JP2000268952A - Heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently heat a toner image and prevent use of a large capacity of alternating magnetic field generating source, and the generation of a leakage magnetic flux in a heating device for heating the toner image on a carrying body having a thin film-like heat generating layer by electromagnetic induction action, and providing an image forming device. SOLUTION: An exciting coil 2 comprising a first coil 2a and a second coil 2b arranged so as to face each other on both sides of a carrying body 1 having a heat generating layer 12 on the inside is installed. The heat generating layer 12 made of a low electric-conductivity material is formed in a thin layer. The exciting coil 2 is pair coil connected by coupling magnetically adding the operations of the first coil 2a and the second coil 2b, and a power source device 3 for applying AC voltage is connected to the exciting coil 2. A magnetic flux being excited with the exciting coil 2 forms a loop passing through the heat generating layer 12, and the heat generating layer 12 is efficiently heated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device for heating an object to be heated carried on a carrier, and an electrophotographic image forming apparatus using the heating device. The present invention relates to a heating device for heating an object to be heated by an electromagnetic induction heating method using a heating layer made of a conductive material, and an image forming apparatus in which the heating device is applied to a toner image transfer fixing device.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine and a printer, a heat fixing device for fixing an unfixed toner image on a recording material has been used. The mainstream of the heat fixing device is, for example, a heat roller system using a halogen lamp. In addition, there is a SURF system in which a belt-shaped heater as a heating source is brought into contact with the inner surface of the endless film to perform fixing.

[0003] The heating device of the heating roller type is basically composed of a rotating roll pair consisting of a heating roll heated by a heat source such as a halogen lamp and adjusted to a predetermined temperature, and a pressure roll pressed against the heating roll. It is. Then, the recording material is introduced into the press-contact nip portion of the two rolls and is nipped and conveyed, so that the unfixed toner image on the recording material is heated and fixed by the heat of the heat roll. Also SUR
In the F system, a belt-shaped heater is brought into contact with the inner surface of an endless film, and the heat is used to heat and fix a toner image on a recording material.

Further, when transferring a toner image from an intermediate transfer member to a recording material, an image forming apparatus is used in which the toner image is heated to simultaneously perform transfer and fixing. The image forming apparatus primarily transfers a toner image on an image carrier to an intermediate transfer member having releasability, and heats and transfers the toner image on the intermediate transfer member.
The toner is melted on the recording material by a pressing means and is fixed simultaneously with the secondary transfer. As the pressurizing / heating means, for example, a heating roll and a pressurizing roll which are pressed through an intermediate transfer body are known. The recording material is separated from the intermediate transfer member by utilizing the releasing effect of the intermediate transfer member. Such an image forming apparatus that simultaneously performs transfer and fixing is disclosed in, for example, JP-A-2-106774, JP-B-64-1027, JP-A-57-163264, and JP-A-50-1.
No. 07936, JP-A-49-78559 and the like.

[0005]

However, the above-mentioned conventional apparatus has the following problems. When a halogen lamp is used as a heating source, a radiant heating method is used, and the efficiency of heat transfer to an object to be heated such as an unfixed toner image is low, and the heat loss is large. Further, since the object to be heated is not directly heated, there is a problem that it takes time to apply a predetermined amount of heat to the object to be heated. When a belt-shaped heater or the like is used, the above problem is solved.However, since the heater itself generates heat by being brought into pressure contact with the object to be heated, and this heat is conducted to the object to be heated, the driving torque is large, It has the disadvantage that it can only be applied to small machines.

As a heating device of an image forming apparatus, there is an intermediate transfer type heating device for simultaneously performing the above-mentioned transfer and fixing. However, a method of applying heat to a heating roll to conduct heat to an intermediate transfer body which is a body to be heated. As a result, the entire intermediate transfer member is heated, so that the heat loss is large.

As a heating means for solving this problem, a heating device of an electromagnetic induction heating system has been proposed. This heating device
An object to be heated is placed on a heating member on which a heating layer made of a conductive material is formed, and an exciting coil is arranged in a non-contact manner with the surface of the object to be heated to apply an alternating magnetic field. An eddy current is generated in the heat generating layer by the alternating magnetic field, and the object to be heated is heated by self-heating of the heat generating layer by electromagnetic induction. A heating device using such an electromagnetic induction heating method,
Since it is a non-contact heating means, there is an advantage that inclusions that impair thermal efficiency are reduced and heat can be directly applied to the object to be heated. In addition, since only a necessary portion of the object to be heated can be heated, the thermal efficiency is high.

However, such an electromagnetic induction type heating device is determined by the problem that the size of the excitation coil of the alternating magnetic field generation source arranged around the heating section becomes large and the heating element arranged near the excitation coil. However, there is a disadvantage that the power factor of the AC circuit to be used is low, and the drive power supply has a large capacity. In addition, when heating is performed by the electromagnetic induction heating method, there is a possibility that a magnetic field leaking from an alternating magnetic field generation source may cause other problems such as heating other metal parts and the like, and adversely affecting the human body. For this reason, it is necessary to sufficiently collect the leakage magnetic flux, and there is a problem that the area around the heating unit becomes large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to efficiently heat a carrier having a heat generating layer that generates heat by electromagnetic induction, and to excite the carrier. An object of the present invention is to provide a heating device that enables a high power factor of an AC circuit including a coil to be set, and prevents an alternating magnetic field generation source in the vicinity of a heat generating portion from being enlarged and generating leakage magnetic flux. Further, by using this heating device, it is possible to reliably transfer and fix the unfixed toner image on the toner image carrying and transporting member to the recording material,
An object of the present invention is to provide an image forming apparatus capable of performing high-speed printing with limited power.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 has a thin heating layer made of a conductive material and moves in a direction parallel to the heating layer. A first excitation coil and a second excitation coil provided at opposite positions on both sides of the carrier;
A power supply device for applying an AC voltage to the first excitation coil and the second excitation coil, wherein the first excitation coil and the second excitation coil are magnetically coupled in a harmonic connection; A heating device is provided in which a magnetic flux excited by these exciting coils is set so as to penetrate the heating layer.

[0011] In such a heating device, the first excitation coil and the second excitation coil provided on both sides of the carrier are magnetically harmonically connected and coupled, so that the magnetic flux generated by these excitation coils is reduced. It easily penetrates through the thin heating layer. As a result, an eddy current is induced in the heat generating layer to generate heat. Then, since the heat generating layer has a thin layer shape, the temperature rises in a short time and is sufficiently heated while passing between the two exciting coils. Further, as described above, when the exciting coils are provided on both sides of the heat generating layer and the magnetic flux penetrates, the volume of the coil (the cross-sectional area of the coil winding × the coil area) is smaller than when the exciting coil is provided only on one side of the heat generating layer. When the winding length is the same, the power factor is improved, and the heating layer can be effectively heated.

In particular, FIG.
As shown in FIG. 1 (a) or FIG. 11 (b), by guiding the magnetic flux in a loop shape so as not to spread on the peripheral surface, more efficient heating becomes possible.

According to a second aspect of the present invention, in the heating apparatus according to the first aspect, the heat generating layer is made of copper, silver, aluminum, or a nonmagnetic material having an electric resistivity equal to or less than these. It is assumed that the thickness of the heat generating layer is 0.1 μm or more and 20 μm or less.

A non-magnetic material having the following resistivity similar to the above-mentioned copper, silver and aluminum includes the above three metals and
Alloys containing these or alloys of metals other than these are included. Aluminum has the largest resistivity among the above three metals (resistivity: 2.66 × 10 ⁻⁸ Ω).
・ Material having a value almost the same as or smaller than m) is applicable.

In such a heating device, the thickness of the heat generating layer is as thin as 0.1 μm to 20 μm, and the heat capacity is small, so that it can be heated to a high temperature in a very short time. Also, it can be cooled rapidly.

It is generally considered that a magnetic material is desirable for the heat generating layer when performing electromagnetic induction heating. However, when the thickness of the heat generating layer is reduced as described above, the electric resistance increases and the eddy current increases. And the effective heating becomes difficult. On the other hand, a material having a lower resistivity than a general magnetic material such as iron or nickel can generate heat more effectively. The present invention has been made by finding such a new fact, and is intended to perform heating and cooling quickly and efficiently with a thin heating layer.

Further, by using a non-magnetic material as the heat generating layer, the skin thickness δ represented by the following equation increases,
The actual heating layer can be made much smaller than this skin thickness. And since the thickness of the heat generating layer is sufficiently smaller than the skin thickness, magnetic flux easily penetrates the heat generating layer, and efficient heating is performed. Skin thickness δ = √ (2 / μσω) = √ (2ρ / μω) = 5
03√ (ρ / fμ _r ) μ: magnetic permeability (H / m) σ: conductivity (1 / Ω · m) ω: angular frequency (= 2πf) (1 / sec) f: frequency (Hz) ρ: Resistance (Ω · m) μ _r : relative magnetic permeability (= μ / μ ₀ ) μ ₀ : magnetic permeability in vacuum (= 4π × 10 ⁻⁷ H / m)

According to a third aspect of the present invention, a toner image formed by attaching toner to a latent image due to a difference in electrostatic potential is carried on an endless peripheral surface, and the peripheral surface moves around. And a second excitation coil provided on the inside and outside of the toner image carrying and conveying member so as to face each other, and the first excitation A power supply device for applying an AC voltage to the coil and the second excitation coil; and a recording medium for transferring the recording medium to the toner at a position downstream of the position where the first and second excitation coils face each other in the circulating direction of the toner image carrier. Pressing means for pressing against the image carrier; the toner image carrier having a thin heating layer made of a conductive material along a peripheral surface; And the second excitation coil is an AC voltage The image forming apparatus is arranged so that the heat generation layer is electromagnetically heated by application of the heat generation layer.

In such an image forming apparatus, since the recording medium is pressed against the toner image carrying and transporting member and the exciting coil constituting the heating device is provided upstream of the position where the toner image is transferred, the endless coil is provided. A sufficient space can be secured both inside and outside of the toner image carrying and transporting body having the peripheral surface, and exciting coils can be provided on both sides of the toner image carrying and carrying body to rapidly heat the toner image carrying and carrying body. Then, by heating the heating layer, the toner carried on the toner image carrier is softened, and when the recording medium is pressed against the pressing means on the downstream side, the softened toner strongly adheres to the recording medium, and the toner is transferred. Fixing is performed simultaneously.

As described above, the heat layer for softening the toner image is reduced by thinning the heat generating layer and rapidly heating immediately before the toner image is pressed against the recording medium, so that efficient transfer and fixing can be performed. Done. Further, since the heat capacity of the toner image carrying / transporting body can be reduced and the toner image carrying / transporting body is an intermediate transfer body and is in close proximity to the photosensitive body, the influence on the photosensitive body is reduced because the toner image carrying / transporting body is cooled rapidly. can do.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the first exciting coil and the second exciting coil are magnetically connected in a harmonically-coupled manner. It is assumed that the magnetic flux excited by the exciting coil is set so as to penetrate the heat generating layer.

In such an image forming apparatus, the first excitation coil and the second excitation coil provided on both sides of the toner image carrying / transporting member are magnetically coupled in a harmony manner.
The magnetic flux generated by these exciting coils easily penetrates the heat generating layer. As a result, an eddy current is induced in the heat generating layer, and the heat generated by the heat generating layer heats the toner image on the toner image carrier. Since the heat generating layer has a thin layer shape, the temperature rises in a short time, and the toner image is sufficiently heated and softened while passing between the two exciting coils. Further, as described above, the excitation coils are provided on both sides of the heat generating layer, and the power factor is improved by penetrating the magnetic flux, so that the heat generating layer can be effectively heated to soften the toner.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the heat generation layer of the toner image carrier has copper, silver, aluminum or an electrical resistivity equal to or less than these. And a non-magnetic material having a thickness of 0.1 μm or more and 2 μm.
It is assumed to be 0 μm or less.

In such an image forming apparatus, since the thickness of the heat generating layer is as thin as 0.1 μm to 20 μm and the heat capacity is small, it can be heated to a high temperature in a very short time and can be cooled rapidly. . In addition, by using a material having a small resistivity, such as copper, silver, or aluminum, as compared with magnetic materials such as iron and nickel, heat can be effectively generated even when the thickness of the heat generating layer is reduced. . Furthermore, since the thickness of the heating layer is sufficiently thinner than the skin thickness, magnetic flux easily penetrates the heating layer,
Efficient heating can be performed.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the third, fourth and fifth aspects, the first excitation coil and the second excitation coil from the power supply device. The AC voltage and the frequency applied to the toner image carrier are set on the toner image carrier, so that the temperature of the toner immediately before being pressed against the recording medium is equal to or higher than the softening point of the toner. By pressing the means,
The range in which the recording medium is pressed against the toner image carrier is set so that the toner temperature is equal to or lower than the softening point at the moment when the recording medium separates from the toner image carrier. I do.

In such an image forming apparatus, by appropriately setting the AC voltage and the frequency to be applied to the first excitation coil and the second excitation coil, the toner image on the toner image carrying and transporting member is rapidly changed. The toner is heated to a temperature equal to or higher than the softening point of the toner. Then, this toner image is pressed against a recording medium at normal temperature at a portion facing the pressing means. If the toner temperature at the moment when the toner comes into contact with the recording medium is lower than the toner softening point temperature, poor adhesion occurs at the interface between the toner and the recording medium due to insufficient adhesive force. Due to the heating, the melted toner penetrates and adheres between the fibers of the recording medium. Further, when the toner image is pressed against the recording medium at normal temperature, the temperature of the toner drops rapidly, and the toner temperature becomes lower than the softening point when the recording medium is separated from the toner image carrying carrier. Since the toner has a low fluidity, the entire amount of the toner adheres to the recording medium as a unit. For this reason, when the recording medium is separated from the toner image carrier, the toner is cut off, and a part of the toner remains on the toner image carrier, so-called offset is prevented. Done.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a heating device according to a first embodiment of the present invention. The heating device includes a cylindrical transport body 1 supported so as to be able to move around, and a first coil 2a and a second coil 2b provided on both sides of the transport body 1 so as to face each other. A main part is constituted by the exciting coil 2 and a power supply device 3 for applying an AC voltage to the exciting coil 2.

The carrier 1 has a thin heat-generating layer 12 which generates heat by electromagnetic induction on a peripheral surface of a cylindrical base material 11 having high heat resistance, and a surface layer 13 thereon. .
The heat generating layer 12 is made of an electric conductor material having a thickness of 10 mm to 0.1 μm and a specific resistance of 10 ⁻¹⁰ to 10 ⁻⁵ Ω · m, and generates Joule heat due to eddy current loss. This layer, for example, as a ferromagnetic or diamagnetic material,
Metals, metal compounds, organic conductors and the like can be used, and more specifically, iron, nickel, cobalt, copper,
Silver, aluminum, or a compound thereof can be selected. Copper, silver,
A material having a low electric resistivity such as aluminum is preferable, and particularly, copper is optimal, and therefore, this embodiment is employed. The thickness of the heat generating layer 12 is preferably as thin as possible, and particularly preferably 0.1 μm to 20 μm.

The excitation coil 2 is composed of a first coil 2a disposed outside the carrier 1 and a second coil 2b disposed inside, and these are magnetically coupled with each other. It is a pair coil. In this case, the magnetic flux excited by these exciting coils 2 penetrates the heat generating layer 12 of the carrier 1.

Further, the first coil 2a and the second coil 2
Ferromagnetic bodies 14a and 14b are provided around b, respectively. The ferromagnetic materials 14a and 14b have high inductance to obtain excellent heating efficiency,
This is for converging the leakage magnetic flux. As the ferromagnetic bodies 14a and 14b, those having extremely small hysteresis loss and eddy current loss such as soft ferrite are used.

The first coil 2a and the second coil 2b
The excitation coil 2 is driven by a single power supply device 3, and a high-frequency AC voltage of 20 kHz to 100 kHz is applied from the power supply device 3. The inductance of the exciting coil 2 is the inductance component of the first coil 2a and the inductance component of the second coil 2a.
Is determined by changing the degree of magnetic coupling with the inductance component of the coil 2b. The degree of magnetic coupling is determined by the distance between the heating layer 12 and the exciting coil and the magnetic field generated by each coil.

The frequency of the AC voltage applied to the exciting coil 2 can be determined by the thickness, the magnetic permeability and the specific resistance of the heat generating layer 12. In this case, if the magnetic flux interlinks perpendicularly to the heat generating layer 12, the eddy current loss increases. For example, when the thickness of the heating layer 12 is a thin film having a thickness of about 50 μm to 0.1 μm, the frequency of the AC voltage is set to a high frequency of 10 kHz or more, and the magnetic flux generated by the exciting coil 2 is vertically linked to the heating layer.

In the above-described heating device, when an AC voltage is applied from the power supply device 3 to the first coil 2a and the second coil 2b which are magnetically coupled in a harmonic connection, the excitation coil 2 The magnetic flux penetrates through the heat generating layer 12 as shown in FIG. An eddy current is generated in the heat generating layer 12 perpendicular to the magnetic flux, and the heat generating layer 12 generates heat by the eddy current and the specific resistance of the heat generating layer. This heating layer 12
Is a thin film, so the temperature rises in a short time,
The carrier 1 is sufficiently heated while passing through the facing portion between the first coil 2a and the second coil 2b.

Next, the basis for selecting the material and thickness of the heat generating layer in the above-described heating device will be described. As described above, the skin thickness δ is the frequency f (Hz), the resistivity ρ
(Ω · m) and δ = 503√ (ρ / fμ _r ) by the relative magnetic permeability μ _r .

[0035] As the material of the heat generating layer, for example, copper, nickel, iron, silver, the resistivity of aluminum ρ and (Ω · m) for relative permeability mu _r is shown as Table 1.

[Table 1]

Further, the skin thickness δ is calculated by changing the frequency f in several steps, as shown in Tables 2 to 6.

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

[0041] From these tables, copper, silver, resistivity such as aluminum ρ is small, by using a material having a high relative magnetic permeability mu _r, the skin depth δ becomes large. Therefore,
By setting the thickness of the heat generating layer sufficiently smaller than the skin thickness δ, the magnetic flux easily penetrates the heat generating layer, and efficient heating is performed. The thickness of the heat generating layer of this embodiment is 0.1 μm.
m to 20 μm, and has a small heat capacity, so that it can be heated to a high temperature in a very short time.

It is generally considered that a magnetic material is desirable for the heating layer when performing electromagnetic induction heating. However, when the thickness of the heating layer is reduced as described above, the electric resistance increases and the eddy current increases. And the effective heating becomes difficult. On the other hand, materials such as copper, silver, and aluminum having a lower resistivity than magnetic materials such as iron and nickel can generate heat more effectively.

Next, the heating device of the present embodiment in which the excitation coil is connected to the outside and inside with the heating layer interposed therebetween, and the conventional heating device in which the excitation coil is disposed only on one of the outside of the heating layer. The result of an experiment for comparison will be described.
In this experiment, copper having a thickness of 2 μm is used as the heating layer.
The distance between the heating layer and the exciting coil and the resistance component of the exciting coil are made equal in both devices of the prior art and the present embodiment, and the heating state is set so that similar conditions are obtained in both devices. The power factor is calculated from the phase difference between the current flowing through the exciting coil and the voltage, and the size of the exciting coil is compared with the outer coil volume. In addition, for both devices, a ferromagnetic material is provided around the exciting coil to prepare conditions for collecting the magnetic flux, and then the average value of the magnetic flux density leaked to the surrounding portion of the exciting coil is measured and compared. Table 7 shows the results.

[0044]

[Table 7]

As shown in Table 7, the power factor of the conventional heating apparatus is about 0.35, whereas the power factor of the heating apparatus of the present embodiment is as high as about 0.85, and the entire coil volume is almost the same. It can be seen that the power factor is improved even in the case of. Therefore, it is possible to reduce the capacity and cost of the power supply device that drives the excitation coil. In addition, it can be seen that the heating device of the present embodiment can significantly reduce the leakage magnetic flux as compared with the conventional heating device. For this reason, it is possible to prevent the device for collecting the leakage magnetic flux from being enlarged.

FIG. 2 is a schematic diagram showing a heating device according to a second embodiment of the present invention. This heating device is different from the heating device shown in FIG. 1 in that a cylindrical carrier 1 is replaced by a carrier 21 made of an endless belt-shaped member.
It has. The transport body 21 has a thin conductive layer 32 that generates heat by electromagnetic induction on a peripheral surface of an endless sheet base 31 having high heat resistance, and a surface layer 33 thereon. Then, by means of a driving means (not shown), it is made to move around in the direction of the arrow shown in FIG. The heating device includes an excitation coil 22 including a first coil 22a and a second coil 22b, a power supply device 23, and ferromagnetic materials 34a and 34b, similarly to the device illustrated in FIG. These components are the same as those shown in FIG.

The heating layer 32 has a thickness of, for example, 20
Silver having three types of μm, 10 μm, and 2 μm is used. The AC voltage applied to the exciting coil 22 includes
A high frequency of 20 kHz to 100 kHz is used.

In such a heating device, the first coil 22a and the second coil 22b are arranged on the outside and inside with the heat generating layer 32 of the carrier 21 therebetween, and these are magnetically connected and connected. Therefore, the magnetic flux generated by these exciting coils passes through the heating layer 32, and the heating layer is rapidly heated by the eddy current. When three types of heat generating layers having different thicknesses were used as described above, good heat generating effects could be obtained in all cases.

FIG. 3 is a schematic configuration diagram showing a heating device according to a third embodiment of the present invention. In this heating device, two independent excitation coils 52 and 53 are arranged in parallel at a position facing an endless belt-shaped carrier 51 instead of the excitation coil 22 of the heating device shown in FIG. The exciting coil 52 includes a first coil 52a outside the carrier 51 and a second coil 52b inside the carrier 51.
These are magnetically coupled in a harmonically connected manner, and the excitation coil 53 is also composed of a first coil 53a on the outside of the carrier 51 and a second coil 53b on the inside. Are magnetically coupled in a harmonic connection. In this apparatus, a carrier 51 having a heating layer 62 and a surface layer 63 on a base material 61 and excitation coils 52 and 53 are provided.
A power supply device 54 for applying an AC voltage to the power supply is provided, and their configurations are the same as those shown in FIG.

In such a heating device, the heating layer 62 is formed by the two exciting coils 52 and 53 facing the carrier 51.
Is heated by electromagnetic induction. Therefore, the carrier 5
1, the heating layer 62 can be heated in a wide range, which is advantageous when a large heating area is desired.

FIG. 4 is a schematic configuration diagram showing a heating apparatus according to a fourth embodiment of the present invention. This heating device includes an excitation coil 72 arranged so that the winding direction of the coil is substantially parallel to the peripheral surface of the carrier 71, instead of the excitation coil 22 of the heating device shown in FIG. The excitation coil 72 is composed of a first coil 72a outside the carrier 71 and an excitation coil 72b inside the carrier 71, each of which is a ferromagnetic material 84a, 84b.
It is wound around. The other configuration of the heating device is the same as the heating device shown in FIG. Also in such a heating device, as shown in FIG. 4, the magnetic flux generated by the excitation coil 72 is guided in a loop penetrating the heating layer 82 of the carrier 71, and the heating layer 82 can be efficiently heated.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention described in claim 3, 4, 5, or 6. This image forming apparatus includes:
An endless belt-shaped intermediate transfer member 105 whose peripheral surface is rotatably supported is provided. Four image forming units for forming yellow, magenta, cyan, and black toner images are provided at positions opposed to the intermediate transfer unit 105. Unit 107Y, 10
7M, 107C and 107B are provided. Each image forming unit has an image carrier 1 on which an electrostatic latent image is formed.
And a charging device 10 for charging the surface of each image carrier 101 substantially uniformly around each image carrier 101.
2, an exposure device 103 for irradiating the surface of the image carrier with image light to form a latent image, and a developing device for selectively transferring toner to the latent image formed on the image carrier to form a toner image 10
4 and a primary transfer roll 106 for transferring the toner image on the image carrier onto the intermediate transfer member 105.

Inside the intermediate transfer member 105, a drive roll 108, a tension roll 109, support rolls 110 and 112, and a secondary transfer roll 113 are arranged. Stretched as possible. At a position facing the secondary transfer roll 113, a pressure roll 114 for pressing the intermediate transfer body 105 against the secondary transfer roll 113 is provided. , Intermediate transfer member 1
There is provided a heating device 120 for heating the toner image transferred on the recording medium 05 by electromagnetic induction. Further, a recording material 116 is applied to a pressure contact portion between the pressure roll 114 and the intermediate transfer body 105.
And a guide member 118 for guiding the recording material in a predetermined transport direction.

As shown in FIG. 6, the intermediate transfer member 105 is provided on the peripheral surface of an endless sheet base 131 having high heat resistance.
A dielectric heating layer 132 that self-heats by electromagnetic induction,
And a surface release layer 133 thereon. The intermediate transfer member 105 is adapted to move around at a speed of 160 mm / s in the direction of the arrow shown in FIG.

The heating device 120 is connected to the intermediate transfer member 105.
The first coil 115a and the second coil 11a are provided with an exciting coil composed of a first coil 115a disposed outside and a second coil 115b disposed inside.
5b is magnetically coupled with a harmonic connection. This heating device 120 is the same as the heating device shown in FIG.

The inductance L of the exciting coil is set such that the magnetic coupling k between the inductance L1 of the first coil 115a and the inductance L2 of the second coil 115b is in the range of 0.65 to 0.95. I do. The magnetic coupling k is represented by the following equation. k = (L−L1−L2) / 2√ (L1 × L2)

The degree of magnetic coupling k is determined by the distance between the heat generating layer 132 and the first and second coils 115a and 115b and the shape of the magnetic field generated by these exciting coils.
As a result, the power factor between the exciting coil and the heating layer is set to 0.4 to
It can be set in the range of 0.9. First coil 1
The excitation coil consisting of 15a and the second coil 115b is driven by a single drive power supply (not shown), and this drive power supply is a high-frequency AC power supply of 20 kHz to 100 kHz.

The toner used in the above image forming apparatus is
It is desirable to use a so-called sharp melt in consideration of the coloring property and the fixing property, and for example, a polyester resin or the like can be used as the binder resin. The softening point of the toner is preferably from 75 to 150 ° C., preferably from 80 to 125 ° C. Here, the toner having a sharp melt property means that the apparent melt viscosity is 10 ³
The temperature at which Pa · s is indicated is T ₁ , and the apparent melt viscosity is 5
When the temperature at which × 10 ² Pa · s is indicated is T ₂ ,
T ₁ = 80 to 140 ° C., and T ₂ −T ₁ = 5 ° C. to 20
A material that satisfies the condition of ° C. The sharp-melt resin having these temperature-melt viscosity characteristics causes an extremely sharp decrease in viscosity when heated. This decrease in viscosity causes appropriate mixing between the uppermost toner layer and the lowermost toner layer on the intermediate transfer member, and furthermore, sharply increases the transparency of the toner layer itself and causes good color mixing.

Further, the air contained in the powder escapes due to the flow of the sharp melt toner, and the thermal conductivity in the toner layer increases. Therefore, even when the toners of the respective colors are superimposed, the entire toner layer is short. It can be melted in a heating time, and is particularly effective in the image forming apparatus of the present embodiment.
Further, such a sharp-melting color toner has a high affinity and is likely to be offset at the time of fixing. However, in the present invention, since the toner is separated from the intermediate transfer member 105 at a temperature lower than the softening point, no offset occurs at all.

Next, the operation of the above-described image forming apparatus will be described. The image information is decomposed into four color images of cyan (C), magenta (M), yellow (Y), and black (K), and each image forming unit 107Y, 107M, 1
By 07C and 107K, toner images of different colors are formed on the image carrier 101, respectively. The intermediate transfer member 105 is circulating in a certain direction, and the toner image is transferred from the image carrier 101 by the action of the primary transfer roll 106.
After the toner images are sequentially transferred from the four image forming units, the superimposed toner images G of four colors are transferred to the intermediate transfer member 10.
By the movement of No. 5, it is transported to a region facing the heating device 120.

In this area, the heat generating layer 132 of the intermediate transfer member 105 generates heat by electromagnetic induction, and the intermediate transfer member 1
The four color toner images on 05 are melted by heating. The melted toner is transferred to a secondary transfer roll 113 and a pressure roll 114.
Is pressed against a recording material at room temperature at a position facing the recording medium, and the toner image instantaneously permeates into the recording material and is transferred and fixed. At the exit of the nip, the temperature of the toner drops due to contact with the recording material, and the cohesive force of the toner increases, so that the toner image is almost completely transferred and fixed onto the recording material without causing offset. You.

Next, in order to confirm the effect of the heating device 120 in the above-described image forming apparatus, an experiment for investigating the power factor was conducted in the same manner as the above-mentioned experiment. In this experiment, the heating layer 132
Is 2 μm thick copper, and the alternating magnetic field source is 80c in total volume
m ³ excitation coil, using a litz wire twisted copper wire of Φ = 0.3 mm, made two 40 cm ³ coils wound in a flat spiral shape, and joined the excitation coil by harmonic coupling,
The heat generating layer 132 was interposed therebetween. At this time, if the frequency of the AC voltage applied to the excitation coil is set to 100 kHz and the distance between the heating layer and the excitation coil is set to 5 mm, the power factor is set to 0.
It was confirmed to be 85.

On the other hand, a single coil wound in the shape of a flat spiral with the same volume was prepared, and the heating layer was set at the same frequency and the distance between the heating layer and the exciting coil from one side on one side. , And the power factor was 0.4. Therefore, a higher power factor can be obtained by the heating device 120 of the present embodiment.

Further, the configuration of the intermediate transfer member may be changed with substantially the same configuration as that of the image forming apparatus. For example, FIG.
As shown in the figure, an endless sheet base material 141 having high heat resistance.
An intermediate transfer member 135 having a four-layer structure including a heat generating layer 142 and a surface release layer 143 on the heat generating layer 142 and a foam layer 144 inside the sheet base 141 may be used. In such an intermediate transfer member 135, the foaming layer 144 functions as a heat insulating layer, preventing the temperature of the intermediate transfer member 135 from lowering and preventing heat conduction to members on the back surface side, thereby obtaining an image forming apparatus with good thermal efficiency. Can be

FIG. 8 is a partial structural view showing the vicinity of a heating device used in an image forming apparatus according to a second embodiment of the present invention. is there. In this image forming apparatus, a secondary transfer roll 152 is disposed inside an endless belt-shaped intermediate transfer body 151, and the secondary transfer roll 152 is provided with a pressure roll 153 for pressing the intermediate transfer body 151. On the upstream side of the pressure roll 153 in the circumferential direction of the intermediate transfer body 151, a first coil 154a which is close to and opposes the peripheral surface of the intermediate transfer body 151, and a second coil disposed inside the secondary transfer roll 152. A heating device 170 having a coil 154b is provided. The secondary transfer roll 152 rotates in the direction of the arrow shown in the figure, and a heat generating layer 152a is provided near the surface. The other configuration of the image forming apparatus is the same as that of the image forming apparatus shown in FIG.

In such an image forming apparatus, the toner image G primary-transferred onto the intermediate transfer member 151 moves in the circumferential direction of the intermediate transfer member, and is moved by the electromagnetic induction at the position where the heating device 170 is provided. Heat generation layer 15 of next transfer roll 152
2a is heated to melt the toner image. This toner image is pressed against a recording material at room temperature at a position where the secondary transfer roll 152 and the pressure roll 153 face each other, and the toner image is transferred and fixed onto the recording material.

FIG. 9 is a partial structural view showing the vicinity of a heating device used in an image forming apparatus according to a third embodiment of the present invention. is there. In this image forming apparatus, a fixed pad 162 is provided inside an endless belt-shaped intermediate transfer member 161, and a pressure roll 163 for pressing the intermediate transfer member 161 is provided on the fixed pad 162. The recording material is fed into the pressure contact portion between the fixed pad 162 and the pressure roll 163. A guide member (not shown) for curving the intermediate transfer body 161 and moving it around is provided near both ends of the intermediate transfer body 161 on the upstream side of the pressure contact portion between the fixed pad 162 and the pressure roll 163. I have. Inside the guide member, a heating device 170 including a first coil 164a and a second coil 164b is disposed so as to be close to and near the center of the intermediate transfer body 161. The intermediate transfer body 161 has the same configuration as that shown in FIG. 6, and has a heat generating layer inside. The other configuration of the image forming apparatus is the same as the apparatus shown in FIG.

In such an image forming apparatus, the toner image G on the intermediate transfer member 161 is heated and melted by electromagnetic induction at the portion where the first coil 164a and the second coil 164b are opposed. Then, by the movement of the intermediate transfer member 161, the recording material 165 at room temperature is pressed by the pressure contact portion between the fixed pad 162 and the pressure roll 163, and the toner image is transferred and fixed onto the recording material 165.

As shown in FIG. 10, a roll-shaped member 172 may be provided in place of the fixed pad 162. In such an apparatus, the toner image G on the intermediate transfer body 171 is conveyed to a position facing the heating device 180 having the first coil 174a and the second coil 174b, and the toner image is fused by electromagnetic induction heating. Is done. This toner image is pressed against a recording material at room temperature at a pressure contact portion between the roll-shaped member 172 and the pressure roll 173, and is satisfactorily transferred and fixed on the recording material.

[0070]

As described above, in the heating device according to the present invention, the exciting coils are provided on both sides of the heating layer, and the magnetic flux generated by the exciting coils penetrates the thin heating layer. The power factor is improved as compared with the case where the excitation coil is provided, and the heating layer can be effectively heated. For this reason, a low-capacity power supply can be designed, the size of the heating device can be reduced, and the leakage magnetic flux can be efficiently collected. Further, such a heating device is applied to an image forming apparatus, and an excitation coil is provided on both sides of a toner image carrier having a heat generating layer to heat the toner image carrier, thereby rapidly melting the toner on the toner image carrier. be able to. Then, the toner image is pressed against the recording medium by the pressing means on the downstream side, so that the softened toner strongly adheres to the recording medium, and the fixing is performed simultaneously with the transfer. For this reason, thermal energy can be reduced, and a good transfer-fixed image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a heating device according to a first embodiment of the present invention described in claim 1 or 2;

FIG. 2 is a schematic configuration diagram showing a heating device according to a second embodiment of the invention described in claim 1 or 2;

FIG. 3 is a schematic configuration diagram showing a heating device according to a third embodiment of the invention described in claim 1 or 2;

FIG. 4 is a schematic configuration diagram showing a heating device according to a fourth embodiment of the invention described in claim 1 or 2;

FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention described in claim 3, 4, 5, or 6;

FIG. 6 is a configuration diagram illustrating an intermediate transfer member used in the image forming apparatus.

FIG. 7 is a configuration diagram illustrating another example of the intermediate transfer member used in the image forming apparatus.

FIG. 8 is a partial configuration diagram showing the vicinity of a heating device of an image forming apparatus according to a second embodiment of the invention described in claim 3, 4, 5, or 6.

FIG. 9 is a partial configuration diagram showing the vicinity of a heating device of an image forming apparatus according to a third embodiment of the present invention.

FIG. 10 is a plan view of a third embodiment of the present invention;
FIG. 10 is a partial configuration diagram illustrating the vicinity of a heating device of an image forming apparatus according to a fourth embodiment of the invention described in FIG.

FIG. 11 is a diagram showing a state of a magnetic flux generated by the heating device of the present invention.

[Explanation of symbols]

1, 21, 51, 71 Carrier 2, 2, 52, 53, 72 Exciting coil 2a, 22a, 52a, 53a, 72a First coil 2b, 22b, 52b, 53b, 72b Second coil 3, 23, 54 Power supply device 11, 31, 61, 81, 131, 141 Base material 12, 32, 62, 82, 132, 142 Heat generation layer 13, 33, 63, 83, 133, 143 Surface layer 14a, 34a, 64a, 65a, 84a Ferromagnetic material 14b, 34b, 64b, 65b, 84b Ferromagnetic material 101 Image carrier 102 Charging device 103 Exposure device 104 Developing device 105, 135, 151, 161, 171 Intermediate transfer member 106 Primary transfer roll 107 Image forming unit 108 Drive roll 109 Tension roll 110, 112 Support roll 113 Secondary transfer roll 114, 53, 173 Pressure rolls 115a, 154a, 164a, 174a First coil 115b, 154b, 164b, 174b Second coil 116, 155, 165, 175 Recording material 117 Paper guide 118 Guide member 120, 160, 170, 180 Heating Apparatus 144 Foam layer 162 Fixed pad 172 Roll-shaped member

Continued on the front page F-term (reference) 2H033 BA11 BA25 BE03 BE06 3K059 AA08 AB00 AB08 AB19 AB20 AC03 AC10 AC12 AC15 AC33 AC73 AD01 AD03 AD32 CD44 CD66 CD73 CD75

Claims (6)

[Claims] 1. A carrier having a thin heating layer made of a conductive material, the carrier moving in a direction parallel to the heating layer, and a first body provided at opposite positions on both sides of the carrier.
An excitation coil and a second excitation coil, and a power supply device for applying an AC voltage to the first excitation coil and the second excitation coil. The first excitation coil, the second excitation coil, Is a heating device characterized in that it is magnetically harmonically connected and coupled, and a magnetic flux excited by these exciting coils is set to penetrate the heating layer. 2. The heat-generating layer is made of copper, silver, aluminum or a non-magnetic material having an electric resistivity equal to or less than these, and the heat-generating layer has a thickness of 0.1 μm or more. The heating device according to claim 1, wherein the heating device has a thickness of 20 μm or less. 3. A toner image formed by adhering toner to a latent image due to a difference in electrostatic potential, carried on an endless peripheral surface, and the peripheral surface is driven to move around. A carrying carrier, a first exciting coil and a second exciting coil provided on the inside and outside of the toner image carrying carrier so as to face each other; the first exciting coil and the second exciting coil A recording medium is pressed against the toner image carrier at a position downstream of a position where the first and second excitation coils oppose each other in a circumferential direction of the toner image carrier. And a pressing means, wherein the toner image carrying and transporting body has a thin heating layer made of a conductive material along a peripheral surface, and the first excitation coil and the second excitation coil are By applying an AC voltage, the heating layer An image forming apparatus, wherein the image forming apparatus is arranged to perform electromagnetic induction heating. 4. The first excitation coil and the second excitation coil are magnetically coupled in a harmonically connected manner, and a magnetic flux excited by these excitation coils is set so as to penetrate through the heat generating layer. The image forming apparatus according to claim 3, wherein: 5. The heat generating layer of the toner image carrying and transporting body is made of copper, silver, aluminum or a non-magnetic material having an electric resistivity equal to or less than these, and the thickness of the heat generating layer is 5. The image forming apparatus according to claim 4, wherein the distance is 0.1 μm or more and 20 μm or less. 6. An AC voltage and a frequency applied from the power supply device to the first exciting coil and the second exciting coil are carried on the toner image carrying conveyance and immediately before being pressed by the recording medium. The temperature of the toner is set to be equal to or higher than the softening point of the toner, and the range in which the recording medium is pressed against the toner image carrying conveyance by the pressing of the pressing means is as follows. The toner temperature is set to be equal to or lower than a softening point at the moment when the toner is separated from the carrier.
The image forming apparatus according to any one of the above.