Printing – Intaglio
Reexamination Certificate
2002-08-01
2004-08-24
Funk, Stephen R. (Department: 2854)
Printing
Intaglio
C101S401100
Reexamination Certificate
active
06779444
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a printing form and a process for producing the printing form.
A suction printing process is a novel gravure printing process, such as is described in detail in the International Publication No. WO 00/40423. A gravure printing process is characterized by depressing those printing form elements which do the printing. The nonprinting form elements lie at a constant level. Before printing, the entire printing form is inked, i.e., flooded with printing ink. Suitable devices, such as wipers or doctor blades, ensure that the printing ink on the nonprinting form elements is removed before printing. Printing ink therefore remains only in the depressions. A high contact pressure and the adhesion forces between the printing material and the ink effect ink transfer from the depressions to the printing material.
The traditional gravure printing process, i.e., gravure printing which is variable only in depth or gravure printing which is variable both in depth and in area are, as printing processes, quite simple, however, the production of the printing form is very expensive. As explained hereinbefore, the gravure printing process is based upon introducing ink into the depressions, which have been engraved in a cylinder or plate in accordance with an image, and then transferred to paper in a comparatively simple printing unit with the aid of an impression cylinder. The production of the printing form is complicated and costly, but the print quality that is achieved is of very high level, and the technology of the printing unit in the rotary gravure printing system is simple when compared with offset printing. In particular, the high costs in the production of the printing form are the reason that the gravure printing process is used only for very large editions in the range of millions of prints.
For this reason, there has been no lack of efforts to simplify the production of the printing form for gravure printing. For example, U.S. Pat. No. 5,233,921 describes a printing form which comprises an easily deformable core and a plate formed with depressions therein, the plate being disposed above the core. The printing form is in the form of a cylinder, and the depressions formed in the plate can be changed depending upon the amount of heat supplied to the depressions. The volume of the individual depressions is consequently controllable in accordance with the respectively supplied heat. A printing form suitable for gravure printing is thereby attained, wherein, in a conventional manner, ink is introduced into the depressions and then applied to printing material via a conventional gravure printing process. The size and the contrast of individual raster dots in the image to be printed can be controlled by the volume of the individual depressions. A difficulty remains, however, in inserting an adequate amount of the ink into the depressions. If the depressions are comparatively small in diameter but long or deep in length, then a medium, such as air, present in the depressions considerably hampers the acceptance or takeup of ink, because the ink introduced into the depressions via the openings thereto prevents the emergence of the air from the depressions, due to which the space for the acceptance or takeup of the ink becomes relatively small.
A remedy is provided herein by the so-called suction printing process, wherein the medium in the depressions serves specifically and selectively for each depression for accepting or taking up the ink. In this regard, use is made of the fact that the volume of the air present as the medium in the depressions depends to a very great extent upon the temperature. If, therefore, the air in the depressions is heated before the ink is accepted or taken up, then the ink will be driven correspondingly forcefully out of the depressions. If the entrance to the depressions is then closed by the ink and the remainder of the medium present in the depressions is cooled, the medium will then contract with the cooling and, accordingly, suck ink into the depressions. This effect is greater, the greater the fluctuation of the temperature in the depressions. In practical terms, if previous high heating occurs in a depression and a high level of cooling of the medium takes place in a respective depression while the ink is being supplied, a comparatively large amount of ink will be sucked into the respective depression. Therefore, principally by controlling the temperature in the depressions, the quantity of ink accepted or taken up in the depressions can also be controlled. The printing form in the suction printing process is therefore rewritten with the aid of a thermal image before each new printing operation, for example, the depressions are irradiated selectively with energetic radiation. It is therefore possible for even very small editions to be printed cost-effectively. By optional additional heating of the depression during the transfer of the ink to the printing medium to be printed, the ink remaining in the depression can also be expelled specifically, so that the heating step has two functions, namely making ready the acceptance or takeup of ink for the next step and, at the same time, ensuring the expulsion of the ink from the depression.
Whereas, in the suction printing process according to the hereinaforementioned International Publication No. WO 00/40423 and also in the case of the hereinaforedescribed process, the image on the printing form can theoretically always change from printing operation to printing operation, this is not the case in the gravure printing process further known from the literature wherein a reusable printing form is employed. This process, amongst others, is described in the Handbook of Print Media by Helmut Kipphan (Springer-Verlag on pages 677, 678). In this heretofore known process, a form cylinder formed uniformly with depressions is provided, whereon the depressions are distributed in the form of a matrix. The depressions, referred to as cells, have a high density in relation to one another, it being possible for about seventy cells to lie on a square centimeter. Before the printing operation, the depressions are filled with a polymer, after which a uniform surface with exposed metallic lands or cross-pieces is produced with a doctor blade. This polymer in the cells is then hardened. The setting of an image or imaging then takes place by vaporizing the polymer in the cells, if necessary or desirable, wholly or only to some extent, by a thermal laser. Consequently, within the predefined or prescribed structure of the cells, individual depressions with different spatial or three-dimensional volumes are formed. The volumes exposed by the laser beam can differ from one another both in the diameter and in the depth thereof, by which a plurality of gray values per pixel can be produced, which permits a correspondingly higher colored or printed image quality.
After a print run or after printing an edition, the printing form is erased by a water jet under high pressure, by which the polymer is released from the cells. The heretoforeknown process is suitable both for direct gravure printing and for indirect gravure printing, wherein the printing image is transferred to paper webs via a transfer cylinder with a rubber coating.
It has been found that the suction printing process has considerable advantages over the other hereinaforedescribed processes. In the suction printing process, assurance is provided that the ink will be introduced in the desired quantity into the depressions. In addition, in this suction printing process, it is possible, by modifying the surfaces of the printing form located between the depressions, to make these surfaces ink-repellant, so that the result here is a printing process which makes use of the advantages of both gravure printing and of offset printing. One difficulty with the suction printing process, however, is that the depressions, preferably arranged in the form of a matrix, must have a considerable depth in comparison with the cr
Ernst Uwe
Hauptmann Gerald Erik
Möller Tobias
Vosseler Bernd
Funk Stephen R.
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Mayback Gregory L.
Stemer Werner H.
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