Image forming apparatus

Abstract

An image forming apparatus is provided. The image forming apparatus includes a transfer member configured to transfer a developer image from an image bearing member to an intermediate transfer belt by applying a current to the intermediate transfer belt in a circumferential direction, and a control unit capable of executing a first mode in which the intermediate transfer belt is rotated and a second mode in which the intermediate transfer belt is rotated at a higher rotational speed than the first mode, and wherein the control unit controls such that an absolute value of a second voltage to be applied from a power source to the transfer member in a case where the one-time transfer is performed in the second mode is smaller than an absolute value of a first voltage to be applied from the power source to the transfer member in a case where the one-time transfer is performed in the first mode.

Description

Technical Field

[0001] This disclosure relates to image forming apparatus such as an electrophotographic copier or printer. Background Technology

[0002] Traditionally, image forming devices such as photocopiers and laser printers are known to use electrophotography to form images.

[0003] In the transfer process, such an image forming apparatus electrostatically transfers a toner image formed on the surface of the photosensitive drum to an intermediate transfer body or recording medium by applying voltage to a transfer member (primary transfer section) arranged in the portion facing the photosensitive drum (primary transfer). The image forming apparatus repeats the transfer process for toner images of multiple colors to form toner images of multiple colors on the intermediate transfer body or recording medium.

[0004] Regarding the transfer process, Japanese Patent Application Publication No. 2006-259639 discusses the construction of an image forming apparatus in which a transfer is performed by causing an electric current to move in a circumferential direction through an annular intermediate transfer belt that serves as an intermediate transfer body.

[0005] However, according to the structure described in Japanese Patent Application Publication No. 2006-259639, if the primary transfer voltage is increased when the current passes through the intermediate transfer belt in the circumferential direction, the electric field may become stronger upstream of the primary transfer section. In this case, image defects may occur, causing the toner on the photosensitive drum to fly outside the intended image area on the intermediate transfer belt before it (is about to) enter the primary transfer section. Summary of the Invention

[0006] One embodiment of this disclosure provides an image forming apparatus that performs a single transfer by applying an electric current to an intermediate transfer belt in the circumferential direction, effectively suppressing toner scattering in multiple modes where the rotation speed of the intermediate transfer belt varies from low to high speed.

[0007] According to one aspect of this disclosure, an image forming apparatus is provided, comprising: an image carrier member configured to carry a developer image; a rotatable annular intermediate transfer belt; a transfer member configured to transfer the developer image from the image carrier member to the intermediate transfer belt by applying a current to the intermediate transfer belt in a circumferential direction; a power supply configured to apply a voltage to the transfer member; and a control unit controlling at least one power supply, wherein the control unit executes a first mode of rotating the intermediate transfer belt and a second mode of rotating the intermediate transfer belt at a rotational speed higher than that of the first mode, and wherein the control unit controls such that the absolute value of the second voltage applied from the power supply to the transfer member when performing one transfer in the second mode is less than the absolute value of the first voltage applied from the power supply to the transfer member when performing one transfer in the first mode.

[0008] Further features will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0009] Figure 1 This is a schematic cross-sectional view of an image forming apparatus according to a first exemplary embodiment of the present disclosure.

[0010] Figure 2 This is a schematic cross-sectional view of an intermediate transfer belt in an image forming apparatus according to a first exemplary embodiment of the present disclosure.

[0011] Figure 3 This is a schematic diagram illustrating the relationship between processing speed and single transfer voltage in an image forming apparatus according to a first exemplary embodiment of the present disclosure under normal environmental conditions (temperature of 23°C and humidity of 50%).

[0012] Figure 4 This is a table showing the volume resistivity of the intermediate transfer belt in various environments of the image forming apparatus according to the second exemplary embodiment disclosed in the present invention.

[0013] Figure 5 This is a table showing the electrical charge of the toner in each environment of the image forming apparatus according to the second exemplary embodiment of this disclosure.

[0014] Figure 6A This is a schematic diagram illustrating the relationship between the processing speed and the primary transfer voltage of the image forming apparatus according to the second exemplary embodiment of the present disclosure under a high temperature and high humidity environment. Figure 6B This is a schematic diagram illustrating the relationship between processing speed and single-pass transfer voltage under low temperature and low humidity conditions.

[0015] Figure 7 This is a table of primary transfer voltages (V) in low-speed mode and normal mode of the image forming apparatus according to the second exemplary embodiment of this disclosure.

[0016] Figure 8 This is a schematic cross-sectional view of a power supply circuit in an image forming apparatus according to a third exemplary embodiment of the present disclosure.

[0017] Figure 9A , Figure 9B and Figure 9C This is a schematic diagram illustrating a primary transfer contrast control according to a third exemplary embodiment of the present disclosure. Detailed Implementation

[0018] In the following description, exemplary embodiments of the present disclosure will be illustrated with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described with respect to the following exemplary embodiments should be appropriately varied depending on the construction of the apparatus to which the present disclosure is applied and various conditions. Therefore, unless otherwise stated, these factors are not intended to limit the scope of the present disclosure to the following exemplary embodiments.

[0019] Figure 1 This is a schematic cross-sectional view of an image forming apparatus according to a first exemplary embodiment of the present disclosure.

[0020] Specifically, Figure 1 An example of a color image forming apparatus 100 is shown. (Refer to...) Figure 1 The configuration and operation of the image forming apparatus 100 are described.

[0021] like Figure 1 As shown, the image forming apparatus 100 is a tandem printer equipped with four image forming stations Sa to Sd. Specifically, the first image forming station Sa forms a yellow (Y) image, the second image forming station Sb forms a magenta (M) image, the third image forming station Sc forms a cyan (C) image, and the fourth image forming station Sd forms a black (Bk) image. Except for the colors of the stored toners, the image forming stations are configured in the same manner. Therefore, the first image forming station Sa will be described below as representative.

[0022] The first image forming station Sa includes a drum-shaped electrophotographic photosensitive element (image carrying component, hereinafter referred to as the photosensitive drum) 1a, a charging roller 2a as a charging unit, an exposure unit 3a, and a developing unit 4a. In the following description, the longitudinal direction or longitudinal width of the components of the image forming apparatus refers to the direction parallel to the rotation axis of the photosensitive drum 1a or the dimension along that direction.

[0023] Photosensitive drum 1a travels at a speed of 180 mm / sec along Figure 1 The image carrier component, driven by the rotational drive in the direction of the arrow shown, carries the toner image. The photosensitive drum 1a has a photosensitive layer and a surface layer on an aluminum tube with a diameter φ of 20 mm. The surface layer is a 20 μm thick thin film layer formed of polycarbonate.

[0024] In this exemplary embodiment, the image forming apparatus 100 has a control unit CTR, such as a controller that performs controls related to the image forming operation.

[0025] Upon receiving an image signal, the control unit CTR initiates an image forming operation, causing the photosensitive drum 1a to rotate. During rotation, the photosensitive drum 1a is uniformly charged to a predetermined potential by the charging roller 2a with a predetermined polarity (negative polarity in this exemplary embodiment). The photosensitive drum 1a is then exposed by the exposure unit 3a according to the image signal. This forms an electrostatic latent image corresponding to the yellow component of the desired color image.

[0026] Then, the electrostatic latent image is developed at the development position by the development unit (yellow development unit) 4a and visualized as a yellow toner image.

[0027] The charging roller 2a abuts against the surface of the photosensitive drum 1a under a predetermined pressure and rotates as the photosensitive drum 1a rotates due to friction with the surface of the photosensitive drum 1a. The charging roller 2a has a rotating shaft to which a predetermined DC voltage from a charging bias power supply (not shown) is applied according to the image forming operation. In this exemplary embodiment, the charging roller 2a is formed by providing a metal shaft with a diameter of 5.5 mm and a thickness of 1.5 mm and a bulk resistivity of approximately 1 × 10⁻⁶. 6 It is formed by making an elastic layer of conductive elastomer with an Ωcm density.

[0028] According to the image forming operation, a DC voltage of -1300V is applied as a charging bias to the rotation axis of the charging roller 2a, thereby charging the surface of the photosensitive drum 1a to -600V (a predetermined potential). The surface potential of the photosensitive drum 1a is measured by a surface electrometer Model 344 manufactured by Trek Corporation. The surface potential of the photosensitive drum 1a at this time (-600V) is the same as that of the photosensitive drum 1a when not forming an image, therefore the toner image is not developed.

[0029] Exposure unit 3a includes a laser driver, a laser diode, a polygon mirror, an optical lens system, etc. Exposure unit 3a irradiates a photosensitive drum with a laser based on image information input from a host computer (not shown). Therefore, an electrostatic latent image is formed on the surface of the uniformly charged photosensitive drum 1a. In this exemplary embodiment, the exposure amount is adjusted so that the image formation potential V1 of the photosensitive drum 1a becomes -100V at the latent image portion after exposure by exposure unit 3a.

[0030] The developing unit 4a is a developing unit that includes a developing roller 41a as a developing component (toner carrier component) and a non-magnetic single-component toner (hereinafter referred to as toner) as a developing agent, and develops the electrostatic latent image into a toner image (developing the photosensitive drum 1a).

[0031] The toner is a non-magnetic toner produced by suspension polymerization and has a negatively charged characteristic (its normal polarity is negative). The toner has a volume average particle size of 7.0 μm and is negatively charged when carried on the developing roller 41a. The volume average particle size of the toner was measured using a Beckman Coulter LS-230 laser diffraction particle size distribution measurement device.

[0032] The developing unit 4a and the main body of the image forming apparatus include a mechanism that controls the contact / separation (development separation) state between the developing roller 41a and the photosensitive drum 1a (not shown), and causes the developing roller 41a and the photosensitive drum 1a to contact or separate from each other according to image forming operations, etc. When the developing roller 41a and the photosensitive drum 1a contact each other, the developing roller 41a is subjected to a pressure of 200 gf.

[0033] The contact portion (hereinafter referred to as the developing clamping portion) between the developing roller 41a and the photosensitive drum 1a has a width of 2 mm in the rotation direction of the photosensitive drum 1a and a width of 234 mm in the longitudinal direction of the photosensitive drum 1a. The developing roller 41a is rotated and driven in the developing clamping portion in the same direction as the surface movement direction of the photosensitive drum 1a (their contact surfaces move in the same direction), such that the surface movement speed (hereinafter, circumferential speed) is 140% of the circumferential speed of the photosensitive drum 1a.

[0034] The developing roller 41a is a roller with an elastic layer made of polyurethane resin disposed on the circumference of a metal core. When the developing roller 41a and the photosensitive drum 1a are in contact with each other during image formation operation, a -300V DC voltage is applied to the metal core of the developing roller 41a as a developing bias voltage from a developing bias power supply (not shown). During image formation, the toner carried on the developing roller 41a is developed in the portion of the photosensitive drum 1a at the image formation potential V1 by the electrostatic force generated due to the difference between the image formation potential (-300V) of the developing bias voltage and the image formation potential V1 (-100V) of the photosensitive drum 1a.

[0035] The supply roller 42a is a sponge roller with a porous elastic layer on the circumference of a metal core. The supply roller 42a is rotated in the opposite direction to the developing roller 41a at the portion in contact with it (where their contact surfaces move in opposite directions). Therefore, the supply roller 42a scrapes toner coating off the developing roller 41a, collects the toner in a developing agent container, and supplies new toner to the developing roller 41a. The amount of toner supplied is controlled by applying a predetermined DC voltage (supply roller voltage Vrs) to the supply roller 42a to control the potential difference (supply roller contrast ΔVrs = Vrs - Vdc) with the voltage applied to the developing roller 41a.

[0036] The developing blade (not shown) abuts against the developing roller 41a and faces in the opposite direction to the developing roller 41a (upstream of the developing roller's rotation direction), thereby adjusting the amount of toner applied and providing charge to the toner through friction.

[0037] The intermediate transfer belt 10 is conductive, stretched by multiple stretching components (drive roller 11, tension roller 12 and opposing roller 13), and is rotatably driven to move in the circumferential direction at the portion opposite to and in contact with the photosensitive drum 1a.

[0038] During a single transfer in the image forming operation, a DC voltage is applied from the single transfer power supply 16 to the single transfer roller 14a (also referred to as the single transfer component 14). The toner image carried on the photosensitive drum 1a is transferred onto the intermediate transfer belt 10 in a single transfer by the electric field formed by the difference between the voltage applied to the single transfer roller 14a by the single transfer power supply 16 and the image forming potential V1 of the photosensitive drum 1a (hereinafter referred to as single transfer contrast). As a transfer component, the single transfer roller 14a together with the single transfer power supply 16 constitutes the voltage application component in this disclosure. In this exemplary embodiment, as Figure 1 As shown, voltage is applied from a shared primary transfer power supply 16 to the four primary transfer rollers 14a to 14d. However, this disclosure is not limited to this configuration. Individual primary transfer power supplies may be provided to the primary transfer rollers 14, or the shared primary transfer power supply may apply voltage to only some of the primary transfer rollers 14.

[0039] The yellow toner image formed on the photosensitive drum 1a is electrostatically transferred to the intermediate transfer belt 10 during the process of passing through the contact portion (hereinafter referred to as the primary transfer portion) between the photosensitive drum 1a and the primary transfer roller 14a (with the intermediate transfer belt 10 in between). In this exemplary embodiment, the primary transfer is performed by applying a voltage (also referred to as the primary transfer voltage) of opposite polarity to the normal charged polarity of the toner from the primary transfer power source 16 to the primary transfer roller 14a. The primary transfer voltage is set according to the detection results of the environment (temperature and humidity) by a temperature sensor (not shown) and a humidity sensor (not shown) mounted on the device body and constituting part of the information acquisition unit S1 of this disclosure.

[0040] The primary transfer component 14a is a cylindrical metal roller with a diameter φ of 6 mm, and is made of nickel-plated SUS. The primary transfer component 14a is positioned 8 mm downstream of the center of the photosensitive drum 1a in the moving direction of the intermediate transfer belt 10, and is wound around the photosensitive drum 1a. The primary transfer component 14a is arranged 1 mm above the horizontal plane formed by the photosensitive drum 1a and the intermediate transfer belt 10 to ensure sufficient winding of the intermediate transfer belt 10 around the photosensitive drum 1a, and to apply a force of approximately 200 gf to the intermediate transfer belt 10.

[0041] The primary transfer component 14a rotates along with the intermediate transfer belt 10. The primary transfer components 14b, 14c, 14d, and 14c arranged in the second image forming station Sb, the third image forming station Sc, and the fourth image forming station Sd are arranged similarly to the primary transfer component 14a.

[0042] Similarly, the magenta toner image as the second color, the cyan toner image as the third color, and the black toner image as the fourth color are formed by the second, third, and fourth image forming stations Sb, Sc, and Sd. Then, the toner images are sequentially transferred and superimposed onto the intermediate transfer belt 10 to obtain a composite color image corresponding to the desired color image.

[0043] During the secondary transfer process, the toner images of four colors on the intermediate transfer belt 10 are transferred together onto the surface of the recording material P supplied by the supply unit 50 through the secondary transfer clamping section formed by the intermediate transfer belt 10 and the secondary transfer roller 15 (secondary transfer). The secondary transfer roller 15, as a secondary transfer component, abuts against the intermediate transfer belt 10 under a pressure of 50N to form a secondary transfer section (hereinafter referred to as the secondary transfer clamping section). The secondary transfer roller 15 rotates as the intermediate transfer belt 10 rotates. When the toner on the intermediate transfer belt 10 is transferred to the recording material P such as paper, a secondary transfer voltage of 1500V is applied to the secondary transfer roller 15 from the secondary transfer power supply (not shown).

[0044] Then, the recording material P carrying the toner images of the four colors is introduced into the fixing unit 30, where it is heated and pressurized, so that the four colors of toner melt and mix, and are fixed (fused) to the recording material P.

[0045] The recording material P can be of the desired type (e.g., plain paper, glossy paper, etc.) and desired size. Plain paper here refers, for example, paper with a basis weight of 60 (g / m³). 2 ) to 90 (g / m 2 Recording materials within the range of ) . Glossy paper refers to recording materials with a basis weight and thickness greater than ordinary paper.

[0046] Glossy paper is thicker and has a higher heat capacity than regular paper, so it requires more heat during the fixing process.

[0047] In this exemplary embodiment, when using glossy paper as the recording material P, the processing speed in the primary transfer process, secondary transfer process, and fixing process is slowed down to 60 mm / sec, which is 1 / 3 of that of ordinary paper, thereby ensuring the heat applied to the glossy paper.

[0048] The cleaning device 17 includes a cleaning scraper, which abuts against the outer peripheral surface of the intermediate transfer belt 10 to scrape off residual toner from the intermediate transfer belt 10 and collect the scraped toner into the intermediate transfer belt cleaning device 17. The intermediate transfer belt cleaning device 17 is configured to collect toner from the intermediate transfer belt 10 (from the intermediate transfer body) on the downstream side of the secondary transfer portion of the intermediate transfer belt 10 in the rotation direction of the intermediate transfer belt 10.

[0049] The above operations generate a full-color printed image.

[0050] Next, the intermediate transfer belt 10 will be described in detail.

[0051] Figure 2 This is a schematic cross-sectional view of an intermediate transfer belt in an image forming apparatus according to a first exemplary embodiment of the present disclosure.

[0052] In this exemplary embodiment, the intermediate transfer belt 10 is a ring-shaped type with a circumference of 700 mm and a thickness of 65 μm. For example... Figure 2 As shown, the intermediate transfer belt 10 includes two layers: a base layer 10a with a thickness of 64 μm and an inner layer 10b with a thickness of 1 μm. The base layer 10a (outer peripheral surface side) abuts against the photosensitive drum 1, and the inner layer 10b (inner peripheral surface side) abuts against the primary transfer component 14.

[0053] The base layer 10a is made of polyethylene terephthalate (PET) resin mixed with an ionic conductive agent as a conductive material. The inner layer 10b is made of polyester resin mixed with carbon, formed inside the base layer 10a, and in contact with the drive roller 11, tension roller 12, and opposing roller 13 (the roller opposite to the secondary transfer roller 15). In this exemplary embodiment, the base layer 10a is made of polyethylene terephthalate (PET) resin, but other materials may be selected as appropriate.

[0054] For example, the base layer 10a can be made of a material such as polyester or acrylonitrile-butadiene-styrene copolymer (ABS) or a mixture of these resins. In this exemplary embodiment, the inner layer 10b is made of polyester resin, but it can also be made of other resins such as acrylic resin.

[0055] In this exemplary embodiment, the resistance of the inner layer 10b is lower than that of the base layer 10a in the intermediate transfer tape 10. The bulk resistivity of the intermediate transfer tape 10 used in this exemplary embodiment is 1×10⁻⁶. 10 Ωcm. The surface resistivity of the inner surface of the intermediate transfer tape 10 is 1.0 × 10⁻⁶. 6 Ω / □.

[0056] In this exemplary embodiment, the indoor temperature in the measurement environment is 23°C and the indoor humidity is 50% (hereinafter also referred to as NN environment).

[0057] Based on the relationship between the resistance and thickness between the base layer 10a and the inner layer 10b, the actual measured volume resistivity of the intermediate transfer belt 10 reflects the resistance value of the base layer 10a. On the other hand, the measured surface resistivity of the inner surface of the intermediate transfer belt 10 reflects the resistance value of the inner layer 10b.

[0058] Volume resistivity was measured using a ring probe type UR (model code MCP-HTP12) used in the Hiresta-UP (MCP-HT450) manufactured by Mitsubishi Chemical Corporation.

[0059] Surface resistivity was measured using the same annular probe type UR100 (model code MCP-HTP16) used in the same measuring instrument used to measure volume resistivity.

[0060] The volume resistivity was measured by applying a probe to the surface side of the intermediate transfer belt 10 at an applied voltage of 100V for 10 seconds.

[0061] Surface resistivity was measured by applying a probe to the inside of the intermediate transfer belt 10 at an applied voltage of 10V for 10 seconds.

[0062] In this exemplary embodiment, the volume resistivity of the intermediate transfer belt 10 is preferably 1×10⁻⁶. 9 Up to 1×10 10 Within the range of Ωcm, the surface resistivity of the inner surface of the intermediate transfer belt 10 is preferably 4.0 × 10⁻⁶. 6 Ω / □ or smaller.

[0063] Next, the phenomenon of toner scattering around the area of ​​a single transfer will be described.

[0064] Toner scattering occurs when toner that has flown from the photosensitive drum onto the intermediate transfer belt 10 bounces off the belt during a single transfer process, or when toner particles collide with each other and fly away from the image (outside the predetermined image area).

[0065] Upstream of the primary transfer section, if the electric field between the photosensitive drum and the intermediate transfer belt 10 causes a phenomenon called "pre-transfer" before reaching the primary transfer clamping section, i.e., the toner on the photosensitive drum flies towards the intermediate transfer belt 10, the toner will significantly scatter. In particular, at the location where pre-transfer occurs, the toner flies a longer distance and moves more violently compared to the usual primary transfer location, so the toner scattering may be more significant.

[0066] Furthermore, the resistance of the intermediate transfer belt 10 in this exemplary embodiment is so low that current can flow through the intermediate transfer belt 10 in the circumferential direction. In this configuration, if the primary transfer voltage is set high, pre-transfer may occur due to the increased electric field strength upstream of the primary transfer clamp.

[0067] When conveying plain paper as the recording material P, the processing speed is three times that of conveying glossy paper. Therefore, the kinetic energy of the dispersed toner increases due to the airflow generated by the accelerated processing speed, making toner dispersion more pronounced.

[0068] In this exemplary embodiment, in order to suppress toner scattering significantly in the high-speed processing mode (M2), the primary transfer voltage is set to be lower than the voltage in the low-speed processing mode (M1), thereby effectively suppressing the occurrence of pre-transfer.

[0069] As described below, from the viewpoint of transferability, unlike the viewpoint of suppressing toner scattering, the necessary transfer electric field is maintained at the primary transfer clamping part while reducing the primary transfer voltage.

[0070] That is, it is preferable to determine the transfer voltage by taking into account toner scattering and transferability at various processing speeds.

[0071] (Control of primary transfer voltage)

[0072] Next, a method for controlling the primary transfer voltage in this exemplary embodiment will be described.

[0073] In this exemplary embodiment, the suppression of toner scattering and the achievement of transferability are achieved by reducing the transfer voltage once in the second mode M2 ​​(hereinafter also referred to as the normal mode) for feeding plain paper (thin paper) to a lower level than the transfer voltage once in the first mode M1 (hereinafter also referred to as the low-speed mode) for feeding glossy paper (thick paper). In other words, the control unit CTR has a first mode M1 and a second mode M2, and can select different processing speed modes for processing according to the type of paper used (i.e., the processing speed corresponding to the type of paper).

[0074] As mentioned above, in the normal mode M2 ​​with a higher processing speed, toner scattering may be more significant than in the low-speed mode M1. Therefore, it is preferable to reduce the primary transfer voltage to a level that does not degrade the transferability.

[0075] Figure 3 This is a schematic diagram illustrating the relationship between processing speed and single transfer voltage in a normal environment NN (at a temperature of 23°C and a humidity of 50%).

[0076] Figure 3Examples are illustrated of the preferred range of processing speed and single-transfer voltage for toner scattering and transferability in an environment NN according to this exemplary embodiment.

[0077] Specifically, such as Figure 3 As shown, at high processing speeds (in mode M2), the primary transfer voltage is lower in absolute value than at low processing speeds (in mode M1). Preferably, the upper limit of the primary transfer voltage range for suppressing toner scattering (e.g., indicated by the dashed line L1) can be set to be lower on the high-speed side (in mode M2) than on the low-speed side (in mode M1).

[0078] Considering the use of high-density images in low-speed mode (M1), the lower limit of the single transfer voltage range with preferred transferability (e.g., indicated by the dashed line L2) can be set higher on the low-speed side (mode M1) than on the high-speed side (mode M2).

[0079] In other words, such as Figure 3 As shown, the primary transfer voltage can be determined within the region where the preferred range of transferability (e.g., the region above the dashed line L2) and the preferred range of toner scattering suppression (e.g., the region below the dashed line L1) overlap.

[0080] In this exemplary embodiment, the primary transfer voltage V1 (first voltage) is set to 300V in low-speed mode M1, and the primary transfer voltage V2 (second voltage) is set to 292V in normal mode M2, such that the primary transfer voltage in normal mode is reduced by 8V (absolute difference) compared to the primary transfer voltage in low-speed mode.

[0081] In other words, in this exemplary embodiment, in terms of absolute value, the first transfer voltage in the low-speed mode M1 (first mode) is lower than the first transfer voltage in the normal mode M2 ​​(second mode) (V1>V2), and the absolute value of the voltage difference (reduction) ΔE1 (=V1-V2) is 8V.

[0082] The transfer voltage in low-speed mode M1 can be the same as that in normal mode M2. However, in low-speed mode M1, high-density image formation using glossy paper or the like is often performed (e.g., photo printing), so it is desirable to make the transfer voltage higher than that in normal mode M2 ​​while having a transfer margin.

[0083] As a condition for forming a high-density image in low-speed mode M1, for example, a color table (conversion table) with a larger data volume than that in normal mode M2 ​​can be used to convert image information input from the host computer (not shown) into cyan, magenta, yellow, and black (CMYK) data. Alternatively, by setting the circumferential speed ratio of the photosensitive drum 1 and the developing roller 41 to be higher than that in normal mode M2, a high-density image with an increased tonal dose to be developed can be output in low-speed mode M1.

[0084] (evaluate)

[0085] Next, we will describe the verification methods and evaluation of toner scattering and transfer properties.

[0086] To verify toner scattering, firstly, a Keyence OneshotVR3000 was used to capture two-point images of the black toner at 80x magnification in high-magnification mode. From the captured images, the toner scattering level can be evaluated and ranked, for example, in descending order of A, B, and C.

[0087] For example, such as Figure 3 As shown, processing speed and single transfer voltage are measured relative to various preset reference values. In the figure, the portion where the toner scattering level is at the highest level A is represented by the dashed line L1. The dashed line L1 can be set as the upper limit of the allowable range for toner scattering. That is, within this range (e.g., the area below the dashed line L1), toner scattering can be reduced more effectively to form a higher quality image.

[0088] On the other hand, for example, a good transferability range can be set by verifying the occurrence of image defects caused by residual toner on the photosensitive drum that was not used for a single transfer (untransferred toner). Specifically, image defects caused by untransferred toner refer to image defects (no cleaner ghosting) where untransferred toner that was not recovered by the developing roller during the process of passing through the developing roller is transferred to the transfer portion after one revolution of the photosensitive drum.

[0089] The evaluation images used were patch images of 190% image data (yellow: 95%, magenta: 95%) in normal mode M2 ​​and patch images of 200% image data (yellow: 100%, magenta: 100%) in low-speed mode M1.

[0090] For example, such as Figure 3As shown, processing speed and single transfer voltage were measured using appropriate settings. In the figure, the portion of the image area where no cleaner ghosting was observed is indicated by the dashed line L2. The dashed line L2 can be considered the lower limit of the preferred range for transferability. That is, within this range (e.g., the area above the dashed line L2), higher transferability can be achieved to form a higher quality image.

[0091] As described above, reducing the primary transfer voltage in normal mode M2 ​​to a level lower than that in low-speed mode M1 effectively suppresses toner scattering.

[0092] Furthermore, setting the voltage based on transferability effectively suppressed toner scattering and achieved high transferability.

[0093] In this exemplary embodiment, the primary transfer contrast is changed by altering the primary transfer voltage. However, this disclosure is not limited thereto. The primary transfer contrast can be changed by altering the image forming potential V1 without altering the primary transfer voltage. Alternatively, the primary transfer contrast can be changed by altering both the primary transfer voltage and the image forming potential V1.

[0094] In this exemplary embodiment, the intermediate transfer belt 10 is configured to perform a single transfer by using an inner layer with a lower resistance than the substrate inside the substrate, such that current flows from the primary transfer roller 14, which serves as a transfer component, to the intermediate transfer belt 10 in the circumferential direction. On the other hand, if current can pass through the intermediate transfer belt 10 in the circumferential direction for a single transfer, the inner layer may not be necessary. For example, if the circumferential resistance corresponding to a circumference of 100 mm for the intermediate transfer belt 10 is 1 × 10⁻⁶... 9 If the Ω or less is used, an inner layer can be used.

[0095] The image forming apparatus in the second exemplary embodiment is substantially similar to the image forming apparatus in the first exemplary embodiment, and therefore the differences will be described below.

[0096] In this exemplary embodiment, environmental information is further considered when setting the primary transfer voltage to allow for suppression of toner scattering.

[0097] Specifically, this exemplary embodiment differs from the first exemplary embodiment in that the reduction in the primary transfer voltage ΔE (difference) of normal mode M2 ​​relative to low speed mode M1 changes according to the detection results of the environmental (temperature and humidity) sensor (information acquisition unit S1).

[0098] In this disclosure, the inventors’ careful research has shown that the degree of toner dispersion may vary depending on the environment (temperature and humidity). According to this exemplary embodiment, the primary transfer voltage in each environment can be more optimally set by changing the amount ΔE of the reduction in primary transfer voltage in each environment.

[0099] Next, we will describe the relationship between toner dispersion and the environment (temperature and humidity).

[0100] The parameters that affect toner dispersion based on environmental factors (temperature and humidity) include the resistance of the intermediate transfer belt 10 and the charge of the toner.

[0101] It is unlikely that toner scattering will be significantly reduced when the energy of the pre-transfer toner is lower. Therefore, it is believed that the higher the resistance of the intermediate transfer belt and the lower the charge of the toner, the less likely toner scattering will occur.

[0102] Figure 4 This is a table showing the volume resistivity of the intermediate transfer belt 10 in various environments within the image forming apparatus according to the second exemplary embodiment of this disclosure. The method for measuring the volume resistivity is the same as that described in the first embodiment.

[0103] like Figure 4 As shown, taking a high-temperature and high-humidity environment of 30°C and 80% humidity (hereinafter also referred to as the HH environment) as an example, the volume resistivity is lower than that in the NN environment. On the other hand, taking a low-temperature and low-humidity environment of 15°C and 10% humidity (hereinafter also referred to as the LL environment) as an example, the volume resistivity is higher than that in the NN environment.

[0104] This is because the ionic conductive agent is incorporated into the intermediate transfer belt 10 as a conductive material, and the ions move as carriers to exert conductivity. In the intermediate transfer belt 10, which is imparted with conductivity by the ionic conductive agent, as it gets closer to the low temperature and low humidity LL environment, the movement of ions becomes slower, and the resistance increases.

[0105] Therefore, from the perspective of belt resistance, it is unlikely that toner scattering will occur in the LL environment with high bulk resistivity of the intermediate transfer belt 10.

[0106] Figure 5 This is a table showing the electrical charge of the toner in each environment of the image forming apparatus according to the second exemplary embodiment of this disclosure.

[0107] like Figure 5 As shown, the charge of the toner varies depending on the environment (temperature and humidity). The charge in the HH environment is less than that in the NN environment, and the charge in the LL environment is greater than that in the NN environment.

[0108] This is because toners readily absorb moisture and experience lower electrical resistance in a high-temperature (HH) environment, while they are less likely to absorb moisture and retain their charge more effectively in a low-temperature (LL) environment. Therefore, from the perspective of the toner's charge, it is unlikely that the toner will disperse in a low-charge (HH) environment.

[0109] Figure 6A This is a schematic diagram illustrating the relationship between processing speed and primary transfer voltage in a high-temperature and high-humidity environment HH of an image forming apparatus according to a second exemplary embodiment of the present disclosure. Figure 6B This is a schematic diagram illustrating the relationship between processing speed and single transfer voltage in a low-temperature and low-humidity environment (LL).

[0110] As shown in Figure 6, in the HH and LL environments, as in the NN environment described with respect to the first exemplary embodiment, toner scattering tends to improve as the primary transfer voltage decreases.

[0111] On the other hand, unlike the NN environment, in the HH and LL environments, compared with the NN environment, the preferred range of toner dispersion (dashed line L1) shifts towards the high voltage side relative to the preferred range of transferability (dashed line L2).

[0112] This is because in the HH environment, the decrease in toner dispersion due to changes in toner charge is greater than the increase in toner dispersion due to changes in toner resistance, and in the LL environment, the increase in toner dispersion due to changes in toner resistance is greater than the increase in toner dispersion due to changes in toner charge.

[0113] Therefore, in HH and LL environments, the reduction in primary transfer voltage (ΔE2, ΔE3) from low-speed mode M1 to normal mode M2 ​​can be less than the reduction (ΔE1) in NN environment (ΔE2≤ΔE1, ΔE3≤ΔE1).

[0114] In this exemplary embodiment, in the HH and LL environments, the reduction amounts ΔE2 and ΔE3 of the primary transfer voltage from low-speed mode M1 to normal mode M2 ​​are set to 3V, and in the NN environment, as in the first exemplary embodiment, the reduction amount ΔE1 of the primary transfer voltage from low-speed mode M1 to normal mode M2 ​​is set to 8V.

[0115] In this way, transfer margin can be provided in normal mode in HH environment (where toner spillage is unlikely and temperature and humidity are higher than in NN environment) and LL environment (where temperature and humidity are lower than in NN environment). Therefore, the reduction in primary transfer voltage in normal mode M2 ​​relative to low-speed mode M1 can be set by ΔE(difference) such that NN environment (ΔE1) ≥ HH environment (ΔE2) ≥ 0 and NN environment (ΔE1) ≥ LL environment (ΔE3) ≥ 0.

[0116] As described above, the primary transfer voltage suitable for each environment can be set by changing the reduction amount ΔE of the primary transfer voltage in normal mode M2 ​​relative to low-speed mode M1 based on the detection results of the environmental (temperature and humidity) sensor (information acquisition unit S1).

[0117] Regarding this exemplary embodiment, how to determine the primary transfer voltage in three environments—NN, HH, and LL—has been described. Furthermore, the reduction in primary transfer voltage ΔE (difference) in normal mode M2 ​​relative to low-speed mode M1 can also be changed in environments other than the three mentioned above.

[0118] Next, we will refer to Figure 7 Example of a table describing the relationship between temperature, humidity (moisture content), and single transfer voltage. Figure 7 This is a table of primary transfer voltages (V) in low-speed mode and normal mode of an image forming apparatus according to a second exemplary embodiment of the present disclosure.

[0119] Specifically, Figure 7 A table showing the primary transfer voltage (V) corresponding to temperature and moisture content (humidity) is provided. Regarding the moisture content, the table of primary transfer voltage (V) shows the primary transfer voltage V1 (first voltage) in low-speed mode M1 on the top and the primary transfer voltage V2 (second voltage) in normal mode M2 ​​on the bottom.

[0120] like Figure 7 As shown, the reduction (ΔE) in normal mode M2 ​​relative to low-speed mode M1 occurs in an environment close to NN (temperature 22℃ to 23℃, water content 9g / m³). 3 Up to 10g / m 3 ), ΔE1 is set to 8V. On the other hand, in an environment close to LL or HH (temperature 15°C to 16°C, water content 1g / m³), 3 Up to 2g / m 3 Or, at a temperature of 30°C to 31°C, the water content is 24 g / m³. 3 Up to 25g / m 3 ΔE3 or ΔE2 is set to 3V. Additionally, in other environments, ΔE is set to 6V.

[0121] Because the single transfer voltage has a larger margin relative to toner scattering in the HH and LL environments compared to the NN environment, the reduction (difference) ΔE in normal mode M2 ​​relative to low-speed mode M1 can be smaller than in the NN environment.

[0122] Furthermore, in low-speed mode M1 and normal mode M2, the single transfer voltage can be adjusted based on temperature and moisture content. Figure 7The environment within the range shown in the table is determined by linear interpolation, and can also be determined by inference in environments outside the table.

[0123] exist Figure 7 In the table (H-side of high temperature and high humidity), the primary transfer voltage can be fixed at a value not less than a predetermined voltage, rather than decreasing linearly. This is because the transferability is improved more in the high temperature and high humidity HH environment, but compared with the NN environment, the degree of improvement tends to decrease under high temperature and high humidity conditions.

[0124] As mentioned above, a table can be used to set a single transfer voltage to suit various environments (humidity: L / N / H and temperature: L / N / H).

[0125] In this exemplary embodiment, the primary transfer contrast is changed by altering the primary transfer voltage. However, this disclosure is not limited to this configuration. The primary transfer contrast can be changed by altering the image formation potential V1 instead of changing the primary transfer voltage. Alternatively, the primary transfer contrast can be changed by altering both the primary transfer voltage and the image formation potential V1.

[0126] In the configurations described in the first and second exemplary embodiments, the primary transfer contrast is changed by altering the primary transfer voltage. Conversely, in the image forming apparatus of the third exemplary embodiment, as... Figure 8 As shown, the primary transfer voltage source is grounded, thereby applying voltage from power supply 200 to photosensitive drums 1a to 1d to control the primary transfer contrast. As described in detail below, even in a configuration without a primary transfer power supply as in this exemplary embodiment, advantageous effects similar to those of the first and second exemplary embodiments can be obtained. Hereinafter, only components different from those in the first exemplary embodiment will be described, and descriptions of components identical to those in the first exemplary embodiment will be omitted. In the following description, as in the description of the first exemplary embodiment, only the first image forming station Sa of the four image forming stations will be represented, except for the different configurations and controls of the four image forming stations.

[0127] Figure 8 This is a schematic diagram illustrating the power supply configuration around the primary transfer portion in an image forming apparatus according to a third exemplary embodiment of the present disclosure. Figure 8 As shown, the primary transfer roller 14a, which is a primary transfer component in this exemplary embodiment, is grounded and its potential is 0V. On the other hand, the photosensitive drum 1a has a metal core (not shown) connected to the power supply 200.

[0128] The image forming potential V1 is determined by the magnitude of the reference potential of the photosensitive drum 1a and the magnitude of the charging bias voltage applied to the charging roller 2a. More specifically, the image forming potential V1 is determined by controlling the charging contrast, which is the difference between the reference potential of the photosensitive drum 1a and the charging bias voltage. For example, if the photosensitive drum 1a is grounded and the reference potential is 0V, the value of the charging bias voltage needs to be changed to control the charging contrast, thereby increasing the absolute value of the image forming potential V1.

[0129] In the configuration of this exemplary embodiment, by applying a –350V drum voltage from the power supply 200 to the metal core of the photosensitive drum 1a, the absolute value of the reference potential of the photosensitive drum 1a is changed to be greater than 0V. In this way, by applying a voltage (reference voltage) having the same polarity as the charging bias voltage (i.e., the same polarity as the normal charging polarity of the toner), an image forming potential V1 with an absolute value greater than the reference voltage can be formed in the primary transfer portion. As a result, the absolute value of the image forming potential V1 can be increased without changing the charging bias voltage. Therefore, it is possible to ensure the difference (hereinafter referred to as primary transfer contrast ΔV) between the primary transfer roller 14a, grounded at a potential of 0V, and the image forming potential V1, for the desired size of the primary transfer.

[0130] Figures 9A to 9C This is a schematic diagram illustrating the relationship between the primary transfer voltage (0V), the developing roller voltage Vdc, the drum voltage Vdr, and the image forming potential V1 on the drum surface in this exemplary embodiment. Figures 9A to 9C In the diagram, the horizontal axis represents the scanning direction of the exposure device 3, and the vertical axis represents the magnitude of the absolute value of each voltage (potential). Figure 9A This is a schematic diagram illustrating the single-transfer contrast ΔV in a configuration that exemplifies this exemplary embodiment. Figure 9B This is a schematic diagram illustrating a method of changing (in this case increasing) the transfer contrast ΔV once in the configuration of this exemplary embodiment. Figure 9C This is a schematic diagram illustrating another method of changing the transfer contrast ΔV in the configuration of this exemplary embodiment.

[0131] First, the description Figure 9A Because the primary transfer roller 14a is grounded, its potential is 0V. Figure 9A In this state, a -350V voltage is applied from the power supply 200 to the metal core (not shown) of the photosensitive drum 1a, the developing roller voltage Vdc is set to -650V, and the image forming potential Vl is set to -450V. The developing roller voltage Vdc and the image forming potential Vl are set with reference to the drum voltage Vdr. Figures 9A to 9CAs shown, in the configuration of this exemplary embodiment, the absolute values ​​of both are set to be greater than the drum voltage Vdr. The absolute value of the difference between the image forming potential V1 and the potential of the grounded primary transfer roller 14a constitutes the primary transfer contrast ΔV (in this exemplary embodiment, Vtr-Vl = 450V). In this way, by applying the drum voltage Vdr from the power supply 200 to the photosensitive drum 1a, the absolute value of the image forming potential V1 can be made greater than the reference voltage, thereby ensuring the primary transfer contrast ΔV required for a primary transfer.

[0132] Then, the description Figure 9B . Reference Figure 9B The contrast ΔV of a single transfer is achieved by changing... Figure 9A The image forming potential V1 is changed (increased) under the given state, rather than by changing the drum voltage Vdr. Specifically, the primary transfer contrast ΔV is increased by increasing the absolute value of the image forming potential V1. For example, with the drum voltage Vdr maintained at -350V, the primary transfer contrast ΔV is changed to 550V by changing the image forming potential V1 to -550V. The image forming potential V1 can be changed by altering the exposure amount of the photosensitive drum 1a by the exposure unit 3a, or by altering the charging bias voltage applied to the charging roller 2a, or by altering both. Figure 9B In the example, as the image forming potential V1 changes, the absolute value of the developing roller voltage Vdc increases with the change in the image forming potential V1 (in this exemplary embodiment, the developing roller voltage Vdc is changed to -750V). However, this disclosure is not limited to this configuration and can be configured so as not to change the developing roller voltage Vdc.

[0133] like Figure 9C As shown, both the drum voltage Vdr and the image forming potential Vl can be changed to... Figure 9A The state change shown increases the absolute value of the primary transfer contrast ΔV. That is, the primary transfer contrast ΔV can be changed to 550V by, for example, changing the drum voltage Vdr to -450V and the image forming potential Vl to -550V. In this way, the drum voltage Vdr does not always need to be fixed, but can be changed as needed.

[0134] As described above, in the configuration of this exemplary embodiment, the primary transfer contrast ΔV can be generated and varied, thereby allowing the toner image to be transferred from the photosensitive drum 1a to the intermediate transfer belt 10 in a single pass using an intermediate transfer belt 10 through which current can flow in a circumferential direction. That is, unlike the first and second exemplary embodiments, even in the configuration of this exemplary embodiment without the primary transfer power supply 16, control can be performed in a similar manner to the first and second exemplary embodiments, and similar advantageous effects can be obtained.

[0135] While this disclosure has been described with reference to exemplary embodiments, it should be understood that this disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims should be given the broadest interpretation to cover all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: An image carrier component configured to carry a developer image; Rotatable annular intermediate transfer belt; The transfer unit is configured to transfer a developer image from an image carrier unit to an intermediate transfer belt by applying an electric current to the intermediate transfer belt in a circumferential direction. The information acquisition unit is used to acquire environmental information about the surrounding environment of the image forming apparatus; A power supply, configured to apply voltage to the transfer components; as well as The control unit controls at least one power source. The control unit executes a first mode that rotates the intermediate transfer belt and a second mode that rotates the intermediate transfer belt at a speed higher than that of the first mode. The control unit controls the process such that the absolute value of the second voltage applied from the power supply to the transfer component during one transfer operation in the second mode is less than the absolute value of the first voltage applied from the power supply to the transfer component during one transfer operation in the first mode. The control unit sets the difference between the absolute values ​​of the first voltage and the second voltage based on the environmental information obtained by the information acquisition unit.

2. The image forming apparatus according to claim 1, wherein, When the information acquisition unit detects environmental information indicating that the temperature is higher than a predetermined temperature or the humidity is higher than a predetermined humidity, the control unit reduces the difference between the absolute values ​​of the first voltage and the second voltage to less than the difference between the absolute values ​​of the first voltage and the second voltage in the environment of the predetermined temperature and predetermined humidity.

3. The image forming apparatus according to claim 2, characterized in that, The predetermined temperature is 17℃~28℃, and the predetermined humidity is 35%~70%.

4. The image forming apparatus according to claim 1, wherein, When the information acquisition unit detects environmental information indicating that the temperature is lower than a predetermined temperature or the humidity is lower than a predetermined humidity, the control unit reduces the difference between the absolute values ​​of the first voltage and the second voltage to less than the difference between the absolute values ​​of the first voltage and the second voltage in the environment of the predetermined temperature and predetermined humidity.

5. The image forming apparatus according to claim 4, characterized in that, The predetermined temperature is 17℃~28℃, and the predetermined humidity is 35%~70%.

6. The image forming apparatus according to claim 1, characterized in that, The circumferential resistance corresponding to the intermediate transfer tape with a circumference of 100 mm is 1 × 10⁻⁶. 9 Ω or less.

7. The image forming apparatus according to any one of claims 1 to 6, wherein, The intermediate transfer tape has multiple layers in the thickness direction, and the resistance of the innermost layer along the thickness direction is lower than that of the other layers.

8. The image forming apparatus according to any one of claims 1 to 6, in, The control unit has a conversion table for converting the color information of the input image data into color information to be represented by multiple color materials, and The data values ​​in the transformation table used for image formation in the first mode are greater than the data values ​​in the transformation table used for image formation in the second mode.

Images