JP2017161918A - Transfer belt unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer belt unit that can suppress the generation of image defects, such as drop out without reducing performance of cleaning performed by a cleaning blade, and an image forming apparatus.SOLUTION: A transfer belt unit 20 comprises: a transfer belt 3 that is formed of a single resin layer and includes an inner peripheral surface and an outer peripheral surface; and a cleaning mechanism 7 that cleans the transfer belt 3. The average diameter of cavities in an area including the cavities on the outer peripheral surface side is smaller than the average diameter of cavities in the center area in the thickness direction of the transfer belt; the average diameter of cavities in an area including the cavities on the inner peripheral surface side with respect to the center area is smaller than the average diameter of cavities in the center area of the transfer belt.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a transfer belt unit using a transfer belt and an image forming apparatus using the transfer belt unit.

  In general, for example, an image forming apparatus using an electrophotographic method includes a transfer belt. In the case of the intermediate transfer method, the developer image formed on the surface of the image carrier is transferred (primary transfer) to a transfer belt, and further transferred (secondary transfer) to a recording medium (for example, printing paper). In the case of the direct transfer method, the developer image formed on the surface of the image carrier is transferred to a recording medium on a transfer belt.

  As a transfer belt, a transfer belt made of a single resin layer such as polyimide (PI) or polyamideimide (PAI) is known.

  However, a transfer belt formed of polyimide or polyamideimide has a high elastic modulus. Therefore, in the step of transferring the developer image of the image carrier to the transfer belt (in the case of the intermediate transfer method) or the step of transferring to the recording medium on the transfer belt (in the case of the direct transfer method), the image carrier and the transfer belt The developer is subjected to a high pressure by the pressing pressure.

  In particular, in the central portion of fine lines (characters, etc.) where the developer is densely packed, the pressure tends to concentrate on the developer as compared with the contour portion, so that plastic deformation may occur in the developer particles (toner particles). . When plastic deformation occurs in the developer particles, the adhesion to the image bearing member becomes strong, and transfer to the transfer belt becomes difficult. As a result, there is a case where a so-called “middle defect” image defect occurs in which a low-density portion occurs at the center of the thin line.

  In order to prevent such hollowing out, a transfer belt having a multilayer structure in which an elastic layer is provided on the surface of the belt base material, and irregularities are formed on the surface by adding a filler to the elastic layer has been proposed (for example, patents). Reference 1).

JP 2013-25274 A (paragraph 0022, FIG. 2)

  On the other hand, conventionally, a cleaning method has been widely used in which a developer (residual toner) remaining on the surface of a transfer belt is scraped off with a cleaning blade. Since blade cleaning is inexpensive and can be performed in parallel with image formation, it is useful as a cleaning method that can cope with high-speed image formation.

  However, as described above, in the transfer belt having irregularities formed on the surface to roughen the surface roughness, it is difficult to efficiently remove the developer remaining on the surface of the transfer belt with a cleaning blade. Therefore, there is a demand for a belt that can suppress the occurrence of image defects such as hollows without deteriorating the cleaning performance of the cleaning blade.

  The transfer belt unit according to the present invention includes a transfer belt formed of a single resin layer and having an inner peripheral surface and an outer peripheral surface, and a cleaning mechanism for cleaning the transfer belt. Compared to the average diameter of the cavities in the central region in the thickness direction of the transfer belt, the average diameter of the cavities in the region having the cavities on the outer peripheral surface side is smaller than that in the central region, and the average diameter of the cavities in the central region of the transfer belt In comparison, the average diameter of the cavities in the region having cavities on the inner peripheral surface side than the central region is smaller.

  According to the present invention, since the average diameter of the cavities in the area having the cavities on the outer peripheral surface side and the inner peripheral surface side is smaller than the average diameter of the cavities in the central area of the transfer belt, the pressure applied to the developer is dispersed. Thus, the occurrence of image defects can be suppressed, and the deterioration of the cleaning performance due to the cleaning belt can be suppressed.

1 is a diagram illustrating a basic configuration of an image forming apparatus including a transfer belt according to a first embodiment of the present invention. It is a figure which shows the structure which cleans the transfer belt in 1st Embodiment. FIG. 3 is a perspective view showing the transfer belt in the first embodiment taken out from the image forming apparatus. It is a figure which shows the cross-section of the transfer belt in 1st Embodiment. FIG. 3 is an enlarged view showing an example of a shape of a cavity of a transfer belt in the first embodiment. It is a figure which shows the other example of the cross-section of the transfer belt in 1st Embodiment. FIG. 3 is a diagram illustrating a cross-sectional structure of a general intermediate transfer belt. It is a schematic diagram for demonstrating the measuring method of the mirror surface degree of a transfer belt. It is a figure which shows the pattern projection plate used for the measurement of the mirror surface degree of a transfer belt. It is a figure which shows the signal waveform used for the measurement of the mirror surface degree of a transfer belt. It is a schematic diagram for demonstrating an example of the manufacturing method of the transfer belt in 1st Embodiment. It is a figure which shows the magnitude | size and occupation rate of the cavity of the transfer belt of Experimental Examples 1-7. It is a figure which shows the evaluation results, such as hollow out, durability, and slipping, using the transfer belt of Experimental Examples 1-7. It is a figure which shows the example of the void of the image formed on the transfer belt, and the void rate.

  Embodiments of the present invention will be described below with reference to the drawings.

<Configuration of image forming apparatus>
FIG. 1 is a diagram showing a basic configuration of an image forming apparatus 1 provided with a transfer belt (intermediate transfer belt) 3 according to the first embodiment of the present invention. The image forming apparatus 1 forms an image using four types of developers of black, yellow, magenta, and cyan by electrophotography. Here, an intermediate transfer method is used as the transfer method.

  The image forming apparatus 1 according to the present embodiment includes four image drum units (hereinafter referred to as ID units) 10K, 10Y, 10M, and 10C as image forming units. The ID units 10K, 10Y, 10M, and 10C are arranged in a line from the right to the left in the drawing along the traveling direction of the transfer belt 3 (described later).

  LED (light emitting diode) heads 13K, 13Y, 13M, and 13C as exposure means are disposed so as to face the ID units 10K, 10Y, 10M, and 10C. The LED heads 13K, 13Y, 13M, and 13C irradiate the photosensitive drums 11 of the ID units 10K, 10Y, 10M, and 10C with light, thereby electrostatic latent images corresponding to black, yellow, magenta, and cyan image data. It forms an image.

  Since the ID units 10K, 10Y, 10M, and 10C have a common configuration except for the developer to be used, they will be collectively referred to as “ID unit 10”. The LED heads 13K, 13Y, 13M, and 13C will be collectively referred to as “LED head 13”.

  The ID unit 10 includes a photosensitive drum 11 as an image carrier, a charging roller 12 as a charging member, a developing unit 14 as a developing unit, and a drum cleaning unit 15.

  For example, the photosensitive drum 11 is obtained by laminating a photosensitive layer (a charge generation layer and a charge transport layer) on the surface of a cylindrical conductive support. The photosensitive drum 11 is rotationally driven in the clockwise direction in the drawing.

  The charging roller 12 is disposed so as to come into contact with the surface of the photosensitive drum 11 and rotates following the rotation of the photosensitive drum 11. A charging voltage is applied to the charging roller 12 to uniformly charge the surface of the photosensitive drum 11.

  The uniformly charged surface of the photosensitive drum 11 is exposed by the LED head 13, so that an electrostatic latent image is formed on the surface of the photosensitive drum 11.

  The developing unit 14 includes a developing roller 14a (developer carrying member) that rotates in contact with the surface of the photosensitive drum 11, and a developer holding portion 14b that holds the developer. A developing voltage is applied to the developing roller 14a. The developing roller 14a attaches a developer to the electrostatic latent image on the surface of the photosensitive drum 11 to form a developer image (toner image).

  Here, the developer is a one-component developer made of toner, but may be a two-component developer made of toner and carrier. The developer image formed on the surface of the photosensitive drum 11 is primarily transferred to the transfer belt 3 as described below.

  The drum cleaning unit 15 removes residual developer remaining on the surface of the photosensitive drum 11 after the primary transfer.

  A transfer belt unit 20 including the transfer belt 3 is provided so as to face the lower side of the ID units 10K, 10Y, 10M, and 10C. The transfer belt 3 is a seamless belt (seamless belt), and the outer peripheral surface thereof is in contact with the photosensitive drums 11 of the ID units 10K, 10Y, 10M, and 10C.

  On the inner peripheral side of the transfer belt 3, primary transfer rollers 21 </ b> K, 21 </ b> Y, 21 </ b> M, 21 </ b> C, a belt driving roller 22, a secondary transfer backup roller 23, and a driven roller 26 are disposed.

  The primary transfer rollers 21K, 21Y, 21M, and 21C face the photoconductive drums 11 of the ID units 10K, 10Y, 10M, and 10C with the transfer belt 3 interposed therebetween. The primary transfer rollers 21K, 21Y, 21M, and 21C have a configuration in which a foamed elastic layer (for example, foamed rubber) is provided around a metal shaft, for example. A primary transfer voltage is applied to the primary transfer rollers 21 </ b> K, 21 </ b> Y, 21 </ b> M, and 21 </ b> C, and a developer image (toner image) on each photosensitive drum 11 is primarily transferred to the transfer belt 3.

  The belt drive roller 22 is rotationally driven by a belt drive motor. As the belt driving roller 22 rotates, the transfer belt 3 travels (circulates) in the direction indicated by the arrow A. The driven roller 26 is for applying tension to the transfer belt 3. The primary transfer rollers 21K, 21Y, 21M, 21C, the secondary transfer backup roller 23, and the driven roller 26 rotate following the movement of the transfer belt 3.

  A secondary transfer roller 24 is disposed on the outer peripheral side of the transfer belt 3 so as to sandwich the transfer belt 3 with the secondary transfer backup roller 23. A secondary transfer voltage is applied to the secondary transfer roller 24. The secondary transfer backup roller 23 and the secondary transfer roller 24 form a secondary transfer portion 25 that transfers the developer image from the transfer belt 3 to the recording medium 8.

  A cleaning blade 7 is arranged on the outer peripheral side of the transfer belt 3 so as to sandwich the transfer belt 3 with the driven roller 26. The cleaning blade 7 scrapes and removes the developer (residual toner) remaining on the surface of the transfer belt 3 after the secondary transfer.

  These transfer belt 3, primary transfer rollers 21 K, 21 Y, 21 M, and 21 C, drive roller 22, secondary transfer unit 25 (secondary transfer backup roller 23 and secondary transfer roller 24), and cleaning blade 7 The transfer belt unit 20 is configured.

  The image forming apparatus 1 also includes a medium supply unit 5 that accommodates a plurality of recording media (for example, printing paper) 8 and conveys the recording media one by one toward the secondary transfer unit 25. The medium supply unit 5 pulls out the recording media 8 one by one from the paper feed cassette 51 (medium storage unit) that stores the recording media 8 in a stacked state, and conveys the recording media 8 toward the secondary transfer unit 25. A paper feed roller 52 (medium supply unit).

  The image forming apparatus 1 also includes a fixing unit 6 that fixes the developer image transferred to the recording medium 8 by the secondary transfer unit 25 to the recording medium 8 by heat and pressure. The fixing unit 6 includes a heating roller 61 and a pressure roller 62. The heating roller 61 has a heating element such as a halogen lamp inside, and heats the recording medium 8. The pressure roller 62 presses the recording medium 8 with the heating roller 61. Further, the image forming apparatus 1 is provided with a medium discharge unit 9 for discharging the recording medium 8 on which the developer image is fixed by the fixing unit 6.

<Basic operation of image forming apparatus>
When receiving a print instruction and image data from an external computer or the like, the image forming apparatus 1 performs an image forming operation as follows. That is, the photosensitive drum 11 and the belt driving roller 22 of each ID unit 10 (10K, 10Y, 10M, 10C) are rotated to apply voltages (charging voltage and developing voltage) to the charging roller 12 and the developing roller 14a, respectively.

  When the photosensitive drum 11 rotates, the developing roller 14 a rotates due to the rotation transmission from the photosensitive drum 11. Further, the charging roller 12 rotates following the rotation of the photosensitive drum 11. Further, the transfer belt 3 travels by the rotation of the belt driving roller 22, and the primary transfer rollers 21 </ b> K, 21 </ b> Y, 21 </ b> M, 21 </ b> C, the secondary transfer backup roller 23, and the secondary transfer roller follow the travel of the transfer belt 3. 24 and the driven roller 26 rotate.

  The charging roller 12 uniformly charges the surface of the photosensitive drum 11. Subsequently, the LED head 13 exposes the uniformly charged surface of the photosensitive drum 11 based on the image data of each color to form an electrostatic latent image. Further, the developing roller 14a of the developing unit 14 attaches the developer to the electrostatic latent image on the surface of the photosensitive drum 11 to form a developer image.

  A primary transfer voltage is applied to the primary transfer rollers 21 (21K, 21Y, 21M, and 21C), and a developer image (toner image) on each photosensitive drum 11 is transferred to the transfer belt 3 (primary transfer). To do. As a result, black, yellow, magenta, and cyan developer images formed by the ID units 10K, 10Y, 10M, and 10C are sequentially transferred onto the transfer belt 3.

  The paper feed roller 52 rotates in synchronization with the timing at which the developer image on the transfer belt 3 reaches the secondary transfer unit 25, and the recording medium 8 is pulled out from the paper feed cassette 51 and conveyed to the secondary transfer unit 25.

  A secondary transfer voltage is applied to the secondary transfer roller 24 of the secondary transfer unit 25. As a result, the developer image on the transfer belt 3 is transferred (secondary transfer) to the recording medium 8 that passes through the secondary transfer portion 25. The recording medium 8 that has passed through the secondary transfer unit 25 is sent to the fixing unit 6.

  In the fixing unit 6, the heating roller 61 and the pressure roller 62 apply heat and pressure to the recording medium 8 to fix the developer image on the recording medium 8. The recording medium 8 on which the developer is fixed by the fixing unit 6 is discharged to the medium discharge unit 9.

<Transfer belt cleaning mechanism>
Next, a cleaning mechanism for cleaning the surface of the transfer belt 3 will be described. The cleaning blade 7 described above is disposed on the downstream side of the secondary transfer portion 25 in the traveling direction of the transfer belt 3 (arrow A). The cleaning blade 7 is disposed so as to sandwich the transfer belt 3 with the driven roller 26.

  FIG. 2 is a diagram illustrating a configuration for cleaning the surface of the transfer belt 3. The cleaning blade 7 is arranged so that its longitudinal direction is parallel to the width direction of the transfer belt 3. The tip 7 a of the cleaning blade 7 is in contact with the surface (outer peripheral surface) of the transfer belt 3.

  The cleaning blade 7 is preferably formed of an elastic material having a rubber hardness in the range of 65 to 100 ° (JIS-A), for example. Here, urethane rubber having a rubber hardness of 78 ° (JIS-A) and a plate thickness of 2.0 mm is used. The cleaning blade 7 is fixed to the main body of the image forming apparatus 1 by a support member 71.

  The method using the cleaning blade 7 made of an elastic material (blade method) is excellent in the function of removing residual developer and foreign matters, and further has an advantage that the configuration is simple, compact, and low in cost. As the elastic material, the above urethane rubber is preferable in that it has high hardness and high elasticity and is excellent in wear resistance, mechanical strength, oil resistance, ozone resistance, and the like.

  The linear pressure (pressing pressure) of the cleaning blade 7 against the transfer belt 3 is preferably 1 to 6 g / mm, and more preferably 2 to 5 g / mm. If the linear pressure is too small, the adhesion between the cleaning blade 7 and the transfer belt 3 is insufficient, which causes a cleaning failure. On the other hand, if the linear pressure is too large, the cleaning blade 7 and the transfer belt 3 come into surface contact with each other, and the frictional resistance increases. Therefore, the cause of troubles such as a crease (deformation of the tip 7a) of the cleaning blade 7 is caused. It becomes. Here, the linear pressure is set to 4.3 g / mm.

  The contact angle θ between the cleaning blade 7 and the transfer belt 3 is preferably 20 ° to 30 °, more preferably 20 ° to 25 °. Here, the cleaning blade 7 is installed so that the contact angle θ is 21 °. The contact angle θ is an angle formed between the cleaning blade 7 and a tangential direction (indicated by an arrow H in FIG. 2) at the contact point between the tip 7a of the cleaning blade 7 and the outer peripheral surface of the transfer belt 3. It is.

  In the example shown in FIG. 2, the cleaning blade 7 is in contact with the curved portion of the transfer belt 3 that is in contact with the driven roller 26. However, the present invention is not limited to this configuration. For example, the cleaning blade 7 may be brought into contact with the horizontal belt surface (plane) of the transfer belt 3.

<Configuration of transfer belt>
Next, the configuration of the transfer belt 3 will be described.
FIG. 3 is a schematic diagram showing the transfer belt 3 taken out from the transfer belt unit 20. The transfer belt 3 has an inner diameter d of, for example, 254 mm and a width (length in the axial direction) W of 350 mm. The thickness T of the transfer belt 3 is preferably 60 μm or more and 200 μm or less. Considering the stress and flexibility applied to the end of the transfer belt 3 during driving, it is more preferably 60 μm or more and 150 μm or less. Here, the thickness T of the transfer belt 3 is 80 μm.

  From the viewpoint of durability and mechanical characteristics, it is preferable that the transfer belt 3 has an elastic deformation amount due to a tension during travel of a predetermined amount or less. Therefore, the Young's modulus of the transfer belt 3 is preferably 2000 Mpa or more, and more preferably 3000 Mpa or more.

  Here, the transfer belt 3 is made of polyamideimide (PAI). In addition, carbon black is added to the polyamide-imide for conductivity.

  FIG. 4 is a diagram showing a cross-sectional structure of the transfer belt 3. The transfer belt 3 is formed of a single resin layer and has a large number of voids 30 therein. In particular, a large number of cavities 30 are formed inside the transfer belt 3 in the thickness direction. On the other hand, the cavity 30 is not formed in the vicinity of the outer peripheral surface 3 </ b> A and the inner peripheral surface 3 </ b> B of the transfer belt 3, or the size of the cavity 30 is smaller than the inside of the transfer belt 3.

  By forming a large number of cavities 30 inside the transfer belt 3 in this way, the pressure applied to the developer is dispersed between the photosensitive drum 11 and the transfer belt 3, and the occurrence of image defects such as voids is suppressed. doing. Further, by not forming the cavity 30 in the vicinity of the surface of the transfer belt 3, the surface of the transfer belt 3 is smoothed and the cleaning performance by the cleaning blade 7 is ensured.

  In other words, the transfer belt 3 has a first layer portion 3C in which the cavity 30 is not formed in the vicinity of the outer peripheral surface 3A and the inner peripheral surface 3B, and in the center of the transfer belt 3 in the thickness direction, It has the 2nd layer part 3D in which many cavities 30 were formed. A single-layer transfer belt 3 is formed by the first layer portion 3C and the second layer portion 3D.

<Cavity size>
Next, the size of the cavity 30 of the transfer belt 3 will be described.
For measurement of the size of the cavity 30, an “electron microscope S-2380N type” manufactured by Hitachi, Ltd., which is a scanning electron microscope (SEM), was used. After performing carbon deposition for 60 seconds on the cut section of the transfer belt 3, the acceleration voltage was set to 15 KV, and observation was performed at a magnification of 3000 times.

  In the cross section of the transfer belt 3 (thickness 80 μm) observed with the SEM, a position P1 (first position) 10 μm from the outer peripheral surface 3A and a position P2 (second position) 40 μm from the outer peripheral surface 3A. The size of the cavity 30 existing in the unit area (10 μm × 10 μm) was measured.

  At this time, as shown in FIG. 5A, when the shape of the cavity 30 in the cross section of the transfer belt 3 is a perfect circle, the diameter of the circle is the size D of the cavity 30. As shown in FIG. 5B, when the shape of the cavity 30 is an ellipse, the length of the major axis of the ellipse is the size D of the cavity 30.

  The size of the cavity 30 was measured at three positions P1 and P2, and the average value at each position was determined. The average value of the measurement results at the positions P1 and P2 is the size of the cavity of the transfer belt 3.

  The size (D) of the cavity 30 in the cross section of the transfer belt 3 is preferably 0.5 μm or more and 5 μm or less. This is because if the size of the cavity 30 is larger than 5 μm, the wear resistance and crack resistance of the transfer belt 3 may be lowered and the life may be shortened. Further, when the size of the cavity 30 is smaller than 0.5 μm, the effect of dispersing the pressure applied to the developer becomes insufficient, and image defects such as voids cannot be sufficiently suppressed.

  Further, the cavity 30 of the transfer belt 3 is preferably large at the central portion in the thickness direction and becomes smaller as it goes toward the outer peripheral surface 3A and the inner peripheral surface 3B. When a large cavity is formed in the vicinity (surface layer) of the outer peripheral surface 3A and the inner peripheral surface 3B of the transfer belt 3, the cavity is exposed to the outer peripheral surface 3A and the inner peripheral surface 3B and becomes an opening, and the surface roughness can be roughened. This is because the cleaning performance of the cleaning blade 7 is deteriorated.

  More specifically, the size A of the cavity 30 existing at a position P1 of 10 μm in the thickness direction from the outer peripheral surface 3A and the inner peripheral surface 3B of the transfer belt 3 and a distance of 40 μm (1/2 of the thickness T). The size B of the cavity 30 present at the position P2 is preferably in a relationship of A <B. As a result, even if an opening derived from the cavity 30 is generated in the outer peripheral surface 3A and the inner peripheral surface 3B, the size of the void can be 1 μm or less, and the mirror surface degree (described later) is 60 or more smooth. A smooth surface can be formed.

  The configuration of the transfer belt 3 is not limited to the configuration shown in FIG. For example, as shown in FIG. 6, the relatively large (preferably 5 μm or less) cavities 30 may be distributed substantially evenly in the portion excluding the outer peripheral surface 3A and the inner peripheral surface 3B of the transfer belt 3.

  FIG. 7 is a diagram showing a cross-sectional structure of a general transfer belt 3G. As shown in FIG. 7, the general transfer belt 3G is not formed with the cavity 30 like the transfer belt 3 of this embodiment (see FIGS. 4 and 6).

<Cavity occupancy>
Next, the occupation ratio of the cavity 30 will be described.
In the cross section of the transfer belt 3 observed with the SEM (see FIG. 4), the area fraction of the cavity 30 in a unit area (10 μm × 10 μm) was determined, and this was used as the occupation ratio of the cavity. Specifically, the image of the cross section of the transfer belt 3 observed with the SEM was binarized, and the cavities and other portions were sorted into black and white. Then, the occupation ratio of the cavity cross-sectional area per unit area (10 μm × 10 μm) was calculated using image processing software “Image-J”.

  The measurement of the occupied area was performed at three locations at a position P1 of 10 μm from the outer peripheral surface 3A of the transfer belt 3 and at three locations at a position P2 of 40 μm from the outer peripheral surface 3A. The average value of the occupation areas at the six locations was defined as the occupation ratio of the cavities 30 of the transfer belt 3.

  The area occupation ratio of the cavity in the cross section of the transfer belt 3 is preferably 3.0% or more and 20% or less. This is because if the occupancy ratio of the cavities 30 is less than 3.0%, the effect of dispersing the pressure applied to the developer is insufficient, and image defects such as voids cannot be sufficiently suppressed. Further, when the occupation ratio of the cavity 30 is larger than 20%, the strength of the transfer belt 3 is lowered and becomes brittle, and it becomes difficult to stably run the transfer belt 3 over a long period of time.

<Specularity>
Next, the specularity of the surface (outer peripheral surfaces 3A and 3B) of the transfer belt 3 will be described.
The specularity is an index that quantitatively represents the surface properties, and is measured by an imaging pattern evaluation method. Further, since the specularity measuring device does not contact the surface of the object to be measured with the stylus unlike the stylus roughness measuring device, the measurement can be performed without damaging the surface of the transfer belt 3. Moreover, since it has a wide measuring range of 200 mm ^{2 as} compared with a stylus type roughness measuring apparatus having a measuring range of several mm, it is useful as a method for evaluating surface properties.

  The specularity of the surface of the transfer belt 3 was measured using a specularity meter “SPOT AHS-100S” manufactured by Arc Harima Co., Ltd. (see Japanese Patent Application Laid-Open No. 2007-225969).

  FIG. 8 is a schematic diagram for explaining a method for measuring the specularity of the transfer belt 3. As shown in FIG. 8, the specularity measuring apparatus 200 includes a pattern projection apparatus 201, a photoelectric conversion element 202, and a signal processing apparatus 203.

  The pattern projection apparatus 201 is provided with a light source 210 and a pattern projection plate 211. As shown in FIG. 9, the pattern projection plate 211 is a stainless steel plate having a thickness of 0.5 mm in which a plurality of openings 211a having a width of 1 mm are arranged in a line. The surface of the pattern projection plate 211 is matte so as not to reflect light. The pattern projection apparatus 201 irradiates the object surface 215 with light at an angle θ. The angle θ can be arbitrarily changed depending on the type of the object to be measured and the measuring method, but here it is 45 °.

  The photoelectric conversion element 202 is held so that its optical axis is on the same plane as the optical axis of the pattern projection device 201 and has an angle of (180-2θ) degrees. For example, the photoelectric conversion element 202 is configured by a CCD array in which a large number of light receiving portions are arranged linearly (one-dimensionally) or two-dimensionally. The photoelectric conversion element 202 captures an image of the pattern projected on the surface 215 to be measured, converts the intensity of the reflected light into an electric signal, and transmits the converted electric signal (intensity signal) to the signal processing device 203.

  The signal processing device 203 includes a receiving unit 205 that receives an electrical signal from the photoelectric conversion element 202, an A / D conversion unit 206 that performs A / D conversion on the received electrical signal, and a digital signal converted by the A / D conversion unit 206. Are subjected to waveform processing, a maximum value (Max) and a minimum value (Min) are selected, a data analysis unit 207 as specularity calculation means for calculating the specularity, and a display unit 208 for displaying the analysis result.

  A parallel light beam is irradiated from the light source 210 onto the pattern projection plate 211 to project a light / dark pattern of light onto the surface 215 of the object to be measured. The light and dark pattern projected on the surface 215 to be measured is imaged by the photoelectric conversion element 202, the intensity of the reflected light is converted into an electric signal, and transmitted to the signal processing device 203. The intensity signal input to the signal processing device 203 is A / D converted by the A / D conversion unit 206 of the signal processing device 203. FIG. 10 is a graph showing the A / D converted data at this time.

  The data analysis unit 207 has an average Max (Ave.) of the maximum values Max (1), Max (2)... Max (n) of the signal waveform A / D converted by the A / D conversion unit 206, and a minimum. The average Min (Ave.) Of the values Min (1), Min (2)... Min (n) is obtained by the following equations, respectively.

Max (Ave.) = ΣMax (n) / n
Min (Ave.) = ΣMin (n) / n

  From the thus obtained Max (Ave.) and Min (Ave.), the specularity of the surface of the object to be measured is obtained by the following equation (1).

  Specularity = [{Max (Ave.) − Min (Ave.)} / {Max (Ave.) + Min (Ave.)}] × 1000 (1)

  The specularity obtained in this way indicates that the surface property is better (ie, smoother) as the specularity is higher than the standard ideal surface specularity of 1000, and the smaller the specularity is, the rougher the surface is. It means that there is.

  The outer peripheral surface 3A of the transfer belt 3 preferably has a mirror surface degree of 60 or more and 200 or less. The specularity of the outer peripheral surface 3A of the transfer belt 3 affects the scraping performance of residual developer (residual toner) by the cleaning blade 7 shown in FIG. 2, that is, the cleaning performance. This is because when the specularity is less than 60, the residual developer may slip through between the transfer belt 3 and the cleaning blade 7. Further, when the mirror surface degree is larger than 200, the contact area between the transfer belt 3 and the cleaning blade 7 increases, so that the frictional force between the two increases, and the cleaning blade 7 is likely to be peeled off.

  Therefore, in the present embodiment, the residual developer can be efficiently scraped off by setting the mirror surface degree of the outer peripheral surface 3A of the transfer belt 3 within the range of 60 to 200. Here, the specularity is in the range of 120 ± 10.

  The inner peripheral surface 3B of the transfer belt 3 does not contact the cleaning blade 7, but contacts the primary transfer rollers 21K, 21Y, 21M, and 21C, the belt driving roller 22, the secondary transfer backup roller 23, and the driven roller 26. To do. Therefore, the inner peripheral surface 3B of the transfer belt 3 is also configured to have the same mirror surface degree as the outer peripheral surface 3A of the transfer belt 3.

<Coefficient of static friction>
Next, the coefficient of static friction on the surface of the transfer belt 3 will be described.
In the present embodiment, an appropriate amount of a fluorine-based or silicone-based water repellent (for example, fluorocarbon) is added to the resin constituting the transfer belt 3 (here, polyamideimide), so that the surface of the transfer belt 3 (the outer peripheral surface 3A and The static friction coefficient μs of the inner peripheral surface 3B) is adjusted.

  Specifically, the static friction coefficient μs of the outer peripheral surface 3A of the transfer belt 3 is set to 0.1 or more and 1.0 or less. This is because if the static friction coefficient μs is smaller than 0.1, the cleaning action by the cleaning blade 7 is not sufficiently exhibited. On the other hand, if the static friction coefficient μs is larger than 1.0, the friction between the transfer belt 3 and the cleaning blade 7 increases, and abnormal noise may occur or the cleaning blade 7 may be scraped. is there.

  However, if the additive is added excessively, a phenomenon that the additive floats on the surface of the transfer belt 3 (bleed-out phenomenon) occurs with the passage of time, and the lifted additive adheres to the photosensitive drum 11 to cause image defects. Cause it to cause. Therefore, the static friction coefficient μs is set in the above range (0.1 to 1.0) while paying attention to the amount of additive added.

  The inner peripheral surface 3B of the transfer belt 3 is also configured to have a static friction coefficient μs similar to that of the outer peripheral surface 3A. As described above, the inner peripheral surface 3B of the transfer belt 3 does not contact the cleaning blade 7, but the primary transfer rollers 21K, 21Y, 21M, and 21C, the belt driving roller 22, the secondary transfer backup roller 23, and the driven roller 26. This is to make contact.

<Transfer belt manufacturing method>
Next, an example of a method for manufacturing the transfer belt 3 in the present embodiment will be described. In addition, the manufacturing method of the transfer belt 3 in this Embodiment is not limited to the example shown below.

  The transfer belt 3 was formed of polyamideimide (hereinafter referred to as PAI) as described above. Polyamideimide was mixed with an appropriate amount of carbon black to develop conductivity, and dispersed in an N-methylpyrrolidone (hereinafter, NMP) solution to produce a material solution. Dispersion was performed using a ball mill.

  FIG. 11 is a schematic diagram illustrating an example of a method for manufacturing the transfer belt 3. Here, a cylindrical mold 101 arranged so that the axial direction is horizontal, a dispenser 102 for dropping a material liquid on the outer peripheral surface of the mold 101, and a material liquid dropped on the outer peripheral surface of the mold 101 A heater 103 for heating and a firing furnace are used.

  The material liquid in which polyamideimide is dispersed in NMP as described above is discharged from the nozzle of the dispenser 102 and dropped (spin coated) on the surface of the rotating mold 101. In FIG. 11, the dispenser 102 is shown dropping the material liquid while moving in the axial direction of the mold 101, but a large number of dispensers 102 may be arranged in the axial direction of the mold 101.

  The dropping of the material liquid from the dispenser 102 to the mold 101 and the heating by the heater 103 (drying of the material liquid) are performed in parallel. The heating temperature is preferably, for example, 180 to 230 ° C. The heat of the heater 103 vaporizes the NMP of the resin material dropped on the mold 101, and a layer portion made of resin is formed on the surface of the mold 101.

  When the mold 101 rotates once, a layer portion 31 having a predetermined thickness is formed on the surface of the mold 101. Here, the mold 101 is rotated a plurality of times, and the layer portions 31 are sequentially laminated on the surface of the mold 101 to form the single-layer transfer belt 3.

  At this time, the size and quantity of the cavities 30 in the transfer belt 3 can be controlled by adjusting the discharge pressure of the material liquid by the dispenser 102 and the heating temperature by the heater 103.

  That is, when forming the layer portion (the first layer portion 3C shown in FIG. 4) near the outer peripheral surface 3A and the inner peripheral surface 3B of the transfer belt 3, the cavity 30 does not exist or the cavity 30 The discharge pressure of the material liquid by the dispenser 102 and the heating temperature by the heater 103 are adjusted so that the size is reduced. Further, when the layer portion (second layer portion 3D shown in FIG. 4) inside the transfer belt 3 is formed, a large number of cavities 30 exist and the size of the cavities 30 is increased by the dispenser 102. The discharge pressure of the material liquid and the heating temperature of the heater 103 are adjusted.

  As a result, it is possible to realize a configuration in which a cavity exists inside the transfer belt 3 and no irregularities appear on the surfaces (the outer peripheral surface 3A and the inner peripheral surface 3B). Even if the transfer belt 3 is formed by laminating a plurality of layer portions as described above, it can be called a “single layer” because all the layers are made of the same material.

  Further, for example, a large cavity exists in the central portion of the transfer belt 3 in the thickness direction, a slightly small cavity exists in the outer region, and is in the vicinity of the surface (the outer peripheral surface 3A and the inner peripheral surface 3B). It is also possible to provide such a distribution that there are almost no cavities.

  By dropping the material liquid from the dispenser 102 onto the surface of the rotating mold 101 as described above, the surface of the transfer belt 3 (the outer peripheral surface 3A and the inner peripheral surface 3B) can be leveled.

  When a plurality of layer portions 31 are laminated on the surface of the mold 101 and the entire thickness (resin layer) reaches a predetermined thickness, the resin layer is removed from the mold 101. Thereafter, the resin layer is put into a baking furnace and heated to a predetermined curing temperature (for example, 250 ° C.). As a result, a seamless belt having an inner diameter d (see FIG. 2) of 254 mm is created. The transfer belt 3 is created by cutting the seamless belt into a predetermined axial length (here, 350 mm).

  The thickness T of the transfer belt 3 is adjusted by the dropping amount of the material liquid from the dispenser 102 or the like. As described above, the thickness T of the transfer belt 3 is preferably 60 μm or more and 200 μm or less (more preferably 60 μm or more and 150 μm or less), and is 80 μm here.

  As is generally known, polyamideimide (PAI) is a polymer in which an imide group and an amide group are bonded via an aromatic ring and polymerized using this as a repeating unit. This polyamideimide is a generally known production method, for example, a method in which an aromatic tricarboxylic acid-anhydride and a diamine are polycondensed and imidized at high temperature in an organic solvent, or an aromatic tricarboxylic acid-anhydride It can be produced by a method of polycondensation and imidization with diisocyanate in an organic solvent at high temperature.

  The mechanical properties of the transfer belt 3 depend on the structure of the imide side chain, the addition amount of a conductive agent such as carbon black, or the molecular weight. By adjusting the reactants and the heating temperature (molding temperature), the transfer belt 3 having different mechanical properties can be produced.

  Here, as shown in FIG. 11, the transfer belt 3 having a single layer is formed by laminating the layer portion 31 on the surface of the mold 101. However, if a resin material in which cavities are easily formed is selected, a resin layer having a smooth surface and having cavities only in the interior can be formed in one step.

  The resin material is not limited to polyamideimide (PAI) and may be formed of other resins. For example, polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyvinylidene fluoride (PVDF), polyamide (PA), polycarbonate (PC), polybutylene terephthalate ( PBT) or a resin obtained by mixing a plurality of these resins.

  The solvent for dispersing the resin material is determined according to the type of the resin material, but an aprotic polar solvent is preferable. In particular, in addition to the above-mentioned NMP, N, N-dimethylacetamide, N, N-diethylformamide, N, N-dimethylsulfoxide, pyridine, tetramethylenesulfone, dimethyltetramethylenesulfone and the like can be mentioned. These may be used alone or as a mixed solvent.

  Examples of the carbon black used as the conductive agent include furnace black, channel black, ketjen black, and acetylene black. These can be used alone or in combination with a plurality of types of carbon black. good.

  The type of these carbon blacks can be appropriately selected depending on the intended conductivity. However, the transfer belt 3 used in the image forming apparatus of the present embodiment has channel black, Furnace black is preferred. Moreover, you may use what improved the dispersibility to a solvent, what prevented oxidation deterioration, such as an oxidation process and a kraft process, according to a use.

  The carbon black content of the transfer belt 3 used in the present embodiment is preferably 3 to 40% by weight, more preferably 3 to 30% by weight, based on the resin solid content, due to its mechanical strength and the like. The means for adding conductivity is not limited to an electronic conduction method using carbon black or the like, and a predetermined conductivity may be imparted by adding an ion conducting agent.

The volume resistivity pv of the transfer belt 3 prepared by the above method is preferably 10 ⁶ or more and 10 ¹⁴ Ω · cm or less, more preferably 10 ⁹ or more and 10 ¹² Ω · cm or less. In general, it is known that a polyamideimide to which carbon black is added for electrical conductivity has a higher elastic modulus and mechanical strength than a polyamideimide to which no carbon black is added.

However, in order to make the volume resistivity pv lower than 10 ⁶ Ω · cm, it is necessary to add a large amount of a conductive agent, so that the amount of the conductive agent relative to the resin becomes excessive, and as a result, the transfer belt 3 becomes brittle. End up. In addition, when ionic conduction is used, it is necessary to add a large amount of a conductive agent, so that the conductive agent may float on the surface of the transfer belt 3 and adhere to the photosensitive drum 11 or the like at high temperature and high humidity. . Further, if the volume resistivity pv is larger than 10 ¹⁴ Ω · cm, the resistance increases in a low temperature and low humidity environment and the resistance increases with the passage of time (seen prominently in ionic conduction), resulting in a higher resistance, resulting in poor transfer. This is not preferable because it may cause

  The toner (developer) used in the present embodiment contains a styrene-acrylic copolymer as a main component, contains a paraffin wax, and is appropriately added with an external additive such as silica for charge adjustment. The average particle diameter of the toner is 7.0 μm and the sphericity is 0.95. The reason for choosing this toner is that it has good transfer efficiency and releasability during fixing, and is excellent in dot reproducibility and resolution in development, taking into account that high-quality images with high sharpness can be obtained. It is.

<Evaluation test>
Using the transfer belt 3 configured as described above, evaluation of voids and durability in the primary transfer process were performed. In the evaluation test, the transfer belt (thickness 80 μm) of Experimental Examples 1 to 7 was used. These transfer belts have different distributions and sizes of cavities by adjusting the discharge pressure and heating temperature of the dispenser 102 in the manufacturing method described above.

  In FIG. 12, in the transfer belts of Experimental Examples 1 to 7, the average value of the size of the cavities at the position (position P1 shown in FIG. 4) 10 μm from the surface (outer peripheral surface 3A, inner peripheral surface 3B) , Mean diameter of the cavity) and mean diameter of the cavity at a position 40 μm from the surface (position P2 shown in FIG. 4). The method for measuring the average diameter of the cavities is as described above.

  FIG. 12 also shows the occupation ratio of the cavity 30. The method for measuring the occupation ratio of the cavity 30 is as described above. The occupancy ratio of the cavity 30 was measured at three places (positions 1, 2, and 3) 10 μm from the surface and three places (positions 4, 5, and 6) 40 μm from the surface, and the average of the six places was obtained.

  The transfer belt 3 of Experimental Example 1 had no cavity at a position 10 μm from the surface or 40 μm from the surface. The average value of the occupation ratio of the cavities 30 was 0%. The transfer belt having no cavity does not belong to the present embodiment, but is referred to as “transfer belt 3” for convenience of explanation.

  In the transfer belt 3 of Experimental Example 2, the average diameter of the cavities at a position of 10 μm from the surface was less than 0.1 μm, and the average diameter of the cavities at a position of 40 μm from the surface was less than 0.5 μm. The average value of the occupation ratio of the cavities 30 was 11%.

  In the transfer belt 3 of Experimental Example 3, the average diameter of the cavities at a position 10 μm from the surface was 1.0 μm, and the average diameter of the cavities at a position 40 μm from the surface was 2.3 μm. The average value of the occupation ratio of the cavities 30 was 25%.

  In the transfer belt 3 of Experimental Example 4, the average diameter of the cavities at a position 10 μm from the surface was 1.1 μm, and the average diameter of the cavities at a position 40 μm from the surface was 2.5 μm. The average value of the occupation ratio of the cavities 30 was 10%.

  In the transfer belt 3 of Experimental Example 5, the average diameter of the cavities at a position 10 μm from the surface was 1.0 μm, and the average diameter of the cavities at a position 40 μm from the surface was 2.5 μm. The average value of the occupation ratio of the cavities 30 was 20%.

  The transfer belt 3 of Experimental Example 6 had an average cavity diameter of 2.6 μm at a position 10 μm from the surface, and an average cavity diameter of 4.8 μm at a position 40 μm from the surface. The average value of the occupation ratio of the cavities 30 was 8%.

  In the transfer belt 3 of Experimental Example 7, the average diameter of the cavities at a position 10 μm from the surface was 2.7 μm, and the average diameter of the cavities at a position 40 μm from the surface was 4.7 μm. The average value of the occupation ratio of the cavities 30 was 5%.

  The transfer belts 3 of these experimental examples 1 to 7 were incorporated in the image forming apparatus 1, and toner image formation by the yellow and magenta ID units 10Y and 10M was started. That is, the belt driving roller 22 was rotated to start the transfer belt 3, and the photosensitive drums 11 of the ID units 10Y and 10M were rotated to start forming a printing pattern.

  The print pattern was a letter “T”, the size was 9 points, and the font was Times New Roman. The reason for selecting the letter “T” is that it includes vertical and horizontal thin lines. The direction of the letter “T” was set so that the horizontal bar was parallel to the moving direction of the transfer belt 3. The print pattern was formed at a temperature of 23 ° C. and a humidity of 50% RH (NN environment).

  In the ID units 10Y and 10M, the surface of the photosensitive drum 11 is uniformly charged by the charging roller 12, and an electrostatic latent image of the letter “T” is formed on the surface of the photosensitive drum 11 by the LED heads 13Y and 13M. . Further, the electrostatic latent image on the surface of each photosensitive drum 11 was developed by each developing unit 14 to form a toner image having a letter “T”.

  Then, a transfer voltage is applied to the transfer rollers 21Y and 21M to transfer the yellow toner image on the photoconductive drum 11 of the ID unit 10Y to the transfer belt 3, and on the magenta of the photoconductive drum 11 of the ID unit 10M. The toner image was transferred.

  After the yellow and magenta (that is, red) toner images were transferred onto the transfer belt 3, the running of the transfer belt 3 was stopped, and the transfer belt 3 was taken out from the image forming apparatus 1. The toner image of the red “T” character formed on the surface (outer peripheral surface 3A) of the taken-out transfer belt 3 and its surroundings were photographed at a magnification of 100 times using a stereomicroscope, and the hollowed out state was observed. evaluated.

  A void is a state in which toner is not present where it should be and a part of the image is missing. The reason for using the toner image of the red character that is the secondary color (yellow and magenta) is that the toner image on the transfer belt 3 is thicker than the single color in the secondary color, This is because the pressure tends to concentrate on the toner between the transfer belt 3 (therefore, voids are likely to occur).

As described above, the binarization processing was applied to the image photographed with the actual microscope (magnification 100 times), and the void ratio (%) was calculated.
Failure rate (%)
= (Area of hollow part) / (Area of “T” character when there is no hollow part) × 100

  The smaller the hollow-out rate, the better the transferability. When the void rate was 5% or less, it was judged that the transferability was good. Further, even when the hollowing out ratio is 5% or more, when it is 10% or less, it was judged that there was no problem in practice.

  FIG. 13 shows the calculation result of the void ratio based on the photographed image for each of Experimental Examples 1 to 7. Further, FIG. 14 shows the calculated hollow ratio and the corresponding hollow state. In FIG. 14, the portion where the void has occurred is shown in black.

  From the evaluation results shown in FIG. 13, when the transfer belt 3 has a cavity 30 inside (Experimental Examples 2 to 7), compared to the case without the cavity 30 (Experimental Example 1), It can be seen that the dropout rate is greatly improved.

  In addition, when the average diameter of the cavities is 0.5 μm or more (Experimental Examples 3 to 7), the average diameter of the cavities of the transfer belt 3 is smaller than 0.5 μm (Experimental Example 2). It can be seen that the effect of improving the omission rate is great and the transferability is good (the omission rate is 5% or less).

<Durability>
Next, evaluation of durability of the transfer belt 3 will be described.
The durability was evaluated by using a PPC (Plain Paper Copy) paper as the recording medium 8 at a temperature of 23 ° C. and a humidity of 50% RH (NN environment), and a 1.5 mm wide horizontal band pattern (in a direction perpendicular to the printing direction). A striped pattern) is printed and a pause (3P / J) job is performed every time three sheets are printed, and the surface of the transfer belt 3 is initially printed at the end of printing 50K sheets, 100K sheets, 150K sheets, and 200K sheets. The presence or absence of cracks was examined by observation. K is 1000 sheets.

  When a crack occurred in the transfer belt 3 during printing, printing was finished at that time. The evaluation results are also shown in FIG.

In addition, the evaluation criteria of durability are as follows.
When no crack was found on the transfer belt 3 at the end of printing 200K sheets, the most excellent a level was obtained.
When cracks occurred on the transfer belt 3 at 150 to 200K sheets, the b level was set.
When cracks occurred on the transfer belt 3 with less than 150K sheets, the c level was set.

  FIG. 13 also shows an observation result of toner slipping between the cleaning blade 7 and the transfer belt 3. The toner slipping was determined based on whether or not dirt other than the pattern portion was observed by observing the horizontal band pattern printed on the PPC paper as the recording medium 8. As shown in FIG. 13, no toner slip was observed in all of Experimental Examples 1 to 7.

Based on the above-described evaluation result of the void and the evaluation result of the durability, a comprehensive determination was performed. The judgment criteria are as follows.
The best A level was obtained when the void ratio was 5% or less and no crack was observed on the transfer belt 3 at the end of printing 200K sheets.
When the cracking rate was 5% or less and cracks occurred on the transfer belt 3 at 150 to 200K sheets, the B level was set.
When the cracking rate was 5% or less and the transfer belt 3 cracked at less than 150K, the C level was set.
Even when no cracks were observed on the transfer belt 3 at the end of printing 200K sheets, the D level was set when the void ratio exceeded 5%.

  From FIG. 13, in the experimental examples 4, 5, 6, and 7, the overall judgment is good at the A level or the B level. From this, the transfer belt 3 satisfying the condition that the size of the cavity 30 is in the range of 1.0 to 5.0 μm and the occupation ratio of the cavity 30 is 20% or less (Experimental Examples 4, 5, 6, and 7). ) Is most preferable in that it can suppress image dropout and maintain the durability of the transfer belt 3.

<Discussion>
The reason why the above results are obtained is considered as follows.
The void in the image is caused by the plastic deformation caused by the contact of the developer particles (toner particles) between the photosensitive drum 11 and the transfer belt 3 when the developer image is transferred from the photosensitive drum 11 to the transfer belt 3. Due to

  In particular, in the vicinity of the center of characters (thin lines) where the developer is densely packed, the pressure is concentrated as compared to the outline portion of the characters, so that the pressure applied to the developer particles is large and plastic deformation is likely to occur. The developer particles that have undergone plastic deformation have increased adhesion to the photosensitive drum 11. The adhesion force increased by plastic deformation does not return even when the pressure is released. As a result, the adhesion force between the developer particles and the photosensitive drum 11 becomes larger than the Coulomb force applied to the developer particles by the transfer electric field, and the developer image is hardly transferred to the transfer belt 3.

  On the other hand, at the contour portion (near the outer periphery) of the character, the pressure is dispersed outside the character, so that the developer particles are not plastically deformed. For this reason, even if the adhesion force between the developer particles and the photosensitive drum 11 increases due to the pressure, it returns to the original state when the pressure is released. Therefore, the developer particles at the outline of the character are easily transferred to the transfer belt by the transfer electric field.

  As a result, a region having a low developer concentration (or no developer is present) is generated near the center of the character, resulting in a void. In particular, in the case of a secondary color such as red, since a plurality of developer images are stacked, it is difficult to disperse the pressure near the center of the character, and it is considered that the void is remarkable.

  On the other hand, since the transfer belt 3 of this embodiment has a cavity 30 inside, it absorbs and disperses the pressure applied to the developer particles between the photosensitive drum 11 and the transfer belt 3. Can do. As a result, it is considered that even in a portion where the pressure is likely to concentrate, such as the central portion of the character (thin line), it was possible to efficiently prevent the void.

  Further, when there is no cavity (Experimental Example 1), the pressure applied to the developer cannot be sufficiently dispersed, so that the hollowing out ratio is considered to be as large as 20% or more. In addition, when the cavity is small (Experimental Example 2), the improvement effect of the hollowing out rate was observed, but it is considered that the improvement effect was small as compared with the case where the cavity was large (Experimental Examples 3 to 7).

  In addition, when the occupation ratio of the cavity 30 exceeded 20% (Experimental Example 3), the durability of the transfer belt 3 was reduced. This is presumably because the ratio of the resin in the transfer belt 3 decreases as the occupation ratio of the cavities 30 increases, and the strength of the transfer belt 3 decreases and becomes brittle.

  From the results shown in Table 13, if the occupancy of the cavity 30 is in the range of 5 to 20% (Experimental Examples 4, 5, 6, and 7), the hollowing out is suppressed without deteriorating the durability of the transfer belt 3. I understand that I can do it. In Experimental Example 7, the occupation ratio of the cavities 30 at the measurement positions 1 and 5 is 3%, and the hollow belt 30 can be suppressed without lowering the durability of the transfer belt 3. It can be considered that the lower limit of 3% is 3%.

  Further, even if the transfer belt 3 of the present embodiment has a cavity 30 inside, the surface has a specularity of 120 ± 10, so that developer is brought into contact with the transfer belt 3 and the cleaning blade 7. It is considered that there was no gap to pass through and the cleaning performance was not deteriorated.

  Further, by setting the static friction coefficient μs on the surface of the transfer belt 3 to 1.0 or less, an excessive frictional force is not applied to the cleaning blade 7, so that stick-slip motion of the cleaning blade 7 is suppressed, and abnormal noise and scratches are generated. It is thought that such abnormalities could be suppressed.

<Effect of the first embodiment>
Since the transfer belt in the present embodiment has a cavity inside the resin layer, the pressure applied to the developer particles between the photosensitive drum 11 and the transfer belt 3 can be absorbed and dispersed. As a result, it is possible to suppress the void in the image due to the concentration of pressure on the developer particles, and to provide a good image.

  In particular, since a cavity is not formed in the vicinity of the surface of the transfer belt, but a cavity is formed in the inside thereof, unevenness on the surface of the transfer belt can be reduced, for example, a smooth surface having a mirror surface degree of 60 to 200 can be obtained. it can. Therefore, the residual developer on the transfer belt can be efficiently cleaned by the cleaning blade.

  That is, it is possible to achieve both improvement in image quality by suppressing the hollowing out phenomenon and maintenance of the cleaning performance by the cleaning blade.

  In addition, since the transfer belt in the present embodiment is formed of a single resin layer, there is an advantage that the configuration is simple and the manufacturing process can be simplified as compared with a transfer belt having a multilayer structure.

  Further, in the multilayer structure in which the coating layer is provided on the surface of the belt base material, the resistance in the thickness direction of the transfer belt is increased, which causes image defects such as dust. Further, since the reflection state of light on the surface of the coating layer is likely to vary, when the developer concentration on the transfer belt is detected by the concentration sensor, it causes variation in the detected density. Further, when the coating layer is thickened, there is a problem that cracks occur or resistance increases.

  Since the transfer belt in the present embodiment is formed of a single resin layer, it is possible to improve the image quality and suppress the cleaning performance without suppressing these problems. it can.

  In the transfer belt according to the present embodiment, the cavity size A at the first position closer to the surface (outer peripheral surface and inner peripheral surface) is larger than the cavity size at the second position farther from the surface. Smaller than B (A <B). Therefore, the surface can be smoothed and the cleaning performance can be maintained while exhibiting the effect of dispersing the pressure of the developer particles by forming cavities inside the transfer belt.

  In addition, since the transfer belt in the present embodiment has a cavity occupancy rate of 20% or less per unit area in the cross section, the occurrence of cracks due to a decrease in strength of the transfer belt can be suppressed.

  In particular, the transfer belt in the present embodiment has a cavity occupation rate per unit area in the cross section in the range of 3 to 20% (more preferably 5 to 20%), so that the pressure applied to the developer particles is dispersed. Generation of cracks due to a decrease in strength of the transfer belt can be suppressed while sufficiently exhibiting the effect of suppressing the hollowing out phenomenon.

  Although the transfer belt used in the intermediate transfer type image forming apparatus has been described in the present embodiment, the present invention can also be applied to a transfer belt used in a direct transfer type image forming apparatus.

  In the direct transfer method, the transfer belt conveys a recording medium (paper), and the developer image is transferred from the photosensitive drum (image carrier) to the recording medium on the transfer belt. Since a recording medium (paper) is interposed between the photosensitive drum and the transfer belt, the concentration of pressure on the developer particles is less likely to occur than in the intermediate transfer method, but there is no possibility that a void will occur. Absent. Therefore, by applying the present invention, an effect of suppressing the hollowing out phenomenon can be obtained.

  Further, the present invention is not limited to the transfer belt of the intermediate transfer system or the direct transfer system but can be applied to, for example, a fixing belt used in a fixing device.

<Usage form>
The belt of the present invention can be applied to an intermediate transfer type or direct transfer type transfer belt, a fixing belt, and other belts.

  DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 3 Transfer belt (belt), 3A outer peripheral surface, 3B inner peripheral surface, 3C 1st layer part, 3D 2nd layer part, 5 Medium supply part, 6 Fixing unit, 7 Cleaning blade, 8 Recording Medium, 10 (10K, 10Y, 10M, 10C) ID unit, 11 photosensitive drum (image carrier), 12 charging roller (charging member), 13 (13K, 13Y, 13M, 13C) LED head (exposure means), 14 Development unit, 20 Transfer belt unit, 21 (21K, 21Y, 21M, 21C) Primary transfer roller, 22 Belt drive roller, 23 Secondary transfer backup roller, 24 Secondary transfer roller, 25 Secondary transfer unit, 26 Driven roller.

Claims (15)

A transfer belt formed of a single resin layer and having an inner peripheral surface and an outer peripheral surface,
Compared to the average diameter of the cavities in the central region in the thickness direction of the transfer belt, the average diameter of the cavities in the region having cavities on the outer peripheral surface side is smaller than the central region,
Compared with the average diameter of the cavities in the central region of the transfer belt, the transfer belt has a smaller average diameter of the cavities in the region having the cavity on the inner peripheral surface side than the central region,
A transfer belt unit comprising a cleaning mechanism for cleaning the transfer belt.   The transfer belt unit according to claim 1, wherein the size of the cavity of the transfer belt is 5.0 μm or less.   The transfer belt unit according to claim 2, wherein a size of the cavity of the transfer belt is 0.5 μm or more and 5.0 μm or less.   4. The transfer belt unit according to claim 1, wherein an occupation ratio of cavities per unit area of a cross section of the transfer belt is 20% or less. 5.   The transfer belt unit according to claim 4, wherein the occupation ratio of the cavities per unit area of the cross section of the transfer belt is 3% or more and 20% or less.   6. The transfer belt unit according to claim 5, wherein an occupation ratio of cavities per unit area of a cross section of the transfer belt is 5% or more and 20% or less.   The transfer belt unit according to any one of claims 1 to 6, wherein the mirror surface of the transfer belt has a mirror surface degree of 60 or more and 200 or less.   The transfer belt unit according to claim 1, wherein a static friction coefficient of the surface of the transfer belt is 0.1 or more and 1.0 or less.   9. The transfer belt unit according to claim 1, wherein a thickness of the transfer belt is not less than 60 μm and not more than 200 μm.   The resin layer includes at least one of polyamide imide, polyimide, polyether imide, polyphenylene sulfide, polyether ether ketone, polyvinylidene fluoride, polyamide, polycarbonate, and polybutylene terephthalate. The transfer belt unit according to any one of 1 to 9.   The transfer belt unit according to claim 10, wherein the resin layer further contains carbon black.   The transfer belt unit according to claim 10 or 11, wherein the resin layer further includes a fluorine-based or silicone-based water repellent.   13. The transfer belt according to claim 1, wherein the transfer belt is an intermediate transfer belt on which a developer image is primarily transferred from the surface of an image carrier and the developer image is secondarily transferred to a recording medium. The transfer belt unit according to any one of the above. The transfer belt unit according to any one of claims 1 to 13, wherein the transfer belt has a volume resistivity of 10 ⁶ Ω · cm or less and 10 ¹⁴ Ω · cm or less. An image forming unit for forming an image;
The transfer belt unit according to any one of claims 1 to 14, wherein the image formed by the image forming unit is directly or indirectly transferred to a medium.
An image forming apparatus comprising: a fixing unit that fixes the image transferred to the medium to the medium.