JPH0651664A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the adhesion of silica to the discharge wire of an electrostatic charger. CONSTITUTION:This image forming device has an image forming section including the discharge type electrostatic charger, exposing means, developing means and transfer device disposed along the rotating direction of a drum-shaped image carrying member on the periphery of this member and a heat fixing section 20 including a fixing roller 21 and a press roller 22 mounted slidingly contactably with this fixing roller 21. The above-mentioned press roller 22 is formed of silicone rubber having the compsn. in which the gaseous low- molecular siloxane evaporated when the fixing roller 21 is operated at 180 to 200 deg.C is generated in <=1000ppm amt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having an image forming section including a discharge type charger and a heat fixing section.

[0002]

2. Description of the Related Art In FIG. 1, reference numeral 1 denotes a main body case which accommodates an image forming section 10 and a heat fixing section 20. Both of these 1
Sheets (P) are fed to the sheets 0 and 20 one by one by the conveying means (conveying roller 8 and conveying path 9). This paper (P)
Are picked up and supplied by the pickup roller 7 from the paper cassette 6 mounted in the entrance 2. In addition, the heat fixing unit 2
The sheet (P) that has passed 0 is discharged to the lower outlet 3 or the upper outlet 4 (sheet receiver 5).

The image forming unit 10 is a drum-shaped image carrier 1.
1, a discharge type charger 12 (discharge wire 12W) arranged around this in the rotation direction, and an exposure unit 13.
The developing device 14 includes a stirring blade 14B and a developing roller 14R, a transfer device 15, a waste toner cleaning device 16 including a blade 16B, and a charge eliminating lamp 17. In the case of the simultaneous development cleaning method, the waste toner cleaning device 16 is unnecessary.

In the image forming section 10, the image carrier 11
The peripheral surface (photosensitive layer) of is charged to, for example, −600 V by the corona discharge action of the charger 12. Subsequently, the electrostatic latent image is drawn by the exposure unit 13. The exposed portion (electrostatic latent image portion) is, for example, −50V, and the unexposed portion remains −600V. Therefore, a toner image is formed when passing through the developing device 14 (14R), and this toner image is transferred onto the paper (P) when passing through the transfer device 15.

On the other hand, the heat fixing device 20 is, as shown in FIG.
The fixing roller 21 includes a heater 21H and is operated at a predetermined temperature (for example, 180 ° C.), a pressure roller 22 biased by a spring 22S, and a separation claw 24. Pressure roller 2
2 is often formed from an elastic member such as silicon rubber for the purpose of its function.

Therefore, the sheet P sent from the image forming section 10 is heated at, for example, 180 ° C. when passing between the rollers 21 and 22. As a result, the toner image is thermally fixed on the paper P.

The toner that has not been thermally fixed on the sheet P adheres to the peripheral surface of the fixing roller 21. Therefore, cleaning means 25 is provided to perform the cleaning. The cleaning unit 25 is configured by impregnating a release agent into a felt material that is slidably attached to the peripheral surface of the fixing roller 21.

[0008]

By the way, in order to perform high-quality image formation in such an image forming apparatus (1, 10, 20), it is premised that each constituent element fully exhibits its function. Therefore, it is carefully assembled and adjusted. Further, it is well known that the components are replaced with new ones as needed.

However, no matter how carefully the assembly and adjustment are performed, the image quality may deteriorate, and it may be difficult to find the cause. One of the reasons is that the corona discharge performance of the charger 12 becomes unstable, and the image carrier 11 is poorly charged. According to the applicant's analysis, the discharge wire 12
It was found that silica (SiO2) adhered to W, which became an electrical insulating material and made corona discharge unstable.

It is an object of the present invention to provide an image forming apparatus which can stabilize the corona discharge performance of a discharge type charger and can always form a high quality image.

[0011]

According to the present invention, the adhesion of silica to the discharge wire is not from the beginning and is gradually generated after image formation, and in the heat fixing section in association with high speed image formation. As a result of repeated tests and studies, paying attention to the fact that the growth proceeds faster as the heating temperature of the toner rises to 180 to 200 ° C., for example, the gas generated from the pressure roller of the heat fixing unit is corona discharge action of the charger In connection with this, it was determined that the cause was that it solidified to become silica and adhered to the discharge wire.

That is, the silicon rubber forming the pressure roller is said to have a dimethylpolysiloxane structure as shown in Chemical formula 1, but when it is heated in the atmosphere, a weight change and a viscosity change occur, and side chain organic compounds are formed. A cross-linking reaction occurs due to the oxidation of the groups. In the higher temperature region, the depolymerization reaction accompanies the formation of a low molecular weight silicon cyclic compound (siloxane) as shown in Chemical formula 2, and the conventionally used silicon rubber becomes a gas with a concentration of 5000 ppm or more. Evaporates and floats inside. This is easily understood from the data shown in Table 1.

[0013]

[Chemical 1]

[Chemical 2]

[Table 1]

In addition, when the low-molecular-weight siloxane gas reaches the charger, it is decomposed by corona discharge, methyl groups (--CH3) are removed, and silica (SiO2) is deposited on the discharge wire. In other words, the conventional pressure roller is selected to be as elastic as possible because the original purpose of pressing the paper against the fixing roller is the primary purpose. For example, it is a low molecular weight siloxane D4 to D10 silicone rubber having the same structure as shown in Table 1.

However, in particular, in order to achieve closer arrangement of the heat fixing portion (pressure roller) and the image forming portion (charging device) and further increase in speed by further downsizing of the present apparatus, the heat fixing temperature is further increased. It has been found that when the conditions of increasing the temperature are overlapped, the gas generated from the heat fixing section and the corona discharge action thereof cause disturbance in the original development in the image forming section. According to the present invention, the amount of low-molecular-weight siloxane evaporated from the pressure roller of the heat fixing unit is minimized to prevent silica from adhering to the discharge wire.

That is, the image forming apparatus according to the present invention is
An image forming unit including a discharge type charger, an exposure unit, a developing unit, and a transfer unit, which are arranged around the drum-shaped image carrier along the rotation direction thereof, a fixing roller, and a fixing roller which can be slidably contacted with the fixing roller. In the image forming apparatus including a heat fixing unit including a pressure roller, the amount of low-molecular-weight siloxane gas evaporated when the pressure roller is operated at a predetermined temperature is 1000 ppm. It is characterized by being formed from silicone rubber having the following composition.

[0017]

In the present invention having the above-mentioned structure, when the image forming section and the thermal fixing section are activated, the charging device starts corona discharge to charge the image carrier. On the other hand, the fixing roller is heated and operated at a high predetermined temperature. Then, the low-molecular-weight siloxane gas is evaporated and scattered from the silicon rubber forming the pressure roller. However, since the generated amount is 1000 ppm or less, even if the gas reaches the charger during corona discharge, silica is not generated and adhered to the discharge wire and the corona discharge is stabilized and uniform. A latent image can be formed. Therefore, a high quality image can be formed at high speed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. This image forming apparatus has a conventional basic structure (see FIG.
2) and the pressure roller 22 has the same siloxane structure D4 to D10 as shown in Table 1 and the fixing roller 21.
Is made of silicon rubber SH200CV (manufactured by Toray Downing Silicone Co., Ltd.), which can reduce the amount of low-molecular siloxane gas generated when it is operated at a predetermined temperature to 1000 ppm or less.

The surface temperature (predetermined temperature) of the fixing roller 21 is selectively switchable within a range of 180 to 200 ° C. Further, it is formed so that the photosensitive layer of the image carrier 11 is charged to −600 V by the corona discharge of the charger 12 (discharge wire 12W). Thus, the heat fixing unit 20
As a result of selecting the temperature of 180 ° C. or 200 ° C. and performing the image forming / heat fixing operation by a conventional method, the corona discharge of the charger 12 was stable and a high quality image could be formed even after printing 10,000 sheets. .

Here, low molecular siloxane structures D4 to D1
0 has a different composition, and the predetermined temperature of the fixing roller 21 (180
The amount of low-molecular-weight siloxane gas that evaporates when operated at ℃) is 5000, 2000, 1000, 500, 2
A comparative test was performed using the pressure roller 22 formed of each silicon rubber different from 00 ppm. Operating conditions were room temperature 24 ° C., humidity 14% RH, and 10000 sheets were printed. The result was determined by whether or not a speckled pattern was formed on the paper sheet that passed through the heat fixing unit 20. The amount of the low-molecular siloxane gas generated was determined by gas chromatography G
It was confirmed by actual measurement with C-14A (made by Shimadzu).

Thus, as shown in FIG. 3, when the amount of silicon rubber conventionally generated from the pressure roller 22 was 5000 ppm, a black spot pattern was generated, and the print content was judged to be unacceptable. The same was true for 2000 ppm. However, in the case of 1000 ppm, it was possible to form an image quality without any problems in practical use. Furthermore, 50
In the case of 0 ppm or less, only the original image was clearly formed even if the image was enlarged and checked.

In the above embodiment, the pressure roller 22 is used.
From the beginning, the composition of the silicone rubber forming the above was selected so that the amount of low-molecular-weight siloxane gas generated was 1000 ppm or less. Gas generation amount is 1000p
It may be pm or less. Therefore, the heat fixing temperature is set to 20 by mounting the pressure roller 22 formed of the silicone rubber having the composition that generates the low-molecular siloxane gas of 2000 ppm.
The experiment was conducted under the condition that the temperature was 0 ° C. and the image forming unit 10 (corona discharge of the charger 12) was stopped. Then, a large amount of low molecular siloxane was generated and adhered to the discharge wire 12W. However, since no corona discharge is performed, the low-molecular siloxane remains as it is and does not become silica SiO 2. It could be easily removed by cleaning with a cloth. And
After operating for one day, the amount of gas generated from the pressure roller 22 was actually measured and could be reduced to 1000 ppm or less. That is, for convenience, this device (10, 2
0) can be used to produce the silicone rubber forming the pressure roller 22.

[0023]

According to the present invention, the pressure roller of the heat fixing section is made of silicone rubber having a composition such that the amount of low-molecular siloxane gas evaporated when the fixing roller is operated at a predetermined temperature is 1000 ppm or less. Since it is formed, silica can be prevented from adhering to the discharge wire of the charger, and the charging can be performed stably. Therefore, a high-quality image can be stably formed, which can contribute to further speeding up.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram for explaining an embodiment of the present invention and a conventional example.

FIG. 2 is also a diagram for explaining a heat fixing unit.

FIG. 3 is a diagram for explaining the effect of the embodiment of the present invention in comparison with the effect of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main body case 10 Image forming part 11 Image carrier 12 Discharge type charger 12W Discharge wire 13 Exposure means 14 Developing device 15 Transfer device 20 Thermal fixing part 21 Fixing roller 22 Pressure roller 25 Cleaning means

Claims (1)

[Claims] 1. A discharge type charging device, an exposing means, a developing device, which is arranged around a drum-shaped image bearing member along the rotation direction thereof.
An image forming apparatus comprising: an image forming unit including a transfer device; and a thermal fixing unit including a fixing roller and a pressure roller that is slidably attached to the fixing roller. The amount of low-molecular-weight siloxane gas that evaporates when the roller is operated at a specified temperature is 1
An image forming apparatus formed of silicon rubber having a composition of 000 ppm or less.