Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-08-09
2004-01-13
Stephens, Juanita (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S047000, C347S065000
Reexamination Certificate
active
06676244
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bubble-jet type inkjet printhead. More particularly, the present invention relates to an inkjet printhead having a hemispherical ink chamber and an anti-wetting film.
2. Description of the Related Art
In general, inkjet printheads are devices for printing a predetermined image by ejecting small droplets of printing ink to desired positions on a recording sheet. Ink ejection mechanisms of an inkjet printer are generally categorized into two different types: an electro-thermal transducer type (bubble-jet type), in which a heat source is employed to form bubbles in ink causing an ink droplet to be ejected, and an electromechanical transducer type, in which an ink droplet is ejected by a change in ink volume due to deformation of a piezoelectric element.
There are multiple factors and parameters to consider in making an inkjet printhead having a bubble-jet type ink ejector. First, it should be simple to manufacture, have a low manufacturing cost, and be capable of being mass-produced. Second, in order to produce high quality color images, the formation of minute, undesirable satellite ink droplets that usually trail an ejected main ink droplet must be avoided. Third, when ink is ejected from one nozzle or when ink refills an ink chamber after ink ejection, cross-talk with adjacent nozzles, from which no ink is ejected, must be avoided. To this end, a back flow of ink in a direction opposite to the direction ink is ejected from a nozzle must be prevented during ink ejection. Fourth, for high-speed printing, a cycle beginning with ink ejection and ending with ink refill in the ink channel must be carried out in as short a period of time as possible. In other words, an inkjet printhead must have a high driving frequency.
The above requirements, however, tend to conflict with one another. Furthermore, the performance of an inkjet printhead is closely associated with and affected by the structure and design of an ink chamber, an ink channel, and a heater, as well as by the type of formation and expansion of bubbles, and the relative size of each component.
In an effort to overcome problems related to the above requirements, various inkjet printheads having different structures have already been suggested. However, while conventional inkjet printheads may satisfy some of the aforementioned requirements, they do not completely provide an improved inkjet printing approach.
FIG. 1
illustrates a cross-sectional view of a conventional bubble type inkjet printhead, schematically illustrating a back-shooting type ink ejector. In a back-shooting type printhead, bubbles grow in a direction opposite to a direction in which ink droplets are ejected.
As shown in
FIG. 1
, in the back-shooting type printhead, a heater
24
is arranged in the vicinity of a nozzle
22
formed on a nozzle plate
20
. The heater
24
is connected to electrodes (not shown) for current application and is protected by a passivation layer
26
made of a predetermined material and formed on the nozzle plate
20
. The nozzle plate
20
is formed on a substrate
10
, and an ink chamber
12
is formed in the substrate
10
to correspond to the nozzle
22
. The ink chamber
12
connected to an ink channel
14
is filled with ink
40
. The surface of the passivation layer
26
for passivating the heater
24
is generally coated with an anti-wetting layer
30
. The anti-wetting layer
30
prevents the ink
40
from adhering to the passivation layer
26
.
In the above-described ink ejector, when current is applied to the heater
24
, the heater
24
generates heat and bubbles
44
are produced in the ink
40
filling the ink chamber
12
. Thereafter, the bubbles
44
continue to grow by the heat supplied from the heater
24
. Accordingly, pressure is applied to the ink
40
so that the ink
40
near the nozzle
22
is ejected through the nozzle
22
in the form of an ink droplet
42
. Then, the ink
40
is supplied to the ink chamber
12
through the ink channel
14
and the ink chamber
12
is refilled.
As described above, in order for the above-described bubble-jet type inkjet printhead to exhibit high quality printing, ink must be ejected in a stable manner, i.e., in the form of droplets. The size, form and surface quality of a nozzle are important factors that greatly affect the performance of the conventional bubble-jet type inkjet printhead, including the size of an ink droplet ejected, ejection stability and continuous ejection efficiency. In particular, the quality of a portion of the surface of the printhead near the nozzle greatly affects the ejection stability and continuous ejection efficiency.
Generally, if a nozzle and a portion of a surface of the printhead near the nozzle have an anti-wetting property, ink can be perfectly ejected in the form of an ink droplet. Accordingly, the accuracy in location of recording paper where an ink droplet lands and the uniformity in ink droplet dispersion are improved, thereby improving overall print quality. In addition, after ink ejection, a meniscus formed around the aperture of a nozzle is rapidly stabilized, thus preventing external air from being pulled back into the ink chamber and preventing a surface of the printhead around the nozzle from being contaminated.
Alternatively, if a portion of a surface of the printhead near the nozzle is not subjected to anti-wetting treatment, the portion is susceptible to contamination by ink or a foreign substance. Accordingly, print quality and efficiency may deteriorate. As shown
FIG. 2
, if the surface of the printhead around a nozzle
62
is not subjected to an anti-wetting treatment, a contact angle &thgr; between an ink droplet
72
and the surface of the printhead is small, so that the ink droplet
72
tends to be easily spread on the surface near the nozzle
62
. In this case, a desirably shaped ink droplet, such as the one illustrated in
FIG. 1
, is not formed, nor is a direction of an ink droplet ejection accurately maintained. Additionally, even after ink droplet ejection, ink may remain on the surface near the nozzle
62
. If the surface near the nozzle
62
is stained with ink or a foreign substance, a sheet of recording paper may also be stained with the ink or foreign substance, resulting in poor print quality.
Accordingly, in order to improve the reliability and print quality of an inkjet printhead, it is necessary to subject a surface of a printhead to an anti-wetting treatment. As a coating for the anti-wetting treatment, a metal such as gold (Au), palladium (Pd) or tantalum (Ta) has been typically used. However, such a metal having a contact angle of less than 90° cannot be suitably used as a coating for an inkjet printhead that is required to have a high anti-wetting property.
SUMMARY OF THE INVENTION
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a bubble-jet type inkjet printhead having a hemispherical ink chamber and an anti-wetting film exhibiting good characteristics while satisfying general requirements of a printhead.
To provide the above feature, the present invention provides a bubble-jet type inkjet printhead including a substrate, in which a manifold for supplying ink, an ink chamber having a substantially hemispherical shape and filled with ink to be ejected, and an ink channel for supplying ink from the manifold to the ink chamber, are incorporated, a nozzle plate, formed on the substrate, having a nozzle, through which ink is ejected, the nozzle formed at a location corresponding to the center of the ink chamber, a heater provided on the nozzle plate and surrounding the nozzle, and electrodes provided on the nozzle plate and electrically connected to the heater to supply pulse current to the heater, wherein an anti-wetting coating including a perfluorinated alkene compound on at least a surface around the nozzle is formed on an exposed surface of the printhead.
Preferably, the perfluorinated alkene compound as an anti-wetting compound is perfluorobutene.
Baek Seog Soon
Kwon Myung-jong
Oh Yong-soo
Lee & Sterba, P.C.
Samsung Electronics Co,. Ltd.
Stephens Juanita
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