JPH11293474A - Production of precoated aluminum strip having excellent formability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating under surface treatment method of a precoated aluminum strip to take place of a chromate treatment which is weak in formability and has a toxicity problem. SOLUTION: After the aluminum strip is subjected to an alkaline treatment and/or pickling treatment, a suspension contg. 0.01 to 50 wt.% inorg. compd. particles of a metal hardly soluble in water of 5<=pH<=9 is adhered thereto and thereafter, the surface is rubbed, by which the strip is made into the state that the inorg. compd. particles of the metal are embedded into at least part of the surface, following which the strip is subjected to a phosphate treatment and coating treatment. Zinc phosphate, etc., are used as the inorg. compd. particles of the metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a precoated aluminum strip for use in building materials, home electric appliances and the like after painting in the state of a strip (coil) and then forming. In this specification, “aluminum” includes not only pure aluminum for industrial use but also aluminum alloys of various compositions.

[0002]

2. Description of the Related Art Ordinary aluminum materials which are formed and used for building materials, home electric appliances, etc. are in the form of strips and are called "alkali degreasing-washing-chemical conversion treatment-washing-drying-painting-baking".
A so-called pre-coated aluminum material, which is formed and processed based on the usage pattern after the coating treatment in the step, is often used. Since it is poor in productivity to paint after forming a shape, a pre-coated aluminum material is used as much as possible except for members subjected to severe forming processing. During this process, as a chemical conversion treatment that corresponds to the base treatment for painting,
Phosphate chromate, chromate chromate and the like are generally used, but recently, the trend toward non-chromate has been shifted due to environmental problems and the like.

[0003]

The method of applying a phosphoric acid chromate or chromate chromate film, which is generally used as a base treatment for coating an aluminum strip, forms a film in a short time and forms the film. When there is no processing, the coating film adhesion and corrosion resistance are excellent. However, in the presence of a forming process, the chromate film itself is inferior in forming processability, so that it cannot follow the deformation of the aluminum material or the coating film, and the coating film is easily cracked or peeled. Furthermore, in recent years, there has been a tendency to restrict the use of chromium due to the problem of harmfulness of chromium. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method of manufacturing a precoated aluminum strip by devising a chemical conversion treatment method as a pretreatment for coating. In addition, before molding an automobile body sheet material or the like to be painted (post-coated), an inorganic compound of a metal having low solubility in alkali and water is adhered using a suspension and rubbed. The present inventors have already applied for a surface treatment method for an aluminum material for phosphating, wherein the particles are at least partially embedded in the surface. (Japanese Patent Application No. 8-289199)

[0004]

SUMMARY OF THE INVENTION The present inventors have found that the poor formability of aluminum coated strips with a chromate coating as a base treatment is due to the continuous formation of the chromate coating. It is considered that the chromate film cannot follow the elongation of the aluminum material due to the processing. In this regard, when the zinc phosphate film is closely observed, it is considered that the formability is improved because the zinc phosphate film is independent of each other and easily follows the elongation of the aluminum material in the forming process. However, phosphate coating is hardly formed on aluminum materials, and if the processing time is not extended, the required amount of coating cannot be secured and productivity will be poor. It has not been done yet. In recent years, as a measure to improve the phosphatability of aluminum materials to reduce the weight of automobiles, a method of improving the phosphatability by applying zinc-based plating to the surface of aluminum in Japanese Patent Application Laid-Open No. 61-157593 has been proposed. Proposed. However, the plating process naturally increases the cost. Therefore, the present inventors considered that the reason for the poor phosphatability of the aluminum strip was that titanium colloid, which is said to function as a nucleus for forming a phosphate film used for surface conditioning before phosphating, did not adhere. The present inventors have found that a phosphate film is formed on the aluminum surface in a short time by mechanically embedding fine particles of a metal inorganic compound instead of a colloid, and have reached the present invention.

Specifically, the invention according to claim 1 is characterized in that after alkali treatment and / or pickling treatment, 0.01 to 50 wt.
A forming process characterized in that the suspension containing the metal is adhered and then rubbed so that the inorganic compound particles of the metal are at least partially embedded in the surface, and then subjected to a phosphate treatment and a coating treatment. This is a pretreatment method for aluminum strips for coating, which has excellent properties.

According to a second aspect of the present invention, in the first aspect, the metal inorganic compound includes titanium oxide, magnesium oxide, tungsten oxide, niobium oxide, aluminum oxide, zinc oxide, cuprous oxide, and cupric oxide. Selected from ferric oxide, molybdenum oxide, magnesium hydroxide, nickel hydroxide, magnesium carbonate, calcium carbonate, zinc phosphate, magnesium oxalate, barium titanate, ferric sulfate, calcium silicate, magnesium hydrogen phosphate It is specified that one or more kinds are used.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The normal phosphating step involves the steps of alkaline degreasing, washing with water, surface conditioning (adhesion of titanium colloid by immersion or spraying), phosphating, washing with water, washing with pure water, drying and painting. . In the case of an aluminum strip, a conventional surface conditioner causes little adhesion of titanium colloid, hardly forms a phosphate film, and requires a processing time of 120 seconds or more. Therefore, instead of this surface conditioning, fine particles of an inorganic compound of a metal which is hardly soluble in water having a pH of 5 ≦ pH ≦ 9 are mechanically partially embedded in the surface of the aluminum strip. It acts as a nucleus for film formation and can form a phosphate film on the surface of the aluminum strip in a short time. Further, when dissolved in water of 5 ≦ pH ≦ 9 and ionized, it does not function as a nucleus for forming a phosphate film, which is considered to function as particles of a metal inorganic compound. Therefore, the inorganic compound of the metal used in the present invention is 5
It is necessary to exhibit poor solubility in water of ≦ pH ≦ 9. As inorganic compounds of metals exhibiting such properties, titanium oxide, magnesium oxide, tungsten oxide, niobium oxide, aluminum oxide, zinc oxide, cuprous oxide, cupric oxide, ferric oxide, molybdenum oxide, hydroxide Magnesium, nickel hydroxide, magnesium carbonate, calcium carbonate, magnesium oxalate, barium titanate, ferric sulfate, calcium silicate, magnesium hydrogen phosphate and the like, and even if used with one selected from these, Also, two or more kinds may be mixed and used. Among the above, zinc phosphate particles have the greatest effect.

The aluminum strip is treated with an alkali and / or
Alternatively, the reason for the pickling treatment is as follows. By removing the aluminum surface oxide film to form an active aluminum surface layer, the fine particles of the inorganic compound of the metal which is hardly soluble in water of 5 ≦ pH ≦ 9 can be easily attached, and the rubbing time can be reduced. If the surface oxide film is present, the hard oxide film is not removed by rubbing with fine particles of the inorganic compound of the metal, so that the inorganic compound particles of the metal are difficult to be planted and a long rubbing time is required. Further, it becomes difficult to attach inorganic compound particles of a metal softer than the oxide film. Further, if the oxide film remains after the metal inorganic compound particles are adhered, no film is formed even after the phosphate treatment. The alkali treatment is carried out using a commercially available degreasing agent such as caustic soda, sodium phosphate, sodium silicate or the like at a concentration of 0.5 to 5% and a temperature of 30 to 30%.
The treatment is preferably performed at 80 ° C. for a time in the range of 5 to 20 sec. In the pickling treatment, nitric acid, sulfuric acid, phosphoric acid or the like is used at a concentration of 0.1%.
5% to 20%, temperature: room temperature to 60 ° C, time: 2 to 15se
It is preferable to process in the range of c. Further, the alkali and the acid treatment may be combined in order. The point is that the oxide film can be removed as described above.

After the alkali and / or pickling treatment, the process proceeds to the next step of depositing inorganic compound particles of a metal in a wet state without drying as much as possible. Oxide film of the aluminum material is in the material containing Mg are mixed is MgO, mostly, hard, coating of dense Al ₂ O _3, harder than aluminum alloy matrix. By removing the hard oxide film by an alkali or acid treatment to expose the surface of the soft aluminum alloy matrix, it becomes easier for zinc phosphate fine particles to adhere. If drying is performed after alkali or pickling treatment, a hard and dense natural oxide film of Al ₂ O ₃ is formed on the aluminum surface in a short time, and the meaning of the alkali or pickling treatment is reduced.
Also, not drying saves energy and time.

[0010] Thereafter, particles of the inorganic compound particles of poorly water-soluble metal having a pH of 5 ≦ pH ≦ 9 having a maximum particle size of 0.0010 to 10 μm are embedded at least partially in the surface at an arbitrary 100 μm ² . Measure so that the coverage area ratio is 20 to 80%. The particle size distribution of the poorly water-soluble metal inorganic compound having a pH of 5 ≦ pH ≦ 9 may range over a wide range, but particles having a particle size of 0.0010 to 10 μm are considered to exhibit the above-mentioned effects. The inorganic compound of the metal present at least partially embedded in the surface of the aluminum material preferably has a maximum particle diameter of 0.0010 to 10 μm. When the particle size is less than 0.0010 μm, it does not function as a nucleus for forming a phosphate film. If the particle size exceeds 10 μm, a phosphate film is formed around the particles to form particles, thereby deteriorating the adhesion of the phosphate film and deteriorating the adhesion after coating and the appearance after coating. For the same reason as described above, the particle diameter of the metal inorganic compound is preferably 0.0050 to 5 μm,
0100-3 μm is more preferred. The coverage of the particles of the metal inorganic compound is ²⁰ to 8 as measured at an arbitrary 100 μm ^2.
0% is preferred. If it is less than 20%, it does not function sufficiently as a nucleus for forming a phosphate film, and does not exhibit a sufficient effect. On the other hand, if the coverage of the particles of the metal inorganic compound exceeds 80%, the particles become continuous and form a large lump, and the number of nucleation sites for forming the phosphate film becomes too small, and the phosphoric acid becomes Inhibits the formation of salt films.

In order to obtain such a surface state, a suspension containing 0.01 to 50% by weight of metal inorganic compound particles is deposited and then rubbed. However, if the wet state is not dried after the alkali or pickling treatment, the inorganic compound particles of the metal can be uniformly coated without forming a suspension.

The method of making the metal particles of the inorganic compound partially embedded in the surface of the aluminum material at a coverage of 20 to 80% as measured at an arbitrary 100 μm ² is as follows. First, a suspension of a metal inorganic compound is deposited.
This is done by spraying the suspension on an aluminum material or immersing the aluminum material in the suspension. By attaching the suspension to the plate surface using the suspension, uniform attachment can be achieved. If the inorganic compound particles of the metal are rubbed on the surface of the aluminum material as a powder without using a suspension, the particles cannot be uniformly adhered, but also damage the surface of the aluminum plate. Although the particle size distribution of the inorganic compound of the metal used as described above may extend over a wide range, since the particles having a particle size of 0.0010 to 10 μm are considered to exhibit the above-mentioned action, the maximum particle size is 0.001 to 0.001 μm. 10
It is preferred to suspend the inorganic compound particles of μm.

Thereafter, the particles are rubbed in a state where they are not completely dried, so that the inorganic compound particles of the metal are at least partially embedded. By rubbing in a state where the plate is not completely dried, the surface of the plate is less likely to be scratched than when rubbing in a completely dry state. In this specification, “rubbing” refers to an operation of mechanically rubbing and embedding particles on the surface of an aluminum material. Specific examples include brushing using a brush roll, light pressure using a rubber roll or a sponge, buff polishing using a polishing cloth, and the like. However, deep scratches on the surface of the aluminum plate may cause breakage during molding, so that the trace depth remaining upon rubbing is preferably less than 10 μm.

The suspension used contains an inorganic compound of a metal at a concentration of 0.
It is contained at a concentration of 01% to 50%. If the concentration of the inorganic compound of the metal is less than 0.01%, the particle coverage is low and there is no effect as a phosphate film forming nucleus or an effect of promoting adhesion of titanium colloid. If the concentration exceeds 50%, not only the cost is increased but also the particle coverage is too high. Therefore, 0.0
The concentration is 1% to 50%, but for the same reason, 0.1% to 1%.
More preferably, it is 0%.

After the above steps, phosphate treatment such as zinc phosphate treatment is performed according to a conventional method. The amount of the phosphate coating is preferably 0.5 to 3 g / m ² . The aluminum material treated according to the present invention has a large number of phosphate nucleation points, so that a uniform film having a phosphate film crystal size of 8 μm or less is formed. Excellent film adhesion.

Thereafter, after washing with water and drying, painting and baking are performed. In the specification of the present application, "painting treatment" is a term including a series of steps of "washing, drying, painting and baking". In addition, it is preferable to wash with industrial water or tap water and then with pure water from the viewpoint of corrosion resistance after coating. The coating is preferably performed in two steps of undercoating and overcoating, and baking may be performed in a two-coat two-bake or two-coat one-bake treatment depending on the paint used. As the paint system, any of a solvent system and a water-soluble paint system may be used, and a commercially available epoxy system, acrylic system, polyester system or the like can be used. Further, the coating film may contain a lubricant for improving the moldability.

The component composition of the precoated aluminum material of the present invention is not particularly limited as long as it is subjected to a phosphate treatment and used for coating purposes. In addition to industrial pure aluminum, various aluminum alloys Can be used. The method for manufacturing the aluminum base material itself is not particularly limited, and the required final thickness may be obtained through ordinary manufacturing steps such as casting, heating, hot rolling, cold rolling, and annealing.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally used JIS-A1050, 3
For the 105 and 5052 aluminum materials, the coating process was performed in a laboratory with a plate thickness of 1 mm, a width of 150 mm, and a length of 300 mm in place of the coating strip, and then the width of 30 mm.
mm and a length of 100 mm were cut into a bending test piece.

The conditions up to the coating treatment are as follows: alkaline degreasing (surf cleaner 322N-8: manufactured by Nippon Paint, 2% solution, 7%
0 ° C 15sec) → Rinse with water → Immerse in zinc phosphate suspension (5% suspension of powder reagent “Zinc phosphate” manufactured by Kanto Chemical Co., Ltd.) and rub with a nylon brush → Zinc phosphate (PB-L3020:
Nippon Parkerizing Chemical Conversion Solution for steel plate, 43 ℃ × 15se
c, dipping) → water washing → pure water washing → drying → painting (resin primer shown in Table 2, top coat: painted with a bar coater) → baking treatment (coating thickness 30 μm). As a comparative material, alkaline degreasing (surf cleaner 322N-8:
Nippon Paint 2% solution, 70 ° C 15sec) → Rinse →
Phosphate chromate (Alodine 407 / Alodine 47: manufactured by Nippon Parkerizing Co .: Cr adhesion amount 30mg / m ² ) → Washing →
Pure water washing → drying → painting (resin primer shown in Table 2, top coat: painted with a bar coater) → baking treatment (coating thickness 30 μm).

The test was performed in accordance with the 6.4 bending test of JIS H 4001, and the following coating film cracking and coating film peeling were observed. Coating Cracking A 180 ° bending test was performed on the painted test piece to evaluate the coating cracking state with a loupe (10 times). In the bending test, the conditions were changed by interposing 0, 1, 2, and 3 spacers having the same plate thickness as the test material. ○ No coating film cracking △ Slight coating cracking × Strong coating cracking

Coating Peeling After the above 180 ° bending test, a cellophane adhesive tape was stuck and immediately peeled off, and the coating peeling state was visually evaluated. ○ No peeling of coating film △ Slight peeling of coating film × Strong peeling of coating film

[0022]

[Table 1]

The results are shown in Table 1. The invention examples in which the concentration of the zinc phosphate suspension is within the range of the present application show good coating film performance without occurrence of coating film cracking and coating film peeling during bending processing. Although not shown in the table in the invention examples and comparative examples 1 and 2, those having a particle diameter of the inorganic compound of 0.001 to 10 μm were used. In the invention examples, the coverage was in the range of 20 to 80%. In Comparative Examples 1 and 2, the coverage was less than 20%. In Comparative Examples 1 and 2 in which the concentration of the zinc phosphate suspension was as low as 0.005%, a sufficient zinc phosphate film was not formed, and thus no cracking of the coating film was caused by bending, but the cellophane adhesive tape was peeled off. Causes the coating to peel off. Further, in Comparative Examples 3 to 6 in which a conventional phosphoric acid chromate film was applied and applied, cracking and peeling of the coating film occurred due to bending.

[0024]

According to the present invention, a chemical conversion treatment method as a pre-coating treatment of a precoated aluminum strip material is carried out by depositing a suspension containing a specific amount of inorganic compound particles of a metal and thereafter rubbing the suspension. At least a part of the inorganic compound particles is embedded in the surface, and the core is used as a nucleus, followed by phosphate treatment to quickly generate a phosphate film, which is a granular film with excellent moldability. Can be done. Therefore, it is not necessary to use a chromate treatment which is weak in molding processing and has problems in toxicity and its use is being regulated. Also, since it is a pre-coated strip, the productivity is high and the painting cost is low. Therefore, the pre-coated aluminum strip of the present invention is most suitable for use in building materials, home electric appliances and the like after molding.

Claims (2)

[Claims] After the alkali treatment and / or the pickling treatment, a suspension containing 0.01 to 50% by weight of inorganic compound particles of a metal which is hardly soluble in water having a pH of 5 ≦ pH ≦ 9 is adhered. By rubbing the inorganic compound particles of the metal at least partially embedded in the surface,
A method for producing a precoated aluminum strip excellent in formability, which comprises a phosphate treatment and a coating treatment. 2. The metal inorganic compound is titanium oxide, magnesium oxide, tungsten oxide, niobium oxide, aluminum oxide, zinc oxide, cuprous oxide, cupric oxide, ferric oxide, molybdenum oxide, magnesium hydroxide. And one or more selected from nickel hydroxide, magnesium carbonate, calcium carbonate, zinc phosphate, magnesium oxalate, barium titanate, ferric sulfate, calcium silicate, and magnesium hydrogen phosphate. The method for producing a precoated aluminum strip according to claim 1.