JP7540294B2 - Developing unit and image forming apparatus - Google Patents

Description

Embodiments of the present invention relate to a developing unit used in electrophotographic printers and copiers, and an image forming apparatus equipped with a developing unit.

An electrophotographic image forming apparatus includes a development unit having a developer carrier that develops a latent image formed on the surface of an image carrier, and a developer supply member that supplies developer to the developer carrier (see, for example, Patent Document 1).

JP 2019-8140 A (see, for example, FIG. 2)

The developer supply member not only supplies developer to the developer carrier, but also has the function of scraping off any developer remaining on the surface of the developer carrier. However, these functions deteriorate over time, resulting in a decrease in image quality.

A developing unit according to an embodiment of the present invention includes a developer carrier that supplies a developer to an electrostatic latent image carrier and develops a latent image on the electrostatic latent image carrier, and a developer supplying member having an outer circumference of φ13 mm that is disposed so as to contact the developer carrier to form a nip region, has an elastic layer made of a conductive foam sponge on its surface, and supplies the developer to the developer carrier;
a stainless steel indenter having a cross-sectional outer diameter of 16 mm and a length of 50 mm is pressed 0.73 mm into the surface of the end portion and the central portion of the elastic layer in the extending direction of the nip region, the ratio of the stress at the end portion to the stress at the central portion is 0.97 or more and 1.23 or less,
When a polishing film with a grain size of 30 μm was fixed to the surface of a stainless steel indenter having a square surface with sides of 50 mm and a thickness of 10 mm, the polishing film was pressed 0.73 mm into the elastic layer, and the developer supply member was rotated at a peripheral speed of 136.1 mm/sec,
The developer supply member is characterized in that the amount of reduction in the outer diameter of the developer supply member when the indenter is separated 250 seconds after the indenter has reached a pressing amount of 0.73 mm is 0.03 mm or less, relative to the outer diameter of the developer supply member before the indenter is pressed in.

Another developing unit according to an embodiment of the present invention includes a developer carrier that supplies a developer to an electrostatic latent image carrier and develops a latent image on the electrostatic latent image carrier, and a developer supplying member having an outer circumference of φ13 mm that is disposed so as to contact the developer carrier to form a nip region, the developer supplying member having an elastic layer made of a conductive foam sponge on a surface thereof, and supplies the developer to the developer carrier,
a stainless steel indenter having a cross-sectional outer diameter of 16 mm and a length of 50 mm is pressed 0.73 mm into the surface of the end portion and the central portion of the elastic layer in the extending direction of the nip region, the ratio of the stress at the end portion to the stress at the central portion is 0.97 or more and 1.23 or less,
After vulcanization of the elastic layer, when a tensile test of JIS-K6251 is performed using a dumbbell-shaped test piece formed from the material before the foaming treatment, the value obtained by dividing the elongation percentage ([%]) at the time when the test piece breaks by the stress ([N/mm2]) at that time is 72.6 [%/N/mm2] or more and 81.6 [%/N/mm2] or less.

According to an embodiment of the present invention, it is possible to suppress degradation of image quality caused by uneven supply of developer by the developer supply member, and by the occurrence of stains and smudges due to reduced developer scraping ability.

1 is a schematic diagram illustrating a configuration of a main part of a printer including a development unit according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing the internal configuration of a developing unit together with a toner cartridge attached to the developing unit; 1 is a block diagram showing a configuration of a main part of a control system of a printer that is related to the present invention; FIG. 2 is an external view showing a main configuration of a supply roller according to the first embodiment; 5 is a flowchart showing a method for manufacturing the supply roller. FIG. 1 shows the spectral intensity distribution obtained by FT-IR (Fourier transform infrared spectroscopy) analysis of a conductive foam layer made of silicone rubber. FIG. 1 is a diagram showing a spectral intensity distribution obtained by FT-IR analysis of a conductive foam layer made of urethane rubber. 11A and 11B are explanatory diagrams illustrating the state of the cell walls of the supply roller during initial printing or continuous printing when the degree of elongation is less than 72.6% or exceeds 81.6%. 10A and 10B are explanatory diagrams illustrating the state of cell walls of a supply roller initially or after a rotational stress test when the rotational stress decay rate is less than 27.0% or exceeds 31.0%. FIG. 1 is a diagram showing the shape of a test piece having a dumbbell No. 1 shape defined in JIS-K6251. FIG. 4 is a schematic diagram illustrating a method for measuring a rotational stress damping rate of a supply roller. FIG. 2A is a schematic diagram illustrating a measurement method for a simple wear test of a supply roller, and FIG. 2B is an external perspective view illustrating the configuration of an indenter. 6 is a flowchart showing a procedure for measuring the amount of change in outer diameter and the amount of change in weight of the supply roller 25. 5A and 5B are schematic diagrams illustrating a method for measuring a rotational stress ratio of a supply roller, in which FIG. 5A is a diagram when testing an end portion, and FIG. 5B is a diagram when testing a central portion. FIG. 2A is a diagram showing a schematic diagram of an image when a 2×2 (halftone) pattern is printed over substantially the entire area of a recording sheet, and FIG. 2B is a partially enlarged view thereof. 1 is a characteristic graph showing the relationship between a toner agitation coefficient k and a rotational stress ratio (B/A).

Embodiment 1.
FIG. 1 is a schematic diagram showing the main configuration of a printer equipped with a development unit according to an embodiment of the present invention.

As shown in FIG. 1, the printer 1 as an image forming device includes developing units 2K, 2C, 2M, 2Y for the colors black (K), cyan (C), magenta (M), and yellow (Y) (these units may be simply referred to as developing units 2 when no particular distinction is required), toner cartridges 3K, 3C, 3M, 3Y for the colors (these units may be simply referred to as toner cartridges 3 when no particular distinction is required), a transfer unit 14, exposure units 5K, 5C, 5M, 5Y (these units may be simply referred to as exposure units 5 when no particular distinction is required), a paper feed cassette 6 that stores and supplies recording paper 10 as a recording medium, and a fixing unit 7 that fixes the toner image on the recording paper 10.

The developing units 2 are arranged along the transport path of the recording paper 10 by the transfer unit 14 (the horizontal portion of the paper transport path 8 shown by the dashed line in the figure) from the supply side (upstream side in the paper transport direction) to the discharge side (downstream side in the paper transport direction) in the order of developing unit 2K, developing unit 2C, developing unit 2M, and developing unit 2Y, and each is configured to be freely attached and detached to the printer 1 main body. Note that for each of the removable or movable components such as the developing unit 2 of the printer 1, the part excluding that component may be referred to as the printer 1 main body.

The toner cartridges 3K, 3C, 3M, 3Y are provided with toner storage sections 31K, 31C, 31M, 31Y (which may simply be referred to as toner storage section 31 when no particular distinction is required) that contain toner 40K, 40C, 40M, 40Y (which may simply be referred to as toner 40 when no particular distinction is required) as unused developer. Each is configured to be detachable from the top of the corresponding developing unit 2K, 2C, 2M, 2Y, and when attached, supplies unused toner 40 to the corresponding developing unit 2.

The developing units 2K, 2C, 2M, and 2Y are all of the same structure, and correspond to the photosensitive drums 21K, 21C, 21M, and 21Y (which may be simply referred to as the photosensitive drum 21 when there is no particular need to distinguish them) as electrostatic latent image carriers, the charging rollers 22K, 22C, 22M, and 22Y (which may be simply referred to as the charging roller 22 when there is no particular need to distinguish them), the developing rollers 23K, 23C, 23M, and 23Y (which may be simply referred to as the developing roller 23 when there is no particular need to distinguish them) as developer carriers, and the developing blades 24K and 24C. , 24M, 24Y (sometimes simply referred to as development blade 24 when no particular distinction is required), supply rollers 25K, 25C, 25M, 25Y (sometimes simply referred to as supply roller 25 when no particular distinction is required) as developer supply members, cleaning blades 27K, 27C, 27M, 27Y (sometimes simply referred to as cleaning blade 27 when no particular distinction is required), and first conveying section 28K, 28C, 28M, 28Y (sometimes simply referred to as first conveying section 28 when no particular distinction is required).

As described below, each first transport section 28 transports waste toner removed by the corresponding cleaning blade 27 toward the top of the paper in FIG. 1 (the positive direction of the Y axis described below), which is the axial direction of the photosensitive drum 21. The second transport section 29 transports all of the waste toner sent from each first transport section 28 to a waste toner container 32 located upstream of the developing unit 2K in the paper transport direction. The waste toner container 32 stores the waste toner transported by the second transport section 29, and is detachably mounted on the printer 1 body.

The X, Y, and Z axes in FIG. 1 are set so that the X axis is the transport direction as the recording paper 10 passes through the four developing units 2, the Y axis is the direction of the rotation axis of each photosensitive drum 21, and the Z axis is a direction perpendicular to these two axes. Furthermore, when the X, Y, and Z axes are shown in other figures described below, these axial directions indicate a common direction. In other words, the XYZ axes in each figure indicate the arrangement direction when the depicted parts of each figure are configured as the printer 1 shown in FIG. 1. Furthermore, here, the Z axis is arranged to be approximately vertical.

Figure 2 is a schematic diagram showing the internal configuration of the development unit 2 together with the toner cartridge 3 attached to the development unit 2. The configuration of the development unit 2 will be further explained with reference to this figure.

The developing unit 2 includes a photosensitive drum 21, a charging roller 22 that uniformly charges the surface of the photosensitive drum 21, a developing roller 23 that develops the electrostatic latent image formed on the surface of the photosensitive drum 21 by the exposure unit 5 (Fig. 1) by adhering toner 40 (Fig. 1), a developing blade 24 that regulates the layer thickness of the toner 40 supplied to the developing roller 23, a supply roller 25 that supplies toner 40 to the developing roller 23, a cleaning blade 27 that removes toner 40 remaining on the photosensitive drum 21 without being transferred to the recording paper 10 (Fig. 1), and a first transport section 28 that transports the toner 40 removed by the cleaning blade 27 as waste toner.

The photosensitive drum 21 is an organic photosensitive body composed of a conductive support and a photoconductive layer, and is configured by sequentially laminating a blocking layer, a charge generating layer as a photoconductive layer, and a charge transport layer on a metal pipe such as aluminum as the conductive support, and rotates in a direction to transport the recording paper 10 in the positive direction of the X-axis (the direction of the arrow in the figure).

The charging roller 22 is connected to a charging roller power source 121 (Figure 3) that applies a bias voltage of the same polarity as the toner 40. It is composed of a metal shaft and a semiconductive rubber layer such as epichlorohydrin rubber, and is positioned so that it contacts the photosensitive drum 21 with a predetermined amount of pressure. It rotates in the direction of the arrow in the figure as the photosensitive drum 21 rotates, and the surface of the photosensitive drum 21 is uniformly charged by the applied bias voltage.

The developing roller 23 is connected to a developing roller power supply 122 (Figure 3) that applies a bias voltage of either the same polarity as the toner 40 or the opposite polarity. The developing roller 23 is composed of a metal shaft, a semiconductive urethane rubber layer, and a surface treatment layer, and is positioned so that it contacts the photosensitive drum 21 with a predetermined amount of pressure. It rotates in the opposite direction to the rotation of the photosensitive drum 21 (the direction of the arrow in the figure) at a predetermined peripheral speed ratio, and the applied bias voltage causes the charged toner 40 to adhere to the electrostatic latent image portion on the photosensitive drum 21, resulting in development.

The developing blade 24 is connected to a developing roller power supply 122 or a supply roller power supply 123 (Figure 3) that applies a bias voltage of either the same polarity as the toner 40 or the opposite polarity, and is a thin metal plate member having a thickness of, for example, 0.08 mm, and having approximately the same width as the longitudinal width of the developing roller 23. Furthermore, one end is fixed, and the other end is arranged so that the surface slightly inside from the tip abuts against the peripheral surface of the developing roller 23, and the toner 40 formed on the peripheral surface of the developing roller 23 is charged by the applied bias voltage and abutment pressure, thereby regulating the layer thickness.

The supply roller 25 is connected to a supply roller power source 123 (Fig. 3) that applies a bias voltage of either the same polarity as the toner 40 or the opposite polarity, and is composed of a metal shaft core 51 (Fig. 4) and a foam layer 52 (Fig. 4) as an elastic layer of conductive foamed silicone sponge. The shaft is parallel to the shaft of the developing roller 23, and is arranged at a position where it abuts with the developing roller 23 with a predetermined amount of pressure so as to form a nip area, and as shown by the arrow in the figure, it rotates in the same direction as the rotation of the developing roller 23 (opposite to the contact surface with the developing roller 23) with a predetermined peripheral speed ratio, and supplies toner 40 replenished from the toner storage unit 31 of the toner cartridge 3 to the developing roller 23 by the applied bias voltage. Therefore, the nip area extends in the axial direction of the supply roller 25.

The supply roller 25 also charges the toner 40 by the frictional force of contact with the developing roller 23, and scrapes off undeveloped toner on the developing roller 23. The supply roller 25 will be described in detail later.

The cleaning blade 27 is a urethane rubber member arranged at a position where one end of the cleaning blade 27 contacts the photosensitive drum 21 with a predetermined amount of pressure. The first transport section 28 transports the toner 40 and adhering matter removed by the cleaning blade 27 as waste toner toward the top of the paper in FIG. 2 (the positive direction of the Y axis), which is the axial direction of the photosensitive drum 21.

The toner storage section 38 is provided with an agitator 37 that agitates the toner 40 supplied from the toner cartridge 3 attached to the development unit 2 through the toner supply port 35, and a conveying screw 36 that uniformly distributes the toner in the Y-axis direction.

Specifically, the toner storage section 38 has a longitudinal length of 150.03 mm and a lateral length of 64.0 mm, and the toner supply port 35 has a longitudinal length of 15.0 mm and a lateral length of 9.7 mm. Here, the ratio of the longitudinal length of the toner supply port 35 to the longitudinal length of the toner storage section 38 is 15.0 mm/150.03 mm=0.099. In this embodiment, the toner supply port 35 is disposed at approximately the center of the toner storage section 38 in the longitudinal direction of the toner storage section 38. Therefore, the toner supply port 35 is shorter than the toner storage section 38 in the longitudinal direction of the toner storage section 38, and toner is not directly supplied to both ends of the toner storage section 38. Furthermore, since the toner supplied from the toner supply port 35 is uniformly distributed in the Y-axis direction by the stirring member 37 and the transport screw 36, there is no configuration for transporting the toner from both ends to the center of the toner storage section 38. Therefore, toner whose characteristics have changed compared to new toner, so-called deteriorated toner, is likely to accumulate at both ends of the toner storage section 38 due to peeling of external additives.

The developing unit 2, toner cartridge 3, and waste toner container 32 are all replaceable units, and can be replaced when the toner is consumed or the components deteriorate and reach the end of their life.

In FIG. 1, the exposure units 5K, 5C, 5M, and 5Y are LED heads equipped with light-emitting elements such as LEDs (Light Emitting Diodes) and lens arrays, and irradiate light onto the surfaces of the corresponding photosensitive drums 21K, 21C, 21M, and 21Y based on the print data input by the printer 1, optically attenuating the potential of the exposed areas to form electrostatic latent images.

The paper feed cassette 6 contains a stack of recording paper 10 inside and is removably attached to the bottom of the printer 1. At the top of the paper feed side of the paper feed cassette 6, a paper feed section (not shown) is provided that includes a hopping roller that separates the recording paper 10 one sheet at a time and feeds it to the paper transport path 8 (shown by the dashed line in the figure). Transport rollers (not shown) are arranged at key points on the paper transport path 8, and transport the recording paper 10 sequentially downstream.

The transfer unit 14 includes a transfer belt 9 that electrostatically attracts the recording paper 10 and transports it downstream, a drive roller 11 that is rotated in the direction of the arrow by a drive unit (not shown) to drive the transfer belt 9, a tension roller 12 that pairs with the drive roller 11 and tensions the transfer belt 9, and transfer rollers 4K, 4C, 4M, and 4Y (which may simply be referred to as transfer rollers 4 when there is no need to distinguish between them) that are arranged in opposing pressure contact with the photosensitive drums 21K, 21C, 21M, and 21Y, respectively, via the transfer belt 9, rotate in the direction of the arrow, and transfer the toner image onto the recording paper 10.

Each transfer roller 4 is connected to a transfer roller power supply 124 (Figure 3) that applies a bias voltage of the opposite polarity to the toner 40, and the applied bias voltage transfers the toner images formed on the corresponding photosensitive drums 21 in succession onto the recording paper 10.

The fixing unit 7 is disposed downstream of the developing unit 2 on the paper transport path 8, and includes a heating roller 7a, a pressure roller 7b, a thermistor and a heater (not shown). The heating roller 7a is formed by covering a hollow cylindrical core metal made of aluminum or the like with a heat-resistant elastic layer of silicone rubber, and then covering that with a PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) tube. A heater such as a halogen lamp is provided within the core metal.

The pressure roller 7b is made of a core metal made of aluminum or the like, covered with a heat-resistant elastic layer of silicone rubber, which is then covered with a PFA tube, and is disposed so that a pressure contact is formed between the pressure roller 7b and the heating roller 7a. The thermistor is a surface temperature detection means for the heating roller 7a, and is disposed in a non-contact manner near the heating roller 7a.

The surface temperature of the heating roller 7a is maintained at a predetermined temperature by a heater that is temperature-controlled by the fixing control unit 127 (Figure 3) based on the surface temperature detected by the thermistor. When the recording paper 10 onto which the toner image has been transferred passes through the pressure contact area formed by the temperature-controlled heating roller 7a and pressure roller 7b, the toner image on the recording paper 10 is fixed by the heat and pressure applied during the passage.

Figure 3 is a block diagram showing the main configuration of the control system of printer 1 that is related to the present invention. Below, this control system will be explained with reference to Figures 1 and 2.

In the figure, the control unit 101 is composed of ROM, RAM, input/output ports, a timer, etc., and receives print data and control commands from a higher-level device (not shown) via an I/F (Interface) control unit 111 to control the sequence of the entire printer 1 and perform printing operations. The receiving memory 112 temporarily records the print data input from the higher-level device via the I/F control unit 111, and the image data editing memory 113 receives the print data recorded in the receiving memory 112 and records the image data, i.e., image data, formed by editing the print data.

The operation unit 114 includes an LED for displaying the status of the printer 1, as well as switches and a display for the operator to give instructions to the printer, and the sensor group 115 includes various sensors for monitoring the operating status of the printer 1, such as a paper position detection sensor, a temperature and humidity sensor, and a density sensor.

The charging roller power supply 121 applies a voltage to the charging roller 22 in response to an instruction from the control unit 101 to charge the surface of the photosensitive drum 21, the developing roller power supply 122 applies a predetermined voltage to the developing roller 23 to cause the toner 40 to adhere to the electrostatic latent image, the supply roller power supply 123 applies a predetermined voltage to the supply roller 25 to supply the toner 40 to the developing roller 23, and the transfer roller power supply 124 applies a predetermined voltage to the transfer roller 4 to transfer the toner image formed on the photosensitive drum 21 to the recording paper 10. The charging roller power supply 121, the developing roller power supply 122, and the supply roller power supply 123 are capable of changing the voltage in response to an instruction from the control unit 101.

The fuse power supply 125 is a fuse power supply that passes a current through the fast acting fuse 130 that determines whether the developing unit 2 is unused or not, and the head drive control unit 126 sends the image data recorded in the image data editing memory 113 to the exposure unit 5 and drives the LED to emit light. The fixing control unit 127 heats and drives the heater of the fixing unit 7 to control the surface temperature of the heating roller 7a and controls the rotation of the pressure roller 7b in order to fix the transferred toner image on the recording paper 10.

The transport motor control unit 128 controls the rotation of a paper transport motor 131 for transporting the recording paper 10, and the transport motor control unit 128 transports and stops the recording paper 10 at a predetermined timing according to instructions from the control unit 101. The drive control unit 129 drives a drive motor 132 for rotating the photosensitive drum 21. When the drive control unit 129 drives the drive motor 132 to rotate, the photosensitive drum 21 rotates in the direction of the arrow as shown in FIG. 2, and the charging roller 22, developing roller 23, and supply roller 25 each rotate in the direction of the arrow at a predetermined rotational speed.

The dot counter 101a counts the number of dots required for printing from the image data editing memory 113, and the drum counter 101b counts the number of rotations of the photosensitive drum 21 that rotates during the printing operation. The calculation unit 101c performs calculations based on the temperature read from the sensor group 115 and the number of rotations of the drum counter 101b, and determines whether or not a rotation flag is generated.

Figure 4 is an external view showing the main configuration of the supply roller 25 in embodiment 1. The configuration of the supply roller 25 will be further explained with reference to this figure.

The supply roller 25 has a core metal 51 of φ6 mm as a support shaft as a conductive support, and a foam layer 52 of φ13 mm and a longitudinal length of 221.4 mm is formed on the outside of the core metal 51. Countless cells exist in the foam outer layer 52a and the inner layer 52b inside the foam layer 52. The rubber material used for the foam layer 52 includes urethane rubber, silicone rubber, EPDM rubber, acrylic rubber, ethylene propylene rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, butadiene rubber, isoprene rubber, acrylic rubber, chloroprene rubber, butyl rubber, etc. In particular, urethane and silicone rubbers have become mainstream in recent years.

The core metal 51 may be any metal that has a certain rigidity and sufficient conductivity, such as iron, copper, brass, stainless steel, aluminum, or nickel. Materials other than metals may also be used as long as they have conductivity and appropriate rigidity, such as resin molded products with dispersed conductive particles, or ceramics. In addition to a roll shape, it may also be an aerial pipe shape. There may also be a gear mounting step on both ends of the core metal 51, or a shape with a pin hole, in which case the diameter of both ends may be narrower than the part with the foam layer 52.

The outer diameter of the foam layer 52 may be constant in the axial direction, or may be a crown shape in which the outer diameter decreases as it approaches the axial end of the supply roller 25, an inverted crown shape in which the outer diameter increases as it approaches the axial end of the supply roller 25, or a tapered shape, or may have different diameters at both ends, but for reasons described below, an inverted crown shape is preferred in this embodiment.

Next, a general method for manufacturing the supply roller 25 will be described. FIG. 5 is a flowchart showing the method for manufacturing the supply roller 25. First, a filler, a foaming agent, and a cross-linking agent are added to the above-mentioned rubber material (step S101).

Fillers include reinforcing fillers and conductive fillers. Reinforcing fillers include, for example, silica (fumed silica or precipitated silica), reinforcing carbon black, etc. Conductive fillers include, for example, conductive carbon black, metal powders such as nickel, aluminum, and copper, metal oxides such as zinc oxide, or barium sulfate, titanium oxide, potassium titanate, etc. coated with tin oxide. Here, titanium, reinforcing carbon black, and conductive carbon black are used as fillers.

As the foaming agent, an azo compound foaming agent (here, azobisisobutylnitrile: AIBN) is used. However, instead of the azo compound foaming agent, a bicarbonate, isocyanate, nitrite, hydrazine derivative, or azide compound foaming agent may be used.

As a crosslinking agent (vulcanizing agent), peroxide and sulfur-based vulcanizing agents are used. However, instead of these, hydrogen siloxane in the presence of a platinum catalyst, or an isocyanate agent, etc. may be used.

The rubber material to which the filler, foaming agent, and cross-linking agent have been added is mixed and kneaded using a pressure kneader or mixing roll (step S102).

The kneaded rubber composition is filled into an extrusion molding machine and extruded around the core metal 51 (step S103). This forms a cylindrical rubber composition on the surface of the core metal 51. Hereinafter, the rubber composition (rubber compound) formed on the surface of the core metal 51 is referred to as a roller body.

Next, the roller body thus formed is placed in a heating furnace and heated to the temperature required for vulcanizing the rubber (step S104). In this process (primary vulcanization process), the rubber is vulcanized, but no foaming occurs.

After the primary vulcanization process, a pre-vulcanization process (step S105) is performed to foam the rubber. In the pre-vulcanization process, the roller body is heated to a temperature higher than that in the primary vulcanization process described above. This causes foaming to occur, forming air bubbles (cells), and the vulcanization of the rubber also progresses. Step S105 and step S1207, which will be described later, are referred to as the foaming process.

After the pre-vulcanization process, the roller body is removed from the heating furnace, and the outer periphery of the foam layer of the roller body is roughly polished (step S106). Here, a range of several mm in thickness on the outer periphery (surface) of the foam layer is removed by rough polishing. In the above-mentioned primary vulcanization process and pre-vulcanization process, a skin layer with small air bubbles is formed on the outer periphery of the foam layer, but this skin layer is removed by rough polishing.

The roughly ground roller body is then placed in a heating furnace and the secondary vulcanization process (step S107) is carried out. In the secondary vulcanization process, the roller body is heated to a temperature higher than the heating temperature in the primary vulcanization process. This causes further foaming and the vulcanization of the rubber also progresses.

In the secondary vulcanization process, the skin layer is removed in advance, which suppresses unevenness (distortion) in the crosslinked state of the rubber and allows bubbles to be formed uniformly (i.e., of uniform size across the entire surface of the foam layer). In addition, in the secondary vulcanization process, low molecular weight siloxane derived from silicone is removed by volatilization, but since the skin layer is removed from the surface of the foam layer as described above, the low molecular weight siloxane can be effectively removed.

After the secondary vulcanization process, the surface of the foam layer of the roller body is polished to obtain a predetermined outer diameter (step S108). This results in the formation of a supply roller 25 in which a conductive foam layer 52 is formed on the surface of the core metal 51 (step S109).

It is also possible to extrude rubber pound into a tube shape and heat it to vulcanize and foam it, form a sponge rubber tube, and then cover the core metal 51 with this to form the supply roller 25. At this time, the core metal 51 and the conductive foam layer 52 may be fixed with an adhesive if necessary. In this embodiment, silicone rubber is used as the rubber material for the conductive foam layer 52. The foam layer 52 of the supply roller 25 that uses silicone rubber has multiple cells in a closed cell state. Since silicone rubber has closed bubbles, it is most preferable to use silicone rubber as the main component.

In the case of a conductive foam layer with open bubbles, the toner can penetrate deep inside the bubbles, so there is a possibility that the toner may become clogged inside the bubbles. Therefore, as the number of sheets printed by the image forming device increases, the amount of toner that becomes clogged inside the bubbles increases, and as a result, the hardness and electrical resistance of the conductive foam layer increase, and image unevenness (blurring) may occur due to insufficient sonar supply. In contrast, in the case of a conductive foam layer with closed bubbles, the toner does not penetrate deep inside the bubbles, so the toner is less likely to become clogged inside the bubbles. Therefore, even if the number of sheets printed by the image forming device increases, there is only a small increase in the hardness and electrical resistance of the conductive foam layer, and the occurrence of image unevenness (blurring) is also suppressed.

Here, we will explain how to calculate the silicone ratio and urethane ratio of the material for the supply roller 25.

A square sample measuring 1 cm on a side was cut out from the conductive foam layer 52 of the supply roller 25 and analyzed by Fourier transform infrared spectroscopy (FT-IR). The analysis range was wave numbers of 400 to 4000 cm ^-1 .

Fig. 6 is a diagram showing a spectral intensity distribution obtained by FT-IR (Fourier transform infrared spectroscopy) analysis of the conductive foam layer ₅₂ made of silicone rubber. In Fig. 6, a SiO2 peak is seen at a wave number of 778 [cm ^-1 ], a Si-O-Si peak is seen at a wave number of 995 [cm ^-1 ], and a SiC peak is seen at a wave number of 1254 [cm ^-1 ].

7 is a diagram showing the spectral intensity distribution obtained by FT-IR analysis of the conductive foamed urethane rubber layer 52. In Fig. 7, a CO peak is seen at a wave number of 1721 [cm ^-1 ], and an NH peak is seen at a wave number of 2937 [cm ^-1 ].

Even if the conductive foam layer 52 of the supply roller 25 contains silicone rubber and other substances (e.g., urethane rubber), it is sufficient that the main component of the silicone rubber is 50% by weight or more. The silicone rubber may also be modified silicone rubber.

In this embodiment, the supply roller 25 has specific elements of the foam layer 52 that are limited in scope as described below. However, various supply rollers that are not limited in scope are distinguished as supply roller 25', and each element is described below.

(Product hardness)
The conductive foam layer 52 of the supply roller 25' is preferably used with a low hardness of 40 to 46 on the Asker F hardness scale. If the hardness of the supply roller 25' is higher than the above range, the load of toner damage increases, resulting in a deterioration in graininess (dot formation), and the pressure applied at the contact portion increases, resulting in increased wear of the toner and components, making it unsuitable for high durability. On the other hand, if the hardness is lower than the above range, the amount of foaming agent used to adjust the hardness becomes excessive, making production difficult, and even if a roller is manufactured, the foaming state inside the roller is largely uneven, making the quality unstable, making it difficult to use as a supply roller.

To adjust the hardness of the supply roller 25', a foaming agent such as AIBN (Azobis isobutylonitrile) is used, and the hardness is adjusted by the amount of foaming agent. By using a foaming agent, the foaming ratio of the sponge increases, and it is possible to change the size of the foam cells and the thickness of the cell walls.

(Regarding stretchability)
The degree of elongation of the supply roller 25' in a solid state is preferably within a range of 72.6 [%/N/ ^mm2 ] to 81.6 [%/N/ ^mm2 ] based on the test results described later. The degree of elongation referred to here refers to the value obtained by dividing the elongation percentage [%] of a rubber test piece at the time of breakage when the solid is stretched in a tensile test by the maximum stress (breaking strength) required to pull the solid to break it. It is considered that the higher this value is, the more easily the rubber will elongate in the direction of rotation when compressed and rotated, and conversely, the lower this value is, the less easily the rubber will elongate in the direction of rotation and the more easily it will break (wear). The method of measuring the degree of elongation will be described in detail later.

Figure 8 is an explanatory diagram that shows the state of the cell walls of the supply roller 25' during initial or continuous printing when the elongation is less than 72.6% or more than 81.6%.

As shown in the figure, if the degree of elongation is less than 72.6 [%/N/ ^mm2 ], the cell walls of the supply roller 25' are difficult to elongate when rotated in a state nipped with the developing roller (developer carrier) 23, and the cell walls are easily torn off by pressure in the rotation direction, i.e., easily worn out. As a result, as the supply roller 25' is used, wear accelerates during continuous printing, the nip width with the developing roller 23 becomes smaller, and undeveloped toner on the developing roller 23 cannot be scraped off, causing stains.

Conversely, if the degree of elongation exceeds 81.6 [%/N/ ^mm2 ], when the supply roller 25' is rotated while being nipped with the developing roller (developer carrier) 23, as shown in FIG. 8, the supply roller 25' itself is likely to elongate in the direction of rotation, and the cell walls lie flat in the direction of rotation during continuous printing, making it prone to sagging. This causes a decrease in stress in the vertical direction, and as a result, stress on the developing roller 23 is reduced. As a result, undeveloped toner on the developing roller 23 cannot be scraped off, causing stains. For these reasons, it is desirable that the degree of elongation of the supply roller 25' in a solid state be within the range of 72.6 [%/N/ ^mm2 ] to 81.6 [%/N/ ^mm2 ].

The term "stain" here refers to the adhesion of toner to the background of an image, i.e., non-image areas of a printed matter, caused by toner that is highly charged compared to normally charged toner, i.e., so-called overcharged toner. In this embodiment, negatively charged toner is used, so "stain" occurs due to excessively negatively charged toner.

(Rotational stress damping rate)
The rotational stress attenuation rate of the conductive foam layer 52 of the supply roller 25' is preferably within a range of 27% to 31% based on the test results described below. The rotational stress attenuation rate here refers to the attenuation rate relative to the initial stress after a rotational stress test in which a metal indenter is pressed 0.73 mm into the foam layer 52 of the supply roller 25' and compressed and rotated for 6 hours. The method for measuring the rotational stress attenuation rate will be described in detail later.

Figure 9 is an explanatory diagram that shows a schematic diagram of the state of the cell walls of the supply roller 25' initially or after a rotational stress test when the rotational stress attenuation rate is less than 27.0% or exceeds 31.0%.

As shown in the figure, when the rotational stress attenuation rate is less than 27%, the supply roller 25' is in a state where it is hard or difficult to deform, so that the conductive foam layer 52 of the supply roller 25' tries to maintain its shape before deformation even when rotating in contact with the developing roller (developer carrier) 23. This causes strong pressure to be applied to contact members such as the developing roller 23, causing a problem of increased load torque on the photosensitive drum 21. This can also cause damage to the surface layer of the developing roller 23, which can cause filming on the developing roller 23 and result in printing defects.

Conversely, if the rotational stress attenuation rate exceeds 31%, the supply roller 25' will have poor distortion, meaning that the elasticity of the pressed-in portion of the foam layer 52 will not recover easily and will easily become worn out. As shown in Figure 9, after 6 hours, the contact pressure with the developing roller (developer carrier) 23 during rotation is weak, and undeveloped toner on the developing roller 23 cannot be sufficiently scraped off, resulting in stains. For these reasons, it is desirable for the rotational stress attenuation rate of the supply roller 25' to be between 27% and 31%.

Here, we will explain the measurement results of a simple wear test that was used to precisely define the "wear (amount)" and "settling" described above.

(Simple abrasion test)
The simple abrasion test measures the weight of the supply roller 25' and the outer diameter of the abutted part before and after pressing the center of the rotating supply roller 25' against a metal indenter with a wrapping film of grain size 30 [μm] (#600) for 250 seconds. The change in weight of the supply roller 25' after the simple abrasion test is indicated as weight change [g], and the change in the outer diameter of the indenter nip part after the abrasion test is indicated as outer diameter change [mm]. The measurement method of the simple friction test will be explained in detail later.

The weight change amount [g] can represent the amount of wear of the conductive foam layer 52 of the supply roller 25'. This weight change amount occurs due to the cell walls of the foam layer 52 being scraped (wearing) when it rotates in contact with the wrapping film.

The amount of change in outer diameter [mm] can represent the state of the conductive foam layer 52 of the supply roller 25' due to wear and the state due to sagging. When the amount of change in outer diameter is large, it means that it has been scraped off due to wear, or that the cell walls have flattened and worn out. When the amount of change in weight of the foam layer 52 and the amount of change in outer diameter are both large, it can be said that the influence of wear is strong. When the amount of change in weight of the foam layer 52 is small but the amount of change in outer diameter is large, it can be said that there is no wear, but the cell walls have flattened and worn out, resulting in a smaller outer diameter.

Based on the test results described below, it is desirable that the change in outer diameter of the supply roller 25' at the nip portion before and after the simple abrasion test be 0.03 mm or less and the change in weight be 0.07 g or less. Any other specification would result in wear or settling, and as explained above, the remaining toner on the development roller (developer carrier) 23 after development would not be scraped off sufficiently, resulting in stains. Therefore, it is desirable that the change in outer diameter of the supply roller 25' at the nip portion before and after the simple abrasion test be 0.03 mm or less and the change in weight of the supply roller 25' be 0.07 g or less.

(Regarding rotational stress ratio)
The ratio B/A (rotational stress ratio) of the central stress A [N] to the end stress B [N] during rotation of the supply roller 25' is preferably 0.97 or more and 1.23 or less, based on the test results described later. The rotational stress here refers to the maximum stress [N] during roller rotation when a metal indenter is pressed 0.73 mm into the conductive foam layer 52 of the supply roller 25' from the reference height, which is the position where the metal roller of φ13.0 (mm) contacts the outermost surface of the supply roller 25'. The rotational stress ratio refers to the ratio (B/A) of the central rotational stress A [N] to the end rotational stress B [N]. The method for measuring the rotational stress ratio will be described in detail later.

When the rotational stress ratio exceeds 1.23, the pressure on the end side of the supply roller 25' becomes stronger, which increases the torque load on the photosensitive drum 21 and increases the toner damage on the end side, causing a deterioration in graininess (dot reproducibility).

When the rotational stress ratio is 0.97 or less, the nip width with the developing roller 23 becomes smaller, and the efficiency of toner supply to the developing roller 23 and the scraping efficiency of the developing roller 23 after development deteriorates. In addition, as continuous printing is performed, the nip width with the developing roller 23 at the end side decreases due to wear on the supply roller 25' side, and the supply and scraping properties decrease, so the durability of the developing unit 2 deteriorates. In particular, when printing with a drum count of 30k or more, uneven toner supply occurs on the end side of the supply roller 25', and partial smearing occurs at the solid end. In addition, the occurrence of this smearing is also due to the fact that old toner is pushed into both ends, which makes it easy for deteriorated toner to accumulate at both ends, and therefore the toner supply to the developing roller 23 decreases. This tendency is particularly noticeable when the toner supply port 35 is provided near the center of the toner storage section 38, as in this embodiment. In addition, in this embodiment, the ratio of the longitudinal length of the toner supply port 35 to the longitudinal length of the toner storage section 38 was set to 0.099, but a larger ratio would improve the toner supply from the toner supply port, thereby further suppressing smearing.

As described above, it is desirable that the ratio B/A (rotational stress ratio) of the central stress A [N] to the end stress B [N] when the supply roller 25' rotates be 0.97 or more and 1.23 or less.

For example, by making the outer diameter of the supply roller 25' thicker at the ends than at the center, and making the stress at the ends higher than at the center, it is possible to suppress the decrease in the nip width with the development roller 23 at the ends due to wear on the supply roller 25' side over continuous printing, thereby maintaining toner supply and enabling a long life for the development unit 2. Furthermore, the larger this rotational stress ratio is within the specified range (the closer it is to 1.23), the higher the toner agitation becomes, and the more easily old toner tends to accumulate at the ends and mix with the center where there is more fresh toner, making it possible to obtain high-quality images with a long life.

Next, we will explain how to measure elongation, rotational stress decay rate, simple abrasion test, and rotational stress ratio.

(Method of measuring stretchability)
In measuring the degree of elongation, a test piece 209 having a No. 1 dumbbell shape as defined in JIS-K6251 was formed as shown in Fig. 10 using a material (solid rubber material) of the rubber material constituting the conductive foam layer 52 of the supply roller 25' after vulcanization and before foaming treatment. The test piece 209 is a plate-like piece that is long in one direction and has a parallel part 209a in the center in the longitudinal direction and gripped parts 209b at both ends in the longitudinal direction. The material after vulcanization and before foaming treatment is the material after the vulcanization step S104 and before the pre-vulcanization step S105 in the manufacturing process described with reference to Fig. 5.

In FIG. 10, the numbers other than the reference numerals 209, 209a, and 209b indicate dimensions in mm. The overall length of the test piece 209 is 120 mm, and the gauge length is 80 mm. The width of the parallel portion 209a of the test piece 209 is 10 mm, and the maximum width of each gripping portion 209b is 25 mm.

The test piece 209 was attached to a tensile tester, and a tensile test based on JIS-K6251 was performed. The gripping portions 209b at both ends of the test piece 209 were gripped by a pair of upper and lower chucks (gripping portions) of the tensile tester, and a tensile force was applied in the longitudinal direction. The distance between the chucks of the test piece 209 was 80 mm. The tensile speed of the tensile tester was 500 mm/min.

When a tensile force is applied to the test piece 209 in this manner and the test piece 209 breaks, the elongation of the test piece 209 is defined as the elongation E [%]. More specifically, the elongation E [%] is the ratio of the length of the test piece 209 at break to the length of the test piece 209 before tension, 120 [mm].

The stress at the time of breakage of the test piece 209 measured by the load cell of the tensile tester is defined as stress S [N/mm ² ].

Here, the elongation degree [%/(N/ ^mm2 )] is defined as the value obtained by dividing the elongation percentage E [%] at break of the test piece 209 by the stress S [N/ ^mm2 ] at break. It is considered that the higher the elongation degree, the more easily the conductive foam layer 52 will elongate and deform in the direction of rotation when compressed and rotated, and the lower the elongation degree, the more difficult it is for the conductive foam layer 52 to elongate in the direction of rotation and the more likely it is to break (wear) when deformed.

(Method of measuring rotational stress damping rate)
A method for measuring the rotational stress damping rate of the supply roller 25' will be described with reference to Fig. 11. Fig. 11 is a schematic diagram for explaining the method for measuring the rotational stress damping rate of the supply roller 25'.

The measurement of the rotational stress decay rate of the supply roller 25' was carried out using an Instron compression tester (model: INSTRON 5543A). As shown in FIG. 11, both ends of the core metal 51 of the supply roller 25' are rotatably placed on the rotating support material 201. In this state, the supply roller 25' is rotated at a rotation speed of 200 rpm (circumferential speed of 136.1 mm/sec), and the indenter 205, which is a SUS cylinder with a cross-sectional outer diameter of 16 mm and a length of 50 mm, is pressed into the rotating foam layer 52 to 0.73 mm at a compression speed of 10 mm/min to create a co-rotating state, and this state is maintained for 6 hours.

The rotational stress attenuation rate indicates how much the stress of the supply roller 25' after six hours has attenuated from the initial stress. That is, the rotational stress attenuation rate can be expressed by the following formula.
Rotational stress attenuation rate [%] = (1 - (stress of supply roller 25 after 6H [N]
/ Initial indentation stress [N]) × 100

(Simple friction test method)
A simple abrasion test method for measuring the amount of change in outer diameter and the amount of change in weight of the supply roller 25' will be described with reference to Fig. 12. Fig. 12(a) is a schematic diagram for explaining the simple abrasion test method of the supply roller 25', and Fig. 12(b) is an external perspective view showing the configuration of an indenter 206.

The simple wear test of the supply roller 25' here was carried out using an Instron compression tester (model: INSTRON 5543A). As shown in FIG. 12(a), both ends of the core metal 51 of the supply roller 25' are rotatably placed on the rotating support material 201. In this state, the supply roller 25' is rotated at a rotation speed of 200 rpm, and the indenter 206 is brought into contact with the rotating foam layer 52.

As shown in Fig. 12(b), the indenter 206 has a square surface with sides of 50 mm, and is made of a 10 mm thick SUS metal plate 206a. A lapping (polishing) film (20 mm x 50 mm) 206b with a grain size of 30 μm (#600) is attached to the center of one side of the metal plate. The indenter 206 is pressed into the foam layer 52 of the supply roller 25' rotating at a rotational speed of 200 rpm (circumferential speed of 136.1 mm/sec) at a compression speed of 10 mm/min to a depth of 0.73 mm, and is maintained in this state for 250 seconds.

Figure 13 is a flowchart showing the procedure for measuring the change in outer diameter and weight of the supply roller 25'. First, before starting the simple wear test, the weight of the supply roller 25' (weight w1) is measured (step S201).

Next, the outer diameter of the supply roller 25' (outer diameter d1) was measured (step S202). In addition, the outer diameter was measured at nine points equally spaced in the axial direction in the contact area C (FIG. 12(a)) of the supply roller 25' with the indenter 206, and the average value was calculated. The outer diameter of the supply roller 25' was measured using an automatic roller diameter measuring device "RM202" manufactured by Apollo Seiko Co., Ltd.

Then, as described above, the supply roller 25' is rotated at a rotational speed of 200 [rpm] (circumferential speed 136.1 [mm/sec]), and the indenter 206 is pressed into the conductive foam layer 52 at a pressing speed of 10 [mm/min]. When the pressing amount reaches 0.73 [mm], the supply roller 25' is rotated for 250 seconds while maintaining this state, and the indenter 206 is separated from the conductive foam layer 52 (step S203).

In this state, the outer diameter (outer diameter d2) of the supply roller 25' is measured (step S204), and further the weight (weight w2) of the supply roller 25' is measured (step S205).
The method of measuring the weight and the outer diameter of the supply roller 25' is as described in steps S201 and S202.

The weight change amount (w1-w2) of the supply roller 25' was calculated from the weights w1 and w2 of the supply roller 25 calculated in steps S201 and S205. The weight loss amount of the supply roller 25 reflects the amount of wear of the supply roller 25'.

The amount of change in the outer diameter of the supply roller 25' (d1-d2) was calculated from the outer diameters d1 and d2 of the supply roller 25' calculated in steps S202 and S204. The amount of decrease in the outer diameter of the supply roller 25' reflects the amount of wear of the supply roller 25 and the degree of collapse (sagging) of the cell walls.

(Method of measuring rotational stress ratio)
Next, a method for measuring the rotational stress ratio of the supply roller 25' will be described with reference to Fig. 14. Fig. 14 is a schematic diagram for explaining the method for measuring the rotational stress ratio of the supply roller 25', in which Fig. 14(a) is a diagram for testing an end portion, and Fig. 14(b) is a diagram for testing a central portion.

The measurement of the rotational stress ratio of the supply roller 25' here was carried out using an Instron compression tester (model: INSTRON 5543A). As shown in FIG. 14, both ends of the core metal 51 of the supply roller 25' are rotatably placed on the rotating support material 201. In this state, the supply roller 25' is rotated at a rotation speed of 200 rpm, and the indenter 205, which is a SUS cylinder with a cross-sectional outer diameter of 16 mm and a length of 50 mm, is pressed into the rotating foam layer 52 to a depth of 0.73 mm at a compression speed of 10 mm/min.

When pressing, the position where it contacts the outermost surface of a φ13.0 [mm] metal roller was estimated in advance as the reference height, and the metal indenter 205 was pressed 0.73 [mm] from that reference height into the conductive foam layer 52 of the supply roller 25' to perform the measurement. As shown in Figures 14 (a) and (b), the above measurement was performed at the center and end sides, and the maximum stress (rotational stress) from the rotating supply roller 25' was measured. At this time, the rotational stress ratio (B/A) was calculated by dividing the rotational stress A [N] at the center by the rotational stress B [N] at the end.

In this embodiment, the length of the foam layer 52 in the longitudinal direction is 221.4 mm, and the length of the indenter 205 in the longitudinal direction is 50 mm. Therefore, measurement at the center here corresponds to measuring the center of the foam layer 52 in the longitudinal direction (110.7 mm ± 20 mm from the end) by overlapping the center of the indenter 205 (25 mm from the end), which is arranged in a center-distributed manner.

Next, we will explain the printing test and the test results that served as the basis for setting the elongation of the supply roller 25' to 72.6 [%/N/ ^mm2 ] or more and 81.6 [%/N/ ^mm2 ] or less, the rotational stress damping rate to 27% or more and 31% or less, and the rotational stress ratio to 0.97 or more and 1.23 or less.

Table 1 lists 13 types of supply rollers 25' with different specifications prepared as test samples, Examples 1 to 6 and Comparative Examples 1 to 7, and the evaluation results of printing tests conducted using these rollers.

As shown in the table, the 13 types of supply rollers 25' as test samples in Examples 1 to 6 and Comparative Examples 1 to 7 have different elongation, rotational stress attenuation rates, and rotational stress ratios. Here, we will explain the 13 types of supply rollers 25' as test samples.

The supply roller 25' of Example 1 has an elongation of 81.6 [%/N/ ^mm2 ], a rotational stress attenuation rate of 28 [%], and a rotational stress ratio of 1.23. The foam layer 52 is thicker at the ends than at the center, the amount of wear in the rubber portion is small, the sample is not worn out, and the toner stirring is also good.
The supply roller 25' of Example 2 has an elongation of 72.6 [%/N/ ^mm2 ], a rotational stress attenuation rate of 29 [%], and a rotational stress ratio of 1.23. The foam layer 52 is thicker at the ends than at the center, the amount of wear in the rubber portion is small, the sample is not worn out, and the toner stirring is also good.
The supply roller 25' of Example 3 has an elongation of 81.6 [%/N/ ^mm2 ], a rotational stress attenuation rate of 28 [%], and a rotational stress ratio of 0.97. The foam layer 52 has the same thickness at the center and the ends, and the rubber part is less worn and not worn out.

The supply roller 25' of Example 4 has an elongation of 72.6 [%/N/ ^mm2 ], a rotational stress attenuation rate of 27 [%], and a rotational stress ratio of 1.09. The foam layer 52 is thicker at the ends than at the center, the amount of wear in the rubber portion is small, the sample is not worn out, and the toner stirring is also good.
The supply roller 25' of Example 5 has an elongation of 72.6 [%/N/ ^mm2 ], a rotational stress attenuation rate of 31 [%], and a rotational stress ratio of 0.98. The amount of wear in the rubber portion is small, and the sample is not worn out.
The supply roller 25' of Example 6 has an elongation of 75.6 [%/N/ ^mm2 ], a rotational stress attenuation rate of 31 [%], and a rotational stress ratio of 1.22. The rubber part has little wear and tear, and the sample is not worn out, and also has good toner agitation.

The supply roller 25' of Comparative Example 1 has an elongation of 81.6 [%/N/ ^mm2 ], a rotational stress decay rate of 28 [%], and a rotational stress ratio of 0.90. This sample has little wear in the rubber part and is not worn out, but because the initial stress on the end side is low, the supply performance of this sample decreases when the end side wears over the course of continuous printing.
The supply roller 25' of Comparative Example 2 has an elongation of 87.0 [%/N/ ^mm2 ], a rotational stress decay rate of 33 [%], and a rotational stress ratio of 0.90. Since the elongation is high and the outer diameter change amount in a simple wear test is 0.05 [mm], this is a sample that is prone to settling.
The supply roller 25' of Comparative Example 3 has an elongation of 65.8 [%/N/ ^mm2 ], a rotational stress attenuation rate of 26 [%], and a rotational stress ratio of 1.01. The sample had a large amount of wear in the rubber part, with an outer diameter change of 0.05 [mm] and a weight change of 0.30 [g] in a simple wear test.

The supply roller 25' of Comparative Example 4 has an elongation of 65.8 [%/N/ ^mm2 ], a rotational stress decay rate of 30 [%], and a rotational stress ratio of 1.10. The sample had a large amount of wear in the rubber part, with an outer diameter change of 0.07 [mm] and a weight change of 0.21 [g] in a simple wear test.
The supply roller 25' of Comparative Example 5 has an elongation of 69.4 [%/N/ ^mm2 ], a rotational stress decay rate of 33 [%], and a rotational stress ratio of 1.03. The simple wear test showed a change in outer diameter of 0.06 [mm] and a change in weight of 0.19 [g], indicating that the rubber portion was significantly worn and prone to settling.
The supply roller 25' of Comparative Example 6 has an elongation of 65.8 [%/N/ ^mm2 ], a rotational stress attenuation rate of 24 [%], and a rotational stress ratio of 1.27. The sample had a large amount of wear in the rubber portion, with an outer diameter change of 0.07 [mm] and a weight change of 0.21 [g] in a simple wear test.
The supply roller 25' of Comparative Example 7 has an elongation of 75.6 [%/N/ ^mm2 ], a rotational stress decay rate of 28 [%], and a rotational stress ratio of 0.69. This sample has little wear in the rubber part and is not worn out, but because the initial stress on the end side is low, the supply performance of this sample decreases when the end side wears over the course of continuous printing.

Next, the image evaluation method will be described. The image evaluation of the supply roller 25' here was performed using an image evaluation device (C650dnw, manufactured by OKI Data Corporation) that has the same basic configuration as the printer 1 shown in Figure 1, and the supply roller 25' was attached as a sample. Therefore, the image evaluation device will be described with reference to the printer 1 shown in Figure 1.

The toner used was magenta (M). The toner had a degree of cohesion in the range of 48% to 56% and a blow-off charge of 75 to 80 μC/g. The toner cartridge 3 was pre-filled with approximately 23.0 g ±0.5 g of toner.

To confirm the effect on the smudges caused by insufficient toner supply due to wear of the supply roller 25' over continuous printing, and on the stains caused by insufficient scraping of undeveloped toner, an image evaluation device (printer 1) equipped with the supply roller 25' was operated and a continuous printing test of 50,000 sheets was performed.

The conditions for the continuous printing test are set as follows (1) to (5).
(1) Print speed: A4 portrait 35 [ppm]
(2) Continuous printing volume per day: 2,500 sheets (this will be done for 20 days)
(3) Print pattern: 0.3% (print image density)
(4) Before starting printing of 2,500 sheets and after completing printing, a 2×2 (halftone) pattern and a solid pattern are printed.
(5) Test environment: temperature 20[°C], relative humidity 50[%]

The image evaluation was carried out as follows.
Before and after printing 2,500 sheets, a 2x2 (halftone) pattern and a solid pattern were printed, and the presence or absence of dirt and blur was judged. When the 2x2 pattern was printed, it was judged whether or not excess toner was developed in the area that should not have been printed at the top edge of the paper. When the solid pattern was printed, it was judged whether or not a blank image was generated from the vertical center to the bottom edge of the A4 paper. At this time, partial blanks at the edge were also counted as having occurred.
In the image evaluation, when either one or more of the stains or the blurring occurred during the continuous printing test of 50,000 sheets, it was judged as "X", and when neither occurred, it was judged as "O".

Here, we will explain 2x2 (halftone) pattern printing and print image density. Figure 15(a) is a schematic diagram of an image 150 when 2x2 (halftone) pattern printing is performed over substantially the entire area of recording paper 10, and Figure 15(b) is a partially enlarged view of the same.

As shown in FIG. 15(b), for example, if an area of 1 dot at a resolution of 600 dpi is divided into 16 squares of 4 dots vertically and 4 dots horizontally, a fixing pattern is generated in 4 squares of each divided area, for example, equivalent to 2 x 2 dots in the center.

In terms of print image density, printing with an area ratio of 100% when printing the entire printable area of a specified region (for example, one circumference of a photosensitive drum or one page of recording paper) is called a print image density of 100%, and printing that corresponds to an area of 1% of this print image density of 100% is called a print image density of 1%. In other words, the print image density is expressed by the following formula: Print image density = [Cm(i)/(Cd x C0)] x 100
It is calculated as follows.
Cm(i): the number of dots actually used in printing when the photosensitive drum rotates Cd times, i.e., the number of exposed dots.
C0: the number of dots per rotation of the photosensitive drum, that is, the number of dots that are potentially possible (in printing) per rotation of the photosensitive drum, regardless of whether exposure is performed or not, and is the number of dots used in the case of a solid image.
Cd x C0 is the number of dots that are potentially possible when the photosensitive drum rotates Cd times.

Next, the toner agitation test will be explained. The toner agitation test for the supply roller 25' here was carried out using an image evaluation device (C650dnw, manufactured by OKI Data Corporation) that has the same basic configuration as the printer 1 shown in Figure 1, and was carried out by mounting the supply roller 25' as a sample. Therefore, the explanation will be given with reference to the printer 1 shown in Figure 1 as the image evaluation device.

The entire upper end of the development unit 2 (see Figure 2) equipped with each supply roller 25' was hollowed out, and 2.5 g of cyan (C) toner (5 g in total) was poured into an area 2.5 cm from both ends of the development unit. From there, 27 g of yellow (Y) toner was poured into the area surrounded by the cyan toner (center). After the toner was poured in, vinyl was laid down to prevent toner from leaking from the hollowed out area, and the unit was then mounted on the image evaluation device (printer 1).

The continuous printing conditions are set as follows (1)-(5).
(1) Print speed: A4 portrait 35 [ppm]
(2) Number of continuous prints at one time: 500 sheets in total (3) Print pattern: 0.3 [%] (print image density)
(4) Print 2x2 (halftone) before starting continuous printing and after printing the 100th and 200th sheets.
(5) Test environment: temperature 20[°C], relative humidity 50[%]

The color agitation test is explained below. The color difference ΔE (L*a*b) was measured near the edge of the 2x2 (halftone) printed before the start of continuous printing and on the 200th sheet using an X-Rite 528 colorimeter (X-Rite). The slope between the two points (a, b) before the start of continuous printing and (a, b) on the 200th sheet was calculated as the toner agitation coefficient k. The higher the toner agitation coefficient, the more likely color changes will occur, so the higher the toner agitation coefficient, the higher the toner agitation property of the roller. Therefore, the toner agitation coefficient was used as an index of toner agitation property this time.

16 is a characteristic graph showing the relationship between the toner agitation coefficient k and the rotational stress ratio (B/A). As shown in the graph, the toner agitation coefficient k changes according to the rotational stress ratio (B/A), and in the average of the group with the degree of elongation of 72.6 [%/N/ ^mm2 ] or more and 81.6 [%/N/ ^mm2 ] or less, the rotational stress ratio (B/A) shows a curve that is minimal at 0.97, and the toner agitation coefficient k increases as the ratio increases or decreases from the boundary of 0.97. However, when the rotational stress ratio (B/A) is less than 0.97, unevenness in toner supply occurs as described above.

Moreover, when the rotational stress ratio exceeds 0.97, the toner agitation coefficient k increases with an increase in the rotational stress ratio. Also, from a comparison of the curve shown by the group average for the degree of elongation of 72.6 [%/N/ ^mm2 ] to 81.6 [%/N/ ^mm2 ] and the curve shown by the group average for the degree of elongation of 61.8 [%/N/ ^mm2 ] to 65.8 [%/N/ ^mm2 ] in the figure, it can be seen that the greater the degree of elongation, the higher the toner agitation coefficient k tends to be.

The test results will be explained.
As shown in Table 1, in contrast to Examples 1 to 6, which did not suffer from printing defects, at least one of blurring and smudges occurred in Comparative Examples 1 to 7. From these results, it was found that good image evaluation results can be obtained if the rotational stress ratio is 0.97 to 1.23, the elongation is 72.6 to 81.6 [%/N/mm2], and the rotational stress attenuation rate is 27 to 31% .

The supply roller 25' of Comparative Example 1 had an elongation degree and a rotational stress attenuation rate within the specified range, but the rotational stress ratio was less than 0.97, and partial smearing occurred. This was because wear over time caused the nip width with the developer carrier to decrease at the end compared to the initial state, causing uneven toner supply from the supply roller 25', and preventing sufficient toner from being supplied to the development roller 23.

The degree of elongation, rotational stress attenuation rate, and rotational stress ratio of the supply roller 25' in Comparative Example 2 are all outside the specified ranges. If the degree of elongation exceeds 81.6 [%/N/ ^mm2 ], the supply roller 25' becomes easily worn out when rotated in a state of being nipped with the developing roller 23, and the stress on the developing roller 23 decreases, so that the remaining toner on the developing roller 23 after development cannot be sufficiently scraped off, causing contamination.

The supply roller 25' of Comparative Example 3 has an elongation and a rotational stress attenuation rate outside the specified range. When the elongation is less than 72.6% [%/N/ ^mm2 ], the nip width with the developing roller 23 is reduced due to wear over time caused by contact rotation with the developing roller 23, and the remaining toner on the developing roller 23 after development cannot be sufficiently scraped off, causing stains. Although the rotational stress ratio of Comparative Example 3 is within the specified range, the specification is prone to wear as described above, so the impact of the reduction in nip amount is large, resulting in stains.

The supply roller 25' of Comparative Example 4 has a degree of elongation outside the specified range. When the degree of elongation is less than 72.6 [%/N/ ^mm2 ], as in Comparative Example 3, the nip width with the developing roller 23 is reduced due to wear over time caused by contact rotation with the developing roller 23, and the remaining toner on the developing roller 23 after development cannot be sufficiently scraped off, resulting in staining. In Comparative Example 4, the rotational stress ratio and rotational stress attenuation rate are within the specified range, but since the specifications are prone to wear as described above, the impact of the decrease in nip amount is large, resulting in staining.

The supply roller 25' of Comparative Example 5 has an elongation degree and a rotational stress attenuation rate outside the specified range. When the elongation degree is less than 72.6 [%/N/ ^mm2 ], the nip width with the developing roller 23 decreases due to wear over time caused by contact rotation with the developing roller 23, as in Comparative Example 3. Furthermore, since the rotational stress attenuation rate exceeds 31%, the elasticity of the pressed-in portion of the foam layer 52 is slow to recover, so the toner after undeveloped on the developing roller 23 cannot be sufficiently scraped off, and stains occur. Although the rotational stress ratio of Comparative Example 5 is also within the specified range, the wear and wear are easily caused as described above, so the influence of these two points is large, resulting in stains.

The supply roller 25' of Comparative Example 6 has an elongation less than 72.6 [%/N/ ^mm2 ], a rotational stress attenuation rate of 27% or less, and a rotational stress ratio exceeding 1.23, all of which are outside the specified range. Therefore, not only does contamination occur, but the load on the photosensitive drum 21 also increases. When the rotational stress ratio exceeds 1.23, the pressure on the end side of the supply roller 25' becomes stronger, the torque load on the photosensitive drum 21 increases, and the load on other contact members also increases, adversely affecting the durability of the development unit 2 itself.

The supply roller 25' of Comparative Example 7 had an elongation degree and a rotational stress decay rate within the specified range, but the rotational stress ratio was less than 0.97, and partial smearing occurred. This was because wear over time caused the nip width with the developer carrier to decrease at the end compared to the initial state, causing uneven toner supply from the supply roller 25', and preventing sufficient toner from being supplied to the development roller 23.

Compared to Comparative Examples 1 to 7, the supply rollers 25' of Examples 1 to 6 produced good images with no image defects. Therefore, the supply rollers 25' of Examples 1 to 6 can satisfy the toner scraping and toner supplying properties, and the numerical ranges of the degree of stretch when the supply roller 25' is solid, which is related to the toner scraping properties, the rotational stress attenuation rate of the conductive foam layer 52 of the supply roller 25', and the rotational stress ratio, which is related to the crannyness and toner supplying properties during durability, as well as the amount of change in outer diameter and the amount of change in weight can be set to the numerical ranges described above. Therefore, the supply rollers 25' of Examples 1 to 6 correspond to the supply roller 25 of this embodiment.

As described above, the supply roller 25 of the present embodiment uses silicone rubber for the foam layer 52, and has a solid elongation of 72.6 [%/N/ ^mm2 ] or more and 81.6 [%/N/ ^mm2 ] or less, an outer diameter change in a simple abrasion test of 0.03 mm or less, a weight change of 0.07 g or less, a stress decay rate in the rubber part after 6 hours when the supply roller 25 is NIP rotated of 27% or more and 31% or less, and a rotational stress ratio B/A of the rotational stress (A) at the center to the rotational stress (B) at the end of 0.97% or more and 1.23 or less, thereby making it possible to maintain toner supplying ability and toner scraping ability up to a drum count of 50k and suppress the occurrence of stains and smears.

In addition, by setting the elongation degree to 72.6 [%/N/ ^mm2 ] or more and 81.6 [%/N/ ^mm2 ] or less, the generation of wear powder from the supply roller and the deterioration of image quality caused by uneven supply due to wear of the supply roller cell wall are suppressed, and by setting the rotational stress ratio B/A to 0.97% or more and 1.23 or less, partial blurring is suppressed.

Furthermore, by limiting the change in outer diameter in a simple wear test to 0.03 mm or less, the occurrence of uneven supply due to a large decrease in outer diameter causing the cell walls to lie flat, i.e., the cell walls of the supply roller becoming worn, is suppressed, and partial smearing is suppressed by setting the rotational stress ratio B/A to 0.97% or more and 1.23 or less.

As described above, the development unit of this embodiment can prevent smudges and blurring in printed images.

In the above-described embodiment 1 of the present invention, an example is shown in which the image forming device is used as a color printer, but the present invention is not limited to this, and can also be used in image processing devices such as copiers, facsimiles, and MFPs. Also, although a color printer has been described, a monochrome printer may also be used.

1 printer, 2 developing unit, 3 toner cartridge, 4 transfer roller, 5 exposure unit, 6 paper feed cassette, 7 fixing unit, 7a heating roller, 7b pressure roller, 8 paper transport path, 9 transfer belt, 10 recording paper, 11 drive roller, 12 tension roller, 14 transfer unit, 21 photosensitive drum, 22 charging roller, 23 developing roller, 24 developing blade, 25 supply roller, 27 cleaning blade, 28 first transport section, 29 second transport section, 31 toner storage section, 32 waste toner storage container, 35 toner supply port, 36 transport screw, 37 stirring member, 38 toner storage section, 40 toner 51 core metal, 52 foam layer, 52a foam outer layer, 52b inner layer, 101 Control unit, 101a dot counter, 101b drum counter, 101c calculation unit, 111 I/F control unit, 112 receiving memory, 113 image data editing memory, 114 operation unit, 115 sensor group, 121 charging roller power supply, 122 developing roller power supply, 123 supply roller power supply, 124 transfer roller power supply, 125 fuse power supply, 126 head drive control unit, 127 fixing control unit, 128 transport motor control unit, 129 drive control unit, 130 fast-acting fuse, 131 paper transport motor, 132 drive motor, 201 rotating support material, 205 indenter, 206 indenter, 206a metal plate, 206b wrapping film, 209 test piece, 209a parallel portion, 209b Gripping part.

Claims (6)

a developer carrier that supplies a developer to the electrostatic latent image carrier and develops the latent image on the electrostatic latent image carrier;
a developer supplying member having an outer circumference of φ13 mm, the developer supplying member being disposed so as to contact the developer carrying member and form a nip region, the developer supplying member having an elastic layer made of a conductive foam sponge on a surface thereof, and supplying the developer to the developer carrying member;
a stainless steel indenter having a cross-sectional outer diameter of 16 mm and a length of 50 mm is pressed 0.73 mm into the surface of the end portion and the central portion of the elastic layer in the extending direction of the nip region, the ratio of the stress at the end portion to the stress at the central portion is 0.97 or more and 1.23 or less,
When a polishing film with a grain size of 30 μm was fixed to the surface of a stainless steel indenter having a square surface with sides of 50 mm and a thickness of 10 mm, the polishing film was pressed 0.73 mm into the elastic layer, and the developer supply member was rotated at a peripheral speed of 136.1 mm/sec,
a developer supply member having an outer diameter reduced by 0.03 mm or less when the indenter is released 250 seconds after the indenter has reached a pressing amount of 0.73 mm, compared to the outer diameter of the developer supply member before the indenter is pressed in. a developer carrier that supplies a developer to the electrostatic latent image carrier and develops the latent image on the electrostatic latent image carrier;
a developer supplying member having an outer circumference of φ13 mm, the developer supplying member being disposed so as to contact the developer carrying member and form a nip region, the developer supplying member having an elastic layer made of a conductive foam sponge on a surface thereof, and supplying the developer to the developer carrying member;
a stainless steel indenter having a cross-sectional outer diameter of 16 mm and a length of 50 mm is pressed 0.73 mm into the surface of the end portion and the central portion of the elastic layer in the extending direction of the nip region, the ratio of the stress at the end portion to the stress at the central portion is 0.97 or more and 1.23 or less,
a developing unit characterized in that, when a tensile test of JIS-K6251 is conducted using a dumbbell-shaped test piece formed from the material before the foaming treatment after the elastic layer has been vulcanized, the value obtained by dividing the elongation percentage ([%]) at the time the test piece breaks by the stress ([N/mm2]) at that time is 72.6 [%/N/mm2] or more and 81.6 [%/N/mm2] or less. The developing unit according to claim 1 or 2, characterized in that the developer supply member has an inverted crown shape. The developing unit according to any one of claims 1 to 3, characterized in that the developer supply member is mainly composed of silicone. The developing unit according to any one of claims 1 to 4, characterized in that the Asker F hardness of the elastic layer is 40 or more and 46 or less. A developing unit according to any one of claims 1 to 5;
a transfer unit that transfers the developer image formed on the electrostatic latent image carrier onto a medium;
a fixing unit that fixes the developer image transferred to the medium onto the medium.

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