Patent Application
20050284551
1. Field of the Invention
The present invention relates to a process for producing an aluminum alloy substrate for a lithographic printing plate, wherein an electrochemically grained surface on the level better than or equal to the levels of known grained surfaces can be realized even when alkali etching corresponding to a pretreatment of a surface-graining treatment is shortened.
2. Description of the Related Art
Generally, a JIS 1000 series aluminum alloy sheet of 0.1 to 0.5 mm in thickness has been used as an aluminum alloy substrate for a lithographic printing plate. Such an aluminum alloy sheet has usually been produced by scalping an ingot prepared by a semicontinuous casting method so that the surface is removed, subjecting the scalped ingot to a homogenization treatment, and subjecting the homogenized ingot to hot rolling, cold rolling, intermediate annealing, and final cold rolling.
The thus produced aluminum alloy substrate for the lithographic printing plate is subjected to a surface-graining treatment through a step composed of either one of or a combination of at least two of a mechanical method, a chemical method, and an electrochemical method. The resulting aluminum alloy substrate is further subjected to an anodization treatment, and optionally to a hydrophilic treatment to give a lithographic printing plate support. In addition, the support is coated with a photosensitive material to form a photosensitive layer. If necessary, the photosensitive layer is strengthened by a heating-burning treatment, so that a photosensitive lithographic printing plate is prepared.
The resulting lithographic printing plate substrate is subjected to a treatment for producing the lithographic printing plate, in which image exposure, development, water washing, lacquering, and the like are conducted sequentially, to give a printing original plate. The photosensitive layer remaining still undissolved after the above-described development is water repellent, and forms image areas serving as an ink-accepting portion which selectively accepts ink alone. The surface of the aluminum alloy support under the photosensitive layer is exposed at the portions where the photosensitive layer is dissolved, and the portions form nonimage areas serving as water-accepting portions due to the hydrophilic property thereof. In this development treatment, the surface of the aluminum alloy support under the photosensitive layer must have a water retention property in order to form a nonimage area serving as a water-accepting portion. Consequently, the surface is made to be a grained surface having uniform asperities by a surface-graining treatment.
In recent years, energy conservation and improvement of productivity have been required particularly in the method for producing a lithographic printing plate.
In order to achieve the above-described energy conservation and improvement of productivity, methods for producing a substrate for a lithographic printing plate have been proposed, in which the time of homogenization treatment of an ingot is shortened, or the time of intermediate annealing treatment is shortened in the cold rolling. However, in each case, the surface of the substrate is dissolved and removed by a long-duration alkali etching corresponding to a pretreatment of a surface-graining treatment. Therefore, these production methods are not satisfactory.
Accordingly, it is an object of the present invention to provide a process for producing an aluminum alloy substrate for a lithographic printing plate, wherein a grained surface on the level better than or equal to the levels of known substrates can be realized even when the heat treatment time of an aluminum alloy plate is shortened or alkali etching corresponding to a pretreatment of a surface-graining treatment is shortened.
In order to achieve the above-described object, a process for producing an aluminum alloy substrate for a lithographic printing plate, according to the present invention, is characterized by including the steps of preparing an aluminum alloy ingot having a JIS 1000 series composition; subjecting the aluminum alloy ingot to a homogenization treatment composed of the first stage of holding at 510° C. to 560° C. for 30 minutes to 2 hours and the latter stage of holding at 460° C. to 500° C. for 30 minutes to 2 hours; starting hot rolling and, thereafter, finishing the hot rolling at a temperature of 360° C. or more; conducting cold rolling; conducting intermediate annealing at a heating temperature of X° C. for a holding time of Y sec in an inert gas atmosphere, where X is 400° C. to 620° C. and Y≧2×108×exp(−0.0284X) is satisfied; and conducting final cold rolling.
It is desirable that the holding time of the homogenization treatment of the above-described ingot is 1 hour or less. This treatment homogenizes simple metallic substances, e.g., Si, Fe, and Cu, or compounds thereof which have been segregated during the casting and have not been adequately homogenized.
Preferably, the inert gas atmosphere of the above-described intermediate annealing treatment is composed of a combustion gas produced by combustion of an inexpensive hydrocarbon gas, e.g., a propane gas and a butane gas, followed by dehydration.
Preferably, the above-described aluminum alloy ingot has a composition composed of 0.1 to 0.50 percent by weight of Fe, 0.03 to 0.30 percent by weight of Si, 0.002 to 0.040 percent by weight of Cu, 0.01 to 0.05 percent by weight of Ti, 0.0001 to 0.02 percent by weight of B, and substantially the balance of aluminum.
According to the present invention, the aluminum alloy ingot having the above-described composition is used, and the homogenization, the hot rolling, the cold rolling, the intermediate annealing, and the final cold rolling are conducted on the conditions in the above-described ranges. Consequently, an aluminum alloy substrate for a lithographic printing plate provided with a grained surface on the level better than or equal to the levels of known substrates can be realized even when the heat treatment time and the pretreatment time of the surface-graining are shortened.
The aluminum alloy in the present invention is a JIS 1000 series alloy. This has a composition suitable for exerting the effect on forming intermetallic compounds of elements, e.g., Fe, Si, Ti, and B, the intermetallic compounds providing strength and electrochemically forming an uniform roughened surface.
In particular, the above-described effect is exerted excellently when Fe is specified to be 0.1 to 0.50 percent by weight, Si is specified to be 0.03 to 0.30 percent by weight, Cu is specified to be 0.002 to 0.040 percent by weight, Ti is specified to be 0.01 to 0.05 percent by weight, and B is specified to be 0.0001 to 0.02 percent by weight.
Elements, e.g., Mg, Mn, Cr, Zr, V, Zn, Ni, Ga, Li, and Be, originated from a base metal and return scraps in the preparation of a melt may be included as unavoidable impurities. However, when the content is such a very small quantity as specified with respect to JIS 1000 series, the effect of the present invention is not adversely affected to a large extent.
The aluminum alloy substrate for a lithographic printing plate in the present invention is produced as described below.
A melt of an aluminum alloy having the above-described composition and prepared by conducting treatments, e.g., degassing and slag removal, is conventionally cast into an ingot. The casting method is not specifically limited, and examples of casting methods include a continuous casting method and a semicontinuous casting method. However, the semicontinuous casting method is desirable. The thickness of the ingot produced by the semicontinuous casting method is not specifically limited. However, the thickness is usually about 500 to 600 mm.
After the surface of the ingot is scalped, a homogenization treatment composed of the first stage of holding at 510° C. to 560° C. for 30 minutes to 2 hours and the latter stage of holding at 460° C. to 500° C. for 30 minutes to 2 hours is conducted.
The heating at 510° C. to 560° C. in the first stage of the homogenization treatment is directed to homogenize elements in the ingot. If the temperature is lower than the lower limit, the above-described effect is reduced, and if the temperature exceeds the upper limit, the thickness of an oxide coating is increased. Therefore, these are not preferable. The holding time is 30 minutes to 2 hours. If the holding time is less than the lower limit, the homogenization effect is reduced, and if the holding time exceeds the upper limit, the thickness of an oxide coating is increased. Therefore, these are not preferable. Preferably, the holding time is 1 hour or less.
The heating at 460° C. to 500° C. in the latter stage is directed to regulate the formation of an oxide coating and to control the temperature of the ingot at a low temperature such that occurrence of recrystallization in the rolled plate is suppressed during the hot rolling and recrystallization is effected to realize a fine recrystallization structure when the hot rolling is finished. If the temperature is lower than the lower limit, the plate temperature becomes too low when the hot rolling is finished and, thereby, it is difficult to realize the fine recrystallization structure. If the temperature exceeds the upper limit, recrystallization occurs in the rolled plate during the hot rolling and, thereby, it is difficult to realize the fine recrystallization structure. The holding time is 30 minutes to 2 hours. If the holding time is less than the lower limit, the temperature of the ingot is significantly varied depending on positions of the ingot and, thereby, it is difficult to realize the fine recrystallization structure all over the surface layer of the rolled plate. If the holding time exceeds the upper limit, the thickness of an oxide coating is increased. Therefore, these are not preferable. Preferably, the holding time is 1 hour or less.
After the homogenization treatment, the hot rolling is conducted generally in at least several rolling passes. The hot rolling is started at the ingot temperature of 460° C. to 500° C., that is, the temperature of the homogenization treatment, and the hot rolling is finished at a temperature of 360° C. or more to effect recrystallization. Preferably, the thickness of the hot-rolled plate is 2 to 10 mm. The rolling reduction rate in the final pass of the hot rolling is desirably at least 55%. This rolling reduction rate causes a large strain in the surface layer of the hot-rolled plate, and a fine recrystallization structure having an average recrystallized grain size of less than 150 μm and a maximum grain size of less than 200 μm in a direction normal to the rolling direction can easily be realized at least in the surface layer of the hot-rolled plate.
In this specification, the surface layer of the hot-rolled plate refers to a region at depths ranging from 200 μm to 800 μm from the surface in the case where the thickness of the hot-rolled plate is 2 to 10 mm. Here, as for the region at depths ranging up to 200 μm from the surface, this value of the depth is in terms of a depth of the hot-rolled plate and corresponds to the depth to be removed by the etching treatment conducted as a pretreatment of the surface-roughening treatment and the depth to be removed by the electrochemical surface-roughening treatment and the like when the hot-rolled plate is finally formed into an aluminum alloy substrate having a thickness of about 0.15 to 0.5 mm by the cold rolling.
The hot-rolled plate having the fine recrystallization structure after completion of the hot rolling is cooled and cold-rolled. The intermediate annealing treatment after the cold rolling is conducted at a heating temperature of X° C. for a holding time of Y sec in an inert gas atmosphere, where X is 400° C. to 620° C. and Y≧2×108×exp(−0.0284X) is satisfied. This treatment is conducted in order to softening the cold-rolled plate having been hardened in cold processing, to realize a fine recrystallization structure, and to homogenize simple metallic substances, e.g., Si, Fe, and Cu, or compounds thereof which have not been adequately homogenized in the homogenization treatment or which have been made heterogeneous during the hot rolling.
The relationship between the heating temperature and the holding time of the intermediate annealing will be described with reference to
In
If the heating temperature is lower than 400° C., a glossy unetched portion results, and if the heating temperature exceeds 620° C., growth of crystal grains is advanced and, thereby, it becomes difficult to realize fine recrystallization.
This intermediate annealing treatment is directed to reduce the thickness of an oxide coating formed on the plate surface by treating in the inert gas atmosphere. The inert gas atmosphere of this intermediate annealing treatment may be composed of an argon gas or a nitrogen gas as long as the gas has a low dew point, for example, the dew point is about −40° C. to −10° C. A combustion gas of hydrocarbon gas, e.g., a propane gas and a butane gas, is preferable because these are inexpensive, if water in the combustion gas is removed. After the intermediate annealing is conducted, final cold rolling is conducted to attain a desired thickness, for example, up to a thickness of 0.15 to 0.5 mm, so that an aluminum alloy substrate for a printing plate is produced.
Examples of the Present Invention
Each aluminum alloy melt was prepared, and a slab having a thickness of 530 mm was cast by a semicontinuous casting method. The composition of the slab is shown in Table 1. Both surfaces of the slab were scalped so that the thickness was decreased by 15 mm per side. A homogenization treatment was conducted by heating and holding at 540° C. for 1 hour and, thereafter, heating and holding at 480° C. for 1 hour. Subsequently, the slab was taken out of a homogenization furnace, and hot rolling was started at a temperature of the homogenization treatment. The rolling reduction rate in the final pass of the hot rolling was 90%, the thickness of the rolled plate was 7 mm, and the temperature was 380° C. at the finish of the hot rolling. After cooling was conducted, cold rolling was conducted up to the thickness of 1 mm. Intermediate annealing was conducted on various conditions and, thereafter, final cold rolling was conducted up to the thickness of 0.3 mm, so that an aluminum alloy substrate was produced. In the intermediate annealing, a nitrogen gas having a dew point of −40° C. was used for constituting the treatment atmosphere. The resulting substrate was taken as the sample of the present invention.
In the condition of preparation of the above-described samples of the present invention, the holding time was set at 1 hour or 12 hours, whereas the temperature of the condition of the homogenization treatment was the same as that of the present invention. Intermediate annealing was conducted on various conditions. The intermediate annealing was conducted in an atmosphere of a nitrogen gas or in an atmosphere of air as in Examples of the present invention, so that samples for comparison were prepared.
Each sample of the above-described Examples of the present invention and Comparative examples was immersed in 10% NaOH aqueous solution at a temperature of 50° C. for 10 seconds. Electrochemical surface graining was conducted through electrolytic etching at an anodic electricity quantity of 150 Coulomb/dm2 in 1% nitric acid aqueous solution at 40° C. by using a power supply having an electrolytic waveform with alternating polarity. The treated sample was cleaned in sulfuric acid and, thereafter, uniformity of asperities of the roughened surface and glossy portions were observed with SEM. As for the glossy portions, a portion having a maximum diameter of 0.5 mm or more was evaluated as an unetched portion. The results are shown in Table 2.
⋆ Asperities of a grained surface were nonuniform and no unetched portion was able to be determined.
As is clear from the results shown in Table 2, as for the substrates (Sample Nos. 1 to 8 and 16 to 22) prepared on the condition according to the present invention, in which the homogenization treatment time is short and the atmosphere of the intermediate annealing is an inert gas, asperities on the roughened surface are uniform and any unetched portion results even when the alkali etching time is reduced, and therefore, the process of the present invention is an excellent process for producing a substrate. On the other hand, it is clear that as for the substrates produced through the intermediate annealing conducted at a low treatment temperature or for a reduced treatment time (Sample Nos. 9 to 12 and 23 to 26), asperities on the roughened surface are uniform but unetched portions result. The samples of Comparative examples (Sample Nos. 13 to 15) in which the atmosphere of the intermediate annealing is air are not suitable for the substrate since asperities on the roughened surface are nonuniform. Furthermore, no unetched portion was able to be determined because of the nonuniformity of asperities.
As described above, the substrate of the present invention is prepared on the condition in which the homogenization treatment time is short and the atmosphere of the intermediate annealing treatment is an inert gas. The process of the present invention can exert the effect of realizing an excellent roughened surface on the level better than or equal to those of known products even when the alkali etching corresponding to a pretreatment of the surface-roughening treatment is shortened. The effect is also exerted on reducing the treatment time in the entire process for producing the substrate and achieving excellent productivity.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-187665 | Jun 2004 | JP | national |
