JP5184169B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic system.

  In recent years, image forming apparatuses such as facsimiles and copiers are used to prevent paper from being wound around rollers due to diversification of paper (for example, recycled paper, double-sided printing of paper, paper thickness, paper size) Separation performance at the transfer section has become strict. In this case, either a grounded static elimination needle or a discharge needle to which a high voltage is applied is usually used for separation at the transfer portion (see Patent Document 1 and Patent Document 2).

JP-A-8-202170 JP-A-7-104585

  However, when a discharge needle to which a high voltage is applied is used, a high-voltage transfer bias flows into the fixing roller at a high current through the sheet in a high humidity environment (the sheet has a high water content and the sheet resistance value is low). As a result, the fixing roller is charged to the same polarity as the transfer bias (toner and the opposite polarity), causing problems such as tailing and electrostatic offset at the fixing unit. Here, the tailing in the fixing unit is a state in which when an unfixed image such as a thin line is fixed by the fixing unit, the toner on the unfixed paper is pulled by the fixing roller and the image flows. The electrostatic offset is a phenomenon in which when the fixing unit fixes, unfixed toner remains on the fixing roller, and when the fixing roller rotates for the second time, the toner moves to the sheet.

  In addition, when the grounded static elimination needle is used, the charging of the sheet becomes high because the transfer bias is a high current and a high voltage. Therefore, the sheet has a strong electric attractive force with the photosensitive drum, and a separation failure is likely to occur at the transfer portion. In particular, when double-sided printing or a low-humidity environment (the water content of the paper is low and the resistance value of the paper is high), the separation failure is remarkable.

  In addition, the adhesion between paper and toner may decrease due to a decrease in toner charge due to high humidity environment or long-term use, or transfer roller deterioration due to long-term use (increased material resistance, paper dust If there is variation in the charging of the paper due to the attachment of the toner or external toner additives, the paper suddenly passes when it passes or contacts the vicinity of the sheet metal (GND) of the transport section in the transport section after the paper is separated or discharged. Is removed, the adhesion between the paper and the toner is reduced, and the toner is scattered, resulting in an image defect. Further, in the rib (insulation) of the conveyance unit, the sheet is abnormally charged due to the contact between the sheet and the rib, and the scattered image is generated by repelling the toner. For these toner scattering, it is desirable to neutralize with GND instead of separation bias OFF (0V). However, a complicated switching circuit is required at a high cost, and separation failure occurs as described above. To do.

  Therefore, the main object of the present invention is to improve the separation performance in the transfer unit, suppress the generation of scattered images in the transport unit after separating and discharging the paper, and further, tailing in the fixing unit, electrostatic offset, etc. It is an object of the present invention to provide an image forming apparatus in which no occurrence occurs.

The invention according to claim 1,
A discharge needle that is disposed downstream of a transfer unit that transfers the developed image on the surface of the image carrier to a sheet, and applies a separation bias to the conveyed sheet;
A static elimination needle disposed downstream of the discharge needle and neutralizing the conveyed paper ,
The static elimination needle is provided in the vicinity of the paper conveyance path so that the tip of the static elimination needle is downstream of the paper conveyance path and the root of the static elimination needle is upstream of the paper conveyance path. The tip is closer to the paper transport path than the base,
The distance between the tip of the discharge needle and the tip of the static elimination needle is greater than the distance between the surface of the image carrier and the tip of the discharge needle,
The discharge needle array pitch is smaller than the discharge needle array pitch,
An image forming apparatus characterized by the above.

  In the conventional case using only a discharge needle to which a high voltage is applied, in a high humidity environment (the paper contains a lot of water and the paper resistance is low), a high voltage transfer bias flows into the fixing roller through the paper at a high current. The fixing roller is charged to the same polarity as the transfer bias (the opposite polarity to the toner), causing problems such as tailing and electrostatic offset at the fixing portion. In the first aspect of the invention, since the static elimination needle is disposed downstream of the discharge needle, a high current and high voltage transfer bias flows to the GND through the static elimination needle. Therefore, a high-current, high-voltage transfer bias does not flow into the fixing roller through the paper, and the fixing roller is not charged with the same polarity (toner and opposite polarity) as the transfer bias. Does not occur.

  Further, the charge of the paper becomes substantially “0” by the grounded static elimination needle, and even if the paper passes or contacts the vicinity of the sheet metal (GND) of the transport unit, the phenomenon that the charge of the paper is suddenly reduced is eliminated. Scattered images caused by a decrease in toner adhesion can be prevented. Further, in the rib (insulation) of the conveying unit, the phenomenon that the paper is abnormally charged due to the contact between the paper and the rib and the scattered image is generated by repelling the toner is eliminated.

  In addition, in the conventional case using only a grounded static elimination needle, the transfer bias is high and the voltage is high, so the sheet is charged, and the sheet has a strong electric adsorption force with the image carrier, It was easy for separation failure to occur. In the first aspect of the invention, since the discharge needle is disposed upstream of the static elimination needle, the paper is easily separated from the image carrier by charging the paper to the same polarity as the image carrier by the discharge needle. .

In addition, since the distance between the tip of the discharge needle and the tip of the static elimination needle is set larger than the distance between the surface of the image carrier and the tip of the discharge needle, leakage between the discharge needle and the static elimination needle can be suppressed. Discharge is performed efficiently.
Moreover, since the arrangement pitch of the static elimination needles is set smaller than the arrangement pitch of the discharge needles, the static elimination effect is further enhanced.

In addition, the static elimination needle is provided in the vicinity of the paper conveyance path, the tip of the static elimination needle is provided on the downstream side of the paper conveyance path, and the root of the static elimination needle is provided on the upstream side of the paper conveyance path. By setting the tip to be closer to the paper transport path than the base of the needle, the tip of the static elimination needle is directed to the paper, so the static elimination electric field from the static elimination needle is efficiently directed to the paper. The static elimination effect is increased.
Further, the invention according to claim 2 is an invention dependent on the invention according to claim 1, wherein the discharge needle is disposed to be inclined toward the image carrier with respect to the normal direction of the sheet conveyance path extending from the transfer portion. In the image forming apparatus, the static elimination needle is arranged to be inclined to the opposite side of the discharge needle with respect to the normal direction.
In the invention of claim 2, since the tip of the discharge needle is directed to the image carrier, the discharge electric field from the discharge needle is efficiently directed to the image carrier, and the discharge effect is enhanced.

  According to the present invention, since the static elimination needle is disposed downstream of the discharge needle, the discharge electric field from the discharge needle is directed to the image bearing member, and the static elimination electric field from the static elimination needle is directed to the paper, In addition, it is possible to improve the separation performance of the image forming apparatus, suppress the generation of scattered images in the transport unit after separating and discharging the paper, and obtain an image forming apparatus that does not generate tailing and electrostatic offset in the fixing unit.

  The above-described object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a main part showing an example of an image forming apparatus according to the present invention. The photosensitive drum (image carrier) 2 is driven at a predetermined speed in a clockwise direction indicated by an arrow in the figure by a driving unit. In the vicinity of the outer periphery of the photosensitive drum 2, a charger 4, a developing device 6, a transfer roller 8, and a cleaning device 10 are provided. The surface of the photosensitive drum 2 is uniformly charged by a charger 4 with a positive bias. A laser scanning unit 12 is disposed on the downstream side of the charger 4 in the rotation direction of the photosensitive drum 2. Laser light L emitted from the laser scanning unit 12 is irradiated onto the photosensitive drum 2 to form an electrostatic latent image.

  A developing device 6 is disposed on the downstream side of the laser scanning unit 12. The developing device 6 is for applying toner to the photosensitive drum 2 by the developing roller 7. The electrostatic latent image is developed by the developing device 6 and visualized as a toner image. A transfer roller 8 is disposed on the downstream side of the developing device 6. A transfer voltage (negative bias) is applied to the transfer roller 8. Further, a cleaning device 10 for removing the toner remaining on the photosensitive drum 2 is disposed on the downstream side of the transfer roller 8.

  In synchronization with the toner image on the photosensitive drum 2 approaching the transfer roller 8, the conveyance timing of the paper P is adjusted and conveyed between the photosensitive drum 2 and the transfer roller 8. As a result, the leading edge of the paper P and the leading edge of the toner image coincide with each other and pass through the transfer roller 8, and the toner image formed on the photosensitive drum 2 is transferred to the paper P. The sheet P to which the toner image has been transferred is separated from the photosensitive drum 2 by the discharge needle 40 and discharged by the charge removal needle 42. Thereafter, the paper P passes through the conveyance unit 50 and is carried into the fixing roller 60, fixed by the fixing roller 60, discharged as a printed matter outside the apparatus, and stacked on a paper discharge tray.

  The discharge needle 40 and the static elimination needle 42 will be described in more detail with reference to FIGS. Here, FIG. 2 is a perspective view showing the discharge needle 40 and the static elimination needle 42, and FIG. 3 is a schematic configuration diagram showing the arrangement relationship thereof.

  A discharge needle 40 for applying a separation bias to the conveyed paper P is disposed downstream of the transfer roller 8. That is, the sheet P conveyed from the transfer roller 8 is in a state of being negatively charged by the transfer bias, and thus is easily wound around the roller. For this reason, a separation voltage (positive bias) is applied from the discharge needle 40 to cancel the negative charge. Since the discharge needle 40 is arranged substantially vertically so that the tip of the discharge needle 40 is directed to the photosensitive drum 2, the discharge electric field E1 from the discharge needle 40 is efficiently directed to the photosensitive drum 2, and the discharge is performed. The effect can be enhanced.

  A grounded static elimination needle 42 is disposed downstream of the discharge needle 40 to neutralize the conveyed paper P. As shown in FIG. 5, the static elimination needle 42 is arranged substantially horizontally, the static elimination needle 42 is in the vicinity of the paper conveyance path R, the tip of the static elimination needle 42 is on the downstream side of the paper conveyance path R, and the static elimination needle 42. Is set so that the root portion is located upstream of the sheet conveyance path R, and the tip end portion is closer to the sheet conveyance path R than the root portion of the static elimination needle 42. That is, it is desirable that the direction of the tip of the static elimination needle 42 is directed to the opposite side of the discharge needle 40 from the normal line H of the paper transport path R because it is easy to prevent the discharge needle 40 and the static elimination needle 42 from leaking. Further, the direction of the tip of the static elimination needle 42 is not parallel to the paper conveyance path R, and the tip of the static elimination needle 42 is directed to the paper P. Therefore, the static elimination electric field E2 from the static elimination needle 42 is efficiently generated on the paper. It can be directed to P, and its charge removal effect can be enhanced.

  The distance b between the tip of the discharge needle 40 and the tip of the static elimination needle 42 is set to be larger than the distance a between the surface of the photosensitive drum 2 and the tip of the discharge needle 40. Since the distance b is set to be larger than the distance a, leakage between the discharge needle 40 and the static elimination needle 42 can be suppressed, and discharge can be performed efficiently. The distance between the paper transport path R and the tip of the discharge needle 40 is set to about 1 mm. This is because if it is smaller than 1 mm, no discharge occurs.

  Furthermore, as shown in FIG. 4, the arrangement pitch of the static elimination needles 42 is set smaller than the arrangement pitch of the discharge needles 40. 2A is a partial front view showing the static elimination needle 42, and FIG. 2B is a partial front view showing the discharge needle 40. FIG. Thereby, the static elimination effect of the static elimination needle 42 further increases.

  Here, in the conventional case using only the discharge needle to which a high voltage is applied, in a high humidity environment (the water content of the paper P is high and the resistance value of the paper P is low), a high current is supplied to the fixing roller 60 through the paper P. A high-voltage transfer bias flows and the fixing roller 60 is charged to the same polarity as the transfer bias (toner and opposite polarity), causing problems of tailing and electrostatic offset at the fixing unit. However, in the image forming apparatus of the present embodiment, since the static elimination needle 42 is disposed downstream of the discharge needle 40, a high current and high voltage transfer bias flows to the GND through the static elimination needle 42. Therefore, a high current and high voltage transfer bias does not flow into the fixing roller 60 through the paper P, and the fixing roller 60 is not charged to the same polarity as the transfer bias (toner and opposite polarity). No electrostatic offset occurs.

  Further, the charge of the paper P becomes substantially “0” by the grounded static elimination needle 42, and even if the paper P passes or contacts the vicinity of the sheet metal (GND) of the transport unit 50, the charge of the paper P rapidly decreases. The scattered image caused by a decrease in the adhesion between the paper P and the toner can be prevented. Further, in the rib (insulation) of the conveyance unit 50, the phenomenon that the paper P is abnormally charged due to the contact between the paper P and the rib and the scattered image is generated by repelling the toner is eliminated.

  In the conventional case using only the grounded static elimination needle 42, the transfer bias is high and the voltage is high, so that the sheet charge is high, and the sheet P has a strong electric adsorption force with the photosensitive drum 2, and the transfer is strong. It was easy for separation failure at the part to occur. However, in the image forming apparatus of the present embodiment, since the discharge needle 40 is disposed upstream of the static elimination needle 42, the paper P is charged to the same polarity as the photosensitive drum 2 by the discharge needle 40, so that the paper P Can be easily separated from the photosensitive drum 2.

  Next, Table 1 shows the evaluation result of the scattered image when the paper P passes or contacts the vicinity of the sheet metal (GND) of the transport unit 50 based on the presence / absence of the discharge needle 40 and the static elimination needle 42. The toner charge at this time was set to 3.5 to 4.0 μc / g for high humidity (humidity: 70%) and 4.0 to 4.5 μc / g for low humidity (humidity: 20%). .

  Comparative Example 1 and Comparative Example 2 are cases where the transfer roller 8 is new and does not include the static elimination needle 42. In this case, a scattered image on the sheet metal (GND) of the transport unit 50 does not occur. Comparative Example 3 and Comparative Example 4 are cases where the transfer roller 8 is old (the transfer roller 8 after printing 100,000 sheets of paper) and the static elimination needle 42 is not provided.

  Comparative Example 3 is a toner in which charging variation of the paper P occurs due to non-uniformity of the electric field of the transfer bias due to deterioration of the transfer roller 8 due to long-term use, and the humidity is caused by a high humidity (humidity: 70%) environment. The adhesion between the paper P and the toner is reduced due to the decrease in charging. As a result, in the conveyance unit 50 after separating the paper P, when the paper P passes or contacts the vicinity of the sheet metal (GND) of the conveyance unit 50, the paper P is suddenly discharged, and the adhesion between the paper P and the toner is reduced. It shows that the toner is scattered to cause an image defect.

  Since Comparative Example 4 is a low humidity (humidity: 20%) environment, the toner charge does not escape, and even when the transfer roller 8 becomes old, the toner does not scatter and image defects do not occur.

  In the first to third embodiments, a static elimination needle 42 is disposed downstream of the discharge needle 40. The reason why the needle pitch of the discharge needle 40 is set to 4 mm is to achieve stabilization of the discharge electric field E1 without causing a local current to flow into the photosensitive drum 2.

  In the case of Example 1, no problem occurred in both the scattered image and the separated conveyance. In the case of Example 2, since the needle pitch of the static elimination needle 42 is wide, the static elimination effect is slightly reduced and toner scattering is improved, but it has not been solved. In the case of Example 3, since the static elimination needle 42 is closer to the discharge needle 40 than the photosensitive drum 2, the discharge current flows not to the photosensitive drum 2 but to the static elimination needle 42. Cause poor separation. Further, since the discharge current from the discharge needle 40 flows through the static elimination needle 42, the paper P is not static neutralized and image scattering occurs.

  In the case of Comparative Example 5 and Comparative Example 6, in Example 1, the static elimination needle 42 is disposed at the position of the discharge needle 40, and nothing is disposed at the position of the static elimination needle 42. Since the transfer bias is a high current and a high voltage, the sheet charge is high, and the sheet P has a strong electric attractive force with the photosensitive drum 2 and a separation failure occurs at the transfer portion.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is carried out within the range of the summary. As shown in FIG. 6, the image forming apparatus may be one in which the discharge needle 40 is disposed substantially vertically and the static elimination needle 42 is disposed substantially vertically. However, in this case, although depending on the voltage setting of the discharge needle 40, the discharge electric field E1 from the discharge needle 40 and the static elimination electric field E2 from the static elimination needle 42 are close to each other, so that both are likely to leak. Therefore, it is necessary to design while paying attention to the positional relationship between the discharge needle 40 and the static elimination needle 42.

1 is a schematic configuration diagram of a main part illustrating an example of an image forming apparatus according to the present invention. It is a perspective view which shows a discharge needle and a static elimination needle. It is a schematic block diagram which shows the arrangement | positioning relationship of a discharge needle and a static elimination needle. (A) is a partial front view which shows a static elimination needle, (B) is a partial front view which shows a discharge needle. It is a schematic block diagram which shows the arrangement | positioning state of a static elimination needle. It is a schematic block diagram which shows another example of the image forming apparatus which concerns on this invention.

Explanation of symbols

2 Photosensitive drum 6 Developer 8 Transfer roller 40 Discharge needle 42 Static elimination needle 50 Conveying section

Claims (2)

A discharge needle that is disposed downstream of a transfer unit that transfers the developed image on the surface of the image carrier to a sheet, and applies a separation bias to the conveyed sheet;
A neutralization needle disposed downstream of the discharge needle and neutralizing the conveyed paper , and
The static elimination needle is provided in the vicinity of the paper conveyance path, the tip of the static elimination needle is provided on the downstream side of the paper conveyance path, and the root part of the static elimination needle is on the upstream side of the paper conveyance path, and The tip is closer to the paper conveyance path than the root of the static elimination needle,
The distance between the tip of the discharge needle and the tip of the static elimination needle is greater than the distance between the surface of the image carrier and the tip of the discharge needle,
The arrangement pitch of the static elimination needles is smaller than the arrangement pitch of the discharge needles,
An image forming apparatus. The discharge needle is disposed to be inclined toward the image carrier with respect to a normal direction of the sheet conveyance path extending from the transfer portion, and the charge eliminating needle is opposite to the discharge needle with respect to the normal direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is inclined to the side .

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