JP2570838B2 - Image heating fixing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image heating apparatus incorporated in an image forming apparatus such as a copying machine, a laser beam printer, a facsimile, a micro film reader printer, an image display (display) device, and a recording device. It relates to a fixing device.

More specifically, a recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, A non-fixed toner image corresponding to the target image information is formed and supported on a surface of a printing paper or the like by a direct method or an indirect (transfer) method, and the unfixed toner image is recorded on a recording material surface carrying the image. And a fixing device of a type for performing a heat fixing process as a permanently fixed image.

2. Description of the Related Art Conventionally, as an image fixing apparatus of a heat fixing type, an unfixed toner is formed by a heating roller maintained at a predetermined temperature and a pressure roller having an elastic layer and pressing against the heating roller. A roller fixing system in which a recording material on which an image is formed is heated while being nipped and conveyed is often used.

However, in this type of apparatus, it is necessary to maintain the heating roller at an optimum temperature in order to prevent the so-called offset phenomenon in which toner is transferred to the heating roller, and the heat capacity of the heating roller or the heating element must be increased. Did not. That is, when the heat capacity of the heating roller is small, the temperature of the heating roller tends to fluctuate greatly to the low temperature side or the high temperature side due to paper passing or other external factors depending on the amount of heat supplied by the heating element. If the temperature fluctuates to a lower temperature, insufficient fixing and melting of the toner will occur due to insufficient softening and melting of the toner.If the temperature fluctuates to a higher temperature, the toner will be completely melted and the cohesive force of the toner will decrease. , Causing hot offset.

If the heat capacity of the heating roller is increased in order to avoid this problem, the time required for heating the heating roller to a predetermined temperature becomes longer, which causes another problem that the standby time becomes longer when the apparatus is used. .

U.S. Pat.
As disclosed in the specification of Patent No. 7, the toner image is brought into contact with a heating element web, heated to its melting point and melted, and after melting, the toner is cooled to a relatively high viscosity, and the tendency of toner to adhere A method of fixing without causing offset is known through a process of peeling off the heating element web in a weakened state.

In the above-mentioned known method, in addition to this, a method is adopted in which the toner image and the recording material are heated without being pressed against and pressed against the heating element, so that the recording material does not need to be heated and compared with other methods. It says that toner can be melted with much less energy. However, as is well known, in the case of contact with the heating element without pressurizing and pressing, the heat transfer efficiency is reduced, and it takes a relatively long time to heat and melt the toner.

Thus, Japanese Patent Publication No. 51-29825 (Japanese Patent Application No. 47-25896)
In addition, it has been proposed to add a well-known press-contact technique to improve the heat transfer coefficient and heat and melt the toner in a short time and sufficiently.

(Problems to be Solved by the Invention) However, in the apparatus disclosed in this publication, a toner image and a recording material are interposed between a pair of heating members in order to heat the toner in a relatively short time and sufficiently. In this method, the heating is stopped while heating is stopped, the heating is stopped, and then the cooling is forcibly performed. This disadvantageously increases the energy required for fixing. In other words, by heating with a pair of heating elements, the toner image is heated from above and below, so it can be considered efficiently at first glance. To heat the toner image from the recording material side, first, heat the recording material sufficiently. Need to do so, which requires a lot of energy. Further, in the cooling step, even if the recording material heated and heated at the time of heating the toner image cannot be separated unless it is cooled, a forced cooling means is required, which wastes much energy.

As described above, a method has been proposed in which a heated toner is cooled and then separated after cooling, thereby fixing without causing high-temperature offset. However, such a method has not been put to practical use because of the drawbacks described above.

In the above two proposals, the heating element is constituted by a heating roller and a web fed by the heating roller and a heat source incorporated in the heating roller, and heating is performed through the web,
It has a function as a web transport roller. For this reason, the method of supplying power to the heat source and the form of contact and support of the temperature detecting element are complicated, and the accuracy of temperature control tends to be poor. Further, in the configuration in which the temperature detecting element slides on the heating roller, there is a problem in safety such as an excessive temperature rise due to disconnection. In addition, both of the above two examples require a heating element having a relatively large heat capacity, so that the heat radiation to the inside of the apparatus is increased, and the temperature inside the apparatus is significantly increased.

The present invention solves the above-mentioned problems of the conventional apparatus, and makes it possible to reduce the heat capacity of the heating element without causing a fixing failure or an offset. As a result, the standby time, the power consumption, and the It is an object of the present invention to provide an image forming apparatus having a small temperature rise in the apparatus and having other remarkable features.

(Means for Solving the Problems) The present invention provides a heating member, a fixing film that moves with a recording material that carries an unfixed toner image while sliding on the heating member,
An image having a pressure member that forms a nip with a heating element via a fixing film, and an energization control unit that controls energization of the heating element so that the temperature of the heating element is maintained at or above the melting point of the toner during fixing. In the heat fixing device, the energization control unit starts energization immediately before the fixing process and temporarily raises the temperature of the heating element to a temperature lower than the melting point of the toner. Image heating and fixing device, characterized in that energization control is performed so as to raise the temperature,
It is.

(Operation) (1) The recording material to be fixed between the fixing film and the pressing member, which is driven in the same direction at the same speed as the recording material conveyance direction, is unfixed toner on the fixing film surface. When the surfaces on the image bearing side are in close contact with each other and the fixing film is overlapped with the fixing film, the heating element and the pressing member receive a mutual pressure contact portion, that is, a fixing nip portion, while being sandwiched by each other, causing surface displacement due to a speed difference therebetween, and wrinkles. It passes over the body without overlapping.

Heating process In the process of passing through the fixing nip, the unfixed toner image on the recording material surface is heated and softened and melted by the heat of the heating section of the heating element via the fixing film. Softens and melts. In this case, the heating member, the fixing film, the toner image, and the recording material are satisfactorily pressed and adhered by the pressing member at the mutual pressure contact portion between the heating member and the pressing member, and the heat is effectively transferred. The toner is sufficiently softened and melted to obtain good fixability. On the other hand, the temperature rise of the recording material itself is extremely small in practice, and the waste of heat energy is small. In other words, the recording material itself is not heated substantially, and only the toner is heated and softened effectively.
The toner image can be satisfactorily fused and heated and fixed with low power.

Here, note the softening and melting of the toner described in the present invention. The temperature, which is conveniently expressed as the "melting point" of the toner, means the minimum temperature required for the toner to be fixed. In some cases. Therefore, even when the term “melting” is used for the sake of convenience for fixing, the viscosity may actually decrease such as softening. The present invention includes such a case. Similarly, when the expression that the toner is cooled and fixed is used for convenience, depending on the toner, it may be more appropriate to increase the viscosity rather than to solidify. The present invention includes such a case.

Cooling process The toner image that has passed through the fixing nip part in close contact with the fixing film surface, and the heated, softened and melted recording material part, even after passing through the fixing nip part, continues to be transported for a while while keeping it in close contact with the fixing film surface. During this period, the cooling process is performed, and the heat of the toner softened and melted in the heating process is radiated to cool and fix the toner. By this cooling and solidification, the cohesive force of the toner becomes very large, and the toner behaves as a group. In addition, while the adhesive / fixing force on the recording material side increases, that on the fixing film side extremely decreases. When the toner is heated and softened and melted in the heating step, the toner is pressed by the pressing member, so that at least a part of the toner image permeates into the recording material surface layer, and the permeated portion is cooled and solidified. The adhesive effect of the solidified toner on the recording material side increases due to the anchor effect of the toner.

Separation (separation) step After the toner image is cooled and solidified by the above-mentioned cooling step, the recording material is sequentially separated from the fixing film surface.
At the time of separation, the toner image has a sufficiently large adhesive / adhesive force to the recording material due to cooling and solidification, and has a very small state with respect to the fixing film, so that the image-fixed recording material portion causes toner offset with respect to the fixing film. It is easily separated one after another.

The recording material to be image-fixed is brought into close contact with the fixing film at the same speed so that the unfixed toner image carrying surface faces the fixing film surface running in this way, and the toner image is heated and melted by a heating element through the fixing film. Since the recording material and the fixing film are separated from each other after the toner image is cooled and fixed, no toner offset occurs with respect to the fixing film, and a heating element having a small heat capacity is used, and power is supplied to the heating element. This method can be performed with a simple configuration, and by maintaining a heating element at a temperature sufficiently high with respect to the temperature (melting point or softening point) at which the toner is to be heated for fixing, the toner image can be efficiently produced. Heating can be performed, and a sufficiently good fixing without a fixing failure can be achieved with a small amount of energy. As a result,
This has the effect of obtaining an image forming apparatus with a small standby time during use of the apparatus, low power consumption, and a small rise in temperature inside the apparatus.

In the above separation step, the toner does not necessarily have to be cooled and solidified at the position of the separation portion between the fixing film and the recording material. If the toner melts sufficiently at a high temperature among the three steps of heating, cooling and separation (if the viscosity of the toner during heating and melting is sufficiently high), the toner is melted at a sufficiently high temperature in the heating step. Immediately thereafter (when the toner temperature is equal to or higher than the melting point), the recording material may be separated from the fixing film surface, and the cooling step after the heating step may be omitted, which belongs to the scope of the present invention.

(2) In the case of an apparatus having a low heat capacity, such as a film heating type image heating and fixing apparatus, it is not necessary to energize the heating element when the apparatus is not used, so that power consumption can be reduced. However, if the heating element is instantaneously heated to a temperature equal to or higher than the melting point of the toner from a state in which the heating element is not warmed, a large current will flow, and a power supply with a large rating will be required.

Therefore, according to the present invention, the energization control means starts energization immediately before the fixing process and temporarily raises the temperature of the heating element to a temperature lower than the melting point of the toner. It is characterized in that the power supply is controlled so as to be heated.

Due to this feature, a large current does not flow when the temperature of the heating element is raised to a temperature equal to or higher than the melting point of the toner, so that a power supply with a small rating is sufficient. Therefore, the maximum power consumption of the fixing device can be reduced, and the size of the power supply can be reduced, and the size and cost of the entire device can be reduced.

(Embodiment) <Embodiment 1> FIG. 3 shows a schematic configuration of an example of an image forming apparatus incorporating an image heating and fixing apparatus 20 according to the present invention. The image forming apparatus of this embodiment is an electrophotographic copying apparatus of a reciprocating type, a rotating drum type, and a transfer type on a document table.

(1) Overall Schematic Configuration of Copying Apparatus In FIG. 3, reference numeral 100 denotes a housing of the apparatus, and 1 denotes a reciprocating original mounting plate made of a transparent plate member such as a glass plate disposed on an upper plate 100a of the housing. It is a mounting table, and is reciprocally driven on the upper surface plate 100a of the machine at a predetermined speed to the right side a and the left side a 'in the drawing.

G is an original, which is placed on the upper surface of the original placing table 1 with the image side to be copied facing downward according to a predetermined placing reference;
The original is set by placing the original cover 1a on top of the cover.

Reference numeral 100b denotes a slit opening serving as a document illuminating unit which is opened on a surface of the machine housing upper plate 100a with a direction perpendicular to the reciprocating movement direction of the document placing table 1 (direction perpendicular to the paper surface) as a longitudinal direction. The downward image surface of the original G placed and set on the original placing table 1 sequentially passes through the position of the slit opening 100b from the right side to the left side during the reciprocating movement of the original placing table 1 to the right side a. the light L ₁ slit opening 100b of the lamp 7 in the passing process, are illuminated and scanned by receiving through a transparent original table 1. The reflected light of the illumination scanning light on the document surface is image-formed and exposed on the surface of the photosensitive drum 3 by the short-focus 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 driven to rotate clockwise as indicated by an arrow b at a predetermined frequency around a center support shaft 3a. The charger 4 was subjected to a uniform charging process of positive or negative polarity, and the uniformly charged surface was subjected to the image forming exposure (slit exposure) of the original image to form an image on the surface of the photosensitive drum 3. An electrostatic latent image corresponding to a document image is sequentially formed.

The electrostatic latent image is sequentially visualized by a toner made of a resin or the like which is softened and melted by heating by the developing device 5, and the developed toner image is transferred to a portion where the transfer discharger 8 as a transfer portion is provided. I will do it.

S denotes a cassette in which transfer material sheets P as recording materials are stacked and stored, and the sheets in the cassette are fed out one by one by the rotation of the feed roller 6, and then the toner on the drum 3 is moved by the registration roller 9. When the leading end of the image forming section reaches the portion of the transfer discharger 8, the leading end of the transfer material sheet P also reaches the position between the transfer discharger 8 and the photosensitive drum 3 and is synchronized in timing so that they coincide with each other. Will be fed. Then, the transfer discharger 8 is applied to the surface of the sheet.
As a result, the toner image on the photosensitive drum 3 side is sequentially transferred.

The sheet to which the toner image has been transferred by the transfer unit is sequentially separated from the surface of the photosensitive drum 3 by a separation unit (not shown), and is guided by a conveyance guide 10 to a fixing device 20 described later to heat the unfixed toner image carried. After being subjected to the fixing process, the sheet is discharged onto a discharge tray 11 outside the apparatus as an image formed product (copy).

On the other hand, the surface of the photosensitive drum 3 after the toner image transfer is subjected to removal of adhering contaminants such as transfer residual toner by a cleaning device 12, repeatedly to erase the residual electrical memory undergoing neutralization by flood exposure L ₂ is made Used for image formation.

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

(2) Fixing Device 20 FIG. 1 is an enlarged view of the fixing device 20 in an image fixing execution state.

Reference numeral 24 denotes a fixing film delivery shaft, in which a fixing film 23 of a desired set length is wound around a roll, and the leading end of the fixing film 23 is locked on a fixing film winding shaft 27. . The fixing film 23 according to the present embodiment is a heat-treated thin plastic long film made of, for example, 6 μm thick PET (polyester) as a base material.

Reference numerals 21 and 22 denote a heating element and a pressure roller, which are disposed on the upper surface side and the lower surface side of the fixing film portion between the shafts 24 and 27 so as to face each other. The heating body 21 and the pressure roller 22 are constantly pressed and urged with the urging means (not shown) sandwiching the fixing film 23 therebetween to apply a desired contact pressure (for example, a total pressure of 4 to 6 kg in A4 width). 26
33 is separated from the upper roller having a large curvature (having a large curvature and a small radius) which is disposed next to the heating element 21 and the pressure roller 22 so as to be opposed to the upper surface side and the lower surface side of the fixing film, respectively. Lower roller. 32 is a pressure roller 22 and a separation lower roller 33
The guide plate is disposed between the heating body 21 and the upper separation roller 26 with a predetermined gap or lightly in contact with the lower surface of the expanded fixing film portion. They face substantially parallel. The pressure roller 22 has an elastic layer made of silicon rubber or the like on a core made of metal or the like. The upper separation roller 26 and the lower separation roller 33 are rotation-free rollers.

The take-up shaft 27 is driven to rotate in a clockwise direction as indicated by an arrow by a drive system (not shown).
The sheet P conveyed from the image forming unit (transfer unit 8) to the fixing device 20 via the guide 10 from the image forming unit (transfer unit 8) via the guide 10 to the winding shaft 27 is wound in the same direction and at the same speed. The pressure roller 22 is driven to rotate in a counterclockwise direction indicated by an arrow at a peripheral speed substantially equal to the conveying speed of the sheet P by a drive system (not shown).

Numeral 30 denotes a remaining amount sensor arm of the fixing film which is brought into contact with the outer surface of the wound fixing film 23 on the sending shaft 24 side, which is sequentially transferred to the winding shaft 27 side by performing the fixing process. The sensor 30a detects the remaining amount from the successive decrease of the winding diameter, and when the film is near the end, a warning display or a warning sound prompts the user to replace the fixing film.

Reference numerals 29 and 25 denote the same levers as sheet detection sensors disposed on the lower surface side of the transfer material transport guide 10 from the toner image transfer unit 8 to the fixing device 20 near the fixing device 20. The distal end of the lever 25 projects from the through hole 10a formed in the guide 10 to the upper surface of the guide 10 in a free state. In this state, the sensor 29 is off. 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 guide 10, and the projecting end of the lever 25 is cut at the end of the sheet P, so that the transfer material sheet P passes through the back side of the sheet P. It sinks into the light 10a and turns. The sensor 29 is turned on by the sinking rotation of the lever 25, and the arrival of the sheet P at the sensor position is detected by a control circuit (not shown). The lever 25 is kept in a squatting and rotating state during contact with and pressed against the back surface of the sheet P until the sheet P has passed through the lever position, so that the ON state of the sensor 29 is maintained. Then sheet P
When the rear end passes through the position of the lever 25 and the edge of the lever 25 is cut off, the lever 25 is in a free state, and returns to the posture in which the front end protrudes from the through hole 10a, and rotates. Due to this return rotation, the sensor 29 is turned off, and the passage of the sheet P to the sensor position is detected by the control circuit.

FIG. 2 is a schematic enlarged cross-sectional view showing the structure of the heating element 21. The heating element 21 of the present example is a horizontally long low heat capacity linear heating element whose longitudinal direction is the transverse direction of the fixing film (the direction perpendicular to the running direction of the fixing film 24).

Reference numeral 52 denotes a heat-resistant and electrically insulating thin heater substrate such as alumina.

Reference numeral 28 denotes a linear or thin line of silver palladium, Ta ₂ N, RuO ₂ , nichrome, or the like formed by a printing method or the like along the length substantially at the center of the lower surface of the substrate 52 (the surface facing the fixing film 23). It is a heating layer (resistance heating element) of a belt-like thin film.

Reference numerals 50 and 50 denote electrodes (for example, gold electrodes) for supplying electricity to the heat generating layer 28, which are also formed on the lower surface of the substrate 52.
The heat generating layer 28 receives a pulse current through the electrodes 50 and generates heat in a pulse shape.

Reference numeral 51 denotes a thin sliding protection layer made of Ta ₂ O ₅ , heat-resistant glass, or the like, which is formed so as to cover the entire lower surface of the substrate 52 provided with the heating layer 28 and the electrodes 50. The outer surface of this protective layer 51 is smooth,
The leading edge and the trailing edge in the running direction of the fixing film are rounded (chamfered) to enable smooth sliding with the fixing film.

Reference numerals 55 and 56 denote a temperature detecting element such as a thermistor or a Pt film or the like having a small heat capacity provided on the upper surface side of the substrate 52 and a temperature detecting element such as a Ta ₂ N
This is an auxiliary heating layer made of a resistance heating element such as a thin film. The temperature detecting element 55 and the auxiliary heat generating layer 56 are arranged close to each other,
Further, it is disposed close to the heat generating layer 28 on the lower surface side of the substrate.

Thus, the above-mentioned substrate structure (52, 28, 50, 55, 56) is used as a heater assembly, which is made of a heat insulating layer 53 made of a material having low heat conductivity, heat resistance, and electric insulation, such as bakelite. , And is attached to the rigid support 54 to form the heating element 21. The surface area on the lower surface of the heater 21 substantially corresponding to the width of the heat generating layer 28 is a heating unit H.

(3) Operation After an image forming start switch is pressed after the necessary setting such as setting of the original G on the original placing table 1, setting of the number of image forming sheets, designation of the size of the sheet P to be used, and designation of the magnification, feeding is performed. Feeding of the sheets P in the cassette S is started by the rollers 6, and the sheet feeding is detected by the sensor PH1. Further, image formation on the surface of the photosensitive drum 3 is started.

In the fixing device 20, the sheet P fed from the cassette S passes through the registration roller pair 9, the transfer unit 8, and the guide 10 when the predetermined time elapses from the sheet feeding detection time by the sensor PH1. When the time required to reach the position in the vicinity of the pressure contact portion between the pressure roller 22 and the pressure roller 22 elapses, the driving system of the fixing device starts rotating the winding shaft 27 and the pressure roller 22 to rotate, and the fixing film 23 is sent out to the shaft 24 side. Then, the sheet is driven to the take-up shaft 27 side at the same speed as the sheet P conveyance speed. Further, the heating element 21 is energized when necessary when the leading end and the trailing end of the conveying sheet P are detected by the sensor 29 and the lever 25 at a time. At this time, the power supply to the heating element may be controlled using the sheet position detection or the like by a sheet feed sensor or the like of the image forming apparatus.

The upper surface of the sheet carrying the unfixed toner image Ta conveyed to the fixing device 20 has a fixing film 23 in a running state.
The heating element 21 and the pressure roller 22 pass through the mutual pressure contact part (fixing nip part) while receiving the pinching pressure in the overlapping state with the fixing film 23 without causing surface deviation or wrinkling due to close contact with the lower surface of the sheet. To go.

The heat of the heating unit H is transmitted to the sheet P side via the fixing film 23 as a heating process in the process of passing the mutual pressure bonding unit, and the heat softening / melting of the toner image described in (1)-of the above (action) is performed. Done.

As described above, the heating step according to the present embodiment
A heating element configured to provide a linear low-heat-capacity heat generating layer on the heat generating layer, and to apply heat to the heat generating layer in a pulsed manner to repeatedly generate heat.
It is done by 21. That is, the toner image Ta on the sheet P conveyed between the fixing film 23 in the fixing nip portion of the fixing device and the pressure roller 22 is sequentially transferred together with the fixing film 23 conveyed without displacement according to the conveying speed of the sheet P. The heating unit H is heated according to the width of the heat generating layer 28 of the heating body 21 to form a softened / melted image Tb.

The sheet portion that has passed through the mutual pressure contact portion between the heating body 21 and the pressure roller 22 stretches forward between the heating body 21 and the separation upper roller 26 until it reaches the position of the separation rollers 26 and 33, and travels forward. The film is conveyed while keeping in close contact with the fixing film portion. The guide plate 32 supports the back of the sheet and fixes the film.
It acts to maintain close contact with 22.

Instead of this guide plate 32, the pressure roller 22 and the separation lower roller 33
The belt can support the back surface of the sheet P to maintain the close contact with the fixing film 23.

This transporting process is defined as a cooling process (1) of the above (action).
As described in section-, the heat of the softened / molten toner Tb is radiated to cool and solidify the toner Tc.

When the fixing film 23 reaches the position of the upper separating roller pair 26, the running direction of the fixing film 23 is turned in a direction away from the sheet P surface along the surface of the separating upper roller 26 having a large curvature, and the fixing film 23 and the sheet P are mutually moved. The paper is separated (separated) and discharged to the paper discharge tray 11. By the time of the separation, the toner is sufficiently cooled and solidified, and as described in the item (1)-of the above-mentioned (action), the adhesion and fixing force of the toner to the sheet P is sufficiently large, and that to the fixing film 23 is extremely small. In this state, separation of the fixing film 23 and the sheet P can be easily and sequentially performed without substantially causing toner offset to the fixing film 23.

The driving for winding and running the fixing film 23 of the fixing device 20 is stopped when the sheet P finishes passing through the fixing device 20 and the trailing end is detected by the sheet discharge detection sensor PH2.

In the present embodiment, the fixing film 23 is fed from the sending shaft 24 side every time the fixing process of the sheet P is executed as described above.
The sheet P is sequentially wound and used at the same speed as the transport speed of the sheet P on the 27 side.

The fixing film winding forward traveling drive control is such that the driving is started when a predetermined first timer time elapses from the paper feeding detection time by the paper feeding detection sensor PH1, and the driving is stopped when a predetermined second timer time elapses. In the meantime, the fixing process of the sheet P is executed, so that the sheet ejection detection sensor PH2
It is also possible to adopt a configuration that does not use.

Further, it is also possible to adopt a configuration in which the drive is controlled by the leading / rear end detection signals of the sheet P by the sensor 29 and lever 25.

In the present embodiment, the linear heating layer 28 of the heating element 21 is instantaneously heated to a sufficiently high temperature relative to the melting point (or fixable temperature) of the toner by the pulsed current, and the non-fixed state when the current is not supplied. Heat transfer to the pressure roller 22 is small. Also, during fixing, the fixing film, toner image and sheet are heated.
Since a steep temperature gradient occurs between the pressure roller 22 and the pressure roller 22 due to the short heating time, the pressure roller 22
The temperature is high and the temperature is maintained below the melting point of the toner even if continuous image formation is performed to the extent necessary for practical use. In the apparatus of this embodiment having such a configuration, the toner image formed of the heat-fusible toner on the sheet P is first heated and melted by the heating body 21 via the fixing film 23, and particularly, the surface layer is completely melted. Softens and melts. At this time, the heating member, the fixing film, the toner image, and the sheet are in good contact with each other by the pressing roller 22, and the heat is efficiently transferred.
Thereby, the heating of the sheet P itself can be suppressed as much as possible, and the toner image can be efficiently heated and melted. In particular, the energy saving can be achieved by limiting the heating time.

A small heating element is sufficient, so the heat dose is small, and there is no need to raise the temperature of the heating element in advance.Therefore, power consumption during non-image formation can be reduced, and temperature rise in the machine can be prevented. become.

In the present embodiment, since the temperature of the pressure roller 22 is maintained lower than the melting point of the toner as described above, heat radiation of the toner image in the cooling step following the toner image heating step can be promoted. . Therefore, the time required for cooling can be reduced, and the size of the apparatus can be reduced.

(4) Power Supply to Heating Element 21 without Power Supply to Auxiliary Heating Layer 56 FIG. 4 is an explanatory diagram showing the mechanism of power supply to the heating layer 28 in the heating element 21 of the present embodiment. Reference numeral 60 denotes a control circuit including a microcomputer. Reference numeral 60 denotes a control circuit including a microcomputer, which controls the first power supply 61 in accordance with the temperature detected by the thermistor 55, and controls the power supplied to the heating layer 28 by changing the pulse width of the power supply to the heating layer 28. I do.

The reason for performing the above-described power control in the present embodiment will be described below. In this embodiment, a heat insulating layer 53 is provided to prevent heat radiation from the heat generating layer 28 to the support 54. The objectives are two points: to save energy by eliminating wasteful heat radiation and increasing energy efficiency; and to reduce the temperature rise in the apparatus due to heat radiation from the support member 54.

However, if the heat is simply insulated without controlling the power supplied to the heat generation layer 28, the heat generation amount significantly exceeds the heat release amount, and the heat generation layer 28 and the heating unit H abnormally increase in temperature. The fixing film may be damaged by heat.
Therefore, in the case where the heat insulating layer 53 is provided, control of power supply to the heat generating layer is effective in order to prevent abnormal heating of the heating section H.

Hereinafter, a power control method according to the present embodiment will be described. In the fixing method using pulse heating according to the present embodiment, as described above, the toner is heated only for a short time on the order of msec, so that the temperature of the heating unit H is dominant in the fixing performance rather than the heating time of the toner. The temperature of the toner layer rises according to the maximum temperature of H. Then, assuming that the temperature of the heating section H when the toner softens to a state sufficient for fixing is T _H0 , the heating layer 28 is maintained such that the maximum temperature of the heating section H is maintained at almost T _H0 during the fixing process. By controlling the power supply to the power supply, it is possible to obtain a sufficient fixing performance without consuming unnecessary power.

Suppose that the temperature of the heating unit H reaches the fixing temperature T _H0 when the temperature of the heating unit H is equal to the reference temperature T ₀ and power is supplied to the heating layer at a constant voltage V for a time t ₀ (see FIG. 5). According to the experiments of the inventors, between T _H0 , T ₀ , t ₀ , It became clear that there was a relationship. Where A, B
Is a constant determined by the power supply condition to the heat generating layer 28 and the heat radiation path from the heating section H.

Consider the case temperature of the heating unit H is T _B.

The pulsed power supply time required to _raise this to _TH0 is τ
_B Was obtained through experiments. Where constants A and B
Was almost equal to the value in the equation (1). When the equation (2) is transformed, Is obtained. Therefore, if T _H0 , A, and B are obtained in advance by experiments and T _B is measured, τ _B can be obtained.

In the present embodiment, as described above, when the heating layer 28 is pulsed with a sufficiently small duty ratio, the heating section H that generates heat in a pulsed manner shows the minimum temperature, that is, the next pulse Immediately before the start, the temperature of the heating unit H becomes substantially equal to the detected temperature of the thermistor 55. Therefore, using the temperature detected by the thermistor 55 at this time, the control circuit 60 shown in FIG. 4 calculates the next energizing time according to the equation (3).
The first power supply 61 supplies power to the heating layer 28 for the calculated time.

FIG. 6 is a diagram showing a graph showing the time change of the temperature of the heating section H during the fixing operation in this embodiment, together with a timing chart of power supply to the heat generating layer 28. In the present embodiment, the heating layer 28
Is constant, and the period τ of the energizing pulse is also constant. Temperature of the heating unit H is the temperature of the heating unit H and the began fixing operation at time t ₀ when T ₀ is uniquely determined from the temperature T _0. After the fixing temperature T _H0 is reached by energization with the pulse width τ _0, the temperature drops to T ₁ higher than T ₀ during a non-power supply time (τ−τ ₀ ) that is sufficiently longer than τ ₀ . Next, at time t ₁ which has undergone from time t ₀ only pulse period tau a second energization tau ₀
By applying a shorter pulse width τ ₁ that is uniquely determined from the temperature T ₁ to the heating layer, the temperature of the heating unit H is again set to T _H0
And then drop with the stop of power supply.

Similarly, after the energization is started, the temperature of the thermistor 55 is read every pulse period τ, and the power is supplied to the heat generating layer 28 with the pulse width determined by the equation (3) according to the detected temperature.
The maximum temperature of the heating section H can be maintained at the fixing temperature T _H0 .

FIG. 7 is a graph showing the temperature of the heating section H and the temperature detected by the thermistor 55 when the heating layer 28 is energized in a pulsed manner in the fixing device of this embodiment. The temperature of the heating section H is based on a measurement value measured in a non-contact manner by an infrared radiation thermometer, and the thermistor detection temperature is based on a value obtained by converting the output power of the thermistor into a temperature. When this graph is obtained, the pulse period is about 10 msec, and the energization time is about 2 msec. After the temperature of the heating section H rises rapidly when energized,
In the present embodiment, the power supply rapidly falls, and the non-energized time is sufficiently longer than the energized time, and the heat insulating layer 53 exists.
When the minimum value of the pulse waveform is obtained, the temperature becomes substantially equal to that of the heating layer 28, the insulating substrate 52, and the thermistor 55. The thermistor used in this embodiment cannot follow a pulse-like temperature change with a short cycle of 10 msec, and indicates a substantially minimum value of the pulse waveform. Therefore, the envelope of the minimum value of the surface temperature of the heating section H substantially matches the detected temperature curve of the thermistor 55.

FIG. 8 is a graph showing, as a comparative example (Comparative Example 1) of the present embodiment, a temporal change in the surface temperature of the heating unit H when the fixing process is performed with the energizing pulse width fixed at a constant value τ ₀ . FIG. 3 is a diagram shown together with a timing chart of power supply to the heat generating layer 28.
In this example, the temperature of the heating unit H is near the initial fixing temperature T _H0 , but the temperature of the heating unit H is fixed because the area around the heated image is warmed and the calorific value is constant despite the minimum temperature rising. As the operation proceeds, the fixing temperature greatly exceeds the fixing temperature _TH0 . Then, it consumes wasted power,
There is a problem that the temperature rise in the machine becomes large. In addition, when many fixing processing operations are performed in connection with each other, there is a possibility that the temperature of the heat generating layer 28 is further significantly increased, and eventually the heat generating layer 28 is damaged. Further, the fixing film 23 pressed against the heating unit H may be thermally deformed.

Operation / Effects of Auxiliary Heating Layer 56 FIG. 9 shows the on / off state of power supply to the heating layer 28 and the auxiliary heating layer 56 when an image forming operation is performed in the image forming apparatus of this embodiment.
FIG. 9 is a diagram also showing a time chart of the sum of the power consumptions of the power supply 61 and the second power supply 62.

As described above, the first power supply 61 is a pulse power supply having a constant DC voltage V, a constant cycle τ, and a variable pulse width. The second power supply 62
AC power. The power consumption of the first power supply 61 was an average power per cycle τ. The reason is as follows. That is, in the case of this type of pulse power supply including this embodiment, a pulse-like voltage output is obtained by charging and discharging the capacitor, but the power required for one discharge and the capacity of the capacitor required for practical use are proportional. The capacity and volume of the capacitor are approximately proportional, and the larger the capacity of the capacitor, the larger the pulse power supply 62 becomes.
Therefore, if the average power per period τ is large, the power supply 62 becomes large almost in proportion thereto.

It is assumed that an image forming operation is started at time t _0. The leading end of the transfer material sheet P to which the toner image has been transferred is time t ₁ by the sheet detection arm 25 and the sensor 29 arranged upstream of the fixing device.
As soon as the power is detected, the control circuit 60 starts power supply from the second power supply 62 to the auxiliary heat generating layer 56. The control circuit 60 turns on / off the output of the second power supply 62 so that the detection temperature of the thermistor 55 is substantially maintained at a temperature T ₀ sufficiently lower than the softening temperature T _{M of the} toner.
Control. Since the thermistor 55 is disposed is near the heating unit H, the temperature of the heating unit H is maintained substantially T _0. From time t ₁ to a predetermined time only the time t ₂ on stopping the output of the second power source 62, to start the pulsed power output of the power supply 61. The control circuit 60 uses the detected temperature of the thermistor 55 to _{operate the} power supply 61 in the above-described manner so that the maximum temperature of the heating unit H is substantially maintained at a temperature T _H0 that is much higher than the softening temperature T _{M of the} toner. Controls the output pulse width. Sheet detection arm 25
And if detecting the trailing edge of the transfer sheet P by the sensor 29, the trailing edge of the sheet P can be calculated the time t ₃ when leaving the heating unit H Taken together with the detection time of the tip. Therefore it stops power output of the power supply 61 at the time t _3, the image forming operation is completed.

In between the time t ₂ when the fixing process is performed until time t _3, the output pulse width of the first power source 61 as described above the time t ₂
And decreases as the fixing process proceeds. Power W defined above therefore takes the maximum value W _MAX at time t _2.

FIG. 9 shows a second comparative example (Comparative Example 2) of this embodiment.
The dotted line shows the time change of the power W 'when the power supply 62 is always turned off. W 'is similarly and W, the maximum value W at time t _2' indicating the _MAX.

'A comparison of the _MAX, W _MAX is W' W _MAX and the W much smaller than _MAX. The reason is that, in the present embodiment, since the heating unit H is previously maintained at the temperature T ₀ sufficiently higher than the room temperature, the first pulse power supply width of the first power supply 61 can be much smaller than that of the comparative example. .

FIG. 10 shows a temporal change in the temperature of the heating unit H when the power control described with reference to FIG. 9 is performed for the image forming apparatus of this embodiment. Temperature of the heating unit H for t ₃ from time t ₀ is maintained below the softening temperature T _M of the toner. When the inventors have conducted practical need a continuous image formation to the extent that is in the image forming apparatus of the present embodiment, the temperature of the heating unit H during non fixing was always T _M or less. Therefore, a pressure roller that contacts the heating unit H via the fixing film 23 during non-fixing
The temperature of 22 is always below T _M. During the fixing process, the fixing film 23, the toner image T, and the transfer material sheet P are interposed between the heat generating portion H and the pressure roller 22, and the heat generation time is short. Due to a sharp temperature gradient, the temperature of the pressure roller 22 hardly rises. Therefore, even when normal continuous image formation is performed, the temperature of the pressure roller is maintained at the toner softening temperature T _M or lower.

In the apparatus of this embodiment having such a configuration, the image formed of the heat-fusible toner on the transfer paper P is first fixed to the fixing film.
It is heated and melted by the heating unit H through 23, and its surface layer, in particular, greatly exceeds the melting point and is completely softened and melted. At this time, the heating element, the fixing film, the toner image, and the transfer material are satisfactorily adhered to each other by the pressure roller 22, and the heat is efficiently transferred.

Thereafter, the heating of the heating element 21 is stopped, and the transfer material is conveyed and separated from the heating element, so that the toner image is radiated and cooled and solidified again.
After passing through 33, the fixing film 23 separates from the transfer paper P. At this time, in this embodiment, since the temperature of the pressure roller 22 is maintained lower than the softening temperature T _{M of the} toner as described above, heat radiation of the toner image can be promoted. Therefore, the time required for cooling can be reduced, and the size of the apparatus can be reduced.

Also, pre-heating time of the heating unit H from time t ₁ performed in this embodiment toward t _2, since it is sufficient only during image formation can reduce power consumption during non-image formation in the image forming apparatus, also machine Temperature rise can also be prevented. Further, since the above-mentioned preheating may be started after the start of image formation, a standby time for the preheating is not required.

(5) Example of execution Next, the results of execution by the apparatus of this embodiment are shown by specific numerical values. A toner image T is formed on a transfer paper having a thickness of 100 μm using a toner which is softened and fixed at about 125 ° C. at a room temperature of 20 ° C. The pulse energizing period is 10 msec, and the maximum temperature of the fixing portion H is reduced.
When a fixing test was performed at a fixing processing speed of 50 mm / sec while controlling the pulse width using the detection temperature of the thermistor 55 so as to reach 300 ° C., an image having no practical problem was obtained. Here, the transfer paper feeds the sheet detection arm 25 and the detection sensor 29 on the conveyance path 150 mm upstream of the heating unit H, and when the leading end of the transfer paper reaches this position, that is, 3 sec before the start of the fixing process of the transfer material. Preheating was started, and the temperature of H at the time of preheating was controlled to be 80 ° C.

FIG. 11 shows the time of the temperature of the toner and the transfer paper, more specifically, the temperature of the central portion in the cross-sectional direction when the fixing process is performed while conveying the transfer paper having the toner layer on the surface using the fixing device 20 of this embodiment. It is the graph which calculated | required the change by calculation. The conditions are as follows.

Heating conditions: 2 ms heated at an energy density 25W / mm ^2.

Fixing temperature of toner: 125 ° C.

Film: PET (6 μm thickness).

Thickness of toner: 20 μm.

Transfer paper thickness: 100 μm. Room temperature: 20 ° C.

In this embodiment, the temperature of the heating unit H rises to about 300 ° C., which is much higher than the fixing temperature of the toner of 125 ° C., so that the toner is sufficiently heated to exceed the fixing temperature, and good fixability is obtained.

On the other hand, the temperature rise of the transfer paper is extremely small, and the waste of energy is small as compared with the conventional heat roller fixing.

Furthermore, in this embodiment, even when the heating time varies the heating energy density and excessive energy is applied, no high-temperature offset occurs and the allowable range of heating control is wide.

<Embodiment 2> The heating body 21 in which the auxiliary heat generation layer 56 and the second power supply 62 are removed from the configuration of the heating body 21 in FIGS.

FIG. 12 and FIG. 13 are output timings and power consumption diagrams of the first power supply 61 at the time of image formation when the heating element 21 is used, respectively.
FIG. 4 is a diagram illustrating a temperature change of a heating unit H. Symbols and the like correspond to FIGS. 9 and 10 of the first embodiment.

t _{1 to} t ₂ : The pulse width is controlled at a constant period τ and a constant voltage V so that the minimum temperature of the heating unit H, that is, the detected temperature of the thermistor 55 becomes T _{0 at} time t ₂ .

t _{2 to} t ₃ : so that the maximum temperature of the heating section H is maintained at _TH0
Control the pulse width. Pulse width, voltage is the same as t ₁ ~t _2.

As shown in FIG. 12, the time t ₁ the power <time t ₂ power.

This configuration also achieves the intended purpose and simplifies the configuration.

<Embodiment-3> Instead of controlling the pulse width in Embodiments 1 and 2, the pulse period and the pulse width may be fixed, and the voltage may be controlled to control the temperature. In short, the temperature may be controlled by controlling the amount of energy per pulse.

As described above, when the heating unit H is heated from the temperature T _B to T _H0 by the pulse power supply of the voltage V ₀ and the time τ ₀ , There is a relationship. Here, assuming that the electrode voltage is generally V, according to the experiments performed by the inventors, the following relationship was obtained: A = kV ² ‥‥ (4). B and K are constants determined by the configuration of the heating element regardless of the voltage.

Then, _assuming that the power supply voltage required to raise the heating unit H from the temperature T _B to the temperature T _H0 by the pulse conduction at the time τ ₀ is V _B. Therefore, if k and B are determined in advance by experiments,
When τ ₀ and T _H0 are set to predetermined values, if T _B is measured, the heating section H can be heated to just T _H0 by applying the voltage V _B obtained by equation (5). .

According to this embodiment, unlike the previous embodiment, the ON / OFF timing of the power supply to the heating element is constant, so that the processing by the microcomputer is easy.

In the first and second embodiments described above, the thermistor 55 is formed integrally with the heating element 21. However, the thermistor 55 is located outside the heating element 21 and close to the heating section H at a position where the transfer of the transfer material is not affected. And may be arranged. For example, a relief portion can be formed in a part of the protective layer, and the thermistor 55 can be disposed there.
In short, it may be arranged at a position where the minimum temperature of the heating unit H can be detected.

Further, the control of the energization pulse width may be performed at an arbitrary time interval longer than the period τ, instead of being performed for each period τ. In this case, the temperature of the heating unit H cannot be accurately maintained at T _H0 , but as described above, even if the maximum temperature slightly changes, no inconvenience occurs in the fixing performance. In short, the heating section H
It is sufficient to keep the temperature in a certain temperature range, including _TH0, at which good fixing performance can be obtained in practical use. From this condition, the upper limit τ _MAX of the control time interval is determined,
The control interval may be selected between τ and τ _MAX .

<Others> The fixing film 23 is sent out from the output shaft 24 to the take-up shaft 27 as shown in the apparatus of the embodiment, and is sequentially taken up and run each time the fixing process is performed. In addition to the take-up replacement type that replaces with 23, since toner offset to the fixing film 23 surface does not substantially occur,
If the thermal deformation or deterioration of the film is small, the used fixing film 23 wound on the winding shaft 27 is sent out in a timely manner and is controlled to be rewound to the shaft 24, or the winding side and the sending side are controlled. It can also be used multiple times, such as by reversing it (rewinding and repetitive use).

Further, it is also possible to adopt a configuration in which an endless belt type is used to be rotated and run to be used for fixing processing.

In the take-up exchange type, the fixing film 23 can be, for example, a thin and inexpensive polyester that has been subjected to heat treatment using a base material, and can be made thinner regardless of durability, and power consumption can be reduced. it can. When this method is adopted, the fixing film remaining amount detecting arm 30 and the sensor 30a detect the remaining amount of the fixing film on the side of the shaft 24, and display a warning or a warning sound to the user when the film is near the end. It is preferable to prompt the user to change the fixing film. When exchanging the fixing film 23, the heating zone
It is desired that the fixing device 20 can be opened and closed about the rotation shaft 31 as shown in FIG. 14 so as to separate the pressure roller 21, the pressure roller 22, and the separation roller pair 26 and 33 from each other.

In the rewinding repeated use type, as a fixing film, for example, a 25 μm thick polyimide resin film is used as a base material having excellent heat resistance, mechanical strength, etc. The provided composite layer film can be used, and it is preferable that the contact pressure between the heating element 21 and the pressure roller 22 is released during reverse rewinding.

When using multiple times such as the rewinding repetition type or the endless belt type, provide a felt pad for cleaning the film surface and impregnate a slight release agent, for example, silicone oil, to abut the pad on the film surface. For example, the film surface may be cleaned and the releasability may be further improved. When the fixing film is made of an insulating fluororesin-treated product, static electricity that disturbs the toner image is likely to be generated on the film. Therefore, in order to cope with the problem, it is preferable to remove the static electricity with a grounded neutralizing brush. A bias voltage may be applied to the brush without grounding to charge the film within a range that does not disturb the toner image. Further, it is also a measure to add conductive powder fibers, for example, carbon black or the like, to the fluororesin to prevent the above-mentioned image disturbance due to static electricity. In addition, the charge roller can be de-charged and made conductive by the same means. Also,
An antistatic agent or the like may be applied or added.

In either case, the fixing film 23 can be easily attached to and detached from a predetermined portion of the fixing device 20 in the form of a cartridge, thereby facilitating the operation of exchanging the fixing film.

If the clay at the time of heating and melting the toner is sufficiently high, the toner temperature at the time of peeling the toner from the fixing film may be equal to or higher than the melting point of the toner. In this case, in the apparatus shown in FIG. 1, the fixing film and the toner image are separated when the transfer paper P passes through the pressure contact portion between the heating body 21 and the pressure roller 22, except for the separation rollers 26 and 33. Such a configuration may be adopted. At this time, it is not necessary that the temperature of the pressure roller 22 be kept below the melting point of the toner. FIG. 16 shows an example in which the fixing film is an endless belt.

The above-described apparatus is a transfer-type electronic copying apparatus.
The image forming process and means are electrofax paper,
An image is formed on a recording material with a heat-fusible toner by a direct type in which a toner image is formed and held directly on an electrostatic recording paper or the like, a magnetic recording image forming type, or any other appropriate image forming process or means, and heated. The present invention can be effectively applied as an image heating fixing device in various image forming apparatuses such as a copying machine of a fixing system, a laser beam printer, a facsimile, a micro film reader printer, a display device, and a recorder.

(Effect of the Invention) As described above, the present invention makes it possible to reduce the heat capacity of the heating element serving as the heating unit without causing a fixing defect or an offset in the toner image heat fixing type image forming apparatus. In addition, an image forming apparatus with a small standby time, low power consumption, and low internal temperature rise can be realized. Further, the fixing film can be repeatedly used for a long period of time without any problem without generation of wrinkles without any problem.

Further, the energization control means starts energization immediately before the fixing process, and temporarily raises the temperature of the heating body to a temperature lower than the melting point of the toner,
Immediately after that, by controlling the energization so that the heating element instantaneously raises the temperature to above the melting point of the toner, a large current does not flow when the temperature of the heating element rises above the melting point of the toner. The maximum power consumption of the fixing device can be reduced, the size of the power supply can be reduced, and the size of the entire device can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a fixing device according to one embodiment, FIG. 2 is a schematic enlarged cross-sectional view showing a configuration of a heating element, FIG. 3 is a schematic configuration diagram of an image forming apparatus incorporating the fixing device, FIG. 4 is a block diagram of a current-carrying system, FIG. 5 is a diagram showing a change over time in the heating section when one pulse is supplied to the electrode, FIG. 6 is a view showing a change over time in the heating section when the pulse width is changed, FIG. 7 is a time-dependent change diagram of the surface temperature of the heating unit and the detected temperature of the temperature detecting element, FIG. 8 is a time-dependent change diagram of the heating unit in the comparative example, FIG. Fig. 11 is a graph showing the change over time in the temperature of the heating unit when power is controlled. Fig. 11 is a graph showing the change in temperature of each unit in the heating process under certain conditions. FIG. 13, FIG. 13 is a diagram showing a change with time of the heating unit temperature, FIG. 14 is a diagram showing a state in which the fixing device is opened, and FIG.
FIG. 15 is a schematic diagram of a fixing device in which a fixing film and a recording material are separated immediately after a heating process, and FIG. 16 is a schematic diagram of a fixing device in which a fixing film is an endless belt type. Reference numeral 3 denotes a photosensitive drum, 8 denotes a transfer discharger, P denotes a transfer material sheet (recording material), 20 denotes an overall reference number of a fixing device, 21 denotes a heating element, 22
Is a pressure roller, 23 is a fixing film, 23 is a take-up shaft (or drive roller), and 24 is a delivery shaft (or driven roller).

Claims (1)

(57) [Claims] 1. A heating element, a fixing film sliding with the heating element and moving together with a recording material carrying an unfixed toner image,
An image having a pressure member that forms a nip with a heating element via a fixing film, and an energization control unit that controls energization of the heating element so that the temperature of the heating element is maintained at or above the melting point of the toner during fixing. In the heat fixing device, the energization control unit starts energization immediately before the fixing process, temporarily raises the temperature of the heating body to a temperature lower than the melting point of the toner, and immediately thereafter, the heating element instantaneously reaches the melting point of the toner or more. An image heating and fixing device, wherein the power supply is controlled so as to increase the temperature.