JP4242653B2 - Metal surface treatment by carboxylation - Google Patents

Abstract

The invention relates to a method for treating a metal surface by carboxylation before forming, said metal being selected from zinc, iron, aluminium, copper, lead and the alloys thereof as well as copper-coated, aluminium-coated, galvanised steels. Said method is carried out in oxidising conditions in relation to the metal by bringing said metal into contact with an aqueous, organic or hydro-organic bath comprising at least one organic acid in free form or in salt form. The inventive method is characterised in that: the organic acid is a saturated or unsaturated aliphatic monocarboxylic or dicarboxylic acid; the organic acid is in solution and/or emulsion in the bath at a concentration greater than 0.1 mole/litre; the pH of the bath is acid.

Description

  The present invention is formed on a metal surface selected from zinc, iron, aluminum, copper, lead, and alloys thereof, and galvanized steel, aluminum-coated steel, and copper-coated steel with very fine crystals. The present invention relates to a method for depositing a conversion coating that makes it possible to produce a conversion coating at high speed.

When carried out before forming the metal plate, these chemical conversion treatments on the metal surface generally have the following effects:
-Improvement of mechanical friction properties by lubrication, for example for stamping metal plates,
-Have at least one temporary protection against corrosion;

For this first type of application, especially the treatment known as phosphoric acid pretreatment in which a metal phosphate coating with a weight per unit area of the order of 1 to 1.5 g / m ² is used is particularly used. Is done.

  However, these chemical conversion treatments can also be performed after the metal plate is formed in order to improve the adhesion of organic coatings to be subsequently coated such as paint. An example of the phosphoric acid treatment will be described. The weight per unit area of the metal phosphate film deposition is larger than that of the phosphoric acid pretreatment.

  These various chemical conversion treatments generally consist of anodic dissolution of surface metal elements, followed by precipitation of compounds formed by reaction of the dissolved metal elements with components present in the chemical bath. Its dissolution requires creating oxidizing conditions for the surface metal and generally occurs in an acidic environment. The precipitation of the metal compound to form the chemical conversion film requires a sufficiently high concentration, and is promoted by an environment where the acidity is locally lowered by the action of dissolution of the metal. It is the nature and structure of the compound deposited on the treated surface that determines the degree of protection against corrosion, improved frictional properties and / or adhesion properties, and other coating properties.

  In order to ensure surface oxidation of the surface to be treated and to promote dissolution thereof, chemicals for metal oxidation are added to the treatment solution and / or the surface is subjected to the action of the treatment solution. It is possible to proceed by chemical or electrochemical methods by electrically polarizing the.

  Apart from what can be an oxidant, the chemical bath essentially contains anions and cations that can form insoluble compounds with the dissolved surface metals. Thus, the main chemical conversion treatment is chromate treatment on zinc-coated steel or aluminum-coated steel, phosphating treatment on non-alloyed non-coated steel or coated steel, or oxalic acid treatment of alloy steel such as stainless steel.

  After contact with the conversion bath, the treated surface is generally washed to remove unreacted components of the surface and / or treatment solution, and the surface is then specifically treated to cure the conversion coating and / or its properties. Dry to improve.

  The conditions of application, the nature and concentration of the additive have a significant influence on the structure, morphology and compactness of the resulting conversion coating and thus its properties.

  The chemical conversion treatment itself generally employs a pretreatment solution that is pre-degreased and cleaned first, followed by creating and / or promoting crystal nucleation sites on the surface to be treated. A pretreatment consisting of an operation known as purification can be performed.

  To this end, titanium salt sols or colloidal suspensions have recently been used on zinc-coated surfaces, allowing subsequent conversion coatings with finer crystals in denser coatings. .

  It is also possible to carry out a post-treatment at the end of the conversion treatment in order to improve the properties of the conversion coating. For example, you may implement the post-processing by chromate on the chemical conversion film obtained by the phosphoric acid process.

International patent application WO 95/21277 is
For treating zinc-coated surfaces containing polyhydroxyarylcarboxylic acids, such as gallic acid or protocatechuic acid, or the depsides of this acid such as tannic acid obtained by reacting it with glucose, and silane-based adhesion promoters The aqueous composition is described.

  Conventional accelerators for zinc coated surfaces such as phosphates, nitrates, fluorides or organic acids are used with this treatment composition.

  Treatments performed with this composition provide not only excellent protection against corrosion, but also excellent paint adhesion.

  Patent application FR 2 465 008 deposits a conversion coating on a zinc coated surface using a treatment solution that may contain a soluble oxalate associated with an activator that is a carboxylic acid, particularly a short chain diacid. Describes the method.

  The concentration of oxalic acid in the described treatment solution is 7.5 g / liter, i.e. less than 0.08 mol / liter.

  The document EP 0 494 431 (Kawasaki) makes it possible to improve the properties of a conversion coating obtained on a zinc-coated surface by adding carboxylic acid to a chromate treatment solution containing colloidal silica and / or It teaches that the chromium content of the solution can be significantly reduced.

The weight of the coating obtained by these various treatments, ie the weight per unit area, varies significantly depending on the main purpose and can vary from 1 g / m ² to 8 g / m ² .

  Various treatments such as chromate treatment, phosphoric acid treatment and oxalic acid treatment according to the prior art generally present a serious disadvantage that these products are toxic to mankind and the environment. Furthermore, when spot welding metal plates with the above conversion coating, this causes the release of toxic fumes.

  Accordingly, it is an object of the present invention to deposit a conversion coating on a metal surface that is not only free of environmentally harmful compounds, but is more effective in corrosion protection and / or pre-lubrication than those obtained by prior art methods. It is to provide a chemical conversion treatment for the metal surface before it is formed using a bath that enables it.

  Another object of the present invention is also that an organic coating having excellent adhesion can be deposited on the surface treated according to the present invention after shaping and degreasing, especially by electrophoresis, provided that the deposited conversion coating is It is assumed that it is easily removed during degreasing.

For this purpose, the present invention provides:
The organic acid is a saturated or unsaturated aliphatic monocarboxylic acid or dicarboxylic acid,
The organic acid is in a concentration of greater than 0.1 mol / l in the bath solution and / or emulsion;
-The pH of the bath is acidic,
Zinc, iron, aluminum, copper, lead, and alloys thereof, and metal surfaces selected from galvanized steel, aluminum-coated steel, and copper-coated steel are subjected to the surface of the metal in oxidation conditions related to the metal. For the treatment by carboxylation prior to molding by contacting with an aqueous, organic or hydro-organic bath containing at least one said organic acid in free or salt form.

  The invention also relates to the use of the surface treatment method by carboxylation for temporary protection against corrosion of the metal surface.

  The present invention further includes a metal plate surface treatment having a surface of a metal selected from zinc, iron, aluminum, copper, lead, and alloys thereof, and galvanized steel, aluminum-coated steel, and copper-coated steel. The present invention relates to a method for producing the shaped metal plate, which is performed according to the invention, and lubricates and forms the treated metal plate. It is particularly preferred to apply this method according to the invention to a steel sheet coated with zinc or a zinc alloy and then form it by stamping.

  The invention will be better understood by reading the following description, given by way of non-limiting example, with reference to the accompanying drawings, in which:

In accordance with the present invention, the conversion coating contacts the surface of the metal with an aqueous, organic or hydro-organic bath containing at least one organic acid in solution or emulsion in oxidizing conditions involving the metal. Precipitates by surface carboxylation by.

  The present invention used aliphatic monocarboxylic acids or dicarboxylic acids that may have one or several unsaturations.

  The acidity constant of the acid is on the order of 4.8 and the normal pH of the bath according to the invention is generally lower than this value. If it is desired to lower the pH further, the treatment bath can be acidified using, for example, nitric acid. The pH of the bath can also be raised, for example, by adding soda. The acidic bath used in the treatment according to the invention must in all cases have a pH value between 1 and 7 which allows the upper limit to avoid the presence of metal hydroxide in the conversion coating. . For the lowest pH, this ensures that the surface metal function ensures sufficient deposition of the conversion coating.

  The at least one organic acid used according to the invention is added at a concentration greater than 0.1 mol / l in the solution in the bath or in the emulsion.

  When the concentration of the organic acid in the treatment bath is less than 0.1 mol / liter, the rate of formation of the conversion film based on the carboxylic acid metal salt is no longer sufficient to obtain a conversion film effectively within the time allowed for the treatment. Absent.

  In a preferred embodiment, the aliphatic organic acid according to the invention is selected from among saturated monocarboxylic acids having 5 to 16 carbon atoms. Hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid and decanoic acid are particularly preferred.

  In another preferred embodiment, the aliphatic organic acid according to the invention is selected among unsaturated monocarboxylic acids having 10 to 18 carbon atoms. Undecenoic acid, oleic acid or linoleic acid is particularly preferred.

  In another preferred mode of embodiment, the aliphatic organic acid according to the invention is selected from saturated dicarboxylic acids having 4 to 12 carbon atoms. Sebacic acid or azelaic acid is particularly preferred.

  In another preferred embodiment, the at least one aliphatic monocarboxylic acid secured is heptanoic acid.

  More preferably, the bath contains decanoic acid or undecenoic acid in addition to heptanoic acid.

  By using a mixture of heptanoic acid and an organic acid such as decanoic acid or undecenoic acid, a denser and more effective conversion coating to protect the metal surface from corrosion is obtained.

The oxidation conditions of the carboxylation bath are as follows:
-Adding to the bath chemicals for oxidation of the metal that are compatible with the properties of the metal, such as perborate tetrahydrate or hydrogen peroxide;
Or alternatively, by causing a current to circulate between the metal surface previously immersed in the bath and at least one counter electrode that is also immersed.

  When the oxidizing conditions for zinc are obtained by adding zinc oxidizing chemicals to the bath, the oxidizing agent and / or accelerator is preferably sodium perborate, sodium nitrite, hydrogen peroxide, hydroxylamine sulfate. And a group comprising nitroguanidine.

In some cases, chemical baths
-Chemicals or buffers for pH adjustment to adjust the conditions for forming a chemical conversion film on the surface,
-Additives such as surfactants that facilitate the performance of the treatment and the distribution of the bath on the surface to be treated;
-Extend the duration of the bath, e.g. chelating agents to delay the precipitation of compounds other than those desired to be obtained in the conversion coating, or additives such as bactericides, and-to accelerate the treatment Contains an agent.

  The chemical conversion bath according to the present invention also includes ethanol, n-propanol, butanol, dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), 4-hydroxy-4-methyl-2-pentanone, diacetone alcohol. , Glycol ethers, or the like, or other organic acids or minerals such as minerals.

Carboxylation treatment bath, + 3 when containing a solution concentration of not less than 1.10 ^-3 mol / liter of the rare earth ion of gadolinium in an oxidized normal, surprising results.

  The resulting conversion coating then constitutes crystals of two different types, possibly different shapes, which are even more effective in resistance to corrosion.

Preferably, the concentration of organic acids in the bath, oxidation conditions for the use conditions and the metal of the bath, so as to obtain a 1 g / m ² and the weight per unit area of between 6 g / m ² carboxylation coating on a metal surface Configure.

  Other advantages of the method according to the invention will become apparent by reviewing the non-limiting examples of the invention provided below.

Materials for obtaining chemical conversion film:
1) Properties of the tested substrates Electrodeposition with or without microalloying, with a thickness between 0.7 mm and 1.2 mm, bare or in chloride or sulfate baths Or a steel plate of ES grade (stamping steel) or HES grade (deep drawing steel) covered with a zinc coating having a thickness of about 10 μm applied by hot dip galvanization.

2) Components of the chemical conversion treatment bath tested a-Solvents and co-solvents The treatment solutions tested are generally based on water as the main solvent and ethanol as the co-solvent, propanol, DMSO, NMP, 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol) Alternatively, other polar solvents that are at least partially miscible with water can also be used as cosolvents.

2. b-Organic acids As examples for describing the invention, it is possible to use heptanoic acid (abbreviation: HC ₇ , Aldrich product, reference number 25,873-3) and / or decanoic acid (abbreviation HC ₁₀ , Rectapur). Company product, reference number 20 243.298, up to 0.1% sulfur ash).

2. c- Substrate Oxidizing Chemical Unless otherwise indicated, 2 g / liter sodium perborate tetrahydrate (NaBO ₃ .4H ₂ O) is used as the chemical for oxidizing zinc. Hydrogen peroxide solution (ie, H ₂ O ₂ ) can also be used.

2. d-pH
Unless indicated, the solution is used at its normal acidic pH, but any increase in pH can be obtained by adding soda.

2. e- Other components and additives Metal cations, Cu ²⁺ , Co ²⁺ , Ni ²⁺ , Fe ²⁺ , Zn ²⁺ , Mn ²⁺ , Al ³⁺ , (rare earth) ^{n +} can also be added.

  3) Standard operation method of treatment with chemical bath

  Ridoline (trademark) is a degreasing aqueous solution containing an alkali metal salt, a surfactant and potassium hydroxide.

  Ridosol ™ is a wet matrix of liquid degreasing agent that contains a mixture of surfactants.

  Fixodine ™ 50CF is an activator (also called a nucleating agent) containing an alkali metal salt-based compound such as a titanium salt.

Method for evaluating the obtained chemical conversion film 1) Weight per unit area of the deposited film In order to measure the weight per unit area, the chemical conversion film formed on a specific surface is dissolved with a complexing solution. The immersion time is such that complete dissolution of the coating is obtained (about 1 minute for a coating generated from HC _{7 at} a rate of 0.3 mg / cm ² ).

The weight per unit area expressed in mg per cm ² is evaluated based on the difference in weight between the coated sample and the same sample after undergoing dissolution treatment.

The composition of the lysis solution is as follows:
-Disodium salt of EDTA (ethylenediaminetetraacetic acid): 0.1M
-MBT (mercaptobenzothiazole) or BZD (benzotriazole): 0.1 g / l. These compounds suppress dissolution of the metal substrate.

  The pH of this solution is adjusted to a value close to 8 by adding soda to obtain optimal complexation of the metal cation.

2) Water corrosion resistance This test consists of periodically measuring the polarization resistance R _p with a potentiometer by a voltage sweep with an amplitude of ± 10 mV in the vicinity of the corrosion potential E _cor .

The equipment used for this evaluation is usually
A window is pierced at the bottom and the standard aqueous electrolyte ASTM D 1384-87 (this electrolyte is 148 mg / liter sodium sulfate (Na ₂ SO ₄ ), 138 mg / liter sodium bicarbonate (NaHCO ₃ ), And a tank made of polymethyl methacrylate containing 165 mg / liter sodium chloride (NaCl) and having a pH close to 8.
A working electrode, a saturated calomel reference electrode (“SCE”), and a supplementary metal surface covered with a conversion coating to be evaluated blocking the bottom window of the cell; 3 electrodes immersed in electrolyte solution, platinum electrode as counter electrode,
-Includes a Princeton (TM) 273 or 263 type potentiostat connected to three electrodes and controlled by software with reference number m352 of EG & G Princeton (TM).

3) Atmospheric corrosion resistance according to DIN standard 51160 First, each cycle has the following characteristics:
-1st part: 8 hours-40 ° C, relative humidity 100%,
-Second part: 16 hours-Place in the humid atmosphere of a humidified greenhouse regulated by a continuous cycle with ambient temperature and humidity.

  Unless indicated, this method consists of continuing to count the number of cycles until it is recorded that at least 10% of the treated surface is covered with white rust.

4) Behavior under friction This test consists of measuring the surface-to-surface friction coefficient by increasing the pressing pressure to 80 MPa.

The sample processed before the test is covered with an oil of reference number 6130 manufactured by QUAKER, and the amount of the oil poured is, for example, about 1 to ² g / m ² .

5) Behavior during stamping This test consists of producing a complete stamping from a sample of a sheet metal blank subjected to chemical conversion treatment. For example, a dish having a diameter of 32 mm and a depth of 25 mm is produced using the first blank having a diameter of 64 mm.

  For the same type of sheet metal blank whose surface treatment is to be tested, the maximum stamping force beyond which the blank will burst during stamping is evaluated from the predetermined pressing force of the blank holder. This maximum value is recorded in a manner of following a curve representing a change in the maximum stamping force Fmax, which is a function of the blank holder force, as shown in FIG.

6) Phosphate treatment suitability after film degreasing Initially, the surface with the conversion coating is prepared by removing the conversion coating in Table 3-"Material for obtaining conversion coating", part 3) "By conversion bath" Degrease according to the procedure specified in Steps 1 and 2- of “Standard Operating Method for Treatment”, and then, on this degreased surface,
-2% by volume Granodine 9580 M / CF (a phosphating mixture containing 10-25% phosphoric acid and a small amount of hydrofluoric acid),
-0.7% by volume Starter 958 / CF (aqueous solution containing zinc salt in the presence of a small excess of nitric acid),
-0.04% by volume of Intensifier No. 1 (Aqueous solution of metal salt in the presence of a small amount of phosphoric acid)
-0.5 vol% Primaire M (aqueous solution containing> 2% sodium hydroxide) to adjust the pH,
-0.05% by volume Compensator M (sodium nitrite aqueous solution, accelerator for crystallization phosphating bath),
A normal phosphoric acid treatment is performed by applying an aqueous composition containing

・ Operating conditions:
-Demineralized water-Immersion treatment 2 minutes-Temperature = 55 ° C ± 2 ° C
• Bath management by chemical analysis The analytical value must be within the following range:
-[Zn ²⁺ ] = 0.9 to 1.1 g / liter-[Mn ²⁺ ] = 0.7 to 0.9 g / liter-[Ni ²⁺ ] = 0.18 to 0.25 g / liter-[F] = 0.25 to 0.35 g / liter Secondly, the quality of the obtained phosphoric acid-treated film is examined with an electron microscope.

7) Suitability for organic coatings by electrophoresis after degreasing and phosphoric acid treatment First, part 3) “Standard operating method of treatment by chemical bath” in Table I-“Materials for obtaining chemical coating” above The surface treated according to the operation method specified in Steps 1 and 2 of the above is degreased to remove the chemical conversion film, and then the degreased surface is subjected to phosphoric acid treatment according to the method of operation specified in 6) above. . Finally, the organic coating is electrophoretically deposited on a phosphated surface according to the following conditions (example of formulation PPG 752-965 1) in the usual manner.

Control bath formulation-43.16 wt% deionized water (up to 10 μS)
-48.18% by weight polyamine urethane-derived binder-8.66% by weight cationic electrodeposition paint paste (pigment dispersion),
Because
-Dry extract = 20-24%
-PH = 5.7 to 6.1 (at 25 ° C)
-Conductivity of the mixture = 1500-2000 mS (at 25 ° C)
・ Painting conditions:
-Bath temperature = 28-35 ° C
-Coating time = 120 to 180 seconds-Anode / cathode ratio = 1/4
-Working voltage = 200-320V
-Nominal baking (T ° level) = 175 ° C, 15 minutes-Target thickness = 18-24 µm

The purpose of this example is to determine the conditions for the carboxylation treatment according to the invention which makes it possible to obtain a conversion coating which is dense and finely crystallized on a zinc-coated plate-like metal surface. Processing zinc coated steel plate is the next step:
-Preparation for treating the surface-Immersion of the prepared surface in a chemical bath-Proceed according to drying and observation of the treatment film obtained.

  The initial preparation process is as described in the successive displays 1 to 4 of Table I. The solvent of the conversion bath is a water / ethanol mixture, and the ratio is adjusted so that the added organic acid is completely dissolved.

  The parameters are variously changed so that the optimum processing conditions can be determined.

1.1 pH
When pH is changed, it turns out that crystallization of a chemical conversion film is inferior, so that pH is high. Furthermore, a pH that is too high can lead to parasitic precipitation of metal hydroxides. This is why this method is actually limited to acidic pH between 1 and 7. The minimum value of pH is set so as to ensure that the chemical conversion film is satisfactorily deposited as a function of the surface metal. For example, in the case of zinc, the treatment is preferably accomplished at a pH between 4 and 6.

1.2 Bath Temperature The bath temperature is varied between 20 ° C. and 80 ° C., and it is observed that increasing the temperature promotes the rate of deposition.

1.3 Concentration of organic acid or corresponding salt It can be seen that varying the concentration of the organic acid should have a concentration range between 0.1M and 1.5M. In fact, as already seen, when the concentration is lower than 0.1M, the rate of formation of the conversion coating based on the metal carboxylate is no longer sufficient to obtain a conversion coating effectively within the time allowed for processing. Absent. Concentrations higher than 1.5M are not possible because the organic acid solubility limit is close to 1.4-1.5M.

  When the organic acid (s) are used in the form of a salt, it is preferred to use chloride, nitrate or sulfate at a concentration of 3 g / liter or less.

1.4 Length of carbon chain of organic acid n
When the length of the carbon chain is changed, the longer the carbon chain of the aliphatic acid (the higher the n), the finer the crystal of the coating, and the weight of the chemical conversion coating increases under the same amount of processing conditions. It can be seen that when the value changes from 7 to 10, the value increases by about 1.5 times.

  Furthermore, the denseness of the conversion coating as well as the corrosion resistance provided by this coating increases with the length of the fatty chain of the carboxylic acid used.

1.5 Properties and concentrations of oxidizing agents Various oxidizing agents such as dissolved oxygen (O ₂ ), nitrite (NO ₂ ⁻ ), hydrogen peroxide (H ₂ O ₂ ) or perborate (BO ₃ ⁻ ) used. It can be seen that the presence of the oxidizing agent or accelerator has a favorable effect on the denseness of the chemical conversion coating.

1.6 Duration of bath immersion or duration of treatment The treated zinc coated surface has the following properties:
-Water / alcohol ratio: 1,
N = 7 (heptanoic acid), [HC ₇ ] = 50 g / liter,
-Oxidizing agent: sodium perborate NaBO ₃ .4H ₂ O 2 g / liter-pH about 4.7
Soak in a bath with a few minutes.

  The duration of the treatment is changed and the weight per unit area of the resulting carboxylated coating is observed.

  It can be seen that an increase in the immersion time in the bath is favorable for the denseness of the coating.

Comparison with prior art At the same time, the following treatment is carried out on the same zinc-coated metal sheet blank under the following conditions.

1. Phosphoric acid-treated metal plate having a film with a weight of about several g / m ² per unit area 6) Normal phosphoric acid treatment on the degreased surface according to the bath conditions specified in 6) (Adequacy of phosphoric acid treatment after film degreasing) Do.

2. Metal plate pretreated with phosphoric acid having a coating weight of about 1 g / m ² per unit area The following conditions:
-A chemical bath consisting of phosphoric acid, Mn and Ni (e.g. Chmetall VP 10118 formulation)
-Drying at 200 ° C-Weight per unit area = 1.1-1.5 g / m ²
Accordingly, phosphoric acid pretreatment is performed on the degreased surface.

  3. With metal plates treated with oxalic acid according to FR 2 465 008, the method follows the mode of operation described in Example 4 of this document with a treatment solution containing a complex fluoride and oxalate.

  4). With a carboxylated metal plate according to WO 95/21177, the method follows the mode of operation described in Example 1 of this document with a treatment solution containing gallic acid and 3-glycidoxypropyltrimethoxysilane.

  By proceeding with the evaluation on the different types of conversion coatings defined in the above method sections 3, 4, 5, 6 and 7, the following results are obtained.

  2.1 Atmospheric corrosion resistance

  It can be seen that the treatment according to the invention provides a better atmospheric corrosion resistance than the treatment according to the prior art.

  2.2 Behavior under friction

  Therefore, the chemical conversion treatment according to the present invention performed before lubrication makes it possible to eliminate stagnation, and at the same time, the friction coefficient is lowered when the pressing pressure is increased.

  It can also be seen that the treatment according to the invention makes it possible to obtain a significantly improved coefficient of friction compared to the phosphoric acid pretreatment.

2.3 Behavior during stamping
-On the one hand, on a carboxylated (duration: 5 minutes) metal plate according to the invention (gradient is symbol △ for no supplementary lubrication, symbol □ for supplementary lubrication with oil QUAKER reference number 6130) Marked by)
The other shows the results obtained on the same untreated metal plate (representing a comparative example by the gradient marked with symbol ◇).

  In general, the lower the slope obtained and the less inclined, the better the behavior during stamping.

  From these three series of tests, it is estimated that the chemical conversion treatment according to the present invention can advantageously replace the conventional phosphoric acid pretreatment and is more likely to avoid the contamination problem caused by the use of phosphoric acid. Is done.

Paintability The metal surface subjected to the chemical conversion treatment according to the present invention is mainly used in the automobile field. It is therefore important to check that these surfaces once coated are compatible with the processes normally used in the industry for the coating of metal plates, in particular zinc-coated metal plates.

3.1 Degreasing properties Molding by stamping generally requires lubrication of the metal surface and then removes all traces of oil from this surface when it is desired to proceed to other operations such as painting or enamel finishing. At the same time, if there is a chemical conversion film formed before molding, it is necessary to remove it. A degreasing step is performed for this purpose, but it is important that the conversion coating should be easily removed for success. Therefore, it is important to check that the chemical conversion film according to the present invention can be easily degreased.

  First, the alkaline degreasing of the metal surface with the conversion coating is specified in steps 1 and 2 of part 3) “Standard operating mode of treatment with conversion bath” in Table I “Materials for obtaining conversion coating”. Perform under conditions.

  Second, the surface of the treated and then degreased sample is observed to see if the conversion coating has disappeared.

  It can be seen that the carboxylated coating according to the invention is completely extinguished.

3.2 Suitability of phosphating after degreasing The procedure according to the method of operation defined in 6) of the method is carried out by treating two surfaces of the sample according to the invention, namely the bare steel surface and the zinc-coated surface. And the conversion coating is observed to provide a suitable range.

3.3 Suitability of organic coating by electrophoresis after degreasing and phosphoric acid treatment Samples treated according to the present invention do not show any special defects when they are degreased, phosphoric acid treated and then coated.

Effect of cosolvent and soaking time on weight per unit area of conversion coating The procedure was performed using heptanoic acid at a concentration of 0.38 mol / liter as described in Materials and Methods.

  After the chemical conversion treatment, purification pretreatment is performed.

As shown in FIG. 2, the weight per unit area of the conversion coating is a function of the time during which the plate metal blank to be treated is immersed in the solution of the present invention as a function of different solvent composition (volume%),
Case 1: 62% water, 38% ethanol (symbol +)
Case 2: Water 61%, 1-propanol 39% (symbol x)
Case 3: 43% water, 57% DMSO (symbol △)
Case 4: Water 56%, NMP 44% (symbol □)
Case 5: 60% water, 40% diacetone alcohol (symbol ○)
Evaluate against.

  The above mixture is optimized for maximum solubilization of over 95% of heptanoic acid.

From the resulting curve,
-The increase in conversion coating is similar in cases 1, 4 and 5;
-It can be concluded that the rate of increase of the coating is lower in cases 2 and 3 than in cases 1, 4 and 5 for an immersion time of less than 280 seconds.

According to observation with a scanning electron microscope, the crystal morphology of the film is
-After 30 seconds of processing for cases 1, 4 and 5,
-Note that after 300 seconds of processing for cases 1, 3 and 4, they are exactly the same.

  Other cosolvents could be envisaged for carrying out the invention, in particular amide solvents such as N-methylformamide, N, N-dimethylformamide or sulfone solvents such as tetramethylsulfone.

Emulsions in chemical conversion solutions In order to avoid the use of solvents that may cause safety problems, it is possible to obtain processing solutions highly concentrated in organic acids according to the invention using suitable surfactants. is there.

  Using 1% by volume of ATOFINA's product FORAFAC 1033D, which is 30% of a perfluorinated anionic surfactant derived from a perfluoroalkyl sulfonic acid mate in water, 50 g / liter heptanoic acid and 2 g / liter perboric acid An emulsion containing sodium tetrahydrate is prepared. The emulsion does not contain any solvent other than water, and the surfactant makes all of the acid into an emulsion and / or solution in water.

  Two treatment solutions having different pHs (first is a normal pH of about 4 and the other is adjusted to about 4.7 by adding soda) are prepared.

  The same metal plate sample as in Example 3 is immersed in the first or other treatment solution for 5 minutes, and then the treated surface is washed and dried.

According to observations made on the treated surface,
At pH about 4, a carboxylated coating of 0.3 mg / cm ² is obtained, which is comparable to that obtained in Example 4 with the same soaking time. The coating appears to contain traces of surfactant, indicating that the chemical is inert with respect to the precipitation reaction.

  -At a pH of about 4.7, the weight per unit area obtained is slightly less (about -30%), but the coating form is comparable to that obtained in Example 4 and the coating is no longer interfacial. Contains no traces of activator.

Carboxylation of substrates under electrochemical oxidation This relates to the production of metal cations generated from metal surfaces by electrochemical means. In this case, the base material, which is a zinc-coated metal plate, is immersed in a treatment solution to apply an electric potential between two titanium plates that are electrically connected and have the same electric potential to generate an anode current. Pass through.

  As the treatment solution, use a solution of 50% water / 50% ethanol containing 0.38% mol / liter heptanoic acid and having a pH between 3.2 and 4.7 depending on the amount of soda added. .

The chemical conversion treatment according to the present invention is performed by applying the operation method described in 3) of the material section, immersing a sample of the metal plate in the treatment solution, and allowing an electric current to pass between the immersed metal plate and the titanium plate. . This procedure at a current density of 10 mA / cm ² and 25mA / cm ^2, performing the processing time of 1, 3, 5 and 10 seconds.

FIG. 3 shows the results obtained for the weight per unit area, the symbol □ indicates the curve obtained at a current density of 10 mA / cm ² and the symbol Δ is obtained at a current density of 25 mA / cm ² . The curve is shown.

  With these results and from observations on the treated surface, the conversion coating obtained after 1 to 10 seconds has a density per unit area, morphology and crystallization comparable to that obtained after 60 to 300 seconds with chemical oxidation. You can see that The mode of application of this treatment according to the invention makes it possible to improve the formation rate of the conversion coating by at least 10 or 100 times and is therefore particularly advantageous.

These observations were confirmed by the test results of atmospheric corrosion resistance of samples treated at a current density of 25 mA / cm ² and are shown in Table III.

Mixture of heptanoic acid and decanoic acid The procedure of Example 4 was carried out using a mixture of 0.38 mol / l of heptanoic acid with an 80/20 mixture of heptanoic acid (abbreviation HC ₇ ) and decanoic acid (abbreviation HV ₁₀ ) (case A) or It is replaced with a 50/50 mixture (Case B) and the immersion time is 5 minutes.

  The sample is evaluated for atmospheric corrosion resistance according to the test in the method section.

Next, water corrosion resistance was evaluated by measuring polarization resistance, and the results are shown in FIG. However,
・ Untreated zinc coated surface is indicated by +
The zinc-coated surface treated according to the invention without post-treatment is
-The one by heptanoic acid is indicated by the symbol △,
-The one by decanoic acid is indicated by the symbol x,
A mixture of heptanoic acid and decanoic acid having a molar ratio of HC ₇ / HC ₁₀ equal to 80/80 is indicated by the symbol *.

  The other gradients in FIG. 4 are dealt with below.

  Comparing these three slopes, it can be seen that the mixture of heptanoic acid and decanoic acid has improved water corrosion resistance compared to heptanoic acid or decanoic acid alone.

  According to observations made on the resulting coating, the coating corresponding to the solution of Case B (50/50) has a very different form than that obtained with only one of heptanoic acid or decanoic acid. You can see that. The conversion coating obtained with this acid mixture appears to be much denser, which explains the improved water corrosion resistance. This effect is more remarkable in case A (8/20). X-ray diffraction of the coatings obtained in these two cases demonstrates not only the presence of zinc decanoate but also that of the mixed species.

Post-treatment It is common to carry out post-treatment to improve the properties of the conversion coating, and the inventors have therefore sought the type of post-treatment that best fits the substrate with the conversion coating according to the invention.

  The zinc coated metal plate is treated by soaking for 5 minutes in a water / ethanol 50/50 solution containing 0.38 mol / l heptanoic acid and 2 g / l sodium perborate hydrate.

  The post-treatment is carried out by immersing in a post-treatment solution whose properties are given in Table V for 60 seconds, followed by a final cleaning in the operating mode described in section 3 of the material.

  After the post-treatment, the treated surface of the sample is observed and / or analyzed, and the water corrosion resistance is evaluated by a potentiometer according to item 2 in the material section.

  It can be seen that the post-treatment of Ti has no effect, but the post-treatment of Si clearly allows a slight improvement in corrosion resistance without any change in the form of the conversion coating.

In the case of post-treatment solutions containing rare earth metals (Gd ^III , Lu ^III ) in the +3 oxidation state, a rare earth coating is observed on the conversion coating when tested at the same concentration and at the same pH. effect on the polarization resistance _{R p} will depend lanthanide as shown in FIG. ^4, a very satisfactory effect cases of significant ^{effects, Gd III} of ^{Lu III.}

In conclusion, it is the solution of Gd ^III that appears to have the greatest impact on the morphology of the carboxylated coating and the water corrosion resistance it provides among the post-treatment solutions evaluated. It also makes it possible to increase the atmospheric corrosion resistance since an improvement of about 10 cycles is observed during the tests conducted in the humidified greenhouse.

Addition of Gadolinium Ions to the Treatment Solution In the material section 2e) it is shown that other compounds or additives can be introduced into the carboxylation solution according to the invention. In the previous examples, the effect of certain compounds was evaluated at the level of the post-treatment operation, but here the effects of these same compounds were used as an additive in the conversion solution, using the level of treatment itself. Evaluate with.

  The treatment according to the invention comprises 0.38 mol / l heptanoic acid, 2 g / l sodium perborate hydrate, and one of the additives listed in Table VI, the pH being nitric acid added By soaking in a solution of water / ethanol 50/50 for 5 minutes.

  The method of operation described in section 3 of the material can be applied without post-processing.

After observation and analysis of the treated surface of the sample, Ti has a negative effect on the carboxylation reaction, while Si and Gd ^III at pH = 4.7 are in contrast to carboxylation without additives. It is recognized that no difference can be seen.

On the other hand, Gd ^{III at} pH = 3.5 gives a conversion coating composed of two types of different compositions and possibly different shapes of crystals. The appearance of this structure is observed at pH higher than 4. By measuring the polarization according to method section 2, a value of R _p approximately 5 times higher than that obtained with a standard sample obtained by carboxylation without additives is obtained.

An evaluation of the behavior of a plate not treated according to the present invention (symbol ◇) and a plate treated according to the present invention and not lubricated (symbol △) or a plate lubricated (symbol □) with respect to stamping, which shows the holding power of the blank It is a graph showing development of the maximum stamping force Fmax as a function of Fs. Zinc and the following co-solvents:-Ethanol (symbol +)-n-propanol (symbol x)-Dimethyl sulfoxide (DMSO, symbol △)-N-methyl-2-pyrrolidone (NMP, symbol □)-Diacetone alcohol (DAA) , Symbol o) is a graph showing the development of the weight P per unit area of the conversion coating obtained according to the invention as a function of the immersion duration Di in the carboxylation solution using the oxidation chemistry means. It relates to an embodiment of the method according to the invention, using electrochemical means to oxidize zinc, to two different current densities (symbol □ = 10 mA / cm ² , symbol Δ = 25 mA / cm ² ). On the other hand, it is a graph which shows expansion | deployment of the weight P per unit area of the chemical conversion film obtained as a function of immersion duration Dc in a carboxylation solution. The following surfaces: • Untreated (“bare”) zinc-coated surface (represented by the symbol +), • Heptanoic acid (symbol Δ),-Decanoic acid (symbol x),-A mixture of heptanoic acid and decanoic acid ( A zinc-coated surface that has been surface-treated by carboxylation according to the invention and without post-treatment using the symbol *), a solution that has been treated by carboxylation using heptanoic acid and contains a rare earth metal (Gd is the symbol □, Lu is the symbol FIG. 6 is a graph showing a potentiometer evaluation of water corrosion resistance in terms of polarization resistance R _p as a function of immersion time in a measured electrolyte solution for a zinc-coated surface post-treated with ◇).

Claims (25)

The bath is aqueous, organic or hydro-organic and comprises at least one organic acid in free or salt form;
The organic acid is a saturated or unsaturated aliphatic monocarboxylic acid or dicarboxylic acid;
The organic acid is present in the bath solution or emulsion at a concentration greater than 0.1 mol / liter;
The pH of the bath is acidic,
Zinc, iron, aluminum, copper, lead, and alloys thereof, as well as surfaces of metals selected from galvanized steel, aluminum coated steel or copper coated steel, perborate tetrahydrate and hydrogen peroxide The oxidation of the metal obtained is effected by adding a chemical selected from the above into the bath or by causing a current to circulate between the surface previously immersed in the bath and at least one counter electrode that is also immersed in the bath. A method of depositing a chemical conversion film consisting essentially of a metal carboxylate on the surface of the metal before forming by bringing it into contact with the bath under conditions that cause it.   The method of claim 1 wherein the bath further comprises a co-solvent.   The method of claim 1, wherein the bath further contains a chemical for oxidizing the metal.   The method according to claim 1, wherein the bath further contains a chemical for pH adjustment. The method of claim 1 wherein the bath further comprises a surfactant . The method of claim 1, wherein the bath further comprises a metal cation selected from Cu ²⁺ , Co ²⁺ , Ni ²⁺ , Fe ²⁺ , Zn ²⁺ , Mn ^2+, or Al ³⁺ .   The method of claim 1, wherein the bath further comprises rare earth ions. The method of claim 1 wherein the bath further comprises a chelating agent . 9. A process according to any one of the preceding claims, wherein the organic acid is selected from saturated monocarboxylic acids having 5 to 16 carbon atoms. 9. A process according to any one of the preceding claims, wherein the organic acid is selected from unsaturated monocarboxylic acids having 10 to 18 carbon atoms. 9. A process according to any one of the preceding claims, wherein the organic acid is selected from saturated dicarboxylic acids having 4 to 12 carbon atoms. The method according to claim 9 , wherein the organic acid is selected from hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid. The method according to claim 10 , wherein the unsaturated organic monocarboxylic acid is undecenoic acid, oleic acid or linoleic acid. The method according to claim 11 , wherein the saturated organic dicarboxylic acid is sebacic acid or azelaic acid. The method according to claim 12 , wherein the organic acid is heptanoic acid. The process according to claim 15 , characterized in that the bath contains decanoic acid or undecenoic acid in addition to heptanoic acid.   The process according to claim 2, wherein the co-solvent is selected from ethanol, n-propanol, dimethyl sulfoxide, N-methyl-2-pyrrolidone or diacetone alcohol. The process according to claim 17 , wherein the co-solvent is diacetone alcohol. The method according to claim 7, wherein the bath contains rare earth ions in the +3 oxidation state at a concentration of 1 × 10 ⁻³ mol / liter or more, and the pH of the bath is higher than 4. 9. The method according to claim 19 , wherein the rare earth ion is a gadolinium ion. The organic acid concentration in the bath, the conditions that cause oxidation of the use conditions and the metal of the bath, as carboxylated coating 6 g / m ² weight per unit area is from 1 g / m ² on the metal surface can be obtained fit 21. The method according to any one of claims 1 to 20 , wherein: At the end of the surface treatment, post-treatment is performed using a bath containing a polyvalent cation in a +3 oxidation state selected from rare earth metals at a concentration of 1 × 10 ⁻³ mol / liter or more. 22. A method according to any one of the preceding claims, characterized in that it is characterized in that 23. Use of the method according to any one of claims 1 to 22 for temporary protection against corrosion of the metal surface. Zinc, iron, aluminum, copper, lead, and their alloys, as well as galvanized steel, carboxylation process of a metal plate having a surface of a metal selected from aluminum-coated steel or copper coated steel claims 1 22 The method of manufacturing the shape | molded said metal plate which is performed according to the method as described in any one of these, and lubricates and shape | molds the said process metal plate. 25. The method according to claim 24 , wherein the metal plate is made from steel coated with zinc or a zinc alloy and is stamped.