JPH0325474A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent offsetting and fixing irregularities by specifying the entire thickness of a fixing film and setting the thickness of a base material layer smaller than that of a releasing layer. CONSTITUTION:A transfer material sheet P carrying an unfixed toner image Ta on a first surface is guided by a guide 29, and advances between the fixing film 24 in a 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, fused image Tb. The fixing film 24 is composed of the base material layer 24a abutting on the heater 20 and the releasing layer 24b abutting on the image side. When the film entire thickness is PF, the base material layer thickness PB and the releasing layer thickness, PC, 7<=P<=50mum, and PB<=PC are satisfied. Consequently, an offsetting phenomenon and fixing irregularities can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device that performs fixing by applying heat to a toner image via a moving film.

[Prior art]

Conventionally, the fixing device used in this type of device uses a heated roller maintained at a predetermined temperature and a pressure roller that has an elastic layer and presses against the heated roller to form an unfixed toner image. A constant fixing method using a heated roller is often used, which heats the transferred transfer device while supporting it.

A belt fixing system described in US Pat. No. 3,578,797 is known.

However, both heat roll fixing and belt fixing have a large heat capacity, so there are problems in that the warm-up time is long and a large amount of electric power is required.

Therefore, the applicant previously proposed a fixing device using a thin heat-resistant film, particularly a film with a thickness of 50 μm or less, in Japanese Unexamined Patent Publication No. 63-313182.

[Problems solved by the invention]

However, when using a heat-resistant film, the release properties of the developed particles (particularly toner) are insufficient, and a so-called offset phenomenon occurs, resulting in image stains and wrapping around the recording device, so a release layer is required. It has been found that depending on the release layer, film transport may become unstable, fixing unevenness, or film damage may occur.

[Embodiments of the invention]

Examples of the present invention will be described below.

FIG. 4 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. 4, reference numeral 100 denotes a device 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 to the right a and to the left a' in the drawing.

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

Reference numeral 100b denotes a slit opening, which serves as a document illumination section, and is opened on the surface of the top plate 100a of the machine casing, with its length extending in a direction perpendicular to the direction of reciprocating movement of the document table 1 (direction perpendicular to the plane of the paper). The downward image surface of the document G set on the document platform 1 passes through the position of the slit opening 100b sequentially from the right side to the left side during the forward movement of the document platform 1 to the right side a. During the passing process, the light L from the lamp 7 is received through the slit opening 100b and the transparent original table l, and the document is illuminated and scanned.

The light reflected from the document surface of the illumination scanning light is image-formed and exposed on the surface of the photosensitive drum 3 by the short-focus, small-diameter imaging element INO2.

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 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 of the original image (slit 1/exposure).
Electrostatic latent images corresponding to the image-formed and exposed original image are sequentially formed on the surface.

This electrostatic latent image is sequentially developed using a toner made of a resin or the like that softens and melts when heated by a developing device 5, and the developed toner image is transferred to a transfer portion of a transfer discharger 8 serving as a transfer portion. attitude".

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. The data is taken and fed synchronously. Then, the toner image (T) on the photosensitive drum 3 side is sequentially transferred onto the surface of the fed sheet by the transfer discharger 8.

The sheet to which the toner image has been transferred in the transfer section is sequentially separated from the surface of the photosensitive drum 3 by a separating means (not shown), and guided to a fixing device 11 (described later) by a conveyance guide 1O, where the unfixed toner image carried thereon is heated. After undergoing fixing processing, the image 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 is transferred is subjected to removal of adhered contaminants such as residual toner by a cleaning device l3, and is used repeatedly for image formation.

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

FIG. 5 is an enlarged sectional view of the fixing device.

Reference numeral 24 denotes an endless belt-shaped fixing film, which includes a driving roller 25 on the left side, a driven roller 26 on the right side, and a low heat capacity linear heating element 20 as a heating element disposed below between the driving roller 25 and the driven roller 26. The four members 25 and 26 and 27 and 20 are suspended and stretched in parallel with each other. This fixing film 24 will be described in detail later.

The driven roller 26 is an endless belt-shaped fixing film 2.
The fixing film 24 is fixed 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. wrinkles, meandering, etc. at the same peripheral speed as the conveyance speed of the transfer material sheet P carrying the
Rotation is driven without speed delay.

Reference numeral 28 denotes a pressure roller having a breaking layer of rubber with good mold releasability, such as silicone rubber, as a pressure member. The lower surface of the transfer material sheet P is pressed against the lower surface of the transfer material sheet P with a total pressure of, for example, 4 to 7 kg by a biasing means (not shown), and is rotated in a forward counterclockwise direction 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). A heater support 27 and a heating element 2 integrally attached and held on the lower surface of the support along the longitudinal direction of the lower surface.
2. It has a heater board 2l equipped with a temperature measuring element 23 and the like.

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), FAI (polyamideimide), PI (polyimide), PEEK (polyetheretherketone), liquid crystal polymer, and composite materials of these resins with ceramics, metals, glass, etc. It can be composed of

The heater substrate 2l has a thickness of 1.5 mm, for example. 0 mm
It is an alumina substrate with a diameter of 10 mm and a length of 240 mm.

The heating element 22 is formed by applying an electrically resistive material such as Ag/Pd (silver palladium) to a thickness of about 10 μm and a width of 1 to 3 mm by screen printing or the like along the length of the lower surface of the substrate 21, for example. A surface protective layer and a heat-resistant glass 21a are coated thereon to a thickness of about 10 μm. The temperature measuring element 23 is, for example, a low heat capacity measuring element such as a PT film coated by screen printing or the like on the upper surface of the substrate 21 (the surface opposite to the surface on which the heating element 22 is provided) approximately at the center. It is a temperature resistor.

As a temperature measuring element, a low heat capacity thermistor etc. board 2 can also be used.
It is also possible to adopt a structure in which it is placed in contact with 1.

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.

The fixing film 24 is not limited to an endless belt shape.
As shown in the figure, the fixing film 24 with an end wound around the feed-out shaft 30 is locked to the take-up shaft 31 between the heating body 20 and the pressure roller 28, and the film is wound from the feed-out shaft 30 side. It may be configured to run toward the take-up shaft 31 side at the same speed as the conveyance speed of the transfer material sheet P.

Next, the fixing operation of the apparatus of this embodiment 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 l1 by the image forming start signal of the apparatus, is moved to the 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 adheres to 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, and the fixing film 24 is moved without surface misalignment or wrinkles.
The heating element 20 and the pressure roller 28 pass through the mutual pressure contact part N of the heating element 20 and the pressure roller 28 while being subjected to a clamping pressure.

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 (curvature radius of about 2 mm) at the edge S of the support 27 with a large curvature (curvature radius of about 2 mm).
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 with the fixing film 24 is separated from the fixing film 24 by the curvature at the edge portion S, and is discharged to the paper discharge tray l2. 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 sufficient to maintain the adhesion of the toner to the fixing film. Extremely greater than force. 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.

Further, in this embodiment, the heat capacity of the heating element 22 and the substrate 21 of the heating element 2o is small, and these are
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.

When such a thin film is used, there are characteristics required for the release layer, which will be explained in detail below.

Figure 1 shows the fixing film (24) in contact with the heating element (20).
) and a pressure roller (28) to fix the toner image (T) on the transfer material (P).

The device will be explained later.

The fixing film consists of a base layer (24a) that comes into contact with the heating element and a release layer (24b) that comes into contact with the image surface side. Specifically, the base material layer is a heat-resistant film made of polyimide resin film such as polyimide, polyetherimide, voriparvanic acid, polyether sulfone, polyether ether ketone, etc., and is used in the form of an end coat or a sheet.

The release layer is made of fluororesin, such as PTFE, PFA, FE.
It is made of P, silicone resin, or rubber, and fluororesin is particularly good. Further, in order to prevent electrostatic image staining and offset while maintaining mold releasability, a conductive substance such as carbon conductive whiskers or graphite 1 may be mixed to reduce the electrical resistance value. Preferably 10”Ω/clTI
1 or less was desirable.

First, if the thickness of the fixing film used is too large,
The following problems arise.

■ Thermal resistance between the heating element and toner increases. Therefore, as the fixing film becomes thicker, the electric power required to soften and melt the 1.ner increases. Therefore, the power supply and the entire device become larger.

■ Unless the peak temperature of the heating element is raised, 1.ner will not soften. Generally, the higher the operating temperature of the heating element, the shorter the lifespan of the heating element, so the thicker the fixing film, the shorter the lifespan of the heating element. When the temperature of the heating element is increased, the temperature of the fixing film, especially on the side of the heating element, also increases. Then, the durability of the fixing film becomes a problem.

■ Heat transfer to toner takes time. Therefore, the time from when the 1.toner passes through the heating element position until the viscosity becomes high again after the toner is softened and melted is also longer. Then, while the toner is being softened and melted, there is a risk that the fixing film and the toner will separate. In order to prevent this, if a member is provided that closely conveys the fixing film and the recording material having the toner image until the toner is completely cooled and solidified, the apparatus becomes complicated.

(2) Recording materials generally have irregularities, and furthermore, toner images are unevenly distributed on the surface. When the fixing film is thin, the fixing film deforms to follow the unevenness of the toner image within the pressure contact area formed by the heating body and the pressure roller. Then, the toner image is heated evenly regardless of its unevenness.
No fixing defects occur. However, if the fixing film is thick, the fixing film will not follow the unevenness of the toner image, and the fixing film will not adhere closely to the toner image. As a result, the toner is heated non-uniformly, which may result in poor fixing or toner offset.

Here, when the total thickness of the fixing film is PF, the base layer is PB, and the release layer is PC, the thickness of PF is limited under the following conditions. That is, as shown in FIG. 2, when considering the total thickness of the film and the temperature of the heating element, the temperature increases as the thickness increases due to the thermal resistance of the film itself. This is because the temperature of the toner contact surface is determined by the toner characteristics.For example, a heating nib of 2 mm is heated to 52 mm/s at 170°C.
When using a toner that obtains fixing properties at a speed of c and a pressure of 6 kg, if the diameter exceeds 50 μm, the temperature will exceed 230°C, and the stability will deteriorate due to the base film and release layer exceeding thermal deterioration or decreasing strength. This is an area where there is a lack of Further, when the thickness is less than 7 μm, the film itself lacks strength (rigidity), and transport of the film becomes unstable, leading to wrinkles and large partial deformation.

Next, it was observed that there are film-specific conditions regarding the relationship between P8 and P0. PC may be less than 1μ as long as it is uniformly formed on the base material and the base material is not exposed, but it may be slightly worn due to contact with the transfer machine or pressure roller, and it is stable for more than 30,000 A4 sheets. In particular, when forming a fluororesin layer, the layer is formed by melting the particles, so to obtain surface uniformity, it is necessary to use at least 2 to 3 μm.
More than μ was required.

However, the release layer does not need to be as thick as it should be, and since the film does not move in concentric circles and heat is applied at the fixing section and not elsewhere, it is stable under various temperature conditions and forms. In particular, fluororesins are more susceptible to thermal deformation than base materials such as polyimide, and when the total thickness of P8 and Pc is less than 50 μm, the deformation of P0 slightly affects TB, resulting in a wavy or bumpy film. As the pattern moves, the pattern is reflected on the fixed image, resulting in subtle differences in gloss, which degrades image quality or causes fixing failure if the amount of deformation is large. Furthermore, if the film is used repeatedly in this state, the release layer may peel off from the base material or the film may be damaged.

Furthermore, when baking a fluororesin, if the temperature is T8 or Tc, curling and shrinkage may become large and dimensional stability may be lost.

Therefore, when the total thickness is 50 μm or less, by setting PF]≦Po, stable image quality and transportability that can withstand repeated use can be obtained.

Further, as shown in FIG. 3, when a bonding layer (24c) is provided for stabilizing the mold release layer and ensuring strong bonding to the base material, the bonding layer + mold release layer is P. It was a closed observation result.

This is considered to be because the bonding layer is similar to the material of the mold release layer rather than to the base material, and this was particularly noticeable for polyimide base materials and fluororesin mold release layers.

[Embodiment 2] FIG. 7 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 4l, 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. 25 is a drive roller that rotates and runs the fixing film, and 26 is a driven roller that always applies an appropriate tension to the fixing film. Note that both the drive roller 25 and the heating roller 32 are
It is rotated clockwise at the same speed as the conveyance speed of the sheet P.

The fixing film 34 has four members 32, 34 parallel to each other.
, 25 and 26.

36 is a pressure roller disposed opposite to the lower side of the heating roller 32; 35 is a lower separation roller disposed opposite to the lower side of the upper separation roller 34; 37 is the pressure roller 36 and the lower separation roller. This is an endless belt-like conveyor belt (backup belt) suspended between 35 and 35. 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 presses the sheet P against the fixing film 34 while moving counterclockwise at the same speed as the conveyance speed of the sheet P. Rotate.

In this embodiment, 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 forming apparatus in response to the image formation or start signal, is heated. In a state where the roller 32 is rotationally driven and therefore the fixing film 24 and the conveyor belt 37 are rotating, the fixing film 24 and the conveyor belt are guided by the guide 29 at the pressure contact portion N between the heating roller 32 and the pressure roller 36. 37, the unfixed toner image surface comes into close contact with the lower surface of the fixing film 24, which is rotating in the same direction at the same speed as the conveyance speed of the sheet P, causing surface misalignment and wrinkles. The film passes through the mutual pressure contact portion N between the heating roller 32 and the pressure roller 36 while being subjected to a pinching pressure, in an overlapping state together with the fixing film 24.

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 heating roller 36 is spread and travels between the pressure roller 32 and the separation upper roller 34 until it reaches the position of the separation upper roller 34. The fixing film continues to be conveyed in close contact with the fixed fixing film part. 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. In this heat dissipation/cooling process, the I/N heat dissipation is natural heat dissipation cooling in this example, but it may be forced heat dissipation cooling by providing heat dissipation 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 in a direction 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 12.

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.
Since it is in an extremely small state with respect to the fixing film 24, the separation of the fixing film 24 and the sheet P is as follows.
This can be done easily and 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 occurs in the conventional heating roller fixing method, thereby improving fixing performance. In addition, the allowable temperature range of the heating element is wide on the high temperature side,
Temperature control can be simplified.

Further, when fixing a multi-color toner image, especially a toner image of three or more colors, it is easy to mix colors because it can be sufficiently melted at a high temperature. Further, since the toner is once melted, cooled and solidified while 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 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 Tc 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 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. 8, 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 1 is small and it is insulated, the temperature rise rate is fast and there is no need for standby temperature control. 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 sheet P from the fixing film 24 more reliably.

FIG. 9 is a diagram showing a third embodiment of the fixing device used in the apparatus of the present invention.

A transparent member such as heat-resistant glass is arranged in place of the heating body 20,
Through this member, the toner image is heated by radiation 7940 such as a halogen lamp placed inside the endless fixing film 24.

In this embodiment, since heating is performed by radiation, the toner can be instantly heated and melted. Therefore, the seat P is the pressure contact part N.
Since it is only necessary to heat the machine when the machine is in the

〔Effect of the invention〕

As described above, according to the present invention, offset and uneven fixing occur.
In other words, a thin film can be used.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a fixing film used in the present invention, FIG. 2 is a diagram for explaining the present invention, FIG. 3 is a sectional view of another fixing film used in the present invention, and FIG. A sectional view of a copying apparatus using a fixing device according to an embodiment of the invention. FIGS. 5 to 9 are sectional views of a fixing device showing other embodiments of the invention. 20...Heating body 24...Fixing film 24a...Fixing film base material 24b...Fixing film release layer 8? Figure l TF (, u777) 28

Claims (1)

[Scope of Claims] Fixing in which a heating body is placed on one side of the film, an image bearing member carrying a toner image is brought into close contact with the other side, and thermal energy is applied to the toner image through the film to perform fixing. In the apparatus, the film is composed of a heat-resistant base material layer and a mold release layer, the total film thickness is P_F, the base material layer thickness is P_B, and the mold release layer is P_C.
A fixing device characterized in that when 7≦P_F≦50 μm and P_B≦P_C.