EP2426227A1

EP2426227A1 - Aluminum alloy sheet forlithographic printing plate, and manufacturing method thereof

Info

Publication number: EP2426227A1
Application number: EP11179125A
Authority: EP
Inventors: Yusuke Namba; Shinya Kurokawa; Hirokazu Sawada; Akio Uesugi; Hirotake Osuga; Yoshikazu Suzuki; Kotaro Kitawaki
Original assignee: Furukawa Sky Aluminum Corp; Fujifilm Corp
Current assignee: Fujifilm Corp; UACJ Corp
Priority date: 2010-09-03
Filing date: 2011-08-29
Publication date: 2012-03-07
Also published as: JP2012072487A; CN102381073A; US20120134875A1

Abstract

An aluminum alloy sheet for a lithographic printing plate which has the excellent ink stain resistance, with a local defect in a photosensitive layer after long-term storage being hard to occur, and excellent the pit uniformity after a roughening and a manufacturing method thereof are provided.

An aluminum alloy sheet for a lithographic printing plate containing a predetermined content of Fe, Si, Cu and Ti as well as one type or more selected from B and C, and composed of remaining Al and inevitable impurities, in which a concentration of an aluminum carbide present in the aluminum alloy sheet is not more than 8 ppm, an area occupancy of aggregation substances present on the aluminum alloy sheet surface after the roughening treatment with respect to an arbitrary circle with a radius 5 µm in the aluminum alloy sheet surface is less than 10%. In a case where the area occupancy is not less than 10%, the aggregation substances are present at a rate of 1 to 2 pieces/50 cm2.

Description

FIELD OF THE INVENTION

The present invention relates to an aluminum alloy sheet used for a lithographic printing plate formed by anodizing a surface of an aluminum alloy sheet subjected to a roughening treatment and by coating it with a photosensitive substance, and a method of manufacturing the aluminum alloy sheet. More specifically, the present invention relates to an aluminum alloy sheet for a lithographic printing plate which is excellent in the pit uniformity after a roughening treatment, the ink stain resistance in a non-image area and the fault tolerance of a photosensitive layer after prolonged storage, and a method of manufacturing the excellent aluminum alloy sheet.

BACKGROUND OF THE INVENTION

In general, as a lithographic printing plate, is used a support which is obtained by subjecting a surface of an aluminum sheet or an aluminum alloy sheet to surface treatments such as a roughening treatment, an anodized film treatment, etc., and which is coated with a photosensitive substance. Among such lithographic printing plates, a so-called PS (Pre-Sensitized) plate comprising a support previously coated with the photosensitive substance is widely used, and thus it can be immediately subjected to an exposing processing.
In actual use of such the lithographic printing plate, it subjected to a variety of plate-making processes such as an exposure processing, a development processing, a gum coat processing, etc. An image forming area on the lithographic printing plate is formed as a lipophilic image forming area for receiving an ink, which is defined by a part of the photosensitive layer which is not dissolved in the development processing. On the other hand, a non-image area on the lithographic printing plate as a hydrophilic non-image area for receiving a fountain solution, from which a part of the photosensitive layer is dissolved and removed in the development processing so that an anodized layer is exposed therefrom. The printing plate fabricated as above is wound around a rotatable plate cylinder of a printing machine. Then, the ink is applied to the image forming area on the wound lithographic printing plate under the presence of the fountain solution. The image formed on the printing plate by the ink is transferred to a rubber blanket, and is then printed on a printing medium.
Conventionally, aluminum alloys such as JIS1050, JIS1100, JIS3003, etc. have been used for an aluminum alloy sheet for the lithographic printing plate. The aluminum alloy sheet is usually roughened by roughening treatments by one or a combination of two or more of a mechanical method, a chemical method and an electrochemical method. The sheet is then subjected to an anodization treatment and a hydrophilic treatment, if necessary, and is used as a support for the lithographic printing plate. A photosensitive coat is applied to a surface of the support for the lithographic printing plate. The original printing plate is obtained by subjecting the support to an exposure processing and a development processing.
Recently, the clearer printing and the printing in a larger number using the same plate are in strong demand. In order to respond to this demand, it is important that ink stains are not caused in the non-image area during printing, that is, the ink stain resistance is excellent. For that purpose, in recent years, a lithographic printing plate of a CTP (Computer To Plate) type in which an image is directly written in the photosensitive layer using a laser writing device and the like has been on an increase.
The photosensitive layer of the CTP-type lithographic printing plate is more sensitive to light and heat than the prior-art lithographic printing plates. Thus, if there is inclusion such as an intermetallic compound on the surface of the aluminum alloy sheet, a defect can easily occur in the photosensitive layer. Particularly, intermetallic compounds such as the single Si and coarse Ti-B-based compounds cause ink stains. Here, the single Si refers to those not forming a solid solution in the alloy but separated as Si grains in Si contained in the aluminum alloy.
Patent Document 1 describes that since a defect occurs in an anodized film by the single Si, which lowers a hydrophilic property in that portion and causes ink stains, a reduction of the single Si in the aluminum alloy sheet is effective. Patent Document 2 describes that by adjusting contents of Mg and Mn so as to be separated as Mg2Si or Al-Mn-Si based compounds, a separation of the single Si can be suppressed.
Patent Document 3 describes a method of continuously casting an aluminum support after removing a coarse Ti-B compound from an aluminum molten metal through a filter. Patent Document 4 describes that, in a continuous casting method including a process where an aluminum molten metal is successively passed through a filtering means, molten metal flow passages, liquid level control means, and a molten metal feed nozzle, trap means for separated grains containing the Ti-B compound present in the molten metal is provided at one or more spots in the liquid level control means and the molten metal feed nozzle, and that time during which the molten metal passes through the molten metal flow passages and a distance of the molten metal flow passages are regulated. However, with the methods in Patent Documents 3 and 4, the removal of the Ti-B aggregation substances is not sufficient, and infusion of coarse aggregation substances cannot be stably prevented.
As described above, ink stains cannot be sufficiently solved even by regulating the inclusion such as the intermetallic compounds.
It has been found out by recent researches that an aluminum carbide affects the ink stain resistance, too. Methods of manufacturing an aluminum alloy sheet for lithographic printing plate in which the aluminum carbide is decreased have been already proposed as disclosed in Patent Documents 5 and 6.
Patent Document 5 describes that an inert gas is blown into a molten metal after an electrolytic refining of an aluminum oxide, a holding time in a holding process is regulated, and a filtration is performed by an in-line degassing treatment and an in-line filter so as to control the aluminum carbide concentration contained in an aluminum alloy sheet manufactured from the molten metal.
Patent Document 6 describes that amounts of oxides and carbides are controlled by performing at least one of a melting process, a holding process, a hydrogen-gas removing process, a filtering process and a casting process in a protective gas atmosphere containing a fluoride gas.
However, with the methods described in Patent Documents 5 and 6, an effect to decrease the aluminum carbide amount is not sufficient, and it is difficult to stably manufacture an aluminum alloy sheet in which the aluminum carbide amount is decreased. Also, an aluminum fluoride indicated in Patent Document 5 and an aluminum fluoride generated by the reaction between the protective gas containing a fluoride gas and the molten metal described in Patent Document 6 are likely to generate a hydrogen fluoride by heating in the the atmosphere. Since the hydrogen fluoride has the extremely strong toxicity to biological bodies and severe corrosiveness, they have problems of a bad influence on human bodies and a damage of a furnace.

LIST OF THE PRIOR ART DOCUMENTS

[Patent Document 1] JPS62-146694A
[Patent Document 2] JPH05-309964A
[Patent Document 3] JPH10-52740A
[Patent Document 4] JP2009-006386A
[Patent Document 5] U52009/0220376A1
[Patent Document 6] JP2007-167863A

SUMMARY OF THE INVENTION

An object of the present invention is to provide an aluminum alloy for a lithographic printing plate which is excellent in the pit uniformity after a roughening treatment, the ink stain resistance in a non-image area and the fault tolerance of a photosensitive layer after prolonged storage by decreasing an amount of an aluminum carbide and preventing an aggregation of at least one of a Ti-B compound and a Ti-C compound and the aluminum carbide.
The inventors have found that the object can be achieved by strictly controlling conditions in a melting process stage of an aluminum alloy and in a treating process stage of a molten metal, and completed the present invention.
According to one aspect of the present invention, an aluminum alloy sheet for a lithographic printing plate contains 0.10 to 0.60 mass% Fe, 0.01 to 0.25 mass% Si, 0.0001 to 0.05 mass% Cu, 0.005 to 0.05 mass% Ti, 0.0001 to 0.0020 mass% of one or more types selected from B and C, the balance of Al, and unavoidable impurities;
wherein the concentration of an aluminum carbide present in the aluminum alloy sheet is not more than 8 ppm; and
wherein when an area occupancy ratio of aggregation substances present on a surface of the aluminum alloy sheet subjected to a roughening treatment to a circle area with a radius of 5 µm arbitrarily set on the surface of the aluminum alloy sheet is less than 10%, the aggregation substances comprising at least one of a Ti-B compound and a Ti-C compound, and the aluminum carbide. In the case where the area occupancy ratio of the aggregation substances is not less than 10%, the aggregation substances are present at a rate of 1 to 2 pieces/50 cm².
According to another aspect of the present invention a method of manufacturing an aluminum alloy sheet for a lithographic printing plate comprises the steps of:

melting an aluminum alloy containing 0.10 to 0.60 mass% of Fe, 0.01 to 0.25 mass% of Si, 0.0001 to 0.05 mass% of Cu, 0.005 to 0.05 mass% of Ti, 0.0001 to 0.0020 mass% of at least one of B and C, and the balance of Al and unavoidable impurities at 680 to 780 °C; and
treating the molten metal of the said aluminum alloy at 680 to 780 °C,

stirring the molten metal of the said aluminum alloy over 5 to 60 minutes by mechanical or electromagnetic means;
holding the stirred molten metal over 10 to 60 minutes;
performing an in-line degassing treatment for the held molten metal;
filtering the in-line degassing-treated molten metal with an in-line filter; and
stirring the molten metal, to which grain-refiners are added, over at least 10 minutes.

The aluminum alloy sheet for a lithographic printing plate according to the present invention is excellent in the pit uniformity after a roughening treatment, with less ink stains occurred in a non-image area during printing, that is, excellent in the ink stain resistance and moreover, less faults of the photosensitive layer occurred in a photosensitive layer if stored under the atmosphere, that is, excellent in the fault tolerance of the photosensitive layer after long-term storage. Also, with the manufacturing method of an aluminum alloy sheet for a lithographic printing plate according to the present invention, the above aluminum alloy sheet for a lithographic printing plate can be obtained reliably and stably.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described below in more detail. First, reasons for limiting the aluminum alloy components used in the present invention will be described.

A. Reasons for Limiting Aluminum Alloy Components

Fe:

The Fe content affects sizes and number densities of Al-Fe-based compounds and Al-Fe-Si-based compounds dispersed in the material, and also largely affects the crystal grain behaviors during re-crystallization and the pit uniformity generated during a roughening treatment. When the Fe content is less than 0.10 mass% (hereinafter referred to simply as "%"), the crystal grain size at re-crystallization is coarsened and the pits generated by the roughening treatment become non-uniform. On the other hand, if the Fe content exceeds 0.60%, coarse Al-Fe-based compounds and Al-Fe-Si-based compounds are increased, and the pits generated by the roughening treatment become non-uniform. Thus, the Fe content should be within a range of 0.10 to 0.60%. The preferable Fe content is within the range of 0.20 to 0.40%.

Si:

When the Si content is less than 0.01%, after a roughening treatment, the pits become non-uniform. On the other hand, if the Si amount exceeds 0.25%, coarse Al-Fe-Si-based compounds are increased, and pits become non-uniform after the roughening treatment. Also, a separation of the single Si can easily occur, which remains in the anodized film and causes film defects. As a result, these defects become starting points of stains in the non-image area during printing, and cause stains in printing. Thus, the Si content should be within a range of 0.01 to 0.25%. The preferable Si content is within the range of 0.07 to 0.15%.

Cu:

Cu is an element which largely affects the roughening properties. When the Cu content is less than 0.0001%, pits generated by a roughening treatment become non-uniform. On the other hand, if the Cu content exceeds 0.05%, the pits generated by the roughening treatment also become non-uniform, and the color tone of the surface becomes too black, which damages merchantability. Thus, the Cu content should be within a range of 0.0001 to 0.05%. The preferable Cu content is within the range of 0.005 to 0.04%.

Ti:

Ti is an element which largely affects roughening properties, and also is an element which largely affects a structural state of an aluminum alloy ingot. When the Ti content is less than 0.005%, after an roughening treatment, the pits become non-uniform. Also, crystal grains of the ingot are not refined, but become coarse crystal grain structures, and band-shaped stripes are generated along the rolling direction, and the band-shaped stripes remain even after the roughening treatment. On the other hand, if the Ti content exceeds 0.05%, not only the above-described effects are saturated, but also coarse Al-Ti-based compounds are formed, and the compounds are distributed in the stripe shape on a rolled plate. As a result, a defect occurs in the anodized film, which causes a defect in a photosensitive layer and ink stains during printing. Thus, the Ti content should be within a range of 0.005 to 0.05%, The preferable Ti content is within the range of 0.005 to 0.03%.

Content of One or More Types Selected from B and C:

In order to refine crystal grain structures, slight amounts of B and/or C are added in a combination with Ti. When the contents of one or more types selected from B and C are less than 0.0001 %, the effect of crystal grain refining cannot be obtained, and the pits become non-uniform after a roughening treatment. On the other hand, if the contents exceed 0.0020%, not only the crystal grain refining effect is saturated, but also an aluminum carbide in a molten metal can easily aggregate with Ti-B-based compounds and Ti-C-based compounds, and a decrease of the aluminum carbide amount from the molten metal becomes insufficient. Also, since the aluminum carbide can be easily separated at a spot where the Ti-B-based compounds and the Ti-C-based compounds are present, ink stains and local defects of a photosensitive layer after long-term storage can easily occur. Also, coarse aggregation substances of the Ti-B-based compounds and the Ti-C-based compounds can cause surface defects. Thus, the contents of one or more types selected from B and C should be within 0.0001 to 0.0020%. The preferable range of the contents is 0.0003 to 0.0012%.

The Other Components:

Mg is an element most of which is present as a solid solution in an aluminum alloy and which improves the strength of the support at normal temperature. Since it plays a role to improve the thermal softening resistance, in order to obtain the desired support strength and the thermal softening resistance, it may be contained in an amount exceeding 0% and not more than 0.5%. In this range, the characteristics of the aluminum alloy sheet for the lithographic printing plate are not damaged.
The pit uniformity after a roughening treatment is considered as the so-called electrolytic graining properties. In order to obtain the further refined pit uniformity by means of an electrolytic operation having a lower current density, one or two or more types of 0.001 to 0.05% In, 0.001 to 0.05% Sn, 0.0001 to 0.01% Be, 0.001 to 0.05% Pb, and 0.001 to 0.05% Ni may be contained.

Inevitable Impurities:

The characteristics of the aluminum alloy sheet for the lithographic printing plate are not damaged by an impurity amount corresponding to JIS1050, that is, at most 0.05% Mn, at most 0.05% Zn, at most 0.05% Zr, at most 0.05% Cr and approximately at most 0.05% in total of the other components.
Subsequently, the aluminum carbide present in the aluminum alloy sheet will be described.

B. Aluminum Carbide

In general, the aluminum carbide is inevitably present in an aluminum metal. This is because, during electrolytic refining such as the three-layer electrolysis, a graphite used as an electrode is dissolved in an aluminum molten metal, and as the molten metal temperature is lowered during transfer or casting, an oversaturated carbon is separated as the aluminum carbide in the aluminum molten metal. Also, an amount of the aluminum carbide in the metal is largely fluctuated depending on metal manufacturers and metal manufacturing conditions. When an aluminum alloy containing a large amount of the aluminum carbide is used for a lithographic printing plate, an anodized film is not properly formed at a spot where the aluminum carbide is present. If the aluminum carbide is in contact with a fountain solution for a long time, the aluminum carbide is oxidized. And, it was found out that, since the hydrophilic nature is lowered in that portion, ink adheres thereto, and thus an ink stain occurs in a non-image area. Also, in the case of long-term storage in a state in which the aluminum carbide is present on the surface of the aluminum alloy sheet after a roughening treatment, the aluminum carbide is oxidized by the reaction with moisture in the atmosphere. As a result, an aluminum hydroxide and CH₄ gas generated by the reaction cause the lower adhesiveness with the photosensitive layer, and can easily cause a local defect in the photosensitive layer.
When a concentration of the aluminum carbide present in the aluminum alloy sheet exceeds 8 ppm, an ink stain caused by the aluminum carbide and a local defect of the photosensitive layer after long-term storage can easily occur. Thus, the aluminum carbide concentration should be at most 8 ppm. Also, it is preferable that an amount of aluminum carbide is low as little as possible, and the concentration of aluminum carbide is preferably at most 5 ppm or more preferably at most 3 ppm.
Subsequently, a distribution of aggregation substances present on the surface of the aluminum alloy sheet after the roughing treatment will be described.

C. Distribution of Aggregation Substances Present on Surface of Aluminum

Alloy Sheet After Roughening Treatment:

Since the aluminum carbide has the extremely low wettability with the aluminum, molten metal, it has the property that of easily existing on a solid-liquid interface between a solid such as a furnace wall, a hearth, a dross mainly composed of aluminum oxide and the like, and on the molten metal and a gas-liquid interface between a gas blown into the molten metal for hydrogen gas removal and the molten metal. When the aluminum carbide is present in the aluminum molten metal as a single body, the aluminum, carbide is discharged from the aluminum molten metal, and an amount of the aluminum carbide in the molten metal is decreased. However, when one or more types of the Ti-B-based compounds and the Ti-C-based compounds are present in the molten metal, the aluminum carbide forms aggregation substances with these compounds. These aggregation substances contain three types, the aggregation substance composed of the aluminum carbide and the Ti-B-based compound, the aggregation substance composed of the aluminum carbide and the Ti-C-based compound, and the aggregation substance composed of the aluminum carbide, the Ti-B-based compound, and the Ti-C-based compound. These aggregation substances have the high wettability with the aluminum molten metal, and are hardly discharged from the molten metal. Also, an oversaturated carbon dissolved in the aluminum molten metal is separated as the aluminum carbide due to a lowered molten metal temperature. As described above, when the Ti-B-based compounds and the Ti-C-based compounds are present in the molten metal, the aluminum carbide is easily separated using these compounds as a starting point.
The above aggregation substance becomes a defect portion of the anodized film and causes an ink stain or a surface defect. Therefore, not only the control of the aluminum carbide concentration in the molten metal but also the control of the Ti content, the B content, and the C content are also required, and thus it is important to control the distribution state of the aggregation substances of the aluminum carbide and the above compounds on the surface of the aluminum alloy sheet.
The distribution of the aggregation substances composed of one or more types of compounds selected from the Ti-B-based compounds and the Ti-C-based compounds and the aluminum carbide is specified by (1) an area occupancy ratio of the aggregation substance on the surface of the aluminum alloy sheet to an area of an arbitrary circle having a radius of 5 µm; and by (2) the number of the aggregation substances present in an arbitrary area of 50 cm² on the surface of the aluminum alloy sheet. When the area occupancy ratio is less than 10%, there is no problem with occurrence of an ink stain or a defect of a photosensitive layer after long-term storage. On the other hand, when the area occupancy ratio is not less than 10%, and when the number of the aggregation substances present in the area of 50 cm² is not more than 2, there is no problem with occurrence of the ink stain or the defect of the photosensitive layer after long-term storage. Also, when the number of the aggregation substances present in the area of 50 cm² is 3 or more, the ink stain and the photosensitive layer defect after long-term, storage occur. Therefore, the distribution of the aggregation substances should be specified that the area occupancy ration is less than 10%, or that the number of the aggregation substances present in the area of 50 cm² is not more than 2, that is, 2 or 1, if the area occupancy ratio is not less than 10%. Here, a circle having a radius of 5 µm was provided around the aggregation substances as the center. The area occupancy ratio was obtained by dividing a value of an area occupied by the aggregation substances by an area of the circle. The area occupancy ratio of the aggregation substances and their number are measured by surface observation and qualitative analysis of the aluminum alloy sheet using an electronic probe microanalyzer (JXA-8200 by JEOL Ltd.). Here, the size of the aggregation substances to be a problem is a radius of not more than 5 µm in equivalent circle diameter. When the radius is larger than 5 µ m, the area of the aggregation substances is too large and it is not a target of the present invention, and the ink stain and the photosensitive layer defect after long-term storage may occur substantially.
Subsequently, a manufacturing method of an aluminum alloy sheet for a lithographic printing plate according to the present invention will be described.

D. Manufacturing Method of Aluminum Alloy Sheet

A method of manufacturing an aluminum alloy sheet for a lithographic printing plate according to the present invention is basically constituted by a melting step, a treatment step, a casting step, a homogenization step, a hot rolling step, an annealing step, a cold rolling step, and a surface treatment step. Since the amounts and the aggregation state of the aluminum carbide, the Ti-B-based compounds, and the Ti-C-based compounds are determined particularly by the melting step of the aluminum metal and the subsequent treatment step, the steps of melting and treatment are important in the present invention.

Aluminum Molten Metal Temperature at Steps of Melting and Treating Molten

Metal:

When the aluminum molten metal temperature at the steps of melting an aluminum metal and treating the molten metal is less than 680 °C, aluminum metals and various master alloys for component adjustment are not fully melted. Also, since the molten metal temperature is further lowered in an in-line degassing treatment process and a filtration treatment process using an in-line filter, which will be described later which is included in the above treatment step, the aluminum alloy sheets cannot be stably produced. On the other hand, when the molten metal temperature exceeds 780 °C, the reaction between the aluminum molten metal and soot caused by imperfect combustion of fuel, carbon-containing compounds and the like in the treatment step is promoted, and the aluminum carbide is caused by the reaction. Also, when the molten metal temperature exceeds 780 °C, an amount of carbon melted in the oversaturated state is increased, and the large amount of aluminum carbide is separated due to a lowered molten metal temperature in a stirring process, a retaining process, an in-line degassing process, and a filtration treatment process using an in-line filter, which are included in the treatment step. As a result, the aluminum carbide cannot be sufficiently removed. Thus, the aluminum molten metal temperature at the stages of melting and treating should be 680 to 780 °C. The preferable molten metal temperature is 680 to 750 °C.

Melting Step of Aluminum Metal:

In an aluminum molten metal obtained by electrolytic refining of bauxite, the melted carbon and the separated aluminum, carbide are present as described above, and, in the aluminum metal prepared from this aluminum molten metal, a large amount of the separated aluminum carbide is contained. By melting this aluminum metal so as to bring the contained aluminum carbide into contact with the atmosphere, the aluminum carbide is oxidized and this aluminum oxide is separated from the aluminum molten metal as dross so that the aluminum carbide can be reduced.
In the treatment step subsequent to the melting step, a stirring process, a retaining process, an in-line degassing treatment process, a filtration treatment process using an in-line filter, and a process of adding and stirring of a crystal grain refining agent are included in this order.

Stirring Process:

The molten metal subjected to the melting process is stirred by mechanical means or electromagnetic means over 5 to 60 minutes. Since a difference in the specific gravity between the aluminum carbide and the aluminum molten metal is small, a separation of the aluminum carbide from the aluminum molten metal takes a long time. Thus, by forcedly stirring the molten metal, the separation of the aluminum carbide from the aluminum molten metal is promoted. By this stirring process, the aluminum carbide separated from the aluminum molten metal is brought into contact with the atmosphere so as to be oxidized, resulting in generation of an aluminum oxide, and, by removing it from the aluminum molten metal, the aluminum carbide is removed, Also, since the aluminum carbide can easily exist in a solid-liquid interface, the aluminum carbide can be also removed from the aluminum molten metal by bringing the aluminum carbide into contact with the dross on the surface of the aluminum molten metal, a furnace wall and a furnace hearth.
As the mechanical means or the electromagnetic stirring means, the means for stirring the aluminum molten metal by operating a forklift, a crane and the like equipped with a stirring jig, or an electromagnetic stirring means using an electromagnetic stirring device and the like. When the stirring time is less than 5 minutes, the above-described stirring effect is not sufficient. On the other hand, when the stirring time exceeds 60 minutes, not only the stirring effect is saturated, inclusion such as oxides might be included easily, which can easily cause linear defects or ink stains derived from the inclusion. Here, as the oxides, reference may be made to an aluminum oxide generated by the reaction with oxygen in the atmosphere, an aluminum hydroxide generated by the reaction with moisture in the atmosphere, an aluminum oxide containing water and the like. Thus, the stirring time should be 5 to 60 minutes. The preferable stirring time is 10 to 50 minutes.
Apart from the in-line degassing treatment, which will be described later, a hydrogen gas removing process may be carried out by blowing an argon gas, a chlorine gas or a mixed gas of them into the aluminum molten metal in the furnace. The stirring effect can be also obtained from this treatment. That is because inclusions such as the aluminum carbide is adsorbed by gas bubbles, and the gas bubbles float in that state so that the inclusions are separated from the aluminum molten metal as the dross.

Holding Process:

After the above stirring process, the aluminum molten metal is subjected to the holding process. Since the aluminum carbide is poor in the wettability with the aluminum molten metal, the aluminum carbide settles down, or floats by fluidization of the molten metal by the holding process. By this settling or floating, the aluminum carbide can be separated. The separation using a difference in the specific gravity between the inclusion such as the aluminum oxide and the aluminum molten metal is also possible. When the holding time is less than 10 minutes, the above-described separation effect is not sufficient. On the other hand, when the holding time exceeds 60 minutes, the effect is saturated, which is not preferable economically. Thus, the holding time should be 10 to 60 minutes. The preferable holding time is 20 to 60 minutes.

In-Line Degassing Treatment Process:

After the above holding process, the molten metal is subjected to the in-line degassing treatment process. As an in-line degassing treating device, those sold in the market with the trademarks such as SNIF or ALPUR can be used. In these devices, while an argon gas or a mixed gas of argon and chlorine is blown into the molten metal, a rotary body with a blade is rotated at a high speed so as to supply the gas in fine bubbles into the molten metal. Removal of hydrogen gas and inclusions can be performed in-line in a short time. By this treatment process, the above stirring effect can be obtained, and the aluminum carbide in the molten metal can be further decreased. When the in-line degassing treatment process is not carried out, removal of hydrogen gas or inclusions such as the aluminum carbide is not sufficient, and a surface defect, ink stains or a defect in the photosensitive layer after long-term storage caused by the aluminum carbide occurs.

Filtration Treatment Process by In-Line Filter:

After the above in-line degassing treatment process, the aluminum molten metal is filtered by an in-line filter. As the in-line filter, a ceramic tube filter, a ceramic foam filter, an alumina ball filter or the like may be used so as to remove inclusions by a cake filtration mechanism or a filter element filtration mechanism. By filtering the aluminum molten metal by the filtration mechanism using a filter, not only the aluminum carbide but also inclusions such oxides including the aluminum oxide can be removed. When the filtration treatment process by the in-line filter is not carried out, removal of inclusions such as the aluminum carbide, oxides and the like is insufficient, ink stains or a defect in the photosensitive layer after long-term storage caused by the aluminum carbide can easily occur, and linear defects of the inclusions or ink stains can be caused.

Process of Addition And Stirring of Crystal Grain Refining Agent:

In order to refine crystal grains of an ingot structure, as a crystal grain refining agent, massive or linear Ti-based aluminum alloys, Ti-B-based aluminum alloys, Ti-C-based aluminum alloys and the like are added. As described above, an added amount as content of one or more types selected from B and C is within a range of 0.0001 to 0.0020%. The Ti-B-based aluminum alloys and the Ti-C-based aluminum alloys have the greater crystal grain refining effect than the Ti-based aluminum alloys, but they also have a defect that surface defects caused by the aggregation substances of the Ti-B-based compounds or the Ti-C-based compounds contained in these aluminum alloys can easily occur.
In the present invention, the aggregation of the Ti-B-based compounds or the Ti-C-based compounds is prevented by controlling the added amount of the crystal grain refining agent or the B amount and the C amount, and by performing a molten metal treatment in which the aggregation is not caused. Specifically, by setting the time during which the crystal grain refining agent is added to the molten metal, and is stirred within 10 minutes, the aggregation by stirring is prevented. Here, as the stirring, there are the above mechanical or electromagnetic stirring process, a bubbling for hydrogen gas removal, and an in-line degassing treatment process. When the aluminum molten metal to which the crystal grain refining agent is added is stirred over more than 10 minutes, the aggregation of the Ti-B-based compound and the Ti-C-based compound occurs, and linear defects can easily occur. Also, since the Ti-B-based compound and the Ti-C-based compound are present as solid in the aluminum molten metal, the aluminum carbide is adsorbed by this solid-liquid interface, which makes the separation from the aluminum molten metal difficult. The aggregation substances of the aluminum carbide and the Ti-B-based compound and the aggregation substances of the aluminum carbide and the Ti-C-based compound can cause ink stains and a photosensitive layer defect after long-term storage easily. The preferable stirring time is within 5 minutes.

Costing:

The molten metal having subjected to the melting and treatment steps as above is cast to an ingot in accordance with a common procedure by a DC casting method and the like. Instead, it may be cast by a continuous casting method using a driving casting mold.
An ingot obtained as above is subjected to the homogenization treatment step, the hot rolling step, the annealing step, the cold rolling step and the like in accordance with a usual procedure as described below, and is finally molded into a rolled sheet having the desired sheet thickness.

Homogenization Treatment Step:

The ingot is usually subjected to the homogenization treatment step at 450 to 620 °C. As a result, impurity elements are diffused, and thus the pit generation in an electrolytic graining is further uniform. Also, crystal grains in an intermediate annealing can be refined more easily. The holding time of the homogenization treatment step can be suitably determined depending on a size of the ingot or the like, but it is usually 0.5 to 20 hours. If the time is less than 0.5 hours, the sufficient homogenization effect cannot be obtained in some cases. On the other hand, when the time exceeds 20 hours, each of the above effects is saturated, which is not preferable economically. Here, after the homogenization treatment step, the ingot may be subjected to a heating treatment process for the hot rolling step after the ingot is once cooled to a room temperature, or the hot rolling step may be performed after the ingot is cooled to 350 to 500 °C after the homogenization treatment step.

Hot Rolling Step:

The hot rolling is preferably started at the temperature of 350 to 500 °C. If the hot rolling start temperature is less than 350 °C, re-crystallization is not realized during the hot rolling step, and crystal grains of the ingot still remain in the hot rolled plate. Thus, when the final hot rolled plate is subjected to an electrolytic graining treatment process, a band-like or stripe-like appearance unevenness (streaks) may occur, which makes the surface appearance of the printing plate non-uniform. On the other hand, if the hot rolling start temperature exceeds 500 °C, re-crystallized grains are made coarse during the hot rolling step, the streaks occur in the surface of the sheet after the electrolytic roughening treatment process, which may make the surface appearance non-uniform,
When the hot rolling end temperature is set at 300 to 350 °C, the self-re-crystallization can be realized by utilizing heat derived from the hot rolling step. As a result, the entire plate after the hot rolling step can be made a refined re-crystallization structure. Due to the self-re-crystallization, the annealing step after the hot rolling step is no longer needed, and a reduction of a manufacturing cost can be expected. When the end temperature is less than 300 °C, the surface of the hot rolled plate is partially re-crystallized, and the appearance after the roughening treatment process may become non-uniform. Also, when only the surface layer region of the plate is re-crystallized, the central region in the plate-thickness is re-crystallized partially, and a fiber structure partially remains. Thus, mass production of an aluminum alloy sheet having the stable strength may become difficult. On the other hand, when the end temperature exceeds 350 °C, the sufficient dislocation is not introduced, and crystal grains on the surface region of the hot rolled plate become coarse. Thus, the appearance after the roughing treatment process may become non-uniform.
By performing the annealing step after the end of the hot rolling step and before the end of the cold rolling step with the hot rolling end temperature at 200 to 300 °C, crystal grains may be further refined as compared with the above-described self-crystallization process material so as to increase uniformity of the appearance after the roughening treatment process. In this case, when the hot rolling end temperature is less than 200 °C, rolling oil is not fully evaporated, but remains on the surface of the final hot rolled plate and might cause surface stains or corrosion. On the other hand, when the end temperature exceeds 300 °C, since the accumulated dislocation is not sufficient, the crystal grains are not refined by the annealing step, and the appearance after the roughening treatment process may become non-uniform.

Annealing Step:

In the above annealing step, by treating the rolled plate at 400 to 550 °C in a continuous annealing furnace for 0 to 60 seconds or at 300 to 500 °C in a batch furnace for 1 to 20 hours after the end of the hot rolling step and before the end of the cold rolling step, crystal grains are refined, and the appearance after the roughening treatment process becomes uniform. In the case of the annealing step in the continuous annealing furnace, when the temperature is less than 400 °C, the effect may not be sufficient. On the other hand, in the case of the annealing step at more than 550 °C or over more than 60 seconds, the effect is saturated, which is not preferable economically. In the case of the annealing step in the batch furnace, when the temperature is less than 300 °C, the single Si can be easily separated, and the effect of crystal grain refining may not be sufficient. Also, when the annealing time is less than 1 hour, the effect of crystal grain refining may not be sufficient. In the case of the annealing step at more than 500 °C or over more than 20 hours, the crystal grains become coarse and the appearance after the roughening treatment process may become non-uniform.

Cold Rolling Step:

Conditions for the cold rolling step are not particularly limited, and it is only necessary to follow a normal procedure. The final cold rolling ratio may be determined in accordance with the required strength or the thickness of the product sheet, and it is only necessary that the cold rolling step is carried out with rolling reduction of 60 to 98%. Straightening with a leveler may be performed after the final cold rolling step.

Surface Treatment Step:

In order to manufacture a lithographic printing plate support from the aluminum alloy sheet for a lithographic printing plate obtained as above, a surface treatment step for roughening, anodization and the like is carried out. This surface treatment method is not particularly limited, and utilizes any one of or two or more in combination of a mechanical method, a chemical method, and an electrochemical method which are performed according to a normal procedure. An etching amount by the surface treatment is preferably 1 to 10 µm from the surface of the aluminum alloy sheet. With the etching amount less than 1 µm, the roughening may be insufficient, and the plate wear resistance may be poor. On the other hand, if the etching amount exceeds 10 µm, the etching amount is too large, which is not preferable economically.
A photosensitive layer is applied to the aluminum alloy sheet for a lithographic printing plate obtained by the above steps, and the resulting plate is dried so that the lithographic printing plate support is obtained.

EXAMPLES

The present invention will be described below in more detail based on examples of the invention and comparative examples. Conditions other than those described in the claims are exemplified in order to explain effects of the present invention in the conditions of a normal procedure, and these conditions do not limit a technical scope of the present invention.

Invention Examples 1 to 22 And Comparative Examples 23 to 33

In production of an aluminum alloy with the compositions A to Z and a to g shown in Table 1, the aluminum metal was melted at 745 °C. Then, the molten metal was mechanically stirred at 745 °C over 30 minutes, using a stirring machine provided with three blades. Moreover, the molten metal was held at 735 °C over 40 minutes. Then, the in-line degassing treatment process was carried out by blowing argon gas into the molten metal, using the in-line degassing treatment device (SNIF), Moreover, the aluminum carbide and oxides were removed by filtering the molten metal by using a ceramic tube filter as an in-line filter. Thereafter, a crystal grain refining agent was added so as to have a concentration as described in each of compositions A to Z and a to g. The stirring time from the addition of the crystal grain refining agent was 0 minutes. The temperature of the molten metal from the in-line degassing treatment process to the addition of the crystal grain refining agent was 700 °C.

[Table 1]

The molten metal having been subjected to the melting and treatment steps as above was cast in accordance with the normal procedure of the DC casting method so as to fabricate an ingot of the aluminum alloy. This ingot was subjected to the homogenization treatment step under the condition of 560 °C and 6 hours. After that, the ingot was cooled to a room temperature once, and was then heated to 430 °C for the hot rolling step. Subsequently, the hot rolling step with the start temperature of 425°C and the end temperature of 320 °C was carried out. Moreover, the cold rolling step with the rolling reduction of 85% was carried out so as to obtain the aluminum alloy sheet for a lithographic printing plate with the thickness of 0.30 mm.

(Measurement And Evaluation of Aluminum Carbide Concentration)

The aluminum carbide concentration was measured in compliance with an alkali hydroxide Cracked gas chromatography method described in LIS A09-1-1971 (LIS: Light Metal Industrial Standard) as follows: An amount of 0.2 g of the aluminum alloy sheet fabricated as above was put into a reaction tank, and air in the inside of the tank is fully replaced with He. After the replacement of air with, a NaOH aqueous solution (20 volumetric %, approximately 20 ml) was dripped using a dripping funnel. Immediately after the dripping, the stirring step was performed by rotating a stirrer, while the reaction tank was heated, so that the aluminum alloy sample containing the aluminum carbide and the NaOH aqueous solution were fully reacted with each other. At this time, CH₄ generated by the reaction between the aluminum carbide and moisture is trapped by an active coal column immersed in liquid N₂. After the aluminum alloy sample and the NaOH aqueous solution have fully reacted, the trapped CH₄ was evaporated by immersing the active coal column in water bath. The quantity of the evaporated CH₄ was determined by a gas chromatography (HP6890 by Hewlett Packard). A CH₄ amount was determined using a calibration curve using a standard gas obtained by diluting CH₄ with N₂ and preparing in advance. Subsequently, this CH₄ amount was converted to the aluminum carbide concentration. Here, as the aluminum carbide, Al4C₃, Al₂C₆, Al₄O₄C and the like can be cited, but as the aluminum carbide converted as the aluminum carbide concentration was represented by Al₄C₃.
The aluminum carbide concentration acquired as above was evaluated, and the concentration not more than 8 ppm is acceptable, while the concentration exceeding 8 ppm is rejected. The results are shown in Table 2. The aluminum carbide concentration in the used aluminum metal was measured in advance, and it was 18 ppm.

[Table 2]

Table 2

	Alloy	Aluminum Carbide Concentration (ppm)	Area Occupancy of the Aggregation Substances with Respect to the Circle Having a Radius of 5 µm (%)	Aggregation Substance Density (Nos./50cm²)	Pit Uniformity after the Roughening	Ink Stain Resistance	Fault Tolerance of the Photosensitive Layer after Long-term Storage
Invention Example 1	A	3.4	<10	-	○	⊚	⊚
Invention Example 2	B	2.8	<10	-	⊚	⊚	⊚
Invention Example 3	C	2.2	<10	-	⊚	⊚	⊚
Invention Example 4	D	3.6	10	1	○	⊚	○
Invention Example 5	E	0.2	<10	-	○	⊚	⊚
Invention Example 6	F	2.7	<10	-	⊚	⊚	⊚
Invention Example 7	G	2.2	<10	-	⊚	⊚	⊚
Invention Example 8	H	1.1	<10	-	○	○	⊚
Invention Example 9	I	3.4	<10	-	○	⊚	⊚
Invention Example 10	J	3.8	22	1	⊚	⊚	○
invention Example 11	K	1.8	<10	-	⊚	⊚	⊚
Invention Example 12	L	0.8	<10	-	○	⊚	⊚
Invention Example 13	M	1.2	<10	-	⊚	⊚	⊚
Invention Example 14	N	0.0	<10	-	⊚	⊚	⊚
Invention Example 15	O	0.5	<10	-	○	○	⊚
Invention Example 16	P	2.4	<10	-	○	⊚	⊚
Invention Example 17	Q	2.2	<10	-	⊚	⊚	⊚
Invention Examples 18	R	3.7	23	1	⊚	⊚	○
Invention Example 19	S	5.8	15,46	2	⊚	○	○
Invention Example 20	T	2.2	<10	-	○	⊚	⊚
Invention Examples 21	U	5.0	100	1	⊚	⊚	○
Invention Example 22	V	6.0	20,50	2	⊚	○	○
Comparative Example 23	W	4.4	35	1	×	⊚	○
Comparative Example 24	X	3.4	<10	-	×	⊚	⊚
Comparative Example 25	Y	3,1	<10	-	×	Ⓞ	Ⓞ
Comparative Example 26	Z	3.3	<10	-	×	×	Ⓞ
Comparative Example 27	a	3.4	<10	-	×	Ⓞ	Ⓞ
Comparative Example 28	b	3.8	15	1	×	Ⓞ	○
Comparative Example 29	c	2.2	<10	-	×	Ⓞ	Ⓞ
Comparative Example 30	d	3.4	<10	-	Ⓞ	×	Ⓞ
Comparative Example 31	e	3.4	<10	-	×	Ⓞ	Ⓞ
Comparative Example 32 *1)	f	8.5	25, 37, 15, 40	4	Ⓞ	×	×
Comparative Example 33 *1)	g	9.1	65, 23, 39, 18, 15	5	Ⓞ	×	×

* 1) A defect occured on the surface.

The obtained aluminum alloy sheet was immersed in a 10 mass% aqueous sodium hydroxide solution at 70 °C for 30 seconds and etched, and was washed with flowing water. Then, the washed sheet was neutralized with a 20 mass% nitric acid aqueous solution, and was further washed with water. This aluminum alloy sheet was subjected to the electrolytic roughening treatment in 1 mass% nitric acid aqueous solution with an electric quantity at an anode of 300 coulomb/dm², using a sinusoidal alternating waveform current under the condition of VA = 12.7 V. The surface roughness was measured, which was 0.45 µm (expressed in terms of Ra). Subsequently, this aluminum alloy sheet was immersed in a 30 mass% sulfuric acid aqueous solution at 55 °C, and is subjected to a desmutting process for 2 minutes. Thereafter, in a 20 mass% sulfuric acid aqueous solution at 33 °C, a cathode was arranged on the grained surface, and the aluminum alloy sheet was anodized at a current density of 5A/dm2 for 50 seconds. The anodized film amount was 2.6 g/m2. The aluminum alloy sheet subjected to the above surface treatment step was made to be a support 1.

(Measurement of Area Occupancy Ratio of Aggregation Substances)

The area occupancy ratio of the aggregation substances of the Ti-B-based compound and the aluminum carbide, the Ti-C-based compound and the aluminum carbide, and the Ti-B-based compound, the Ti-C-based compound and the aluminum carbide distributed within 50 cm² on the surface of the aluminum alloy sheet subjected to the above surface treatment step were measured using an electronic probe microanalyzer. Measurement spots were determined by arbitrarily selecting 20 pieces of the aggregation substances. A circle having a radius of 5 µm was provided around the selected the aggregation substances as the center, and the area occupancy ratio of the aggregation substances with respect to the circle was measured. The area occupancy ration was obtained by dividing a value of an area occupied by the each aggregation substances by an area of the circle. The each area occupancy ration less than 10% was rated as acceptable. The result is shown in Table 2.

(Measurement of Number of Present Aggregation Substances)

In the above measurement, when there are the aggregation substances with the area occupancy ratio of not less than 10%, the number thereof was counted. The number of the aggregation substances present within a range of 50 cm² being 1 or 2 was rated as acceptable, while the number exceeding 2 was rated as rejected. The result was shown in Table 2. The measurements of the area occupancy ratio and the number of the aggregation substances on the surface of the aluminum alloy sheet are preferably made on the support 1 which is subjected to the above surface treatment step, but since fine scars or projections and recesses caused by the roughening treatment are present, the discrimination may be difficult. In that case, the measurement may be made on the surface which is subjected to a smoothing treatment. The smoothing treatment method includes mechanical polishing, electrolytic polishing and the like. Also, the polishing depth should be 1 to 10 µm, and it is important that it should be equal to the depth to be etched by the above surface treatment step. Also, since the aluminum carbide is oxidized by the reaction with moisture and oxygen in the atmosphere, the measurement needs to be made quickly after the surface treatment step.

(Evaluation of Pit Uniformity After Roughening)

a piece having a certain size (30 x 30 cm) was cut out of the aluminum alloy sheet subjected to the above surface treatment step as a test piece, and the pit uniformity was evaluated. Evaluation was made by visually observing the appearance of the test piece over the entire width, and the piece with the favorable pit uniformity over the entire width was rated as very good (⊚), the piece which was partially poor but practically has no problem as good (○), and the pieces which was poor over the entire width was rated as poor (×). The pieces with ⊚ and ○ were rated as acceptable, while those with × were rated as rejected. The result is shown in Table 2.
This support 1 was coated with a base coating liquid having the following composition so that a dried application amount becomes 2 mg/m² using a bar coater and was dried at 80 °C for 20 seconds, to thereby obtain a support 2.

(Composition of Base Coating Liquid)

Polymer (P1) (chemical structure is shown below)··· 0.3 mass parts
Purified Water ··· 60.0 mass parts
Methanol ··· 939.7 mass parts

This support 2 was coated with a photosensitive substance having the following composition using a bar coater, and then it was dried at 90 °C for 1 minute, to thereby form a photosensitive layer. The mass of the dried photosensitive layer was 1.35 g/m².

(Composition of Photosensitive Substance)

Polymerizable compound (1) <chemical structure is shown below> (PLEX6661-O, by Degussa Japan Co., Ltd.) ··· 1.69 mass parts
Binder Polymer (1) <chemical structure is shown below> ··· 1.87 mass parts
Sensitizing Dye (1) <chemical structure is shown below> ··· 0.13 mass parts
Polymerization Initiator (1) <chemical structure is shown below> ··· 0.46 mass parts
Chain Transfer Agent (1) <chemical structure is shown below> ··· 0.44 mass parts
Dispersed Substance of ε-Phthalocyanine Pigment ··· 1.70 mass parts
(pigment: 15 mass parts, dispersing agent (allyl methacrylate/methacrylic acid copolymer (mass average molar weight: 60 thousands, copolymerization molecular ratio: 83/17)): 10 mass parts, cyclohexanone: 15 mass parts)
Thermal Polymerization Inhibitor (N-nitrosophenyl hydroxylamine aluminum salt) ··· 0.012 mass parts
Dispersed Substance of Yellow Pigment ··· 0.5 mass parts (yellow pigment Novoperm Yellow H2G (by Clariant): 15 mass parts, dispersing agent (allyl methacrylate/methacrylic acid copolymer (mass average molar weight: 60 thousands, copolymerization molecular ratio: 83/17)): 10 mass parts, cyclohexanone: 15 mass parts)
Fluorine Surfactant (1) (mass average molecular weight: 10 thousands) <chemical structure is shown below> ··· 0.03 mass parts
Methyl Ethyl Ketone ··· 27.0 mass parts
Propylene Glycol Monomethyl ether ··· 26.7 mass parts

This photosensitive layer was coated with a protective layer application aqueous solution having the following composition using a bar coater so that a dried application mass becomes 2.5 g/m², and was dried at 120 °C for 1 minute, to thereby obtain a photosensitive lithographic printing plate original plate.

(Composition of Protective Layer Application Aqueous Solution)

PVA105 (polyvinyl alcohol, saponification degree 98 molar%, by Kuraray Co., Ltd.) ··· 1.80 mass parts
PVP-K30 (polyvinyl pyrrolidone, by BASF) ··· 0.40 mass parts
Emalex 710 (by Nihon Emulsion Co., Ltd.) ··· 0.03 mass parts
Luviskol VA64W (by BASF) ··· 0.04 mass parts
The Above Polymer (P1) ··· 0.05 mass parts
Purified Water ··· 36.5 mass parts

The obtained photosensitive printing plate was adjusted with Vx9600CTP by Fuji Film Corporation (light-source wavelength: 405 nm) so that an exposure amount on a sensitizing material is 0.05 mJ/cm² and drawing was made in an image state. Thereafter, a preheating was performed within 30 seconds, and a development was made by the developing solution at 25 °C using PS processor Inter Plater 850HD by G&J in which an alkali developing solution having the following composition was incorporated.

(Composition of Alkali Developing solution)

Potassium Hydroxide ··· 0.15 g
Polyoxyethylene Naphthyl ether (n = 13) ··· 5.0 g
Chelest 400 (chelating agent) ··· 0.1 g
Water ··· 94.75 g

(Ink Stain Resistance)

The developed lithographic printing plate was washed with water and dried, and a printing test using 100 thousand copies was carried out using an offset rotary press. Thereafter, a degree of dot-like stains in a non-image area was visually evaluated. Evaluation was made such that a favorable copy without dot-like stains over the entire non-image area was rated as very good (⊚), a copy with some dot-like stains but without a practical problem was rated as good (○), and a copy with dot-like stains causing a practical problem was rated as poor (×). The ⊚ and ○ marks were rated as acceptable, while the × mark was rated as rejected. The result is shown in Table 2.

(Fault Tolerance of Photosensitive Layer After Long-Term Storage)

Moreover, the lithographic printing plate on which the photosensitive layer was formed as above was stored for three months under the atmosphere at a room temperature and the humidity within a range of 20 to 90%, and occurrence of a defect in the photosensitive layer was evaluated. Evaluation was made such that a plate without defects in the photosensitive layer was rated as very good (⊚), a plate with some defects but without a practical problem was rated as good (○), and a plate with defects causing a practical problem was rated as poor (×). The ⊚ and ○ marks were rated as acceptable, while the × mark was rated as rejected. The result is shown in Table 2.
In Invention Examples 1 to 22, the aluminum carbide concentration was not more than 8 ppm, the area occupancy ratio of the aggregation substances was less than 10%. Although, the area occupancy ratio is not less than 10%, the density of the aggregation substances was not more than 2 per 50 cm². Both the cases were acceptable. Moreover, the pit uniformity after the roughening, the ink stain resistance, and the fault tolerance of the photosensitive layer after long-term storage were all acceptable.
In Comparative Example 23, since the Fe content of the aluminum alloy W was too small, the pits generated by the roughening treatment were non-uniform.
In Comparative Example 24, since the Fe content of the aluminum alloy X was too large, the pits generated by the roughening treatment were non-uniform.
In Comparative Example 25, since the Si content of the aluminum alloy Y was too small, the pits generated by the roughening treatment were non-uniform.
In Comparative Example 26, since the Si content of the aluminum alloy Y was too large, the pits generated by the roughening treatment were non-uniform, and also the single Si was separated, to thereby causing ink stains.
In Comparative Example 27, since the Cu content of the aluminum alloy a was too small, the pits generated by the roughening treatment were non-uniform.
In Comparative Example 28, since the Cu content of the aluminum alloy b was too large, the pits generated by the roughening treatment were non-uniform.
In Comparative Example 29, since the Ti content of the aluminum alloy c was too small, the pits generated by the roughening treatment were non-uniform,
In Comparative Example 30, since the Ti content of the aluminum alloy d was too large, the coarse Al-Ti-based compound was formed, and ink stains occurred.
In Comparative Example 31, since the total contents of B and C of the aluminum alloy e was too small, the pits generated by the roughening treatment were non-uniform.
In Comparative Example 32, since the content of B of the aluminum alloy f was too large, the total contents of B and C were too large, too. As a result, the aluminum carbide concentration was too high, the aggregation density of the Ti-B-based compound was also too large, and ink stains and a local defect in the photosensitive layer after long-term storage occurred. Moreover, a defect occurred on the surface by an aggregation of the Ti-B-based compound.
In Comparative Example 33, since the content of C of the aluminum alloy g was too large, the total contents of B and C were too large, too. As a result, the aluminum carbide concentration was too high, the aggregation density of the Ti-C compound was also too large, and ink stains and a local defect in the photosensitive layer after long-term storage occurred. Moreover, a defect occurred on the surface by an aggregation of the Ti-C-based compound.

Invention Examples 34 to 49 and Comparative Examples 50 to 60

In production of an aluminum alloy containing 0.35% Fe, 0.09% Si, 0.025% Cu, 0.010% Ti, and 0.0005% B, the aluminum metal was subjected to the melting step and the treatment step described in Table 3. Here, the molten metal temperature in the stirring process after the melting process was the same as the temperature in the melting process. Also, after the crystal grain refining agent was added, the molten metal temperature in the stirring process was the same as the molten metal temperature in the filtration treatment process using the in-line filter. The molten metal subjected to the melting process and the treatment processes as above was cast in compliance with the normal procedure of the DC casting method, to thereby fabricate an ingot of the aluminum alloy.

[Table 3]

The obtained ingot was subjected to the homogenization treatment step under the condition of 540 °C and 3 hours. Thereafter, the ingot was cooled to a room temperature once, and was then heated to 420 °C for the hot rolling step. Subsequently, the ingot was subjected to the hot rolling step with the start temperature of 415 °C and the end temperature of 330 °C. Moreover, the hot rolled aluminum alloy plate was subjected to the cold rolling step with rolling reduction of 80% to thereby obtain an aluminum alloy sheet for a lithographic printing plate with the thickness of 0.3 mm.
The obtained aluminum alloy sheet for a lithographic printing plate was subjected to the same surface treatment step as in the above-described Invention Example 1, and was made to be the aluminum alloy sheet support 1. The area occupancy ratio of aggregation substances of the Ti-B-based compound and the aluminum carbide, the Ti-C-based compound and the aluminum carbide, and the Ti-B-based compound, the Ti-C-based compound and the aluminum carbide on the surface of the support 1 were measured and evaluated similarly to the example 1. Moreover, when the area occupancy of the aggregation substances is not less than 10%, the number of the aggregation substances was measured and evaluated similarly to the example 1. Moreover, the pit uniformity after the roughening was also evaluated similarly to the example 1. The results are shown in Table 4.

[Table 4]

Table 4

No.	Condition	Aluminum Carbide Concentration (ppm)	Area Occupancy of the Aggregation Substances with Respect to the Circle Having a Radius of 5 µm (%)	Aggregation Substance Density (Nos./50cm²)	Pit Uniformity after the Roughening	Ink Stain Resistance	Fault Tolerance of the Photosensitive Layer after Long-term Storage
Invention Example 34	1	0.8	<10	-	⊚	⊚	⊚
Invention Example 35	2	0.0	<10	-	⊚	⊚	⊚
Invention Example 36	3	5.7	27,48	2	⊚	○	○
Invention Example 37	4	5.5	42,39	2	⊚	○	○
Invention Example 38	5	2.9	<10	-	⊚	⊚	⊚
Invention Example 39	6	3.9	32	1	⊚	⊚	○
Invention Example 40	7	4.2	45	1	⊚	○	○
Invention Example 41	8	3.5	10	1	⊚	⊚	○
Invention Example 42	9	3.4	<10	-	⊚	⊚	⊚
Invention Example 43	10	5.9	60,40	2	⊚	○	○
Invention Example 44	11	5.3	55, 34	2	⊚	○	○
Invention Example 45	12	5.0	100	1	⊚	⊚	○
Invention Example 46	13	1.5	<10	-	⊚	⊚	⊚
Invention Example 47	14	2.3	<10	-	⊚	⊚	⊚
Invention Example 48	15	5.8	15,50	2	⊚	○	○
Invention Example 49	16	6.2	23,57	2	⊚	○	○
Comparative Example 50	17	8.9	18, 24, 32, 44	4	⊚	×	×
Comparative Example 51 *²⁾	18	-	-	-	-	-	-
Comparative Example 52	19	9.5	25, 29, 31, 44, 20	5	⊚	×	×
Comparative Example 53 *³⁾	20	1.9	<10	-	⊚	×	⊚
Comparative Example 54	21	9.2	38, 45, 22, 33	4	⊚	×	×
Comparative Example 55	22	8.7	15, 18, 29, 59	4	⊚	×	×
Comparative Example 56 *²⁾	23	-	-	-	-	-	-
Comparative Example 57	24	8.9	20, 44, 35, 30	4	⊚	×	×
Comparative Example 58 *³⁾	25	8.5	22, 23, 49, 32	4	⊚	×	×
Comparative Example 59	26	8.2	34, 59, 25	3	⊚	×	×
Comparative Example 60 *³⁾	27	8.1	41, 48, 31	3	⊚	×	×

* 2) The aluminum alloy plate counld not produced stably.
* 3) A defect occured on the surface.

Similarly to the example 1, the support 1 was coated with the base coating liquid, and was dried to thereby obtain the support 2. Moreover, similarly to the example 1, the support 2 was coated with the photosensitive composition, and was dried to thereby form the photosensitive layer. Finally, similarly to the example 1, the formed photosensitive layer was coated with the protective layer application aqueous solution, and was dried to thereby obtain the photosensitive lithographic printing plate original plate.
Similarly to the example 1, drawing was made in an image state on the obtained photosensitive lithographic printing plate, this was developed, washed with water, and dried. A printing test using 100 thousand copies was carried out using an offset rotary press. Similarly to the example 1, the photosensitive lithographic printing plate obtained as above was tested and evaluated for the ink stain resistance and the fault tolerance of the photosensitive layer after long-term storage. The result is shown in Table 4.
In Invention Examples 34 to 49, the aluminum carbide concentration was not more than 8 ppm, the area occupancy ratio of the aggregation substances was less than 10%. Although, the area occupancy ratio is not less than 10%, the density of the aggregation substances was not more than 2 per 50 cm². Both the cases were acceptable. Moreover, the pit uniformity after the roughening, the ink stain resistance, and the fault tolerance of the photosensitive layer after long-term storage were all acceptable.
In Comparative Example 50, due to the fact that the molten metal temperature during the melting stage was too high, soot caused by imperfect combustion of fuel, carbon-containing compounds and the like were reacted with the molten metal, and the aluminum carbide was generated, resulting in increase in its concentration. Further, the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains at printing and defects in the photosensitive layer after long-term storage occurred.
In Comparative Example 51, since the molten metal temperature during the melting stage was too low, an aluminum metal and a mother alloy were not fully melted, and the aluminum alloy sheet could not be produced stably.
In Comparative Example 52, since the stirring time after the melting stage was too short, the effect of the aluminum carbide removal by stirring was not sufficient, the concentration became high, and the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains at printing and defects in the photosensitive layer after long-term storage occurred.
In Comparative Example 53, since the stirring time after the melting stage was too long, inclusions was included. As a result, ink stains occurred. Moreover, defects were caused on the surface.
In Comparative Example 54, due to the fact that the molten metal temperature in the retaining process was too high, soot caused by imperfect combustion of fuel, carbon-containing compounds and the like were reacted with the molten metal, the aluminum carbide was generated, resulting in increase in its concentration. Further, the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains at printing and defects in the photosensitive layer after long-term storage occurred.
In Comparative Example 55, since the retaining time was too short, a separation of the aluminum carbide was insufficient, the concentration became high. Further, the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains at printing and defects in the photosensitive layer after long-term storage occurred.
In Comparative Example 56, since the molten metal temperature in the in-line degassing treatment process was too low, the molten metal was coagulated, and the aluminum alloy sheet could not be produced stably.
In Comparative Example 57, due to the fact that the molten metal temperature in the in-line degassing treatment process was too high, soot caused by imperfect combustion of fuel, carbon-containing compounds and the like were reacted with the molten metal, and the aluminum carbide was generated, resulting in increase in its concentration. Further, the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains at printing and defects in the photosensitive layer after long-term storage occurred.
In Comparative Example 58, due to the fact that the in-line degassing treatment was not performed, the decrease effect of the aluminum carbide was insufficient, and the concentration became high. Further, the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains at printing and defects in the photosensitive layer after long-term storage occurred. Also, hydrogen gas removal was not sufficient, and a surface defect occurred.
In Comparative Example 59, due to the fact that the filtration treatment using an in-line filter was not performed, removal of the aluminum carbide, inclusions such as oxides and the like was not sufficient, resulting in increase in the concentration of aluminum carbide. Further, the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains caused by the aluminum carbide and defects in the photosensitive layer after long-term storage occurred. Also, inclusions caused surface defects and ink stains.
In Comparative Example 60, due to the fact that the stirring time of the aluminum molten metal after the addition of the crystal grain refining agent was too long, the concentration of the aluminum carbide became high. Further, the aggregation substance density with the Ti-B-based compound was too high. As a result, ink stains and defects in the photosensitive layer after long-term storage occurred. Also, an aggregation of the Ti-B compound occurred, which caused a surface defect.

INDUSTRIAL APPLICABILITY

According to the present invention, an aluminum alloy sheet for a lithographic printing plate which is excellent in the pit uniformity after roughening, the ink stain resistance in a non-image area during printing, and the fault tolerance of a photosensitive layer in storage under the atmosphere can be obtained. Also, according to the manufacturing method of an aluminum alloy sheet for a lithographic printing plate according to the present invention, the aluminum alloy sheet for the lithographic printing plate can be obtained reliably and stably.

Claims

An aluminum alloy sheet for a lithographic printing plate containing 0.10 to 0.60 mass% Fe, 0.01 to 0.25 mass% Si, 0.0001 to 0.05 mass% Cu, 0.005 to 0.05 mass% Ti, and one or more types selected from B and C: 0.0001 to 0.0020 mass% of one or more types selected from B and C, the balance of A1, and unavoidable impurities,
wherein the concentration of an aluminum carbide present in the aluminum alloy sheet is not more than 8 ppm; and
wherein when an area occupancy ratio of aggregation substances present on a surface of the aluminum alloy sheet subjected to a roughening treatment to a circle area with a radius of 5 µm arbitrarily set on the surface of the aluminum alloy sheet is less than 10%, said aggregation substances comprising at least one of a Ti-B compound and a Ti-C compound, and the aluminum carbide.
An aluminum alloy sheet for a lithographic printing plate containing 0.10 to 0.60 mass% Fe, 0.01 to 0.25 mass% Si, 0.0001 to 0.05 mass% Cu, 0.005 to 0.05 mass% Ti, and one or more types selected from B and C: 0.0001 to 0.0020 mass% of one or more types selected from B and C, the balance of Al, and unavoidable impurities,
wherein the concentration of an aluminum carbide present in the aluminum alloy sheet is not more than 8 ppm; and
wherein when an area occupancy ratio of aggregation substances present on a surface of the aluminum alloy sheet subjected to a roughening treatment to a circle area with a radius of 5 µm arbitrarily set on the surface of the aluminum alloy sheet is not less than 10%, said aggregation substances are present at a rate of 1 to 2 pieces/50 cm².
A method of manufacturing an aluminum alloy sheet for a lithographic printing plate comprises the steps of:
melting an aluminum alloy containing 0.10 to 0.60 mass% Fe, 0.01 to 0.25 mass% Si, 0.0001 to 0.05 mass% Cu, 0.005 to 0.05 mass% Ti, 0.0001 to 0.0020 mass% of at least one of B and C, and the balance of Al and unavoidable impurities at 680 to 780 °C; and

treating the molten metal of the said aluminum alloy at 680 to 780°C,
wherein said steps of treating includes:
stirring the molten metal of the said aluminum alloy over 5 to 60 minutes by mechanical or electromagnetic means;
holding the stirred molten metal over 10 to 60 minutes;
performing an in-line degassing treatment for the held molten metal;
filtering the in-line degassing-treated molten metal with an in-line filter; and
stirring the molten metal, to which grain-refiners are added, over at least 10 minutes.