JPH087511B2 - Fixing roll and fixing device for electrophotographic apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing roll used for melting and fixing an unfixed toner powder image on a copy paper and an electrophotographic apparatus using the fixing roll. The present invention relates to a fixing device.

[Conventional technology]

2. Description of the Related Art Conventionally, a heat roll fixing method has been generally adopted for a fixing device of an electrophotographic apparatus.

In this fixing type device, a halogen heater or the like is built in a hollow cylindrical thin metal core, and a fluorine resin such as perfluoroalkoxy resin (PFA) or polytetrafluoroethylene resin (PTFE) is provided on the surface of the core, For heating rolls provided with an offset prevention layer made of silicone rubber, fluorine rubber, or a mixture of fluorine resin and fluorine rubber, the thickness elasticity of silicone rubber, fluorine rubber, a mixture of fluorine resin and fluorine rubber, etc. on a metal cored bar In addition to the layers, if necessary, a pressure roll provided with a non-adhesive layer such as a fluororesin tube is provided so as to face each other so as to be in pressure contact.

In such a fixing device, when the pressure roll is brought into pressure contact with the heating roll, the thick elastic layer on the surface thereof is dented, and the contact area between the rolls increases. Then, when the copy paper carrying the unfixed toner powder image is passed between the heating roll and the pressure roll, the toner powder is melted by heat and pressure, and is pressed onto the copy paper for fixing.

By the way, in these hot roll fixing methods, it is desired that the heating roll is heated in a short time after power-on,
This is particularly important in low speed electrophotographic devices and the like.

To solve this problem, there is a method to reduce the thickness of the core metal to enable rapid heating, but the temperature rise is fast because the heat capacity of the roll is small, but the heat distribution of the heater appears on the surface as it is. There is a problem that it is difficult to make the temperature distribution uniform. Therefore, it is necessary to add means for adjusting the heat generation distribution of the heater to make the surface temperature uniform.

Further, the toner powder usually shows a good fixing operation when it is fused within the range of 165 ° to 195 ° C. However, below this temperature, low temperature offset occurs, and above this temperature range, high temperature offset occurs. It occurs. Therefore, in general, a temperature sensor such as a thermistor is brought into contact with the surface of the heating roll to detect the surface temperature of the roll during operation, and the surface of the heating roll is adjusted within the range of 180 ° to 200 ° C.

However, when a large number of copies are made at high speed, heat is taken by the copy paper and the temperature of the heating roll surface partially drops.
At this time, if the decrease in the surface temperature is detected and the amount of heat generated by the heater is increased, the temperature will be too high in regions other than the region through which the copy paper has passed, and a high temperature offset will occur partially. Therefore, in a high-speed type apparatus, a method of improving the phenomenon that the temperature distribution collapses due to heat loss due to copy paper by increasing the heat capacity by increasing the wall thickness of the core bar is often adopted. In this case, there is a drawback that the temperature rising time becomes long and the temperature difference between the core metal surface and the inner surface becomes large, resulting in large overheating after the temperature rise.

In order to meet the contradictory requirements of shortening the temperature rising time of the heating roll which cannot be dealt with by such a conventionally known technique and compensating the heat loss due to the copy paper and making the surface temperature uniform, for example, A heat pipe type roll in which a heat medium liquid is sealed between the outer cylinder and the inner cylinder, and a halogen heater or the like is arranged at the center of the inner cylinder (JP-A-54-86352), and a plurality of heat pipes are contacted with the inner surface of the outer cylinder. Rolls arranged in the center of which a heat source is provided (Japanese Patent Laid-Open No. 56-46989), heat rolls in which a plurality of heat pipes are evenly arranged in a thick outer cylinder (Shokai 58-38165), etc. have been proposed. .

However, these heat pipe type rolls have a drawback that when using a large heat pipe having a large diameter, the temperature difference in the circumferential direction of the roll cannot be made sufficiently uniform and the temperature rise time is slow, and the diameter is large. When a thin heat pipe is used, the working fluid is unevenly distributed and the temperature difference in the axial direction of the roll cannot be eliminated, which is a drawback. Also, it is difficult and expensive to make grooved wicks or wire mesh wicks in a thin heat pipe, and single-line or bundle-type wicks can be easily inserted, but the rotation of the roll In addition to the drawbacks such as the generation of noise, all of them have a problem that the temperature difference on the roll surface cannot be completely eliminated.

[Problems to be Solved by the Invention]

As described above, the fixing roll used in the conventional electrophotographic apparatus cannot not completely eliminate the temperature difference on the surface, but also cannot sufficiently meet the requirements of rapid temperature rise and avoidance of overshoot. It was In order to compensate for any such defects, if an attempt is made to accurately adjust the temperature by directly detecting the temperature of the fixing roll surface using a temperature sensor, the offset prevention layer on the fixing roll surface will be worn or scratched. However, there is a problem in that a trouble such as a disorder of a fixed image occurs due to such a problem.

The present invention solves such a problem, achieves uniform surface temperature distribution without increasing the temperature rising time of the fixing roll, and prevents occurrence of fixing failure due to disordered surface temperature distribution after mass copying. It is an object of the present invention to provide a fixing roll for an electrophotographic device that can be used, and a fixing device for an electrophotographic device that can stably obtain a high-quality fixed image using the fixing roll.

[Means for solving the problem]

In order to achieve the object of the present invention, the fixing roll for an electrophotographic apparatus of the present invention has a plurality of heat pipes embedded in parallel with the axis in the thick wall of a hollow cylindrical cored bar provided with a heater inside. The heat pipe comprises a metal pipe body having a hairpin-shaped wick formed by bending an elastic metal wire so as to gradually increase the mutual distance from the central portion to the free end and a working fluid. It is characterized by becoming.

Further, in the fixing roll of the present invention, the thickness of the wall extending from the outer surface of the hollow cylindrical core to the heat pipe is larger than the thickness of the wall extending from the inner surface of the hollow cylindrical core to the heat pipe. It is preferable to have such a constitution, and it is particularly preferable to set it to 3 mm or more. As a result, even if the heat pipe expands and breaks due to overheating, the outer shape of the fixing roll itself is distorted and the function of the fixing roll is impaired.

Further, it is preferable to embed a plurality of heat pipes in the thick wall of the hollow cylindrical cored bar at equal intervals, whereby the temperature distribution along the circumference of the fixing roll can be further equalized. By forming the wall thickness of the hollow cylindrical cored bar where the heat pipe is not embedded to be thinner than that where the heat pipe is embedded, the heating time is shortened and the heat loss due to the copy paper is quickly compensated. An excellent fixing roll can be obtained.

The fixing roll of the present invention uses, for example, a core metal having good thermal conductivity such as aluminum or copper, and a surface thereof is mixed with a filler for improving abrasion resistance, thermal conductivity, electrical conductivity and the like. It is preferable to form and provide an offset prevention layer made of a fluororesin or the like.

The heat pipe embedded in the fixing roll of the present invention has a structure as shown in FIGS. 1a and 1b, and the hairpin-shaped wick 3 enclosed therein may be only one, There may be a plurality. If the hairpin-shaped wick 3 is formed by bending the central portion 3a and then twisting it so that the leg pieces 3b gradually increase in mutual distance toward the free end, a further better effect can be obtained. The tube 5 and the wick 3 which constitute such a heat pipe are preferably made of copper or phosphor bronze, and the working fluid 6 is preferably water or the like.

Further, in the fixing device for an electrophotographic apparatus of the present invention, the fixing roll of the present invention as described above is used as a heating roll, and a copy paper carrying an unfixed toner powder image is nipped and conveyed between the heating roll and a pressure roll. The toner powder image is fused onto the copy paper, and the temperature sensor is brought into contact with the surface portion of the fixing roll which is not in contact with the copy paper. It is possible to reduce the occurrence of wear and scratches and prevent fixing failure.

[Action]

According to the present invention, a plurality of heat pipes having a special structure are embedded parallel to the axis in the thick wall of the core metal of the fixing roll, and the heat pipe also rotates as the fixing roll rotates, but FIG. 5a. And, as shown in FIG. 5b, the wick 3 having a special shape works so as to cause the working fluid 6 enclosed in the heat pipe to recirculate in the direction parallel to the axis as the fixing roll rotates. Further, since the wick 3 does not hinder the vapor of the working fluid sealed in the heat pipe from moving in the direction parallel to the axis, the working fluid circulates smoothly in the heat pipe, and the liquid runs out due to evaporation. (Dry out) hardly occurs, and the temperature distribution of the fixing roll is remarkably uniformed. Therefore, even if a partial heat loss occurs due to contact with the copy paper, the temperature distribution is quickly compensated and no disturbance occurs.

[Example 1] An inner diameter of 35 mm, an outer diameter of 60 mm, a wall thickness of 12.5 mm, and a length of 500 mm made of an aluminum hollow cylindrical cored bar 4 evenly in the circumferential direction.
Equal thickness from outer and inner surfaces (3.25 m)
a heat pipe with a diameter of 6 mm and a length of 480 mm is embedded so that the wall of (m) is left, and a PFA with a thickness of 30 μm is further attached to the surface of the core metal.
A fixing roll A having a cross-sectional shape shown in FIG. 2 was formed by coating a resin (MP-10, manufactured by Mitsui DuPont Fluorochemicals).

The heat pipe 2 used here is, as shown in FIGS. 1a to 1b, a phosphor bronze wire with a diameter of 1.5 mm is bent in the center of a copper tube 5 with a thickness of 0.8 mm to form a hairpin shape. The twisted product is inserted as the wick 3, and the amount of water corresponding to 20% of the internal volume is sealed as the hydraulic fluid 6. Further, in the wick 3 here, the leg pieces 3b are in contact with the inner surface of the tube 5 in a loose vine shape, and a part thereof is immersed in the hydraulic fluid 6.

[Example 2] Minimum inner diameter 35 mm, maximum inner diameter 50 mm, outer diameter 60 mm, length 500 mm
Then, using an aluminum cored bar provided with three thick parts and three thin parts evenly in the circumferential direction of the inner surface, the thick part 3 of this cored bar is used.
A fixing roll B having the cross-sectional shape shown in FIG. 3 was formed, which has exactly the same structure as in Example 1 except that holes were axially formed in the places and the heat pipes similar to those in Example 1 were buried and inserted.

[Embodiment 3] The same structure as in Embodiment 1 except that the heat pipe is inserted at a position where a wall portion having a thickness of 4.0 mm from the outer surface and a wall portion having a thickness of 2.5 mm from the inner surface are left. The fixing roll C having the cross-sectional shape shown in FIG. 4 was formed.

[Comparative Example 1] The structure is exactly the same as that of Example 1 except that an aluminum core having an inner diameter of 40 mm, an outer diameter of 60 mm, and a length of 500 mm is coated with 30 μm of PFA resin and no heat pipe is embedded. ,
A control fuser roll D was formed.

[Comparative Example 2] A comparative fixing roll E having the same structure as in Example 1 except that a heat pipe in which a wick is not inserted is buried is formed.

[Comparative Example 3] Fixing of a control having the same structure as in Example 1 except that a heat pipe having a rope-like wick with a diameter of about 1 mm, which is formed by bundling 50 copper wires with a diameter of 0.1 mm and twisting the bundle, is used. Roll F was formed.

〔Evaluation test〕

A halogen lamp with an output of 1.2 kw was installed as a heater inside the six types of fixing rolls prepared as described above. On the other hand, as the pressure roll to be combined with the fixing roll, a stainless steel core having a diameter of 50 mm and a length of 500 mm coated with silicone rubber to a thickness of 5 mm was used.
A fixing device for an electrophotographic apparatus was assembled as shown in the figure. Here, 7 is a temperature sensor, 8 is a separation claw for copying paper, and 9 is
Is a drive gear and 4 is a heater.

The fixing rolls A, B, and C of the present invention were provided with the temperature sensor 7 so as to be in contact with the non-sheet passing portion of the fixing roll. A temperature sensor was provided so as to come into contact with the sheet passing portion of the fixing roll.

The results of various tests conducted using the thus-assembled fixing device were as follows.

[Test 1] Temperature rising time from the start of energizing the heater of the fixing roll at room temperature until the roll surface temperature reaches 200 ° C, and the non-communication with the paper passing part when the roll surface temperature is stabilized at 200 ° C. The temperature difference of the paper portion was measured, and the results are shown in FIGS.

The temperature rising time from room temperature to 200 ° C. is fixing roll A (Example 1) 6 minutes 20 seconds B (Example 2) 5 minutes 30 seconds D (Comparative Example 1) 6 minutes 20 seconds E (Comparative Example 2) 6 Minutes 20 seconds F (Comparative Example 3) It was 6 minutes 20 seconds, and it can be seen that the temperature rising time of the fixing device equipped with the fixing roll B was short.

Further, when the roll surface temperature is stabilized at 200 ° C., the temperature difference between the paper passing portion and the non-paper passing portion is fixing roll A (Example 1) 2.5 ° C. B (Example 2) 3 ° C. D (Comparative Example 1) ) 21 ° C. E (Comparative Example 2) 7 ° C. F (Comparative Example 3) 5 ° C., and the temperature difference due to overshoot at the time of rising was within 3 ° C. in the fixing roll of the present invention, while in the control It can be seen that the difference is as much as 21 ° C. in the fixing roll D, and 5 to 7 ° C. in the other fixing rolls.

[Test 2] After 100 sheets of A4 copy paper were continuously passed in the lateral direction, the sheet was paused for 20 seconds, and when this cycle was repeated, the temperature change of the paper passing portion and the temperature change of the non-paper passing portion were compared. The result is
Shown in Figures 12-16.

From this result, in the case of the present invention, almost no temperature difference is observed in the fixing roll A, and the fixing roll B is also within the range of 1 to 2 ° C. Further, it can be seen that the temperature of the paper-passing portion and the non-paper-passing portion rises stably even during copying suspension, and the recovery of the fixing temperature is very excellent.

However, in each control fixing roll, the temperature of the paper passing part gradually decreases, whereas in the non-paper passing part, the temperature once decreases and then starts to rise, and in the worst case, the temperature reaches 20 ° C. The difference is coming.

[Test 3] Generation of high-temperature offset when 500 sheets of A4 copying paper were passed in the lateral direction and then A3 copying paper was copied and the fixing roll A of the present invention was used and the fixing roll D of the control was used. Were compared.

As a result, a satin-like offset was generated on the fixing roll D, but a good fixed image was obtained on the fixing roll A.

From this, in the fixing device using the fixing roll of the present invention, the temperature difference between the paper passing portion and the non-paper passing portion is small, and after passing a large amount of small size copying paper, the large size copying paper is It was confirmed that even if copying was carried out using the same, stable copying was possible without causing a change in fixing performance.

[Test 4] The temperature fuse was removed from the fixing device, the temperature was set to infinity, and the heater was runaway.

As a result, the heat pipe expanded and lost its function,
In each of the fixing rolls of the present invention, there is no change in the surface of the core metal, and at the position where the heat pipe is inserted on the inner surface of the core metal.
A swell of about 0.2 mm was discovered. As a result, it was confirmed that the function as the conventional fixing roll is maintained even if the temperature adjusting function by the heat pipe is lost.

[Effect of the present invention]

According to the present invention, the temperature rising time of the fixing roll after the power is turned on can be shortened, and the temperature on the surface of the fixing roll can be made uniform over the entire surface. Further, since there is almost no temperature difference between the paper passing portion and the non-paper passing portion, a uniform fixed image can be obtained even if a large amount of small size copying paper is copied and then a large size copying paper is copied. I was able to do it.

Furthermore, since the temperature of the surface of the fixing roll is uniform, even if the temperature sensor is brought into contact with the part of the fixing roll where the copy paper does not pass, no problem occurs in the fixing operation. The occurrence of wear and scratches on the offset prevention layer and the resulting defective fixing are eliminated.
It has become possible to significantly extend the service life.

Further, even when the function of the temperature controller is lost and thermal runaway occurs, the fixing roll of the present invention can maintain at least the same function as the conventional fixing roll.

[Brief description of drawings]

FIGS. 1a and 1b are sectional views of a heat pipe used in the fixing roll according to the present invention, FIGS. 2 to 4 are cross-sectional views of examples of the fixing roll according to the present invention, FIGS. 5a and 5b. FIG. 6 is a vertical cross section and a horizontal cross section showing the posture of the wick in the heat pipe that changes according to the rotation of the fixing roll. FIG. 6 is a top view of the fixing device according to the present invention, and FIGS. 7 to 11 are the present invention. Graphs showing the temperature rising characteristics of the fixing roll and the control fixing roll, FIGS. 12 to 16 are the paper passing portion and the non-paper passing portion during the intermittent fixing operation of the fixing roller according to the present invention and the control fixing roller. 3 is a graph showing the surface temperature change characteristics of 1 ... Core metal, 2 ... Heat pipe, 3 ... Wick, 3a
... central part, 3b ... leg pieces, 4 ... heater, 5 ... tube, 6 ... hydraulic fluid, 7 ... temperature sensor, 8 ... separation claw, 9 ... drive gear.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-55-117179 (JP, A) JP-A-59-19978 (JP, A) JP-A-53-129052 (JP, A) JP-A-60- 55368 (JP, A) JP 62-194195 (JP, A) JP 61-52587 (JP, A) JP 61-15089 (JP, A) Actual Kaihei 4-40253 (JP, U) Actually open 63-109871 (JP, U) Actually open 63-12076 (JP, U) Actually open 58-27666 (JP, U) Actually open 2-7484 (JP, U)

Claims (8)

[Claims] 1. A heating roll in which a plurality of heat pipes are embedded parallel to an axis in a thick wall of a hollow cylindrical cored bar having a heater inside, wherein the heat pipe is made of an elastic metal wire. A fixing roll for an electrophotographic apparatus, comprising a hairpin-shaped wick formed by bending such that a mutual distance gradually increases from a central portion to a free end, and a metal tube in which a working fluid is sealed. 2. The thickness of the wall extending from the outer side surface of the hollow cylindrical cored bar to the heat pipe is greater than the thickness of the wall extending from the inner side surface of the hollow cylindrical cored bar to the heat pipe. A fixing roll for an electrophotographic apparatus as described. 3. A fixing roll for an electrophotographic apparatus according to claim 1, wherein a plurality of heat pipes are embedded in the thick wall of the hollow cylindrical cored bar at equal intervals. 4. The hollow cylindrical core metal is formed by forming a wall thickness of a portion where the heat pipe is not embedded, to be thinner than a portion where the heat pipe is embedded. A fixing roll for an electrophotographic apparatus according to any one of 1. 5. The fixing roll for an electrophotographic apparatus according to claim 1, wherein the heat pipe has a plurality of hairpin-shaped wicks enclosed therein. 6. The hairpin-shaped wick is formed by bending the center portion of the wick and adding a twist so that the mutual distance gradually increases toward the free end. A fixing roll for an electrophotographic apparatus according to Crab. 7. A fixing device for sandwiching and conveying a copy paper carrying an unfixed toner powder image between a heating roll and a pressure roll to fuse the toner powder image onto the copy paper, the heating device comprising: A fixing device for an electrophotographic apparatus, comprising the fixing roll for an electrophotographic apparatus according to any one of claims 1 to 6 as a roll. 8. The fixing device for an electrophotographic apparatus according to claim 7, wherein the temperature sensor is brought into contact with a surface portion of the fixing roll which is not in contact with the copy paper.