JPH09274343A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device which prevents toner offset by means of a relatively simple structure even in a case of high-resistance paper and exhibits stable image-quality. SOLUTION: Paper 35 is passed between a photoreceptive drum 19 and a transfer bias roll 29, and, at this time, a toner image is transferred to it. This paper 35 is destatized from back by means of a destaticizing needle 41, and passed along first and second carrying guides 71 and 72, respectively, in that order, and then between a heat roll 42 and a pressure roll 43, so that the toner image is fixed to the paper. The core metal 79 of the pressure roll, the first carrying guide 71 and second carrying guide 72, and a destaticizing brush 78 are grounded via a first diode 77. The first diode 77 makes the pressure roll and so on hold proper-polarity charges, and prevents offset in a fixing device 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer or a facsimile machine which forms a toner image using an electrostatic latent image, transfers the toner image onto a recording material such as paper and then fixes the toner image. In particular, the present invention relates to an image forming apparatus in which a toner image is transferred onto a recording material by a transfer roll and a recording material is fixed by a fixing device using a roll such as a heat roll.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic system can output a high-quality image at high speed and is widely used in various devices such as an electrophotographic copying machine and a printer. In such an image forming apparatus, an image carrier represented by a photoconductor drum or a photoconductor belt (hereinafter simply referred to as a photoconductor or a photoconductor drum) is first charged, and this is charged by using light such as a laser beam. Exposed to form an electrostatic latent image. This electrostatic latent image is developed by selectively adsorbing toner to form a toner image. This toner image is transferred from a photosensitive drum to a recording material typified by plain paper (hereinafter, referred to as paper except for special cases) and fixed by heat or pressure.

Conventionally, in such an image forming apparatus,
Corona dischargers are used to realize various processes such as charging and transfer. Corona dischargers generally cause the following problems. Since the voltage applied to this corona discharger is high in order to use the discharge phenomenon, it is necessary to use a special circuit. When negative discharge is performed with a corona discharger, the amount of ozone generated is particularly large. Therefore, a filter is required to prevent the generated ozone from being emitted to the outside of the image forming apparatus. The corona discharger uses a thin wire for discharge called a corotron wire. Since this wire is arranged in the image forming apparatus, it is easily contaminated with particles such as toner, and if it contaminates, discharge failure occurs. Therefore, regular maintenance is required to keep the corona discharger in good condition. Also, the corotron wire may break if it is handled carelessly during cleaning.

Since the corona discharger has such a problem, a device for charging the surface of the photosensitive member or transferring a toner image without using discharge has been devised. A contact charging device or a contact transfer device is a typical one of them. These contact type devices are equipped with a charging or transfer member that comes into pressure contact with the photoconductor. In the case of charging, a predetermined bias voltage is applied to the charging member to charge the surface of the photoconductor. In the case of transfer, a predetermined bias voltage is applied to the transfer member via the paper to the toner image adsorbed on the surface of the photoconductor to transfer the toner particles to the paper. Hereinafter, the transfer bias roll as a transfer member that is pressed against the photosensitive drum will be described as an example.

As described above, the toner image transferred onto the paper is fixed by the fixing device. The mainstream of the fixing device is a heating roll type device using a heating roll (hereinafter referred to as a heat roll) and a pressure roll in pressure contact with the heating roll. In many cases, oil such as silicone oil was used to clean the surface of the heat roll, but recently these oils have not been used to facilitate maintenance and downsize the fixing device. There are many things.

A carrying path is provided between the contact transfer device and the fixing device for carrying the unfixed paper on which the toner image is adhered. This conveyance path is for guiding the sheet passing between the photoconductor drum and the transfer bias roll between the heat roll and the pressure roll while slidingly contacting the conveyance guide by the driving force of the transfer bias roll. . The transport guide normally uses a grounded sheet metal member such as a sheet metal in order to electrostatically attract the charged sheet at the time of transferring the toner image and perform stable transport.

However, if the front surface of the sheet metal comes into direct contact with the back surface of the paper, the transfer charge adsorbing the toner image transferred to the paper escapes. As a result, the toner image may be disturbed, or the toner may move to the heat roll side to cause an offset when the paper passes between the heat roll and the pressure roll. Therefore, A has been conventionally used on the surface of the conveyance guide.
The ribs are made of a high resistance material having a resistance of 10 ¹⁰ Ω · cm or more, which is represented by a resin such as BS (acrylonitrile / butadiene / styrene) or polycarbonate. As a result, ordinary paper, which does not have a particularly high resistance, is transported in the transport path while being in contact with the ribs, and is electrostatically and indirectly adsorbed to the grounded sheet metal to ensure stable transport. Secured.

However, the OHP (overhead program)
(E.g. paper) resin film and low humidity low temperature environment
100 g / of the cardboard that has been left to stand and dried.
cm ^TwoUsing the above items, the above heat roll
The toner image is electrostatically transferred from this heat roll as it passes through
Transferring to the surface, the phenomenon that offset occurs
I do. In particular, such an offset phenomenon is
Heater without a cleaning mechanism using oil such as oil
It occurs remarkably on the troll and is transferred to the heat roll surface.
Toner is transferred to the paper again, so-called fixing ghost
To generate dirt. This is due to the volume resistance of the paper
Is very high, such as OHP paper, the transfer bar
The transfer charge of the Yassroll reaches the toner side of the paper sufficiently.
And the electrostatic binding force between the toner and the paper
This is because it will decrease. For this, use with heat roll
Toner on the paper is generated by the triboelectric potential generated between the paper.
Easily transfer to the surface of the heat roll.

Various proposals have been made to prevent such an offset phenomenon. For example, applying a voltage of the same polarity to the heat roll to electrostatically prevent its adhesion, or grounding the heat roll via a low-capacity element such as a diode causes the same polarity voltage to be biased. In this way, a proposal has been made to prevent the offset. It is also considered to prevent the offset by increasing the electrostatic binding force between the paper and the toner. In this proposal, the bias voltage of the transfer bias roll is increased to raise the charging potential of the paper. However, the charging of the paper is several KV (kilovolts)
If a high resistance rib is formed on the conveyance guide, a leak will occur from the sheet toward the sheet metal for electrostatic attraction if the rib is formed to have a high resistance. For this reason, the toner image is disturbed at this portion, and this proposal has not been put to practical use.

[0010]

Therefore, proposals for applying a bias to the heat roll by some method are being studied. The method of applying a bias to the heat roll generally has the following problems.

First, when OHP paper or thick paper that has been left to stand in a low-humidity and low-temperature environment is used as a paper for transferring a toner image, the electric potential of the paper after transfer changes depending on the pattern to be printed or the density of the printing portion, A potential of opposite polarity to transcription may occur. In such a case, if you try to apply a voltage of the opposite polarity to the heat roll by using a power source or a diode to prevent the offset, it is necessary to apply a voltage higher than the potential remaining after the transfer to the paper to the heat roll. is there. Such a voltage is extremely high, for example, −2 KV or more when negatively charged toner is used. Therefore, a leak is likely to occur in the temperature detecting element such as the thermistor or the pressure roll arranged so as to be in contact with the heat roll. When a leak occurs, the image forming apparatus itself tends to malfunction.
Further, in order to prevent such malfunction, it is necessary to add a mechanism or a circuit for preventing leakage, which causes a problem that the device becomes complicated and the cost increases.

Next, if the rib of the conveyance guide is devised so that the distance between the paper and the sheet metal for electrostatic attraction can be increased, leakage can be prevented, but the distance between the paper and the sheet will be reduced by the length of the distance. This will reduce the electric attraction. As a result, inconveniences such as a phenomenon (smudge) in which the trailing edge of the sheet floats up after passing through the transfer bias roll and comes into contact with a member such as a cleaning device located on the upper side of the conveyance path to scrape off the toner image (smudge) Will be generated. Further, when the leading edge of the sheet floats, there is a problem that the sheet cannot properly enter between the heat roll and the pressure roll.

In the above description, a resin sheet such as an OHP sheet or a thick paper left to stand in a low-humidity and low-temperature environment is used as the high-resistance paper, but the present invention is not limited to this. Needless to say, the same problem occurs when printing is performed on a sheet that is dried by passing through the fixing device and has a high resistance subsequently, as in the case of double-sided printing.

Therefore, an object of the present invention is to provide an image forming apparatus capable of preventing toner offset even with high resistance paper with a relatively simple structure and exhibiting stable image quality. Especially.

[0015]

According to a first aspect of the invention, (a) an electrostatic latent image holding member such as a photosensitive drum holding an electrostatic latent image, and (b) this electrostatic latent image holding member. The developing means for forming a toner image corresponding to the electrostatic latent image on the electrostatic latent image forming portion of (3), and (c) the electrostatic latent image holding member are contacted via the recording material and developed by the developing means. It comprises a transfer means such as a transfer bias roll for transferring the toner image onto the recording material, and (d) a pair of rotating bodies composed of a heat roll and a pressure roll arranged on the downstream side of the transferring means. A fixing means for passing the recording material between the fixing means and the fixing means, and (e) at least a part thereof for guiding the recording material on which the toner image is transferred and arranged between the transfer means and the fixing means to the fixing means. A guide member composed of a conductive member, and The inner member and the surface of the rotating body that does not come into direct contact with the toner image out of the pair of rotating bodies that form the fixing unit both discharge electric charges of the same polarity as the electric potential of the toner image, and charge of the opposite polarity to them. The image forming apparatus is provided with a rectifying element connected in a holding direction.

That is, according to the first aspect of the invention, from the transfer of the toner image on the recording material (paper) to the fixing,
A part of the guide member is conveyed on a guide member made of a conductive member. Then, of the pair of rotators forming the guide member and the fixing unit, the surface of the rotator which is not in direct contact with the toner image releases a charge having the same polarity as the potential of the toner image, and a charge having a polarity opposite to this. The rectifying element is connected in such a direction as to hold them. As a result, first OH
Even if the recording material has a relatively high resistance, such as P paper and thick paper that has been left to dry in an environment of low humidity and low temperature, a stable conveyance is ensured by the appropriate suction action of the guide member. It is possible to prevent smudging due to lifting from the guide member. Further, since the fixing means holds the electric charges of proper polarity, it is possible to effectively prevent the offset of the toner. That is, by removing the excessively charged electric charge existing on the peeling surface of the recording material after the transfer of the toner image, the recording material is prevented from floating from the guide member, and the removed electric charge is accumulated and offset by the fixing means. Is supplied with a charge of effective polarity.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a conductive member including a brush for static elimination is provided at a charging portion of the fixing unit with the rotating body on the side not in direct contact with the toner image. The conductive members are arranged so as to face each other, and the conductive members are connected to the rectifying element in such a direction that charges having the same polarity as the potential of the toner image are discharged from the facing rotating body and charges having the opposite polarity are held. This makes it possible to maintain the surface of this rotating body made of a pressure roll or the like at an electric potential of an appropriate polarity and prevent offset.

According to the third aspect of the invention, in the image forming apparatus according to the second aspect, the pair of rotating bodies is a heating rotating body such as a heat roll which comes into contact with the surface of the recording material on which the toner image is transferred. , A pressure-applying rotary member such as a pressure roll that presses the recording material against the heating rotary member, and the pressurizing rotary member has an elastic layer disposed on a cored bar, and a high-resistance release layer on the elastic layer. It is characterized by having layers.

According to a fourth aspect of the present invention, the guide member of the image forming apparatus according to the first aspect is a first guide member in which an insulating material protruding from a part of a conductor surface is arranged, and the first guide member. And a second guide member which is disposed on the downstream side of the conductor and whose conductor surface is exposed on the entire surface. Both of these conductor portions are grounded via a rectifying element. The insulator protruding from the conductor surface of the first guide member prevents the recording material from coming into contact with the conductor.

According to a fifth aspect of the invention, in the image forming apparatus according to the fourth aspect, the first guide member is inclined downward as it goes downstream, and the second guide member is upward as it goes downstream. The recording material, which is inclined by the electrostatic latent image holding member and the transfer means, projects into the inclined surface of the first guide member at an inclination angle larger than the inclination angle of the first guide member, and the second guide The member has a recording material conveying surface area smaller than that of the first guide member, and the extended surface of the inclined surface of the second guide member substantially coincides with the rolling contact position of the pair of rotating bodies of the fixing unit. Is characterized by. That is, by making the overall shape of the guide member V-shaped in the transport direction, it is possible to prevent the recording material from floating above the surface of the guide member, and
With a relatively high attraction force by directly contacting the conductor surface of the second guide member so that the rolling contact position of the pair of rotating bodies exists within the allowable range on the extension of the conductor surface of the second guide member. In addition to stabilizing the direction, the tip of the recording material is surely guided to the fixing device.

According to a sixth aspect of the invention, the rectifying element in the image forming apparatus according to the first, second or fourth aspect is a diode. Of course, it is also possible to use another semiconductor element which substantially functions as a diode.

The protrusion amount of the insulator protruding from a part of the conductor surface of the first guide member in the image forming apparatus according to claim 4 may be in the range of 0.5 mm to 2.5 mm. Within this range, effective effects are often obtained. Within this range, in a normal image forming apparatus, in order to prevent the recording material from directly contacting the conductor surface, in order to secure the electrostatic adsorption force by the conductor surface in an appropriate range, and in the recording material It is effective to receive the supply of electric charges for preventing the offset from.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows an outline of the configuration of a laser printer as an image forming apparatus in one embodiment of the present invention. The laser printer 11 has a device body 1
Laser scanning device 1 for emitting a laser beam into 2
3 are arranged. A semiconductor laser (not shown) is arranged in the laser scanning device 13. The semiconductor laser outputs a laser beam modulated based on print data sent through a network such as a personal computer (not shown) connected to the laser printer 11 or a LAN (local area network). There is. This laser beam is incident on the polygon mirror 15 that rotates at a high speed, and is deflected according to this rotation. The reflected light of the polygon mirror 15 passes through the fθ lens 16 and is corrected in the scanning direction of the laser beam.
The light is sequentially reflected by the first mirror 17 and the second mirror 18 and emitted toward the photosensitive drum 19. It should be noted that the illustration and description of the optical lens are omitted in this figure. A laser beam emitted from the laser scanning device 13 and from the laser scanning device 13 is indicated by a chain line 21.

The photosensitive drum 19 is a cylindrical photosensitive member that rotates in a clockwise direction indicated by an arrow at a constant speed by a main motor (not shown), and the laser beam repeats in the axial direction (main scanning direction) of the drum at its exposure position 22. To be scanned. A charging roll 23 is in rolling contact with the drum surface slightly upstream of the exposure position 22 to uniformly charge the drum surface. The photoconductor drum of this embodiment uses an organic photoconductor. Since this photosensitive member has a characteristic that it should be negatively charged, a negative DC bias voltage is applied to the charging roll 23 by superimposing a negative DC bias voltage.

The surface of the photosensitive drum 19, which has been uniformly negatively charged, is selectively exposed at the exposure position 22 to form an electrostatic latent image. This electrostatic latent image is developed by the developing device 25 arranged on the downstream side of the exposure position 22. In the developing device 25, the developing roll 26 and the toner supply mechanism 2 are provided.
7 are arranged. Here, the toner supply mechanism 27 is a mechanism for sequentially supplying the toner in the developing device 25 containing the toner in the form of a cartridge to the developing roll 26. The developing roll 26 is a roll for magnetically raising the toner to bring this portion into contact with or close to the electrostatic latent image forming region of the photoconductor drum 16 for development.
A predetermined developing bias is applied to the developing device 25. In the case of the present embodiment, an AC voltage with a negative DC bias voltage superimposed thereon is used. In this embodiment, the photosensitive drum 19 is negatively charged to form an electrostatic latent image, and the potential of the exposed portion is close to zero. Since the negative DC bias voltage is applied to the developing device 25, the exposed portion is relatively charged to the positive side, and the negatively charged toner is adsorbed to the portion.

The toner image developed on the drum surface by the developing device 25 moves to the position where the transfer bias roll 29 is in rolling contact with the drum surface by the rotation of the photosensitive drum 19. Here, the toner image is transferred to the sheet sent through the registration roll 31. The sheet conveying path 32 is shown by a broken line in FIG.

The sheet conveying path of the image forming apparatus 11 will be described. At the bottom of the device body 12, a cassette tray 33
Are removably arranged. Paper 35 cut into a predetermined size is stacked on the cassette tray 33. Paper 35 placed on the uppermost layer of cassette tray 33
Are sent one by one to the right in the figure by intermittent rotation of the half-moon roll 36 having a half-moon shape. In addition to the half-moon roll 36, another roll such as a retard roll or a mechanism for adsorbing and feeding the paper 35 may be used.

The paper 35 delivered from the cassette tray 33 is conveyed to the registration roll 31 through the conveyance rolls 38 and 39 in order, and after being temporarily stopped there, it is exposed in synchronism with the rotational position of the photosensitive drum 19. Body drum 19
Transported in the direction of A predetermined positive DC bias voltage is applied to the transfer bias roll 29 only when the paper 35 passes between the photosensitive drum 19 and the transfer bias roll 29. As a result, the toner image formed of the negatively charged toner particles on the photoconductor drum 19 is electrostatically attracted to the transfer bias roll 29, and the transfer is performed.

The paper 35 on which the toner image has been transferred is neutralized from behind by the static elimination needle 41 arranged adjacent to the exit side of the transfer bias roll 29, and is peeled off from the drum surface. Then, it advances along the conveyance path 32, and the fixing device 4
0 and the heat roll 42 and the pressure roll 43
Enter the contact point of. The heat roll 42 is kept at a constant high temperature, the pressure roll 43 presses the paper 35 against the heat roll 42, and efficient heat transfer is performed in the area where the two are nipped to fix the toner image. . The sheet 35 after fixing passes through the transport roll 47 and is then transported upward in the transport path 32 in a state where the switching piece 44 is arranged at the position shown by the solid line in the figure. Then, the paper is ejected to the ejection tray 48 arranged on the upper part of the apparatus main body 12 through the transport roller 45 and the ejection roller 46 in order. This is,
This is a conveyance path for printing on only one side of the paper 35.

When printing is performed on both sides of the paper 35, the paper 35 on which the toner image is transferred and fixed on the first surface
Is transported once upward from the switching piece 44 through the transport path 32. Then, after passing through the transport roll 45, the rear end is the switching piece 4
The conveyance is temporarily stopped at the position where the position 4 is removed. In this state, the switching piece 44 is switched to the position shown by the broken line, and the transport roll 45 rotates in the opposite direction to transport the paper 35 downward this time. As a result, the sheet of paper 35 travels along the transport path 51 indicated by the alternate long and short dash line, passes through the transport rolls 52, 53, 54 in order, and reaches the transport roll 38 used for the first surface.
The sheet is conveyed along the conveying path 32 from here onward and again passes between the photosensitive drum 19 and the transfer bias roll 29.
At this time, the toner image is transferred onto the second surface opposite to the first surface onto which the toner image is transferred onto the tip of the paper 35. After that, the conveyance is performed as in the case where the printing is performed on only one side described above, and the sheet 35 on which the second fixing is performed is ejected onto the ejection tray 48.

On the other hand, the toner remaining on the surface of the photosensitive drum 19 even after the toner image is transferred by the transfer bias roll 29 is transferred to the transfer bias roll 29 and the charging roll 2.
And a cleaning device 56 disposed between the two, so as to be scraped off from the drum surface. The photosensitive drum 19 whose surface has been cleaned in this way is uniformly charged again by the charging roll 23, and is ready for the next image forming process.

FIG. 2 shows a device portion from the vicinity of the transfer bias roll to the fixing device, which is the main part of the laser printer described above. In the present embodiment, the roll portion of the transfer bias roll 29 that is in contact with the photosensitive drum 19 is a rubber material such as urethane, EPDM (polyisoprene blended elastomer), CR (chloroprene rubber), silicone rubber, or a foam sponge of these materials. It consists of The hardness of this roll is JIS
Asker (ASKER) C, which is a standard, is used with a weight of around 500 degrees and a weight of around 40 degrees. This hardness not only stabilizes the conveyance performance of the paper 35 (FIG. 1), but also
This is effective for preventing the phenomenon of missing characters when the toner image is transferred and for preventing the photoconductor drum 19 from being scraped. The resistance value of the transfer bias roll 29 is preferably about 10 ⁷ to 10 ¹⁰ Ω by the measuring method described below.

FIG. 3 shows the principle for measuring the resistance value of this transfer bias roll. The transfer bias roll 29 to be measured is placed on the metal plate 61, and the force 63 of 500 g load is applied downwardly to the rotation shaft 62 thereof as described above. In this state, a DC voltage of + 1000V is applied to one end of the rotary shaft 62. At this time, an ammeter 64 is attached to the sheet metal 61 as a conductor.
Is connected to measure the current flowing therethrough, and the resistance value of the transfer bias roll 29 is calculated from the voltage and the measured current.

The transfer bias roll 29 has 10 ⁷ to 10 ¹⁰
The reason why a resistance value of about Ω is preferable is that a good transfer characteristic can be obtained even when the paper 35 has a high resistance. High resistance paper is, for example, OHP
High resistance resin film for (overhead projector), paper left in low temperature and low humidity environment, heat fixing after transfer of the toner image on the first side when double-sided printing is performed, and water content decreases. One example is paper with high resistance.

When the transfer of the electric charge from the transfer bias roll 29 to the paper 35 when the toner image formed on the photosensitive drum 19 is transferred to the paper 35 is performed in the area where the transfer bias roll 29 is nipped. There is not much paper 35
Mostly move in areas that are slightly separated on both sides near the nip. That is, Pasc
According to Hen's law, the main cause is that electric charges move due to electric discharge due to dielectric breakdown of air. Due to such a principle, a sufficient transfer charge can be obtained by applying a voltage of about 2 KV to the transfer bias roll 29.

Photosensitive drum 19 and transfer bias roll 2
If the resistance value of the transfer bias roll 29 is too low in the transfer state in which the paper 35 exists between 9 and 9, it is related to the width of the paper 35, but in a region where the photosensitive drum 19 and the transfer bias roll 29 are directly nipped. A situation occurs in which a large amount of transfer current flows into the drum surface. As a result, the photosensitive layer of the photosensitive drum 19 is damaged. When such damage occurs, the toner adheres to the drum surface at the time of the next development at the side portion of the paper 35, that is, at the boundary portion of the region where the photosensitive drum 19 and the transfer bias roll 29 are in direct contact with each other. . This causes a problem that the side portion of the paper 35 is soiled with the toner. In addition, there is a problem that unevenness in image density occurs due to the damage of the photosensitive layer.

On the other hand, if the resistance value of the transfer bias roll 29 is too high, the transfer current does not flow when the above-mentioned voltage of about 2 KV is applied, which causes transfer failure. Therefore, the resistance value of the transfer bias roll 29 has an optimum value, which is a resistance value of about 10 ⁷ to 10 ¹⁰ Ω. Transfer bias roll 29 in this range
The voltage applied to the
The optimum range is 0V to 5KV.

As shown in FIG. 2, the transfer bias roll 29
At the exit side of the sheet, two conveyance guides, a first conveyance guide 71 and a second conveyance guide 72, are arranged in this order along the conveyance path, and a heat roll 42 for fixing and a pressure roll 43 are provided ahead of them. Are arranged.

FIG. 4 shows the structure of the first conveyance guide. The first transport guide 71 is an integrally-molded resin including a plurality of ribs 73 of the same shape that are inclined in the sheet transport direction and are arranged in parallel with each other, and a support plate 74 that supports one end of each of the ribs 73. It is composed of a manufacturing member and a metal plate 75 arranged in parallel to an inclined surface formed by connecting inclined end surfaces of the ribs 73 and slightly below the inclined surface. As the resin member, a high resistance material of 10 ¹⁰ Ω · cm or more such as ABS resin or polycarbonate is used. Each rib 73 projects from the sheet metal 75 at a height in the range of 0.5 mm to 2.5 mm.

The ribs 73 and the supporting plate 74 which also projects from the sheet metal 75 are provided to prevent the sheet 35 from directly contacting the sheet metal 75. Each rib 73
However, when the sheet metal 75 protrudes from the sheet metal 75 at a height of less than 0.5 mm, the sheet 35 is generally formed depending on the distance between the ribs 73.
If the paper sheet droops during transportation, it may come into contact with the sheet metal 75 and cause a problem. If the protrusion is higher than 2.5 mm, the action of the sheet metal 75 to adsorb the sheet 35 may be too weak.

On the other hand, the second conveyance guide 72 is used for the paper 35.
Is a sheet metal having a width slightly larger than the maximum width of the above-mentioned No. Sheet metal 7 of the first transport guide 71
5 is connected to the cathode side of the first diode 77 whose anode side is grounded. This is because positive charges are stored, and the first diode 77 is connected in a direction in which the positive charges are not released. The static elimination needle 41 is connected to a negative power source or grounded. The first diode 77 preferably has a low capacitance,
The meaning will be described later. Second transport guide 7
The base portion of the static elimination brush 78 is fixed to 2 via a mounting member (not shown). The tip of the static elimination brush 78 is arranged so as to face the surface of the pressure roll 43 with a slight distance therebetween, and removes electric charges from the surface of the pressure roll 43. The cathode of the first diode 77 is connected to the first transport guide 71 and the second transport guide 7.
2, static elimination brush 78 and core bar 79 of pressure roll
Is connected to

FIG. 5 shows an equivalent circuit of the first diode of this embodiment. The first diode 77 is
It is equivalent to a CR circuit including a capacitor C whose one end is grounded and a resistor R whose one end is connected to the other end of the capacitor C. That is, the reason for disposing the first diode 77 is to prevent the offset, and to accumulate and retain the electric charge of the polarity on the side where the current does not flow. This is a state in which a reverse voltage is applied across the terminals of the first diode 77. At this time, a capacitance component is present between the terminals, and the first diode 77
Is equivalent to a CR circuit. In this Figure, the potential V _in applied to one end of the resistor R, the charge potential heat roll 42 and pressure roll 43 of the induced potential or sheet 35 in the guide member or the like by charging the sheet 35 shown in FIG. 2 The voltage V _{out that} is applied and is applied to the other end is an offset countermeasure potential that the heat roll 42 and the pressure roll 43 have.

FIG. 6 shows the countermeasure potential V for the applied potential V _in .
_It represents the relationship of _out . The countermeasure potential V _out shown by the curve 80 can be expressed by the following equation (1), where R is the resistance of the resistor R and C is the capacitance of the capacitor C. However, the symbol t represents time.

[0046]

[Equation 1]

The capacitance component when the reverse voltage is applied differs depending on what kind of diode is selected as the first diode 77. From this equation (1), the smaller the capacitance component C, the better the response of the rise of the countermeasure potential V _out . The offset suppressing effect in the heat roll 42 depends on the countermeasure potential V _out , and the offset is reduced as the countermeasure potential V _out is larger and closer to the applied potential V _in . For this reason, the first diode 77 has a low capacitance capacitor component.

Returning to FIG. 2, the description will be continued. The heat roll 42 and the pressure roll 43 are housed in a pair of fixing device cases 81 and 82 which are vertically separated. A temperature detecting element 83 is attached to the inner surface of the upper fixing device case 81 so as to make light contact with the surface of the heat roll 42. The surface of this heat roll 42 is
It is connected to the anode side of the second diode 85 whose cathode side is grounded. Such electrical connection may be performed through a material such as a conductive fiber that is in sliding contact with the surface of the heat roll 42, or may be performed through the temperature detection element 83.

The second diode 85 has a charge of the same polarity as the toner (minus in this embodiment) and the polarity opposite to the applied voltage (plus in this embodiment) at the time of transfer by the transfer bias roll 29. Is a low-capacity diode arranged in a direction to prevent the movement of the. The meaning of the low capacitance is the same as that described above for the first diode 77. By grounding the surface of the heat roll 42 via the second diode 85, the offset of the toner with respect to the heat roll 42 is prevented. However, the use of the second diode 85 allows the heat roll 42
When the paper 35 is passed between the heat roll 4 and the pressure roll 43, a low charge of +300 V or less induced on the surface of the heat roll 42 by frictional charging is applied to the heat roll 4.
The purpose is not to remain on the surface of 2. Therefore, the second diode 85 is omitted, and the heat roll 42 is omitted.
It is also possible to directly ground.

The heat roll 42 has a release layer of PFA (perfluoroalkoxy), PTFE (polytetrafluorocotylene) or the like on the outer surface of a hollow cylindrical member made of aluminum, stainless steel or the like with a thickness of 10 to 50 μm. And is heated by a heating member 86 such as a halogen heater. The surface temperature of the heat roll 42 is controlled by a temperature control circuit (not shown) within a predetermined temperature range based on the surface temperature detected by the temperature detection element 83 such as a thermistor. Pressure roll 43
Has a structure in which a heat resistant elastic body layer of silicone rubber, silicone sponge or the like is provided on a cored bar 79 made of stainless steel or iron. The fixing device 40 including the heat roll 42 and the pressure roll 43 is loaded so that the surface of the paper 35 on which the toner image is transferred faces the heat roll 42, and is heated and fixed at the nip portion of both rolls.

Since the pressure roll 43 is made of the above-mentioned material, the pressure roll 43 generates a high potential on the same polarity side as the toner due to the frictional charging with the paper 35. In order to prevent the toner offset phenomenon with respect to the heat roll 42, it is desirable that the surface of the pressure roll 43 be charged with a polarity opposite to that of the toner (plus in this embodiment). For this reason, the tip of the static elimination brush 78 has the pressure roll 4
3 is disposed so as to face the surface of the transfer bias roller 3 and is grounded via a first diode 77 disposed in a direction in which movement of charges having the same polarity as the transfer bias roll 29 is blocked.
As a result, the accumulation of charges having the same polarity as the transfer bias roll 29 on the surface of the pressure roll 43 is promoted, and the generation of charges having the same polarity as the toner is blocked.

The structure of the pressure roll 43 having such a function is effectively as follows. (1) A configuration in which a conductive or high-resistance elastic layer is disposed on the cored bar 79 and grounded via a low-capacity rectifying element such as a diode. Here, the diode is the transfer bias roll 29.
Will be arranged in such a direction as to block the movement of charges having the same polarity as. (2) A conductive or high resistance elastic layer is disposed on the cored bar 79, and a high resistance layer such as a PFA tube or FEP (polyfluorinated ethylene propylene) tube having a thickness of 20 to 100 μm is separated from the release layer. Coat layers. The cored bar 79 is grounded or is grounded via a diode as described in (1).

In the present embodiment, the durability of the pressure roll 43, that is, the viewpoint of preventing contamination by toner and enabling long-term use, and the slipperiness for suppressing frictional electrification with the paper 35 are taken into consideration. The configuration of (2) is adopted. Also, a high-resistance silicone rubber was used for the elastic layer from the viewpoint of ease of manufacture, and the surface thereof was covered with a PFA tube having a thickness of 50 μm to form the pressure roll 43. Further, in order to further enhance the offset prevention function, the core metal 79 of the pressure roll 43 is grounded via the first diode 77.

Now, the inclined surface of the first transport guide 71 is
The angle does not coincide with the tangential direction of the photosensitive drum 19 and the transfer bias roll 29 shown by the broken line 87, and the angle is gentler than this. Therefore, the leading edge of the sheet 35 conveyed in the direction of the tangent line 87 has the rib 73 of the first conveying guide 71.
The metal sheet 75 is pressed against the inclined end surface of the sheet metal so that the sheet metal 75 is electrostatically attracted thereto. This prevents the leading edge of the paper 35 from floating during the transportation by the first transport guide 71, and the paper 35 contacts the cleaning device 56 shown in FIG. 1 to disturb the unfixed toner image. It is preventing the situation. Similarly, the transport surface of the first transport guide 71 and the transport surface of the second guide 72 are not arranged on the same plane, but are bent so that the cross section has a V shape. Therefore, the first
The sheet 35 that has been conveyed on the inclined surface of the conveyance guide 71 is conveyed so that the leading end portion thereof is pressed against the second conveyance guide 72, and the leading end portion floats and touches the fixing device case 81. It is also attempted to prevent the unfixed toner image from being disturbed.

Moreover, the sheet 35 of the second transport guide 72
When the extension direction of the latter half of the sheet is conveyed by another broken line 88, the contact position between the heat roll 42 and the pressure roll 43 exists on the extension line of the broken line 88. As a result, the sheet 35 is not likely to contact the unfixed toner image with the member located above the transport path until the sheet 35 is carried to the position where the heat roll 42 and the pressure roll 43 are nipped, and the above-mentioned problem called smudge occurs. It never happens. The rear half of the paper 35 is first
Existing on the conveyance guide 71, and the front half of the sheet 35 is accurately conveyed by the waist of the sheet 35 along the second conveyance guide 72 to the position where the heat roll 42 and the pressure roll 43 are nipped. Therefore, unlike the conventional case, there is no possibility that the leading edge of the sheet 35 once abuts against the heat roll 42 or the pressure roll 43 and then enters these nip portions. In addition, since the paper 35 does not hit in the middle of conveyance in this way, there is no fear that the image at the time of transfer is disturbed due to a temporary delay in the transport speed, and the transfer image is disturbed called smear. .

In the image forming apparatus of this embodiment, the cathode side of the first diode 77 is in contact with the metal plate 75 of the first transport guide 71. A rib 73 exists between the sheet metal 75 and the sheet 35 being conveyed. Against this, the first
The second transport guide 72, which contacts the cathode side of the diode 77, directly contacts the paper 35 being transported. The reason why the ribs are arranged only on the first conveyance guide 71 is that the total area of the first conveyance guide 71 contacting the paper 35 is wide. That is, when the contact area between the conveyance guide (conductive member) and the paper 35 is large, the electrostatic attraction force becomes too large, and the leading end of the paper 35 is attracted to the conveyance guide (conductive member) and conveyed to the fixing device 40. There may be a situation where the operation is not performed smoothly.

Therefore, as shown in FIG. 2, ribs 73 are arranged on the first conveyance guide 71 having a larger facing area to the paper 35, and a distance from the paper 35 is set so that the electrostatic adsorption is performed. It has a configuration that reduces the power to some extent. On the other hand, regarding the second conveyance guide 72, in order to allow the leading edge of the sheet to accurately and reliably rush into the rolling contact position of both rolls 42 and 43 of the fixing device 40, the conductive area having a small facing area is used. A sheet metal as a flexible member is used, and the sheet is conveyed while being in close contact with the second conveyance guide 72. In addition, these first and second transport guides 7
The conductive members 1 and 72 are electrically connected to each other, and are grounded via the first diode 77 having a low capacity.

Next, although a part of the description is repeated, the influence of static electricity on the conveyance of the sheet 35 will be considered in detail. In the present embodiment, the sheet 35 as a recording material is controlled by the transfer bias roll 29 so that the charge is reduced by the charge eliminating needle 41 arranged on the downstream side after the charge is applied by the transfer bias roll 29. This is because the charging potential of the transfer bias roll 29 varies greatly depending on the type of the paper 35. That is, when a high resistance resin film for OHP or a thick paper having high resistance is used as the paper 35, the surface thereof may be charged to +5 KV or more. When the sheet 35 comes into contact with a member such as the fixing device case 81 at the time of such high charging, or approaches these conductive members, the charged charge leaks and the unfixed toner image is disturbed. There is a possibility that the paper may be lifted from the conveyance guides 71 and 72, and the leading end of the sheet of paper 35 may not enter the fixing portion, causing a jam. However, when the charging potential of the paper 35 is low, the attraction force with the toner is low, so that the offset tends to occur. Therefore, static elimination needle 4
1 has a charging potential of + 2K regardless of the type of the paper 35.
It is generally configured so as to be maintained at about V.

However, even in the case of the paper 35 whose charge potential is controlled by the static elimination needle 41 in this way, when the guide member used in the conveying path to the fixing device 40 is made of a high resistance resin material. Induces high charge of the same polarity on the resin side, and causes the resin to float up from the guide member. Further, when such a guide member is made of a conductive member and is directly grounded, the paper is formed in a portion having a minute gap of about 0 to 0.3 mm between the paper 35 and the conductive guide member. A gap discharge leak occurs from 35. Due to this gap discharge leak, the unfixed toner image on the sheet 35 is disturbed.

In the present example, it was concluded from the results of the above examination that the following two points are necessary to suppress these obstacles. At least the surface of the guide member existing from the transfer bias roll 29 to the fixing device 40 facing the paper 35 has conductivity, and the facing surface does not generate frictional electrification or excessive induced electrification. The conductive member having conductivity should be grounded with a high resistance of 10 ¹⁰ Ω · cm or more.

Therefore, in the present embodiment, the guide member existing from the transfer bias roll 29 to the fixing device 40 is made of a conductive member so as to be electrically connected, and the diode in the direction of holding the electric charge having the same polarity as the transfer voltage is used. It is designed to be grounded through. As a result, the transfer bias roll 2
9, the charge potential of the sheet 35 after being controlled by the charge eliminating needle 41 so as to reduce the positive charge is maintained without changing to the fixing device 40, and also from the conveyance guide due to the above-mentioned leak or discharge. It becomes possible to carry without rebounding and lifting.

The offset phenomenon is caused by the pressure roll 43.
Excluding the frictional electrification of the sheet 35 and the sheet 35 depends on the potential induced on the heat roll 42 and the pressure roll 43 by the electric charge held by the sheet 35 after the transfer. Therefore, in the case of the diode connection as in the present embodiment, the offset is more difficult to occur as the following condition is satisfied. The charge on the polarity side of the transfer voltage of the paper 35 is high. The potential on the polarity side of the transfer voltage generated on the surface of the heat roll 42 is low. The potential on the polarity side of the transfer voltage induced on the surface of the pressure roll 43 is high.

The charging potential of the paper 35 shown by the above is usually controlled to about 2 KV because it is necessary to suppress the accompanying trouble as already described. In the configuration of the present exemplary embodiment, it is possible to carry the sheet in a highly charged state up to about 4 KV, and therefore, it is possible to further reduce the offset generated in the fixing device 40.

Further, the first and second conveyance guides 71 and 72 from the transfer bias roll 29 to the fixing device 40 are electrically connected to the static elimination brush 78 arranged close to the pressure roll 43. Therefore, the paper 35 charged on the polarity side of the transfer voltage is transferred to the first and second transport guides 7.
When the sheets 1 and 72 are being conveyed, the conveying guides 71 and 72 and the static elimination brush 78 have a potential substantially equal to the charging potential of the paper 35. Further, there is no change in the potential on the side of the paper separation surface during the conveyance of the guide, and the disturbance of the unfixed image due to the electrostatic action at the guide boundary does not occur. As a result, charges on the polarity side of the transfer voltage are supplied from the static elimination brush 78 to the surface of the pressure roll 43 facing the static elimination brush 78. The charge is supplied by the first and second transport guides 7
This is performed while the sheet 35 is present on either of Nos. 1 and 72. Therefore, from the front end to the rear end of the paper 35, the pressure roll 43 that is always charged on the offset suppression side.
The fixing will be performed using the surface of the.

With this effect, it is possible to stably maintain the potential on the polarity side of the transfer voltage induced on the surface of the pressure roll 43, which is synergistic with the maintenance of the charging potential of the paper 35. Since offset is also added, offset can be completely prevented.

Next, the influence of the heat roll 42 on the offset will be described. When the sheet 35 is conveyed to the rolling contact position of the heat roll 42 and the pressure roll 43 and is fixed, frictional charging with the sheet 35 causes the surface of the heat roll 42 to have the same polarity side as the transfer voltage of 300.
A voltage of about V is induced. This is the charging behavior in the direction of deteriorating the offset. However, as described in this embodiment, the heat roll 42 is directly grounded,
Alternatively, if the charges on the polarity side of the transfer voltage are made to be cancelable by grounding the diode on the same polarity side as the transfer voltage to prevent charging, the offset will not occur.

The prior art of the present invention includes a heat roll 42.
There has also been proposed a method of applying a voltage having a polarity opposite to that of the toner charge to generate a repulsive force with respect to the toner to obtain an offset preventing effect. However, power supply and wiring cost increase, influence on transfer performance when using hydrous paper in high temperature and high humidity environment, or to sensor member terminals such as temperature sensor or thermostat arranged on the surface of heat roll 42. There are many concerns such as leaks. Therefore, it is desirable to prevent the offset without requiring such an arrangement.

FIG. 7 shows the first part of the fixing device of this embodiment.
And the action of the second diode. Based on this figure, these first and second diodes 7
The function of 7, 85 will be described. Toner 92 is electrostatically adsorbed on the upper surface of the paper 35 conveyed in the direction of the arrow 91 in the negatively charged state. Since the paper 35 itself is positively charged, the pressure roll 43 that comes into contact with the paper 35 is also normally positively charged. On the other hand, the surface of the heat roll 42 is usually negatively charged.

The core of the pressure roll 43, and the first diode 77 having the cathode side connected to the static elimination brush 78 arranged opposite to the surface of the pressure roll 43,
It is preferable that the sheet 35 has the ability to have the same potential as that of the sheet 35 when it arrives. For this purpose, it is preferable that the capacitance of the first diode 77 is extremely small. In the case of the present embodiment, the second conveyance guide 72 (see FIG. 2) that is in sliding contact with the paper 35 for this purpose is
It was confirmed that the capacitance of 100 pF or less with respect to the ground plane is particularly preferable.

The first diode 77 is connected to the paper 35.
It is preferable that the potential becomes substantially the same as that of the first diode when it arrives, but this does not mean that, for example, the first diode can be replaced with a capacitor having a high breakdown voltage and a low capacitance. The charging relationship as shown in FIG. 7 is an ideal form in terms of preventing offset, but it is not always maintained in such a polarity relationship. That is, for example, the pressure roll 43 is basically supposed to give the charged electric charge from the paper 35 and to obtain the electric charge by frictional electrification, but it is not always the case depending on the type of the paper 35 or the use environment and history of the machine. In many cases, electric charges having an unfavorable polarity are supplied.

When there are charges of undesired polarities, it is necessary to release these charges. Therefore, the first diode 77 having the anode side connected to the pressure roll 43 and the cathode side grounded is used. If an element such as a capacitor having a bidirectional insulating property is used instead of this, electric charges cannot be released regardless of the polarity, which is not preferable. For the same reason, the second diode 85 is also connected to the heat roll 42. Of course, it has already been explained that this can be omitted.

Modification

FIG. 8 corresponds to FIG. 4 and shows a modification of the first transport guide. First of this modification
The conveyance guide 71A of the sheet metal 101 has one end (FIG.
The transfer bias roll 29 side shown in FIG. 2) is bent at a substantially right angle, and a slope is formed toward the other end side (the side reaching the fixing device 40 in FIG. 2). A band-shaped insulating film 102 having a predetermined width is attached to the surface of the sheet metal 101 with an adhesive. 10 for the film 102
It preferably has a resistance of ¹⁰ Ω · cm or more. Also,
This thickness and the distance between the films 102 is
The size (see FIG. 2) is set so as not to come into direct contact with the sheet metal 101 portion when being conveyed on the first conveying guide 71A.

Insulating film 1 having desired resistance value
For example, a PET (polyethylene terephthalate) film, a FEP film or a PVdF (polyvinylidene fluoride) film is effective as 02, but it is also possible to use another film having an equivalent function.

The first transport guide 71A of this modification is
Compared with the first transport guide 71 of the previous embodiment, there are advantages that the manufacturing is simple and the cost can be reduced.

Although the laser printer is shown as the image forming apparatus in the embodiment, the invention is not limited to this, and for example, for a printer using a light beam other than a laser, an electrophotographic copying machine or an electrostatic recording device. The present invention can be similarly applied. Further, although the photoconductor drum is used as the photoconductor in the embodiments, the present invention can be applied to an image forming apparatus using another photoconductor such as a photoconductor belt. Further, in the embodiment, a heat roll having a built-in heater is used as the fixing device, but it is not suitable for a device using a film for heat generation on the surface of the rotating body or a device using another fixing device such as a belt-like one. Of course, the present invention is also applicable.

Further, in the embodiment, the tip of the static elimination brush 78 and the surface of the pressure roll 43 are not in contact with each other, but it goes without saying that they may be brought into contact with each other. Further, in the embodiment, the case where the transfer bias roll supplies a positive charge has been described. However, the present invention is an image forming apparatus for recording with a charge having a polarity opposite to that of the embodiment, depending on the type of the photoconductor or the difference in charging polarity. It goes without saying that the same can be applied to the above.

[0078]

As described above, according to the first aspect of the invention, the rotation of the guide member from the transfer of the toner image to the recording material until the fixing is performed and the rotation of the side of the fixing device which is not in contact with the toner image. Since the bodies are connected in common, it is possible to uniformly control the potential of the portion that comes into contact with the recording material throughout the transportation of the recording material. Then, of the pair of rotators forming the guide member and the fixing unit, the surface of the rotator which is not in direct contact with the toner image releases a charge having the same polarity as the potential of the toner image, and a charge having a polarity opposite to this. Since the rectifying element is connected in such a direction as to hold them, even a relatively high resistance recording material made of OHP paper or thick paper left to stand and dried in an environment of low humidity and low temperature. Therefore, it is possible to stably convey by a proper suction action, and it is possible to prevent smudging due to lifting from the guide member. Further, since the fixing means holds the electric charges of proper polarity, it is possible to effectively prevent the offset of the toner. Therefore, not only the cleaning member for cleaning the surface of the rotating body can be removed from the fixing device, but also a circuit for grounding the sheet metal for electrostatic attraction of the recording material with high resistance and an offset are prevented. Therefore, an additional device for applying a bias to a predetermined rotating body becomes unnecessary, and the configuration of the image forming apparatus can be simplified and the cost can be reduced. It also contributes to downsizing of the device.

According to the second aspect of the invention, since the conductive member such as the brush for discharging electricity is arranged to face the rotating body on the side which does not directly contact the toner image in the fixing means, the potential of this rotating body is improved. It is possible to control and to prevent offset more thoroughly, and to secure high-quality recording.

Further, the invention according to claim 3 is characterized in that the rotating body for pressurization has an elastic layer arranged on a cored bar, and has a high resistance release layer on the elastic layer. Therefore, the toner image is less crushed as compared with a so-called pressure fixing roller, and good recording can be ensured by preventing offset.

According to the fourth aspect of the present invention, it is possible to prevent escape of the transfer charge generated when the conductive member and the recording material are in direct contact with each other. Therefore, when a toner image is transferred by a transfer means such as a transfer bias roll, it is possible to effectively avoid the occurrence of a defect such as a transfer failure or a disorder of the toner image on the recording material. As a result, it becomes possible to use a metal member even in a portion that may become hot, such as a guide member near the fixing device, and it is necessary to use a relatively expensive material such as a heat resistant resin. The cost of the image forming apparatus can be reduced also in this sense. Further, since the problem of thermal deformation of the guide member is eliminated, it is not necessary to provide a space between the guide member and the fixing device, and there is an advantage that it contributes to downsizing and increases flexibility in design.

Further, in the invention according to claim 5, the first guide member of the guide members arranged on the upstream side is inclined downward toward the downstream side, and the second guide member is arranged on the downstream side. The recording material is inclined upward as it goes, and the recording material sent out by the electrostatic latent image holding member and the transfer means plunges into the slope of the first guide member at an inclination angle larger than the inclination angle of the first guide member, The second guide member has a recording material conveying surface area smaller than that of the first guide member, and the extended surface of the inclined surface of the second guide member coincides with the rolling contact position of the pair of rotating bodies of the fixing means. ing. Therefore, even if there is no special suction mechanism for sucking the recording material, the recording material can be effectively pressed against the surface of the guide member and can be effectively prevented from rising from the surface. Further, since the rolling contact position of the pair of rotating bodies exists on the extension of the conductor surface of the second guide member, the leading end of the recording material is surely guided to the fixing device, and the occurrence of jam is prevented. be able to.

Further, since the second guide member is inclined upward, when the heating roller is arranged on the upper side of the fixing device, the second guide member can enter toward this roller relatively from the lower side. The side wall of the case that covers the heating roller can be extended to the lower side. As a result, it is possible to keep the fixing device warm and suppress the radiation of heat to the outside.

According to the sixth aspect of the invention, since the capacitance of the diode is small, the responsiveness is good and it is possible to sufficiently cope with the speeding up of recording.

When the protrusion amount of the insulator protruding from a part of the conductor surface of the first guide member in the image forming apparatus according to claim 4 is in the range of 0.5 mm to 2.5 mm, Since the preferable value of the protrusion amount of the insulator protruding from a part of the conductor surface in the guide member 1 is relatively wide, it is easy to process and assemble, and the recording material is stabilized by the electrostatic attraction force. Since it can be transported as it is, it contributes to downsizing of the apparatus.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a laser printer as an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a partial cross section of a device portion from the vicinity of a transfer bias roll to a fixing device.

FIG. 3 is an explanatory diagram showing a principle for measuring a resistance value of a transfer bias roll.

FIG. 4 is a perspective view showing a structure of a first conveyance guide of the present embodiment.

FIG. 5 is a circuit diagram showing an equivalent circuit of a first diode of this embodiment.

FIG. 6 is a countermeasure potential V for an applied potential V _{in in} this embodiment.
It is a characteristic view showing the relationship of _out .

FIG. 7 illustrates first and second fixing devices according to the present exemplary embodiment.
FIG. 6 is an explanatory view showing the function of the diode of FIG.

FIG. 8 is a perspective view showing a modified example of the first transport guide.

[Explanation of symbols]

19 ... Photosensitive drum, 29 ... Transfer bias roll, 35
... paper, 40 ... fixing device, 41 ... static elimination needle, 42 ... heat roll, 43 ... pressure roll, 71, 71A ... first
Transport guide 72, second transport guide 73, rib,
74 ... Support plate, 75, 101 ... Sheet metal, 77 ... First diode, 78 ... Static elimination brush, 79 ... Core metal, 85 ... Second diode, 102 ... Insulating film

Claims (6)

[Claims] 1. An electrostatic latent image holding member for holding an electrostatic latent image, and a toner image corresponding to the electrostatic latent image is formed on a portion of the electrostatic latent image holding member where the electrostatic latent image is formed. Developing means, transfer means for contacting the electrostatic latent image holding member via the recording material and transferring the toner image developed by the developing means onto the recording material, and a pair arranged downstream of the transfer means. Fixing means for fixing the recording material by passing the recording material between these rotating bodies, and a fixing means for fixing the recording material on which the toner image is transferred between the transfer means and the fixing means. A guide member at least a part of which is made of a conductive member for guiding the guide member and a surface of the rotary member on the side which does not come into direct contact with the toner image among the pair of rotary members which constitute the guide member and the fixing unit. It releases a charge of the same polarity as the potential of the toner image. Shikore an image forming apparatus characterized by comprising a rectifying element connected in a direction to retain these electric charges of the opposite polarity. 2. A conductive member disposed opposite to a charging portion of the rotating member on the side not directly contacting the toner image in the fixing unit, the conductive member having a charge having the same polarity as the potential of the toner image. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is connected to the rectifying element in a direction such that the charge is emitted from the facing rotating body and holds a charge having a polarity opposite to that of the charge. 3. The heating rotator that contacts the surface of the recording material on which the toner image is transferred,
The recording material is composed of a pressurizing rotary member that presses the recording material against the heating rotary member, and the pressurizing rotary member has an elastic layer disposed on a core metal and a high resistance release layer on the elastic layer. The image forming apparatus according to claim 2, wherein the image forming apparatus comprises: 4. The guide member comprises a first guide member having a protruding insulator disposed on a part of the conductor surface, and a first guide member disposed on the downstream side of the first guide member with the conductor surface exposed to the entire surface. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is composed of two guide members, and these conductor portions are both grounded via the rectifying element. 5. The electrostatic latent image holding member, wherein the first guide member is inclined downward as it goes downstream, and the second guide member is inclined upward as it goes downstream. And the recording material sent out by the transfer means protrudes into the slope of the first guide member at an inclination angle larger than the inclination angle of the first guide member, and the second guide member forms the recording material more than the first guide member. 5. The image forming according to claim 4, wherein the area of the conveying surface is small, and the extended surface of the inclined surface of the second guide member substantially coincides with the rolling contact position of the pair of rotating bodies of the fixing means. apparatus. 6. The image forming apparatus according to claim 1, wherein the rectifying element is a diode and has an electrostatic capacity of 100 pF or less.