1. Field of the Invention
This invention relates to a liquid jet head used for a liquid jet recording apparatus and, more particularly, to a liquid jet head using recording liquid with fine particles dispersed therein, a liquid jet recording apparatus for the liquid jet head, and a recording liquid (ink) used for the liquid jet head.
2. Description of the Related Art
Non-impact recording methods have recently gained attention since the noise created from the methods during recording is so little that the noise is almost unnoticeable. Among such methods, the so-called inkjet recording method is known as an effective recording method which records with high speed and requires no special fixing process when recording to plain paper. Various types of inkjet recording methods have been proposed and improved. Some have been introduced to the market as actual products, while others are still being developed for practical use.
The inkjet recording method records by ejecting droplets of recording liquid (so-called ink) onto a recording medium. Various types of inkjet recording methods are described below. The various types of inkjet recording methods can be classified according to methods for creating the droplets, or methods for controlling the flight direction of the droplets.
In the prior art, for example in U.S. Pat. No. 3,060,429, a Tele-type method, which is an electrostatic attraction type method, is known as a method that creates droplets of ink by electrostatic attraction, controls the droplets by controlling an electric field according to recording signals, and allows the droplets to selectively adhere to a recording medium, to thereby achieve recording.
Furthermore, U.S. Pat. Nos. 3,596,275 and 3,298,030) disclose a Sweet type method which is a continuous stream and charge-controlled type method. The method creates droplets of recording liquid having electric charges thereof controlled by a continuous vibration method, and allows the electrically charged controlled droplets of the recording liquid to fly between deflection-electrodes applied with a uniform electric field, to thereby record to a recording medium.
As for another example, U.S. Pat. No. 3,416,153 discloses a Hertz type method which applies an electric field to a discharge port and a ring-like electrode, and creates a mist of droplets of recording liquid with use of a continuous vibration method, to thereby provide a recording image on a recording medium. That is, the strength of the electric field applied between the discharge port and the electrode is modulated according to recording signals, to thereby create a gradation in the recording image.
Furthermore, as another method, for example, U.S. Pat. No. 3,747,120 discloses a Stemme type method. This method is based on a principle different from those of the above-described three types. That is, all of the above-described three types employ electrical control of droplets ejected from a discharge port during their flight from the discharge port to thereby allow the droplets corresponding to the recording signals to selectively adhere to a recording medium. Meanwhile, the Stemme type is a method which ejects droplets of recording liquid only when requested in accordance with recording signals. That is, in recording with the Stemme type, electric recording signals are applied to a piezo vibration element provided to a recording head having a discharge port for discharging recording liquid, and the electric recording signals are changed to mechanical vibration of the piezo vibration element, to thereby allow droplets of recording liquid to eject from the discharge port in accordance with the mechanical vibration, and adhere to a recording medium. This type is referred as a “drop on demand type”.
Furthermore, Japanese Patent Publication No.56-9429 discloses another type which is a type previously proposed by the applicant of the present invention. This type is also a “drop on demand type” which records by allowing droplets of recording liquid to eject from a discharge port according to recording signals. This type is a so-called “bubble inkjet type” which heats ink inside a liquid chamber, and creates bubbles inside the ink, to thereby allow a reaction of the bubbles to eject droplets of the ink from a discharge port.
As described above, many types of inkjet recording methods may be provided depending on the principle upon which the method is based. What is common with the inkjet recording methods is that the methods are performed by ejecting a recording liquid (so-called ink) and adhering the recording liquid to a recording medium. Furthermore, a recording liquid having a water-soluble dye dissolved therein is typically employed as a recording liquid (so-called ink) Recently, however, water-fastness and light-fastness of the ink are becoming more important. Therefore, a pigment having durable properties is anticipated to be used as a colorant of a recording liquid for inkjet recording.
For example, Japanese Patent Laid-open Application No. 2-255875 discloses a water-soluble pigment based ink for inkjet recording which fulfills basic requirements such as printing quality, ejection property, storage stability, and fixation.
However, unlike a dye-based ink in which dye can stably dissolve in a liquid medium, this pigment-based ink does not dissolve, but rather has particles thereof dispersed inside a liquid medium. Accordingly, this pigment-based ink has a disadvantage of instability in a liquid medium, and has yet to resolve problems such as pigment aggregation, sedimentation, and separation of the pigment in the ink, or clogging at a nozzle portion.
Meanwhile, a conventional discharge port (nozzle) of a recording head has an orifice typically ranging from Φ33 μm-Φ34 μm (approximately 900 μm2 in terms of area of a nozzle orifice) to Φ50 μ-Φ51 μm (approximately 2000 μm2 in terms of area of a nozzle orifice). However, owing to the recent advances in image quality and precision of inkjet recording, a recording head with a smaller discharge port is desired. In such a case, clogging would be no problem if a conventional water-soluble dye was employed as a recording liquid since the dye dissolves in a liquid medium. In contrast, clogging heretofore has been a grave problem for a pigment-based ink where a smaller discharge port is used (for example, an orifice no more than Φ25 μm).
Furthermore, since a water-soluble dye-based ink allows dye to dissolve in a liquid medium, droplets of the ink are able to penetrate fibers of a paper serving as a recording medium when the ink contacts and adheres to the paper, and thereby achieve satisfactory pixel formation/image formation. In contrast, with the recording liquid having pigment particles dispersed therein, the pigment particles, unlike dye, does not dissolve, but merely disperses in a liquid medium. Therefore, although the liquid medium of the ink may penetrate into fibers of a paper, pigment particles and solid content in the ink are unable to penetrate the fibers of the paper. Accordingly, color pixels are formed in a manner where particles and solid content of the ink are accumulated on the surface of the paper.
Therefore, a suitable pixel shape cannot be obtained unless the size of the pigment particles is optimized. For example, satisfactory round pixels would be difficult to obtain and high quality printing cannot be achieved if ink (recording liquid) which contains pigment particles with an order of magnitude equal to that of pixels to be formed on paper is used in forming the pixels.