JPH0762338A - Ink composition - Google Patents

Abstract

PURPOSE:To obtain an ink composition which can develop a relatively large electroviscous effect at a smaller electric power consumption by dispersing specified carbonaceous particles in an electric insulating liquid phase. CONSTITUTION:60-1wt.% carbonaceous particles having a particle diameter of 0.01-100/mum and a C/H ratio of 1.0-10 are dispersed in 40-99wt.% at least one liquid phase selected from among an aliphatic hydrocarbon, an aromatic hydrocarbon, a halohydrocarbon, a silicone oil, etc., to obtain them objective composition having a viscosity of 0.5-1000cSt at 25 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an ink composition whose viscosity can be changed by applying a voltage, and is suitable for use in recording technology such as printing and printing in which the flow of ink is controlled by the voltage. It is a thing.

[0002]

2. Description of the Related Art A suspension in which a finely divided dielectric solid is dispersed in an electrically insulating liquid, the viscosity of which changes extremely rapidly and reversibly under the action of a sufficiently strong electric field. The fluid is known as an electrorheological fluid. Examples of the electrorheological fluid include U.S. Pat.No. 2,417,850, U.S. Pat.No. 3,047,507, U.S. Pat.No. 3,397,147, U.S. Pat.No. 3,970,573, U.S. Pat.
-31211 or West German Laid-Open Patent No. 3,427,499, the adsorbed water from the particle surface and made into fine particles of cellulose, starch, silica gel, ion exchange resin, polyacrylic acid lithium, etc. , Butyl sebacate, hydrocarbon oil, chlorinated paraffin, and silicone oil are known to be dispersed in an insulating liquid. The principle of increasing viscosity by applying voltage has not been clarified yet, but as voltage is applied, the positive and negative charges in the particles move and the particles polarize, attracting each other and forming a beaded pattern between the electrodes. It is believed that chain formation increases the apparent viscosity.
This phenomenon is generally referred to as an electrorheological effect, and it is expected that this characteristic will be applied to components for controlling devices and parts such as clutches, shock absorbers, and various anti-vibration rubbers.

However, the electrorheological fluids disclosed herein are
Since the ions in the particles move and the particles are polarized, water that is indispensable for ionization of the ions must be contained in the particles. Since the expression of the electrorheological effect depends on the water content, the water content changes due to the adsorption or drying of the water in the air, and the characteristics are not stable over time. In order to solve this, a dispersed phase particle that does not require water has been proposed, but none has been put to practical use yet.

Several proposals have been made for the application of this electrorheological fluid. For example, in JP-A-2-212149, it is used as an ink used in an ink jet recording apparatus. This shows a suspension in which carbon black particles as an electrorheological fluid are dispersed and contained in an insulating solvent. However, it is difficult to say that the electrorheological effect can be reliably obtained by using the carbon black particles as the disperse phase component in this way, and a large electrorheological effect is not exhibited. Further, it has been found that there is a problem that a large current flows when a high voltage is applied because of the high conductivity of the carbon black particles. for that reason,
In order to put it into practical use, the device must be upsized and consumes a lot of power.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art. It is possible to reliably obtain a large electrorheological effect with a small amount of power consumption, and to control discharge or fluidity by an electric field. It is an object of the present invention to provide an ink composition that can contribute to downsizing of a device and energy saving in a printing and printing device that controls printing.

[0006]

According to the present invention, an electrically insulating liquid phase has an atomic ratio of carbon atoms to hydrogen atoms of 1.0 to 10.
An ink composition comprising a dispersed phase of carbonaceous particles.

In the present invention, the dielectric particles constituting the dispersed phase component have an atomic ratio of carbon atoms and hydrogen atoms in elemental analysis (hereinafter referred to as "C / H ratio" for convenience) of 1.
0 to 10 carbon atom particles, preferably 1.2 to
5, more preferably 1.75 to 3.5. If the C / H ratio is less than 1.0, the carbonaceous particles cannot exhibit the function as a dielectric, and a sufficient electrorheological effect cannot be obtained. On the other hand, when the C / H ratio exceeds 10, too much current flows in the ink, and when used for practical purposes, the energy efficiency is low and there is a risk of dielectric breakdown.

Specifically, C / H suitable as a dispersed phase component
Carbonaceous substances having a ratio include coal tar pitch,
Various carbonaceous mesophases obtained by heat treatment of petroleum pitch, synthetic pitch, pitch obtained by thermally decomposing polyvinyl chloride or tar components, and pulverized products thereof, phenol resin, furan resin, polyacrylonitrile, cellulose, polychlorination Examples are so-called various low-temperature treated carbon materials obtained by heating and carbonizing a polymer material having a high residual carbon ratio such as vinylidene at 300 to 700 ° C. in an inert atmosphere. It is preferable that the composition of the carbonaceous substance is uniform, and therefore, for example, it is necessary to previously remove free carbon (also called free carbon) originally contained in coal tar pitch, which is a raw material of carbonaceous particles, during application of an electric field. It is effective in reducing the power consumption.

More specifically, free carbon is amorphous carbon fine particles with extremely advanced carbonization, which is pyrolyzed in a coke oven at a temperature of 1000 ° C. or higher. According to the analysis by the present inventors, C The / H ratio has an extremely large value, and when carbonaceous powder is used as the disperse phase component, the inclusion of such free carbon increases the current value during application of an electric field.

In the present invention, the suitable particle size of the dielectric particles constituting the dispersed phase component is 0.01 to 100 μm.
m, and preferably 0.1 to 10 μm. 100
The use of particles of μm or larger makes the suspension unstable, and the use of particles of 0.01 μm or smaller greatly increases the initial viscosity.

Further, in the present invention, in order to limit the current value when a voltage is applied, part or all of the surface of the carbonaceous particles can be coated with an insulator such as a synthetic polymer.

On the other hand, the electrically insulating liquid phase of the present invention includes aliphatic hydrocarbons such as petroleum ether, kerosene, n-hexane, n-heptane, isooctane and ligroin, or aromatic hydrocarbons such as toluene and xylene. Hydrocarbons, carbon tetrachloride, dichloroethane, trifluoroethane,
Examples thereof include halogenated hydrocarbons such as bromonaphthalene or a mixture thereof, and silicone oils such as polydimethylsiloxane. These can be used alone or in combination of two or more.

The viscosity of the ink composition having the electrorheological effect of the present invention is 0.5 to 1000 centistokes (cSt) at 25 ° C., preferably 1 to 20.
Those having a viscosity of 0 centistokes, more preferably 2 to 50 centistokes are used. In order to produce an ink composition having a low viscosity, it is necessary to use a liquid phase having high volatility, which deteriorates long-term stability. On the other hand, if the viscosity of the fluid becomes high, it becomes difficult to discharge from the orifice, which is not preferable in practice. Moreover, the dispersed phase can be efficiently suspended by using a liquid phase having an appropriately low viscosity.

The proportion of the dispersed phase and the liquid phase constituting the ink composition of the present invention is such that the content of the dispersed phase is 1 to 60% by weight and the content of the liquid phase which is an oil medium is 40 to 99% by weight. Preferably, the content of the dispersed phase is 10 to 40% by weight and the content of the liquid phase is 60 to 90% by weight. The dispersed phase content is 1
If it is less than 60% by weight, the electroviscous effect is small, and if it exceeds 60% by weight, the initial viscosity in the absence of an electric field is significantly increased, which is not preferable.

Although the above-mentioned carbonaceous particles are used as they are as the coloring material element of the ink composition of the present invention (black), other coloring material elements can be appropriately added. Further, the ink composition of the present invention may contain other disperse phase or dispersant, and additives such as other inorganic salts within a range that does not impair the effects of the present invention.

[0016]

According to the above constitution of the present invention, the C / H ratio is 1.0 as the dispersed phase component of the ink composition having the electrorheological effect.
By using carbonaceous particles of 10 to 10, this ink composition can surely exhibit a large electrorheological effect with a small current value by the application of an external electric field. Therefore, when applied to an ink jet recording apparatus, ink ejection control can be reliably performed and a clear image can be obtained. Further, it consumes less power and can contribute to downsizing of the device and energy saving.

Further, since the ink composition of the present invention uses the carbonaceous material in which hydrogen atoms are appropriately left as the dispersed phase particles, the electrons in the carbonaceous particles move due to the voltage application, and the particles undergo interfacial polarization. It develops an electrorheological effect.
Therefore, it is not necessary to add water to the dispersed phase particles, and the characteristics over time are stable. Since the characteristics of the recording apparatus do not change over time, a desired discharge amount and discharge operation can be easily secured without making a complicated adjustment each time the recording apparatus is used, and a simple apparatus can be provided.

[0018]

EXAMPLES Hereinafter, more specific examples will be described. The present invention is not limited to the examples below.

Example Coal tar containing no free carbon was heat-treated at 450 ° C. in a substantially inert atmosphere. The resulting heat-treated product was extracted and filtered using tar-based medium oil (boiling range 120 to 250 ° C). The extraction / filtration residue was reheat-treated at a temperature of 450 ° C. under a nitrogen stream to further pulverize and classify the carbonaceous powder. The carbon / hydrogen atom ratio of the carbonaceous fine particles thus obtained was 2.40, and the average particle size was 2.9 μm. 20% by weight of such carbonaceous fine particles is used as an electric insulating liquid phase of kerosene 8
The ink composition was suspended in 0% by weight to obtain an ink composition. A printing test was conducted on the obtained ink composition using a recording apparatus having the head structure shown in FIG. In FIG. 1, a DC voltage is turned on / off according to an image signal to an electrode 2 provided near the nozzle 1, and a pressure P is applied to the ink to eject the ink 5 onto the recording paper 4. The image obtained using this ink was clear.

Comparative Example 20% by weight of carbon black (carbon / hydrogen atom ratio 15.2) was suspended in 80% of kerosene,
An ink composition was obtained. When an image was formed using this ink composition in the same manner as in the example, even if a voltage was applied, a current would flow too much, the electrorheological effect would not be exhibited, and the ejection of ink from the nozzle 1 could not be controlled. I couldn't get a good image.

The electrorheological effect was measured for each ink composition used in the above Examples and Comparative Examples. For the electrorheological effect, a double cylinder type rotational viscometer is used and the same shear rate (366 sec) is applied when a voltage is applied between the inner and outer cylinders.
^-1 ), the viscosity at room temperature was measured, and at the same time, the current flowing between the inner and outer cylinders was measured. Table 1 shows the viscosity when no voltage is applied (initial viscosity), the viscosity when a voltage of 2 kV / mm is applied, and the current value when a voltage of 2 kV / mm is applied.

[0022]

[Table 1]

In Table 1, in the comparative example, too much current was applied and measurement was impossible, and no change in viscosity was observed. On the other hand, in the case of this example, the electrorheological effect is surely exhibited, and the current does not flow too much as in the comparative example.

[0024]

As described above, the ink composition of the present invention can exhibit a relatively large electrorheological effect with low power consumption, and by using this ink composition, ejection control or fluidity is controlled by an electric field. It is possible to realize downsizing and energy saving of the printing and printing devices that are used.

[Brief description of drawings]

FIG. 1 is an example of an apparatus suitable for using the ink composition of the present invention.

[Explanation of symbols]

 1 Nozzle 2 Electrode 3 DC power supply 4 Recording paper 5 Ink P Pressure

Claims (1)

[Claims] 1. An ink composition, wherein carbonaceous particles having an atomic ratio of carbon atoms and hydrogen atoms of 1.0 to 10 are dispersedly contained in an electrically insulating liquid phase.