JP3342288B2 - Image forming device - Google Patents

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 a printer for transferring a toner image to a transfer material and outputting a recorded image, and a copying machine for outputting a copy of a document.

[0002]

2. Description of the Related Art In a color image forming apparatus using an intermediate transfer member, a plurality of intermediate transfer members are formed by repeating a process of forming a transferable image on a first image carrier and a primary transfer process of the image onto the intermediate transfer member. In some cases, after forming a color (multicolor) toner image composed of a color developer, the image is secondarily transferred collectively to a transfer material. According to this method, color image information can be synthesized and reproduced, and an image free from misalignment (color misalignment) can be obtained by superimposing each component color image.
This is extremely effective as a color image forming apparatus.

However, in an image forming apparatus using an intermediate transfer member, after secondary transfer from the intermediate transfer member to a transfer material such as paper, transfer residual toner is present on the intermediate transfer member. Removal is one technical issue.

Means for solving the above problems include:
For example, Japanese Patent Application Laid-Open No. 56-15335 discloses a blade cleaning means of a type in which an elastic blade (cleaning blade) is brought into contact with an intermediate transfer member to scrape off toner on the intermediate transfer member.
No. 7, JP-A-5-303310, and the like.

Further, a fur brush which comes in contact with and separates from the intermediate transfer member is provided, and a bias having a polarity opposite to that of the secondary transfer residual toner on the intermediate transfer member is applied to collect the residual toner. There is also a configuration in which the remaining toner is attached and then scraped off with a blade.

As an auxiliary means for reducing the load caused by cleaning only with the blade cleaning means, the residual toner on the intermediate transfer member is charged to a polarity opposite to the potential on the photosensitive member as the first image carrier. A method of returning the residual toner to the photosensitive member by the action of an electric field after the completion of the transfer step has been proposed in, for example, JP-A-4-340564 and JP-A-5-297739.

Further, Japanese Patent Laid-Open Publication No. 1-105980 discloses that
By providing a charger for charging the remaining toner on the intermediate transfer body to a polarity opposite to the charging potential of the photoconductor without providing a similar cleaning device on both the intermediate transfer body and the photoconductor,
The residual toner after the secondary transfer on the intermediate transfer member is reduced to 1
A configuration has been proposed in which the image is returned to the photoconductor when the next transfer is not performed. According to this publication, in this cleaning configuration, the process of charging the residual substance on the intermediate transfer member and returning the residual toner to the photosensitive member may be performed once during one (one) copy process. It is described that the intermediate transfer member can be made to be in a cleaner state by performing it a plurality of times.

[0008]

However, the above-described conventional intermediate transfer body cleaning device has the following problems.

In a cleaning device of the type in which the toner on the intermediate transfer member is scraped off using a cleaning blade, when the blade that has come into contact with the cleaning member separates, the toner accumulated on the blade portion is removed. Since it remains on the upper surface, there is a problem that blade marks are generated on an image produced in the next image forming process. In addition, since the blade and the surface of the intermediate transfer member that the blade is in contact with are worn over a long period of time, problems such as occurrence of poor cleaning and deterioration of transfer efficiency due to deterioration of the surface of the intermediate transfer member also occur. .

Further, the cleaning device for recovering the residual toner on the intermediate transfer member by the fur brush has a disadvantage that the cleaning device is large and complicated, which leads to an increase in size and cost of the entire image forming apparatus.

A cleaning device that performs cleaning by returning a residual toner on an intermediate transfer member to a photosensitive drum by using a corona charger or a bias roller as auxiliary means for blade cleaning is a mechanical cleaning method as described above. It is effective because it is different from the above.However, after the normal image forming step is completed, a separate intermediate transfer body cleaning step is required, and in an image forming mode in which different patterns are continuously output, the throughput is significantly reduced. There is a disadvantage that.

On the other hand, a charger described in JP-A-1-105980 for charging the remaining toner on the intermediate transfer member to a polarity opposite to the charging potential of the photosensitive member is provided. The configuration in which the secondary transfer residual toner on the intermediate transfer member is returned to the photoreceptor only by the device is considered to be a very simple and effective means. However, this publication states that once (one)
After the image forming (printing) step is completed, one or more cleaning steps are performed (sequential cleaning).

Therefore, in the configuration described in the above publication, the cleaning is performed sequentially after the end of the primary transfer, so that the throughput is reduced during continuous printing of different patterns.

An object of the present invention is to solve the above-mentioned problem of an image forming apparatus having an intermediate transfer member.

Another object of the present invention is to shorten the time required for image formation by reducing the time required for cleaning the toner remaining after the transfer in the intermediate transfer.

Still another object is to simplify the structure of the entire apparatus by configuring the apparatus without providing a dedicated container for collecting and storing the toner remaining on the intermediate transfer member.

[0017]

According to the present invention, there is provided an image forming apparatus for forming a toner image on a transfer material using an intermediate transfer member, comprising: an image carrier; A toner image forming means for forming an image with toner, an intermediate transfer member which moves endlessly in contact with the image carrier, and a toner image formed on the image carrier at a first transfer position of the intermediate transfer member. Bias applying means for primary transfer to a transfer member, transfer means for secondly transferring the toner image transferred to the intermediate transfer member to a transfer material at a second transfer position of the intermediate transfer member, and intermediate transfer after transfer. And a residual toner charging means for charging the residual toner remaining on the transfer body to a polarity opposite to the original polarity of the toner. After the secondary transfer, the residual toner on the intermediate transfer body is charged to the original polarity of the toner. Is charged to the opposite polarity by the above-mentioned remaining toner charging means. 1 electrodeposition been residual toner during the primary transfer
By passing through the next transfer position, the residual toner is reverse-transferred to the image carrier at the same time as the next primary transfer, thereby removing the residual toner on the intermediate transfer member.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic sectional view of a color laser beam printer utilizing an electrophotographic process, which is an embodiment of the color image forming apparatus of the present invention.

In this embodiment, the printer includes a rotating drum type electrophotographic photosensitive member 1 (hereinafter referred to as "photosensitive drum") repeatedly used as a first image carrier. It is rotationally driven at a predetermined peripheral speed (process speed) in the counterclockwise direction indicated by the arrow.

The photosensitive drum 1 is uniformly charged to a predetermined negative polarity and potential by the primary charging roller 2 during the rotation process. Next, an image exposure means (FIG. 1) comprising a color separation image of a color original image, an image formation exposure optical system, a scanning exposure system using a laser scanner for outputting a laser beam modulated in accordance with a time-series electric digital pixel signal of image information, and the like. Not shown)
Receives the image exposure 3 by. As a result, an electrostatic latent image corresponding to the first color component image of the target color image, for example, a yellow component image is formed.

In this embodiment, a yellow developing device 41, a magenta developing device 42, a cyan developing device 43, and a black developing device 4
A so-called rotary developing device equipped with a developing device 4 is used, and each developing device is rotated in the direction of an arrow in the figure by a rotation driving device (not shown), and each developing device faces the photosensitive drum 1 in a developing process. It is configured to be located at a position. In FIG. 1, the yellow developing device 41 is located at the developing position.

The electrostatic latent image formed on the photosensitive drum is developed by a first developing device, in this embodiment, a yellow developing device 41, using a first color yellow toner Y, to form a yellow toner image.

The first color yellow toner image on the photosensitive drum 1 passes through a nip portion between the photosensitive drum 1 and the intermediate transfer member 5, and a primary transfer bias applied to the intermediate transfer member 5 Due to the electric field and pressure formed by 29,
The intermediate transfer is performed on the outer peripheral surface of the intermediate transfer body 5. Hereinafter, this process is referred to as “primary transfer”.

In the present embodiment, the intermediate transfer member 5 is an elastic roller having a medium resistance, and is driven to rotate in the clockwise direction indicated by an arrow at the same peripheral speed as the photosensitive drum 1.

Hereinafter, similarly, the magenta toner image of the second color, the cyan toner image of the third color, and the black toner image of the fourth color are sequentially superimposed and transferred onto the intermediate transfer member 5, and each color corresponding to the target color image Is formed on the intermediate transfer member 5.

In this embodiment, a transfer belt 6 is disposed below the intermediate transfer member 5. The transfer belt 6
It is stretched and supported by a bias roller 62 and a tension roller 61. A desired secondary transfer bias is applied to the bias roller 62 by the secondary transfer bias source 28, and one tension roller 61 is grounded.

First transfer from the photosensitive drum 1 to the intermediate transfer member 5
The primary transfer bias for sequentially superimposing and transferring the toner having negative charge of the fourth color to the fourth color has a polarity opposite to that of the toner.
That is, in the present embodiment, the positive polarity is applied, and the voltage is applied from the bias power supply 29.

First transfer from the photosensitive drum 1 to the intermediate transfer member 5
The transfer belt 6 and the intermediate transfer body cleaning roller 8 of the present invention, which will be described in detail later, are separated from the intermediate transfer body 5 in the step of sequentially transferring the toner images of the colors from the first color to the fourth color.

In transferring the color toner image superimposed on the intermediate transfer member 5 onto the transfer material P, the transfer belt 6 is brought into contact with the intermediate transfer member 5. And a paper cassette (not shown)
The transfer material P is fed at a predetermined timing from a contact nip portion between the intermediate transfer body 5 and the transfer belt 6 through a registration roller 11 and a pre-transfer guide 10 at the same time, and at the same time, a secondary transfer bias is applied to a bias power supply 28. Is applied to the bias roller 62. The toner image formed on the intermediate transfer member 5 is transferred to the transfer material P by the secondary transfer bias. Hereinafter, the step of transferring the toner image from the intermediate transfer body to the transfer material is referred to as “secondary transfer”.

The transfer material P on which the superimposed color toner images are collectively transferred is introduced into the fixing device 15 and is heated and fixed, and then carried out of the apparatus.

After the image transfer to the transfer material P is completed, the intermediate transfer body 5 is brought into contact with an intermediate transfer body cleaning roller 8 in this embodiment, which is an intermediate transfer body cleaning means.
The toner remaining on the intermediate transfer member 5, that is, the transfer residual toner, is charged by the intermediate transfer member cleaning roller 8 to a polarity opposite to that of the toner for developing the latent image on the photosensitive drum. Set up in the process.

The intermediate transfer member cleaning which is a feature of the present invention will be described below.

According to the present invention, the intermediate transfer member cleaning means 8 performs the intermediate transfer member 5 simultaneously with the primary transfer from the photosensitive drum 1 to the intermediate transfer member 5, that is, while performing the primary transfer.
The mechanism of transferring the above-mentioned secondary transfer residual toner to the photosensitive drum 1 and returning it will be described.

The toner remaining on the intermediate transfer member after the secondary transfer, that is, the residual toner, receives a strong electric field having a polarity opposite to that of the toner when the toner is transferred from the intermediate transfer member 5 to the transfer material P on the transfer belt 6. Therefore, there are many toners which are charged to a polarity (positive in this embodiment) opposite to the normal charging polarity (negative in this embodiment) and remain on the intermediate transfer member 5. However, not all toners are inverted to the positive polarity, and some toners are partially neutralized and have no charge, and other toners maintain the negative polarity.

This phenomenon was confirmed by performing the following experiment.

The laser beam printer having the structure shown in FIG. 1 performs continuous printing of two sheets of a monochromatic text pattern and a solid white pattern. When the intermediate transfer body cleaning unit 8 is not provided, the transfer residual toner of the text pattern of the previous print appears on the second solid white pattern like a positive ghost. At this time, the secondary transfer bias value was changed with respect to a preset value, and the generation level of a ghost image due to the residual toner appearing in a positive shape was observed. As a result, the degree of occurrence of the generated positive ghost image depends on the bias value, and the level of the positive ghost image generated at a transfer bias higher than the transfer bias showing the maximum transfer efficiency is most improved. Was observed. Conventionally, transfer efficiency has a peak at a certain transfer bias value,
It is known that transfer efficiency is reduced when an excessive bias is applied.

As described above, since the behavior of the occurrence of the positive ghost in the above examination was different from the behavior of the conventional transfer efficiency, the inventors of the present invention carried out the transfer on the intermediate transfer member 5 and the photosensitive drum 1 after the secondary transfer. The upper toner was observed.

When transfer was performed with an excessively large secondary transfer bias, the amount of toner on the intermediate transfer member 5 was very large, but the photosensitive drum 1 from which primary transfer was to be completed at the same time
There was also toner on top. Judging from the state of the toner pattern on the photosensitive drum, it was confirmed that the secondary transfer residual toner on the intermediate transfer member 5 was clearly transferred to the photosensitive drum 1 and returned.

From the above examination results, it has been confirmed that the secondary transfer residual toner has a behavior of being reversed to the opposite polarity during transfer by a strong secondary transfer bias.

However, the secondary transfer residual toner on the intermediate transfer member 5 includes neutralized toner and toner maintaining negative polarity, as described above, so that all of the toner remains on the photosensitive drum 1. Does not return, and appears as a positive ghost in the next succeeding print image during continuous mode printing. Also,
If a transfer bias higher than such an optimum transfer bias is used, image deterioration due to an excessive transfer current becomes severe, so that it is not practical.

Accordingly, the present inventors have considered that, of the residual toner after the secondary transfer on the intermediate transfer member 5, the neutralized toner having no charge and the toner maintaining the negative polarity are also regarded as the original toner. A charging means for reversing the polarity is provided after the secondary transfer. As a result, the present inventors have confirmed that it is possible to return all of the residual toner after the secondary transfer to the photosensitive drum 1.

The oppositely charged positive toner on the intermediate transfer member 5 and regular negative toner to be primarily transferred from the photosensitive drum 1 to the intermediate transfer member 5 are transferred to the photosensitive drum 1 by the intermediate transfer. In the primary transfer nip portion with the body 5, the toner reversely charged by the cleaning unit 8 is charged to the photosensitive drum 1 and to a regular negative charge without neutralizing the charge by exchanging the charge between the toners. It was found that the transferred toner was reverse-transferred and transferred to the intermediate transfer member 5 in this nip portion.

This phenomenon occurs because the toner has an insulating property, so that the toners of opposite polarities do not cancel each other in a short time to reverse the polarity or neutralize. It is. That is, by lowering the primary transfer bias, the electric field applied between the photosensitive drum 1 and the intermediate transfer member 5 at the primary transfer nip is weakened, and the toner is charged in an undesirable direction by the discharge at the nip. When the toner passes through the primary transfer nip, the neutralization effect by the exchange of the charge between the toners does not work, so that the toner on the photosensitive drum 1 and the intermediate transfer member 5
This is because the upper toners take an independent behavior.

In this embodiment, 2
As a means for charging the residual toner after the next transfer, a contact-type charging means, specifically, an intermediate transfer body cleaning roller 8 including an elastic roller having a plurality of layers is used.

FIG. 2 is a schematic sectional view of the intermediate transfer member cleaning roller 8 actually used in the present invention.

In this embodiment, the intermediate transfer member cleaning roller 8 is, for example, a cylindrical or columnar conductive support 8.
3 has a roller shape having at least an elastic layer 82 made of rubber, elastomer and resin, and further having one or more coating layers 81 on the upper layer of the elastic layer 82.

The cylindrical or columnar conductive support 83 is
Any material may be used as long as the material can be abutted with rigidity such that the nip becomes uniform in the longitudinal direction without bending to the intermediate transfer member 5.
Metals or alloys such as aluminum, iron, copper, and stainless steel, and conductive resins in which carbon, metal particles, and the like are dispersed can be used.

The elastic layer 82 only needs to have a hardness capable of abutting on the intermediate transfer member 5 without a gap, and further have a certain electrical withstand voltage against an applied bias.

Specific rubber materials that can be used as the elastic layer 82 include acrylonitrile-butadiene rubber (N
BR), styrene butadiene rubber, butadiene rubber, ethylene propylene rubber, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, acrylonitrile butadiene rubber, acrylic rubber, fluorine rubber, urethane rubber, urethane sponge, and the like. The resistance value is 10 ⁵ to 10 ^11, preferably 10 ⁵ to 10 in volume resistivity.
10 ⁷ Ω · cm (when 1 kV is applied) is desirable. The resistance value required for the intermediate transfer member cleaning roller 8 will be described later.

The material of the coating layer 81 is an important factor in cleaning the intermediate transfer member. This is because the function required of the intermediate transfer body cleaning roller 8 is the same as that of the charging roller 2 that charges the photosensitive drum 1.

The charging roller for charging the photosensitive drum 1 has a very stable resistance value, and if there is no microscopic resistance unevenness on the surface, a roller having a single layer structure can satisfy the function. . This is because the charging is due to the discharge that occurs when a voltage is applied between the material of the photosensitive drum surface and the material of the charging roller, and the capacitance that contributes to the discharge is determined by the resistance value.

Therefore, in order to control the resistance and suppress the microscopic unevenness of the resistance on the surface, the function of each layer is separated by forming the charging roller into a two-layer structure, and the resistance of the lower elastic layer 82 is roughly controlled. It is also desirable to make the surface coating layer 81 have a function of finely adjusting the resistance value from the viewpoint of manufacturing such as expansion of material options and cost.

In view of the above, the present embodiment adopts a two-layer structure, but the material used for the coating layer 81 is nylon resin, urethane resin, fluororesin, etc., titanium oxide as conductive material, It is desirable to disperse a metal oxide such as tin oxide and control the resistance.

Further, a type in which a sheet-shaped or tube-shaped resin is wound as the coating layer 81 may be used.

The resistance of the coating layer 81 needs to have a sufficient surface resistance to be discharged in contact with the intermediate transfer member 5. An effective surface resistance value is 10 ⁶ to 10 ^15, preferably 10 ¹¹ to 10 ¹⁵ Ω / cm ² (when 1 kV is applied).

For the measurement of the surface resistance, a sample was prepared by applying a coating layer on a 100 × 100 mm conductive sheet under the same conditions, and R8340A and R8340A manufactured by Advantest were used.
12704, applied voltage 1 kV, discharge
e 5sec, charge30sec and measu
It is a value measured under conditions of re 30 sec.

The structure of the cleaning roller 8 used in the present embodiment is such that a 3 mm thick urethane sponge (volume resistivity 10 ⁵ Ω · cm (1 kV) is formed on a stainless steel core 83 having an outer diameter of 14 mm as an elastic layer 82. (At the time of application)), and as the coating layer 81, a material obtained by dispersing titanium oxide in methoxymethylated polyamide as a nylon resin was used. Its thickness is 10 μm and its surface resistance is 10 ¹³ Ω / c.
m ² . The outer diameter of the roller 8 was about 20 mm.

The actual resistance of the cleaning roller 8 used for cleaning the intermediate transfer member was measured by the method shown in FIG. Here, the “actual resistance” refers to the resistance of the cleaning roller 8 including the elastic layer 82 and the coating layer 81.

In FIG. 3, the aluminum cylinder 71 is rotated by a drive source such as a motor (not shown), and the cleaning roller 8 is driven to rotate accordingly. The contact pressure is
It is equivalent to the actual use condition, and the total pressure is 1 kgf.
A constant DC voltage Vdc is applied to the core of the intermediate transfer member cleaning roller 8 from the high voltage power supply 73. The current flowing through the elastic layer and the coating layer of the cleaning roller 8 flows into the aluminum cylinder 71 and is grounded via the standard resistor 72. The voltage across the standard resistor 72 is Vr
(V), the resistance value Rc of the cleaning roller 8
(Ω) is given by the following equation.

Rc (Ω) = 10 ⁶ / Vr (V) As a result of the measurement, the actual use resistance of the cleaning roller 8 was 4 × 10 ⁸ Ω.

According to the study of the present inventors, the actual use resistance value desired for the cleaning roller 8 is 5 × 10 ⁵ to 1 × 10 ^10, preferably 10 ⁸ to 10 ¹⁰ Ω according to the measurement method.
It turned out that it can be used in the range.

The thickness of the coating layer 81 is 5 to 100 μm
It was confirmed that it was effective.

Next, the intermediate transfer member 5 used in this embodiment will be described with reference to FIG.

The intermediate transfer member 5 used in this embodiment also has, for example, an elastic layer 52 made of at least rubber, elastomer, or resin on a rigid cylindrical conductive support 53, and furthermore, the elastic layer 52. One or more coating layers 5 on top of
1.

As the cylindrical conductive support 53, a metal or alloy such as aluminum, iron, copper and stainless steel, a conductive resin in which carbon and metal particles are dispersed, and the like can be used. Examples thereof include a cylindrical shape as described above, a shape in which an axis passes through the center of the cylinder, and a shape in which the inside of the cylinder is reinforced. Core metal 5 used in this embodiment
1 was obtained by reinforcing the inside of a 3 mm-thick aluminum cylinder.

The thickness of the elastic layer 52 used for the intermediate transfer member 5 is preferably 0.5 to 7 mm from the viewpoints of transfer nip formation, color shift due to rotation, material cost, and the like.
The film thickness is preferably a thin layer in order to further convey the flexibility of the lower elastic layer 52 to the upper layer or the surface of the photosensitive drum 1, and more specifically, 5 to 100 μm. The elastic layer 52 of the intermediate transfer member 5 used in this embodiment is used.
Is 5 mm, and the thickness of the surface layer 51 is 10 μm.
In this embodiment, the total outer diameter of the intermediate transfer member 5 is 180 m
m.

The elastic layer 52 was made of a material in which resistance was controlled by dispersing ketjen black as a conductive material in acrylonitrile-butadiene rubber (NBR), focusing only on the resistance value. Other usable rubber materials for the elastic layer 52 include the same materials as the elastic layer of the cleaning roller 8 described above.

Further, as the conductive material, for example, carbon black, aluminum powder, nickel powder and the like can be used. It is also conceivable to use a conductive resin instead of dispersing a conductive agent in the resin. Specifically, quaternary ammonium salt-containing polymethyl methacrylate,
Polyvinylaniline, polyvinylpyrrole, polydiacetylene, polyethyleneimine and the like can be mentioned.

The measurement of the volume low efficiency is performed by setting the elastic layer 52 to 1
Cut out into a sheet of appropriate thickness of 00 x 100 mm,
R8340A and R12704 manufactured by Advantest
Using an applied voltage of 1 kV and a discharge of 5 sec.
c, charqe 30 sec and measure 3
It was measured under the condition of 0 sec.

The surface layer 51 of the intermediate transfer member 5 is important because it greatly affects the cleaning ability of the secondary transfer residual toner. For the surface layer 51, a material obtained by dispersing aluminum borate whiskers as a conductive material for controlling resistance and PTFE powder for the purpose of improving releasability using a urethane resin as a binder was used.

When the surface resistance was measured by the same measuring method as described above, it was 10 ¹² Ω (when 1 kV was applied). According to the study of the present inventors, the surface resistance is 10 ⁸ to 10 ¹² Ω.
It was found that the cleaning property was good if it was within the range.

The actual resistance including the elastic layer 52 and the surface layer 51 was 10 ⁷ Ω (when 1 KV was applied). The method of measuring the actual use resistance of the intermediate transfer member 5 was the same as that of the cleaning roller 8 described above, using the same method as the measurement system shown in FIG.

Next, the toner used in this embodiment will be described.

The toner used in this embodiment was manufactured from a styrene resin binder by a pulverization method, and had a shape factor SF1 of 153, a shape factor SF2 of 145, and a particle size of 7 μm.
m is a non-magnetic toner having an irregular shape, and oil-treated silica is externally added. Then, as a comparative toner, a magnetic material such as magnetite was added to a styrene-butyl acrylate-butyl maleate half-ester copolymer binder by 100%.
An amorphous magnetic toner externally added with oil-treated silica having a shape factor SF1 of 150 to 160, a shape factor SF2 of 140 to 150, and a particle size of 5 to 7 μm, which was internally added and manufactured by a pulverization method, was used.

The shape factor SF1 here is a numerical value indicating the ratio of the roundness of the shape of the spherical material as shown in FIG. 5, and is an elliptical shape formed by projecting the spherical material on a two-dimensional plane. The square of the maximum length MXLNG of the figure is the figure area AREA
, And multiplied by 100π / 4. That is, the shape factor SF1 is given by the following equation: SF1 = {(MXLNG) ² / AREA} × (100π
/ 4).

As shown in FIG. 6, the shape factor SF2 is a numerical value indicating the proportion of irregularities in the shape of a substance, and the square of the perimeter PERI of a figure formed by projecting a substance on a two-dimensional plane is represented by a figure area AREA. , And multiplied by 100π / 4. That is, the shape factor SF2 is expressed by the following equation: SF2 = {(PERI) ² / AREA} × (100π /
4) It is defined by.

The shape factor described in this embodiment is obtained by using a FE-SEM (S-800) manufactured by Hitachi, Ltd.
The sample is randomly sampled and the image information is sent via an interface to an image analyzer manufactured by Nicole (LUSE ×
This is calculated by the above equation by analyzing the data introduced in 3).

The tribo of the two types of toners used in this embodiment on the photosensitive drum 1 before the primary transfer is approximately -1.
It was 5 μC / g.

Next, the photosensitive drum 1 used in this embodiment
Is an OPC having an outer diameter of 60 mm and a charge generation layer (Carr).
ier Generation Layer)
A phthalocyanine compound having a thickness of 0.2 to 0.3 μm is used, and a charge transport layer (Carrier Transfe) on the upper layer is used.
r Layer) has a hydrazone compound dispersed in a polycarbonate polycarbonate as a binder, and has a thickness of 15 to 25 μm.
m was used.

In this embodiment, the transfer belt 6 is used as the secondary transfer means. The bias roller 62 and the tension roller 61 supporting the transfer belt 6 may be made of the same material or may be made of another material. In this embodiment, an NBR having a volume resistivity of 5 × 10 ⁷ (when 1 kV is applied) is used.
Was used. The hardness is 30 to 35 degrees according to JIS-A.
Both rollers 61 and 62 were formed with an NBR layer on a SUS core having a diameter of 8 mm so as to have an outer diameter of 20 mm.

The material of the rollers 61 and 62 must be such that the volume resistivity is controlled at 1 × 10 ⁴ to 1 × 10 ⁹ Ω · cm (when 1 kV is applied) and the voltage dependence of the resistance value is extremely large. I just need. Other materials include E
Any suitable conductive agent such as PDM, urethane rubber, and CR may be used as long as it is dispersible.

Next, regarding the transfer belt 6, the transfer belt 6 used in this embodiment has an outer diameter of 80 mm.
Tube shape of 300mm width, thickness 100μ
m, the volume resistivity is 10 ⁸ Ω · cm to 10 ¹⁵ Ω · cm (1
kV).

In the present embodiment, carbon is dispersed in silicon-modified polycarbonate, and the volume resistivity is 10 ¹¹ Ω · c.
m, and a resin belt whose surface resistance was controlled to 10 ¹² to 10 ¹³ Ω / cm ² was used.

Other materials usable as the transfer belt 6 include polycarbonate (PC), nylon (PA), polyester (PET), polyethylene naphthalate (PEN), polysulfone (PSU), and polyether sulfone ( PEI), polyetherimide (PEI), polyethernitrile (PEN), polyetheretherketone (PEEK), thermoplastic polyimide (TPI), thermosetting polyimide (PI), PES alloy, polyvinylidene fluoride (PVdF), There are ethylene tetrafluoroethylene copolymer (ETFE) and the like,
Elastomers include polyolefin-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyurethane-based thermosetting elastomers, and polystyrene-based thermoplastic elastomers.
Examples thereof include a polyamide thermoplastic elastomer, a fluorine thermoplastic elastomer, a polybutadiene thermoplastic elastomer, a polyethylene thermoplastic elastomer, an ethylene vinyl acetate thermoplastic elastomer, and a polyvinyl chloride thermoplastic elastomer.

Other conditions are as follows: contact pressure of the intermediate transfer member 5 against the photosensitive drum 1: 2 k
gf, a contact pressure of the cleaning roller 8 used for cleaning the intermediate transfer member with the intermediate transfer member 1: 1 kgf, a contact pressure of the transfer belt 6 with the intermediate transfer member 5: 5 kg
f,

Dark potential on the photosensitive drum (non-image portion potential due to primary charging): Vd = -600 V Bright potential on the photosensitive drum (image portion potential by laser exposure): Vl = -250 V Development method 1 component jumping development ・ Development bias: Vdc = −400V, Vac = 160
0 Vpp, frequency = 1800 Hz, process speed: 120 mm / sec, primary transfer bias: +100 V.

Under the conditions described in detail above, the effect of cleaning the intermediate transfer member in the laser beam printer having the configuration shown in FIG. 1 was confirmed.

The timing of the contact of the cleaning roller 8 with the intermediate transfer member 5 is determined in the single color continuous pattern mode (a mode in which a plurality of sheets are continuously printed in a single color). The transfer member 5 was brought into contact. This is to prevent the image being transferred from being disturbed by the contact shock. In the four-color multiple transfer mode (a mode in which a single print outputs a color image obtained by superimposing four color toners), the four colors are brought into contact at the same time as the primary transfer is completed. .

FIG. 7 is a graph showing the secondary transfer bias dependence of the residual toner concentration (amount) after the secondary transfer on the intermediate transfer member 5 for the above-described non-magnetic toner and magnetic toner. The measurement of the residual toner concentration is actually performed by
The toner remaining after the next transfer is adhered to an adhesive tape and collected, and the measurement is performed using a Macbeth densitometer.

In FIG. 7, the range of the secondary transfer bias at which the secondary transfer residual density is minimum is wider for the non-magnetic toner than for the magnetic toner, and the secondary transfer residual density at that time is also lower. At this time, the toner amount (mg / cm ² ) on the intermediate transfer member 5 before the secondary transfer was set to 0.7 mg / cm ² .

In order to clean the intermediate transfer member, the secondary transfer residual toner on the intermediate transfer member 5 should be as small as possible. When the residual toner amount is large, it is necessary to apply a strong cleaning bias to the intermediate transfer member cleaning roller 8 in order to charge the residual toner by the intermediate transfer member cleaning roller 8 and reversely transfer the toner back to the photosensitive drum 1. . When the residual toner of the intermediate transfer member is charged for the cleaning with such a strong bias, the remaining toner, which has already been charged to the opposite polarity (positive in this embodiment) in the secondary transfer, is further removed. Since the toner is strongly charged, toner having a very high positive charge is generated in the residual toner of the intermediate transfer member. FIG. 12 is a diagram schematically illustrating this phenomenon.

This phenomenon will be described with reference to FIG. Tribo of toner 94 on photoconductor drum 1 before primary transfer (μC /
When g) is −15 μC / g, the tribo just after the primary transfer hardly changes. This is because the primary transfer bias is +
This is because the value is as low as 100 V. This is because, when the primary transfer bias is increased, the ratio of the inverted toner among the toners on the intermediate transfer body 5 after the primary transfer is higher than on the photosensitive drum 1, and as a result, the secondary transfer efficiency is increased. Since the phenomenon of reduction was confirmed, the primary transfer bias was set to the bias value.

The toner primarily transferred to the intermediate transfer member 5 is
While the tribo is maintained at 15 μC / g, the secondary transfer process starts and the image is transferred onto the transfer material P.

Secondary transfer residual toner 95 on intermediate transfer member 5
Is mainly dominated by positive polarity toner which has been inverted to the polarity opposite to the normal polarity in the secondary transfer process. The tribo on the intermediate transfer member 5 at this time was +10 to 20 μC / g.

Further, by applying a bias to the cleaning roller 8 and inverting most of the secondary transfer residual toner 95 to the opposite polarity, the tribo of the toner 96 after passing through the cleaning roller 8 is +40 to +50 μC / g. To rise.

As described above, since the residual toner has a strong positive charge, the secondary transfer residual toner 96 is efficiently re-transferred to the photosensitive drum 1 and returned.

However, if the amount of toner is large, or abnormally strong positively charged toner is generated, as shown in FIG. 12, the toner 94 to be primarily transferred during the primary transfer and the photosensitive member Toner 96 returning to drum 1
Is the toner 96 to be returned in the primary transfer nip.
Since the charge amount of the toner itself is large, the primary transfer is completed in such a manner that the toner 94 to be primarily transferred to the intermediate transfer member is attracted and returned to the photosensitive drum 1. Under such conditions, if continuous printing is set as an actual image, the image of the remaining toner image at the time of the immediately preceding print is a negative ghost image Will appear like The present inventors have called this phenomenon "cleaning ghost".

Therefore, in order to clean the toner remaining on the intermediate transfer member of the present invention, it is necessary to prevent both the cleaning failure and the cleaning ghost from occurring. The present inventors have achieved these by optimizing the transfer bias and the bias value applied to the cleaning roller 8 and using a non-magnetic toner.

As for the secondary transfer bias, the range of the bias which takes the minimum value of the curves of the two types of toner in FIG.
This is the optimum secondary transfer bias used in this embodiment. Specifically, 8 μA was used for the non-magnetic toner used in the present example, and 4 μA was used for the magnetic toner listed as a comparative example.

Table 1 shows the result of observing the occurrence of cleaning failure and cleaning ghost when the bias value applied to the cleaning roller 8 was changed for the non-magnetic toner and the magnetic toner.

[0102]

[Table 1]

In Table 1, when a magnetic toner was used as the developer, cleaning failure occurred at any of the cleaning bias values for charging the residual toner of the intermediate transfer member. Therefore, simultaneous primary transfer cleaning in the present invention was not possible. It was possible. On the other hand, in the case of non-magnetic toner,
Cleaning failure occurs at 0 to 20 μA, and a cleaning ghost occurs at 40 μA or more. When the cleaning bias value is 30 μA, simultaneous primary transfer and reverse transfer, that is, cleaning of remaining toner, is established.

The degree of occurrence of cleaning failure and cleaning ghost differs depending on the type of developer.
This is considered to be due to the toner amount (mg / cm ² ) of the next transfer residual toner 95. As can be seen from FIG. 7, the magnetic transfer toner has more secondary transfer residual toner 95 at the optimum secondary transfer bias than the non-magnetic toner. As a result, even if the cleaning current is increased, in the case of the non-magnetic toner, the charging polarity of all the secondary transfer residual toner 95 cannot be made positive, and it is considered that the occurrence of the cleaning failure cannot be prevented. Can be

As described above, according to the present embodiment,
(1) Since the residual toner on the intermediate transfer member can be cleaned simultaneously with the primary transfer, it can be used for continuous printing with a color laser beam printer, a color copier, or the like.
There is no need to perform a step of cleaning the residual toner on the intermediate transfer member when the primary transfer is not performed each time a sheet is printed out. From this, it is possible to improve the throughput in the continuous print mode. or,
(2) Since the remaining toner on the intermediate transfer member 5 can be cleaned only by the charger irrespective of contact or non-contact, the configuration is very simple and a low-cost cleaning means can be provided. Further, (3) compared to conventional blade cleaning, fur brush cleaning, etc., there is no mechanical damage to parts to be used, so that it is possible to provide a stable means for cleaning the intermediate transfer member which can sufficiently withstand long-term use. it can. The effect was obtained.

In this embodiment, a roller having an outer diameter of 20 mm is used as the cleaning roller 8. However, according to studies by the present inventors, a roller having an outer diameter of about 12 to 30 mm can perform the same function. confirmed.

Further, in this embodiment, the cylindrical photosensitive drum 1 and the intermediate transfer member 5 are used. However, it is needless to say that a belt-like photosensitive member or an intermediate transfer member has no problem and the same effect can be obtained. .

Although the belt transfer method is used as the secondary transfer means, the effect of the present invention does not change even if a conventional corona transfer or transfer roller method is used.

Although the present embodiment has been described with respect to a system that performs reversal development, a similar effect can be obtained in a system that performs regular development. Hereinafter, the case of the regular development will be described.

The toner used in the regular development is charged to a polarity opposite to that of the electrostatic latent image formed on the photosensitive drum. When the latent image has a negative polarity as in the above embodiment, a positive polarity toner is applied. Further, in the normal development, the background exposure is employed, so that the light portion potential and the dark portion potential have an opposite relationship to the time of the reversal development.

The bias for the primary transfer applied to the intermediate transfer member has a polarity opposite to that of the toner, that is, the same polarity as the potential of the latent image on the photosensitive drum and in a direction more negative than the potential of the latent image. , A high negative voltage is applied. For example, when the potential of the latent image is -600 V, the potential of the intermediate transfer member is -700 to -700 V.
A primary transfer bias of about -800 V is applied.

Similarly, in the secondary transfer, a negative bias is applied to transfer the final toner image to the transfer material.

After the completion of the secondary transfer in this way,
The polarity of the toner remaining on the intermediate transfer member is in an unstable state due to the mixture of positive and negative polarities. For this reason, also in the removal of the residual toner, the residual toner is charged to a polarity opposite to the original polarity of the toner, as in the above embodiment.

The residual toner charged as described above has a higher potential on the photosensitive drum side than the residual toner when passing through the primary transfer position. For this reason, at the time of the next primary transfer, the residual toner on the intermediate transfer body is reversely transferred to the photosensitive drum simultaneously with the primary transfer.

Embodiment 2 A second embodiment of the present invention is directed to a case where the shape factor SF is used as a developer.
1 is 150 to 170, shape factor SF2 is 140 to 160
The amorphous polymerized toner produced by the suspension polymerization method is used.

The resin used was a polymerized toner of styrene-butyl acrylate. When actually used, silica treated with oil is externally added for stabilizing the tribo.

FIG. 8 shows the dependence of the secondary transfer residual toner concentration on the secondary transfer bias for the amorphous non-magnetic polymer toner used in this embodiment. As a comparison, an amorphous non-magnetic toner obtained by a pulverization method used in Example 1 is cited.

In FIG. 8, the minimum value of the secondary transfer residual density of the non-magnetic polymerized toner is lower than that of the non-magnetic toner obtained by the pulverization method. At this time, the toner amount (mg / cm ² ) on the intermediate transfer member 5 before the secondary transfer was 0.7 mg / cm ² .

As the secondary transfer bias, an optimum secondary transfer bias as shown in FIG. 8 was used for each toner. Specifically, 8 μA was used for both the amorphous polymerized toner used in this example and the non-magnetic toner obtained by the pulverization method described as a comparative example.

Table 2 shows the occurrence of cleaning defects and cleaning ghosts when the bias value applied to the intermediate transfer member cleaning roller 8 was changed for the amorphous non-magnetic toner and the amorphous non-magnetic polymerized toner. It is a table of the result of having performed.

[0121]

[Table 2]

In Table 2, when a non-magnetic toner prepared by a pulverization method is used as a developer, cleaning failure occurs when the cleaning bias value for charging the residual toner on the intermediate transfer member is 0 to 20 μA, and when the cleaning bias value is 40 μA or more, the cleaning ghost is generated. Has been confirmed, and the primary transfer simultaneous cleaning is established when the cleaning bias value is 30 μA.

On the other hand, in the case of an amorphous polymerized toner, 0 to
Cleaning failure occurs at 10 μA, and a cleaning ghost occurs at 40 μA or more. Therefore, when the cleaning bias value is 20 to 30 μA, cleaning of the remaining toner is established at the same time as primary transfer, and cleaning with a lower cleaning bias value is performed. Is possible.

Embodiment 3 (Embodiment 1) In Embodiment 1 of the third embodiment of the present invention, the developer contains a low softening point substance at 5 to 30% by weight, a shape factor SF1 of 110 to 120, and a Coefficient SF2
Having a particle size of 5 to 100 produced by a suspension polymerization method.
A substantially spherical non-magnetic one-component polymerized toner of 7 μm is used.

When the shape of the toner approaches a spherical shape as much as possible,
It is said that the transfer efficiency is increased. It is considered that this is because the surface energy of each toner is reduced, the fluidity is increased, the attraction force (mirror force) on the photosensitive drum or the like is weakened, and the toner is easily affected by the transfer electric field.

FIG. 13 is a schematic structural view of the polymerized toner. As shown in FIG. 13, the polymerized toner 9 has a spherical shape due to its manufacturing method.

In this embodiment, the core 93 contains an ester wax, the resin layer 92 is made of styrene-butyl acrylate, and the surface layer 91 is made of styrene-polyester. Its specific gravity is about 1.05. 3
The reason why the layer structure is adopted is that by enclosing the core 93 with wax, an offset preventing effect in the fixing step is obtained, and by providing a resin layer on the surface layer 91, charging efficiency is improved. Yes, and at the time of actual use, oil-treated silica is externally added for stabilizing the tribo.

FIG. 9 shows the dependency of the secondary transfer residual toner concentration on the secondary transfer bias for the substantially spherical non-magnetic polymer toner used in this embodiment. As a comparison, the amorphous non-magnetic polymerized toner used in Example 2 is cited.

In FIG. 9, the minimum value of the concentration of the secondary transfer residual toner is lower in the substantially spherical non-magnetic polymer toner than in the amorphous non-magnetic polymer toner. At this time, the intermediate transfer member 5
The toner amount (mg / cm ² ) before the secondary transfer is 0.7
mg / cm ² .

As the secondary transfer bias, the optimum secondary transfer bias as shown in FIG. 9 was used for each toner. Specifically, 14 μA was used for the substantially spherical polymerized toner used in this example, and 8 μA was used for the amorphous polymerized toner mentioned as a comparative example.

Table 3 shows that the intermediate transfer member cleaning roller 8 is used for the irregular polymerized toner and the substantially spherical polymerized toner.
6 is a table showing the results of observing the occurrence of cleaning defects and cleaning ghosts when the bias value applied to the laser beam was changed.

[0132]

[Table 3]

In Table 3, when an amorphous polymerized toner is used as the developer, cleaning failure occurs when the cleaning bias value for charging the residual toner on the intermediate transfer member is 0 to 10 μA, and when the cleaning bias value is 40 μA or more, the cleaning ghost is not generated. Occurrence has been confirmed. When the cleaning bias value is 20 to 30 μA, cleaning of the remaining toner is established simultaneously with the primary transfer of the bias value.

On the other hand, in the case of a substantially spherical polymerized toner, when the bias value is 0 to 5 μA, the cleaning becomes poor.
Since the cleaning ghost occurs at 40 μA or more, the primary transfer simultaneous cleaning is established when the intermediate transfer cleaning bias is 10 to 30 μA, and the remaining toner can be cleaned with a lower cleaning bias value.

According to the study of the present inventors, the effect of the substantially spherical toner described in the present embodiment is the same even in a substantially spherical polymerized toner containing no low softening point substance. That was confirmed.

(Embodiment 2) In Embodiment 2 of the third embodiment of the present invention, after a developer is produced from a styrene-based resin binder by a pulverization method, it is subjected to a mechanical impact force, a hot air flow or a high temperature. Shape factor SF by spheroidizing treatment in liquid
1 is 140 to 150, shape factor SF2 is 120 to 130
A substantially spherical non-magnetic toner having a particle size of 5 to 7 μm was used.

FIG. 10 shows characteristics of the substantially spherical non-magnetic toner used in the present embodiment, in which the concentration of the residual toner on the intermediate transfer member after the secondary transfer depends on the secondary transfer bias. For comparison, the amorphous non-magnetic toner used in Example 1 is cited.

In FIG. 10, the minimum value of the secondary transfer residual density is lower in the substantially spherical non-magnetic polymer toner than in the amorphous non-magnetic polymer toner. At this time, the amount of toner (mg / cm ² ) on the intermediate transfer member before the secondary transfer is 0.7 mg / c.
It was m ^2.

As the secondary transfer bias, the optimum secondary transfer bias as shown in FIG. 10 was used for each toner. Specifically, 12 μA was used for the substantially spherical non-magnetic toner used in this example, and 8 μA was used for the amorphous non-magnetic toner mentioned as a comparative example.

Table 4 shows the results of observing the occurrence of defective cleaning and the occurrence of cleaning ghosts when the bias value applied to the cleaning roller 8 was changed for the amorphous non-magnetic toner and the substantially spherical non-magnetic toner. It is the table shown.

[0141]

[Table 4]

In Table 4, when an amorphous non-magnetic toner is used as the developer, cleaning failure occurs when the cleaning bias value for charging the residual toner of the intermediate transfer member is 0 to 20 μA, and when the cleaning ghost is 40 μA or more, the cleaning ghost is generated. Has been confirmed, and the primary transfer simultaneous cleaning is established when the cleaning bias value is 30 μA.

On the other hand, in the case of a substantially spherical non-magnetic toner,
Since cleaning failure occurs at 0 to 10 μA and cleaning ghost occurs at 40 μA or more, cleaning of the remaining toner is established at the same time as primary transfer at the cleaning bias value of 20 to 30 μA.
Cleaning with a lower cleaning bias value is possible.

Example 4 In a fourth example of the present invention, a magnetic material such as magnetite was internally added as a developer to a styrene-butyl acrylate-butyl maleate half ester copolymer binder by 100 parts, and the mixture was pulverized by a pulverization method. produced. This toner is subjected to mechanical impact force, spheroidization in hot air flow or high temperature liquid,
Shape factor SF1 is 140 to 150, shape factor SF2 is 1
This is a substantially spherical magnetic toner having a particle size of 5 to 7 μm and a particle size of 20 to 130. Oil-treated silica is externally added as an external additive. As a comparative toner, a magnetic material such as magnetite was added to a styrene-butyl acrylate-butyl maleate half ester copolymer binder.
00 parts internally added, shape factor SF1 manufactured by the pulverization method
Is 150 to 160, the shape factor SF2 is 140 to 150,
An amorphous magnetic toner externally added with oil-treated silica having a particle size of 5 to 7 μm is mentioned.

FIG. 11 shows the characteristic that the concentration of the residual toner after the secondary transfer depends on the secondary transfer bias for the substantially spherical magnetic toner used in the present embodiment and the amorphous magnetic toner as the comparative example. Show.

In FIG. 11, the minimum value of the secondary transfer residual density is lower in the substantially spherical magnetic toner than in the amorphous magnetic toner. At this time, the toner amount (mg / cm ² ) on the intermediate transfer member before the secondary transfer was 0.7 mg / cm ² .

As the secondary transfer bias, the optimum secondary transfer bias as shown in FIG. 11 was used for each toner. Specifically, 4 μA was used for both the substantially spherical magnetic toner used in this example and the amorphous polymerized toner mentioned as a comparative example.

Table 5 shows that the intermediate transfer member cleaning roller 8 is used for the irregular magnetic toner and the substantially spherical magnetic toner.
4 is a table showing the results of observing the occurrence of cleaning defects and cleaning ghosts when the bias value applied to the laser beam was changed.

[0149]

[Table 5]

In Table 5, when an amorphous magnetic toner was used as the developer, cleaning failure occurred at any of the cleaning bias values for charging the residual toner of the intermediate transfer member. Cleaning was not possible. On the other hand, in the case of the substantially spherical magnetic toner, cleaning failure occurs when the bias value is 0 to 30 μA, and a cleaning ghost occurs when the bias value is 50 μA or more.
At μA, the cleaning of the remaining toner is established simultaneously with the primary transfer.

The cleaning according to the present invention is realized by performing the spheroidizing process also on the magnetic toner.

Embodiment 5 Next, as a configuration for further improving the effect of the present invention, a case where a release layer is applied to the surface of a photosensitive drum will be described below.

The photosensitive drum 1 used in this embodiment will be described with reference to FIG.

In this study, two types of photosensitive drums were prepared.

First, as a photosensitive drum (hereinafter referred to as a first photosensitive drum) of a comparative example with respect to the present embodiment, an outer diameter of about 60
[Mm] a charge generating layer 1b made of a phthalocyanine compound having a thickness of 0.2 [μm] as a photosensitive layer on a core metal 1a made of aluminum having a thickness of 25 [mm].
[Μm] was used in which a charge transport layer 1c in which a hydrazone compound was dispersed in polycarbonate as a binder was used.

The photosensitive drum of the present embodiment (hereinafter referred to as a second photosensitive drum)
The photoreceptor drum of the above-described first photoreceptor drum was prepared by dispersing 10% of Teflon as fluorine particles in the charge transport layer 1c.

The purpose of this is to improve the releasability of the surface of the photosensitive drum, but the amount of Teflon to be added is 20 in order not to impair the original characteristics of the charge transport layer.
[%] Is preferably set to the upper limit.

The contact angles of water and the slipperiness of the surfaces of the two types of photosensitive drums 1 were measured.
The contact angle of the photosensitive drum was 85 [゜], the slip property was not slippery, and measurement was impossible, and the contact angle of the second photosensitive drum was 95 [゜] and the slip property was 0.8. Was.

Here, the slip property is measured by a slip property tester manufactured by Haydon Co., Ltd., and the slip property of an object to be measured is defined assuming that the slip property of polyethylene terephthalate (PET) is 1. It is indicated by a PET ratio, and the smaller the value, the better the slipperiness.

The results of various experiments using the image forming apparatus shown in FIG. 1 having the above configuration will be described below. The contact timing of the cleaning roller 8 with the surface of the intermediate transfer member 5 is determined for the monochrome printing. At the time of continuous printing, it was configured to contact the intermediate transfer body 5 at the same time as the primary transfer. This is to prevent the image from being disturbed by the influence of blur due to the contact. In the case of the four-color multiple transfer, the contact is made at the same time when the primary transfer of the fourth color is completed.

First, FIG. 15 shows the dependence of the primary transfer efficiency on the primary transfer bias when the toner on the surface of the photosensitive drum 1 is primarily transferred to the surface of the intermediate transfer body 5 without cleaning the intermediate transfer body. Shows sex.

Here, the primary transfer efficiency is obtained by measuring the toner concentration D1 on the surface of the photosensitive drum 1 after the primary transfer and the toner concentration D2 on the surface of the intermediate transfer member 5 after the primary transfer. Next transfer efficiency = D ₂ / (D ₁ + D ₂ ) × 100

The toner concentration was measured by tapping the toner on the surface of the photosensitive drum 1 and the surface of the intermediate transfer member 5 and measuring them using a Macbeth densitometer. D1 and D2 The value of was obtained by subtracting the concentration of the collecting tape itself from the actual measured concentration, that is, 0.1 in this experiment.

According to this, the first photosensitive drum and the second photosensitive drum
In comparison with the photoreceptor drum, it can be seen that high transfer efficiency can be obtained with a relatively low primary transfer bias when the second photoreceptor drum is used.

This is presumably because the fluorine particles added to the charge transport layer of the second photosensitive drum improved the releasability.

As described above, the high primary transfer efficiency and the low primary transfer bias can be obtained because the toner is not charged with the polarity opposite to the normal polarity in the primary transfer step. The secondary transfer efficiency is also improved, and the density of the image output as a result can be made sufficiently high.

Next, the secondary transfer bias dependency of the secondary transfer residual toner concentration remaining on the surface of the intermediate transfer member 5 when the toner on the surface of the intermediate transfer member 5 is secondarily transferred to the surface of the transfer material P is shown in FIG. As shown in the figure, the toner concentration was measured by collecting the secondary transfer residual toner on the surface of the intermediate transfer member 5 by taping and measuring it with a Macbeth densitometer. Means that there is little secondary transfer residual toner remaining. At this time, the toner amount M / S [mg / cm ² ] on the surface of the intermediate transfer member 5 is 0.5 [mg / cm ² ] for single color and 1.4 [mg / cm ² ] for four colors.
cm ² ].

According to this, the residual toner density is minimum at the secondary transfer bias of about 10 to 15 [μA], in other words, the secondary transfer efficiency is maximum at the time of single color and four color multiple transfer. You can see that.

As described above, it is preferable that the residual toner on the surface of the intermediate transfer member 5 be as small as possible in order to clean the intermediate transfer member satisfactorily in this embodiment.

When the amount of the residual toner is large, it becomes necessary to apply a strong electric field when the residual toner is charged by the cleaning roller 8 and pulled back to the photosensitive drum 1.

In the case where the cleaning is performed with such a strong electric field, a part of the toner already charged to the opposite polarity (positive) at the time of the secondary transfer is more strongly charged. In this case, a toner having a high electric charge is present, and the phenomenon of a cleaning ghost described later is likely to occur. From the above viewpoints, in the subsequent studies, the secondary transfer bias is set to 1
It was fixed at 2 [μA].

Next, the results of an experiment on cleaning of the intermediate transfer member, which is a feature of the present invention, will be described. In this experiment, from the above experimental results, the first photosensitive drum was used for the primary transfer bias. 300 if there was
[V], 100 when the second photosensitive drum is used
In [v], the secondary transfer bias was set to 12 [μA], and the dependency of the cleaning bias applied to the cleaning roller 8 under this condition was confirmed.

FIG. 17 shows the result when the first photosensitive drum is used, and FIG. 18 shows the result when the second photosensitive drum is used. The residual toner after the secondary transfer remaining on the surface of the transfer member 5 cannot be returned to the surface of the photosensitive drum 1 even by the action of the cleaning roller 8. This shows a problem that a positive ghost image appears on the second solid white image.

According to this, no matter which one of the first and second photosensitive drums is used, the cleaning failure,
The appropriate range of the bias value applied to the cleaning roller 8 which can prevent the occurrence of both cleaning ghosts is:
It can be seen that there is a shift to a slightly higher region when four colors are multiplexed than when single colors are used.

This is because the electric field received by the toner on the surface of the intermediate transfer member 5 at the time of the secondary transfer is different. This is because the amount of toner on the surface of the transfer member 5 is large, and the amount of toner charged to the opposite polarity slightly decreases.

Further, when the second photosensitive drum is used, the above-mentioned appropriate range, particularly the upper limit of the occurrence of the cleaning ghost, is wider than when the first photosensitive drum is used.

The reason for this is that the cleaning ghost can
The primary transfer bias acting on the toner to be primarily transferred from the surface of the photosensitive drum 1 to the surface of the intermediate transfer member 5 at the next transfer position, and the ease of separation of the toner from the surface of the photosensitive drum 1, in other words, the photosensitive The balance between the releasability of the surface of the body drum 1 and the effect of being electrostatically attracted to the toner drawn back from the surface of the intermediate transfer body 5 to the surface of the photosensitive drum 1 contributes.

That is, as described above, in the case of the second photosensitive drum, the fluorine particles added to the charge transport layer 1c cause
Since the releasability is improved, it is possible to lower the primary transfer bias. This suppresses the generation of toner whose polarity is inverted by the primary transfer, and prevents the toner remaining on the intermediate transfer member 5 after the secondary transfer from being present with a toner having a high positive charge. Will be. Therefore, the appropriate range of the bias applied to the cleaning roller 8 can be set wide.

As described above, the fact that the appropriate range of the cleaning bias value can be set broadly depends on the manufacturing fluctuation of the resistance values of the intermediate transfer member 5 and the cleaning roller 8.
It is very effective when considering the resistance value change due to these environmental changes, the change in the amount of toner on the surface of the intermediate transfer member 5, and the like. From this viewpoint, it is possible to use a photosensitive drum having a surface having excellent releasability. It is effective to use.

A continuous image print test of 100,000 sheets was conducted using the above-described cleaning roller 8 and the second photosensitive drum 1 having a release layer on its surface. The cleaning of the intermediate transfer member can be performed.
Since the rotation was driven by rotation of the intermediate transfer member 5, no wear was observed.

With the configuration described above,
Since the intermediate transfer body can be cleaned at the same time as the primary transfer, even in the case of continuous printing with a color laser printer, a color copying machine, or the like, a step of cleaning the surface of the intermediate transfer body 8 every time one sheet is printed out. Since the setting does not need to be made, a significant improvement in throughput can be realized.

Although the polymerized toner manufactured by the suspension polymerization method was used as the toner, the same method can be used by optimizing the cleaning bias of the intermediate transfer member even if a toner manufactured by a normal pulverization method is used. The effect is obtained.

Embodiment 6 Hereinafter, another embodiment relating to the improvement of the surface of the photosensitive drum of the present invention will be described. The same members as those described above are designated by the same reference numerals, and description thereof will be omitted. In this embodiment,
The apparatus according to the fifth embodiment is characterized in that the photosensitive drum 1 having a surface release layer 1d formed on the outer peripheral surface of the charge transport layer 1c shown in FIG. 19 is used.

In the photosensitive drum 1 shown in this embodiment, a charge generation layer 1b having a thickness of 0.2 [μm] is formed on a core metal 1a made of aluminum having an outer diameter of approximately 60 [mm]. A charge transport layer 1c having a thickness of 15 μm is formed on the upper layer, and a thickness of 3 μm is further formed on the upper layer by dipping.
m] is obtained by forming the surface release layer 1d.

The surface protective layer 1d is composed of a binder made of acrylic having ultraviolet curability, and dispersed with 35% of Teflon (trade name) having a particle diameter of about 0.3 μm as fluorine particles. Let me do it.

As described above, by separating the charge transport layer and the surface release layer for improving the releasability into two layers, a large amount of fluorine particles can be added to the surface release layer. This makes it possible to improve the surface slipperiness as compared with the case where fluorine particles are added to the charge transport layer shown in the first embodiment.

Specifically, the contact angle of water on the surface of the photoreceptor drum used in this example and the slipperiness were measured. The contact angle was 100 ° and the slipperiness was 0.4. .

When the amount of fluorine particles added to the surface release layer is too large, the film strength decreases and the film becomes brittle because the binding force of the binder is relatively weakened. Therefore, it is preferable to set the upper limit to about 45%.

Here, using the photosensitive drum 1 described above,
FIG. 20 shows experimental results showing that the cleaning effect on the surface of the intermediate transfer member depends on the cleaning bias applied to the cleaning roller 8.

The experimental method, experimental conditions, and the like are the same as those in the fifth embodiment, and a description thereof will not be repeated.

According to this, according to the second embodiment shown in the fifth embodiment,
The appropriate range of the intermediate transfer member cleaning bias, particularly the upper limit side of the occurrence of the cleaning ghost, is wider than when the photosensitive drum is used.

It is considered that this is because the surface releasability of the second photosensitive drum was improved as compared with the second photosensitive drum shown in the fifth embodiment, as is clear from the measurement results of the contact angle and the slipperiness described above. .

A continuous print test of 100,000 images was performed using the above-mentioned photosensitive drum in the same manner as described in the fifth embodiment. As a result, good and stable cleaning of the intermediate transfer member 5 could be realized. Was.

Embodiment 7 Another embodiment according to the present invention will be described below. In this embodiment, a surface release layer 1d is formed on the outermost layer of the photosensitive drum 1 in the same manner as in Embodiment 6. However, it is characterized in that the forming method is a spray method. The configuration of the apparatus other than the photosensitive drum 1 is the same as that of the fifth embodiment.

More specifically, a charge generation layer 1b having a thickness of 0.2 [μm] is formed on a core metal 1a made of aluminum having an outer diameter of approximately 60 [mm]. (Μ
m], and a surface release layer 1d having a thickness of 3 [μm] formed thereon by spraying. This surface protective layer 1d is made of a binder made of polycarbonate, and a Teflon (trade name) having a particle diameter of about 0.3 [μm] as a fluorine particle.
5% is dispersed. When the contact angle of the surface with water and the slipperiness were measured, the contact angle was 10
4 [゜], the slip property was 0.2.

It is considered that this value is better than that of the photoreceptor drum used in Example 6 because polycarbonate itself as a binder has better slipperiness than acrylic itself.

FIG. 21 shows experimental results showing that the cleaning effect of the intermediate transfer member 5 using the photosensitive drum depends on the cleaning bias applied to the cleaning roller 8. The experimental method, experimental conditions, and the like are the same as those in the fifth embodiment, and the description is omitted here.

According to this, as in the case of the photosensitive drum shown in the sixth embodiment, the bias value to the cleaning roller 8 is smaller than that in the case where the second photosensitive drum shown in the fifth embodiment is used. The appropriate range, particularly the upper limit of the occurrence of cleaning ghost, is wide.

It is considered that this is because the surface releasability of the second photosensitive drum was improved as compared with the second photosensitive drum shown in Example 5, as is clear from the measurement results of the contact angle and the slipperiness described above. .

Here, a continuous print test of 100,000 sheets was conducted using the photosensitive drum 1 in the same manner as described in Example 5, and a good and stable cleaning of the intermediate transfer member could be realized. .

Next, the toner applied to the photosensitive drums of Examples 5 to 7 will be described.

As shown in the above embodiment, the primary transfer bias value can be reduced by using a photosensitive drum 1 having releasability and using a substantially spherical toner. For this reason, secondary transfer efficiency is increased because the toner tribo on the intermediate transfer member 5 is less neutralized, and substantially the same cleaning as the primary transfer of the present invention, that is, the above-described reverse transfer becomes possible. .

The developing method used was a well-known one-component non-contact developing method (jumping developing method).

The toner that can be used is a toner obtained by further spheroidizing a conventional pulverized toner. As substitute properties, the shape factor SF-1 is 110 to 180, and the shape factor SF-2 is 1
10 to 140. More preferably, the shape factor SF-
1 was 120 to 160, and SF-2 was 115 to 140. The volume average diameter of the used toner was 6 to 7 μm.

The toner used in the above examples was prepared by adding a magnetic material such as magnetite to a styrene-butyl acrylate-butyl maleate half-ester copolymer binder.
After being internally added and manufactured by a pulverization method, the shape factor SF-1 is 140 to 150 and the shape factor SF-2 is 120 by mechanical impact force or spheroidizing treatment in a hot air flow or a high-temperature liquid.
It was a substantially spherical magnetic toner having a particle size of 5 to 7 μm. Oil-treated silica was used as an external additive.

According to this embodiment, it is possible to lower the primary transfer bias by using the photosensitive drum 1 having releasability and applying the substantially spherical developer as described above. Therefore, the secondary transfer efficiency is increased because the toner is less likely to neutralize the tribo of the toner on the intermediate transfer member 8, and the cleaning of the intermediate transfer member by the primary transfer and the secondary transfer of the present invention can be substantially performed. It becomes possible.

[0207]

In the above embodiment, the case where the present invention is applied to a full-color printer to which a digital optical system is applied has been described. However, an image forming apparatus using each of red, blue, yellow and black toners, This is also effective for an apparatus using toner. That is, even if the apparatus can reproduce only a single color, if the mode for outputting an image as described above is a continuous mode, it is effective in improving the reduction of the throughput time.

As a means for removing the toner which has cleaned the toner secondary-transferred onto the image carrier from the image carrier, a known cleaning means such as a conventional blade or brush can be applied.

Further, the intermediate transfer member is not limited to a drum-shaped one, but may be a belt-shaped one. The transfer material may be a resin sheet, an envelope, a card, or a postcard other than plain paper. As the image carrier, other than the electrophotographic photosensitive member, a dielectric for electrostatic recording, a magnetic for magnetic recording, or the like can be applied.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a laser beam printer as an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view of an intermediate transfer member cleaning roller incorporated in the laser beam printer of the first embodiment.

FIG. 3 is a schematic cross-sectional view of an intermediate transfer member cleaning roller used in the present invention and an actual use resistance measuring device of the intermediate transfer member.

FIG. 4 is an enlarged sectional view of the intermediate transfer member.

FIG. 5 is an explanatory diagram of a shape factor SF1.

FIG. 6 is an explanatory diagram of a shape factor SF2.

FIG. 7 is a graph showing a relationship between a secondary transfer current and a secondary transfer residual density on an intermediate transfer member in Example 1.

FIG. 8 is a graph showing a relationship between a secondary transfer current and a secondary transfer residual density on an intermediate transfer member in Example 2.

FIG. 9 is a graph showing the relationship between the secondary transfer current and the residual secondary transfer density on the intermediate transfer member in Examples 3 and 1.

FIG. 10 is a graph showing the relationship between the secondary transfer current and the residual secondary transfer density on the intermediate transfer member in Examples 3 and 2.

FIG. 11 is a graph showing a relationship between a secondary transfer current and a secondary transfer residual density on an intermediate transfer member in Example 4.

FIG. 12 is a diagram illustrating a mechanism of a cleaning negative ghost.

FIG. 13 is a schematic sectional view of a polymerized toner used in the present invention.

FIG. 14 is a schematic configuration diagram of a photosensitive drum according to the present invention.

FIG. 15 is a diagram showing the dependence of primary transfer efficiency on primary transfer bias.

FIG. 16 is a diagram illustrating the dependence of the secondary transfer residual toner concentration on the secondary transfer bias.

FIG. 17 is a view showing the cleaning bias dependency of the cleaning performance of the surface of the intermediate transfer member when the first photosensitive drum is used.

FIG. 18 is a view showing the cleaning bias dependency of the cleaning performance of the surface of the intermediate transfer member when the second photosensitive drum is used.

FIG. 19 is a schematic configuration diagram showing another embodiment of the photosensitive drum according to the present invention.

FIG. 20 is a diagram illustrating the cleaning bias dependency of the cleaning performance of the surface of the intermediate transfer member when a photosensitive drum having a surface release layer is used.

FIG. 21 is a diagram illustrating the cleaning bias dependence of the cleaning performance of the surface of the intermediate transfer member when another photosensitive drum having a surface release layer is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging roller 3 Laser beam 41-44 Developing device 5 Intermediate transfer body 6 Transfer belt 8 Intermediate transfer body cleaning roller 9 Toner

──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuhiko Nishimura, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Tatsuya Sakamaruko 3-30-2, Shimomaruko, Ota-ku, Tokyo (56) References JP-A-1-105980 (JP, A) JP-A-4-340564 (JP, A) JP-A-5-297739 (JP, A) JP-A-5-333706 (JP) , A) JP-A-7-244435 (JP, A) JP-A-9-50167 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16-15/16 103

Claims (31)

(57) [Claims] An image forming apparatus for forming a toner image on a transfer material using an intermediate transfer body, an image carrier, a toner image forming means for forming an image on the image carrier with a non-magnetic toner, and an image carrier An intermediate transfer member that moves endlessly by contacting the intermediate transfer member; a bias applying unit that performs primary transfer of the toner image formed on the image carrier to the intermediate transfer member at a first transfer position of the intermediate transfer member; The toner image transferred to the transfer member is transferred to the second transfer member of the intermediate transfer member.
Transfer means for secondary transfer to the transfer material at the transfer position, and residual toner charging means for charging residual toner remaining on the intermediate transfer body after transfer to a polarity opposite to the original polarity of the toner, After the secondary transfer, the residual toner on the intermediate transfer member is charged to the polarity opposite to the original polarity of the toner by the residual toner charging means, and the charged residual toner is transferred to the primary transfer position during the primary transfer. The image forming apparatus removes the residual toner on the intermediate transfer body by reverse-transferring the residual toner to the image carrier at the same time as the primary transfer by passing the toner. 2. The image bearing member according to claim 1, wherein said image bearing member is an electrophotographic photosensitive member having a releasable property on its surface, is charged to the same polarity as that of the toner, and forms a toner image by reversal development. Image forming device. 3. The image forming apparatus according to claim 1, wherein a bias having a polarity opposite to the polarity of the toner is applied to the bias applying unit for performing the primary transfer. 4. The image forming apparatus according to claim 3, wherein the intermediate transfer member has a conductive layer, and a bias for primary transfer is applied to the conductive layer by bias applying means. 5. The image bearing member according to claim 1, wherein the image bearing member is an electrophotographic photosensitive member having a releasable surface, is charged to a polarity opposite to the polarity of the toner, and forms a toner image by regular development. Image forming device. 6. The image forming apparatus according to claim 5, wherein a bias having a polarity opposite to the polarity of the toner is applied to the bias applying unit for performing the primary transfer. 7. The image forming apparatus according to claim 6, wherein the intermediate transfer member has a conductive layer, and a bias for primary transfer is applied to the conductive layer by bias applying means. 8. The image forming apparatus according to claim 1, wherein the remaining toner charging unit is a rotating roller that comes into contact with and separates from the intermediate transfer member. 9. An image forming apparatus according to claim 1, wherein said remaining toner charging means is a corona charger. 10. The image forming apparatus according to claim 1, wherein the toner is a spherical polymerized toner. 11. The toner according to claim 1, wherein the shape factor SF-1 is 1
00 to 180, the shape factor SF-2 is 100 to 140
The image forming apparatus according to claim 10, wherein: 12. The toner according to claim 1, wherein the shape factor SF-1 is 1
10 to 180, the shape factor SF-2 is 110 to 140
The image forming apparatus according to claim 11, wherein: 13. The toner according to claim 1, wherein the shape factor SF-1 is 1
20 to 160, the shape factor SF-2 is 115 to 140
The image forming apparatus according to claim 12, wherein: 14. The image forming apparatus according to claim 1, wherein the photoconductor has fluorine resin particles on the surface to obtain releasability. 15. An image forming apparatus for forming a toner image on a transfer material using an intermediate transfer member, wherein the toner image forming device forms a color toner image with a plurality of non-magnetic color toners on the image carrier. Means, an intermediate transfer body that moves endlessly in contact with the image carrier, and a toner image formed on the image carrier is sequentially transferred to the intermediate transfer body at a first transfer position of the intermediate transfer body for each color. Bias applying means for primary transfer, and a toner image transferred to the intermediate transfer member,
Transfer means for collectively transferring the toner to the transfer material at the transfer position, and remaining toner charging means for charging the residual toner remaining on the intermediate transfer body after the transfer to a polarity opposite to the original polarity of the toner. In the first image forming mode in which an image is formed with the single-color toner, the toner image is secondarily transferred to the transfer material each time the toner image by the single-color toner is transferred to the intermediate transfer material. In the second image forming mode in which an image is formed by using the color toners, after a plurality of color toners are sequentially transferred to the intermediate transfer material, the toner images are collectively secondarily transferred to the transfer material, and then the intermediate transfer is performed. The residual toner on the body is charged to the polarity opposite to the original polarity of the toner by the residual toner charging means, and the charged residual toner is passed through the primary transfer position during the primary transfer, so that the primary toner is charged. At the same time as the transfer, this residual toner Image forming apparatus for removing residual toner on the intermediate transfer member by reverse transcription into. 16. The image forming apparatus according to claim 15, wherein the toner is a spherical polymerized toner. 17. The toner according to claim 1, wherein the shape factor SF-1 is 1
00 to 180, the shape factor SF-2 is 100 to 140
The image forming apparatus according to claim 15, wherein: 18. The toner according to claim 18, wherein the shape factor SF-1 is 1
10 to 180, the shape factor SF-2 is 110 to 140
The image forming apparatus according to claim 17, wherein: 19.18, the toner has a shape factor SF-1 of 120 to 160,
The shape factor SF-2 is 115 to 140. 19. The image forming apparatus according to claim 15, wherein the photoreceptor has fluorine resin particles on the surface to obtain releasability. 20. The image forming apparatus according to claim 15, wherein the color toners are yellow, magenta, and cyan. 21. An image forming apparatus for forming a toner image on a transfer material using an intermediate transfer member, comprising: an image carrier which is an electrophotographic photosensitive member; and a toner image comprising black toner and a plurality of non-magnetic toners on the image carrier. A transfer device that forms an image, an intermediate transfer member that moves endlessly in contact with the image carrier, and a toner image formed on the image carrier is firstly transferred to the intermediate transfer member at a first transfer position of the intermediate transfer member. A bias application mechanism for transferring the toner image transferred to the intermediate transfer member;
Transfer means for secondary transfer to the transfer material at the transfer position, and a residual toner charger for charging the residual toner remaining on the intermediate transfer body after the transfer to a polarity opposite to the original polarity of the toner, In the first image forming mode for forming an image with the single color toner, each time the toner image of the single color toner is transferred to the intermediate transfer material, the toner image is secondarily transferred to the transfer material. In the second image forming mode in which an image is formed by a plurality of color toners, the plurality of color toners are sequentially transferred to the intermediate transfer material, and then the toner images are collectively secondarily transferred to the transfer material. The residual toner is charged to the polarity opposite to the original polarity of the toner by the residual toner charger, and the charged residual toner is passed through the primary transfer position during the primary transfer, thereby simultaneously with the primary transfer. This residual toner is reversely transferred to the image carrier. Image forming apparatus for removing residual toner on the intermediate transfer member by. 22. The image forming apparatus according to claim 21, wherein the image carrier is charged to the same polarity as the toner and forms a toner image by reversal development. 23. The image forming apparatus according to claim 21, wherein the image carrier is charged to a polarity opposite to the polarity of the toner, and forms a toner image by regular development. 24. The image forming apparatus according to claim 21, wherein the color toners are yellow, magenta, and cyan. 25. The image forming apparatus according to claim 24, wherein the remaining toner charging unit is a rotating roller that is not in contact with the intermediate transfer member until the set number of primary transfers is completed. 26. The image forming apparatus according to claim 21, wherein the remaining toner charger is a corona charger. 27. The toner has a shape factor SF-1 of 1
00 to 180, the shape factor SF-2 is 100 to 140
22. The image forming apparatus according to claim 21, wherein 28. The toner according to claim 28, wherein the shape factor SF-1 is 1
10 to 180, the shape factor SF-2 is 110 to 140
The image forming apparatus according to claim 27, wherein: 29. The toner has a shape factor SF-1 of 1
20 to 160, the shape factor SF-2 is 115 to 140
The image forming apparatus according to claim 28, wherein: 30. When a plurality of images are continuously formed in the first image forming mode using the single-color toner, the residual toner charging device operates on the intermediate transfer member every time the secondary transfer process is completed. 22. The image forming apparatus according to claim 21, wherein the residual toner is charged. 31. The image forming apparatus according to claim 21, wherein the photoreceptor has fluorine resin particles on the surface to obtain releasability.