JP6295843B2 - Method for forming a film on aluminum or aluminum alloy, pretreatment liquid used therefor, and member obtained thereby - Google Patents

Description

  The present invention relates to a method for forming a film on aluminum or an aluminum alloy, a pretreatment liquid used therefor, and a member obtained therefrom, and more specifically, plugs pores present in an anodized film formed on the surface of aluminum or aluminum alloy. The present invention relates to a sealing process.

  Anodizing treatment is a method for improving the corrosion resistance of aluminum and aluminum alloys. Anodizing treatment forms an anodized film on the surface of this aluminum or aluminum alloy, but this anodized film has a porous layer with a large number of fine pores, which contributes to a decrease in corrosion resistance. Yes. Therefore, for the purpose of further improving the corrosion resistance, a sealing process for closing the fine holes after the anodizing process is performed.

  As a sealing treatment method, there is a high temperature hydration type sealing treatment method in which an aluminum member on which an anodized film is formed is immersed in boiling water. However, this method has a problem that a treatment time of 10 minutes or more is required and a large amount of energy is required to maintain the boiling state of boiling water. Therefore, in order to solve these problems, a method using an aqueous solution containing lithium ions as a sealing treatment liquid has been developed as disclosed in JP 2010-077752. This sealing treatment method is excellent in terms of production efficiency and energy consumption because the sealing treatment can be performed even when the temperature of the treatment liquid is 25 ° C. and the treatment time is 1 minute.

  Japanese Patent Laid-Open No. 2013-1957 discloses a method for sealing the surface of an anodized film formed on the surface of an aluminum member. The sealing solution used in this method is lithium ion. And a reaction accelerator A selected from polyoxyethylene alkyl ether or the like and a reaction accelerator B selected from polyvinyl alcohol or the like. In addition, as reaction conditions, it is described that the sealing treatment liquid has a weak alkaline pH of 8.0 to 10.0, and that the immersion time in the sealing treatment liquid is 30 minutes.

JP 2010-077752 A JP 2013-1957 A

  The sealing treatment method using lithium ions disclosed in Japanese Patent Application Laid-Open No. 2010-077752 is a method in which a part of an anodized film is dissolved to form a compound with lithium ions and rapidly sealed. For this reason, the amount of the sealing product generated in the hole varies between the bottom and the surface of the hole, and a large amount of sealing product is generated near the surface of the anodized film, so that anodization after sealing is performed. The film changes to a white and cloudy color. As a result, there is a problem that the appearance deteriorates when a colorless coating is applied on the anodized film or when it is not applied.

  Although the sealing treatment method disclosed in Japanese Patent Application Laid-Open No. 2013-1957 can prevent the anodized film from changing to a white and cloudy color tone, it has the following problems. Since the sealing treatment liquid has a weak alkaline pH of 8.0 to 10.0, the anodizing treatment liquid remains in the object to be treated even after washing with water after the anodizing treatment. It is inevitable that strongly acidic or strongly basic anodizing treatment liquid is mixed in the treatment liquid. Therefore, the pH of the sealing treatment liquid fluctuates greatly and it is difficult to maintain it within a predetermined pH range. is there. It is described that when the pH of the sealing treatment liquid is 12.0, film dissolution occurs in the surface layer portion of the anodized film, resulting in a white and uneven finish.

  Therefore, the object of the present invention is to prevent a change in the color tone of the surface of the anodized film after the sealing treatment, to shorten the time required for the sealing treatment, and to control the pH of the sealing treatment liquid. It is also possible to provide a method of forming a film on aluminum or an aluminum alloy, a pretreatment liquid used therefor, and a member obtained therefrom.

  In order to achieve the above object, the present invention, as one aspect thereof, is a method of forming a film on the surface of aluminum or aluminum alloy, the step of forming an anodized film on the surface of aluminum or aluminum alloy, The step of pretreating the aluminum or aluminum alloy on which the anodized film has been formed in a pretreatment liquid and the anodized film on the surface of the aluminum or aluminum alloy that has been pretreated are sealed with lithium ions. The pretreatment liquid contains phosphate ions and a reaction regulator, and has a pH in a neutral to acidic range, and the reaction regulator is included. Is a compound which generates a hydroxide ion in a compound having a carboxy group or a salt thereof or an aqueous solution.

The concentration of the phosphate ion is preferably 0.1 to 4.0 mol / L. The concentration of the reaction modifier is preferably 0.05 mol / L or more. The temperature of the pretreatment liquid is preferably 10 to 50 ° C. The time for immersion in the pretreatment liquid is preferably 1.5 minutes or longer. The compound having a carboxy group is preferably a carboxylic acid or a salt thereof. The compound that generates hydroxide ions in the aqueous solution is preferably a hydroxide. The anodic oxide film may have a thickness of 3 to 40 μm. In the sealing treatment step, a sealing product is generated in the holes present on the surface of the anodic oxide film, and the sealing product is lithium-aluminum containing at least LiH (AlO ₂ ) ₂ .5H ₂ O. Hydrates may also be used. The pretreatment liquid is preferably a buffer solution.

  Another aspect of the present invention is a pretreatment liquid used for the pretreatment when performing the sealing treatment of the anodic oxide film using the sealing treatment liquid containing lithium ions. A compound containing acid ions and a reaction modifier, having a pH in a neutral to acidic range, wherein the reaction modifier is a compound having a carboxy group or a salt thereof, or a compound that generates hydroxide ions in an aqueous solution. Is included.

  In another aspect, the present invention provides an aluminum or aluminum alloy member comprising aluminum or an aluminum alloy and an anodized film formed on the surface thereof, the anodized film formed on the aluminum or aluminum alloy. The surface pores are sealed with a sealing product, and the sealing product contains lithium-aluminum hydrate, and the lithium-aluminum hydrate is anodized in the pores. It is uniformly generated from the surface to the bottom of the hole.

  As described above, according to the present invention, the pretreatment step is performed before the sealing treatment step, and the phosphate ion and the reaction modifier are added to the pretreatment liquid in the pretreatment step, and neutral to acidic. In addition, by using a compound having a carboxy group or a salt thereof or a compound that generates hydroxide ions in an aqueous solution as a reaction regulator, phosphate ions are moderately added to the anodized film in the pretreatment step. This phosphate ion has an effect of suppressing the formation of a sealing product such as lithium-aluminum hydrate generated in the sealing treatment step, and thus a plurality of fine particles present on the surface of the anodized film. The sealed product can be evenly generated in the pores from the surface of the coating to the bottom of the pores. This can prevent the color tone of the anodized film from changing. In addition, since the pretreatment process and the sealing treatment process are in a short time of about several minutes and the pretreatment liquid has a pH in a neutral to acidic range, the pH of the sealing treatment liquid can be easily managed. be able to.

It is sectional drawing which shows typically the anodized film by which the sealing process obtained by the film forming method which concerns on this invention was carried out. It is sectional drawing which shows typically the anodized film by which the sealing process obtained by the conventional film formation method was carried out. In an Example and a control example, it is a photograph which shows the surface appearance of the anodized film by which the sealing process was carried out. In an Example, it is an electron micrograph which copied the surface of the anodic oxide film by which the sealing process was carried out. In an Example and a comparative example, it is a photograph which shows the surface appearance of the anodized film by which the sealing process was carried out in the corrosion resistance test.

  Hereinafter, an embodiment of a film forming method according to the present invention will be described. The film forming method of the present embodiment includes a step of forming an anodized film on the surface of aluminum or an aluminum alloy, and pretreating the aluminum or aluminum alloy on which the anodized film is formed by immersing it in a pretreatment liquid. And a step of sealing the anodized film on the surface of the aluminum or aluminum alloy subjected to the pretreatment with a sealing treatment liquid.

  The target for forming the film may be aluminum alloy as well as aluminum. It does not specifically limit as an aluminum alloy, Components, such as a silicon and copper, can be included widely. Further, the production method of aluminum or aluminum alloy is not particularly limited, and the present method can be applied to a wrought material, a cast material, and a die-cast material.

  In the step of forming the anodized film, the anodized solution is electrolyzed in the anodized solution using aluminum or an aluminum alloy as a working electrode. Thereby, an anodized film mainly composed of aluminum oxide can be formed on the surface of aluminum or aluminum alloy. The anodizing solution is not particularly limited. For example, an acid bath such as sulfuric acid, oxalic acid, phosphoric acid, or chromic acid, or an alkaline bath such as sodium hydroxide, sodium phosphate, or sodium fluoride is used. Also good.

  The method of electrolysis is not particularly limited, and any of DC electrolysis, AC electrolysis, AC / DC superposition electrolysis, Duty electrolysis and the like may be used. Moreover, it is preferable to perform water washing at least once after the electrolytic treatment. By washing with water, the anodizing treatment liquid adhering to the aluminum or aluminum alloy can be removed to some extent, or the concentration of the treatment liquid that could not be removed can be reduced, and the amount mixed into the next step can be reduced. The water used in the water washing is preferably water with few impurities such as ion exchange water and pure water.

  Although the film thickness of an anodized film is not specifically limited, 3-40 micrometers is preferable. Since sealing treatment is performed using lithium ions for the anodized film, the anodized film needs to have a certain thickness. If the thickness of the anodized film is 3 μm or more, the anodized film will not disappear even if the sealing treatment is performed using lithium ions. In addition, when the thickness is at least 40 μm, a sufficient function as a film of aluminum or an aluminum alloy can be exhibited, and the time required for film formation can be shortened, and productivity can be improved.

  In the pretreatment step, the aluminum or aluminum alloy on which the anodic oxide film is formed includes a phosphate ion and a reaction modifier before the anodized film is sealed, and has a pH in the acidic to neutral range. Immerse in a pretreatment liquid having

  By immersing the anodized film in such a pretreatment liquid, phosphate ions are taken into the surface and pores of the anodized film. Phosphate ions have the effect of suppressing the hydration reaction, so the formation reaction of lithium-aluminum hydrate, which is a sealed product that requires a large amount of water molecules, becomes gentle, and the bottom and surface of the pores in the pores It is possible to suppress variation in the amount of the sealed product generated in the part. Therefore, the color tone change of the anodized film due to reflection or refraction of light hitting the film can be suppressed.

  As the phosphate ion source, phosphate or phosphate containing phosphate ions soluble in water is preferable. Examples thereof include orthophosphoric acid, disodium hydrogen phosphate, sodium dihydrogen phosphate, trisodium phosphate, potassium phosphate, calcium dihydrogen phosphate, lithium phosphate, ammonium phosphate and the like. Preferably, it is a sodium salt of phosphoric acid from the viewpoint of being inexpensive and easy to handle, and more preferably sodium dihydrogen phosphate.

  The concentration of phosphate ions in the pretreatment liquid is preferably 0.1 to 4.0 mol / L. By setting the concentration of phosphate ions to 0.1 mol / L or more, a necessary amount of phosphate ions is incorporated into the anodized film, and the effect of suppressing the hydration reaction can be exhibited. In addition, by setting the phosphate ion concentration to 4.0 mol / L or less, it is possible to prevent phosphate ions from being excessively taken into the anodized film and to appropriately proceed with the sealing treatment in the next step. be able to.

  As described above, phosphate ions have an effect of suppressing the hydration reaction. Therefore, if they are taken into the anodic oxide film more than necessary, the sealing treatment time may be prolonged or the sealing reaction may be stopped. However, it is difficult to completely adjust the amount of phosphate ions taken into the anodized film only by adjusting the concentration of phosphate ions. Therefore, in the present invention, a reaction regulator is added to the pretreatment liquid to prevent excessive phosphate ions from being taken into the anodized film.

  The reaction regulator is a compound having a carboxy group or a salt thereof or a compound that generates hydroxide ions in an aqueous solution. Such a compound having a carboxy group or a compound that generates hydroxide ions in an aqueous solution has an appropriate amount of phosphate ions in the solid-liquid interface between the anodized film and the pretreatment liquid. Consume and thereby prevent phosphate ions from being excessively incorporated into the anodized film.

  As the compound having a carboxy group, carboxylic acid is preferable because it is easy to handle and acidic. Examples of the carboxylic acid include saturated carboxylic acids such as formic acid, acetic acid, propionic acid and butyric acid, dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid and fumaric acid, benzoic acid, salicylic acid and phthalic acid. Aromatic carboxylic acids such as trimesic acid, citric acid, lactic acid, glycolic acid, malic acid, hydroxy acids such as tartaric acid, and other compounds, as well as pyruvic acid, acetoacetic acid, and aconitic acid can be widely used. Alternatively, a compound having a relatively low solubility in water such as benzoic acid or salicylic acid may be replaced by a carboxylate such as sodium benzoate or sodium salicylate.

  As a compound that generates hydroxide ions in an aqueous solution, ammonia, carbonates such as sodium hydrogen carbonate, metal salts that generate hydroxide ions, and the like can be widely used. Among the compounds that generate hydroxide ions in an aqueous solution, hydroxide is preferred because it is soluble in water and easy to handle. Examples of the hydroxide include sodium hydroxide, calcium hydroxide, magnesium hydroxide, and potassium hydroxide. Among these, sodium hydroxide is preferable because it is easy to obtain and inexpensive.

  The reaction regulator may be a compound having both a carboxy group and a hydroxy group. Examples of such compounds include hydroxy acids such as citric acid, lactic acid, glycolic acid, malic acid and tartaric acid described above, and aromatic hydroxy acids such as salicylic acid. Among these, citric acid is preferable because it is easily available and easy to handle.

  The concentration of the reaction control agent in the pretreatment liquid is preferably 0.05 mol / L or more. By setting the concentration to 0.05 mol / L or more, phosphate ions can be prevented from being excessively taken into the anodized film. The upper limit of the concentration of the reaction modifier is not particularly limited, but if the concentration of the reaction modifier is too high, the viscosity of the pretreatment liquid becomes high, and it becomes difficult to remove the pretreatment liquid by washing with water. Therefore, the upper limit of the concentration of the reaction modifier is preferably 10 mol / L or less, more preferably 7 mol / L or less, and still more preferably 4 mol / L or less.

  The ratio of the concentration of phosphate ions to the concentration of reaction modifier is not particularly limited. For example, phosphate ion: reaction modifier may be in the range of 1: 0.25 to 1: 4.

  The pH of the pretreatment liquid is in the acidic to neutral range, for example, pH 1-7. This is because, when the pH of the pretreatment liquid is alkaline, it may adversely affect the sealing treatment in the next step, and the holes present in the anodized film may not be properly blocked, or the color tone of the film may change. Because there is. In addition, by setting the pretreatment liquid in an acidic to neutral range, for example, when a carboxylate is added to the pretreatment liquid, the carboxylate is ionized into carboxylate anions and metal ions in the pretreatment liquid. The equilibrium of the carboxylate anion in this ionized state is inclined to the carboxy group, and there is an effect of preventing phosphate ions from being excessively taken into the anodized film.

  Further, the pH of the pretreatment liquid is preferably in a weakly acidic to neutral range, for example, pH 5-7. In this way, by changing the pretreatment liquid from weakly acidic to neutral, even if the pretreatment liquid is mixed in the sealing treatment liquid in the next step, it is possible to suppress a change in pH of the sealing treatment liquid.

  In addition to adjusting the types and concentrations of phosphate ions and reaction modifiers to adjust the pH of the pretreatment solution to an acidic to neutral range, acids such as sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid, and hydrogen carbonate A base such as sodium, sodium carbonate, or ammonia may be used. In addition, a silicate compound such as sodium silicate cannot be used as the acid or base for adjusting the pH. When a silicate compound is used, there is a possibility of hindering the sealing treatment.

  In addition, since the pretreatment liquid contains phosphate ions that act as conjugate bases, the buffer ions may be combined with phosphate ions and weak acids or weak bases. Even if a strongly acidic or strongly alkaline anodizing solution is mixed in the pretreatment liquid, it can be pretreated by using a phosphate buffer solution having a pH of 5 to 7 and having a wide buffer capacity in a weakly acidic to neutral region. The change in pH of the liquid can be suppressed, and the pH of the pretreatment liquid can be maintained within a predetermined range.

  Although the temperature of a pretreatment liquid is not specifically limited, 10-50 degreeC is preferable. By making it 10 degreeC or more, the activity of the phosphate ion in a pretreatment liquid can be made active, and a phosphate ion can be taken in into an anodized film appropriately. Moreover, by making it 50 degrees C or less, while being able to prevent that a large amount of phosphate ion is taken in into an anodized film, an anodized film melt | dissolves in a pre-processing liquid, and it is because a micro unevenness | corrugation is made on the surface. It is possible to prevent the color change of the film. The temperature of the pretreatment liquid is more preferably 15 to 40 ° C. By setting this temperature range, the temperature can be easily maintained, and the energy required for maintaining the temperature can be reduced because the temperature is close to normal temperature.

  As for time to immerse in a pretreatment liquid, 1.5 minutes or more are preferred. By setting the immersion time to 1.5 minutes or longer, phosphate ions in the pretreatment liquid can be sufficiently taken into the anodized film. Although the upper limit of immersion time is not specifically limited, When production efficiency is considered, 20 minutes or less are preferable.

  After the immersion in the pretreatment liquid, it is preferable to perform the sealing treatment in the next step after washing with water at least once, as in the step of forming the anodized film.

  In the sealing treatment step, the anodic oxide film formed on the surface of aluminum or aluminum alloy is sealed with a sealing treatment liquid containing lithium ions, whereby fine pores existing on the surface of the anodic oxide film are formed. Can be closed. As the lithium ion source, lithium sulfate, lithium chloride, lithium nitrate, lithium carbonate, lithium phosphate, lithium hydroxide, or a hydrate thereof can be used. Of these, lithium hydroxide and lithium carbonate are preferred because the aqueous solution is alkaline and non-toxic.

  The lithium ion concentration of the sealing treatment liquid is preferably 0.02 to 20 g / L, and more preferably 0.08 to 10 g / L. The pH of the sealing treatment liquid is preferably 10.5 or more, more preferably 11 or more, and still more preferably 12 or more. Although the upper limit of pH is not specifically limited, 14 or less is preferable. Since the pH varies depending on the lithium ion source, the pH of the sealing treatment solution can be adjusted using an acid such as sulfuric acid, oxalic acid, or chromic acid, or a base such as sodium hydroxide, sodium carbonate, or sodium fluoride. .

  The sealing treatment method includes immersing aluminum or aluminum alloy on which the anodized film is formed in the sealing treatment liquid, spraying the sealing treatment liquid on the surface of the anodized film, or applying it with a brush, etc. Then, the sealing treatment liquid may be attached to the anodized film. The temperature of the sealing treatment liquid is preferably 10 to 65 ° C, and more preferably 25 to 50 ° C. The sealing treatment time is preferably 0.5 to 5 minutes. After the sealing treatment liquid is adhered, the anodized film is preferably washed with water or hot water and dried with an air blower or a drier.

By such a sealing treatment, as shown in FIG. 1, the plurality of fine holes 24 existing on the surface of the anodized film 22 formed on the aluminum or aluminum alloy 10 are evenly distributed from the film surface to the hole bottom. A sealed product 26 can be generated. Examples of the sealing product 26 include lithium-aluminum hydrate 26a and boehmite 26b. Examples of the lithium-aluminum hydrate 26a include LiH (AlO ₂ ) ₂ .5H ₂ O. Further, as boehmite 26b, for example, there is AlO.OH.

This LiH (AlO ₂ ) ₂ · 5H ₂ O is a pentahydrate and requires 5 equivalents of water molecules relative to lithium molecules to form. Phosphate ions incorporated into the anodic oxide film in the pretreatment step have the effect of suppressing the hydration reaction, and many water molecules have a great influence on the formation of the required lithium-aluminum hydrate. Hydrate formation can be moderated. As a result, the conditions (required amount of phosphoric acid and reaction inhibitor, immersion time, solution temperature) for suppressing changes in the color tone of the anodized film can be reduced, shortened, and lowered.

  Further, as described above, the sealing product 26 includes boehmite 26b in addition to the lithium-aluminum hydrate 26a. In the conventional method, as shown in FIG. 2, since a large amount of lithium-aluminum hydrate 26a is generated near the surface of the anodized film 22, it affects light refraction and the film appears white. . On the other hand, in the present invention, as shown in FIG. 1, since the lithium-aluminum hydrate 26a is uniformly formed in the holes 24 of the anodized film, the color tone of the anodized film by the sealing treatment is consequently obtained. The change of can be suppressed. As described above, according to the present invention, it is possible to prevent the color tone of the anodized film from changing and to manufacture aluminum or an aluminum alloy member having high corrosion resistance.

(Test Example 1: Influence of reaction modifier in pretreatment liquid)
An aluminum alloy A1100 material was used as a test piece. This is because when an alloy component is contained in a large amount, the anodized film is colored black or yellow due to the influence of the alloy component. Therefore, an A1100 material that hardly contains an alloy component and can form a transparent film is used. Therefore, the effect (inhibition of color tone change) according to the present invention can be easily determined visually.

In Test Example 1, the test piece of A1100 material was immersed as an anode in a sulfuric acid bath having a concentration of 200 g / L, and a direct current having a current density of 1.5 A / dm ² was applied for 10 minutes. As a result, an anodized film having a thickness of 10 μm was formed on the surface of the test piece. Next, for pretreatment, using various phosphate ion sources (reagent 1) and reaction modifier (reagent 2) shown in Table 1, the phosphate ion concentration was 0.5 mol / L, and the reaction modifier A pretreatment liquid (20 ° C.) that is an aqueous solution having a concentration of 0.25 or 0.5 mol / L and a pH of 1 to 5 was prepared. When the aqueous solution was alkaline, sulfuric acid was added to adjust the pH to be acidic. After immersing the test piece in this pretreatment liquid for 5 minutes, the pretreated test piece is put into a sealing treatment liquid (20 ° C.) which is an aqueous solution having a lithium ion concentration of 0.8 g / L and pH of 13, It was immersed for 1 minute (Examples 1 to 9).

  For comparison, a series of treatments of the test pieces were performed in the same manner as in the above-described examples except that a pretreatment liquid was prepared using a compound not corresponding to the reaction modifier of the present invention (Comparative Examples 1 to 3). 2).

  About each test piece of an Example and a comparative example, it was evaluated whether the color tone change of the anodized film was suppressed and whether the anodized film was sealed. The evaluation of suppression of color tone change of the film was made by visual comparison of the color tone with the test pieces of Control Example 1 and Control Example 2 below.

The control example 1 is a test piece of only anodizing treatment. Specifically, in Control Example 1, a test piece of A1100 material was immersed as an anode in a sulfuric acid bath having a concentration of 200 g / L, and a direct current was applied at a current density of 1.5 A / dm ² for 10 minutes to obtain 10 μm An anodized film is formed.

Control Example 2 is a test piece that was subjected to a sealing treatment without performing a pretreatment after the anodizing treatment. Specifically, in Control Example 2, a test piece of A1100 material was immersed as an anode in a sulfuric acid bath having a concentration of 200 g / L, and a direct current was applied at a current density of 1.5 A / dm ² for 10 minutes to obtain a 10 μm After forming the anodic oxide film, it was immersed in a sealing treatment solution having a lithium ion concentration of 0.8 g / L, pH 13, and a temperature of 20 ° C. for 1 minute to perform sealing treatment.

  The evaluation criteria for determining whether or not the change in the color tone of the film could be suppressed is effective when the color of the test piece of the example or comparative example is close to the test piece of the control example 1 (in the table, a circle mark). ), When it was close to Control Example 2, it was judged that there was no effect (in the table, x mark). FIG. 3 shows the appearance of each test piece of Control Example 1 and Control Example 2 and the appearance of a test piece judged to be effective for reference (Example 40 described later).

  Moreover, the sealing state observed the surface of the anodic oxide film with the electron microscope, and confirmed whether the anodic oxide film was sealed. In addition, when a sealing product sufficient to block a plurality of fine holes existing on the surface of the anodized film is generated by the sealing treatment, as shown in FIG. 4, a flaky shape is formed on the surface of the anodized film. Substance is observed. Therefore, in this test, the sealing state was evaluated based on the presence or absence of the flaky material. Table 1 shows the results of the above evaluations.

  As shown in Table 1, in Examples 1 to 9 in which pretreatment liquids were prepared using various phosphate ion sources and various compounds that generate hydroxide ions in a carboxylic acid or aqueous solution, the color tone change of the anodized film It was possible to perform sealing while suppressing this. On the other hand, in Comparative Examples 1 and 2 in which a pretreatment liquid was prepared using a compound that does not have a carboxy group such as sulfuric acid or boric acid and that does not generate hydroxide ions alone in an aqueous solution, it is incorporated into the film. The amount of phosphate ions could not be adjusted, and a large amount of phosphate ions was taken in, and could not be sufficiently sealed.

(Test Example 2: Effect of pH of pretreatment liquid)
Prepare an aqueous solution (20 ° C.) using phosphoric acid and citric acid as the pretreatment liquid so that the concentration of phosphate ions is 0.5 mol / L and the concentration of carboxylic acid is 0.25 mol / L. By adding sodium hydroxide to this in the range of 0-3.5 mol / L, except that the pretreatment liquid in which the pH of the aqueous solution was changed to 1-13 was prepared, the same as in Test Example 1 described above A series of treatments of the test pieces were performed (Example 1, Examples 10 to 14, and Comparative Examples 3 to 6). And about each test piece of these Examples and a comparative example, evaluation of suppression of the color tone change of a film | membrane and evaluation of a sealing state were performed similarly to Test Example 1. FIG. The results are shown in Table 2.

  As shown in Table 2, in Examples 1 and 10 to 14, in which the pH of the pretreatment liquid is in the acidic to neutral range of 1 to 7, sealing can be performed while suppressing the color tone change of the anodized film. did it. In particular, when the pH was 2 to 4, the discoloration suppressing effect was high, and more preferable results were obtained. In Comparative Examples 4 to 7 in which the pH of the solution is 8 or more, the surface of the film is dissolved in the pretreatment liquid, and a large number of minute irregularities are generated, and the color tone of the film changes, which is not preferable. Further, in Comparative Examples 3 to 6 having a pH of 8 or more, sealing was not performed. This is because the anodized film becomes alkaline when immersed in an alkaline pretreatment liquid, and the pH gradient is eliminated with respect to the same alkaline sealing liquid as the film, so that the sealing liquid penetrates into the film. It is thought that it became difficult to be done.

(Test Example 3: Effect of pretreatment liquid concentration)
The concentration of phosphate ion is 0-5 mol / L using sodium dihydrogen phosphate or phosphoric acid, and the concentration is 0 using citric acid (carboxylic acid) or sodium hydroxide (hydroxide). Except that the pretreatment liquid was prepared so as to be ˜3 mol / L, a series of treatments of the test pieces were performed in the same manner as in Test Example 1 described above (Example 3, Examples 15 to 33, Comparative Examples 7 to 13). The pH of the pretreatment liquid was 3-4. And about each test piece of these Examples and a comparative example, evaluation of suppression of the color tone change of a film | membrane and evaluation of a sealing state were performed similarly to Test Example 1. FIG. The results are shown in Table 3.

  As shown in Table 3, Examples 3 and 15 to 33 in which the concentration of phosphate ions is 0.1 to 4 mol / L and the total concentration of carboxylic acid or hydroxide is 0.05 to 4 mol / L. Then, it was possible to perform sealing while suppressing a change in color tone of the anodized film. On the other hand, in Comparative Examples 10 to 12 where the concentration of phosphate ions is less than 0.1 mol / L, the amount of phosphate ions taken into the film is reduced, so that the sealing reaction proceeds rapidly. The film turned white. In Comparative Example 13 in which the concentration of phosphate ions exceeds 4 mol / L and Comparative Examples 7 to 9 in which the concentrations of carboxylic acid and hydroxide are less than 0.05 mol / L, phosphate ions are excessively applied to the film. Since it was taken in, it was not sealed.

(Test Example 4: Effect of temperature of pretreatment liquid)
Using sodium dihydrogen phosphate and citric acid, a pretreatment solution was prepared so that the phosphate ion concentration was 0.5 mol / L, the carboxylic acid concentration was 0.25 mol / L, and the pH was 3. The test piece was subjected to a series of treatments in the same manner as in Test Example 1 described above except that the test piece was immersed by changing the point and the temperature of the pretreatment liquid in the range of 5 to 60 ° C. (Example 3, Examples 34 to 37, Comparative Examples 14 to 15). And about each test piece of these Examples and a comparative example, evaluation of suppression of the color tone change of a film | membrane and evaluation of a sealing state were performed similarly to Test Example 1. FIG. The results are shown in Table 4.

  As shown in Table 4, in Examples 3 and 34 to 37 in which the temperature of the pretreatment liquid was 10 to 50 ° C., sealing could be performed while suppressing a change in the color tone of the anodized film. On the other hand, in Comparative Example 14 in which the temperature was less than 10 ° C., the activity of phosphate ions in the pretreatment liquid was slow, and phosphate ions were difficult to be taken into the film, so that the rapid sealing reaction could not be suppressed, and the film The color of has changed. Further, in Comparative Example 15 where the temperature was higher than 50 ° C., the activity of phosphate ions became too active, and a large amount of phosphate ions was taken into the film, and thus was not sealed. In addition, the anodized film was dissolved in the pretreatment liquid, and many fine irregularities were formed on the surface, and the color tone of the film was changed.

(Test Example 5: Influence of immersion time in pretreatment liquid)
Using sodium dihydrogen phosphate and citric acid, a pretreatment solution was prepared so that the phosphate ion concentration was 0.5 mol / L, the carboxylic acid concentration was 0.25 mol / L, and the pH was 3. Except for the point and the point in which the immersion time of the test piece in the pretreatment liquid was changed in the range of 1 to 20 minutes, a series of treatments of the test piece were performed in the same manner as in Test Example 1 described above (Example 3, Examples 38-43, comparative example 16). And about each test piece of these Examples and a comparative example, evaluation of suppression of the color tone change of a film | membrane and evaluation of a sealing state were performed similarly to Test Example 1. FIG. The results are shown in Table 5.

  As shown in Table 5, in Examples 3 and 28 to 43 in which the immersion time in the pretreatment liquid was 1.5 minutes or more, sealing could be performed while suppressing a change in the color tone of the anodized film. On the other hand, in Comparative Example 16 in which the immersion time was less than 1.5 minutes, the amount of phosphate ions taken into the anodized film was small, and the sealing reaction could not be suppressed, and thus the color tone of the film changed. .

(Test Example 6: Corrosion resistance test)
Since the aluminum alloy A1100 material used in Test Examples 1 to 5 is an alloy that hardly corrodes, in Test Example 6 that evaluates corrosion resistance, ADC12 material, which is one of the commonly used aluminum alloys, was used as a test piece. . In Test Example 6, the test piece of ADC12 material was immersed as an anode in a sulfuric acid bath having a concentration of 200 g / L, and a direct current with a current density of 1.5 A / dm ² was applied for 10 minutes. As a result, an anodized film having a thickness of 4 μm was formed on the surface of the test piece. Next, for pretreatment, using only sodium dihydrogen phosphate, a pretreatment liquid (20 ° C.) that is an aqueous solution having a phosphate ion concentration of 0.5 mol / L and a pH of 4, and phosphoric acid Using sodium dihydrogen and citric acid, prepare a pretreatment liquid (20 ° C) that is an aqueous solution with a phosphate ion concentration of 0.5 mol / L, a citric acid concentration of 0.25 mol / L, and a pH of 3. did. After immersing the test piece in these pretreatment liquids for 5 minutes, the pretreated test piece is put into a sealing treatment liquid (20 ° C.) which is an aqueous solution having a lithium ion concentration of 0.8 g / L and pH of 13, Soaked for 1 minute.

  And about each test piece after a sealing process, the salt spray test was done for 120 hours based on JISZ2371, and the corrosion resistance evaluation by the presence or absence of white rust was performed. The appearance of the surface of the test piece at this time is shown in FIG. Moreover, it was also evaluated whether the anodized film was sealed with an electron microscope.

  In the test piece when the pretreatment liquid was only phosphate ions, white rust was generated after the corrosion resistance test, as shown in FIG. This is because phosphate ions were excessively taken into the film and the sealing reaction did not occur. On the other hand, in the test piece in which the pretreatment liquid contains both phosphate ions and citric acid, the sealing reaction occurred, the corrosion resistance was improved, and no white rust was generated as shown in FIG. . In addition, in ADC12 material, since the film | membrane of a blackish color produced | generated, it was not able to evaluate about the color tone change of a film | membrane. Also, in the observation of the film surface using an electron microscope, when the pretreatment liquid is only phosphate ions, the sealing cannot be confirmed, and when the pretreatment liquid contains both phosphate ions and citric acid, It was confirmed that these were consistent with the results of the actual corrosion resistance test.

10 Aluminum or aluminum alloy 20 Sealed film 22 Anodized film 24 Hole 26 Sealed product

Claims (12)

A method of forming a film on the surface of aluminum or an aluminum alloy,
Forming an anodized film on the surface of aluminum or aluminum alloy;
A step of pretreating the aluminum or aluminum alloy on which the anodized film has been formed by immersing it in a pretreatment liquid;
Sealing the anodized film on the surface of the aluminum or aluminum alloy that has been subjected to the pretreatment with a sealing treatment liquid containing lithium ions,
The pretreatment liquid, along with containing phosphate ions and reaction modifiers, have a pH in the range from neutral acidic, the reaction modifier is a compound having a carboxyl group or a carboxylic acid salt or an aqueous solution A method comprising a compound that generates hydroxide ions in   The method according to claim 1, wherein a concentration of the phosphate ion is 0.1 to 4.0 mol / L.   The method according to claim 1 or 2, wherein the concentration of the reaction modifier is 0.05 mol / L or more.   The method according to any one of claims 1 to 3, wherein the temperature of the pretreatment liquid is 10 to 50 ° C.   The method according to any one of claims 1 to 4, wherein a time of immersion in the pretreatment liquid is 1.5 minutes or more.   The method according to any one of claims 1 to 5, wherein the compound having a carboxy group is a carboxylic acid.   The method according to any one of claims 1 to 5, wherein the compound that generates hydroxide ions in the aqueous solution is a hydroxide.   The method according to claim 1, wherein the anodized film has a thickness of 3 to 40 μm. In the sealing treatment step, a sealed product is generated in the holes present on the surface of the anodized film, and the sealed product contains at least LiH (AlO ₂ ) ₂ .5H ₂ O. It is a hydrate, The method as described in any one of Claims 1-8.   The method according to claim 1, wherein the pretreatment solution is a buffer solution. A pretreatment liquid used for the pretreatment when performing sealing treatment of an anodized film using a sealing treatment liquid containing lithium ions, the pretreatment liquid containing phosphate ions and a reaction modifier. together, they have a pH in the range from neutral acidic, the reaction modifier, before a compound having a carboxyl group or a carboxylic acid salt or an aqueous solution is intended to include compounds which produce a hydroxide ion treatment liquid.   An aluminum or aluminum alloy member comprising aluminum or an aluminum alloy and an anodized film formed on the surface thereof, wherein the pores on the surface of the anodized film formed on the aluminum or aluminum alloy are sealed products. The sealed product contains lithium-aluminum hydrate, and the lithium-aluminum hydrate is uniformly formed from the surface of the anodized film to the bottom of the hole in the hole. Aluminum or aluminum alloy member.