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
2000-06-23
2003-06-10
Ashton, Rosemary (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
C430S272100, C430S273100, C430S278100, C430S302000, C430S348000, C430S944000, C430S945000, C101S453000, C101S454000, C101S455000, C101S463100, C101S466000, C101S467000
Reexamination Certificate
active
06576395
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat mode recording material for making a lithographic plate for use in lithographic printing. The present invention further relates to a method for imaging said heat mode recording material e.g. by means of a laser.
BACKGROUND OF THE INVENTION
Lithographic printing is the process of printing from specially prepared surfaces, some areas of which are capable of accepting ink (oleophilic areas) whereas other areas will not accept ink (hydrophilic areas). According to the so called conventional or wet printing plates, both water or an aqueous dampening liquid and ink are applied to the plate surface that contains hydrophilic and oleophilic areas. The hydrophilic areas will be soaked with water or the dampening liquid and are thereby rendered oleophobic while the oleophilic areas will accept the ink.
When a laser heat mode recording material is to be used as a direct offset master for printing with greasy inks, it is necessary to have oleophilic-hydrophilic mapping of the image and non-image areas. In the case of heat mode laser ablation it is also necessary to completely image wise remove a hydrophilic or oleophilic topcoat to expose the underlying oleophilic respectively hydrophilic surface of the laser sensitive recording material in order to obtain the necessary difference in ink-acceptance between the image and non-image 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 a printing press without further processing. The plate is called a “direct negative” plate because the areas of the recording material that have been exposed are rendered ink accepting.
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 include e.g. U.S. Pat. No. 4,341,183, 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 have on an anodized aluminum support a hydrophilic layer. The disclosed heat mode recording materials are image-wise exposed using a laser. Laser exposure renders the exposed areas insoluble and ink receptive, whereas the non exposed image portions remain hydrophilic and water soluble allowing to be removed by the dampening liquid during printing exposing the hydrophilic support. Such plates can be used directly on the press without processing.
DD-A-155 407 discloses a laser heat mode “direct negative” printing plate where a hydrophilic aluminum oxide layer is rendered oleophilic by direct laser heat mode imaging. These printing plates may also be used on the press without further processing.
From the above it can be seen that a number of proposals have been made for making a ‘direct negative’ offset printing plate by laser heat mode recording. They have such disadvantages as low recording speed and/or the obtained plates are of poor quality.
Another way of making direct lithographic plates is by laser ablation.
EP-A-580 393 discloses a 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. The lithographic properties of said material are not very good.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a material for a heat mode recording material of high sensitivity and high lithographic quality, especially in regard to little toning at start-up.
SUMMARY OF THE INVENTION
According to the present invention there is provided a heat-sensitive material for making lithographic plates comprising in the order given on a support an IR-sensitive oleophilic layer and an ablatable cross-linked hydrophilic layer comprising an inorganic pigment and a hardener, characterized in that the ratio of said inorganic pigment over the hardener is comprised between 95/5 and 75/25 by weight.
DETAILED DESCRIPTION OF THE INVENTION
In this invention it has been found that by using a lithographic base in combination with a high ratio of inorganic pigment over hardener in the hydrophilic layer, little toning at start-up is obtained.
The IR-sensitive oleophilic layer amounts preferably to a dry weight between 0.1 and 0.75 g/m
2
, more preferably between 0.15 and 0.5 g/m
2
.
The IR-sensitive oleophilic layer comprises a binder and a compound capable of converting light into heat.
Suitable compounds capable of converting light into heat are preferably infrared absorbing components having an absorption in the wavelength range of the light source used for image-wise exposure. Particularly useful compounds are for example dyes and in particular infrared dyes as disclosed in EP-A-908 307 and pigments and in particular infrared pigments such as carbon black, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and oxides structurally related to the bronze family but lacking the A component e.g. WO
2.9
. It is also possible to use conductive polymer dispersion such as polypyrrole or polyaniline-based conductive polymer dispersions. The lithographic performance and in particular the print endurance obtained depends i.a. on the heat-sensitivity of the imaging element. In this respect it has been found that carbon black or graphite yields very good and favorable results.
Preferably the binder is selected from the group consisting of polyvinyl chloride, polyesters, polyurethanes, novolac, polyvinyl carbazole etc., copolymers or mixtures thereof.
Most preferably the polymeric binder in the recording layer is heat sensitive: e.g. a polymer containing nitrate ester groups (e.g. self oxidizing binder cellulose nitrate as disclosed in GB-P-1 316 398 and DE-A-2 512 038); e.g. a polymer containing carbonate groups (e.g. polyalkylene carbonate); e.g. a polymer containing covalently bound chlorine (e.g. polyvinylidene chloride). Also substances containing azo or azide groups, capable of liberating N
2
upon heating are favorably used.
Different kinds of hardened hydrophilic surface layers are suitable in connection with the present invention. The hydrophilic coatings are preferably cast from aqueous compositions containing hydrophilic binders having free reactive groups including e.g. hydroxyl, carboxyl, hydroxyethyl, hydroxypropyl, amino, aminoethyl, aminopropyl, carboxymethyl, etc. along with suitable cross-linking or modifying agents including e.g. hydrophilic organotitanium reagents, aluminoformyl acetate, dimethylol urea, melamines, aldehydes, hydrolyzed tetraalkyl orthosilicate, etc.
Suitable polymers for hydrophilic layers may be selected from the group consisting of gum arabic, casein, gelatin, starch derivatives, carboxymethyl cellulose and Na salt thereof, cellulose acetate, sodium alginate, vinyl acetate-maleic acid copolymers, styrene-maleic acid copolymers, polyacrylic acids and salts thereof, polymethacrylic acids and salts thereof, hydroxyethylene polymers, polyethylene glycols, hydroxypropylene polymers, polyvinyl alcohols, and hydrolyzed polyvinylacetate having a hydrolyzation degree of at least 60% by weight and more preferably at least 80
Damme Marc Van
Vermeersch Joan
Agfa-Gevaert
Ashton Rosemary
Breiner & Breiner L.L.C.
Gilliam Barbara
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