In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
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 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.RTM. and polyimide-siloxane, or a monomolecular layer of a material that chemically binds to the nozzle plate, e.g., alkyl thiols, alkyl trichlorosilanes and partially fluorinated alkyl silanes.
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 that are created when the primary ink drop impacts recording material. Ink drops accumulating on the nozzle plate can also potentially attract contaminants such as paper fibers 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.
In order to solve this problem, the nozzle plates are periodically wiped clean. Several wiping methods are known including wet wiping techniques utilizing inks as a cleaning solvent. While inks and ink solvents used to dilute inks may be used as a cleaning liquid, they are not optimized for this purpose. Inks may contain additives such as, for example, ethylene glycol, diethylene glycol, and diethylene glycol monobutyl ether which may be environmentally undesirable when released during cleaning in unventilated areas such as a home or an office.
Further, 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 anti-wetting coating on the nozzle plate may be severely contaminated and compromised by ink residue. The ink-fouled coating is therefore unable to prevent the spreading of ink from orifices.
It has also been discovered that hydrophobic coatings on an ink jet print head nozzle plate are susceptible to fouling by certain ink jet inks, such as those containing copper phthalocyanine dyes. The fouling of the nozzle plate by the ink can lead to excessive spreading by ink on to the nozzle plate during normal use, further aggravating drop placement problems. Another disadvantage in using inks as a cleaning solution is that they are expensive.
There remains a need for a simple, economical ink jet nozzle plate cleaning solution that will help maintain the anti-wetting character of 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.