US20090252642A1 - Aluminum alloy sheet for lithographic printing plate and method of producing the same

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Abstract

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Claims

US20090252642A1

Publication number: US20090252642A1
Application number: US11/990,905
Authority: US
Inventors: Akio Uesugi; Hirokazu Sawada; Hiroshi Ougi; Atsushi Hibino
Original assignee: Fujifilm Corp; Sumitomo Light Metal Industries Ltd
Current assignee: Fujifilm Corp; Sumitomo Light Metal Industries Ltd
Priority date: 2005-08-30
Filing date: 2006-08-16
Publication date: 2009-10-08
Also published as: WO2007026574A1

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/m². 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 (mm²).

TECHNICAL FIELD

The present invention relates to an aluminum alloy sheet for a lithographic printing plate. More particularly, the present invention relates to an aluminum alloy sheet for a lithographic printing plate which can be surface-roughened uniformly by an electrochemical etching treatment and exhibits excellent strength and thermal softening resistance, and a method of producing the same.

BACKGROUND ART

An aluminum alloy sheet is generally used as a support for a lithographic printing plate (including an offset printing plate). Such a support is surface-roughened from the viewpoint of improving adhesion to a photosensitive film and improving the water retention properties in a non-image area. As the surface roughening method, a mechanical surface roughening method such as ball graining, brush graining, or wire graining has been employed. In recent years, a method of roughening the surface of a support aluminum alloy sheet by an electrochemical etching treatment has been increasingly developed due to excellent plate-making applicability (fitness), excellent printing performance, and a continuous treatment capability using a coil material.
The electrochemical etching treatment is performed using hydrochloric acid or an electrolyte mainly containing hydrochloric acid (hereinafter referred to as “hydrochloric acid-based electrolyte”), or nitric acid or an electrolyte mainly containing nitric acid (hereinafter referred to as “nitric acid-based electrolyte”). An A1050 (aluminum purity: 99.5%) equivalent material which can be relatively uniformly surface-roughened by electrolysis is used as a support. It is possible to obtain hundreds of thousands of clear printed matters by appropriately selecting a photosensitive layer applied to the support.
In order to improve the plate wear of a printing plate, a printing plate using an aluminum alloy sheet as a support is subjected to exposure and development using a normal method, followed by a high-temperature heat treatment (burning treatment) to strengthen an image area. The burning treatment is generally performed at 200 to 290° C. for 3 to 9 minutes. An aluminum alloy sheet used as a support is required to exhibit heat resistance (burning resistance) which maintains the strength of the support during the burning treatment.
In recent years, the printing speed has increased along with the proceed in printing technology so that stress applied to a printing plate mechanically secured to each side of a plate cylinder of a printer has increased. Therefore, a support having a high strength has been desired. If the strength of the support is insufficient, the secured portion of the support may be deformed or damaged, whereby a printing variation or the like may occur. Accordingly, an increase in strength of the support is indispensable together with the burning resistance.
In order to satisfy such a demand, an aluminum alloy support of which the components are adjusted based on an A1050 equivalent material has been proposed (see JP-A-2005-15912, for example). An attempt has been made which adjusts the components based on an A1050 equivalent material and adjusts the depth of oil pits in the sheet surface in order to satisfy the above demand (JP-A-2004-35936).

DISCLOSURE OF THE INVENTION

In order to further improve the above-mentioned aluminum alloy support, the inventors of the present invention have utilized an aluminum alloy support based on an A1050 equivalent material and conducted studies on the relationship between the surface properties of a cold-rolled sheet and etch pits obtained by the electrolytic surface-roughening treatment. As a result, the inventors have found that an aluminum powder remaining on the surface of the rolled sheet affects etch pit formation, and a uniform pit pattern is obtained by limiting the amount of aluminum powder.
The present invention has been achieved as a result of further experiments and studies based on the above findings. An object of the present invention is to provide an aluminum alloy sheet for a lithographic printing plate which allows pits to be more uniformly formed by an electrochemical surface-roughening treatment, exhibits more excellent adhesion to a photosensitive film and water retention properties, and shows excellent thermal softening resistance (burning resistance), and a method of producing the same.
In order to achieve the above object, an aluminum alloy sheet for a lithographic printing plate according to claim 1 comprises 0.1 to 1.5% of Mg, 0.5% or less 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/m².
An aluminum alloy sheet for a lithographic printing plate according to claim 2 comprises 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/m².
In the aluminum alloy sheet according to claim 2, 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 (mm²).
In the aluminum alloy sheet according to claim 2 or 3, the quantity of Fe in solid solution (the amount of Fe dissolved) in the aluminum alloy sheet is 20 to 100 ppm.
In the aluminum alloy sheet according to any one of claims 2 to 4, 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.
In the aluminum alloy sheet according to any one of claims 1 to 5, 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 (mm²).
The aluminum alloy sheet according to any one of claims 1 to 6 further comprises more than 0.05% and 0.3% or less of Mn.
In the aluminum alloy sheet according to any one of claims 1 to 7, 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.
The aluminum alloy sheet according to any one of claims 1 to 8 further comprises one or more elements selected from Pb, In, Sn, and Ga in an amount of 0.005 to 0.05% in total.
The aluminum alloy sheet according to any one of claims 3 to 9 has a 0.2% proof stress of 120 MPa or more after being subjected to a heat treatment at 270° C. for seven minutes.
A method of producing an aluminum alloy sheet for a lithographic printing plate according to claim 11 comprises casting an aluminum alloy having the composition according to any one of claims 2, 7, and 9 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.
A method of producing an aluminum alloy sheet for a lithographic printing plate according to claim 12 comprises casting an aluminum alloy having the composition according to any one of claims 2, 7, and 9 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.
A method of producing an aluminum alloy sheet for a lithographic printing plate according to claim 13 comprises casting an aluminum alloy having the composition according to any one of claims 2, 7, and 9 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 subjected to the homogenization treatment 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.
A method of producing the aluminum alloy sheet according to claim 14 is a method of producing the aluminum alloy sheet according to claim 1 or 2, the method comprising subjecting the aluminum alloy sheet to final cold rolling using a rolling oil with a viscosity of 1 to 6 cSt.
A method of producing the aluminum alloy sheet according to claim 15 is a method of producing the aluminum alloy sheet according to claim 1 or 2, 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”.
A method of producing the aluminum alloy sheet according to claim 16 is 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 6 cSt.
A method of producing the aluminum alloy sheet according to claim 17 is 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”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a wiping method for measuring the amount of aluminum powder.

FIG. 2 is a flowchart showing a phenol residue analysis method for measuring the Fe content and the Si content of intermetallic compounds.

BEST MODE FOR CARRYING OUT THE INVENTION

The meanings and the reasons relating to the limitations on the alloy components of the aluminum alloy sheet for a lithographic printing plate according to the present invention are given below. Specifically, most Mg is dissolved in aluminum to improve strength and thermal softening resistance. The term “strength” used herein refers to the tensile strength of a printing plate support at room temperature. The strength is preferably 160 MPa or more in practical applications. The term “thermal softening resistance” used herein is also called burning resistance, and refers to 0.2% proof stress after heating at about 280° C. The thermal softening resistance is preferably 90 MPa or more in practical applications. The Mg content is preferably 0.1 to 1.5%. If the Mg content is less than 0.1%, Mg may not exhibit a sufficient effect. If the Mg content exceeds 1.5%, the uniformity of pits obtained by the surface-roughening treatment may decrease, whereby a non-image area may easily become dirty.
Most Zn is dissolved in aluminum in the same manner as Mg. On the other hand, Zn does not improve strength and thermal softening resistance, but affects an oxide film formed on the surface of aluminum. The oxide film formed on the surface of aluminum is classified as an oxide film formed when allowed to stand at room temperature (spontaneous oxide film) and an oxide film formed during a heat treatment performed in the production process. Zn affects both of these oxide films.
Specifically, an aluminum alloy containing Mg tends to produce an oxide film mainly formed of an Mg oxide (MgO) during a heat treatment such as heating during homogenization or hot rolling or process annealing. Since such an oxide film is active and porous, wettability with a treatment liquid is improved during the electrolytic surface-roughening treatment so that surface roughening is promoted. On the other hand, pits tend to become non-uniform. Zn improves non-uniformity of the surface-roughened structure, and suppresses activation due to the Mg oxide. The Zn content is preferably 0.5% or less. If the Zn content exceeds 0.5%, an effect of suppressing activation due to the Mg oxide may increase so that surface roughening may become non-uniform. Moreover, since coarse intermetallic compounds tend to be produced, large pits may be formed during the electrolytic treatment, whereby surface-roughening uniformity may be further impaired. The Zn content is more preferably more than 0.05% and 0.5% or less, and still more preferably 0.06 to 0.5%.
Fe produces Al—Fe intermetallic compounds, and produces Al—Fe—Si intermetallic compounds together with Si. These compounds are dispersed to refine the recrystallization structure. Pits are uniformly formed from these compounds as starting points and are finely distributed during the electrolytic treatment. The Fe content is preferably 0.1 to 0.6%. If the Fe content is less than 0.1%, the distribution of the compounds may become non-uniform so that an unetched area may occur during the electrolytic treatment. As a result, formation of pits may become non-uniform. If the Fe content exceeds 0.6%, coarse compounds may be produced, whereby the uniformity of the surface-roughened structure may decrease.
Si produces Al—Fe—Si intermetallic compounds together with Fe. These compounds are dispersed to refine the recrystallization structure. Pits are uniformly formed from these compounds as starting points and are finely distributed during the electrolytic treatment. The Si content is preferably 0.03 to 0.15%. If the Fe content is less than 0.03%, the distribution of the compounds may become non-uniform so that an unetched area may occur during the electrolytic treatment. As a result, formation of pits may become non-uniform. If the Si content exceeds 0.15%, coarse compounds may be produced. Moreover, precipitation of Si tends to occur, whereby the uniformity of the surface-roughened structure may decrease.
Cu is easily dissolved in aluminum. When the Cu content is 0.0001 to 0.10%, Cu exhibits a pit refinement effect. If the Cu content exceeds 0.10%, pits may become large and non-uniform during the electrolytic treatment, and an unetched area may occur. In the present invention, the amount of Cu mixed from an ingot employed to obtain the above Fe content and Si content is about 5 to 100 ppm (0.0005 to 0.01%).
Ti refines an ingot structure and crystal grains. As a result, Ti makes formation of pits uniform during the electrolytic treatment to prevent occurrence of streaks during printing using the resulting printing plate. The Ti content is preferably 0.0001 to 0.05%. If the Ti content is less than 0.0001%, Ti may not exhibit a sufficient effect. If the Ti content exceeds 0.05%, coarse Al—Ti compounds may be produced, whereby the surface-roughened structure tends to become non-uniform. When adding B together with Ti in order to refine the ingot structure, the Ti content is preferably 0.01% or less.
Mn increases strength and thermal softening resistance. The Mn content is preferably more than 0.05% and 0.3% or less. If the Mn content is less than 0.05%, Mn may not exhibit a sufficient effect. If the Mn content exceeds 0.3%, coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds may be easily produced, whereby surface roughening during the electrolytic treatment may become non-uniform. The Mn content is more preferably 0.06 to 0.3%.
In the aluminum alloy sheet for a lithographic printing plate according to the present invention, the Mg content and the Zn content preferably satisfy the relationship “4%×Zn %−1.4%≦Mg %≦4×Zn %+0.6%”. If the Mg content and the Zn content satisfy this relationship, formation of pits during the electrolytic treatment becomes more uniform so that an excellent surface-roughened structure can be obtained. If 4×Zn %−1.4%>Mg %, since the Zn content is in excess with respect to the Mg content, an effect of suppressing activation of the Mg oxide increases, whereby formation of pits during the electrolytic treatment may become non-uniform. As a result, formation of a roughened surface may become non-uniform. If Mg %>4×Zn %+0.6%, since the Mg content is in excess with respect to the Zn content, an effect of suppressing activation of the Mg oxide decreases, whereby formation of pits during the electrolytic treatment may become non-uniform. As a result, formation of a roughened surface may become non-uniform.
The aluminum alloy sheet for a lithographic printing plate according to the present invention exhibits improved electrolytic graining properties by adding one or more of Pb, In, Sn, and Ga in an amount of 0.005 to 0.05% in total. Therefore, a desired pit pattern can be obtained with a small amount of electricity. If the total amount of one or more elements selected from the group consisting of Pb, In, Sn, and Ga is less than 0.005%, the effect of addition may be insufficient. If the total amount of one or more elements selected from the group consisting of Pb, In, Sn, and Ga exceeds 0.05%, the shape of pits may be deformed.
The aluminum alloy sheet for a lithographic printing plate according to the present invention is produced by casting the above aluminum alloy by continuous casting or the like to obtain an ingot, homogenizing the resulting ingot, hot-rolling the homogenized product, and cold-rolling the hot-rolled product. It is important to adjust the amount of aluminum powder on the surface of the rolled sheet after final cold rolling to 0.1 to 3.0 mg/m². The term “aluminum powder” used herein refers to an aluminum alloy powder which is produced from the aluminum alloy rolled sheet during final cold rolling and remains on the surface of the rolled sheet. In the aluminum alloy according to the present invention which contains Mg, if the amount of aluminum powder is less than 0.1 mg/m², an effect of preventing abrasion of a coil may be insufficient when the rolled sheet is wound as a coil after final cold rolling. If the amount of aluminum powder exceeds 3.0 mg/m², the aluminum powder may not be removed sufficiently during a degreasing process and remain on the surface of the sheet, whereby formation of pits may become insufficient or non-uniform in the area in which the aluminum powder remains during the electrolytic surface-roughening treatment, and an inferior appearance due to an unetched area or an irregular pattern may occur after electrolytic graining. Moreover, an excessive aluminum powder may contaminate the production line.
In order to adjust the amount of aluminum powder on the surface of the sheet after final cold rolling to the above range, it is necessary to adjust the degree of final cold rolling, the properties of the rolling oil, and the amount of rolling oil supplied depending on the composition in addition to adjusting the components. In particular, the viscosity of the rolling oil used for final cold rolling is important. It is preferable to use a rolling oil with a viscosity of 1 to 6 cSt. If the viscosity is less than 1 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet decreases, a lubrication failure occurs, whereby a large amount of aluminum powder tends to be produced. If the viscosity exceeds 6 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the amount of aluminum powder produced tends to decrease.
If the Mg content (Mg %) of the aluminum alloy and the viscosity p of the rolling oil used for final cold rolling have the relationship (−2×Mg %+2)>ρ, deformation resistance decreases and the amount of rolling oil introduced between the roll and the rolled sheet decreases, whereby a large amount of aluminum powder tends to be produced. If ρ>(−2×Mg %+8), since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the amount of aluminum powder produced tends to decrease.
In the present invention, 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 (mm²), more uniform etch pits can be formed during the electrolytic treatment. If the number of precipitates is less than 10,000 per square millimeter, an unetched area tends to occur, whereby a number of large pits may be formed. If the number of precipitates exceeds 100,000 per square millimeter, it may be difficult to form uniform pits, thereby making it difficult to obtain an aluminum alloy sheet suitable as a lithographic printing support.
In the present invention, burning resistance can be maintained by setting the quantity of Fe in solid solution at 20 to 100 ppm so that uniform etch pits can be formed by the electrolytic treatment. If the amount of Fe dissolved is less than 20 ppm, burning resistance tends to decrease. If the amount of Fe dissolved exceeds 100 ppm, the pit pattern becomes non-uniform due a decrease in electrolytic surface-roughening properties. This makes it difficult to obtain an aluminum alloy sheet suitable as a lithographic printing support.
More uniform pits can be formed by the electrolytic treatment when some or all of the elements of the aluminum alloy sheet according to the present invention 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.
If the content of Fe which forms an intermetallic compound is less than 50% of the total Fe content, since a sufficient number of intermetallic compounds as pit starting points may not be obtained, large pits tend to be formed. If the content of Fe which forms an intermetallic compound exceeds 99.8% of the total Fe content, since a large number of intermetallic compounds are produced, it may be difficult to obtain a uniform pit pattern. If the content of Si which forms an intermetallic compound is less than 5% of the total Si content, since the amount of Si dissolved increases, the potential difference between the matrix and the intermetallic compound decreases, whereby electrochemical solubility decreases. Moreover, precipitation of Si occurs to a large extent, whereby ink contamination tends to occur. If the content of Si which forms an intermetallic compound exceeds 40% of the total Si content, since a large number of intermetallic compounds are produced, it may be difficult to obtain a uniform pit pattern.
The Al—Fe intermetallic compound has an electrochemical solubility higher than that of the Al—Fe—Si intermetallic compound to more positively act as a pit starting point as compared with the Al—Fe—Si intermetallic compound. If the ratio (B %/A %) of the content (B %) of Fe which forms the Al—Fe—Si intermetallic compound to the content (A %) of Fe which forms the Al—Fe intermetallic compound is larger than 0.9, since pit formation efficiency decreases, large pits tend to be formed.
In the present invention, etch pits formed by the electrolytic surface-roughening treatment can be made more uniform by adjusting 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 after final cold rolling to 50 or less per square millimeter (mm²). Since the aluminum alloy according to the present invention contains Mg, large oil pit with a diameter of 30 μm or more tend to remain as large pits after electrolytic graining. If the number of such large pits exceeds 50 per square millimeter (mm²), etch pits formed by the electrolytic surface-roughening treatment tend to become non-uniform.
In order to adjust the number of oil pits with a diameter (circle equivalent diameter) of 30 μm or more to 50 or less per square millimeter (mm²), it is necessary to adjust the degree of final cold rolling, the configuration of the roll, the properties of the rolling oil, and the amount of rolling oil supplied. When using an aluminum alloy which contains Mg and has a relatively high deformation resistance as that of the aluminum alloy according to the present invention, it is preferable to use a roll having a roll surface with an arithmetic average roughness Ra of 0.2 to 0.5 μm during final cold rolling and to perform cold rolling using a rolling oil with a viscosity of 1 to 6 cSt.
If the roll surface has an arithmetic average roughness Ra exceeding 0.5 μm, the oil film breaks due to an increase in local contact pressure in the contact arc length, whereby the metal contact area increases. As a result, a lubrication failure tends to occur. If the arithmetic average roughness Ra is less than 0.2 μm, since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the number of large oil pits may increase. If the viscosity of the rolling oil is less than 1 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet decreases, a lubrication failure occurs. If the viscosity of the rolling oil exceeds 6 cSt, since the amount of rolling oil introduced between the roll and the rolled sheet increases to a large extent, the number of large oil pits may increase.
As the rolling oil used during final cold rolling, it is preferable to use a rolling oil which ensures that the Mg content (Mg %) of the aluminum alloy sheet and the viscosity ρ of the rolling oil satisfy the relationship “ρ≦2×Mg+4”. If ρ>(2×Mg+4), deformation resistance decreases. Moreover, since the amount of rolling oil introduced between the roll and the rolled sheet increases, a number of large pits tend to be formed.
In the present invention, occurrence of an inferior appearance after electrolytic graining due to irregular surface quality and streaks can be suppressed by specifying the grain size with respect to the surface of the sheet. Specifically, the average grain size in the direction perpendicular to the rolling direction with respect to the surface of the sheet is adjusted to be 100 μm or less, and the average grain size in the direction parallel to the rolling direction with respect to the surface of the sheet is adjusted to be 2 to 20 times the average grain size in the direction perpendicular to the rolling direction. If the average grain size in the direction perpendicular to the rolling direction with respect to the surface of the sheet exceeds 100 μm, the surface quality may become irregular. If the average grain size in the direction parallel to the rolling direction with respect to the surface of the sheet is less than twice the average grain size in the direction perpendicular to the rolling direction, the strength necessary for a printing plate support may not be obtained. If the average grain size in the direction parallel to the rolling direction with respect to the surface of the sheet is more than 20 times the average grain size in the direction perpendicular to the rolling direction, streaks may occur.
The aluminum alloy sheet for a lithographic printing plate according to the present invention is produced by casting the above aluminum alloy by continuous casting or the like to obtain an ingot, homogenizing the resulting ingot, hot-rolling the homogenized product, and cold-rolling the hot-rolled product.
It is preferable to face each rolling-side surface of the ingot by 3 to 15 mm. If the amount of scalping is less than 3 mm per side, since coarse crystal grains (coarse crystal) in the vicinity of the ingot surface may be removed to only a small extent, the faced surface may have a non-uniform structure, whereby streaks may occur. If the amount of scalping exceeds 15 mm per side, economic efficiency may be impaired due to a decrease in yield.
When producing the aluminum alloy sheet in which 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 (mm²), the operation from the ingot homogenization treatment to hot rolling is preferably carried out as follows.
The temperature increase rate of the ingot during the homogenization treatment is preferably 20 to 60° C./hr. This is effective to obtain the above precipitate distribution. If the temperature increase rate is less than 20° C./hr, precipitation proceeds so that the diameter of the precipitate tends to exceed 1 μm and the number of precipitates decreases. Moreover, economic efficiency may be impaired since heating requires time. If the temperature increase rate exceeds 60° C./hr, it is difficult to obtain specific precipitates since precipitation does not proceed due to too high a temperature increase rate.
The homogenization treatment is preferably performed at 450 to 580° C. for one hour or more. The homogenization treatment causes Fe and Si which have been dissolved to supersaturation to uniformly precipitate. As a result, etch pits formed during the electrolytic treatment have a minute circular shape, whereby plate wear is improved. If the homogenization treatment temperature is less than 450° C., precipitation of Fe and Si which serve as pit starting points may be insufficient so that an unetched area may be formed during the electrolytic treatment. As a result, the pit pattern may become non-uniform. If the homogenization treatment temperature exceeds 580° C., since the quantity of Fe in solid solution increases, the number of minute precipitates which serve as pit starting points decreases. If the homogenization treatment time is less than one hour, precipitation of Fe and Si becomes insufficient, whereby the pit pattern may become non-uniform.
The hot rolling start temperature is preferably 400 to 520° C. If the hot rolling start temperature is less than 400° C., precipitation of Fe and Si which serve as pit starting points may be insufficient so that an unetched area may be formed during the electrolytic treatment. As a result, the pit pattern may become non-uniform. Moreover, since the degree of rolling cannot be increased due to an increase in deformation resistance, the number of rolling passes increases, whereby economic efficiency may be impaired. If the hot rolling start temperature exceeds 520° C., since coarse recrystallized grains are produced during hot rolling, streaks tend to occur due to the streak-shaped non-uniform structure.
The hot rolling finish temperature is preferably 320 to 400° C. If the hot rolling finish temperature is less than 320° C., recrystallization may occur only partially, whereby an unrecrystallized area may cause streaks. Moreover, since the amount of strain accumulated after final cold rolling may increase, the recrystallizing temperature may decrease, whereby burning resistance may decrease. If the hot rolling finish temperature exceeds 400° C., recrystallization occurs over the entire surface. However, since coarse crystal grains are produced, streaks may occur. The thickness of the sheet when finishing hot rolling is preferably 5 mm or less. If the thickness of the sheet when finishing hot rolling is 5 mm or more, the rolling rate during hot rolling may become insufficient so that the amount of strain introduced may decrease, whereby recrystallized grains may become coarse.
When producing the aluminum alloy sheet in which the quantity of Fe in solid solution is adjusted to 20 to 100 ppm, the operation from the ingot homogenization treatment to hot rolling is preferably carried out as follows.
The temperature increase rate of the ingot during the homogenization treatment is preferably 20 to 60° C./hr. This is effective to obtain the above specific dissolution state. If the temperature increase rate is less than 20° C./h, the amount of dissolution may decrease to a large extent due to an increase in the amount of precipitation. Moreover, economic efficiency may be impaired since heating requires time. If the temperature increase rate exceeds 60° C./hr, it is difficult to obtain the above specific dissolution state since precipitation does not proceed due to too high a temperature increase rate.
The homogenization treatment is preferably performed at 450 to 580° C. for one hour or more. By the homogenization treatment, Fe and Si which have been dissolved to supersaturation, are uniformly and minutely precipitated. As a result, etch pits formed during the electrolytic treatment have a minute circular shape, whereby plate wear is improved. If the homogenization treatment temperature is less than 450° C., precipitation of Fe and Si (i.e., a reduction in the quantity of Fe and Si in solid solution) may be insufficient. As a result, the pit pattern may become non-uniform. If the homogenization treatment temperature exceeds 580° C., since the quantity of Fe in solid solution may increase to a large extent, the pit pattern may become non-uniform. If the homogenization treatment time is less than one hour, the dissolution state of Fe and Si in the longitudinal direction and the width direction becomes non-uniform, whereby the pit pattern may become non-uniform.
It is possible to control precipitation of Fe and Si by decreasing the temperature to room temperature after the homogenization treatment, whereby the desired dissolution state can be obtained.
The hot rolling start temperature is preferably 350 to 500° C. If the hot rolling start temperature is less than 350° C., since the degree of rolling cannot be increased due to an increase in deformation resistance, the number of rolling passes increases, whereby economic efficiency may be impaired. If the hot rolling start temperature exceeds 500° C., since coarse recrystallized grains are produced during hot rolling, streaks tend to occur due to the streak-shaped non-uniform structure.
The hot rolling finish temperature is preferably 300 to 380° C. If the hot rolling finish temperature is less than 300° C., recrystallization may occur only partially, whereby an unrecrystallized area may cause streaks. Moreover, since the amount of strain accumulated after final cold rolling may increase, the recrystallizing temperature may decrease, whereby burning resistance may decrease. If the hot rolling finish temperature exceeds 380° C., recrystallization occurs over the entire surface. However, since coarse crystal grains are produced, streaks may occur. The thickness of the sheet when finishing hot rolling is preferably 5 mm or less. If the thickness of the sheet when finishing hot rolling is 5 mm or more, the rolling rate during hot rolling may become insufficient so that the amount of strain introduced may decrease, whereby recrystallized grains may become coarse.
When producing the aluminum alloy sheet in which 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, the operation from the ingot homogenization treatment to hot rolling is preferably carried out as follows.
The homogenization treatment is preferably performed at 450 to 580° C. for three hours or more. The homogenization treatment causes Fe and Si which have been dissolved to supersaturation to uniformly precipitate. As a result, etch pits formed during the electrolytic treatment have a minute circular shape, whereby plate wear is improved. If the homogenization treatment temperature is less than 450° C., precipitation of Al—Fe—Si intermetallic compounds which serve as pit starting points to only a small extent may proceed so that large pits may be formed due to a decrease in pit formation efficiency. As a result, the pit pattern may become non-uniform. If the homogenization treatment temperature exceeds 580° C., since the quantity of Fe in solid solution increases, precipitation of Al—Fe intermetallic compounds which serve as pit starting points to a large extent decreases. If the homogenization treatment time is less than three hours, precipitation of Fe and Si becomes insufficient, whereby the pit pattern may become non-uniform.
It is preferable to decrease the temperature of the ingot to the hot rolling start temperature at a temperature decrease rate of 20 to 60° C./hr after the homogenization treatment, and to start hot rolling at 400 to 500° C. Precipitation proceeds when decreasing the temperature of the ingot after the homogenization treatment. In particular, precipitation of not only Fe but also Si proceeds when decreasing the temperature of the ingot to 400 to 450° C. If the temperature decrease rate is less than 20° C./hr, precipitation of Al—Fe—Si intermetallic compounds proceeds to a large extent. When precipitation proceeds further, the diameter of the precipitate may exceed 1 μm and the number of precipitates decreases. Moreover, economic efficiency may be impaired since heating requires time. If the temperature decrease rate exceeds 60° C./hr, the period of time for precipitation may be insufficient. Moreover, since the temperature of the ingot may become non-uniform, precipitation of Fe and Si also may become non-uniform. As a result, recrystallization during the subsequent hot rolling may become non-uniform, whereby streaks tend to occur.
The hot rolling start temperature is preferably 400 to 500° C. If the hot rolling start temperature is less than 400° C., since the degree of rolling cannot be increased due to an increase in deformation resistance, the number of rolling passes increases, whereby economic efficiency may be impaired. If the hot rolling start temperature exceeds 500° C., since coarse recrystallized grains are produced during hot rolling, streaks tend to occur due to the streak-shaped non-uniform structure.
The hot rolling finish temperature is preferably 300 to 400° C. If the hot rolling finish temperature is less than 300° C., recrystallization may occur only partially, whereby an unrecrystallized area may cause streaks. Moreover, since the amount of strain accumulated after final cold rolling may increase, the recrystallizing temperature may decrease, whereby burning resistance may decrease. If the hot rolling finish temperature exceeds 400° C., recrystallization occurs over the entire surface. However, since coarse crystal grains are produced, an irregular pattern or streaks may occur. The thickness of the sheet when finishing hot rolling is preferably 5 mm or less. If the thickness of the sheet when finishing hot rolling is 5 mm or more, the rolling rate during hot rolling may become insufficient so that the amount of strain introduced may decrease, whereby recrystallized grains may become coarse.
The aluminum alloy sheet subjected to hot rolling as described above is cold-rolled without being subjected to process annealing. Cold rolling is performed after hot rolling in order to provide a strength which prevents breakage when winding a support around a plate cylinder and adjusting the length of crystal grains produced during hot rolling or immediately after hot rolling in the direction parallel to the rolling direction when applying the aluminum alloy sheet as a lithographic printing support. The degree of rolling is preferably 50 to 98%. If the degree of rolling is less than 50%, it is difficult to provide a strength which prevents breakage when winding the support around a plate cylinder. If the degree of rolling exceeds 98%, crystal grains produced after hot rolling extend to a large extent along the direction parallel to the rolling direction, whereby streaks tend to occur. After cold rolling, finish cold rolling may be performed using a roll provided with a special pattern on the surface to obtain an aluminum alloy sheet having a surface roughness indicated by an arithmetic average roughness Ra of 0.15 to 0.30 μm, an average elevation/depression dimension RSm of 50 μm or less in the direction perpendicular to the rolling direction, a maximum depression depth Rv of 1 μm or less, and a maximum height Rz of 1.5 to 2.5 μm.
The amount of aluminum powder on the surface of the sheet, the precipitate distribution, the quantity of Fe in solid solution, the relationship between the intermetallic compounds and the Fe content and the Si content, the oil pit distribution, and the crystal grain size as specified above are obtained by combining the above composition and production steps, whereby a 0.2% proof stress after a heat treatment at 270° C. for seven minutes of 120 MPa or more is achieved. The above strength properties are important for a printing plate support. If the 0.2% proof stress is less than 120 MPa, the secured portion of the printing plate may be deformed or damaged during printing, whereby incorrect printing or the like may occur.

EXAMPLES

Examples according to the present invention are described below in contrast with comparison examples to demonstrate the effects of the present invention. Note that these examples illustrate only preferred embodiments of the present invention. The present invention is not limited to these examples.

Example 1 and Comparison Example 1

As a specimen aluminum alloy, an aluminum alloy having a composition shown in Table 1 was melted and cast. Each rolling side of the resulting ingot was faced by 5 mm to reduced to the thickness of the ingot to 500 mm. The ingot was heated to 530° C. at a temperature increase rate of 35° C./hr. The ingot was then subjected to homogenization at 530° C. for 3.5 hours.
The temperature of the ingot was decreased to 515° C. (hot rolling start temperature) at a temperature decrease rate of 35° C./hr from the homogenization treatment temperature (530° C.). The ingot was then hot-rolled to a thickness of 3 mm. Hot rolling was finished at 346° C. The hot-rolled product was cold-rolled to a thickness of 0.3 mm without being subjected to process annealing. The arithmetic average roughness Ra of a roll used for cold rolling was 0.3 μm, and the viscosity of a rolling oil was 3 cSt. In Table 1, a value outside the condition according to the present invention is underlined. A case where the relational equation “(4×Zn %−1.4%)≦Mg %≦(4×Zn %+0.6%)” relating to the Mg content and the Zn content was satisfied is indicated by “Good”, and a case where the relational equation “(4×Zn %−1.4%)≦Mg %≦(4×Zn %+0.6%)” relating to the Mg content and the Zn content was not satisfied is indicated by “Bad”.
The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the following methods. The results are shown in Table 2. The burning resistance of the resulting aluminum alloy sheet was evaluated, and the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling was observed. The results are shown in Table 3. In Table 2, the term “crystal length” indicates the crystal grain size (GL) in the direction parallel to the rolling direction with respect to the surface of the sheet, the term “crystal width” indicates the crystal grain size (GT) in the direction perpendicular to the rolling direction, and the term “ratio” indicates the ratio (GL/GT) of the crystal grain size (GL) to the crystal grain size (GT). A value outside the condition according to the present invention is underlined.
Measurement of amount of aluminum powder: As a quantitative analysis of residual powder on the surface of the sheet, a specific area of the surface of the sheet was wiped off with an absorbent cotton immersed in a solvent, and the aluminum content of the absorbent cotton was measured. FIG. 1 shows a wiping method.
Measurement of number of precipitates with a diameter (circle equivalent diameter) of 0.1 to 1.0 μm: After degreasing and washing the surface of the aluminum alloy sheet, the surface of the aluminum alloy sheet was etched for 10 seconds using an aqueous solution (Keller's reagent) prepared by mixing nitric acid, hydrofluoric acid, and hydrochloric acid, and was photographed using an optical microscope at a magnification of 1000. The particle diameter distribution of precipitates was measured using an image analyzer (Luzex 500 manufactured by Nireco Corporation). The diameter of the precipitate was converted into the diameter of a circle having the same area as that of the precipitate in the photograph (i.e., circle equivalent diameter), and the intermetallic compound distribution density was determined from the results.
Measurement of number of oil pits: After degreasing and washing the surface of the aluminum alloy sheet, the surface of the aluminum alloy sheet was observed using a scanning electron microscope (SEM) at a magnification of 500. The number of oil pits and their distribution were measured by an intercept method.
Measurement of crystal grain size: After degreasing and washing the surface of the aluminum alloy sheet, the surface of the aluminum alloy sheet was mirror-polished and then anodized using Parker's reagent. The crystal grains were observed in a polarization mode of an optical microscope, and the crystal grain size in the direction perpendicular or parallel to the rolling direction was determined using an intercept method.
Evaluation of burning resistance: As an index of thermal softening resistance, the aluminum sheet was heated in an atmospheric furnace maintained at 270° C. for seven minutes, and was subjected to a tensile test to measure the 0.2% proof stress. The burning resistance of a support was evaluated based on the 0.2% proof stress. The proof stress was measured in the direction (direction L) parallel to the rolling direction of the aluminum alloy sheet. A case where the 0.2% proof stress after heating at 270° C. for seven minutes was 120 MPa or more was evaluated as “Good”, and a case where the 0.2% proof stress was less than 120 MPa was evaluated as “Bad”.
Observation of the presence or absence of coil scratches due to rubbing: A case where scratches due to rubbing were observed in a specific area of the surface of the sheet with the naked eye was evaluated as “Bad”, and a case where scratches due to rubbing were not observed was evaluated as “Good”.
The resulting aluminum alloy sheet was subjected to degreasing (solution: 5% sodium hydroxide, temperature: 60° C., time: 10 seconds), neutralization (solution: 10% nitric acid, temperature: 20° C., time: 30 seconds), an alternating-current electrolytic surface-roughening treatment (solution: 2.0% hydrochloric acid, temperature: 25° C., frequency: 50 Hz, current density: 60 A/dm², time: 20 seconds), a desmut process (solution: 5% sodium hydroxide, temperature: 60° C., time: 5 seconds), and an anodizing process (solution: 30% sulfuric acid, temperature: 20° C., time: 60 seconds). The aluminum alloy sheet was then washed with water, dried, and cut to a specific size to prepare a specimen.
The presence or absence of an irregular pattern and streaks was observed for each specimen. The surface of the specimen was observed using a scanning electron microscope (SEM) at a magnification of 500. The surface of the specimen was photographed so that the field of view was 0.04 mm². Occurrence of an unetched area and uniformity of etch pits were evaluated based on the resulting photograph. The results are shown in Table 3.
Observation of the presence or absence of irregular pattern: A case where a significant irregular pattern was observed on the surface of the specimen with the naked eye was evaluated as “Bad”, a case where no significant irregular pattern was observed was evaluated as “Good”, and a case where no irregular pattern was observed was evaluated as “Excellent”.
Observation of the presence or absence of streaks: A case where streaks were observed on the surface of the specimen with the naked eye was evaluated as “Bad”, and a case where streaks were not observed was evaluated as “Good”.
Evaluation of occurrence of unetched area: A case where the percentage of an unetched area exceeded 20% was evaluated as “Bad”, a case where the percentage of an unetched area was 15 to 20% was evaluated as “Good”, and a case where the percentage of an unetched area was less than 15% was evaluated as “Excellent”.
Evaluation of uniformity of etch pits: A case where the area ratio of large pits with a circle equivalent diameter exceeding 10 μm was more than 10% with respect to all pits was evaluated as “Bad”, a case where the area ratio was 5 to 10% was evaluated as “Good”, and a case where the area ratio was less than 5% was evaluated as “Excellent”.

	TABLE 1

	Composition (wt %)

Pb +

Relational

In +

Alloy

Mg

Zn

Fe

Si

Cu

Ti

Mn

equation

Pb

In

Sn

Ga

Sn + Ga

Remarks

A	0.22	0.110	0.31	0.06	0.0050	0.0130	0.002	Good	0.0002	0.0003	0.0003	0.010	0.0108	Example
B	0.13	0.070	0.16	0.03	0.0002	0.0007	0.006	Good	0.0006	0.0006	0.0001	0.013	0.0143	Example
C	0.51	0.200	0.28	0.09	0.0021	0.0140	0.080	Good	0.0003	0.0009	0.0004	0.019	0.0206	Example
D	1.40	0.120	0.40	0.07	0.0007	0.0053	0.003	Bad	0.0004	0.0002	0.0010	0.014	0.0156	Example
E	0.21	0.450	0.33	0.07	0.0009	0.015	0.006	Bad	0.0031	0.0011	0.0011	0.014	0.0193	Example
F	0.002	0.0003	0.30	0.06	0.0008	0.0200	0.003	Good	0.0001	0.0016	0.0006	0.017	0.0193	Comparative Example
G	2.54	0.490	0.25	0.05	0.0300	0.0310	0.008	Good	0.0015	0.0001	0.0009	0.020	0.0225	Comparative Example
H	1.40	0.650	0.31	0.07	0.0011	0.0140	0.003	Good	0.0011	0.0000	0.0008	0.021	0.0229	Comparative Example
I	0.12	0.140	0.06	0.01	0.0730	0.0009	0.010	Good	0.0017	0.0004	0.0018	0.016	0.0199	Comparative Example
J	0.92	0.310	0.81	0.21	0.0263	0.0072	0.180	Good	0.0005	0.0003	0.0023	0.018	0.0211	Comparative Example
K	0.21	0.100	0.30	0.07	0.1500	0.0009	0.180	Good	0.0019	0.0010	0.0007	0.020	0.0236	Comparative Example
L	0.67	0.230	0.25	0.13	0.0110	0.1249	0.220	Good	0.0010	0.0005	0.0001	0.017	0.0186	Comparative Example
M	1.22	0.420	0.37	0.05	0.0140	0.0101	0.410	Good	0.0005	0.0006	0.00042	0.0009	0.0143	Comparative Example
O	1.10	0.39	0.12	0.11	0.0067	0.0005	0.160	Good	0.0089	0.0092	0.0055	0.040	0.0636	Comparative Example

TABLE 2

								Number of oil
			Viscosity			Amount of		pits with	Crystal	Crystal
			ρ of	Relationship I	Relationship II	aluminum		diameter of 30 μm	length	width
		Ra of roll	rolling oil	between	between	powder	Precipitate	or more	GL	GT	Ratio
Specimen	Alloy	(μm)	(cSt)	Mg and ρ	Mg and ρ	mg/m²	(/mm²)	(/mm²)	(μm)	(μm)	GL/GT

1	A	0.3	3	Good	Good	2.50	65520	40	678	68	10.0
2	B	0.3	3	Good	Good	2.80	28040	45	810	79	10.3
3	C	0.3	3	Good	Good	2.01	73000	35	649	64	10.1
4	D	0.3	3	Good	Good	0.12	67860	8	676	63	10.7
5	E	0.3	3	Good	Good	2.62	71150	38	667	70	9.5
6	F	0.3	3	Bad	Good	4.02	62660	75	729	77	9.5
7	G	0.3	3	Bad	Good	0.02	60100	2	740	70	10.6
8	H	0.3	3	Good	Good	0.25	60000	10	730	70	10.4
9	I	0.3	3	Good	Good	3.06	6980	46	1200	123	9.8
10	J	0.3	3	Good	Good	1.08	159980	21	552	51	10.8
11	K	0.3	3	Good	Good	2.39	66250	42	675	62	10.9
12	L	0.3	3	Good	Good	1.67	57700	33	613	59	10.4
13	M	0.3	3	Good	Good	0.70	80310	20	580	57	10.2
14	O	0.3	3	Good	Good	2.30	60070	30	1110	93	11.9

Note:
Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad)
Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 3

	Burning resistance
Specimen	(MPa)	Scratch	Unetched area	Pit uniformity	Irregular pattern	Streaks

1	149	Good	Excellent	Excellent	Good	Good
2	130	Good	Excellent	Excellent	Good	Good
3	170	Good	Excellent	Excellent	Good	Good
4	226	Good	Good	Good	Good	Good
5	140	Good	Good	Good	Good	Good
6	85	Good	Bad	Bad	Bad	Good
7	241	Bad	Good	Bad	Good	Good
8	220	Good	Good	Bad	Good	Good
9	98	Good	Bad	Bad	Bad	Good
10	219	Good	Good	Bad	Good	Good
11	148	Good	Bad	Bad	Good	Good
12	183	Good	Good	Bad	Good	Good
13	209	Good	Good	Bad	Good	Good
14	175	Good	Good	Bad	Good	Good

As shown in Table 3, specimens No. 1 to No. 5 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface.
On the other hand, specimen No. 6 exhibited inferior burning resistance due to low Mg content. Moreover, the amount of aluminum powder increased, and formation of pits became non-uniform. An inferior appearance due to an unetched area and an irregular pattern occurred after electrolytic graining. Specimen No. 7 exhibited inferior pit uniformity due to high Mg content. Moreover, the amount of aluminum powder decreased, and coil scratches due to rubbing occurred. Specimen No. 8 was non-uniformly surface-roughened due to high Zn content. Specimen No. 9 had a small number of precipitates due to low Fe content and low Si content. The distribution of Al—Fe intermetallic compounds and Al—Fe—Si intermetallic compounds became non-uniform, whereby formation of pits became non-uniform. Moreover, the amount of precipitation and the amount of dissolution decreased due to low Fe content, resulting in insufficient burning resistance. Specimen No. 10 produced a large number of precipitates due to high Fe content and high Si content to produce coarse compounds. Therefore, uniformity of the surface-roughened structure decreased. In specimen No. 11, pits became large and non-uniform and an unetched area occurred during the electrolytic treatment due to high Cu content. Specimen No. 12 produced coarse Al—Ti compounds due to high Ti content, whereby the surface-roughened structure became non-uniform. Specimen No. 13 produced coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds due to high Mn content, whereby surface roughening during the electrolytic treatment became non-uniform. In specimen No. 14, the shape of pits was deformed and became non-uniform since the total amount of Pb, In, Sn, and Ga exceeded 0.05%.

Example 2 and Comparative Example 2

An ingot of an aluminum alloy A cast in Example 1 was subjected to scalping of rolling surface, homogenization, and hot rolling under conditions shown in Table 4. The hot-rolled product was cold-rolled to a thickness shown in Table 4 without being subjected to process annealing. Table 5 shows the surface roughness of a roll and the viscosity of a rolling oil used for cold rolling. In Tables 4 and 5, a value outside the condition according to the present invention is underlined.
The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The results are shown in Table 5. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 6.

TABLE 4

		Cold
Homogenization treatment	Hot rolling	rolling

	Amount of	Temperature			Temperature	Start	Finish	Sheet	Sheet
	scalping	increase rate	Temperature	Time	decrease rate	temperature	temperature	thickness	thickness
Specimen	(mm/side)	(° C./hr)	(° C.)	(hr)	(° C./hr)	(° C.)	(° C.)	(mm)	(mm)	Remarks

15	5	37	538	3	35	470	355	3	0.3	Example
16	10	40	460	5	35	384	336	5	0.3	Example
17	1.5	31	502	2	35	450	340	2	0.3	Comparative Example
18	6	10	580	4	35	491	370	4	0.3	Comparative Example
19	7	70	580	4	35	479	366	4	0.3	Comparative Example
20	7	34	410	3	35	400	329	3	0.3	Comparative Example
21	8	35	610	3	35	411	333	3	0.3	Comparative Example
22	4	37	538	0.5	35	473	350	3	0.3	Comparative Example
23	9	29	595	5	35	331	272	3	0.3	Comparative Example
24	9	27	598	5	35	515	420	3	0.3	Comparative Example
25	12	40	460	5	35	388	341	6.5	0.3	Comparative Example
26	5	35	545	3	35	470	355	3	0.3	Comparative Example
27	5	35	545	3	35	465	339	3	0.3	Comparative Example
28	5	35	545	3	35	468	342	3	0.3	Comparative Example
29	5	35	545	3	35	475	332	3	0.3	Comparative Example

TABLE 5

							Number of oil
		Viscosity			Amount of		pits with
	Ra	ρ of	Relationship I	Relationship II	aluminum		diameter of 30 μm	Crystal	Crystal
	of roll	rolling oil	between	between	powder	Precipitate	or more	length GL	width GT	Ratio
Specimen	(μm)	(cSt)	Mg and ρ	Mg and ρ	(mg/m²)	(/mm²)	(/mm²)	(μm)	(μm)	GL/GT

15	0.3	3	Good	Good	2.42	67920	41	641	62	10.3
16	0.3	3	Good	Good	1.95	97850	32	1621	90	18.0
17	0.3	3	Good	Good	2.64	76400	47	368	51	7.2
18	0.3	3	Good	Good	1.50	113700	32	1052	79	13.3
19	0.3	3	Good	Good	1.78	8080	29	979	76	12.9
20	0.3	3	Good	Good	2.88	9160	33	910	89	10.2
21	0.3	3	Good	Good	2.35	4520	22	822	76	10.8
22	0.3	3	Good	Good	1.64	5910	18	626	66	9.5
23	0.3	3	Good	Good	2.74	54220	35	Not	Not	—
								recrystallized	recrystallized
24	0.3	3	Good	Good	2.56	60030	42	1190	125	9.5
25	0.3	3	Good	Good	1.39	81250	31	4115	189	21.8
26	0.05	3	Good	Good	0.07	63600	71	400	54	7.4
27	0.6	3	Good	Good	10.05	69450	6	512	55	9.3
28	0.3	0.5	Bad	Good	3.80	60900	6	620	63	9.8
29	0.3	7	Bad	Bad	0.04	7170	96	385	50	7.7

Note:
Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad)
Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

TABLE 6

	Burning resistance
Specimen	(MPa)	Scratch	Unetched area	Pit uniformity	Irregular pattern	Streaks

15	143	Excellent	Excellent	Excellent	Good	Good
16	126	Good	Good	Good	Good	Good
17	140	Excellent	Good	Good	Good	Bad
18	94	Good	Good	Bad	Good	Good
19	156	Good	Bad	Bad	Good	Good
20	160	Excellent	Bad	Bad	Good	Good
21	159	Excellent	Bad	Bad	Good	Good
22	166	Good	Bad	Bad	Good	Good
23	89	Excellent	Good	Good	Bad	Bad
24	165	Excellent	Good	Good	Bad	Good
25	125	Good	Good	Good	Bad	Good
26	130	Bad	Good	Bad	Good	Good
27	125	Excellent	Bad	Bad	Bad	Good
28	146	Excellent	Bad	Bad	Bad	Good
29	135	Bad	Good	Bad	Good	Good

As shown in Table 6, specimens No. 15 and No. 16 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. Specimen No. 17 produced streaks due to a small amount of scalping. In specimen No. 18, since the temperature increase rate of the ingot during the homogenization treatment was low, the diameter of the precipitates exceeded 1 μm and the number of precipitates decreased. Formation of pits was non-uniform due to the presence of an unetched area. Moreover, since the amount of precipitation increased to a large extent, the quantity of Fe in solid solution became insufficient, whereby burning resistance decreased. In specimen No. 19, since the temperature increase rate of the ingot during the homogenization treatment was high, precipitation did not proceed sufficiently so that pit starting points were insufficiently formed. An unetched area was formed during the electrolytic treatment, and uniformity of pits was impaired. In specimen No. 20, since the homogenization treatment temperature was low, precipitation of Fe and Si which serve as pit starting points was insufficient so that an unetched area was formed during the electrolytic treatment. As a result, the pit pattern became non-uniform. In specimen No. 21, since the homogenization treatment temperature was high, The quantity of Fe in solid solution increased. As a result, the number of minute precipitates which serve as pit starting points decreased. An unetched area was formed, and the pit pattern became non-uniform. In specimen No. 22, since the homogenization treatment time was short, precipitation of Fe and Si became insufficient, whereby the pit pattern became non-uniform due to formation of an unetched area. In specimen No. 22, since the hot rolling start temperature was low, the hot rolling finish temperature decreased. As a result, recrystallization occurred only partially, whereby streaks occurred. Moreover, since the amount of strain accumulated after final cold rolling increased, the recrystallizing temperature decreased, whereby burning resistance decreased. In specimen No. 24, since the hot rolling start temperature was high, the hot rolling finish temperature increased. Although recrystallization occurred over the entire surface, coarse crystal grains were formed, whereby irregular surface quality and streaks occurred. In specimen No. 25, since the thickness of the sheet when finishing hot rolling was large, the rolling rate during hot rolling became insufficient so that the amount of strain introduced decreased, whereby recrystallized grains became coarse. As a result, the surface quality became irregular. In specimen No. 26, since the arithmetic average roughness of the roll surface was small, the amount of rolling oil introduced between the roll and the rolled sheet increased to a large extent, whereby the number of large oil pits increased. As a result, etch pits formed during the electrolytic surface-roughening treatment became non-uniform. Moreover, since the amount of powder decreased, scratches due to rubbing were observed. In specimen No. 27, since the arithmetic average roughness of the roll surface was large, the amount of rolling oil introduced between the roll and the rolled sheet decreased, whereby a lubrication failure occurred. As a result, the amount of powder increased, whereby formation of pits became non-uniform. An inferior appearance due to an unetched area or an irregular pattern occurred after electrolytic graining. In specimen No. 27, since the viscosity of the rolling oil was low, the amount of rolling oil introduced between the roll and the rolled sheet decreased, whereby a lubrication failure occurred. As a result, the amount of aluminum powder increased, whereby formation of pits became non-uniform. An inferior appearance due to an unetched area or an irregular pattern occurred after electrolytic graining. In specimen No. 29, since the viscosity of the rolling oil was high, the amount of rolling oil introduced between the roll and the rolled sheet increased to a large extent, whereby the number of large oil pits increased. As a result, etch pits formed during the electrolytic surface-roughening treatment became non-uniform. Moreover, since the amount of powder decreased, coil scratches due to rubbing were observed.

Example 3 and Comparative Example 3

Each rolling side of an ingot of an aluminum alloy (Table 1) cast in Example 1 was faced by 5 mm to reduce the thickness of the ingot to 500 mm. The ingot was heated to 530° C. at a temperature increase rate of 35° C./hr. The ingot was then subjected to homogenization at 530° C. for 3.5 hours.
The ingot was heated to 469° C. (hot rolling start temperature) and was then hot-rolled to a thickness of 3 mm. Hot rolling was finished at 353° C. The hot-rolled product was cold-rolled to a thickness of 0.3 mm without being subjected to process annealing. The arithmetic average roughness Ra of a roll used for cold rolling was 0.3 μm, and the viscosity of a rolling oil was 3 cSt.
The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The quantity of Fe in solid solution was measured according to the following method. The results are shown in Table 7. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 8. In Table 7, a value outside the condition according to the present invention is underlined.
Measurement of the quantity of Fe in solid solution: The aluminum alloy sheet was dissolved in hot phenol, and the Fe content of the filtrate was measured. The details are described in “Measurement of amount of dissolution by wet chemical analysis” in Light Metal vol. 50 (2000), pages 518 to 526.

TABLE 7

							Number of oil
		Viscosity			Amount of		pits with
		ρ of	Relationship I	Relationship II	aluminum		diameter of 30 μm	Crystal	Crystal
	Ra of roll	rolling oil	between	between	powder	Precipitate	or more	length GL	width GT	Ratio
Specimen	(μm)	(cSt)	Mg and ρ	Mg and ρ	(mg/m²)	(/mm²)	(/mm²)	(μm)	(μm)	GL/GT

30	0.3	3	Good	Good	2.35	70030	41	35	63	10.4
31	0.3	3	Good	Good	2.78	31200	30	46	75	10.7
32	0.3	3	Good	Good	1.92	73510	53	38	65	9.7
33	0.3	3	Good	Good	0.10	66780	92	7	61	11.3
34	0.3	3	Good	Good	2.71	73150	47	40	70	9.4
35	0.3	3	Bad	Good	4.20	60060	30	88	67	10.6
36	0.3	3	Bad	Good	0.02	62390	26	2	73	10.4
37	0.3	3	Good	Good	0.30	60840	44	15	70	10.6
38	0.3	3	Good	Good	3.24	7120	15	51	135	10.7
39	0.3	3	Good	Good	1.00	167000	120	20	48	10.9
40	0.3	3	Good	Good	2.51	65110	30	40	62	10.6
41	0.3	3	Good	Good	1.59	59430	28	29	59	10.0
42	0.3	3	Good	Good	0.66	81000	86	23	57	10.5
43	0.3	3	Good	Good	2.30	62070	21	34	97	10.8

Note:
Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad)
Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

30	140	Good	Excellent	Excellent	Good	Good
31	132	Good	Excellent	Excellent	Good	Good
32	166	Good	Excellent	Excellent	Good	Bad
33	210	Good	Good	Good	Good	Good
34	138	Good	Good	Good	Good	Good
35	88	Good	Bad	Bad	Bad	Good
36	243	Bad	Good	Bad	Good	Good
37	205	Good	Good	Bad	Good	Good
38	95	Good	Bad	Bad	Bad	Good
39	200	Good	Good	Bad	Good	Good
40	142	Good	Bad	Bad	Good	Good
41	189	Good	Good	Bad	Good	Good
42	209	Good	Good	Bad	Good	Good
43	171	Good	Good	Bad	Good	Good

As shown in Table 8, specimens No. 30 to No. 34 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. On the other hand, specimen No. 35 exhibited inferior burning resistance due to low Mg content. Moreover, the amount of aluminum powder increased, and formation of pits became non-uniform. An inferior appearance due to an unetched area and an irregular pattern occurred after electrolytic graining. Specimen No. 36 exhibited inferior pit uniformity due to high Mg content. Moreover, the amount of aluminum powder decreased, and coil scratches due to rubbing occurred. Specimen No. 37 was non-uniformly surface-roughened due to high Zn content. Specimen No. 38 had a small number of precipitates due to low Fe content and low Si content. The distribution of Al—Fe intermetallic compounds and Al—Fe—Si intermetallic compounds became non-uniform, whereby formation of pits became non-uniform due to formation of an unetched area. Moreover, since the quantity of Fe in solid solution was small, burning resistance was insufficient. Specimen No. 39 produced a large number of precipitates due to high Fe content and high Si content to produce coarse compounds. Therefore, uniformity of the surface-roughened structure decreased. Moreover, since the quantity of Fe in solid solution was large, the pit pattern became non-uniform. In specimen No. 40, an unetched area occurred during the electrolytic treatment due to high Cu content so that pits became large and non-uniform. Specimen No. 41 produced coarse Al—Ti compounds due to high Ti content, whereby the surface-roughened structure became non-uniform. Specimen No. 42 produced coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds due to high Mn content, whereby surface roughening during the electrolytic treatment became non-uniform. In specimen No. 43, the shape of pits was deformed and became non-uniform since the total amount of Pb, In, Sn, and Ga exceeded 0.05%.

Example 4 and Comparative Example 4

An ingot of an aluminum alloy B cast in Example 1 was subjected to scalping of rolling surface, homogenization, and hot rolling under conditions shown in Table 9. The hot-rolled product was cold-rolled to a thickness shown in Table 9 without being subjected to process annealing. The ingot was cooled to room temperature after the homogenization treatment, and was then heated to the hot rolling start temperature. Table 10 shows the surface roughness of a roll and the viscosity of a rolling oil used for cold rolling. In Tables 9 and 10, a value outside the condition according to the present invention is underlined.
The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the quantity of Fe in solid solution, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The results are shown in Table 10. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 11.

	TABLE 9

	Homogenization treatment	Hot rolling

		Amount of	Temperature		Temperature	Start	Finish		Cold rolling
		scalping	increase rate	Temperature	decrease rate	temperature	temperature	Sheet thickness	Sheet thickness
Specimen	Alloy	(mm/side)	(° C./hr)	(° C.)	(° C./hr)	(° C.)	(° C.)	(mm)	(mm)	Remarks

44	B	5	35	535	3	475	355	3	0.3	Example
45	B	5	44	455	10	475	355	3	0.3	Example
46	B	5	10	550	5	475	355	3	0.3	Comparative
										Example
47	B	5	80	580	2	475	355	3	0.3	Comparative
										Example
48	B	5	38	405	3	475	355	3	0.3	Comparative
										Example
49	B	5	30	615	3	475	355	3	0.3	Comparative
										Example
50	B	5	33	553	0.5	475	355	3	0.3	Comparative
										Example

TABLE 10

								Number of
							Quantity	oil pits with
		Viscosity			Amount of		of	diameter
	Ra	ρ of	Relationship I	Relationship II	aluminum		Fe in solid	of 30 μm	Crystal	Crystal
	of roll	rolling oil	between	between	powder	Precipitate	solution	or more	length GL	width GT	Ratio
Specimen	(μm)	(cSt)	Mg and ρ	Mg and ρ	(mg/m²)	per mm²	(ppm)	(/mm²)	(μm)	(μm)	GL/GT

44	0.3	3	Good	Good	2.38	55230	26	50	735	73	10.1
45	0.3	3	Good	Good	1.80	69410	21	40	843	90	9.4
46	0.3	3	Good	Good	1.71	9830	17	35	1120	98	11.4
47	0.3	3	Good	Good	1.67	3120	172	36	964	92	10.5
48	0.3	3	Good	Good	2.93	7040	116	38	900	89	10.1
49	0.3	3	Good	Good	2.40	3950	129	24	850	87	9.8
50	0.3	3	Good	Good	1.59	3760	30	21	671	63	10.7

Note:
Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad)
Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

44	130	Excellent	Good	Good	Good	Good
45	122	Good	Good	Good	Good	Good
46	72	Good	Bad	Bad	Good	Good
47	123	Good	Bad	Bad	Good	Good
48	136	Excellent	Bad	Bad	Good	Good
49	140	Excellent	Bad	Bad	Good	Good
50	144	Good	Bad	Bad	Good	Good

As shown in Table 11, specimens No. 44 and No. 45 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. In specimen No. 46, since the temperature increase rate of the ingot during the homogenization treatment was low, the diameter of the precipitates exceeded 1 μm and the number of precipitates decreased. Therefore, an unetched area was formed so that uniformity of pits was poor. Moreover, since the amount of precipitation increased to a large extent, the quantity of Fe in solid solution became insufficient, whereby burning resistance decreased. In specimen No. 47, since the temperature increase rate of the ingot during the homogenization treatment was high, precipitation became insufficient, whereby the pit pattern became non-uniform due to formation of an unetched area during the electrolytic treatment. In specimen No. 48, since the homogenization treatment temperature was low, precipitation of Fe and Si (i.e., a reduction in the quantity of Fe and Si in solid solution) became insufficient, whereby the pit pattern became non-uniform due to formation of an unetched area during the electrolytic treatment. In specimen No. 49, since the homogenization treatment temperature was high, the quantity of Fe in solid solution increased. As a result, the number of minute precipitates which serve as pit starting points decreased. An unetched area was formed, and the pit pattern became non-uniform. In specimen No. 50, since the homogenization treatment time was short, the dissolution state of Fe and Si in the longitudinal direction and the width direction became non-uniform, whereby the pit pattern became non-uniform.

Example 5 and Comparative Example 5

Each rolling side of an ingot of an aluminum alloy (Table 1) cast in Example 1 was faced by 5 mm to reduce the thickness of the ingot to 500 mm. The ingot was heated to 530° C. at a temperature increase rate of 35° C./hr, and was then subjected to homogenization at 530° C. for 3.5 hours.
The temperature of the ingot was decreased to 490° C. (hot rolling start temperature) at a temperature decrease rate of 35° C./hr. The ingot was then hot-rolled to a thickness of 3 mm. Hot rolling was finished at 346° C. The hot-rolled product was cold-rolled to a thickness of 0.3 mm without being subjected to process annealing. The arithmetic average roughness Ra of a roll used for cold rolling was 0.3 μm, and the viscosity of a rolling oil was 3 cSt.
The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the quantity of Fe in solid solution, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, and the crystal grain size of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The content (%) of Fe (Fe compound) which formed an intermetallic compound with respect to the total Fe content, the content (%) of Si (Si compound) which formed an intermetallic compound with respect to the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which formed an Al—Fe—Si intermetallic compound to the content (A %) of Fe which formed an Al—Fe intermetallic compound were determined according to the following method. The results are shown in Table 12. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 13. In FIG. 12, a value outside the condition according to the present invention is underlined.
Measurement of Fe content and Si content relating to intermetallic compound: The Fe content and the Si content of the total intermetallic compounds were determined using a phenol residue analysis method shown in FIG. 2. The ratio (Fe content (wt %) of Al—Fe—Si intermetallic compounds)/(Fe content (wt %) of Al—Fe intermetallic compounds) of the total intermetallic compounds was determined.

TABLE 12

		Viscosity					Quantity
		ρ			Amount of		of Fe in
	Ra	of rolling	Relationship	Relationship	aluminum		solid	Fe
	of roll	oil	I between	II between	powder	Precipitate	solution	compound
Specimen	(μm)	(cSt)	Mg and ρ	Mg and ρ	(mg/m²)	(/mm²)	(ppm)	(%)

51	0.3	3	Good	Good	2.43	67430	53	98.3
52	0.3	3	Good	Good	2.91	30060	29	98.2
53	0.3	3	Good	Good	1.88	74600	61	97.8
54	0.3	3	Good	Good	0.20	62890	80	98.0
55	0.3	3	Good	Good	2.58	72650	40	98.8
56	0.3	3	Bad	Good	4.11	61120	33	98.9
57	0.3	3	Bad	Good	0.03	64210	27	98.9
58	0.3	3	Good	Good	0.26	59330	39	98.7
59	0.3	3	Good	Good	3.19	5300	13	97.8
60	0.3	3	Good	Good	0.99	139720	162	98.0
61	0.3	3	Good	Good	2.47	67940	31	99.0
62	0.3	3	Good	Good	1.81	58040	36	98.6
63	0.3	3	Good	Good	0.55	82180	92	97.5
64	0.3	3	Good	Good	2.51	61040	20	98.3

			Number of oil
			pits with
	Si		diameter of 30 μm	Crystal	Crystal
	compound		or more	length GL	width GT	Ratio
Specimen	(%)	B %/A %	(/mm²)	(μm)	(μm)	GL/GT

51	20.0	0.23	38	661	64	10.3
52	23.3	0.27	47	820	77	10.6
53	17.8	0.38	33	634	68	9.3
54	35.7	0.43	6	679	63	10.8
55	34.3	0.53	42	632	58	10.9
56	18.3	0.21	71	733	66	11.1
57	20.0	0.24	3	756	79	9.6
58	31.4	0.51	13	727	78	9.3
59	60.0	0.93	49	1220	131	9.3
60	7.1	0.10	23	529	47	11.3
61	32.9	0.58	45	603	60	10.1
62	12.3	0.44	30	601	60	10.0
63	22.0	0.17	19	588	55	10.7
64	10.0	0.78	33	1075	99	10.9

Note:
Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad)
Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

51	155	Good	Excellent	Excellent	Good	Good
52	140	Good	Excellent	Excellent	Good	Good
53	162	Good	Excellent	Excellent	Good	Good
54	220	Good	Good	Good	Good	Good
55	134	Good	Good	Good	Good	Good
56	90	Good	Bad	Bad	Bad	Good
57	233	Bad	Good	Bad	Good	Good
58	198	Good	Good	Bad	Good	Good
59	93	Good	Bad	Bad	Bad	Good
60	204	Good	Good	Bad	Good	Good
61	147	Good	Bad	Bad	Good	Good
62	186	Good	Good	Bad	Good	Good
63	199	Good	Good	Bad	Good	Good
64	175	Good	Good	Bad	Good	Good

As shown in Table 13, specimens No. 51 to No. 55 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. On the other hand, specimen No. 56 exhibited inferior burning resistance due to low Mg content. Moreover, the amount of aluminum powder increased, and formation of pits became non-uniform. An inferior appearance due to an unetched area and an irregular pattern occurred after electrolytic graining. Specimen No. 57 exhibited inferior pit uniformity due to high Mg content. Moreover, the amount of aluminum powder decreased, and coil scratches due to rubbing occurred. Specimen No. 58 was non-uniformly surface-roughened due to high Zn content. Specimen No. 59 had a small number of precipitates due to low Fe content and low Si content. The distribution of Al—Fe intermetallic compounds and Al—Fe—Si intermetallic compounds became a non-uniform, whereby formation of pits became non-uniform due to formation of an unetched area. Moreover, since the quantity of Fe in solid solution was small, burning resistance was insufficient. Since the content of Fe which formed an intermetallic compound was more than 40% of the total Fe content, precipitation of Al—Fe—Si intermetallic compounds which serve as pit starting points to only a small extent proceeded so that large pits were formed due to a decrease in pit formation efficiency. As a result, the pit pattern became non-uniform. When 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 larger than 0.9, large pits tend to be formed due to a decrease in pit formation efficiency. Specimen No. 60 produced a large number of precipitates due to high Fe content and high Si content to produce coarse compounds. Therefore, uniformity of the surface-roughened structure decreased. Moreover, since the quantity of Fe in solid solution was large, the pit pattern became non-uniform. In specimen No. 61, an unetched area occurred during the electrolytic treatment due to high Cu content so that pits became large and non-uniform. Specimen No. 62 produced coarse Al—Ti compounds due to high Ti content, whereby the surface-roughened structure became non-uniform. Specimen No. 63 produced coarse Al—Fe—Mn compounds or Al—Fe—Mn—Si compounds due to high Mn content, whereby surface roughening during the electrolytic treatment became non-uniform. In specimen No. 64, the shape of pits was deformed and became non-uniform since the total amount of Pb, In, Sn, and Ga exceeded 0.05%.

Example 6 and Comparative Example 6

An ingot of an aluminum alloy C cast in Example 1 was subjected to scalping of rolling surface, homogenization, and hot rolling under conditions shown in Table 14. The hot-rolled product was cold-rolled to a thickness shown in Table 14 without being subjected to process annealing. The ingot was cooled to room temperature after the homogenization treatment, and was then heated to the hot rolling start temperature. Table 15 shows the surface roughness of a roll and the viscosity of a rolling oil used for cold rolling. In Tables 14 and 15, a value outside the condition according to the present invention is underlined.
The amount of aluminum powder on the surface of the sheet after cold rolling, the number of precipitates with a diameter of 0.1 to 1.0 μm, the quantity of Fe in solid solution, the content (%) of Fe (Fe compound) which formed an intermetallic compound with respect to the total Fe content, the content (%) of Si (Si compound) which formed an intermetallic compound with respect to the total Si content, and the ratio (B %/A %) of the content (B %) of Fe which formed an Al—Fe—Si intermetallic compound to the content (A %) of Fe which formed an Al—Fe intermetallic compound, the number of oil pits with a diameter of 30 μm or more formed in the surface of the sheet, the crystal grain size, the content of Fe which formed an intermetallic compound, the content of Si which formed an intermetallic compound, and the ratio of the content of Fe which formed an Al—Fe—Si intermetallic compound to the content of Fe which formed an Al—Fe intermetallic compound of the resulting aluminum alloy sheet (specimen) were measured according to the above-described methods. The results are shown in Table 15. Evaluation of burning resistance, observation of the presence or absence of scratches due to rubbing which occurred on a coil wound after cold rolling, an irregular pattern, and streaks, and evaluation of etching properties were conducted according to the above-described methods. The results are shown in Table 18.

TABLE 14

Homogenization treatment	Hot rolling	Cold rolling

		Amount of	Temperature			Temperature	Start	Finish	Sheet	Sheet
		scalping	increase rate	Temperature	Time	decrease rate	temperature	temperature	thickness	thickness
Specimen	Alloy	(mm/side)	(° C./hr)	(° C.)	(hr)	(° C./hr)	(° C.)	(° C.)	(mm)	(mm)	Remarks

65	C	5	35	535	3	35	465	343	3	0.3	Example
66	C	5	35	455	10	44	465	343	3	0.3	Example
67	C	5	35	405	5	30	465	343	3	0.3	Comparative
											Example
68	C	5	35	615	2	33	465	343	3	0.3	Comparative
											Example
69	C	5	35	550	0.5	38	465	343	3	0.3	Comparative
											Example
70	C	5	35	580	3	10	465	343	3	0.3	Comparative
											Example
71	C	5	35	553	3	80	465	343	3	0.3	Comparative
											Example

TABLE 15

							Quantity
		Viscosity ρ			Amount of		of Fe in
		of rolling	Relationship	Relationship	aluminum		solid
	Ra of roll	oil	I between	II between	powder	Precipitate	solution
Specimen	(μm)	(cSt)	Mg and ρ	Mg and ρ	(mg/m²)	(/mm²)	(ppm)

65	0.3	3	Good	Good	1.98	73240	24
66	0.3	3	Good	Good	1.41	88780	31
67	0.3	3	Good	Good	1.29	7330	120
68	0.3	3	Good	Good	1.26	3420	168
69	0.3	3	Good	Good	2.55	4040	55
70	0.3	3	Bad	Good	2.00	9650	19
71	0.3	3	Bad	Good	0.98	8870	80

				Number of oil
				pits with
	Fe	Si		diameter of 30 μm	Crystal	Crystal
	compound	compound		or more	length GL	width GT	Ratio
Specimen	(%)	(%)	B %/A %	(/mm²)	(μm)	(μm)	GL/GT

65	99.1	13.3	0.26	30	514	53	9.7
66	98.9	21.1	0.48	25	875	90	9.7
67	95.7	33.3	1.12	19	1130	108	10.5
68	94.0	8.9	0.17	16	836	82	10.2
69	98.0	10.0	0.18	20	713	66	10.8
70	99.3	32.2	0.97	14	850	87	9.8
71	97.1	8.9	0.16	10	547	52	10.5

Note:
Relationship I between Mg and ρ: −2 × Mg % + 2 ≦ ρ ≦ −2 × Mg % + 8 (satisfied: Good, not satisfied: Bad)
Relationship II between Mg and ρ: ρ ≦ 2 × Mg % + 4 (satisfied: Good, not satisfied: Bad)

65	148	Excellent	Good	Good	Good	Good
66	123	Good	Good	Good	Good	Good
67	140	Good	Bad	Bad	Good	Good
68	145	Good	Bad	Bad	Good	Good
69	137	Excellent	Good	Bad	Good	Good
70	79	Excellent	Good	Bad	Good	Good
71	126	Good	Bad	Bad	Good	Bad

As shown in Table 16, specimens No. 65 and No. 66 according to the present invention did not show scratches due to rubbing, exhibited excellent burning resistance, did not produce an irregular pattern and streaks, exhibited excellent etching properties after the electrolytic treatment, and had uniform etch pits over the entire surface. In specimen No. 67, since the homogenization treatment temperature was low, precipitation of Fe and Si which serve as pit starting points was insufficient so that an unetched area was formed during the electrolytic treatment. As a result, the pit pattern became non-uniform. In specimen No. 68, since the homogenization treatment temperature was high, the quantity of Fe in solid solution increased. As a result, the number of minutes precipitates which serve as pit starting points decreased. An unetched area was formed, and the pit pattern became non-uniform. In specimen No. 69, since the homogenization treatment time was short, precipitation of Fe and Si became insufficient, whereby the pit pattern became non-uniform. In specimen No. 70, since the temperature decrease rate of the ingot to the hot rolling start temperature after the homogenization treatment was low, precipitation of Al—Fe—Si intermetallic compounds proceeded, whereby the diameter of the precipitates exceeded 1 μm and the number of precipitates decreased. Moreover, the quantity of Fe in solid solution decreased. As a result, burning resistance became insufficient, and pits became non-uniform. In specimen No. 71, since the temperature decrease rate of the ingot to the hot rolling start temperature after the homogenization treatment was high, the period of time for precipitation was insufficient. Moreover, since the temperature of the ingot became non-uniform, precipitation of Fe and Si also became non-uniform. As a result, recrystallization during the subsequent hot rolling became non-uniform, whereby streaks occurred. In addition, the pit pattern became non-uniform.

INDUSTRIAL APPLICABILITY

According to the present invention, an aluminum alloy sheet for a lithographic printing plate which allows pits to be more uniformly formed by an electrochemical surface-roughening treatment, exhibits more excellent adhesion to a photosensitive film and water retention properties, and shows excellent strength and thermal softening resistance which achieve improved image clarity and plate wear, and a method of producing the same are provided.

Burning resistance

Unetched area

Pit uniformity

Irregular pattern

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/mm².

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/m².

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 (mm²).

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 (mm²).

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”.