JP2007193233A - Image forming apparatus and intake and exhaust system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously form high quality image by preventing degradation in the charging function of a charger, caused by foreign matters sticking to the charger. <P>SOLUTION: The image forming apparatus includes: a photoreceptor drum 3 with an electrostatic latent image formed on its surface; a developing unit that develops the electrostatic latent image with toner; and a charger 5 that charges the surface of a photoreceptor drum 3 by corona discharge. Further, the image forming apparatus uses toner to which silica is added, the silica having a surface subjected to hydrophobic treatment with a trimethylsilyl group. The image forming apparatus also uses, as the charger 5, a saw-tooth charger having a saw-tooth discharge electrode. The image forming apparatus further includes a gas flow creating means. The gas flow creating means blows gas into the charger 5 from the outside of the image forming apparatus and discharges the gas inside the charger 5 to the outside of the image forming apparatus, such that gas flows from the outside of the image forming apparatus, flows into the charger 5, and flows from the charger 5 to the outside of the image forming apparatus. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a suction / exhaust system including a saw-tooth charger for charging an image carrier.

  Conventionally, a corona charging method has been used as a charging method in an image forming apparatus employing an electrophotographic method, an electrostatic recording method, or the like.

This corona charging method is a charging method in which ions generated by corona discharge are led to the surface of an electrostatic latent image carrier such as a photoconductor to be charged. For this reason, by repeatedly performing charging, O ₃ , NOx, toner, paper dust, etc. generated during corona discharge are floated in the vicinity of the corona charger, charging unevenness occurs in the corona charger, and image defects occur. The problem arises.

For example, in the case of a saw-tooth charger, which is a kind of corona charger, foreign matter such as O ₃ and NOx adheres to the tip of the discharge needle, causing defective discharge and uneven charging at that portion, and the electrostatic latent image carrier Charging failure and further image failure occur. This is because the corona discharge by the corona charger discharges the generated O ₃ , NOx, and a gas containing floating substances such as toner and paper powder floating in the image forming apparatus while collecting dust.

Therefore, in Patent Document 1, an exhaust unit that exhausts O ₃ , NOx, and the like floating in the vicinity of the image carrier is provided in the image forming apparatus.

Further, in Patent Document 2, a blow-in fan that blows air toward the charging unit and a suction fan that sucks air near the charging unit are provided in the image forming apparatus.
JP 09-026731 (released January 28, 1997) JP 2000-206841 (released July 28, 2000)

  Here, silica is added to the toner as an external additive for imparting chargeability and fluidity. This silica has a problem that charging characteristics are deteriorated by moisture during use. Therefore, the surface of silica is hydrophobized with a hydrophobizing agent having a trimethylsilyl group.

  When such a toner to which silica is added is used and a sawtooth charger is used as a charger, when about 20,000 sheets are printed, dust-like foreign matter starts to adhere to the tip of the sawtooth electrode. Thereafter, the cotton dust grows in a cotton hat shape as printing is repeated.

  When the saw-tooth charger enters such a state, the electric field strength is greatly reduced, and charging failure occurs. In particular, in a high-speed machine that performs printing at a speed of 30 sheets / minute or more, it is necessary to smoothly charge the photosensitive member by passing a large current through the saw-tooth charger, and the influence of charging failure due to a decrease in electric field strength is significant. Become.

  In addition, as one of the dust-like foreign substances adhering to the tip of the sawtooth electrode, the hydrophobizing agent floating in the machine can be considered. That is, it is considered that the hydrophobizing agent having a trimethylsilyl group has a low melting point, evaporates in a fixing process in which the toner is heated and fixed on the recording paper, and floats in the apparatus and adheres to the sawtooth electrode. Alternatively, it is conceivable that when the toner is stirred in the developing device, the toner is scattered from the toner and floats in the machine and adheres to the sawtooth electrode.

However, in Patent Document 1, since only the exhaust means are provided for removing O _3, NOx, etc. floating in the vicinity of the image bearing member, sufficiently remove O _3, NOx, etc., and to sawtooth electrode The adhesion of dust-like foreign matter cannot be prevented.

Moreover, in patent document 2, as shown in FIG. 1 described in the literature, it has the structure by which the blowing fan and the suction fan were arrange | positioned closely. For this reason, even if the gas in the vicinity of the primary charger 2 is sucked by the suction fan F2, the gas including a part of the gas is blown near the primary charger 2 by the blow-in fan F1 provided in the immediate vicinity. . For this reason, as the usage frequency of the primary charger 2 increases, O ₃ and NOx, the above-mentioned foreign substances, and the like are accumulated in the vicinity of the primary charger 2, and the charging failure caused by the primary charger 2 is appropriately corrected. Cannot be resolved.

  Therefore, the present invention prevents the charging function of the charging unit from deteriorating due to the adhesion of foreign matter to the charging unit even when the usage frequency of the charging unit increases, and can continue to form a high-quality image. The purpose is to provide.

  In order to solve the above problems, an image forming apparatus of the present invention includes an image carrier on which an electrostatic latent image is formed on a surface, a developing unit that develops the electrostatic latent image with toner, and the image carrier. In an image forming apparatus provided with a charger for charging the surface by corona discharge, a toner with externally added silica whose surface is hydrophobized with a trimethylsilyl group is used as the toner, and a sawtooth discharge is used as the charger. A saw-tooth charger having an electrode, and sucks air from outside the image forming apparatus and blows air into the charger and exhausts the gas in the charger to the outside of the image forming apparatus. A gas flow generating means for generating a gas flow into the charger and a gas flow from the charger to the outside of the image forming apparatus is provided.

  Further, the intake / exhaust system of the present invention develops the image bearing member on which an electrostatic latent image is formed on the surface, and the toner to which the electrostatic latent image is made externally added with silica whose surface is hydrophobized with a trimethylsilyl group. Provided in an image forming apparatus having a developing device and a saw-tooth charger that charges the surface of the image carrier by corona discharge from a saw-shaped discharge electrode, and sucks air from outside the image forming apparatus and blows air into the charger In addition, by exhausting the gas in the charger to the outside of the image forming apparatus, a gas flow from the outside of the image forming apparatus to the charger and a gas flow from the charger to the outside of the image forming apparatus. It is characterized by comprising a gas flow generating means for generating

  According to the above configuration, the gas flow generation unit generates a gas flow from the outside of the image forming apparatus to the inside of the charger and a gas flow from the inside of the charger to the outside of the image forming apparatus by intake and exhaust. Therefore, the gas in the charger can always be ventilated with the gas outside the image forming apparatus.

Here, silica is added to the toner as an external additive for imparting chargeability and fluidity, and the surface of the silica is hydrophobized with a hydrophobizing agent having a trimethylsilyl group. Therefore, the hydrophobizing agent floats inside the image forming apparatus, and the hydrophobizing agent tends to cause foreign matter (for example, foreign matter that grows in a cotton cap shape) at the tip of the sawtooth electrode of the charger. Further, since the charger is a corona discharge system, O ₃ , NOx, etc. are generated by the operation of the charger.

However, in the configuration of the present invention, the above-described ventilation function for the charger by the gas flow generating means causes the hydrophobic treatment agent floating in the image forming apparatus, O ₃ , NOx, and the like to float in the charger. Can be prevented. Therefore, even if frequency of use of the charger is increased, since the suspended matter, such as hydrophobizing agent and O _3, NOx discharge electrodes of the charger is hardly accumulated, the occurrence of improper charging (charge unevenness) in the charger As a result, it is possible to continue to form high-quality images without image deterioration due to uneven charging.

  In the image forming apparatus, the gas flow generation unit includes a blower that generates the gas flow, an intake duct that guides gas sucked from outside the image forming apparatus into the charger, It is good also as a structure provided with the exhaust duct which guide | induces gas to the exterior of an image forming apparatus.

  According to the above configuration, since the gas flow generating means includes the blower, the intake duct, and the exhaust duct, the gas outside the image forming apparatus is efficiently introduced into the charger, and the gas in the charger is It can be efficiently discharged outside the image forming apparatus. Thereby, it becomes possible to reduce the charging failure of the charger with a small amount of energy.

  In the image forming apparatus, the blower may include an intake fan provided in the intake duct and an exhaust fan provided in the exhaust duct.

  According to the above configuration, since the intake duct is provided with the intake fan and the exhaust duct is provided with the exhaust fan, it is possible to appropriately control the wind speed of the intake and exhaust.

  In the image forming apparatus, the charger includes a charger case having a U-shaped cross section surrounding the discharge electrode from three directions, and an end portion of the intake duct is connected to one end portion of the charger case. It is good also as a structure by which the edge part of the said exhaust duct is connected to the other end part.

  According to the above configuration, for the charger having the charger case, the operation of introducing the gas outside the image forming apparatus into the charger and the operation of discharging the gas inside the charger to the outside of the image forming apparatus. Furthermore, it can carry out efficiently.

  In the above image forming apparatus, the wind speed of the intake air into the charger may be set to be higher than the wind speed of the exhaust gas from the charger.

According to the above configuration, since the wind speed of the intake air into the charger is faster than the wind speed of the exhaust gas from the charger, the gas introduced from the outside of the image forming apparatus overflows from the charger. Become. As a result, the hydrophobic treatment agent generated inside the image forming apparatus and floating substances such as O ₃ and NOx can be reliably prevented from entering the charger, and these floating substances are accumulated in the discharge electrodes of the charger. Thus, it is possible to more reliably prevent the occurrence of charging failure.

  The image forming apparatus may have a configuration in which a plurality of the chargers are arranged for one image carrier.

  The configuration provided with the gas flow generation means of the present invention can be suitably used for an image forming apparatus in which a plurality of chargers are arranged for one image carrier. Examples of such an image forming apparatus include a high-speed printing apparatus that needs to charge the surface of the image carrier at high speed.

  The image forming apparatus may include a plurality of the image carriers, and the chargers may be arranged on the image carriers.

  The configuration provided with the gas flow generating means of the present invention can be suitably used for an image forming apparatus in which a plurality of image carriers are provided and a charger is disposed on each of the image carriers. Examples of such an image forming apparatus include a tandem type image forming apparatus in which an image carrier is provided for each ink in order to form a color image.

  The image forming apparatus may include a cleaning device that collects toner remaining on the surface of the image carrier, and the charger is disposed at a position lower than the cleaning device.

  The configuration including the gas flow generating means of the present invention is an image forming apparatus in which the charger is disposed at a position lower than the cleaning device, that is, toner scattered during cleaning, toner leaked from the cleaning device, or scattered from the toner. It can be suitably used for a configuration in which suspended substances such as external additives easily enter the charger.

  In the above image forming apparatus, the charger may be disposed at a position lower than the developing unit.

  The structure having the gas flow generation means of the present invention is an image forming apparatus in which the charger is disposed at a position lower than the developing unit, that is, toner scattered during development, toner leaked from the developing unit, or scattered from the toner. It can be suitably used for a configuration in which suspended substances such as external additives easily enter the charger.

  In the above image forming apparatus, the air pressure in the charger may be higher than the air pressure around the charger.

According to the above configuration, since the atmospheric pressure in the charger is higher than the atmospheric pressure around the charger, the hydrophobic treatment agent generated inside the image forming apparatus and the suspended matter such as O ₃ and NOx are charged by the charger. It is possible to surely prevent the intrusion into the inside, and it is possible to more reliably prevent a situation in which these floating substances are accumulated on the discharge electrode of the charger and a charging failure occurs.

  As described above, the image forming apparatus according to the present invention uses, as the toner, a toner to which silica whose surface has been hydrophobized with a trimethylsilyl group is externally added, and has a sawtooth discharge electrode as the charger. A charger is provided, and air is sucked from the outside of the image forming apparatus and blown into the charger, and gas in the charger is exhausted to the outside of the image forming apparatus. And a gas flow generating means for generating a gas flow from the inside of the charger to the outside of the image forming apparatus.

Therefore, the ventilation function by the gas flow generating means can prevent the hydrophobic treatment agent floating in the image forming apparatus, O ₃ , NOx, and the like from floating in the charger. As a result, even if the frequency of use of the charger increases, it becomes difficult to accumulate the hydrophobizing agent and floating substances such as O ₃ and NOx on the discharge electrode of the charger. Occurrence can be reduced, and as a result, it is possible to continue forming high-quality images without image deterioration due to uneven charging.

An embodiment of the present invention will be described as follows.
FIG. 2 is an explanatory diagram showing a configuration of the image forming apparatus A according to the present embodiment. Here, as an example of the image forming apparatus A, a laser printer that forms a multicolor or single color image on a sheet (recording paper) based on image data input from the outside or image data obtained by reading a document will be described as an example. To do.

  As shown in the figure, the image forming apparatus A includes an exposure unit 1, a developing device 2 (2a, 2b, 2c, 2d), a photosensitive drum 3 (3a, 3b, 3c, 3d), and a charger 5 (5a, 5d). 5b, 5c, 5d), a cleaner unit 4 (4a, 4b, 4c, 4d), an intermediate transfer belt unit 8, a fixing unit 12, a sheet conveying path S, a paper feed cassette 10, a paper discharge tray 15, and the like.

  The image data of a color image handled in the image forming apparatus A corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the developing device 2 (2a, 2b, 2c, 2d), the photosensitive drum 3 (3a, 3b, 3c, 3d), the charger 5 (5a, 5b, 5c, 5d), the cleaner unit 4 (4a, 4b, 4c and 3d) are provided four by four so as to form four types of latent images corresponding to the respective colors. The symbols a to d correspond to a being black, b being cyan, c being magenta, and d being yellow. It is configured.

  In the image station, the photosensitive drum 3 is disposed on the upper part of the image forming apparatus A. The charger 5 uniformly charges the surface of the photosensitive drum 3 to a predetermined potential. As the charger 5, a charger type as shown in FIG. 2 is used. Details of the charger 5 will be described later.

  The exposure unit 1 includes, for example, an EL or LED writing head in which light emitting elements are arranged in an array, in addition to a method using a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror as shown in FIG. Some techniques are used. The exposure unit 1 exposes the charged photosensitive drum 3 according to the input image data, thereby forming an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum 3.

  Each developing device 2 visualizes the electrostatic latent image formed on each photoconductor drum 3 with K, C, M, and Y toners. The cleaner unit 4 removes and collects the toner remaining on the surface of the photosensitive drum 3 after the development and image transfer processes. The toner used in each developing device 2 is a toner to which silica whose surface is hydrophobized with a trimethylsilyl group is externally added.

  An intermediate transfer belt unit 8 is disposed above the photosensitive drum 3. The intermediate transfer belt unit 8 includes an intermediate transfer roller 6 (6a, 6b, 6c, 6d), an intermediate transfer belt 7, an intermediate transfer belt driving roller 71, an intermediate transfer belt driven roller 72, an intermediate transfer belt tension mechanism 73, and an intermediate transfer belt. A transfer belt cleaning unit 9 is provided.

  The intermediate transfer roller 6, the intermediate transfer belt drive roller 71, the intermediate transfer belt driven roller 72, the intermediate transfer belt tension mechanism 73, and the like stretch the intermediate transfer belt 7 and rotate it in the direction of arrow B.

  The intermediate transfer roller 6 is rotatably supported by an intermediate transfer roller mounting portion in the intermediate transfer belt tension mechanism 73 of the intermediate transfer belt unit 8. The intermediate transfer roller 6 provides a transfer bias for transferring the toner image on the photosensitive drum 3 onto the intermediate transfer belt 7.

  The intermediate transfer belt 7 is provided so as to be in contact with each photosensitive drum 3. A color toner image (multicolor toner image) is formed on the intermediate transfer belt 7 by sequentially transferring the toner images of the respective colors formed on the photosensitive drum 3 in a superimposed manner. The intermediate transfer belt 7 is formed in an endless shape using a film having a thickness of about 100 μm to 150 μm.

  Transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by the intermediate transfer roller 6 in contact with the back side of the intermediate transfer belt 7. A high voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image. The intermediate transfer roller 6 is formed based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm, and the surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, the intermediate transfer roller 6 can uniformly apply a high voltage to the intermediate transfer belt 7. In this embodiment, a roller-shaped transfer electrode (intermediate transfer roller 6) is used as the transfer electrode, but a brush or the like can also be used.

  As described above, the electrostatic latent images on the respective photosensitive drums 3 are visualized with toners corresponding to the respective hues to become toner images, and these toner images are stacked on the intermediate transfer belt 7. As described above, the stacked toner images are moved to the contact position between the conveyed sheet and the intermediate transfer belt 7 by the rotation of the intermediate transfer belt 7, and the transfer roller 11 arranged at this position moves the sheet onto the sheet. Is transcribed. In this case, the intermediate transfer belt 7 and the transfer roller 11 are pressed against each other at a predetermined nip, and a voltage for transferring the toner image onto the paper is applied to the transfer roller 11. This voltage is a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner.

  In order to obtain the nip constantly, either the transfer roller 11 or the intermediate transfer belt drive roller 71 is made of a hard material such as a metal, and the other is a soft material such as an elastic roller (an elastic rubber roller or a foaming resin roller). ).

  The toner adhering to the intermediate transfer belt 7 due to the contact between the intermediate transfer belt 7 and the photosensitive drum 3 and the toner image remaining on the intermediate transfer belt 7 without being transferred when the toner image is transferred from the intermediate transfer belt 7 to the sheet. The toner is removed and collected by the intermediate transfer belt cleaning unit 9 because it causes toner color mixing in the next step. The intermediate transfer belt cleaning unit 9 is provided with a cleaning blade as a cleaning member that comes into contact with the intermediate transfer belt 7. The portion of the intermediate transfer belt 7 in contact with the cleaning blade is supported by an intermediate transfer belt driven roller 72 from the back side.

  The paper feed cassette 10 is for storing sheets used for image formation, such as recording paper, and is provided below the image forming unit and the exposure unit 1. On the other hand, the paper discharge tray 15 provided on the upper part of the image forming apparatus A is for placing printed sheets face down.

  Further, the image forming apparatus A is provided with a sheet conveyance path S for sending the sheets of the paper feed cassette 10 and the sheets of the manual feed tray 20 to the paper discharge tray 15 via the transfer roller 11 and the fixing unit 12. . In a portion from the sheet feeding cassette 10 to the sheet discharge tray 15 in the sheet conveyance path S, a pickup roller 16, a registration roller 14, a transfer unit including a transfer roller 11, a fixing unit 12, a conveyance roller 25, and the like are arranged. Yes.

  The conveyance rollers 25 are small rollers for promoting and assisting conveyance of the sheet, and a plurality of conveyance rollers 25 are provided along the sheet conveyance path S. The pickup roller 16 is a drawing roller that is provided at the end of the paper feed cassette 10 and supplies sheets from the paper feed cassette 10 to the sheet conveyance path S one by one. The registration roller 14 temporarily holds the sheet conveyed in the sheet conveyance path S, and conveys the sheet to the transfer unit at a timing when the leading edge of the toner image on the photosensitive drum 3 and the leading edge of the sheet are aligned.

  The fixing unit 12 includes a heat roller 31, a pressure roller 32, and the like. The heat roller 31 and the pressure roller 32 rotate with a sheet interposed therebetween. The heat roller 31 is controlled by a control unit (not shown) so as to have a predetermined fixing temperature. This control unit controls the heat roller 31 based on a detection signal from a temperature detector (not shown). The heat roller 31 heat-presses the sheet together with the pressure roller 33 to melt, mix, and press the color toner images transferred to the sheet, and heat-fix the sheet. The sheet on which the multicolor toner image (each color toner image) has been fixed is conveyed to the reverse sheet discharge path of the sheet conveyance path S by the plurality of conveyance rollers 25 and is reversed (the multicolor toner image is on the lower side). Are discharged onto the paper discharge tray 15.

  Next, the sheet conveyance operation by the sheet conveyance path S will be described, including processing in each unit. As described above, the image forming apparatus A is provided with the paper feed cassette 10 that stores sheets in advance and the manual feed tray 20 that is used when printing a small number of sheets. The pickup rollers 16 (16-1, 16-2) are respectively disposed in both of these, and these pickup rollers 16 supply sheets one by one to the sheet conveyance path S.

(For single-sided printing)
The sheet conveyed from the sheet feeding cassette 10 is conveyed to the registration roller 14 by the conveyance roller 25-1 in the sheet conveyance path S, and the registration roller 14 and the toner images stacked on the intermediate transfer belt 7 by the registration roller 14. Is conveyed to the transfer section at the timing of alignment with the leading edge of the sheet. In the transfer portion, a toner image is transferred onto the sheet, and this toner image is fixed on the sheet by the fixing unit 12. Thereafter, the sheet is discharged from the discharge roller 25-3 onto the discharge tray 15 through the conveyance roller 25-2.

  Further, the sheet conveyed from the manual feed tray 20 is conveyed to the registration roller 14 by a plurality of conveyance rollers 25 (25-6, 25-5, 25-4). Thereafter, the sheet is discharged to the discharge tray 15 through the same process as that of the sheet supplied from the sheet cassette 10.

(For duplex printing)
As described above, the single-sided printing is completed, and the sheet that has passed through the fixing unit 12 is chucked at the trailing edge by the paper discharge roller 25-3. Next, the sheet is guided to the transport rollers 25-7 and 25-8 by the reverse rotation of the paper discharge roller 25-3, and is printed on the back surface through the registration roller 14, and then discharged to the paper discharge tray 15. Is done.

  Here, the charger 5 will be described below with reference to FIGS. 3 and 4. Since the four chargers (5a to 5d) provided in the image forming apparatus A shown in FIG. 2 have the same configuration, the following description will be made as the charger 5 without distinction.

  FIG. 3 is a cross-sectional view schematically showing the configuration of the charger 5 and its periphery. The charger 5 is a corona discharge type charger, and has a length substantially equal to the length of the cylindrical photosensitive drum 3 in the longitudinal direction (perpendicular to the paper surface in FIG. 3), and extends along the photosensitive drum 3. is set up.

  The charger 5 includes a charge generation unit 50 that generates charges, a mesh grid electrode 54 that is interposed between the charge generation unit 50 and the photosensitive drum 3, and a grid electrode that fixes the grid electrode 54 to the charge generation unit 50. A holding member 55 is provided.

  The charge generation unit 50 includes a charger case 51, a discharge electrode 53, and a discharge electrode holding member 52 that fixes the discharge electrode 53 to the charger case 51. The charger case 51 is formed in a U-shaped cross section, and is arranged so that the opening portion faces the photosensitive drum 3.

  The grid electrode holding member 55 and the discharge electrode holding member 52 are insulating members and insulate between the charge generation unit 50 and the grid electrode 54 and between the discharge electrode 53 and the charger case 51.

  A first DC power supply 56 is connected to the grid electrode 54 and the charger case 51, and a voltage having a potential difference Vg (Vg <0) is applied to the ground potential. A second DC power source 57 is connected to the discharge electrode 53, and a voltage having a potential difference Vc (Vc <Vg <0) is applied to the ground potential. As a result, an electric field is generated between the charger case 51 and the discharge electrode 53, the atmosphere is ionized by the electric field, and negative charges (negative ions) are generated around the discharge electrode 53. The generated negative charge moves toward the photosensitive drum 3 while being attracted to the grid electrode 54 and spreads, and what passes through the grid electrode 54 reaches the surface of the photosensitive drum 3.

  The surface of the photosensitive drum 3 is made of a member having semiconductivity when not exposed and having conductivity when exposed. As described above, the surface of the photosensitive drum 3 is initialized and charged by the negative charge reaching the surface of the photosensitive drum 3, and becomes a predetermined initialization charging potential VO. When the surface of the initialized photosensitive drum 3 is exposed, the portion (bright portion) becomes conductive, and the negative charge moves to the ground. In the portion where the negative charge has moved, the potential changes in the positive direction and becomes the bright portion potential VE. An electrostatic latent image is formed by a portion where the negative charge is present and a portion where the negative charge is not present on the surface of the photosensitive drum 3, that is, a portion of the initialization charging potential VO and a portion of the bright portion potential VE.

  As shown in FIG. 4, the discharge electrode 53 of the charger 5 is formed in a sawtooth shape, and discharge is performed from the tip portion 53a of the sawtooth. That is, the charger 5 is a sawtooth charger in which the discharge electrode 53 has a sawtooth shape.

Here, silica is added to the toner as an external additive for imparting chargeability and fluidity, and the surface of the silica is hydrophobized with a hydrophobizing agent having a trimethylsilyl group. Therefore, the hydrophobizing agent floats inside the image forming apparatus, and the hydrophobizing agent tends to cause foreign matter (for example, foreign matter that grows in a cotton cap shape) at the tip of the sawtooth electrode of the charger. In general, in corona discharge, O ₃ , NOx, and the like are generated when ions are generated. As the number of discharges increases, the amount of O ₃ and NOx accumulated in the tip 53a of the charger 5 also increases. When the above-mentioned deposit (accumulated matter) is generated at the tip 53a of the charger 5, the discharge cannot be sufficiently performed, and there is a risk that uneven charging (charge unevenness) to the photosensitive drum 3 by the charger 5 may occur. is there. In addition to the above, toner and paper powder are also floating in the vicinity of the charger 5, and even if the toner or paper powder adheres to the tip 53 a of the charger 5, Reduce performance.

Therefore, in the present embodiment, as shown in FIG. 1, the longitudinal direction of the photosensitive drum 3 as the image carrier (the axis of the photosensitive drum 3) in the charger 5 (in the charger case 51) by intake and exhaust. (Direction) gas (air) flow (gas flow) is generated. As a result, O ₃ , NOx, and other floating substances generated by corona discharge of the charger 5 and floating in the charger 5 (in the charger case 51) are caused to flow in the charger 5 (in the charger case 51) by the gas flow. Since it can be discharged from (inside), it is possible to always maintain an optimum charged state.

  The gas flow can be realized by an intake / exhaust system 60 (gas flow generating means) as shown in FIG.

  FIG. 5 is a diagram illustrating an outline of the intake / exhaust system 60 with respect to the charger 5, and FIG. 6 is a cross-sectional view taken along the line XX in the intake / exhaust system 60 illustrated in FIG. 5. In FIG. 6, the discharge electrode 53 and the like in the charger 5 are omitted, and only the charger case 51 is displayed.

  As shown in FIG. 5, the intake / exhaust system 60 includes ducts (61, 62) at both ends of each charger case 51 in order to generate a gas flow in the longitudinal direction of the charger 5 (5 a to 5 d). Is provided. An intake duct 61 for taking in gas outside the image forming apparatus A is provided on the intake side of the charger 5, and the gas in the charger 5 is supplied to the exhaust side of the charger 5 in the image forming apparatus A. An exhaust duct 62 for discharging to the outside is provided.

  That is, the intake / exhaust system 60 includes an intake duct 61 for introducing gas from outside the image forming apparatus A into the charger 5 (in the charger case 51), and gas in the charger 5 (in the charger case 51). And an exhaust duct 62 for exhausting the air to the outside of the image forming apparatus A. Then, in order to appropriately perform the intake from the outside of the image forming apparatus A and the exhaust to the outside of the image forming apparatus A, an end portion on the intake side of the intake duct 61 is formed in the casing of the image forming apparatus A. The end of the exhaust duct 62 on the exhaust side reaches the vicinity of the exhaust port (not shown) formed in the housing of the image forming apparatus A. . The intake port and the exhaust port are formed in one and the other of a pair of wall portions facing each other in the housing of the image forming apparatus A, for example.

  An intake fan 63 for taking in gas from the outside is provided at the intake side end of the intake duct 61. The intake duct 61 is connected to the charger case 51 of each charger 5 via connection ducts 61a to 61d. As the intake fan 63, for example, a fan of model number BG0703-B054 manufactured by Minebea Co., Ltd. can be used.

  On the other hand, an exhaust fan 65 for exhausting the gas from each charger 5 through an ozone filter 64 is provided at the exhaust side end of the exhaust duct 62. The exhaust duct 62 is connected to the charger case 51 of each charger 5 via connection ducts 62a to 62d. As the exhaust fan 65, for example, a fan of model number: D10F-24PM manufactured by Nidec Corporation can be used.

In the intake / exhaust system 60 having the above configuration, first, the gas taken in from the outside of the image forming apparatus A by the intake fan 63 flows from the intake duct 61 into the chargers 5 through the connection ducts 61a to 61d. Next, the gas flowing into each charger 5 is drawn toward the exhaust duct 62 by the exhaust fan 65 via the connection ducts 62a to 62d. Thereafter, the gas passes through the ozone filter 64 and is discharged from the exhaust fan 65 to the outside of the image forming apparatus A. The ozone filter 64 adsorbs O ₃ generated in the charger 5.

Here, in the intake / exhaust system 60, it is possible to reliably remove O ₃ , NOx, and the like by appropriately setting the velocity of the gas passing through each charger 5 (inside the charger case 51), that is, the wind velocity. It becomes. This wind speed can be controlled by the rotational speeds of the intake fan 63 and the exhaust fan 65. Experiments relating to these optimum wind speed values will be described later.

  The rotation speeds of the intake fan 63 and the exhaust fan 65 are controlled by the control device 100 shown in FIG.

  The control device 100 includes an intake fan drive motor (first motor) 101 that rotates the intake fan 63, an exhaust fan drive motor (second motor) 102 that rotates the exhaust fan 65, and the rotation speed of the first motor. Is connected to a first motor rotation number setting unit 103 for setting the second motor rotation number setting unit 104 for setting the rotation number of the second motor.

  That is, by setting the rotation speeds of the intake fan drive motor 101 and the exhaust fan drive motor 102 by the first motor rotation speed setting section 103 and the second motor rotation speed setting section 104, the inside of the charger 5 in the intake / exhaust system is set. The wind speed is set.

Note that the amount of accumulated O ₃ , NOx, and other floating substances, that is, the floating amount of floating substances differs between the initial charging state and the state after time has elapsed, so the wind speed in the charger 5 is not constant. May be. In other words, the wind speed when the floating amount of O ₃ and NOx and other suspended matter is small small, by increasing the wind speed when the floating amount of O ₃ and NOx and other suspended matter is large, O ₃ Ya according to the situation NOx and other suspended matters can be appropriately exhausted from the inside of the charger 5.

Specifically, the chargers 5, provided with a NOx concentration detection sensor 106 for detecting the concentration of ozone concentration detection sensor 105, NOx for detecting the concentration of O _3, according to the detected values from the sensors The rotation speed of each motor in the first motor rotation speed setting section 103 and the second motor rotation speed setting section 104 may be set.

Thus, if the rotation speed of each motor is controlled in accordance with the O ₃ concentration or NOx concentration in the charger 5, it is possible to reduce the noise caused by the rotation of the motor and reduce the power consumed by each motor. There is an effect.

  For example, even when the noise of the intake fan 63 increases as the wind speed increases, it is only necessary to temporarily increase the wind speed. Noise can be reduced.

  Hereinafter, the relationship between the wind speed and the charging unevenness in the intake / exhaust system 60 provided in the vicinity of the charger 5 in the image forming apparatus A having the above configuration will be described with reference to each experimental example described later.

  First, the apparatus for measuring the wind speed in the intake / exhaust system used for this experiment is demonstrated based on FIG. 8 and FIG. Here, the wind speed inside the charger 5 and the wind speed inside the intake duct 61 and the exhaust duct 62 constituting the intake / exhaust system are measured.

  As shown in FIG. 8, the charger 5, the intake duct 61 and the exhaust duct 62 are provided with a sensor 201 for detecting the wind speed. The value detected by the sensor 201 is input to the processing unit 202, and after predetermined processing is performed, information indicating the wind speed is displayed on the monitor 203.

  As shown in FIG. 9, the sensor 201 has a structure in which a propeller-shaped rotating part 201b is provided in a cylindrical part 201a, and measures the wind speed inside the cylindrical part 201a, that is, the charger 5. That is, the sensor 201 outputs an electrical signal from the rotating unit 201b rotated by the gas passing through the cylinder unit 201a to the processing unit 202 as a detection value obtained by detecting the wind speed.

  As this sensor 201, for example, a sensor whose model number is THERM 2285-2 manufactured by Ashburn Mess- und Regelugstechnik GmbH can be used.

  In the following description, symbols for determining the degree of charging unevenness (hereinafter referred to as charge unevenness) will be described with reference to FIG.

  In FIG. 10, “◯” indicates a state in which no streak is generated, “○ Δ” indicates a state in which several thin streaks are generated, and “Δ” indicates that a thin streak is entirely present. “Δ ×” indicates a state in which a dark streak is generated, and “×” indicates a state in which a dark streak is generated as a whole. In addition, these charge nonuniformity was judged visually by printing a 16-tone pattern on paper as a print sample. When the above “Δ” is determined, it is determined that charge unevenness has occurred, and the experimental results will be described below.

  FIG. 11 to FIG. 13 show the relationship between the difference in wind speed in the intake / exhaust system (difference between the intake side and the exhaust side) and the number of printed sheets until the charge unevenness Δ level is reached (hereinafter referred to as “charge unevenness reached number”). Show about.

  FIG. 11 shows the wind speed of the intake section (intake duct 61 side) in the intake / exhaust system, the wind speed of the exhaust section (exhaust duct 62 side), the wind speed in the charger 5 (MC), and the number of charge unevenness arrivals. It is the table | surface which showed the measured result. Here, a live-action AGING test was performed by repeating a 4-sheet continuous multi of A4 size originals using only black toner. The reference original used for printing used a 5% band pattern. The evaluation criterion was the number of sheets generated when the charge unevenness reached the “Δ” level. Further, the wind speed in the exhaust section is constant (2.12 m / s), and the wind speed in the intake section is changed to cause a wind speed difference in the MC.

  From the results shown in FIG. 11, it can be seen that the faster the wind speed in the charger 5 (MC), the greater the number of charge unevenness arrivals. That is, it can be seen that the charge unevenness is less likely to occur as the wind speed in the charger 5 (MC) increases. The wind speed in the charger 5 (MC) is the speed of the gas flow flowing in the charger case 51 in the longitudinal direction of the charger case 51.

  Assuming that the wind speed in the MC is x (m / s), the number of charge unevenness arrival (the number of images until an image formed according to a predetermined standard is determined to be poorly charged) is y (thousand). When the result shown in FIG. 11 is graphed, a graph as shown in FIG. 12 is obtained. Here, the predetermined reference is the reference shown in FIG. 10, and in this case, Δ.

When an approximate expression is obtained from the graph shown in FIG. 12, y = 12.0e ^1.4x . The scope of a preferred relationship between the wind speed and charge unevenness reach number in MC from the graph, the range indicated by y ≦ 12.0e ^1.4x (range in the lower right of the graph).

  Further, since it is considered that the inside of the MC is turbulent, in this case, it is necessary to change the above relational expression. That is, a result obtained by raising the wind speed in the MC shown in FIG. 11 to the power of 1.75 may be expressed as x ′ (m / s). The relationship between x 'and the number of charge unevenness arrivals y is a graph as shown in FIG. When an approximate expression is obtained from this graph, y = 47.4x ′ + 7.2. A range indicating a preferable relationship between x ′ and the number of reached charge unevenness is a range represented by y ≦ 47.4x ′ + 7.2 (a lower right range in the graph).

  From the above results, it can be seen that uneven charging is less likely to occur as the wind speed in the charger 5 increases.

  Here, based on the results shown in FIG. 11, the wind speeds of the intake and exhaust sections are set so that the wind speed of the intake section is in the range of 1.9 to 4.2 times the wind speed of the exhaust section. It turns out that is preferable. That is, when the wind speed of the intake section is 4.00 m / s and the wind speed of the exhaust section is 2.12 m / s, the wind speed of the intake section is about 1.9 times the wind speed of the exhaust section. When the wind speed of the intake section is 8.92 m / s and the wind speed of the exhaust section is 2.12 m / s, the wind speed of the intake section is about 4.2 times the wind speed of the exhaust section. Further, if the wind speed in the intake section is greater than about 4.2 times the wind speed in the exhaust section, initial charge unevenness occurs. That is, the charge unevenness from the initial state refers to a state in which the charge unevenness has occurred from the initial state, and is not caused by the adhesion of foreign matter to the discharge portion, but is caused by the wind speed becoming too high. That is, since the vibration is applied to the grid portion of the charger due to the influence of the wind speed, the charging control to the photosensitive member becomes unstable, potential fluctuations occur in the longitudinal direction of the photosensitive member, and the light and shade that cannot withstand actual use. Unevenness appears.

  Further, the wind speed of the gas flow in the MC is preferably set to be 1 m / sec or more and less than 2.5 m / sec for the following reason. This is because when the wind speed of the gas flow in the MC is less than 1 m / sec, almost no effect (an effect of reducing charging unevenness) appears, and when 2.5 m / sec or more, charging unevenness occurs from the beginning. is there.

  Here, the result of having experimented by setting variously the wind speed of the intake part of the intake / exhaust system in this invention and the wind speed of an exhaust part is shown.

  Experiment No. 1 shown in FIG. No. 1 is a measurement in which only the exhaust wind speed is defined by the current process (a process not using the intake duct 61 and the exhaust duct 62), and the number of charge unevenness arrivals is measured. There are two types of process speeds: high (225 mm / s) and low (167 mm / s). This point is the following experiment No. 2-Experiment No. 2 It is the same up to 6. In this experiment No. In No. 1, the charge unevenness arrival number was 10k at any process speed.

  In addition, Experiment No. 2-Experiment No. 2 5, the exhaust air speed is kept constant at 2.21 m / s and the intake air speed is gradually increased to 0 m / s, 4 m / s, 6 m / s, and 8.92 / using the intake / exhaust system shown in FIG. In this way, the number of charged unevenness reached is measured. Among these experiments, those exceeding about 30k, which is the number of charge unevenness at the practical level, are shown in Experiment No. 4). Experiment No. It was 5.

  Experiment No. 5, it was found that the number of charge unevenness reached 79k or more at any process speed. And experiment no. 2-Experiment No. 2 5 has the most preferable relationship between the intake air speed and the exhaust air speed. It turned out to be 5.

  In addition, Experiment No. 6 shows the exhaust wind speed in Experiment No. 2-Experiment No. 2 It is faster than the exhaust wind speed up to 5, set to 5.05 m / s, the intake wind speed is set to 0 m / s, and the number of charge unevenness arrivals is measured. In this experiment No. In No. 6, it was found that the charge unevenness reaching number was 20k when the process speed was low, whereas the charge unevenness reaching number was 10k when the process speed was high.

  In the above experiment No. 2-Experiment No. 2 From the experimental results up to 5, the relationship between the intake air speed and the number of charge unevenness arrivals is shown in the table shown in FIG. 17, and the result is shown in FIG. Here, the influence of the intake air speed on the number of charge unevenness arrivals is shown. That is, it can be seen that the charge unevenness reaching number tends to increase as the intake air speed increases.

  Subsequently, the experiment No. 1 shown in FIG. 7 to Experiment No. Up to 12, experiment no. 1 to Experiment No. 1 Unlike FIG. 6, this is a process for forming a color image, that is, an experiment for confirming the number of charged unevennesses when there are four chargers 5. Therefore, the exhaust wind speed and the intake wind speed are set for each charger 5 corresponding to each color.

  Experiment No. No. 7 is a measurement in which only the exhaust wind speed is defined by the current process (a process that does not use the intake duct 61 and the exhaust duct 62), and the number of charge unevenness arrivals is measured. The process speed is 167 mm / s for color development and 225 mm / s for monochrome development. This point is the following experiment No. 8 to Experiment No. It is the same up to 12. In this experiment No. 7, the number of charge unevenness reached was 10k.

  In addition, Experiment No. 8 to Experiment No. No. 10 is a measurement of the number of charge unevenness arrivals using the intake / exhaust system shown in FIG. 1 while making the exhaust wind speed faster than the intake wind speed. None of these experiments exceeded about 30k, which is the number of charge unevenness achieved at a practical level.

  Experiment No. 11 is an experiment no. 7, only the exhaust air speed is defined by the current process (a process not using the intake duct 61 and the exhaust duct 62), and the number of charge unevenness arrivals is measured.

  Experiment No. No. 12 is an experiment No. for both the intake air velocity and the exhaust air velocity. 11, but in order to increase the exhaust efficiency, the charger case 51 of the charger 5 is sealed with a urethane seal, and the number of charge unevenness arrivals is measured.

  In addition, Experiment No. 1 shown in FIG. 1, the intake air speed was measured at the inlet of the intake fan 63 of the intake duct 61 with respect to the charger 5 corresponding to only black using the intake and exhaust system shown in FIG. Wind velocity) and the exhaust wind speed are set to 6.50 m / s, and the number of charge unevenness arrivals is measured. In this experiment No. In No. 13, the number of charge unevenness reaching the practical level was not reached.

  The above experiment No. 6-13 and Experiment No. The experimental results in 2 are summarized in the table shown in FIG.

  As can be seen from the results shown in FIG. 19, in the case where the exhaust wind speed was made higher than the intake wind speed, the number of charge unevenness arrivals did not reach the practical level (about 30 k). That is, it can be seen that the wind speed in the charger 5 cannot be increased only by increasing the exhaust wind speed.

  From the above, the intake / exhaust system 60 of the image forming apparatus according to the present embodiment generates a gas flow in the longitudinal direction of the charger 5 in the charger 5 by the intake and exhaust air. It becomes possible to always exhaust the gas.

Here, as described above, the hydrophobizing agent is suspended inside the image forming apparatus. Further, since the charger 5 is a corona discharge type, when the charger 5 operates, O ₃ , NOx, etc. are generated by the corona discharge. In such a case, the floating substance is exhausted by the gas flow generated in the longitudinal direction in the charger 5 as described above.

  As a result, even if the usage frequency of the charger 5 (printing frequency in the image forming apparatus) increases, the floating matter is less likely to be accumulated in the charger 5, so that charging failure (charging unevenness) occurs in the charger 5. As a result, it is possible to continue to form a high-quality image without image deterioration due to uneven charging.

  The intake / exhaust system 60 includes an intake duct 61 for guiding a gas from outside the image forming apparatus A into the charger 5 (in the charger case 51) and an image of the gas from the charger 5 (in the charger case 51). An exhaust duct 62 for exhausting the outside of the forming apparatus A is provided. In this way, with the configuration in which intake is performed via the intake duct 61, the gas can be efficiently guided into the charger 5 (inside the charger case 51) compared to a configuration in which intake is not performed via the intake duct 61. Further, in the configuration in which the exhaust is performed through the exhaust duct 62, the gas existing in the charger 5 (in the charger case 51) can be efficiently exhausted as compared with the configuration in which the exhaust is not performed through the exhaust duct 62. it can. As a result, even if the same wind speed of the gas on the intake side and the same wind speed of the gas on the exhaust side are provided, the wind speed of the gas flowing in the charger 5 (inside the charger case 51) can be reduced by providing the intake duct 61 and the exhaust duct 62. Can be increased. Therefore, it is possible to efficiently reduce charging defects with a small amount of energy.

  Further, in order to efficiently increase the wind speed of the gas flowing in the charger 5 (in the charger case 51), the intake fan 61 may be provided in the intake duct 61 and the exhaust fan 5 may be provided in the exhaust duct 62.

  The intake / exhaust system 60 may be configured such that the intake duct 61 and the exhaust duct 62 are not provided, the intake fan 63 is provided on the intake side in the gas flow, and the exhaust fan 65 is provided on the exhaust side of the gas flow. Good.

  Also in this case, although not as much as when the intake duct and the exhaust duct are provided, the wind speed of the gas in the charger 5 (in the charger case 51) can be increased as compared with the case where each fan is not provided.

  Further, from the above various experiments, in order to increase the wind speed of the gas in the charger 5 (in the charger case 51), the wind speed on the intake side for introducing the gas into the charger 5 is changed to the gas from the charger 5. What is necessary is just to set it larger than the wind speed of the exhaust side which exhausts.

  Furthermore, the wind speed on the intake side is preferably set to be 1.9 times or more and 4.2 times or less of the wind speed on the exhaust side.

In this case, if the wind speed on the intake side is less than 1.9 times the wind speed on the exhaust side, the wind speed of the gas in the charger 5 cannot be sufficiently increased, so that O ₃ or the like is accumulated and charging failure occurs. Is likely to occur.

  On the other hand, if the wind speed on the intake side is greater than 4.2 times the wind speed on the exhaust side, the wind speed of the gas in the charger 5 becomes too high and an initial charging failure tends to occur. This initial charging failure refers to a state where charging unevenness has always occurred from the initial state.

  From the above, in the image forming apparatus according to the present embodiment, even if the charging device 5 is used for a long time, the floating matter floating in the charging device 5 can be appropriately discharged. It is possible to form a high-quality image without influence.

As described above, the present invention is suitably used for a laser printer or the like, and in particular, is used for an electrophotographic image forming apparatus that employs a charging method in which O ₃ , NO x, or the like is easily generated by corona discharge.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can be applied to an electrophotographic image forming apparatus, and in particular, can be applied to an image forming apparatus including a charger adopting a corona discharge method.

1, showing an embodiment of the present invention, is a schematic configuration diagram showing a configuration of an intake / exhaust system in an image forming apparatus. FIG. 1 is a schematic longitudinal sectional view showing a configuration of an image forming apparatus of the present invention. FIG. 3 is a schematic diagram showing a positional relationship between a charger and a photosensitive drum provided in the image forming apparatus shown in FIG. 2. FIG. 4 is a schematic perspective view of the charger illustrated in FIG. 3. It is a top view which shows the whole structure of the intake / exhaust system shown in FIG. FIG. 6 is a cross-sectional view taken along line XX in FIG. 5. FIG. 3 is a block diagram of a control device provided in the image forming apparatus shown in FIG. 2. It is a schematic explanatory drawing of the apparatus for measuring a wind speed. It is a front view of the wind speed sensor with which the apparatus shown in FIG. 8 is provided. It is a figure which shows the criteria for judgment of charge nonuniformity. It is a figure which shows the result of the charge non-uniformity arrival number obtained by the wind speed of each part in the said intake / exhaust system. It is a graph which shows the relationship between the wind speed in MC obtained based on the result shown in FIG. It is a graph which shows the relationship between the wind speed in MC obtained based on the result shown in FIG. Experiment No. 1 to Experiment No. 1 It is a figure which shows the experimental result to 6. Experiment No. 7 to Experiment No. It is a figure which shows the experimental result to 12. Experiment No. It is a figure which shows 13 experimental results. Experiment No. 2-Experiment No. 2 5 is a diagram showing the results of the intake air speed and the number of charge unevenness arrivals in FIG. FIG. 18 is a graph of intake air speed and charge unevenness arrival number obtained from the result shown in FIG. 17. Experiment No. 2, Experiment No. 6 to Experiment No. It is a figure which shows the comparison result of the experimental result to 13.

Explanation of symbols

1 Exposure Unit 2 Development Device (Developer)
3 Photosensitive drum (image carrier)
4 Cleaner Unit 5 Charger 50 Charge Generation Unit 51 Charger Case 52 Discharge Electrode Holding Member 53 Discharge Electrode 53a Tip 54 Grid Electrode 55 Grid Electrode Holding Member 56 First DC Power Supply 57 Second DC Power Supply 60 Intake / Exhaust System (Gas Flow Generation Means)
61 Intake ducts 61a to 61d Connection duct 62 Exhaust ducts 62a to 62d Connection duct 63 Intake fan 64 Ozone filter 65 Exhaust fan 100 Control device (wind speed control means)
DESCRIPTION OF SYMBOLS 101 Intake fan drive motor 102 Exhaust fan drive motor 103 1st motor rotation speed setting part 104 2nd motor rotation speed setting part 105 Ozone concentration detection sensor 106 NOx concentration detection sensor 201 Sensor 201a Tube part 201b Rotation part 202 Processing part 203 Monitor

Claims (11)

An image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed; a developing unit that develops the electrostatic latent image with toner; and a charger that charges the surface of the image carrier by corona discharge. ,
As the toner, a toner externally added with a silica whose surface is hydrophobized with a trimethylsilyl group is used, and a serrated charger having a serrated discharge electrode is provided as the charger,
The flow of gas from the outside of the image forming apparatus to the inside of the charger by sucking air from the outside of the image forming apparatus and blowing the air into the charger and exhausting the gas in the charger to the outside of the image forming apparatus. An image forming apparatus comprising: a gas flow generating means for generating a gas flow from the inside of the charger to the outside of the image forming apparatus.   The gas flow generation means includes a blower that generates the gas flow, an intake duct that guides gas sucked from outside the image forming apparatus into the charger, and gas inside the charger outside the image forming apparatus. The image forming apparatus according to claim 1, further comprising an exhaust duct leading to   The image forming apparatus according to claim 2, wherein the blower includes an intake fan provided in the intake duct and an exhaust fan provided in the exhaust duct.   The charger has a U-shaped charger case surrounding the discharge electrode from three directions, an end of the intake duct is connected to one end of the charger case, and the exhaust is connected to the other end of the charger case. The image forming apparatus according to claim 2, wherein ends of the ducts are connected.   The image forming apparatus according to claim 3, wherein the wind speed of the intake air into the charger is set to be higher than the wind speed of the exhaust gas from the charger.   2. The image forming apparatus according to claim 1, wherein a plurality of the chargers are arranged for one image carrier.   The image forming apparatus according to claim 1, wherein a plurality of the image carriers are provided, and the chargers are arranged on the image carriers.   The image forming apparatus according to claim 1, further comprising a cleaning device that collects toner remaining on the surface of the image carrier, wherein the charger is disposed at a position lower than the cleaning device.   The image forming apparatus according to claim 1, wherein the charger is disposed at a position lower than the developing unit.   The image forming apparatus according to claim 1, wherein the air pressure in the charger is higher than the air pressure around the charger. An image carrier on which an electrostatic latent image is formed on the surface, a developing device for developing the electrostatic latent image with a toner having a surface hydrophobized with a trimethylsilyl group, and a sawtooth discharge electrode Provided with an image forming apparatus having a saw-tooth charger for charging the surface of the image carrier by corona discharge.
The flow of gas from the outside of the image forming apparatus to the inside of the charger by sucking air from the outside of the image forming apparatus and blowing the air into the charger and exhausting the gas in the charger to the outside of the image forming apparatus. And a gas flow generating means for generating a gas flow from the inside of the charger to the outside of the image forming apparatus.

Images