Image forming apparatus, transfer roller, and image forming method

Abstract

To provide an image forming apparatus excellent in toner cleaning property of a roller constituting a transfer member.SOLUTION: The image forming apparatus includes a transfer member for transferring an image on an image carrier 440 to a recording material S, and transfers a toner image on the image carrier 440 to the recording material S by applying a voltage between the image carrier 440 and the transfer member 450 across the recording material S. The toner is negatively charged, the transfer member 450 includes a secondary transfer roller 424 that rotates around a rotation shaft 483, at least one rubber layer 481 is provided on the rotation shaft 483 side of the secondary transfer roller 424, a coating layer 482 is provided on an outermost surface of the secondary transfer roller 424, the coating layer 482 contains at least a urethane resin and a silicone compound, and an average particle diameter of an aggregate of the silicone compound is less than 7 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, a transfer roller, and an image forming method, and more particularly to an image forming apparatus, a transfer roller, and an image forming method that are excellent in toner cleaning properties of a roller that constitutes a transfer member. [Background technology]

[0002] With the demand for light-duty printing machines, image forming devices that form images using electrophotography are required to improve performance, such as higher speed, higher quality, and longer life. Achieving higher speed means, for example, shortening the time it takes for the transfer medium to pass through the fixing device. Therefore, image forming devices are required to fix toner images with less energy. Hereinafter, "transfer medium" will also be referred to as "recording material."

[0003] In order to meet the demand for fixing toner images with less energy as described above, there is a tendency to study lowering the melting temperature and melt viscosity of the binder resin of the toner. By lowering the melting temperature and melt viscosity of the binder resin of the toner, the toner can be fixed at a low temperature. To achieve both low-temperature fixability and heat-resistant storage stability of the toner, the addition of a polyester resin to the binder resin has been studied (see, for example, Patent Document 1).

[0004] On the other hand, studies have been conducted to prevent toner filming on the roller by coating the outermost surface of the secondary transfer roller with urethane or the like to suppress the tackiness of the rubber (see, for example, Patent Document 2).

[0005] Furthermore, a cleaning method has also been considered in the past, in which an electric field is applied to the toner adhering to the secondary transfer roller, causing it to return to the intermediate transfer belt (see, for example, Patent Document 3). This method of cleaning by applying an electric field to the toner is advantageous for paper transport because the torque required for running the secondary transfer roller is lower than a method of mechanically cleaning the secondary transfer roller with a blade, and it also allows for a compact, low-cost design, making it an effective means. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-249726 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-317627 [Patent Document 3] Japanese Patent Application Publication No. 2017-90811 Summary of the Invention [Problem to be solved by the invention]

[0007] In response to the above-mentioned needs for low-temperature fixation of toner and long life for components constituting image forming apparatuses, the problem of toner filming occurring on secondary transfer rollers during use is becoming apparent. Here, toner filming refers to a phenomenon in which toner adheres to the surface of a transfer roller or the like in the form of a thin film due to repeated image formation, resulting in film-like contamination.

[0008] For this reason, there is an increasing demand for improved cleaning performance of transfer rollers in image forming apparatuses, and there is a demand for the development of an image forming apparatus and an image forming method that are excellent in toner cleaning performance of rollers that constitute transfer members.

[0009] The present invention has been made in view of the above problems and circumstances, and an object of the present invention is to provide an image forming apparatus, a transfer roller, and an image forming method that are excellent in toner cleaning performance of a roller that constitutes a transfer member. [Means for solving the problem]

[0010] The present inventors have investigated the causes of the above problems in order to solve the above problems. They have found that applying a urethane coating to the outermost surface of a roller constituting a transfer member and adding a silicone compound to the urethane coating changes the charge of the toner, thereby improving the cleaning properties of the roller. Specifically, the above problems according to the present invention are solved by the following means.

[0011] 1. An image forming apparatus that includes a transfer member that transfers an image on an image carrier to a recording material, and transfers a toner image on the image carrier to the recording material by applying a voltage between the image carrier and the transfer member, with the recording material sandwiched therebetween, The toner is negatively charged the transfer member has a roller that rotates around a rotation axis, has at least one rubber layer on the rotation axis side of the roller, and has a coating layer on the outermost surface of the roller; 1. An image forming apparatus, wherein the coating layer contains at least a urethane resin and a silicone compound, and the average particle size of the aggregates of the silicone compound is less than 7 μm.

[0012] 2. The image forming apparatus according to claim 1, wherein the toner image on the image carrier is transferred from a photosensitive member.

[0013] 3. The image-forming apparatus according to item 1 or 2, wherein the coating layer contains the silicone compound in an amount of 0.5 to 50% by mass relative to the total mass of the coating layer.

[0014] 4. The image forming apparatus according to item 1 or 2, wherein the coating layer of the transfer member has a thickness of 1 to 20 μm.

[0015] 5. The image forming apparatus according to item 1 or 2, wherein the roller has a surface roughness of 1 to 12 μm.

[0016] 6. An image forming apparatus as described in item 1 or 2, characterized in that it is provided with an electric field control means that controls the electric field between the image carrier and the transfer member in a direction that returns the toner on the transfer member to the image carrier when there is no recording material between the image carrier and the transfer member.

[0017] 7. The image forming apparatus according to item 6, wherein the toner contains a polyester resin as a binder resin.

[0018] 8. The image forming apparatus according to item 7, wherein the toner contains a styrene acrylic resin as the binder resin.

[0019] 9. The image-forming apparatus according to item 1 or 2, wherein the coating layer does not contain an organic fluorine compound.

[0020] 10. A transfer roller of an image forming apparatus that transfers a toner image on an image carrier to a recording material by applying a voltage between the image carrier and the transfer roller, with the recording material sandwiched therebetween, A transfer roller characterized in that it has at least one rubber layer on the rotation axis side of the transfer roller and a coating layer on the outer periphery thereof, the coating layer containing a urethane resin and a silicone compound, and the average particle size of the aggregates of the silicone compound is less than 7 μm.

[0021] 11. An image forming method including a step of transferring a toner image on an image carrier to a recording material by applying a voltage between the image carrier and a transfer member sandwiching the recording material, The toner is negatively charged the transfer member has a roller that rotates around a rotation axis, has at least one rubber layer on the rotation axis side of the roller, and has a coating layer on the outermost surface of the roller; 1. An image forming method, wherein the coating layer contains at least a urethane resin and a silicone compound, and the average particle size of the aggregates of the silicone compound is less than 7 μm. [Effects of the Invention]

[0022] The above-described means of the present invention can provide an image forming apparatus and an image forming method that are excellent in toner cleaning properties of the roller that constitutes the transfer member. Also, the above-described means of the present invention can provide a transfer roller that is excellent in toner cleaning properties.

[0023] The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is speculated as follows.

[0024] In the image forming apparatus of the present invention, the transfer member has a roller that rotates around a rotation axis, and the roller has at least one rubber layer on the rotation axis side and a coating layer on the outermost surface of the roller. The coating layer contains at least a urethane resin and a silicone compound, and the average particle diameter of the aggregate of the silicone compound is less than 7 μm. Hereinafter, the roller that constitutes the transfer member described above may be referred to as a "transfer roller."

[0025] The silicone compound contained in the material constituting the coating layer of the transfer roller is more negatively charged than the toner material in the charge hierarchy. Therefore, by providing a coating layer containing a silicone compound on the outermost surface of the transfer roller, the charge of the toner adhering to the transfer roller is more easily transferred to the transfer roller. When the charge of the toner is transferred to the transfer roller, the charge of the toner decreases, and the toner adhesion strength decreases. Therefore, it is presumed that the toner cleaning ability of the transfer roller is improved.

[0026] In the image forming apparatus of the present invention, the method for cleaning the transfer roller is not particularly limited. For example, it may be a cleaning method in which an electric field is applied to the toner adhering to the transfer roller to return it to the intermediate transfer belt, or a cleaning method in which a cleaning blade is brought into contact with the transfer roller to mechanically remove the toner adhering to the transfer roller. For example, if an electric field is applied to the toner to return it to the intermediate transfer belt, the adhesive force of the toner is reduced, making it easier for the toner to move to the intermediate transfer belt when an electric field is applied to move it to the intermediate transfer side, which is thought to improve toner cleaning properties. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus. [Figure 2] FIG. 2 is a schematic diagram of a secondary transfer unit in the image forming apparatus. [Figure 3] FIG. 1 is a block diagram illustrating an example of the configuration of an image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0028] An embodiment of the image forming apparatus of the present invention includes a transfer member that transfers an image on an image carrier to a recording material, and transfers the toner image on the image carrier to the recording material by applying a voltage between the image carrier and the transfer member, with the recording material sandwiched between them. In the image forming apparatus of this embodiment, the toner is negatively charged. The transfer member has a roller that rotates around a rotation axis, with at least one rubber layer on the rotation axis side of the roller and a coating layer on the outermost surface of the roller. The image forming apparatus of this embodiment is characterized in that the coating layer contains at least a urethane resin and a silicone compound, and the average particle diameter of the aggregates of the silicone compound is less than 7 μm. This feature is a technical feature common to or corresponding to each of the following embodiments.

[0029] The image forming apparatus of this embodiment has a coating layer containing the above-described silicone compound on the outermost surface of the roller of the transfer member, which reduces the toner adhesion to the roller and provides excellent toner cleaning properties. If the average particle diameter of the silicone compound aggregates contained in the coating layer exceeds 7 μm, the silicone particles in the coating layer become less firmly fixed, making them more likely to peel off from the surface of the coating layer. For these reasons, if the average particle diameter of the silicone compound aggregates contained in the coating layer exceeds 7 μm, it becomes difficult to obtain good toner cleaning properties.

[0030] In the image forming apparatus of this embodiment, from the viewpoint of efficiency in forming a multicolor image, it is preferable that the toner image on the image carrier is one that has been transferred from a photosensitive member.

[0031] There are no particular restrictions on the content of the silicone compound contained in the coating layer. However, from the viewpoint of the strength of the coating layer, the coating layer preferably contains 0.5 to 50% by mass of the silicone compound relative to the total mass of the coating layer.

[0032] There are no particular restrictions on the thickness of the coating layer of the transfer member, but from the viewpoint of durability, the thickness of the coating layer is preferably 1 to 20 μm.

[0033] There are no particular restrictions on the surface roughness of the roller constituting the transfer member, but from the viewpoint of uniformity of the transfer electric field formed in the transfer area, for example, the surface roughness of the roller is preferably 1 to 12 μm.

[0034] The image forming apparatus of this embodiment may include an electric field control unit that controls the electric field between the image carrier and the transfer member in a direction that returns the toner on the transfer member to the image carrier when there is no recording material between the image carrier and the transfer member. By including such an electric field control unit, toner adhering to the transfer roller or the like that constitutes the transfer member can be returned to the image carrier such as the intermediate transfer belt, making it easy to clean the transfer member.

[0035] In the image forming apparatus of this embodiment, for example, from the viewpoint of improving the low-temperature fixability of the toner, it is preferable to use a toner containing a polyester resin as a binder resin, and it is more preferable to use a toner containing a styrene acrylic resin as a binder resin.

[0036] Furthermore, for example, from the viewpoint of adhesion between the coating layer and the rubber layer, it is preferable that the coating layer does not contain an organic fluorine compound.

[0037] Next, an embodiment of the transfer roller of the present invention will be described. The transfer roller of this embodiment is a transfer roller of an image forming device that transfers a toner image on an image carrier to a recording material by applying a voltage between the image carrier and the transfer roller, with the recording material sandwiched between them. The transfer roller of this embodiment has at least one rubber layer on the rotation shaft side of the transfer roller and a coating layer on its outer periphery. The coating layer is characterized by containing a urethane resin and a silicone compound, and the average particle size of the aggregates of the silicone compound is less than 7 μm.

[0038] Next, an embodiment of the image forming method of the present invention will be described. The image forming method of this embodiment includes a step of transferring a toner image on an image carrier to a recording material by applying a voltage between the image carrier and a transfer member, with the recording material sandwiched therebetween. In the image forming method of this embodiment, the toner is negatively charged. The transfer member has a roller that rotates around a rotation axis, and has at least one rubber layer on the rotation axis side of the roller, and a coating layer on the outermost surface of the roller. The coating layer is characterized by containing at least a urethane resin and a silicone compound, and the average particle size of the aggregate of the silicone compound is less than 7 μm.

[0039] Hereinafter, an example of an embodiment of the image forming apparatus of the present invention will be described, but the present invention is not limited to the following example.

[0040] [Configuration of image forming device] FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to this embodiment. FIG. 2 is a schematic diagram of a secondary transfer unit in the image forming apparatus. FIG. 3 is a block diagram showing an example of the configuration of the image forming apparatus. As shown in FIGS. 1 to 3, the image forming apparatus 1 is an intermediate transfer type color image forming apparatus that uses electrophotographic process technology. That is, the image forming apparatus 1 primarily transfers toner images of each color, Y (yellow), M (magenta), C (cyan), and K (black), formed on a photosensitive member 413, onto an intermediate transfer belt 421, and then superimposes the four color toner images on the intermediate transfer belt 421, and then secondarily transfers the toner images onto a recording material S, thereby forming an image.

[0041] The image forming apparatus 1 employs a tandem system in which photosensitive elements 413 corresponding to the four colors YMCK are arranged in series in the running direction of an intermediate transfer belt 421, and each color toner image is transferred sequentially to the intermediate transfer belt 421 in a single step.

[0042] The image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a conveying unit 50, a fixing unit 60, and a control unit 100.

[0043] The image reading unit 10 is configured to include an automatic document feeder 11 called an ADF, and an original image scanning device 12 such as a scanner. "ADF" is an abbreviation for "Auto Document Feeder."

[0044] The automatic document feeder 11 transports the documents D placed on the document tray using a transport mechanism and sends them to the document image scanning device 12. The automatic document feeder 11 makes it possible to continuously read the images of multiple documents D placed on the document tray all at once.

[0045] The document image scanning device 12 optically scans a document transported from the automatic document feeder 11 onto the contact glass or a document placed on the contact glass. Then, light reflected from the document is focused on the light receiving surface of the CCD sensor 12a, and the document image is read. The image reading unit 10 generates input image data based on the results of reading by the document image scanning device 12. This input image data is subjected to predetermined image processing in the image processing unit 30. Note that "CCD" is an abbreviation for "Charge Coupled Device," meaning a charge-coupled device.

[0046] The operation display unit 20 is configured, for example, by a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image states, operation statuses of various functions, etc., in accordance with display control signals input from the control unit 100. The operation unit 22 has various operation keys such as a numeric keypad and a start key, and accepts various input operations by the user and outputs operation signals to the control unit 100.

[0047] The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, under the control of the control unit 100, the image processing unit 30 performs gradation correction based on gradation correction data and a gradation correction table. In addition to gradation correction, the image processing unit 30 also performs various correction processes such as color correction and shading correction, as well as compression, on the input image data. The image forming unit 40 is controlled based on the image data that has undergone these processes.

[0048] The image forming section 40 includes image forming units 41Y, 41M, 41C, and 41K for forming images with color toners of Y, M, C, and K components based on input image data, an intermediate transfer unit 42, and the like.

[0049] The image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components have the same configuration. For ease of illustration and explanation, common components are denoted by the same reference numerals, and when distinguishing between them, the reference numerals are suffixed with Y, M, C, or K. In Figure 1, only the components of the image forming unit 41Y for the Y component are denoted by reference numerals, and the components of the other image forming units 41M, 41C, and 41K are not denoted by reference numerals.

[0050] The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive member 413, a charging device 414, a drum cleaning device 415, and the like.

[0051] The photoreceptor 413 is, for example, a negatively charged organic photoreceptor in which an undercoat layer, a charge generating layer, and a charge transport layer are sequentially laminated on the peripheral surface of an aluminum conductive cylinder.

[0052] The charging device 414 generates a corona discharge to uniformly charge the surface of the photoconductor 413, which has photoconductivity, to a negative polarity.

[0053] The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photoconductor 413 with laser light corresponding to an image of each color component. Positive charges are generated in the charge generation layer of the photoconductor 413, and are transported to the surface of the charge transport layer, thereby neutralizing the negative charges that are the surface charges of the photoconductor 413. An electrostatic latent image of each color component is formed on the surface of the photoconductor 413 due to the potential difference with the surrounding area.

[0054] Developing device 412 is a two-component reversal type developing device, and visualizes the electrostatic latent image to form a toner image by adhering toner of each color component to the surface of photoconductor 413. Developing device 412 forms a toner image on the surface of photoconductor 413 by supplying toner contained in the developer to photoconductor 413.

[0055] Drum cleaning device 415 has a drum cleaning blade or the like that is brought into sliding contact with the surface of photoreceptor 413, and removes untransferred toner remaining on the surface of photoreceptor 413 after primary transfer.

[0056] The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, and a belt cleaning device 426. In the image forming apparatus 1, the photosensitive member 413 and the intermediate transfer belt 421 correspond to an image carrier 440. The primary transfer roller 422 and the secondary transfer roller 424 correspond to a transfer member 450.

[0057] The intermediate transfer belt 421 is an endless belt that is stretched in a loop around multiple support rollers 423. At least one of the multiple support rollers 423 is a drive roller, and the others are driven rollers. As the drive roller rotates, the intermediate transfer belt 421 runs at a constant speed in direction A.

[0058] Intermediate transfer belt 421 is a conductive and elastic belt. Intermediate transfer belt 421 is driven to rotate by a control signal from control unit 100. Note that there are no limitations on the material, thickness, or hardness of intermediate transfer belt 421, as long as it is conductive and elastic.

[0059] The primary transfer roller 422 faces the photoconductor 413 of each color component and is disposed on the inner peripheral surface side of the intermediate transfer belt 421. The primary transfer roller 422 is pressed against the photoconductor 413 with the intermediate transfer belt 421 sandwiched therebetween, thereby forming a primary transfer nip for transferring a toner image from the photoconductor 413 to the intermediate transfer belt 421.

[0060] Secondary transfer roller 424, which serves as transfer member 450, is disposed on the outer circumferential surface of intermediate transfer belt 421, facing opposing roller 423B, which is disposed downstream of drive roller 423A in the belt running direction. Secondary transfer roller 424 and opposing roller 423B constitute a secondary transfer unit that transfers the toner image carried on intermediate transfer belt 421 to recording material S. Here, the term "secondary transfer unit" is a general term for parts related to secondary transfer. Specifically, the secondary transfer unit includes secondary transfer roller 424, opposing roller 423B, and the like. Meanwhile, parts related to primary transfer, including the above-described primary transfer roller 422, and the like, are sometimes collectively referred to as the "primary transfer unit." The primary transfer unit and secondary transfer unit are also collectively referred to simply as the "transfer unit," and the components of such a transfer unit, such as secondary transfer roller 424 and primary transfer roller 422, are also referred to as transfer member 450.

[0061] Secondary transfer roller 424 moves between a contact position where it contacts intermediate transfer belt 421 and a separation position where it is separated from intermediate transfer belt 421. Secondary transfer roller 424 is located at the separation position when not printing, and is controlled to move to the contact position in accordance with the printing operation.

[0062] The belt cleaning device 426 removes the residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer.

[0063] When intermediate transfer belt 421 passes through the primary transfer nip, the toner image on photoconductor 413 is primarily transferred onto intermediate transfer belt 421 in a sequentially overlapping manner. Specifically, a primary transfer bias is applied to primary transfer roller 422, and a charge of the opposite polarity to the toner is applied to the back side of intermediate transfer belt 421, that is, the side that contacts primary transfer roller 422, so that the toner image is electrostatically transferred onto intermediate transfer belt 421.

[0064] Thereafter, when the recording material S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred onto the recording material S.

[0065] The fixing section 60 includes an upper fixing section 60A having a fixing surface side member arranged on the side on which the toner image is formed, which is the fixing surface of the recording material S, and a lower fixing section 60B having a back surface side support member arranged on the side opposite the fixing surface, which is the back surface of the recording material S. When the back surface side support member is pressed against the fixing surface side member, a fixing nip is formed that holds and transports the recording material S.

[0066] The fixing unit 60 fixes the toner image onto the recording material S by applying heat and pressure to the conveyed recording material S at a fixing nip after the toner image has been secondarily transferred. The fixing unit 60 is disposed as a unit inside the fixing device F. The fixing device F may also be provided with an air separation unit that blows air to separate the recording material S from the fixing surface side member or the back surface side support member.

[0067] The upper fixing unit 60A has an endless fixing belt 61, which is a fixing surface side member, a heating roller 62, and a fixing roller 63. The fixing belt 61 is stretched between the heating roller 62 and the fixing roller 63.

[0068] The heating roller 62 has a built-in heat source such as a halogen heater and heats the fixing belt 61. The heating roller 62 is heated by the heat source, and as a result, the fixing belt 61 is heated.

[0069] The fixing roller 63 rotates in a clockwise direction under the driving control of the control unit 100. When the fixing roller 63 rotates, the fixing belt 61 and the heating roller 62 are driven to rotate in the clockwise direction.

[0070] The lower fixing unit 60B has a pressure roller 64 which is a back surface support member. The pressure roller 64 forms a fixing nip between the pressure roller 64 and the fixing belt 61 to sandwich and transport the recording material S. The pressure roller 64 is driven and controlled by the control unit 100 to rotate in a counterclockwise direction.

[0071] The conveying section 50 includes a paper feed section 51, a paper discharge section 52, and a conveying path section 53. The three paper feed tray units 51a to 51c that make up the paper feed section 51 store recording materials S, identified based on basis weight, size, etc., according to a preset type. Examples of the recording materials S include standard paper and special paper. The conveying path section 53 includes a plurality of conveying roller pairs, such as a registration roller pair 53a.

[0072] The recording materials S contained in the paper feed tray units 51a to 51c are fed one by one from the top and transported to the image forming unit 40 by the transport path unit 53. At this time, a registration roller unit having a registration roller pair 53a corrects the inclination of the fed recording materials S and adjusts the transport timing. Then, in the image forming unit 40, the toner images on the intermediate transfer belt 421 are secondarily transferred all at once onto one side of the recording materials S, and a fixing process is performed in the fixing unit 60. The recording materials S with the images formed thereon are discharged outside the apparatus by the paper discharge unit 52 having a paper discharge roller 52a.

[0073] [Secondary transfer roller] Next, the configuration of secondary transfer roller 424 as transfer member 450 will be described. Here, Fig. 2 is a schematic diagram of a secondary transfer unit in image forming apparatus 1 for secondarily transferring a toner image onto recording material S. As shown in Fig. 2, in the secondary transfer unit, secondary transfer roller 424 and opposing roller 423B transfer the toner image carried on intermediate transfer belt 421 onto recording material S.

[0074] Secondary transfer roller 424 as transfer member 450 has at least one rubber layer 481 on the roller's rotation shaft 483 side, and has coating layer 482 on the outermost surface of the roller. Coating layer 482 contains at least a urethane resin and a silicone compound, and the average particle diameter of the aggregate of the silicone compound is less than 7 μm. In secondary transfer roller 424, for example, rubber layer 481 is arranged so as to surround the outer periphery of a core metal as a shaft body, which is rotation shaft 483 of secondary transfer roller 424, and coating layer 482 is arranged so as to surround the outer periphery of rubber layer 481.

[0075] By having the above-described structure, the secondary transfer roller 424 can contact the recording material S and the intermediate transfer belt 421 with a substantially uniform nip pressure in the axial direction, and also has excellent toner cleaning properties.

[0076] (rubber layer) The rubber layer 481 constituting the secondary transfer roller 424 is formed, for example, by covering a shaft body, such as a core metal, which is the rotating shaft 483, and is made of a solid elastic body. Examples of the rubber layer 481 include rubber made of adhesive rubber, conductive rubber made by adding a conductive material to non-adhesive rubber, or semi-conductive rubber. Examples of rubber that can be used include nitrile rubber (NBR), ethylene-propylene rubber (EPDM), hydrin rubber, urethane rubber, acrylic rubber, and chloroprene rubber. Examples of adhesive rubber that can be used include nitrile rubber (NBR), ethylene-propylene rubber (EPDM), or the like, to which a tackifier such as phenol resin, coumarone resin, acetylene resin, or terpene resin has been added. It is preferable that the rubber layer 481 be made of a solid elastic body made of the above-mentioned rubber.

[0077] Rubber layer 481 can be formed using any of the above-mentioned various rubbers as a main component. Rubber layer 481 may contain 1 to 100 parts by mass of a conductive material such as carbon black or quaternary ammonium to ensure conductivity, per 100 parts by mass of the main component.

[0078] Furthermore, the main component may contain, but is not limited to, 0.3 to 5 parts by mass of a crosslinking agent such as sulfur, 1 to 10 parts by mass of a crosslinking aid such as zinc oxide, and 0.5 to 3 parts by mass of a crosslinking accelerator such as thiazoles, dithiocarbamates, or thiurams.

[0079] Furthermore, various additives such as lubricants and inorganic fillers may be appropriately blended into the base material as required.

[0080] (coat layer) Coat layer 482 is a layer that constitutes the outermost surface of secondary transfer roller 424. Coat layer 482 contains at least a urethane resin and a silicone compound. In coat layer 482, the average particle diameter of the aggregate of the silicone compound is less than 7 μm.

[0081] The urethane resin can be obtained by polymerizing polyisocyanate and polyol, and serves as a matrix material for the coating layer 482, which contains at least the urethane resin and the silicone compound.

[0082] Examples of the polyisocyanate include aromatic polyisocyanates such as phenylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, polymethylene polyphenyl polyisocyanate, and carbodiimidized diphenylmethane polyisocyanate; and aliphatic or alicyclic polyisocyanates such as hexamethylene diisocyanate, lysine diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, dimer acid diisocyanate, and norbornene diisocyanate. These polyisocyanates may be used alone or in combination of two or more.

[0083] Examples of the polyol include polyether polyol, polyester polyol, polyacrylic polyol, polycarbonate polyol, polybutadiene polyol, etc. These polyols may be used alone or in combination of two or more.

[0084] Coat layer 482 contains a silicone compound in addition to the urethane resin described above. A silicone compound is a compound having a siloxane bond in its main skeleton. For example, the silicone compound may be a silicone compound having a polyorganopolysiloxane structure.

[0085] The silicone compound is contained in the coating layer 482 as an aggregate of silicone compounds. For example, the aggregate of silicone compounds may be particulate, such as polysiloxane or silicone rubber, or oily, such as dimethyl silicone or methylphenyl silicone. Furthermore, the aggregate of silicone compounds may be mixed at the molecular level with a urethane resin as a matrix material. An example of the aggregate of particulate silicone compounds is powder-like particles. An example of the aggregate of oily silicone compounds is liquid silicone oil at room temperature of 25°C and normal pressure.

[0086] In the coating layer 482, the average particle diameter of the silicone compound aggregates is less than 7 μm. If the average particle diameter of the silicone compound aggregates exceeds 7 μm, the silicone compound aggregates in the coating layer 482 are not firmly fixed, and the silicone compound aggregates are more likely to detach from the surface of the coating layer 482. For this reason, if the average particle diameter of the silicone compound aggregates contained in the coating layer exceeds 7 μm, it becomes difficult to obtain good toner cleaning properties. On the other hand, if the average particle diameter of the silicone compound aggregates is less than 7 μm, the silicone compound aggregates are well dispersed in the urethane resin used as the matrix material, the toner adhesion force to the coating layer 482 is reduced, and good toner cleaning properties are achieved.

[0087] The average particle size of the silicone compound aggregates in the coating layer 482 is measured by the following method. First, platinum / palladium is vapor-deposited onto the surface of the coating layer 482 to form a metal coating. Next, the coating layer 482 and the rubber layer 481 disposed below it are cut parallel to the axial direction of the rotation shaft 483. Next, the cut cross sections of the coating layer 482 and rubber layer 481 are polished using cryo-ion milling. The polished cross sections of the coating layer 482 and rubber layer 481 are observed with a scanning electron microscope over a 1 mm width in the axial direction of the roller. Hereinafter, the scanning electron microscope is also referred to as "SEM." "SEM" stands for Scanning Electron Microscope. In SEM observation, the coating layer 482 is defined as the area between the platinum / palladium metal coating vapor-deposited on the surface of the coating layer 482 and the rubber layer 481 disposed below the coating layer 482. The SEM observation magnification was set to 2000x, and SEM observation was performed while changing the observation field. During this SEM observation, the major and minor axes of particles observed in the coating layer 482 within the field of view were measured, and the average value was taken as the particle diameter of each particle. Regarding particle diameter measurement, when the number of particles observed in the coating layer 482 within the field of view was 50 or less, all particles were measured. On the other hand, when the number of particles observed in the coating layer 482 within the field of view was more than 50, 50 particles were randomly selected and measured. For example, when the silicone compound aggregates are oily, the particle diameter of the silicone compound aggregates may be so small that they cannot be observed as particles during SEM observation at 2000x magnification. Therefore, when the presence of a silicone compound can be confirmed in the coating layer 482 but particles cannot be observed during SEM observation, the particle diameter of the silicone compound aggregates is considered to be below the detection limit for that observation. The particle size detection limit in the above-mentioned SEM observation at a magnification of 2000 times is 0.5 μm. For example, if no aggregate particles of the silicone compound can be confirmed in such SEM observation, it can be determined that the silicone compound is dispersed at the molecular level.After measuring the particle diameters of up to 50 particles by SEM observation in the manner described above, the arithmetic mean of the measured particle diameters is calculated, and the calculated arithmetic mean value is used as the average particle diameter of the aggregate of silicone compounds.

[0088] Furthermore, whether or not the coating layer 482 contains a silicone compound can be confirmed by X-ray photoelectron spectroscopy of the coating surface, infrared method, solid-state NMR, GCMS, or the like.

[0089] There are no particular restrictions on the content of the silicone compound in the coating layer 482. For example, the silicone compound is preferably contained in an amount of 0.5 to 50 mass %, more preferably 3 to 50 mass %, and particularly preferably 20 to 50 mass %, relative to the total mass of the coating layer 482. By setting the content of the silicone compound within the above numerical range, better toner cleaning properties are achieved.

[0090] There are no particular restrictions on the thickness of coating layer 482, but it is preferably 1 to 20 μm, more preferably 3 to 15 μm, and particularly preferably 5 to 10 μm. For example, if coating layer 482 is too thin, it may be difficult to maintain quality due to durability due to abrasion, etc. On the other hand, if coating layer 482 is too thick, cracks, etc. may easily occur in the coating agent.

[0091] The thickness of the coating layer 482 can be measured by the following method. First, platinum / palladium is vapor-deposited onto the surface of the coating layer 482 to form a metal coating. Next, the coating layer 482 and the rubber layer 481 disposed below it are cut parallel to the axial direction of the rotation shaft 483. Next, the cut cross sections of the coating layer 482 and rubber layer 481 are polished using cryo-ion milling. The polished cross sections of the coating layer 482 and rubber layer 481 are observed using an SEM over a 1 mm width in the axial direction of the roller. In the SEM observation, the coating layer 482 is defined as the space between the platinum / palladium metal coating vapor-deposited on the surface of the coating layer 482 and the rubber layer 481 disposed below the coating layer 482. The magnification of the SEM observation is 1000x, and 10 fields of view are observed by changing the observation field. In each of the 10 SEM observations, the thickness of the coating layer 482 is measured at 20 points. As described above, the arithmetic mean of the thickness of a total of 200 points measured at 20 points each in 10 visual fields of SEM observation is calculated, and the calculated arithmetic mean value is set as the thickness of the coating layer 482.

[0092] The surface roughness of secondary transfer roller 424 is determined by the surface roughness of coating layer 482 provided on the outermost surface of secondary transfer roller 424. There are no particular restrictions on the surface roughness of secondary transfer roller 424, but it is preferably 1 to 12 μm, and particularly preferably 5 to 10 μm. If the surface roughness of secondary transfer roller 424 is too high, the distance between the toner and the intermediate transfer belt at the convex portions of the surface of secondary transfer roller 424 will be longer at the concave portions. This may result in insufficient transfer electric field at the concave portions of the surface of secondary transfer roller 424.

[0093] The surface roughness of the secondary transfer roller 424 can be measured by the following method: The average value of the ten-point average height (JIS B0601 1994) measured under the following conditions is defined as the surface roughness of the secondary transfer roller 424. [Surface roughness measurement conditions] Measurement locations: 3 locations along the longitudinal axis (12.5 mm from the 50 mm position toward the nearest end, and 12.5 mm across the center) x 3 locations along the circumference (at the apex, 0°, 120°, and 240°) for a total of 9 locations Measuring instrument: Surfcom1400g (Tokyo Seimitsu Co., Ltd.) Stylus shape: cone (angle 60°, tip radius 2μm) High-pass filter cutoff value: 2.5 mm ·Measurement speed: 0.2mm / sec Evaluation length: 12.5mm

[0094] Coat layer 482 may contain various additives such as a filler dispersant, a reinforcing agent, a resistance adjuster, a leveling agent, etc. On the other hand, it is preferable that coat layer 482 does not contain an organic fluorine compound.

[0095] For example, the coating layer 482 can be formed using a coating layer-forming material containing at least a urethane resin and a silicone compound. For example, the coating layer 482 can be formed by preparing a coating layer-forming material containing at least a urethane resin and a silicone compound, applying the prepared coating layer-forming material to the outer peripheral surface of the rubber layer 481 to a desired thickness, and then heating and curing the coating layer.

[0096] (shaft body) The shaft that becomes the rotation shaft 483 of the secondary transfer roller 424 is not particularly limited and may be solid or hollow. The material from which the shaft is made is also not particularly limited and examples include iron, plated iron, stainless steel, aluminum, and copper. An adhesive or primer is usually applied to the surface of the shaft. The shaft usually has an outer diameter in the range of 4 to 15 mm and a length in the range of 230 to 500 mm.

[0097] [Opposite roller] Next, the configuration of opposing roller 423B will be described. Opposing roller 423B is configured to include a core made of a conductive material that is a shaft body as rotating shaft 484, and a conductive elastic layer that covers the circumferential surface of the core. The elastic layer is configured, for example, from a rubber layer made of a single solid rubber such as nitrile rubber (NBR) or a single foam rubber, a porous elastic layer such as sponge, or a porous elastic layer with a rubber layer attached to the surface thereof.

[0098] The surface of opposing roller 423B may be coated with a low-friction material, such as tetrafluoroethylene resin, melamine resin, nylon, polyethylene, urea resin, polyacetal, ABS resin, vinyl chloride resin, polypropylene, phenolic resin, polycarbonate, polystyrene, acrylic resin, or epoxy resin.

[0099] The surface hardness of the opposing roller 423B is preferably, for example, 30° or more. The hardness of the opposing roller is measured using an Asker Rubber Hardness Tester Type C manufactured by Asker Corporation, adjusted to a total load of 1 kg. The hardness is measured at five equally spaced points along the axial length of the opposing roller 423B, and then rotated 90° from each of the five points in the circumferential direction to measure at four points, for a total of 20 points. The average value of the 20 measured points is then taken as the hardness of the opposing roller.

[0100] [Intermediate transfer belt] Next, a description will be given of the configuration of intermediate transfer belt 421 as image carrier 440. Intermediate transfer belt 421 can be made of, for example, a material containing various resins.

[0101] There are no particular limitations on the resin that constitutes the intermediate transfer belt 421. Examples of resins that can be used to constitute the intermediate transfer belt 421 include polyimide, polyamideimide, polycarbonate, polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer, polyamide, and polyphenylene sulfide. The resin that constitutes the intermediate transfer belt 421 may be one selected from the above-mentioned resins and used alone, or may be a mixture containing two or more resins. Among these resins, at least one selected from the group consisting of polyimide, polyamideimide, and polyamide is preferred.

[0102] Furthermore, the intermediate transfer belt 421 preferably contains a conductive material to impart conductivity. Examples of conductive materials include conductive carbonaceous materials such as carbon black and graphite, and metals and alloys such as aluminum and copper. Examples of conductive materials include conductive metal oxides such as tin oxide, zinc oxide, antimony oxide, indium oxide, potassium titanate, antimony oxide-tin oxide composite oxide (ATO), and indium oxide-tin oxide composite oxide (ITO). These conductive materials may be used alone or in combination of two or more. Among these conductive materials, conductive carbonaceous materials are preferred, and carbon black is more preferred. The content of the conductive material in the intermediate transfer belt 421 is not particularly limited. For example, the content of the conductive material in the intermediate transfer belt 421 may be 5 to 30% by mass.

[0103] The intermediate transfer belt 421 can be formed by molding a base layer-forming composition containing a resin, a solvent, and additives that are added as needed into a desired belt shape.

[0104] The thickness of intermediate transfer belt 421 is set appropriately taking into consideration the stress applied to the belt during driving and durability against external forces, and is, for example, 30 to 160 μm, preferably 30 to 120 μm, and more preferably 50 to 100 μm.

[0105] Furthermore, if necessary, a surface layer may be provided on the toner transfer surface of intermediate transfer belt 421. The resin contained in the surface layer is not particularly limited, and for example, existing resins such as acrylic resin, polyester resin, polysiloxane resin, fluororesin, polyamideimide resin, and polyimide resin can be used.

[0106] [Electric field control means] 1 may have an electric field control unit that controls the electric field between image carrier 440 and transfer member 450 in a direction that returns toner on transfer member 450 to image carrier 440 when transfer is not being performed. Specifically, the image forming apparatus 1 may have an electric field control unit that controls the electric field between image carrier 440 and transfer member 450 in a direction that returns toner on transfer member 450 to image carrier 440 when no recording material S is present between image carrier 440 such as intermediate transfer belt 421 and transfer member 450 such as secondary transfer roller 424.

[0107] The image forming apparatus may also be configured to mechanically remove toner adhering to the transfer roller by bringing a cleaning blade into contact with the transfer roller, such as the drum cleaning device 415 described above.

[0108] [Electrostatic image developing toner] The image forming apparatus is not particularly limited, but is suitable for forming an image using a toner for developing an electrostatic image. Hereinafter, "toner for developing an electrostatic image" may also be simply referred to as "toner."

[0109] Toner is used to develop an electrostatic image (electrostatic latent image) formed on an image carrier such as a photoreceptor. The toner is negatively charged. The toner may be a one-component developer or a two-component developer having carrier particles and toner particles. Note that toner particles are toner base particles to which an external additive has been added, and an aggregate of toner particles is called a toner. Generally, toner base particles can be used as they are, but it is preferable to use toner particles to which an external additive has been added.

[0110] The toner base particles may contain, for example, a toner base particle precursor containing a binder resin, and other components such as a pigment, a release agent, and a charge control agent.

[0111] (binder resin) The binder resin constituting the toner base particles is preferably a thermoplastic resin. Examples of thermoplastic resins include styrene resins, vinyl resins such as acrylic resins and styrene-acrylic resins, polyester resins, olefin resins, polyamide resins, and epoxy resins. The binder resin may be an amorphous resin or a crystalline resin. The binder resin constituting the toner base particles preferably contains a polyester resin, and more preferably contains a polyester resin and a vinyl resin such as an acrylic resin or a styrene-acrylic resin.

[0112] The vinyl resin hardens the toner base particles, inhibiting the embedding of external additives in the toner base particles and further enhancing the effect of the external additives in improving chargeability. The vinyl resin is not particularly limited as long as it is a polymer of a vinyl compound, and examples thereof include (meth)acrylic acid ester resin, styrene (meth)acrylic acid ester resin, and ethylene vinyl acetate resin. These may be used alone or in combination of two or more. In this specification, "(meth)acrylic" refers to both "acrylic" and "methacrylic."

[0113] Here, a crystalline resin refers to a resin that has a melting point in an endothermic curve obtained by differential scanning calorimetry. Hereinafter, "differential scanning calorimetry" may be referred to as "DSC." "DSC" is an abbreviation for Differential scanning calorimetry.

[0114] The endothermic curve can be measured using a known DSC measuring instrument. For example, a Diamond DSC (trade name) manufactured by PerkinElmer can be used as a DSC measuring instrument. Specifically, 3.0 mg of the resin sample is sealed in an aluminum pan and set in the sample holder of the DSC measuring instrument. An empty aluminum pan is used as a reference. The endothermic curve is obtained under measurement conditions that, in this order, involve a first heating step in which the temperature is increased from 0°C to 200°C at a heating rate of 10°C / min, a cooling step in which the temperature is decreased from 200°C to 0°C at a cooling rate of 10°C / min, and a second heating step in which the temperature is increased from 0°C to 200°C at a heating rate of 10°C / min.

[0115] The melting point of a crystalline resin refers to a clear endothermic peak observed during heating in an endothermic curve. A clear endothermic peak refers to a peak with a half-width of 15°C or less in an endothermic curve obtained by DSC measurement when the temperature is increased at a rate of 10°C / min.

[0116] The glass transition temperature of a resin can be determined as follows: Based on the endothermic curve obtained by DSC measurement, an extension of the baseline before the rise of the first endothermic peak during each temperature rise process is drawn, and a tangent line showing the maximum slope between the rise of the first peak and the peak apex is drawn, and the intersection of these lines is taken as the glass transition temperature.

[0117] On the other hand, an amorphous resin refers to a resin in which, in an endothermic curve obtained by performing differential scanning calorimetry similar to that described above, a baseline curve indicating the occurrence of glass transition is observed, but no clear endothermic peak as described above is observed.

[0118] (Other components of toner) The toner base particles may contain a release agent such as wax, a colorant, a charge control agent, and the like.

[0119] (mold release agent) The release agent can improve the releasability of the toner from a fixing member, etc. Examples of the release agent include hydrocarbon waxes such as polyethylene wax, paraffin wax, microcrystalline wax, and Fischer-Tropsch wax, dialkyl ketone waxes such as distearyl ketone, carnauba wax, montan wax, ester waxes such as behenyl behenate, behenic acid behenate, trimethylolpropane tribehenate, pentaerythritol tetramyristate, pentaerythritol tetrastearate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate, trimellitate tristearyl, and distearyl maleate, and amide waxes such as ethylenediamine dibehenylamide and trimellitate tristearylamide.

[0120] The content of the release agent is preferably 2% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less, based on the total mass of the toner base particles. When the content of the release agent is 2% by mass or more, the releasability of the toner from the fixing member is sufficiently improved. When the content of the release agent is 30% by mass or less, a sufficient amount of binder resin can be contained in the toner base particles, thereby sufficiently improving the fixability of the image.

[0121] (coloring agent) The toner base particles may contain a colorant. When the toner base particles are configured to contain a colorant, various known colorants such as carbon black, magnetic materials, black iron oxide, dyes, and pigments can be used as the colorant.

[0122] Examples of carbon black include channel black, furnace black, acetylene black, thermal black, and lamp black. Examples of magnetic materials that can be used include ferromagnetic metals such as iron, nickel, and cobalt, alloys containing these metals, and ferromagnetic metal compounds such as ferrite and magnetite. Examples of black iron oxides include magnetite, hematite, and titanium iron trioxide.

[0123] Examples of dyes include CI Solvent Red 1, 49, 52, 58, 63, 111, and 122; CI Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, and 162; and CI Solvent Blue 25, 36, 60, 70, 93, and 95.

[0124] Examples of pigments include CI Pigment Red 5, 48:1, 48:3, 53:1, 57:1, 81:4, 122, 139, 144, 149, 150, 166, 177, 178, 222, 238, 269, CI Pigment Orange 31, 43, CI Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 156, 158, 180, 185, CI Pigment Green 7, CI Pigment Blue 15:3, 60, and the like.

[0125] The colorants for obtaining the toner of each color may be used singly or in combination of two or more.

[0126] The content of the colorant is preferably 1 to 10 parts by mass, more preferably 2 to 8 parts by mass, per 100 parts by mass of the binder resin in the toner base particles. When the content of the colorant is within the above range, the desired coloring power is easily obtained in the resulting toner. Furthermore, the colorant is less likely to be liberated or adhere to the carrier, which may have little effect on the chargeability, and liberation or adhesion of the colorant to the carrier is less likely to occur.

[0127] (charge control agent) The charge control agent can adjust the chargeability of the toner base particles. Examples of the charge control agent include nigrosine dyes, metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, quaternary ammonium salt compounds, azo metal complexes, metal salicylate salts, or metal complexes thereof.

[0128] The content of the charge control agent is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less, relative to the total mass of the binder resin. Note that, if an attempt is made to control the chargeability of the toner by, for example, adding an excessive amount of charge control agent, other properties of the toner base particles may change significantly. In contrast, in this embodiment, by adjusting the chargeability of the toner with alumina, it is possible to adjust the chargeability of the toner to a desired level while satisfying other required properties.

[0129] (external additives) The toner base particles can be used as a toner as they are, but it is preferable to attach an external additive to the surface of the toner base particles in order to improve the fluidity, chargeability, cleaning properties, etc. of the toner. Examples of the external additive include known fine particles such as inorganic fine particles and organic fine particles, and lubricants. Various external additives may be used in combination.

[0130] Preferred examples of inorganic fine particles include inorganic fine particles made of silica, titanium oxide, alumina, strontium titanate, zinc titanate, calcium titanate, etc. Two or more of these may be combined. The number-average primary particle size of the inorganic fine particles is preferably about 10 to 100 nm. The number-average primary particle size of the inorganic fine particles can be measured, for example, by calculating the horizontal Feret diameters of 100 particles from an image photographed using a scanning electron microscope (SEM) using an image processing analyzer or the like, and then calculating the average value.

[0131] These inorganic fine particles may be hydrophobized by surface modification as needed. By using hydrophobized inorganic fine particles, for example, adhesion of white toner base particles to each other due to moisture adsorption caused by hydroxy groups present on the surfaces of inorganic oxide particles can be suppressed.

[0132] Examples of surface modifiers used to modify the surface of inorganic fine particles include silane coupling agents and titanium coupling agents. Preferred silane coupling agents include dimethyldimethoxysilane, hexamethyldisilazane (HMDS), methyltrimethoxysilane, isobutyltrimethoxysilane, and decyltrimethoxysilane. Higher fatty acids and silicone oils can also be used as surface modifiers. Examples of silicone oils that can be used include organosiloxane oligomers, octamethylcyclotetrasiloxane, or cyclic compounds such as decamethylcyclopentasiloxane, tetramethylcyclotetrasiloxane, and tetravinyltetramethylcyclotetrasiloxane, as well as linear or branched organosiloxanes.

[0133] The amount of the external additive added is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, based on 100 parts by mass of the toner base particles.

[0134] (Method for producing toner base particles) The toner base particles can be produced in the same manner as known toners by methods such as kneading and pulverization, suspension polymerization, solution suspension, polyester elongation, emulsion polymerization aggregation, and emulsion aggregation. In particular, the emulsion polymerization aggregation and emulsion aggregation methods are more preferred in that they provide excellent dispersibility of colorant particles in the dispersion of the colorant contained in the toner base particles. The emulsion polymerization aggregation and emulsion aggregation methods are also superior in that they can form toner base particles while maintaining excellent dispersibility of the colorant particles, even when the colorant particles and the binder resin particles are aggregated and fused together.

[0135] In the emulsion polymerization aggregation method, first, a dispersion of binder resin particles obtained by emulsion polymerization and a dispersion of pigment particles are mixed together with particles of a release agent and a charge control agent, which are optionally added. Then, these are aggregated, associated, or fused together until particles of a desired particle size are obtained, thereby producing toner base particles. Then, external additives are added to the toner base particles to obtain toner particles.

[0136] In the emulsion aggregation method, first, a binder resin solution in which a binder resin is dissolved is dropped into a poor solvent to obtain a dispersion of binder resin particles. Next, the obtained dispersion of binder resin particles is mixed with a dispersion of pigment particles and, optionally, particles of a release agent and a charge control agent. These are then aggregated, associated, or fused until particles of the desired particle size are obtained, thereby producing toner base particles. Thereafter, external additives are added to the toner base particles to obtain toner particles.

[0137] (flocculant) The flocculant used in the emulsion polymerization flocculation method and emulsion flocculation method is not particularly limited, but is preferably selected from metal salts such as alkali metal salts and alkaline earth metal salts. Examples of metal salts include monovalent metal salts such as sodium, potassium, and lithium; divalent metal salts such as calcium, magnesium, manganese, and copper; and trivalent metal salts such as iron and aluminum. Specific metal salts include sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, zinc chloride, copper sulfate, magnesium sulfate, and manganese sulfate. Among these, it is particularly preferred to use divalent metal salts, as they can more stably promote flocculation. These may be used alone or in combination of two or more.

[0138] (Career) The carrier is mixed with the toner particles to form a two-component magnetic toner, and may be any known magnetic particle that can be contained in a toner.

[0139] Examples of magnetic particles include particles containing magnetic materials such as iron, steel, nickel, cobalt, ferrite, and magnetite, as well as alloys of these with aluminum, lead, etc. The carrier may be a coated carrier in which the surface of particles made of a magnetic material is coated with a resin or the like, or a resin-dispersed carrier in which a magnetic material is dispersed in a binder resin. Examples of coating resins include olefin resins, styrene resins, styrene-acrylic resins, silicone resins, polyester resins, and fluororesins. Examples of binder resins include acrylic resins, styrene-acrylic resins, polyester resins, fluororesins, and phenolic resins.

[0140] The average particle size of the carrier is preferably 20 μm or more and 100 μm or less, and more preferably 25 μm or more and 80 μm or less, on a volume basis. The average particle size of the carrier can be measured using a laser diffraction particle size distribution analyzer equipped with a wet disperser. For example, an example of a laser diffraction particle size distribution analyzer is "HELOS (product name)" manufactured by Sympatec Co., Ltd.

[0141] The content of the carrier is preferably 2% by mass or more and 10% by mass or less with respect to the total mass of the toner particles and the carrier.

[0142] [System block diagram of image forming device] Next, a description will be given of a block diagram of an example configuration of the image forming apparatus 1 shown in Fig. 2. As shown in Fig. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a conveying unit 50, a fixing unit 60, a storage unit 70, and a control unit 100. Note that, in the following, descriptions of the configuration that overlap with the description of the image forming apparatus 1 shown in Fig. 1 above will be omitted.

[0143] The control unit 100 of the image forming apparatus 1 is composed of, for example, a CPU, RAM, ROM, etc. (not shown). Here, CPU stands for Central Processing Unit. RAM stands for Random Access Memory. ROM stands for Read Only Memory. The CPU of the control unit 100 reads various processing programs stored in the ROM and loads them into the RAM. Then, in accordance with the loaded programs, the CPU comprehensively controls the operations of the image reading unit 10, operation display unit 20, image processing unit 30, image forming unit 40, conveying unit 50, fixing unit 60, memory unit 70, etc., which are connected via a system bus.

[0144] The storage unit 70 is composed of non-volatile memory such as an EEPROM or flash memory. EEPROM is an abbreviation for Electrically Erasable Programmable Read Only Memory. The storage unit 70 stores programs executed by the control unit 100 and is also used as a work area for the control unit 100. The storage unit 70 also stores image formation conditions set in an image formation job, recording material information including the size and type of the recording material S, and the like. Further, the image formation conditions stored in the storage unit 70 include, for example, execution conditions for the image forming unit 40, including the interval between successive images formed on the recording material S, and execution conditions for the fixing unit 60.

[0145] Furthermore, the control unit 100 acquires image data from the input job information and performs image processing. The control unit 100 performs image processing such as shading correction, image density adjustment, and image compression on the acquired image data as necessary. The image data processed by the control unit 100 is then sent to the image forming unit 40.

[0146] The conveying section 50 conveys the recording material S to the image forming section 40, the fixing section 60, etc., under the control of the control section 100.

[0147] The image forming section 40 receives image data that has been image-processed by the control section 100, and forms an image on the recording material S that has been conveyed to the image forming section 40 by the conveying section 50 based on this image data.

[0148] The operation display unit 20 displays various operation buttons, device status indication, operation status of each function, etc. on the display screen in accordance with instructions of a display signal input from the control unit 100. Furthermore, the operation display unit 20 accepts input of various instructions, characters, numbers, and other data by user operation, and outputs the input signal to the control unit 100. [Example]

[0149] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0150] <Toner Production> Toner (1) and toner (2) were prepared by the following method. Toner (1) contains an amorphous polyester (Pes) and a crystalline polyester (Pes) as binder resins. Toner (2) contains a styrene-acrylic resin (St-Ac), an amorphous polyester (Pes), and a crystalline polyester (Pes) as binder resins.

[0151] [Preparation of colorant particle dispersion] 226 parts by weight of sodium dodecyl sulfate was added to 1600 parts by weight of ion-exchanged water, and 420 parts by weight of copper phthalocyanine (CI Pigment Blue 15:3) was gradually added while stirring. A colorant particle dispersion (P1) was prepared by dispersing the mixture using a Clearmix stirrer (manufactured by M Technique Co., Ltd., "Clearmix" is a registered trademark of the company). The colorant particles in the dispersion had a volume-based median diameter of 110 nm.

[0152] [Preparation of amorphous resin particle dispersion] (Preparation of amorphous polyester resin particle dispersion (a1)) Bisphenol A ethylene oxide 2.2 mole adduct: 40 mole parts Bisphenol A propylene oxide 2.2 mole adduct: 60 mole parts Dimethyl terephthalate: 60 parts by mole Dimethyl fumarate: 15 parts by mole Dodecenyl succinic anhydride: 20 mole parts Trimellitic anhydride: 5 mole parts

[0153] A reaction vessel equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube was charged with the above monomers except for dimethyl fumarate and trimellitic anhydride, and tin dioctylate in an amount of 0.25 parts by mass per 100 parts by mass of the above monomers. After reaction at 235°C for 6 hours under a nitrogen gas stream, the temperature was lowered to 200°C, and the above amounts of dimethyl fumarate and trimellitic anhydride were added and reacted for 1 hour. The temperature was then raised to 220°C over 5 hours and polymerization was continued under a pressure of 10 kPa until the desired molecular weight was reached, yielding a pale yellow, transparent amorphous polyester resin (A1). The amorphous polyester resin (A1) had a mass average molecular weight of 35,000, a number average molecular weight of 8,000, and a glass transition temperature (Tg) of 56°C.

[0154] Next, 200 parts by weight of the amorphous polyester resin (A1), 100 parts by weight of methyl ethyl ketone, 35 parts by weight of isopropyl alcohol, and 7.0 parts by weight of a 10% by weight aqueous ammonia solution were placed in a separable flask and thoroughly mixed and dissolved. Then, while heating and stirring at 40°C, ion-exchanged water was added dropwise at a rate of 8 g / min using a liquid pump, and the addition was stopped when the amount of liquid reached 580 parts by weight. The solvent was then removed under reduced pressure to obtain an amorphous polyester resin particle dispersion. Ion-exchanged water was added to the dispersion to adjust the solid content to 25% by weight, thereby preparing amorphous polyester resin particle dispersion (a1). The volume-based average particle diameter of the amorphous polyester resin (A1) in the amorphous polyester resin particle dispersion (a1) was 156 nm.

[0155] (Preparation of styrene acrylic resin particle dispersion (b1)) (First stage polymerization) A 5 L reaction vessel equipped with a stirrer, a temperature sensor, a condenser, and a nitrogen introducing device was charged with 8 parts by mass of sodium dodecyl sulfate and 3,000 parts by mass of ion-exchanged water, and the internal temperature was raised to 80° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. After the temperature was raised, a solution prepared by dissolving 10 parts by mass of potassium persulfate in 200 parts by mass of ion-exchanged water was added, and the liquid temperature was again raised to 80° C., and the following mixed liquid of monomers was added dropwise over 1 hour. Styrene: 480.0 parts by mass n-Butyl acrylate: 250.0 parts by mass Methacrylic acid: 68.0 parts by mass

[0156] After the dropwise addition of the mixed liquid, the mixture was heated at 80° C. for 2 hours with stirring to polymerize the monomers, thereby preparing a vinyl resin particle dispersion liquid S1.

[0157] (Second stage polymerization) A 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introducing device was charged with 100 parts by mass of ion-exchanged water and 55 parts by mass, in terms of solid content, of the vinyl resin particle dispersion S1 prepared in the first-stage polymerization, and heated to 87°C.

[0158] Next, a mixture of the following monomers, chain transfer agent, and release agent was dissolved at 85°C. This mixture was mixed and dispersed for 10 minutes using a mechanical disperser with a circulation path to prepare a dispersion containing emulsified particles as oil droplets. The chain transfer agent used was n-octyl-3-mercaptopropionate. The release agent was paraffin wax, HNP0190 (product name) manufactured by Nippon Seiro Co., Ltd. The mechanical disperser used was CLEARMIX (product name) manufactured by M-Technique Co., Ltd. The prepared dispersion was then added to the 5-L reaction vessel, and a polymerization initiator solution consisting of 5.4 parts by weight of potassium persulfate dissolved in 103 parts by weight of ion-exchange water was added. The system was heated and stirred at 87°C for 1 hour to polymerize. In this way, vinyl resin particle dispersion S1' was prepared. Styrene: 256.5 parts by weight 2-Ethylhexyl acrylate: 95.3 parts by mass Methacrylic acid: 38.2 parts by mass Chain transfer agent: 4.0 parts by mass Release agent: 375 parts by weight

[0159] (Third stage polymerization) A solution of 7.3 parts by weight of potassium persulfate dissolved in 157.9 parts by weight of ion-exchanged water was added to the vinyl resin particle dispersion S1' obtained by the second-stage polymerization. Furthermore, a mixture of the following monomers and chain transfer agent was added dropwise over 90 minutes at a temperature of 84°C. The chain transfer agent used was n-octyl-3-mercaptopropionate. Styrene: 370.0 parts by mass n-Butyl acrylate: 165.0 parts by mass Methacrylic acid: 40.0 parts by mass Methyl methacrylate: 47.2 parts by mass Chain transfer agent: 8.6 parts by mass

[0160] After the dropwise addition was completed, polymerization was carried out by heating and stirring for 2 hours, and then the mixture was cooled to 28°C to obtain microparticles made of amorphous vinyl resin containing a release agent. The obtained microparticles were composed of 89% by mass of amorphous vinyl resin and 11% by mass of release agent. Ion-exchange water was added to the dispersion to adjust the solid content to 30% by mass, obtaining amorphous vinyl resin particle dispersion (b1).

[0161] [Preparation of crystalline resin particle dispersion] (Preparation of Crystalline Polyester Resin Particle Dispersion (c1)) Dodecanedioic acid: 50 mole parts 1,6-Hexanediol: 50 parts by mole

[0162] The monomers were placed in a reactor equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, and the atmosphere inside the reactor was replaced with dry nitrogen gas. Next, titanium tetrabutoxide (Ti[O(CH2)3CH3]4) was added in an amount of 0.25 parts by mass per 100 parts by mass of the monomers. After stirring and reacting for 3 hours at 170°C under a nitrogen gas stream, the temperature was further increased to 210°C over 1 hour, the pressure inside the reactor was reduced to 3 kPa, and the mixture was stirred and reacted under reduced pressure for 13 hours to obtain crystalline polyester resin (C1). Crystalline polyester resin (C1) had a mass average molecular weight of 25,000, a number average molecular weight of 8,500, and a melting point of 71.8°C.

[0163] Next, 200 parts by weight of crystalline polyester resin (C1), 120 parts by weight of methyl ethyl ketone, and 30 parts by weight of isopropyl alcohol were placed in a separable flask and thoroughly mixed and dissolved at 60°C. Then, 8 parts by weight of a 10% by weight aqueous ammonia solution was added dropwise. The heating temperature was lowered to 67°C, and while stirring, ion-exchanged water was added dropwise at a rate of 8 g / min using a liquid pump. When the amount of liquid being fed reached 580 parts by weight, the addition of ion-exchanged water was stopped. The solvent was then removed under reduced pressure to obtain a crystalline polyester resin particle dispersion. Ion-exchanged water was added to the dispersion to adjust the solid content to 25% by weight, thereby preparing crystalline polyester resin particle dispersion (c1). The volume-based average particle diameter of the crystalline polyester resin (C1) in the crystalline polyester resin particle dispersion (c1) was 198 nm.

[0164] [Preparation of release agent particle dispersion (W1)] Paraffin wax: 270 parts by weight Anionic surfactant: 13.5 parts by weight (60% active ingredient, 3% paraffin wax) Ion-exchanged water: 21.6 parts by weight

[0165] The above materials were mixed and the release agent was dissolved in a pressure discharge homogenizer at an internal liquid temperature of 120°C. The mixture was then dispersed at a dispersion pressure of 5 MPa for 120 minutes, followed by 40 MPa for 360 minutes, and cooled to obtain a dispersion. The pressure discharge homogenizer used was a "Gaulin Homogenizer (trade name)" manufactured by Gaulin. Ion-exchanged water was then added to adjust the solid content to 20%, thereby preparing a release agent dispersion (W1). The volume average particle diameter of the particles in the release agent dispersion (W1) was 215 nm. The paraffin wax used was "HNP0190 (melting temperature: 85°C)" manufactured by Nippon Seiro Co., Ltd. The anionic surfactant used was "Neogen RK (trade name)" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0166] [Preparation of toner base particles] (Preparation of Toner Base Particles (1)) Amorphous polyester resin particle dispersion (a1): 1,120 parts by mass Crystalline polyester resin particle dispersion (c1): 320 parts by mass Release agent particle dispersion (W1): 200 parts by weight Colorant particle dispersion (P1): 335 parts by weight Anionic surfactant: 40 parts by weight Ion-exchanged water: 1,500 parts by weight

[0167] The above materials were placed in a 4-liter reaction vessel equipped with a thermometer, pH meter, and stirrer, and a 1.0% by mass aqueous solution of nitric acid was added at 25°C to adjust the pH to 3.0. Subsequently, while dispersing at 3000 rpm with a homogenizer, 100 parts by mass of a 2.0% by mass aqueous solution of aluminum sulfate was added as a flocculant over 30 minutes. After the dropwise addition, the mixture was stirred for 10 minutes to thoroughly mix the raw materials and flocculant. The homogenizer used was an "Ultra Turrax T50 (trade name)" manufactured by IKA.

[0168] A stirrer and mantle heater were then installed in the reaction vessel. The temperature was increased at a rate of 0.2°C / min up to 40°C, and then at a rate of 0.05°C / min after 40°C, while adjusting the stirrer rotation speed to ensure sufficient stirring of the slurry. Particle size was measured every 10 minutes using a particle size analyzer. A Beckman Coulter Coulter Multisizer 3 (trade name) was used as the particle size analyzer. The particle size was measured using an aperture diameter of 100 μm. When the volume-based average particle size reached 5.9 μm, the temperature was maintained and a premixed liquid of the following materials was added over a 20-minute period. Amorphous polyester resin particle dispersion (a1): 160 parts by mass Anionic surfactant: 15 parts by weight The anionic surfactant added twice was Dowfax 2A1 (20% aqueous solution) manufactured by The Dow Chemical Company.

[0169] Next, after maintaining the temperature at 50°C for 30 minutes, 8 parts by mass of a 20% by mass EDTA (ethylenediaminetetraacetic acid) aqueous solution was added to the reaction vessel, followed by the addition of a 1 mol / L aqueous sodium hydroxide solution to control the pH of the raw material dispersion to 9.0. Thereafter, the temperature was increased to 85°C at a rate of 1°C / min while adjusting the pH to 9.0 every 5°C, and the temperature was maintained at 85°C.

[0170] Thereafter, when the shape factor measured using a particle size analyzer reached 0.970, the mixture was cooled at a temperature decreasing rate of 10°C / min to obtain toner base particle dispersion liquid (1). The particle size analyzer used was "FPIA-3000 (trade name)" manufactured by Malvern Instruments.

[0171] The toner base particle dispersion (1) was then filtered, and the resulting solid was thoroughly washed with ion-exchanged water. The solid was then dried at 40°C to obtain toner base particles (1). The volume-based average particle diameter of the obtained toner base particles (1) was 6.0 μm. The average circularity of the toner base particles (1), measured using the above-mentioned particle size analyzer, was 0.972.

[0172] (Preparation of Toner Base Particles (2)) Amorphous polyester resin particle dispersion (a1): 500 parts by mass Styrene acrylic resin particle dispersion (b1): 650 parts by mass Crystalline polyester resin particle dispersion (c1): 320 parts by mass Colorant particle dispersion (P1): 335 parts by weight Anionic surfactant: 40 parts by weight Ion-exchanged water: 1,500 parts by weight

[0173] The above materials were placed in a 4-liter reaction vessel equipped with a thermometer, pH meter, and stirrer, and a 1.0% by mass aqueous solution of nitric acid was added at 25°C to adjust the pH to 3.0. Subsequently, while dispersing at 3000 rpm using a homogenizer, 100 parts by mass of a 2.0% by mass aqueous solution of aluminum sulfate was added as a flocculant over 30 minutes. The homogenizer used was an "Ultra Turrax T50 (trade name)" manufactured by IKA. After the dropwise addition, the mixture was stirred for 10 minutes to thoroughly mix the raw materials and flocculant.

[0174] A stirrer and mantle heater were then installed in the reaction vessel. The temperature was increased at a rate of 0.2°C / min up to 40°C, and then at a rate of 0.05°C / min after 40°C, while adjusting the stirrer rotation speed to ensure sufficient stirring of the slurry. Particle size was measured every 10 minutes using a particle size analyzer. A Beckman Coulter Coulter Multisizer 3 (trade name) was used as the particle size analyzer. The particle size was measured using an aperture diameter of 100 μm. When the volume-based average particle size reached 5.9 μm, the temperature was maintained and a premixed liquid of the following materials was added over a 20-minute period. Amorphous polyester resin particle dispersion (a1): 160 parts by mass Anionic surfactant: 15 parts by weight The anionic surfactant added twice was Dowfax 2A1 (20% aqueous solution) manufactured by The Dow Chemical Company.

[0175] Next, after maintaining the temperature at 50°C for 30 minutes, 8 parts by mass of a 20% by mass EDTA (ethylenediaminetetraacetic acid) aqueous solution was added to the reaction vessel, followed by the addition of a 1 mol / L aqueous sodium hydroxide solution to control the pH of the raw material dispersion to 9.0. Thereafter, the temperature was increased to 85°C at a rate of 1°C / min while adjusting the pH to 9.0 every 5°C, and the temperature was maintained at 85°C.

[0176] Thereafter, when the shape factor measured using a particle size analyzer reached 0.970, the mixture was cooled at a temperature decreasing rate of 10°C / min to obtain toner base particle dispersion liquid (2). The particle size analyzer used was "FPIA-3000 (trade name)" manufactured by Malvern Instruments.

[0177] The toner base particle dispersion (2) was then filtered, and the resulting solids were thoroughly washed with ion-exchanged water. The solids were then dried at 40°C to obtain toner base particles (2). The volume-based average particle diameter of the obtained toner base particles (2) was 6.0 μm. The average circularity of the toner base particles (2), measured using the above-mentioned particle size analyzer, was 0.972.

[0178] [Creating the carrier] (Preparation of core particles) MnO: 35.0 mol% MgO: 14.5 mol% Fe2O3: 50.0 mol% SrO: 0.5 mol% The raw materials were weighed to achieve the above ratio, mixed with water, and then pulverized in a wet media mill for 5 hours to obtain a slurry.

[0179] The resulting slurry was dried using a spray dryer to obtain spherical particles. After adjusting the particle size, the particles were heated at 950°C for 2 hours and pre-fired in a rotary kiln. They were then pulverized in a dry ball mill using 0.3 cm diameter stainless steel beads for 1 hour. Subsequently, 0.8 mass% of polyvinyl alcohol (PVA) was added as a binder based on the solid content, followed by water and a polycarboxylic acid dispersant, and the mixture was pulverized using 0.5 cm diameter zirconia beads for 30 hours. The resulting powder was granulated and dried using a spray dryer and then fired in an electric furnace at 1050°C for 15 hours.

[0180] The fired powder was crushed and further classified to adjust the particle size, and then low magnetic particles were separated by magnetic separation to obtain core particles, which had a volume average particle size of 30 μm.

[0181] The volume-average particle diameter of the core particles was measured by a wet method using a laser diffraction particle size analyzer (HEROSKA, product name) manufactured by Nippon Laser Corporation. Specifically, a focal length of 200 mm was selected, and the measurement time was set to 5 seconds. The core particles to be measured were then added to a 0.2% by mass aqueous solution of sodium dodecyl sulfate and dispersed for 3 minutes using an ultrasonic cleaner to prepare a sample dispersion for measurement. The ultrasonic cleaner used was a US-1 (product name) manufactured by Asone Corporation. A few drops of this dispersion were fed into the laser diffraction particle size analyzer, and measurement was initiated when the sample concentration gauge reached the measurable range. A cumulative distribution was created from the obtained particle size distribution, starting from the smallest diameter, for each particle size range (channel), and the particle diameter at 50% of the cumulative concentration (D50) was defined as the volume-average particle diameter.

[0182] (Preparation of coating resin) Cyclohexyl methacrylate and methyl methacrylate were added to a 0.3% by mass aqueous solution of sodium benzenesulfonate in a mass ratio (copolymerization ratio) of 70:30, and potassium persulfate was added in an amount equivalent to 0.5% by mass of the total amount of monomers to carry out emulsion polymerization. The resulting mixture was then spray-dried to produce a coating resin. The weight-average molecular weight of the coating resin was 500,000.

[0183] (Carrier production) 100 parts by mass of the prepared core particles and 4.5 parts by mass of the prepared coating resin were added to a high-speed agitating mixer equipped with horizontal agitating blades, and mixed and stirred for 15 minutes at 22°C under conditions where the peripheral speed of the horizontal rotor was 8 m / sec. The mixture was then mixed at 120°C for 50 minutes to coat the surfaces of the core particles with the coating material through the action of mechanical impact force, and then cooled to room temperature to produce a carrier. The mechanical impact force was obtained by a mechanochemical method.

[0184] [Preparation of toner for developing electrostatic images] (Preparation of Toner (1)) 1.0 parts by weight of alumina and 1.5 parts by weight of silica were added to 100 parts by weight of toner base particles (1) and mixed for 20 minutes using a Henschel mixer. The silica used had a number-average particle diameter of 20 nm. The mixture was then mixed with the carrier to a toner concentration of 7% by weight, and mixed for 30 minutes at 25°C using a V-type mixer manufactured by Tokuju Kosakusho Co., Ltd. to produce toner (1) as a toner (developer) for developing electrostatic images.

[0185] (Preparation of Toner (2)) Toner (2) was prepared in the same manner as toner (1), except that toner base particles (2) were used instead of toner base particles (1).

[0186] <Secondary transfer roller> [Making base roller 1] A rubber layer forming material was prepared by kneading 60 parts by mass of NBR, 40 parts by mass of epichlorohydrin, 10 parts by mass of XFC carbon, 10 parts by mass of calcium carbonate, 5 parts by mass of zinc oxide, 1 part by mass of stearic acid, 1 part by mass of sulfur, 2 parts by mass of dibenzothiazole sulfide as a crosslinking accelerator, and 1 part by mass of tetramethylthiuram monosulfide as a crosslinking accelerator using a kneader, and then further kneading using a roll. The NBR used was "Nipol DN3335 (trade name)" manufactured by Nippon Zeon Co., Ltd. The epichlorohydrin used was "Hydrin T3106 (trade name)" manufactured by Nippon Zeon Co., Ltd. The XFC carbon used was "Vulcan P (trade name)" manufactured by Cabot Corporation.

[0187] The rubber layer forming material prepared above was co-extruded onto the outer periphery of a mandrel of a predetermined diameter, wound around the mandrel, and molded into a tube of a predetermined length. A metal shaft was used as the mandrel. The tubular molded product was then vulcanized by heating at 160°C for 40 minutes in a steam oven. The mandrel was then removed, and the molded product was cut to a length that matched the dimensions of the roller to obtain a solid layer tube. Air was blown into the inside of the obtained solid layer tube, and a core was inserted while expanding the diameter. The surface of the solid layer tube was then finish-polished to obtain a base roller 1 in which a rubber layer was disposed so as to surround the outer periphery of the core as a shaft.

[0188] [Preparation of Coating Layer Forming Material 1] Coat layer forming material 1 was prepared by adding 4 g of silicone particles with an average particle size of 0.7 μm to 300 g of urethane emulsion (solid content 30% by mass) and mixing using a planetary centrifugal mixer. The urethane emulsion used was "W6020 (trade name)" manufactured by Mitsui Chemicals, Inc. The silicone particles used were "X-52-854 (trade name)" manufactured by Shin-Etsu Chemical Co., Ltd. Coat layer forming material 1 was prepared so that the concentration of the silicone compound relative to the resin solid content was 4.3% by mass.

[0189] [Preparation of Coating Layer Forming Material 2] Coat layer forming material 2 was prepared by adding 90 g of silicone particles with an average particle size of 0.7 μm to 300 g of urethane emulsion (solid content 30% by mass) and mixing using a planetary centrifugal mixer. The urethane emulsion and silicone particles used were the same as those used to prepare coat layer forming material 1. Coat layer forming material 2 was prepared so that the concentration of the silicone compound relative to the resin solid content was 50% by mass.

[0190] [Preparation of Coating Layer Forming Material 3] Coat layer forming material 3 was prepared by adding 23 g of silicone particles with an average particle size of 5 μm to 300 g of urethane emulsion (solid content 30% by mass) and mixing using a planetary centrifugal mixer. The urethane emulsion used was "W6020 (product name)" manufactured by Mitsui Chemicals, Inc. The silicone particles used were "X-52-1621 (product name)" manufactured by Shin-Etsu Chemical Co., Ltd. Coat layer forming material 3 was prepared so that the concentration of the silicone compound relative to the resin solid content was 20.4% by mass.

[0191] [Preparation of Coating Layer Forming Material 4] Coat layer forming material 3 was prepared by adding 23 g of silicone particles with an average particle size of 23 μm to 300 g of urethane emulsion (solid content 30% by mass) and mixing using a planetary centrifugal mixer. The urethane emulsion used was "W6020 (trade name)" manufactured by Mitsui Chemicals, Inc. The silicone particles used were "Silcrush-A150G (trade name)" manufactured by Nikko Rica Corporation. Coat layer forming material 4 was prepared so that the concentration of the silicone compound relative to the resin solid content was 20.4% by mass.

[0192] The compositions of coating layer forming materials 1 to 4 are shown in Table 1 below.

[0193] [Table 1]

[0194] [Example 1: Preparation of secondary transfer roller 1] First, any rubber shavings or dust that had adhered during polishing of the surface of the base roller 1 was thoroughly removed. Then, the above-mentioned coating layer forming material 1 was spray-coated onto the outer peripheral surface of the rubber layer that constitutes the base roller 1, so that the thickness of the coating layer after baking would be 7 μm. The coated layer forming material 1 was then cured by heating at 120°C for 30 minutes, forming a coating layer, thereby obtaining the secondary transfer roller 1. The configuration of the secondary transfer roller 1 is shown in Table 2. In Table 2, the average particle size (μm) of the silicone compound is the average particle size (μm) of the silicone compound aggregates determined by SEM observation of the coating layer described above. In the "Average particle size (μm) of the silicone compound" column, "ND" indicates that the particle size was below the detection limit by SEM observation.

[0195] [Table 2]

[0196] [Examples 2 to 5, Comparative Example 2: Preparation of Secondary Transfer Rollers 2 to 5, 7] Secondary transfer rollers 2 to 5 and 7 were produced in the same manner as secondary transfer roller 1, except that instead of coating layer forming material 1, coating layer forming materials 2 to 5 shown in Table 2 were used and each coating layer forming material 2 to 5 was applied so that the thickness of the coating layer after firing would be the value shown in Table 2.

[0197] In the production of the secondary transfer roller 5, "NTBX-139 (product name)" manufactured by Okitsumo Co., Ltd. was used as the coating layer forming material 5. "NTBX-139 (product name)" manufactured by Okitsumo Co., Ltd. is a material containing urethane and silicone oil.

[0198] Comparative Example 1: Preparation of Secondary Transfer Roller 6 Secondary transfer roller 6 was produced in the same manner as secondary transfer roller 1, except that instead of coating layer forming material 1, only urethane emulsion (solid content 30% by mass) was used and applied so that the thickness of the coating layer after baking would be the value shown in Table 2. The urethane emulsion used was "W6020 (product name)" manufactured by Mitsui Chemicals, Inc.

[0199] (Surface roughness of the coating layer) The surface roughness (μm) of the coating layer of secondary transfer rollers 1 to 7 was determined by the following method. The results are shown in Table 2. The surface roughness (μm) of the coating layer was taken as the average value of the ten-point average height (JIS B0601 1994) measured under the following conditions: [Surface roughness measurement conditions] Measurement locations: 3 locations along the longitudinal axis (12.5 mm from the 50 mm position toward the nearest end, and 12.5 mm across the center) x 3 locations along the circumference (at the apex, 0°, 120°, and 240°) for a total of 9 locations Measuring instrument: Surfcom1400g (Tokyo Seimitsu Co., Ltd.) Stylus shape: cone (angle 60°, tip radius 2μm) High-pass filter cutoff value: 2.5 mm ·Measurement speed: 0.2mm / sec Evaluation length: 12.5mm

[0200] <evaluation> The following image formation tests were carried out using the combinations of secondary transfer rollers and toners shown in Table 2 above. Specifically, toners (1) and (2) were filled into toner cartridges, respectively. Furthermore, a modified image forming apparatus (AccurioPress C7100, manufactured by Konica Minolta, Inc.) was used for the image formation tests. The above-described secondary transfer rollers 1 to 7 were installed in this modified apparatus, respectively, to form the image forming apparatuses for evaluation in Examples 1 to 5 and Comparative Examples 1 and 2.

[0201] Using the image forming apparatus for evaluation described above, 350,000 cyan monochrome images with a 20% coverage were printed on Konica Minolta A4-size J paper in an environment with a temperature of 30°C and humidity of 80%, and then another 350,000 cyan monochrome images with a 20% coverage were printed in an environment with a temperature of 10°C and humidity of 20%. The surface conditions of secondary transfer rollers 1 to 7 were then observed. The observed surface conditions of secondary transfer rollers 1 to 7 were evaluated for "toner filming" and "surface cracking of the coating layer" as follows. The evaluation results are shown in Table 2. For the evaluation of "toner filming," results of A, B, and C according to the following evaluation criteria were deemed acceptable. For the evaluation of "surface cracking of the coating layer," results of A and B according to the following evaluation criteria were deemed acceptable. Furthermore, a sample that passed both the evaluations of "toner filming" and "surface cracking of the coating layer" according to the following evaluation criteria was deemed acceptable in the overall evaluation.

[0202] [Toner filming (cleaning)] A: No toner filming was observed in the visual evaluation, and the printed matter was good. B: Slight toner filming was observed by visual inspection, but the printed matter was good. C: Filming was observed by visual inspection, but the print was good. D: Toner filming and poor cleaning were confirmed by visual inspection, and noise occurred on the printed matter during the test.

[0203] [Cracks on the surface of the coating layer] A: Visual inspection revealed no or only slight cracks, and the printed matter was in good condition. B: Cracks were observed by visual inspection, but the printed matter was in good condition. C: Visually evaluated, multiple thick cracks occurred, and noise appeared on the printed matter during the durability test.

[0204] (result) As shown in Table 2, secondary transfer rollers 1 to 5 of Examples 1 to 5 have a coating layer containing a urethane resin as a matrix material and a silicone compound having an average particle size of a certain value or less. In image formation tests using such secondary transfer rollers 1 to 5, good results were obtained in the evaluations of both "toner filming" and "cracks on the surface of the coating layer" described above. In particular, when secondary transfer rollers 1 to 4 of Examples 1 to 4 have a coating layer containing silicone particles as the silicone compound, exceptionally good results were obtained in the evaluation of "toner filming."

[0205] On the other hand, the secondary transfer roller 6 of Comparative Example 1, whose coating layer was composed only of urethane resin, failed the evaluation of "toner filming." Furthermore, although the evaluation of "cracks on the surface of the coating layer" met the pass standard, it did not reach the evaluation results of Examples 1 to 3 and 5.

[0206] The secondary transfer roller 7 of Comparative Example 2 has a coating layer containing a urethane resin and silicone particles with an average particle size of 23 μm. In an image formation test using the secondary transfer roller 7 of Comparative Example 2, the evaluations of "toner filming" and "cracks on the surface of the coating layer" were both unsatisfactory. In particular, visual observation in the evaluation of "cracks on the surface of the coating layer" confirmed that the silicone particles in the coating layer were not firmly fixed, and some of the silicone particles had peeled off.

[0207] The present invention is not limited to the configurations described in the above embodiments, and various modifications and changes are possible without departing from the scope of the present invention. [Industrial Applicability]

[0208] According to the present invention, it is possible to provide an image forming apparatus, a transfer roller, and an image forming method that are excellent in toner cleaning properties of a roller that constitutes a transfer member. [Explanation of symbols]

[0209] 1. Image forming device 10 Image reading unit 20 Operation display section 30 Image processing section 40 Image forming unit 42 Intermediate transfer unit 50 Conveying section 60 Fixing unit 70 Memory section 100 control section 411 Exposure equipment 412 Developing device 413 Photoreceptor 414 Charging device 415 Drum cleaning device 421 Intermediate transfer belt 422 Primary transfer roller 423 Support Roller 423A Drive Roller 423B Opposed Roller 424 Secondary transfer roller 426 Belt cleaning device 440 Image carrier 450 Transfer material 481 Rubber layer 482 Coat layer 483 Rotational Axis 484 Rotational Axis S recording material

Claims

1. An image forming apparatus including a transfer member that transfers an image on an image carrier to a recording material, and that transfers a toner image on the image carrier to the recording material by applying a voltage between the image carrier and the transfer member with the recording material sandwiched therebetween, The toner is negatively charged the transfer member has a roller that rotates around a rotation axis, has at least one rubber layer on the rotation axis side of the roller, and has a coating layer on the outermost surface of the roller; 1. An image forming apparatus, wherein the coating layer contains at least a urethane resin and a silicone compound, and the average particle size of the aggregates of the silicone compound is less than 7 μm.

2. 2. The image forming apparatus according to claim 1, wherein the toner image on the image carrier is transferred from a photosensitive member.

3. 3. The image forming apparatus according to claim 1, wherein the coating layer contains the silicone compound in an amount of 0.5 to 50% by mass relative to the total mass of the coating layer.

4. 3. The image forming apparatus according to claim 1, wherein the coating layer of the transfer member has a thickness of 1 to 20 μm.

5. 3. The image forming apparatus according to claim 1, wherein the surface roughness of the roller is 1 to 12 μm.

6. 3. The image forming apparatus according to claim 1, further comprising an electric field control means for controlling an electric field between the image carrier and the transfer member in a direction that returns the toner on the transfer member to the image carrier when there is no recording material between the image carrier and the transfer member.

7. 7. The image forming apparatus according to claim 6, wherein the toner contains a polyester resin as a binder resin.

8. 8. The image forming apparatus according to claim 7, wherein the toner contains a styrene acrylic resin as the binder resin.

9. 3. The image forming apparatus according to claim 1, wherein the coating layer does not contain an organic fluorine compound.

10. A transfer roller of an image forming apparatus that transfers a toner image on an image carrier to a recording material by applying a voltage between the image carrier and the transfer roller, the toner image being transferred from the image carrier to the recording material, A transfer roller characterized in that it has at least one rubber layer on the rotation axis side of the transfer roller and has a coating layer on the outer periphery thereof, the coating layer containing a urethane resin and a silicone compound, and the average particle diameter of the aggregates of the silicone compound is less than 7 μm.

11. 1. An image forming method including a step of transferring a toner image on an image carrier to a recording material by applying a voltage between an image carrier and a transfer member sandwiching the recording material therebetween, The toner is negatively charged the transfer member has a roller that rotates around a rotation axis, has at least one rubber layer on the rotation axis side of the roller, and has a coating layer on the outermost surface of the roller; 1. An image forming method, wherein the coating layer contains at least a urethane resin and a silicone compound, and the average particle size of the aggregates of the silicone compound is less than 7 μm.

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