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
2001-04-06
2004-08-17
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
C430S287100, C430S302000, C430S306000, C430S326000, C430S014000, C430S292000, C430S905000, C430S909000, C430S926000, C430S944000, C101S456000, C101S457000, C101S465000, C101S467000, C101S470000
Reexamination Certificate
active
06777164
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates to lithographic printing forms and to precursors thereto, having aluminum supports bearing imagable coatings. The invention relates further to the manufacture of such precursors, and their use.
Typical lithographic printing form precursors are prepared as follows.
Aluminum sheet is subjected to a graining or roughening treatment. This may be a mechanical graining treatment, for example brush graining or ball graining, or an electrograining treatment (also called electrochemical etching or electrochemical roughening) in a mineral acid. The sheet is then anodised, to provide a hard hydrophilic surface, which has a microporous “honeycomb” structure. Anodising may typically take place in a sulphuric acid or phosphoric acid electrolyte. A post-anodic treatment (PAT) is then carried out, using, for example, a silicate or a phosphate composition. Subsequently a different composition, containing a polymeric substance, is applied in a liquid form, a solvent being removed therefrom to leave the imagable coating as a dry film on the aluminum sheet, which may be cut into individual lithographic printing form precursors. The resultant precursors may be imaged and developed, to provide the lithographic printing forms which are printed from. During development, portions of the coating are selectively removed. In positive working systems portions which were exposed are removed. In negative working systems portions which were not exposed are removed. In most systems, whether positive or negative, the remaining portions of the coating are preferentially ink-accepting.
Many coatings contain dyes and these may be employed for several distinct reasons. A dye may alter the properties of the polymeric substance, for example by rendering it insoluble in a developer, but such that after imaging, the coating is soluble in the developer. Examples of such dyes are given in PCT/GB97/39894. A dye may function as an absorber of imaging radiation, either as a “spectral sensitizer”, to emit radiation of a different wavelength which triggers a desired chemical reaction to alter the properties of the coating, or as a compound which converts the absorbed radiation to heat, which alters the properties of the coating. Examples of dyes functioning as spectral sensitizers are given in U.S. Pat. No. 5,200,292. Examples of dyes converting imaging radiation to heat are given in PCT/GB97/39894. Additionally, a dye may be used to color a coating, with the result that after development a positive or negative image can be seen on the printing plate, from the color contrast. From this the printer can gain an impression of whether imaging and development has been successful and can identify and correct faults.
If the PAT step is not carried out colored dye present in the coating may be seen in the regions from which the portions of the coating are removed on development; the dye may form an absorbed or residual layer on the anodised surface. This is undesirable as it reduces the color contrast between exposed and unexposed portions of the printing plates and makes it harder for the printer to determine whether imaging and development has been successful, and to identify and correct faults. Furthermore dye which is present in uncoated areas may attract ink and cause poor printing performance.
SUMMARY OF THE INVENTION
The invention relates to the use in a lithographic printing form precursor of a polymeric compound comprising pendent colorant groups. This gives the required color contrast. Free colorant dye is not needed and it is not necessary to employ a PAT step, in the preparation of an aluminum lithographic support.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with a first aspect of the present invention there is provided a lithographic printing form precursor having an imagable coating on an aluminum support, wherein the imagable coating comprises a polymeric substance comprising colorant groups, wherein the aluminum support on which the coating is provided is anodized but not subsequently modified by means of a post-anodic treatment compound, and wherein the coating does not comprise a free colorant dye.
Such a polymeric substance of the invention is referred to herein as a “colorant tagged polymer”.
By “colorant dye” we mean a dye which reduces the color contrast between exposed and unexposed portions of a printing plate after development of the plate, when retained on the developed plate. By “free colorant dye” we mean a colorant dye which is not pendent on the polymeric substance.
The term “aluminum” as used herein includes aluminum alloys.
Preferably both sides of the aluminum sheet are anodised, to reduce the risk of corrosion attack in a developer.
Preferably a graining step is carried out prior to the anodising step, for example mechanical graining or electrograining, as described briefly above. Preferably electrograining is carried out. The anodising step which follows may suitably take place in a phosphoric acid or, especially, a sulphuric acid electrolyte. The technology of graining and anodising is very well known to the skilled person but if background information is needed, the reader may refer to “The Surface Treatment and Finishing of Aluminum and its Alloys”, S. Wernick et al, 5
th
edition; 1987,ISBN 0-904477-09-6, pp 184-189.
As well as avoiding staining and removing a manufacturing step we have found that the printing form precursors of the invention yield, after steps of imaging and development, printing forms which have longer run lengths than similar printing forms, employing a polymeric substance without colorant groups thereon, employing an admixed colorant dye, and which have had a post-anodic chemical treatment step.
A precursor made by a method in accordance with the invention may have a coating formed as a single layer or as two, or more, layers.
In accordance with the examples herein good results were found with positive working compositions, which are preferred embodiments of the invention, but a precursor made by a method in accordance with the invention may be positive working or negative working.
Preferably the corresponding polymeric substance without any pendent colorant groups (referred to herein as the parent polymer), has nucleophilic groups Y, able to react with a colorant compound or moiety, having a halogen atom, for example a chlorine atom. Preferably the parent polymer has groups Y selected from —SO
2
NHR, —NHR, —SH and —OH, where R represents a hydrogen atom or a C
1—4
alkyl group, for example a methyl group. Preferably R represents a hydrogen atom. More preferably the parent polymer has sulfonamido groups or hydroxyl groups Y, or both.
Since it is unlikely or undesirable, or both, that all such groups of the parent polymer are functionalized by the reaction, preferably the colorant-tagged polymer also has such groups Y. Most preferably, the parent polymer has hydroxyl groups Y.
A hydroxyl group-containing polymer, useful as a parent polymer may comprise a phenolic resin or co-polymer thereof. Other polymers suitable as parent polymers include poly-4-hydroxystyrene; copolymers of 4-hydroxystyrene, for example with 3-methyl-4-hydroxystyrene or 4-methoxystyrene; copolymers of (meth)acrylic acid, for example with styrene; copolymers of maleiimide, for example with styrene; hydroxy or carboxy functionalised celluloses; dialkylmaleiimide esters; copolymers of maleic anhydride, for example with styrene; and partially hydrolysed polymers of maleic anhydride.
Particularly useful phenolic resins in this invention are the condensation products from the interaction between phenol, C-alkyl substituted phenols (such as cresols and p-tert-butyl-phenol), diphenols (such as bisphenol-A) and aldehydes and ketones (such as formaldehyde and acetone). Depending on the preparation route for the condensation a range of phenolic materials with varying structures and properties can be formed, as will be well understood to those skilled in the art. One useful class is pyrogallol/acetone condensates. Particularly useful in this invention are novol
Bayes Stuart
Horne Geoffrey
Monk Alan Stanley Victor
Ray Kevin Barry
Faegre & Benson LLP
Huff Mark F.
Kodak Polychrome Graphics LLC
Lee Sin J.
LandOfFree
Lithographic printing forms does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lithographic printing forms, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lithographic printing forms will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3353755