DE2452483A1 - METHODS AND MEANS FOR SURFACE TREATMENT OF METALS - Google Patents

Description

Process and means for the surface treatment of

Metals

The invention addresses the problem of surface treatment of metals for the purpose of increasing their resistance to corrosion. In particular, the invention relates to a Chromate resin composition for use as a paint coating on the surface of metals such as steel, zinc and aluminum.

It has been found that the conventional chromate resin coating compositions, currently used as a primer for metal surfaces, have certain disadvantages. point. If so, the chromate resin composition in view of is chosen based on its ability to protect the metal surface against corrosion, then the adhesive strength of the Color on the metal surface often turned out to be too weak. On the other hand, when the chromate resin composition is im With regard to their strength was selected, it was found that the protection of the metallic surface against Corrosion was only weak. The invention is therefore based on the object to provide a chromate synthetic resin composition which not only protects the metal against corrosion but also ensures perfect adhesion to the metallic surface.

According to the invention, the composition is for surface treatment of metals from an aqueous solution, which

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Has chromium ions with a Cr to Cr ion ratio,

between 2: 1 and lsi, together with one water-soluble organic synthetic resin.

According to a further feature of the invention, the method for the surface treatment of a metal is carried out in such a way that an aqueous solution is applied to the metal surface which contains chromium ions, which convert a Cr to Cr Have ion ratio which is between 2: 1 and 1: 1, together with a water-soluble organic synthetic resin and that finally the solution is dried to form a film.

The aqueous solution can include chromium ions in any of the following three forms, although other forms are not excluded should be:

a) a hexavalent chromium compound that is partially reduced to a trivalent state,

b) a trivalent chromium compound which is partially oxidized to the hexavalent state,

c) a mixture of hexavalent and trivalent chromium compounds .

The aqueous solution can be applied to the metal surface by any conventional method, for example by dipping, spraying, squeezing or winding.

. The, temperature at which the solution is applied, can be between ambient temperature and 6o ° C range, and preferably the solution is dried after it is applied, namely at a suitable temperature 25O ⁰ C does not exceed "the generated Chromium weight on drying Film of the solution is usually between

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0.03 to 0.20 g / m, while the total film weight is between Is 0.1 and 0.5 g.

Preferably, the Cr to Cr ion ratio of the aqueous solution is selected to be within a range is between 2: 1 to 3: 2 and expediently the solution contains the chromium ions in the form of a partially reduced one hexavalent chromium compound.

Conveniently, the organic synthetic resin material of; a mixed polymer of acrylonitrile, citridic acid, buty! urea and acrylamide. The synthetic resin can; 30 to 60% by weight of acrylonitrile, between 30 and 60% by weight Citridic acid, between 5 and 30 weight ^ butylurea and contain between 5 to 20 weight acrylics. ;

The solution can be a partially reduced hexavalent chromium compound be in an amount which is between 3 to 20 g / l, preferably in the range between 5 and 10 g / l and the synthetic resin may be present in an amount comprised between 10 and 50 g / l, preferably in the range between 10 and 30 g / l. The solution can also be a hydrofluoric acid as a corrosion inhibitor in an amount which is, for example, between 2 and 5 g / l, but preferably in a range between 2 and 3 g / l.

Sugar has been shown to be an effective way of reducing the compound when present in the solution. A suitable sugar for this is dextrose.

Other compounds, e.g. ammonium fluoride, 1,2-bipyridyl, 1,10-phenanthroline and fluoroboric acid can also be introduced into the solution to improve the corrosion resistance of the coated metal surface. The ammonium fluoride can be provided in an amount in the area

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between 0.5 and 2.0 g / l, the 1,2-bipyridyl and 1,10-phenanthrolln can be present in amounts ranging between 0.25 and 1.0 g / l while the fluoroboric acid is in an amount between 1 and 5 g / l can be present.

If the metal surface is to be painted, the ratio of Cr to Cr ions has proven to be important, so that a good adhesion between the paint and the metal surface is achieved and thus the coated surface opposite Corrosion effects are saved. A higher than the specified ratio tends to adversely affect the corrosion resistance, while a lower ratio the adhesion of the paint to the metal is reduced. The water-soluble synthetic resin is also useful Part of the composition according to the invention, since the paint adhesion improves and the corrosion resistance of the metal surface increase.

Embodiments of the invention are detailed below described:

Example 1.

100 grams of chromic acid are dissolved in one liter of water and 5 g of D (+) - dextrose was added to the solution. The mixture was boiled for two hours to dissolve the dextrose, thereby partially reducing the chromic acid and turning a Cr to Cr Ion ratio of 5: 2 was obtained.

This solution was used to prepare another solution with the following composition:

Solution A.

Partially reduced chromic acid solution (with a Cr to Cr Ion ratio of 2: 2 and the concentration based on the original chromic acid concentration) 6 g / l.

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Water-soluble organic synthetic resin 10g / l (Copolymers of citridic acid $ 40, acrylonitrile $ 40, Acrylamide $ 10 and Butylurea $ 10).

Hydrofluoric acid HgSiPg 2.5 g / l Ammonium fluoride NHwF 1 s / l

1.10 phenanthroline 0.5 g / l.

Four cold rolled mild steel sheets were cleaned and one was coated by spraying Solution "A" at ambient temperature. A second panel was treated with a conventional chromate resin system, the third with a conventional chromate silicon system, and the fourth panel was left untreated. The coated panels were then ^{dried at 150 °} C. and the four panels were exposed to an atmosphere of condensing moisture for 168 hours, after which the corrosion products were removed by the Clarks solution (11 concentrated hydrochloric acid, 10 g antimony chloride and 10 g tin chloride) and the weight loss was measured .

Table 1 shows the weight loss in each case. It turns out that the panel treated with solution "A" is much less was more corroded than the other panels.

Table J
Coating solution weight loss in mg / ft

Untreated 2130

Solution A 138

Come 1 i before s

Chrome synthetic resin system 210

Conventional chromate silicate

system 173

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Example 2

Four cold rolled mild steel sheets were selected and three of them were cleaned and coated as in Example 1, while one was left untreated after cleaning. Then the panels were painted with acrylic resin and then tested for adhesion and corrosion resistance in a humid atmosphere, in a salt spray atmosphere and in an SO ₂ room.

In order to be able to determine the adhesion characteristics, a small piece of each panel was cross-hatched using a scriber and it became an Eriehsen notch of 9 now over the surface The cross hatching attached® Attempts were then made to remove the color from the cross hatching by means of an adhesive tape to remove. The values recorded in Table II show the percentage of cross-hatched squares, their color was removed.

The humidity test was carried out for 2000 hours and the salt spray test for 1000 hours. The SOY space trial was after The corrosion characteristics of each carried out 20 cycles Chalkboards were made by visual inspection of a scribe section, determined for each panel. The results are also shown in Table II, where frequencies and The size of the color bubbles was expressed as follows;

Frequency of the bubbles: Fi few; Mz medium; D: dense;

Size of the bubbles; 8th; tiny; 6: medium size;

2: very large;

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Type of attempt

- 7 - Table II

Untreated solution A

Chromate

synthetic resin

system

Chromate silicate system

adhesion
humidity

Salt spray

space

$ 100

Dense rust in the grooves D8 bubbles

Slightly strong rust
Rust in the in the
Groove writing and writing grooves

Dense rust. Strong, strong rust in the write- Rust in in the grooving the writing writing D6 bubbles grooving grooving

Dense rust Rust in rust in the grooves in the writing- writing- writing grooves grooves D2 bubbles · ⁰ ^ bubbles d6 bubbles

Heavy rust in the writing grooves

Very strong rust in the writing area

Rust in the writing grooves D8 bubbles.

It can be seen from Table II that the panel treated with Solution "A" gave excellent adhesion values and that it corroded much less than other panels.

Example III

Panels made of hot-dip galvanized steel, electro-galvanized steel and hot-dip aluminized steel have been cleaned and treated with the Solution "A" coated by the procedure of Example 1 and three more panels were cleaned and cleaned with conventional reduced chromate synthetic resin systems. Then the panels were coated with an acrylic resin and an alkyd paint and checked as in Example II. The results are shown in Table III, using the same scales of Bubble size and frequency was used. The Adhäsionser-

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results relate to the Erichsen recess, the over a cross hatch area was made before Paint can be removed with an adhesive tape.

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Table III

Substrate

Hot-dip galvanized galvanized steel

Experimental method

Adhesion moisture

Salt sprinkling

SCL

Solution 1 acrylic alkydic

7 ram 8 mm

no change. no change

no change - no change

Bubbles Dß bubbles

Conventional chromate resin, acrylic alkydic

6mm
no change

6 mm

Ρβ blisters near the writing called out

no change no change

D8 bubbles

Ώβ bubbles

cn -
O Electrogalva
nized steel adhesion 8 mm 8 mm 6 mm DS bubbles in the
Near the writing
called 9820 humidity no change
tion no change
tion 1) 8 bubbles in the
Near the writing
called υ ² ! · Bubbles —S. Salt sprinkling F8 bubbles Where bubbles D4 bubbles Fo bubbles ..
in O
O
• Ρ- • so ₂ f6 bubbles Buttocks bubbles f6 bubbles ro
9mm ⁴ ^ ¹ Fire aluminum
ized steel adhesion 9mm Stan, 9mm no change co
FS bubbles humidity
Salt sprinkling no change
tion
Ρβ bubbles no change
tion
Ρβ bubbles no change
F8 bubbles low rust in
the writing letters
FS bubbles red rust
in the
write
called
Fo bubbles Rust in the
Writing letters
F8 bubbles
'.P Rust in the
Writing letters
F8 bubbles

It can be seen that the panels coated with solution A a superior aggression and superior corrosion properties compared to conventional chromate resin coatings.

Patent claims:

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Claims (17)

Patent claims: 1) Agent for the surface treatment of metals consisting of an aqueous solution, characterized in that the aqueous solution contains chromium ions with a Cr to Cr ion ratio that is between 2KEi 2il and 1: 1 together with a water-soluble organic synthetic resin. 2) means according to claim 1, characterized in that that the chromium ions are contained in one of the following forms: a) a hexavalent chromium compound, some of which is trivalent Condition has been reduced, b) a trivalent chrome alloy that has been partially oxidized to the hexavalent state, e) a mixture of hexavalent and trivalent chromium bonds 3) Agent according to claims 1 or 2, characterized in that the chromium ^ ¹ to chromium ¹¹¹ ratio is chosen so that it is in the range between 2: 1 and 5: 2. 4) Agent according to claims 1 to 3 *, characterized in that the organic synthetic resin is a copolymer of acrylonitrile, citridic acid, butylurea and acrylamide. 5) means according to claims 1 to 4, characterized in that that the solution contains hydrofluoric acid as corrosion protection. 509820/1004 ./. 6) Means according to claims 1-5 * characterized in that the solution contains sugar as Reducing agent works. 7) means according to claims 1-6, characterized in that the solution has one or more of the following Compounds contains: Ammonium fluoride, 1,2-bipyridyl, 1,10-phenanthroline and Fluoroboric acid. 8) Process for the surface treatment of metals by
Applying an aqueous solution to the metal surface and drying the solution to form a film, characterized in that the aqueous
Solution of chromium ions with a Cr to Cr ion ratio
contains between 2: 1 and 1: 1 together with a water-soluble organic synthetic resin, 9) Method according to claim 8, characterized in that that the chromium ions are contained in one of the following forms: a) a hexavalent chromium compound that has been partially reduced to the trivalent state, b) a trivalent chromium alloy that has been partially oxidized to the hexavalent state, c) a mixture of hexavalent and trivalent chromium compounds. 10) Method according to claims 8 or 9> characterized in that the solution is at an intermediate temperature and 6o ° C lying temperature is applied. 11) Method according to claims 8 to 10, characterized in that the solution after application at
a ^{temperature not exceeding 250 0} C is dried. 509820/1004 ./. 12) Method according to claims 8 to 11, characterized in that g e k e η η shows that the chromium weight of the film produced on drying the solution is in the range between 0.03 and'0.20 g / m, the total film thickness in one Range between 0.1 and 0.5 g / lm. 13) Process according to claims / to 12, characterized in that the chromium to chromium ratio is chosen to be in the range between 2: 1 and 3: 2. 14) Process according to claims 8 to IJ, characterized in that g e k e η η indicates that the organic synthetic resin material is a copolymer of acrylonitrile, citridic acid, Butylurea and acrylamide. 15) Method according to claims 8 to 13, "thereby g e k e η η shows that the solution contains hydrofluoric acid as corrosion protection. 1β) Method according to claims 8 to 15 »thereby g e k e η η draws that the solution contains sugar, which acts as a reducing agent. 17) Method according to claims 8 to 16, characterized in that g e k e η η draws that the solution is one or more of the following Compounds contains: Ammonium fluoride, 1,2-bipyridyl, 1,10-phenaniroline and Fluoroboric acid. 509820/1004 ORtGlNAL IISJSPibTED