JPS6256579A - Acidic aqueous solution and method for passivating surface of zinc or zinc/aluminum alloy - Google Patents

Abstract

An aqueous acidic treating solution for forming a chromium-containing passivate coating on the surface of zinc or zinc-aluminium alloys contains chromium ions of which the predominant proportion are in the hexavalent state, preferably in an amount 2-20 g/l., nitrate ions, preferably in an amount 0.5-6 g/l., and phosphate ions, preferably in an amount 1-15 g/l. The solution may also contain fluoride ions, molybdate ions and tungstate ions. The phosphide may be an alkali metal or ammonium phosphate, a polyphosphate or phosphoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION (Background of the Invention) The present invention provides an acidic aqueous solution used to form a passive film on the long surface of zinc or zinc-aluminum alloy to improve its corrosion resistance, and an acidic aqueous solution used to improve the corrosion resistance of the zinc or zinc-aluminum alloy. We focus on methods to form a passive film on surfaces.

In the art, the purpose is to form a chromium-containing passive film on zinc surfaces, such as galvanized steel and dull galvanized steel, to improve the surface resistance to corrosion, electrical discharge and white rust. It is known to form a passive film by treating the metal surface with an acidic solution containing chromium. In the present specification, the term "zinc surface" includes relatively pure zinc as well as surfaces of zinc that do not contain alloying elements. The well-known liquid composition commercially available for the above-mentioned one-paste contains chromium salt ions, halonic acid and hydrofluoric acid as main components. It has been found that the acidic aqueous solution according to this type of prior art is satisfactory for treating substantially pure zinc-gold and high surfaces as a treatment solution, but commercially available zinc-aluminum It has now been found to be unsatisfactory for the passivation of alloy coated steel sheets. Zinc in this building
As one of the aluminum alloys, there is one commercially available under the trade name of ``Galvalyume J'', which is approximately 55% aluminum by weight.
Approximately 43.5% by weight of zinc and approximately 1.5% by weight of silicon
It contains. Substantially pure galvanized steel is treated with a conventional passivating aqueous solution to form a passive film on the surface of the zinc-aluminum alloy, which is then exposed to the atmosphere under standard conditions in an uncoated state. It has been observed that rapid darkening and/or discoloration of the surface cannot be effectively prevented when the surface is removed.

This type of discoloration and/or darkening of the surface is undesirable.

The present invention provides novel passivating acidic aqueous solutions capable of substantially improving the corrosion resistance of zinc or zinc-aluminum alloy surfaces and preventing surface darkening and/or discoloration upon exposure of those surfaces to the atmosphere. and a passivation method using the aqueous solution.

(Summary of the Invention-) The benefits and effects of the present invention are that a chromium-containing passive film is formed on the surface of zinc or zinc-aluminum alloy with an acidic aqueous solution containing chromium ions, nitrate ions, and phosphate ions mainly composed of hexavalent chromium. Obtained by forming. The acidic water door solution may optionally further contain fluoride, molybdate or tungstate ions effective to promote the film-forming action.

In a preferred embodiment of the present invention, the treatment liquid (acidic aqueous solution) can be prepared by diluting a liquid concentrated acidic aqueous solution with water.

According to the method of the present invention, the surface of a clean zinc or zinc-aluminum alloy surface, such as a galvanized steel sheet or a zinc-aluminum alloy coated steel sheet, is treated with the acidic aqueous solution or treatment liquid of the present invention, and then the liquid film is dried. Ru. The treatment time, the temperature of the solution, the concentration of the active ingredient, and the liquid film present on the treated metal surface are controlled so that the desired amount of chromium coverage becomes an immobile, stateless film using, for example, a squeeze roll, without subsequent rinsing with water. .

(Description of Preferred Embodiment 5) According to the characteristics of the passivating composition of the present invention, the passivating acidic water bath Z night contains hexavalent chromium ions, nitrate ions, and phosphoric acid as its essential components. It contains io:/ and indicates a pH value on the acidic side due to hydrogen ions. The solution may optionally further contain fluoride ions, molybdate ions and tungstate ions or mixtures thereof to promote the film forming reaction on the zinc-aluminum base metal surface.

Chromium ions can be introduced in the form of soluble chromium compounds, such as chromic acid, alkali metal salts of chromic acid and dichromic acid, ammonium salts or mixtures thereof. Preferably the chromium ions are introduced as chromic acid or chromium trioxide which further imparts acidity to the solution. The chromium ions in the passivating acidic aqueous solution are mainly hexavalent ones. Chromium ions are added as hexavalent chromium, but some trivalent chromium ions are present due to the reduction of hexavalent chromium to trivalent -'\ which occurs during the film forming reaction. The degree of chromium ion in the processing solution can range over a wide range, from about 2 to about 20 grams per liter (1/L), but concentrations of about 11/1 are typical. Nitrate ions are added to an acidic aqueous solution (·τ) in the form of nitric acid, an alkali gold salt or ammonium salt of nitric acid, or a mixture of these salts. In particular, it is preferable to use nitric acid. About 0.5 to about 61 inside
, / , 1 (typically about 3 ?/l) is preferably present. 1) The ion is preferably an alkali metal or ammonium salt or more preferably f() of phosphoric acid or polyphosphoric acid.

1-, which can be introduced in the form of phosphoric acid as a compound, general:・
The phosphate ion concentration in the treatment solution is about 1 to about 15 f.
,'t (approximately 7 i//
``'' is another representative example.

The processing solution is acidic and maintained at a pH of about 2 or less.

For this purpose, the pH is adjusted by adding the acid component used in the acidic aqueous solution of the present invention, or the acid component and its salts.

Experiments have shown that the acidic aqueous solution of the present invention is suitable for treating zinc or zinc-aluminum alloy surfaces. Therefore, the treatment liquid can also be used to passivate both galvanized steel strip and zinc-aluminum alloy coated steel strip.

When treating zinc-aluminum alloy surfaces such as "Galvalum", it is advantageous to use a treatment solution containing activated ions that further promote the film-forming reaction and contribute to the formation of a passivation film. It turns out that there is something.

Additives for this activation, ie, activators, include fluoride ions (additional amount of about 0.54/l to about 0.7?/l1, typically hydrofluoric acid), molybdate ions (additional amount of About 0.5 to about 0.7?/l, specific examples include alkali metal salts of molybdic acid, ammonium salts, etc., but economically molybdic acid is preferable), tungstate ion ( about 0.29./l sodium tungstate (preferably), and one or both of these compounds can be added to the processing solution.

The treatment solution is produced by first preparing a concentrated aqueous solution and diluting this with water to a desired concentration. Suitable acidic concentrated water bath solutions include 30.4% by weight of chromium trioxide (approximately 2199 chromium ions/l), approximately 4.35% by weight of 100% nitric acid (approximately 59r/A of nitrate ions), and approximately 10% by weight of 100% phosphoric acid. It is composed of .65% by weight (approximately 142?/l of phosphate ions) and water. The concentrated composition has a specific gravity of about 1.383.

In preparing the treatment solution, the above-mentioned thick rock solution can be diluted with water until the concentrated aqueous solution weighs about 1 to about 10 volume cents of the treatment solution.

According to the invention, a treatment liquid is applied to a clean zinc-aluminum alloy surface by, for example, spraying, dipping, flooding, brushing, roller coating, etc., and then excess treatment liquid is removed by, for example, a squeegee. - removed by rolls; By controlling the coating solution with a squeegee roll, a relatively thin and uniform liquid film can be produced, and by controlling the thickness of the liquid film, it is possible to adjust the amount of chromium deposited in the dried film to a desired amount. Chromium coverage is also influenced by the length of time the solution is in contact with the surface, the temperature of the treatment solution and the concentration of active ingredients therein.

Generally, the processing liquid is about 38 to about 88°C (about 100° to about 1
90°F), with temperatures of about 54°C to about 71°C (about 130°F to about 160°F) being particularly preferred.

Typically the processing liquid is controlled at about 60°C (about 140°F).

Depending on the desired thickness of the chromium-containing passivation coating, the contact time with the processing liquid can range from as little as about 0.5 seconds to about 1 minute or more. After removing the excess liquid film using, for example, a squinol roll, the remaining liquid film is dried.

In common industrial processing operations, the steel strip is typically first cleaned with a solvent cleaner to remove the protective oil film on the metal surface, and then the steel strip is cleaned with a suitable cleaning treatment, such as an alkaline cleaner. Thereafter, the copper strip is washed and dried and immersed in a molten zinc-aluminum alloy bath for hot-dip plating. Once the zinc-aluminum alloy plating has solidified, the plated steel strip can be brought into direct contact with the treatment solution of the present invention to passivate the metal surface.

In order to further specifically explain the present invention, the following examples are presented.

Example 1 In the Calvalume test, the board was first wiped with mineral spirits to remove any protective oil film and contaminants, and then treated with ParC'O Cleaner 338 (P).
arker Chemical C! Cleaned by spraying for 10 seconds at a temperature of approximately 130° F. After that, the cleaned test plate was heated to about 19°C.
(approximately 120° F.) for 5 t'2. Next, the surface was cleaned, and the plate was coated with about 0.7 chromium trioxide.
1 layer (chromium ion approx. 3.7 t/l)), 68% nitric acid (approximately 0.15% by weight of nitric acid ions) and 75% phosphoric acid (approx. 2.
4? /l) and about 000 to the treatment solution containing residual water.
Soaked at a temperature of about 140°F. Excess treatment solution was squeezed off and the remaining liquid film was dried at room temperature. In addition, during the treatment, the dry film amount should be set in advance as the amount of chromium deposited, approximately 10, smg/m” (approximately 1
The immersion time and swiping conditions were adjusted so that the immersion time and sifting conditions were adjusted to 100 mV/ft2). The barked and treated test board was heated to approx.
Cut to dimensions of 6 cm x 19 cm (approximately 3.5 x 7.5 inches) and use the trade name "Castrol Ru5tillo" DW.
-924HF J's Vanishing Oil/l/ (Van
ishing oil: 1) was applied.

The test plates were then tested using corrosion tests established by suppliers of zinc and zinc-aluminum alloy coated steel sheets to predict weather resistance. That is, these test plates were first cleaned with mineral spirits to remove the protective oil film, and then placed in a glass dish containing 0.75 t of distilled water (
Dimensions: 4.5 x 8.5 x 3 inches (deep). It was then placed in a humidity cabinet maintained at a temperature of 37.7°C (100°F).

During the duration of the tests described above, the surfaces of the treated test panels were periodically checked for darkening and/or discoloration. The degree of darkening and discoloration of the test plate surface is rated from 1 to 8, with no discernible darkening being rated 8, and those showing complete darkening being rated 1 and 1-. is.

Example 2 A "Gulparium" plated test plate was treated in the same manner as in Example 1 except that the following treatment liquid was used, and then an accelerated corrosion test was conducted. The treatment liquid contains 0.65 fi amount of chromium trioxide (
Chromium ion approx. 3.4 f/l), 68 nitric acid approx. 0.14
75% by weight (approximately 0.93 nitrate ions/l), 75% by weight phosphoric acid (approximately 2.42/l phosphate ions, 70% by weight)
% hydrofluoric acid by weight of approx. 0.07% (common ion approx. 0
．． 5? /l), sodium molybdate dihydrate approx.
0.09% by weight (approximately 0.6"i/l of molybdate ions) and approximately 0.03"i of sodium tungstate dihydrate (approximately 0.22"i/l of tungstate ions).

Comparative Example 3 For comparison, a "Gulparium" plated test plate was treated and tested in the same manner as in Example 1, except that the following treatment liquid was used. The treatment solution is a typical passivation solution conventionally used to passivate the surface of galvanized steel sheets, and contains 0.38% chromium trioxide (approximately 2r/z chromium ions), Acid approximately 0.11% by weight and 7
It is an aqueous solution containing about 0.11% hydrofluoric acid by weight.

Comparative Example 4 For comparison, a "Galupalium" plated test plate was first wiped with mineral spirits and then subjected to an alkaline cleaning treatment, followed by washing with water, according to the same process as described in Example 1. The surface was not subjected to immobilization or transformation treatment. For this cleaning only test, Example 1~
Corrosion tests were conducted in the same manner as in Comparative Example 2 and Comparative Example 3.

Table 1 shows the results of the chromium deposition amount and corrosion condition of Examples 1 and 2 and Comparative Examples 3 and 4.

Corrosion of first skin film≠1 14.7 (1,37) 7.
5 7.3$2 10.7 (0,9
9) 8 7.8 Comparative example≠3 1.1.1 (1,03)
3.9 2.5 Cleaning only test plate is simply 168
After some time, the color darkened completely. After 1400 hours of testing, the test panel treated with the passivating solution of ActiS 1*11 showed only a very slight darkening, as indicated by a 7.5 degree of staining, compared with Example 2. Passivation treatment liquid,・
Test results showed a rating number of 8 with no visible discoloration.

On the other hand, in Comparative Example 3, the sample 1 horizontal plate treated with the passivation treatment solution based on the prior art showed a rating number of 3.9, that is, significant discoloration, after 1.10 tons) of time. The benefits of the inventive treatment solution as illustrated in Examples and 2 demonstrate clear superiority over Comparative Example 3. It is proven that it is further extended from the 2,164 hour test results.

Claims (19)

[Claims] (1) Contains chromium ions, nitrate ions, and phosphate ions mainly consisting of hexavalent chromium, and each of these is contained in amounts sufficient to form a chromium-containing passive film on the surface of zinc or zinc-aluminum alloy. Acidic aqueous solution for passivating zinc or zinc-aluminum alloy surfaces. (2) Chromium ions are about 2 to about 20 g/l, nitrate ions are about 0.5 to about 6 g/l, and phosphate ions are about 1
An acidic aqueous solution for passivating a zinc or zinc-aluminum alloy surface according to claim 1, comprising from about 15 g/l to about 15 g/l. (3) Zinc or zinc according to claim 1, which contains hydrogen ions until the pH becomes about 2 or less.
Acidic aqueous solution for passivating aluminum alloys. (4) The acidic aqueous solution for passivating the surface of zinc or zinc-aluminum alloy according to claim 1, which further contains fluoride ions in an amount effective to promote the formation of a chromium-containing passive film. (5) The acidic aqueous solution for passivating zinc or zinc-aluminum alloy according to claim 4, which contains about 0.5 g/l of the fluoride ions. (6) Acidic aqueous solution for passivating the surface of zinc or zinc-aluminum alloy according to claim 1, further containing molybdate ions in an amount effective to promote the formation of a chromium-containing passive film. . (7) The molybdate ion is about 0.5 to about 0.
7 g/l of the acidic aqueous solution for passivating the surface of zinc or zinc-aluminum alloy according to claim 6. (8) Acidic aqueous solution for passivating the surface of zinc or zinc-aluminum alloy according to claim 1, further containing tungstate ions in an amount effective to promote the formation of a chromium-containing passive film. . (9) The acidic aqueous solution for passivating the surface of zinc or zinc-aluminum alloy according to claim 8, which contains about 0.2 g of the tungstate ion. (10) A concentrated acidic aqueous solution used to passivate the surface of zinc or zinc-aluminum alloy, in an amount necessary to form a chromium-containing passive film on the metal surface by diluting the composition with water. A concentrated acidic aqueous solution for passivating the surface of zinc or zinc-aluminum alloy, characterized in that it can be made into an acidic aqueous solution containing chromium ions, nitrate ions and phosphate ions mainly composed of hexavalent chromium. (11) Chromium ion approximately 219g/l, nitrate ion approximately 5
11. A concentrated acidic aqueous solution for passivating zinc or zinc-aluminum alloy surfaces as claimed in claim 10, containing 9 g/l and about 142 g/l of phosphate ions. (12) The process consists of a process of treating a clean zinc or zinc-aluminum alloy surface with an acidic aqueous solution containing chromium ions, nitrate ions, and phosphate ions mainly composed of hexavalent chromium, and a process of drying the film. A method for passivating the surface of zinc or zinc-aluminum alloy for increasing the corrosion resistance of the metal. (13) Treatment with an acidic aqueous solution containing about 2 to about 20 g/l of chromium ions, about 0.5 to about 6 g/l of nitrate ions, and about 1 to about 15 g/l of phosphate ions. A method for passivating a surface of zinc or zinc-aluminum alloy as described in 2. (14) The method for passivating the surface of zinc or zinc-aluminum alloy according to claim 12, which comprises the step of controlling the pH of the acidic aqueous solution to about 2 or less. (15) further comprising a compound selected from the group consisting of fluorides, molybdates, tungstates, and mixtures thereof in an amount effective to promote the formation of a chromium-containing film on the zinc or zinc-aluminum alloy surface. Claim 1, which is treated with an acidic aqueous solution containing
The method for passivating a surface of zinc or zinc-aluminum alloy according to item 2. (16) Adjust the temperature of the acidic insoluble solution to about 38 to about 88°C (about 10
13. A method for passivating a zinc or zinc-aluminum alloy surface as claimed in claim 12, including the step of controlling the temperature within a range of 0 to about 190 degrees Fahrenheit. (17) Adjust the temperature of the acidic aqueous solution to about 54 to about 71 °C (about 13
13. A method for passivating a zinc or zinc-aluminum alloy surface as claimed in claim 12, including the step of controlling the temperature within a range of 0 to about 160 degrees Fahrenheit. (18) When dry, the amount of chromium deposited is approximately 10.8 mg/
13. The method of passivating a zinc or zinc-aluminum alloy surface as claimed in claim 12, comprising a control step to achieve a coating of about 1 mg/ft^2. (19) An article having a chromium-containing passive film formed on its surface by the method according to claim 12.