DE1936633A1 - Process for the surface treatment of metals - Google Patents

Description

Dr. Werner Häßler

PATENTAN WAIT
588 LöDENSCHEID

Ludenscheid, July 15, 1969 A69 3o8

Applicant: Ea. Yawata Iron & Steel Co., Ltd. No. 1, 1-chome, Marunouchi, Chiyoda-ku, Tokyo, Japan

. Process for surface treatment

handling of metals. '...

The invention relates to a method for the surface treatment of metals. .. ■ '.

The field of application of the invention is the surface treatment of zinc and zinc alloys. This is in particular about the chemical surface treatment of metals with a zinc layer, where the formation of so-called white rust occurs the surface should be switched off under the influence of moisture.

Usually zinc and zinc alloys are widely used as plating materials, with electroplating the article is done by hot dipping or electroplating is made. This application of zinc is more common than the direct use of the metallic one Zinc. However, it is corrosion resistance in both applications not unrestricted, because white rust forms on the surface. This formation represents a serious disadvantage for the use of zinc and its Alloys.

White rust forms on the surface of galvanized steel sheets, especially when used during transport Lake out; such formations show up very often when used in a higher environment. Moisture, e.g. in Japan .. To Various treatments have been proposed to suppress this formation. However, nowadays exists

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the need for a process that makes all of these materials - " high corrosion resistance and good paint adhesion confers.

To suppress the formation of white rust is mainly a Chromate treatment with chromic acid or its salts applied, but a satisfactory process is not yet known

Advantageous properties of galvanized steel sheets are the high corrosion resistance and the good paint adhesion, both before and after processing. The processors of such steel sheets make these demands so the above properties without subsequent chromate treatment is available from the processors. Since baked-on paints have recently also been used, the Color substance can be kept in a state of high corrosion resistance even after baking.

In summary, the surface treatment must be galvanized Steel sheets provide a good looking, corrosion resistant surface with good paint adhesion. i) ie high corrosion resistance and good paint adhesion should be retained even after processing, and high corrosion resistance even after baking. "- ■.

On the other hand, the continuous surface treatment of galvanized steel sheets for corrosion protection should normally be included high processing speed; because it is a surface treatment with drying by nip rollers to the usual surface treatment with water rinsing and drying • preferable for various reasons. As part of This customary process can use other treatment options for uniform application instead of squeegee rollers the treatment solution is applied to the "fabric to be treated" be, for example a gas drying; such a method for uniform application of a treatment solution can be used at a steel sheet of any kind can be used, in particular especially in the case of a prefabricated part with a simple shape, ■ '

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BAD ORJGINAL

There are a considerable number of patents relating to the surface treatment of galvanized parts; however, most relate to post-processing surface treatment of clad parts, and few relate to continuous surface treatment where nip roll drying is applicable. The Armco Steel Corp. process is widely used for continuous surface treatment. using pure chromic acid (Japanese Patent 5857-1956). Starting from this chromic a further relates to the use of a chromic acid-water glass bath in accordance with the United States Patent \ 665 232. However, the processes described therein do not provide the expected effect in terms of corrosion resistance and paint adhesion of the treated materials after processing. The corrosion resistance after applying a coat of paint is not as good in terms of * the blistering of the paint layer after corrosion tests have been carried out. If a chromic acid water glass bath is used as the treatment solution, the treated metal surface will look poor due to the action of the Na ions from the water glass. This deterioration increases with time after the simple nip treatment and drying. As a result, rinsing of the treated surface with water after drying cannot be dispensed with in this dissolving treatment; if the water rinse is omitted, the corrosion resistance and the paint adhesion of the product deteriorate. Such a deterioration in the corrosion resistance and the paint adhesiveness of the product is attributable to the Na ions of the water glass.

When a great corrosion resistance for the finished product under treatment with the chromic acid water glass solution. no rinsing treatment is required after drying comes the so-called two-solution process, where the objects first immersed in water glass and then in a chromic acid solution will. Γ-This method is however in the application to { of course; the loss of the treatment solution is very great, * wa ^ is disadvantageous in this two-solution process. !

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The object of the invention is to provide a method .for the surface treatment of zinc and zinc alloys, after which within a short treatment time and in a simple manner a chromate layer with good paint adhesion and appearance on the surface of metallic zinc, zinc alloys or galvanized sheet steel is formed.

This object is achieved according to the invention is that the surface of a metal of the group of zinc and Zinkle- _(-ierungen with a mixed solution of chromic acid and silica colloid is coated and in that a drying of the solution applied takes place to form a thin surface film.

The chromate layer formed by the process according to the invention has a high corrosion resistance, i.e. it is free from white rust formation after other treatment methods Can hardly be suppressed in the case of galvanized steel sheets; the chromate layer has good paint adhesion. After this chromate layer has been applied, the product retains the high level of corrosion resistance even after baking a paint application to the same extent.

: he treatment according to the invention is carried out so that a treatment solution with chromic acid as a main component and a Silica colloid additive to the surface of the zinc metal, zinc alloy, or a zinc-plated or zinc-coated Sheet steel is applied. J) ie applied solution is squeezed off with the aid of nip rollers so that a uniformly thin layer is obtained; the sheet steel with this layer is then dried, whereby a chromate layer forms on the surface of the treated product trains. This treatment according to the invention does nothing Water rinsing of the treated product following the Application and drying of the mixed solution required Application of the Miachlösung and drying take place within very short time.

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With regard to the components of the mixture and the concentration ranges for the mixed solution, a solution with a low concentration, namely with 1. to 20 g / l chromic acid and 1 to 70 g / l silica colloid (as SiO ₂ ), is preferable for items that are not further under shaping. ' ■ work after the surface treatment has been carried out, but can be used in their original form. A solution of higher concentration, namely with more than 18 g / l chromic acid and more than 56 g / l silica colloid, is useful for products that are further processed under shaping should be...,

If a good look the by the treatment after the In the invention produced layer is desired, the concentration ratio between chromic acid and silica colloid should be less than 1: 3 within the mixed solution.

In the context of the treatment of the invention is an aqueous solution of chromic anhydride or einem- material which is mainly composed of chromic anhydride ,, used together with a silica colloid * hieraŭ is a solution useful by removing the Efatriumionen from a ITaSiO ₉ -Losung (waterglass ) is prepared with the help of ion exchange resins, * commercially available silica colloids can also be used, the "Lüdox" commodity from EI du Pont de Nemours & Co., Inc., Wilmington, Delaware, USA} furthermore, substances that can be used by uniform dispersion of silica gel in an alkali solution are prepared \ - namely by neutralizing water glass with. a Na-ion-free acid, - Furthermore there is the possibility of the dispersion of solid SiO ₂ as well as the possibility of dialysis of water glass, In each case the SiOp. be uniformly dispersed so that a colloidal phase is present in the solution. The solution becomes even more effective if part of the contained Seohswertigen.Chroms is reduced to trivalent chromium by any method, without harmful oxidation products may occur in the solution; such a reduction can be achieved with a

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The treatment solution according to the invention is also at comparative low concentration so "effective that the treated product has good corrosion resistance and Has paint adhesion. However, a solution of higher concentration also reduces the retention of these properties expect further processing. "

An embodiment of the treatment solution of low concentration with hexavalent chromium ions contains 0.5 to 10 g / l metallic tyirom with a silica colloid addition of 1 to fo g / l based on SiO «. Even if a solution in this concentration range is extremely effective, see the later examples 1) and 2), the effect in terms of maintaining the above-mentioned properties after further processing is not as high as can be achieved with a solution of higher concentration.

The treatment described above is carried out in such a way that the workpiece to be treated is degreased with a zinc or 'galvanized * surface and rinsed with water so that the surface is clean; then thawing takes place in the treatment bath at room temperature for a period of about 30 seconds; finally, the excess treatment solution adhering to the surface is removed with Guinmi rollers or other scrapers, and the product is dried.

The application of the treatment solution described above makes A water rinse after drying is superfluous. to maintain good paint adhesion. Subject of the invention can rather, the product has excellent corrosion resistance and • paint adhesion even without water rinsing can be achieved after drying the treatment solution.

The two-stage process, the treatment of the objects

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next only with silica colloid and then with chromic acid, . "Doesn't make such a big difference with the above - mentioned properties compared to the one-step procedure. According to the invention, however, the double drying is saved in both types of the known treatment, resulting in a simplification of the process and a temporal shortening results.

For the coating of the surface of the respective object to be treated, not only dipping into the solution is useful, but also spraying or brush application of the solution; drying can take place after the excess solution on the surface has been removed. - ■■

j) The following individual examples of the invention relate to a low concentration solution:

Example ii,

Chromic anhydride 5 g / l

Silica colloid (as SiO ₂ ) 2o g / l water remainder

Solution temperature 25 ° C

Dive duration 5 seconds

Example 2:

Chromic acid anhj ^ drid. . 5 g / l sucrose ^ 1 f / 1

Silica colloid (as SiO ₂ ) 20 g / l water solution, temperature 25 ° C

Diving daiiar 5 seconds

Bi® © fig solution is made by heating chromic anhydride. Sucrosey where diaselbess react with each other, and

ίθϊΜ @ia "galvanized Eiseablsch, that with the above solution ©! I & iiQelt is examined after the salt water spray o.ver3ueh / j.

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bath

There is no white rust formation 12o hours after the spray treatment. For comparison, a galvanized iron sheet that was made with pure chromic acid without added silica colloid was treated, tested in the same way, the formation of white rust began after 10 to 12 hours; after 24 hours 2o to 3o percent of the surface were covered with white rust.

In the case of the coated samples, the paint adherence decreased the Erichsen trial using a color from the Melamine alkyd resin series determined, which means for samples that were treated in a chromic acid bath with a silica colloid content, good paint adhesion was demonstrated. The tests showed that the requirements in terms of paint adhesion were completely met. "

The chromium fraction deposited is 0.2 mg / dm for Examples 1 and 2 and also 0.2 mg / dm for a treatment without it Silica collord additive.

The following description relates to the treatment with a high concentration solution. Metallic zinc, zinc alloys and galvanized steel sheets are, in a solution with a Chromic acid content of more than 18 g / l and a silica content treated by more than 50 g / l (as SiO «); Then it will be the excess solution standing on the surface for the purpose of uniform application of the solution to the surface underneath

squeezed off with rubber rollers at a pressure of about 0.52 kg / cm, whose hardness is between 40 ° and 60 °, measured with a spring hardness tester (Japanese industrial standard K.43o1) i then drying takes place without prior rinsing (preferably at a temperature between 70 ° C and 250 ° C for a period of less than 10 seconds). For even In addition to the squeeze rollers mentioned, methods such as spray treatment can also be used to apply the solution; particularly A spray treatment with a gas jet using a gas at a higher temperature is expedient; • -then the drying level can be shortened or omitted.

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Mr a hot dip of a galvanized sheet steel purpose Treatment according to the invention., The same can be used, the thickness of the coating layer adjusted with normal rollers is; but then the result is a particularly uniform one Thickness of the application layer when using the setting a gas jet "takes place. Hot-dipped, galvanized steel

Sheets and zinc electroplated steel sheets result in finished parts with good properties at a layer thickness of ρ * · ρ.

'about 10 mg / m to 70 mg / m (for Cr) on each side of the Surface when these steels continuously mil ;: a throughput speed from 15 to 150 m / min.

If, with the exclusive use of pure chromic acid, the concentration exceeds 15 g / l, the result is a total. gradual yellowing of the treated steel sheets. At the same time, there are uneven deposits of chromic acid, so-called chroic acid stains. When the chromic acid concentration reaches 18 g / l, the proportions become poor and there is a noticeable decrease in the appearance of the finished product. This phenomenon is evident with galvanized sheet metal as well as with zinc-plated steel sheets and cannot be prevented even if the squeezing with rollers is controlled in the course of the treatment; the type of rollers also has no influence. This phenomenon depends only on the chromic acid concentration. . ^: "-;:

There is consequently a limit to using pure chromic acid for the separated chromium content, which also has a limiting effect on the corrosion resistance of the product. If the deposited portion exceeds the limit value, the appearance of the product becomes uneven, which means the market value of the product is reduced.

The maximum proportion of chromium deposits during treatment with pure chromic acid solution is
one surface) for chrome metal.

2 with pure chromic acid solution is below 1 ο mg / m "(based on

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In contrast to this, the experiments with the solution of the chromic acid-silica colide series show that "at such a high chromic acid concentration of 15 g / l and even more of 18 g / l _f <where a pure chromic acid solution is no longer applicable,""■ the addition of silica colloid leads to a noticeable reduction in chromic acid stains and yellowing in comparison with pure odorous acid treatment, if the chromium concentration continues to rise, there is only a uniform color change on the entire surface of the treated object.

As a result, silica colloid is found to be effective for an even application of the treatment solution the surface, chromic acid is effective. for suppression the color change to yellow. ■ '

To increase the amount of chromium deposited to more than 1o mg / m - (based on a surface) must therefore be a solution _the choric acid-silica colloid series instead of a pure one Ohromic acid solution can be used. r.

The special effect of the silica colloid is that it is also effective in a comparatively small proportion and that the effect increases when the concentration ratio between chromic acid and silica colloid is less than 1/5 » in this case the yellow color will turn back into the interference ' coloring converted. - V

Based on the experiments with series of solutions of chromic acid-silica colloid In manufacturing plants it could be shown after the above that silica colloid causes a uniform application of the treatment solution and a discoloration of the treated object is eliminated. This makes it possible to have a high concentration of watchomic acid in the production of galvanized products Use steel sheets with a high sales value. .. '■

Further attempts concerned the structure of the chromic acid oil - ^ ' erjäekollaid-Bades when using solutions with higher

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; OhroiUBäurekonzentiation compared to Examples 1) and 2) .- Deibiai was again the far-reaching improvement of the situation the corrosion & resistance after further processing the fortunes confirmed. However, the processing affects

. outer _; This would change the corrosion resistance and the adhesive properties (even if these properties were much lower than before processing).

The use of high concentration chromic acid within the meaning of the invention with more than 20 g / l with a silica colloid additive to achieve a good appearance of the objects after further processing is, however, for the improvement of the corrosion resistance at a concentration ratio between chromic acid and Silica colloid less than 1: 5 very effective * It is desirable that acids (with. Phosphate urns and other * ions containing chloride ions), iia ions and individual amino groups should not be included in the silica colloid. For example, the Na content must be less than ö »o5 ^c ß> . The above concentration ratio of 1: 5 is important for improving the decolorization effect.

Even if the chromic acid concentration is increased, will a corresponding silica colloid addition enables the production of galvanized Ensure steel sheets, the appearance of which the commercial requirements as well as treated differently Substances met, namely a uniform yellow color, üie improved corrosion resistance remains even after further processing obtain.

An improvement results in ⁸ ^ Cn for the paint adhesion of the treated object after its further processing and for the corrosion resistance after the application of paint. The I-.eß-'values of such tests are given in Table 1. As can be seen from the fact .man needs at very high concentration of chromic acid is not "xn ice Konsentrationsverhältnis clipboard ^ chromic acid and Kieseleraekolloid νοϊχ 1 to haltsn s 3 when the corrosion resistance and the Furbhaftfähigkeit nacl ^ '

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Further processing should be retained. For example, if the chromic acid concentration is 35 g / l, 70 g / l "silica colloid will suffice in this case. However, if high treatment efficiency and good appearance of the treated objects are taken into account, a ratio is close to 1: 3 to be preferred_ -, _s

Examples of an optimal composition of the treatment solution are 20 g chromic acid and 60 g silica colloid; 35 Z chromic acid and 1 oo silica colloid. In order to increase the separated proportion of chromium, it is advisable to increase the concentrations of these substances with regard to the drying time, which should be as short as possible for a continuous process.

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Table 1) shows the tests with different galvanized -'- ■■ Steel sheets used in hot baths to improve corrosion resistance and paint adhesion after a Further processing as well as the corrosion resistance one application of paint ". In the columns of the table the following sizes are given:

Corrosion resistance test after further processing of the workpieces

Erichsen attempt

Column 1 salt water spray test Column 2 Wet container test · Skin peeling

Column 3 salt water spray test Column 4 wet container test Bending test

Column 5 Salt water spray test Paint adhesion test after skin detachment Column 6 Du Pont impact test Column 7 Treatment after the Irichsen test Corrosion resistance test after applying paint to the material (reinforcement of the paint layer) Column 8 salt water spray test

Column 9 wet container test *

The following applies in detail:

Skin detachment: about 15 1 ° reduction.

Bending test: 180 °

Erichsen test: less than 21 mm from the break of the sheet.

Paint application; about 2QyU, thick of color number 36 white polymeline_

(Trade name) of International Corporation. Salt water spray test: according to the Japanese. Germany t

Industry standard Z 2371 * ■

Humidity test: 49 ° G, relative humidity 100 ° C. ' Results: (?) Very good, O good, Δ bad, X very bad. . '

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The salt water spray test and the FeuchtbehalterVsreVe ^. warn] continuously for a period of 72 hours bsv? 1 rfoche |

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carried out, with the exception of those with the sign " X " and »· 'Δ>' *, which have not been treated for that long because rust began to form after just 24 hours. The character (S) indicates that even after the long-term test only an east formation from 0 to 5. $> occurred.

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Claims (6)

Claims o he; Process for the surface treatment of metals, thereby characterized in that the surface of a metal of the group of "ink and zinc alloys with a mixed solution Chromic acid and silica colloid is coated and that drying of the applied solution with formation a thin surface film takes place. 2. The method according to claim 1, characterized in that the Mixed solution with a chromic acid content of 1 g / l to 2o g / l * based on the chromium metal and a silica colloid content of 1 g / l to 70 g / l based on SiOp. 3. The method according to claim 2, characterized in that chromic acid more than 18 g / l, chromium and the Kieselerde- _u ^t colloid more than 5o g / l SiO ₉ contains. .. 4 «Method according to claim 2, characterized by a concentration ratio of chromic acid to silica ^ colloid in the mixed solution of 1: more than 3 « 5. The method according to any one of claims 1 to 4, characterized in that by a dip-spray or brush-on treatment for application des überzuijs. 6. The method according to any one of claims 1 to 5, characterized in, that the metal surface is the surface of zinc or a zinc alloy, with which · Merkstoff the surface of iron or steel "coated, or ■ 'is plated. '* 0 018 0 8 / 16A7 BATH ORIGINAL