CA1047174A - Process for the production of planographic printing forms - Google Patents

Abstract

Abstract of the Disclosure This invention relates to a process for the preparation of a planographic printing plate which comprises imagewise exposing a light-insensitive hydrophilic layer on a carrier to electron rays, to thereby form an image in said layer from which prints may be made in an offset printing machine without further treatment.

Description

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~ 47~74 PROCES$ FOR THE PRODUÇTION OF PLANOGRAPHIC PRINTING FORMS
The invention relates to a process for the production of plano-graphic printing forms, in which a carrier covered with a hydrophilic layer is imagewise exposed to radiation and oleophilic image areas are thereby produced.
During the photomechanical production of planographic printing forms, copying material with a light-sensitive layer is usually image-wise exposed to light and then developed with a suitable developer solution, whereby oleophilic image areas and hydrophilic non-image areas are obtained. The oleophilic image areas are usually the layer areas which remain after the development, whereas the non-image areas are the areas of the carrier surface bared during the development.
For the development, usually organic solvents or alkaline or acidic aqueous solutions are used, according to the nature of the layer.
Work with these solutions must always be carried out with considera-tion of certain safety measures such as distillation, neutralization and the like. Therefore, it is desirable to eliminate such developer solutlons .
It is already known as well - for example from Canadian Patent Nos.
716,~0 & 771,590, Example 4- to develop exposed presensitized offset printing forms by wiping them over with pure water. For this, however, it is always necessary to use light-sensitive copying layers which have only a limited storage quality and still can be copied after being stored a little too long but can be no longer developed with pure water. In any case, here too the washed-out parts of the light-sensitive layer, which contain for example diazonium salts, acids, metal salts and the like, must be removed.

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~L~47~74 The purpose of the present invention is to propose a process for the production of planographic printing orms by imagewise exposure to radiation, for which no light-sensitive material and no development step are necessary.
According to the present invention, there is provided a process for the preparation of a planographic printing plate which comprises image-wise exposing a light-insensitive hydrophilic layer on a carrier to electron rays of an intensity and for a period such that the hydrophilic material in the exposed areas is ~ransformed into a hydrophobic material, to thereby form an image in said layer from which prints may be made in an offset printing machine without further development of said image, the carrier being hydrophilic if the hydrophilic layer is water-soluble.
The process of the invention affords a new and unusually simple proceclure for producing planographic printing forms. The recording material used in this process is insensitive to daylight and artifical light, as well as to aging. It practically has an unlimited storage life. The only pro-cessing step is the imagewisc exposure of the material to electron rays.
Thus, the hydrophilic surface layer is hardened in the exposed areas so that it becomes hydrophobic or oleophilic and absorbs printing ink.
Without further treatment, the exposed plate is put into an offset machine, and oily or greasy printing ink and fountain solution are applied in the usual manner. If the original surface layer was water-soluble, this layer can be removed by the fountain solution. In ~;" ~ J~
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this case, the surface layer underneath must be hydrophilic as well.
If the hydrophilic layer is insoluble in water, practically no removal of substance by the fountain solution takes place, the une~posed areas serving directly as the lmage background.
For excellent hydrophilic layers there is no fountain sotution needed in the offset machine, i.e., one also can print ln the dry off-set process.
By rAeans of electron exposure, a hydrophilic surface with very durable oleophilic properties can be obtained, so that very often extremely large numbers of prints can be achieved.
Layers and surfaces of various kinds can be regarded c15 hydro-philic layers in the sense of the invention.
An lmportant group are the layers of water-soluble organic sub-stances, which can be monomeric or polymeric and which are suitable for producing even, thin, and non-crystallizing films.
Suitable water-soluble polymers are, for example, polyvinyL
alcohol, polyvinyl pyrrolidone, polyalkylene oxides, polyalkyLene imines, cellulose ether, as well as carboxymethyl cellulose or hydroxy-ethyl cellulose, polyacrylamide, polyacrylic acid, polymethacrylic acid, starah, wheat gluten, dextrin, casein, gelatin, gum arabic and tannin.
Suitable monomeric or low-molecular weight water-soluble sub-stances are, for example, water-soluble dyes such as Rhodamine B, Methylene Blue, eosine, triphenyl methane dyes, e.g Crystal Violet as well as the film-forming low-molecular weight organic substances, which are described in Canadian Patent Number 976,799.
Above atl, monomeric and oligomeric carbohydrates belong to them, includlng the reduction and oxidation products deri~red therefrom an their esters, ethers, salts and the like, e.g. arabite, sorbilol, ~3471 ~ K-2244 pentaerythritol, dipentaerythritol, tetramethylol cyclopentanol, tetra-methylol cyclohexanol, anhydroenneaheptit, gluconic acid, galactonic acid, galacturonic acid, mucic acid, and the alkali and ammonium salts thereof, glucose, galactose, fructose, mannose, arabinose, saccharose, lactose, maltose, methyl glucose, hydroxyethyl glucose, saccharose monolaurate, saccharose monopalmitate, saccharose-mono-12-hydroxy-stearate; furthermore wetting agents such as saponine, sodium salts of alkylated sulfo-succinic acids and alkylated aryl sulfonic acids, poly-glycols, polyglycol alkylphenolether, polyoxyethylene sorbitan fatty acid ester, and the like.
It is also advantageous to use water-insoluble hydrophilic layers, which may be of inorganic or organic nature~
Sultable organic water-insoluble hydrophilic substances are, for example, association products of phenolic resins and polyethyLene oxides, as described in German Offenlegungsschrift No. 1,447,978, of Movember 7, 1968, to Union Carbide Corp., NewYork, N. Y., hardened melamine-formaldehyde resins according to British Patent No. 907,289, or amine urea-formaldehyde resins, as described in German Auslegeschrift No.
1,166,217, of March 26, 1964, to Lithoplate Inc., El Monte, Calif.;
furthermore cross-linked hydrophilic colloids, e.g. cross-linked poly-vinyl alcohol, which may contain hydrophilic inorganic pigments.
In addition to this water-insoluble hydrophilic inorganic pigment layers are suitable, which are embedded in the surface of the carrier, è.g. of a plastic sheet or a paperwith a plastic surface, e.g. Iayers made of pyrogenic silicic acid.
An especially important and preferred group of water-insoluble hydrophilic layers which can be used in accordance with the invention are the layers which have been obtained by the reaction of metal sur-faces, particularly aluminum surfaces, with monomeric or polymeric h~ .

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organic or inorganic acids or their salts or with certain complex acids or complex salts. Such layers are well known in planographic printing and are commonly used for the pretreatment of metal carriers for the applica-tion of light-sensitive layers. Examples of suitable treatment agents are alkali silicates (German Patent Mo. 907,147, of February 11, 1954, to 3M Co., St. Paul, Minn.), phosphonic acids or their derivatives (Can.
Patents Nos . 716,010 & 771,590), titanium or zirconium hexahalides (German Auslegeschriften Nos. 1,183,919, of :December 23, 1964, and 1,192,666, of January 13, 1966, bothtoPolychromeCorp., NewYork, N.Y.), organic polyacids (German Patent No. 1,091,433, of April 20, 1961, to 3 M Co., St. Paul, Minn.), monomeric carboxylic acids or their derivatives, phosphomolybdates, silicomolybdates, and the like.
For the purpose of this invention, however, treating solutions which have higher concentrations of the substances given than usual are generally used, preferably solutions with a content of about 3 to 15 per cent by weight .
Boehmite layers are also suitable as hydrophilic layers and are produced on aluminum carriers, possibly after anodic oxidation, by treating them with hot water or hot aqueous solutions.
In general, the hydrophilic layers must, according to the inventlon fulfill the condition that during the planographic or offset printing process, with simultaneous action of printing ink based on oil, and of fountain solution, they are wetted only by the latter. Layers with this property are sufficiently known as carrier or background surfaces for planograph-ic printing plates. Moreover, as mentioned above, Layers of water-soluble film-forming organic substances fulfill this condition as well.
The next condition which the hydrophilic layers have to fulfill in order to be used in the process of the invention is the capacity, under exposure to electron rays, of changing their surface tension with B respect to water and printing ink in such a way that they are no longer - `~

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wetted by water but only by printing ink based on oil or fat, i.e. that they become hydrophobic or oleophilic.
Although there does not exist any definite concept of the nature of the change caused by exposure to electrons, it can be assumed that a polymerization or a cross-linking takes place, accompanied by the splitting-off or conversion of hydrophilic groups, especially of OH-groups, into hydrophobic groups. Hence, it follows that hydrophilic layers, the hydrophilic properties of which do not depend upon the presence of cross-linkable hydrophilic groups, e.g. metal surfaces such as chromium or pure anodically produced oxide areas on alumlnum, are not suitable for the process according to the invention.
Suitable carriers for the hydrophilic layers are the materials commonly used in planographic printing, e.g. paper coated with cellu-lose acetate, zinc, magnesium, aluminum, chromium, copper, brass, steet, multimetal, plastics or plastic/metal composite foils or films.
Preferably aluminum, roughened mechanically, chemically, or by means of electric curren-t, and/or anodized, is used. If water-soluble hydro-philic layers are used, it is necessary for the carrier surface to be permanently hydrophilic. Otherwise, it can be chosen at will.
The hydrophilic layers are imagewise exposed to electrons with a charge density of about 10 to 10 Coul/cm with an accelerating vottage of about 5 to 50 kv. According to the sensitivity of the layers applied, times of 0.005 to 10 seconds per 2 cm are required with beam current intensities of 1 ~A to 1,000 ~A. As the layers are insensitive to light and to ultraviolet light as wetl, the exposure can be carried out in daylight. It is useful to control the electron beam by means of a given programmed line and/or screen movement.

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A special advantage of the process of the invention is that the imagewise exposed carrier can be immediately placed in an offset printing machine and printing can be started at once. A dev01Opment or decoating of the image-free areas of the carrier, as is known from the customer-coated and most of the presensitized offset printing plates and which is often carried out in bulky and expenslve developing machines, is completely eliminated. This advantage considerably supports the efforts made to realize higher speed and more rationality in off set printing .
~Nhen the exposed materials are processed in the offset print-ing machine, printing is carried out either according to the dry offset process or in the presence of fountaln solution. When the hydrophilic non-image areas are wetted by fountain solution, either no material at all ls removed (water-insoLuble layers), or there are only relatively small quantities taken up by fountain solution (water-soluble layers), which in many cases can be easily removed and discharged into the sewer. Unlike this, the development of the known light-sensitive layers generally produces considerably more toxic substances, the removal of which requires additional steps in order not to adversely affect the environment.
~, The following examples relate to preferred embodiments of the process of the invention. Percentages are, unless otherwise stated, per cent by weight. 1 g is 1 part by weight, if 1 cm is 1 part by volume .
Example 1 i An aluminum plate of a thickness of 0.3 mm is mechanically roughened by brushing and is immersed in 20% trisodium phosphate solution forthree minutes at a temperature of 70C, rins0d withwater, \

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treated for 15 seconds with 70~ nitric acid and, after a second rinsing with warm water, treated for three minutes in 10% sodium silicate solution at a temperature of 85 C, then rinsed with wa-ter,and dried.

The light-insensitive coated aluminum plate, which can be stored for years, is now imagewise exposed to electrons of a medium speed with energies around 10-15 kv in a high vacuum (about 10 5 Torr). The beam current intensity is 200/uA and the deflection speed is 1.0 sec/2 cm.

After the exposure, the printing plate is placed in an offset machine without further treatment and the printing is begun, the ex posed areas accepting greasy printing ink. Several thousand prints are obtained.

! Example 2 A rolled aluminum web is continuously roughened and anodized and coated with a 5% solution of polyvinyl 20 pyrrolidone in water, and dried.

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,The light-insensitive material is cut into pieces and, as described in Example 1, is imagewise exposed to electrons of a medium speed, but at a deflection speed of 5 sec/2 cm. After the exposure, the aluminum sheet is placed in an offset printing machine and printing is begun immediately.

Similar results are obtained if instead of polyvinyl pyrrolidone the copolymers thereof or casein or 2.5%
of wheat gluten or 5~ of tannin dissolved in water are used for the coating.

Example 3 A mechanically grained aluminum plate is coated by immersion in 5.0% aqueous polyvinyl phosphonic acid solution at 80 C, dried, and imagewise exposed to an electron beam. The beam has an amperage of 200/uA and a deflection speed of 0.5 sec/2 cm. The impinged areas are oleophilic and accept greasy print-ing ink during the printing process.

~xample 4 An aluminum / chromium plate is coated with an aqueous 2.5% polyvinyl alcohol solution and ex-posed to electrons of 100/uA at a ~47~
deflection speed of 5 sec/2 cm. Then printing is begun immediately, as described above.
Similar results are obtained if, instead of polyvinyl alcohol, a 6% solution of dextrin, an 18% solution of gum arabic, a 5% solution of starch, a 2.5% solution of wheat gluten or a 0.1% solution of hydroxyethyl cellulose is used for the coating.
Example 5 An anodized aluminum plate is coated with a 5% solution of poly-ethylene glycol having a medium molecularweight of 3,900 to 4,800 and ex-posed to electrons of 200 ~A at a deflection speed of 5 sec/2 cm. The exposed plate is immediately used as an offset printing form.
Similar results are obtained if a 2.5% solution of polyacrylic acid is used for the coating.
Example 6 An anodized aluminum plate is immersed in very pure water for 60 seconds at a temperature of 95C in order to produce a boehmite layer of a thickness at least ten times greater than that of an air oxide layer, and is dried. After imagewise exposure to electrons of 20 yA, the exposed areas are oleophilic and accept printing ink in the offset printing machine.
Instead of an anodized plate, an aluminum plate with a boehmite layer and roughened by nylon brushes in a pumice suspension can be processed as above.
Example 7 A paper sheet suitable for use as a printing plate, which has a coating of a hydrophilic colloidal binder with a finely divided inorganic pigment, according to the disclosure of U.S. Patent No.

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2,534,558, dated December 19, 1950, to the S. D. Warren Company, is exposed to electrons of 25~A and thereafter printed as described in Example 1.
Example 8 A polyethylene terephthalate film provicled with a hydrophilic adhesive layer according to German Patent No. 1,228,414, dated November 10, 1966, to Ozalid Company Limited, Loughton, Essex, is exposed to electrons of 50~A and further treated as in Example 1. Prints of similar quality as in Example 1 are obtained.
Example 9 A mechanically roughened aluminum plate is coated with a 2 %
aqueous Crystal Violet solution and dried. Exposure is carried out with electrons of a beam current lntensity of 100,~A. Thereafter, the printing plate is placed ln an offset printing machine and wiped over with a wet sponge. The dye layer, readily soluble in water, is there-by removed from the non-exposed areas, while it is hardened and oleophilic in the exposed areas.
The wiping over with the wet sponge is not necessary, but with an introduction lnto the machine without previous wiping over, the machine may in the long run be contaminated by the dye residue.
More than 100,000 flawless prints are obtained.
Instead of Crystal Violet, the dyes Rhodamine B, Methylene Blue and eosine can be employed in the same concentration and with the same result.
Example 10 A mechanically roughened aluminum plate is aoated with a 5%
sorbitol solution, dried and, as described in Example 1, exposed to electrons. Printing in an offset machine can be begun without further treatment .
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Solutions with the same concentration of cane, grape and milk sugar and/or maltose can be employed instead of the sorbitol solution with the same good result.
It wilL be obvious to those skilled in the art that many modifi-~ations may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications .

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of a planographic printing plate which comprises imagewise exposing a light-insensitive hydrophilic layer on a carrier to electron rays of an intensity and for a period such that the hydrophilic material in the exposed areas is transformed into a hydrophobic material, to thereby form an image in said layer from which prints may be made in an offset printing machine without further development of said image, the carrier being hydrophilic if the hydrophilic layer is water-soluble.

2. A process according to claim 1 in which said hydrophilic layer comprises a water-soluble, film-forming compound.

3. A process according to claim 1 in which said hydrophilic layer comprises a water-soluble organic compound of high molecular weight.

4. A process according to claim 1 in which said carrier is metallic.

5. A process according to claim 4 in which the carrier and hydrophilic layer are composed of a reaction product of the metal surface with a mono-meric or polymeric acid or salt thereof.

6. A process according to claim 4 in which the carrier is aluminum.