JP2002333788A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device suitable for a color image forming device whose rising time is short by reducing the heat capacity of a heating member while securing the contact area of the heating member with a fixing belt. SOLUTION: The endless fixing belt 2 is sufficiently heated by the heating member 3 constituted by using a surface heating element on the upstream side of a nip between a pressure roller 5 and the belt 2, and an image is fixed at the nip by the belt 2 heated to specified temperature, then only the belt having the small heat capacity existing on a surface layer is heated so that the rise time is shortened by as long as time obtained because the elastic layer 4b of a fixing roller 4 is not heated. Since the image is fixed at the nip after the belt 2 is sufficiently heated by the member 3, the temperature is instantaneously recovered even when the temperature of the belt 2 is lowered at paper passing time, temperature stability becomes excellent, and the fixing property and the gloss of a fixed image are stabilized. Since the member 3 is the surface heating element, the heat capacity is reduced and responsiveness is improved. By arranging the member 3 proximately to the roller 4, space saving and the reduction of cost are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an image forming apparatus, and more particularly, to a belt-type fixing device for shortening a rise time in color fixing.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional belt fixing device. The fixing device 1 is disclosed, for example, in Japanese Patent Application Laid-Open No. 10-307496, and includes a fixing belt 2 between a fixing roller 4 and a heating roller 10.
, And the fixing roller 4 and the pressure roller 5 are in sliding contact with each other via the fixing belt 2. Reference numeral 6 denotes a heater in the pressure roller 5, and reference numeral 11 denotes a heater in the heating roller 10.

In the configuration of the fixing device 1, the rising time is increased by pre-heating the fixing belt 2 having a small heat capacity and then fixing the toner on the paper passed through the nip portion between the heating roller 10 and the fixing roller 4. It has a feature that it can be fixed at a low temperature due to its short and wide nip width. However, in order to obtain a contact area between the heater 11 for the heating roller and the fixing belt 2, the outer diameter of the heating roller 10 is required to some extent. At the same time as the heat capacity of the roller 10 and the fixing belt 2 increases, the size of the apparatus also increases.

That is, in order to further reduce the rise time in this method, it is conceivable to reduce the heat capacity of the heating roller 10 as much as possible. When the contact area between the heating roller 10 and the fixing belt 2 is small, the paper and the toner on the paper deprive the heat at the nip portion between the two, and the fixing belt 2 whose temperature has decreased makes one revolution. However, there is a problem that the temperature does not recover and the fixability of the fixing belt after the second rotation deteriorates. Therefore, the contact area between the heating roller 10 and the fixing belt 2 needs to be larger than at least the nip formed by the fixing belt 2 and the pressure roller 10.

It is also conceivable to reduce the heat capacity by reducing the thickness of the heating roller 10. However, if the thickness of the heating roller 10 is reduced to a certain degree or more, the rigidity of the heating roller 10 decreases, and problems such as deformation and bending of the roller occur. However, there is a problem that processing of a thin pipe is difficult, and the processing cost increases.

Further, a halogen heater is often used as the heater 11 which is a heat source of the heating roller 10.
Halogen heaters have poor responsiveness because tungsten reaches a high temperature, and cannot be said to be suitable for high-speed startup because of the large heat capacity of the heater itself.

Further, when small-sized paper is continuously passed through the maximum paper-passing width, the width of the small-sized paper is heated by a heating member by an amount corresponding to the loss of heat, and the temperature recovers. On the other hand, since the outside of the small-sized paper is heated by the heating roller 10 even though the heat is not taken away, a phenomenon occurs in which only the both ends of the fixing belt 2 become hot.

Although there is not much problem when the heat conduction between the fixing belt 2 and the heating roller 10 is very good, when the fixing belt 2 and the heating roller 10 are thin, the heat conduction is small, and this phenomenon becomes remarkable. Therefore, two halogen heaters having a heat generation distribution corresponding to the paper passing size are provided, and when small-sized paper is continuously passed, a method of supplying heat with a heater for small-sized paper is adopted. The cost is increased by the use of the heater, and the heat capacity of the heat source is also increased.

The present invention has been made in view of the above-mentioned conventional problems,
An object of the present invention is to provide a fixing device suitable for a color image forming apparatus having a short rise time while reducing the heat capacity of the heating member while securing a contact area between the heating member and the fixing belt.

[0010]

According to a first aspect of the present invention, there is provided a fixing device comprising: an endless fixing belt stretched between a fixing roller and a heating member; A pressure member facing the fixing roller via a belt-shaped fixing belt, and a heating device for heating and pressing an unfixed toner image carried on a recording material in a nip formed by the fixing belt and the pressure member Wherein the heating member is a substantially semicircular sheet resistance heating element, and the heating member is disposed close to the fixing roller so as to slide.

According to a second aspect of the present invention, in order to achieve the above object, the fixing device according to the first aspect, wherein a radius of curvature of the heating member is equal to or larger than a radius of the fixing roller. .

According to a third aspect of the present invention, in order to achieve the above object, in the fixing device of the first aspect, a contact area between the heating member and the fixing belt is made larger than the nip. It is characterized by the following.

According to a fourth aspect of the present invention, there is provided a fixing device according to any one of the first to third aspects, wherein the heating member comprises an electric insulating layer and a resistive heating layer formed on a substrate. It is a planar heating element formed by laminating layers, wherein the resistance heating layer is formed on the fixing belt side with respect to the substrate.

According to a fifth aspect of the present invention, there is provided a fixing device according to any one of the first to fourth aspects, wherein the base material of the fixing belt is made of a heat-resistant resin such as polyimide or polyamide. It is characterized by being formed.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In the following, description will be made by assigning common reference numerals to parts common to the related art. FIG. 1 is a sectional view showing an embodiment of the fixing device according to the present invention. Fixing device 1
An endless fixing belt 2 that conveys the transfer paper 8, a heating member 3 that stretches the fixing belt 2, a fixing roller 4, and a pressure roller that is disposed to face the fixing roller 4 via the fixing belt 2. Five.

As the base 2a of the fixing belt 2, an endless belt-like base made of a heat-resistant resin is used. As the material of the heat-resistant resin, polyimide, polyamideide, polyetherketone (PEEK), or the like can be used. The thickness of the base 2a is 30 to 10 in consideration of the balance between heat conduction and strength.
It is desirable that the thickness is 0 μm. Since the surface of the fixing belt 2 is brought into pressure contact with the transfer paper 8 and the toner 9, the surface of the fixing belt 2 is covered with a surface release layer 2c such as a fluorine-based resin as a surface release layer having excellent heat resistance and durability. Further, an elastic layer 2b of heat resistant rubber such as silicone rubber or fluoro rubber of about 100 to 300 μm is provided under the surface release layer 2c in order to obtain image uniformity.

The fixing roller 4 has a diameter of, for example, φ30 mm.
A heat-insulating elastic member 4b made of a soft heat-resistant material, for example, foamed silicone rubber, is provided on the outer periphery of the cored bar 4a in order to make the nip width sufficiently large. For example, the thickness of the heat insulating elastic member 4b is about 3 to 6 mm,
Has a surface hardness of about 30 to 50 Hs with AskerC.

The pressure roller 5 is formed by forming a heat-resistant elastic layer 5b made of a fluororesin or silicone rubber on the outer periphery of a cored bar 5a and a surface release layer 5c made of a fluororesin or the like. In order to improve the releasability of the transfer paper 8 from the fixing belt 2, the surface hardness of the pressure roller 5 is made harder than that of the fixing roller 4, and a downward fixing nip portion between the fixing belt 2 and the pressure roller 5. Is formed. Elastic layer 5 of pressure roller 5
b has a thickness of about 1 mm and a surface hardness of Ask
erC is about 70 to 90 Hs. Although a halogen heater 6 for accelerating the temperature rise of the pressure roller is provided in the pressure roller, this is not essential in the present invention.

The heating member 3 is arranged so as to be longer than the maximum sheet passing width of the transfer sheet 8 and to extend along the width direction of the transfer sheet 8. The heating member 3 has a substantially semi-circular outer shape when viewed from the axial direction, and is disposed substantially above a nip formed by the fixing roller 4 and the pressure roller 5 so as to be upwardly tensioned by a base (not shown). is there. Both ends of the heating member 3 in the paper passing direction are provided with R as shown to be curved in an arc shape to maintain rigidity.

The heating member 3 is formed by laminating an electric insulating layer 3b and a resistance heating layer 3c on a thin metal plate 3a made of Fe or Al and having a thickness t of 0.3 to 0.8 mm. It is. The electric insulating layer 3b is made of a material having both heat resistance and electric insulation, such as ceramic or polyimide.

As a method of forming the thin metal layer of the resistance heating layer 3c in a pattern, painting, screen printing, or the like can be used. The resistance heating layer 3c is formed on the side of the heating member 3 that is in contact with the fixing belt 2, and is connected to a power supply unit (not shown).

As shown in FIG. 2, for example, at least two systems of the resistance heating layer 3c are formed in a maze pattern on the electric insulating layer 3b. The end of the resistance heating layer 3c is provided with a terminal for connection to a power supply unit, and power supply can be controlled independently for each system. In the present embodiment, a system that generates heat only at the center and a system that generates heat only at both ends are formed separately.

Each of the above-mentioned resistance heating layers 3c is kept insulative from the heating member 3 by the electric insulating layer 3b, and generates heat when heated by the power supply unit to heat the heating member 3. As described above, when small-sized paper is continuously passed with respect to the maximum paper-passing width, the width of the small-sized paper is heated by the heating member as much as the heat is removed, and the temperature recovers. On the other hand, since the outside of the small-sized paper is heated by the heating member 3 even though the heat is not taken away, a phenomenon occurs in which only the both ends of the fixing belt 2 become hot, but in this embodiment, Since the resistance heating layer 3c is divided into a system that generates heat only at the center and a system that generates heat only at both ends, when a small-size transfer paper is passed, only the system that generates heat only at the center resistance heating element 3c is used. To make the temperatures of the fixing belt 2 and the heating member 3 uniform so as to cope with the above-mentioned problem.

It is to be noted that if an electric insulating layer is further provided on the resistance heating layer 3c and the resistance heating layer 3c is sandwiched between two electric insulation layers, a more preferable structure from the viewpoint of safety.

It is also preferable to provide a low friction layer between the heating member 3 and the fixing belt 2 for suppressing abrasion. For example, the low friction layer 25 is thinly formed of a heat-resistant and low-friction material such as a fluororesin on the outside of the heating member 3 or on the inside of the fixing belt 2. The low friction layer 25 may be provided on the contact surface side of the fixing belt 2 or the heating member 3, but is preferably provided on the heating member 3 in order to reduce the installation area.

In the fixing device having such a configuration, the fixing belt 2 is heated by the heating member 3 and rotates in the direction of the arrow in the figure, so that the toner 9 on the transfer paper 8 is heated and melted and fixed on the transfer paper 8. . In the present embodiment, the heating member 3 has a low heat capacity, and at the same time, the heating member 3 is arranged near the fixing roller 4 to reduce the size of the apparatus and the peripheral length of the fixing belt. The rise time is shortened by the minute. In addition, since the surface area of the fixing belt 2 is reduced, heat radiation loss is also reduced. Further, as the circumference of the fixing belt 2 is reduced, the cost is reduced and the belt transportability is improved. That is, since the heating member 3 is close to the fixing roller 4, the fixing roller 4 is warmed by radiant heat and convection from the heating member 3, and a drop in the temperature of the fixing belt 2 during rotation is suppressed. Further, the heating member 3 as a heat source is a planar heating element having excellent responsiveness, which is advantageous for shortening the rise time.

That is, the endless fixing belt 2 is sufficiently heated by the heating member 3 upstream of the nip, and fixing is performed at the nip by the fixing belt 2 having a predetermined temperature. Since only the belt is heated, the rise time is shortened by the amount that the elastic layer 4b of the fixing roller 4 is not heated. Further, since the fixing belt 2 is sufficiently heated by the heating member 3 and then fixed at the nip, even if the temperature of the fixing belt 2 decreases during paper passing, the temperature can be recovered instantaneously, and the temperature stability is excellent. Stability of image fixability and gloss can be achieved. In addition, since the heating member 3 upstream of the nip is a planar heating element, the heating member 3 can be heated without reducing the contact area between the fixing belt 2 and the heating member 3, in other words, without impairing the temperature stability of the fixing belt 2. The heat capacity of the member 3 is reduced and the response is improved, and the rise time is shortened. Further, the heating member 3 of the sheet heating element is connected to the fixing roller 4.
The fixing belt 4
The heat roller 3 is heated by radiation and convection from the heating member 3 to further reduce the rise time.

FIG. 3 is a sectional view showing another embodiment of the fixing device according to the present invention. In this embodiment, the heating member 3 is located on the upstream side in the rotation direction of the nip portion, and the fixing belt 2 is wound around the pressure roller 5. Therefore, unlike the previous embodiment, the nip can be widened by winding the fixing belt 2 and the set temperature can be lowered.

Further, by pressing the heating member 3 against the pressure roller 5 via the fixing belt 2 and pressing and heating the toner 9 at the tip of the nip, the toner 9 is melted to some extent, and the pressure of the toner 9 is reduced. This prevents the toner 9 from shifting in a nip with a small pressure formed by the roller 6.

Further, similarly to the previous embodiment, the semicircular heating member 3 having a large radius of curvature is located near the fixing roller 4 so that the peripheral length of the fixing belt 2 is shortened. The heating and the convection heat the fixing roller 4 to shorten the rise time.

[0031]

As described above, in the fixing device according to the first aspect, the endless fixing belt is sufficiently heated by the heating member including the planar heating element upstream of the nip with the pressing member. Since fixing is performed at the nip by the fixing belt that has reached a predetermined temperature, only the belt having a small heat capacity in the surface layer is heated, and the rising time is shortened by not heating the surface layer of the fixing roller. Since the fixing belt is fixed sufficiently at the nip after the fixing belt is sufficiently heated, even if the temperature of the fixing belt decreases during paper passing, the temperature can be recovered instantaneously, the temperature stability is excellent, and the fixing property and gloss of the fixed image are improved. There is an effect that stabilization is possible.
Further, since the heating member is a planar heating element, the heat capacity of the heating member 3 can be reduced and the responsiveness can be improved without reducing the contact area between the fixing belt and the heating member, that is, without impairing the temperature stability of the fixing belt. This also has the effect that the rise time can be shortened. Furthermore, since the heating member of the sheet heating element can be arranged close to the fixing roller, it is possible to reduce the diameter of the fixing belt, reduce the heat capacity, save space, and reduce the cost, and fix the fixing member by radiation and convection from the heating member. There is an effect that the rise time can be further reduced by heating the roller.

In the fixing device according to the second aspect, in addition to the above-described common effects, as described above, the heating member is formed in a semicircular arc shape having a larger radius of curvature than the fixing roller, so that contact with the fixing belt is achieved. It is possible to obtain an area and to be close to the fixing roller, so that the circumference of the fixing belt can be shortened, so that there is an effect that the rising time can be shortened and the space for the fixing device can be saved.

In the fixing device according to the third aspect, in addition to the above-described common effects, as described above, the contact area between the heating member and the fixing belt is set to be smaller than the nip formed by the fixing belt and the pressing member. By adopting a wider width, there is an effect that heat can be sufficiently conducted from the heating member to the fixing belt, and the temperature of the fixing belt can be stabilized even during continuous paper feeding.

In the fixing device according to the fourth aspect, in addition to the above-mentioned common effects, as described above, by forming the resistance heating layer outside the electrical insulating layer, heat from the heating layer to the fixing belt can be obtained. There is an effect that transmission of information is improved.

In the fixing device according to the fifth aspect, in addition to the above-described common effects, as described above, the base material of the fixing belt is made of a heat-resistant resin, so that unlike the metal belt, the sheet-like resistance heat is generated. It is easy to ensure insulation with the body, the slidability between the fixing belt and the heating member is improved, and the service life of the belt and the heating member is prolonged.

[Brief description of the drawings]

FIG. 1 is a sectional view (A) showing an embodiment of a fixing device according to the present invention, and enlarged sectional views (B, C).

FIG. 2 is an enlarged plan view showing a pattern of a resistance heating layer (A).
And an enlarged sectional view (B).

FIG. 3 is a sectional view showing another embodiment of the fixing device according to the present invention.

FIG. 4 is a sectional view showing a conventional belt fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing apparatus 2 Fixing belt 2a Fixing belt base 2c Same surface release layer 2b Same elastic layer 3 Heating roller 3a Thin metal plate 3b Electrical insulating layer 3c Resistance heating layer 4 Fixing roller 4a Core 4b Elastic member 5 Pressure roller 5a Core Gold 5b Heat-resistant elastic layer 5c Surface release layer 6 Heater (for pressure roller) 7 Power supply unit 8 Transfer paper 9 Toner 10 Heat roller 11 Heater (for heat roller)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiko Baba 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Takashi Kikuchi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Inside Ricoh Company (72) Inventor Hirokazu Ikegami 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Inside Ricoh Company (72) Takashi Fujita 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (72) Inventor Jun Nakato 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2H033 AA30 BA11 BA12 BA25 BA26 BB18 BB21 BB30 BB38 3K058 AA02 BA18 DA01

Claims (5)

[Claims] An endless fixing belt stretched between a fixing roller and a heating member; and a pressing member opposed to the fixing roller via the endless fixing belt. In a fixing device that heats and presses an unfixed toner image carried on a recording material in a nip formed by a pressing member, the heating member is a substantially semicircular planar resistance heating element, and the heating member is A fixing device, which is disposed so as to slide close to a fixing roller. 2. The fixing device according to claim 1, wherein a radius of curvature of the heating member is equal to or larger than a radius of the fixing roller. 3. The fixing device according to claim 1, wherein a contact area between the heating member and the fixing belt is wider than the nip. 4. The fixing device according to claim 1, wherein the heating member is a planar heating element formed by laminating an electric insulating layer and a resistance heating layer on a base material, A fixing device, wherein a layer is formed on the fixing belt side with respect to the base material. 5. The fixing device according to claim 1, wherein a base material of the fixing belt is formed of a heat-resistant resin such as polyimide or polyamide.