Aluminum alloy sheet for lithographic printing plate and method of producing the same

Abstract

An aluminum alloy sheet for a lithographic printing plate which allows pits to be more uniformly formed by an electrochemical surface-roughening treatment and exhibits more excellent adhesion to a photosensitive film and water retention properties, and a method of producing the same are disclosed. The aluminum alloy sheet includes 0.1 to 1.5% of Mg, more than 0.05% and 0.5% or less of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.10% of Cu, and 0.0001 to 0.05% of Ti, with the balance being aluminum and impurities, the Mg content and the Zn content satisfying a relationship “4×Zn %−1.4%≦Mg %≦4×Zn %+0.6%”, and the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/m 2 . It is more effective when precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm are dispersed on the surface of the sheet in a number of 10,000 to 100,000 per square millimeter (mm 2 ).

1 . An aluminum alloy sheet for a lithographic printing plate, the aluminum alloy sheet comprising 0.1 to 1.5% (mass %; hereinafter the same) of Mg, 0.5% or less (excluding 0%; hereinafter the same) of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.1% of Cu, and 0.0001 to 0.1% of Ti, with the balance being aluminum and impurities, the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/mm 2 . 
     
     
         2 . An aluminum alloy sheet for a lithographic printing plate, the aluminum alloy sheet comprising 0.1 to 1.5% of Mg, more than 0.05% and 0.5% or less of Zn, 0.1 to 0.6% of Fe, 0.03 to 0.15% of Si, 0.0001 to 0.10% of Cu, and 0.0001 to 0.05% of Ti, with the balance being aluminum and impurities, the Mg content and the Zn content of the aluminum alloy sheet satisfying a relationship “4×Zn %−1.4%≦Mg %≦4×Zn %+0.6%”, and the amount of aluminum powder on the surface of the aluminum alloy sheet being 0.1 to 3.0 mg/m 2 . 
     
     
         3 . The aluminum alloy sheet according to  claim 2 , wherein precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm are dispersed on the surface of the aluminum alloy sheet in a number of 10,000 to 100,000 per square millimeter (mm 2 ). 
     
     
         4 . The aluminum alloy sheet according to  claim 2 , wherein the quantity of Fe in solid solution in the aluminum alloy sheet is 20 to 100 ppm. 
     
     
         5 . The aluminum alloy sheet according to  claim 2 , wherein some or all of the elements of the aluminum alloy sheet form intermetallic compounds, the content of Fe which forms an intermetallic compound is 50 to 99.8% of the total Fe content, the content of Si which forms an intermetallic compound is 5 to 40% of the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which forms an Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms an Al—Fe intermetallic compound is 0.9 or less. 
     
     
         6 . The aluminum alloy sheet according to  claim 1 , wherein the number of oil pits with a diameter (circle equivalent diameter) of 30 μm or more formed in the surface of the aluminum alloy sheet is 50 or less per square millimeter (mm 2 ). 
     
     
         7 . The aluminum alloy sheet according to  claim 1 , wherein the aluminum alloy sheet further comprises more than 0.05% and 0.3% or less of Mn. 
     
     
         8 . The aluminum alloy sheet according to  claim 1 , wherein the average grain size of the aluminum alloy sheet in a direction perpendicular to a rolling direction with respect to the surface of the aluminum alloy sheet is 100 μm or less, and the average grain size in a direction parallel to the rolling direction with respect to the surface of the aluminum alloy sheet is 2 to 20 times the average grain size in the direction perpendicular to the rolling direction. 
     
     
         9 . The aluminum alloy sheet according to  claim 1 , wherein the aluminum alloy sheet further comprises one or more elements selected from Pb, In, Sn, and Ga in an amount of 0.005 to 0.05% in total. 
     
     
         10 . The aluminum alloy sheet according to  claim 3 , wherein the aluminum alloy sheet has a 0.2% proof stress of 120 MPa or more after being subjected to a heat treatment at 270° C. for seven minutes. 
     
     
         11 . A method of producing an aluminum alloy sheet for a lithographic printing plate, the method comprising casting an aluminum alloy having the composition according to  claim 2  to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. at a temperature increase rate of 20 to 60° C./hr and keeping the ingot at 450 to 580° C. for one hour or more, hot-rolling the resulting product to a thickness of 5 mm or less under conditions where the hot rolling start temperature is 400 to 520° C. and the hot rolling finish temperature is 320 to 400° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing. 
     
     
         12 . A method of producing an aluminum alloy sheet for a lithographic printing plate, the method comprising casting an aluminum alloy having the composition according to  claim 2  to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. at a temperature increase rate of 20 to 60° C./hr and keeping the ingot at 450 to 580° C. for one hour or more, cooling the resulting product to room temperature, heating the cooled product to 350 to 500° C. and hot-rolling the product to a thickness of 5 mm or less under conditions where the hot rolling finish temperature is 300 to 380° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing. 
     
     
         13 . A method of producing an aluminum alloy sheet for a lithographic printing plate, the method comprising casting an aluminum alloy having the composition according to  claim 2  to obtain an ingot, scalping a rolling-side surface of the ingot by 3 to 15 mm, subjecting the ingot to a homogenization treatment which includes heating the ingot to 450 to 580° C. and keeping the ingot at 450 to 580° C. for three hours or more, cooling the resulting product to a hot rolling start temperature at a temperature decrease rate of 20 to 60° C./hr, hot-rolling the cooled product to a thickness of 5 mm or less under conditions where the hot rolling start temperature is 400 to 500° C. and the hot rolling finish temperature is 300 to 400° C., and cold-rolling the hot-rolled product without subjecting the hot-rolled product to process annealing. 
     
     
         14 . A method of producing the aluminum alloy sheet according to  claim 1 , the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil with a viscosity of 1 to 6 cSt. 
     
     
         15 . A method of producing the aluminum alloy sheet according to  claim 1 , the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil, the Mg content (Mg %) of the aluminum alloy sheet and the viscosity p of the rolling oil satisfying a relationship “−2×Mg %+2≦ρ≦−2×Mg %+8”. 
     
     
         16 . A method of producing the aluminum alloy sheet according to  claim 6 , the method comprising subjecting the aluminum alloy sheet to final cold rolling using a roll having a roll surface with an arithmetic average roughness Ra of 0.2 to 0.5 μm and a rolling oil with a viscosity of 1 to cSt. 
     
     
         17 . A method of producing the aluminum alloy sheet according to  claim 6 , the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil, the Mg content (Mg %) of the aluminum alloy sheet and the viscosity p of the rolling oil satisfying a relationship “ρ≦2×Mg+4”.