Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2001-04-18
2002-06-25
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S303000, C430S348000, C430S944000, C430S945000, C430S964000, C101S463100
Reexamination Certificate
active
06410208
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing plates. More particularly, it relates to lithographic plates capable of direct imaging using digitally controlled laser output. More specifically, it relates to lithographic plates comprising on a substrate a thermo-deactivatable photosensitive layer, and methods of processing such lithographic plates.
BACKGROUND OF THE INVENTION
Lithographic printing plates (after process) generally consist of ink-receptive areas (image areas) and ink-repelling areas (non-image areas). During printing operation, an ink is preferentially received in the image areas, not in the non-image areas, and then transferred to the surface of a material upon which the image is to be produced. Commonly the ink is transferred to an intermediate material called printing blanket, which in turn transfers the ink to the surface of the material upon which the image is to be produced.
Lithographic printing can be further divided into two general types: wet lithographic printing (conventional lithographic printing) and waterless lithographic printing. In wet lithographic printing plates, the ink-receptive areas consist of oleophilic materials and the ink-repelling areas consist of hydrophilic materials; fountain solution (consisting of primarily water) is required to continuously dampen the hydrophilic materials during printing operation to make the non-image areas oleophobic (ink-repelling). In waterless lithographic printing plates, the ink-receptive areas consist of oleophilic materials and the ink-repelling areas consist of oleophobic materials; no dampening with fountain solution is required.
At the present time, lithographic printing plates (processed) are generally prepared from lithographic printing plate precursors (also commonly called lithographic printing plates) comprising a substrate and a photosensitive coating deposited on the substrate, the substrate and the photosensitive coating having opposite surface properties (such as hydrophilic vs. oleophilic, and oleophobic vs. oleophilic). The photosensitive coating is usually a photosensitive material, which solubilizes or hardens upon exposure to an actinic radiation, optionally with further post-exposure overall treatment. In positive-working systems, the exposed areas become more soluble and can be developed to reveal the underneath substrate. In negative-working systems, the exposed areas become hardened and the non-exposed areas can be developed to reveal the underneath substrate. The exposed plate is usually developed with a liquid developer to bare the substrate in the non-hardened or solubilized areas.
On-press developable lithographic printing plates have been disclosed in the literature. Such plates can be directly mounted on press after exposure to develop with ink and/or fountain solution during the initial prints and then to print out regular printed sheets. No separate development process before mounting on press is needed. Among the patents describing on-press developable lithographic printing plates are U.S. Pat. Nos. 5,258,263, 5,516,620, 5,561,029, 5,616,449, 5,677,110, 5,811,220, 6,014,929, and 6,071,675.
Conventionally, the plate is exposed with an actinic light (usually an ultraviolet light from a lamp) through a separate photomask film having predetermined image pattern which is placed between the light source and the plate. While capable of providing plate with superior lithographic quality, such a method is cumbersome and labor intensive.
Laser sources have been increasingly used to imagewise expose a printing plate that is sensitized to a corresponding laser wavelength. This allows the elimination of the photomask film, reducing material, equipment and labor cost.
Among the laser imagable plates, infrared laser sensitive plates are the most attractive because they can be handled and processed under white light. Infrared laser sensitive plates are also called thermosensitive plates or thermal plates because the infrared laser is generally converted to heat to cause a certain chemical or physical change (such as hardening, solubilization, ablation, phase change, or thermal flow) needed for imaging formation on a plate. Various thermosensitive plates have been disclosed in the patent literature. Examples of thermosensitive plates are described below.
U.S. Pat. No. 5,379,698 describes a lithographic plate comprising a top polymer layer, a thin metal layer, and a substrate. The top polymer layer and the substrate have opposite affinity to ink. The plate is imaged by exposing with an infrared laser to thermally ablate the thin metal layer and the top polymer layer, baring the substrate in the exposed areas. While this plate can eliminate the use of photomask, it has the disadvantage of producing hazardous ablation debris during laser exposure, and often requires a cleaning step after exposure.
U.S. Pat. No. 5,705,309 describes a lithographic plate having on a substrate a thermosensitive layer comprising a photocrosslinkable polymeric binder having pendant ethylenic groups, a polyazide photoinitiator, and an infrared absorbing compound. This plate can be exposed with an infrared laser and then developed with a liquid developer to form a negative plate. While this plate allows digital imaging without the use of photomask, it requires a cumbersome liquid development process and has limited press run length.
U.S. Pat. No. 5,491,046 describes a lithograghic plate having on a substrate a photosensitive layer comprising a resole resin, a novolac resin, a haloalkyl substituted s-triazine, and an infrared absorber. This plate is sensitive to ultraviolet and infrared radiation and capable of functioning in either a positive-working or negative working manner. The plate can be imagewise exposed with an infrared laser followed by development to form a positive plate, or can be imagewise exposed with an infrared laser and then baked at an elevated temperature followed by development to form a negative plate. While this plate is capable of digital imaging and can act as both positive and negative plate, it requires a cumbersome baking process to achieve high press run length.
U.S. Pat. No. 4,132,168 describes a lithographic plate consisting of on a substrate an ultraviolet light (UV) sensitive layer and a top mask layer that is opaque to UV light and is capable of being removed or rendered transparent to UV light by a non-actinic laser radiation. While this plate is capable of digital imaging, it requires two cumbersome chemical processes after exposure, namely a mask layer removal process and a development process.
U.S. Pat. Nos. 5,674,658 and 5,677,106 describe a lithographic printing plate having on a porous hydrophilic substrate an oleophilic imaging layer. The imaging layer comprises a polymeric binder and an infrared absorbing dye, and is capable of bonding to the porous substrate surface through thermal flow upon exposure to a radiation. The non-exposed areas are capable of removal from the substrate by contacting with ink or by peeling. While this plate is useful, it suffers from poor press durability because the image layer in the exposed areas is not hardened (crosslinked) and can be quickly washed off during press operation.
U.S. Pat. No. 6,117,610 describes a lithographic printing plate having an imaging layer comprising a non-basic infrared radiation absorbing material and a phenolic resin that is either mixed or reacted with an o-diazonaphthoquinone derivative. The plate can be imagewise exposed with an infrared laser, followed by development with an aqueous developer, to remove the imagewise exposed areas of the image layer to form a positive plate. Alternatively, the plate can be imagewise exposed with an infrared laser and then overall exposed with an actinic radiation, followed by development with an aqueous developer, to remove the non-imagewise exposed areas of the image layer to form a negative plate. While this plate allows direct digital imaging, it has limited press run length because the imaging layer in the imaging areas is not fully crosslinked.
U.S.
Baxter Janet
Gilmore Barbara
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