JPH11258933A - Heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a bad effect as a result of a non-paper passing part heating-up by restraining the non-paper passing part heating-up so far as possible in a heating device of film heating system. SOLUTION: In this heating device provided with fixedsupported heating bodies 1, the film 2 sliding through the heating bodies, an elastic pressure member 4 forming a nip part with the heating bodies 1 across the film 2, capable of insert/holding material to be heated P between the film and the elastic pressure member 4 in the nip part, and heating the material to be heated by heat from the heating bodies across the film, the device is allowed to make the width Na of the nip part in transporting direction of the material to be heated in the case of holding no material to be heated between the film and the elastic member in the nip part, so as to become beyond 60% of the width Nb in the case of holding the material to be heated whose thickness is 0.5 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film heating type heating device and an image forming apparatus such as a copying machine or a laser beam printer having the heating device as image fixing means.

[0002]

2. Description of the Related Art Conventionally, for example, a heating device for a recording material for heating and fixing an image includes a heating roller maintained at a predetermined temperature and a pressure roller which presses the heating roller through an elastic layer. Thus, a heat roller method of heating while nipping and conveying a recording material as a material to be heated is often used. Also,
In addition, flash heating method, open heating method,
Various systems and configurations such as a hot plate heating system are known and are in practical use.

[0003] In recent years, a film heating type heating device has been devised in place of such a method and put into practical use (Japanese Patent Application Laid-Open No. 63-313182, Japanese Patent Application Laid-Open No. 1-26).
Nos. 3679, 2-15778, and 4-4
Nos. 4075-44083 and 4-204980-2
No. 04984).

[0004] The heating device includes a fixedly supported heating element, a film that slides on the heating element, an elastic pressure member (pressure roller) that forms a nip with the heating element via the film, A device in which the material to be heated is nipped and conveyed between the film and the elastic pressing member of the nip portion, and the material to be heated is heated by heat from the heating body through the film,
It can be used as a means for heat-fixing an unfixed toner image as a permanently fixed image on a recording material surface carrying the image. Further, for example, as an image heating device for heating a recording material carrying an image to improve the surface properties such as gloss, an image heating device for a hypothetical deposition process, and other means for heating a sheet-like heating material. Can be widely used.

[0005] In such a film heating type heating apparatus, a heating element having a low heat capacity and a thin film such as a so-called ceramic heater can be used, and the temperature of the heating element rises in a short time. Eliminating the need for conducting heating of the heating body during standby eliminates the need to heat the heating body sufficiently to a predetermined temperature until the recording material reaches the fixing portion even if the recording material as the heated material is immediately passed. This machine, such as an image forming apparatus, can reduce power consumption and shorten the wait time (quick start property) as compared with conventional contact heating systems such as a heat roller system and a belt heating system. This has the advantage that the temperature rise in the machine can be reduced, and is effective.

[0006]

However, in the above-described film heating type heating device typified by the heat fixing device, there is a problem due to the so-called "non-paper-passing portion temperature rise" as a problem.

That is, in the apparatus, a recording material (small size cardboard) which is narrower and thicker than the axial length of the film.
When the heating and fixing process is executed by continuously feeding paper, a large amount of heat is taken by the recording material of the continuous paper in the paper passing portion of the fixing nip portion, so that a large amount of power is supplied to the heating body, The temperature of the heating element corresponding to the paper passing section is adjusted so that a predetermined fixing temperature is maintained. On the other hand, the same large amount of power is supplied to the non-sheet passing area as for the sheet passing section, but the heat is not deprived by the recording material, and the nip width is reduced compared to the sheet passing section. The effect of transferring heat to the rollers is deteriorated, and the portion corresponding to the non-sheet passing portion of the heating body becomes much higher in temperature than the portion corresponding to the sheet passing portion. This is "non-sheet passing portion temperature rise".

For this reason, when a normal-size recording material is passed immediately after the temperature of the non-paper-passing portion is extremely high, the toner in the recording-material portion corresponding to the non-paper-passing region is abnormally melted. As a result, an inconvenient state occurs in the image due to hot offset or the like. If toner adheres to the film due to hot offset, the toner will adhere again to the rear end of the recording material or to the front and back of the next recording material.

Also, cracks may occur in the heater substrate due to thermal expansion stress (thermal stress) due to a local temperature difference of the heater substrate (heater crack). That is, when the heating element is a ceramic heater using a ceramic material such as alumina as the substrate, when the temperature of the non-sheet-passing heating element becomes high, the width between the resistance heating element of the heating element and the ceramic substrate increases. A large temperature difference occurs in the direction, and a thermal stress is applied in the longitudinal direction of the ceramic substrate due to the temperature difference. If the thermal stress exceeds the breaking strength of the ceramic substrate, there is a problem that the heating element is broken.

Further, if the temperature rise in the non-sheet passing portion is deteriorated, the heating member supporting member (heater stay), the film, the pressure roller and the like may be damaged (heat loss).

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heating apparatus of a film heating type, in which the non-sheet-passing portion is heated as much as possible to prevent the problem caused by the non-sheet-passing portion.

[0012]

According to the present invention, there is provided a heating apparatus and an image forming apparatus having the following constitutions.

(1) The nip comprises a fixedly supported heating element, a film sliding on the heating element, and an elastic pressure member forming a nip portion with the heating element via the film. In a heating device in which a material to be heated is sandwiched and conveyed between the film and the elastic pressing member of the portion, and the material to be heated is heated by heat from the heating body through the film, the film of the nip portion When the heated material is not sandwiched between the elastic material and the elastic pressing member, the width of the nip portion in the heated material transport direction is 60% of the width when the heated material having a thickness of 0.5 mm is sandwiched therebetween. A heating device characterized by the above.

(2) An image forming apparatus comprising the heating device according to (1) as image fixing means.

<Operation> That is, when the material to be heated is not sandwiched between the film at the nip and the elastic pressing member, the width of the nip in the material transport direction of the nip is 0.5 mm thick. By setting the width to be 60% or more of the width when the material to be heated is sandwiched, a decrease in the nip width of the non-sheet passing portion with respect to the nip width of the sheet passing portion when passing small-sized thick paper is suppressed, and The heat transfer efficiency from the heating element portion to the film and the elastic pressing member in the section can be increased to suppress the temperature rise in the non-sheet passing section, and the problem caused by the temperature rise in the non-sheet passing section, that is, in the heat fixing device, Can prevent inconvenience on an image due to hot offset or the like, cracking of a heating element (heater), and generation of heat loss of a heating element supporting member, a film, a pressure roller, and the like.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (FIGS. 1 to 6) (1) Overall Schematic Configuration of Heating Device FIG. 1 shows a film heating type heating device (image fixing device) according to the present invention. It is a schematic structure figure of an example. FIGS. 2A and 2B are enlarged cross-sectional schematic diagrams of a main part, in which FIG. 2A shows a state in which a recording material is not sandwiched in a fixing nip portion, and FIG.

The heating device 10 of this embodiment is disclosed in Japanese Patent Application Laid-Open No. 4-44075.
This is a so-called tensionless type device disclosed in Japanese Patent Nos. 44083 and 4-204980 to 204984. The tensionless type device uses an endless belt or cylindrical heat-resistant film, and at least a part of the peripheral length of the film is always tension-free (in a state where tension is not applied). This is a device that is driven to rotate by a driving force. The heating device 10 of this example has a maximum paper passing width of A3 size.

1 is a ceramic heater as a heating element, 2
Is a heater supporting member (heater stay) having a trough-shaped cross-section, and 3 is a cylindrical heat-resistant film (fixing film).
Reference numeral 4 denotes an elastic pressure roller as an elastic pressure member.

The ceramic heater as the heating element 1 will be described in detail in the following section (2).

The support member 2 is made of a heat-resistant and electrically insulating rigid material capable of withstanding a high load, for example, PPS (polyphenylene sulfide), PAI (polyamide imide),
The heating element 1 is made of PI (polyimide), PEEK (polyetheretherketone), or the like, and the heating element 1 is exposed with its front surface facing downward in a groove 2 a provided along the longitudinal direction of the support member at a substantially central portion of the lower surface of the support member 2. It is fitted and fixedly supported.

The cylindrical film 3 has a film thickness of 100 μm or less, preferably 50 μm or less and preferably 20 μm or more and has a single layer of heat-resistant PTFE, PFA, FEP or the like in order to reduce the heat capacity and improve the quick start property. Film or polyimide, polyamide imide, PEE
PTF on the outer surface of film such as K, PES, PPS
A composite layer film coated with E, PFA, FEP or the like can be used. In this example, a polyimide film having an outer peripheral surface coated with PTFE was used.

The cylindrical film 3 is externally fitted to the support member 2 including the heating element 1. The inner peripheral length of the cylindrical film 3 and the outer peripheral length of the supporting member 2 including the heating element 1 are larger than that of the film 3 by, for example, about 3 mm. I have.

The elastic pressure roller 4 is a film outer surface contact driving means for forming a pressure contact nip portion (fixing nip portion) N with the film 3 sandwiched between the heat roller 1 and the film 3 and driving the film 3 to rotate. The film driving roller and pressure roller 4 includes a cored bar 4a and an elastic layer 4 made of silicon rubber or the like.
b, and an outermost release layer 4c. The film 3 is sandwiched with a predetermined pressing force by a bearing means and a biasing means (not shown), and is disposed in pressure contact with the surface of the heating element 1.

The pressure roller 4 is driven by a driving means M to rotate in the counterclockwise direction indicated by an arrow. The cylindrical film 3 is pressed by the frictional contact between the outer surface of the roller 4 and the outer surface of the film 3 at the nip N by the rotation of the pressure roller 4.
, The film 3 slides while the inner surface of the film 3 is in close contact with the downward surface of the heating element 1 at the nip portion N and substantially corresponds to the rotational peripheral speed of the pressure roller 4 in the clockwise direction a shown by the arrow. With the set peripheral speed, the support member 2 is rotated outside (pressure roller driving method).

The support member 2 also serves as a film guide for holding the heating element 1 and improving the transport stability of the film 3 during rotation.

Further, a small amount of a lubricant such as heat-resistant grease can be interposed between the inner surface of the film 3 and the downward surface of the heater 1 in order to reduce the sliding resistance.

When the pressure roller 4 is driven to rotate, the cylindrical film 3 rotates around the outer periphery of the supporting member 2, and electricity is supplied to the heating element 2 to generate heat at the nip portion. In a state where the temperature of N has risen to a predetermined temperature and the temperature has been adjusted, a recording material P as a heated material carrying an unfixed toner image t is introduced into the nip portion N, and the toner image of the recording material P is carried in the nip portion N. The front side is in close contact with the outer surface of the film 3 and the nip N is conveyed together with the film 3.

In the nipping and conveying process, the heat of the heating element 1 is applied to the recording material P via the film 3, and the unfixed toner image t on the recording material P is heated and pressed.

After passing through the nip N, the recording material P is conveyed from the outer surface of the film 6 with a curvature separated.

(2) Configuration of Heating Element 1 FIG. 3 (a) is a diagram illustrating a surface side model view of a partially cut-away heating element 1 and a block diagram of an energizing system, and FIG. It is a model figure on the back side.

The heating element 1 of this embodiment is a ceramic heater using a ceramic material such as alumina (Al ₂ O ₃ ) or aluminum nitride (AlN) as the heating element substrate 1a, and has a low heat capacity and a rapid temperature rise as a whole. It is.

The heating body substrate 1a is horizontally long and thin with a longitudinal direction (film width direction) perpendicular to the film / recording material transport direction a in the nip portion N. In this embodiment, the thickness is 1 mm.・ Width 12mm ・ Length 330mm
This is an elongated thin plate member.

Reference numerals 1b and 1c denote two parallel first and second resistance heating elements provided on the front side of the substrate 1a along the length of the substrate. The resistance heating elements 1b and 1c are, for example, A
g / Pd (silver palladium), RuO ₂ , Ta ₂ N or other electric resistance material by screen printing or the like to a thickness of about 10 μm.
It is formed by applying and firing a linear or narrow band pattern having a width of 1 to 3 mm.

Reference numerals 1d and 1e denote first and second electrode patterns arranged side by side on one longitudinal end of the substrate surface. First
The electrode pattern 1d is electrically connected to one end of the first resistance heating element 1b, and the second electrode pattern 1e is electrically connected to one end of the second resistance heating element 1c. Also, the first
The other ends of the first and second resistance heating elements 1b and 1c are electrically connected to a common third electrode pattern 1f.

Accordingly, the first electrode pattern 1d → the first resistance heating element 1b → the third electrode pattern 1f,
A parallel electric circuit (AC line) is formed from the electrode pattern 1e → the second resistance heating element 1c → the third electrode pattern 1f.

Reference numeral 1g denotes a heat-resistant overcoat layer on which the resistance heating elements 1b and 1c are formed and which protects the surface of the heating element. For example, a heat-resistant glass layer having a thickness of about 10 μm.

Reference numerals 1h and 1i denote fourth and fifth electrode patterns, respectively, which are juxtaposed at the other longitudinal end of the substrate surface. The fourth and fifth electrode patterns are respectively formed in through holes 1j.
Conduction is made to the two parallel conductor patterns 11 and 1m formed on the back side of the substrate via 1k to reach the approximate center of the substrate length. A thermistor 1n as a temperature detecting element is provided between the tip portions of the two parallel conductor patterns.

Thus, the fourth electrode pattern 1h → the through hole 1j → the conductor pattern 11 → thermistor 1n →
A series electric path (DC line) of the conductor pattern 1m → the through hole 1k → the fifth electrode pattern 1i is formed.

The thermistor 1n is made of cobalt, manganese,
Particles of alloys such as nickel, ruthenium, oxides, ceramics such as platinum or barium titanate are mixed with a glass paste material and screen-printed on the back surface of the substrate to form a thin layer type or chip type thermistor. can do.

The first to fifth electrode patterns 1d and 1
e, 1f, 1h, 1i and the conductor patterns 11l, 1m are formed by applying a silver (Ag) paste in a predetermined pattern on a front surface side and a rear surface side of a substrate in a predetermined pattern by screen printing or the like, and baking. I have.

The first and second resistance heating elements 1b and 1c and the temperature detecting element 1n are located in the nip portion N.

Thus, power is supplied between the first and second electrode patterns 1d and 1e and the third electrode pattern 1f of the AC line from a power supply circuit including a commercial power supply (AC power supply) 5, a triac 6.7 and the like. The first and second resistance heating elements 1
b and 1c generate heat, and the predetermined effective length region of the heating element 1 rises in temperature.

The temperature rise is detected by a thermistor 1n as a temperature detecting element of the DC line, and the output of the thermistor 1n is set to A.
/ D converted and taken into the CPU 8, and the first and second resistance heating elements 1b.
The temperature control of the heating element 1 is performed by controlling the heating element energizing power by controlling the AC voltage of the AC power supply 5 energizing 1c by controlling the phase and the wave number. That is, by controlling the energization so that the temperature of the heating element 1 rises when the temperature detected by the temperature detecting element 1n is lower than a predetermined set temperature, and to lower the temperature when the temperature is higher than the predetermined temperature, the temperature of the heating element 1 is controlled at a fixed temperature during fixing. Is done.

In a state where the temperature of the heating element 1 rises to a predetermined value and the rotation peripheral speed of the film 3 is stabilized by the rotation of the pressure roller 4, the heating element 1 and the pressure roller 4, a recording material P to be fixed as an image to be heated is introduced between the film 3 and the pressure roller 4 in the press-contact nip portion N formed by The heat of the heating body 1 is applied to the recording material P via the film 3 by being nipped and conveyed by the press-contact nip N, and the unfixed visible image (toner image) on the recording material P
t is fixed on the surface of the recording material P by heating. The recording material P that has passed through the pressure nip N is separated from the surface of the film 3 and conveyed.

(3) Nip Width By the way, as described above, in the conventional heating device of this type, when a small-sized thick paper is passed as the recording material P, the heat is taken by the recording material in the non-paper passing portion of the nip portion N. In addition, the heat transfer efficiency from the heating element 1 to the film 3 and the pressure roller 4 deteriorates due to the small nip width with respect to the paper passing section, and the heating element becomes extremely hot (the non-paper passing section rises). Temperature). When the temperature of the heating element in the non-sheet passing portion becomes high, inconvenience on an image due to hot offset or the like occurs. In addition, a large temperature difference occurs in the width direction between the resistance heating element and the ceramic substrate serving as the heating element substrate, and a thermal stress is applied in the longitudinal direction of the ceramic substrate due to the temperature difference. If the temperature exceeds the range, a problem that the heating element is damaged (heater cracking) occurs. Further, if the temperature rise in the non-sheet passing portion is deteriorated, heat loss of the heater supporting member 2, the film 3, and the pressure roller 4 may be caused.

In this embodiment, as shown in FIG. 2A, the recording material is placed between the film 3 and the pressure roller 4 in order to suppress the nip reduction in the non-sheet passing portion when the small size thick paper is passed. When the width (nip width) of the nip portion Na in the recording material conveyance direction when the P is not sandwiched between the recording materials (sheets) P having a thickness of 0.5 mm is sandwiched therebetween as shown in FIG. Of the nip width of 60% or more.

The nip portion N is formed by pressing the heating element 1 with a predetermined pressing force against the elasticity of the pressing roller 4 with the film 3 interposed between the pressing roller 4 and as shown in FIG. The nip width Nx is determined geometrically if the pressing amount x of the pressing roller 4 is determined, and increases as the pressing amount x or the diameter 2r of the pressing roller 4 increases according to the equation (1).

R ² = (Nx / 2) ² + (r−x) ² (1) In general, the pressing amount x increases as the pressing force increases and the hardness of the pressing roller 4 decreases. And the thickness of the elastic layer 4b.

As an example, in the heating device of this embodiment,
The diameter of the pressure roller 4 is 25 mm, and the length in the longitudinal direction is 317.
mm, the thickness of the elastic layer 4b is 4 mm, and the hardness is ASKER.
FIGS. 5 and 6 show graphs obtained by calculating the relationship between the pressing force, the nip width, and the amount of indentation when a configuration of 48 ° is measured by a −C type tester. The pressing force is a value of the total pressure.

FIG. 5 shows the relationship between the pressing force and the nip width, and FIG. 6 shows the relationship between the pressing force and the pushing amount. It can be seen that both the nip width and the pushing amount increase as the pressing force increases.

The recording material P between the film 3 and the pressure roller 4
2 (FIG. 2B), the pressing amount becomes larger by the thickness of the recording material P than when the recording material P is not sandwiched (FIG. 2A). The nip width also increases (Nb> Na). That is, if the nip width Na when the recording material P is not sandwiched between the film 3 and the pressure roller 4 is known, the nip width Nb when the recording material P is sandwiched is also determined.

Therefore, the nip width Na when the recording material P is not sandwiched between the film 3 and the pressure roller 4 is 60 times the nip width Nb when the sheet having a thickness of 0.5 mm is sandwiched therebetween.
%, The combination of the pressing force, the hardness and diameter of the pressure roller 4, the thickness of the elastic layer 4b, and the like may be selected. For example, if the pressing force is set to 13 kgf in the configuration of the diameter, the length, the hardness, and the thickness of the elastic layer of the pressing roller 4 described above, the recording material P is sandwiched between the film 3 and the pressing roller 4. When there is no pushing amount x is 0.36m,
The nip width Na becomes about 6.0 mm. In addition, the thickness is 0.
When a 5 mm sheet P is sandwiched between the film 3 and the pressure roller 4, the pushing amount x increases by 0.5 mm, so that the pushing amount x is about 0.86 mm, and the nip width Nb is about 9.2 mm.
The nip width Na when the recording material P is not sandwiched between the film 3 and the pressure roller 4 is about 65% of the nip width Nb when a sheet having a thickness of 0.5 mm is sandwiched therebetween.

The ratio of the nip width Na when the recording material P is not sandwiched to the nip width b when the recording material P is sandwiched between the film 3 and the pressure roller 4 is determined by the configuration in which the nip width is large, that is, the pressing force Is large or when the pressure roller 4 has a low hardness.

Regarding the nip width when the recording material P is narrower than the axial length of the film 3, the paper passing portion sandwiches the recording material P between the film 3 and the pressure roller 4. Since the non-sheet passing portion corresponds to the nip width Na when not sandwiching the recording material P, the ratio of the nip width Na of the non-sheet passing portion to the nip width Nb of the sheet passing portion is as described above. The ratio of the nip width Na when the recording material P is not sandwiched to the nip width Nb when the recording material P is sandwiched between the film 3 and the pressure roller 4 that has been sandwiched between the film 3 and the pressure roller 4 is as follows. )> (Nip width N of non-sheet passing area)
a).

For example, in the configuration of the diameter, the length, the hardness, the thickness of the elastic layer, and the pressing force of the pressure roller 4 described above, the thickness of the film 3 is smaller than the axial length of the film 3. 5mm
, The nip width Nb of the paper passing portion is 9.2.
mm, the nip width Na of the non-sheet passing portion is 6.0 mm, and (the nip width Na of the non-sheet passing portion) / (the nip width N of the sheet passing portion)
b) = 65%.

That is, the nip width Na when the recording material P is not sandwiched between the film 3 and the pressure roller 4 is 60 times the nip width Nb when a sheet having a thickness of 0.5 mm is sandwiched therebetween.
% Or more, a thickness of 0.5
The nip width Na of the non-sheet passing portion when a sheet of mm is sandwiched can be 60% or more of the nip width of the sheet passing portion.

After all, by adopting the configuration of this embodiment,
It is possible to suppress a decrease in the nip width Na of the non-sheet passing portion with respect to the nip width Nb of the sheet passing portion when the small size thick paper is passed. When the decrease in the nip width Na of the non-paper passing portion is small, the efficiency of heat transfer from the heating element 1 to the film 3 and the pressure roller 4 in the non-paper passing portion is increased, and therefore, the temperature rise of the non-paper passing portion is suppressed. Can be.

Further, by suppressing the temperature rise in the non-sheet passing portion, it is possible to prevent inconvenience on the image due to hot offset or the like caused by the temperature rise. Further, it is possible to prevent breakage of the heater 1 (heater crack) due to thermal stress and heat loss of the heater support member 2, the film 3, and the pressure roller 4.

(Comparative Example 1) In the heating device of the embodiment described in the first embodiment, by changing the pressing force, the thickness of the film 3 is reduced to 0.5 mm, which is narrower than the axial length of the film 3.
Is changed when the ratio of the nip width Nb of the non-sheet passing portion and the nip width Na of the sheet passing portion when the sheet is sandwiched between the film 3 and the pressure roller 4 is changed, the effect of preventing the heater crack is different. Are shown below.

Here, the diameter of the pressure roller 4 is 25 mm,
The length in the longitudinal direction is 317 mm, and the thickness of the elastic layer 4b is 4
mm, hardness is 48 ° as measured by ASKER-C tester
Was used.

In the heating apparatus having the above configuration, an acceleration test for cracking of the heater was performed while changing the pressing force. Table 1 shows the results of this heater cracking acceleration test.

In the accelerated test, three sheets of A4 size 157 g / m ² thick paper were stacked vertically in an environment of a temperature of 15 ° C.
The cycle of passing the sheets continuously and cooling with a fan for 15 minutes was repeated. By repeating a cycle in which the temperature of the heating body 1 is increased and cooled at a stretch from a cold state, thermal stress is intermittently applied to the ceramic substrate 1a (alumina), and the heating body 1 is easily broken.
The values of the nip widths of the non-sheet passing portion and the sheet passing portion in Table 1 are values obtained when a sheet having a thickness of 0.5 mm is sandwiched between the film 3 and the pressure roller 4.

[0063]

[Table 1] In Table 1, the ratio of the nip width between the non-sheet passing portion and the sheet passing portion is 6
A configuration of 0% or more is an embodiment of the present invention. It should be noted that if the pressure is increased, the fixing property is improved.
In each of the configurations, the fixing temperature was set lower as the pressing force was increased so that the fixing property was the same.

As can be seen from Table 1, the configuration of the present invention (60% or more of the nip width of the non-sheet passing portion when the sheet having a small width of 0.5 mm is sandwiched between the nip width of the sheet passing portion). It can be seen that by applying (2), the heater crack is not generated and the margin for the heater crack is increased.

The lower the fixing temperature, the smaller the temperature rise in the non-sheet-passing portion and the less likely it is for the heater to crack. In the heater crack acceleration test of this comparative example, in order to verify whether or not the heater crack did not occur in the configuration of the present invention because of the low fixing temperature, the same heater crack was performed in all the configurations with the same fixing temperature. An accelerated test was performed. Table 2 shows the results.

[0066]

[Table 2] As can be seen from Table 2, the results are the same as in Table 1. In the heater cracking acceleration test in which the fixing temperature was changed in each configuration, the heater cracking did not occur in the configuration of the present invention because the fixing temperature was low. Is not the main factor. Even when only the pressing force is changed with the same fixing temperature,
It can be seen that by applying the configuration of the present invention, a heater crack does not occur and a margin for the heater crack is increased.

(Comparative Example 2) In the heating device of the embodiment described in the first embodiment, by changing the hardness of the pressing roller 4, the thickness of the film 3 is smaller than the axial length of the film 3. When the ratio of the nip width of the non-paper passing portion and the nip width of the paper passing portion when a .5 mm sheet is sandwiched between the film 3 and the pressure roller 4 is changed, how does the effect of preventing the heater cracking differ? Are shown below.

Here, the diameter of the pressure roller 4 is 25 mm,
The length in the longitudinal direction is 317 mm, and the thickness of the elastic layer 4b is 4
mm and a total pressure of 13 kgf.

In the heating device having the above configuration, the same heater cracking acceleration test as in Comparative Example 1 was performed while changing the hardness of the pressure roller 4. Table 3 shows the results. As in Comparative Example 1, the nip width values of the non-sheet passing portion and the sheet passing portion in Table 2 are as follows.
This is the value when sandwiched between. The value of the second pressure roller hardness is a value measured by an ASKER-C tester.

[0070]

[Table 3] In Table 3, the ratio of the nip width between the non-sheet passing portion and the sheet passing portion is 6
A configuration of 0% or more is an embodiment of the present invention. If the hardness of the pressure roller 4 is low, the nip width becomes large and the fixability is improved. Therefore, in the seven configurations listed in Table 3, the hardness of the pressure roller 4 is low so that the fixability is the same. The lower the fixing temperature, the higher the fixing temperature.

As can be seen from Table 3, the configuration of the present invention (60% or more of the nip width of the non-sheet passing portion when a sheet having a small width of 0.5 mm is sandwiched between the nip width of the sheet passing portion). It can be seen that by applying (2), the heater crack is not generated and the margin for the heater crack is increased.

The heater crack acceleration test in each of the configurations performed in Comparative Example 1 at the same fixing temperature was also performed in this comparative example. The purpose is the same as in Comparative Example 1. Table 4 shows the results.

[0073]

[Table 4] As in Comparative Example 1, the results in Table 4 are the same as in Table 3. Even when only the hardness of the pressure roller 4 is changed while keeping the fixing temperature the same, by applying the configuration of the present invention,
It can be seen that there is no heater cracking and the margin for heater cracking is large.

<Second Embodiment> (FIG. 7) FIGS. 7 (a), (b) and (c) show other structural examples of a film heating type heating apparatus.

9A, an endless belt-like heat-resistant film 3 is suspended between a heating element 1 held by a support member 2, a driving roller 11, and a driven roller (tension roller) 12. In this configuration, the film 3 is stretched and driven to rotate the film 3 by the driving roller 11. M is a driving unit of the driving roller 11. The pressure roller 4 is a film 3
It is driven and rotated with the rotational movement of.

(B) shows an endless belt-shaped heat-resistant film 3 suspended between a heating member 1 held by a supporting member 2 and a driving roller 11 to form a driving roller 1.
1 and is driven to rotate. Pressure roller 4
Rotates following the rotation of the film 3.

In the case of (c), a long rolled end film is used as the heat-resistant film 3, and the heat-resistant film 3 is wound through the heating element 1 held on the support member 2 from the feeding shaft 13 side. It is configured to travel at a predetermined speed to the take-up shaft 14 side. M is a drive unit of the winding shaft 14.

The present invention can be applied to the above-mentioned heating devices (a) to (c).

<Third Embodiment> (FIG. 8) The heating element 1 may be other than a ceramic heater. In this embodiment, an electromagnetic induction heating member is used.

In FIG. 8, reference numeral 1 denotes a horizontally long electromagnetic induction heating member as a heating element, for example, a horizontally long iron plate. Reference numeral 15 denotes an excitation coil, and reference numeral 16 denotes a core (excitation iron core) of the excitation coil. The horizontally long electromagnetic induction heating member 1 as a heating element generates electromagnetic induction heat by the action of a high frequency magnetic field generated by supplying a high frequency current from an excitation circuit (not shown) to the excitation coil 15. The heat of the electromagnetic induction heating member 1 is applied to the recording material P via the film 3, and the unfixed toner image t on the recording material P is heated and pressed and fixed.

The present invention can be applied to such a heating device.

<Fourth Embodiment> (FIG. 9) FIG. 9 is a schematic structural view of an example of an image forming apparatus provided with, for example, the heating device 10 of the first embodiment as an image heating and fixing device. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 21 denotes a rotating drum type electrophotographic organic photosensitive member (hereinafter, referred to as a photosensitive drum) as an image carrier.
It is rotationally driven at a predetermined peripheral speed (process speed) in the clockwise direction of the arrow.

The photosensitive drum 21 is uniformly charged with negative charges by a charging roller 22 as a charging member during the rotation process, and the charged surface of the photosensitive drum 21 is exposed to the laser exposure device 2.
3 receives a laser beam scanning exposure L corresponding to the target image information. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photosensitive drum 21.

The laser exposure device 23 outputs a laser beam L whose intensity is modulated in accordance with a target image information signal (a time-series electric digital pixel signal) sent from an external device such as a host computer (not shown). The uniformly charged surface of the rotating photosensitive drum 21 is scanned and exposed to light (raster scanning). The intensity of the laser beam and the diameter of the irradiation spot are appropriately set according to the resolution of the printer and the desired image density.

The portion irradiated with the laser beam on the uniformly charged surface of the rotary photosensitive drum 21 is attenuated to a bright portion potential, and the other portion is maintained at the dark portion potential charged by the charging roller 22. Thus, an electrostatic latent image is formed.

The electrostatic latent images formed on the surface of the rotating photosensitive drum 21 are sequentially developed in reverse by the developing device 24. The toner (such as a one-component magnetic toner) in the developing device 24 includes a developing sleeve 24a, which is a toner supply rotating body, and a developing blade 24.
b, the toner layer thickness and tribo are controlled, and a uniform toner layer is formed on the developing sleeve 24a. The developing blade 24b is usually made of metal or resin, and the resin blade is in contact with the developing sleeve with an appropriate contact pressure. The toner layer formed on the developing sleeve faces the photosensitive drum 21 with the rotation of the developing sleeve itself, and a portion having a light portion potential is generated by the voltage applied to the developing sleeve 24a and the electric field formed by the surface potential of the photosensitive drum 21. Only the image is selectively visualized (reversal development).

The toner image formed on the surface of the rotating photosensitive drum 21 is recorded at a transfer portion, which is the opposing portion between the photosensitive drum 21 and the transfer roller 25, at a predetermined control timing with respect to the transfer portion. It is sequentially transferred to a material (transfer material) P.

Reference numeral 27 denotes a paper feed cassette mounted in the lower part of the printer, in which recording materials P are stacked and stored. The recording material P in the paper feed cassette 27 is separated and fed one by one by a paper feed roller 28 and a separating member, and is transferred to a transfer portion at a predetermined control timing along a path of a sheet path 29, a pair of registration rollers 30, and a sheet path 31. Will be fed.

The recording material P on which the toner image has been transferred at the transfer portion is sequentially separated from the surface of the rotating photosensitive drum 21 and introduced into the heating and fixing device 10 as a heating device to fix the toner image (heating and heating). Pressure permanent imaging)
The sheet is sent to a sheet discharge tray 34 via a sheet path 32 and a sheet discharge roller 33.

On the other hand, the rotating photosensitive drum 21 after the recording material is separated
The surface is the cleaning blade 26 of the cleaning device 26.
The cleaning is performed by removing the adhered residue such as the toner remaining after transfer by a, and the image is repeatedly provided for image formation.

<Others> a) Resistance heater 1 of ceramic heater as heater 1
b · 1c may have a single-line configuration or a multi-line configuration of three or more.

B) As a means for protecting the heating element 1 from overheating, a safety element, for example, a temperature fuse or a thermoswitch is interposed in series with the power supply line for the AC line of the heating element 1 and brought into contact with or close to the heating element 1. It may be arranged by making it.

C) The pressing member need not be a roller. For example, it can be a belt member.

D) The reference for transporting the material to be heated may be the one-side transport reference or the two-side transport reference.

E) In the present invention, the heating device is not limited to the heat fixing device of the embodiment, but may be an image heating device for heating a recording material carrying an image to improve the surface properties such as gloss.
Means and devices for heating the material to be heated, such as an image heating device to be assumed, a heating and drying device for the material to be heated, and a heating laminating device, are widely included.

[0097]

As described above, according to the present invention, in a film heating type heating apparatus, the reduction of the nip width of the non-sheet passing portion with respect to the nip width of the sheet passing portion when passing small-sized thick paper is suppressed. The efficiency of heat transfer from the heating element to the film and the pressure member in the paper passing portion can be increased, the temperature rise in the non-paper passing portion can be suppressed, and the adverse effect due to the temperature rise in the non-paper passing portion can be prevented.

That is, in the heat fixing device, it is possible to prevent the occurrence of inconvenience on the image due to hot offset or the like, and it is possible to prevent the heating element (heater) from cracking and the heat loss of the heating element supporting member, the film, the pressure roller and the like. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of a heating device (film heating type image heating and fixing device) according to the present invention.

FIGS. 2A and 2B are enlarged cross-sectional schematic diagrams of a main part, in which FIG. 2A is a diagram when a recording material is not sandwiched in a fixing nip portion, and FIG.

FIG. 3A is a front side model diagram and a block diagram of an energization system in which a middle part of the heating element is omitted and partially cut away, and FIG.

FIG. 4 is an explanatory diagram of a nip width and a pushing amount of an elastic pressure roller.

FIG. 5 is a diagram showing a relationship between a pressing force and a nip width.

FIG. 6 is a diagram showing a relationship between a pressing force and a pushing amount.

FIGS. 7A, 7B, and 7C are schematic diagrams of another configuration example of a film heating type heating device.

FIG. 8 is a schematic view of a main part of an example of a heating apparatus using an electromagnetic induction heating member as a heating body.

FIG. 9 is a schematic diagram of an example of an image forming apparatus.

[Explanation of symbols]

Reference Signs List 1 heating element (ceramic heater or electromagnetic induction heating member) 2 support member (heater stay) 3 film 4 elastic pressure roller P material to be heated (recording material) N, Na, Nb, Nx nip portion or nip width

Claims (2)

[Claims] 1. A nip portion comprising a fixedly supported heating element, a film sliding on the heating element, and an elastic pressing member forming a nip with the heating element via the film. In a heating device in which a material to be heated is sandwiched and conveyed between the film and the elastic pressing member, and the material to be heated is heated by heat from the heating body through the film, the film in the nip portion and When the heated material is not sandwiched between the elastic pressing member and the nip portion, the width in the heated material transport direction is 60% or more of the width when the heated material having a thickness of 0.5 mm is sandwiched therebetween. A heating device, characterized in that: 2. An image forming apparatus comprising the heating device according to claim 1 as image fixing means.