EP0097318A2

EP0097318A2 - Aluminum sheet for offset lithographic printing

Info

Publication number: EP0097318A2
Application number: EP83105837A
Authority: EP
Inventors: Motohiro Nabae; Mitsuya Miyamoto; Chozo Fujikura
Original assignee: Furukawa Aluminum Co Ltd; Fuji Photo Film Co Ltd
Current assignee: Furukawa Aluminum Co Ltd; Fujifilm Holdings Corp
Priority date: 1982-06-18
Filing date: 1983-06-14
Publication date: 1984-01-04
Also published as: JPH0147545B2; JPS58221254A; EP0097318A3

Abstract

An aluminum sheet for offset lithographic printing essentially consists of 0.02 - 0.15 wt.% of Si, 0.1 - 1.0wt.% of Fe, not more than 0.003 wt.% of Cu as impurity, and the balance of Al and inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION:

The present invention relates to an aluminum sheet used as the printing plate for the offset lithographic printing and in particular an aluminum sheet for the offset printing featured in that an uniform grained surface formed by a graining treatment enhances an adhesion of a photosensitive coating to the grained surface and prevents scumming non-image area of the printing plate during printing, and results in a high print quality at the image area of the printing plate.
Al is widely used as the printing plate for the offset lithographic printing since it has advantage of light weight and excellent mechanical strength, surface treatment and corrosion resistance. Al sheet used as the printing plates have been the plates in 0.1 - 0.3 mm thickness consisting of JIS 1050 of pure Al (pure Al not less than 99.5 wt.% of purity), JIS 1100 (Al-0.05 - 0.20 wt.%Cu). These Al sheet are usually subjected to a surface roughening by treatment using a mechanical, a chemical or a electrochemical graining and coated with photosensitive material, and subjected to imagewise exposure and development to be made as printing plates.
The printing plates thus prepared as the above are subsequently mount on the presscylinder and stuck with ink on the image area of the plates under existence of a fountain solution, and thereafter ink is transfered imagewisely on rubber blanket cylinder, then printed on papers. The printing plates such as the above is provided with a press life for about 30,000 sheets of copies and the grained surface mentioned above enhances an adhesion of the photosensitive material and a water retaining property during printing and further a tone reproduction, which are indispensable requirements to allow the sheet to have functions of the printing plates. In order to enhance the press life, the plate may be subjected to an anodic oxidation treatment after the graining to form anodic oxide films of approximately 1 - 3 µm in thickness thereon, and then coated with the photosensitive material and the plate was then subjected to the exposure and, after the development, to be prepared as the printing plates.
The printing plates subjected to the anodic oxidation treatment have a press life for about 70,000 - 150,000 sheets of copies.
The Al sheet for printing such as the above are required with the following characteristics.

(A) The graining treatment forms an uniform grained surface.
(B) The adhesion of the photosensitive material is excellent.
(C) Prevents scumming on the non-image area during printing.
(D) The tone reproduction on the image area is excellent.
(E) When the image area is investigated after development, a color tone (color tone after the graining treatment) on the paper basis becomes white to be easy to see the drawing portion.

Among those characteristics, (A) is a basic feature and, if the grained surface becomes uneven it affects the features of (B) - (D) and results in failing to obtain a good press life. In order to obtain the uniformly grained surface by means of the electrochemical graining, the selection of the sheet are important and the Al sheet corresponding to JIS 1050 of containing impurities indicated in Table 1 are generally used.
However, even when Al sheet corresponding to JIS 1050 are used, drawbacks have been found in (A), (C), (D) and (E) of the above features. Namely, the electrochemical graining has formed an uneven and rather rugged surface and made the color tone. Still more, there have been drawbacks that the printing plates allow the ink to stick on the non-image area during printing and the tone reproduction of the image area becomes worse.
In the light of the above results, after intensive studies and examinations, the inventors have developed Al sheet for offset printing to improve the above features of (A) -(D) and further satisfy the feature (E), the composition of which is essentially 0.02 - 0.15 wt.% of Si (hereinafter the term "%" designates "% by weight".), 0.1 -1.0% of Fe, not more than 0.003% of Cu as impurity, and the balance of Al and inevitable impurities.
As a result of these studies, we have confirm that the dot-form stain is caused by dot-form defects present at the surface of the support. The dot-form defects result from certain impurities distributed in the aluminum alloy plates. On the basis of this finding knowledge, we have examined the impurities affected to the dot-form stain and found that, where Cu as impurity is contained in the Al sheet, the amount of Cu content lowers anticorrosion as the content increases, if it is minimum for the printing plates, and results in increasing the dot-form stain on the non-image area of the printing plates during printing. For example, Al base metals of not less than 99.70% of Al purity were selected according to from minimum to larger quantity of Cu content and added with Cu to form Al sheet of different Cu content. These Al sheet were subjected to various tests, which revealed that the printing plates made of these sheet increased the formation of the dot-form stain on the printed matters during printing as the Cu content increased such as 0.005%, 0.01% and 0.05%, and the electrolytic etching also formed uneven rugged surface.
On the basis of these knowledges, by means of restricting the amount of Cu content as impurity of the Al sheet strictly, we have uniformalized the formation of rugged surfaces in the electrochemical graining and improved the color tone after graining of the Al sheet, the adhesion of the photosensitive coating and prevention of stains on the non-image area during printing. Further, by means of restricting the amounts of Fe and Si contents contained in the Al sheet to a specific range, the Al printing plates are provided with a sufficient strength to prevent a cracking near the line along which the plate is bent for clamping to the press cylinder during mounting and press running without impairing the above features.
The composition of the Al sheet for this invention is restricted as mentioned above for the following reasons.
The amount of Cu as impurity is restricted to not more than 0.03% since an amount of exceeding 0.003% Cu makes the grained surface formed by the electrochemical graining uneven and lowers the color tone after graining, and worsens dot-form stains on the non-image area during printing. Further, the amount of Si content is restricted to 0.02 - 0.15% and that of Fe content to 0.1 - 1.0% since either one of the elements being under the minimum limit causes the break at the bending portion of the printing plate during printing which is formed when the printing plate being mount on the press cylinder, and either one of the elements being above the maximum limit fails to obtain an uniformly grained surface by the electrochemical graining.
Furthermore, in the manufacture of the Al sheet for this invention, it is necessary that the final sheet is composed of Cu not more than 0.003%, Fe content being 0.1 - ₁._0% and Si content being 0.02 - 0.15. Therefore, it is preferable that Al is selected from Al base metals not less than ₉₉.₇0% of Al purity or Fe and Si elements may be added as required to the above limits. As to the impurities other than Cu, Si and Fe, their content range in the Al base metals corresponding to JIS 1050 (not more than 0.05% Mn, not more than 0.05% Mg, not more than 0.05% Zn and not more than 0.03 Ti) will never impair that features required for the Al sheet of this invention.
The Al sheet of this invention will be described in detail with reference to the following embodiments.

Embodiment 1:

Al base metals of various grades (not less than 99.50% of Al purity, not less than 99.70% and not less than 99.90%) were used and Cu, Si and Fe were added as required, and subjected to an ordinary smelting and casting to obtain ingots of the compositions indicated in Table 2 in connection with Cu, Si and Fe. The ingots were faced up to 350 mm in thickness, 1,000 mm in width and 2,000 mm in length, and homogenized, then subjected to hot rolling, and subsequently to repeated cold rolling and process annealing to finish Al sheet of 0.2 mm thickness for printing. The Al sheet were treated under the following condition and then measured as to an uniformity of a grained surface due to the electrochemical graining and a lightness after the electrochemical graining.
The Al sheet were further subjected to the exposure and the development and the Al printing plates were mount on the press cylinder and used for printing 30,000 sheets of copies, and then the dot-form stain on the printed matters were examined.
The results of the above items were indicated in the Table 2. The lightness (L value) due to the electrochemical graining was measured by the tone (lightness) meter of Hunter type.
Treatment condition:

After removing grease on the surface with commercial detergent the Al sheet subjected to etching with 5% dilute solution of sodium hydroxide at 50°C for 60 sec, and subsequently subjected to AC electrochemical graining for one minute at current density of 30A/dm² in 1.5% dilute solution of nitric acid at 20°C liquid temperature. Thereafter, smudges on the surface were removed for 5 minutes in 25% dilute solution sulfuric acid at 50°C. Then the aluminum plate was rinsed and dried. The plates were further coated with photosensitive material thereon, then the plate was exposed and developed to prepare the printing plates.

Apparent from the Table 2, the blank plates of Nos. ₁- 7 were high in the lightness (L) after the electrochemical graining and uniform in the surface roughness due to the electrochemical graining, and formed none of the dot-form stain on the printed matters and none of the bending break at the bending portion which is formed when the printing plates being mount on the press cylinder.
On the contrary, it was found that the comparative sheet of Nos. 8, 10, 12, 14, 16 and 18 and the conventional sheet of No. 20 all made dot-form stain on the printed matters during printing as the printing plates if the amount of Cu content exceeded 0.003% in whatever amounts of Si and Fe contents. Further, it is discovered that the comparative sheet of Nos. 9, 10, 11, 12 and 19 were broken at the bending portions which were formed when the printing plates being mount on the press cylinder if the amount of Si or Fe content was lower than the range restricted by this invention even if the amount of Cu content was not more than 0.003%, and the comparative sheet of Nos. 13, 14, 15, 16, 1,7 and 18 and the conventional sheet of No. 20 all formed uneven grained surface due to the electrochemical graining if the amount of Si or Fe content was higher than the range restricted by this invention.

Embodiment 2:

The ingots of the composition indicated in the Table 2 were treated in a same manner as the embodiment 1 and formed into sheet in 0.2 mm thickness for printing, which were subjected to the electrochemical graining and the removal of smudges, and thereafter subjected to DC anodizing for three minutes with 30A/dm² of current density in 15% dilute solution bath of sulfuric acid at 20°C to form anodic oxide films thereon in approx 1µ thickness. The plates were further coated with photosensitive material and exposed and developed to prepare printing plates. The printing plates mount on the press cylinder were used for printing.
As the result, it is known that the printing plates of this invention made no dot-form stain on the printed matters providing with high lightness and no bending break at the bending portions formed when the plates being mount on the press cylinder, and formed uniform grained surface due to the electrochemical graining.
On the contrary, the comparative and conventional sheet all made dot-form stain on the printed matters during printing if the amount of Cu content exceeded 0.003% in whatever amounts of Si and Fe contents and were broken at the bending portions which were formed when the printing plates being mount on the press cylinder if the amount of Si or Fe content was lower than the range restricted by this invention, and all formed uneven grained surface due to the electrochemical graining if the amount of Si or Fe content was higher than the range restricted by this invention.
As the foregoing description, the Al sheet for printing of this invention are provided with the conspicuous effects that, by means of restricting the amounts of Cu, Fe and Si contents as impurities contained in Al to a specific range, the surface roughening treatment attains to form uniform grained surfaces to improve the adhesion of the photosensitive material and prevent the formation of the dot-form stain on the non-image area during printing.as the printing plates, and simultaneously improve the tone, the tone reproduction and the color tone.

Claims

1. An aluminum sheet for offset lithographic printing, said plate consisting of a composition of 0.02 - 0.15 wt.% of Si, 0.1 - 1.0 wt.% of Fe, not more than 0.003 wt.% of Cu as impurity, and the balance of Al and inevitable impurities.

₂. The aluminum sheet, as recited in claim 1, wherein the content of Si is 0.03 to 0.14 wt.% of the total composition.

3. The aluminum sheet, as recited in claim 1, wherein the content of Fe is 0.2 to 0.8 wt.% of the total composition.

4. The aluminum sheet, as recited in claim 1, wherein the content of Cu contaminated as impurity of Al is 0.001 to 0.003 wt.% of the total composition.