JP2007065085A - Transfer device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer device having a wide application range of the device, by effectively suppressing the occurrence of density uneveness, spot-like defects and blurs, even when applying to an image forming apparatus or the like that performs printing processing at high speed. <P>SOLUTION: In the transfer device, a difference between a common logarithm value of surface resistivity after 10 sec of voltage application and a common logarithm value of surface resistivity after 30 msec is 0.2 (LogΩ/square) or lower in absolute value, an electric field of a bias roll (V=It×Rv) is 3,000 V or lower, and the voltage change for 1 sec of the bias roll is 300 V or higher. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transfer device used in an image forming apparatus using an electrophotographic system such as an electrophotographic copying machine, a laser printer, a facsimile, and a composite OA apparatus thereof, and an image forming apparatus including the transfer device.

  An image forming apparatus using an electrophotographic method forms a uniform charge on an image carrier, which is a photoconductive photosensitive member made of an inorganic or organic material, and uses an electrostatic image with a laser beam or the like that modulates an image signal. Then, the electrostatic latent image is developed with a charged toner to obtain a visualized toner image. Then, the toner image is electrostatically transferred to a transfer material such as a recording sheet through an intermediate transfer member, or a required reproduction image is obtained. In particular, there is known an image forming apparatus that employs a system in which a toner image formed on the image carrier is primarily transferred to an intermediate transfer member, and a toner image on the intermediate transfer member is secondarily transferred to a recording sheet (for example, , See Patent Document 1).

  As a belt material used in the image forming apparatus adopting the intermediate transfer body method, when a thermoplastic resin conductive material such as polycarbonate resin or PVDF (polyvinylidene fluoride) is used, the mechanical characteristics are inferior. Belt deformation with respect to stress is large, and high-quality transfer image quality cannot be obtained stably. Further, although an elastic belt with a reinforcing material formed by laminating a woven fabric such as polyester and an elastic member has been proposed, there may be a problem of color misregistration due to creep deformation of the belt material over time.

Further, an intermediate transfer belt in which a conductive filler is dispersed in a polyimide resin excellent in mechanical properties and heat resistance has been proposed (see, for example, Patent Documents 2 and 3).
In an image forming apparatus employing the intermediate transfer system, the charge during primary transfer affects the surface potential of the photoconductor, which may cause insufficient charging or spotted defects. For this reason, by using a belt-shaped intermediate transfer member with a high degree of design freedom and arranging the photosensitive member and the first transfer roller offset, the influence on the surface potential of the photosensitive member during the primary transfer can be reduced. it can. By offsetting, the transfer function has a close relationship with the surface resistance of the intermediate transfer belt.

However, even in an image forming apparatus in which the photosensitive member and the primary transfer roller are offset, in the case of an apparatus that performs printing at high speed, density unevenness and blur (toner scattering) occur in addition to the above-mentioned spotted defects. There was a problem to do.
JP-A-62-206567 JP-A-5-77252 Japanese Patent Laid-Open No. 10-63115

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, an object of the present invention is to provide a transfer device that does not generate density unevenness, spotted defects, and blur, and has a wide application range of the device, and an image forming apparatus including the transfer device.

  As a result of intensive studies, the present inventors have found that the following present invention solves the above problems, and have completed the present invention.

That is, the present invention
<1> A transfer apparatus having an intermediate transfer belt in which carbon black is dispersed and a bias roll, and performing a transfer current at a constant current (It), the surface resistance of the intermediate transfer belt after 10 seconds of voltage application The difference between the common logarithm of the rate and the common logarithm of the surface resistivity after 30 msec is 0.2 (LogΩ / □) or less in absolute value, and the electric field given by V = It × Rv of the bias roll (V) is 3000 V or less, and the change in potential of the bias roll for 1 sec is 300 V or more.

  <2> First transfer means for primary transfer of the toner image formed on the image carrier to the intermediate transfer belt, and second transfer means for secondary transfer of the toner image transferred to the intermediate transfer belt to the transfer body An image forming apparatus comprising the transfer device according to claim 1 as the first transfer unit.

  According to the present invention, for example, even when applied to an apparatus that performs printing processing at high speed, the generation of density unevenness, spotted defects, and blur can be effectively suppressed, and a transfer apparatus having a wide application range of the apparatus, and An image forming apparatus including the transfer device can be provided.

  In the following description of the present invention, the transfer device of the present invention will be described in detail, and then the image forming apparatus of the present invention equipped with the transfer device will be described.

≪Transfer device≫
The transfer apparatus of the present invention has an intermediate transfer belt and a bias roll, and the common logarithmic value of the surface resistivity of the intermediate transfer belt is 0.2 (LogΩ / □) in absolute difference between 10 seconds after voltage application and after 30 msec. ), The electric field (V = It × Rv) of the bias roll when the transfer current is performed at a constant current (It) is 3000 V or less, and the potential change for 1 sec of the bias roll is 300 v or more. It is characterized by that.
By using this transfer device, it is possible to improve the occurrence of density unevenness, spotted defects, and blur (toner scattering).

As described above, the intermediate transfer belt has an essential requirement that the difference between the common logarithm values of the surface resistivity between 30 msec and 10 sec after voltage application is 0.2 LogΩ / □ or less in absolute value.
In recent years, the time of the electric field applied in the primary transfer in the image forming apparatus has become extremely short, and the electrical resistance when the electric field is applied in a short time is related to the actual transfer. However, the electric resistance is time-dependent, and the resistance value rises with the electric field application time. Particularly in a so-called high-speed machine that performs high-speed printing, an electric field is applied for a short time, and the difference in rising of the belt resistance is emphasized, resulting in density unevenness in image quality. It was found that the electrical resistance at this time has a relationship with the surface resistance rather than the volume resistance which has been conventionally considered since it has an offset in the device configuration. Therefore, by reducing the rise of the belt surface resistivity, that is, by making the difference between the common logarithm values of the surface resistivity of the intermediate transfer belt 0.2 or less (LogΩ / □) in absolute value, the density generated in the high-speed machine In addition to suppressing unevenness, it can cope with printing speeds other than high-speed printing, and the intermediate transfer belt has a wide application range of the apparatus.

In addition, the bias roll is required to have an electric field expressed by V = It × Rv of 3000 V or less and a potential change for 1 sec of 300 v or more.
The spotted defect occurs when a discharge is generated in a gap generated between the belt and the photoconductor, or between the belt and the bias roll, and a charge history is given to the photoconductor. The cause of the discharge is that the discharge limit voltage is exceeded by the air gap. The surface potential is determined by the belt volume resistance value and the bias roll volume resistance value, but the contribution of the transfer belt having a small film thickness is small and mainly depends on the volume resistance of the bias roll. During image formation, in primary transfer, the current is controlled by a constant current in order to stabilize the transfer. For this reason, a bias roll with large environmental fluctuations is disadvantageous in terms of discharge due to resistance fluctuations due to resistance fluctuations. In order to prevent troubles caused by discharge, the bias roll electric field (V = It × Rv) in the primary transfer of the constant current (It) needs to be 3000 V or less. Therefore, it is necessary to adjust the volume resistance Rv of the bias roll.
Further, the potential after passing through the Nip region becomes equal to the bias roll shaft potential, and when the bias roll material has a capacitor component, a charging current is generated and the potential rises. The bias roll electric field is an electric field after charging, during which the potential is rising. When the potential change for 1 sec is 300 V or more, the above-described discharge phenomenon can be suppressed.

  Further, with respect to the occurrence of blur, a new function that greatly improves in the combination of the transfer belt and the bias roll has been confirmed. This mechanism is not fully understood, but is interpreted as follows.

First, the difference in the common logarithm of the surface resistivity after 30 msec and 10 sec after voltage application to the transfer belt is 0.2 LogΩ / □ or less in absolute value, so that an electric field for holding toner at the post Nip portion can be obtained. , Toner scattering can be reduced. If it exceeds 0.2 LogΩ / □, an effective resistance cannot be obtained and the toner cannot be held.
On the other hand, since the transfer is already completed in the post Nip portion, an electric field is not particularly required. When the potential suddenly rises at this time, current is injected into the toner charge, and repulsion due to polarity reversal or nonuniform charge distribution occurs. Occurs and causes toner scattering. When the resistance change of the bias roll is 300 V or more, since the resistance change of the bias roll is in the volume direction, a potential is applied gently, and charge injection and uneven distribution can be prevented.
Therefore, blur suppression can be achieved only by a combination of a transfer belt and a bias roll.
Hereinafter, the transfer belt and the bias roll will be described in detail.

<Intermediate transfer belt>
(Surface resistivity)
The intermediate transfer belt according to the present invention has a difference between the common logarithm of the surface resistivity after 10 seconds of voltage application and the common logarithm of the surface resistivity after 30 msec (hereinafter referred to as “the difference between the common logarithm of the surface resistivity according to the present invention”). ) Is 0.2 (LogΩ / □) or less in absolute value, preferably 0.15 (LogΩ / □) or less, and preferably 0.10 (LogΩ / □). The following is more preferable. When the difference between the common logarithm values of the surface resistivity in the present invention exceeds 0.2 in absolute value, unevenness in image density occurs when high-speed printing is performed.

  As a result of intensive studies, the present inventors have found that the occurrence of density unevenness in image formation is derived from the effective belt resistivity at the time of primary transfer. That is, the electric resistivity of the intermediate transfer belt is conventionally controlled by the surface resistivity after 10 sec of the primary transfer and the volume resistivity after 30 sec. However, the electric field applied by the primary transfer in the actual image forming apparatus. This time is extremely short, and the electrical resistance when an electric field is applied in a short time is related to the actual transfer. However, the electric resistance is time-dependent, and the resistance value rises with the electric field application time. In particular, in a so-called high-speed machine that performs high-speed printing, an electric field is applied for a short time, and the difference in rising of the belt resistance is emphasized, resulting in density unevenness in image quality. Further, since the electrical resistance at this time has an offset depending on the apparatus configuration, it has a relationship with the surface resistance, not the volume resistance which has been conventionally considered. For this reason, by reducing the rise of the belt surface resistivity, that is, by making the difference in the common logarithm of the surface resistivity in the present invention 0.2 or less (LogΩ / □) in absolute value, density unevenness generated in a high-speed machine In addition, it is possible to cope with printing speeds other than high-speed printing, and the intermediate transfer belt has a wide application range of the apparatus.

In addition, the difference of the common logarithm value of the surface resistivity in this invention can be controlled to the above-mentioned value by the kind of carbon black mentioned later and the dispersion method of carbon black.
The rise of the surface resistivity in a short time after the voltage application is affected by the conductivity of the carbon black, and the rise is delayed as the amount of carbon black in the belt increases. For this reason, carbon black is preferably made into fine particles and added in a small amount, and in order to reduce the added amount, it is preferable to select and use one having high conductivity.
A preferable type of carbon black and a dispersion method will be described in detail later.

  The intermediate transfer belt of the present invention preferably has a common logarithmic value of surface resistivity of 9 to 13 (LogΩ / □), more preferably 10 to 12 (LogΩ / □) after 30 msec of voltage application. preferable. If the common logarithm value of the surface resistivity after the voltage application 30 msec exceeds 13 (LogΩ / □), the recording medium and the intermediate transfer belt may be electrostatically adsorbed during the secondary transfer, and the recording medium may not be peeled off. is there. On the other hand, if the common logarithm of the surface resistivity after 30 msec of voltage application is less than 9 (Log Ω / □), the holding power of the toner image primarily transferred to the intermediate transfer belt is insufficient, and the graininess of the image quality and the image disturbance May occur. The common logarithmic value of the surface resistivity after 30 msec of voltage application can be controlled by the type of carbon black described later and the amount of carbon black added.

In the present invention, the surface resistivity can be measured according to JIS K6911 (1995) using a circular electrode (for example, “UR probe” of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd.). A method for measuring the surface resistivity will be described with reference to the drawings. FIG. 1 is a schematic plan view (a) and a schematic cross-sectional view (b) showing an example of a circular electrode. The circular electrode shown in FIG. 1 includes a first voltage application electrode A and a plate-like insulator B. The first voltage application electrode A has a cylindrical electrode portion C and a cylindrical ring electrode having an inner diameter larger than the outer diameter of the cylindrical electrode portion C and surrounding the cylindrical electrode portion C at a constant interval. Part D is provided. An intermediate transfer belt T is sandwiched between the plate-shaped insulator B and the cylindrical electrode portion C and the ring-shaped electrode portion D in the first voltage application electrode A, and the cylindrical electrode portion C and the ring in the first voltage application electrode A The current I (A) that flows when a voltage V (V) is applied to the electrode portion D is measured, and the surface resistivity ρs (Ω / Ω) of the transfer surface of the intermediate transfer belt T is calculated by the following equation (1). □) can be calculated. Here, in the following formula (1), d (mm) indicates the outer diameter of the cylindrical electrode portion C, and D (mm) indicates the inner diameter of the ring-shaped electrode portion D. In the present invention, the current I (A) is measured 10 seconds after application of the voltage V (V) and 30 milliseconds later.
Formula (1) ρs = π × (D + d) / (D−d) × (V / I)

(Volume resistivity)
The intermediate transfer belt of the present invention preferably has a common logarithmic value of volume resistivity of 8 to 13 (Log Ωcm). If the common logarithmic value of the volume resistivity is less than 8 (Log Ωcm), the electrostatic force that holds the charge of the unfixed toner image transferred from the image carrier to the intermediate transfer belt becomes difficult to work. The electrostatic repulsive force between them or the fringe electric field near the image edge may cause the toner to scatter around the image and form a noisy image. On the other hand, if the common logarithmic value of the volume resistivity exceeds 13 (Log Ωcm), the charge holding force is large, and therefore the surface of the intermediate transfer belt is charged by the transfer electric field in the primary transfer, so that a static elimination mechanism is necessary. There is a case. The common logarithmic value of the volume resistivity can be controlled by the type of carbon black described later and the amount of carbon black added.

In the present invention, the volume resistivity can be measured according to JIS K6911 (1995) using a circular electrode (for example, UR probe of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd.). A method for measuring volume resistivity will be described with reference to the drawings. FIG. 2 is a schematic plan view (a) and a schematic cross-sectional view (b) showing an example of a circular electrode. The circular electrode shown in FIG. 2 includes a first voltage application electrode E and a second voltage application electrode F. The first voltage application electrode E includes a cylindrical electrode portion G. The intermediate transfer belt T2 is sandwiched between the cylindrical electrode part G and the second voltage application electrode F in the first voltage application electrode E, and the cylindrical electrode part G and the second voltage application electrode F in the first voltage application electrode E are sandwiched. The current I (A) flowing when the voltage V (V) is applied between the two is measured, and the volume resistivity ρv (Ωcm) of the intermediate transfer belt T2 can be calculated by the following equation (2). Here, in the following formula (2), d (mm) indicates the outer diameter of the cylindrical electrode portion G, and t indicates the thickness of the intermediate transfer belt T2.
Formula (2) ρv = πd ² / 4t × (V / I)

(Young's modulus)
The intermediate transfer belt according to the present invention is required to have a high elastic force and little change, particularly when multicolor toners are sequentially placed thereon. Specifically, the Young's modulus is 3500 MPa to 10,000 MPa. preferable. If the Young's modulus is less than 3500 MPa, the toner position may be shifted between colors, and color registration may deteriorate.
The Young's modulus E can be calculated from the following formula (3) by measuring the force ΔS applied to the unit cross-sectional area and the elongation Δa in the unit length.
Formula (3) E = ΔS / Δa

Here, ΔS is calculated from the load F, the film thickness t of the sample, and the sample width w, ΔS = F / (w × t
), And Δa is based on the sample reference length L and the sample elongation ΔL when a load is applied.
It is represented by ΔL / L.

Here, for the measurement of the thickness of the intermediate transfer belt, a general contact type or non-contact type film thickness meter can be used. In the present invention, an eddy current film thickness meter CTR-1500E manufactured by Sanko Denshi Co., Ltd. was used.
In addition, a commercially available tensile tester can be used for Young's modulus measurement. In the present invention, a tensile tester MODEL-1605N manufactured by Aiko Engineering Co., Ltd. was used.

(Thickness)
The intermediate transfer belt in the present invention preferably has a total thickness of 0.05 to 0.5 mm, more preferably 0.06 to 0.30 mm, and further preferably 0.06 to 0.15 mm. preferable. If the total thickness of the belt is less than 0.05 mm, the intermediate transfer belt may not satisfy the required mechanical properties. If it exceeds 0.5 mm, the stress on the belt surface is caused by deformation at the roll bending portion. Concentration may cause problems such as generation of cracks in the surface layer.

(Surface micro hardness)
The intermediate transfer belt in the present invention preferably has a transfer surface hardness of 30 or less in terms of surface microhardness, and more preferably 25 or less. The surface microhardness is not a method of obtaining the diagonal length of the indentation like the Vickers hardness widely used for measuring the hardness of metal materials, but how much the indenter has entered the sample. It can be determined by the measurement method. When the test load is P (mN) and the penetration amount (indentation depth) of the indenter into the sample is D (μm), the surface microhardness DH is defined by the following formula (4).
Formula (4) DH≡αP / D ²
Here, α is a constant depending on the shape of the indenter, and α = 3.8854 (used indenter: in the case of a triangular pyramid indenter).

A more specific measurement method is shown below. The intermediate transfer belt is cut into about 5 mm square, and the small piece is fixed to the glass plate with an instantaneous adhesive, and the micro hardness of the sample surface is measured using an ultra micro hardness meter DUH-201S (manufactured by Shimadzu Corporation). To do. The measurement conditions are as follows.
Measurement environment: 22 ° C, 55% RH
Working indenter: Triangular pyramid indenter Test mode: 3 (soft material test)
Test load: 0.70 gf
Load speed: 0.0145 gf / sec
Holding time: 5 sec

  This surface microhardness is the hardness obtained from the load and indentation depth in the process of indenting the indenter, and represents the strength characteristics of the material including not only plastic deformation of the sample but also elastic deformation. is there. In addition, the measurement area is very small, and more accurate hardness measurement is possible within a range close to the toner particle diameter. The surface microhardness obtained here has a correlation with the generation level of the holocharacter, and when the surface microhardness of the transfer surface of the intermediate transfer belt is 30 or less, the secondary transfer portion is caused by the pressing force of the bias roller. The transfer surface of the intermediate transfer belt is deformed, whereby the pressing force concentrated on the toner on the intermediate transfer belt is dispersed. For this reason, the toner does not aggregate, and it is possible to prevent the occurrence of image quality defects such as a holocharacter in which the line image is lost.

(Resin material)
The resin material that is the main component of the intermediate transfer belt in the present invention is not particularly limited, and a polyimide resin, a polyamide resin, a polyamideimide resin, a polyether ether ester resin, a polyallelate resin, a polyester resin, and a reinforcing material are added. The polyester resin etc. which can be mentioned can be mentioned, but a polyimide resin is especially preferable among these.

In addition, in this invention, the resin material used as a main component means that it is 50 mass% or more in all the resins. When the polyimide resin is the main component, the ratio of the polyimide resin in the total resin is preferably 70% by mass or more, and more preferably 90% by mass or more.
Since the polyimide resin is a high Young's modulus material, it is less susceptible to deformation due to stresses such as a support roll and a cleaning blade during driving. Therefore, when used as a main component, an intermediate transfer belt that is less prone to image defects such as color misregistration and the like. Become.

  The polyimide resin is usually obtained as a polyamic acid solution by polymerizing an equimolar amount of tetracarboxylic dianhydride or its derivative and a diamine in a solvent. As tetracarboxylic dianhydride, what is shown by the following general formula (I) is mentioned, for example.

  In the general formula (I), R is a tetravalent organic group, and is an aromatic, aliphatic, cycloaliphatic, a combination of aromatic and aliphatic, or a substituted group thereof.

  Specific examples of the tetracarboxylic dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetra. Carboxylic dianhydride, 2,3,3 ′, 4-biphenyltetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic Acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) sulfonic acid dianhydride, perylene-3,4,9, Examples thereof include 10-tetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, and ethylenetetracarboxylic dianhydride.

On the other hand, specific examples of the diamine include 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylmethane, 3,3′-dichlorobenzidine, 4,4′-diaminodiphenyl sulfide. 3,3′-diaminodiphenylsulfone, 1,5-diaminonaphthalene, m-phenylenediamine, p-phenylenediamine, 3,3′-dimethyl4,4′-biphenyldiamine, benzidine, 3,3′-dimethylbenzidine 3,3′-dimethoxybenzidine, 4,4′-diaminodiphenylsulfone, 4,4′-diaminodiphenylpropane, 2,4-bis (β-aminotert-butyl) toluene, bis (p-β-amino- Tert-butylphenyl) ether, bis (p-β-methyl-Δ-aminophenyl) benzene, bi -P- (1,1-dimethyl-5-amino-benzyl) benzene, 1-isopropyl-2,4-m-phenylenediamine, m-xylylenediamine, p-xylylenediamine, di (p-aminocyclohexyl) Methane, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, diaminopropyltetramethylene, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 2,11-diaminododecane, 1,2-bis-3-aminopropoxyethane, 2,2-dimethylpropylenediamine, 3-methoxyhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 3-methylheptamethylenediamine, 5-methylnonamethylenediamine 2 , 17-diaminoeicosadecane, 1,4-diaminocyclohexane, 1,10-diamino-1,10-dimethyldecane, 12-diaminooctadecane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane , _{piperazine, H 2 N (CH 2)} 3 O (CH 2) 2 O (CH 2) NH 2, H 2 N (CH 2) 3 S (CH 2) 3 NH 2, H 2 N (CH 2) 3 _{N (CH 3) 2 (CH} 2) 3 NH 2 and the like.

  As the solvent for the polymerization reaction of the tetracarboxylic dianhydride and the diamine, a polar solvent (organic polar solvent) is preferably mentioned from the viewpoint of solubility. As the polar solvent, N, N-dialkylamides are preferable, and specific examples thereof include N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethyl which are low molecular weight compounds thereof. Formamide, N, N-diethylacetamide, N, N-dimethylmethoxyacetamide, dimethylsulfoxide, hexamethylphosphortriamide, N-methyl-2-pyrrolidone, pyridine, tetramethylenesulfone, dimethyltetramethylenesulfone, etc. Among these, N-methyl-2-pyrrolidone is preferable from the viewpoint of properties. These can be used singly or in combination.

(Carbon black)
In the intermediate transfer belt of the present invention, carbon black such as ketjen black and acetylene black is dispersed as a conductive agent, and may further contain other conductive agents as long as the effects of the present invention are not impaired. Good. As the other conductive agent, conductive or semiconductive fine powder can be used, and if the desired electrical resistance can be stably obtained, the conductivity is not limited, but metals such as aluminum and nickel, oxidation Examples thereof include metal oxide compounds such as tin and potassium titanate. These may be used alone or in combination.

  In the present invention, the absolute value of the difference between the common logarithmic values of the surface resistivity in the present invention can be made 0.2 (LogΩ / □) or less by dispersing carbon black by the dispersion method described later.

  The carbon black is preferably oxidized carbon black in that it has high conductivity and can lower the difference in common logarithm of surface resistivity in the present invention.

[Oxidized carbon black]
The oxidation-treated carbon black preferably has a pH of 5 or less, and can be produced by oxidizing the carbon black to impart a carboxyl group, a quinone group, a lactone group, a hydroxyl group, or the like to the surface. This oxidation treatment is an air oxidation method in which contact is made with air in a high temperature atmosphere to react, a method of reacting with nitrogen oxides or ozone at room temperature, and air oxidation at high temperature, followed by ozone oxidation at a low temperature. It can be performed by a method or the like. Specifically, the oxidized carbon black can be produced by a contact method.

  Examples of the contact method include a channel method and a gas black method. Oxidized carbon black can also be produced by a furnace black method using gas or oil as a raw material. Further, if necessary, after performing these treatments, a liquid phase oxidation treatment with nitric acid or the like may be performed. Acidic carbon black can be produced by a contact method, but is usually produced by a closed furnace method. In the furnace method, only carbon black having a high pH and a low volatile content is usually produced, but the pH can be adjusted by subjecting it to the above-mentioned liquid phase acid treatment. For this reason, carbon black obtained by furnace method production and adjusted to have a pH of 5 or less by post-treatment is also preferably used.

  As described above, the oxidation-treated carbon black preferably has a pH of 5.0 or less, more preferably has a pH of 4.5 or less, and even more preferably has a pH of 4.0 or less. Oxidized carbon having a pH of 5.0 or lower has oxygen-containing functional groups such as a carboxyl group, a hydroxyl group, a quinone group, and a lactone group on the surface, so that the dispersibility in the resin is good and good dispersion stability is obtained. The resistance variation of the semiconductive belt can be reduced, the electric field dependency is also reduced, and the electric field concentration due to the transfer voltage is less likely to occur.

  The pH of carbon black is obtained by adjusting an aqueous suspension of carbon black and measuring it with a glass electrode. Moreover, the pH of carbon black can be adjusted by conditions, such as processing temperature and processing time in an oxidation treatment process.

  The oxidized carbon black preferably has a volatile component content of 1 to 25% by mass, more preferably 2 to 20% by mass, and still more preferably 3.5 to 15% by mass. . When the content of the volatile component is less than 1% by mass, the effect of the oxygen-containing functional group attached to the surface is lost, and the dispersibility in the binder resin may be reduced. On the other hand, when the content of the volatile component exceeds 25% by mass, it is decomposed when dispersed in a polyimide resin or the like, or the amount of water adsorbed on the oxygen-containing functional group on the surface increases. Problems such as deterioration of the appearance of the resulting molded product may occur. Therefore, the dispersion | distribution to a polyimide resin etc. can be made more favorable by content of the said volatile component shall be 1-25 mass%. This volatile component can be determined by the ratio of organic volatile components (carboxyl group, hydroxyl group, quinone group, lactone group, etc.) that come out when carbon black is heated at 950 ° C. for 7 minutes.

  In the intermediate transfer belt of the present invention, two or more types of carbon black may be contained. At that time, these carbon blacks are preferably substantially different in conductivity from each other, for example, those having different physical properties such as the degree of oxidation treatment, DBP oil absorption, specific surface area by BET method utilizing nitrogen adsorption, etc. It is preferable to use it. When two or more types of carbon blacks having different conductivity are added in this way, for example, carbon black that expresses high conductivity is preferentially added, and then carbon black with low conductivity is added to adjust the surface resistivity. And so on. Even when two or more types of carbon black are contained in this way, the mixing and dispersion of all the carbon blacks to be added can be enhanced by using at least one type of oxidized carbon black.

  Specific examples of the oxidized carbon black include “Printex 150T” (pH 4.5, volatile content 10.0%) and “Special Black 350” (pH 3.5, volatile content 2.2) manufactured by Degussa. %), “Special Black 100” (pH 3.3, volatile content 2.2%), “Special Black 250” (pH 3.1, volatile content 2.0%), “Special Black 5” (pH 3. 0, volatile content 15.0%), "Special Black 4" (pH 3.0, volatile content 14.0%), "Special Black 4A" (pH 3.0, volatile content 14.0%), " "Special Black 550" (pH 2.8, volatile content 2.5%), "Special Black 6" (pH 2.5, volatile content 18.0%), "Color Black FW200" (pH 2.5, volatile content 20) . %), “Color Black FW2” (pH 2.5, volatile content 16.5%), “Color Black FW2V” (pH 2.5, volatile content 16.5%), “MONARCH1000” (pH 2. 5, volatile content 9.5%), “MONARCH 1300” (pH 2.5, volatile content 9.5%) manufactured by Cabot, “MONARCH 1400” (pH 2.5, volatile content 9.0%) manufactured by Cabot, “ MOGUL-L "(pH 2.5, volatile matter 5.0%)," REGAL400R "(pH 4.0, volatile matter 3.5%) and the like.

  In addition, the carbon black to be used can be purified. Here, purification refers to removal of impurities mixed in the carbon black production process, such as residual oxidant, impurities such as treatment agents and by-products, and other inorganic and organic impurities. For example, a method for removing impurities by an inert gas or high-temperature heat treatment in a vacuum of about 500 to 1000 ° C., an organic solvent treatment such as carbon disulfide or toluene, a mixing of a water slurry, or a mixing treatment in an organic acid aqueous solution. Etc. The purification method may be any method, but is not limited to these. However, since the heat treatment of the powder is difficult to handle in the manufacturing process and uses a lot of energy, A treatment mainly comprising water is preferred as a purification method. In particular, a water-based treatment method is preferable from the viewpoint of safety. It is preferable to use ion-exchanged water, ultrapure water, distilled water, ultrafiltered water, or the like, in order to prevent impurities from being mixed in.

[Addition amount of oxidized carbon black]
The oxidation-treated carbon black has better dispersibility in the resin composition due to the effect of the oxygen-containing functional group present on the surface as described above, compared with general carbon black. The effect of using oxidation-treated carbon black that can suppress variations can be maximized.
In the present invention, by containing 10 to 30% by mass of the oxidized carbon black, the effects of the oxidized carbon black such as suppressing in-plane variation in the surface resistivity of the semiconductive belt can be exhibited. When the content of the oxidized carbon black is less than 10% by mass, the uniformity of electrical resistance is lowered, and in-plane unevenness of the surface resistivity and electric field dependency may increase. Moreover, when it exceeds 30 mass%, it may become difficult to obtain a desired resistance value.

[Carbon black particle size]
In the transfer belt of the present invention, the average particle diameter of the carbon black is preferably 500 nm or less, more preferably 300 nm or less, in order to improve the surface resistivity in a short time after voltage application. The thickness is preferably 150 to 250 nm.

  Here, the average particle diameter of carbon black was measured using a dynamic light scattering type measuring device PAR-III manufactured by Otsuka Electronics. The measurement conditions are: clock rate: 100 μs, accumulate time: 10 times, correlate ch: 128, temperature: 20 ° C., solvent: NMP.

(Method for manufacturing intermediate transfer belt)
The intermediate transfer belt in the present invention generally uses a resin such as polyimide or polyamideimide as a main component. For example, in the case of a polyimide resin, carbon black is dispersed in a polyamic acid (polyimide precursor) solution and dispersed. After the liquid is prepared and the dispersion is developed in a ring shape, the film is dried and formed into a belt shape, and further heated to effect imide conversion. Hereinafter, a method for manufacturing an intermediate transfer belt using a polyimide resin will be described in the order of steps.

[Method for preparing carbon black dispersion]
In the intermediate transfer belt according to the present invention, it is preferable to uniformly and finely disperse carbon black in the polyamic acid solution, which is a polyimide precursor, in order to satisfy the difference in the common logarithmic value of the surface low efficiency according to the present invention.
Examples of a method for preparing a dispersion by dispersing carbon black in a polyamic acid solution include the following methods, but are not particularly limited in the present invention.

= Dispersion method by collision type disperser =
In addition, in the method of manufacturing the intermediate transfer belt, a method of dispersing carbon black by mixing the carbon black-containing polyamide resin solution divided into two or more by colliding with each other at 150 MPa or more is also preferable.

  In the mixing step, first, carbon black is mixed with a polyamide resin solution which is a polyimide precursor, and the mixed solution is divided into two or more. Then, the two or more divided carbon black-containing polyamide resin solutions are collided with each other at 150 MPa or more and mixed. Thus, it is considered that the carbon black can be finely dispersed in the polyamic acid solution by causing them to collide with each other at 150 MPa or more and to mix them.

  The carbon black-containing polyamide resin solutions divided into two or more are collided with each other at a pressure of 150 MPa or more, and are preferably collided with each other at a pressure of 150 to 250 MPa, more preferably 180 to 220 MPa. If the pressure causing the collision with each other is less than 150 MPa, fine dispersion of carbon black in the polyamic acid solution may be insufficient.

  Further, the collided mixed solution may be further divided into two or more, and the divided solutions may be collided with each other at 150 MPa or more and mixed. By repeating this operation twice or more, carbon black can be finely dispersed in the polyamic acid solution more efficiently.

  Such a division / mixing mechanism that divides the carbon black-containing polyamide resin solution divided into two or more and collides with each other and mixes the mixture and further divides the mixed solution into two or more will be described with reference to the drawings. FIG. 3 is an explanatory view for explaining a mechanism for dividing and mixing the carbon black-containing polyamic acid solution in the method for producing a transfer member of the present invention.

  The dividing / mixing mechanism shown in FIG. 3 includes two first flow path pipes 50 connected at one point from upstream to downstream, a connection pipe 52 constituting a connection portion, and two from one end of the connection pipe 52. By dividing the carbon black-containing polyamide resin solution into the flow path constituted by the second flow path pipe 54 branched as described above, the division and mixing are performed.

  First, a carbon black-containing polyamide resin solution is caused to flow through each of the two first flow path pipes 50, and the flow pressure at this time is set to 150 MPa or more, so that the pressure is 150 MPa or more in the vicinity of one end 52a of the connection pipe 52 constituting the connection part. Collide each other's solution. Then, the collided liquid mixture passes through the connecting pipe 52 and flows into the second flow path pipe 54 branched into two or more, and is divided into two again. The mixed solution divided into two again can be further flowed to the first flow path pipe 50, and the mixing and division can be repeated a plurality of times.

  In such a dividing / mixing mechanism shown in FIG. 3, the carbon black-containing polyamide resin solution is caused to flow through the two first flow path pipes 50 connected to one point from upstream to downstream at a pressure of 150 MPa or more. Thus, it is possible to apply a collision force at a pressure of 150 MPa or more together with a shearing force to the solution, and to disperse carbon black efficiently and uniformly.

Further, the mixed liquid that has collided passes through the connecting pipe 52, but the connecting portion of the two first flow path pipes 50 (in the vicinity of one end 52a of the connecting pipe 52 in the figure), that is, two solutions are present. By setting the minimum cross-sectional area of the colliding portion to 0.07 mm ² or less (preferably 0.007 to 0.05 mm ² , more preferably 0.015 to 0.04 mm ² ), carbon in the polyamic acid solution Black can be finely dispersed. The reason for this is not clear, but when colliding each other's solutions at a pressure of 150 MPa or more, by reducing the area, shearing force and pressure at the time of collision can be efficiently added to the solution. It is considered that carbon black can be finely dispersed therein. Here, the minimum cross-sectional area of the collision portion where the two solutions collide corresponds to the cross-sectional area of the flow channel pipe 50 in the vicinity of the inlet of the connecting pipe 52 in the drawing.

  As a collision type disperser having such a dispersion / mixing mechanism, for example, “Geanus PY” manufactured by Genus can be suitably cited. In addition, as a collision type disperser, a Sugino Machine optimizer, a Nanomizer nanomizer, and the like can be used.

  In the carbon black-containing polyamic acid solution dispersed by the collision type disperser, a carbon black aggregate of several tens of μm, which is considered to be due to the impact of the collision, may occur. Even if this exists, there is no major problem, but the carbon black-containing polyamic acid solution that has been divided and mixed is passed through, for example, a filter having an opening of 25 μm or less, thereby removing carbon black aggregates and making the carbon black finer. Can be in a dispersed state.

  A polyamide acid solution in which carbon black is dispersed is prepared by dissolving and polymerizing a diamine component and an acid dianhydride component, which are polyimide precursors, in the obtained carbon black dispersion. In this case, the monomer concentration (concentration of the diamine component and the acid dianhydride component in the solvent) is set according to various conditions, but is preferably 5 to 30% by mass. Moreover, it is preferable to set reaction temperature to 80 degrees C or less, Especially preferably, it is 5-50 degreeC, and reaction time is 5 to 10 hours.

  Moreover, after adding carbon black directly to the polyamic acid solution which is a polyimide precursor and performing a dispersion process, it can also prepare by the method of diluting and stirring with the said organic polar solvent. This method is the difference until the polyamic acid solution is prepared, and the drying and imidization steps described later can be performed by the same method. Also, the carbon black dispersion method and conditions can be performed by the same methods and conditions as the former.

[Molding process and firing process]
Since the polyamic acid solution in which the carbon black is dispersed is a high-viscosity solution, the air bubbles mixed at the time of production do not spontaneously escape, and defects such as belt protrusions, dents and holes due to the air bubbles occur due to the application. For this reason, defoaming is desirable. Defoaming is preferably performed immediately before application as much as possible.

  When producing a seamless belt as the intermediate transfer belt of the present invention, for example, a method in which a polyamic acid solution is immersed in the outer peripheral surface of a cylindrical mold, a method in which it is applied to the inner peripheral surface, a method in which centrifugation is further performed, or a casting mold It is developed into a ring shape by an appropriate method such as a method of filling in, and the developed layer is dried and formed into a bell-shaped shape, and the molded product is heat-treated to convert the polyamic acid into an imide from the mold. The intermediate transfer belt of the present invention can be produced by an appropriate method according to the conventional method such as a recovery method (Japanese Patent Laid-Open Nos. 61-95361, 64-22514, and 3-180309). ). In the production of the seamless belt, a mold release treatment can be performed.

  Further, imide conversion is generally performed at a high temperature of 200 ° C. or higher. If it is 200 ° C. or lower, sufficient imide conversion may not be obtained. On the other hand, high-temperature treatment is advantageous for imide conversion, and stable characteristics can be obtained.However, since heat energy is used, the thermal efficiency is low and the cost is high, so the heat treatment temperature is considered in consideration of the characteristics and productivity of the intermediate transfer belt. It is necessary to decide.

<Bias roll>
The bias roll in the present invention is characterized in that the electric field given by V = It × Rv is 3000 V or less and the potential change for 1 sec is 300 V or more, and it is particularly limited as long as it satisfies these requirements. Although it is not a thing, it is preferable that it is the aspect by which the electroconductive elastic layer formed by adding a electrically conductive agent to an elastic material was provided in the outer peripheral surface of the metal roll axis | shaft at least.

(Conductive elastic layer)
Examples of the elastic material include silicone rubber, fluorine rubber, urethane rubber, EPDM, NBR, ECO rubber, CR, chlorinated polyisoprene, isoprene rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber, hydrogenated polybutadiene, and butyl rubber. A material obtained by blending one kind or two or more kinds of these rubber materials can be used.
In addition to the conductive agent, materials that can be usually added to rubber materials such as a curing agent, a plasticizer, and a vulcanization accelerator may be added to these.

  In order to stably obtain an electric resistance value in the elastic material, it is preferable to disperse a conductive agent as described above. As the conductive agent, an electron conductive conductive agent or an ion conductive conductive agent can be added.

  In the bias roll according to the present invention, since it is an essential requirement that the electric field is 3000 V or less, it is not preferable to use an ion conductive conductive agent whose resistance value changes in the usage environment. It is desirable to control the resistance with a combination of an electron conductive agent and an electron conductive agent.

  Moreover, the control of the potential change during the 1 second can be realized by mixing a conductive agent, a filling material, and the like so that the granular material and the elastic material have an interface.

  Examples of the electron conductive conductive agent include carbon black, graphite, aluminum, nickel, copper alloys and other metals or alloys, tin oxide, zinc oxide, potassium titanate, tin oxide-indium oxide, or tin oxide-antimony oxide composite oxide. Among these, carbon black and graphite are more preferable, and carbon black is particularly preferable from the viewpoint of being inexpensive and easily available.

Examples of the ion conductive conductive agent include sulfonates and ammonia salts, and various surfactants such as cationic, anionic, and nonionic surfactants.
Furthermore, there is a method of blending a conductive polymer as a conductive agent. Examples of the conductive polymer include various (for example, styrene) copolymers with (meth) acrylates that bind a quaternary ammonium base to a carboxyl group, Polymers that bind quaternary ammonium bases such as copolymers of maleimide and methacrylate that bind to quaternary ammonium bases, polymers that bind alkali metal salts of sulfonic acids such as sodium polysulfonate, and at least alkyl oxides in the molecular chain A polymer that binds a hydrophilic unit of, for example, a polyethylene oxide, a polyethylene glycol-based polyamide copolymer, a polyethylene oxide-epichlorohydrin copolymer, a polyether amide imide, a block polymer having a polyether as a main segment, Raniwa, mention may be made of polyaniline, polythiophene, polyacetylene, polypyrrole, polyphenylene vinylene and the like. These conductive polymers can be used in an undoped state or in a doped state.

  By using one or more of the conductive agents in combination, the electrical resistance value can be stably obtained as described above.

  In addition, a filler such as molybdenum disulfide, mica, graphite, boron nitride, potassium titanate, alumina, silicon carbide, or the like can be added. As described above, the potential change for 1 second can be controlled by addition.

The total amount of the conductive agent and filler dispersed in the conductive elastic layer is in the range of 5 to 50 parts by mass with respect to 100 parts by mass of the elastic material from the viewpoint of obtaining desired electrical resistance and roll hardness. Preferably, 10-30 mass parts is more preferable.
In addition, the ratio of the conductive agent in the total addition amount of the conductive agent and the filler is preferably in the range of 15 to 30% by mass from the viewpoint of resistance control.
Further, from the viewpoint of controlling the bias roll electric field within a desired range, the ratio of the electron conductive conductive agent to the total amount of the conductive agent added is preferably 20 to 100% by mass, more preferably 40 to 100% by mass, 60-100 mass% is especially preferable.

  As a method of dispersing the conductive agent and filler in the elastic material, a method such as kneading using a super mixer, a Banbury mixer, a two roll, a pressure kneader, a two roll, a three roll or the like is applied. That's fine. Note that the elastic layer preferably has a cylindrical shape. A base layer can be formed by covering the cored bar through the elastic layer and the cored bar.

The volume resistance value of the conductive elastic layer in the present invention is adjusted according to the current (constant current) value passed through the transfer device so as to satisfy the requirement that the electric field (V = It × Rv) of the bias roll is 3000 V or less. In addition, the value is preferably in the range of 10 ⁶ to 10 ⁹ Ωcm, and more preferably in the range of 10 ⁶ to 10 ⁸ Ωcm.

The volume resistance value Rv (Ω) of the bias roll is determined by placing a bias roll on a conductor such as a metal plate, applying a load of 500 g to both ends of the bias roll, and applying a voltage V of 1.0 kV to the roll axis. The current value I (A) flowing between the roll shaft and the metal plate was read and obtained from the following equation.
Rv = V / I

  Further, the potential change for 1 sec was obtained as follows. First, a transfer current is applied to the bias roll, and a resistance value every 30 msec from 30 msec to 10 sec is measured using a digital ultrahigh resistance / microammeter (trade name: R8340A, manufactured by Advantest Corporation). The potential was calculated by applying a constant current value and plotted in a table, and the difference between 0 sec and 1 sec was obtained from the table.

The conductive elastic layer preferably has an Asker C hardness of 70 ° or less. When the Asker C hardness is higher than 70 °, for example, the nip uniformity with the intermediate transfer member may be impaired, and image quality defects may occur.
The Asker C hardness was measured under the condition of a load of 1000 g by bringing a pusher of an Asker C type hardness meter (manufactured by Kobunshi Keiki Co., Ltd.) into contact with the surface of a measurement sheet having a thickness of 3 mm.

  The conductive elastic layer preferably has a thickness of 1 to 20 mm, more preferably 3 to 10 mm. If the thickness is less than 1 mm, the deformation at the nip portion due to the nip pressure is small, which may cause a problem that the nip cannot be stably formed. On the other hand, when the diameter exceeds 20 mm, the outer diameter of the bias roll is larger than 40 mm, which may cause problems such as an increase in the size of the apparatus and an increase in cost.

  The bias roll may have a conductive coating layer on the surface. As the conductive coating layer material, for example, resin materials such as polyimide, polyphenylene sulfide, polyether sulfide, polyether imide, and polyarylate can be used. The conductive agent described above can be used for imparting conductivity.

(Roll axis)
The roll shaft is a cylindrical metallic member that functions as an electrode and a support member of a bias roll, and as a material thereof, for example, a metal alloy such as aluminum, iron, copper alloy, SUS, or the surface thereof is chromium, Examples include known ones having conductivity such as metal plated with nickel or the like. It is preferable that the outer diameter of the roll shaft is usually in the range of 6 to 20 mm.

  The bias roll in the present invention is preferably produced by forming a conductive elastic layer on at least the outer periphery of the metal roll shaft. When the bias roll is pressed against the image carrier constituting the image forming apparatus, a predetermined nip width is formed. The toner transfer efficiency corresponds to the nip width. If a non-uniform nip width is formed between the transfer roll and the image carrier, transfer unevenness occurs. Therefore, from the viewpoint of obtaining a stable nip width, it is preferable that the bias roll in the present invention has a low elastic repulsion force and a low hardness.

<Image forming apparatus>
An image forming apparatus according to the present invention first-transfers a toner image formed on an image carrier to primary transfer onto an intermediate transfer belt, and secondary-transfers the toner image transferred onto the intermediate transfer belt onto a transfer target. An image forming apparatus comprising at least a second transfer unit, wherein the transfer device of the present invention is used as the first transfer unit.

  The image forming apparatus of the present invention is not particularly limited as long as it is an intermediate transfer type image forming apparatus having the above-described configuration. For example, a monocolor image forming apparatus in which only a single color toner is contained in a developing device, A color image forming apparatus that sequentially repeats primary transfer of a toner image carried on an image carrier onto an intermediate transfer belt, and a tandem in which a plurality of image carriers equipped with developing units for respective colors are arranged in series on the intermediate transfer belt Type color image forming apparatus.

A specific example of the tandem type color image forming apparatus will be described below with reference to the drawings.
FIG. 4 is a schematic configuration diagram showing an example of the image forming apparatus of the present invention. The image forming apparatus shown in FIG. 4 includes four toner cartridges 1, a pair of fixing rolls 2, a backup roll 3, a tension roll 4, a secondary transfer roll (secondary transfer means) 5, a paper path 6, a paper tray 7, Laser generator 8, four photoconductors (image carrier) 9, four primary transfer rolls (bias rolls) 10, drive roll 11, transfer cleaner 12, four charging rolls 13, photoconductor cleaner 14, developer 15 The intermediate transfer belt 16 and the like are included as main constituent members. In the image forming apparatus shown in FIG. 4, the intermediate transfer belt is used as an intermediate transfer belt 16 that functions as a toner image overlapping unit and a toner image transfer unit.

  Next, the configuration of the image forming apparatus shown in FIG. 4 will be sequentially described. First, around the photoreceptor 9, a primary transfer roll (bias roll) 10 and a photoreceptor cleaner 14 are disposed counterclockwise via a charging roll 13, a developing device 15, and an intermediate transfer belt 16, These one set of members form a developing unit corresponding to one color. Each developing unit is provided with a toner cartridge 1 for replenishing the developer in the developing unit 15, and the photosensitive member 9 of each developing unit is exposed to a photosensitive member between the charging roll 13 and the developing unit 15. A laser generator 8 that can irradiate the surface of the body 9 with laser light corresponding to image information is provided.

  Four developing units corresponding to four colors (for example, cyan, magenta, yellow, and black) are arranged in series in a substantially horizontal direction in the image forming apparatus. An intermediate transfer belt 16 is provided so as to pass through the nip portion with the transfer roll (bias roll) 10. The intermediate transfer belt 16 is stretched by a backup roll 3, a tension roll 4, and a drive roll 11 provided on the inner peripheral side thereof in the following order in the counterclockwise direction. The four primary transfer rolls are positioned between the backup roll 3 and the tension roll 4. A transfer cleaner 12 for cleaning the outer peripheral surface of the intermediate transfer belt 16 is provided on the opposite side of the drive roll 11 via the intermediate transfer belt 16 so as to be in pressure contact with the drive roll 11.

  A toner image formed on the outer peripheral surface of the intermediate transfer belt 16 on the surface of the recording paper conveyed from the paper tray 7 via the paper path 6 to the opposite side of the backup roll 3 via the intermediate transfer belt 16. A secondary transfer roll 5 for transferring the ink is provided so as to be in pressure contact with the backup roll 3.

  In addition, a paper tray 7 for stocking recording paper is provided at the bottom of the image forming apparatus, and a backup roll 3 and a secondary transfer roll 5 that constitute a secondary transfer unit via the paper path 6 from the paper tray 7. It can supply so that it may pass a press-contact part. The recording sheet that has passed through the press contact portion can be further transported by a transport means (not shown) so as to pass through the press contact portions of the pair of fixing rolls 2 and can be finally discharged out of the image forming apparatus.

  Next, an image forming method using the image forming apparatus of FIG. 4 will be described. The toner image is formed for each developing unit. After uniformly charging the surface of the photoconductor 9 rotating counterclockwise by the charging roll 13, the photoconductor 9 charged by the laser generator 8 (exposure device) is used. A latent image is formed on the surface, and then this latent image is developed with a developer supplied from a developing device 15 to form a toner image, and a pressure contact between the primary transfer roll (bias roll) 10 and the photosensitive member 9 is formed. The toner image conveyed to the portion is transferred onto the outer peripheral surface of the intermediate transfer belt 16 that rotates clockwise. The photosensitive member 9 after the transfer of the toner image is cleaned with toner or dust adhered to the surface by the photosensitive member cleaner 14 to prepare for the formation of the next toner image.

  The toner images developed for each color developing unit are sequentially superimposed on the outer peripheral surface of the intermediate transfer belt 16 so as to correspond to the image information, and are conveyed to the secondary transfer unit by the secondary transfer roll 5. The image is transferred from the paper tray 7 to the surface of the recording paper conveyed via the paper path 6. The recording paper on which the toner image has been transferred is further fixed by being heated by pressure when passing through the pressure contact portion of the pair of fixing rolls 2 constituting the fixing portion, and an image is formed on the surface of the recording medium. Then, it is discharged out of the image forming apparatus.

  The intermediate transfer belt that has passed through the secondary transfer portion is prepared for the transfer of the next toner image after the outer peripheral surface is cleaned by the transfer cleaner 12.

Here, as the photoreceptor (image carrier) 9, a conventionally known one can be used, and as the photosensitive layer, a known one such as an organic type or amorphous silicon can be used. When the image carrier is cylindrical, it can be obtained by a known manufacturing method such as surface processing after extrusion molding of aluminum or an aluminum alloy. It is also possible to use the belt-shaped image carrier.
The charging roll 13 (charging means) is not particularly limited. For example, a contact-type charger using a conductive or semiconductive roller, brush, film, rubber blade, a scorotron charger using corona discharge, Known chargers such as a corotron charger can be used. Among these, a contact-type charger is preferable in terms of excellent charge compensation capability. The charging unit normally applies a direct current to the photoconductor 9, but an alternating current may be applied in a superimposed manner.

  There is no restriction | limiting in particular as the laser generator 8 (exposure means), For example, on the surface of the said electrophotographic photoreceptor, light sources, such as a semiconductor laser beam, LED light, a liquid-crystal shutter light, or these light sources are passed through a polygon mirror. Examples thereof include optical equipment that can be exposed to a desired image.

  The developing device 15 (developing means) can be appropriately selected according to the purpose. For example, the developing device 15 is developed by bringing a one-component developer or a two-component developer into contact or non-contact with each other using a brush, a roller or the like. A well-known developing device etc. are mentioned.

  Examples of the secondary transfer roll 5 (second transfer unit) include a contact transfer charger, a scorotron transfer charger, and a corotron transfer charger. Among these, a contact type transfer charger is preferable. If the contact-type transfer charger such as a transfer roll is pressed strongly, the image transfer state can be maintained in a good state. Also, when a contact type transfer charger such as a transfer roller is pressed at the position of the roller that guides the intermediate transfer belt 16, the toner image is transferred from the intermediate transfer belt 16 to the transfer target (paper) in a good state. It becomes possible to do in.

  Further, in the image forming apparatus shown in FIG. 4, a charge eliminating unit can be installed on the outer peripheral surface of the intermediate transfer belt 16 between the backup roll 3 and the drive roll 11, for example, a tungsten lamp, an LED, or the like. Examples of the light quality used in the light neutralization process include white light such as a tungsten lamp, red light such as LED light, and the like. The irradiation light intensity in the photostatic process is usually set to output several times to about 30 times the amount of light indicating the half exposure sensitivity of the electrophotographic photosensitive member.

The fixing roll 2 (fixing means) is not particularly limited, and examples thereof include known fixing devices such as a heat roller fixing device and an oven fixing device.
The cleaning means 12 is not particularly limited, and a known cleaning device or the like may be used.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In the following examples, “part” means “part by mass” unless otherwise specified.

(Manufacture of belts 1 to 4)
An NMP solution of polyamic acid shown in Table 1 (both solid content concentration 20% by mass) and carbon black were dispersed (150 MPa, 5 pass) with a wet jet mill disperser (Genus PY), and carbon black-dispersed polyamic acid A solution was obtained. This was passed through a stainless steel 20 μm mesh to remove foreign substances and carbon black aggregates. Further, vacuum defoaming was performed for 15 minutes with stirring to prepare a final coating solution.

In Table 1, “carbon black content” is the amount of polyamic acid with respect to 100 parts of NMP solution, and “surface resistivity after 10 seconds” represents the common logarithm of surface resistivity after 10 seconds of voltage application, The “10 sec-30 msec surface resistivity difference” represents the difference between the common logarithmic value of the surface resistivity after 10 seconds of voltage application and the common logarithm of the surface resistivity after 30 msec. Abbreviations described in Table 1 are as follows.
BPDA: biphenyltetracarboxylic dianhydride PDA: p-phenylenediamine ODA: oxydianiline SB250: special black 250 (manufactured by Degussa)
SB4A: Special Black 4A (Degussa)

  Next, the obtained polyamic acid solution in which carbon black is dispersed is applied to a cylindrical mold inner surface (inner diameter 302 mm, length 500 mm, wall thickness 10 mm) through a dispenser so that the thickness becomes 0.5 mm, After rotating at 1500 rpm for 15 minutes to form a spread layer having a uniform thickness, while rotating at 250 rpm, hot air of 60 ° C. was applied from the outside of the mold for 30 minutes, and then heated at 150 ° C. for 60 minutes. It was removed and demolded as a semi-cured state. Thereafter, the removed belt was placed on an iron core and heated to a firing temperature (300 ° C.) to convert the imide to obtain desired polyimide belts (intermediate transfer belts) 1 to 4. The belt thickness was about 80 μm.

(Measurement of belt surface resistivity)
The surface resistivity of the obtained belts 1 to 4 was measured by the method described above. In detail, a circular electrode (UR probe of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd .: outer diameter Φ16 mm of the cylindrical electrode C, inner diameter Φ30 mm of the ring electrode portion D, outer diameter Φ40 mm) is used at 22 ° C./55 Under a% RH environment, a voltage of 100 V was applied, and the resistance values at 30 msec and 10 sec were measured after the application. Table 1 shows the common logarithm values of the surface resistivity after 10 seconds after application, and the common logarithm values of the surface resistivity after 10 seconds and 30 msec after application.

(Manufacture of bias roll 1)
100 parts of acrylonitrile-butadiene rubber (NBR: Nipol DN-219: manufactured by Nippon Zeon Co., Ltd.), 1 part of sulfur (200 mesh manufactured by Tsurumi Chemical Industry Co., Ltd.) and a vulcanization accelerator (Noxeller M manufactured by Ouchi Shinsei Chemical Co., Ltd.) A mixture obtained by adding 1.5 parts, 22 parts of carbon black (Printex 150T manufactured by Degussa Co., Ltd.) as an electron conductive conductive agent, and 6 parts of benzenesulfonyl hydrazide as a foaming agent and kneading with an open roll has a diameter of 10 mm. It was wound around a roll shaft made of SUS and press vulcanized and foamed at 160 ° C. for 20 minutes. A bias roll 1 having a roll outer diameter of 18.8 mm was obtained.

(Manufacture of bias roll 2)
By containing an ethylene oxide group, 60 parts of epichlorohydrin rubber (ECO: epichromer CG-102: manufactured by Daiso Corporation) and 30 parts of acrylonitrile-butadiene rubber (NBR: Nipol DN-219: manufactured by Nippon Zeon Corporation) having high ion conductivity 1 part of sulfur (200 mesh manufactured by Tsurumi Chemical Co., Ltd.), 1.5 part of a vulcanization accelerator (Noxera-M manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.), and carbon black ( Degussa Special Black 250) 28 parts and benzenesulfonyl hydrazide 6 parts as a foaming agent were added and kneaded with an open roll. The mixture was wound around a SUS roll shaft of φ10 mm and pressed at 160 ° C. for 20 minutes. Sulfur foamed. A bias roll 2 having a roll outer diameter of 18.8 mm was obtained.

(Manufacture of bias roll 3)
By containing an ethylene oxide group, 60 parts of epichlorohydrin rubber (ECO: epichromer CG-102: manufactured by Daiso Corporation) and 30 parts of acrylonitrile-butadiene rubber (NBR: Nipol DN-219: manufactured by Nippon Zeon Corporation) having high ion conductivity 1 part of sulfur (200 mesh manufactured by Tsurumi Chemical Co., Ltd.), 1.5 part of a vulcanization accelerator (Noxera-M manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.), and carbon black ( Degussa Special Black 4A) 24 parts and 6 parts of benzenesulfonyl hydrazide as a blowing agent were added and kneaded with an open roll. The mixture was wound around a SUS roll shaft with a diameter of 10 mm and pressed at 160 ° C. for 20 minutes. Sulfur foamed. A bias roll 3 having a roll outer diameter of 18.8 mm was obtained.

(Manufacture of bias roll 4)
By containing an ethylene oxide group, 70 parts of epichlorohydrin rubber (ECO: epichromer CG-102: manufactured by Daiso Corporation) and 30 parts of acrylonitrile-butadiene rubber (NBR: Nipol DN-219: manufactured by Nippon Zeon Corporation) having high ion conductivity are contained. As a foam vulcanizing agent, 1 part of sulfur (200 mesh manufactured by Tsurumi Chemical Co., Ltd.), 1.5 part of a vulcanization accelerator (Noxera-M manufactured by Ouchi Shinsei Chemical Co., Ltd.), foaming A mixture obtained by adding 6 parts of benzenesulfonylhydrazide as an agent and kneading with an open roll was wound around a roll shaft made of SUS having a diameter of 10 mm, and press vulcanized and foamed at 160 ° C. for 20 minutes. A bias roll 4 having a roll outer diameter of 18.8 mm was obtained.

(Bias roll resistance measurement)
As for the volume resistance value (Rv) of the bias roll, a voltage of 1000 V (V) was applied by applying a load of 500 g to both ends of the bias roll shaft on an aluminum plate in a low temperature and low humidity (10 ° C., 15% RH) environment. The current value I (A) up to 10 seconds later was read with an ammeter (manufactured by Advantest, digital ultra-high resistance / microammeter R8340A), and the volume resistance was calculated from Rv = V / I.
Further, the potential change for 1 sec was obtained as follows. First, a transfer current is applied to the bias roll, and a resistance value every 30 msec from 30 msec to 10 sec is measured using a digital ultrahigh resistance / microammeter (trade name: R8340A, manufactured by Advantest Corporation). The potential was calculated by applying a constant current value and plotted in a table, and the difference between 0 sec and 1 sec was obtained from the table.

(Evaluation of copy quality)
The intermediate transfer belt and bias roll described in Table 3 and Table 4 were mounted on Docu Center Color a450 manufactured by Fuji Xerox Co., Ltd., and the transfer current applied was set to the values described in Table 3 and Table 4. In a low-temperature, low-humidity (10 ° C, 15% RH) environment, Cyan and Magenta 50% halftone images were output to Fuji Xerox C2 paper, and the following criteria were used to visually evaluate density unevenness, spot defects, and blurring. . The results are shown in Tables 3 and 4.

[Density unevenness]
○: Density unevenness is not confirmed.
X: Slight density unevenness was confirmed.
XX: Density unevenness was clearly confirmed.

[Speckle defect]
○: Spot defect is not confirmed.
X: Spot defects were slightly confirmed.
XX: Spot defects were clearly confirmed.

[Blur (Toner Scatter)]
○: Toner scattering is not confirmed.
X: Toner scattering was slightly confirmed.
XX: Toner scattering was clearly confirmed.

(Surface electric field)
The surface electric field (V) was calculated by V = It × Rv from the bias roll volume resistance (Rv) and the transfer current (It), assuming that the surface electric field after transfer is equipotential with the bias roll. The calculation results are shown in Tables 3 and 4.

  From Tables 3 and 4, it can be seen that in Examples 1 and 2 using the transfer device of the present invention, density unevenness, spot defects and blur were reduced.

(A) is a schematic plan view which shows an example of a circular electrode, (b) is the schematic sectional drawing. (A) is a schematic plan view which shows an example of a circular electrode, (b) is the schematic sectional drawing. It is explanatory drawing for demonstrating the division | segmentation and mixing mechanism of a carbon black containing polyamic acid solution. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus.

Explanation of symbols

1 toner cartridge 2 fixing roll 3 backup roll 4 tension roll 5 secondary transfer roll (secondary transfer means)
6 Paper path 7 Paper tray 8 Laser generator 9 Photoconductor (image carrier)
10 Primary transfer roll (bias roll)
11 Driving Roll 12 Transfer Cleaner 13 Charging Roll 14 Photoconductor Cleaner 15 Developer 16 Intermediate Transfer Belt 50 First Flow Pipe 52 Connecting Pipe 54 Second Flow Pipe A, E First Voltage Application Electrode B Plate Insulator C, G Cylindrical electrode part D, H Ring-shaped electrode part F Second voltage application electrode T, T2 Intermediate transfer belt

Claims (2)

A transfer device having an intermediate transfer belt in which carbon black is dispersed and a bias roll, and performing a transfer current at a constant current (It);
The difference between the common logarithm of the surface resistivity after 10 seconds of voltage application and the common logarithm of the surface resistivity after 30 msec of the intermediate transfer belt is 0.2 (LogΩ / □) or less in absolute value.
The electric field (V) given by V = It × Rv of the bias roll is 3000 V or less,
The transfer apparatus is characterized in that the potential change of the bias roll for 1 sec is 300 V or more. A first transfer unit that primarily transfers a toner image formed on the image carrier to an intermediate transfer belt; and a second transfer unit that secondarily transfers the toner image transferred to the intermediate transfer belt to a transfer target. An image forming apparatus comprising:
An image forming apparatus using the transfer device according to claim 1 as the first transfer unit.

Images