Printing – Printing members – Blanks and processes
Reexamination Certificate
2002-05-28
2004-03-02
Funk, Stephen R. (Department: 2854)
Printing
Printing members
Blanks and processes
C101S395000, C219S121760, C347S239000, C347S255000
Reexamination Certificate
active
06698354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and a device for the production of a printing block. The printing block may, for example, be a flexible or inflexible printing block, which can act as a relief printing or gravure printing block.
2. Description of the Relevant Art
To produce the flexographic printing block with the aid of a conventional CO
2
laser it is already generally well known for material to be burned out directly from a printing plate, which may be a polymer plate for instance, in order in this manner to produce a relief in the printing plate. In this process, the CO
2
laser is permanently power-modulated to obtain recesses bounding the relief in the surface of the printing plate.
SUMMARY OF THE INVENTION
Furthermore, for the production of a flexographic printing block PCT/EP96/05277 already discloses the use of two laser beam sources in order with the first laser beam source to obtain fine structures in a desired profile, while by means of the second laser beam source lower-level regions in the profile are produced.
The state of the art further includes methods for placing small raster dots in a relief at a lower level. This is done in that focused beams staggered close beside one another strike corresponding regions and remove the material in conformity with the focused course of the beams. This then gives rise to a sort of cone whose conical apex is located at a greater or lesser depth in the relief. If in subsequent printing an add-on is arranged under the printing block, that is to say a kind of underlay, then due to this underlay the tip of the cone is lifted back again into the region of the print area. However, printing material adheres quite poorly to this cone tip so that a less than sharp printed image results. Cone tips representing raster dots of this kind are provided by way of example in the vicinity of full print areas so that in subsequent printing the full print areas may be given more prominence. In subsequent printing the said underlay comes to lie beneath a full print area so that during printing a high contact pressure is obtained. Where the depth of the raster dots surrounding the full print area not reduced in advance the latter would press too heavily against the subsequent print area and buckle which would likewise adversely affect the printed image.
It is an object of the invention to specify a method for the production of a printing block, in particular a flexographic printing block, with which fine relief structures to be given prominence in subsequent printing may be produced in such a way that they result in a flawless printed image. Moreover, a corresponding device for producing such printing blocks is to be provided.
In a method according to the invention for producing a printing block, in particular a flexographic printing block, a relief is introduced into the surface of a blank of the printing block in that material of the printing block blank is removed in regions along tracks by radiation in order by this means to form recesses between which plateaus come to lie. Now, according to the invention the surface of the printing block blank located between the recesses is also removed by radiation in such a way that as a result lower-lying plateaus are obtained.
Thus, contrary to the most recently described state of the art fine raster dots later to be given prominence in the relief are not produced in that due to conical and closely adjacent beams more or less low-lying cone tips are blocked in the relief, but rather in that initial plateaus between the respective recesses located initially in the surface of the printing block blank are lowered in depth more or less uniformly in order to obtain lower-lying plateaus whose plateau surface comes to lie as before more or less parallel to the surface of the printing block blank. If, during subsequent printing, these plateaus are lifted, that is to say lifted into the print area, then sufficient printing material remains adhering to them to yield a sharp printed image. This procedure is used when, for example, a relatively large full print area is surrounded by a fine raster so that the full print area is given more prominence.
According to a refinement of the invention, in order to set the depth of the lower-lying plateaus the surface of the printing block blank located between the recesses can be removed by radiation whose intensity or power can be correspondingly adjusted. Thus, if the plateaus lying between the recesses are to be burned away to a greater depth the intensity or power of the beam must be increased and vice versa.
According to another refinement of the invention, in order to set the depth of the lower-lying plateaus the surface of the printing block blank lying between the recesses can also be removed by repeated irradiation. Thus, this multiple irradiation of the printing block blank in the region of the plateaus to produce the lower-lying plateaus ensues with a time delay or successively so that a lower-lying plateau is obtained as it were by repeated scooping out.
Since the lower-lying plateaus of the relief structure are carved out by repeated exposure to radiation or burning off the power of the beam can be relatively low which has the consequence that even very fast modulators, precisely whose beam power when used has to be limited in order to save the modulators from destruction, acousto-optical modulators for instance, can be used for switching the beam power on and off. Due to repeated and hence relatively gentle erosion of the plateau it is also achieved that after each removal operation the printing block material cools again before removal of material starts afresh which has the result that the printing block material in the region of the plateau does not heat up so much and hence the relief can be built up in decidedly exact manner or true to shape. Between the individual burn-off operations the material stripped off can also be taken away, eg sucked off, which allows more precise working in the next removal operation and results in structures of better quality.
In doing so the irradiation of the plateaus can ensue along a particular track using one and the same beam which is guided repeatedly along a track. However, it is also possible for irradiation along a track to be done using a plurality of beams which are conveyed one after the other along the same track. For this purpose it is possible in principle for a plurality of stations to be arranged beside one another in a direction running transverse to the longitudinal direction of the track when a corresponding relative shift between track and beams ensues. However, a plurality of beams located alongside one another in a direction running in the longitudinal direction of the track may also be used.
According to a refinement of the invention the depth of the lower-lying plateaus may be set differently as a function of their position in the relief. Thus, by way of example the depth of the lower-lying plateaus may increase in the direction towards a full print area located in the surface of the printing block blank in order to ensure that during subsequent printing the lower-lying plateaus in the vicinity of the full print area are lifted just into the print area when an add-on or underlay is located under the full print area.
It should be pointed out that the recesses in the surface of the printing block blank present between the plateaus may also be constructed by multiple irradiation of the surface of the printing block blank. This multiple irradiation of the printing block blank to produce the lower-lying recesses then occurs with a delay or successively so that a lower-lying recess is obtained as it were by repeated scooping out. However, the recesses could also be obtained by appropriate control of the power of the beam over the region of a recess.
In a further development of the invention the exposure of the printing block blank to radiation is done using laser radiation since in this manner the requisite radiation energy can be readily made available
Juffinger Josef
Thaler Karl
Birch & Stewart Kolasch & Birch, LLP
Funk Stephen R.
Schablonentechnik Kufstein Aktiengesellschaft
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