KR940010610B1 - Set temperature changeable image fixing apparatus - Google Patents

Abstract

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Description

Variable set temperature image fixing device

1 is a cross-sectional view of an image fixing device according to an embodiment of the present invention.

2 is a cross-sectional view of an image fixing apparatus according to another embodiment of the present invention.

3 is an enlarged cross-sectional view of a temperature detector for detecting a fixing film temperature.

4 is a graph of the fixing film temperature, the heater temperature, the high temperature offset temperature and the minimum fixing temperature immediately before the fixing nip.

5 is a graph of the fixing film temperature and the driven roller temperature during the fixing operation and the non-fixing operation.

6 is a partial view of a fixing device illustrating a temperature detector for a driven roller.

7 is a related graph between image fixing film temperature, heater temperature, high temperature offset temperature and minimum settable temperature.

8 is a cross-sectional view of an embodiment of an image forming apparatus.

9a and 9b are graphs of the relationship between the time period of the fixing film in the nip and the fixing film surface temperature when the thickness of the fixing film is 40 microns and 80 microns.

The present invention relates to an image heat-fixing apparatus in which a recording material holding an image goes to a heater through a film and fixes the image.

Regarding an image fixing apparatus used in an image forming apparatus such as a copying machine or an electrophotographic printing machine, a thermal-roller type image fixing system is widely used.

However, such a system suffers from a long wait until the surface of the roller to be heated reaches a predetermined temperature.

US Application Serial No. 206,767, assigned to the assignee of the present application; 387,970; 409,341; 416,539; 426,028; 435,247; 430,437; 440,380; 440,678; 444,802 and 446,449 have proposed low temperature capacity heaters and thin films, and image stabilization devices with significantly reduced or eliminated waiting periods.

In such a film fixing system, when the temperature of the heater is constantly controlled, the amount of heat applied to the toner image by the nip changes when the temperature of the fixing film changes.

The inventors performed thermal analysis on the surface temperature of the fixing film immediately before the nip (the surface temperature of the fixing film capable of contacting the toner image of the recording material), that is, the relationship between the initial surface temperature, and the temperature increased with time after entering the nip. do.

The results are shown in FIGS. 9A and 9B, where FIG. 9A relates to a fixing film having a thickness of 40 microns, and FIG. 9B relates to a fixing film having a thickness of 80 microns. In the graph, the curve 1 indicates the film surface temperature at which image fixing operation is possible (fixable temperature which is almost 200 ° C. in this embodiment).

Curve 2 shows the surface temperature of the fixing film when the initial surface temperature is 130 ° C .:

Curve 3 shows the fixing film surface temperature when the initial surface temperature is 20 ° C.

As understood from the graphs of FIGS. 9A and 9B, when the fixing film temperature before entering the nip is low, the time for the fixing film temperature to reach the fixable temperature during the passage of the nip becomes long, thus effective toner image The heating period is shortened. In the case where the fixing film becomes much thicker, the fixable temperature does not reach until the fixing film passes through the nip (curve 9 in FIG. 9b).

Since the temperature of the fixing film is lowered immediately after the main switch is activated or the device is not used, a low temperature toner offset may occur when the toner is not sufficiently melted.

In the case where the temperature of the heater is increased in the apparatus in which the recording plate is separated from the film when the temperature of the toner is higher than the glass transition point, a high temperature toner offset may occur because the toner melts excessively when a continuous fixing operation is performed.

Accordingly, it is a primary object of the present invention to provide an image fixing device in which an approximately equal amount of heat can be applied to an image irrespective of the initial temperature of the fixing film.

Another object of the present invention is to provide an image fixing apparatus in which a power source provided to a heater can be changed according to a temperature of a fixing film.

Still another object of the present invention is to provide an image fixing device in which a fixing temperature of a heater changes according to a temperature of a fixing film.

Still another object of the present invention is to provide an image fixing apparatus in which the temperature of the fixing film is controlled based on the output of the detecting means.

These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention in connection with the accompanying drawings.

8 shows an image forming apparatus using an image fixing apparatus according to an embodiment of the present invention. The image forming apparatus is an image transfer type electrophotographic apparatus composed of a reciprocating original support carriage and a rotatable drum.

The device consists of a case 100, a reciprocating original support carriage 1 made of a transparent material such as glass attached on the top 100a of the case 100. The original support carriage 1 is reciprocable in the left and right directions a-a 'on the upper end 100a.

The original G is placed upside down in accordance with the reference position on the original support carriage 1. Then, the original is covered by the original cover 1a.

A slit opening 100b is formed in the upper end 100a and extends in a direction perpendicular to the reciprocating motion of the original carriage 1 (direction perpendicular to the sheet of the drawing). The original is illuminated through the slit 100b.

The surface of the original image of the original G located in the original carriage 1 is passed by the slit opening 100b from right to left during the forward movement a of the original carriage 1. While doing so, the original image receives light L through the slit 100b and through the transparent original carriage 1 so that the original is scanned.

The light reflected by the original is illuminated on the surface of the photosensitive drum 4 through an array of image elements 2 having a short focal point and a small diameter.

The photosensitive drum 4 has a photosensitive layer such as a zinc oxide photosensitive layer or an organic photosensitive layer, and is rotatable in the direction indicated by the arrow b at a predetermined peripheral speed with respect to the central axis 4a.

During rotation, the photosensitive member is uniformly charged with either positive or negative charge. Thus, the surface of the charged photosensitive member is exposed to the light of the image from the original through the slit so that a latent image of static electricity is formed on the photosensitive drum 4.

The latent image of static electricity is continuously developed by the developing apparatus 6 having a toner made of a heat-softening and meltable resin material or the like. Then, the toner image (developed image) is moved to the image transfer site having the transfer discharger 9.

The cassette S contains a transfer sheet material (recording material). From the cassette S, the sheets come out one by one by the rotation of the pickup roller, and when the leading edge of the toner image reaches the position of the transfer discharger 9, the leading edge of the electronic sheet P and the transfer discharger 9 In this temporal relationship arriving at the position between the photosensitive drums 4, it is fed to the photosensitive drum 4 by the matching roller 8. On the surface of the transfer sheet thus fed, the toner image is continuously transferred from the photosensitive drum 4 by the transfer discharger 9.

The transfer sheet which receives the transferred image is separated from the surface of the photosensitive drum 4 by invisible separating means, and performs an image operation operation by heat to fix the unfixed toner image Ta. It is moved by the moving device 10. Finally, it is emitted as a print (copy) to the release plate outside the device through the guide 43 and the release roller 44.

After the image transfer, the surface of the photosensitive drum 4 is cleaned by the cleaning device 13, whereby the remaining toner or dirt is removed, thereby preparing for the image forming operation again.

According to this embodiment, an image fixing apparatus is described.

1 shows a cross-sectional view of the fixing device 11.

The fixing film 25 formed of the continuous belt has a low heat capacity linear heater 20 fixed downward between four parallel members, that is, the left driving roller 26, the right driven roller 27, and the rollers 26 and 27. And a guide roller 26a positioned below the drive roller 26.

The driven roller 27 also acts as a roller that extends the film 25. The fixing film 25 has a field of view of the driving roller 26 at a peripheral speed equal to the moving speed of the transfer sheet P (recording material) having an unfixed toner image Ta moved from the image forming place 9. It is rotated clockwise without folding or wriggling movement or delay by rotation in the direction.

The pressing member 28 formed of the pressing roller has a resilient rubber layer made of silicone rubber or the like having good separation characteristics.

This presses the lower end of the fixing film 25 to the lower surface of the heater 20 by pressure means having a total pressure of 4-7 kg, for example. This rotates in the same direction as the transfer sheet P movement, that is, counterclockwise.

Since the continuous belt type fixing film 25 is repeatedly used to heat and fix the toner image, it has sufficient heat-durability, separation characteristics and durability. In general, the total thickness thereof is about 100 microns, preferably about 40 microns.

It may be a single layer film of a heat resistant resin such as PI (polyimide, PEI (polyether imide) or PFA (tetrafluoro ethylene-perfluoro vinyl ether copolymer), or at least 10 microns on the side in contact with the image It is made of a multilayer film comprising a 20 micron thick film covered with a separation layer of, and the coating layer is made of PTFE resin (tetrafluoroethylene resin) to which an electrically conductive material is added.

The heater 20 constitutes the heater support 21 extended in the lateral direction (fixing film 25, the direction perpendicular to the moving direction), and has high rigidity, heat-durability, and insulation characteristics. The heater substrate 22 of good heat conducting material is mounted on the bottom surface of the support along the length of the support 21.

The heat generating resistor 23 is mounted on the film surface side of the heater substrate 22, and the heat generating resistor 23 generates heat instantaneously by its power supply. On the opposite side of the heater substrate 22, a temperature detecting element 24 is provided for detecting the temperature of the heater substrate 22.

Heater substrate 21 provides the total mechanical strength of the heater and includes heat-resistant resin materials such as PPS (polyphenylene sulfide), PAI (polyamideimide), PI (polyimide), PEEK (polyether ether ketone) Or mixtures such as liquid crystal polymer materials or resin materials and materials such as ceramics, metals, glass and the like.

One example of the heater substrate 22 is made of alumina with a thickness of 10.0 mm, a width of 10 mm and a length of 240 mm.

An example of the heat generating element is formed of an electrical resistive material such as Ag / Pt, RuO₂, Ta ₂ N, etc. applied to the bottom surface of the substrate 22 along the centerline of the substrate 22 having a width of 1.0 mm by screen printing or the like. do. Therefore, the heat generating element 23 is a linear or strip element having a low heat capacity and is activated by a power source.

The temperature detecting element 24 is composed of a temperature sensor having a low heat capacity formed of platinum film or thermistor. It is formed at the top of the substrate 22 (opposite in the heat generating element 23 side) along the nearly center length direction line of the top. In this embodiment, the temperature of the substrate 22 having good thermal conductivity is detected as the temperature of the heater 20 by the temperature sensor 22.

In this embodiment, the heat generating element 23 is in contact with the power source at the opposite lengthwise direction to generate heat along the entire length of the heat generating element 23. Energy loss is compensated by supplying power to the heat generating element based on the output of the fixing film temperature detector 31 and the set (target) temperature which will be described below.

The fixing film 25 is not limited to the form of the continuous belt. The construction of the film wound on the feed shaft 41 and the feed shaft 42 and spanned between them and between the heater 20 and the press roller 28 below the guide roller 26a is shown in FIG. In this case, the fixing film 23 is moved from the supply shaft 41 to the supply / demand shaft 42 at the same speed as that of the transfer sheet P. FIG.

In order to prevent abrasion and loss of the heat generating element 23, the heater 20 has a protective layer made of Ta ₂ O ₅ from the side contactable to the fixing film 25.

In operation, by pressing a copy switch (not shown), it is effective to reach the set temperature of the heater determined by the means described below by the power supply when an image forming signal is generated.

After reaching the set temperature, the power supply is controlled to maintain the set temperature.

The transfer sheet P is moved from the transfer place 9 to the fixing device 11 by an image forming operation in response to the start of image forming, and the nipple N formed between the fixing film 25 and the pressure roller 28 ( And a heater 20 and a pressure roller 28, the heater 20 is temperature-controlled. The sheet P having an unfixed toner image is combined with the heater 20 in close contact with the bottom surface of the fixing film 25 that moves at the same speed as the movement speed of the sheet P without collapsing with the surface. The branch passes through the fixing nip N between the heater 20 and the pressure roller 28. During this, the sheet P is pressurized.

At the bottom of the heater, the heat generating element 23 has a width W. The heat generating element 23 is in the contact area between the width of the fixing nip N, that is, the lower surface of the heater 20 and the upper surface of the pressure roller 28 through which the fixing film 25 passes.

The toner image holding surface of the sheet P receives heat from the heat generating element 23 through the fixing film 25, which passes through the fixing nip N having pressure-contact therebetween. The toner image is melted and softened by the high temperature and adhered onto the surface Tb of the sheet P.

In this embodiment, the separation between the sheet P and the fixing film 25 occurs at the time when the sheet P passes through the fixing nip N.

At this time of separation, since the temperature of the toner Tb is higher than the glass transition point of the toner, the adhesion (bonding force) between the sheet P and the fixing film 25 becomes small. Therefore, the sheet P is gently separated with little toner offset and almost no wrapping of the sheet P on the surface of the fixing film 25 due to improper separation.

Since the toner Tb has a higher temperature than the glass transition point has suitable rubber properties, this is moderately rough because the toner image surface at the time of separation does not completely follow the surface properties of the fixing film. Maintaining surface properties, the toner image is cooled and stuck. Therefore, the quality of the toner image surface after fixing is not excessively shiny.

After the sheet P is separated from the fixing film 25, it is moved along the guide 43 to the discharge roller pair 44. In doing so, the temperature of the toner Tb is increased from the temperature above the glass transition point and reduced by automatically cooling below the point below the glass transition point. Therefore, this is fixed in the toner image Tc. The sheet P having a fixed image is discharged to the plate.

The temperature control of the heater will be explained.

1 and 2, the temperature detecting element 31 is shown in contact with the inner surface of the fixing film 25 above the fixing nip N with respect to the moving direction of the fixing film.

The temperature detecting device 31 is composed of a silicone sponge 32, a temperature detecting element 33 sandwiched therein, and a PTFE tape 34 having good sliding characteristics.

The device 31 contacts the fixing film and detects the temperature of the inner surface of the fixing film immediately before the fixing nip N, before which the heater is supplied with power.

The information of the detected temperature is fed back to the microcomputer of the heater control system as a control element.

In the inventor's experience using commercially available toners for Canon FC copiers, when the fixing film has a temperature of 20 ° C. immediately before the nip, sufficient image fixing operation results in the heater 20 having a temperature of 190 ° C. (minimum fixable). Temperature); If the temperature is not lower than 210 ° C, it appears that the toner melts too much resulting in toner offset.

As shown in FIG. 5, each temperature varies depending on the temperature of the fixing film immediately before the nip.

In this embodiment, the set temperature of the heater control system is changed by using a microcomputer in accordance with the temperature of the fixing film detected by the temperature detector 31 according to Table 1 determined based on the result shown in FIG. do.

In particular, when the temperature of the fixing film at the start of the fixing operation is not higher than 30 ° C, as in the case where the fixing apparatus is not used for a long time, the set temperature is selected to maintain 200 ° C during the fixing operation.

When the temperature of the fixing film is increased so that it is 31-60 ° C, a temperature of 195 ° C is selected, and when the temperature is 61-100 ° C, the temperature is selected as 190 ° C.

When the temperature of the fixing film is not lower than 101 ° C, the control temperature is lowered to 185 ° C.

TABLE 1

Thus, even if the amount of heat absorbed from the fixing film changes, a good fixing image can be formed without inappropriate image fixing due to the low temperature of the fixing film during a long continuous fixing operation and without high temperature toner offset due to excessive high temperature of the fixing film. .

Another embodiment is described.

In the previous example, the temperature of the fixing film was directly detected. However, when the thickness of the fixing film is very small, for example, about 20 microns, the fixing film may be damaged by slipping of the temperature detecting device 31. When the temperature is detected without contact, a constant gap (eg 0.3 mm) is not easily maintained in consideration of the wave motion of the fixing film. Therefore, the temperature is not always detected correctly.

In order to solve this problem, this embodiment tends to be particularly important that the temperature of the driven roller, the member other than the fixing film 25, or the temperature of the pressure roller is changed by a method similar to the fixing film temperature. At this time, member temperatures other than the fixing film 25 are detected so as to switch the control temperature for the heater to be switched.

5 shows the temperature change of the fixing film 25 and the driven roller 27 when stopping after the fixing apparatus is operated for 10 minutes. As will be appreciated, the temperature change is similar.

As shown in FIG. 6, in the apparatus of this embodiment, the temperature detecting element 41 is used to detect the temperature of the driven roller 27. As shown in FIG. When it detects that the temperature is not higher than 60 ° C., heater 20 is controlled to be 193 ° C .; When this is higher than 60 ° C, the heater 20 is controlled to be 188 ° C.

The system in which the temperature of the fixing film is predicted based on the temperature detected for the portions other than the fixing film 25 does not require the temperature detecting element to contact the fixing film 25, and the durability of the fixing film 25 is reduced. There is an advantage to be improved.

In this embodiment, although the temperature of the driven roller 27 is detected, it is also possible to alternately detect the temperature of the neighborhood of the fixing film 25, that is, the temperature of the driving roller 26 or the pressure roller 28. .

In a fixing apparatus in which the movement of the fixing film 25 is stabilized so that the gap between the temperature detecting element 31 and the fixing film 25 can be kept constant, a non-contact type temperature sensor is effectively used.

Another embodiment is described. When the fixing apparatus is stopped and the power of the heater is ineffective, the temperature of the heater 20 changes similarly to the fixing film.

Therefore, in this embodiment, the temperature detecting element 24 for the heater 20 is used to detect the heater before the start of the image fixing operation, and the set temperature during the fixing operation is changed based on the detection.

This embodiment eliminates the need for a special temperature detector.

When the heat fixing toner A (Canon Corp.) is used, when the temperature of the fixing film is not higher than 60 ° C, the optimum temperature of the heater is shown in FIG. 7 which shows the relationship between the fixing film temperature and the heater temperature. 190 ° C. as shown. However, when the temperature of the fixing film is not lower than 140 ° C, the temperature of 190 ° C of the heater is too high, and the temperature of 185 ° C is appropriate.

Therefore, in this embodiment, when the fixing film temperature detected by the temperature detecting element 24 for the heater 20 is not higher than 60 ° C before the start of the image fixing operation, the power is supplied such that the temperature of the heater 20 becomes 190 ° C. do. When the temperature of the fixing film is not lower than 60 ° C already before the start of the fixing operation, the heater 20 is controlled to be 185 ° C from the first radiation. By doing so, sufficient image fixing force without toner offset can be provided.

In the image fixing apparatus of this embodiment, the temperature of the fixing film is increased to almost 60 DEG C by the power supply for one minute (corresponding to five sheet treatments) so that the temperature of the fixing film reaches almost 140 DEG C. In view of this, the continuous energy supply period is calculated from the start of operation by the microcomputer during the continuous operation, on the basis that the temperature of the film can be predicted. When the predicted temperature reaches 60 ° C, the control temperature for the heater 20 is switched to 185 ° C.

By predicting the temperature rise of the fixing film 25 in this way, even if the control temperature is controlled based on the temperature of the heater 20 before the start of the fixing operation, and even if the fixing operation continues to be executed, a high temperature offset does not occur. Do not.

In this embodiment, the temperature of the fixing film 25 is predicted based on the continuous power supply period, but this may be effective based on the number of sheets processed continuously. As for the control method, the set temperature of the control system is changed in the above embodiment, but it is also possible to alternately provide the same effect by changing the power source based on the detection of the film temperature or the like.

While being described with reference to the structures disclosed herein, this does not limit the detailed description described, which may be modified or altered within the scope of the claims or claims for improvement.

Claims (11)

An image fixing apparatus comprising: a heater for fixing an unfixed region; Control means for adjusting a power supply to the heater to maintain a predetermined fixing temperature; A film heated by the heater through the film, the film being in contact with the heater and movable with the recording material accompanying the image; A temperature detecting element for detecting a temperature of the film or a member in contact with the film; And changing means for changing the fixing temperature based on the output of the temperature detecting element before starting the image fixing operation of the image fixing apparatus. 2. An image fixing apparatus according to claim 1, wherein said temperature detecting element detects a temperature of said heater and, during the fixing operation, said control means controls the power supply to said heater. An image fixing apparatus according to claim 1, wherein said fixing temperature is determined by said changing means before starting supplying power to said heater. The image fixing apparatus according to claim 1, wherein the temperature detecting element detects a temperature of one surface of the film that is in contact with the image. The image fixing apparatus according to claim 1, wherein the temperature detecting element detects a temperature of a member in contact with one surface of the film in a direction opposite to the other surface of the film capable of contacting the image. The image fixing apparatus according to claim 1, wherein the heater is fixed during the fixing operation and the film is in sliding contact with the heater. 7. The heater according to claim 6, wherein the heater is composed of a heat generating resistance layer on the film side of the base plate which generates heat by the base plate and the power source, and heat from the heat generating resistance layer is transferred to the image without an air layer therebetween. Image fixing apparatus characterized in that the. An image fixing apparatus according to claim 1, wherein the image consists of a toner of powder and the recording material is separated from the film while the temperature of the toner is higher than the glass transition point of the toner. The image fixing apparatus according to claim 1, wherein the film is formed of a continuous belt. 8. The apparatus of claim 7, wherein the thickness of the film is no greater than 100 microns. 11. An apparatus according to claim 10, wherein the film has a thickness no greater than 40 microns.

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