JPH10186911A - Heat fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of tailing of images, to obviate the crack of a heater and to well maintain fixability by providing the device with an electric exothermic resistance layer so as to protrude to the upstream side of the flow of a recording material to be passed from a fixing nip. SOLUTION: A fixing film 13 of a small heat capacity consists of films of polyimide, polyamide imide, etc., having heat resistance and thermoplasticity in order to enable a quick start. The heater 11 for heating is the member for electrical heating obtd. by forming the electric exothermic resistance layer 11b on the front surface 11a of a high isolation ceramic substrate 11b consisting of aluminum nitride or silicon carbide by screen printing, etc., along the longitudinal direction. The electric exothermic resistance layer 11b is formed to protrude to the upstream side of the flow of the recording material to be passed from the fixing nip. A temp. detecting element, such as thermistor, for detecting the temp. of the ceramic substrate 11a heated up according to the heat generation of the electric exothermic resistance layer 11b is disposed on the rear surface of the ceramic substrate 11b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus employing an image forming process such as an electrophotographic system or an electrostatic recording system. An unfixed toner image of image information formed and carried on a transfer method or a direct method on an electrostatic recording paper, etc.
The present invention relates to a heat fixing device that performs a heat fixing process as a fixed image.

[0002]

2. Description of the Related Art Conventionally, as a heat fixing device of an image forming apparatus employing an electrophotographic or electrostatic recording type image forming process, a heat roller type or a film heating type has been widely used. In particular, a method in which power is not supplied to the heat fixing device during standby and power consumption is kept as low as possible, specifically, a film heating method in which a toner image on a recording material is fixed through a film between a heater and a pressure roller. The heat fixing method is described in JP-A-63-313182 and JP-A-Hei 2
JP-A-157878 / JP-A-4-44075 /
It is proposed in Japanese Patent Application Laid-Open No. 4-204980. FIG. 9 shows a schematic configuration of a main part of this apparatus. That is, in FIG. 9, a heating member (heater, hereinafter referred to as a heater) fixedly supported by a stay holder (support) 42 in FIG.
41, and an elastic pressure roller 50 that presses the heater 41 with a heat-resistant thin film (hereinafter, referred to as a fixing film) 43 therebetween to form a nip portion (fixing nip portion) N having a predetermined nip width. The heater 41 is heated and controlled to a predetermined temperature by energization. The fixing film 43 is conveyed and moved in the direction of arrow a while being in close contact with and sliding on the surface of the heater 41 at the fixing nip portion N by a driving means (not shown) or the rotational force of the pressure roller 50. Alternatively, it is a rolled end-shaped web-shaped member.

[0003] The heater 41 is heated and controlled to a predetermined temperature,
With the fixing film 43 conveyed and moved in the direction of the arrow, the recording material P on which the unfixed toner image t is formed and carried between the fixing film 43 in the fixing nip portion N and the pressure roller 50 is heated. When the recording material P is introduced as described above, the recording material P is brought into close contact with the surface of the fixing film 43 and is nipped and conveyed together with the fixing film 43 at the fixing nip N by the pressing roller 50. In the fixing nip portion N, the recording material P and the toner image t are heated by the heater 41 via the fixing film 43, and the toner image t on the recording material P is heated and fixed.
The recording material that has passed through the fixing nip N is peeled off from the surface of the fixing film 43 and is conveyed.

Generally, a ceramic heater is used as the heater 41 as a heating member. The ceramic heater includes, for example, an energization heating resistor layer 41b such as silver palladium (Ag / Pd) / Ta ₂ N on the surface of the ceramic substrate 41a made of alumina on the side of the fixing film 43 along the substrate length (direction perpendicular to the drawing). It is formed by screen printing or the like, and the surface on which the heat generating resistance layer is formed is further covered with a thin glass protective layer 41c. When the ceramic heater 41 is energized, the energized heating resistor layer 41b generates heat, and the entire heater including the ceramic substrate 41a and the glass protection layer 41c rapidly rises in temperature. The temperature rise of the heater 41 is detected by the temperature detecting means 44 provided on the back surface of the heater 41 and is fed back to a power supply control unit (not shown). The energization control unit controls the power supply to the energization heating resistance layer 41b so that the heater temperature detected by the temperature detection unit 44 is maintained at a predetermined substantially constant temperature (fixing temperature), and the heater 41 is heated to the predetermined fixing temperature.・ The temperature is adjusted.

The fixing film 43 has a very small thickness of 20 to 70 μm in order to efficiently apply the heat of the heater 41 to the recording material P as the material to be heated in the fixing nip portion N. The fixing film 43 has a three-layer structure including a film base layer, a primer layer, and a release layer. The film base layer is on the heater side, and the release layer is on the pressure roller side. The film base layer is a glass protective layer 41c of the heater 41.
Higher insulating polyimide, polyamide imide, PE
It is made of EK or the like and has heat resistance and high elasticity. Also,
The mechanical strength such as the tear strength of the entire fixing film 43 is maintained by the film base layer. The primer layer has a thickness of 2
It is formed of a thin layer of about 6 μm. The release layer is a toner offset prevention layer for the fixing film 43,
Fluororesin such as PFA, PTFE, FEP, etc.
m.

The stay holder 42 is formed of, for example, a heat-resistant plastic member and holds the heater 41 and also serves as a conveyance guide for the fixing film 43.

In a film heating type heating apparatus using such a thin film 43 for fixing, the pressing roller 50 having the elastic layer 51 is used for the high rigidity of the ceramic heater 41 as a heating member. Following the flat lower surface of the pressed heater 41, the flattening is performed at the pressing portion to form a fixing nip portion N having a predetermined width, and only the fixing nip portion N is heated, thereby realizing quick-start heat fixing.

The structure of the heater 41 used in the above-described film heating apparatus will be described in detail with reference to FIG. FIG.
The width W of the current-carrying resistance layer 41b of the heater 41
Are included in a fixing nip N for fixing a toner image on a recording material via the fixing film 43. As a result, the heat generated by energizing the current-carrying resistance layer 41b of the heater 41 is applied to the recording material P conveyed between the fixing film 43 and the pressure roller 50 between the fixing nips N. It acts to melt and fix the upper toner image t.

Further, as shown in FIG. 10, on the back surface of the heater 41, a temperature detecting element 44 such as a thermistor and a thermal fuse or a thermoswitch for shutting off the power supply to the electric heating resistor layer 41b of the heater 41 at the time of runaway. The thermo protectors 45 are in contact with each other, and are disposed in the transport area of the recording material P having the minimum width that can be transported by the image forming apparatus.

The temperature detecting element 44 heats and fixes the toner image t on the recording material P at an appropriate fixing temperature without causing problems such as poor fixing and high-temperature offset. Is disposed on the back of the heater 41 substantially at the center. On the other hand, as with the temperature detecting element 44, the thermo-protector 45 also includes
Is disposed on the back surface of the heater 41 at substantially the center of the width W.

[0011]

In the above conventional example, the following problems occur. That is, in the film-type fixing device, a transfer material such as paper on which an unfixed image is placed is fixed to a fixing nip (hereinafter abbreviated as nip) formed between a fixing heater and a pressure roller via a film. Heating and fixing is performed while performing predetermined temperature control when passing the toner. However, in a fixing heater using a ceramic substrate made of alumina, the ceramic substrate may be broken if the heating element is not completely within the nip. Because if the heating element is outside the nip,
This is because the protruding portion does not lose heat to the transfer material or the pressure roller, so that the temperature rapidly rises, and only a part of the ceramic substrate expands to apply stress. In order to prevent this, the heating element needs to be thinner than the nip width. On the other hand, if the heating element is made thinner, the fixing property tends to deteriorate. Therefore, it is necessary to supply sufficient electric power to the heating element and heat the heating element to maintain the fixing property in a good condition. In such a case, water vapor spouts from the transfer material rapidly heated in the nip, for example, paper, toward the upstream side of the flow of the transfer material in the nip, thereby causing an image defect called tailing that blows and disturbs the unfixed image ( See FIG. 11). This image distortion problem is particularly noticeable when the paper squeezes in a high humidity environment.
The feature is that the horizontal line is interrupted in some places and the toner is scattered on the upstream side, that is, on the lower side of the paper. The tailing can be eliminated by lowering the power supplied to the heater or lowering the regulated temperature, but this deteriorates the fixing property.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problem of trailing an image, to prevent a heater from cracking, and to maintain good fixability.

[0013]

According to the present invention, the recording material on which an unfixed image is formed is passed between a fixing nip where a fixing member having a heating means and a pressing member are pressed against each other, thereby achieving the above-mentioned object. In a heat fixing device for fixing an unfixed image as a permanent image on a recording material, the fixing member includes:
It consists of a thin film and a heater in which an energized heating resistance layer that generates heat by energization is formed on a substrate made of ceramics of aluminum nitride or silicon carbide, and the energized heating resistance layer passes through the fixing nip and passes through the fixing nip. A heat fixing device is provided so as to protrude upstream of a flow of a recording material to be made.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the heat fixing apparatus having the above-described structure, the heating element of the heater is located on the upstream side of the flow of the recording material passed through the nip (hereinafter, may be simply referred to as upstream).
The so-called pre-heating effect, in which the unfixed image before the nip enters through the film, is preliminarily heated, and the so-called pre-heating effect acts on the heat of the portion formed so as to improve the image problem of the tailing described above. Is possible. On the other hand, regarding substrate cracking due to protrusion from the nip portion of the heating element, which has been a problem with ceramic substrates of alumina conventionally,
Aluminum nitride or silicon carbide ceramics have no problem since they have high thermal conductivity and low thermal expansion coefficient.

Hereinafter, a specific example of the device according to the present invention will be described as an example.

[0016]

【Example】

Embodiment 1 FIG. 1 is a configuration diagram of an example of an image forming apparatus according to the present invention.

In FIG. 1, reference numeral 1 denotes a photosensitive drum;
A photosensitive material such as PC, amorphous Se, and amorphous Si is formed on a cylindrical substrate made of aluminum, nickel, or the like. The photosensitive drum 1 is driven to rotate in the direction of the arrow, and its surface is uniformly charged by a charging roller 2 as a charging device. Next, ON / OFF according to the image information
Scanning exposure is performed by the laser beam 3 controlled to be OFF, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a development method, a jumping development method, a two-component development method, an FEED development method, or the like is used, and a combination of image exposure and reversal development is often used.

The visualized toner image is transferred from the photosensitive drum 1 onto the recording material P conveyed at a predetermined timing by a transfer roller 5 as a transfer device. At this time, the recording material P is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressing force. Recording material P to which this toner image has been transferred
Is transported to the fixing device 6 and fixed as a permanent image.
On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

FIG. 2 shows the configuration of the heat fixing device 6 according to the present invention. 2, the fixing member 10 includes the following members. Reference numeral 13 denotes a fixing film having a small heat capacity. Polyimide, polyamideimide, PEEK, PES, PPS, PFA, P having heat resistance and thermoplasticity with a thickness of 100 μm or less to enable quick start.
It is made of a film such as TFE and FEP. A film having sufficient strength to form a long-life heat fixing device and having excellent durability must have a thickness of 20 μm or more. Therefore, the thickness of the fixing film 13 is 20 μm.
It is optimal that the thickness is at least m and at most 100 μm. Furthermore, in order to prevent offset and ensure the separation of the recording material, the surface layer is made of PF.
A, PTFE, FEP, or a heat-resistant resin having good release properties such as silicone resin is mixed or coated alone.
Numeral 11 denotes a heating heater provided inside the fixing film 13, which heats a nip portion where the toner image on the recording material is melted and fixed. Details of the configuration of the heater 11 will be described later. 12 is a heater 11 for heating
And a heat insulating stay holder for preventing heat radiation in the direction opposite to the nip, and is formed of a liquid crystal polymer, a phenol resin, PPS, PEEK, or the like, and the fixing film 13 is loosely fitted around the fixing film 13 with a margin. , Are rotatably arranged in the direction of the arrow. Fixing film 1
3 rotates while rubbing against the internal heater 11 and the heat-insulating stay holder 12, so that the frictional resistance between the heater 11 and the heat-insulating stay holder 12 and the fixing film 13 must be reduced. Therefore, a small amount of lubricant such as heat-resistant grease is interposed between the surfaces of the heater 11 and the heat insulating stay holder 12. Thus, the fixing film 13 can rotate smoothly.

The pressing member 20 comprises an elastic layer 22 formed by foaming heat-resistant rubber such as silicon rubber or fluorine rubber or silicon rubber on the outside of a cored bar 21.
A release layer 23 of FA, PTFE, FEP or the like may be formed. The pressing member 20 is sufficiently pressed in the direction of the fixing member 10 by pressing means (not shown) from both ends in the longitudinal direction so as to form nip portions necessary for heat fixing. , And is rotationally driven in the direction of the arrow by a rotational drive (not shown) through a metal core 21. As a result, the fixing film 13 is driven and rotated on the outside of the stay holder 12 in the direction of the arrow in the figure. Or fixing film 13
A driving roller (not shown) is provided in the inside, and the fixing film 13 is rotated by rotating the driving roller.

Next, the structure of the heater 11 according to the present invention will be described with reference to FIG. In FIG. 3, a heater 1 for heating is used.
Reference numeral 1 denotes a heat-generating heat source such as Ag / Pd (silver palladium), RuO ₂ , or Ta ₂ N on the surface of a highly insulating ceramic substrate 11a (about 0.64 mm in thickness) of aluminum nitride or silicon carbide. The resistance layer 11b is formed to a thickness of about 10 μm and a width of 1 to 5 by screen printing or the like.
It is a current-carrying heating member formed by applying a linear or narrow band of about mm. In this example, the current-carrying resistance layer 11b is 5
mm pattern.

On the back surface of the ceramic substrate 11a, a temperature detecting element 1 such as a thermistor for detecting the temperature of the ceramic substrate which has been heated in accordance with the heat generated by the current-generating resistance layer 11b.
4 are provided. In response to the signal from the temperature detecting element 14, the duty ratio, the wave number, etc. of the voltage applied to the energizing heat generating resistance layer 11b from the electrode portion 11d formed of Ag / Pt (silver / platinum) at the longitudinal end portion. By appropriately controlling the temperature, the temperature regulation temperature in the fixing nip is kept almost constant,
Heating necessary for fixing the toner image on the recording material is performed.
DC conduction from the temperature detection element 14 to a temperature control unit (not shown) is achieved by a connector (not shown) via a DC conduction unit 14a and a DC electrode unit 14b. On the surface of the heat-generating resistance layer 11b of the heater 11, an insulating protective layer 11c such as a thin glass coat which is electrically insulated and can withstand rubbing with the fixing film is provided.

Heating resistance layer 11b of heater 11
FIG. 4 is a sectional view showing the positional relationship between the fixing nip and the fixing nip.
In FIG. 4, dotted lines indicate the fixing nip, the width of the heating element, and the protruding portion of the heating element that protrudes from the nip on the upstream side of the flow of the recording material to be passed. The heating element has a width of 5 mm as described above. The nip width was about 5 mm, and the heating element was formed so as to protrude about 2 mm upstream from the nip. As a result of examining the tailing level by changing the amount of protrusion of the heating element in the above configuration, it was found in Table 1 that the material of the substrate was almost the same regardless of whether the material was aluminum nitride or silicon carbide.

[0024]

[Table 1] The protrusion amount of the heating element of -1 mm means that the upstream side of the heating element is located at a position 1 mm inside from the nip end. When the protrusion amount of the heating element was in the range of -1 mm to 0 mm, the tailing level was poor. This bad level is a level that is not practical for an image having many horizontal lines due to severe tailing as shown in FIG. 11 depending on the paper type (recycled paper or thick paper). Heating element protrusion 0.5m
The level of "m" is a level that is noticeable if pointed out under similar conditions and does not need to be a particular problem. When the extruding amount of the heating element is 1.0 mm or more, the tailing is improved to a level that does not cause any problem.

FIG. 5 shows a portion where preheating is performed.
FIG. 5 shows the fixing film 13 and the pressure roller 20 in FIG.
Only shows. Preheating is performed in the portion circled in FIG. The jet of water vapor that causes tailing occurs mainly near the start of the nip portion that is pressed by the pressure roller. According to the present invention, the width of the heating element is increased to about 2 mm outside the nip on the upstream side of the nip, so that when the paper enters the nip portion, the toner of the unfixed image has already been supposedly attached by the preheating effect, There is no worry about being blown away. 2m like this
The reason why the heating element could be provided upstream of the nip by as much as about m was that the thermal conductivity of aluminum nitride (AlN) or silicon carbide as the raw material of the substrate was about 9 to 9 as compared with alumina (Al ₂ O ₃ ). 14 times, the coefficient of thermal expansion is about 6/10 to 5/10
Therefore, it is possible to prevent the heat near the heating element outside the nip from being conducted around, thereby preventing the temperature from being abnormally high, and the low thermal expansion, so that the deformation of the ceramic substrate is small and there is no danger of cracking. Table 2 shows the thermal characteristics of aluminum nitride and silicon carbide.

[0026]

[Table 2] For comparison, the relationship between the amount of protrusion of the heating element upstream of the nip and the tailing was examined using a heater using a conventional ceramic substrate using alumina. Table 3 shows the results.

[0027]

[Table 3] As can be seen from Table 3, when the heating element was pushed out of the nip in an attempt to improve the tailing, it was confirmed that the heater was cracked and could not withstand use.

As described above, the heater using the aluminum nitride or silicon carbide substrate is provided with the heating element protruding from the nip upstream of the nip, so that the unfixed image on the recording material before the nip is provided. The assumption of the preheating effect can solve the problem of tailing that disturbs the image.

Embodiment 2 Next, a second embodiment of the present invention will be described. The configuration of the entire apparatus is the same as that of FIG. 1 shown in the first embodiment, and the configuration in the heat fixing device and the configuration of the heater for heating are also the same as those of FIG. I do.

FIG. 6 shows a cross section of an aluminum nitride heater and a fixing device which are features of this embodiment. The feature of the heater 11 using the aluminum nitride ceramic substrate of the present example is that the fixing nip has an aluminum nitride substrate directly via the film 13, and the heating element 11b is provided on the surface of the substrate opposite to the nip. The material, width and dimensions of the heating element are the same as in the first embodiment. Glass 11c is coated on the heating element for insulation.

In the first embodiment, the heat generated by the heating element is transmitted through glass having a thickness of about 0.06 mm. In this embodiment, the heat is transmitted through a ceramic substrate of aluminum nitride having a thickness of about 0.6 mm. Although this configuration may seem inefficient at first glance, aluminum nitride is about 10 times less than glass.
Since the thermal conductivity is 0 times larger, even if the thickness is 10 times, the thermal efficiency is improved 10 times. In this example, an experiment was performed on the amount of protrusion and the level of tailing in the same manner as in the previous example, and the results shown in Table 4 were obtained.

[0032]

[Table 4] In this example, since the heat conduction of the substrate itself was good, the preheating effect was exhibited even if the amount of protrusion of the heating element was small. That is, even when the protrusion amount is +0.5 mm, the tailing level is improved, and it can be seen that the good heat conduction of the substrate enhances the preheating effect.

As described above, even in the configuration in which the heating element is provided on the side opposite to the nip of the aluminum nitride ceramic substrate, the heating element is formed so as to protrude upstream of the nip, so that the unfixed image before the nip enters the nip. The preheat effect works to improve the tailing problem.

Embodiment 3 A third embodiment of the present invention will be described. The configuration diagram of the device is the same as in FIGS. FIG. 7 shows a cross-sectional view of the vicinity of the nip portion of this example. It is characterized in that the heating element of the heater is not a single type with a width of 5 mm in the above two examples, but a folded type with a width of 2.5 mm. The pattern of the heating element of the heater is as shown in FIG. Table 5 shows the experimental results of the relationship between the amount of protrusion of the heating element and the tailing level when the substrate material was aluminum nitride in this example.

[0035]

[Table 5] The effect on tailing was the same as in Example 1. When the protrusion amount is +2.5 mm, the upstream heating element is completely outside the nip upstream. At this time, it was feared that the fixing property might be deteriorated. However, since the aluminum nitride substrate had good heat conduction, heat was transmitted between the two heating elements, and the fixing was sufficiently performed in the fixing nip. The problem of poor fixability did not occur.

[0036]

As described above, according to the present invention,
Heat generated from the heating element outside the nip upstream of the nip of the heater heating element preliminarily heats the unfixed image immediately before entering the nip through the film and presumably attaches the image, so that the so-called preheating effect works to tail the image. Problem can be improved. Also, there is no occurrence of substrate cracking which has conventionally been a problem with alumina ceramic substrates.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of a heat fixing device according to the present invention.

FIG. 3 is a schematic configuration diagram of a heater according to the present invention.

FIG. 4 is a schematic cross-sectional view showing a first example near a fixing nip portion in the present invention.

FIG. 5 is a diagram showing a portion where preheating is performed in the present invention.

FIG. 6 is a schematic cross-sectional view showing a second example near the fixing nip portion in the present invention.

FIG. 7 is a schematic cross-sectional view showing a third example near the fixing nip portion in the present invention.

FIG. 8 is a schematic configuration diagram of a heater according to the present invention.

FIG. 9 is a schematic configuration diagram of a heat fixing device according to a conventional example.

FIG. 10 is a schematic configuration diagram of a heater in a conventional example.

FIG. 11 is an explanatory diagram of tailing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Image exposure 4 Developing device 5 Transfer roller 6 Fixing device 7 Cleaning device (cleaner) 10 Fixing member 11 Heater 11a Ceramic substrate 11b Electric heating resistance layer 11c Insulation protection layer 11d Electrode section 12 Heat insulation stay holder 13 Fixing Film 14 Temperature detecting element 14a DC conducting part 14b DC electrode part 20 Pressing member 21 Core metal 22 Elastic layer 23 Releasable layer 41 Heating member (heater) 41a Ceramic substrate 41b Electric heating resistor layer 41c Glass protective layer 42 Stay holder 43 Thin film (fixing film) 44 Temperature detecting means 45 Thermo protector 50 Pressure roller N Fixing nip (nip) P Recording material t Toner image

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masami Takeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (1)

[Claims] An unfixed image is formed on a recording material by passing the recording material on which the unfixed image is formed through a fixing nip where a fixing member having a heating unit and a pressing member are pressed against each other. A fixing device, wherein the fixing member comprises a heater having a current-carrying resistance layer formed on a substrate made of ceramics of aluminum nitride or silicon carbide, and a thin film. A heating and fixing device, wherein the heating and heating resistance layer is provided so as to protrude from a fixing nip to an upstream side of a flow of the recording material to be passed.