JPS60194478A - Fixing device using heat roller - Google Patents

Abstract

PURPOSE:To prevent offset by forming an insulating layer of a press roller pressed against a heat roller so that paper powder is adhered to the surface of the insulating layer. CONSTITUTION:The titled device is provided with the heat roller 4 obtained by forming a releasing type layer on a core material and the press roller 7 obtained by forming an insulating layer on its core material. A rubber-like elastic body such as natural rubber and synthetic rubber, e.g. silicone rubber, is used as the insulating layer of the press roller 7 and the surface is made rough. Although paper powder of copying paper which is previously collected may be used as the paper powder S adhered to the surface of the press roller 7, inorganic substances may be used instead of cellulose as a main component of the paper powder S and kaoline and talc as additives. After charging electrostatically the surface of the roller 7 by corona electrostatic charge or triboelectrification the paper powder S is forcedly adhered to the surface of the roller 7 by rubbing the surface with cloth to which the paper powder S is adhered.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a heat roller fixing device in an electrophotographic copying machine, an electronic printer, etc. Specifically, as shown in FIG. A releasable layer 2 is formed.
A heating roller 4 with a built-in heater 3 and a pressure roller 7 having an insulating layer 6 formed on a core material 5 and in pressure contact with the heating roller 4 are provided to hold the copy paper P holding the positively charged toner image T. Both rollers 4, so that the surface P faces the heating roller 4,
The present invention relates to a heat roller fixing device that fixes a positively charged toner image T onto a copy paper P by passing the toner image T through a roller. In the diagram,
Reference numeral 9 indicates a separation claw, 10 a guide plate, and 11 a paper discharge roller.

Conventional technology This type of heat roller fixing device has a good releasability on the roller surface and can prevent toner from melting and adhesion, so there is no need to apply anti-offset liquid such as silicone oil, and even if it is used, only a small amount of offset will occur. It is enough to apply the preventive liquid,
There is no stain on the copy paper P, and the texture of the copy paper P after fixing is good. However, the releasable layer 2 is a resin layer that is fixed to the core material 1 directly or through a primer layer 8, and since it is an insulator, it can be used as an insulating layer 6 on the surface of the pressure roller 7, copy paper P, etc. The toner image T is triboelectrically charged by the insulator, and initially charged negatively, the positively charged toner image T is electrostatically attracted to the surface of the heating roller 4 and an offset occurs, and after a certain period of time, it becomes positively charged. A phenomenon is observed in which offset is no longer generated due to electrostatic repulsion.

In order to prevent the offset of the positively charged toner image, the present inventor attempted to charge the release layer 2 positively even during the initial period, and has already reported in Japanese Patent Laid-Open No. 57
-150869, JP-A-58-134673, etc. However, these methods involve adding carbon black, for example, to the layer of the heating roller 4 or pressure roller 7, and therefore cannot be applied directly to conventional heating roller fixing devices. be.

Summary of the Invention The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to prevent offset by positively charging a heating roller using a simple method.

The inventors of the present invention focused on the fact that, as mentioned above, the frictional charging of the heating roller in the conventional device becomes negative during the initial period, but then reverses and maintains the positive polarity, and the heating roller becomes positively charged. As a result of various studies on the causes of this, it was discovered that paper dust adhering to the pressure roller surface was a major factor. In other words, paper dust generated from the copy paper adheres to the surface of the pressure roller each time the copy paper is passed, and the amount increases when the polarity is reversed to positive. We have arrived at what makes positive charging possible.

From this, we believe that if paper powder is attached to the surface of the pressure roller before the paper starts passing, it will be positively charged during the initial period.
This has led to the completion of the present invention.

The present invention includes a heating roller having a releasable layer formed on a core material, and a pressure roller that is in pressure contact with the heating roller and having an insulating layer formed on the core material, and is capable of producing a positively charged toner image. In a heat roller fixing device that fixes the toner image on the copy paper by passing the copy paper to be held between the two rollers so that the toner image holding surface thereof faces the heating roller, the insulating layer of the pressure roller is It is characterized by consisting of an insulating layer with paper powder adhered to its surface.

As the core material of the heating roller and the pressure roller, aluminum, aluminum alloy, iron alloy such as stainless steel, and other metals are used. - As the mold release resin, it is best to use a fluororesin with excellent heat resistance and mold release properties, such as tetrafluoroethylene-perfluoroalkoxytyrene copolymer (PFA resin).

As the primer for the mold release resin, a primer mainly composed of a fluororesin, which is commercially available as an adhesive undercoat for the metal materials such as iron alloys and aluminum alloys, is used. Specifically, DuPont Tackware (
Primer A) 459-=5-882, MP902BN manufactured by Mitsui Fluorochemicals, etc. are used.

The insulating layer of the pressure roller is made of a commonly used material exhibiting rubber-like elasticity such as natural rubber or synthetic rubber, such as silicone rubber, but any material having a rough surface may be used.

The filter paper powder adhering to the surface of the pressure roller may be made of paper powder collected in advance from copying paper used in electrophotographic copying machines, electronic printers, etc.; Cellulose (cellulose expressed as (CsHxoCi)n)
and kaolin as an additive (AI!2S12ns(OH
)4.nH+o) and talc (3Mg0.4 SiO2
・H2O) and inorganic substances are used.

There are two methods for attaching paper powder to the pressure roller surface: After charging the roller surface with corona charging and frictional charging, paper powder is electrostatically attached to the roller surface. For the rubbing, a method of forcibly adhering the paper powder or a method of adhering the paper powder while pressing it onto the roller surface with a blade can be adopted, but it is sufficient that the paper powder is taken into minute recesses on the roller surface.

Example Examples of the present invention will be described below along with comparative examples.

Comparative example.

A 5μ thick layer of fryer (MPG-RD manufactured by Mitsui Fluorochemicals) is applied onto an aluminum roller as a core material, and a layer of PFA resin (MPIQ manufactured by Mitsui Fluorochemicals) is applied on top of that.
) was used to manufacture a heating roller with a diameter of 32 cm, which was made by laminating a release resin layer with a thickness of about 30 μm, and separately, the surface of the roller made of aluminum as a core material was laminated with a commercially available silicone rubber layer with a thickness of 5 μm. A pressure roller having a diameter of 40 cm was manufactured and was used to construct the heat roller fixing device shown in FIG. Note that the pressing force of the pressing roller is set to 40~. Using this device, a positively charged toner image (toner: mainly composed of styrene/acrylic resin, average particle size 14μ, charge amount 10-12μ) was formed by electrophotography.
c/g) A4 size copy paper that holds 11crn
When 12 sheets per minute were passed between the two rollers at a speed of 1/2 and the fixing process was performed at a heating roller temperature of 170.degree. C., offset occurred up to about 120 sheets.

When the charge and potential of the heating roller at that time were measured using a vibrating surface electrometer, results as shown by the curve CR in FIG. 2 were obtained.

From this result, after 5 minutes of continuous paper feeding, the charging potential of the heating roller reaches a maximum of 1200V, and after 10 minutes, the positively charged toner reaches a maximum of 125V due to the strong electrostatic force generated between the surface of the heating roller and the heating roller. It is thought that it is electrostatically attracted to the surface and an offset phenomenon occurs.

Example 1 An integrated mixture consisting of 91% cellulose as paper powder S, 6% kaolin, and 3% talc was applied to the silicone rubber surface of the pressure roller in a heat roller fixing device configured in the same manner as Comparative Example 2. As shown in FIG. 3, approximately 10 μm of the film was deposited substantially uniformly. After that, turn the heating roller to 170
Both rollers were rotated in contact with each other for 20 minutes at a speed of 11 cm/sec without passing copy paper while the temperature was maintained at a high temperature of .degree. Even after this contact rotation, paper powder remains attached to the surface of the pressure roller.

This is because the paper powder has entered the recesses on the silicone rubber surface of the pressure roller.

The measurement result of the charging potential of the heating roller at that time was 1 on the curve in FIG. 4, confirming that the surface of the heating roller was positively charged by the paper powder.

That is, when the contact rotation is 5 minutes, the voltage is 75V, and when the contact rotation is 10 minutes, it is 120V.
It is positively charged to 130V in 15 minutes and 150V in 20 minutes. Moreover, this positively charged heating roller exhibits almost no potential attenuation even after two weeks in a room temperature environment of 25° C. and 50% humidity.

Note that the curve CR shows the charging characteristics when contact rotation is performed in the same manner without adhering paper powder. This shows that the heating roller is normally negatively charged.

Next, we investigated the temperature dependence of positive charging of the heating roller due to paper dust. As a result, curves R2 and R3 show the charging characteristics when the heating roller was heated to 155°C and 140°C, respectively, after paper powder was attached. Since the positive charging efficiency is poor at a temperature lower than this, it can be said that it is preferable to carry out the charging at a higher temperature.

Example 2 Based on Example 1, using a heating roller that was positively charged by contact rotation for 5 minutes, that is, positively charged from 1 to 75 V according to the curve in FIG. As a result, clear images without phase offset were obtained from the first image.

The measurement result of the charging potential of the heating roller at that time is shown by the curve in FIG.

From this result, it is confirmed that the heating roller is positively charged even during the initial period, and that the positively charged toner image T is electrostatically repelled and no offset occurs.

However, it should be taken into consideration here that the charging potential of the heating roller tends to decrease immediately after continuous copy paper passes, so the positive charging potential due to paper dust is
It is important to take this potential reduction into account when setting.

Note that similar results were obtained even when paper dust from copy paper collected in advance was used as the paper dust.

10- Effects As described above, the present invention makes it possible to positively charge the heating roller even during the initial period of continuous sheet feeding by attaching paper powder to the surface of the pressure roller of the heating roller fixing device in advance. Therefore, there is an advantage that offset of positively charged toner can be prevented by a simple method and that it can be applied as is to a conventional heat roller fixing device.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional device, Fig. 2 is a comparative example of a heating roller and a charging characteristic diagram of an embodiment of the present invention, and Fig. 3 is a comparative example of main parts in which the present invention is applied to the device shown in Fig. 1. FIG. DESCRIPTION OF SYMBOLS 1... Core material, 2... Mold release layer, 4... Heating roller, 5... Core material, 6... Insulating layer, 7... Pressure roller,
■...Positively charged toner, P...Copying paper, S...Paper powder Applicant Minolta Camera Co., Ltd.=11- g槁D-Ir'Ginchi-Hayabusaε

Claims (1)

[Claims] 1. A heating roller having a releasable layer formed on a core material, and a pressure roller that is in pressure contact with the heating roller and having an insulating layer formed on the core material, A heat roller fixing device that fixes the toner image onto the copy paper by passing the copy paper holding the positively charged toner image between the two rollers so that the toner image holding surface faces the heating roller, A heat roller fixing device characterized in that the insulating layer of the pressure roller is made of an insulating layer having paper powder adhered to its surface. , 2L. The heat roller fixing device according to claim 1, wherein the paper powder consists of cellulose as a main component and an inorganic substance as an additive. 6. The heat roller fixing device according to claim 2, wherein the inorganic substance is kaolin and talc.