JP3527442B2 - Image heating device and image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus for reducing the warming-up time, and more particularly to an image heating apparatus suitable for a fixing apparatus for fixing an unfixed image used in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus. The present invention relates to an apparatus and an image forming apparatus using the apparatus.

[0002]

2. Description of the Related Art As an image heating apparatus represented by a heat fixing apparatus, a contact heating method such as a heat roller method or a belt method has been generally used.

In recent years, a belt system which can set a small heat capacity has been attracting attention due to demands for shortening warm-up time and energy saving.

Japanese Laid-Open Patent Publication No. 6-318001 is an example of such a structure, and its structure is shown in FIG. Endless rotating belt 1
01 is stretched between the fixing roller 102 and the heating roller 103, and the heating source H1 in the heating roller 103 heats the heating roller 103 to heat the belt 101 to a predetermined temperature.

In this conventional example, by using a belt having a small heat capacity, it is intended to achieve the fixing without offset with a constitution in which the oil application is small.

Further, an electromagnetic induction heating system, which has the possibility of rapid heating and high efficiency heating, has been attracting attention.
23861 is an example thereof, and its structure is shown in FIG. An exciting coil 114 is arranged inside the heating roller, and an AC magnetic field is generated by this and a core 117 made of ferrite or the like to generate an eddy current in the heating roller 112 to generate heat. The recording material 110 carrying the unfixed toner image 111 is passed through the pressure contact portion of the heating roller 112 and the pressure roller 113 to fix the recording material 110.

[0007]

In general, the belt system including the above-mentioned conventional examples has an advantage that the heat capacity of the belt can be set small in order to shorten the warm-up time, and the belt itself can be heated to a predetermined temperature in a short time. You can On the other hand, however, the smaller the heat capacity, the stronger the tendency that the belt temperature is likely to drop due to the heat absorbed by the recording material when the toner image is fixed. For reliable fixing, it is necessary to stably and uniformly return the belt temperature lowered at this time to a temperature required before reaching the fixing unit again.

A further big problem is how the temperature of the belt decreases when passing through the fixing section, the recording material at that time,
That is, it greatly changes depending on the temperature state of the member used for the pressurizing means. Regardless of these temperature conditions, that is, even if the temperature of the belt decreases drastically after passing through the fixing unit, when bringing the belt to the fixing unit again, the belt is always returned to the constant temperature optimum for fixing. Is necessary for stable fixing.

In order to uniformly and stably return the belt to a predetermined temperature, the structure of heat transfer from the heat generating part to the belt and the structure of the heat generating part itself are important. No special consideration was given to this in the heating device.

In addition, in the belt system including the above-mentioned conventional example, the heat capacity of the film is generally set to be small in order to shorten the warm-up time, but this causes a problem of uneven temperature and partial excessive temperature rise. . This becomes a more remarkable problem when a recording material having a narrow width with respect to the width of the image heating device in the depth direction of FIG. 12 is continuously passed. That is, the portion through which the recording material passes must be heated accordingly in order for the recording material to absorb heat, but if the portion where the recording material does not pass through is heated similarly, the heat capacity of the heating element is small. The temperature rises steadily. Then, if it rises abnormally, hot offset may occur if a wide recording material is passed through in that state.

On the other hand, if the heat generation is limited to prevent hot offset, the temperature of the portion where the heat is taken by the recording material becomes low, which may cause cold offset or unfixed.

The present invention solves the problems associated with reducing the heat capacity of these conventional belt type image heating apparatuses.

Further, as in the case of the second conventional example, in which the heat roller is heated by using induction heating, a heating element such as the heat roller is directly heated by electromagnetic induction. It is said that the heat conversion efficiency is high and the heat roller surface can be quickly raised to the fixing temperature with less electric power as compared with.

However, it is difficult to remarkably shorten warm-up as compared with the conventional halogen lamp system in the structure in which the ordinary metal roller is simply heated by electromagnetic induction as in the conventional example. Improving efficiency by induction heating is not enough to make the temperature rising time faster,
It is necessary to reduce the heat capacity of the roller itself. When the heat capacity is reduced, temperature unevenness and partial excessive temperature rise pose problems as in the case of the belt.

The problem of this temperature unevenness becomes more remarkable when a recording material having a width smaller than the width of the heat roller is continuously passed, and power is supplied to maintain the temperature of the central portion where the recording material receives heat. If it continues to be added, an abnormal temperature rise may be caused at a place where heat absorption at both ends is small. This leads to damage to the bearings and the like at both ends, resulting in partial unevenness of the fixed image and deteriorating the image quality.

The present invention also solves the problems associated with reducing the heat capacity of these conventional roller type image heating devices.

[0017]

In order to solve the above-mentioned problems, the present invention has a belt, a pressurizing means for press-contacting the belt to form a nip on the surface side of the belt, and magnetic permeability. A heating roller that movably suspends the belt, a conductive member, and an exciting unit that excites the heating roller, the conductive member being within a range of a magnetic field of the exciting unit .
And a second position which is different from the first position and is outside the range of the magnetic field of the exciting means , and an image forming apparatus using the same. It is a device.

Further, the present invention comprises a heat-generating roller having magnetic permeability, a pressure member for pressing the heat-generating roller to form a nip, a conductive member, and an exciting means for exciting the heat-generating roller. , The conductive member is the magnetic field of the excitation means .
A first position in the range of, this is different from the first position, using the same and an image heating apparatus characterized by taking a second position which is outside of the magnetic field of the excitation means The image forming apparatus.

The present invention also relates to a belt and a pressure applied to the belt.
Pressurizing means for contacting and forming a nip on the surface side of the belt
And has magnetic permeability and heat generated by suspending the belt so that the belt can move.
A roller and an arc portion installed inside the heat roller.
Through a conductive member having a substantially semicircular cross section and the belt
Excitation means for exciting the heat roller from the outside.
However, in the conductive member, the arcuate portion is opposed to the exciting means.
The first position facing away from the first position,
Take a second position where the arc portion does not face the excitation means.
An image heating apparatus characterized by the above (Claim 3). Also
The present invention relates to a heat generating roller having magnetic permeability and the heat generating roller.
Pressure member that presses against the roller to form a nip, and the heat generating roller.
Is placed inside the roller and has a semi-circular cross section with an arc.
An electrically conductive member and the heat generating roller from outside the heat generating roller.
Exciting means for exciting the conductive member,
A first position where the circular arc portion faces the excitation means, and
The arc portion, which is different from the first position, is opposed to the exciting means.
Image heating device characterized by taking a second position that does not face
(Claim 4). The present invention also provides a belt,
Form a nip on the surface side of the belt by pressing it against the belt
And a magnetically permeable belt that movably suspends the belt.
A heat generating roller to be mounted and an exciting hand for exciting the heat generating roller.
The excitation means is provided so as to take a different position from the step.
For transmitting the magnetic flux generated from the heat generating roller
The heat generating roller is permeable to the magnetic flux.
The member for causing the second position to be far from the excitation means.
If the magnetic field of the exciting means is out of the range,
The magnetic flux generated from the exciting means penetrates through the heating roller.
The first heat generation state in which the heat generation roller generates heat by
And the member for transmitting the magnetic flux is the excitation hand.
At a first position close to the step, of the magnetic field of the excitation means
Of the magnetic flux generated from the excitation means when it is within the range
The heat generated by a member that partially transmits the magnetic flux
The remaining magnetic flux passes through the roller and penetrates inside the heat roller.
The second heat generation state in which the heat generation roller generates heat by
The image heating device is characterized in that
(Claim 14). The present invention also relates to a heat generating roller having magnetic permeability.
And a heating roller that presses the heat roller to form a nip.
The pressure member and the excitation means for exciting the heat roller are different from each other.
It is installed so that the
A member for transmitting the generated magnetic flux through the heat generating roller,
And the heat-generating roller is for transmitting the magnetic flux.
The member is in a second position remote from said excitation means,
When the magnetic field of the exciting means is out of the range, the exciting means is
That the magnetic flux generated from the penetrating inside the heating roller
The first heat generation state in which the heat generation roller generates heat,
A member for transmitting magnetic flux is close to the excitation means
The first position is within the range of the magnetic field of the exciting means.
Part of the magnetic flux generated from the excitation means
The inside of the heat roller due to the member for transmitting the magnetic flux
And the remaining magnetic flux penetrates the inside of the heat roller.
A second heat generation state in which the heat generation roller generates heat by
The image heating device is characterized by
Item 15). The present invention also relates to a belt and pressure contact with the belt.
Means for forming a nip on the front side of the belt
And has magnetic permeability and heat generated by suspending the belt so that the belt can move.
Conductive part provided so as to take a different position from the roller
Excitation for exciting the heating roller through the material and the belt.
Normal operation of outputting an image to a recording material having magnetic means
Sometimes the conductive member is in the range of the magnetic field of the excitation means.
The first position inside is taken, and the normal operation is possible.
During non-normal operation until
Take a second position outside the magnetic field of the excitation means.
And an image heating device characterized by (claim 24). Also
The present invention relates to a heat generating roller having magnetic permeability and the heat generating roller.
Position different from the pressure member that presses against the la to form the nip
And a heat-generating roller
And an excitation means for exciting the
During normal operation, the conductive member is
Taking the first position within the range of the magnetic field, the normal operation is
In non-normal operation until possible state,
The member is in a second position outside the range of the magnetic field of the excitation means.
The image heating device according to claim 2,
5). Further, the present invention provides a belt and a pressure contact with the belt.
A pressing means for forming a nip on the surface side of the belt, and a transparent member.
A heat-generating roller that has magnetism and movably suspends the belt.
And a conductive member provided so as to take a different position,
Exciting means for exciting the heating roller via the belt
And, wherein the conductive member has a magnetic field of the excitation means.
A first position within the range and the range of the magnetic field of the excitation means
Is configured to assume a second outer position,
The temperature of the heat roller is close to the Curie temperature of the heat roller.
When the conductive member is raised to the second position,
It is controlled to switch to the first position from the
It is an image heating device as a characteristic (claim 26). The present invention
Is a magnetically permeable heat generating roller, and
Takes a different position from the pressure member that contacts and forms a nip
Exciting the heat generating roller and the conductive member
An exciting means for
A first position within the magnetic field of the means, and the excitation means
Configured to assume a second position outside the range of the magnetic field of
And the temperature of the heat roller is close to the Curie temperature of the heat roller.
When raised to the side, the conductive member is
Controlled to switch from position to first position
An image heating device characterized in that (claim 27).

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

FIG. 12 is a sectional view of an image forming apparatus using the image heating apparatus of the embodiment of the present invention as a fixing device. The configuration and operation of this device will be described below.

Reference numeral 1 is an electrophotographic photosensitive member (hereinafter referred to as photosensitive drum). The surface of the photosensitive drum 1 is uniformly charged to a predetermined negative dark potential V0 by the charger 2 while being rotationally driven in the direction of the arrow at a predetermined peripheral speed.

A laser beam scanner 3 outputs a laser beam modulated in accordance with a time series electric digital pixel signal of image information input from a host device such as an image reading device or a computer (not shown). The surface of the photosensitive drum 1 which is uniformly charged as described above is scanned and exposed by this laser beam, and the absolute value of the potential in the exposed portion becomes small and becomes the bright potential VL, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. It is formed.

Next, the latent image is reversely developed by the developing device 4 with the negatively charged powder toner to be visualized.

The developing device 4 is a developing roller 4a which is rotationally driven.
And a thin layer of toner having a negative charge is formed on the outer peripheral surface of the roller to oppose the surface of the photosensitive drum 1, and the developing roller 4a has an absolute value of the absolute value.
By applying a developing bias voltage that is smaller than the dark potential V0 and larger than the bright potential VL, the toner on the developing roller 4a is transferred only to the bright potential VL portion of the photosensitive drum 1 and the latent image becomes visible. To be done.

On the other hand, the recording material 15 is fed one by one from the paper feed section 10, passes through the registration roller pairs 11 and 12, and then to the nip portion between the photosensitive drum 1 and the transfer roller 13 brought into contact with the photosensitive drum 1. It is sent at an appropriate timing synchronized with the rotation of the photosensitive drum 1. By the action of the transfer roller 13 to which the transfer bias is applied, the toner images on the photosensitive drum 1 are sequentially transferred to the recording material 15. The recording material 15 that has passed through the transfer portion is separated from the photosensitive drum 1 and is introduced into the fixing device 16 to fix the transferred toner image. The recording material 15 on which the image is fixed and fixed is output to the paper discharge tray 17.

After the recording material is separated, the surface of the photosensitive drum 1 is cleaned by a cleaning device 5 after removal of residual toner such as transfer residual toner on the surface of the photosensitive drum, and is repeatedly used for the next image formation.

Next, the image heating apparatus of the embodiment of the present invention will be described in detail.

FIG. 1 is a sectional view of a fixing device as an image heating device according to the first embodiment of the present invention.

The thin belt 20 is an endless belt having a base material 21 made of polyimide resin and has a diameter of 50 mm and a thickness of 5 mm.
As shown in the cross section in FIG. 2, the release layer 22 having a thickness of 5 μm made of a fluororesin is coated on the surface of the release layer at 0 μm so as to provide the release property. As the material of the base material 21, in addition to heat-resistant polyimide, fluororesin, or the like, a very thin metal such as nickel produced by electroforming can be used. Further, the release layer 22 on the surface may be coated with a resin or rubber having a good release property such as PTFE, PFA, FEP, silicon rubber, and fluororubber, either alone or as a mixture. Only the releasability is required for fixing a monochrome image, but it is desirable to impart elasticity when used for fixing a color image, and in that case, it is necessary to form a slightly thick rubber layer. .

Reference numeral 23 denotes an exciting coil as an exciting means, which uses a litz wire formed by bundling thin wires, and has a sectional shape formed so as to cover the belt 20 as shown in FIG. A core material 24 composed of is installed. The core material 24 may be made of a material having a high magnetic permeability such as permalloy. FIG. 3 is a view of the structure of the core member 24 and the exciting coil 23 as seen from the front side of the belt, and the exciting coil 23 is formed along the central core member 24 as shown in the figure over substantially the entire length of the heat generating roller. The core material on the back surface is present only in part and is configured to capture the magnetic flux leaking to the outside. An alternating current of 30 kHz is applied to the exciting coil 23 from the exciting circuit 25.

Returning to FIG. 1, the belt 20 has a low thermal conductivity fixing roller 43 having a diameter of 20 mm, which is made of elastic silicone rubber having a low hardness (JIS A30 degrees) and an alloy described later. It is suspended with a predetermined tension between the heating roller 44 having a diameter of 20 mm and is rotatable in the direction of arrow B. The heat generating roller 44 is made of a magnetic material having a high magnetic permeability and made of an iron / nickel / chromium alloy having a thickness of 0.4 mm, and its Curie temperature is adjusted to 220 degrees by the amount of chromium mixed in the material. Are manufactured. Inside the heat roller 44,
Arc part 45 with a gap of 0.5 mm from the heating roller 44
A conductive member 45 having a substantially circular cross section having a and made of aluminum having a higher conductivity than the heat generating roller 44 is provided. The conductive member 45 has an axial length that is substantially the same as or slightly shorter than the exciting range of the exciting coil 23, and is rotatably supported by a shaft 46.
The phase with 3 is fixed at a predetermined position, and the phase can be switched by the switching means 53.

As shown in FIG. 4, the heat generating roller 44 and the conductive member 45 are supported at both ends by flanges 47 and 48 made of a heat-resistant resin having a small heat conductivity such as bakelite. The generated heat is hard to be transferred to the conductive member 45. Heating roller 44
Is rotatably driven by a drive means of the apparatus body (not shown).

In FIG. 1, the pressure roller 49 has a hardness of JI.
It is made of silicon rubber having an SA of 65 degrees, and presses against the fixing roller 43 via the belt 20 as shown in FIG. 1 to form a nip. The pressure roller 49 was rotatably supported around the metal shaft 50 in this state. Pressure roller 4
The material of 9 may be made of other heat resistant resin such as fluororubber or fluororesin or rubber. The surface of the pressure roller 49 is made of PFA or PTF to improve wear resistance and releasability.
Resins or rubbers such as E and FEP may be coated alone or as a mixture. Pressure roller 49 to prevent heat dissipation
Is preferably composed of a material having low thermal conductivity.

In this embodiment, this portion has a self-temperature control characteristic due to the constitution of the heat generating roller portion.
The operation will be described below with reference to FIGS.

The conductive member 45 is fixed in a phase in which an arc portion 45a having a substantially equal distance from the heat generating roller 44 faces the exciting coil 23. Here, the operation of the image forming apparatus for outputting an image on a recording material is referred to as a normal operation, and the operation of warming up to a state in which normal operation is possible is referred to as an abnormal operation. For warming up from room temperature (non-normal operation), first, a heating roller 44, a fixing roller 43, a pressure roller 49, and
When the belt 20 is moved, the exciting circuit 25 drives the exciting coil 23 with an alternating current having a frequency of 25 to 30 kHz by the exciting circuit 25 to start heating, and in FIG. 5, heat generation facing the exciting coil 23 of the heat generating roller 44 is performed. Since the portion 44a is at a temperature below the Curie point and the magnetic flux generated by the magnetic field generated by the exciting coil 23 is magnetized by the heat generating roller 44, almost all the heat is generated in the heat generating roller 44 as indicated by arrows D and D'in the figure. The disappearance is repeated, and the induced current generated thereby flows almost only on the surface of the heat generating roller 44 due to the skin effect, and Joule heat is generated at that portion.

Here, in FIG. 8, the curve μ shows the relationship between the magnetic permeability and the temperature of the magnetic material made of an alloy of iron, nickel and chromium used for the heat generating roller 44. In this figure,
The horizontal axis represents the temperature of the material of the heat generating roller, and the vertical axis represents the magnetic permeability. When the temperature of the heat generating roller 44 is low, the magnetic permeability shows a high value, the magnetic flux generated by the exciting coil 23 penetrates through the heat generating roller 44 as described above, and the induced current is mostly concentrated on the surface thereof and heat is generated by Joule heat. The roller 44 heats up rapidly. The point Tk in the figure represents the Curie temperature, and above this temperature, the magnetic permeability is almost the same as in air. That is, the magnetic flux generated by the exciting coil 23
4 and diverges to the conductive member 45, and the induced current flows out predominantly in the conductive member 45 having high conductivity.

In FIG. 6, the heat generating portion 4 of the heat generating roller 44 is used.
Since the magnetic permeability of 4a becomes close to the Curie temperature, the magnetic flux diverges toward the conductive member 45 inside as shown by arrows E and E'in the figure, and the induced current has a high conductivity. It flows overwhelmingly in 45, and at this time, the conductivity is high, that is, the resistance is small, so if the current is limited to a constant value, heat generation is significantly reduced, and the temperature stabilizes. According to the calculation, the depth of the portion where the current flows due to the skin effect is about 0.3 mm when the frequency of the exciting current is 30 kHz. If the thickness of the heat generating roller 44 is equal to or larger than this skin depth, most of the current is generated in the heat generating roller 44 at low temperature. The higher the current frequency, the smaller the skin depth, and the thinner heating roller can be used. However, if the frequency of the exciting current is too high, cost will be incurred, and noise emitted to the outside will also be large.

The magnetic permeability is about 140 as shown by the curve μ in FIG.
Although the same value is represented up to the degree, from here to the Curie point Tk, a gentle curve is drawn to decrease. That is, the magnetic permeability gradually decreases, and accordingly, the amount of the magnetic flux that passes through the heat generating roller 44 also gradually increases, so that the magnetic flux passing through the conductive member 45 increases and the induced current generated in the conductive member 45 increases. . As a result, the rate of temperature rise of the heating roller gradually becomes slower from around 140 degrees, and the temperature stabilizes near 190 degrees.

FIG. 9 shows the temperature rise time of the heat generating roller 44,
The horizontal axis represents the temperature rise time, and the vertical axis represents the temperature of the heat generating roller. In FIG. 9, the curve A represents the heating time when the arc portion 45a of the conductive member 45 and the exciting coil 23 are in opposite phases, as described above, and the temperature gradually rises after about 140 degrees. The speed slows down and is stable around 190 degrees.

Here, the conductive member 45 is formed as shown in FIG.
When the arc portion 45a having a substantially constant distance from the heat generating roller 44 is fixed at a position where it does not face the exciting coil 23 and the exciting coil 23 is energized, when the temperature of the heat generating roller 44 is low, the magnetic flux is indicated by arrows D and D'in the figure. Even if the magnetic flux penetrates through the heat generating roller 44 and the magnetic permeability decreases as the temperature rises, the distance from the arc portion 45a of the conductive member 45 is long, that is, outside the magnetic field range of the exciting coil 23. Therefore, there is almost no magnetic flux passing through the conductive member 45 as indicated by arrows E and E ′ in the figure, so that almost no induced current flows in the heating roller 44, and the temperature rising rate hardly changes. A curve B in FIG. 9 shows a case where the circular arc portion 45a of the conductive member 45 does not face the exciting coil 23. In the present embodiment, the heat generating roller 4 takes about 14 seconds.
4 climbed to 190 degrees and continued to climb thereafter.

Here, when the energization is started from the state where the energizing coil 23 is not energized (during the non-normal operation), the conductive member 45 is made to face the second position, that is, the circular arc portion 45a is opposed to the exciting coil 23. Without heat, the heat roller 4
4 is near the Curie temperature. In this case, when the temperature approaches 190 degrees (during normal operation), the arc portion 45a of the conductive member 45 is raised to the first position, that is, the position facing the exciting coil 23. When the warm time was shown, it became like the curve C of FIG. In the present embodiment, with the above setting, the heat generating roller was raised to 190 degrees in about 15 seconds, and after a slight overshoot, stable temperature control could be realized at about 190 degrees.

As described above, the arc portion 45a of the conductive member 45 is formed.
The warm-up (non-normal operation) is started at a phase (second position) where the heat roller 4 is not opposed to the exciting coil 23.
When the surface temperature of 4 rises to near the Curie temperature (during normal operation), the arc portion 45a of the conductive member 45 is switched to the phase (first position) facing the exciting coil 23,
The temperature rise time is almost the same as when the self temperature control is not performed,
The effect of self-temperature control such that the steady temperature is stable can be obtained.

The fixing device having the above-described structure is shown in FIG.
Material 15 to which a toner image has been transferred by the image forming apparatus of
As shown in FIG. 1, the surface on which the toner 35 is present is made to protrude from the direction of the arrow F to fix the toner on the recording material 15.

According to the above embodiment, since the heat-generating roller itself has the self-temperature control characteristic, the heat-generating portion does not become abnormally high temperature, and the temperature control of the temperature close to the fixing temperature is automatically performed. It can be done. The conductive member has almost the same length as the exciting width of the exciting coil, and acts on the partial temperature difference in the depth direction of FIG. As a result, even if a narrow recording material is continuously passed, the portion where the recording material does not pass does not become abnormally hot, and hot offset does not occur thereafter even when the recording material is wide. .

Further, since the material and thickness of the heat generating roller can be set independently of the belt, the optimum material and thickness for controlling the self temperature can be selected, and the heat capacity of the belt is also different from that. Since it can be set, the optimum value can be selected.

On the other hand, since the fixing roller itself has a low thermal conductivity and is made of foam, the presence of internal voids makes it difficult for heat generated by the belt to escape and is efficient.

In this embodiment, in order to achieve the object of shortening the warm-up time, the heat capacity of the belt is set as small as possible, and the thickness of the heat generating roller is made small so that the heat capacity is also set small. When the thickness of the heat-generating roller is reduced to reach the same level as the heat capacity of the belt in order to speed up the start-up, the amount of heat stored in the heat-generating roller becomes very small. Even if heat is stored in the heat generating roller, the temperature usually immediately drops. That is, in the method of heating the heating roller once by applying heat to the heating roller at a place other than the contact portion with the belt, it is necessary to heat the heating roller itself to a considerably high temperature in order to give a sufficient amount of heat to the belt. There is. Furthermore, the belt cooled when passing through the nip portion may be cooled to a temperature greatly different depending on the temperature of the pressure roller and the fixing roller and the temperature state of the recording material at that time. Therefore, in the above method, the temperature of the heat-generating roller must be set to a temperature greatly different accordingly.

In the present embodiment, however, heat is generated in the portion of the heat generating roller that is in contact with the belt, so that the heat required for the belt is immediately transmitted, and it is not necessary to raise the temperature of the heat generating roller more than necessary. In addition, since there is almost no heat generation at the position where the heating roller passes the contact portion with the belt, the temperature of this portion is controlled to be kept constant, so that the belt temperature plunging into the nip portion is always kept constant. Therefore, stable fixing can be performed regardless of the temperature condition of the pressure roller and the like.

In the present embodiment, since the heat capacity of the belt is small, the recording material begins to take heat when the belt starts to come into contact with the recording material, and when the belt passes through the nip portion and leaves, the considerable temperature decreases, and the toner Will not be hot offset.

Although the belt is made of resin in this embodiment,
If a metal is used instead, a part of heat is generated in this belt, but if the thickness is extremely small, most of the magnetic flux described above penetrates this and reaches the heat generating roller. Can perform various actions.

Further, in the present embodiment, the heat generating portion is inside the belt, but the exciting coil and the core material can be installed outside the belt. Can be kept stable.

Further, in this embodiment, the heat generating roller 44 and the conductive roller 45 are thermally separated from each other, but the self-temperature control characteristic can be similarly obtained even if they are closely contacted with each other.
In this case, the heat capacity of the heat-generating roller portion is slightly large, and the warm-up time is correspondingly long.

Next, the image heating apparatus of the second embodiment will be described with reference to FIG.

In the second embodiment, the parts having the same structures and the same functions as those of the fixing device of the first embodiment are designated by the same reference numerals, and the detailed description thereof will be omitted.

Reference numeral 44 is a heat-generating roller made of iron having a thickness of 0.4 mm.
nickel. It is made of a magnetic material made of a chromium alloy, and is manufactured with its Curie point adjusted to 250 degrees. The diameter of the heat generating roller 44 is 30 mm, and the surface of the heat generating roller 44 is covered with a releasing layer of fluororesin having a thickness of 15 μm in order to impart releasability. PTF as the release layer on the surface
Resins or rubbers having good releasability such as E, PFE, FEP, silicone rubber and fluororubber may be coated alone or in combination. As a fixing device for monochrome images, it is only necessary to ensure releasability, but when it is used as a fixing device for color images, it is desirable to impart elasticity. In that case, it is necessary to form a slightly thick rubber layer. There is.

Reference numeral 23 denotes an exciting coil as an exciting means, which uses a litz wire formed by bundling thin wires, and has a sectional shape formed to cover the heat generating roller 44 as shown in FIG. A core material 24 made of ferrite is installed. Similar to the first embodiment, the exciting coil 23 is formed along the central core member 24 over substantially the entire length of the heat generating roller 24, and the rear core member 24 is present only in a part and prevents the magnetic flux leaking to the outside. It is configured to supplement. Similarly, an alternating current of 25 to 30 KHz is applied to the exciting coil 23 from the exciting circuit 25.

Inside the heat generating roller 44, the heat generating roller 44 is provided.
And a conductive member 45 made of aluminum, which has a semicircular cross section having an arc portion 45a with a gap of 0.5 mm and has a higher conductivity than the heat generating roller 44, is provided. The conductive member 45 is rotatably supported by a shaft 46, the phase with the exciting coil 23 is fixed at a predetermined position, and the phase can be switched by a switching unit 53.

In FIG. 11, the length in the width direction of the conductive member 45 corresponds to the position where the non-recording material 15 passes, and is approximately the same length from the outside of the minimum width of the recording material 15 as the center core material 24. Over the length, it is formed at both ends of the shaft 46.

Both ends of the heat generating roller 44 and the conductive member 45 are supported by flanges 47 and 48 made of a heat-resistant resin having a small heat conductivity such as bakelite, and the heat generated by the heat generating roller 44 is difficult to be transmitted to the conductive member 45. Has become.

The heat generating roller 44 is rotatably supported by a bearing 51, and is rotationally driven by a driving means (not shown) of the apparatus main body.

Referring again to FIG. 10, the pressure roller 49 is made of low hardness (JIS A 30 degrees) silicone rubber, and is pressed against the heat roller 44 to form a nip.
The pressure roller 49 was rotatably supported around the metal shaft 50 by being driven. The pressure roller 44 may be made of other heat resistant resin such as fluororubber or fluororesin or rubber, or may be made of foam. Further, on the surface of the pressure roller 49, in order to improve wear resistance and releasability, PFA, PTF
A resin such as E or FEP or rubber may be coated alone or in combination.

Reference numeral 52 denotes a temperature detecting sensor, which is a heat generating roller 44.
The heat generating roller 44 is disposed substantially at the center in the axial direction so as to detect the surface temperature thereof. This temperature sensor 52
The detection output of is input to the excitation circuit 23 and is configured to control the electric power supplied to the excitation coil.

In this embodiment as well, as in the first embodiment, the heat generating portion is constructed so that this portion has a self-temperature control characteristic. The operation will be described below.

In the conductive member 45, the heat generating roller 44 is rotated by a driving means (not shown) while the arc portion 45a is fixed in a phase (second position) that does not face the exciting coil 23. When the exciting coil 23 is driven with an alternating current of 30 kHz to generate heat (non-normal operation), the heating portion 44a of the heating roller 44 facing the exciting coil 23 is at a temperature below the Curie point in FIG. The magnetic flux generated by the exciting coil 23 almost penetrates the heating roller 44 as shown by arrows D and D ′ in the figure, and heats the heating roller 44. In this case, the conductive member 45 is located far from the exciting coil 23, is almost outside the magnetic field, and regardless of the shape of the conductive member 45 in the width direction, most of the magnetic flux penetrates the heating roller 44. To do. When the temperature of the heat generating roller 44 is increased and the output of the temperature sensor 52 detects that the temperature is increased to a predetermined temperature (190 degrees in the case of this embodiment), the exciting circuit 25 thereafter determines the surface temperature of the heat generating roller 44. The output is controlled so as to be maintained at a predetermined temperature, and the surface temperature of the heat generating roller 44 is maintained at a predetermined temperature. Until the temperature sensor 52 detects a predetermined temperature, even if the temperature of the heat generating roller rises, the magnetic flux is far from the arc portion 45a of the conductive member 45 and the exciting coil 23 as shown in FIG. The magnetic field generated by the coil 23 is almost outside the range, and there is almost no magnetic flux passing through the conductive member 45 as indicated by arrows E and E ′ in the figure. Therefore, almost no eddy current flows in the heat generating roller 44, and the temperature rising rate also changes. The heating roller 44 is heated almost uniformly over the excitation width. When the temperature sensor 52 detects a predetermined temperature, a normal operation state is set, and the arc portion 45a of the conductive member 45 is moved to a position (first position) facing the exciting coil 23 by the switching unit 53. Can be switched.

The fixing device having the above-described structure is shown in FIG.
The recording material 15 having the minimum width, to which the toner image is transferred by the image forming apparatus, is continuously projected in the direction of arrow F with the surface having the toner 35 facing upward as shown in FIG. The upper toner was fixed.

The surface temperature of the heating roller 44 at the portion where the recording material 15 has passed is lowered, the temperature is detected by the temperature sensor 52, and the exciting circuit 25 supplies electric power to recover the lowered amount. Then, a strong magnetic flux flows to both end portions of the heat generating roller 44 other than the portion through which the recording material 15 passes, but most of the magnetic flux is the non-recording material as indicated by arrows E and E'in FIG. 15 radiates to the conductive member 45 formed outside the position corresponding to 15, and the induced current flows overwhelmingly in the conductive member 45 having high conductivity, and if the current is limited to a constant value, heat is not generated. The temperature was remarkably reduced, the temperature was stable, and in this example, it was almost stable at 220 degrees.

The temperature of the portion of the heat generating roller 44 passing through the recording material 15 is lowered, and the magnetic permeability is larger than that at both ends, and since it does not face the conductive member 45, the arrows D and D'in FIG. As described above, the magnetic flux almost penetrates the heat generating roller 44, the induced current flows in the heat generating roller 44, the surface temperature is recovered, and the output of the temperature sensor 52 causes a predetermined temperature (190 degrees in the case of this embodiment). When it is detected that the heat generation roller 44 has been recovered, the exciting circuit 25 thereafter controls its output so as to maintain the surface temperature of the heat generating roller 44 at a predetermined temperature, and the surface temperature of the heat generating roller 44 is maintained at the predetermined temperature.

In this embodiment, the warm-up is started (non-normal operation) in a phase (second position) where the arc portion of the conductive member is not opposed to the exciting coil, and the temperature of the heat generating roller reaches a predetermined temperature. Is detected and the conductive member is switched to the phase (first position) facing the exciting coil (during normal operation), the temperature rise time is almost the same as when self-temperature control is not performed, and damage due to abnormal high temperature Safety is secured.

In this embodiment, since the conductive member is formed from the outer side of the minimum width of the recording material to the excitation range of the heat generating roller, almost all the magnetic flux is constantly generated on the heat generating roller in the portion where the recording material passes. Since more magnetic flux passes through the heating roller, more magnetic flux passes through the heating roller than the case where a conductive member is formed over the entire width, and when the recording material passes continuously, the recording material passes through. Even if the speed is high, it is possible to recover the temperature of the heat generation roller, and it is possible to cope with a higher speed range.

In this embodiment, the heat generating roller itself has a self-temperature control characteristic and acts on the partial temperature difference in the depth direction of FIG. 10 to cause a partial difference in the heat generating action. Even if you continuously pass through a narrow recording material, the area where the recording material does not pass does not become abnormally hot, and the heat capacity of the heating roller is made small, so that the power supply was stopped or reduced. In this case, the temperature of the heat-generating roller drops quickly, and hot offset does not occur even after passing through a wide recording material.

Also, since there is almost no heat generation at the position where the exciting coil of the heat generating roller passes through the opposing portion, the temperature of this heat generating roller is controlled so as to be kept constant, so that the temperature of the heat generating roller entering the nip portion can be controlled. It can be kept constant, and stable fixing can be performed regardless of the temperature state of the pressure roller or the like.

Further, in the present embodiment, the exciting coil and the core material are installed outside the heat generating roller, and the exciting coil and the like are hardly affected by the temperature of the heat generating part and the temperature is not easily raised, and the amount of heat generated is kept stable. You can

In the first and second embodiments, the conductive member is provided inside the heat generating roller and the exciting coil is provided outside. However, the exciting coil may be provided inside the heating roller and the conductive member may be provided outside. It is possible to obtain a similar effect.

Although aluminum is used as the conductive member in the first and second embodiments, other highly conductive metals such as copper can be used. Further, the heat generating roller can also obtain the same effect with other alloys which can set the Curie temperature.

Further, in the first and second embodiments, the temperature of the heat generating roller is set as the object for detecting the timing of switching the position of the conductive member. However, the change in magnetic permeability, the change in current, the amount of electric power, etc. are detected. However, there is no problem, and the most suitable target in the configuration may be adopted.

Further, in the first and second embodiments, the conductive member has a substantially semicircular cross section having arc portions whose distances from the inner surface of the heat generating roller are substantially equal to each other. It is possible to obtain the same effect with the difference of.

Further, in the first and second embodiments, the position (phase) of the conductive member and the exciting coil is switched between facing and non-facing depending on the first position and the second position. The same effect can be obtained by switching between the case of moving away from and the case of moving away from.

In the first and second embodiments, the entire conductive member having a substantially semicircular cross section is made of a highly conductive metal. However, conductivity is required only in the portion facing the heat generating roller and being in contact with or separated from it. The same effect can be obtained even if the other portions are made of other materials, such as synthetic resin.

Although the first and second embodiments describe the image heating apparatus for a monochrome image, the surface of the belt or the surface of the roller may be changed to sufficiently serve as an image heating apparatus for a color image. It can be used.

[0086]

As described above, in the present invention, the heat capacities of the belt, which is the object to be heated, and the heat generating roller, which is the heat generating member, can be set to be extremely small, so that it is possible to warm up quickly and to reach the fixing temperature. The up time can be extremely small. Further, even if the heat capacity of the heat generating roller is set small, the temperature of the heat generating roller can be set low due to the heat generated at the belt contact portion.

By setting the thickness of the heat-generating roller to be larger than the skin depth, uniform heat generation can be achieved.

Further, by the self-temperature control, stable temperature control is achieved, and even if the recording material having a narrow width is continuously passed, a portion where the recording material does not pass is not excessively heated, and hot offset occurs or heat is generated. The quantity does not become unstable and damage to the exciting coil due to heat can be prevented.

Regarding the increase in warm-up time due to the decrease in the amount of heat generated near the Curie point for self-temperature control, the phase of the conductive member is switched to cause an induction current to flow through the conductive member, and the time is concentrated on the heat generating roller. By switching to the case where it is carried out, it is possible to obtain the warm-up time which is almost the same as the case where the self-temperature control is not carried out and the work is suppressed to the minimum.

Further, since the exciting means and the core material can be installed outside the belt, a stable heat generation amount can be obtained without exposing the exciting means and the core material to high temperature.

[Brief description of drawings]

FIG. 1 is a sectional view of an image heating apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a belt used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 3 is a front view showing an exciting coil and a core member used in the image heating apparatus according to the first and second embodiments of the present invention.

FIG. 4 is a sectional view of a heat roller used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 5 is a diagram for explaining the flow of magnetic flux passing through the heat roller used in the image heating apparatus of the first and second embodiments of the present invention when the conductive member is in the second position and in the low temperature state.

FIG. 6 is a diagram illustrating a flow of magnetic flux passing through a heat generating roller used in the image heating apparatus of the first and second embodiments of the present invention when the conductive member is at the second position and in a high temperature state.

FIG. 7 shows the first aspect of the present invention when the conductive member is in the first position.
And a diagram for explaining the flow of magnetic flux passing through the heat generating roller used in the image heating apparatus of the second embodiment.

FIG. 8 is a diagram showing a relationship between magnetic permeability and temperature of a heat generating roller used in the image heating apparatus according to the first embodiment of the present invention.

FIG. 9 is a diagram showing the temperature rise time of the heat roller used in the first embodiment of the present invention.

FIG. 10 is a sectional view of an image heating apparatus according to a second embodiment of the present invention.

FIG. 11 is a cross-sectional view of a heat generating roller of an image heating apparatus used in the second embodiment of the present invention.

FIG. 12 is a sectional view of an image forming apparatus using the image heating apparatus according to the first and second embodiments of the present invention.

FIG. 13 is a sectional view of an image heating apparatus of a first conventional example.

FIG. 14 is a sectional view of an image heating apparatus of a second conventional example.

[Explanation of symbols]

1 photosensitive drum 16 Fixing device 20 belts 23 Excitation coil 24 core material 43 fixing roller 44 Heat roller 45 Conductive member 49 Pressure roller 53 switching means 15 Recording material

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideki Tatematsu 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP 10-74011 (JP, A) JP 10- 74009 (JP, A) JP-A-9-197869 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20 H05B 6/00-6/44

Claims (35)

(57) [Claims] 1. A belt, a pressurizing unit that presses against the belt to form a nip on the surface side of the belt, a heat-generating roller that has magnetic permeability and movably suspends the belt, and a conductive member. An exciting means for exciting the heat roller, the conductive member being in a range of a magnetic field of the exciting means, the first position being different from the first position. An image heating apparatus, which is located at a second position outside the range of the magnetic field of the exciting means. 2. A heat-generating roller having magnetic permeability, a pressure member that presses against the heat-generating roller to form a nip, a conductive member, and an exciting unit that excites the heat-generating roller. The elastic member has a first position within the magnetic field of the exciting means and a second position different from the first position and outside the magnetic field of the exciting means. An image heating device characterized by the above. 3. A belt, a pressurizing unit that presses against the belt to form a nip on the surface side of the belt, a heat-generating roller having magnetic permeability and suspending the belt so as to be movable, and inside the heat-generating roller. And an exciting member for exciting the heat roller from the outside through the belt, the conductive member being installed in the arc member. The image heating apparatus has a first position facing the exciting means and a second position different from the first position in which the arc portion does not face the exciting means. 4. A heat-generating roller having magnetic permeability, a pressure member that presses against the heat-generating roller to form a nip, and a conductive member that is disposed inside the heat-generating roller and has an arc portion and has a substantially semicircular cross section. And a magnetizing means for exciting the heat generating roller from the outside of the heat generating roller, wherein the conductive member has a first position where the arcuate portion faces the magnetizing means, and the first position. And a second position in which the arc portion does not face the excitation means, which is different from the above. 5. The first position is a position where the conductive member is within the range of the magnetic field of the exciting means.
The image heating device according to any one of 3 to 4. 6. The second position is a position where the conductive member is outside the range of the magnetic field of the exciting means.
The image heating device according to any one of 3 to 4. 7. The image heating apparatus according to claim 1, wherein the conductive member is in the first position during a normal operation of outputting an image on a recording material. 8. The conductive member is in the second position during an abnormal operation, which is a warming-up state from when the energization of the exciting means is started to when the normal operation becomes possible. Item 7. An image heating device according to any one of items 1 to 4 and 6. 9. The conductive member is controlled so as to switch from the second position to the first position when the temperature of the heat generating roller rises to near the Curie temperature of the heat generating roller. The image heating device according to any one of 1 to 4. 10. The image heating apparatus according to claim 1, wherein the conductive member is arranged inside the heat roller and the exciting means is arranged outside the heat roller. 11. The image heating apparatus according to claim 3, wherein the arcuate portions of the conductive member are substantially equal in distance from the inner surface of the heat roller. 12. The image heating apparatus according to claim 1, wherein the length of the conductive member in the width direction is substantially equal to or less than the exciting width of the heat generating roller. 13. The conductive member is formed at a position corresponding to the recording material, outside the minimum width of the recording material, and substantially equal to or less than the excitation range of the heat roller. The image heating apparatus according to claim 1. 14. A belt, a pressurizing unit that presses against the belt to form a nip on the surface side of the belt, a heat-generating roller that has magnetic permeability and movably suspends the belt, and the heat-generating roller. Exciting means for exciting, and a member for allowing the magnetic flux generated from the exciting means to pass through the heat-generating roller, provided so as to take different positions, and the heat-generating roller for transmitting the magnetic flux. When the member is at the second position far from the exciting means and is out of the range of the magnetic field of the exciting means, the magnetic flux generated from the exciting means penetrates the inside of the heat generating roller to cause the heat generating roller to move. When the first heat generating state in which heat is generated and the member for transmitting the magnetic flux are at the first position close to the exciting means and are within the range of the magnetic field of the exciting means, the exciting means. It passes through the heating roller by a member for a portion of al generated magnetic flux is transmitted through the magnetic flux, and a second heating state the heating roller is heated by the remaining magnetic flux passing through the heating roller in,
An image heating device characterized by the following. 15. A heat-generating roller having magnetic permeability, a pressure member that presses against the heat-generating roller to form a nip, and an exciting means that excites the heat-generating roller are provided at different positions. A member for transmitting the magnetic flux generated by the means to the heat generating roller, wherein the heat generating roller has a member for transmitting the magnetic flux at a second position far from the exciting means, A first heat generation state in which the heat generating roller generates heat when the magnetic flux generated from the magnetizing means penetrates the inside of the heat generating roller when it is outside the range of the magnetic field of the magnetizing means, and a member for transmitting the magnetic flux. At a first position close to the exciting means and within the range of the magnetic field of the exciting means, a part of the magnetic flux generated from the exciting means acts as a member for transmitting the magnetic flux. The second heating state in which the heat generating roller generates heat when the remaining magnetic flux passes through the heat generating roller and the remaining magnetic flux penetrates the heat generating roller. 16. The image heating apparatus according to claim 14, wherein the member for transmitting the magnetic flux is in the first position during a normal operation for outputting an image on a recording material. apparatus. 17. The member for transmitting a magnetic flux is in the second position during a non-normal operation which is a warming-up state from when energization of the exciting means is started until when normal operation is possible. The image heating device according to any one of claims 14 to 15, characterized in that the image heating device comprises: 18. The member for transmitting magnetic flux is controlled so as to switch from the second position to the first position when the temperature of the heat generating roller rises to near the Curie temperature of the heat generating roller. Claims 14 to 15
The image heating device according to any one of 1. 19. The image heating apparatus according to claim 14, wherein the length of the member for transmitting the magnetic flux in the width direction is substantially equal to or less than the exciting width of the heat generating roller. 20. The member for transmitting magnetic flux is formed at a position corresponding to the recording material, outside the minimum width of the recording material, and substantially equal to or less than the excitation range of the heat roller. The image heating device according to any one of claims 14 to 15, wherein: 21. The image heating apparatus according to claim 14, wherein the member for transmitting the magnetic flux is a conductive member disposed inside the heat generating roller. 22. The image heating apparatus according to claim 21, wherein the conductive member is arranged inside the heat generating roller, and the exciting means is arranged outside the heat generating roller. 23. The conductive member has a substantially semicircular cross section having an arcuate portion that is substantially equal in distance from the inner surface of the heat generating roller, and the arcuate portion faces the exciting means at the first position,
22. The image heating apparatus according to claim 21, wherein the arcuate portion does not face the exciting means in the second position. 24. A belt, a pressurizing unit that presses against the belt to form a nip on the surface side of the belt, and a heat-generating roller that has magnetic permeability and suspends the belt so as to be movable. And an exciting means for exciting the heat-generating roller via the belt, and during the normal operation of outputting an image to a recording material, the conductive member is provided with the exciting means. The first position within the range of the magnetic field, and during the non-normal operation until the normal operation becomes possible, the conductive member has the second position outside the range of the magnetic field of the exciting means. An image heating device characterized by: 25. A heat-generating roller having magnetic permeability, a pressure member that presses against the heat-generating roller to form a nip, a conductive member provided at different positions, and an excitation that excites the heat-generating roller. In a normal operation of outputting an image to a recording material, the conductive member takes a first position within the range of the magnetic field of the exciting means, and the normal operation is possible. The image heating device is characterized in that, during the non-normal operation up to, the conductive member assumes a second position outside the range of the magnetic field of the exciting means. 26. A belt, a pressurizing unit that presses against the belt to form a nip on the surface side of the belt, and a heat-generating roller that has magnetic permeability and suspends the belt so as to be movable. A conductive member provided as described above, and an exciting unit that excites the heat roller via the belt, wherein the conductive member has a first position within a range of a magnetic field of the exciting unit. A second out of range of the magnetic field of the excitation means
When the temperature of the heat generating roller rises to near the Curie temperature of the heat generating roller, the conductive member is controlled so as to switch from the second position to the first position. An image heating device characterized by the following. 27. A heat-generating roller having magnetic permeability, a pressure member that presses against the heat-generating roller to form a nip, a conductive member that is provided at different positions, and an excitation that excites the heat-generating roller. A first position within the range of the magnetic field of the exciting means, and a second position outside the range of the magnetic field of the exciting means.
When the temperature of the heat generating roller rises to near the Curie temperature of the heat generating roller, the conductive member is controlled so as to switch from the second position to the first position. An image heating device characterized by the following. 28. When the temperature of the heat generating roller rises to near the Curie temperature of the heat generating roller, the conductive member is provided with the second member.
26. The image heating apparatus according to claim 24, wherein the image heating apparatus is controlled so as to switch from the position of 1 to the first position. 29. The image heating apparatus according to claim 26, wherein the conductive member is in the first position during a normal operation of outputting an image on a recording material. 30. The conductive member is in the second position during the non-normal operation which is a warming-up state from when the excitation means is energized until when the normal operation is possible. Item 28. An image heating device according to any one of items 26 to 27. 31. The image heating apparatus according to claim 24, wherein the conductive member is arranged inside the heat generating roller, and the exciting means is arranged outside the heat generating roller. 32. The conductive member has a substantially semicircular cross section having an arc portion having a substantially equal distance from the inner surface of the heat roller, and the arc portion faces the exciting means at the first position,
28. The image heating apparatus according to claim 24, wherein the arc portion does not face the exciting means in the second position. 33. An image heating apparatus according to claim 24, wherein the length of the conductive member in the width direction is substantially equal to or less than the exciting width of the heat generating roller. 34. The conductive member is formed at a position corresponding to the recording material, outside the minimum width of the recording material, and substantially equal to or less than the excitation range of the heat roller. An image heating apparatus according to any one of claims 24 to 27. 35. An image forming apparatus comprising: an image forming means for forming and carrying an unfixed image on a recording material; and a heat fixing device for thermally fixing the unfixed image on the recording material, wherein the heat fixing device is claimed. An image forming apparatus, which is the image heating apparatus according to any one of items 1 to 34.