JP2668555B2 - Chemical treatment agent and chemical treatment bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a chemical conversion treatment agent and a chemical conversion treatment used for forming a chemical conversion film on a metal surface such as iron and an iron-based alloy, particularly a tin-plated iron surface. Regarding bath

[Prior Art] Iron cans are widely used as containers for filling various canned goods, soft drinks, juices and the like. As a steel can, a thin iron plate processed into a can shape or a can (DI can) formed by drawing and ironing is used. However, since the material itself is inferior in corrosion resistance, a coating for corrosion prevention is used. It is usually applied. As a coating for anticorrosion, a thin film of an epoxy resin or the like is generally formed on the surface of a can body. However, such a resin coating is not formed directly on the surface of an iron plate, but is subjected to a surface treatment. Have been applied to. As such a surface treatment, it is preferable to perform a chemical conversion treatment from the viewpoint of corrosion protection, coating film adhesion, etc.
Such a chemical conversion treatment is often performed on a tin-plated iron can.

By the way, as a typical example of the chemical conversion treatment, there is a method of treating with a solution containing chromic acid and phosphoric acid. According to this method, it is possible to obtain a film having good adhesion and corrosion resistance to the coating film, but since it uses highly toxic hexavalent chromium, it has a problem on the human body and wastewater treatment. There is. Therefore, various solutions containing no hexavalent chromium have been developed so far.

For example, a method of chemically treating tin plating cans with an aqueous solution containing at least one of orthophosphoric acid and salts thereof and at least one of phytic acid and salts thereof at pH 3 to 5 (Japanese Patent Publication No. 58-39231), , Acidic alkaline phosphates,
One or more of chlorate and bromate, tin ion,
And a pH 3 to 6 metal surface film forming treatment solution containing chloride ions (JP-B-58-41352), hexafluorozirconium (IV) acid salt, phytic acid or its salt, phosphoric acid or its salt, and chlorate A method for chemical conversion treatment of a metal surface such as tin-plated iron with an acidic aqueous solution containing JP-A-59-83
No. 775) is known.

[Problems to be solved by the invention]

However, when treated by the method described in JP-B-58-39231, although the corrosion resistance is good, salts are generated by phytic acid in the treatment bath and tin and iron eluted from the tin plating can, and There is a problem that the salt (hereinafter the same) adheres to the can and the can cannot be transported smoothly. Further, when the can is printed, the adhered matter is transferred to the rubber blanket, which causes a problem that printing is not smoothly performed.

Further, when a chemical conversion treatment is carried out with the treatment solution described in JP-B-58-41352, the corrosion resistance of the metal surface, particularly when not coated, is insufficient.

Furthermore, according to the method described in JP-B-59-83775, although good results can be obtained at the beginning of the treatment, when tin and iron eluted from the tin plating can accumulate in the treatment bath, the treatment bath There is a problem that a precipitate is formed by zirconium, phytic acid and phosphoric acid, which are components for forming a film, and the life of the treatment bath is shortened.

Therefore, an object of the present invention is to solve the problems of the prior art, and salts that cause various obstacles to the processing step are not generated in the processing bath, and have excellent corrosion resistance and good coating film adhesion. An object of the present invention is to provide a chemical conversion treatment agent and a chemical conversion treatment bath capable of forming a chemical conversion film.

[Means for solving the problem]

As a result of intensive studies to solve the above problems, the present inventor has formulated orthophosphate and / or a salt thereof, oxalic acid and / or a salt thereof, and divalent tin ions in a specific ratio as a chemical conversion bath. As a result, the present inventors have found that a chemical conversion film having little iron elution and having good corrosion resistance and good coating film adhesion can be provided, and reached the present invention.

That is, the chemical conversion treating agent of the present invention is orthophosphoric acid and / or
Or 1 to 30 parts by weight of a salt thereof PO ₄ terms, 0.005 part by weight of oxalic acid and / or salts thereof with oxalic acid converted, and the divalent tin ions, characterized in that it contains 0.005 to 0.5 parts by weight.

Moreover, chemical treatment bath of the present invention, 1 to 30 g / orthophosphoric acid and / or its salt PO ₄ terms, oxalic acid and / or its salt with oxalic acid in terms 0.005 to 0.5 / and divalent tin ions 0.00
It is characterized by containing 5 to 0.5 g / content and having a pH of 3 to 5.

 Hereinafter, the present invention will be described in detail.

The chemical conversion treating agent of the present invention is used particularly for the surface treatment of tin-plated iron cans and the like, and contains the following components at a predetermined ratio and is diluted to an appropriate concentration to prepare a chemical conversion bath.

The first component is orthophosphoric acid and / or its salts. Examples of the salts of orthophosphoric acid include sodium salts, potassium salts, lithium salts, ammonium salts and the like. Orthophosphoric acids which are neutralized with caustic alkali, alkali carbonate and the like may also be used. Orthophosphoric acid and salts thereof can be used either alone or in combination, and two or more salts may be used in combination. The first component is 1-3 in terms of PO _4.
0 parts by weight (concentration in the chemical conversion bath is 1 to _{4 in} terms of PO ₄
30 g /, the same below), preferably 3-10 parts by weight (3-10
g /). Orthophosphoric acid and / or in the chemical conversion bath
When the content of the salt is less than 1 g /, not only the formation of the chemical conversion film is insufficient, but also the corrosion resistance of the obtained chemical conversion film is low. On the other hand, if it exceeds 30 g /, the etching of the metal surface is promoted, the appearance is impaired, and the corrosion resistance and the adhesion of the coating film are reduced.

The second component is oxalic acid and / or its salt. Examples of the salt of oxalic acid include sodium salt, potassium salt, lithium salt, ammonium salt, tin salt and the like. The second component has a content of 0.005 to 0.5 part by weight (0.005 to 0.5 g /), preferably 0.02 to 0.1 part by weight (0.02 to 0.1 g /) in terms of oxalic acid.
The content of oxalic acid and / or its salt in the chemical conversion bath is
If it is less than 0.005 g / s, sufficient corrosion resistance and coating film adhesion cannot be obtained. On the other hand, when it exceeds 0.5 g /, etching of the metal surface is promoted, the appearance is impaired, and the corrosion resistance is lowered.

Further, the chemical conversion treating agent (chemical conversion bath) of the present invention contains 0.005 to 0.5 part by weight (0.005 to 0.5 g /), preferably 0.01 to 0.05 part by weight (0.01 to 0.05 g /) of a divalent component as the third component. Contains tin ions. Examples of the divalent tin ion include stannous chloride, stannous sulfate, tin oxalate and the like. Note that tin ions need to be divalent, and tetravalent tin ions are inappropriate because they result in excessive etching of the tin-plated surface. When the content of divalent tin ions in the chemical conversion treatment bath is less than 0.005 g /, the resulting chemical conversion film has insufficient corrosion resistance and coating film adhesion. On the other hand, 0.5g /
If the amount exceeds the above range, there is no further effect, and conversely, a large amount of sludge is generated in the treatment bath, and the treatment efficiency is reduced.

The chemical conversion bath of the present invention needs to have a pH of 3 to 5, preferably 3.0 to 3.5. If the pH is less than 3, the etching of the metal surface is promoted too much, resulting in poor appearance, and the resulting chemical conversion film has low corrosion resistance. If the pH exceeds 5, the chemical conversion reaction does not proceed satisfactorily, and it becomes difficult to form a chemical conversion film.

The chemical conversion treating agent of the present invention is prepared by adding each of the above-mentioned components to water and mixing to form an aqueous concentrated solution (concentration of about 10 to 100 times), which is diluted with an appropriate amount of water to a predetermined concentration. Thereafter, the pH is adjusted as necessary to obtain the chemical conversion treatment bath of the present invention. The phosphoric acid component that is particularly easily consumed in the treatment bath can be kept at a constant concentration by automatic replenishment. Further, divalent tin ions are eluted from the tin plating layer of the can into the treatment bath during the film forming reaction, and thus do not need to be replenished.

In order to apply the chemical conversion bath of the present invention to a metal surface such as tin-plated iron, the metal surface is first degreased and washed with water, and then the treatment bath is applied by any method such as a dipping method or a spray method. The treatment temperature is generally room temperature to 80 ° C, preferably 40 to
60 ° C, treatment time is usually about 5 seconds to 2 minutes, preferably 20 to 60
Seconds. Then, the treatment is completed by washing with water, washing with pure water and drying.

(Operation)

When the tin-plated can surface is treated with the chemical conversion bath of the present invention,
The tin plating layer is mainly etched by oxalic acid, and the tin is eluted into the treatment bath, and the insoluble tin phosphate is formed by the eluted tin and phosphoric acid, and this tin phosphate forms a chemical conversion film on the exposed iron surface of the tin plating can. Coating as. As a result, the exposed surface of iron is eliminated, and the corrosion resistance and coating film adhesion are improved. Oxalic acid also has a function of retaining tin in the treatment bath as divalent tin ions.

The divalent tin ions serve to suppress overetching of the tin plating can by oxalic acid and phosphoric acid, and to maintain an appropriate balance between the etching reaction and the film formation reaction.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

In the following examples and comparative examples, (1) appearance (2) uncoated corrosion resistance, (3) coating corrosion resistance, and (4) coating film adhesion were evaluated as follows.

(1) Appearance The appearance of the can after treatment and drying in a chemical conversion bath was visually observed and evaluated according to the following three grades.

○: Glossy △: No gloss remaining ×: Glossy, yellowing occurred (2) Unpainted corrosion resistance Treated with a chemical conversion bath, cut the side of the can after drying into a size of 3 cm x 4 cm, and the inner surface of the can was 1 cm It was sealed with tape so that it was exposed in the range of 1 cm. This test piece was immersed in a 2.8 g / phosphoric acid aqueous solution (pH adjusted to 2.4 with NaOH) at 40 ° C. for 48 hours, and then the corrosion state was observed and evaluated according to the following five grades.

5: Corrosion area is 0% 4: Corrosion area is less than 5% 3: Corrosion area is 5% or more and less than 20% 2: Corrosion area is 20% or more and less than 50% 1: Corrosion area is 50% or more (3) Paint Corrosion Resistance A commercially available epoxy paint was applied to the inner surface of the can after being treated with a chemical conversion treatment bath and dried so as to have a film thickness of 4 to 5 μm, and baked at 210 ° C. Next, cut the side of the paint can into a size of 5cm x 5cm, seal the back edge with tape, and scratch the paint surface with a sharp blade laterally to the can to a length of 3cm until it reaches the base. It was The test piece was immersed in a 1.3 g / citric acid aqueous solution (adjusted to pH 3.6 with NaOH) at 40 ° C. for 30 days, and then the corrosion state was observed and evaluated according to the following five grades.

5: Corrosion width less than 5mm 4: Corrosion width 5mm or more, less than 10mm 3: Corrosion width 10mm or more, less than 15mm 2: Corrosion width 15mm or more, less than 20mm 1: Corrosion width 20mm or more (4) Coating adhesion Properties (3) The same side of the coating can as that used for the evaluation of coating corrosion resistance was cut into a size of 5 cm × 10 cm, and this test piece was immersed in a 50 g / acetic acid aqueous solution in a boiling state for 30 minutes. After that, until reaching the substrate with a sharp blade on the painted surface,
I made scratches to make 100 grids of 1mm x 1mm.
Next, an adhesive tape was strongly pressed thereon, and the state of peeling of the coating when the tape was suddenly peeled was observed, and evaluated by the following five grades.

5: Peeling area is 0% 4: Peeling area is less than 5% 3: Peeling area is 5% or more and less than 20% 2: Peeling area is 20% or more and less than 50% 1: Peeling area is 50% or more ~ 8, Comparative Examples 1-7 Tin plating with tin weight of # 25 / # 50 (2.8g / m ² /5.6gm ² ).
DI can was degreased with 10 g / solution of alkaline degreasing agent (Nippon Paint Co., Ltd., Ridolin SN311), washed with water,
Spraying was performed at 50 ° C for 30 seconds in a chemical conversion bath having the composition and pH shown in the table. In Table 1, PO ₄ was H ₃ PO ₄ , oxalic acid was H ₂ C ₂ O ₄ , Sn ²⁺ was SnCl ₂ .2H ₂ O, and the pH was adjusted with NaOH. Next, after washing with tap water and washing with pure water, it was dried at 200 ° C. for 3 minutes.

The appearance and unpainted corrosion resistance of each dried can were evaluated. The results are shown in Table 2.

Thereafter, the commercially available epoxy-based paint was applied to the chemical conversion-treated DI can so as to have a thickness of 4 to 5 μm, and baked at 210 ° C.

The obtained coating can was evaluated for coating corrosion resistance and coating film adhesion. Table 2 shows the results.

When treated with the chemical conversion bath of the present invention (Examples 1 to 8)
No more occurrence of salt or precipitate in the treatment bath, and the life of the treatment bath was not shortened. Further, even if the salt is formed, it can be easily washed off with water, so that it does not adhere to the can. Therefore, there is no problem in transporting and printing the can due to the adhesion of the salt. Furthermore, as is clear from the above results, good results were obtained in terms of appearance, corrosion resistance, and coating adhesion.

[Effect of the Invention] By using the chemical conversion treatment agent and the chemical conversion treatment bath of the present invention, a chemical conversion film having excellent corrosion resistance can be formed on the metal surface. Further, when coating is applied on this film, very strong adhesion of the film can be obtained.

Further, in the chemical conversion treatment bath of the present invention, since it is unlikely that salt or precipitate is generated during the treatment, the adhesion of salt causes
It does not hinder the transportation and printing of cans or shorten the life of the processing bath.

The chemical conversion treatment agent and the chemical conversion treatment bath having such characteristics are suitable for the treatment of the tin-plated iron surface, particularly for the chemical conversion treatment of tin-plated drawn ironed iron cans (DI cans).

Claims (2)

(57) [Claims] 1. A 0.00 orthophosphoric acid and / or a salt thereof 1 to 30 parts by weight PO ₄ terms, oxalic acid and / or its salt with oxalic acid in terms
A chemical conversion treating agent comprising 5 to 0.5 parts by weight and 0.005 to 0.5 parts by weight of divalent tin ion. 2. An orthophosphoric acid and / or a salt thereof is 1 to 30 g / PO ₄ equivalent, and an oxalic acid and / or a salt thereof is 0.005 equivalent as oxalic acid.
A chemical conversion treatment bath containing 0.5 to 0.5 g / and 0.005 to 0.5 g / of divalent tin ions, and having a pH of 3 to 5.