JP2010044329A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the deterioration of image quality. <P>SOLUTION: A common logarithm value of volume resistivity of each of primary transfer rolls 105 to 105d is in a range of 7 to 8.5 LogΩ cm. An intermediate transfer belt 107 includes a plurality of layers laminated one another in a thickness direction, and among the plurality of layers, a common logarithm value of surface resistivity of the innermost layer located on the innermost peripheral side of the belt is smaller than that of the outermost layer located on the outermost peripheral side. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus using an electrophotographic method, conventionally, an electrostatic latent image is formed on an image carrier such as an electrophotographic photosensitive member, the electrostatic latent image is developed with toner, and the obtained toner image is transferred to an endless belt. 2. Description of the Related Art Image forming apparatuses are known that form an image after electrostatically transferring (primary transfer process) onto an intermediate transfer belt, and then transferring again to a transfer medium such as transfer paper (secondary transfer process). . In particular, an intermediate transfer belt is preferably used in an image forming apparatus of a system (tandem system) that obtains a full color image by superimposing different color toner images. In this type of image forming apparatus, an intermediate transfer belt having conductivity has been widely used.

In an intermediate transfer belt, in order to obtain a stable and good output image over a long period of time, electrical strength such as surface resistivity and volume resistivity as well as mechanical strength such as flexibility, folding resistance and tensile breaking strength are provided. Properties are important.
For example, a technique is disclosed in which the common logarithmic value of the surface resistivity of the outer peripheral surface of the intermediate transfer belt is 8 LogΩ / □ or more and 12 LogΩ / □ or less, and the common logarithm of the surface resistivity of the inner peripheral surface is 5 LogΩ / □ or more and 10 LogΩ / □ or less. (For example, refer to Patent Document 1). Further, the common logarithm of the surface resistivity of the intermediate transfer member 10LogΩ / □ or more 14LogΩ / □ or less, the common logarithm value of the volume resistivity is less 13LogΩ · cm, and 10 ^X Ω / □ surface resistivity, volume resistivity technologies that X ≦ Y when representing the rate at 10 ^Y Ω · cm has been disclosed (e.g., see Patent Document 2).

Further, in Patent Document 3, in a primary transfer process in which a toner image on a photosensitive drum is transferred onto a high-resistance intermediate transfer belt composed of a single layer by a transfer roll, the photosensitive drum is sandwiched between the intermediate transfer belts. On the other hand, a technique for improving the image quality by disposing a primary transfer roll at the most downstream transfer nip position is disclosed.
JP-A-8-30109 JP 2004-46277 A JP 2005-189563 A

  In the primary transfer process, in the primary transfer region between the primary transfer roll arranged in contact with the inner peripheral surface side of the intermediate transfer belt and the image carrier arranged opposite to the intermediate transfer belt, the image on the image carrier As each toner constituting the toner image moves to the intermediate transfer belt, the toner image is transferred to the intermediate transfer belt. In this primary transfer step, the charge amount of the intermediate transfer belt increases due to peeling discharge between the transfer roll disposed in contact with the inner peripheral surface of the intermediate transfer belt and the inner peripheral surface of the intermediate transfer belt. The toner transferred from the image carrier to the intermediate transfer drum may be scattered or aggregated, and there has been concern about image quality deterioration. Specifically, discharge occurs between the transfer roll placed in contact with the inner peripheral surface of the intermediate transfer belt and the back surface of the intermediate transfer belt, thereby disturbing the toner image on the outer peripheral surface of the intermediate transfer belt, thereby causing image quality degradation. There was a case.

  Such a phenomenon tends to occur especially as the deviation between the image carrier and the primary transfer roll arranged opposite to each other via the intermediate transfer belt is larger. Deviation may occur due to variations in time, and improvement has been expected.

  An object of the present invention is to provide an image forming apparatus in which image quality deterioration is suppressed.

The invention according to claim 1
An image carrier on which an electrostatic latent image is formed;
Developing means for developing the electrostatic latent image formed on the image carrier with toner to form a toner image;
An intermediate transfer belt on which the toner image on the image holding member is transferred and holding the transferred toner image;
A primary transfer roll that is disposed in contact with the inner peripheral surface of the intermediate belt so as to sandwich the intermediate transfer belt with the image carrier, and transfers the toner image from the image carrier to the intermediate transfer belt;
A secondary transfer roll for transferring the toner image held on the intermediate transfer belt to a recording medium;
With
The common logarithm of the volume resistivity of the primary transfer roll is 7 LogΩ · cm or more and 8.5 LogΩ · cm or less,
The intermediate transfer belt is composed of a plurality of layers laminated in the thickness direction, and the common logarithm of the surface resistivity of the innermost layer on the innermost surface side of the plurality of layers is the outermost layer on the outermost surface side. The image forming apparatus is smaller than the common logarithm of the surface resistivity.

The invention according to claim 2
The image forming apparatus according to claim 1, wherein the intermediate transfer belt satisfies the following formulas (1) to (3).

11.6 LogΩ / □ ≦ ρs ≦ 14.0 LogΩ / □ (1)
10.3 LogΩ · cm ≦ ρv ≦ 14.0 LogΩ · cm (2)
9.8 LogΩ / □ ≦ ρexs ≦ 13.4 LogΩ / □ (3)

  In the above formulas (1) to (3), ρs represents a common logarithm of the surface resistivity of the outermost layer of the intermediate transfer belt, ρv represents a common logarithm of the volume resistivity of the intermediate transfer belt, ρexs represents a common logarithmic value of the creeping resistivity of the inner peripheral surface of the intermediate transfer belt.

  The invention according to claim 3 is the image forming apparatus according to claim 2, wherein the outermost layer and the innermost layer satisfy the following formula (4).

1.2 ≦ du / dl ≦ 4.0 (4)
In the above formula (4), du represents the film thickness (μm) of the outermost layer, and dl represents the film thickness (μm) of the innermost layer.

  According to the first aspect of the present invention, the common logarithmic value of the surface resistivity of the outermost layer of the intermediate transfer belt is made smaller than that of the innermost layer, and the volume resistance value of the primary transfer roller is within the range of the first aspect. As compared with the case where the above is not applied, the peeling discharge between the inner peripheral surface of the intermediate transfer belt and the primary transfer roll is suppressed, and the image quality deterioration due to the peeling discharge is suppressed.

  According to the second aspect of the present invention, as compared with the case without the configuration of the present invention, the secondary transfer roll that is in contact with the inner peripheral surface of the intermediate transfer belt and the intermediate transfer belt are sandwiched and opposed to each other. Gap discharge with the roll is suppressed, image quality deterioration during secondary transfer is also suppressed, and further image quality deterioration can be suppressed.

  According to the third aspect of the present invention, compared to the case without the configuration of the present invention, image defects at the time of secondary transfer by the secondary transfer roll are further suppressed, and further image quality deterioration can be suppressed. There is an effect.

Hereinafter, preferred embodiments will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram illustrating an example (one embodiment) of a configuration of an image forming apparatus according to a preferred embodiment. The image forming apparatus 100 according to the present embodiment is a so-called tandem system, and sequentially around the four image holding bodies 101a to 101d made of an electrophotographic photosensitive member along the rotation direction, the charging devices 102a to 102d, and the exposure. Devices 114a to 114d, developing devices 103a to 103d, primary transfer devices (primary transfer rolls) 105a to 105d, and image carrier cleaning devices 104a to 104d are arranged. Note that a static eliminator may be provided in order to remove residual potential remaining on the surfaces of the image carriers 101a to 101d after transfer.

  Further, the intermediate transfer belt 107 is stretched around the tension rolls 106a to 106d, the drive roll 111, and the backup roll 108 to form an annular body stretching apparatus (belt stretching apparatus). With these tension rolls 106a to 106d, drive roll 111, and backup roll 108, the intermediate transfer belt 107 is in contact with the surfaces of the image carriers 101a to 101d, and the image carriers 101a to 101d and primary transfer rollers 105a to 105d. Are conveyed in the direction of arrow X.

  The primary transfer rolls 105a to 105d are arranged in contact with the inner peripheral surface side of the intermediate transfer belt 107 so as to sandwich the intermediate transfer belt 107 between each of the image carriers 101a to 101d. A region between each of the primary transfer rolls 105a to 105d and each of the image carriers 101a to 101d is a primary transfer region (details will be described later). A primary transfer current is applied to each of the primary transfer regions by each of the primary transfer rolls 105 a to 105 d, whereby the toner image held on each of the image carriers 101 a to 101 d is transferred to the intermediate transfer belt 107. Transcribed above.

  Further, as a secondary transfer device, a backup roll 108 and a secondary transfer roll 109 are disposed to face each other with an intermediate transfer belt 107 and a secondary transfer belt 116 interposed therebetween. The transfer medium 115 such as paper is conveyed in the direction of arrow Z between the intermediate transfer belt 107 and the secondary transfer roll 109 while contacting the surface of the intermediate transfer belt 107, and then passes through the fixing device 110. The area where the secondary transfer roll 109 comes into contact with the backup roll 108 via the intermediate transfer belt 107 and the secondary transfer belt 116 is the secondary transfer area, and the secondary transfer roll 109 and the backup roll 108 are in contact with the secondary transfer roll 109. A transfer voltage is applied. Further, intermediate transfer belt cleaning devices 112 and 113 are arranged so as to come into contact with the intermediate transfer belt 107 after transfer.

  In the full-color image forming apparatus 100 having this configuration, the image carrier 101a rotates in the direction of arrow Y, and the surface is uniformly charged by the charging device 102a, and then the first color is applied by the exposure device 114a such as laser light. Electrostatic latent image is formed. The formed electrostatic latent image is developed (visualized) with toner by a developing device 103a containing toner corresponding to the color to form a toner image. The developing devices 103a to 103d contain toners (for example, yellow, magenta, cyan, and black) corresponding to the electrostatic latent images of the respective colors.

  The toner image formed on the image carrier 101a is electrostatically transferred (primary transfer) onto the intermediate transfer belt 107 by the primary transfer roll 105a when passing through the primary transfer region. Thereafter, the first, second and third color toner images are primarily transferred onto the intermediate transfer belt 107 holding the first color toner image by the primary transfer rolls 105b to 105d so that the toner images of the second color, the third color, and the fourth color are sequentially superimposed. Finally, a full color multiple toner image is obtained.

  The multiple toner images formed on the intermediate transfer belt 107 are electrostatically collectively transferred to the transfer medium 115 when passing through the secondary transfer portion. The transfer medium 115 onto which the toner image has been transferred is conveyed to the fixing device 110, fixed by heating and / or pressurization, and then discharged outside the apparatus.

  Residual toner is removed from the image carriers 101a to 101d after the primary transfer by the image carrier cleaning devices 104a to 104d. On the other hand, residual toner is removed from the intermediate transfer belt 107 after the secondary transfer by the intermediate transfer belt cleaning devices 112 and 113 to prepare for the next image forming process.

  Each configuration will be described below. In the following description, when a configuration (member) having the same function is described, the symbols a to d are omitted. For example, the image holders 101a to 101d will be described as the image holder 101 when collectively referred to.

[Intermediate transfer belt]
As shown in FIG. 3, the intermediate transfer belt 107 in the present embodiment has a configuration in which a plurality of layers are stacked in the thickness direction.
For example, as shown in FIG. 3A, the intermediate transfer belt 107 is configured by laminating an outermost layer 107A positioned on the outermost surface side on an innermost layer 107B positioned on the innermost surface side. ing. In the intermediate transfer belt 107 attached to the image forming apparatus 100, the image carrier 101 is disposed in contact with the outermost layer 107A and at a predetermined interval in the conveyance direction of the intermediate transfer belt 107 (the arrow X direction in FIG. 1). It becomes the state of being arranged with a gap. The primary transfer roll 105 is disposed in contact with the inner peripheral surface of the intermediate transfer belt 107 so as to sandwich the intermediate transfer belt 107 with the image carrier 101.

The common logarithm value of the surface resistivity of the innermost layer 107B of the intermediate transfer belt 107 is adjusted in advance so as to be smaller than the common logarithm value of the surface resistivity on the outer peripheral surface side of the outermost layer 107A.
Although the details will be described later, the common logarithm of the surface resistivity on the inner peripheral surface side of the innermost layer 107B is made smaller than the common logarithm of the surface resistivity on the outer peripheral surface side of the outermost layer 107A. By adjusting in advance, the peeling discharge between the primary transfer roll 105 and the intermediate transfer belt 107 in contact with the inner peripheral surface side is suppressed, and image quality deterioration due to the peeling discharge is suppressed.

  In the present embodiment, “the common logarithm value of the surface resistivity of the outermost layer 107A” indicates the common logarithm value of the surface resistivity on the outer peripheral surface side surface of the outermost layer 107A, and “the surface resistance of the innermost layer 107B”. The “common logarithm of rate” indicates the common logarithm of the surface resistivity on the inner peripheral surface side surface of the innermost layer 107B.

  The common logarithm value of the surface resistivity of the outermost layer 107A depends on the graininess and paper peelability, and the value is not limited. However, for reasons of graininess, high resistance (“high resistance” is specifically Is preferably 11.6 LogΩ / □ or more, and is preferably in the range of 12.4 or less, and more preferably in the range of 11.9 or more and 12.4 or less, for reasons of paper peelability.

  In the intermediate transfer belt 107 of the image forming apparatus 10 of the present embodiment, the common logarithm of the surface resistivity on the outer peripheral surface side of the outermost layer 107A is the common logarithm of the surface resistivity on the inner peripheral surface side of the innermost layer 107B. However, for the reason of suppressing variation due to disturbance, the common logarithmic value of the surface resistivity on the outer peripheral surface side of the outermost layer 107A is 0.6 LogΩ / □ or more than the surface resistivity on the inner peripheral surface side of the innermost layer 107B. It is preferably large, and more preferably 1.0 LogΩ / □ or larger.

  Note that the layer structure of the intermediate transfer belt 107 may be a plurality of layers (two or more layers), and is not limited to the two layers as shown in FIG. 3A, but as shown in FIG. A three-layer structure, a four-layer structure illustrated in FIG. 3C, or a layer structure including five or more layers may be employed. For example, in the case of a three-layer structure, as shown in FIG. 3B, the intermediate transfer belt 107 may be configured by laminating the innermost layer 107B, the intermediate layer 107C, and the outermost layer 107A in this order. In the case of a four-layer structure, as shown in FIG. 3C, the intermediate transfer belt 107 is formed by laminating the innermost layer 107B, the intermediate layer 107D, the intermediate layer 107C, and the outermost layer 107A in this order. That's fine.

  Even when the layer configuration of the intermediate transfer belt 107 is three or more, as described above, the surface resistivity on the outer peripheral surface side of the outermost layer 107A is larger than the surface resistivity on the inner peripheral surface side of the innermost layer 107B. And any resistance relationship may be used. For example, the surface resistivity may be adjusted so as to increase continuously from the inner peripheral surface side toward the outer peripheral surface side, or may be adjusted so as to increase stepwise.

Further, it is preferable that the intermediate transfer belt 107 satisfies all of the following formulas (1), (2), and (3).
11.6 LogΩ / □ ≦ ρs ≦ 14.0 LogΩ / □ (1)
10.3 LogΩ · cm ≦ ρv ≦ 14.0 LogΩ · cm (2)
9.8 LogΩ / □ ≦ ρexs ≦≦ 13.4 LogΩ / □ (3)
(In the above formulas (1) to (3), ρs is a common logarithm of the surface resistivity of the outermost layer of the intermediate transfer belt 107, ρv is a common logarithm of the volume resistivity of the intermediate transfer belt 107, and ρexs. Represents a common logarithm value of the creeping resistivity of the inner peripheral surface of the intermediate transfer belt 107.)

  The “ρs” is more preferably 11.9 LogΩ / □ ≦ ρs ≦ 12.4 LogΩ / □.

  If ρs ≧ 11.6 LogΩ / □, in the secondary transfer step, the transfer electric field applied from the secondary transfer roll 109 wraps around the toner on the intermediate transfer belt 107, so that the toner scatters around the transfer medium. Although deterioration of the graininess caused by the toner image transferred in a blurred state is avoided, the 1-grade graininess is further improved by setting ρs ≧ 11.9 LogΩ / □.

  Note that “1 grade graininess” indicates the degree of dot dispersion (image unevenness).

  Further, when ρs> 12.4 LogΩ / □, a sheet peeling defect is likely to occur in the secondary transfer step, and can be avoided by providing a charge eliminating unit on the inner surface of the intermediate transfer belt 107 downstream of the secondary transfer roll 109. However, by satisfying ρs ≦ 12.4 LogΩ / □, the sheet peeling failure is suppressed without using the static eliminating means.

The “ρv” is more preferably 11.0 LogΩ · cm ≦ ρv ≦ 13.0 LogΩ · cm. If ρv ≧ 11.0 LogΩ · cm, image quality defects such as scattering of line images (image blurring) that are likely to occur when ρv is low (ρv <11.0 LogΩ · cm) can be suppressed, and high image quality can be achieved.
When ρv> 13.0 Log Ω · cm, the amount of charge on the surface of the intermediate transfer belt 107 increases, and self-static charge cannot be performed. This can be avoided by providing the charge eliminating means on the inner surface of the transfer belt 107. However, by setting ρv ≦ 13.0 Log Ω · cm, the occurrence of sheet peeling defects can be suppressed without using the charge eliminating means.

  The ρexs is more preferably 10.6 LogΩ / □ ≦ ρexs ≦ 13.0 LogΩ / □. If ρexs ≧ 10.6 LogΩ / □, the occurrence of image quality defects such as white spots occurring in the primary transfer process under high temperature and high humidity environmental conditions is suppressed. If ρexs ≦ 13.4 LogΩ / □, a discharge occurs between the backup roll 108 that contacts the inner peripheral surface of the intermediate transfer belt 107 and the back surface of the intermediate transfer belt 107 in the secondary transfer step, and the The toner image is disturbed, and the image quality defect that occurs as a scale-like density unevenness is reduced to an acceptable level. Further, by setting ρexs ≦ 13.0 LogΩ / □, the scale-like density unevenness is substantially eliminated.

  The intermediate transfer belt 107 in this embodiment desirably has a total film thickness of 60 μm or more and 120 μm or less. If the total film thickness is 50 μm or more, sufficient mechanical strength can be maintained, and a better output image can be obtained even in long-term use in the image forming apparatus. If the total film thickness is 130 μm or less, sufficient flexibility can be maintained, and the intermediate transfer belt 107 can be stretched even when it is stretched for a long time in the image forming apparatus. Therefore, a better output image can be obtained.

Furthermore, it is desirable that the layer thicknesses of the outermost layer 107A and the innermost layer 107B satisfy the following formula (4).
1.2 ≦ du / dl ≦ 4.0 (4)
(In the above formula (4), du represents the film thickness (μm) of the outermost peripheral layer, and dl represents the film thickness (μm) of the innermost peripheral layer.)

The “du / dl” preferably satisfies 1.5 ≦ du / dl ≦ 3.0, and more preferably 1.6 ≦ du / dl ≦ 2.7.
Here, in the secondary transfer process, the charge flowing in from the backup roll 108 in contact with the inner peripheral surface of the intermediate transfer belt 107 is accumulated between the outermost layer and the innermost layer of the intermediate transfer belt, and thereby locally. An electric field is generated. When the electric field strength of the local electric field exceeds a threshold value, electric charges flow into the outermost peripheral layer at once, and a discharge is generated between the secondary transfer roll 109. The inventors of the present invention have found that when the toner in the discharge region is charged to the opposite polarity and is not transferred to the transfer medium, a region (HT unevenness) in which the toner image is missing on the output image occurs.

  When 1.2 ≦ du / dl, in the secondary transfer step, the occurrence of discharge between the secondary transfer roll 109 and the outer peripheral surface of the intermediate transfer belt 107 is suppressed, and the toner is prevented from having a reverse polarity. For this reason, a region (white point) from which the toner image is missing does not occur, and a good output image is obtained. In addition, when du / dl ≦ 4.0, the charge flowing in from the backup roll 108 is not accumulated between the outermost and innermost layers of the intermediate transfer belt 107, and therefore, between the secondary transfer roll 109 and the intermediate transfer belt 107. Since no discharge is generated and the toner is prevented from having a reverse polarity, a region (HT unevenness) in which the toner image is missing does not occur and a good output image is obtained.

  Examples of the material of the intermediate transfer belt 107 include polycarbonate resin, polyvinylidene fluoride resin, polyalkylene phthalate resin, polycarbonate / polyalkylene phthalate blend material, thermoplastic resin such as ethylene tetrafluoroethylene copolymer, polyimide, polyimide, and the like. A material obtained by dissolving or dispersing a conductive agent in a thermosetting resin such as a copolymer of polyamide and polyamide is used.

  Examples of the conductive agent include conductive particles such as carbon black, graphite, aluminum, nickel, copper, tin oxide, zinc oxide, titanium oxide, or potassium titanate, and organic conductive substances such as polyaniline and polythiophene. It is done. Among these, the intermediate transfer belt 107 in which polyimide resin is the main component (the main component indicates that the polyimide resin content in the intermediate transfer belt exceeds 50 mass%) and conductive particles such as carbon black are dispersed. However, it is particularly preferably used because of its excellent mechanical strength, high elastic modulus, and excellent creep resistance (a property that resists the phenomenon that strain increases with time when a continuous stress acts on an object).

  The common logarithm of the surface resistivity, the common logarithm of the volume resistivity, and the common logarithm of the creeping resistivity of each layer of the conductive agent (the outermost layer 107A and the innermost layer 107B of the intermediate transfer belt 107) are contained in each layer. It is adjusted by the amount of the conductive agent.

Specifically, the common logarithmic value of the surface resistivity and the common logarithm of the volume resistivity of the outermost layer 107A are adjusted according to the amount of the conductive material contained in the outermost peripheral layer, and the conductivity contained in the innermost layer 107B. Ρexs and the common logarithm of the surface resistivity of the innermost layer 107B are adjusted by the amount of the agent.
Furthermore, when drying the coating liquid 16 coating film formed on the outer peripheral surface of the cylindrical tube 11, ρs is controlled independently of ρv and ρexs by setting to a predetermined temperature. More specifically, when the drying temperature is increased, ρs is increased, and when the drying temperature is decreased, ρs is decreased. The independent control of ρs, ρv and ρexs is more preferably used when a polyimide precursor is used as the coating liquid 16 resin material and carbon black is used as the conductive material. In the case of using a polyimide precursor and carbon black, ρs is controlled independently of ρv and ρexs by adjusting the temperature in the drying step while keeping the amount of residual solvent after the drying step constant.

The method for manufacturing the intermediate transfer belt 107 according to the present embodiment is not particularly limited, but is preferably manufactured by, for example, a spin coating method as shown in FIG. 2 using a polyimide precursor solution.
In this method, a cylindrical tube 11 having an outer diameter corresponding to the length of the intermediate transfer belt 107 is prepared. A nozzle 15 for discharging the coating liquid 16 onto the outer peripheral surface of the cylindrical molding tube 11 is disposed at a position along the outer peripheral surface of the cylindrical molding tube 11, and the nozzle 15 is connected to the coating liquid container 14 through the pipe. The coating solution container 14 is connected to a pressurizing device 17 through a pipe. A blade 18 for leveling the discharged coating liquid 16 on the outer peripheral surface of the cylindrical tube 11 is disposed below the nozzle 15.

The cylindrical forming tube 11 is rotated in the direction of the cylindrical forming tube rotation (arrow D), the coating liquid 16 is discharged from the nozzle 15 onto the outer peripheral surface of the cylindrical forming tube 11, and the blade 18 is uniformly applied onto the outer peripheral surface of the cylindrical forming tube 11. The The nozzle 15 and the blade 18 move at a constant speed in the nozzle and blade movement direction (arrow E), and the coating liquid 16 is applied on the outer peripheral surface of the cylindrical tube 11 with a constant thickness. The coating liquid 16 is adjusted so that a predetermined amount is discharged from the nozzle 15 by the pressurizing device 17. Thereby, the coating liquid 16 coating film is formed on the outer peripheral surface of the cylindrical tube 11.
The obtained coating liquid 16 is dried by heating, and after cooling, is peeled off from the cylindrical tube 11 and cut at a predetermined width to obtain the intermediate transfer belt 107. In addition, when using a polyimide precursor as a resin material of the coating liquid 16, after forming the coating liquid 16 coating film on the outer peripheral surface of the cylindrical tube 11, the solvent is removed by drying at 80 ° C. or higher and 170 ° C. or lower. (Drying step), and further heated to 250 ° C. or higher and 350 ° C. or lower for imide conversion (firing step) to form a polyimide resin film. After cooling, the obtained polyimide resin film is peeled off from the cylindrical tube 11 and cut at a predetermined width, whereby the intermediate transfer belt 107 is obtained.

  The solid content concentration of the coating liquid 16 is, for example, 10 mass% to 40 mass%, and the viscosity is 1 Pa · s to 100 Pa · s. In addition, a predetermined amount of conductive particles such as carbon black is dispersed in the coating liquid 16 in accordance with the required common logarithm of the surface resistivity of the intermediate transfer belt. As a dispersion method, a known method such as a jet mill, a roll mill, a ball mill, a vibrating ball mill, an attritor, a sand mill, a colloid mill, or a paint shaker is used.

  In the method of manufacturing the intermediate transfer belt 107, it is desirable that the drying temperature is 100 ° C. or higher and 170 ° C. or lower. If the drying temperature is too low in the drying step, the solvent in the polyimide precursor does not dry, and even if the drying time is extended, it is difficult to reach a predetermined residual solvent amount. In addition, if the drying temperature is too high, a dry film may be generated on the surface of the polyimide precursor at the very beginning of the drying process, and the solvent inside the polyimide precursor may not be sufficiently dried. The surface of the film is pulled, and wrinkle-like defects are easily generated on the surface of the coating film. By setting the drying temperature to 100 ° C. or more and 170 ° C. or less, a polyimide precursor film having a predetermined residual solvent amount and a better coating film is obtained.

  In the present embodiment, as described above, the intermediate transfer belt 107 has at least two layers. Even when forming the intermediate transfer belt 107 having two or more layers, the materials used are the same as described above. In addition, the multilayer structure film of two or more layers is formed by coating the coating liquid 16 on the outer peripheral surface of the cylindrical tube 11 and drying it to form the innermost peripheral layer, and then repeating the coating and drying process, A desired constituent film is obtained. When a polyimide precursor containing carbon black is used as the coating solution 16, the coating / drying process is repeated, and after the desired configuration is obtained, the desired constituent film is obtained through the firing step.

  The thickness of the intermediate transfer belt 107 is adjusted by the discharge amount of the coating liquid 16, the moving speed of the nozzle 15 and the blade 18, and the solid content concentration of the coating liquid 16. The thickness of the intermediate transfer belt 107 is preferably not less than 50 μm and not more than 130 μm from the viewpoint of maintaining dimensional accuracy even in repeated image output.

(Image carrier)
As the image carrier 101, known electrophotographic photoreceptors are widely used. As the electrophotographic photoreceptor, an inorganic photoreceptor having a photosensitive layer made of an inorganic material, an organic photoreceptor having a photosensitive layer made of an organic material, or the like is used. In the organic photoconductor, a function-separated type organic photoconductor in which a charge generation layer that generates charges upon exposure and a charge transport layer that transports charges are stacked, and a function that generates charges and a function that transports charges are the same. A single layer type organic photoreceptor fulfilled by the layer is preferably used. In addition, as the inorganic photoconductor, a photoconductive layer composed of amorphous silicon is preferably used.

  The shape of the image carrier is not particularly limited, and a known shape such as a cylindrical drum shape, a sheet shape, or a plate shape is employed.

[Charging device]
The charging device 102 is not particularly limited, and is, for example, conductive (here, “conductive” means, for example, a volume resistivity of less than 10 ⁷ Ω · cm. In this specification, unless otherwise specified) The same), or semiconductive (here, “semiconductive” means, for example, a volume resistivity of 10 ⁷ to 10 ¹³ Ωcm. In this specification, the same applies unless otherwise specified.) Known chargers such as contact chargers using rollers, brushes, films or rubber blades, scorotron chargers using corona discharge and corotron chargers can be widely applied. Among these, a contact charger that generates less ozone and can perform efficient charging is preferable.

  The charging device 102 normally applies a direct current to the image carrier 101, but an alternating current may be applied in a superimposed manner.

[Exposure equipment]
The exposure device 114 is not particularly limited. For example, a light source such as a semiconductor laser light, an LED light, or a liquid crystal shutter light, or a desired light source from these light sources via a polygon mirror is provided on the surfaces of the image carriers 101a to 101d. A known exposure apparatus such as an optical system apparatus for imagewise exposure is widely applied.

[Development equipment]
The developing device 103 is selected according to the purpose. For example, a known developing device that develops a one-component developer or a two-component developer in contact or non-contact with a brush, a roller, or the like can be used.

  The toner (developer) used in the image forming apparatus 100 of the present embodiment is not particularly limited, and includes, for example, a binder resin and a colorant.

  Examples of the binder resin include homopolymers or copolymers such as styrenes, monoolefins, vinyl esters, α-methylene aliphatic monocarboxylic acid esters, vinyl ethers, and vinyl ketones. Typical binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer. Examples thereof include coalescence, polyethylene, and polypropylene. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax, and the like can be given.

  Colorants include magnetic powders such as magnetite and ferrite, carbon black, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black. Rose Bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 17, C.I. I. Pigment blue 15: 1 or C.I. I. Pigment Blue 15: 3 is a typical example.

  The toner may be internally added or externally added with known additives such as a charge control agent, a release agent, and other inorganic particles.

  Typical examples of the release agent include low molecular polyethylene, low molecular polypropylene, Fischer-Tropsch wax, montan wax, carnauba wax, rice wax, and candelilla wax.

  Known charge control agents are used, but azo metal complex compounds, metal complex compounds of salicylic acid, and resin type charge control agents containing polar groups are used.

As other inorganic particles, small-diameter inorganic particles having an average primary particle size of 40 nm or less are used for the purpose of powder fluidity, charge control, and the like. Inorganic or organic particles may be used in combination. As these other inorganic particles, known ones are used.
In addition, the surface treatment of the small-diameter inorganic particles is effective because the dispersibility becomes high and the effect of increasing the powder fluidity increases.

  As a method for producing the toner, a polymerization method such as an emulsion polymerization aggregation method or a dissolution suspension method is preferably used because high shape controllability can be obtained. In addition, a manufacturing method may be performed in which the toner obtained by these methods is used as a core, and agglomerated particles are further adhered and heat-fused to have a core-shell structure.

  In addition, when adding an external additive, it manufactures by mixing a toner and an external additive with a Henschel mixer or a V blender. In addition, when the toner is manufactured by a wet method, external addition may be performed by a wet method.

[Primary transfer roll]
The primary transfer roll 105 may be either a single layer or a multilayer. For example, in the case of a single layer structure, it is composed of a roll in which an appropriate amount of conductive particles such as carbon black is blended in foamed or non-foamed silicone rubber, urethane rubber, ethylene-propylene-diene rubber (EPDM), or the like.

The volume resistance value of the primary transfer roll 105 is in the range of 7 LogΩ to 8.5 LogΩ, and more preferably in the range of 7.4 LogΩ to 7.9 LogΩ.
When the volume resistance value of the primary transfer roll 105 is 7 LogΩ or more and 8.5 LogΩ or less, it is an environmental condition of high temperature and high humidity (environment satisfying at least one of 27 ° C. or more and 80% RH or more. The same shall apply hereinafter). In this case, the resistance of the intermediate transfer belt and the primary transfer roll is too low to suppress a transfer electric field (voltage) sufficient to transfer the toner image on the image holding member 101 to the intermediate transfer belt 107, and Transfer defects (unevenness) are suppressed. Conversely, the resistance of the intermediate transfer belt and the primary transfer roll is too high even under low temperature and low humidity (environment satisfying at least one of 15 ° C. or less and 30% RH or less, the same shall apply hereinafter). In addition, an excessive transfer electric field (voltage) formed between the image carrier 101 and the primary transfer roll 105 is suppressed. As a result, charge is injected into the toner constituting the toner image (reverse polarity), and the toner image is transferred partially (fine white dots) from the image carrier 101 to the intermediate transfer belt 107. The occurrence of image quality defects such as discharge marks that are not performed is suppressed.

  That is, by setting the volume resistance value of the primary transfer roll 105 to 7 LogΩ or more and 8.5 LogΩ or less, the transfer defect (unevenness) at high temperature and high humidity and the occurrence of the discharge mark at low temperature and low humidity can be allowed. It can be suppressed. Furthermore, the transfer defect (unevenness) and the discharge mark are suppressed by setting the volume resistance value of the primary transfer roll 105 to 7.4 LogΩ or more and 7.9 LogΩ or less.

  For example, a current of 30 μA or more and 60 μA is applied to the primary transfer roll 105, and the toner image held on the image holding body 101 is transferred to the primary transfer roll by an electric field (voltage) formed between the primary transfer roll 105. 105 is transferred.

  The outer diameter (diameter) of the primary transfer roll 105 is preferably 18 mm or more and 30 mm or less, and more preferably 26 mm or more and 30 mm or less from the viewpoint of life.

[Image carrier cleaning device]
The image carrier cleaning device 104 is for removing residual toner adhering to the surface of the image carrier 101 after the primary transfer process, and in addition to a cleaning blade, brush cleaning or roll cleaning can be used. . Among these, it is preferable to use a cleaning blade. Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicone rubber.

[Secondary transfer roll]
The layer structure of the secondary transfer roll 109 is not particularly limited. For example, in the case of a three-layer structure, the secondary transfer roll 109 includes a core layer, an intermediate layer, and a coating layer covering the surface. The core layer is a foamed material such as silicone rubber, urethane rubber, or EPDM in which conductive particles are dispersed, and the intermediate layer is composed of these non-foamed materials. Examples of the material for the coating layer include tetrafluoroethylene-hexafluoropropylene copolymer and perfluoroalkoxy resin. The volume resistivity of the secondary transfer roll 109 is preferably 10 ⁷ Ωcm or less. Moreover, it is good also as a two-layer structure except an intermediate | middle layer.

[Backup roll]
The backup roll 108 forms a counter electrode of the secondary transfer roll 109. The layer structure of the backup roll 108 may be either a single layer or a multilayer. For example, in the case of a single layer structure, it is composed of a roll in which an appropriate amount of conductive particles such as carbon black is blended in silicone rubber, urethane rubber, EPDM, or the like. In the case of a two-layer structure, it is composed of a roll in which the outer peripheral surface of the elastic layer composed of the rubber material as described above is covered with a high resistance layer. The surface resistivity of the backup roll 108 is preferably in the range of 10 ⁷ Ω / □ to 10 ¹¹ Ω / □.

  A voltage of 1 kV to 6 kV is normally applied between the shafts of the backup roll 108 and the secondary transfer roll 109. Instead of applying a voltage to the shaft of the backup roll 108, a voltage can be applied between the electrically conductive electrode member brought into contact with the backup roll 108 and the secondary transfer roll 109. Examples of the electrode member include a metal roll, a conductive rubber roll, a conductive brush, a metal plate, or a conductive resin plate.

[Fixing device]
As the fixing device 110, for example, a known fixing device such as a heat roller fixing device, a pressure roller fixing device, or a flash fixing device is widely applied.

[Intermediate transfer belt cleaning device]
As the intermediate transfer belt cleaning devices 112 and 113, in addition to a cleaning blade, brush cleaning, roll cleaning, and the like can be used. Among these, it is preferable to use a cleaning blade. Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicone rubber.

  In the above-described embodiments, a so-called tandem image forming apparatus including a plurality of image carriers has been described. However, the intermediate transfer belt rotates and forms an image by one image carrier and the number of colors. The image forming apparatus may be a so-called multi-cycle method (for example, a 4-cycle method) that performs the process.

  Next, a mechanism for preventing image quality degradation that occurs in the primary transfer unit in the image forming apparatus 100 of the present embodiment will be described.

  In the image forming apparatus 100, as shown in FIG. 9, each of the primary transfer rolls 105 (primary transfer rolls 105a to 105d) is intermediately transferred to each of the image carriers 101 (image carriers 101a to 101d). The belt 107 is disposed so as to be shifted by an offset amount D in the transport direction X of the belt 107.

  Specifically, as shown in FIG. 9, each of the image carriers 101 and each of the corresponding primary transfer rolls 105 arranged from the rotation center a of the image carrier 101 toward the intermediate transfer belt 107. The distance between the intersection A of the intermediate transfer belt 107 and the intermediate transfer belt 107, and the intersection B of the intermediate transfer belt 107 with the perpendicular extending from the rotation center b of the primary transfer roll 105 toward the intermediate transfer belt 107. They are arranged at positions shifted by a certain “offset amount D”. The primary transfer roll 105 is disposed on the downstream side in the transport direction X of the intermediate transfer belt 107 with respect to the image carrier 101.

  The offset amount D is not zero “0” as described above, and the rotation center a of the image carrier 101 and the rotation center b of the primary transfer roll 105 are shifted toward the conveyance direction X of the intermediate transfer belt 107. It is preferable that it is in the state. This is because the primary transfer area between each of the image carriers 101 and the intermediate transfer belt 107 is sufficiently secured to transfer the toner image from the image carrier 101 to the intermediate transfer belt 107 efficiently and stably. .

  Here, like the intermediate transfer belt in the conventional image forming apparatus, the common logarithm of the surface resistivity on the outer peripheral surface side and the common logarithm of the surface resistivity on the inner peripheral surface side are substantially the same (± 1%) In the case of a single layer configuration, for example, the rotation of the image carrier 101 in the arrow Y direction, the rotation of the intermediate transfer belt 107 in the arrow X direction, and the primary transfer roll Due to the rotation of 105 in the direction of arrow P, peeling discharge occurs between the image carrier 101 and the intermediate transfer belt 107 and between the intermediate transfer belt 107 and the primary transfer roll 105 at the time of peeling. The peeling discharge generates charges (charges having a polarity opposite to the charge polarity of each toner constituting the toner image transferred from the image holding member 101 to the intermediate transfer belt 107), thereby degrading image quality. Similarly, peeling discharge occurs in the peeling area where the intermediate transfer belt 107 and the primary transfer roll 105 are peeled off, and image quality deterioration occurs.

  Specifically, as shown in FIG. 10, the peeling area H between the image carrier 101 and the intermediate transfer belt 107 and the peeling area I between the primary transfer roll 105 and the intermediate transfer belt 107 are substantially the same area. (When the offset amount D is “0” or close to “0” as much as possible), the potential balance is balanced between the side of the intermediate transfer belt 107 in contact with the image carrier 101 and the side of contact with the primary transfer roll 105. Therefore, the toner image transferred on the intermediate transfer belt 107 is intermediate even after the primary transfer area E is added along with the conveyance of the intermediate transfer belt 107. The toner image transferred onto the transfer belt 107 is not disturbed.

However, as shown in FIG. 11, the image carrier 101 and the primary transfer roll 105 arranged correspondingly via the intermediate transfer belt 107 are shifted by an “offset amount D” (the offset amount D is When the offset amount D is larger, the combined resistance of the intermediate transfer belt 107 and the primary transfer roll 105 in the primary transfer region E is zero “0”. Alternatively, it is higher than when the image carrier 101 and the primary transfer roll 105 are arranged so as to have a value close to “0”.
For this reason, in the intermediate transfer belt in the conventional image forming apparatus, even when the voltage having the same current value is supplied to the primary transfer roll 105, the voltage value of the voltage flowing to the primary transfer region E increases as the offset amount D increases. In some cases, image quality deterioration may occur due to variations in the offset amount D. As the offset amount D increases, an excessive voltage is applied to the toner image transferred onto the intermediate transfer belt 107, and fine white spot (discharge mark) image quality defects may occur.

  Further, in the single-layer intermediate transfer belt in the conventional image forming apparatus, the primary transfer roll 105 is disposed on the downstream side in the transport direction X of the intermediate transfer belt 107 with respect to the image carrier 101. The separation region I between the intermediate transfer belt 107 and the primary transfer roll 105 is located downstream of the separation region H between the intermediate transfer belt 107 and the intermediate transfer belt 107 in the transport direction X of the intermediate transfer belt 107. For this reason, the charge amount by peeling discharge also becomes large. As a result, the highly charged intermediate transfer belt 107 leaks to a nearby grounding member, and the charge of the toner image on the intermediate transfer belt 107 decreases in the form of tree branches, and the charge decreases at the subsequent secondary transfer portion. The portion of the tree was not transferred to the paper, and a white branch in the form of a branch of the tree occurred.

  Here, in the single-layer intermediate transfer belt in the conventional image forming apparatus, as shown in FIG. 12, even if the voltage of the same current value is applied to the primary transfer roll 105 as the offset amount D decreases, the intermediate transfer belt 107. As a result, the above-described “fine white spot (discharge mark)” image quality defect is suppressed. However, in the embodiment of FIG. 12, the primary transfer region E is narrower than that of FIG. 11, and particularly high resistance (in this embodiment, “high resistance” indicates that the volume resistivity is 11.6 or more. When the intermediate transfer belt 107 is used, the intermediate transfer belt 107 remains highly charged even after the separation region I between the intermediate transfer belt 107 and the primary transfer roll 105 has passed. For this reason, when the intermediate transfer belt 107 is peeled from the image carrier 101 in this highly charged state, the toner image on the intermediate transfer belt 107 is disturbed by the peeling discharge, and the image quality defect of “arc-shaped white spot” is caused. appear.

  On the other hand, in the image forming apparatus 10 of the present embodiment, as described above, the intermediate transfer belt 107 is composed of a plurality of layers, and the surface resistivity of the innermost layer is greater than the surface resistivity of the outermost layer as described above. The small intermediate transfer belt 107 is used, and the common logarithmic value of the volume resistivity of the primary transfer roll 105 is 7 LogΩ or more and 8.5 LorΩ or less. With this configuration, it is possible to suppress the charge amount on the inner peripheral surface side of the intermediate transfer belt 107 from being excessively increased due to the peeling discharge. In particular, a “fine white spot (discharge) generated when the offset amount D is large. The occurrence of image quality defects such as “marks” and “branched white spots on trees” and “arc-shaped white spots” that occur when the offset amount D is small are suppressed. Further, since the outermost layer 107A of the intermediate transfer belt 107 has a higher surface resistivity and volume resistivity than the innermost layer 107B, another image quality defect (very fine) due to excessive charge injection in the secondary transfer portion. White spots: micro white spots) are also suppressed.

  In the above-described embodiment, a so-called tandem type image forming apparatus including a plurality of image carriers 105 has been described. However, in the image forming apparatus 100 according to the present embodiment, the image carrier 105 has one image carrier 105. The present invention is also applicable to a so-called four-cycle image forming apparatus in which the intermediate transfer belt 107 rotates and forms an image for the number of colors.

  Hereinafter, although an example and a comparative example are explained, the present invention is not limited to the following examples.

  In the following examples and comparative examples, the common logarithm of the surface resistivity, the common logarithm of the volume resistivity, the common logarithm of the creeping resistivity of the extreme surface, and the common logarithm of the volume resistivity of the primary transfer roll The measurement was performed by the following method.

(Measurement of common logarithm value ρs of surface resistivity)
FIG. 4 shows a schematic cross-sectional view of the surface resistivity measuring apparatus. An insulating sheet 24 is disposed on the back electrode 23 connected to the GND, and a measurement sample 27 is disposed thereon. The front surface electrode 21 and the guard electrode 22 are arranged on the measurement sample 27, and the measurement sample 27 is sandwiched between the back surface electrode 23, the front surface electrode 21, and the guard electrode 22 via the insulating sheet 24. In the following examples and comparative examples, instead of the measurement sample 27, a measurement object is sandwiched, a DC voltage is applied by a DC power source 25 connected to the guard electrode 22, and the surface electrode 21 is applied after the DC voltage is applied. The surface resistivity was calculated from the measurement result of the amount of current measured by the microammeter 26 connected to.

Details are shown below. FIG. 7 shows a schematic plan view of electrodes used in the surface resistivity measuring apparatus shown in FIG. A guard electrode 22 is arranged concentrically with the surface electrode 21 as the center. Here, d1 to d3 represent the diameter of the center electrode 21, the diameter of the inner circumference of the guard electrode 22, and the diameter of the outer circumference of the guard electrode 22, respectively. These values can be arbitrarily set according to the size and shape of the measurement sample. In addition, in the measurement of the surface resistivity in a present Example and a comparative example, UR probe (made by Mitsubishi Chemical Corporation) was used, and d1-d3 was made into the following value, respectively.
d1 = 16mm, d2 = 30mm, d3 = 40mm

And surface resistivity was computed by following formula (5), and the common logarithm value of the obtained surface resistivity was calculated | required as (rho) s.
Surface resistivity = [π (d2 + d1) / (d2−d1)] × (V / I) (5)

  Here, in Expression (5), V represents a voltage value (V) applied to the center electrode 21, and I represents a current value (A) detected by the microammeter 26. In the measurement of the surface resistivity in the examples of the present invention, the voltage applied to the center electrode 21 was 500V. The current value I was 10 seconds after the voltage V was applied. The surface resistivity was measured in an environment at a temperature of 20 ° C. and a relative humidity of 40%.

(Measurement of common logarithm value ρv of volume resistivity)
FIG. 5 shows a schematic sectional view of the volume resistivity measuring apparatus. A measurement sample 27 is placed on the back electrode 23 connected to the GND via the DC power supply 25. The front surface electrode 21 and the guard electrode 22 are arranged on the measurement sample 27, and the measurement sample 27 is sandwiched between the back surface electrode 23, the front surface electrode 21, and the guard electrode 22. The guard electrode 22 is connected to GND. A DC voltage is applied by a DC power source 25 connected to the back electrode 23, the amount of current flowing by the microammeter 26 connected to the front electrode 21 is measured, the volume resistivity is calculated, and the calculated volume resistivity is commonly used. The logarithmic value was determined as ρv.

Details will be described below. FIG. 7 shows a schematic plan view of electrodes used in the volume resistivity measuring apparatus. A guard electrode 22 is arranged concentrically with the surface electrode 21 as the center. Here, d1 to d3 represent the diameter of the center electrode 21, the diameter of the inner circumference of the guard electrode 22, and the diameter of the outer circumference of the guard electrode 22, respectively. These values can be arbitrarily set according to the size and shape of the measurement sample. In addition, in the measurement of the volume resistivity in a present Example and a comparative example, UR probe (made by Mitsubishi Chemical Corporation) was used, and d1-d3 was made into the following value, respectively.
d1 = 16mm, d2 = 30mm, d3 = 40mm

The volume resistivity was calculated by the following formula (6), and the common logarithm value of the calculated volume resistivity was obtained as ρv.
Volume resistivity = [(π × d12) / 4] × (V / I) × (1 / t) (6)

  Here, in Expression (6), V is a voltage value (V) applied to the center electrode 21, I is a current value (A) detected by the microammeter 26, and t is a film thickness (cm) of the measurement sample. Respectively. In the measurement of the surface resistivity in the examples of the present invention, the voltage applied to the center electrode 21 was 500V. The current value I was 10 seconds after the voltage V was applied. For measuring the film thickness t of the measurement sample, any known method such as a micrometer or an eddy current film thickness system is preferably used. In the embodiment of the present invention, the eddy current film thickness meter ISOSCOPE MP30 is used. The film thickness was measured by (manufactured by FFischer). The volume resistivity was measured in an environment at a temperature of 20 ° C. and a relative humidity of 40%.

(Measurement of common logarithm value ρexs of creeping resistivity on the pole surface)
FIG. 6 is a schematic cross-sectional view of a creeping resistivity measuring device on the pole surface. A measurement sample 27 is disposed on the back electrode 23 connected to the GND. The voltage application electrode 28 and the current measurement electrode 29 are arranged on the measurement sample 27, and the measurement sample 27 is sandwiched between the back electrode 23, the voltage application electrode 28, and the current measurement electrode 29. A direct current voltage was applied from a direct current power source 25 connected to the voltage application electrode 28, and the amount of current flowing by the microammeter 26 connected to the current measurement electrode 29 was measured, and the creeping resistivity on the pole surface was calculated.

Details are shown below. FIG. 8 shows a schematic plan view of an electrode used in a creeping resistivity measuring device on the pole surface. A current measuring electrode 29 is arranged around the voltage applying electrode 28 and parallel to the voltage applying electrode 28 on both sides thereof. Here, d4 to d6 represent the width of the voltage application electrode 29 and the current measurement electrode 29, the length of the voltage application electrode 29 and the current measurement electrode 29, and the distance between the voltage application electrode 28 and the current application electrode 29, respectively. These values can be arbitrarily set according to the size and shape of the measurement sample. In addition, in the measurement of the surface resistivity in a present Example and a comparative example, d4-d6 was set as the following value, respectively.
d4 = 10mm, d5 = 50mm, d6 = 10mm

And the creeping resistivity of the pole surface was calculated by the following formula (7), and the common logarithm of the calculated value was obtained as ρexs.
Creeping resistivity of pole surface = V / (I / 2) × (d5 / d6) = 2 × (V / I) × (d5 / d6) (7)

  In the above formula (7), V represents a voltage value (V) applied to the voltage application electrode 29, and I represents a current value (A) detected by the microammeter 26. In the measurement of the creeping resistivity on the pole surface in this example, the voltage applied to the voltage application electrode 28 was 500V. The current value I was 15 seconds after the voltage V was applied. The creepage resistivity on the pole surface was measured in an environment at a temperature of 20 ° C. and a relative humidity of 40%.

  The creeping resistivity on the pole surface is different from the so-called surface resistivity that has been measured in the past by adopting the electrode shape and measurement conditions as described above. ) To measure resistivity.

(Measurement of common logarithmic value R of volume resistivity of primary transfer roll)
FIG. 13 shows a schematic cross-sectional view of an apparatus for measuring the volume resistance of the primary transfer roll 105. The primary transfer roll 105 is placed on the flat plate 32, and a load (500 gf weight: 1000 gf in total) is put on both ends of the metal shaft of the primary transfer roll 105, and then the primary transfer roll from the high resistance meter (resistance measuring device) 33. After applying a voltage of 1 kV to 105 metal shafts for 10 seconds, the common logarithm of the value measured by the resistance measuring device 33 was used as the common logarithm of the volume resistivity of the primary transfer roll. The high resistance meter was measured using R8340A manufactured by Advantest. The volume resistivity was measured in an environment with a temperature of 22 ° C. and a relative humidity of 55%.

(A1 production of intermediate transfer belt)
N-methyl-2-pyrrolidone (NMP) solution of polyamic acid composed of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminodiphenyl ether (the solid content ratio after imide conversion is 18 mass%), carbon black (Special Black 4: manufactured by Degussa) is added to 100 mass parts of the solid content of polyamic acid so as to be 80 mass parts, and a jet mill disperser (Geanus PY [minimum part of the collision part] is added. Cross-sectional area 0.032 mm2]: manufactured by Genus Co., Ltd.) was used to disperse and mix by passing the dispersion unit part 5 times at a pressure of 200 MPa to obtain dispersion (A). An NMP solution of polyamic acid composed of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminodiphenyl ether (solid after imide conversion) was added to the obtained dispersion (A). 18 mass%) is added so that carbon black is 22.5 parts by weight with respect to 100 parts by weight of polyamic acid, and mixed and stirred using a planetary mixer (Aiko mixer manufactured by Aikosha Seisakusho). By doing so, a carbon black-dispersed polyimide precursor solution for the innermost layer was prepared.

  On the other hand, an aluminum cylindrical body having an outer diameter of 366 mm, a length of 600 mm, and a thickness of 6 mm was prepared as the cylindrical molded tube 11 shown in FIG. Such an aluminum cylinder has a surface roughened to Ra: 0.40 μm by blasting with spherical glass particles. A silicone release agent (trade name: KS700, manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to the surface of the cylindrical molded tube 11 and baked at 300 ° C. for 1 hour to produce an aluminum cylindrical body. Furthermore, as a spin coating process, as shown in FIG. 2, the cylindrical molded tube 11 was rotated at 50 rpm in the direction of the arrow 12 with the axial direction horizontal. The blade 18 is made of SUS having a width of 20 mm and a thickness of 0.5 mm, and has elasticity. The blade 18 was pressed against the cylindrical molding tube 11, and the carbon black-dispersed polyimide precursor solution for the innermost layer was used as the polyimide precursor solution 16 and extruded from the container 14 through the nozzle 15 having a diameter of 2 mm. When the polyimide precursor solution passed through the blade 18, the blade 18 was spread and a gap was formed between the blade 18 and the cylindrical tube 11.

  Next, the nozzle 15 and the blade 18 were moved in the direction of arrow 13 at a speed of 120 mm / min. In addition, in the case of application | coating, the non-application area | region of 20 mm was provided in the both ends of the cylindrical shaping | molding pipe | tube 11. As shown in FIG. Next, the cylindrical molded tube 11 coated with the carbon black-dispersed polyimide precursor solution for the inner circumferential layer is kept horizontal and heated and dried at 125 ° C. for 40 minutes while rotating at 6 rpm to dry the innermost layer carbon black-dispersed polyimide precursor. A membrane was obtained. In addition, the film thickness of the innermost-layer carbon black-dispersed polyimide precursor dry film was adjusted by the amount of extrusion liquid from the nozzle 15 at the time of application so that the film thickness after imidization described later has a desired value. Moreover, the amount of residual NMP in the innermost layer carbon black-dispersed polyimide precursor dry film was 24.0% by mass. The residual NMP amount was calculated from the weight difference of the cylindrical molded tube 11 after drying from the weight of the cylindrical molded tube 11 after the innermost layer application.

  Next, an NMP solution of polyamic acid composed of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminodiphenyl ether (after imide conversion) was added to the dispersion (A). The solid content is 18% by mass), and 100% by mass of polyamic acid is added so that the carbon black is 18.7 parts by mass, and mixed using a planetary mixer (Aiko mixer manufactured by Aikosha Seisakusho). By stirring, a carbon black-dispersed polyimide precursor solution for the outermost layer was prepared. Using the obtained carbon black-dispersed polyimide precursor solution for the outermost layer, except that the rotational speed of the cylindrical tube 11 was 40 rpm and the moving speed of the nozzle 15 was 90 mm / min, It apply | coated on the innermost layer carbon black dispersion | distribution polyimide precursor dry film | membrane.

  Next, the outermost carbon black-dispersed polyimide precursor solution is dried by heating at 120 ° C. for 40 minutes while rotating the cylindrical tube 11 coated with the carbon black-dispersed polyimide precursor solution for outermost layer in a horizontal state at 6 rpm. Got. The film thickness of the outermost carbon black-dispersed polyimide precursor dry film was adjusted by the amount of extrusion liquid from the nozzle 15 at the time of coating so that the film thickness after imidization described later has a desired value. The amount of residual NMP after drying was 35.2% by mass. In addition, since this residual NMP amount is measured after the outermost layer is dried, it is a residual NMP amount that combines the innermost layer and the outermost layer.

  The cylindrical molded tube 11 obtained by laminating the outermost carbon black-dispersed polyimide precursor dry film on the innermost carbon black-dispersed polyimide precursor dry film obtained as described above was placed at 200 ° C. for 30 minutes and at 260 ° C. for 30 minutes. This was heated at 300 ° C. for 30 minutes and at 320 ° C. for 20 minutes to form a carbon black-dispersed polyimide film. Thereafter, when the temperature of the cylindrical molded tube 11 was cooled to room temperature (25 ° C.), the polyimide resin film was peeled off from the cylindrical molded tube 11. The obtained polyimide resin film was cut to a width of 362 mm to obtain an intermediate transfer belt a. Two intermediate transfer belts “a” obtained were joined to obtain an intermediate transfer belt A1 having a circumference of 2111 mm.

  Further, when the film thicknesses of the outermost layer and the innermost layer were measured using the remaining cut ends of the intermediate transfer belt a, they were 31.2 μm and 64.9 μm, respectively. Further, when ρs, ρv, and ρexs were measured, they were 12.58 LogΩ / □, 13.27 LogΩ · cm, and 11.58 LogΩ / □, respectively. The results are shown in Table 1.

(Preparation of intermediate transfer belts A2 to A12)
In the production of the intermediate transfer belt A1, the amount of carbon black contained in the innermost layer, the amount of carbon black contained in the outermost layer, and the drying temperature and time after coating when forming the innermost layer carbon black-dispersed polyimide precursor dry film Intermediate transfer belts A2 to A12 were prepared in the same manner as the intermediate transfer belt A1, except that the values were changed to the values shown in Table 1, respectively. In the intermediate transfer belts A2 to A16, the drying conditions for the innermost layer and the outermost layer were the same, and the drying conditions shown in Table 1 were used. When the common logarithm values of the outermost layer thickness, the innermost layer thickness, ρs, ρv, ρexs, and the surface resistivity of the innermost layer were measured, the values shown in Table 1 were obtained.

(Preparation of intermediate transfer belt B1)
In the production of the intermediate transfer belt A1, a single-layer intermediate transfer belt B1 is formed in the same manner as the intermediate transfer belt A1 and the conventional intermediate transfer belt, except that polyaniline is used instead of carbon black as the conductive agent and the film thickness is 80 μm. Produced. The results of measuring the resistivity in the same manner as in Example A1 are shown in Table 1. In the intermediate transfer belt B1, the conductive agent is polyaniline, but it is not necessary to be limited, and carbon black may be used. Also, the coating and drying conditions need not be limited, and the relationship between the common logarithmic value ρs of the outermost layer surface resistivity and the common logarithm ρi of the innermost layer surface resistivity is ρs as shown in Table 1 in a single layer. As long as ≦ ρi, the manufacturing method is not limited.

Example 1
The above-described adjusted intermediate transfer belt A1 and a common logarithmic value of volume resistivity of 7.0 LogΩ are added to the image quality evaluation machine obtained by remodeling a full-color multifunction peripheral (DocuColor 8000 Digital Press: manufactured by Fuji Xerox Co., Ltd.) having the basic configuration shown in FIG. Equipped with a primary transfer roll.

Using this image quality evaluation machine, A3 paper (J paper: manufactured by Fuji Xerox Co., Ltd.)
An offset amount D (see FIGS. 9 to 11 and the like) between the image carrier 101 and the primary transfer roll 105 in each environment of a temperature of 28 ° C. and a humidity of 85% RH, and 10 ° C. and 15% RH. , 3.0 mm, 3.5 mm, and 4.5 mm, and 12 sheets were continuously printed in each.
During printing, the transfer current applied to the primary transfer roll is 45 μA in an environment of temperature 28 ° C. and humidity 85% RH, 45 μA in each environment of 10 ° C. and 15% RH, and applied to the secondary transfer roll. The transfer voltage was set to 1.5 kV under the environment of temperature 28 ° C. and humidity 85% RH, and set to 3.0 kV under each environment of 10 ° C. and 15% RH. As an output image, halftone pattern 1 (Magenta 20% density) and full-color gradation pattern 1 are printed in an environment of temperature 28 ° C. and humidity 85% RH, and half in an environment of 10 ° C. and 15% RH. Tone pattern 2 (Red 40% density) and full-color gradation pattern 1 were printed, and image defects were evaluated for the 12th formed image. As the image defect evaluation, each of transfer unevenness, arc-shaped white spots, tree branch white spots, and fine white spots (discharge marks) were evaluated. The evaluation criteria were as follows.

<Evaluation of transfer unevenness>
Transfer fullness was evaluated by visually evaluating the formed full-color gradation pattern 1. The evaluation criteria were as follows.
<Evaluation criteria for transfer unevenness>
○: No transfer unevenness occurred.
(Triangle | delta): The transcription | transfer nonuniformity which is very slight (a level which can be confirmed visually cannot be seen) generate | occur | produces within 20% or less of the whole image area | region.
X: Transfer unevenness that can be clearly discriminated visually is generated, or very slight transfer unevenness occurs in an area exceeding 20% of the entire image area.

<Evaluation of arc-shaped white spots>
Transfer unevenness was evaluated by visually evaluating the formed halftone pattern 1. The evaluation criteria were as follows.
<Evaluation criteria for arc-shaped white spots>
○: Arc-shaped white spots have not occurred.
X: One or more arc-shaped white spots are observed.

<Evaluation of branching of trees>
The formed halftone pattern 2 was visually evaluated to evaluate the branching white of the tree. The evaluation criteria were as follows.
<Evaluation criteria for branching of trees>
○: No branching of trees has occurred.
X: One or more branch white spots are observed.

<Evaluation of fine white spots (discharge marks)>
A fine white spot (discharge mark) was evaluated by visually evaluating the formed full-color gradation pattern 1. The evaluation criteria were as follows.
<Evaluation criteria for fine white spots (discharge marks)>
○: Fine white spots (discharge marks) have not occurred.
Δ: Fine white spots (discharge marks) are observed within 20% or less of the entire image area.
X: A fine white spot (discharge mark) is observed in an area exceeding 20%.

  The above evaluation results are shown in Tables 2 to 4.

(Example 2 to Example 3)
In place of the primary transfer roll used in Example 1, a common logarithmic value of volume resistivity is 7.7 LogΩ, and a primary transfer roll is used as Example 2, and the common logarithm of volume resistivity is 8.5 LogΩ. Using a primary transfer roll as Example 3, image formation was performed under the same conditions as in Example 1, and evaluation was performed. The evaluation results are shown in Tables 2 to 4.

(Example 4 to Example 6)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A2 was used instead of the intermediate transfer belt A1. Were designated as Examples 4 to 6, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 7 to Example 9)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A3 was used instead of the intermediate transfer belt A1. Were designated as Examples 7 to 9, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 10 to Example 12)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A4 was used instead of the intermediate transfer belt A1. Were designated as Examples 10 to 12, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 13 to Example 15)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3 except that the intermediate transfer belt A5 was used instead of the intermediate transfer belt A1. Were designated as Examples 13 to 15, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 16 to Example 18)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A6 was used instead of the intermediate transfer belt A1. Were designated as Examples 16 to 18, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 19 to Example 21)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A7 was used instead of the intermediate transfer belt A1. Were designated as Examples 19 to 21, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 22 to Example 24)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3 except that the intermediate transfer belt A8 was used instead of the intermediate transfer belt A1. Were designated as Examples 22 to 24, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 25 to Example 27)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A9 was used instead of the intermediate transfer belt A1. Were taken as Examples 25 to 27, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 28 to Example 30)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A10 was used instead of the intermediate transfer belt A1. Were designated as Examples 28 to 30. The evaluation results are shown in Tables 2 to 4.

(Example 31 to Example 33)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A11 was used instead of the intermediate transfer belt A1. Were designated as Examples 31 to 33, respectively. The evaluation results are shown in Tables 2 to 4.

(Example 34 to Example 36)
In Examples 1 to 3, images were formed and evaluated under the same conditions as in Examples 1 to 3, except that the intermediate transfer belt A12 was used instead of the intermediate transfer belt A1. Were designated as Examples 34 to 36, respectively. The evaluation results are shown in Tables 2 to 4.

(Comparative Examples 1 to 2)
In place of the primary transfer roll used in Example 1, a common logarithmic value of volume resistivity of 6.9 LogΩ was used as Comparative Example 1, and a common logarithm of volume resistivity was 8.6 LogΩ. Using a primary transfer roll as Comparative Example 2, image formation was performed under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 4.

(Comparative Example 3 to Comparative Example 7)
In place of the primary transfer roll used in Example 1, a common logarithmic value of volume resistivity of 6.9 LogΩ was used as Comparative Example 3, and the common logarithm of volume resistivity was 7.0 LogΩ. The one using the primary transfer roll is Comparative Example 4, the common logarithm of volume resistivity is 7.7 LogΩ, and the one using the primary transfer roll is Comparative Example 5, and the common logarithm of volume resistivity is 8.5 LogΩ. The one using a primary transfer roll is referred to as Comparative Example 6, and the one using a primary transfer roll having a common logarithmic value of volume resistivity of 8.6 LogΩ is referred to as Comparative Example 7, and the intermediate transfer belt B1 is used instead of the intermediate transfer belt A1. Except for the above, image formation was performed under the same conditions as in Example 1, and evaluation was performed as Comparative Examples 3 to 7. The evaluation results are shown in Table 4.

  As shown in Tables 2 to 4, the common logarithm of the surface resistivity of the innermost layer of the intermediate transfer belt is adjusted to be smaller than the common logarithm of the surface resistivity of the outermost layer, and the primary transfer In Examples 1 to 36 in which the common logarithmic value of the volume resistivity of the roll is in the range of 7 LogΩ to 8.5 LogΩ, the common logarithmic value of the volume resistivity of the primary transfer roll is less than 7 LogΩ or more than 8.5 LogΩ. Comparative Example 1 and Comparative Example 2 that are values, the common logarithm of the surface resistivity of the innermost layer is larger than the common logarithm of the surface resistivity of the outermost layer, compared with Comparative Examples 3 to 7, as an image quality evaluation Even when the offset amount fluctuated for all the evaluation items of the transferred unevenness, the arc-shaped white spot, the tree branch white spot, and the fine white spot, always good results were obtained.

Specifically, for example, when the volume resistance value of the primary transfer roll is 7.7 LogΩ, in Examples 1 to 36, the offset amount D is any of 3 mm, 3.5 mm, and 4.5 mm. However, it can be seen that a good result is obtained and that a range (allowable range) in which a good image is obtained even when the offset amount D varies is wide. On the other hand, in Comparative Example 1 in which the common logarithmic value of the volume resistance value of the primary transfer roll is less than 7 LogΩ, transfer unevenness is observed regardless of the offset amount D. Further, in Comparative Example 2 in which the common logarithmic value of the volume resistance value of the primary transfer roll exceeds 8.5 LogΩ, when the offset amount is larger than 3.5 mm, branching white spots or fine white spots (discharge marks) of the tree are formed. It has occurred.
In Comparative Examples 2 to 4, good results were obtained for all items as image quality evaluation results, one point each (3 mm in Comparative Example 2, 3 mm in Comparative Example 5, and 3 mm in Comparative Example 6). Alternatively, when there is no settable range (Comparative Example 3, Comparative Example 4, and Comparative Example 7), and there is a variation in the offset amount D due to variations in manufacturing the image forming device, good image quality is obtained in all the image forming devices. It turns out that it cannot be said that it is obtained.
From the above, in the embodiment, compared with the comparative example, even if the offset amount D varies, a good image quality can be obtained, and the allowable range of the offset amount D (allowable range for obtaining good image quality) is compared. It can be said that it is wider than the example.

  Further, the common logarithm of the surface resistivity of the innermost layer of the intermediate transfer belt is adjusted to be smaller than the common logarithm of the surface resistivity of the outermost layer, and the common logarithm of the volume resistivity of the primary transfer roll. In Examples 1 to 18 in which the intermediate transfer belt satisfies all of the above formulas (1) to (3) among Examples 1 to 36 in which is in the range of 7 LogΩ to 8.5 LogΩ. As compared with Examples 19 to 36 that do not satisfy at least one of the formulas (1) to (3), further favorable results were obtained for all the image evaluation items.

1 is a schematic cross-sectional view showing a preferred embodiment of an image forming apparatus of the present embodiment. FIG. 3 is a schematic cross-sectional view showing an embodiment of a cylindrical tube-applying device used for producing the intermediate transfer belt of the embodiment. FIGS. 3A to 3C are schematic cross-sectional views illustrating an example of an intermediate transfer belt of the present embodiment. 1 is a schematic cross-sectional view of a surface resistivity measuring device for an intermediate transfer belt according to an embodiment. 1 is a schematic cross-sectional view of a volume resistivity measuring device for an intermediate transfer belt according to an embodiment. 1 is a schematic cross-sectional view of a creeping resistivity measuring device for a pole surface of an intermediate transfer belt according to an embodiment. FIG. 3 is a schematic plan view of electrodes used in the surface resistivity and volume resistivity measuring device of the intermediate transfer belt of the present embodiment. FIG. 3 is a schematic plan view of electrodes used in a creeping resistivity measuring device on the pole surface of the intermediate transfer belt of the present embodiment. FIG. 3 is a schematic diagram illustrating an example of a primary transfer unit in the image forming apparatus according to the present embodiment. FIG. 10 is a schematic diagram illustrating an example of a primary transfer unit in a conventional image forming apparatus. FIG. 3 is a schematic diagram illustrating an example of a primary transfer unit in the image forming apparatus according to the present embodiment. FIG. 10 is a schematic diagram illustrating an example of a primary transfer unit in a conventional image forming apparatus. It is a schematic diagram showing an example of a measuring device for measuring the volume resistance of the primary transfer roll 105.

Explanation of symbols

101a to 101d Image carriers 103a to 103d Developing devices 105a to 105d Primary transfer roll 107 Intermediate transfer belt 109 Secondary transfer roll

Claims (3)

An image carrier on which an electrostatic latent image is formed;
Developing means for developing the electrostatic latent image formed on the image carrier with toner to form a toner image;
An intermediate transfer belt on which the toner image on the image holding member is transferred and holding the transferred toner image;
A primary transfer roll that is disposed in contact with the inner peripheral surface of the intermediate belt so as to sandwich the intermediate transfer belt with the image carrier, and transfers the toner image from the image carrier to the intermediate transfer belt;
A secondary transfer roll for transferring the toner image held on the intermediate transfer belt to a recording medium;
With
The common logarithm of the volume resistivity of the primary transfer roll is 7 LogΩ · cm or more and 8.5 LogΩ · cm or less,
The intermediate transfer belt is composed of a plurality of layers laminated in the thickness direction, and the common logarithm of the surface resistivity of the innermost layer on the innermost surface side of the plurality of layers is the outermost layer on the outermost surface side. An image forming apparatus smaller than the common logarithm of the surface resistivity. The image forming apparatus according to claim 1, wherein the intermediate transfer belt satisfies the following formulas (1) to (3).
11.6 LogΩ / □ ≦ ρs ≦ 14.0 LogΩ / □ (1)
10.3 LogΩ · cm ≦ ρv ≦ 14.0 LogΩ · cm (2)
9.8 LogΩ / □ ≦ ρexs ≦ 13.4 LogΩ / □ (3)
(In the above formulas (1) to (3), ρs represents a common logarithm of the surface resistivity of the outermost layer of the intermediate transfer belt, and ρv represents a common logarithm of the volume resistivity of the intermediate transfer belt. , Ρexs represents a common logarithm of the creeping resistivity of the inner peripheral surface of the intermediate transfer belt.) The image forming apparatus according to claim 2, wherein the outermost layer and the innermost layer satisfy the following expression (4).
1.2 ≦ du / dl ≦ 4.0 (4)
(In the above formula (4), du represents the film thickness (μm) of the outermost layer, and dl represents the film thickness (μm) of the innermost layer.)

Images