Image forming apparatus

Abstract

To provide an image forming apparatus that can reduce accumulation of toner on an electrifying member and prevent occurrence of abnormal images over a long period.SOLUTION: An image forming apparatus has: an image carrier; an electrifying member that is arranged in contact with the image carrier and electrifies the image carrier; latent image forming means that forms a latent image on the surface of the image carrier; developing means that applies toner to the image carrier, and develops the latent image formed on the surface of the image carrier to form a toner image; and transfer means that transfers the toner image to a transfer target body, and the image forming apparatus recovers a transfer residual toner remaining on the image carrier after the transfer by using the developing means. The toner includes an external additive including inorganic fine particles. The external additive is included in the toner in an amount of 1.8 mass% or more. The electrifying member satisfies 2≤Sk+Spk≤16, where Sk [μm] and Spk [μm] are defined in JIS B0671-2:2002 (ISO 25178-2:2012).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In an electrophotographic image forming apparatus, it is known to charge a photoreceptor (image carrier) by a charging member such as a charging roller, supply toner to the photoreceptor by developing means, and transfer the toner on the photoreceptor to a recording medium or an intermediate transfer member.

[0003] In the prior art, for example, it is known to clean the toner adhering to the photoreceptor with a cleaning means such as a cleaning blade. In recent years, from the viewpoint of miniaturization of the apparatus, etc., a so-called cleanerless method has been proposed that does not include a cleaning means for specifically cleaning the photoreceptor.

[0004] In a cleanerless image forming apparatus, it is known to recover the transfer residual toner remaining on the photoreceptor after transfer by developing means. In such a cleanerless image forming apparatus, since the transfer residual toner is recovered by the developing means and reused, waste toner can be suppressed. For this reason, user maintenance can be simplified, a waste toner container becomes unnecessary, and waste can be reduced.

[0005] In a cleanerless image forming apparatus, there is a problem that an abnormal image is generated when the transfer residual toner stains a charging member (for example, a charging roller). In contrast, for example, the technique of Patent Document 1 has been proposed.

[0006] Patent Document 1 discloses that a linear velocity difference is provided between the charging roller and the photoreceptor to charge the transfer residual toner with a normal polarity and promote the recoverability by the developing means. In Patent Document 1, the linear velocity difference of the charging roller is made faster than the linear velocity difference of the photoreceptor. According to Patent Document 1, it is expected to suppress the contamination of the charging roller even in the cleanerless method.

[0007] Patent Document 2 discloses the configuration of an image forming apparatus using a cleanerless method and the toner composition. Patent Document 2 uses a predetermined toner in the cleanerless method and states that it can suppress the occurrence of abnormal images over a long period of time.

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the prior art, when image formation is continued over a long period of time, the chargeability of the toner decreases, resulting in poor electric field response of the toner at the nip portion between the charging roller and the photoreceptor. As a result, toner gradually accumulates on the surface of the charging roller, and the accumulated toner becomes toner contamination, which reduces the charging performance. For this reason, there has been a problem that abnormal images are generated due to charging abnormalities.

[0009] Therefore, an object of the present invention is to provide an image forming apparatus that can reduce the accumulation of toner on a charging member and suppress the occurrence of abnormal images over a long period of time.

Means for Solving the Problems

[0010] To solve the above problems, the image forming apparatus of the present invention includes an image carrier, a charging member disposed in contact with the image carrier for charging the image carrier, a latent image forming means for forming a latent image on the surface of the image carrier, a developing means for applying toner to the image carrier and developing the latent image formed on the surface of the image carrier to form a toner image, a transfer means for transferring the toner image to a transfer medium, and is an image forming apparatus that recovers the residual transfer toner remaining on the image carrier after the transfer by the developing means, wherein the toner contains an external additive containing inorganic fine particles, the external additive is contained in the toner in an amount of 1.8 mass% or more, The charging member satisfies the following conditions with respect to the surface roughness Sk [μm] and Spk [μm] defined in JIS B0671-2:2002 (ISO 25178-2:2012): 2 ≦ Sk + Spk ≦ 16 and is characterized by this.

Effect of the Invention

[0011] According to the present invention, it is possible to reduce the accumulation of toner on the charging member and suppress the occurrence of abnormal images over a long period of time.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 4

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Figure 5B

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Figure 7A

Figure 7B

Figure 7C

Figure 7D

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Figure 9

Figure 10

Mode for Carrying Out the Invention

[0013] Hereinafter, the image forming apparatus according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments shown below, and can be changed within the range that those skilled in the art can conceive, such as other embodiments, additions, modifications, deletions, etc., and is included in the scope of the present invention as long as the functions and effects of the present invention are achieved in any aspect.

[0014] The image forming apparatus of the present invention is an image carrier, a charging member disposed in contact with the image carrier to charge the image carrier, a latent image forming means for forming a latent image on the surface of the image carrier, a developing means for applying toner to the image carrier and developing the latent image formed on the surface of the image carrier to form a toner image, a transfer means for transferring the toner image to a transfer body, and has an image forming apparatus for recovering transfer residual toner remaining on the image carrier after the transfer with the developing means, the toner contains an external additive containing inorganic fine particles, the external additive is contained in the toner in an amount of 1.8 mass% or more, the charging member has, in terms of surface roughness Sk [μm] and Spk [μm] defined in JIS B0671-2:2002 (ISO 25178-2:2012), 2 ≦ Sk + Spk ≦ 16 satisfies and is characterized by this.

[0015] The image forming apparatus may also be referred to as an electrophotographic apparatus, a printing apparatus, a printer, etc. Further, the image forming apparatus of the present invention can be a cleanerless type image forming apparatus. The cleanerless method may also be referred to as a cleanerless system, a cleanerless imaging system, etc.

[0016] Hereinafter, a charging roller will be described as an example of the charging member. As the image carrier, a photoreceptor and a photoreceptor drum will be described as examples. The image carrier may sometimes be referred to as an electrostatic latent image carrier. Also, in the following examples, the developing means has a developing roller as the developer carrier. The developing means may also be referred to as a developing apparatus, etc. In the following examples, the transfer means has a transfer roller as the transfer member. In the following examples, the latent image forming means has an exposure means. The exposure means exposes the charged photoreceptor.

[0017] When the content of the external additive is 1.8 mass% or more in the toner, it can be said that the amount of the external additive in the toner is large. By increasing the amount of the external additive in the toner, the charging performance of the toner is improved. On the other hand, if the amount of the external additive becomes too large, the external additive itself may cause contamination of the surface of the charging roller. When the surface of the charging roller is contaminated, the charging of the photoreceptor cannot be performed well, and abnormal images are generated.

[0018] In the present embodiment, the aim is to solve the problems that secondarily occur when using a toner (the amount of the external additive is 1.8 mass% or more) that improves the electrical responsiveness. The problems that secondarily occur are that a large amount of the external additive adheres to the charging roller, and as a result, the charging characteristics of the charging roller and the electrical response characteristics of the toner are adversely affected. That is, in the present embodiment, when using a toner that improves the electrical responsiveness, while taking advantage of the advantages of the toner, in order to solve the problems that secondarily occur, the characteristics of the surface shape of the charging roller are adjusted.

[0019] In a cleanerless system, it is desirable to improve the electrical responsiveness of toner in order to move the toner electrically. As a method for this, there is a method of increasing the content of an external additive containing inorganic fine particles. However, when the content of the external additive is increased, the degree of separation of the external additive from the toner increases, and a large amount of the external additive adheres to the charging roller and contaminates it. For this reason, it affects the electrical responsiveness of the toner and the charging characteristics of the photoreceptor.

[0020] Therefore, in the present embodiment, the surface of the charging roller has a three-dimensional concavo-convex structure and a surface shape that satisfies the above relationship of surface roughness. Specifically, it has a three-dimensional concavo-convex shape with the surface roughness Sk [μm] and Spk [μm] of the surface of the charging roller being 2 ≤ Sk + Spk ≤ 16. As a result, the toner can enter the concave portion of the charging roller, and the pressure applied to the toner at the nip portion (also referred to as a charging nip, charging nip portion, etc.) between the charging roller and the photoreceptor can be reduced. For this reason, when the transfer residual toner attached to the photoreceptor passes through the charging nip, it is less likely to adhere to the charging roller, and it is possible to suppress the charging roller from being contaminated with the transfer residual toner. For this reason, it is possible to suppress charging failures caused by contamination of the charging roller and to suppress abnormal images caused by charging failures. Note that Sk and Spk will be described later.

[0021] Also, according to the present embodiment, when the transfer residual toner passes through the charging nip portion, the transfer residual toner adhering to the charging roller can be reduced, so that the recovery rate at the developing roller can be improved. Also, in the present embodiment, since the content of the external additive is increased, the electrical responsiveness of the toner is improved, so that the efficiency of electrical recovery from the photoreceptor to the developing roller is improved.

[0022] Further, according to the present embodiment, since the external force applied to the toner passing through the charging nip portion is reduced, it becomes difficult for the external additive to separate from the toner. As a result, it is possible to suppress the charging roller from being contaminated by the external additive, and it is possible to suppress the influence on the electrical responsiveness of the toner and the charging characteristics of the photoreceptor. According to the present embodiment, even if the amount of the external additive of the toner is increased, it is possible to suppress the charging roller from being contaminated by the external additive, and it is possible to satisfactorily recover the toner by the developing means in the cleanerless system. According to the present embodiment, it is possible to suppress the occurrence of abnormal images caused by the contamination of the charging roller and the occurrence of abnormal images caused by the residual transfer toner over a long period of time.

[0023] Since the toner used in the present embodiment has good electrical responsiveness, it becomes easier to perform the recharging of the residual transfer toner as intended. The recharging of the residual transfer toner is a discharge process performed between the charging roller and the photoreceptor in order to recover the residual transfer toner by the developing means. The recharging may be referred to as pre-charging discharge or the like. In the present embodiment, since the chargeability of the toner can be improved, the toner responsiveness to the electric field at each nip of the charging roller and the developing roller is improved. Therefore, it is possible to easily move the toner.

[0024] The effects when the surface roughness of the charging roller is 2 ≦ Sk + Spk ≦ 16 will be supplemented below. There are some parts that overlap with the above description. By making the surface shape of the charging roller as described above, the toner enters into the three-dimensional uneven shape of the charging roller, and it becomes difficult for the pressure between the charging roller and the image carrier to be applied to the toner. As a result, a region where the pressure is reduced is formed in the pressure distribution within the charging nip, and it is possible to reduce the adhesion force of the toner to the photoreceptor due to the physical adsorption force (van der Waals force). Therefore, the van der Waals force between the toner and the charging roller can be reduced.

[0025] Even when a large amount of toner adheres to the surface of the charging roller, a minute gap necessary for charging the photoreceptor can be formed. In a state where the minute gap is formed, by recharging the toner near the convex portion, the toner can be moved from the charging roller to the photoreceptor by electric field control. As a result, it becomes easier to remove the toner on the surface of the charging roller. That is, even when the amount of toner adhering to the charging roller increases, discharge due to charging can be generated at the convex portions in the three-dimensional unevenness. Since the convex portions are dispersed on the surface of the charging roller, it becomes possible to preferentially recharge the toner around the convex portions and discharge it from the charging roller by an electric field. Thereby, it becomes easier to move the toner on the charging roller by an electric field.

[0026] Also, since the pressure between the toner and the charging roller is suppressed, the amount of external additive that separates from the toner and adheres to the surface of the charging roller can be reduced.

[0027] Further, when the charging performance of the toner is improved, when a recovery means (which may be referred to as a cleaning member or the like) for recovering the toner on the charging roller is used, the voltage responsiveness of the toner to the recovery means is improved. As a result, the toner recovery rate of the recovery means is improved. Furthermore, it becomes easier to sweep the toner from the recovery means to the charging roller, and it becomes easier to recover the toner from the recovery means through the charging roller and the photoreceptor to the developing means.

[0028] In the present embodiment, in an image forming apparatus using a cleanerless system, in addition to the regulation of the amount of external additive of the toner, regulation by the arithmetic surface roughness of the charging member (for example, a charging roller) is added. In the case of the roughness on a one-dimensional line, only the roughness along the ridge line of the roller is regulated, so the condition of the roughness in the circumferential direction could not be regulated. In the case of two-dimensional surface roughness, conditions can be given as a composite roughness characteristic of the roughness along the ridge line of the charging roller and the roughness in the circumferential direction.

[0029] The additional condition is the sum of Sk representing the core roughness and Spk indicating the roughness (height) protruding more than that. By satisfying the condition of the sum of Sk and Spk, the charging quality can be maintained even when an external additive adheres to the charging roller.

[0030] When Sk + Spk is 2 μm or more, the convex portions on the surface of the charging roller can be exposed even when an external additive adheres to the charging roller. For example, when the charging member is a charging rubber roller, when it is 2 μm or more, the rubber agent of the charging roller can be exposed even when an external additive adheres. When Sk + Spk is less than 2 μm, the contact pressure between the charging roller and the toner becomes high at the charging nip portion, and the van der Waals force of the toner on the charging roller becomes strong. For this reason, it becomes difficult to discharge the toner due to the electric field response, and it becomes difficult for the toner to move from the charging roller to the photoreceptor.

[0031] When Sk + Spk is 16 μm or less, the quality of the charging member can be maintained and abnormal images can be reduced. When Sk + Spk is larger than 16 μm, it becomes difficult to form the minute space necessary for charging between the charging roller and the photoreceptor, the charging becomes unstable, and abnormal images are likely to occur.

[0032] It is preferable that the charging roller satisfies 5 ≦ Sk + Spk ≦ 12. In this case, the above effects are further improved. For example, the pressure on the toner passing through the charging nip portion can be further reduced, and the generation of abnormal images can be further reduced.

[0033] When the weight average particle diameter of the toner is D [μm], it is preferable to satisfy D ≦ Sk + Spk ≦ 3D. In this case, good results can be obtained from the viewpoint of the toner entering the concave portion, the pressure on the toner passing through the charging nip portion can be further reduced, and the generation of abnormal images can be further reduced.

[0034] It is more preferable that the charging roller satisfies 5 ≦ Sk + Spk ≦ 12 and also satisfies D ≦ Sk + Spk ≦ 3D. In this case, the pressure on the toner passing through the charging nip portion can be further reduced, and the adhesion of the residual transfer toner to the charging roller can be further reduced.

[0035] The toner can be appropriately selected, but it is preferably a toner that satisfies the following formulas (1) to (3). In the particle size distribution of the primary particles of the inorganic fine particles, there are a plurality of peaks between 5 nm and 50 nm. Among the peaks, the highest peak is peak n1, the second highest peak is peak n2, the particle size (nm) at the apex of peak n1 is n1d, the particle size (nm) at the apex of peak n2 is n2d, the height at the apex of peak n1 is n1h, and the height at the apex of peak n2 is n2h. When n1d > n2d (1) 10 < (n1d + n2d) (2) 30 ≤ {(n2h / n1h) × 100} < 100 (3) is satisfied. In this case, for example, the stress resistance of the toner can be improved, and contamination of the image carrier can be sufficiently suppressed.

[0036] In the present embodiment, the content of the external additive in the toner is 1.8% by mass or more. When it is less than 1.8% by mass, it becomes difficult to transfer the toner from the charging roller to the photoreceptor, and the toner accumulates on the charging roller over time. The content of the external additive in the toner is preferably greater than 1.8% by mass, and more preferably 3.0% by mass or more. The upper limit value of the content of the external additive in the toner is not particularly limited, but for example, it is preferably 8.0% by mass or less, and more preferably 6.0% by mass or less.

[0037] The charging member is a contact-type charging rubber roller, and the resistance is 1×10 4 Ω or more and 1×10 7 Ω or less. In this case, abnormal images due to charging contamination can be suppressed. The resistance of the charging roller will also be described in the following evaluation.

[0038] In this embodiment, it is preferable to have a recovery means that contacts the charging roller and recovers the toner on the charging roller. In this case, the charging roller can be made cleaner. Examples of the recovery means include a recovery brush described later. In this embodiment, since the electrical responsiveness of the toner is good, it becomes easier to move the toner recovered by the recovery means in the order of the charging roller, the photoreceptor, and the developing roller. Therefore, when the recovery means is used, the recovery means and the charging roller can be kept cleaner.

[0039] Next, a cleanerless image forming apparatus used in the present invention will be described with reference to the drawings. In the following description, a charging roller is exemplified as the charging member for explanation. The developing means has, for example, a developing roller, and in the following description, the explanation is made using the developing roller. As the image carrier, a photoreceptor or a photoreceptor drum is exemplified for explanation. As the transfer body, for example, paper or recording paper is exemplified for explanation, but as the transfer body, an intermediate transfer body (for example, an intermediate transfer belt) or the like can also be used.

[0040] FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention. As shown here, a printer as an example of the image forming apparatus according to this embodiment includes a paper feeding means 4, a registration roller pair 6, a photoreceptor drum 10 as an image carrier, a transfer roller 62, a fixing device 12, and the like.

[0041] Further, it is provided with a charging power source 21 for supplying a bias voltage necessary for image formation, a developing power source 22, a cleaning power source 23, a transfer power source 24, etc., and their outputs are controlled by a control unit 25.

[0042] The charging power source 21 is an example of a charging voltage applying means, and applies a voltage to the charging roller 160. The charging roller 160 is an example of a charging member. The voltage applied to the charging roller 160 may be referred to as a charging bias voltage or the like. The developing power supply 22 is an example of developing voltage applying means, and applies a voltage to the developing means. The developing device 61 is an example of the developing means, and has, for example, a developing roller 72. Although the developing power supply 22 is described as applying a voltage to the developing means, the developing power supply 22 may apply a voltage to the developing roller 72. The voltage applied to the developing roller 72 may be referred to as a developing bias voltage or the like. The transfer power supply 24 is an example of transfer voltage applying means, and applies a voltage to the transfer roller 62. The transfer roller 62 is an example of a transfer member, and a voltage is applied thereto for transfer. The voltage applied to the transfer roller 62 may be referred to as a transfer bias voltage or the like.

[0043] The paper feeding means 4 has a paper feeding tray 14 in which sheets P as recording paper are stored in a stacked state, and a paper feeding roller 15 or the like that separates and feeds out the recording papers 105 stored in the paper feeding tray 14 one by one in order from the topmost one. The recording paper is an example of a transfer body, and may be referred to as a recording medium, a recording material, a medium, or the like.

[0044] The recording paper 105 fed out by the paper feeding roller 15 is temporarily stopped by the registration roller pair 6, and after the posture deviation is corrected, at a timing synchronized with the rotation of the photosensitive drum 10, that is, at a timing when the leading end of the toner image formed on the photosensitive drum 10 coincides with a predetermined position at the leading end in the conveyance direction of the paper Pa, it is sent to the transfer site N3 by the registration roller pair 6.

[0045] Around the photosensitive drum 10, in the order of the rotation direction indicated by the arrow, a charging roller 160 as charging means, a developing device 61 including a developing roller 72, and a transfer roller 62 are arranged. Among these, the charging roller 160 and the developing roller 72 are provided in contact with the photosensitive drum 10. Further, a recovery brush 161 (which may also be referred to as a brush roller, a cleaning brush, a cleaning member, etc.) is provided in contact with the charging roller 160. The recovery brush 161 is an example of recovery means.

[0046] Between the charging roller 160 and the developing device 61, exposure light Lb is irradiated onto the surface of the photosensitive drum 10 from the exposure means 5 and is scanned.

[0047] When the photoreceptor drum 10 starts to rotate, a charging bias voltage is applied from the charging power supply 21 to the charging roller 160, and the surface of the photoreceptor is uniformly charged in the charging area N1. Based on the image information, exposure light Lb is irradiated from the exposure means 5 onto the surface of the photoreceptor drum 10, and an electrostatic latent image is formed by discharging the portion of the photoreceptor surface corresponding to the image to be created. This electrostatic latent image moves to the development area N2 due to the rotation of the photoreceptor drum 10. At this time, a development bias voltage is applied from the development power supply 22 to the development roller 72 provided in the developing device 61.

[0048] In the development area N2, the negatively charged toner held on the development roller is supplied from the development roller 72 to the photoreceptor drum 10 according to the potential difference between the potential of the exposed portion and the development bias voltage, and a toner image is formed on the photoreceptor drum 10. The toner image formed on the photoreceptor drum 10 moves to the transfer area N3 at a predetermined timing. At this time, a transfer bias voltage is applied from the transfer power supply 24 to the transfer roller 62, and the toner image is transferred onto the recording paper 105 that has entered the transfer area N3.

[0049] The recording paper 105 carrying the toner image is conveyed toward the fixing device 12, fixed by the fixing device 12, and then discharged and stacked on the paper discharge tray. The residual toner remaining on the photoreceptor drum 10 without being transferred to the recording paper 105 in the transfer area N3 reaches the charging area N1 as the photoreceptor drum 10 rotates. In the charging area N1, the residual toner is charged to a negative polarity by the microdischarge of the charging bias voltage applied to the charging roller 160 and is returned to the development area N2.

[0050] In the development area N2, the residual toner moves onto the development roller 72 according to the potential difference between the potential of the unexposed portion (the non-exposed site) and the development bias voltage and is collected into the developing device 61.

[0051] In the charging area N1, it is difficult to completely align the charging of the residual toner to the negative polarity, and the toner with a positive polarity adheres to the charging roller 160 side. Therefore, it is preferable to use a recovery brush 161 for scraping off the dirt on the charging roller 160. A cleaning bias voltage is applied from the cleaning power supply 23 to the recovery brush 161, and the positive-polarity toner attached to the charging roller 160 is cleaned by the potential difference and mechanical scraping. By using the recovery brush 161, the charging roller 160 can be made cleaner.

[0052] FIG. 2(A) is a block diagram for explaining the hardware configuration of the control unit 25 in the present embodiment. The control unit 25 includes, for example, a CPU which is a central element for performing arithmetic processing, and memories such as a ROM and a RAM which are storage elements (storage units). The sensor detection results, arithmetic results, etc. are stored in the RAM, and the control program, pre-determined data tables, etc. are stored in the ROM. The control unit 25 controls, for example, the charging power supply 21, the developing power supply 22, the cleaning power supply 23, and the transfer power supply 24. The control unit 25 controls the ON / OFF and output values of the outputs of each power supply. The control unit 25 controls the exposure means 5. The control unit 25 controls the discharging lamp 64 (discharging means), and for example, discharges the photosensitive drum 10 in the pre-charging discharge.

[0053] FIG. 2(B) is a block diagram showing an example of the hardware configuration of the control unit 25.

[0054] The control unit 25 has a CPU (Central Processing Unit) 110, a RAM (Random Access Memory) 111, a ROM (Read Only Memory) 112, and a storage unit 113 connected via a bus 117.

[0055] The CPU 110 is an arithmetic unit that controls the operation of the entire image forming apparatus 100. The RAM 111 is a volatile storage medium that enables high-speed reading and writing of information. When the CPU 110 processes information, the RAM 111 is used as the working area of the CPU 110. The ROM 112 is a read-only non-volatile storage medium in which programs such as firmware are stored.

[0056] The storage unit 113 is a non-volatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The storage unit 113 is, for example, an SSD (Solid State Drive), an HDD (Hard Disk Drive), or the like.

[0057] In the image forming apparatus of the present embodiment, transfer residual toner remaining on the image carrier is recovered by the developing means. The image forming apparatus of the present embodiment is configured not to use cleaning means (for example, a cleaning blade) for cleaning the image carrier (also referred to as an electrostatic latent image carrier, a photoreceptor, etc.). In this case, there are advantages such as miniaturization of the apparatus.

[0058] Hereinafter, a method that does not use cleaning means for cleaning the image carrier may also be referred to as a cleanerless method. However, means for cleaning the charging member and means for cleaning the intermediate transfer belt may be provided, and even in the case where these means are provided, they are included in the cleanerless method.

[0059] The basic configuration and operation of the cleanerless image forming apparatus will be described with reference to FIG. 3. FIG. 3 is a diagram for explaining an example of a process of forming an image. As the charging member, for example, a charging roller can be used, and in the following description, the charging roller is taken as an example for explanation.

[0060] First, the charging roller 160 uniformly charges the photosensitive drum 10 serving as an image carrier. The charging roller 160 in this example is arranged to contact the photosensitive drum 10 and applies, for example, a DC voltage to the photosensitive drum 10. The charging in this example is a contact-type DC charging method. The exposure device 121 exposes the photosensitive drum 10 to the exposure light L to form an electrostatic latent image on the photosensitive drum 10. The exposure device 121 is not particularly limited, but for example, an LED is used.

[0061] The developing roller 72 is an example of a developer carrier included in the developing device 61. The developing roller 72 has a developing bias applied thereto by an applying means and supplies the toner 200 to the photosensitive drum 10. Thereby, a toner image (also referred to as a visible image) is formed on the photosensitive drum 10. The developing device 61 may have, for example, a stirring roller 73 and stir the toner within the developing device 61. The rotation direction of the stirring roller 73 can be appropriately selected, and it may be in contact with or non-contact with the developing roller 72. The transfer roller 62 transfers the toner image on the photosensitive drum 10 to the recording paper 105. The discharging lamp 64 discharges the potential of the photosensitive drum 10. For example, it discharges by irradiating the discharging light QL.

[0062] The above configuration is the basic configuration of a cleanerless type image forming apparatus. In such an apparatus, after the transfer process, cleaning means such as a cleaning grade for cleaning the photosensitive drum 10 is not provided.

[0063] In the example shown in FIG. 3, for example, -300 V is applied to the developing roller 72 and -1100 V is applied to the charging roller 160. For example, the surface of the photosensitive drum 10 becomes about -50 V when discharged and about -500 V when charged. Note that the image forming apparatus of this embodiment may include a recovery brush 161 (recovery means) for recovering the toner on the charging roller 160. In the example shown in FIG. 3, since the recovery brush 161 is not provided, it is shown by a broken line in the figure.

[0064] Here, an example of the toner flow in the example shown in FIG. 3 will be described. For the sake of explanation, the reference numerals of the toner in the figure are changed according to the position and state of the toner. The developing roller 72 carries the toner 200, and the toner 200 carried on the developing roller 72 is supplied to the photosensitive drum 10. The toner supplied to the photosensitive drum 10 forms a toner image (visible image) according to the electrostatic latent image (toner 201). The toner 201 on the photosensitive drum 10 is transferred to the recording paper 105. The toner 202 transferred to the recording paper 105 is fixed to the recording paper 105 in a later process.

[0065] The toner that has not been transferred in the transfer process remains on the photosensitive drum 10 as the remaining transfer toner 203. After passing through the charge elimination process, the remaining transfer toner 203 adheres to the charging roller 160 at the contact point (or in the vicinity) between the photosensitive drum 10 and the charging roller 160. Among the remaining transfer toner 203, there is also toner 206 that does not adhere to the charging roller 160, and this toner 206 remains on the photosensitive drum 10. This toner 206 is recovered by the developing roller 72.

[0066] Next, an example of a method for recovering the remaining transfer toner in a cleanerless type image forming apparatus will be described with reference to FIGS. 4, 5A, and 5B. FIG. 4 is a schematic diagram for explaining the state after FIG. 3, and is a diagram schematically showing the state during printing. The term "during printing" as used here means the state in which the apparatus is operating, and includes not only the process of transferring toner to the recording paper but also the process of preparing to transfer toner to the recording paper. FIG. 4 is a diagram for explaining the process performed between the transfer to the previous recording paper and the transfer to the next recording paper.

[0067] As described with reference to FIG. 3, the toner that has not been transferred in the transfer process remains on the photoreceptor drum 10 as residual transfer toner 203. In FIG. 4, it is shown that the residual transfer toner 203 remains on the photoreceptor drum 10 on the downstream side of the transfer roller 62. After transferring onto the previous recording paper 105, the surface of the photoreceptor drum 10 is discharged by the discharge lamp 64. As a result, the potential difference between the charging roller 160 and the photoreceptor drum 10 widens, and a discharge occurs between the charging roller 160 and the photoreceptor drum 10 before charging. In the figure, the discharge is schematically illustrated.

[0068] Due to the discharge before charging, the residual transfer toner 203 becomes negatively charged (not shown in FIG. 4). Among the residual transfer toner 203, there are those that become negatively charged, for example, due to the discharge before charging, and those that remain slightly positively charged. The residual transfer toner 203 that remains slightly positive adheres to the charging roller 160 at the point (or in the vicinity) where the charging roller 160 and the photoreceptor drum 10 come into contact. The toner adhering to the charging roller 160 is illustrated as toner 204.

[0069] Note that the arrow a in the figure schematically illustrates that the residual transfer toner 203 on the photoreceptor drum 10 adheres to the charging roller 160. The adhesion of the residual transfer toner 203 on the photoreceptor drum 10 to the charging roller 160 may also be referred to as moving or the like.

[0070] The image forming apparatus in this example has a recovery brush 161 for recovering the toner adhering to the charging roller 160. The positively charged toner 204 adhering to the charging roller 160 is recovered by the recovery brush 161. The arrow b in the figure schematically illustrates that the toner 204 on the charging roller 160 is recovered by the recovery brush 161. The recovery of the toner 204 on the charging roller 160 by the recovery brush 161 may also be referred to as moving or the like. A recovery bias is applied to the recovery brush 161. The value of the recovery bias is not particularly limited and can be appropriately selected.

[0071] Of the transfer residual toner 203 on the photoreceptor drum 10, the toner charged negatively does not adhere to the charging roller 160 and remains on the photoreceptor drum 10. This toner is illustrated as toner 206. Note that both toner 203 and toner 206 are transfer residual toner.

[0072] The toner 206 remaining on the photoreceptor drum 10 is recovered by the developing roller 72. The toner recovered by the developing roller 72 is illustrated as toner 208. The fact that the toner is recovered by the developing roller 72 may be referred to as moving or the like. The toner 206 passing between the photoreceptor drum 10 and the developing roller 72 moves to the side of the developing roller 72 due to the potential difference between the photoreceptor drum 10 and the developing roller 72. The arrow c in the figure schematically illustrates that the toner 206 on the photoreceptor drum 10 is recovered by the developing roller 72.

[0073] To recover with the developing roller 72 as described above, for example, a method of adjusting the potential of each member can be mentioned. As an example, for example, the surface of the photoreceptor drum 10 after discharging is set to -50V, the charging roller 160 is set to -1100V, the recovery brush 161 is set to -1300V, the surface of the photoreceptor drum 10 after charging is set to -500V, and the developing roller 72 is set to -300V. In FIG. 4, the potential is illustrated as this example, but it is not limited to this.

[0074] In the image forming apparatus of the present invention, it is preferable to have the recovery brush 161, but the recovery brush 161 is not essential. When there is no recovery means (for example, the recovery brush 161) for recovering the toner existing on the charging roller 160, it is preferable to adjust the potential so as to reduce the toner moving to the charging roller 160.

[0075] Next, with reference to FIGS. 5A and 5B, the movement of the toner during apparatus shutdown and an example of toner recovery will be described. As described with reference to FIG. 4, the positively charged transfer residual toner 203 (the same applies to toner 206) that became negative during discharge before charging adheres to the charging roller 160 and is recovered by the recovery brush 161. During printing, since this recovery is repeated, the positively charged toner 207 accumulates on the recovery brush 161.

[0076] During apparatus shutdown, the potential difference between the recovery brush 161 and the charging roller 160 is adjusted to move the slightly positively charged toner 207 toward the charging roller 160. This is indicated by arrow d in the figure.

[0077] The toner 205 that has moved to the charging roller 160 moves to the photosensitive drum 10 due to the potential difference between the charging roller 160 and the photosensitive drum 10. This is indicated by arrow e in the figure. The moved toner is shown as toner 209 in the figure. During apparatus shutdown, since the photosensitive drum 10 is not discharged by the discharge lamp 64, the potential difference between the charging roller 160 and the photosensitive drum 10 is adjusted in consideration of this.

[0078] The positively charged toner 209 on the photosensitive drum 10 is not recovered by the developing roller 72 and passes through the developing roller 72 as it is. Further, the toner 209 passes through the transfer roller 62. Thus, during apparatus shutdown, there will be positively charged toner 209 on the photosensitive drum 10.

[0079] In FIGS. 4, 5A, and 5B, toner 203, 206, and 209 are shown on the photosensitive drum 10. All of these are considered as transfer residual toner. Toner 209 is the one that moved onto the photosensitive drum 10 again after the transfer residual toner 203 was recovered by the recovery brush 161, and such toner may also be included in the transfer residual toner.

[0080] In order for the toner to move as in the example shown in FIG. 5A, for example, a method of adjusting the electric potential of each member can be mentioned. For example, the electric potential of the recovery brush 161 is -150V, the electric potential of the charging roller 160 is -350V, the electric potential of the surface of the photosensitive drum 10 is 500V, and the electric potential of the developing roller 72 is +250V. In FIG. 5A, the electric potential is illustrated as this example, but it is not limited thereto.

[0081] Next, in the apparatus shutdown, the recovery of the toner on the photosensitive drum 10 will be described with reference to FIG. 5B. FIG. 5B is a continuation of FIG. 5A. As shown in the figure, the photosensitive drum 10 is discharged by the discharge lamp 64 at a predetermined timing. By performing the discharge, the potential difference between the charging roller 160 and the photosensitive drum 10 widens, and discharge occurs between the charging roller 160 and the photosensitive drum 10. In the figure, the discharge is schematically illustrated. Note that the discharge shown in the figure is not the discharge performed for image formation, but the discharge performed for toner recovery.

[0082] Due to the above discharge, the toner 209 is charged negatively. Similar to FIG. 4, among the toner 209, the toner that is not charged negatively and remains positively charged adheres to the charging roller 160 and is recovered by the recovery brush 161 (arrows g and h in the figure).

[0083] The toner 209 charged negatively by the above discharge remains on the photosensitive drum 10 without moving to the charging roller 160. Then, the toner 209 charged negatively is recovered by the developing roller 72 to which the developing bias is applied (arrow i in the figure). The toner recovered by the developing roller 72 is shown as toner 208 in the figure.

[0084] In order for the toner to move as in the example shown in FIG. 5B, for example, a method of adjusting the potential of each member can be mentioned. For example, the potential of the recovery brush 161 is -1300V, the potential of the charging roller 160 is -1100V, the surface of the photoreceptor drum 10 after discharging is -50V, the potential of the surface of the photoreceptor drum 10 is 500V, and the potential of the developing roller 72 is -300V. In FIG. 5B, the potential is illustrated as this example, but it is not limited to this.

[0085] Note that the discharge lamp 64 is an example of a discharging device. The discharging device may also be referred to as a discharging means or the like.

[0086] The recovery of the transfer residual toner described with reference to FIG. 3 is a method of controlling the charging polarity of the toner and moving and recovering it by an electric field in each process. Thereby, toner contamination of the charging roller is prevented. One of the purposes of the present embodiment is to control the toner behavior in the charging nip portion by an electric field response, and to more reliably perform the recovery of the transfer residual toner described with reference to FIG. 3.

[0087] The charging roller and the photoreceptor drum are in a pressed state in order to form a minute gap for generating discharge on the surface of the photoreceptor drum. When the transfer residual toner attached to the surface of the photoreceptor drum passes between the nips, the toner is crushed by both the photoreceptor drum and the charging roller. At this time, if the surface of the charging roller is smooth, pressure from the charging roller is applied to all the transfer residual toner, and the adhesion force to the charging roller due to physical adsorption force (van der Waals force) other than the electric field acts strongly. Therefore, most of the transfer residual toner adheres to the charging roller not by the electric field response but by the physical adsorption force (van der Waals force). In this case, even if an attempt is made to recover it onto the photoreceptor drum again by utilizing the action of the electric field response, it does not function well.

[0088] FIG. 6 is a diagram for explaining the attachment of toner to the charging roller. In the figure, the portion surrounded by the dashed rectangle is the portion where the charging roller 160 and the photoreceptor drum 10 face each other. An enlarged view of the portion between the charging roller 160 and the photoreceptor drum 10 is shown below the paper surface. In the enlarged view shown by the lower dashed line, the unevenness on the surface of the charging roller 160 is schematically illustrated.

[0089] Also, in the enlarged view, the transfer residual toner 203 on the photoreceptor drum 10 is illustrated. In the figure, toner 203a is the toner that has contacted the convex portion of the charging roller 160, and toner 203b is the toner that has contacted the concave portion of the charging roller 160. The toner 203a that has contacted the convex portion of the charging roller 160 is attached to the charging roller 160 under pressure from both the charging roller 160 and the photoreceptor drum 10. On the other hand, toner 203b is less likely to receive the pressure from the charging roller 160 and the photoreceptor drum 10 and is less likely to adhere to the charging roller 160. Therefore, in order to suppress the attachment to the charging roller 160, it is required to appropriately set the surface shape of the charging roller 160.

[0090] Although it has been described that toner 203b is the toner that has contacted the concave portion of the charging roller 160, it may be considered as the toner that has not contacted the charging roller 160 due to the concave portion of the charging roller 160.

[0091] Therefore, three-dimensionally unevenness is formed on the surface of the charging roller, and the surface roughness Sk + Spk is designed to be 2 to 16 μm. As a result, it becomes possible to provide a region weak in the distribution of the nip pressure between the charging roller and the photoreceptor drum, and it is possible to prevent toner attachment due to the physical adsorption force (van der Waals force) of the transfer residual toner during nip passage. Also, even if toner adheres to the charging roller side, since the physical adsorption force (van der Waals force) is weak, it becomes easy to move the toner onto the photoreceptor drum by electric field control again.

[0092] In terms of line roughness, only the local unevenness in the axial or circumferential direction of the charging roller can be expressed. On the other hand, in terms of surface roughness defined in JIS B0671-2:2002 (ISO 25178-2:2012), the three-dimensional uneven shape considering both the axial and circumferential directions of the charging roller can be numerically expressed. Therefore, it is possible to more accurately grasp the shape factor of the surface of the charging roller. The shape factor of the surface of the charging roller is specified by the surface roughness, and the pressure at the nip portion between the charging roller and the photoreceptor is adjusted. Since the shape factor of the surface of the charging roller cannot be specified accurately by the line roughness, the roughness of the three-dimensional surface is defined.

[0093] Sk and Spk will be explained. Regarding Sk and Spk, explanations can be found not only on the homepage of Keyence Corporation (https: / / www.nsfellows.com / files / user / site / hyoumenarasa.pdf) but also on the homepage of EVIDENT Corporation. Sk and Spk used in the present invention may follow the definitions explained therein, but here, for simplicity, examples will be given to explain below. In the following explanations, there are some parts that are schematically explained from the perspective of facilitating understanding, but they may follow the known definitions.

[0094] Fig. 7A is a diagram schematically showing a certain cross-section in the three-dimensional cross-sectional profile of the charging roller. The horizontal axis is the X-axis or the Y-axis. Fig. 7B(1) is a diagram showing the load curve obtained for an example of the charging roller. The horizontal axis represents the load area ratio, and the vertical axis represents the height. Fig. 7B(1) can also be said to be a plot with the horizontal axis representing the distribution number and the vertical axis representing the height for the height of the cross-sectional profile. Also, in Fig. 7B(1), the ratio of the load area at a certain height c is represented as the load area ratio Smr(c). The load curve can also be said to be the ratio of the solid part to the void part when horizontally cut at a certain height c in the unevenness of the cross-section as shown in Fig. 7A, for example. For example, at the height m in Fig. 7A, since there is no solid part, the load area ratio is 0%, and at the height n in Fig. 7A, since it is all solid part, the load area ratio is 100%.

[0095] Figure 7B(2) is a diagram showing a secant line of a load curve with a difference in load area ratio of 40%. The secant line is, for example, a straight line drawn along the load curve from a load area ratio of 0% with a difference in load area ratio of 40%. The secant line is moved from a load area ratio of 0% to 100%, and the position where the slope of the secant line becomes the gentlest is determined.

[0096] Figure 7B(3) is a diagram showing the position where the slope of the secant line becomes the gentlest. The position where the slope of the secant line becomes the gentlest is referred to as the central portion of the load curve. The straight line with the gentlest slope of the secant line may also be referred to as the gentlest slope straight line or the like. Also, in Figure 7B(3), an equivalent line is shown. The equivalent line is a straight line where the sum of the squares of the deviations in the vertical axis direction is minimized in the central portion.

[0097] Figure 7C(4) is a diagram showing point a1 which is the point of 0% load area ratio on the equivalent line and point b1 which is the point of 100% load area ratio on the equivalent line. Although it is an image, the portion corresponding to the core part is from the height position of b1 to the height position of a1. The portion protruding above the core part is the protruding peak part, and the portion sunken below the core part is the protruding valley part. The core part can also be said to be the surface obtained by removing the region not included in the range of the height of 0% to 100% load area ratio of the equivalent line.

[0098] Figure 7C(5) is a diagram showing Smr1 and Smr2. Smr1 is the load area ratio where the protruding peak part and the core part are separated, and Smr2 is the load area ratio where the protruding valley part and the core part are separated. Smr1 is the load area ratio at the intersection of the height above the core part and the load curve. Smr2 is the load area ratio at the intersection of the height below the core part and the load curve. In Figure 7C(5), Sk is shown. Sk is the level difference of the core part, which is the value obtained by subtracting the minimum height from the maximum height of the core part (height of a1 - height of b1), and is calculated by the height difference between 0% and 100% load area ratio of the equivalent line.

[0099] FIG. 7C(6) is a diagram for explaining the images of the core portion, the protruding peak portion, and the protruding valley portion, and is a diagram showing the corresponding portions of the core portion, the protruding peak portion, and the protruding valley portion with respect to FIG. 7A. The portion protruding upward from the core portion corresponds to the protruding peak portion, and the portion recessed downward from the core portion corresponds to the discharge valley portion.

[0100] FIG. 7D is a diagram showing Sk and Spk. Sk can be calculated as shown in FIGS. 7C(4) and (5). Spk is the height of the protruding peak portion, and as shown in the figure, it is the position from the highest position (a1) of the core portion in the height direction to the point where it intersects the load curve. Spk can also be said to be the average height of the protruding peak portion.

[0101] In addition, in FIG. 7D, Svk is shown. Svk is the height of the protruding valley portion and can also be said to be the average depth of the protruding valley portion. Also, in FIG. 7D, the cross-sectional area of the protruding peak portion and the cross-sectional area of the protruding valley portion are represented by diagonal lines. Sk can also be said to be the main uneven height of the surface shape of the charging roller. Also, Spk can be said to be the portion protruding more than the main uneven height of the surface shape of the charging roller.

[0102] For measuring the surface roughness, a measuring device that can arithmetically measure the surface roughness is used, using a device that can measure the vertical height profile on a plane observation screen, such as a confocal laser scanning microscope. Representative examples include the OLS series (OLS4000, OLS4100, OLS5000, OLS5100, etc.) manufactured by Olympus Corporation and the VK series (VKX-100, VKX-200, VKX-3000, etc.) manufactured by Keyence Corporation. A range of 600 μm × 600 μm or more is specified as the observation range, and the surface roughness Sk and Spk are measured after performing three-dimensional measurement by laser scanning.

[0103] In order to make the surface roughness Sk + Spk of the charging member fall within the scope of the present invention, for example, a method of injecting a material into a mold processed into a predetermined uneven shape to produce the charging member can be mentioned. When the charging member is a charging roller, a method of injecting a rubber material into a mold processed with the required uneven shape and molding it into a roller shape can be considered.

[0104] For example, there is also a method of applying a surface coating agent mixed with particles for forming irregularities on the surface after molding the charging member in a smooth shape. For example, there is also a method of shaping the surface of the charging member with a high-output laser. For example, there is also a method of partially changing the composition of a material (for example, rubber) with a high-output laser and then performing polishing with a file.

[0105] (Evaluation) Next, the following evaluations were performed on the present invention.

[0106] (Examination of the amount of external additive) Using the image forming apparatus shown in FIG. 1, the evaluation of abnormal images due to contamination of the charging roller was performed when the amount of external additive was changed as shown in Table 1 below. The amount of external additive in Table 1 represents the content of the external additive in the toner. An evaluation chart for evaluation was prepared. The evaluation criteria are as follows. ○ was regarded as passing. In the evaluation of Table 1, a charging roller that satisfies the requirements of Sp + Spk was used.

[0107] [Evaluation criteria] 〇: No abnormality △: Density decrease ×: Toner contamination occurs in the non-image area

[0108] [Table 1]

[0109] As shown in Table 1, when the amount of external additive is 1.6% by mass, abnormal images due to contamination of the charging roller occur. When the amount of external additive is small, the accumulation of toner on the charging roller increases, and the contact property between the charging roller and the surface of the photosensitive drum decreases. For this reason, charging failure occurs and the image density begins to decrease. Furthermore, when the contamination of the charging roller progresses, toner is developed in the non-image area. Therefore, when the amount of external additive is lower than 1.6% by mass, the result may be ×. From this, the amount of external additive in the toner needs to be 1.8% by mass or more.

[0110] (Examination of surface roughness) Next, the evaluation results of the surface roughness of the charging roller will be described. First, the surface roughness Sk + Spk of the charging roller was set to around 12 μm, and evaluation charts were created using Toners A to C with different amounts of external additive, and the images were evaluated. In the evaluation, the decrease in image density and the state of toner contamination in the non-image area were confirmed for each toner. Toner A (△) has an external additive amount of 2.4% by mass in the toner, Toner B (□) has an external additive amount of 2.0% by mass in the toner, and Toner C (〇) has an external additive amount of 1.8% by mass in the toner.

[0111] Each toner used in the evaluation satisfies the following. In the particle size distribution of the primary particles of the external additive, there are a plurality of peaks between 5 nm and 50 nm. Among the peaks, the highest peak is Peak n1, the second highest peak is Peak n2, the particle size (nm) at the apex of Peak n1 is n1d, the particle size (nm) at the apex of Peak n2 is n2d, the height at the apex of Peak n1 is n1h, and the height at the apex of Peak n2 is n2h. When the following mathematical formulas (1) to (3) are all satisfied. n1d > n2d (1) 10 < (n1d + n2d) (2) 30 ≤ {(n2h / n1h) × 100} < 100 (3) The above mathematical formulas (1) to (3) mean that the inorganic fine particles as the external additive contain at least two types of small particle sizes and large particle sizes, and in the external additive, more large particle size inorganic fine particles are contained than small particle size inorganic fine particles.

[0112] The production of the toner used in the evaluation will be described. Parts refers to parts by mass.

[0113] - Preparation of toner base particles - 87 parts of polyester resin 3 parts of rice wax (TOWAX - 3F16, manufactured by Toagosei Co., Ltd.) 8 parts of carbon black (#44, manufactured by Mitsubishi Chemical Corporation) 2 parts of azo iron compound (T - 77, manufactured by Hodogaya Chemical Co., Ltd.)

[0114] The toner raw materials of the above formulation were preliminarily mixed using a Henschel mixer (manufactured by Mitsui Miike Chemical Machinery Co., Ltd., FM20B), and then melted and kneaded at a temperature of 120 °C using a twin-screw kneader (manufactured by Ikegai Corporation, PCM-30). The obtained kneaded product was rolled to a thickness of 2.7 mm using rollers, cooled to room temperature using a belt cooler, and coarsely pulverized to 200 μm - 300 μm using a hammer mill. Subsequently, it was finely pulverized using a supersonic jet mill Labojet (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and then classified using an air classifier (manufactured by Nippon Pneumatic Mfg. Co., Ltd., MDS-I) while appropriately adjusting the louver opening so that the weight average particle diameter became 5.8 ± 0.2 μm, thereby obtaining toner base particles.

[0115] - Preparation of toner - To 100 parts of the above toner base particles, 1.00 part of inorganic fine particle 1 and 0.03 part of inorganic fine particle 2 were added as external additives, and they were stirred and mixed using a Henschel mixer to prepare a toner for evaluation. The amounts of the external additives were appropriately changed to obtain toners A - C. Note that according to 1.03 / (100 + 1.03) = 1.03 / 101.03 ≒ 0.01019, the ratio of the external additives to the toner is 1.0 mass%. Also, the above inorganic fine particle 1 and inorganic fine particle 2 were obtained as follows.

[0116] <Manufacture of inorganic fine particle 1> - Manufacture of silica particles - Octamethylcyclotetrasiloxane, which is a silica compound, was heated and vaporized, and after mixing oxygen and nitrogen, it was introduced into the central tube of a concentric triple-tube burner. Hydrogen and nitrogen were mixed and introduced into the second annular tube arranged on the outer periphery of the central tube. Further, air was introduced into the third annular tube arranged on the outer periphery of the second annular tube. The silica particles obtained by these combustions were collected and recovered using a metal filter.

[0117] - Surface treatment - The silica particles obtained above were placed in a fluidized bed reactor, and dimethyl silicone oil was fed into the reactor heated to 250°C at a rate of 8 g / min for 40 minutes under a nitrogen atmosphere to subject the silica particle surfaces to hydrophobic treatment. In this way, inorganic fine particles 1 were obtained.

[0118] The volume average particle size of the obtained inorganic fine particles 1 was 26 nm, and the BET specific surface area was 50 m 2 / g.

[0119] <Production of Inorganic Fine Particles 2> Using the same method as inorganic fine particles 1, the volume average particle size was 12 nm, the BET specific surface area was 300 m 2 / g of inorganic fine particles 2 were obtained.

[0120] FIG. 8 is a diagram showing the evaluation results. In the figure, the horizontal axis is the durable print count, and the vertical axis is the image density. In the figure, △ is toner A, □ is toner B, and ○ is toner C. The durable print count refers to the number of printed sheets at the time of image evaluation. For example, the plot for the durable print count of 10kp (10,000 sheets) is obtained by printing 10,000 evaluation charts and measuring the image density of the 10,000th evaluation chart. From the results in FIG. 8, it can be seen that when the amount of external additive is 1.8 mass % or more, it is possible to suppress abnormal images and reduction in image density caused by contamination of the charging roller.

[0121] Next, image evaluation was performed by changing the surface roughness Sk+Spk of the charging roller using the above toner C. The results are shown in Table 2. The evaluation criteria are as follows.

[0122] [Evaluation Criteria] 〇: No abnormalities △: Concentration decrease ×: Toner stains occur in non-image areas

[0123] [Table 2]

[0124] If the surface roughness Sk + Spk of the charging roller is small, the contact pressure between the charging roller and the toner at the roller nip portion increases, and the van der Waals force of the toner on the charging roller becomes stronger. For this reason, it becomes difficult to sweep out the toner by the electric field response, and it becomes difficult for the toner to move from the charging roller to the photosensitive drum. On the contrary, if the surface roughness Sk + Spk of the charging roller is too large, it becomes difficult to form the minute space necessary for charging between the charging roller and the photosensitive member. For this reason, charging is not stable and abnormal images tend to occur. From the results in Table 2, it is appropriate that the surface roughness Sk + Spk of the charging roller is 2 μm to 16 μm.

[0125] Although not shown in Table 2, when the surface roughness Sk + Spk of the charging roller was 6 μm and 12 μm, abnormal images could be suppressed at a higher level compared to other examples (for example, 2 μm and 16 μm).

[0126] Next, using toner with the amount of external additive adjusted to 2.2 mass%, image evaluation was performed on charging rollers with different surface roughnesses Sk + Spk. For each charging roller, an evaluation chart was created, and the state of density reduction and toner contamination in the non-image area was confirmed. The results are shown in Fig. 9. In the figure, the horizontal axis represents the number of durable printed sheets, and the vertical axis represents the image density. Charging roller A (△) has a surface roughness Sk + Spk of 28 μm, charging roller B (□) has a surface roughness Sk + Spk of 12 μm, and charging roller C (〇) has a surface roughness Sk + Spk of 1 μm.

[0127] As shown in the results of Fig. 9, in charging roller A (△), toner contamination occurred in the non-image area when the number of durable printed sheets was 45 kp and 60 kp. When the surface roughness Sk + Spk exceeds 16 μm, it becomes difficult to form the minute space necessary for charging between the charging roller and the photosensitive member, charging is not stable, and abnormal images occur. Also, in charging roller C (○), the image density decreased after the number of durable printed sheets reached 30 kp. When the surface roughness Sk + Spk is less than 2 μm, it becomes difficult for the toner to be ejected from the charging roller to the photosensitive member, the accumulation of toner on the charging roller increases, and charging failure and a decrease in image density occur. From the results of Fig. 9, it can be seen that when the surface roughness Sk + Spk satisfies the scope of the present invention, the reduction of the image density can be prevented over a long period of time, the toner contamination of the non-image area can be prevented, and the abnormal image can be prevented.

[0128] Thus, in the present invention, by using a toner in which the content of the external additive in the toner is 1.8% by mass or more and using a charging roller with a surface roughness Sk + Spk of 2 to 16 μm, the accumulation of toner on the charging roller can be reduced, and the occurrence of abnormal images can be suppressed over a long period of time.

[0129] <Examination of the Resistance of the Charging Roller> Next, the evaluation results of the resistance of the charging roller will be described. When the external additive adheres to the charging roller and the resistance of the charging roller increases, charging failure may occur. Therefore, when the resistance of the charging roller is within an appropriate range, charging failure can be suppressed. Using a toner with the amount of the external additive adjusted to 2.2% by mass, setting the surface roughness Sk + Spk of the charging roller to around 12 μm, and changing the resistance of the charging roller to conduct image evaluation. Also, a contact-type charging rubber roller was used as the charging roller. The results are shown in Table 3. The evaluation criteria are as follows.

[0130] [Evaluation Criteria] 〇: No abnormality △: Density reduction ×: Toner contamination occurs in the non-image area

[0131]

Table 3

[0132] From the evaluation results in Table 3, the resistance of the charging roller is preferably 1×10 4 Ω or more and 1×10 7 Ω or less. By setting the resistance of the charging roller within the above range, charging failure can be suppressed, and the occurrence of abnormal images can be further suppressed. Also, when the charging member is a contact-type charging rubber roller and the resistance of the charging roller is 1×10 4 Ω or more and 1×10 7It is more preferably Ω or less. However, when the resistance of the charging roller is 1×10 3 Ω, 1×10 8 Ω, 1×10 9 Ω, these cases are also included in the present invention. Although the results are inferior in Table 3, these cases were also at the passing level.

[0133] To measure the resistance of the charging roller, for example, an electric resistance measuring device jig as shown in FIG. 10 is used. The conditions are as follows, for example. Applied voltage: DC - 500V Rotation speed: 29 r / m Measurement point: 185 (circumferential direction) Measurement time: 6 seconds Resistance value: Average value of the measurement points when a load of 4.9 N (500 g) is applied to both ends of the metal roller 170

[0134] (Toner) Next, a detailed example of the toner used in the present invention will be described.

[0135] <External additive> As described above, the toner used in the present invention contains an external additive containing inorganic fine particles, and the external additive is contained in the toner in an amount of 1.8% by mass or more. Further, the toner used in the present invention contains, for example, toner base particles containing a binder resin and an external additive containing inorganic fine particles. The inorganic fine particles as the external additive preferably contain at least two types of small particle size and large particle size. In the external additive, it is preferable that the large particle size inorganic fine particles are contained more than the small particle size inorganic fine particles.

[0136] In the particle size distribution of the primary particles of the external additive, it preferably has a plurality of peaks between 5 nm and 50 nm. Among the peaks, the highest peak is peak n1, the second highest peak is peak n2, the particle size (nm) at the apex of peak n1 is n1d, the particle size (nm) at the apex of peak n2 is n2d, the height at the apex of peak n1 is n1h, and the height at the apex of peak n2 is n2h. When defined as such, it is preferable to satisfy all of the following mathematical formulas (1) to (3). n1d > n2d (1) 10 < (n1d + n2d) (2) 30 ≤ {(n2h / n1h) × 100} < 100 (3) The mathematical formulas (1) to (3) mean that the inorganic fine particles as an external additive contain at least two types of small particle sizes and large particle sizes, and in the external additive, more large particle size inorganic fine particles are contained than small particle size inorganic fine particles.

[0137] In the prior art, small particle size inorganic fine particles were made to play a role in imparting stress resistance, and large particle size inorganic fine particles were added thereto as spacers to prevent the small particle size inorganic fine particles from being buried in the toner surface. Therefore, more small particle size inorganic fine particles were added than large particle size inorganic fine particles. However, it was difficult for the prior art to sufficiently suppress the burial of small particle size inorganic fine particles.

[0138] As a result of intensive studies by the present inventors, it has been found that even large particle size inorganic fine particles can improve the stress resistance of the toner and sufficiently suppress contamination of the electrostatic latent image carrier if the addition amount thereof is set within a specific range. Large particle size inorganic fine particles are less likely to be buried in the toner surface and can sufficiently exhibit the effect. Such an effect is improved by satisfying the mathematical formulas (1) to (3).

[0139] The particle size distribution of the inorganic fine particles referred to in the present invention is a number-based particle size distribution targeting the primary particles thereof, and can be measured by sequentially passing through the following steps (1) to (3).

[0140] (1) With inorganic fine particles attached to the toner surface, an image of the toner is obtained using a scanning electron microscope SU8200 series (Hitachi High-Technologies Corporation). (2) The obtained image is binarized with image processing software A Image-kun (Asahi Kasei Engineering Corporation), and the equivalent circle diameter of the inorganic fine particles is calculated. The equivalent circle diameter of the inorganic fine particles is measured for 1000 particles. (3) Next, the number of classes is determined according to the following formula, a histogram is created, and the particle size distribution is obtained. Number of classes = 1 + log2n (n represents the number of data on the equivalent circle diameter of inorganic fine particles)

[0141] As the inorganic fine particles used in the present invention, the particle size (nm) at the peak of the peak n1, n1d, is preferably 15 nm to 50 nm, more preferably 20 nm to 40 nm. Also, the particle size (nm) at the peak of the peak n2, n2d, is preferably 5 nm to 50 nm, more preferably 10 nm to 20 nm.

[0142] Also, the difference between n1d and n2d is preferably 10 nm to 45 nm, more preferably 13 nm to 30 nm.

[0143] Further, from the viewpoint of improving the effect of the present invention, more preferable forms of the above formulas (2) and (3) are represented by the following formulas (20) and (30).

[0144] 20 < (n1d + n2d) Formula (20) 40 < {(n2h / n1h) × 100} < 90 Formula (30)

[0145] In the particle size distribution of the primary particles of the inorganic fine particles, in order to have a plurality of peaks between 5 nm and 50 nm and satisfy all of the above formulas (1) to (3), for example, means such as preparing two or more kinds of inorganic fine particles having different average particle sizes and adjusting the blending amounts so as to satisfy the conditions can be mentioned. Note that the inorganic fine particles are preferably of the same kind.

[0146] As described above, in the present invention, a toner having high toner chargeability due to a large amount of external additive and a charging roller having a three-dimensional concavo-convex shape on the surface are combined. Thereby, the electrical responsiveness is improved, toner contamination on the charging roller in the cleanerless system is suppressed, and good charge stability is obtained.

[0147] To improve the electrical responsiveness, it is required to ensure the charge amount as toner and to have a low electrical resistance. As a countermeasure for the external additive for this purpose, for example, increasing the chargeability by making the surface treatment of silica a silicone oil type can be mentioned. In addition, it can be mentioned that including titania in the external additive lowers the charge amount and reduces the electrical resistance. Examples of the external additive for which such an effect can be expected include the following external additives.

[0148] The type of inorganic fine particles used in the present invention is not particularly limited, and examples thereof include silica, alumina, titania, barium titanate, magnesium titanate, calcium titanate, strontium titanate, iron oxide, copper oxide, zinc oxide, tin oxide, silica sand, clay, mica, wollastonite, diatomaceous earth, chromium oxide, cerium oxide, red iron oxide, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride, and the like. Among them, from the viewpoint of improving stress resistance, at least one selected from silica (including hydrophobic silica), alumina, and titania is preferable.

[0149] The inorganic fine particles can also be subjected to a hydrophobization treatment. The hydrophobization treatment can be obtained, for example, by treating hydrophilic fine particles with a silane coupling agent such as methyltrimethoxysilane, methyltriethoxysilane, octyltrimethoxysilane. Also, the inorganic fine particles can be heat-treated with silicone oil to perform a hydrophobization treatment.

[0150] Examples of the silicone oil include dimethyl silicone oil, methylphenyl silicone oil, chlorophenyl silicone oil, methylhydrogen silicone oil, alkyl-modified silicone oil, fluorine-modified silicone oil, polyether-modified silicone oil, alcohol-modified silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, epoxy-polyether-modified silicone oil, phenol-modified silicone oil, carboxyl-modified silicone oil, mercapto-modified silicone oil, methacryl-modified silicone oil, α-methylstyrene-modified silicone oil, and the like.

[0151] Commercially available inorganic fine particles can be used. Examples of silica include R972, R974, RX200, RY200, R202, R805, R812 (all manufactured by Nippon Aerosil Co., Ltd.). Examples of titania include P-25 (manufactured by Nippon Aerosil Co., Ltd.), STT-30, STT-65C-S (all manufactured by Titanium Industry Co., Ltd.), TAF-140 (manufactured by Fuji Titanium Industry Co., Ltd.), MT-150W, MT-500B, MT-600B, MT-150A (all manufactured by Teika Co., Ltd.). Examples of hydrophobized titania fine particles include T-805 (manufactured by Nippon Aerosil Co., Ltd.), STT-30A, STT-65S-S (all manufactured by Titanium Industry Co., Ltd.), TAF-500T, TAF-1500T (all manufactured by Fuji Titanium Industry Co., Ltd.), MT-100S, MT-100T (all manufactured by Teika Co., Ltd.), IT-S (manufactured by Ishihara Sangyo Co., Ltd.).

[0152] From the viewpoint of improving stress resistance, the specific surface area of the inorganic fine particles by the BET method is preferably 20 m 2 / g to 500 m 2 / g, and more preferably 30 m 2 / g to 400 m 2 / g.

[0153] In addition to the inorganic fine particles, other external additives such as fatty acid metal salts (e.g., zinc stearate, aluminum stearate, etc.) and fluoropolymers can also be used in combination.

[0154] Also, the volume average particle diameter of the external additive is preferably 5 nm or more and 50 nm or less.

[0155] <Toner mother particles> The toner mother particles in the present invention contain, for example, a binder resin, a colorant, a charge control agent, a release agent, and the like. Known materials can be used for the toner mother particles.

[0156] [Binder resin] Examples of the binder resin include polymers of styrene and its substituents such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene; styrene-based copolymers such as styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-methyl α-chloromethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, and styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, epoxy resin, epoxy polyol resin, polyurethane, polyamide, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc. These can be used alone or in combination.

[0157] [Colorant] As the coloring agent, all known dyes and pigments can be used. For example, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, loess, lead yellow, titanium yellow, polyazo yellow, oil yellow, Hansa yellow (GR, A, RN, R), pigment yellow L, benzidine yellow (G, GR), permanent yellow (NCG), Balkan fast yellow (5G, R), tartrazine lake, quinoline yellow lake, anthrazane yellow BGL, isoindolinone yellow, red lead, minium, vermilion, cadmium red, cadmium mercury red, antimony vermilion, permanent red 4R, para red, phthalein red, para chloro ortho nitroaniline red, resorcin fast scarlet G, brilliant fast scarlet, brilliant carmine BS, permanent red (F2R, F4R, FRL, FRLL, F4RH), fast scarlet VD, Balkan fast rubine B, brilliant scarlet G, resorcin rubine GX, permanent red F5R, brilliant carmine 6B, pigment scarlet 3B, Bordeaux 5B, toluidine maroon, permanent Bordeaux F2K, heliobordeaux BL, Bordeaux 10B, bon maroon light, bon maroon medium, eosin lake, rhodamine lake B, rhodamine lake Y, alizarin lake, thioindigo red B, thioindigo maroon, oil red, quinacridone red, pyrazolone red, polyazo red, chrome vermilion, benzidine orange, perinone orange, oil orange, cobalt blue, cerulean blue, alkaline blue lake, peacock blue lake, victoria blue lake, metal-free phthalocyanine blue, phthalocyanine blue, fast sky blue, indanthrene blue (RS, BC), indigo, ultramarine, dark blue, anthraquinone blue, fast violet B, methyl violet lake, cobalt violet, manganese violet, dioxane violet, anthraquinone violet, chrome green, zinc green, chromium oxide, pyridine, emerald green, pigment green B, naphthol green B, green gold, acid green lake, malachite green lakePhthalocyanine green, anthraquinone green, titanium oxide, zinc white, lithopone, and mixtures thereof can be used. The amount used is generally 0.1 to 50 parts by mass with respect to 100 parts by mass of the binder resin.,

[0158] [Charge control agent] Known ones can also be used as the charge control agent. For example, nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxyamines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides, simple substances or compounds of phosphorus, simple substances or compounds of tungsten, fluorine-based activators, metal salts of salicylic acid, and metal salts of salicylic acid derivatives can be mentioned.

[0159] The amount of the charge control agent used in the present invention is determined by the type of the binder resin, the presence or absence of additives used as necessary, and the toner production method including the dispersion method, and is not uniformly determined. Preferably, it is used in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin, and preferably in the range of 2 to 5 parts by mass. Further, if necessary, a plurality of charge control agents may be used in combination.

[0160] [Release agent] In the present invention, a release agent may be used to impart releasability to the toner. The softening point of the release agent used is preferably 70 to 100°C.

[0161] Examples of the release agent include synthetic waxes such as low molecular weight polyethylene and polypropylene and their copolymers, vegetable waxes such as candelilla wax, carnauba wax, rice wax, wood wax, and jojoba wax, animal waxes such as beeswax, lanolin, and spermaceti wax, mineral waxes such as montan wax and ozokerite, and oil waxes such as hydrogenated castor oil, hydroxystearic acid, fatty acid amide, and phenol fatty acid ester.

[0162] From the perspective of chemical structure, hydrocarbon waxes, ester waxes, amide waxes, etc. are known, but ester waxes are suitable when evaluated in terms of storage stability, image quality, fixing temperature range, etc.

[0163] The amount of the release agent is preferably 1 to 6 parts by mass based on the total toner.

[0164] The method for manufacturing the toner in the present invention may be a conventionally known method, and examples include a manufacturing method that goes through the steps of mixing, kneading, roll cooling, pulverizing, and classifying toner raw materials. For example, after mixing the raw materials, they are kneaded with a twin-screw kneader, cooled with a belt cooler, pulverized with a jet mill, and classified to obtain the toner.

[0165] The weight average particle diameter of the toner is preferably 4 μm to 10 μm, and more preferably 5 μm to 8 μm.

[0166] Aspects of the present invention are as follows, for example. <1> An image carrier, A charging member disposed in contact with the image carrier to charge the image carrier, A latent image forming means for forming a latent image on the surface of the image carrier, Developing means for applying toner to the image carrier and developing the latent image formed on the surface of the image carrier to form a toner image, Transfer means for transferring the toner image to a transfer body, and having An image forming apparatus that recovers transfer residual toner remaining on the image carrier after the transfer with the developing means, The toner contains an external additive containing inorganic fine particles, The external additive is contained in the toner in an amount of 1.8% by mass or more, The charging member is in terms of the surface roughness Sk [μm] and Spk [μm] defined in JIS B0671-2:2002 (ISO 25178-2:2012), 2 ≤ Sk + Spk ≤ 16 Satisfying An image forming apparatus characterized by this. <2> The toner contains toner base particles containing a binder resin and the external additive. In the particle size distribution of the primary particles of the inorganic fine particles, there are a plurality of peaks between 5 nm and 50 nm. Among these peaks, the highest peak is peak n1, the second highest peak is peak n2, the particle size (nm) at the apex of peak n1 is n1d, the particle size (nm) at the apex of peak n2 is n2d, the height at the apex of peak n1 is n1h, and the height at the apex of peak n2 is n2h. When n1d > n2d (1) 10 < (n1d + n2d) (2) 30 ≦ {(n2h / n1h) × 100} < 100 (3) is satisfied The image forming apparatus according to <1>, characterized in that. <3> The charging member 5 ≦ Sk + Spk ≦ 12 is satisfied The image forming apparatus according to <1> or <2>, characterized in that. <4> When the weight average particle size of the toner is D [μm], D ≦ Sk + Spk ≦ 3D is satisfied The image forming apparatus according to any one of <1> to <3>, characterized in that. <5> The charging member is a contact charging rubber roller, and the resistance is 1 × 10 4 Ω or more and 1 × 10 7 Ω or less The image forming apparatus according to any one of <1> to <4>, characterized in that. <6> It has a recovery means for recovering the toner on the charging member in contact with the charging member. The image forming apparatus according to any one of <1> to <5>, characterized in that.

Explanation of reference numerals

[0167] 10 Electrostatic latent image carrier (photoconductor drum) 28 Fixing device 61 Developing device 62 Transfer roller 64 Charge removal lamp 72 Developing roller 73 Stirring roller 105 Recording paper 121 Exposure device 160 Charging roller 161 Recovery brush

Prior art documents

Patent documents

[0168]

Patent Document 1

Patent Document 2

Claims

1. An image carrier, a charging member disposed in contact with the image carrier to charge the image carrier, a latent image forming means for forming a latent image on the surface of the image carrier, a developing means for applying toner to the image carrier and developing the latent image formed on the surface of the image carrier to form a toner image, a transfer means for transferring the toner image to a transfer material, and having, an image forming apparatus for recovering the residual transfer toner remaining on the image carrier after the transfer by the developing means, wherein the toner contains an external additive containing inorganic fine particles, the external additive is contained in the toner in an amount of 1.8% by mass or more, the charging member is in terms of the surface roughness Sk [μm] and Spk [μm] defined in JIS B0671-2:2002 (ISO 25178-2:2012), 2 ≤ Sk + Spk ≤ 16 is satisfied, an image forming apparatus characterized by this.

2. the toner contains toner base particles containing a binder resin and the external additive, in the particle size distribution of the primary particles of the inorganic fine particles, there are a plurality of peaks between 5 nm and 50 nm, and among the peaks, the highest peak is peak n1, the second highest peak is peak n2, the particle size (nm) at the apex of peak n1 is n1d, the particle size (nm) at the apex of peak n2 is n2d, the height at the apex of peak n1 is n1h, and the height at the apex of peak n2 is n2h, then n1d > n2d (1) 10 < (n1d + n2d) (2) 30 ≤ {(n2h / n1h) × 100} < 100 (3) is satisfied, the image forming apparatus according to claim 1, characterized by this.

3. the charging member, 5 ≤ Sk + Spk ≤ 12 is satisfied, the image forming apparatus according to claim 1, characterized by this.

4. when the weight average particle diameter of the toner is D [μm], D ≤ Sk + Spk ≤ 3D is satisfied, the image forming apparatus according to claim 1, characterized by this.

5. The charging member is a contact-type charging rubber roller, and has a resistance of 1×10 ４ Ω or more and 1×10 ７ Ω or less. the image forming apparatus according to claim 1, characterized by this.

6. having a recovery means for contacting the charging member and recovering the toner on the charging member, the image forming apparatus according to claim 1, characterized by this.

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