JP2005233991A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which discharge phenomenon (short circuit) does not occur even when the distance between members to be electrified to high potential is narrowed. <P>SOLUTION: The image forming apparatus 10 is provided with a scraper 42, which is not grounded, cleaning residue remaining on a transfer body 38 to which specified bias is applied and a wiping member 46, attached to a grounded paper carrying guide 44 and carrying out auxiliary cleaning of residue remaining on the transfer body 38 in the vicinity of the scraper 42. The scraper 42 or the surface of the paper carrying guide 44 is covered by an insulating member 48 in a discharging range of the scraper 42 and the paper carrying guide 44. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers using an electrophotographic system (electrostatic transfer system) are widely known. In such an image forming apparatus, the toner image is transferred onto the recording paper by the final transfer member, and the toner image is fixed by the fixing device, whereby a toner image as a permanent image is formed on the recording paper.

  In such an image forming apparatus, it is necessary to control a toner image forming process in order to prevent fluctuations in environmental conditions such as temperature and humidity and fluctuations in image density due to changes over time. As a means for controlling the toner image formation process, for example, a test toner patch is formed on the surface of the final transfer member, the toner patch is detected by an optical density sensor, and a resist patch is detected based on the position and density of the toner patch. It is conceivable to control the image quality by so-called process control that performs adjustment control and toner image density control. Here, in order to obtain good results, it is necessary to keep the surface of the final transfer member clean, and residual toner on the surface of the final transfer member is always cleaned with a metal scraper or the like. (For example, refer to Patent Document 1).

  However, as the neutral papermaking of recording paper has been promoted in recent years, it has been added for the purpose of improving various properties such as recording paper surface smoothness, printability (ink acceptability), whiteness, and opacity. There is a tendency that the amount of calcium carbonate added has increased. That is, as the amount of calcium carbonate added as a paper component increases, the above characteristics are improved, but the possibility of calcium carbonate peeling off from the recording paper increases during the conveyance of the recording paper. If this peeled calcium carbonate adheres to each conveyance roll, the conveyance capability will fall, and also various problems generate | occur | produce by adhering to another member.

  In particular, when calcium carbonate or silica oxide, which is an external additive of toner, adheres to the surface of the final transfer body, the attached calcium carbonate scrapes the edge of the scraper, so that wear of the edge is accelerated. As described above, when the edge of the scraper is dulled, or when calcium carbonate, residual toner, or an external additive adheres to the edge, the adhesion between the edge and the final transfer member is lowered, resulting in poor cleaning.

  In addition, if calcium carbonate or silica oxide adheres to the final transfer body, the surface reflectance of the final transfer body decreases, so the reflected light intensity of the toner patch formed on the final transfer body decreases and accurate measurement can be performed. This causes a problem that the process control described above becomes difficult.

  Furthermore, even if calcium carbonate, silica oxide, or the like does not adhere to the final transfer body, the calcium carbonate attached to the edge of the scraper wears the surface of the final transfer body or scratches the surface of the final transfer body. Therefore, the surface reflectance is lowered, and similarly, the reflected light intensity of the toner patch formed on the final transfer member is lowered and accurate measurement cannot be performed, so that the process control described above becomes difficult.

As described above, when calcium carbonate or the like, which is the paper component of the recording paper, stays on the final transfer member, various problems occur. Therefore, as shown in FIG. 6, the paper transport guide 44 positioned on the downstream side of the scraper 42. A wiping member 46 is provided at the front end 44 </ b> A for auxiliary wiping of calcium carbonate, silica oxide or the like remaining on the surface of the final transfer body 38. According to this, adhesion of calcium carbonate, silica oxide or the like to the surface of the final transfer member 38 can be prevented, and fine scratches can be prevented from being attached to the final transfer member 38.
JP 2001-75448 A

  However, when such a wiping member 46 is provided, the front end 44A of the paper transport guide 44 falls downward due to its weight, and is in a state of being extremely close to the metal scraper 42 (the front end 44A of the paper transport guide 44). The shortest distance D to the scraper 42 is 1.5 mm or less). For this reason, there arises a problem that a discharge phenomenon (leakage) occurs between the two.

That is, the paper transport guide 44 is made of a metal plate, and is normally grounded (grounded) via a varistor or the like so as to eliminate the charge and not charge the recording paper transported to the transfer position. On the other hand, a voltage of +1200 V to +6000 V is applied to the final transfer body 38 so that a transfer current of 10 μA to 30 μA is secured. In particular, in a low temperature and low humidity environment, the resistance of the final transfer body 38 increases (usually 10 ⁸ Ω but 10 ⁹ Ω), so a voltage of +3500 V to +6000 V is applied. At this time, since the scraper 42 is always in contact with the final transfer member 38, the scraper 42 is charged to a high potential of + 3500V to + 6000V.

  Therefore, if the tip 44A of the paper transport guide 44 and the scraper 42 are arranged close to each other, a discharge phenomenon (leakage) occurs between them, and a part of the voltage applied to the final transfer member 38 is impaired. There is a problem in that a sufficient transfer current cannot be obtained and a transfer failure to a recording sheet occurs. Moreover, in recent years, since the downsizing and unitization of the image forming apparatus has been promoted without providing the wiping member 46 as described above, the distance between the members charged to a high potential tends to be extremely narrow. Therefore, there is a high possibility that such a discharge phenomenon (leakage) occurs.

  In view of the above problems, an object of the present invention is to obtain an image forming apparatus in which a discharge phenomenon (leakage) does not occur even when the distance between members charged to a high potential is reduced.

  In order to achieve the above object, an image forming apparatus according to claim 1 of the present invention includes a non-grounded scraper for cleaning a residue remaining on a member to which a predetermined bias is applied, and a grounded. In the image forming apparatus, comprising: a wiping member that is attached to the conductive member and that supplementarily cleans the residue remaining on the member in the vicinity of the scraper. The discharge of the scraper and the conductive member is possible. The surface of the scraper or the conductive member in the region is covered with an insulating member.

  According to the first aspect of the present invention, the residue remaining on the member to which a predetermined bias is applied is cleaned with a scraper that is not grounded. For this reason, the scraper is also charged, but since the surface of the scraper or the conductive member in the dischargeable region between the scraper and the grounded conductive member is covered with the insulating member, the distance between the two can be reduced. No discharge phenomenon (leakage) occurs.

  The image forming apparatus according to claim 2 is the image forming apparatus according to claim 1, wherein the member to which the bias is applied is a transfer body, and the conductive member is a sheet conveyance guide. It is said. According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the sheet transport guide is made of metal.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, the first imaginary line drawn from the center of the transfer body to the paper transfer position, and the transfer body An angle formed by the second imaginary line drawn from the center to the wiping member is 90 degrees or more.

  In the invention of claim 4, the angle formed by the first imaginary line drawn from the center of the transfer body to the sheet transfer position and the second imaginary line drawn from the center of the transfer body to the wiping member is 90 degrees or more. Yes. This is because if the angle is less than 90 degrees, the paper transport guide is pressed from the back side by the wiping member, so that the paper transport guide is deformed (changes in the paper transport path), and recording at the writing position is performed. This is because the leading edge position of the paper (the leading edge position of the image to be formed) varies. Therefore, occurrence of such a problem is prevented by setting the angle to 90 degrees or more.

  An image forming apparatus according to a fifth aspect is the image forming apparatus according to any one of the first to fourth aspects, wherein the bias is 3500 V or more.

  As described above, according to the present invention, it is possible to provide an image forming apparatus in which a discharge phenomenon (leakage) does not occur even when the distance between members charged to a high potential is narrowed.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below in detail based on the embodiments shown in the drawings. FIG. 1 is a schematic configuration diagram showing a main part of a tandem type full color printer 10 as an image forming apparatus according to the present invention. The printer 10 is roughly divided into an image forming unit 12, an intermediate transfer device 14, a final transfer unit 16, a fixing device 18, and a paper feeding unit (not shown). In addition, the arrow in a figure has shown the rotation direction of each rotation member.

  The image forming unit 12 includes an image forming unit 20Y having photosensitive drums (image carriers) 22Y, 22M, 22C, and 22K for yellow (Y), magenta (M), cyan (C), and black (K). 20M, 20C, 20K, primary charging charging rolls (contact type charging devices) 24Y, 24M, 24C, 24K that are in contact with the photosensitive drums 22Y-22K, yellow (Y), magenta (M), cyan ( C) and a laser optical unit (exposure device) (not shown) that irradiates laser light of each color of black (K), and developing devices 30Y, 30M, 30C, and 30K.

  The intermediate transfer device 14 includes a first primary intermediate transfer drum (intermediate transfer body) 32 that contacts the two photosensitive drums 22Y and 22M among the four photosensitive drums 22Y to 22K, and the remaining two photosensitive drums. A second primary intermediate transfer drum (intermediate transfer body) 34 that contacts the body drums 22C and 22K, and a secondary intermediate transfer drum (intermediate transfer body) 36 that contacts the first and second primary intermediate transfer drums 32 and 34. It consists of and.

  The final transfer unit 16 includes a final transfer roll (final transfer member) 38 that contacts the secondary intermediate transfer drum 36. A fixing device 18 is disposed downstream of the final transfer unit 16 in the conveyance direction of the recording paper S.

  The photoconductor drums 22Y to 22K are arranged at a constant interval so as to have a common tangential plane, and the first primary intermediate transfer drum 32 and the second primary intermediate transfer drum 34 each have a rotation shaft. Are arranged so as to be parallel to the rotational axes of the photosensitive drums 22Y to 22K and symmetrical with respect to a predetermined target surface. The secondary intermediate transfer drum 36 is arranged so that the rotation axis thereof is parallel to the photosensitive drums 22Y to 22K.

  A signal corresponding to the image information for each color is rasterized by an image processing unit (not shown) and input to the laser optical unit. In this laser optical unit, laser light of each color of yellow (Y), magenta (M), cyan (C), and black (K) is modulated and irradiated to the corresponding photosensitive drums 22Y to 22K.

  Around each of the photosensitive drums 22Y to 22K, an image forming process for each color is performed by a known electrophotographic method. First, as the photoconductor drums 22Y to 22K, for example, photoconductor drums (image carriers) using OPC photoconductors having a diameter of 20 mm are used, and the photoconductor drums 22Y to 22K have a rotational speed of, for example, 95 mm / sec. Is driven to rotate. The surfaces of the photosensitive drums 22Y to 22K are charged to, for example, about -300V by applying a DC voltage of about -840V to the charging rolls 24Y to 24K as contact type charging devices.

  In addition, examples of the contact-type charging device include a roll type, a film type, and a brush type, but any type may be used. In this embodiment, a charging roll generally used in an electrophotographic apparatus in recent years is employed. In addition, in order to charge the surfaces of the photosensitive drums 22Y to 22K, in the present embodiment, a charging method in which only DC is applied is employed, but a charging method in which AC + DC is applied may be employed.

  In this way, laser light corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is irradiated by the laser optical unit as an exposure apparatus, whereby the photosensitive drums 22Y to 22K. An electrostatic latent image corresponding to input image information for each color is formed on the surface. When an electrostatic latent image is written on the photosensitive drums 22Y to 22K by the laser optical unit, the surface potential of the image exposure portion is neutralized to about −60V or less.

  Thereafter, the electrostatic latent images corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) formed on the surfaces of the photosensitive drums 22Y to 22K are developed with the corresponding color developing devices. Developed by 30Y to 30K, and visualized as toner images of yellow (Y), magenta (M), cyan (C), and black (K) on the photosensitive drums 22Y to 22K.

  In this embodiment, as the developing devices 30Y to 30K, a magnetic brush contact type two-component developing method is adopted. However, the developing devices 30Y to 30K are not limited to the two-component developing method. Other development methods such as a one-component development method and a non-contact development method may be adopted.

  The developing devices 30Y to 30K are filled with yellow (Y), magenta (M), cyan (C), and black (K) toners of different colors and a developer composed of a carrier. That is, when toner is supplied to each developing device 30Y to 30K from a toner cartridge (not shown), the supplied toner is sufficiently agitated with the developer by the augers 26Y, 26M, 26C, and 26K and frictionally charged. The

Further, inside the developing devices 30Y to 30K, a magnet roll (not shown) in which a plurality of magnetic poles are arranged at a predetermined angle is fixed. Then, the developer conveyed to the vicinity of the surface of the developing rolls 28Y, 28M, 28C, and 28K by the paddles 27Y, 27M, 27C, and 27K is conveyed to the developing unit by the developer amount regulating members 29Y, 29M, 29C, and 29K. The amount to be regulated. In this embodiment, the amount of the developer is a ^{30g / m 2 ~50g / m 2} , the charge amount of the toner present on the developing roll 28Y~28K this time, generally -20μC / g~-35μC / g Degree.

  Here, as the toner used in the developing devices 30Y to 30K, a so-called “spherical shape” having a shape factor SP1 defined by the following equation of 100 to 140, for example, about SP1 = 130 and an average particle diameter of 3 μm to 10 μm. "Toner" is used.

SP1 = (absolute maximum length of particle) ² / (projected area of particle) × (π / 4) × 100

  The toner supplied onto the developing rolls 28Y to 28K is in the form of a magnetic brush composed of developer and toner by the magnetic force of the magnet roll, and this magnetic brush is in contact with the photosensitive drums 22Y to 22K. . Then, an AC + DC developing bias voltage is applied to the developing rolls 28Y to 28K, and the toner on the developing rolls 28Y to 28K is developed into electrostatic latent images formed on the photosensitive drums 22Y to 22K. An image is formed. In this embodiment, the developing bias voltage is set such that AC is 4 kHz, 1.5 kVpp, and DC is about −230 V.

  Next, the yellow (Y), magenta (M), cyan (C), and black (K) toner images formed on the photosensitive drums 22Y to 22K are transferred to the first primary intermediate transfer drum 32 and The secondary transfer is electrostatically performed on the second primary intermediate transfer drum 34. That is, the yellow (Y) and magenta (M) toner images formed on the photoconductive drums 22Y and 22M are formed on the photoconductive drums 22C and 22K on the first primary intermediate transfer drum 32. The cyan (C) and black (K) toner images are transferred onto the second primary intermediate transfer drum 34, respectively.

  Accordingly, on the first primary intermediate transfer drum 32, a single color image transferred from either the photosensitive drum 22Y or the photosensitive drum 22M and two colors transferred from both the photosensitive drum 22Y and the photosensitive drum 22M. A double color image is formed by superimposing the toner images. In addition, similar single-color images and double-color images are formed on the second primary intermediate transfer drum 34 from the photosensitive drums 22C and 22K.

  Here, the surface potential necessary for electrostatically transferring the toner images from the photosensitive drums 22Y to 22K onto the first and second primary intermediate transfer drums 32 and 34 is about + 250V to + 500V. This surface potential is set to an optimum value depending on the charged state of the toner, the ambient temperature, the humidity, and the like. The ambient temperature, humidity, and the like can be easily known by detecting the resistance value of a member having a characteristic that the resistance value varies depending on the ambient temperature, humidity, and the like. Incidentally, when the charge amount of the toner is in the range of −20 μC / g to −35 μC / g and is in a normal temperature and humidity environment, the surface potential of the first and second primary intermediate transfer drums 32 and 34 is + 380V is desirable.

The first and second primary intermediate transfer drums 32 and 34 used in this embodiment are formed with an outer diameter of 42 mm, for example, and a resistance value of about 10 ⁸ Ω. The first and second primary intermediate transfer drums 32 and 34 are cylindrical rotating bodies having a single layer or a plurality of layers whose surfaces are flexible or elastic, and are generally made of Fe, Al, or the like. A low resistance elastic rubber layer (R = 10 ² Ω to 10 ³ Ω) typified by conductive silicon rubber or the like is provided on a metal pipe as a metal core to be formed to a thickness of about 0.1 mm to 10 mm. Configured.

Further, the surfaces of the outermost layers of the first and second primary intermediate transfer drums 32 and 34 are typically a high release layer (R = 10) having a thickness of 3 μm to 100 μm of fluororubber in which fluororesin fine particles are dispersed. ⁵ Ω to 10 ⁹ Ω) and bonded with a silane coupling agent adhesive (primer). Note that what is important here is the resistance value and the surface releasability, and the resistance value of the high release layer is about R = 10 ⁵ Ω to 10 ⁹ Ω, so long as the material has a high releasability. The material is not limited.

  In any case, the single-color or double-color toner images thus formed on the first and second primary intermediate transfer drums 32 and 34 are electrostatically transferred onto the secondary intermediate transfer drum 36. Next transferred. Therefore, on the secondary intermediate transfer drum 36, a final full color toner image from a single color image to a quadruple color image of yellow (Y), magenta (M), cyan (C), and black (K) is obtained. Will be formed.

  On the other hand, the surface potential necessary for electrostatically transferring the toner images from the first and second primary intermediate transfer drums 32 and 34 onto the secondary intermediate transfer drum 36 is about + 600V to + 1200V. This surface potential is an optimum value depending on the charging state of the toner, the ambient temperature, the humidity, etc., as in the case of transferring from the photosensitive drums 22Y to 22K to the first primary intermediate transfer drum 32 and the second primary intermediate transfer drum 34. Set to

  Also, since what is necessary for the transfer is a potential difference between the first and second primary intermediate transfer drums 32 and 34 and the secondary intermediate transfer drum 36, the first and second primary intermediate transfer drums 32 and 34 have different potentials. It is necessary to set the value according to the surface potential. As described above, the toner charge amount is in the range of −20 μC / g to −35 μC / g, and the surface potential of the first and second primary intermediate transfer drums 32 and 34 is +380 V in a normal temperature and humidity environment. The surface potential of the secondary intermediate transfer drum 36 is about +880 V, that is, the potential difference between the first and second primary intermediate transfer drums 32 and 34 and the secondary intermediate transfer drum 36 is +500 V. It is desirable to set the degree.

The secondary intermediate transfer drum 36 used in this embodiment is formed to have the same outer diameter of 42 mm as that of the first and second primary intermediate transfer drums 32 and 34, for example, and the resistance value is set to about 10 ¹¹ Ω. . Similarly to the first and second primary intermediate transfer drums 32 and 34, the secondary intermediate transfer drum 36 is also a single-layered or cylindrical rotating body having a plurality of layers of flexible or elastic surfaces. There is generally a low resistance elastic rubber layer (R = 10 ² Ω to 10 ³ Ω) typified by conductive silicon rubber on a metal pipe as a metal core made of Fe, Al or the like, A thickness of about 0.1 mm to 10 mm is provided.

  Further, the surface of the outermost layer of the secondary intermediate transfer drum 36 is typically formed by forming fluororubber in which fluororesin fine particles are dispersed as a high release layer having a thickness of 3 μm to 100 μm, and bonding with a silane coupling agent. It is composed by bonding with an agent (primer). Here, the resistance value of the secondary intermediate transfer drum 36 needs to be set higher than that of the first and second primary intermediate transfer drums 32 and 34. Otherwise, the secondary intermediate transfer drum 36 will charge the first and second primary intermediate transfer drums 32, 34, making it difficult to control the surface potential of the first and second primary intermediate transfer drums 32, 34. Become. The material is not particularly limited as long as the material satisfies such conditions.

  Next, a final toner image from a single color image to a quadruple color image formed on the secondary intermediate transfer drum 36 is recorded on the recording sheet S passing through the sheet conveyance path by a final transfer roll 38 as a final transfer body. Third transfer (final transfer). The recording sheet S passes through the registration roll pair 56 through a sheet feeding process from the sheet feeding unit, and is guided by a metal sheet conveyance guide 44 that is grounded (grounded) via a resistor, a zener diode, or a varistor. Then, it is fed into the nip portion (transfer position) between the secondary intermediate transfer drum 36 and the final transfer roll 38. After this final transfer step, the final toner image formed on the recording paper S is fixed by heat and pressure by the fixing device 18, and a series of image forming processes is completed.

Here, the final transfer roll 38 has an outer diameter of 20 mm, for example, and a resistance value of about 10 ⁸ Ω. The final transfer roll 38 is provided with a semiconductive coating layer made of urethane rubber or the like on a metal shaft, and has a surface microhardness equal to or higher than a value corresponding to a polyimide resin or a polyetherimide resin on the coating layer. The tube which it has is coat | covered and comprised. Specifically, a tube made of polyimide resin or polyetherimide resin is used.

  The optimum voltage applied to the final transfer roll 38 is approximately + 1200V to + 6000V, although the optimum value varies depending on the ambient temperature, humidity, paper type, etc. (resistance value, etc.). In this embodiment, a constant current method is employed, and a current of about +6 μA is applied in a room temperature and humidity environment to obtain a substantially appropriate transfer voltage (+1600 V to +2000 V).

  In these series of transfer processes, when the toner image passes through the transfer part of each transfer process, a part of the positive toner in the negatively charged toner image is positively charged with a reverse polarity due to Paschen discharge or charge injection. May become toner. The positively charged toner flows back upstream without being transferred to the next process, and therefore adheres and accumulates on the charging rolls 24Y to 24K having the highest negative potential.

  The portions of the charging rolls 24Y to 24K to which the toner is attached are actively discharged, and the surface potential of the photosensitive drums 22Y to 22K tends to increase. Unevenness occurs in the surface potentials of the photosensitive drums 22Y to 22K at portions where toner is not attached. If unevenness occurs in the surface potentials of the photosensitive drums 22Y to 22K, the latent image potentials are uneven even if the image is uniformly exposed on the surfaces of the photosensitive drums 22Y to 22K in order to form an electrostatic latent image. As a result, a difference in the development amount occurs, and density unevenness is particularly noticeable when a halftone image is developed.

  Therefore, in order to prevent the occurrence of density unevenness due to the residual toner adhering to the charging rolls 24Y to 24K, in this embodiment, a predetermined timing such as before a printing operation, after a printing operation, and every predetermined number of continuous prints. Therefore, the following cleaning operation is performed.

  That is, the charging roller 24Y to 24K, the photosensitive drums 22Y to 22K, the first and second primary intermediate transfer drums 32 and 34, the secondary intermediate transfer drum 36, and the final transfer roll 38, the final transfer roll 38 has the most negative potential. In order to increase the voltage, a voltage with a potential gradient is applied in order, and the positively charged toner having the opposite polarity adhered and deposited on the charging rolls 24Y to 24K during the printing operation is transferred to the final transfer roll 38 in order. To move it.

  Specifically, for example, the surface potential of the charging rolls 24Y to 24K is 0V, the surface potential of the photosensitive drums 22Y to 22K is −300V, the surface potential of the first and second primary intermediate transfer drums 32 and 34 is −800V, The surface potential of the secondary intermediate transfer drum 36 is set to -1300V, and the surface potential of the final transfer roll 38 is set to -2000V.

  A cleaning device 40 having a metal scraper 42, a toner recovery box (not shown), a charge eliminating device (not shown), and the like is disposed below the final transfer roll 38. The remaining toner thus peeled off is scraped off by a scraper 42 provided so as to be always in contact with the final transfer roll 38 and is collected in a toner collection box.

  The scraper 42 is preferably a stainless steel blade, and the thickness is preferably set to 0.08 mm, the biting angle is set to a doctor direction of 30 degrees, and the biting amount is set to 0.8 mm. Further, the scraper 42 is manufactured by an etching method, and the accuracy of the edge is strictly controlled. As a material for that purpose, a tension annealing treatment material is used.

  Further, the potential gradient is obtained by a system in which a voltage is supplied to the metal part (shaft, pipe) of each member. For example, the first and second primary intermediate transfer drums 32 and 34 or the secondary intermediate transfer drum In the case where a desired surface potential is obtained by electrically floating 36 and the like and the relationship between the resistance values of these members, such a method may be employed. In any case, the negative application cleaning mode, that is, the positively charged toner collecting mode having the opposite polarity, can prevent the occurrence of density unevenness due to the residual toner adhering to the charging rolls 24Y to 24K.

  The image forming process in the full-color printer 10 has been described above. However, in the xerographic method or the like, the static image is used, and thus the image density is likely to change due to environmental changes and aging. For this reason, it is desirable to control the process with respect to environmental fluctuations and changes with time.

  As one of the methods, a test toner patch is formed on the surface of an image density detection medium such as the photosensitive drum 22, the intermediate transfer drums 32, 34, and 36, or the final transfer roll 38, and the density is changed to an optical density. There is a method of detecting and controlling with a sensor. In this embodiment, a test toner patch is transferred onto the final transfer roll 38, and the density is detected by the optical density sensor 50.

  The test toner patch is a non-image area, here, at a timing when an image is not formed, and under the same charging, exposure, development, and transfer conditions as in the image formation, yellow (Y), magenta (M), cyan (C ) And black (K) are formed on the final transfer roll 38 at an interval of 12 mm × 12 mm and 3 mm so that the image density is 40%.

  The optical density sensor 50 is mounted in a fixed state in a holder (not shown), and is positioned on the axially central portion of the final transfer roll 38 and on the radial extension line on the outer periphery of the final transfer roll 38. It is arranged.

  As shown in FIG. 2, the optical density sensor 50 is a specular reflection type sensor that detects specular reflection light, and is inclined by a predetermined incident angle θ with respect to the detection position on the surface of the final transfer roll 38. In order to detect the specular reflected light that is emitted from the light emitting element 52 to the detection position on the surface of the final transfer roll 38 and is specularly reflected from the detection position, the final transfer is performed. It is composed of a light receiving element 54 made of a phototransistor or the like that is disposed at an angle of reflection equal to a predetermined incident angle θ with respect to the detection position on the surface of the roll 38.

  The optical density sensor 50 may be a diffuse reflection type sensor that detects diffused light. Further, both a specular reflection type sensor and a diffuse reflection type sensor may be used. In this case, the toner density detection accuracy can be further improved by detecting the toner density based on both the specular reflection component and the scattered light component.

  In any case, the toner patch is detected by such a configuration. If the toner patch forming area provided on the surface of the final transfer roll 38 is stained with toner or the like, the optical density sensor 50 accurately detects the toner patch forming area. There is a possibility that the toner patch cannot be detected. Therefore, in order to avoid this, it is necessary to always clean the surface of the final transfer roll 38 by the scraper 42, and further, a wiping member 46 for assisting cleaning of the surface of the final transfer roll 38 is provided. Yes.

  That is, the rotation direction of the final transfer roll 38 on the downstream side in the rotation direction of the final transfer roll 38 of the metal scraper 42 and the rotation direction upstream of the nip portion (transfer position) between the secondary intermediate transfer drum 36 and the final transfer roll 38. A wiping member 46 for wiping off deposits adhering to the surface of the final transfer roll 38 is attached in the vicinity of the tip 44 </ b> A of the sheet conveyance guide 44 positioned at the position.

  The wiping member 46 is formed of a material such as urethane foam. Specifically, a high-density foamed urethane foam (trade name: Polon (grade: ML-32 / tensile strength: 0.68 MPa)) manufactured by Inoac Corporation is preferably used. This is a sheet having a thickness of 3 mm and a length of 4 mm (length approximately along the circumferential direction of the final transfer roll 38), and is set to bite 0.8 mm.

  The wiping member 46 set in this manner presses the surface of the final transfer roll 38 with a predetermined pressure, thereby removing deposits adhering to the final transfer roll 38. The deposits wiped off by the wiping member 46 are calcium carbonate, which is a paper component of the recording paper S, and the wiper is used to wipe out such deposits. Such troubles are prevented from occurring.

  Further, as shown in FIG. 3, a first imaginary line K1 drawn from the center of the final transfer roll 38 to the nip portion (transfer position) with the secondary intermediate transfer drum 36, and a wiping member from the center of the final transfer roll 38 The second imaginary line K2 drawn to 46 (the second imaginary line K2 is a normal line of the surface to which the wiping member 46 of the paper transport guide 44 is attached in the side view of FIG. 3). The angle α is 90 degrees or more.

  This is because if the angle α is less than 90 degrees, the attachment position of the wiping member 46 moves upward, so that the paper conveyance guide 44 is pressed from the back side by the wiping member 46 and deformed, and the paper This is because the transport path changes. That is, when such a phenomenon occurs, the leading edge position of the recording paper S with respect to the writing position varies, and the leading edge position of the formed image varies. Therefore, the angle α is set to 90 degrees or more. Thus, the occurrence of such a problem is prevented.

  However, by providing the wiping member 46 at such a position, the front end 44A of the paper transport guide 44 falls downward due to the weight of the wiping member 46, and is the shortest distance (interval) from the metal scraper 42. D (see FIG. 6) is very narrow. Specifically, the shortest distance (interval) D is D = 1.5 mm or less.

The paper transport guide 44 is made of a metal plate, and is grounded by, for example, a 1000V varistor so as not to discharge and charge the recording paper S transported to the nip portion (transfer position). Yes. The scraper 42 is always in contact with the final transfer roll 38 to which a voltage of +1200 V to +6000 V is applied. In particular, in the low temperature and low humidity environment, the resistance of the final transfer roll 38 increases (from 10 ⁸ Ω to 10 ⁹ Ω). Therefore, in order to obtain an appropriate transfer current (10 μA to 30 μA), the final transfer roll 38 has + 3500V. A voltage of ~ + 6000V is applied. Therefore, when the scraper 42 and the leading end 44A of the paper transport guide 44 are arranged close to each other, a discharge phenomenon (leakage) occurs between them.

Therefore, as shown in FIGS. 3 and 4, in order to prevent a discharge phenomenon (leakage) between the scraper 42 and the paper transport guide 44 (tip 44 </ b> A), on the upper surface (surface) of the scraper 42, In addition, an insulating sheet 48 as an insulating member is attached to an area where discharge is possible by an adhesive means such as double-sided tape. The insulating sheet 48 has a thickness of 0.1 mm, and as its material, for example, a resin such as PET having a volume resistance of 10 ¹⁰ Ω · cm or more can be suitably used.

  The insulating sheet 48 is attached in a dischargeable area, but if the scraper 42 is longer than the paper transport guide 44 in the width direction (perpendicular to the plane of FIG. 3), the entire width of the paper transport guide 44 is used. You may stick so that the above range may be insulated. Further, instead of sticking the insulating sheet 48 to the above range of the scraper 42 with a double-sided tape or the like, a fluorine-based insulating paint resin may be applied by a method such as spraying. In other words, the above range of the scraper 42 may be covered with the insulating resin film. Furthermore, a method such as attaching a polyimide tape or a Teflon (registered trademark) tape as an insulating member to the above range of the scraper 42 may be employed.

  Further, in order to prevent a discharge phenomenon (leakage) between the scraper 42 and the paper transport guide 44 (front end 44A), as shown in FIG. 5, the front end 44A of the paper transport guide 44 has a full width (FIG. 5). (The direction perpendicular to the paper surface) may be covered with an insulating resin film 49 as an insulating member. As the material at this time, a fluorine-based insulating paint resin or the like can be preferably used. What is necessary is just to apply | coat this coating material on the upper surface of the front-end | tip 44A periphery of the paper conveyance guide 44, the lower surface, an end surface, and both sides by methods, such as spraying.

  Further, for example, a method of immersing the tip 44A of the paper transport guide 44 in a container filled with a vinyl chloride insulating paint resin and applying the paint may be employed. Further, a method may be employed in which a polyimide tape, a Teflon (registered trademark) tape or the like as an insulating member is attached to the front end 44A of the paper transport guide 44 and the front end 44A is covered.

  In any case, the scraper 42 which is always in contact with the final transfer roll 38 and is charged to a high potential (+3500 V to +6000 V), which is not grounded (grounded), and the tip 44A of the grounded (grounded) paper transport guide 44, Even if the shortest distance (interval) D is reduced by the weight of the wiping member 46, the downsizing and unitization of the printer 10, the scraper 42 or the paper transport guide 44 (the tip 44A) in the dischargeable area of both of them. Since the surface is covered with an insulating member such as the insulating sheet 48 and the insulating resin film 49, no discharge phenomenon (leakage) occurs between the portions. Accordingly, there is no problem that the voltage applied to the final transfer roll 38 is impaired, and a sufficient transfer current can be obtained, so that transfer failure to the recording paper S does not occur.

Schematic configuration diagram showing the main parts of the printer Schematic explanatory diagram showing the structure of the optical density sensor Schematic side view showing a scraper coated with an insulating member and a paper transport guide Schematic perspective view showing a scraper coated with an insulating member and a paper transport guide Schematic side view showing a paper transport guide and a scraper coated with an insulating member Schematic side view showing the final transfer body of a conventional printer

Explanation of symbols

10 Printer (image forming device)
12 Image forming unit 14 Intermediate transfer device 16 Final transfer unit 18 Fixing device 20 Image forming unit 22 Photosensitive drum 24 Charging roll 28 Developing roll 30 Developing device 32 First primary intermediate transfer drum 34 Second primary intermediate transfer drum 36 Second Next intermediate transfer drum 38 Final transfer roll (transfer body)
40 Cleaning device 42 Scraper 44 Paper transport guide 46 Wiping member 48 Insulating sheet (insulating member)
49 Insulating resin film (insulating material)
50 Optical density sensor

Claims (5)

An ungrounded scraper that cleans any residue remaining on the member to which a predetermined bias is applied;
A wiping member attached to a grounded conductive member to assist in cleaning residue remaining on the member in the vicinity of the scraper;
In an image forming apparatus comprising:
An image forming apparatus, wherein a surface of the scraper or the conductive member in a dischargeable region between the scraper and the conductive member is covered with an insulating member.   The image forming apparatus according to claim 1, wherein the member to which the bias is applied is a transfer body, and the conductive member is a paper conveyance guide.   The image forming apparatus according to claim 2, wherein the sheet conveyance guide is made of metal.   The angle formed by the first imaginary line drawn from the center of the transfer body to the transfer position and the second imaginary line drawn from the center of the transfer body to the wiping member is 90 degrees or more. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 1, wherein the bias is 3500 V or more.

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