KR930002251B1 - Image fixing apparatus - Google Patents

Abstract

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Description

Image fixing device

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

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

3 is a cross-sectional view of an image forming apparatus combined with an image fixing apparatus according to an embodiment of the present invention.

4 and 5 are cross-sectional views of an image fixing apparatus according to the prior art.

* Explanation of symbols for the main parts of the drawings

11: image fixing device 20: heating assembly

21: heater 21a: bottom plate

21b: heating element 22: support member

25: fixing film 29: press roller

P: Recording material N: Fixing nip

The present invention relates to an image fixing apparatus that can be used with an image forming apparatus such as a copying machine, a laser beam printer, a microfilm reader / printer, a facsimile recorder, or an image display, which corresponds to object image information and directly or indirectly. Passionate unfixed toner images contained in recording materials such as print sheets, transfer material sheets, electrostatic lock sheets, and print sheets are passionately attached as permanent settling images.

Background Art [0002] A conventionally used image fixing apparatus in which a toner image is fixed on a recording medium supporting an unfixed toner image, includes a heating roller in which the recording material is maintained at a predetermined temperature, and a pressurization or backup roller in which the toner image is pressurized in contact with the heating roller. It passes through the nip formed in between. However, the heating roller fixing system has a problem that the heating time required to reach a predetermined temperature on the surface of the heating roller is long. In order to solve this problem, US application No. 206,767 proposes a new image fixing apparatus, wherein a toner image is melted using a small heat capacity heater and an image fixing film relatively slippery to the heater. This fixing device is composed of a heat generating resistor placed on a low heat capacity base plate.

4 shows an example of such an image fixing apparatus using a fixed heater with a low heat capacity and a thin film.

This device is composed of a fixing film 25 in the form of an endless belt that performs the same function as the film described above.

The film 25 extends around the drive roller 26, the driven roller 27, the heating assembly 20 lying below between these rollers, and the guide roller 28 lying underneath the drive roller 26. The driven roller 27 functions as a tension roller for the fixing film 25. The apparatus further includes a pressurizing roller that pressurizes the fixing film 25 effectively to the heating assembly at its bottom.

The heating assembly 20 includes a low heat capacity linear heater 21 as a main part and a support member 22 for supporting the heater insulated. The heat generating resistor material 21b is mounted on the base plate 21a and generates heat in accordance with the supply of power.

The heat generating resistor material 21b immediately rises in temperature upon power supply, and the fixing film 25 is thin and thus has a low heat capacity, so that the fixing operation becomes possible as soon as the power supply is started.

The fixing film 25 is not limited to the endless belt, but may be in the form of a roll film as shown in FIG. 5, wherein the film is wound around the supply shaft 30, and the free end thereof is disposed between the heating assembly and the pressure roller 29. It is fixed to the winding shaft 31 by the nip so that the fixing film 25 is moved from the supply shaft 30 toward the winding shaft 31 at the same speed as the conveying speed of the recording material P.

In the examples of FIGS. 4 and 5, the sliding surface of the fixing film is aligned so that the surface of the heater 21 is aligned with the surface of the supporting member 22 so that the entire sliding surface is smoothed so that the fixing film 25 can slide the sliding surface. It is supposed to be.

However, due to the required processing and assembly precision, it is difficult to make the surface of the heater 21 and the surface of the support member 22 completely match.

If only a small portion of the edge of the heater protrudes beyond the surface, the film may be scratched or torn, thereby reducing the life of the fixing film.

If the base plate 21a is made of a ceramic material such as alumina, it is straightforward to smoothly round the edge portion of the ceramic base plate 21a.

The edge of the heater is particularly important.

Similar problems exist for the edge portion of the support member 22.

If the film is partially folded or partially protruded by the edge portion during the passage, an unfixed toner image on the recording material introduced into the fixing apparatus may be scratched and a damaged image may be obtained. Scratched toner can contaminate the film or recording material and the pressure roller.

Therefore, the present invention has a main object to provide an image fixing device that the fixing film can slide smoothly on the heater.

It is another object of the present invention to provide an image fixing apparatus in which a heater can be used without rounding its edge portion. Still another object of the present invention is to provide an image fixing apparatus in which a fixing film can move without sliding contact with an edge portion.

These and other objects, features and advantages of the present invention will become apparent from the following preferred embodiments of the present invention which will be described in conjunction with the accompanying drawings.

Preferred embodiments of the present invention will be described with reference to the drawings, in which like reference numerals will be given to members with corresponding functions.

3 is a cross-sectional view of an image forming apparatus incorporating an image fixing apparatus according to Embodiment 1 of the present invention.

The illustrated image forming apparatus is an electrophotographic copying apparatus in which an original support platen is reciprocable, a rotatable drum is used, and an image is transferred therefrom.

The apparatus consists of a reciprocating original support platen (1) made of a transparent member such as a glass plate placed on the housing (100) and the top plate (100a) of the housing 100, wherein the original support platen (1) It can be reciprocated from side to side on the top plate (100a) at the speed of.

The original G is placed on the original support platen 1 with its surface facing down according to a predetermined position indication and covered with the original cover 1a.

A slit opening 100b is formed on the top plate 100a extending in a direction perpendicular to the reciprocating direction of the original support platen (perpendicular to the drawing sheet). The slits form part of the original research system.

The screen of the original picture, with the screen facing down on the original support platen 1, passes through the slit opening 100b while moving to the right side (a) of the original support platen 1. While passing, the light rays of the lamp 7 are irradiated to the original 1 through the slit opening 100b and the transparent original supporting platen 1.

The rays reflected by the originalization form an image on the surface of the photosensitive drum 3 through the array 2 of image elements having a short focal length and a small diameter. The photosensitive drum 3 is covered with a photosensitive layer such as a zinc oxide photosensitive layer or an organic photoelectric body photosensitive layer. It rotates around the central axis 3a at a predetermined main speed in the clockwise direction b.

During rotation, the photosensitive drum 3 is uniformly charged to the cathode or the anode by the charger 4, and the uniformly charged surface is exposed to the image light of the original through the slit opening so that the electrostatic latent image corresponding to the ray image It is formed continuously on the surface of this photosensitive drum 3.

The electrostatic latent image is visualized as a toner image by a thermal softening or a hot melt resin by the developing apparatus 5, and the visible toner image is conveyed to an image delivery station having a transfer discharger 8.

The transfer material sheet P is placed in the cassette 5.

The sheet is discharged one by one from the cassette by the rotation of the pickup roller 6 so that when the head of the toner image forming portion on the drum 3 reaches the delivery discharger 8, the leading edge of the delivery sheet P is transferred to the delivery discharger ( 8) and the photosensitive drum 3 is conveyed to the photosensitive drum 3 in a timely relationship such that the position between the photosensitive drum 3 is reached. The toner image is sequentially transferred onto the sheet conveyed from the photosensitive drum 3 by the transfer discharger 8.

The sheet containing the toner image is sequentially separated from the surface of the light sensing drum 3 by a separating member (not shown) and guided to the image fixing apparatus 11 by the conveying device 10, where the fixing toner image is heated. Settles down.

Thereafter it is discharged by the guide 35 and the release roller 36 onto the discharge tray outside of the device as a final print (copy).

On the other hand, the surface of the photosensitive drum 3 used in the toner image transfer operation is cleaned by the cleaning device 13 to remove excess toner or other contaminants to prepare for the next image forming operation.

The fixing device 11 according to the present embodiment will be described with reference to FIG.

Except for the heater 20, its basic structure is similar to that of FIG.

In this operation, when an image forming start signal is generated in the image forming apparatus, an image forming operation is started in which an unfixed visible image (powder toner image in this embodiment) is formed on the recording material.

The recording material is conveyed to the image fixing device 11 with the screen side facing upwards and guided into the fixing device along the guide.

The leading edge portion of the recording material P is detected by a recording material detection sensor (not shown) located in the recording material passage adjacent to the fixing device 11 just before it enters the fixing device 11.

In response to the detection signal, the endless belt-like fixing film 25 starts to rotate clockwise.

The rotational speed for driving the fixing film is substantially the same as the conveying speed of the recording material P to the fixing device 11. The fixing film 25 rotates without folding or snaking. In addition, power supply control for the heat generating member 21b of the heater of the heater assembly 20 is started.

The bottom surface of the fixing film 25 is fine while the recording material P enters the nip formed between the fixing film 25 and the pressure roller 29 and is transported together with the fixing film 25 through the nip N. It is brought into contact with the toner image under pressure.

While the recording material P is passed through the fixing nip N, the toner image supporting side of the recording material is thinned by the thermal energy provided by the heater 21 of the heater assembly 20 so that the fixing film 25 is thin. The toner image Ta is melted and thereby becomes a toner image Tb that is melted and fixed to the surface of the recording material P. When separated, the temperature of the molten toner Tb is lower than when it is at the position of the heat generating member 21b, but is higher than the glass transition point of the toner, so that the toner Tb has sufficient rubbery property and thus recording at the separation point. The toner image support side of the material P does not follow the surface of the fixing film and has a suitable surface roughness.

The toner image Tb is further cooled to become a solid image Tc in which proper surface roughness is maintained. Therefore, the fixing toner image is not glossy and therefore the image quality is excellent.

Low temperature offset does not occur because the toner is sufficiently heated and melted by the heater.

In addition, the recording material is separated from the fixing film after the temperature of the toner is sufficiently lowered, whereby no hot offset occurs.

The recording material P separated from the fixing film 25 is guided to the emission roller 36 along the guide 35, during which the temperature of the toner Tb higher than the glass transition point is automatically lowered than the glass transition point. This hardens | cures by solidification (Tc). The recording material P having recorded image information is discharged onto the discharge tray 12.

Power control of the heating element 21b of the heater 21 is stopped after a predetermined time has elapsed, and this time is set after the sensor detects the trailing edge of the recording material P. Depends on how long it takes to pass. At this time, the rotation of the fixing film 25 is stopped. The fixing device 11 is in the standby state until the head portion of the next recording material is detected by the sensor.

In this embodiment, gloss of the image is prevented by separating the recording material from the film while the temperature of the toner is higher than the glass transition point.

However, it is possible to keep the recording material P from being moved in close contact with the recording material P until after the recording material P passes through the fixing nip N, and the toner Tb softened or melted in the meantime. Heat is radiated to cool the toner with the solidified toner Tc, which is subsequently separated from the surface of the fixing film 25. In this case, the coagulation force of the toner solidified by the cooling step is sufficiently large that the toner behaves as agglomerates, thereby increasing the adhesion to the recording material, while the adhesion to the fixing film is considerably reduced.

When the toner is heated and softened or melted, it is pressed by the pressing member so that at least a part of the toner constituting the image penetrates into the surface layer of the recording material, and the mounting effect by cooling and solidifying the penetrated portion is effectively applied to the recording material of the toner. Increases the adhesion of

As a result, the portion of the recording material on which the image is fixed is easily separated from the fixing film without generating toner offset in the fixing film sequentially.

In this case the image will have a gloss and can be used if gloss is desired. As can be appreciated, the temperature of the heater 21 is simultaneously increased to a temperature which can be settled immediately (quick start) as soon as power is supplied to the heating element 26, thereby making the preheating of the heater unnecessary.

In addition, the heat transfer to the pressure roller 29 during this image fixing operation is small. During the fixing operation, the fixing film, the toner image, and the recording material are in the fixing nip N between the heater 21 and the pressure roller 29, and in addition, the heat generation time is short due to the high temperature gradient, and thus the pressure roller 29 ) Does not easily rise in temperature. The temperature of the press roller is kept lower than the melting point of the toner even when the image forming operation is continuously performed by a practical method.

In the apparatus having such a structure, the toner image made of the hot melt toner on the recording material P is first heated and melted by the heat generating member through the fixing film 25, in particular the surface portion thereof is completely softened and melted.

At this time, the pressure roller 29 forms a close contact between the heater, the fixing film, the toner image, and the recording material so that heat transfer becomes effective. Therefore, the toner image is effectively heated and melted while minimizing the heating of the recording material P. FIG.

In particular, by limiting the power supply can save heat cycle and energy consumption. The size of the heater can be small and so its heat capacity is small. For this reason, it is not necessary to preheat the heater in advance, and the power consumption during non-imaging is minimized, and in addition, the temperature rise in the apparatus can be prevented.

Now, the fixing film used in the present embodiment will be described. The fixing film 25 is composed of a thin film having good heat resistance and good separation property to the visualizing agent (toner).

It is highly durable against repeated use when it is shaped as an endless belt that is used repeatedly.

For the purpose of reducing the heat capacity to be a quirkstart device, the thickness should preferably not be greater than 100 microns and more preferably less than 40 microns.

It is a single layer film of a heat resistant resin such as PI (polyimide), PET (polyetherimide), PES, copolymer of tetrafluoroethylene-perfluor-alkylvinylether (PFA), or is coated with a 10 micron separation layer that can contact at least one side of the recording material. It may be a multi-layer film comprising a 20 micron thick base film, which is a tetrafluoroethylene resin, PFA or another fluorinated resin added with an electrically conductive material.

The press roller 29 has a rubber elastic layer made of silicone rubber having good separation characteristics. The pressure roller 29 is pressurized to the bottom surface of the heater assembly 20 under a total pressure of 4 to 7 kg through a fixing film 25 interposed by a pressure means not shown. The pressure roller 29 is rotated as the fixing film 25 moves, or is driven at a main speed that generally corresponds to the moving speed of the film 25.

The fixing nip N is formed by pressing the pressure roller 29 toward the bottom surface of the heater assembly 20. The width of the heater 21 is within the width range of the fixing nip N.

The heater assembly 20 will be described in more detail.

The heater assembly 20 is composed of a low heat capacity linear heater 21 and a support member 22 for fixedly supporting the heater 21. The heater 21 includes a low heat capacity and a high heat resistance, and a high thermal conductivity base plate 21a. More specifically, the heater 21 includes a stretched alumina base plate having a thickness of 1 mm, a width of 10 mm, and a length of 240 mm and having a heating element 21 b on one side. More specifically, for example, it includes a heat-resisting element such as silver palladium of 1mm in width which is generally processed by screen printing along the length of the base plate at the center of the base plate width.

A temperature detecting element is provided on the side of the base plate 21a opposite to the side having the heat generating resistor. The power supply to the heat generating resistive material is controlled so that the temperature detecting element detects a constant temperature.

The support member 22 which fixedly supports the heater 21 is a molded heat resistant resin having sufficient rigidity, high thermal resistance and low thermal conductivity.

Usable materials include polyethylene terephtralate (PET), bakelite,

Polyphenylenesulfide (PPS), polyimide amide (PAI), PI, polyether (PEEK)

ether ketone) resins.

Grooves 22a are formed in the bottom surface of the fixing film which is in contact with the side surface of the support member 22.

The heater 21 generally extends along the length of the support member 22 at the center of the width (as measured in the fixing film moving direction).

The groove 22a has a depth greater than the thickness of the heater 21.

The heater 21 is installed to be fixed to the support member 22 by a double-sided adhesive tape or adhesive in the groove 22a in the direction in which the heat generating element 21b is directed outward.

The overall strength and rigidity of the heater assembly 20 is ensured by the support member 22.

The heater assembly 20 includes the outer surface of the heater 21 at the mounting portion of the cast assembly provided at the predetermined position so that the bottom surface of the support member faces outwardly. Is mounted on.

While the fixing film 25 of the endless belt type rotates, its inner surface slides on the bottom surface of the support member 22 including the outer surface of the heater 21 of the heater assembly 20. The heating element 21b of the heater 21 generates heat when power is supplied through an electrode connected to the opposite end in the longitudinal direction thereof.

The heater 21 is recessed in the groove 22a so that the portions 22b and 22c of the support member 22 which surround the heater 21 in the fixing film moving direction come out of the outer surface of the heater 21. It is done. In other words, the step d is formed at the connection portion with the outer surface of the heater. The height of the step d is preferably 0.1 to 2 mm.

The parts 22b, 22c of the support member comprise parts (1), (2), (3), (4), (5) and (6) and the corners of the part, as in FIG. 1, have a radius R = It is rounded to 0.2 to 5 mm to form curved portions 1, 3, 4, and 6.

The surface roughness of the surface portions 2, 5 and the curved portions 1, 3, 4, 6 is not greater than 3.2 S, so the surface is smooth.

In this way, projections are provided over the outer surface of the heater toward the recording material, guiding the film toward the recording material upstream and downstream of the heater with respect to the direction of movement thereof, so that the film does not slide to the edge of the heater.

Therefore, the heater can be used without rounding its edges. This makes it possible to use a low workability material such as a ceramic material in the heater.

The protrusion is made by molding a resin supporting member having excellent workability and productivity. Because of this, the machining and assembly steps are simple since no machining steps need to be added.

In the manner as described above, damage or abrasion of the inner surface of the film is prevented, which greatly increases the life of the film. In addition, scratches on unfixed toner images or burns on the recording material, which are likely to occur in the image fixing operation due to the edges of the heater or the supporting member, are prevented, and the possibility of contamination of the film, the pressing member and the recording material due to the toner scratches is eliminated. do.

Moreover, the stability of film movement is increased, and the recognition and reliability of the fixing operation are improved.

Referring to FIG. 2, another embodiment of the present invention is shown.

In this embodiment, smoothly rotatable rollers 22d and 22e for guiding the fixing film are provided on the support member at the up and down portions of the heater 21 with respect to the movement of the film.

These rollers protrude outward beyond the outer surface of the heater 21 and form a step d with the outer surface of the heater. The height of the step is 0.1 to 2 mm.

According to this embodiment, since the number of parts of the apparatus is increased because of providing the separate guide rollers 22d and 22e, the required driving force for sliding the film is reduced due to the rotating roller, so that the required driving force for the film can be reduced.

In this embodiment, the stepless fixing film has been described, but it is also applicable to the case where the stepless film as shown in FIG.

If the fixing film 25 is not unauthorized, a replaceable roll film may be employed, in which all fixing films 25 may be wound from the supply rail 30 onto the winding rail 31 and a roll of new film is mounted. (Cold and exchange type).

In this type, the thickness of the fixing film can be significantly reduced irrespective of the durability of the fixing film, so that power consumption can be reduced.

For example, this type of fixing film can be made from materials such as heat-resistant polyester (PET) films that are less expensive and less than 12.5 microns thick. As another alternative, the used fixing film wound on the winding shaft can be rewound on the feeding shaft, or the winding shaft and the feeding shaft are replaced with each other so that the fixing film can be used repeatedly unless the fixing film is significantly deteriorated due to heat deformation or heat. (Rewind and repeat type).

In this type, the fixing film is preferably composed of a multilayer film coated with a separation layer made of a fluorinated resin or the like, wherein the swamp is a 25 micron-thick polyimide resin film having heat resistance and mechanical strength. do.

The pressure contact release mechanism is provided to automatically release the pressure contact between the heater and the pressure roller during the rewinding operation.

When the fixing film is repeatedly used in the rewind and repeat use type and the endless belt type, felt pede is provided to clean the surface of the film, and oil can be leached onto the pad to apply a silicone oil or other separating agent to the slider mount. The surface of the film can be derived to be clean and have good separability. When the fixing film is treated with an insulating fluorinated resin, an electric charge is easily generated in the film and the electric charge disturbs the toner image.

In this case, the fixing film is rubbed with an electrically grounded discharge brush to discharge the film. In contrast, the film can be electrically charged by applying a bias voltage to such a brush without grounding so long as the toner image is not disturbed.

By applying carbon black or the like to the fixing film, it is possible to cope with image disturbance due to electric charging. The same means can be applied to the electric charging of the pressure roller.

As another alternative, an anti-electrification agent may be used or added. In any of the above endless belt type, winding and replacing type, rewinding and repeating use type, the fixing film may be in the form of a cartridge that is detachably mounted at a predetermined position of the mounting apparatus 11 in order to expedite the replacement operation. .

The heater 21 or the heating element 21b may be in the form of a ceramic chip array having PTC characteristics. The power source may be an on-off power source of direct current or alternating voltage as well as in the form of a pulsed power supply.

Although the present invention has been described with reference to the embodiments disclosed herein, it is intended to be illustrative, and the present invention extends from the invention disclosed in the claims to all equivalent inventions that can be easily modified or changed.

Claims (13)

A heater having a heat generating resistor that generates heat in accordance with a power supply and a base plate for supporting a heat generating resistor, and a film which can be slid from the heater, wherein a recording material supporting a visualized image is heated by the heater through the film. ; And a projection protruding toward the recording material to guide the film so that the film moves without contacting the edge of the base plate. An image fixing apparatus according to claim 1, wherein said base plate is made of a ceramic material. The image fixing apparatus according to claim 1, wherein the bottom plate has high thermal conductivity and a temperature detecting element for controlling power to the heat generating resistor is provided on an opposite side of the side supporting the heat generating resistor. The image fixing apparatus according to claim 1, wherein the apparatus further comprises a supporting member for supporting the heater, wherein the supporting member is provided with the protrusion. An image fixing apparatus according to claim 4, wherein said support member is a heat insulating material. The image fixing apparatus according to claim 1, wherein the protrusion includes a protruding portion surrounding the heater in a moving direction of the film. An image fixing apparatus according to claim 1, wherein said apparatus further comprises a pressing member for pressing said heater, said film and recording material. The image fixing apparatus according to claim 1, wherein the visualized image is a toner image and the temperature when the recording material is separated from the film of the toner forming the toner image is higher than the glass transition point of the toner. The image fixing apparatus of claim 1, wherein the film is not thicker than 100 microns. 10. An apparatus according to Claim 9, wherein said film is no thicker than 40 microns. The image fixing apparatus according to claim 1, wherein the film is in the form of an endless belt. The image fixing device according to claim 1, wherein the protrusion blocks toward the film without a corner. The image fixing apparatus according to claim 12, wherein the protrusion is round.

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