JPH11258944A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely and stably obtain the effect of restricting a toner offset phenomenon and scatter phenomenon even in a high humidity environment in an image forming device equipped with a fixing device which applies a voltage with the opposite polarity of the toner electrification polarity to a pressure roll. SOLUTION: A specific output-limit-resistance-element R5 and a constant- voltage element TD are connected to a power source 14 which applies a bias voltage to the pressure roll 30, an aluminum base material with a hard-anodized- aluminum layer formed on it is used as the base material 21 of a heat roll 20, and the resistance value of the conductive surface layer 33 of the pressure roll 30 is specified. Besides them, an insulation surface layer is formed on a conductive guide member on the sheet-ejection side or a constant-voltage element, etc., are connected to it, and a restriction member for restricting the position of the entry of a recording sheet into a nip is provided. Otherwise, the structures above are properly combined.

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 a copying machine, a printer, a facsimile, and a multifunction machine using an electrophotographic process. The present invention relates to an improvement in an image forming apparatus capable of reliably suppressing a toner offset phenomenon, a scattering phenomenon, and the like generated in a fixing device.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic process is well known. This type of image forming apparatus includes:
Basically, as shown in FIG. 25, a charging device (for example, a charging roll) 101 and an image exposing device (for example, a laser beam writing device) are provided around an image carrier 100 formed of a drum-shaped or belt-shaped photoconductor. 102, a developing device 103, a transfer device (for example, a transfer roll) 104, a fixing device 105, a cleaning device 106, and the like are sequentially arranged.

In forming the image, first,
The image carrier 100 is charged by the charging device 101, and the charged image carrier 100 is exposed to a light image corresponding to image information from the image exposure device 102 to form an electrostatic latent image. The toner image T is formed by developing the image with a developer (finally, toner) supplied from the developing device 103. Next, the unfixed toner image T formed on the image carrier 100 is transferred to the image carrier 100 and the transfer device 1.
After being transferred onto a recording sheet P such as a transfer sheet supplied and conveyed during the time period 04 (transfer section), the recording sheet P is sent to a fixing device 105 disposed downstream of the image carrier 100 by The transferred unfixed toner image T is fixed on the recording sheet P to form an image. Reference numeral 107 in the figure denotes a static elimination terminal of a static eliminator for neutralizing the recording sheet P after transfer to facilitate separation from the image carrier 100.

In this type of image forming apparatus, as a fixing device 105, a heating roll 110 having a heating source 115 and a pressure roll 12 as shown in FIG.
The recording sheet P carrying the unfixed toner image T is fed and passed through a nip portion N formed by the two rolls 110 and 120, which is arranged so as to rotate in a state where the roller 110 is pressed against the fixing roller 110. Roll-type fixing devices that perform the above-mentioned processes are frequently used.

However, when such a fixing device 105 is used, a so-called offset phenomenon occurs in which a part of the unfixed toner is transferred to and adheres to the heating roll 110 at the time of fixing, or the nip is generated. When the sheet P described in the section N enters, the arrangement of the toner on the recording sheet P is disturbed, and the toner scatters, that is, a so-called scatter phenomenon occurs.

[0006] The offset phenomenon and the scattering phenomenon of the toner occur particularly when the amount of retained electric charge of the toner is not sufficient and the unfixed toner immediately after the power supply of the image forming apparatus main body is turned on or immediately after the toner is supplied to the developing device 103. When the adhesion of the toner image to the recording sheet P is weak, when the recording sheet P has a high water content due to moisture absorption or the like, and the holding power of the recording sheet P with respect to the toner is low, It tends to occur when they overlap. Also,
Regarding the toner scattering phenomenon, particularly when the recording sheet is in a water-containing state, when the recording sheet is heated by the heating roll, moisture in the sheet evaporates to generate an air current, and the air flow causes the recording sheet P to enter the nip portion N. It has been confirmed that this is caused by disturbing the arrangement of the above unfixed toner. Moreover, such scattering of toner is particularly
It tends to occur in a thin line extending in the direction (axial direction of the roll) perpendicular to the traveling direction of the recording sheet.

Therefore, conventionally, as a measure for preventing such an offset phenomenon and a scattering phenomenon of the toner, for example, as shown in FIG. A method of applying a polarity bias voltage has been proposed (Japanese Patent Laid-Open No. 5-22 / 1990).
No. 4546).

That is, the fixing device according to this proposal has a transfer device 104 (or a charging device) as shown in FIG.
The voltage divided by the resistors R1 and R2 from the power supply 130 is applied to the metal core 120a of the pressure roll 120. Heating roll 120 in this fixing device
For example, a core metal 120a on which a conductive elastic layer 120b and an insulating surface layer 120c are coated in this order is used.

According to this fixing device, a charge having the same polarity as the charged polarity of the toner is induced in the conductive surface layer 110a of the grounded heating roll 110, and the unfixed toner image on the recording sheet P is transferred to the recording sheet P. An electric field is generated in a direction to attract the toner to the side, so that the toner is less likely to be transferred to the heating roll 110 side, thereby suppressing the toner offset phenomenon. Further, as described above, the pressing roll 120
Applying a voltage of the opposite polarity to the charge polarity of the toner to
It has been confirmed that the present invention is effective not only in preventing the toner offset phenomenon but also in preventing the toner scattering phenomenon as described above.

For this reason, the present inventors also prototyped an image forming apparatus having a configuration as shown in FIG. 27 and tested whether or not there was an effect of preventing the toner offset phenomenon and the scattering phenomenon.

The prototype image forming apparatus is the same as the apparatus illustrated in FIG. 25 described above, except that a voltage obtained by dividing the bias power source 140 by resistors R1 and R2 (the reverse of the charging polarity of the toner) as shown in FIG. (Polarity voltage) is applied to the pressure roll 120 via one power supply member 141 including a power supply brush and the like disposed to be in contact with one end surface of the pressure roll 120.

In this image forming apparatus, the heating roll 110 is a core bar 110a made of aluminum.
A pressure roll having a coating formed thereon with an insulating surface layer 110b was used, and a pressure roll 120 having a cored bar 120a coated with an insulating elastic layer 120d and a conductive surface layer 120e was used. Among them, the insulating surface layer 110b
As the conductive surface layer 120e, a conductive tube formed of a synthetic resin alone or a conductive tube formed by dispersing a conductive agent (such as carbon black) in the synthetic resin was used. Further, in this image forming apparatus, a voltage for removing the charge of the transferred recording sheet P to a predetermined level from the power supply 150 is applied to the charge removing terminal 106 via the resistor R3.

[0013]

However, when a test was performed using the image forming apparatus thus prototyped,
Despite the bias voltage being applied to the pressure roll in the fixing device by resistive voltage division, the following problems were found.

That is, especially in a high humidity environment,
When the recording sheet P enters the nip portion N of the fixing device 105 and passes therethrough, the bias power supply 140
Voltage fluctuates greatly (see FIG. 5).
reference). Then, due to the fluctuation of the voltage, the pressure roll 1
Since the electric field in the direction of attracting the unfixed toner image to the recording sheet P as described above is not stably formed between the heat roller 20 and the heating roll 110, the effect of preventing the toner offset phenomenon and the scattering phenomenon can be obtained. It turned out that it was not possible to obtain it sufficiently and stably.

Such a voltage fluctuation is caused by the pressure roll 12
The charge induced by the bias voltage applied to 0 is
In a high humidity environment, the surface of the recording sheet P or the heating roll 1
It is presumed that the outflow easily occurs through the surface or the like of 10 as a main factor.

According to various studies by the present inventors regarding this voltage fluctuation, the higher the bias voltage applied to the pressure roll, the greater the effect of suppressing toner scattering on the recording sheet, but the bias voltage is reduced. When the voltage is increased, the current load is increased, whereas the load resistance is substantially reduced in the resistance voltage dividing circuit as described above, so that the outflow of charges as described above becomes remarkable, and as a result, the voltage further varies. It turned out to be easier. In addition, in this case, if there is a static eliminator that neutralizes the transferred recording sheet P as in the above-described example of the image forming apparatus, the recording sheet P is moved to the nip portion of the static eliminator (the static elimination terminal 107) and the fixing device 105. It has also been found that, when a state of straddling occurs, the charge of the pressure roll 120 may be transmitted through the recording sheet P and flow from the charge removing terminal 106 to the charge removing device side.

When such a bias voltage is continuously applied to the pressure roll 120 for a long period of time, the surface of the heating roll 110 (insulating surface layer 110b) in contact with the pressure roll 120 is locally applied. It has been confirmed that dielectric breakdown and the like caused by bubbles occur, and a bias voltage leaks at that portion to cause a voltage drop. Such a voltage drop also occurs when a pinhole exists in the insulating surface layer.

Further, at the time of fixing, the pressure roll 120 itself is heated by a nip portion with the heating roll 120 to change its temperature state, or a bias voltage is applied in contact with the pressure roll 120. It was confirmed that the bias voltage was not uniformly and sufficiently applied to the pressure roll 120 (particularly in the vicinity of the nip portion) due to a difference in the arrangement position of the power supply member 141 and the like.

In addition, if a conductive guide member for guiding and discharging the fixed recording sheet P is provided on the sheet discharge side of the fixing device 105, a part of the guide member is provided at the sheet rear end. It was confirmed that the bias voltage fluctuated due to the contact of the fixed recording sheet P whose portion was in the nip portion. Further, the fixing device 10 for the recording sheet P
It was also confirmed that there was a difference in the effect of suppressing the toner offset phenomenon and the scattering phenomenon depending on the attitude (angle) of entering the nip portion into the nip portion.

The present invention has been made in view of the above-mentioned situation, and an object of the present invention is to apply a voltage having a polarity opposite to the charge polarity of the toner to the pressure roll of the fixing device to thereby cause the toner offset phenomenon. It is an object of the present invention to provide an image forming apparatus capable of more reliably and stably obtaining the effect of suppressing the phenomenon of scatter and scattering, even in a high humidity environment.

[0021]

An image forming apparatus according to a first invention (an invention according to claim 1) capable of achieving the above object carries an unfixed toner image formed according to image information. An image carrier, a transfer device for transferring an unfixed toner image on the image carrier to a recording sheet, and a recording sheet after the transfer by the transfer device is completed. A fixing device for fixing the unfixed toner image on a recording sheet by passing through a nip portion between a formed heating roll and a pressure roll having a conductive surface layer formed on a conductive roll substrate, and the fixing device And a bias power supply for applying a bias voltage having a polarity opposite to the charging polarity of the unfixed toner image via a power supply member disposed in contact with the conductive surface layer of the pressure roller. (Hereafter, this is referred to as )), An output limiting resistance element having a resistance value within a range of 1 to 15 Ω is connected in series between the output of the bias power supply device and the power supply member, and the current limiting resistance element is connected to the output limiting resistance element. A constant voltage element is connected between the power supply member and the power supply member in a grounded state.

Here, the image bearing member is usually a photosensitive member on which a toner image is directly formed by an electrophotographic process. After the toner image formed on the photosensitive member is once held, the toner image is formed on a recording sheet. It may be a so-called intermediate transfer member for retransfer. The transfer device may be a corona discharger or the like in addition to the roll type. The insulating surface layer and the conductive surface layer may be formed by coating by powder coating or the like in addition to the tube-shaped one. The thickness of the insulating surface layer is preferably in the range of 10 to 60 μm. Further, the thickness of the conductive surface layer is preferably in the range of 20 to 120 μm. The power supply member may be in the form of a conductive film in addition to the brush.

As the above-mentioned output limiting resistance element, any resistance element having a resistance value within the above-mentioned specific range may be used. The resistance value of this resistance element is more preferably in the range of 5 to 15?. As the above-mentioned constant voltage element, a Zener diode is usually used, but other than this, for example, a varistor or the like may be used.

According to the first aspect of the present invention, a stable bias voltage is always applied to the pressure roll from the bias power supply device even when the factors causing the charge to flow out may increase in a high humidity environment or the like. Can be applied. Further, since the resistance value of the output limiting resistance element is set to 1 MΩ or more, it is possible to reliably suppress the occurrence of leakage between the output limiting resistance element and the heating roll. In addition, since the resistance value is set to 15 ° Ω or less, it is possible to reliably suppress the voltage drop when the water-containing recording sheet passes through the inside of the fixing device. Therefore, an electric field in the direction of attracting the unfixed toner image to the recording sheet is stably formed between the pressure roll and the heating roll.

Further, the image forming apparatus according to the first aspect of the present invention is disposed so as to be close to the back side of the recording sheet after the transfer, and at least a voltage having the same polarity as the charging polarity of the unfixed toner image is supplied from a power supply device. In the case where a static eliminator is provided for neutralizing the recording sheet via the neutralizing terminal to be applied, a resistance value within a range of 5 to 100 Ω between the output of the power supply device and the neutralizing terminal in the neutralizer. It is desirable that the current limiting resistance elements be connected in series.

As the current limiting resistance element, any resistance element having a resistance value within the above specific range may be used. The resistance value of this resistance element is more preferably in the range of 5 to 50?. The neutralizing terminal is an electrode plate or a discharge wire when the neutralizing device is a corona discharger.

In this case, even if the recording sheet P straddles the charge removing terminal of the charge removing device and the nip portion of the fixing device, the charge induced by the bias voltage applied to the pressure roll is generated. Can be suppressed from flowing through the recording sheet and flowing from the static elimination terminal to the static elimination device side, and the voltage drop due to such charge inflow is eliminated. Further, since the resistance value of the current limiting resistance element is set to 5 MΩ or more,
The inflow of charges transmitted from the pressure roll via the recording sheet into the charge removing device can be reliably suppressed. Moreover,
Since the resistance value is set to 100 ° Ω or less, a voltage for discharging can be instantaneously transmitted from the power supply device of the static eliminator to the static elimination terminal without loss during the transfer operation. As a result, a delay in the rise of the charge removing device during the transfer operation does not occur.

The image forming apparatus according to the second invention (the invention according to claim 3) which can achieve the above-mentioned object, in addition to the common elements premised on the first invention, further includes a heating roller in the fixing device. The roll base material is an aluminum roll base material having a hard alumite layer formed on its surface.

The hard anodized layer is an anodic oxide film formed by performing an anodic oxidation treatment included in a hard class when the aluminum is classified as hard or soft in the anodic oxidation treatment of aluminum. This hard alumite layer is desirably formed so that its thickness is in the range of 10 to 30 μm. In order to form such a hard alumite layer, the temperature of the electric field bath in the anodic oxidation treatment is 0 to 20 ° C., and the current density is 2 to 12 A / d.
m ² and the processing time may be appropriately set within a range of 5 to 30 minutes.

According to the second aspect of the present invention, the insulating surface layer can be formed on the roll base on which the hard alumite layer is formed, as compared with the heating roll composed of the roll base on which the soft alumite layer is formed. Can be formed with adhesive strength,
In addition, the generation of bubbles between the surface layer and the roll substrate can be suppressed. Thereby, it is possible to reliably prevent the dielectric breakdown and the occurrence of pintle in the heating roll.

Further, in the image forming apparatus of the second invention, the aluminum roll base material is subjected to a fine roughening treatment on the surface of the roll base material before the formation of the hard alumite layer. It is desirable.

The above-mentioned fine rough surface treatment refers to surface roughness Ra
Is about 1 μm. Such a rough surface treatment can be usually performed by blast processing,
It may be performed by other methods.

In this case, as compared with a heating roll in which a hard alumite layer is simply formed without performing the roughening treatment,
The adhesive strength of the insulating surface layer to the roll substrate can be further improved, and the generation of bubbles between the surface layer and the roll substrate can be suppressed more reliably. Also,
Since the surface of the hard anodized layer becomes rough due to the effect of the roughening treatment, and fine voids are present between the surface layer and the surface layer, even if bubbles are generated between the surface layer and the roll base material, It is released through the void and does not remain between the surface layer and the roll substrate.

Further, in the image forming apparatus of the second invention, the insulating surface layer of the heating roll is coated up to the end of the conductive roll base material, and the contact angle with water is 100.
It is desirable to have a surface physical property of not less than °.

This is particularly effective in an image forming apparatus in which the width of the heating roll is wider than the width of the pressure roll, and both ends of the heating roll project from both ends of the pressure roll.

In this case, even if moisture or the like that evaporates from the recording sheet at the time of fixing is attached to the surfaces of both ends of the heating roll, the surface becomes hydrophobic with a contact angle of 100 ° or more. Therefore, although the water becomes fine and independent water droplets, it does not form a continuous water film. Therefore, the bias voltage applied to the pressure roll does not discharge along the surfaces of both ends of the heating roll.

The image forming apparatus according to the third invention (the invention according to claim 6), which can achieve the above object, has the following features: The conductive surface layer is a layer in which a conductive agent is dispersed in a fluorine-based resin or a silicone-based resin, and has a resistance of 3ΜΩ or less at a temperature of 0 to 30 ° C. .

As the above-mentioned fluororesin, PFA (perfluoroalkoxyethylene copolymer resin), FEP (ethylene tetrafluoride / hexafluoropropylene copolymer resin) and the like are used. Examples of the conductive agent include carbon black, polyacetylene, poly-p-phenylene, polythiazole, etc. The conductive surface layer is made of PFA.
Most preferably, carbon black is dispersed therein.
Further, the resistance value of the conductive surface layer at the above temperature is 3Μ.
The value of Ω or less can be obtained by adjusting the dispersion state of the conductive agent, but is not limited to this.

According to the third aspect, even if the surface of the pressure roll is heated by the heat of the heating roll in the nip portion and the temperature rises, the resistance value of the conductive surface layer of the heating roll is large. Since there is no fluctuation (increase) (the amount of change is at least within 50 times), the bias voltage can be more stably applied to the entire pressure roll.

The image forming apparatus according to a fourth invention (an invention according to a seventh aspect), which can achieve the above-mentioned object, has a configuration in which, in addition to the common elements premised on the first invention, the power supply member includes One or more rolls are provided at both ends of the roll.

According to the fourth aspect, the bias voltage can be reliably applied in the axial direction of the pressure roll.

In the image forming apparatus according to a fourth aspect of the present invention, it is preferable that the power supply member is disposed at least in the vicinity of the nip portions at both ends of the pressure roll. The vicinity of the nip portion is preferably near the nip portion on the sheet entry side, and more preferably, within the peripheral surface region within 90 ° with respect to the circumferential direction of the pressure roll around the nip portion. It is desirable that

In this case, the bias voltage is reliably applied to the vicinity of the nip of the pressure roll. As a result, an electric field due to the bias voltage is satisfactorily formed between the pressure roll and the heating roll near the nip portion, and the effect of suppressing the toner scattering phenomenon can be reliably obtained.

Further, in the image forming apparatus according to a fourth aspect of the present invention, at least two power supply members are arranged in the circumferential direction of the roll in the circumferential direction including the nip portion at both ends of the pressure roll. It is desirable to be installed.

In this case, the bias voltage is more reliably applied near the nip of the pressure roll. As a result, an electric field due to the bias voltage is more favorably formed between the pressure roll and the heating roll near the nip portion, and the effect of suppressing the toner scattering phenomenon and the effect of suppressing the offset phenomenon can be reliably obtained.

The image forming apparatus according to a fifth aspect (an invention according to a tenth aspect), which can achieve the above-described object, has the same structure as the first aspect, except that A conductive guide member for guiding a recording sheet to be discharged is provided, and an insulating surface layer is formed on at least a sheet contact portion of the conductive guide member that can contact the recording sheet. It is. It is preferable to form a layer having a resistance value of 10 ⁹ Ωcm or more as the insulating surface layer.

According to the fifth aspect, even if the recording sheet in the process of being discharged from the nip portion comes into contact with the conductive guide member, the charge induced on the pressure roll by the application of the bias voltage causes the recording sheet to be charged. Then, it flows to the guide member side. As a result, there is no voltage fluctuation due to the electric charge flowing into the guide member.

The image forming apparatus according to the sixth invention (the invention according to the eleventh aspect) which can achieve the above object can be obtained by replacing the fifth embodiment with the formation of the insulating surface layer on the conductive guide member. A constant voltage element or a high resistance element is connected between the conductive guide member and the grounding portion. A Zener diode or the like is used as the constant voltage element. It is preferable to use a high resistance element having a resistance value of 10 ⁹ Ω or more.

According to the sixth aspect, even if the recording sheet in the process of being discharged from the nip portion comes into contact with the conductive guide member, the charge induced on the pressure roll by the application of the bias voltage causes the recording sheet to be charged. It is suppressed that it is transmitted to the guide member side and grounded. As a result, there is no voltage fluctuation due to the electric charge flowing into the guide member.

An image forming apparatus according to a seventh invention (an invention according to a twelfth aspect), which can achieve the above object, has, in addition to the common elements premised on the first invention, a sheet entrance side in the fixing device. A regulating member for regulating a posture of the recording sheet when the recording sheet enters the nip portion so as to be changeable. By this regulating member, the recording sheet after at least the sheet leading end portion enters the nip portion is separated from the sheet by the nip. The angle of the tangent to the center of the section is restricted to an approaching posture of 5 ° or more toward the heating roll side.

The restricting member can be constructed by displacing a sheet guide member disposed on the sheet entry side, but can also be displaced separately from the sheet guide member. A member may be provided, and the guide member and the movable member may be used in combination.

According to the seventh aspect, the attitude (entrance angle) of the recording sheet approaching the heating roll side by the regulating member.
, The toner image bearing surface side of the recording sheet is preliminarily heated by heat radiation of a heating roll just before the nip portion. As a result, the unfixed toner on the recording sheet is slightly melted and physically adheres strongly to the recording sheet, so that the toner scattering phenomenon is suppressed and the toner is easily fixed on the recording sheet. Become.

An image forming apparatus according to an eighth invention (an invention according to claim 13) which can achieve the above object is the image forming apparatus according to the first invention, wherein the image forming apparatus according to the second invention and the third invention are provided. Each of the above-mentioned components is added and combined. That is, in the image forming apparatus of the first invention, the conductive surface layer of the heating roll is an aluminum roll base material having a hard alumite layer formed on the surface thereof, and the conductive surface layer of the pressure roll is a silicone resin. Or a layer in which a conductive agent is dispersed in a fluororesin,
The resistance value at a temperature of 30 ° C. is 3ΜΩ or less.

According to the eighth aspect, the respective effects of the first, second, and third aspects can be simultaneously and synergistically obtained. As a result, the toner Can be more reliably and stably suppressed.

In addition, in order to achieve the above object,
By appropriately combining at least two or more of the above-described first to seventh inventions, it is possible to more reliably realize the invention.

[0056]

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

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

[Configuration of the Entire Apparatus] The laser beam printer includes a photosensitive drum 1 made of selenium or an organic photoconductor on which a toner image corresponding to image information is formed by an electrophotographic process. This photosensitive drum 1
It is supported so as to rotate in the direction of the arrow in the figure, and is uniformly charged by a charging roll 2 arranged to rotate while contacting the outer surface of the drum. The exposure and scanning of the laser beam LB corresponding to the image information output from the laser exposure device 3 causes the charge to disappear and an electrostatic latent image to be formed.
A voltage obtained by superimposing a negative DC bias voltage on an AC voltage is applied to the charging roll 2 from a charging power supply device (not shown).

Downstream from the exposure position of the photosensitive drum 1, a developing device 4 for storing a one-component or two-component developer (toner) for developing an electrostatic latent image is provided. I have. The developing device 4 is provided with a developing roll 4a that rotates in proximity to the photosensitive drum 1, a toner supply member (not shown) that supplies toner to the developing roll 4a, and the like. The electrostatic latent image is developed by a toner supplied from a developing roll 4a of the developing device 4 at a position facing the developing device 4 to become a toner image T.
A developing bias in which a negative DC bias voltage is superimposed on an AC voltage is applied to the developing roll 4a from a developing power supply device (not shown), and a negatively charged toner is used. Therefore, the developing device 4 performs development by so-called reversal development in which toner is attached to an exposed area (latent image) of the photosensitive drum 1.

Further, a transfer roll 5 as a transfer device for transferring the toner image on the photosensitive drum 1 to the recording sheet P is provided downstream of the developing device 4 of the photosensitive drum 1. A transfer bias in which a positive DC bias voltage is superimposed on an AC voltage is applied to the transfer roll 5 during transfer from a transfer power supply device (not shown). As a result, the unfixed toner image T on the photosensitive drum 1 is transferred to the recording sheet P at a position facing the transfer roll 5.

The recording sheets P are fed out one by one from a paper feeding unit such as a cassette or tray (not shown) via a paper feeding roll 6 or a sheet conveying path, and sent out in synchronization with the photosensitive drum 1 by a registration roll 7. Is supplied so as to pass between the photosensitive drum 1 and the transfer roll 5 at a desired paper feed timing. The dashed line in FIG. 1 is the conveyance path of the recording sheet. Then, during this passage, the transfer bias described above is applied to the transfer roll 5, whereby
The toner image on the photosensitive drum 1 is electrostatically transferred to the recording sheet P side.

After the transfer of the toner image, the photosensitive drum 1 has a residual toner which has not been transferred to the recording sheet P side, but the toner is downstream of the transfer roll 5 of the photosensitive drum 1. It is removed and cleaned by the cleaning device 8 disposed at the side position. The photosensitive drum 1 after the cleaning by the cleaning device 8 is performed.
It is uniformly charged again by the charging roll 2, and the process proceeds to the next image forming cycle.

On the other hand, at a position downstream of the transfer roll 5,
A static eliminator 9 is disposed to neutralize the transferred recording sheet P from the back side (the surface opposite to the toner image carrying surface). The static eliminator 9 is provided on the recording sheet P of the photosensitive drum 1.
A static elimination plate 10 serving as a static elimination terminal, which is disposed so as to be close to the rear surface of the sheet at a point where the sheet is peeled off, and whose leading end adjacent to the sheet is formed in a saw-tooth shape; And a power supply unit 11 for applying a bias voltage having the same polarity (minus in this example) as the charging polarity of the unfixed toner image T from the power supply unit 11. Therefore, the recording sheet P after the transfer is removed from the surface of the photosensitive drum 1 after the charge is removed by the charge removing plate 10 of the charge removing device.

On the downstream side of the transfer position of the photosensitive drum 1 from the transfer position in the sheet conveying direction, a roll-type fixing device 12 including a heating roll 20 and a pressure roll 30 which rotates while being pressed against each other.
Are arranged.

As shown in FIG. 2, the heating roll 20 has a structure in which a conductive roll base material 21 is coated with an insulating surface layer 22, and is disposed inside the roll base material 21. The heater 23 is heated to a predetermined temperature (about 160 to 220 ° C.) by a heating source 23 such as a lamp. As the roll base material 21, a material made of aluminum, iron, copper, or the like can be used. In this example, a material made of aluminum was used. Insulating surface layer 22
A tube in which carbon black was dispersed in PFA (thickness: about 30 μm) was used. The heating roll 20 grounds the roll base 21.

On the other hand, as shown in FIG. 2, the pressure roll 30 is formed by coating a conductive roll base 31 with an insulating elastic layer 32 and a conductive surface layer 33 in this order. Is pressed by a biasing means (not shown) at a predetermined pressure to form a nip portion N having a predetermined width with the heating roll 20. As the roll base material 31, a material made of aluminum, iron, copper, or the like can be used. In this example, a material made of aluminum is used. As the insulating elastic layer 32, a layer made of silicone sponge was used. As the conductive surface layer 33, PFA in the form of a tube (about 20 μm in thickness) was used. The pressure roller 30 is provided with a power supply brush 13 as a power supply member that comes into contact with an end of the pressure roll 30.
3, a bias voltage having a polarity (plus in this example) opposite to the charging polarity of the toner image T is applied from the bias power supply device 14. The bias power supply device 14 may be a dedicated power supply device different from the power supply device 11 of the static elimination device 9 as illustrated in FIGS.
1 (secondary power supply circuit).

Further, on the sheet entrance side of the fixing device 12,
An entry guide member 15 for guiding the transferred recording sheet P into the nip portion N without fail is provided. On the other hand, on the sheet discharge side, a discharge guide member 16 for guiding the transferred recording sheet P from the nip N to be surely discharged is provided.

In the fixing device 12, the transferred recording sheet P is guided by the entry guide member 15, enters the nip portion N formed by the heating roll 20 and the pressure roll 30, and is then moved by the two rolls 20, 30. It is pinched and transported.
At this time, the recording sheet P is conveyed so that the toner image carrying surface side faces the heating roll 20. As a result, the unfixed toner image T on the recording sheet P is fixed on the sheet surface by heating and pressing.

Further, in the fixing device 12, since a bias voltage having a polarity (plus) opposite to the charging polarity of the toner image is applied to the pressure roll 30 from the fixing power supply device 14 via the power supply brush 13, In the nip portion N of the heating roll 20 and the pressure roll 30 and the area before and after the nip portion N, a positive polarity charge is stored on the conductive surface layer 33 side of the pressure roll 30, and the charge base material 21 side of the heating roll 20 is A negative polarity charge is induced. As a result, an electric field is formed in a direction in which the negative polarity toner constituting the toner image T on the recording sheet P is repelled from the heating roll 20 and is attracted to the recording sheet P side. The occurrence of the phenomenon is suppressed, and the occurrence of the scattering phenomenon of the toner on the recording sheet P is suppressed.

The recording sheet P on which the toner image has been fixed as described above is guided by the discharge guide member 16 and discharged to a discharge tray or the like through a discharge port (not shown).

[Structure of Principal Parts] In this printer, in order to more effectively suppress the occurrence of the toner offset phenomenon and the scattering phenomenon, the following detailed structure is employed.

First, when a bias voltage is applied to the pressure roll 30 of the fixing device 12 through a resistance voltage dividing circuit (see FIG. 27) as in the prior art, as shown in FIG. At the time (S) when the recording sheet P passes through the nip N, the bias voltage applied to the pressure roll 30 fluctuates greatly. The data shown in FIG. H. In this environment, the current was measured based on the current flowing through the power supply brush 13 in contact with the heating roll 30. The bias voltage is +340 V
Is applied.

Therefore, in this printer, as shown in FIG. 2, in a bias power supply 14 for applying a bias voltage to the pressure roll 30 of the fixing device 12, the bias power supply 14 is connected between the output side of the power supply 14 and the power supply brush 13. Is connected to a resistance element R5 for limiting output, and a zener diode TD as a constant voltage element is connected between the resistance element R5 and the power supply brush 13. Thereby, the power supply device 14
The bias voltage applied to the pressure roll 30 from FIG.
As shown in FIG. 5, it was confirmed that the recording sheet P was extremely stable without being affected even when the recording sheet P passed.

Further, even when the output side of the bias power supply device 14 is configured by connecting the resistance element R5 and the Zener diode TD as described above, depending on the resistance value of the resistance element R5, the output to the pressure roll 30 may be changed. It was confirmed that the applied voltage slightly fluctuated. FIG. 7 shows that the resistance element R5 is 3
This shows the state of the applied voltage when a resistance of 0 MΩ is used. From the results shown in FIG. 7, it can be seen that the voltage slightly fluctuates at the time S when the recording sheet P passes. The applied voltage also fluctuates regularly during the sheet non-passing time when the recording sheet P has not passed (between the passing time S and the next passing time S). This is caused by a difference in resistance value caused by a fold in the surface layer 32 of the pressure roll 30.

Therefore, as the resistance element R5, 10 MΩ
To use the resistor. Thereby, the power supply device 1
8, it was confirmed that the bias voltage applied to the pressure roll 30 was extremely stable without being affected even when the recording sheet P passed, as shown in FIG. Also,
As a result of various studies, it has been found that this resistance element R5 has at least 1
It has been found that good results are obtained when the resistance value is in the range of ~ 15 ° Ω. Note that the data shown in FIG. 8 does not show the record fluctuation at the time of non-passing of the sheet as shown in FIG. 7, but this is solved by improving the arrangement of the power supply brush 13 as described later. It is.

Next, the bias power supply device 14 connecting the resistance element R5 (10 MΩ) and the Zener diode TD is connected.
The bias voltage to be applied to the pressure roll 30 and the effect of suppressing the toner scattering phenomenon were confirmed using FIG. 9. As shown in FIG. 9, as the bias voltage was increased, the effect of suppressing the toner scattering was improved. It was confirmed that. However, on the other hand, it was confirmed that when the bias voltage was higher than 400 V, the toner image transferred onto the recording sheet P blurred.

For this reason, in this printer, the bias voltage applied to the pressure roll 30 was set to 340V. The toner scattering level in FIG. 9 is obtained by printing out a sample image, examining the degree of toner scattering generated in the obtained image, and determining the result at that time.
In the case where no toner splattering occurs, the grade is 0, and the case in which the worst splattering occurs is the highest grade 6, and a total of 6 levels within this range (grade 0 to 0)
The level was evaluated in section 5).

Further, in this printer, there is a neutralizing device 9 for neutralizing the recording sheet P after the transfer, and the recording sheet P is temporarily removed from the neutralizing device 9 (the neutralizing plate 10) and the nip portion of the fixing device 105. There may be a situation in which the straddle is straddled. Therefore, the electric charge of the pressure roll 30 is transferred to the charge removing plate 1
The situation of flowing from 0 to the static eliminator 9 was examined.

FIG. 10 shows the power supply device 1 in the static eliminator 9.
The result of measuring the state of the current flowing into the static eliminator 9 when the resistance value of the current control resistive element R6 (FIG. 2) connected between the output side of No. 1 and the static elimination plate 10 is changed is shown. Things. In this measurement, an AC / DC high-voltage power supply device (trade name: 610C) was used instead of the power supply device 11.
Was used to check the state of the voltage (current) displayed on the monitor of the device. At this time, 3 k is applied from the high-voltage power supply to the static elimination plate 10.
A voltage of around V was applied.

From the results shown in FIG. 10, the resistance element R6
It can be understood that the inflow current can be suppressed to 8 μA or less by setting the resistance value of at least 5 MΩ or more.
When the inflow current was 8 μA or less, it was confirmed that the fluctuation of the voltage applied to the pressure roll 30 was small, and the effect of suppressing the toner offset phenomenon and the scattering phenomenon was favorably obtained. When the resistance value of the resistance element R1 exceeds 32 MΩ, the subsequent inflow current becomes substantially constant and hardly changes.

Therefore, in this printer, a resistance of 22 MΩ was used as the resistance element R6 in the power supply unit 11 for static elimination. In addition, as a result of various studies, the resistance element R
It has been found that good results are obtained when No. 6 has a resistance value in the range of at least 5 to 100 ° Ω.

Next, as a heating roll 20 in such a printer, as shown in FIG. 4, an aluminum roll base material 20 is anodized to form an alumite layer 21a on the base material surface. A roll base material 21 in which a tube in which carbon black is dispersed in PFA was coated and formed as a conductive surface layer 22 was used, but air bubbles or bubbles were locally formed between the roll base material 20 and the conductive surface layer 22. Layer delamination was confirmed, and it was confirmed that the voltage applied to the pressure roll 30 leaked due to dielectric breakdown at that portion, causing a voltage drop.

Therefore, in this printer, the heating roll 2
As the roll substrate 21 of No. 0, a surface obtained by subjecting the surface to a fine roughening treatment by a blast method and then forming a hard alumite layer 21a on the roughened surface was used.

FIG. 11 shows the peel strength of the conductive surface layer 22 in the form of a tube as described above, when the hard alumite layer is formed, when the soft alumite layer is formed, and when the blast treatment is performed. It is the result of comparing and examining the cases where no treatment was performed. The peel strength at this time is such that when a cut is formed on the surface layer 22 corresponding to three sides of a square with a side of 10 mm and the middle one of the three cuts is gripped and pulled, the cut is made. The tensile load when the surface layer 22 to be peeled off from the roll base material 21 was measured. FIG.
In the case of a bubble generated between the roll base material 21 and the conductive surface layer 22, the case where a hard alumite layer is formed and the case where a soft alumite layer is formed, and the case where a blast treatment is performed are not performed. This is the result of comparing and examining the cases. Regarding the state of bubble generation at this time, it is checked whether or not bubbles are generated in each of the pressure rolls 30 obtained according to each of the above manufacturing conditions, and the number of bubbles generated at that time is one. Times are shown as "Yes", and those with more numbers are shown as "Very Many".

From the results shown in FIGS. 11 and 12, it is understood that when the hard alumite layer is formed and when the blast treatment is performed, good results are obtained in both the peel strength and the bubble generation state. This is advantageous in suppressing the voltage drop of the voltage applied to the pressure roll, which is likely to occur due to the occurrence of bubbles or delamination locally between the roll base material 21 and the conductive surface layer 22.

[0086] The roll base material 21 is first subjected to a fine rough surface treatment such that the surface roughness Ra of the surface of the aluminum roll base material 21 is about 1 µm by a blast method (shot particle size: # 200). After that, anodizing treatment for forming a hard alumite layer (electric bath: sulfuric acid 10-3)
0%, current density 2-12 A / dm ² , bath temperature 0-10 ° C.
(A processing time of 15 to 30 minutes) to form a hard alumite layer 20a having a thickness of about 20 μm.
And the heating roll 20 using this roll base material 21
Can be manufactured by applying a primer on the surface of the roll base material 21 and then coating the above-mentioned tube as the insulating surface layer 22.

Next, the pressure roll 3 in this printer
The resistance value of the conductive surface layer 33 of the pressure roll 30
It was confirmed that this is an important factor from the viewpoint of suppressing the fluctuation of the voltage applied to the substrate. That is, the conductive surface layer 33
Having a resistance value of 8.6 MΩ at a temperature of 0 to 30 ° C. (a PFA tube in which carbon black is dispersed)
Is used, the state of the voltage applied to the pressure roll 30 fluctuates at the time of passing the sheet S as shown in FIG.

Therefore, in this printer, the pressure roll 3
As the 0 conductive surface layer 33, one having a resistance value of 1.6 MΩ at a temperature of 0 to 30 ° C. (a PFA tube in which carbon black is dispersed) was used. Thus, the state of the voltage applied to the pressure roll 30 hardly fluctuates even when the sheet passes through the sheet S as shown in FIG.

Such a variation in the applied voltage is caused by the fact that the temperature state fluctuates (increases) as the pressure roll 30 is heated by the pressure roll 20 in the nip portion N. It is presumed to be caused by a change in the value. Actually, when the temperature dependence of a plurality of conductive surface layers 33 having different resistance values at a temperature of 0 to 30 ° C. was examined, the results shown in FIG. 15 were obtained. From the results shown in FIG.
It can be seen that the resistance value increases as the temperature approaches the fixing temperature (160 to 220 ° C.). In addition, the rise range is 0 to
It can also be seen that the resistance increases at a temperature of 30 ° C. as the resistance increases. As a result of various studies based on this finding, as long as the conductive surface layer 33 has a resistance value of 3 MΩ or less at a temperature of 0 to 30 ° C., the fluctuation of the voltage applied to the pressure roll 30 is suppressed. It was confirmed that. At this time, the resistance value of the conductive surface layer 33 can be set, for example, by adjusting the dispersion state of a conductive agent such as carbon black.

In the printer having the above configuration,
Even in a high humidity environment, the fluctuation of the bias voltage applied to the pressure roll 30 is reduced, and the pressure roll 3
Since the electric field in the direction of attracting the toner image to the recording sheet P is stably formed between 0 and the heating roll 20, the toner offset phenomenon and the scattering phenomenon hardly occur for a long time.

In this printer, the effect of suppressing the toner offset phenomenon and the scattering phenomenon as described above is based on the configuration of the bias power supply 14 described above,
Even when the configuration relating to the static eliminator 9 is used alone, it can be obtained reliably and sufficiently. Similarly, even when the configuration relating to the roll base material 21 of the heating roll 20 and the configuration relating to the conductive surface layer 33 of the pressure roll 30 are individually employed, a reliable and sufficient result can be obtained. .

Other Embodiments In this printer, in order to more effectively suppress the occurrence of the toner offset phenomenon and the scattering phenomenon, the following configurations are appropriately selected and adopted.

[Embodiment Regarding Power Feeding Brush] First, it was confirmed that the arrangement condition of the power feeding brush 13 in this printer is an important factor from the viewpoint of suppressing the fluctuation of the voltage applied to the pressure roll 30. FIG. 16 shows the result of an investigation on the state of toner scattering on the recording sheet P when the arrangement condition of the power supply brush 13 is changed. That is, as shown in FIG. 17, when one power supply brush 13a is arranged on the rear side of the pressure roll 30,
When a single power supply brush 13b is disposed on the front side of the pressure roll 30 in addition to the power supply brushes 13a, when a total of two power supply brushes are disposed, pressure is applied in addition to the two power supply brushes 13a and 13b. When three power supply brushes are arranged in total by arranging one power supply brush 13c closer to the nip portion N than the power supply brush 13a on the rear side of the roll 30, the three power supply brushes 13a,
13b, 13c and a power supply brush 13d near the nip portion N on the rear side and the front side of the pressure roll 30 one by one.
Were arranged and a total of five power supply brushes were arranged, and the number of scattered toner particles was measured. The measurement of the number of toner scattered was performed by printing out a test image and actually counting the number of toner scattered in the image at that time.

As can be seen from the results shown in FIG. 16, when the number of the power supply brushes 13 is one, the toner scatters most, and further, as the power supply brush 13a is located on the roll end side opposite to the side where the power supply brush 13a is disposed (front side). It can be seen that toner scattering increases. Further, scattering of the toner can be further suppressed by arranging the power supply brushes at both ends of the pressure roll 30, by arranging the nip near the nip portion N, or by arranging a plurality of brushes near the nip portion N. I understand.

Therefore, in this printer, the power supply brush 1
3 are arranged at least on both right and left ends of the pressure roll 30 as shown in FIG. In FIG. 3, the symbol W indicates the maximum width of the recording sheet P passing through the nip. Further, from the viewpoint of reliably preventing toner scattering, the power supply brush 13 is desirably disposed near the nip portion N on the sheet entry side.

Further, regarding the power supply brush 13,
As shown in FIG. 18A, it is desirable that at least two or more rolls 30 are arranged in the semi-peripheral surface region E including the nip portion N at both ends of the pressure roll 30 in the circumferential direction of the roll 30. In addition, as shown in FIG. 18B, in addition to disposing the power supply brush 13 on the entry side of the recording sheet P in the semi-peripheral surface area E of the pressure roll 30, the side opposite to the sheet entry side (discharge side) It is desirable to dispose it in the vicinity of the nip portion N).

In particular, when at least two power supply brushes 13 are disposed in the semi-peripheral surface area E of the pressure roll 30 in the circumferential direction of the roll 30, the pressure roll 30 is formed of a tube. Variations in the bias voltage (see FIG. 7) caused by the folds of the conductive surface layer 33 can be suppressed (see FIG. 8).

This is because the conductive surface layer 33 has a tube shape.
Is to cover the insulating elastic layer 32 of the pressure roll 30 via an adhesive, as a means for applying the adhesive to the tube, after immersing the surface layer 33 in the adhesive solution, When a method is used in which the tube-shaped surface layer 33 is crushed into a plate shape and squeezed to remove the excess solution, two folds formed when the tube-shaped surface layer 33 is crushed are used. It is formed at the position facing. Since the resistance value of these two fold portions is higher than that of other portions, the resistance value is caused by the resistance value. For example, the fold portions appear as regular fluctuations of the bias voltage as shown in FIG. In this regard, if at least two or more power supply brushes 13 are arranged in the semi-peripheral surface area E of the pressure roll 30 in the circumferential direction of the roll 30, one power supply brush is provided on the surface layer 33 corresponding to the fold. 13 is always in contact with the surface layer 33 other than the portion where the other power supply brush 13 folds,
The application of the bias voltage can always be performed through the surface layer 33 other than the fold. Thus, even when the pressure roll 30 having the creased surface layer 33 is used, the fluctuation of the bias voltage caused by the crease can be suppressed.

[Other Embodiments Regarding Heating Roll] In the above-described heating roll 20, as shown in FIG. 3, the insulating surface layer (tube of PFA) 22 is extended to the end of the conductive roll base material 21. In addition to coating, the contact angle of water on the surface of the surface layer 22 was set to 100 ° or more. As a result, as shown in the figure, the insulating surface layer 22 having the above-described surface properties also exists in the end region G of the heating roll 20 that protrudes from the end of the pressure roll 30.

When the heating roll 20 is configured as described above, even in a high-humidity environment, the charge induced by the bias voltage applied to the pressure roll 30 is charged by the end of the grounded pressure roll 20. Since the current does not flow out from the portion (particularly, the end region G) along the surface thereof, the fluctuation of the bias voltage due to the flow of the electric charge is eliminated. It is confirmed that when the contact angle of the insulating surface layer 22 in the end region G of the heating roll 20 is less than 90 °, creeping conduction in which electric charges flow through the surface of the end region G occurs. I have.

[Other Embodiments for Pressure Roll] As the conductive surface layer 33 of the pressure roll 30 described above, the above-described foldable surface layer was not used, but the unfolded surface layer 33 was used. . The pressure roll 30 having such a surface layer 33 can be used for covering the tube-shaped surface layer 33 on the insulating elastic layer 32 without using an adhesive. Layer 33
Is obtained by irradiating the inner peripheral surface with laser light. When the pressure roll 30 is used, the bias voltage does not fluctuate due to the fold.

[Embodiment relating to Guide Member on Sheet Discharge Side] As shown in FIG. 19, the conductive guide member 16 on the sheet discharge side in the fixing device is discharged from the nip portion N after fixing among the guide members. An insulating surface layer 40 was formed at a position where the recording sheet P to be contacted was used. In this example, a Teflon material having a thickness of 8 is formed on the surface side of the guide member 16 as the insulating surface layer 40.
It was formed by coating so as to have a thickness of about 0 μm. The resistance of the insulating layer 40 is about 10 ¹¹ Ωcm.

Thus, when the conductive guide member 16 without the insulating surface layer 40 is used, FIG.
As shown in FIG. 1, at time F when the fixed recording sheet P is discharged from the nip portion N and passed through the guide member 16, the voltage applied to the pressure roll fluctuated. When the conductive guide member 16 on which the layer 40 was formed was used, as shown in FIG. 22, the fluctuation of the voltage applied to the pressure roll at the sheet passing time F was suppressed. This effect is achieved by the conductive guide member 16.
Even when the recording sheet P after fixing contacts, the electric charge induced on the pressure roll 30 by the application of the bias voltage is prevented from flowing along the recording sheet P and flowing into the guide member 16 side. It is supposed to be.

As shown in FIG. 20, a conductive guide member 16 having a zener diode 45 as a constant voltage element connected between the guide member 16 and a ground portion was used. This Zener diode 45
Alternatively, a high resistance element may be connected.

Also in this case, similarly to the case of the guide member 16 on which the insulating surface layer 40 is formed, the timing when the fixed recording sheet P is discharged from the nip N and passes through the guide member 16 is used. The fluctuation of the voltage applied to the pressure roll 30 in the above is suppressed. This effect is particularly so that, even if the fixed recording sheet P comes into contact with the conductive guide member 16, the charge induced in the pressure roll 30 is transmitted through the recording sheet P and grounded from the guide member 16, and the Zener diode 45. It is presumed to be obtained by being suppressed by

[Embodiment Regarding Guide Member on Sheet Entry Side] The guide member 15 on the sheet entry side in the above-described fixing device is completely fixed, but instead of this guide member 15, FIG. As shown in FIG. 5, a variable guide 50 is provided as a restricting member for restricting the entry posture when the recording sheet P enters the nip portion N so as to be changeable.

The variable guide 50 is a guide plate that is swingably mounted around a support shaft 51 on the sheet entry side of a nip portion N formed between the heating roll 20 and the pressure roll 30 of the fixing device. Yes, electromagnetic solenoid 52
As a result, it can be displaced to one of the initial position X shown in FIG. 23A and the swing position Y shown in FIG. 23B. The initial position X is a restriction position for restricting the approach posture until the leading end of the fixed recording sheet P enters the nip portion N. The initial position X is set at a position where the sheet can be guided and guided so as to be fed into the nip n after the sheet leading end Pa comes into contact with the heating roll 20 slightly upstream of the nip N. On the other hand, the swing position Y is a regulating position for regulating the approach posture of the sheet portion after the leading end of the recording sheet P enters the nip portion N. In particular, for the swing position Y, the angle α between the sheet P and the tangent L at the center of the nip portion N after the sheet leading end portion Pa has entered the nip portion N is closer to the heating roll 20 side. It is set at a position that can be restricted to an approach posture of 5 ° or more (5 to 8 ° in this example).

Therefore, the variable guide 50 is located at the initial position X until the leading end Pa of the fixed recording sheet P enters the nip N, and when the sheet leading end Pa enters the nip N. Is set so as to be displaced to the swing position Y. The swing timing at this time is set based on, for example, a detection signal from a sheet passage detection sensor or the like disposed on the sheet entry side of the fixing device.

According to the variable guide 50, the variable guide 50 is located at the initial position X as shown in FIG. 23A until the recording sheet P after fixing enters the nip portion N. Thereby, the recording sheet P once abuts against the heating roll 20 slightly before the nip portion N so that the leading end portion Pa is guided by the guide 50 at the initial position X, as shown in FIG. FIG. A), and thereafter, it is fed into the nip N (FIG. B).

When the leading end P of the recording sheet enters the nip N, the variable guide 50 is actuated by the electromagnetic solenoid 52 as shown in FIG.
It is displaced to the closer swing position Y. As a result, the rear end side of the recording sheet P is sent to the nip portion N in a posture approaching the heating roll 20. As a result, the toner image bearing surface side of the recording sheet P is preliminarily heated by heat radiation of the heating roll 20 just before the nip portion N, and the unfixed toner on the recording sheet P is slightly melted and physically It becomes a state of being strongly adhered. As a result, the toner scattering phenomenon is suppressed, and the toner is easily fixed on the recording sheet.

[Other Embodiments] In a printer employing the configuration according to each of the above-described embodiments independently (except in the case where the configuration in which the variable guide 50 is provided alone is employed), the case of the first embodiment is also applicable. Similarly to the above, the fluctuation of the bias voltage applied to the pressure roll 30 is reduced regardless of the high humidity environment, and as a result, the offset phenomenon and the scattering phenomenon of the toner hardly occur for a long time. Further, even in a printer in which only the variable guide 50 is provided, the occurrence of the toner offset phenomenon and the scattering phenomenon can be sufficiently suppressed.

Further, the configuration according to each of the above embodiments can be appropriately combined with each other, or can be appropriately combined with the first embodiment.
In this case, the effect of suppressing the toner offset phenomenon and the scattering phenomenon as described above can be obtained more reliably and sufficiently.

[0113]

As described above, according to any of the first to seventh aspects of the present invention, by applying a voltage having a polarity opposite to the charge polarity of the toner to the pressure roll of the fixing device, the offset phenomenon and the scattering The effect of suppressing the phenomenon can be obtained more reliably and stably even in a high humidity environment. Then, when the image forming apparatus of the invention is used, it is possible to form an image with excellent image quality even in a high humidity environment.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a printer according to a first embodiment.

FIG. 2 is an explanatory diagram illustrating a configuration of a main part of the printer according to the first embodiment.

FIG. 3 is a partial cross-sectional explanatory view showing each configuration related to a fixing device.

FIG. 4 is an enlarged explanatory view of a main part showing respective components relating to a heating roll and a pressure roll.

FIG. 5 is a graph showing a result of measuring a state of fluctuation of a voltage applied to a pressure roll when a conventional resistance voltage dividing circuit is used.

FIG. 6 is a graph showing a result of measuring a fluctuation state of an applied voltage to a pressure roll when the bias voltage device according to the first embodiment is used.

FIG. 7 shows that the resistance element R5 of the bias voltage device is “30M”.
FIG. 7 is a graph showing the results of measuring the state of fluctuation of the voltage applied to the pressure roll when “Ω”.

FIG. 8 shows that the resistance element R5 of the bias voltage device is “10M”.
FIG. 7 is a graph showing the results of measuring the state of fluctuation of the voltage applied to the pressure roll when “Ω”.

FIG. 9 is a graph showing a relationship between a bias voltage applied to a pressure roll, a toner scattering level, and occurrence of transfer bleeding.

FIG. 10 is a graph showing a relationship between a resistance element R6 of the static eliminator and a current flowing into the static eliminator;

FIG. 11 is a graph showing the relationship between the type of alumite layer in the base material of the heating roll, the presence or absence of blast treatment, and the peel strength of the insulating surface layer.

FIG. 12 is a graph showing the relationship between the type of alumite layer in the base material of the heating roll, the presence or absence of blasting, and the generation of bubbles at the interface between the roll base material and the insulating surface layer.

FIG. 13 shows that the conductive surface layer of the pressure roll is “8.6M”.
FIG. 7 is a graph showing the results of measuring the state of fluctuation of the voltage applied to the pressure roll when “Ω”.

FIG. 14 shows that the conductive surface layer of the pressure roll is “1.6M”.
FIG. 7 is a graph showing the results of measuring the state of fluctuation of the voltage applied to the pressure roll when “Ω”.

FIG. 15 is a graph showing the relationship between the resistance of the conductive surface layer of the pressure roll and the temperature.

FIG. 16 is a graph showing a relationship between the arrangement condition of the power supply brush and the number of toner scattered.

FIG. 17 is a perspective view showing an arrangement condition of a power supply brush.

FIG. 18 is an explanatory diagram showing an arrangement condition of a power supply brush.

FIG. 19 is an explanatory view showing one embodiment of a conductive guide member having an insulating surface layer formed thereon.

FIG. 20 is an explanatory diagram showing one embodiment of a conductive guide member to which a constant voltage element is connected.

FIG. 21 is a graph showing a result of measuring a state of fluctuation of a voltage applied to a pressure roll when a conventional conductive guide member is used.

FIG. 22 is a graph showing the results of measuring the state of fluctuation of the voltage applied to the pressure roll when the conductive guide member of FIG. 19 is used.

FIG. 23 shows an embodiment of a variable guide.
(A) is an explanatory view showing a state at an initial position, and (b) is an explanatory view showing a state at a swing position.

FIG. 24 is an explanatory view showing the operation and operation of the variable guide.

FIG. 25 is an explanatory diagram illustrating an overall configuration of a conventional image forming apparatus.

FIG. 26 is an explanatory view of a main part showing another example of a conventional image forming apparatus.

FIG. 27 is an explanatory view of a main part showing another example of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum (image carrier), 5 ... Transfer roll (transfer device), 9 ... Static elimination device, 10 ... Static elimination plate (static elimination member), R6 ... Current control resistance element, 13 ... Power supply brush (power supply member), 14: bias power supply device, R5: output limiting resistance element, TD: zener diode (constant voltage element), 2
0: heating roll, 21: conductive roll substrate, 21a: hard alumite layer, 22: insulating surface layer, 30: pressure roll, 31: conductive roll substrate, 33: conductive surface layer, 4
0: insulating surface layer; 45: constant voltage element (or high resistance element); 50: variable guide (regulating member); P: recording sheet; T: unfixed toner image.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Mitsugu Haga 2274 Hongo, Ebina-shi, Kanagawa Prefecture, within Fuji Xerox Co., Ltd. (72) Inventor Shuichi Suzuki 2274 Hongo, Ebina-shi, Kanagawa Prefecture, within Fuji Xerox Co., Ltd. 72) Inventor Yoshio Shiina 2274 Hongo, Ebina City, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd. (72) Inventor Toshika Tsukiji 2274 Hongo, Ebina City, Kanagawa Prefecture, inside Fuji Xerox Co., Ltd.

Claims (13)

[Claims] An image carrier for carrying an unfixed toner image formed in accordance with image information, a transfer device for transferring the unfixed toner image on the image carrier to a recording sheet, and a transfer by the transfer device After finishing the recording sheet,
The unfixed toner image is recorded on a recording sheet by passing through a nip portion between a heating roll having an insulating surface layer formed on a conductive roll base and a pressure roll having a conductive surface layer formed on the conductive roll base. A fixing device for fixing the toner image on the non-fixed toner image via a power supply member disposed in contact with the conductive surface layer of the fixing device. And a bias power supply for applying the voltage, wherein 1 is provided between an output of the bias power supply and the power supply member.
An output limiting resistance element having a resistance within a range of ~ 15ΜΩ is connected in series, and a constant voltage element is connected between the current limiting resistance element and the power supply member in a grounded state. Characteristic image forming apparatus. 2. The apparatus according to claim 1, wherein the power supply device is provided with at least a voltage having the same polarity as the charged polarity of the unfixed toner image, which is disposed close to the back side of the transferred recording sheet. A static eliminator for neutralizing the recording sheet through the static elimination terminal provided, and a current limiting resistor having a resistance value in a range of 5 to 100 Ω between the output of the power supply device and the static elimination terminal in the static eliminator. An image forming apparatus, wherein the elements are connected in series. 3. An image carrier for carrying an unfixed toner image formed according to image information, a transfer device for transferring the unfixed toner image on the image carrier to a recording sheet, and a transfer by the transfer device After finishing the recording sheet,
The unfixed toner image is recorded on a recording sheet by passing through a nip portion between a heating roll having an insulating surface layer formed on a conductive roll base and a pressure roll having a conductive surface layer formed on the conductive roll base. A fixing device for fixing the toner image onto the toner image, and a bias voltage having a polarity opposite to the charging polarity of the unfixed toner image is applied to a pressure roller of the fixing device via a power supply member disposed in contact with the conductive surface layer. An image forming apparatus comprising: a bias power supply device for applying a voltage; and a conductive roll base material of a heating roll in the fixing device is an aluminum roll base material having a hard alumite layer formed on a surface thereof. 4. The apparatus according to claim 3, wherein the aluminum roll substrate has been subjected to a fine roughening treatment on the surface of the roll substrate prior to the formation of the hard alumite layer. An image forming apparatus comprising: 5. The device according to claim 3, wherein
The insulating surface layer of the heating roll is coated up to the end of the conductive roll base material and has a contact angle with water of 10
An image forming apparatus having surface properties of 0 ° or more. 6. An image carrier for carrying an unfixed toner image formed according to image information, a transfer device for transferring the unfixed toner image on the image carrier to a recording sheet, and a transfer by the transfer device After finishing the recording sheet,
The unfixed toner image is recorded on a recording sheet by passing through a nip portion between a heating roll having an insulating surface layer formed on a conductive roll base and a pressure roll having a conductive surface layer formed on the conductive roll base. A fixing device for fixing the toner image onto the toner image, and a bias voltage having a polarity opposite to the charging polarity of the unfixed toner image is applied to a pressure roller of the fixing device via a power supply member disposed in contact with the conductive surface layer. A bias power supply device for applying a voltage, wherein the conductive surface layer of the pressure roll in the fixing device is a layer in which a conductive agent is dispersed in a fluorine-based resin or a silicone-based resin, at a temperature of 0 to 30 ° C. Resistance value is 3Μ
An image forming apparatus characterized in that the resistance is Ω or less. 7. An image carrier for carrying an unfixed toner image formed in accordance with image information, a transfer device for transferring the unfixed toner image on the image carrier to a recording sheet, and transfer by the transfer device After finishing the recording sheet,
The unfixed toner image is recorded on a recording sheet by passing through a nip portion between a heating roll having an insulating surface layer formed on a conductive roll base and a pressure roll having a conductive surface layer formed on the conductive roll base. A fixing device for fixing the toner image onto the toner image, and a bias voltage having a polarity opposite to the charging polarity of the unfixed toner image is applied to a pressure roller of the fixing device via a power supply member disposed in contact with the conductive surface layer. A bias power supply device for applying the voltage, wherein the power supply member is provided at both ends of the pressure roll,
An image forming apparatus, wherein at least one is provided. 8. The image forming apparatus according to claim 7, wherein a power supply member is provided at least near a nip portion at both ends of the pressure roll. 9. The apparatus according to claim 7, wherein at least two power supply members are disposed in a semi-peripheral surface area including a nip portion at both ends of the pressure roll, and are arranged back and forth in the circumferential direction of the roll. An image forming apparatus comprising: 10. An image carrier for carrying an unfixed toner image formed in accordance with image information, a transfer device for transferring the unfixed toner image on the image carrier to a recording sheet, and a transfer by the transfer device After finishing the recording sheet,
The unfixed toner image is recorded on a recording sheet by passing through a nip portion between a heating roll having an insulating surface layer formed on a conductive roll base and a pressure roll having a conductive surface layer formed on the conductive roll base. A fixing device for fixing the toner image onto the toner image, and a bias voltage having a polarity opposite to the charging polarity of the unfixed toner image is applied to a pressure roller of the fixing device via a power supply member disposed in contact with the conductive surface layer. And a conductive guide member for guiding the recording sheet discharged from the nip portion in the fixing device.
An image forming apparatus, wherein an insulating surface layer is formed on at least a sheet contact portion of the conductive guide member that can contact a recording sheet. 11. A constant-voltage element or a high-resistance element is connected between the conductive guide member and the ground part, instead of forming an insulating surface layer on the conductive guide member according to claim 10. An image forming apparatus comprising: 12. An image carrier for carrying an unfixed toner image formed in accordance with image information, a transfer device for transferring the unfixed toner image on the image carrier to a recording sheet, and transfer by the transfer device After finishing the recording sheet,
The unfixed toner image is recorded on a recording sheet by passing through a nip portion between a heating roll having an insulating surface layer formed on a conductive roll base and a pressure roll having a conductive surface layer formed on the conductive roll base. A fixing device for fixing the toner image onto the toner image, and a bias voltage having a polarity opposite to the charging polarity of the unfixed toner image is applied to a pressure roller of the fixing device via a power supply member disposed in contact with the conductive surface layer. A bias power supply device for applying a voltage, and a regulating member that regulates a changeable entry posture of the recording sheet when entering the nip portion on the sheet entry side of the fixing device. The angle between the sheet and the tangent to the center of the nip after the recording sheet has entered the nip is 5 ° toward the heating roll.
An image forming apparatus, wherein the image forming apparatus is restricted to the approach posture described above. 13. The fixing device according to claim 1, wherein the conductive roll base material of the heating roll in the fixing device is an aluminum roll base material having a hard alumite layer formed on a surface thereof. The conductive surface layer of the pressure roll is a layer in which a conductive agent is dispersed in a silicon-based resin or a fluorine-based resin, and has a resistance of 3 at a temperature of 0 to 30 ° C.
An image forming apparatus characterized by having a resistance of ΜΩ or less.