JP4725420B2 - Charging device and image forming apparatus - Google Patents

Description

  The present invention relates to a charging device that performs charging, and an image forming apparatus that forms an image composed of a fixed toner image on a recording medium.

In recent years, image forming apparatuses such as printers and copiers have been widely used, and technologies relating to various elements constituting such image forming apparatuses have also been widely used. Among image forming apparatuses that employ an electrophotographic method, a pattern to be printed by forming an electrostatic latent image having a potential different from the surrounding potential on a photosensitive member such as a photosensitive drum. The electrostatic latent image formed in this way is developed with toner, and finally transferred onto a recording medium.

Among image forming apparatuses that perform such image formation, a non-contact charging type charging device using corona discharge is used to charge a photosensitive member to form an electrostatic latent image or after image formation. There is an image forming apparatus that performs a pre-cleaning process for adjusting the charge of toner particles remaining on a photoreceptor to a charge suitable for cleaning. In such a non-contact charging type charging device, a corona discharge is caused by applying a high voltage to a wire called a corona wire. As the corona discharge is repeated, silica (SiO ₂ ) and other corona discharges are generated. The various substances produced become attached to the corona wire.

  FIG. 1 is a diagram showing a corona wire and the surrounding deposits.

  As shown in FIG. 1, the deposit 210 adheres so as to cover the surface of the corona wire 21. When the amount of the deposit 210 increases, the corona discharge is inhibited, and the charging performance is uneven in the direction along the corona wire. In order to prevent the occurrence of such uneven charging performance, there is a charging device equipped with a means for cleaning a corona wire as a non-contact charging type charging device (see, for example, Patent Document 1 and Patent Document 2). Here, the situation where the corona wire is cleaned by the cleaning means conventionally employed will be described.

  FIG. 2 is a diagram illustrating how the corona wire is cleaned.

In FIG. 2, a cleaning pad 211 ′ is shown as a cleaning means that has been conventionally employed, and the cleaning pad 211 ′ is in contact with the corona wire 21 from the up and down direction of the corona wire 21. The cleaning pad 211 ′ can be moved in a direction perpendicular to the drawing by a mechanism (not shown) in such a state that the cleaning pad 211 ′ is in contact with the corona wire 21. 210 is scraped off the corona wire 21.
JP 2004-109721 A JP 2000-221757 A

  In the corona wire cleaning method shown in FIG. 2, the vicinity of the upper part and the lower part of the corona wire 21 in contact with the cleaning pad 211 ′ is cleaned around the corona wire 21. The adhering material 210 attached to the left and right of the wire 21, that is, the position not in contact with the cleaning pad 211 ′ remains on the corona wire 21 without being removed because there is no contact with the cleaning pad 211. If there is a deposit that remains without being removed in this manner, the electric field around the corona wire changes depending on the direction along the corona wire due to the deposit, and charging performance unevenness occurs in this direction. Occurrence of uneven charging performance appears as it is as charging unevenness of a charged body such as a photoconductor, and causes troubles in image formation such as development failure.

  In view of the above circumstances, an object of the present invention is to provide a charging device in which uneven charging performance is reduced, and an image forming apparatus that has such a charging device and performs good image formation.

To achieve the above object, the charging device of the present invention comprises:
A corona wire extending in a direction intersecting a predetermined discharge direction and causing corona discharge;
A shield that extends along a direction intersecting the predetermined discharge orientation at a distance from the corona wire, and that surrounds the corona wire except for the discharge orientation;
A conical or frustum-shaped protrusion has a surface structure aligned in a predetermined direction, and the surface abuts on the corona wire while the predetermined direction is inclined with respect to the corona wire, and moves along the corona wire. And a cleaning member that removes deposits adhering to the corona wire.

  In the charging device of the present invention, when the cleaning member strongly contacts the corona wire, the corona wire is fitted between the two protrusions, and both the protrusions and the corona wire come into contact with each other. When the corona wire is cleaned in this state, the deposits are removed at two or more locations around the corona wire, thereby realizing high cleaning performance.

  Further, in the charging device of the present invention, “the cleaning member has a protruding portion in which abrasive particles are bound with a resin as the protruding portion” is a preferable mode.

  The protruding portion formed by binding abrasive particles with resin is the protruding portion that can be most easily formed, and the cleaning member having the above-described surface structure is easily configured.

  Further, in the charging device of the present invention, “the cleaning member is separated from the corona wire while the corona wire is causing corona discharge” is a preferable mode.

  According to such a form, the cleaning member can avoid the influence of the high voltage applied to the corona wire during corona discharge.

  Further, in the charging device of the present invention, “the corona wire is made of tungsten containing rhenium and the surface is subjected to oxidation treatment” is a preferable embodiment, and “the corona wire is made of rhenium. The form of “having a weight ratio of 30% to 60 μm in which the surface is oxidized and made of tungsten containing 1% to 26% by weight” is a more preferable form.

  When the corona wire contains rhenium, the tensile strength of the corona wire is improved. Moreover, it becomes difficult to attach a deposit to the corona wire because the surface is oxidized. In particular, when the corona wire contains rhenium in a weight ratio of 1% to 26%, the effect of improving the tensile strength is great. In this region, when rhenium is contained at around 3%, the tensile strength is increased. The effect of improving is the largest.

  In the charging device of the present invention, a form of “the cleaning member has a surface structure in which quadrangular pyramid-shaped or quadrangular pyramid-shaped protrusions are aligned” may be employed. The cleaning member may have a surface structure in which a plurality of rows of protrusions aligned in the predetermined direction are parallel to each other.

  Further, in the charging device of the present invention, “the cleaning member has a surface structure in which the protrusions are aligned at equal intervals in the vertical and horizontal directions, and the aligned protrusions are advanced one by one in the vertical and horizontal directions and plural in the other. The form of “the surface abuts against the corona wire in a state where the corona wire is along the direction” is a preferable form.

  According to such a form, when the cleaning member is in strong contact with the corona wire, the portions that come into contact with the corona wire surface appear periodically, and high cleaning performance is realized.

  In the charging device of the present invention, “the cleaning member has a surface structure in which the protrusions are aligned at equal intervals in the vertical and horizontal directions, and the aligned protrusions are advanced one by one in the vertical and horizontal directions and four in the other. The form that the corona wire is in contact with the corona wire in the advancing direction is a preferred form, and `` the cleaning member has a surface structure in which the protrusions are aligned at equal intervals in the vertical and horizontal directions, The form that “the corona wire contacts the corona wire in a state in which the aligned protrusions are advanced one by one in the vertical and horizontal directions and three in the other direction” is a more preferable form. The cleaning member has a surface structure in which the protrusions are aligned at equal intervals in the vertical and horizontal directions, and the aligned protrusions are advanced one by one in the vertical and horizontal directions and two in the other direction. Form of the is "intended to abut on the corona wires in a state in which the corona wire along are especially preferred form.

  When the cleaning member has a surface structure in which the protrusions are aligned at equal intervals in the vertical and horizontal directions, the state in which the aligned protrusions are advanced one by one in the vertical and horizontal directions and three in the other is in contact with the corona wire. While the number of protrusions is the largest, the corona wire is fitted between the protrusions and is in a contact state that is difficult to come off, so that the highest cleaning performance is achieved. In the state in which the aligned protrusions are advanced one by one in the vertical and horizontal directions and three in the other, the high cleaning performance is exhibited next to the above-described state in which the other two are advanced in the other. In the state of proceeding one by one and proceeding four to the other, the high cleaning performance is exhibited next to the above-described state of proceeding three to the other.

In order to achieve the above object, an image forming apparatus of the present invention comprises:
The rotating image carrier is charged by a charging device, an electrostatic latent image is formed on the image carrier by exposure, the electrostatic latent image is developed with toner, and a toner image is formed. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing the recording medium on the recording medium.
A corona wire for causing corona discharge, wherein the charging device extends in a direction intersecting a predetermined discharge direction;
A shield that extends along a direction intersecting the predetermined discharge orientation at a distance from the corona wire, and that surrounds the corona wire except for the discharge orientation;
A conical or frustum-shaped protrusion has a surface structure aligned in a predetermined direction, and the surface abuts on the corona wire while the predetermined direction is inclined with respect to the corona wire, and moves along the corona wire. And a cleaning member that removes deposits adhering to the corona wire.

  Since the image forming apparatus of the present invention includes the above-described charging device, the charging performance is stable, and favorable image formation is possible.

  According to the present invention, uneven charging performance is reduced with a simple configuration, and favorable image formation is possible.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 is a diagram showing a schematic configuration of a full-color image forming apparatus corresponding to an embodiment of the image forming apparatus of the present invention.

  The image forming apparatus 1 shown in FIG. 3 includes a photoreceptor 10 and an intermediate transfer belt 2. The photoconductor 10 is a laminated photoconductor for electrophotography, and rotates in the direction of arrow A in the figure at the time of image formation. The intermediate transfer belt 2 is an endless belt member mainly composed of a polyimide resin, which is stretched around backup rolls 60a, 60b, and 60c. Circulate to A primary transfer roll 40a is disposed at a position facing the photoconductor 10 with the intermediate transfer belt 2 interposed therebetween, and a secondary transfer roll 40b is provided below (lower side in the figure). Yes. These are respectively applied with a bias voltage from the primary transfer bias voltage application unit 41a and the secondary transfer bias voltage application unit 41b.

  Around the photoconductor 10, a developing rotary 50, a scorotron 20, an exposure device 32, and a cleaning blade 31 are disposed. The scorotron 20 is a corona discharger for negatively charging the photoconductor 10 when receiving a high voltage. The scorotron 20 corresponds to an embodiment of the charging device according to the present invention. The developing rotary 50 is a rotation in which developing devices 51 to 54 each containing a developer having colored toners of black (BK), yellow (Y), magenta (M), and cyan (C) are arranged along the circumferential direction. It is a composite developing device of the type, and the developing device that performs development in the vicinity of the photoreceptor 3 can be switched by the rotation of the developing rotary 50. Each colored toner has a charging characteristic of charging the negative electrode, and each colored toner is added with external additive particles smaller than toner particles such as a lubricant, a transfer aid, and a cleaning aid. The exposure device 32 is responsible for irradiating the surface 10b of the photoreceptor 10 with laser light, and the cleaning blade 31 is in contact with the photoreceptor 10 and serves to scrape off the toner on the photoreceptor 10.

  Next, an image forming operation in the image forming apparatus 1 will be described.

  The image forming apparatus 1 forms an image by receiving input of image information representing one or more images having image signals of four colors of yellow, magenta, cyan, and black. When these image signals are input, the photoconductor 10 starts to rotate, and the surface of the rotating photoconductor 10 is charged by the scorotron 20. Of the input four-color image signals, laser light corresponding to the cyan image signal is first irradiated from the exposure unit 32 toward the photosensitive member 10, and this irradiation causes the surface of the photosensitive member 10 to have a potential from the surroundings. An electrostatic latent image having a high height is formed. Further, by the rotation of the developing rotary 50, the developing device 54 containing cyan toner comes close to the photoconductor 10 and develops the electrostatic latent image with cyan toner. When developing the electrostatic latent image, the developing device 54 containing cyan toner is applied with a bias voltage by a developing bias applying unit (not shown), and the potential is higher than the potential of the electrostatic latent image. The potential is low and higher than the potential of the photoconductor 10. For this reason, the cyan toner in the developing device 54 adheres to the electrostatic latent image after leaving the developing device 54 due to a potential difference between the electrostatic latent image and the developing device 54 containing cyan toner. A cyan toner image is formed.

  Next, the formed cyan toner image is primarily transferred from the photoreceptor 10 to the intermediate transfer belt 2 by the primary transfer roll 40a. At the time of the primary transfer, the primary transfer bias is applied to the primary transfer roll 40a so that the potential of the primary transfer roll 40a is higher than the potential on the photoreceptor 10 where the cyan toner image is located. The primary transfer is realized by applying a bias voltage by the voltage application unit 41a.

  Although there is residual toner remaining on the photoconductor 10 without being primarily transferred, the residual toner is scraped off from the photoconductor 10 by the cleaning blade 31.

  After the residual toner is removed by the cleaning blade 31, the surface of the photoconductor 10 is again charged by the scorotron 20, and by the rotation of the developing rotary 50, the developing device 53 containing magenta toner is now moved to the photoconductor 10. A magenta toner image is formed in the same manner as the cyan toner image described above. This magenta toner image is formed when the cyan toner image on the intermediate transfer belt 2 passes through the backup rolls 60a, 60b, 60c after the primary transfer and returns to the position of the primary transfer roll 40a. The timing is adjusted so that the magenta toner image is primarily transferred over the cyan toner image. After the magenta toner image is primarily transferred and superimposed on the cyan toner image, the yellow toner image and the black toner image are formed in the same manner and are superimposed on the magenta toner image and the cyan toner image. As a result, a multicolor toner image is formed on the intermediate transfer belt 2 by superimposing cyan, magenta, yellow, and black toner images.

  Subsequently, the multicolor toner image is secondarily transferred onto the sheet fed from the tray 6 by the paper feed roll 61 at a position sandwiched between the secondary transfer roll 40b and the backup roll 60c. At the time of the secondary transfer, the secondary transfer roll 40b has a potential that is higher than the potential on the intermediate transfer belt 2 on which the multicolor toner image is positioned, with respect to the secondary transfer roll 40b. The secondary transfer is realized by the application of the bias voltage by the secondary transfer bias voltage application unit 41b.

  The sheet that has undergone the secondary transfer of the multicolor toner image is subjected to heat and pressure by the fixing device 62 that is provided in the rightward position of the secondary transfer roll 40b in FIG. Fixing processing is performed. Then, the sheet subjected to the fixing process is output in the right direction of the image forming apparatus as indicated by an arrow.

  Next, the scorotron 20 shown in FIG. 3 will be described.

  The scorotron 20 is a corona wire 21 having a diameter of 40 μm for generating negative ions by corona discharge to negatively charge the photosensitive member 10, and an electrode provided between the corona wire 21 and the photosensitive member 10, and passes therethrough. A grid 23 having an aperture ratio of 90% for adjusting the potential of the photosensitive member by controlling the amount of negative ions, and a shield 22 having a thickness of 1 mm surrounding the corona wire 21 are provided. The corona wire 21 is a ReW mirror-polished wire made of an alloy containing tungsten as a main component and containing 3% rhenium in a weight ratio, and the surface thereof is oxidized. Thus, a corona wire with a high tensile strength is implement | achieved because a corona wire contains rhenium. The scorotron 20 causes corona discharge by applying a high voltage to the corona wire 21, but as the corona discharge is repeated, various substances generated during the corona discharge become attached to the corona wire 21. When the amount of deposits increases, it becomes an obstruction factor for corona discharge, and uneven charging performance occurs in the direction along the corona wire 21. In the corona wire 21, the surface of the ReW mirror-polished wire is subjected to oxidation treatment, thereby realizing a state in which deposits are difficult to adhere to the surface when the ReW mirror-polished wire is used as a corona wire. Further, the scorotron 20 is provided with a cleaning pad for removing such deposits from the corona wire 21. Hereinafter, cleaning of the corona wire by the cleaning pad will be described.

  FIG. 4 is an explanatory view of the cleaning of the corona wire by the cleaning pad.

  Part (a) of FIG. 4 and part (b) of FIG. 4 show the state of the end of the corona wire 21, and part (a) of FIG. 4 shows the corona wire 21 and two parts at the time of corona discharge. The positional relationship with the cleaning pad 211 is shown. Part (b) of FIG. 4 shows the positional relationship between the corona wire 21 and the two cleaning pads 211 during cleaning.

  The cleaning pad 211 provided on the upper side of the corona wire 21 is attached to the inner wall 201 on the upper side of the figure of the support member 200 whose inside is hollow so that the corona wire 21 can pass through the inside. As shown in part (a) of FIG. 4, it is at a position separated from the corona wire 21. On the other hand, the cleaning pad 211 provided on the lower side of the corona wire 21 is fixed to the pad holding member 24, and the pad holding member 24 is rotated around the rotation shaft 240 by a mechanism (not shown). The rotation shaft 240 is also fixed to the support member 200. At the time of corona discharge, as shown in part (a) of FIG. 4, the cleaning pad 211 provided on the lower side of the corona wire 21 also remains at a position separated from the corona wire 21. At the time of cleaning, the pad holding member 24 rotates around the rotation shaft 240 in the direction of arrow C in Part (a) of FIG. 4, and the cleaning pad 211 fixed to the pad holding member 24 by this rotation. However, as shown in part (b) of FIG. 4, the corona wire 21 is abutted so as to be pushed up from below. As the corona wire 21 is pushed up, the corona wire 21 is lifted upward and is strongly pressed against the cleaning pad 211 provided on the upper side of the corona wire 21. The support member 200 can move along the corona wire 21 by a mechanism (not shown), and in the state of the part (b) in FIG. 4, while the corona wire 21 is squeezed, the left side of the part (b) in FIG. The corona wire 21 is cleaned. Such cleaning of the corona wire 21 is performed once every time image formation for 5000 sheets is performed.

  Next, the structure of the cleaning pad on the contact surface with the corona wire will be described. Here, the cleaning pad 211 provided below the corona wire 21 among the two cleaning pads shown in FIG. 4 will be described as an example.

  FIG. 5 is a schematic diagram showing the structure of the cleaning pad shown in FIG. 4 on the contact surface with the corona wire.

  An abrasive 2111 is bonded to the contact surface of the cleaning pad 211 with the corona wire by a resin 210a which is a kind of urethane resin, and has a quadrangular pyramid shape like the quadrangular pyramid 100 shown in FIG. It is provided with a surface structure that is regularly arranged vertically and horizontally. Such a surface structure is provided on the support 2110. The quadrangular pyramid 100 is a regular quadrangular pyramid having a square bottom surface and all four side faces being the same triangle, and has a side length L of 0.48 mm and a height h of 0.4 mm. The distance d between adjacent quadrangular pyramids is 0.02 mm.

  6 is a plan view showing a series of quadrangular pyramids arranged on the surface of the cleaning pad shown in FIG.

  In this figure, the quadrangular pyramids arranged on the surface of the cleaning pad are represented by a square having a side length L. Further, the ridge line of the quadrangular pyramid is expressed by the diagonal line of the square, and the intersection of the two diagonal lines corresponds to the vertex. On the surface of the cleaning pad, eight quadrangular pyramids are arranged in the vertical direction of the figure. In the figure, among the four quadrangular pyramid rows, seven quadrangular pyramids 100, ..., 107, 110 are shown. , ..., 117, 120, ..., 127, 130, ..., 137, 140, ..., 147, 150, ..., 157, 160, ..., 167 are shown. When the corona wire 21 is cleaned, the corona wire 21 comes into contact with the cleaning pad 211 so as to come into contact with the quadrangular pyramid as much as possible.

  FIG. 7 is a diagram illustrating a state where a series of quadrangular pyramids illustrated in FIG. 6 is in contact with a corona wire.

In this figure, a continuous cross section of the quadrangular pyramid shown in FIG. 6 at the position (height) of the corona wire 21 measured from the bottom surface of the quadrangular pyramid shown in FIG. As shown in this figure, when the corona wire 21 is cleaned, the corona wire 21 is between the two quadrangular pyramids 100 and 101 in the first row from the left, and the two quadrangular pyramids in the second row from the left. 112, 113, the corona wire of the cleaning pad 211 so as to pass between the two quadrangular pyramids 124, 125 in the third column from the left and between the two quadrangular pyramids 136, 137 in the fourth column from the left. 21 are oriented adjustment of the contact surface between the corona wire 21, these and eight pyramids, eight contacts _{a 0, ..., a 3,} B 0, ..., in contact respectively with _{B 3} Yes.

  FIG. 8 is a diagram when the positional relationship between the corona wire and the cleaning pad in FIG. 7 is viewed from a direction along the corona wire.

In this figure, two quadrangular pyramids 100 and 101 of eight quadrangular pyramids contacting the corona wire 21 are shown. As shown in this figure, the corona wire 21 is pushed all the way to the bottom of the figure, and the two quadrangular pyramids 100 and 101 are corona with two contacts A ₀ and B ₀ so as to sandwich the corona wire 21. The wire 21 is in pressure contact. Similar to the two quadrangular pyramids 100 and 101 shown in FIG. 8, two quadrangular pyramids 112 and 113 in the second column from the left in FIG. 7, two quadrangular pyramids 124 and 125 in the third column from the left, and 4 from the left A pair of quadrangular pyramids 136 and 137 in a row is in pressure contact with the corona wire 21 so as to sandwich the corona wire 21, and the positional relationship between the corona wire 21 and the cleaning pad 211 in FIG. Then, a state in which four pairs of quadrangular pyramids are in pressure contact with the corona wire 21 is realized.

  In the above, the cleaning pad 211 provided on the lower side of the corona wire 21 of the two cleaning pads shown in FIG. 4 has been described as an example, but the cleaning pad 211 provided on the upper side of the corona wire 21 is also illustrated in FIG. 6 and the surface structure similar to that shown in FIG. 6, and the corona wire 21 and the cleaning pad 211 are arranged from the upper side of the corona wire 21 with respect to the corona wire 21 so that the positional relationship of FIG. Abut.

  As described above, the two cleaning pads 211 provided on the upper side and the lower side of the corona wire 21 are in a state where the four pairs of quadrangular pyramids on the surface of each cleaning pad 211 are in pressure contact with the corona wire 21. It moves along the corona wire 21 as shown in FIG. By this movement, the deposit on the corona wire 21 is scraped off.

  In the conventional example shown in FIG. 2, in the vicinity of the corona wire 21, the vicinity of the upper portion of the corona wire 21 that comes into contact with the upper cleaning pad 211 in the drawing and the lower portion of the corona wire 21 that comes into contact with the lower cleaning pad 211 in the drawing. Only the deposits attached to two places are removed, but in this embodiment, the lower cleaning pad 211 in FIG. 4 is attached to the lower two places around the corona wire 21 as shown in FIG. The attached matter is removed, and the upper cleaning pad 211 in FIG. 8 removes the attached matter on the upper two places around the corona wire 21, so that the attached matter is removed at four places in total. It will be. When the deposits are removed at four locations around the corona wire 21, substantially the same effect as that obtained when the entire periphery of the corona wire 21 is cleaned is obtained, and high cleaning performance is exhibited. It will be. Therefore, the scorotron 20 shown in FIG. 3 is a scorotron that hardly causes uneven charging performance even when the number of times of charging increases.

  Next, in the positional relationship between the corona wire 21 and the cleaning pad 211 as shown in FIG. 7, the height of the corona wire 21 measured from the bottom surface of the quadrangular pyramid will be described.

  9 is a cross-sectional view of the quadrangular pyramid shown in FIG.

  As described above, the quadrangular pyramid 100 is a regular quadrangular pyramid having a square bottom surface and all four side faces being the same triangle. In FIG. 9, the cross section of the quadrangular pyramid 100 has a height h and a base. Is an isosceles triangle of length L. The distance d between adjacent quadrangular pyramids is also shown in this figure. As described above, the side length L is 0.48 mm, the height h is 0.4 mm, and the distance d between adjacent quadrangular pyramids is 0.02 mm. In the following, for convenience of explanation, instead of specific numerical values, the length L of the bottom square, the height h, and the adjacent quadrangular pyramids are represented by three variables L, h, and d representing the length. The distance d between is described and described, and the above specific numerical values are substituted as necessary.

  When t is a parameter in the range of 0 to 1, the cross section at the height (t × h) of the quadrangular pyramids on the surface of the cleaning pad 211 shown in FIG. 6 is a square. The length of the side of this square is the length of a line segment in which the line of height (t × h) is cut out by the isosceles triangle of FIG. 9, and (1-t) × L from the figure. I understand that Here, the period of a series of squares is the same as the period of a series of square pyramids (L + d).

  FIG. 10 is a view showing a cross section at a height (t × h) of a series of quadrangular pyramids on the surface of the cleaning pad.

This figure shows a state in which squares whose side length is (1−t) × L are arranged in a cycle (L + d). The square located in the lower left of this figure is a cross section at a height (t × h) of the square pyramid 100 located in the lower left of the series of square pyramids shown in FIG. The top left vertex of the square of this quadrangular pyramid 100 is taken as the origin O of the coordinate system that describes the position in the plane shown in FIG. 10, and when viewed from this origin O, the right direction of the figure is the x axis and the upward direction of the figure is Take the y-axis. The coordinates of the square vertex B ₀ ′ of the second quadrangular pyramid 101 in the first column from the left and the square vertex A ₁ ′ of the square pyramid 112 in the second column from the left in the second column from the left are: If the x and y coordinates of each vertex are expressed as (x, y),
B ₀ ′: ((1−t) × L, (d + L) × t)
A ₁ ': (L + d, 2L + 2d)
It is expressed. Here, as in the corona wire 21 shown in FIG. 7, the lower left quadrangular pyramid 100, the second quadrangular pyramid 101 from the bottom in the first column from the left, and the third pyramid from the bottom in the second column from the left. The straight line in contact with all of the quadrangular pyramids 112 is a straight line when the straight line OB ₀ ′ and the straight line OA ₁ ′ coincide with each other, and is a straight line in which these two inclinations are the same. From the condition that the slopes match,
(D + L * t) / ((1-t) * L) = 2 * (L + d) / (L + d) = 2
The following formula is established. Solving this equation for t,
t = 2 / 3-d / (3L)
It is obtained. Accordingly, as in the corona wire 21 shown in FIG. 7, the lower left quadrangular pyramid 100, the second quadrangular pyramid 101 from the bottom in the first column from the left, and the fourth pyramid from the bottom in the second column from the left. The height at which a straight line in contact with all of the pyramids 112 appears is h × (2 / 3−d / (3L)). Here, if h = 0.4 mm, d = 0.02 mm, and L = 0.48 mm are substituted, this height is 0.261 mm. In this way, the straight line passing through the origin O and the two vertices B ₀ ′ and A ₁ ′ is a square of the fourth pyramid 124 in the third column from the left and the fifth from the bottom due to the periodicity of the series of squares. Vertex A ₂ ′, square vertex A ₃ ′ of the fourth pyramid 136 from the bottom in the fourth column from the left, and square vertex B ₁ of the fourth pyramid 113 from the bottom in the second column from the left ', The square vertex B ₂ ' of the fourth pyramid 125 in the third row from the left and the sixth square pyramid 125 from the bottom, and the square vertex B ₃ 'of the seventh pyramid 137 in the fourth row from the left also passes. It will be in contact with all 8 squares.

  In the above description, the thickness of the corona wire 21 is ignored, but considering the thickness of the corona wire 21, the position of the center of the circular cross section of the corona wire 21 shown in FIG. 7 and a cleaning pad as shown in FIG. 7 when it belongs to an area of 0.301 mm or less obtained by adding the thickness of the corona wire 21 (diameter 40 μm) to 0.261 mm. The positional relationship is almost realized.

  In the positional relationship between the corona wire 21 and the cleaning pad 211 described above, the corona wire 21 has an inclination of almost 2 in the coordinate system of FIG. Nearly four corona wires 21 are also feasible.

  FIG. 11 is a diagram showing the positional relationship between the cleaning pad and the corona wire whose inclination is approximately 3 in the coordinate system of FIG.

The corona wire 21 shown in this figure has a square vertex C _{0 of} the first quadrangular pyramid 100 from the bottom in the first column from the left, and a square vertex of the square pyramid 101 in the second column from the bottom in the first column from the left. D ₀ , the square vertex C ₁ ′ of the fourth pyramid 113 from the bottom in the second column from the left, the square vertex D ₁ ′ of the square pyramid 114 in the second column from the left and the fifth square pyramid 114 from the bottom, left By touching each quadrangular pyramid at the vertex C ₂ of the square pyramid 126 of the sixth square pyramid 126 from the bottom in the third row and from the square vertex D ₂ of the square pyramid 127 seventh from the bottom in the third row from the left It is in contact with six square pyramids in total. Compared to eight in the positional relationship between the corona wire 21 and the cleaning pad 211 shown in FIG. 7, the number of the quadrangular pyramids in contact with the corona wire 21 and the cleaning pad 211 is slightly smaller, but the cleaning performance is slightly lower than the positional relationship shown in FIG. Even in the positional relationship between the wire 21 and the cleaning pad 211, as shown in FIG. 8, the cleaning is performed at two places below the corona wire 21, and sufficient cleaning performance is exhibited. The parameter t for determining the height of the corona wire 21 measured from the bottom surface of the quadrangular pyramid at this time is for the inclination of the straight line OB ₀ ′ and the inclination of the straight line OC ₁ ′ to coincide in the coordinate system shown in FIG. Conditional expression,
(D + L * t) / ((1-t) * L) = 3 * (L + d) / (L + d) = 3
From this conditional expression,
t = 3 / 4−d / (4L)
It is obtained. Therefore, if the thickness of the corona wire 21 is ignored, the height of the corona wire 21 shown in FIG. 11 is h × (3 / 4−d / (4L)). Here, if h = 0.4 mm, d = 0.02 mm, and L = 0.48 mm are substituted, this height is 0.296 mm. In consideration of the thickness of the corona wire 21, the center position of the circular cross section of the corona wire 21 as shown in FIG. 8 is 0.296 mm or more, and the thickness of the corona wire 21 is 0.296 mm. When it belongs to the region of 0.336 mm or less including the diameter of 40 μm), the positional relationship between the corona wire 21 and the cleaning pad as shown in FIG. 11 is almost realized.

  Also in the positional relationship between the corona wire 21 and the cleaning pad 211 shown in FIG. 11, image formation and cleaning of the corona wire 21 are performed in the same manner using the same configuration as the configuration shown in FIG. 3 and FIG.

  FIG. 12 is a diagram showing the positional relationship between the cleaning pad and the corona wire having an inclination of about 4 in the coordinate system of FIG.

The corona wire 21 shown in this figure has a square vertex E _{0 of} the first quadrangular pyramid 100 from the bottom in the first column from the left, and a square vertex of the second quadrangular pyramid 101 from the bottom in the first column from the left. F ₀ , at the vertex E ₁ ′ of the square pyramid 114 in the second column from the left and the fifth square pyramid 114 from the bottom, and at the vertex F ₁ ′ of the square of the sixth pyramid 115 from the bottom in the second column from the left, It is in contact with four quadrangular pyramids. Compared to eight in the positional relationship between the corona wire 21 and the cleaning pad 211 shown in FIG. 7, the number of quadrangular pyramids in contact is small, and the cleaning performance is slightly lower than the positional relationship shown in FIG. However, even in the positional relationship between the corona wire 21 and the cleaning pad 211 in FIG. 12, the cleaning is performed at two places below the corona wire 21, as shown in FIG. At this time, t for determining the height of the corona wire 21 measured from the bottom surface of the quadrangular pyramid is a condition for the inclination of the straight line OB ₀ ′ and the inclination of the straight line OE ₁ ′ in the coordinate system shown in FIG. formula,
(D + L × t) / ((1-t) × L) = 4 × (L + d) / (L + d) = 4
From this conditional expression,
t = 4 / 5-d / (5L)
It is obtained. Therefore, if the thickness of the corona wire 21 is ignored, the height of the corona wire 21 shown in FIG. 12 is h × (4 / 5−d / (5L)). Here, if h = 0.4 mm, d = 0.02 mm, and L = 0.48 mm are substituted, this height becomes 0.317 mm. Considering the thickness of the corona wire 21, the center position of the circular cross section of the corona wire 21 as shown in FIG. 8 is 0.317 mm or more, and the thickness of the corona wire 21 is 0.317 mm. When it belongs to the region of 0.357 mm or less including the diameter of 40 μm), the positional relationship between the corona wire 21 and the cleaning pad as shown in FIG. 12 is almost realized.

  Also in the positional relationship between the corona wire 21 and the cleaning pad 211 shown in FIG. 12, image formation and cleaning of the corona wire 21 are performed in the same manner using the same configuration as the configuration shown in FIG. 3 and FIG.

  FIG. 13 is a diagram showing the positional relationship between the corona wire having an inclination of approximately 1 in the coordinate system of FIG. 10 and the cleaning pad.

  The corona wire 21 shown in this figure is in contact with a total of 14 quadrangular pyramids in an oblique direction. Compared with the eight in the positional relationship between the corona wire 21 and the cleaning pad 211 in FIG. However, the sandwiching angle when the corona wire 21 is sandwiched between two quadrangular pyramids as shown in FIG. For this reason, even when the cleaning pad 211 is in pressure contact with the corona wire 21 as shown in part (b) of FIG. 4, if a slight external vibration is applied, the corona wire 21 is placed on the surface of the cleaning pad 211. It is easy to come off from the quadrangular pyramid, and the cleaning performance is reduced as compared with the positional relationship between the corona wire 21 and the cleaning pad 211 shown in FIG. However, even in the positional relationship shown in FIG.

The height t of the corona wire 21 shown in FIG. 13 that determines the height measured from the bottom of the quadrangular pyramid is a condition for the inclination of the straight line OB ₀ ′ and the inclination of the straight line OG ₁ ′ in the coordinate system shown in FIG. formula,
(D + L × t) / ((1-t) × L) = 1 × (L + d) / (L + d) = 1
From this conditional expression,
t = 1 / 2-d / (2L)
It is obtained. Therefore, if the thickness of the corona wire 21 is ignored, the height of the corona wire 21 shown in FIG. 11 is h × (1 / 2−d / (2L)). Here, if h = 0.4 mm, d = 0.02 mm, and L = 0.48 mm are substituted, this height is 0.192 mm. When the thickness of the corona wire 21 is taken into consideration, the position of the center of the circular cross section of the corona wire 21 as shown in FIG. When it belongs to the region of 0.232 mm or less including the diameter of 40 μm, the positional relationship between the corona wire 21 and the cleaning pad as shown in FIG. 13 is almost realized.

  In the positional relationship between the corona wire 21 and the cleaning pad 211 shown in FIG. 13, image formation and cleaning of the corona wire 21 are performed in the same manner using the same configuration as that shown in FIG. 3 and FIG. 4.

In the cleaning method described above, a cleaning pad having a surface structure in which eight quadrangular pyramids are arranged in the vertical direction in the figure as shown in FIG. 6 is used. However, the contact with the corona wire is not used. In order to further increase the cleaning performance by increasing the number, a cleaning pad having a surface structure in which eight or more quadrangular pyramids are arranged in the vertical direction may be employed. 7, 11, 12, and 13, the slopes of the straight lines representing the corona wire 21 in the coordinate system of FIG. 10 are 2, 3, 4, and 1, respectively. By increasing the number of quadrangular pyramids arranged in the, the inclination of the corona wire 21 can be further increased. When the inclination of the corona wire 21 is an integer m, the height t of the corona wire 21 measured from the bottom surface of the quadrangular pyramid in this case is determined by the inclination of the straight line OB ₀ ′ in the coordinate system shown in FIG. A conditional expression for becoming an integer m,
(D + L × t) / ((1-t) × L) = m
From this conditional expression, t = m / (m + 1) −d / ((m + 1) × L) (1)
It is obtained. Therefore, if the thickness of the corona wire 21 is ignored, the height of the corona wire 21 shown in FIG.
h × (m / (m + 1) −d / ((m + 1) × L)) (1)
It becomes. Considering the thickness of the corona wire 21, the position of the center of the circular cross section of the corona wire 21 as shown in FIG. 8 is not less than the height determined by the above equation (1) and the above equation (1). The contact points between the corona wire 21 and the quadrangular pyramid are the largest when they belong to a region below the height obtained by adding the thickness of the corona wire 21 (the diameter of 40 μm) to the determined height.

  In the cleaning method described above, as shown in FIG. 6, the two cleaning pads 211 come into contact with each other at different positions on the corona wire 21, and the corona wire 21 moves in a rugged manner. Although cleaning has been performed, it is also possible to employ a method in which two cleaning pads sandwich the same position on the corona wire 21 from the top and bottom of the corona wire for cleaning. Hereinafter, such a sandwiching type cleaning method will be described.

FIG. 14 is an explanatory view of a sandwiching type cleaning method.
Part (a) of FIG. 14 shows the positional relationship between the corona wire 21 and the two cleaning pads 211a and 211b during corona discharge, and part (b) of FIG. 14 shows the corona wire 21 and the corona wire 21 during cleaning. The positional relationship between the two cleaning pads 211a and 211b is shown. The two cleaning pads 211a and 211b are supported by a support member 200 ′, and can be brought into contact with and separated from the corona wire 21 by a mechanism (not shown) provided in the support member 200 ′. Further, the support member 200 ′ can move along the corona wire 21 in the direction indicated by the double-headed arrow in the figure. During the corona discharge, the support member 200 ′ can obstruct the operation of charging the photosensitive member. It is located near the end of the corona wire 21 so as not to become. In the vicinity of this end, the cleaning pads 211a and 211b are separated from the corona wire 21 as shown in part (a) of FIG. 14 to avoid the influence of a high voltage during corona discharge. When the corona wire 21 is cleaned, as shown in part (b) of FIG. 14, the two cleaning pads 211 a and 211 b are in contact with each other from the vertical direction of the corona wire 21. With the cleaning pads 211a and 211b in contact with the corona wire 21 as described above, the support member 200 ′ moves along the corona wire 21, and along with this movement, deposits on the corona wire 21 are removed from the cleaning pad 211a. , 211b.

  On the surfaces of the cleaning pads 211a and 211b that come into contact with the corona wire 21, there are four pyramid frustums shown in FIG. 6 in which the vicinity of the apex of the quadrangular pyramid 100 shown in FIG. It has a surface structure that is connected in the same way as a series of pyramids. When the cleaning pad 211a on the left side of FIG. 14 and the corona wire 21 come into contact with each other, the series of pyramidal pyramids on the cleaning pad 211a on the left side of FIG. 14 corresponds to the corona wire 21 and the corona wire 21 shown in FIG. And the positional relationship between the cleaning pad 211 and the cleaning pad 211. On the other hand, for the cleaning pad 211b on the right side of FIG. 14, when the corona wire 21 comes into contact with the corona wire 21, the corona wire 21 is placed on the right-side cleaning pad 211b of FIG. The direction of the contact surface of the right cleaning pad 211b with the corona wire 21 is adjusted so as to be placed on each flat top portion.

  FIG. 15 is a diagram illustrating a state where the corona wire and the quadrangular frustum are in contact with each other in a plane perpendicular to the corona wire.

As shown in this figure, the corona wires 21, two truncated pyramid 100 on the cleaning pad 211a of the bottom of FIG. ', 101' and the contact _{A 0} ', the contact _{B 0'} in contact with, on the other hand, a truncated pyramid 100b on the upper cleaning pad 211b of FIG, are in contact with contacts _{Z 0.} Thus, the cleaning pads 211a and 211b move along the corona wire 21 in the state where they are in contact with the corona wire 21 at the three contacts A ₀ ′ and B ₀ ′ contact Z ₀ . Scrub off the kimono.

  In such a sandwiching type cleaning method, cleaning is performed at three locations around the corona wire 21, and only two cleaning operations are performed near the top of the corona wire 21 and near the bottom of the corona wire 21 as shown in FIG. Compared with the cleaning method of the example, the cleaning property is improved. For this reason, the scorotron adopting the above-described sandwiching type cleaning method is a scorotron that is less likely to cause uneven charging performance even if the number of times of charging increases.

  The positional relationship between the cleaning pad 21a on the lower side of FIG. 15 and the corona wire 21 is not limited to the positional relationship as shown in FIG. The direction of the contact surface of the pad 211a with the corona wire 21 may be adjusted.

  The structure of the scorotron and the image forming apparatus adopting such a sandwich type cleaning method is the same as that of the scorotron 20 and the image forming apparatus 1 shown in FIGS. 3 and 4 except that the corona wire cleaning mechanism is different. Therefore, the redundant description is omitted here.

  Next, by providing a surface structure on the contact surface of the cleaning pad with the corona wire that increases the number of contacts with the corona wire, charging performance unevenness can be suppressed even if the number of times of charging by corona discharge increases. Will be described based on specific experimental data.

In this experiment, an output test for continuously outputting 1 million monochrome images having an image ratio of 1% to 4% is performed under the following two conditions.
(Example) The output test is performed using the image forming apparatus 1 shown in FIG.
(Comparative Example) The above output test is performed using an image forming apparatus having the same configuration as the image forming apparatus 1 except that the cleaning pad 211 ′ shown in FIG. In this image forming apparatus, as with the scorotron 22 employed in the image forming apparatus 1 shown in FIG. 3, the corona wire is cleaned each time image formation for 5000 sheets is performed.

  For each of these examples and comparative examples, each time 100,000 sheets are output, the potential on the surface of the photoconductor is measured at each position on the photoconductor along the axial direction of the corona wire. Then, the average value, the maximum value, and the minimum value of the potential of the photoreceptor surface obtained by the measurement are obtained, and the ratio (percentage) of the difference between the maximum value and the minimum value to the average value is calculated. This ratio represents the non-uniformity of charging on the surface of the photoconductor, and this ratio is hereinafter simply referred to as non-uniformity (unit: percent).

  FIG. 16 is a diagram showing the transition of non-uniformity according to the number of output sheets for each of the example and the comparative example.

  As shown in FIG. 16, in the comparative example, the non-uniformity suddenly increases when the number of output sheets exceeds 500,000, and the non-uniformity is 30% when the number of output sheets is 800,000 or more. Is over. On the other hand, in the example, the non-uniformity increases as the number of output sheets increases, but the rate of increase is moderate compared to the comparative example, and the non-uniformity is maintained at approximately 10% or less up to 1 million sheets. I'm leaning.

  From this result, the number of times of electrification by corona discharge is increased by providing the cleaning pad with a surface structure on the contact surface with the corona wire that increases the number of contacts with the corona wire as in the embodiment. It can also be seen that uneven charging performance is suppressed.

  The scorotron described above is a scorotron that performs corona discharge using only one corona wire, but the charging device of the present invention may be a scorotron that performs corona discharge using a plurality of corona wires.

  The charging device of the present invention is not limited to the scorotron, and may be a corotron, for example. Further, the charging device of the present invention may be a charging device whose charging object is other than the photoconductor, for example, a pre-cleaning charge for adjusting the charge of the toner particles remaining on the photoconductor to a charge suitable for cleaning. It may be a device.

  Further, although the image forming apparatus of the present embodiment is a full-color image forming apparatus, the image forming apparatus of the present invention may be applied to a monochrome image forming apparatus. In the above description, an example of an image forming apparatus that forms an image via an intermediate transfer belt is shown. However, the present invention directly transfers from a photoreceptor to a recording medium without using an intermediate transfer belt. The present invention may be applied to a direct transfer type image forming apparatus.

It is a figure showing a corona wire and the deposit | attachment of the circumference | surroundings. It is a figure showing a corona wire and the cleaning means which removes a deposit | attachment from this corona wire. 1 is a diagram illustrating a schematic configuration of a full-color image forming apparatus corresponding to an embodiment of an image forming apparatus of the present invention. It is explanatory drawing of the cleaning of the corona wire by a cleaning pad. It is the schematic diagram which showed the structure on the contact surface with the corona wire of the cleaning pad shown in FIG. FIG. 5 is a view when a series of quadrangular pyramids arranged on the surface of the cleaning pad shown in FIG. 4 is looked down from above the cleaning pad. FIG. 7 is a diagram illustrating a state where a series of quadrangular pyramids illustrated in FIG. 6 is in contact with a corona wire. It is a figure when the positional relationship of the corona wire and cleaning pad of FIG. 7 is seen from the direction along the corona wire. It is sectional drawing of the square pyramid shown in FIG. It is a figure showing the section in height txh of a series of square pyramids on the surface of a cleaning pad. FIG. 11 is a diagram showing a positional relationship between a corona wire having an inclination of approximately 3 in the coordinate system of FIG. 10 and a cleaning pad. FIG. 11 is a diagram showing a positional relationship between a corona wire having an inclination of about 4 in the coordinate system of FIG. 10 and a cleaning pad. FIG. 11 is a diagram illustrating a positional relationship between a corona wire having an inclination of approximately 1 in the coordinate system of FIG. 10 and a cleaning pad. It is explanatory drawing of the pinching type cleaning system. It is a figure showing a mode that a corona wire and a quadrangular frustum have touched in a plane perpendicular to a corona wire. It is the figure showing the change of the nonuniformity according to the number of output about each of an Example and a comparative example.

Explanation of symbols

1 Image forming apparatus,
10: Photoconductor,
2 ... Intermediate transfer belt,
20 ... Scorotron,
200, 200 '... support member,
201 ... inner wall,
210 ... deposits,
21 ... Corona wire,
211, 211a, 211b, 211 '... cleaning pads,
210a ... Resin,
2110 ... support,
2111 ... abrasive,
22 ... Shield,
23 ... Grid,
24. Pad holding member,
240 ... rotating shaft,
31 ... Cleaning blade,
32 ... exposure unit,
40a ... primary transfer roll,
40b ... secondary transfer roll,
41a ... Primary transfer bias voltage application unit,
41b ... Secondary transfer bias voltage application unit,
50: Development rotary,
51, 52, 53, 54 ... developer,
60a, 60b, 60c ... backup roll,
6 ... Tray,
61: Paper feed roll,
62 ... Fixer,
100 to 107, 110 to 117, 120 to 127, 130 to 137 ... square pyramid,
140-147, 150-157, 160-167 ... quadrangular pyramid,
100 ', 101', 100b ... square pyramid

Claims (2)

A corona wire extending in a direction intersecting a predetermined discharge direction and causing corona discharge;
A shield that extends along a direction intersecting the predetermined discharge orientation at a distance from the corona wire, and that surrounds the corona wire except for the discharge orientation;
A conical or frustum-shaped protrusion has a surface structure aligned in a predetermined direction, and the surface abuts on the corona wire while the predetermined direction is inclined with respect to the corona wire, and moves along the corona wire. And a cleaning member that removes deposits attached to the corona wire. The rotating image carrier is charged by a charging device, an electrostatic latent image is formed on the image carrier by exposure, the electrostatic latent image is developed with toner, and a toner image is formed. In an image forming apparatus for forming an image composed of a fixed toner image on a recording medium by transferring and fixing the recording medium on the recording medium.
A corona wire for causing corona discharge, wherein the charging device extends in a direction intersecting a predetermined discharge direction;
A shield that extends along a direction intersecting the predetermined discharge orientation at a distance from the corona wire, and that surrounds the corona wire except for the discharge orientation;
A conical or frustum-shaped protrusion has a surface structure aligned in a predetermined direction, and the surface abuts on the corona wire while the predetermined direction is inclined with respect to the corona wire, and moves along the corona wire. An image forming apparatus comprising: a cleaning member that removes deposits attached to the corona wire.

Images