Incremental printing of symbolic information – Ink jet – Combined
Reexamination Certificate
1999-09-23
2002-10-08
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Combined
C347S101000
Reexamination Certificate
active
06460957
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the production of an ink jet image for use in graphic arts prepress.
BACKGROUND OF THE INVENTION
In graphic arts reproduction processes the original image appearing to have a continuous tone gradation is reproduced by a collection of a large number of dots and/or lines. The tone of the reproduced image is influenced by both the size of the dots and/or lines and their density. The technique by which each particular area of a continuous tone original is broken up into a large number of small dots is called screening. The obtained image is called a halftone image.
In a commonly used halftone screening technique, the continuously changing tone values of the original are modulated with periodically changing tone values of a superimposed two-dimensional screen. The modulated tone values are then subject to a thresholding process wherein tone values above the treshold value will be reproduced and those below will not be reproduced. The process of tone-value modulation and thresholding results in a two-dimensional arrangement of equally spaced “screen dots” whose dimensions are proportional to the tone value of the original at that particular location. The number of screen dots per unit distance determines the screen frequency or screen ruling. This screening technique wherein the screen frequency is constant and inversely proportional to the halftone elementary cell size is referred to as amplitude-modulation screening or autotypical screening. This technique can be implemented photo-mechanically or electronically.
The photo-mechanical implementation involves an analog process wherein a screen of equally spaced dots is physically superimposed, in contact or in projection with the original. Screen dots are formed when this combination is photographically reproduced in a system wherein thresholding is achieved through the use of special photographic films and developing chemicals producing a very high photographic contrast resulting in a sharp distinction between tone values above and below a certain level.
The electronic implementation of autotypical screening is a digital process whereby the continuous tone values of the original are broken up into discrete tone-value levels, specified at discrete areal coordinates within the original image. Each tone value is compared with an electronic threshold level, and values above the threshold are reproduced while those below the threshold are not. Screen dots are formed when a specific pattern of threshold values is defined in a two-dimensional array corresponding to the size of a halftone cell, and this threshold pattern is periodically applied across the image.
It will further be clear that in order to reproduce a color image using lithographic printing it will be required to separate the image in three or more part-images corresponding to primary colors which when printed over each other yield the desired color at any place within the image. Each of these colour separations has to be screened as described above.
When using conventional amplitude modulation halftoning some unwanted artifacts can occur in the reproduced photographic image and hence also in the final print for which the photographic film serves as intermediate. Without going into further detail effects called subject Moiré, colour Moiré, and micro Moiré or “rosette” can occur. These artefacts can be avoided by using an alternative technique, called frequency modulation screening.
Frequency modulation screening, also called stochastic screening, is a technique in which the continuously changing tone values of an original are reproduced by means of equally sized micro dots, the number of which, not the size, is proportional to the tone value of the original image. The name frequency modulation refers to the fact that the number of micro dots per unit surface (the frequency) fluctuates in relation to the tone value in the corresponding area of the original. A commercial implementation of frequency modulation screening is CrystalRaster, registered trade name of Agfa-Gevaert N.V.
The dots and lines of screened images must exhibit sufficient high density since no substantial amount of light may be transmitted trough the dots and lines in a further exposure cycle. Therefore, a photographic element with high gradation is required. Furthermore the dots must exhibit a well-shaped form and sharp edges. This most desired combination of high contrast and excellent dot quality is commonly termed “lith quality”. The goal of achieving optimal lith quality is reached, in conventional photographic prepress, by the combination of so-called specially designed photographic materials and appropriate processing systems. A first group of such processing systems consists of the traditional “lith developers” characterized by the presence of hydroquinone as the sole developing agent and a low but critical sulphite ions content giving rise to an infectious development mechanism. However these conventional lith developers are rather instable in time and require complicated replenishment systems for both oxidation and exhaustion. Furthermore their developing capacity is rather limited due to the fact that they contain hydroquinone as the sole developing agent. Therefore, some 10-15 years ago so-called “hybrid systems” or “hard dot Rapid Access” developers were introduced on the market combining a good stability and lith quality in the reproduction of lines and screen dots. Examples of such developers and corresponding appropriate photographic materials include the GRANDEX system, marketed by Fuji Photo Co., AGFASTAR, marketed by Agfa-Gevaert N.V., and the ULTRATEC system, marketed by Eastman Kodak Co. However, this type of developers had a rather high pH and was more or less corrosive to the processing tank. In still more recent years hard dot systems were conceived wherein the developer more and more resembles a conventional Rapid Accesss developer as to pH and composition. Examples are the Kodak RA 2000 system, the Fuji HD system, and the IMPOWER system developed by the former prepress division of DuPont, now owned by Agfa-Gevaert AG.
When the screen dots are recorded electronically from digitally stored information a Rapid Access developing system will be adequate in most cases for obtaining sufficient dot quality provided the laser exposure source of the image-setter is of high quality and able to write screen dots with strong geometrical precision. A suitable image-setter is the AVANTRA, marketed by Agfa-Gevaert N.V., and a suitable recorder film is ALLIANCE HN, marketed by the same company.
Photomechanically or electronically produced halftone images are used as a master for the direct exposure of a printing plate, e.g. a planographic printing plate, or for the exposure of a photographic intermediate such as a contact film.
It will be clear that the photographic production of halftone images brings along a complicated and expensive work flow. The use of expensive exposure devices, films and chemicals is inevitable. Furtheron, the use of processing chemicals is ecollogically suspect according to modern standards. As a consequence, a cumbersome and expensive disposal procedure is needed. An alternative to the photographic method would be welcome.
OBJECTS OF THE INVENTION
It is the object of the present invention to provide an alternative system for the production of an image which can serve as a master for the exposure of a printing plate or intermediate contact film, or printed circuit board (PCB) precursor, said system being simple, inexpensive and involving no wet processing steps.
SUMMARY OF THE INVENTION
The above mentioned objects are realised by providing a method for the production of a UV sensitive printing plate, said method comprising exposing said plate through a screened image, or through an intermediate which itself is exposed through said screened image, said image having a full area Dmax of at least 3.5 in the ultra-violet spectral region, characterized in that said image has been obtained by jetting information-wise an ink comp
Graindourze Marc
Oelbrandt Leo
Quintens Dirk Cyriel
Agfa-Gevaert
Barlow John
Guy Joseph T.
Nexsen Pruet Jacobs & Pollard LLC
Shah Manish S
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