JP2000056585A - Transfer member and image forming device using the member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the local reduction in surface resistance of a transfer member and the void of image accompanying it by providing a conductive layer having a volume resistivity lower than the volume resistivities of a base layer and a surface layer between the base layer and the surface layer. SOLUTION: This transfer member is provided with a base layer 1a, a surface layer 1c provided on the circumference of the base layer 1a, and a conductive layer 1b interposed between the base layer 1a and the surface layer 1c and having a volume resistivity lower than the volume resistivities of the base layer 1a and the surface layer 1c and 107Ωcm or less. As the surface layer 1c, a one formed of a rubber or resin base material and a resistance regulating agent of electron conductive type filler is effective. Either one of the base layer 1a and the surface layer 1c is mainly formed of polyimide resin, and a material having a tensile elasticity of 1470 N/mm2 or more is used for either one of the base layer 1a and the surface layer 1c. The conductive layer 1b is preferably formed of a material capable of adhering the base layer 1a to the surface layer 1c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer member for electrostatically carrying a developed image such as a toner image and a recording material in an image forming apparatus such as a copying machine or a printer using an electrophotographic method. The present invention relates to an image forming apparatus using the same.

[0002]

2. Description of the Related Art As a conventional intermediate transfer type image forming apparatus, for example, a photosensitive drum on which a toner image corresponding to an electrostatic latent image is formed, and a toner image on the photosensitive drum are intermediately transferred. An intermediate transfer belt, a primary transfer device for transferring the toner image on the photosensitive drum to the intermediate transfer belt, and a secondary transfer device for collectively secondary transferring the toner image transferred on the intermediate transfer belt to paper A device having a transfer device is known (see, for example, JP-A-5-323704).

In this type of image forming apparatus, the intermediate transfer belt has an insulating (dielectric) or semiconductive property in order to electrostatically carry and transport the toner image transferred from the photosensitive drum. In particular, a type having a semiconductivity that does not need to remove a transfer charge applied for transferring a toner image is widely used. As a semiconductive intermediate transfer belt of this kind, an electron conductive filler such as carbon or metal oxide or an ionic conductive material such as quaternary ammonium salt or lithium perchlorate is used as a base material made of resin or rubber. A material in which a substance is dispersed and whose electric resistance value is adjusted is used.

Here, in the former type in which the electron conductive type filler is dispersed, the strength of the intermediate transfer belt can be improved by the dispersion, and the amount of change in the electric resistance value due to environmental changes is small. On the other hand, the latter type, in which the ionic conductive substance is dispersed, can disperse the ionic conductive substance at the molecular level with respect to the base material such as resin or rubber. Is very small.

However, in the case of the type in which the ionic conductive material is dispersed, it is difficult to set the transfer parameters and the like due to a large amount of change in the electric resistance due to the surrounding environment, particularly the change in humidity. There is a possibility that the conductive substance is easily deposited on the surface of the intermediate transfer belt, and the deposited ion conductive substance is transferred to the surface of the photoconductor drum and contaminates the surface of the photoconductor drum.

[0006] Also, JP-A-8-50419 discloses that
It has been proposed to use epichlorohydrin rubber, which is an ion conductive substance, and carbon, metal oxide, or the like, which is an electron conductive filler. However, epichlorohydrin rubber, which is an ion conductive substance, has a large amount of change in electric resistance due to a change in humidity as described above,
It is not practical because it is a highly sticky material.
For this reason, as a conventional intermediate transfer belt, a type in which an electron conductive type filler is dispersed in resin or rubber is widely used.

[0007]

However, when an intermediate transfer belt in which an electron conductive type filler is dispersed is used,
In a low-temperature, low-humidity environment, for example, a temperature of 15 ° C. or less and a humidity of 20%
Under the following environment, the electrical resistance of the intermediate transfer belt, particularly the surface resistivity, tends to decrease due to the two types of discharge described below, and the decrease in the surface resistivity makes it impossible to hold the transfer charge, resulting in poor transfer. There is a technical problem of getting lost.

1) Discharge inside the toner layer (reduction in resistance of the intermediate transfer belt at the time of primary transfer) FIG. 2A is a schematic diagram of an intermediate transfer belt in which an electron conductive filler is dispersed. In the figure, reference numeral 200 denotes an intermediate transfer belt, 201 denotes an insulating resin serving as a base of the intermediate transfer belt 200, 202 denotes a conductive electron-conductive filler dispersed inside the intermediate transfer belt 200,
03 is a primary transfer device (primary transfer roll). Here, paths (current paths) P _a , P _b , P _c ... Are formed in the intermediate transfer belt 200 in a substantially vertical direction in the figure by a chain of electron conductive fillers 202. Normal time,
The intermediate transfer belt 200, and flows transfer current I _t by the primary transfer bias. At this time, the transfer current I _t is, among the paths formed inside the intermediate transfer belt 200, so that the flow through the closest path P _b to the primary transfer position T _r.

On the other hand, when, for example, yellow, magenta, and cyan toners are transferred onto the intermediate transfer belt 200, a toner layer having a thickness of about 60 μm is laminated thereon. Voids are formed. In a low-temperature and low-humidity environment, the system resistance of the primary transfer unit including the primary transfer device (primary transfer roll) 203 and the intermediate transfer belt 200 increases, so that the primary transfer bias required for the primary transfer reaches several kV. Under such circumstances, if the relationship between the primary transfer bias and the gap inside the toner layer satisfies the Paschen rule near the primary transfer position _Tr , discharge occurs inside the stacked toner layers (hereinafter referred to as internal discharge). Occurs.

[0010] In this way, the internal discharge occurs, the intermediate transfer belt 200, a transfer current I _t by the primary transfer bias, and internal discharge current I _d caused by the internal discharge,
At the same time so that the flow into the path P _b of the primary transfer position neighborhood. However, there is a limit to the amount of current that can be the path P _b shed, if it exceeds allowable current amount of the path P _b, excessive current, the path P _b and another path (e.g., P _a , P _c ) flows into the resin 201 (shown by a broken line in the figure). Since this phenomenon occurs particularly actively near the surface of the intermediate transfer belt 200, it is considered that a dielectric breakdown of the resin 201 occurs at a portion where an excessive current has flowed, and the surface resistance of the intermediate transfer belt 200 is reduced. Thus, the intermediate transfer belt 200
In the area where the resistance is lowered, the transfer charge cannot be held, so that the toner image cannot be held. Since the reduction in resistance due to the internal discharge occurs in the area where the toner image is carried, white spots occur in the area (toner mark).

2) Peeling discharge of transfer material (reduction in resistance of intermediate transfer belt during secondary transfer) In a low-temperature and low-quality environment, the electrical resistance of the paper increases due to a decrease in the water content of the paper. The secondary transfer bias at the time of the next transfer requires several kV. When the sheet is separated from the intermediate transfer belt after the secondary transfer, several k
Since a gap that satisfies the Paschen rule is generated between the recording material charged to V and the intermediate transfer belt, a discharge (hereinafter, referred to as a peeling discharge) occurs between the sheet and the intermediate transfer belt.

At this time, the current generated by the peeling discharge (hereinafter referred to as the peeling discharge current) and the secondary transfer current flow into the intermediate transfer belt, and exceed the amount of current that can pass through the path in the intermediate transfer belt. If so, it is considered that the resin is subjected to dielectric breakdown due to the excessive current as in the case of the occurrence of the internal discharge, and the surface resistance of the portion is reduced. Since the decrease in resistance due to the peeling discharge occurs in the area where the paper is carried on the intermediate transfer belt, the area (paper trace)
White spots occur on the surface. Further, it is considered that at the time of the secondary transfer, the surface resistance is reduced due to the discharge inside the toner layer at the same time as the surface resistance is reduced due to the peeling discharge of the paper.

Incidentally, such a technical problem can occur not only in an intermediate transfer member having a drum shape but also in an intermediate transfer member having a drum shape. A recording material transporting body that is circulated and transported is disposed at a portion facing one or a plurality of image forming units, and the recording material transported electrostatically on the recording material transporting body, and the recording material transported by the image forming unit, The same can occur in a recording material transporter of an image forming apparatus that transfers a formed image. Further, such a technical problem is particularly remarkable in a type in which an electron conductive filler is dispersed in a resin or rubber which is likely to cause dielectric breakdown because a path in an intermediate transfer member is fixed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and by devising the structure of the transfer member, a local decrease in the surface resistance value of the transfer member and an image associated therewith are reduced. And an image forming apparatus using the same.

[0015]

That is, as shown in FIG. 1, the present invention provides at least a base layer 1a, a surface layer 1c provided on the outer periphery of the base layer 1a, and a space between the base layer 1a and the surface layer 1c. And a conductive layer 1b which is lower than the volume resistivity of the base layer 1a and the surface layer 1c and has a volume resistivity of 10 ⁷ Ωcm or less.

In such technical means, as the base layer 1a and the surface layer 1c of the transfer member 1 in the present application, an electron conductive type filler is dispersed in both, and an electron conductive type filler is dispersed in at least one of them. It encompasses any of the types. In addition, the shape of the transfer member 1 to which the present invention is applied may be appropriately selected, such as a belt shape and a drum shape. Further, the transfer member 1 transfers and carries the target 2 by electrostatic force. Examples of the target 2 include a developer such as a toner and a recording material such as a sheet.

The base layer 1a has a volume resistivity higher than a volume resistivity of the conductive layer 1b described later from the viewpoint of preventing leakage of a transfer current or a discharge current to another functional member. On the other hand, from the viewpoint of preventing accumulation of excessive charges on the base layer 1a and eliminating the need for a charge removing mechanism of the transfer member 1, the volume resistivity is set to 1
It is preferable to set it to 0 ¹² Ωcm or less. Here, the material constituting the base layer 1a may be appropriately selected as long as it satisfies the above-mentioned volume resistivity condition. However, from the viewpoint of environmental stability of electric resistance, resin, rubber, or the like may be used. It is preferable to use a type in which an electron conductive filler is dispersed in a base material.

Furthermore, the surface layer 1c has a surface resistivity of 10 to prevent the charge for electrostatically carrying the object 2 from being immediately removed due to the conductivity of the surface layer 1c itself. preferably set to ¹⁰ Omega / □ or more, whereas, from the viewpoint that prevents the accumulation of excess charge on the surface layer 1c eliminates the need for neutralizing mechanism of the transfer member 1, the surface resistivity of 10 ¹⁵ It is preferably set to Ω / □ or less. Furthermore, the volume resistivity of the surface layer 1c needs to be set higher than the volume resistivity of the conductive layer 1b, which will be described later, as in the case of the base layer 1a. From the viewpoint of preventing the accumulation of charges and eliminating the need for the charge elimination mechanism of the transfer member 1, 1
It is preferable to set it to 0 ¹³ Ωcm or less.

Here, the material constituting the surface layer 1c may be appropriately selected as long as it satisfies the above conditions of the volume resistivity and the surface resistivity.
However, it is effective to apply to a type composed of a base material made of rubber or resin and a resistance adjuster made of an electron conductive type filler. In such an embodiment,
As the base material, for example, polyethylene, polypropylene, polystyrene, polyisobutylene, polyester, polyurethane, polyamide, polyimide, polyamideimide, alcohol-soluble nylon, polycarbonate, polyarylate, phenol, polyoxymethylene, polyetheretherketone, polyphosphazene,
Thermoplastic resins and thermosetting resins such as polysulfone, polyether sulfide, polyphenylene oxide, polyphenylene ether, polyparabanic acid, polyallylphenol, polybenzimidazole, urea, fluorine, polyurea, ionomer, silicone, and the like;
Examples include a mixture or a copolymer composed of at least one kind, and as the resistance adjuster, for example, carbon black,
Examples thereof include conductive fillers such as acetylene black, graphite, metal oxides, composite metal oxides, and metal powders, and semiconductive fillers alone or in an appropriate combination.

Examples of the method for producing the base layer 1a and the surface layer 1c include extrusion molding, injection molding, casting, centrifugal molding, and film-like molding by inflation.
It may be appropriately selected from various manufacturing methods. Further, the thicknesses of the base layer 1a and the surface layer 1c may be appropriately selected, but if the base layer 1a and the surface layer 1c are too thick, for example, when the transfer member 1 has a belt shape stretched over a plurality of roll members. Is caused by the difference in speed between the inner circumference and the outer circumference of the belt near the stretched portion due to the roll,
Further, since the elastic deformation of the transfer member 1 is reduced with respect to the pressing force of the transfer roll at the transfer portion, the pressing force is concentrated on the toner image, so that toner aggregation may occur, and a line image may drop out. There is. From the viewpoint of reliably preventing such defects, the base layer 1a
And the thickness of the surface layer 1c is 10 mm or less, preferably 5 m
m or less.

The conductive layer 1b has a resistance of 10 ⁷ Ωc
m is required, but this has been found by the present inventor. As will be described later, in those having a volume resistivity of 10 ⁸ Ωcm or more, white It has also been found that dropout cannot be prevented. Here, from the viewpoint of reliably preventing white spots,
Preferably, the conductive layer 1b has a volume resistivity of 10 ⁵ Ωcm or less.

Further, the material constituting the conductive layer 1b may be appropriately selected as long as it can be adjusted to the above-described volume resistivity. For example, the material for the base layer 1a and the surface layer 1 may be selected.
You may comprise from the same material as c. Here, from the viewpoint of simplifying and facilitating the manufacture of the transfer member 1,
The conductive layer 1b is preferably made of a material that bonds the base layer 1a and the surface layer 1c. Specific examples of the configuration of the adhesive type conductive layer 1b include, for example, a resin component having an adhesive force such as acrylic, polyester, urethane, polyamide, polyolefin, and silicon, and conductive carbon, a metal piece, and a metal oxide. And a conductive filler dispersed therein. In such an embodiment, the thickness of the conductive layer 1b may be any range as long as it is set in a range where an adhesive force sufficient to bond the base layer 1a and the surface layer 1c is obtained, for example, 10 to 1000 μm, Preferably, it may be appropriately selected from the range of 10 to 500 μm.

Further, when the transfer member 1 has, for example, an endless belt shape, if the resistance (strength) against load fluctuation (stress) during driving is low, the transfer member 1 may be elongated and permanently deformed. When the transfer member 1 is used as an intermediate transfer member, for example, such elongation may cause a shift of a superimposed toner image, that is, a so-called registration shift. From the viewpoint of reliably preventing such misregistration, at least one of the base layer 1a and the surface layer 1c of the transfer member 1 has a thickness of 1470 N / mm.
It is preferable to use a material having a tensile modulus of ² or more.

Here, the tensile modulus is defined by JIS K-7.
127 is a value obtained by the following equation. Tensile modulus Em = Δσ / Δε where Em: Tensile modulus (N / mm ² ) Δσ: Difference in stress due to the original average cross-sectional area between two points on a straight line (N / mm ² ) Δε: Between the same two points Difference (tensile speed: 100 mm /
min)

The relationship between the tensile modulus of the transfer member 1 and the amount of displacement (elongation) of the transfer member 1 due to a load change (stress) during driving is expressed as follows. Displacement Δl = P · l · α / (t · w · Em) where Δl: belt displacement (μm) P: load (N) l: belt length (mm) between two tension rolls α: Coefficient t: Belt thickness (mm) w: Belt width (mm) Em: Tensile elastic modulus (N / mm ² ) of belt material

From the above equation of displacement amount, the displacement amount of the transfer member 1 due to the load variation during driving is inversely proportional to the tensile elastic modulus of the transfer member 1, and the material having the larger tensile elastic modulus is caused by the load variation during driving. It is clear that the amount of displacement of the transfer member 1 can be reduced. The present inventor pays attention to this relationship, and in the case of the combination of the base layer 1a, the conductive layer 1b, and the surface layer 1c of the present invention, at least one of the base layer 1a and the surface layer 1c has a tensile modulus of 1470 N / m
It has been found that, when it is set to m ² or more, the displacement amount (elongation) of the transfer member 1 can be suppressed, so that the misregistration can be prevented.

The upper limit of the tensile modulus of the base layer 1a or the surface layer 1c may be appropriately selected, but generally, when the tensile modulus is increased, the toughness is lost and the material may become very brittle. From the viewpoint of preventing such problems, the upper limit of the tensile modulus of the surface layer 1a and the base layer 1c is 9807 N / cm ² or less, preferably 78.
It is preferred to be 45 N / cm ² or less.

As a material having a high tensile modulus, a low water absorption and a good surface smoothness, a polyimide resin can be used. Therefore, it is preferable to use a resin mainly composed of polyimide for at least one of the base layer 1a and the surface layer 1c.

Further, the transfer member 1 includes an image carrier on which a toner image corresponding to image information is formed, an intermediate transfer member disposed to face the image carrier and carrying the toner image, and
An image forming apparatus including a primary transfer unit for sequentially transferring a toner image on an image carrier to an intermediate transfer body, and a secondary transfer unit for collectively transferring a toner image transferred and held on the intermediate transfer body onto a recording material It is preferable to apply the present invention to the intermediate transfer member.

Further, the transfer member 1 has one or a plurality of image forming units, and a recording material conveying body circulated and conveyed is disposed at a portion facing the image forming unit. For recording materials carried and transported on the body,
It is preferable to apply the present invention to a recording material transporting body of an image forming apparatus which transfers an image formed by the image forming unit.

There is a prior art in which an intermediate transfer member (corresponding to the transfer member 1 in the present invention) is composed of two or more layers (see JP-A-8-50419), but this is different from the present invention. Because there is, it is explained just in case. That is, Japanese Patent Application Laid-Open No. H8-50419 discloses a method for forming a visible developed image comprising two or more layers in order to solve the technical problem of image unevenness due to variation in resistance of an intermediate transfer member. There is disclosed a technology relating to an intermediate transfer member in which the specific resistance of the uppermost layer to be formed is equal to or higher than the specific resistance of the lower layer located below the uppermost layer (claim 1). This prior art may certainly be similar to the present invention in that the specific resistance of the lower layer located below the uppermost layer is set smaller than that of the uppermost layer. However, this prior art does not mention any technical problem of a decrease in the resistance of the transfer member 1 due to a discharge inside the toner layer or a peeling discharge of a recording material such as paper. conductive layer 1b with 10 ⁷ [Omega] cm or less in volume resistivity lower than the volume resistivity of the two layers between the characteristic point of the present application base 1a and the surface layer 1c for solving issues
Since there is no suggestion about the provision of the above, the technical problem and the solution thereof are different between the above prior art and the present invention.

The above prior art discloses a technique in which the uppermost layer of the intermediate transfer member is composed of at least a polymer component and epichlorohydrin rubber in order to solve the technical problem that the resistance of the intermediate transfer member decreases over time. Is also disclosed (Claim 3). This may be said to be similar to the technical problem of the present invention in terms of preventing the resistance of the intermediate transfer member (the transfer member 1 in the present invention) from decreasing with time.
However, this prior art merely discloses that the uppermost layer of the intermediate transfer member is composed of a polymer and epichlorohydrin rubber, and that the uppermost layer of the intermediate transfer member is located between the base layer 1a and the surface layer 1c, which is a feature of the present invention. Conductive layer 1b having a volume resistivity of 10 ⁷ Ωcm or less lower than the volume resistivity of both layers
Since there is no suggestion about the provision of the above, the above-mentioned prior art and the present invention are different in the means of solving the problem.

Next, the operation of the above-mentioned technical means will be described with reference to a transfer member 1 of a type in which an electron conductive filler is dispersed in the surface layer 1c. FIG. 2B shows a transfer member 1 in which an electron conductive filler is dispersed inside a surface layer 1c.
FIG. In the figure, reference numeral 1d denotes a base material made of an insulating resin or the like serving as a base of the surface layer 1c, 1e denotes an electron conductive type filler dispersed inside the surface layer 1c, and 3 denotes a conductive material for flowing a current. It is assumed to be a member. Further, inside the surface layer 1c, the electron conductive type filler 1 is provided.
The path (current path) in the direction substantially vertical in the figure by the chain of e
P _a , P _b , P _c ... Are formed. And the current I
Flow from the position _Tr of the surface layer 1c toward the conductive member 3.

[0034] When current flows I is small, the current I flows to the position T after passing through the path P _b of the nearest surface 1c to _r, the conductive member 3 via the conductive layer 1b and the base layer 1a. On the other hand, current flows I increases and exceeds the allowable current amount of the path P _b, excessive current is generated that can not flow only path P _b. This excess current, the path P _b and another path (e.g. P _a, P _c) to try to flow into in the base material 1d that exists between. However, according to the present invention, the transfer member 1 has a surface
0 ⁷ for Ωcm conductive layer 1b having the volume resistivity is provided, the path P _a than the base material 1d, the direction of P _c is the resistance has become low, an excessive current, a high resistance based Instead of the material 1d, it flows into the paths P _a and P _{c having} low resistance. As described above, when an excessive current is generated, the excessive current flows through another path and does not flow into the base material 1d of the surface layer 1c, so that a reduction in resistance at the relevant portion is prevented.

Further, the volume resistivity of the base layer 1a is
Is set to be higher than the volume resistivity of the transfer member 1, even if the conductive member indicated by reference numeral 4 is arranged in contact with the transfer member 1, the current flowing into the conductive layer 1b is It does not flow into. Note that, even when the current flows in the opposite direction, the excess current flows through another path, so that it does not flow into the base material 1d of the surface layer 1c, and a reduction in resistance at the portion is prevented. .

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 3 shows a schematic configuration of a color image forming apparatus (a color electrophotographic apparatus in the present embodiment) to which the present invention is applied. In FIG. 1, reference numeral 11 denotes a photosensitive drum, and a charging device 12 and a beam 1
An electrostatic latent image corresponding to image information is formed by a well-known electrophotographic process such as No. 3. Further, developing devices 14 to 1 corresponding to black (Bk), yellow (Y), magenta (M), and cyan (C) are provided around the photosensitive drum 11.
The electrostatic latent image formed on the photosensitive drum 11 is developed by one of the developing devices 14 to 17 to form a toner image. Reference numeral 18 denotes a drum cleaner that collects residual toner remaining on the photosensitive drum 11 without being primary-transferred.

Reference numeral 20 denotes an intermediate transfer belt disposed in contact with the surface of the photosensitive drum 11, and is stretched over a plurality of (four in the present embodiment) rolls 21 to 24 in the direction of arrow B. It is designed to rotate. Here, in the present embodiment, reference numeral 21 denotes a driving roll of the intermediate transfer belt 20, reference numeral 22 denotes a driven roll, reference numeral 23 denotes an opposing roll (backup roll) for secondary transfer, and reference numeral 24 denotes a constant tension of the intermediate transfer belt 20. It is a tension roll to be controlled.

Further, at a portion (primary transfer position) where the photosensitive drum 11 and the intermediate transfer belt 20 face each other, a primary transfer roll 25 is provided as a primary transfer device on the back side of the intermediate transfer belt 20. By applying a voltage having a polarity opposite to the charging polarity of the toner to the primary transfer roll 25, the toner on the photosensitive drum 11 is transferred to the intermediate transfer belt 20.
Is electrostatically attracted.

A secondary transfer device 40 is provided at a secondary transfer position of the intermediate transfer belt 20 facing the conveyance path of the sheet P as a recording material. And a counter roll (backup roll) 23 disposed on the back side of the intermediate transfer belt 20 and serving as a counter electrode of the secondary transfer roll 26. ing. Further, a bias voltage having the same polarity as that of the toner is stably supplied to the backup roller 23 via the power supply roller 27. The secondary transfer roll 26 includes the secondary transfer roll 2
6 Remove toner adhering to the surface, for example, polytan,
A cleaning blade 28 made of silicon is provided.

In the present embodiment, the paper transport system takes out the paper P from the supply tray 50 by the pickup roll 51, temporarily stops the positioning by the registration roll 52, and then moves to the secondary transfer position at a predetermined timing. And the sheet P are sent.
Is transported to the fixing device 53 via a transport belt (not shown). Further, the secondary transfer roll 26 and the belt cleaner 29 are disposed so as to be able to freely contact and separate from the intermediate transfer belt 20 by a retracting device (not shown). These members are separated from the intermediate transfer belt 20 until the previous toner image T passes through the secondary transfer roll 26 and the belt cleaner 29.

FIG. 4 is a sectional view of the intermediate transfer belt 20 according to the present embodiment. In the present embodiment,
The intermediate transfer belt 20 includes a base layer 20a that comes into contact with the rolls 21 to 24 and the primary transfer roll 25, and a surface layer 20c on the outer peripheral surface side of the base layer 20a on which the toner T transferred from the photoconductor drum 11 is carried. A conductive layer 20b is provided between the base layer 20a and the surface layer 20c. In particular, in the present embodiment, the conductive layer 20b is made of an adhesive, and the base layer 20a and the surface layer 20c are bonded via the conductive layer 20b.

In the present embodiment, the base layer 20a, the conductive layer 20b, and the surface layer 20c are each formed by dispersing an electron conductive filler in a base material such as resin or rubber. The base layer 20a has a volume resistivity of 10 ⁸ Ωcm to 1 Ωcm.
0 ¹² is set in a range of [Omega] cm, also the surface layer 20c has a surface resistivity of ^{10 10 Ω / □ ~10 15 Ω} / □ range, setting the range of the volume resistivity 10 ⁸ Ωcm~10 ¹³ Ωcm Further, the conductive layer 20b has a volume resistivity of 10
It is set to ⁵ Ωcm or less.

Next, an image forming process of the color image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. More specifically, if the electrostatic latent image written on the photosensitive drum 11 corresponds to, for example, yellow image information, the electrostatic latent image is yellow (Y).
The toner is developed by the developing device 15 containing the toner, and a yellow toner image T is formed on the photosensitive drum 11. Then, the unfixed toner image T formed on the photosensitive drum 11
Is transferred from the photosensitive drum 11 to the surface of the intermediate transfer belt 20 by the transfer electric field formed by the primary transfer roll 25 at the primary transfer position where the photosensitive drum 11 and the intermediate transfer belt 20 are in contact with each other.

At this time, when forming a monochrome image,
The toner image T primarily transferred to the intermediate transfer belt 20 is immediately secondary-transferred. However, when a color image in which toner images of a plurality of colors are superposed is formed, the photosensitive drum 1
The process of forming the toner image on the surface 1 and the primary transfer of the toner image is repeated by the number of colors. For example, when forming a toner image in which three color toner images are superimposed, yellow, magenta, and cyan toner images T are formed on the photosensitive drum 11 at each rotation thereof, and these toner images T The primary transfer is sequentially performed on the intermediate transfer belt 20. On the other hand, the intermediate transfer belt 20 rotates at the same cycle as the photosensitive drum 11 while holding the yellow toner image T which has been primarily transferred first, and the magenta and cyan Is superimposed and transferred.

The toner image T primarily transferred to the intermediate transfer belt 20 in this manner is conveyed to a secondary transfer position as the intermediate transfer belt 20 rotates. On the other hand, the paper P is supplied to the secondary transfer position at a predetermined timing by the registration roll 52, and the secondary transfer roll 26 nips the paper P with respect to the backup roll 23. Then, at the secondary transfer position, the secondary transfer roll 26 and the backup roll 2
The toner image T carried on the intermediate transfer belt 20 is transferred onto the sheet P by the action of the transfer electric field formed between the sheet P.
After that, the sheet P on which the toner image T is transferred is fixed to the fixing device 53.
To fix the toner image. On the other hand, the toner remaining on the intermediate transfer belt 20 after the transfer is cleaned by the belt cleaner 29.

In the image forming process, a current due to a transfer electric field flows through the intermediate transfer belt 20 passing through the primary transfer position. Further, when a discharge occurs inside the toner layer superimposed and transferred on the intermediate transfer belt 20 passing through the primary transfer position, a current due to the internal discharge also flows. On the other hand, a current due to the transfer electric field also flows through the intermediate transfer belt 20 passing through the secondary transfer position. Further, when a discharge occurs when the sheet P is peeled off from the intermediate transfer belt 20 that has passed the secondary transfer position, a current due to the peeling discharge also flows.

These currents flow through paths (current paths) formed by a chain of electron conductive fillers dispersed inside the surface layer 20c. Since the current tends to flow in the path closest to the primary transfer position or the secondary transfer position, if the current concentrates on a specific path, it flows into an area (base material) where no path is formed, which may cause dielectric breakdown. was there. However, in the present embodiment, since the conductive layer 20b whose volume resistivity is set to 10 ⁷ Ωcm or less, which is lower than that of the surface layer 20c, is provided on the back side of the surface layer 20c, the primary transfer is performed more than the resistance of the base material. The resistance of another pass near the position or the secondary transfer position is lower. For this reason, the electric current flows not in the base material having a high resistance but in another path, so that dielectric breakdown of the base material does not occur. Therefore, the resistance of the intermediate transfer belt 20 does not decrease, and no white spots on the image occur. Further, since the volume resistivity of the base layer 20a is set higher than the volume resistivity of the conductive layer 20b, the current does not leak to the rolls 21 to 24.

Second Embodiment FIG. 5 shows a second embodiment of the color image forming apparatus to which the present invention is applied. In the figure, a color image forming apparatus according to the present embodiment includes a plurality of image forming units 100 (specifically, each forming a color component toner image by an electrophotographic method on a paper transport path C along a horizontal direction, for example). Typically, 1
00Y, 100M, 100C, and 100Bk) are arranged in parallel, and the respective color component toner images formed by the respective image forming units are sequentially transferred onto the paper P conveyed on the transfer / conveying belt 120. This is to form a polymerized color image.

In this embodiment, the image forming unit 100 for each color component includes a charger 102 around which the photosensitive drum 101 is uniformly charged, and an electrostatic latent image on the photosensitive drum 101. A laser writing device 103 for writing an image, a developing device 104 that contains each color component toner and visualizes the electrostatic latent image on the photosensitive drum 101, and a cleaner that removes residual toner and the like on the photosensitive drum 101 106 are sequentially arranged.

In the present embodiment, a transfer conveyance belt 120 circulating in the direction of arrow D along the paper conveyance path C is disposed at a position corresponding to each photosensitive drum 101 of each image forming unit 100. Have been. The transfer conveyance belt 120 is stretched over a pair of tension rolls 121 and 122. In the present embodiment, the tension roll 121 on the entrance side of the paper transport path C is a driven roll and the tension roll on the exit side. The frame roll 122 is a drive roll. In the present embodiment, an endless belt having a three-layer structure shown in FIG. This configuration and characteristics are the same as those of the intermediate transfer belt described in the first embodiment.

Further, a transfer roller 105 is provided on the back side of the transfer / conveyance belt 120 corresponding to the photosensitive drum 101 of each image forming unit 100. The transfer / transfer is performed between the transfer roller 105 and the photosensitive drum 101. Belt 12
The paper P above the nip is held in the nip. A transfer bias power supply (not shown) is connected to the transfer roll 105 so that a predetermined transfer bias is applied at an appropriate timing.

Further, in the paper transport system in the present embodiment, the paper P from the supply tray 150 is taken out by the pick-up roll 151, temporarily stopped by the registration roll 152, and then transferred to the transfer transport belt 120 at a predetermined timing. The paper P is fed, and after the paper P is transported on the transfer transport belt 120,
The sheet is conveyed to the fixing device 153 and is fixed.

Further, in the present embodiment, the sheet suction device (sheet suction roll) 1
11 are provided. This paper suction roll 111 is
A paper suction roll 111 is disposed at a position corresponding to the tension roll 121 on the entrance side of the paper transport path C of the transfer transport belt 120, and a bias power source (not shown) is supplied between the paper suction roll 111 and the tension roll 121. By applying a bias voltage, the paper P is attracted onto the transfer / conveying belt 120. Also,
A belt cleaner 131 for cleaning the surface of the transfer conveyance belt 120 is provided at a position off the paper conveyance path C of the transfer conveyance belt 120.

In this embodiment, the paper P is transported along the paper transport path C in a state where the paper P is adhered to the transfer transport belt 120 by the paper suction roller 111, and the toner image formed by each image forming unit 100 is The sheet P is transferred by the transfer roll 105 provided in the image forming unit.
Transcribed above. After passing through all the image forming units, the sheet P is separated from the transfer / conveyance belt 120 and is fixed by the fixing device 153.

In this image forming process, a current due to a transfer electric field flows through the intermediate transfer belt 20 passing through each transfer position. Further, when a discharge occurs inside the toner layer that is overlaid and transferred on the intermediate transfer belt 20 passing through each transfer position, a current due to the internal discharge also flows. On the other hand, if a discharge occurs when the paper P that has passed through all the transfer positions is separated from the transfer conveyance belt 120, a current due to the separation discharge also flows.

In this embodiment, since the transfer / transport belt 120 has the same configuration as that of the intermediate transfer belt of the first embodiment, the resistance of the transfer / transport belt 120 does not decrease, and the white color of the image is not changed. No omission occurs. Further, the current does not leak to the rolls 121 and 122.

[0057]

Examples ◎ Example 1 10 parts by weight of conductive carbon was mixed with polyimide varnish for heat-resistant coating (U Varnish-S, Ube Industries, Ltd.), and both were sufficiently mixed by a mixer. Put this stock solution at 30 ° C
And centrifugally molded while heating to 130 ° C.
The mold is released in a semi-cured state, and then the removed belt is covered with an iron core and heated at 380 ° C. for 30 minutes to have a thickness of 100 μm.
m, a seamless belt having a width of 320 mm was produced. The characteristics of the obtained belt in a low-temperature and low-humidity environment (10 ° C., 15% RH) are as follows. Surface resistivity 7 × 10 ¹¹ Ω / □ Volume resistivity 8 × 10 ⁹ Ωcm Tensile elasticity 3432 N / mm ²

Separately from the above, 7 parts by weight of conductive carbon and 1 part by weight of a silicon-based additive were blended with polyarylate, and a semiconductive film having a thickness of 100 μm and a width of 320 mm was prepared by extrusion molding. Here, the silicon-based additive is added to improve the releasability of the film. The characteristics of the obtained belt in a low-temperature and low-humidity environment (10 ° C., 15% RH) are as follows. Surface resistivity 5 × 10 ¹² Ω / □ Volume resistivity 7 × 10 ¹⁰ Ωcm Tensile modulus 1961 N / mm ²

The above-mentioned surface resistivity and volume resistivity were measured using a Hirester IP resistance measuring instrument and an HR probe (both manufactured by Mitsubishi Yuka) with an applied voltage of 100 V and an applied time of 30 hours.
This is a value obtained from the measurement value in seconds (the same applies to the subsequent measurement results).

Next, a conductive adhesive made by dispersing conductive carbon in an acrylic resin on the outer periphery of the above polyimide-based seamless belt as a base layer (in a low-temperature and low-humidity environment (10 ° C.,
The volume resistivity at 5% RH) is 1 × 10 ⁷ Ωcm).
After uniformly coating to a thickness of 0 μm, the polyarylate-based semiconductive film is laminated and an endless belt comprising a base layer (polyimide resin), a conductive layer (acrylic adhesive), and a surface layer (polyalate resin) I got The endless belt thus obtained is attached to the position of the intermediate transfer belt 20 of the full-color image forming apparatus shown in FIG.
It was subjected to a durability test of 10,000 sheets under the following conditions. Process speed 220mm / sec Image pattern A-4 3c on vertical paper (plain paper)
Three mx 3 cm process plaque (yellow, magenta, cyan) solid patches are produced at equal intervals (see Fig. 6). Primary transfer 32μA constant current Secondary transfer 3.5kv constant voltage

After the endurance test, the area of the surface of the endless belt where the paper P is carried and the solid patch is formed (hereinafter referred to as an image area AG),
The surface resistivity was measured in a region where no solid patch was formed (hereinafter, referred to as a paper passing portion AP) and in a region where the paper P was not supported (hereinafter, referred to as a non-paper passing portion AN). . As a result, in the present embodiment, the surface resistivity of the intermediate transfer belt 20 after the durability test is
G, paper passing area AP and non-paper passing area AN were almost the same as before the endurance test.

Example 2 Ethylene propylene rubber (EPD)
A semiconductive rubber sheet containing M) as a main component and having a thickness of 300 μm was produced. EPDM 100 parts by weight Conductive carbon 8 parts by weight Reinforcing carbon 20 parts by weight Vulcanizing agent 1 part by weight Vulcanization accelerator 2 parts by weight Vulcanizing aid 2 parts by weight Dispersing aid 0.5 part by weight Plasticizer 20 parts by weight The properties of the obtained sheet are as follows. Volume resistivity 2 × 10 ⁸ Ωcm Tensile modulus 294 N / mm ²

Next, the ethylene / propylene rubber (EP
(DM) sheet as a base layer, and a conductive adhesive obtained by dispersing conductive carbon in an acrylic resin on the outer periphery (volume resistivity in a low-temperature and low-humidity environment (10 ° C., 15% RH) is 3 × 10 ⁵
Ωcm) to a uniform thickness of 200 μm, and then adhere the polyimide seamless belt produced in Example 1 to the base layer (EPDM rubber), conductive layer (acrylic adhesive), and surface layer (polyimide resin). Was obtained. The endless belt thus obtained was attached to the position of the intermediate transfer belt 20 of the full-color image forming apparatus shown in FIG. 2, and subjected to a durability test of 30,000 sheets under the same conditions as in Example 1.

After the endurance test was performed, the surface resistivity of the image area AG, the sheet passing section AP, and the non-sheet passing section AN were measured in the same manner as in Example 1. As a result, the durability test was performed in the same manner as in Example 1. The surface resistivity of the intermediate transfer belt 20 after that was almost the same as that before the durability test in all of the image portion AG, the paper passing portion AP, and the non-paper passing portion AN.

Example 3 The polyimide seamless belt produced in Example 1 was
A conductive adhesive prepared by dispersing conductive carbon in silicone resin in a gap between the two (prepared in a low-temperature and low-humidity environment (10 ° C.,
The volume resistivity at 5% RH) was poured at 5 × 10 ³ Ωcm) to obtain an endless belt composed of a base layer (polyimide resin), a conductive layer (silicone resin adhesive), and a surface layer (polyimide resin). . The endless belt thus obtained was attached to the position of the intermediate transfer belt 20 of the full-color image forming apparatus shown in FIG. 2 and subjected to a durability test of 50,000 sheets under the same conditions as in Example 1.

After the endurance test was performed, the surface resistivity of the image area AG, the sheet passing area AP, and the non-sheet passing area AN were measured in the same manner as in Example 1. As a result, the durability test was performed in the same manner as in Example 1. The surface resistivity of the intermediate transfer belt 20 after that was almost the same as that before the durability test in all of the image portion AG, the paper passing portion AP, and the non-paper passing portion AN.

Comparative Example An endless belt in which the conductive adhesive of the endless belt of Example 1 was changed to a urethane adhesive (the volume resistivity in a low-temperature and low-humidity environment (10 ° C., 15% RH) was 2 × 10 ⁸ Ωcm) A belt was manufactured, and this endless belt was attached to the position of the intermediate transfer belt 20 of the full-color image forming apparatus shown in FIG. 2, and subjected to a durability test of 10,000 sheets under the same conditions as in Example 1.

After the endurance test was carried out, the surface resistivity of the image portion AG, the paper passing portion AP, and the non-sheet passing portion AN were measured in the same manner as in Example 1. As a result, the surface of the endless belt after the endurance test was measured. The resistivity is two digits in the image area AG compared to before the endurance test,
In the paper-passing section AP, each digit decreased. The non-sheet passing portion was hardly changed. For this reason, when a halftone image of the entire surface is formed on the endless belt after the endurance test, the electric resistance of the image portion AG is significantly lower than the electric resistance of the paper passing portion AP. The density was very low, and an image with a uniform density could not be obtained.

[0069]

As described above, according to the present invention,
The transfer member has at least a base layer, a surface layer provided on the outer periphery of the base layer, and a layer interposed between the base layer and the surface layer, having a volume resistivity lower than the volume resistivity of the base layer and the surface layer and not more than 10 ⁷ Ωcm. And the conductive layer having the conductive layer, the current flowing into the transfer member can be dispersed and allowed to flow, and local dielectric breakdown of the transfer member can be prevented. The accompanying white spots on the image can be prevented. Further, since the life of the transfer member can be prolonged, the replacement time can be greatly extended, and the running cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of a transfer member according to the present invention.

FIG. 2A is a diagram illustrating a current flowing through an intermediate transfer belt having a single-layer structure, and FIG. 2B is a diagram illustrating a current flowing through a transfer member according to the present invention.

FIG. 3 is an explanatory diagram illustrating an outline of an image forming apparatus used in the first embodiment;

FIG. 4 is a configuration diagram (cross-sectional view) of the intermediate transfer belt according to the first embodiment.

FIG. 5 is an explanatory diagram illustrating an outline of an image forming apparatus used in a second embodiment.

FIG. 6 is an explanatory diagram showing an outline of a patch pattern used in the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transfer member, 1a ... Base layer, 1b ... Conductive layer, 1c ... Surface layer, 2 ... Object, 11 ... Photoconductor drum, 20 ... Intermediate transfer belt, 20a ... Base layer, 20b ... Conductive layer, 20c ... Surface layer, 23 ... Backup roll, 25: primary transfer roll, 26: secondary transfer roll, T: toner, P: paper, 1
01 photoreceptor drum, 105 transfer roll, 120 transfer belt

Claims (7)

[Claims] At least a base layer, a surface layer provided on an outer periphery of the base layer, and a volume resistivity interposed between the base layer and the surface layer, which is lower than the volume resistivity of the base layer and the surface layer and is 10 ⁷ Ωcm or less. And a conductive layer having the following formula: 2. The transfer member according to claim 1, wherein the surface layer is composed of a base material made of rubber or resin and a resistance adjuster made of an electron conductive filler. 3. The transfer member according to claim 1, wherein at least one of the surface layer and the base layer is 1
A transfer member having a tensile modulus of 470 N / mm ² or more. 4. The transfer member according to claim 1, wherein at least one of the surface layer and the base layer is mainly made of a polyimide resin. 5. The transfer member according to claim 1, wherein the conductive layer is made of a material that adheres a surface layer and a base layer. 6. An image carrier on which a toner image corresponding to image information is formed, an intermediate transfer member disposed opposite to the image carrier and carrying the toner image, and an intermediate image between the toner image on the image carrier. An image forming apparatus comprising: a primary transfer unit that sequentially transfers to a transfer body; and a secondary transfer unit that collectively transfers a toner image transferred and held on an intermediate transfer body onto a recording material, wherein the intermediate transfer body is An image forming apparatus comprising the transfer member according to any one of claims 1 to 5. 7. A recording material having one or a plurality of image forming units, a recording material transporting body circulated and transported at a portion facing the image forming unit, and a recording material carried and transported by the recording material transporting body. An image forming apparatus configured to transfer an image formed by the image forming unit, wherein the recording material transport body is configured by the transfer member according to any one of claims 1 to 5. Characteristic image forming apparatus.