JP2008026588A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in which rising of a fixing belt heated by an electromagnetic induction heating system is further improved, and an image forming apparatus. <P>SOLUTION: The fixing device includes: a first induction heating section 24 which generates magnetic flux; the fixing belt 22 which is stretched over a plurality of roller members 20, 21 and heated by the first induction heating section 24; a pressure belt 42 which is stretched over a plurality of roller members 30, 41 and applies pressure on a recording medium P transported between the pressure belt 42 and the fixing belt 22; and a second induction heating section 34 which heats the pressure belt 42 by generating magnetic flux. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  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 composite machine thereof, and a fixing device installed therein, and more particularly to a fixing device and an image forming apparatus using an electromagnetic induction heating method. It is.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, an electromagnetic induction heating type fixing device has been widely used for the purpose of reducing the rise time of the device and saving energy (see, for example, Patent Document 1). .)

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device includes a fixing belt stretched by a support roller (heating roller) and a fixing auxiliary roller (fixing roller), and an induction facing the support roller via the fixing belt. A heating unit (induction heating device), a pressure roller that presses the fixing auxiliary roller through a fixing belt, and the like are included. The induction heating unit includes a coil unit (excitation coil) extending in the width direction (a direction orthogonal to the conveyance direction of the recording medium), a core unit (core material) facing the coil unit, and the like. The

The fixing belt is heated at a position facing the induction heating unit. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, magnetic lines of force are formed at the positions of the fixing belt and the support roller facing the coil portion, and an eddy current is generated on the surface of the support roller. When an eddy current is generated in the support roller, Joule heat is generated by the electrical resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat.
A fixing device using such an electromagnetic induction heating method has higher heat conversion efficiency than other methods such as a heat roller method (heater lamp heating method), and requires less energy consumption and a shorter rise time. It is known that the surface temperature (fixing temperature) can be raised to a desired temperature.

  On the other hand, Patent Document 1 and the like are electromagnetic induction heating type fixing devices that have a technique of heating a pressure roller with a heater lamp provided in the pressure roller for the purpose of maintaining the fixing temperature during standby. It is disclosed.

JP 2005-173445 A

In the fixing device described in Patent Document 1 and the like described above, the heating roller that is heated by the radiant heat from the heater lamp has a rising time (a time required to reach a fixing temperature from a predetermined temperature). Since the rise time of the belt is very long, the temperature rise characteristic of the fixing belt has not been improved so much.
That is, in order to further improve the rising of the fixing belt heated by the electromagnetic induction heating method, heating the pressure roller by the heater lamp method has no significant effect. In particular, when the fixing device is started up after the fixing device is left for a long time (after the fixing temperature is sufficiently lowered), the above-described phenomenon becomes remarkable.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a fixing device and an image forming apparatus in which the rising of the fixing belt heated by the electromagnetic induction heating method is further improved.

  According to a first aspect of the present invention, a fixing device includes a first induction heating unit that generates a magnetic flux, and a plurality of roller members that are stretched by the magnetic flux generated by the first induction heating unit. The recording conveyed between the fixing belt that is directly or indirectly heated to melt the toner image and is fixed on the recording medium, and the fixing belt that is stretched between a plurality of roller members and press-contacted. A pressure belt that pressurizes the medium, and a second induction heating unit that generates magnetic flux and heats the pressure belt directly or indirectly by the magnetic flux.

  The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the fixing belt is stretched between a first support roller and a fixing auxiliary roller, and the pressure belt is 2 It is stretched between a supporting roller and a pressure auxiliary roller, and the fixing auxiliary roller and the pressure auxiliary roller are in pressure contact with each other via the fixing belt and the pressure belt.

  According to a third aspect of the present invention, in the fixing device according to the second aspect, the first induction heating unit is opposed to the first support roller via the fixing belt, and the fixing is performed. At least one of the belt and the first support roller is electromagnetically heated, and the second induction heating unit faces the second support roller through the pressure belt, and the pressure belt and the second support roller. At least one of the support rollers is heated by electromagnetic induction.

  According to a fourth aspect of the present invention, in the fixing device according to the second or third aspect, at least one of the auxiliary fixing roller and the auxiliary pressure roller is rotationally driven to rotate the fixing belt. And the pressure belt is made to travel.

  According to a fifth aspect of the present invention, there is provided the fixing device according to any one of the first to fourth aspects, wherein the first induction heating unit and the second induction heating unit are provided when the apparatus is started up. After energization and the apparatus is started up, at least one of the first induction heating unit and the second induction heating unit is controlled to be energized.

  A fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, wherein the rising time of the fixing belt heated by the first induction heating unit is This is configured to be shorter than the rise time of the pressure belt heated by the second induction heating unit.

  A fixing device according to a seventh aspect of the invention is the fixing device according to any one of the first to sixth aspects, wherein the first induction heating unit and the second induction heating unit are connected to a commercial power source. The power is supplied from at least one of the main power source and the auxiliary power source capable of charging / discharging the power.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to any one of the first to seventh aspects, wherein the toner relating to the toner image is a pre-made of a modified polyester resin in an organic solvent. Solvent from a dispersion obtained by dissolving or dispersing a polymer, a compound obtained by extending or cross-linking the prepolymer, and a toner composition, and subjecting the solution or dispersion to a cross-linking reaction and / or an extension reaction in an aqueous medium. In which the dispersed particle diameter of the pigment-based colorant dispersed therein is 0.5 μm or less in number average diameter, and the number average diameter is 0.7 μm or more. It is formed so that the ratio is 5% by number or less.

  According to a ninth aspect of the present invention, there is provided the fixing device according to the eighth aspect, wherein the toner has a dispersed particle diameter of the pigment-based colorant of 0.3 μm or less in terms of number average diameter. The number average diameter is 0.5 μm or more, and the number ratio is 10% by number or less.

  According to a tenth aspect of the present invention, in the fixing device according to the eighth or ninth aspect, the dispersion is obtained by dissolving a polyester-based resin that is non-reactive with amines. .

The fixing device according to an eleventh aspect of the present invention is the fixing device according to any one of the first to tenth aspects, wherein the number of toners related to the toner image is a number having a weight average particle diameter Dv (μm). When the average particle diameter is Dn (μm),
3.0 ≦ Dv ≦ 7.0
1.00 ≦ Dv / Dn ≦ 1.20
It is formed so that the following relationship is established.

  A fixing device according to a twelfth aspect of the present invention is the fixing device according to any one of the first to eleventh aspects, wherein the toner related to the toner image has a circularity of 0.900 to 0.960. It was formed so as to be within the range.

  The fixing device according to a thirteenth aspect of the invention is the fixing device according to any one of the first to twelfth aspects of the invention, wherein the toner relating to the toner image can be a tetrahydrofuran of polyester resin contained therein. In the molecular weight distribution of the solute, a main peak is present in the molecular weight range of 2500 to 10,000, and the number average molecular weight is in the range of 2500 to 50000.

  The fixing device according to a fourteenth aspect of the present invention is the fixing device according to any one of the first to thirteenth aspects, wherein the toner related to the toner image is a glass transition of a polyester resin contained therein. The point is 40 to 65 ° C., and the acid value is 1 to 30 mgKOH / g.

  An image forming apparatus according to a fifteenth aspect of the present invention includes the fixing device according to any one of the first to fourteenth aspects.

  An image forming apparatus according to a sixteenth aspect of the invention is the image forming apparatus according to the fifteenth aspect of the invention, which contains a developer composed of a carrier and toner relating to the toner image and is formed on the image carrier. The image forming apparatus includes a developing unit that develops the latent image.

  In the present invention, a pressure belt having a smaller heat capacity than that of the pressure roller is installed, the fixing belt is heated by the electromagnetic induction heating method, and the pressure belt is heated by the electromagnetic induction heating method. It is possible to provide a fixing device and an image forming apparatus in which the temperature characteristics are further improved.

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 1 denotes an apparatus main body of a tandem color copier as an image forming apparatus, 2 a writing unit that emits laser light based on input image information, and 3 an original conveying unit that conveys an original D to an original reading unit 4. 4 is a document reading unit that reads image information of the document D, 7 is a paper feeding unit that accommodates a recording medium P such as transfer paper, 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 11Y, 11M, and 11C. , 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, and 13 is each photosensitive drum. A developing unit that develops electrostatic latent images formed on 11Y, 11M, 11C, and 11BK, and a toner image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK Transfer bias roller for transferring superimposed on the recording medium P, 15 denotes each of the photosensitive drums 11Y, 11M, 11C, cleaning unit for collecting the untransferred toner on 11BK, a.

  Reference numeral 16 denotes a transfer belt cleaning unit that cleans the transfer belt 17, reference numeral 17 denotes a transfer belt that conveys the recording medium P so that toner images of a plurality of colors are carried on the recording medium P, and reference numeral 19 denotes the recording medium P. 1 shows an electromagnetic induction heating type fixing device that fixes a toner image (unfixed image) of the toner.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport rollers of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document D placed on the contact glass 5.

  Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light (exposure light) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (this is a charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (development process). .) In this embodiment, each developing unit 13 contains a two-component developer composed of toner and carrier. Then, after the toner and the carrier are sufficiently frictionally charged in the developing unit 13 while stirring and mixing, the toner is electrostatically attached to the electrostatic latent image formed on the photosensitive drum 11.
Thereafter, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the transfer belt 17. Then, the toner images of the respective colors formed on the photoconductive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the recording medium P on the transfer belt 17 at the position of the transfer bias roller 14 (transfer process). .)

Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

On the other hand, the recording medium P on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are transferred (carrying) is run in the direction of the arrow in the drawing and reaches a position facing the separation charger 18. . Then, the charge accumulated in the recording medium P is neutralized at a position facing the separation charger 18, and the recording medium P is separated from the transfer belt 17 without causing toner dust or the like.
Thereafter, the surface of the transfer belt 17 reaches the position of the transfer belt cleaning unit 16. Then, the deposit adhered on the transfer belt 17 is collected by the transfer belt cleaning unit 16.

Here, the recording medium P transported onto the transfer belt 17 is transported from the paper feeding unit 7 via the registration rollers 9 and the like.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P passes through a conveyance guide (not shown) and is guided to the registration roller 9. The recording medium P that has reached the registration roller 9 is conveyed toward the position of the transfer belt 17 in time.

The recording medium P to which the full color image has been transferred is separated from the transfer belt 17 and then guided to the fixing device 19. In the fixing device 19, the color image (toner) is fixed on the recording medium P between the fixing belt and the pressure belt (a fixing nip portion).
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a discharge roller (not shown), and a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 19 installed in the image forming apparatus main body 1 will be described in detail.
As shown in FIG. 2, the fixing device 19 includes a fixing auxiliary roller 20, a first support roller 21 (first heating roller), a fixing belt 22, a first induction heating unit 24, a pressure auxiliary roller 30, and a second support roller. 41 (second heating roller), a pressure belt 42, a second induction heating unit 34, and the like.

  Here, the fixing auxiliary roller 20 is formed by forming an elastic layer such as silicone rubber on the surface of a cored bar made of stainless steel or the like. The elastic layer of the auxiliary fixing roller 50 is formed so as to have a thickness of 1 to 5 mm and an Asker hardness of 30 to 60 degrees.

  The first support roller 21 is a hollow cylindrical member formed of a magnetic metal material such as iron, cobalt, nickel, or an alloy thereof. The first support roller 21 rotates in the clockwise direction in FIG. The first support roller 21 is heated by electromagnetic induction by the magnetic flux emitted from the first induction heating unit 24.

The fixing belt 22 is stretched and supported by the first support roller 21 and the auxiliary fixing roller 20 (two roller members). The fixing belt 22 is an endless belt having a multilayer structure in which a heat generation layer, an elastic layer, a release layer, and the like are laminated from the inner peripheral surface side.
As a material for the heat generating layer of the fixing belt 22, a magnetic metal material such as iron, cobalt, nickel, or an alloy thereof can be used.
The elastic layer of the fixing belt 22 is made of silicone rubber, fluorosilicone rubber or the like, and is formed to have a layer thickness of 50 to 500 μm and an Asker hardness of 5 to 50 degrees. Thereby, a uniform image quality without gloss unevenness can be obtained in the output image.
The release layer of the fixing belt 22 includes tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene / hexafluoropropylene copolymer (FEP). Or the like, a mixture of these resins, or a dispersion of these resins in a heat resistant resin. The layer thickness of the release layer 22d is 5 to 50 μm (preferably 10 to 30 μm). Thereby, the toner releasability on the fixing belt 22 is ensured and the flexibility of the fixing belt 22 is ensured.
A primer layer or the like can be provided between the layers of the fixing belt 22.

The fixing belt 22 travels clockwise in FIG. The fixing belt 22 (heat generation layer) is electromagnetically heated by the magnetic flux emitted from the first induction heating unit 24.
Thus, the fixing belt 22 in the present embodiment functions as a fixing member that melts the toner image, and also functions as a heat generating member that is directly electromagnetically heated by the first induction heating unit 24.
The fixing belt 22 is also indirectly heated (received heat) by the first support roller 21 heated by electromagnetic induction by the first induction heating unit 24.

  In the present embodiment, the heat generating layer of the fixing belt 22 has a single layer structure made of a magnetic metal material. On the other hand, the heat generating layer of the fixing belt 22 may have a two-layer structure including a first nonmagnetic layer and a second nonmagnetic layer. In that case, as the first nonmagnetic layer, SUS304, SUS301, SUS316 (all of which are nonmagnetic stainless steel) or the like can be used. As the second nonmagnetic layer, copper (Cu), silver (Ag), aluminum (Al), or the like can be used. Furthermore, in order to prevent oxidation of the heat generating layer, an oxidation preventing layer made of nickel (Ni) or the like can be formed on the heat generating layer.

The first induction heating unit 24 is disposed so as to face the first support roller 21 with the fixing belt 22 interposed therebetween. The first induction heating unit 24 includes a coil unit 25 (excitation coil), a core unit 26 (excitation coil core), a coil guide 27, a cover member 28, and the like. The coil portion 25 is formed by winding a litz wire bundled with thin wires and extending in the width direction (in the direction perpendicular to the paper surface of FIG. 2). The coil guide 27 is made of a heat-resistant resin material or the like, and holds the coil portion 25 on the side facing the fixing belt 22. The core portion 26 is made of a ferromagnetic material such as ferrite (having a relative permeability of about 1000 to 3000), and is a center core for forming an efficient magnetic flux toward the fixing belt 22 and the first support roller 21. And side cores are provided. The core part 26 is installed so as to face the coil part 25 extending in the width direction. The cover member 28 is configured to cover the coil portion 25 and the core portion 26.
An internal core made of a ferromagnetic material such as ferrite can be installed inside the first support roller 21 or a magnetic flux shielding member that covers a part of the outer periphery of the internal core can be installed.

  Although not shown, a thermistor is in contact with the surface of the fixing belt 22. The thermistor is a temperature sensitive element with high thermal responsiveness, and detects the temperature on the fixing belt 22 (fixing temperature). And based on the detection result by a thermistor, the heating amount by the 1st induction heating part 24 is adjusted.

  The auxiliary pressure roller 30 is formed by forming an elastic layer 31 such as fluorine rubber or silicone rubber on a cylindrical member 32 made of aluminum, copper or the like. The elastic layer 31 of the auxiliary pressure roller 30 is formed to have a thickness of 0.5 to 2 mm and an Asker hardness of 60 to 90 degrees. The pressure auxiliary roller 30 is in pressure contact with the fixing auxiliary roller 20 via the fixing belt 22 and the pressure belt 42. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure belt 42.

  Similar to the first support roller 21, the second support roller 41 is a hollow cylindrical member formed of a magnetic metal material such as iron, cobalt, nickel, or an alloy thereof. The second support roller 41 rotates counterclockwise in FIG. The second support roller 41 is heated by electromagnetic induction by the magnetic flux generated from the second induction heating unit 34.

The pressure belt 42 is stretched and supported by the second support roller 41 and the pressure auxiliary roller 30 (two roller members). Similar to the fixing belt 22, the pressure belt 42 is a multi-layered endless belt in which a heat generation layer, an elastic layer, a release layer, and the like are laminated from the inner peripheral surface side. The configuration of each layer of the pressure belt 42 is substantially the same as that of the fixing belt 22.
The pressure belt 42 travels counterclockwise in FIG. The pressure belt 42 (heat generation layer) is electromagnetically heated by the magnetic flux generated from the second induction heating unit 34.
As described above, the pressure belt 42 in the present embodiment functions as a pressure member that pressurizes the recording medium P conveyed to the fixing nip portion, and is directly electromagnetically heated by the second induction heating unit 34. It also functions as a heat generating member.
The pressure belt 42 is also indirectly heated (received heat) by the second support roller 41 that has been electromagnetically heated by the second induction heating unit 34.

The second induction heating unit 34 is disposed so as to face the second support roller 41 with the pressure belt 42 interposed therebetween. Similar to the first induction heating unit 24, the second induction heating unit 34 includes a coil unit 35, a core unit 36, a coil guide 37, a cover member 38, and the like. The coil portion 35 is formed by winding a litz wire in which fine wires are bundled and extending in the width direction. The coil guide 37 is made of a highly heat-resistant resin material or the like, and holds the coil portion 35 on the side facing the pressure belt 42. The core portion 36 is made of a ferromagnetic material such as ferrite (having a relative permeability of about 1000 to 3000), and a center for forming an efficient magnetic flux toward the pressure belt 42 and the second support roller 41. A core and a side core are provided.
An internal core made of a ferromagnetic material such as ferrite can be installed inside the second support roller 41, or a magnetic flux shielding member that covers a part of the outer periphery of the internal core can also be installed.

  Since the heat loss from the fixing member side to the pressure member side is reduced by heating the pressure belt 42 by the second induction heating unit 34 in this way, the rise time of the fixing belt 22 is shortened. . In particular, in the present embodiment, since the pressure belt 42 having a smaller heat capacity than that of the roller-shaped pressure member (pressure roller) is heated by the electromagnetic induction heating method, the fixing belt 22 (fixing device) The temperature rise characteristic is further improved.

The fixing device 19 configured as described above operates as follows.
When the auxiliary fixing roller 20 is rotationally driven by a drive motor (not shown), the fixing belt 22 runs in the clockwise direction in FIG. 2 and the first support roller 21 also rotates in the clockwise direction. Further, the pressure belt 42 travels counterclockwise, and the pressure auxiliary roller 30 and the second support roller 41 also rotate counterclockwise. The fixing belt 22 is heated at a position facing the first induction heating unit 24, and the pressure belt 42 is heated at a position facing the second induction heating unit 34.

  Specifically, a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) is supplied from the power supply unit (not shown) to the coil unit 25, so that the coil unit 25 supplies the first support roller 21 and the fixing belt 22. The magnetic field lines are formed so as to alternately switch in both directions. By forming an alternating magnetic field in this way, an eddy current is generated on the surface of the first support roller 21 and the heat generating layer of the fixing belt 22, and Joule heat is generated by the electrical resistance of the first support roller 21 and the heat generating layer. Thus, the first support roller 21 and the heat generating layer are heated. In this way, the fixing belt 22 is heated by the heat received from the first supporting roller 21 that has generated heat and the heat generated by its own heat generation layer. That is, the fixing belt 22 is directly heated by the first induction heating unit 24 and indirectly heated by the first induction heating unit 24 (heated via the first support roller 21).

Thereafter, the surface of the fixing belt 22 heated by the first induction heating unit 24 reaches a contact portion with the pressure belt 42. Then, the toner image T (toner) on the conveyed recording medium P is heated and melted.
The surface of the fixing belt 22 that has passed through the fixing position then reaches the position facing the first induction heating unit 24 again.

  On the other hand, a high frequency alternating current of 10 kHz to 1 MHz (preferably, 20 kHz to 800 kHz) is supplied from the power supply unit to the coil unit 35 of the second induction heating unit 34, and the second support roller 41 is supplied from the coil unit 35. In addition, the magnetic field lines are formed alternately in both directions toward the pressure belt 42. By forming an alternating magnetic field in this way, an eddy current is generated on the surface of the second support roller 41 and the heat generating layer of the pressure belt 42, and Joule heat is generated by the electrical resistance of the second support roller 41 and the heat generating layer. Then, the second support roller 41 and the heat generating layer are heated. Thus, the pressure belt 42 is heated by the heat received from the second support roller 41 that has generated heat and the heat generated by its own heat generation layer. That is, the pressure belt 42 is directly heated by the second induction heating unit 34 and indirectly heated by the second induction heating unit 34 (heated via the second support roller 41). .

Thereafter, the surface of the pressure belt 42 heated by the second induction heating unit 34 reaches a contact portion with the fixing belt 22. Then, the recording medium P conveyed toward the fixing nip is pressurized.
The surface of the pressure belt 42 that has passed through the fixing position then reaches the position facing the second induction heating unit 34 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process (the step of fixing the toner image by heating and pressing on the recording medium P).

  Thus, in this embodiment, since the pressure belt 42 is heated by the second induction heating unit 34, heat loss from the fixing member side to the pressure member side is reduced. For this reason, the heating time of the fixing belt 22 heated by the electromagnetic induction heating method is further shortened. In particular, since the fixing belt 22 and the pressure belt 42 have a smaller heat capacity than the fixing roller and the pressure roller, the temperature rise characteristic of the fixing belt 22 (fixing device) is further improved.

  In the present embodiment, the fixing belt 22 and the pressure belt 42 are caused to travel in a predetermined direction by rotating only the fixing auxiliary roller 20 with a driving motor. On the other hand, the fixing belt 22 and the pressure belt 42 can be run by rotating only the pressure auxiliary roller 30 with a driving motor, or both the fixing auxiliary roller 20 and the pressure auxiliary roller 30 are driven motors. The fixing belt 22 and the pressure belt 42 can be caused to travel by being driven to rotate. Also in those cases, the fixing belt 22 and the pressure belt 42 run well.

  In the present embodiment, both the first induction heating unit 24 and the second induction heating unit 34 are used when the fixing device is started up (when the operation is started and the temperature increase range is large). Can be controlled such that at least one of the first induction heating unit 24 and the second induction heating unit 34 is energized after the fixing device is activated. That is, when large heat energy is required to raise the temperature of the fixing belt 22 to a desired temperature, the first induction heating unit 24 and the second induction heating unit 34 are fully operated, and the temperature of the fixing belt 22 is reduced with small heat energy. Is maintained, the operating rates of the first induction heating unit 24 and the second induction heating unit 34 are reduced. Thereby, the electric power consumed in the 1st induction heating part 24 and the 2nd induction heating part 34 can be reduced efficiently.

  In the present embodiment, the rising time of the fixing belt 22 heated by the first induction heating unit 24 is set to be shorter than the rising time of the pressure belt 42 heated by the second induction heating unit. be able to. Specifically, the power supplied from the power supply unit to the first induction heating unit 24 can be set to be larger than the power supplied from the power supply unit to the second induction heating unit 34. Then, when the fixing belt 22 reaches a desired fixing temperature, the above-described fixing process is performed. This is because the thermal energy required for the pressure belt 42 is smaller than the thermal energy required for the fixing belt 22 that directly melts the toner image. That is, by allocating the power of the power supply unit so that the startup of the fixing belt 22 is prioritized, efficient power consumption can be performed and the entire fixing device can be started up efficiently.

Here, in the present embodiment, a power supply unit that supplies power to the first induction heating unit 24 and the second induction heating unit 34 is constituted by a main power supply 61 and an auxiliary power supply 62.
Specifically, referring to FIG. 3, the first induction heating unit 24 and the second induction heating unit 34 include a main power source 61 connected to a commercial power source and an auxiliary power source 62 capable of charging and discharging power. Power is supplied from at least one.

As shown in FIG. 3, the induction heating units 24 and 34 are connected to a main power supply 61 and an auxiliary power supply 62 via a switch circuit 65 having a plurality of switches 65 </ b> A to 65 </ b> C. The main power supply 61 is connected to an outlet (commercial power supply) provided at a setting location of the image forming apparatus. The auxiliary power supply 62 is provided with a chargeable / dischargeable capacitor. As the capacitor of the auxiliary power source 62, an electric double layer capacitor (for example, manufactured by Nippon Chemi-Con) having a capacitance of about 2000F and sufficient capacity to supply power for several seconds to several tens of seconds is used. be able to.
Then, by switching a plurality of switches 65A to 65C of the switch circuit 65, power is supplied to or cut off from the main power supply 61 or / and the auxiliary power supply 62 to the induction heating units 24, 34, or the main power supply 61 is connected to the auxiliary power supply. Power is supplied to 62 to charge the auxiliary power supply (capacitor).

FIG. 4 is a waveform diagram showing the amount of power supplied from the main power supply 61 and the auxiliary power supply 62 to the induction heating units 24 and 34.
Referring to FIG. 4, when the operation of induction heating units 24 and 34 is started, only first switch 65A of switch circuit 65 is connected, and power supply from main power supply 61 to induction heating units 24 and 34 is performed. It is carried out. As a result, the fixing belt 22 and the pressure belt 42 are heated to a desired temperature by heating by the induction heating units 24 and 34, and a predetermined fixing process is performed.
When the induction heating units 24 and 34 are in a standby state (a state in which large heating is not required), the second switch 65B is connected, and power is supplied from the main power supply 61 to the auxiliary power supply 62 so that the auxiliary power supply is supplied. 62 is charged.
When the induction heating units 24 and 34 start heating again from the standby state, the first switch 65A and the third switch 65C are connected to supply power from the main power supply 61 to the induction heating units 24 and 34. Then, power is supplied (discharged) from the auxiliary power source 62 to the induction heating units 24 and 34.

  Here, unlike the secondary battery, the capacitor of the auxiliary power source 62 has the following excellent characteristics because it does not involve a chemical reaction. In other words, when a secondary battery (for example, a nickel-cadmium battery) is used as an auxiliary power source, it takes several hours even if rapid charging is performed. However, when a capacitor is used as an auxiliary power source, rapid charging takes about several minutes. Is possible. Therefore, when the standby state and the heating state are repeated within the same time, by using a capacitor as an auxiliary power source, power can be reliably supplied from the auxiliary power source to the induction heating unit, and the induction heating unit can be operated for a short time. Can be raised to a predetermined temperature. Moreover, since secondary batteries, such as a nickel-cadmium battery, have 500 to 1000 charge / discharge cycles, they have a short life as an auxiliary power source, which requires labor and cost for replacement. On the other hand, capacitors have a long life, little deterioration due to repeated charge and discharge, and no need for liquid replacement or replenishment like lead-acid batteries, so there is almost no maintenance and can be used stably. .

Here, in the present embodiment, toner formed by the following manufacturing method is used as the toner (developer for forming a toner image) in the developer stored in the developing unit 13. .
That is, the toner in the present embodiment is obtained by dissolving or dispersing a prepolymer composed of a modified polyester resin in an organic solvent, a compound obtained by extending or cross-linking the prepolymer, and a toner composition, and dissolving or dispersing the dispersion or dispersion. It was obtained by removing the solvent from the dispersion obtained by crosslinking and / or elongation reaction in an aqueous medium. Furthermore, the dispersed particle diameter of the pigment-based colorant dispersed therein is 0.5 μm or less in terms of the number average diameter, and the number ratio in which the number average diameter is 0.7 μm or more is 5% by number or less. It has been done.
The toner thus formed is excellent in low-temperature fixability, charging stability, and fluidity, and can provide a high-quality image. In particular, in a color image forming apparatus, a color image having excellent transparency and excellent gloss can be obtained.

  Further, a toner formed so that the dispersed particle diameter of the above-mentioned pigment-based colorant is 0.3 μm or less in number average diameter and the number ratio of the number average diameter is 0.5 μm or more is 10% by number or less is used. As a result, a higher quality image can be obtained. Such toner is excellent in image resolving power and is suitable for a digital image forming apparatus. In particular, in a color image forming apparatus, a color image having excellent resolution and transparency and excellent color reproducibility can be obtained.

  In the toner production method described above, the dispersion (oil-based dispersion) can be obtained by dissolving a polyester-based resin that is non-reactive with amines. By using the toner formed in this way, it is possible to improve the low fixing property and the hot-offset resistance.

Further, the toner used in the present embodiment has a weight average particle diameter of Dv (μm) and a number average particle diameter of Dn (μm).
3.0 ≦ Dv ≦ 7.0
1.00 ≦ Dv / Dn ≦ 1.20
It is formed so that the following relationship is established. The toner thus formed is excellent in heat-resistant storage stability, low-temperature fixability and hot offset resistance, and can provide a color image excellent in glossiness. In addition, even when toner is consumed and replenished for a long time in a two-component developer, there is little fluctuation in the particle size of the toner in the developer, and stable developability is maintained even if stirring is performed for a long time in the developing section. Is done.
The weight average particle diameter and number average particle diameter of the toner can be determined using a particle size distribution measuring device “Coulter Counter TA-2”, “Coulter Multisizer 2” (both manufactured by Coulter, Inc.) and the like.

In addition, the toner used in the present embodiment is a substantially spherical toner, and is formed so that its circularity is in the range of 0.900 to 0.960. By using such a toner, a high-quality image having excellent transferability and no dust can be obtained.
The circularity of the toner is a value obtained by dividing the perimeter of an equivalent circle having the same area as the projected area by the perimeter of the actual particles, and is a flow type particle image analyzer “FPIA-2000” (manufactured by Sysmex Corporation). Etc. can be obtained.

  Further, the toner used in the present embodiment has a main peak in the molecular weight range of 2500 to 10,000 in the molecular weight distribution of the tetrahydrofuran-soluble portion of the polyester resin contained therein, and the number average molecular weight thereof. It is formed to be in the range of 2500 to 50000. By using such a toner, heat-resistant storage stability is optimized, and good low-temperature fixability and hot offset resistance can be obtained.

  The toner used in the present embodiment is formed such that the polyester resin contained therein has a glass transition point of 40 to 65 ° C. and an acid value of 1 to 30 mg KOH / g. It is. By using such a toner, it is possible to improve the low fixing property and the resistance to hot offset.

Hereinafter, in FIG. 5, an experiment conducted by the present inventor in order to confirm the effect of shortening the heating time of the fixing device by heating the pressure belt 42 by the second induction heating unit 34 will be described. To do.
FIG. 5 is a graph showing the temperature rise characteristics of the pressure auxiliary roller (or pressure roller). In FIG. 5, a solid line R indicates a temperature rise characteristic of the auxiliary pressure roller 30 in the fixing device (the fixing device in the present embodiment) that heats the pressure belt 42 by the second induction heating unit 34. A broken line S indicates a temperature rise characteristic of the pressure roller in a fixing device (a fixing device in Patent Document 1 described above) in which a halogen lamp (heater lamp) is provided in the pressure roller.

The fixing device related to the solid line R and the fixing device related to the broken line S were the same except for the heating method of the pressure member. The image forming linear speed (and the recording medium conveyance speed) in both image forming apparatuses was set to 185 mm / sec. Here, when 0.9 mg / cm ² of toner adheres to the recording medium P having a thickness (paper thickness) of 100 g / m ² (when a solid image is formed), the fixing property is satisfied. Therefore, the temperature of the auxiliary fixing roller 20 needs to reach 165 ° C., and the temperature of the auxiliary pressing roller 30 (or the pressing roller) needs to reach 80 ° C. In the experiment, the temperature increase of the fixing belt 22 and the pressure belt 42 (or pressure roller) was started from the state where the room temperature and the apparatus internal temperature were 20 ° C. Specifically, 1100 W of electric power was supplied to the first induction heating device 24 and 350 W of electric power was supplied to the second induction heating device 34 (or halogen heater).

As a result, in the fixing device using the halogen heater, the temperature rising time until the pressure roller surface reaches 80 ° C. is 40 seconds, whereas in the fixing device in the present embodiment, the pressure auxiliary roller surface is The temperature rising time until reaching 80 ° C. was 30 seconds. At this time, the time required for the temperature of the auxiliary fixing roller 20 and the fixing belt 22 to reach 165 ° C. (fixable temperature) is 28 seconds for the fixing device using the halogen heater. It was 26 seconds for the fixing device in No. 1. This is because the amount of heat on the fixing member side is less likely to move as much as the temperature rise on the pressure member side is faster.
Thus, by heating the pressure belt 42 by the second induction heating unit 34, the time required from warm-up to the start of image formation is shortened. Further, the fixing device that heats the pressure belt 42 using the electromagnetic induction heating method intermittently turns on and off the heater in the pressure roller for the purpose of shortening the rise time as in the fixing device using the halogen heater. Since there is no need to do so, energy saving is improved.

  As described above, in the present embodiment, the pressure belt 42 having a small heat capacity is installed, the fixing belt 22 is heated by the electromagnetic induction heating method, and the pressure belt 42 is heated by the electromagnetic induction heating method. Therefore, it is possible to provide a fixing device and an image forming apparatus in which the temperature rise characteristics are further improved.

  In the present embodiment, both the fixing belt 22 and the first support roller 21 are electromagnetically heated by the first induction heating unit 24, and both the pressure belt 22 and the second support roller 41 are subjected to the second induction heating. The part 34 is configured to be heated by electromagnetic induction. In contrast, only one of the fixing belt 22 and the first support roller 21 is heated by electromagnetic induction by the first induction heating unit 24, and only one of the pressure belt 42 and the second support roller 41 is heated. A configuration in which electromagnetic induction heating is performed by the second induction heating unit 34 may also be adopted. For example, when the heat generating layer is not provided on the fixing belt 22 or the pressure belt 42, only the first support roller 21 or the second support roller 41 is heated by electromagnetic induction by the induction heating units 24 and 34, and the fixing belt 22 or It functions as a heating member that heats the pressure belt 42. Even in such a case, the same effect as the present embodiment can be obtained.

  In the present embodiment, the induction heating units 24 and 34 are arranged at positions facing the outer peripheral surfaces of the fixing belt 22 and the pressure belt 42, but induction is performed so as to oppose the outer peripheral surfaces of the support rollers 21 and 41. The heating parts 24 and 34 can also be provided. That is, the induction heating units 24 and 34 can be directly opposed to the support rollers 21 and 41 without using the fixing belt 22 or the pressure belt 42. Even in such a case, the same effect as this embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a block diagram illustrating a main power source and an auxiliary power source that supply power to the fixing device. It is a wave form diagram which shows the electric power supply amount supplied from a main power supply and an auxiliary power supply. It is a graph which shows the temperature rising characteristic of a pressure auxiliary roller.

Explanation of symbols

1 image forming apparatus body (apparatus body),
19 fixing device,
20 Fixing auxiliary roller (roller member),
21 first support roller (roller member),
22 fixing belt,
24 1st induction heating part,
25, 35 coil part, 26, 36 core part,
30 Pressure auxiliary roller (roller member),
34 Second induction heating unit,
41 second support roller (roller member),
42 pressure belt,
61 Main power, 62 Auxiliary power.

Claims (16)

A first induction heating unit for generating magnetic flux;
A fixing belt stretched over a plurality of roller members and heated directly or indirectly by the magnetic flux generated by the first induction heating unit to melt and fix the toner image on a recording medium;
A pressure belt that is stretched between a plurality of roller members and pressurizes the recording medium conveyed between the pressure-contacting fixing belt;
A second induction heating unit that generates magnetic flux and heats the pressure belt directly or indirectly by the magnetic flux;
A fixing device comprising: The fixing belt is stretched between a first support roller and a fixing auxiliary roller,
The pressure belt is stretched between a second support roller and a pressure auxiliary roller,
The fixing device according to claim 1, wherein the auxiliary fixing roller and the auxiliary pressure roller are in pressure contact with each other via the fixing belt and the pressure belt. The first induction heating unit faces the first support roller via the fixing belt, and electromagnetically heats at least one of the fixing belt and the first support roller,
The second induction heating unit opposes the second support roller via the pressure belt, and electromagnetically heats at least one of the pressure belt and the second support roller. Item 3. The fixing device according to Item 2.   4. The apparatus according to claim 2, wherein at least one of the fixing auxiliary roller and the pressure auxiliary roller is rotationally driven to run the fixing belt and the pressure belt. 5. Fixing device.   When starting up the device, the first induction heating unit and the second induction heating unit are energized, and after starting up the device, at least one of the first induction heating unit and the second induction heating unit is energized. The fixing device according to claim 1, wherein the fixing device is controlled as described above.   The rising time of the fixing belt heated by the first induction heating unit is configured to be shorter than the rising time of the pressure belt heated by the second induction heating unit. The fixing device according to claim 1.   The first induction heating unit and the second induction heating unit are configured such that power is supplied from at least one of a main power source connected to a commercial power source and an auxiliary power source capable of charging and discharging power. The fixing device according to any one of claims 1 to 6, wherein the fixing device.   The toner relating to the toner image is obtained by dissolving or dispersing a prepolymer composed of a modified polyester resin in an organic solvent, a compound obtained by extending or crosslinking the prepolymer, and a toner composition, and then dissolving or dispersing the solution or dispersion in an aqueous system. It is obtained by removing the solvent from the dispersion obtained by crosslinking reaction and / or elongation reaction in the medium, and the dispersed particle diameter of the pigment-based colorant dispersed therein is the number average diameter. The number average diameter is 0.5 μm or less, and the number ratio of 0.7 μm or more is formed so that the number ratio is 5 number% or less. Fixing device.   The toner is formed so that the dispersed particle diameter of the pigment-based colorant is 0.3 μm or less in number average diameter, and the number ratio of the number average diameter is 0.5 μm or more is 10% by number or less. The fixing device according to claim 8.   The fixing device according to claim 8, wherein the dispersion is obtained by dissolving a polyester-based resin that is non-reactive with amines. The toner relating to the toner image has a weight average particle diameter of Dv (μm) and a number average particle diameter of Dn (μm).
3.0 ≦ Dv ≦ 7.0
1.00 ≦ Dv / Dn ≦ 1.20
The fixing device according to claim 1, wherein the fixing device is formed so as to satisfy the following relationship.   12. The fixing device according to claim 1, wherein the toner related to the toner image is formed so that a circularity thereof is in a range of 0.900 to 0.960.   The toner relating to the toner image has a main peak in the molecular weight range of 2500 to 10,000 in the molecular weight distribution of the tetrahydrofuran-soluble portion of the polyester resin contained therein, and the number average molecular weight is in the range of 2500 to 50000. The fixing device according to claim 1, wherein the fixing device is formed as follows.   The toner relating to the toner image is formed such that a polyester resin contained therein has a glass transition point of 40 to 65 ° C. and an acid value of 1 to 30 mg KOH / g. The fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to claim 1. The image forming apparatus according to claim 15, further comprising a developing unit that stores a developer composed of a carrier and toner related to the toner image and develops a latent image formed on the image carrier.

Images