Patent Publication Number: US-2019196367-A1

Title: Image bearing member and image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The entire disclosure of Japanese Patent Application No. 2017-245260 filed on Dec. 21, 2017 is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     The present invention relates to an image bearing member and an image forming apparatus. 
     Description of Related Art 
     Generally, an image forming apparatus (a printer, a copier, a facsimile machine, or the like) utilizing electrophotographic process technology irradiates (exposes) a charged photoconductor drum with laser light based on image data, thereby forming an electrostatic latent image. Then, toner is supplied from a developing device to the photoconductor drum on which the electrostatic latent image is formed, whereby the electrostatic latent image is visualized to form a toner image. Furthermore, after this toner image is directly or indirectly transferred to sheet, the toner image is fixed by heating and pressurizing, whereby an image is formed on the sheet. 
     Furthermore, in the image forming apparatus, a toner adhesion amount is optically detected by a sensor in the photoconductor drum or an intermediate transfer belt (image bearing member), image forming operation is controlled on the basis of a detection result and image quality is improved. 
     For example, in an image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2014-109586 (hereinafter referred to as “Patent Literature 1”), for a base material layer including polyimide (PI) (sometimes referred to as a base layer), the use of an intermediate transfer belt coated with a surface layer (sometimes referred to as a superficial layer or a coat layer) containing silicon dioxide (SiO 2 ) as a main component has been studied. 
     As in Patent Literature 1, in the intermediate transfer belt having the base material layer and the surface layer, toner adhesion force is reduced and transfer efficiency is improved. However, in the case of detecting the toner adhesion amount in the intermediate transfer belt having the base material layer and the surface layer described above, there is a problem that reflected light beams generated as a result that incident light emitted from a light emitting side of the sensor is reflected by each of the base material layer and the surface layer are interfered with each other, sensor noise is generated on a light receiving side of the sensor and the toner adhesion amount cannot be accurately detected. 
     SUMMARY 
     An object of the present invention is to provide an image bearing member and an image forming apparatus capable of accurately detecting a toner adhesion amount. 
     In order to realize at least one of the above objects, an image bearing member includes: 
     a base material layer; and 
     a surface layer disposed on the base material layer and including an inorganic oxide containing an organic component, in which
         a ten-point average roughness of the surface layer is 69% or more of a wavelength of incident light emitted from a sensor for detecting an amount of toner adhering to the image bearing member and less than 20% of an average particle diameter of the toner.       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention: 
         FIG. 1  is a view schematically illustrating an overall configuration of an image forming apparatus according to one embodiment; 
         FIG. 2  is a diagram illustrating a main part of a control system of the image forming apparatus according to the one embodiment; 
         FIG. 3  is a diagram schematically illustrating a cross section of an intermediate transfer belt; 
         FIG. 4  is a diagram for describing interference that occurs in the intermediate transfer belt; 
         FIG. 5  is a diagram illustrating an example of a cross section of an intermediate transfer belt according to the one embodiment; 
         FIG. 6  is a table illustrating an example of evaluation results of cleanability and sensor noise according to the one embodiment; 
         FIG. 7  is a graph illustrating an example of relationship between the content of an organic component in a surface layer and the hardness of the surface layer; 
         FIG. 8  is a diagram for describing a principle of improving transfer efficiency by the surface layer; 
         FIG. 9  is a table illustrating an example of an evaluation result of transferability and occurrence of a crack according to a first modification of the one embodiment; 
         FIG. 10  is a table illustrating an example of an evaluation result of transferability according to a third modification of the one embodiment; and 
         FIG. 11  is a graph illustrating an example of relationship between the content of the organic component in the surface layer and a film thickness of the surface layer. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. 
       FIG. 1  is a view schematically illustrating an overall configuration of image forming apparatus  1  according to an embodiment of the present invention.  FIG. 2  is a diagram illustrating a main part of a control system of image forming apparatus  1  according to the present embodiment. Image forming apparatus  1  illustrated in  FIGS. 1 and 2  is an intermediate transfer type color image forming apparatus utilizing electrophotographic process technology. That is, image forming apparatus  1  primarily transfers each color toner image of yellow (Y), magenta (M), cyan (C), and black (K) formed on photoconductor drum  413  to intermediate transfer belt  421  (image bearing member), superimposes the four color toner images on intermediate transfer belt  421 , and secondarily transfers the toner images to sheet S (recording medium), thereby forming an image. Note that image forming apparatus  1  may be an image apparatus that forms a single color image (for example, monochrome image). 
     In image forming apparatus  1 , a tandem system in which photoconductor drums  413  corresponding to the four colors of YMCK are disposed in series in a running direction of intermediate transfer belt  421  and the toner image of each color is sequentially transferred to intermediate transfer belt  421  in a single procedure has been adopted. 
     As illustrated in  FIG. 2 , image forming apparatus  1  includes image reading section  10 , operation display section  20 , image processing section  30 , image forming section  40 , sheet conveying section  50 , fixing section  60 , and control section  100 . 
     Control section  100  includes central processing unit (CPU)  101 , read only memory (ROM)  102 , random access memory (RAM)  103 , and the like. CPU  101  reads a program corresponding to processing contents from ROM  102 , develops the program in RAM  103 , and centrally controls the operation of each block of image forming apparatus  1  in cooperation with the developed program. At this time, various data stored in storage section  72  is referred to. Storage section  72  includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive. 
     Control section  100  transmits/receives various data to/from an external device (for example, personal computer) connected to a communication network such as a local area network (LAN) and a wide area network (WAN) via communication section  71 . For example, control section  100  receives image data transmitted from the external device and form an image on sheet S on the basis of image data (input image data). Communication section  71  includes, for example, a communication control card such as a LAN card. 
     Image reading section  10  is configured by including automatic document feeding device  11  called an auto document feeder (ADF), document image scanning device  12  (scanner). 
     Automatic document feeding device  11  conveys document D placed on a document tray by a conveyance mechanism and sends document D to document image scanning device  12 . Automatic document feeding device  11  can continuously read images (including both surfaces) of a large number of documents D placed on the document tray at once. 
     Document image scanning device  12  optically scans the document conveyed on contact glass from automatic document feeding device  11  or the document placed on the contact glass, causes light reflected from the document to form an image onto a light receiving surface of charge coupled device (CCD) sensor  12   a , and reads a document image. Image reading section  10  generates input image data on the basis of a reading result by document image scanning device  12 . The input image data is subjected to predetermined image processing in image processing section  30 . 
     Operation display section  20  includes, for example, a liquid crystal display (LCD) with a touch panel and functions as display section  21  and operation section  22 . Display section  21  displays various operation screens, image status, operation status of each function, and the like according to a display control signal input from control section  100 . Operation section  22  includes various operation keys such as numeric keys and a start key, accepts various input operations by a user, and outputs an operation signal to control section  100 . 
     Image processing section  30  includes a circuit and the like that performs digital image processing according to an initial setting or a user setting on the input image data. For example, under the control of control section  100 , image processing section  30  performs tone correction on the basis of tone correction data (tone correction table). Furthermore, in addition to the tone correction, image processing section  30  subjects the input image data to various correction processing such as color correction, shading correction and compression processing. Image forming section  40  is controlled on the basis of the image data subjected to these kinds of processing. 
     Image forming section  40  includes image forming units  41 Y,  41 M,  41 C, and  41 K for forming images with color toners of a Y component, an M component, a C component, and a K component on the basis of the input image data, intermediate transfer unit  42  and the like. 
     Image forming units  41 Y,  41 M,  41 C, and  41 K for the Y component, the M component, the C component, and the K component have a similar configuration. For convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and in a case where the constituent elements are distinguished from one another, the constituent elements are represented with Y, M, C, or K added to the reference numerals. In  FIG. 1 , only the constituent elements of image forming unit  41 Y for the Y component are denoted by reference numerals, and the reference numerals of the constituent elements of other image forming units  41 M,  41 C,  41 K are omitted. 
     Image forming unit  41  includes exposure device  411 , developing device  412 , photoconductor drum  413 , charging device  414 , drum cleaning device  415 , and the like. 
     Exposure device  411  includes, for example, a semiconductor laser, and irradiates photoconductor drum  413  with a laser beam corresponding to an image of each color component. As a result, an electrostatic latent image of each color component is formed on a surface of photoconductor drum  413  due to a potential difference from surroundings. 
     Developing device  412  is, for example, a two-component reversal type developing device, and attaches toner of each color component to the surface of photoconductor drum  413 , whereby the electrostatic latent image is visualized to form a toner image. Developing device  412  includes a developing sleeve disposed so as to face photoconductor drum  413  via a developing region. For example, a direct current developing bias having the same polarity as a charging polarity of charging device  414 , or a developing bias in which a direct current voltage having the same polarity as the charging polarity of charging device  414  is superimposed on an alternate current voltage is applied to the developing sleeve. As a result, reversal development in which toner is attached to the electrostatic latent image formed by exposure device  411  is performed. 
     Photoconductor drum  413  includes, for example, an organic photoreceptor in which a photosensitive layer including a resin containing an organic photoconductor is formed on an outer peripheral surface of a drum-shaped metal base. 
     Control section  100  controls a driving current supplied to a driving motor (not illustrated) that rotates photoconductor drum  413 , thereby rotating photoconductor drum  413  at a constant peripheral speed. 
     Charging device  414  is, for example, an electrification charger, and generates corona discharge, thereby uniformly charging the surface of photoconductor drum  413  into negative polarity. 
     Drum cleaning device  415  is in contact with the surface of photoconductor drum  413 , has a flat plate-shaped drum cleaning blade and the like including an elastic body, and removes the toner that is not transferred to intermediate transfer belt  421  and remains on the surface of photoconductor drum  413 . 
     Intermediate transfer unit  42  includes intermediate transfer belt  421 , primary transfer roller  422 , a plurality of support rollers  423 , secondary transfer roller  424 , belt cleaning device  426 , and the like. 
     Intermediate transfer belt  421  includes an endless belt and is stretched in a loop shape around a plurality of support rollers  423 . At least one of the plurality of support rollers  423  includes a driving roller and the others include a driven roller. For example, support roller  423 A disposed on a downstream side of primary transfer roller  422  for the K component in a belt running direction is preferably a driving roller. This makes it easier to keep the running speed of the belt in a primary transfer section constant. The rotation of driving roller  423 A causes intermediate transfer belt  421  to travel at a constant speed in a direction of arrow A. 
       FIG. 3  is a diagram schematically illustrating a cross section of intermediate transfer belt  421 . As illustrated in  FIG. 3 , intermediate transfer belt  421  has at least two layers of base material layer  421   a  and surface layer  421   b  disposed on base material layer  421   a . For base material layer  421   a , for example, a synthetic resin in which a conductive material such as a polyimide (PI) resin, a polyamideimide resin, a polyphenylene sulfide resin, a polyamide resin or the like is dispersed is used. Base material layer  421   a  may have a single layer configuration or a multi-layer configuration. Furthermore, for surface layer  421   b , for example, a material containing silicon dioxide (SiO 2 ) as a main component is used. For example, for surface layer  421   b , a siloxane compound such as methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane may be used as silicon oxide containing an alkyl group. Furthermore, surface layer  421   b  has at least light permeability. 
     Note that materials used for base material layer  421   a  and surface layer  421   b  are not limited to these materials. 
     Primary transfer roller  422  is disposed on an inner peripheral surface side of intermediate transfer belt  421  such that primary transfer roller  422  faces photoconductor drum  413  of each color component. A primary transfer nip for transferring the toner image from photoconductor drum  413  to intermediate transfer belt  421  is formed by pressing primary transfer roller  422  against photoconductor drum  413  across intermediate transfer belt  421 . 
     Secondary transfer roller  424  is disposed on an outer peripheral surface side of intermediate transfer belt  421  such that secondary transfer roller  424  faces backup roller  423 B disposed on the downstream side of driving roller  423 A in the belt running direction. A secondary transfer nip for transferring the toner image from intermediate transfer belt  421  to sheet S is formed by pressing secondary transfer roller  424  against backup roller  423 B across intermediate transfer belt  421 . 
     When intermediate transfer belt  421  passes through the primary transfer nip, the toner image on photoconductor drum  413  is sequentially superimposed and primarily transferred to intermediate transfer belt  421 . Specifically, a primary transfer bias is applied to primary transfer roller  422 , and a charge having a polarity opposite to a polarity of the toner is imparted to a back side of intermediate transfer belt  421  (side in contact with primary transfer roller  422 ), whereby the toner image is electrostatically transferred to intermediate transfer belt  421 . 
     Thereafter, when sheet S passes through the secondary transfer nip, the toner image on intermediate transfer belt  421  is secondarily transferred to sheet S. Specifically, a secondary transfer bias is applied to secondary transfer roller  424 , and a charge having a polarity opposite to that of the toner is imparted to a back side of sheet S (side in contact with secondary transfer roller  424 ), whereby the toner image is electrostatically transferred to sheet S. Sheet S to which the toner image is transferred is conveyed toward fixing section  60 . 
     Belt cleaning device  426  removes transfer residual toner remaining on the surface of intermediate transfer belt  421  after the secondary transfer. Note that instead of secondary transfer roller  424 , a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is stretched in a loop shape on a plurality of support rollers including a secondary transfer roller may be adopted. 
     Fixing section  60  includes upper fixing section  60 A having a fixing surface-side member disposed on a side of a fixing surface of sheet S (surface on which the toner image is formed), lower fixing section  60 B having a back surface-side support member disposed on the back side of sheet S (surface opposite to the fixing surface), heating source  60 C, and the like. By pressing the back surface-side support member against the fixing surface-side member, a fixing nip for sandwiching and conveying sheet S is formed. 
     In fixing section  60 , sheet S on which the toner image is secondarily transferred and that is conveyed is heated and pressurized at the fixing nip, whereby the toner image is fixed on sheet S. Fixing section  60  is disposed as a unit in fixing device F. Furthermore, an air separation unit that separates sheet S from the fixing surface-side member or the back surface-side support member may be disposed on fixing device F by blowing air. 
     Sheet conveying section  50  includes sheet feed section  51 , sheet ejecting section  52 , conveyance path section  53 , and the like. Sheet S (standard sheet, special sheet) identified on the basis of a basis weight, a size, and the like is accommodated in each of three sheet feed tray units  51   a  to  51   c  constituting sheet feed section  51  for each preset type. Conveyance path section  53  has a plurality of a pair of conveyance rollers such as a pair of registration rollers  53   a.    
     Sheets S accommodated in sheet feed tray units  51   a  to  51   c  are sent one by one from the uppermost portion and are conveyed to image forming section  40  by conveyance path section  53 . At this time, the inclination of fed sheet S is corrected and the conveyance timing is adjusted by a registration roller section in which the pair of registration rollers  53   a  is arranged. Then, in image forming section  40 , the toner image of intermediate transfer belt  421  is secondarily transferred collectively to one side of sheet S, and the fixing step is performed in fixing section  60 . Sheet S on which an image is formed is ejected to the outside of image forming apparatus  1  by sheet ejecting section  52  having sheet ejection roller  52   a.    
     Toner adhesion amount detecting section  73  faces intermediate transfer belt  421  and detects a toner adhesion amount on intermediate transfer belt  421 . For example, an image density control (IDC) sensor, a charge coupled device (CCD) image sensor, or the like is used for toner adhesion amount detecting section  73 . For example, toner adhesion amount detecting section  73  includes a light sensor including a light emitting element and a light receiving element. In intermediate transfer belt  421 , light having an intensity corresponding to the amount of toner adhering to intermediate transfer belt  421  is reflected. For example, as the toner adhesion amount on intermediate transfer belt  421  becomes smaller, stronger light is reflected on intermediate transfer belt  421 . Toner adhesion amount detecting section  73  detects the toner adhesion amount on intermediate transfer belt  421  on the basis of a reflection intensity (for example, voltage value) of the reflected light received by the light receiving element. The higher the reflection intensity of the reflected light received by the light receiving element, the smaller the toner adhesion amount detected by toner adhesion amount detecting section  73  becomes. 
     Control section  100  controls transfer operation (for example, transfer bias) and the like in image forming section  40  on the basis of a detection result (toner adhesion amount) of toner adhesion amount detecting section  73 . 
     As illustrated in  FIG. 3 , in intermediate transfer belt  421  having base material layer  421   a  and surface layer  421   b , interference between light reflected on the surface of surface layer  421   b  and light that passes through surface layer  421   b  and is reflected on base material layer  421   a  occurs. Due to the interference of the reflected light, sensor noise is generated in the light receiving element of toner adhesion amount detecting section  73 . 
       FIG. 4  is a diagram for describing a mechanism of generation of the sensor noise. 
     In  FIG. 4 , the wavelength (sensor wavelength) of incident light (sensor light) emitted from the light emitting element (not illustrated) included in toner adhesion amount detecting section  73  is λ, the refractive index of surface layer  421   b ) is n, and the film thickness of surface layer  421   b  (thickness of the coat layer) is d. Furthermore, an angle (refraction angle) at which light is incident inside surface layer  421   b  is θ r . 
     In this case, a condition under which the light reflected on surface layer  421   b  and the light that passes through surface layer  421   b  and is reflected on base material layer  421   a  interfere with each other is expressed by the following equations. 
       2 nd  cos θ r   =mλ   (1)
 
       2 nd  cos θ r =( m +(½))λ  (2)
 
     In the equations (1) and (2), m is an integer of 0 or more (0, 1, 2, . . . ). 
     Here, variations (for example, nm to μm order) in the thickness of surface layer  421   b  coated on base material layer  421   a  necessarily occur in intermediate transfer belt  421 . Due to variations in the thickness of surface layer  421   b , variations in an interference condition as illustrated in  FIG. 4  also occur in intermediate transfer belt  421 . For this reason, variations in the toner adhesion amount detected by toner adhesion amount detecting section  73  (sensor noise) also occur in intermediate transfer belt  421 . 
     Therefore, in order to accurately detect the toner adhesion amount, it is desirable to reduce the sensor noise caused by the variations in film thickness d of surface layer  421   b.    
     Therefore, in the present embodiment, in order to reduce the sensor noise, roughness is imparted to the surface of surface layer  421   b  that is the outermost layer surface of intermediate transfer belt  421 . 
       FIG. 5  illustrates an example of a cross section of intermediate transfer belt  421  according to the present embodiment. As illustrated in  FIG. 5 , the roughness is imparted to surface layer  421   b  (outermost layer surface). 
     As illustrated in  FIG. 5 , by imparting the roughness to surface layer  421   b  of intermediate transfer belt  421 , the sensor light incident from toner adhesion amount detecting section  73  (light emitting element) is scattered on the surface of surface layer  421   b.    
     Similarly, as illustrated in  FIG. 5 , among the sensor light, light that passes through surface layer  421   b  and is reflected on base material layer  421   a  (represented by a broken line arrow) is scattered on the surface of surface layer  421   b.    
     As described above, the sensor light incident from the light emitting element and the reflected light from base material layer  421   a  are each scattered on the surface to which the roughness is imparted in surface layer  421   b . Therefore, the light reflected from the surface of surface layer  421   b  and the light that passes through surface layer  421   b  and is reflected on base material layer  421   a  becomes difficult to interfere with each other. Therefore, occurrence of the sensor noise due to the interference at surface layer  421   b  can be suppressed. As a result, toner adhesion amount detecting section  73  can accurately measure the amount of toner adhering to intermediate transfer belt  421 . 
     Here, the larger surface roughness “Rz” of surface layer  421   b  is, the larger the degree of scattering of the incident sensor light in surface layer  421   b  and the reflected light from base material layer  421   a  becomes, and the sensor noise is further reduced. However, the larger surface roughness Rz of surface layer  421   b  is, the deeper a groove formed on the surface of surface layer  421   b  becomes. Therefore, for example, in belt cleaning device  426 , the transfer residual toner easily passes through without being removed and there is a possibility of a cleaning failure. 
     Therefore, surface roughness Rz of surface layer  421   b  is desirably designed in consideration of at least both reduction of the sensor noise in toner adhesion amount detecting section  73  and ensuring of cleanability in belt cleaning device  426 . 
     The present inventors evaluated the sensor noise in toner adhesion amount detecting section  73  and the cleanability in belt cleaning device  426  by the following method and criteria. 
     Note that in the following description, surface roughness Rz (μm) of surface layer  421   b  is a ten-point average roughness measured by a surface roughness measuring device Surfcorder SE3500 manufactured by Kosaka Laboratory Ltd. Furthermore, as measurement conditions of surface roughness Rz of surface layer  421   b , a feed speed is 0.2 mm/sec, a trace length is 12.5 mm, a cutoff value λc is 2.5 mm, and an evaluation length is a length obtained by multiplying a cutoff value by 5. 
     Furthermore, a method (manufacturing method) of imparting surface roughness Rz of surface layer  421   b  includes a dip coating method, a spray method, an atmospheric pressure plasma enhanced chemical vapor deposition (CVD) method, and the like, but is not limited to these methods. 
     Furthermore, the resistance (surface resistivity) of base material layer  421   a  is preferably, for example, 9.0 to 12.0 log Ω/□. Furthermore, the resistance of surface layer  421   b  is preferably a value higher by 0.5 to 2.0 log Ω/□ than the resistance of base material layer  421   a . Furthermore, the resistance of intermediate transfer belt  421  in a state in which base material layer  421   a  and surface layer  421   b  are laminated is preferably 9.1 to 12.1 log Ω/□, more preferably 9.5 to 11.0 log Ω/□. Note that with a resistivity measuring device (Hiresta-UP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.), the resistance of intermediate transfer belt  421  was determined by applying a voltage of 500 V with insulating plates facing each other. Furthermore, the resistance of surface layer  421   b  alone was obtained by making an opposing plate conductive. 
     Table 1 illustrates each parameter of image forming apparatus  1  (evaluator) used in the evaluation of the sensor noise and the cleanability. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Machine 
                 Full color machine adopting intermediate 
               
               
                   
                 transfer member 
               
               
                 Speed 
                 400 mm/sec 
               
               
                 Intermediate transfer belt 421 
                 Described separately 
               
            
           
           
               
               
               
               
            
               
                 Secondary transfer 
                 Backup roller 
                 Material 
                 Acrylonitrile-butadiene rubber (NBR) 
               
               
                 section 
                 423B 
                 Shape 
                 φ 38 straight 
               
               
                   
                   
                 Physical 
                 Aske-C71°, 7.5 logΩ 
               
               
                   
                   
                 property 
               
               
                   
                 Secondary transfer roller 
                 Material 
                 SUS Roller 
               
               
                   
                 424 
                 Shape 
                 φ 38 straight 
               
               
                   
                   
                 Physical 
                 — 
               
               
                   
                   
                 property 
               
            
           
           
               
               
               
            
               
                   
                 Pressing force 
                 80 N 
               
               
                 Belt cleaning device 
                 Blade material 
                 Urethane rubber 
               
               
                 426 
                 Contact force 
                 20 N 
               
               
                   
                 Contact angle 
                 20° 
               
               
                 Toner adhesion amount 
                 Wavelength 
                 870 nm 
               
               
                 detection section 73 
                 Incidence angle 
                 10° 
               
               
                   
                 Output voltage 
                 0 to 4 V 
               
            
           
           
               
               
            
               
                 Stretching roller 
                 SUS-made φ 38 straight 
               
               
                   
               
            
           
         
       
     
     Base material layer  421   a  of intermediate transfer belt  421  uses a material including a polyimide resin and having a film thickness of 65 μm and resistance of 10.2 log Ω/□. Surface layer  421   b  of intermediate transfer belt  421  uses a material containing silicon dioxide as a main component and having a material having a film thickness of 1.6 μm. 
     Furthermore, for the material used for surface layer  421   b , both masses of tetraalkoxysilane (Si(OR) 4 ) and methyltrimethoxysilane ((CH 3 ) 3 SiCH 3 ) to be blended are adjusted such that the content of an organic component in surface layer  421   b  is 20 mass %. Note that a reason why the organic component is contained in surface layer  421   b  is to prevent a crack from occurring in a case where the component of surface layer  421   b  cannot follow the fluctuations of intermediate transfer belt  421  stretched around the roller in a case where the component of surface layer  421   b  is only silicon dioxide. 
     Under the above conditions, intermediate transfer belt  421  was manufactured by varying surface roughness Rz of surface layer  421   b  in the range of 0.4 to 1.5 μm (patterns (1) to (11)). 
       FIG. 6  illustrates the results of evaluating the cleanability and the sensor noise in image forming apparatus  1  according to the following evaluation criteria with respect to the patterns (1) to (11). 
     Specifically, as a cleanability evaluation method, according to a state of a wiping residue in a case where the toner adhesion amount on intermediate transfer belt  421  was 8 gsm and the toner was made to rush into belt cleaning device  426 , the cleanability was evaluated as follows.
         A: No wiping residue   B: Although there is a wiping residue, the wiping residue is acceptable in actual operation.   D: There is a wiping residue, which is not acceptable in actual operation.       

     Furthermore, as a sensor noise evaluation method, intermediate transfer belt  421  is driven while the sensor light is emitted from toner adhesion amount detecting section  73 , sensor reflection intensity (voltage value) on the bare surface of intermediate transfer belt  421  is measured, and the sensor noise was evaluated as follows according to a difference [V] between the maximum value of the measured values and the minimum value thereof.
         A: Less than 0.1 V   B: 0.1 to 0.15 V   D: Larger than 0.15 V       

     As illustrated in  FIG. 6 , the cleanability was “A” when surface roughness Rz of surface layer  421   b  was 1.2 μm or less (patterns (1) to (8)), “B” when surface roughness Rz of surface layer  421   b  was 1.3 μm (pattern (9)), and “D” when surface roughness Rz of surface layer  421   b  was 1.4 μm or more (patterns (10) and (11)). That is, from the viewpoint of the cleanability, surface roughness Rz of surface layer  421   b  is preferably 1.3 μm or less. 
     Furthermore, as illustrated in  FIG. 6 , the sensor noise was “D” when surface roughness Rz of surface layer  421   b  was 0.5 μm or less (patterns (1) and (2)), “B” when surface roughness Rz of surface layer  421   b  was 0.6 μm (pattern (3)), and “A” when surface roughness Rz of surface layer  421   b  was 0.7 μm or more (patterns (4) to (11)). That is, from the viewpoint of the sensor noise, surface roughness Rz of surface layer  421   b  is preferably 0.6 μm or more. 
     From the above, in the evaluation results illustrated in  FIG. 6 , in consideration of both of the cleanability and the sensor noise, surface roughness Rz of surface layer  421   b  is desirably a value in the range of 0.6 μm or more and 1.3 μm or less. That is, when surface roughness Rz is less than a lower limit value thereof (0.6 μm), the degree of scattering of light on the surface of surface layer  421   b  becomes small and it becomes difficult to suppress the sensor noise. Furthermore, in a case where surface roughness Rz is larger than an upper limit value thereof (1.3 μm), the cleanability by belt cleaning device  426  deteriorates. 
     Furthermore, as illustrated in  FIG. 6 , surface roughness Rz of surface layer  421   b  is more desirably a value in the range of 0.7 μm or more and 1.2 μm or less. By setting surface roughness Rz of surface layer  421   b  within the range of 0.7 μm or more and 1.2 μm or less, good performance (“A”) can be obtained in terms of both of the cleanability and the sensor noise. 
     Here, as illustrated in  FIG. 6 , the lower limit value of surface roughness Rz is determined by the sensor noise. Furthermore, the sensor noise varies depending on the wavelength λ of the sensor. For example, under the conditions illustrated in Table 1, the sensor wavelength λ is 0.87 μm, and as illustrated in  FIG. 6 , the lower limit value of surface roughness Rz is 0.6 μm. Therefore, a study by the inventors of the present invention has found that surface roughness Rz needs to be 69% or more with respect to the sensor wavelength. 
     Furthermore, as described above, the upper limit value of surface roughness Rz is determined due to the cleanability. Furthermore, the cleanability varies depending on a toner particle size to be used. For example, an average particle diameter of the toner used in the evaluation illustrated in  FIG. 6  is 7 μm, and as illustrated in  FIG. 6 , the upper limit value of surface roughness Rz is 1.4 μm (that is, pattern (9) in  FIG. 6 ). Therefore, a study by the present inventors has found that surface roughness Rz needs to be less than 20% with respect to the toner particle size. 
     Therefore, in the present embodiment, it suffices that that surface roughness (ten-point average roughness) Rz of surface layer  421   b  of intermediate transfer belt  421  is 69% or more of the wavelength λ of incident light emitted from toner adhesion amount detecting section  73  to intermediate transfer belt  421  and less than 20% of the average particle size of the toner to be used. 
     As a result, in the present embodiment, image forming apparatus  1  can accurately detect the toner adhesion amount by suppressing a sensor noise level in intermediate transfer belt  421  with respect to toner adhesion amount detecting section  73 , good cleanability can be obtained in belt cleaning device  426 . 
     For example, image forming apparatus  1  can accurately control the transfer operation by accurately detecting the toner adhesion amount. Therefore, image forming apparatus  1  can form an electric field enough for the toner to move with respect to a depressed portion of paper having depressed and raised portions (for example, embossed paper) and ensure good transferability. 
     Note that in the present embodiment, a case where the content of the organic component in surface layer  421   b  is 20 mass % has been described, but the embodiment of the present invention is not limited to the case. Here, there is a tendency that the larger the content of the organic component in surface layer  421   b  becomes, the more the transferability deteriorates. A mechanism in which the transferability tends to deteriorate may be as follows. 
       FIG. 7  illustrates an example of relationship between the content of the organic component [mass %] in surface layer  421   b  and the hardness (indentation hardness) [N/mm 2 ] of surface layer  421   b . As illustrated in  FIG. 7 , it can be seen that the larger the content of the organic component becomes, the smaller the hardness of surface layer  421   b  becomes. As illustrated in  FIG. 7 , in a case where the content of the organic component is large and surface layer  421   b  is soft, a contact area between surface layer  421   b  and the toner increases, as compared with the case where the content of the organic component is small and surface layer  421   b  is hard. Therefore, the larger the content of the organic component becomes, the larger the contact area between surface layer  421   b  and the toner becomes. As a result, the physical adhesion of the toner to surface layer  421   b  increases, resulting in deterioration of the transferability. 
     For example, conventionally (for example, in the case of an intermediate transfer belt having only a base material layer), the indentation hardness of a polyimide (PI) resin that has been used as a base material layer is about 320 N/mm 2 . Therefore, in the present embodiment, the hardness of surface layer  421   b  is desirably 320 N/mm 2  or more in a similar manner. In  FIG. 7 , in a case where the content of the organic component exceeds 30 mass % (range surrounded by a dotted line in  FIG. 7 ), the hardness of surface layer  421   b  is less than 320 N/mm 2 . That is, in a case where the content of the organic component in surface layer  421   b  exceeds 30 mass %, there is a possibility that the transferability in intermediate transfer belt  421  deteriorates. 
     Therefore, the content of the organic component in surface layer  421   b  needs to be 30 mass % or less. Meanwhile, in a case where the content of the organic component in surface layer  421   b  is too small, a crack is likely to occur as described above. Therefore, for example, the content of the organic component needs to be 10 mass % or more. Therefore, in the present embodiment, the content of the organic component in surface layer  421   b  may be in the range of 10 mass % or more and 30 mass % or less (range surrounded by a solid line illustrated in  FIG. 7 ). 
     (First Modification) 
     In a first modification, a design range of a film thickness of surface layer  421   b  is defined. 
     As illustrated in  FIG. 8 , in a case where intermediate transfer belt  421  includes base material layer  421   a  (PI layer) and surface layer  421   b  (coating layer) having resistance higher than that of base material layer  421   a , since the resistance of surface layer  421   b  is high, when toner adheres to intermediate transfer belt  421  by primary transfer, a counter charge opposite to a charge of the toner (+Q) is generated in base material layer  421   a.    
     Here, electrostatic adhesion force F between the toner and intermediate transfer belt  421  is represented by the following equation (3). 
     
       
         
           
             
               
                 
                   F 
                   = 
                   
                     
                       1 
                       
                         4 
                          
                         πɛ 
                       
                     
                     × 
                     
                       
                         q 
                         2 
                       
                       
                         r 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     That is, the longer distance r between the toner and the counter charge opposite to the charge of the toner is, the smaller electrostatic adhesion force F between the toner and intermediate transfer belt  421  becomes. When electrostatic adhesion force F between the toner and intermediate transfer belt  421  is reduced, transfer efficiency (transferability) is improved. Therefore, in intermediate transfer belt  421  illustrated in  FIG. 8 , the larger film thickness (“d”) of surface layer  421   b  is, the longer distance r between the toner and the counter charge opposite to the charge of the toner becomes. As a result, the transfer efficiency (transferability) improves. 
     Meanwhile, an organic component is included in surface layer  421   b  of intermediate transfer belt  421  in order to prevent occurrence of a crack. However, even if surface layer  421   b  includes the organic component, there is a possibility that a crack of surface layer  421   b  occurs due to stress caused by curvature of a stretched roller, pressing force at a transfer nip (primary transfer nip or secondary transfer nip), and the like. In particular, the larger film thickness d of surface layer  421   b  is, the more a crack is likely to occur. 
     Therefore, film thickness d of surface layer  421   b  is desirably designed in consideration of at least both ensuring of good transferability and prevention of occurrence of a crack in surface layer  421   b . Therefore, in the first modification, the design of the film thickness of surface layer  421   b  that can ensure good transferability while preventing occurrence of a crack in surface layer  421   b  will be described. 
     The present inventors evaluated transferability and occurrence of a crack by the following method and criteria. Note that in the first modification, materials and each parameter of image forming apparatus  1  (evaluator) used in evaluating transferability and occurrence of a crack are similar to those in the above embodiment (for example, Table 1). 
     Furthermore, in the first modification, surface roughness Rz of surface layer  421   b  is 0.6 μm. However, surface roughness Rz is not limited to 0.6 μm and may be a value within the range described in the above embodiment. 
     Under the above conditions, intermediate transfer belt  421  was manufactured by varying film thickness d of surface layer  421   b  in the range of 0.4 to 3.4 μm (patterns (1) to (13)). Note that film thickness d is an average value of film thicknesses measured at any 12 places on intermediate transfer belt  421 . 
       FIG. 9  illustrates the results of evaluating transferability and occurrence of a crack in image forming apparatus  1  according to the following evaluation criteria with respect to patterns (1) to (13). 
     Specifically, as a transferability evaluation method, a solid image was output to embossed paper (LEATHAC 66, white, 302 gsm, manufactured by Tokushu Tokai Paper Co., Ltd.) (“LEATHAC” is a registered trademark of the company) a degree of blank in a depressed portion was taken as transferability and transferability was evaluated with rankings as follows.
         A: There is no problem with the entire surface.   B: There is a blank portion depending on place, but this is acceptable in actual operation.   C: There is a blank portion, which is not acceptable in actual operation.   D: There are blanks on the entire surface.       

     Furthermore, as an evaluation method of a crack in surface layer  421   b , primary transfer and secondary transfer were crimped, and with voltages of 2 kV and 3 kV applied respectively to the primary transfer and the secondary transfer, idling for 200 hr was performed. Thereafter, by visual observation of the surface, the presence or absence of a crack was evaluated as follows.
         A: There is a crack.   D: There is no crack.       

     As illustrated in  FIG. 9 , the transferability was “D” when the film thickness of surface layer  421   b  was 0.4 μm (pattern (1)), “C” when the film thickness of surface layer  421   b  was 0.6 μm and 0.8 μm (patterns (2) and (3)), “B” when the film thickness of surface layer  421   b  was 1.0 μm and 1.2 μm (patterns (4) and (5)), and “A” when the film thickness of surface layer  421   b  was 1.4 μm or more (patterns (6) to (13)). That is, from the viewpoint of ensuring the transferability, the film thickness of surface layer  421   b  is preferably 1.0 μm or more. 
     In other words, by setting the film thickness of surface layer  421   b  to 1.0 μm or more, image forming apparatus  1  can ensure good transferability also for the depressed portion of the embossed paper. 
     Furthermore, as illustrated in  FIG. 9 , the crack evaluation in surface layer  421   b  was “B” when the film thickness of surface layer  421   b  was 3 μm or less (patterns (1) to (11)), and “D” when the film thickness of surface layer  421   b  was 3.2 μm or more (patterns (12) and (13)). That is, from the viewpoint of the crack evaluation in surface layer  421   b , the film thickness of surface layer  421   b  is preferably 3.0 μm or less. 
     From the above, in the evaluation results illustrated in  FIG. 9 , if both of the transferability and the prevention of occurrence of a crack are taken into consideration, the film thickness of surface layer  421   b  is desirably in the range of 1.0 μm or more and 3.0 μm or less. That is, when the film thickness of surface layer  421   b  is less than the lower limit value thereof (1.0 μm), for example, distance r illustrated in  FIG. 8  becomes short, electrostatic adhesion force F between the toner and intermediate transfer belt  421  increases, and the transferability deteriorates. Furthermore, in a case where the film thickness of surface layer  421   b  is larger than the upper limit value (3.0 μm), a crack occurs. 
     Furthermore, as illustrated in  FIG. 9 , the film thickness of surface layer  421   b  is more desirably in the range of 1.4 to 3.0 μm. By setting the film thickness of surface layer  421   b  within the range of 1.4 to 3.0 μm, good transferability (“A”) can be obtained without occurrence of a crack. 
     As described above, according to the first modification, image forming apparatus  1  can ensure good transferability while preventing occurrence of a crack in intermediate transfer belt  421 . 
     (Second Modification) 
     In a second modification, intermediate transfer belt  421  adopts a configuration in which an intermediate layer (not illustrated) is disposed between base material layer  421   a  and surface layer  421   b  in addition to base material layer  421   a  and surface layer  421   b.    
     The intermediate layer may have, for example, an elastic layer. The elastic layer may include, as a main component, for example, rubber in which a conductive material or the like is dispersed. Furthermore, as the rubber constituting the elastic layer, acrylonitrile-butadiene rubber, butadiene rubber, chloroprene rubber, urethane rubber, and the like may be used, but the rubber is not limited thereto. 
     The inventors of the present invention evaluated the transferability of intermediate transfer belt  421  including the intermediate layer by the following method and criteria. Note that in the second modification, materials, each parameter, and an evaluation method of transferability of image forming apparatus  1  (evaluator) used in the evaluation of transferability are similar to those in the first modification. 
     Furthermore, in the second modification, the intermediate layer uses NBR, a material having a film thickness of 150 μm and resistance of 10.2 log Ω/□. Furthermore, surface roughness Rz of surface layer  421   b  is 0.8 μm and the film thickness is 1.5 μm. However, surface roughness Rz and the film thickness of surface layer  421   b  are not limited to these values. 
     As the evaluation result of the second modification, the transferability was “A”: There is no problem with the entire surface” (not illustrated). As described above, according to the second modification, by providing intermediate transfer belt  421  with the intermediate layer, good transferability can be obtained. 
     (Third Modification) 
     In a third modification, a resistance value difference between surface layer  421   b  and base material layer  421   a  is defined. 
     As described above, it has been found that in a case where the content of the organic component in surface layer  421   b  is large (for example, in a case where the content of the organic component in surface layer  421   b  exceeds 30 mass %), transferability deteriorates when continuous paper passing (continuous printing) is performed. This deterioration of the transferability is presumably caused by that the resistance of surface layer  421   b  decreases due to energization of a transfer section. More specifically, in surface layer  421   b , bonding force with an inorganic component portion of Si—O is very strong, but bonding force with an organic component portion of Si—R is weak. For this reason, the bonding of Si—R is cut by the energization of the transfer section and conductivity is exhibited, whereby the resistance of the whole of surface layer  421   b  decreases. This decrease in the resistance of the whole of surface layer  421   b  is thought to cause the deterioration of the transferability. When the resistance of surface layer  421   b  decreases, a difference in resistance between surface layer  421   b  and base material layer  421   a  disappears and the principle as described with reference to  FIG. 8  (that is, principle that the counter charge opposite to the charge of the toner appears not in surface layer  421   b  but in base material layer  421   a ) no longer works. 
     Furthermore, as described in the first modification ( FIG. 9 ), the larger the film thickness of surface layer  421   b  is, the better transferability can be obtained. Therefore, the larger the film thickness of surface layer  421   b  is, the more conspicuous a tendency that the transferability deteriorates due to the decrease in the resistance of surface layer  421   b  due to continuous paper passing becomes. 
     Therefore, in the third modification, in a case where the content of the organic component in surface layer  421   b  is large (for example, in the case of 30 mass % or more), the larger the film thickness of surface layer  421   b  is, the lower resistance of base material layer  421   a  is designed. In other words, in a case where the content of the organic component in surface layer  421   b  is large, the larger the film thickness of surface layer  421   b  is, the larger the resistance value difference between surface layer  421   b  and base material layer  421   a  is made. 
     As a result, even in a case where the resistance of surface layer  421   b  decreases due to energization of the transfer section described above, the resistance value difference (resistance gap) between surface layer  421   b  and base material layer  421   a  can be maintained. Therefore, the principle as described with reference to  FIG. 8  works and good transferability can be maintained. 
     The present inventors evaluated the transferability in the third modification by the following method and criteria. Note that in the third modification, materials and each parameter of image forming apparatus  1  (evaluator) used in the evaluation of the transferability are similar to those in the first modification. 
     Furthermore, in the third modification, base material layer  421   a  of intermediate transfer belt  421  includes a material having a polyimide resin, a film thickness of 65 μm, and resistance of 9.5 log Ω/□, and surface layer  421   b  of intermediate transfer belt  421  uses a material containing silicon dioxide as a main component and having a film thickness of 3.0 μm is used. 
     Furthermore, for the material used for surface layer  421   b , both masses of tetraalkoxysilane (Si(OR) 4 ) and methyltrimethoxysilane ((CH 3 ) 3 SiCH 3 ) to be blended are adjusted such that the content of an organic component is 35 mass %. 
     Under the above conditions, intermediate transfer belt  421  was manufactured. In this case, 11.8 log Ω/□ was obtained as a resistance value of surface layer  421   b . That is, the resistance value difference between surface layer  421   b  and base material layer  421   a  is 2.3 digits. 
     Furthermore, in the evaluation of the transferability, as a comparative example with the third modification, intermediate transfer belt  421  in a case where the surface resistivity of base material layer  421   a  is 10.2 log Ω/□ was also manufactured. That is, in the comparative example, the resistance value difference between surface layer  421   b  and base material layer  421   a  is in 1.6 digits smaller than that of the third modification (2.3 digits). 
       FIG. 10  illustrates the results of evaluating the transferability in the third modification and the comparative example according to the following evaluation criteria. 
     Specifically, as a transferability evaluation method, the transferability at the time of continuous printing from the time of print start (start) until the printing number of prints 4 kp were evaluated (evaluated with “A”, “B”, “C”, and “D” as with the first modification). 
     As illustrated in  FIG. 10 , the transferability in the third modification was “A” until the number of prints reached 1.0 kp and “B” when the number of prints was 1.5 kp to 4.0 kp. That is, in the third modification, good transferability can be maintained at least until the number of prints reaches 4.0 kp. Meanwhile, the transferability in the comparative example was “A” until the number of prints reached 0.5 kp, “B” when the number of prints was 1.0 kp to 1.5 kp, “C” when the number of prints was 2.0 kp to 3.0 kp, and “D” when the number of prints was 4.0 kp. That is, in the comparative example, good transferability cannot be maintained after the number of prints reaches 2.0 kp. 
     Here, the measured value of the resistance of surface layer  421   b  alone after the number of prints passed 4 kp as illustrated in  FIG. 10  was 10.5 log Ω/□. Meanwhile, there is no change in the resistance of base material layer  421   a . The resistance of base material layer  421   a  is 9.5 log Ω/□ in the third modification and 10.2 log Ω/□ in the comparative example. That is, in the third modification, even in a case where the resistance of surface layer  421   b  decreases due to energization of the transfer section at the time of continuous printing, the resistance value difference between surface layer  421   b  and base material layer  421   a  can be maintained to be one digit. In contrary to this, in the comparative example, since the resistance of surface layer  421   b  decreased due to energization of the transfer section at the time of continuous printing, the resistance value difference between surface layer  421   b  and base material layer  421   a  was reduced to 0.3 digits. 
     As described above, in the third modification, even in a case where the resistance of surface layer  421   b  decreases due to energization of the transfer section like at the time of continuous printing, good transferability can be maintained by maintaining the resistance value difference between surface layer  421   b  and base material layer  421   a.    
     Furthermore, in  FIG. 10 , a case where the film thickness of surface layer  421   b  is 3.0 μm and the resistance value difference between surface layer  421   b  and base material layer  421   a  is 2.3 digits has been described, but the embodiment of the present invention is not limited to these values. For example, in a case where the content of the organic component in surface layer  421   b  is more than 30 mass %, the film thickness of surface layer  421   b  is C [μm], the resistance value difference between surface layer  421   b  and base material layer  421   a  is D [log Ω/□], it suffices to satisfy the relationship of formula (4), 
       0.6 ×C+ 0.2 ≤D    (4).
 
     By satisfying the relationship of formula (4), good transferability can be maintained in intermediate transfer belt  421 . 
     (Fourth Modification) 
     In a fourth modification, relationship between the content of an organic component and a film thickness in surface layer  421   b  is defined. 
     As described above, it has been found that the larger the content of the organic component in surface layer  421   b  becomes, the more transferability deteriorates (for example, see  FIG. 7 ). Meanwhile, as described above, it has been found that as film thickness d of surface layer  421   b  is made larger, the transferability improves (for example, see  FIG. 8 ). 
     Therefore, in the fourth modification, the larger the content of the organic component in surface layer  421   b  becomes, the larger the film thickness of surface layer  421   b  is made. 
       FIG. 11  illustrates an example of the relationship between the content [mass %] of the organic component in surface layer  421   b  and the film thickness [μm] of surface layer  421   b.    
     As illustrated in  FIG. 11 , in a case where the film thickness of surface layer  421   b  is small, the transferability is likely to deteriorate and in a case where the film thickness of surface layer  421   b  is large, a crack is likely to occur. In addition, as illustrated in  FIG. 11 , as the content of the organic component in surface layer  421   b  increases, the hardness of surface layer  421   b  decreases. Therefore, a crack is less likely to occur, but the transferability is likely to deteriorate. 
     For example, as illustrated in  FIG. 11 , it can be seen that in a case where the film thickness of surface layer  421   b  is 1 μm, good transferability is obtained when the content of the organic component in surface layer  421   b  is 15 mass %, whereas good transferability cannot be obtained when the content of the organic component is 25 mass % that is more than 20 mass %. Meanwhile, as illustrated in  FIG. 11 , it can be seen that in a case where the content of the organic component in surface layer  421   b  is 25 mass %, good transferability can be obtained when the film thickness of surface layer  421   b  is 2 μm. 
     As described above, by making the film thickness of surface layer  421   b  larger as the content of the organic component in surface layer  421   b  is larger, deterioration of transferability due to the content of the organic component in surface layer  421   b  can be supplemented by improvement of the transferability due to the film thickness of surface layer  421   b , and good transferability can be ensured. 
     For example, in a case where the content of the organic component in surface layer  421   b  is A [mass %] and the film thickness of surface layer  421   b  is B [μm], it suffices to satisfy the relationship of formula (5), 
       0.05 ×A&lt;B&lt; 0.05 ×A+ 2   (5).
 
     By satisfying the relationship of the formula (5), good transferability can be ensured in intermediate transfer belt  421 . 
     Each modification of the present embodiment has been described above. 
     Note that in the above embodiment, intermediate transfer belt  421  may further include a protective layer on surface layer  421   b . This makes it possible to suppress deterioration of surface layer  421   b.    
     Furthermore, in the above embodiment, intermediate transfer belt  421  (intermediate transfer member) has been described as an image bearing member including base material layer  421   a  and surface layer  421   b  disposed on base material layer  421   a . However, an embodiment of the present invention is not limited to the above embodiment and the embodiment of the present invention can be applied also to other image bearing members (for example, photoconductor drum  413 ) on which a toner image adhesion amount is detected. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purpose of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.