low resistance (such as moisture absorption) is used, there is a disadvantage that electric charges leak from the transfer material via the separation claw 8a, thereby causing transfer omission.

An object of the present invention is to insert a separation claw between a transfer material onto which an image has been transferred and a transfer material carrier, and apply a separation bias to a separation / elimination means to remove electricity from the transfer material and the transfer material carrier. An object of the present invention is to provide an image forming apparatus capable of separating a transfer material by preventing a separation claw mark of an image or a transfer omission when separating a transfer material.

[0021]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A transfer electric field is applied by a transfer electric field applying means to a transfer material carried and conveyed on the transfer material carrier to transfer an image formed on the image carrier, and thereafter, the transfer material carrier and the transfer material And a separation bias in which an AC voltage and a DC voltage are superimposed is applied to the separation and static elimination means provided near the separation claw, so that the transfer material and the transfer material carrier are neutralized. In the image forming apparatus for separating the transfer material,
The image forming apparatus is characterized in that the separation bias is applied to the separation / elimination unit with its DC component reduced or set to 0 during a non-separation operation other than the transfer material separation operation.

According to the present invention, the separation claw has a resistance of 10 ⁵ to 10 ¹⁰ Ω / cm. The non-separation operation may be one or two of the timings of pre-rotation and post-rotation immediately before, immediately after the separation operation during image formation, and before and after image formation.
More than one time.

[0023]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 2 is a sectional view showing an image forming apparatus suitable for embodying the present invention. This image forming apparatus is a full-color copying machine, and has a digital color image reader at the top and a digital color printer at the bottom. The reader unit and the printer unit are separable, and can be used alone or in combination by connecting them via a network or the like.

In the reader unit, the original 30 is placed on an original platen glass 31, and the reflected light from the original 30 obtained by exposing and scanning with an exposure lamp 32 is passed through a lens 3.
The light is condensed on the full color sensor 34 by 3 to obtain a color separation image signal. The color-separated image signal is amplified by an amplifier circuit (not shown), processed by a video processing unit (not shown), and sent to the printer unit.

In the printer section, a photosensitive drum 1 as an image carrier is installed. This photosensitive drum 1 has an optical semiconductor layer such as an organic photosensitive layer provided on a conductive substrate such as an aluminum cylinder, has an outer diameter of 100 mm, and rotates at a peripheral speed of 100 mm / sec in the direction of the arrow in the figure. Driven.

Around the photosensitive drum 1, a pre-exposure lamp 11 for electrically initializing the surface of the photosensitive drum 1, and a charger 2 (corona charging in this example) for uniformly charging the surface of the photosensitive drum 1 to a negative value. A charging roller or a charging brush can be used), a laser exposure optical system 3 for forming an electrostatic latent image on the photosensitive drum 1 (an LED or the like can be used), a surface potential of the photosensitive drum 1 Potential sensor 1 for detecting
2. Four developing devices 4 containing developers (toners) of different colors for developing the electrostatic latent image formed on the photosensitive drum 1
Developing device having Y, 4M, 4C, 4K, photosensitive drum 1
A light amount detecting means 13 for detecting the amount of toner above, a transfer device 5 including a transfer drum 5a as a recording material carrier, a cleaner 6 for removing residual toner on the photosensitive drum 1, and the like are provided respectively.

In this embodiment, the laser exposure optical system 3 comprises a polygon mirror 3a, a lens 3b, a mirror 3c, etc., and outputs a laser output modulated by a color image signal for each color separated from the reader unit. Laser light (light image corresponding to image information) E from the
Then, the light is reflected on the surface of the photosensitive drum 1 through the lens 3b and the mirror 3c to form an electrostatic latent image corresponding to a color image signal of each color.

To form an image in the printer unit, first, the photosensitive drum 1 is rotated, the surface of the photosensitive drum 1 is neutralized by a pre-exposure lamp 11, initialized, and uniformly charged by a charger 2, and a laser exposure is performed. The optical system 3 sequentially irradiates the optical image E with the electrostatic latent image on the surface of the photosensitive drum 1 in a predetermined color order, for example, magenta (M), cyan (C), yellow (Y), black (K). To form

Next, corresponding to this, the developing units 4M, 4M
The latent images are developed by sequentially operating C, 4Y, and 4K, and yellow, magenta, cyan, and black toner images are sequentially formed on the photosensitive drum 1.

The developer used in the developing units 4Y to 4K may be a one-component developer composed of only toner. However, in order to further stabilize the charge of the toner, the developer is mixed with a carrier and used as a two-component developer. I have.

The toner is made up of particles of a resin such as polyester or styrene acryl as a base material and a coloring material for producing each color. Silica is used as an external additive to assist fluidity and chargeability. Alumina, titanium oxide, and the like are added in an amount of about 0.1% to several% with respect to the weight of the toner to obtain a product toner. A pulverization method or a polymerization method is used as a method for producing the toner, and the particle diameter of the toner is adjusted to a size of about 6 to 10 μm in volume average particle diameter.

The carrier has a magnetic material such as ferrite as a base material, and has a surface coated with a coating for stabilizing the toner charge, and has a volume average particle size of about 30 to 60.
Those having a size of about μm are used. The two-component developer is formed by mixing the weight ratio of the carrier and the toner to about 97: 3 to 85:15.

The developing units 4Y, 4M, 4C, 4
K indicates that a developing device of a color corresponding to the latent image formed on the photosensitive drum 1 is selectively brought closer to the photosensitive drum 1 by the operation of the eccentric cams 24Y, 24M, 24C, and 24K, and the developing operation of the latent image is performed. It is configured to perform.

The transfer device 5 is provided with a transfer drum 5a having an outer diameter of 200 mm and a transfer material carrying sheet (abbreviated transfer sheet) 5f formed of a dielectric sheet stretched around the transfer drum 5a as shown in FIG. In the direction of rotation, the suction charging brush 5c (corona charger or suction blade) of the suction charging means and the suction roller 5g, the transfer charging brush 5b of the transfer charging means (corona charger or transfer charger blade, etc.) Possible), separation static eliminator 5h, separation claw 8a, separation pushing roller 8b, inner static eliminator 5d, outer static eliminator 5
e, a cleaner 16 and a backup brush 17 are provided.

The transfer charging brush 5b and the adsorption charging brush 5c are made of a conductive brush using elastic conductive fine fibers. In the present embodiment, conductive fibers which were obtained by dyeing acrylic fine fibers with copper sulfide and conducting the treatment were used. Other conductive fibers include stainless steel fibers having a diameter of about 8 to 15 μm, or fibers obtained by applying metal plating to resin fibers such as acryl, nylon, polyester and rayon, and conductive fine particles such as carbon and metal powder in the resin. Can be kneaded or compounded into fibers, and furthermore, carbon fibers or the like obtained by carbonizing resin fibers or the like and imparting conductivity can be used.

The volume resistivity of the conductive fiber is 10 ¹⁰ Ωcm
The following can be used, but preferably 10 ⁸ Ωcm or less.

In parallel with the formation of the toner image on the photosensitive drum 1, the transfer material cassette 7a, 7b or 7c shown in FIG.
From (sometimes by manual feed), through a transport system consisting of a pickup roller, paper feed guide, paper feed roller, etc.
The transfer material is conveyed to the transfer drum 5a, and the suction charging brush 5
The transfer roller 5g sucks and carries the transfer sheet 5f on the surface of the transfer drum 5a. The transfer material carried on the transfer drum 5a is conveyed to a transfer portion facing the photosensitive drum 1 with the rotation of the transfer drum 5a, where the toner image on the photosensitive drum 1 is transferred by the action of the transfer charging brush 5b. Is transferred to the surface of

As the transfer drum 5a continues to rotate, the transfer material is repeatedly conveyed to the transfer section to transfer toner images of each color. In this manner, a color image in which toner images for four colors of magenta, cyan, yellow, and black are superimposed on the surface of the transfer material is obtained.

Next, the transfer material onto which the four color toner images have been transferred is separated from the transfer sheet 5f by the action of the separation claw 8a, the separation push-up roller 8b and the separation neutralizer 5h. 9 The transfer material then fuses and fixes the toner image to form a full-color permanent image, and is then discharged onto a tray 10 outside the printer. On the other hand, the photosensitive drum 1 on which the transfer of the toner image has been completed.
After the residual toner on the surface is cleaned and removed by the cleaning device 6, the toner is again provided for image formation.

The transfer device 5 will be further described with reference to FIG. 3. The transfer sheet 5f is stretched on the outer peripheral surface of the transfer drum 5a of the transfer device 5 as described above, and the transfer material is placed on the transfer sheet 5f. The transfer material is conveyed in the direction of arrow C in FIG. The front and rear ends of the transfer sheet 5f are attached to a connecting member 5j connecting two rings of the transfer drum 5a.

In this embodiment, the transfer sheet 5f has a thickness of 1
50 μm, volume resistivity 10 ¹⁵ Ωcm or more, dielectric constant 2.8
A flexible polycarbonate (PC) film was used. Generally, tensile modulus (Young's modulus)
Has 2 MPa or more, more preferably 5 MPa or more,
And a dielectric constant of 3.0 to 13.0 and a volume resistivity of 10 ¹⁰ to 1
A dielectric film satisfying the conditions of 0 ¹⁶ Ωcm and a thickness of 70 to 200 μm, for example, polyvinylidene fluoride resin (P
VdF), polyethylene terephthalate resin (PE
T), polyethylene phthalate resin (PEN), polyurethane resin, polyether sulfone resin (PE
S), polyimide resin (PI), polyetherimide resin (PEI), polysulfone resin (PSF), polyetheretherketone resin (PEEK), polyphenylsulfide resin (PPS), and the like.

The transfer sheet 5f is neutralized by an outer static eliminator 5e and an inner static eliminator 5d prior to image formation. AC high voltages of, for example, 12 kVpp and 500 Hz are applied to the outer static eliminator 5 e and the inner static eliminator 5 d in opposite phases to each other, whereby the surface potential of the transfer sheet 5 f is reduced to almost 0 V.

The transfer material transported to the transfer drum 5a by the transport system is fed to the transfer drum 5a in the direction of arrow B.
At the same time, the suction roller 5g is brought into close contact with the surface of the transfer sheet 5f by a driving source (not shown), is driven to rotate, and a suction current of +15 μA is injected from the back surface of the transfer sheet 5f from the suction charging brush 5c.

The suction roller 5g is made of a conductive material such as a metal such as SUS and has an outer diameter of 12 mm, and is electrically grounded. For this reason, the transfer sheet 5f which is a dielectric
When a suction current is injected from the suction charging brush 5c opposed to the transfer material, the current in the opposite direction (reverse polarity) to the current flowing through the suction charging brush 5c is induced to the suction roller 5g. Then, the transfer material is electrostatically attracted onto the transfer sheet 5f.

Next, when the transfer material adsorbed and carried on the transfer sheet 5f is conveyed to the transfer section and reaches the transfer nip between the photosensitive drum 1 and the transfer sheet 5f, a high-voltage power supply (not shown) is applied to the transfer charging brush. , A transfer current of +10 μA is injected, and as described above, the negatively charged toner image formed on the photosensitive drum 1 is transferred to the transfer material. When performing multiple transfer, this transfer operation is repeated a desired number of times.

When the transfer material having been transferred the desired number of times has approached the separation push-up roller 8b, as shown in FIG. 4, the separation push-up roller 8b is driven by driving means (not shown) to move the transfer sheet 5f. It is pushed up to the separation claw 8a side as a peeling member. Almost synchronized with this timing,
The separation claw 8a is operated by a driving unit (not shown) and descends in the direction of the transfer sheet 5f. At this time, the separation claw roller 8c attached to the rear surface of the leading end of the separation claw 8a is moved by the transfer sheet 5f.
The contact in the direction prevents the tip of the separation claw 8a from damaging the transfer sheet 5f.

The separation push-up roller 8b is made of polyacetal resin (POM) or ethylene propylene dimethyl rubber (E
(PDM) and the like, and are formed of resin, high hardness rubber, or the like. The separation claw 8a is made of resin such as polycarbonate resin (PC), polybutylene phthalate resin (PBT), polyacetal resin (POM), and polyamide imide resin (PAI) by adding fiber, carbon, or the like to reduce strength and resistance. It is preferably formed of an adjusted resin and adjusted to have a resistance per cm of 10 ⁵ to 10 ⁸ Ω.

In the present invention, for measuring the resistance of the separation claw 8a,
High resistance meter 3116 and probe 913 manufactured by HIOKI
The probe was arbitrarily taken on the separation nail using
1 cm of the separation claw by making contact with two points at a cm interval and applying a voltage of 500 V between the probes and measuring the resistance value.
The resistance value per cm was obtained. The resistance value per 1 cm of the separation claw 8a in the following description is based on this measuring method.

During the separation operation of the transfer material, a separation bias in which a DC voltage of +2 kV is superimposed on an AC voltage of 10 kVpp and 500 Hz is applied to the separation charge eliminator 5 h, thereby discharging by the separation charge eliminator 5 h and transferring. It neutralizes the ions generated by the discharge peeling off from the sheet 5f and prevents the occurrence of discharge unevenness and the like.

When a series of transfer / separation operations is completed, the cleaner 16 mounted on the transfer sheet 5f is rotated by a drive motor (not shown), and the cleaner 16 is moved by the separation / contact means (not shown). The residual toner on the transfer sheet 5 is cleaned and removed by the action of the cleaner 16 and the backup brush 17 that is in contact with the surface of the transfer sheet 5f via the transfer sheet 5f.

The inner and outer static eliminators 5d and 5e operate before and after the above-described series of suction, transfer and separation operations to electrically initialize the transfer sheet 5f.

The features of the present invention will be described with reference to FIG. 1 showing a method of applying a separation charging bias.

The inventor first examined the relationship between the resistance value of the separation claw 8a and the trace of the separation claw. When the relationship was described, as described in the section of the problem to be solved by the present invention, the separation claw 8a When the resistance value of the separation claw is 10 ⁴ Ω or less, a claw mark occurs on the transfer material having low resistance, and the resistance value of the separation claw is 1
At 0 ¹¹ Ω or more, the charging potential of the separation claw rises too quickly,
For example, a large-sized transfer material in the transfer material advancing direction, for example, A
In the transfer material 3 such as, gradually toward the image rear end portion scratch is there is a problem that intensifies, both of the intermediate ¹⁰⁵
It has been found that even with a resistance value of 〜１０10 ¹⁰ Ω, nail marks are generated at the time of continuous image output.

Therefore, in this embodiment, the resistance of the separation claw is 1
0 ⁵ to 10 ¹⁰ Ω, and even in the condition of continuous image output, in order to prevent the separation claw trace from being generated, immediately before the separation operation on the transfer material, that is, the separation operation by the separation claw 8a and the push-up roller 8b. , And immediately before the AC + DC discharge from the separation static eliminator 5h, the separation bias (AC 10 kVpp, 500 Hz + DC2
By cutting off the DC component of kV), only the AC component is applied, and the separation claw 8a is discharged.

More specifically, as shown in FIG. 1, multiple transfer is performed on the transfer material on the transfer drum 5a, and the leading end of the transfer material onto which the final color black toner image (K) has been transferred is moved to the separation section. 0.5 seconds earlier than the arrival time S1,
At h, only the AC component of the separation bias is turned on to remove electricity from the separation claw, and 0.5 seconds after that, that is, when the leading end of the transfer material reaches the separation portion, the DC component of the separation bias is turned on.
Then, an original separation bias is applied. While the transfer material passes through the separation section, the application of the separation bias is continued, and when the transfer material passes, the separation bias is turned off.

In this embodiment, as described above, one transfer material,
Immediately before one sheet is separated, only the AC component of the separation bias is turned on in the separation neutralizer 5h, and the separation operation is performed in a state where the separation claw 8a is neutralized. It was possible to suppress the charge-up of the nail and obtain a good image without traces of the separated nail.

In the above description, the separation bias AC
Although only the component was applied to remove electricity from the separation claw, the same effect was obtained even when the DC component of the separation bias was reduced from +2 kV to +0.5 kV, and the separation claw was suppressed.

Second Embodiment In the first embodiment, the charge of the separation claw 8a is removed immediately before the separation of the transfer material. However, in this embodiment, the DC component of the separation bias is changed immediately after the separation of the transfer material.

As shown in FIG. 5, when the transfer material on which the final color black toner image (K) has been transferred to the transfer member on the transfer drum 5a is subjected to multiple transfer, the transfer material is separated. At the same time when the separation bias (AC + DC) is turned on to the static eliminator 5h, the separation claw 8a and the lifting roller 8
b, the transfer material is separated from the transfer sheet 5f, and after the rear end of the transfer material passes through the separation portion, the DC component of the separation bias becomes O.
FF is performed, and thereafter, the separation claw 8a is discharged while the separation bias AC component remains ON, and the DC component is turned OFF.
After a second, the AC component is turned off.

In the above description, the delay application time of the AC component is set to 0.
Although the time is set to 5 seconds, the optimum value of the delay time slightly changes depending on parameters such as the transfer speed of the transfer material, the resistance of the separation claw, the magnitude of the DC component of the separation bias, and the rising characteristics of the separation bias high-voltage power supply. Generally, 0.3 seconds or more is preferable.

Subsequently, when the next multiply-transferred transfer material reaches the separation section, the separation bias (AC + DC) is turned on in the separation neutralizer 5h, and at the same time, the separation claw 8a and the push-up roller 8b are operated by the neutralization. The transfer material is separated from the transfer sheet 5f and the DC component of the separation bias is turned off, but the AC component is output as it is.
Five seconds later, after the separation claw 8a is neutralized, the AC component is also turned off.

In this embodiment, as described above, one transfer material,
Immediately after one sheet is separated, only the separation bias AC is turned on to the separation neutralizer 5h, and the separation operation is performed in a state where the separation nail is neutralized. It was possible to obtain a good image without separation nail traces by suppressing the up-up.

In the above description, the separation bias AC
Although only the component was applied to remove electricity from the separation claw, the same effect was obtained even when the DC component of the separation bias was reduced from +2 kV to +0.5 kV, and the separation claw was suppressed.

Embodiment 3 This embodiment is different from Embodiments 1 and 2 in the case of an intermittent image forming operation such as when two small-size transfer materials and one large-size transfer material are used. That is.

In such an intermittent image forming operation, it is preferable to use the pre-rotation time and the post-rotation time from when the copy button is turned ON to when the image formation of the discharge of the transfer material after fixing is completed.

Therefore, in this embodiment, only the AC component of the separation bias or the DC
After applying a separation bias with reduced components to remove electricity from the separation claw, the transfer material was separated. As a result, Example 1,
As with 2, suppress the charge-up of the separation claw,
A good image without separation nail marks could be obtained.

In the above description, the charge is removed from the separation claw by using any one of the timings immediately before, immediately after the transfer material separating operation, or during the rotation before and after the image forming operation. It is apparent that the same effect can be obtained.

[0069]

As described above, according to the present invention,
A separation claw is inserted between the transfer material on which the image has been transferred and the transfer material carrier that carries the image, and a separation bias in which AC and DC are superimposed is applied to the separation and static elimination means to eliminate the transfer material and the transfer material carrier. When the transfer material is separated, the AC component of the separation bias is applied to the separation / de-electrification unit by using any time immediately before or immediately after the transfer material separation operation, or during the pre-rotation or post-rotation of the image forming operation. Only the separation bias is applied or the DC component is reduced, and the transfer material is separated in a state where the separation claw is de-electrified. It has become possible to obtain good images without these defects.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method of applying a separation bias in one embodiment of the present invention.

FIG. 2 is a sectional view showing an image forming apparatus suitable for realizing the present invention.

3 is a cross-sectional view illustrating an arrangement of devices around a transfer drum installed in the image forming apparatus of FIG. 2;

FIG. 4 is a cross-sectional view illustrating an operation of separating a transfer material from the transfer drum of FIG.

FIG. 5 is an explanatory diagram showing a method of applying a separation bias in another embodiment of the present invention.

FIG. 6 is an explanatory diagram illustrating a relationship between a separation claw and a potential of a transfer material before and after separation in a conventional transfer material separation operation.

[Explanation of symbols]

 Reference Signs List 5 transfer drum 5f transfer sheet 5h separation static eliminator 8a separation claw S1 separation operation start time S2 separation operation end time

Claims (6)

[Claims] A transfer electric field applying means for applying a transfer electric field to a transfer material carried and conveyed on the transfer material carrier to transfer an image formed on the image carrier; The separation claw is inserted between the carrier and the transfer material, and a separation bias in which the AC voltage and the DC voltage are superimposed is applied to the separation and static elimination means provided near the separation claw to transfer the transfer material and the transfer material. In the image forming apparatus for separating the transfer material while the body is being neutralized, the separation bias is applied to the separation and static elimination means during a non-separation operation outside the separation operation of the transfer material.
An image forming apparatus characterized in that components are reduced or applied at a reduced level. 2. The separation claw according to claim 1, wherein the separation claw is 10 ⁵ to 10 per cm.
^2. The image forming apparatus according to claim 1, which has a resistance of ¹⁰ Ω. 3. The image forming apparatus according to claim 1, wherein the time of the non-separation operation is a time immediately before the time of the separation operation during image formation. 4. The image forming apparatus according to claim 1, wherein the non-separation operation is a time immediately after the separation operation during image formation. 5. The image forming apparatus according to claim 1, wherein the time of the non-separation operation is a timing of pre-rotation and post-rotation before and after image formation. 6. The non-separating operation is at least two of timings before, immediately after, and before and after image formation before and after the separation operation during image formation. Or the image forming apparatus of 2.