An aluminium alloy support for a lithographic printing plate

Abstract: An aluminium alloy support for a lithographic printing plate, suitable for an electrochemical roughening treatment and excellent in fatigue resistace, heat softening resistance and printability, is provided which comprises aluminium and contains 0.05 to 1% by weight of Mn, not more than 0.2% by weight of Si, not more than 0.5% by weight of Fe and unavoidable traces of impurities.

Description: This invention relates to a lithographic printing plate comprising a support of an aluminium alloy, which has an excellent fatigue resistance, thermoplastic properties and printability. Lithographic printing plates which have generally been used are obtained by submitting so-called pre-sensitized printing plates (which will hereinafter be referred to as "PS plates") to plate making processes such as the steps of imagewise exposure, developing and gum coating. The PS plates are prepared by coating light-sensitive materials onto aluminium plates which have their surfaces subjected to surface treatments such as surface roughening and anodic oxidation and then drying. It is well known that an area where the light-sensitive layer remains undissolved after the above described developing step forms an image portion and the other area where the light-sensitive layer is removed to expose the underlying aluminium surface becomes hydrophilic and thus forms a non-image portion. As the supports for such a lithographic printing plate, lightweight aluminium plates have generally been used which have an excellent adaptability to surface treatments and machining, as well as corrosion resistance. Conventional materials used for this purpose are aluminium alloy plates having a thickness of 0.1-0.8 mm according to JIS A 1050 (Al alloys of a purity of at least 99.5 wt. %), JIS A 1100 (Al-0.05-0.20 wt. % Cu alloys) and JIS A 3003 (Al-0.05-0.20 wt. % Cu-1.5 wt. % Mn alloys) the surfaces of which are roughened by one or more of mechanical, chemical and electrochemical treatments, and then subjected to anodic oxidation. JP-A-5239403 describes a printing plate of an aluminium alloy containing 0.8 - 1.5% by weight Mn and less than 1.5% by weight of impurities. EP-A-0069320 describes the coating of aluminium support materials for offset printing plates with a hydrophilic salt-type phosphorus or sulphur organic polymer. Suitable aluminium supports for coating comprise 0 to 0.3% Mg, 0.8 to 1.5% Mn, impurities and the balance of aluminium. More specifically, aluminium lithographic printing plates have hitherto been proposed which are subjected in sequence to a mechanical surface roughening treatment, chemical etching treatment and anodically oxidized film forming process such as described in U.S. Patent No. 3,834,998; which are subjected in sequence to a chemical etching treatment and anodically oxidized film forming process as described in Japanese Patent Application OPI (Kokai) No. 61304/1976; which are subjected in sequence to an electrochemical treatment, aftertreatment and anodically oxidized film forming process as described in Japanese Patent Application OPI (Kokai) No. 146234/1979; which are subjected in sequence to an electrochemical treatment, chemical etching treatment and anodically oxidized film forming process as described in Japanese Patent Application OPI (Kokai) No. 28123/1973; and which are subjected to a mechanical surface roughening treatment and subsequently to the treatments described in Japanese Patent Application OPI (Kokai) No. 28123/1973. Up to 100,000 sheets of clear prints can be obtained by providing a suitable light-sensitive layer on such a support, but it is still desired to obtain a further number of prints from one printing plate (improvement of printing resistance). To achieve this, it has been proposed to subject a PS plate using an aluminium alloy plate as a support to exposure, development and heat treatment at a high temperature, i.e. so-called burning treatment, thereby strengthening the image portion, as described in detail in Japanese Patent Publications Nos. 27243/1969 and 27244/1969. In this burning treatment, the heating temperature and time, depend upon the resin used for forming the image, but are generally in the range of from 200 to 280°C and 3 to 7 minutes. Recently, it has been required that this burning treatment is carried out at a high temperature over a short period of time so as to shorten the time for the burning treatment. When the commonly used aluminium alloy plates are heated at a high temperature, e.g. 280°C or higher, however, recrystallization of aluminium takes place, the strength thereof is significantly lowered and the printing plates are not firm, thus resulting in the drawbacks that the handling thereof is very difficult and it is impossible to position them in printing machines or to place them in register in multicolour printing. Therefore, the demand for a support consisting of an aluminium alloy plate which is stable and has an excellent heat resistance is increasing. Recently, printing speeds have increased with the progress of the printing techniques. Accordingly, this causes an increase in the stress applied to the printing plate which is fixed mechanically to both the ends of a rotating cylinder installed in a printing machine and when the strength of the aluminium printing plate is insufficient under the increased stress, deformation or breaking of the printing plate occurs at the fixed parts, resulting in a shear in printing and cracking of the printing plate due to repeated stress at the bent part thereof, which makes it impossible to continue printing. The aluminium alloy plates of the prior art according to JIS A 1050 can provide a uniformly rough surface and suitable surface roughness in an electrochemical surface roughening treatment and can avoid the stains on a non-image area during printing, but are inferior in their fatigue resistance and heat softening resistance. On the other hand, the aluminium alloy plates of the prior art according to JIS A 3003 have a sufficient fatigue resistance and heat softening resistance, but suffer from the disadvantages that a uniformly rough surface and suitable surface roughness are scarcely produced by an electrochemical surface roughening treatment and stains tend to occur on the non-image areas during printing. We have now developed a lithographic printing plate comprising an aluminium alloy support, whereby the above described disadvantages can be overcome, which support has a sufficient fatigue resistance as well as a high heat softening resistance as a printing plate, and which is capable of acquiring a uniformly rough surface and a suitable surface roughness by a surface roughening treatment, and which is free from stains on the non-image areas thereof during printing. Accordingly, the present invention provides a presensitized lithographic printing plate comprising a support having thereon a light sensitive layer, wherein the support comprises an aluminium alloy which consists of 0.05 to 0.8% by weight of Mn, with the exception of 0.8% by weight of Mn, not more than 0.2% by weight of Si, not more than 0.5% by weight of Fe, not more than 0.1% by weight of Ti, not more than 0.02% by weight of B, unavoidable traces of impurities and the balance of aluminium. Preferably the aluminium alloy used in the lithographic plate of the invention contains 0.05 to 0.8% by weight of Mn, with the exception of 0.8% by weight of Mn, 0.02 to 0.15% by weight of Si, 0.05 to 0.25% by weight of Fe, not more than 0.1% by weight of Ti, not more than 0.02% by weight of B, unavoidable traces of impurities and the balance of aluminium. All percentages referred to hereinafter are to be taken as those by weight. Mn is added to aluminium for the purpose of improving the strength and heat softening resistance without unfavourably affecting the surface roughening treatment and printing properties or printability. If the quantity of Mn is less than 0.05%, the strength is insufficient, while if it is more than 1% a uniformly rough surface cannot be obtained by an electrochemical roughening method and a coarse compound of Al₆Mn is formed which causes stains during printing. Fe serves to raise the fatigue resistance. If the amount of Fe exceeds 0.5% and Si exceeds 0.2%, however, these components form compounds of Al-Fe-Si, Al-Si and Al-Fe, thus often resulting in stains. The aluminium alloy used in the lithographic plates of the present invention may contain impurities in s such a quantity such as contained in commercially available aluminium alloys. Ti and B, generally used as a fine crystal forming agent in the production of an ingot, may be included, respectively in proportions of up to 0.1% and 0.02%. The aluminium alloy used in the lithographic plates of the present invention is formed into a thin plate by a continuous casting process using a mold or by a process comprising solidification between a pair of cooled rolls or plates and then hot rolling and cold rolling, optionally with intermediate annealing. In the aluminium alloy support used in the present invention, it is effective in order to further improve the fatigue resistance as well as the heat softening resistance to reduce the residual stress accumulated in the support. When the material strength and elongation are varied by varying the extent of a finishing cold rolling and the finishing annealing temperature, it is found that the fatigue life is sufficient if the elongation amounts to at least 5%. The stiffness as a support for a lithographic printing plate presents no problems in practical use at a stress resistance of at least 10 kg/mm². A preferred stress resistance is at least 15 kg/mm². A useful way of obtaining these desired properties comprises effecting a finishing cold rolling in a proportion of 10 to 50% after the intermediate annealing, or effecting a softening treatment (finishing annealing) at a temperature of 200 to 320°C after the finishing cold rolling step. Processes for the surface treatment of the aluminium alloy support of the present invention are described in detail below. Examples of the surface treatment which can be applied to the aluminium alloy support of the present invention include electrochemical processes, in which roughening is carried out in an electrolytic solution containing hydrochloric acid or nitric acid by passing an electric current therethrough, and mechanical processes such as a wire brush roughening process wherein the aluminium surfaces are scratched by a metal wire, a ball process wherein the aluminium surfaces are rubbed by abrasive balls and abrasives, or a brush process wherein aluminium surfaces are rubbed by a nylon brush and abrasives. These roughening processes may be employed independently or in combination. The electrochemical processes have the advantages that a uniformly rough surface and suitable surface roughness can be obtained and stains hardly occur on the non-image areas during printing. After the surface treatment, the aluminium plate is subjected to a chemical etching process using an acid or alkali. If an acid is used as the etching agent, it takes a very long time to destroy the fine structure. Accordingly, it is generally preferred to use an alkali as the etching agent. Examples of the alkali which can advantageously be used in the present invention include sodium hydroxide, sodium carbonate, sodium aluminate, sodium metasilicate, sodium phosphate, potassium hydroxide or lithium hydroxide. Of these sodium aluminate is preferred. A preferred concentration of such an alkali in the etching solution and a preferred temperature for the etching process range, respectively, from 1 to 50% and 20 to 100°C, so as to dissolve the aluminium in an amount of 5 to 20 g/m². After the etching process, the aluminium alloy plate is pickled with an acid to remove any dirt remaining on its surface. Examples of the acid which can be used for this purpose include nitric acid, sulfuric acid, phosphoric acid, chromic acid, hydrofluoric acid and borofluoric acid. For the removal of dirt, in particular, after an electrochemical surface roughening treatment, a method as described in Japanese Patent Application OPI (Kokai) No. 12739/1958, can be used in which the dirt is removed by contact with 15 to 65 wt. % sulfuric acid at a temperature of from 50 to 90°C, and an alkali etching method as described in Japanese Patent Publication No. 28123/1973. The thus processed aluminium plates are used as the support for a lithographic printing plate and if necessary, they are preferably submitted further to an anodic oxidation film forming process or a chemical process. The anodic oxidation process can be carried out using techniques which are known in the art. For example, an anodically oxidized film can be formed on the surface of an aluminium support by passing a DC or AC current through the aluminium support in an aqueous or non-aqueous solution of sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid or a mixture of two or more of these acids. The process conditions for the anodic may be changed depending on what electrolytic solution is used and, therefore, they cannot be determined indiscriminately. However, as a general guide, an electrolytic solution having a concentration of from 1 to 80 wt. %, a solution temperature of from 5 to 70°C. a current density of from 0.5 to 60 ampere/dm², a voltage of from 1 to 100 V and an electrolysis time of from 10 to 100 seconds can produce preferable results. Particularly effective anodically oxidized film forming processes are those described in British Patent No. 1,412,768, wherein anodic oxidation is carried out in sulfuric acid at a high current density, and described in US Patent No. 3,511,661, wherein anodic oxidation is carried out using phosphoric acid as an electrolytic bath. The aluminium plate which has been anodically oxidized may further be treated with an aqueous solution of an alkali metal silicate such as sodium silicate in conventional manner, e.g. by dipping as described in US Patent Nos. 2,714,066 and 3,181,461. Alternatively, a layer made of hydrophilic cellulose (e.g., carboxymethyl cellulose) containing a water-soluble metal salt (e.g., zinc acetate) can additionally be provided on the anodically oxidized aluminium plate, as described in US Patent No. 3,860,426. The aluminium alloy support used for the lithographic printing plate according to the present invention is then provided with a light-sensitive layer which is known to have been used for PS plates to produce a presensitized lithographic printing plate. The lithographic printing plate obtained by subjecting this PS plate to a plate making process has an excellent performance. Suitable examples of the composition of the'above described light-sensitive layer are described below: (1) Light-sensitive layer comprising a diazo resin and a binder Preferably, a condensate of formaldehyde and diphenylamine-p-diazonium salt, or the reaction product of a diazonium salt and an organo condensing agent containing a reactive carbonyl group, such as an aldol or an acetal (so-called light-sensitive diazo resin) is used as described in US Patent Nos. 2,063,631 and 2,667,415. Other useful condensed diazo compounds are described in Japanese Patent Publication Nos. 48,001/1974, 45,322/1974 and 45,323/1974. The light-sensitive diazo compounds of this type can be obtained in the form of a water-soluble inorganic salt and can thus be coated from an aqueous solution. Alternatively, the water-soluble diazo compounds may be reacted with an aromatic or aliphatic compound having at least one of a phenolic hydroxyl group or a sulfonic acid group and the both by the process described in Japanese Patent Publication No. 1,167/1972 and the resulting reaction products, i.e. substantially water-insoluble light-sensitive diazo resins can be used. In addition, the water-soluble diazo compounds can be used as reaction products with hexafluorophosphates or tetrafluoroborates, as described in Japanese Patent Application OPI (Kokai) No. 121,031/1981. (2) Light-sensitive layer comprising an o-quinone-diazide compound Particularly preferred examples include o-naphthoquinonediazide compounds as described in US Patent Nos. 2,766,118, 2,767,092, 2,772,972, 2,859,112, 2,907,665, 3,046,110, 3,046,111, 3,046,115, 3,046,118, 3,046,119, 3,046,120, 3,046,121, 3,046,122, 3,046,123, 3,061,430, 3,102,809, 3,106,465, 3,635,709, 3,647,443 (incorporated by reference) and many other publications. (3) Light-sensitive layer comprising a composition containing an azide compound and a binder (macromolecular compound) Specific examples of these compositions include compositions comprising azide compounds and water-soluble or alkali-soluble macromolecular compounds which are described in British Patent Nos. 1,235,281 and 1,495,861 and Japanese Patent Application OPI (Kokai) Nos. 32,331/1976 and 36,128/1976, and compositions comprising azide group-containing polymers and macromolecular compounds as binders which are described in Japanese Patent Application OPI (Kokai) Nos. 5,102/1975, 84,302/1975, 84,303/1975 and 12,984/1978. (4) Light-sensitive layers comprising other light-sensitive resinous compositions Specific Examples include polyester compounds described in US Patent No. 4,101,326, polyvinyl cinnamate ester resins described in British Patent Nos. 1,112,277, 1,313,309, 1,341,004 and 1,377,747, and photopolymerizable photopolymer compositions described in US Patent Nos. 4,072,528 and 4,072,527 (incorporated by reference). The amount (thickness) of the light-sensitive layer to be provided on the support is controlled to about 0.1 to about 7 g/m², preferably 0.5 to 4 g/m². PS plates, after imagewise exposure, are subjected to processing, including a developing step in a conventional manner, to form resin images. For example a PS plate having light-sensitive layer (1) constituting a diazo resin and a binder has unexposed portions of the light-sensitive layer removed by development after imagewise exposure to produce a lithographic printing plate. On the other hand, a PS plate having a light-sensitive layer (2) has exposed portions of the light-sensitive layer which are removed by development with an alkaline aqueous solution after imagewise exposure to produce a lithographic printing plate. The following examples are given in order to illustrate the present invention in detail without limiting the same. Example 1 An alloy shown in Table 1 was cast in conventional manner and subjected to cutting of both the surfaces to form an ingot with a thickness of 500 mm, a width of 1000 mm and a length of 3500 mm, optionally homogenizing, hot rolling to a thickness of 1.5 mm, intermediate annealing at 360°C for 1 hour, finishing cold rolling and finishing annealing to obtain a plate with a thickness of 0.30 mm shown in Table 2. Sample No. 1 was further subjected to intermediate annealing at a thickness of 0.5 mm and Sample Nos. 2, 3, 4 and 6 were subjected to finishing annealing at 240 to 280°C for 3 hours. These aluminum alloy plates were then subjected to assessment of the electrochemical etching property, fatigue resistance, heat softening resistance and printability according to the following procedures, thus obtaining results shown in Table 2. (1) Electrochemical etching property The surface state is observed by means of a scanning electron microscope to assess the uniformity of pits. Better: ○; good; Δ; bad: X. (2) Fatigue resistance One end of a sample piece bent in 90 degrees at a corner of 2 mmR is repeatedly loaded with a tensile load of 5 kg/mm² at 25 Hz and the repeated number of loading is measured until broken. Practically, a repeated number of 80,000 is desirable. (3) Heat softening resistance A sample is heated at 300°C for 7 minutes in a burning processor (Burning Processor 1300-commercial name-having a heat source of 12 kW manufactured by Fuji Photo Film Co.) and cooled to examine the heat softening property sensuously by hands. (4) Printability A printing plate is processed by the following procedure and charged in an offset press KOR (commercial name) to examine the degree of stains on a non-image area. The printing plate was prepared as follows: An aluminum alloy plate was subjected to a graining treatment in a suspension of pumice stone and water using rotated nylon brushes and then etched with a 20% aqueous solution of sodium hydroxide so that the amount of aluminum dissolved was 8 g/m². After the plate was washed thoroughly with running water, it was pickled with a 25% aqueous solution of nitric acid and subsequently washed with water to prepare a base plate. The thus prepared base plate was then subjected to AC electrolysis in an electrolytic bath containing 0.5 to 2.5% of nitric acid with a current density of 20 A/dm² or more, as described in Japanese Patent Application OPI (Kokai) No. 146,234/1979, and subsequently, the surface of the base plate was cleaned by dipping in a 15% aqueous solution of sulfuric acid at 50°C for 3 minutes and processed to provide an oxidized film at a coverage of 3 g/m² in an electrolytic bath containing 20% sulfuric acid as a major component at a bath temperature of 30°C. On the thus processed sample was provided a light-sensitive layer having the following composition to give a coating thickness of 2.5 g/m² on dry basis: The thus obtained presensitized printing plate was imagewise exposed for 60 seconds by means of a metal halide lamp of 3 kW placed at a distance of 1 meter, developed with an aqueous solution of sodium silicate having an SiO₂/Na₂O molar ratio of 1.2 and an SiO₂ content of 1.5 wt. %, washed with water, dried and subjected to gum coating. Sample Nos. 1 to 4 using Alloy A in accordance with present invention each have a higher fatigue resistance, better heat softening resistance, better electrochemical etching property and better printability, while Sample No. 6 using Comparative Alloy B is a commonly used material and Sample No. 6 is a material obtained by subjecting the same to finishing annealing to improve the fatigue life, which is not suitable, however, for practical use because of its low material strength and stains occurring during printing. Sample Nos. 2 to 4 according to the present invention are examples wherein the fatigue resistance is largely improved with holding the strength (stiffness) sufficient by subjecting to a finishing annealing treatment. Example 2 An alloy ingot shown in Table 3 was subjected to hot rolling and cold rolling to a thickness of 1.0 mm, intermediate annealing at 360°C for 1 hour, finishing cold rolling in 70% and finishing annealing at 280°C to obtain an aluminum alloy plate with a thickness of 0.30 mm. The resulting alloy plates were subjected to assessment of the properties in an analogous manner to Example 1. Alloy Sample Nos. 7 to 10 in accordance with present invention, in which amounts of Si and Fe are specified and suitable amounts of Mn are added to control the strength and elongation, exhibit more excellent properties in all of the electrochemical etching property, fatigue resistance, heat softening resistance and printabilty as compared with Comparative Sample Nos. 11 and 12. Example 3 Alloy Nos. J, K and L in accordance with present invention and Comparative Alloy Nos. M, N, O and P shown in Table 5 were respectively melted and cast, and subjected to cutting of both the surfaces to form an ingot with a thickness of 500 mm, a width of 1000 mm and a length of 3500 mm, optionally homogenizing, hot rolling to a thickness of 4 mm, cold rolling to a thickness of 0.3 mm and finishing annealing at a heating rate of 20°C/hr with holding conditions of 230-260°C×5 hrs, thus obtaining aluminum alloy plates J-1, K-1, L-1, M-1, N-1, O-1 and P-1. These aluminum alloy plates were surface-treated in an analogous manner to Example 1 to obtain printing plates. The thus resulting printing plates were subjected to assessment of the electrochemical etching property, fatigue resistance, heat softening resistance and printability in an analogous manner to Example 1. Example 4 Of the alloys having the compositions shown in Table 5, Alloys J, K, L, M, N and O were respectively converted into hot rolled plates with a thickness of 4 mm in an analogous manner to Example 3, then cold rolled in a thickness of 0.6 mm, subjected to intermediate annealing at a heating rate of 20°C/hr with holding conditions of 390°C×2 hrs and cold rolled in a thickness of 0.3 mm to obtain aluminum alloy plates J-2, K-2, L-2, M-2, N-2 and 0-2. Printing plates were prepared therefrom in an analogous manner to Example 1 and subjected to examination of the properties, thus obtaining results as shown in Table 7: Example 5 The alloys having the compositions shown in Table 5 were respectively converted into hot rolled plates with a thickness of 4 mm in an analogous manner to Example 3, then cold rolled in a thickness of 0.6 mm, subjected to intermediate annealing by heating up to 390°C at a heating rate of 20°C/sec and immediately cooling at a cooling rate of 20°C/sec, and then further cold rolled in a thickness of 0.3 mm to obtain aluminum alloy plates J-3, K-3, L-3, M-3, N-3, O-3 and P-3. Printing plates were prepared therefrom in an analogous manner to Example 1 and subjected to assessment of the properties, thus obtaining results shown in Table 8: As is evident from the results of Examples 3 to 5, the aluminum alloys used in present invention satisfy all of the electrochemical etching property, fatigue resistance, heat softening resistance and printability, while the comparative aluminum alloys do not satisfy two or more of these properties.

Claims: A presensitized lithographic printing plate comprising a support having thereon a light-sensitive layer, wherein the support comprises an aluminium alloy which consists of 0.05 to 0.8% by weight of Mn, with the exception of 0.8% by weight of the Mn, not more than 0.2% by weight of Si, not more than 0.5% by weight of Fe, not more than 0.1% by weight of Ti, not more than 0.02% by weight of B, unavoidable traces of impurities and the balance of aluminium. A lithographic printing plate as claimed in claim 1 wherein the aluminium alloy contains 0.05 to 0.8% by weight of Mn, with the exception of 0.8% by weight of Mn, 0.02% to 0.15% by weight of Si, 0.05 to 0.25% by weight of Fe, not more than 0.1% by weight of Ti, not more than 0.02% by weight of B, unavoidable traces of impurities and the balance of aluminium. A lithographic printing plate as claimed in any one of the preceding Claims wherein the stress resistance of the support is at least 10 kg/mm² and the elongation at break is at least 5%. A lithographic printing plate as claimed in Claim 3 wherein the stress resistance of the support is at least 15 kg/mm². A lithographic printing plate as claimed in any one of the preceding Claims wherein a finishing cold rolling of the support is carried out with a ratio of 10 to 50% after an intermediate annealing step. A lithographic printing plate as claimed in any one of the preceding Claims wherein a finishing annealing of the support is carried out at a temperature in the range of from 200 to 320°C after a finishing cold rolling step. A lithographic printing plate as claimed in any one of the preceding claims wherein the surface of the aluminium alloy support is roughened and anodically oxidized. A lithographic printing plate as claimed in Claim 7 wherein the surface of the aluminium alloy support is roughened by an electrochemical treatment.

Inventors: ABE YUJI, MATSUO MAMORU, SAKAKI HIROKAZU, TAJIRI AKIRA, TAKIZAWA KAZUSHIGE, TSUCHIDA SHIN, ABE, YUJI, MATSUO, MAMORU, SAKAKI, HIROKAZU, TAJIRI, AKIRA, TAKIZAWA, KAZUSHIGE, TSUCHIDA, SHIN
Applicants: FUJI PHOTO FILM CO LTD, SKY ALUMINIUM, SUMITOMO LIGHT METAL IND, FUJI PHOTO FILM CO., LTD., SKY ALUMINIUM CO., LTD., SUMITOMO LIGHT METAL INDUSTRIES, LTD.
Application year: 1985
Main classification: C22C21
IPC codes: C22C21, B41N1