JPH0514287Y2 - - Google Patents

Description

[Detailed explanation of the idea]

Technical Field This invention relates to a heat roller fixing device for an electrostatic recording device. BACKGROUND ART In electrostatic recording devices such as electrophotographic copying machines, facsimile machines, and electrostatic printers, a toner image formed on a photoreceptor by an electrophotographic process is transferred to a transfer material and fixed, thereby completing a recording. This fixing device has a fixing device that presses against each other, a transfer material carrying a toner image is passed between pressure rollers, the toner is melted by a heat source inside the fixing roller, and the pressure between the fixing roller and pressure roller is used to melt the toner. A hot roller fixing device that fuses molten toner to the surface of a transfer material is widely used. FIG. 1 is a diagram showing a schematic configuration of this type of fixing device, in which an unfixed image is placed in a nip portion 4 of a roller pair consisting of a fixing roller 2 having a heater 1 inside and a pressure roller 3 in pressure contact with the fixing roller 2. A transfer paper 6 carrying a toner image 5 on its upper surface is guided by an upper guide plate 7 and a lower guide plate 8 and fed. Now, the transfer material generally has curls on either side, and in particular it often curls upwardly. In this case, as shown in FIG. The guided, unfixed toner image is therefore disturbed. As a means to prevent this, for example, as shown in Fig. 2,
There is a device in which a plurality of spurs 9 are provided at appropriate intervals under the corner portion of the upper entrance guide plate 7, but this does not provide a fundamental solution because the image shows marks where the tips of the teeth of the spurs made contact. In addition, as shown in FIG. 3, the upper guide plate 7 is made longer so that the trailing edge of the transfer material comes into sliding contact with the lower surface of the upper guide plate to prevent the image surface from being rubbed. As shown in the figure, there is an example in which the surface of the transfer material is moved away from the upper guide plate by tilting the fixing roller 2 and the pressure roller 3 in the tangential direction with respect to the direction in which the transfer material is carried in, but this poses problems in conveyance performance, etc. , I can't say it's perfect. In particular, this problem becomes more acute as the diameter of the roller becomes smaller due to miniaturization of the apparatus and the space near the entrance of the transfer material becomes narrower. Purpose The present invention has been developed in view of the above-mentioned problem of preventing the surface of an unfixed image from sliding against the upper entrance guide member of a conventional heat roller fixing device. It is an object of the present invention to provide a fixing device that prevents this from occurring. Structure In order to achieve the above object, the present invention is characterized in that the upper guide member at the entrance of the heat roller fixing device is made of an insulating material, and the lower guide member is made of a conductor. Hereinafter, embodiments of the present invention will be described in detail based on the drawings. According to experiments conducted by the present inventors, in a conventional fixing device that uses metal guide plates at the top and bottom, the contact of the transfer paper to the guide plates is not only due to curling of the transfer paper, but also due to the contact of the transfer paper with the photoreceptor. When toner is transferred from the drum or separated from the photoreceptor drum, the transfer paper is charged with static electricity due to separation, transfer charge, etc., and when the transfer paper enters the fixing device, it approaches the fixing device. It is pulled by a conductor (metal) by electrostatic induction,
We have discovered a phenomenon in which this promotes image rubbing. Therefore, the upper guide plate and the lower guide plate were made of a conductor and an insulator, respectively, and when these were combined, transfer paper carrying a toner image was passed through the paper and the image rubbing situation was observed in each case. The results shown are obtained.

[Table] In other words, when the lower guide plate is a conductor and the upper guide plate is an insulator, as in combination number 3, the transfer paper is pulled toward the lower guide plate by electrostatic induction, and the upper guide plate is transferred. It repels paper and gives the best rating. Example In the fixing device having the configuration shown in FIG. 1, the surface of the fixing roller 2 is made of silicone rubber, the surface layer of the pressure roller 3 is made of tetrafluoroethylene, and the diameter of each roller is 40 mm.
mm. The upper guide plate 7 is made of polycarbonate, and the lower guide plate 8 is made of zinc-plated iron. When this device was installed in an actual copying machine with a distance of 10 mm between the two, no image rubbing occurred and good results were obtained. Obtained. Note that the material of the insulator forming the guide plate may be any material as long as it satisfies strength and heat resistance.
Various materials other than the polycarbonate mentioned in the examples can be used. Also, regarding the lower guide plate,
A tetrafluoroethylene coating may be applied on the metal, and it is also possible to use a conductive resin. The shape of the lower guide plate is the same as shown in Fig. 5, which is conventionally implemented and is effective against image scratching.
You may use the shape shown in . Effects As described above, according to the present invention, image rubbing by the fixing section entrance guide can be reliably prevented with a simple structure in which the upper guide plate is made of an insulator and the lower guide plate is made of metal. be able to.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a schematic configuration of a fixing device to which the present invention is applied, and FIGS.
The figures are sectional views showing conventional measures for preventing image rubbing, and FIG. 5 is a plan view showing another example of the shape of the lower guide plate. 2... Fixing roller, 3... Pressure roller, 4...
Nip portion, 5... unfixed toner image, 6... transfer material, 7... upper guide plate, 8... lower guide plate.

Claims (1)

[Scope of utility model registration request] A fixing device in which a transfer member carrying a toner image on its upper surface is guided and passed through by a pair of upper and lower inlet guide members between fixing and pressure rollers that are in pressure contact with each other, and the toner image is thermally fused to the surface of the transfer material. A fixing device characterized in that an upper entrance guide member is made of an insulating material, and a lower guide member is made of a conductor.