Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-10-08
2004-04-13
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S302000, C430S964000, C101S462000, C101S467000
Reexamination Certificate
active
06720130
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat-sensitive lithographic printing plate precursor, which requires no development-processing and can ensure a long press life and high stain resistance. More specifically, the present invention relates to a lithographic printing plate precursor which enables non-ablative recording of images by scanning exposure to radiation, such as infrared laser beams based on digital signals and, after the images are recorded therein, can be mounted in a printing machine (i.e. a printing press) without undergoing development-processing, and subjected to printing operations.
2. State of the Art
Various methods have been proposed concerning a lithographic printing plate precursor of the kind which enables image formation by heat and can be mounted in a printing machine without development-processing after the image formation. One method among them is a method of utilizing an ablation phenomenon, which comprises exposing a printing plate precursor containing a compound capable of converting light to heat by means of a high-output solid-state laser, e.g., a semiconductor laser or a YAG laser, to make the exposed area evolve heat by the compound capable of converting light to heat, thereby causing decomposition and evaporation, namely ablation, in the exposed area.
In negative-working compositions, a water-receptive layer is provided on a substrate having an oleophilic ink-receptive layer and the water-receptive layer is removed by ablation.
Reference is made to U.S. Pat. No. 6,397,749 and EP 1,110,719, both assigned to Fuji Photo Film, Ltd. which disclose heat sensitive lithographic printing plate precursors for on-press development, having a substrate supporting an ink-receptive or oleophilic layer and having thereover a crosslinked hydrophilic layer. In U.S. Pat. No. 6,397,749, a third water soluble overcoat layer is further provided to facilitate development on press.
Reference is also made to published EP Patent Applications 1,065,049 to 1,065,053 and to U.S. Pat. No. 5,985,515, all assigned to AGFA-Gevaert, N.V. These references also disclose heat-imageable lithographic printing plates having a support, a heat-sensitive oleophilic layer and a hydrophilic top layer containing a cross-linked hydrophilic polymer. In U.S. Pat. No. 5,985,515 and EP 1,065,052, the hydrophilic layer is heat-ablatable.
In EP 1,110,049 the hydrophilic layer contains heat-meltable, dispersed hydrophobic polymer particles which melt to form hydrophobic, oleophilic image areas. In EP 1,110,050 the thickness of the heat-sensitive oleophilic layer is regulated to permit the hydrophilic properties of the hydrophilic support to reduce toning in the non-imaged areas of the plate and thereby increase the run length of the imaged plate. In EP 1,110,051, the two-layer heat-sensitive material is covered by a third hydrophilic layer comprising an organic compound containing cationic groups.
A major disadvantage of ablation processes is contamination of the imaging device. Vacuum cleaning systems are generally required to avoid such contamination. Another disadvantage is that the decomposition of the plate layer(s) in the exposed areas results in the scattering of scum particles produced during decomposition, which scum particles attract printing ink to the non-image areas of the developed plate surface, resulting in background staining of the printed copies. This is alleviated to some extent by the application of a water-soluble overcoat layer.
It is also known in U.S. Pat. No. 6,107,001 to Presstek Inc., dated Aug. 22, 2000, to avoid the disadvantages of ablation or decomposition of the plate layers in the heat developed image areas by providing two layers, such as a hydrophilic top layer and an oleophilic bottom layer, the top layer becoming irreversably-debonded from the bottom layer in the heat-imaged areas.
None of the above cited references discloses interlayer chemical bonding between the hydrophilic and oleophilic layers.
SUMMARY OF THE INVENTION
The present invention relates to a radiation sensitive lithographic printing plate precursor preferably having only two polymeric layers on a support. The first (bottom) layer is composed of oleophilic polymer(s) and a photothermal converter which converts radiation to heat. The second polymeric layer (top) is composed of crosslinked hydrophilic polymer(s) which absorb aqueous fountain solution and repel ink. The oleophilic polymer(s) in the first layer contain functional groups, which chemically bond with the second layer to provide interlayer adhesive bonding between the two layers.
The plate is imagewise exposed to electromagnetic radiation, such as with an IR laser, resulting in non-ablative weakening of the adhesive bonding between the two layers so that it can be developed by fountain solution and/or ink on press. After development, the top layer in the exposed area is removed to reveal the underlying ink-receptive image area. The top layer in the unexposed area remains as non-image area.
The top hydrophilic layer has an opposite affinity for printing ink or ink-adhesive fluid from the heat-sensitive oleophilic, hydrophobic layer therebeneath. Preferably, both the top and bottom layers remain in place after the plate precursor is heat-imaged with no ablation of either layer. Any detachment of the top layer from the bottom layer in the heat-images areas is reversible to some extent by heating to elevated temperatures, as described in the examples.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The novel lithographic printing plate precursors of the present invention comprise:
(1) a substrate, which is dimensionally stable and can be aluminum or another metal or alloy. Preferentially electrochemically and/or mechanically grained and anodized aluminum is used in the present invention. Hydrophilization of the aluminum substrate is not required, but may be useful for enhancing adhesion of the base layer to the substrate.
Furthermore in connection with the present invention, the support can be a flexible support. As flexible support in connection with the present embodiment it is particularly preferred to use a polymeric film e.g. substrated polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, poly-styrene film, polycarbonate film, polyethylene film, polypropylene film, polyvinyl chloride film, polyether sulphone film. The plastic film support may be opaque or transparent. The polymeric film is preferably subbed with subbing layers as described in EP-A-619 524, EP-A-619 525 and EP-A-620 502.
Still further paper or glass of a thickness of not more than 1.2 mm can also be used.
(2) an olephilic base layer comprising an oleophilic polymer containing functional reactive groups, and a photothermal converter material, such as dye or pigment capable of absorbing electromagnetic radiation and converting it to heat, and
(3) a hydrophilic overlayer comprising a crosslinked hydrophilic polymer capable of absorbing aqueous lithographic fountain solution, in which said crosslinked hydrophilic polymer is interlayer chemically bonded with the functional reactive groups of said oleophilic polymer in the base layer to provide interlayer adhesive bonding between said layers, imagewise exposure of said printing plate precursor to laser radiation resulting in non-ablative weakening of said adhesive bonding between said layers in the exposed areas whereby said hydrophilic overlayer can be removed by fountain solution or ink on a lithographic printing press to reveal the oleophilic ink-receptive base layer.
Preferably the oleophilic polymer of the base layer composition and the crosslinkable hydrophilic polymer of the overlayer or top layer are both organic polymers.
Suitable oleophilic organic polymers for the base layer include acrylic polymers and copolymers, methacrylic polymers and copolymers, epoxy polymers, phenolic polymers, polyurethanes, polyureas and polyesters, most preferably such polymers contain at least one of —COOH and —OH functional reactive groups.
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Pappas S. Peter
Saraiya Shashikant
Zhong Xing-Fu
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
Schilling Richard L.
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