JP4128258B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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, or a complex machine using an electrophotographic process, and more particularly, a toner generated in a roll type fixing device that fixes an unfixed toner image on a recording sheet. The present invention relates to an improvement of an image forming apparatus that can surely suppress the offset phenomenon and the scattering phenomenon.
[0002]
[Prior art]
Conventionally, an image forming apparatus using an electrophotographic process is well known. As shown in FIG. 25, this type of image forming apparatus basically includes a charging device (for example, a charging roll) 101 and an image exposure device for the periphery of an image carrier 100 formed of a drum-like or belt-like photoconductor. (For example, a laser beam writing device) 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 disposed.
[0003]
When forming the image, first, the image carrier 100 is charged by the charging device 101, and the charged image carrier 100 is exposed to an optical image corresponding to the image information from the image exposure device 102, thereby electrostatic latent image. After the image is formed, the electrostatic latent image is developed with a developer (finally toner) supplied from the developing device 103 to form a toner image T. Next, after the unfixed toner image T formed on the image carrier 100 is transferred to a recording sheet P such as transfer paper supplied and conveyed between the image carrier 100 and the transfer device 104 (transfer unit). The recording sheet P is sent to a fixing device 105 disposed on the downstream side of the image carrier 100 to fix the transferred unfixed toner image T on the recording sheet P, thereby forming an image. It has become. Reference numeral 107 in the figure denotes a charge removal terminal of a charge removal apparatus for removing the charge from the image carrier 100 by removing charge from the recording sheet P after transfer.
[0004]
By the way, in this type of image forming apparatus, the fixing device 105 is generally arranged so as to rotate in a state in which a heating roll 110 having a heating source 115 and a pressure roll 120 are in pressure contact with each other as shown in FIG. In many cases, a roll type fixing device is used in which a recording sheet P carrying an unfixed toner image T is fed into and passed through a nip portion N formed by both rolls 110 and 120.
[0005]
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 adhered to the heating roll 110 at the time of fixing, or at the nip portion N. When the recording sheet P enters, the arrangement of the toner on the recording sheet P is disturbed and the toner is scattered, so-called scattering phenomenon occurs.
[0006]
This toner offset phenomenon and splatter phenomenon are not particularly sufficient when the toner holding charge amount is not sufficient, such as immediately after the image forming apparatus main body is turned on or immediately after the developing apparatus 103 is replenished with toner. When the adhesive force to the recording sheet P is weak, or when the recording sheet P is in a state where the moisture content is high due to moisture absorption or the like, and the holding power of the recording sheet P with respect to the toner is weak, or when both of these states overlap It tends to occur easily. As for the toner scattering phenomenon, particularly when the recording sheet is in a water-containing state, the moisture in the sheet evaporates when heated by a heating roll, and an air current is generated. It has been confirmed that this occurs when the arrangement of unfixed toner on the sheet P is disturbed. In addition, such toner scattering tends to occur particularly in a thin line extending in a direction (axial direction of the roll) perpendicular to the traveling direction of the recording sheet.
[0007]
Therefore, conventionally, as a countermeasure for preventing such toner offset phenomenon and scattering phenomenon, for example, as shown in FIG. 26, a bias having a polarity opposite to the charged polarity of the toner is applied to the pressure roll 120 of the fixing device. A method of applying a voltage has been proposed (Japanese Patent Laid-Open No. 5-224546).
[0008]
That is, in the fixing device according to this proposal, as shown in the figure, the voltage divided by the resistors R1 and R2 from the power supply 130 of the transfer device 104 (or charging device) is applied to the core metal 120a of the pressure roll 120. It is made to apply. As the heating roll 120 in this fixing device, a cored bar 120a is coated with a conductive elastic layer 120b and an insulating surface layer 120c in this order.
[0009]
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 attracted to the recording sheet P side. Since an electric field in the direction is generated, it is difficult for the toner to transfer to the heating roll 110, thereby suppressing the toner offset phenomenon. Further, the application of a voltage having a polarity opposite to the charging polarity of the toner to the pressure roll 120 in this way is effective not only in preventing the toner offset phenomenon but also preventing the toner scattering phenomenon as described above. It has been confirmed that the above can be effective.
[0010]
For this reason, the present inventors also prototyped an image forming apparatus having a configuration as shown in FIG. 27 and tested it for the effect of preventing the toner offset phenomenon and the scattering phenomenon.
[0011]
The prototype image forming apparatus is a voltage obtained by dividing the bias power supply 140 by resistors R1 and R2, as shown in FIG. ) Is applied to the pressure roll 120 via one power supply member 141 made of a power supply brush or the like disposed so as to be in contact with the surface of one end portion of the pressure roll 120.
[0012]
In this image forming apparatus, the heating roll 110 is a core metal 110a made of aluminum and coated with an insulating surface layer 110b. The pressure roll 120 is an insulating material on the core metal 120a. A material in which an elastic layer 120d and a conductive surface layer 120e are coated is used. Among these, for the insulating surface layer 110b and the conductive surface layer 120e, a conductive tube form made only of a synthetic resin or a conductive tube form in which a conductive agent (carbon black or the like) is dispersed in the synthetic resin, We used what we did. Further, in this image forming apparatus, a voltage for discharging the recording sheet P after transfer from the power source 150 to a predetermined level is applied to the discharging terminal 106 via the resistor R3.
[0013]
[Problems to be solved by the invention]
However, when a test was performed using the prototype image forming apparatus as described above, the following problems may be encountered despite the fact that the bias voltage is divided and applied to the pressure roll in the fixing device. found.
[0014]
That is, particularly in a high humidity environment, when the recording sheet P enters and passes through the nip portion N of the fixing device 105, the voltage applied from the bias power source 140 to the pressure roll 120 varies greatly. (See FIG. 5). Due to this voltage fluctuation, the electric field in the direction in which the unfixed toner image as described above is attracted to the recording sheet P side is not stably formed between the pressure roll 120 and the heating roll 110. It has been found that the effect of preventing the offset phenomenon and the scattering phenomenon cannot be obtained sufficiently and stably.
[0015]
Such a variation in voltage is likely to cause the charge induced by the bias voltage applied to the pressure roll 120 to flow out through the surface of the recording sheet P, the surface of the heating roll 110, or the like in a high humidity environment. It is speculated that this is the main factor.
[0016]
Further, 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 the toner scattering on the recording sheet, but when the bias voltage is increased, Whereas the current load becomes large, the resistance voltage dividing circuit as described above has a substantially low load resistance, so that the outflow of charges as described above becomes significant, and as a result, the voltage is more likely to fluctuate. There was found. In addition, in this case, if there is a static eliminator that neutralizes the transferred recording sheet P as in the above-described image forming apparatus example, the recording sheet P is connected to the static eliminator (the neutralization terminal 107) and the nip portion of the fixing device 105. It has also been found that, when a state that extends over the sheet occurs, the charge of the pressure roll 120 may flow through the recording sheet P and flow from the charge removal terminal 106 to the charge removal apparatus.
[0017]
Further, if such a bias voltage is continuously applied to the pressure roll 120 for a long time, bubbles are locally generated on the surface of the heating roll 110 (insulating surface layer 110b) in contact with the pressure roll 120. It was confirmed that a dielectric breakdown occurred, and the bias voltage leaked at that portion, resulting in a voltage drop. Such a voltage drop also occurs when pinholes are present in the insulating surface layer.
[0018]
Further, the pressure roll 120 itself is heated by a nip portion with the heating roll 120 at the time of fixing, and the temperature state thereof changes, or a power supply member 141 that applies a bias voltage in contact with the pressure roll 120. It was confirmed that the bias voltage was not evenly and sufficiently applied to the pressure roll 120 (particularly in the vicinity of the nip portion) due to the difference in the arrangement position and the like.
[0019]
In addition, if a conductive guide member that guides and discharges the recording sheet P after fixing is provided on the sheet discharge side of the fixing device 105, the rear end of the sheet is a nip part of the guide member. It was confirmed that the bias voltage fluctuated by touching the recording sheet P after fixing in the section. Further, it was also confirmed that there is a difference in the effect of suppressing the toner offset phenomenon and the scattering phenomenon depending on the approaching angle (angle) of the recording sheet P to the nip portion of the fixing device 105.
[0020]
The present invention has been made paying attention to the above-described actual situation, and the object of the present invention is to apply a voltage having a polarity opposite to the charging polarity of the toner to the pressure roll of the fixing device, thereby causing the toner offset phenomenon and the scattering phenomenon. It is an object of the present invention to provide an image forming apparatus that can more reliably and stably obtain the effect of suppressing the above-described problem even in a high humidity environment.
[0021]
[Means for Solving the Problems]
The image forming apparatus according to the first invention (the invention according to claim 1) capable of achieving the above object includes an image carrier that carries an unfixed toner image formed according to image information, and the image carrier. A transfer device for transferring the upper unfixed toner image onto a recording sheet, and a heating roll and a conductive roll in which an insulating surface layer is formed on a conductive roll base material. A fixing device for fixing the unfixed toner image on a recording sheet by passing through a nip portion with a pressure roll having a conductive surface layer formed on a base material; A bias power supply device 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 surface layer; The recording sheet is neutralized through a neutralizing terminal which is disposed close to the back side of the recording sheet after transfer and to which at least a voltage having the same polarity as the charging polarity of the unfixed toner image is applied from the power supply device. With a static eliminator An output limiting resistance element having a resistance value in the range of 1 to 15Ω is connected in series between the output of the bias power supply device and the power supply member, and between the current limiting resistance element and the power supply member. Connected to the constant voltage element in a grounded state. In addition, a current limiting resistor element having a resistance value in the range of 5 to 100 Ω is connected in series between the output of the power supply device and the charge removal terminal in the charge removal device. It is characterized by this.
[0022]
The image carrier is usually a photoreceptor on which a toner image is directly formed by an electrophotographic process. The toner image formed on the photoreceptor is temporarily held and then re-transferred to a recording sheet. A so-called intermediate transfer member may be used. The transfer device may be a corona discharger in addition to a roll. 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 shape. The layer thickness of the insulating surface layer is preferably in the range of 10 to 60 μm. The layer 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 that in the form of a brush.
[0023]
As the output limiting resistance element, any element may be used as long as the resistance element has a resistance value within the specific range described above. The resistance value of this resistance element is more preferably in the range of 5 to 15Ω. 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.
[0024]
As the current limiting resistance element, any resistance element having a resistance value within the specific range described above may be used. The resistance value of this resistance element is more preferably in the range of 5 to 50Ω. In addition, the static elimination terminal is an electrode plate or a discharge wire when the static elimination device is a corona discharger. .
[0025]
According to the first invention as described above, a stable bias voltage can always be applied from the bias power supply device to the pressure roll even if the factor of the outflow of charges increases in a high humidity environment or the like. Can do. Moreover, since the resistance value of the output limiting resistance element is set to 1 MΩ or more, the occurrence of a leak with the heating roll can be reliably suppressed. In addition, since the resistance value is 15 Ω or less, it is possible to reliably suppress a voltage drop when the water-containing recording sheet passes through the fixing device. Accordingly, an electric field in a direction in which the unfixed toner image is attracted toward the recording sheet is stably formed between the pressure roll and the heating roll. .
[0026]
Even when the recording sheet P is in a state where the recording sheet P extends over the discharging terminal of the discharging device and the nip portion of the fixing device, the charge induced by the bias voltage applied to the pressure roll is transmitted to the recording sheet and the discharging is performed. Inflow from the terminal to the static eliminator can be suppressed, and voltage drop due to such charge inflow is eliminated. .
[0027]
Moreover In addition, since the resistance value of the current limiting resistance element is 5 MΩ or more, it is possible to reliably suppress the inflow of the charge transmitted from the pressure roll through the recording sheet into the static eliminator. In addition, since the resistance value is set to 100 ΩΩ or less, the voltage for discharging can be instantaneously sent from the power supply device of the static eliminator to the static eliminator terminal during the transfer operation. As a result, a delay in rising of the static eliminator during the transfer operation does not occur.
[0028]
A second invention capable of achieving the above object (claim) 2 The image forming apparatus according to the invention) An image carrier that carries an unfixed toner image formed in accordance with image information, a transfer device that transfers the unfixed toner image on the image carrier to a recording sheet, and after the transfer by the transfer device is completed The recording sheet is passed through a nip portion between a heating roll in which an insulating surface layer is formed on a conductive roll base and a pressure roll in which a conductive surface layer is formed on the conductive roll base. A fixing device for fixing an image on a recording sheet, and a charging roller having a reverse polarity 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 of the fixing device And a bias power supply device that applies a bias voltage (hereinafter referred to as “common element”). 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 the surface thereof.
[0029]
The hard anodized layer is an anodized film formed by performing an anodizing treatment included in a hard class when the aluminum is classified as hard or soft in the anodizing treatment of aluminum. The hard alumite layer is desirably formed so that the layer thickness is in the range of 10 to 30 μm. Moreover, in order to form such a hard alumite layer, the temperature of the electric field bath in the anodizing treatment is 0 to 20 ° C., and the current density is 2 to 12 A / dm. ² The processing time may be appropriately set within a range of 5 to 30 minutes.
[0030]
According to such 2nd invention, compared with the heating roll which consists of a roll base material in which the soft alumite layer was formed, an insulating surface layer is provided with favorable adhesive strength on the roll base material in which the hard alumite layer was formed. In addition, it is possible to suppress the generation of bubbles between the surface layer and the roll base material. As a result, dielectric breakdown and pins in the heating roll Ho Can be reliably prevented.
[0031]
In the image forming apparatus according to the second aspect of the invention, it is desirable that the aluminum roll base material is obtained by subjecting the surface of the roll base material to a fine rough surface treatment prior to the formation of the hard alumite layer. .
[0032]
The above-described fine rough surface treatment refers to a treatment with a surface roughness Ra of about 1 μm. Such rough surface treatment can be usually performed by blasting, but may be performed by other methods.
[0033]
In this case, the adhesive strength of the insulating surface layer to the roll base material can be further improved as compared with a heating roll in which a hard anodized layer is simply formed without performing the roughening treatment, and the surface layer And the generation of bubbles between the roll base materials can be more reliably suppressed. In addition, the surface of the hard anodized layer becomes rough due to the effect of the rough surface treatment, and fine voids exist between the surface layer, so even if bubbles are generated between the surface layer and the roll base material. , It is released through the gap and does not remain between the surface layer and the roll base material.
[0034]
Furthermore, the image forming apparatus according to the second aspect of the present invention has a surface physical property in which the insulating surface layer of the heating roll is covered to the end of the conductive roll base material, and the contact angle with respect to water is 100 ° or more. It is desirable that
[0035]
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 the both ends of the heating roll protrude from the both ends of the pressure roll.
[0036]
In this case, even if moisture that evaporates from the recording sheet at the time of fixing may adhere to the surfaces of both ends of the heating roll, the surface has a hydrophobic contact angle of 100 ° or more. Although the water becomes fine independent water droplets, it does not form a continuous water film. For this reason, the bias voltage applied to the pressure roll does not discharge along the surfaces of both ends of the heating roll.
[0037]
A third invention capable of achieving the above object (claim) 5 The image forming apparatus according to the present invention 2 In addition to the common elements as the premise of the invention, 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 resin or a silicone resin, and a temperature of 0 to 30 ° C. The lower resistance value is 3ΜΩ or less.
[0038]
As the fluororesin, PFA (perfluoroalkoxyethylene copolymer resin), FEP (tetrafluoroethylene / hexafluoropropylene copolymer resin, etc.) are used, and silicone rubber is used as the silicone resin. Examples of the conductive agent include carbon black, polyacetylene, poly-p-phenylene, polythiazole, etc. The conductive surface layer is most preferably one in which carbon black is dispersed in PFA. The resistance value of the conductive surface layer at the above temperature can be adjusted to 3 Ω or less by adjusting the dispersion state of the conductive agent, but is not limited thereto.
[0039]
According to such a third invention, even when the surface of the pressure roll is heated by the heat of the heating roll at the nip portion, the temperature rises. Pressure Since the resistance value of the conductive surface layer of the roll does not fluctuate (increase) greatly (contains a change amount of at least 50 times), the bias voltage can be more stably applied to the entire pressure roll. it can.
[0040]
The fourth embodiment that can achieve the above-mentioned object Mysterious The image forming apparatus 2 In addition to the common elements as the premise of the invention, one or more of the power supply members are disposed at both ends of the pressure roll.
[0041]
According to such 4th invention, a bias voltage can be reliably applied over the axial direction of a pressurization roll.
[0042]
In the image forming apparatus according to the fourth aspect of the invention, it is desirable that the power supply member is disposed at least near the nip portion at both ends of the pressure roll. The vicinity of the nip portion is desirably the vicinity of the nip portion on the sheet entry side, and further within the peripheral surface region that is within 90 ° with respect to the circumferential direction of the pressure roll with the nip portion as the center. It is desirable that
[0043]
In this case, the bias voltage is surely applied in the vicinity of the nip portion of the pressure roll. Thereby, an electric field due to the bias voltage is favorably formed between the pressure roll and the heating roll in the vicinity of the nip portion, and in particular, the effect of suppressing the toner scattering phenomenon can be surely obtained.
[0044]
Further, in the image forming apparatus of the fourth invention, at least two or more power supply members are disposed in the circumferential direction of the roll in the circumferential direction including the nip portions at both ends of the pressure roll. It is desirable.
[0045]
In this case, the bias voltage is more reliably applied to the vicinity of the nip portion of the pressure roll. As a result, an electric field due to the bias voltage is more satisfactorily formed between the pressure roll and the heating roll in the vicinity of the nip portion, and the effect of suppressing the offset phenomenon as well as the effect of suppressing the toner scattering phenomenon can be reliably obtained.
[0046]
A fifth embodiment capable of achieving the above object Mysterious The image forming apparatus 2 In addition to the common elements as the premise of the invention, a conductive guide member for guiding the recording sheet discharged from the nip portion in the fixing device is provided, and at least the conductive guide member can be in contact with the recording sheet. An insulating surface layer is formed at the sheet contact portion. As an insulating surface layer, 10 ⁹ It is preferable to form a layer having a resistance value of Ωcm or more.
[0047]
According to the fifth aspect of the invention, even if the recording sheet in the process of being discharged from the nip portion contacts the conductive guide member, the charge induced in the pressure roll by the application of the bias voltage is transmitted through the recording sheet and guided. It will flow into the member side. As a result, voltage fluctuation due to the inflow of electric charge to the guide member is eliminated.
[0048]
A sixth embodiment capable of achieving the above-mentioned object Mysterious In the image forming apparatus, instead of forming the insulating surface layer on the conductive guide member in the fifth invention, a constant voltage element or a high resistance element is connected between the conductive guide member and the grounding portion. It is characterized by. 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.
[0049]
According to the sixth aspect of the invention, even if the recording sheet in the process of being discharged from the nip portion contacts the conductive guide member, the charge induced in the pressure roll by the application of the bias voltage is transmitted through the recording sheet and guided. Inflow to the member side and grounding are suppressed. As a result, voltage fluctuation due to the inflow of electric charge to the guide member is eliminated.
[0050]
A seventh embodiment capable of achieving the above object Mysterious The image forming apparatus 2 In addition to the common elements as the premise of the invention, on the sheet entry side in the fixing device, there is provided a regulating member that regulates the entry posture when the recording sheet enters the nip portion so as to be changeable. The recording sheet after the leading edge of the sheet has entered the nip portion is restricted to an approach posture in which an angle between the sheet and the tangent of the center of the nip portion is 5 ° or more on the heating roll side.
[0051]
The restricting member can be configured by displacing the sheet guide member disposed on the sheet entry side. In addition, a movable member that can be displaced is provided separately from the sheet guide member. The guide member and the movable member may be used in combination.
[0052]
According to the seventh aspect of the invention, the recording sheet enters the nip portion with the posture (approach angle) approaching the heating roll side by the regulating member, so the toner image carrying surface side of the recording sheet is in front of the nip portion. Then, it is preliminarily heated by heat radiation of the heating roll. As a result, the unfixed toner on the recording sheet is slightly melted and physically strongly adhered to the recording sheet, so that the toner scattering phenomenon is suppressed and the toner is easily fixed on the recording sheet. Become.
[0053]
An eighth invention that can achieve the above object (claim) 6 The image forming apparatus according to the present invention 2 In the image forming apparatus of the invention, In the third invention It is featured in Structure This is a combination of components. I.e. 2 In the image forming apparatus of the invention, the conductive surface layer of the heating roll is an aluminum roll base material having a hard anodized layer formed on the surface, and the conductive surface layer of the pressure roll is a silicon-based resin or a fluorine-based resin. The conductive material is dispersed in a layer having a resistance value of 3 to Ω or less at a temperature of 0 to 30 ° C.
[0054]
According to the eighth aspect, the functions and effects of the first, second and third aspects can be obtained simultaneously and synergistically. As a result, the toner offset phenomenon And the scattering phenomenon can be more reliably and stably suppressed.
[0055]
In addition, in order to achieve the above-mentioned object, it is possible to realize more reliably by combining at least two or more of the first to seventh inventions as appropriate.
[0056]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0057]
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.
[0058]
[Configuration of the entire device]
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. The photosensitive drum 1 is supported so as to rotate in the direction of the arrow in the figure, and after being uniformly charged by a charging roll 2 disposed so as to rotate in contact with the drum surface circle, The charged drum surface is exposed and scanned with a laser beam LB corresponding to image information output from the laser exposure device 3, whereby the charge is lost and an electrostatic latent image is 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).
[0059]
A developing device 4 that accommodates a one-component or two-component developer (toner) for developing the electrostatic latent image is disposed downstream of the exposure position of the photosensitive drum 1. The developing device 4 is provided with a developing roll 4a that rotates in the vicinity of the photosensitive drum 1, a toner supply member (not shown) that supplies toner to the developing roll 4a, and the like. The previous electrostatic latent image is developed into a toner image T by toner supplied from the developing roll 4a of the developing device 4 at a position facing the developing device 4. A developing bias obtained by superimposing a negative DC bias voltage on an AC voltage is applied to the developing roll 4a from a developing power supply device (not shown), and a negatively chargeable toner is used. Therefore, in the developing device 4, development is performed by so-called reversal development in which toner is attached to an exposed area (latent image) of the photosensitive drum 1.
[0060]
Further, on the downstream side of the developing device 4 of the photosensitive drum 1, a transfer roll 5 is disposed as a transfer device that transfers the toner image on the photosensitive drum 1 to the recording sheet P. 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.
[0061]
The recording sheets P are fed out one by one from a sheet feeding unit such as a cassette or a tray (not shown) via a sheet feeding roll 6 or a sheet conveying path, and are sent out in synchronism with the photosensitive drum 1 by a registration roll 7 to obtain a desired sheet. The sheet is supplied so as to pass between the photosensitive drum 1 and the transfer roll 5 at the sheet feeding timing. A one-dot chain line in FIG. 1 is a recording sheet conveyance path. Then, at the time of passing, the above-described transfer bias 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.
[0062]
The photosensitive drum 1 after the transfer of the toner image is not transferred to the recording sheet P side, but there is residual toner, but the toner is positioned downstream of the transfer roll 5 of the photosensitive drum 1. It is removed and cleaned by the cleaning device 8 arranged in the above. Further, the photosensitive drum 1 after the cleaning by the cleaning device 8 is uniformly charged again by the charging roll 2 and proceeds to the next image forming cycle.
[0063]
On the other hand, at a position downstream of the transfer roll 5, a static eliminating device 9 that neutralizes the transferred recording sheet P from its back side (surface opposite to the toner image carrying surface) is disposed. The static eliminator 9 is disposed so as to be close to the back side of the sheet at the point where the recording sheet P of the photosensitive drum 1 is peeled off, and the leading end adjacent to the sheet is formed in a sawtooth shape. The neutralization plate 10 as a neutralization terminal and the neutralization power supply device 11 that applies a bias voltage of the same polarity (minus in this example) as the charging polarity of the unfixed toner image T from the power supply device 11 to the neutralization plate 10. It is configured. Therefore, after the transfer, the recording sheet P is discharged from the surface of the photosensitive drum 1 after being discharged by the discharging plate 10 of the discharging device.
[0064]
On the downstream side of the sheet conveying direction from the transfer position of the photosensitive drum 1, a roll type fixing device 12 including a heating roll 20 and a pressure roll 30 that are rotated in pressure contact with each other is disposed.
[0065]
Among these, as shown in FIG. 2, the heating roll 20 has a structure in which a conductive roll base 21 is coated with an insulating surface layer 22, and is disposed inside the roll base 21. It is heated to a predetermined temperature (about 160 to 220 ° C.) by a heating source 23 such as a lamp. Although what consists of aluminum, iron, copper, etc. can be used as the roll base material 21, what consists of aluminum was used in this example. As the insulating surface layer 22, a tube shape (thickness of about 30 μm) in which carbon black is dispersed in PFA was used. The heating roll 20 has its roll base 21 grounded.
[0066]
On the other hand, as shown in FIG. 2, the pressure roll 30 is formed by covering a conductive roll base 31 with an insulating elastic layer 32 and a conductive surface layer 33 in this order. A nip portion N having a predetermined width is formed with the heating roll 20 by being pressed by a biasing means (not shown) with a predetermined pressure. As the roll base material 31, one made of aluminum, iron, copper or the like can be used, but in this example, one made of aluminum was used. As the insulating elastic layer 32, a layer made of silicone sponge was used. As the conductive surface layer 33, a PFA in the form of a tube (thickness of about 20 μm) was used. In addition, the pressure roller 30 is provided with a power supply brush 13 as a power supply member that comes into contact with the end of the pressure roll 30. The power supply brush 13 has a polarity opposite to the charging polarity of the toner image T from the bias power supply device 14 ( In this example, a positive bias voltage is applied. The bias power supply device 14 may be a dedicated device different from the power supply device 11 of the static eliminator 9 as illustrated in FIG. 1 or FIG. Circuit).
[0067]
Further, on the sheet entry side of the fixing device 12, an entry guide member 15 that guides the transferred recording sheet P so as to surely enter the nip portion N is disposed. On the other hand, on the sheet discharge side, a discharge guide member 16 for guiding the transferred recording sheet P to be reliably discharged from the nip portion N is disposed.
[0068]
In the fixing device 12, the recording sheet P after the transfer is guided by the guide member 15 for entering and enters the nip portion N by the heating roll 20 and the pressure roll 30, and then is nipped and conveyed by the both rolls 20 and 30. The 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 being heated and pressed.
[0069]
Further, in the fixing device 12, a bias voltage having a polarity (plus) opposite to the charging polarity of the toner image is applied from the fixing power supply device 14 to the pressure roll 30 via the power supply brush 13. In the nip portion N of the pressure roll 30 and the front and back regions thereof, positive charge is stored on the conductive surface layer 33 side of the pressure roll 30, while negative polarity is stored on the roll base 21 side of the heating roll 20. A charge is induced. As a result, an electric field is formed in the 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 attracted to the recording sheet P side. The occurrence of the phenomenon is suppressed, and the occurrence of the toner scattering phenomenon on the recording sheet P is suppressed.
[0070]
The recording sheet P on which the toner image has been fixed in this manner is guided by the discharge guide member 16 and discharged to a discharge tray or the like through a discharge port (not shown).
[0071]
[Configuration of main parts]
By the way, this printer employs a configuration as described in detail below in order to more effectively suppress the occurrence of the toner offset phenomenon and the scattering phenomenon.
[0072]
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 toner passes through the nip portion N, the bias voltage applied to the pressure roll 30 varies greatly. The data shown in FIG. H. , Measured based on the current flowing through the power supply brush 13 in contact with the heating roll 30. Also, + 340V is applied as the bias voltage.
[0073]
Therefore, in this printer, as shown in FIG. 2, in the bias power supply 14 that applies a bias voltage to the pressure roll 30 of the fixing device 12, the output is limited between the output side of the power supply 14 and the power supply brush 13. A resistance element R5 is connected, and a Zener diode TD as a constant voltage element is connected between the resistance element R5 and the power supply brush 13. As a result, it was confirmed that the bias voltage applied to the pressure roll 30 from the power supply device 14 is extremely stable without being influenced by the passage of the recording sheet P as shown in FIG. .
[0074]
Even when the output side of the bias power supply 14 is configured by connecting the resistor element R5 and the Zener diode TD as described above, the voltage applied to the pressure roll 30 depends on the resistance value of the resistor element R5. Was confirmed to fluctuate slightly. FIG. 7 shows the state of applied voltage when a resistance of 30 MΩ is used as the resistance element R5. From the result of FIG. 7, it can be seen that the voltage slightly fluctuates when the recording sheet P passes through. Note that the applied voltage fluctuates regularly even in the sheet non-passing time (between the passing time S and the next passing time S) when the recording sheet P does not pass, but this will be described later. This occurs due to a difference in resistance value caused by a crease in the surface layer 32 of the pressure roll 30.
[0075]
Therefore, a resistance of 10 MΩ is used as the resistance element R5. As a result, it was confirmed that the bias voltage applied from the power supply device 14 to the pressure roll 30 is extremely stable without being influenced by the passage of the recording sheet P as shown in FIG. Further, as a result of various studies, it has been found that a satisfactory result can be obtained when the resistance element R5 has a resistance value in the range of at least 1 to 15Ω. In the data shown in FIG. 8, the record fluctuation at the time of non-passage of the sheet appearing in FIG. 7 does not appear, but this is solved by improving the arrangement of the power supply brush 13 as will be described later. It is.
[0076]
Next, using the bias power supply device 14 in which the resistor element R5 (10 MΩ) and the Zener diode TD are connected, the effect of suppressing the bias voltage to be applied to the pressure roll 30 and the toner scattering phenomenon was confirmed. As shown in the graph, it was confirmed that the higher the bias voltage, the better the toner scattering suppression effect. On the other hand, however, it was confirmed that when the bias voltage is higher than 400 V, the toner image transferred onto the recording sheet P is blurred.
[0077]
Therefore, in this printer, the bias voltage applied to the pressure roll 30 is set to 340V. The toner splatter level in FIG. 9 is determined after the sample image is printed out, and the degree of toner splattering in the obtained image is checked. The result is that no toner splattering occurs. When the case is grade 0, and the case where the most severe scattering occurs is the highest grade 6, the level is evaluated by classifying into 6 stages (grades 0 to 5) within this range.
[0078]
Further, in this printer, there is a static eliminating device 9 that neutralizes the recording sheet P after transfer, and the recording sheet P temporarily spans between the neutralizing device 9 (the neutralizing plate 10) and the nip portion of the fixing device 105. May occur. For this reason, the state in which the charge of the pressure roll 30 flows from the neutralization plate 10 to the neutralization device 9 via the recording sheet P in the straddled state was examined.
[0079]
FIG. 10 shows the flow into the static eliminator 9 when the resistance value of the resistance element R6 (FIG. 2) for current control connected between the output side of the power source device 11 and the static eliminator plate 10 in the static eliminator 9 is changed. The result of having measured the state of the electric current to perform is shown. This measurement was carried out by using an AC / DC high-voltage power supply device (manufactured by Trek Co., Ltd .: 610C) instead of the power supply device 11 and examining the state of the voltage (current) displayed on the monitor in the device. At this time, a voltage of about 3 kV was applied from the high-voltage power supply device to the charge removal plate 10.
[0080]
From the results shown in FIG. 10, it is understood that the inflow current can be suppressed to 8 μA or less by setting the resistance value of the resistance element R6 to at least 5 MΩ or more. If this 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 could be obtained well. When the resistance value of the resistance element R1 exceeds 32 MΩ, the inflow current thereafter becomes substantially constant and hardly changes.
[0081]
Therefore, in this printer, a resistance of 22 MΩ is used as the resistance element R6 in the static elimination power supply device 11. Further, as a result of various studies, it has been found that the resistance element R6 can obtain good results when the resistance value is at least in the range of 5 to 100Ω.
[0082]
Next, as the heating roll 20 in such a printer, as shown in FIG. 1 After anodizing and forming an alumite layer 21a on the surface of the base material, a tube in which carbon black was dispersed in PFA on the roll base material 21 was used as a conductive surface layer 22 was used. The roll base 2 1 It is confirmed that bubbles and delamination are locally observed between the conductive surface layer 22 and the conductive surface layer 22, and the voltage applied to the pressure roll 30 leaks due to the occurrence of dielectric breakdown at that portion, resulting in a voltage drop. It was done.
[0083]
Therefore, in this printer, as the roll base material 21 of the heating roll 20, a surface obtained by subjecting the surface to a fine rough surface treatment by a blast method and then forming a hard alumite layer 21a on the roughened surface is used. did.
[0084]
FIG. 11 shows the case where the hard anodized layer is formed, the case where the soft anodized layer is formed, and the case where the blast treatment is performed and the case where the blast treatment is not performed. It is the result of comparing and examining each. The peel strength at this time is determined by forming a cut surface corresponding to three sides of a square having a side of 10 mm on the surface layer 22, and holding and pulling the middle one of the cut sides of the three sides. The tensile load when the surface layer 22 to become peeled off from the roll base material 21 is measured. FIG. 12 shows the state of bubbles generated between the roll base material 21 and the conductive surface layer 22 when a hard anodized layer is formed, when a soft anodized layer is formed, and a blast treatment is performed. It is the result of investigating by comparing the case with no case. Regarding the state of bubble generation at this time, it is checked whether or not bubbles are generated in each pressure roll 30 obtained according to each of the above manufacturing conditions, and the number of bubbles generated at that time is one. The time was classified as “Yes”, and the number of times larger than that was classified as “Very many”.
[0085]
From the results of FIGS. 11 and 12, it can be seen that when a hard anodized layer is formed and when a blast treatment is performed, good results are obtained in both peel strength and bubble generation. This is advantageous in suppressing the voltage drop of the applied voltage to the pressure roll, which is likely to occur due to local generation of bubbles and delamination between the roll base material 21 and the conductive surface layer 22.
[0086]
Such a roll base 21 first, after the surface of the aluminum roll base 21 is subjected to a fine rough surface treatment such that the surface roughness Ra is about 1 μm by a blasting method (shot particle size: # 200), Anodizing treatment to form a hard anodized layer (electric field bath: sulfuric acid 10-30%, current density 2-12 A / dm ² And a hard alumite layer 20a having a thickness of about 20 μm is obtained by applying a bath temperature of 0 to 10 ° C. and a processing time of 15 to 30 minutes. And the heating roll 20 using this roll base material 21 can be produced by coating the above-mentioned tube as the insulating surface layer 22 after applying a primer to the surface of the roll base material 21.
[0087]
Next, it was confirmed that the resistance value of the conductive surface layer 33 of the pressure roll 30 in this printer is an important factor from the viewpoint of suppressing fluctuations in the voltage applied to the pressure roll 30. That is, when a conductive surface layer 33 having a resistance value of 8.6 MΩ at a temperature of 0 to 30 ° C. (PFA tube in which carbon black is dispersed) is applied to the pressure roll 30. As shown in FIG. 13, the voltage state fluctuates in the sheet passing time S.
[0088]
Therefore, in this printer, the conductive surface layer 33 of the pressure roll 30 has a resistance value of 1.6 MΩ at a temperature of 0 to 30 ° C. (PFA tube in which carbon black is dispersed). As a result, the voltage applied to the pressure roll 30 hardly fluctuates even when the sheet passes S as shown in FIG.
[0089]
Such a change in the applied voltage is caused by the pressure roll 30 being heated by the pressure roll 20 in the nip portion N, and the temperature state fluctuates (rises). It is presumed that it happens by doing. Actually, when the temperature dependency of the plurality of conductive surface layers 33 having different resistance values at a temperature of 0 to 30 ° C. was examined, the result shown in FIG. 15 was obtained. From the results shown in FIG. 15, it can be seen that the resistance value of each conductive surface layer 33 increases as it approaches the fixing temperature (160 to 220 ° C.). Moreover, it turns out that the increase width increases as the resistance value under the temperature of 0-30 degreeC becomes high. As a result of various investigations based on this finding, if the conductive surface layer 33 has a resistance value of 3 MΩ or less at a temperature of 0 to 30 ° C., fluctuations in the voltage applied to the pressure roll 30 are suppressed. It was confirmed. The resistance value of the conductive surface layer 33 at this time can be set, for example, by adjusting the dispersion state of a conductive agent such as carbon black.
[0090]
In the printer having the above-described configuration, the fluctuation of the bias voltage applied to the pressure roll 30 is reduced even in a high humidity environment, and a toner image is formed between the pressure roll 30 and the heating roll 20. Since the electric field in the direction of attracting the toner toward the recording sheet P is stably formed, the toner offset phenomenon and the scattering phenomenon hardly occur over a long period of time.
[0091]
In addition, in this printer, the suppression effect of the toner offset phenomenon and the scattering phenomenon as described above can be reliably achieved even when the configuration related to the bias power supply device 14 or the configuration related to the charge removal device 9 is employed alone. And you can get enough. Similarly, even when the configuration related to the roll base material 21 of the heating roll 20 and the configuration related to the conductive surface layer 33 of the pressure roll 30 are each independently employed, it can be reliably and sufficiently obtained. .
[0092]
◎ 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.
[0093]
[Embodiment related to power supply brush]
First, it was confirmed that the arrangement condition of the power supply brush 13 in this printer is an important element from the viewpoint of suppressing fluctuations in the voltage applied to the pressure roll 30. FIG. 16 shows the result of examining the toner scattering state 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 disposed on the rear side of the pressure roll 30, one power supply brush 13b is disposed on the front side of the pressure roll 30 in addition to the power supply brush 13a. When two power supply brushes are arranged in total, in addition to the two power supply brushes 13a and 13b, one power supply brush 13c is disposed closer to the nip portion N than the power supply brush 13a on the rear side of the pressure roll 30. Thus, when three power supply brushes are arranged in total, in addition to the three power supply brushes 13a, 13b, 13c, one power supply brush 13d is provided near the nip portion N on the rear side and front side of the pressure roll 30 one by one. When a total of five power supply brushes were arranged, the number of scattered toner was measured for each. The number of scattered toner was measured by printing out a test image and actually counting the number of toner scattered in the image at that time.
[0094]
From the results shown in FIG. 16, when the number of the power supply brush 13 is one, the toner scatters most, and the toner scatters toward the roll end on the side opposite to the side where the power supply brush 13a is disposed (front side). It can be seen that increases. Further, the scattering of the toner can be further suppressed by arranging the power supply brush at both ends of the pressure roll 30, arranging the power supply brush near the nip portion N, and arranging a plurality of them closer to the nip portion N. I understand.
[0095]
In view of this, in this printer, the power supply brushes 13 are arranged at least one on each of the left and right ends of the pressure roll 30 as shown in FIG. In FIG. 3, the symbol W indicates the maximum width of the passage width when passing through the nip portion of the recording sheet P. The power supply brush 13 is desirably disposed in the vicinity of the nip portion N on the sheet entry side from the viewpoint of reliably preventing toner scattering.
[0096]
Further, as shown in FIG. 18 a, at least two or more of the power supply brushes 13 are arranged back and forth in the circumferential direction of the roll 30 in the half circumferential surface region E including the nip portion N at both ends of the pressure roll 30. It is desirable to do. Further, as shown in FIG. 18B, in addition to the power supply brush 13 being arranged on the entry side of the recording sheet P in the half circumferential surface region E of the pressure roll 30, the side opposite to the sheet entry side (discharge side) ) In the vicinity of the nip portion N).
[0097]
In particular, when at least two or more power supply brushes 13 are arranged back and forth in the circumferential direction of the roll 30 in the half circumferential surface region E of the pressure roll 30, the conductive surface layer having a tube shape of the pressure roll 30. Fluctuations in bias voltage (see FIG. 7) due to the 33 folds can be suppressed (see FIG. 8).
[0098]
In the case where the conductive surface layer 33 in the form of a tube is to be coated and mounted on the insulating elastic layer 32 of the pressure roll 30 via an adhesive, the surface is used as a means for applying the adhesive to the tube. After the layer 33 is immersed in the adhesive solution, the tube-shaped surface layer 33 is squeezed in a state of being crushed into a plate shape in order to remove the excess solution. Two creases formed when squeezed are formed at opposite positions. The two fold portions have a resistance value higher than that of the other portions, which is the cause, and for example, appears as regular fluctuations in the bias voltage as shown in FIG. In this regard, if at least two or more power supply brushes 13 are disposed in the circumferential direction 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 portion corresponding to the fold. When 13 is in contact, the other power supply brush 13 is always in contact with the surface layer 33 portion other than the portion hitting the fold, so that the bias voltage can always be applied through the surface layer 33 portion other than the fold. Thereby, even when the pressure roll 30 having the surface layer 33 with a fold is used, fluctuations in the bias voltage due to the fold can be suppressed.
[0099]
[Other Embodiments Regarding Heating Roll]
As shown in FIG. 3, the heating roll 20 covers the insulating surface layer (PFA tube) 22 up to the end of the conductive roll base 21 and water on the surface of the surface layer 22. The contact angle with respect to was set to 100 ° or more. As a result, as shown in the figure, the insulating surface layer 22 having the above surface properties is also present in the end region G protruding from the end of the pressure roll 30 in the heating roll 20.
[0100]
In the case where the heating roll 20 is configured in this way, even in a high humidity environment, the charge induced by the bias voltage applied to the pressure roll 30 causes the end of the pressure roll 20 to be grounded (particularly, Since the end region G) does not flow out along the surface, the bias voltage does not fluctuate due to the charge outflow. In addition, when the contact angle of the insulating surface layer 22 in the end region G of the heating roll 20 is less than 90 °, it is confirmed that creeping conduction in which charges flow along the surface of the end region G occurs. Yes.
[0101]
[Other Embodiments Regarding Pressure Roll]
As the conductive surface layer 33 of the pressure roll 30 described above, the surface layer 33 without the folds was used without using the folds as described above. The pressure roll 30 provided with such a surface layer 33 has a PFA tube-shaped surface without using an adhesive when the tube-shaped surface layer 33 is coated on the insulating elastic layer 32. It is obtained by attaching the laser beam after irradiating the inner peripheral surface of the layer 33 with a laser beam. When the pressure roll 30 is used, the bias voltage does not fluctuate due to the fold.
[0102]
[Embodiment relating to guide member on sheet discharge side]
As the conductive guide member 16 on the sheet discharge side in the fixing device described above, as shown in FIG. 19, an insulating surface layer is formed on the portion of the guide member that contacts the recording sheet P discharged from the nip portion N after fixing. What formed 40 was used. In this example, the insulating surface layer 40 is formed by coating a Teflon material on the surface side of the guide member 16 so that the thickness is about 80 μm. The insulation layer 40 has a resistance of about 10 ¹¹ Ωcm.
[0103]
Accordingly, when the conductive guide member 16 that does not form the insulating surface layer 40 is used, the fixed recording sheet P is discharged from the nip portion N and passes through the guide member 16 as shown in FIG. The applied voltage to the pressure roll fluctuated at the time F when the conductive guide member 16 having the insulating surface layer 40 formed thereon was used, as shown in FIG. The variation in the voltage applied to the pressure roll at the sheet passing time F was suppressed. This effect is that even if the recording sheet P after fixing comes into contact with the conductive guide member 16, the charge induced in the pressure roll 30 by application of the bias voltage is transmitted through the recording sheet P to the guide member 16 side. It is presumed that it is obtained due to the disappearance of.
[0104]
Further, as the conductive guide member 16 described above, a member in which a Zener diode 45 as a constant voltage element is connected between the guide member 16 and a grounding portion as shown in FIG. 20 was used. Instead of the zener diode 45, a high resistance element may be connected.
[0105]
Also in this case, as in the case of the guide member 16 on which the insulating surface layer 40 is formed, pressurization is performed when the recording sheet P after fixing is discharged from the nip portion N and passes through the guide member 16. Variations in the voltage applied to the roll 30 are suppressed. This effect is that, even if the recording sheet P after fixing contacts the conductive guide member 16, the electric charge induced in the pressure roll 30 is transmitted through the recording sheet P and grounded from the guide member 16. It is presumed to be obtained because of being suppressed by the above.
[0106]
[Embodiment related to guide member on sheet entry side]
Although the guide member 15 on the sheet entry side in the fixing device described above is completely fixed and arranged, the recording sheet P is placed in the nip portion N as shown in FIG. A variable guide 50 is provided as a restricting member that restricts the approach posture when entering.
[0107]
The variable guide 50 is a guide plate that is attached to the nip portion N formed on the heating roll 20 and the pressure roll 30 of the fixing device so as to be swingable about the support shaft 51. The solenoid 52 is displaced to either the initial position X shown in FIG. 23a or the swing position Y shown in FIG. The initial position X is a restriction position for restricting the approach posture until the leading edge of the recording sheet P after fixing enters the nip portion N. The initial position X is set at a position where the sheet leading end portion Pa can be guided and regulated so as to be fed into the nip portion n after contacting the heating roll 20 slightly upstream of the nip portion N. On the other hand, the swing position Y is a restriction position for restricting the approach posture of the sheet portion after the leading end portion of the recording sheet P enters the nip portion N. In particular, for this swing position Y, the angle α between the sheet P and the tangent L of the center of the nip N after the sheet leading end Pa enters the nip N is set to the heating roll 20 side. It is set at a position that can be regulated to an approach posture of 5 ° or more (5 to 8 ° in this example).
[0108]
Therefore, the variable guide 50 is positioned at the initial position X until the leading end Pa of the recording sheet P after fixing enters the nip N, and swings when the leading end Pa of the sheet enters the nip N. It is set to be displaced to 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.
[0109]
According to such a variable guide 50, until the recording sheet P after fixing enters the nip portion N, the variable guide 50 is positioned at the initial position X as shown in FIG. Thus, as shown in FIG. 24, the recording sheet P is once abutted against the heating roll 20 just before the nip portion N so that the leading end Pa thereof is guided by the guide 50 at the initial position X (same as above). After that, it is fed into the nip portion N (FIG. B).
[0110]
When the leading end portion P of the recording sheet enters the nip portion N, the variable guide 50 is displaced to the swing position Y near the heating roll 20 by the operation of the electromagnetic solenoid 52 as shown in FIG. As a result, the rear end side of the recording sheet P is fed into the nip portion N in a posture approaching the heating roll 20. As a result, the toner image carrying surface side of the recording sheet P is preliminarily heated by the heat radiation of the heating roll 20 before the nip portion N, and the unfixed toner on the recording sheet P is slightly melted and physically applied to the recording sheet P. It will be in the state which adhered strongly. As a result, the toner scattering phenomenon is suppressed and the toner is easily fixed on the recording sheet.
[0111]
[Other Embodiments]
Even in a printer that employs the configuration according to each of the above embodiments independently (except when the configuration in which the variable guide 50 is provided is employed alone), as in the case of the above-described first embodiment, the printer is in a high humidity environment. Regardless, the fluctuation of the bias voltage applied to the pressure roll 30 is reduced, and as a result, the toner offset phenomenon and the scattering phenomenon hardly occur over a long period of time. Further, even in a printer in which only the variable guide 50 is provided, the occurrence of toner offset phenomenon and scattering phenomenon can be sufficiently suppressed.
[0112]
In addition, the configuration according to each of the above embodiments can be appropriately combined with each other, or can be appropriately combined with the above-described 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]
【The invention's effect】
As explained above, the first to the first 8 According to any of the inventions, the effect of suppressing the toner offset phenomenon and the scattering phenomenon by applying a voltage having a polarity opposite to the toner charging polarity to the pressure roll of the fixing device, even in a high humidity environment. It becomes possible to obtain more reliably and stably. When the image forming apparatus of each 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 diagram illustrating each configuration relating to the fixing device.
FIG. 4 is a main part enlarged explanatory view showing each configuration relating to a heating roll and a pressure roll.
FIG. 5 is a graph showing a result of measuring a fluctuation state of a voltage applied to a pressure roll when a conventional resistance voltage dividing circuit is used.
6 is a graph showing the results of measuring the fluctuation state of the voltage applied to the pressure roll when the bias voltage device according to Embodiment 1 is used. FIG.
FIG. 7 is a graph showing the results of measuring the fluctuation state of the voltage applied to the pressure roll when the resistance element R5 of the bias voltage device is “30 MΩ”.
FIG. 8 is a graph showing the result of measuring the fluctuation state of the voltage applied to the pressure roll when the resistance element R5 of the bias voltage device is “10 MΩ”.
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 an inflow current to 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 blast treatment, and the state of bubble generation at the interface between the roll base material and the insulating surface layer.
FIG. 13 is a graph showing the results of measuring the fluctuation state of the voltage applied to the pressure roll when the conductive surface layer of the pressure roll is “8.6 MΩ”.
FIG. 14 is a graph showing the results of measuring the fluctuation state of the voltage applied to the pressure roll when the conductive surface layer of the pressure roll is “1.6 MΩ”.
FIG. 15 is a graph showing the relationship between resistance and temperature of a conductive surface layer of a pressure roll.
FIG. 16 is a graph showing the relationship between the power supply brush arrangement condition and the number of scattered toner.
FIG. 17 is a perspective view showing an arrangement condition of the power supply brush.
FIG. 18 is an explanatory diagram showing the arrangement conditions of the power supply brush.
FIG. 19 is an explanatory view showing an embodiment of a conductive guide member having an insulating surface layer formed thereon.
FIG. 20 is an explanatory view showing an embodiment of a conductive guide member to which a constant voltage element is connected.
FIG. 21 is a graph showing the result of measuring the fluctuation state of the voltage applied to the pressure roll when a conventional conductive guide member is used.
22 is a graph showing the results of measuring the fluctuation state of the voltage applied to the pressure roll when the conductive guide member of FIG. 19 is used.
FIGS. 23A and 23B show an embodiment of a variable guide, where FIG. 23A is an explanatory view showing a state at an initial position, and FIG. 23B is an explanatory view showing a state at a swing position.
FIG. 24 is an explanatory view showing the operation of the variable guide and its action.
FIG. 25 is an explanatory diagram showing an overall configuration of a conventional image forming apparatus.
FIG. 26 is a main part explanatory view showing another example of a conventional image forming apparatus.
FIG. 27 is a main part explanatory view showing another example of a conventional image forming apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier), 5 ... Transfer roll (transfer apparatus), 9 ... Static elimination apparatus, 10 ... Static elimination plate (static elimination member), R6 ... Current control resistance element, 13 ... Power feeding brush (power feeding member), DESCRIPTION OF SYMBOLS 14 ... Bias power supply device, R5 ... Output limiting resistance element, TD ... Zener diode (constant voltage element), 20 ... Heating roll, 21 ... Conductive roll base material, 21a ... Hard anodized layer, 22 ... Insulating surface layer, 30 ... Pressure roll, 31 ... Conductive roll base material, 33 ... Conductive surface layer, 40 ... Insulating surface layer, 45 ... Constant voltage element (or high resistance element), 50 ... Variable guide (regulating member), P ... Recording sheet, T ... unfixed toner image.

Claims (1)

An image carrier that carries an unfixed toner image formed according to image information;
A transfer device for transferring an unfixed toner image on the image carrier to a recording sheet;
The recording sheet after the transfer by the transfer device is completed, between a heating roll in which an insulating surface layer is formed on a conductive roll base and a pressure roll in which a conductive surface layer is formed on the conductive roll base. A fixing device that passes through the nip portion and fixes the unfixed toner image on the recording sheet;
A bias power supply device that applies a bias voltage having a polarity opposite to the charging polarity of the unfixed toner image to a pressure roll of the fixing device via a power supply member disposed in contact with the conductive surface layer;
Discharging the recording sheet through a discharging terminal that is disposed close to the back side of the recording sheet after transfer and is applied with at least a voltage having the same polarity as the charging polarity of the unfixed toner image from the power supply device. With the device,
The recording sheet is configured to temporarily generate a state where the recording sheet straddles the static elimination terminal of the static elimination device and the nip portion of the fixing device,
An output limiting resistor element having a resistance value in the 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 output of the bias voltage is 400 V or less. A constant voltage element is connected between the limiting resistance element and the power supply member in a grounded state,
In addition, when a state where the recording sheet straddles between the output of the power supply device and the charge removal terminal in the charge removal device, an inflow current flowing into the power supply device side of the charge removal device via the record sheet is 8 μA or less. An image forming apparatus, wherein current limiting resistance elements each having a resistance value within a range of 5 to 100 Ω are connected in series.

Images