JP2656947B2 - Dimethyl silicone oil, consisting of release agent for electrophotographic heat roll fixing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to dimethyl silicone oil and a release agent for fixing an electrophotographic heat roll containing dimethyl silicone oil as a main component.

(Prior art)

In the electrophotographic method, generally, a fixing unit that transfers a toner image formed on an image forming member by development to a transfer paper such as a plain paper and applies heat, pressure, and the like to the transfer paper is adopted. Such heat fixing and pressure fixing have both advantages and disadvantages due to their different means,
The former heat-fixing method, particularly the heat-roll fixing method, is widely used in dry electrophotography because of its good heat transfer efficiency and high safety.

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). And (2) moving to the surface of a pressure roll which forms a pair with a heat roll and presses against the surface of the roll to stain the back surface of the transfer paper. Has inconvenience.

In order to avoid such inconveniences, the surface of the heat roll is formed of a material having excellent releasability from toner such as fluorine resin and silicone resin, and an anti-offset liquid such as silicone oil is applied to the surface during thermal fixing. A coating method using a felt, a roll, a blade, or the like is 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. But
It has been pointed out that in this case, because of insufficient strength of the silicone rubber itself and softening due to the impregnating oil, the roll is worn by fixing at most several hundred sheets.

Therefore, the method of applying dimethyl silicone oil with a kinematic viscosity of 50 to tens of thousands of centistokes (25 ° C) to the heat fixing roll is now considered in consideration of the release agent and the applicability to the heat fixing roll. Generally adopted.

However, when conventional dimethyl silicone oil is used as a release agent and thermally fixed, corona discharge unevenness occurs over time, and as a result, image density decreases and density unevenness occurs. Is the actual situation.

〔Purpose〕

The present invention is free from the above disadvantages, and
It is an object of the present invention to provide a hot roll fixing release agent capable of obtaining a high-quality image for a long period of time.

〔Constitution〕

A first aspect of the present invention is a dimethyl silicone having a kinematic viscosity of 300 to 60,000 centistokes (cSt) and a structural unit of dimethylsiloxane having a molecular weight of 2,000 or less and a content of 300 ppm or less. Oil.

A second aspect of the present invention is a release agent for fixing an electrophotographic heat roll, comprising the above dimethyl silicone oil.

By the way, the present inventors re-examined the silicone oil which has been conventionally used as a releasing agent for hot roll fixing, and found that dimethyl siloxane Molecular weight in dimethyl silicone oil with
There is a low molecular weight component of 2000 or less, which evaporates by the heat roll and grows as SiO ₂ on the charge wire, causing uneven charging, and further, 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.

The present invention will be described in more detail below. The release agent of the present invention is composed of dimethyl silicone oil having dimethyl siloxane as a structural unit, and as can be easily inferred from the above, a low molecular weight component is contained here. (Molecular weight 20
00 or less) is 300 ppm or less, preferably 200 ppm
It has been removed as much as possible. This dimethyl silicone oil has a kinematic viscosity (25
° C) is between 300 and 60,000 centistokes (cSt), preferably 50
~ 50,000 centistokes (cSt). In order to remove dimethylsiloxane having a molecular weight of 2000 or less (low molecular weight component) from dimethylsilicone oil, the dimethylsilicone oil is heated at about 150 ° C. for 20 hours or more (preferably at 150 ° C. for 24 hours or more) with sufficient stirring. What is necessary is just to volatilize a low molecular weight component.

Kinematic viscosity can be measured with an Ostwald viscometer.

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

Here, the method of measuring the weight average molecular weight of the sample (dimethyl silicone oil) by GPC will be described for reference as follows. First, at a temperature of 25 ° C, a solvent (tetrahydrofuran) is flowed at a flow rate of 1 ml per minute,
8 mg as a 0.4 g / dl tetrahydrofuran sample solution
Inject and measure. 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 by the NBS706 polystyrene standard sample (Mw = 2
Mw / Mn of 8.8 × 10 ⁴ , Mn = 13.7 × 10 ⁴ , Mw / Mn = 2.11) is 2.11
Confirm by being ± 0.10. Mn is a number average molecular weight.

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

〔Example〕

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

Example 1 A mixture composed of 85 parts of a styrene-n-butyl methacrylate copolymer resin, 12 parts of carbon, and 3 parts of a chromium-containing azo dye was kneaded, dried and pulverized to obtain a toner having an average volume particle size of about 13 μm.

On the other hand, a ferrite core material having an average particle size of about 100 μm was coated with a methyl methacrylate resin at a thickness of about 1 μm to form a coated carrier.

The toner and the coated carrier are mixed with the toner by about 3
The two-component developer was prepared by mixing so as to obtain a ratio of 2% by weight, and the developer was placed in an electrophotographic copying machine FT6200 manufactured by Ricoh Co., Ltd. to perform a continuous running test.

In order to prevent offset in the fixing device and prevent the paper from wrapping 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 has a kinematic viscosity of 300 centistokes, a weight average molecular weight of 11,000, and a molecular weight of 2
A low molecular weight component having a ratio of 169 ppm or less was used.

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.

Also, remove the charge wire after running,
Observation of the surface with a scanning electron microscope revealed no growth of needle-like foreign matter.

Comparative Example 1 For comparison, a running test was performed in exactly the same manner as in Example 1 except that the following release agent, 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. Was.

As a result, the hot male set and the paper wrapping around the roller did not occur during the running, but after the 40,000 sheets were run, the stripe-shaped density unevenness began to be generated on the black solid portion, and after the 70,000 sheets were run, the density was high. Running was stopped because the difference from the low 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.
Needle-like foreign matters having a length of m were growing. FT-
Analysis by IR and X-ray microanalyzer confirmed that the main component was SiO ₂ .

Example 2 A running test of 100,000 sheets was performed in the same manner as in Example 1 except that felts impregnated with the release agent shown below 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, no hot offset or paper wrapping around rollers occurs during running 100,000 sheets, and even after running High image quality without image density reduction or density unevenness was maintained.
Also, no growth of foreign matter was observed on the charge wire.

Comparative Example 2 A running test 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: 48,000 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 rollers were not a problem, but after running about 50,000 sheets Streaked density unevenness began to appear in the solid black area, and after running 80,000 sheets, the difference between the high density area and the low density area was 0.3 as measured by a Macbeth densitometer, so running was stopped.

When observing the surface of the charge wire, it was about 15μm
Needle-like foreign matter having a length of was formed. As a result of the analysis, the foreign substance was mainly composed of SiO ₂ .

〔effect〕

The present invention provides a kinematic viscosity as a release agent for fixing an electrophotographic heat roll.
300-60,000 centistokes (25 ° C), preferably 50-5
By using 10,000 centistokes of dimethyl silicone oil, hot offset can be prevented, paper wrapping around the roll can be prevented, and the content of low molecular weight dimethylpolysiloxane having a molecular weight of 2000 or less is 300 ppm or less, preferably 200 ppm or less. Pressing can prevent needle-like SiO ₂ from growing on the charge wire of the corona discharger.

In addition, by adopting a method in which such dimethyl silicone oil is applied to the surface of the heat fixing roll and the toner on the transfer paper is pressed and heated, high-quality copying can be performed satisfactorily, and a high-quality copy without image density reduction or density unevenness is obtained. be able to.

Claims (2)

(57) [Claims] 1. A dimethyl silicone oil having a kinematic viscosity of 300 to 60,000 centistokes and a dimethylsiloxane having a molecular weight of 2,000 or less and a content of 300 ppm or less as a structural unit. 2. A release agent for fixing an electrophotographic heat roll, comprising the dimethyl silicone oil according to claim 1.