Image forming apparatus

Abstract

To provide an image formation device which can reduce an influence of paper powder and a transfer residual toner without increasing manufacturing cost, can suppress an abnormal image such as lateral black stripes, and has high temporal durability.SOLUTION: An image formation device has: an image carrier 10; a charging member 20 which is arranged so as to be brought into contact with the image carrier and charges the image carrier; development means 200 which supplies a toner to the image carrier, and forms a toner image on the image carrier; and transfer means 62 for transferring the toner image on the image carrier onto a recording medium or an intermediate transfer body. The development means recovers a transfer residual toner remaining on the image carrier after the transfer. Surface roughness Rz of the charging member is 5 μm or more and 16 μm or less and an electric resistance value of the charging member is 0.1 MΩ or more and 1.6 MΩ or less, or surface roughness Rz of the charging member is 5 μm or more and 18 μm or less and an electric resistance value of the charging member is 0.1 MΩ or more and 1.4 MΩ or less.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD

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

[0002] Conventionally, there has been known an image forming apparatus that adopts a method of charging an image bearing member by bringing a charging member such as a charging roller applied with a voltage into contact with the surface of a photoconductor (the image bearing member).

[0003] In such image forming apparatuses, there are technologies for cleaning toner adhered to the surfaces of the photoconductor and the charging roller. In the conventional art, it is known to clean toner adhered on a photoconductor by means of a cleaning unit such as a cleaning blade, for example. In recent years, from the perspective of downsizing the apparatus, a so-called cleaner-less system, which is not provided with a dedicated cleaning unit for cleaning the photoconductor, has been proposed.

[0004] In a cleaner-less image forming apparatus, when printing is continuously performed on paper containing a large amount of paper dust, not only residual toner after transfer but also a large amount of paper dust adheres to the charging member. When a large amount of paper dust adheres to the charging member, the electric resistance of the paper dust prevents uniform charging from the charging member to the photoconductor, resulting in abnormal images such as horizontal black streaks. To avoid such abnormal images, for example, the following Patent Documents 1 and 2 have been proposed.

[0005] Patent Document 1 discloses that in an image forming apparatus using a cleaner-less system in which a developer remaining on the surface of an image bearing member is collected by the developing device, the surface treatment of the contact charging member portion corresponding to the non-image forming area within the contact area between the contact charging member and the image bearing member is different from the surface treatment of the contact charging member portion corresponding to the image forming area. Patent Document 1 also discloses that the ten-point average roughness Rz of the surface of the contact charging member portion differs between the non-image forming area and the image forming area, and the Rz of the non-image forming area is 3 µm or more and 12 µm or less.

[0006] Patent Document 2 discloses a paper dust removal means for removing paper dust by contacting the surface of an image carrier, a bias application means for applying a bias to the paper dust removal means to form a potential difference between the paper dust removal means and the image carrier, and a control means for controlling the bias application means to change the potential difference according to the amount of image formation. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in image forming apparatuses using a cleanerless system, if the roughness Rz of the charged member differs between the non-image forming area and the image forming area, as in Patent Document 1, the manufacturing process increases, thus increasing manufacturing costs. Also, if paper dust removal means, bias application means, and control means are provided, as in Patent Document 2, the number of parts increases, thus increasing manufacturing costs. Furthermore, if the system continues to operate with a large amount of paper dust adhering to the charged component, the electrical resistance of the charged roller will fluctuate locally depending on the amount of paper dust adhering to its surface. This prevents uniform charging of the entire charged component. To avoid this, providing a paper dust removal mechanism as described above would increase manufacturing costs. Furthermore, in the case of a cleanerless image forming apparatus, it is necessary to maintain good charging of the charging roller over time, and to achieve this, it is necessary to minimize the effects of paper dust and residual toner. If the effects of paper dust and residual toner become significant, for example, the lifespan of the process unit in a cleanerless system will be shortened and its durability over time will be reduced.

[0008] Therefore, the present invention aims to provide an image forming apparatus that can reduce the effects of paper dust and transfer residue toner without increasing manufacturing costs, suppress abnormal images such as horizontal black streaks, and have high durability over time. [Means for solving the problem]

[0009] To solve the above problems, the image forming apparatus of the present invention comprises an image carrier, a charging member positioned in contact with the image carrier and charging the image carrier, developing means for supplying toner to the image carrier and forming a toner image on the image carrier, and transfer means for transferring the toner image on the image carrier to a recording medium or an intermediate transfer body. A collection means for collecting toner from the charged member, The developing means has a surface roughness Rz of 5 μm or more and 16 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.6 MΩ or less, or the surface roughness Rz of the charging member is 5 μm or more and 18 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.4 MΩ or less. The toner comprises a matrix particle and an external additive, the external additive being present in the toner at a concentration of 1.8% by mass or less, and during printing, the residual toner on the image carrier is moved to the charging member, the residual toner on the charging member is moved to the recovery means for collection, and when the device is shut down, the recovery means moves the collected residual toner to the charging member, the residual toner on the charging member is moved to the image carrier, and the residual toner on the image carrier is moved to the developing means for collection. It is characterized by the following: [Effects of the Invention]

[0010] According to the present invention, it is possible to reduce the effects of paper dust and residual toner without increasing manufacturing costs, suppress abnormal images such as horizontal black streaks, and provide an image forming apparatus with high durability over time. [Brief explanation of the drawing]

[0011] [Figure 1] This figure illustrates one embodiment of the image forming apparatus of the present invention. [Figure 2] This figure illustrates another embodiment of the image forming apparatus of the present invention. [Figure 3A] This figure illustrates another embodiment of the image forming apparatus of the present invention. [Figure 3B] This figure illustrates another embodiment of the image forming apparatus of the present invention. [Figure 4] This figure shows an example of an abnormal image occurring in the relationship between the surface roughness Rz of a charged roller and its electrical resistance. [Figure 5] This is a diagram illustrating one embodiment of a process cartridge. [Modes for carrying out the invention]

[0012] The image forming apparatus according to the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to the embodiments shown below, and can be modified, added, altered, or deleted to the extent that a person skilled in the art can conceive of it. Any embodiment that achieves the function and effects of the present invention is included within the scope of the present invention.

[0013] The image forming apparatus of this embodiment comprises an image carrier, a charging member positioned in contact with the image carrier and charging the image carrier, a developing means for supplying toner to the image carrier and forming a toner image on the image carrier, and a transfer means for transferring the toner image on the image carrier to a recording medium or an intermediate transfer body, wherein the developing means recovers the transfer residue toner remaining on the image carrier after the transfer, and the charging member is characterized in that the surface roughness Rz of the charging member is 5 μm or more and 16 μm or less and the electrical resistance of the charging member is 0.1 MΩ or more and 1.6 MΩ or less, or the surface roughness Rz of the charging member is 5 μm or more and 18 μm or less and the electrical resistance of the charging member is 0.1 MΩ or more and 1.4 MΩ or less.

[0014] In this embodiment of the image forming apparatus, residual toner remaining on the image carrier is recovered by a developing means. This embodiment of the image forming apparatus does not use a cleaning means (e.g., a cleaning blade) to clean the image carrier (also referred to as an electrostatic latent image carrier, photoreceptor, etc.). In this case, there are advantages such as miniaturization of the apparatus.

[0015] Hereinafter, a method that does not use a cleaning means to clean the image carrier will be referred to as a cleanerless method, cleanerless configuration, etc. Furthermore, a charging roller can be used as the charging member, and the following explanation uses a charging roller as an example.

[0016] Figure 1 is a diagram showing an example of an image forming apparatus according to this embodiment, and illustrates an example of the image forming process in a cleanerless image forming apparatus.

[0017] First, the charging roller 20 uniformly charges the photosensitive drum 10 serving as an image carrier. The charging roller 20 of this example is arranged so as to be in contact with the photosensitive drum 10, and applies a DC voltage to the photosensitive drum 10, for example. The charging in this example adopts a contact DC charging method.

[0018] The exposure device 21 exposes the photosensitive drum 10 to exposure light L and forms an electrostatic latent image on the photosensitive drum 10. There is no particular limitation on the exposure device 21, and an LED is used, for example.

[0019] The developing roller 72 is an example of a developer carrier provided in the developing device 61. A developing bias is applied to the developing roller 72 by an applying means, and the developing roller 72 supplies toner 200 to the photosensitive drum 10. As a result, a toner image (also referred to as a visible image) is formed on the photosensitive drum 10.

[0020] The developing device 61 includes, for example, a stirring roller 73, which may stir the toner in the developing device 61. The rotation direction of the stirring roller 73 can be appropriately selected, and the stirring roller 73 may be in contact with the developing roller 72 or may be non-contact therewith.

[0021] The transfer roller 62 transfers the toner image on the photosensitive drum 10 onto the recording paper 105. The static eliminating lamp 64 eliminates the potential on the photosensitive drum 10. For example, it emits static eliminating light QL to perform static elimination.

[0022] The above configuration is the basic configuration of a cleaner-less image forming apparatus. Such an apparatus does not include a cleaning means such as a cleaning blade for cleaning the photosensitive drum 10 after the transfer process.

[0023] Although there is no particular limitation, in the example shown in FIG. 1, for example, -300 V is applied to the developing roller 72, and -1200 V is applied to the charging roller 20. For example, after static elimination, the surface potential of the photosensitive drum 10 becomes about -50 V, and after charging, the surface potential becomes about -500 V.

[0024] In this embodiment, the image forming apparatus is preferably equipped with a cleaning brush 161 (brush member) for scraping off dirt from the charging roller 160. In this case, the stability of image quality over time is improved.

[0025] Here, we will explain an example of toner flow in the example shown in Figure 1. For illustrative purposes, the toner symbols in the figure are changed depending on the position and state of the toner. The developing roller 72 carries toner 200, and the toner 200 carried on the developing roller 72 is supplied to the photoreceptor drum 10. The toner supplied to the photoreceptor drum 10 forms a toner image (visible image) (toner 201) according to the electrostatic latent image. The toner 201 on the photoreceptor 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.

[0026] Toner that is not transferred during the transfer process remains on the photoreceptor drum 10 as transfer residue toner 203. After the static discharge process, the transfer residue toner 203 adheres to the charging roller 20 at the point of contact (or nearby) between the photoreceptor drum 10 and the charging roller 20. Of the transfer residue toner 203, there is also toner 206 that does not adhere to the charging roller 20, and this toner 206 remains on the photoreceptor drum 10. This toner 206 is recovered by the developing roller 72, as described later.

[0027] Next, an example of a method for recovering residual toner in a cleanerless image forming apparatus will be explained using Figures 2, 3A, and 3B.

[0028] Figure 2 is a schematic diagram illustrating the state after Figure 1, and schematically shows the state during printing. In this context, "during printing" means the state in which the device is running, and includes not only the process of transferring toner to the recording paper, but also the process of preparing the recording paper for toner transfer. Figure 3 is a diagram illustrating the process performed between the transfer to the previous recording paper and the transfer to the next recording paper.

[0029] As explained in Figure 1, toner that is not transferred during the transfer process remains on the photoreceptor drum 10 as transfer residue toner 203. In Figure 2, the transfer residue toner 203 remains on the photoreceptor drum 10 downstream of the transfer roller 62.

[0030] After transferring the image to the previous recording paper 105, the surface of the photoreceptor drum 10 is destaticized by the destaticizing lamp 64. This widens the potential difference between the charging roller 20 and the photoreceptor drum 10, causing a discharge to occur between the charging roller 20 and the photoreceptor drum 10 before charging. The discharge is schematically illustrated in the figure.

[0031] Due to the discharge before charging, the transfer residue toner 203 becomes negatively charged (not shown in Figure 2). In the transfer residue toner 203, due to the discharge before charging, some remains negatively charged, while others remain slightly positively charged. The transfer residue toner 203 that remains slightly positively charged adheres to the charging roller 20 at the point (or nearby) where the charging roller 20 and the photoreceptor drum 10 come into contact. The toner adhering to the charging roller 20 is shown as toner 204.

[0032] The arrow a in the figure schematically illustrates the adhesion of the residual toner 203 on the photoreceptor drum 10 to the charging roller 20. The adhesion of the residual toner 203 on the photoreceptor drum 10 to the charging roller 20 may also be described as movement.

[0033] The image forming apparatus in this example has a cleaning brush 161 for collecting toner adhering to the charging roller 20. The positive toner 204 adhering to the charging roller 20 is collected by the cleaning brush 161. Arrow b in the figure schematically illustrates the collection of toner 204 on the charging roller 20 by the cleaning brush 161. The collection of toner 204 on the charging roller 20 by the cleaning brush 161 may also be referred to as movement.

[0034] A recovery bias is applied to the cleaning brush 161. The value of the recovery bias is not particularly limited and can be selected as appropriate.

[0035] Of the transfer residue toner 203 on the photoconductor drum 10, the negatively charged toner does not adhere to the charging roller 20 and remains on the photoconductor drum 10. This toner is shown as toner 206. Both toner 203 and toner 206 are transfer residue toners.

[0036] 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 shown as toner 208. The recovery by the developing roller 72 may also be referred to as movement. The toner 206 passing between the photoreceptor drum 10 and the developing roller 72 moves towards 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 the recovery of toner 206 on the photoreceptor drum 10 by the developing roller 72.

[0037] As described above, there are no particular limitations on how the developing roller 72 can recover the material, but one method is to adjust the potential of each component. For example, the surface of the photoreceptor drum 10 after static discharge may be set to -50V, the charging roller 20 to -1100V, the cleaning brush 161 to -1300V, the surface of the photoreceptor drum 10 after charging to -500V, and the developing roller 72 to -300V. Figure 2 illustrates the potentials as in this example, but it is not limited to this.

[0038] Next, using Figures 3A and 3B, we will explain the movement of toner during device shutdown and an example of toner recovery.

[0039] As explained in Figure 2, the positively charged residual toner 203 (and similarly toner 206) that did not become negative during the discharge before charging adheres to the charging roller 20 and is collected by the cleaning brush 161. During printing, this collection is repeated, so positively charged toner 207 accumulates on the cleaning brush 161.

[0040] During shutdown, the potential difference between the cleaning brush 161 and the charging roller 20 is adjusted to move the slightly positively charged toner 207 towards the charging roller 20. This is indicated by arrow d in the figure.

[0041] The toner 205 that has moved to the charging roller 20 moves to the photoreceptor drum 10 due to the potential difference between the charging roller 20 and the photoreceptor drum 10. This is indicated by arrow e in the figure. This moved toner is shown as toner 209 in the figure. Note that when the device is shut down, the photoreceptor drum 10 is not discharged by the discharge lamp 64, so the potential difference between the charging roller 20 and the photoreceptor drum 10 is adjusted to take this into consideration.

[0042] The positively charged toner 209 on the photoreceptor drum 10 is not collected by the developing roller 72, but passes directly through the developing roller 72. Furthermore, the toner 209 passes through the transfer roller 62. Thus, when the device is shut down, positively charged toner 209 remains on the photoreceptor drum 10.

[0043] In Figures 2, 3A, and 3B, toners 203, 206, and 209 are shown on the photoconductor drum 10. These are all considered as transfer residue toner. Toner 209 is formed when transfer residue toner 203 is collected by the cleaning brush 161 and then moved back onto the photoconductor drum 10; however, such toner may also be included as transfer residue toner.

[0044] As shown in the example in Figure 3A, there are no particular limitations on how the toner moves, but one method is to adjust the potential of each component. For example, the potential of the cleaning brush 161 could be set to -150V, the potential of the charging roller 20 to -350V, the potential of the surface of the photoreceptor drum 10 to 500V, and the potential of the developing roller 72 to +250V. Figure 3A illustrates the potentials in this example, but it is not limited to this.

[0045] Next, we will explain, using Figure 3B, how toner is collected on the photoreceptor drum 10 during the shutdown of the device. Figure 3B is a continuation of Figure 3A.

[0046] As shown in the figure, the photoreceptor drum 10 is discharged by the static discharge lamp 64 at a predetermined timing. By performing static discharge, the potential difference between the charging roller 20 and the photoreceptor drum 10 widens, and a discharge occurs between the charging roller 20 and the photoreceptor drum 10. The discharge is schematically illustrated in the figure. Note that the static discharge shown is not static discharge performed for image formation, but static discharge performed for toner recovery.

[0047] As a result of the discharge described above, the toner 209 becomes negatively charged. As in Figure 2, any toner 209 that remains positively charged and does not become negatively charged adheres to the charging roller 20 and is collected by the cleaning brush 161 (arrows g and h in the figure).

[0048] The toner 209, which has become negatively charged due to the discharge described above, remains on the photoreceptor drum 10 without moving to the charging roller 20. The negatively charged toner 209 is then collected by the developing roller 72 to which a developing bias is applied (arrow i in the figure). The toner collected by the developing roller 72 is shown as toner 208 in the figure.

[0049] As shown in the example in Figure 3B, there are no particular restrictions on how the toner moves, but one method is to adjust the potential of each component. For example, the potential of the cleaning brush 161 could be set to -1300V, the potential of the charging roller 20 to -1100V, the surface of the photoreceptor drum 10 after static discharge to -50V, the potential of the surface of the photoreceptor drum 10 to 500V, and the potential of the developing roller 72 to -300V. Figure 3B illustrates the potentials in this example, but it is not limited to this.

[0050] In this embodiment of the image forming apparatus, the cleanerless method described above can be employed. The cleanerless method described above controls the charging characteristics of the toner and moves and recovers the toner using an electric field in each process. This removes the transfer residue toner on the photoreceptor drum 10.

[0051] By using a cleanerless image forming apparatus as described above, there is no need to have a cleaning blade to clean the photoreceptor, which offers advantages such as miniaturization of the apparatus and omission of parts. However, in a cleanerless image forming apparatus, as printing continues, paper dust adheres to the charging roller, and if a large amount of paper dust adheres, the electrical resistance of the paper dust causes uneven charging from the charging roller to the photoreceptor drum 10. This results in abnormal images such as horizontal black streaks. In response to this, conventional technology has proposed providing a paper dust removal brush or different surface treatments for the image forming area and non-image forming area of ​​the charged component. However, this has the problem of increasing manufacturing costs. In addition, if a large amount of paper dust adheres to the charging roller, the charging performance of the charging roller locally deteriorates, shortening the lifespan of the cleanerless unit, but if conventional technology is used to address this, manufacturing costs increase.

[0052] Therefore, the inventors conducted diligent research and found that by defining the characteristic values ​​of the charged material, particularly the electrical resistance and surface roughness Rz in combination, it is possible to reduce the effects of paper dust and transfer residue toner at a lower cost without adding new materials or creating different surface treatments for the charged material, thereby avoiding horizontal black streaks.

[0053] Furthermore, according to this embodiment, durability over time can be increased without increasing manufacturing costs. According to this embodiment, the effects of paper dust and transfer residue toner can be reduced, and the charged component can maintain a state in which it can be charged properly over time. For this reason, even when a cleanerless system is used, the lifespan of the process unit including the charged component can be extended.

[0054] The process unit includes an image carrier, a charging member, a developing means, etc., and may also be called an image forming unit. An example of a process unit is the process cartridge described later.

[0055] In this embodiment, the surface roughness Rz of the charging member is 5 μm or more and 16 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.6 MΩ or less, or the surface roughness Rz of the charging member is 5 μm or more and 18 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.4 MΩ or less. Detailed examples are described below.

[0056] <Evaluation (1): Tests when both surface roughness Rz and electrical resistance are changed> Tests were conducted using an image forming apparatus with the configuration shown in Figure 1, where both the surface roughness Rz and electrical resistance of the charging roller were varied. In evaluation (1), the apparatus with varying surface roughness Rz and electrical resistance of the charging roller was used, and after performing the durability process as described below, an image was formed and the occurrence of horizontal black streaks was evaluated. In evaluation (1), paper with a high amount of paper dust (e.g., HighWhite) was used as the recording medium. Furthermore, the image forming apparatus used in evaluation (1) was equipped with a cleanerless process cartridge and used a charged rubber roller as the charging roller.

[0057] The durability process is an acceleration condition designed to generate horizontal black streaks caused by paper dust when a large amount of paper dust adheres to the charged roller, and it consists of two steps. The first step is the paper feeding durability process, and the second step is the humidity control process. After the durability process, an image is formed and evaluated to confirm the durability against horizontal black streaks in the cleanerless system.

[0058] In the first step of the durability process (paper threading durability process), 8,000 sheets of paper are threaded through the device at a temperature of 27°C and 80% humidity to allow a large amount of paper dust and transfer toner residue to adhere to the charged components. Specifically, 1,000 sheets of paper are threaded through the device per day for a total of 8 days in an environment (temperature 27°C, humidity 80%) where paper dust and transfer toner residue are likely to adhere to the charged components. In the second step of the durability process (humidity control process), after the first step, humidity control was performed in a low-temperature, low-humidity environment (temperature 10°C, humidity 15%) where the electrical resistance of the charging roller was highest. Specifically, the device was left in this low-temperature, low-humidity environment for more than 8 hours.

[0059] After humidity control, images (blank paper, halftone images) were printed in a low-temperature, low-humidity environment, and the printable images were visually inspected to see if horizontal black streaks appeared at the intervals between the electrostatic rollers.

[0060] The results are shown in Figure 4(A). In Figure 4(A), the horizontal axis represents electrical resistance (MΩ), and the vertical axis represents surface roughness Rz (μm). The dashed lines in the figure indicate the points where the electrical resistance is 0.1 MΩ and the surface roughness Rz is 5 μm. The evaluation criteria are as follows: ● indicates a pass. [Evaluation Criteria] ●: No horizontal black streaks have appeared. ▲: Halftones are visible (horizontal black streaks are not present in the white areas (non-image-forming areas)). ×: Horizontal black streaks appear in both halftone and white areas.

[0061] In evaluation (1), if horizontal black streaks are visible in the blank areas or halftone images (▲, ×) under the accelerated conditions of the durability process, it means that the cleanerless process cartridge has not achieved a long lifespan. As in this embodiment, by using a charging roller configuration with a surface roughness Rz and electrical resistance MΩ as shown by ●, the lifespan of the cleanerless process cartridge can be extended, and its durability over time can be increased.

[0062] In evaluation (1), the surface roughness Rz and electrical resistance of the charged roller were measured as follows. The surface roughness Rz (μm) of the electrostatic roller was measured using a stylus-type surface roughness meter under the following conditions. Measurement method: Rz according to the old JIS B0601-1982 Measurement conditions: Axial measurement length: 2.5 mm, Feed rate: 0.1 mm / sec, Cutoff value: 0.8λc, Filter type: 2CR, Resolution: L / 8000 (L: Evaluated length)

[0063] The electrical resistance (MΩ) of the charged roller was measured using an electrical resistance measuring device under the following conditions. This measurement method allows for the determination of the electrical resistance of the entire charged roller, including the shaft. Measurement environment: 23±3℃, 55±10% (temperature and humidity control time was set to 4 hours or more) Applicable voltage: DC-500V Rotation speed: 29 r / m Measurement points: 185 locations (circumferential direction) Measurement time: 6sec Resistance measurement: Average value of measurement points when the jig load is 4.9N (500g) at both ends.

[0064] As shown in Figure 4(A), the ●▲× pattern occurs in the region where the surface roughness Rz is 18 μm and the electrical resistance is around 1.6 MΩ. Therefore, it can be seen that there is a threshold in this region.

[0065] Figure 4(B) is a diagram illustrating the passing region in Figure 4(A). In the figure, rectangular region a is the region where the surface roughness Rz of the charging roller is 5 μm or more and 16 μm or less, and the electrical resistance of the charging roller is 0.1 MΩ or more and 1.6 MΩ or less. Rectangular region b is the region where the surface roughness Rz of the charging roller is 5 μm or more and 18 μm or less, and the electrical resistance of the charging roller is 0.1 MΩ or more and 1.4 MΩ or less.

[0066] From the results in Figure 4(A), black horizontal streaks can be avoided if the surface roughness Rz of the charging roller is 5 μm or more and 16 μm or less, and the electrical resistance of the charging roller is 0.1 MΩ or more and 1.6 MΩ or less, or if the surface roughness Rz of the charging roller is 5 μm or more and 18 μm or less, and the electrical resistance of the charging roller is 0.1 MΩ or more and 1.4 MΩ or less.

[0067] The reason why horizontal black streaks appear when the electrical resistance of the charging roller is high is thought to be as follows: It is known that when the electrical resistance of a charging roller is high, when a certain voltage is applied to the charging roller, the photoreceptor cannot be properly charged, resulting in charging failure. For this reason, even if there is no problem with the electrical resistance of the charging roller itself, charging failure may occur in a cleanerless configuration. In a cleanerless configuration, paper dust adheres to the charging roller as printing is repeated, and the apparent electrical resistance of the entire charging roller increases. This increase in the apparent electrical resistance of the entire charging roller causes partial charging failure, resulting in horizontal black streaks.

[0068] The reason why horizontal black streaks occur when the surface roughness Rz of the charging roller is large is thought to be as follows: When paper dust gets into the grooves on the surface of the charging roller, the electrical resistance of the groove containing the paper dust becomes relatively higher than that of other areas, reducing the charging ability of the photoreceptor surface. When the charging ability decreases, partial charging failures occur, resulting in the appearance of horizontal black streaks. The larger the groove (Rz) of the charging roller, the greater the absolute amount of paper dust that can get into the groove, making horizontal black streaks more likely to occur. Furthermore, if the surface roughness Rz of the charging roller is large, it becomes easier to scrape off external additives and paper dust from the photoreceptor, resulting in a larger amount of external additives and paper dust adhering to the charging roller. This makes it easier for horizontal black streaks to occur.

[0069] <Evaluation (2): Test when only the electrical resistance value is changed> Next, we will describe the test when only the electrical resistance value of the charged roller is changed. Using an image forming apparatus with the same configuration as in evaluation (1), tests were conducted by changing the electrical resistance value of the charging roller. In evaluation (2), the surface roughness Rz of the charging roller was set to 18 μm for the tests. In evaluation (2), after performing the same durability process as in evaluation (1), images were formed and the presence or absence of abnormal images was evaluated. The electrical resistance value was measured in the same way as in evaluation (1).

[0070] The results are shown in Table 1. The evaluation criteria are as follows. ○ indicates a passing grade. [Evaluation Criteria] ○: No abnormalities △: Density reduction occurs, and horizontal black streaks appear in the white areas (non-image-forming areas) (localized toner staining). ×: Toner smudges (generalized charging failure, not localized) occur in the blank area (non-image forming area).

[0071] [Table 1]

[0072] As shown in Table 1, increasing the electrical resistance of the charging roller resulted in uneven charging of the photoreceptor, leading to charging defects, reduced density, and toner smudging. Conversely, if the electrical resistance of the charging roller was too low, the resistance was too low for the applied voltage, resulting in a large current flow and leakage.

[0073] In a cleanerless configuration, residual toner passes through the charging roller, making it easy for external additives and paper dust added to the toner to adhere to the charging roller. The adhesion of external additives and paper dust to the charging roller increases its electrical resistance, making charging failures more likely. The amount of paper dust adhering to the charging roller is related to the appearance of horizontal black streaks; a large amount of paper dust makes horizontal black streaks more likely. On the other hand, specifying only the electrical resistance value makes it difficult to predict how much paper dust will adhere to the charging roller during the durability period of repeated printing. Since it is difficult to guarantee quality with only the electrical resistance value, specifying both the surface roughness Rz of the charging roller and the electrical resistance value can ensure quality.

[0074] <Evaluation (3): Test when only the surface roughness Rz is changed> Next, we will describe the test when only the surface roughness Rz of the electrostatic roller is changed. Using an image forming apparatus with the same configuration as in evaluation (1), tests were conducted by changing the electrical resistance value of the charging roller. In evaluation (3), the electrical resistance value of the charging roller was set to 1.4 MΩ. In evaluation (3), after performing the same durability process as in evaluation (1), an image was formed and the presence or absence of abnormal images was evaluated. The surface roughness Rz was measured in the same way as in evaluation (1).

[0075] The results are shown in Table 2. The evaluation criteria are as follows. ○ indicates a passing grade. [Evaluation Criteria] ○: No abnormalities △: Concentration decrease ×: Toner smudges (generalized charging failure, not localized) occur in the blank area (non-image forming area).

[0076] [Table 2]

[0077] As shown in Table 2, abnormal images occurred when the surface roughness Rz of the charging roller was large. As the surface roughness Rz of the charging roller increases, the unevenness increases, creating gaps at the contact surface between the photoreceptor and the charging roller, resulting in uneven contact. Therefore, proper charging cannot occur, and abnormal images are produced.

[0078] Furthermore, reducing the surface roughness of the electrostatic roller increases the time and process required for polishing the roller's surface, thus increasing manufacturing costs. The smaller the surface roughness Rz of the electrostatic roller, the higher the manufacturing cost. As shown in Table 2, when the surface roughness Rz is 2 μm, the manufacturing cost is even higher than when it is 4 μm because it requires an increase in the number of grinding wheel types.

[0079] When paper dust adheres to a charging roller, its apparent electrical resistance increases, causing horizontal black streaks. Therefore, a small surface roughness Rz of the charging roller is desirable. However, if only surface roughness Rz is specified, while the amount of paper dust adhering to the charging roller can be easily controlled, it becomes difficult to specify how small the surface roughness Rz should be, and it becomes necessary to make it as small as possible. The acceptable level of surface roughness Rz largely depends on the electrical resistance of the charging roller, so the design ends up being one that makes the surface roughness Rz as small as possible. In order to reduce the surface roughness Rz, the time and process of polishing the surface of the charging roller increases, which increases manufacturing costs.

[0080] Furthermore, if the surface roughness Rz of the charging roller is large, in a contact charging method, the charging roller will scrape off a large amount of paper dust and external additives from the photoreceptor, making the charging roller prone to contamination. For this reason, it is necessary to provide a cleaning blade to clean the photoreceptor and prevent the charging roller from becoming contaminated, which increases the number of parts and thus increases manufacturing costs.

[0081] Considering the above, in a cleanerless configuration, by specifying both the surface roughness Rz and electrical resistance value of the charging roller, it is possible to create a device configuration that ensures quality while suppressing increases in manufacturing costs.

[0082] <Amount of external additives in toner> Next, we will describe a preferred configuration for the amount of external additives in the toner. The method for recovering residual toner after transfer, as explained in Figure 2 above, involves controlling the charge polarity of the toner and moving it using an electric field in each process for recovery. This prevents toner from contaminating the charging roller. However, it is difficult to control the charge polarity of external additives released from the toner in the same way as the toner itself. Therefore, the movement of external additives cannot be controlled during the toner recovery and discharge operations to the charging roller after transfer, and the external additives adhere to the charging roller. If printing continues for a long period of time, the adhesion of external additives to the charging roller accumulates, resulting in uneven density due to poor charging.

[0083] Therefore, in this embodiment, the toner contains matrix particles and an external additive, and it is preferable that the external additive is present in the toner at a concentration of 1.8% by mass or less. By using a toner with a small amount of external additive in a cleanerless configuration, it is possible to suppress soiling of the charging roller and reduce density unevenness due to charging failure.

[0084] <Evaluation (4): Tests when the amount of external additives in the toner is changed> Using an image forming apparatus with the same configuration as in evaluation (1), the test was conducted by changing the amount of toner additive. In evaluation (4), the same durability process as in evaluation (1) was performed, and after humidity control, an image was formed and the occurrence of abnormal images was evaluated.

[0085] The results are shown in Table 3. The evaluation criteria are as follows: [Evaluation Criteria] ○: No abnormalities △: Concentration decrease ×: Toner smudges (generalized charging failure, not localized) occur in the blank area (non-image forming area).

[0086] [Table 3]

[0087] As shown in Table 3, when the amount of external additive is 1.8% by mass or less, no abnormal images occur. When the amount of external additive is 1.8% by mass or less, the amount of external additive released from the toner can be minimized, so the amount of external additive that moves to the charging roller can also be suppressed, and contamination of the charging roller by external additive can be suppressed. On the other hand, when external additive adheres to the charging roller, the apparent electrical resistance of the charging roller increases, causing charging failure and a decrease in density. Furthermore, as the contamination of the charging roller progresses, toner is developed on the white paper, and horizontal black streaks appear.

[0088] Furthermore, when the amount of external additive is small, it is also effective in terms of adhesion of the external additive to the developing roller (filming). Although not shown in Table 3 above, when the amount of external additive was 1.8% by mass or less, developing and filming tended to improve.

[0089] Furthermore, if the amount of external additive is 1.8% by mass or less, the amount of external additive adhering to the charging roller over time can be reduced, thereby improving durability over time. This also extends the lifespan of the process cartridge even when using a cleanerless system.

[0090] The following describes an example of toner preparation used in the above evaluation. - Toner matrix particle preparation - The toner matrix particles were prepared using the following raw materials as described below. "Parts" refers to "parts by mass."

[0091] Polyester resin 87 parts Rice wax (TOWAX-3F16, manufactured by Toa Kasei Co., Ltd.) 3 parts Carbon black (#44, manufactured by Mitsubishi Chemical Corporation) 8 parts Azo iron compound (Hodogaya Chemical Co., Ltd. T-77) 2 parts

[0092] The toner raw materials of the above formulation were pre-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 Co., Ltd., PCM-30). The resulting kneaded material was rolled to a thickness of 2.7 mm using rollers, cooled to room temperature using a belt cooler, and then coarsely ground to 200 μm to 300 μm using a hammer mill. Next, it was finely ground using a supersonic jet pulverizer LabJet (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and then classified using an airflow classifier (manufactured by Nippon Pneumatic Mfg. Co., Ltd., MDS-I) while appropriately adjusting the louver opening so that the weight-average particle size was 5.8 ± 0.2 μm, to obtain toner matrix particles.

[0093] -Toner production- To 100 parts of the above-mentioned toner matrix particles, 1.00 part of inorganic fine particles 1 and 0.03 parts of inorganic fine particles 2 were added, and the mixture was stirred and mixed in a Henschel mixer to prepare a toner for evaluation. Furthermore, since 1.03 / (100+1.03)=1.03 / 101.03 ≈ 0.01019, the ratio of the external additive to the toner is 1.0% by mass.

[0094] Furthermore, the volume-average particle size of the external additive used in this embodiment is preferably between 5 nm and 50 nm. By keeping it within this range, the external additive is less likely to detach from the parent particles, thereby suppressing contamination of the electrostatic roller by the external additive.

[0095] (toner) Next, a detailed example of the toner used in the present invention will be described.

[0096] <External additives> The external additive used in the present invention preferably contains inorganic fine particles. The inorganic fine particles preferably have multiple peaks in the particle size distribution of primary particles in the range of particle size from 5 nm to 50 nm, and preferably satisfy all of the following equations (1) to (3) when the highest peak is n1, the second highest peak is n2, the particle size (nm) at the top of peak n1 is n1d, the particle size (nm) at the top of peak n2 is n2d, the height at the top of peak n1 is n1h, and the height at the top of peak n2 is n2h. n1d>n2d Equation (1) 10<(n1d+n2d) Equation (2) 30≦{(n2h / n1h)×100}<100 Equation (3)

[0097] The particle size distribution of inorganic fine particles as referred to in this invention is a particle size distribution based on the number of primary particles, and can be measured by sequentially following the steps (1) to (3) below. (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 images are binarized using the image processing software A-Image-kun (Asahi Kasei Engineering Co., Ltd.) and the equivalent circle diameter of the inorganic microparticles is calculated. The equivalent circle diameter of the inorganic microparticles is measured for 1000 particles. (3) Next, determine the number of classes according to the following formula, create a histogram, and obtain the particle size distribution. Number of classes = 1 + log2n (where n represents the number of data points for the equivalent circular diameter of inorganic particles)

[0098] As inorganic fine particles used in the present invention, the particle size (nm) n1d at the peak of peak n1 is preferably 15 nm to 50 nm, and more preferably 20 nm to 40 nm. Furthermore, the particle size (nm) n2d at the peak of peak n2 is preferably 5 nm to 50 nm, and more preferably 10 nm to 20 nm.

[0099] Furthermore, the difference between n1d and n2d is preferably 10nm to 45nm, and more preferably 13nm to 30nm.

[0100] Furthermore, from the viewpoint of improving the effects of the present invention, more preferred forms of formulas (2) and (3) are represented by the following formulas (20) and (30). 20<(n1d+n2d) Equation (20) 40<{(n2h / n1h)×100}<90 Equation (30)

[0101] In the present invention, means to ensure that the particle size distribution of the primary particles of inorganic fine particles has multiple peaks between 5 nm and 50 nm and satisfies all of the above formulas (1) to (3) include, for example, preparing two or more types of inorganic fine particles with different average particle sizes and adjusting their blending amounts to satisfy the conditions. It is preferable that the inorganic fine particles are of the same type.

[0102] The types of inorganic fine particles used in the present invention are not particularly limited, but examples 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, and silicon nitride. Among these, at least one selected from silica (including hydrophobic silica), alumina, and titania is preferred from the viewpoint of improving stress resistance.

[0103] Inorganic microparticles can also be hydrophobized. Hydrophobization can be achieved, for example, by treating hydrophilic microparticles with silane coupling agents such as methyltrimethoxysilane, methyltriethoxysilane, or octyltrimethoxysilane. Alternatively, inorganic microparticles can be hydrophobized by heat treatment with silicone oil.

[0104] Examples of the silicone oils mentioned above 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, methacrylic-modified silicone oil, and α-methylstyrene-modified silicone oil.

[0105] Commercially available inorganic nanoparticles can be used. For example, silica can be R972, R974, RX200, RY200, R202, R805, or R812 (all manufactured by Nippon Aerosil Co., Ltd.). For titania, examples 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, or MT-150A (all manufactured by Teika Co., Ltd.). Examples of hydrophobized titania microparticles 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 (both manufactured by Fuji Titanium Industry Co., Ltd.), MT-100S, MT-100T (both manufactured by Teika Co., Ltd.), and IT-S (manufactured by Ishihara Sangyo Co., Ltd.).

[0106] The specific surface area of ​​inorganic microparticles obtained by the BET method is 20 m², from the viewpoint of improving stress resistance. 2 / g~500m 2 It is preferable that it be / g, which is 30m 2 / g~400m 2 It is even more preferable that it be / g.

[0107] In addition to the inorganic fine particles mentioned above, other external additives such as fatty acid metal salts (e.g., zinc stearate, aluminum stearate, etc.) and fluoropolymers can also be used in combination.

[0108] Furthermore, as mentioned above, the content of the external additive is preferably 1.8% by mass or less in the toner. Furthermore, as mentioned above, the volume average particle size of the external additive is preferably 5 nm or more and 50 nm or less.

[0109] <Toner matrix particles> The toner matrix particles in this invention include, for example, a binder resin, a colorant, a charge control agent, a release agent, etc. Any known material can be used for the toner matrix particles.

[0110] [Binding resin] The binder resins include polymers of styrene and its substituted derivatives such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene; 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-α-chloromethacrylate copolymer, styrene-acrylonitrile copolymer, and styrene-vinylmethyl methyl methacrylate copolymer. Examples include styrene copolymers such as ketone copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers, styrene-maleic acid copolymers, and styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, epoxy resins, epoxy polyol resins, polyurethanes, polyamides, polyvinyl butyral, polyacrylic acid resins, rosin, modified rosin, terpene resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffin, and paraffin wax, which can be used individually or in combination.

[0111] [Coloring agent] All known dyes and pigments can be used as colorants, for example, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, ochre, yellow lead, titanium yellow, polyazo yellow, oil yellow, Hansa yellow (GR, A, RN, R), pigment yellow L, benzidine yellow (G, GR), permanent yellow (NCG), Vulcan fast yellow (5G, R), tartrazine lake, quinoline yellow lake, anthrazane yellow BGL, isoindolinoin Yellow, Red Iron, Red Lead, Red Lead, Cadmium Red, Cadmium Mercury Red, Antimony Red, Permanent Red 4R, Para Red, Faise Red, Parachloro-orthonitroaniline Red, Risol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmine BS, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Belkan Fast Rubin B, Brilliant Scarlet G, Risol Rubin GX, Permanent Red F5R, Brilliant Carmine 6B, Po Gument Scarlet 3B, Bordeaux 5B, Toluidine Maroon, Permanent Bordeaux F2K, Helio Bordeaux 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, Perinon Orange, Oil Orange, Cobalt Blue, Cerulean Blue, Alkali Blue Lake, Peacock Blue - Lake, Victoria Blue Lake, Metal-free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue (RS, BC), Indigo, Ultramarine, Navy Blue, Anthraquinone Blue, Fast Violet B, Methyl Violet Lake, Cobalt Purple, Manganese Purple, Dioxane Violet, Anthraquinone Violet, Chrome Green, Zinc Green, Chromium Oxide, Pyridian, Emerald Green, Pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake,Phthalocyanine green, anthraquinone green, titanium dioxide, zinc oxide, lithobone, and mixtures thereof can be used. The amount used is generally 0.1 to 50 parts by mass per 100 parts by mass of the binder resin.

[0112] [Static Control Agent] Known charge control agents can also be used, such as 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, elemental or compound phosphorus, elemental or compound tungsten, fluorine-based surfactants, metal salicylic acid salts, and metal salts of salicylic acid derivatives.

[0113] The amount of charge control agent used in this invention is determined by the type of binder resin, the presence or absence of additives used as needed, and the toner manufacturing method including the dispersion method, and is not uniformly determined. However, it is preferably used in the range of 0.1 to 10 parts by mass, and more preferably in the range of 2 to 5 parts by mass, per 100 parts by mass of binder resin. In addition, multiple charge control agents may be used in combination as needed.

[0114] [Release agent] In this invention, a release agent may be used to impart release properties to the toner. The softening point of the release agent used is preferably 70 to 100°C.

[0115] Examples of mold release agents include synthetic waxes such as low molecular weight polyethylene and polypropylene and their copolymers; plant waxes such as candelilla wax, carnauba wax, rice wax, wood wax, and jojoba wax; animal waxes such as beeswax, lanolin, and whale wax; mineral waxes such as montan wax and ozokerite; and oily waxes such as hydrogenated castor oil, hydroxystearic acid, fatty acid amides, and phenolic fatty acid esters.

[0116] From a chemical structural standpoint, various types of waxes are known, including hydrocarbon waxes, ester waxes, and amide waxes. However, ester waxes are preferred when evaluated in terms of storage properties, image quality, and fixing temperature range.

[0117] The amount of release agent is preferably 1 to 6 parts by mass relative to the total amount of toner.

[0118] The toner manufacturing method in the present invention may be any conventionally known method, and may include a manufacturing method that goes through the steps of mixing, kneading, rolling and cooling, grinding and classifying the toner raw materials. For example, after mixing the raw materials, they may be kneaded in a twin-screw kneader, cooled in a belt-type cooler, ground in a jet mill, and classified to obtain toner.

[0119] The weight-average particle size of the toner is preferably 4 μm to 10 μm, and more preferably 5 μm to 8 μm.

[0120] (Developer) The developer in the present invention contains a toner that can be used in the present invention and can be used, for example, as a dry one-component developer and a dry two-component developer. When used as a dry two-component developer, it is preferable to mix the carrier and the toner of the present invention so that the toner particles adhere to the carrier surface of the carrier particles and occupy, for example, 30 to 90% of their surface area.

[0121] Conventional carriers such as iron powder, ferrite, and glass beads can be used. These carriers may also be coated with resin. In this case, the resins used may be polyfluorocarbon, polyvinyl chloride, polyvinylidene chloride, phenolic resin, polyvinyl acetal, silicone resin, etc.

[0122] In any case, the appropriate mixing ratio of toner to carrier is approximately 0.5 to 6.0 parts by mass of toner per 100 parts by mass of carrier.

[0123] (Other examples of image forming apparatus) Next, another example of the image forming apparatus of the present invention will be described. The image forming apparatus of the present invention also includes a configuration that includes a process cartridge. In this embodiment, the process cartridge refers to a unit that integrates an image carrier (electrostatic latent image carrier, photoreceptor), a charging member, and a developing means, and contains toner. The process cartridge may further include exposure means and the like. The process cartridge is an example of a process unit.

[0124] In the present invention, when a cleaning-less process cartridge (for example, one that does not have a cleaning blade for cleaning the image carrier) is used, the lifespan of the cleaner-less process cartridge can be extended and its durability over time can be increased. According to the present invention, the effects of paper dust and transfer residue toner can be reduced without increasing manufacturing costs, and the charged component can maintain a state in which it can be charged well over time.

[0125] Next, Figure 5 shows one embodiment of the process cartridge. As shown in Figure 5, the process cartridge of this embodiment incorporates an electrostatic latent image carrier 101, a charging device 102, a developing device 104, and further includes other means as needed. In Figure 5, reference numeral 103 denotes exposure from the exposure device, and reference numeral 105 denotes recording paper.

[0126] For example, the electrostatic latent image carrier 101 can be one of those described later. Furthermore, any charging member can be used for the charging device 102. The image formation process using the process cartridge shown in Figure 5 will now be explained. The electrostatic latent image carrier 101 rotates clockwise, and an electrostatic latent image corresponding to the exposed image is formed on its surface by charging with a charging device 102 and exposure 103 with an exposure means (not shown). This electrostatic latent image is developed by the developing device 104, and the developed toner is transferred to the recording paper 105 by the transfer roller 108 and printed out. Then, the static electricity is removed by the static elimination means, and the above operation is repeated again.

[0127] The image forming apparatus of the present invention comprises an image carrier, a charging member positioned in contact with the image carrier and charging the image carrier, a developing means for supplying toner to the image carrier and forming a toner image on the image carrier, and a transfer means for transferring the toner image on the image carrier to a recording medium or an intermediate transfer body. Furthermore, the developing means in this embodiment recovers the remaining toner on the image carrier after the transfer. The apparatus also includes other means as appropriate, such as static elimination means, recycling means, and control means.

[0128] The image forming method used in the present invention comprises a charging step of charging an image carrier, a developing step of supplying toner to the image carrier and forming a toner image on the image carrier, and a transfer step of transferring the toner image on the image carrier to a recording medium or an intermediate transfer medium. Furthermore, it includes other means as appropriate, such as static elimination means and control means. Furthermore, it includes other steps as appropriate, such as static elimination steps and control steps.

[0129] In the following explanation, the charging process and the exposure process will be collectively referred to as the electrostatic latent image formation process, and the charging means and the exposure means will be collectively referred to as the electrostatic latent image formation means.

[0130] -Electrostatic latent image formation process and electrostatic latent image formation means- The electrostatic latent image formation step is a step of forming an electrostatic latent image on an electrostatic latent image carrier. The electrostatic latent image carrier (sometimes referred to as "electrophotographic photoreceptor," "photoreceptor," or "image carrier") is not particularly limited in terms of its material, shape, structure, size, etc., and can be appropriately selected from known materials. A drum shape is preferred, and examples of materials include inorganic photoreceptors such as amorphous silicon and selenium, and organic photoreceptors (OPCs) such as polysilane and phthalopolymethine. Among these, organic photoreceptors (OPCs) are preferred because they can obtain higher-resolution images.

[0131] The formation of the electrostatic latent image can be carried out, for example, by uniformly charging the surface of the electrostatic latent image carrier and then exposing it to image-like light, and can be performed by an electrostatic latent image forming means. The electrostatic latent image forming means includes, for example, at least a charging means (charger) for uniformly charging the surface of the electrostatic latent image carrier, and an exposure means (exposurer) for exposing the surface of the electrostatic latent image carrier to an image-like state.

[0132] The charging can be performed, for example, by applying a voltage to the surface of the electrostatic latent image carrier using the charger. The charger may also be called a charging member. There are no particular limitations on the charger, and it can be appropriately selected depending on the purpose. Examples include contact chargers that are known themselves and are equipped with conductive or semiconducting rolls, brushes, films, rubber blades, etc. Among these, it is preferable to use a charging roller, and more preferably a charging rubber roller. Preferably, the charger is positioned in contact with the image carrier and charges the surface of the electrostatic latent image carrier by applying a DC voltage. Alternatively, DC and AC voltages may be superimposed.

[0133] The exposure can be performed, for example, by exposing the surface of the electrostatic latent image carrier in an image-like manner using the exposure device. The exposure device is not particularly limited as long as it can expose the surface of the electrostatic latent image carrier, which has been charged by the charger, in the manner of the image to be formed, and can be appropriately selected according to the purpose. Examples of exposure devices include copying optical systems, rod lens array systems, laser optical systems, liquid crystal shutter optical systems, and various other types of exposure devices. In addition, in the present invention, a back-facing method may be employed in which the electrostatic latent image carrier is exposed in an image-like manner from the back side.

[0134] -Developing process and developing means- The development step is a step of developing the electrostatic latent image using the toner to form a visible image (which may also be called a toner image, etc.). The formation of the visible image can be performed, for example, by developing the electrostatic latent image using the toner, and this can be done by the developing means. The developing means preferably includes, for example, a developer that contains the toner and is capable of applying the toner to the electrostatic latent image by contact or non-contact, and more preferably a developer equipped with a toner container.

[0135] The developer may be a single-color developer or a multi-color developer. For example, a suitable developer may have an agitator that frictionally agitates and charges the toner, and a rotatable magnetic roller. Within the developing unit, for example, the toner is mixed and stirred, and the friction during this process causes the toner to become charged, which is then held in a brush-like state on the surface of a rotating magnetic roller, forming a magnetic brush. Since the magnetic roller is positioned near the electrostatic latent image carrier (image carrier, photoreceptor), a portion of the toner that constitutes the magnetic brush formed on the surface of the magnetic roller moves to the surface of the electrostatic latent image carrier (image carrier, photoreceptor) by electrical attraction. As a result, the electrostatic latent image is developed by the toner, and a visible image is formed on the surface of the electrostatic latent image carrier (image carrier, photoreceptor) by the toner.

[0136] -Transfer process and transfer means- The transfer step is a step of transferring the visible image to a recording medium, and it is preferable to use an intermediate transfer body, first transfer the visible image onto the intermediate transfer body, and then second transfer the visible image onto the recording medium. More preferably, the toner is two or more colors, preferably full-color toner, and the transfer step includes a first transfer step of transferring the visible image onto the intermediate transfer body to form a composite transfer image, and a second transfer step of transferring the composite transfer image onto the recording medium. The transfer can be performed, for example, by charging the electrostatic latent image carrier (image carrier, photoreceptor) with the visible image using a transfer charger, and can be performed by the transfer means. The transfer means preferably comprises a first transfer means for transferring the visible image onto an intermediate transfer body to form a composite transfer image, and a second transfer means for transferring the composite transfer image onto a recording medium. There are no particular restrictions on the intermediate transfer material, and it can be appropriately selected from known transfer materials depending on the purpose. For example, a transfer belt is a suitable example.

[0137] The transfer means (the primary transfer means, the secondary transfer means) preferably includes at least a transfer device that exfoliates and charges the visible image formed on the electrostatic latent image carrier (photoreceptor) toward the recording medium. The transfer means may be one or two or more. Examples of the aforementioned transfer devices include corona discharge transfer devices, transfer belts, transfer rollers, pressure transfer rollers, adhesive transfer devices, and the like.

[0138] There are no particular restrictions on the recording medium, and any known recording medium (recording paper) can be appropriately selected. Recording media include cardboard, postcards, envelopes, plain paper, thin paper, coated paper (such as coated paper or art paper), tracing paper, etc. In addition, OHP sheets and OHP films can also be used.

[0139] - Fixing process and fixing means - The fixing step is a step of fixing the visible image transferred to the recording medium using a fixing device, and may be performed for each color developer after the image has been transferred to the recording medium, or it may be performed simultaneously for each color developer in a stacked state. There are no particular restrictions on the fixing device, and it can be appropriately selected according to the purpose, but known heating and pressing means are preferred. Examples of the heating and pressing means include a combination of a heating roller and a pressing roller, a combination of a heating roller, a pressing roller and an endless belt, and so on. Preferably, the fixing device comprises a heating element equipped with a heating element, a film in contact with the heating element, and a pressurizing member that presses against the heating element via the film, and is a means for heating and fixing by passing a recording medium on which an unfixed image has been formed between the film and the pressurizing member. The heating temperature in the heating and pressing means is usually preferably 80°C to 200°C. In addition, in the present invention, depending on the purpose, a known optical fuser may be used together with or instead of the fixing step and fixing means.

[0140] -Other processes and other means- The static discharge step is a step of discharging static electricity by applying a static discharge bias to the electrostatic latent image carrier, and can be suitably carried out by static discharge means. There are no particular limitations on the static elimination means; it is sufficient that a static elimination bias can be applied to the electrostatic latent image carrier, and it can be appropriately selected from known static eliminators, for example, a static elimination lamp is a suitable example.

[0141] It is preferable to include a brush member for scraping off dirt from the charged component. For example, the cleaning brush described above can be used as the brush member. Using such a brush member improves the stability of image quality over time. The brush member may rotate or may be fixed without rotating. Furthermore, such a brush member may be configured to collect toner.

[0142] In addition to the brush member described above, the device may also have a recovery means for recovering toner remaining on the charged member. The recovery means is not particularly limited and only needs to be able to remove the toner remaining on the charged member. It can be appropriately selected from known options, and examples of preferred recovery means include magnetic brushes, electrostatic brushes, magnetic rollers, blades, webs, etc.

[0143] The control step is a step that controls each of the steps, and each step can be suitably carried out by control means. The control means are not particularly limited as long as they can control the movement of each of the means, and can be appropriately selected according to the purpose. Examples include devices such as sequencers and computers.

[0144] Examples of the present invention are as follows: <1> Image carrier and, A charging member is positioned so as to be in contact with the image carrier and to charge the image carrier, A developing means that supplies toner to the image carrier and forms a toner image on the image carrier, The system includes a transfer means for transferring the toner image on the image carrier to a recording medium or an intermediate transfer medium, The developing means collects the transfer residue toner remaining on the image carrier after the transfer, The surface roughness Rz of the charging member is 5 μm or more and 16 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.6 MΩ or less, or The surface roughness Rz of the charging member is 5 μm or more and 18 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.4 MΩ or less. An image forming apparatus characterized by the following features. <2> The toner comprises matrix particles and an external additive. The aforementioned external additive is characterized by being present in the toner at a concentration of 1.8% by mass or less. <1> The image forming apparatus described above. <3> The toner comprises matrix particles and an external additive. The volume-average particle size of the external additive is 5 nm or more and 50 nm or less. <1> or <2> The image forming apparatus described above. <4> This feature is characterized by not having a cleaning blade for cleaning the image carrier. <1> from <3> An image forming apparatus as described in any of the following. <5> The aforementioned charging member is characterized by having a brush member for scraping off dirt. <1> from <4> An image forming apparatus as described in any of the following. <6> The charging member is characterized by being a charging rubber roller. <1> from <5> An image forming apparatus as described in any of the following. <7> The process cartridge comprises the image carrier, the charging member, and the developing means, all integrated together. The process cartridge is characterized by not being equipped with a cleaning blade for cleaning the image carrier. <1> from <6> An image forming apparatus as described in any of the following. [Explanation of Symbols]

[0145] 10 Image carrier (photosensitive drum) 20 Electrostatic Rollers 62 Transfer Roller 72 Developing Roller 161 Cleaning Brush [Prior art documents] [Patent Documents]

[0146] [Patent Document 1] Japanese Patent Publication No. 2004-126104 [Patent Document 2] Patent No. 3596535

Claims

1. Image carrier and, A charging member is positioned so as to be in contact with the image carrier and to charge the image carrier, A developing means that supplies toner to the image carrier and forms a toner image on the image carrier, A transfer means for transferring the toner image on the image carrier to a recording medium or an intermediate transfer medium, The system includes a recovery means for recovering toner from the charged member, The developing means collects the transfer residue toner remaining on the image carrier after the transfer, The surface roughness Rz of the charging member is 5 μm or more and 16 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.6 MΩ or less, or The surface roughness Rz of the charging member is 5 μm or more and 18 μm or less, and the electrical resistance of the charging member is 0.1 MΩ or more and 1.4 MΩ or less. The toner comprises matrix particles and an external additive. The aforementioned external additive is contained in the toner at a concentration of 1.8% by mass or less. During printing, the residual toner on the image carrier is moved to the charging member, the residual toner on the charging member is moved to the recovery means for collection, and when the device is shut down, the recovery means moves the collected residual toner to the charging member, the residual toner on the charging member is moved to the image carrier, and the residual toner on the image carrier is moved to the developing means for collection. An image forming apparatus characterized by the following features.

2. The image forming apparatus according to Claim 1, characterized in that the volume average particle diameter of the external additive is 5 nm or more and 50 nm or less.

3. The image forming apparatus according to claim 1, characterized in that it does not include a cleaning blade for cleaning the image carrier.

4. The image forming apparatus according to claim 1, characterized in that the recovery means is a brush member for scraping off dirt from the charged member.

5. The image forming apparatus according to claim 1, characterized in that the charging member is a charged rubber roller.

6. The process cartridge comprises the image carrier, the charging member, and the developing means, all integrated together. The image forming apparatus according to claim 1, characterized in that the process cartridge does not include a cleaning blade for cleaning the image carrier.

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