Patent Publication Number: US-9891579-B2

Title: Cleaning member and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2014-235385 filed Nov. 20, 2014. 
     BACKGROUND 
     Technical Field 
     The present invention relates to cleaning members and image forming apparatuses. 
     SUMMARY 
     A cleaning member according to an aspect of the invention includes a base member comprised of a first material that has a peak temperature of tan δ less than approximately zero degrees Celsius; and a contact portion comprised of a second material that has a higher hardness than the first material and a tear strength of approximately 49 kilonewtons per meter or higher, the contact portion contacting an image carrier and cleaning the image carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates the entire configuration of an image forming apparatus according to an exemplary embodiment of the invention; 
         FIG. 2  illustrates the configuration of a drum cleaner; 
         FIG. 3  illustrates the structure of a plate member; 
         FIGS. 4A to 4D  illustrate examples of the shape of a contact portion of the plate member; 
         FIG. 5  is a graph of the crack resistance index of the contact portion with respect to the peak temperature of tan δ of a first material, represented with different symbols corresponding to types of a second material; 
         FIG. 6  is a graph of the peak temperature of tan δ of the first material with respect to the tear strength of the second material, represented with different symbols sorted by the crack resistance index; 
         FIG. 7  illustrates the thickness of the contact portion; 
         FIG. 8  illustrates the contact portion in a manner enlarged in the direction of the thickness from the surface; and 
         FIG. 9  is a graph of the crack resistance index with respect to the thickness of the contact portion. 
     
    
    
     DETAILED DESCRIPTION 
     1. Exemplary Embodiment 
     1-1. Entire Configuration of Image Forming Apparatus 
     The configuration of an image forming apparatus  1  according to an exemplary embodiment of the invention is described below. In the drawings, the space in which components of the image forming apparatus  1  are disposed is represented as a xyz right-handed coordinate system space. Among the coordinate symbols illustrated in the drawings, an encircled dot denotes an arrow directing from the back to the front of the sheet. In the space, the direction along the x axis is represented as an x-axis direction. Part of the x-axis direction in which the x component increases is represented as a +x direction, whereas part of the x-axis direction in which the x component decreases is represented as a −x direction. Similarly, a y-axis direction, a +y direction, a −y direction, a z-axis direction, a +z direction, and a −z direction represent the directions defined in accordance with the above definition relating to the y or z component. 
       FIG. 1  illustrates the entire configuration of the image forming apparatus  1  according to an exemplary embodiment of the invention. As illustrated in  FIG. 1 , the image forming apparatus  1  includes a developing portion  13 , a transfer portion  14 , a fixing portion  15 , and a transporting portion  16 . 
     The transporting portion  16  includes a container and transport rollers. The container holds paper sheets P serving as media. The paper sheets P contained in the container are picked up one by one by a transport roller in response to a command from a controller, not illustrated, and transported to the transfer portion  14  through a sheet transport path. The media are not limited to paper sheets and may be sheets comprised of, for example, resin. In short, any media that is capable of recording images on their surfaces may be used. 
     The developing portion  13  includes an image carrier  31 , a charging device  32 , an exposing device  33 , a developing device  34 , a first transfer roller  35 , and a drum cleaner  36 . The image carrier  31  is a photoconductor drum having an electric-charge generating layer and an electric-charge conveying layer. The image carrier  31  is rotated by a driving portion, not illustrated, in the direction of an arrow D 13  around the axis extending in the x-axis direction of  FIG. 1 . The charging device  32  charges the surface of the image carrier  31 . The exposing device  33  includes components such as a laser-beam emitting source and a polygon mirror, not illustrated. The exposing device  33  irradiates the image carrier  31  charged by the charging device  32  with a laser beam in accordance with an image data under the control of a controller, not illustrated. Thus, a latent image is held on the image carrier  31 . 
     The above-described image data may be the one that the image forming apparatus  1  receives from an external apparatus via a communicating portion, not illustrated. Examples of the external apparatus here include a reading device that reads an original image or a storage device that stores data representing an image. The developing device  34  supplies a developer to the image carrier  31 . Thus, an image is formed (developed) on the image carrier  31 . 
     The first transfer roller  35  causes a predetermined potential difference at a position at which an intermediate transfer belt  41  of the transfer portion  14  faces the image carrier  31 . Thus, the first transfer roller  35  transfers the image to the intermediate transfer belt  41  using the potential difference. The drum cleaner  36  removes toner remaining on the surface of the image carrier  31  without being transferred after the image has been transferred and eliminates static from the surface of the image carrier  31 . 
     The transfer portion  14  includes an intermediate transfer belt  41 , a second transfer roller  42 , belt transport rollers  43 , a backup roller  44 , and a belt cleaner  49 . The transfer portion  14  transfers an image formed by the developing portion  13  to a paper sheet P. The belt transport rollers  43  and the backup roller  44  are disposed so as to be rotatable around respective axes extending in the x-axis direction of  FIG. 1 . The intermediate transfer belt  41  is an endless belt member and is stretched around the belt transport rollers  43  and the backup roller  44 . 
     At least one of the belt transport rollers  43  and the backup roller  44  includes a driving portion (not illustrated) to move the intermediate transfer belt  41  in the direction of an arrow D 14  of  FIG. 1 . The remaining roller or rollers  43  and/or  44  that do/does not include a driving portion are/is rotated in accordance with the movement of the intermediate transfer belt  41 . Rotating the intermediate transfer belt  41  in the direction of the arrow D 14  of  FIG. 1  moves the image on the intermediate transfer belt  41  to a position at which the image is nipped between the second transfer roller  42  and the backup roller  44 . 
     The second transfer roller  42  transfers the image on the intermediate transfer belt  41  to a paper sheet P transported from the transporting portion  16  using the potential difference between the second transfer roller  42  and the intermediate transfer belt  41 . A belt cleaner  49  removes toner remaining on the surface of the intermediate transfer belt  41  without being transferred. The transfer portion  14  or the transporting portion  16  transports to the fixing portion  15  the paper sheet P to which the image has been transferred. The fixing portion  15  fixes to the paper sheet P by heating the image that has been transferred to the paper sheet P. 
     1-2. Configuration of Drum Cleaner 
       FIG. 2  illustrates the configuration of the drum cleaner  36 . As illustrated in  FIG. 2 , the drum cleaner  36  includes a casing  360 , a plate member  361 , and a support member  362 . The drum cleaner  36  may also include components such as a mechanism that eliminates static from the surface of the image carrier  31  and a mechanism that supplies a lubricant to the surface. 
     The casing  360  is a housing that includes a support member  362  and has an opening  3600  on the side facing the image carrier  31 . The support member  362  has one end fixed to the inside of the casing  360 . The other end of the support member  362  is a free end and supports one end of the plate member  361 . The other end of the plate member  361  is exposed through the opening  3600  of the casing  360 . The plate member  361  supported by the support member  362  is in contact with the image carrier  31  at a predetermined pressure and at a predetermined angle (hereinafter referred to as a contact angle θ). The support member  362  does not have to support the plate member  361  throughout the full length in the x-axis direction. 
       FIG. 3  illustrates the structure of the plate member  361 . The point at which the plate member  361  comes into contact with the image carrier  31  is a contact point P 0 . The contact point P 0  may be any point on the surface of the image carrier  31 . Here, the contact point P 0  is regarded as a point furthest in the +y direction. The contact angle θ is an angle formed between the tangent plane F 0  at the contact point P 0  of the image carrier  31  and a direction in which the plate member  361  extends. The contact angle θ is an acute angle, that is, an angle less than a right angle. 
     The plate member  361  is an example of a cleaning member according to an exemplary embodiment of the invention. The plate member  361  is a plate-shaped cleaning blade and includes a contact portion  3611  and a base member  3612 . 
     The base member  3612  is a member comprised of, for example, rubber. The base member  3612  includes a portion that is attached or bonded to the support member  362 . Since this portion of the base member  3612  is attached or bonded to the support member  362 , the plate member  361  is supported in a fixed position at a predetermined position in the casing  360 . The material of the base member  3612  is hereinafter referred to as a first material. The first material is not limited to rubber and may be any material that satisfies the conditions described below. 
     The contact portion  3611  is a portion of the plate member  361  that comes into contact with the contact point P 0  of the image carrier  31  and is comprised of a second material having a hardness higher than that of the first material. Specifically, the contact portion  3611  is formed by changing the quality of part of an original base member, which has the shape of the plate member  361 , on the surface or surfaces facing the image carrier  31 . In this case, the base member  3612  is a remaining portion of the original base member whose quality has not been changed in the quality change. The quality change is a process during which the hardness of the first material forming the base member  3612  is enhanced to form a second material. Examples of the quality change include various types of oxidation treatment such as ultraviolet irradiation, corona discharge, plasma emission, or ozone atmosphere exposure and isocyanate resin impregnation. 
     The contact portion  3611  may be formed by coating the base member  3612  with any of various types of resin, low frictional agents, and particles. However, desirably, the contact portion  3611  is formed by changing the quality of the first material into the second material on the surface of the base member  3612 . This is because the contact portion  3611  formed by quality change is generally less likely to be detached at the boundary between itself and the base member  3612  than in the case of a contact portion formed through coating. 
     The contact portion  3611  removes an object such as toner adhering to the surface of the image carrier  31  by coming into contact with the image carrier  31  at the contact point P 0 . The object that has been scraped off by the contact portion  3611  of the plate member  361  is held in the casing  360  and removed from the image forming apparatus  1  at the time of maintenance. Specifically, the contact portion  3611  is comprised of a second material having a hardness higher than that of the first material. The contact portion  3611  is an example of a contact portion that cleans the image carrier by coming into contact with the image carrier in motion. 
     The contact portion  3611  may have any shape as long as it extends to a contact point P 0 .  FIGS. 4A to 4D  illustrate examples of the shape of the contact portion  3611  of the plate member  361 . Among the surfaces of the plate member  361 , one that faces the image carrier  31  and in the −z direction is referred to as a surface F 1  whereas one that faces the image carrier  31  and in the +z direction is referred to as a surface F 2 . Among the surfaces of the plate member  361 , one that faces away from the image carrier  31  and in the −z direction is referred to as a surface F 3  whereas one that faces away from the image carrier  31  and in the +z direction is referred to as a surface F 4 . 
     The contact portion  3611  may be disposed so as to extend over all the surfaces F 1  to F 4 , as illustrated in  FIG. 4A , or may be disposed so as to extend over the entireties of the surfaces F 1  and F 2  facing the image carrier  31 , as illustrated in  FIG. 4B . Alternatively, the contact portion  3611  may be disposed so as to extend over only the entirety of the surface F 1 , as illustrated in  FIG. 4C , or may be disposed so as to extend over only the entirety of the surface F 2 , as illustrated in  FIG. 4D . 
     2. Results of Experiment 
       FIG. 5  is a graph of the crack resistance index of the contact portion  3611  with respect to the peak temperature (referred to as “tan δ peak temperature”) of tan δ of the first material forming the base member  3612 , represented with different symbols corresponding to types of the second material forming the contact portion  3611 . Types of the second material are sorted into a A based material and a B based material by the original materials of the first material. What kind of effect is exerted on the crack resistance index was checked as a result of variously changing the conditions (factors such as process duration or liquid concentration) under which the quality change is performed on the first material. During measurement of the crack resistance index, the thickness of the contact portion  3611  was determined as 0.05 millimeters. This thickness is a thickness determined by a dynamic ultramicro hardness tester, described below. 
     The tan δ peak temperature is a temperature falling within the glass transition range of a certain material at which tan δ is maximum. The “δ” of tan δ denotes a loss angle. 
     Specifically, the tan δ peak temperature of a material was measured using an automatic dynamic viscoelastometer RHEOVIBRON (manufactured by Orientec Co., Ltd.), at the frequency of 10 Hz while the temperature is increased 0.1° C./min from the lower side (−45° C.) to the higher side (35° C.). 
     Tan δ at each temperature was obtained by the following method. Both end portions of each test piece were fixed to the viscoelastometer. A predetermined tension was applied to the test piece, the test piece was strained at the frequency of 10 Hz, and the stress thus caused in the test piece was measured. This stress was decomposed into an elastic stress based on which the storage elastic modulus and the loss elastic modulus were calculated. Tan δ was obtained by dividing the loss elastic modulus by the storage elastic modulus. The highest temperature of the obtained tan δ at each temperature was designated as the tan δ peak temperature. 
     The crack resistance index is an index that represents how easily the cleaning member, which cleans the image carrier, is likely to crack as a result of coming into contact with the image carrier in motion. The crack resistance index was measured in the following method. 
     The plate member  361  was mounted on DocuCentre-IVC5575 manufactured by Fuji Xerox Corporation, the contact pressure was adjusted to 2.0 gf/mm, the contact angle was adjusted to 11°, and the measurement was performed under the temperature of 10° C. and the relative humidity of 15%. Conical protrusions were provided on the surface of the image carrier  31 . Every time after the image carrier  31  makes 25 rotations, the blade end, that is, the portion of the contact portion  3611  that comes into contact with the image carrier  31  was observed. The number of rotations after which a crack was observed was determined as a cracking cycle number. The value obtained by dividing the obtained cracking cycle number by 250 was determined as a crack resistance index. 
     Sapphire was used as the material of the protrusions. The angle at the end of the protrusions was 60 degrees, the radius of curvature was 0.05 millimeters, and the height was 0.05 millimeters. 
     For example, if the contact portion  3611  is found to be cracked after the image carrier  31  has made first 25 rotations, the cracking cycle number is represented as “25” and the crack resistance index is represented as “0.1”. The sample having a crack resistance index of 0.2 or higher is regarded as being practically tolerable and the sample having a crack resistance index of 0.1 or lower is regarded as being practically unacceptable. 
     As illustrated in  FIG. 5 , when the tan δ peak temperature is used alone as an index, the conditions under which the crack resistance index is 0.2 or higher are not found regardless of the type of the second material. This is probably because, although the same material is used, the difference in conditions between the ways of the quality change changes the crack resistance of a finally obtained contact portion  3611 . 
       FIG. 6  is a graph of the tan δ peak temperature of the first material with respect to the tear strength of the second material, represented with different symbols sorted by the crack resistance index. The samples are sorted into three groups, a group having a crack resistance index of 0.1, a group having a crack resistance index within the range of 0.2 to 0.6, and a group having a crack resistance index of 0.7 or higher. The samples in each group were denoted by the same symbols. 
     The tear strength (kilonewton per meter [kN/m]) was measured in accordance with JIS-K6252 “Rubber, Vulcanized or Thermoplastic, Determination of Tear Strength” while the rate at which a test-piece gripper moves is determined at 500±50 millimeters per minute [mm/min], an uncut angle test piece was stretched, and the maximum tear strength at which the test piece is broken was read. The tear strength TR was obtained from the following equation (1):
 
 TR=F/t   (1).
 
     Here, F (newton [N]) is the maximum tear strength described above and t (millimeters [mm]) is the thickness of the test piece. Strograph AE elastomer manufactured by Toyo Seiki Seisaku-sho, Ltd. was used as a testing machine. 
     As illustrated in  FIG. 6 , it is found that the crack resistance index of the contact portion  3611  is 0.2 or greater when the tan δ peak temperature of the first material is less than 0 degrees Celsius and the tear strength of the second material is 49 kilonewtons per meter or higher. 
     Thus, a cleaning member that is less likely to crack is produced by selecting the material and the conditions (factors such as process time and liquid concentration) of the quality change at the design stage of the plate member  361 , serving as a cleaning member, in such a manner that the peak temperature of tan δ of the first material forming the base member  3612  is determined to be less than 0 degrees Celsius and the tear strength of the second material forming the contact portion  3611  is 49 kilonewtons per meter or higher. 
     3. Modified Example 
     An exemplary embodiment has been described thus far, but the contents of the exemplary embodiment may be modified in the following manner. Modified examples may be combined together. 
     3-1. Modified Example 1 
     In the above-described exemplary embodiment, the image forming apparatus  1  includes only one developing portion  13  but may include multiple developing portions  13 . In this case, the image forming apparatus  1  may include, in one-to-one correspondence with the multiple developing portions  13 , image carriers  31 , charging devices  32 , exposing devices  33 , developing devices  34 , first transfer rollers  35 , and drum cleaners  36 . The multiple developing portions  13  may form toner images of different colors. In this case, the toner images of different colors are transferred to the intermediate transfer belt  41  in a stacked manner, so that a color image is formed on a medium such as a paper sheet P. 
     3-2. Modified Example 2 
     In the above-described exemplary embodiment, the plate member  361  is included in the drum cleaner  36 , but may be included in the belt cleaner  49 . In this case, the plate member  361  may remove an object adhering to the intermediate transfer belt  41  instead of the image carrier  31 . Here, the image carrier  31  and the intermediate transfer belt  41  are examples of an image carrier that holds an image that is to be formed on a medium. 
     3-3. Modified Example 3 
     Desirably, the thickness of the contact portion  3611  is 0.1 millimeters or less.  FIG. 7  illustrates the thickness of the contact portion  3611 . As illustrated in  FIG. 4B , for example, the contact portion  3611  extends over the entireties of the surfaces F 1  and F 2  from the contact point P 0 . The direction of the depth in the surface F 1  is defined as a +v direction and the direction of the depth in the surface F 2  is defined as a +w direction. The contact point P 0  is a ridge extending in the x-axis direction of the plate member  361 . Thus, this space is represented by the x axis, the v axis, and the w axis. 
       FIG. 8  illustrates the contact portion  3611  in a manner enlarged in the direction of the thickness from the surface F 1 . The +v direction, which is the direction of the thickness from the surface F 1 , is a direction along the normal to the surface F 1 . 
     Using a dynamic ultramicro hardness tester DUH-W201S manufactured by Shimadzu Corporation, the dynamic ultramicro hardness DH of the contact portion  3611  was measured at each section formed by being scraped per 0.01 millimeters from the surface F 1 . The portion that has a dynamic ultramicro hardness DH 30% less than that of the previously measured portion, that is, the portion that is 0.01 millimeters shallower is determined as being no longer the contact portion  3611 . 
     For example, in  FIG. 8 , measured portions F 11 , F 12 , F 13 , and F 14  are sections respectively positioned at the depth of 0.01, 0.02, 0.03, and 0.04 millimeters from the surface F 1  in the v direction. Here, if the dynamic ultramicro hardness DH measured at the measured portion F 14  is 30% less than the dynamic ultramicro hardness DH measured at the measured portion F 13 , the thickness of the contact portion  3611  ends at the measured portion F 13 . 
     The dynamic ultramicro hardness DH is a hardness calculated from the following equation (2) using the indent depth D micrometers [μm] at the time when a diamond triangular pyramid indenter (inter-ridge angle of 115 degrees and α of 3.8584) is indented at the pressing speed of 0.047399 millinewtons per second [mN/s], at the testing load P=4.0 millinewtons [mN], and under the environmental temperature of 23° C.:
 
 DH=α×P/D 2  (2),
 
where α denotes a constant relating to the shape of the indenter.
 
       FIG. 9  is a graph of the crack resistance index with respect to the thickness of the contact portion  3611  assessed by the dynamic ultramicro hardness. The experiment was performed on three types of second material and in which the crack resistance index was measured while the thickness of the contact portion  3611  was changed in four stages of 0.02, 0.05, 0.1, and 0.2 millimeters. The selected three types of second material are those respectively having crack resistance indexes of 0.2, 0.3, and 1.3 (all of which are 0.2 or higher, regarded as being “practically bearable”) when the thickness of the contact portion  3611  is 0.05 millimeters. 
     As illustrated in  FIG. 9 , at the thickness of 0.1 millimeters, all the types of material have maintained the same crack resistance indexes as those at the thickness of 0.05 millimeters. However, at the thickness of 0.2 millimeters, all the types of material have reduced their crack resistance indexes to 0.1. Specifically, it is desirable that the thickness of the contact portion  3611  be 0.1 millimeters or less. The material having a thickness of 0.2 millimeters or greater is found to be practically unacceptable in terms of the crack resistance index. 
     The depth by which the material wears as a result of a contact with the image carrier is approximately several tens of micrometer at most. Thus, wear negligibly affects the material even when the thickness of the contact portion  3611  is 0.1 millimeters or less. The +w direction, which is the direction of the thickness from the surface F 2  is also defined similarly to the case of the v direction. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.