JP2848855B2 - Fixing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device provided in a copying machine or the like, and more particularly, to a fixing device for a color copying machine capable of performing a color image copying process and a black and white image copying process. It relates to a fixing device.

[Conventional technology]

FIG. 3 shows a curl correcting mechanism for correcting transfer paper curled by a fixing process in a conventional fixing device (Japanese Patent Laid-Open Publication No.
57-204073), wherein the fixing device comprises a heating roller 301 having a heater 302 therein,
A pressing roller 303 for applying a certain pressure to the heating roller 301, a separation claw 304 for separating transfer paper adhered to the heating roller 301 from the heating roller 301 by the fixing process, and a curl of the transfer paper generated by the fixing process. Straightening roller pair 305 to straighten,
306.

In the above configuration, a predetermined pressure is applied to the pressure roller 303, and the pressure roller 303 made of an elastic body is deformed with respect to the heating roller 301 to form a predetermined nip with the heating roller 301. I do. The heating roller 301 is maintained at a predetermined temperature by a heater 302 provided inside the heating roller 301, and the transfer paper is passed between the nips to perform a fixing process by applying pressure and heating.

At this time, since the heating roller 301 which is a rigid roller is arranged above and the pressing roller 303 which is an elastic roller is arranged below, the rollers 301, 301
The nip between 303 is formed upwards, so that the separation claw 3
The transfer paper separated and discharged from the heating roller 301 by 04 is curled in a downward convex shape.

Therefore, in the curl correcting mechanism according to the prior art, a pair of correcting rollers 305 and 306 that form a nip in a direction opposite to the fixing roller pair 301 and 303 are installed, and the fixing roller pair 305 and 306 are passed through to make the above-mentioned transfer paper transfer. Corrects downward convex curls.

FIG. 4 is for correcting transfer paper curled by the fixing process of the fixing device in the same manner as the curl correcting mechanism of FIG. 3 (Japanese Patent Laid-Open No. 59-34572). That is, a nip portion is formed by the heating roller 402 having the heater 401 and the pressing roller 403, and the transfer paper passing through the nip portion has a downward convex curl. Therefore, in the prior art shown in FIG. 4, after the transfer paper adhered to the heating roller 402 is separated by the separation claw 404, a guide member 405 having a curve opposite to the downward convex curl is provided, and the transfer paper is removed. The transfer paper 406 is conveyed in the direction of the arrow along the guide member 405 to correct the downward convex curl in the transfer paper.

[Problems to be solved by the invention]

However, in the first prior art, when the degree of curl after the fixing process is large, the correction roller pair 30
When the paper passes through 5,306, wrinkles may be generated on the transfer paper.
Since 5,306 must be arranged, it becomes a cause to hinder miniaturization of the device.

Next, a guide member 405 having a curvature opposite to that of the curl generated after the fixing process is provided, and in the second related art in which the transfer paper is transported along the guide member 405, the curl after the fixing process is performed. When the degree is large, there is a problem that the effect of correcting the curl is insufficient.

At present, many copying machines equipped with both color image copying and black-and-white image copying functions have been developed.

Here, since the amount of the developer adhering to the transfer paper is different between the transfer paper on which the color image processing has been performed and the transfer paper on which the black-and-white image processing has been performed, the degree of the curl is different. In this case, there is a problem that the curl correction cannot be appropriately performed on each of the transfer images.

Further, the fixing device itself is heated by a heater inside the heating roller, and a predetermined pressure is applied by a pressure roller. Therefore, the degree of wear is higher than that of other portions, and good fixing processing is continuously performed for a long period of time. It is difficult. As a result, an incomplete fixing process may be caused, and a fixing defect of an image on the discharged transfer paper may occur.

The present invention has been made in view of the above, and has been made to prevent the occurrence of wrinkles due to curl correction, improve the efficiency of curl correction of transfer paper, and perform curl correction based on a fixing process suitable for each of a color image and a black and white image. And to reduce the frequency of maintenance and inspection by prolonging the life of the fixing device, preventing the occurrence of defective fixing due to long-term use.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a fixing device including a heating roller having a heat source and a pressing roller for applying a constant pressure to the heating roller. And a second fixing unit in which the surface hardness of the pressure roller is higher than the surface hardness of the heating roller.
And a fixing device provided with the fixing unit.

[Action]

In the fixing device according to the present invention, when a large amount of developer adheres to a color image copy or the like, the fixing process is performed by a first fixing processing unit in which the surface hardness of the pressure roller is higher than the surface hardness of the heating roller. If the amount of the developer adhered is small, such as when copying a black and white image, the image fixing process is performed by a second fixing unit in a combination in which the surface hardness of the pressure roller is lower than the surface hardness of the heating roller. Execute

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a structural explanatory view of a color copying machine equipped with a fixing mechanism according to the present invention.

This color copier includes a contact glass 101 on which a document (not shown) is placed, an optical scanning system (light source lamp, mirror, lens, etc.) 102 for reading the contents of the document on the contact glass, and an optical scanning system 102 Color separating means 103 for separating the contents of the original read by
A photosensitive drum 104 for forming an electrostatic latent image by receiving the light decomposed by 03, and a charger for uniformly charging the surface of the photosensitive drum 104 before forming an electrostatic latent image on the photosensitive drum 104
A black developing device 106 for storing a black developer for developing an electrostatic latent image formed by being charged by the charging device 105 and thereafter being exposed by the information light L from the color separation means; A cyan developing device 107 for storing the agent,
A magenta developing device 108 for storing a magenta developer, a yellow developing device 109 for storing a yellow developer, and a developed image formed on the surface of the photosensitive drum 104 by a developing process is transferred to the transfer paper 113 a plurality of times. Therefore, a transfer drum 110 for holding the transfer paper 113, a cleaning device 111 for cleaning the photosensitive drum 104 for the next process after the transfer of the transfer drum 110, and a photosensitive drum for the transfer drum 110 After transferring the visible image on 104 and combining each color,
Transfer device 1 that transfers an image to transfer paper 113 that is transported
12, a transfer means 125 for transferring the transfer paper 113 from the paper feeding unit to the transfer unit, a separation claw 114 for separating the transfer paper 113 electrically attracted onto the transfer drum 110, and a separation claw 115
And a fixing device 116 for fixing the image on the transfer paper 113 separated by the separation claws 114 and 115.

The transfer paper 113 separated by the separation claw 114 advances to the A route fixing unit, and the transfer paper 113 separated by the separation claw 115 advances to the B route fixing unit.

The fixing device 116 includes a pressure roller 117 of the A route fixing unit.
And a dual-purpose roller 119 having a heat source 118 therein and serving as a heating roller for the A-root fixing unit and a pressure roller for the B-root fixing unit, and a heating roller 121 for the B-root fixing unit having a heater 120 therein. It is configured.

In the A route fixing section, the hardness of the surface of the pressure roller 117 is set lower than that of the surface of the dual-purpose roller 119.
In the root fixing section, the surface hardness of the dual-purpose roller 119 is set higher than that of the heating roller 121.

The operation of the fixing process in the above configuration will be described.

When a full-color image copying process is performed using the color copying machine shown in FIG. 1, charging, exposure,
Each step of development and transfer is repeated a plurality of times.
The color development formed thereon is transferred by the transfer device 112 onto the transfer paper 113 transported by the transport means 125,
Thereafter, the separation claw 115 separates the transfer paper 113 on which the full-color image has been transferred from the transfer drum 110, and transfers the transfer paper 113 to the B
It is transported to the root transfer unit. In the B-route fixing section, the transfer paper 113 is subjected to a fixing process by a heating roller 121 and a dual-purpose roller 119 serving as a pressure roller, and is discharged outside the copying machine. At this time, since the dual-purpose roller 119 plays a role as a pressure roller, the built-in heater 118 is turned off.

Thus, in the full-color image fixing process, the second
As shown in the figure, the saturated adhesion amount of the solid black portion on the transfer paper is about 2.0 to 3.0 mg / cm ² , and as a result, the curl amount of the transfer paper 113 is large. .

Next, when executing the fixing process of the black and white image,
Transfer paper 113 that has undergone black and white image transfer processing on a transfer drum
Is separated from the transfer drum 110 by a separation claw 114 and discharged to the outside of the apparatus via an A-root fixing unit constituted by a dual-purpose roller 119 serving as a heating roller and a pressure roller 117. At this time, since the dual-purpose roller 119 plays a role as a heating roller, the built-in heater 118 is operated.

In this way, in the black-and-white image fixing process, as shown in FIG.
~0.9mg / cm is about ^2, so that the transfer sheet 113 not very large curling amount is, can achieve the purpose of sufficiently curl correction by Route A fixing unit.

In addition, one of three colors of yellow, magenta, and cyan is one to two.
When a single color copying process is performed using colors, the amount of toner adhered is large in the yellow, magenta, and cyan copying processes, and the B route fixing unit is used similarly to the full color copying process. Among the single colors, violet, red, and green use a relatively small amount of toner, so the A route fixing unit is used.

In other words, for example, in the case where the amount of the developer adhered to the transfer paper is very large with respect to the solid black portion as in a full-color copying process, if the heat fixing process is executed by the A route fixing unit, as shown in FIG. Thus, the transfer paper curls greatly toward the image side. For example, if the conditions such as A3 size vertical feed, large image area, and large toner adhesion amount overlap, after the toner is discharged from the copying machine, the toner attached is cooled and contracts. Further, the paper may be curled into a cylindrical shape due to the moisture absorption on the back side of the copy paper. However, when this is fixed in the B-root fixing unit, as shown in FIG. I can do it.

Further, regarding the heating roller, when the rubber hardness of the elastic layer of the surface rubber is high, the life of the roller itself is generally long, and when the rubber hardness is low, the life is short.

Therefore, in the present invention, for example, when a control unit (not shown) such as a microcomputer has a large amount of toner adhering to the transfer paper 113 and passes through the A route fixing unit, the transfer paper
Only when it is determined that the curl of 113 becomes an allowable level or more, control is performed so that the transfer paper 113 is conveyed to the B route fixing unit. As a result, the amount of copy is relatively large (in the prediction, the ratio of color image copy processing to black and white image copy processing is 1: 9 to 3:
7) Black-and-white image processing uses the A route, so that the frequency of roller replacement can be significantly reduced for the entire fixing device, and maintenance time for the fixing device as a whole copying machine can be reduced. it can.

By the way, the life of the heating roller (the rubber hardness in this case is about 40 to 50 degrees) when only the A-root fixing section is used is about
There are 100,000 to 300,000 sheets, and the life of the heating roller (the rubber hardness in this case is about 25 to 35 degrees) when only the B-root fixing section is used is about 20 to 50,000 sheets, which is a large difference.

The rubber hardness of the pressure roller is preferably 25 to 40 degrees with respect to the heating roller when only the A-route fixing unit is used.

〔The invention's effect〕

As described above, according to the fixing device of the present invention,
A first fixing processing section in which the surface hardness of the pressure roller is lower than the surface hardness of the heating roller, and a second fixing processing in which the surface hardness of the pressure roller is higher than the surface hardness of the heating roller. The processing unit prevents the occurrence of wrinkles due to the curl correction, improves the efficiency of the curl correction of the transfer paper, and executes the curl correction based on the fixing process suitable for each color image or black and white image.
It is possible to extend the life of the fixing device, prevent occurrence of defective fixing due to long-term use, and reduce the frequency of maintenance and inspection.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the structure of a color copying machine provided with a fixing device according to the present invention and capable of performing color and black-and-white image copying processing, and FIG. 2 shows the degree of curl of a transfer sheet after passing through the fixing processing. FIG. 3 and FIG. 4 are explanatory diagrams showing a curl correction method for transfer paper in a conventional fixing device. EXPLANATION OF SYMBOLS 104 Photosensitive drums 106, 107, 108, 109 Developing device 110 Transfer drum 112 Transfer device 113 Transfer paper 114, 115 Separating claw 116 Fixing device 117 Pressure roller for A route 118: Dual-purpose roller heater 119: Dual-purpose roller 120: B-route heating roller heater 121: B-root heating roller

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 13/20 G03G 15/20

Claims (1)

(57) [Claims] An image forming apparatus comprising: a heating roller having a heat source; and a pressure roller for applying a predetermined pressure to the heating roller, wherein the fixing device executes a fixing process on an image on a transfer sheet after the transfer process. A first fixing processing unit in which the surface hardness of the pressure roller is lower than the surface hardness of the heating roller, and a second fixing processing unit in which the surface hardness of the pressure roller is higher than the surface hardness of the heating roller. A fixing device comprising: