DE2758628A1 - DRAWING PROCEDURE - Google Patents

Description

The invention relates to the formation of organic coatings on metallic surfaces and in particular the deposition of organic coatings on metallic surfaces Bringing the metallic surfaces into contact with an acidic, aqueous coating solution containing dispersed particles an organic coating-forming material such as shark particles contains.

A relatively recent development in the coating art is the provision of coating compositions Water-based which, without the aid of electricity, form organic coatings on immersed therein, metallic surfaces are effective, these organic coatings increasing in strength or weight,

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the longer the surfaces are immersed in the compositions will. For the sake of simplicity, a coating composition of this type is hereinafter referred to as "self-depositing composition" designated, and one formed with the help of such a composition The coating is hereinafter referred to as "self-deposited coating". Generally it can be said that in this Kind of effective compositions include acidic, aqueous coating solutions that contain particles of an organic material such as resin particles dispersed therein. Even secluded ones. Coatings are made from such compositions as Formed as a result of their ability to attack the metallic surface and to dissolve metal ions from it in such quantities, which cause the particles to be deposited on the surface in such a way that a continuous structure of the organic coating takes place on the surface.

Coatings formed from such compositions differ completely from coatings, which by immersing the metallic Surfaces are formed in conventional latices, i.e. in compositions which are solid dispersed in water Contain resin particles. The weight or thickness of a through Immersion of a metallic surface in a conventional latex-formed coating is not affected by the length of time for which the surface is immersed in the latex is affected. It is mainly determined by the amount of in that resin solids dispersed in aqueous medium.

Coatings made from self-depositing compositions are also completely different from coatings formed from previously known acidic, aqueous coating solutions containing dispersed solid resin particles and relatively high amounts of water-soluble corrosion inhibitors such as hexavalent Chromium-containing compounds. 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

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like coatings cannot be obtained. Therefore have resinous coatings formed by dipping metallic surfaces in such compositions are the same Properties like the coatings obtained by immersion of the metallic Surfaces were formed in conventional latices because they also do not grow with increasing immersion time.

The use of self-precipitating compositions offers a number of advantages. For example, self-precipitating Compositions containing relatively small amounts of coating-forming solids for the application of relatively thick, organic coatings on metallic surfaces in a relatively can be used for a short period of time and in a one-step process. Furthermore, the coating thickness can be controlled by that the immersion time of the metallic surface in the self-depositing composition is varied. Additionally edges of the metallic substrate can be provided with a coating in a simple manner. In general, coatings can be obtained which have good corrosion-resistant properties and good aesthetic appearance. Furthermore you can such coatings can be made without the use of electricity, as is required in electroplating. this are just some of the advantages that result from the use of self-deposition, i.e. the coating process which the Includes formation of self deposited coatings without the use of electricity.

Although self-depositing compositions are capable of forming organic coatings of excellent quality, it has been found that coatings with defects or flaws are formed under certain conditions. Examples of such defects or defects are holes, bubbles and / or craters.

In some applications, such errors can only be minor or be of no importance at all. However, there are also applications

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genes in which coatings exhibiting such defects are not can be tolerated or are at least undesirable. Such defects generally set the corrosion resistance properties the covers come down. In applications where these properties are essential, these would be coatings are therefore not suitable. They would also be in applications not suitable where the appearance of the coating has a smooth, uninterrupted film target.

The object of the invention is to prevent the formation of defects or flaws in a self-precipitating composition to reduce or prevent formed coatings.

According to the invention, a substrate or a base that can accommodate a self-deposited coating is included Acid pretreated before exposing the substrate to the self-precipitating composition. 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 coatings with defects such as bubbles, craters and / or holes has been found to be effective in reducing or preventing the formation of such defects.

The inventive acid pretreatment of the substrate or the base can be carried out in a suitable manner so that the substrate or the base of an aqueous Solution is exposed to the acid.

A variety of acids or mixtures of acids can be used in the pretreatment stage * The use of Phosphoric acid is particularly preferred.

It should be noted that acid pretreatment of metal surfaces has long been used in order to

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surfaces of undesired materials such as carbonaceous deposits and metal oxides, e.g. scale and rust, to clean before the surface coating compositions get abandoned. Defects of the aforementioned type occurred on self deposited coatings / those on clean, initially Metal surfaces not containing such materials have been formed, i.e. on surfaces which are usually a Have not been subjected to acid cleaning pretreatment. This is shown in more detail using the following examples.

As can be seen from the following examples, there are applications of the self-deposition method in which error-free coatings are formed. However, under certain Conditions self-deposited coatings formed that Have errors.

One of the most common in the formation of flawed coatings occurring factors depend on the type of metal surface to be treated. Plating defects occurred when metal surfaces coated that had been processed, e.g. a molding process, punching, bending, drawing, shearing or have been subjected to similar work processes. Machining the metal surface generally results in pressure and tensile stresses in the metal and can result in scratching, surface imperfections (nicks) or fretting of the surface entail. The more the surface has been processed, the greater the inclination, since the one formed on it coatings have defects. In general, the defects are limited to the areas of the coating that are over the machined areas or sections of the metal surface. For example, in one application, which only results in a section of the metal surface during a punching process seizure due to pressure occurred, the defects were only observed in these sections of the coating, the notches caused by the seizure lay, otherwise the coating was free of defects.

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Defects in self-deposited coatings were also found encountered when plating metal surfaces that are in a roughened state for reasons other than one Processing of these templates. Objects produced by casting processes often have roughened surfaces as Follow the rough surfaces of the walls of the mold in which the article was made.

Defects in self-deposited coatings on metal surfaces of the type described above may take various forms depending on the particular accept the application occurring here. For example, the defects can be holes, bubbles and / or craters appear in the coating. The term used here "Crater" refers to a defect that looks like a collapsed bubble. In some applications there are no defects on the moist, not melted or not baked on coating, but they do occur Appearance after the coating has been baked by treatment at an elevated temperature. In other applications The moist coating may have bubbles that form holes (small holes similar to pores) during the baking of the coating at elevated temperatures, or the vesicles may remain in the coating after baking. In still other applications, such pinholes have been observed in the moist, unbaked coating.

Applied in the process of self-deposition of coatings Steps often include rinsing steps of the moist, self-deposited coating after the metal object has self-deposited Composition was brought into contact. For example, a moist or partially dried coating rinsing with water and / or contact with an aqueous, chromium-containing solution for the purpose of improvement subjected to the corrosion resistance properties of the coating will. In some applications this problem is so severe that the portions of the coating which are over

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the sections of the metal surface leading to the aforementioned type of defects, when in contact with the liquid composition, i.e. parts of the coating are removed during the rinsing treatment. In such cases the defect appears as an uncoated section of the metal surface.

There are a number of factors which play a role in whether or not to encounter defects in self deposited coatings are or not and, if encountered, affect the extent or severity of their occurrence. How out As can be seen from the following examples, there are applications in which errors are encountered when using a special type of self-precipitating composition, while they do not occur when another type of self-precipitating composition Composition is applied. The temperature of the self-precipitating composition can also play a role play here, in general, the higher the temperature of the composition, the greater the tendency for errors to occur is. The thickness of the coating can also have an influence on the likelihood of occurrence of The greater the thickness of the coating, the smaller the defects. The coating thickness, in turn, can vary from one to the other Factors such as the time of contact of the metal surface with the self-precipitating composition, the content of the solids forming the coating in the self-precipitating Composition and temperature of the self-precipitating composition.

With every special application that the coating of Concerns metal surfaces of the type described above and on which coating defects of the type specified above occur, can the acid pretreatment of the surface according to the invention can be used to prevent or inhibit the formation of such errors. The following examples show that including a great variety of acids

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organic and inorganic acids can be applied. Mixtures of acids can also be used. The entirety of the metal surface or only the portions of the surface that give rise to a problem with the defects, can be brought into contact with the acid pretreatment material. Although the contact of the metal surface with a acidic material can be achieved in various ways, it has been found advantageous to use the surface to bring an aqueous solution of the acid into contact.

There are numerous factors that go into determining the effective acid concentration of the pretreatment solution to play. Such factors include the strength of the particular acid used, 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 The numerous factors that play a role, however, should be noted that experience or ease of use Preliminary tests for a particular application are sufficient to determine the optimum acid concentration and the treatment conditions to be determined. In general, the lower application temperatures and shorter contact times can be used, the the higher the acid concentration of the solution. In the same way, less concentrated acid solutions can be used at higher levels temperatures and longer contact times can be used.

As a general guideline, it is recommended that an acid pretreatment be used solution is used, which is at least about 0.1 vol .-% Contains acid, and that the temperature of the solution is within the range of about 18.3 ° C to about 93.3 ° C, and that the Contact time between the solution and the metal surface is about 30 seconds to about 3 minutes.

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

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den, a solution containing 10% by volume acid may be required be. It should be noted, however, that higher concentrations are also possible of acid including undiluted acid can be used. However, the acid concentration should not lie so high that the metal surface is adversely affected.

It is believed that for most applications, working within the parameters given above will result in the development of Prevents or inhibits coating defects. However, it should be noted that that because of the numerous factors at play, as mentioned above, beneficial results occur Use of both lower and higher acid concentrations and / or shorter or longer contact times achieved can be.

For use in carrying out the method according to the invention phosphoric acid is particularly preferred. Phosphoric acid is relatively safe to handle and gives off relatively few vapors and does not pose any particular problems in wastewater treatment. In case some phosphate ions happen to be in the self deposition bath are dragged over, their presence therein is also relatively harmless.

When using phosphoric acid, it is recommended that the treatment conditions include the use of an aqueous solution containing about 1 to about 5 vol .-% of phosphoric acid at a temperature of about 51.7 ° C to about 71.1 ⁰ C for a contact time from about 1 to about 2 minutes.

An optional ingredient that can be used in the acidic solution is a surfactant. Any suitable surfactants that help improve the wetting of the metal surface of the solution be used. The surfactant can be used in relatively small amounts, e.g., about 0.001 to about 1% by volume of the solution.

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The pre-treatment of the metal surface can also be used for the Effectively reduces the tendency of the coatings to form bridges be. Bridging occurs in coatings that are formed on objects that are not in the same Have flat, but intersecting surfaces, and it occurs at the cutting line. The bridging shows by peeling off the coating from the underlying metallic surface at this cutting line.

Coating compositions that are effective in producing self-deposited coatings are known per se. Examples of such coating compositions are in the US patents: 3,585,084, 3,592,699, 3,709,743 and 3,776,848, in British Patent 1,241,991, in South African Patent 72/1146 and the Belgian patent (Additional patent) 811 841.

In general, it can be said that the acidic, aqueous coating compositions of the aforementioned type act to attack the metallic surface brought into contact therewith and to dissolve metal ions therefrom in sufficient quantities to directly or indirectly prevent the deposition of organic particles in the area of the metallic Surface thereupon in a continuous manner, ie in such a way that an increase in the amount of organic material deposited on the surface occurs the longer the surface is in contact with the composition. This deposition of the organic material on the metallic surface is achieved by the chemical action of the coating composition on the metallic surface. The use of electricity, which is otherwise required when performing some plating methods such as the electro-plating method, is not necessary in this case.

It can be seen that the process of the invention is the most powerful is applied in connection with coatings made of self-precipitating Compositions were formed, which are solid particles of resin dispersed in a dissolved fluoride and trivalent Aqueous solution containing iron are dispersed, see e.g. South African patent specification 72/1146. Preferably contains

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the aqueous phase of the coating composition is a surfactant Agent in an amount below the critical micelle concentration (hereinafter referred to as "CMC"), and particularly preferred is the concentration of the surfactant in the aqueous phase of the composition below the surfactant concentration which is the inflection point on a graph of surface tension versus logarithm of surfactant concentration in corresponds to the composition. Preferably the composition contains an anionic surfactant, and the The source of the resin dispersion of the composition is a latex which contains surfactant in such an amount that the aqueous phase of a self-precipitating composition formulated from the latex has a concentration of surfactant Means below the "CMC" and preferably below the inflection point concentration of the surfactant having.

A preferred composition for use in the invention The method is described in US patent application 664,613, which is incorporated herein by reference. The preferred composition has a surfactant concentration as previously described, as well as one pH from about 1.6 to about 4, and it is made from water, an iron (III) -containing compound, particularly preferably iron (III) fluoride, in an amount such that it contains the equivalent of about 0.5 to about 3.5 g / l of trivalent iron, about 0.2 to about 5 g / l of HF, optionally a pigment such as carbon black and about 50 to about 125 g / l of resin particles, these resin particles being substantially all of the same size and being substantially chemically homogeneous, i.e. each particle consists of the same monomeric components, which are present in practically the same proportions, or of resin particles, made by copolymerization of the following monomers:

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1) about 25 to about 70, and preferably about 40 to about 65% by weight of a conjugated diene having, for example, 4 to about 9 carbon atoms such as butadiene or isoprene;

2) about 5 to about 70 and preferably about 30 to about 65% by weight CH ₂ = CHR, where R is an aryl radical or a cyano group, for example styrene or acrylonitrile;

3) about 1 to about 50, and preferably about 3 to about 15 weight percent of a vinyl halide such as vinyl chloride or Vinylidene chloride and

4) about 0.5 to about 15, and preferably about 1 to about

4 wt .-% of a monoethylene-like unsaturated monomer with a functional group in the form of amide or Carboxyl groups, e.g. acrylamide, methacrylamide, octylic acid maleate and monoethylene-like unsaturated monocarbon and dicarboxylic acids having from about 3 to about 12 carbon atoms, and preferably from about 3 to about 5 Carbon atoms such as acrylic acid, cinnamic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid ,.

The resin is most suitably used in the form of a latex, which can be prepared according to procedures known per se can.

A particularly preferred latex contains resin particles made from the aforementioned monomers, which particles are chemically and physically homogeneous. The resin particles of the preferred latex are made from styrene, butadiene, vinylidene chloride and methacrylic acid. Furthermore, the content of emulsifier or surface-active agent of the preferred latex is about 1 to about 4%, based on resin solids, and comprises at least 90% by weight and particularly preferably 100% by weight of an anionic emulsifier such as a sulfonate, e.g. sodium dodecylbenzenesulfonate or a sulfosuccinate , for example sodium oleoyl isopropanolamide sulfosuccinate, or a mixture thereof.

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A particularly preferred self-precipitating composition has a surfactant concentration accordingly of the description given above and a pH in the range of about 2 to about 3.2, and includes about 50 to about 125 g / l resin solids, ferric fluoride in an amount equivalent to about 0.5 to about 2 g / L trivalent iron, and about 0.7 to about 3 g / L HF.

Regarding the cause of coating defects in self-deposited Coatings are believed to be the portions of a metal surface that have been machined against the coating composition are more sensitive than sections that have not been processed. In other words, it it is believed that the machined portions or parts of the surface are more reactive and easier to pass through the coating composition can be attacked with the result that in these sections hydrogen ions become hydrogen are reduced in greater amounts than occurs in other, less reactive sections of the surface. It it is believed that excess amounts of hydrogen are also formed when roughened surfaces of the previously specified type are coated and also when surfaces of the type that lead to bridging defects are coated.

For difficult applications that require the coating of machined or roughened surfaces, where relatively high amounts of hydrogen are generated, are defects such as small holes or pores visible in the moist or unbaked coating. For less difficult applications it seems to be such that the hydrogen remains trapped beneath or within the coating until the coating cures or is burned at a higher temperature, in which case the hydrogen expands. Depending on various factors can the hydrogen cause the formation of small holes or pores, bubbles or craters in the coating.

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

As previously described, one of the factors that play a role in the development of coating defects is temperature, in which the self-precipitating composition is brought into contact with the metal surface. In this context It should be pointed out that self-deposition compositions are used for the formation of coatings on metal surfaces are effective over a wide range of temperatures, including temperatures which are close to the boiling point of the

..., _m ^ which which approach, are approaching reduction ratio, and temperatures, / in which the aispergierten, organic, the coating-forming particles are coagulated in an undesirable manner. There are advantages to working at elevated temperatures. In general, it can be said that the higher the temperature of the composition, the greater the thickness of the coating. Therefore, at higher temperatures, the time required to form coatings of a given thickness is shorter. On the other hand, the use of higher temperatures usually leads to a deteriorated condition in terms of plating defects when plating metal surfaces of the type in which this problem is a concern. 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, since application of such a temperature in the absence of acid pretreatment would normally produce coating defects.

Although the coating composition with the metal surface may be contacted in various ways including, for example, spraying or flow coating

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believed that the most common contact method is to immerse the metal surface in the coating composition at about room temperature. As described above, the build-up of the coating thickness is greater, the longer the metal surface in the coating composition is immersed. It is believed that the desired coating thickness will work through in most applications Immersing 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 periods of time also can be applied.

The stirring or keeping in motion of the composition assists maintaining their uniformity. There is also a stirring or stirring of the composition effective in improving the uniformity of the coatings produced.

Various factors should be considered in determining whether to clean the metal surface or not should not be cleaned, and the extent of cleaning prior to contact with the self-separating Composition, including, for example, the type of foreign materials that may be 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 the corrosion resistance of the resinous or plastic-like coatings in a negative way as a result the presence of foreign materials on the metal surface during the plating step. In general, it can be said that coatings of improved quality can then be safely obtained, ever the surface is cleaner. Excellent results can

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can be safely achieved by subjecting the metal surface to a cleaning process which results in a surface on which a water-free film can be formed. The choice of detergent and
the type of application thereof on the metal surface depends on the type of foreign materials present on the metal surface. Available cleaning agents can be used in accordance with the technology known per se. Therefore, depending on the type of dirt or foreign matter present, acidic, alkaline or other may be used
Detergents are used. For example, dilute phosphoric acid can be used to clean easily rusted parts, and hot, alkaline compositions can be used to remove oils, greases, fingerprints and other organic deposits.

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

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

Rinsing the coated surface with water after it is removed 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 residues are left on the coated surface, they can alter or adversely affect the quality of the coating. For a specific application, an investigation can be carried out to determine whether residues have negative influences that cannot be tolerated. If this is the

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If so, they should be removed, e.g. by rinsing with Water using either tap water or deionized water.

If this is not the case, this level of removal can be used be omitted from this.

If so desired, the properties of corrosion resistance can be added the coated surface can be improved by treating the coated surface with an acidic, aqueous rinsing solution containing hexavalent chromium. Such rinsing solutions can be made of chromium trioxide or a water soluble dichromate or chromate salt such as ammonium, sodium and potassium salts. Also can a chromium composition can be used, which by treating a concentrated, aqueous solution of chromic acid with formaldehyde to reduce some of the hexavalent chromium * This type of rinse composition that in U.S. Patent 3,063,877 Chromium in the hexavalent state and reduced chromium in aqueous solution. It was also stated that the durability a baked or melted, resin-like coating as opposed to spray treatment with water and salt It can be improved that the non-baked or non-fused top coat with a solution, preferably one aqueous solution, contacted by 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 rinse steps applied after removing the coated surface from the composition the coating should be dried. Melting down or burning in the resinous top layer converts it into a continuous coating around, increasing its corrosion resistance

and its adhesion to the underlying metal surface be improved.

The conditions under which the drying and / or Brennbzw. Melting process is carried out depends to some extent on the type of resin used. Generally, heat is required to melt the coating. The corrosion resistance properties of coatings baked at elevated temperatures have been found to be better than those of coatings that have been air dried. However, there are applications in which air dried coatings can be used satisfactorily. The melting of the coating should be carried out below temperatures which cause the degradation or destruction of the resinous coating. Exemplary conditions that are in melting or burning of the invention produced coatings applied are temperatures within the range of about 100 ° C to about 200 ⁰ C for periods of time within the range of about 10 to about 30 minutes, this being from the Mass of the coated part depends. Baking the coating for such a period of time until the metal surface has reached the temperature of the heated environment has advantageously been used.

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

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Examples 1 and 2, Comparative Games C-1 through C-8

The first group of examples shows acid pretreatment of metal objects according to the invention and the application thereof to self-deposited coatings. For comparison purposes, this group of examples also shows the pretreatment of metal objects with alkaline cleaning materials.

Each of the articles used in this group of examples were made from hot rolled steel sheet that was pressed into the cup was drawn, made. The objects had seizure marks along the connection between the deep-drawn sections and the lip portions on the convex side of the articles. The objects were soiled with molding oil and workshop dirt, however, they were not rusted. Soiling of this type was generally removed by cleaning the objects with alkaline Cleaning solutions are removed.

Acid pretreatment solutions were made of the following composition manufactured:

Composition A

Components Amount (% by weight)

Phosphoric acid (75% strength by weight) 33.5

Ethylene glycol butyl ether 7.9

(Butyl cellosolve)

Nonylphenol ethoxylate
(Triton N-100) 0.5

Sodium alkylbenzenesulfonate

(ültraWett 45DS) 0.3

Oleyl alcohol (technical grade) 0.1

Water 57.7

The pretreatment solutions and the conditions used for the order are listed in Table I below.

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Pre-treatment material

Composition A (as indicated)

Pretreatment solution of Example 1 plus 2.5 Vol.-2 21 wt% HF

highly alkaline, spray cleaner

Pretreatment solution of Ex. CI plus 1 vol .-% of an aqueous solution of 38 wt .-% NH ₃ chlorinated, alkaline cleaner ^ 'amount of pretreatment material in the
aqueous pretreatment solution

Vol. Part on

Parts by volume of water

15 g / l

g / l
g / l
44.9 g / l

oxidized, alkaline cleaner (3)

strongly alkaline immersion cleaner ^ ' *

Pretreatment solution of Ex. C-5 plus 1% by weight sodium alpha-glucoheptonate (Glucoquest AC)

Pretreatment solution of Ex. C-5 plus 1% by volume ethylenediaminetetraacetic acid type chelate cleaner for iron (Hampenol OH-I)

Caustic rust remover of 120 g / l gluconate type ' Terms of engagement

3 min immersion at 43.3 ° G

3 min immersion at 43.3 ° C

Spray at 71.1 ° C. for 3 min

Spray at 71.1 ° C for 3 min

Spray at 71.1 ° C for 3 min

Spray at 71.1 ° C for 3 min

5 min immersion at 87.8 ⁰ C

3 min immersion at 71.1 ° C

3 min immersion at 71.1 ° C

Immersion at 87.8 ⁰ C (time not noted)

Commercially available product in the form of a powder mixture of caustic soda, Soda, sodium orthosilicate and surfactant (phosphate free) ^ A commercial product from Amchem Products, Inc. named Ridoline 529Ö7

Powder cleaner, commercial product (Amchem Products, Inc. name RL 69-364)

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Powder cleaner containing sodium perborate (commercial product of Amchem Products, Inc., designation RL-69-390)

Powder mixture of sodium tripolyphosphate, caustic soda, sodium gluconate and wetting agent (commercial product from Amchem, Inc. with the Designation Ridoline 27)

Commercially available powder cleaner (product of Amchem Products, Inc., Designation Ridoline 32)

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The articles treated with the acid pretreatment solutions of Examples 1 and 2 were first washed with the alkaline detergent solution of Example C-5 by immersing the articles in the cleaning solution for 5 minutes at a temperature of 71.1C purified. The cleaned items were then rinsed with tap water followed by the solutions of the examples 1 and 2 suspended.

After the objects have been given the pretreatment solutions given in Table I. After being exposed, they were immersed in moving tap water for about 30 seconds rinsed and then further rinsed with an atomized steel deionized water for 5 seconds Articles coated by immersing them in a 3000 liter bath of a stirred, self-depositing composition for about 90 seconds which contained per 1:

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

The resin or plastic used in this composition Latex contained about 62% styrene, about 30% butadiene, about 5% vinylidene chloride, and about 3% methacrylic acid. On off film formed on the resin is soluble in refluxing chlorobenzene in an amount of about 13%. The networking of the Resin is shown by its insolubility in the Soxhlet extraction with chlorobenzene. The water-soluble part of the latex is about 2% based on the weight of the dried resin, with the water-soluble portion being about 10% sodium phosphate, about 13% sodium oleyl isopropanolamide sulfosuccinate and about 75% sodium dodecylbenzenesulfonate constitutes, wherein the component mentioned in the first place is a buffering agent that is used in the manufacture of the latex is used, 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 dynes / cm. The average particle size of the resin was about 2000 S.

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The carbon black pigment dispersion used in this composition was an aqueous dispersion having a total solids content of about 36%. The carbon black made up about 30% of the dispersion. It had a pH of about "10-11.5 and a specific gravity of about 1.17. The dispersion contains a nonionic one Dispersant for the solids and is a commercial product (trade name Aquablak 115).

After the resin-coated objects from the self-deposition After the composition had been taken out, they were air-dried in tap water for about 1 minute immersed 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 surfactant solution, namely an aqueous solution of Octylphenoläthoxylat (trade name Triton X102) and 3 vol .-% of an aqueous, chromium-containing Concentrates containing about 8.6% by weight of CrO., About 8.6% by weight of CrO. Reduced with formaldehyde, and about 3.9% by weight of phosphoric acid contained, included. After rinsing with the chromium solution, the items were placed in a forced air oven at a temperature of about 135 ° C for about 20 minutes Fusing the resin coating arranged.

Upon removal from the oven, an inspection of the coated items showed that the coatings were coated with the solution of Examples C-1 to C-8 pretreated articles had hundreds of pinholes extending through the coating extended to the underlying metal surface. The holes or pores were in such portions of the coatings arranged, which were above the feed marks on the objects. On the other hand, the coatings on the objects which had been treated according to the invention (pretreatment solutions of Examples 1 and 2), only a few Pores that resided in some of the portions of the coatings that were located over the seizure marks. Thus, a pretreatment resulted of articles according to the invention a great improvement in preventing the formation of pores.

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Unless otherwise indicated, various steps used in these examples were also used in the following Examples applied, i.e. in the following examples the same rinsing steps with water were carried out following the alkaline cleaning, the same rinsing stages with water after cleaning with acid, the same self-separating Composition and the same application conditions, the same air drying conditions and the same Steps of rinsing with water and with a chromium-containing solution following the self-deposition and the same stoving conditions Applied In all examples the self-depositing compositions were at a temperature within the range from 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 achieved with the alkaline cleaning

at
supply of metal surfaces / either upstream or downstream acid pretreatment, furthermore the results achieved only with acid pretreatment. In this group of examples the following acid pretreatment solution was used:

Pretreatment Solution A

H ₃ PO ₄ (85% by weight) 5.0% by volume

HF (21% by weight) 2.5% by volume

Nonylphenol ethoxylate
(Triton N-100) 1.0% by volume

Antifoam agent (Makon NF 12) 1.0% by volume

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

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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 for 71.1 ° C for 5 minutes. The cleaned article is then sprayed with the above-mentioned acid pretreatment solution A at 71.1 ⁰ C for 3 minutes. The examination of the article provided with the self-deposited coating after the baking stages showed that the coating did not contain any pores or holes.

Example 4

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

Example 5. ·.

The article was sprayed with the aforementioned acid pretreatment solution A for 3 minutes at 71.1 ° C. The inspection of the object provided with the self-deposited coating
after the baking step showed that the number of pores, although the coating contained a few pores, was far fewer than in
acid pretreatment not carried out was obtained.

Examples 6 to 12

The next group of examples includes the acid pretreatment of articles of the type described in the previous examples for various periods of time and demonstrates the results obtained. Each of the articles used in this series of tests was initially cleaned by soaking the article for 5 minutes in an alkaline cleaning solution, this cleaning solution having been prepared as described in Example C-5 of Table I and one
Temperature of 71.1 ⁰ C had. In the following Table II are

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3Cr

the acid pretreatment solutions used and the immersion times of the objects in the solutions. Every the solution was kept at a temperature of 71.1 ° C.

Table II

Acid pretreatment solution

H-PO., 85 wt%, interfacial HF, 21 wt% immersion results E.g. , __. active agent (vol .-%) time

^ ^{Voi / c)} <Vol.-Z) (min)

6th , 5 0.1 1 1 Holes or
Pores 7th 5 o.i 1 2 no holes
or pores 8th 5 0.1 1 3 no holes
or pores 9 5 0.1 no 3 no holes
or pores 10 10 0.1 no 1 Holes or
Pores U 1 * 0.1 no 1 Holes or
Pores 12th 1 0.1 1 1 Holes or
Pores

Agent containing octylphenol ethoxylate (trade name Triton X102)

For the aforementioned examples 6, 10, 11 and 12 it was also observed that that the resin-like coatings, in addition to the holes or pores, also lifted off, i.e. the sections lying over the seizure marks the coatings were so loose that pieces of the coatings fell off the items when the items passed the steps of the Rinsing with water and chromium-containing solution were subjected to subsequent removal of the objects from the self-separating Composition were carried out. The results of the examples in Table II show that the length of the period for which the item is exposed to the acid pretreatment solution may affect the results obtained.

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Examples 13-18

The next group of examples includes ratings of corrosion resistance of self deposited coatings applied to backing, some of which have been acid pretreated and others have not been pretreated. The substrates used were cold-rolled steel sheets (unpolished Q-sheets) which were free from rolling marks and other defects which generally lead to the formation of holes or pores in self-deposited coatings. The metal sheets were first cleaned by immersing them for 2 minutes in an aqueous, alkaline cleaning agent solution at a temperature of 65.6 ° C., the solution containing 30 g / l of the alkaline immersion cleaner of Example C-5 in Table I above. The acid pre-treatment solutions used had a temperature of 71.1 ⁰ C and consisted of an acidic aqueous solution containing 5 vol .-% phosphoric acid (85 wt .-% strength) und.0,17 vol .-% of a Octylphenoläthoxylat containing surfactant Means (trade name Triton X102) contained. The autodeposition composition used was the same as that previously described in the examples, except that the concentrations of the latex and FeF _{3 were} 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 carried out using an arbitrary scale from 0 to 10, the designation "10" denoting a perfect coating.

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Immersion time in
Acid pretreatment
solution
(min) 33 Salt spray test
5% at 35 ° C,
Cross-cut 275.81 0 Table III 6.3 E.g. 2 Immersion time in
self-parting
the togetherness
composition
(min) 7.3 ASTM B-117 standard
336 h
area 13th 3 1 7.0 5.0 34 0 1 7.8 6.3 15th 2 ' 1 8 * 0 5.3 16 3 2 7.1 7.6 17th 2 2.3 ⁺ 18th 2 8.3

This rating is considered abnormal and cannot be explained. The ratings for the three panels were 0, 0, and 7.

It can be seen from the results in Table III that acid pretreatment generally improves corrosion resistance properties of the coated sheets did not have a negative effect. In fact, in most cases there were improvements the corrosion resistance 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 (unpolished Q-sheets) and hot-rolled steel sheets were scratched by grinding them with a belt sander provided with an emery paper 60 (60 grit). 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. and containing 30 g / l of an alkaline, commercially available cleaner (trade name Ridoline 1727). The sheets were then acid pretreated by immersing them for 3 minutes in an aqueous, acidic pretreatment solution with a temperature of 71.1 ° C, which 5 vol .-% H ₃ PO ₄ (85 wt .-%) and 0.1 % By volume of a

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Octylphenoläthoxylat containing surfactant (commercial product with the name Triton X102) contained. Thereafter, the scored panels were immersed for 90 seconds in a self-depositing composition similar to that of the compound with the composition described in Examples 1 and 2 corresponded. The coated sheets were of a different kind Rinse with an aqueous chromium solution as previously described was subjected, namely with a solution containing 3 vol .-% of an aqueous, chromium-containing concentrate, which

+6 150 g / l Na ₂ Cr ₃ O ₇ .2H ₂ O and a mixture of Cr with formaldehyde-reduced Cr in such an amount that the total Cr concentration of the mixture in the concentrate is 50 g / l at about 50 wt .-% 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 having a temperature of 71.1 ⁰ C for 15 or 20 minutes. For comparison purposes, the same process steps as previously described were used in the treatment of further sheets with the exception that some of the sheets had neither been ground nor pretreated with acid and other sheets, although ground, were not pretreated with acid. The results of these tests are shown in Table IV below.

>. sheet Table IV Acid pretreatment Holes or Bsi art sanded Pores cold rolled no no 19th η no no many 20th η Yes Yes no 21st hot rolled Yes no in traces 22nd H no no moderate 23 Il Yes Yes in traces 24 Yes

In addition to Table IV, it should be added that when of pores in the self-deposited coatings these in the sections the coatings occurred over the scratched areas

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the sheets were. From Table IV it can be seen how indented areas are used to form the small Guide holes or pores, and how effective the invention in eliminating or preventing the formation of such Is a coating defect.

Examples 25 and 26

Previously it was stated that there are several factors which play a role in development or non-development play of defects in self-deposited coatings, and that the specific type of self-deposited coatings used Composition can be a factor. The next group of examples shows this in education of defect-free coatings from a specific type of self-depositing composition. In these examples was the same type of scribed metal sheet and process steps as previously used in connection with the Examples 19 to 24 were described, with the exception that the sheets were used in the following described, autodeposition composition were immersed for 3 minutes and that in addition the one minute air drying step between removal of the panels from the autodeposition Composition and its rinsing with tap water was omitted. It was an approach of 4 1 of the self-depositing composition made from the same type of latex and the same carbon black pigment dispersion as they were used in the autodeposition composition of the previous examples. This contained per liter Composition:

Latex 180 g

H ₂ O ₂ (35% strength by weight) 6 ml

HF (21% by weight) 10 ml

Carbon black pigment dispersion 5 g.

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Example 25

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

Example 26

A self deposited coating formed from this composition on a cold rolled steel sheet which is not acidic had been pretreated had no pores.

Examples 27 to 40

The next group of examples shows the application 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 before in connection with the examples 19 to 24 described, applied. The used, special, aqueous, acidic pretreatment solutions are in the Table V below. In addition to the ingredients contained in the solutions given in Table V below all solutions with the exception of the acetic acid solution and the monosodium phosphate solution 0.1% by volume of a surfactant By means of (Triton X102). The sheets were in the solutions for Immersed for 3 minutes at a temperature of 71.1 ° C.

8 0 9 8 l \ l 0 9 6 6

^ SS 50 ml / 1 98% by weight H ₂ SO ₄ 275 Table V 50 ml / 1 98% by weight H ₂ SO ₄ E.g Tin-type aqueous acid pretreatment solution 50 ml / 1 37% by weight HCl Pores 27 cold rolled 50 ml / 1 37% by weight HCl no 28 when rolled 50 ml / 1 49% by weight HF no 29 cold rolled 50 ml / 1 49% by weight HF no 30th hot rolled 50 ml / 99% by weight acetic acid no 31 cold rolled 50 ml / 1 99% by weight acetic acid no 32 hot rolled 50 g / l citric acid monohydrate no 33 cold rolled 50 g / l citric acid monohydrate no 34 hot rolled 50 g / l oxalic acid dihydrate no 35 cold rolled 50 g / l oxalic acid dihydrate no 36 hot rolled 25 g / l NaH ₂ PO ₄ -H ₀ O no 37 cold rolled 25 g / l NaH ₂ PO ₄ -H ₂ O no 38 hot rolled no 39 cold rolled no 40 hot rolled traces way (D some craters

The examples in Table V show the effectiveness of several 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 others 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 indicated above, the inventive method is also Applicable to other metal surfaces including e.g. zinc and aluminum.

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Overall, it can be stated that the present invention provides an effective way to measure the quality by itself to improve deposited coatings, as shown by the numerous examples.

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Claims (19)

Claims 1. Coating process in which a self-deposited coating on a metal surface by bringing that surface into contact is formed with a self-depositing composition and the nature of this surface is such that from a upper layers formed with such a composition show defects, characterized in that the surface with an acidic material prior to contacting the surface with the composition. 2. The method according to claim 1, characterized in that that at least a part or section of the surface was machined Metal surface is. 3. The method according to claim 1, characterized in that that at least a portion or part of the surface is roughened and not machined. 4. The method according to claim 1, characterized in that that the surface includes intersecting surface sections, which lie in different planes, and that the defect is a bridging of this section of the coating includes that over the portion of the metal surface where the surfaces intersect, lies. 5. coating process, characterized in that it includes: (a) contacting a clean metal surface with an acidic material and then (b) the formation of a self deposited coating on the surface by contacting the surface with a self-precipitating composition. 80982 ^ 0966 6. The method according to claim 5, characterized in that that the metal surface is brought into contact with an aqueous solution of an acid. 7. The method according to claim 6, characterized in that the concentration of the acid in the solution is about 0.1 to about 10 vol .-%, and that the solution has a temperature of about 18.3 ° C to about 93.3 ⁰ C and that the surface is contacted with the solution for about 30 seconds to about 3 minutes. 8. The method according to claim 7, characterized in that that the concentration of the acid in the solution is no greater than about 5% by volume. 9. The method according to claim 5, characterized in that that the acidic material is phosphoric acid. 10. The method according to claim 9, characterized in that that the surface is brought into contact with an aqueous phosphoric acid solution. 11. Covering process, * in which a self-deposited, Resin-like coating on a cleaned, machined metal surface or a cleaned, unmachined, roughened one Metal surface by immersing the surface in a self-precipitating composition, which is an acidic, aqueous solution containing dissolved fluoride and dissolved trivalent iron with resin solids dispersed therein contains, and in which the composition for forming coatings with defects including Blisters, craters, holes or pores or uncoated sections of the metal surface on the surface tends, characterized in that the acidic metal surface with an aqueous solution of acid before the Immersing the surface in the composition. 80982 ^ / 0966 12. The method according to claim 11, characterized in that that the concentration of the acid in the solution is from about 0.1 to about 10% by volume, that the solution has a temperature from about 18.3 ° C to about 93.3 ° C, and that the surface with the solution for about 30 seconds to about 3 minutes is brought into contact. 13. The method according to claim 12, characterized in that that the concentration of the acid in the solution is no greater than about 5% by volume. 14. The method according to claim 11, characterized in, that the metal surface has a ferrous surface and that the acid is phosphoric acid. 15. The method according to claim 14, characterized in that the solution contains about 1 to about 5 vol .-% phosphoric acid, and that the surface with the acid at a temperature of about 51.7 ° C to about 71.1 ⁰ C for contacting for a period of about 1 to about 2 minutes. 16. The method according to claim 11, characterized in that that before the metal surface is brought into contact with the aqueous solution of the acid, this surface with an alkaline one Cleaning material is cleaned. 17. The method according to claim 11, characterized in that that the composition has a pH within the range of about 2 to about 3.2 and about 50 to about 125 g / l of resin solids, ferric fluoride in one amount equivalent to about 0.5 to about 2 g / l of trivalent iron and about 0.7 to about 3 g / l of HF, and that an anionic, surfactant in the aqueous phase of the composition is present in an amount below the critical micelle concentration. 80982 ^ 0966 18. The method according to claim 17, characterized in that the concentration of the surfactant in the aqueous phase is below the concentration of surfactant which is the inflection point on a diagram of the surface tension versus the logarithm
corresponds to the concentration of surfactant in the composition. 19. The method according to claim 11, characterized in, that the composition contains crack pigment; and that the resin solids are styrene-butadiene resin solids. 8 0 9 8 2V0 9 6 6