DE2758628C3 - Coating process - Google Patents

Description

The invention relates to a coating method in which a self deposited coating is applied to a Metal surface by bringing this surface into contact with an acidic, self-precipitating one Is formed and the nature of this surface is such that from such a composition coatings formed have defects.

A relatively recent development in the field (of coatings is the provision of coating compositions water-based, which without the aid of electricity in the formation of organic Coatings are effective on metallic surfaces immersed therein, these Organic coatings increase in strength or weight the longer the surfaces are in the compositions be immersed. For the sake of simplicity, a coating composition is used (of this type hereinafter referred to as "self-precipitating composition" and a coating formed with the aid of a composition is used In the following referred to as "self-deposited coating". In general it can be said that in (These types of effective compositions include acidic, • aqueous coating solutions, the particles of a organic material such as resin particles dispersed therein. Even deposited coatings • ground from such compositions as a result here Ability formed to attack the metallic surface and from this metal ions in such quantities to dissolve, which cause the deposition of the particles on the surface in such a way that a continuous build-up of the organic coating takes place on the surface.

Over formed from such compositions

trains are completely different from coatings, which

conventional latices are formed, d. H. in compositions, which contain solid resin particles dispersed in water. The weight or the Thickness of one formed by dipping a metallic surface in a conventional latex Coating is not affected by the period of time for which the surface is immersed in the latex.

H) flows. You will mainly get through the crowd the resin solids dispersed in the aqueous medium.

Coatings made from self-depositing compositions are still entirely of

ij different coatings, those from previously known, acidic, aqueous coating solutions were formed, which dispersed, solid resin particles and relatively high amounts of water-soluble corrosion inhibitors such as compounds containing hexavalent chromium, contained. The use of relatively high levels of corrosion inhibitors in such solutions prevents the attack on the metallic surface to such an extent that over time increasing, resinous coatings cannot be obtained.

Thus, resinous coatings have been softened by immersing metallic surfaces in such compositions have the same properties as the coatings formed by immersion the metallic surfaces in conventional lati-

jo ces were formed, as they also increased with increasing Immersion time does not grow.

The use of self-precipitating compositions offers a number of advantages. For example can self-precipitating compositions, the relatively small amounts of coating-forming Contains solids for the application of relatively thick, organic coatings on metallic surfaces can be used in a relatively short period of time and in a one-step process. Farther

the coating thickness can be controlled by adjusting the immersion time of the metallic surface in the self-precipitating composition is varied. In addition, edges of the metallic base in a simple way with a cover

hen will. In general, coatings can be obtained which have good corrosion-resistant properties and have a good aesthetic appearance. Furthermore, such coatings can be used without application produced by electricity, as is the case with elec-

■ 50 dry coats required. These are just a few the benefits derived from the use of self-separation, d. H. the coating process, which involves the formation of self deposited coatings without the application of electricity.

Although self-depositing compositions are capable of producing organic coatings with excellent To train quality, it has been found that under certain conditions coatings with defects or errors are formed. Examples of such

Wed defects h / w errors are 1 hole, bubbles and / or Crater.

In some applications, such errors may be of little or no importance. However there are also applications where such

-s flawed coatings are not tolerated may or at least are undesirable. Such defects generally set the corrosion resistance properties the coverings down. When arriving

Twists in which these properties are essential

sina, if such coatings would be suitable for revenge. They would also not be suitable for applications in which the appearance of the coating smooths one out, shouldn't have interrupted film.

From the German Offenlegungsschrift 2621970 is a method of making self-deposited Compositions on surfaces by means of acidic coating compositions known such However, self-deposited coatings show defects such as holes, bubbles under certain conditions and / or scratches.

The object of the invention is the formation of such defects or errors in formed of a self-depositing composition coatings herabzu- ^| put ^r> or prevent.

The method according to the invention, which is characterized in that, serves to solve this problem the metal surface with an acidic material prior to contact with that forming the coating Composition is treated.

The acid pretreatment of the substrate or the base according to the invention in applications in which a self-precipitating composition for the formation of defects such as bubbles, craters 2ΐ and / or holes prone to coatings, has in reducing or preventing such Error found to be effective.

The acid pretreatment of the substrate or the base according to the invention can be carried out in a suitable μ manner in such a way that the substrate or the base is exposed to an aqueous solution of the acid.

A variety of acids or mixtures of acids can be used in the pretreatment step will. The use of phosphoric acid is particularly preferred.

It should be noted that acid pretreatment of metal surfaces has long been used is used to remove metal surfaces from undesirable materials such as carbonaceous deposits and metal oxides, e.g. B. scale and rust, to be cleaned before the surface coating compositions get abandoned. Errors of the aforementioned type occurred in self-deposited Coatings formed on clean metal surfaces initially not containing such materials were, d. H. on surfaces that do not normally undergo acid cleaning pretreatment were subjected. This is shown in more detail using the following examples.

As can be seen from the following examples, there are applications of the self-separation method, in which flawless coatings are formed. However, under certain conditions even deposited coatings formed which have defects.

One of the factors involved in the formation of defective coatings depends on this Type of metal surface to be treated from Coating defects occurred when metal surfaces were coated that had been processed, e.g. B. a molding process, punching, bending, drawing, Sheared or subjected to similar operations. Processing the metal surface generally causes compressive and tensile stresses in the metal and can scratch and surface defects (Nicks) or fretting of the surface. The more the surface is processed became, the greater the tendency that the coatings formed thereon have defects. In general the defects are limited to the areas of the coating over the machined areas or Sections of the metal surface lies. For example, in an application that only works in a section of the metal surface suffered from pressure seizure as a result of a punching operation, the defects were observed only in these sections of the coating caused by the seizure above it There were notches, otherwise the coating was free from defects.

Defects in self-deposited coatings were also encountered when coating metal surfaces, which were in a roughened state for reasons other than machining. Objects produced by casting processes often have roughened surfaces as a result of the rough surfaces of the walls of the mold in which the article was made.

Defects in self-deposited coatings produced on metal surfaces of the type previously described may have different forms depending on the particular one that is occurring here Accept application. For example, the defects can appear as holes, bubbles and / or craters in the coating appear. The term "crater" used here refers to an error that looks like a collapsed bubble. In some applications, errors are due to the damp, non-melted or not baked-on coating not detectable, but they do appear, after the coating has been baked by treatment at an elevated temperature. In other applications, the moist coating can have bubbles that lead to holes (small holes similar to pores) are converted during the baking of the coating at elevated temperatures, or the vesicles may remain in the coating after baking. For other applications as well such pinholes were observed in the moist, unbaked coating.

Steps used in the process of self-deposition of coatings often include rinsing steps moist, self-deposited coating after the metal object with the self-deposited Composition was brought into contact. For example, a moist or partially dried Coating of a spool with water and / or contact with an aqueous, chromium-containing solution for the purpose of improving the corrosion resistance properties of the coating. In some applications this problem is so severe that the portions of the coating which are above the sections of the metal surface leading to the aforementioned type of defects, lift off on contact with the liquid composition, d. H. Parts of the coating removed during rinsing treatment. In such cases, the error occurs as a non-exaggerated section the metal surface in appearance

There are a number of factors which play a role in whether or not to fail in self-deposited Coatings may or may not be encountered and, if encountered, the extent or strength of theirs Affect occurrence. As can be seen from the following examples, there are applications in which

errors occur in the use of a particular type of self-precipitating composition, while they do not occur when another type of self-precipitating composition is applied will. The temperature of the self-precipitating composition can also play a role play here, in general, the higher the tendency for errors to occur, the greater the The temperature of the composition is. The thickness of the coating can also have an influence on the The greater the thickness of the coating, the lower the probability of defects occurring. The coating thickness can in turn depend on various factors such as e.g. B. the time of contact the metal surface with the self-depositing composition, the content of the coating forming it Solids in the self-precipitating composition and the temperature of the self-precipitating Composition.

In any particular application involving the plating of metal surfaces as previously described Type relates and where coating defects of the type specified above occur, the inventive Acid pretreatment of the surface can be applied to prevent the formation of such defects to prevent or inhibit. From the following examples it can be seen that a wide variety of Acids including organic and inorganic acids can be applied. Also is the application of mixtures of acids possible. The entirety of the metal surface or just cie sections the surface, which give rise to the problem with the errors, can or can with the Acid pretreatment material are brought into contact. Although the contact of the metal surface can be achieved in various ways with an acidic material, it has been found to be advantageous bringing the surface into contact with an aqueous solution of the acid.

There are numerous factors to consider in determining the effective acid concentration of the pretreatment solution play a role. Such factors include the strength of the particular, applied Acid, the temperature of the pretreatment solution, the contact time between the solution and the metal surface and the type of metal surface to be treated. With regard to the numerous, here However, factors that play a role should be pointed out to the fact that experience or simple preliminary tests in a particular application sufficient to achieve the optimum acid concentration and the treatment conditions to be determined. In general, the lower the application temperatures and the shorter the contact times, the higher is the acid concentration of the solution. In the same way, less concentrated acid solutions can be used can be used at higher application temperatures and longer contact times.

As a general guideline, it is recommended that an acid pretreatment solution be used, which contains at least 0.1% by volume of acid, and that the temperature of the solution is half of the range of 18.3 ° C to 93.3 ° C and that the contact time between the solution and the metal surface is 30 seconds to 3 minutes.

Advantageous results have been achieved with solutions which contain no more than 5% by volume of acid. In some cases where the problem is severe and / or where temperatures are relatively low and

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Volume% acid containing solution may be required. However, the acid concentration should not be that high lie that the metal surface is attacked in a disadvantageous manner.

Phosphoric acid is particularly useful for use in carrying out the process of the invention preferred. Phosphoric acid is relatively safe in the

ίο Handling, emits and brings relatively little fumes no particular problems in wastewater treatment with them. If some phosphate ions happen to be are carried over into the autodeposition bath, their presence therein is also relatively innocuous.

When using phosphoric acid, it is recommended that the treatment conditions include the Verwendung'einer aqueous solution .-% phosphoric acid at a temperature of 51.7 ⁰ C to 71.1 ° C for a contact time of I which 1 to 5 by volume to Include 2 minutes.

An optional ingredient that can be used in the acidic solution is a surfactant Middle. Any suitable surfactant that improves wetting of the Metal surface of the solution supported can be used. The surfactant can be used in relatively small amounts, e.g. B. 0.001 to 1 vol. % of the solution.

jo The pre-treatment of the metal surface can also help to reduce the inclination of the coatings be effective for bridging. Bridging occurs in coatings that are on objects are formed which are not in the same plane, but intersecting surfaces and it occurs at the cutting line. The bridging can be seen when the Coating from the underlying, metallic surface at this cutting line.

AO coating compositions that are effective in producing self-deposited coatings are known per se. Examples of such coating compositions are described in U.S. Patents 3585084, 3592699, 3709743 and 3,776,848, British Patent 1,241,991, South African Patent 72/1146 and Belgian Patent (additional) 811841.

In general it can be said that the acidic,

Aqueous coating compositions of the aforesaid type act to bring them into contact therewith Attack brought metallic surface and dissolve from it metal ions in sufficient quantity to directly or indirectly the deposition of organic particles in the area of the metallic surface then to evoke in a continuous manner, d. H. in such a way that a build-up of the amount of organic, material deposited on the surface ■ occurs, the longer the surface with the

ho setting is in contact. This deposit of the organic Material on the metallic surface is made by chemical action of the coating composition reached on the metallic surface. The use of electricity that would otherwise

some coating methods such as the electro-coating method is required, is not necessary in this case.

It is understood that the inventive method

most commonly used in conjunction with coatings made from self-depositing compositions were formed, which solid particles of resin, dispersed in a dissolved fluoride and trivalent iron containing aqueous solution are dispersed, see e.g. B. South African patent specification 72/1146. Preferably the aqueous phase of the coating composition contains a surfactant Agent in an amount below the critical micelle concentration (hereinafter referred to as "CMC" denotes) and particularly preferably the concentration of the surface-active agent is in aqueous phase of the composition below the surfactant concentration, which the inflection point on a graph of surface tension versus logarithm of concentration of surfactant in composition. Preferably contains the Composition an anionic, surface-active

g, g ccinates, e.g. B. sodium oleoyl isopr

ves agent, and the source of the resin dispersion of the additive 20 amide sulfosuccinate, or a mixture thereof,
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Acrylic acid, cinnamic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid.

The resin is most suitably used ^r in the form of a latex> which can be prepared according to known procedures.

A particularly preferred latex contains resin particles made from the aforementioned monomers, the particles being chemically and physically homogeneous. The resin particles of the preferred latex are made from styrene, butadiene, vinylidene chloride and methacrylic acid. Furthermore, the emulsifier or surfactant content of the preferred latex is about 1 to about AVt, based on resin solids , and comprises at least 90% by weight and particularly preferably H) U% by weight of an anionic emulsifier such as a sulfonate, ζ. Β. Sodium dodecylbenzenesulfonate or a sulfosuccinate, e.g. B. Sodium oleoylisopropanol

composition is a latex which contains surfactant in an amount such that the aqueous phase of a self-precipitating composition formulated from the latex has a concentration of surfactant below 2-1 the χ CMC «and preferably below the inflection point concentration of the surfactant.

A preferred composition for use in the method according to the invention is disclosed in jo DE-OS 2612995 described, to which reference is hereby made. The preferred composition has a surfactant concentration as described above particularly preferred, self-precipitating composition has a concentration of surfactant as described above and a pH in the range from about 2 to about 3.2 and comprises from about 50 to about 125 grams per liter of resin solids, ferric fluoride in an amount equivalent to about 0.5 to about 2 g / l of trivalent iron, and about 0.7 to about 3 e / l of HF.

With regard to the cause of coating defects in self-deposited coatings, it is assumed that that the portions of a metal surface that have been machined against the coating composition are more sensitive than sections where

Exercise and a pH of about 1.6 to about 4.35 no processing was carried out. Differently

and it is pressed out of water, an iron (III) -containing one, it is believed that the worked

Compound, particularly preferably iron (III) fluoride, - - in such an amount that it is the equivalent of

about 0.5 to about 3.5 g / l of trivalent iron makes sections or parts of the surface more reactive and are more easily attacked by the coating composition with the result

holds, about 0.2 to about 5 g / l of HF, optionally 40 that hydrogen ions to what one in these sections Pigment such as carbon black and about 50 to 125 g / l of hydrogen are reduced in greater amounts than this Resin particles produced with these resin particles in other, less reactive portions of the practically all are of the same size and have practically a surface area. It is believed to be overchemical are homogeneous, d. H. Each particle is made up of excessive amounts of hydrogen as well from the same monomeric ingredients that are used in 45 when roughened surfaces of the previously impractical the same proportions are present or given type are coated and also if composed of resin particles formed by copolymerization of the fol surfaces of the type that give rise to bridging defects The following monomers were produced: lead, be coated.

1. about 25 to about 70 and preferably about 40 In difficult applications that require the over bis about 65% by weight of a conjugated diene 50 pulls from machined or roughened surfaces z. B. 4 to about 9 carbon atoms such as beeches, in which relatively high amounts of hydrogen tariien "of the Isonren; "~" -

2. about 5 to about 70 and preferably about 30 to about 65 wt .-% CH ₂ = CHR, where R is an aryl radical or a cyano group, z. B. styrene or acrylonitrile;

3. from about 1 to about 50, and preferably from about 3 to about 15 weight percent of a vinyl halide such as vinyl chloride or vinylidene chloride; and

05 bi

are defects such as small holes or pores in the moist or not baked-in Cover visible. In less difficult applications it appears that the hydrogen remains trapped beneath or within the coating until the coating cures or is fired at a higher temperature, in which case the hydrogen expands. In dependence of

y;

4. about 0.5 to about 15 and preferably about 1 ω different factors, the hydrogen can be the BiI-bi 4 G% i h

up to about 4% by weight of a monoethylene type unsaturated one Monomers with a functional group in the form of amide or carboxyl groups, z. B. acrylamide, methacrylamide, octylic acid maleate and monoethylene-like unsaturated Monocarboxylic and dicarboxylic acids having from about 3 to about 12 carbon atoms and preferably about 3 to about 5 carbon atoms such as e.g. B.

cause small holes or pores, bubbles or craters in the coating.

It is believed that the acid pre-treats the surface of the relatively reactive portions the surface deactivated, so that in this way the production of excess hydrogen is inhibited or prevented, which in turn leads to the formation of coatings of improved quality.

As previously described, one of those playing a role in the development of coating defects is Factors the temperature at which the self-precipitating composition with the metal surface is brought into contact. In this context it should be noted that self-precipitating Compositions for forming coatings on metal surfaces in a wide range of temperatures effective including temperatures which are close to the boiling point of the composition approach, and temperatures approaching those at which the disperse, organic, the coating forming particles are undesirably coagulated. There are advantages to working at elevated levels Temperatures. In general it can be said that the thickness of the coating is the greater, the higher the temperature of the composition. Therefore, at higher temperatures it is necessary to train the time required for coatings of a given thickness is shorter. On the other hand, the Use of higher temperatures usually leads to a deteriorated condition the plating failure when plating metal surfaces of the type which have this problem Role play. One of the advantages of the process of the present invention is that the coating composition can be used effectively at a temperature which would otherwise be avoided because when using such a temperature in the absence of acid pretreatment normally Plating defects would be formed.

Although the coating composition is in contact with the metal surface in various ways brought 'verden, including z. B. Spraying or flow coating, it is believed that the most common contact method is to immerse the metal surface in the coating composition at about room temperature. As previously described, the structure is the coating thickness the longer the metal surface is immersed in the coating composition, the greater. It will believed that in most applications the desired coating thickness could be obtained by dipping the Metal surface in the composition for a period of time within the range of about 30 seconds until about 3 minutes can be reached. However, it should be noted that longer or shorter Time periods can also be used.

Stirring the composition helps maintain their uniformity. There is also a holding in motion or stirring the composition for improvement

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rials on the metal surface are adversely affected during the plating step. Generally it can be said become that coatings with improved quality can certainly be obtained, the purer the Surface is. Excellent results can be safely achieved by removing the metal surface is subjected to a cleaning process which results in a surface on which there is no water break comprising film can be formed. The choice of detergent and the type of Application of this to the metal surface depend on the type of material present on the metal surface Foreign materials. Available cleaning agents can according to the known technology be used. Therefore, depending on the type of dirt or the present Foreign materials, acidic, alkaline or other cleaning agents are used. For example Diluted phosphoric acid can be used to clean rusted parts, and it can hot, alkaline compositions for removing oils. Fats, fingerprints and other organic Deposits are used.

The type of deposits on the metal surface can be such that the acid pretreatment according to Invention for their removal is not effective. In either case, it is preferred that the metal surface is clean when it is subjected to the acid pretreatment according to the invention.

After contact with the self-tapping composition, the coated metal surface can further processing stages, as they are known per se, are subjected. Such stages are briefly explained below.

Rinsing the coated surface with water after removing it from the composition and before any significant drying occurs, is to remove residues such as acids or other ingredients in the bath that adhere to the coated surface. If such Any residue left on the coated surface can affect the quality of the coating change or affect negatively. An investigation can be made for a specific application whether residues have negative influences that cannot be tolerated. If this is the If so, they should be removed, e.g. B. by rinsing with water either using tap water or using deionized water.

If this is not the case, this removal step can be omitted.

If this is desired, the properties

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effective.

Various factors should be considered in determining whether to clean the metal surface or should not be cleaned, and the amount of cleaning prior to contact with the self-precipitating composition including e.g. B. the type of possibly on the Foreign materials present on the surface and the desired quality of the coating. Foreign materials, present on the metal surface can lead to the formation of non-uniform coatings. Furthermore, the adhesive properties and the properties of corrosion resistance can be resinous or plastic-like coatings in a negative manner as a result of the presence of the foreign matter surface can still be improved by the fact that the coated surface with an acidic, aqueous Rinsing solution is brought into contact, which contains hexavalent chromium. Such rinsing solutions can come from Chromium trioxide or a water soluble dichromate or chromate salt, e.g. B. ammonium, sodium and Potassium salts. A Chromium composition can be used, which by treatment of a concentrated, aqueous Solution of chromic acid with formaldehyde to reduce part of the hexavalent chromium became. This type of rinse composition, described in U.S. Patent 3,063,877, contains Chromium in the hexavalent state and reduced chromium in aqueous solution. Furthermore, it was stated

ben that the resistance of a stoved or melted, resinous coating to a Spray treatment with water and salt can be improved in that the non-baked or unfused coating with a solution, preferably an aqueous solution, of phosphoric acid See U.S. Patent 3,647,567. The recommended amount of phosphoric acid in the solution is from about 0.25 to about 7% by weight based on the total weight of the solution.

Following any rinsing stages that occur after the coated surface has been removed from the Composition applied, the coating should be dried. Melting down or baking of the resinous coating converts it into a continuous coating, whereby its Corrosion resistance and its adhesion to the underlying metal surface can be improved.

The conditions under which the drying and / or firing or melting process is carried out depends to some extent on the type of resin used. In general, heat is for Melting of the coating required. The corrosion resistance properties of at increased Temperature fired coatings have been found to be better than those of coatings \ 3which have been air dried. However, there are applications in which air dried coatings are used satisfactorily can. The melting of the coating should be carried out below temperatures, which cause the degradation or destruction of the resinous coating. Exemplary conditions used in the Melting or baking of coatings produced according to the invention are used Temperatures within the range of about 100 ° C to about 200 ° C for times within of the range from about 10 to about 30 minutes, wherein this depends on the mass of the coated part. Baking in the coating for such a period of time until the metal surface has reached the temperature of the heated environment, has been advantageous applied.

The invention is explained in more detail by means of the following examples and comparative examples.

Examples 1 and 2,
Comparative Examples CI to C-8

The first group of examples shows the acid pretreatment of metal articles according to the Lnindur. "Iiv.a the application thereof on seihst deposited coatings. For comparison purposes, this group of examples also shows the pretreatment of metal objects with alkaline cleaning materials.

Each of the items used in this group of examples were made from hot rolled steel sheet, which had been cup deep drawn by pressing. The items had feet marks along the connection of the deep-drawn sections and the lip sections on the convex side of the Objects on. The items were soiled with molding oil and workshop grime, but they were not rusted dirt this ax would generally be cleaned by cleaning the objects with alkaline Cleaning solutions are removed.

Acid pretreatment solutions were prepared from the following composition:

Composition A

Components Amount (wt .-%) Phosphoric acid (75% by weight) 33.5 Ethylene glycol butyl ether (Butyl cellosolve) 7.9 Nonylphenol ethoxylate 0.5 Sodium alkylbenzenesulfonate 0.3 Oleyl alcohol (technical quality) 0.1 water 57.7

The pre-treatment solutions and the applied terms of the order are in the following Table 1 compiled.

20th E.g. Pretreatment Amount of Order lung Pretreatment conditions material lung material in the water ⁷ ) rigen before treatment solution 1 Together 1 part by volume 3 min a setting A on 2 VoI.- dive into JO (as stated) Share water 43.3 ° C 2 Pretreatment 3 min a solution dive into of example 1 43.3 ° C + 2.5 vol .-% 35 21 weight percent HR C-I strong alka 15 g / l 3 min lischer spray hen at cleaner ¹ '' 7i, rc 40 C-2 Pretreatment 3 min Be solution spray at from Ex. C-I 71, TC plus 1% by volume one wäßri • Γ) gene solution from 3S weight percent NH, C-3 chlorinated. 15 g / l 3 min Be Ϊ0 more alkaline spray at Cleaner ^{1: i} 71.1 ° C C-4 oxidized. 15 g / l 3 min Be aikai spray at Cleanser"' 71.1 ° C 55 C-5 strong alka 44.9 g / l 5 min a lic diving dive into cleaner ¹ "" S7, S ° C C-6 Pretreatment 3 min a solution dive into 60 of Ex. C-5 71.1 ° C plus 1 wt .- <% Sodium- alpha- glucohepto- 65 nat C-7 Pretreatment 3 min a solution dive into of Ex. C-5 71.1 ° C

- "ι

E.g. Pretreatment Amount of Order lung Pretreatment conditions material lung material in the water rigen before treat solution plus 1% by volume Chelate cleanser from the ethylene diamine tetra acetic acid- type for iron C-8 more caustic 12Og-! Immersion Rust removal from at 87.8 "C vjiiiconst " (Time not type ' ^M written down)

II)

⁽ "Commercially available product in the form of a powder mixture of caustic soda, soda, sodium orthosilicate and surface-active agent (phosphate-free) ⁽²¹ Powder cleaner, commercially available product
⁽ "Powder cleaner containing sodium perborate

⁽⁴⁾ Sodium tripolyphosphate powder mixture. Caustic soda, sodium gluconate and wetting agents

⁽⁵⁾ Commercially available powder cleaner

The articles treated with the acid pretreatment solutions of Examples 1 and 2 became first with the alkaline cleaning solution of Example C-5 by dipping the objects in the cleaning solution cleaned for 5 minutes at a temperature of 71.1 ° C. The cleaned items were then rinsed with tap water and then exposed to the solutions of Examples 1 and 2.

After the articles have been exposed to the pretreatment solutions given in Table I. were, they were immersed in tap water kept in motion for about 30 seconds rinsed and then further rinsed with an atomized jet of deionized water for 5 seconds. Thereafter the articles were coated by immersing them in a 3000 liter bath for about 90 seconds stirred, self-precipitating composition containing per 1: 4S

About 54% solids latex 180 g

Iron (III) fluoride 3 g

Hydrofluoric acid 2.1 g

Carbon black pigment dispersion 5 g

Water on 1 1 so

The resin or plastic of the latex used in this composition contained about 62% ot.yröi, Ctw * a _> w 'rc uutailiCn, £ tw ~ a D / c. ν ϊΠγ'ιϊιιβΠΟιιΐο- rid and about 3% methacrylic acid. A film formed from the resin is soluble in refluxing chlorobenzene in an amount of about 13%. The crosslinking of the resin is shown by its insolubility in the Soxhlet extraction with chlorobenzene. The water-soluble portion of the latex is about 2%, based on the weight of the dried resin, the water-soluble portion making up about 10% sodium phosphate, about 13% sodium oleylisopropanolamide sulfosuccinate and about 75% sodium dodecylbenzenesulfonate, the first component being a buffering agent is used in the manufacture of the latex, and the latter two ingredients are emulsifiers. The pH of the latex was about 7.8 and the interfacial tension thereof was about 45-50 niN / m. The average particle size of the resin was about 200 nm.

The carbon black pigment dispersion used in this composition was an aqueous dispersion with a total solids content of about 36%. The carbon black made up about 30% of the dispersion. She owned one pH around 10-11.5 and a specific gravity of about 1.17. The dispersion contains a nonionic dispersant for the solids and is a commercially available product.

After the resin-coated articles were removed from the self-depositing composition, they were air-dried for about 1 minute, immersed in tap water for about 30 seconds, and then immersed in an aqueous chromium-containing solution for about 30 seconds. The chromium-containing solution was an aqueous solution containing 0.1% by volume of an aqueous solution of a surfactant, namely an aqueous solution of octylphenol ethoxylate and 3% by volume of an aqueous, chromium-containing concentrate containing about 8.6% by weight of Cr (X, containing about 8.6% by weight of formaldehyde-reduced CrO ₁ and about 3.9% by weight of phosphoric acid. After rinsing with the chromium solution, the objects were placed in a forced-air oven at a temperature of about 135% ° C for about 20 minutes to fuse the resin coating.

Upon removal from the oven, inspection of the coated articles showed that the Coatings of the articles pretreated with the solution of Examples C-I to C-8 were hundreds of small Had holes which extended through the coating to the underlying metal surface. The holes or pores were arranged in those sections of the coatings, which over the food marks were on the objects. On the other hand, the covers of the objects had which had been treated according to the invention (pretreatment solutions of Examples 1 and 2), only a few Pores that lay in some of the portions of the coatings located over the seizure marks was. Thus, pretreatment of articles in accordance with the invention resulted in a great improvement to prevent the formation of pores.

Unless otherwise specified, various steps were used in these examples also used in the following examples, i. H. in the following examples the the same rinsing stages with water after the alkaline cleaning, the same rinsing stages with Wassci nii connection to the purification πίϊΐ acid, the same self-precipitating composition and the same conditions of use, the same conditions when drying in air and the same stages of rinsing with water and with chromium-containing Solution following the self-deposition and the same stoving conditions applied in all For example, the self-depositing compositions were at a temperature in the range of about 22.2 ° C to about 23.9 ° C.

Examples 3 to 5

The following group of examples (Examples 3, 4 and 5) shows the results obtained with the alkaline Cleaning of metal surfaces with either upstream or downstream acid pre-

action, the results obtained only with an acid pretreatment. In this group of Examples was the following acid pretreatment ■ solution used:

Pretreatment Solution A

H ₃ PO ₄ (85% by weight)
HF (21% by weight)
Nonylphenol ethoxylate
Antifoam agents

5.0% by volume 2.5% by volume 1.0% by volume 1.0% by volume

The metal objects used in Examples 3, 4 and 5 were of the same type as those in FIG the previous examples were used.

Example 3

The article was cleaned by immersing it in an alkaline cleaning solution similar to that of Example C-5 in Table I above was the same while cleaning 71.1 ° C for 5 minutes. Of the The cleaned item was then cleaned with the aforementioned acid pretreatment solution A at 71.1 ° C sprayed for 3 minutes. The inspection of the object provided with the self-deposited coating after the baking steps showed that the coating contained no pores or holes.

Example 4

The article was treated with the aforementioned acid pretreatment solution A for 3 minutes 71.1 ° C sprayed and then the described in Example 3, subjected to alkaline cleaning. The examination of the self-deposited coating The article after the baking step showed that the coating had no small holes or pores exhibited.

Example 5

The article was treated with the aforementioned acid pretreatment solution A for 3 minutes Sprayed 71.1 ° C. The inspection of the object provided with the self-deposited coating after the baking step showed that although the coating contained some pores, the number of pores was far lower than was obtained when the acid pretreatment was not carried out.

Examples 6 to 12

The next group of examples includes the acid pretreatment of articles in the previous examples for different periods of time and shows the here achieved results. Each of the items used in this series of investigations became Start cleaned by soaking the object for 5 minutes in an alkaline cleaning solution, this cleaning solution having been prepared as described in Example C-5 of Table I. and had a temperature of 71.1 ° C. In the following Table II are the acid pretreatment solutions used and the immersion times of the objects in the solutions are compiled. Each of the solutions was at a temperature of Maintained 71.1 ° C.

Tables

Acid pretreatment solution H ₃ PO ₄ , limit HF, one results

E.g.

8th?
Weight

(Vol.

flat 21

area weight

active% ig

Mean =

(VoI.-

(VoI .-%)

diving

Time

(min)

6 5

7 5

8 5

9 5

10 10

11 1

12 1

0.1
0.1
0.1
0.1
0.1
0.1
0.1

1 1

1 2

1 3

no 3

no 1

no 1

1 1

Holes or pores

no holes or pores no holes or pores no holes or pores Holes or pores

Holes or pores

Holes or pores

^s Agent containing octylphenol ethoxylate

For the aforementioned Examples 6, 10, 11 and 12, it was also observed that the resinous

Coatings also lifted off in addition to the holes or pores, d. H. those lying above the eating marks Sections of the coatings were so loose that pieces of the coatings fell off the articles when the objects to the stages of rinsing with water

J5 and chromium-containing solution, which are im Following the removal of the articles from the self-depositing composition carried out became. The results of the examples in Table II show that the length of time for which

the object exposed to the acid pretreatment solution can affect the results obtained.

Examples 13-18

The next group of examples includes the corrosion resistance ratings of on Self-deposited coatings applied to underlays, some of which are pretreated with acid and others have not been pretreated. The supports used were cold rolled steel sheets (unpolished Q-plates) that were free from rolling marks and other defects, which in general for the formation of holes or pores in themselves

lead deposited coatings. The panels were first immersed by immersing them for 2 minutes Purified in an aqueous, alkaline cleaning solution at a temperature of 65.6 ° C, the Solution 30 g / l of the alkaline immersion cleaner of Example C-5 of the aforementioned Table I contained. the Acid pretreatment solutions used had a temperature of 71.1 ° C and consisted of one acidic, aqueous solution containing 5% by volume of phosphoric acid (85% by weight) and 0.17% by volume of an octylphenol ethoxylate containing surfactant. The one used, self-precipitating Composition corresponded to the composition previously described in the examples with the

130 217/244

E.g. Immersion Immersion Salt spray test time in time in ASTM standard Acid pre self B-IΠ 5% at treat outgoing 35 ° C, 336 h solution Together Grid surface (min) settlement cut (min)

0 2 3 0 2 3

6.3
7.3
7.0
7.8
8.0
7.1

5.0
6.3
5.3
7.6

2.3 *
8.3

* This rating is considered abnormal and cannot be explained. The reviews for the three sheets were 0, 0 and 7.

From the results in Table III it can be seen that the acid pretreatment generally improves the properties did not adversely affect the corrosion resistance of the coated sheets. Indeed In most cases, improvements in corrosion resistance were achieved.

Examples 19 to 24

The next series of examples shows how scratch marks on metal surfaces promote the formation of small holes or pores in self-deposited coatings. Cold-rolled steel sheets (non-polished Q-sheets) and hot-rolled steel sheets were scribed by grinding them with a belt sander provided with an emery paper 60. The scratched metal sheets were cleaned by immersing them for 1 to 5 minutes in an alkaline cleaning solution at a temperature of 71.1 ° C. which contained M) g / l of an alkaline, commercially available cleaning agent. The sheets were then acid pretreated by immersing them for 3 minutes in an aqueous, acidic pretreatment solution at a temperature of 71.1 ° C, which 5 vol .-% H ₃ PO ₄ (85 wt .-%) and 0.1 % By volume of a surfactant containing octylphenol ethoxylate. The scratched sheets were then immersed for 90 seconds in an autodeposition composition which corresponded to the composition described in connection with Examples 1 and 2. The coated sheets would be

Assume that the concentrations of the latex and FeF _{3 are} about 150 g / L and about 2.2 g / L, respectively. The resinous coatings were melted by placing the coated articles in an oven at a temperature of about 140 ° C for 10 minutes. The immersion times for the panels in the acid pretreatment solutions and in the composition for the self deposited coating are given in Table III below. For each example, three panels were subjected to the process steps indicated above and then the salt spray tests indicated in Table III were carried out on them. The corrosion resistance ratings reported in Table III are the average of the three values obtained. The ratings were made on an arbitrary scale from 0 to 10, with the designation "10" meaning a perfect coating.

Table III

subjected to a different type of rinsing with an aqueous chromium solution than was previously described, namely with a solution which contained 3% by volume of an aqueous, chromium-containing concentrate which contained 150 g / l Na ₂ Cr ₂ O ₇ .2H ₂ O and a mixture of Cr ^{+ 6} with formaldehyde-reduced Cr in such an amount that the total Cr concentration of the mixture in the concentrate was 50 g / l at about 50% by weight of the Cr in reduced form, and 25 g / l contained 75% strength by weight H ₃ PO ₄ . The coatings on the cold-rolled steel sheets and those on the hot-rolled steel sheets were baked in an oven at a temperature of 71.1 ° C for 15 and 20 minutes, respectively. For comparison purposes, the

the same process steps as described above, used in the treatment of other sheets with the exception that some of the sheets are not ground had been pretreated with acid and other sheets were ground, but

had not been pretreated with acid. The results of these tests are shown in Table IV below compiled.

Table IV

E.g. sheet type

acid holes or created pores
fen handy.

no

no
no

19 cold rolled
20 cold rolled

21 cold rolled yes yes
hot rolled no no
hot rolled yes

24 hot rolled yes

no
Yes

no

many

no

in traces

moderate

in traces

In addition to Table IV, it should also be added that when pores appeared in the coatings that had been deposited, these occurred in the sections of the coatings which lay over the scratched areas of the Aa sheets. From Table IV it can be seen how incised areas result in the formation of the pinholes or pores and how effective the invention is in eliminating or preventing the formation of such coating defects.

Example 25 and 26

Previously it was stated that there are various factors that play a role in the development or Failure to develop errors in self-separated

coatings and that the specific type of self-depositing composition used Can be a factor. The next group of examples shows this in the formation of error-free Coatings made from a specific type of self-adhesive

T, outgoing composition. In these examples was the same type of scored metal sheet and the same process steps as previously related with Examples 19 to 24 were described, with the exception that the BIe

bo before in the self-precipitating described below Composition was immersed for 3 minutes, plus the one minute air drying step between the removal of the sheets from the self-precipitating composition

(, 5 and their rinsing with tap water omitted became. A batch of 4 liters of the self-depositing composition of the same type of latex was used and the same carbon black pigment dispersion produced,

as it is in the self-separating composition, e.g. sheet metal type

of the previous examples were used.

This composition contained per liter:

Latex 180 g

H ₂ O ₂ (35% strength by weight) 6 ml

HUF (21% by weight) 10 ml

Carbon black pigment dispersion 5 g.

Example 25

A self-deposited coating formed from this composition on a sanded, hot-rolled steel sheet that had not been pretreated with acid had no pores.

Example 26

A self deposited coating formed from this composition on a cold rolled one Steel sheet that had not been pretreated with acid had no pores.

aqueous acid pretreatment solution

Pores

20th

Examples 27 to 40

The next group of examples shows the use of a variety of acidic compositions for the acid pretreatment of metal surfaces according to the invention. In this group of examples became the same type of ground, cold-rolled steel sheets and ground, hot-rolled Steel sheets and the same process steps as previously described in connection with Examples 19 to 24, applied. The special, aqueous, acidic pretreatment solutions used are in the Table V compiled below. In addition to the ingredients listed in Table V below Solutions contained all solutions except the acetic acid solution and the monosodium phosphate solution 0.1% by volume of a surfactant. The sheets were used in the solutions for Immersed for 3 minutes at a temperature of 71.1 ° C.

Table V

E.g. sheet metal type

aqueous acid pretreatment solution

Pores

27 cold-rolled 50 ml / 1 98% by weight none

H ₂ SO ₄

28 hot-rolled 50 ml / 1 98% by weight none

H ₂ SO ₄

29 cold rolled 50 ml / 1

30 hot rolled 50 ml / 1

31 cold rolled 50 ml / 1

32 hot rolled 50 ml / 1

33 cold rolled 50 ml / 1

34 hot rolled 50 ml / 1

35 cold rolled 50 g / l

36 hot rolled 50 g / l

37 cold rolled 50 g / l

38 hot rolled 50 g / l

39 cold rolled 25 g / l

40 hot rolled 25 g / l

37 wt% HCl

37 wt% HCl

49 wt% HF

49 wt% HF

99% by weight acetic acid 99% by weight acetic acid Citric acid monohydrate Citric acid monohydrate Oxalic acid dihydrate Oxalic acid dihydrate NaH ₂ PO ₄ -H ₂ O NaP ₂ PO ₄ -H ₂ O

no

no

no

no

no

none ⁽¹⁾

no

no

no

no

no trace of ' ^1Y

^(I) some craters

The examples in Table V show the effectiveness of various types of acidic materials, including inorganic and organic acidic compounds in the acid pretreatment process according to the invention. It should be noted that the aforementioned acids are only examples and that other acids can also be used. Examples of other acidic compounds that can be used in the process include tartaric acid, sulfamic acid, sodium bisulfate and nitric acid.

In addition to the pretreatment of ferrous surfaces of the type specified above, that is according to the invention Process also applicable to other metal surfaces including e.g. B. zinc and Aluminum.

Overall, it can be stated that the present invention provides an effective way to achieve the To improve the quality of self-deposited coatings, as demonstrated by the numerous examples was shown.

Claims (4)

uuuc 1. Coating process in which a self-deposited coating is applied to a metal surface by contacting this surface with an acidic, self-precipitating composition is formed and the nature of this surface is such that from such a composition formed coatings have defects, characterized in that the metal surface treated with an acidic material prior to contacting the composition will. 2. The method according to claim 1, characterized in that an aqueous material is used as the acidic material Solution of an acid is used, the concentration of the acid in the solution being 0.1 to 10 Vol .-%, and that the solution has a temperature of 18.3 ° C to 93.3 ° C, and that the Surface is brought into contact with the solution for 30 seconds to 3 minutes. 3. The method according to claim 2, characterized in that an acid is used, the Concentration in the solution is not greater than 5% by volume. 4. The method according to claim 2, characterized in that the acidic, aqueous solution Phosphoric acid is used.