GB2098627A

GB2098627A - Anodized supports for production of lithographic printing plates

Info

Publication number: GB2098627A
Application number: GB8213896A
Authority: GB
Original assignee: Polychrome Corp
Current assignee: Polychrome Corp
Priority date: 1981-05-15
Filing date: 1982-05-13
Publication date: 1982-11-24
Also published as: AU8323982A; NL190150C; FR2509229A1; GB2098627B; DE3217870A1; CA1193571A; NL190150B; FR2509229B1; JPS57195697A; NL8201961A

Abstract

A support suitable for reception of a radiation sensitive composition comprises an anodized surface that has been treated before, during or after anodization with an alkali salt of a condensed aryl sulfonic acid (e.g. dinaphthylmethanedisulfonic acid). The invention allows preparation of long running lithographic printing plates which are free of background contamination.

Description

SPECIFICATION Anodized supports suitable for production of lithographic printing plates This invention relates to lithographic printing plates. More particularly it relates to an improved support for use in the preparation of such plates, radiation-sensitive elements prepared from such supports and lithographic printing plates prepared from said elements.

Radiation sensitive elements, which may be converted to lithographic printing plates, comprise a radiation-sensitive reproduction layer, in which the printing image is photomechanically produced, and a support which, from the production of the material until its processing into a printing plate, carries the reproduction layer and is stored therewith until the material is used. After the production of the printing image, the support carries the printing image and simultaneously forms the image background in the image-free areas. It is a requirement of a support suitable for the production of a printing plate that the printing image areas developed from the reproduction layer of the material adhere thereto very firmly.

Further, it must have a hydrophilic surface and the repelling effect thereof with respect to oleophilic printing inks must not be reduced in efficiency under the multiple requirements of the printing procedure. the support must have a surface structure which is porous so that the surface can retain sufficient water to have an adequate repelling effect with respect to the printing inks used for printing.

Aluminum oxide layers prepared by anodic-oxidation of aluminum sheets or foils are extraordinarily abrasion-resistant and such anodized sheets have been found very useful in the production of long running printing plates. However, such plates suffer from disadvantages caused by too great a penetration of the radiation-sensitive composition into the pores of the support.

In the past such disadvantages have been obviated by, for example, treating the anodized support with an aqueous solution of sodium silicate, ammonium or alkali bichromate, iron ammonium oxalate or a dyestuff which can react chemically with the Al oxide surfaces, prior to coating with the radiation-sensitive composition.

However, these processes also suffer from disadvantages. Thus, treatment with alkali silicate entails the requirement of thorough rinsing with water when the support obtained is to be provided with a storable light-sensitive layer adapted to be stored in the thus sensitized state over a long period without deterioration. But even after thorough rinsing with water, or even neutralization with dilute acids, the silicate layer, or perhaps alkali residue remaining from the silicate solution, effect a certain deterioration.

When the mentioned aqueous chromate solutions are used a barely hydrophilic intermediate layer is obtained, the chromate content of which presumably because of its oxidizing effect, often adversely affects the light-sensitive layer to be applied in that the layer is discolored, which impairs the light-permeability thereof so that the light-sensitivity of the layer is reduced.

Furthermore, the use of chromium containing compositions is now considered environmentally undesirable. Similar considerations, except for the environmental, apply to treatment with an iron ammonium oxalate solution, the iron content of which may cause a dark discoloration. When using aqueous solution of dyestuffs which chemcially react with the aluminum oxide surface, the hydrophilic properties of the aluminum layer are reduced partially with the result that a printing plate material produced with a support pretreated in this manner tends to scum during printing more than a printing plate whole surface has not been so pretreated. Furthermore, the aluminum oxide surfaces chemically altered by means of dyestuffs cannot be easily corrected.

The improved support according to the present invention has been found to overcome the above disadvantages.

A support according to the invention is suitable for reception of a radiation sensitive composition and comprises an anodized surface that has been treated with an alkali salt of a condensed aryl sulfonic acid. The support may be made by anodizing an appropriate surface and treating the surface with the salt prior to or, preferably, during or after the anodizing. The treatment is normally effected by contacting the surface with an aqueous solution of the salt.

A radiation sensitive element according to the invention comprises the treated support coated with a radiation sensitive composition.

A lithographic printing plate according to the invention may be made by exposing such an element to radiation through a mask and developing the exposed element to remove areas of greater solubility.

By the invention it is possible to prepare long running lithographic printing plates which are free of background contamination.

The arylsulfonic acid salts useful according to the instant invention include the naphthalene sulfonates in which two or more naphthalene nuclei are joint by alkylene groups. The prototype of this class is dinaphthylmethanedi-sulfonic acid (methylene di-naphthyl sulphonic acid). This has a formula as follows:

Products of this class are of indefinite composition. They may be manufactured by heating naphthalene, formaldehyde, and sulfuric acid together, or by treating naphthalene sulfonic acids with formaldehyde. Thus three or more naphthalene nuclei may be joined together by alkylene groups to yield a condensation polymer.

Lower alkylated naphthalenes may also be used in the reaction. An example is monoisopropylnaphthalene. In place of naphthalene, other aromatic hydrocarbons may be employed such as benzene, diphenyl, anthracene, phenanthrene, fluorene, etc., or homologues or derivatives thereof. The salts of the foregoing acids, such as the sodium salts possess similar properties. The production of dispersing agents of this type is described in detail in the literature and in prior art patents including U.S. Patent No. 2,802,845 and representative compounds are available in the trade under the trademarks Tamol, Leukanol and Daxad.

Particuiarly useful for the instant invention are the sodium salts of condensed naphthalene sulfonic acids known as Tamol SN and Tamol N Micro which are available commercially from Rhom and Hass.

The support material may be any of those known in the art, including aluminum and its ailoys. A preferred support material is selected from aluminum and its lithographically suitable alloys.

If desired, the support material may be subjected to one or more treatments prior to, or after, said salt treatment, selected from the group comprising graining e.g., chemical, mechanical, or electrochemical, degreasing, desmutting, and the like.

The anodization may be effected in any manner known in the art including immersion of the substrate in an aqueous bath comprising H2SO4, HsPO4, and the like, and mixtures thereof and subjecting it to a current density in an AC or DC field.

According to one embodiment of the invention an anodized support material is prepared by subjecting a metal sheet or web which may have been pretreated as indicated above, to a current density of about 1 to about 4 A/dm2 at about 10 to about 40 volts DC, in an aqueous acid bath of about 15 to about 30% wt. concentration for about 0.5 to about 5 minutes. The thus anodized support is then treated with an aqeuous solution of the alkali salt of the condensed aryl sulfonic acid whose concentration is about 5 to about 10% wt. The pH of the sulfonic acid bath is adjusted to about 1.5 by addition of H2SO4.

Preferably the anodization is effected in a bath of about 20%wt. aqueous H2SO4 at about 2.6 A/dm2 and about 20 volts DC for about 1 minute while the sulfonic acid comprises about 7.5% wt.

aqueous solution. The salt solution may be applied to the anodized support material by any means including dipping, sponging and squeegeeing.

In an alternative modification of the instant invention, the anodization and sealing processes are effected approximately simultaneously by inclusion of the arylsulfonic acid salt in the anodization bath. According to this modification the bath comprises from about 1 5 to about 30% wt. H2SO4 and about 0.5 to about 1 owt of the sulfonic acid salt. Preferably the bath comprises about 20%wt. H2SO4 and about 1 %wt. sulfonic acid salt.

According to the instant invention there is also provided an improved radiation-sensitive element which comprises any of the improved supports upon which has been coated any radiationsensitive composition as known in the art, e.g., positive-acting compositions, such as are described, e.g., in U.S. Patents 4,189,320 (issued February 19, 1980) and 3,785,825 (issued January 1 6, 1 974) and negative-acting compositions, such as are described, e.g., in U.S.

Patent 3,382,069 (issued May 7, 1968). Said coatings are applied to the support material by any method known to the art including which coating, meniscus coating and the like.

The instant invention also provides a method for the preparation of improved lithographic printing plates which comprises the steps of imagewise exposing any of the above elements, in accordance with the invention, to radiation through a mask, development of said imagewise exposed element to remove the less soluble areas of the coating and, if desired, post-treating the developed element to produce a desirable lithographic printing plate.

The methods for exposure, development and post-treatment of the elements may by any of those known in the art including, e.g., the post curing procedure described in U.S. Patent No.

4,233,390 issued November 11, 1980.

The following examples illustrate and are not meant to limit the invention as claimed.

Example 1 A sheet (25cmx25cm) of Al alloy AA 1050 was grained using a wet slurry of pumice and then anodized in an aqueous bath comprising 20% wt. H2SO4 at 3.8 A/dm2 for a period of 1 minute.

The thus anodized sheet was then dipped, at room temperature into a bath comprising 50 to 100gel of TamolTMSN, which was adjusted to a pH of 1.5 with H2S04,for 30 seconds.

After the above treatment the sheet was rinsed and dried and coated with a radiation-sensitive composition comprising a 1 to 1 mixture of a cresol formaldehyde resin with the condensation product of naphthoquinone-1 ,2-(diazide 2)-5 sulfonyl chloride with a pyrogallol acetone resin, to yield a radiation-sensitive element which after image-wise exposure, development and posttreatment by means well known in the art yielded a lithographic printing plate, having a clean nonimage area, which produced 65,000 acceptable impressions.

Example 2 The method of Example 1 was repeated except that the anodizing bath comprised 20% wt. H2SO4 and 1 %wt. Tamol SN, and the dipping step was deleted. Similar results were obtained.

Claims

1. A support suitable for reception of a radiation sensitive composition and comprising an anodized surface that has been treated with an alkali salt of a condensed aryl sulfonic acid.

2. A support according to claim 1 in which the acid is methylene di-naphthyl sulphonic acid.

3. A support according to claim 1 or claim 2 in which the surface is of aluminium or aluminium alloy.

4. A support according to any preceding claim and which has been made by anodizing the surface and then treating the surface with the salt.

5. A support according to any of claims 1 to 3 in which the support has been made by anodizing the surface and treating the surface with the salt during anodizing.

6. A radiation sensitive element comprising a support according to any preceding claim coated with a radiation sensitive composition.

7. A method of making a lithographic printing plate comprising exposing an element according to claim 6 to radiation through a mask and developing the exposed element to remove the areas of greater solubility.