BRPI0902046A2 - alloy, lithographic plate, and method for processing a lithographic plate - Google Patents

Abstract

ALLOY, LITHOGRAPHIC PLATE, AND METHOD FOR PROCESSING A LITHOGRAPHIC PLATE. An alloy suitable for processing on a lithographic plate is described, the alloy having a wt.% composition of: Fe 0.16 to 0.40 Si to 0.25 Cu to 0.01 Mn to 0.05 Ti to 0.015 Mg 0.02 to 0.10 Zn to 0.06; other components not specified to 0,03 each; The equilibrium is aluminum, where the minimum Al content is 99.3.

Description

"ALLOY, LITHOGRAPHIC PLATE, AND METHOD FOR PROCESSING A LITHOGRAPHIC PLATE"

This invention relates to an alloy suitable for processing on a lithographic plate, an alloy to form a thin rolled aluminum strip, particularly for use by offset printing plate manufacturers, and a method for processing such a lithographic plate.

It is well known that aluminum alloy in the form of a thin strip of laminated aluminum is used by offset printing plate manufacturers.

In order to process a rolled aluminum plate into a lithographic plate, platemakers initially degreased or matched the aluminum strip, typically in an alkaline solution. This process prepares the surface of aluminum for granulation and uniformises the imperfections of the mirrored surface.

Electrogranulation is then performed to create a surface topography with convoluted hemispheric point corrosions. This is typically performed on a hydrochloric acid-based or nitric acid-based electrolyte.

Electrogranulation is performed using an alternating current (AC) through an electrolyte cell containing the aluminum strip. Electrochemical reactions that occur in each half cycle effectively remove aluminum from the surface by dissolution.

Alternatively, the surface of the aluminum strip may be mechanically roughened, for example by brushing. However, this process is less common.

The function of the punctual corrosions formed on the surface of the aluminum strip is to increase the surface area of the aluminum strip, and to retain water. In other words, because of the presence of punctual corrosions, the aluminum strip becomes hydrophilic. A smoothness reduction step can then be performed in order to remove aluminum hydroxide dirt created during the electrogranulation process.

Then the aluminum strip is anodized. This results in the growth of porous anodic oxide on the surface with occasional corrosions of aluminum. This provides a wear-resistant coating that improves the service life and print quality of a Hograph plate formed from the aluminum strip. It also allows better adhesion to light-sensitive coating and makes the plate chemically more inert, thus improving its shelf life.

Normally, a photosensitive polymeric coating is then applied to the aluminum strip. This coating repels water but attracts oil. The Ht plate needs to attract oil since the printing ink is oil based.

At this stage, the Htographic plate comprises a hydrophilic anodized aluminum layer covered by a photosensitive oleophilic layer.

In its simplest form, an image is created by removing parts of the coating, for example by exposure to light. This means that the coating must be easy to remove to reveal the hydrophilic anodized layer underneath. However, the coating also has to be wear resistant in order to retain a well-defined image during printing runs.

Therefore, it is important that the aluminum strip used to form the Htographic plate has sufficient traction and proper surface functionality.

The term "surface functionality" is used to describe the ability of an electrogranular material well to provide a uniform distribution in the size of point corrosions without any risk or directionality being formed. This is important for the quality of the resulting printed images.

Most plate manufacturers use an HC1-based solution as the electrolyte during the electrogranulation process. However, the use of HN03-based electrolyte is also known. The mechanism by which the granulation process takes place is different in each electrolyte. It is advantageous for the material to be well electrogranulated in both electrolytes.

In the lithographic plate production industry, it is particularly well known to use two types of alloy. The first type of alloy is known as AA1050 and has the composition shown in table 1 below. AA1050 exhibits good electrogranulation behavior.

If a material has "good electrogranulation behavior", it means that the material has the ability to produce a surface with uniform point corrosion "over a wide range of conditions. Such a material should also be able to electrogranulate on both hydrochloric acid and acid nitric electrodes .

<table> table see original document page 4 </column> </row> <table>

Table 1

A second type of alloy is known as AA3XXX and comprises AA3103 or AA3003 alloys with the compositions shown in tables 2 and 3 below. AA3XXX has better traction compared to AA1050 traction. However, the electroplating properties of AA3XXX are not as good as those of the A1010 alloy type. <table> table see original document page 5 </column> </row> <table>

Table 2 <table> table see original document page 5 </column> </row> <table> Table 3

Alloy type AA1050 is traditionally used in the markets of Europe, Asia and South America. This type of electrogranule alloys well in both H1 and HN03 based solutions, but has lower traction compared to other alloys. This is considered a potential problem in situations where alloys should be used to form a lithographic plate for longer running runs.

The AA3XXX alloy type is traditionally used in North America. It is more difficult to electrogranulate this type of alloy and therefore it is most often used when mechanical roughness formation processes can be applied.

AA3XXX alloys can be electrogranulated in HCl, but the electrogranulation process can produce lines on the surface. These alloys, therefore, have relatively poor electrogranulation behavior, chew a high gross traction and high cooking traction.

The tensile wear of the photosensitive coating is generally improved by firing the lithographic plate. However, this process may have an adverse effect on aluminum substrate traction. This practice is more common in North America and tends to explain the greater use of A3XXX. The traction on cooking of an alloy is typically measured using a standard cooking test. The standard baking test involves heating the alloy for ten minutes at 240 ° C.

It is important that alloys to be used for lithographic plate processing do not soften significantly during cooking so that the alloy traction is not adversely affected. Significant softening and associated microstructural changes in the aluminum alloy substrate could also have a negative impact on the dimensional properties of the printing plate. This can be detrimental to fatigue failure.

In general, it has been observed that an alloy that exhibits good electrogranulation behavior may not have the required traction, whereas an alloy with the required traction may have poor electrogranulation behavior.

According to a first aspect of the present invention there is provided an Al alloy suitable for processing on a lithographic plate, the alloy having a weight% composition of:

Fe 0.16 to 0.40

Si up to 0.25

Cu to 0.01

Mn to 0,05

Ti to 0.015

Mg 0.02 to 0.10

Zn to 0.06;

other components not specified to 0,03 each.

The equilibrium is aluminum, where the minimum Al content is 99.3.

With a high percentage of aluminum in the alloy, there is a correspondingly lower level of other components. This results in an alloy that is more versatile during recycling after use. Preferably, the minimum aluminum content is 99.45% by weight. More preferably, the minimum aluminum content is 99.50% by weight.

With a higher percentage weight of aluminum in the alloy, the alloy's aversatility is further increased during recycling thereafter.

Magnesium is used to improve granulation performance of the alloy, but has a limited influence on alloy traction. However, magnesium improves the mechanical properties (such as traction) of both cooked and cooked alloys, and therefore their presence in the alloy is important. However, limiting the magnesium range to 0.10% by weight is important as it does not compromise the alloy's versatility for recycling purposes.

An alloy according to the present invention may contain up to 0.099% by weight of magnesium.

Preferably, the magnesium content is in the range 0.02 to 0.05 wt%.

Zinc also improves alloy granulation performance, but also has limited influence on alloy traction. The inventors have found that the weight percentage of up to 0.05 zinc in the aluminum alloy may have beneficial effects with respect to the alloy's electrochemical properties.

Advantageously, the minimum zinc content is 0.02% by weight.

The ratio of zinc to magnesium in the alloy may be substantially in the range 0.1 to 2.3.

It was observed that by controlling the zinc and magnesium content, it is possible that the resulting aluminum alloy will have good electrogranulation behavior.

The presence of iron in the aluminum alloy also serves two purposes. The first is to ensure the formation of iron intermetallic compounds that are essential for the development of a structure with homogeneous cavities during the electrogranualation step (increasing roughness) of the plate manufacturing process. The second is to ensure that there is sufficient iron in the solid solution in the material that is beneficial for good temperature stability properties, and particularly for retention of traction after baking.

An advantage of alloy with minimal iron content is that a sufficient number of second phase intermetallic compounds are present in the alloy structure. This, in turn, can be achieved only when the level of iron solubility in aluminum is exceeded.

Increasing the iron content of the alloy is advantageous in that it provides a hardening effect on aluminum alloys, thereby increasing the tensile strength of the alloy.

However, it is not advantageous to increase iron beyond the superior strength of 0.4 wt% because such an extra addition has no additional positive effect on the alloy structure and has a minimal additional increase in traction. An additional disadvantage of increasing iron content beyond 0.4% by weight is that it compromises the versatility of the alloy recycling purposes.

It was observed that the presence of copper in an aluminum alloy may affect the morphology of the roughened cavities, but, on the other hand, may improve the traction of the material in both raw and cooked conditions. The inventors have noted that if the percentage by weight of copper remains at 0.01 or less, the alloy may benefit from better traction because of the presence of copper, while at the same time the adverse effects of copper on cavity morphology are maintained. at a minimum.

The presence of titanium in an aluminum alloy is necessary to ensure proper metallurgical grain size control. However, too much titanium can have an adverse effect on the electrochemical performance of the alloy. The inventors have observed that if the weight percent of titanium is not more than 0.015, the alloy may benefit from the grain size control achieved by titanium, but at the same time the adverse effects on electrochemical performance are kept to a minimum.

An alloy according to the present invention may contain up to 0.049 wt% manganese.

Preferably, the minimum manganese content is 0.005% by weight.

The presence of manganese in the alloy serves to increase both raw and cooked alloy traction. However, manganese may have a negative impact on the electrogranulation behavior of the alloy and therefore the level of manganese in the alloy should not be too high.

Preferably, the manganese content falls within the range of from 0.005 to 0.030% by weight.

Advantageously, the manganese to magnesium ratio is substantially in the range of 0.08 to 1.63.

According to a second aspect of the present invention there is provided a Htograph plate formed of an alloy according to the first aspect of the present invention.

According to a third aspect of the present invention, there is provided a method for processing a Ht plate formed of a slight according to the first aspect of the present invention.

The invention will be described by way of example only with reference to the following examples.

The following are details of the composition of four examples of preferred embodiments of the invention showing the weight percent of alloying components.

<table> table see original document page 10 </column> </row> <table>

Table 4

The invention will be described in detail only by way of non-limiting example with reference to the accompanying figures, in which:

Figure 1 is a graphical representation showing the maximum tensile strength in the longitudinal direction of the identified 1, 2, 3 and 4 supers, in an uncooked raw state and after having been cooked each of 200 ° C, 220 ° C, 240 ° C and 260 ° C for ten minutes compared to known alloy groups AA3XXX and AA1050.

Figure 2 is a graphical representation showing a limited elasticity by displacing a longitudinal elasticity limit (Rp) and longitudinal direction of the above-identified examples 1, 2, 3 and 4, in an uncooked raw state and after having been cooked every 200 ° C, 220 ° C, 240 ° C and 260 ° C for ten minutes compared to a group of the known alloy AA1050.

Figure 3 is a graphical representation showing the maximum tensile strength in the transverse direction of the identified examples 1, 2, 3 and 4, in an uncooked raw state and after having been cooked each of 200 ° C, 220 ° C, 240 ° C and 260 ° C for ten minutes, purchased as known alloy group AA1050.

Figure 4 is a graphical representation showing the elasticity limit by displacing an elasticity limit (Rp) in the transverse direction of the above-identified examples 1, 2, 3 and 4 in an uncooked bruton state and after having been cooked at each 200 °. C, 220 ° C, 240 ° C and 260 ° C for ten minutes compared to the known alloy group AA1050.

Figures 5 and 5a are micrographs, each showing a cross section of a sample of an AA1050 alloy after being subjected to a bend test. Figure 5 is magnified by 200x and Figure 5a is magnified by 100x.

Figures 6 and 6a are micrographs, each showing a cross section of a sample from example 1, above identified, then subjected to a folding test. Figure 6 is magnified by 200x and Figure 6a is magnified by 100x.

Figure 7 is a micrograph showing the more detailed outer-folding surface of the AA1050 sample shown in Figure 5; and is up by 112.5x.

Figure 8 is a micrograph showing the more detailed outer-folding surface of the sample from example 1 shown in Figure 6. Figure 8 is at an enlargement of 112.5 x.

Tensile strength, or ultimate tensile strength / stress (UTS) is the largest load applied to a material in the course of a tensile test, divided by the original cross-sectional area of the material. In fragile or tough materials, it coincides with the fracture point, but usually the extension continues with a decreasing stress after the UTS passes.

The elasticity limit by displacing an elasticity limit (Rp) is the stress required to produce a certain amount of permanent deformation (plastic deformation) in metals that do not have a distinct elasticity limit. In the accompanying figures 2 and 4, the deelasticity limit by displacing an elasticity limit is the stress that produces a 0.2% strain (Rp 0.2).

As mentioned earlier, the standard cooking test takes ten minutes at 240 ° C. In Figures 1 to 4, additional temperatures, namely 200, 220, and 260 ° C, are also examined to show the tensile behavior of each alloy, and how it reduces with different cooking conditions. As shown in Figure 1, each One of the examples 1 to 4 has a higher maximum tensile strength in the longitudinal direction, both in the uncooked state and at the identified temperatures, when compared with the AA1050 group of alloys. The AA3XXX group of alloys, however, has no higher traction than examples 1 to 4.

Figure 2 shows that each of Examples 1 to 4 has a higher yield strength by displacing a yield strength in the longitudinal direction, both in the uncooked state and at identified temperatures, than the AA1050 group of alloys.

Figure 3 shows that each of Examples 1 to 4 has a higher maximum tensile strength in the transverse direction, both in the uncooked state and at the indicated temperatures, than the AA1050 group of alloys.

Figure 4 shows that each of Examples 1 to 4 has a higher yield strength by shifting a yield strength in the transverse direction than the AA1050 group of alloys, both in the raw state and at the indicated temperatures.

It has been realized that bending properties are more important than traction in terms of press performance but not as straightforward to measure. Therefore, traction is generally used as an approximate guideline. However, simple folding tests have been performed on the identified examples.

The fold test used is a static test based on performing and examining a fold that is used to attach a placalithographic to a printing press.

A static test is considered to be most appropriate as the nature of the material (eg alloy composition, tempering, and alloy processing method) has a significant impact on initial bending, also a limited impact on fatigue. It should be understood that fatigue failure is basically determined by bending dimensions and material thickness.

In order to perform bending tests, a plate formed of a particular alloy was bent according to a restricted set of parameters. If dimensions vary greatly from projected values, including a specified thickness, then this may compromise the test results.

The thickness measurements of the samples were kept as constant as possible, ranging between 0.275 and 0.280 mm.

The inner bend radius and thickness roughly determine the amount of deformation on the outer folding surface. This can vary significantly only with a slight change in configuration parameters. Therefore, the internal bend radius is kept constant.

In use, the aluminum lithographic plate would be folded using a plate folding device. A plate folding device is associated with a printing press and is the piece of equipment that is used to form the folding. In this test, a single 60 ° bend around an established radius was made to simulate the plate bending device. 60 ° is in the region of typically used folding angles.

The tests were performed in two directions, with the eixogeometric folding parallel and perpendicular to the plate lamination direction. The rolling direction is the direction in which the aluminum plate is processed during rolling.

The tests were compared with tests performed on the A1050 alloy group.

Once the tests were performed, a bend in an alloy was evaluated in terms of its cross-sectional and external surface appearance using optical microscopy.

Micrographs showing bend test data for a sample of an AA1050 alloy and for a sample from example 1 identified above are shown in figures 5 to 8.

Figures 5 and 5a are micrographs showing a cross section of the AA1050 alloy sample after being subjected to a bending test as described above. From these figures it can be seen that there is an inward distortion on the inner surface of the alloy caused by the compressive deformation of the inner folding surface. This distortion is the circled area identified by reference number 1. Compressive deformation can be measured by the level of inward distortion.

It can also be seen that there are ridges formed on the outer surface of the alloy by shear deformation on the outer surface, as shown in area 2. The level of shear deformation can be measured by the depth of the formed ridges.

It is believed to be an advantage that a material does not form deformation. This is because the ridges are thought to be able to behave as stress concentrators and act as a weakness point for the initiation of print plate failure.

Figures 6 and 6a show a cross section of an example 1 sample as previously identified after passing a similar bend test. It can be seen from these figures that there is the least internal bending strain shown in area 3, and the outer surface is smoother, as shown in area 4, when compared to the outer surface of the AA1050 alloy sample shown in figures 5 and 5a.

Figures 7 and 8 show in more detail the outer bending surface of the AA1050 alloy sample and a sample from example 1, respectively. Again, it can be seen from figure 7, in the circled areas labeled with reference numeral 5, that there are deep ridges in the AA1050 alloy sample when compared to the sample in example 1.

An analysis of micrographs such as those shown in Figures 5 to 8 is quite qualitative. However, the observed shear and cracking deformation levels varied among different materials, allowing a direct comparison between the different alloys. Wrinkle measurements were also performed on the outer surface of the bend for each alloy, and the peak peak to valley distances of the shear-forming crest on the outer surface of the bends were measured.

These topographic measurements of the external folding surface were made using a white light interferometer. In this application, interferometry is used as a noncontact method of measuring surface roughness.

The results of roughness measurements are given in table 5 below.

<table> table see original document page 12 </column> </row> <table>

Table 5

A summary of the test results is given below in Table 6. As can be seen from the table, the AA1050 group of alloys show moderate formation during such bending tests. It is understood that the AA3XXX alloy group has very little bending deformation.

<table> table see original document page 12 </column> </row> <table>

Table 6

As explained above, it is important that the surface with uniform, line-free pitting corrosions be achieved by electrogranulation of the alloy in both a hydrochloric acid and a nitric acid solution to produce a well-functioning surface.

The electrogranulation performance of Examples 1 to 4 compared to both AA1050 and AA3XXX alloy groups is shown below.

The results described below are based on laboratory testing of alloys on an HCl-based electrolyte.

The following electrogranulation performance measurement scale was used.

<table> table see original document page 16 </column> </row> <table>

Table 7

Results for three different examples are given below.

All conditions use a charge density of 1,000C / dm2, but electrogranulation is performed at different time durations.

The "easy" laboratory condition is achieved by electrogranulation for 24 seconds.

The "intermediate" condition is reached by electrogranulation for 9.5 seconds.

The "hard" condition is reached by 6.5 second electrogranulation. <table> table see original document page 17 </column> </row> <table>

Table 8

The results show that each of Examples 1 to 4 has electrogranulation properties at least as good under certain conditions as better than the AA1050 group of alloys.

The electrogranulation behavior of each of examples 1 to 4 in all cases is better than that of the AA3XXX alloy group.

The present invention therefore provides an aluminum alloy with better tensile strength compared to alloy type AA1050 and better electrogranulation behavior compared to alloy type AA3XXX.

A process for forming a lithographic plate according to the present invention will now be briefly described. The process can serve as three subprocesses: alloy production and slab casting; production of rolled aluminum sheet; and the production of a chapalitographic. These processes will now be described in additional detail.

Alloy and Plate Casting Production

Thin strip ingot rolling is done by cast aluminum direct casting (CC) casting.

The elemental composition of the metal is controlled at the levels described by the appropriate additions.

Ingots are typically between 400-650 mm thick.

Rolled Aluminum Thin Strip Production

Laminating sheet ingot chipping is performed to improve surface quality and uniformity by removing the delingotation skin. Up to 25 mm in total is removed from both surfaces.

Preheating is performed to reach dometal temperatures at the outlet of 400-600 ° C for hot rolling.

The ingot is hot rolled in multiple passes to a plate thickness of 11-18 æm.

In-line tempering reduces the plate temperature to <50 ° C.

The plate is then cold rolled to an intermediate thickness.

Intercritical batch annealing can be performed. Target metal temperature is between 350-550 ° C.

Additional cold rolling steps are used to dye the final product thickness between 0.1-0.5 mm.

The coil can then be played and degreased prior to supply for lithographic plate production.

Lithographic Plate Production

The surface is prepared for increased roughness by an alkaline-based etching process.

Increased roughness is preferably achieved by electrogranulation. This is performed on a hydrochloric acid-based electrolyte or a nitric acid-based electrolyte. An AC current is applied to the electrogranulation flange to achieve increased roughness.

The electrogranulated surface is anodized to increase wear appeal.

Several other inline treatments may be applied to improve plaque properties between some or each of the basic process steps described.

A photosensitive coating is applied.

Once the plate has been converted to an image, it can be fired to improve the wear resistance of the photosensitive coating.

Claims (16)

1. Al alloy suitable for processing on a platalitograph, characterized in that the alloy has a wt.% Composition of: Fe 0.16 to 0.40Si to 0.25Cuate to 0.01Mn to 0.05Ti to 0.015Mg 0.02 to 0.10Zn to 0.06, other components not specified to 0.03 each, the equilibrium is aluminum, where the minimum Al content is 99.3. Alloy according to claim 1, characterized in that the minimum aluminum (Al) content is 99.45% by weight. Alloy according to claim 1 or claim 2, characterized in that the minimum aluminum content is 99.50% by weight. Alloy according to any of the preceding claims, characterized in that it contains up to 0.099% by weight of magnesium. Alloy according to any one of the preceding claims, characterized in that the magnesium content is preferably in the range 0.02 to 0.05% by weight. Alloy according to any one of the preceding claims, characterized in that the minimum zinc (Zn) content is 0.02% by weight. Alloy according to any one of the preceding claims, characterized in that the ratio of zinc to magnesium in the alloy is substantially in the range 0.1 to 2.3. Alloy according to any one of the preceding claims, characterized in that it contains up to 0.049% by weight of manganese. Alloy according to any one of the preceding claims, characterized in that the minimum manganese (Mn) content is 0.005% by weight. Alloy according to any one of the preceding claims, characterized in that the manganese (Mn) content falls within the range of 0.005 to 0.030% by weight. Alloy according to any one of the preceding claims, characterized in that the ratio of manganese to magnesium is substantially in the range 0.08 to 1.63. Lithographic plate, characterized in that it is a alloy form as defined in any of the preceding claims. 13. Method for processing a lithographic plate, characterized in that the lithographic plate is as defined in claim 12. 14. Alloy, characterized in that it is substantially above described with reference to the accompanying drawings. 15. Lithographic plate, characterized by the fact that it is substantially in the manner described above with reference to the attached drawings. 16. Method, characterized in that it is substantially as described above with reference to the accompanying drawings.