JPH04145473A - Fixing device - Google Patents

Abstract

PURPOSE:To realize a uniform temp. distribution in the longitudinal direction of a heating roller and to surely fix a toner image over the total sheet width by, at least, setting the effective length of the heating part of a heater inserted/ provided in the shaft direction of the heating roller longer, nearby both end parts of the roller. CONSTITUTION:The heater 23 has heat resistance, and a constitution that a nichrome wire 25 as a heating body is inserted into a glass tube 24 meandering like a wave, when it is viewed from a side surface, is adopted. The amplitude of the wave of the tube 24 is properly determined so as to be housed in the hollow part of the heating roller 21. On the other hand, the nichrome wire 25 is required for strongly heating nearby both end parts of the heating roller, so that the number of the turns of the nichrome wire 25 nearby the corresponding both end parts, is increased. Besides, for heating the whole of the roller part of the roller 21 without having irregularities, the total length of the heating part H of the heater 23 is a little longer than that of the roller part. Thus, the quantity of heat to supplied to both end parts of the roller 21 can remarkably be increased. Consequently, the dropping of a temp. nearby both end parts of the roller 21 is surely prevented.

Description

[Detailed Description of the Invention] Lord! The Emperor's desk ■Tateno's invention is installed in, for example, electrophotographic printers.
The present invention relates to a fixing device that fixes transferred toner to paper.

In a conventional electrophotographic printer, recorded information is exposed on a photoreceptor drum to form an electrostatic latent image on the exposed area, and then toner is supplied to this to obtain a visible image (toner image). , this toner image is transferred onto a sheet of paper by a transfer device to obtain a single copy.

Incidentally, toner transfer is performed by applying an electric charge having a polarity opposite to the charged polarity to the paper, and generating an electrostatic force between the toner and the paper. In this case, the transferred toner loses its charge on the paper, so that the toner simply adheres to the paper. Therefore, in order to make the transferred toner image a permanent image as recorded information, a fixing step is provided after the transfer step.

Generally, in the fixing process, heat and pressure are applied to the paper onto which the toner has been transferred to fuse the toner to the paper to obtain a permanent image. The device used in this step is a fixing device. FIG. 5 is a side sectional view showing a conventional example of a fixing device. As shown in the figure, the fixing device 30 is composed of an upper heating roller 31 that rolls into contact with the transfer surface of a sheet of paper, and a lower pressure roller 32 that is pressed against the heating roller 31 through the sheet of paper.

Further, the heating roller 31 has a hollow structure, and an elongated tubular heater 33 is inserted into the hollow portion.

FIG. 6 is a side view showing a conventional example of the heater 33. The heater 33 has a form in which a nichrome wire 35 is inserted into a heat-resistant glass tube 34, and when power is supplied, the nichrome wire 35 generates heat and heats the glass tube 34. The heated glass tube 34 heats the air around it, and the heated air heats the inner surface of the heating roller 31.

This heat is transferred to the surface of the heating roller 31 (the surface temperature is normally adjusted to about 170° C.), and heat is supplied to the rolling contact surface with the paper sheet. As a result, the toner is fused to the paper and the toner image is fixed.

By the way, as shown in the figure, the nichrome wire 35 is set so that the number of turns near both ends thereof is greater than that near the center. This is because near the longitudinal center of the heating roller 31 having the above structure, the heater 33
Since the heat supplied from the heating roller 31 is trapped inside the heating roller 31,
While the temperature tends to rise, heat is dissipated to the surrounding areas near both ends of the heating roller 31.
This measure was taken in consideration of the phenomenon of a large drop in temperature.

However, even if the heater configured as described above is used, the temperature drop near both ends of the heating roller 31 can be considerably reduced, but it is still not sufficient. That is, regarding the temperature distribution in the longitudinal direction of the heating roller 31, the tendency for the temperature near the center to be higher than near both ends remains.

If the temperature distribution in the longitudinal direction of the heating roller 31 is not kept approximately uniform as described above, the degree of fixation of the toner to the paper will be uneven, resulting in a significant deterioration in image quality. This will lead to drawbacks.

The present invention has been made in order to eliminate such drawbacks, and an object of the present invention is to provide a fixing device that can realize a uniform temperature distribution in the longitudinal direction of a heating roller and can reliably fix a toner image over the entire width of a sheet of paper. shall be.

In the present invention, a heating roller and a pressure roller are disposed facing each other,
In a fixing device that fixes the toner image transferred on the paper to the paper at the same time as the paper is conveyed through the rollers, a heater inserted in the axial direction of the heating roller,
The roller is characterized in that the effective length of the heat generating portion is increased at least near both ends of the roller.

According to the above configuration, since the effective length of the heater is long near both ends of the heating roller, the amount of heat generated at that portion increases significantly. Along with this, the amount of heat supplied to the vicinity of both ends of the heating roller also increases significantly. As a result, the amount of heat dissipated from both ends of the heating roller to its periphery is sufficiently covered, and a drop in temperature near both ends of the heating roller is reliably prevented. Therefore, the temperature difference between the ends of the heating roller and the center of the heating roller becomes extremely small, and a substantially uniform temperature distribution in the longitudinal direction of the heating roller is realized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a side sectional view showing an example in which the fixing device according to the present invention is applied to a printer.

When a print switch (not shown) is turned on, the photosensitive drum 2 provided at the center of the printer 1 rotates in the direction shown by arrow A, and the charger 3 charges the surface of the photosensitive drum 20 accordingly. Next, an optical writing unit 4 consisting of an LED array emits light in response to an image signal given from a scanner section (not shown), and exposes the surface of the photoreceptor drum 2. Thus, an electrostatic latent image is formed in the exposed area. Next, a developing device 5 installed on the upper right side of the photoreceptor drum 2 in the figure supplies toner to the electrostatic latent image to form a toner image (visible image).

Meanwhile, in synchronization with this image forming process, the feed roller 7 feeds out the paper (not shown) stored in the paper feed cassette 8,
It is supplied to the registration roller 9.

The registration rollers 9 transport the paper to the transfer device 6 in synchronization with the rotation of the photosensitive drum 2.

The transfer device 6 is provided opposite to the photoreceptor drum 2, and transfers the toner image formed on the photoreceptor drum 2 onto a sheet of paper.

The paper onto which the toner image has been transferred is then subjected to a toner image fixing process in a fixing device 10. After the fixing process, the paper is conveyed in a U-turn by a vapor guide 11 and a discharge roller 12, and is discharged onto a paper discharge tray 13 attached to the upper part of the main body. In addition, in the figure, the path line P of the paper is indicated by the dashed dotted line.

Next, details of the fixing device according to the present invention will be explained with reference to FIGS. 2 to 4. FIG. 2 is a side sectional view showing the fixing device 10, and FIG. 3 is a side view showing the heater 23. Moreover, FIG. 4 is a side view showing a modified example of the heater 23.

As shown in FIG. 2, the fixing device 10 includes an upper heating roller 21 provided on the transfer surface side of a sheet of paper, and a lower pressure roller 2 that is pressed against the heating roller 21 from below through the sheet of paper.
It consists of 2. Then, the paper is conveyed to the next process through between these rollers. In addition, the heating roller 21
has a hollow structure, and a heater 23 is inserted in the axial direction of the hollow portion.

As shown in FIG. 3, the heater 23 is heat resistant and has a structure in which a nichrome wire 25 serving as a heat generating element is inserted into a glass tube 24 which is meandering in a wavy manner when viewed from the side. The amplitude of the wave of the glass tube 24 is appropriately determined so that it fits within the hollow part of the heating roller 21. In addition, the nichrome wire 25 is
In order to strongly heat the vicinity of both ends of the heating roller, the number of turns is increased near the corresponding ends. The total length of the heat generating portion H of the heater 23 is set to be slightly longer than the total length of the roller portion in order to evenly heat the entire roller portion of the heating roller 21.

According to the heater 23 configured as described above, the vicinity of both ends of the heater 23 are formed in a wave shape, so the effective length of the heat generating part in that part is long, and in addition, the number of turns of the nichrome wire 25 in this part is increased. Therefore, the amount of heat generated near both ends of the heater 23 increases significantly. In addition, since the glass tube 24 is meandering in a wavy manner, the heat generating portion is connected to the heating roller 2.
Since the heat generating area increases as it approaches the inner surface of the heater 23, the heating efficiency of the air around the heater 23 becomes extremely high. Therefore, the amount of heat supplied to both ends of the heating roller 21 can be significantly increased. As a result, heating roller 2
Temperature drop near both ends of 1 is reliably prevented.

4 shows a modified example of the heater, in which a spiral glass tube 26 is used in place of the glass tube 24. Such a glass tube 26 is relatively easy to manufacture;
Moreover, since the air in the center formed by the flexible tube is effectively heated, the heating efficiency of the air in the surrounding area of the heater is further increased.

In this embodiment and the modified examples, the shape of the heat-resistant glass tube into which the nichrome wire is inserted is wavy or spiral, but the heater is not limited to these shapes. For example, any tube shape may be used, such as a zigzag shape, as long as it can lengthen the effective length of the heat generating section provided near both ends of the heater.

In addition, it is not necessarily necessary to form a curved pipe over the entire length of the heater, but it is sufficient that the heat generating portion has an effective length to the extent that a temperature drop near both ends of the heating roller can be prevented.
Only that part may be a bent pipe.

According to the above-described invention, in a fixing device consisting of a heating roller and a pressure roller, the effective length of the heat generating portion of the heater inserted into the heating roller is long near both ends of the roller.
It is possible to strongly heat the vicinity of both ends of the heating roller. As a result, it is possible to reliably prevent the temperature drop at both ends of the heating roller due to heat dissipation to the surrounding areas.

Therefore, it is possible to maintain substantially uniform temperature distribution in the width direction of the heating roller, so that the toner image transferred to the paper can be reliably fixed as a permanent image over the entire width of the paper. As a result, image quality can be further improved.

4,

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an example in which the fixing device according to the present invention is applied to a printer, FIG. 2 is a side sectional view showing the fixing device, FIG. 3 is a side view showing the heater, and FIG. 4 is a side view of the heater. FIG. 7 is a side view showing a modified example. FIG. 5 is a side sectional view showing a conventional example of a fixing device, and FIG. 6 is a side sectional view showing a conventional example of a heater. DESCRIPTION OF SYMBOLS 1... Printer, 10... Fixing device, 21... Heating roller, 22 Pressure roller, 23... Heater, D...
・Paper.

Claims (1)

[Claims] (1) In a fixing device in which a heating roller and a pressure roller are disposed facing each other, and a sheet is conveyed between the rollers and a toner image transferred onto the sheet is fixed to the sheet at the same time, the fixing device is inserted in the axial direction of the heating roller. A fixing device characterized in that a heater provided has a long effective length of a heat generating section at least near both ends of the roller.