Inkjet recording method and apparatus

1. An inkjet recording method in which droplets made of an ink composition are ejected to record on a recording medium, comprising:

using insulating ink prepared by dispersing colorant particles capable of being charged in a solvent as said ink composition;

allowing an electrostatic force to act on said ink composition to form a thread of said ink composition; and

providing a stimulus to said thread at a frequency in a range of 100 kHz to 800 kHz to separate said thread into said droplets.

2. The inkjet recording method according to claim 1 , wherein an equation:

f=v/{ 8.89 ×a ×(1+3η/(2σρ a ) (1/2) ) (1/2) }

is satisfied assuming that said frequency is f[Hz], a fly speed of said droplets is v[m/s], a radius of said thread is a[m], a viscosity of said ink composition is η[Pa·s], a surface tension of said ink composition is σ[N/m], and a density of said ink composition is ρ[kg/m 3 ].

3. The inkjet recording method according to claim 1 , wherein said stimulus comprises vibrations generated by using one of a piezoelectric element, a magnetostrictor, and an electrostatic actuator.

4. The inkjet recording method according to claim 1 , wherein said stimulus comprises heating with a heater that generates heat periodically.

5. The inkjet recording method according to claim 1 , wherein said stimulus comprises application of a high-frequency voltage at said frequency so that said high-frequency voltage is superimposed on one of a control voltage applied for controlling ejection of said droplets and a charging voltage applied for charging said recording medium with an opposite polarity to that of said control voltage.

6. The inkjet recording method according to claim 1 , wherein, when at least two kinds of ink compositions that are different from each other are used as said ink composition, physical properties of said at least two kinds of ink compositions are previously adjusted so that frequencies of said stimulus becomes identical.

7. An inkjet recording apparatus in which an electrostatic force is allowed to act on an ink composition to eject ink droplets, thereby recording on a recording medium, comprising:

an inkjet head which is placed at a position where said inkjet head is opposed to said recording medium, and which includes ejection ports through which said ink droplets are ejected and control electrodes for applying control voltages for allowing said ink droplets to be ejected;

an electrode substrate placed on a side of said recording medium opposite to a side facing said inkjet head, for applying a charging voltage with a polarity opposite to that of said control voltages to said recording medium; and

stimulus providing means for providing a stimulus at a frequency in a range of 100 kHz to 800 kHz to threads of said ink composition formed from said ejection ports toward said recording medium by electric forces generated from said control electrodes.

8. The inkjet recording apparatus according to claim 7 , wherein said stimulus providing means provides said stimulus at said frequency f[Hz] satisfying an equation:

f=v /{8.89 ×a ×(1+3η/(2 σρa ) (1/2) ) (1/2) }

where a fly speed at which said ink droplets fly from one of said ejection ports is v[m/s], a radius of one of said threads formed from said one of said ejection ports is a[m], a viscosity of said ink composition is η[Pa·s], a surface tension of said ink composition is σ[N/m], and a density of said ink composition is ρ[kg/m 3 ].

9. The inkjet recording apparatus according to claim 7 , wherein said stimulus providing means comprises one of a piezoelectric element, a magnetostrictor, and an electrostatic actuator provided in said inkjet head.

10. The inkjet recording apparatus according to claim 7 , wherein said stimulus providing means comprises a heater that generates heat periodically.

11. The inkjet recording apparatus according to claim 7 , wherein said stimulus providing means comprises a high-frequency power source for applying a voltage at said frequency so that said voltage is superimposed on one of said control voltages and said charging voltage.

12. The inkjet recording apparatus according to claim 7 , wherein said inkjet head includes respective ink guides extending through said ejection ports.