EP0257957A1

EP0257957A1 - Aluminium alloy support for lithography, process for producing thereof and lithographic printing plate using the same

Info

Publication number: EP0257957A1
Application number: EP87307277A
Authority: EP
Inventors: Toshiki c/o Sky Aluminium Co. Ltd. Muramatsu; Mamoru c/o Sky Aluminium Co. Ltd. Matsuo; Kazushige§c/o Fuji Photo Film Co. Ltd. Takizawa; Hirokazu§c/o Fuji Photo Film Co. Ltd. Sakaki
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1986-08-18
Filing date: 1987-08-18
Publication date: 1988-03-02
Also published as: JPS6347349A

Abstract

An aluminum alloy support for a lithographic printing plate is disclosed, wherein the aluminum alloy support comprises 0.30 wt% to less than 1.0 wt% of Mg, more than 0.3 wt% up to 1.3 wt% of Si, 0.003 wt% tp 0.10 wt% of Cu, the balance being Al and usual impurities. Preferably the average width of the grain perpendicular to the rolling direction is at most 40 µm. A process for producing the support via various rolling and annealing steps and a lithographic printing plate with a light-sensitive coating using the support are also disclosed.

Description

FIELD OF THE INVENTION

The present invention relates to an aluminum alloy support for lithography. More particularly, the present invention relates to an aluminum alloy support for lithography which can be electrochemically roughened to provide a roughened surface having a uniform appearance and excellent fatigue resistance, heat softening resistance, and printing durability.

BACKGROUND OF THE INVENTION

Conventional lithographic printing plates are generally obtained by subjecting an aluminum alloy sheet to a surface treatment such as roughening and anodic oxidation, coating a light-sensitive material on the aluminum alloy sheet, drying the light-sensitive material to form a PS plate, and then subjecting the PS plate to a plate-making process such as by imagewise exposure to light, development, and gumming-up treatment. In the processing of such a lithographic plate, the light-sensitive layer which is left undissolved after development forms an image portion, while the exposed surface of the aluminum alloy plate which has lost the light-sensitive layer and is hydrophilic forms a water-receptive non-image parts.
As a support for such a lithographic printing plate there is generally employed a light aluminum alloy plate excellent in surface-treatability, workability, and corrosion resistance. Examples of such an aluminum alloy material include aluminum alloy plates having a thickness of 0.1 to 0.8 mm specified by JIS A 1050 (Aℓ alloy having a purity of at least 99.5 wt%), JIS A 1100 (Aℓ alloy comprising 0.05 to 0.20 wt% of Cu), and JIS A 3003 (Aℓ alloy comprising 0.05 to 0.20 wt% of Cu and 1.5 wt% of Mn) (the term "JIS" as used herein refers to a "Japanese Industrial Standard). These aluminum alloy plates are roughened by at least one of mechanical, chemical and electrochemical roughening processes, and then are subjecged to anodic oxidation.
Specific examples of such aluminum lithographic printing plates include an aluminum lithographic printing plate obtained by a process including mechanical roughening, chemical etching, and anodic oxidation as described in Japanesr Patent Application (OPI) No. 49501/73 (the term "OPI" as used herein means an "unexamined published Japanese patent application"); an aluminum lithographic printing plate obtained by a process including chemical etching, and anodic oxidation as described in Japanese Patent Application (OPI) No. 61304/76; an aluminum lithographic printing plate obtained by a process including electrochemical processing, after-treatment, and anodic oxidation as described in Japanese Patent Application (OPI) No. 146234/79; an aluminum lithographic printing plate obtained by a process including electrochemical processing, chemical etching, and anodic oxidation as described in Japanese Patent Publication No. 28123/73; and an aluminum lithographic printing plate obtained by a process including mechanical roughening followed by a processing described in Japanese Patent Publication No. 28123/73.
Up to 100,000 sheets of clear prints can be obtained by printing using a printing plate prepared by providing a suitable light-sensitive layer on such a support, but it is still desired to obtain a further great number of prints using a printing plate, i.e., the printing plate is desired to have a good printing durability. To this end, aluminum PS plates (presensitized plate) may be subjected to a heat treatment at an elevated temperature ("burning") after being subjected to ordinary exposure to light and development, so that the image parts thereof are effectively reinforced. Specific examples of such a process are described in Japanese Patent Publication Nos. 27243/69 and 27244/69. The heating temperature and time of such a burning treatment generally depend on the type of resin used to form the image, but are generally in the range of 200 to 280°C and 3 to 7 minutes, respectively.
In recent years, it has become desirable to perform such a burning treatment at a higher temperature in a short er period of time in order to reduce the time of treatment. However, conventional aluminum alloy plates show an abrupt drop in strength by recrystallization when heated at a high temperature of 280°C or above. Such an aluminum alloy plate is insufficient in firmness and it is difficult to set on a printing machine, or to subject to registration in a multicolor printing process. For this reason, a stable aluminum alloy support which has better heat resistance, particularly heat temperature softening resistance, than conventional aluminum alloy support is desired.
As the printing speed has been raised with the development of printing technique, a higher stress results in being imposed to the printing plate, which is mechanically fixed on the both ends of the printing cylinder in the printing machine. If the aluminum printing plate has low strength, the fixed portion by which it is mounted on the plate cylinder is subject to deformation or damage, which causes shear in printing. A repeated stress on the bending portion of the printing plate can cause a break which stops printing entirely. Thus, an aluminum alloy support excellent in strength, particularly fatigue strength is eagerly sought.
Aluminum alloy plates according to JIS A 1050 can provide a unform roughened surface or suitable surface-roughness when subjected to an electrochemical roughening process. The non-image part on such a roughened surface is less susceptible to stain during printing. In other words, such aluminum alloy plates can provide excellent printing durability. However, such aluminum alloy plates are disadvantageous in that they have poor fatigue resistance and poor heat softening resistance. On the contrary, aluminum alloy plates according to JIS A 3003 provide sufficient fatigue resistance and sufficient heat softening resistance. However, such aluminum alloy plates are disadvantageous in that they cannot provide a uniform roughened surface or properly roughened surface when subjected to an electrochemical roughening process. Such aluminum alloy plates are also disadvantageous in that they are susceptible to stain of the non-image parts during printing. Further, printing plates using Aℓ-Mg-Si alloy are known as is described in Japanese Patent Application (OPI) Nos. 26746/86, 157212/75 and 80255/87, and Japanese Patent Publication Nos. 42745/83 and 220395/84, as correlated applications to the present application.

SUMMARY OF THE INVENTION

Therefore there remains a need in the art for an aluminum alloy support for lithography having excellent printing durability, sufficient fatigue resistance and good heat softening resistance; that is capable of providing a uniformly and properly roughened surface when subjected to a roughening process, particularly an electrochemical roughening process; and that has low susceptibility to stain of the non-image parts during printing.
With a view to overcoming the drawbacks of the prior art, the present invention provides an aluminum alloy support containing Mg in an amount of 0.3 to less than 1.0 wt%, preferably 0.5 to less than 1.0 wt%; Si in an amount of more than 0.3 up to 1.3 wt%, preferably from more than 0.3 up to 0.6 wt%, Cu in an amount of 0.003 to 0.10 wt% preferably 0.003 to 0.03 wt%; and the balance being Aℓ and impurities.
In a preferred embodiment the average width of grain perpendicular to the rolling direction is at most 40 µm, preferably at most 30µm.
These and other features of the present invention will become more apparent from the following detailed description and examples.

DETAILED DESCRIPTION OF THE INVENTION

Although not desiring to be bound by theory, it is considered that the present aluminum alloy support for lithography requires the above mentioned components for the following reasons:

Mg

Mg is an element effective for improving strength, handling properties, and fatigue strength, and to provide a finely and uniformly roughened surface by electrochemical roughening process. If the Mg content is less than 0.30 wt%, these effects are insufficient. On the contrary, if the Mg content is 1.0 wt% or more, the electrochemically roughened surface can be non-uniform. Therefore, the Mg content of the present aluminum alloy support for lithography is in the range of 0.30 wt% to less than 1.0 wt%.

Si

Si is an element effective for obtaining finely and uniformly roughened surface by electrochemical roughening process. Si also contributes to improvement in strength by combining with Mg. If the Si content is 0.3 wt% or less, these effects cannot be sufficient. On the contrary, if the Si content is more than 1.3 wt%, the electrochemically roughened surface can be nonuniform and large elemental Si constituents result in stain during printing. Therefore, the Si content of the present aluminum alloy support is in the range of more than 0.3 up to 1.3 wt%.

Cu

Cu is an element effective for improving strength and making finely and uniformly roughened surface by electrochemically roughening process. If the Cu content is less than 0.003 wt%, these effects are not sufficient. On the contrary, if the Cu content exceeds 0.10 wt%, the diameter of pits in the electrochemically roughened surface tends to be large and the surface is nonuniform. Therefore, the Cu content of the present aluminum alloy support is in the range of 0.003 wt% to 0.10 wt%.
Besides these elements, Cr may be optionally present in the aluminum alloy if desired. Cr is effective for improving strength, and refining recrystallized grain and producing fine and uniform electrochemically roughened surface by electrochemical roughening process. However, when the Cr content is more than 0.25 wt%, large intermetallic compounds (A₃Cr) are crystallized in casting, causing defects on the surface of the aluminum alloy plate. Therefore, if Cr is present in the aluminum alloy as necessary, its contents preferably at most 0.25 wt%, and more preferably 0.05 wt% to 0.25 wt%.
In general, aluminum alloys contain Fe as an unavoidable impurity. The Fe content is preferably limited to 0.50 wt% or less, particularly 0.30 wt% or less. Fe is effective for improving strength and fatigue strength. However, if the Fe content exceeds 0.50 wt%, large intermetallic compounds of an Aℓ-Fe-(Si) system are formed, providing a nonuniform electrochemically-roughened surface. This also renders the aluminum alloy plate more susceptible to stain during printing, and is the reson why the Fe content is preferably about 0.50 wt% or less. The content of impurities other than Fe may be near the value used in commercially available industrial pure aluminum.
In the production of an aluminum alloy ingot, Ti or Ti-B is added as a grain refiner. The present aluminum alloy support for lithography optionally may contain Ti and/or B as a grain refiner of ingot. However, the Ti content and the B content are preferably at most 0.1 wt% and 0.02 wt%, and more preferably 0.005 wt% to at most 0.1 wt% and 0.0005 wt% to 0.02 wt%, respectively.
As other impurities which may be contained in the alloy of the present invention are, for example, at most 0.15 wt% of Zn, at most 50 ppm of Be and at most 0.15 wt% of Zr, Vand Mn.
In a preferred embodiment of the present invention, the average width of grain (in the direction) perpendicular to the rolling direction is 40 µm or less, more preferably at most 30 µm. To this end, the grain size obtained at intermediate annealing before final cold rolling step must be at most 40 µm. By minimizing the grain size of aluminum alloy sheet at intermediate annealing to be 40 µm or less namely the average width of grain of final cold rolled sheet, perpendicular to the direction of final cold rolled sheet to be 40 µm or less, the aluminum alloy support gets a uniformly and finely roughened surface when subjected to etching with an acid or alkali or electrochemical etching, further inhibiting the generation of uneven tone or streaks.
As to the minimum average width of grain perpendicular to the rolling direction, smaller one is preferred, but it is generally difficult to produce grains having 5 µm or less of the average width of grain in manufacturing. In other words, the fine grains allow the aluminum alloy support to be better roughened. Thus, a substrate for a printing plate support having an excellent external appearance can be obtained. The average width of grain is measured by intercept procedure.
The process for the preparation of the present aluminum alloy support for lithography is now described in greater detail.
A molten aluminum alloy containing the above mentioned components is subjected to any ordinary casting process. The casting may be accomploished by a semi-continuous casting process. In order to save energy or improve the mechanical properties of the aluminum alloy support, continuous sheet casting may be effected. The resulting ingot is subjected to homogenization, hot rolling, cold rolling, intermediate annealing asn so on to obtain a sheet having preferably a thickness of 0.10 to 0.50 mm, more preferably 0.15 to 0.35 mm. The homogenization treatment is preferably conducted at a tempreature of 450 to 610°C for 1 to 48 hours so that the grain size are fine at intermediate annealing and non segregation of Fe, Si, Mg in the ingot occurs to obtain a uniform distribution of the components, and thereby the aluminum alloy support is uniformly roughened when subjected to electrochemical etching. The heat treatment for the homogenization and the hot rolling process can be conducted in two stages or one stage. In any case, the hot rolling preferably begins at a temperature of 400 to 550°C.
After the hot rolling is finished, the aluminum alloy support is generally subjected to a first cold rolling, intermediate annealing, and then a final cold rolling. However, two or more intermediate annealing steps may be conducted between the first cold rolling and the final rolling steps. In this process, if the average grain size after intermediate annealing and before final cold rolling is at most 40 µm, the average width of the grain perpendicular to the rolling direction of the final cold rolling results in being at most 40 µm, so that the aluminum alloy support can provide a uniformly and finely roughened surface when subjected to an electrochemical etching process. The intermediate annealing temperature is preferably in the range of 300 to 600°C for at most 5 hours. If the intermediate annealing temperature is below 300°C, recrystallization is insufficient. If the annealing temperature is above 600°C, a violet oxidation discolors the surface of the aluminum alloy sheet, and large recrystallized grains are formed, fibing undesirable results. The intermediate annealing may be either an ordinary batch annealing (average heating rate: 20 to 50°C/hr) or a continous annealing (average heating rate: a few degree c/sec. to several tens of degrees c/sec.). In order to make the average grain size before final cold rolling at most 40 µm or less, continuous annealing is preferably used rather than batch annealing. Continuous annealing is also preferably effected in order to improve strangth by precipitation of Mg₂Si. If continuous annealing is used, the intermediate annealing temperature is preferably 380°C or above for recrystallization, more preferably 380°C to 550°C, most preferably 450°C to 550°C in order to improve strength by precipitation of Mg₂Si. If a batch annealing process is used, the soaking temperature is preferably higher than the ordinary temperature in order to obtain finer recrystallized grains.
The intermediate annealing conditions are important in making the average grain size of 40 µm or less. However, the cold reduction ratio in thickness before the intermediate annealing must also be considered. The cold reduction ratio means a reduction ratio in thickness of sheet subjected to cold rolling and is obtained according to the following formula: Cold reduction ratio = (t₀ - t₁)/t₀ x 100 (t₁ represents a thickness after cold rolling; t₀ represents a thickness before cold rolling). That is, in order to make the average grain szie of the recrystallized grain of at most 40 µm, the cold rolling is preferably conducted at a cold reduction ratio at least 30%, more preferably at least 40%, and most preferably at least 50%, before the intermediate annealing. The larger cold reduction ratio is preferred, but in practically the maximum reduction ratio is about 95%, in a manufacturing technique and in considering a characteristics of support for a lithographic printing plate.
In order to obtain the toughness or firmness necessary for an aluminum alloy support for lithographic printing plate, the final cold rolling needs to be conducted at a cold reduction ratio sufficient to provide a proof stress of 15 kgf/mm² is obtained. To this end, the cold reduction ratio at the final cold rolling needs to be at least 20%, more preferably at least 30% and most preferably at least 40%. The larger cold reduction ratio is preferred, but in practically the maximum reduction ratio is about 95%, in a manufacturing technique and in considering a characteristics of support for a lithographic printing plate. The temper may be any one of H1n, H2n, and H3n (alloys which are not subjected to heat treatment and defined in JIS H 0001) so long as a proof stress of at least 15 kfg/mm² can be obtained.
The method for surface processing of the present lithographic support is now described in detail.
Examples of graining processes which can be used in the present invention include an electrochemical graining process by electrochemically roughening the material in a hydrochloric acid or nitric acid electrolyte; and a mechanical graining process such as a wire brush graining process which includes scratching the surface of aluminum with a metal wire, a ball graining process which includes roughening the surface of aluminum with abrasive balls and abrasive agents; and a brush graining process which includes roughening the surface of aluminum with a nylon brush and an abrasive agent. These graining processes may be used, singly or in combination. The electrochemical etching process is advantageous in that it provides a uniformly and properly roughened surface. It is also advantageous in that the non-image parts thus obtained is less susceptible to stain during printing.
The aluminum thus roughened or grained is then chemically etched with an acid or alkali. It takes a longer time to destroy the fine structure by acid etching, therefore, in general, it is desirable that an alkali be used as an etching agent.
Examples of suitable alkali agents which can be used in the present invention include caustic soda, sodium carbonate, sodium aluminate, sodium metasilicate, sodium phosphate, potassium hydroxide, and lithium hydroxide. The concentration of such an alkali agent is preferably in the range of 1 to 50 wt% based on an etching solution. The temperature of such an alkali agent is preferably in the range of 20 to 100°C. The condition of such an alkali agent is preferably such that aluminum is dissolved in an amount of 5 to 20 g/m².
After being etched, the aluminum is normally washed with an acid to remove remaining contaminants (smut) from the surface thereof. Examples of an acid which can be used in this washing process include nitric acid, sulfuric acid, phosphoric acid, chromic acid, hydrofluoric acid, and borofluoric acid. Particularly, the removal of smut after the electrochemical roughening process is preferably accomplished by a process as described in Japanese Patent Application (OPI) No. 12739/78 which includes bringing the material into contact with a 15 to 65 wt% sulfuric acid solution at a temperature of 50 to 90°C, or a process as described in Japanese Patent Publication No. 28123/73 which includes etching with an alkali.
The aluminum alloy plate thus processed can be used as a support for lithography. However, the aluminum alloy plate may be further subjected to a processing step such as anodic oxidation, if desired.
The anodic oxidation can be accomplished by any suitable method which has been heretofore used in this field. For example, the aluminum alloy plate may be processed in an aqueous or nonaqueous solution of sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, or benzenesulfonic acid, or a combination thereof with a d.c. or a.c. current passing therethrough so that an anodized film is formed on the surface thereof.
The conditions of the anodic oxidation depend on the electrolyte used and cannot be specifically defined. In general, the anodic oxidation is preferably effected at an concentration of 1 to 80 wt% of electrolyte based on an electrolytic solution, an electrolyte temperature of 5 to 70°C, and a current density of 0.5 to 60 A/dm² on 1 to 100 V for an electrolysis time of 10 to 100 seconds.
Preferred examples of such an anodic oxidation process include a process as described in British Patent 1,412,768, which includes anodic oxidation with a high current density in sulfuric acid, and a process as described in U.S. Patent 3,511,661, which includes anodic oxidation in phosphoric acid as an electrolytic bath.
The aluminum alloy plate thus anodized may be further subjected to a processing step as described in U.S. Patents 2,714,066 and 3,181,461, which includes dipping the aluminum in an aqueous solution of metallic silicate such as sodium silicate, or a processing step as described in U.S. Patent 3,860,426, which includes applying an undercoat layer of a hydrophilic cellulose (e.g., carboxymethyl cellulose) containing a water-soluble metallic salt (e.g., zinc acetate) on the aluminum alloy support.
Any conventional light-sensitive layer which has been heretofore known as a light-sensitive layer for a PS plate may be coated on the lithographic aluminum alloy support according to the present invention to obtain a light-sensitive lithographic plate. Such a light-sensitive lithographic plate can then be subjected to any conventional plate-making process to obtain a lithographic plate having excellent properties.
Examples of the above mentioned light-sensitive layer are now described in detail, although the present invention is not to be construed as being limited thereto.

(1) Light-sensitive layer containing a diphenylamine-p-diazonium salt

A product of condensation of a diphenylamine-p-diazonium salt as described in U.S. Patents 2,063,631 and 1,667,415 (the product of the reaction of a diazonium salt with an organic condensing agent containing a reactive carbonyl group such as an aldol and an acetal) with formaldehyde ("light-sensitive diazo resin") is preferably used. Other useful examples of condensed diazo compounds are disclosed in Japanese Patent Application (OPI) Nos. 48001/74, 45322/74 and 45232/74.
Such light-sensitive diazo compounds can be normally obtained in the form of a water-soluble inorganic salt and thus can be coated on a support in the form of an aqueous solution. Alternatively, these water-soluble diazo compounds may be reacted with an aromatic or aliphatic compound containing one or more phenolic hydroxyl groups and/or sulfonic acid groups in a process as disclosed in Japanese Patent Publication No. 1167/72. This reaction produces a substantially water-insoluble light-sensitive diazo resin which can be used in the present light-sensitive layer. As described in Japanese Patent Application (OPI) No. 121031/81, these water-soluble diazo compounds can be used as products of reaction with hexafluorophosphate or tretrafluoroborate. Diazo resins as described in British Patent 1,312,925 may be preferably used.

(2) Light-sensitive layer containing an o-quinonediazide compound

Particularly preferred examples of such an o-quinonediazide compound include an o-naphthoquinonediazide compound. Examples of suitable o-naphthoquinonediazide compounds are described in U.S. Patents 2,766,118, 2,767,092, 2,772,972, 2,859,112, 2,907,665, 3,046,110, 3,046,111, 3,046,115, 3,046,118, 3,046,119, 3,046,120, 3,046,121, 3,046,122, 3,046,123, 3,061,430, 3,102,809, 3,106,465, 3,635,709, and 3,647,443.

(3) Light-sensitive layer containing an azide compound and a binder (high molecular compound)

Examples of such a light-sensitive layer composition include a composition containing an azide compound as described in British Patents 1,235,281 and 1,495,861, and Japanese Patent Application (OPI) Nos. 32331/76 and 36128/76 and a water-soluble or alkali-soluble high molecular compound, and compositions containing a polymer containing an azide group as described in Japanese Patent Application (OPI) Nos. 5102/75, 84302/75, 84303/75 and 12984/78 and a high molecular compound as a binder.

(4) Other light-sensitive resin layers

Other useful light-sensitive resin layer compositions include polyester compounds as disclosed in Japanese Patent Application (OPI) No. 96696/77 polyvinyl cinnamate resins as described in British Patents 112,277, 1,313,309 1,341,004 and 1,377,747, and photopolymerizable photopolymers as described in U.S. Patents 4,072,527 asnd 4,072,528.
The amount of the above light-sensitive compositions in the light-sensitive layer to be formed on the support is 0.2 to 7.0 g/m², preferably 0.5 to 4 g/m².
After being imagewise exposed to light, the PS plate is subjected to any conventional processing steps including development so that a resin image is formed. For example, in the case of a PS plate having the above mentioned light-sensitive layer (1) containing a diazo resin and a binder, after imagewise exposure, the unexposed portion of the light-sensitive layer is removed by development to obtain a lithographic plate. In the case of a PS plate having the above mentioned light-sensitive layer (2), after the imagewise exposure, the unexposed portion is removed by development with an alkaline aqueous solution to obtain a lithographic plate.
The present invention will be further illustrated in the following examples, but the present invention is not to be construed as being limited thereto. Unless otherwise indicated, all parts, percents and ratios are by weight.

EXAMPLE 1

The alloy specimens A to E shown in Table 1 were casted by DC casting and scalped on both sides thereof to obtain alloy ingots 500 mm thick, 1,000 mm wide, and 3,500 mm long. These ingots were then subjected homogenization at a temperature of 560°C for 10 hours. These ingots thus homogenized were heated to a temperature of 480°C and then hot-rolled to 4 mm thick plates. These alloy plates were cold-rolled to 1.5 mm thick plates. These alloy plates were intermediate-annealed at a temperature of 470°C in a continuous annealing process. These annealed alloy plates were then cold-rolled to 0.3 mm thickness. These aluminum alloy plates were evaluated for electrolytic etching properties, appearance of roughened surface, fatigue strength, heat softening resistance, and printing durability by the methods specified below. The results are shown in Table 2.

(1) Electrolytic etching property

The surface condition of the specimens was observed by means of a scanning electron microscope to evaluate the uniformity of pitting. Excellent uniformity is indicated by the symbol ○. Good uniformity is indicated by the symbol Δ. Poor uniformity is indicated by the symbol X.

(2) Appearance of roughened surface

The surface appearance of the aluminum alloy supports for lithography after anodization by the undermentioned method (5) was visually judged for streaks and unevenness in color tone. Streaks are marks developed in the rolling direction due to nonuniformity in chemical etching or electrolytic etching or nonuniformity in the micro-structure of aluminum alloy sheet. The condition without streaks is indicated by the symbol ○, and the condition of many streaks is indicated by the symbol X. The condition of nonuniform color tone on the roughened surface, or poor evenness, is indicsated by the symbol X. The condition of uniform color tone, or excellent evenness, is indicated by the symbol ○. The appearance of both streaks and unevenness is undesirable for aluminum alloy supports for lithography.

(3) Fatigue strength

A tensile load of 5 Kgf/mm² was repeatedly applied at a frequency of 25 Hz to one end of specimens which had been bent at 2 mm radius with right - angle until the specimens were broken. The number of repetitions of stress before breakage represents the fatigue strength of the specimens. In practical use, this value is preferably 80,000 or more.

(4) Heat softening resistance

The specimens were heated to a temperature of 270°C for 7 minutes in Burning Processor Model 1300 (Fuji Photo Film Co., Ltd.'s burning processor equipped with a 12-kw heat source). After being allowed to cool, the specimens were measured for proof strength to evaluate their heat softening resistance.

(5) Printing Durability

Printing plates which had been subjected to the undermentioned processing were mounted in an offset printer KOR (made by Heidelberg Co.). After being printed, the printing plates were evaluated for strain of the non-image parts.
The printing plates used were prepared in the following manner:
The aluminum alloy plates used were roughened with a rotary brush in a suspension of pumice and water. The aluminum alloy plates thus processed were then etched with a 20 wt% aqueous solution of caustic soda based on an etching solution in such a manner that the aluminum was dissolved in the solution in an amount of 8 g/m². The aluminum alloy plates thus etched were thoroughly washed with running water, then washed with a 25 wt% aqueous solution of nitric acid, and then washed with water. These substrates were then subjected to an AC electrolysis with a current density of 20 A/cm² in an electrolytic bath containing 0.5 to 2.5 wt% of nitric acid based on an electrolytic solution as described in Japanese Patnet Application (OPI) No. 1462134/79. These substrates were subsequently dipped in a 15 wt% aqueous solution of sulfuric acid at a temperature of 50°C for 3 minutes so that the surface thereof were cleaned. These substrates were then processed in an electrolytic bath mainly containing 20 wt% sulfuric acid based on an electrolytic solution at a bath temperature of 30°C to form an anodized film thereon in an amount of 3 g/m².
The specimens thus prepared were coated with the following light-sensitive layer composition in an amount of 2.5 g/m².

Light sensitive layer composition

Ester compound of naphthoquinone-1,2-diazide-5-sulfonylchloride with a pyrogallolacetone resin (as described in Example 1 in U.S. Patent 3,635,709) 0.75 g
Cresol novolak resin 2.00 g
Oil Blue + 603 (Orient Kagaku) 0.04 g
Ethylene dichloride 16 g
2-Methoxyethylacetate 12 g
These light-sensitive lithographic plates thus prepared were imagewise exposed to light from a 3-kw metal halide lamp placed at a distance of 1 meter therefrom for 60 seconds, developed with an aqueous solution of sodium silicate having an SiO₂/Na₂O molar ratio of 1.2 and containing 1.5 wt% of SiO₂, washed with water, dried, and then rubberized.
As is aparent from Table 2, the present alloy specimens A and B both had a high fatigue strength as well as excellent heat softening resistance, electrolytic etching properties, surface appearance, and printing durability. On the contrary, the comparative alloy specimen C exhibited poor fatigue strength as well as poor heat softening resistance. The comparative alloy specimens D and E had poor electrolytic etching properties, surface appearance, and printing durability.

EXAMPLE 2

Ingots of the alloy specimen B shown in Table 1 were processed under various preparation conditions so that 0.3-mm thick aluminum alloy plates having different width of grain were obtained. These aluminum alloy plates were evaluated for electrolytic etching property, surface appearance, fatigue strength, heat softening resistance, and printing durability as in Example 1. Table 3 shows the various preparation conditions and the average width of the grain perpendicular to the rolling direction. Table 4 shows the results of the evaluation.
As apparent from Tables 3 and 4, the plates prepared under conditions producing an average width of the grain perpendicular to the rolling direction of 40 µm or less had a high fatigue strength as well as excellent heat softening resistance, electrolytic etching properties, surface appearance, and press life. In contrast, since in the preparation conditions 2 and 3, too high intermediate annealing temperature is employed (in condition 2) and the cold reduction ratio provided by a cold rolling before intermediate annealing is too low (in conditions 2 and 3), the size of grains thus obtained is too large to obtain the aluminum sheet having superior surface appearance.
As has been described, the aluminum alloy supports for lithography of the present invention have a fatigue resistance and heat softening resistance that is sufficient for use as printing plate supports, as well as excellent electrolytic etching properties, which provide a uniformly and properly roughened surface, particularly when electrochemically roughened. Furthermore, lithographic plates containing the present aluminum alloy support have excellent printing durability, and are less susceptible to stain of the non-image portion. Thus, the present aluminum alloy plates are extremely excellent lithographic support.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

1. An aluminum alloy support for a lithographic printing plate, comprising 0.30 wt% to less than 1.0 wt% of Mg, more than 0.3 wt% up to 1.3 wt% of Si, 0.003 wt% to 0.10 wt% of Cu, and a balance of Al and impurities.

2. The aluminum alloy support as claimed in claim 1, wherein Mg is 0.5 wt% to less than 1.0 wt%.

3. The aluminum alloy support as claimed in claim 1, wherein Si is more than 0.3 wt% to 0.6 wt%.

4. The aluminum alloy support as claimed in claim 1, wherein Cu is 0.003 wt% tp 0.03 wt%.

5. The aluminum alloy support as claimed in claim 1, wherein the average width of the grain perpendicular to the rolling direction is at most 40 µm.

6. An aluminum alloy support as claimed in claim 1, wherein said aluminum alloy further comprises at least one of at most 0.25 wt% of Cr, at most 0.50 wt% of Fe, at most 0.10 wt% of Ti, and at most 0.02 wt% of B.

7. A process for producing an aluminum alloy support for lithography, comprising the step of:

(a) casting an aluminum alloy comprising 0.30 wt% to less than 1.0 wt% of Mg, more than 0.3 wt% to 1.3 wt% of Si, 0.003 wt% to 0.10 wt% of Cu, and a balance of Al and impurities;

(b) homogenizing said body at a temperature of 450 to 610°C for 1 to 48 hours;

(c) hot rolling said homogenized body at about 400 to 500°C;

(d) cold rolling said rolled body;

(e) intermediate annealing said cold rolled body at a temperature of 300 to 600°C for at most 5 hours; and

(f) cold rolling said annealed body such that the average grain width perpendicular to the rolling direction is at most 40 µm.

8. The process as claimed in claim 6, wherein said intermediate annealing is a continuous annealing conducted at a temperature of at least 380°C.

9. The process as claimed in claim 8, wherein said intermediate annealing is conducted at a temperature of 380 to 550°C.

10. The process as claimed in claim 7, wherein said first cold rolling step (d) is performed at a reduction ratio of at least 30 wt%, and said final cold rolling step (f) is conducted at a reduction ratio at least 20 wt%.

11. The process as claimed in claim 10, wherein said final cold rolling step (f) is conducted at a reduction ratio of at least 40 wt%.

12. The process as claimed in claim 7, further comprising the steps of:

(g) graining the surface of said sheet;

(h) chemically etching the grained surface of said sheet;

(i) washing said etched sheet with an acid; and

(j) anodic oxidation

13. A lithographic printing plate comprising an aluminum alloy support comprising 0.30 wt% to less than 1.0 wt% of Mg, more than 0.3 wt% of Si, 0.003 wt% to 0.10 wt% of Cu, and a balance of Al and impurities, and a light-sensitive layer thereon.

14. The lithographic printing plate as claimed in claim 13, wherein said light-sensitive layer comprises a light-sensitive composition selected from (a) a diazo dye and a binder; (b) an o-quinonoediazide compound; (c) an azide compound and a binder; (d) a light-sensitive polyester compound; (e) a light-sensitive polyvinyl cinnamate resin; and (f) a photopolymerizable photopolymer.

15. The lithographic printing plate as claimed in claim 14, wherein said light-sensitive layer comprises said light-sensitive composition in an amount of from 0.1 to 7.0 g/m².