Simple electrostatic ink jet printing head having low cost

Details Simple electrostatic ink jet printing head having low cost Simple electrostatic ink jet printing head having low cost

1997-01-28

2001-04-24

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

Reexamination Certificate

active

06220696

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to an electrostatic ink jet printing head, and more particularly, to an electrostatic ink jet printing head which adheres toner particulates to a recording medium.
DESCRIPTION OF THE RELATED ART
A non-impact printing method has recently become interesting because the non-impact printing method makes negligable undesired sounds when printing. An ink jet printing method as the non-impact printing method can, in high speed, directly print to a sheet of plain paper by a simple mechanism. An electrostatic ink jet printing method is known as the ink jet printing method. The electrostatic ink jet printing method comprises printing electrodes and a counter electrode. When the printing electrodes are selectively supplied with printing pulse voltages, electric fields are caused between the printing electrodes and the counter electrode. A sheet of recording paper is positioned on the counter electrode. A small amount of coloring material such as ink is filed by electrostatic forces of the electric fields and adhered to the recording paper.
In the manner which will later be described in more detail, first, second, and third conventional electrostatic ink jet printing heads are known. The first conventional electrostatic ink jet printing head comprises a substrate and a covering member. The covering member has an internal surface defining, in cooperation with the substrate, an ink receiving space which receives ink containing coloring particulates. A plurality of printing electrodes are, in parallel, positioned in the ink receiving space. Front ends of the substrate and the covering member form an ink ejecting nozzle of a slit type. Each of the printing electrodes is formed in the shape of a needle. At a time of printing, the printing electrodes are selectively supplied with printing pulse voltages.
A counter electrode is positioned to counter the printing electrodes. A sheet of printing paper is positioned between the printing electrodes and the counter electrode so that the printing paper is in contact with the counter electrode. When the printing electrodes are supplied with printing pulse voltages, electric fields occur between the printing electrodes and the counter electrode. In this event, the electric field is concentrated at a front edge of the printing electrode. Thereby, electric charges in the ink are stored at a vicinity of the front edge of the printing electrode.
The second conventional electrostatic ink jet printing head is described in Japanese Unexamined Patent Prepublication (koukai) No. 228162/1985. The second conventional electrostatic ink jet printing head comprises a substrate, a covering member, printing electrodes, protruding portions, and reinforcement boards. The protruding portions are formed on the front end of the substrate so that the protruding portions correspond to front edges of the printing electrodes. The protruding portions give the ink meniscus preformed irregularities to concentrate the electric field at the vicinities of the front edges of the printing electrodes.
The third conventional electrostatic ink jet printing head comprises a substrate, a covering member, printing electrodes, and meniscus forming members. The meniscus forming members are positioned to correspond to the printing electrodes. The printing electrodes are formed by sputtering conductive material such as chromium to the whole surface of the substrate and by patterning the conductive material by photolithography. The meniscus forming members are formed by laminating a photosensitivity macromolecular film on the substrate and by patterning the photosensitivity macromolecular film by photolithography.
However, since the above conventional electrostatic ink jet printing heads comprise printing electrodes which are formed by sputtering conductive material such as chromium to the whole surface of the substrate and by patterning the conductive material by photolithography, and since the above conventional electrostatic ink jet printing heads comprise meniscus forming members that are formed by laminating a photosensitivity macromolecular film on the substrate and by patterning the photosensitivity macromolecular film by photolithography, the above conventional electrostatic ink jet printing heads have a complex manufacturing process and a high cost. In addition, since, in the above conventional electrostatic ink jet printing heads, the meniscus forming members are made of the photosensitivity macromolecular film, the thickness of the meniscus forming members is limited by a thickness of the photosensitivity macromolecular film. As a result, in the above conventional electrostatic ink jet printing heads, only a limited amount of ink can be ejected.
Referring to
FIGS. 1
,
2
,
3
,
4
, and
5
, first, second, and third conventional electrostatic ink jet printing heads will be described in order to gain a better understanding of this invention.
In
FIG. 1
, the first conventional electrostatic ink jet printing head comprises a substrate or base board
1
and a covering member
2
. The covering member
2
has an internal surface defining, in cooperation with the substrate
1
, an ink receiving space
3
which receives ink containing coloring particles. A plurality of printing electrodes
4
are, in parallel, positioned in the ink receiving space
3
. Front ends of the substrate
1
and the covering member
2
form an ink ejecting nozzle of a slit type. Each of the printing electrodes
4
is formed in a shape of a needle. At a time of printing, the printing electrodes are selectively supplied with printing pulse voltages.
On the other hand, a counter electrode
5
is positioned to counter the printing electrodes
4
. A sheet of printing paper
6
is positioned between the printing electrodes
4
and the counter electrode
5
so that the printing paper
6
is in contact with the counter electrode
5
. When the printing electrodes are supplied with printing pulse voltages, electric fields occur between the printing electrodes
4
and the counter electrode
5
. In this event, the electric field is concentrated at a front edge of the printing electrode
4
. Thereby, electric charges in the ink are stored at a vicinity of the front edge of the printing electrode
4
.
Processes of storing the electric charges in the ink are different due to kinds of the ink used. In case of conductive ink, storing the electric charges is due to electrostatic induction. Also, in case of dielectric ink, storing the electric charges is due to polarization. In addition, in case of ink having colored particles which are dispersed in the ink, storing the electric charges is due to inherent charges of the coloring particles that are caused by zeta potential.
In any case, the ink or the coloring particles in the ink are, by Coulomb's force which acts the stored electric charges, strained in a direction of the counter electrode
5
, namely, the printing paper
6
. When Coulomb's force is stronger than surface tension of the ink, a small amount of the ink is flied to be adhered on the printing paper
6
. In this case, the printing pulse voltages which are supplied to the printing electrodes are appropriately controlled in response to printing images.
However, since electric conductivity and dielectric constant of the ink for use in printing is greater than electric conductivity and dielectric constant of air, a location at which the electric charges are concentrated is not determined by only position of the printing electrode
4
, but is also influenced by a state of an ink meniscus at the ink ejecting nozzle. Namely, although it is expected that the ink meniscus is homogeneous in a longitudinal direction of the ink ejecting nozzle, minute irregularities of the ink meniscus are really caused due to machining accuracies of the ink ejecting nozzle, due to vibrations the ink meniscus after ejecting the ink, and due to natural fluctuations of the ink meniscus.
In this case, the electric field is more concentrated at minute convex portions of the ink meniscus in the

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