JP2003228249A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of preventing an excessive temperature increase of a fixing belt and surely fixing a toner image and to provide an image forming apparatus having the fixing device. <P>SOLUTION: The fixing belt 1 is rotatably stretched between a heat roller 2, as a heat source for heating a sheet, and a fixing roller 3 and heated by the heat roller 2. Using the heated fixing belt 1, the sheet passed through a pressure contact portion between the fixing roller 2 and the pressure roller 3 is heated, thereby fixing a toner image to the sheet. At least two heat generation sources 51, 52 of different distributions in heat generation are disposed within the heat roller. Also, the at least two heat generation sources 51 and 52 are independently controlled by a control means 55 according to the size of a sheet. In addition, a specific portion of the fixing belt 1 other than the contact portion of it with the heat roller 2 is heated by a heating means 6. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device and an image forming apparatus having the same, and more particularly to a fixing device for fixing a toner image onto a sheet.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine, a printer and a facsimile, a toner image transferred onto a recording paper or a transfer material sheet is heated and pressed. A fixing device for fixing the sheet is provided. As such a fixing device, for example, there is one that has a fixing roller also called a heating roller that heat-melts the toner on the sheet, and a pressure roller that presses the fixing roller to nip the sheet.

The fixing roller is formed in a hollow shape, and on the center axis of the fixing roller, a tubular heating heater such as a halogen lamp is provided, which generates heat when a predetermined voltage is applied. Are held by the holding means.

Since the heating element (halogen lamp) is located on the central axis of the fixing roller, the heat generated by the heating element is uniformly radiated to the inner wall of the fixing roller, resulting in the outer circumference of the fixing roller. The temperature distribution on the surface becomes uniform in the circumferential direction. Further, the fixing roller is heated until the temperature of the outer peripheral surface reaches a temperature suitable for fixing (for example, 150 to 200 ° C.).

Then, the fixing roller and the pressure roller, which are heated in this way, rotate in opposite directions while being in pressure contact with each other, and sandwich the sheet to which the toner is attached. As a result, the toner on the sheet is melted by the heat of the fixing roller at the pressure contact portion (hereinafter referred to as the nip portion) between the fixing roller and the pressure roller, and is fixed on the sheet by the pressure acting from both rollers.

By the way, particularly in a fixing device for fixing color toners, it is necessary to sufficiently melt and mix the toners of respective colors and to discharge the sheet without winding it around the fixing roller. For this reason, a thick elastic layer is provided on the fixing roller and the pressure roller, and a sufficient nip width and good paper discharge performance are obtained by the deformation of the elastic layer.

On the other hand, in a fixing roller having a heating element composed of a halogen lamp or the like, the inner surface of the fixing roller core metal is heated by utilizing the radiant heat from a heat source arranged inside the fixing roller to The heat is transmitted to the surface of the fixing roller through the elastic layer.

However, since the thick elastic layer has poor thermal conductivity, when heat is transferred from the core metal to the surface of the fixing roller via the elastic layer, the temperature at the interface between the fixing roller core metal and the elastic layer is The temperature will be higher than the surface temperature. Therefore, when the elastic layer at the core metal interface is continuously used at high temperature,
The elastic body causes hardening deterioration and liquefaction, which shortens the life. Furthermore, these phenomena become more prominent in a fixing device that performs high-speed fixing.

Therefore, as a fixing device for solving such a problem, a belt provided with a fixing belt and a heating roller for heating the fixing belt is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-228293. A fixing device has been proposed.

FIG. 11 is a diagram showing the configuration of such a conventional belt fixing device. In this belt fixing device, a thin fixing belt 100 having a low heat capacity is wound around a heating roller 101 to be heated and heated. The fixing belt 100 heats the sheet on which the toner image has been transferred at the nip portion between the fixing roller 102 and the pressure roller 103 to fix the toner image on the sheet.

In the belt fixing device having such a structure, the heat is not transferred from the inner surface of the thick elastic layer, but the fixing belt 100 in the vicinity of the surface is conveyed to the nip portion to convey the sheet. Since it is heated, it is possible to prevent the elastic body of the fixing roller elastic layer from being hardened and deteriorated or causing a liquefaction phenomenon. Further, since the nip shape can be made to be an upward convex shape depending on the thickness and hardness of the elastic layers of the fixing roller 102 and the pressure roller 103, good paper discharge performance can be obtained.

[0012]

However, even in such a conventional belt fixing device, for example, 40 minutes per minute.
When performing high-speed fixing of more than one sheet or high-speed continuous fixing of thick paper, the fixing belt 100 passes through the winding portion (contact portion) of the heating roller 101 in order to increase the rotation speed of the fixing belt 100. Is short, and it becomes difficult to supply the amount of heat required for fixing. As a result, there is a problem that the toner image is not properly fixed.

In order to solve such a problem, for example, the heating roller 101 is enlarged to have an outer shape.
The length of the circumference of 01 is lengthened to fix the fixing belt 100 and the heating roller 1.
The contact time with 01 or the length of the contact portion may be increased, but if the outer shape is increased in this way, the outer shape of the fixing belt 100 is also increased, and energy loss due to an increase in heat radiation or , There is a risk of causing an abnormal rise in the internal temperature of the main unit. Further, since the large diameter roller and the large diameter belt are used, the fixing device itself becomes large.

On the other hand, since the fixing belt 100 is made of a thin material having a low heat capacity, its thermal conductivity is extremely poor, and when a sheet having a size smaller than the set maximum width is continuously fed, the non-sheet feeding area (of the heating roller). Since the heat is not taken by the sheet at the end portion, there is a problem that the temperature rises excessively. Note that this was more serious in the case of continuous fixing at high speed.

Therefore, the present invention has been made in view of the above circumstances, and a fixing device capable of preventing an excessive temperature rise of the fixing belt and reliably fixing a toner image, and the fixing device. An object of the present invention is to provide an image forming apparatus provided with.

[0016]

SUMMARY OF THE INVENTION The present invention comprises a fixing roller and a pressure roller in pressure contact with the fixing roller, and a sheet on which a toner image is transferred is pressed into contact with the fixing roller and the pressure roller. In a fixing device for fixing the toner image on the sheet by heating while passing a sheet, a heating roller serving as a heat source for heating the sheet, and rotatably installed between the heating roller and the fixing roller. A fixing belt that heats the sheet that is heated by the heating roller and that passes through the pressure contact portion between the fixing roller and the pressure roller, and two or more heat generations provided in the heating roller and having different heat distributions. And a control means for independently controlling the two or more heat sources according to the size of the sheet.

Further, the present invention is characterized by comprising heating means for heating a predetermined portion of the fixing belt other than the contact portion with the heating roller.

The present invention is also characterized in that the heating means is an electromagnetic induction heating member having an induction coil and performing induction heating by an alternating current applied to the induction coil.

Further, the present invention is characterized in that the heating means is provided with a resistance heating element that generates heat by electric resistance, and heats the fixing belt by bringing the resistance heating element into contact with the fixing belt. It is what

Further, the present invention is characterized in that the fixing belt includes a conductive layer in at least a part thereof.

Further, the present invention is characterized in that the fixing belt includes a metal layer made of nickel, magnetic SUS, iron and alloys thereof.

Further, the present invention is characterized in that the fixing belt has an elastic layer made of an elastic material such as silicon rubber or fluororubber on the base layer.

Further, the present invention is characterized by comprising a pressing roller for pressing the fixing belt against the pressure roller.

Further, the present invention is an image forming apparatus, wherein an image forming section for forming a toner image and a sheet on which the toner image formed by the image forming section is transferred are heated and pressed to form the toner image. The fixing device according to any one of the above for fixing to a sheet is provided.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a view showing the arrangement of a fixing device according to the first embodiment of the present invention, and 50 is a fixing device for fixing a toner image onto a sheet by using the fixing belt 1.
The fixing device 50 is used, for example, in a color image forming device that forms a color image by an electrophotographic method, and is provided downstream of an image forming unit (not shown) in charge of an image forming process.

The fixing device 50 includes a fixing roller 3, a heating roller 2 serving as a heat source for heating the sheet through the fixing belt 1, and the fixing roller 3 and the fixing roller installed on the heating roller 2. A belt 1 and a pressure roller 4 that is in pressure contact with the fixing roller 3 and holds the fixing belt 1 together with the fixing roller 3 are provided.

In a color image forming apparatus (not shown), the original image is read by the original reading unit, a toner image corresponding to the original image is formed by the image forming unit, and toner is applied to the sheet supplied from the paper feeding unit. After the image is transferred, the toner image is heated and fixed on the sheet at the nip portion (hereinafter referred to as the fixing nip portion) between the fixing roller 3 and the pressure roller 4 of the fixing device 50. The sheet on which the toner image has been fixed by the fixing device 50 in this manner is then discharged to the paper discharge unit.

In the figure, 7 is a sheet separating claw disposed on the sheet exit side of the fixing nip portion so as to come into contact with or close to the surfaces of the fixing belt 1 and the pressure roller 4, and 8 is a sheet. A conveyance guide for conveying to the fixing nip portion, 9 is an oil application mechanism for applying release oil contained in an oil tank (not shown) onto the fixing belt 1, 10
Is a cleaning web for cleaning the offset toner on the fixing belt 1.

Reference numeral 11 denotes a temperature detecting element, which is a fixing device 50.
The control means 55 provided at a predetermined position detects the temperature of the surface of the fixing belt 1 on the basis of the output signal of the temperature detection element 11, and the main control means 51, 52 and induction heating which will be described later are operated via the temperature control circuit. The output of the member 6 is controlled.

In this embodiment, the fixing belt 1 laid over the fixing roller 3 and the heating roller 2 has a conductive layer (not shown) and nickel, magnetic SUS, at least in part.
It includes a metal layer made of iron and an alloy thereof, for example, a metal layer serving as a base layer of a thin film-shaped body made of nickel and having a thickness of 10 to 100 μm. Further, the fixing belt 1 has an elastic body such as silicon rubber or fluororubber on the surface of the base layer, for example
It has a release layer of silicon rubber having a thickness of 0 to 700 μm and has both good thermal response, flexibility and good release properties.

The heating roller 2 has an outer diameter of φ40 and a thickness of 3
The fixing roller 3 has an aluminum core and an elastic layer such as sponge or heat-resistant silicone rubber 5 to 5
It is composed of a φ50 roller having 10 mm and is driven by a drive motor (not shown).

The pressure roller 4 is a roller having an outer diameter of 50, and like the fixing roller 3, it has an elastic layer of 2 to 10 mm such as silicon rubber or sponge on an aluminum cored bar.
The outermost layer has a silicone rubber release layer that has good toner release properties and good oil affinity.

In the fixing nip portion formed by the pressure roller 4 and the fixing roller 3, the pressure roller 4 moves the fixing roller 3 through the fixing belt 1 from 500N to 1N.
It is formed by pressing with a pressure load of 000 N to deform the elastic layers of the fixing roller 3 and the pressure roller 4. Further, by setting the hardness of the pressure roller 4 to be higher than that of the fixing roller 3, the shape of the fixing nip can be made parallel to
It is possible to make it upwardly convex, and it is possible to obtain good paper discharge properties.

By the way, inside the heating roller 2, there are arranged a main heater 51 and a sub-heater 52 which are heat sources composed of halogen heaters having different light distribution characteristics as shown in FIG.

The light distribution characteristics of the main heater 51 are as follows.
As shown in FIG. 2A, for example, the amount of light is higher at the central portion and lower at the end portions in the longitudinal direction (L) of the heating roller 2. The light distribution characteristic of the sub-heater 52 is low at the center and high at the ends, as shown in FIG.

As a result, when the main heater 51 is energized, the central portion of the heating roller 2 is warmed to a temperature higher than the end portion, and when the sub-heater 52 is energized, the end portion of the heating roller 2 is warmed to a temperature higher than the central portion. To be In other words, these 2
The two heaters 51 and 52 act to complement each other.

Then, the two heaters 51 and 52, which act to supplement each other in this way, are independently turned ON / OFF by the control means 55 (see FIG. 1), and the main heater 5 is controlled.
By changing the lighting ratio of 1 and the sub-heater 52, it becomes possible to control the temperature of each of the central portion and the end portion of the heating roller 2.

For example, A3 having a normal maximum sheet width
When the sheets are continuously fed, the maximum heating width of the heating roller 2 can be uniformly heated by setting the lighting ratio of the main heater 51 and the sub heater 52 to 1: 1. on the other hand,
In A4 longitudinal paper (A4R), the lighting ratio of the main heater 51 and the sub heater 52 is 4: 1.

Then, the main heater 51 and the sub heater 5
By setting the lighting ratio of 2 to such a ratio, the central portion of the heating roller 2 is intensively heated, and as a result, the abnormal temperature rise of the non-sheet passing portion of the heating roller 2 is prevented. You can In addition, the lighting ratios of the main heater 51 and the sub heater 52 with respect to the main sheet size are shown in Table 1 below.

[0041]

[Table 1]

By the way, when the fixing belt 1 is wound around the heating roller 2 and heat is supplied to the fixing belt 1 only at the contact portion between the heating roller 2 and the fixing belt 1, it is sufficient that the moving speed of the fixing belt 1 becomes high. Cannot supply enough heat. For example, the moving speed of the fixing belt 1 is 200 mm / s.
When the speed is ec or more, the heat supply becomes insufficient, and the temperature of the fixing belt 1 decreases, which may cause a problem such as constant temperature offset.

Therefore, in the present embodiment, as shown in FIG. 1, an induction heating member 6 as a heating means is arranged in the vicinity of the fixing belt 1, and the induction heating member 6 serves as a heating roller 2 for the fixing belt 1. A predetermined part other than the contact part is heated.

Here, as shown in FIG. 3, the induction heating member 6 includes an induction coil 61, an excitation core 62, and a coil holder 6 for holding the induction coil 61 and the excitation core 62.
3 and 3.

By disposing the induction coil 61 using the Litz wire that is flatly wound into an elliptic shape in the transverse E-shaped exciting core 62 that is projected on both sides of the center of the coil, as shown in FIG. A unit such as is formed. As the exciting core 62, one having a high magnetic permeability and a low residual magnetic velocity density such as ferrite or permalloy is used, whereby the loss in the induction coil 61 and the exciting core 62 can be suppressed, and the fixing belt 1 can be efficiently used. Can be heated.

The coil holder 63 is made of a heat-resistant resin such as PPS, PEEK, phenol resin or the like, which is a non-magnetic and non-conductive heat-resistant material, so that the fixing belt may not come into contact with the fixing unit frame (not shown). It is fixed.

By the way, FIG. 5 is a diagram for explaining the heat generation principle of the induction heating member 6. Here, when a high-frequency (several KHz to hundreds of KHz) current is passed through the induction coil 61, a magnetic flux A perpendicular to the traveling direction of the fixing belt 1 is generated according to the "law of Ampere's right screw". Furthermore, this magnetic flux A
In response to this, a vortex-shaped induced current is generated in the fixing belt 1 in accordance with the "Lenz's law" so that a magnetic flux is generated in the direction opposite to the magnetic flux A. The induced current is converted into Joule heat by the specific resistance of the fixing belt 1, and the fixing belt 1 generates heat.

In the structure shown in FIG.
Since the magnetic flux is concentrated in the vicinity of the side surface of No. 1, a local heat distribution is obtained as shown in FIG. Here, the current generated by such electromagnetic induction has a distribution in the plate thickness direction according to the material, and the penetration depth δ of the magnetic flux is (κμf)
^It is proportional to the reciprocal of ^1/2 . Note that κ is the conductivity, μ is the relative permeability, and f is the frequency.

That is, the higher the frequency, the more the induced current collects on the surface. Therefore, if the thickness of the heat generating part is set to a value close to the penetration depth of the magnetic flux, most of the generated magnetic flux can be used effectively within that thickness, so the member that generates the induced eddy current according to the frequency is optimal. It is desirable to set the thickness to a proper value.

Here, in the present embodiment, the induction heating member 6 is provided with a heating roller 2 and a fixing roller 3 outside the fixing belt 1 which is a predetermined portion as shown in FIG. 7A.
It is arranged so as to heat the substantially flat surface portion upstream of the fixing nip portion stretched by.

Then, the induction heating member 6 is placed at such a position.
7B, the heating width for heating the fixing belt 1 is increased as compared with the configuration shown in FIG. 7B in which heat is supplied only at the contact portion between the heating roller 2 and the fixing belt 1. It is possible to supply a sufficient amount of heat to the fixing belt 1 even during high-speed fixing in which the rotating roller rotates at a high speed.

Although the induction heating member 6 is provided so as to uniformly heat the area corresponding to the maximum paper width, it is difficult to arbitrarily control the heat generation distribution within the heat generation area.
However, as described above, by independently controlling the main heater 51 and the sub-heater 52, which form the heat source in the heating roller and have different heat distributions, the heating roller 2 is prevented while preventing an abnormal temperature rise in the non-sheet passing portion. By using the induction heating of the flat portion of the fixing belt 1, it is possible to maintain a high-speed fixing property while maintaining a small size.

In this way, by independently controlling the main heater 51 and the sub heater 52 having different heat distributions,
It is possible to prevent an abnormal temperature rise in the non-sheet passing portion, and by enlarging the heating region by the induction heating member 6, it is possible to supply a sufficient amount of heat required for high-speed fixing.

As a result, the toner image can be reliably fixed on the sheet. In addition, by non-contact heating a predetermined portion other than the heating roller by the induction heating member 6,
Efficient heating with less heat loss can be performed without damaging the fixing belt 1.

Next, a second embodiment of the present invention will be described.

FIG. 8 is a diagram for explaining the configuration of the fixing device according to the present embodiment. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts.

In the figure, reference numeral 31 denotes a pressing roller which is arranged upstream of the fixing nip portion and presses the fixing belt 1 against the pressure roller 4. By pressing the fixing belt 1 against the pressure roller 4 in this way, the nip portion is pressed. Is wide. By widening the nip width in this way, good fixability can be maintained even when a large amount of heat is required for fixing such as high-speed fixing and thick paper fixing.

For example, by increasing the heating width by using the enlarging nip using the winding roller 31 and the heating roller 2 and the induction heating member 6 as described above, 50 sheets of 250 g thick paper per minute (A4 width). It is possible to maintain good fixability even when continuous fixing is carried out.

In the present embodiment, since the light distribution of the peak portion is high in both the main heater 51 and the sub heater 52, even when the nip portion is widened to cope with high-speed fixing, the fixing belt It becomes possible to supply a large amount of heat to 1, so that the temperature drop during continuous fixing can be suppressed and the apparatus can be downsized.

In the above description, the case where the induction heating member 6 supplies a sufficient amount of heat to the fixing belt 1 has been described, but the present invention is not limited to this, and the induction heating member 6 is replaced. Alternatively, other heating means may be used.

Next, a third embodiment of the present invention in which other heating means is used instead of the induction heating member 6 will be described.

FIG. 9 is a diagram for explaining the configuration of the fixing device according to the present embodiment. The same reference numerals as those in FIG. 8 indicate the same or corresponding parts.

In the figure, 13 is a sheet heating element which is another heating means. As shown in FIG. 10, this sheet heating element 13 has one surface of the substrate 132 on the film sliding side. And Ta ₂ N.
A planar low-heat-capacity resistance heating element layer 13 provided by coating (screen printing, etc.) an electric resistance material such as silver palladium
1 is a resistance heating element.

The sheet heating element 13 is provided with a glass layer 133 on the side where the belt contacts and slides. By providing such a glass layer 133, the sheet heating element 13 is connected to the fixing belt 1. The lubricity can be improved, and thus the inner surface of the belt can be prevented from being scraped and the resistance heating element layer 131 can be prevented from being worn.

Further, the glass layer 133 is composed of the pressure roller 4 and the resistance heating layer 131 when the fixing belt 1 is broken.
It also serves as an insulating layer that prevents electrical short circuit and leakage due to direct contact with.

In the above description, the case where the two heaters 51 and 52 are used as the heat source has been described, but the present invention is not limited to this, and three or more heaters may be used.

[0067]

As described above, according to the present invention, the heating roller for heating the fixing belt has different heat generation distributions.
By providing one or more heat sources and independently controlling the two or more heat sources according to the size of the sheet, it is possible to prevent excessive temperature rise of the fixing belt. Further, by heating a predetermined portion of the fixing belt other than the contact portion of the heating roller with the heating means, it is possible to supply a sufficient amount of heat required for high-speed fixing and thick paper fixing, and to reliably fix the toner image. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing light distribution characteristics of a main heater and a sub heater provided inside a heating roller of the fixing device.

FIG. 3 is an exploded view of an induction heating member provided in the fixing device.

FIG. 4 is a side sectional view of the induction heating member.

FIG. 5 is a view for explaining the heat generation principle of the induction heating member.

FIG. 6 is a diagram showing a heat generation distribution of the induction heating member.

FIG. 7 is a diagram showing a heating region of a fixing belt provided in the fixing device.

FIG. 8 is a diagram showing a configuration of a fixing device according to a second embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a fixing device according to a third embodiment of the present invention.

FIG. 10 is a side sectional view showing a configuration of a sheet heating element provided in the fixing device.

FIG. 11 is a diagram showing a configuration of a conventional fixing device.

[Explanation of symbols]

1 fixing belt 2 heating roller 3 fixing roller 4 pressure roller 6 induction heating member 13 Sheet heating element 31 pressing roller 50 fixing device 51 Main heater 52 Sub heater 55 Control means

Front page continued (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 6/14 H05B 6/14 F term (reference) 2H033 AA02 BA11 BA12 BA25 BA26 BA27 BB18 BE06 CA17 CA27 CA48 3K058 AA86 BA18 CA12 CA22 CB02 CB19 DA02 DA04 DA06 GA03 GA06 3K059 AB19 AB26 AD25 CD75

Claims (9)

[Claims] 1. A fixing roller and a pressure roller that is in pressure contact with the fixing roller, and a sheet on which a toner image is transferred is passed while heating a pressure contact portion between the fixing roller and the pressure roller. In a fixing device for fixing the toner image on the sheet, a heating roller serving as a heat source for heating the sheet, rotatably installed between the heating roller and the fixing roller, and heated by the heating roller. A fixing belt that heats the sheet that passes through the pressure contact portion between the fixing roller and the pressure roller; two or more heat generation sources provided in the heating roller and having different heat generation distributions; A fixing device comprising: a control unit that independently controls a heat source according to the size of the sheet. 2. The fixing device according to claim 1, further comprising heating means for heating a predetermined portion of the fixing belt other than a contact portion with the heating roller. 3. The fixing device according to claim 2, wherein the heating unit is an electromagnetic induction heating member including an induction coil and performing induction heating by an alternating current applied to the induction coil. 4. The heating means includes a resistance heating element that generates heat by electric resistance, and heats the fixing belt by bringing the resistance heating element into contact with the fixing belt. Item 2. The fixing device according to item 2. 5. The fixing device according to claim 1, wherein at least a part of the fixing belt includes a conductive layer. 6. The fixing belt is made of nickel or magnetic SU.
The fixing device according to claim 1, further comprising a metal layer made of S, iron and an alloy thereof. 7. The fixing device according to claim 1, wherein the fixing belt has an elastic layer made of an elastic material such as silicon rubber or fluororubber on a base layer. 8. The fixing device according to claim 1, further comprising a pressing roller that presses the fixing belt against the pressure roller. 9. The image forming unit for forming a toner image, and the sheet on which the toner image formed by the image forming unit is transferred is heated and pressed to fix the toner image on the sheet. 9. An image forming apparatus, comprising: the fixing device according to any one of 8 above.