Image forming device

Abstract

To provide a configuration that can select a mode of preferentially achieving the extension of the life of a cartridge and preventing abnormal discharge occurring on the upstream side of a primary transfer unit in the direction of rotation of a photoconductor drum.SOLUTION: A control unit 200 can have a first mode for controlling such that the peripheral speed ratio of the peripheral speed of a developing roller 3 to the peripheral speed of a photoconductor drum 1 is a first peripheral speed ratio and the first peripheral speed ratio becomes larger than 50% and smaller than 100%, and the potential difference between a development potential and a surface potential of an area of the photoconductor drum 1 where an electrostatic latent image is formed by a laser unit 7 becomes a first potential difference, and a second mode for controlling such that the peripheral speed ratio is a second peripheral speed ratio larger than the first peripheral speed ratio and the second peripheral speed ratio becomes less than 150%, and when the potential difference becomes a second potential difference smaller than the first potential difference.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, such as a laser printer, a copier, or a facsimile, which obtains a recorded image by primarily transferring a toner image formed on an image carrier using an electrophotographic method or the like to an intermediate transfer body and then secondarily transferring the toner image to a recording material. [Background technology]

[0002] In image forming devices that form images on recording materials using electrophotography, such as copiers, printers, and facsimiles, there is a known configuration that includes a developing device that visualizes an electrostatic latent image using toner. One such developing device includes a developing roller that carries and transports toner, and a toner supply roller surrounding the developing roller. In this developing device, toner is supplied from the toner supply roller to the developing roller, and the supplied toner is regulated to a fixed amount on the developing roller by a toner regulating member. The regulated toner is transported to a development area of ​​a photosensitive drum and applied to an electrostatic latent image on the photosensitive drum to form a toner image.

[0003] Conventionally, a process cartridge system has been adopted in which a photosensitive drum and a process means acting on the photosensitive drum are integrated into a cartridge, and the cartridge is detachably mountable to an image forming apparatus. In recent years, there has been a demand for shortening the travel distance of the developing roller in order to extend the life of the process cartridge (hereinafter referred to as the cartridge). For example, a technology has been disclosed in which the peripheral speed of the developing roller is slowed when the amount of toner required according to the image data is small, and the peripheral speed of the developing roller is increased when the amount of toner required is large. This technology aims to extend the life of the cartridge by shortening the travel distance of the developing roller as much as possible (see Patent Document 1).

[0004] On the other hand, in recent years, in order to further shorten the travel distance of the developing roller, the peripheral speed of the developing roller is sometimes made slower than that of the photosensitive drum (i.e., the ratio of the peripheral speed of the developing roller to that of the photosensitive drum is less than 100%).In order to maintain the amount of toner carried (supplied) to the photosensitive drum even when the peripheral speed of the developing roller is made slower than that of the photosensitive drum, it is first necessary to increase the amount of toner carried on the developing roller after it has passed through the toner regulating member (position).One method for achieving this is to increase the surface roughness of the developing roller. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-75358 Summary of the Invention [Problem to be solved by the invention]

[0006] However, increasing the surface roughness of the developing roller can cause unevenness in the amount of toner carried on the developing roller. In particular, when the peripheral speed of the developing roller is slower than that of the photosensitive drum, unevenness in the amount of toner carried on the developing roller due to the surface characteristics of the developing roller tends to affect the photosensitive drum during development. This unevenness in the amount of toner carried on the photosensitive drum can induce abnormal discharge upstream of the primary transfer portion in the rotational direction of the photosensitive drum, potentially resulting in poor image quality.

[0007] For this reason, there is a demand for a mode that prioritizes extending the life of the cartridge, while also having a mode that suppresses abnormal discharge that occurs upstream of the primary transfer portion in the rotation direction of the photosensitive drum.

[0008] The present invention was made under these circumstances, and aims to provide a configuration that allows the selection of a mode that prioritizes extending the life of the cartridge or suppresses abnormal discharge that occurs upstream of the primary transfer section in the rotation direction of the photosensitive drum. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention has the following configuration. (1) An image forming apparatus comprising: a rotatable image carrier; an exposure unit that exposes the surface of the image carrier to light to form an electrostatic latent image on the surface of the image carrier; a rotatable developing unit that applies a developer to the surface of the image carrier to develop the electrostatic latent image; an application unit that applies a development voltage to the developing unit; a drive unit that drives the developing unit to rotate; and a control unit that controls the drive unit, wherein the control unit controls the image forming apparatus to rotate the image carrier such that a peripheral speed ratio of the peripheral speed of the developing unit to the peripheral speed of the image carrier is a first peripheral speed ratio, and An image forming apparatus capable of having a first mode in which a first peripheral speed ratio is greater than 50% and less than 100%, and a potential difference between the surface potential of the image carrier in an area where the electrostatic latent image is formed by the exposure means and the development potential is controlled to be a first potential difference, and a second mode in which the peripheral speed ratio is a second peripheral speed ratio greater than the first peripheral speed ratio, the second peripheral speed ratio being less than 150%, and the potential difference is controlled to be a second potential difference smaller than the first potential difference. [Effects of the Invention]

[0010] According to the present invention, a configuration can be provided that allows selection of a mode that prioritizes extending the life of the cartridge or suppresses abnormal discharge that occurs upstream of the primary transfer portion in the rotation direction of the photosensitive drum. [Brief explanation of the drawings]

[0011] [Figure 1] Schematic cross-sectional view of an image forming apparatus according to Examples 1 to 4 [Figure 2] Schematic cross-sectional views of cartridges of Examples 1 to 4 [Figure 3] Schematic diagram of the primary transfer section in Examples 1 to 4 [Figure 4] Schematic diagram of uneven toner amount on the photosensitive drum and abnormal discharge in Examples 1 to 4 [Figure 5]Schematic diagram of the difference in peripheral speed and unevenness in toner amount in Examples 1 to 4 [Figure 6] 10 is a flowchart showing mode switching control in the third embodiment. [Figure 7] 10 is a flowchart showing mode switching control in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail by way of examples with reference to the accompanying drawings. [Example]

[0013] [Basic configuration of image forming device] Figure 1 is a cross-sectional view of an example of an image forming apparatus that transfers a toner image formed on a rotatable image carrier to a recording material. In Example 1, toner is used as the developer and an intermediate transfer belt is used as the intermediate transfer body. The following describes printing operations in full color mode. In the following description, peripheral speed refers to the speed on the surface of the photosensitive drum or developing roller when it is rotating, i.e., linear speed.

[0014] The toner image forming unit 30 forms a multi-color toner image, here a superimposed toner image of four colors: yellow (Y), magenta (M), cyan (C), and black (K), on the moving intermediate transfer belt 8. The toner image forming unit 30 includes four process cartridges PY, PM, PC, and PK that are detachably attached to the image forming apparatus 100. The toner image forming unit 30 also includes an intermediate transfer belt unit 40 that uses the intermediate transfer belt 8. The four cartridges PY, PM, PC, and PK have the same structure and each cartridge contains yellow (Y), magenta (M), cyan (C), and black (K) toner to form an image. In Example 1, negative toner with a particle size of 7 μm, for example, is used. In the following description, the letters Y, M, C, and K suffixed to the reference numerals indicate the toner color and are omitted when describing matters common to the four colors.

[0015] FIG. 2 is a cross-sectional view of a cartridge P in an image forming apparatus 100. The cartridge P has a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotated in the direction of arrow A (clockwise) at a speed of, for example, 300 mm / s (hereinafter referred to as the peripheral speed). The cartridge P has a charging roller 2 as a charging means for charging the photosensitive drum 1. The charging roller 2 uniformly charges the surface of the photosensitive drum 1 by applying a negative high voltage from a high-voltage power supply (not shown). Next, a laser unit 7 as an exposure means irradiates the photosensitive drum 1 with laser light in accordance with image data, forming an electrostatic latent image on the surface of the photosensitive drum 1. A negative developing voltage is applied to the developing roller 3 as a developing means by a voltage application unit 80, which is an application means for applying a developing voltage. The potential on the surface of the developing roller 3 to which the developing voltage is applied is referred to as the developing potential. The developing roller 3 is rotated in the direction of arrow B (counterclockwise) by a motor 70, which is a driving means, and the charged toner coated on its surface adheres to the electrostatic latent image on the surface of the photosensitive drum 1. This causes the electrostatic latent image to become a visible image (developer image). The detection unit 90 is a detection means for detecting the number of rotations of the developing roller 3. Hereinafter, the visible image formed by the toner will be referred to as a toner image. The developing roller 3 in Example 1 has an average surface roughness Rz of 12 μm, for example. The developing roller 3 may have a surface roughness Rz of 8.0 μm to 15.0 μm.

[0016] The base layer of the photosensitive drum 1 is grounded, and a positive voltage is applied to the primary transfer roller 6 (which serves as a transfer means) by a primary transfer voltage application unit 60 (hereinafter referred to as the voltage application unit 60). This creates an electric field at the nip between the primary transfer roller 6 and the photosensitive drum 1, transferring the toner image from the photosensitive drum 1 to the intermediate transfer belt 8 (referred to as primary transfer). Any toner remaining on the surface of the photosensitive drum 1 that is not transferred to the intermediate transfer belt 8 during the primary transfer is removed from the photosensitive drum 1 by a drum cleaning blade 4 and collected in a waste toner container 23. The toner supply roller 24 replenishes toner to the developing roller 3 by rotating in the direction of arrow C (clockwise). The agitator 25 replenishes toner to the toner supply roller 24 by rotating in the direction of arrow D (clockwise). Because the toner regulating blade 26 is fixed, the developing roller 3 rubs against the toner regulating blade 26 as it rotates. The portion where the developing roller 3 rubs against the toner regulating blade 26 is referred to as the rubbing portion. The amount of toner coated on the surface of the developing roller 3 is regulated while being negatively charged at this rubbing portion, thereby enabling development with a stable density.

[0017] Returning to Figure 1, the intermediate transfer belt unit 40 is composed of a flexible, endless intermediate transfer belt 8, and a drive roller 9 and a driven roller 10 that wrap around and stretch the intermediate transfer belt 8. Furthermore, primary transfer rollers 6 are disposed inside the intermediate transfer belt 8, facing the photosensitive drums 1, and each of them abuts against the corresponding photosensitive drum 1 via the intermediate transfer belt 8. The abutment point between each photosensitive drum 1 and the intermediate transfer belt 8 is the primary transfer portion.

[0018] Polyethylene naphthalate was used as the base material for the intermediate transfer belt 8 in Example 1. Other examples include polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene-1, polystyrene, polyamide, polysulfone, polyarylate, polybutylene terephthalate, and polyimide. Other examples include thermoplastic resins such as polybutylene naphthalate, polyphenylene sulfide, polyether sulfone, polyether nitrile, thermoplastic polyimide, polyether ether ketone, thermotropic liquid crystal polymer, and polyamic acid. Two or more of these may also be mixed and used.

[0019] These thermoplastic resins are impregnated with an ion-conductive material that exhibits ion conductivity. In Example 1, an alkali metal salt was used as the ion-conductive material. Specifically, potassium perfluorobutanesulfonate (potassium nonafluorobutanesulfonate; CFSOK) was used. This material is commercially available as "KFBS" (manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.). Furthermore, from the viewpoint of increasing the surface hardness and improving durability (abrasion resistance) of the intermediate transfer belt 8, the intermediate transfer belt 8 may have a surface layer made of a thermosetting material or a curable material that is cured by irradiation with energy rays such as ultraviolet rays or electron beams.

[0020] The intermediate transfer belt 8 has a thickness of 70 μm, a circumference of 790 mm, a width of 250 mm, and a volume resistivity of 1.0×10 9 Ω cm, surface resistivity 1.0×10 10 The resistivity is Ω / □. Here, the circumference is the length in the rotation direction of the intermediate transfer belt 8 (direction of arrow E), and the width is the length in the direction perpendicular to the rotation direction of the intermediate transfer belt 8. Measurements were taken using a Hiresta·UP MCP-HT450 (manufactured by Mitsubishi Chemical Corporation) at a temperature of 23°C, a relative humidity of 50%, and an applied voltage of 500V. The surface resistivity is a value measured from the back side of the intermediate transfer belt 8.

[0021] The intermediate transfer belt 8 is rotated (moved) in the direction of arrow E (counterclockwise) by the rotational drive of the drive roller 9 at a rotational speed of 300 mm / s corresponding to the peripheral speed of the photosensitive drum 1. The toner images formed on the photosensitive drums 1 are sequentially superimposed and primarily transferred onto the intermediate transfer belt 8 at the primary transfer unit. That is, four color toner images of Y, M, C, and K are formed superimposed in this order on the surface of the intermediate transfer belt 8. The four color toner images are transported by the rotation of the intermediate transfer belt 8 to the secondary transfer unit 18, which is the contact point between the intermediate transfer belt 8 and a secondary transfer roller 11 serving as a secondary transfer member.

[0022] The feeding / conveying device 12 has a feeding roller 14 that feeds the recording material S from a cassette 13 that stores a stack of sheet-like recording materials S, and a pair of conveying rollers 15 that convey the fed recording material S. The recording material S is conveyed from the feeding / conveying device 12 at 300 mm / s, which corresponds to the rotation speed of the intermediate transfer belt 8, and is introduced into a secondary transfer unit 18 at a predetermined timing by a pair of registration (hereinafter referred to as registration) rollers 16. The recording material S is sandwiched and conveyed between a secondary transfer roller 11 and the intermediate transfer belt 8. A positive voltage is applied to the secondary transfer roller 11 by a secondary transfer voltage application unit 61 (hereinafter referred to as voltage application unit 61). As a result, the toner image, in which the four colors on the intermediate transfer belt 8 are superimposed, is transferred all at once (secondary transfer) onto the recording material S being sandwiched and conveyed by the secondary transfer unit 18. After the intermediate transfer belt 8 rotates in the direction of arrow E, the toner that was not transferred from the intermediate transfer belt 8 to the recording material S by the secondary transfer is scraped off by a cleaning blade 21 as a cleaning means and collected in a waste toner collection container 22. The recording material S on which an unfixed toner image has been formed by the secondary transfer is introduced into a fixing device 17. The recording material S, which has had the toner image heat-fixed by the fixing device 17, is discharged onto a discharge tray 50 by a pair of discharge rollers 20.

[0023] The image forming apparatus 100 includes a control unit 200 that controls the above-described components to control the entire image forming apparatus 100, including the image forming operation and the conveyance operation of the recording material S. The control unit 200 includes, for example, a CPU 200a, which controls timing using a timer 200d and executes a program stored in a ROM 200b while using a RAM 200c as a temporary work area. The control unit 200 controls the motor 70 so that the peripheral speed ratio between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the developing roller 3 is a predetermined ratio. For example, when the peripheral speed ratio is controlled to 1:1, if the peripheral speed of the photosensitive drum 1 is 300 mm / s, the control unit 200 controls the motor 70 so that the peripheral speed of the developing roller 3 is also 300 mm / s. Note that the configuration of the image forming apparatus 100 is not limited to the configuration shown in FIG. 1.

[0024] [Mechanism of abnormal discharge upstream of primary transfer] Below, we will explain image defects caused by abnormal discharge (hereinafter referred to as abnormal discharge) that occurs upstream of the primary transfer section (hereinafter referred to as the primary transfer upstream section) in the rotation direction of the photosensitive drum 1 (in other words, the direction of arrow E, which is the rotation direction of the intermediate transfer belt 8). Figure 3 is an enlarged view of the primary transfer section. Abnormal discharge occurs when a large potential difference occurs between the photosensitive drum 1 in the primary transfer upstream section and the intermediate transfer belt 8. When abnormal discharge occurs, the toner image that was present at the location of the occurrence is disturbed, and this becomes apparent on the intermediate transfer belt 8 as, for example, fine vertical streaks.

[0025] Three features of this abnormal discharge are explained below. First, abnormal discharge is likely to occur in solid images. This is because solid images have a large amount of toner on the photosensitive drum 1, and the negative potential of the surface of the photosensitive drum 1, including the toner layer, is high. This causes a large potential difference between the photosensitive drum 1 and the intermediate transfer belt 8.

[0026] The second point is that abnormal discharge is more likely to occur when the toner has a large charge amount. This is because a large charge amount in the toner increases the potential difference between the photosensitive drum 1 and the intermediate transfer belt 8. The charge amount of the toner changes depending on the number of times the cartridge P has been used (also known as the number of pages it can handle) and the operating environment, so whether or not abnormal discharge occurs depends on these conditions.

[0027] The third point is that abnormal discharge is likely to occur when there is significant unevenness in the amount of toner carried on the photosensitive drum 1. Figure 4 shows a schematic diagram of the unevenness in the amount of toner carried on the photosensitive drum 1 and abnormal discharge, as well as a schematic diagram of the corresponding potential. The upper part of Figure 4 is a schematic diagram showing the intermediate transfer belt 8 and the photosensitive drum 1 to which toner has been applied, and the lower part is a graph showing the relationship between the position and potential of the intermediate transfer belt 8 and the photosensitive drum 1. The lower graph shows the potential of the intermediate transfer belt 8 (belt potential), the potential of the surface of the photosensitive drum 1 (drum potential), and the potential of the toner layer on the photosensitive drum 1 (potential of the toner layer).

[0028] FIG. 4(A) shows a case where the unevenness of the toner deposition on the photosensitive drum 1 is large, and FIG. 4(B) shows a case where the unevenness of the toner deposition on the photosensitive drum 1 is small. Note that the toner deposition amount on the photosensitive drum 1 is under the same conditions in FIGS. 4(A) and 4(B). The toner deposition amount is the weight of toner per unit area on the photosensitive drum 1. The measurement method was a measurement of an area of ​​approximately 10 cm. 2 Measure the weight of the toner in mg / cm 2 Toner application unevenness refers to the unevenness caused by the way the toner is applied.

[0029] In Figure 4(A), where there is significant unevenness in toner placement, the potential difference with the intermediate transfer belt 8 becomes large locally at the toner peaks (convex portions), causing current to concentrate at the peaks and resulting in abnormal discharge. In actual measurements, the distance between the toner peaks and the adjacent toner peaks was approximately 50 μm, and the height of the peaks was approximately 14 μm. On the other hand, in Figure 4(B), where there is minimal unevenness in toner placement, the surface has a uniform potential, making abnormal discharge less likely to occur. This mechanism makes abnormal discharge more likely to occur when there is significant unevenness in toner placement.

[0030] One way to reduce uneven toner deposition on the photosensitive drum 1 is to increase the circumferential speed of the developing roller 3 relative to the circumferential speed of the photosensitive drum 1. Figure 5(A) shows a case where the circumferential speed of the developing roller 3 is slow relative to the circumferential speed of the photosensitive drum 1. In this case, the uneven toner deposition on the developing roller 3 remains spread out on the photosensitive drum 1. On the other hand, Figure 5(B) shows a case where the circumferential speed of the developing roller 3 is fast relative to the circumferential speed of the photosensitive drum 1. In this case, the gaps between the uneven toner deposition on the developing roller 3 are narrowed on the photosensitive drum 1, allowing a uniform toner layer to be formed.

[0031] [1st mode and 2nd mode] The following describes the first and second printing modes in Example 1. The ratio of the peripheral speed of the developing roller 3 to the peripheral speed of the photosensitive drum 1 is called the drum-developing peripheral speed ratio (hereinafter referred to as the peripheral speed ratio), and the difference between the surface potential (light area potential) of the photosensitive drum 1 after exposure of a solid image and the developing voltage applied to the developing roller 3 is called the development contrast.

[0032] If the peripheral speed ratio is increased, the amount of toner carried on the photosensitive drum 1 increases, resulting in a larger amount of toner consumed. Therefore, in the first embodiment, the development contrast is changed so that a constant amount of toner consumed is maintained even if the peripheral speed ratio changes. For example, the development contrast is set to 270V at a peripheral speed ratio of 90%, and 220V at a peripheral speed ratio of 110%. In other words, by decreasing the development contrast as the peripheral speed ratio increases, the toner carried amount is maintained at a constant 0.45 mg / cm at either setting value. 2 The development contrast can be controlled by the exposure amount in the laser unit 7 and the development voltage applied by the voltage application section 60.

[0033] [Table 1]

[0034] Table 1 shows the drum-development peripheral speed ratio (%) and whether or not abnormal discharge images occur in single-color solid images when the development contrast is changed so that the amount of toner carried on the photosensitive drum 1 remains constant in accordance with the peripheral speed ratio. The first column of Table 1 shows the drum-development peripheral speed ratio %, the second column shows the development contrast (V), and the third column shows whether or not abnormal discharge images occur (× (occurred), △ (OK), ○ (not occurred)). Note that "△ (OK)" means that abnormal discharge was confirmed compared to ○, but the quality did not deteriorate to the extent of ×.

[0035] When the peripheral speed ratio was 50%, no results were obtained because image formation was impossible. This was because when the peripheral speed ratio was reduced to 50%, the amount of toner developed on the photosensitive drum 1 became extremely small, and even when the development contrast was increased, the amount of toner carried on the photosensitive drum 1 could not be kept constant. When the peripheral speed ratio was between 60% and 95%, some abnormal discharge occurred, but no image defects were observed. On the other hand, when the peripheral speed ratio was between 100% and 140%, no abnormal discharge occurred. This is because the unevenness of the toner carried on the photosensitive drum 1 was reduced as the peripheral speed ratio increased. Then, at 150%, abnormal discharge began to occur again. This is because the toner was charged by rubbing between the photosensitive drum 1 and the developing roller 3 as the peripheral speed ratio increased, increasing the amount of charge on the toner.

[0036] From the above results, the range of the peripheral speed ratio set for the first mode is greater than 50% and less than 100%. The range of the peripheral speed ratio set for the second mode is greater than or equal to 100% and less than 150%. In other words, the first mode is a mode that emphasizes (prioritizes) extending the life of the cartridge P, and the second mode is a mode that suppresses abnormal discharge images while reducing the amount of toner consumed. Note that, in Example 1, the development contrast is uniquely set for the peripheral speed ratio to keep the amount of toner carried constant, but this is not limited to this.

[0037] [Effects of Example 1] Table 2 explains Example 1 and Comparative Example 1. Comparative Example 1 shows a case where only the first mode with a peripheral speed ratio of 90% and a development contrast of 270 V is provided. Example 1 shows a case where both the first mode and the second mode with a peripheral speed ratio of 110% and a development contrast of 220 V are provided, and the user can switch between modes depending on the purpose of use.

[0038] [Table 2] Table 2 shows the results of Comparative Example 1 and Example 1 as either good (Excellent) or possible (Good) for two points: the occurrence of image defects (abnormal discharge images) due to abnormal discharge, and the extension of the lifespan of cartridge P. In Comparative Example 1, it was possible to extend the lifespan of cartridge P by slowing the peripheral speed ratio, and although abnormal discharge occurred, image formation was possible. On the other hand, in Example 1, it was possible to extend the lifespan of cartridge P by switching to the first mode, and it was possible to suppress abnormal discharge images by switching to the second mode, and both were good results.

[0039] As described above, the control unit 200 performs image formation in a first mode or a second mode. The first mode is a mode in which the motor 70 is controlled so that the peripheral speed ratio is a first peripheral speed ratio (e.g., 90%), and the laser unit 7 and / or the voltage application unit 80 are controlled so that the development contrast is a first potential difference (e.g., 270 V). The second mode is a mode in which the motor 70 is controlled so that the peripheral speed ratio is a second peripheral speed ratio (e.g., 110%), and the laser unit 7 and / or the voltage application unit 80 are controlled so that the development contrast is a second potential difference (e.g., 240 V). Here, the second peripheral speed ratio is greater than the first peripheral speed ratio, and the second potential difference is smaller than the first potential difference. In the first mode, the first peripheral speed ratio is equal to or greater than 60% and less than 100%, and in the second mode, the second peripheral speed ratio is equal to or greater than 100% and less than 140%. The weight of toner applied per unit area to the photosensitive drum 1 in the first mode is equal to the weight of toner applied per unit area to the photosensitive drum 1 in the second mode.

[0040] As mentioned above, the circumstances under which abnormal discharge occurs vary depending on the amount of toner and the magnitude of the toner charge. The amount of toner varies depending on the image to be printed, and the toner charge varies depending on the number of pages the cartridge P can print and the usage environment. In Comparative Example 1, the peripheral speed of the developing roller 3 is slowed (90%), which achieves a long life for the cartridge P, but abnormal discharge occurs depending on the circumstances. On the other hand, in Example 1, it is possible to switch to the second mode as necessary in a situation where abnormal discharge images occur. Therefore, it is possible to suppress abnormal discharge images while minimizing the impact on the life of the cartridge P.

[0041] As described above, according to Example 1, it is possible to provide a configuration that allows the selection of a mode that prioritizes extending the life of the cartridge or suppresses abnormal discharge that occurs upstream of the primary transfer portion in the rotation direction of the photosensitive drum. [Example]

[0042] In recent years, with the diversification of the market, there has been an increasing need for wide color gamut printing, such as in photo printing. Wide color gamut printing allows for the expansion of the image color gamut and the production of higher quality images. In wide color gamut printing, the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 is controlled to be higher than that during normal image formation. Therefore, in addition to a first mode that prioritizes the life of the cartridge P and a second mode that suppresses abnormal discharge images while taking toner consumption into consideration, a third mode is also provided. The third mode achieves a wide color gamut by increasing the peripheral speed ratio and increasing the development contrast. The basic configuration of the image forming apparatus 100 is the same as in the first embodiment, and therefore the same components are designated by the same reference numerals and will not be described again.

[0043] [Third Mode] In the third mode, for example, the peripheral speed ratio is set to 110% and the development contrast is set to 300V. The amount of toner carried on the photosensitive drum 1 is increased by increasing the peripheral speed ratio, increasing the developable amount, and increasing the development contrast. The first and second modes are the same as in the first embodiment, so a description thereof will be omitted. The amount of toner carried on the photosensitive drum 1 in the first and second modes is 0.45 mg / cm. 2 whereas in the third mode, it is 0.55 mg / cm 2 In the third mode, the peripheral speed ratio is set to 110%, so that the toner deposition unevenness on the photosensitive drum 1 is small and abnormal discharge can be suppressed.

[0044] [Effects of Example 2] Example 2 and Comparative Example are explained in Table 3. Comparative Example 1 is as described above. Example 2 has a third mode in addition to the first and second modes similar to Example 1, and shows a case where the user can switch modes depending on the purpose of use.

[0045] [Table 3] Table 3 shows the two points of occurrence of abnormal discharge images and the long life of cartridge P, as well as the results of wide color gamut printing, such as good (Excellent) and acceptable (Good) for Comparative Example 1 and Example 2, respectively.

[0046] In Comparative Example 1, it is possible to minimize the impact on the lifespan of the cartridge P, and although abnormal discharge images occur, images can be formed, but wide color gamut printing is not supported. In Example 2, by providing the third mode, it is possible to minimize the impact on the lifespan of the cartridge P, suppress abnormal discharge, obtain good results, and support wide color gamut printing. As described above, Example 2 can be adapted to a wider variety of markets.

[0047] As described above, when wide color gamut printing is performed, the control unit 200 performs image formation in the third mode. The third mode is a mode in which the motor 70 is controlled so that the peripheral speed ratio becomes the third peripheral speed ratio (e.g., 110%), and the laser unit 7 and / or the voltage application unit 80 are controlled so that the development contrast becomes the third potential difference (e.g., 300 V). The third peripheral speed ratio is greater than the first peripheral speed ratio, and the third potential difference is greater than the first potential difference. The weight of toner applied per unit area to the photosensitive drum 1 in the third mode is greater than the weight of toner applied per unit area to the photosensitive drum 1 in the first and second modes.

[0048] As described above, according to the second embodiment, it is possible to provide a configuration that allows the selection of a mode that prioritizes the long life of the cartridge and suppresses abnormal discharge that occurs upstream of the primary transfer portion in the rotation direction of the photosensitive drum. [Example]

[0049] As explained in the mechanism of abnormal discharge in the upstream portion of the primary transfer in the first embodiment, abnormal discharge is likely to occur in solid images and becomes apparent when the solid image is present over a wide area. A solid image includes not only a toner image formed over the entire image-formable area of ​​the photosensitive drum 1, but also a toner image formed continuously over a predetermined area. Therefore, in the third embodiment, an example will be described in which the first mode and the second mode are automatically switched depending on the image data to be printed. The basic configuration of the image forming apparatus 100 is the same as in the first embodiment, and the same components are designated by the same reference numerals and will not be described again.

[0050] [Solid image data and abnormal discharge image] Table 4 shows the difference in visibility of the abnormal discharge image depending on the area of ​​the solid image in the first mode described above.

[0051] [Table 4] In Table 4, the area of ​​the solid image (mm 2) and the second column indicates the occurrence of abnormal discharges (△ indicates that the discharge occurred but was not significant, ◯ indicates that the discharge was not confirmed).

[0052] In the evaluation of Example 3, a solid image of the same shape, here a square, was used. 2 No abnormal discharge was observed below 400mm. 2 Above this threshold, abnormal discharge occurs, but it is not significant. In other words, when the area of ​​a solid image of the same shape is changed, the first threshold for determining whether abnormal discharge occurs or not is set to, for example, 400 mm 2 This indicates that abnormal discharge occurs when a solid image exists over a relatively large area. Even if abnormal discharge occurs, it is not significant. The first threshold is 400 mm 2 The number of times is not limited to the above, and is set depending on the specifications of the image forming apparatus 100, etc.

[0053] Next, Table 5 shows the solid image with an equal area of ​​400mm 2 This shows the difference in visibility of the abnormal discharge image due to the difference in shape when the rectangle is used. [Table 5] In Table 5, the first column shows the diagonal distance (mm) of the solid image shape, and the second column shows whether or not abnormal discharge occurred. Here, ◯ indicates that no abnormal discharge was confirmed, and △ indicates that abnormal discharge occurred but was not significant.

[0054] The difference in shape is expressed by the diagonal distance. It can be seen that abnormal discharge is noticeable when the diagonal distance is 51 mm or less, but does not occur when it is 80 mm or more. In other words, when the diagonal distance is changed for a solid image of the same area, the second threshold for determining whether or not abnormal discharge will occur is, for example, 51 mm. This shows that abnormal discharge is less likely to occur in elongated shapes, and the closer the shape is to a square, the more abnormal discharge will occur. Furthermore, even if abnormal discharge does occur, it is not noticeable. From the above results, it can be seen that when a solid image area of ​​400 mm 2was set as the threshold value for determining whether to switch modes. In addition, in order to accommodate shapes other than polygons, the distance between the furthest points in the solid image area, for example, a diagonal line, was used for the determination, and the length of the diagonal line (diagonal distance) of 51 mm was set as the threshold value for determining whether to switch modes. Note that the second threshold is not limited to 51 mm, and is set depending on the specifications of the image forming apparatus 100, etc.

[0055] [Mode switching control] FIG. 6 shows a flowchart of a process for switching between the first mode and the second mode according to image data. The first mode and the second mode are the same as those in the first embodiment. In step (hereinafter, S) 101, the control unit 200 acquires image data from a host device (not shown) such as a personal computer (hereinafter, PC) when the image forming apparatus 100 acquires image data. In S102, the control unit 200 determines whether the image data acquired in S101 contains a solid image area of ​​any of the colors YMCK. If the control unit 200 determines in S102 that there are no solid image areas of any of the four colors, it proceeds to S103. If the control unit 200 determines that there are solid image areas of at least one color, it proceeds to S104. In S103, the control unit 200 selects the first mode, executes printing in the first mode, and ends the process.

[0056] In S104, the control unit 200 determines whether the solid image area is continuously larger than the first threshold value (for example, 400 mm 2 If the control unit 200 determines in S104 that the number of consecutive solid image areas is less than the first threshold, the process proceeds to S103, and if the number is greater than or equal to the first threshold, the process proceeds to S105.

[0057] In S105, the control unit 200 determines whether the distance between the farthest points in the solid image area (e.g., diagonal distance) is less than or equal to a second threshold value (e.g., 51 mm). If the control unit 200 determines in S105 that the diagonal distance is greater than the second threshold value, the process proceeds to S103; if the control unit 200 determines that the diagonal distance is less than or equal to the second threshold value, the process proceeds to S106. In S106, the control unit 200 selects the second mode, performs printing in the second mode, and ends the process.

[0058] In the third embodiment, the solid image, in other words, the density, the area of ​​the density (solid image area), and the shape of that area are determined using specific thresholds, but the present invention is not limited to this. Adjustments may be made depending on the physical properties of the toner used, the resistance of the intermediate transfer belt, the primary transfer voltage, the configuration of the cartridge P, and the environment. Also, as shown in FIG. 6, a determination process may be provided for two or more conditions, or a determination process may be provided for one condition.

[0059] [effect] Table 6 explains Comparative Example 1 and Example 3. Comparative Example 1 is as described above.

[0060] [Table 6] Table 6 shows the automatic mode switching in addition to the two points of occurrence of abnormal discharge images and extending the life of cartridge P. For Comparative Example 1 and Example 3, the respective realizations are shown as excellent (◯ (Excellent)), possible (△ (Good)), compatible (◯), and not compatible (-).

[0061] Example 3 has both the first mode and the second mode, and shows a case where the mode is automatically switched according to the image data by the above-mentioned control. In Example 3, when an image is likely to cause abnormal discharge, it is automatically printed in the second mode. On the other hand, Comparative Example 1 can achieve a long life of the cartridge P, but cannot suppress abnormal discharge images, and does not have multiple modes (is not compatible), so automatic switching is not possible.

[0062] As described above, the control unit 200 switches between the first mode and the second mode according to the image data. Specifically, the control unit 200 switches between the first mode and the second mode according to the area of ​​a continuous region in the toner image. The control unit 200 forms an image in the first mode when the area of ​​the continuous region in the toner image is less than a first threshold. The control unit 200 also switches between the first mode and the second mode according to the shape of the continuous region. When the area of ​​the continuous region in the toner image is equal to or greater than the first threshold, the control unit 200 forms an image in the first mode if the distance between the two most distant points in the shape of the region is greater than a second threshold. On the other hand, when the distance between the two most distant points in the shape of the region is equal to or less than the second threshold, the control unit 200 forms an image in the second mode.

[0063] As described above, according to the third embodiment, it is possible to provide a configuration that allows the selection of a mode that prioritizes the extension of the cartridge life or that suppresses abnormal discharge that occurs upstream of the primary transfer portion in the rotation direction of the photosensitive drum. [Example]

[0064] As with the mechanism of abnormal discharge in the upstream portion of primary transfer in Example 1, abnormal discharge is affected by the amount of charge on the toner, and therefore changes depending on the usage status (endurance status) of the cartridge P. Therefore, Example 4 describes an example in which the first mode and the second mode are switched depending on the endurance status. Note that the basic configuration of the image forming apparatus 100 is the same as in Example 1, so the same reference numerals are used for the same components and their description will be omitted.

[0065] [Cartridge life and abnormal discharge images] [Table 7] Table 7 shows the lifespan of cartridge P (hereinafter referred to as cartridge lifespan) and whether or not abnormal discharge images occurred. Cartridge lifespan is expressed as a percentage, and for each cartridge lifespan, it indicates that no abnormal discharge was confirmed (◯) or that abnormal discharge occurred but was not significant (×).

[0066] In the third embodiment, the cartridge life detection means detects the life using, for example, the number of rotations of the developing roller 3 detected by the detection unit 90. That is, the higher the number of rotations of the developing roller 3, the shorter (or more consumed) the cartridge life becomes. Note that the life of an unused, brand new cartridge is set to 100%, and this value decreases as the cartridge P is used more. The cartridge life detection means is not limited to a detection means based on the number of rotations of the developing roller 3, but may be another detection means that obtains a detection result that shows a correlation with the cartridge life, such as the number of sheets of recording material S on which an image is formed. The control unit 200 stores the cartridge life (e.g., 70%) obtained by the cartridge life detection means in a storage means such as the RAM 200c.

[0067] As shown in Table 7, abnormal discharge occurs when the cartridge life is 100%, but is not significant, and abnormal discharge no longer occurs when the cartridge life is 50% or less. In other words, as the cartridge life decreases, the third threshold for determining whether abnormal discharge will occur is, for example, 60%. As the number of sheets of recording material S conveyed (hereinafter referred to as the number of sheets passed) increases (progresses), the amount of charge on the toner decreases due to friction between the developing roller 3 and the toner regulating blade 26, or between the developing roller 3 and the photosensitive drum 1, due to the shape of the toner surface and the detachment of external additives. Therefore, abnormal discharge becomes less likely to occur as the cartridge life decreases.

[0068] [Mode switching control] 7 is a flowchart showing the process of switching between the first mode and the second mode depending on the cartridge life. The first mode and the second mode are the same as those in the first embodiment. In S201, the control unit 200 acquires the cartridge life stored in a cartridge life storage unit (e.g., RAM 200c) in the image forming apparatus 100. In S202, the control unit 200 determines whether the cartridge life acquired in S201 is equal to or greater than a third threshold (e.g., 60%). If the control unit 200 determines in S202 that the cartridge life is less than the third threshold, the process proceeds to S203; if the control unit 200 determines that the cartridge life is equal to or greater than the third threshold, the process proceeds to S204.

[0069] In S203, the control unit 200 selects the first mode, executes printing in the first mode, and ends the process. In S204, the control unit 200 selects the second mode, executes printing in the second mode, and ends the process. Note that in the third embodiment, the cartridge life is determined using the third threshold of 60%, but this is not limited to this. The third threshold may be adjusted depending on the toner properties used, the resistance of the intermediate transfer belt, the primary transfer voltage, the cartridge configuration, the environment, etc.

[0070] [effect] Table 8 explains Comparative Example 1 and Example 4. Comparative Example 1 is as described above. [Table 8] Table 8 shows whether Comparative Example 1 and Example 4 are good (Excellent) or acceptable (Good) in terms of the occurrence of abnormal discharge images and the extension of the lifespan of cartridge P. It also shows whether automatic mode switching is supported (Good) or not (-).

[0071] The fourth embodiment has both the first mode and the second mode, and shows a case where the mode is automatically switched depending on the cartridge lifespan through the above-mentioned control. In the fourth embodiment, when a nearly new, early stage cartridge P is used, which may cause abnormal discharge, printing is automatically performed in the second mode, thereby reducing the chance of abnormal discharge occurring. Note that the control of the third embodiment, i.e., the control of switching modes depending on the area and shape of the image to be formed, may be combined with the control of the fourth embodiment.

[0072] As described above, the control unit 200 switches between the first mode and the second mode according to the information regarding the lifespan of the cartridge P. The information regarding the lifespan of the cartridge P is expressed such that the value when the cartridge P is new is greater than the value when the cartridge P has been used for some time. The control unit 200 performs image formation in the first mode when the information regarding the lifespan of the cartridge P is less than the third threshold value, and performs image formation in the second mode when the information regarding the lifespan of the cartridge P is equal to or greater than the third threshold value. The control unit 200 obtains the information regarding the lifespan of the cartridge P based on the detection result of the detection unit 90 that detects the number of rotations of the developing roller 3.

[0073] As described above, according to the fourth embodiment, it is possible to provide a configuration that allows the selection of a mode that prioritizes the long life of the cartridge and suppresses abnormal discharge that occurs upstream of the primary transfer portion in the rotation direction of the photosensitive drum. [Explanation of symbols]

[0074] 1 Photosensitive drum 3 Developing roller 7 Laser Unit 70 Motor 80 Voltage application section 200 control section

Claims

1. a rotatable image carrier; an exposure unit for exposing the surface of the image carrier to light to form an electrostatic latent image on the surface of the image carrier; a rotatable developing means for applying a developer to the surface of the image carrier and developing the electrostatic latent image; an application means for applying a development voltage to the developing means; a driving means for rotating the developing means; a control means for controlling the driving means; An image forming apparatus comprising: The control means a first mode in which a peripheral speed ratio of the peripheral speed of the developing means to the peripheral speed of the image carrier is a first peripheral speed ratio, and the first peripheral speed ratio is greater than 50% and less than 100%, and a potential difference between a surface potential of the image carrier in an area where the electrostatic latent image is formed by the exposure means and a development potential is controlled to be a first potential difference; and, a second mode in which the peripheral speed ratio is controlled to a second peripheral speed ratio that is greater than the first peripheral speed ratio and is less than 150%, and the potential difference is controlled to a second potential difference that is smaller than the first potential difference.

2. 2. The image forming apparatus according to claim 1, wherein the developing unit comprises a developing roller having a surface roughness Rz of 8.0 μm to 15.0 μm.

3. 3. The image forming apparatus according to claim 1, wherein the weight of the developer applied per unit area to the image carrier in the first mode is equal to the weight of the developer applied per unit area to the image carrier in the second mode.

4. the control unit is capable of forming an image on the recording material in a third mode in which the peripheral speed ratio is controlled to a third peripheral speed ratio that is larger than the first peripheral speed ratio, and the potential difference is controlled to a third potential difference that is larger than the first potential difference, 4. The image forming apparatus according to claim 3, wherein the weight of the developer applied per unit area to the image carrier in the third mode is greater than the weight of the developer applied per unit area to the image carrier in the first mode and the second mode.

5. 4. The image forming apparatus according to claim 1, wherein the control unit switches between the first mode and the second mode in accordance with image data.

6. 6. The image forming apparatus according to claim 5, wherein the control means switches between the first mode and the second mode depending on the area of ​​a continuous region in the developer image.

7. 7. The image forming apparatus according to claim 6, wherein the control unit performs image formation in the first mode when the area is less than a first threshold value.

8. 8. The image forming apparatus according to claim 7, wherein the control unit switches between the first mode and the second mode depending on the shape of the continuous area.

9. When the area is equal to or greater than the first threshold value, the control means 9. The image forming apparatus according to claim 8, wherein image formation is performed in the first mode when the distance between the two farthest points in the shape is longer than a second threshold, and image formation is performed in the second mode when the distance is equal to or less than the second threshold.

10. a cartridge including the image carrier and the developing means, 10. The image forming apparatus according to claim 5, wherein the control unit switches between the first mode and the second mode in accordance with information relating to the life of the cartridge.

11. The information is expressed such that a value when the cartridge is new is greater than a value when the cartridge has been used; The image forming apparatus according to claim 10, wherein the control unit performs image formation in the first mode when the information is less than a third threshold value, and performs image formation in the second mode when the information is equal to or greater than the third threshold value.

12. a detection means for detecting the number of rotations of the developing means, 12. The image forming apparatus according to claim 10, wherein the control unit obtains the information based on the detection result of the detection unit.

Images