JPWO2000073535A1 - Phosphate-treated zinc-plated steel sheet with excellent corrosion resistance and paintability - Google Patents

Abstract

(57) [Abstract] Provided are phosphate-treated zinc-based plated steel sheets with excellent corrosion resistance and paintability. The phosphate-treated zinc-based plated steel sheets with excellent corrosion resistance and paintability are characterized by having a phosphate coating formed on the surface of a zinc or zinc-based alloy plated steel sheet in an amount of 0.5 g/ ^m2 or more, the phosphate coating containing 2 wt% or more of Mg, 0.5 wt% or more of Ni and/or Mn, and a total of 4 wt% or more of Mg, Ni and/or Mn. The phosphate-treated zinc-based plated steel sheets with excellent corrosion resistance and paintability are characterized by having a phosphate coating formed on the surface of a zinc or zinc-based alloy plated steel sheet in an amount of 0.3 g/ ^m2 or more, preferably 1 g/ ^m2 or more, the phosphate coating containing 2 wt% or more of Mg, 0.5 wt% or more of Ni and/or Mn, and a total of 5 wt% or more of Mg, Ni and/or Mn.

Description

Description: TECHNICAL FIELD The present invention relates to a phosphate-treated zinc-plated steel sheet having excellent corrosion resistance and paintability, which is used in applications such as automobiles, home appliances, and building materials.

BACKGROUND ART Zinc-plated steel sheets used in applications such as automobiles, home appliances, and building materials have often been subjected to phosphate treatment, chromate treatment, and even organic coating treatment to improve added value such as corrosion resistance and paintability. In recent years, due to environmental concerns, chromate-treated steel sheets in particular have tended to be disliked because they may contain hexavalent chromium, and there has been an increasing demand for phosphate treatment.

However, conventional phosphate treatment of zinc-plated steel sheets does not necessarily provide sufficient corrosion resistance and paintability, and various methods for improving this have been proposed. For example, Japanese Patent Publication No. 60-34912 discloses a method in which a phosphate film is formed and then treated with an inhibitor. Also, Japanese Patent Laid-Open Nos. 60-50175 and 8-13154 disclose methods in which Ni, Mn, etc. are made to coexist in the phosphate film.

Although the above methods have some effect, they are not sufficient in view of the recent stricter requirements for corrosion resistance, and in particular, they have almost no effect in improving the corrosion resistance of bare steel.

In addition, in Japanese Patent Laid-Open No. 1-312081 and Japanese Patent Laid-Open No. 3-107469,
Although zinc phosphate coatings containing Mg have been disclosed, the corrosion resistance improvement effect is insufficient and the paintability is also insufficient. Furthermore, Japanese Patent Laid-Open Publication No. 9-49086 discloses a method for forming zinc phosphate coatings containing Ni and Mg,
In this case too, there is a problem of insufficient corrosion resistance.

DISCLOSURE OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide a phosphate-treated zinc-plated steel sheet that is excellent in corrosion resistance and paintability.

The present inventors first performed a phosphate treatment on a zinc-based plated steel sheet by making a large amount of Mg ions and Ni ions coexist in the treatment bath, thereby achieving a Mg ion concentration not found in the prior art.
As a result of attempts to form a phosphate coating with a high Mg and Ni content, it was found that increasing the content of both Mg and Ni in the phosphate coating improved both corrosion resistance and paintability. Furthermore, it was found that by applying an aqueous phosphate solution containing Mg and/or Ni after forming a Mg- and Ni-containing phosphate coating and drying it without rinsing with water, a phosphate coating with an even higher Mg and Ni content could be obtained, and that by setting the Mg and Ni contents in the phosphate coating thus obtained within specific ranges, extremely good corrosion resistance and paintability not previously known could be obtained. It was also found that using Mn instead of Ni produced the same effect.

The present invention has been completed based on the above-mentioned new findings, and the gist of the present invention is to provide a zinc or zinc-based alloy plated steel sheet containing 2 wt % or more of Mg and Ni on the surface thereof.
and/or Mn is 0.5 wt% or more, and Mg and Ni and/or Mn
a phosphate-treated zinc-based plated steel sheet having excellent corrosion resistance and paintability, characterized in that a phosphate coating containing 4 wt% or more of the above in total is formed on the steel sheet at 0.5 g/ ^m2 or more;
and a zinc or zinc alloy plated steel sheet having 2 wt% or more of Mg and Ni on the surface thereof.
The present invention provides a phosphate-treated zinc-based plated steel sheet having excellent corrosion resistance and paintability, characterized in that a phosphate coating containing 0.5 wt % or more of Mg and/or Mn and 5 wt % or more in total of Mg, Ni and/or Mn is formed in an amount of 0.3 g/m ² or more, preferably 1 g/m ² or more.

BEST MODE FOR CARRYING OUT THE INVENTION There is no particular limitation on the zinc-based plated steel sheet used in the present invention, and either pure zinc plating or alloy plating can be used. Furthermore, the method of pure zinc plating or zinc alloy plating can be any method, including electrical plating, melting, vapor deposition, etc.

In the present invention, the phosphate coating formed on the zinc-based plating layer usually contains zinc dissolved from the plating layer and in the phosphate treatment bath, but also Mg
The content of these metals in the total weight of the phosphate coating is 2 wt % or more for Mg and 0 wt % or less for Ni and/or Mn.
It is necessary that the total content of Mg, Ni and/or Mn is 4 wt% or more, and that the total content of Mg, Ni and/or Mn is 4 wt% or more. If either of the lower limits is exceeded, corrosion resistance and paintability will be significantly deteriorated. It is more preferable that the total content of Mg, Ni and/or Mn is 5 wt% or more.

The upper limit is not particularly limited, but Mg and Ni may be about 10 wt % alone or in total, and Mg and Mn and/or Ni may be about 15 wt % in total.
%, and it has been technically difficult to increase the content beyond this.

The weight of the phosphate coating containing 4 wt% or more of Mg and Ni and/or Mn in total must be 0.5 g/ ^m2 or more; if it is less than this value, the corrosion resistance will be insufficient. Also, the weight of the phosphate coating containing 5 wt% or more of Mg and Ni and/or Mn in total must be 0.3 g/ ^m2 or more.
If the value is less than this, the corrosion resistance will be insufficient. It is more preferable that the value is 1 g/m2 or ^more . There is no particular upper limit, but in consideration of weldability, it is generally 2.5
It is preferable that the density is about g/m ² or less.

Since Ni and Mn have the same effect, the following description will be made on the case where only Ni is used without Mn as a representative example.

The Mg- and Ni-containing phosphate treatment coating of the present invention can be obtained by treatment with a phosphate treatment bath containing Mg ions and Ni ions. Prior to such treatment, it is preferable to carry out a known pretreatment such as titanium colloid treatment or brushing treatment. The phosphate treatment bath may be, for example, a treatment bath containing Zn ions, phosphate ions, fluorides, oxidizing agents (nitrates, nitrites, chlorates, etc.), etc., in which Mg is added.
An example of such a bath is one containing Zn ions and Ni ions. In this case, the concentration ratio (weight ratio) of each metal ion is 1:1, where Mg ions are 10 to 50, Ni ions are 1:1, and
The ion concentration is preferably about 1 to 10. Using such a treatment bath, examples of the treatment method include a spray method and an immersion method, and a zinc phosphate treatment film can be formed on a zinc-plated steel sheet by these methods. In this method, when Mg and Ni are present together, the total weight ratio of the two metals in the formed film is industrially limited to about 5%, and any inclusion of a higher ratio is not only difficult but also undesirable because it is likely to cause poor deposition of the film and the generation of a large amount of sludge.

When larger amounts of Mg and Ni are to be present together, Mg and Ni are first mixed by the method described above.
and Ni, or after treatment in a conventional phosphate bath not containing Mg or Ni, a composite phosphate coating is preferably formed by applying an aqueous phosphate solution containing Mg and/or Ni and then drying the resulting sheet temperature at 90 to 150°C without rinsing with water. The aqueous solution to be applied is preferably a primary phosphate (also called dihydrogen phosphate or biphosphate) of each metal. The preferred application method is a roll coater method. Such application may be performed on both sides or on one side. In cases where corrosion resistance of the inner surface is more important, such as in the case of automotive steel sheets, it is also preferable to apply only to the surface corresponding to the inner surface. When applying an aqueous phosphate solution, the total weight of the phosphate coating in the present invention is the total weight of the coating formed by the initial phosphate treatment coating and the subsequent application of the aqueous phosphate solution, and the respective contents of Mg and Ni are
The total content of each component in the initial phosphate treatment coating and the subsequently applied phosphate coating is divided by the total weight of both coatings to obtain a percentage. As long as the respective contents and the total coating weight are within the ranges of the present invention, similarly good corrosion resistance and paintability can be obtained.

As already mentioned, Mn may be used in place of Ni, and the same effect can be obtained by using Ni and Mn in combination.

Examples The following are examples of the present invention.

In all Examples, electrogalvanized steel sheets with a coating weight of 30 g/m ² (per side) were used as test materials.

[Sample Preparation] (Examples 1 to 8) Galvanized steel sheets were pretreated using a commercially available titanium colloid-based treatment agent (PL-Zn, manufactured by Nihon Parkerizing Co., Ltd.), and then phosphate treatment was carried out by spraying with the phosphate treatment bath shown in Table 1. The spray time was adjusted to 1.5 to 10 seconds, and the treatment bath temperature was adjusted to between 60°C and 70°C, so that the weight after drying was 0.2 to 1.7 g depending on each example.
After the treatment, the plate was rinsed with water and dried, and then an aqueous magnesium biphosphate solution (a 50% aqueous magnesium biphosphate solution manufactured by Yoneyama Chemical Co., Ltd. was diluted five-fold and used) was applied using a ^roll coater, adjusting the rotation speed to give a dried coating weight of 0.3 to 1.5 g/ ^m2 , and the plate was dried at a temperature of 110°C.

(Example 9) In the same manner as above, a phosphate coating having a dry weight of 0.7 g/ ^m2 was formed using the phosphate treatment bath in Table 1, with a spray time of 2 seconds and a treatment bath temperature of 60°C. After rinsing with water and drying, manganese biphosphate (manganese dihydrogen phosphate tetrahydrate manufactured by Yoneyama Chemical Co., Ltd.) was further mixed with an aqueous magnesium biphosphate solution (a 50% aqueous magnesium biphosphate solution manufactured by Yoneyama Chemical Co., Ltd.) at a solids weight ratio of 2:1, and the mixture was diluted with water to prepare an aqueous solution with a solids concentration of 10%, which was then applied using a roll coater so that the dry weight of the coating would be 1 g/ ^m2 . The final plate temperature was 100°C.
The temperature was kept at 10°C and the mixture was dried.

Example 10: In the phosphate treatment bath shown in Table 1, 4 g/l of Mn ions were used instead of Ni ions.
Similarly, the spray time was 2 seconds, the treatment bath temperature was 65°C, and the weight after drying was 1 g/m
After rinsing with water and drying, ^an aqueous solution of magnesium biphosphate (a 50% aqueous solution of magnesium biphosphate manufactured by Yoneyama Chemical Co., Ltd. was diluted five-fold and used) was applied using a roll coater so that the weight of the coating after drying would be 0.7 g/ ^m2 , and the plate was dried at a temperature of 110°C.

(Example 11) Phosphate treatment was carried out by spraying using the phosphating bath shown in Table 2. The spray time was 1.5 seconds, and the treatment bath temperature was 60°C. After drying, a phosphate coating weighing 1.0 g/ ^m2 was formed. After rinsing with water and drying, an aqueous magnesium biphosphate solution (
Manganese diphosphate (manganese dihydrogen phosphate tetrahydrate, manufactured by Yoneyama Chemical Industry Co., Ltd.) was mixed with magnesium diphosphate (50% aqueous solution, manufactured by Yoneyama Chemical Industry Co., Ltd.) at a solids weight ratio of 2:1, and the mixture was diluted with water to prepare an aqueous solution with a solids concentration of 10%, which was then applied using a roll coater and dried so that the plate temperature reached 110°C, yielding a coating with a dry weight of 1 g/ ^m2 .

(Examples 12 and 13) The phosphate treatment baths shown in Table 3 were sprayed onto steel sheets to perform phosphate treatment. The spray times were 4 seconds and 2 seconds, and the treatment bath temperature was 70°C. The weight after drying was 1.4 g/
A phosphate coating of 0.6 g/m ² (Example 12) and 0.6 g/m ² (Example 13) was formed. After the treatment, the plate was washed with water and dried.

(Example 14) After carrying out the same treatment as in Example 13, an aqueous magnesium biphosphate solution (
(Used 50% aqueous solution of magnesium biphosphate (manufactured by Yoneyama Chemical Industry Co., Ltd.) diluted 5 times)
was applied using a roll coater so that the weight of the coating after drying would be 1 g/m ² , and dried so that the ultimate plate temperature would be 110°C.

(Example 15) A spray phosphate treatment was performed using the phosphate treatment bath shown in Table 3. The spray time was 2 seconds, and the treatment bath temperature was 65°C, and after drying, a phosphate coating weighing 0.4 g/ ^m2 was formed. After treatment, the steel was rinsed with water and dried.

(Example 16) A spray phosphate treatment was performed using the phosphate treatment bath shown in Table 3. The spray time was 1.5 seconds, and the treatment bath temperature was 60°C, forming a phosphate coating weighing 0.2 g/ ^m2 after drying. After rinsing with water and drying, an aqueous solution containing magnesium biphosphate and manganese biphosphate adjusted to a solids weight ratio of 1:1 was applied so that the coated coating would weigh 0.1 g/ ^m2 after drying, and the plate was dried to an ultimate temperature of 110°C.

(Comparative Example 1) A treatment bath having the same concentration and composition as in Table 3 was used, except that the Ni ion concentration was 0 g/l.
The phosphate treatment was carried out by spraying. The spray time was 6 seconds, and the treatment bath temperature was 65°C.
After drying, a phosphate coating having a weight of 1.5 g/m ² was formed. After treatment, the substrate was washed with water and dried.

(Comparative Example 2) Using the treatment bath shown in Table 1, a phosphate coating was formed with a dry weight of 0.1 g/ ^m² at a spray time of 0.5 seconds and a bath temperature of 55°C. After rinsing with water and drying, an aqueous magnesium biphosphate solution (a 50% aqueous magnesium biphosphate solution manufactured by Yoneyama Chemical Co., Ltd. was diluted 10 times and used) was applied with a roll coater, and the dry weight of the coating was 0.1 g/m².
The coating was adjusted to give a coating amount of g/m ² , and the coating was dried so that the ultimate plate temperature reached 110°C.

Comparative Example 3 A phosphate coating was formed in the same manner as in Example 5, except that the aqueous magnesium biphosphate solution was not applied after the phosphate treatment.

(Comparative Example 4) Phosphate treatment was performed by spraying using the phosphating bath shown in Table 4. The spray time was 4 seconds, and the treatment bath temperature was 70°C, forming a phosphate coating weighing 1.5 g/ ^m2 after drying. After treatment, the steel was rinsed with water and dried.

(Comparative Example 5) Phosphate treatment was performed by spraying using the phosphating bath shown in Table 5. The spray time was 4 seconds, and the treatment bath temperature was 65°C, forming a phosphate coating weighing 1.5 g/ ^m2 after drying. After treatment, the steel was rinsed with water and dried.

[Performance evaluation method] Film weight: ammonium dichromate 20 g/l and 25% ammonia 490 g/l
The sample was immersed in 1 of the mixed aqueous solution (stripping solution) to strip off the entire phosphate film.
The amount of the coating was calculated from the difference in sample weight before and after peeling.

Film components (Mg, Ni, Mn): Nitric acid was added to the stripping solution containing the film, and after heating, the amounts of Mg, Ni, and Mn were determined by ICP and their weight percentages relative to the total film amount were calculated.

Paint adhesion (primary): Samples were degreased with alkali (SD2 manufactured by Nippon Paint Co., Ltd.).
After leaving the specimen for one day, scratches reaching the steel substrate were made into the substrate with 2 mm intervals (100 squares), and the specimen was then pushed out 7 mm using an Erichsen tester, after which it was peeled off with cellophane tape.
(Evaluation XX: 100 squares peeled off, ×: 99 to 6 squares peeled off, △: 1 to 5 squares peeled off, ○: No squares peeled off but peeling around the cut flaw, ⊚: No peeling at all)
.

Paint adhesion (secondary): After electro-deposition coating as above, soak in 50°C hot water for 1 minute.
The sample was immersed for 0 days, and then evaluated in the same manner as above.

Corrosion resistance after painting: The test piece was subjected to the same process as in the above paint adhesion evaluation up to the electrodeposition coating stage, and after leaving it for one day, a cross-cut scratch was made with an NT cutter reaching the steel substrate.
The salt spray test No. 1 was carried out for 20 days. After that, the test piece was peeled off with Selehan tape, and the maximum peeled width of the coating film from the crosscut area (one side) was evaluated. (×: more than 10 mm, △: 3
10mm or less, ○: less than 3mm) Bare corrosion resistance: After sealing the edges and backside of the sample with tape,
The number of days until 5% red rust appeared was measured in a salt spray test using No. 71. (XX: within 1 day, ×: within 2 days, Δ: 2 to 5 days, ○: 5 to 10 days, ⊚: 10 days or more) The evaluation results are shown in Table 6. The examples of the present invention exhibited good paintability and corrosion resistance, whereas the comparative examples outside the scope of the present invention exhibited deterioration in either performance.

The present invention makes it possible to obtain phosphate-treated zinc-plated steel sheets with unprecedentedly good corrosion resistance and paintability. The steel sheets of the present invention do not use harmful substances such as hexavalent chromium, are produced by a simple and cost-effective method, and are suitable for a variety of applications, including automobiles, home appliances, and automobile parts.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (3)

[Claims] [Claim 1] A phosphate-treated zinc-based plated steel sheet with excellent corrosion resistance and paintability, characterized in that a phosphate coating containing 2 wt% or more of Mg, 0.5 wt% or more of Ni and/or Mn, and a total of 4 wt% or more of Mg, Ni and/or Mn is formed on the surface of zinc or zinc-based alloy plated steel sheet in an amount of 0.5 g/ ^m2 or more. [Claim 2] A phosphate-treated zinc-based plated steel sheet with excellent corrosion resistance and paintability, characterized in that a phosphate coating containing 2 wt% or more of Mg, 0.5 wt% or more of Ni and/or Mn, and a total of 5 wt% or more of Mg and Ni and/or Mn is formed on the surface of zinc or zinc-based alloy plated steel sheet in an amount of 0.3 g/ ^m2 or more. [Claim 3] A phosphate-treated zinc-based plated steel sheet with excellent corrosion resistance and paintability, characterized in that a phosphate coating containing 2 wt% or more of Mg, 0.5 wt% or more of Ni and/or Mn, and a total of 5 wt% or more of Mg and Ni and/or Mn is formed on the surface of zinc or zinc-based alloy plated steel sheet in an amount of 1 g/ ^m2 or more.