JP2012256003A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain a paper powder and an external additive material from directly attaching to an outer peripheral surface of an intermediate transfer belt at a secondary transfer position for transferring a toner image to a recording material in a constitution comprising a blade for cleaning the intermediate transfer belt even when a lubricant is supplied to the intermediate transfer belt to suppress excess rubbing by the blade.SOLUTION: An image forming apparatus comprises: an image carrier 11 for carrying a toner image; an elastic intermediate transfer belt 16 for having the toner image transferred on an outer peripheral surface thereof; a secondary transfer outer member 26 for transferring the toner image from the intermediate transfer belt 16 to a recording material P; a blade 27 for cleaning the intermediate transfer belt 16; supply means 25 for supplying a lubricant to the intermediate transfer belt 16; and supply means counter member 24 for stretching the intermediate transfer belt 16 at a counter position of the supply means 25 across the intermediate transfer belt 16. The curvature at an area where the supply means counter member 24 contacts with the intermediate transfer belt 16 is larger than that at an area where a secondary transfer inner member 22 contacts with the intermediate transfer belt 16.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that forms an image using an electrophotographic system, and more particularly to an image forming apparatus that uses an intermediate transfer member.

  In order to cope with various recording materials, there is a configuration in which an intermediate transfer belt that carries a toner image is provided. However, if the outer peripheral surface of the intermediate transfer belt is to be cleaned with a cleaning blade, the surface friction becomes excessive and the cleaning blade may turn over. Therefore, there is a method of supplying a lubricant to the outer peripheral surface of the intermediate transfer belt in order to suppress excessive friction between the intermediate transfer belt and the cleaning blade. Japanese Patent Application Laid-Open No. 2005-228561 includes a supply unit that supplies a lubricant to the outer peripheral surface of the intermediate transfer belt, and a supply unit facing member that stretches the intermediate transfer belt at a position facing the supply unit via the intermediate transfer belt. Is described.

JP2007-140317A

  However, when the belt surface supplied with the lubricant reaches the secondary transfer position where the toner image is transferred to the recording material, the belt surface may extend. In this case, since the region where the lubricant is supplied on the belt is extended and the concentration of the lubricant per unit area is lowered, the paper dust is not on the lubricant at the secondary transfer position. It becomes easy to adhere directly to the belt surface. As a result, there is a possibility that the paper dust enters a minute recess on the belt and is difficult to be cleaned.

  In order to solve the above problems, the present invention provides an image carrier that carries a toner image, an elastic intermediate transfer belt that is rotatable and transfers a toner image from the image carrier to an outer peripheral surface, and the intermediate A secondary transfer outer member that is disposed on the outer peripheral surface side of the transfer belt and transfers a toner image from the intermediate transfer belt to a recording material, and the intermediate transfer belt is stretched from the inner peripheral surface side, and the intermediate transfer belt A secondary transfer inner member that faces the secondary transfer outer member via a blade, and a blade that is provided downstream of the transfer inner member in the rotational direction in which the intermediate transfer belt rotates, and that cleans the intermediate transfer belt; A supply means for supplying a lubricant to the intermediate transfer belt; and a supply means facing member that stretches the intermediate transfer belt at a position facing the supply means via the intermediate transfer belt. In forming apparatus, the curvature in the region in contact with the intermediate transfer belt of the supply means opposing member, being larger than the curvature in the region in contact with the intermediate transfer belt of the secondary transfer member.

  According to the present invention, in a configuration in which a blade for cleaning the intermediate transfer belt is provided, secondary transfer that transfers a toner image to a recording material even if a lubricant is supplied to suppress excessive sliding of the blade. It is possible to suppress the paper dust from directly adhering to the outer peripheral surface of the belt at the position.

It is the figure which showed schematic sectional structure of the apparatus which implements this invention. It is the figure which showed the schematic cross-sectional structure of the lubricant coating device. FIG. 5 is a diagram showing the relationship between the amount of elongation on the surface of the intermediate transfer belt and the radius of curvature. It is the figure which showed the gross reduction rate at the time of 60k sheets by R2 / R1. It is the figure which showed transition of the gross reduction rate obtained in the structure of Embodiment 1. FIG. It is the figure which showed schematic sectional structure of the apparatus used in Embodiment 2. FIG. It is the figure which showed the gross reduction rate at the time of 60k sheets by R3 / R1. It is a figure showing transition of the gross reduction rate obtained in the structure of Embodiment 2. FIG. FIG. 5 is a diagram illustrating a schematic cross-sectional configuration of an intermediate transfer belt used in Embodiment 3. It is a figure showing transition of the gross reduction rate obtained in the structure of Embodiment 3. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
(Image formation process)
The image forming apparatus in this embodiment is an electrophotographic four-color full-color image forming apparatus. The overall configuration and operation of image formation will be described with reference to FIG.

  The image forming apparatus includes four (four color) image forming stations, that is, image forming stations Y, M, and Y that form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. C and K are provided.

  Each of the image forming stations Y, M, C, and K includes drum-type photosensitive members (hereinafter referred to as photosensitive drums) 11Y, 11M, 11C, and 11K as image carriers (photosensitive members and photosensitive drums). In each of the photosensitive drums 11Y, 11M, 11C, and 11K, OPC (organic optical semiconductor) is applied as a photosensitive layer on the outer peripheral surface of an aluminum cylinder having an outer diameter of 30 mm, and a curable resin is used as a resin for the charge transport layer. Used configuration.

  The photosensitive drums 11Y, 11M, 11C, and 11K are in contact with charging rollers 12Y, 12M, 12C, and 12K having an outer diameter of 14 mm that are pressed against the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K. The battery is uniformly charged by applying a charging bias on which a DC voltage is superimposed.

  After the photosensitive drums 11Y, 11M, 11C, and 11K are uniformly charged by the charging rollers 12Y, 12M, 12C, and 12K, laser light having a wavelength of 780 nm is exposed from the exposure devices 13Y, 13M, 13C, and 13K according to image information. Irradiation is performed on the drums 11Y, 11M, 11C, and 11K, and electrostatic latent images corresponding to the respective colors are formed.

  The electrostatic latent images formed on the photosensitive drums 11Y, 11M, 11C, and 11K are supplied with toners of respective colors by developing devices 14Y, 14M, 14C, and 14K that contain yellow, magenta, cyan, and black toners, respectively. Attached and developed as a toner image. Reference numerals 18Y, 18M, 18C, and 18K denote toner supply containers that store toners to be supplied to the developing devices 14Y, 14M, 14C, and 14K of the respective colors.

  As the developer, a two-component developer for transporting toner particles mixed with a magnetic carrier by magnetic force and developing the toner particles in contact with the photosensitive drum was used. From the viewpoint of obtaining good image quality, it is preferable to use a spherical toner. The external additive added to the toner preferably has a particle size of 1/10 or less of the weight average particle size of the toner particles from the viewpoint of durability when added to the toner. The particle size of the external additive means the average particle size obtained by observing the surface of the toner particles with a microscope. The external additive is used in an amount of 0.01 to 15 parts by weight, preferably 0.05 to 12 parts by weight, based on 100 parts by weight of the toner. As the external additive, aluminum oxide, titanium oxide, other materials, and the like can be used.

In this embodiment, a negatively charged toner is used, and an average charge amount (charge amount per unit weight; hereinafter referred to as Q / M) charged by friction with a carrier is −1.0 × 10 ⁻² C / kg to − The thing of 6.0 * 10 ^<-2 > C / kg was used.

  Below the four image forming stations Y, M, C, and K described above, an intermediate transfer member 16 that carries a toner image is disposed. Primary transfer rollers 15Y, 15M, 15C, and 15K for transferring a toner image having an outer diameter of 18 mm onto the intermediate transfer member are in contact with positions corresponding to the photosensitive drums 11Y, 11M, 11C, and 11K with the intermediate transfer member 16 interposed therebetween. It is arranged. When a positive primary transfer bias is applied from the primary transfer bias power source, the respective toner images on the photosensitive drums 11Y, 11M, 11C, and 11K are primarily transferred by the primary transfer portion N1.

  In this embodiment, an intermediate transfer belt having a single elastic layer is used as the intermediate transfer body 16. As the elastic layer, urethane rubber having a thickness of 500 μm is used, but natural rubber and other materials can be used.

  When the thickness is less than 20 μm, the elastic layer cannot sufficiently contract, and the fluctuation of the contact pressure with respect to the intermediate transfer belt 16 on the photosensitive drums 11Y, 11M, 11C, and 11K cannot be sufficiently absorbed. On the other hand, if the thickness exceeds 1000 μm, the intermediate transfer belt 16 does not bend appropriately at the support shaft regardless of the hardness, and the running becomes unstable.

The intermediate transfer belt 16 is stretched around a drive roller 21, a secondary transfer counter roller 22 as a secondary transfer inner member, a cleaning device counter roller 23, and a lubricant application device counter roller 24. Reference numeral 21 denotes a driving roller as a driving stretch member for driving the intermediate transfer belt. The driving roller 21 is rotated by a driving force transmitted from a driving motor (not shown), and the intermediate transfer belt 16 can rotate in the direction of the arrow by rotating clockwise. Reference numeral 22 denotes a secondary transfer counter roller that faces the secondary transfer roller via the intermediate transfer belt 16. A cleaning device facing roller 23 faces the cleaning device through the intermediate transfer belt 16. Reference numeral 24 denotes a lubricant application device facing roller 24 that faces the lubricant application device via the intermediate transfer belt. The drive roller 21 has a conductive rubber layer on a metal core, is a 10 ² to 10 ⁶ Ω roll, and the core is grounded. A lubricant application device 25 for applying lubricant to the surface of the intermediate transfer belt 16 is disposed in contact with the lubricant application device facing roll 24 on the intermediate transfer belt 16. Yes. Details of the lubricant application device 25 will be described later.

The cleaning device facing roll 23 and the lubricant applying device facing roller 24 have outer diameters of 30 mm and 20 mm, respectively, and are formed by covering an insulating roller with a semiconductive thin film. This thin film is formed to a thickness of 10 μm to 200 μm, and its surface resistivity is adjusted to 10 ⁷ to 10 ¹¹ Ω / □ (□: unit area).

  A secondary transfer roller 26 as a secondary transfer outer member for transferring a toner image having an outer diameter of 24 mm to a recording material is disposed at a portion of the intermediate transfer belt 16 facing the secondary transfer counter roller 22. Are arranged opposite to each other as a backup roller. That is, the secondary transfer roller 26 is disposed on the outer peripheral surface side of the intermediate transfer belt, and the secondary transfer counter roller 22 is disposed on the inner peripheral surface side of the intermediate transfer belt. The secondary transfer counter roller 22 and the secondary transfer roller 26 serve as secondary transfer means for transferring the toner image transferred to the intermediate transfer body belt 16 onto the recording material. The transfer material P is supplied to the secondary transfer portion N2 by a registration roller so that the four color toner images are aligned on the intermediate transfer belt 16 with good timing. The toner image on the intermediate transfer belt 16 is secondarily transferred onto the surface of the transfer material P when a secondary transfer bias voltage is applied to the secondary transfer roller 26 from a secondary transfer bias power source.

  The toner image transferred to the transfer material P is fixed to the transfer material P by receiving heat and pressure with a fixing device. Thereafter, the sheet is discharged outside the apparatus main body.

  The secondary transfer residual toner and the lubricant that have not been secondarily transferred to the transfer material P at the secondary transfer portion N2 are removed by the cleaning blade 27 that presses the intermediate transfer belt 16.

(Detection sensor)
In this embodiment, in order to control the density of an image, an adjustment toner image is formed on the intermediate transfer member, and then the adjustment toner image is irradiated with light, and its specular reflection light component and scattered light component The image forming conditions are adjusted from the relationship between the light quantity and the density.

  Reference numeral 19 denotes a detection sensor for detecting the density of the toner images sequentially transferred from the photosensitive drums 11Y, 11M, 11C, and 11K onto the intermediate transfer belt 16. A detection sensor is provided with the irradiation part which irradiates light toward a belt surface, and the detection part which detects light. The irradiating unit irradiates light toward the belt surface, and the detecting unit detects specularly reflected light. The amount of specularly reflected light differs between a region where the adjustment toner image is not formed and a region where the adjustment toner image is formed. Then, the adjustment unit calculates the density of the toner image for adjustment using the difference Δ of the regular reflection light, and adjusts the image forming conditions.

(Lubricant application device)
In the present embodiment, an elastic belt is used as the intermediate transfer belt 16 in order to cope with various recording materials. Therefore, the friction between the intermediate transfer belt 16 and the cleaning blade 27 is increased, and the cleaning blade 27 may be turned up. In order to prevent the cleaning blade 27 from turning up, a lubricant application device 25 for applying the lubricant to the outer peripheral surface of the belt is provided as supply means for supplying the lubricant to the outer peripheral surface of the intermediate transfer belt. ing. As a result, the friction between the intermediate transfer belt and the cleaning blade 27 is reduced, and the cleaning blade 27 is prevented from turning up.

  FIG. 2 is a partially enlarged view of the lubricant application device 25 used in the present invention, and lubrication for applying the solid lubricant 28, the solid lubricant holding member 29, and the solid lubricant 28 onto the intermediate transfer belt 16. Brush roller 30 as agent application means (brush-like member), pressure spring 31 for pressurizing the lubricant to the brush roller, anti-scattering sheet 32 for preventing the lubricant from scattering, intermediate from the brush roller 30 A leveling blade 33 for leveling the lubricant supplied on the transfer belt 16 is provided.

  As the lubricant, zinc stearate is used, which is molded into a solid bar shape. The solid lubricant 28 is held by a lubricant holding member 29, and is pressed against the brush roller 30 through the lubricant holding member by a pressure spring 31 with a pressurizing force of 300 gf. Then, the lubricant is applied onto the intermediate transfer belt 16. When the applied lubricant passes the contact position of the leveling blade 33 on the downstream side in the moving direction of the surface of the intermediate transfer belt 16, the surface is leveled and uniformly spread, and thickness unevenness is suppressed. Is done.

  The brush roller 30 is provided in contact with the intermediate transfer member belt 16, and the solid lubricant 28 is scraped to the brush roller 30 side by the rotation of the brush roller 30, and the lubricant adhered to the brush roller 30 is transferred to the intermediate transfer member. It adheres to the surface of the intermediate transfer belt 16 from the contact portion with the belt 16.

  As for the rotation direction of the brush roller 30, it does not matter with respect to the present invention whether the intermediate roller belt 16 is rotated in the same direction or in the reverse direction.

  As the solid lubricant 28, a dry solid hydrophobic lubricant can be used. For example, a lubricant having a stearic acid group such as zinc stearate and barium stearate can be used. In addition, lead oleate having the same fatty acid group, metal salt of fatty acid, and the like can be used. In addition, plant waxes such as candelilla wax, carnauba wax, rice wax, tree wax, buckwheat oil, and animal waxes such as beeswax and lanolin can be used.

  Further, since the pressure applied to the belt surface that is required for leveling is lower than that for cleaning, the leveling blade 33 abuts in the forward direction with respect to the moving direction of the surface of the intermediate transfer belt 16. Therefore, there is no possibility that the leveling blade 33 will turn over.

(Stretch member radius and belt outer surface elongation)
In this embodiment, since an elastic belt member is used as the intermediate transfer belt, the outer peripheral surface of the belt expands and contracts along the stretching member. The relationship between the curvature of the tension member and the elongation of the belt outer peripheral surface will be described with reference to FIG.
FIG. 3 shows the relationship between the belt outer peripheral surface of the intermediate transfer belt and the size of the stretching roller. r is the radius of the tension roller, t is the thickness of the intermediate transfer belt 35, and θ is a sector formed by the center of the tension roller 34 and the contact point between the tension roller 34 and the intermediate transfer belt 35. Is the central angle. Further, L1 is the length of the arc inside the stretched portion of the stretching roller 34 and the intermediate transfer belt 35 having the radius r, and L2 is the length of the arc outside the intermediate transfer belt 35. L1 and L2 are respectively L1 = rθ
L2 = (r + t) θ
It is expressed.

Here, the amount of elongation on the outer peripheral surface of the intermediate transfer belt is expressed using an elongation rate α based on the natural length of the outer peripheral surface of the intermediate transfer belt 35. The relationship between the elongation amount and the elongation rate α is a relationship that the elongation amount of the belt outer peripheral surface increases as the elongation rate α increases. Elongation rate α is
α = L2 / L1 = 1 + (t / r)
It is expressed. In the present embodiment, since the thickness t of the intermediate transfer belt 35 is substantially constant, the extension amount of the belt decreases as the radius r of the stretching roller 34 increases. Here, the radius of curvature R of the outer peripheral surface of the intermediate transfer belt at the tension position by the tension roller is:
R = r + t
It is represented by The relationship between the radius of curvature R and the curvature X representing the degree of curvature of the curve or curved surface is as follows.
X = 1 / R
That is, the larger the radius of curvature R of the surface of the intermediate transfer belt 35 is, the smaller the curvature X is and the smaller the amount of elongation with respect to the natural length. The flat shape is represented by curvature = 0.

(Curvature of lubricant coating device facing means and curvature of secondary transfer facing roller)
As already described, in the present embodiment, the lubricant applying device 25 applies the lubricant to the outer peripheral surface of the belt in order to prevent the cleaning blade 27 from turning up.

  However, when the belt surface supplied with the lubricant reaches the secondary transfer position where the toner image is transferred to the recording material, the belt surface may extend. In this case, since the region where the lubricant is supplied on the belt is extended and the concentration of the lubricant per unit area is lowered, the paper dust is not on the lubricant at the secondary transfer position. It becomes easy to adhere directly to the belt surface. As a result, there is a possibility that the paper dust enters a minute recess on the belt and is difficult to be cleaned.

  Therefore, in the present embodiment, the radius r1 of the lubricant application device facing roller 24 as the supply means facing member facing the supply means is set to be smaller than the radius r2 of the secondary transfer facing roller 22. In other words, the curvature χ1 in the region where the lubricant application device facing roller 24 contacts the intermediate transfer belt is set to be larger than the curvature χ2 in the region where the secondary transfer facing roller 22 contacts the intermediate transfer belt. That is, the radius of curvature R1 of the outer peripheral surface of the intermediate transfer belt 16 at the lubricant supply portion for supplying the lubricant is smaller than the radius of curvature R2 of the outer peripheral surface of the intermediate transfer belt 16 at the secondary transfer portion for secondary transfer. . In other words, the curvature X1 of the outer peripheral surface of the intermediate transfer belt at the lubricant supply unit is set to be larger than the curvature X2 at the secondary transfer unit.

  As a result, the elongation rate at the lubricant application portion is larger than the elongation rate at the secondary transfer portion. Even if the belt outer peripheral surface is bent at the secondary transfer portion, it is possible to prevent the belt outer peripheral surface from being largely exposed at the secondary transfer portion. Since the paper dust and the external additive adhering to the surface of the intermediate transfer belt 16 from the secondary transfer outer roller adhere on the lubricant coated on the surface, direct adhesion to the outer peripheral surface of the belt is suppressed. Since these adhering substances are removed together with the lubricant applied to the surface of the intermediate transfer belt 16 by the cleaning device 27, accumulation of paper dust and external additives and the contamination of the intermediate transfer belt are suppressed.

FIG. 4 shows the relationship between the reduction rate of the gloss and the size ratio of the curvature radii R1 and R2. The horizontal axis indicates the ratio of the radius of curvature R1 at the lubricant application portion to R2 at the secondary transfer portion. The vertical axis represents the result of measuring the gloss value on the intermediate transfer belt 16 at 20 points when 60,000 sheets were passed using plain paper CLC80 (basis weight 80 g / cm ² ). As the paper dust and the external additive accumulate on the belt surface, the gloss of the belt surface decreases, so the degree of contamination on the belt surface can be determined by the gloss value on the vertical axis. The gloss value on the intermediate transfer member belt 16 is measured at an input / output angle of 45 degrees with respect to the vertical direction of the image surface of the transfer material using a gloss meter PG-3D manufactured by Nippon Denshoku Co., Ltd. The so-called 45 degree measurement value defined the gloss value. The gloss reduction rate was calculated by using the lowest gloss value among the measurement points on the basis of the gloss value on the surface of the intermediate transfer belt 16 before passing paper.

  As shown in FIG. 4, as the value of the radius of curvature R2 of the belt outer peripheral surface at the secondary transfer portion becomes smaller than the radius of curvature R1 of the belt outer peripheral surface at the lubricant application portion, the gloss reduction rate increases. . When R2 / R1 is 1 or more, the gross reduction rate is about 8%, which is sufficiently low. On the other hand, when R2 / R1 is smaller than 1.0, the gloss reduction rate is a value of around 18%, which is high.

  However, there may be unevenness in the application of the lubricant. When R2 / R1 is set to 1, a region where the lubricant is not applied may be generated due to uneven application, and the belt surface may be exposed at the secondary transfer portion. Therefore, in order to prevent the outer peripheral surface of the intermediate transfer belt 35 from being exposed at the secondary transfer portion even if coating unevenness occurs, it is desirable to use a range of R2 / R1> 1.

  In this embodiment, the radius r1 of the lubricant application device facing roller 24 is set to 10 mm, and the radius r2 of the secondary transfer facing roller 22 is set to 15 mm. The curvature corresponding to each roller is χ1 = 1/10 and χ2 = 1/15. That is, the radius of the lubricant application device facing roller 24 is set to be smaller than the radius of the secondary transfer facing roller 22. In other words, the curvature χ 1 of the lubricant application device facing roller 24 is set to be larger than the curvature χ 2 of the secondary transfer facing roller 22. Since the thickness t of the intermediate transfer belt is 0.5 mm, R1 = 10 + 0.5 = 10.5 mm and R2 = 15 + 0.5 = 15.5 mm. Further, the curvature X1 of the outer peripheral surface of the intermediate transfer belt at the position of the lubricant application device facing roller 24 is 1 / 10.5, and the curvature X2 of the outer peripheral surface of the intermediate transfer belt at the position of the secondary transfer counter roller 22 is 1/15. 5

  As a result, R2 / R1 = X1 / X2 = (15.5 / 10.5) ≈1.5. That is, the radius of curvature of the outer peripheral surface of the intermediate transfer belt at the lubricant application portion is set to be smaller than the radius of curvature of the outer peripheral surface of the intermediate transfer belt at the secondary transfer portion. In other words, the curvature of the outer peripheral surface of the intermediate transfer belt at the lubricant application portion is set to be larger than the curvature of the outer peripheral surface of the intermediate transfer belt at the secondary transfer portion.

  FIG. 5 shows the relationship between the gloss reduction rate and the number of formed images in the configuration of the present embodiment. The gloss value was measured up to 300,000 sheets every 20,000 using the same measurement method as in FIG. As a result, the image quality deterioration due to the decrease in gloss on the surface of the intermediate transfer belt 16 that was a concern did not occur.

  Therefore, according to the present invention, even in a system using an intermediate transfer belt having an elastic layer, a gloss reduction that deteriorates image quality does not occur, and a high-quality image can be obtained stably stably.

  In the present embodiment, the lubricant application device facing roll 24 and the secondary roll 24 satisfy the relationship of R1 <R2 so that the radius of curvature R1 at the lubricant supply portion on the outer peripheral surface of the intermediate transfer belt and R2 at the secondary transfer portion are satisfied. The case where the radius of the transfer counter roller 22 is set to 10 mm and 15 mm has been described, but the radius of the lubricant applicator counter roller 24 and the secondary transfer counter roller 22 can be freely selected as long as the relationship of R1 <R2 is satisfied. be able to. When the radius of the secondary transfer counter roller is large, the belt surface of the intermediate transfer belt at the secondary transfer position approaches a flat shape. As a result, the recording material after transfer may stick to the intermediate transfer belt side and cause separation failure. Therefore, in order to suppress the separation failure, it is desirable to set the radius r2 of the secondary transfer counter roller to a certain extent so that the curvature χ2 is larger than zero. More preferably, the radius r2 of the secondary transfer counter roller is 20 mm or less and the curvature χ2 ≧ 1/20> 0. As a result, the curvature X2> 0 of the outer peripheral surface of the intermediate transfer belt at the secondary transfer portion in the region where the secondary transfer counter roller is in contact with the intermediate transfer belt, and separation failure is suppressed.

<Embodiment 2>
The description overlapping with the first embodiment will be omitted. Differences from the first embodiment will be described.

  In the present embodiment, the radius r1 of the lubricant applicator facing roller is set to be not less than the radius r3 of the cleaning device facing roller as the blade facing member. In other words, the curvature χ1 of the lubricant application device facing roller is set to be equal to or less than the curvature χ3 of the cleaning device facing roller. That is, the radius of curvature R1 of the outer peripheral surface of the intermediate transfer belt at the lubricant application portion is set to be greater than or equal to the radius of curvature R3 of the outer peripheral surface of the intermediate transfer belt at the cleaning portion. In other words, the curvature X1 of the outer peripheral surface of the intermediate transfer belt at the lubricant application portion is set to be equal to or less than the curvature X3 of the outer peripheral surface of the intermediate transfer belt at the cleaning portion.

  The reason for this setting will be described below. When the belt surface supplied with the lubricant reaches the cleaning portion, it bends along the curvature of the cleaning device facing roller 22. If the curvature of the cleaning device facing roller 22 is smaller than the curvature of the lubricant applying device facing roller 24, the belt outer peripheral surface contracts at the cleaning portion, so that the cleaning performance of the belt outer peripheral surface may be deteriorated. As a result, the gloss on the outer peripheral surface of the belt may be reduced. Therefore, in this embodiment, the radius r1 of the lubricant application device facing roller is set to be equal to or larger than the radius r3 of the cleaning device facing roller. That is, the relationship between the curvature radius R3 of the outer peripheral surface of the intermediate transfer belt 16 formed by the cleaning device facing roller 23 and the curvature radius R1 of the outer peripheral surface of the intermediate transfer belt 16 formed by the lubricant application device facing roll 24 is R3 ≦ R1 is set. As a result, the area where the lubricant is applied can be improved in advance by the cleaning device 27.

  FIG. 7 shows the relationship between the decrease in gloss and the size ratio of the radius of curvature R1 at the lubricant supply portion of the outer peripheral surface of the intermediate transfer belt and the size of R3 at the cleaning portion. The horizontal axis represents the ratio of the curvature radius R1 of the belt outer peripheral surface at the lubricant application portion to the curvature radius R3 of the belt outer peripheral surface at the cleaning portion. The vertical axis represents the gloss reduction rate of the outer peripheral surface of the intermediate transfer belt at the time when 60,000 sheets are passed. The gloss value was measured and calculated using the same method as in FIG.

  As shown in FIG. 7, the gloss reduction rate increased as the value of R1 decreased with respect to R3. When R1 / R3 was 1 or more, the gloss reduction rate was almost constant. On the other hand, when R1 / R3 is smaller than 1, the gloss reduction rate tends to increase. That is, in order to suppress the gloss reduction rate, it is desirable that R1 / R3 is set to 1 or more.

  Therefore, in this embodiment, R1 / R3 = X3 / X1≈1.5 is set. More specifically, in this embodiment, as shown in FIG. 6, the radius of the cleaning device facing roller 23 that contacts the cleaning device 27 of the intermediate transfer belt 16 via the intermediate transfer belt 16 is set to 15 mm. . That is, the radius of curvature R3 of the surface of the intermediate transfer belt 35 formed by the cleaning device facing roller 23 is R3 = 15 + 0.35 = 15.35 mm. The curvature X3 of the belt outer peripheral surface of the intermediate transfer belt 24 is X3 = 1 / R3 = 1 / 15.35. In response, R1 / R3 = X3 / X1 = 30.35 / 20.35≈1.5.

  FIG. 8 shows the relationship between the gloss reduction rate and the number of formed images in the configuration of the present embodiment. The measurement was performed in the same manner as in FIG.

  There was no deterioration in image quality due to a decrease in gloss on the surface of the intermediate transfer belt 16 which was a concern. In addition, the gloss reduction rate can be made smaller than that of the first embodiment.

  Therefore, according to the present invention, even in a system using an intermediate transfer belt having an elastic layer, a gloss reduction that deteriorates the image quality does not occur, and a high-quality image can be obtained stably stably.

  In the present embodiment, the radii of the lubricant application device facing roller 24 and the cleaning device facing roller 23 are set to 20 mm and 15 mm, respectively, in order to satisfy the relationship of curvature radii R1 and R3 with R3 ≦ R1. That is, the radius of the lubricant application device facing roller 24 is larger than the radius of the cleaning device facing roller 23. In other words, the curvature of the lubricant application device facing roller 24 is smaller than the curvature of the cleaning device facing roller 23. Of course, it is not intended to limit to this value. If the relationship of R3 <R1 is satisfied, the radii of the lubricant application device facing roller 24 and the cleaning device facing roller 23 can be freely selected.

<Embodiment 3>
In this embodiment, the intermediate transfer belt used in Embodiments 1 and 2 is changed to a multilayer structure. In the first and second embodiments, an intermediate transfer belt having a single-layer structure including only an elastic layer is used. However, in a single-layer structure including only an elastic layer, the image cannot be removed by cleaning the elastic layer when image formation is repeated. External additives, paper dust, lubricant, and the like are deposited to induce fusing and filming, and gloss deterioration and transfer efficiency are changed to affect image quality. In order to reduce this, the elastic layer may be coated with a material having high releasability. Therefore, the surface layer of the intermediate transfer belt 16 can be improved by covering the elastic layer with a surface layer having high releasability. In addition, the elastic layer may be deteriorated due to ozone generated during charging or transfer, or fatigue wear may occur due to repeated stretching. As a result, there is also a problem that the elastic characteristics are deteriorated. Therefore, in the present embodiment, the intermediate transfer belt 16 is not an intermediate transfer belt having a single elastic layer, but an intermediate layer having a multilayer structure having an elastic layer as an intermediate layer and having a high releasability. A transfer belt was used. By making the intermediate transfer belt 16 have a multilayer structure having a surface layer and a substrate, it is possible to suppress functional deterioration of the elastic layer due to ozone exposure or the like, and to maintain a high-quality image over a longer period.

  The intermediate transfer belt 16 used in the present embodiment has a cross-sectional configuration as shown in FIG. 9, and has a base 36 molded to 150 μm in thickness made of polyimide resin, and 300 μm in thickness made of urethane rubber on the upper surface thereof. An elastic layer 37 and a surface layer 38 made of a fluororesin and having a thickness of 10 μm were provided. In the present embodiment, a polyimide resin is used as the substrate 36. Other materials may be used.

Further, urethane rubber was used as the elastic layer 37. Other materials may be used. Furthermore, the volume resistivity of the intermediate transfer belt 16 can be appropriately adjusted with a conductive filler such as carbon, ZnO, SnO ₂ and TiO ₂ as necessary. When the thickness is less than 20 μm, the elastic layer 37 cannot sufficiently contract, and the fluctuation of the contact pressure of the photosensitive drums 11Y, 11M, 11C, and 11K with respect to the intermediate transfer belt 16 cannot be sufficiently absorbed. On the other hand, if the thickness exceeds 1000 μm, the intermediate transfer belt 16 does not bend appropriately at the support shaft regardless of the hardness, and the running becomes unstable.

  In the present embodiment, up to 500,000 images are formed in the same manner as in Embodiments 1 and 2, and the output image is confirmed and the intermediate transfer belt 16 after the secondary transfer on the intermediate transfer belt 16 is transferred every 20,000 sheets. As a result of observation, the lubricant is still present on the intermediate transfer belt 16 even after the secondary transfer, and image degradation due to a decrease in gloss on the surface of the intermediate transfer belt 16 that was concerned as shown in FIG. Was not confirmed.

  Therefore, according to the present invention, even in a system using an intermediate transfer belt having an elastic layer, a gloss reduction that deteriorates the image quality does not occur, and a high-quality image can be obtained stably stably.

11Y, 11M, 11C, 11K Photosensitive drum 12Y, 12M, 12C, 12K Charging roller 13Y, 13M, 13C, 13K Exposure device 14Y, 14M, 14C, 14K Developer 15Y, 15M, 15C, 15K Primary transfer roller 16 Intermediate transfer member Belt 17Y, 17M, 17C, 17K Photosensitive drum cleaning device 18Y, 18M, 18C, 18K Toner supply container 19 Concentration detection sensor 20 Toner image after primary transfer 21 Drive roller 22 Secondary transfer counter roller 23 Cleaning device counter roller 24 Lubricant Application device opposing roller 25 Lubricant application device 26 Secondary transfer roller 27 Intermediate transfer belt cleaning device 28 Lubricant 29 Lubricant holding member 30 Lubricant application member 31 Lubricant pressure spring 32 Lubricant scattering prevention sheet 33 Leveling blade 34 Frames roller 35 the intermediate transfer belt 36 base 37 elastic layer 38 surface

Claims (4)

An image carrier for carrying a toner image;
An elastic intermediate transfer belt that is rotatable and has a toner image transferred from the image carrier to an outer peripheral surface;
A secondary transfer outer member disposed on the outer peripheral surface side of the intermediate transfer belt and transferring a toner image from the intermediate transfer belt to a recording material;
A secondary transfer inner member that stretches the intermediate transfer belt from the inner peripheral surface side and faces the secondary transfer outer member via the intermediate transfer belt;
A blade provided on the downstream side of the secondary transfer inner member in the rotational direction in which the intermediate transfer belt rotates, and for cleaning the intermediate transfer belt;
Supply means for supplying a lubricant to the intermediate transfer belt;
An image forming apparatus comprising: a supply means facing member that stretches the intermediate transfer belt at a position facing the supply means via the intermediate transfer belt.
2. An image forming apparatus according to claim 1, wherein a curvature of the supply means facing member in a region in contact with the intermediate transfer belt is larger than a curvature in a region of the secondary transfer inner member in contact with the intermediate transfer belt. A blade facing member that stretches the intermediate transfer belt at a position facing the blade via the intermediate transfer belt;
The image forming apparatus according to claim 1, wherein a curvature of the supply unit facing member is equal to or less than a curvature of the blade facing member.   3. The image forming apparatus according to claim 1, wherein the supply unit facing member is a roller. 4. The image forming apparatus according to claim 1, wherein a curvature of a region of the secondary transfer inner member in contact with the intermediate transfer belt is greater than zero. 5.

Images