Printing – Planographic – Lithographic printing plates
Reexamination Certificate
2002-03-01
2004-02-03
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic printing plates
C101S462000, C101S467000
Reexamination Certificate
active
06684785
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to printing apparatus and methods, and more particularly to imaging of lithographic printing-plate constructions on- or off-press using controlled laser output.
BACKGROUND OF THE INVENTION
In offset lithography, a printable image is present on a printing member as a pattern of ink-accepting (oleophilic) and ink-rejecting (oleophobic) surface areas. Once applied to these areas, ink can be efficiently transferred to a recording medium in the imagewise pattern with substantial fidelity. Dry printing systems utilize printing members whose ink-repellent portions are sufficiently phobic to ink as to permit its direct application. Ink applied uniformly to the printing member is transferred to the recording medium only in the imagewise pattern. Typically, the printing member first makes contact with a compliant intermediate surface called a blanket cylinder which, in turn, applies the image to the paper or other recording medium. In typical sheet-fed press systems, the recording medium is pinned to an impression cylinder, which brings it into contact with the blanket cylinder.
In a wet lithographic system, the non-image areas are hydrophilic, and the necessary ink-repellency is provided by an initial application of a dampening fluid to the plate prior to inking. The dampening fluid prevents ink from adhering to the non-image areas, but does not affect the oleophilic character of the image areas.
To circumvent the cumbersome photographic development, plate-mounting and plate-registration operations that typify traditional printing technologies, practitioners have developed electronic alternatives that store the imagewise pattern in digital form and impress the pattern directly onto the plate. Plate-imaging devices amenable to computer control include various forms of lasers.
For example, U.S. Pat. No. 5,493,971 discloses wet-plate constructions that extend the benefits of ablative laser imaging technology to traditional metal-based plates. Such plates remain the standard for most of the long-run printing industry due to their durability and ease of manufacture. As shown in
FIG. 1
, a lithographic printing construction
100
in accordance with the '971 patent includes a grained-metal substrate
102
, a protective layer
104
that can also serve as an adhesion-promoting primer, and an ablatable oleophilic surface layer
106
. In operation, imagewise pulses from an imaging laser (typically emitting in the near-infrared, or “IR” spectral region) interact with the surface layer
106
, causing ablation thereof and, probably, inflicting some damage to the underlying protective layer
104
as well. The imaged plate
100
may then be subjected to a solvent that eliminates the exposed protective layer
104
, but which does no damage either to the surface layer
106
or to the unexposed protective layer
104
thereunder. By using the laser to directly reveal only the protective layer and not the hydrophilic metal layer, the surface structure of the latter is preserved; the action of the solvent does not damage this structure.
This construction relies on removal of the energy-absorbing layer to create an image feature. Exposure to laser radiation may, for example, cause ablation—i.e., catastrophic overheating—of the ablated layer in order to facilitate its removal. Accordingly, the laser pulse must transfer substantial energy to the absorbing layer. This means that low-power lasers must be capable of very rapid response times, and imaging speeds (i.e., the laser pulse rate) must not be so fast as to preclude the requisite energy delivery by each imaging pulse.
In order to reduce or even obviate the need for substantial ablation as an imaging mechanism, U.S. application Ser. No. 09/564,898, now U.S. Pat. No. 6,378,432, the entire disclosure of which is hereby incorporated by reference, discloses a construction combining the benefits of simple construction, the ability to utilize traditional metal base supports, and amenability to imaging with low-power lasers that need not impart ablation-inducing energy levels. As shown in
FIGS. 2A-2C
and
3
A-
3
B, in one embodiment, a printing member includes a hydrophilic metal substrate
302
, a topmost layer
306
that does not significantly absorb imaging radiation, and an intermediate layer
304
that does absorb imaging radiation. The radiation-absorbing layer
304
comprises a radiation-absorptive material (which may be graded through the thickness of layer
304
if desired). In one version as shown in
FIGS. 2A-2C
, in response to an imaging pulse the absorbing layer
304
debonds from the surface of the adjacent metal substrate; in another version as shown in
FIGS. 3A-3B
, an interior split is formed within the absorbing layer, facilitating removal of the portion of that layer above the split. In neither case does the absorbing layer undergo substantial ablation. Remnants of the absorbing layer and the overlying layer (or layers) are readily removed by post-imaging cleaning to produce a finished printing plate.
BRIEF SUMMARY OF THE INVENTION
The cost of manufacturing a printing plate is generally a function of the number of plate layers. Because each layer is individually applied in a separate process step, elimination of a layer can materially reduce overall production costs. In accordance with the present invention, the functions performed by layers
304
and
306
are combined into a single layer.
In particular, the present invention provides a printing member having a single radiation-absorptive multiphase layer over a substrate layer that may be imaged with or without ablation. The multiphase layer may be in contact with the substrate layer along an interface. The multiphase layer comprises a polymer-rich phase and an inorganic-rich phase dispersed within the polymer-rich phase. To provide a lithographic image, the printing member is subjected to imaging radiation in an imagewise pattern. The radiation removes or facilitates removal of at least a portion of the multiphase layer but does not affect the substrate. Following imaging, a cleaning step may be used to remove remnants of the portion of the multiphase layer, thereby creating an imagewise lithographic pattern on the printing member. The printing member may now be used for printing.
In preferred embodiments, a printing member in accordance with the invention comprises a multiphase layer and a substrate. In one embodiment, the substrate is a metal substrate. Suitable metal substrates include, but are not limited to, aluminum, copper, steel, and chromium. In a preferred embodiment, the metal substrate is grained, anodized, and/or silicated. For example, the substrate may be aluminum. In another embodiment, the substrate is a polymer substrate. Suitable polymer substrates include, but are not limited to, polyesters, polycarbonates, and polystyrene. In a preferred embodiment, the substrate is a polyester film, and preferably a polyethylene terephthalate film. In still another embodiment, the substrate is a paper substrate.
The multiphase layer may comprise a polymer-rich phase and an inorganic-rich phase. Suitable materials for the polymer-rich phase include, but are not limited to, polyvinyl alcohols, copolymers of polyvinyl alcohol, polyvinyl pyrrolidone and its copolymers, and polyvinylether and copolymers thereof. In a preferred embodiment, the polymer is a polyvinyl alcohol. The inorganic-rich phase contains one or more inorganic oxides, typically formed as a reaction product of an initially soluble complex. Such inorganic oxides may include, for example, zirconium oxide (typically ZrO
2
), aluminum oxide (typically Al
2
O
3
), silicon dioxide and titanium oxide (typically TiO
2
), as well as combinations and complexes thereof. It should also be noted that these oxides may exist in hydrated form. In a preferred embodiment, the inorganic-rich phase comprises “nodules” rich in zirconium oxide. Preferably, the nodules are dispersed within the polymer-rich phase. In one embodiment, the inorganic-rich phase further comprises an inorga
Funk Stephen R.
Presstek Inc.
Testa Hurwitz & Thibeault LLP
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