JP2511825B2 - Fixing device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, a facsimile, a microfilm reader printer, an image display (display) device, and a recording machine.
A recording material (electrofax sheet, electrofax sheet, etc.) is formed by using a developing material (toner) made of a heat-meltable resin or the like by an appropriate image forming process means such as electrophotography, electrostatic recording or magnetic recording.
An unfixed image (toner image) corresponding to the target image information formed and carried on the surface of the electrostatic recording sheet, transfer material sheet, printing paper, etc. directly or indirectly (transfer) is permanently fixed to the surface of the recording material. The present invention relates to a fixing device that heats and fixes an image.

More specifically, it has a heater provided with a heating element that heats the substrate when energized, and a film that slides on the heater, and an unfixed image is formed on the recording material by the heat from the heater through the film. The present invention relates to a film heating type fixing device for fixing to a sheet.

(Prior Art) A film heating type fixing device as described above is disclosed in
Known in JP-A-59-68766 and JP-A-59-157678, it has a quick start characteristic and can reduce power consumption in comparison with a heating roller type fixing device. It has the feature that it can suppress

(Problems to be Solved by the Invention) In such a film heating type fixing device,
There is a problem that when the film slides on the heater, the film is damaged at the edge of the heater.

The present invention solves this film damage problem.

(Means for Solving Problems) In a fixing device in which an unfixed image is fixed on a recording material by heat from a heater through a film, the heater is preferably heat-insulated and supported by a supporting member in order to improve thermal efficiency.

In view of this, the present invention focuses on a support member that heat-insulates the heater, and provides the support member with a protrusion that protrudes toward the recording material side from the substrate of the heater, and guides the movement of the film by this protrusion. It was done.

(Operation) As a result, the film can be prevented from being damaged by the substrate (mainly the edge) of the heater without providing a member separately from the supporting member for supporting the heat insulation of the heater, and the film can be protected with a simple structure. be able to.

(Embodiment) (1) Fixing device 11 FIG. 1 is a model view of the fixing device 11 of this embodiment, and FIG. 2 is an enlarged model view of a heating unit portion.

In FIG. 1, reference numeral 25 denotes an endless belt-shaped fixing film, which includes a driving roller 26 on the left side, a driven roller 27 on the right side, and a heating unit 20 fixedly supported below the rollers 26, 27. And a guide roller 26a disposed below the drive roller 26, and is stretched between the four members 26, 27, 20 and 26a parallel to each other.

The driven roller 27 is an endless belt-shaped fixing film 25.
The fixing film
Reference numeral 25 denotes a predetermined peripheral speed in the clockwise direction in accordance with the clockwise rotation of the drive roller 26, that is, the transfer speed of the transfer material sheet P carrying the unfixed toner image Ta conveyed from the image forming section 8 side on the upper surface. It is driven to rotate with the same peripheral speed as wrinkles, meandering and speed delay.

Reference numeral 28 denotes a pressure roller as a pressure member having a rubber elastic layer having a good releasability such as silicon rubber, which sandwiches the film portion on the descending side of the endless belt-shaped fixing film 25 of the heating unit 20. Bottom heater (heater) H
On the other hand, for example, a pressing force of not shown is applied to the transfer material sheet P so that the transfer material sheet P is rotated in a counterclockwise direction.

Endless belt-shaped fixing film 25 driven to rotate
Since the toner is repeatedly used for heat fixing of the toner image, it is excellent in heat resistance, releasability and durability, and is generally 100 μm or less, preferably thinner than 40 μm. For example, a single-layer film of a heat-resistant resin such as polyimide, polyetherimide, PES, or PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin) or a composite layer film, for example, at least the image contact surface side of a 20 μm thick film And a 10 μm-thick release coating layer obtained by adding a conductive material to a fluororesin such as PTFE (tetrafluoroethylene resin) and PAF.

The heating unit 20 of this example is a heater supporting member 24 having laterally long rigidity, high heat resistance, and heat insulating property, the longitudinal direction of which is the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film 25), and this supporting member. A heater H is integrally attached and held on the lower surface side of the member 24 along the length of the lower surface.

The heater H includes a substrate 21, a heating element 22 that is provided on the front surface side of the substrate 21 and generates heat when energized, a temperature measuring element 23 that is provided on the back surface side of the substrate 21, and the like.

The heater H is supported on the lower surface of the heater support member 24 by exposing the surface side provided with the heating element 22.

The heater support member 24 ensures the overall strength of the heater H,
Heat-insulating support, such as PPS (polyphenylene sulfide), PAI (polyamide imide), PI (polyimide), PEEK (polyether ether ketone), liquid crystal polymer and other high heat resistant resins, and these resins and ceramics metal / glass Etc. can be made of a composite material.

As shown in FIG. 2, the heater support member 24 has protrusions a and a that protrude from the substrate 21 of the heater H toward the recording material P, and guides the movement of the fixing film 25.

The heater substrate 21 has a thickness of 1.0 mm, a width of 10 mm, and a length of 2 as an example.
It is a 40 mm alumina substrate.

The heating element 22 is, for example, a linear or strip-shaped member provided by coating (screen printing, etc.) an electric resistance material such as Ta ₂ N with a width of 1.0 mm along the length in the substantially central portion of the lower surface of the substrate 21. It is an electric heating element with a low heat capacity.

The temperature measuring element 23 is, for example, a Pt film or the like provided by coating (screen printing or the like) along the length in a substantially central portion of the back surface of the substrate 21 (the surface opposite to the side on which the heating element 22 is provided). It is a resistance thermometer with low heat capacity.

In the case of the present example, the linear or belt-like heating element 22 is energized from both longitudinal ends thereof to generate heat over the entire length.

Energization is a pulsed waveform with a cycle of 20 msec of DC 100 V, a desired temperature controlled by the temperature measuring element 23, and a pulse width corresponding to the amount of energy released is given to the energization control circuit configuration, and the pulse width is About 0.5-5msec
The heating element 22 is heated in the range of 200 to 300 ° C. instantly every time a pulse is input.

Further, in this example, a sheet front and rear end detection sensor (not shown) is provided on the upstream side of the fixing device 11 in the transfer material sheet conveying direction, and the sheet detection signal of the sensor is used to energize the heating element 22. Sheet P is the fixing device for the period 11
Is controlled only during the required period of powering.

The fixing film 25 is not limited to the endless belt shape,
As shown in the figure, the end fixing film 25 wound around the delivery shaft 30 in a roll is locked between the heating body 20 and the pressure roller 28 and under the guide roller 26a, and is locked to the winding shaft 31. The transfer material sheet P from the delivery shaft 30 side to the winding shaft 31 side.
It may be configured to run at the same speed as the transport speed of.

(2) Fixing Execution Operation The unformed toner image Ta conveyed from the image forming section (transfer section) 8 side to the fixing apparatus 11 by the image forming apparatus main body performing an image forming operation by the image formation start signal is displayed on the upper surface. When the leading end of the transfer material sheet P carried on the sheet is detected by the above-mentioned sensor (not shown) arranged near the fixing device, the fixing film 25 starts to rotate (or travel) and the transfer material sheet P is guided. It is guided by 29 and enters between the fixing sheet 25 and the pressure roller 28 at the pressure contact portion N (fixing nip portion) between the heater H and the pressure roller 28, and the unfixed toner image surface is the conveying speed of the sheet P. Fixing film 25 that moves in the same direction at the same speed as
While passing through the fixing nip portion N between the heater H and the pressure roller 28 in a state of overlapping with the fixing film 24 without coming into close contact with the lower surface of the sheet and causing the surface shift or wrinkling, the fixing nip portion N is passed.

w is the width dimension of the heating element 22 provided on the lower surface of the heater H, and the heating element 22 is in the mutual pressure contact width area between the lower surface of the heater H and the upper surface of the pressure roller 28, that is, the width of the fixing nip portion N. It exists in the area.

The toner image bearing surface of the sheet P is a heating element in the process of passing through the fixing nip portion N while being pressed and closely attached to the fixing film surface.
The heat of 22 is received through the fixing film 24, and the toner image is melted at a high temperature and softened and adhered to the surface of the sheet P Tb.

In the case of the apparatus of this example, a recording material sheet P and a fixing film
The separation from the sheet 24 is performed when the sheet P passes through the fixing nip portion N and exits.

At the time of this separation, the temperature of the toner Tb is still higher than the glass transition point of the toner, and therefore the bonding force (adhesive force) between the sheet P and the fixing film 25 at the time of this separation.
Since the sheet P is small, the sheet P hardly causes toner offset to the surface of the fixing film 25, and the sheet P is always smoothly separated without being wound and jammed while being adhered to the surface of the fixing film 25 due to separation failure. Go.

And, since the toner Tb in a state of a temperature higher than the glass transition point has an appropriate rubber property, the toner image surface at the time of separation has an appropriate uneven surface property without following the fixing film surface, and this surface property is improved. Since the toner image is maintained and cooled and solidified, a proper image gloss is not generated on the fixed toner image surface, and high quality image is obtained.

The sheet P separated from the fixing film 25 is guided by the guide 35 and reaches the discharge roller pair 36. The temperature of the toner Tb higher than the glass transition point naturally lowers (natural cooling), and the temperature is lower than the glass transition point. Then, the solidified Tc is reached, and the sheet P on which the image has been fixed is output onto the tray 12.

In this embodiment, the linear heating element 22 of the heater H instantly rises to a sufficiently high temperature with respect to the melting point (or fixing temperature) of the toner when energized, so that preheating of the heater H is unnecessary. There is little heat transfer to the pressure roller 28 during non-fixing.

Also during fixing, a fixing film, a toner image, and a sheet are present in the fixing nip portion N between the heater H and the pressure roller 28, and a short heat generation time causes a rapid temperature gradient. It is difficult for 28 to rise in temperature, and the temperature is maintained below the melting point of the toner even when continuous image formation is carried out to the extent practically required.

In the apparatus of this embodiment having such a structure, the toner image formed of the heat-fusible toner on the sheet P is first heated and melted by the heater H through the fixing film 25, and in particular, the surface layer portion thereof is completely softened. To melt. At this time, the heater, the fixing film, the toner image, and the sheet are in good contact with each other by the pressure roller 28, 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.

It is sufficient for the heater H to be small in size, so that the heat capacity becomes small and it is not necessary to raise the temperature of the heater H in advance. Therefore, it is possible to reduce the power consumption during non-image formation,
Further, the temperature rise inside the machine can be prevented.

(3) Function of the heater supporting member 24 As described above (FIG. 2), the heater supporting member 24 has the fixing film 25 with the protruding portions aa protruding from the heater substrate 21 of the supporting member 24 toward the recording material side. Can also be used as a conveyance guide member.

That is, the chamfered curvature and smoothness of the corners 24a are easier than that of the heater substrate 21, and the sliding abrasion of the fixing film when it is used as the sliding conveyance guide member of the fixing film 25 can be prevented.

As a result, it is possible to prevent the film from being damaged by the substrate 21 (mainly the edge) of the heater H without providing a member separately from the support member 24 that heat-insulates and supports the heater H, and the film 25 can be protected easily. Can be done at.

Further, the separation angle θ (FIG. 2) from the surface of the fixing film 25 after heat fixing of the sheet P as a recording material is arbitrary (0 <θ <
180 °) can be set. In an experiment by the present inventors, thin paper (46 g
/ m ² ), the sheet P could be prevented from being wrapped around the fixing film 25 by the rapid peeling of about θ = 30 ° or more in the horizontal black (the right angle in the traveling direction) and the solid black tip (with the toner image). That is, the separating claw was unnecessary. Further, in the conventional heat roller, the curl curl which occurs on the sheet P due to its curvature can be prevented by making the heating portion (fixing nip portion N) flat and increasing the separation angle θ of the fixing film 25.

Regarding the heater H, the smaller the heat capacity of the heater substrate 21, the heating element 22 and the temperature detecting element 23 is, the better the energy capacity is. However, this portion alone is against the pressure of the pressure roller 28 as a heating member. In some cases, the strength is insufficient. In this case, the heater H is integrally attached to the support member 24 as a strength member to secure the overall strength of the heater H.

The support member 24 can be provided with the following features in addition to the strength member.

. The support member 24 is made of a material having poor heat conduction such as PPS, bakelite, or ceramic to act as a heat insulator, which can improve the heat efficiency to the fixing film side and prevent the temperature rise due to heat diffusion to other than the heating portion. .

. In some cases, the positional accuracy between the fixing nip portion N and the heating element is important as a device, and the center of the pressing member and the heater H can be accurately measured.
The centers need to be aligned. In the case of the above-described heater H having a small heat capacity, it may be difficult for the heater itself to provide the position reference / installation strength. In such a case, the support member 24 may be provided with a dimensional reference (for example, a pin) of the device. It is possible.

(4) Others a) Regarding the heater H, the substrate 21 may be made of heat-resistant glass or heat-resistant resin such as PI / PPS in addition to alumina.

The heating element 22 may be a resistor such as nichrome, RuO ₂ , Ta ₂ N, etc., in addition to Ag / Pd.

As the temperature detecting element 23, a bead thermistor having a low heat capacity or the like can be used in addition to the resistance temperature detector such as a Pt film.

It is preferable to provide a slide protection film layer such as a thin heat resistant glass layer on the lower surface of the heater on which the fixing film 25 slides.

The heating element 22 is arranged on the back side of the substrate 21 (the side opposite to the fixing film facing side of the substrate 21), and the temperature detecting element 23 is arranged on the front side of the substrate 21 (fixing film facing side of the substrate 21). Alternatively, the heating element 22 and the temperature measuring element 23 may be arranged on the lower surface side of the substrate 21.

The energization of the heating element 22 may be controlled by normal energization control instead of pulse energization.

b) When an endless fixing film 25 is used as in the apparatus shown in FIG. 3, when the fixing film on the delivery shaft side is almost completely wound on the winding shaft side and used, a new roll winding film is used. It is also possible to use a method of exchanging (winding exchange type).

In the case of such a take-up exchange type, the thickness can be reduced regardless of the durability of the fixing film, and the power consumption can be reduced. For example, an inexpensive base material such as a PET (polyester) film or the like may be used as the fixing film, and a heat-treated thin film having a thickness of about 12.5 μm or less may be used.

Or, since the toner offset to the fixing film surface does not substantially occur as described above, if the thermal deformation or deterioration accompanying the use of the fixing film is small, the used sheet wound on the take-up shaft side can be removed in a timely manner. And rewinding control to the shaft side,
Alternatively, it can be used a plurality of times by reversing the winding shaft side and the sending shaft side, etc. (rewinding repetitive use type).

In the rewinding repeated use type, as the fixing film, for example, a 25 μm thick polyimide resin film is used as a base material having excellent heat resistance, mechanical strength, etc., and a release layer made of a highly releasable fluororesin or the like on its surface. It is preferable to automatically control the pressure release mechanism during reverse rewinding to keep the contact between the heating element and the pressure roller in the released state.

In the case of multiple use such as a rewinding repetitive use type or an endless belt type, a felt pad is provided for cleaning the film surface, and a slight release agent, for example, silicon oil is impregnated to contact the pad with the film surface. For example, the film surface may be cleaned and the releasability may be further improved.

When the fixing film is an insulative fluororesin-treated product, static electricity that disturbs the toner image is easily generated in the film. Therefore, it is also possible to remove the static electricity with a grounded static elimination brush.

A bias voltage may be applied to the brush without being grounded to charge the film within a range that does not disturb the toner image. Further, it is one 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, depressurization and conductivity of the pressure roller can be performed by the same means. Further, an antistatic agent or the like may be applied or added.

Fixing film is endless belt type, rewindable type,
Regardless of the rewinding and reusing type, the fixing film can be easily replaced at a predetermined portion of the fixing device 11 so that the fixing film can be easily replaced.

(5) Example of image forming apparatus FIG. 4 shows a schematic configuration of an example of an image forming apparatus in which the fixing device 11 is incorporated in the examples of FIGS.

The image forming apparatus of this example is a reciprocating platen / rotating drum type / transfer type electrophotographic copying apparatus.

Reference numeral 100 is a machine casing, and 1 is a reciprocating type document placing table made of a transparent plate member such as a glass plate disposed on the top plate 100a of the casing. a, left a '
Each of them is driven to reciprocate at a predetermined speed.

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 pressure plate 1a is placed on top of it and pressed down to set it.

Reference numeral 100b denotes a slit opening serving as a document illuminating section which is opened on the surface of the machine housing upper surface plate 100a with a direction perpendicular to the reciprocating direction of the document placing table 1 (direction perpendicular to the paper surface) as a longitudinal direction. The downward image surface of the document G placed and set on the document placing table 1 sequentially passes through the position of the slit opening 100b from the right side to the left side in the forward movement process of the document placing table 1 to the right a. The light L of the lamp 7 is passed through the slit opening 100b and the transparent document placing table 1 and is illuminated and scanned during the passage. The light reflected from the document surface of the illumination scanning light is image-wise exposed on the surface of the photosensitive drum 3 by the short-focus small-diameter image-forming 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 peripheral speed 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.

Reference numeral S denotes a cassette in which transfer material sheets P as recording materials are stacked and housed, the sheets in the cassette are fed out and fed one by one by the rotation of the feeding roller 6, and then the toner on the drum 3 is fed by the registration roller 9. When the leading edge of the image forming portion reaches the portion of the transfer discharger 8, the leading edge of the transfer material sheet P also reaches the position between the transfer discharger 8 and the photosensitive drum 3 and is timed and synchronized so as to coincide with each other. Be delivered. Then, the transfer discharger 8 is attached to the surface of the fed sheet.
Thus, the toner images on the photosensitive drum 3 side are sequentially transferred.

The sheet to which the toner image has been transferred in the transfer unit is sequentially separated from the surface of the photosensitive drum 3 by a separation unit (not shown),
The unfixed toner image carried by the fixing device 11 is heated and fixed by the above-mentioned fixing device 11 through the guide 35 and the discharge roller 36 as an image-formed product (copy), and then on the discharge tray 12 outside the machine. Is discharged to.

On the other hand, the surface of the photosensitive drum 3 after the transfer of the toner image is repeatedly used for image formation after the adhering contaminants such as the transfer residual toner are removed by the cleaning device 13.

The fixing apparatus of the present invention is not limited to the transfer type electrophotographic apparatus illustrated in FIG. 4, and the image forming process / means may be a direct type in which a toner image is directly formed and carried on an electrofax paper or electrostatic recording paper. Copiers, laser beam printers, facsimiles, microfilm reader printers of the type that forms an image with a heat-melting toner on a recording material by a magnetic recording image forming method or other appropriate image forming process / means and heat-fixes it. It can be effectively applied as an image heating and fixing device in various image forming devices such as display devices and recorders.

(Effects of the Invention) As described above, in the film heating type fixing device of the present invention, the heater supporting member that heat-insulates and supports the heater is provided with the protruding portion protruding toward the recording material side from the heater substrate, and the protruding portion forms the film. Since the movement is guided, it is possible to prevent the film from being damaged by the substrate (mainly the edge) of the heater without providing a member separately from the supporting member for thermally insulating the heater, and the film can be protected with a simple structure. be able to.

[Brief description of drawings]

FIG. 1 is a schematic configuration model diagram of a fixing device according to an embodiment, FIG. 2 is an enlarged model diagram of a heating unit portion, FIG. 3 is a schematic configuration model diagram of a fixing device having another configuration, and FIG. 4 is an image forming apparatus. It is a schematic block diagram of an example. 11 is the whole number of the fixing device, 20 is a heating unit, H is a heater, 25 is a fixing film, 28 is a pressure roller, P is a sheet,
Ta is unfixed toner, Tb is heat-softened / melted toner, Tc is solidified toner, and N is a fixing nip portion.

Continuation of front page (56) Reference JP-A-59-68766 (JP, A) JP-A-58-105178 (JP, A) JP-A-48-94438 (JP, A) JP-A-59-157678 (JP , A)

Claims (1)

(57) [Claims] 1. A heater provided with a heating element for generating heat upon energization of a substrate, and a support member for heat-insulating and supporting the heater.
In a fixing device having a film that slides with the heater, and fixing an unfixed image on a recording material by heat from the heater through the film, the support member is closer to the recording material than a substrate of the heater. The fixing device is characterized in that it has a projecting portion projecting to the inside, and this projecting portion guides the movement of the film.