JPH0996979A - Heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly heat a material which is to be heated, in a heating device which carries the material while changing an amount of nip in order to carry it without making a wrinkle. SOLUTION: The heating device carries a film 2 and a material P, which is to be heated, by rotating a pressure roller 4 which makes a nip N set so that the nip width of the roller middle part is smaller than that of each of the roller ends, and it heats the material P in the nip N by means of a heater 3 (heating means). In the heating device, a uniform quantity of heat is transferred to the material P by changing, according to the nip widths, a quantity of heat that is transferred to the material P from the heater 3.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to heating a heat-resistant film on one surface side, and bringing a material to be heated into close contact with the other surface side,
The present invention relates to a heating device for applying heat energy to the heated material through the film, and more particularly to a technique for fixing an unfixed toner image carried on the heated material of an image forming apparatus using an electrophotographic method.

[0002]

2. Description of the Related Art A conventional heating device for heating a recording material for fixing an image, for example, has a heating roller maintained at a predetermined temperature and an elastic layer. A heat roller method is widely used in which a recording material is held and conveyed by a pressure roller that is in pressure contact with a heating roller while heating.

In addition, various systems and configurations such as a flash heating system, an oven heating system, and a hot plate heating system are known and put to practical use.

Recently, a heating means fixed and supported, a heat-resistant film (fixing film) conveyed while being pressed against the heating means, and a pressure member for closely contacting a recording material with the heating means via the film. A fixing device of a system / structure that heats and fixes the unfixed image formed and carried on the recording material surface by transferring the heat of the heating means to the recording material through the film (film heating Method) has been adopted.

In such a film heating system,
As the heating means, one having a relatively low heat capacity can be used. For this reason, it is possible to quickly raise the temperature to a predetermined temperature as compared with the conventional heating method which is a heating roller method, and it is possible to save power and shorten the wait time (quick start).

[0006]

In the film heating apparatus, a recording material carrying a toner image is nipped and conveyed to a fixing nip composed of a fixing film and a pressure roller to heat and fix the recording material.

However, when the width of the fixing nip is larger in the central portion than in the end portions, wrinkles occur on the conveyed recording material. This is because when the nip width in the central portion becomes larger than the end portions, a biasing force acts from the both end portions toward the central portion on the fixing film and the recording material.

In order to prevent this wrinkle, the width of the fixing nip may be made smaller in the central portion than in the end portions. Therefore, for example, a method is used in which both ends of the pressure roller are pressed by springs to increase the width of the fixing nip at the ends, or the center of the pressure roller is made slightly smaller than both ends. Has been done.

However, since the size of the fixing nip width is closely related to the fixing property, if the central nip is made thin, the amount of heat transferred to the recording material will be different, and as a result, the fixing at the end portion and the central portion will be fixed. There is a problem that uniform fixing cannot be performed because of different properties.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to heat a material to be heated without wrinkling by changing the nip amount and carrying it. In the above, it is possible to uniformly heat the material to be heated.

[0011]

In order to achieve the above object, in the present invention, a film for transferring heat from a heating means which is in contact with one surface to a material to be heated which is in contact with the other surface. And the other surface of the film to press the material to be heated to form a nip having a narrower width at the center of the roller than at the end of the roller. A heating device for transporting the film and the material to be heated by rotating the pressure roller, and heating the material to be heated in the nip; The amount of heat transmitted to the heated material is changed in accordance with the nip width to transfer a uniform amount of heat to the material to be heated.

However, it is also preferable to make the thermal conductivity of the film larger in the central portion of the film than in the end portions of the film in the direction orthogonal to the conveying direction.

It is also preferable to make the thickness of the film smaller in the central portion of the film than in the end portions of the film in the direction orthogonal to the transport direction.

It is also preferable that the heat generation distribution of the heating means is made larger in the central portion of the heating means than in the end portions of the heating means in the direction orthogonal to the carrying direction.

It is also preferable to make the width of the heating means in the carrying direction larger in the central part of the heating means than in the end part of the heating means in the direction orthogonal to the carrying direction.

Further, the heating means is provided with a protective layer for protecting the contact surface with the film, and the thickness of the protective layer is made thinner at the central portion of the heating means than at the end portions of the heating means in the direction orthogonal to the conveying direction.

The image forming apparatus is provided with the above-mentioned heating device and image forming means for forming an image on the recording material, and an unfixed image of the recording material on which the image is formed is fixed by the heating device. Let

Therefore, a uniform amount of heat is transferred from the heating means to the material to be heated, regardless of the size of the nip width in the direction perpendicular to the direction in which the material to be heated is conveyed.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(Embodiment 1) A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a sectional view of a heating device according to an embodiment of the present invention.

In FIG. 1, reference numeral 2 denotes an endless tubular heat-resistant film, which is a heater 3 as a heating means.
Is externally fitted to the stay 1 including. The inner peripheral length of the endless heat-resistant film 2 and the outer peripheral length of the stay 1 including the heater 3 are larger than those of the film 2 by, for example, about 3 mm. Therefore, the film 2 has a margin for the peripheral length of the stay 1. It fits loosely.

The film 2 has a thickness of 100 μm in order to reduce the heat capacity and improve the quick start property.
m, preferably 20 μm or more and 50 μm or less, and the material is a single layer of PTFE, PFA, FEP, or polyimide, polyamide imide, PEE
K, PES, PTFE, PFA,
A composite layer film coated with FEP or the like can be used. In this embodiment, the outer peripheral surface of the polyimide film is coated with PTFE.

The heater 3 is formed by coating an electric resistance material such as Ag / Pd (silver palladium) on the surface of a substrate made of alumina or the like with a thickness of about 10 μm and a width of 1 to 5 mm by screen printing or the like. The protective layer 7 is coated with glass, fluororesin or the like.

A pressure roller 4 is brought into pressure contact with the heater 3 at an opposed position across the film 2 to form a nip. The pressure roller 4 is composed of a cored bar 4a and a heat-resistant rubber 4b having a good releasability such as silicone rubber, and is driven by a driving means (not shown) from the end of the cored bar 4a.
Along with this driving, the film 2 is also rotated at the same time.

In the temperature control in the apparatus of this embodiment, the output of the thermistor 5 which is the temperature detecting means provided on the heater 3 is A / D converted and the CPU 1 which is the temperature controlling means.
It is performed by setting the AC voltage applied to the heater 3 by the triac 11 to a desired value by phase, wave number control, etc. based on the information.

That is, if the temperature detected by the thermistor 5 is lower than a predetermined set temperature, the heater 3 is heated, and if it is high, the heater 3 is cooled by controlling the energization to fix the temperature of the heater. Sometimes the temperature is adjusted to keep it constant.

Therefore, the sheet-shaped recording material P as a heated material carrying the unfixed powder toner image is conveyed to the nip portion N between the heater 3 and the pressure roller 4 formed via the film 2. Then, the unfixed powder toner image PT on the recording material P is melted by the application of heat and pressure in the nip portion N and is fixed on the recording material P.

As described above, the image heating apparatus according to the present embodiment can be used as a fixing device of an image forming apparatus such as a copying machine or a printer, and a print command is issued after the main switch of the image forming apparatus is turned on. The heater 3 is started to be energized, and the heater 3 is stopped in a standby state waiting for a print command.

By the way, the nip formed by the heater, the fixing film, and the pressure roller must be made narrower in the central portion than in the end portions when the nip is passed through as described in the section of the prior art. The recording material P is wrinkled. FIG.
FIG. 4 is a diagram showing a mechanism of wrinkles. Here, in order to describe the case where the nip width of the central portion is narrower than the nip width of the end portion, the left side of the drawing is the end portion and the right side of the drawing is the central portion.

Since the larger the nip width is, the larger the conveying force is. Therefore, when the nip width is different between the end portion and the central portion, the conveying force is different between the end portion and the central portion. As a result, the center axis of the film is inclined by α ° with respect to the stay, depending on the degree of difference between the inner circumference of the film and the circumference of the stay. The force F perpendicular to the longitudinal direction of the pressure roller causes the film to be biased by a force of F sin α °.

The recording material P passing through the nip is also subjected to the same offset force. That is, the recording material P approaches the side with the larger nip width. Therefore, if the nip width in the central portion is smaller than that in the end portion, the recording material P will be closer to the end portion from the central portion, and wrinkles will not occur.

The heat generated by the heater 3 is transferred to the recording material P via the film 2. Therefore, the amount of heat transferred to the recording material P changes depending on the thermal conductivity of the film 2. Therefore, by using a film in which the thermal conductivity of the central portion having a smaller nip width than that of the end portion is increased, heat can be transferred to the recording material P at the same degree as that of the end portion even in the central portion.

FIG. 3 is a diagram showing the nip width N1 and the thermal conductivity C1 of the film of the heating device of the present embodiment along the direction perpendicular to the transport direction. Since the fixing property of the heating device is affected by both the nip width N1 and the thermal conductivity C1 of the film, the effects of both are canceled as in T1 of FIG. 3, and the fixing property becomes substantially uniform in the direction perpendicular to the conveying direction. .

The thermal conductivity of the film is such that the polyimide film has a filler for improving the thermal conductivity, such as BN.
It can be improved by adding (boron nitride). It is also possible to give the distribution of the thermal conductivity of the fixing film in the direction perpendicular to the paper conveying direction by continuously changing the amount of the filler mixed.

As described above, by making the nip width smaller in the central portion than in the end portions and improving the thermal conductivity of the film in the central portion from the end portions, wrinkles do not occur,
In addition, uniform fixability can be secured at any position in the direction perpendicular to the transport direction.

(Embodiment 2) As a method of compensating for the difference in fixing property in the direction perpendicular to the carrying direction by changing the width of the nip at the end and the center, the heat generation distribution of the heater 3 is changed from the end to the center. You may use the method of enlarging.

FIG. 4 is a view showing the nip width N2 and the heat generation distribution H2 of the heater of the heating device of the present embodiment along the direction perpendicular to the carrying direction. Fixing property of heating device is nip width N
2 and the heat generation distribution H2 of the heater, the effects of both are offset as shown by T2 in FIG. 4, and the fixability becomes substantially uniform in the direction perpendicular to the paper conveyance direction.

In order to give the heater a desired heat generation distribution, it is necessary to give the heater an appropriate resistance value distribution. Specifically, a method of giving a distribution to the resistance value of the electric resistance material which is a heating element, a method of giving a distribution to the volume resistance of the electric resistance material (a heating element width or a heating element thickness), or a heater A method such as giving a distribution to the thickness of the protective layer can be applied. In the present embodiment, the heater has a heat generation distribution by providing a distribution in the thickness of the heating element.

(Embodiment 3) As a method of compensating for the difference in fixing property in the direction perpendicular to the conveying direction by changing the nip width at the end and the central part, the width of the heating element of the heater from the end to the central part. You may use the method of enlarging.

FIG. 5 is a view showing the nip width N3 of the heating device of the present embodiment and the heating element width HW3 of the heater along the direction perpendicular to the carrying direction. The larger the heating element width HW3, the longer the heating time, and the better the fixability.

Since the fixing property of the heating device is influenced by both the nip width N3 and the heating element width HW3 of the heater, the influences of the both are canceled as in T3 of FIG. 5, and the fixing is performed in the direction perpendicular to the conveying direction. The properties are almost uniform.

However, if the heating element is not inside the nip, the contribution to the fixing property is small. Therefore, it is preferable that the heating element is inside the nip.

If the width of the heating element is simply widened, the resistance value of the heater in that portion is lowered and the amount of heat generation is reduced. In order to prevent this, as the width of the heating element of the heater is increased, the heating element must be thinned, or an electric resistance material having a high volume resistance value must be used. In the present embodiment, the thickness of the heating element is reduced as the heating element width of the heater is increased, so that the heater has a substantially uniform heat generation distribution in the direction perpendicular to the transport direction.

(Embodiment 4) As a method of compensating for the difference in fixing property in the direction perpendicular to the conveying direction by changing the nip width at the end and the center, the film is made thinner at the center than at the end. Any method may be used.

FIG. 6 is a view showing the nip width N4, the film thickness F4 and the amount of heat transfer C4 thereof in the heating device of the present embodiment along the direction perpendicular to the transport direction. Since the fixing property of the heating device is affected by both the nip width N4 and the heat transfer amount C4 of the film, the effects of both are canceled out as in T4 of FIG. 6, and the fixing property is substantially uniform in the direction perpendicular to the transport direction. Becomes

(Embodiment 5) As a method of compensating for the difference in fixability between the conveyance direction and the direction perpendicular to the nip width by changing the nip width between the end portion and the central portion, the thickness of the heater protective film is changed from the end portion to the central portion. You may use the method of thinning.

FIG. 7 is a diagram showing the nip width N5 of the heating device of the present embodiment, the thickness HT5 of the protective film of the heater, and the heat generation amount C5 of the heater surface along the direction perpendicular to the carrying direction. Since the fixability of the heating device is influenced by both the nip width N5 and the heat generation amount C5 of the heater surface, the influences of both are canceled out as in T5 of FIG. 7, and the fixability is almost equal in the direction perpendicular to the transport direction. Be uniform.

(Embodiment 6) FIG. 8 shows an example of an image forming apparatus incorporating a heat fixing device 115 as a film heating type heating device to which the present invention is applied as shown in the first embodiment. The schematic structure is shown.

The image forming apparatus of this embodiment is an electrophotographic copying apparatus in which a document table reciprocates and a process cartridge is detachable.

Reference numeral 100 denotes an apparatus casing, 101 denotes a reciprocating type document placing table made of a transparent plate member such as a glass plate disposed on an upper surface plate 102 of the apparatus casing, and the apparatus casing upper surface plate 102.
The upper part is driven to reciprocate to the right a and the left a'in the drawing at a predetermined speed.

A document G is placed on the upper surface of the document placing table 101 with the image side to be copied facing downward in accordance with a predetermined placing reference, and the document pressing plate 103 is put on the document and pressed down. Set.

Reference numeral 104 denotes a slit opening serving as a document illuminating section which is opened on the surface of the upper surface plate 102 of the machine casing in a direction perpendicular to the reciprocating direction of the document placing table 101 (direction perpendicular to the paper surface) as a document illuminating section.

The downward image surface of the document G placed and set on the document placing table 101 sequentially passes through the position of the slit opening 104 from the right side to the left side in the reciprocating process of the document placing table 101 to the right a. In the course of the passage, the light L of the lamp 105 is received through the slit opening 104 and the transparent original placing table 101 to be illuminated and scanned, and the original surface reflected light of the illumination scanning light is reflected by the image element array 106 by the photosensitive drum 107. The image is exposed on the surface.

The photosensitive drum 107 is coated with a photosensitive layer such as a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer, and is rotated in a clockwise direction indicated by an arrow b at a predetermined peripheral speed around the central support shaft 108. During the rotation process, the charging device 109 receives a uniform positive or negative charging process, and the uniformly charged surface is subjected to the image formation exposure (slit exposure) of the original image, so that the surface of the photosensitive drum 107 is formed. An electrostatic latent image corresponding to the image-exposed original image is sequentially formed.

The electrostatic latent image is sequentially visualized by a developing device 110 with toner made of resin or the like that is softened and melted by heating, and the toner image as the visualized image is provided with a transfer discharge device 111 as a transfer portion. It moves to the part.

Reference numeral S denotes a cassette in which transfer material sheets P as recording materials are stacked and housed. The sheets in the cassette S are fed out one by one by the rotation of the feeding roller 112, and then the drum is moved by the registration rollers 113. When the leading edge of the toner image forming portion on 107 reaches the portion of the transfer discharger 111, the leading edge of the transfer material sheet P also arrives at the position between the transfer discharger 111 and the photosensitive drum 107 so that they both coincide with each other. It is returned and is synchronously fed.

Then, the toner images on the side of the photosensitive drum 107 are sequentially transferred onto the surface of the fed sheet by the transfer discharger 111.

The sheet to which the toner image has been transferred at the transfer portion is sequentially separated from the surface of the photosensitive drum 107 by a separating means (not shown), and the conveying device 114 performs the same heating and fixing device as that described in the first to fifth embodiments. The unfixed toner image carried to 115 is heated and fixed, and is discharged as an image-formed product (copy) through a discharge roller 116 onto a discharge tray 117 outside the apparatus.

The surface of the photosensitive drum 107 after the image transfer is subjected to removal of adhered contaminants such as transfer residual toner by the cleaning device 118, and is repeatedly used for image formation.

The PC is a process cartridge which is attached / detached to / from the cartridge attaching / detaching portion 120 in the apparatus main body 100.
In the case of the present embodiment, the apparatus main body 10 includes four process devices including a photosensitive drum 107 as an image carrier, a charger 109, a developing device 110, and a cleaning device 118.
0 is detachable and exchangeable.

[0061]

EFFECT OF THE INVENTION The present invention has the above-mentioned configuration and action. In order to convey a heated material without wrinkles, a heating device for changing the nip amount and carrying out heating conveyance is provided in the conveying direction of the heated material. A uniform amount of heat is transferred from the heating means to the material to be heated regardless of the size of the nip width in the perpendicular direction.

Further, in the image forming means provided with this heating means as a heat fixing device, wrinkles do not occur in the conveyed recording material, and moreover, uniform fixing is carried out in the direction perpendicular to the conveying direction of the heated material. It becomes possible.

[Brief description of drawings]

FIG. 1 is a sectional view of a heating device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a mechanism of a film and a recording material leaning toward each other according to the first embodiment of the present invention.

FIG. 3 shows the nip width in the direction perpendicular to the transport direction, the thermal conductivity of the film in the first embodiment of the present invention,
It is a figure which shows distribution of fixability.

FIG. 4 is a diagram showing a nip width in a direction perpendicular to the carrying direction, a heat generation distribution of a heater, and a fixing property distribution in the second embodiment of the present invention.

FIG. 5 is a diagram showing a distribution of a nip width, a heater heating element width of a heater, and a fixing property in a direction perpendicular to the conveyance direction in a third embodiment of the present invention.

FIG. 6 is a diagram showing distributions of a nip width, a film thickness, a heat transfer amount of a film, and a fixability in a direction perpendicular to a transport direction in a fourth embodiment of the present invention.

FIG. 7 is a diagram showing a nip width in a direction perpendicular to the conveyance direction, a thickness of a heater protective film, a heat generation amount on a heater surface, and a distribution of fixability in a fifth embodiment of the present invention. .

FIG. 8 is a schematic view of an example of an image forming apparatus incorporating a heat fixing device as a film heating type heating device according to the present invention.

[Explanation of symbols]

 1 stay as film guide member 2 film 3 heating means 4 pressure roller 5 thermistor (temperature detection means) 10 CPU (temperature control means) P recording material PT toner image

Claims (7)

[Claims] 1. A material to be heated is pressed between a film for transferring heat from a heating means abutting on one surface to a material to be heated which contacts the other surface, and the other surface of the film. ,
A nip having a narrower width is formed at the center of the roller than at the end of the roller. The pressure roller is provided at a position facing the heating means, and the pressure roller is rotated. In a heating device that conveys the film and the material to be heated and heats the material to be heated in the nip, the amount of heat transferred from the heating means to the material to be heated is changed according to the nip width, and a uniform amount of heat is applied to the material to be heated. A heating device characterized by transmitting heat. 2. The heating device according to claim 1, wherein the thermal conductivity of the film is made larger in the central portion of the film than in the end portion of the film in the direction orthogonal to the transport direction. 3. The heating device according to claim 1, wherein the thickness of the film is smaller in the central portion of the film than in the end portion of the film in the direction orthogonal to the transport direction. 4. The heating device according to claim 1, wherein the heat generation distribution of the heating means is made larger in the central portion of the heating means than in the end portions of the heating means in the direction orthogonal to the conveying direction. 5. The heating device according to claim 1, wherein the width of the heating means in the carrying direction is made larger in the central part of the heating means than in the end part of the heating means in a direction orthogonal to the carrying direction. 6. The heating means is provided with a protective layer for protecting the contact surface with the film, and the thickness of the protective layer is made thinner in the central portion of the heating means than in the end portion of the heating means in the direction orthogonal to the transport direction. The heating device according to claim 1 or 4, wherein. 7. An image forming device, comprising: the heating device according to claim 1, 2, 3, 4, 5 or 6, and an image forming means for forming an image on a recording material. An image forming apparatus, wherein an unfixed image on a recording material is fixed by the heating device.