JP3021363B2 - 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 using an electrophotographic method, and more particularly, to a transferable image (toner image) formed on a first image carrier, which is temporarily used as a second image carrier. A primary transfer is performed on the intermediate transfer body, and a transfer material as a third image carrier is pressed against the intermediate transfer body with a contact transfer member, and is secondarily transferred to the transfer material to obtain an image formation (copy / print). The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

In the above, the first image carrier is, for example, an electrophotographic photosensitive member, an electrostatic recording dielectric, a magnetic recording magnetic material, or the like.

The process of forming a transferable image on the first image carrier is, for example, an electrophotographic process, an electrostatic recording process, a magnetic recording process, or the like.

An intermediate transfer member as a second image carrier is
A roller-shaped body (drum-shaped body) and a belt-shaped body.

The transfer material as the third image carrier is a transfer paper, a recording paper, a printing paper, a card, an envelope, a postcard, and the like.

[0006]

2. Description of the Related Art An image forming apparatus using an intermediate transfer member as described above performs an intermediate transfer by forming a transferable image on a first image carrier and repeating a primary transfer step of the image onto the intermediate transfer member. After forming a color image (or a multicolor image) composed of a plurality of color developers on the body, the image is subjected to secondary transfer collectively to a transfer material, thereby outputting an image formed product in which color image information is synthesized and reproduced. Although the image forming apparatus is provided with a color image forming function, it is effective as an image forming apparatus, and can obtain an image without overlapping deviation (color deviation) of each component color image.

As a full-color image forming apparatus using an intermediate transfer member, there is known a device using a drum-shaped roller as an intermediate transfer member, as described in US Pat. No. 5,187,526. Have been.

FIG. 16 shows a schematic configuration of the image forming apparatus. That is, the electrophotographic photosensitive drum 1 as a first image carrier, which is driven to rotate in the clockwise direction of the arrow, is uniformly charged by a corona charger 22 according to a known electrophotographic method, and is obtained by exposure 3. The developed electrostatic latent image is developed by a developing device 4 into a developer (hereinafter, referred to as toner) composed of colored charged particles.
And visualized. The toner image is transferred to an intermediate transfer roller 5 as a second image carrier that rotates synchronously in the forward direction at the same peripheral speed as the photosensitive drum in contact with or close to the photosensitive drum 1 at a first transfer nip area N1. The primary transfer is performed. That is, the intermediate transfer roller 5 is composed of a core metal 51 and a surface layer 52 made of a thin layer of conductive polyurethane, and applies a bias voltage having a polarity opposite to that of the toner by the power supply 29 to electrostatically transfer the toner image on the photosensitive drum 1. Transcribe.

The formation of the toner image on the photosensitive drum 1 and the primary transfer process of the toner image to the intermediate transfer roller 5 are repeatedly performed by the required number of component colors of the target full-color image information, thereby executing the intermediate transfer roller. A full-color image corresponding to the target color image information is synthesized and formed on the surface 5 by superimposing and transferring the toner images of the respective component colors. Developing device 4
The developing device containing the toner of the corresponding color is replaced with the developing position of the photosensitive drum 1 every time the component color toner image is formed on the photosensitive drum 1.

When the final primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer roller 5 is performed, a second transfer nip area between the intermediate transfer roller 5 and the transfer roller 7 as a contact transfer member is provided. A transfer material P such as a transfer paper is fed to the N2 from a paper supply unit (not shown) at a predetermined timing, and the full-color image formed on the intermediate transfer roller 5 is secondarily transferred to the transfer material P.

The transfer roller 7 is constituted by a core layer 71 and a surface layer 72 made of a thin layer of conductive polyurethane. At the time of primary transfer of the toner image from the photosensitive drum 1 onto the intermediate transfer roller 5, the switch layer 90 causes the core layer 71 to move. When the secondary transfer of the full-color image from the intermediate transfer roller 5 to the transfer material P is performed by the switch 90, the core 71 has the opposite polarity to the toner and the power supply 2 for the core 51 of the intermediate transfer roller 5 is connected to the ground 91.
9 is coupled to a bias power supply 92 having a voltage greater than the applied voltage.

The transfer material P to which the full-color image has been transferred from the intermediate transfer roller 5 is introduced into a fixing device (not shown) and undergoes image fixing processing to form a full-color image formed product.

Reference numeral 13 denotes a cleaner for the photosensitive drum 1. 8
Reference numeral 0 denotes a cleaner for the intermediate transfer roller 5, and the cleaner 8
0 is moved toward and away from the intermediate transfer roller 5 by a shift means (not shown), and at least after the primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer roller 5 is started, Until the secondary transfer of the full-color image to the transfer material P is completed, it is moved and held at a position separated from the intermediate transfer roller 5. The transfer roller 7 is also moved toward and away from the intermediate transfer roller 5 by the shift means, and is brought into pressure contact with the intermediate transfer roller 5 during the secondary transfer of the full-color image from the intermediate transfer roller 5 to the transfer material P. It can also be moved and held at a position where it has been moved.

The use of the drum-shaped intermediate transfer roller 5 as the intermediate transfer member for the above-described apparatus does not require a mechanism for correcting the traveling accuracy as compared with the belt-shaped intermediate transfer member, and has a simple configuration and no misalignment. There is an advantage that a full-color image can be obtained. Further, the image forming apparatus is not limited to forming a color image, and primary-transfers an image formed on a first image carrier to an intermediate transfer member, and further secondary-transfers the image to a transfer material. This is effective for a transfer material in which it is difficult to directly transfer the formed image to the transfer material, for example, a very thin paper or sheet, or a very thick paper. That is, such a transfer material is
This is because it is not easy to support and transport around the image carrier. Further, such an image forming apparatus is also effective in that, when the transfer material is paper, paper dust does not adhere to the first image carrier.

[0015]

However, such a two-transfer image forming apparatus requires high transfer efficiency of an image. Further, it is required that the image quality does not deteriorate even in the two transfer operations.

Accordingly, it is an object of the present invention to provide an image forming apparatus having high transfer efficiency and no image quality deterioration at the time of transfer.

[0017]

According to the present invention, an image formed on a first image bearing member is formed on an intermediate transfer member serving as a second image bearing member, and then the image is transferred to a transfer material by using a contact transfer means. In the image forming apparatus for transferring, the dielectric constant of the surface layer of the first image carrier is ε _d , the dielectric constant of the surface layer of the intermediate transfer body ε _ITD and the dielectric constant of the surface layer of the secondary contact transfer means are ε _Tr. And these have a relationship of ε _d ≦ ε _ITD ≦ ε _Tr , and the volume resistivity of the intermediate transfer member is 10 ⁶ Ω · cm to ^{10 10} Ω · c.
m (when 1 kV is applied) when the volume resistivity of the contact transfer means is 1
An image forming apparatus which is a ^{0 8 Ω · cm~10 15 Ω ·} cm ( at 1kV is applied).

When the intermediate transfer member and the contact transfer means are composed of a single layer, their surface layers are the single layer itself.

By using the image forming apparatus according to the present invention, it is possible to execute a process with no transfer unevenness and high transfer efficiency, to save toner consumption, and to reduce waste toner. . Further, since the secondary transfer efficiency is particularly high, the cleaner for the intermediate transfer member can be simplified. Furthermore, in each color image superimposed on the intermediate transfer body, both the toner near the surface and the toner in the lower layer in contact with the intermediate transfer body are transferred to the transfer material, and the color reproducibility which is most important in the color image is transferred. Is excellent.

The transfer efficiency and image quality of an image forming apparatus using an intermediate transfer member greatly depend on the resistance and dielectric constant of the member. That is, the volume resistance value of the intermediate transfer member is 10 ⁶ Ω · c
m (when 1 kV is applied), the transfer efficiency of the toner from the intermediate transfer body to the transfer material (hereinafter referred to as the secondary transfer efficiency) decreases. When the volume resistance value is 10 ¹¹ Ω · cm (when 1 kV is applied) or more, the transfer efficiency of toner from a first image carrier such as a photosensitive drum to an intermediate transfer member (hereinafter, 1)
Next transfer efficiency) is reduced. This phenomenon is considered to occur because when a high-resistance substance rotates in contact with a high voltage applied state, a discharge according to Paschen's rule occurs at the time of separation, a retransfer phenomenon occurs due to a peeling discharge, and an increase in reversal toner is caused. . In the transfer step using a low voltage, no re-transfer phenomenon occurs because peeling discharge does not occur. When the volume resistance value of the intermediate transfer member is 10 ¹¹ Ω · cm (when 1 kV is applied) or more, the primary transfer bias increases, and the secondary transfer bias is also applied in a primary superimposed manner. , It is necessary to apply a higher bias than when the resistance is low, which adversely affects the image quality and increases the cost due to an increase in the high-voltage power supply performance.

Therefore, it is desirable that the resistance values of the intermediate transfer member and the secondary transfer means be set as low as image quality allows, including environmental fluctuations, so that both the primary transfer efficiency and the secondary transfer efficiency are set to high values. In order to satisfy the above condition, the resistance value of the intermediate transfer member should be 10 ⁶ Ω · cm (when 1 kV is applied) or more and 10 ¹⁰ Ω · c
m (when 1 kV is applied).

Also in the so-called secondary transfer step of transferring from the intermediate transfer member to a third image carrier such as transfer paper, the resistance value of the secondary transfer means has a great influence on transfer efficiency and image quality. Needless to say. Volume resistivity is 10 ⁸ Ω
When the voltage is less than cm (at the time of applying 1 kV), the volume efficiency of the paper in a low-humidity environment is lower than the efficiency of the paper. The volume resistivity is 10 ¹⁵ Ω · cm (when 1 kV is applied)
In the case described above, similarly to the transfer of the intermediate transfer member, the secondary application bias becomes large, so that retransfer by peeling discharge easily occurs, and the power supply cost also increases.

Therefore, in order to satisfy the secondary transfer efficiency with a high value in the secondary transfer means, the resistance value of the secondary transfer means should be 10 ⁸ Ω · cm (when 1 kV is applied) or more and 10 ¹⁵ Ω ·
cm (at the time of applying 1 kV).

In the present invention, in order to obtain high transfer efficiency at a low transfer voltage, attention was paid to the relative dielectric constant of the first and second image carriers and the final contact transfer means. This is because the transfer electric field can be increased without applying a high transfer bias.

The reason why the transfer efficiency is improved by increasing the relative dielectric constant is considered as follows. That is,
The electric field applied between the first image bearing member and the intermediate transfer member is represented by E
1. Assuming that the electric field applied between the intermediate transfer member and the final contact transfer means is E2, E1 and E2 can be written as follows.

[0026] _{E 1 = (V d -V ITD1} ) / (d d / ε d + d tl / ε t + d ITD / ε ITD + d e / ε e + g 1) ... (1) E 2 = (V ITD2 -V _T ) / (d _ITD / ε _ITD + de / ε _e + d ₁₂ / ε _t + d _p / ε _p + d _Tr / ε _Tr + g ₂ ) (2) where V _d : surface on the first image carrier Potential V _ITD1 : Surface potential on intermediate transfer member V _ITD2 : Surface potential on intermediate transfer member V _T : Surface potential on final transfer means d _d : Recording layer of first image carrier (recording of electrophotographic photosensitive member) The layer is a photosensitive layer, and the recording layer of an electrophotographic photosensitive member having an overcoat layer is a laminate of the overcoat layer and the photosensitive layer.) Thickness d _t1 : thickness of the toner layer on the first image carrier d _ITD : intermediate transfer member the thickness d _e of the coating layer: thickness of the elastic layer of the intermediate transfer member d _12: thickness of the toner layer on the intermediate transfer member d _P: thickness of the transfer material d _Tr: Final thickness of the transfer means epsilon _d: the intermediate transfer member: a first image bearing member having a relative dielectric constant of the surface layer epsilon _t: toner layer of the dielectric constant epsilon _ITD: relative permittivity of the coating layer of the intermediate transfer member epsilon _e Relative dielectric constant of the elastic layer ε _P : relative dielectric constant of the transfer material ε _Tr : relative dielectric constant of the surface layer of the final transfer means g1: gap width between the first image carrier and the intermediate transfer member g2: intermediate between the transfer material and the intermediate material Gap width with transfer body The transfer efficiency in electrostatic transfer of toner is proportional to the electric field E applied to the gap between the transfer material and the toner layer. Then, as is clear from the equations (1) and (2), it is found that when the relative dielectric constant ε is increased, E1 and E2 are increased.
Further, the capacitance C and the relative permittivity ε are given by C = εε ₀ S / d (S
Is a unit area, d is a thickness, and ε ₀ constant: dielectric constant of vacuum. Therefore, when the capacitance C of the first image carrier, the intermediate transfer member, and the final contact transfer unit is increased,
It can be seen that the value of the electric field E increases and the transfer efficiency improves.

By the way, when the magnitude of the electric field E on the surface of the image carrier is constant, in order to increase the transfer efficiency, the charge density appearing on the surface of the downstream transfer means is increased in both the primary transfer and the secondary transfer. Is considered effective. According to Gauss's theorem, when the charge density on the surface is σ, σ is expressed as σ = εε ₀ E, and it is understood that it is effective to increase the relative dielectric constant also here.

This relationship can be applied to the relationship between the first image carrier and the intermediate transfer member and the relationship between the intermediate transfer member and the secondary contact transfer means.

Therefore, in the present invention, when the relative permittivity of the first image carrier is ε _d , the relative permittivity of the intermediate transfer member ε _ITD and the relative permittivity of the secondary contact transfer means are ε _Tr , , Ε _d ≦ ε _ITD ≦ ε _Tr . This relationship is preferably ε _d <ε _ITD ≦ ε _Tr , particularly preferably ε _d +1
<Ε _ITD , ε _ITD +1 <ε _Tr .

In the present invention, the capacitance was determined according to the following measurement procedure.

FIG. 15 is a schematic diagram of a capacitance measuring device. The measuring method is described below.

1) A sample whose capacitance is to be measured is connected to a capacitor having a known capacitance as shown in FIG. 15, and the sample is charged by a corona charger.

2) With the SW turned off, measure the surface potential of the sample with a surface voltmeter. The measured value at this time is V
Let it be 1.

3) Next, the switch is turned on, and the surface potential of the sample is measured again with the surface voltmeter. The measured value at this time is V
Let it be 2.

The calculation method is as follows.

V1 = V ₀ + V _X = q / C ₀ + q / C _X (3) V2 = V _X = q / C _X (4) When q is deleted from the above equations (3) and (4), a _{C X = [(V1-V2} ) / V2] · C 0. In order to determine the relative permittivity from the capacitance, ε _x = C _X · d / (ε ₀ · S) where d is the thickness of the sample and S is the surface area of the sample. The calculations performed to determine the relative permittivity ε are all
Performed in MKS unit system.

As described above, the resistance value of the intermediate transfer member is 10 ⁶ Ω · cm to ^{10 10} · cm (when 1 kV is applied). The resistance value of the secondary contact transfer means is 10 ⁸ Ω · cm to 10 ¹⁵ Ω · cm (when 1 kV is applied), the relative permittivity of the surface layer of the first image carrier is ε _d , the relative permittivity of the surface layer of the intermediate transfer body ε _ITD, and the relative permittivity of the surface layer of the secondary contact transfer means. When the ratio is ε _Tr , by giving them a relationship of ε _d ≦ ε _ITD ≦ ε _Tr , high primary transfer efficiency and high secondary transfer efficiency can be obtained in a wide transfer bias region. Further, even if there is a portion where the toner is multiplex-transferred and a single-layer portion of the toner on the intermediate transfer member, a good quality transfer image can be obtained without any transfer failure. Further, an image without transfer unevenness and transfer omission can be obtained even in a low humidity / high humidity environment.

[0038]

(Embodiment 1) FIG. 1 is a schematic sectional view of a color image forming apparatus (copier or laser printer) using an electrophotographic process. Medium resistance elastic roller 5 as intermediate transfer member
And a transfer belt as a secondary contact transfer means.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) which is repeatedly used as a first image carrier, and has a predetermined peripheral speed (process speed) in a counterclockwise direction indicated by an arrow. It is driven to rotate.

In the course of rotation, the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the primary charging roller 2, and then is subjected to image exposure means (not shown) for color separation of a color original image.
A first exposure of a target color image by receiving an image exposure 3 by an imaging exposure optical system, a scanning exposure system using a laser scanner that outputs a laser beam modulated in accordance with a time-series electric digital pixel signal of image information, and the like. (For example, a yellow component image) is formed.

Next, the electrostatic latent image is transferred to the first developing device 41.
(Yellow developing device) to develop with the first color yellow toner Y. Developing devices 41, 42, 43, 44
Each of the developing units (yellow, magenta, cyan, and flack) is rotated in a direction indicated by an arrow in the drawing by a rotation driving device (not shown), and each developing unit is disposed so as to face the photosensitive drum 1 in a developing process. I have.

The intermediate transfer member 5 is driven to rotate at the same peripheral speed as the photosensitive drum 1 in the clockwise direction indicated by the arrow.

FIG. 2 is a schematic sectional view of the intermediate transfer member 5 of this embodiment. In FIG. 2, the intermediate transfer member 5 includes a pipe-shaped core metal 51 and an elastic layer 52 formed on the outer peripheral surface thereof.

The above-described first type formed and carried on the photosensitive drum 1
In the process of passing through the nip portion between the photosensitive drum 1 and the intermediate transfer member 5, the yellow toner image of the color is formed on the intermediate transfer member 5 by an electric field formed by the primary transfer bias 29 applied to the intermediate transfer member 5. Intermediate transfer is performed on the outer peripheral surface.

After the transfer of the first color yellow toner image corresponding to the intermediate transfer member 5, the surface of the photosensitive drum 1 is cleaned by the cleaning device 13.

Thereafter, 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 are synthesized corresponding to the target color image. A color toner image is formed.

Reference numeral 6 denotes a transfer belt, which is provided in parallel with the intermediate transfer member 5 so as to be in bearing with the lower surface thereof. The transfer belt 6 includes a bias roller 62 and a tension roller 6.
1, a desired secondary transfer bias is applied to the bias roller 62 by the secondary transfer bias source 28, and the tension roller 61 is grounded.

First transfer from the photosensitive drum 1 to the intermediate transfer body 20
The primary transfer bias for the sequential superimposed transfer of the toner images of the fourth to fourth colors has a polarity (+) opposite to that of the toner and a bias power source 2
9. In the step of sequentially transferring the toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer member 5, the transfer belt 6 and the intermediate transfer member cleaner 8 can be brought into contact with and separated from the intermediate transfer member 5.

The transfer of the composite color toner image superimposedly transferred onto the intermediate transfer member 5 onto the transfer material P is carried out by bringing the transfer belt 6 into contact with the intermediate transfer member 5 and transferring the image data from a paper cassette (not shown) to a registration roller. 11, the transfer material P is fed at a predetermined timing to the contact nip between the intermediate transfer body 5 and the transfer belt 6 through the pre-transfer guide 10, and at the same time, the secondary transfer bias is applied from the bias power supply 28 to the bias roller 62. Applied. The composite color toner image is transferred from the intermediate transfer member 5 to the transfer material P by the secondary transfer bias. The transfer material P to which the toner image has been transferred is introduced into the fixing device 15 and is fixed by heating.

After the image transfer to the transfer material P is completed, the transfer residual toner on the intermediate transfer member 5 is cleaned by contacting the intermediate transfer member cleaner 8. The intermediate transfer member cleaner 8 has a fur brush 81, and is rotated with a peripheral speed difference in a direction opposite to that of the intermediate transfer member by a rotation driving unit (not shown) to scrape off toner on the intermediate transfer member. It has become.

The intermediate transfer member used in the present invention will be described with reference to FIG.

The intermediate transfer member used in the present invention comprises, for example, at least a rubber, an elastomer,
It has a roller shape having an elastic layer made of a resin, and further has a roller shape having one or more coating layers on the elastic layer.

FIG. 3 is a schematic sectional view of the intermediate transfer member 5,
Is a rigid cylindrical conductive support, 52 is an elastic layer, 53
Is a release layer.

As the cylindrical conductive support, metals and alloys such as aluminum, iron, copper and stainless steel, conductive resins in which carbon and metal particles are dispersed, and the like can be used. Such a cylinder, a cylinder having a shaft penetrating the center of the cylinder, a cylinder having a reinforced interior, and the like can be given. The core metal 51 used in this embodiment is obtained by reinforcing the inside of a 3 mm-thick aluminum cylinder.

The thickness of the elastic layer used for the intermediate transfer member is desirably 0.5 to 5 mm in terms of formation of a transfer nip, color misregistration due to rotation, material cost, and the like. It is preferable to make the elastic layer thinner in order to transmit the flexibility of the elastic layer to the surface of the photoreceptor, and specifically, it is desirable that the thickness be 50 to 200 μm.

The resistance value of the intermediate transfer member used in the present invention is 10
^It is necessary to adjust the resistance to ⁶ Ω · cm to ^{10 10} Ω · cm (when 1 kV is applied). However, as the intermediate transfer member of the present embodiment, the elastic layer 52 is made of only acrylonitrile-butadiene rubber (NBR), focusing only on the resistance value. Ketjen black was used as a conductive material and the volume resistivity was controlled.

Other usable rubber materials for the elastic layer 52 include styrene butadiene rubber, butadiene rubber, ethylene propylene rubber, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, acrylonitrile butadiene rubber, acrylic rubber, fluorine rubber, and urethane rubber. And the like. 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. Specific examples include quaternary ammonium salt-containing polymethyl methacrylate, polyvinylaniline, polyvinylpyrrole, polydiacetylene, and polyethyleneimine.

The volume resistivity was measured by cutting a laminate of the elastic layer and the release layer into a sheet of 100 × 100 mm, and measuring the insulation resistance (trade name: R8340A, Advantages).
t) and a guard electrode (trade name: R1)
2704). The measurement procedure is as follows: after the measurement electrode sandwiching the sheet is released for 5 seconds to set the initial state,
A voltage of kV is applied between the measurement electrodes sandwiching the sheet. A current measurement circuit is connected to the applied voltage system 30 seconds after the start of voltage application, and the volume resistivity is calculated from the current value 30 seconds after the connection. The sheet to be measured is referred to in Table 1
ence indicates an elastic layer (base rubber layer).
In the case of the belt of the above, it is a base layer or a laminate of a base layer and a surface layer.

The photosensitive layer of the photosensitive drum 1 is composed of a charge generation layer and a charge transport layer.

In order to increase the primary transfer efficiency from the photosensitive drum 1, the charge transport layer (C
arrier Transfer Layer Below C
The relative permittivity of the substance used for the binder of the (T layer) is relevant. The photosensitive drum 1 used in this embodiment has an outer diameter of φ
60 OPCs (Organic Photocondu)
0.2 μm to 0.3 μm on an aluminum drum
μm-thick charge generation layer (Carrier Generator)
As the ion layer, a layer in which a phthalocyanine compound is dispersed and contained on a polyvinyl butyral resin is used, and a hydrazone compound is dispersed in a polycarbonate (hereinafter referred to as PC) as a binder in the upper CT layer to have a thickness of 15 to Those having a thickness of 25 μm were used. The relative permittivity of the CT layer is about 3. In addition, this relative permittivity is 1 degree for the CT layer.
What was directly applied and formed on a 00 × 100 mm aluminum sheet was measured by the above-described capacitance measuring method. The measurement conditions are the same as those for the release layer described below.

The relative dielectric constant of the intermediate transfer member, which is a feature of this embodiment, was controlled by the release layer 53 on the surface.

The release layer 53 is composed of 33 parts (coulomb) of a urethane resin as a binder, 11 parts of potassium titanate whiskers as a conductive material for controlling the resistance, and PT for improving the releasability.
What dispersed 56 parts of FE powder was used. The urethane resin has a higher dielectric constant than PC, and the relative dielectric constant ε of the release layer was about 5 when measured using the aforementioned capacitance measurement method. For the measurement, the release layer was spray-coated to a thickness of 100 μm on an aluminum sheet of 100 × 100 mm,
Applied bias DC 150μA constant current control to corona charger, 1 × 10 capacitance of reference capacitor
^The capacitance was measured under the condition of ⁻¹² F.

Other resins having a high relative permittivity include:
Examples include polyvinylidene fluoride, polyamide, vinyl chloride, vinylidene chloride, polyamide imide, and polyurethane.

Examples of the filler having a high dielectric constant include fine powders of inorganic compounds such as calcium titanate, strontium titanate, barium titanate, and titanium oxide, and organic compounds such as polyvinylidene fluoride. Among them, particularly, calcium titanate, strontium titanate, and those obtained by sintering barium titanate once to a fine powder have a very high relative dielectric constant of several thousands to ten thousands, so that a small amount of Can increase the relative dielectric constant of the intermediate transfer member.

Table 1 and FIG. 4A show the results obtained when the primary transfer efficiency was measured by changing the resistance of the elastic layer 52 of the intermediate transfer member and changing the overall volume resistivity.

As another condition, the outer diameter of the intermediate transfer member is φ
180, a PC having a relative dielectric constant of about 3 is used for the binder of the CT layer on the surface of the photosensitive drum, as described above.
The upper potential relationship is set as follows.

Dark potential on photoreceptor (non-image portion potential by primary charging): Vd = −700 V Bright potential (image portion potential by laser exposure): Vl = −150 V Development method: non-magnetic one-component jumping development Development bias: Vdc = −450 V Vac = 1600 Vpp Frequency = 1800 Hz Process speed: 120 mm / sec

The toner used in this embodiment is a non-magnetic one-component pulverized toner containing styrene acrylic resin as a binder, carbon black as a colorant, a metal salicylate compound as a charge control agent, and a low molecular weight polyolefin as a release agent. Approximately 2 titanium oxides to improve fluidity
% Externally added.

The transfer efficiency is measured by comparing the image density a of the transferred toner on the intermediate transfer member with the remaining toner concentration b on the photosensitive drum, and a / (a + b) × 100 (%)
Was calculated.

The measurement environment was assumed to be a normal office environment of 23 ° C. and 50% RH.

[0071]

[Table 1]

As shown in Table 1, when the volume resistivity of the intermediate transfer member is in the range of 1 × 10 ⁶ Ω · cm to 1 × 10 ¹⁰ Ω · cm (when 1 kV is applied), the relative value of the relative dielectric constant of the surface layer of the photosensitive drum 1 is used. By setting it large, high primary transfer efficiency can be obtained in a wide transfer voltage application range.

Next, the secondary transfer from the intermediate transfer member to the transfer material will be described.

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, NBR having a volume resistivity of 5 × 10 ⁷ (when 1 kV is applied) is used. The hardness is 30 to 35 degrees according to JIS A. Both rollers were configured to have an outer diameter of φ20 on a φ8 SUS cored bar.

As the material of the roller, the volume resistivity is controlled at 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω · cm (when 1 kV is applied), and the voltage dependency (resistance decreases when a high voltage is applied) is remarkable. Good if not bad. As other materials, any suitable conductive agent such as EPDM, urethane rubber, and CR can be dispersed.

Next, the transfer belt 6 was in the form of a tube with an outer diameter of φ80 × 300 mm, and the thickness was arbitrarily variable.

In the present invention, the volume resistivity is set to 10 ⁸ Ω.
・ Cm to 10 ¹⁵ Ω ・ cm (at 1kV mark) and
A material having a large relative dielectric constant must be used.

The present inventors used the transfer belt 6 as a material.
The resin system is polycarbonate (PC), nylon (P
A), polyester (PET), polyethylene naphthalate (PEN), polysulfone (PSU), polyethersulfone (PEI), polyetherimide (PE)
I), polyether nitrile (PEN), polyether ether ketone (PEEK), thermoplastic polyimide (T
PI), thermosetting polyimide (PI), PES alloy,
There are polyvinylidene fluoride (PVdF), ethylene tetrafluoroethylene copolymer (ETFE) and the like.
Polyester-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polystyrene-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, fluorine-based thermoplastic elastomer, polybutadiene-based thermoplastic elastomer, polyethylene-based thermoplastic elastomer, ethylene-vinyl acetate-based thermoplastic elastomer, And polyvinyl chloride-based thermoplastic elastomers.

Some of the above materials have a high relative dielectric constant from the beginning, but most of them have a dielectric constant of 3 to 5 or less. Therefore, dispersing a filler having a high dielectric constant to increase the relative dielectric constant is not frustrating. The specific filler is the same as that for filling the above-mentioned intermediate transfer member, and therefore the description thereof is omitted here.

In this embodiment, three types of belts were prepared for each of a belt having a higher relative dielectric constant and a lower belt than that of the intermediate transfer member.
The measuring methods of the volume resistivity and the relative permittivity are the same as those of the above-described intermediate transfer member.

Belt: Ketjen black as a conductive agent and titanium oxide as a dielectric constant controlling agent are dispersed in a PC base, and have a volume resistivity of 5 × 10 ¹³ Ω · cm (when 1 kV is applied) and a relative dielectric constant of about 7. . Belt thickness is 150μm
It is.

Belt: Belt reference, PC
And Ketjen Black as a conductive agent dispersed therein, and the volume resistivity is 5 × 10 ¹³ Ω · cm (when 1 kV is applied) as in the above value.
We also prototyped a belt set at. The relative permittivity of the belt is about 3, which is lower than the relative permittivity of the intermediate transfer member of about 5.
The thickness of the belt is 150 μm.

Belt: Ketjen black as a conductive agent and titanium oxide as a dielectric constant controlling agent are dispersed in an ETFE base, and have a volume resistivity of 1 × 10 ¹⁵ Ω · cm (when 1 kV is applied) and a relative dielectric constant of about 9. . The thickness of the belt is 75 μm.

Belt: belt reference, ET
Ketjen black is dispersed as a conductive agent in the FE base, and the volume resistivity is 1 × 10 ¹⁵ Ω · cm (when 1 kV is applied);
The dielectric constant is about 4. The thickness of the belt is 75 μm.

Belt: A two-layered base layer having a thickness of 500
μm, carbon black dispersed as a conductive agent in an ester-based urethane resin binder, the surface layer was 50 μm thick, PVd
A mixed resin layer of F-based fluororesin and PTFE-based fluororesin,
Volume resistivity 5 × 10 ⁸ Ω · cm combining surface layer and base layer
(At the time of applying 1 kV), and the relative dielectric constant is about 9.

Belt: A belt reference, a two-layer structure, a base layer having a thickness of 500 μm, a carbon black dispersed as a conductive agent in an ester-based urethane base, a surface layer having a thickness of 50 μm, a PTFE-based fluororesin layer, and a surface layer / base layer. Volume resistivity 5 × 10 ⁸ Ω · cm (when 1 kV is applied),
The dielectric constant is about 5.

The measurement of the secondary transfer efficiency was performed using the above-described intermediate transfer member sample, and all other conditions were fixed. The transfer material is 80 g / m ² coated paper (Canon designated C
LC paper).

The secondary transfer bias is controlled by constant current control.
In the measurement of the next transfer efficiency, assuming that the residual toner density on the intermediate transfer member is b 'and the density of the transferred image on paper is c, c / (b'
+ C) × 100 (%).

FIG. 4 (b) shows the relationship between the relative dielectric constant and volume resistivity of the transfer belt and the secondary transfer efficiency. The transfer efficiency shown in FIG. 4B is for the belt to the belt.

[0090]

[Table 2]

From Table 2, it can be seen that the secondary transfer efficiency greatly changes depending on the relative dielectric constant of the transfer belt. Also,
It can be seen that the transfer bias application area in which the transfer efficiency of 90% or more can be ensured is greatly expanded.

When the laser printer using the intermediate transfer member and the transfer belt was similarly evaluated in a low humidity environment and a high humidity environment, the order of the intermediate transfer member and the transfer belt did not change.

As described above, the relative permittivity of the first image carrier is ε _d , the relative permittivity of the intermediate transfer member ε _ITD and the relative permittivity of the transfer belt as the secondary contact transfer means are ε _Tr. In this case, the relationship of ε _d ≦ ε _ITD ≦ ε _Tr is provided, and the resistance value of the intermediate transfer member is 10 ⁶ Ω · cm to ^{10 10} Ω · cm (when 1 kV is applied). The resistance value of the transfer belt is 10 ⁸ By controlling between Ω · cm and 10 ¹⁵ Ω · cm (when 1 kV is applied), both primary and secondary transfer can be performed.
High transfer efficiency can be obtained in a wide transfer bias region. In addition, even when a portion where the toner is multiplex-transferred and a portion where the toner is a single layer are present on the intermediate transfer member, a high-quality transferred image can be obtained without any transfer failure. Further, an image without transfer unevenness and transfer omission can be obtained even in a low humidity / high humidity environment.

(Embodiment 2) FIG. 5 is a schematic sectional view of a laser printer for explaining a second embodiment of the present invention.

The present embodiment is characterized in that a belt-type intermediate transfer member is used, and a conventional transfer roller is used as a secondary transfer means.

In FIG. 5, since the approximate functions in each step are the same as those in the first embodiment, the description of the intermediate transfer belt 20 and the transfer roller 30 will be mainly given here.

As in the first embodiment, the yellow toner image of the first color formed and carried on the photosensitive drum 1 passes through the nip between the photosensitive drum 1, the intermediate transfer belt 20, and the bias roller 21 on the back surface thereof. In the process, the intermediate transfer is performed on the outer peripheral surface of the intermediate transfer belt 20 by the electric field formed by the primary transfer bias 29 applied to the bias roller 21.

The surface of the photosensitive drum 1 on which the transfer of the first color yellow toner image corresponding to the intermediate transfer belt 20 has been completed is cleaned by the cleaning device 13.

Thereafter, 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 on the intermediate transfer member 5, and are synthesized corresponding to the target color image. A color toner image is formed.

Reference numeral 30 denotes a transfer roller, which is provided in parallel with the intermediate transfer belt and in contact with the lower surface thereof. A desired secondary transfer bias is applied to the transfer roller 30 by a secondary transfer bias source 28.

First transfer from the photosensitive drum 1 to the intermediate transfer member 20
The primary transfer bias for the sequential superimposed transfer of the toner images of the fourth to fourth colors has a polarity (+) opposite to that of the toner and a bias power source 2
9.

In the step of sequentially transferring the toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer belt 20, the transfer roller 30 and the intermediate transfer belt cleaner 8 can be brought into contact with and separated from the intermediate transfer belt 20.

The transfer of the composite color toner image superimposedly transferred onto the intermediate transfer belt 20 onto the transfer material P is performed by bringing the transfer roller 30 into contact with the intermediate transfer belt 20 and moving the registration roller 11, the transfer material P is fed at a predetermined timing to the contact nip between the intermediate transfer belt 20 and the transfer roller 30 through the pre-transfer guide 10, and at the same time, the secondary transfer bias is applied to the bias power supply 28 or the transfer roller 30. Applied. The composite color toner image is transferred from the intermediate transfer belt 20 to the transfer material P by the secondary transfer bias.

Since the photosensitive drum 1 used in this embodiment is the same as that used in the first embodiment, its relative dielectric constant is about 3.

The intermediate transfer belt 20 is, as shown in FIG.
Supported by four support shafts (21, 22, 23, 24),
It is rotated in the direction of the arrow in the figure by a rotation drive device (not shown). The support shafts (21, 22, 23, 24) are all made of the same material, and the other three except the bias roller 21 are electrically floated. Support shafts (21, 22, 23, 2
4) may be made of the same material or another material. In this embodiment, the volume resistivity is 5 × 10
NBR of ⁷ (at the time of applying 1 kV) was used. Hardness is JIS
A is 30 to 35 degrees. Both rollers were configured to have an outer diameter of φ16 on a φ8 SUS cored bar.

As the material of the roller, the volume resistivity is controlled at 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω · cm (when 1 kV is applied), and the voltage dependency (resistance decreases when a high voltage is applied) is remarkable. Good if not bad. As other materials, any suitable conductive agent such as EPDM, urethane rubber, and CR can be dispersed.

The volume resistivity of the intermediate transfer belt 20 is 10 ⁶
Ω · cm to ^{10 10} Ω · cm (when 1 kV is applied), and the relative dielectric constant is desirably higher than that of the CT layer (about 3 for PC) of the photosensitive drum 1. In this embodiment, as the material of the intermediate transfer belt 20, a belt formed by coating a conductive urethane sheet having a thickness of 2 mm and a PTFE-based fluororesin layer having a thickness of 50 μm as a release layer was used. The volume resistivity of the release layer is 2 ×
10 ⁹ Ω · cm (when 1 kV is applied), the relative permittivity of the release layer is about 4.5.

The transfer roller 30 is made of EPDM with a thickness of 6 mm on a SUS cored bar of φ8. The volume resistivity in a single layer state is determined by dispersing Ketjen black and zinc oxide whiskers as conductive agents. , 6 × 10 ⁶ Ω · c
m (when 1 kV is applied).

The EPDM single layer had a low relative dielectric constant of about 2.2, and it was difficult to obtain a high relative dielectric constant. Specifically, the thickness is 200 μm and the volume resistivity is 1 ×
A PVdF sheet of 10 ¹² Ω · cm (when 1 kV is applied)
Adhered to PDM surface. As a result, the relative dielectric constant of the surface of the transfer roller 30 became about 9. The volume resistivity of the transfer roller as a whole is approximately the volume resistivity of the PVdF sheet.

The primary and secondary transfer efficiencies were measured by incorporating the photosensitive drum, the intermediate transfer belt and the transfer roller into the laser printer shown in FIG. In the experiment, it had the same volume resistivity of 1 × 10 ⁷ Ω · cm (when 1 kV was applied),
A single-layer roller having a low relative dielectric constant was compared with a two-layer roller having a high relative dielectric constant.

The results are shown in FIGS. 6 (a) and 6 (b). The potential condition of the photosensitive drum, toner, measurement environment, paper type, and the like are all the same as those in the first embodiment.

As shown in FIG. 6, it can be seen that the higher the relative dielectric constant of the transfer roller is, the higher the transfer efficiency is, and the wider the transfer bias application area is.

Similar evaluations were made in a low-humidity environment and a high-humidity environment. As a result, there was no change in the order of the transfer rollers. In particular, the combination of the intermediate transfer belt and the transfer roller has advantages such as better space efficiency, a simpler configuration, and lower cost than the combination of the first embodiment. Therefore, the combination with the present invention is considered to be effective.

As described above, even when the belt type is used as the intermediate transfer member and the transfer roller is used as the secondary contact transfer means, the relative permittivity of the first image carrier is ε _d , the dielectric constant of the transfer roller is the relative dielectric constant epsilon _ITD and secondary contact transfer means when the epsilon _Tr of, to have the relationship of _{ε d ≦ ε ITD ≦ ε Tr} , the resistance value of the intermediate transfer belt 10 ⁶ Ω · cm to ^{10 10} Ω · cm (when 1 kV is applied) By controlling the resistance value of the transfer roller to 10 ⁸ Ω · cm to 10 ¹⁵ Ω · cm (when 1 kV is applied), the primary and secondary resistances are controlled. For both the next transfer,
High transfer efficiency can be obtained in a wide transfer bias region. In addition, even when a portion where the toner is multiplex-transferred and a portion where the toner is a single layer are present on the intermediate transfer member, a high-quality transferred image can be obtained without any transfer failure. Further, an image without transfer unevenness and transfer omission can be obtained even in a low humidity / high humidity environment.

The present invention is not limited to the structure of the photosensitive drum, the intermediate transfer body, and the contact transfer means, and may be implemented by, for example, a photosensitive belt, an intermediate transfer body, a transfer belt ( Rollers) The present invention is also effective in a configuration such as a photoreceptor belt, an intermediate transfer belt, and a transfer belt (roller).

(Embodiment 3) A feature of the third embodiment of the present invention is that a polymerized toner as shown in FIG. 7 manufactured by a polymerization method is applied to the apparatus shown in FIG.

The non-magnetic polymerized toner contains, for example, 5 to 30% by weight of a low-softening substance produced by a suspension polymerization method, and has a shape factor SF1 of 100 to 120 and a shape factor SF2 of 10%.
A substantially spherical non-magnetic one-component fine particle polymerized toner having a particle diameter of 0 to 120 and an average particle diameter of 5 to 7 μm is preferred. In this example, SF1 and SF2 having a mean particle size of 110 and 6 μm were used.

When the shape of the toner approaches the 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.

The shape factor SF1 referred to here is the same as that in FIG.
Is a numerical value indicating the ratio of the roundness of the shape of the spherical substance, and the square of the maximum length MXLNG of an elliptical figure formed by projecting the spherical substance on a two-dimensional plane is divided by the figure area AREA to obtain 100π / 4 multiplied by the value.

That is, it is defined by the following equation for the shape factor SF1: SF1 = {(MXLNG) ² / AREA} × (100π / 4)

As shown in FIG. 10, the shape factor SF2 is a numerical value indicating the proportion of irregularities in the shape of a substance, and is obtained by dividing the perimeter PERI of a figure formed by projecting a substance on a two-dimensional plane by the figure area AREA. And multiplied by 100π / 4.

That is, it is defined by the following equation for the shape factor SF1: SF2 = {(PERI) ² / AREA} × (100π / 4)

In this embodiment, the FE-SEM manufactured by Hitachi, Ltd. is used.
Using (S-800), the toner in the developing container is sampled at random, and the image information is introduced into an image analyzer (LUSEX3) manufactured by Nicole Co., Ltd. via an interface to collect 100 toner particles in total. The analysis is performed, SF1 and SF2 are calculated for 100 toners from the above equation, and the schematic configuration diagram of the polymerized toner employing the average value is shown in FIG.
Shown in

As shown in FIG. 7, the polymerized toner has a spherical shape due to its production method. In this embodiment, the core contains an ester wax, and the resin layer contains styrene-butyl acrylate.
A polymerized toner having a structure of polyester was used for the surface layer.
Its specific gravity is about 1.05. The reason for the three-layer configuration is that the core contains wax so that an offset preventing effect can be obtained in the fixing process, and that the charging efficiency is improved by providing a resin layer on the surface layer.
When actually used, 1.2 wt% of silica treated with silicone oil is added externally for stabilizing the tribo.

This polymerized toner was manufactured as follows.

In a 2-liter four-necked flask equipped with a high-speed stirring device, 710 parts by weight of ion-exchanged water and 0.1 mol /
450 parts by weight of a 1-Na ₃ PO ₄ aqueous solution was added, and the number of rotations was set to 1
It was adjusted to 2000 revolutions and heated to 65 ° C. 68 parts by weight of a 1.0 mol / 1-CaCl ₂ aqueous solution was gradually added thereto to prepare a dispersion medium system containing a minute water-insoluble dispersant Ca ₃ (PO ₄ ) ₂ . On the other hand, the dispersoid system includes styrene monomer 165 parts by weight n-butyl acrylate monomer 35 parts by weight C.I. I. Pigment Blue 15: 3 14 parts by weight Saturated polyester 10 parts by weight {teriftalic acid-propylene oxide modified bisphenol A, acid value 15, peak molecular weight: 6000} salicylic acid metal compound 2 parts by weight The following compound 60 parts by weight

[0127]

[Outside 1]

After the above mixture was dispersed for 3 hours using an attritor, a dispersion obtained by adding 10 parts by weight of 2,2′-azobis (2.4-dimethylvaleronitrile) as a polymerization initiator was added to a dispersion medium. 15 while maintaining the rotation speed
Granulated for minutes. Thereafter, the agitator was changed from a high-speed agitator to a propeller stirring blade, the internal temperature was raised to 80 ° C., and the polymerization was continued at 50 rotations for 10 hours. Thereafter, 2 parts by weight of a styrene monomer was added to complete the polymerization. After the polymerization was completed, the slurry was cooled, and diluted hydrochloric acid was added to remove the dispersant.

Further, after washing and drying, a polymerized toner was produced. Instead of Pigment Blue, other colorants such as C.I. I. Pigment Yellow 17, C.I.
I. By using Pigment Red 122 and carbon black, a yellow toner, a magenta toner, and a black toner can be manufactured, respectively.

The toner used in this example has a tribo (Q / M) of about −20 μC / g. The toner is incorporated into the laser printer described in the first embodiment,
The secondary transfer efficiency was measured.

The intermediate transfer member used in the study was the same as the sample in Example 1. To be more specific, the acrylonitrile-butadiene rubber (NB) was used as the elastic layer.
R) was prepared by dispersing Ketjen black as a conductive material. The thickness is 0.5 mm. The release layer contains a urethane resin as a binder, potassium titanate whiskers as a conductive material for controlling the resistance, and PTF for the purpose of improving the releasability.
A dispersion of E powder was used. Release layer thickness is 2
00 μm, and the relative dielectric constant of the surface layer is about 5.

The transfer belt used in the study was a belt P
Ketjen black as a conductive agent and titanium oxide as a dielectric constant controlling agent are dispersed in a C base, and the volume resistivity is 5 × 10 ¹³
Ω · cm (when 1 kV is applied) and a relative dielectric constant of about 7. The thickness of the belt is 150 μm.

The primary transfer bias was controlled by a constant voltage control, and the secondary transfer bias was controlled by a constant current control.

The photosensitive drum used was a PC having a relative dielectric constant of about 3 as a binder for the surface CT layer, and the potential relationship on the photosensitive drum 1 was set as follows.

Dark potential on photoreceptor (non-image portion potential due to primary charging): Vd = −700 V Bright potential (image portion potential by laser exposure): Vl = −150 V Development method: non-magnetic one-component jumping development Development bias: Vdc = −450 V Vac = 1600 Vpp Frequency = 1800 Hz Process speed: 120 mm / sec

As a reference, a non-magnetic one-component pulverized toner (about 2% of titanium oxide was externally added) using the styrene resin as a binder and used in Example 1 was similarly measured. Tribo (Q / M) is about -20 μC / g, which is the same as that of the polymerized toner. The particle size of the toner is 8 μm, the shape factor SF1 is 170, and the shape factor SF2 is 160.

The measurement environment was a normal office environment of 23 ° C. and 50% RH.

The transfer material whose secondary transfer efficiency was measured was 80 g
/ M2 coated paper (Canon-designated CLC paper).

FIG. 9 shows the results. FIG. 9A shows the primary transfer efficiency, and FIG. 9B shows the secondary transfer efficiency.

As shown in FIG. 9, the transfer efficiency as well as the primary and secondary transfer efficiencies was about 5% higher than that of the conventional pulverized toner. Also, the transfer bias application range in which high transfer efficiency can be maintained has been widened.

As described above, even when the polymerization toner having a substantially spherical shape is used as the toner, the relative permittivity of the first image carrier is ε _d and the relative permittivity of the intermediate transfer member is ε _ITD.
And the relative dielectric constant of the transfer belt is a secondary contact transfer means when the _{εT r, ε d ≦ ε ITD} ≦ εT r to have a relationship, the resistance value of the intermediate transfer member 10 ⁶ Ω · cm~ 10 ¹⁰ Ω · cm (when 1 kV is applied) By controlling the resistance value of the transfer belt to between 10 ⁸ Ω · cm and 10 ¹⁵ Ω · cm (when 1 kV is applied), it is possible to reduce the toner produced by the conventional pulverization method. Also, higher transfer efficiency can be obtained.

As described in the second embodiment, it is needless to say that the same effect can be obtained when an intermediate transfer belt is used instead of the roller-type intermediate transfer member and a transfer roller is used instead of the transfer belt. No.

(Embodiment 4) A feature of the fourth embodiment of the present invention is that a toner obtained by forming a conventional one-component magnetic toner into a substantially spherical toner is applied to the apparatus shown in FIG. Hereinafter, this toner is referred to as a magnetic spherical toner.

The magnetic spheroidized toner used in the present study is one in which the irregularities on the toner surface are removed by, for example, heat or mechanically, so as to approximate a substantially spherical shape. As means for spheroidization by heat, there are a hot water bath method in which the toner is dispersed in an aqueous system 5 to 10 degrees higher than the glass transition temperature of the toner, and a surffusion method in which the toner is brought into contact with a hot air stream at 200 to 400 ° C. As a mechanical method, there are a method of spheroidizing by deformation due to a mechanical impact force, a method of spheroidizing and pulverizing from the beginning, and the like. In this embodiment, among the sphering means by mechanical force, a method of spheroidizing by deformation due to mechanical impact force, that is, the non-spherical toner formed by pulverization is moved at high speed in the minute gap and the side wall is formed. This is a method in which the toner is brought into contact and a convex portion on the toner surface is pressed into a spherical shape. To carry out this method, for example, a mechanical surface modifier (trade name: hybr)
idizer, Nara Machinery C
o. Is used. In the above-described processing, it is possible to add an effect of heat (set at 5 to 10 degrees higher than the glass transition temperature) in addition to mechanical force.

The magnetic spheronized toner is prepared by adding magnetite to 10
A magnetic one-component toner containing 100 parts of a styrene acrylic resin and containing 0 parts (by weight) and 2 parts of a metal salicylate compound, and preferably has a shape factor SF1 of 140 to 150 by treatment with the mechanical surface modifier. Is characterized in that the shape factor SF2 is deformed to 120 to 130, and the shape is not spherical, but rather has a quad (surface unevenness). The average particle size is between 5 and 7 μm. In the present embodiment, the sample 1 used had an SF1 of 145, an SF2 of 125 and an average particle size of 6 μm. At the time of use, 1.2 parts by weight of silica treated with silicone oil was added to 100 parts by weight of the toner.

When the surface irregularities in the toner shape are reduced, the surface energy of each toner is reduced as in the case of the polymerized toner, the fluidity is increased, and the attraction force (mirror force) to the photosensitive drum or the like is increased. ) Is weakened, and is likely to be affected by the transfer electric field.

Tribo (Q / M) of the magnetic spherical toner
Is about −15 μC / g, and under the same conditions as in Example 3,
The primary and secondary transfer efficiencies were measured.

FIG. 11 shows a comparison result of transfer efficiency with a conventional magnetic toner (containing 100 parts of magnetite. Magnetic one-component toner using a styrene-based resin as a binder). FIG. 11A shows the primary transfer efficiency, and FIG. 11B shows the secondary transfer efficiency. The particle diameter of the reference magnetic toner was 7 μm, the shape factor SF1 was 160, and SF2 was 150, and the tribo was about −15 μC / g, which was the same as that of the magnetic spherical toner.

As shown in FIG. 11, the primary and secondary transfer efficiencies were about 3% higher than the conventional pulverized toner. Further, the transfer bias application range in which high transfer efficiency can be maintained is widened.

As described above, even when a magnetic spheroidized toner having few surface irregularities is used as the toner shape, the relative permittivity of the first image carrier is ε _d and the relative permittivity of the intermediate transfer body is the dielectric constant of the transfer belt is epsilon _ITD and secondary contact transfer means when the εT _r, to have the relationship of _{ε d ≦ ε ITD ≦ εT r} , the resistance of the intermediate transfer member 10 ⁶ Omega · cm ^{10 to} 10 ¹⁰ Ω · cm (when 1 kV is applied) By controlling the resistance value of the transfer belt to between 10 ⁸ Ω · cm and 10 ¹⁵ Ω · cm (when 1 kV is applied), the transfer belt is manufactured by a conventional pulverization method. It is possible to obtain higher transfer efficiency than the toner. The magnetic toner has the advantages of a simpler developing device configuration and can be manufactured at lower cost than conventional non-magnetic one-component pulverized toner or polymerized toner. Is big.

As described in the second embodiment, it goes without saying that the same effect can be obtained when an intermediate transfer belt is used instead of the roller-type intermediate transfer member and a transfer roller is used instead of the transfer belt. No.

(Embodiment 5) The feature of the fifth embodiment of the present invention is that the overcoat layer (Ov
In this embodiment, a photosensitive drum having a er Coat Layer (hereinafter referred to as OCL) and having a reduced relative dielectric constant on the surface is applied to the apparatus of FIG.

The OCL is originally used for the purpose of preventing abrasion of the photoreceptor drum and preventing poor cleaning, and the thickness is preferably 2 to 5 μm. In this example, 3 parts (by weight) of an acrylic resin in a binder
The purpose was to disperse 5 parts of PTFE having a low relative dielectric constant together with 5 parts of tin oxide to lower the relative dielectric constant of the surface layer of the photosensitive drum. The particle size of PTFE is about 0.3 μm and that of tin oxide is about 0.03 μm. The purpose of mixing tin oxide is P
This is because TFE can be easily dispersed in the acrylic resin.

FIG. 12 is a schematic sectional view of the photosensitive drum 1 with the OCL used in this embodiment. In the photosensitive drum 1 of FIG. 12, 101 is an OCL, 102 is a CT layer as a conventional charge transport layer, and 102 is a CG layer as a charge generation layer. Each thickness is OCL: 3 μm, CT layer: 25 μm
m, CG layer: 3 μm.

FIG. 13 is a schematic enlarged sectional view of the OCL 101, and shows a state in which tin oxide surrounds PTFE and is dispersed in an acrylic resin.

The relative permittivity of the OCL used in this embodiment is about 2, which is almost the same as that of PTFE. As an effect of the present invention, although the secondary transfer efficiency from the intermediate transfer body to the paper is not replaced by the conventional one, the effect of increasing the primary transfer efficiency is obtained.

The photosensitive drum having the OCL was incorporated in the laser printer described in the third and fourth embodiments, and the primary transfer efficiency was compared with that of the conventional photosensitive drum having a PC binder in the CT layer. The toner used in this embodiment is the polymerized toner described in Embodiment 3 as a color toner. As the black toner, the magnetic spherical toner described in Example 4 was used.

The polymerized toner contains 5 to 30% by weight of a low-softening substance produced by a suspension polymerization method, and has a shape factor SF1 of 11%.
0, a substantially spherical non-magnetic one-component polymerized toner having a shape factor SF2 of 110 and an average particle diameter of 6 μm. Oil-treated silica is added externally for tribo stabilization, and the tribo (Q / M) is about -20 μC / g.

The magnetic spheronized toner is composed of 10 magnetites.
A magnetic one-component toner containing a styrene-acrylic resin as a binder and containing 0 part and 2 parts of a salicylate metal compound. The HB treatment causes the shape factor SF1 to be changed to 145 and the shape factor SF2 to be changed to 125. 6 μm. Oil treated silica was externally added. The toner has a tribo (Q / M) of about −15 μC / g.

Since other various conditions are described in detail in the third embodiment, the description is omitted here.

FIG. 14 shows the measurement results of the primary transfer efficiency in the above configuration. FIG. 14A shows a polymerized toner and FIG. 14B shows a magnetic spheroidized toner, which are compared between a conventional drum and a drum having an OCL.

Referring to FIG. 14, in the case of the polymerized toner, the transfer efficiency itself did not increase, but the voltage application range in which the high transfer efficiency could be maintained became wider. In the case of the magnetic spherical toner, the transfer efficiency increased by about 5%.

The secondary transfer efficiency was the same as that in Examples 3 and 4.

As described above, when the voltage application range in which high transfer efficiency can be maintained is widened, two types of toners having different tribos and having different properties can be used together. As in the present embodiment, when a polymerized toner using a non-magnetic one-component developing method is used as a color toner and a magnetic spherical toner using a magnetic one-component developing method is used as a black toner, the optimum transfer bias of the toner is different. There is a fear that high transfer efficiency cannot be realized and the waste toner capacity increases. However, by setting the relationship between the OCL and the relative dielectric constant of the intermediate transfer member properly, it can be avoided. .

[0165]

As described above, according to the present invention,
In an image forming apparatus that performs multiple transfer, the relative permittivity of the surface layer of the first image carrier is ε _d , the relative permittivity of the surface layer of the intermediate transfer body ε _ITD, and the ratio of the surface layer of the secondary contact transfer unit. the dielectric constant is taken as _{εT r, ε d ≦ ε ITD} ≦ εT r to have a relationship, the resistance value of the intermediate transfer member ^{10 6 Ω · cm~10 10 Ω ·} cm ( at 1kV is applied) of the transfer roller By controlling the resistance value between 10 ⁸ Ω · cm and 10 ¹⁵ Ω · cm (when 1 kV is applied), the primary transfer efficiency and the secondary transfer efficiency can be made compatible at a high value. (1) Since the amount of waste toner is reduced, the amount of consumed toner per page can be reduced. (2) Transfer residual toner is small. Therefore, the size of the cleaning device for the intermediate transfer member can be reduced. (3) Since the toner in the lower layer is sufficiently transferred by overlapping the colors during multiple transfer, a print image with high color reproducibility of the color image can be obtained.

Further, according to the present invention, by using a toner having a substantially spherical shape or a surface with few surface irregularities,
The above operation and effect can be enhanced, and the effect can be further improved by providing an OCL having a low relative dielectric constant on the surface layer of the photosensitive drum.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a laser printer according to a first embodiment of the present invention.

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

FIG. 3 is an enlarged sectional view of an intermediate transfer member.

FIG. 4 shows primary and secondary transfer efficiencies of the first embodiment.

FIG. 5 is a schematic sectional view of a laser printer according to a second embodiment of the present invention.

FIG. 6 shows primary and secondary transfer efficiencies of the second embodiment.

FIG. 7 is a schematic sectional view of a polymerized toner according to a third embodiment.

FIG. 8 is an explanatory diagram of a shape factor SF1.

FIG. 9 shows primary and secondary transfer efficiencies of the polymerized toner of the third embodiment.

FIG. 10 is an explanatory diagram of a shape factor SF2.

FIG. 11 shows the primary and secondary magnetic spherical toners of the fourth embodiment.
Next transfer efficiency.

FIG. 12 is a schematic enlarged sectional view of a photosensitive drum having an OCL.

FIG. 13 is a schematic enlarged sectional view of the OCL.

FIG. 14 shows primary transfer efficiency with and without OCL due to toner difference.

FIG. 15 is a principle diagram of a capacitance measuring device under a DC voltage.

FIG. 16 is a schematic cross-sectional view of an image forming apparatus that performs multiple transfer using a conventional intermediate transfer roller.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Katsuhiko Nishimura, inventor Canon Inc. 3- 30-2 Shimomaruko, Ota-ku, Tokyo (56) References JP-A-6-295132 (JP, A) JP-A-6 -202489 (JP, A) JP-A-4-324885 (JP, A) JP-A-61-295584 (JP, A) JP-A-55-18633 (JP, A) (58) Fields investigated (Int. . ^7, DB name) G03G 15/16 - 15/16 103 G03G 15 / 01,15 / 014 G03G 5/147 - 5/147 506

Claims (10)

(57) [Claims] 1. An image forming apparatus for forming an image formed on a first image carrier on an intermediate transfer body as a second image carrier, and then transferring the image to a transfer material using a contact transfer unit. Assuming that the dielectric constant of the surface layer of the first image carrier is ε _d , the dielectric constant of the surface layer of the intermediate transfer member ε _ITD and the dielectric constant of the surface layer of the secondary contact transfer means are ε _Tr , _d ≦ ε _ITD ≦ ε _Tr , and the volume resistivity of the intermediate transfer body is 10 ⁶ Ω · cm to ^{10 10} Ω · cm (when 1 kV is applied). The volume resistivity of the contact transfer means is 10 ⁸ Ω. The image forming apparatus is characterized in that the pressure is within a range of from about 10 cm to about 10 ¹⁵ Ωcm (when 1 kV is applied). 2. The image forming apparatus according to claim 1, wherein an image formed on the first image carrier is sequentially formed on an intermediate transfer member in a plurality of colors from a first color, and then transferred collectively to a transfer material. 3. The intermediate transfer member according to claim 1, wherein said intermediate transfer member has a roller shape.
Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the surface layer of the intermediate transfer member is a release layer, and has an elastic layer below the release layer. 5. A shape factor SF1 of 100 to 120, SF
2. The image forming apparatus according to claim 1, wherein a non-magnetic developer having a substantially spherical shape of 2 to 100 is used. 6. A shape factor SF1 of 140 to 150, SF
2. The image forming apparatus according to claim 1, wherein the magnetic developer 2 comprises 120 to 130 magnetic developers. 7. The method according to claim 1, wherein a surface protective layer having a low dielectric constant is provided on a surface layer of the surface of the first image carrier.
Image forming apparatus. 8. The image forming apparatus according to claim 7, wherein the surface protective layer has a relative dielectric constant of 3 or less. 9. The image forming apparatus according to claim 1, wherein ε _d , ε _ITD and ε _Tr have a relationship of ε _d <ε _ITD ≦ ε _Tr . 10. The image forming apparatus according to claim 9, wherein ε _d , ε _ITD and ε _Tr have a relationship of ε _d + 1 ≦ ε _ITD and ε _ITD + 1 ≦ ε _Tr .