Aluminum alloy sheet for lithographic printing plate, and manufacturing method thereof

Abstract

An aluminum alloy sheet for a lithographic printing plate which has excellent ink stain resistance, with a local defect in a photosensitive layer after long-term storage being hard to occur, and excellent the pit uniformity after a roughening and a manufacturing method thereof are provided. An aluminum alloy sheet for a lithographic printing plate containing a predetermined content of Fe, Si, Cu and Ti as well as one type or more selected from B and C, and composed of remaining Al and inevitable impurities, in which a concentration of an aluminum carbide present in the aluminum alloy sheet is not more than 8 ppm, an area occupancy of aggregation substances present on the aluminum alloy sheet surface after the roughening treatment with respect to an arbitrary circle with a radius 5 μm in the aluminum alloy sheet surface is less than 10%. In a case where the area occupancy is not less than 10%, the aggregation substances are present at a rate of 1 to 2 pieces/50 cm2.

1 . An aluminum alloy sheet for a lithographic printing plate containing about 0.10 to about 0.60 mass % Fe, about 0.01 to about 0.25 mass % Si, about 0.0001 to about 0.05 mass % Cu, about 0.005 to about 0.05 mass % Ti, and one or more types selected from B and C: about 0.0001 to about 0.0020 mass % of one or more types selected from B and C, the balance of Al, and unavoidable impurities,
 wherein the concentration of an aluminum carbide present in the aluminum alloy sheet is not more than 8 ppm; and   wherein when an area occupancy ratio of aggregation substances present on a surface of the aluminum alloy sheet subjected to a roughening treatment to a circle area with a radius of 5 μm set on the surface of the aluminum alloy sheet is less than 10%, said aggregation substances comprising at least one of a Ti—B compound and a Ti—C compound, and the aluminum carbide.   
     
     
         2 . An aluminum alloy sheet for a lithographic printing plate containing about 0.10 to about 0.60 mass % Fe, about 0.01 to about 0.25 mass % Si, about 0.0001 to about 0.05 mass % Cu, about 0.005 to about 0.05 mass % Ti, and one or more types selected from B and C: about 0.0001 to about 0.0020 mass % of one or more types selected from B and C, the balance of Al, and unavoidable impurities,
 wherein the concentration of an aluminum carbide present in the aluminum alloy sheet is not more than 8 ppm; and   wherein when an area occupancy ratio of aggregation substances present on a surface of the aluminum alloy sheet subjected to a roughening treatment to a circle area with a radius of 5 μm set on the surface of the aluminum alloy sheet is not less than 10%, said aggregation substances are present in an amount of 1 to 2 pieces/50 cm 2 .   
     
     
         3 . A method of manufacturing an aluminum alloy sheet for a lithographic printing plate comprises the steps of:
 melting an aluminum alloy containing about 0.10 to about 0.60 mass % Fe, about 0.01 to about 0.25 mass % Si, about 0.0001 to about 0.05 mass % Cu, about 0.005 to about 0.05 mass % Ti, about 0.0001 to about 0.0020 mass % of at least one of B and C, and the balance of Al and unavoidable impurities at about 680 to about 780° C.; and   treating the molten metal of the aluminum alloy at about 680 to about 780° C.,   wherein said steps of treating includes:   stirring the molten metal of the aluminum alloy over about 5 to about 60 minutes by mechanical or electromagnetic means;   holding the stirred molten metal over about 10 to about 60 minutes;   performing an in-line degassing treatment for the held molten metal;   filtering the in-line degassing-treated molten metal with an in-line filter; and
 stirring the molten metal, to which grain-refiners are added, over at least 10 minutes.