JPH0325472A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent irregularities in picture gloss and fixing defects by specifying a rate of circumferential length to width in an endless film wherein a toner image is heated via the endless film and fixed. CONSTITUTION:A transfer material sheet P carrying an unfixed toner image Ta on an upper surface is guided by a guide 29, and advances between a fixing film 24 in the press-contact part N between a heater 20 and a pressure roller 28, and the pressure roller 28. The toner image Ta is heated in the press-contact part N to turn into a softened and fused image Tb. Here, the rate of circumferential length to width in the endless film 28 is specified to be more than 1/3 and less than 8/3. Gloss irregularities arising from the waving of the film 24 and heating defects because of wrinkles can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field of the Invention] The present invention relates to a fixing device that fixes a toner image by applying heat to it via an endless film.

[Prior art]

Conventionally, as a fixing device for fixing a toner image, a heat roller fixing method consisting of a heat roller and a pressure roller that is in pressure contact with the heat roller has been widely used.

Further, a fixing device has also been considered, which fuses a toner image via a thin film that moves together with a recording material on which the toner image is formed, as described in Japanese Patent Application Laid-Open No. 63-313182.

[Problems solved by the invention]

However, such thin walls, especially those with a thickness of 100μ
In a fixing device using a film with a diameter of 1.5 m or less, since the film lacks rigidity, "waving" or "sagging" may occur during feeding, resulting in uneven gloss on the image.

In addition, if ``wavy'' or ``sagging'' continues to deteriorate, it may become ``wrinkled'' and result in poor fixation.

[Means to solve problems]

The present invention, which solves the above problems, includes an endless film in contact with the toner image and a heating body in contact with the endless film, and heat from the heating body is applied to the toner image via the endless film to fix the toner image. The fixing device is characterized in that the ratio of the circumferential length to the width (peripheral length/width) of the endless film is 1/3 or more and 8/3 or less.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a sectional view of an electrophotographic copying apparatus to which a fixing device according to an embodiment of the present invention is applied.

In FIG. 2, reference numeral 100 denotes an apparatus housing, and l denotes a reciprocating type document mounting table made of a transparent plate member such as a glass plate, which is disposed on the upper plate 100a of the machine housing. are driven to reciprocate at predetermined speeds in the right direction a and the left direction a' in the drawing, respectively.

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

1. O O b is a slit opening as a document illumination section, which is opened on the surface of the top plate 100a of the machine casing with its length extending in a direction perpendicular to the reciprocating direction of the document loading table l (direction perpendicular to the plane of the paper). Original G placed on the original placing table L
The downward image surface of the document table 1 passes through the slit 1 and the opening 100b sequentially from the right side to the left side in the forward movement process to the right side a of the document table 1, and in the process of passing, the light of the lamp 7 L is received through the slit 1, the opening 100b, and the transparent original table l, and is scanned by illumination.

The illumination scanning light reflected from the document surface is imaged and exposed on the surface of the photosensitive drum 3 by the short focus and small diameter imaging element array 2.

The photosensitive drum 3 is coated with a photosensitive layer such as a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer, and is rotated clockwise as indicated by an arrow b around a central support shaft 3a at a predetermined circumferential speed. The surface of the photosensitive drum 3 is uniformly charged with positive or negative polarity by the charger 4, and the uniformly charged surface is exposed to image formation (slit exposure) of the original image. Electrostatic latent images corresponding to the original image are sequentially formed.

This electrostatic latent image is sequentially developed by a developing device 5 using a toner made of a resin etc. that is softened and melted by heating, and the developed toner image is transferred to a location where a transfer discharger 8 is provided as a transfer section. It will transition.

S is a cassette loaded with transfer material sheets P as recording materials, and the sheets in the cassette are fed and fed one by one by the rotation of the feeding roller 6, and are then fed onto the drum 3 by the registration roller 9. The timing is set so that when the leading edge of the toner image forming section reaches the position of the transfer discharger 8, the leading edge of the transfer material sheet P also reaches a position between the transfer discharger 8 and the photosensitive drum 3, and the two coincide. and then synchronously fed. Then, the 1.toner image on the photosensitive drum 3 side is sequentially transferred onto the surface of the fed sheet by the transfer discharger 8.

The sheet to which the toner image has been transferred in the transfer section is sequentially separated from the surface of the photosensitive drum 3 by a separating means (not shown), and is transferred to a fixing device 1 (described later) by a conveyance guide IO! The unfixed 1/toner image carried thereon is subjected to a heat fixing process and is discharged onto a paper discharge tray 12 outside the machine as an image formed product (copy).

On the other hand, the surface of the photosensitive drum 3 after the toner image has been transferred is subjected to removal of adhering contaminants such as residual toner by a cleaning device 13, and is used repeatedly to form images.

Next, a fixing device according to an embodiment of the present invention will be described in detail.

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

Reference numeral 24 designates an endless belt-shaped fixing film, which includes a drive roller 25 on the left side, a driven roller 26 on the right side, and a low heat capacity linear heating element as a heating element disposed below between the drive roller 25 and the slave roller 26. The body 20 is suspended between the four members 25, 26, 27, and 20 that are parallel to each other.

The slave opening 26 is an endless belt-like fixing film 2.
The fixing film 24 is rotated clockwise at a predetermined circumferential speed as the drive roller 25 rotates clockwise, that is, the unfixed toner image Ta conveyed from the image forming section 8 side. It is rotationally driven at the same circumferential speed as the conveyance speed of the transfer material sheet P carrying on the upper surface thereof without meandering or speed delay.

Reference numeral 28 denotes a pressure roller having a rubber elastic layer such as silicone rubber with good mold releasability as a pressure member, and the pressure roller 28 pinches the downward film portion of the endless belt-shaped fixing film 24 and presses the heating body 20. The lower surface is pressed against the lower surface by a biasing means (not shown) with a total pressure of, for example, 4 to 7 kg, and is rotated forward and counterclockwise in the conveyance direction of the transfer material sheet P.

The low heat capacity linear heating body 20 as a heating body in this example has rigidity, high heat resistance, and heat insulation properties and is horizontally long with the length extending in the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film 25). It has a heater support 27 and a heater substrate 2l equipped with a heating element 22, a temperature measuring element 23, etc., which is integrally attached and held on the lower surface side of the support along the longitudinal length of the lower surface.

The heater support 27 supports the heating body 20 insulatingly with respect to the fixing device 11 and the entire copying device, and is, for example, pps (
Highly heat-resistant resins such as polyphenylene sulfide), PAI (polyamideimide), PI (polyimide), PEEK (polyetheretherketone), liquid crystal polymer, and composite materials of these resins with ceramics, metals, glass, etc. It can be composed of

As an example, the heater board 2l has a thickness of 1.0 mm.
It is an alumina substrate with a width of 10 mm and a length of 240 mm. The heating element 22 is made of an electrically resistive material such as Ag/Pd (silver palladium) approximately 10 μm thick and 1 to 3 times wide along the length of the lower surface of the substrate 2l, for example.
mm by screen printing or the like, and a heat-resistant glass 21a of about 10 μm is coated thereon as a surface protective layer. For example, the temperature sensing element 23 is mounted on the upper surface of the substrate 21 (the heating element 2
A low heat capacity temperature measuring resistor such as a PT film is provided approximately at the center of the surface (opposite to the surface on which 2 is provided) by coating by screen printing or the like. As the temperature measuring element, a thermistor or the like having a low heat capacity may be arranged in contact with the substrate 2l.

In the case of this example, for the linear or band-shaped heating element 22,
Electricity is applied from both ends in the longitudinal direction to cause the heating element 22 to generate heat over substantially its entire length. The energization is ACIOOV, and the energizing power is controlled by controlling the phase angle of energization by an energization control circuit (not shown) including a triac in accordance with the temperature detected by the temperature measuring element 23.

Next, this fixing operation will be explained.

The transfer material sheet P carrying the unfixed toner image Ta on its upper surface, which is conveyed from the transfer section 8 to the fixing device 11 by the image formation operation of the device in response to an image formation or start signal, is moved to a guide 29.
The pressure contact portion N between the heating body 20 and the pressure roller 28 is guided by
enters between the fixing sheet 24 and the pressure roller 28,
The unfixed toner image surface closely contacts the lower surface of the fixing film 24, which is moving in the same direction at the same speed as the conveyance speed of the sheet P, so that the fixing film 24 can be moved without surface misalignment or wrinkles.
The heating body 20 and the pressure roller 28 pass through the mutual pressure contact portion N of the heating body 20 and the pressure roller 28 while being subjected to a clamping force.

Since the heating body 20 is energized and heated at a predetermined timing in response to an image formation start signal, the toner image Ta is heated at the pressure contact portion N.
It is heated to become a softened and melted image Tb.

The fixing film 24 has a steep angle (
When the bending angle θ is approximately 45°), the traveling direction is changed.

Therefore, the sheet P conveyed through the pressure contact portion N while overlapping the fixing film 24 is separated from the fixing film 24 by the curvature at the edge portion S, and is ejected to the paper ejection tray 12. By the time the paper is ejected, the toner has sufficiently cooled and solidified and is completely fixed on the sheet P (toner image T
c).

The toner used in this example has a sufficiently high viscosity when melted by heating, so even if the toner temperature when separated from the fixing film 24 is higher than the melting point of the toner, the adhesion force between the toners is strong enough to prevent the toner from sticking to the fixing film 24. Extremely greater than adhesive strength.

Therefore, when the fixing film 24 and the sheet p are separated, toner offset with respect to the fixing film 24 does not substantially occur.

Furthermore, in this embodiment, the heat capacity of the heating element 22 and the substrate 2l among the heating elements 20 is small, and these
Since the surface temperature of the heating body 20 at the pressure contact portion N is adiabaticly supported by the toner, the surface temperature of the heating body 20 at the pressure contact portion N rises to a high enough temperature relative to the melting point of the toner (or the temperature at which it can be fixed to the sheet P) in a short time. There is no need to raise the temperature of the heating element in advance (so-called standby temperature control), saving energy.
Moreover, it also prevents the temperature inside the aircraft from rising.

Next, the endless belt-shaped fixing film 24 used in this embodiment will be explained.

The fixing film 24 has heat resistance, releasability, durability, etc.
Generally, single-layer or multi-layer films with a thickness of 100 μm or less, preferably 40 μm or less can be used.

FIG. 4 is a schematic cross-sectional view of the layer structure of an example of a composite layer film, in which 24a is a heat-resistant layer as a base film of the fixing film, and 24b is the outer surface of the heat-resistant layer 24a (facing the toner image). This is a release layer laminated on the side surface).

The heat-resistant layer 24a is made of, for example, polyimide, polyetheretherketone (PEEK), polyethersulfone (F'E
S), polyetherimide (PEI), polyvalabanic acid (PPA), and other highly heat-resistant resin films, and N1/SU
S-AI! Metals with excellent strength and heat resistance can be used, such as metals such as .

The release layer 24b is preferably made of, for example, fluororesin such as PTFE (polytetrafluoroethylene)/PFA@FEP, silicone resin, or the like. The laminated form of the release layer 24b with respect to the heat-resistant layer 24a is the adhesive laminate of the release layer film and the stability of the release layer material. ! Painting (coating), vapor deposition, C
This can be carried out by lamination using a film-forming technique such as VD, or by co-extrusion of a heat-resistant layer material and a release layer material to form a two-layer film.

Note that the resistance value of the surface of the fixing film 24 may be lowered by mixing a conductive agent such as carbon black, graphite, or conductive whiskers into the release layer 24b. In this case, charging of the toner contacting surface of the fixing film 24 can be prevented. When the toner contact surface of the fixing film 24 is insulative, the surface of the fixing film is electrically charged, which may disturb the toner image on the sheet P or transfer the toner image to the fixing film 24 (so-called charging offset). However, these problems can be avoided by taking the above measures.

A thin film of 100 μm or less has no rigidity, so unless it is rotated while applying a certain amount of tension evenly in the middle direction, it may generate waves, which may cause wrinkles.

In experiments by the present inventors, we experimented with different film thicknesses and materials, and found that for films with a thickness of 100μ or less, any of the above-mentioned materials could have a tension of 1.8 x 10-2 kg/mm per unit length at least in the width direction. If it was not applied evenly, waves would occur.

Further, in order to apply such tension uniformly in the width direction, it is necessary to prevent the drive roller 25, driven roller 26, and heater stay 30 from being "deflected" during rotation of the film. According to the inventors' experiments, these 5
When a deflection of 0μ or more occurred, there was insufficient tension in that area and the film produced waves.

In this example, the length is 3 30 based on the above results.
mm, a certain driving roller 25 and driven roller 26 from SUS with a diameter of 20 mm and an SU of 330 x 20 x 20
Width 300 m using heater stay 30 from S
An endless film 24 made of PI with a circumferential length of 150 mm and a circumferential length of 150 mm is suspended and stretched.

For example, when a film 24 with a circumferential length of 100 mm or less is used, it is impossible to make each roller diameter 15 mm or more, so the deflection cannot be reduced to 50 μ or less (that is, waves occur). However, if the inside of the film is 210 mm, each roller will not deflect more than 50μ if it is made of SUS with a diameter of 10 mm or more.
A tension of 1.8xlO-''kg/mm was applied uniformly.In other words, a film with a width of 210mm was applied with a tension of 70
If it has a circumferential length of mm or more, it is possible to rotate it while applying sufficient tension uniformly.

As mentioned above, by setting the width to circumference length ratio to 1/3 or more in an endless film with a thickness of 100μ or less, it becomes possible to rotate while applying sufficient tension uniformly in the width direction. No longer produces waves that cause wrinkles.

When rotating an endless film, a problem arises in that the film gradually shifts in the axial direction. In this embodiment, as a means to solve this problem, the driven roller 2 is
By moving one side of the film 24 up and down with the force of the solenoid 40 and running the film at an angle of θ on only one side as shown in the figure, the state in which the film 24 is wrapped around the driven roller 26 is changed and shifted. I am trying to return the film to its original position.

In addition, here, the film circumference 11 is the width I! If it is significantly longer than 2, the angle α (α = d/j?z) will become too large when creating the angle θ (tan θ = d/i + ) necessary to return the shifted film, and the film will A problem arises in that the strain in the axial direction becomes large and wrinkles are more likely to form.

In other words, the amount of movement d of the driven roller must be increased as the film circumference becomes longer, but as d increases, the axial inclination α increases, and the distortion at this time causes wrinkles in the film. It is something. According to the authors' experiments, the ratio of film width 12 and d is d/l.
When 2>1/50, wrinkles occurred. For example, the width is 30
For 0mm film, d≦6mm, 200
For a film of mm, d must be 4 mm. Further, the angle θ sufficient to return the shifted film could only be 1 when d≦6 mm and ≦800 mm, and 11≦530 mm when d≦4 mm.

In this way, in order to return the film that has been shifted in the axial direction to its original position without wrinkles, the ratio of the film circumference l1 and width l2 must be set to 11.
It is necessary to satisfy /i2≦8/3.

As explained above, in a fixing device that rotates an endless film of 100μ or less, the circumference l and the width l2
By setting 1/3≦1 + / l 2≦8/3, it is possible to prevent uneven gloss on the image due to the film waving, and heating defects due to wrinkles.

FIG. 5 is a diagram showing a second embodiment of the fixing device used in the apparatus of the present invention.

Reference numeral 32 denotes a heating roller as a heating body, which has a built-in heater 33, and by causing the heater 33 to generate heat appropriately according to the heating roller surface temperature detected by the temperature measuring element 41, the surface of the heating roller 32 is brought to a predetermined temperature. Can be maintained.

Reference numeral 34 denotes a small-diameter separation upper roller disposed downstream of the heating roller 32 in the conveying direction of the sheet P. Reference numeral 25 denotes a tension roller, which is a driven roller that constantly applies an appropriate tension to the fixing film and controls meandering by moving one side up and down when the film shifts too much in the axial direction.

The fixing film 34 is suspended and stretched, and is rotated clockwise at the same speed as the sheet P by rotation of the heating roller 32.

36 faces the lower side of the heating roller 32. 35 is a lower separation roller arranged opposite to the lower side of the upper separation roller 34; 37 is an endless roller suspended between the pressure roller 36 and the lower separation roller 35. This is a belt-shaped conveyor belt (backup belt). Pressure roller 36
is a roller whose surface layer is made of an elastic material such as silicone rubber. The downward film portion of the endless belt-shaped fixing film 24 is sandwiched between the pressure roller 36 and the heating roller 32, and a total contact pressure of, for example, 4 to 7 kg is obtained by a biasing means (not shown). ing. The pressure roller 36 rotates as a result of the rotation of the heating roller 32, and the conveyor belt 37 also rotates counterclockwise at the same speed as the conveyance speed of the sheet P while pressing the sheet P against the fixing film 34. move.

Next, the fixing operation of this embodiment will be explained.

The transfer material sheet P carrying the unfixed toner image Ta on its upper surface is transported from the transfer section 8 to the fixing device 11 by the image forming operation of the device in response to the image formation start signal, and is rotated by the heating roller 32. Therefore, when the fixing film 24 and the conveyor belt 37 are rotating, the guide 29
The unfixed toner image surface enters between the fixing film 24 and the conveyor belt 37 at the pressure contact portion N between the heating roller 32 and the pressure roller 36, and the unfixed toner image surface is moved at the same speed as the conveyance speed of the sheet P. The heating roller 32 and the pressure roller 36 are in close contact with the lower surface of the fixing film 24 rotating in the same direction, without causing surface misalignment or wrinkles, and in an overlapping state with the fixing film 24 between the heating roller 32 and the pressure roller 36. It passes through while being under pressure.

In the process of passing through the mutual pressure contact portion N, the toner image Ta on the sheet P is heated and becomes a softened and melted image Tb.

The sheet portion that has passed through the mutual pressure contact portion N between the heating roller 32 and the pressure roller 36 is spread and travels between the heating roller 32 and the upper separating roller 34 until it reaches the position of the upper separating roller 34. The fixing film continues to be conveyed in close contact with the part of the fixing film that is being fixed. The conveyor belt 37 functions to support the back surface of the sheet P and maintain close contact between the sheet P and the fixing film 24. During this conveyance process, the heat of the softened/melted toner image Tb is radiated and becomes a cooled/solidified toner image Tc. The toner heat radiation in this heat radiation/cooling process is natural radiation cooling in this example, but it may be forcibly radiation cooled by using radiation fins, air blowing means, or the like.

When the fixing film 24 is conveyed to the position of the upper separation roller 34, the traveling direction of the fixing film 24 is turned away from the surface of the sheet P along the surface of the upper separation roller 34 having a large curvature.
The fixing film 24 and the sheet P are separated from each other, and the sheet P is conveyed to the paper discharge tray l2. By the time of this separation, the toner has sufficiently cooled and solidified, and the adhesion and adhesion of the toner to the sheet P is sufficiently large, and the strength to the fixing film 24 is extremely small. The separation of one toner P is easily performed sequentially without substantially causing toner offset to the fixing film 24.

In this embodiment, it is possible to set the temperature of the heating roller, which is a heating element, higher than the temperature at which high-temperature offset 1. occurs in the conventional heating roller fixing method, thereby improving fixing performance. Furthermore, the allowable temperature range of the heating element is wide on the high temperature side, making it possible to simplify temperature control.

Further, when fixing a multi-color image, particularly a 1.color image of three or more colors, it is easy to mix colors because it can be sufficiently melted at a high temperature.

Furthermore, since the toner is once melted, cooled and solidified in a state in close contact with the fixing film, and then peeled off from the fixing film, it is possible to make the surface properties of the 1. toner image similar to the surface properties of the fixing film. Therefore, for example, by smoothing the surface of the fixing film, it is possible to give the surface of the toner image Te a gloss similar to that of a silver halide photograph.

Further, by making the fixing film 24 thin as described above, heat accumulation in the fixing film is prevented and the cooling process of the toner image is made more efficient. Furthermore, when a thin resin film was used as the fixing film, the adhesion to the toner image was improved and the heat transfer efficiency was improved.

Note that the heating body 32 is not limited to the heating roller, and as shown in FIG. 6, the fixed heating body 20 shown in the first embodiment may be used. In that case, in addition to the above effects, the heating element 22 and the substrate 2
Since the heat capacity of l is small and the heat is insulated, there is an advantage that the temperature rise rate is fast and standby temperature control is not required. Further, by arranging a separation stay 38 having an end face with a larger curvature in place of the upper separation roller 34, it becomes possible to separate the seal I-P from the fixing film 24 more reliably.

In this embodiment, the film 32 and the belt 37 must be in complete contact with each other within the distance C.

For example, when the film 32 becomes wavy in the cooling process C, a space is created between the film and the belt, and a portion is created where the film and the image carrier P are separated before the toner Tb is sufficiently cooled, resulting in an offset. will occur.

Further, a method in which the fixing film is separated after the toner has sufficiently cooled, as in this embodiment, generally produces a glossy image, but if there are portions where the toner separates before cooling due to waves, significant uneven gloss will result.

In this way, in this example, offset! - In order to prevent uneven gloss, it is necessary to make the corrugations smaller than in Example 1 described above. Therefore, the length ratio between the film circumference l and the film width l2 is 1/3≦E + / R 2≦8/3
preferably 2/3≦12 r /
12 2≦5/3 is good.

〔Effect of the invention〕

As explained above, the present invention makes it possible to rotate the endless film while applying uniform and sufficient tension by setting the length ratio between the circumference and the width of the endless film to be 1/3 or more and 8/3 or less. This prevents the endless film from meandering without causing wrinkles.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a fixing device according to an embodiment of the present invention. FIG. 2 is a sectional view of a copying machine to which the embodiment of FIG. 1 is applied. FIG. 3 is a sectional view of the fixing film used in this example. FIG. 4 is a model diagram showing control of film meandering. FIG. 5 is a sectional view of a fixing device according to another embodiment of the present invention. In the figure 20... Heating body 25... Drive roller 26...Followed roller 28...pressure roller ? 4-■■■

Claims (1)

[Claims] (1) In a fixing device that has an endless film in contact with a toner image and a heating body in contact with the endless film, and performs fixing by applying heat from the heating body to the toner image via the endless film, the above-mentioned A fixing device characterized in that the ratio of the circumference to the width (perimeter/width) of the endless film is 1/3 or more and 8/3 or less.