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
2001-11-02
2004-09-14
Huff, Mark F. (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
C430S278100, C430S302000, C430S348000, C430S944000, C430S945000, C101S453000, C101S463100, C101S467000
Reexamination Certificate
active
06790595
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a negative-working heat-sensitive material which is suitable for making a lithographic printing plate by direct-to-plate recording and to a method for imaging said heat-mode recording material by means of an infrared laser.
BACKGROUND OF THE INVENTION
Lithographic printing is the process of printing from specially prepared surfaces, which contain a lithographic image consisting of areas that are capable of accepting ink (oleophilic areas) and areas that do not accept ink but are water-accepting (hydrophilic areas). In so-called wet lithographic printing methods, both water or an aqueous dampening liquid (also called fountain solution) and ink are applied to the plate surface that contains the hydrophilic and oleophilic areas. The hydrophilic areas are soaked with water or the dampening liquid and are thereby rendered oleophobic.
Various heat-mode plate materials are known which can be used as a lithographic master for printing with greasy inks. Ablative plates are the best known examples of so-called processless plates, i.e. plates which do not require any processing and therefore can be used as a printing plate immediately after exposure. The heat, which is generated in the recording layer of such ablative plates by light absorption of a laser beam, removes a hydrophilic or oleophilic topcoat to expose an underlying oleophilic respectively hydrophilic surface, thereby obtaining the necessary differentiation of ink-acceptance between the image (printing) and non-image or background (non-printing) areas.
For example DE-A-2 448 325 discloses a laser heat-mode ‘direct negative’ printing plate comprising e.g. a polyester film support provided with a hydrophilic surface layer. The disclosed heat-mode recording material is imaged using an Argon laser thereby rendering the exposed areas oleophilic. An offset printing plate is thus obtained which can be used on an printing press without further processing. The plate is called a ‘direct negative’ plate because it is suitable for direct exposure by a laser beam (“computer-to-plate”, no film mask required) and because the areas of the recording material that have been exposed to the laser are rendered ink-accepting and define the image areas, i.e. the printing areas.
Other disclosures in DE-A-2 448 325 concern “direct negative” printing plates comprising e.g. hydrophilic aluminum support coated with a water soluble laser light (Argon-488 nm) absorbing dye or with a coating based on a mixture of hydrophilic polymer and laser light absorbing dye (Argon-488 nm). Further examples about heat-mode recording materials for preparing “direct negative” printing plates have been described in e.g. DE-A-2 607 207, DD-A-213 530, DD-A-217 645 and DD-A-217 914. These documents disclose heat-mode recording materials that contain an anodized aluminum support and a hydrophilic recording layer provided thereon. Laser exposure renders the exposed areas insoluble and ink-receptive, whereas the non-exposed areas remain hydrophilic and water-soluble. Such plates can also be used directly on the press without processing, because the non-exposed areas are removed by the dampening liquid during printing, thereby revealing the anodized aluminum support.
DD-A-155 407 discloses a processless heat-mode ‘direct negative’ printing plate where a hydrophilic aluminum oxide layer is rendered oleophilic by direct laser heat-mode imaging.
The above heat-mode ‘direct negative’ lithographic printing plate are characterized by a low recording speed and/or the obtained plates are of poor quality and durability.
EP-A-580 393 discloses an ablative lithographic printing plate directly imageable by laser discharge, the plate comprising a topmost first layer and a second layer underlying the first layer wherein the first layer is characterized by efficient absorption of infrared radiation and the first and second layer exhibit different affinities for at least one printing liquid.
EP-A-683 728 discloses a heat-mode recording material comprising on a support having an ink receptive surface or being coated with an ink receptive layer a substance capable of converting light into heat and a hardened hydrophilic surface layer having a thickness not more than 3 &mgr;m.
U.S. Pat. No. 4,034,183 describes a processless lithographic plate that comprises a light-absorbing hydrophilic top layer coated on a support which is exposed to a laser beam to convert the absorber from an ink repelling to an ink receiving state. All of the examples and teachings require a high power laser, and the run lengths of the resulting lithographic plates are limited.
U.S. Pat. No. 3,832,948 describes both a printing plate with a hydrophilic layer that may be ablated by strong light from a hydrophobic support and also a printing plate with a hydrophobic layer that may be ablated from a hydrophilic support. However, no examples are given,
U.S. Pat. No. 3,964,389 describes a processless printing plate based on the principle of laser transfer of material. This process is very sensitive to transfer defects and requires an additional donor sheet.
U.S. Pat. No. 4,054,094 describes a process for making a lithographic printing plate by using a laser beam to etch away a thin top coating of polysilicic acid on a polyester base, thereby rendering the exposed areas receptive to ink. No details of run length or print quality are given, but it is expected that an non-crosslinked polymer such as polysilicic acid will wear off rapidly and give a short run length.
U.S. Pat. No. 4,081,572 describes a method for preparing a printing master on a substrate by coating the substrate with a hydrophilic polyamic acid and then image-wise converting the polyamic acid to melanophilic polyimide with heat from a flash lamp or a laser. No details of run length, image quality or ink/water balance are given.
Japanese Kokai No. 55/105560 describes a method of preparation of a lithographic printing plate by laser beam removal of a hydrophilic layer coated on a melanophilic support, in which the hydrophilic layer contains colloidal silica, colloidal alumina, a carboxylic acid, or a salt of a carboxylic acid. The only examples given use colloidal alumina alone, or zinc acetate alone, with no crosslinkers or addenda. No details are given for the ink/water balance or limiting run length.
WO 92/09934 describes and broadly claims any photosensitive composition containing a photo acid generator, and a polymer with acid labile tetrahydropyranyl groups. This would include a hydrophobic/hydrophilic switching lithographic plate composition. However, such a polymeric switch is known to give weak differentiation between hydrophilic and oleophilic areas.
All the examples mentioned in the prior art fail to prepare a processless direct imageable printing plate which has a high sensitivity, good start-up behaviour and offers a high run length.
Unpublished EP-A no. 99202109, filed on 29.06.99, discloses a negative-working heat-sensitive material for making lithographic plates comprising in the order given a lithographic base having a hydrophilic surface, an oleophilic imaging layer and a cross-linked hydrophilic upper layer. The heat generated during exposure in the imaging layer removes the hydrophilic upper layer by ablation. However, the water-acceptance of the non-exposed areas is insufficient and, as a result, the plate has an inferior start-up behaviour, i.e. the non-exposed areas to a certain extent accept ink (a defect known as “toning”) while printing the first 10 to 50 copies, which are lost due to bad print quality.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a processless material that is suitable for heat-mode direct-to-plate recording and is characterized by a high lithographic quality, especially with regard to start-up behaviour. This object is realized by the material defined in claim 1. Preferred embodiments thereof are defined in the dependent claims.
DETAILED DESCRIPTION OF THE INVENTION
The lithographic printing plate of the present invention comprises in the
Aert Huub Van
Damme Marc Van
Sap Wim
Agfa-Gevaert
Gilliam Barbara
Huff Mark F.
Leydig , Voit & Mayer, Ltd.
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