JPH023073A - Toner for developing electrostatic images - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a toner for developing electrostatic images, and more particularly to a toner for developing electrostatic images containing a specified dimethyl silicone oil.

[Prior art]

In electrophotography, a toner image formed on an image forming member by development is generally transferred to a transfer paper such as plain paper, and then a fixing means is employed which applies heat, pressure, etc. to the toner image. Since these heat fixing and pressure fixing methods are different, they both have advantages and disadvantages.
The former type of heat fixing, particularly the heat roll fixing method, is widely used in dry electrophotography because of its good heat transfer efficiency and high safety.

The toner (-component toner, two-component toner) used in this dry electrophotography method is made mainly of a colorant and a binder resin.

However, in this hot roll fixing method, a heated roll is directly brought into close contact with the toner image to perform fixing, so some of the molten toner adheres to and transfers to the surface of the fixing roll (thermal roll) (offset phenomenon). This may (i) transfer again to the next transfer paper, causing image stains, or (ii) transfer to the surface of the pressure roll, which is paired with the heat roll and comes into pressure contact with the surface of the roll, staining the back side of the transfer paper. It has the disadvantage of being stored away.

In order to avoid these inconveniences, (a) toner containing silicone oil (Japanese Patent Application Laid-Open No. 54-48245,
(described in publications such as JP-A No. 59-197048)
(b) Addition of silica surface treated with silicone oil (
Toner with internal or external addition
(described in publications such as No. 59) have been proposed. These will solve the above-mentioned inconvenience.

It is intended to improve the fluidity of the toner and to prevent the toner from filming on the carrier and image forming member (photoreceptor).

As a silicone oil, - For boat fishing, the kinematic viscosity is 5 to 5.
Examples include 100,000 centistokes (at 25°C) methyl silicone oil, dimethyl silicone oil, phenylmethyl silicone oil, chlorphenylmethyl silicone oil, alkyl-modified silicone oil, fatty acid-modified silicone oil, polyoxyalkylene-modified silicone oil, etc. One type or a mixture of two or more types have been used, and among them, dimethyl silicone oil is most suitable.

However, when a conventional toner containing (adding) dimethyl silicone oil is used and heat-fixed, uneven corona discharge occurs over time.
As a result, the actual situation is that a decrease in image source density and uneven density occur.

〔the purpose〕

The present invention provides a toner for developing electrostatic images that does not cause the above-mentioned unevenness in corona discharge and allows a large number of high-quality images to be obtained over a long period of time.

〔composition〕

The present invention provides a toner for developing electrostatic images containing a color viewing agent and a binder resin as main components, which has a kinematic viscosity of about 30 to about 60,000 centistokes (at 25°C) and a molecular weight of about 2,000 or less. It is characterized by containing 0.01 to 360% by weight of dimethylsilicone oil having dimethylsiloxane as a structural unit and having a content of about 300 ppm or less.

Incidentally, the inventors of the present invention have reexamined silicone oil, which has traditionally been used as an additive in toner, and have found that dimethylsilicone oil, which has dimethylsiloxane as a structural unit, contains a low molecular weight component with a molecular weight of about 2,000 or less. It has been found that a considerable amount of is present, and this is evaporated by the hot roll, reacts with oxygen on the charge wire of the corona charger, and grows as 5in2, causing charging unevenness. The present invention has been made based on this.

The present invention will be explained in more detail below. The dimethylsilicone oil in the toner of the present invention has dimethylsiloxane as a structural unit, but as can be easily inferred from the above, it contains low molecular weight components (molecular weight about 2000 Low molecular weight components are removed as much as possible so that the content of 30
to 60,000 centistokes (CS) preferably 50 to 5
In order to remove dimethylsiloxane (low molecular weight component) with a molecular weight of about 2,000 or less, which is CS), from dimethylsilicone oil, dimethylsilicone oil is heated at about 150°C with sufficient stirring for 15 hours or more (preferably l
5 (at 1° C. for 24 hours or more) to volatilize such low molecular weight components.

The kinematic viscosity can be measured using an Ostwald viscometer.Dimethylsilicone oil is a mixture of dimethylsiloxanes with different molecular weights represented by the above structural formula, and the molecular weight Mw (weight average molecular weight) of this oil is Gel permeation chromatography method (GPC)
) is expressed as a value measured from

Here, the method for measuring the weight average molecular weight of a sample (dimethyl silicone oil) by GPC will be explained as follows for reference. First, at a temperature of 25°C,
A solvent (tetrahydrofuran) is flowed at a flow rate of 1 mΩ/min, and a sample weight of 8 mg of a tetrahydrofuran sample solution with a concentration of 0.4 g/dQ is injected, and measurement is performed. When measuring the molecular weight of a sample, select measurement conditions in which the molecular weight distribution of the sample falls within a range where the logarithm of the molecular weight and the count number of a calibration curve prepared using several types of monodisperse polystyrene standard samples are linear. . In addition, the reliability of this measurement was determined using the NB5706 boristyrene standard sample (M++=28.8X10', Mn=13
．． 7X 10', M w / M n = 2.11)
Confirm that w/Mn is 2.11±0.10. In addition, Mn is a number average molecular weight.

The amount of dimethyl silicone oil according to the present invention obtained as described above added to the toner is 0.01 to 3.0% by weight, preferably 0.1 to 2.0% by weight. If the amount added is less than 0.01% by weight, hot offset tends to occur, while if it is more than 3.0% by weight, the fluidity of the toner will be impaired. The dimethyl silicone oil can be added to the toner either internally or externally, but internally is preferable. As mentioned above, the method of addition is to add it directly when the toner forming material is mixed, or to add it by attaching it to the surface of hard fine powder (silica, alumina, titanium oxide, etc.). Vine.

Next, examples and comparative examples will be shown. Parts here are parts by weight.

Example 1 A mixture consisting of 12 parts and 3 parts of a carbon-containing chromium azo dye was kneaded, dried, and pulverized and classified to obtain a toner having an average particle diameter of about 12 μm.

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

A two-component developer is prepared by mixing these toners and coated carrier so that the toner accounts for approximately 3% by weight, and this developer is applied to an electrophotographic copying machine manufactured by Ricoh Co., Ltd., FT6.
200 and conducted a continuous running test. In addition,
The fuser roll has a core metal coated with Teflon to a thickness of approximately 25 μm, and the application of a release agent was omitted.6 As a result, during the running of 100,000 sheets, there were no image stains due to hot offset or paper wrapping on the roller. It does not occur at all,
Even after running, high image quality was maintained without any reduction in image density or density unevenness.

In addition, after running, the charge wire of the corona charger was removed and the surface was observed using a scanning electron microscope.
No growth of needle-like foreign bodies was observed.

Comparative Example 1 For comparison, the following dimethyl silicone oil has a kinematic viscosity of about 20,000 centistokes (at 25°C), a weight average molecular weight of 13,000, and a proportion of low molecular weight components with a molecular weight of about 2,000 or less, 1,800.
A running test was conducted in exactly the same manner as in Example 1 except that ppmm was used.

As a result, hot offset and paper wrapping around the roller did not occur during running, but after 50,000 sheets, sushi-like density unevenness began to appear in the black solid area, and after 80,000 sheets, there were high and low density areas. The difference between the two points was 0.3 when measured using a Macbeth densitometer, so I stopped running. At this time, when the surface of the charge wire of the corona charger was examined using a scanning electron microscope, it was found that approximately 1
A needle-like foreign body with a length of 5 μm was growing. When this foreign material was analyzed using FT-IR and XM microanalyzer, it was confirmed that the main component was 5in2.

Example 2 A running test was conducted in the same manner as in Example 1 except that the dimethyl silicone oil shown below was used.

(Dimethyl silicone oil) Kinematic viscosity: approx. 10,000 centiTokes (at 25°C) Weight average molecular weight: 40,000 Ratio of low molecular weight components with a molecular weight of approx. 2,000 or less: approx. 80 pp
+i As a result, no hot offset or paper wrapping around the roller occurred during the 100,000-sheet run, and high image quality was maintained without any reduction in image density or density unevenness even after the run. Further, no foreign matter was observed to grow on the charge wire of the corona charger.

Comparative Example 2 The amount of dimethyl silicone oil added was varied from 1.5 parts to 3.
A running test was conducted in the same manner as in Example 2 except that the amount was changed to 0 parts.

As a result, although hot offset and paper wrapping on the roller were not a problem, the initial image density of 1.40 was reduced to 300.
The density was 1.10 in a run of 0 copies, and 0.72 in a run of 5,000 copies, and a decrease in density was observed as the number of copies increased.

〔effect〕

The toner of the present invention contains dimethyl silicone oil with a kinematic viscosity of 300,000 to 60,000 centistokes (at 25°C), and the content of low molecular weight dimethyl polysiloxane having a molecular weight of about 2,000 or less is suppressed to 300 ppm or less. As a result, hot offset can be prevented, paper can be prevented from being wrapped around the roll, and the growth of needle-like Sio on the charge wire of the corona discharger can also be prevented.

Further, by employing a method of pressing and heating using such toner, fixing is performed well, and a high-quality copy without a decrease in image density or density unevenness can be obtained.

Claims (1)

[Claims] 1. In a toner whose main components are a binder resin and a colorant, the kinematic viscosity is about 30 to about 60,000 centistokes, and the content of molecular weight of about 2,000 or less is about 30,000 centistokes.
0.01 to 3.0% by weight of dimethylsilicone oil whose structural unit is dimethylsiloxane with a content of 0 ppm or less
A toner for developing an electrostatic image, comprising: