Ink jet method with improved tonal range

Details Ink jet method with improved tonal range Ink jet method with improved tonal range

1999-09-01

2002-04-30

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Controller

C347S100000, C347S105000

Reexamination Certificate

active

06378974

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an ink jet method with improved tonal range and high obtainable maximal density. The method is useful for the rendering of medical diagnostic information.
BACKGROUND OF THE INVENTION
In the majority of applications printing proceeds by pressure contact of an ink-loaden printing form with an ink-receiving material which is usually plain paper. The most frequently used impact printing technique is known as lithographic printing based on the selective acceptance of oleophilic ink on a suitable receptor.
In recent times however so-called non-impact printing systems have replaced classical pressure-contact printing to some extent for specific applications. A survey is given e.g. in the book “Principles of Non Impact Printing” by Jerome L. Johnson (1986), Palatino Press, Irvine, Calif. 92715, USA.
Among non-impact printing techniques ink jet printing has become a popular technique because of its simplicity, convenience and low cost. Especially in those instances where a limited edition of the printed matter is needed ink jet printing has become a technology of choice. A recent survey on progress and trends in ink jet printing technology is given by Hue P. Le in Journal of Imaging Science and Technology Vol. 42 (1), January/February 1998.
In ink jet printing tiny drops of ink fluid are projected directly onto an ink receptor surface without physical contact between the printing device and the receptor. The printing device stores the printing data electronically and controls a mechanism for ejecting the drops image-wise. Early patents on ink jet printers include U.S. Pat. No. 3,739,393, U.S. Pat. No. 3,805,273 and U.S. Pat. No. 3,891,121.
The jetting of the ink droplets can be performed in several different ways. In the early 1960s, Dr. Sweet of Stanford University demonstrated that by applying a pressure wave pattern to an ink stream which is jetted continuously through a small nozzle. This ink stream could be broken in droplets which are uniform in size and spacing. The droplet stream is image-wise divided into droplets that are electrostatically charged and deflected, and into droplets that remain uncharged and continue their way undeflected. This process is known as continuous ink jet printing. In one embodiment the uncharged undeflected droplet stream forms the image while the charged deflected stream is recollected. Alternatively, the charged deflected stream forms the image and the uncharged undeflected jet is recollected. In still a further variant of the latter system several jets are deflected to a different degree and thus record the image (multideflection system). Sweet's invention led to the introductions of A.B. Dick VideoJet and the Mead DIJIT products. In the 1970s IBM licensed the technology and adapted it for their computer printers. At approximately the same time, Prof. Hertz of the Lund Institute of Technology in Sweden and his associates independently developed several continuous ink jet techniques that had the ability to modulate the ink flow characteristics for gray-scale printing by controlling the number of drops deposited in each pixel. This method was licensed to companies such as Iris Graphics/Scitex and Stork to produce high-quality colour images.
As an alternative for continuous ink jet the ink droplets can be created “on demand” (“DOD” or “drop on demand” method) whereby the printing device ejects the droplets only when they are used in imaging on a receiver thereby avoiding the complexity of drop charging and deflection hardware. In drop-on-demand the ink droplet can be formed by means of a piezoelectric transducer (so-called “piezo method”), or by means of discrete thermal pushes (so-called “bubble jet” method, or “thermal jet” method). Zoltan, Kyser and Sears are the pioneers of the first method. In these printers, on the application of voltage pulses, ink drops are ejected by a pressure wave created by the mechanical motion of a piezoelectric ceramic. In 1979, Endo and Hara of Canon Co. invented a drop-on-demand ink jet method wherein ink drops were ejected from a nozzle by the growth and collapse of a water vapor bubble on the top surface of a small heater located near the nozzle. Canon called the technology the bubble jet. During the same time period or shortly thereafter Hewlett-Packard developed a similar ink jet technology, commercialized in 1984 in the Thinkjet printer. They named the technology thermal ink jet.
Ink jet printing technologies are used in a wide range of applications such as desktop publishing at home or at office, industrial printing of packings, e.g. with barcodes, printing of cables, prints from photographs generated from an electronic camera, outdoor advertisement, textile printing; three-dimensional printing, etc. An emerging market is surely ink jet printing of electronically stored medical information. Key players are the companies Scitex/Iris and Sterling Diagnostics. Also Misubishi Plastics recently announced the development of a film that can be imaged with ink jet to print medical images (Japan Chemical Week, (Apr. 9, 1998, p. 1). Hitherto images comprising medical information were conventionally produced by classical photographic techniques. The most commonly used is silver halide technology. After image-wise exposure by X-rays, converted to actinic radiation by means of a phosphor screen, or by a laser beam the film must be processed in baths containing dissolved chemicals. This however is a cumbersome and ecologically undesired procedure. Therefore environmently friendlier materials were recently introduced based on thermographic or photothermographic technologies such as Imation Dryview films and Agfa Drystar. These technologies however need expensive apparatuses based on laser or thermal head imaging. Ink jet could be an inexpensive and ecologically acceptable alternative to the systems mentioned above provided it would be capable of producing continuous tone images with a sufficient number, preferably at least 100, of grey levels, high maximal transmission density, low noise level, and neutral grey tone.
As already mentioned above grey-scale printing can be performed by the Hertz method by controlling the number of droplets deposited in each pixel. A sufficient number of grey levels can also be obtained by combining droplets of different inks having the same colorant but in different concentrations. The principle was already disclosed in U.S. Pat. No. 3,404,221, priority U.S. Pat. No. 22.10.1965. Specific embodiments of the method of combinations of several inks of different densities are disclosed e.g. in DE 3415778, DE 3415775, U.S. Pat. No. 4,533,923, U.S. Pat. No. 4,695,846, U.S. Pat. No. 4,714,964, U.S. Pat. No. 4,686,538, U.S. Pat. No. 4,952,942, U.S. Pat. No. 4,860,026, EP 388978, EP 606022, U.S. Pat. No. 5,606,351, U.S. Pat. No. 5,625,397, and EP 750995. Furtheron grey scale images can be produced by modulation of the ink droplet size as explained in the article “Photo-realistic ink jet printing through dynamic spot size control”, by D. Wallace et al., presented at IS & T's Eleventh International Congress on Advances in Non-Impact Printing, Oct. 29-Nov. 3, 1995, Hilton Head, South Carolina. Furtheron combinations of these different methods can be used.
According to the article “Continuous Ink Jet Printing of Medical images” presented at the RSNA congress, November 1993, in Chicago Dr. Philp Drew of Scitex Co. demonstrated the production of multi-grey images by the UniTone ink jet printer based on the combinations of black and grey inks, meaning neutral inks with different colorant concentrations, in combinations with variable dot sizes. These images however were printed on reflective receivers. In this case the reflection density does not increase indefinitly in a linear way as a function of the number of dots per pixel, but becomes almost constant at a density of about 1.6, as explained in the article “Enhanced Density Resolution with Continuous Ink Jet Printing Using Dual Ink Densities” by T. Kirkhorn et al., J. Imag. Sci. Tech., Vol. 36

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