JPH0349989B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for anticorrosive surface treatment of iron or iron alloys. Specifically, the present invention relates to a method for anticorrosion treatment of metal surfaces, which comprises forming a zinc or zinc alloy coating on the surface of iron or iron alloy, and then treating the surface with a non-aqueous chromate treatment agent. BACKGROUND OF THE INVENTION It is well known to hot-dip or electroplate zinc for corrosion protection on steel surfaces. Relatively recently, one of the applicants of the present application has developed a collection of independent particles made of iron or iron alloy as a core and zinc or zinc alloy deposited around this core through an iron-zinc alloy layer. A zinc coating method for iron or iron alloy surfaces was developed, which consists of projecting a blasting material consisting of iron-zinc particles (hereinafter referred to as iron-zinc blasting material) onto the surface of iron or iron alloys (Japanese Patent Laid-Open No. 1983-1999).
45372). This method is referred to herein as the blast zinc coating method. This method is an innovative method with low equipment costs, low energy consumption, and minimal environmental pollution. However, the zinc coating formed by this method does not have sufficient corrosion resistance, and At a coating weight of ² , red rust occurs within 24 hours in a salt spray test. This is thought to be due to the fact that the zinc coating formed by this method is an iron-zinc alloy and is porous. Therefore, a sufficient anticorrosion effect cannot be obtained by the blast zinc coating method alone, and some other treatment must be performed in combination with this method. A relatively simple method is chromate treatment, of which baking type chromate treatment, aqueous chromate treatment, and non-aqueous chromate treatment are known. Baking-type chromate treatment is a mixture of a water-soluble chromic acid compound, a reducing agent, and water, which is applied to the surface of the object to be treated and then heated by baking, which reduces the water-soluble chromic acid compound and converts it into water-insoluble chromate. It produces a film. As this processing agent,
Some well-known examples include Pennwalt's ``Hinatsuk'' and Diamond Shamlokk's ``Dacromet 100''. The formation of a film in baking-type chromate treatment involves the reduction of chromic acid heated in the presence of a reducing agent, so even if the substrate is an iron-zinc alloy formed by the plasto zinc coating method, , the reduction is achieved without any problems. However, since these are water-based treatment agents, they require a step to remove residual droplets after being applied to the untreated object, and a baking step that also serves as drying. The disadvantages are that heat energy consumption is large and processing costs are high. Water-based chromate treatment is a process of treating the surface of galvanized steel with a mixture of a water-soluble chromic acid compound, strong acid, and water. It is disclosed in books such as Nikkan Kogyo Shimbun (published by Nikkan Kogyo Shimbun). Water-based chromate treatment is effective for pure zinc, but iron
For zinc-based materials, the film produced varies widely and is not as effective as it is for pure zinc. Water-based chromate treatment is a mixture of water, a water-soluble chromate compound, and a strong acid such as sulfuric acid. Zinc on the surface of the coating reacts with the strong acid to produce nascent hydrogen, which reduces the chromic acid and removes the chromate coating from the surface. Since the reaction occurs at the interface of the galvanized surface, it is difficult to form a thick film. In addition, water-based chromate treatment generates wastewater containing a large amount of chromic acid, and requires a large amount of equipment and management costs to counteract this. It is not suitable for combination with the dry blast zinc coating method. Non-aqueous chromate treatment consists of a chromate compound, an organic solvent (mainly halogenated hydrocarbon solvent), and alcohol as a solubilizer, and optionally contains stabilizers and reaction accelerators to form a chromate coating. It forms the
-5288 (DuPont), Special Publication Showa 42-3363 (DuPont),
JP-A-56-62970 (Tokuyama Soda), JP-A-55-97476
(Nippon Paint), Japanese Patent Application Laid-Open No. 556-139679 (Nippon Paint), etc. Relatively recently, one of the present applicants has developed an extremely stable non-aqueous chromate treatment agent using fluorinated chlorinated hydrocarbon as a solvent (Japanese Patent Application No. 1983). While any non-aqueous chromating agent can be used in the present invention, it is advantageous to use fluorinated chlorinated hydrocarbon solvents. The present inventors have investigated various treatment methods that exhibit excellent corrosion prevention effects in combination with blast zinc coating, and have discovered that the combination with non-aqueous chromate treatment exhibits the most excellent corrosion prevention effects. completed. Structure of the Invention That is, according to the present invention, particles are made of an aggregate of independent adhered particles having iron or an iron alloy as a core and zinc or a zinc alloy around the core through an iron-zinc alloy layer. A zinc coating film is formed on the surface of iron or iron alloy by projecting a blasting material of A method for surface treatment of iron alloys is provided. The method of the present invention can compensate for the corrosion resistance effect, which is the weak point of the blast zinc coating method, without sacrificing its advantages. DETAILED DESCRIPTION OF THE INVENTION The blast zinc coating method is described in detail in the above-mentioned published patent application and will not be described in detail here. The organic solvent used in the non-aqueous chromate treatment of the present invention is a halogenated hydrocarbon containing chlorine and/or fluorine having 1 to 2 carbon atoms, such as methylene chloride, chloroform, carbon tetrachloride, trichloroethane, trichloroethylene, perchloride, etc. Ethylene, trichlorotrifluoroethane, trichloromonofluoromethane, dichlorotetrafluoroethane, tetrachlorodifluoroethane, mixtures thereof, and the like can be suitably used. Considerations in selecting a solvent include that it forms a homogeneous solution with the other ingredients, and that it is liquid at a temperature at which the chromate reaction proceeds at a significant rate. The chromic acid used in the method of the present invention is called chromic anhydride or chromium trioxide, and has the chemical formula
It is equivalent to _CrO3 . The chromic anhydride is used in an amount of 0.01 to 10 parts, preferably 0.1 to 10 parts, per 100 parts by weight of the halogenated hydrocarbon solvent (hereinafter simply referred to as parts).
Used at a concentration of 5 parts. The amount of chromic anhydride
If it is less than 0.01 part, the rate of the chromate reaction will be slow, and if it is more than 10 parts, the decomposition of the halogenated hydrocarbon solvent and solubilizer in the bath will be significant, preventing normal film formation and reducing corrosion resistance. This gives rise to a tendency to The solubilizing agent used in the process of the invention is a secondary or tertiary alcohol soluble in the halogenated hydrocarbon solvent and having 3 to 20 carbon atoms. Generally, secondary propanol, tertiary butanol, tertiary amyl alcohol, triphenyl carbinol, etc. are preferably used, but they uniformly dissolve the components of the treatment liquid of the present invention and are stable even during long-term use. Tertiary butanol (hereinafter referred to as t-butanol) is most preferred because it has a regular price. Solubilizer is 100 parts of halogenated hydrocarbon solvent,
At least 1 part or more is required, and the amount may be 20 parts or more. The larger the amount of solubilizer is, the more chromic anhydride is dissolved. If the amount of solubilizer is less than 1 part, the solubilizing power will be insufficient and it will be difficult to dissolve the ingredients uniformly.It is possible to use 20 parts or more, but it may be flammable depending on the usage conditions. It is preferable to set the upper limit to this point. The stabilizers used in the method of the present invention include amines,
Many known compounds such as quinones, nitro, azo or azoxy aromatic compounds, thioureas, dienes, organic nitrites, zinc fluoride, zinc oxide, etc. are stable in the case of chlorinated fluorinated hydrocarbon solvents. There is no need to use a curing agent, which is advantageous in this respect. Examples of these compounds include N-nitrodiphenylamine, azoxybenzene, hydroquinone, diisobutylamine, pentadiene, amyl nitrite, and many others. These can be used alone or in combination
It can be used in combination of more than one species, and the amount thereof is 0.001 to 5 parts per 100 parts of halogenated hydrocarbon solvent.
part is preferred. Use of amounts outside this range will have little or no expected effect or will be wasteful beyond the limits of effectiveness. The reaction accelerator used in the method of the present invention is hydrogen fluoride, organic acid, water, etc., and these compounds may be used alone or in a mixture of two or more, and depending on the situation, they may not be used at all. good. The organic acid may be any organic acid having 1 to 20 carbon atoms as long as it is soluble in the mixture of the above components. General formula, R-
In (COOH) _o , R may have a linear, branched, or cyclic structure, and may also have a substituent. Also, n is 1~
3 is preferred. Examples of these organic acids include the following. formic acid, acetic acid,
Lactic acid, stearic acid, oxalic acid, fumaric acid, malic acid. These reaction accelerators are preferably used in an amount of 0.001 part or more per 100 parts of the halogenated hydrocarbon solvent, and in the case of hydrogen fluoride and organic acids, it is preferably used in an amount of 0.12 parts or less. In such cases, it is preferable to use within a range that can maintain a uniformly dissolved system. If it is less than these ranges, the effect cannot be expected, and if it exceeds it, defects such as significant corrosive effects on the object to be treated or the equipment or inability to maintain a homogeneous system will occur. The chromate treatment liquid used in the method of the present invention is substantially non-aqueous, the halogenated hydrocarbon solvent performs the task of degreasing and cleaning, renders the treatment liquid non-flammable, and the solubilizer uniformly dissolves all components. It is essential that all components of the treatment liquid are dissolved uniformly; if they are not uniform, the coating will be formed unevenly and the corrosion resistance will deteriorate. In the method of the present invention, the treatment liquid is maintained at any temperature from 5°C to the boiling point, and the untreated metal is brought into contact with it for 1 second to 60 minutes, preferably 30 seconds to 5 minutes, and then the metal surface is dried. . The processing liquid is
If the temperature is lower than 5°C, substantially no chromating reaction will proceed, if the contact time is shorter than 1 second, substantially no effective coating will be obtained, and if the contact time is longer than 60 minutes, the coating will not proceed. This may result in non-uniformity and is not practical from a productivity standpoint. It is preferable that the metal to be treated is previously degreased and cleaned, and in particular a not excessive amount of oil is degreased by the treatment liquid during the chromate treatment. After the chromate treatment, the object to be treated can be further heated or subjected to post-treatment such as irradiation with ultraviolet rays to improve corrosion resistance. As described above, since all steps in the method of the present invention are substantially non-aqueous treatments, wastewater treatment measures are not required and an excellent corrosion-resistant coating can be formed at low cost. Comparing the product () produced using the metal surface anticorrosion treatment method of the present invention with a hot dip galvanized product () and a product () coated with hot dip zinc plating and further subjected to non-aqueous chromate treatment, () has the best corrosion resistance. Excellent, followed by (), and () is the worst. But in terms of price, () is ()
It costs about three times as much. In normal applications, () has insufficient corrosion protection, but () has excessive quality. Specific Description of the Invention The present invention will be illustrated in more detail below using Examples and Comparative Examples, but the present invention is not limited thereto. The test piece was an M10 x 40 mm hexagonal mild steel bolt. After vapor degreasing with trichloroethane, the above-mentioned iron-zinc blasting material was projected for 30 minutes, and the surface was heated to 100 mm.
An iron-zinc alloy film is produced with a basis weight of mg/dm ² and subjected to a non-aqueous chromate treatment. Five treated specimens were subjected to the following corrosion resistance test. (1) Salt spray test Judgment and evaluation were performed according to the following criteria according to the test method of JIS-Z-2371. 5 points No red rust 4 points 3 points with pinhole-shaped red rust within 10 spots 2 points where the rust spreads and some rust fluid begins to flow 1 point where the rust fluid flows significantly Front surface is covered with red rust (2) Cast test JIS-D -0201-1971 test method. However, the pH of the spray liquid was set to 3.5. The criteria for determining rust are the same as above. (3) Outdoor water sprinkling test A sprinkler is placed on the asphalt pavement surface exposed to sunlight, and test pieces are arranged in a concentric circle around the sprinkler within a circumference of 1.4 m, and tap water is poured at 0.3 to 0.4 m.
It was applied continuously at a rate of m ³ /hr. (4) Cycle test Continuous salt spray test specified in JIS-Z-2371 for 4 hours, drying at 60℃ for 2 hours, 50
℃ and 90% or more humidity test for 2 hours, and this cycle was repeated. Example 1 100 parts of trichlorethylene, 0.5 parts of chromic anhydride
1 part, 0.01 part of zinc fluoride, and 10 parts of t-butanol were prepared, and the bolts blasted with the iron-subsalt alloy were heated to 1 part at reflux temperature.
After being immersed for a minute and subjected to steam cleaning, it was taken out and cooled to room temperature. The various tests described above were conducted on the samples thus prepared, and the results shown in Table 1 were obtained. Example 2 A treatment solution was prepared in the same manner as in Example 1 except that 100 parts of methylene chloride was used, and samples were prepared and tested in the same manner, and the results shown in Table 1 were obtained. Example 3 A treatment solution similar to that in Example 1 was prepared except that 100 parts of perchlorethylene was used, and samples were prepared and tested in the same manner to obtain the results shown in Table 1. Example 4 For 100 parts of trichlorotrifluoroethane,
A treatment solution containing 15 parts of t-butanol and 2 parts of chromic anhydride dissolved uniformly was prepared and treated in the same manner as in Example 1 to obtain the results shown in Table 1. Example 5 To 100 parts of trichlorofluoroethane, t-
15 parts of butanol, 2 parts of chromic anhydride, oxalic acid
A treatment solution containing 0.01 part of the solution was prepared and heated to the boiling point, and the same test as in Example 1 was conducted, and the results shown in Table 1 were obtained. Example 6 In Example 5, 0.01 part of fumaric acid was used instead of oxalic acid, and the reaction was carried out at 40°C (below the boiling point) to obtain the results shown in Table 1.

【table】

[Table] Note; * Samples with iron-zinc blasting only and no chromate treatment
** Sample of iron-zinc blast bolt subjected to aqueous chromate treatment

Claims (1)

[Claims] 1 A blasting material consisting of an aggregate of independent deposited particles made of iron or iron alloy as a core and zinc or zinc alloy deposited around this core through an iron-zinc alloy layer is applied to the surface of iron or iron alloy. A method for surface treatment of iron or iron alloys, which comprises forming a zinc coating on the surface of iron or iron alloys by spraying on the surface of iron or iron alloys, and subjecting the thus formed surfaces to non-aqueous chromate treatment.