JP4109966B2 - Heat fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic printer, a copying machine, and an electrostatic recording apparatus, and a heat fixing apparatus used in the image forming apparatus for fixing toner or the like on a recording material.
[0002]
[Prior art]
Conventionally, many electrophotographic copying machines, printers, etc. have a contact heating type heat roller fixing method with good thermal efficiency and safety as a heat fixing means, and quick start property (on-demand property). It uses an energy-saving film heating method that keeps power consumption as low as possible without supplying power to the equipment.
[0003]
A heat roller fixing type heat fixing apparatus includes a heating roller (hereinafter referred to as a fixing roller) as a heating rotating body including a halogen heater therein, and an elastic pressure roller (hereinafter referred to as a pressing rotating body) pressed against the heating roller. , A pressure roller). The pair of rollers is rotated, and a recording material (transfer material sheet / electrostatic recording material) as a heated material in which an unfixed image (toner image) is formed and supported in a fixing nip portion that is a pressure nip portion of the pair of rollers・ Introducing electro-fax paper, printing sheets, etc.), and nipping and transporting the toner image onto the recording material surface as a permanently fixed image by heat from the fixing roller and the pressure applied to the fixing nip. is there.
[0004]
On the other hand, film heating type heat fixing devices are disclosed in, for example, JP-A-63-313182, JP-A-2-157878, JP-A-4-44075-44083, JP-A-4-204980-204984. As described in the above, a heat-resistant film (hereinafter referred to as a fixing film) that is a rotating body for heating is applied to a heating body such as a ceramic heater (hereinafter referred to as a heater) that is fixedly arranged. A recording material carrying a toner image in a fixing nip portion, which is a pressure nip portion formed by a heating body and a pressure roller, with a fixing film interposed therebetween. Then, the toner image is transported together with the fixing film, and the toner image is fixed to the recording material surface as a permanently fixed image by heat and pressure by the heat from the heating body applied through the fixing film and the pressing force of the fixing nip portion.
FIG. 10 shows a schematic configuration of an example of a film heating type heat fixing device 11. The heating assembly 11a includes a heater 20 as a heating body, a film guide 22 as a guide member that supports the heater, and a flexible rotating body that includes the film guide 22 and is in contact with the heater 20. The assembly includes a cylindrical fixing film 25 and a flange member (not shown) that supports the fixing film 25 at both ends and is fitted to the film guide 22. The heater 20 is a so-called ceramic heater having a horizontally long and thin wall having a direction perpendicular to the conveyance direction (arrow K direction) of the recording material P as a longitudinal direction and having a low heat capacity as a whole. The fixing film 25 includes a release layer, a conductive layer, and a base material layer from the surface. The elastic pressure roller 26 as a pressure member includes a metal core 26a, an elastic layer 26b, and an insulating release layer 26c on the surface.
[0005]
The heater 20 and the pressure roller 26 on the side of the heating assembly 11a are opposed to each other and are pressed against each other with the fixing film 25 interposed therebetween to form a fixing nip portion N. The pressure roller 26 is rotationally driven in a counterclockwise direction indicated by an arrow R26 by a driving means (not shown). Due to the rotational drive of the pressure roller 26, the rotational force acts on the fixing film 25 by the frictional force between the pressure roller 26 and the outer surface of the fixing film 25 in the fixing nip portion N, and the inner peripheral surface of the fixing film 25 is fixed to the fixing nip. In the portion N, the outer periphery of the film guide 22 is rotated in the clockwise direction indicated by the arrow R25 while sliding in close contact with the surface of the heater 20 at a peripheral speed substantially corresponding to the peripheral speed of the pressure roller 26.
[0006]
A recording material P having an unfixed toner image T formed and supported on the surface is introduced between the fixing film 25 and the pressure roller 26 in the fixing nip portion N, and is nipped and conveyed. In this nipping and conveying process, the unfixed toner image T on the recording material P is heated by the heater 20 through the fixing film 25 in the fixing nip portion N, and is fixed by the pressure of the fixing nip portion N.
[0007]
Here, there are the following problems in image quality that occur during fixing in both the heat roller system and the film heating system.
[0008]
(1) A phenomenon in which the toner T on the recording material P is partially blown to the downstream side in the recording material conveyance direction immediately before the fixing nip introduction portion (hereinafter, rear toner scattering).
(2) A part of the toner T on the recording material P adheres to the fixing film 25 or the fixing roller side without being fixed, and when the portion where the toner has adhered next contacts the recording material, Image failure (hereinafter referred to as offset) in which the toner on the fixing roller is transferred to the recording material side.
As a countermeasure for suppressing these phenomena, conventionally, a method of increasing the electrostatic adhesion force of the toner T to the recording material P has been tried.
[0009]
For example, the film heating type heat fixing apparatus shown in FIG. 10 described above will be described as an example. A neutralizing means 33 such as a conductive roller grounded downstream of the fixing nip portion N in the recording material conveyance direction is provided. The conductive layer of the fixing film 25 is composed of the release layer 25a, the conductive layer 25b, and the base material layer 25c from the front surface so that the charge removing means 33 contacts the back surface of the printing surface of the recording material P after passing through the fixing nip. At least the recording material P passes through the fixing nip portion N via a safety circuit (not shown) from the bias power supply 32 and a power supply means 31 such as a conductive brush in the portion 25b, and has the same polarity as the toner T (here, negative polarity). By applying a predetermined amount of the fixing bias, a reverse polarity (here, positive polarity) charge to the bias applied from the grounding portion of the charge eliminating means 33 via the resistance of the recording material P is applied to the back surface of the printing surface of the recording material P. Induced A method of attracting and fixing toner T having a reverse charge and a reverse polarity to the recording material P is performed.
[0010]
The greater the amount of fixing bias applied, the greater the effect for suppressing the back toner scattering phenomenon. On the other hand, if the amount is too large, the offset tends to deteriorate. is there. This is because, due to the application of the fixing bias, a positive current having a polarity opposite to that of the toner T flows from the static elimination means 33 to the fixing film 25 side via the recording material P. This is considered to be reversed by this current and easily attached to the fixing film 25 side.
[0011]
Therefore, if the fixing bias setting is optimized for the offset phenomenon, the rear toner scattering phenomenon occurs remarkably. On the other hand, if the fixing bias setting is optimized for the rear toner scattering phenomenon, the offset phenomenon occurs remarkably. End up. Therefore, the fixing bias application amount is set to a balanced value between the offset level and the rear toner scattering level.
[0012]
[Patent Document 1]
JP-A-63-313182
[Patent Document 2]
Japanese Patent Laid-Open No. 2-157878
[Patent Document 3]
JP-A-4-44075
[Patent Document 4]
JP-A-4-204980
[Problems to be solved by the invention]
In the heat fixing apparatus as described above, as shown in FIG. 11a), the fixing bias is applied to the conductive layer 25b portion of the fixing film 25 to control the surface potential of the intermediate resistance release layer 25a. Therefore, when the fixing bias is turned OFF, as shown in FIG. 11 (b), a positive charge having a polarity opposite to that of the applied bias induced during the bias application remains on the surface of the release layer 25a having a medium resistance. The surface potential of 25 tends to reverse. This is because when the surface potential of the fixing film 25 is high and held for a long time, the amount of the positive charge with the opposite polarity that is induced increases. This also increases the time required for attenuation.
[0013]
For this reason, when a recording material (small size media) narrower than the maximum sheet passing width of the heat fixing device is passed and heated and fixed, recording on the surface of the fixing film is performed as shown in FIGS. 12 (a) and 12 (b). In the area (sheet passing area) through which the material has passed, a voltage drop occurs due to the current path through the recording material, and the potential on the surface of the fixing film decreases during the sheet passing. However, the surface potential tends to decay. However, the area on the surface of the fixing film where the recording material does not pass (non-sheet passing area) has no current path through the recording material, and the potential on the surface of the fixing film does not change even when the sheet is passed. Even if it is turned off, the surface potential is difficult to attenuate.
[0014]
Therefore, when the next fixing bias is applied while the surface potential of the continuous print is not attenuated, as shown in FIG. 13, there is a difference in the surface potential between the sheet passing area and the non-sheet passing area of the fixing film. As a result, the non-sheet passing area has a lower surface potential than the applied fixing bias. This tendency becomes conspicuous due to the continuous passage of small-size media.
[0015]
In such a state where the surface potential of the fixing film is uneven, when a recording material (large size media) wider than the recording material is passed, the passing area of the small size media passed before that However, since the surface potential is lower than the predetermined value in the non-sheet passing area, the rear toner scattering phenomenon in the non-sheet passing area is deteriorated. Further, if the bias application amount is increased so that the non-sheet passing area has a predetermined surface potential in order to suppress the back toner scattering phenomenon in the non-sheet passing area, the offset phenomenon in the sheet passing area is deteriorated. .
[0016]
In recent years, the increase in the fixing temperature and the enlargement of the fixing nip due to the increase in the printing speed worsen the back scattering phenomenon. Therefore, as a means for suppressing this, the transfer charge for holding the toner T on the recording material P is released. The resistance of the release layer of the fixing film is increased so that the conductive layer 25b under the layer 25a is less likely to leak. This increase in the resistance of the release layer delays the decay of the surface potential after the fixing bias is turned off. Therefore, the unevenness of the surface potential of the fixing film after passing through the small-size media described above tends to be further worsened. It was.
[0017]
Therefore, the present invention solves the above-described problems, and its object is to heat a large-size medium printed after a small-size medium so as to obtain a good image in which an offset phenomenon and a rear toner scattering phenomenon are balanced. A fixing device is provided.
[0018]
[Means for Solving the Problems]
A typical configuration according to the present invention for achieving the above object is as follows: A heating rotator having a heating member disposed therein; a pressure member that presses the print surface of the recording material on which the toner image is formed in contact with the heating rotator to fix the toner image; Bias voltage applying means for applying a bias voltage having the same polarity as that of the toner image to the recording material via the heating rotator, and the recording material in the pressure nip portion where the heating rotator and the pressure member are pressed against each other. A conductive member that contacts a back surface of the recording material passing through the pressure nip portion at a position downstream of the conveying direction and induces a charge having a polarity opposite to that of the toner to the recording material, and applies the bias voltage The means applies a first bias voltage to the recording material when the width of the recording material in the direction perpendicular to the conveyance direction of the recording material is the first size, and the second is smaller in width than the first size. For the first bias voltage Applying even lower second bias voltage having an absolute value It is characterized by doing.
[0019]
That is, by controlling the amount of bias applied to the recording material by the width of the recording material passing through the fixing nip portion, the unevenness of the surface potential of the fixing film after passing through the small-sized medium is suppressed, and after the small-sized medium In a large-sized medium to be printed, a good image in which the offset phenomenon and the rear toner scattering phenomenon are balanced can be obtained.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0021]
[First Embodiment]
FIG. 1 shows an image forming apparatus according to the present invention, that is, an image forming apparatus provided with a fixing device according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a laser beam printer (hereinafter, image forming apparatus) as an example of an image forming apparatus according to the present invention.
[0022]
{Image forming device}
First, the configuration of the image forming apparatus will be described with reference to FIG. The image forming apparatus shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in the direction of the arrow R1 by a driving unit (not shown). Around the photosensitive drum 1, a charging roller (charging device) 2, an exposure unit 3, a developing device 4, a transfer roller (transfer device) 5, and a cleaning device 6 are arranged almost sequentially along the rotation direction. Yes. A feeding cassette 7 that stores a sheet-like recording material P such as paper is disposed below the apparatus main body M. A feeding roller 15 is sequentially provided from the upstream side along the conveyance path of the recording material P. , A transport roller 8, a top sensor 9, a transport guide 10, a fixing device 11, a discharge sensor 16, a transport roller 12, a discharge roller 13, and a discharge tray 14 according to the present invention are arranged.
[0023]
Next, the operation of the image forming apparatus having the above configuration will be described. The photosensitive drum 1 that is rotationally driven in the direction of the arrow R1 by a driving unit (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 2. The surface of the charged photosensitive drum 1 is subjected to image exposure L based on image information by an exposure means 3 such as a laser optical system on the surface thereof, and the charge of the exposed portion is removed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller 4a, and a developing bias is applied to the developing roller 4a to attach toner to the electrostatic latent image on the photosensitive drum 1 and develop (visualize) the toner image. . The toner image is transferred to the recording material P such as paper by the transfer roller 5. The recording material P is stored in the feeding cassette 7, fed by the feeding roller 15, conveyed by the conveying roller 8, and is interposed between the photosensitive drum 1 and the transfer roller 5 via the top sensor 9. It is conveyed to the transfer nip part. At this time, the leading edge of the recording material P is detected by the top sensor 9 and is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.
[0024]
The recording material P carrying the unfixed toner image on the surface by the transfer is transported to the fixing device 11 along the transport guide 10, where the unfixed toner image is heated and pressurized and fixed on the surface of the recording material P. . The fixing device 11 will be described in detail later.
[0025]
The recording material P after the toner image is fixed is transported by the transport roller 12 and discharged onto the discharge tray 14 on the upper surface of the apparatus main body M by the discharge roller 13.
[0026]
On the other hand, after the toner image is transferred, the toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording material P is removed by the cleaning blade 6a of the cleaning device 6 and used for the next image formation.
[0027]
By repeating the above operations, image formation can be performed one after another.
[0028]
{Fusing device}
Next, an example of the fixing device 11 according to the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view taken along the conveyance direction (arrow K direction) of the recording material P. A fixing device 11 shown in FIG. 2 is a pressure roller driving type heat fixing device using a flexible endless belt as a fixing film.
[0029]
The fixing device 11 includes a fixing film 25 as a heating member that is a rotating body including a ceramic heater (hereinafter referred to as a heater) 20 that heats toner, and a pressure member that is in contact with the fixing film 25. The pressure roller 26 is configured as a main constituent member.
[0030]
The heater 20 and the pressure roller 26 on the heating assembly 11a side are in pressure contact with each other with the fixing film 25 interposed therebetween to form a fixing nip portion N. When the pressure roller 26 is rotationally driven in the counterclockwise direction indicated by the arrow R26, a rotational force acts on the fixing film 25 by the pressure frictional force at the fixing nip N between the pressure roller 26 and the fixing film 25. The fixing film 25 is driven to rotate in the clockwise direction indicated by the arrow R25 while sliding with its inner surface being in close contact with the downward surface of the heater 20.
[0031]
In a state where the pressure roller 26 is driven to rotate, the fixing film 25 is driven and rotated, and electric power is supplied to the heater 20, and the heater 20 is heated to a predetermined temperature. The recording material P carrying the unfixed toner image T is introduced between the fixing film 25 and the pressure roller 26 in the fixing nip N, and the toner image carrying surface side of the recording material P is the fixing film 25 in the fixing nip N. The fixing nip portion N is nipped and conveyed together with the fixing film 25 in close contact with the outer surface. In this nipping and conveying process, the heat of the heater 20 is applied to the recording material P through the fixing film 25, and the unfixed toner image T on the recording material P is heated and pressurized on the recording material P to be melted and fixed. . The recording material P that has passed through the fixing nip N is separated from the fixing film 25 by curvature.
[0032]
(heater)
The heater 20 as a heating element is a heating element in which a heating paste is printed on a ceramic substrate, and a glass coating layer for ensuring protection and insulation of the heating element is sequentially formed. Heat is generated by supplying a power-controlled AC current. As a material of the ceramic substrate, aluminum nitride, aluminum oxide or the like is used. A temperature control thermistor (temperature detection element) 21 is in contact with the back of the ceramic substrate. The heater 20 is long in the left-right direction perpendicular to the conveyance direction (arrow K direction) of the recording material P, and is longer than the width of the recording material P. The heater 20 is supported by a film guide 22 attached to the apparatus main body M. The film guide 22 is a member formed in a semicircular shape with a heat-resistant resin, and also functions as a guide member for guiding the rotation of the fixing film 25 described later.
[0033]
(Fixing film)
The fixing film 25 is formed of a heat-resistant resin such as polyimide in a cylindrical shape, and is loosely fitted to the heater 20 and the film guide 22 described above. The fixing film 25 is pressed against the heater 20 by a later-described pressure roller 26 so that the back surface of the fixing film 25 comes into contact with the lower surface of the heater 20. The fixing film 25 is configured to rotate in the arrow R25 direction as the recording material P is conveyed in the arrow K direction by the rotation of the pressure roller 26 in the arrow R26 direction. Note that both left and right end portions of the fixing film 25 are regulated by a flange member (not shown) fitted to the film guide 22 so that the fixing film 25 does not come off in the longitudinal direction of the heater 20. Further, grease is applied to the inner surface of the fixing film 25 in order to reduce the sliding resistance between the heater 20 and the heater holder 22.
[0034]
The fixing film 25 has a conductive primer layer 25b on the surface of a heat-resistant resin film (base film) 25a having a low heat capacity such as polyimide, polyamideimide, PEEK, PES, etc. as shown in the layer configuration model diagram of FIG. And a release layer 25c in which a conductive member such as carbon black is mixed in PTFE, PFA, FEP or the like. The release layer 25c is designed to have an optimum resistance value so as not to cause various image defects. Further, as shown in FIG. 3B, the fixing film 25 exposes the conductive primer layer 25b to a part of the surface of the fixing film and makes it contact with the power supply means 31 such as a conductive brush in order to apply a fixing bias described later. ing.
[0035]
The fixing film 25 may be a metal sleeve in which the release layer is coated on the surface of a thin metal element tube such as stainless steel via a primer layer. In this case, the metal base tube is partially exposed on the surface of the metal sleeve for grounding the fixing film and applying a bias.
[0036]
(Pressure roller)
The pressure roller 26 has an insulating layer made of a fluororesin such as PFA, PTFE, FEP, etc. with an elastic layer 26b of a heat-resistant rubber such as silicone rubber or a foamed sponge elastic layer sandwiched between the outer peripheral surface of a metal cored bar 26a. And a fixing nip portion N between the fixing film 25 and the fixing film 25 by pressing the fixing film 25 against the heater 20 from below by the outer peripheral surface of the releasing layer 26c. . If the width (nip width) in the fixing nip portion N in the rotation direction of the pressure roller 26 is a, the nip width a is such that the toner on the recording material P can be suitably heated and pressed. Is set. In order to suppress the charge-up on the surface of the insulating release layer 26c, the elastic layer 26b is preferably mixed with a conductive member such as carbon black to be conductive, and the cored bar is grounded.
[0037]
(Fixing bias application means)
The toner T is brought into contact with a conductive primer layer 25b (see FIG. 3) partially exposed on the surface of the fixing film 25 from a bias power source 32 through a safety circuit (not shown) and a power supply means 31 such as a conductive brush. Is applied to the fixing film 25. The fixing bias is applied at least while the recording material P is in contact with the fixing film 25. The amount of bias applied is variable by the control means 42 described later.
[0038]
(Static removal means)
On the downstream side in the conveyance direction (arrow K direction) of the recording material P in the fixing nip N, a grounded conductive roller or the like is in contact with the back surface of the printing surface of the recording material P that has passed through the fixing nip N. Conductive member A neutralizing means 33 is provided. As a form of the charge removal means 33, a form such as a brush or a guide may be used as long as it has conductivity.
[0039]
(Recording material width size detection means)
Reference numeral 41 denotes a control circuit unit of the image forming apparatus, which controls image forming operation sequence control of the entire image forming apparatus. In addition, a width sensor that operates when the recording material has a predetermined width or more is provided in the recording material conveyance path from the unillustrated feeding unit to the fixing device 11, and the control circuit unit 41 has this width. The width size of the recording material to be passed through the fixing device 11 is detected by a sensor signal or a sensor signal provided in a feeding cassette (not shown).
[0040]
(Correlation between fixing bias application amount and image quality depending on recording material width size)
Here, regarding the correlation between the fixing bias application amount and the image quality (back toner scattering, offset) depending on the width size of the recording material, the A4 / LTR compatible fixing device and the maximum sheet passing width of A4 size paper and the maximum sheet passing width are used. Since evaluation was performed on A5 size paper having a width smaller than the paper width, the result is shown in FIG. In FIG. 4, “◯” indicates an OK level, “Δ” indicates a level having no practical problem, and “×” indicates an NG level. The rear toner splattering phenomenon is caused by printing a pattern in which lines are arranged in a direction perpendicular to the paper transport direction on plain paper that has been left for 24 hours or more in an environment of 23 ° C./60% RH. The offset phenomenon is printed on plain paper that has been left for 24 hours or more in an environment of 23 ° C / 60% RH, and a pattern with a 100mm leading edge and solid white is printed on the plain paper. Evaluation was performed by observing the offset state of the character pattern to the part.
[0041]
As a result, the fixing bias required to suppress the offset does not change depending on the width of the recording material, but the fixing bias required to suppress the backside toner scatter is lower for small-size media than for large-size media. It was confirmed that it was good.
[0042]
This is because the non-sheet passing area of the small size medium in the pressure roller 26 is heated by passing the small size medium. It is considered that the shape of the pressure roller 26 is reverse crowned due to the thermal expansion of the elastic layer of the pressure roller 26, and the conveyance speed at both ends is faster than the central portion.
[0043]
In other words, when the conveyance speeds at the center and both ends are equal, the recording material has a slight undulation in the direction perpendicular to the conveyance direction, and the peak portion (the portion near the fixing film) is affected by heat before entering the fixing nip. Water vapor is gradually released before entering the fixing nip.
[0044]
On the other hand, since the valley portion (the portion far from the fixing film) is hardly affected by heat, it hardly releases water vapor before entering the fixing nip. When a portion that releases almost no water vapor in front of the fixing nip, such as this valley, enters the fixing nip, the water vapor is released at the moment when it enters the fixing nip, and the water vapor blows off unfixed toner upstream with a strong force. End up.
[0045]
However, if the conveyance speed at both ends is faster than that at the center, the recording material is conveyed while being pulled at both ends, so that the above-described crests and troughs do not exist and the level of rear toner scattering is thought to improve. It is done. Therefore, when a small size medium is passed, the rear toner scattering phenomenon can be suppressed with a lower fixing bias application amount than when a large size medium is passed.
[0046]
(Fixing bias control method)
From the detection of the recording material width size in the control circuit unit 41 and the correlation between the fixing bias application amount and the image quality based on the recording material width size, for example, in the fixing device 11 compatible with A4 / LTR, the maximum sheet passing width A4 or LTR size recording material (large size media) is passed, and B5 or A5 size recording material (small size media) narrower than the maximum paper passing width is passed. Then, the bias power supply control means 42 is controlled so as to change the amount of fixing bias applied from the bias power source 32 to the fixing film 25. An example of the control method is shown in FIG. 5 (a) (corresponding to Embodiment 1 and Embodiment 2).
[0047]
{Comparison experiment with conventional example}
As in the present embodiment, the bias amount applied to the recording material depending on the width of the recording material passing through the fixing nip portion is − when the fixing bias application amount is not less than the A4 size width as shown in FIG. When the voltage is less than 600V and A4 size width, the bias amount applied to the recording material is constant (−) regardless of the width that passes through the fixing nip portion of the recording material as in the conventional example. In the case of 600V), the evaluation of the offset phenomenon and the backward scattering phenomenon in the large-sized medium continuously printed after the small-sized medium was performed by changing the number of sheets of the small-sized medium, and the result is shown in FIG. Shown in (b).
[0048]
Here, using an A4 / LTR compatible fixing device, A4 size paper was used as a large size medium having a maximum sheet passing width, and A5 size paper was used as a small size medium having a width narrower than the maximum sheet passing width. In FIG. 5B, ◯ indicates an OK level, Δ indicates a level having no practical problem, and × indicates an NG level.
[0049]
The rear toner splattering phenomenon is caused by printing a pattern in which lines are arranged in a direction perpendicular to the paper transport direction on plain paper that has been left for 24 hours or more in an environment of 23 ° C./60% RH. The offset phenomenon is printed on plain paper that has been left for 24 hours or more in an environment of 23 ° C / 60% RH, and a pattern with a 100mm leading edge and solid white is printed on the plain paper. Evaluation was performed by observing the offset state of the character pattern to the part.
[0050]
As a result, compared with the conventional example, the present embodiment makes it possible to achieve both the offset phenomenon and the rear toner scattering phenomenon in the large-sized medium continuously printed after the small-sized medium even if the number of sheets passing through the small-sized medium increases. I was able to confirm.
[0051]
This is because, in the present embodiment, when a small size medium is passed, a lower fixing bias than that of a large size medium is applied to the surface potential of the fixing film in the conventional example shown in FIG. As shown in FIGS. 6 (a) and 6 (b), the surface potential of the fixing film is rapidly attenuated in the non-sheet passing area of the fixing film surface due to the fixing bias OFF after passing the small-size media. The difference in surface potential from the sheet passing area of the fixing film can be reduced.
[0052]
Therefore, even when a fixing bias for a large-size medium is applied to pass a large-size medium in a state where the surface potential of continuous printing or the like is not attenuated, as shown in FIG. The difference in surface potential between the paper area and the non-paper passing area is small, and can be set to a level that does not affect the image quality.
[0053]
[Second Embodiment]
Next, as a second embodiment, another example of a fixing bias control method when a small-size medium is passed will be described. In addition, the part which has the same function as 1st Embodiment mentioned above uses the same code | symbol, and uses description.
[0054]
{Correlation between fixing bias application amount and image quality during continuous feeding of small size media}
Here, with respect to the correlation between the amount of fixing bias applied when continuously passing small-size media and the image quality (backward toner scattering, offset) when a predetermined number of sheets are used, the A4 / LTR compatible fixing device is used for the small-size media. Since A5 size paper was evaluated, the result is shown in FIG. In FIG. 8 (a), ◯ indicates an OK level, Δ indicates a level having no practical problem, and × indicates an NG level.
[0055]
The rear toner splattering phenomenon is caused by printing a pattern in which lines are arranged in a direction perpendicular to the paper transport direction on plain paper that has been left for 24 hours or more in an environment of 23 ° C./60% RH. The offset phenomenon is printed on plain paper that has been left for 24 hours or more in an environment of 23 ° C / 60% RH, and a pattern with a 100mm leading edge and solid white is printed on the plain paper. Evaluation was performed by observing the offset state of the character pattern to the part.
[0056]
From this result, the fixing bias necessary for suppressing the offset does not change depending on the number of continuously passing small-size media. However, the fixing bias required for suppressing the backward toner scattering is increased by increasing the number of continuously passing small-sized media. It was confirmed that the applied amount may be low.
[0057]
This is because, as described in the first embodiment, the reverse crowning of the pressure roller shape due to the passing of small size media increases the amount of reverse crown due to the increase in the number of continuously passing small size media. It is done.
[0058]
{Fixing bias control method when passing through small-size media}
From the above-described correlation between the amount of fixing bias applied during continuous feeding of small-size media and image quality, for example, in a fixing device compatible with A4 / LTR, a B5 or A5 size recording material (small size media) that is narrower than the maximum sheet passing width. ) Is continuously controlled, the amount of fixing bias applied is controlled in accordance with the number of small-size media to be passed. An example of the control method is shown in FIG. 8B (corresponding to Embodiment 3). For large size media, the application amount shown in FIG. 5A is used as in the first embodiment.
[0059]
{Comparison experiment}
As in the first embodiment, the bias amount applied to the recording material depending on the width of the recording material passing through the fixing nip portion is as shown in FIG. 5A when the fixing bias application amount is equal to or larger than the A4 size width. When the control is made to be −400 V when the width is less than −600 V and A4 size, and the bias amount to be applied according to the number of sheets of small size media in addition to the first embodiment as in the present embodiment, FIG. As shown in Fig. 8 (b), when the number of sheets is 1 to 5 sheets, it is controlled as -400V, when it is between 6 and 10 sheets, it is controlled as -300V, and when it is 11 sheets or more, it is controlled as -200V. Regardless of the width of the material passing through the fixing nip, the offset phenomenon and backward scattering in large-sized media that are continuously printed after small-sized media when the amount of bias applied to the recording material is constant (−600 V) The evaluation of the phenomenon The results are shown in FIG. 9 because the number of sheets was changed.
[0060]
Here, using an A4 / LTR compatible fixing device, A4 size paper was used as a large size medium having a maximum sheet passing width, and A5 size paper was used as a small size medium having a width narrower than the maximum sheet passing width. In FIG. 9, “◯” indicates an OK level, “Δ” indicates a level having no practical problem, and “×” indicates an NG level.
[0061]
The rear toner splattering phenomenon is caused by printing a pattern in which lines are arranged in a direction perpendicular to the paper transport direction on plain paper that has been left for 24 hours or more in an environment of 23 ° C./60% RH. The offset phenomenon is printed on plain paper that has been left for 24 hours or more in an environment of 23 ° C / 60% RH, and a pattern with a 100mm leading edge and solid white is printed on the plain paper. Evaluation was performed by observing the offset state of the character pattern to the part.
[0062]
As a result, compared with the first embodiment and the conventional example, the present embodiment further increases the number of small-size media passing through the offset phenomenon and the rear toner scattering phenomenon in the large-size media continuously printed after the small-size media. It has been confirmed that even if it increases, both can be achieved.
[0063]
This is because, as described in the first embodiment, when a small-size medium is passed, a fixing bias lower than that of a large-size medium is applied, and the applied amount is further decreased stepwise when continuous paper is passed. Even if the number of small-size media to be passed increases, the difference in surface potential of the fixing film can be set to a level that does not affect the image quality.
[0065]
In addition, the film heating type heat fixing device in the above-described embodiment is a pressure rotating body driving method, but a driving roller is provided on the inner peripheral surface of the endless fixing film and driven while applying tension to the film. The apparatus of a system may be sufficient, and the apparatus of the system of making a film into the end-web of roll winding and driving this may be sufficient.
[0066]
Further, in the present invention, the image heating apparatus is not limited to the film heating method, and the image on the recording material can be conveyed by sandwiching and conveying the recording material carrying the image at the nip between the heating member and the pressure member, such as a heat roller method. Any image heating apparatus may be used.
[0067]
Furthermore, the heater is not limited to a ceramic heater. For example, an electromagnetic induction heat generating member such as an iron plate may be used. By using an electromagnetic induction heat generating member such as an iron plate as a heater, this is disposed at the position of the fixing nip portion, and a high frequency magnetic field generated by an electromagnetic coil and a magnetic core as an alternating magnetic flux generating means is applied thereto. An apparatus configuration that generates heat can also be used. Also, the film itself as the moving member can be made into an electromagnetic induction heat generating member so as to generate heat by the alternating magnetic flux generating means.
[0068]
The image heating apparatus of the present invention includes not only a fixing device that heats and fixes an unfixed image as a permanent image on a recording material, but also a heating device that presupposes an unfixed image on a recording material, and a recording that carries the image. Also included is a heating device that reheats the material to improve image surface properties such as gloss.
[0069]
The image forming method of the image forming apparatus is not limited to the electrophotographic method, and may be an electrostatic recording method, a magnetic recording method, or the like, or may be a transfer method or a direct method.
[0070]
Embodiment
Next, preferred embodiments to which the present invention can be applied are listed below.
[0071]
[Embodiment 1] A heating member that heats a recording material, and a pressure member that presses the recording material against the heating member. An unfixed toner image is formed at a pressure nip portion between the heating member and the pressure member. In a heating and fixing apparatus that heat-fixes the unfixed toner image on the recording material by passing the recording material on which
Means for applying a bias to the recording material at least while the recording material passes through the pressure nip portion;
Neutralizing means provided on the downstream side of the pressure nip portion in the recording material conveying direction;
Have
A heating and fixing apparatus, wherein a bias amount applied to the recording material is controlled by a width of the recording material passing through the press-contact nip portion.
[0072]
[Embodiment 2] The heat fixing apparatus according to Embodiment 1, wherein the bias amount applied to the recording material is smaller in the narrow recording material than in the wide recording material.
[0073]
[Embodiment 3] The heat fixing apparatus according to Embodiment 2, wherein the bias amount applied to the recording material having a narrow width is gradually reduced in accordance with the number of recording materials to be conveyed.
[0074]
[Embodiment 4] In an image forming apparatus for transferring a toner image to a recording material and fixing the recording material by a heat fixing device,
An image forming apparatus using the heat fixing apparatus according to any one of Embodiments 1 to 3 as the heat fixing apparatus.
[0075]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a good image in which the offset phenomenon and the rear toner scattering phenomenon are balanced on a large-sized medium that is continuously printed after a small-sized medium.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an electrophotographic image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the heat fixing device according to the first embodiment of the present invention.
FIGS. 3A and 3B are a layer configuration model diagram of a fixing film and a model diagram of a primer layer exposed portion. FIG.
FIG. 4 is a table showing the results of an experiment in which A4 size paper having the maximum paper passing width and A5 size paper having a narrower width than the maximum paper passing width were evaluated.
FIG. 5A is a table showing the relationship between the fixing bias application amount controlled according to the size of the recording material and the recording material size according to the embodiment of the present invention.
(b) is a table showing the results of evaluating the offset phenomenon and the backward scattering phenomenon in a large-sized medium continuously printed after the small-sized medium while changing the number of sheets passing through the small-sized medium.
FIG. 6 is a graph showing changes in surface potential of the fixing film when a small-size medium is passed in the first embodiment of the present invention.
FIG. 7 is a graph showing changes in surface potential of a fixing film when a small-size medium is passed in the first embodiment of the present invention.
FIG. 8A is a table showing experimental results of correlation between the amount of fixing bias applied when continuously passing small-size media and the image quality when a predetermined number of sheets are passed.
(b) is a table showing the experimental results of the correlation of image quality when an image is formed by changing the fixing bias application amount in accordance with the number of sheets of small size media to be passed.
FIG. 9 is a table showing experimental results of correlation comparing image quality related to bias control of the second embodiment and image quality related to bias control of the first embodiment with image quality of a conventional example.
FIG. 10 is a cross-sectional view of a heat fixing device in a conventional example.
FIGS. 11A and 11B are model diagrams illustrating reversal of the surface potential of a fixing film by ON / OFF of a fixing bias.
FIGS. 12A to 12B are changes in surface potential of a fixing film when a small-size medium is passed in a conventional example.
FIG. 13 is a graph showing changes in surface potential of a fixing film when a small-size medium is passed in a conventional example.
[Explanation of symbols]
L ... Image exposure
M ... Main unit
N: Fixing nip
P: Recording material
T: Toner
a: Nip width
1 ... Photosensitive drum
2 ... Charging roller
3 Exposure means
4 ... Developing device
4a: Developing roller
5: Transfer roller
6 ... Cleaning device
6a Cleaning blade
7 ... Feed cassette
8: Conveyance roller
9 ... Top sensor
10… Conveyance guide
11… Fixing device
11a… heating assembly
12… Conveying roller
13… discharge roller
14… discharge tray
15 ... Feed roller
16… discharge sensor
20… Heater
21… Thermistor
22… Film guide
25… Fixing film
25a ... heat resistant resin film
25b ... Conductive primer layer
25c ... release layer
26… Pressure roller
26a ... Metal core
26b ... elastic layer
26c ... release layer
31… Power supply means
32… Bias power supply
33 ... Static elimination means
41… Control circuit section
42… Control means

Claims (1)

A heating rotator with a heating element disposed therein;
A pressure member that presses the printing surface of the recording material on which the toner image is formed in contact with the heating rotator to fix the toner image;
Bias voltage applying means for applying a bias voltage having the same polarity as the toner image to the recording material via the heating rotator;
Contact the back surface of the recording material passing through the pressure nip at a position downstream of the pressure nip where the heating rotator and pressure member are in pressure contact with each other in the conveying direction of the recording material. A conductive member for inducing the charge of the recording material,
Have
The bias voltage applying unit applies a first bias voltage to the recording material when the width of the recording material in a direction orthogonal to the conveyance direction of the recording material is the first size, and the width is smaller than the first size. And a second bias voltage having an absolute value lower than that of the first bias voltage is applied when the second size is small .

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