Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
1999-12-13
2002-03-05
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S273100, C430S281100, C430S022000
Reexamination Certificate
active
06352815
ABSTRACT:
The present invention relates to a process for the production of large-format composite relief printing plates by applying individual photopolymerizable relief printing plates to a large-format substrate, the image information being transmitted to the individual relief printing plates by means of a laser. The present invention furthermore relates to a process in which the individual photopolymerizable relief printing plates are positioned on the substrate with the aid of a laser. The present invention also relates to a composite of relief printing plates comprising a substrate, a laser-structurable layer applied thereon and insoluble in printing inks and printing plate developers, and relief printing plates applied thereon and having an IR-ablatable layer.
For printing on very large surfaces with relief printing plates, for example on corrugated board for cardboard packaging with flexographic printing plates, correspondingly large printing plates are required. These are difficult to handle and are expensive. Frequently, printing is to be effected on only one or more small portions of a large total area. The following procedure is customary for this purpose: the printing plates required for the portions to be printed on are produced from individual, small photopolymer printing plates and adhesively bonded to a mounting sheet in the position where the printed image is to appear within the total area. The mounting sheet with the individual plates bonded thereon is hooked into the printing cylinder by means of an angle bar fastened to it and is fastened to said printing cylinder in a defined position. In the case of multicolor printing, such a mounting sheet with corresponding plates is produced for each color.
However, the mounting of the printing plates is extremely time-consuming and labor-intensive. In the case of multicolor compositions, mounting must be carried out with very exact positioning so that the various color dots precisely match one another in the print. Mounting exactly to the dot has to date required mounting apparatuses with video cameras for detection of the register marks. Mounting exactly in register must be tested in a complicated procedure by superposed printing in a proof press. If a color is not printed exactly in register, then the corresponding printing plate must be removed from the mounting sheet and stuck on again in an improved position. After such a correction, proof printing of all colors for a further check is necessary again.
WO 98/01792 has therefore proposed carrying out the production of large-area printing plates by means of an inkjet process. Here, an inkjet printer applies marks for positioning the individual plates on a mounting sheet. After individual photopolymer plates, i.e. plates not yet exposed and developed, have been stuck on, a photomask is applied to the individual photopolymer plates by means of an inkjet printer. The plate composite as a whole is then exposed and developed. The recording of images on photopolymer relief printing plates by means of an inkjet process has been disclosed, for example, also by EP-A 465 949, WO 97/25206 or JP-A
63-109 052.
However, the disadvantage of image recording by means of an inkjet process is the low resolution, which is limited to about 600 dpi in the case of the inkjet printer. The print quality is therefore subject to limits.
It is known that higher resolutions can be achieved by image recording on printing plates by means of IR ablation, for example disclosed by EP-A 767 407 or U.S. Pat. No. 5,262,275. However, these advantages could not be utilized to date in the production of large-format printing plates on a mounting sheet since they were cancelled out by the mounting problems described above and poor registration.
It is an object of the present invention to provide a process which permits the production of large-format composite relief printing plates by direct image recording from a digital data stock with substantially higher resolution than that known in the prior art.
We have found that this object is achieved by the process described at the outset and the composites described at the outset and comprising photopolymerizable relief printing plates.
In the novel process, a dimensionally stable substrate is first provided with marks for positioning the photopolymer printing plates. The term dimensionally stable is to be understood as meaning that the substrate should not distort under the influence of environmental conditions, for example temperature variations or variations in the atmospheric humidity. In particular, those materials which are also advantageously used as substrates for flexographic or letterpress printing plates are employed as dimensionally stable substrates. Examples of such materials are foils of metals such as steel, aluminum, copper or nickel or sheets of plastics such as polyethylene terephthalate (PET), polybutylene terephthalate, polyamide or polycarbonate. Particularly suitable dimensionally stable substrates are polyethylene terephthalate sheets. These substrate sheets are in general from 100 to 500 &mgr;m, preferably from 200 to 500 &mgr;m, for example 250 &mgr;m, thick.
The choice of a suitable method by means of which the dimensionally stable substrate can be provided with positioning marks is not limited. In principle, any method which leaves marks on the substrate which are so clearly visible that these marks are detectable with the naked eye without technical aids can be used. For example, the positioning marks can be applied manually, if necessary assisted by suitable drawing or marking tools. The position of the mark is advantageously calculated by means of a computer with the aid of the layout data stocks. Furthermore, marks can be applied, for example, by means of suitable drawing apparatuses or plotters.
In a preferred embodiment, the positioning marks are written with the aid of an IR laser. This embodiment also comprises the use of a dimensionally stable substrate which is itself laser-structurable. Such a substrate contains components which can interact with the IR laser. The preferred embodiment of the invention furthermore comprises the coating of a dimensionally stable substrate with a laser-structurable layer.
The laser-structurable layer on the substrate is insoluble and preferably also non-swellable in the printing inks used, for example flexographic printing inks based on water, alcohols and esters, and in the developers usually used for developing the relief printing plates, for example those based on chlorinated hydrocarbons or high-boiling hydrocarbon solvents.
The laser-structurable layer on the substrate can be written on by means of an IR laser. Suitable laser-structurable layers are, for example, thermochromic layers which undergo an irreversible color change on exposure to an IR laser, or are IR-ablative layers which are removed or evaporated on exposure to an IR laser, with the result that the substrate underneath becomes visible again.
The thermochromic layers contain thermochromic systems. In general, such thermochromic systems consist of organic layers which, under the influence of activators, for example of free radicals, acids, bases or oxidizing agents, undergo irreversible rearrangement or conversion into a form which has different absorption behavior with respect to light. In this way, an irreversible color change is achieved. Under the influence of heat, the activators result in the conversion of the absorbing substances. Suitable thermochromic systems are disclosed, for example, in DE-A 33 42 579. An example of such a system is Michler's ketone with benzyl tosylate as activator.
Suitable IR-ablative layers on the substrate sheet contain IR-absorbing materials and have high absorption in the wavelength range from 750 to 20000 nm. Furthermore, in the visible range of the spectrum, i.e. in the wavelength range from 400 to 750 nm, the layer has an optical density of at least 0.5, preferably at least 1.0. Examples of suitable IR-absorbing materials are dyes which absorb in the IR range, such as phthalocyanine compo
Feil Markus
Telser Thomas
Weidmann Albrecht
BASF Drucksysteme GmbH
Baxter Janet
Gilmore Barbara
Keil & Weinkauf
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