Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N1/00—Printing plates or foils; Materials therefor
  • B41N1/04—Printing plates or foils; Materials therefor metallic
  • B41N1/08—Printing plates or foils; Materials therefor metallic for lithographic printing
  • B41N1/083—Printing plates or foils; Materials therefor metallic for lithographic printing made of aluminium or aluminium alloys or having such surface layers
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/06—Alloys based on aluminium with magnesium as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent

Definitions

• This invention relates to an Al alloy suitable for processing into a lithographic sheet, which exhibits good mechanical properties with good electrograining characteristics.
• the lithographic sheet market largely consists of products in the 1XXX and 3XXX alloy range.
• the 1XXX alloys are used with both nitric and hydrochloric acid electrolytes and generally have the better graining response.
• the 3XXX alloys mainly AA3103, are used where greater strength is demanded by the printer but can only be grained in hydrochloric acid, and even then not by all platemakers.
• an Al alloy suitable for processing into a lithographic sheet having a composition in wt%:
• the alloy is relatively cheap to produce as it contains alloying elements in smaller amounts compared with AA3103. Furthermore, the alloy has an added commercial benefit by providing the potential for reduced inventories for manufacturers and their customers. The alloy has also been found to resist the softening encountered during stoving or heating at temperatures of about 240°C or even 270°C.
• magnesium and manganese are sufficient to attain much improved mechanical properties while still allowing adequate electrograining in hydrochloric acid, and preferably in nitric acid in some embodiments.
• Magnesium is preferably present in an amount of 0.06 to 0.30wt%, even more preferably 0.10 to 0.30-wt%. Magnesium is the element influencing work hardening in the alloy. However, if the magnesium level is raised too far, then electrograining becomes increasingly difficult especially in nitric acid electrolyte.
• Manganese is present in an amount of 0.05 to 0.25wt%, preferably in an amount of 0.05 to 0.20wt%. In either case, the lower limit of Mn may optionally be 0.06wt%. Manganese provides maximum stoved strength, and a minimum drop in strength compared with the as cold rolled sheet. The optimum upper level of manganese is determined by a balance between the desirable stoving resistance on the one hand and the onset of an undesirable level of streaking and discolouration after electrograining on the other hand.
• copper is present in an amount up to 0.005%, more preferably up to 0.003%.
• Ti is present in total amounts of up to 0.03wt%.
• up to 0.028wt% of the titanium is free i.e. present in solid solution and not tied up for example as the boride, TiB 2 .
• titanium is present in a total amount up to 0.015 wt%, even more preferably 0.010 wt%.
• Grain refiner may or may not be present; if it is, some additional titanium is present over that found in virgin metal.
• the free titanium content is too high, this may have a detrimental effect on the ability to grain the formed lithographic sheet in nitric acid, although it may still be grainable in hydrochloric acid.
• the level of titanium preferably needs to be controlled. If too much free titanium is present it is detrimental to graining; titanium combined with boron is not detrimental.
• B is preferably present in an amount up to 0.002.
• zinc may be present in an amount of up to 0.05wt%.
• a zinc content in the range of 0.01 to 0.15wt% has been found to be advantageous in order that the alloy can be satisfactorily grained by electrograining in nitric acid.
• the zinc content of the alloy will typically be in the range of from 0.01 to 0.1wt% and more preferably from about 0.01 to 0.08wt%.
• Especially preferred zinc contents will be in the range of from 0.015 to 0.06wt% and most preferably from about 0.02 to about 0.05wt%.
• Zirconium may typically be present in amounts up to 0.019wt%, for example up to 0.015wt%, particularly up to 0.005wt%. In a preferred embodiment, there is no deliberate addition of zirconium.
• iron is present in an amount of 0.20 to 0.40%.
• Silicon may be present in an amount of 0.05 to 0.15%, for example 0.09 to 0.15%.
• Such alloys have been found to exhibit good strength properties in both the as-rolled and stoved embodiments, and are reasonably cost effective for use in high volume production of lithographic sheet.
• Silicon in solution alters the reactivity of the sheet during electrograining. If the amount of silicon present is too small, too many pits form during graining and the surface is not suitable for lithographic sheet. If the amount of silicon present is too great, too few pits form during electrograining and they are too large.
• Iron in solution has a similar effect to silicon as regards electrograining.
• iron forms intermetallic phases present as particles in the sheet. The presence of too many of these iron containing particles is detrimental to graining.
• a lithographic sheet formed from the alloy in such a lithographic sheet, titanium may be present in an amount sufficient to enable the sheet to be capable of being electrograined in nitric acid, although it should be borne in mind that in some embodiments of the invention the presence of titanium is not essential to the ability to electrograin in nitric acid.
• free Ti is present up to 0.028wt% in general but only up to 0.019wt%, for example up to 0.015wt%, for nitric acid graining.
• TiB 2 is, in one embodiment, present up to 170ppm, but it can be higher.
• a DC cast ingot comprising the alloy.
• a method of processing an Al alloy as defined above comprises the steps of: casting, optional homogenising, optional hot rolling, cold rolling, optional interannealing.
• the casting step is, in one embodiment, a DC casting step.
• the DC cast ingots are scalped prior to the homogenising step. Homogenising is used to get the right amount of Fe and Mn in solid solution. Other casting options include roll casting or belt casting. If these continuous casting processes are used, then homogenising and scalping may not be necessary. This is because the rapid cooling in continuous casting holds a lot of Fe and Mn in solid solution.
• Heat treatment after casting and before hot rolling affects both the strength loss during stoving and the response to electrograining. To some extent the effects are contradictory and an optimum treatment has to be found.
• Two alternative homogenising treatments are envisaged. Firstly, there is a two stage homogenisation designated Type 2. This involves slow heating of the alloy to a temperature higher than the rolling temperature and holding at this temperature. During heating to this temperature and during holding, Mn is taken into solution. The ingot is then cooled to the hot rolling temperature and rolled either after holding for a period or immediately on reaching the hot rolling temperature. Some Mn will come out of solution during cooling but the process is slow and most will remain in supersaturated solution.
• An example of this treatment is: slow heat to 550 to 610°C and holding in that temperature range for typically 1 to 10 hours. This is followed by cooling to the rolling temperature and hot rolling at a temperature of between 450 to 550°C.
• the homogenisation may be carried out with a heat-to-roll practice (designated Type 1 ). This involves heating the alloy as cast (and scalped) to the hot rolling temperature, typically 450 to 550°C, by ramped heating and holding at that temperature for 1 to 16 hours prior to hot rolling. This treatment consumes less energy and take less time than the Type 2 treatment and is therefore less expensive.
• Type 1 treatment minimises the amount of Mn taken into solution. This benefits electrograining but the strength loss during subsequent stoving is greater. Variations or combinations of these two treatments may be required to achieve the optimum combination of strength after stoving and good electrograining response.
• an intermediate annealing step it may be carried out immediately after hot rolling or during cold rolling.
• the interannealing may be carried out as batch interannealing, in which case it is preferably carried out at 300 to 500°C, for example for 1 to 5 hours.
• the interannealing may be continuous, in which case it is preferably carried out at 450 to 600°C, preferably for less than 10 minutes, for example for up to 5 minutes, even more preferably up to 1 minute.
• at least forced air quenching is used. It is preferred to cool rapidly in order to hold Mn and Fe in solid solution.
• the cold roll reduction of the sheet thickness is greater than 30%, preferably greater than 50%.
• An electrograining step may also be provided.
• the alloy is capable of being electrograined in hydrochloric acid, even more preferably in both hydrochloric and nitric acids.
• Further steps which may be provided are anodising and stoving. Stoving trials are typically carried out at 240°C for 10 minutes or even 270°C for 10 minutes to harden the photosensitive coating prior to printing.
• stoving is simulated by heating the plate to 240°C for 10 minutes or, where noted, to 270°C for 10 minutes.
• Printers use less time than 10 minutes, typically 3 minutes in continuous ovens, up to 7 minutes in others, and therefore the simulated stoving is a particularly severe test because the degree of softening increases with both time and temperature of stoving.
• the plate softens via the mechanisms of recovery and recrystallisation of the microstructure and the inherent anisotropy in the plate can lead to off-flatness problems. As mentioned above, the present invention minimises such problems. Generally, as low a drop in proof strength as possible is required.
• a method of forming a lithographic sheet comprising electrograining an aluminium metal sheet formed of the above-mentioned alloy in a nitric acid electrolyte until a total charge input of above 82kC/m 2 is applied, wherein the surface of the lithographic sheet comprises a pitted structure.
• the total charge input is about 87kC/m 2 .
• the pitted structure may provide total coverage of the surface of the material and sufficient roughness to allow good adhesion of a light-sensitive coating, together with good wear resistance and water retention following anodising and post anodic treatment.
• Figures 1a and 1 b show, respectively, the proof strength and ultimate tensile strength at final gauge in the as-rolled (H18 - that is with an interanneal) condition and after stoving for Mg or Mn additions;
• Figures 2a and 2b show, respectively, the proof strength and ultimate tensile strength at final gauge in the as rolled condition and after stoving for other Mg and/or Mn additions;
• FIGS 3a and 3b show similar properties in the H19 condition (without interanneal);
• Figures 4a to 4d show proof strength and nitric acid graining response for various alloy compositions for different homogenising and annealing conditions
• Figures 5a and 5b show, respectively, the proof strength and ultimate tensile strength for various treatments in the H18 condition against total Ti content
• FIGS. 6a and 6b show similar properties in the H19 condition
• Figure 7 shows the ultimate tensile strength of various alloys under varying treatment conditions
• Figure 8 shows the ultimate tensile strength of various alloys under various treatment conditions against the annealing temperature.
• Figures 9a - c show the softening behaviour of various alloys against stoving temperature.
• Zn, Cu, Cr and Zr all 0.001 wt% for all variants shown in Table *Free Ti is the Ti in the Al solid solution and not including Ti combined with B as TiB 2 particles.
• compositions given in Table 1 are rounded to the nearest significant figure and Std means typical AA1050A with the compositions shown.
• Rolling blocks approximately 70mm thick by 180mm wide by 200mm long were scalped from ingots cast in large book moulds.
• the rolling blocks were homogenised by heating slowly to 600°C and holding for several hours followed by a 2 hour cool to 500°C for 10 hours to allow equilibration of solute to occur, prior to hot rolling.
• This two-stage homogenisation is an example of a Type 2 pre-heat.
• the rolling blocks were hot rolled to an intermediate gauge of about 9mm with a finish temperature of about 150°C and allowed to air cool. Subsequent cold rolling to a final gauge of 0.3mm was done with an intermediate anneal at about 2mm gauge by heating to 450°C and holding for 2 hours.
• the tensile properties of the final gauge sheet, before and after a simulated stoving treatment for 10 minutes at 240°C, were measured in the longitudinal and transverse orientations (with respect to the rolling direction).
• Figures 1a and 1 b show, respectively, the proof strength and tensile strength at final gauge in the as rolled (H18) condition and after stoving for the Mn and Mg additions. It can be seen that even small Mg additions give significant work hardening effect and thus a higher as rolled strength. However on stoving the drop in strength is also large. The maximum stoved strength (and minimum drop in strength) is seen in the Mn containing alloys.
• *Free Ti is the Ti in the Al solid solution and not including Ti combined with B as TiB 2 particles.
• compositions given in Table 2 are rounded to the nearest significant figure and Std means typical AA1050A with the additions shown.
• Rolling blocks were manufactured in a similar manner to that described in Example 1.
• a set of blocks were homogenised with a heat-to-roll practice (Type 1 ). This consists of a ramped heating to the rolling temperature of 500°C and holding for a few hours (total heating cycle about 16 hours).
• the blocks were either rolled to final gauge with an interanneal, as above, to give material in the H18 condition, or without any interanneal to give material in the H19 condition.
• the H19 route is more economical while the H18 route gives an opportunity to control solute and grain structure, and hence stoving response and surface streakiness in the final gauge product.
• Pre-heat Type 1 in general gives lower stoved strength as compared with pre-heat Type 2
• Type 2 pre-heat results in the lowest drop during softening. This is consistent with the recovery being controlled via solute rather than dispersoids.
• Figures 4a to 4d illustrate property-electrograining maps for homogenising treatments Type 1 and Type 2 in the H18 or H19 condition.
• Figures 4a and 4b show graining and proof strength results after stoving for 10 minutes at 240°C for Type 1 and Type 2 homogenisation respectively in H18 conditions.
• Figures 4c and 4d show similar results for Type 1 and 2 homogenisation respectively in the H19 condition. There is sufficient overlap between the good strength properties and the good graining response in the alloy range tested.
• Ti is an important element in electrograining response in nitric acid. So a middle level Mn/Mg variant was chosen and ingots were cast with a range of Ti levels, as shown in Table 4 and heat treated and rolled as in Example 2: TABLE 4. Ti Uniallov Variants
• Type 2 pre-heat gives higher strength, most notably for H19 samples.
• Material destined to be in the H18 condition was hot rolled to 4.2 mm and then cold rolled to a final gauge of 0.28 mm with an interanneal at about 2.2 mm.
• Material destined to be in the H19 condition was hot rolled to 3.5 mm and then cold rolled to a final gauge of 0.28 mm without an inter-anneal.
• Figure 8 shows that the final gauge stoving response of the alloy labelled 1 st version in Table 6 is independent of the interannealing temperature compared to the AA1050A alloy. This is consistent with the stoving resistance being controlled by manganese in solid solution, which has a high solid solubility over this temperature range. Fe has a very low solubility resulting in a high driving force for Fe precipitation during inter-anneal. Consequently a high interannealing temperature is usually used to keep Fe solute levels high in the AA1050A product.
• An advantage of the new alloy is that it could be supplied in the H18 condition for intermediate strength applications by using a relatively low inter-anneal temperature thus saving production costs.
• the blocks were either rolled to final gauge with an interanneal, as above, to give material in the H18 condition, or without interanneal to give material in the H19 condition. Stoving was carried out for 10 minutes at various temperatures to simulate the actions of a printer and the results are shown in Figures 9a - c. From this it can be seen that material in the H19 condition for the alloys shown has a higher strength than in the H18 condition. At higher baking temperatures the material containing Mn in the H19 condition has much better mechanical properties than the comparison material in a similar condition.
• compositions I, II and III were prepared using a Type 2 homogenisation and were electrograined as described in Example 3 with the exception that the voltage applied was lower than standard, in order to demonstrate the sensitivity.

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• 2001
  • 2001-12-11 ES ES01270197T patent/ES2259311T3/es not_active Expired - Lifetime
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