Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Finishing or perfecting composition or product
Reexamination Certificate
2000-10-13
2001-11-13
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Finishing or perfecting composition or product
C430S404000, C430S466000
Reexamination Certificate
active
06316171
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of lithography, and more particularly to an aqueous developer for lithographic printing plates. More specifically, this invention relates to a novel aqueous developer for removing the non-image area of negative lithographic printing plates.
BACKGROUND OF THE INVENTION
In lithographic printing plates, oleophilic image areas materially corresponding to an image and hydrophilic non-image areas are formed in the same plane. The oleophilic image area is ink-receptive and water-repellent, the hydrophilic non-image area is ink-repellent and water-receptive. In the printing process, the ink that is adhered to the image areas is transferred to the printing-paper via a rubber blanket, whereas the non-image areas are wetted with water and do not transfer any ink to the paper. Lithographic printing plates are formed by a light-sensitive layer that is coated on a suitable support. The photosensitive layers can be divided into two types:
Positive working layer, in which the unexposed area remains on the plate after development and thus forms the image area
Negative working layer, in which the unexposed area is removed in the development process to reveal the non-image area.
Developer compositions are usually water-based systems, because of environmental and safety reasons. In many cases they contain one or more surfactants and an (low amount of) organic solvent. In the U.S. Pat. No. 4,186,006 , benzyl alcohol and the sodium salt of t-Butyl-naphtalene sulphonic acid are described for usage in developer as solvent and surfactant respectively.
Because of the nature of the lithographic plate, binders are usually hydrophobic of nature, which poses the problem that they do not readily dissolve in aqueous systems. To overcome this problem, it is possible to incorporate into the binder some acidic side-groups, which yield a water soluble compound when treated with an alkaline liquid. Examples of these systems can be found in U.S. Pat. Nos. 4,631,245 and 4,902,602. These compounds however tend to have a lower sensitivity and less ink receptivity than binders without acidic side-groups. The less materials groups will result in a higher sensitivity and better ink receptivity, but a poorer solubility in a developer.
Binders that do not dissolve into the developer liquid sufficiently, will form coagulates: they will stick together, forming large, insoluble particles. These particles have an affinity for parts in the automatic development machine that have a hydrophobic surface: brushes, rubber rollers, tank walls. The insoluble particles will adhere to these parts, accumulate, and in time will redeposit on the non-image area of the printing plate, yielding undesired image formation. It costs a lot of effort to clean the developing machine. So higher frequency of and longer time for cleaning will be necessary when that problem remains.
In EP 0004014, a developing composition is described consisting of a water soluble polymer, an anionic surfactant and a water miscible organic solvent, which is characterized by the water soluble polymer being either poly-N-vinyl-N-methylacetamide or polyvinylalcohol. It is further suggested to add 0.01-2 wt % of gelatin. Also in EP 323836, addition of natural polymers including gelatin is mentioned as a thickener. But the effect thereof is insufficient to prevent the problems discussed above.
SUMMARY OF THE INVENTION
The present invention is directed to improving the performance of a developer for binders that are not sufficiently soluble in the developer liquid. This performance improvement is reached by a developing composition which is comprised at least of
(a) an organic solvent
(b) a surfactant
(c) a gelatine, which comprises more than 3% of the
total developer weight.
The present invention has the surprising advantage that the binder is dispersed better, the tendency of the binder components to form coagulates is reduced, and the affinity of the binder-particles for brushes, rubber rollers and other hydrophobic parts of the automatic development machine is lowered. This way accumulation of the binder on these parts will occur more slowly or is even prevented, resulting in a low frequency and shorter time for cleaning the development machine and less deposit of developer sludge on the plate
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention, the development solution, which is used for the development of negative lithographic printing plates, preferably contains, next to water, an organic solvent, a surfactant, a gelatine and other agents. The organic solvent is preferably an alcohol and has preferably a boiling point of higher than 120° C. Specific examples of this type of solvent include benzyl alcohol, di-acetone alcohol, 2-methoxy ethanol, 2-ethoxy ethanol, 2-butoxy ethanol, 2-phenoxy ethanol, 1-methoxy-2-propanol, and so on. The preferable amount of these solvents as described here ranges from 1% by weight (b/w) to 7%b/w, more preferably 2%b/w to 5%b/w on the basis of the total weight of developers used.
The surfactant is preferably an anionic surfactant. Specific examples of anionic surface active agents include fatty acid salts such as potassium rhodinate, potassium oleate, sodium stearate etc.; sodium alkylarylsulphonates (e.g. sodium isopropylnaphtalene sulphonate, sodium salt of dodecyl-p-benzenesulphonate etc.); the salts of sulphates of aliphatic and aromatic alcohols (e.g. sodium salt of lauryl alcohol sulphate, ammonium salt of lauryl alcohol sulphate, sodium salt of oleyl alcohol sulphate, sodium salt of octyl alcohol sulphate, sodium salt of xylenol sulphate etc.), sodium alkyl sulphonates; monosodium salts of N,N-dihydroxyethylglycine; sodium alkylpolyoxythylene sulphates; sodium dialkylsulfosuccinates; etc. The concentration of such anionic surfactant ranges from 0.5 %b/w to 10%b/w, preferably from 2%b/w to 8%b/w, more
preferably from 4%b/w to 6%b/w on the basis of the total weight of developers used.
The gelatine consists of gelatine molecules selected from the group consisiting of natural gelatine, alkaline processed gelatine, acid processed gelatine, hydrolysed gelatine, peptised gelatine resulting from enzymatic treatment and recombinant gelatine. It can originate from bovine or porcine matter. The intrinsic viscosity of gelatine, measured as the low-shear (<1/s) viscosity of a 6.67%b/w solution at 40° C., ranges preferably from 3 to 9 mPa.s.
The pH of the developer solution ranges from 4 to 12, preferably from 7 to 11. The pH can be regulated by addition of alkali or acidic agents, e.g. potassium silicate, sodium silicate, potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium tertiary phosphate, sodium secondary phosphate, sodium meta silicate, sodium hydrogen carbonate and other inorganic alkalis, ammonia water and organic amine compounds such as mono-ethanol amine, diethanol amine, triethanol amine for the preparation of alkali developers; by inorganic acids such as hydrochloric acid, sulphuric acid, nitric acid, boric acid; organic acids as citric acid, alkyl-carboxylic acids, (alkyl-)aryl-carboxylic acids, alkylsulphonic acids, (alkyl-)arylsulphonic acids and the like.
REFERENCES:
patent: 3800359 A1 (1988-08-01), None
patent: 0004014 (1979-02-01), None
patent: 0323836 (1989-01-01), None
patent: 0923001 A1 (1998-12-01), None
Sekiya Toshiyuka
Toda Yuzo
Wiegers Ronald
Fuji Photo Film B.V.
Le Hoa Van
Merchant & Gould P.C.
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