JPS6197678A - Fixing device - Google Patents

Abstract

PURPOSE:To form a high-quality picture image which is free from disturbance in the fixed image, by carrying a sheet material into a fixing section by means of an entrance guide made of a ceramic material having semiconductor characteristics. CONSTITUTION:A sheet material 2, to which an unfixed toner image 1 is transferred, is carried into the contacting section between fixing rollers 5 and 6 by means of an earthed entrance guide 4 backed by a metallic base plate 3 and fixed. The entrance guide 4 is made of a ceramic material having a varister characteristic. Therefore, the electrostatic attractive force between the unfixed toner image 1 and sheet material 2 is kept excellent and a high-quality picture image which is free from disturbance in fixed image is formed. Moreover, the heat-resistant property and durability of the entrance guide 4 can be improved sharply.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a fixing device used in an electrophotographic copying machine and the like, and more particularly to a fixing device entrance guide for introducing transfer paper into a fixing section.

[Background of the invention]

Conventionally, the entrance guide of a fixing device such as an electrophotographic copying machine has been molded with a material that has semiconductor properties, such as by mixing carbine into heat-resistant resin, or the contact surface with the paper sheet material is made of metal and a bias is applied to this material. It was common to use it by applying a voltage. The reason for this is that if the entrance guide is grounded, the charge applied to the sheet material during transfer will leak through the guide, weakening the bond between the sheet material and the toner carried on it, and as a result, the sheet material This is because the toner image on the material is easily disturbed.On the other hand, if the entrance guide is insulated or non-grounded, the contact between the entrance guide and the sheet material may be poor, or frictional electrification may occur between the two. This is because the opposite effect may cause instability in guiding the sheet material into the fixing device, or may cause wrinkles in the sheet material.

However, in the above-mentioned bias application method, the use of a bias power supply increases the number of parts on the device and increases costs, and when using a carbon-containing resin entrance guide, It is difficult to manufacture the resin with a constant resistance value, for example, it is usually 10Ω/α for a setting of 1
0 to 103 (106''' (2 to 3)) Ω·α remains as a tolerance, which has the disadvantage of affecting as an unstable factor.

[Purpose of the invention]

The main technical idea of the present invention is to maintain a stable potential state of the entrance guide, and it solves the above-mentioned difficulties and allows stable introduction guidance of the sheet material into the fixing device with a relatively simple and inexpensive configuration. The purpose is to provide a realized entrance guide.

[Summary of the invention]

The gist of the present invention, which has been made to achieve the above object, is to provide an inlet that contacts the back surface of a sheet material carrying an unfixed toner image on its surface and guides the sheet material to a fixing section. The fixing device includes a guide, wherein the entrance guide has a circuit that grounds a surface that contacts the sheet material and includes a ceramic material exhibiting semiconductor properties.

In the present invention, the entrance guide itself is made of a conductor, and in addition to the structure in which a ceramic material exhibiting semiconductor properties is interposed between the conductor and the ground, the entrance guide itself is made of a ceramic material exhibiting semiconductor properties. The ceramic exhibiting semiconducting properties used in the present invention may be reinforced with a metal plate or the like if necessary. A material that does not weaken the ceramic and exhibits characteristics that prevent the effects of frictional electrification, etc. is selected, and although it depends on the shape of the ceramic, the resistance value is generally 10'Ω・cIr1 to 109
A material in the range of Ω·α, particularly a ceramic having varistor properties, is preferably used.

[Embodiments of the invention]

FIG. 1 is a diagram schematically showing an embodiment of the present invention, in which a toner image 1 is transferred from a photoreceptor (not shown) to a sheet material 2 by a transfer charger (not shown), It is transported to a position of a ceramic entry guide 4 lined with a substrate 3.

The metal substrate 3 is grounded. Thereafter, the sheet material 2 reaches the mutually rotating portion of the upper fixing roller 5 and the lower fixing port 26, is fixed thereon, and is then discharged. The upper fixing roller 5 has a heater 7 inside and is controlled to a constant temperature, thereby fixing the toner image 1. Here, the material of the entrance guide 4 is ceramics having varistor properties, such as ZnO.
It is constructed of -810 series or V205 series ceramics, and by appropriately selecting the thickness of the input guide 4, the varistor voltage (constant voltage value of the constant voltage characteristic of the varistor) can be set to a desired value.

In the present invention, the voltage may normally be set to several 100 volts.

FIG. 2 is a diagram showing an outline of another embodiment of the present invention, in which the plate-shaped entrance guide 8 is made of a conductive member (for example, a metal plate), and the entrance guide 8 made of the conductive member is made of a ceramic material. The structure is the same as the previous embodiment except that the structure is grounded via the block 9. The ceramic material includes the above-mentioned Zn0-
Bi 203 series or V203 series are preferably used, and the shape can be set appropriately considering its constant voltage characteristics.

In addition to ceramic materials that exhibit varistor properties, the ceramic materials described above can be used as long as they can maintain a predetermined constant voltage on the contact surface with the sheet material of the entrance guide. In the above embodiment, there is an advantage that not only the effect based on the electrical properties but also the preferable properties regarding the sheet material conveyance guide can be utilized by variously selecting mechanical properties such as surface frictional resistance.

Other configurations may be adopted as long as they bring the guide itself into a stable potential state as described above.

〔Effect of the invention〕

According to the present invention having the above-mentioned configuration, the introduction guidance of the sheet material to the fixing section can be carried out more stably and reliably than in the past, and the gap between the unfixed toner image and the 7-t material is Since the electrostatic adhesion force can also be maintained well, there is an effect that a high-quality image can be obtained without disturbing the fixed image.

Further, since a ceramic material is used, heat resistance and durability are greatly improved, and the device design is also facilitated.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG. 2 is a schematic diagram showing another embodiment. l: toner image, 2: sheet material, 3.8: entrance guide, 4: backing metal plate, 5: fixing upper n-ra,
6: Lower fixing roller, 7: Heater, 9: Ceramic, block. Figure 1 Figure 2

Claims (1)

[Claims] A fixing device comprising an entrance guide that comes into contact with the back side of a sheet material carrying an unfixed toner image on its surface and guides the sheet material to a fixing section, the entrance guide having a surface that contacts the sheet material. A fixing device characterized in that a circuit for grounding includes a ceramic exhibiting semiconductor characteristics.