JP4277694B2 - Fixing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a heating apparatus used for heating and pressure-fixing an unfixed toner image in an image recording apparatus such as a copying machine, a printer, or a facsimile employing an electrophotographic system, and a fixing apparatus using the same. In particular, the present invention relates to a heating device using a thin belt-like member as a member to be heated, a fixing device using the same, and an image recording device.

JP 11-316509 A JP 2000-321895 A JP 2000-181258 A JP 2000-29332 A JP 7-295411 A JP-A-8-69190 JP 11-38827 A Japanese Patent No. 3426229 JP 2001-343847 A Japanese Patent Laid-Open No. 2002-148983

  Conventionally, for example, in an image recording apparatus such as a copying machine, a printer, or a facsimile employing an electrophotographic method, a heating device used for heating and pressure-fixing an unfixed toner image and a fixing device using the same In addition, a heating source such as a halogen lamp is provided inside the heating roll having at least a metal core, the heating roll is heated from the inside, and the pressure roll is disposed so as to be in pressure contact with the heating roll. By passing the recording material on which the unfixed toner image is transferred between the nip formed by the heating roll and the pressure roll, the unfixed toner image is fixed on the recording material with heat and pressure, and then fixed. The one configured to obtain an image is mainly used.

  Here, in the heating device of the fixing device, the member to be heated is instantaneously heated to a predetermined temperature from the viewpoint of energy saving or not causing the user to wait when using the image recording apparatus, and the waiting time (warm There is a demand for an apparatus that can reduce the (uptime) to zero, but the method of heating the heating roll with a heating source such as a halogen lamp disposed therein cannot be achieved for the following reason. .

  That is, the heating roll as a heating member is a member to which a pressure member such as a pressure roll is pressed, so that it needs to maintain a predetermined rigidity and has a metal core having a certain thickness or more. . Therefore, the heating roll cannot reduce the heat capacity so much, and the halogen lamp as a heating source is provided inside the heating roll, and the heating roll is heated from the inside. It takes time to transfer heat to the surface of the. Accordingly, the waiting time is inevitably long, and furthermore, since the halogen lamp for heating the heating roll usually has a glass tube, the halogen lamp itself has a certain heat capacity, It takes time to warm the halogen lamp itself.

  For this reason, the conventional fixing device has a problem that it takes time to warm up and the waiting time becomes long. Further, when a halogen lamp is used as a heating source, there is a problem that a so-called “flicker” phenomenon occurs in which an energization current flows transiently when the halogen lamp is turned on / off.

  Therefore, in recent years, as a heating unit used in such a fixing device, a heating unit using an induction heating method instead of a halogen lamp has been studied. This is to heat a heated member by electromagnetic induction by applying a magnetic field generated by a magnetic field generating means to a heated member (heating element) having a conductive layer. This is a very effective heating means in order to provide a fixing device with a short waiting time because only the object to be heated can be instantaneously heated.

  In addition, the heating means such as the halogen lamp can be used only in a state where the circumference of 360 ° such as the inside of the heating roll is covered, whereas in the case of the induction heating method, the magnetic field generating means is not covered. As long as a magnetic field can be applied to the heating member, it may be provided not only inside the member to be heated but also outside, and can be arranged at an arbitrary position according to the configuration of the fixing device. That is, in the case of a heating means adopting the above induction heating method, it is arranged at an arbitrary position, and a magnetic field is applied only to a portion to be heated to selectively heat only a desired portion. Has the advantage of being able to

  As described above, the magnetic field generating means in the induction heating method can be arranged at an arbitrary position with respect to the heating roll as the member to be heated, so that the degree of freedom in designing the apparatus can be expanded. Further, as compared with a fixing device using a halogen lamp or the like as a heating source, only the heating roll to be heated is selectively heated, so that the warm-up time can be shortened by about 10 to 30%.

  As a fixing device employing such an induction heating method, for example, as shown in FIG. 25, a coil 310 is disposed in a non-contact manner inside or outside a rigid iron roll 300 having a thickness of about 0.5 to 2 mm. Depending on the shape of the coil, there may be mentioned a heating device that heats the roll as a whole in the circumferential direction or locally heats a part in the circumferential direction. There is also a heating device that heats the roll as a whole in the circumferential direction depending on the shape of the coil (see, for example, Patent Document 1). As another example, as shown in FIG. 26, a belt 320 having a heat generation layer made of nickel having a thickness of about 50 μm is induction-heated by a coil 310 inserted inside the belt. There is also a heating device (see, for example, Patent Document 2). Furthermore, as another example, a heating means having conductivity, a pressure contact means that is in pressure contact with the heating means, a magnetic field generation means that is formed in a coil shape with a conductive wire and causes a generated magnetic field to act on the heating means, There has been proposed a magnetic field blocking means for blocking the magnetic field generated by the magnetic field generating means, and arranged so that the magnetic field generating means is sandwiched between the heating means and the magnetic field blocking means (for example, Patent Document 3). reference). Furthermore, a fixing device is also proposed in which a magnetic field generating means is disposed outside or inside a heating roll as a heating means having conductivity (see, for example, Patent Document 4). Furthermore, a fixing device using an endless film belt as a fixing member (see, for example, Patent Documents 5 to 7) and arrangement of coils and cores in such a fixing device have also been proposed (for example, patents). Reference 8-10).

  The heating layers of the heating devices used in these fixing devices are all made of a magnetic metal, and the thickness thereof is equal to or greater than the skin depth. In any fixing device, it is not possible to complete the warm-up time in 10 seconds or less.

  Here, the skin depth refers to the depth at which the electromagnetic field can enter the conductor, and specifically refers to the distance at which the electromagnetic field incident on a certain material attenuates to 1 / e = 0.37.

  In general, a heating apparatus using electromagnetic induction has been conventionally known, and most of the heat generating layer that performs induction heating uses a magnetic metal such as iron or nickel. As a conventional heat generation layer thickness of the magnetic metal, a thickness of about 50 μm to 2 mm is adopted. This thickness is approximately equal to or greater than the thickness for induction heating of the heat generating layer, that is, the skin depth. In this way, when the heating layer thickness is equal to or greater than the skin depth, the electromagnetic field due to electromagnetic induction converges inside the heating layer, and the magnetic flux almost leaks from the opposite side of the heating layer coil. Absent. The conventional heat generating layer in which “the magnetic flux hardly leaks” refers to a heat generating layer having a thickness equal to or greater than the skin depth.

  Due to energy saving in recent years, it is desirable that the heating device can heat the non-heated object with a minimum amount of heat. However, in a fixing device of an electrophotographic image recording apparatus, for example, since the heat capacity of the member to be heated is large, heating exceeding a necessary amount of heat is performed. For this reason, there is a problem that the time (warm-up time) until a state where predetermined heating can be performed becomes long, and the convenience in using the heating device is poor. Therefore, it is conceivable to reduce the thickness of the heat generating layer of the member to be heated to reduce the heat capacity and further reduce the weight.

  However, in order to shorten the warm-up time, if the heat capacity is reduced, that is, if the heat generating layer (metal) is made thinner, the heat generating layer having a small specific resistance value is required. For example, a ferromagnetic metal such as iron or nickel has a high specific resistance value. Therefore, when the layer is thinned to about 10 μm, electromagnetic induction heating becomes difficult for a high-frequency power source having high versatility. Metals that can be heated by electromagnetic induction even with a thickness of about 10 μm are nonmagnetic metals typified by AL, Cu, Ag, etc. When the nonmagnetic heating layer of this thickness is heated by electromagnetic induction, the skin depth Since it is sufficiently thinner than that, the magnetic field leaks and spreads on the side opposite to the coil of the heat generating layer, which adversely affects efficiency reduction and electromagnetic induction to the surroundings. The present invention provides a technique capable of performing electromagnetic induction heating of a metal thinner than the skin depth, particularly a non-magnetic thin film metal, stably.

  In addition, a heating device using electromagnetic induction heating has a problem that the cost increases because there are many functional members unique to electromagnetic induction heating. The present invention is intended to provide a heating apparatus that is excellent in energy saving and convenience, and that is reduced in cost while being reduced in weight.

  Further, the conventional fixing device has the following problems. That is, for example, in the case of the fixing devices disclosed in Patent Documents 1 to 4, since the induction heating method is employed, the warm-up time is faster than when a heating source such as a halogen lamp is used. However, since the heating roll itself has a metal core with a thickness greater than a certain thickness in order to maintain rigidity, it has a certain heat capacity, which limits the reduction in warm-up time. Further, there is a problem that it is difficult to set the warm-up time for completing preparation for fixing an unfixed toner image to 10 seconds or less.

  On the other hand, the fixing devices disclosed in Patent Documents 5 to 7 use a conductive film as a fixing member, and the heat capacity of the film itself is 1/2 to that of the fixing roll of an equivalent class fixing device. The film is reduced to about 1/10. Further, by directly heating the film by induction heating, the film as a fixing member can be raised to a desired temperature in about 20 to 30 seconds.

  However, even when the image heating film having a small heat capacity including the magnetic metal heat generating layer is heated by the exciting coil as described above, the warm-up time has not been sufficiently shortened.

  Similarly, in the fixing device adopting the arrangement of coils and cores disclosed in Patent Documents 8 to 10, the warm-up time has not been sufficiently shortened yet.

  Reducing the standby time, especially achieving a warm-up time of 10 seconds or less, requires only power to be used when actually using the fixing device or image recording device. It is possible to provide an apparatus that is highly convenient. This is an important element from the viewpoint of energy saving, and does not require residual heat when not in use, and the significance of providing a heating device that inputs energy only when it is used, a fixing device using the same, and an image recording device is used. large.

  In view of the above-described problems of the prior art, the present invention provides a heating device capable of ensuring a stable induction heating state while extremely shortening the warm-up time, a fixing device using the same, and image recording An object is to provide an apparatus.

In order to achieve the above object, a heating device of the present invention is an endless heated member including a conductive heating layer, and the heating member has a thickness that is thinner than the skin depth thereof. The heating device includes an excitation coil that generates a varying magnetic field along the thickness direction of the heat generating layer of the member to be heated and electromagnetically heats the heat generating layer, and the excitation coil is disposed outside the member to be heated. are arranged, the surface and the non-contact of the heating member, along Ikatsu wire so as to follow the surface shape is formed by winding a magnetic path of the fluctuating magnetic field generated by the pre Ki励 magnetic coil on the surface A first magnetic path forming member and a second magnetic path forming member that shield the magnetic field, and the first magnetic path forming member and the second magnetic path forming member are made of a magnetic material. Formed to follow the surface shape of the heated member, and the heated member The first magnetic path forming member is disposed in the longitudinal direction of the exciting coil in a non-contact manner with the material and arranged to face each other across the exciting coil and the heated member. The second magnetic path forming member is arranged on the opposite side of the exciting coil from the heated member side, and is opposed to the exciting coil of the heated member. A portion of the surface opposite to the surface to be opposed does not face the first magnetic path forming member, and faces the nonmagnetic metal member . The nonmagnetic metal member may be a support member that supports the first magnetic path forming member.

  In general, in order to reduce the warm-up time as close as possible to 0 and to 10 seconds or less, it is most important to reduce the heat capacity of the heat generating layer (metal) that is heated by electromagnetic induction. For this purpose, it is possible to realize a metal layer that contributes to heat generation within a total range of 30 μm or less, preferably 2 to 20 μm. Further, when there is one layer that mainly generates heat, the layer is preferably about 10 μm in view of manufacturability (yield and uniformity of layer formation) and cost.

  For example, there may be a plurality of layers (metal layers) that contribute to heat generation for manufacturing reasons or strength reinforcement reasons. The number of layers that generate heat due to electromagnetic induction is preferably one from the viewpoint of cost. However, when there are a plurality of layers that contribute to heat generation due to the above reasons, the total thickness of each layer is preferably 30 μm or less. . In the present invention, even if there are a plurality of layers that contribute to heat generation, a layer that can obtain an electromagnetic induction heat generation amount of 50% or more of the total heat generation amount is referred to as a “main heat generation layer” as a main heat generation layer. All the contributing layers are collectively referred to simply as “heat generation layer”.

  A high-frequency power source (eg, a quasi-E class parallel resonant circuit power source used in an electromagnetic cooker or the like) made of a conductor in which a main heat generating layer contributing to heat generation is thinned to about 10 μm, that is, a metal or a metal mixture, is highly versatile It is necessary to use a nonmagnetic metal in order to perform induction heating in step (1). When the magnetic metal is made thin, the magnetic metal has a high specific resistance value, so that an induced eddy current hardly flows and heating becomes difficult. If it is attempted to inductively heat the heat generating layer that is difficult to flow, it is necessary to apply a high voltage to the coil, and problems such as an increase in the voltage of the power source occur, making it difficult to actually adapt. Although an eddy current due to electromagnetic induction flows when an alternating electromagnetic field is applied to all metals, in order to design a heating device using Joule heat generation, it is important to give conditions that easily generate heat. In contrast, non-magnetic metals such as aluminum, copper, and silver have low specific resistance values, and are suitable for induction heating by being sufficiently thinner than the skin depth. Specifically, for example, about 10 μm. It becomes easy to heat by thinning.

For example, when a non-magnetic metal copper is taken as an example of a single heat generating layer, the skin depth δ at which the electromagnetic field penetrates into the copper layer in the frequency band of 20 to 100 kHz is expressed by the following equation: μ = 1 , Ρ = 1.67 × 10 −8 Ωm, which is 200 to 500 μm, and the thickness of the heat generating layer is sufficiently smaller than the skin depth.

However, non-magnetic metals having a low specific resistance value typified by aluminum, copper, silver, etc., are generated from an excitation coil that is an alternating magnetic field generating means when induction heating is performed on a metal whose heating layer is thinner than the skin depth δ. The reaction magnetic field due to the magnetic field and the induced eddy current leaks from the side opposite to the coil across the heating layer. Table 1 shows the difference in magnetic flux density with and without the magnetic path forming member, but it can be seen that when there is no magnetic path forming member, a strong magnetic field is generated around the heat generating layer. This magnetic field is generated by the magnetic field generated by the coil and the magnetic field generated by the eddy current flowing in the heat generating layer, and leaks from the heat generating layer.

  Therefore, the heating device of the present invention configured as described above is a heated member including a conductive heat generating layer, and the heated member having a heat generating layer whose thickness is thinner than the skin depth, In a heating mode of a heating device having an exciting coil for electromagnetically heating the heat generating layer by generating a variable magnetic field along the thickness direction of the heat generating layer of the heating member, at least the heat generating layer, the coil and the magnetic path forming member For example, a magnetic flux path is formed by alternating magnetic field generating means (excitation coil) -heating layer-magnetic path forming member with a structure sandwiched between, for example, soft ferrite (hereinafter sometimes referred to as ferrite). Therefore, a stable induction heating state can be realized. Accordingly, it is possible to provide a heating device that can obtain a safe and stable induction heating state even with a nonmagnetic metal that is sufficiently thinner than the skin depth.

  Here, the member to be heated has an endless belt shape and is formed so as to be movable in a predetermined direction, and both ends of the magnetic path forming member are opposed to each other before and after the moving direction. Each may extend beyond both ends of the coil.

  In this case, since both ends of the magnetic path forming member extend beyond both ends of the exciting coils facing each other before and after the predetermined moving direction of the heated member, the width of the magnetic path forming member is When the metal that is larger than the coil width (heating width) and the heat generating layer is thinner than the skin depth δ is induction-heated, magnetic flux leakage due to the reaction magnetic field that leaks from the opposite side of the exciting coil across the heat generating layer is more effective. Therefore, a magnetic flux path with less leakage can be formed, and the shielding effect can be improved.

  The member to be heated formed in the endless belt shape may be cylindrical.

  The magnetic path forming member may be formed of soft ferrite.

  In this case, a heating apparatus having a magnetic path forming member using a suitable material for collecting and shielding magnetic flux can be provided.

  Furthermore, the heat generating layer of the member to be heated is mainly formed of copper having a thickness of 2 to 15 μm, and the frequency of the alternating current applied to the exciting coil is 20 to 100 kHz. Good.

  In this case, a heating device capable of stable heating can be provided in the relationship between the copper layer thickness and the applied frequency.

  The heating device of the present invention is a member to be heated including a conductive heat generating layer, and the member to be heated has a thickness that is thinner than the skin depth of the member to be heated, and the heat generating layer of the member to be heated. In a heating device having an exciting coil for electromagnetically heating the heat generating layer by generating a variable magnetic field along the thickness direction, the exciting coil is in non-contact with the surface of the heated member, And a magnetic path forming member that forms a magnetic path of a variable magnetic field generated by the exciting coil and shields the magnetic field, and formed the exciting coil and the magnetic path formed. The member is formed so as to follow the surface shape of the member to be heated, and is disposed in non-contact with the member to be heated, and the magnetic path forming member sandwiches the excitation coil and the member to be heated. It has a part that faces And wherein the door.

  If it is necessary to obtain a more stable heating state as required by the heating device, a magnetic path forming member is further arranged on the side opposite to the heat generating layer of the alternating magnetic field generating means (excitation coil), and the heat generating layer and the alternating magnetic field are generated. It is desirable to adopt a heating configuration in which the means is sandwiched, that is, a magnetic path forming member-alternating magnetic field generating means (excitation coil) -heating layer-magnetic path forming member. By sandwiching the exciting coil and the heat generating layer with the magnetic path forming member, a magnetic path with respect to the electromagnetic field by the exciting coil and the heat generating layer is formed, and the stable heating can be performed safely.

  Therefore, in the heating device of the present invention configured as described above, an excitation coil and a magnetic path forming member are formed so as to follow the surface shape of the member to be heated, and arranged in non-contact with the member to be heated, Further, since the magnetic path forming member is arranged so as to have a portion facing each other with the exciting coil and the heated member sandwiched therebetween, a magnetic flux path with less leakage is formed, and the magnetic flux leaking from the exciting coil is effectively prevented. The shielding effect can be improved.

  Here, the magnetic path forming member includes a first magnetic path forming member and a second magnetic path forming member arranged so as to face each other with the excitation coil and the heated member interposed therebetween, The first magnetic path forming member may be disposed on the heated member side, and the second magnetic path forming member may be disposed on the exciting coil side.

  In this case, the magnetic path forming member is composed of the first magnetic path forming member arranged on the heated member side and the second magnetic path forming member arranged on the exciting coil side. The magnetic path forming member for collecting and shielding the magnetic flux leaking from the exciting coil can be used more efficiently.

  The heated member has an endless belt shape and is formed so as to be movable in a predetermined direction, and the first magnetic path disposed at least on the heated member side before and after the moving direction. Both ends of the forming member may extend beyond both ends of the exciting coils facing each other.

  In this case, at least both ends in the circumferential direction of the first magnetic path forming member arranged on the heated member side are respectively beyond both ends of the exciting coils facing each other before and after the predetermined moving direction of the heated member. Therefore, when induction heating is performed on a metal whose heat generation layer is thinner than the skin depth δ, magnetic flux leakage due to the reaction magnetic field that leaks from the opposite side of the excitation coil across the heat generation layer is more effectively prevented. , The shielding effect can be improved.

  The member to be heated formed in the endless belt shape may be cylindrical.

  Further, at least one of the first and second magnetic path forming members is composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially perpendicular to the moving direction of the heated member. You may be comprised by the small piece member group.

  In this case, at least one of the first and second magnetic path forming members is composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially orthogonal to the moving direction of the heated member. Since it is composed of small piece member groups, the individual magnetic path forming members can be made smaller, thereby facilitating the molding of the individual magnetic path forming members and the dimensional accuracy thereof. In addition, it is possible to provide a heating device that can reduce the amount of expensive magnetic path forming members used and can be reduced in weight and cost.

  Further, each of the first and second magnetic path forming members is composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially orthogonal to the moving direction of the heated member. In the small piece member group, the small piece member group constituting the first or second magnetic path forming member, and the small piece member group constituting the second or first magnetic path forming member. You may arrange | position so that each gap | interval which two small piece members adjacent to each other may mutually oppose.

  In this case, each of the first and second magnetic path forming members is a small piece composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially perpendicular to the moving direction of the heated member. Each of the small piece members of the small piece member group constituting the first or second magnetic path forming member and the small piece member group constituting the second or first magnetic path forming member Since the gaps formed by two adjacent small piece members are arranged so as to face each other, an appropriate magnetic path is formed to prevent temperature unevenness due to concentration of magnetic flux and an expensive magnetic path It is possible to provide a heating device that enables effective use of the forming member while reducing the amount of use of the forming member.

  Further, each of the first and second magnetic path forming members is composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially orthogonal to the moving direction of the heated member. The small piece member group is composed of a small piece member group, and the small piece member group of the first magnetic path forming member and the small piece member group of the second magnetic path forming member are spaced from each other on the opposing magnetic path forming member. May be arranged so as to complement.

  Also in this case, each of the small piece member groups of the first and second magnetic path forming members is arranged so as to complement the gap between the opposing magnetic path forming members facing each other. It is possible to provide a heating device that can prevent the occurrence of temperature unevenness and can effectively use the magnetic path forming member while reducing the amount of use of the expensive magnetic path forming member.

  Still further, each of the small piece member groups of the first and second magnetic path forming members has a magnetic path on the opposite side whose centers in a direction substantially orthogonal to the moving direction of the heated member are opposed to each other. You may arrange | position so that it may correspond substantially with the center of the gap | interval of a formation member group.

  In this case, it is possible to provide a heating device that more effectively prevents the occurrence of temperature unevenness due to the concentration of magnetic flux and enables more effective use of the magnetic path forming member.

  In the above, the magnetic path forming member may be formed of soft ferrite.

  In this case, a heating apparatus having a magnetic path forming member using a suitable material for collecting and shielding magnetic flux can be provided.

  The heating layer of the member to be heated is mainly made of copper having a thickness of 2 to 15 μm, and the frequency of the alternating current applied to the exciting coil is 20 to 100 kHz. Good.

  In this case, a heating device capable of stable heating can be provided in the relationship between the copper layer thickness and the applied frequency.

In addition, the fixing device of the present invention includes an endless fixing belt having a release layer on at least the outermost surface and including a conductive heat generation layer, and the thickness of the heat generation layer is thinner than the skin depth. In a fixing device having an exciting coil for electromagnetically heating the heat generating layer by generating a variable magnetic field along the thickness direction of the heat generating layer of the fixing belt, pressurizing a recording material carrying an unfixed toner image A nip portion that heats and presses between the member and the fixing belt to fix the unfixed toner image, and a pressing member that is disposed opposite to the pressure member and the fixing belt to form the nip portion; A first magnetic path forming member and a second magnetic path forming member that form a magnetic path of a fluctuating magnetic field generated by the exciting coil and shield the magnetic field, and the exciting coil is disposed outside the fixing belt. Of the fixing belt The first magnetic path forming member and the second magnetic path forming member are made of a magnetic material so as to be non-contact with the surface and wound along the surface so as to follow the surface shape. Formed so as to follow the surface shape of the fixing belt, arranged so as to be in non-contact with the fixing belt and opposed to each other with the excitation coil and the fixing belt interposed therebetween, and forming the first magnetic path The member is supported by a support member made of a non-magnetic metal member inside the fixing belt and is partially disposed in the longitudinal direction of the excitation coil, and the second magnetic path forming member is A first magnetic path forming member disposed on the opposite side of the surface of the fixing belt opposite to the side of the fixing belt, of the surface opposite to the surface of the fixing belt facing the excitation coil; The non-opposing part Has support members facing made of a magnetic metal member, further, the support member is characterized by supporting said pressing member opposite to the side which supports the first magnetic path forming member .

  According to another aspect of the present invention, there is provided an image recording apparatus including the above-described fixing device and an image forming unit that forms an unfixed toner image on a recording material.

  According to the present invention, in a heating device that heats a main heat generating layer made of a non-magnetic material (metal) and a heat generating layer thinner than its skin depth, heating can be performed in a very short time and stable induction heating can be performed. A heating device capable of obtaining a state can be realized, and by applying this heating device to a fixing device and an image recording device, the warm-up time can be reduced to 10 seconds or less. Further, it is possible to realize a heating device that is energy-saving and convenient, and that only needs to input energy when it is necessary for heating, and a fixing device and an image recording device using the heating device.

Embodiments of the present invention will be described below with reference to the drawings.
<First embodiment>

  First, a first embodiment of a fixing device to which a heating device according to the present invention is applied will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a first embodiment of a fixing device according to the present invention.

  The first embodiment 10 of the fixing device according to the present invention aims at shortening the warm-up time and ensuring the separation performance of the recording material, and as a fixing member for fixing the toner image, a flexible material having a small heat capacity. A (flexible) belt-shaped member is used, and the belt-shaped member is configured so that a member for removing heat is not disposed as much as possible. In other words, the endless belt member (heat fixing belt) is disposed without stretching members such as drive rolls on the inner side thereof, and is disposed so as to face the pressure member, and the fixing nip portion is provided. Only a pad member (pressing member) to be formed is basically provided. Further, a heating layer is provided inside the belt-like member so that the belt-like member to be heated can be directly heated, and this heating layer is induction-heated by a variable magnetic field generated by an exciting coil.

  Specifically, as shown in FIG. 1, a thin hollow cylindrical heat-fixing belt 20 having a heat generating layer, and a pressure disposed so as to be in pressure contact with a lower outer surface of the heat-fixing belt 20 in the figure. An elastic member 24 that is in contact with the inner surface of the heat-fixing belt 20 that is provided with a roll 23 and faces the pressure roll 23 is supported by a support member 22 and disposed. Inside the heat fixing belt 20 opposite to the surface facing the pressure roll 23 (upper part in the drawing), excitation is performed so as to face a part of the inner surface without contacting the inner surface of the heat fixing belt 20. A coil 1A is provided. Further, outside the heat fixing belt 20 facing the exciting coil 1A, the ferrite 41, which is a magnetic path forming member, is not in contact with the outer surface of the heat fixing belt 20 and faces a part of the outer surface. Is arranged.

  In the fixing device 10 configured as described above, the nip portion 1Y is formed by holding the heat fixing belt 20 with the pressure roll 23 and the elastic member 24, and unfixed toner is formed in the nip portion 1Y. By passing the recording material 27 onto which the image 25 has been transferred, the unfixed toner image 25 is fixed on the recording material 27 by heat and pressure, and a fixed image is formed. The thin heating and fixing belt 20 having the heat generation layer is heated by electromagnetic induction heating with a fluctuating magnetic field generated by the exciting coil 1A, so that heating for fixing an unfixed toner image is performed. .

  Next, details of constituent members of the fixing device 10 will be described below.

  First, the heat fixing belt 20 as a heat fixing member is formed as an endless belt having a heat generating layer. Specifically, as shown in FIG. 2, the heat generation is a base layer 20a made of a sheet-like member having high heat resistance and a single heat generation layer laminated on the base layer 20a from the inside. At least three layers of the layer 20b and the uppermost surface release layer 20c are provided and formed as an endless belt having a diameter of 30 mm. As shown in FIG. 3, an elastic layer 20d made of, for example, silicon rubber having a rubber hardness of 35 ° may be further provided between the heat generating layer 20b and the surface release layer 20c. Further, in the present embodiment, although not shown, the end portions of the endless heat fixing belt 20 are abutted against the edge guides, whereby the meandering of the heat fixing belt 20 is regulated and used.

  Here, the base material layer 20a of the heat-fixing belt 20 is, for example, a sheet having a thickness of 10 to 100 μm, more preferably a thickness of 50 to 100 μm (for example, 75 μm) and a high heat resistance, such as polyester, polyethylene terephthalate, It can be formed from a synthetic resin having high heat resistance such as polyether sulfone, polyether ketone, polysulfone, polyimide, polyimide amide, polyamide.

  The heat generating layer 20b is a conductive layer that generates heat by electromagnetic induction of a magnetic field generated by the exciting coil 1A, and is formed of copper with a thickness of about 2 to 15 μm. If a uniform layer is to be formed by plating, vapor deposition or the like, if it is 2 μm or less, there will be problems in terms of poor manufacturing yield, ensuring film thickness accuracy, quality control and cost. Further, if it is 15 μm or more, the heat capacity becomes large, which affects the achievement of warm-up for 10 seconds or less, and the flexibility of the heat generating layer deteriorates. Is less than 15 μm. Further, when the thickness is 15 μm or more, the induction heating performance at a frequency of 20 k to 100 kHz is deteriorated. This is because eddy current flows through the entire metal layer with a thickness sufficiently thinner than the skin depth, but the resistance value decreases as the thickness increases, making it difficult to obtain Joule heat loss due to eddy current. To do. In other words, Joule heating is determined by multiplying the square value of the eddy current by the resistance value of the main path through which the eddy current flows. Therefore, if the resistance value is too low, no heat will be generated no matter how much eddy current flows. It is.

  In this embodiment, although not shown in FIGS. 2 and 3, a nickel layer having a thickness of about 0.1 to 5 μm is provided on the surface release layer side of the heat generating layer 20b which is a copper layer. The heat fixing belt was also used. The nickel layer is provided to improve the strength of the heat-fixing belt, and contributes to heat generation due to electromagnetic induction, but has a small effect on electromagnetic induction characteristics (changes in inductance and resistance in the induction state). Is approximately 10% or less). As an actual example, when comparing the electromagnetic induction characteristics of a heat-fixing belt having two layers contributing to heat generation in which a nickel layer of 5 μm is provided on a copper layer of 10 μm and a heat-fixing belt having a single copper layer of 10 μm, The change in inductance and resistance in the inductive state is 5% or less, and the difference from a single copper layer is very small. Even if such a layer is provided, the layer that generates heat mainly becomes the copper layer of the heat generating layer 20b, so there is almost no problem in the embodiment of the present invention.

  Here, the relationship between the copper layer thickness and the applied frequency will be further described with reference to FIG. FIG. 4 is a diagram showing the change of the power factor equivalent amount with respect to the frequency, and is a characteristic diagram showing the ease of heat generation when the copper layer thickness is 2 μm to 15 μm.

  In FIG. 4, stable heating is possible if the heat factor corresponding to the power factor reaches 0.5 over the frequency band of 20 k to 100 kHz, but the thickness is as shown in the figure. It can be seen that the frequency is about 60 kHz to 100 kHz in the case of 2 μm, and about 30 kHz or less in the case of 15 μm.

  Therefore, the frequency of the current applied to the coil is desirably 20 kHz to 100 kHz. If it is 20 kHz or less, the oscillation noise sound cannot be adopted because it enters the human audible region, and if it is 100 kHz or more, the switching loss of the induction heating power source that applies current to the coil increases, affecting peripheral devices. This is because the radiation noise exerted increases, the skin resistance of the coil increases, and the loss due to these increases.

  In the present embodiment, the heat fixing belt 20 needs to follow the shape of the nip portion inside the nip portion formed by the pad member and the pressure roll. For this reason, it is necessary to be a flexible belt, and the heat generating layer 20b is preferably as thin as possible. Therefore, in the present embodiment, as the heat generation layer 20b, copper having high conductivity is plated on the base material layer 20a made of the above-described polyimide with an extremely thin thickness of about 10 μm so as to increase the heat generation efficiency. Is used.

  Further, since the release layer 20c is a layer in direct contact with the unfixed toner image transferred onto the recording material, it is necessary to use a material having good release properties. Examples of the material constituting the release layer 20c include tetrafluoroethylene perfluoroalkyl vinyl ether polymer (PFA), polytetrafluoroethylene (PTFE), silicon copolymer, or a composite layer thereof. The release layer 20c is a layer appropriately selected from these materials and provided on the uppermost layer of the belt with a thickness of 1 to 50 μm. On the other hand, if the thickness of the release layer 20c is too thin, the durability is poor in terms of wear resistance, and the life of the heat fixing belt 20 is shortened. Conversely, if the thickness is too large, the heat capacity of the belt is reduced. Increases the warm-up time.

  In the present embodiment, a 20 μm thick tetrafluoroethylene perfluoroalkyl vinyl ether polymer (PFA) is used as the release layer 20 c of the heat-fixing belt 20 in consideration of the balance between wear resistance and the heat capacity of the belt. in use.

  Further, an elastic member 24 as a pad (pressing member) made of, for example, silicon rubber or the like is provided inside the heat fixing belt 20 configured as described above. In this embodiment, as the elastic member 24, a silicon rubber having a rubber hardness of 35 ° in JIS-A is laminated on a support member 22 having a rigidity made of a metal such as SUS / iron or a synthetic resin having high heat resistance. Things are used. As the elastic member 24 made of silicon rubber, for example, one having a uniform thickness is used. The support member 22 is arranged in a state of being fixed to a frame of a fixing device (not shown), but a spring or the like (not shown) is used so that the elastic member 24 is pressed against the surface of the pressure roll 23 with a predetermined pressing force. You may press toward the surface of the pressure roll 23 by a biasing means.

  In the present embodiment, the surface of a solid iron roll having a diameter of 26 mm as the pressure roll 23 is coated with a tetrafluoroethylene perfluoroalkyl vinyl ether polymer (PFA) having a thickness of 30 μm as the release layer. Things are used. The pressure roll 23 is rotationally driven by a driving unit (not shown) while being pressed against the elastic member 24 via the heat fixing belt 20 by a pressing unit (not shown).

  The pressure roll 23 may be provided with a metal roll (not shown) made of a metal such as aluminum or stainless steel having good thermal conductivity so as to be able to contact and separate. This metal roll stops at a position away from the pressure roll 23 when the temperature of the heat fixing belt 20 or the pressure roll 23 is cooled to the room temperature, for example, in the morning when the energization of the fixing device is started. Yes. In the fixing device, when the fixing device is used, for example, when a small-size sheet is continuously fixed, the temperature along the axial direction is applied to the heat fixing belt 20 and the pressure roll 23. When the difference occurs, the metal roll may be configured to contact the pressure roll 23.

  The heat fixing belt 20 as a member to be heated is circulated in a predetermined direction following the rotation of the pressure roll 23. Therefore, in this embodiment, a sheet material having high friction resistance and good slidability, for example, Teflon (registered trademark) resin, is used between the heat fixing belt 20 and the elastic member 24 to improve the slidability. By interposing a glass fiber sheet impregnated with (Nakako Kasei Kogyo: FGF400-4, etc.) and further applying a release agent such as silicon oil as a lubricant to the inner surface of the heat fixing belt 20, It is configured to improve. In this way, during actual heating, the driving torque during idling of the pressure roll 23 can be reduced from about 6 kg · cm to about 3 kg · cm. Therefore, the heat fixing belt 20 is driven without sliding with the pressure roll 23 and can circulate and move at a speed equal to the rotation speed of the pressure roll 23.

  Next, as shown in FIG. 5, the exciting coil 1A is formed so as to follow the outer surface of the thin cylindrical heating and fixing belt 20 by winding a linear member having a core material made of a ferromagnetic material. The coil support member 26 supports the heat fixing belt 20 with the direction orthogonal to the rotation direction (circumferential direction) as the longitudinal direction. The heat fixing belt 20 that is a member to be heated is disposed so as to face the surface of the heat fixing belt 20 while maintaining a gap of about 0.5 mm to 3 mm. Here, as the exciting coil 1A, for example, one in which a predetermined number of litz wires obtained by bundling 90 copper wires having a diameter of 0.16 mm that are insulated from each other in a straight line are arranged in parallel is used. The method of winding the litz wire is not limited to a single winding method. For example, the litz wire may be wound in a spiral shape, and the variable magnetic field H generated by the alternating current flowing through the exciting coil 1A is illustrated with respect to the heating layer 20b. It should work as follows. Further, it is desirable to use a heat-resistant nonmagnetic material as the coil support member 26, and for example, a heat-resistant resin such as ceramics, heat-resistant glass, polycarbonate, LCP, polyimide, PPS or the like is used.

When an alternating current having a predetermined frequency is applied to the exciting coil 1A through the exciting circuit 30, a fluctuating magnetic field H is generated around the exciting coil 1A. When crossing 20b, an eddy current B is generated in the heat generating layer 20b of the heat-fixing belt 20 so as to prevent the change of the magnetic field H by electromagnetic induction. When this eddy current B flows through the heat generating layer 20b of the heat fixing belt 20, Joule heat is generated with electric power (W = I ² R) proportional to the resistance of the heat generating layer 20b, and the member to be heated (heat generating body). A certain heat fixing belt 20 is heated. The frequency of the alternating current applied to the exciting coil 1A is set, for example, to 20 to 50 kHz. In this embodiment, the frequency of the alternating current is set to 30 kHz. In the present embodiment, it has been confirmed that electromagnetic induction heating can be performed extremely well even when a low-cost parallel resonance type excitation circuit power source is used as the excitation circuit 30. Such a parallel resonance type high-frequency power source has a track record in an electromagnetic cooker or the like, and can be constructed at a low cost as a power source for electromagnetic induction heating, and is highly practical and versatile.

  Referring to FIG. 1 again, as the magnetic path forming member 41, a magnetic material such as iron, cobalt, nickel, or ferrite can be used, but the most desirable is soft ferrite. Soft ferrite has ferromagnetism, high magnetic permeability, and very high electric resistance, so that eddy current B due to electromagnetic induction does not flow easily. In addition, the hysteresis loss due to the alternating magnetic field is small, which is most suitable for forming a magnetic path on the opposite side of the coil 1A of the heat generating layer 20b. This magnetic path forming member 41 collects the magnetic flux generated by the exciting coil 1A and the surrounding magnetic flux with a high magnetic flux density of the reaction magnetic field due to the eddy current to form a magnetic path, enabling efficient heating. At the same time, the magnetic flux leaks to the outside of the fixing device 10 to prevent the peripheral members from being unintentionally heated.

  Here, both end portions 41e in the circumferential direction of the magnetic path forming member 41 extend in the circumferential direction beyond the region facing between the end portions 1Ae in the circumferential direction of the exciting coil 1A. Yes. That is, both ends 41e of the magnetic path forming member 41 extend beyond both ends 1Ae of the exciting coil 1A facing each other before and after the moving direction of the heat fixing belt 20 (circumferential direction).

Specifically, as schematically shown in FIG. 6, the relationship between the ferrite width m2 of the magnetic path forming member 41 and the coil width m1 of the exciting coil 1A is set to satisfy m2> m1. . This is because if m2 is shorter than m1, the magnetic path is not sufficiently formed, and there is a possibility that efficiency may be reduced and guidance to peripheral members may be caused. Table 2 shows the measurement results of the magnetic flux density around the heating region in the case of m1 <m2 and m1> m2. As shown in Table 2, it can be seen that when m1 <m2, the leakage magnetic flux is small and a good shielding effect can be obtained.

  As described above, since both end portions 41e of the magnetic path forming member 41 extend beyond the region facing the exciting coil 1A and further in the circumferential direction of the heat fixing belt 20, the width of the magnetic path forming member 41 is increased. Is larger than the width (heating width) of the exciting coil 1A, and when the heat generating layer 20b induction heats a metal thinner than the skin depth δ, the reaction leaks from the opposite side of the exciting coil 1A across the heat generating layer 20b. Magnetic flux leakage due to a magnetic field can be more effectively prevented, a magnetic flux path with less leakage can be formed, and the shielding effect can be improved.

The first embodiment of the fixing device according to the present invention has been described above. However, the positional relationship between the exciting coil 1A and the magnetic path forming member 41 with respect to the heat fixing belt 20 is not limited to the above. For example, FIG. 7 is a view showing a modification 10A of the first embodiment of the fixing device according to the present invention. The fixing device 10A in the present modification is one in which the magnetic path forming member 40 is disposed inside the heat-fixing belt and the exciting coil 1A is disposed outside the heat-fixing belt 20. The arrangement relationship between the exciting coil 1A and the magnetic path forming member 41 is reversed. Even in such a configuration, the same effect as described above can be obtained, and at the same time, the heat dissipation of the exciting coil 1A can be improved.
<Second Embodiment>

  Next, a second embodiment of the fixing device according to the present invention will be described with reference to FIG.

  In the second embodiment of the fixing device according to the present invention, as shown in FIG. 8, the two magnetic path forming members 55 and 57 are arranged so as to face each other with the exciting coil 1A and the heat fixing belt 20 interposed therebetween. It is composed. For simplicity, members having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The fixing device 50 according to the second embodiment is intended to collect magnetic flux generated by the exciting coil 1A more efficiently and to increase the heating efficiency.

  Specifically, as shown in FIG. 8, a thin-walled hollow cylindrical heat-fixing belt 20 having a heat generating layer 20b, and a press-fit member disposed so as to be in pressure contact with the lower outer surface of the heat-fixing belt 20 in the figure. A pressure roll 23 is provided, and a support member 22 is disposed at the center of the heat fixing belt 20. The support member 22 supports the elastic member 24 that forms a nip by contacting the inner surface (lower part in the figure) of the heat fixing belt 20 facing the pressure roll 23 and vice versa. On the side (upper part in the figure), a ferrite 55 which is a substantially semi-cylindrical first magnetic path forming member formed so as to follow the curved surface shape of the inner surface of the heat fixing belt 20 is supported. Further, a substantially semi-cylindrical coil formed on the upper portion of the ferrite 55 so as to follow the curved surface shape of the inner surface of the heat-fixing belt 20 through an exciting coil 1A formed in a hollow spiral shape, for example. The support member 26 is disposed so as not to contact the inner surface of the heat fixing belt 20 and to face a part of the inner surface. The coil support member 26 has a protrusion 26A on the side facing the ferrite 55 at the center, and the excitation coil 1A is connected to the ferrite 55 by disposing a hollow portion of the excitation coil 1A on the protrusion 26A. The exciting coil 1A is held. Further, a second magnet disposed outside the heat-fixing belt 20 facing the exciting coil 1A so as to face a part of the outer surface without contacting the outer surface of the heat-fixing belt 20. A ferrite 57 which is a path forming member is provided.

  In the case of the fixing device 50 configured as described above, the magnetic path forming member sandwiching the exciting coil 1 </ b> A and the heat fixing belt 20 is the first magnetic path forming member 55 disposed inside the heat fixing belt 20. And the second magnetic path forming member 57 disposed outside the exciting coil 1A, the magnetic path forming for collecting and shielding the magnetic flux leaking from the exciting coil 1A more effectively. The member can be used more efficiently.

  Further, both end portions 57e in the circumferential direction of the ferrite 57 disposed on the heat fixing belt 20 side are formed so as to extend further in the circumferential direction beyond the region facing the exciting coil 1A.

  In this case, at least the circumferential ends 57e of the ferrite 57, which is the second magnetic path forming member disposed at least on the heat fixing belt 20 side, exceed the opposite ends 1Ae of the exciting coil 1A facing each other. Since it extends in the direction, as in the previous embodiment, when the heat generating layer 20b induction heats a metal thinner than the skin depth δ, the reaction leaks from the opposite side of the exciting coil 1A across the heat generating layer 20b. Magnetic flux leakage due to a magnetic field can be more effectively prevented, and the shielding effect can be improved.

  Further, by arranging the ferrite 55 and the ferrite 57 so as to face each other with the exciting coil 1A and the heat fixing belt 20 interposed therebetween, the frequency of the high frequency power source for applying an alternating current to the exciting coil 1A can be lowered, or the exciting coil 1A. The number of turns can be reduced, and further, cost reduction can be realized through downsizing the power source and downsizing the exciting coil 1A.

  In the present embodiment, the magnetic path forming member is formed by the first and second magnetic path forming members 55 and 57, but the magnetic path forming member sandwiches the exciting coil 1A and the heat fixing belt 20. What is necessary is just to have the part which has opposed, for example, you may form integrally in U shape so that the side surface of the heat fixing belt 20 may be covered.

  In order to further improve the shielding effect, both circumferential ends 55e of the ferrite 55 arranged on the exciting coil 1A side extend further in the circumferential direction beyond the region facing the exciting coil 1A. You may form as follows.

Further, as shown in a modified example 50A of FIG. 9, the exciting coil 1A may be disposed outside the heat fixing belt 20. In this case, the same effect as described above can be obtained, and the heat dissipation of the exciting coil 1A can be improved.
<Third embodiment>

  Next, a third embodiment of the fixing device according to the present invention will be described with reference to FIGS.

  The third embodiment is intended to provide a highly practical heating device and a fixing device using the same, in which the second embodiment is configured at a lower cost and considering cost reduction. The fixing device 70 according to this embodiment is different from the configuration of the fixing device 50 shown in the second embodiment in the form of the magnetic path forming member. In this embodiment, the amount of the magnetic path forming member used is smaller. Thus, a cheaper and lighter heating device and a fixing device using the same are provided.

  FIG. 10 is a schematic side view of the fixing device 70 according to the third embodiment, and FIG. 11 is a cross-sectional view taken along the line H-H ′. For simplification, the members (excitation coil support member 26, excitation coil 1A, magnetic path forming member 77) above the heat fixing belt 20 shown in FIG. 11 are separated upward in FIG. It is shown in the figure.

  In this embodiment, since the configuration other than the magnetic path forming member is substantially the same as that of the second embodiment, the description thereof will be omitted, and the magnetic path forming member and its peripheral constituent members will be mainly described below.

  As shown in FIGS. 10 and 11, the exciting coil 1 </ b> A has a hollow spiral shape composed of 90 litz wires, each of which is a bundle of 90 insulated wires (copper wires) having a diameter of φ0.16 mm that are insulated from each other. The coil 1 </ b> A is coiled by being wound and press-molded. The hollow portion 1 </ b> Ac of the exciting coil 1 </ b> A is disposed on the convex portion 26 </ b> A of the exciting coil support member 26, and is curved following the curved shape of the surface of the exciting coil support member 26 The shape is retained. In addition, a magnetic path forming member 77 is disposed on the upper surface of the exciting coil 1A so as to substantially cover the curved shape of the coil so as to cover the exciting coil 1A. 1A and the exciting coil support member 26 are disposed in contact with the outer surface of the heat-fixing belt 20 that moves around and is not in contact with the outer surface.

  Further, a magnetic path forming member 75 is disposed inside the heat fixing belt 20 along the inner surface of the belt so as to face the inner surface in a non-contact manner. The magnetic path forming member 75 and the magnetic path forming member 77 are disposed. Are opposed to each other with the exciting coil 1A and the heat fixing belt 20 interposed therebetween.

  Further, the magnetic path forming member 75 is supported by a nonmagnetic insulating member or a nonmagnetic metal member (resin, aluminum, copper, or the like) support member 22, and this support member 22 is also an elastic member that forms a fixing nip. The load from 24 is supported. Here, since the supporting member 22 supports the pressing load of the fixing nip, the supporting member 22 needs to be a member having high rigidity, high heat resistance, and high creep resistance, and is difficult to form with a resin material. It is desirable to be formed by. In the present embodiment, aluminum is used in consideration of cost, ease of manufacture, and rigidity. The reason for using aluminum or copper, which is a nonmagnetic metal, as the metal member is that the support member 22 is located at a position where the magnetic field generated by the eddy current B of the heating layer 20b in the heating coil 20 and the exciting coil 1A is likely to act. In the case of a magnetic metal, heat is generated by the action of this magnetic field. Therefore, by using a nonmagnetic metal having a large skin depth, eddy current loss can be extremely reduced.

  Here, as shown in FIGS. 10 and 11, the magnetic path forming member 77 arranged on the exciting coil 1A side is formed of a continuous body that covers the coil 1A. On the other hand, the magnetic path forming member 75 arranged on the heat fixing belt 20 side is divided into a plurality of small piece arcuate members 75A, and has an interval of 16 mm in the rotation axis direction substantially orthogonal to the moving direction of the heat fixing belt 20. There are 13 open. The small piece 75A of the magnetic path forming member group 75 has an arcuate shape with a thickness of 3 mm and a gentle curvature, and the width along the longitudinal direction of the exciting coil 1A is 10 mm. The small arcuate member 75A on the support member 22 is placed on the support member 22 and is in non-contact with the inner surface of the heat-fixing belt 20, and substantially corresponds to the opposing surface of the exciting coil 1A along the inner surface. Is arranged. With the magnetic path forming member 75 arranged in this way, for example, the magnetic path in the H-H ′ cross section of FIG. 10 is formed as shown by a broken line in FIG. 12.

  Here, the reason why the small bow members 75A of the magnetic path forming member 75 are arranged at intervals is to form a magnetic path by applying a magnetic flux evenly in the direction of the rotation axis of the heat fixing belt 20. The usage amount of the small pieces 75A constituting the magnetic path forming member 75 is only required to be able to prevent electromagnetic induction to the peripheral metal member with a small number.

  Below, the usage-amount of this magnetic path formation member 75 is examined with reference to FIG. FIG. 13 is a diagram showing the degree of induction to the support member 22 with respect to the usage amount of the magnetic path forming member 75A. The support member 22 is made of aluminum, and the inductivity to the support member metal 22 referred to in this figure is affected by the electromagnetic induction action of the exciting coil 1A. This is a characteristic indicating that it has not been received. Moreover, the usage-amount of a magnetic path formation member has shown the state when the surface of the supporting member 22 is covered by the same length as a coil length with respect to a coil length, for example.

  In the case of the present embodiment, the coil length is 350 mm, and a total of 13 small arch members 75A of the magnetic path forming member 75 having a width of 10 mm are used. Therefore, the usage amount of the magnetic path forming member 75 is 10 × 13 mm / 350 mm × 100≈37%.

  In the case where the inductive degree (0.9) of the dotted line in the figure is less than or equal to 0.9, this is a region where reactive power increases due to the inductive action on the support member 22 and causes a reduction in power supply efficiency. If it is 30% or more, it turns out that there is no problem. Further, if the usage amount is 30% or more, the leakage magnetic field is small, and induction to a metallic component other than the support member 22 can be almost eliminated.

  Therefore, also in the third embodiment in which the amount of magnetic path forming member 75 used is reduced in this way, it is possible to provide a heating device that can obtain a stable heating state and a fixing device using the same.

  Further, in the present embodiment, at least the magnetic path forming member 75 disposed on the heat fixing belt 20 side is provided with a plurality of small piece members 75 </ b> A with a gap between them in the direction of the rotation axis of the heat fixing belt 20. Therefore, the individual magnetic path forming members 75A can be made small, thereby facilitating the molding of the individual magnetic path forming members 75A and increasing the dimensional accuracy thereof. In addition, it is possible to provide a heating device that can reduce the amount of ferrite used as an expensive magnetic path forming member, reduce the weight, and reduce the cost, and a fixing device using the heating device.

  As in the previous embodiment, both circumferential ends 75e of the ferrite 75 disposed on the heat fixing belt 20 side extend further in the circumferential direction beyond a region facing the exciting coil 1A. Thus, when the heat generating layer 20b induction heats a metal having a skin depth less than δ, magnetic flux leakage due to the reaction magnetic field leaking from the side opposite to the exciting coil 1A across the heat generating layer 20b is more effectively performed. It is possible to prevent and improve the shielding effect.

Further, the exciting coil 1A may be disposed outside the heat fixing belt 20, or the magnetic path forming member 77 disposed outside the heat fixing belt 20 is formed of a small piece arcuate member group, and the heat fixing belt 20 is formed. The magnetic path forming member 75 disposed on the inner side may be formed of a continuous body.
<Fourth embodiment>

  Next, a fourth embodiment of the fixing device according to the present invention will be described with reference to FIGS.

  The fourth embodiment is intended to provide a highly practical heating device and a fixing device using the same, in which the third embodiment is configured at a lower cost and considering cost reduction. . The fixing device 90 according to this embodiment is different from the configuration of the fixing device 70 shown in the third embodiment in the form of the magnetic path forming member. In this embodiment, the amount of the magnetic path forming member used is smaller. Thus, a cheaper and lighter heating device and a fixing device using the same are provided.

  FIG. 14 is a schematic side view of a fixing device 90 according to the fourth embodiment, FIG. 15 is a cross-sectional view taken along line JJ ′, and FIG. 16 is a cross-sectional view taken along line KK ′. FIG. FIG. 17 is a side view schematically showing the positional relationship between the magnetic path forming member groups in order to visually explain the meaning of the designation “staggered arrangement” in the fourth embodiment. Here, in FIG. 17, for simplification, members (excitation coil support member 26, excitation coil 1A, magnetic path forming member 97) above the heat fixing belt 20 shown in FIGS. In FIG. 17, it is shown separated upward.

  In this embodiment, since the configuration other than the magnetic path forming member is substantially the same as that of the third embodiment, the description thereof will be omitted, and the magnetic path forming member and its peripheral constituent members will be mainly described below.

  As shown in FIG. 14, in the present embodiment, the magnetic path forming member 95 and the magnetic path forming member 97 arranged so as to face each other are divided into a plurality of small piece arcuate members 95A and 97A, respectively. There are 14 magnetic path forming members 97 arranged on the exciting coil 1A side and 13 magnetic path forming members 95 arranged on the heating and fixing belt side with an interval of 16 mm in the direction of the rotation axis of 20 respectively. Has been.

  The mutual positional relationship between the magnetic path forming member 95 and the magnetic path forming member 97 is a so-called “staggered arrangement” as shown in FIGS. 14 and 17, and the opposing magnetic path forming member group 95 </ b> A. 97A is asymmetric with respect to the heat-fixing belt 20, and the gap 95As of the small arch member 95A forming the magnetic path forming member 95 is the small arch shape forming the magnetic path forming member 97. The members 97A are arranged in a positional relationship such that they are substantially interpolated. In other words, each of the small piece arcuate member 95A and the small piece arcuate member 97A is disposed so as to correspond to the gaps 97As and 95As of the opposing ferrites 97 and 95 facing each other.

  More specifically, as shown in FIG. 17, the center positions 95Ac and 97Ac of the small piece arcuate member 95A and the small piece arcuate member 97A correspond to the centers of the gaps 97As and 95As of the opposing mating ferrites 97A and 95A. It arrange | positions so that it may correspond substantially.

  In this way, when the magnetic path forming members 95 and 97 are divided into a plurality of small piece arcuate members 95A and 97A and arranged with a gap therebetween, the influence of electromagnetic induction on the surrounding members due to leakage of the magnetic field can be considered. .

  Therefore, the verification results on the influence of electromagnetic induction on the surrounding members when the number of the small bow members 95A and 97A is changed to provide a gap will be described below.

  First, a characteristic change depending on the number of small piece bow members 97A of the magnetic path forming member 97 disposed on the exciting coil 1A side will be described with reference to FIG. FIG. 18 shows the induction when a metal member such as iron or aluminum having the same size as that of the coil 1A is brought close to the distance of 5 to 10 mm from the excitation coil 1A when a constant alternating current is applied to the excitation coil 1A. It shows the result of investigating the influence of electromagnetic induction on surrounding metal members from change information such as the inductance value, resistance value, and phase difference between current and voltage. In FIG. 18, as a representative characteristic indicating the degree of induction to the surrounding metal with respect to the ratio of covering the coil length, the inductance value (a) in the induction state when the metal member is brought close to the usage amount of the magnetic path forming member and the resistance The change in value (b) is shown. For example, in the present embodiment, 14 small piece bow members 97A each having a width of 10 mm and a coil 1A are covered with a gap of 350 mm with respect to the coil length of 350 mm, so that 10 mm × 14 pieces / 350 mm = 40% magnetic path formation. This is the amount of material used (corresponding to 40% share area 40% on the horizontal axis in the figure). Here, the close metals are aluminum and iron. When these metals are brought close to each other, as shown in FIGS. 18A and 18B, if at least 40% or more of the magnetic path forming member is used, the surroundings of the electromagnetic field in the AC frequency component applied to the coil It was found that the impact on the level was negligible.

  Next, FIG. 19 shows the result of investigating the degree of influence of electromagnetic induction on the surrounding members of the magnetic path forming member 95 in the same manner with the usage amount of the magnetic path forming member 97 being 40%. The degree of influence of electromagnetic induction on the surrounding members of the magnetic path forming member 95 is such that the supporting member 22 that holds the magnetic induction is made of a metal such as aluminum or iron, and the magnetic field H generated by the magnetic field of the exciting coil 1A or the eddy current B of the heat generating layer 20b. The effect on the support metal 22 was investigated. The degree of induction to the support member metal 22 in this figure is a characteristic indicating that the smaller the degree of induction, the less the influence of the electromagnetic induction action is received. This is almost the same as the typical characteristic shown in FIG. 18, and shows the ratio of change in the inductance value and resistance value in the inductive state when the metal member is brought closer. Here, if the degree of induction is 0.9 or more, the influence on the induction can be ignored. As shown in FIG. 19, when the magnetic path forming member 95 is used at about 35%, the induction degree becomes 0.9 or more, and it has been found that the influence of electromagnetic induction on the surrounding members can be extremely reduced.

  From the above-described verification results, it can be seen that the magnetic path forming member 95 and the magnetic path forming member 97 may be disposed with appropriate gaps in appropriate amounts. It is also necessary to consider the heat generation distribution. For example, as shown in FIG. 20, the magnetic path forming member 95 and the magnetic path forming member 97 are in the same positional relationship with respect to the rotation axis direction of the heat fixing belt 20 (the small bow members 95A and 97A are opposed to each other). When the magnetic path forming members 95 and 97 are orthogonally projected onto the heat-fixing belt, the magnetic flux concentrates on the portions (portions where the small bow members 95A and 97A face each other), This portion is heated excessively, resulting in a temperature difference (temperature unevenness).

  When the heating device of the present embodiment is applied to a fixing device, if such a temperature difference occurs, problems such as uneven coloring of a toner image to be fixed occur, which is not desirable. Therefore, as shown in FIG. 21, the arrangement relationship between the magnetic path forming member 95A and the magnetic path forming member 97A is arranged so as not to have the same positional relationship with respect to the rotation axis direction of the heat fixing belt 20, and particularly shown in the drawing. Thus, it is desirable to adopt a so-called “staggered arrangement” in which the gaps 95As and 97As are arranged to complement each other. In the case of the arrangement as shown in FIG. 21, as shown in the schematic diagram of FIG. 22, the magnetic field of the coil acts on the heat generating layer 20b of the heat fixing belt 20 evenly, and the temperature difference of the heat fixing belt 20 is reduced. This makes it possible to stably heat the image without causing problems such as uneven coloring of the fixed image.

  Further, if the magnetic path forming member 95A and the magnetic path forming member 97A are arranged so as to complement the gaps 95As and 97As of each other, the positions of the mutual portions are partially as shown in the schematic diagram shown in FIG. 23, for example. You may arrange | position so that it may overlap. FIG. 23 shows an example in which the amount of use of the small piece arcuate member 95A that forms the magnetic path forming member 95 is increased as compared with the case of FIG. 21, but the amount of use of the small piece arcuate member 97A that forms the magnetic path forming member 97 is shown. You may arrange with increasing.

  As described above, when the magnetic path forming member is divided into small pieces such as the magnetic path forming member 95A and the magnetic path forming member 97A and provided with a gap, the mutual positional relationship is considered as described above. A heating device capable of forming an appropriate magnetic path, preventing occurrence of temperature unevenness due to concentration of magnetic flux, reducing the amount of expensive magnetic path forming members, and enabling its effective use, and application thereof The fixing device can be provided.

  Further, as shown in FIG. 16, both end portions 95e in the circumferential direction of the ferrite 95 disposed on the heat fixing belt 20 side extend further in the circumferential direction beyond the region facing the exciting coil 1A. As in the previous embodiment, the reaction magnetic field leaks from the side opposite to the exciting coil 1A across the heat generating layer 20b when the heat generating layer 20b induction heats a metal having a skin depth less than δ. Can effectively prevent the leakage of magnetic flux and improve the shielding effect.

  In any of the embodiments of the fixing device to which the heating device according to the present invention described above is applied, the warm-up time can be made equal to almost zero of 10 seconds or less and good fixing can be performed as follows. In addition, it is possible to reliably prevent the occurrence of defective peeling.

  That is, in the fixing device according to these embodiments, for example, as illustrated in FIG. 1, the pressure roll 23 is rotationally driven by a driving source at a process speed of 100 mm / s. The heat fixing belt 20 is in pressure contact with the pressure roll 23 and is circulated and moved at a speed of 100 mm / s, which is equal to the movement speed of the pressure roll 23.

  In the fixing device, the recording material 27 onto which the unfixed toner image 25 is transferred by a transfer device (not shown) passes through the nip portion 1Y formed between the heat fixing belt 20 and the pressure roll 23, While the recording material 27 passes through the nip portion 1Y, the toner image 25 is fixed on the recording material by being heated and pressed by the heat fixing belt 20 and the pressure roll 23. Yes.

  At that time, in the fixing device, the temperature of the heat fixing belt 20 is controlled to about 160 ° C. to 200 ° C. at the entrance of the nip portion 1Y during the fixing operation by the frequency of the high frequency current flowing through the exciting coil 1A. .

  In such a fixing device, simultaneously with the input of the image forming signal, the pressure roll 23 starts to rotate and a high-frequency current is applied to the exciting coil 1A. For example, when 1000 W of electric power is applied to the exciting coil 1A, the temperature of the heat-fixing belt 20 reaches the fixable temperature in about 8 seconds or less from room temperature by induction heating action. That is, the warm-up is completed within the time required for the recording material 27 to move from the paper feed tray to the fixing device. Accordingly, the fixing device can perform the fixing process without causing the user to wait.

  Further, when the recording material 27 having a large amount of toner such as a color solid image entered into a thin paper of about 60 gms enters the nip portion 1Y of the fixing device, the toner and the release layer on the surface of the heat fixing belt 20 are transferred. In general, the attracting force increases, and it becomes difficult to peel off the recording material from the surface of the heat fixing belt 20. However, in the fixing device according to the present invention, the heat fixing belt 20 is formed to have a concave shape inside the nip portion 1Y, while the heat fixing belt 20 has a convex shape outside the nip portion 1Y. That is, in the nip portion 1Y, the direction of the recording material 27 is a direction wound around the pressure roll 23, and the direction of the heat fixing belt 20 is changed from a concave shape to a convex shape at the outlet portion of the nip portion 1Y. Since the recording material 27 changes abruptly, the recording material 27 can not keep up with the rapid shape change of the heat fixing belt 20 due to the stiffness (rigidity) of the recording material itself, and is naturally separated from the heat fixing belt 20. Thereby, it is possible to reliably prevent the problem of the peeling failure of the recording material 27.

  Further, when the small size recording material 27 is continuously fixed, the temperature of the heat fixing belt 20, the elastic member 24, the pressure roll 23, etc. in the non-sheet passing area rises. By bringing the metal roll 28 (see FIG. 11) provided on the side into contact with the surface of the pressure roll 23, the heat of the high temperature portion of the pressure roll 23 can be absorbed by the metal roll 28, and the heat Therefore, the temperature distribution in the axial direction becomes small, and the temperature of the pressure roll 23 and the temperature of the heat fixing belt 20 can be prevented from becoming higher than a predetermined temperature.

  Although the heat fixing belt 20 in the above embodiment is formed in a thin cylindrical shape, the belt shape is naturally not limited to a cylindrical shape. For example, the heat fixing belt 20 extends between a plurality of rollers. A heat fixing belt may be formed by stretching the belt.

  Next, an embodiment of an image recording apparatus to which the present invention is applied will be described with reference to FIG. FIG. 24 is a diagram showing a schematic configuration of the image recording apparatus 100 according to an embodiment of the present invention.

  As shown in FIG. 24, the image recording apparatus 100 includes, for example, a photosensitive drum 121 that rotates in the direction of an arrow in the figure, a charger 122 such as a corotron that precharges the photosensitive drum 121, and each color component image. An image writing device such as a laser scanning device (ROS) (not shown) that writes an electrostatic latent image corresponding to each color component on the photosensitive drum 121 based on the information (in this example, a beam is attached to the beam from the device). And a rotary type developing device 124 in which developing units 241 to 244 corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are mounted on a rotary holder 245, and An electrostatic latent image for each color component of yellow, magenta, cyan, and black is formed on the body drum 121, and the corresponding developing devices 241 to 244 in the rotary developing device 124 After each electrostatic latent image is visualized with a color toner, the image is sequentially primary-transferred onto the intermediate transfer belt 130, and the superimposed transfer image of each color component toner image on the intermediate transfer belt 130 is secondarily transferred onto the recording material P. The image is transferred and fixed by the fixing device 160.

  Here, the recording material P is transported from the recording material tray 150 to a predetermined transport path by the feed roll 151, and once stopped by a registration roll (registration roll) 152 in the transport path, the recording material P is then transported to a predetermined transport path. The recording material P is conveyed to the secondary transfer position 140 at the timing, and is guided to the conveyance belt 153 after the secondary transfer, and is conveyed to the fixing device 160 by the conveyance belt 153. When the secondary transfer process is completed, residual toner on the photosensitive drum 121 is cleaned by the drum cleaner 125, and residual toner on the intermediate transfer belt 130 is cleaned by the belt cleaner 141.

  In the image recording apparatus 100 configured as described above, by applying the heating device and the fixing device according to the present invention to the heating unit and the fixing unit, an image recording that has a short warm-up time and can be stably fixed by heating. An apparatus can be provided.

  The image recording apparatus to which the present invention is applicable is not limited to the rotary type described above, and can be applied to various image recording apparatuses within the scope of the object of the present invention. For example, the same effects can be obtained even when applied to a so-called tandem type image recording apparatus.

  As described above, by providing the fixing device with the heating device of the present invention, it is possible to design an energy-saving fixing device that can reduce the warm-up time to 10 seconds or less. In addition, it is possible to design a highly practical heating apparatus that can realize cost reduction. Further, by providing such a heating device and a fixing device, it is possible to provide an image recording apparatus that is excellent in stability and safety and has an extremely short warm-up time.

1 is a schematic cross-sectional view showing a first embodiment of a heating device and a fixing device according to the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration of a fixing belt. FIG. 6 is a schematic cross-sectional view showing another configuration of the fixing belt. It is a characteristic view which shows the relationship between the applied frequency to a heating apparatus, and heat_generation | fever. It is a schematic diagram which shows the structure of a heat generating apparatus. It is a schematic diagram which shows the relationship between the width | variety of an exciting coil and the width | variety of a magnetic path formation member. FIG. 6 is a schematic cross-sectional view showing a modification of the first embodiment of the heating device and the fixing device according to the present invention. It is a typical sectional view showing a second embodiment of a heating device and a fixing device concerning the present invention. It is a typical sectional view showing a modification of a second embodiment of a heating device and a fixing device according to the present invention. It is a typical side view which shows 3rd embodiment of the heating apparatus and fixing device which concern on this invention. It is typical sectional drawing along the H-H 'line | wire of FIG. It is typical sectional drawing which shows the formation state of a magnetic path. It is a figure which shows the relationship between the usage-amount of a magnetic path formation member, and the induction | guidance | derivation degree to a supporting member. FIG. 6 is a schematic side view showing a fourth embodiment of a heating device and a fixing device according to the present invention. FIG. 15 is a schematic cross-sectional view taken along line J-J ′ in FIG. 14. It is typical sectional drawing along the K-K 'line | wire of FIG. It is a typical side view which shows the arrangement | positioning relationship of a component. It is a figure which shows the change of the inductance value (a) of an induction | guidance | derivation state, and resistance value (b) when a metal member is brought close with respect to the usage-amount of a magnetic path formation member. It is a figure which shows the relationship between the usage-amount of a magnetic path formation member, and the induction | guidance | derivation degree to a supporting member. Side surface schematic diagram showing the degree of influence of electromagnetic induction on the surrounding metal members when each of the small piece arcuate members of the magnetic path forming members facing each other is arranged in the same positional relationship with respect to the rotation axis direction of the heat fixing belt It is. It is a side surface schematic diagram which shows the influence degree of the electromagnetic induction to a surrounding metal member when each of the small piece arch-shaped members of the opposing magnetic path forming member is staggered with respect to the rotation axis direction of the heat fixing belt. FIG. 6 is a schematic side view showing a state in which the magnetic field generated by the exciting coil acts on the heat generating layer of the heat-fixing belt evenly in the “staggered arrangement”. It is a typical side view which shows the example which increased and used the usage-amount of one small piece bow-shaped member of the opposing magnetic path formation member. 1 is a diagram showing a schematic configuration of an image recording apparatus according to the present invention. It is a figure which shows an example of the conventional electromagnetic induction heating apparatus. It is a figure which shows another example of the conventional electromagnetic induction heating apparatus.

Explanation of symbols

1A: exciting coil, 1Y: nip portion, 1Ae: circumferential end portions, 1Ac: hollow portion, 10, 10A: fixing device, 20: heat fixing belt, 20a: base material layer, 20b: heating layer, 20c: release Layer, 20d: elastic layer, 22: support member, 23: pressure roll, 24: elastic member, 25: toner image, 26: excitation coil support member, 26A: convex portion, 27: recording material, 28: metal roll, 30: Excitation circuit, 40: Magnetic path forming member, 41: Magnetic path forming member, 41e: Both ends in the circumferential direction, 50: Fixing device, 55: Magnetic path forming member, 55e: Both ends in the circumferential direction, 57: Magnetic path forming Member, 57e: both ends in the circumferential direction, 70: fixing device, 75: magnetic path forming member, 75A: small piece bow member 75e: both ends in the circumferential direction, 77: magnetic path forming member, 90: fixing device, 95, 97: magnetic Road forming member, 95A, 97A: Small bow Member, 95Ac, 97Ac: center position, 97As, 95As: gap, 100: image recording device, 121: photosensitive drum, 122: charger, 124: rotary developing device, 125: drum cleaner, 130: intermediate transfer belt, 140: Secondary transfer position, 141: Belt cleaner, 150: Recording material tray, 151: Feed roll, 153: Conveyor belt, 160: Fixing device, 241-244: Each developer, 245: Rotating holder, m1: Coil width , M2: ferrite width

Claims (10)

And having a at least on the outermost surface release layer, seen containing a conductive heating layer, the thickness of the heat generating layer, and a fixing belt of a thin endless than its skin depth, of the heat generating layer of the fixing belt thickness In a fixing device having an exciting coil for electromagnetically heating the heat generating layer by generating a variable magnetic field along a direction,
A recording material carrying an unfixed toner image is heated and pressed between a pressure member and the fixing belt, and the nip portion for fixing the unfixed toner image is opposed to the pressure member via the fixing belt. A pressing member that is disposed to form the nip portion, a first magnetic path forming member that forms a magnetic path of a variable magnetic field generated by the exciting coil and shields the magnetic field, and a second magnetic path forming member;
With
The exciting coil is disposed outside of the fixing belt, the surface and non-contact of the fixing belt is formed by winding a wire so as to follow the along and the surface shape on the surface,
Wherein a first magnetic path forming member and the second magnetic path forming member made of a magnetic material, the fixing belt is formed so as to follow the surface shape of the fixing belt and the contact to the said excitation coil and said It is arranged to face each other across the fixing belt ,
The first magnetic path forming member is supported by a support member made of a nonmagnetic metal member inside the fixing belt, and is partially disposed in the longitudinal direction of the excitation coil. The path forming member is disposed on the side opposite to the fixing belt side of the excitation coil,
Of opposite side of the exciting coil and the opposing surfaces of the fixing belt, the partially deployed first magnetic path forming member not facing portion, the support member and the facing comprising the non-magnetic metal member And the support member supports the pressing member on the side opposite to the side supporting the first magnetic path forming member.   The fixing belt is formed so as to be movable in a predetermined direction, and at least both ends of the first magnetic path forming member arranged on the fixing belt side before and after the moving direction are opposed to each other. The fixing device according to claim 1, wherein the fixing device extends beyond both ends of the coil. The fixing device according to claim 1, wherein the fixing belt has a cylindrical shape . At least one of the first and second magnetic path forming members is a small piece member group composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially perpendicular to the moving direction of the fixing belt. The fixing device according to claim 1 , wherein the fixing device is configured as follows . Each of the first and second magnetic path forming members is a small piece member group composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially perpendicular to the moving direction of the fixing belt. 2 each adjacent to each other in each small piece member of the small piece member group constituting the first or second magnetic path forming member and the small piece member group constituting the second or first magnetic path forming member. The fixing device according to claim 4 , wherein the gaps formed by the two small piece members are arranged to face each other . Each of the first and second magnetic path forming members is a small piece member group composed of a plurality of small piece members arranged with a predetermined gap therebetween in a direction substantially perpendicular to the moving direction of the fixing belt. The small piece member group of the first magnetic path forming member and the small piece member group of the second magnetic path forming member are configured to complement each gap of the opposing magnetic path forming member facing each other. The fixing device according to claim 4 , wherein the fixing device is disposed on the fixing device. Each of the small piece member groups of the first and second magnetic path forming members has a center in a direction substantially orthogonal to the moving direction of the fixing belt, and the opposite magnetic path forming member group is opposed to each other. The fixing device according to claim 1 , wherein the fixing device is disposed so as to substantially coincide with a center of the gap . The fixing device according to claim 1, wherein the magnetic path forming member is made of soft ferrite . The heat generating layer of the fixing belt is mainly formed of copper having a thickness of 2 to 15 μm, and the frequency of the alternating current applied to the exciting coil is 20 to 100 kHz. The fixing device according to claim 1 .   An image recording apparatus comprising: the fixing device according to claim 1; and an image forming unit that forms an unfixed toner image on a recording material.

Images