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  Method of manufacturing lithographic printing plate supportRelated Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Object Protection, Rotary, Barrels And Rotary Receptacles, Swinging Or Tilting ReceptaclesThe Patent Description & Claims data below is from USPTO Patent Application 20060049037. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The entire contents of the documents cited in this specification are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] The present invention relates to a method of manufacturing a lithographic printing plate support. More specifically, the invention relates to a method of manufacturing a lithographic printing plate support used for a presensitized plate which has both an excellent scumming resistance and a good press life. [0003] An aluminum support for lithographic printing plates used for a lithographic printing plate (hereinafter referred to simply as "a lithographic printing plate support") is manufactured by subjecting an aluminum plate to graining treatment and other surface treatments. Examples of a known graining treatment include mechanical graining treatment, electrochemical graining treatment (hereinafter also referred to simply as "electrolytic graining treatment"), chemical graining treatment (chemical etching), and a combination thereof. [0004] Among others, mechanical graining treatment is effective for the improvement of lithographic printing plates in press life. In a method for mechanical graining treatment which is generally known, a slurry of an abrasive is sprayed between a rotating nylon brush and an aluminum plate. It is also known to combine an electrolytic graining treatment with a mechanical graining treatment using a nylon brush and an abrasive (see, for instance, JP 2001-1663 A (the term "JP XXXX-XXXXXX A" as used herein means an "unexamined published Japanese patent application")). [0005] JP 2001-1663 A proposes "a method of manufacturing an aluminum support for lithographic printing plate, comprising steps of mechanically graining an aluminum plate; subjecting the ground plate to alkali etching, and then to electrolytic etching in which a three-phase alternating current is used to carry out etching in an electrolyte containing 25 to 90 g/L of hydrochloric acid, 50 to 240 g/L of nitric acid, and 25 to 60 g/L of aluminum ions, with the hydrochloric acid and the nitric acid being present in the electrolyte in amounts of 1 to 1.5 parts by weight and 2 to 4 parts by weight with respect to one part by weight of aluminum ions, respectively; and subjecting the etched plate to desmutting, and subsequent anodizing treatment". It is described in Examples of the published patent that "an aluminum plate in web form having a thickness of 0.24 mm is alkali degreased and then mechanically ground using a nylon brush rotating at a revolution number of 250 rpm and an abrasive chiefly composed of alumina and silica". [0006] The above method using a nylon brush and an abrasive has indeed the advantage of being performed at a high speed and low cost. In the method, however, it is difficult to control the particle size of the abrasive and mixed abrasive particles with large sizes are liable to form deep recesses locally. If deep recesses are locally formed on the surface of a lithographic printing plate support, some problems will arise. Specifically: The presensitized plate obtained by providing a positive-type image recording layer on such a support is hard to be developed in deeply recessed local portions of the non-image area. In the case of the presensitized plate with a negative-type image recording layer, its image formability is limited in deeply recessed local portions of the image area. [0007] In other words, the presensitized plate using a support obtained by the manufacturing method of JP 2001-1663 A is inferior in developability (sensitivity) and scumming resistance as well, even though excellent in press life. A presensitized plate which fully meets the users' requirements is still awaited. SUMMARY OF THE INVENTION [0008] It is an object of the present invention to provide a method of manufacturing a lithographic printing plate support by subjecting an aluminum plate to a mechanical graining treatment with a brush and a slurry containing an abrasive and an electrolytic graining treatment, which makes it possible to obtain a presensitized plate of high sensitivity which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate. [0009] In order to achieve the above and other objects, the present inventors have intensively studied to finally find out that the rate of deep recess formation in a mechanical graining treatment with a nylon brush and an abrasive is higher as the average surface roughness (R.sub.a) is increased. To be more specific: If the average surface roughness R.sub.a after mechanical graining treatment (for instance, mechanical grinding using a nylon brush rotating at a revolution number of 250 rpm and an abrasive chiefly composed of alumina and silica as described in Examples of JP 2001-1663 A) is large (e.g., 0.45 .mu.m), many deep recesses are recognized on the treated surface of an aluminum plate. If the average surface roughness R.sub.a after mechanical graining treatment is small (e.g., 0.30 .mu.m), almost no deep recesses are recognized on the treated surface of an aluminum plate even if the average surface roughness R.sub.a is increased (to 0.45 .mu.m, for instance) by a subsequent electrolytic graining treatment. [0010] Based on the findings as above, the present inventors have found that a presensitized plate of high sensitivity which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate can be obtained by using a lithographic printing plate support which is manufactured by subjecting an aluminum plate to at least a mechanical graining treatment which uses a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R.sub.a is 0.25 .mu.m or more but less than 0.40 .mu.m, and an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R.sub.a is 0.40 to 0.55 .mu.m, with the treatments being performed in this order. The present invention has been thus accomplished. [0011] It has been found in particular that a presensitized plate will have a higher sensitivity as well as a higher scumming resistance, a better press life and further an excellent cleaner resistance when made into a lithographic printing plate, if it is obtained by using a lithographic printing plate support which is manufactured by subjecting an aluminum plate to at least a mechanical graining treatment which uses a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R.sub.a is 0.25 .mu.m or more but less than 0.40 .mu.m, an etching treatment in an aqueous alkali solution (hereinafter also referred to simply as "alkali etching treatment"), an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R.sub.a is 0.40 to 0.55 .mu.m, an alkali etching treatment, an electrochemical graining treatment in an aqueous solution containing hydrochloric acid, an alkali etching treatment, and an anodizing treatment, with the treatments being performed in this order. [0012] Accordingly, the present invention provides the followings (1) to (3). [0013] (1) A method of manufacturing a lithographic printing plate support, comprising a step of subjecting an aluminum plate to at least: [0014] a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R.sub.a is 0.25 .mu.m or more but less than 0.40 .mu.m, and [0015] an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R.sub.a is 0.40 to 0.55 .mu.m (first hydrochloric acid electrolysis), with the treatments being performed in this order, so as to obtain a lithographic printing plate support. [0016] (2) A method of manufacturing a lithographic printing plate support, comprising a step of subjecting an aluminum plate to at least: [0017] a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R.sub.a is 0.25 .mu.m or more but less than 0.40 .mu.m, [0018] an first etching treatment in an aqueous alkali solution (first alkali etching treatment), [0019] an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R.sub.a is 0.40 to 0.55 .mu.m (first hydrochloric acid electrolysis), [0020] an second etching treatment in an aqueous alkali solution (second alkali etching treatment), [0021] an electrochemical graining treatment in an aqueous solution containing hydrochloric acid (second hydrochloric acid electrolysis), [0022] an third etching treatment in an aqueous alkali solution (third alkali etching treatment), and [0023] an anodizing treatment, with the treatments being performed in this order, so as to obtain a lithographic printing plate support. [0024] (3) The method of manufacturing a lithographic printing plate support according to the above (2), wherein a desmutting treatment is performed subsequent to at least one of the first etching treatment in an aqueous alkali solution, the second etching treatment in an aqueous alkali solution and the third etching treatment in an aqueous alkali solution. [0025] According to the present invention, a method can be provided of manufacturing a lithographic printing plate support allowing a presensitized plate of high sensitivity which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate, as will be described below. In addition, the energy required for the first hydrochloric acid electrolysis can be reduced by performing a specified mechanical graining treatment using a brush and a slurry containing an abrasive. The present invention is thus very useful. [0026] Above all, the alkali etching treatments and the second hydrochloric acid electrolysis can provide a presensitized plate which has a higher sensitivity as well as a higher scumming resistance, a better press life and further an excellent cleaner resistance when made into a lithographic printing plate. BRIEF DESCRIPTION OF THE DRAWINGS [0027] In the accompanying drawings: [0028] FIG. 1 is a side view conceptually showing processes of brush graining in the method of manufacturing a lithographic printing plate support according to the present invention; [0029] FIG. 2 is a schematic cross-sectional view of an apparatus for rinsing with a free-falling curtain of water that is used for rinsing in the method of manufacturing a lithographic printing plate support according to the present invention; [0030] FIG. 3 is a graph showing an example of an alternating current waveform that is used in electrochemical graining treatment in the method of manufacturing a lithographic printing plate support according to the present invention; Continue reading... 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