ITMI941715A1 - ACID WATER PHOSPHATIC SOLUTION AND METALLIC SURFACE PHOSPHATION PROCESS USING IT - Google Patents

Description

Patent application for Industrial Invention entitled:

"Acidic aqueous phosphate solution and metal surface phosphating process using it."

FIELD OF THE INVENTION

The present invention relates to an acidic aqueous phosphate solution and a phosphating process which uses it to obtain a phosphate film on metal surfaces capable of developing excellent resistance to corrosion and high adhesiveness towards coatings, in particular those obtained with electrophoretic painting. The phosphating process carried out at low temperatures, both on iron-based metal surfaces as well as on zinc, aluminum or steel-based, has the surprising ability to eliminate the phenomenon of white spots, which is a very serious problem especially in industry. automotive.

STATE FROM TECHNIQUE

The use of coatings obtained by applying aqueous phosphate solutions to prevent corrosion and short life of metal surfaces, as well as to improve the adhesion of the paint layer, dates back to 1917: the surface of the metal reacts with the solution to form a amorphous or crystalline phosphate layer, depending on the operating conditions used.

Some phosphate solutions have acquired a notable diffusion and commercial importance; such solutions usually contain phosphate, zinc and / or manganese ions and possibly a component selected from nickel, cobalt, copper, magnesium, calcium, nitrite, nitrate, chlorate, and fluoride.

At present, although the phosphate solutions have reached satisfactory quality levels, there is a continuous request for improvements especially from the automotive industry, following the new needs dictated by the evolution of the metal substrates used. Furthermore, the current average life time of a car is more than 10 years, while a treatment of the bodies capable of preventing corrosion and extending their life for such a long period of time is not known to date.

The metal supports currently used are based on iron, aluminum and zinc, and preferably galvanized steels (galvanized or electro-galvanized), which prove to be the most suitable for obtaining a better resistance to corrosion, after the application of the paints. The particular effectiveness of the zinc coating in preventing corrosive phenomena and its bucna adhesiveness are due to the reactivity of the zinc itself with CO2 and oxygen in the air, which leads to the formation of zinc-hydroxy-carbonate, which adheres quickly to the metal surface, inhibiting further corrosive phenomena. Furthermore, zinc plays a cathodic protection role towards steel, acting as an anode and corroding itself instead of the steel itself.

The mechanisms involved in the phosphating process seem to be, in the case of solutions with a low zinc content:

on steel

In crystalline phosphating processes, an accelerator is always used, generally consisting of an oxidizing agent of an inorganic or more rarely organic nature, aimed at obtaining the surface conversion process in shorter, industrially acceptable times. The accelerator achieves the dual objective of depolarizing the treated metal surface, acting in particular in the areas with high electronic density (microcathodic), and at the same time oxidizing the metals dissolved in the microanodic etching area and causing them to precipitate as insoluble phosphate salts.

The use of the most varied accelerators, both of an oxidizing and reducing nature, or even mixtures of oxidants and reducing agents, is known in the state of the art.

Until now, nitrite (preferably in the form of sodium salt) has been the most used among the external components with an accelerating function in microcrystalline phosphating processes.

The success of nitrite finds valid reasons in its easy availability, low cost and marked oxidizing power. However, the use of nitrite and / or nitro-derivatives finds an insuperable limit in the onset of ecological problems, irreconcilable with the most recent regulations on the subject. In fact, this compound presents a series of technical and ecological contraindications due to its limited thermal stability in commonly used operating conditions, instability that inevitably leads to the formation of nitrogen oxides: nitrogen oxide vapors of general formula Ν0χ emitted into the atmosphere are strongly polluting and aggressive. Furthermore, nitrite has a tendency to transform into nitrate ions in processing baths, which require subsequent difficult disposal in purification plants. These problems, added to the high level of danger in the handling and industrial storage of nitrite (a toxic and oxidizing substance according to the current classification in accordance with the EEC), entail high management costs and the difficulty of operating in compliance with current regulations. matter.

In the light of the aforementioned problems, the need to find an alternative accelerator system free from nitro-derivatives, capable of offering technological performances at least equivalent to those of traditional nitrite-based processes, appears evident.

With this in mind, hydroxylamine has returned to be taken into consideration, a product used as an accelerator in phosphating processes since the early 1950s and certainly absolutely safe from an ecological point of view.

However, the procedures that use hydroxylamine have proved to be inapplicable in the phosphating of galvanized steels, as well as aluminum and iron-based surfaces, due to the onset of "white spots", that is, small, point-like, white-colored outgrowths of varying sizes, with average diameter of 50-150 um and with average height of 100-400 um, which are found statistically distributed on the galvanized surface after the phosphating phase (D. Saatweber.Galvaniced sheet and cationic ED primer: synergism for finishing optimization, ATA 27 / 02/1989 in Milan Surface Finishing and Corrosion Protection in Automobilistic). The subsequent electro-cathodic painting, instead of correcting these defects, faithfully reproduces the extrusions, likewise replicating the layer and thus making the finished product absolutely unacceptable.

The chemical nature of this phenomenon, also known in the state of the art as "white specking" or "nubbing", has not yet been fully clarified, even if it seems to have electrochemical origins: it has in fact been observed that the cathodic polarization of galvanized surfaces it can prevent the formation of white spots (W. Rausch, Industrie Lackerbetrieb, 1981, 12, 413). It has been found that at the entrance to the phosphating bath the metal surfaces to be treated, in particular those based on zinc, usually have non-uniform residual areas of oxides. Thus, preferential polarities are created during the phosphating process, which always involves a first "pickling" step, in which the phosphoric acid generated by the phosphatic system conducts an acid surface attack. Local anodic corrosion develops in the acid medium, leading to the formation of small point craters characterized by a zinc vacancy of the surface layer. In the points of the surface where the iron remains exposed, a "galvanic cell" probably acts between the iron itself and the metallic zinc, thus allowing the continuation of the zinc dissolution. Consequently, it is possible that there is an excessive precipitation of phosphates and zinc hydroxides, which accumulate at the limits of the crater. Small blackish craters characterized by whitish lateral deposits, mainly consisting of phosphates and zinc hydroxides, would form on the final phosphated surfaces, which would cause the typical vaporous outgrowth of the phenomenon (Guy Lorin, La phosphatation des metaux, 20-21, Edition Eyrolles 1973)

As previously mentioned, it was found that this phenomenon is strongly accentuated by the use of hydroxylamine as a phosphating accelerator.

According to the known art, the remedy for the white spots arising after phosphating can only be of a mechanical type, eg. sanding or destroying the efflorescence by rubbing with fabric or paper. It is clear that such a manual procedure involves labor costs that are too high to be industrially acceptable.

Different solutions of the problem of white spots have also been indicated in specific cases.

Eg. European patent EP 228.151 describes a phosphating bath containing zinc, ΡΟ4 ion, manganese and fluoride ions; it provides for the use of various accelerators, including nitrite and nitro-derivatives, but does not provide for the use of hydroxylamine. However, the problem of the presence of white spots is highlighted, which can be partially contained, according to the inventors, by reducing the concentration of chloride ions in the phosphate solution and, obviously, also of chlorate ions, which by reduction slowly generate chlorides.

The British patent application GB 2,179,680 also identifies in the presence of chloride ions one of the major causes of the formation of white spots and proposes a phosphating solution for the coating of galvanized metal surfaces capable of reducing the occurrence of said phenomenon. This result, however not totally satisfactory, would be achieved by canceling the effect of the chlorides with proportional additions of fluorides. The solution described must in fact contain fluorides in such an amount that the weight ratio F <_> / Cl- is at least 8: 1; furthermore, the concentration of chloride ions cannot be higher than 50 ppm, preferably lower than 20 ppm, and any pre-treatment of the metal surface must be carried out with solutions whose chloride content is lower than 100 ppm. These limits are difficult to propose at an industrial level, as the value of 20 or 50 ppm is often exceeded by the salinity of the mains water used alone, and is in any case easily reached even in a phosphating tank prepared with demineralized water due to drag. -out of the previous washing phases with mains water.

The European patent EP 0264 151 seeks the solution to the problem of white spots in the pre-treatment phase of the metal surface and describes a rinse, prior to the activation phase, with a solution containing a mixture of nitrites, borates and sodium silicates.

The European patent EP 0224190, on the other hand, provides for the use of an activating solution based on titanium phosphates, with the addition of disodiotetraborate or other alkaline borates in such quantities that the PO4 / B4O7 ratio is greater than or equal to 1. The addition of B ^ Oy reduces the formation of white spots to spots, but is not able to completely eliminate the phenomenon. Furthermore, the serious problem of pollution due to the high quantities of Na2B4Oo710 H2O envisaged by this patent (4-8 g / 1) is highlighted.

None of the aforementioned patents use hydroxylamine as an accelerator.

However, it is clear that the problem of white spots is an unsolved problem and that in particular no solution exists for the case in which hydroxylamine is used as an accelerator, which makes the problem particularly serious.

SUMMARY

The Applicant has now surprisingly found that in an acidic aqueous phosphate solution, the simultaneous presence of hydroxylamine phosphate and a cationic surfactant, in particular a quaternary ammonium surfactant, allows to obtain, in times compatible with industrial requirements, phosphate coatings with good resistance. corrosion and adhesion to the paint layer, without any onset of white spots.

The present invention also relates to a spray or immersion process for the phosphating of metal surfaces which uses the above solution, at a temperature between 40 and 55 ° C, in a time of 1-5 minutes.

DETAILED DESCRIPTION OF THE INVENTION

The characteristics and advantages of the phosphating solution and of the process which uses it, according to the present invention, will be better illustrated in the course of the following detailed description.

The present invention relates to an acidic aqueous phosphate solution containing hydroxylamine phosphate and a cationic surfactant, in particular a quaternary ammonium surfactant, in certain concentrations and in certain ratios between them. More precisely, the present invention relates to phosphating solutions containing from 0.6 to 3.0 g / l of hydroxylamine phosphate and from 0.001 to 1 g / l of a cationic surfactant, and preferably from 0.005 to 0.1 g / l. The weight ratio between hydroxylamine phosphate and the cationic surfactant can vary between 0.6 and 1000, and preferably between 10 and 200.

The solution may possibly also contain from 0.003 to 0.08 g / 1 of copper ions, from 0.05 g / 1 to 0.3 g / 1 of at least one polyfunctional sequestering agent selected from the group consisting of aminated polyacid complexing agents with accelerating functions , such as EDTA, and organic polyacids, such as tartaric and citric acid, and preferably EDTA and / or tartaric acid, in quantities ranging from 0.08 to 0.1 g / 1, and a non-ionic emulsifying agent with foam limiting functions , compatible with the phosphating process and the common subsequent passivation and painting treatments, in a quantity equal to 10-30% by weight with respect to the weight of said cationic surfactant.

The phosphating compositions according to the present invention advantageously have a composition comprised within the following limits:

- from 5 to 25 g / 1 of phosphate ions;

- from 0.5 to 2.0 g / l of zinc ions, and preferably from 0.5 to 1.5 g / l;

- from 1.5 to 4.0 g / l of nitrate ions;

- from 0.3 to 1.2 g / 1 of manganese ions;

- from 0.001 to 0.1 g / 1 of iron ions;

- from 0.4 to 1.1 g / l of nickel ions;

- from 0.3 to 1.2 g / l of total fluoride ions, deriving from hydrofluoric acid, fluosilicic acid or other suitable sources;

- from 0.6 to 3.0 g / l of hydroxylamine phosphate; And

from 0.001 to 1 g / l of a cationic surfactant, and preferably from 0.005 to 0.1 g / l.

In the phosphating compositions of the invention, said nickel ions can be replaced by a combination of cobalt and magnesium ions, in which cobalt ions are present in variable quantities from 0.05 to 0.2 g / 1 and magnesium ions in variable quantities from 0.5 to 1.5 g / 1-Since, as previously said, the nature of the white spots has not yet been clarified, it is also difficult to understand what type of action the hydroxylamine phosphate / cationic surfactant system generates.

This is even more surprising when you consider that only hydroxylamine phosphate and no other hydroxylamine salts lead to the desired result. It is difficult to hypothesize any chemical mechanism of action in which the hydroxylamine phosphate acts and not, for example, the corresponding sulphate. It is also surprising that among the different types of surfactants tested, the anionic surfactants even have a tendency to enhance the phenomenon of white spots, while the non-ionic surfactants are indifferent to the onset of this phenomenon. Among the cationic surfactants, the ammonium surfactants selected from the group comprising:

- Coccodibenzylammonium chloride, with an alkyl chain consisting of 12-14 carbon atoms;

- Polypropoxylates and polyethoxylates of alkylammonium chloride and phosphate;

- Benzalkonium chloride and derivatives, with side chain consisting of 12-14 carbon atoms;

- N-alkylammonium chloride, with an alkyl residue consisting of 12-18 carbon atoms and the remaining consisting of H and / or methyl;

- Alkyl polyglycol ethers of ammonium chloride and sulphate, of general formula (I):

C20 · which prove to be extremely effective in eliminating white spots.

Furthermore, the cationic surfactants according to the present invention can form in situ, in the phosphating solution. by addition to the phosphating bath of a surfactant of the formula:

in which R and n have the meanings reported above.

Although it has not been possible to demonstrate a clear link between the chlorides present and the formation of white spots, it has nevertheless been found that it is possible to obtain the complete elimination of white spots in the presence of a quantity of the cationic surfactant such that the cationic surfactant weight ratio / chlorides is equal to 1/3

It has also been found that the presence of the copper ion in the solution of the invention helps to improve the quality of the phosphatic layer, making it more conductive. The certainly advantageous use of the copper ion is made possible by the presence of the hydroxylamine phosphate / cationic surfactant system, which however inhibits the formation of white spots. In the absence of such a system, copper ions cause the formation of white spots already in concentrations of 0.003-0.005 g / 1.

The phosphate solution according to the present invention has a total acidity value between 10 and 28 points, a free acidity value between 0.5 and 2.0 points, with an acid ratio (ratio between total acidity and free acidity) included between 5 and 56 points. With such acidity values the phosphate film can be obtained in an economical way, without excessive corrosion of the metal surface taking place.

In the present description, the total acidity value refers to the number of ml of 0.1 N NaOH (points) needed to titrate 10 ml of the phosphate solution of the invention to the change of phenophthalein; the free acidity value, on the other hand, refers to the number of ml of 0.1 N NaOH (points) needed to titrate 10 ml of the phosphate solution of the invention when the methyl yellow color changes.

The phosphating process according to the present invention can be carried out either by spraying or by immersion or also by combination of the first two treatments, for a time of 1-5 minutes, at a temperature between 40 and 55 "C. Temperatures lower than said interval would require long processing times to obtain an acceptable coating, while a higher temperature would accelerate the decomposition of the phosphating accelerator, unbalancing the concentrations of the components of the solution and making it difficult to obtain satisfactory phosphate films.

The microcrystalline phosphate layer obtained with the process of the invention is 1.5 ~ 5.0 g / m.

The process of the invention produces an effect of total elimination of white spots, with a practical factor higher than $ 8%, both with spray application and by immersion.

The phosphate film is applied with satisfactory results even on objects with a complex shape, such as the bodywork of a motor vehicle.

When the phosphating process of the invention is carried out by immersion, the operating temperature is preferably between 45 and 50 ° C, for a time of 2-5 minutes.

The acid aqueous phosphate solution used in this treatment preferably contains from 13 to 15 g / 1 of phosphate ions, from 1.0 to 1.5 g / 1 of zinc ions, from 2.5 to 3.5 g / 1 of nitrate ions, 0.6 to 1.1 g / 1 of manganese ions, 0.001 to 0.05 g / 1 of iron ions, 0.4 to 0.6 g / 1 of nickel ions, 0.6 to 0, 8 g / 1 of fluoride ions, 1 to 2 g / 1 of hydroxylamine phosphate, 0.01 to 0.1 g / 1 of a cationic surfactant. The solution can also contain from 0.003 to 0.006 g / l of copper ions and from 0.05 to 0.3 g / l of a polyfunctional organic sequestering agent, preferably EDTA and / or tartaric acid.

Again in the case of the immersion process, the total acidity value is preferably between 18 and 22 points, while the free acidity is preferably between 1 and 2 points. Said immersion process gives rise to microcrystalline phosphate layers having a weight of between 1.5 and 3.5 g / m on iron substrates and having a weight of between 2 and 5 g / m on pre-coated sheets.

When the phosphating process of the invention is carried out by spraying, the operating temperature is preferably between 45 and 50 ° C, for a time of 1-3 minutes, with a spray pressure between 1 and 2.5 atm.

The acidic aqueous phosphate solution used in this treatment preferably contains from 9.0 to 11.2 g / 1 of phosphate ions, from 0.8 to 1.2 g / 1 of zinc ions, from 1.7 to 3.0 g / 1 of ions nitrate, 0.4 to 0.7 g / 1 of manganese ions, 0.001 to 0.04 g / 1 of iron ions, 0.4 to 0.5 g / 1 of nickel ions, 0.4 to 0.7 g / l of fluoride ions, 0.8 to 1.6 g / l of hydroxylamine phosphate, 0.01 to 0.1 g / l of a cationic surfactant. The solution can also contain from 0.003 to 0.006 g / l of copper ions and from 0.05 to 0.3 g / l of a polyfunctional organic sequestering agent, preferably EDTA and / or tartaric acid. Again in the case of the spray process, the total acidity value is preferably between 13 and 14 points, while the free acidity is preferably between 0.6 and 0.8 points. Said spray process gives rise to microcrystalline phosphate layers having a weight between 1 and 3.5 g / m2 on iron substrates and a weight between 1.5 and 3.5 g / m for ferrous sheets coated with zinc by electrolytic galvanizing.

The dipping and dipping / spraying treatments are preferred to the spraying and spraying / dipping treatments in the process of the invention.

Finally, a treatment that combines spraying and immersion can be carried out with an immersion of 100-200 seconds, at a temperature of 45 "50 ° C, followed by a spray of 20-50 seconds, at a temperature of 45" 50. ° C; or the treatment may include a 20-50 second spray, at a temperature of 45-50 <e> C, followed by a 100-200 second immersion, at a temperature of 45 ~ 50 ° C. The combination that provides the treatment immersion followed by spraying is particularly advantageous for objects of complex shape, such as the bodywork of a motor vehicle.

The elements constituting the acid aqueous phosphate solution according to the present invention can be obtained by adding the following compounds:

- Hydroxylamine phosphate is a stable salt that can be

Here we want to emphasize once again the impossibility of using a hydroxylaramine salt other than phosphate in the phosphate solutions of the invention. In particular, it would be desirable, from an industrial point of view, to use hydroxylamine sulphate, a stable, low-cost and easily commercially available salt. However, it has been ascertained that this is impossible as the sulphate ions favor the formation of white spots if present in quantities greater than 500 ppm, essentially carrying out the same action as the chloride ions. - Phosphoric anhydride, phosphoric acid, zinc phosphate, zinc monohydrogen phosphate, zinc dihydrogen phosphate, manganese phosphate, manganese monohydrogen phosphate, manganese dihydrogen phosphate etc., preferably phosphoric acid, can be used as a source of phosphate ion.

- Zinc oxide, zinc carbonate etc. can be used as a source of zinc, preferably zinc oxide.

- Manganese carbonate, manganese oxide, the aforementioned manganese phosphates etc., preferably manganese carbonate, can be used as a source of manganese.

- Ferric nitrate is preferably used as a source of iron; however, during the initial stage of preparation of the phosphating bath, the iron may not even be added to this bath, since the iron ions can spontaneously arise from the iron-based surfaces subjected to the phosphating processes following the acid attack.

- Nickel nitrate, nickel carbonate, nickel phosphate etc. can be used as a source of nickel, preferably nickel nitrate.

- Fluosilicic acid, hydrofluoric acid, fluoboric acid and their metal salts, preferably fluosilicic acid, can be used as a source of fluoride ions.

- The copper ion is preferably added to the solution in the form of copper nitrate.

Finally, any modifications or additions to the solution, aimed at obtaining the acidity values mentioned above, can be obtained by means of alkali metal hydroxides and ammonium hydroxide, preferably by means of sodium hydroxide. The metal surfaces treated according to the present invention comprise surfaces based on iron, zinc, aluminum and / or their respective alloys. Such metal surfaces can be treated both separately and in combination. The new process is particularly advantageous if the treatment is carried out on an article which includes both an iron-based surface and a zinc-based surface, such as occurs for example in the bodywork of a motor vehicle.

Examples of zinc-based surfaces are galvanized steel sheet, pass-through steel sheet, galvanized steel sheet for electroplating, zinc alloy plated steel sheet for electroplating and complex galvanized steel sheet for electroplating.

The acidic aqueous phosphate solutions according to the present invention can be suitably prepared by diluting an aqueous concentrate containing the quantities of elements of the solution in the due weight ratios to each other and finally adding some necessary elements, such as pH adjusters or accelerators.

The present process advantageously provides for the pre-treatment steps of the metal surfaces, which consist of a degreasing step which can be carried out with weakly or strongly alkaline degreasing agents or with acid degreasers, followed and / or preceded by rinsing with water. Then the surfaces can be subjected to a conditioning treatment with a solution of titanium or zirconium. A solution containing 0.0003-0.05% titanium on a phosphate support and preferably containing 0.0005-0.001% titanium is particularly suitable for the purpose.

Furthermore, after the phosphating process of the invention, especially in cases where a subsequent coating step is envisaged, the phosphated surfaces are advantageously subjected to post-treatments such as rinsing with a dilute chromic solution, containing for example 0.025-0, 1% chromium in the form of chromium (III), chromium (VI) or a mixture thereof. Alternatively, rinses can be carried out which provide for washing with aqueous solutions containing poly-4-vinylphenols or the condensation products of the latter with an aldehyde or a ketone.

Furthermore, passivation treatments can be carried out using metal salts such as aluminum, zirconium etc. After the aforementioned final rinses, the surfaces show good resistance to corrosion and good adhesiveness to the paint layer subsequently applied by electro-cathodic painting, since there is no onset of white spots.

For illustrative but not limitative purposes of the present invention, the following examples are reported.

EXAMPLE 1

Influence of anionic, cationic and non-ionic surfactants on the formation of WS.

Materials and methods

The tests were carried out using steel sheets coated with an electrolytic galvanizing process on both faces with a thickness of 8-10 um of zinc. The aforementioned sheets were treated according to the following operating cycle:

DEGREASING PHASE

A solution of a degreasing agent containing:

Sodium Disodium Phosphate approx. 7 g / 1

Sodium Metasilicate-5 H2O ca. 7 g / 1

Sodium Trisodium Phosphate · 12 H2O ca. 3 g / 1

Sodium Neutral Pyrophosphate approx. 1.8 g / 1

Non-ionic surfactants ca. .1 g / 1

Hydrotropics approx. 1 g / 1

The treatment was carried out by immersion at a temperature between 55 and 60 ° C, for a time of 3 "5 minutes.

ACTIVATION PHASE

An activating solution was used containing:

Titanium 5-6 mg / 1

PO4 150-200 mg / 1

<P> 3O10 450-500 mg / 1

The treatment was carried out by immersion at a temperature of 20 ° C for 1 minute.

PHOSPHATATION PHASE

The phosphating treatment was carried out by immersion at a temperature of 50'C, for a time of 3 minutes, using normal 5-liter trays of antacid material, suitably heated electrically, under magnetic stirring.

Three different phosphating solutions were used containing: PO4 ca. 13-15 g / 1

Zinc approx. 1-1.2 g / 1

NO3 approx. 3-3.5 g / 1

Manganese approx. 1-1.2 g / 1

Nickel approx. 0.4-0.5 g / 1

Iron ca. 0.005-0.02 g / 1

Total fluorides approx. 660-715 mg / 1

Total acidity 18 points

Free Acidity 1.8 points

To the above solutions was added hydroxylamine phosphate (2 g / 1), 100 ppm of chloride ions (0.1 g / 1) and a surfactant in a concentration of 0.1 g / 1:

- a non-ionic emulsifying agent consisting of a block copolymer of ethylene oxide - propylene oxide was added to BATH 1;

- a cationic surfactant which falls within the present invention, and in particular chloride of alkyl polyglycol ether of ammonium of formula (I), has been added to BATH 2, with R = 0 ^ 2 * n = 11 and m = 1;

- an anionic surfactant was added to BATH 3, and in particular sodium dodecylbenzenesulphonate.

After being subjected to the aforementioned phases of the operating cycle, the sheets were analyzed.

The detection of white spots is easily implemented even with the naked eye, but preferably with an optical microscope, because it consists of point-like efflorescences in the shape of micro domes, with a diameter of 0.5 "1.5 nim, which stand out clearly as white efflorescences on the gray surface of the electro-galvanized phosphated sheet.

Results:

The results of this test show that the non-ionic surfactants do not prevent the formation of white spots, while the anionic surfactants favor it and the cationic surfactants of the invention inhibit it.

EXAMPLE 2

Determination of the ratio between the cationic surfactant of the invention and chloride ions, effective in eliminating the phenomenon of white spots.

Materials and methods

The tests were carried out using FePO / | steel sheets coated with electrolytic galvanizing process on both faces with a thickness of 8-10 pm of zinc. The degreasing and activating pre-treatment cycle followed is similar to that reported in Example 1.

The phosphating treatment was carried out by immersion at a temperature of 50 ° C, for a time of 3 minutes, using normal 5 liter tubs of antacid material, suitably heated electrically, under magnetic stirring.

described in Example 1, 2 g / 1 of hydroxylamine phosphate and 100 ppm of chloride ions (0.1 g / 1) were added. Subsequent additions of ammonium polyglycol ether alkyl chloride of formula (I) where R = C12 were also made. n = ll and m = l, to determine the concentration of cationic surfactant necessary for the total elimination of white spots even in the presence of chloride ions, which seem to create the worst situation.

The results of this test indicate that a ratio of 1/3 between the cationic surfactant of the invention and chloride ions is sufficient to eliminate the phenomenon of white spots.

EXAMPLE 3

Determination of the maximum amount of the cationic surfactant of the invention acceptable in the phosphating of iron.

Materials and methods

Two types of ferrous sheets were analyzed:

TYPE 1 - cold rolled type FePO4, in compliance with the UNI 5961-67 standard (April 1967), commonly used in motor vehicles;

TYPE 2 - cold-rolled ferrous sheet with a thickness of 0.8 mm, type R, marketed by the company Q-Panel (U.K.), in accordance with the 750 standard

Said sheets were treated according to the same degreasing and activating pre-treatment cycle described in Example 1. The phosphating treatment was carried out by immersion at a temperature of 50 ° C, for a time of 3 minutes, using normal trays of antacid material to be 5 liters, suitably heated electrically, under magnetic stirring. A phosphating solution was used containing:

To the above solution were added 2 g / 1 of hydroxylamine phosphate, 150 ppm of chloride ions (0.15 g / 1) and ammonium polyglycol ether alkyl chloride of formula (I), where R = C12, n = ll and m = l, in increasing quantities; after each addition of the cationic surfactant, the suitably pretreated laminations were phosphated according to the aforementioned methods and the nature of the phosphated layer thus obtained was observed. Results:

surfactant quality of the phosphate layer (mg / 1) TYPE 1 TYPE 2

0 good good

300 good good 500 good good 700 good good 1000 good good

These results show that the cationic surfactants according to the present invention do not affect the phosphating of iron; there are therefore no limits to their concentration in the phosphating bath up to 1000 ppm (1 g / 1).

EXAMPLE 4

Influence of the cationic surfactants of the invention on the phosphating of iron sheets and galvanized sheets.

Materials and methods

The tests were carried out using ferrous sheets coated with zinc on two faces by the process of The sheets were previously treated according to the degreasing and activation steps described in Example 1. Then they were subjected to the phosphating step in the presence and absence of the cationic surfactant of the invention of formula (I), where R - C-12 n = 11 and m = 1.

The phosphating treatment was carried out by immersion at a temperature of 50 ° C, for a time of 3 minutes, using normal 5 liter trays of antacid material, suitably heated electrically, under magnetic stirring. A phosphating solution was used containing:

To the above solution, 50 ppm (solution A), 100 ppm solution B) and 150 ppm of chloride ions (solution C) were added respectively.

For comparison, solutions containing the above mentioned amounts of chloride were prepared, together with the cationic surfactant of the present invention, added in increasing quantities equal to 30 ppm (solution A '), 60 ppm (solution B'} and 90 ppm (solution C In these last three solutions a foam limiter was also added. After having subjected the aforementioned sheets to the operating cycle described, the presence of white spots was evaluated with the naked eye.

Results:

These results show that the cationic surfactants according to the present invention efficiently inhibit the formation of white spots.

EXAMPLE 5

Influence of the cationic surfactants of the invention on the corrosion resistance and wet adhesion of the phosphate layers after painting.

Materials and methods

The tests were carried out using three types of sheets: TYPE 1 - FePO4 cold rolled steel panels;

TYPE 2 - electro-galvanized steel panels on both sides, with a thickness of 7 of zinc;

TYPE 3 ~ hot dip galvanized steel panels with smooth finish, 10-11 pm zinc thickness.

The aforementioned sheets were treated according to the following operating cycle:

DEGREASING PHASE

A solution of a degreasing agent containing:

Sodium Disodium Phosphate approx. 7 g / 1

Sodium Metasilicate-5 f ^ O approx. 7 g / 1

Sodium Trisodium Phosphate-12 H2O ca. 3 g / 1

Sodium Neutral Pyrophosphate approx. 1.8 g / 1 Non-ionic surfactants approx. 1 g / 1

Hydrotropics approx. 1 g / 1

The treatment was carried out by immersion at a temperature between 50 and 60 ° C, for a time of 2-5 minutes.

RINSE PHASE

The rinsing was carried out with tap water at room temperature.

ACTIVATION PHASE

An activating solution was used containing:

The treatment was carried out by immersion at a temperature between 20 and 40 ° C, for a time between 30 seconds and 120 seconds.

PHOSPHATATION PHASE

The phosphating phase was carried out both by spraying (A) and by immersion / spray (B).

A) The phosphating process was carried out by spraying at a temperature of about 50 ° C, for a time of 180 seconds.

A phosphating solution was used containing:

*

Said cationic surfactant is ammonium polyglycol ether alkyl chloride of formula (I), where R = C12 n = 11 and m = 1.

B) The phosphating treatment was carried out by immersion / spray: the first immersion phase was carried out at a temperature of about 50 ° C, for a time of 180 seconds., Using normal 5-liter trays of antacid material, or unfortunately heated electrically, under magnetic stirring, followed by the second spray phase for 30 seconds.

A phosphating solution was used containing:

Said cationic surfactant is ammonium polyglycol ether alkyl chloride of formula (I), where R = C12 n = 11 and m = 1.

RINSE PHASE

The rinsing was carried out with tap water at room temperature.

PASSIVATION PHASE

The treatment was carried out at a temperature of 20-40 ° C, for a time of 30-120 seconds, by immersion in a passivating solution containing:

RINSE PHASE WITH DEI0NIZED WATER

The washing was carried out by immersion in deionized water at room temperature, for a time of 10-60 seconds.

The aforementioned sheets were subjected to the phases of the operating cycle described above, obtaining phosphate layers of uniform appearance and microcrystalline morphology, with phosphate weights ranging from 1.5 to 3.5 g / m on ferrous sheets and from 2 to 4.5 g / m on electro-galvanized or hot-dip galvanized sheets.

The weights of the phosphate layers obtained, calculated according to the UNI / IS03892 rule, are shown below:

The sheets were then painted with a typical three-coat cycle for motor vehicles (epoxy cathode primer, epoxy primer and alkyd enamel topcoat), obtaining a total thickness of 95-105 um, and were subsequently subjected to adhesion and corrosion tests. accelerated.

Corrosion resistance test after impact with solid bodies and engraving (scab corrosion test)

The sheets, painted as previously described, were subjected to a corrosion test according to the FIAT 500412 standard (test method 50493/02), based on the appearance of corrosion in the areas of the specimens affected by the impact of solid bodies and on the evaluation of corrosion propagation beyond a score line.

The specimens in question were preliminarily conditioned by immersion in demineralized water at 38'C, for 120 hours; they were then dried and their edges protected with adhesive tape or wax. After allowing at least an hour to elapse from said pre-treatment, stones of standardized size were thrown onto half the surface of the specimen by means of an air spray device in a "gravellometer", while the remaining half of the specimen was drilled with a tip. of incision, an incision at 45 ° with respect to the edges of the specimen, until the support metal is exposed.

The specimens were then placed on a special rack for placement to atmospheric agents, exposed to the open so that it would not be wet by any rain, and were wetted twice a week with a 5% NaCl solution. an exposure period of 6 months, the sub-film penetration was measured, i.e. the extent of corrosion propagation beyond the incision line and around the oxidized impact points, obtaining the following results:

In consideration of the fact that the maximum penetration granted by the aforementioned FIAT standard is 8 mm after an exposure period of 1 month, the results obtained are satisfactory.

Wet Adhesion Test

The aforementioned sheets, after at least 48 hours from painting, were subjected to a wet adhesion test in order to verify the adhesion of the paint film to the metal layer, through the grid incision of the same with a special six knife blades (by Braive Instruments - Belgium) until they reach the base metal, and two subsequent tears with adhesive tape made to adhere with pressure of the nail to the surface (Scoth Brand Tape 610), after artificial aging. This aging was carried out by immersing the test samples in demineralized water for a period of 120 hours, at a temperature of 50 ± 2 “C.

Tape Test, according to the ANSI / ASTM D 3359 "76 method, obtaining the following results:

*

According to the adhesion scale of the aforementioned ANSI / ASTM standard, 5 indicates no detachment of the engraved paint surface of the sample, while 0 indicates a detachment greater than 65% of said surface.

Resistance test of the paint film to stone blows The sheets, painted as described above, were subjected to a resistance test to stone blows in a special "gravellometer", according to the ASTM D 3170-7 * + standard.

The evaluation of the resistance to stone hits was carried out by means of the degree of chipping, given by the combination of the number and diameter of the chipping found. The definition of the degree of chipping was carried out by visual comparison with reference photographs: 1 D indicates more than 250 chips with a diameter greater than 6mm, on a 5 x 5 cm specimen; 3 C indicates 100-150 chips with a diameter between 3 and 6 mm, always on a surface of 5 x 5 cm; 5 B indicates 50-7 * 1 chips of 1-3: nm in diameter; finally 7 A indicates 10-24 chips with a diameter of less than 1 mm.

EXAMPLE 6

Influence of the cationic surfactants of the invention on the corrosion resistance of the phosphate layers of the invention after painting.

Materials and methods

The tests were carried out using two types of sheets: TYPE 1 - FePO ^ cold rolled steel panels;

TYPE 2 - electro-galvanized steel panels on both sides, with a thickness of 7 pm of zinc.

The aforementioned sheets were treated according to the following operating cycle:

DEGREASING PHASE

A solution of a degreasing agent containing:

The treatment was carried out by immersion at a temperature of 50 ° C, for a time of 3 minutes.

RINSE PHASE

The rinsing was performed with tap water at room temperature for a period of 1 minute.

ACTIVATION PHASE

An activating solution was used containing:

The treatment was carried out by immersion at a temperature of 20 ° C, for a time of 1 minute.

PHOSPHATATION PHASE

The phosphating step was carried out by immersion at a temperature of 50 ° C, for a time of 3 minutes, using normal 5 liter trays of antacid material, or unfortunately electrically heated, under magnetic stirring.

The aforesaid sheets were phosphated in the absence (Process A) and in the presence of 0.09 g / 1 of the cationic surfactant of the invention of formula (I), where R = C12 n = 11 and m «1 (Process B),

In both cases, the phosphating solutions contained:

RINSE PHASE

The rinsing was carried out by immersion in mains water at room temperature, for a time of 1 minute, and subsequently by immersion in deionized water at room temperature, for 3 minutes.

The passivation step was not carried out in order to make the comparison between the results obtained using the above phosphating solutions more severe, in the presence or absence of the cationic surfactant of the invention.

The aforesaid sheets were subjected to the phases of the operating cycle described above, giving phosphate layers of uniform appearance and microcrystalline morphology.

PAINTING PHASE

The sheets were then subjected to a typical painting cycle used in the automotive sector:

- epoxy cataphoretic primer, polymerized at a temperature of 180 ° C for 30 minutes, having a thickness of 30-35 µm;

- melamine alkyd enamel, polymerized at a temperature of 160eC for 20 minutes, with a thickness of 35-40 µm.

The sheets were finally subjected to various corrosive tests. Corrosion test

The sheets, painted as described above, were subjected to the Salt Spray Test according to the ASTM B 117 standard. After an exposure period of 1000 hours in a salt fog chamber, the sub-cellular penetration, i.e. corrosion (mm ) along the score line, on both sides, obtaining the following results:

The two cycles gave similar and satisfactory results to the Salt Spray Corrosion Test. These data prove that the phosphate layers obtained using the phosphating solution according to the present invention, which prevents the formation of white spots, have excellent adhesion to the paint layer. and excellent resistance to corrosion.

Corrosion resistance test after impact with solid bodies and engraving (Scab Corrosion Test)

The sheets, painted as described above, were subjected to the corrosion test according to the FIAT 500412 standard (test method 50493/02), as reported in Example 5-After an exposure period of 4 months, the penetration was measured sub-film, i.e. the extent of corrosion propagation beyond the incision line and around the oxidized impact points, obtaining the following results:

Considering that the maximum penetration allowed by the aforementioned FIAT standard is 8 mm after an exposure period of 4 months, the results obtained are satisfactory. The two operating cycles (A) and (B) give similar and satisfactory results to the Scab Corrosion Test described above, which demonstrate that the phosphate layers obtained using the phosphating solution according to the present invention show excellent adhesion to the paint layer and a excellent resistance to corrosion.

Claims (5)

CLAIMS 1. Acid aqueous phosphate solution, suitable for the formation of compact and resistant phosphate layers on metal surfaces, in the absence of white spots, characterized by the fact that it contains hydroxylamine phosphate in association with a cationic surfactant. 2. Phosphate solution according to claim 1, wherein said hydroxylamine phosphate is contained in an amount ranging from 0.6 to 3 g / 1 and said cationic surfactant is contained in an amount ranging from 0.001 to 1 g / 1. 3. Phosphate solution according to claims 1 and 2, wherein said hydroxylamine phosphate and said cationic surfactant are contained in a weight ratio ranging from 10 to 200. 4. Phosphate solution according to claim 2, wherein said cationic surfactant is contained in an amount ranging from 0.005 to 0.1 g / l. 5. Phosphate solution according to claim 1, wherein said cationic surfactant is selected from the group comprising: - Coccodibenzylammonium chloride, with an alkyl chain consisting of 12-14 carbon atoms; - Polypropoxylates and polyethoxylates of alkylammonium chloride and phosphate; - Benzalkonium chloride and derivatives, with side chain consisting of 12-14 carbon atoms; - N-alkylammonium chloride, with an alkyl residue consisting of 12-18 carbon atoms and the remaining consisting of H and / or methyl; - Alkyl polyglycol ethers of ammonium chloride and sulphate, of general formula (I): 6. Phosphate solution according to claim 5, wherein said cationic surfactant is an alkyl polyglycol ether of amount chloride or sulfate of formula (I), where n = 10-12, m = 1 or 2, R1, R2 R3 = H and / or methyl and R = C12-C20 alkyl. 7. Phosphate solution according to claim 1, wherein said cationic surfactant is formed in situ, by addition to said phosphate solution of a surfactant of formula: in which n is between 4 and 18 and R is a linear or branched alkyl, consisting of 10-22 carbon atoms. 8. Phosphate solution according to claim 1, containing: - 0.6-3 g / 1 of hydroxylamine phosphate; - 0.001-1 g / l of a cationic surfactant; - 5-25 g / 1 of phosphate ions; - 0.5 "2.0 g / 1 of zinc ions; - 1.5-4.0 g / 1 of nitrate ions; - 0.3-1.2 g / 1 of manganese ions; - 0.001-0.1 g / 1 of iron ions; - 0.4-1.1 g / 1 of nickel ions; And - 0.3 "1.2 g / 1 of total fluoride ions. 9. Phosphate solution according to claim 8, having a total acidity value comprised between 10 and 28 points and a free acidity value comprised between 0.5 and 2.0 points. 10. Phosphate solution according to claim 8, wherein said zinc ions are contained in a quantity ranging from 0.5 to 1.5 g / l. 11. Phosphate solution according to claim 8, wherein said nickel ions are replaced by a combination of 0.05-0.2 g / 1 of cobalt ions and 0.5 "1.5 g / 1 of magnesium ions. 12. Phosphate solution according to claim 8, further containing 0.003-0.08 g / 1 of copper ions. 13. Phosphate solution according to claim 8, further containing a suitable anti-foaming agent, in an amount comprised between 10 and 30% by weight with respect to the cationic surfactant. 14. Phosphate solution according to claim 8, further containing 0.05-0.3 g / l of an organic sequestering agent 15. Phosphate solution according to claim 14, wherein said polyfunctional organic sequestering agent is EDTA and / or tartaric acid, in quantities ranging from 0.08 to 0.1 g / l. 16. Process for the formation on metal surfaces of a compact and resistant layer of phosphating, in the absence of formation of white spots, characterized by the fact that said surfaces are treated, after the appropriate pre-treatments, with an aqueous phosphate solution containing hydroxylamine phosphate in association with a cationic surfactant. 17. Process according to claim 16, wherein said phosphate solution contains said hydroxylamine phosphate in an amount ranging from 0.6 to 3 g / 1 and said cationic surfactant in an amount ranging from 0.001 to 1 g / 1. 18. Process according to claims 16 and 17, wherein said phosphate solution contains said hydroxylamine phosphate and said cationic surfactant in a weight ratio ranging from 10 to 200. 19. Process according to claim 17. wherein said cationic surfactant is contained in an amount ranging from 0.00f> to 0.1 g / l. 20. Process according to claim 16, wherein said phosphate solution contains: - 0.6-3.0 g / l of hydroxylamine phosphate; - 0.001-1 g / l of a cationic surfactant; - 0.5-2.0 g / 1 of zinc ions; - 1.5 - ^. 0 g / 1 of nitrate ions; - 0.3-1.2 g / 1 of manganese ions; - 0.001-0.1 g / 1 of iron ions; - 0.4-1.1 g / 1 of nickel ions; e - 0.3-1.2 g / 1 of total fluoride ions. 21. Process according to claim 20, wherein said phosphate solution has a total acidity value comprised between 10 and 28 points and a free acidity value comprised between 0.5 and 2.0 points. 22. Process according to claim 20, wherein said zinc ions are contained in quantities ranging from 0.5 to 1.5 g / l. 23- Process according to claim 20, wherein said nickel ions are replaced by a combination of 0.05-0.2 g / l of cobalt ions and 0.5-1.5 g / l of magnesium ions. 24. Process according to claim 16, wherein said metal surfaces are based on iron and / or zinc and / or aluminum. 25- Process according to claim 16, in which the treatment with said phosphate solution is carried out at a temperature of 40-55 ° C, for a time of 1-5 minutes. 26. Process according to claim 16, wherein the treatment is carried out by immersing the metal surfaces in the aqueous phosphate solution. treatment is carried out by spraying the aqueous phosphate solution on the metal surfaces. 28. Process according to claim 16, in which the treatment is carried out by immersing the metal surfaces in the aqueous phosphate solution for 100-200 seconds at 45-50 ° C and subsequent spray application of the same solution for a time of 20- 50 seconds, at 45-50 ° C. 29. Process according to claim 16, wherein the pre-treatment consists of a degreasing step with alkaline degreasing agents and a conditioning step with a solution of titanium or zirconium salts. 30. Process according to claim 16, wherein the pretreated and phosphated metal surfaces are further rinsed, passivated and electro-painted.