JP6171815B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Conventionally, a charging member made of a single-layer conductive foam having a low hardness and a restoring force that does not cause image defects in order to widen a nip portion with an object to be charged has been known ( Patent Document 1). An image forming apparatus having a conductive roller including a conductive shaft and a conductive elastic layer provided on the outer periphery of the shaft is known (see Patent Document 2).

JP 2006-154441 A

JP 2003-195601 A

  An object of the present invention is to provide an image forming apparatus capable of suppressing an increase in volume resistance value of a transfer member.

In order to achieve the above object, an image forming apparatus according to claim 1 is provided with a transfer member having a conductive core shaft to which a positive voltage is applied and an ion conductive material wound around the core shaft, and facing the transfer member. And a contact area between the ion conductive material and the counter member is larger than a half of a contact area between the core shaft and the ion conductive material.

  2. The image forming apparatus according to claim 1, wherein the diameter of the core shaft is D, and the nip width between the ion conductive material and the opposing member is W, in the image forming apparatus according to claim 1. And the said opposing member is comprised so that the relationship of (pi) D <2 <W may be satisfy | filled.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, further comprising a load member that applies a constant load to a central portion in a longitudinal axis direction of the transfer member.

The image forming apparatus according to claim 4, in the image forming apparatus according to any one of claims 1 to 3, before Symbol transfer member is characterized in that onto a recording medium negatively charged toner image.

  According to the first aspect of the present invention, an increase in the volume resistance value of the transfer member can be suppressed.

  According to the invention of claim 2, an increase in the volume resistance value of the transfer member can be suppressed.

  According to the invention of claim 3, it is possible to prevent unevenness of the transferred image due to the deflection of the transfer member.

  According to the invention of claim 4, it is possible to suppress an increase in volume resistance value of the transfer member to which a positive voltage is applied.

1A is a configuration diagram of an image forming apparatus according to the present embodiment. FIG. 2B is a schematic configuration diagram of a photosensitive drum, a transfer roller, and a load roller. (A) And (B) is a schematic diagram of the apparatus used in Experiment 1. FIG. 6 is a graph showing an experimental result of Experiment 1. (A) And (B) is a schematic diagram of the apparatus used in Experiment 2. FIG. (C) is a figure which shows the method of measuring the volume resistance value of rubber | gum. 10 is a graph showing an experimental result of Experiment 2. It is an enlarged view of a transfer roller and a photosensitive drum. (A)-(C) is a figure showing composition of a transfer device. It is a graph which shows the verification result of a comparative example, and the verification result of Example 1. FIG. It is a graph which shows the verification result of Example 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1A is a configuration diagram of an image forming apparatus according to the present embodiment.

  The image forming apparatus 1 in FIG. 1A is, for example, a printer, but may be a copier or a multifunction machine. The image forming apparatus 1 includes a photosensitive drum 10 as an image carrier, a charging roller 11 that uniformly charges the surface of the photosensitive drum 10, and an exposure device 12 that forms an electrostatic latent image on the photosensitive drum 10. A developing device 13 for forming a toner image corresponding to the electrostatic latent image, a transfer roller 14 as a transfer member for transferring the toner image to a recording medium and conveying the recording medium, and a longitudinal axis of the transfer roller 14 A load roller 15 as a load member for applying a constant force to the central portion in the direction, a transfer bias power source (that is, a DC power source) 16 for supplying a transfer current to the shaft of the transfer roller 14, and a toner image on the recording medium. A heating roller 17 and a pressure roller 18 for fixing to a recording medium are provided. The recording medium in FIG. The photosensitive drum 10 is rotationally driven in the arrow A direction, and the sheet S on which the toner image is formed is conveyed in the arrow B direction. The toner image is negatively charged.

  Here, the image forming apparatus 1 is a direct transfer type, but may be an intermediate transfer type image forming apparatus. In the direct transfer type image forming apparatus 1, the opposing member of the transfer roller 14 is the photosensitive drum 10, but in the intermediate transfer type image forming apparatus, the opposing member of the transfer roller is a transfer belt or a backup roller. .

  FIG. 1B is a schematic configuration diagram of a photosensitive drum, a transfer roller, and a load roller.

  The transfer roller 14 is a cylindrical transfer roller, and includes a metal core shaft 141 and a semiconductive (that is, ionic conductive) urethane foam 142 having a volume resistance value of 6.0 to 8.0 LogΩ. Has been. The urethane foam 142 as an ionic conductive material is wound around the core shaft 141. The urethane foam 142 is a deformable elastic layer.

  The load roller 15 is disposed at a position facing the central portion of the transfer roller 14 in the longitudinal axis direction, and at a position opposite to the photosensitive drum 10 via the transfer roller 14. When the transfer roller 14 is pressed against the photosensitive drum 10, a load is applied to both ends of the core shaft 141, so that the transfer roller 14 bends and an appropriate load is not applied to the central portion in the longitudinal axis direction of the transfer roller 14. This causes unevenness of the transferred image. Therefore, the load roller 15 loads the central portion of the transfer roller 14 in the longitudinal axis direction to the photosensitive drum 10 side with a constant force in order to prevent unevenness of the transfer image.

  By the way, the volume resistance value of the ionic conductive urethane foam 142 increases with time due to the current supply from the transfer bias power source. This is a cause of transfer failure, and is a determinant of the life of the transfer roller.

  In view of this, the present inventor first conducted several experiments in order to find out a factor for increasing the volume resistance value of the transfer roller. Hereinafter, this experiment will be described.

  <Experiment 1> In Experiment 1, the inventor examined the amount of increase in the volume resistance value of the transfer roller caused by the difference in voltage application direction. The laboratory temperature was 22 ° C. and the humidity was 55%.

  2A and 2B are schematic views of the apparatus used in Experiment 1. FIG. This apparatus includes a transfer roller 20, a counter roller 21, a power source 22, and an ammeter 23.

  The transfer roller 20 includes a core shaft 201 and foamed rubber 202. The foam rubber 202 is composed of a mixture of nitrile rubber (NBR), epichlorohydrin rubber (ECO) and an ionic conductive agent. The Asker C hardness of the foam rubber 202 is 35 °. The foam rubber 202 has a diameter Φ of 10 mm and a length of 220 mm. The core shaft 201 is lead-free steel subjected to electroless Ni plating. The diameter Φ of the core shaft 201 is 5 mm and the length is 240 mm.

  The counter roller 21 is a metal pipe made of aluminum (Al) having a diameter Φ of 50 mm. The facing roller 21 is in contact with the transfer roller 20. The counter roller 21 is rotated by a motor (not shown), and the transfer roller 20 is rotated along with the rotation of the counter roller 21. A general-purpose high-voltage power supply (Trek 610) was used as the power supply 22. As the ammeter 23, a digital ammeter (8340A manufactured by ADC) was used.

  In FIG. 2A, the power source 22 applied a positive voltage of 1000 V to the core shaft 201 of the transfer roller 20 continuously for 120 minutes. In FIG. 2B, the power supply 22 applied a negative voltage of 1000 V to the core shaft 201 of the transfer roller 20 continuously for 120 minutes. The ammeter 23 read the current value once per minute, and converted the current value into a resistance value (LogΩ). The transfer roller 20 and the counter roller 21 were continuously rotated for 120 minutes during the experiment. The rotational speed is 60 revolutions per minute.

  FIG. 3 is a graph showing the experimental results of Experiment 1. The vertical axis in FIG. 3 indicates the volume resistance value (LogΩ) of the transfer roller 20, and the horizontal axis indicates the energization time.

  3 indicates a volume resistance value of the transfer roller 20 when the power source 22 applies a positive voltage of 1000 V to the core shaft 201 (see FIG. 2A), and reference numeral 102 indicates the power source 22 is the core shaft. A volume resistance value of the transfer roller 20 when a negative voltage of 1000 V is applied to 201 is shown (see FIG. 2B).

  From this experimental result, the amount of increase in the resistance of the foam rubber 202 of the transfer roller 20 varies depending on the direction of voltage application. Compared with the case where a positive voltage is applied to the core shaft 201, the foam rubber 202 is applied when a negative voltage is applied to the core shaft 201. It can be seen that the increase in resistance can be suppressed.

  Here, foamed rubber composed of nitrile rubber (NBR), epichlorohydrin rubber (ECO) and an ionic conductive agent is used. However, these rubber materials do not limit the present invention, and ionic conductivity is not limited. The same results are shown for rubber materials showing. For example, even when an elastic body composed of urethane and an ionic conductive agent is used, an experimental result showing the same tendency as described above can be obtained.

  <Experiment 2> In Experiment 2, the present inventor examined the amount of increase in the volume resistance value of rubber caused by the difference in the size of the electrode area. The laboratory temperature was 22 ° C. and the humidity was 55%.

  4A and 4B are schematic views of the apparatus used in Experiment 2. FIG. This apparatus includes an ion conductive rubber 30, electrodes 31 and 32, a power source 22, and an ammeter 23. The specifications of the power source 22 and the ammeter 23 are as described above.

  The electrode 31 is made of metal (aluminum). The electrode 31 has a length of 40 mm and a width of 20 mm. The electrode 32 is made of metal (aluminum). The electrode 32 has a length of 40 mm and a width of 10 mm.

  The rubber 30 is composed of a mixture of nitrile rubber (NBR), epichlorohydrin rubber (ECO) and an ionic conductive agent. However, the rubber 30 is not foamed. The rubber 30 has a length of 40 mm, a width of 40 mm, and a thickness of 2 mm.

  First, as shown in FIG. 4C, the inventor creates a rubber sheet of 40 mm (length) × 80 mm (width) × 2 mm (thickness), and divides the rubber sheet to obtain 2 A sheet of rubber 30 was prepared. And this inventor changes the volume resistance value of rubber | gum 30 twice by changing the application direction of a voltage as shown in FIG.4 (C) by arrangement | positioning of the electrodes 31 and 32 shown in FIG.4 (A). The volume resistance value of the rubber 30 was measured twice by changing the voltage application direction as shown in FIG. 4C with the arrangement of the electrodes 31 and 32 shown in FIG. 4B.

  In FIG. 4A, the power source 22 applied a positive voltage of 1000 V to the electrode 31 continuously for 15 minutes. In FIG. 4B, the power source 22 applied a positive voltage of 1000 V to the electrode 32 continuously for 15 minutes. The ammeter 23 read the current value once every 2 seconds, and converted the current value into a resistance value (LogΩ).

  FIG. 5 is a graph showing the experimental results of Experiment 2. The vertical axis in FIG. 5 indicates the amount of increase (LogΩ) in the volume resistance value of the rubber 30, and the horizontal axis indicates the energization time.

  Reference numeral 103 in FIG. 5 indicates the amount of increase in the volume resistance value of the rubber 30 when the power supply 22 applies a positive voltage of 1000 V to the electrode 31 and the surface of the rubber 30 is in contact with the electrode 31. Reference numeral 104 indicates an increase in the volume resistance value of the rubber 30 when the power source 22 applies a positive voltage of 1000 V to the electrode 31 and the back surface of the rubber 30 is in contact with the electrode 31. Reference numeral 105 indicates the amount of increase in the volume resistance value of the rubber 30 when the power source 22 applies a positive voltage of 1000 V to the electrode 32 and the surface of the rubber 30 is in contact with the electrode 31. Reference numeral 106 indicates an increase in the volume resistance value of the rubber 30 when the power source 22 applies a positive voltage of 1000 V to the electrode 32 and the back surface of the rubber 30 is in contact with the electrode 31.

  From this experimental result, it can be seen that the resistance increase amount of the rubber 30 varies depending on the relationship between the positive and negative electrode areas, and that the resistance increase amount of the rubber 30 can be suppressed when the area of the negative electrode is larger than the area of the positive electrode (reference numeral 105). , 106 graph).

  Here, foamed rubber composed of nitrile rubber (NBR), epichlorohydrin rubber (ECO) and an ionic conductive agent is used. However, these rubber materials do not limit the present invention, and ionic conductivity is not limited. The same results are shown for rubber materials showing. For example, even when an elastic body composed of urethane and an ionic conductive agent is used, an experimental result showing the same tendency as described above can be obtained.

  Based on the results of Experiment 1 and Experiment 2, the present inventor found that when ions (charges) flow through the foamed rubber 202, the contact area between the core shaft 201 of the transfer roller 20 and the foamed rubber 202 is half (that is, the opposing roller). If the contact area between the foam rubber 202 and the counter roller 21 is smaller than the contact area of the portion facing the roller 21, the cation is unevenly distributed inside the foam rubber 202 near the counter roller 21, and the volume resistance of the foam rubber 202 is reduced. The value was estimated to rise.

  Accordingly, the present inventor has devised an image forming apparatus capable of suppressing an increase in the volume resistance value of the transfer roller based on this estimation.

  Specifically, in the image forming apparatus 1, as shown in FIG. 6, a photosensitive body corresponding to half S1 of the contact area between the core shaft 141 of the transfer roller 14 and the urethane foam 142 (that is, corresponding to a half circumference of the core shaft 141). An increase in the volume resistance value of the transfer roller 14 is suppressed by increasing the contact area S2 between the urethane foam 142 and the photosensitive drum 10 than the contact area of the portion facing the drum 10. In other words, when the diameter of the core shaft 141 of the transfer roller 14 is D and the transfer nip width is W, the transfer roller 14 and the photosensitive drum 10 are configured to satisfy the relationship of W> πD / 2. As a result, an increase in the volume resistance value of the transfer roller 14 is suppressed.

  Hereinafter, an example in which suppression of an increase in the volume resistance value of the transfer roller 14 is verified and a comparative example will be described. The laboratory temperature used for verification was 22 ° C. and the humidity was 55%.

<Comparative example>
(1) First, as shown in FIG. 7A, the present inventor created a transfer roller 41 having a core shaft 441 and a single-layer foamed urethane 442. The core shaft 441 is a metal shaft having a diameter Φ of 15 mm and a length of 80 mm. The Asker C hardness of the single layer urethane foam 442 is 12 °. Single-layer urethane foam 442 was mixed with quaternary ammonium perchlorine as a conductive agent, and its volume resistance value was controlled to 7.8 LogΩ. Moreover, the diameter Φ of the single layer urethane foam 442 was 30 mm, and the length was 50 mm.

  (2) The inventor used a facing roller 40 having a diameter Φ of 80 mm and formed of a metal pipe as the facing member of the transfer roller 41. In the transfer apparatus 100 as shown in FIG. 7A, the transfer roller 41 and the counter roller 40 were installed so that the nip width between the transfer roller 41 and the counter roller 40 was 5 mm. A load of 0.3 kgf is applied to both ends of the transfer roller 41 in the longitudinal axis direction, and the transfer roller 41 presses the opposing roller 40. The power source 22 and the ammeter 23 are the same as those used in Experiment 1 and Experiment 2.

  (3) Next, a motor (not shown) rotated the counter roller 40 at 50 revolutions per minute. The transfer roller 41 rotates with the rotation of the opposing roller 40. The power supply 22 applied a voltage of 1900 V so that a current of 30 μA flows through the transfer device 100. Thereafter, a voltage of 1900 V was continuously applied for 25 hours under constant voltage control. The ammeter 23 read the current value once every 10 minutes and converted the current value into a resistance value (LogΩ). For 25 hours during verification, the transfer roller 41 and the counter roller 40 continuously rotated.

  FIG. 8 is a graph showing the verification result of the comparative example and the verification result of Example 1 described later. The vertical axis in FIG. 8 represents the volume resistance value (LogΩ) of the transfer roller 41, and the horizontal axis represents the energization time.

  The current value 25 hours after the start of verification was 8 μA, and the volume resistance value was 8.4 LogΩ.

<Example 1>
(1) First, the present inventor created a transfer roller 14 including a core shaft 141 and a single layer urethane foam 142 as shown in FIG. The core shaft 141 is a metal shaft having a diameter Φ of 4 mm and a length of 80 mm. The Asker C hardness of the single layer urethane foam 142 is 12 °. Single-layer foamed urethane 142 was mixed with quaternary ammonium perchlorine as a conductive agent, and its volume resistance value was controlled to 7.8 LogΩ. Moreover, the diameter Φ of the single-layer foamed urethane 142 was 30 mm, and the length was 50 mm.

  (2) The present inventor used a counter roller 40 having a diameter Φ of 80 mm and made of a metal pipe as the counter member of the transfer roller 14. In the transfer apparatus 100 as shown in FIG. 7B, the transfer roller 14 and the counter roller 40 were installed so that the nip width between the transfer roller 14 and the counter roller 40 was 12 mm. A load of 2.2 kgf is applied to both ends of the transfer roller 14 in the longitudinal axis direction, and the transfer roller 14 presses the opposing roller 40. The power source 22 and the ammeter 23 are the same as those used in Experiment 1 and Experiment 2.

  (3) Next, a motor (not shown) rotated the counter roller 40 at 50 revolutions per minute. The transfer roller 14 rotates with the rotation of the counter roller 40. The power supply 22 applied a voltage of 1900 V so that a current of 30 μA flows through the transfer device 100. Thereafter, a voltage of 1900 V was continuously applied for 25 hours under constant voltage control. The ammeter 23 read the current value once every 10 minutes and converted the current value into a resistance value (LogΩ). For 25 hours during verification, the transfer roller 14 and the counter roller 40 continuously rotated.

  The current value 25 hours after the start of verification was 26 μA, and the volume resistance value was 7.9 LogΩ as shown in FIG.

  From the verification result of FIG. 8, the urethane foam and the counter roller are more than half the contact area between the core shaft of the transfer roller and the urethane foam (that is, the contact area of the portion facing the counter roller corresponding to the half circumference of the core shaft). It has been clarified that the increase in the volume resistance value of the transfer roller is suppressed by increasing the contact area.

<Example 2>
In the comparative example and Example 1, the transfer rollers 41 and 14 and the opposing roller 40 were small in size. In Example 2, the transfer roller and the counter roller were made large (that is, the actual product size). Hereinafter, only the changes from the first embodiment will be described.

  (1) The length of the core shaft 141 was 350 mm, and the length of the single layer urethane foam 142 was 310 mm. Moreover, the volume resistance value of the single layer urethane foam 142 was controlled to 7.0 LogΩ.

  (2) Further, as shown in FIG. 7C, the load roller 15 applied the central portion in the longitudinal axis direction of the transfer roller 14 to the counter roller 40 side with a constant force (4 kgf). The diameter Φ of the load roller 15 was 20 mm, and the length was 100 mm.

  (3) The power source 22 applied a voltage of 500 V so that a current of 50 μA flows through the transfer apparatus 100. Thereafter, a voltage of 500 V was continuously applied for 25 hours under constant voltage control. Other verification conditions are the same as those in the first embodiment.

  The current value 25 hours after the start of verification was 46 μA, and as shown in FIG. 9, the volume resistance value of the transfer roller 14 was about 7.0 LogΩ. That is, even after 25 hours from the start of verification, the volume resistance value of the transfer roller 14 hardly changed.

  From the verification result of FIG. 9, the urethane foam and the counter roller are more than half the contact area between the core shaft of the transfer roller and the urethane foam (that is, the contact area of the portion facing the counter roller corresponding to the half circumference of the core shaft). It has been clarified that the increase in the volume resistance value of the transfer roller is suppressed by increasing the contact area.

  As described above, according to the present embodiment, the image forming apparatus 1 is opposed to the transfer roller 14 having the conductive core shaft 141 and the urethane foam 142 wound around the core shaft 141, and the transfer roller 14. The contact area between the urethane foam 142 and the photoreceptor drum 10 is half the contact area between the core shaft 141 and the urethane foam 142. Is also big. Accordingly, an increase in the volume resistance value of the transfer roller 14 is suppressed.

  Note that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Photosensitive drum 11 Charging roller 12 Exposure apparatus 13 Developer 14 Transfer roller 15 Load roller 16 Transfer bias power supply 17 Heating roller 18 Pressure roller 141 Core shaft 142 Foam urethane

Claims (4)

A transfer member having a conductive core shaft to which a positive voltage is applied and an ionic conductive material wound around the core shaft;
A counter member disposed to face the transfer member,
An image forming apparatus, wherein a contact area between the ion conductive material and the facing member is larger than half of a contact area between the core shaft and the ion conductive material.   When the diameter of the core shaft is D and the nip width between the ion conductive material and the facing member is W, the transfer member and the facing member are configured to satisfy the relationship of πD / 2 <W. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, further comprising a load member that applies a constant load to a central portion in a longitudinal axis direction of the transfer member. Before SL transfer member The image forming apparatus according to any one of claims 1 to 3, characterized in that onto a recording medium negatively charged toner image.

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