JP2983181B2 - Electrophotographic image fixing method, image forming method and image forming apparatus using dimethyl silicone oil as release agent - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image fixing method, an image forming method, and an image forming apparatus using a release agent for fixing an electrophotographic heat roll containing dimethyl silicone oil as a main component.

[0002]

2. Description of the Related Art In an electrophotographic method, generally, a toner image formed on an image forming member by development is transferred to a transfer paper such as plain paper, and a fixing means for applying heat, pressure and the like to the transfer paper is employed. Have been. Such heat fixing and pressure fixing have both advantages and disadvantages because their means are different, but the former heat fixing, especially the heat roll fixing method,
Due to its good heat transfer efficiency and high safety, it is widely used in dry electrophotography.

However, in this method, since the heated roll is directly adhered to the toner image for fixing, a part of the melted toner adheres and transfers (offset phenomenon) to the surface of the fixing roll (heat roll). This causes (i) re-transfer to the next transfer paper to generate image stains, or (ii) transfer to the surface of a pressure roll which forms a pair with a heat roll and presses against the roll surface to stain the back surface of the transfer paper. Inconvenience.

In order to avoid such inconveniences, the surface of the heat roll is formed of a material having excellent releasability with respect to the toner such as a fluororesin or a silicone resin.
A method of applying an anti-offset liquid such as silicone oil to the surface thereof using a felt, a roll, a blade, or the like has been performed. However, so-called "oil-less fixing rolls" have been used in which the silicone rubber is impregnated with silicone oil or the like before or after curing so that the oil is constantly leached on the surface and the supply of the release agent is omitted. However, it is pointed out that the roller is worn by fixing at most several hundred sheets due to insufficient strength of the silicone rubber itself and softening by impregnating oil.

Therefore, dimethyl silicone oil having a kinematic viscosity of 50 to tens of thousands of centistokes (at 25 ° C.) is applied to the heat fixing roll in consideration of the releasability and the coating property to the heat fixing roll. Is generally adopted. However, when conventional dimethyl silicone oil is used as a release agent and used for heat fixing, corona discharge unevenness occurs over time,
As a result, the fact is that the phenomenon of image density reduction and density unevenness is caused.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for fixing an electrophotographic image using a releasing agent for fixing a hot roll, which is free from the above-mentioned disadvantages and can provide a high quality image for a long period of time. , An image forming method and an image forming apparatus.

[0007]

SUMMARY OF THE INVENTION The present invention firstly provides a kinematic viscosity of 300 to 60,000 centistokes and a molecular weight of 20 to 60 centistokes.
The toner image on the transfer paper is fixed by using a fixing roll formed by applying dimethylsilicone oil having dimethylsiloxane having a content of not more than 300 ppm or less as a structural unit to the surface as dimethylsiloxane oil as a release agent. Secondly, an electrophotographic image forming method using the above fixing method, and thirdly, a kinematic viscosity of 300 to 60,000 centistokes and a molecular weight of 2,000
This is an electrophotographic image forming apparatus equipped with a fixing roll in which dimethyl silicone oil containing dimethylsiloxane having a content of the following as 300 ppm or less as a structural unit is present on the surface as a release agent.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors reexamined silicone oil, which has been conventionally used as a releasing agent for heat roll fixing, and found that dimethylsiloxane

Embedded image Molecular weight in dimethyl silicone oil with
There are low molecular weight components of 2000 or less, which evaporate by the heat roll and grow as SiO ₂ on the charge wire, causing uneven charging. In addition, this low molecular weight component contributes to prevention of offset phenomenon I confirmed that there was little to do. The present invention has been made based on this.

Hereinafter, the present invention will be described in more detail.
The release agent used in the present invention is composed of dimethyl silicone oil having dimethyl siloxane as a structural unit. As can be easily inferred from the above description, the content of the low molecular weight component (those having a molecular weight of 2000 or less) is included here. Is 300 ppm or less, preferably 200 ppm or less. This dimethyl silicone oil has a kinematic viscosity (25 ° C.) of 300 to 60,000 centistokes (cSt), preferably 500 to 50,000 centistokes (cSt).
It is. In order to remove dimethylsiloxane (low molecular weight component) having a molecular weight of 2000 or less from the dimethylsilicone oil, the dimethylsilicone oil is stirred for about 15 minutes.
It may be heated at 0 ° C. for 20 hours or more (preferably at 150 ° C. for 24 hours or more) to volatilize low molecular weight components. Kinematic viscosity can be measured with an Ostwald viscometer.

Dimethyl silicone oil is a mixture of dimethylsiloxanes represented by the above structural formulas having different molecular weights, and the molecular weight Mw (weight average molecular weight) of the mixture is measured by gel permeation chromatography (GPC). It is represented by the value given.

Here, a method for measuring the weight average molecular weight of a sample (dimethyl silicone oil) by GPC will be described for reference as follows. First, at a temperature of 25 ° C., a solvent (tetrahydrofuran) is caused to flow at a flow rate of 1 ml per minute, and 8 mg of a tetrahydrofuran sample solution having a concentration of 0.4 g / dl is injected as a sample to perform measurement. In measuring the molecular weight of a sample, select a measurement condition in which the molecular weight distribution of the sample is included in a range in which the logarithm of the molecular weight and the count number are linear in a calibration curve prepared from several types of monodisperse polystyrene standard samples. .

In this measurement, the reliability was determined based on the NBS706 polystyrene standard sample (Mw
= 28.8 × 10 ⁴ , Mn = 13.7 × 10 ⁴ , Mw / Mn = 2.11)
Confirm by Mn being 2.11 ± 0.10. Note that Mn
Is the number average molecular weight.

The dimethyl silicone oil of the present invention obtained as described above can be widely used as a release agent in an electrophotographic method in a heat roller fixing device. For example, the release agent can be applied not only to the surface of the fixing heat roller but also to the pressure roller.

[0014]

EXAMPLES Examples and comparative examples are shown below. Parts here are parts by weight.

Example 1 A mixture composed of 85 parts of styrene-n-butyl methacrylate copolymer resin, 12 parts of carbon, 3 parts of chromium-containing azo dye was kneaded, dried and pulverized to obtain a toner having an average volume particle diameter of about 13 μm. . On the other hand, the average particle size is about 1
A 00 μm ferrite core material was coated with a methyl methacrylate resin at a thickness of about 1 μm to form a coated carrier.

A two-component developer is prepared by mixing the toner and the coated carrier so that the toner has a ratio of about 3% by weight, and the developer is charged into an electrophotographic copying machine FT6200 manufactured by Ricoh Company. A continuous running test was performed. In order to prevent the offset in the fixing device and prevent the paper from being wound around the heat roll, a release agent (dimethyl silicone oil) was put in a tank, and the surface was coated on a Teflon-made fixing roll via felt. The release agent used had a kinematic viscosity of 300 centistokes, a weight average molecular weight of 11,000, and a low molecular weight component having a molecular weight of 2000 or less and a ratio of 160 ppm.

As a result, during the running of 100,000 sheets, no image contamination due to hot offset or paper wrapping around the roller occurred at all, and high image quality without image density reduction and density unevenness was maintained even after the running. The charge wire after the running was removed, and the surface was observed with a scanning electron microscope. As a result, no growth of acicular foreign matter was observed.

Comparative Example 1 For comparison, the following release agent was run in exactly the same manner as in Example 1 except that a kinematic viscosity of 20,000 centistokes, a weight average molecular weight of 11,000, and a ratio of low molecular weight components having a molecular weight of 2,000 or less of 2030 ppm were used. Tested.

As a result, hot offset and paper wrapping around the roller did not occur during the running, but after the running of 40,000 sheets, the stripe-shaped density unevenness began to appear on the black solid portion, and the density was high after the running of 70,000 sheets. The running was stopped because the difference between the lower part and the lower part became 0.3 as measured by the Macbeth densitometer. At this time, the surface of the charge wire of the corona charger was observed with a scanning electron microscope. As a result, needle-like foreign matters having a length of about 20 μm had grown.
When this foreign substance was analyzed by FT-IR and X-ray microanalyzer, it was confirmed that the main component was SiO ₂ .

Example 2 A running test of 100,000 sheets was performed in exactly the same manner as in Example 1 except that felts impregnated with the following release agent were replaced every 5,000 sheets. (Release agent) Kinematic viscosity: 20,000 centistokes Weight average molecular weight: 48000 Ratio of low molecular weight components having a molecular weight of 2,000 or less 90 ppm

As a result, hot offset and paper wrapping around the roller did not occur at all during the running of 100,000 sheets, and high image quality without image density reduction and density unevenness was maintained after the running. Also, no growth of foreign matter was observed on the charge wire.

Comparative Example 2 A running test was conducted in exactly the same manner as in Example 1 except that felts impregnated with the following release agent were replaced every 5,000 sheets. (Release agent) Kinematic viscosity: 20,000 centistokes Weight average molecular weight: 48000 Ratio of low molecular weight components having a molecular weight of 2,000 or less: 1500 ppm

As a result, hot offset and paper wrapping around the roller did not cause any problem, but after about 50,000 sheets of running, a streaky density unevenness began to appear on the black solid portion, and after 80,000 sheets of running, the density was not uniform. Running was stopped because the difference between the high and low parts was 0.3 as measured by a Macbeth densitometer. Observation of the surface of the charge wire revealed that needle-like foreign matters having a length of about 15 μm had been formed. As a result of the analysis, the foreign substance was mainly composed of SiO ₂ .

[0024]

According to the present invention, a hot roll is obtained by using dimethyl silicone oil having a kinematic viscosity of 300 to 60,000 centistokes (25 ° C.), preferably 500 to 50,000 centistokes, as a releasing agent for fixing an electrophotographic heat roll. Prevents offset, prevents paper wrapping around rolls, and has a molecular weight of 2000
Reduce the content of the following low molecular weight dimethylpolysiloxane to 300p
By keeping the pressure at pm or less, preferably at 200 ppm or less, the growth of acicular SiO _{2 on} the charge wire of the corona discharger can be prevented. In addition, by adopting a method in which dimethyl silicone oil is applied to the surface of the heat fixing roll and the toner on the transfer paper is pressed and heated, good fixation is performed, and a high-quality copy without image density reduction or density unevenness is obtained. be able to.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 13/20 G03G 15/20 C08G 77/04

Claims (3)

(57) [Claims] 1. A dimethyl silicone oil having a kinematic viscosity of 300 to 60,000 centistokes and a molecular weight of 2,000 or less and a content of dimethyl siloxane having a content of 300 ppm or less as a structural unit is applied to a surface as a release agent. An electrophotographic image fixing method, comprising fixing a toner image on a transfer sheet using a fixing roll. 2. An electrophotographic image forming method using the fixing method according to claim 1. 3. A dimethylsilicone oil having a kinematic viscosity of 300 to 60,000 centistokes and a molecular weight of 2,000 or less and a content of dimethylsiloxane of 300 ppm or less as a structural unit is present on the surface as a release agent. An electrophotographic image forming apparatus equipped with a fixing roll.