Litho strip with high cold-rolling pass reduction

Abstract

Provided is a method for production of an aluminium strip for lithographic printing plate supports from an aluminium alloy including (in wt %): 0.05%Si0.25%, 0.2%Fe1%, Cu max. 400 ppm, Mn0.30%, 0.10%Mg0.50%, Cr100 ppm, Zn500 ppm, Ti<0.030%, the remainder aluminium and unavoidable impurities individually at most 0.03%, in total at most 0.15%. In the method, a rolling ingot is cast from an aluminium alloy, and the rolling ingot is homogenised. Further, the rolling ingot is hot rolled to a hot strip final thickness, and the hot strip is cold rolled to final thickness of between 0.1 mm and 0.5 mm. The product of the relative final thicknesses of the aluminium strip after the first and after the second cold rolling pass of the aluminium strip is 15% to 24%.

Claims

1. A method for production of an aluminium strip for lithographic printing plate supports from an aluminium alloy, wherein the aluminium alloy of the aluminium strip for lithographic printing plate supports comprises the following alloy constituents in % by weight: 0.05%Si0.25%, 0.2%Fe1%, Cu max. 400 ppm, Mn0.30%, 0.10%Mg0.50%, Cr100 ppm, Zn500 ppm, Ti<0.030%, the remainder aluminium and unavoidable impurities individually at most 0.03%, in total at most 0.15%, with at least the following steps: casting of a rolling ingot from an aluminium alloy, homogenising of the rolling ingot, hot rolling of the rolling ingot to a hot strip thickness, and cold rolling of the hot strip to final thickness, wherein the final thickness of the aluminium strip after cold rolling is between 0.1 mm and 0.5 mm, wherein on cold rolling, the product of the relative final thicknesses of the aluminium strip from a first and second cold rolling pass is 17% to 22%.

2. The method according to claim 1, wherein the hot strip thickness is 2.3 mm to 3.7 mm.

3. The method according to claim 1, wherein on cold rolling, the first cold rolling pass is carried out with a pass reduction of maximum 65%.

4. The method according to claim 1, wherein the second cold rolling pass has a pass reduction of maximum 60%.

5. The method according to claim 1, wherein three cold rolling passes to final thickness are performed, and the final thickness of the aluminium strip after cold rolling is 0.2 mm to 0.4 mm.

6. The method according to claim 1, wherein four cold rolling passes to final thickness are performed, and the final thickness of the aluminium strip after cold rolling is less than 0.2 mm.

7. The method according to claim 1, wherein, during cold rolling, no intermediate annealing is performed.

8. The method according to claim 1, wherein a third or fourth cold rolling pass has a maximum pass reduction of 52%.

9. The method according to claim 1, wherein the aluminium alloy of the aluminium strip for lithographic printing plate supports has a magnesium content of 0.15%Mg0.45%.

10. The method according to claim 1, wherein the aluminium alloy of the aluminium strip for lithographic printing plate supports has a magnesium content of 0.24% to 0.45% by weight.

11. The method according to claim 1, wherein the hot strip thickness is from 2.5 mm to 3.0 mm.

12. The method according to claim 1, wherein the aluminium alloy of the aluminium strip for lithographic printing plate supports has a magnesium content of 0.26% to 0.35% by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in more detail below with reference to exemplary embodiments in conjunction with the drawing. The drawing shows in:

(2) FIG. 1 shows a diagrammatic view, the basic method steps for production of an aluminium strip for lithographic printing plate supports;

(3) FIG. 2 shows a diagrammatic sectional view, the performance of a cold rolling pass with one or more cold rolling passes; and

(4) FIGS. 3a)-3c) show a comparison of SEM images of surface regions, which are considered good and poor, of an aluminium strip for lithographic printing plate supports.

DETAILED DESCRIPTION

(5) FIG. 1 shows diagrammatically the various method steps in the production of an aluminium strip for lithographic printing plate supports. Firstly, according to step 1, the aluminium alloy is cast into a rolling ingot. In step 2, the rolling ingot is subjected to homogenisation, wherein the rolling ingot is heated to temperatures from 450 C. to 600 C. for a duration of at least 1 hour. The homogenised rolling ingot is prepared for hot rolling and then hot-rolled at temperatures of over 280 C. At the start of the hot rolling, the temperature of the ingot is around 450 C. to 550 C. The hot rolling final temperature is usually from 280 C. to 350 C. The hot strip final thickness may lie between 2 mm and 9 mm; however, hot strip thicknesses from 2.3 mm to 3.7 mm are preferred. The hot strip is sent for cold rolling in step 4. In cold rolling, the hot strip is cold-rolled to final thickness. Cold rolling and in particular the last cold rolling pass determine the surface properties of the cold-rolled aluminium strip, since the surface topography of the cold roll is directly transferred to the cold-rolled aluminium strip. During the rolling pass, in cold rolling, defects can occur which are then transferred to the surface or remain directly visible on the surface. Because of this circumstance, previously only moderate pass reductions of at most 50% for the individual cold rolling step were provided, since it is known that if the pass reduction is too high, there is either a risk of damaging the cold rolls or regions of the surface of the aluminium strip are broken away, leading to surface defects. In view of the high requirements for homogeneity of the surface of lithographic printing plate supports, surfaces with uneven appearance, for example streaky surfaces, are unacceptable.

(6) Cold rolling according to step 4 may take place both with and without intermediate annealing. Intermediate annealing is performed at temperatures of 230 C. to 490 C. for at least 1 hour in a chamber furnace, or continuously in a continuous belt furnace for at least 10 seconds, usually before the last cold rolling pass. Intermediate annealing allows the final strength of the aluminium strip for lithographic printing plate supports to be set within certain ranges before the last cold rolling pass. However, intermediate annealing also entails costs, so particularly cost-efficient production is preferably performed without intermediate annealing.

(7) Usually, for cold rolling, rolls stands are used which perform a single cold rolling pass, and the aluminium strip is rewound immediately after the cold rolling pass. FIG. 2 shows a corresponding roll stand 5 which has an uncoiling reel 6, a coiling reel 7, and a roll arrangement 11 with two working rolls 9 and 10. FIG. 2 shows as an example a quarto roll stand. The roll arrangement may also be configured as a duo, quarto or sexto roll stand. An additional roll arrangement 11 is also indicated, so that after passing through the roll arrangement 11, the strip 8 may undergo a further rolling pass in the roll arrangement 11, i.e. in total a multiple pass. Usually however, as already stated, individual cold rolling passes are performed and the aluminium strip 8 is then coiled into a coil on the coiling reel 7. In some cases, after cooling of the aluminium strip 8 in the coil after the cold rolling pass, the aluminium strip may be supplied to a further cold rolling pass.

(8) FIGS. 3a) to 3c) show scanning electron microscope images of cold-rolled aluminium strips for lithographic printing plate supports. FIG. 3a) shows, at the same magnification as FIG. 3b), a strip considered to be inconspicuous from the surface. The roll webs of the ground rolls which have been imprinted into the aluminium strip are clearly evident. However, almost no structures are present perpendicular to the roll direction, so the overall impression of the surface is considered non-streaky.

(9) FIGS. 3b) and 3c) in contrast show a surface region of an aluminium strip which is regarded as uneven, which leads to a streaky appearance of the aluminium strip. A corresponding strip would not meet the surface requirements for lithographic printing plate supports. FIGS. 3b) and 3c) show surface defects, in particular magnified in FIG. 3c), which have regions extending transversely to the roll direction in which the material has been removed from the surface of the strip. It is assumed that these defects are attributable to the cold rolling. The width of the problematic region is around 20 m perpendicular to the rolling direction and is evident on a visual inspection.

(10) Aluminium strips were produced from six different aluminium alloys A to H using the method steps 1 to 3 explained above and depicted in FIG. 1. The aluminium strips were produced without intermediate annealing on cold rolling, wherein the hot strip final thickness and the pass reductions on cold rolling were varied. The aluminium alloys differ in particular in the differing contents of silicon, iron, manganese and magnesium. The different alloy compositions are shown in Table 1 with their alloy constituents as percentages by weight. In addition, all alloys contained chromium at less than 50 ppm, and unavoidable impurities individually at most 0.03% by weight and in total at most 0.15% by weight.

(11) TABLE-US-00001 TABLE 1 Alloy wt % Si Fe Cu Mn Mg Zn Ti A 0.092 0.438 0.0019 0.039 0.262 0.0114 0.0051 B 0.084 0.420 0.0019 0.255 0.244 0.0124 0.0051 C 0.077 0.435 0.0018 0.040 0.264 0.0093 0.0072 D 0.128 0.429 0.0016 0.040 0.285 0.0087 0.0068 E 0.085 0.374 0.0016 0.003 0.196 0.0090 0.0050 F 0.116 0.438 0.0015 0.040 0.324 0.0136 0.0075 G 0.119 0.436 0.0010 0.040 0.323 0.0137 0.0058 H 0.085 0.374 0.0016 0.003 0.196 0.0090 0.0050

(12) The hot strip final thickness of the produced aluminium strips varied from 2.3 mm to 3.0 mm, and from the hot strips of varying thickness, aluminium strips for lithographic printing plate supports were produced by cold rolling without intermediate annealing and with a final thickness from 0.274 mm to 0.285 mm. The pass reductions of the first and second cold rolling passes were selected such that, starting from the hot strip final thickness, a maximum of three cold rolling passes to final thickness were required, wherein the last cold rolling pass had a maximum pass reduction of 51%. As Table 2 shows, the product P of the relative final thicknesses after the first and after the second cold rolling passes, because of the pass reductions in the first two cold rolling passes, was 18.57% to 21.74%. This means that because of the first two cold rolling passes, the strip was rolled to an intermediate thickness of 18.57% to 21.74% of the hot strip final thickness.

(13) Table 2 shows the exemplary embodiments according to the invention and the associated pass reductions, and the values for the product of the relative end thicknesses after the first and second cold rolling passes.

(14) TABLE-US-00002 TABLE 2 Hot strip 1st cold 2nd cold 3rd cold Final final rolling rolling Prod- rolling thick- thickness pass (a1) pass (a2) uct P pass ness No. Alloy [mm] [%] [%] [%] [%] [mm] 1 A 2.3 57 50 21.74 45 0.275 2 B 2.3 57 50 21.74 45 0.275 3 C 2.8 57 53 20.00 51 0.274 4 C 2.8 57 53 20.00 51 0.274 5 C 2.8 57 53 20.00 51 0.274 6 D 2.8 57 53 20.00 51 0.274 7 D 2.8 57 53 20.00 51 0.274 8 D 2.8 57 53 20.00 51 0.274 9 D 2.8 57 53 20.00 51 0.274 10 E 2.8 50 60 20.00 51 0.275 11 F 2.8 64 48 18.57 45 0.285 12 F 2.8 64 48 18.57 45 0.285 13 G 2.8 64 48 18.57 45 0.285 14 G 2.8 64 48 18.57 45 0.285 15 H 3.0 60 53 18.67 51 0.275

(15) In order to examine the surfaces in relation to their suitability for lithographic printing plate supports, two tests were developed to evaluate the streakiness S of the surfaces of the cold-rolled aluminium strips. The test methods serve to highlight possible streakiness defects by surface preparation and make these more easily identifiable visually.

(16) In the so-called K test, the grain streakiness of the aluminium alloy strips was investigated. For this, the surfaces must be specifically prepared to expose the grain structure. Firstly, rectangular specimens 250 mm long in the roll direction and 45 mm wide were cut from the strips. The specimens were taken both from the edge and from the centre of the strips in relation to the roll direction. The K test aims to reveal whether, because of the grain distribution, a streakiness effect can be seen in the surface.

(17) The specimens thus cut out were ground initially for 60 seconds using an orbital sander, wherein the oscillating sander was wrapped in a damp cloth and scouring agent was used to polish the specimens. The scouring agent used here may be a simple domestic scouring agent. After rinsing the surface with water, the specimens were immersed in a 30% soda lye at a temperature of 60 C. for 15 seconds and then rinsed with water. Macro etching then took place in a macro etching solution. This consists of:

(18) 40 ml water,

(19) 300 ml HCl with a concentration of 37%,

(20) 133.6 ml HNO.sub.3 with 65% concentration, and

(21) 43.34 ml of 40% hydrofluoric acid.

(22) The macro etching took place at around 25 to 30 C. for 30 seconds. The specimen was then rinsed with water again and immersed for 15 seconds in the 30% soda lye at a temperature of 60 C. Subsequent neutralisation took place with a solution of 40.5 ml of 85% phosphoric acid and 900 ml water at room temperature for around 60 seconds. The specimen was then rinsed with water and dried at room temperature. After drying, the specimens were visually assessed for streakiness. Reference samples with value numbers from 1 to 10 were used for assessment of the streakiness in the K test. A comparison was made between the reference sample and the specimen using the human eye. The specimens were then assigned the value number of the nearest reference sample. The value number of 10 here means not streaky. The value number of 1 corresponds to a streaky appearance. This streakiness, as already stated, is caused by the grain distribution of the aluminium strips and can be easily assessed using this test.

(23) As evident from Table 3, the exemplary embodiments with high pass reductions of 64% in the first cold rolling pass indeed show good values in relation to the value number of the K test. Their surface as a whole however is somewhat poorer than the exemplary embodiments with lower pass reductions in the first cold rolling pass.

(24) It was found that, in addition to the established K test, a further test must be used since in particular the surface defects from cold rolling, shown in FIGS. 3b) and 3c), were evidently not revealed by the previous K test. This is shown by the results of the newly developed test.

(25) An additional pickling test was developed. The specimen was a rectangular cut-out of 250 mm edge length in the rolling direction and 80 mm edge length perpendicular to the rolling direction, which was first subjected to degreasing in a watery solution with a degreasing medium, here under the brand name Nabuclean 60S, at 60 C. for 10 seconds. The concentration of the degreasing medium is 15 g/l. After rinsing with water, the specimen was immersed in a soda lye solution and etched for around 10 seconds at 50 C. The soda lye concentration was 50 g/l. Then rinsing with water took place followed by drying in the drying cabinet at around 70 C. After drying, the specimens were evaluated, wherein again reference samples were used to which values from 0 to 5 were assigned, wherein the value 0 is considered not streaky and the value 5 refers to a surface regarded as streaky. In the pickling test, the specimens were compared with reference samples and evaluated before and after pickling.

(26) No surfaces with value number 5 were found in the pickling test. In experiments 11 to 14, a cold rolling pass reduction of 64% was used in the first cold rolling pass, which had a significant effect on the surface quality in the evaluation of the specimens in the pickling test, both before performance of the pickling test and after pickling. In comparison with experiments 1 to 10 produced with the lower pass reductions, experiments 11 to 14 showed results with value numbers 3-4 and 3 in the pickling test. These indicate a poorer surface quality in this test. A pass reduction of 65% in the first cold rolling pass must therefore be regarded as the maximum. Any increase above this level, according to our present knowledge, leads to significant disadvantages in relation to surface quality.

(27) All other specimens showed values of 2-3 or 3 after the pickling test and hence sufficiently good surface qualities. This means that as the pass reductions in the first cold rolling pass reduce, the surface quality in the pickling test increases. In general, it was found that pass reductions of at most 60% in the first and second cold rolling passes, despite the omission of one cold rolling pass, gave good surfaces in the pickling test.

(28) Thus, for various aluminium alloys which contain magnesium with different hot strip final thicknesses, it could be shown that a cold rolling pass could be omitted in the production of cold-rolled aluminium strips for lithographic printing plate supports without influencing the surface quality too greatly. As a result, therefore, a production method can be provided which, by saving one cold rolling pass, may provide cheaper aluminium strips for lithographic printing plate supports.

(29) TABLE-US-00003 TABLE 3 K Test Pickling test No. Alloy Edge Centre before after 1 A 5 3-4 1 2-3 2 B 4-5 4 1 3 3 C 2-3 2 1 2-3 4 C 2-3 2-3 2 2-3 5 C 3 3 0 3 6 D 3-4 3 2 2-3 7 D 2-3 3 2 2-3 8 D 3 3-4 0 3 9 D 4 3-4 0 2-3 10 E 5 1-2 1-2 2-3 11 F 7 3-4 3 3 12 F 6-7 4 3 3 13 G 7 4-5 2 3-4 14 G 7 4-5 3 2-3 15 H 5-6 2 1-2 2-3

(30) All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

(31) The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(32) Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.