JPH03173778A - Method for chemical conversion of metal substrate, conversion bath suitable for use in said method and condensate suitable preparation of said bath - Google Patents

Abstract

Chemical conversion process characterised in that it comprises the use, at the time of the actual phosphatising stage, of a zinc conversion bath containing phosphate and nitrate ions as well as ferrous or ferric ions and from approximately 21 to approximately 100 g/l of at least one organic chelating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention aims to improve corrosion resistance, deformation adaptability, or both at the same time.
In particular, it relates to methods for chemically converting metal substrates based on iron or galvanized steel.

The invention also relates to chemical conversion baths preferably used in the process as well as concentrates suitable for the preparation of this bath.

BACKGROUND OF THE INVENTION It is already known to chemically convert metal substrates by traditional crystalline phosphating processes in which a film of insoluble phosphate is created on the surface of the metal.

This known crystalline phosphating process generally uses an acid bath containing at least the following ingredients:

- Orthophosphoric acid H3PO4 - Monophosphate ion H1PO, - - Selected from zinc, iron, manganese, nickel, copper, cobalt, and calcium! or several metals; - at least one accelerating agent consisting of an oxidizing agent such as chlorate ions, nitrate ions, nitrites or sodium metanitrobenzenesulphonate; This can be done by soaking.

The above process is part of a series of operating steps consisting of the following steps:

・One to several degreasing steps ・One to several water washing steps ・Optionally one to several pickling steps followed by a water washing step ・Optionally one surface conditioning step ・Original phosphating step ・l one or more water washing steps; optionally a passivation step, generally in a chromic acid medium, and a water washing step; optionally a drying or heat-drying step. The substrate thus treated may be used as is, or Suitable for subsequent application of lubricants, protective oils or paints.

The nature and composition of the resulting insoluble phosphate film depends essentially on: the nature of the substrate; the composition of the phosphate bath; the type of application of the product (spraying or dipping); and the characteristics of the pretreatment process.

The existing art discloses various improvements to chemical conversion baths to improve their performance.

Incidentally, according to French patent FR-A-1362,202, the corrosion resistance of the phosphating film is limited to a small amount (less than 2%,
This is improved by the addition of an organic complexing agent (preferably 0.5% to 5%). The patent calls for so-called "salt spray" (standard ASTM-B-117) for 25 hours or less.
) was recorded.

According to French patent FR-A-1585,660, the so-called film weight is increased by adding an organic polyacid to a phosphating bath enriched with chlorate and almost free of divalent iron ions. be able to. This patent is, in effect,
This invention relates to phosphating treatment of cold-worked metals. It should be noted that the phosphating treatment produces a film with a film weight of +6.1 to 32.2 g/m'', and it is known that this film shows only slight resistance to salt spray when tested as is. ing.

Finally, according to French patent FR-2531,457, when a chelating agent and a soluble polyphosphate are used together,
Coatings with considerably improved resistance to corrosion can be obtained. For example, it is stated that even simply phosphated metal parts can resist salt spray for up to 310 hours.

The last mentioned French patent discloses that an excess of polyphosphate prevents the formation of a crystalline film and that the pH before use is
It is proposed to age the bath as required by the changes in

Since this intended maturation does not occur instantaneously, the bath regeneration process is discontinuous, which is a drawback since most industrial baths are continuously regenerated.

OBJECT OF THE INVENTION The object of the invention is inter alia to overcome this drawback and to provide a chemical conversion bath which exhibits performance comparable to the process disclosed in French patent FR-A-2531,457 and which can be continuously regenerated. It is by providing the following.

[Means for solving the problem] In order to achieve this objective, the applicant believes that phosphate ions,
It has been fortunately discovered that it is necessary to add at least 20 g/l of an organic chelating agent to a zinc conversion bath containing nitrate ions and divalent or trivalent iron ions.

Accordingly, the chemical conversion process according to the present invention involves, during the actual phosphating step, phosphoric acid and nitrate ions as well as divalent or trivalent iron ions and at least one organic chelate in an amount of about 21 to about 100 g/l. It is characterized by the use of a zinc conversion bath containing an agent.

The zinc conversion bath of the present invention is characterized in that it comprises phosphoric acid and nitrate ions, divalent or trivalent iron ions, and about 21 to about 100 g/4 of at least one organic chelating agent. is selected from the group consisting of:

- Polycarboxylic acids, including citric acid, oxuic acid, malic acid, glutamic acid, tartaric acid, aspartic acid, malonic acid, and salts thereof, with citric acid being preferred.

・Polyhydroxycarboxylic acid, including gluconic acid,
Glucoheptonic acid, mucilage acid and their salts, with gluconic acid being preferred.

The salts of polycarboxylic acids and polyhydroxycarboxylic acids mentioned above are salts of alkali and alkaline earth metals, ammonium,
Selected from iron, zinc, manganese, molybdenum, cobalt and nickel salts.

The zinc ions used in a proportion of 0.5 to 25 g/l can be introduced in any convenient manner, in particular in the form of salts with nitric, phosphoric, carbonic, gluconic or oxalic acids, or in the form of oxides. can do.

The zinc ions can be used in combination with metals currently used in phosphate baths, such as manganese, nickel, cobalt, calcium, and magnesium.

The iron ions used in a proportion of 0.1 to 15 g/1 can be introduced by dissolving iron in solid form, such as iron pieces, iron powder, iron parts or iron strings. Iron ions can also be introduced as salts of iron with sulfuric, hydrofluoric, phosphoric or nitric acids.

The iron ions may be divalent iron ions or trivalent iron ions or a mixture of both.

Both phosphate and nitrate ions are used in the bath in proportions of up to 40 g/l.

The baths of the present invention also contain hydrofluoric acid, hydrofluoric acid,
It can also contain fluorosilicic acid, fluoroboric acid or mixtures of these acids.

The bath of the invention contains: - up to 500 g/l of an organic chelating agent, in particular citric acid or gluconate ions; - up to 200 g/l phosphate ions; - up to 125 g/l zinc ions; - up to 200 g/l nitrate ions. It is prepared by dilution starting from a concentrate characterized by:

The coatings obtained when practicing the present invention are capable of continuous regeneration and have a resistance to salt spray comparable to that obtained by patent FR-A-2531,457 within the objective of testing according to standard ASTM B-117. shows resistance to

Substrates treated with the method of the invention can be stored and used without the need for further protective measures. However, it is also possible to coat the substrate in order to further increase its resistance to corrosion. These substrates can be cold worked after optionally applying a lubricant.

A preferred exchange column consists of:

5 to 40 g/A phosphate ions, 21 to 100 g/l citrate and/or gluconate ions 2 to 40 g/fl nitrate ions, 0.5 to 25 g/l zinc ions, 0.1 to 15 g Depending on the iron correction of /l, the bath contains 0.02 to 3 g/l of cobalt or copper.

A particularly preferred bath consists of:

5 to 20 g/l phosphate ion, 21 to 60 g/l citrate ion 2 to 40
g/I2 nitrate ions, 2 to 10 g/l zinc ions, 0.1 to 15 g/I2 iron.One particularly preferred bath has the following composition.

5 to 20 g/ε phosphate ion, 30 to 80 g/l gluconate ion 2 to 4
0g/j! 2 to 10 g/l of nitrate ions and 0.1 to 15 g/l of iron.The chemical conversion bath of the present invention can be prepared by spraying onto the metal substrate to be treated or by immersing the substrate in the bath. Use with. Among these, immersion is preferred.

The chemical conversion method of the present invention consists of a series of processing steps. 1 or several degreasing steps; 1 or several water washing steps; optionally 1 or several activation or pickling steps; 1 water washing step; the original chemical reaction using the conversion bath of the present invention. Conversion Step/Water Washing Step/Drying Step Owing to the excellent resistance to conversion of the phosphate coating obtained using the bath of the present invention, this method is superior to existing techniques for chemical phosphate conversion. This method simplifies the process by omitting the chromic acid passivation and protection steps required in the above method.

Preferably, the temperature of the bath according to the invention is between 40 and 100°C, more preferably between 70 and 90°C.

The invention will be better understood by the following non-limiting examples in which advantageous embodiments of the baths of the invention are disclosed.

[Example] A conversion bath based on the existing technology of "X1 Takumi" Kitakami was prepared. In addition to water, the bath contains the following ions:

Zn": 6g/E Total POa: 16.7g/12 NOs-: IQg/l & Total Fe: Ig/12N5": 0.2g/, and the temperature of the bath is raised to 95°C. Bring the free acidity to within the desired range corresponding to 8.0 points using concentrated sodium hydroxide (free acidity is measured by adding 10w1 of a room temperature solution to the desired range of 8.0 points).
/10 (determined by titration with sodium hydroxide solution until pH reaches 3.6).

A cold-rolled steel plate containing 0.02% carbon and corresponding to the ZES quality normally used in the automotive industry - length and width of the steel plate 150+mm x 14h+m-5 is subjected to the following series of processing steps.

alkaline degreasing in an aqueous solution based on the degreasers marketed by the applicant under the trademarks Bimodal Uniridrin 1550 CF/2 (1,5% by volume basis) and Lidosol 550 CF (1,5% by volume pace); Temperature = 60℃ Processing time: 3 minutes 1 liter: 2 minutes room temperature washing with tap water 1: Nitric acid pickling, Pickling agent: 60% nitric acid in aqueous solution (10% volume basis) Temperature: 20℃ Processing time 710 seconds Process A: Wash with tap water for 1 minute at room temperature 2 2: Wash with tap water at room temperature for 30 minutes at a temperature of 95°C Original conversion process 1: Wash with tap water at room temperature for 10 seconds TJLL = Dry in a drying box for 10 minutes at a temperature of 95°C The treated steel plate is subjected to a salt spray with a concentration of 5% (according to standard ASTM B-117).

After 1 hour of exposure to salt spray, a very homogeneous 50% rust development is observed.

A conversion bath is prepared according to existing technology by adding 10g/fl of citric acid to the bath of Example 1 for 1 hour. The free acidity of this bath is brought to 15.0 points. When the same cold-rolled steel sheet is subjected to the same treatment as described above and exposed for 8 hours, 50% homogeneous rust formation is observed.

A conversion bath according to the invention is prepared by adding citric acid in an amount of 30 g/l to the bath of Example 1. When a cold rolled steel plate is treated as in Example 1, bringing the free acidity of this new bath to 18/19 points, local rusting of 10% is observed after 150 hours of exposure.

Table 1 This example is intended to demonstrate the possibility of applying this method to various industrial parts.

Carburized steel HRC55 (contains 0.55% carbon in it)
and cold rolled steel sheet XC10 (contains 0.1% carbon)
Processing of parts.

The following three compositions are prepared - Slow-burning A 56.7 g of water are mixed with 20 g of citric acid and 22.3 g of 75% strength phosphoric acid. An amount of Ig of metallic iron is dissolved in this mixture.

46.7 g of soybean water is mixed with 30 g of citric acid and 22.3 g of 75% strength phosphoric acid. An amount of Ig of metallic iron is dissolved in this mixture.

An amount of 7.5 g of zinc oxide and an amount of Ig of nickel nitrate containing 20% nickel are dissolved in a mixture of 74.8 g of water and 16.7 g of nitric acid with a concentration of 60%.

The series of processing is similar to that shown in Example 1, but
(The nitric acid pickling in Step 3 was carried out at 60°C for 2 minutes in an aqueous solution containing 7.75% phosphoric acid by volume.
It is replaced by aqueous phosphoric acid pickling carried out at a temperature of .

The bath used during the actual conversion step is constructed as follows.

Bath 1: - 800 tafl of water - 100 ml of composition A - 100 mI2 of composition C Bath 2: - 800 tafl of water - 100 o + fl of composition B - 100 mI2 of composition C Two types of composition corresponding to the qualities of XC10 and HRC55, respectively The steel parts were previously subjected to the series of treatments described in Example 1, in which bath 1 was used for parts made of XC10 steel and bath 2 was used for parts made of ■Rc 55 steel; It is then subjected to a salt spray test according to standard ASTM B-117. Record the time when red rust begins to appear.

The results are shown in Table 1I.

It can be seen that using a citrate ion concentration of more than 20 g/l in the bath of the invention, rather than using a difficult to process steel such as IRC55 type carburized steel, the resistance to corrosion is significantly improved. .

Past JJ soup 25g/fl citric acid 10g/ε NOs ion 16, 7g/l P04 ion 1g/! Prepare an aqueous solution bath containing 6 g of Fe++ ions/1 g of Zn4+ ions of I2/Mn41i ions of I2 (heavy ffi/vol!!k).

The bath is heated to 95° C. and the free acidity is brought to a value equal to 20 points using sodium hydroxide.

A ZES type cold rolled galvanized steel sheet was subjected to the same series of treatments as described in Example 1 (the conversion step used the bath described above), but (steps 3 and 4 were omitted, and after this treatment The steel plate is subjected to a salt spray test (Standard ASTM B-117) and shows no rust even after 400 hours of exposure.

Parts made of cold-rolled galvanized steel of type X-Arashi ZES, parts made of low-carbon content steel of type XC10, and parts made of high-carbon content steel (0.55% carbon) of type XC55 are subjected to the following process. It will undergo a further conversion process.

1 Alkaline degreasing with an aqueous solution based on the degreasers marketed by the applicant under the trademarks Uniridrin 1550 CF (2-1.5% by volume) and Lidosol 550 CF (0,1S% by volume), temperature = 60℃ Processing time: 4 minutes Step 1: Washing with tap water at room temperature for 2 minutes Fifth day: Pickling with phosphoric acid in aqueous solution, Pickling agent: Phosphoric acid with a concentration of 75% (7.75% volume basis) Temperature = 55 °C Processing time: 4 minutes A: Washing with tap water at room temperature for 1 minute ■2: Pickling with nitric acid in an aqueous solution Pickling agent: Nitric acid with a concentration of 60% (10% volume basis) Temperature: 20°C Processing time: 20 seconds 1! + washing with tap water for 1 minute at room temperature 1: original conversion at 95°C for 15 minutes washing with tap water at room temperature for 10 seconds drying: drying in a drying box at a temperature of about 95°C for 10 minutes The conversion bath of No. 7 also has the following composition: 51 g/ll
gluconate ions 3.6 g/It l1i lead ions 8.2 g/j2 phosphate ions 16.9 g/ft nitrate ions 0.5 g/It iron ions The pH of this bath is 2.7.

Parts and sheets processed under these conditions are standard ^STM
Subjected to salt spray by B-117.

Record the time when rust begins to appear.

The results are shown in Table m.

Claims (11)

[Claims] 1. A zinc conversion bath consisting of phosphate ions, nitrate ions, divalent or trivalent iron ions and at least one chelating agent in an amount of about 21 to about 100 g/l is used during the actual phosphating step. A method for chemical conversion of metal substrates. 2. A chemical zinc conversion bath for use in the process of claim 1, comprising phosphate and nitrate ions, divalent or trivalent iron ions, and from about 21 to about 100 g/l of at least one organic chelating agent. 3. 3. The bath of claim 2, wherein the organic chelating agent is selected from the group consisting of polycarboxylic acids and their salts and polyhydroxycarboxylic acids and their salts. 4. 3. A bath according to claim 2, wherein the organic chelating agent is selected from the group consisting of oxuic acid, malic acid, glutamic acid, tartaric acid, aspartic acid, malonic acid and preferably citric acid. 5. 3. A bath according to claim 2, wherein the organic chelating agent is selected from the group consisting of glucoheptonic acid, mucilage acid and preferably gluconic acid. 6. Claim in which the organic chelating agent is selected from the group consisting of alkali and alkaline earth metal salts, ammonium salts, iron salts, zinc salts, manganese salts, molybdenum salts, cobalt salts and nickel salts of polycarboxylic acids and polyhydroxycarboxylic acids. 2. The bath according to 2. 7.・5 to 40 g/l phosphate ions ・21 to 100 g/l citric acid and/or gluconate ions ・2 to 40 g/l nitrate ions ・0.5 to 25 g/l zinc ions ・0.1 to 100 g/l nitrate ions 3. A bath according to claim 2, comprising 15 g/l iron. 8.・5 to 20 g/l phosphate ion ・21 to 60 g/l citrate ion ・2 to 40 g/l nitrate ions ・2 to 10 g/l zinc ions ・0.1 to 15g/l iron 3. The bath according to claim 2, comprising: 9. - Consists of 5 to 20 g/l of phosphate ions, 30 to 80 g/l of gluconate ions, 2 to 40 g/l of nitrate ions, 2 to 10 g/l of zinc ions, and 0.1 to 15 g/l of iron. A bath according to claim 2. 10. During the actual conversion step, the bath according to claim 2 contains 40
Process according to claim 1, characterized in that the bath has a temperature of from 70 to 100°C, preferably from 70 to 99°C, and is used in a spraying or dipping manner for at least 10 seconds. 11. - an organic chelating agent, in particular citrate ions or gluconate ions, of up to 500 g/l; - phosphate ions, up to 200 g/l; - zinc ions, up to 125 g/l; - nitrates, as claimed in claim 2, comprising up to 200 g/l. Concentrate for preparing baths.