Incremental printing of symbolic information – Ink jet
Reexamination Certificate
2000-10-31
2001-12-11
Yoon, Tae H. (Department: 1714)
Incremental printing of symbolic information
Ink jet
C347S073000, C523S161000, C106S031650, C106S031870, C106S031890
Reexamination Certificate
active
06328393
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to aqueous ink compositions. More specifically, the present invention is directed to pigmented aqueous ink compositions particularly suitable for use in ink jet printing processes.
BACKGROUND
Ink jet printing is a non-impact method that produces droplets of ink that are deposited on a substrate such as paper or transparent film in response to an electronic digital signal. Thermal or bubble jet drop-on-demand ink jet printers have found broad application as output for personal computers in the office and the home.
In existing thermal ink jet printing, the printhead typically comprises one or more ink jet ejectors, such as disclosed in U.S. Pat. No. 4,463,359, and each ejector includes a channel communicating with an ink supply chamber, or manifold, at one end and an opening at the opposite end, referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each of the channels at a predetermined distance from the nozzles. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. As the bubble grows, the ink rapidly bulges from the nozzle and is momentarily contained by the surface tension of the ink as a meniscus. This is a very temporary phenomenon, and the ink is quickly propelled toward a print substrate. As the bubble begins to collapse, the ink still in the channel between the nozzle and bubble starts to move towards the collapsing bubble, causing a volumetric contraction of the ink at the nozzle and resulting in the separation from the nozzle of the bulging ink as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides the momentum and velocity for propelling the ink droplet in a substantially straight line direction towards a print substrate, such as a piece of paper. Because the droplet of ink is emitted only when the resistor is actuated, this type of thermal ink-jet printing is known as “drop-on-demand” printing. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. Nos. 4,601,777, 4,251,824, 4,410,899, 4,412,224, 4,532,530, and 5,281,261, the disclosures of which are totally incorporated herein by reference. Other types of ink-jet printing, such as continuous-stream or acoustic, are also known.
In an ink jet printing apparatus, the printhead typically comprises a linear array of ejectors, and the printhead is moved relative to the surface of the print sheet, either by moving the print sheet relative to a stationary printhead, or vice-versa, or both. In some types of apparatuses, a relatively small ink jet printhead moves across a print sheet numerous times in swathes to form a line image. A partial (e.g. checkerboard) or a desired line image can be produced on the print sheet in each swath. After each line image is completed, the print sheet is advanced and the process is repeated until the entire image is printed. This type of ink jet printing is known as multiple pass (multi-pass) printing or checkerboard printing.
In some cases, an array of ejectors is formed by butting together several printheads, forming a printhead bar. This increases the number of ink jet nozzles so that the printing speed can be increased. The length of the printhead bar may cover only a part of the width of the print substrate. This type of ink jet printhead is called a partial-width printhead. The partial-width printhead can be used in the aforementioned multiple pass printing or checkerboard printing with increased print speed.
Alternatively, a printhead which consists of an array of ejectors and extends to the full width of the print substrate may be used. Ink can be deposited onto the print substrate one line at a time by the full-width array printhead until full-page images are completed. This is called a single pass method of printing. The ink jet printer which uses one or more full-width array printheads is known as a “full-width array” (FWA) printer. When the full-width array printhead and the print substrate are moved relative to each other, image-wise digital data is used to selectively activate the thermal energy generators in the printhead over time so that the desired image will be created on the print substrate. Several full-width array ink jet printheads can be employed in a multi-color ink jet printing system.
With the demand for higher resolution printers, the nozzles of printheads, partial-width printheads and full-width array printheads in ink jet printers are decreasing in size. Nozzle openings are typically about 50 to 80 micrometers in diameter or size for 300 spot per inch (spi) printers. With the advent of high resolution (e.g., >360 spi, including 400 spi and 600 spi) printers, these nozzle openings in a printhead are typically about 10 to about 49 micrometers in diameter or size. These high resolution printheads, partial-width printheads, and full-width array printheads with small nozzle dimensions or sizes require special inks that do not easily clog the small openings. These special inks are more difficult to make than the ink jet inks used in low resolution printheads (e.g. ≦360 spi), which have less stringent requirements.
One of the critical requirements for an ink jet ink is the ability of the ink to remain in a fluid and jettable condition in a printhead opening which is exposed to air. Latency is the maximum idling time that still allows a printhead to function without failure at 15% relative humidity (RH), jetting an ink with a speed ≧5 m/s (equivalent to an ink traveling a distance of 0.5 mm in ≦100 microseconds) after a period of non-use or idling. Long latency is required in order to reduce maintenance of the printhead, especially when there are some infrequently utilized nozzles. A major concern with all ink jet printheads is plug formation or clogging of nozzles, both during operation and between operations of the ink jet printhead. Plug formation is caused by evaporation of water or an organic solvent from the opening of the nozzle. In dye-based inks, this can cause crystallization or precipitation of soluble components such as dye or solid additives as well as an increase in the viscosity of the ink composition. In pigment based inks, this evaporation can cause precipitation of the pigment particles, flocculation or aggregation of the pigment particles, or precipitation of solid ink additives, as well as an increase in the viscosity of the ink composition.
Initial evaporation generally causes an increase in viscosity which affects the ability of the printhead to fire a drop of ink through a nozzle. Some additives have been developed which reduce the rate of evaporation from the ink. However, these additives do not totally eliminate the problem of evaporation from the ink, and, thus, clogging of the nozzles remains a problem, especially with regard to pigment based inks and printheads with small nozzle openings.
The inception of plug formation may cause distortion of the image or alphanumeric characters. This may appear as a drop of ink which is displaced from its intended position. Sometimes two ink drops will be formed equally spaced from the intended target position. Sometimes small numerous satellite drops are produced. On some occasions, the drop may even reach its intended position but at a lower drop volume, producing a lower optical density image. Ultimately, the plugged nozzle will fail to fire and no image will be generated.
Ink jet printers are normally designed to prevent excessive evaporation of water and humectant or solvent from printhead nozzles by sealing the printhead in an air-tight chamber when not in use. These devices may become ineffective with continued printer use because dried ink deposits can be formed at the front face of a printhead and on the rubber seals, causing the system to lose its air-tight condition. However, the system may still be used in an ink jet printer to slow down ink evaporation at the printhead nozzles. Another device used to prevent clogging of the nozzle is a f
Fague Gary R.
Lin John Wei-Ping
Wong Raymond R.
Oliff & Berridg,e PLC
Xerox Corporation
Yoon Tae H.
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