JP2003295652A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which efficiently fixes and image by means of a simple and low-cost structure. <P>SOLUTION: In the fixing device A which fixes an image to a recording material by bringing a fixing member into contact with the image carrying face of the material P, the fixing member 1 is heated from its surface by a heating member 3 of a low heat capacity. The fixing device A further has a pressing member 2 which forms a pressure nip N1 together with the fixing member 1. The heating member 3 can abut on the fixing member 2 in a position that is upstream from the pressure nip formed by the fixing member 1 and pressure member 2. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus using, for example, an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art For example, as a problem that has become more important in recent years in electrophotographic image forming apparatuses used in copying machines, printers, fax machines, etc., there is a problem of energy saving.

The fixing device used in such an image forming apparatus consumes electric power directly as heat energy in order to melt the toner and fix it on the recording material, and is used in the entire image forming apparatus main body. Power consumption accounts for a large proportion.

As one direction for reducing energy consumption, the image forming apparatus has been made on-demand in recent years. For example, the fixing member is formed into a thin roller, a thin belt, or a film to reduce the heat capacity, accelerate the rising time, and simultaneously suppress the power consumption during that period.

By achieving on-demand, the image forming apparatus can start printing immediately after receiving a print signal with almost no waiting time. Therefore, it is not necessary to keep the fixing member at a high temperature near the printing temperature during non-printing, and it may be kept at room temperature or at a proper low temperature at best. The heat radiation during the heat retention of the fixing device increases in proportion to the temperature difference between the environmental temperature and the set temperature of the fixing member, and therefore power is always consumed even in the non-printing state. Therefore, in a situation where printing is repeated intermittently, the on-demand operation brings about a great power saving effect.

In the image forming apparatus as described above, a method of heating the heater from the inner surface of a roller-shaped fixing member (fixing roller) is generally used. And
A recording material is nipped and conveyed by a pressure nip formed by a fixing member that is heated and a pressure member that is in pressure contact with the fixing member, and an image is fixed on the recording material. When using a halogen lamp and a fixing roller, the glass surface of the halogen lamp is 200 ° C.
However, the actual temperature control is performed at about 180 ° C. by detecting the surface temperature of the roller.

On the other hand, in the on-demand system configuration in which the surface of the recording material is directly heated by using a ceramic heater and a fixing film which have been commercialized in recent years, the heater temperature is 190 to 20.
At a low temperature of about 0 ° C, the same fixability as the former is obtained. From this, it can be said that the latter system, which can reduce the top temperature to almost the fixing temperature, is more efficient with less heat loss.

Similarly, a system in which the fixing member itself generates heat, for example, a system using a self-heating element or magnetic induction heating, is a highly efficient system which can lower the top temperature. In addition, since it is possible to directly heat the vicinity of the surface of the fixing member, the thermal response is improved, stable temperature control with less ripple is possible compared to roller fixing by normal halogen lamp heating, and high temperature offset The latitude between the region and the low temperature offset region can be effectively taken. As a result, it is possible to obtain a stable image with high fixability without uneven gloss.

[0009]

However, the roller fixing described above is mechanically stable and has no problem such as slipping even when the pressure in the nip portion is increased as compared with belt fixing, and the structure is simple. Because it has the advantage that
It is considered that this technology will be widely used in products in the future.

Therefore, the present inventors have made earnest studies to achieve the efficiency of the fixing device such as the improvement of the fixing property and the energy saving while taking advantage of the roller fixing. Then, the present inventors have paid attention to the following points in roller fixing from the viewpoint of efficiency.

Normally, in roller fixing, there is a temperature gradient such that the roller surface has the lowest temperature and the core metal has the highest temperature during printing. However, in practice, only the vicinity of the surface needs to have a certain suitable temperature for fixing, and it can be said that useless energy is required to raise the core metal temperature higher than that. This extra heat causes an overshoot after printing, and eventually it is not effectively utilized and is radiated to the outside.

Further, as described above, on-demanding is preferable in terms of energy saving and high efficiency. However, in the structure of directly heating and fixing from the image side of the recording material using the conventional ceramic heater and film, the fixed image is fixed. There has been a problem that a phenomenon in which a myriad of fine air bubbles are generated on the surface, that is, a so-called "sun" or uneven gloss is generated. Therefore, a monochrome image has no practical problem, but there is still a problem in obtaining a high quality color image.

Therefore, it is an object of the present invention to provide a fixing device which is generally simple and has a low cost, and which can perform fixing efficiently.

Another object of the present invention is to prevent surface overshoot due to heat moving from the inner side to the surface side of the fixing member after image formation, and at the same time, effectively utilize thermal energy for energy saving. It is to provide a fixing device that can do this.

Another object of the present invention is to provide a fixing device having an appropriate on-demand property.

Another object of the present invention is that when a fixed image does not have uneven gloss, it is possible to form a high-quality color image, and when it is applied to an on-demand system that also uses a ceramic heater and a film. Another object of the present invention is to provide a fixing device capable of mitigating a temperature difference in the lengthwise direction of a heater when passing a recording material and preventing heater cracking.

[0017]

The above object can be achieved by the fixing device according to the present invention. In summary, the present invention relates to a fixing device for fixing an image on a recording material by bringing the fixing member into contact with the image bearing surface of the recording material, wherein the fixing member is heated from the surface by a heating member having a lower heat capacity. The fixing device is characterized in that

According to an embodiment of the present invention, the fixing member may be a roller or an endless belt. The fixing member preferably has at least an elastic layer,
In one embodiment, the fixing member has at least a release layer and an elastic layer in this order from the side in contact with the recording material.

In the present invention, it is preferable that the heating member contacts the fixing member to heat the fixing member by contact. In one embodiment, the heating member comprises a roller or an endless film having at least a heating element and a releasable surface, which has a lower heat capacity than the fixing member, preferably the elastic layer portion thereof.

According to a preferred embodiment of the present invention, the fixing device further includes a pressure member forming a pressure nip with the fixing member, and the heating member includes the fixing member and the pressure member. The fixing member is abutted at a position upstream of the pressure nip. Further, in one embodiment, the heating member is arranged in the vicinity of the recording material conveyance path immediately before the pressure nip between the fixing member and the pressure member. According to another embodiment of the present invention, the pressure member includes a film having at least a heating element and a releasable surface, which has a lower heat capacity than the fixing member, preferably the elastic layer portion thereof.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The fixing device according to the present invention will now be described in more detail with reference to the drawings.

Embodiment 1 In this embodiment, the present invention is embodied in a fixing device used in an electrophotographic image forming apparatus. However, the present invention is not limited to this, and can be applied to a fixing device used in any image forming apparatus such as an electrostatic recording method that requires heating and pressure fixing of a developer image.

An electrophotographic image forming apparatus typically has a schematic structure shown in FIG. That is, the image forming apparatus 100 has a drum-type electrophotographic photosensitive member (photosensitive drum) 101 as an image bearing member. Photosensitive drum 1
01 rotates in the direction of the arrow in the figure, and its surface is uniformly charged by the charger 102 as a charging means. The charged surface of the photoconductor drum 101 is scanned and exposed by a laser beam L according to image information, for example, by a laser scanner 103 as an exposure unit, and an electrostatic latent image is formed on the surface of the photoconductor drum 101. The electrostatic latent image formed on the photosensitive drum 101 is then developed by the developing device 1 as a developing unit.
By supplying the developer (toner) by the developing roller 104a included in 04, the toner image is visualized as a toner image.

On the other hand, a recording material P stored in a recording material storage portion (not shown) such as a tray or a recording material storage cassette,
For example, a recording paper, an OHP sheet, or the like is synchronized with the formation of the toner image on the photosensitive drum 101, and
01 and the transfer charger 105 serving as a transfer unit are conveyed to a facing portion (transfer position).

The toner image formed on the photosensitive drum 101 is electrostatically transferred to the recording material P by the action of the transfer charger 105. Recording material P on which the toner image is transferred
Is then conveyed to the fixing device A, where it is heated and pressed, and the toner image is fixed on the surface thereof.

The recording material P on which the toner image is fixed is then discharged to the outside of the apparatus. Further, the toner remaining on the surface of the photosensitive drum 101 after the transfer of the toner image (transfer residual toner)
Are removed by a cleaning device 106 having cleaning means such as a cleaning blade 106a and a cleaning roller 106b, and the photosensitive drum 101 is repeatedly used for image formation.

FIG. 1 shows a schematic cross section of an embodiment of the fixing device A according to the present invention. The fixing device A is a fixing member.
It has a fixing roller 1 which is rotationally driven by a driving means (not shown). Also, for the driven fixing roller 1,
The pressure roller 2 is pressed as a pressure member, and the pressure roller 2 is driven to rotate by the rotation of the fixing roller 1.
By heating and pressurizing the recording material P via the contact portion (pressure nip portion) N1 of the fixing roller 1 and the pressure roller 2, the unfixed toner image carried by the recording material P is recorded on the recording material P. Fix it.

Next, the fixing device A in this embodiment will be described in detail.

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems in conventional roller fixing, and as a result,
The minimum required heating is performed from the surface side of the fixing member, and the surface of the fixing member is at a high temperature, and the inside, that is, in the case of a roller-like fixing member (fixing roller), has a thermal gradient such that the core side is rather low temperature. It has been found that fixing can improve thermal efficiency and save energy.

Through many experiments and researches conducted by the present inventors, typically, a heating member in which a surface release layer is formed on a thin-walled, small-diameter metal roller having a built-in heating element (halogen lamp heater, etc.) and having a rapid rise. The (heat roller) is brought into contact with the surface of the fixing member at a position upstream of the pressure nip formed by the fixing member (fixing roller, fixing belt, etc.), and the fixing member is heated from the surface while rotating. I decided to do it. As a result, it has been found that it is possible to obtain a temporary fixability. In this specification, such a fixing method is
Called the surface heating method.

In this embodiment, the fixing roller 1 is heated by the surface heating method. The surface of the fixing roller 1 is heated by bringing the heat roller 3 as a heating member into contact with the upstream side of the pressure nip portion N1. The heat roller 3 has a halogen lamp heater as a heating element 4 inside. In this way, the contact portion (heating portion) between the fixing roller 1 and the heat roller 3
In N2, the fixing roller 1 is contact-heated from the surface.
The fixing temperature control is performed by controlling the heating of the heating element 4 of the heat roller 3 based on the temperature detection signal of the thermistor 5 as the temperature detection means that is in contact with the heat roller 3. The fixing device A further has a fixing inlet guide 6 for guiding the recording material P to the pressure nip portion N1.

Here, the upstream side of the pressure nip N1 with respect to the position of the heating portion N2 is a direction of the fixing member (fixing roller) in the direction opposite to the moving direction of the surface of the fixing member (fixing roller) from the pressure nip N1. It is a position along the outer circumference up to about half of its circumference.

In the surface heating method of this embodiment, the heating roller 3 heats the surface of the fixing roller 1 sufficiently to heat the upper layer (surface layer) of high thermal conductivity of the fixing roller 1 upstream of the pressure nip portion N1. The heat accumulated in the pressure nip portion N1 moves to the recording material P while the heat is transferred without being diffused in the lower layer of low thermal conductivity, and the accumulated heat is released to the recording material P in the pressure nip portion N1. To do. This process is continuous during fusing.

In this embodiment, the fixing roller 1 has a diameter of 30φ.
(Mm), the core metal 1c is a hollow cylinder so as to reduce the heat capacity while ensuring the necessary nip. The layer structure of the fixing roller 1 will be further described. The surface release layer (surface layer) 1a of the fixing roller 1 has an F of about 10 to 30 μm.
EP (tetrafluoroethylene-hexafluoropropylene copolymer resin) or PTFE (tetrafluoroethylene resin), CP
It is formed as a fluororesin tube or coat layer of TFE (trifluorochloroethylene resin), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin) or the like. Then, an elastic layer made of an elastic material having low thermal conductivity is formed thereunder.

As a material for such an elastic layer, low heat conductive LTV (low temperature vulcanization type) or HTV (high temperature vulcanization type) silicone rubber can be preferably used. In this embodiment, the thermal conductivity of 1.2 × 1 is provided below the surface release layer 1a.
H of 0 ^-3 cal / cm / s / K (≈ 0.5 W / m / K)
An elastic layer (lower layer) 1b having a thickness of 2 t (mm) was formed using TV (high temperature vulcanizing type) silicone rubber.

The elastic layer 1b has a thickness of 0.5 t.
It has been found that it is possible to sufficiently accumulate the heat necessary for fixing if it is about (mm) or more. Further, according to the study by the present inventors, the effect of improving the fixing property was recognized in the range of about 0.2 to 0.8 t (mm). In this embodiment, the thickness of the elastic layer 1b is further increased to 2t (mm) in order to secure the nip amount. In this embodiment, the core metal 1c of the fixing roller 1 is made of aluminum 6063 and has a thickness of 2.0 t (mm). At this time, the heat capacity of the fixing roller 1 was 240 J / K.

Although not limited, according to the studies by the present inventors, from the viewpoint of more effectively storing heat,
The material for forming the elastic layer 1b has a thermal conductivity of 0.9.
× 10 ^-3 cal / cm / s / K (≈ 0.37 W / m /
K) The following are preferable. Further, since the filler for improving the heat resistance strength is externally added, the thermal conductivity of the material forming the elastic layer 1b is 0.3 × 10 ⁻³ cal / cm / s /
K or above. More preferably, the thermal conductivity is 0.5 × 1
0 ^-3 cal / cm / s / K or more, 0.7 × 10 ^-3 cal
/ Cm / s / K or less is used.

The pressure roller 2 has a diameter of 30 mm (mm), and an elastic layer 2b of HTV silicone rubber is formed under the surface release layer 2a similar to the fixing roller 1 to have a thickness of 2.0 t (mm). It is a layered structure. The heat capacity of the pressure roller 2 is 240 J
Was / K.

The heat roller 3 has a diameter of 16φ (mm),
The hollow cylindrical member 3b is made of aluminum and has a thickness of 1.0 t (mm), and has a halogen heater as a heating element 4 therein. Further, the surface of the heat roller 3 has a fluororesin release layer tube 3a having a thickness of 50 μm. The heat capacity of the heat roller 3 was 32 J / K.

With such a layer structure, the fixing roller 1 is driven and rotated in a state in which the pressure roller 2 is pressed against the fixing roller 1 to form the pressure nip portion N1 therebetween. In this embodiment, the peripheral speed of the fixing roller 1 is 30 to 120 mm / s, and the pressing force at the pressure nip portion N1 is 40 kgf (≈392).
Pa). The nip width of the pressure nip portion N1 in the stationary state (the recording material P conveying direction) was 7.6 mm in the central portion.

In this embodiment, the fixing temperature is controlled to 190 ° C. by controlling the temperature of the heat roller 3 to 205 ° C. based on the temperature detection signal of the thermistor 5.

Further, in the present embodiment, in order to achieve on-demand at the time of rising, it is necessary to set a time interval of about several tens of seconds.
It was necessary to send a large electric power of about 000W. Once the printing temperature is reached, 80 ~ 1 to keep it warm
It was necessary to send electric power of about 00 W, and about 400 to 500 W during fixing.

It took about 90 seconds to rise from the room temperature to the printing temperature of 190 ° C. This is because the surface temperature of the fixing roller 1 rises fairly quickly, but in the configuration in which the pressure roller 2 does not have a heat source, the fixing property becomes low when the pressure roller 2 is in a cold state.
This is because a rise time of about 1 minute or more is required for heating by the multiple rotations before. The surface temperature ripple of the fixing roller 1 was about ± 4 ° C.

On the other hand, in the system in which the halogen lamp heater having the same power is built in the fixing roller 1 and the heating is performed from the inside, the rising time is 165 seconds. Compared with the fixing device A of the present embodiment, in the method of the present embodiment, although another member (heat roller 3) is provided outside the fixing roller 1, it does not go through heat conduction inside the elastic layer 1b, Direct fixing roller 1
It was found that the heat transfer to the surface of the roller is improved because heat is injected into the surface of, and the rise time is about half. In this case, the heat capacity of the heat roller 3 is equal to that of the fixing roller 1.
It is very important to improve the start-up, which is considerably smaller than 1/8. The heat capacity of the heat roller 3 is about 1/4 of the heat capacity of the elastic layer 1b, which has a poorer heat conduction than the metal core 1c of the fixing roller 1 (here, 125 J / K). At least half the heat capacity of the elastic layer 1b is preferable. When the heat capacity of the heat roller 3 is larger than that of the fixing roller 1, preferably the elastic layer 1b thereof, the effect of shortening the rise time is significantly reduced.

In this surface heating method, in order to further improve the efficiency and the fixing property, the amount of heat sent from the heating element 4 to the surface of the fixing roller 1 and the recording material of the fixing roller 1 at the pressure nip portion N1. It has been found to be important to increase the amount of heat sent to P, for example, recording paper, OHP sheet, cloth, etc., to the amount necessary for fixing. In order to improve the fixing property, it is desirable that the heat once sent by the heating unit N2 does not diffuse so much into the fixing roller 1 while being conveyed to the pressure nip unit N1. For that, the heating unit N2
It is considered preferable to make the distance between the pressure nip portion N1 and the pressure nip portion N1 as close as possible.

The present inventors have arranged the heating portion N2 on the upstream side of the pressure nip portion N1, and set the contact position (heating portion) N2 between the fixing roller 1 and the heat roller 3 as the pressure nip portion. By shifting in the N1 direction, the fixing efficiency during printing was gradually improved. Although not limited, the heating unit N2 is provided on the downstream side of the pressure nip N1 (a position other than the “upstream side position of the pressure nip N1” along the outer periphery of the fixing member (fixing roller)). When arranged, the fixing temperature and the heating speed are likely to be insufficient, and the heating element 4 having a higher temperature may be required. Therefore, the heating unit N2 is added in each point of on-demand, energy saving, and cost reduction. It is preferably arranged on the upstream side of the pressure nip N1.

In addition, the heating unit N2 approaches the conveyance path such as the fixing entrance guide 6 for the recording material P, so that the recording material P is preheated before entering the pressure nip portion N1 and the fixing property is improved. I got the effect. This is considered to be because the fixing inlet guide 6 and the like are radiatively heated by bringing the heat roller 3 closer to the conveyance path of the recording material P. In the structure of this embodiment, when the distance between the heating portion N2 and the recording material P is set to 15 mm or less, the fixing inlet guide 6 facing each other is radiantly heated to 60 ° C. or more, and this effect is obtained.

As described above, in the surface heating method of this embodiment, unlike the fixing roller generally used in the past,
Since the surface of the fixing roller 1 has a high temperature and the inner surface or the inside has a reverse temperature gradient such as a low temperature, surface overshoot due to heat moving from the inner side to the surface side after printing is prevented and at the same time. By suppressing the unnecessary heating of the inner surface and performing the minimum required heating from the surface side of the fixing roller 1, it is possible to effectively use the thermal energy and save energy. Further, since the fixing roller 1 needs to heat only the vicinity of the surface, it takes about 1 minute to start up, which is an intermediate characteristic between the heat roller system, which takes several minutes in the past, and the on-demand system, which requires several tens of seconds or less. And
It has an appropriate on-demand property. Further, by disposing the heating source (heating element) 4 for the surface of the fixing roller 1 on the upstream side of the pressure nip portion N1 as in the present embodiment, the heat of the surface of the fixing roller 1 is applied from the heating portion N2. It is possible to prevent heat dispersion during the movement to the pressure nip portion N1 and further improve the thermal efficiency. At the same time, by disposing the heating element 4 in the vicinity of the conveying path before the recording material P enters the pressure nip portion N1, the fixing property can be improved by the preliminary heating effect.

As described above, according to this embodiment, fixing can be efficiently performed with a simple and low-cost structure.

Embodiment 2 Next, another embodiment of the present invention will be described. In this embodiment, like the first embodiment, the present invention is embodied in a fixing device used in an electrophotographic image forming apparatus. Since the configuration and operation of the image forming apparatus are similar to those of the first embodiment, the description of the first embodiment will be used here.

FIG. 2 is a fixing device A of the present embodiment, which is a modified application example of the surface heating method to the upper and lower heating in the first embodiment.
2 shows a schematic cross section of. In this embodiment, the heating member 3'is also provided on the pressure roller 2 side. That is, the halogen heater 4 ′ is built in as a heating element, and the surface of the pressure roller 2 is heated in the heating portion N2 ′ by using the heat roller 3 ′ whose temperature is controlled by the thermistor 5 ′ as the temperature detecting means. , The fixability is improved.

In this embodiment, the fixing roller 1 has the same structure as that of the first embodiment. In this embodiment, the pressure roller 2 has the same structure as the fixing roller 1.

As a result, in this embodiment, the insufficient heat flow due to the surface heating of only the fixing roller 1 at the initial stage of start-up can be compensated by heating the back surface of the recording material P from the back surface to improve the fixability. it can. Alternatively, the roller surface temperature can be lowered even in normal time as compared with the case of heating only above,
It has the effect of preventing high temperature offset. Further, even during printing, a heat flow can be sent from both sides of the recording material P at a constant temperature, and more stable fixing is possible.

Further, the heat roller 3 ′ can indirectly enhance the effect of preheating the recording material P by indirectly heating the fixing entrance guide 6 from the back surface. It is possible to preheat up to.

As described above, according to this embodiment, it is possible to obtain the same effects as those described in the first embodiment, and improve the fixing property by heating the surface of the pressure roller 2 as well. You can

In the first and second embodiments described above, the principle of the present invention is applied to the oilless fixing system. However, the present invention is not limited to this, and the same applies to the oil fixing system. Application is also possible.

In the oil fixing system, the layer structure of the fixing roller 1 is, for example, the surface layer (surface release layer) of the fixing roller 1.
1a is a high thermal conductivity RTV (room temperature vulcanizing type) or LTV
Silicone rubber is used, and as shown in FIG. 3, oil is applied to the surface by an oil applying mechanism such as an existing oil applying roller 7 so as to provide releasability. Alternatively, as shown in FIG. 4, instead of the oil applying roller 7,
The heat roller 3 is contacted with a doctor blade 8 for regulating the amount of oil, or an oil-impregnated felt (not shown) is contacted with the heat roller 3 to replenish the oil, and thus the surface of the fixing roller 1 The structure can be simplified by providing both functions of heating and applying oil to the surface release layer 1a of the fixing roller 1.

Also in this case, the elastic layer (lower layer) 1b is
Use low heat conductive LTV or HTV silicone rubber. In the conventional roller fixing, the fixing roller 1 is heated from the inside, and the interface temperature between the core metal 1c and the lower layer 1b becomes high. Therefore, when oil permeates to the lower layer 1b, the adhesiveness between the two deteriorates. May cause peeling of the lower layer 1b. Therefore, an intermediate barrier layer such as fluororubber can be separately provided between the surface layer 1a and the lower layer 1b so that oil does not permeate to the lowermost layer. However, in the present invention, since the interface temperature is kept lower than the surface by the surface heating, the intermediate layer is unnecessary, peeling of the lower layer 1b is prevented, and the structure of the fixing roller 1 is further simplified. Further, since the internal temperature of the lower layer 1b is low, the generation of oil mist is reduced accordingly, and the fluctuation of the roller diameter due to the oil swelling of the fixing roller 1 is prevented.

As described above, the present invention can exhibit the same effect whether it is an oil fixing system using oil (silicone oil or the like) as a release agent or an oilless fixing system.

Embodiment 3 Next, another embodiment of the present invention will be described. In this embodiment, like the first and second embodiments, the present invention is embodied in a fixing device used in an electrophotographic image forming apparatus. Since the configuration and operation of the image forming apparatus are similar to those of the first embodiment, the description of the first embodiment will be used here.

The present inventors have found that the same result can be obtained even if a heating element such as a ceramic heater is brought into contact with the surface of the fixing member instead of the heating roller 3 used in Examples 1 and 2. It was However, the toner accumulated between the heating element and the surface of the fixing member may slip through to cause streak-shaped image defects in the image, or the two may stick to each other when cooled. It was In this case, the endless thin film having a releasable surface was wrapped around the heating element, and the film was pressed against the fixing member and slid at the same speed as the fixing member, thereby preventing the accumulation of toner. . In this case, since the film has a smaller heat capacity than the heat roller, the effect of more rapidly rising the surface temperature of the fixing member, that is, the effect of further improving the on-demand property can be obtained.

FIG. 3 shows a schematic cross section of the fixing device A of this embodiment. In this embodiment, instead of the heat roller 3 (3 ′) in the first and second embodiments, the fixing roller 1 is constituted by a heating member including a ceramic heater 11 as a heating element and an endless film 13 as a releasing member. Surface heating. In this embodiment, the fixing roller 1 and the pressure roller 2 are the same as those in the first embodiment.

In this embodiment, the ceramic heater 11 is
The structure is such that a band of a conductive heat generating layer is provided on the surface of alumina or aluminum nitride of about 0.6 to 0.8 t (mm), and an insulating protective layer of silica or glass is provided thereon. In this embodiment, the heat capacity of the ceramic heater 11 is about 10 J.
Was / K.

A thermistor 12 as a temperature detecting means is pressed against the back surface of the ceramic heater 11, that is, the side opposite to the side facing the fixing roller 1. Then, the heater temperature control is performed based on the temperature detection signal of the thermistor 12.

The ceramic heater 11 is brought into contact with the surface of the fixing roller 1 through the endless film 13 to heat the surface. As the endless film 13, 25-
A thin heat-resistant resin film such as polyimide having a thickness of about 60 μm coated with a release layer such as a fluororesin can be preferably used. In this example, the heat capacity of the endless film 13 was 6 J / K.

The endless film 13 is the fixing roller 1
Along with the rotation, the frictional force follows the circumference of the film guide 14 as a film holder, and slides while contacting the ceramic heater 11. With the endless film 13 and the ceramic heater 11, the additional heat capacity is minimized, and the start-up is faster,
Moreover, thermal efficiency can be improved.

In this embodiment, the temperature of the ceramic heater 11 is set to 200 ° C. based on the temperature detection signal of the thermistor 12.
The fixing temperature was controlled to 180 ° C.
Further, in the fixing device A of this embodiment, at the time of rising,
The fixing roller 1 reached the fixing temperature in about 20 seconds by supplying power of about 00W. Moreover, about 450 W of electric power was required for fixing.

Conventionally, there is an on-demand type fixing system in which a recording material P on which an image is formed is directly heated by a ceramic heater through a film. However, in this method, when a thick paper or thick envelope that does not meet the specifications of the image forming apparatus is passed as the recording material P, or when the paper is erroneously double-fed by the paper feeding unit, the recording material P itself is lost. Since the heat capacity becomes high, a large temperature difference may occur in the portion corresponding to the edge portion of the recording material P in the length direction of the heater, and a large thermal strain may occur inside the ceramic heater to cause heater cracking. . In this embodiment, the ceramic heater 11 and the endless film 13 are used as the fixing roller 1.
Even in the above-mentioned case, the heater crack is prevented because the heat fixing is indirectly performed via the heater.

Further, normally, in the idle rotation heating, the temperature of the surface of the endless film 13 reaches 185 to 195 ° C. when the heater set temperature is set to 200 ° C., so that the fixing inlet immediately before the pressure nip portion N1. By disposing the endless film 13 in the vicinity of the conveyance path of the recording material P such as the guide 6, the recording material P can be preheated before entering the pressure nip portion N1. According to a study by the present inventor, the distance between the endless film 13 and the recording material P conveyance path is preferably 30 mm or less. More preferably, it is 20 mm or less. In the present embodiment, by setting the distance between the endless film 13 and the fixing entrance guide 6 in the above range, the surface of the fixing entrance guide 6 can be heated to 60 ° C. or higher, and the effect of flying heating the recording material P is achieved. was gotten.

The holding shape of the film is not limited to the cylindrical shape described above, but may be, for example, an elliptic cylindrical shape as shown in FIG. 8 or the preheating surface may be planarized to increase the preheating distance. By doing so, the effect of further improving the fixing property can be obtained.

FIG. 6 shows a schematic cross section of a fixing device in which the surface heating method using the ceramic heater 11 and the endless film 13 shown in FIG. 5 or 8 is applied to the vertical heating. As shown in the figure, a heating member 10 ′ including a ceramic heater 11 ′, a thermistor 12 ′, an endless film 13 ′, and a film guide 14 ′ is also provided for the pressure roller 2. In this case, the pressure roller 2 has the same structure as the fixing roller 1. As described in the second embodiment, the fixing property can be improved by heating not only the fixing roller 1 but also the pressure roller 2 by the surface heating method. In this case, the upper and lower ceramic heaters 11 and 11 'are prevented from cracking.

As described above, according to the present embodiment, the same operational effects as those of the first or second embodiment are obtained, and the additional heat capacity is minimized, so that the rise is quicker and the thermal efficiency is improved. Further, according to this embodiment, since the fixing roller 1 has the elastic layer 1b, the fixing roller 1 can be directly heated and fixed from the image surface side by using the hard ceramic heater and the film, as can be seen in a normal on-demand system. It should be noted that a phenomenon in which countless fine air bubbles are generated on the surface of the fixed image, that is, so-called "sun" or gloss unevenness does not naturally occur, and a high quality color image can be dealt with. Further, in an on-demand system using a ceramic heater and a film, it is possible to prevent the heater from cracking by relaxing the temperature difference in the length direction of the heater when the recording material P passes (when the paper is passed). Play.

Embodiment 4 FIG. 7 shows still another modified application example. In this embodiment, the ceramic heater 11 and the endless film 13 are used as the heating (upward heating) from the image surface side of the recording material P.
The heating member 10 is used to heat the surface of the fixing roller 1 and heat the recording material P from the back side of the image side (lower heating).
From the back surface of the recording material P to the ceramic heater 11 ″
And heating member 10 "using a film and a film 13"
Back heating is performed directly by. Similar to the heating member 10 (10 ′) described in the third embodiment, the heating member 10 and the pressure / heating member 10 ″ further include a thermistor 12 (12 ″) and a film guide 14 (14 ″). ing. The structure of the fixing roller 1 is the same as that of the first embodiment.

Since the image surface side of the recording material P is heated and pressed by the fixing roller 1 having an elastic layer, a normal on-demand operation of directly heating and fixing from the image surface side using a hard ceramic heater and a film. As seen in the system,
It is possible to prevent a phenomenon in which innumerable fine air bubbles are generated on the surface of the fixed image, that is, so-called "drop" or uneven gloss. Therefore, a high-quality image can be obtained regardless of whether the fixed image is a monochrome image or a color image.

At this time, the ceramic heater 11 and the endless film 13 provide the preheating effect on the upstream side of the pressure nip N1 as described in the third embodiment. In addition, from the back surface of the recording material P, the ceramic heater 11 '
Since the back surface is heated by the endless film 13 ', the fixing property is improved.

Since it is possible to fix the thin sheet as the recording material P by heating only the back surface, it is possible to minimize extra heating to the fixing roller 1.
Further, even if the recording material P is a thick sheet or an OHP transmissive sheet, if the fixing speed is set to a low speed mode reduced to a fraction of the normal mode, fixing can be performed by heating only the back surface.

The cracking of the heater can be prevented by using an aluminum nitride type heater, which has much higher thermal conductivity than a normal alumina type ceramic heater. However,
Since the latter is slightly expensive, it is preferable to use a cheaper alumina type ceramic heater 11 for the upper heating and an aluminum nitride type ceramic heater 11 '' for the lower heating.

As described above, also with the structure of this embodiment, the same effects as those of the above-described embodiments can be obtained, and further fixability,
On-demand property can be improved.

In each of the above embodiments, the fixing member is described as a roller, but the present invention is not limited to this. For example, the fixing member may be an endless belt (or film). In this case as well, the fixing member is provided with an elastic layer having a low thermal conductivity, and the fixing member is heated by the surface heating method described in each of the above-described embodiments, whereby the same effect as each of the above-described embodiments can be obtained. it can.

[0080]

As described above, according to the present invention,
Prevents surface overshoot due to heat moving from the inside to the surface of the fixing member after image formation, and at the same time,
Energy can be saved by effectively utilizing thermal energy. Further, the fixing device of the present invention has an appropriate on-demand property. Furthermore, according to the present invention, uneven gloss does not occur in a fixed image, it is possible to form a high quality color image, and when applied to an on-demand system using a ceramic heater and a film, a recording material is used. It is possible to prevent the heater from cracking by mitigating the temperature difference in the length direction of the heater when passing. As described above, according to the present invention, there is provided a fixing device capable of efficiently performing fixing with a simple and low-cost configuration.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of a fixing device according to the present invention.

FIG. 2 is a schematic cross-sectional view of another embodiment of the fixing device according to the present invention.

FIG. 3 is a schematic sectional view of another embodiment of the fixing device according to the present invention.

FIG. 4 is a schematic cross-sectional view of another embodiment of the fixing device according to the present invention.

FIG. 5 is a schematic sectional view of another embodiment of the fixing device according to the present invention.

FIG. 6 is a schematic cross-sectional view of another embodiment of the fixing device according to the present invention.

FIG. 7 is a schematic sectional view of another embodiment of the fixing device according to the present invention.

FIG. 8 is a schematic sectional view of another embodiment of the fixing device according to the present invention.

FIG. 9 is a schematic cross-sectional view of a main part of an example of an image forming apparatus to which the fixing device according to the present invention can be applied.

[Explanation of symbols]

1 Fixing roller (fixing member) 2 Pressure roller (pressure member) 3, 3'heat roller (heating member) 4,4 'Halogen heater (heating element) 5,5 'Thermistor (temperature detection means) 6 Entrance guide 11, 11 'Ceramic heater (heating element) 12, 12 'Thermistor (temperature detection means) 13, 13 'Endless film (release member) 14, 14 'film guide (film holder)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shoji Kimura             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F term (reference) 2H033 AA30 AA32 BA25 BA26 BA32                       BB05 BB06 BB15 BB18 BB21                       BB23 BE03

Claims (9)

[Claims] 1. A fixing device for fixing an image on a recording material by bringing a fixing member into contact with an image bearing surface of the recording material, wherein the fixing member is heated from the surface by a heating member having a lower heat capacity. And fixing device. 2. The fixing device according to claim 1, wherein the fixing member is a roller or an endless belt. 3. The fixing device according to claim 1, wherein the fixing member has at least an elastic layer. 4. The fixing device according to claim 1, wherein the fixing member has at least a release layer and an elastic layer in this order from the side in contact with the recording material. 5. The fixing device according to claim 1, wherein the heating member contacts and heats the fixing member. 6. The fixing device according to claim 5, wherein the heating member has a roller or an endless film having a heat capacity lower than that of the fixing member or an elastic layer portion thereof and having at least a heating element and a releasable surface. . 7. A pressure member that forms a pressure nip with the fixing member, wherein the heating member is provided on the fixing member at a position upstream of the pressure nip between the fixing member and the pressure member. The fixing device according to claim 5, wherein the fixing device is brought into contact with the fixing device. 8. The fixing device according to claim 7, wherein the heating member is arranged in the vicinity of the recording material conveying path immediately before the pressure nip between the fixing member and the pressure member. 9. The fixing member according to claim 7, wherein the pressing member has an endless film having a heat capacity lower than that of the fixing member or an elastic layer portion thereof, the endless film having at least a heating element and a releasable surface. apparatus.