JPH02103579A - Image forming device - Google Patents

Abstract

PURPOSE:To improve durability of fixing film by providing a film drive controlling means which controls a toner picture heating and fixing means to rewind, reversely travel and drive the fixing film by a rewinding amount different from the rewinding amount by which the fixing film is rewound, normally traveled and driven. CONSTITUTION:The fixing film drive and control means is provided which controls the toner picture heating and fixing means 20 to rewind, reversely travel and drive the fixing film 23 as follows: a recording material P is fixed, while the fixing film 23 is rewound, normally traveled and driven. After the trailing edge of the recording material P separates from the fixing film 23 and before the leading edge of a fresh recording material P to be fixed enters the fixing means 20, fixing is carried out for each recording material P by a rewinding amount different from the rewinding amount when the fixing film 23 is rewound, normally traveled and driven. As a result, the same side of the fixing film is used repeatedly in order, whereby the durability of the fixing film can be improved and the replacement frequency of the fixing film can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to image forming apparatuses such as copying machines, laser beam printers, facsimile machines, microfilm reader printers, image display devices, and recording machines.

More specifically, recording materials (electrofax sheets, electrostatic recording sheets, transfer material sheets,・A recording material that carries an unfixed toner image corresponding to the target image information by direct or indirect (transfer) method on a printing paper, etc., and carries the unfixed toner image. The present invention relates to an image forming apparatus that performs heat-fixing processing to form a permanently fixed image on a surface.

(Prior Art) Conventionally, a fixing device used in this type of apparatus uses a heating roller maintained at a desired temperature and a pressure roller having five elastic layers pressed against the heating roller. A roller fixing method is often used in which a recording material on which an unfixed toner image is formed is heated while being nipped and conveyed.

However, in this type of device, in order to prevent the so-called off-yield phenomenon in which toner transfers to the heating roller,
It is necessary to maintain the heating roller at an optimum temperature, and the heat capacity of the heating roller or heating element must be increased. In other words, the heat capacity of the heating roller! 4 is small, the temperature of the heating roller tends to fluctuate greatly from low temperature AL to high temperature (IL) due to paper passing or other external factors depending on the relationship with the amount of heat supplied by the heating element.If it fluctuates to the low temperature side, Insufficient softening and melting of the toner causes poor fixing and low-temperature offset, and when the temperature changes to the high temperature side, the toner is completely melted and the cohesive force of the toner decreases, resulting in high-temperature offset.

In order to avoid this problem, increasing the heat capacity of the heating roller increases the time it takes to heat the heating roller to a predetermined temperature, leading to another problem of increasing standby time when using the device. .

As a measure to solve this problem, US Patent No. 3,578
, No. 797, (1) bringing the toner image into contact with a heating body web and heating it to its melting point to melt it, (2) cooling the toner after melting to give it a relatively high viscosity, and (2) making the toner image relatively high in viscosity. A method is known in which the adhesive is adhered to the off-cera 1 without causing it by going through the process of peeling it off from the heating web in a state where the tendency to adhere is weakened.

In the known method described in 1-1, in addition to this, for the heating body,
Since it uses a method of heating the toner image and recording material without pressurizing them, there is no need to heat the recording material, and the toner can be melted with far less energy than other methods.

However, as is well known, when the toner is brought into contact with a heating body without being pressurized, the heat transfer efficiency decreases and it takes a relatively long time to heat and melt the toner.

Therefore, Special Publication No. 51-29825 Publication No. 111I (Special Patent Application No. 47
25896), it has been proposed to add a known pressure welding technique to this in order to improve the heat transfer coefficient and heat and melt the toner in a short time and sufficiently.

(Problem to be solved by the invention) However, in the apparatus disclosed in this publication, in order to heat the toner sufficiently in a relatively short time, This method involves heating the recording material by sandwiching it under pressure, and (2) stopping the heating and then forcibly cooling it, resulting in the inconvenience that the energy required for fixing increases. That is, by heating the toner image with a pair of heating elements, the toner image is heated from below -F, which may seem efficient at first glance, but on the other hand, in order to heat the toner image from the recording material side, the recording material must first be heated sufficiently. It is necessary to heat the material to a certain temperature, which requires a large amount of energy. Furthermore, in the cooling process, the recording material heated to a raised temperature when heating the toner image cannot be separated unless it is cooled.
A forced cooling method is required, resulting in a large waste of energy.

As mentioned above, a method has been proposed in which the heated toner is cooled and then separated to fix the toner without causing high-temperature offset. do not have.

Furthermore, in the two examples mentioned above, the heat-resistant web for fixing, which is interposed between the heating roller and the toner image and performs heat transfer, is composed of an endless member (belt). Problems tend to occur in runnability, and as a countermeasure to this problem, it was necessary to increase the thickness of the heat-resistant web. As the thickness of the heat-resistant web increases, its heat capacity inevitably increases, which reduces the heat transfer efficiency and requires a large amount of energy.In addition, as the latent heat of the heat-resistant web increases, the temperature inside the machine increases unnecessarily. Ta.

The present invention solves the problems of the conventional apparatus described above, and makes it possible to reduce the heat capacity of the heating element without causing fixing failure or offset. As a result, standby time, power consumption, and It is an object of the present invention to provide an image forming apparatus that has a low internal temperature of 91°C and has other remarkable features.

(Means for Solving the Problems) The present invention provides an image forming means for forming an unfixed toner image corresponding to target image information by supporting a toner made of heat-melting resin or the like on the surface of a recording material. , a heating body, a fixing film that is run forward and backward by a winding means and an unwinding means, and arranged on a side opposite to the heating body with the fixing film inside, and with respect to the heating body. a pressure member that brings the unfixed toner image bearing side of the recording material into close contact with each other through the fixing film; m at the same speed
(l) a toner image heat fixing means that causes the fixing film to run forward, introduces the recording material between the forward running fixing film and the pressure member, and heats and fixes the unfixed toner image onto the surface of the recording material; The rewinding and reverse driving of the nη fixing film of the toner image heat fixing means is performed at least under the negative recording material fixing process or the fixing film winding forward driving, and the rear end of the recording material is What is the winding amount for each interval of recording material after it rolls up from the fixing film until the leading edge of the next recording material to be fixed enters the fixing means, and by the forward running drive of the fixing film? An image forming apparatus comprising: a fixing film drive control unit configured to perform rewinding with different amounts of rewinding.

(Function) (1) The recording material on which the image is to be fixed is introduced between the fixing film in the normal running state and the pressure member, and the unfixed toner image bearing side of the recording material is in close contact with the fixing film surface. The heating body and the pressure member pass through the mutual pressure contact portion of the heating member and the pressure member while being subjected to a squeezing force while being overlapped together.

The fixing film runs forward at the same speed as the recording material conveyance speed (
Since the recording material and the fixing film are moved in the same direction as the recording material transport direction), the recording material and the fixing film overlap and are in close contact with each other without causing surface misalignment or wrinkles due to speed differences, and are pressed against the heating body. It passes through the mutual pressure contact area with the member.

■Heating process During this process of passing through the reciprocal contact area, the unfixed toner image on the surface of the recording material is heated and softened and melted by the heating body via the fixing film, and in particular, the surface layer exceeds the toner melting point and is completely softened and melted. do. In this case, the heating body, fixing film, toner image, and recording material are well pressed together by the pressure member at the mutual pressure contact portion of the heating member and the pressure member, and heat is transferred effectively, so that the heat is heated for a short time. The toner is sufficiently softened and melted to provide good fixing properties.

On the other hand, the temperature rise of the recording material itself is actually extremely small and there is little waste of thermal energy. In other words, the recording material itself is not heated substantially, only the toner is effectively heated to soften and melt, and the toner image can be successfully heat-fixed with low power.

Here, a note will be made regarding the softening and melting of the toner described in the present invention. The temperature, which is conveniently expressed as the "melting point" of a toner, means the minimum temperature required for the toner to fix, and there are cases where the viscosity decreases to the extent that it can be said to be melted at the minimum fixing temperature. In some cases, the viscosity decreases to the extent of softening. Therefore, even if it is conveniently expressed as melting during fixing, the viscosity may actually decrease to the extent of softening. The present invention also includes such cases. Similarly, even when it is conveniently expressed that the toner is cooled and fixed, depending on the toner, it may be more appropriate to say that the toner has become highly viscous rather than solidified. The present invention also includes such cases.

■Cooling process The toner image that is in close contact with the fixing film surface and sequentially passes through the mutual pressure contact area of the heating body and the pressure member.The recording material portion that has been heated, softened and melted is kept in close contact with the fixing film even after passing through the pressure contact area. The conveyance is continued for a while, and this period is used as a cooling process, in which the heat of the toner softened and melted in the heating process is radiated, and the toner is cooled and fixed. This cooling and solidification greatly increases the cohesive force of the toner, causing it to behave as a group, and while the adhesion and fixing force to the recording material side increases, the cohesive force to the fixing film side extremely decreases. When applied to the recording material, the toner is heated and softened and melted in the heating process, and is then pressurized by the pressure member, so at least a portion of the toner image permeates into the surface layer of the recording material, and the permeation valve The anchor effect caused by cooling and solidification increases the adhesion and adhesion of the cooled assimilated toner to the recording material side.

(2) Separation (Separation) Step - After the toner image is cooled and solidified in the cooling step described in (1), the recording material is sequentially separated from the fixing film.

At this time, the toner image is cooled and solidified and has a sufficiently large adhesion and adhesion force to the recording material, but the adhesion and adhesion force to the fixing film is extremely small, so toner offset occurs to the part of the recording material where the image has been fixed to the fixing film. They are easily separated one after another without having to do anything.

In this way, the recording material on which the image is to be fixed is made to run in close contact with the fixing film at the same speed so that the unfixed toner image bearing surface faces the running fixing film surface, and the toner image is heated and melted by a heating body through the fixing film. In addition, since the recording material and the fixing film are separated after the toner image is cooled and fixed, toner offset with respect to the fixing film does not occur, and a heating element with a small heat capacity is used, and power is supplied to the heating element. This can be done with a simple configuration, and by maintaining the heating element at a temperature sufficiently high compared to the temperature (melting point or softening point) at which the toner should be heated for fixing, the toner image can be improved efficiently. As a result, it is possible to achieve sufficiently good fusing with less energy and no fusing defects, resulting in an image forming device that requires less standby time during use, less power consumption, and less internal temperature rise. This effect is achieved.

(2) A thin heat-resistant film can be used as the fixing film, and in the present invention, the fixing film is configured to run forward and backward by a winding means and a reversing means. It is possible to run the toner image in the same direction as the transport direction of the recording material and at the same speed as the transport speed of the recording material and use it to heat and fix the toner image as described above, and then rewind it at a predetermined time and run it in the reverse direction for repeated use. It is possible.

By using the structure in which the fixing film is used by winding the film in the forward direction and rewinding it in the reverse direction using the winding means and the unwinding means, the winding means, the pressure member, the heating body, the rewinding means, etc. Even if there is a slight deviation in the transport direction of the fixing film or wrinkles are likely to occur due to component precision or positional precision such as mutual parallelism, the fixing film may be easily rolled up after it has been wound up by the specified amount. Since rewinding is performed using the same member as the one used in the rewinding process, slight deviations during winding must be corrected each time. Excellent, stable running of the fixing film over a long period of time can be realized. As a result, even thin fixing films that are prone to wrinkles and lack running stability can be used repeatedly over long periods of time, resulting in further energy savings. .

(3) In the rewinding and reverse running drive of the fixing film, at least the fixing process of the - recording material is performed under the winding forward running drive of the fixing film, and the trailing edge of the recording material is separated from the fixing film. After that, the unwinding process is performed for each recording material interval until the leading edge of the next recording material to be fixed enters the fixing means, and with a different winding amount from the winding forward drive of the fixing film. As a result, the fixing film mounted between the winding means and the unwinding means is gradually updated by a length corresponding to the difference between the winding amount and the rewinding amount, and the recording material is sequentially updated. It is then subjected to a fixing process. This allows the same side of the fixing film to be used by turning over the edge one after another, improving the durability of the fixing film (several times the number of durable sheets), and increasing the number of times the fixing film is replaced.
frequency).

(Embodiment) The drawing shows an apparatus according to an embodiment of the present invention, which is an electrophotographic copying machine having a reciprocating document table, a rotating drum type, and a transfer type.

(1) Overall schematic configuration of the device (Fig. 1) In Fig. 1, 100 is a device housing, and 1 is a reciprocating motion consisting of a transparent plate member such as a glass plate disposed on the top plate 100a of the machine housing. It is a document mounting table of the type, and the upper surface plate 100a of the machine casing is placed on the right side a in the drawing.
, are driven to reciprocate in the left direction a at predetermined speeds.

G is a document, which is placed by placing the image side to be copied facing down on the top surface of the document table 1 according to a predetermined placement standard, and placing the document pressure bonding plate 1a on top of it and pressing it down. .

Reference numeral 100b denotes a slit opening, which serves as a document illumination section, and is opened on the surface of the top plate 100a of the machine casing, with its length extending in a direction perpendicular to the direction of reciprocating movement of the document table 1 (direction perpendicular to the plane of the paper). The downward image surface of the original G placed on the original placing table 1 passes through the position of the slit opening 100b sequentially from the right side to the left side during the forward movement of the original placing table l to the right side a. During the passing process, the light L1 from the lamp 7 is received through the slit opening 100b and the transparent original table 1, and the document is illuminated and scanned. The illumination scanning light reflected from the document surface is imaged and exposed on the surface of the photosensitive drum 3 by the short focus and small diameter imaging element array 2.

The photosensitive drum 3 is coated with a photosensitive layer such as a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer, and is rotated clockwise around a central support shaft 3a at a predetermined peripheral speed in the clockwise direction shown by the arrow, and is charged during the rotation process. The surface of the photosensitive drum 3 is subjected to image-forming exposure (slit exposure) with an original image written on the surface of the charged surface. Electrostatic latent images corresponding to the original image are sequentially formed.

This electrostatic latent image is sequentially visualized by a developing device 5 using toner made of a resin or the like that softens and melts when heated, and the developed toner image is transferred to a location where a transfer discharger 8 is provided as a transfer section. I will do it.

S is a cassette loaded with transfer material sheets P as recording materials, and the sheets in the cassette are fed one by one by the rotation of the feeding roller 6, and then the toner on the drum 3 is transferred by the registration roller 9. When the leading edge of the image forming section reaches the position of the transfer discharger 8, the leading edge of the transfer material sheet P also reaches the open position of the transfer discharger 8 and the photosensitive drum 3 and is synchronized so that they are aligned. be sent. Then, the toner image on the photosensitive drum 3 side is sequentially transferred onto the surface of the fed sheet by the transfer discharger 8.

The sheet to which the toner image has been transferred in the transfer section is sequentially separated from the surface of the photosensitive drum 3 by a separating means (not shown), and guided by a conveyance guide 1O to a fixing device 20, which will be described later, to heat the unfixed toner image carried thereon. After being subjected to fixing processing, the image is output onto a paper output tray 11 outside the machine as an image-formed product (copy).

On the other hand, the surface of the photosensitive drum 3 after the toner image has been transferred is subjected to removal of adhering contaminants such as residual toner by the cleaning device 12, and electricity is removed by full-surface exposure L2 to erase the electrical residual memory and repeat the image formation process. Used in formation.

PH1 is a paper feed detection sensor (for example, a photo sensor) disposed in the sheet path section between the feed roller 6 and the registration roller 9, and PH2 is a paper discharge detection sensor (for example, a photo sensor) disposed next to the fixing device 20. It is.

(2) Fixing device (2) Structure FIG. 2 is an enlarged view of a portion of the fixing device 20 in an image fixing state.

21 is a heating element with a width of, for example, 160 μm on its lower surface side.
, has a length (length in the direction perpendicular to the plane of the paper) of 216 mm, is made of, for example, Ta2N, and has a resistance heating element 28 in the form of a line or band arranged with a component perpendicular to the conveying direction, and the surface thereof is covered with a sliding protective layer. For example, Ta20. , is covered with. Heating element 210 The heating element 28 has a small heat capacity, and is energized in a pulsed manner by the energizing circuit 28A of the Luno control system 42, and the temperature rises instantaneously to around 2600C each time.

Reference numeral 22 denotes a pressure roller as a pressure member disposed opposite to one side of the heating body 21, which has an elastic layer made of silicone rubber etc. on a core material made of metal etc., as will be described later. It is driven counterclockwise in the forward direction and clockwise in the reverse direction. The heating body 21 and the pressure roller 22 are pressed against each other with a predetermined contact pressure via a fixing film 23 or a fixing film 23 and a sheet P as a recording material, which will be described later. A fixed body is used, and a heating body 21 is a movable body that is constantly pressed against this pressure roller 22 by a pressure spring 40 to obtain a predetermined contact pressure (for example, a total pressure of 4 to 6 kg for A4 width). .

Reference numeral 41 designates an electromagnetic solenoid as a means for releasing the contact pressure between the heating body 21 and the pressure roller 22, and when the solenoid is energized by the control circuit 42, the plunger 4
1a, the heating element 21 is lifted from above the pressure roller 22 by the lever 43 and the lifting rod 44 against the pressure spring 40 as shown in FIG. 3, and separated from the pressure roller 22. ,
The contact pressure between both 21 and 22 is maintained in a released state.

When the current to the solenoid 41 is cut off, the pressure spring 40
As a result, the pressure contact state of the predetermined contact pressure is restored again.

24 is on the right side of the heating element 21 (on the flow side in the conveyance direction of the sheet P)
A rewinding shaft as a means for rewinding the fixing film disposed in the
Reference numeral 27 indicates a take-up shaft as a fixing film winding means disposed on the left side of the heating body 21 (on the F flow side thereof), and 26 indicates a take-up shaft located approximately midway between the heating body and the winding lug 27 from the take-up shaft 27. This is a separation roller with a strong curvature (small radius) and which is free to rotate.

Reference numeral 23 denotes a fixing film, which is initially fully embedded in the rewinding shaft 24 side, and its tip side passes through the space between the heating element 21 and the pressure roller 22 and the F side of the separation roller 26. It is locked to the winding shaft 27. The fixing film 23 has a thin wall (for example, 10 to
30 μm) or a composite layer film that has been subjected to desired surface treatment or lamination treatment. For example, about 12.
This is a composite layer film made of a 5 μm thick polyimide (P-based single layer film) and a release layer added to the surface of the film using tetrafluoroethylene (PTFE). sensor, 52 is the rewinding shaft 24
This is a film trailing edge detection sensor located on the side. The detection sensors 51 and 52 are both light sources 51a and 52a and light receiving elements 5.
It is a reflective sensor including 1b and 52b. Winding shaft 27
The fixing film 23 (
Usually transparent or translucent film) leading and trailing ends nν1
As shown in FIG. 9, a leading edge display black band 23a and a trailing edge display black band 23b are provided, respectively, and these black bands 23a and 23b are used for the fixing film 23 or for rewinding @24hai1. The sensors 51 and 52 are used at the beginning of the winding operation when the film is sufficiently wound, and at the end of the winding when almost the entire length of the fixing film is wound from the unwinding shaft 24 side to the winding shaft 27 side as the winding progresses. The leading edge and trailing edge of the film 23 are detected by light detection.

Reference numeral 33 indicates a free rotation auxiliary roller disposed opposite to the lower side of the separation roller 26, and 32 indicates a pressure roller 22 and an auxiliary roller 33.
This guide plate is arranged between the heating body 21 and the separation roller 26 with a predetermined gap between them, or with a slight contact with the lower surface of the stretched fixing film part. facing in parallel.

Reference numerals 29 and 25 are the same levers as the sheet detection sensors disposed on the lower surface side of the transfer material conveyance guide 10 from the toner image transfer section 8 to the fixing device 20 near the fixing device 20. In the free state, the tip of the lever 25 projects from the through hole 10a provided in the guide 10 to the upper surface side of the guide 10. In this state, sensor 29 is off. Guide 1
The transfer material sheet P is conveyed from the transfer unit 8 side to the fixing device 20 side along the upper surface of the sheet P, and the protruding tip of the lever 25 is cut by the tip of the sheet P, so that it goes into the back side of the sheet P and forms a through hole. It sinks into 1 Oa and rotates. This lever 25
The sensor 29 is turned on by the downward rotation of the sheet P, and the control circuit 42 detects whether the sheet P has reached the sensor position. The lever 25 is pressed against the back surface of the sheet P until the sheet P passes through the lever position, so that the lever 25 is kept in a sunken and rotating state during that time, and therefore the sensor 29 is kept in the on state. Thereafter, when the rear end of the sheet P passes the position of the lever 25 and is separated from the lever 25, the lever 25 becomes free and rotates again, returning to the position in which the tip protrudes from the through hole 10a. This return rotation causes sensor 2
9 is turned off, and the control circuit 42 detects that the sheet P passes the sensor position.

■Drive system Figure 4 shows the above-mentioned rewinding shaft 24, take-up shaft 27, and pressure roller 22 being driven in the normal direction (III! 1 I24 and 27 are rotated clockwise in Figure 2, and the pressure roller 22 is driven in the clockwise direction in Figure 2). This figure shows the gear train part of the drive system that rotates in the counterclockwise direction) and in reverse (rotates in the opposite direction to the above).

G is a first VL wheel as a power gear, which is driven to rotate clockwise in the direction of arrow X at a predetermined circumferential speed by an unillustrated drive source.
Rotation stop is controlled. G2 is the second gear meshed with the first gear.
Gears G3 and G4 are the third and fourth gears as two planetary gears for the second guide wheel G2. This third and fourth
Both gears are connected to the first arm 36. of a lever 36 which is rotatably supported by the l1ilII35 of the second gear G2 around the shaft.
and the second barrel 362, respectively, and the second gear G2
It meshes with the G5 is a fifth gear that is concentrically integrated with the fourth gear G4, G6 is a sixth gear that is in contact with the third gear G3, and G7
- G8 are the seventh and eighth gears meshed with the sixth gear G6, G9, G, o are the ninth and tenth gears meshed with the eighth gear G8 in sequence, G1. is the ii1st wheel which is concentrically integrated with the 10th gear Glo, and the 5th gear east G5 approaches and separates from this gear.

The seventh gear G7, the ninth gear G9, and the tenth gear G1° serve as driving gears for the winding @27, the pressure roller 22, and the unwinding shaft 24, respectively. Reference numeral 37 denotes an electromagnetic solenoid, and a link 39 connects the tip of the reciprocating plunger 37a to the central shaft 38 of the fourth gear G4 supported by the second arm 362 of the marking lever 36.

When the plunger 37a moves backward, the lever 36
is rotated counterclockwise around the shaft 35, and the third gear G3 meshes with the sixth gear G6 as shown by the solid line, and the fifth gear G5 is separated from the 11th gear G5 and its edge is cut off. Become. This is the first switching state.

Conversely, when the plunger 37a moves forward Z, the lever 36
rotates clockwise about the shaft 35, the third gear G3 separates from the sixth gear G6 and its edge is cut off, as shown by the two-dot chain line, and the fifth gear G5 moves to the eleventh gear G1. It will be in a state where it is meshed with.

This is the second switching state.

The plunger 37a is normally kept in the reverse position, so that the gear train is kept in the first switching state shown by the solid line. In this first switching state, the first gear G is rotationally driven in the clockwise direction of arrow
The winder 1M27 is driven to rotate in the normal direction. Further, the rotational force of the gear G6 is transmitted to the gear G9 via the gear G8, and the pressure roller 22 is driven to rotate in the normal direction. Furthermore, gear G
The rotational force of 9 is transmitted to gears G and o to drive the rewinding shaft 24 in normal rotation. That is, the fixing film 23 is rotated in the normal direction by the winding shaft 27, the pressure roller 22, and the rewinding shaft 24.
is wound up from the unwinding shaft 24 (Ill) to the winding shaft 27 at a predetermined speed (same speed as the conveying speed of the sheet material P to be fixed) and becomes a forward running state.

The seventh gear G7, which serves as a driving gear for the winding shaft 27, is connected to the winding shaft 27 via a slip mechanism so that the circumferential speed of the winding shaft 27 is slightly higher than the circumferential speed of the pressure roller 22. is set to . That is, pressure roller 2
The fixing film conveyed by No. 2 at a predetermined conveyance speed is wound up under a predetermined tension by a slip mechanism. Here, a braking member is further loaded on the winding shaft 27, and the braking load can be changed by changing the pressure of the friction plate, and the braking load is reduced during film winding.

a tenth gear G as a drive gear for the unwinding shaft 24; is the rewind @24 as in the case of the seventh (II4tG7) above.
The fixing film is connected to the fixing film via a slip mechanism, and is provided with a braking member, which applies tension to the fixing film by increasing the braking load during film winding. Here, the 10th gear G. is a rewind IP! Either the circumferential speed of the II 24 is set to be greater than the circumferential speed of the pressure roller 22, or the slip mechanism is activated by the braking force of the braking member, and the speed corresponds to the speed at which the fixing film is conveyed by the pressure roller 22. The rewinding shaft 24 is configured to rotate.

With the above-mentioned configuration, in this embodiment, even if the fixing film 23 is a thin film, it can be wound up without wrinkles because it is fed with an appropriate tensioning force and travels in the forward direction.

・Next, the plunger 37a is moved forward Z and the gear train is held in the second switching state shown by the two-dot chain line, and the first gear Gl
When is rotationally driven in the clockwise direction of arrow X, the first @car G1
The rotational driving force of the 2nd TiI car G2 and the 4th TK car G4
・Gear G→GIO→G via the 5th gear G
9 → G8 → G6 → G7 are transmitted in the reverse order of the film winding process to the rewinding shaft 24 and the pressure roller 2.
2. The winding shaft 27 is driven in the reverse direction, whereby the fixing film 23 is rewound from the winding shaft 27 side to the unwinding shaft 24 side, and is in a reverse running state.

In this case, in this embodiment, the fourth and fifth gears G4 and G
5 is a small-diameter and large-diameter two-stage gear, and the 10th and 11th gears are
Since the gears G, -G, are two-stage gears with large and small diameters, the number of reverse rotations of the rewind@24, pressure roller 22, and take-up shaft 27 is the same as the number of normal rotations during film winding. , and the film rewind time is shortened. Further, the braking load on the rewinding shaft 24 is reduced, and the braking load on the winding shaft 27 is increased. With this configuration, in this embodiment, the film can be rewound without wrinkles in the same manner as when the film is wound, and the film can be rewound in a short time.

(2) Operation FIG. 10 is a flowchart for controlling the operation of the image forming apparatus.

After turning on the main power switch of the device and performing surface operations such as setting the original, setting the number of images to be formed, and selecting the sheet size to be used, when the image formation start switch is pressed (the first
0, step ■), the feed roller 6 starts feeding the sheet P in the cassette S (step ■), and the sensor P
Paper feeding is detected by H1 (YES in step ①).

Also, image formation on the photosensitive drum 3 is started (step 2). The fixing device 20 operates when a predetermined timer period elapses from the time when the sensor PH1 detects paper feeding, that is, when the sheet P fed from the cassette S is transferred to the registration roller pair 9 and the transfer unit 8.
- When the time required for the tip of the guide 10 to reach a position near the pressure contact portion between the heating body 21 and the pressure roller 22 has elapsed, the rotational drive X of the first gear G of the drive system (FIG. 4) is started. Ru.

The gear train of the drive system of the fixing device 20 is always maintained in the first switching state, and the first gear G1 is stopped from rotating, so that the winding shaft 27, the unwinding shaft 24, and the pressure roller 22 is in a standby state where it has stopped rotating. By starting the drive X of the first gear G, the fixing device 20 enters a winding drive state in which the fixing film 23 travels forward at the same speed as the conveyance speed of the sheet P (step 2). Further, when the sensor 29 detects whether the leading edge of the sheet P conveyed to the fixing device 20 reaches the position of the sensor lever 25 or the trailing edge passes, the heating element 28 is energized at the appropriate timing.

In the above driving state, the leading edge of the sheet P smoothly enters between the fixing film 23 in a bad forward running state and the pressure roller 22 in a forward running state, and the upper surface of the sheet P carries the unfixed toner image Ta. is in close contact with the lower surface of the fixing film 23 in the forward running state, and the mutual pressure contact portion of the heating body 21 and the pressure roller 22 is subjected to a clamping force while overlapped with the fixing film 23 without causing surface deviation or wrinkles. It passes by.

This process of passing through the mutual crimping part is referred to as the heating process (action).
The toner image is heated to soften and melt as described in item (1)-0. As mentioned above, in the heating process in this practical hh example, the heating body 21 is provided with the linear heating element 28, and the heating body 21 is
The heating element 2 is configured to repeatedly generate heat by supplying electricity in a pulsed manner to the heating element 28 having a low heat capacity and integrally formed with the heating element 28.
It is carried out by 1. As shown in FIG. 5, the toner image Ta of the sheet P conveyed at a conveyance speed V, (+nm/s) is sequentially transferred to the heating body 21 along with the fixing film 23, which is conveyed without deviation according to the conveyance speed of the sheet P. It is fed into the effective width Q of the linear heating section, which is determined according to the width of the heating element 28, and is heated to become a softened and melted image Tb.

The sheet portion that has passed through the mutual pressure contact between the heating body 21 and the pressure roller 22 is a fixing film that is spread between the heating body 21 and the separation roller 26 and is traveling forward until it reaches the position of the separation roller 26. It continues to be transported while remaining in close contact with the part. The guide plate 32 functions to support the back surface of the sheet P and maintain close contact with the fixing film 23. Instead of this guide plate 32, a rotary guide belt 34 is stretched around the pressure roller 22 and the auxiliary roller 33 as shown in the example in FIG.
The belt 34 can also support the back surface of the sheet P to maintain close contact with the fixing film 23.

This conveyance process is used as a cooling process in the above (action) (1)-
As described in item 0, the heat of the softened/melted toner Tb is radiated, and the toner is cooled and solidified Tc.

When the fixing film 23 reaches the position of the separation roller 26, the running direction of the fixing film 23 is turned away from the surface of the sheet P along the surface of the separation roller 26, which has a strong curvature, and the fixing film 23 and the sheet P are separated from each other (separated). ) I'm going. By the time of separation, the toner has been sufficiently cooled and solidified as described above (
As described in (1)-0 of section 2.1, the adhesion and adhesion of the toner to the sheet P is sufficiently large, and the fixing film 2
3, the separation of the fixing film 23 and the sheet P can be easily and sequentially performed without substantially generating toner offset with respect to the fixing film 23.

The above heating process of the sheet P introduced into the fixing device 20
As the cooling process/separation process progresses, the trailing edge of the sheet P separates from the surface of the fixing film 23 that is being wound and driven forward, and then the sensor PH2 detects when the trailing edge passes the sheet discharge detection sensor PH2 ( Discharge detection, YES in step ■
), the fixing film 23 starts to rewind and travel in reverse based on that signal (step (2)).

To rewind the fixing film 23, the electromagnetic solenoid 41 as a pressure fixing means is energized in response to a paper discharge detection signal while the first IfiJ vehicle G1 is being driven, and the electromagnetic solenoid 37 of the drive system is also energized. This is executed by energizing.

By energizing the electromagnetic solenoid 41 as a pressure release means, the heating body 21 is activated as described above (FIG. 3).
is lifted from above the pressure roller 22 and the pressure roller 22
Then, the contact pressure between the two members 21 and 22 is released.

That is, the clamping force of both members 21 and 22 of the fixing film 23 is released, and the electromagnetic solenoid 37 of the drive system (FIG. 4)
When the plunger 37a is energized, the plunger 37a moves forward Z, and while the solenoid 37 is energized, the gear train is maintained in the second switching state shown by the two-dot chain line in FIG.

In this state, the fixing film 23 is reversely rewound from the take-up shaft 27 side to the rewind shaft 24 side by the rotational drive X of the first gear G1. When the fixing film 23 is unwound and runs in reverse, the heating body 21 and the pressure roller 2 are
Since the contact pressure between the heating element 21 and the fixing film 23 is released, the unwinding torque of the fixing film 23 is reduced, and wear and scratches on the heating element 21 and the fixing film due to unnecessary mutual sliding are prevented, thereby improving durability. can be improved.

In this embodiment, the above-mentioned fixing film rewinding reverse running is executed at a faster speed than the film winding forward running as described above, and the winding shaft 27 side is Film winding length ff1
It is stopped when the length e/2 of J2 (that is, the length approximately corresponding to the length of one fed sheet P) has been rewound.

This rewinding stop is performed by stopping the driving of the first gear G1, and at the same time, the electromagnetic solenoid 4
Power to 1.37 was also cut off.

If the set number of images to be formed is multiple sheets (multi-copy), after detecting paper ejection in step ■ in +i7f (YES), return to the start of paper feeding in step ■ from YES in step ■, and repeat the operation cycle of steps ■ to ■. is executed repeatedly for the set number of images to be formed.

In this case, in each image forming operation cycle, the fixing film is rewound by 172 minutes, which was started at the discharge detection (YES) in step The process is completed by the time the leading edge reaches the fixing device 20.

In this way, the fixing film 23 is gradually updated by the length corresponding to the difference between the winding length 1 and the unwinding length iJZ/2 as shown in FIG. The sheet P is wound up to the side and sequentially subjected to the fixing process (winding use mode). After approximately the entire length of the fixing film on the rewinding shaft 24 side is wound and transferred to the winding shaft 27 side, and the trailing edge of the film is detected by reading the trailing edge display black band portion 23b by the sensor 52, , in this embodiment, the unwinding length is 3 with respect to the film winding length I.
The unwinding shaft 2 is rotated from the winding shaft 27 side while being gradually reversed and updated by a length corresponding to the difference between the winding length h[42 and the unwinding length 5i311/2.
The sheet P is rewound to the 4th side and sequentially subjected to the fixing process (rewind use mode).

In this way, each time the leading end of the film is detected by the sensor 51 and the trailing end of the film is detected by the sensor 52, the above-mentioned winding use mode and rewinding use mode are repeated.

In this embodiment, the effective length of the fixing film 23 for fixing is set to 4Il. For example, when fixing 12 sheets, the part near the center of the effective length of the fixing film is used most often. However, four sheets are subjected to the fixing process. Therefore, in the case of this embodiment, the effective length of the fixing film is set to 1, which is the length of one sheet, and the entire β portion is repeatedly used for fixing. By making 42 times the number, you can obtain three times the number of durable sheets.

After the ejection of the final sheet is detected in multi-copying or after the ejection of that sheet is detected in monocopy, the path becomes image forming path Y (YES in step 2). →Step ■), the image forming apparatus enters a standby state.

In the paper feed detection in step (2), if the sensor PH1 does not detect the paper feed even after the predetermined timer period has elapsed since the paper feed start signal (No in step (2)), it is assumed that the paper feed is defective and a message to that effect is displayed on the console. This is done on the display section of the panel section (step [phase]), and at the same time, an emergency stop of the device operation is made (step ■).

In addition, in the paper ejection detection in step (2), if the paper ejection is not detected even after a predetermined timer period has elapsed from the time of paper feeding detection in step (2) or the time when the leading or trailing edge of the sheet is detected by the sensors 25 and 29 (step (NO), the sheet conveyance is defective and a message to that effect is displayed on the console panel (step @), and at that point, the operation of the apparatus is stopped urgently (step 2).

When the device is forced to stop due to a paper feed failure or conveyance failure as described above, image formation can be restarted by pressing the circuit reset button and pressing the image formation start switch again after recovering from the failure. It will be done.

The timing for starting rewinding of the fixing film 23 (step ■) can be determined not only by the paper ejection detection signal from the paper ejection detection sensor PH2 as in the embodiment apparatus, but also by using a timer from the time of the paper feed detection signal from the paper feed detection sensor PH1, for example. It can be set as appropriate, such as starting the circuit and taking the elapsed signal when a predetermined timer time corresponding to the time required for the fed sheet to be ejected to the paper ejection tray 11 has elapsed.

To release the contact pressure between the heating body 21 and the pressure roller 22 as a pressure member when rewinding the fixing film, the pressure roller 22 as a pressure member is moved from the heating body 21 in the interlayer direction as a movable side. Alternatively, both the heating body 21 and the pressure roller 22 may be moved in the interlayer direction.

The front and rear ends of the fixing film 23 can be detected by optical means as in the embodiments, as well as electrical means such as capacitance detection, magnetic means such as magnetic pattern detection, mechanical means such as unevenness, etc. as appropriate. can be selected.

FIG. 12 shows another example of driving the fixing film. In this example, a long fixing film is used repeatedly because it is gradually updated in the winding use mode in the relationship between the unwinding length and the winding length. By setting the unwinding length according to the durability of the fixing film, it is possible to use a thin fixing film while sequentially rewinding it, and by making the film thinner, it is possible to reduce thermal energy, making it possible to use rewinding. This improves economic efficiency.

Specifically, it is assumed that the fixing film 23 can be reused four times, and the length of the next unwinding is 31174 for the film winding length of 1 during the fixing process for one sheet.
It is set to . When the use of the fixing film 23 progresses and the trailing edge of the film is detected by the sensor 52, the fixing film is replaced with a new one.

(3) Example of implementation Figure 7 shows that in the configuration of this example, a 12.5 μm thick polyimide sheet is used as the fixing film 23 to fix 20 μm toner with a minimum fixing temperature of 80°C onto a 100 μm thick transfer paper P. It shows the change in temperature over time in the case of heating, and the surface layer part of the effective width of the heating section, the middle layer part of the toner, and the middle layer part of the recording material are calculated and shown.

FIG. 8 shows the temperature of toner and transfer paper (for details, , temperature at the center in each cross-sectional direction) over time. The fixing conditions are as follows:
It is as follows.

Heating conditions: energy temperature density 25vI/++on2 at 2.5rnskJ thermal toner fixing temperature 280°C Film: Polyimide (thickness 25μm) Toner layer thickness = 20μm Transfer paper thickness 2100μm Room temperature: 20'C In the example, the temperature is raised to 360'C, which is much higher than the toner fixing temperature of 800C, so it takes an extremely short time of 2ms.
By heating for a short period of time, the toner is sufficiently heated above the fixing temperature and good fixing properties are obtained.

On the other hand, the temperature rise of the transfer paper is extremely small, and there is less wasted energy than in conventional heat roller fixing.

Furthermore, in this embodiment, even if excessive energy is applied due to fluctuations in the heating time or the temperature of the heating element, high temperature offset does not occur and the tolerance range is wide.

In addition, in FIG. 8, compared to the conditions in FIG. 7, the energy density was changed to 20 Vl/lnm2, heating was performed for 2 ms, the fixing film thickness was changed to 12.5 μm, and other conditions were kept the same, but the same favorable conditions were used. The results were obtained.

As is clear from this example, the heating element according to the present invention can be small enough to have a small heat capacity, and there is no need to raise the temperature of the heating element in advance. Power consumption can also be reduced, and temperature rise inside the machine can also be prevented.

Further, in this embodiment, by providing the separation roller 26, cooling time for the toner image Tb in a heated, softened and melted state is ensured until the separation roller 26 is provided.
By increasing the curvature of 6, it is possible to easily separate the fixing film 23 and the recording material P, and, combined with the above-mentioned effect, it is possible to prevent offset at the separating portion.

However, the heating part (heating element part) 28 and the fixing film 2
If the heat capacity of the recording material P is sufficiently small and the fixing processing speed is low, the toner image will be softened and melted by heating within a short range after the recording material P passes through the heating section, without the need for special means such as the separation roller 26. Since Tb is cooled and solidified Tc, offset-free fixing processing is possible even if the separation roller 26 shown in this embodiment is omitted. That is, toner image T
Once a is heated to soften and melt Tb, it is again heat-radiated and solidified T.
It is only necessary that the fixing film 23 and the recording material P can be separated after C.

Next, the results obtained using the apparatus of this embodiment will be shown with specific numerical values. A toner image Ta was formed using a wax toner for PPCPG-30 (trade name) manufactured by Canon Co., Ltd., and the heat generation amount was approximately 3000 J per sheet of A4 size paper at a fixing processing speed of 15 mm/sec. , 10m5
When a fixing test was conducted by heating in a pulsed manner at a rate of 2 ms each time, an image with no practical problems was obtained.

Due to this energization, the temperature of the heating element 28 rises to about 260° C., and since the heat capacity is small, the temperature decreases by stopping the energization for 8 ms. Therefore, no waiting time is required to heat the heating element 21. In the above case, the temperature of the toner image exceeds, even momentarily, the temperature that is conventionally said to cause high-temperature offset, but as mentioned above, it is recorded on the fixing film 23 after being sufficiently cooled and fixed again. Since the material P is separated, there is no offset. The wax, which is the main component of the toner used in this example, has a temperature of about 80°C when heated.
It has a melting point of 260% and also has a low viscosity when melted.
When heated by the heating elements 28 before and after 'C, in conventional heat fixing devices, the molten toner penetrates into the recording material too much, causing problems such as image blurring or show-through, resulting in a decrease in toner. However, in this example, the heat capacity of the heating element 28 is small and the heating time is short, so the temperature gradient is large, and only the surface layer of the transfer paper is heated for a short time. , the above-mentioned disadvantages caused by excessive toner penetration do not occur.

Although the above-described embodiment is a transfer type electrophotographic copying device,
The image forming process/means is electrofax paper/
An image is formed using heat-fusible toner on a recording material using a direct method in which a toner image is directly formed and carried on electrostatic recording paper, a magnetic recording image forming method, or other appropriate image forming process or means, and then heated. The present invention can be effectively applied to various image forming apparatuses such as fixing type copying machines, laser beam printers, facsimiles, microfilm printers, display devices, and recording machines.

(Effects of the Invention) As described above, the present invention makes it possible to reduce the heat capacity of the heating body, which is the heating means, without causing fixing failure or offset in a toner image heat fixing type image forming apparatus. , it is possible to realize an image forming apparatus with low standby time, low power consumption, and low internal temperature rise. Furthermore, the thin fixing film can be used repeatedly for a long period of time without any problem of wrinkles.

The fixing film rewinding reverse running drive is performed at least after the fixing process of the negative recording material is performed under the fixing film winding forward running drive and the trailing edge of the recording material is separated from the fixing film. The rewinding process is performed for each recording material interval until the leading edge of the recording material to be subjected to the next fixing process enters the fixing means, and with an amount of rewinding that is different from the amount of rewinding by the forward drive for winding the fixing film. Therefore, the fixing film installed and set between the winding means and the rewinding means is gradually updated by the length corresponding to the difference between the winding amount and the rewinding amount, and is subjected to the fixing process of the recording material one after another. To go. This allows the same side of the fixing film to be used repeatedly, improving the durability of the fixing film (several times the number of durable sheets), and reducing the number of times (frequency) the fixing film needs to be replaced. It is effective and the intended purpose is well achieved.

[Brief explanation of drawings]

The drawings show an embodiment of the apparatus; FIG. 1 is an overall schematic diagram of the apparatus, FIG. 2 is an enlarged view of the fixing device in the fixing state, and FIG. 3 is a diagram showing the arrangement of the heating body and pressure roller. FIG. 4 is a diagram of the gear train of the drive system, FIG. 5 is a schematic enlarged sectional view of the pressure contact portion between the heating body and the pressure roller, and FIG. 6 is a partial enlarged view of the state in which the contact pressure is released. Figure 7 is a diagram of an example in which a guide belt is suspended between the pressure roller and the auxiliary roller; The figure shows temperature changes along the same line under other conditions.
FIG. 9 is a perspective view of the leading and trailing black display bands provided on the leading and trailing ends of the fixing film, FIG. 10 is a flowchart of the operation of the embodiment apparatus, and FIG. 11 is a fixing film. FIG. 12, which is a state diagram of film winding/rewinding travel control, is the same as the above diagram of another example. 20 is a heat fixing device, 21 is a heating element, 28 is a heating element, 2
2 is a pressure roller, 23 is a fixing film, 24 is a rewinding shaft, 7 is a winding shaft, is an electromagnetic plunger as a pressure release means, and P is a transfer material sheet as a recording material.

Claims (1)

[Claims] (1) An image forming means for forming an unfixed toner image corresponding to target image information by carrying toner made of heat-melting resin or the like on the recording material surface, a heating body, a winding means, and an unwinding means. A fixing film that is run forward and backward by a means,
a pressure member disposed on a side opposite to the heating body with the fixing film therein, and bringing the unfixed toner image bearing side of the recording material into close contact with the heating body via the fixing film; and causing the fixing form to travel forward at the same speed as the conveyance speed of the recording material carrying the unfixed toner image conveyed from the image forming means side, between the fixing film in the forward travel and the pressure member. a toner image heat fixing means for heating and fixing an unfixed toner image on the surface of the recording material by introducing the recording material into the recording material; and a rewinding and reverse running drive of the fixing film of the toner image heat fixing means for at least one recording. After the fixing process of the recording material is performed under the normal winding drive of the fixing film and the trailing edge of the recording material leaves the fixing film, the leading edge of the next recording material to be fixed enters the fixing means. An image forming apparatus comprising: a fixing film drive control unit configured to perform rewinding for each recording material interval up to and with a rewinding amount that is different from the rewinding amount by the forward winding drive of the fixing film.