JPH0243375A - Surface treating liquid for galvanized steel sheet - Google Patents

Abstract

PURPOSE:To improve the blackening resistance and corrosion resistance of a plated surface by treating the galvanized steel sheet with an aq. alkaline soln. contg. metal ions of Ni, Co, etc., and specific amine compd., then treating the steel sheet with an acetic acid-contg. chromate treating liquid. CONSTITUTION:The plated surface of the galvanized steel sheet or hot dip Zn-Al alloy coated steel sheet is treated with the aq. alkaline soln. which contains 0.01-2.5% ions of the metals of at least one kind of the Ni or Co, further contains >=0.05% amine compd. of at least one kind among 2-12C alkylene diamine, 2-10C polyalkylene polyamine and 2-10C alkanol amine, and has 10-14pH value. this steel sheet is then treated with the acetic acid-contg. chromate liquid which contains 0.1-5% acetic acid and 0.1-10% chromic acid to form the chromate film. The galvanized steel sheet having the excellent blackening resistance and corrosion resistance is thus obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a surface treatment solution for hot-dip galvanized steel sheets that are hot-dipped with pure zinc or zinc alloys such as Zn-AQ, and more specifically, The present invention relates to a surface treatment liquid that can impart excellent blackening resistance and corrosion resistance to steel plates.

In addition, in this specification, pure zinc plating and zinc alloy plating are collectively referred to as zinc-based alloy plating.

(Conventional technology) Hot-dip galvanized steel sheets were called galvanized iron in the past and were mainly used for building materials such as roofs and exterior walls, as well as for everyday miscellaneous goods such as brushes.However, in recent years, as their quality has improved, especially their corrosion resistance, they have been used in a wide variety of applications. It has come to be used for. In addition, fused Zn-AC has further improved corrosion resistance! Hot-dip galvanized steel sheets, such as alloy-plated steel sheets, have also been developed.

These hot-dip galvanized steel sheets exhibit corrosion resistance by delaying the occurrence of rust on the steel plate due to the sacrificial anti-corrosion action of Zn, but by applying chromate treatment after plating with hot-dip Zn or Zn-AQ alloy, the occurrence of rust can be further inhibited. can delay the process and improve the adhesion of the paint film. Due to its excellent corrosion resistance, chromate-treated hot-dip galvanized steel sheets are used in a wide range of products that we see every day, such as automobiles, building materials, home appliances, and others.

However, when chromate treatment is applied to hot-dip galvanized steel sheets, if they are left in a humid place for a long time during subsequent storage or after being processed into the desired product, the plating surface becomes black, a so-called blackening phenomenon. , the appearance becomes inferior and the product value is lost.

This black discoloration is characterized by a grayish-black color especially at specific crystal orientations in the spangles on the plating surface, so minimizing the spangles by a well-known method is effective to some extent. In addition, there are PB particles in the spangles where black discoloration occurs, and the presence of these PB granules also promotes the occurrence of black discoloration.
It is also known that black discoloration is less likely to occur at a concentration of less than 1%). However, many users prefer spangled products for hot-dip galvanized steel sheets, and the addition of PB to the plating bath is unavoidable. Furthermore, in molten Zn-Q alloy plating, if the AQ concentration in the plating layer is high, it is thought that black discoloration occurs due to the local battery action of Zn and AQ. In view of the above circumstances, it has been desired to solve the problem of blackening of hot-dip zinc and zinc alloy coated steel sheets, and various methods have been proposed to date to prevent blackening.

Japanese Patent Application Laid-Open No. 55-131178 discloses that after a light reduction is performed on a hot-dip galvanized steel sheet for the purpose of shape correction, improvement of appearance, improvement of mechanical properties, etc. with a reshape roller or skin pass roll, the galvanized steel sheet is once removed. It is described that chromate treatment is performed after heating to prevent blackening. This method prevents blackening by heating the plating surface that has deteriorated during rolling, but it is not sufficiently effective and requires heating equipment and energy, making it economically disadvantageous. It is.

JP-A-57-114695 describes a method in which after hot-dip zinc plating, the surface is treated with an alkali metal carbonate solution to dissolve and remove oxides on the plating surface, and then electrogalvanized. This method makes the plating surface uniform and prevents blackening, and is a very effective method. However, it requires an electroplating line in addition to the hot-dip plating line, and requires manufacturing equipment and processes. It becomes complicated and costs significantly more.

For the purpose of improving blackening resistance, corrosion resistance, etc., it has been proposed to treat hot-dip galvanized steel sheets with an aqueous solution containing metal ions such as Ni, Co, Fe, etc., followed by chromate treatment. For example, JP-A-59-1773
No. 81 discloses that after hot-dip zinc plating, Ni is applied to the surface.
A method is described in which Ni and/or Co is deposited on the plated surface by treatment with a solution containing ions, Co ions, or both, followed by chromate treatment.

In the method described in JP-A-61-110777, N
A hot-dip galvanized steel sheet is cleaned with an alkaline aqueous solution containing i ions, and at the same time the AQ on the surface of the plating is eluted and the Ni
is deposited on the surface, and then chromate treatment is performed.

JP-A No. 62-20881 discloses a method in which after hot-dip zinc plating, the surface is immediately treated with an alkaline aqueous solution containing both Fe ions and Ni ions to precipitate Fe and Ni on the surface, followed by chromate treatment. is listed.

The mechanism of preventing blackening by these methods is that the active Zn surface exposed on the plating surface by skin bath etc.
It is thought that the coating is formed by precipitation of Ni, Go, etc. by substitution reaction, and as a result, corrosion due to the local battery action of Zn is suppressed and blackening is prevented. Furthermore, when an alkaline aqueous solution is used, it is thought that the removal of M on the plating surface layer by the alkali also contributes to the prevention of blackening.

However, none of the above methods could sufficiently prevent blackening of hot-dip galvanized steel sheets. especially,
When processing is performed after mechanical processing such as skin pass, the plating surface is already smooth, so Ni and G precipitate due to a substitution reaction with weak bonding strength.

Due to insufficient adhesion between the metal coating and the plated surface, the precipitated metal and chromate coating were removed during subsequent coiling and pressing, resulting in localized blackness (blackening). It was done.

(Problems to be Solved by the Invention) The purpose of the present invention is to provide improved blackening resistance than before, which is less likely to cause blackening even when subjected to slipping during coiling or press processing, and to solve the problem of corrosion resistance. It is an object of the present invention to provide a surface treatment solution for a hot-dip galvanized steel sheet that does not cause the occurrence of oxidation.

(Means for Solving the Problem) As a result of intensive studies to solve the above object, the present inventors found that treatment with an alkaline aqueous solution containing a small amount of Ni and/or Co ions and a specific amine compound;
After learning that acetic acid-containing chromate treatment can produce a hot-dip galvanized steel sheet that has excellent blackening and corrosion resistance, and maintains blackening resistance even in slips during coiling and ironing during pressing, we developed the present invention. Completed.

Herein, the gist of the present invention is that in one embodiment, a small amount by weight of Ni and CO (both 0.01 to 2.5% of one metal ion) and a C2 to C2-C10 alkylene diamine. , C2-C1o polyalkylene polyamine, and 0.05% or more of at least one amine compound selected from 02-C10 alkanolamine. This alkaline aqueous solution is used prior to chromate treatment, as in conventional surface treatment methods, and is referred to herein as a pretreatment solution.

In another embodiment, according to the invention, 0.0% by weight of acetic acid.
A surface treatment solution for hot-dip galvanized steel sheet consisting of an acetic acid-containing chromate solution containing 1 to 5% of chromic acid and 0.1 to 10% of chromic acid is provided. Since it is used after being treated with a treatment liquid, it is called a post-treatment liquid.

(Function) The present invention will be explained in more detail below. In addition, in the following description, % is weight % unless otherwise specified.

The surface treatment solution according to the present invention is applied to ordinary hot-dip galvanized steel sheets, that is, 8Q: 0.08-0.20% and Pb:
It is applicable to both galvanized steel sheets manufactured from hot-dip galvanizing baths containing 0.2% or less Zn and the balance, and hot-dip zinc alloy-plated steel sheets such as Zn- to Q alloy-plated steel sheets. A typical example of hot-dip Zn-Q alloy plated steel sheet is 8Q: 0.3-6.0%, trace amounts of La, Ce.
, low N Zn-continuous alloy plated steel sheet manufactured from a hot-dip plating bath consisting of elements such as Mg, Si, and the remainder Zn, and a hot-dip plating bath consisting of AQ: 55%, Pb: 17%, and the remainder Zn. This is a high AQ Zn-Q alloy plated steel sheet.

As mentioned above, hot-dip galvanized steel sheets and hot-dip Zn-M alloy-plated steel sheets with spangles, zero or minimum spangles containing Pb, and especially high AQ Zn-alloy-plated steel sheets, have a strong tendency to blacken. When the surface treatment liquid of the invention is applied to such a plated steel sheet, a particularly remarkable blackening prevention effect is observed. Similarly, the effects of the surface treatment liquid of the present invention are also exhibited when applied to other hot-dip galvanized steel sheets.

The surface treatment liquid according to the present invention is characterized in that it consists of a combination of a pretreatment liquid consisting of an alkaline aqueous solution containing a specific polyamine or alkanolamine together with Ni and/or Co ions, and an acetic acid-containing chromate solution.

The present inventors have developed hot-dip galvanized steel sheets with spangle and zero-spangle surfaces that are prone to blackening due to the presence of PB, Q-Zn coated steel sheets with 5% Q-Zn as lower alloy coated steel sheets, and 55% Q-Zn coated steel sheets as high AQ alloy coated steel sheets. %M-Zn
Using a plated steel sheet, we investigated additives that are effective in preventing blackening by combining an alkaline pre-treatment liquid and a chromate-based post-treatment liquid as in the past. As a result, for any of the hot-dip galvanized steel sheets, the alkaline pretreatment liquid contains metal ions consisting of Ni, Co, or both, and at least one amine compound selected from alkylene diamines, polyalkylene polyamines, and alkanolamines. It has been found that blackening can be significantly prevented by containing .

The amine compounds used in the surface treatment liquid for pretreatment of the present invention include C2-C2-C12 alkylene diamine, C2-C
OO polyalkylene polyamines and C2-Cl11 alkanolamines. To give specific examples of useful amine compounds, examples of alkylene diamines include ethylene diamine, 1,3-diaminopropane, 1.4 diaminobutane, 1,5-diaminopencune, 2-C106-diamithexane, 1.7 -Diaminohebutane, 1.8-diaminooctane, 1,9-diaminononane, 1.10-diaminodecane, 1.11-diaminoundecane, 1,12
-diaminododecane, etc.; examples of polyalkylene polyamines are diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexazine, etc.; examples of alkanolamines are monoethanolamine, jetanolamine, triethanolamine, etc. It is. These amine compounds may be used alone or in combination of two or more.

The presence of such an amine compound is essential in the surface treatment liquid for pretreatment of the present invention, and it has been proposed in the prior art to add it as a complexing agent to an alkaline surface treatment liquid containing Ni and Co. When other organic compounds such as the typical complexing agents ammonia, ethylenediaminetetraacetic acid, nitrilotriacetic acid, glycol etherdiaminetetraacetic acid, diethylenetriaminepentaacetic acid, etc. are used in combination with Ni and/or Co. In this case, the blackening resistance is not substantially improved, and the aqueous solution may become unstable and precipitate may occur. Moreover, when these are used in combination with the amine compound used in the present invention, a decrease in blackening resistance may be observed. Therefore, in the alkaline surface treatment liquid of the present invention, it is preferable that the organic additive is only the above-mentioned amine compound.

In the surface treatment liquid for pretreatment, this amine compound is 0
．． It is contained in an amount of 0.05% or more, preferably 0.1% or more. When the content of the amine compound becomes less than 0.05%,
The solubility of Ni and Co deteriorates, and precipitation of these metals on the plating surface becomes insufficient, making it impossible to sufficiently prevent blackening. The upper limit of the content of the amine compound is not particularly limited because the amine compound does not have any adverse effects even if it is present in excess. When two or more types of amine compounds are used together, the total amount thereof should be 0.005% or more.

The metal ions present in the alkaline pretreatment surface treatment liquid are Ni, Co, or both, and other metal ions such as Cu, Ti, Fe, Sn,
.

When Mn and the like are present in an alkaline processing solution in combination with the above-mentioned amine compound, no improvement in blackening resistance can be obtained. Therefore, it is preferable that the alkaline aqueous solution used as the pretreatment liquid in the present invention does not substantially contain metal ions other than Ni and Co.

The metal ion selected from Ni and Co is 0.01~
It is present in the alkaline aqueous solution of the present invention at a concentration of 2.5% (total concentration when both Ni and Co coexist).

If it is less than 0.01%, a sufficient blackening prevention effect cannot be obtained. On the other hand, if the concentration of these metal ions exceeds 2.5%, corrosion resistance deteriorates and white rust is likely to occur.

Ni and/or Co ions are added to the alkaline aqueous solution as various salts, oxides, or hydroxides. Examples of salts that can be used are chlorides, nitrates, sulfates, phosphates, acetates, oxalates, and the like.

The pH of the surface treatment liquid for pretreatment is 10 to 14.

If the pH of the aqueous solution is less than 10, the blackening resistance will be poor.

A particularly preferred pH range is 10-13.5. If necessary, the pH of the aqueous solution can be adjusted to 1 by adding any alkaline inorganic substance that does not adversely affect the performance of the surface treatment solution.
Adjust to a value between 0 and 14. The pH is usually adjusted by the addition of alkali metal hydroxides such as sodium and potassium hydroxide. However, since a basic amine compound is used as an additive in the present invention, depending on the type and amount of the amine additive, the pH of the aqueous solution may be maintained at 10 or higher even without such pH adjustment. There is also.

This alkaline surface treatment liquid for pretreatment is applied to the hot-dip galvanized steel sheet by an appropriate method such as spraying or dipping. The treatment time may be a very short time of about 1 second to several seconds, and thereby Ni and/or Co metals are deposited on the plating surface. The amount of Ni and/or Co precipitated on the plated surface is 0.1 to 30 ng/+ per side in terms of metal.
It is preferably within the range of y+, more preferably from 0.4 to 10
■It is within the range of /IT+.

When Ni and Co are used together, the total amount of both should be within this range.

The mechanism of prevention of blackening by the surface treatment liquid of the present invention is essentially the same as that by conventionally known alkaline aqueous solutions containing Ni and/or Co, that is, the mechanism of prevention of blackening by the surface treatment liquid is due to the elution of AQ in the surface layer by the alkali and the precipitation of the above metals. It is conceivable that in the case of the treatment liquid of the present invention, the addition of the amine compound may cause the precipitated metal to adhere more firmly to the plating surface than in conventional surface treatment liquids.

The temperature conditions for this treatment are not particularly limited. That is, the hot-dip galvanized steel sheet to be treated may be at room temperature or at a high temperature of about 350°C. Therefore, the surface treatment liquid can also be applied to a zinc-based plated steel sheet while it is still at a high temperature immediately after hot-dip plating. In addition, the temperature of the alkaline surface treatment liquid can range from room temperature to 100'
Temperatures up to c. If necessary, heat drying is performed after surface treatment.

The surface treatment liquid for post-treatment of the present invention is an acetic acid-containing chromate liquid containing acetic acid and chromic acid. If a normal chromate solution that does not contain acetic acid is used, the blackening and corrosion resistance will not be sufficient, and blackening and white rust will easily occur in areas that are subjected to strong friction, such as the parts where the plates are rubbed together and the pressed areas. Become. To sufficiently improve blackening resistance and corrosion resistance, a chromic acid concentration of 0.1% or more and an acetic acid concentration of 0.1% or more are required. On the other hand, if the concentrations of chromic acid and acetic acid become too high, the surface of the steel sheet becomes yellowish, reducing its commercial value. This phenomenon occurs when the chromic acid concentration is 1
It becomes noticeable when the concentration of chromic acid exceeds 0% and the concentration of acetic acid exceeds 5%, so the concentration of chromic acid is 0.1 to 10% and the concentration of acetic acid is 0.1 to 5%.
shall be. Preferably, the chromic acid concentration is 0.3-3.0%
, the acetic acid concentration is 0.5-35%.

A part of the chromium in this chromate solution may be a water-soluble trivalent chromium compound to promote the formation of a chromate film. Moreover, this chromate-1 liquid can also be used as a coating type chromate liquid by containing silica sol. However, it is preferable to avoid the addition of various inorganic strong acids (sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, etc.) and fluorine compounds, which have been conventionally added to chromate solutions to enhance the etching effect. When an acetic acid-containing chromate solution is used, the chromate on the surface of the Zn or Zn-edge alloy plating film reacts as aluminum acetate, and this aluminum acetate is thought to be effective in preventing black discoloration and white rust. This is because this effect may be inhibited by the addition of .

The treatment operation and conditions using the post-treatment liquid, that is, the acetic acid-containing chromate liquid, may be the same as those for ordinary chromate treatment.

That is, the treatment can be carried out at room temperature to slightly high temperature by appropriate means such as dipping, coating, and spraying. The processing time is about several seconds to 10 minutes, and in the case of a coating type, the processing time is about 10 minutes.
It is usually less than a second, or longer in the case of a reactive type. The amount of chromate film deposited is within the range of 1 to 100 mg/n (calculated as Cr metal) per side, especially 5-
It is preferably within the range of 60*/m. After chromate treatment,
If necessary, perform heat drying to dry the chromate film.

Next, the present invention will be explained in more detail with reference to Examples.

The hot-dip galvanized steel sheets used in the examples are of the following four types (all are double-sided plated steel sheets). All base copper plates have a thickness of 1. It was a low carbon cold-rolled steel sheet with a diameter of 0.0 mm.

On U plate: Spangled Zn-plated steel plate produced on a continuous hot-dip Zn plating line Plating bath composition M: 0.05%, pb・0010
%, Fe: 0.02-0.03%, remaining Zn plating bath temperature 470℃ Line speed 100 m/m1n Zn deposition amount 2708hd (one side amount) Skin pass building ratio 1.0% Post-treatment No chromate treatment jliLM! = Zero-spangled Zn-plated steel plate plating bath composition manufactured on a continuous hot-dip Zn plating line AQ: 0.15%, PB: o, i
o%, Fe: 0.02-0.03%, remaining Zri plating bath temperature 470℃ Line speed 100 m/m1n Zn coating amount 270 g/mt (single side amount) Skin pass building ratio 1.0% Post treatment No chromate treatment Bumper plate 1 = 5% A manufactured on a continuous hot-dip Zn plating line (
! -Zn alloy plated steel plate plating bath composition 8Q: 5%, Pb: 0.01% or less, Fe: 0.02% or less, Misosu Metal 70.
06%, remaining Zn Plating bath temperature 460℃ Line speed 70 m/min Plating deposition amount 90 g/m2 (one side amount) Skin bath construction rate 0.8% Post-treatment New version without chromate treatment (: by hot-dip plating in the laboratory 55%A produced
(!-Zn alloy plated steel plate plating bath composition Q: 55%, Si: 1.7% or less, remaining Zn Plating bath temperature 600℃ Coating amount 175 g/m2 (single side amount) Skin bath construction rate 0.8% Post-treatment No chromate treatment This example shows the effect of the type of organic additive added to the pre-treatment liquid on blackening resistance and corrosion resistance.

Using the above-mentioned four types of hot-dip galvanized steel sheet test materials, treatment with a pretreatment liquid and subsequent chromate treatment were performed in the following manner.

The alkaline aqueous solution used for pretreatment contained 0.05% of NiC] and 2.5% of various organic amines or other organic or inorganic compounds, and was adjusted to pH 13 with sodium hydroxide. It is an aqueous solution.

As the chromate solution, acetic acid 1.0% and chromic acid 5%
An aqueous solution containing % was used.

First, each test material at room temperature was immersed in the above alkaline aqueous solution at a liquid temperature of 20° C. for 10 seconds to pre-treat the plated steel sheet. Next, after washing with water and draining, chromate treatment was performed by immersing the sample in the acetic acid-containing chromate solution at room temperature for 1 minute, and after draining, it was dried at 60° C. for 10 minutes to form a chromate film.

Thereafter, the obtained surface-treated plated steel sheet was stored in a desiccator at room temperature for 7 days, and then tested for blackening resistance in the following manner.

Mouse degeneration wiping: A test piece was wrapped in white clay kneaded with water, placed in a nylon bag, and immersed in warm water at 80°C for 24 hours, then taken out and the occurrence of black discoloration was visually determined.

The test results were evaluated based on the following criteria.

○: Good (no black discoloration) △: Slightly good (black discoloration area rate less than 40%) ×: Bad (
black discoloration area rate of 40% or more).

Furthermore, after each of the prepared alkaline treatment solutions was left at room temperature for 7 days, the stability of the treatment aqueous solutions was determined by visually observing the solutions according to the following criteria.

○: Stable (no precipitate observed) △: A slight amount of precipitate was formed.

×: Precipitate was formed.

The test results are shown in Table 1 below. Note that among the additives used in Table 1, the compounds marked with * are amine compounds used in the present invention. Table 1 shows the results when the test steel sheet is Steel Sheet 3 (5% Q-Zn alloy coated steel sheet), but the test results also apply when other hot-dip galvanized steel sheets are used. It was confirmed that similar trends were shown.

From the results in Table 1, it can be seen that only when the amine compound of the present invention is added to the alkaline aqueous solution for pretreatment, the occurrence of blackening is effectively suppressed and the treatment solution is also stably maintained. Unexpectedly, when ethylenediaminetetraacetic acid and nitrilotriacetic acid, which are commonly used as complexing agents to stably maintain Ni in a solution state in alkaline aqueous solutions, were added, the stability of the solution was good. However, no effect on suppressing the occurrence of black discoloration was observed.

(Left below blank) Table 1 Table 1 (Continued) 1 Soup 1 The same experiment as in Example 1 was repeated. However, the test steel plate is Steel Plate 3, and the alkaline aqueous solution for pretreatment contains N.
Various metal chlorides were used in place of 1ce2, and triethylenetetramine was used as an additive. The amount of metal chloride added was 0.05% in metal terms, the amount of triethylenetetramine added was 2.5%, and the pH of the solution was adjusted to 13 with sodium hydroxide. Other conditions were the same as in Example 1, and the blackening resistance of the obtained surface-treated plated steel sheet was determined in the same manner as in Example 1. The results are shown in Table 2 below.

From the results shown in Table 2, it can be seen that when the metals are Ni and Go, an excellent blackening prevention effect is obtained, and when the other metals are used, blackening is not prevented.

Implementation Group 1 The same experiment as in Example 1 was repeated. However, the test steel sheet was Steel Sheet 3, and chlorides of Ni and Co as metal compounds and ethylenediamine or ethylenediaminetetraacetic acid were added as additives to the alkaline aqueous solution for pretreatment. The amounts of Ni and Go added were 0.05%, ethylenediamine and ethylenediaminetetraacetic acid were each 2.5%, and the pH was adjusted to 10 or 13 with sodium hydroxide. The obtained surface-treated plated steel sheet was evaluated not only for blackening resistance but also for white rust resistance in the following manner.

7: Test specimens were subjected to salt spray test at 35"C for 120
After carrying out the test for a certain period of time, the occurrence of white rust was visually observed. The results were evaluated in three stages: O1, Δ, and ×, using the same criteria as the blackening resistance test.

Table 3 Table 3 shows the same trends as in Tables 1 and 2 above. That is, the alkaline treatment liquid for pretreatment is Ni
When containing Co and/or Co and the amine compound of the present invention, ethylenediamine, the blackening resistance was improved, but when the organic compound is changed to ethylenediaminetetraacetic acid, this improvement is no longer obtained. The occurrence of black discoloration cannot be prevented by acetic acid-containing chromate treatment alone.

Example 4 0.01% (as Ni” and Co2+) NiC
l2, CoC:I□ and various amounts of ethylenediamine were added to water and the pH was adjusted to 13 with sodium hydroxide to obtain an alkaline aqueous solution for pretreatment.

The stability of this solution was determined by the same method as in Example 1. The results are shown in Table 4 below.

A hot-dip galvanized steel sheet (test steel sheet 2) was surface-treated in the same manner as in Example 1, except that the fourth surface was added. After the acetic acid-containing chromate treatment, the plated steel sheet was tested for blackening resistance in the same manner as in Example 1. The test results are shown in Table 5 below.

Table 5 When 0.05% or more of the amine compound is added, Ni,
Co was able to be stably maintained in a solution state.

To prevent blackening, add 2.5% of ethylenediamine as an additive to the alkaline aqueous solution for pretreatment, and add various amounts of NiC2 to C12 and CoCl2 as metal compounds. At least 0. (11% or more Ni”
, it can be seen that it is necessary to include CO2+ in the pretreatment liquid.

Example 6 A solution containing an amine compound or other additives in addition to Ni, Co, or both compounds was used as the alkaline aqueous solution for pretreatment, and a molten zinc-based solution was prepared in the same manner as in Example 1 in Table 6. The surface of the plated mesh plate was treated.

The plated steel plate used in this example is the steel plate 3 (5
% AQ-Zn alloy plated steel sheet), and the pretreatment was carried out by spraying an alkaline aqueous solution (adjusted to pH 13 with Na leaf or KOI +) at a liquid temperature of 60 °C on the plated steel plate at room temperature for 2 seconds, and the subsequent treatment The operation was similar to Example 1. The surface-treated plated steel sheet obtained after the chromate treatment was left in a desiccator at room temperature for 7 days, and then the blackening resistance and corrosion resistance (white rust resistance) were evaluated in the same manner as above.

The results are summarized in Table 6 below along with the types of additives.

As can be seen from the results in Table 6, when the surface treatment liquid of the present invention was used (examples of the present invention), black discoloration was effectively prevented and the occurrence of white rust was also suppressed. Within the scope of the present invention, N
When i and Go were used in combination, when a metal compound other than chloride was used, and even when the pH was adjusted with KOH, excellent effects similar to those of the previous examples were obtained. However, if an additive outside the scope of the present invention is used, or the amount of metal species added is outside the scope of the present invention, black discoloration and white rust cannot be suppressed at the same time.

That is, the amount of metal species (Ni, Co) added is 0°01
If this amount is less than 2.5%, no improvement in blackening resistance will be observed, and if this amount exceeds 2.5%, corrosion resistance (white rust resistance) will deteriorate.

0.05% Ni as an alkaline aqueous solution for pre-treatment of snoring
”contains N1Ch and triethanolamine at a concentration of 2
．． The surface treatment of the steel plate 3 specimen was carried out in the same manner as in Example 6, except that aqueous solutions containing 5% and various pH values were used. p
H was adjusted with NaOH. After the acetic acid-containing chromate treatment, blackening resistance and corrosion resistance were tested in the same manner as in Example 6. The results are shown in Table 7 below.

From the results in Table 7, it can be seen that when the pH is lower than 10, the effect of preventing blackening cannot be obtained. When p I-1 approached 14, the corrosion resistance deteriorated somewhat.

Example 8 The surface treatment described in Example 6 was repeated. However, as the alkaline treatment liquid, a pH 13 aqueous solution containing 0.05% CO"?Mf degree COCl2 and 2.5% ethylenediamine was used, and the chromate solution for post-treatment was 1.0% acetic acid. The experiment was carried out using an acetic acid-containing chromate solution containing 3% chromic acid or a normal chromate solution.The composition of the normal chromate solution used was 3% chromic acid, 0.3% phosphoric acid, and 10.1% phosphoric acid. %.The test results are shown in Table 8 below.

This will greatly contribute to improving the quality and expanding the applications of hot-dip zinc plating.

Table 8

Claims (3)

[Claims] (1) 0.01 to 2.5% by weight of at least one metal ion selected from Ni and Co, and C_2 to C
A hot-dip galvanized steel sheet consisting of an aqueous solution with a pH of 10 to 14 containing 0.05% or more of at least one amine compound selected from _1_2 alkylene diamine, C_2-C_1_0 polyalkylene polyamine, and C_2 to C_1_0 alkanolamine. Surface treatment liquid. (2) By weight, acetic acid 0.1-5% and chromic acid 0.1-5%
A surface treatment solution for hot-dip galvanized steel sheets consisting of an acetic acid-containing chromate solution containing 10%. (3) (a) 0.01 to 2.5% by weight of at least one metal ion selected from Ni and Co; and C_
2~C_1_2 alkylene diamine, C_2~C_1_
0 polyalkylene polyamine, and C_2 to C_1_
(b) a pretreatment liquid consisting of an aqueous solution with a pH of 10 to 14 containing at least one amine compound selected from 0.0 alkanolamines and 0.05 or more of alkanolamine; and (b) 0.1 to 5% by weight of acetic acid and chromic acid. 0.1～
A surface treatment solution for hot-dip galvanized steel sheets consisting of two solutions: a post-treatment solution consisting of an acetic acid-containing chromate solution containing 10%;