JPH0372389A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of curling or creases of a transfer material by improving respective structures and relative arrangement relations of elements around a fixing device from a transfer material rush guide plate for the fixing device to a heat roll, a pressure roll, and a paper ejecting roll. CONSTITUTION:The carrying path from a photosensitive drum to a transfer material guide plate 1 is concaved upward, and small-diameter straight rolls are used as a heat roll 4 and a pressure roll 5, and the line connecting centers of the heat roll 4 and the pressure roll 5 is inclined at about 27 deg. to the perpendic ular line, and the upper face straight part on the lower transfer material guide plate 1, the contact part between the heat roll 4 and the pressure roll 5, and that between a paper eject driving roll 6 and a paper eject inverted roll 7 are approximately placed on the normal of this line. Consequently, a fixing device 2 and transfer material guide structures before and after the fixing device 2 are simplified, and elements around the fixing device are compactly collected. Thus, the device is easily unitized, and the occurrence of curling or creases of the transfer material is prevented.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a fixing device of an electrophotographic image forming apparatus, in particular, a method in which a transfer material that has been developed with toner from a photosensitive drum undergoes fixation of a toner image in the fixing device. relates to an improvement in paper feeding in the vicinity of a fixing device until it is ejected from an image forming apparatus by a paper ejection roller.

[Conventional technology]

In an electrophotographic image forming apparatus, a transfer material onto which a toner image has been transferred from a photosensitive drum by a transfer corotron is then guided to a fixing device for fixing the toner image onto the transfer material.

The fixing device consists of a heating roller and a pressure roller that are pressed together, a transfer material having a toner image transferred thereto is introduced between these rollers, and the toner image is fixed onto the transfer material by pressure and heat.

By the way, the pressure roller used in such a fixing device has an outer circumferential surface formed of an elastic material, and when it comes into pressure contact with the heating roller, the pressure roller deforms along the circumferential shape of the heating roller. , forming a nip.

When the transfer material passes through such a nip, the transfer material may curl into four sides depending on the shape of the heating roller, and the paper may wrinkle due to the application of heat and pressure.

In order to prevent the occurrence of such curls and wrinkles, in the past, for example, as shown in Fig. 4, a heating roller with a smaller diameter at the center side than the diameter at both ends was used; 63-148932, as shown in FIG. 5, the tip extension surface of the guide member that conveys the transfer material between both rollers is 90 degrees parallel to the plane containing the center lines of both rollers.
The position where the transfer material that has passed through the pressure contact portion of both rollers is separated from the pressure roller is shifted by a certain angle toward the delivery side from a plane that includes the center line of both rollers. .

[Problem to be solved by the invention]

However, in the conventional example, even if a heating roller with a center diameter smaller than the diameters of both ends is used as a heating roller as shown in Fig. 4, it is not a perfect countermeasure against curls and wrinkles. Compared to a normal heating roller with a constant diameter, the heating roller has the drawback that it is more difficult to manufacture and therefore more expensive.Also, in the conventional example shown in Fig. 5, before the transfer material enters between the two rollers, Another problem was that the transfer particles in the unfixed area came into contact with the heating roller, resulting in a wavy image with a difference in gloss. Furthermore, the entry position of the transfer material is shifted from the center of both rollers,
Since a loop is attached to the transfer material, there is a problem that a load is applied to the transfer material and the transfer material tends to be skewed.

The present invention comprehensively improves the individual structure and relative arrangement of various elements surrounding the fixing device, from the guide plate for introducing the transfer material into the fixing device, to the heating roller and pressure roller, and further to the paper ejection roller. It is an object of this invention to provide a fixing device which eliminates the defects of the conventional example and which does not cause curls or wrinkles.

〔Example〕

An embodiment of the present invention will first be described with reference to FIG. The transfer material on which the toner image has been transferred from the photosensitive drum in close contact with the photosensitive drum is peeled off from the photosensitive drum by a separation belt or the like, and then enters the fixing device 2 along the transfer material guide plate 1 . The fixing device 2 has a heater 3 inside, and a transfer material having an unfixed image on its surface is heated between a heating roller 4 whose surface is coated with Teflon and a pressure roller 5 whose surface has an elastic member. As a result, the toner is thermally fused and the image is fixed on the transfer material. The transfer material leaving the fixing device 2 is then discharged onto a tray outside the image forming apparatus by a paper discharge drive roller 6 and a paper discharge driven roller 7.

In this structure for feeding the transfer material around the fixing device, the structural features of the present invention are as follows.First of all, the heating roller 4 and the pressure roller 5 have a diameter of 20 to 25 mm.
The roller has a considerably smaller diameter than the conventional roller having a diameter of 30+ am or more, and is characterized in that the releasability of both rollers and the transfer material is greatly improved.

Second, conventionally, the heating roller 4 is tapered by approximately several tens of microns from the center toward the sides, as shown exaggeratedly in FIG. 4, so that the transfer material passes between the two rollers. In the present invention, such a taper of the heating roller 4 is eliminated, and a straight roller is used to apply pressure instead. The structure is such that the contact pressure on both sides of the roller is substantially higher than the contact pressure on both sides of the roller by appropriate means. As a result, the nip width on both sides of both rollers is made larger than the nip width at the central portion, and an effect similar to that obtained when the heating roller is provided with a taper to prevent the occurrence of paper wrinkles is obtained. Therefore, in the present invention, since the complicated taper processing of the heating roller 4 is omitted, the manufacturing cost is significantly reduced.

Thirdly, the line connecting the center of the pressure roller 4 located at the top and the center of the pressure roller 5 located at the bottom of both rollers whose diameters have been reduced in this way is a vertical line as shown in FIG. On the other hand, it is characterized by having an offset of about 27 degrees. This increases the inclination by 9 degrees compared to the applicant's conventional offset angle of 18 degrees, but by increasing the transfer material discharge angle in this way, it is possible to reduce the diameter of the roller. This eliminates the need for a transfer material peeling member on the pressure roller 5 side.

Fourth, in the present invention, the line connecting the centers of the paper discharge driving roller 6 and the paper discharge driven roller 7 is parallel to the line connecting the centers of the two rollers. On the other hand, the transfer material guide plate 1 disposed upstream of the heating roller 4 and the pressure roller 5, the straight portion on the upper surface side of the fixing device side, the heating roller 4
The conveyance path of the transfer material is formed in a substantially straight line from the contact point of the pressure roller 5 to the contact point of the paper ejection driving roller 6 and the paper ejection driven roller 7. As a result, when the transfer material is introduced into the fixing device 2, the transfer material is guided slightly toward the heating roller side, and a loop is attached to the leading edge of the transfer material to give stiffness to the transfer material and prevent paper wrinkles. With this type, when the paper enters, the transfer material comes into contact with the heating roller in the unfixed area first, which tends to result in images with different gloss and skewed movement of the transfer material in the fixing device. Preventing.

Note that the same effect can be obtained even if the upper surface of the transfer material guide plate on the fixing device side is not only an extension of the straight line connecting the contact point of the roller pair of the fixing device and the contact point of the paper ejection roller pair, but also slightly below the straight line. is obtained.

Fifth, the transfer material conveyance path 8 provided from the photoreceptor drum to the paper guide plate 1 disposed downstream thereof has a structure in which the transfer material is guided downward and then changes its direction upward. This is designed to release the stress generated in the transfer material when it is peeled off from the photosensitive drum, and then direct the transfer material to the fixing device 2.

Finally, as an additional feature of the present invention, a paper ejection guide (chute) 9 is provided between the fixing device and both paper ejection rollers as shown in FIG. It is characterized by being supported by That is, in the conventional example, a paper peeling claw was also installed on the pressure roller 5, but in the present invention, by considering the diameters of both rollers and their installation angles, this is no longer necessary, and a paper ejection guide (chute) is installed instead. ) has an end close to the pressure roller, and has a structure in which it can rotate around the pressure roller axis, and the other end is placed on a pin by its own weight, so that the pressure roller 4 Even if thermal expansion occurs, the end shaft of the pressure roller 4 also expands, so the paper ejection guide (chute) 9 supported by it also has a structure that can maintain a relative gap distance.

〔Effect of the invention〕

As detailed above, according to the present invention, since the fixing device and the guide structure for the transfer material before and after the fixing device are simplified,
The fixing device and its surroundings can be made more compact than in the conventional example, making it easier to form a unit, and also preventing the transfer material from curling or wrinkling.

[Brief explanation of drawings]

FIG. 1 is a front view showing an embodiment of the fixing device and its surroundings according to the present invention, FIG. 2 is a schematic diagram showing the offset of the centers of both rollers according to the present invention, and FIG. 3 is a transfer material ejection guide according to the present invention. FIG. 4 is a schematic diagram showing the contact relationship between a conventional heating roller and a pressure roller, and FIG. 5 is a front view of the conventional example. In the figure, 1 is a transfer material guide plate, 2 is a fixing device, 3 is a heater,
4 is a heating roller, 5 is a pressure roller, 6 is a paper discharge drive roller, 7 is a paper discharge driven roller, 8 is a conveyance path, 9 is a paper discharge guide (
Shoots) are shown respectively. Figure 4

Claims (1)

[Claims] 1. Transfer material feeding structure around the fixing device, from the photosensitive drum to the conveyance path, the transfer material guide plate, the heating roller and pressure roller of the fixing device, and the paper ejection drive roller and paper ejection driven roller. The conveyance path from the photosensitive drum to the transfer material guide plate is concave upward, and the heating roller and pressure roller are small-diameter straight rollers, with the center line between the heating roller and the pressure roller being a vertical line. On the other hand, the upper straight part of the downstream side of the transfer material guide plate, the contact part of the heating roller and the pressure roller, and the contact part of the paper ejection driving roller and the paper ejection driven roller are approximately 27 degrees inclined and the upper straight part of the transfer material guide plate is approximately on the normal line of this center line. 1. A fixing device for an image forming apparatus, characterized in that the fixing device is configured such that the fixing device is positioned in a fixed position. 2. A transfer material discharge guide is provided on the downstream side of the fixing device, one end of which is rotatably supported on the shafts at both ends of the pressure roller, and the other end of which is freely placed on a fixed pin. The fixing device for an image forming apparatus according to claim 1.