Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-12-31
2001-12-04
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S047000, C347S044000, C347S100000
Reexamination Certificate
active
06325490
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ink jet printing and, more particularly, to ink jet nozzle plates in ink jet print heads modified by deposition of a self-assembled monolayer comprising mixtures of hydrophobic and ionic molecules.
BACKGROUND OF THE INVENTION
An ink jet printer produces images on a receiver by ejecting ink droplets onto the receiver in an imagewise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
In this regard, “continuous” ink jet printers utilize electrostatic charging tunnels that are placed close to the point where ink droplets are being ejected in the form of a stream. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the recording medium.
In the case of “on demand” ink jet printers, at every orifice a pressurization actuator is used to produce the ink jet droplet. In this regards either one of two types of actuators may be used. These two types of actuators are heat actuators and piezoelectric actuators. With respect to heat actuators, a heater placed at a convenient location heats the ink and a quantity of the ink will phase change into a gaseous steam bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled to the recording medium. With respect to piezoelectric actuators. A piezoelectric material is used, which piezoelectric material possess piezoelectric properties such that an electric field is produced when a mechanical stress is applied. The converse also holds true; that is, an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
A continuing problem with ink jet printers is the accumulation of ink on ink jet nozzle plates, particularly around the orifice from which ink drops are ejected. The result of ink drops accumulating on the nozzle plate surface around the orifice is that it becomes wettable causing ink drops to be misdirected, degrading the quality of the printed image. To limit or prevent the spreading of ink from the orifice to the nozzle plate, it is common practice to coat the ink jet nozzle plate with an anti-wetting layer. Examples of anti-wetting layers are coatings of hydrophobic polymer materials such as Teflon and polyimide-siloxane, or a monomolecular layer (self-assembled monolayer) of a material that chemically binds to the nozzle plate. Self assembled monolayers of alkyl thiols, alkyl trichlorosilanes and partially fluorinated alkyl silanes have previously been disclosed in the patent literature for the treatment of inkjet nozzle plates (see, e.g., U.S. Pat. Nos. 4,643,948, 5,136,310, and 5,598,193).
Ink jet nozzle plates are also contaminated by ink drops that land on the nozzle plate. These “satellite ink” drops are created as a by-product of the drop separation process of the primary ink drop that is used to print. Another source of contaminating ink are tiny ink drops created when the primary ink drop impacts recording material. Where the whole nozzle plate surface has been treated with a non-wetting layer, such additional ink drops will bead-up for easy removal. Ink drops accumulating on nozzle plates can also potentially attract dirt such as paper fibers, however, which cause the nozzles to become blocked. Partially or completely blocked nozzles can lead to missing or misdirected drops on the print media, either of which degrades the quality of the print. The particulate debris thus needs to be cleaned from the surface and orifice to restore proper droplet formation.
In order to solve this problem, the nozzle plates are periodically cleaned. This cleaning is commonly accomplished by brushing, wiping, spraying, vacuum suction, and/or spitting of ink through the orifices. Several wiping methods are known including wet wiping techniques utilizing inks and ink solvents used to dilute inks as a cleaning solvent. Even with the presence of hydrophobic non-wetting surfaces, inks often contain various materials which may leave an undesirable residue on the ink jet print head nozzle plate. Thus while wiping removes ink drops from the nozzle plate, the hydrophobic non-wetting coating may be severely contaminated and compromised by ink residue. Such resulting “ink-fouled” coatings may subsequently be unable to effectively prevent the spreading of the ink firm the orifices.
It has been discovered, e.g., that hydrophobic coatings on ink jet print head nozzle plates are susceptible to fouling by certain ink jet inks, such as those containing copper phthalocyanine dyes. U.S. Pat. Nos. 4,643,948 and 5,589,193, e.g., relate to modification of an ink jet nozzle plate with organic hydrophobic materials. U.S. Pat. No. 5,589,193 in particular discloses the use of non-polar and polar alkyl thiols to produce non-wetting or wetting layers, respectively, and discloses that such compounds may be either ionic or nonionic. However, there is a problem in that the non-wetting layers containing organic hydrophobic materials disclosed therein have been found to be prone to ink-fouling upon contact with copper phthalocyanine ink jet ink. The fouling of the nozzle plate by the ink can lead to excessive spreading by ink onto the nozzle plate during normal use, further aggravating drop placement problems. The lone specific ionic compound (Compound No. 9) disclosed in U.S. Pat. No. 5,589,193 is described as the “most wetting”, and there is no suggestion to use such compound as a component in a non-wetting layer.
There remains a need for a simple, economical ink jet nozzle plate with a reduced propensity to foul upon contact with inks. The preferred coating should render anti-wetting and anti-ink-fouling characters to ink jet nozzle plates so that an ink jet print head will consistently deliver accurate and reproducible drops of ink to a receiver resulting in photographic quality images.
SUMMARY OF THE INVENTION
An object of this invention is to provide a method for treating an ink jet print head nozzle plate with a hydrophobic coating that inhibits ink-fouling. This method comprises applying self-assembled monolayers that are hydrophobic and anti-ink-fouling to an ink jet nozzle plate. In accordance with one embodiment of the invention, an ink jet nozzle plate is provided comprising an outer surface having a self-assembled monolayer thereon comprising a mixture of at least one hydrophobic compound and at least one ionic compound, which monolayer renders the outer surface non-wetting with respect to aqueous ink solutions. In accordance with preferred embodiments, the self-assembled monolayers comprises a mixture of hydrophobic alkyl thiols and charged alkyl thiols. An advantage of coatings in accordance with the invention is that they provide improved non-wetting characteristics after contact with ink. Another advantage is that because the coatings are not compromised after contact with ink, they do not need to be cleaned using specially formulated cleaning solutions which may be environmentally hazardous. Yet another advantage is the reduced cost of maintaining the anti-wetting character of the print head.
REFERENCES:
patent: 4643948 (1987-02-01), Diaz et al.
patent: 4961785 (1990-10-01), Skene et al.
patent: 5108504 (1992-04-01), Johnson et al.
patent: 5136310 (1992-08-01), Drews
patent: 5598193 (1997-01-01), Halko et al.
patent: 6074040 (2000-06-01), Usui et al.
Penner Thomas L.
Sharma Ravi
Yang Zhihao
Anderson Andrew J.
Barlow John
Eastman Kodak Company
Shah Manish S.
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