METHOD FOR PAINTING ARTICLE TO BE TREATED

Abstract

An object of the present invention is to unify sealing treatment and degreasing treatment by treating an anodic oxide film of an article to be treated made from aluminum or an aluminum alloy with a strongly basic treatment liquid containing a lithium ion, and simplify a pretreatment step for painting. A method for painting the article to be treated, by forming the anodic oxide film on the article to be treated made from aluminum or the aluminum alloy, and painting the article to be treated by using the anodic oxide film as a substrate, includes a first step including anodic treatment S1 and a second step including painting treatment S3, wherein sealing treatment and degreasing treatment are conducted in a unified way with the use of a strongly basic bath containing the lithium ion.

Description

PRIORITY CLAIM

This patent application claims priority to Japanese Patent Application No. 2011-040450, filed 25 Feb. 2011, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field

Disclosed embodiments relate to a technology of painting an article to be treated made from aluminum or an aluminum alloy, and particularly relates to a method for painting the article to be treated, which has simplified a pretreatment for the painting of the article to be treated that is a component made from aluminum or the aluminum alloy.

2. Related Art

Conventionally, an exterior component such as an outboard motor or the like made from aluminum or an aluminum alloy is subjected to an anodizing treatment so as to provide a coated film formed thereon which works as a substrate (surface) for painting, in order to increase a rust-preventing capability of the outer surface of the component.

The anodizing treatment is a treatment (anodic oxide coating treatment) in which the article to be treated as an anode is immersed in a treatment liquid, and an electric current is passed through the article so as to oxidize the surface of the article to be treated thereby to form the film on the surface of the article. The surface of the anodic oxide film is porous, and accordingly, the surface of the oxide film is generally subjected to a sealing treatment beforehand and is then painted.

In general, the anodizing treatment process including the sealing treatment is ordinarily conducted in a batch process. The reason why the batch process is applied is because the anodizing treatment needs an electrical energization and accordingly the energization needs a special jig, and because the anodic oxide film is an unstable porous film and accordingly the pores need to be subjected to a sealing treatment thereby to be promptly sealed so as to be plugged immediately after the film has been formed.

In a painting step after the sealing treatment, the jig is changed, and the painting step is conducted as a continuous line. In this case, there is the possibility that dirt adheres and deposits on the article to be treated in the changing operation of the jig, and accordingly the article results in indispensably needing to be degreased as a pretreatment for painting when the article is painted.

In a conventional method for painting the article to be treated, the article to be treated is dried as a technique of preventing a treatment liquid and water droplets from dropping from the article to be treated when the jig is changed or the article is transferred between steps.

In a case where the article to be treated is dried by means of a heater, there are needed a heating facility, process control and energy such as heat, which causes such problems that the corrosion of the article to be treated is promoted by heating, a stain due to drying is formed, and an extra period of time is needed for cooling after the drying step.

In addition, in a case where the article to be treated is dried by air blow, there may be posed following problems. An air facility is needed, and besides, water trapped by the article to be treated spreads and scatters, corrosion progresses due to insufficient drying or the like, and dust and dirt adhere and deposit on the article to be treated due to air. Thus, any drying technique causes many problems when being applied.

Because of these problems, it is desirable to omit the drying step, but when the drying step is omitted, such problems occur that not only water droplets drop in a degreasing bath but also a sealing liquid (sealing bath) is carried into the degreasing bath. In general, the sealing bath is acidic, and even if the article is sufficiently washed with water, there is a tendency that the acid sealing bath is carried into a basic degreasing bath and the degreasing bath quickly deteriorates, because there are cases that the sealing bath remains in the article to be treated when the shape of the article is complicated and also in the pores of the anodic oxide film.

In addition, in a case where the sealing bath remains in the pores of the anodic oxide film, the basic degreasing bath quickly deteriorates, and the anodic oxide film tends to be easily attacked because the reactivity of the sealing liquid with a basic degreasing agent is enhanced. Because of this problem, in a conventional method for painting the article to be treated, water content is necessary to be sufficiently removed by drying.

FIG. 6 is a process chart for illustrating a method of painting a component (anodized aluminum component) made from aluminum or an aluminum alloy, which has the anodic oxide film formed thereon by a conventional technology.

Conventionally, as is illustrated in FIG. 6, as a first step (I), aluminum or the aluminum alloy is subjected to anodizing treatment (i) with the use of an electrical energization jig and sealing treatment (ii).

Due to the anodizing treatment (i) and the sealing treatment (ii), the surface of the anodic oxide film, which is the surface to be treated of the aluminum or aluminum alloy component, is made into a flat surface having no pores thereon.

After the sealing treatment (ii), the treated surface is dried (D), and the jig is changed.

FIGS. 7 (A) and (B) are schematic views for specifically describing the conventional pretreatment for the painting of the article to be treated.

FIG. 7 (A) is a cross-sectional view illustrating a state of an aluminum substrate (base material) 101 which has an anodic oxide film 102 formed thereon by using the energization jig in the first step (I) illustrated in FIG. 6. The anodic oxide film 102 is formed on the surface of the aluminum substrate 101. The surface portion of the anodic oxide film 102 is porous and has many pores 103 formed therein.

As for FIG. 7 (B), the anodic oxide film 102 which has been subjected to the anodic treatment (i) in the first step (I) is subjected to the sealing treatment (ii). In the sealing treatment (ii), the sealing bath (sealing agent, sealer) 104 penetrates into the pore (103) of the anodic oxide film 102, the sealer 104 is accumulated in the pore 103, and then the pore is sealed.

In the second step (II) after the jig has been changed, a degreasing step (iii) and a painting step (iv) are conducted with the use of a hanger for degreasing and a hanger for painting or the like which are not illustrated.

Such conventional process is disclosed in a patent literature 1: Japanese Patent Application (Laid-Open) No.2010-77532.

In a conventional technology for painting the article to be treated, the article to be treated is dried after having been subjected to sealing treatment, in order to prevent a treatment liquid and water droplets from dropping from the article to be treated when the jig is changed or the article is transferred between steps.

However, when the article to be treated is dried by means of a heater, a facility for heating the article to be treated, process control and energy such as heat are needed.

In addition, when the article to be treated is heated, there are posed such problems that the corrosion of the article to be treated is promoted by heating, a stain due to drying is formed on the article to be treated, and an extra period of time is needed for cooling after the drying step.

In addition, when the article to be treated is dried by air blowing method, an air facility is needed, and there are concerns that water spreads during the air blowing operation and corrosion progresses due to insufficient drying.

Furthermore, dust and dirt will deposit on the article to be treated due to air. Thus, any drying technique has many problems. Because of this reason, it is desirable to omit the drying step, but when the drying step is omitted, there are posed such problems that water droplets drop and a sealing bath is carried into a degreasing bath.

Furthermore, the sealing bath is generally acidic, and accordingly even if the article is sufficiently washed with water, there is a possibility that the acidic sealing bath is carried into a basic degreasing bath and the degreasing bath quickly deteriorates, because the sealing bath remains in the article to be treated when the shape of the article is complicated and also remains in the pores of the anodic oxide film.

When the sealing bath (sealer) remains in the pores of the anodic oxide film, the reactivity of the sealing liquid with the basic degreasing bath is enhanced, so that the degreasing bath quickly deteriorates, and the anodic oxide film tends to be easily attacked. Accordingly, in a conventional method, the water content needs to be removed by drying.

SUMMARY

Disclosed embodiments provide a method for painting an article to be treated, which unifies sealing treatment and degreasing treatment by sealing an anodic oxide film of the article to be treated made from aluminum or an aluminum alloy with a strongly basic treatment bath containing lithium ions, thereby to provide a method of painting the article in which the pretreatment step for painting can be simplified.

One disclosed embodiment provides a method for painting the article to be treated, which can treat the article to be treated made from aluminum or the aluminum alloy continuously from an anodic treatment step to a painting step, and eliminates the need for the drying step.

The present invention has been achieved for solving the problems occurred in the above-described circumstances, and the disclosed embodiments provide a method for painting an article to be treated, by forming an anodic oxide film on the article to be treated made from aluminum or an aluminum alloy, and painting the article to be treated by using the anodic oxide film as a substrate, the method comprising a first step including anodic treatment and a second step including painting treatment, wherein sealing treatment and degreasing treatment are conducted in a unified way with the use of a strongly basic bath containing a lithium ion.

In this method for painting the article to be treated, it is desirable to omit a drying step between the first step including the anodic treatment and the second step including the painting treatment, and conduct the anodic treatment, the sealing/degreasing treatment and the painting treatment as a continuous process.

In the disclosed method for painting the article to be treated, the anodic treatment is not particularly limited to a treatment which uses a specific anodizing bath. As for the electrolysis condition, any of a direct current, an alternating current and a superimposed direct current on an alternating current may be used. Further, as long as the film can be formed, the electrolysis condition is not particularly limited. The film thickness of the anodic oxide film is also not limited in particular, but is desirably controlled to 3 μm or more and 40 μm or less.

In addition, in the disclosed method for painting the article to be treated, it is desirable to control the concentration of the lithium ions in a sealing liquid used for the sealing treatment which also serves as degreasing treatment to 0.02 g/L or more and 20 g/L or less, a pH value of the strongly basic sealing bath is controlled to 10.5 or more, and a treatment temperature is controlled to 10° C. or higher and 65° C. or lower.

Furthermore, in the disclosed method for painting the article to be treated, it is desirable to employ lithium hydroxide or lithium carbonate as a source of the lithium ion.

In addition, in the disclosed method for painting the article to be treated, as for the painting treatment, there are various painting methods such as an immersion method, a spray method and a roll coating method. Further, as for paint, there are various types of paints such as urethane-based paint, epoxy-based paint and acrylic-based paint or the like. However, the painting method is not limited to a method using a particular painting method or paint.

The disclosed method for painting the article to be treated unifies the sealing treatment and the degreasing treatment by sealing the anodic oxide film of the article to be treated made from aluminum or the aluminum alloy with the strongly basic bath containing the lithium ions. Therefore, the present invention can simplify the pretreatment for painting, and can adequately keep corrosion resistance and the adhesiveness of the paint film without leaving (remaining) a degreasing component in the anodic oxide film.

In addition, the disclosed method for painting the article to be treated can save energy and save the space by omitting the drying step in the pretreatment for the painting of the article to be treated made from aluminum or the aluminum alloy. Therefore, the present invention can enhance production efficiency by simplifying the pretreatment for the painting and reducing the number of steps, so that the quality of a formed film can be greatly enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process drawing (chart) illustrating a method for painting an article to be treated;

FIG. 2A and FIG. 2B are magnified and enlarged cross-sectional views illustrating specific examples of sealing and degreasing steps illustrated in FIG. 1;

FIG. 3 is a view illustrating results of having verified a degreasing effect by using test examples, and illustrating results of an adhesiveness test of a paint film;

FIG. 4 is an explanatory drawing which collectively illustrates results of having evaluated Example and Comparative Examples by test pieces of an article to be treated;

FIG. 5 is a view which illustrates results of the adhesiveness test of the Example and the Comparative Examples illustrated in FIG. 4;

FIG. 6 is an explanatory view illustrating a process in a conventional technology; and

FIG. 7A and FIG. 7B are cross-sectional views for describing sealing treatment in a conventional technology.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

Disclosed embodiments will be described below with reference to FIG. 1 to FIG. 5.

FIG. 1 is a process drawing (process chart) for describing a method for painting an article to be treated according to one disclosed embodiment.

As is illustrated in FIG. 1, in the method for painting the article to be treated, the article 1 to be treated is treated in a continuous process which includes an anodizing step (S1), a sealing and degreasing step (S2) and a painting step (S3), as main treatment steps.

The article to be treated is, for instance, an exterior aluminum component part of an outboard motor, and is made from aluminum or an aluminum alloy. In the anodizing step (S1) of the article to be treated, the surface of the article to be treated is oxidized to form an anodic oxide film, by being immersed as an anode in an anodizing liquid, and being electrically energized with the use of an energization jig.

The treatment liquid to be used in the anodizing step S1 may be any one of an acidic bath such as a sulfuric acid bath, an oxalic acid bath and a phosphoric acid bath, or a basic bath such as a sodium hydroxide bath, a sodium phosphate bath and a sodium fluoride bath. In the method for painting the article to be treated according to the disclosed embodiment, the anodic treatment is not limited to a treatment which uses a specific anodizing bath (treatment liquid).

In addition, as for the electrolysis condition in the anodizing step S1, any of a direct current, an alternating current and a superimposed direct current on an alternating current may be used, and as long as the oxide film is formed, any electrolysis condition may be employed. In an anodizing step, a necessary amount of an electric current is passed to a substrate 2 of aluminum or an aluminum alloy, which is an article to be treated, thereby the substrate is anodized, and an anodic oxide film having a necessary film thickness is formed on the aluminum substrate 2. The thickness of the oxide film formed in the anodic treatment is not limited in particular, but the oxide film having a thickness of 3 to 40 μm is normally formed by controlling an energization period of time.

After the aluminum substrate 2 has been subjected to the anodic treatment of the anodizing step S1 and has acquired the anodic oxide film having a necessary film thickness formed on the surface, the anodic oxide film 3 on the article 1 to be treated is subjected to sealing treatment, as is illustrated in FIG. 2. FIG. 2A illustrates the initial state of the sealing treatment, in which a strongly basic sealing bath (sealing liquid) 5 penetrates into the anodic oxide film 3, and FIG. 2B illustrates the state in which the sealing bath 5 causes a chemical reaction and the compound 6 has sealed the pores 4. The pores 4 in the porous anodic oxide film 3 are covered with the compound 6 that has been formed by the chemical reaction between the strongly basic sealing bath (strongly basic aqueous solution) 5 and the anodic oxide film 3, which occurs by the penetration of the strongly basic sealing bath (strongly basic aqueous solution) 5, and thus are sealed with the basic sealing bath.

As is illustrated in FIG. 2A, the anodic oxide film 3 having a film thickness of 3 to 40 μm is formed on the surface of the aluminum substrate 2 in the anodizing step S1. The anodic oxide film 3 is porous and has many pores 4 therein. The strongly basic sealing bath (sealing liquid) 5 containing lithium ions penetrates into the pores 4, and the pores 4 are sealed and are plugged. The strongly basic sealing bath 5 containing the lithium ions is an aqueous solution of lithium hydroxide or an aqueous solution of lithium carbonate, enters the pores of the anodic oxide film 3, forms the compound in the pores 4 and seals the pores 4.

The sealing liquid described in Japanese Patent Laid-Open No. 2010-77532 is used as the strongly basic sealing bath 5, and the concentration of the lithium ions needs to be set at 0.02 to 20 g/L. When the concentration of the lithium ions is 0.02 g/L or more, the chemical reaction in the sealing treatment is promoted. The lower limit of the concentration of the lithium ions is 0.02 g/L, and is optionally 2 g/L. The upper limit of the concentration of the lithium ions is 20 g/L, but is optionally 10 g/L. When the sealing liquid having the concentration of the lithium ions exceeding 10 g/L is used, the chemical reaction rapidly progresses, and the dissolution of the aluminum substrate (basis metal) having no anodic oxide film occurs.

A pH value of the sealing liquid needs to be set at 10.5 or more. The pH value of the sealing liquid may be 11 or more, and optionally is 12 or more which means that the liquid is strongly basic. The upper limit of the pH value is 14, which means that the liquid is strongly basic. The sealing liquid is optionally strongly basic, then the sealing liquid easily reacts with the anodic oxide film 3 to promptly produce the compound 6 in pores, and accordingly the sealed anodic oxide film shows high corrosion resistance. However, the sealing liquid having a pH value of less than 10.5 which means that the liquid is weakly basic shows an inefficient effect of enhancing the corrosion resistance, and the sealed anodic oxide film shows a high corrosion rate. In addition, the pH value differs according to the source of the lithium ion, and accordingly the pH value can be adjusted by using a base such as sodium hydroxide, sodium phosphate and sodium fluoride or the like.

The temperature of the sealing liquid needs to be set at 10° C. or higher and 65° C. or lower. The temperature of the sealing liquid is optionally 25° C. to 50° C. When the anodic oxide film is treated with the sealing liquid at a temperature of 10° C. or lower, the activity of the sealing liquid is low and the reaction becomes weak, but some degree of corrosion resistance is expected. On the contrary, when the temperature exceeds 65° C., the dissolution of the anodic oxide film 3 progresses from its surface, and the film disappears, so that the high corrosion resistance can not be obtained.

According to one disclosed embodiment, a film having excellent corrosion resistance can be formed by the sealing treatment which brings an anodic oxide film 3 on the aluminum substrate 2 into contact with the strongly basic sealing bath (sealing liquid) 5 for a short period of time. At the same time, the strongly basic sealing bath 5 can show a degreasing effect by decomposing oil with the strongly basic bath. In this sense, the strongly basic sealing bath 5 is constituted so as to serve also as a strongly basic degreasing bath, and accordingly can conduct the sealing treatment and the degreasing treatment at the same time by sealing the pores 4 of the anodic oxide film 3. Accordingly, the strongly basic (treatment) bath containing the lithium ions can conduct both the sealing treatment and the degreasing treatment.

The strongly basic sealing bath 5 containing the lithium ions can decompose dirt such as oil (grease), and can provide a sealing effect and the degreasing effect at the same time, which is different from a general sealing bath such as a sealing bath of nickel acetate, which is a commercially available sealer. Accordingly, the manufacturing process which unifies a sealing step and a degreasing step can be structured, and the strongly basic (sealing) bath 5 containing the lithium ions can conduct the sealing/degreasing treatment simultaneously at one time.

A period of treatment time (immersion time) in the strongly basic sealing bath (sealing liquid) may be at least 0.5 minute. Then, the sealing bath can show both of the degreasing effect and the sealing effect, accordingly can secure the adhesiveness of the paint film and can provide high corrosion resistance. The upper limit of the period of the treatment time is approximately 5 minutes. When the period of the treatment time exceeds 5 minutes, the dissolution of the anodic oxide film 3 progresses, and the adhesiveness and corrosion resistance of the paint film are disadvantageously lowered.

According to this disclosed method for painting the article to be treated, the sealing treatment and the degreasing treatment (S2) can be conducted at the same time in a unified way by subjecting the anodic oxide film 3 to the sealing treatment with the use of the strongly basic sealing bath (sealing liquid) 5 containing the lithium ions. Because the unified treatment (S2) of the sealing treatment and the degreasing treatment becomes possible, the degreasing treatment to be solely conducted before painting becomes unnecessary.

In addition, in the sealing treatment with the use of the strongly basic sealing bath 5, the sealing bath chemically reacts with the anodic oxide film to form the compound 6. Accordingly, a degreasing component does not remain in the film, and a drying step can be omitted. Because the drying step can be omitted, a heating facility and an air facility become unnecessary. Accordingly, the energy and the space can be saved.

Because the sealing treatment for the pores 4 of the anodic oxide film 3 and the degreasing treatment for the anodic oxide film 3 are conducted at the same time in a unified way, and besides, a drying step can be omitted, the pretreatment for painting can be simplified and the period of the treatment time can be shortened. After that, in a painting step (S3), painting treatment can be conducted by using urethane-based paint, epoxy-based paint or acrylic-based print, in an immersion method, a spraying method, a roll coating method or the like. There are various types for the method for painting the article to be treated, and the painting step does not limit the painting method and the paint to special ones.

According to the disclosed method for painting the article to be treated, the sealing treatment and the degreasing treatment are unified and can be conducted at the same time, by sealing the pores 4 in the porous anodic oxide film with the strongly basic (sealing) bath 5 containing the lithium ions, in a process of manufacturing a component of aluminum or an aluminum alloy, which forms the anodic oxide film on the substrate for painting.

Accordingly, the sealing treatment and the degreasing treatment are conducted at the same time by subjecting the component to the sealing treatment with the use of the strongly basic (sealing) bath 5 containing the lithium ions, a drying step can be omitted, so that the pretreatment step for painting is simplified. A manufacturing process having a small number of manufacturing steps becomes possible by unifying the sealing step and the degreasing step. The component of the strongly basic (sealing) bath 5 enters into the pores 4 of the porous anodic oxide film 3 and chemically reacts with the anodic oxide film to form the compound 6 in the pores 4 and on the surface, and accordingly the degreasing component does not remain in the oxide film.

In addition, because the anodic oxide film 3 of the aluminum substrate 2 is sealed with the strongly basic (sealing) bath 5 containing the lithium ions, a liquid drip does not occur. The sealing treatment and the degreasing treatment can be conducted at the same time, which has enabled the sealing treatment to be conducted in a painting line as the pretreatment for painting. Furthermore, the sealing treatment for the anodic oxide film 3 can be conducted with a hanger jig, and accordingly the drying step before painting can be omitted by changing the jig after the anodic treatment and unifying the sealing treatment and the degreasing treatment.

According to one disclosed method for painting the article to be treated, the sealing treatment after the anodic (anodizing) treatment of the article to be treated is unified with the degreasing treatment before painting, and accordingly a manufacturing process is shortened and simplified. The manufacturing process can be integrated by eliminating the drying step between the anodic treatment and the painting treatment via the sealing/degreasing treatment, so that the number of manufacturing steps is reduced, whereby the space can be saved, a manufacturing line can be shortened, and the tact time can be shortened.

In addition, the drying step which has existed between the first step including the anodic treatment and the second step including the painting treatment can be omitted by the integration, so that a heating facility and an air facility become unnecessary, and the energy and the space can be advantageously saved. Accordingly, corrosion due to insufficient drying can be prevented from occurring, corrosion due to exposure to a high temperature environment can be prevented from being promoted, and a stain due to drying can be prevented from occurring.

In a general alkaline degreasing step for a conventional pretreatment for painting, a degreasing agent remains in the pores of the anodic oxide film in the degreasing step after the sealing step, so that there may be a case where the adhesiveness of the paint film is occasionally lowered. However, in the present embodiment, the lithium ion in the strongly basic (sealing) bath (treatment liquid) containing the lithium ions chemically reacts with the anodic oxide film to form the compound 6, and accordingly no degreasing component remains, which can prevent the lowering of the adhesiveness of the paint film.

In addition, there are merits of facilitation and simplification also in a process control of a manufacturing process. In a conventional manufacturing process, an acid sealing liquid is carried into an alkaline degreasing bath, so that a pH value is changed and varied, whereby the degradation of the degreasing bath is accelerated. In addition, there have been many cases in which the sealing liquid is carried to the degreasing treatment, because the anodic oxide film is formed to be porous, and the sealing liquid in the pores cannot be fully removed even though having been subjected to washing in water.

However, in the disclosed method for painting the article to be treated, control items can be reduced by unifying the sealing treatment and the degreasing treatment. In the sealing treatment for the anodic oxide film using the strongly basic (sealing) bath 5 containing the lithium ions, the sealing bath chemically reacts with the anodic oxide film to form the compound 6, and accordingly has an effect of enhancing the corrosion resistance of the anodic oxide film 3. A general strongly-basic bath to be used for degreasing attacks and dissolves the anodic oxide film to reduce the thickness of the film and/or decrease the effect of sealing. As a result, the corrosion resistance of the anodic oxide film is disadvantageously lowered.

In the strongly basic (sealing) bath containing the lithium ions, although the bath is strongly basic, the anodic oxide film is not attacked and the pores of the film can be sealed and plugged, so that the corrosion resistance of the anodic oxide film can be enhanced. In the method for painting the article to be treated in the present embodiment, the sealing treatment and the degreasing treatment can be conducted at the same time in a unified way, the component in the sealing bath chemically reacts with the anodic oxide film to form the compound 6, and the degreasing component does not remain in the anodic oxide film. Accordingly, the anodic oxide film can be prevented from being attacked in the degreasing treatment before painting, and the product of the treated article having a stable quality can be provided.

[Experiment 1]

Next, in Experiment 1, the degreasing effect was verified by an adhesiveness test of the paint film of a test piece.

An exterior aluminum component of an outboard motor and the like are subjected to an anodic treatment for a substrate (base surface) of painting, in order to enhance a rust-preventing capability. An anodic oxide film is painted after having been subjected to sealing treatment because of being porous, but degreasing treatment has been conventionally conducted as a pretreatment for painting.

In this example, the sealing treatment is abolished, and a jig is changed after the anodic treatment is conducted and subsequently water is drained off. A test piece having the anodic oxide film formed thereon was subjected to the degreasing treatment before painting with the use of a strongly basic treatment bath of an aqueous solution of lithium hydroxide, and then was subjected to the painting by a spray of an acrylic lacquer. The sealing treatment and the degreasing treatment can be conducted at the same time, by using the strongly basic treatment bath of the lithium hydroxide solution even though the degreasing treatment before painting is omitted, and the production process can be shortened.

When the strongly basic treatment bath is used, the bath (treating liquid) penetrates into each pore of the anodic oxide film and can dissolve oil and the like, and furthermore, the strongly basic treatment liquid chemically reacts with the anodic oxide film to form a compound (solidified material) thereby to seal the pores, even if the sealing treatment is abolished. Accordingly, the sealing treatment is conducted with the degreasing treatment simultaneously with the use of the strongly basic treatment liquid, and the sealing step and the degreasing step before painting can be unified. The method becomes a method for painting the article to be treated which is equivalent to what was shown by the present embodiment. This Example corresponds to Test Example 4.

As for Test Examples 1 to 4, the anodic oxide film of approximately 10 μm was formed on each test piece by anodic treatment, and then in the verification of the degreasing effect illustrated in FIG. 3, the test piece was subjected to each treatment after an engine oil was applied onto the anodic oxide film for a malicious test of the adhesiveness of the paint film, was painted and was subjected to the adhesiveness test. The adhesiveness of the paint film in the adhesiveness test was evaluated according to the cross-cut testing method in JIS-K5400.

In the verification of the degreasing effect, the case in which the degreasing treatment was not conducted was illustrated in the column of “no degreasing” of Test Example 1, and the case in which the degreasing effect was confirmed by nickel acetate that was a commercial sealer was illustrated in the column of “nickel acetate” of Test Example 2.

In addition, the case in which the degreasing treatment was conducted by using “MAXCLEEN (NG-30)” made by Kizai Corporation, which is a commercial degreasing agent, and by immersing the test piece in the solution at 50° C. for approximately 3 minutes was illustrated in the column of “NG-30” of Test Example 3. Furthermore, the case in which the treatment was conducted by using the strongly basic treatment liquid to be used in the present example was illustrated in the column of “lithium” of Test Example 4. Each test piece was subjected to a peeling test of the paint film in accordance with the above described cross-cut testing method.

According to the adhesiveness test result, it was confirmed that the degreasing treatments of “NG-30” of Test Example 3 and “lithium” of Test Example 4 (Example) did not show peeling and showed an adequate adhesiveness. In contrast, the test pieces of the degreasing treatment of “no degreasing” of Test Example 1 and “nickel acetate” of Test Example 2 showed perfect (complete) and large peeling phenomena, respectively.

As a result of the adhesiveness test, it was suggested that a product which does not cause the peeling of the paint film and has a sufficient quality could be supplied by employing the condition of the test pieces of “Test Examples 3 and 4”, as illustrated in “Test Examples 1, 2, 3, and 4” in the upper column of FIG. 3. Test Example 3 showed the adequate adhesiveness but the lowered corrosion resistance. Test Example 4 corresponded to the Example, was prepared in a few steps, and was confirmed to have also superior corrosion resistance and adhesiveness. The corrosion resistance of each test piece of “Test Examples 1, 2, 3, and 4” is evaluated as illustrated in the lower column of FIG. 3, and Test Examples 2 and 4 show excellent corrosion resistance. When the performance including the adhesiveness was evaluated, it was confirmed that the test piece of Test Example 4 which corresponded to the Example was excellent.

[Experiment 2]

In Experiment 2, the adhesiveness test of the paint film was conducted for each test piece by a cross cut test.

Die-casting material ADC12 of an aluminum alloy, which is used for the exterior aluminum component of the outboard motor, was used for the test piece. The adhesiveness to the paint film of the test piece was evaluated according to the cross-cut testing method in JIS-K5400.

In the adhesiveness test of the paint film, the adhesiveness of the Example and Comparative Examples 1 to 4 was evaluated, as illustrated in FIG. 4. The FIG. 5 illustrated the result of the adhesiveness test of the paint film of the Example and Comparative Examples 1 to 4.

EXAMPLE

In the Example, a test piece which was treated with the disclosed method was subjected to the adhesiveness test of the paint film with a cross cut test.

Aluminum alloy ADC12 was used for the test piece. The test piece was immersed as an anode in 200 g/L of a sulfate bath, and the anodic oxide film 3 having a film thickness of 10 μm was formed on the test piece by passing an electric current to the test piece for 20 minutes under the condition of a current density of 2 A/dm². Then, an engine oil was applied onto the surface to be evaluated (the surface of the anodic oxide film of the test piece) assuming that dirt deposited due to the change of the jig after the anodic treatment, in order to evaluate the degreasing effect of the strongly basic sealing bath 5 for the anodic oxide film 3.

After that, the sealing treatment and the degreasing treatment were conducted at the same time by immersing the oil-applied test piece into the strongly basic (sealing) bath which contains 2 g/L of lithium ions and has a pH of 13, at a temperature of 25° C. for 1 minute. In the painting treatment, the acrylic lacquer made by Nippe Home Products Co, Ltd. was sprayed. The adhesiveness of the paint film was evaluated according to the cross-cut testing method in JIS-K5400.

According to the test piece of the above described Example, it became possible to decrease the number of manufacturing steps to three steps which were anodizing, sealing/degreasing and painting steps and to provide a product having such a high quality that the paint film was not peeled and the adhesiveness was sufficiently high as illustrated in FIG. 5.

Comparative Example 1

In Comparative Example 1, a test piece which was prepared according to the conventional method illustrated in FIG. 6 was subjected to the adhesiveness test of the paint film.

The engine oil was applied onto the surface to be evaluated of the anodic oxide film having a film thickness of 10 μm in a similar way to that in the test piece of the Example, and the sealing treatment was conducted by using a sealer of nickel acetate (TOP SEAL H-298 made by Okuno Chemical Industries Co., Ltd.) which is a commercially available sealer, and immersing the oil-applied test piece into the solution at a temperature of 90° C. for 10 minutes.

After that, the test piece after the sealing treatment was subjected to drying treatment to be dried for 20 minutes, and after the drying for 20 minutes, the engine oil was applied onto the surface, because it was assumed that dirt deposited when the jig was changed. Furthermore, after the drying treatment, the oil-applied test piece was subjected to the degreasing treatment with the use of a commercial degreasing agent, to the painting treatment by a spray of an acrylic lacquer, and subjected to the adhesiveness test. “MAXCLEEN NG-30” made by Kizai Corporation, which is commercially available, was used as the degreasing agent, and the oil-applied test piece was immersed in the solution at 50° C. for 3 minutes.

As a result of this adhesiveness test, as illustrated in FIG. 5, the paint film was not peeled. However, this test piece needs each treatment of anodizing, sealing, drying, degreasing and painting for the manufacture, and there is such a problem that the number of manufacturing steps is large.

Comparative Example 2

Comparative Example 2 was conducted for confirming whether the sealing treatment and the degreasing treatment could be conducted at the same time or not by using a commercial sealing agent in a continuous process shown in the 1st embodiment (refer to FIG. 1). Specifically, the anodic oxide film having a film thickness of 10 μm was formed on a test piece, the engine oil was applied to the surface to be evaluated of the anodic oxide film, and the sealing treatment and the degreasing treatment were conducted at the same time in a similar way to that in the test piece of Example, by using a commercial sealing liquid of nickel acetate and immersing the oil-applied test piece in the solution at a temperature of 90° C. for 10 minutes.

After that, the resultant test piece was subjected to painting treatment by a spray of the acrylic lacquer, and then subjected to an adhesion test. As a result, the most part of the paint film of the test piece was peeled as illustrated in FIG. 5, and it was confirmed that the commercial sealing agent did not show the degreasing effect and the sufficient quality could not be obtained.

Comparative Example 3

In Comparative Example 3, the degreasing effect of a commercial degreasing agent was confirmed in the continuous process illustrated in FIG. 1, in order to evaluate only the degreasing effect of Example, though the commercial degreasing agent does not show an effect of enhancing corrosion resistance. The engine oil was applied onto the anodic oxide film having a film thickness of 10 μm in a similar way to that in the above described Example, and the degreasing treatment was conducted by using the degreasing agent without conducting the sealing treatment. After that, the painting treatment was conducted by a spray of the acrylic lacquer, and the adhesiveness test of the paint film was conducted. “MAXCLEEN NG-30” made by Kizai Corporation, which is commercially available, was used as the degreasing agent, and the test piece was immersed in the solution at 50° C. for 3 minutes.

As a result of the adhesiveness test of the paint film, as illustrated in FIG. 5, the paint film of the test piece of Comparative Example 3 was not peeled, and a similar result to that of the test piece of Example was obtained. It was confirmed that the test piece of Comparative Example 3 had acquired a sufficient degreasing effect. However, the test piece showed inferior corrosion resistance because the test piece was not subjected to the sealing treatment.

Comparative Example 4

In Comparative Example 4, a test piece which skipped (omitted) the degreasing treatment so as to decrease the attack of the degreasing agent to the anodic oxide film was subjected to the evaluation for the adhesiveness of the paint film. The engine oil was applied onto the anodic oxide film having a film thickness of 10 μm in a similar way to that in the test piece of the above described Comparative Example 3, the oil-applied test piece was directly subjected to the painting treatment by a spray of an acrylic lacquer without conducting the sealing treatment and the degreasing treatment, and the painted test piece was subjected to the adhesion test. As a result, the paint film was all peeled (refer to FIG. 5).

According to the present embodiment, the sealing treatment and the degreasing treatment are unified by subjecting the anodic oxide film of the article to be treated made from aluminum or an aluminum alloy to the sealing treatment (or degreasing treatment) with the use of the strongly basic treatment bath containing lithium ions, and the sealing/degreasing treatment can be conducted at the same time, each treatment of anodizing, sealing/degreasing and painting for the article to be treated can be integrated and unified, and the treatment process can be effectively simplified.

In addition, by conducting the sealing/degreasing treatment for the article to be treated in a unified way with the strongly basic treatment bath containing the lithium ions, the drying treatment can be omitted. Furthermore, degreasing treatment before painting does not need to be solely or independently conducted, so that the energy and the space can be saved.

Furthermore, the reduction of the film thickness of the anodic oxide film is prevented, a degreasing component does not remain in the film, and the deterioration of the adhesiveness to the paint film is prevented, because the anodic oxide film of the article to be treated is treated by using the strongly basic treatment bath containing the lithium ions to make the component of the bath chemically react with the anodic oxide film to form a compound.

Moreover, the tact time can be shortened, thereby the productive efficiency is enhanced, and the quality of the formed film is enhanced without producing corrosion which is caused by a stain due to drying and the insufficiency of drying.

Claims

1. A method for painting an article to be treated, by forming an anodic oxide film on the article to be treated made from aluminum or an aluminum alloy, and painting the article to be treated by using the anodic oxide film as a substrate, the method comprising:

a first step including anodizing treatment; and

a second step including painting treatment,

wherein sealing treatment and degreasing treatment are conducted in a unified way with the use of a strongly basic bath containing a lithium ion.

2. The method for painting the article to be treated according to claim 1, wherein a drying step between the first step including the anodizing treatment and the second step including the painting treatment is omitted, and the anodizing treatment, the sealing/degreasing treatment and the painting treatment are conducted as a continuous process.

3. The method for painting the article to be treated according to claim 1, wherein a film thickness of the anodic oxide film formed in the anodizing treatment is 3 μm or more and 40 μm or less.

4. The method for painting the article to be treated according to claim 1, wherein

a concentration of the lithium ion in the strongly basic bath to be used in the sealing/degreasing treatment is set to 0.02 g/L or more and 20 g/L or less,

a pH value of the strongly basic bath is set to 10.5 or more, and

a treatment temperature is set to 10° C. or higher and 65° C. or lower.

5. The method for painting the article to be treated according to claim 1, wherein lithium hydroxide or lithium carbonate is employed as a source of the lithium ion.

6. The method for painting the article to be treated according to claim 3, wherein in the painting treatment, an immersion method, a spray method or a roll coating method is employed as a painting method, and urethane-based paint, epoxy-based paint or acrylic-based paint is employed.