JP5874105B2 - Trivalent chromium chemical conversion solution particularly suitable for zinc-nickel alloy plating and tin-zinc alloy plating - Google Patents

Description

  The present invention relates to a chemical and a method for forming a trivalent chromium chemical conversion coating on a zinc member, a zinc alloy member, a galvanized product or a zinc alloy plated product. The present invention relates to a drug and a method thereof which are particularly effective for forming a chemical conversion film on zinc alloy plating.

  Generally, zinc or zinc-based alloy plating (for example, zinc-iron alloy plating, zinc-nickel alloy plating, tin-zinc alloy plating) is widely used as a rust prevention method for iron-based materials and parts. However, zinc is a metal that is easily rusted, and white rust, which is rust of zinc, is generated immediately when used as it is, so that it is common to form a protective film.

  In the field of chemical conversion coatings, hexavalent chromate was once widely used, but for the reasons such as environmental problems, trivalent chromium chemical conversion coatings are currently mainstream. Examples thereof include JP 2003-166074, JP 2003-313675, JP 2004-10937, and the like. However, none of them exhibits sufficient performance when applied to zinc-nickel alloy plating. On the other hand, Japanese Patent Application Laid-Open No. 2005-240068 can be cited as an example of a trivalent chromium conversion coating corresponding to zinc-nickel alloy plating. However, even if the expansion of the white rust range is slow, white rust generation is early and the performance is still satisfactory. However, when the nickel eutectoid rate is relatively high, such as 10 to 25%, there is a defect that stable and satisfactory performance cannot be obtained in terms of appearance and corrosion resistance. In addition, regarding the trivalent chromium conversion coating treatment for tin-zinc alloy plating, at present, the standard of corrosion resistance, etc. required by each manufacturer by directly applying the trivalent chromium conversion coating treatment used for zinc or other zinc-based alloy plating. Since most of the cases can be cleared, there is a history that has hardly been studied. However, in the future, higher corrosion resistance than that which has already been achieved at the present time is required, and it is considered that a chemical conversion film treatment suitable for tin-zinc alloy plating is required.

JP 2003-166074 A JP 2003-313675 A JP 2004-10937 A Japanese Patent Laid-Open No. 2005-240068

  The present invention relates to a chemical conversion treatment solution, a chemical conversion treatment method, and a chemical-treated product for forming a trivalent chromium chemical conversion coating suitable for zinc and zinc-based alloy plating, particularly zinc-nickel alloy plating and tin-zinc alloy plating.

  The present inventors paid attention to carboxylic acid that may be contained in the trivalent chromium chemical conversion coating solution. It has been known for some time that the effect of adding carboxylic acid to a chemical conversion coating solution has improved appearance, corrosion resistance, and the like. However, there have been very few examples of intentional use of multiple carboxylic acids, and there are examples that consider the use of multiple types of carboxylic acids. The carboxylic acid was simply picked up.

  In the present invention, paying attention to the acidity of each carboxylic acid, by intentionally using a plurality of carboxylic acids having a certain difference or more in acidity, it is possible to stably increase the resistance to alloy plating, particularly zinc-nickel alloy plating. We succeeded in obtaining a high performance chemical conversion film. In the case of zinc-based alloy plating, especially zinc-nickel alloy plating, it is difficult to uniformly apply the usual trivalent chromium conversion coating due to the difference in reactivity between zinc and nickel, and satisfactory appearance and corrosion resistance There was no way to get it. In addition, the higher the nickel eutectoid rate (that is, the lower the zinc eutectoid rate), the more difficult it is to obtain a uniform appearance, and particularly good appearance and corrosion resistance for plating films with a high nickel eutectoid rate exceeding 10%. There is no method that can stably obtain the above. Although the principle is unknown, it is possible to minimize the influence of differences in the reactivity of each metal in alloy plating containing multiple types of metals by using two or more types of carboxylic acids with different acidities at the same time. Conceivable.

  Furthermore, one or more metals selected from the group consisting of alkali metals, alkaline earth metals, titanium, zirconium, vanadium, molybdenum, tungsten, manganese, iron, cobalt, nickel, gold, silver, copper, tin, and aluminum It is also possible to contain a silicon compound, and there is no particular limitation. In addition, pretreatment with a treatment liquid containing a surfactant, inorganic acid ions, hydroxides, metal ions, etc. for the purpose of cleaning, activation, etc., and overcoat in consideration of corrosion resistance, appearance, etc. Is also possible.

The present invention contains (A) trivalent chromium, (B) two or more carboxylic acids or derivatives thereof, and (C) one or more selected from chloride ions, chlorine oxyacid ions, sulfate ions, and nitrate ions. , (B) and in the number of carboxyl groups of a carboxylic acid total of the three or more contained group of carboxyl group, except those in the most pKa smaller carboxyl group and the carboxyl group within the same molecule, then The present invention relates to a chemical conversion coating solution for a zinc-based alloy plating in which the difference in pKa of carboxyl groups having a large pKa is 1.2 or more.
In addition, in a carboxylic acid having two or more carboxyl groups, there are a plurality of dissociation stages. In this case, the dissociation stage 1 having the lowest pKa is the pKa of the first carboxyl group, and then the pKa is low. Dissociation stage 2 is regarded as the pKa of the second carboxyl group, and so on.

  Although there is no restriction | limiting in particular in the density | concentration of each component, 0.01-4 g / L is preferable for trivalent chromium, and 5-100 g / L for the anion which belongs to the (C) group is suitable. Although there is no restriction | limiting in the suitable density | concentration of the carboxylic acid contained 2 or more types, 0.1-15 g / L of the sum total of carboxylate ion density | concentration is suitable, More preferably, it is 0.5-10 g / L. In zinc-nickel alloy plating, the preferred concentration varies depending on the nickel eutectoid rate and the type of carboxylic acid used. However, setting the concentration of the carboxyl group having the lowest pKa, in other words, the most acidic, in many cases, often gives good results (a carboxylic acid having the smallest pKa or a derivative thereof): (Other The weight ratio of the carboxylic acid or its derivative) is preferably 1.5: 1 to 100: 1, more preferably 2: 1 to 50: 1.

  Although there is no restriction | limiting in particular about the pH of a process liquid, pH 0.5-6.0 is suitable, Furthermore, in order to fully exhibit the effect of this invention, since high pH is more suitable in many cases, pH 2 0.5 to 6.0 is preferable, and pH 3.5 to 5.0 is more preferable. The temperature is preferably 10 to 50 ° C. The treatment time varies depending on the purpose, but is preferably 10 to 120 seconds, more preferably 20 to 90 seconds. The metal to be treated is not limited as long as it is zinc or zinc-based alloy plating, but the present invention is excellent in alloy plating, particularly when the weight of a specific metal is 95% or less of the total weight of metals in plating. Exerts a particularly excellent effect at 90% or less.

  Carboxylic acids included in group (B) that can be used in the present invention include, but are not limited to, the following. Oxalic acid (pKa 1.04, 3.82), citric acid (pKa 2.9, 4.35, 5.69), succinic acid (pKa 3.99, 5.2), tartaric acid (pKa 2.87, 3.97) , Malonic acid (pKa 2.6, 5.29), lactic acid (pKa 3.64), acetic acid (pKa 4.57), maleic acid (pKa 1.84, 5.83), malic acid (pKa 3.23, 4.77) Etc., but are not limited to these. However, since these alone do not produce sufficient effects, a combination satisfying the above conditions must be selected from them. In addition, the numerical value of pKa displayed here referred to the description of the revised 5th edition chemical manual basics (Maruzen Co., Ltd.).

  Hereinafter, the present invention will be described with reference to examples mainly composed of zinc-nickel alloy plating and tin-zinc alloy plating in which the effects of the present invention are most prominent. In the test, the test piece is subjected to appropriate pretreatment such as degreasing and acid dipping, galvanizing (Hyper Zinc; Nippon Surface Chemical Co., Ltd.), zinc iron alloy plating (Strong Zinc; Nippon Surface Chemical Co., Ltd.), zinc nickel Alloy plating (Stron Ni zinc, High Ni zinc depending on the required Ni eutectoid rate; both use Nihon Surface Chemical Co., Ltd.) and tin zinc alloy plating (TZ-400; Nihon Surface Chemical Co., Ltd.) After applying appropriate pretreatment, trivalent chromium conversion treatment was performed. The pH was adjusted with a suitable acid selected from sulfuric acid, nitric acid and hydrochloric acid and sodium hydroxide. The plating film thickness was 8 to 10 μm for any plating, and the corrosion resistance evaluation was a salt spray test according to JIS Z2731.

  Example 1 A galvanized product was made of chromium sulfate 3 g / L, chromium nitrate 3 g / L, sodium nitrate 15 g / L, cobalt nitrate 3 g / L, vanadate ammonium 2 g / L, nickel chloride 1 g / L, citric acid 1 g / L, The treatment was performed by dipping in a treatment solution containing 8 g / L of oxalic acid. This was performed under the conditions of a temperature of 30 ° C., an immersion time of 40 seconds, and a pH of 2.0. After washing with water and drying, a film having a good appearance was obtained. In the corrosion resistance test, there was no white rust for 240 hours.

  Example 2 A zinc-iron alloy plated product (iron eutectoid rate of 0.5%) was chromium sulfate 2 g / L, chromium nitrate 2 g / L, sodium nitrate 10 g / L, cobalt chloride 2.5 g / L, nickel sulfate 0.5 g. / L, succinic acid 1 g / L, oxalic acid 8 g / L was immersed in a treatment solution for treatment. It was performed under the conditions of a temperature of 35 ° C., an immersion time of 40 seconds, and a pH of 2.2. After washing with water and drying, a film having a good appearance was obtained. In the corrosion resistance test, there was no white rust for 360 hours.

  Example 3 The chemical conversion treatment was performed while greatly varying the nickel eutectoid rate and the bath composition of the zinc-nickel alloy plated product. Hereinafter, for a plated product with a nickel eutectoid rate of 15%, chromium chloride 2.5 g / L, potassium nitrate 8 g / L, cobalt nitrate 5 g / L, nickel sulfate 1 g / L, oxalic acid 8 g / L, tartaric acid 1 g / L It was immersed in the processing liquid containing and processed. It was performed under the conditions of a temperature of 30 ° C., an immersion time of 40 seconds, and a pH of 4.0. After washing with water and drying, a film having a good appearance was obtained. In the corrosion resistance test, there was no white rust for 720 hours.

In the following, the chemical conversion treatment was performed with the specific conditions varied greatly with Example 3 as a reference.
Example 4: Chromium chloride concentration 0.3 g / L, Example 5: Chromium chloride concentration 20 g / L, Example 6: Potassium nitrate is changed to sodium nitrate, Example 7: Potassium nitrate 0.5 g / L, Example 8: Potassium nitrate 40 g / L, Example 9: No cobalt nitrate, Example 10: Cobalt nitrate 30 g / L, Example 11: No nickel sulfate, Example 12: Nickel sulfate 10 g / L, Example 13: Oxalic acid 0.5 g / L, Example 14: Oxalic acid 14 g / L, Example 15: Tartaric acid 0.05 g / L, Example 16: Tartaric acid 8 g / L, Example 17: Tartaric acid was changed to citric acid, Example 18: Tartaric acid Example 19: Tartaric acid changed to lactic acid, Example 20: Tartaric acid changed to succinic acid, Example 21: Tartaric acid changed to acetic acid, Example 22: Oxalic acid changed to maleic acid, Tartaric acid changed to malonic acid Change to oxalic acid, Example 23: Change oxalic acid to malonic acid, tartaric acid to succinic acid, Example 24: change oxalic acid to malic acid, tartaric acid to butyric acid, Example 25: change temperature to 15 ° C, Example 26: Temperature changed to 50 ° C, Example 27: Changed to pH 2.5, Example 28: Changed to pH 3.5, Example 29: Changed to pH 5.0, Example 30: Changed to pH 6.0, Example 31: The test was performed by changing the processing time to 20 seconds, and Example 32: changing the processing time to 90 seconds. The appearance was all good, and the corrosion resistance of Examples 4, 9, 25, 30, and 31 was no white rust for 600 hours, and the others were all white rust for 720 hours.

  As a comparative example, Example 3 was carried out under the same conditions except that tartaric acid was removed from Example 3, and this was designated as Comparative Example 1. As a result, white rust occurred in 120 hours. The appearance was also more noticeable than in any of Examples 3 to 32. As mentioned above, when not using carboxylic acid together, the appearance and corrosion resistance are reduced.

  The same tests as in Examples 3 to 32 were also performed on zinc-nickel alloy plated products having nickel eutectoid rates of 5, 7, 10, 20, and 25% (that is, zinc eutectoid rate of 75 to 95%). Appearance is all good, corrosion resistance is 5% for nickel eutectoid, 25%, no white rust for 600 hours, 7, 10, 20% corresponds to Examples 4, 9, 25, 30, 31 Under conditions, no white rust was generated for 600 hours, and under other conditions, white rust was not generated for 720 hours. On the other hand, when Comparative Example 1 was performed on zinc nickel alloy plating with these nickel eutectoid rates, white rust was generated in 120 hours when the nickel eutectoid rate was 5, 7, 10%, and 20, 25%. In some cases, white rust occurred in 96 hours. The appearance was also uneven in any of the comparative examples.

Chemical conversion treatment was also performed on tin-zinc alloy plated products. For a plated product with a tin eutectoid rate of 75%, a treatment containing 2.5 g / L of chromium chloride, 8 g / L of potassium nitrate, 5 g / L of cobalt nitrate, 1 g / L of nickel sulfate, 8 g / L of oxalic acid, and 1 g / L of tartaric acid It was immersed in the liquid and processed. It was performed under the conditions of a temperature of 30 ° C., an immersion time of 40 seconds, and a pH of 4.0. After washing with water and drying, a film having a good appearance was obtained. In the corrosion resistance test, there was no white rust for 240 hours and no red rust for 800 hours.
On the other hand, when tartaric acid was removed, white rust was generated in 72 hours and red rust was generated in 240 hours.

Claims (10)

  (A) Two or more types of trivalent chromium, (B) carboxylic acid or derivatives thereof, (C) one or more types selected from chloride ions, oxyacid ions of chlorine, sulfate ions, nitrate ions, ) When the total number of carboxyl groups of the carboxylic acid included in the group is 3 or more, the difference in pKa from the carboxyl group having the smallest pKa is 1.2 or more, which is different from the carboxyl group having the smallest pKa. A chemical conversion film treatment solution for zinc-based alloy plating having a carboxyl group having the smallest pKa in the molecule and having a pH in the range of 4-6.   (A) Two or more types of trivalent chromium, (B) carboxylic acid or derivatives thereof, (C) one or more types selected from chloride ions, oxyacid ions of chlorine, sulfate ions, nitrate ions, ) When the total number of carboxyl groups of the carboxylic acid included in the group is 3 or more, the difference in pKa from the carboxyl group having the smallest pKa is 1.2 or more, which is different from the carboxyl group having the smallest pKa. Chemical film treatment for zinc-based alloy plating that is in a molecule, has a carboxyl group with the smallest pKa in the molecule, has a pH in the range of 2.2 to 6, and does not contain quinoline-based compounds and derivatives thereof liquid.   The chemical conversion film treatment solution according to claim 2, wherein the pH is in the range of 4-6.   The carboxyl group having the smallest pKa in the molecule having the smallest pKa according to any one of claims 1 to 3 and the carboxyl group according to any one of claims 1 to 3 The chemical conversion film treatment solution according to any one of claims 1 to 3, wherein the difference in pKa is 0.4 or more.   5. The chemical conversion film treatment solution according to claim 1, wherein the weight ratio of the carboxylic acid having the smallest pKa or derivative thereof: other carboxylic acid or derivative thereof is 1.5: 1 to 100: 1.   Furthermore, it contains one or more metals selected from the group consisting of alkali metals, alkaline earth metals, titanium, zirconium, vanadium, molybdenum, tungsten, manganese, iron, cobalt, nickel, gold, silver, copper, tin and aluminum The chemical film treatment liquid according to any one of claims 1 to 5.   The metal to be treated is zinc-based alloy plating, and the abundance ratio of the metal having the largest abundance in the plating layer with respect to the entire metal in the plating layer is 95% or less. The chemical film treatment liquid described in 1.   The conversion coating solution according to claim 7, wherein the metal to be treated is zinc-nickel alloy plating.   A chemical conversion film forming method using the chemical conversion film treatment liquid according to claim 1. A method for producing a zinc-based alloy plating product,
The method in which a chemical conversion film is formed on a zinc-based alloy plated article using the method according to claim 9.