JP6794787B2 - Fixing device and image forming device - Google Patents

Description

The present invention relates to a fixing device for fixing an image on a recording material, and an image forming device such as a copying machine, a printer, a facsimile, or a multifunction device having at least two functions thereof equipped with the fixing device. ..

In recent years, there has been an increasing market demand for image forming devices for energy saving and high speed.
In the image forming apparatus, unfixed toner images are transferred to recording paper, printing paper, photosensitive paper, electrostatic recording paper, etc. by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. Form on recording material. As a fixing device for fixing an unfixed toner image, a contact heating type fixing device such as a thermal roller method, a film heating method, and an electromagnetic induction heating method is widely adopted.

Recent issues in such a fixing device include the following.
-The warm-up time, which is the time required to reach the specified printable temperature (reload temperature) from the normal temperature state when the power is turned on, and the printing operation is performed after receiving the printing request and the printing is completed. Further shortening of the first print time, which is the time required for printing (Problem 1).
-As the speed of the image forming apparatus increases, the number of sheets to be passed per unit time increases and the required amount of heat increases. Therefore, the amount of heat is insufficient especially at the beginning of continuous printing, which is a problem of so-called temperature drop (problem 2).

In order to solve the above problems, a thin film-like endless belt with a low heat capacity is configured to be directly heated without using a metal thermal conductor that also serves as a support, and is mounted on a high-production image forming apparatus. However, a fixing device capable of obtaining good fixing property has been proposed (for example, Patent Document 1). In this fixing device, the pressure roller arranged on the outer peripheral side of the endless fixing belt and the nip forming member fixedly arranged inside the fixing belt (inside the loop) are pressed against each other via the fixing belt to obtain a fixing nip. Is forming.

The fixing configuration using an endless belt with a low heat capacity without providing a metal thermal conductor that also serves as a support inside has excellent thermal efficiency, but keeps the temperature distribution in the longitudinal direction uniform during paper passing. It has difficulty. That is, in the region through which the small-sized recording material passes (paper-passing region), heat is consumed to heat the recording material and the unfixed toner on the recording material, but in the non-paper-passing region, heat is generated by the recording material or the like. Since it is not deprived, heat accumulates in the fixing belt and the pressure roller, and the temperature of the nip part in the non-paper-passing area becomes higher than the temperature of the nip part in the paper-passing area maintained at a predetermined temperature. A so-called end temperature rise occurs.

In response to such a problem of temperature rise at the end, a member made of a highly thermally conductive material is attached to the fixing nip side of the nip forming member that is in pressure contact with the fixing belt, and heat is not provided without providing a new drive mechanism or gripping mechanism. It has been proposed to increase the transfer and endothermic capacity to prevent the end temperature from rising (for example, Patent Document 2). This is because the heat transfer in the width direction of the fixing belt, that is, in the longitudinal direction / axial direction of the nip forming member is facilitated by the high thermal conductive material, so that the heat transfer is not taken by the paper passing and the end region remains heated. The heat is transferred in the longitudinal direction to make the temperature distribution as smooth as possible.

However, in such a method using an endless belt having a low heat capacity, in a configuration in which a high thermal conductive member is used for the nip portion and the fixing belt is slidably contacted with the fixing belt under a high load, high thermal conduction is achieved between the nip forming member and the fixing belt. By interposing the sex member, the amount of heat transferred from the fixing belt to the nip forming member that does not contribute to fixing increases, resulting in waste in power consumption.

Therefore, the present invention reduces the amount of heat transfer to the nip forming member and reduces the amount of power consumption in the fixing device having a structure in which a high thermal conductive member is interposed between the endless belt having a low heat capacity and thin film-like shape and the nip forming member. The purpose is to do.

In order to achieve the above object, in the present invention, a flexible endless belt, a fixing heat source disposed inside the belt and heating the belt by radiant heat, a nip forming member and the inner circumference of the belt. A nip forming unit having a heat transfer assisting member that slides in contact with a surface and transfers heat in the longitudinal direction thereof, and a pressure member that press-contacts the nip forming unit with the belt in between to form a fixing nip. In a fixing device for fixing an unfixed image on a recording material by passing a recording material carrying an unfixed image through the fixing nip.
A contact heat transfer type end heat source is provided at the longitudinal end of the nip forming member, and the heat transfer assisting member is a surface of each of the nip forming member and the end heat source facing the inner peripheral surface of the belt. The nip forming member is arranged on the side opposite to the fixing nip side of the heat transfer assisting member, and is made of a heat-resistant resin mixed with a hollow filler.

According to the present invention, since the nip forming member arranged on the side opposite to the fixing nip side of the heat transfer assisting member is formed of a heat-resistant resin mixed with a hollow filler, the thermal conductivity of the nip forming member The amount of heat transferred to the nip forming member that does not contribute to fixing is reduced, and the amount of power consumption in the fixing device can be reduced.

It is the schematic which shows the whole structure of the image forming apparatus which concerns on one Embodiment of this invention. It is sectional drawing which shows one Embodiment of the fixing device. It is an exploded perspective view which shows the basic positional relationship of a nip forming member, a support member, a heat transfer assisting member, and an end heater which make up a nip forming unit. It is sectional drawing of the nip forming member containing hollow filler and the heat transfer assisting member. It is sectional drawing of the nip forming member containing hollow filler and the heat transfer assisting member which concerns on another structural example. It is sectional drawing of the nip forming member and the heat transfer assisting member which concerns on still another structural example, and is the sectional view at the end position of the nip forming member which supports an end heater. It is sectional drawing which shows the other embodiment of the fixing device which can use the nip forming member which concerns on each form.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view showing an overall configuration of an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 1 is a color laser printer, and four image forming portions 4Y, 4C, 4M, and 4K are juxtaposed in the center of the printer body along the extension direction of the intermediate transfer belt 30. There is. Each image forming unit 4Y, 4C, 4M, 4K accommodates developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, it has the same configuration.

Specifically, each image processing unit 4Y, 4C, 4M, 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 for charging the surface of the photoconductor 5. A developing device 7 that supplies toner to the surface of the photoconductor 5 and a cleaning device 8 that cleans the surface of the photoconductor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4K are assigned color codes, and the other image forming units 4Y, 4C, and 4M have a color code. The code is omitted.

Below the image-creating portions 4Y, 4C, 4M, and 4K, an exposure apparatus 9 for exposing the surface of the photoconductor 5 is arranged. The exposure apparatus 9 has a light source, a polygon mirror, an f−θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

A transfer device 3 is arranged above the image forming portions 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

The intermediate transfer belt 30 is an endless belt, and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, by rotating the secondary transfer backup roller 32, the intermediate transfer belt 30 orbits (rotates) in the direction indicated by the arrow in the figure.

Each of the four primary transfer rollers 31 has an intermediate transfer belt 30 sandwiched between the four primary transfer rollers 31 and the photoconductors 5 to form a primary transfer nip. Further, a power supply of the printer main body is connected to each primary transfer roller 31, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. ..

The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Further, similarly to the primary transfer roller 31, the power supply of the printer main body is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It is supposed to be done.

The belt cleaning device 35 has a cleaning brush and a cleaning blade arranged so as to come into contact with the intermediate transfer belt 30.
A bottle accommodating portion 2 is provided on the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K accommodating replenishing toner are detachably attached to the bottle accommodating portion 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development is performed from each toner bottle 2Y, 2C, 2M, 2K via this replenishment path. Toner is replenished to the device 7.

On the other hand, in the lower part of the printer main body, a paper feed tray 10 containing the paper P as a recording material, a paper feed roller 11 for carrying out the paper P from the paper feed tray 10, and the like are provided. Here, the recording material includes, in addition to plain paper, thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, and the like. Further, as is well known, a manual paper feed mechanism may be provided.

A transport path R for passing the paper P from the paper feed tray 10 through the secondary transfer nip and discharging the paper P to the outside of the apparatus is provided in the printer main body. In the transport path R, a pair of resist rollers 12 as transport means for transporting the paper P to the secondary transfer nip are arranged on the upstream side in the paper transport direction from the position of the secondary transfer roller 36.

Further, a fixing device 20 for fixing the unfixed image transferred to the paper P is arranged on the downstream side in the paper transport direction from the position of the secondary transfer roller 36. Further, a pair of paper ejection rollers 13 for ejecting the paper to the outside of the apparatus are provided on the downstream side of the transport path R in the paper transport direction with respect to the fixing device 20. Further, on the upper surface of the printer body, a paper ejection tray 14 for stocking the paper ejected outside the apparatus is provided.

The basic operation of the printer according to this embodiment is as follows. When the image-drawing operation is started, each of the photoconductors 5 in each image-forming unit 4Y, 4C, 4M, and 4K is rotationally driven clockwise in the figure, and the surface of each photoconductor 5 is brought to a predetermined polarity by the charging device 6. It is uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure apparatus 9, and an electrostatic latent image is formed on the surface of each photoconductor 5. At this time, the image information to be exposed to each photoconductor 5 is monochromatic image information obtained by decomposing a desired full-color image into yellow, cyan, magenta, and black color information. By supplying toner to the electrostatic latent image formed on each photoconductor 5 in this way by each developing device 7, the electrostatic latent image is visualized (visualized) as a toner image. ..

When the image-drawing operation is started, the secondary transfer backup roller 32 is rotationally driven counterclockwise in the drawing to rotate the intermediate transfer belt 30 in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed at the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

After that, when the toner image of each color on the photoconductor 5 reaches the primary transfer nip with the rotation of each photoconductor 5, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. The intermediate transfer belt 30 is sequentially superposed and transferred. Thus, a full-color toner image is supported on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be completely transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. The surface of each photoconductor 5 is then statically eliminated to initialize the surface potential.

At the lower part of the image forming apparatus, the paper feed roller 11 starts rotational driving, and the paper P is sent out from the paper feed tray 10 to the transport path R. The paper P sent out to the transport path R is timed by the resist roller 12 and sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, whereby a transfer electric field is formed in the secondary transfer nip.

After that, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 goes around, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed at the nip. Is collectively transferred onto the paper P. Further, the residual toner on the intermediate transfer belt 30 that could not be transferred to the paper P at this time is removed by the belt cleaning device 35, and the removed toner is conveyed to the waste toner container placed in the printer main body. , Will be recovered.

After that, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged to the outside of the device by the paper ejection roller 13 and is stocked on the paper ejection tray 14.

The above description is an image forming operation when forming a full-color image on paper, but a monochromatic image can be formed by using any one of four image forming units 4Y, 4C, 4M, and 4K. It is also possible to form a two-color or three-color image using two or three image-forming sections.

FIG. 2 is a schematic cross-sectional configuration diagram showing an embodiment of the fixing device 20.
The fixing device 20 has an endless fixing belt 21 which is a thin and flexible tubular fixing member, and a pressure roller 22 which is a pressure member which abuts from the outer peripheral side of the fixing belt 21. ing. The fixing belt 21 is heated by the radiant heat of the heaters 23A and 23B as a plurality of heat sources arranged inside (inside the loop). As the heat source, a halogen heater is generally used, but it may be an induction heating device, a resistance heating element, a carbon heater, or the like.

Further, inside the fixing belt 21, a nip forming member 24 that forms a fixing nip N with a pressure roller 22 via the fixing belt 21 and a stay 25 (supporting member) that supports the nip forming member 24 are arranged. ing. The nip forming member 24 arranged in the width direction of the fixing belt 21 is fixedly supported by the stay 25 to prevent the nip forming member 24 from bending due to the pressure from the pressure roller 22 and to be applied. A uniform nip width can be obtained over the axial direction (longitudinal direction) of the pressure roller 22. The nip forming member 24 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or higher, particularly a heat-resistant resin such as a polyimide (PI) resin or a polyetheretherketone (PEEK) resin, which is reinforced with glass fiber. It is composed of the plastic. As a result, deformation of the nip forming member 24 due to heat is prevented in the toner fixing temperature range, a stable fixing nip state is ensured, and output image quality is stabilized. Further, the stay 25 and the heaters 23A and 23B are fixedly held at both ends in the longitudinal direction by a side plate of the fixing device 20 or a holder provided separately. End heaters 26 as end heat sources separate from the main heat source (fixing heat source) are integrally attached to both ends of the nip forming member 24 in the longitudinal direction. The end heat source is generally a contact heat transfer heater such as a ceramic theta.

A heat transfer assisting member 27, which is also called a heat equalizing member that facilitates heat transfer in the longitudinal direction of the fixing belt, forms each surface of the nip forming member 24 and the end heater 26 facing the inner peripheral surface of the fixing belt 21. It is arranged so as to cover it, preventing heat from staying in the end region of the fixing belt 21 when passing small-sized paper or lighting the end heater 26, and positively in the width direction of the fixing belt 21, that is, Heat is transferred in the longitudinal direction of the heat transfer assisting member 27 to eliminate temperature non-uniformity in the longitudinal direction. Therefore, the heat transfer assisting member 27 is made of a material having high thermal conductivity that enables heat transfer in a short time, and copper or aluminum is assumed. In the description of FIG. 2, the surface of the heat transfer assisting member 27 facing the inner peripheral surface of the fixing belt 21 is a surface that directly contacts the fixing belt 21, is a nip forming surface, and is formed flat. However, it may have a concave shape or other shape. With the concave nip-forming surface, the discharge direction of the paper tip is closer to the pressure roller, the separability is improved, and the occurrence of jam is suppressed.

As is well known, a temperature sensor 29 for detecting the belt temperature is provided at an appropriate position on the outer peripheral side of the fixing belt 21, and the paper P from the fixing belt 21 is provided on the downstream side in the paper transport direction of the fixing device 20. A separating member 40 for separating the two members is arranged, and a releaseable pressurizing means for pressurizing the pressurizing roller 22 against the fixing belt 21 is also provided.

In order to reduce the heat capacity, the endless fixing belt 21 which is thin and has a small diameter like a film has an inner peripheral side base material made of a metal material such as nickel or SUS or a resin material such as polyimide, and PFA. It is composed of a release layer on the outer peripheral side formed of (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), or the like. An elastic layer made of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber may be interposed between the base material and the release layer. If the thickness of the elastic layer is set to about 100 μm, minute irregularities on the belt surface can be absorbed due to the elastic deformation of the elastic layer when the unfixed toner is crushed and fixed, and the occurrence of uneven gloss can be avoided. From the viewpoint of reducing the heat capacity, the fixing belt 21 is set to have a thickness of 1 mm or less and a diameter of 20 to 40 mm as a whole. The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in the ranges of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, respectively. In order to further reduce the heat capacity, it is desirable that the thickness of the entire fixing belt 21 is 0.2 mm or less, and more preferably 0.16 mm or less, and the diameter is 30 mm. It is desirable to do the following.

The stay 25 having a T-shaped cross section has an upright portion 25a on the side opposite to the fixing nip N side, and the heaters 23A and 23B as fixing heat sources are arranged so as to be separated by the upright portion 25a. One of the heaters 23A and 23B has a heat generating region in the central portion in the longitudinal direction corresponding to the small size paper, and the other has a heat generating region in both ends in the longitudinal direction corresponding to the large size paper. The heaters 23A and 23B are configured to generate heat by controlling the output by a power supply unit provided in the printer main body, and the output control detects the temperature of the belt surface by a temperature sensor provided on the outer circumference of the fixing belt 21. It is done based on the result. By controlling the output of such a heater, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

Further, reflective members 28A and 28B are arranged between the stay 25 and the heaters 23A and 23B to increase the heating efficiency of the heaters 23A and 23B for the fixing belt 21, and the stay 25 is heated by the radiant heat from the heaters 23A and 23B. It suppresses wasteful energy consumption due to this. The same effect can be obtained by performing heat insulation or mirror surface treatment on the surface of the stay 25 instead of providing the reflective members 28A and 28B.

The pressure roller 22 is formed of a core metal, an elastic layer made of foamable silicone rubber, fluororubber, etc. provided on the surface of the core metal, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. It is configured. At a position where the pressure roller 22 is pressed against the fixing belt 21 by the spring of the pressing means and is in pressure contact with the fixing belt 21, the elastic layer of the pressure roller 22 is crushed to form a fixing nip N having a predetermined width. There is. The pressurizing roller 22 is configured to be rotationally driven by a drive source such as a motor provided in the printer main body. When the pressurizing roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 by the fixing nip N, and the fixing belt 21 is driven to rotate. The fixing belt 21 is sandwiched between the fixing nip N and rotates, and is guided by the side plate flanges arranged at both ends and travels except for the fixing nip N.

In the present embodiment, the pressure roller 22 is a solid roller, but a hollow roller may be used. In that case, a heat source such as a halogen heater may be arranged inside the pressurizing roller 22. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because it has higher heat insulating properties and is less likely to take away heat from the fixing belt 21.

In the nip forming unit composed of the nip forming member 24, the stay 25, the heat transfer assisting member 27, and the end heater 26, as can be seen from FIG. 3 showing the basic configuration thereof, the nip forming member 24 and the fixing nip N side The surface on the opposite side is integrated with the flat surface on the fixing nip N side of the stay 25. At this time, uneven shapes such as bosses and pins may be formed on each surface, and these may be fitted in a shape-constrained manner. The heat transfer assisting member 27 arranged on the fixing nip side of the nip forming member 24 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 24 facing the inner peripheral surface of the fixing belt 21. .. The heat transfer assisting member 27 and the nip forming member 24 may be integrally formed by providing claws or the like to engage with each other, but adhesive or the like may be used. Recesses 24a and 24b as stepped portions are formed at both ends of the nip forming member 24 in the longitudinal direction, and end heaters 26a and 26b are housed and fixed in these portions. The surface of the heat transfer assisting member 27 facing the inner peripheral surface of the fixing belt 21 is configured as the belt sliding contact surface 27a, but in terms of mechanical strength, the nip forming surface is substantially the nip forming surface. The surface 24c facing the compression roller 22.

As described above, the heat transfer assisting member 27 has the purpose of transferring heat in the longitudinal direction to eliminate temperature non-uniformity in the longitudinal direction, and is formed of a material having high thermal conductivity such as copper or aluminum. Has been done. However, when the heat of the fixing belt 21 is transferred to the heat transfer assisting member 27, the amount of heat transferred from there to the nip forming member 24 also increases. Since the heat transferred from the heat transfer assisting member 27 to the nip forming member 24 does not contribute to the fixing of the toner, it becomes wasteful heat energy. That is, the power consumption used for fixing is increased. Therefore, suppressing the amount of heat that does not contribute to such fixing is energy saving of the fixing device and, by extension, the image forming device.

An example of the configuration for that purpose is shown in FIG. The nip forming member 24 shown in FIG. 4 has a hollow filler 24d mixed inside the resin material. Since the hollow filler 24d has air inside and has a very low thermal conductivity, the thermal conductivity of the entire nip forming member 24 is significantly lower than that of the nip forming member in which the hollow filler is not mixed. Therefore, the amount of heat transferred to the heat transfer assisting member 27 to the nip forming member can be reduced, and the amount of power consumption can be reduced. The degree of mixing of the hollow filler 24d is set according to the strength of the nip forming member 24 and the degree of heating, that is, the heat resistance condition.

The rising portion 27d of the heat transfer assisting member 27 extends from the base portion 27c to the stay 25 side. The nip forming member 24 in which the hollow filler 24d is mixed includes a portion 24f facing the rising portion 27d of the heat transfer assisting member, a heat transfer assisting member side portion 24g forming a surface facing the heat transfer assisting member 27, and a stay 25. A surface facing the stay 25 is formed, and the stay side portion 24h substantially parallel to the base portion 27c of the heat transfer assisting member 27 and the stay side portion 24h facing the stay 25 extend toward the stay 25, and the tip is in contact with the stay 25. It has a protruding portion 24i. The stay-side portion 24h of the nip-forming member 24 extends from the vicinity of the stay-side tip of the rising portion 24f located at one end of the nip-forming member 24 to the vicinity of the tip of the rising portion 24f located at the other end. The rising portion 24f and the stay side portion 24h have the same height in the figure, but either of them may be higher. A separate member may be interposed between the tip of the protrusion 24i and the stay 25 so as to come into contact with each other. The portion of the projecting portion 24i in contact with the stay protrudes so as to be higher toward the stay side in the pressing direction than the tip of the rising portion 24d of the heat transfer assisting member. In other words, the stay 25 does not enter the concave shape formed by the base portion 27c and the rising portion 27d of the heat transfer assisting member.

Here, the significance of the hollow filler will be described in detail. In a configuration in which a heat transfer assisting member is interposed between a resin nip forming member that functions as a pressure pad and a fixing belt, and the heat transfer assisting member is directly rubbed against the belt, the resin nip forming member Compared to the conventional configuration in which the fixing belt is rubbed and the conventional configuration in which a sliding sheet is interposed between the heat transfer assisting member and the fixing belt, the heat equalizing performance in the longitudinal direction is greatly improved, but the heat equalizing plate is used. Since the heat absorption of a certain heat transfer assisting member in the thickness direction is also increasing, problems such as an increase in warm-up time and a decrease in energy saving performance occur, and there is a trade-off between heat equalization in the longitudinal direction and rapid heat in the thickness direction. It ends up. Therefore, improving the heat insulating performance of the nip forming member existing on the back surface of the heat transfer assisting member suppresses the increase in endothermic property while maintaining the heat soaking performance by the heat transfer assisting member, and increases the warm-up time and energy saving performance. It can be extremely effective in minimizing the decrease in the amount of heat. When there is no heat transfer assisting member or a sliding sheet with poor thermal conductivity is interposed between the heat transfer assisting member and the fixing belt as in the conventional case, the heat absorption performance is extremely low in the first place, so that the nip forming member There is almost no effect of improving warm-up time and energy-saving performance due to the improvement of heat insulation performance. In particular, since the heat absorption performance in a short time has a great influence on the warm-up time, it means that the fixing belt reaches a predetermined temperature before sufficient heat is transferred to the heat transfer assisting member at the time when the sliding sheet is interposed. Does not form. Therefore, in combination with the heat transfer assisting member, the heat insulation of the nip forming member can exert a great effect. Here, as a method for insulating the nip forming member, by mixing the hollow filler with the resin material, not only the thermal conductivity but also the heat capacity of the nip forming member can be lowered to obtain a further heat insulating effect. it can.

Further, reducing the heat capacity by mixing the resin material of the nip forming member with the hollow filler reduces the rigidity of the nip forming member and lowers the pressing force, which is the original function. However, in the configuration in which the heat transfer assisting member is fitted, the rigidity of the heat transfer assisting member itself is high because the heat transfer assisting member is a metal material, and the rigidity obtained by combining the nip forming member and the heat transfer assisting member is added. It can fully fulfill the function of pressure. That is, the heat transfer assisting member may be provided with both heat equalizing performance and pressing functions, and the nip forming member may be heat-insulated by mixing a hollow filler as much as possible while compensating for the insufficient strength. As described above, by utilizing the combination of the heat transfer assisting member and the nip forming member mixed with the hollow filler, it is possible to optimize the heat soaking performance, the heat insulating performance, and the pressing force.

For the hollow filler 24d, it is desirable to use a glass balloon made of a glass material or a glass microhollow body called a glass bead. This is because the glass balloon has high hardness and excellent heat resistance. The glass balloon can achieve both high strength and low thermal conductivity by controlling the film thickness and particle size of the glass. For example, a glass balloon having a size of about 35 μm to 135 μm is mixed inside the nip forming member 24. The deflection temperature under load of the nip forming member 24 is 300 ° C. or higher, and the bending strength is, for example, about 90 Mpa (23 ° C.) or higher.

FIG. 5 shows another configuration example of the nip forming member. In addition to using a resin material in which the hollow filler 24'd is mixed, the nip forming member 24'extends in the longitudinal direction on the surface on the side in contact with the heat transfer assisting member 27, that is, the surface on the fixing nip side. A plurality of large grooves 24'e are formed. The groove 24'e is provided in a range in the longitudinal direction in which the nip forming member 24 faces the heat transfer assisting member 27. The groove 24'e is formed parallel to the longitudinal direction of the nip forming member 24', but may be formed obliquely with respect to the longitudinal direction thereof. By forming the groove 24'e in this way and providing an air layer while reducing the contact surface between the heat transfer assisting member 27 and the nip forming member 24', the amount of heat transferred to the nip forming member can be further reduced. .. Since the heat transfer assisting member 27 is a metal material such as copper or aluminum, it has higher rigidity than resin, and a load is applied to a region that is not in contact with the nip forming member, that is, a region that is not supported by the nip forming member. Is also configured to maintain nip formation with its own strength. The number and area of the non-contact regions of the heat transfer assisting member 27 may be determined from the permissible value of the amount of deflection caused by applying a load to the regions not in contact with the heat transfer assisting member 27. The basic shapes of the heat transfer assisting member 27 and the nip forming member 24'are the same except for the groove 24'e, and by adding the same subscript code as the subscript code in FIG. 4, their description is omitted. To do.

FIG. 6 shows yet another configuration example of the nip forming member. This figure shows a cross section of a nip forming member that supports an end heater at an end position. In FIG. 6, the end heater 26 is supported on the back surface of the heater in a state of being fitted into the nip forming members 24 ”at both end positions in the longitudinal direction, and the front surface of the heater is in contact with the back surface of the heat transfer assisting member 27. The heat generation region 26c of the end heater 26 exists on the back surface of the heater, and the heat of the heat generation region 26c is transferred to the surface of the heater and the heat transfer assisting member 27. On the other hand, the heat of the heat generation region 26c forms a nip that supports the heater. Although it is transmitted to the member 24 ", since the nip forming member 24" is made of a resin material containing a hollow filler, the heat conductivity is low, so that the heating efficiency of the fixing belt by the end heater 26 can be improved. The basic shape of the heat transfer assisting member 27 and the nip forming member 24 "is the same except for the end heater 26, and has the same subscript code as the subscript code in FIG. Therefore, those explanations will be omitted. Further, except for the portion where the end heater 26 of FIG. 6 is located, a part of the nip forming member 24 "in the longitudinal direction may have the configuration shown in FIG. 4, and a groove may be provided in a part as shown in FIG. ..

The heat transfer assisting member and the nip forming member according to each of the above-described forms can be applied not only to a fixing device having an end heater in the nip forming member, but also, of course, a known fixing not provided with an end heater. It can also be applied to devices. FIG. 7 shows a schematic cross section of the fixing device 80 not provided with an end heater. This fixing device is basically different from the fixing device 20 having the end heater 26 in the nip forming member 24 shown in FIG. 2 only in the presence or absence of the end heater and the number of fixing heat sources. Therefore, refer to each member. The description will be omitted by adding a code. In the case of this configuration, the end portion of the nip forming member does not have the configuration of FIG. 6 described above, and the configuration of FIG. 4 can be formed up to the end portion. Further, even when the groove as shown in FIG. 5 is provided, the length and shape of the groove can be set more freely because the end heater 26 is not provided. It is also possible to provide a groove in a part of the cross section of the nip forming member as shown in FIG. 4 and another part as shown in FIG.

20 Fixing device 21 Fixing belt 22 Pressurizing roller 23 Heater 24 Nip forming member 25 Stay 26 End heater 27 Heat transfer assisting member

Japanese Unexamined Patent Publication No. 2010-32631 JP 2015-64561

Claims (4)

A flexible, endless belt, a fixing heat source that is arranged inside the belt and heats the belt by radiant heat, and a nip forming member and the inner peripheral surface of the belt are in sliding contact with each other to generate heat in the longitudinal direction thereof. A recording material that includes a nip forming unit having a moving heat transfer assisting member and a pressurizing member that press-contacts the nip forming unit with the belt to form a fixing nip and carries an unfixed image is fixed. In a fixing device that fixes an unfixed image on a recording material by passing it through a nip.
A contact heat transfer type end heat source is provided at the longitudinal end of the nip forming member, and the heat transfer assisting member is a surface of each of the nip forming member and the end heat source facing the inner peripheral surface of the belt. The fixing device is characterized in that the nip forming member arranged on the side opposite to the fixing nip side of the heat transfer assisting member is formed of a heat-resistant resin mixed with a hollow filler. The fixing device according to claim 1, wherein the hollow filler is a glass balloon. The fixing device according to claim 1 or 2, wherein a groove extending in the longitudinal direction is formed on the surface of the nip forming member on the fixing nip side. An image forming apparatus having the fixing apparatus according to any one of claims 1 to 3 .

Images