JP2008020482A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an antistatic and discharging mark from being left and jamming or the like from occurring while eliminating density irregularity in the width direction of material to be recorded with simple constitution. <P>SOLUTION: An opposed space between the discharge electrode or the antistatic holder of an antistatic means 17 and a photoreceptor drum is set to differ in the direction of the rotary shaft of the photoreceptor drum, that is, in the width direction of the material to be recorded so that the density of the material to be recorded may differ in the width direction in advance. Thus, density is balanced between a center side area and both end side areas by paper passing in a fixing device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a charge removing unit that removes charges charged in an image carrier or a recording material.

  In various image forming apparatuses including electrostatic recording apparatuses and electrophotographic apparatuses such as copying machines and laser beam printers, a toner image formed on a recording material is fixed to obtain a final image. In the heat roller fixing method widely used, the heat fixing roller in which a heating element such as a halogen lamp is encapsulated inside a hollow roller made of aluminum, iron, or the like, and a pressure roller having an elastic layer are fixed. A nip is formed, and a recording material is guided to the fixing nip to be nipped and conveyed to fix the toner image.

  Recently, a resistance heating element is formed on an insulating substrate such as alumina or aluminum nitride, and a heating element that controls the temperature by energization control is arranged so as to be in pressure contact with the fixing nip through a heat-resistant film having a low heat capacity. Film heating and fixing system that improves the thermal response from the heating element to the fixing nip, thereby saving power and shortening the time from the start of energization to the fixing temperature. Is being adopted (see Patent Documents 1 and 2 below).

  An outline of such a film fixing device will be described with reference to FIG. FIG. 9 is a cross-sectional view of the main part of the film heating / fixing device when used in an electrophotographic apparatus. The heater unit 1 includes a heating heater 2, a fixing film 3, and a film guide 4 and pressurization. The roller 5 is formed of a core metal 5a, a silicone rubber 5b, and a PFA tube 5c. A chip thermistor 2b is bonded to the back surface of the substrate 2a of the heater 2, and its resistance value is A / D converted. After that, the control is performed on the triac 6a by a control signal from a DC controller (not shown) that is input to the CPU 6 and the energization control to the heater 2 is performed according to the input value.

  In such a film fixing device, a driving force for conveying the recording material P is transmitted from a motor and a driving gear train (not shown) to the metal core 5a of the pressure roller 5, and the surface of the pressure roller 5 The recording material P and the fixing film 3 are conveyed by the frictional force acting between the fixing film 3 and the recording material P.

JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878

However, after fixing using such a heat fixing device, density unevenness tends to occur in the toner image in the width direction of the recording material. For example, FIG. 10 shows an example of the result of measuring the image density before and after passing through the fixing device when the film fixing device is used. In this case, plain paper for a printer (basis weight 64 g / m ² ) is used as a recording material, and the test environment is a room temperature and normal humidity environment with a temperature of 25 ° C. and a humidity of 55%. % Solid black was uniformly measured on one side of A3-sized plain paper, and was measured at 26 locations using a spectrodensitometer (Amtech) X-Lite 504/508. As is clear from this figure, a decrease in density (vertical axis) before and after fixing is observed particularly in both end regions in the width direction (horizontal axis; longitudinal direction) of the recording material, and in the width direction of the recording material. When the density difference after fixing is compared between the center side area and the both end side areas, it can be seen that there is a difference of about 0.15 at the maximum.

  In view of the above problems, the present invention suppresses toner image density unevenness after fixing in the width direction of the recording material without adding and complicating the mechanical configuration of the main body apparatus and the heating apparatus, and improves density uniformity. An object of the present invention is to provide an image forming apparatus which can be improved.

  In order to achieve the above object, in the image forming apparatus according to the present invention, transfer means for transferring a toner image formed on the surface of a rotationally driven image carrier to a recording material, and the image carrier or the recording material. A plurality of discharge electrodes for discharging the charged charges, arranged so as to face the surface of the image carrier at an appropriate interval, and the discharging unit includes the discharging unit and the transfer unit. In the image forming apparatus supported by the static eliminator holder arranged so as to partition between the discharge electrode and the static eliminator, the discharge electrode or the static eliminator holder of the static eliminator is a distance between the discharge electrode or the static eliminator holder and the image carrier Are arranged differently along the rotation axis direction of the image carrier.

  According to the image forming apparatus having such a configuration, the transfer efficiency with respect to the recording material differs in the rotation axis direction, that is, the paper width direction, which is the longitudinal direction of the image carrier, so that the density of the recording material differs in the paper width direction. For example, by reducing the transfer efficiency of the central area, for example, by reducing the density of the central area in advance at the time of an unfixed image before fixing, and making a density difference in the paper width direction of the recording material in advance, As the density of the both end side regions is reduced by passing the fixing device, the density balance between the central side region and the both end side regions is made uniform as a result.

  As described above, in the image forming apparatus according to the present invention, the facing distance between the discharge electrode or the static elimination holder of the static elimination means and the image carrier is different along the rotation axis direction of the image carrier, that is, the width direction of the recording material. Since the density of the recording material is set to be different in the width direction in advance and the density is balanced between the center side area and the both end side areas by passing the fixing device, a simple configuration is provided. The density unevenness in the width direction of the recording material can be eliminated by setting the wall-shaped portion of the static elimination holder high to prevent the occurrence of static elimination discharge traces and jams, and the reliability of the image forming apparatus. Can be improved.

[Embodiment 1]
First, the overall structure of an image forming apparatus using a charge eliminating member according to the present invention will be schematically described.

  An electrophotographic photosensitive drum 10 provided as an image carrier in the laser printer shown in FIG. 1 includes a developing device 11 having a developing sleeve 11a and a developing container 11b, and a cleaning having a waste toner container 12b having a cleaning blade 12a incorporated therein. The process cartridge is integrated with the apparatus 12 so as to constitute a process cartridge, and the entire process cartridge is detachable from the main body of the image forming apparatus. It is not always necessary to integrate all of these elements as a process cartridge. The process cartridge can be configured by integrating the photosensitive drum 10 and the developing device 11 as the minimum elements, and the other elements and charging devices can be used. A configuration in which 13 and the like are appropriately integrated can also be employed.

  The outer peripheral surface of the photosensitive drum 10 described above is uniformly charged by the charging device 13 while rotating in the direction of the arrow, and the laser light emitted from the laser exposure device 14 is reflected by the reflection mirror 14a and is reflected on the photosensitive drum 10. The outer peripheral surface is irradiated and an electrostatic latent image is formed on the photosensitive drum 10. The toner container 11b of the developing device 11 is filled with the toner 11c, and an appropriate amount of the toner 11c is appropriately charged as the developing sleeve 11a rotates, whereby the toner on the developing sleeve 11a is transferred to the photosensitive drum 10. The latent image is developed on the electrostatic latent image and visualized as a toner image.

  In addition, the paper cassette 15 which is a recording material stacking unit such as cut paper is configured so that the paper feeding roller 15a feeds the recording material one by one at a timing. The correspondingly arranged separation pads 15b are adjusted so that the friction coefficient, the installation angle, and the shape of the outer peripheral surface are fed only once for each recording medium.

  When the toner image visualized as described above moves to the contact portion with the transfer roller 16, the recording material is inserted between the photosensitive drum 10 and the transfer roller 16 in accordance with the timing. At the same time, when a positive bias voltage is applied to the transfer roller 16 by the positive voltage application power source 16a, the transfer roller 16 is charged to the positive side, whereby toner is applied to the recording material in contact with the transfer roller 16. The toner image on the photosensitive drum 10 is attracted and transferred to the recording material side.

  Further, as shown in FIG. 2, in the vicinity of the side of the transfer roller 16 and on the downstream side in the rotation direction of the photosensitive drum 10 (the left side in the drawing), the rotation shaft of the photosensitive drum 10 is arranged. A static elimination member 17 made of a plate-like member arranged along the extending direction is provided. The neutralizing member 17 is configured to be applied with a negative bias from a negative voltage application power source 17a, and by discharging negative charges to the recording material after transfer described above, neutralization of the recording material is performed. As a result, the recording material is separated from the photosensitive drum 10. Such a charge removal member 17 constitutes a main part of the present invention and will be described in detail later.

  On the other hand, the untransferred toner remaining on the photosensitive drum 10 without being transferred is stored in the waste toner container 12b by the scraping action of the cleaning blade 12a, and the photosensitive drum 10 whose surface has been cleaned is repeatedly subjected to the next image forming process. to go into. Further, the recording material on which the fixed toner image is placed is subjected to a heating / pressing action by a fixing device (see FIG. 9) having a film structure as shown in the conventional example so that the toner image is permanently fixed. It has become.

  Incidentally, as described above, since the transfer roller 16 and the charge removal member 17 are disposed at positions close to each other, the negative charge discharged from the charge removal member 17 affects the positive charge supplied to the transfer roller 16. Can be considered. In order to cancel such an influence, the transfer bias voltage applied to the transfer roller 16 described above is set to be relatively high, and as shown in FIGS. A standing wall-like portion (partition plate) 18 a of the static elimination holder 18 is arranged so as to partition the static elimination member 17.

  The static elimination holder 18 is disposed so as to surround the main body side other than the upper end portion of the static elimination member 17 shown in the figure, and prevents the static elimination member 17 from deforming or contacting with the transfer roller 16 during processing such as a paper jam. Has been made. The entire static elimination holder 18 is formed of a resin such as PPS, and the above-described standing wall-like portion (partition plate) 18a sandwiches the static elimination member 17 from the front and rear in the sheet passing direction indicated by the arrow in FIG. It is comprised from a pair of plate-shaped member arrange | positioned like this.

  The standing wall-like portion (partition plate) 18a of the static elimination holder 18 in the present embodiment is formed so as to be integrated with a main body frame 18b for guiding a recording material from the transfer portion to the fixing device. The main body frame 18b also has a function of avoiding the influence of the charge removing member 17 on the transfer roller 16.

  In particular, as shown in FIG. 3, a transport rib 20 that bridges a pair of plate-like members constituting the standing wall-like portion (partition plate) 18a of the static elimination holder 18 in the recording material passing direction is provided. The recording material is provided at a position X of 50 mm from both end positions in the width direction of the recording material. Each of the transport ribs 20 is disposed at a position higher than the upper end position of the static elimination member 17, whereby the recording material is conveyed in contact with the static elimination member 17, or the leading end of the recording material in the conveyance direction. The edge is prevented from entering a jammed state by entering downward.

  Here, as described above, the charge eliminating member 17 according to the present embodiment is disposed on the downstream side in the conveyance direction of the recording material with respect to the transfer nip formed at the contact portion between the photosensitive drum 10 and the transfer roller 16. In addition, the neutralization member 17 is provided along the paper width direction, which is the extending direction of the rotating shaft of the photosensitive drum 10, and the charge eliminating member 17 has good conductivity such as SUS plate, Ulster steel gold, aluminum plate, for example. For example, it is formed in a shape as shown in FIG.

  That is, as shown in FIG. 4, the static eliminating member 17 has an elongated plate-like substrate portion 17b extending along the width direction of the recording material, and the substrate portion 17b is shown in the drawing. A large number of needle-like or sawtooth-shaped spire-shaped discharge electrodes 17c are provided on the edge portion, that is, the edge on the recording material conveyance side, so as to form a periodic protruding shape.

  Specific examples of dimensions of the spire-shaped discharge electrode 17c include, for example, an adjacent pitch p of 1.0 mm and a plate thickness of 0.5 mm. If the sharpness of each spire-shaped discharge electrode 17c is high, the tip of the electrode The concentration of the electric field is strengthened, and gas molecules interposed between the recording material and the electrode tip are ionized to become ions. Once gas molecules are ionized, they receive a force from an electric field according to their electric polarity and are accelerated and collide with an electrode or recording material. In other words, the recording material is neutralized by a current flowing between the recording material and the spire-shaped discharge electrode 17c via ions.

  Thus, the adjacent pitch p or the electrode height (depth) d of the spire-shaped discharge electrode 17c is an important factor for determining the effective static elimination range of the electrode, and the distance between the recording material and the static elimination member 17 is determined. It will be decided according to the required static elimination capacity. The effective static elimination range of the static eliminator provided with the static elimination member 17 is an approximate range that covers the static elimination capability of one spire-shaped discharge electrode 17c. For example, as shown in FIG. 5, the upper end of the spire-shaped discharge electrode 17c It is represented by a region indicated by a dotted line extending from the center.

  That is, when the recording material is located at a position A in the drawing that is very close to the upper end position of the pinnacle-like discharge electrode 17c of the charge removal member 17, the charge removal ranges of two adjacent pinnacle-like discharge electrodes 17c are connected. Therefore, there is a range F in which static elimination is not sufficiently performed because of no overlap. On the other hand, if the recording material is separated to the position B shown in the figure, the effective charge removal ranges of the individual spire-shaped discharge electrodes 17c overlap each other, so that the surface of the recording material can be completely discharged. It becomes possible. However, the further away the recording material is from the spire-shaped discharge electrode 17c, the weaker the electric field between the recording material and the spire-shaped discharge electrode 17c, so that the neutralization effect is reduced. If a good static elimination effect is to be obtained in a state where the distance is long, a higher voltage bias is applied to the spire-shaped discharge electrode 17c so that the static elimination effect is exhibited even if there is a distance. However, in order to achieve high output, the capacity of the negative voltage application power source is required, which greatly increases the cost.

  With regard to the structure of the pinnacle-shaped discharge electrode 17c of the charge eliminating member 17, in this embodiment, the electrode height that is the position of the upper end of the pinnacle-shaped discharge electrode 17c is the width direction of the recording material, that is, the rotation of the photosensitive drum 10. The central region in the axial direction is formed so as to be higher than the both end regions, and the spire-shaped discharge electrode 17c of the charge removal member 17 has an opposing distance between the spire-shaped discharge electrode 17c and the photosensitive drum 10 described above. It arrange | positions so that it may differ along the width direction, and the opposing space | interval in a center side area | region is set so that it may become narrower than a both-ends side area | region.

  More specifically, the static elimination member in the both end side region from the both end positions of the maximum sheet passing width of the recording material to the position of about 50 mm toward the inner side in the sheet width direction (for example, refer to the symbol X in FIG. 3). The electrode height in the center side region inside the both end side regions is set to be higher by 0.8 mm than the electrode height of the 17 spire-shaped discharge electrodes 17c.

  FIG. 6 shows an image in the case where the image density output by the image forming apparatus using the structure of the conventional charge removal member and the spire-like discharge electrode 17c of the charge removal member 17 are configured to be high as in the above-described embodiment. It is the diagram which showed the relationship with a density | concentration. In the conventional structure, the distance relationship between the recording material and the discharge electrode of the charge removal member is set so as to be the optimum value of the charge removal capability, for example, the position of symbol B in FIG. When the tip height of the discharge electrode is gradually set higher (the horizontal axis in the figure), the distance between the recording material and the tip of the charge removal portion is reduced, and thus the above-mentioned range F is approached where charge removal is not sufficient. As a result, the static elimination ability of the recording material tends to decrease, and as a result, the image density (vertical axis in the drawing) also decreases.

  Furthermore, as in the present embodiment described above, the electrode height of the spire-shaped discharge electrode 17c of the static elimination member 17 is set higher in the central region than in the both end regions in the arrangement direction of the spire-shaped discharge electrode 17c. And the amount of neutralization between the positive charge from the transfer roller 16 and the negative charge from the charge removal member 17 performed on the standing wall-like portions (partition plates) 18a and 18a of the charge removal holder 18 by the spire-shaped discharge electrode 17c in the central region. As a result, the amount of positive charge from the transfer roller 16 is reduced, and the efficiency of toner transfer onto the recording paper is lower than at both end regions. For this reason, the unfixed image on the recording material before the fixing device is inserted has a higher image density in the both end regions than in the central region, and the image density in the both end regions decreases after passing through the fixing device. In addition, the density unevenness between the center side region and the both end side regions can be suppressed substantially uniformly.

  FIG. 7 is a diagram showing the result of measuring the image density in the width direction (longitudinal direction) before and after passing through the fixing device of the image forming apparatus using the present invention. As described above, by changing the discharge electrode 17b of the static elimination member 17 in the width direction, the concentration in the central region is lowered, and the difference from the concentration in the both end regions is improved to about 0.07. In addition, although the neutralization capability in the central region tends to decrease, when narrow paper is used, the stiffness of the paper is relatively strong and can be sufficiently separated even if the conventional optimum separation setting is not used. It was found that the density reduction in the central region when the height of the central region of the static elimination member 17 was increased satisfied the concentration standard sufficiently and there was no problem.

[Embodiment 2]
In the second embodiment of the present invention shown in FIG. 8, the height of the standing wall-like portion (partition plate) 18a of the static elimination holder 18 described in the first embodiment is set to be higher than the central region in the width direction. Is also set higher in both end regions, the height at which the standing wall-shaped portion (partition plate) 18a partitions the transfer roller 16 and the charge eliminating member 17 is lower in the central region than both end regions. In (a) of the figure, the height is increased stepwise in both end regions, and in (b), the height is continuously increased from the central region to both end regions. Also in the second embodiment, since the charge neutralization amount between the charge eliminating member 17 and the transfer roller 16 can be increased only in the central region, the transfer efficiency can be lowered. Similar effects can be obtained.

  As mentioned above, although the embodiment of the invention made by the present inventor has been specifically described, the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the scope of the invention. Nor.

  For example, each of the embodiments described above applies the present invention to a printer, but the present invention is not limited to this, and can be similarly applied to other image forming apparatuses.

  As described above, the present invention can be widely applied to a wide variety of image forming apparatuses including the printer according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-sectional explanatory diagram showing the overall structure of a laser printer as an example of an image forming apparatus to which the present invention is applied. FIG. 2 is an explanatory longitudinal cross-sectional view illustrating an enlarged schematic structure of a static elimination member used in the laser printer shown in FIG. 1 and a static elimination holder that supports the static elimination member. FIG. 3 is an external perspective explanatory view showing an enlarged discharge electrode portion of the charge removal member shown in FIG. 2. It is side surface explanatory drawing showing the whole static elimination member shape shown by FIG. 2 and FIG. FIG. 5 is a front explanatory view schematically showing a charge removal range for a recording material based on a positional relationship between a charge removal member and a recording paper. It is a diagram showing the relationship between the tip height of the discharge electrode of the charge removal member and the image density. It is a diagram showing an example of the result of measuring the image density before and after passing through the fixing device when the neutralizing member according to the present invention is used for the film fixing device. It is front explanatory drawing showing the structure of the standing wall-like part (partition plate) of the static elimination holder in the 2nd Embodiment of this invention. It is a longitudinal cross-sectional explanatory drawing showing the principal part structure of the film heating fixing device used for an electrophotographic recording device. It is a diagram showing an example of the result of measuring the image density before and after passing through the fixing device when a conventional static eliminating member is used for the film fixing device.

Explanation of symbols

10 Electrophotographic photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 11 Developing device 11a Developing sleeve 11b Developing container 11c Toner 12 Cleaning device 12a Cleaning blade 12b Waste toner container 13 Charging device 14 Laser exposure device 14a Reflecting mirror 15 Paper cassette 15a Feed roller 15b Separation pad 16 Transfer roller 16a Positive voltage application power source 17 Static elimination member 17a Negative voltage application power source 17b Substrate part 17c Spire-shaped discharge electrode 18 Static elimination holder 18a Standing wall part (partition plate)
18b Body frame 20 Transport rib

Claims (5)

Transfer means for transferring a toner image formed on the surface of a rotationally driven image carrier to a recording material, and a plurality of discharge electrodes for discharging charges charged on the image carrier or the recording material. In the image forming apparatus, the charge removing means arranged so as to face the surface with an appropriate interval,
The image forming apparatus, wherein the discharge electrode of the charge eliminating unit is arranged so that a facing distance between the discharge electrode and the image carrier is different along a rotation axis direction of the image carrier.   The image forming apparatus according to claim 1, wherein the facing interval is set such that a central region in a rotation axis direction of the image carrier is narrower than both end regions. Transfer means for transferring a toner image formed on the surface of a rotationally driven image carrier to a recording material, and a plurality of discharge electrodes for discharging charges charged on the image carrier or the recording material. Neutralizing means arranged so as to oppose the surface at an appropriate interval,
In the image forming apparatus provided with a partition plate arranged so as to partition the charge removing unit and the transfer unit in a wall shape,
An image forming apparatus, wherein the partition plate is arranged so that a height of partitioning between the charge eliminating unit and the transfer unit is different along a rotation axis direction of the image carrier.   The height of the partition plate between the charge eliminating unit and the transfer unit is set such that a central region in the rotation axis direction of the image carrier is lower than both end regions. The image forming apparatus according to claim 3. It has a heating element, a heat-resistant film that slides in contact with the heating element on one side, and a support that holds the heating element. The heated object contacts the other side and moves with the heat-resistant film. The image forming apparatus according to claim 1, further comprising: a heating device that transmits heat of the heating body to the heated body.

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