JP2014224280A - Composition for phosphate chemical-conversion treatment bath and method for forming phosphate chemical-conversion film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a phosphate chemical-conversion film on a material other than iron and steel (1), to improve the corrosion resistance of a coating (2), to shorten phosphate chemical-conversion treatment time (3), and to secure the stability of a treatment bath (4).SOLUTION: A composition for an electrolytic phosphate chemical-conversion treatment bath, which is constituted of phosphate ion, zinc ion, nickel ion and nitrate ion, and characterized in that the weight ratio of total zinc/phosphoric acid is within the range of 0.35-0.65, is obtained through a step (1) for forming an assembly of phosphoric acid and zinc: [HPO-Zn-HPO-..] by dissolving or chemically combining zinc oxide into a phosphoric acid solution in a ratio of zinc/phosphoric acid (weight ratio) of 0.26-0.35, a step (2) for adding nitric acid to a solution containing [the assembly of phosphoric acid and zinc] obtained in the step (1) to dissolve the solution containing the assembly, a step (3) for adding zinc nitrate into a solution obtained in the step (2) to dissolve the zinc nitrate therein, and a step (4) for dissolving nickel nitrate into a solution obtained in the step (3).

Description

The phosphate chemical conversion bath composition of the present invention is a composition for mainly forming a coating film containing phosphate on the surface of steel or aluminum, and more specifically, it can be used for coating base treatment. Composition.

The phosphate chemical conversion treatment includes an electroless treatment method and an electrolytic treatment method. The current state of practical use is mostly electroless. However, the present invention relates to electrolytic phosphate chemical treatment.
As an existing technique (patent) of the electrolytic method, there is Patent Document 1.

Patent document 1 shows the basic matter of the electrolytic phosphate chemical conversion technology put into practical use. The feature is that metal ions (for example, sodium ions) that do not become film components are not substantially contained in the treatment bath. In addition, it contains metal ions that form complexes with phosphate ions such as phosphate, nitrate ion, and zinc, and form metal films (such as nickel) that do not form phosphates but precipitate as films. It shows that a coating film containing phosphate is formed by electrolytic treatment using an external power source using a treatment bath.

Patent Document 1 discloses that coating corrosion resistance is improved by applying electrolytic phosphate treatment to performing phosphate treatment by electroless treatment. (Examples 1, 3, 4, 5 and Comparative Examples 1, 3)

Patent Document 2 is a countermeasure against the problem in the practical application facility of Patent Document 1, and shows that it is excellent in the same manner as Patent Document 1 for coating corrosion resistance.
In Patent Documents 1 and 2, the target part is a steel material, and the corrosion resistance is evaluated by a salt water immersion test (after 240 hours of immersion in 55% 5% saline solution, the tape is peeled off and the coating corrosion resistance is evaluated by the size of the peel width). Is going. Further, the film formation time in the electrolytic treatment is 120 seconds or more.

Patent Document 3 is obtained by shortening the electrolytic treatment time. The electrolytic treatment time is 50 seconds and 30 seconds. In order to shorten the electrolytic phosphate treatment, the composition of the treatment bath is nickel> zinc and nitrate ion> phosphoric acid. Moreover, the corrosion resistance of the coating is evaluated by a salt spray test. Corrosion resistance is excellent in the salt spray test 2000 hours. However, the electrolytic phosphating treatment for 30 seconds and the electrodeposition coating for 45 seconds have a coating peeling width of 10 mm after 1250 hours, which exceeds the general standard of 5 mm. Moreover, the metal material which also makes patent document 3 object is only steel.
Patent Document 4 attempts to change the dissociation state of phosphoric acid in a phosphating bath. Up to 25 parts of zinc from zinc oxide were dissolved in 100 parts by weight of phosphoric acid. Then, it was possible to form a film with an electrolytic treatment time of 30 seconds.

Patent Documents 1 and 2 evaluate corrosion resistance in a salt water immersion test, while Patent Document 3 evaluates corrosion resistance in a salt water spray test. None of the documents evaluates the corrosion resistance of aluminum materials.

JP 2000-234200 A JP 2002-322593 A JP 2007-46149 A JP 2006-302789 A

Transition and Trend of Chemical Treatment Technology for Aluminum Toshiaki Shimakura: Surface Technology, 61, 223 (2010) Chemical conversion treatment for aluminum wheels Masanobu Sugawara: Surface Technology, 61, 251 (2010) Zinc phosphate treatment for automobile bodies Hitoshi Ishii: Surface Technology, 61, 232 (2010) Basics of Phosphate Treatment Hitoshi Ishii: Surface Technology, 61, 216 (2010) Development of small lot and compact forging line for global production Koichi Morishita: Plasticity and processing, vol. 52 1247 (2011) Current status and future prospects of DENSO parts processing technology Yoshitaka Kuroda: Denso Technical Review Vol. 11 No. 2, 14 (2006)

The main problems to be solved by the present invention are: (1) Phosphate conversion film formation on materials other than steel (2) Improvement of coating corrosion resistance, (3) Reduction of phosphate conversion treatment time, and (4) Ensuring stabilization of the treatment bath.

(1) “Formation of phosphate conversion coating on materials other than steel”
In recent years, automobiles have a tendency to improve the ratio of using metals other than steel with weight reduction. The proportion of aluminum used in automobile bodies is increasing. The current automobile body coating employs a conventional method of forming a phosphate film by electroless treatment. Electroless treatment can form a phosphate film on a steel material, but basically a phosphate film cannot be formed on the surface of an aluminum material. The current automobile body is an iron-aluminum composite material with an aluminum material ratio of 10% or less, and a phosphate film is also formed on the aluminum material part along with the phosphate film formation on the iron material part. In this situation, a phosphate film is formed on the aluminum material. Further, in the current electroless treatment, fluorine ions are contained because it is necessary to ensure the reactivity of the aluminum material surface. In the electroless treatment, the treatment bath is heated to about 45 ° C. or higher. And sludge is produced | generated with film formation. From these things, it is a processing method that discharges environmental pollutants with high energy consumption.

Moreover, the electroless phosphating treatment cannot form a phosphate chemical conversion film on an aluminum single material. Therefore, a coating based on zirconium or the like is employed as a coating ground treatment film for coating ground treatment on an aluminum single material (for example, an automobile wheel). Even in such non-phosphate surface treatment, the electroless treatment bath generally contains fluorine ions in order to remove the oxide film on the aluminum surface.

(2) “Improvement of coating corrosion resistance”
It is described in Patent Document 2 that the coating corrosion resistance of the steel material is superior to that in the case where the coating using electrolytic phosphate treatment is electroless treatment. However, there is no comparison of coating corrosion resistance against aluminum materials. The present invention develops an effective electrolytic phosphating treatment for aluminum alone. That is, the coating corrosion resistance is superior to that of a conventional non-phosphate coating electroless treatment film (for example, a zirconium-based film).

(3) “Reduction of phosphate chemical conversion treatment time”
In recent years, automobiles are being produced all over the world. Along with this, the production of automobile parts is also required to be compatible with production in various parts of the world.
The above non-technical documents 5 and 6 describe that production facilities are to be downsized in order to cope with global production. Machine processing such as plastic working can reduce the number of treatments per hour without reducing the processing time, and can reduce the size of the equipment. In fact, both documents are downsizing the equipment, but no mention is made of shortening the machining time.
However, it is difficult to reduce the size of chemical processing equipment without shortening the processing time. Therefore, the above technical literature does not mention downsizing of the chemical treatment facility accompanied by a chemical reaction. The automobile parts production line is a production line including not only machining equipment but also chemical treatment equipment. For these reasons, it is necessary to reduce the size of the chemical processing equipment, and in order to achieve this, it is necessary to shorten the chemical processing (chemical reaction) time.

The conventional electroless treatment phosphate treatment time is 2 minutes or longer (Patent Document 1, Comparative Example 1, and Non-Patent Document 4).
Moreover, the processing time of the electrolytic phosphate treatment for the coating base has been reported as short as 30 seconds. (Patent Document 3)

The solution of the present invention is to form a film having coating corrosion resistance in an electrolysis time of 30 seconds or less (preferably about 15 seconds). Then, by applying the ground treatment, an electrodeposition coating time is reduced to 60 seconds (1/2 of the conventional one) or less to form a good coating film. And it is applicable also to materials (for example, aluminum material) other than steel.

(4) “Ensuring stabilization of treatment bath”
Ensuring stabilization of the treatment bath is prevention of sludge formation accompanying electrolytic treatment. In the electrolytic phosphate treatment of the present invention, zinc or nickel metal is placed in a treatment bath as an anode, an object to be treated is placed on the cathode, a voltage of at least 5 V is applied between both electrodes, and the surface of the object to be treated To form a phosphate conversion coating. The difference from the prior art of electrolytic treatment is that a good film is formed in a time of 30 seconds or less. Therefore, it has a composition different from the conventional treatment bath composition. It is devised so as not to cause a useless reaction between the treatment bath and the electrode both when the voltage is applied and when the voltage is not applied. In particular, it is important to suppress the reaction between the treatment bath and the electrode (zinc) when the treatment is not performed.

In the present invention, zinc oxide is dissolved or combined in a phosphoric acid solution in a range of zinc / phosphoric acid (weight ratio) = 0.26 to 0.35, and an aggregate of phosphoric acid and zinc: “H ₂ PO ₄ ⁻ −Zn ²⁺ −”. H ₂ PO ₄ ^{- -} ·· "step of forming a (1) a step of dissolving a solution containing meeting adding nitric acid incorporated into a solution aggregate" including a "phosphoric acid and zinc obtained in the step (1) (2) obtained by the step (3) of adding zinc nitrate to the solution obtained in the step (2) and dissolving the solution and the step (4) of dissolving nickel nitrate in the solution obtained in the step (3); Electrolytic phosphate chemical treatment bath composition comprising phosphate ions, zinc ions, nickel ions and nitrate ions, wherein the weight ratio of total zinc / phosphoric acid is in the range of 0.35 to 0.65 It is.

The electrolytic phosphate chemical treatment bath composition should have phosphoric acid of 40 to 120 g / L, total zinc of 20 to 78 g / L, nickel of 0.3 to 30 g / l, and nitrate ions of 13 to 90 g / L. preferable.

Zinc oxide is dissolved or combined in a phosphoric acid solution in the range of zinc / phosphoric acid (weight ratio) = 0.30 to 0.35, and an aggregate of phosphoric acid and zinc: “H ₂ PO ₄ ⁻ −Zn ²⁺ −H ₂ PO ₄ ^- - ... "it is preferred to have the step (1) to form a.

In the present invention, the electrolytic phosphate chemical treatment bath described above is used, zinc or nickel is used as an anode, an object to be treated is connected to the cathode via a DC power source, and energization is performed for 5 to 30 seconds on the surface of the object to be treated. It is also an electrolytic phosphate treatment method characterized by forming a phosphate film.

(1) A coating base treatment technology that is applicable to steel and materials other than steel and has excellent coating corrosion resistance in a treatment time of 30 seconds or less has been developed: electrolytic phosphate treatment technology. The treatment time of 30 seconds or less, and the formation of a phosphate conversion coating other than steel contributes to the downsizing of the equipment.
(2) Zn (ZnO) / H ₃ PO ₄ : The ratio (weight ratio) of zinc dissolved from zinc oxide to phosphoric acid is 0.26 or more, preferably 0.3 or more, and the total Zn / H ₃ PO ₄ : Electrolytic phosphating treatment that prevents dissolution of metal electrodes (zinc, nickel) used for electrodes by using a treatment bath in which the ratio (weight ratio) of total zinc to phosphoric acid is 0.35 or more. Bathing and processing techniques were developed.

It is a figure which shows formation of a phosphate-zinc aggregate and the abundance ratio of free phosphoric acid. It is a schematic diagram which shows the range of the chemical conversion treatment bath of this invention. It is a figure which shows the salt water immersion test result in an Example and a comparative example. It is a figure which shows the salt spray test result in an Example and a comparative example. It is a figure which shows the salt water immersion test result in an Example and a comparative example. It is a figure which shows the salt spray test result in an Example and a comparative example. It is a figure which shows the salt water immersion test result in an Example and a comparative example. It is a figure which shows the peeling result after the A6061 salt water immersion test of the comparative example 7. It is a figure which shows the peeling result after the SPCC salt water immersion test of the comparative example 7. It is a figure which shows the peeling result after the A6061 salt water immersion test of Example 3. It is a figure which shows the peeling result after the SPCC salt water immersion test of Example 3. FIG. It is a figure which shows the peeling result after the A6061 salt spray test of the comparative example 7. It is a figure which shows the peeling result after the SPCC salt spray test of the comparative example 7. It is a figure which shows the peeling result after the A6061 salt spray test of Example 3. FIG. It is a figure which shows the peeling result after the SPCC salt spray test of Example 3. It is a figure which shows the peeling result after the A6061 salt water immersion test of the comparative example 15. It is a figure which shows the peeling result after the SPCC salt water immersion test of the comparative example 15. It is a figure which shows the peeling result after the A6061 salt water immersion test of Example 11. FIG. It is a figure which shows the peeling result after the SPCC salt water immersion test of Example 11. It is a figure which shows the peeling result after the A6061 salt spray test of the comparative example 15. It is a figure which shows the peeling result after the SPCC salt spray test of the comparative example 15. It is a figure which shows the peeling result after the A6061 salt spray test of Example 11. It is a figure which shows the peeling result after the SPCC salt spray test of Example 11. It is a figure which shows the peeling result after the A6061 salt water immersion test of the comparative example 17. It is a figure which shows the peeling result after the SPCC salt spray test of the comparative example 18. It is a figure which shows the peeling result after the A6061 salt spray test of the comparative example 17. It is a figure which shows the peeling result after the SPCC salt spray test of the comparative example 18. It is a figure which shows the peeling result after the A6061 salt spray test of a reference example. It is a figure which shows the state after the test of the zinc electrode used by Comparative Examples 1-8. It is a figure which shows the state after the test of the zinc electrode used in Examples 1-8.

(1) Means for forming phosphate film on metal other than steel It is clearly shown in Patent Document 1 that formation of phosphate film on steel other than steel is possible by electrolytic treatment (Examples 2, 3, 4). . However, the application of the corrosion resistance of the phosphate chemical coating is not clearly shown and is unknown.

"Analysis and operation of phosphate chemical film formation mechanism"
In order to form a phosphate chemical conversion film on a material other than steel, the phosphate film can be formed by the same reaction mechanism as that of the steel material. The reason why a phosphate conversion coating cannot be formed on an aluminum material by electroless treatment is that the reaction behavior of the aluminum material in a phosphate treatment bath (electroless) is different from that of an iron material.
The phosphating treatment reaction (film formation reaction) is an electrochemical reaction. In steel materials, iron is dissolved by immersing steel in a treatment bath, and electrons are supplied to the reaction system to form an electrochemical reaction system.

  However, aluminum cannot be dissolved in the treatment bath. The reaction (2) does not occur.

It is natural that the dissolution of the metal material differs depending on the composition of the treatment bath. Existing electroless phosphating baths for steel materials react (dissolve) with steel materials, but do not dissolve with aluminum materials. Therefore, the electroless treatment bath for steel materials cannot be applied to aluminum materials alone.
Why is it necessary to dissolve the material to be treated in electroless treatment? This is because the phosphating treatment reaction is an electrochemical reaction. An electrochemical reaction involves the movement of electrons. In the electroless treatment bath, electrons are not supplied to the reaction system from the outside through a power source. Therefore, it is necessary to dissolve the material itself and supply electrons.

On the other hand, an external power source is used in the present invention. Therefore, in the electrolytic phosphating treatment, since the supply of electrons to the reaction system is supplied from an external power source, it is not necessary to dissolve the material to be treated. And a phosphate membrane | film | coat can be formed, without dissolving a to-be-processed material. Therefore, a phosphate film can be formed even on a metal (such as an aluminum material) that does not dissolve in the phosphating bath.

(2) Means for improving coating corrosion resistance It is clearly disclosed in Patent Document 1 that coating corrosion resistance is improved by performing electrolytic phosphate treatment and including a nickel component in the film. (Examples 4 and 5) Nickel improves the adhesion of the film to the metal to be treated. However, in order to improve the coating corrosion resistance, it is more important that the phosphate conversion coating is reliably formed in the form of a metal material. Electrolytic phosphate treatment uses electrons (e) in the reaction system using an external power source. As a result, the phosphate chemical conversion film can be reliably formed on the metal material.

(3) Shortening of phosphating time: 30 seconds or less Improve the electrochemical reaction rate related to phosphating.
The components of the treatment bath of the present invention are basically that the cation is zinc ion or nickel ion, and the anion is phosphate ion or nitrate ion.

The phosphate chemical conversion treatment is an electrochemical reaction.
The electrochemical reaction includes an anode reaction (oxidation reaction) and a cathode (reduction reaction).
The phosphating anodic reaction is a phosphoric acid dissociation reaction (3).

The formation of the phosphoric acid film is that phosphoric acid ions are combined with zinc ions as phosphoric acid is dissociated, and is collectively shown in (4).

The corresponding cathodic reaction is the reduction of nitrate ions (5).

Therefore, promptly performing the phosphate treatment is to rapidly perform the electrochemical reactions (3) and (5) related to phosphoric acid and nitrate ions.

The necessity of controlling the reduction reaction of (5) has already been described in Patent Document 2. However, the present invention needs to further improve the reduction reaction rate. The reason is explained below.
The general chemical reaction formula does not indicate the reaction rate. However, it can be convinced that the simple reaction route to the final product has a faster reaction rate than the complicated route. Moreover, the necessity for the final reduction state of NO ₃ ⁻ being NO (g) is that it is necessary to escape from the reaction system as a gas in the final state. NO has a boiling point of −151 ° C. and easily escapes from the treatment bath. However, even when the intermediate state is a gas (eg, N ₂ O ₄ (g)), it is slow to escape from the treatment bath.
The reduction reaction of nitrate ions is finally summarized in (5), but there are several routes to the final state of NO (g). This is shown below.

Reactions other than (6) are reactions that produce an intermediate product that reaches the final product. For example, HNO ₂ (aq) produced in (7) reaches the final product in the reaction of (10).

Therefore, (6) should be used to reduce nitrate ions rapidly.
The oxidation (dissociation) of phosphoric acid, which is an anodic reaction, proceeds through the following route.

However, phosphoric acid is an “weak acid” and is an acid with little acid dissociation.
The acid dissociation state of phosphoric acid is indicated by an acid dissociation constant, and is shown in (12), (13) and (14) below. pKa is the acid dissociation constant.

Phosphoric acid is normally present in the solution in the equilibrium state shown in (12). Then, (12), phosphoric acid 1mol is present in about PH2 state, H ₃ PO ₄ (aq) is ^{_{99%, H 2 PO 4 -}} (aq) be present in a ratio of about 1% Indicates.

Phosphating, (11) it is a final state of dissociation of phosphoric acid as shown formula PO ₄ ^{3 -} is to (aq) until oxidation (dehydrogenation). This is performed by cathodic electrolysis by causing phosphoric acid to undergo an anodic reaction.
An object of the present invention is to form an effective film by carrying out a phosphating treatment rapidly in 30 seconds or less. Therefore, devise to dissociate phosphoric acid quickly.

(12) Among the dissociated states of phosphoric acid shown in (13) and (14), (12) relates to the phosphating bath. The phosphating bath of the present invention dissolves zinc ions and nickel ions. Since they are supplied with nitrates, they will contain nitrate ions. If zinc ions and nickel ions are all supplied as nitrates, the phosphoric acid in the treatment bath exists in an equilibrium state of the equation (12). The electrolytic reaction of phosphating is a rate reflecting the state of (12) (the state where H ₃ PO ₄ (aq) is present at a ratio of 99% and H ₂ PO ₄ ⁻ (aq) at a ratio of about 1%). . In that situation, the dissociation of phosphoric acid will be spent much on (12). And even if the equilibrium of (12) shifts to the right, dissociation of phosphoric acid is insufficient in that state. If most of the electrolysis current is spent moving (12), a phosphate conversion coating cannot be formed in 30 seconds or less.

In order to increase the reaction rate, the state of phosphoric acid in the treatment bath should be as close as possible to the right side of (12). One end of this idea is described in Patent Document 4. However, the method of Patent Document 4 is insufficient, and the present invention takes further measures.
In Patent Document 4, zinc oxide is dissolved in a phosphoric acid solution to form a phosphoric acid solution (H ₂ PO ₄ ⁻ + Zn ²⁺ ).

In Patent Document 4, the amount of zinc dissolved in phosphoric acid is the maximum amount dissolved in 25 parts by weight of zinc per 100 parts by weight of phosphoric acid. ([0025]) Therefore, the method of Patent Document 4 can only dissolve up to 25 g of zinc per 100 g of phosphoric acid.

The present invention does not use the concept of dissolving zinc in a phosphoric acid solution. Instead, the concept of forming “phosphate-zinc aggregates” from zinc oxide is adopted. Therefore, we develop a method of associating with 25g or more of zinc to 100g of phosphoric acid to the limit of the formation of "phosphate-zinc aggregate".
The “phosphate-zinc aggregate” is formed by associating phosphoric acid with zinc oxide (or zinc metal, zinc hydroxide). The reaction is (16), indicating the state of the aggregate.

If the reaction (16) is performed reliably, 1 mol of zinc corresponds to 2 mol of phosphoric acid. This forms a new “phosphate-zinc” aggregate in which 65.4 parts by weight (1 mole) of zinc are bound to 196 parts by weight (2 moles) of phosphoric acid. The above aggregate can theoretically be formed up to 2 mol of phosphoric acid per 1 mol of zinc. That is, up to 33.3 parts by weight of zinc per 100 parts by weight of phosphoric acid. (Zinc: 1 mol / phosphoric acid: 2 mol = 65.4 / 196 = 0.333)

The idea of “phosphate-zinc aggregate” is not the dissolution of zinc (solid) in a phosphate solution but the formation of an aggregate. The aggregate is present in a solution state up to 25 parts by weight of zinc with respect to 100 parts by weight of phosphoric acid. However, it is necessary to devise to maintain the solution state at 25 parts by weight or more.

The formation status of “phosphate-zinc aggregate” and the status of phosphoric acid are shown in FIG.
FIG. 1 shows the formation status of “phosphate-zinc aggregate” when phosphoric acid and zinc (from zinc oxide) are associated to form a “phosphate-zinc aggregate”. The vertical axis of FIG. 1 represents the weight ratio of Zn / H ₃ PO _4, the horizontal axis is "phosphate - zinc ^{_{associate": [H 2 PO 4 - -}} Zn 2+ - H 2 PO 4 -] "free of The ratio of phosphoric acid: H ₃ PO4 is shown.
At a Zn / H ₃ PO ₄ : weight ratio of 0.33, the abundance of free phosphoric acid is zero. In the Zn / phosphoric acid: weight ratio of 0.25 in Patent Document 4, phosphoric acid bound to a phosphoric acid-zinc aggregate is 25/33 = 0.76, and 24% phosphoric acid is in an active state. Similarly, at a Zn / phosphoric acid: weight ratio of 30, the phosphoric acid bound to the phosphoric acid-zinc aggregate is 30/33 = 0.91 and 9% phosphoric acid is in the active state.
The present invention aims to speed up the reaction by reducing the ratio of “free phosphoric acid: H ₃ PO ₄ ” in the treatment bath as much as possible.

In the state of Patent Document 4, 24% of the total phosphoric acid is “free phosphoric acid: H ₃ PO ₄ ”. A method for decreasing “free phosphoric acid” and increasing the ratio of “phosphate-zinc aggregate” will be described below.

Method for Producing “Phosphate-Zinc Aggregate” A state containing zinc that can be dissolved in a normal state can be obtained as a gel-like substance at room temperature. The method is schematically shown.
More than 25 parts by weight of zinc from zinc oxide is gradually mixed into the stirred solution of 100 parts by weight of phosphoric acid.
At this time, the form of zinc added is limited to zinc oxide, zinc hydroxide, and metal zinc. Only those zinc species promote the dissociation of phosphate.

The solution is heated to about 50 ° C. or higher and held. By maintaining the temperature at 50 ° C. or higher, it is possible to dissolve up to 29 parts by weight of zinc. However, the solution stops heating and enters a gel state when cooled to room temperature. Moreover, a slight insoluble state exists at 30 parts by weight or more of zinc. These insoluble substances are also stirred for a long time and become a gel state when cooled.

The gel substance cannot be used as a phosphating bath as it is. The phosphating bath is premised on a state in which ions are dissolved: a transparent state. The gel state is dissolved by adding a minimum amount of nitric acid. The amount of nitric acid required for dissolution is adjusted by the ratio of zinc associated with phosphoric acid.

For example, when phosphoric acid is 80 g / L and zinc / phosphoric acid is 0.3 (weight ratio), adding 9.5 g / L of nitric acid (HNO ₃ ) dissolves the gel and the solid content to obtain a transparent solution. Further, when phosphoric acid is 80 g / L and zinc / phosphoric acid is 0.34, if 19 g / L of nitric acid (HNO ₃ ) is added, the gel and solid matter dissolve and a transparent solution is obtained.
The amount of nitric acid is preferably in a range where the weight of nitric acid does not exceed the weight of phosphoric acid.

The actual phosphating bath adjusts the total zinc content and nickel content relative to the phosphoric acid of the solution obtained by the above-described process. This is done by adding nitrate. The treatment bath of the present invention has the amount of zinc to phosphoric acid (a) “Zn (ZnO) / H ₃ PO ₄ : zinc / phosphoric acid ratio from zinc oxide” and (b) “total Zn / H ₃ It is indicated by two indicators of “PO ₄ ”.

(A) relates to the formation of “phosphate-zinc aggregate”, and the ratio “Zn (ZnO) / H ₃ PO ₄ ” is 0.26 to 0.35.
(B) is the ratio of the total Zn / H ₃ PO ₄ required to form the phosphate conversion coating. In this case, the ratio of all Zn / H ₃ PO ₄ is set to 0.35 to 0.65.
(B) is an index of total zinc / phosphoric acid (weight ratio) after adding the zinc shortage of (a) as zinc nitrate.
The exact zinc / phosphate ratio (weight ratio) of “phosphate-zinc aggregate” = [H ₂ PO ₄ ⁻ −Zn ²⁺ −H ₂ PO ₄ ⁻ ] is 0.333. However, in the present invention, the upper limit of the ratio is set to 0.35 in order to ensure that “free phosphoric acid” is zero.

Zinc nitrate is added to a solution in which a “phosphate-zinc aggregate”, which is a gel substance, is dissolved in nitric acid, and is easily dissolved. And the solubility (transparency) of a processing bath is ensured.
Further, nickel nitrate is added to the treatment bath and dissolved as necessary. Since nickel nitrate is also easily dissolved, the solubility (transparency) of the treatment bath is ensured.

"Intention of nitric acid addition"
Nitric acid is a so-called “strong acid”. The acid dissociation constant of nitric acid is (17).

(17) indicates that nitric acid exists in a state in which it moves to the right in a normal state. It shows that the active acid (H ⁺ ) has a strong dissolving action. Therefore, nitric acid dissolves the gel-like “phosphate-zinc aggregate” produced above. However, the “phosphate-zinc aggregate” is not decomposed. Nitric acid forms a “phosphate-zinc aggregate” and then is added to the solution to dissolve the aggregate. The amount necessary for dissolution varies depending on the component ratio, but the amount of nitric acid added is preferably the minimum amount for dissolving the aggregate.

"Addition of nickel"
A suitable phosphate coating for the paint substrate is zinc phosphate (Zn ₃ (PO ₄ ) ₂ ) + nickel (Ni). Zinc phosphate, which is the main component of the phosphate chemical film, is formed by dissociation (oxidation) of phosphoric acid. Nickel does not form phosphate crystals, but is formed by a reduction reaction different from phosphate in the phosphating reaction system.

And it exists in a phosphate chemical conversion film as metallic nickel. That will reinforce the adhesion of the phosphate conversion coating and contribute to the coating corrosion resistance. In addition, it is preferable that nickel addition amount is 0.3-30 g / l as needed. It is added to the treatment bath as nickel nitrate.

"Creation of phosphate chemical treatment bath"
1. The procedure for preparing the “phosphate-zinc aggregate” will be described in the preparation of a 1 L treatment bath. The following adjustment method is an example for description, and the present invention is not limited to the following method.
(I) 1 mol of phosphoric acid is dissolved in an amount of 4.2 to 6.5 mol of water. This is to make 72-117 g of water correspond to 98 g of phosphoric acid. When making an 80 g / L phosphoric acid solution, the 85% phosphoric acid solution is 55.7 ml. A solution obtained by adding about 100 ml of water to it. The reason for adjusting the amount of water relative to phosphoric acid is not to dissolve phosphoric acid in water but to create a “phosphate-zinc aggregate”.

(Ii) Add 30 g of zinc oxide (ZnO) to the above solution, and heat and stir so that the solution is about 50 ° C to 75 ° C. This will add 24g of Zn. With this addition, a solution of Zn (ZnO) / H ₃ PO ₄ = 24/80 = 0.3 is prepared. Zinc oxide dissolves in the phosphoric acid solution with heat generation, but becomes transparent while leaving a slight solid content. When the solution is continuously stirred and cooled, it becomes a gel-like solution. The dissolved aggregate [H ₂ PO ₄ ⁻ −Zn ²⁺ −H ₂ PO ₄ ⁻ ] becomes a gel by stirring and cooling.

(Iii) Next, 7.5 ml of a 70% nitric acid solution (9.5 g as HNO ₃ ) is added. By this operation, the remaining solid content and the like are dissolved. Stop heating the solution once it is clear. Note that the gel-like solution is similarly dissolved by the addition of nitric acid.

(Iv) Add water to make the amount of solution about 500-650 ml.
(V) 36.4 g of zinc nitrate hexahydrate (Zn (NO ₃ ) ₂ · 6H ₂ O) is added and dissolved. This will add 8 g of Zn (from zinc nitrate). With this addition, the total zinc ion amount is 32 g. The total Zn / H ₃ PO ₄ ratio (weight ratio) = 0.4.
(Vi) Next, 50 g of nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O) is added and dissolved.
The amount of nickel ion added is 10 g.
(Vii) The total amount of the solution is 1L.

(Viii) The composition of the obtained solution was phosphoric acid: 80 g / L, Zn ion: 32 g / l, Ni ion: 10 g / l, nitrate ion: 45.7 g / L, and Zn (ZnO) / H ₃ PO ₄ = 0.3, total Zn / H ₃ PO ₄ = 0.4.

The treatment bath of the present invention is prepared in accordance with the above procedure. Zn (ZnO) / H ₃ PO ₄ = 0.26 to 0.35, total Zn / H ₃ PO ₄ = 0.35 to 0.65, and phosphoric acid 50 to 120 g / L And an electrolytic phosphate chemical treatment bath composition having zinc of 20 to 78 g / L, nickel of 0.3 to 30 g / l, and nitrate ions of 13 to 90 g / L. Zn (ZnO) / H ₃ PO ₄ is more preferably 0.30 to 0.35.

The phosphating bath can contain manganese as a metal ion, and an appropriate amount can be added in the form of manganese nitrate. In addition, in the case of anions, it is possible to add an appropriate amount of fluorine ions in order to assist the ion permeability of materials having an oxide film on the surface such as aluminum, stainless steel, and titanium. Fluorine ions are preferably added in the form of zinc fluoride. The fluorine ion content is preferably 0 to 0.5 g / L.

"Electrolysis method"
The electrolysis method of the present invention is a cathodic electrolysis treatment using zinc or nickel as an anode and a metal workpiece such as steel or aluminum as a cathode. A phosphate conversion film is formed on the surface of the metal object by electrolytic treatment within a voltage range of approximately 5v to 15v for 30 seconds or less. The reason for limiting the anode to zinc or nickel is to maintain electrolytic efficiency. In order to form a film in a short time of 30 seconds or less, it is necessary to select an electrode material that can efficiently flow current at an appropriate voltage. Since zinc and nickel are components of the treatment bath, there is little resistance between the anode surface and the solution, and an electrolytic current can flow efficiently.

In addition, since the electrolytic phosphate treatment supplies the treatment bath component to the treatment bath as a chemical (liquid), the electrode component is slightly dissolved. In electroplating, since no chemicals are supplied, an anode component is formed as a film. For example, in zinc plating, zinc is used as an anode and dissolved. At that time, zinc is not replenished in the form of chemicals. The difference between electroplating and electrolytic phosphating is that the form of replenishment of film components is different. The electrolytic phosphating anode is basically selected with the intention of replenishing components mainly because the electrolytic current flows efficiently. Therefore, zinc and nickel are selected for the electrode.

(4) Ensuring stabilization of electrolytic phosphate chemical treatment bath In the electrolytic phosphate treatment of the present invention, zinc or nickel metal is placed in the treatment bath as an anode, and an object to be treated is placed at the cathode. Then, a voltage of at least 5 V or more is applied between both electrodes to form a phosphate chemical conversion film on the surface of the object to be processed. The difference from the prior art of the electrolytic treatment is that the film is formed in a time of 30 seconds or less, so that it has a composition different from the conventional treatment bath composition. That is, a device is devised so that a wasteful reaction does not occur between the electrode (anode) and the treatment bath both when the voltage is applied and when the voltage is not applied: when the voltage is not applied.

The idea is to make the abundance ratio of free (active) H ₃ PO ₄ shown in FIG. 1 as small as possible. Free H ₃ PO ₄ has the effect of delaying the formation of a phosphate conversion film “when a voltage is applied”. In addition, when “no voltage is applied: at rest”, it reacts with zinc as an electrode material, and zinc phosphate (Zn ₃ (PO ₄ ) ₂ ) is formed on the surface of the electrode. The zinc phosphate crystal formed on the electrode surface is an insulating material. The presence of an insulator on the electrode surface hinders the flow of current during electrolysis. This reduces the electrolysis efficiency. When the electrolytic phosphating bath is not used (holidays, etc.), the electrolytic bath is moved to another bath (circulation / preliminary bath) in order to prevent the reaction between the processing bath and the electrode. Therefore, the electrode surface is exposed to the atmosphere and dried. Zinc phosphate crystals formed by reaction of free active phosphoric acid on the electrode surface become a solid film firmly bonded to the electrode surface when left in the atmosphere. Such a membrane (zinc phosphate) is not zinc and interferes with the electrolysis on the zinc surface.

In addition, if zinc phosphate crystals are detached from the electrode and transferred to the treatment bath, it becomes sludge. Then, if the sludge moves and adheres to the surface of the workpiece as it is, it forms a non-adhesive chemical film in which the solid content is gently joined instead of the phosphate chemical film produced from the solution (ionic state). This reduces the adhesion of the phosphate conversion coating and reduces the corrosion resistance after painting. From these things, it is better that the free H ₃ PO ₄ in the treatment bath is as small as possible.

Patent document 4 aims at the reduction | restoration of the free (active) phosphoric acid said by this case in a processing bath. Up to 25 parts by weight of Zn from zinc oxide (ZnO) is dissolved in 100 parts by weight of H ₃ PO ₄ . However, the situation is the state of H ₃ PO ₄ in which 24% of the total phosphoric acid is active.

In the present invention, a “phosphate-zinc aggregate”: [H ₂ PO ₄ ⁻ − Zn ²⁺ − H ₂ PO ₄ ⁻ ] is formed to form a colloidal “phosphate-zinc aggregate”. Add the minimum amount of nitric acid to dissolve the aggregates and form a clear phosphating bath. This reduces the free (active) H ₃ PO ₄ in the treatment bath.

That is, Zn from zinc oxide (ZnO) is added from 0.255 to 0.35 with respect to 100 parts by weight of H ₃ PO ₄ , dissolved by heating, and a nitric acid solution is added to dissolve the “phosphate-zinc aggregate”. And create a treatment bath. Therefore, a treatment bath in which free H ₃ PO ₄ is reduced as compared with Patent Document 4 is used. Therefore, stabilization of the treatment bath is achieved.

  The chemical conversion treatment using the electrolytic phosphate chemical treatment bath composition of the present invention does not particularly limit the object to be processed, and any metal can be applied as long as it is a normal metal. For example, it can be applied to steel, stainless steel, copper, aluminum and the like. Especially, it is suitable for the chemical conversion treatment of the raw material for painting.

  Before performing the treatment with the electrolytic phosphate chemical treatment bath composition of the present invention, if necessary, ordinary pretreatment commonly performed in chemical conversion treatment such as degreasing, pickling and surface adjustment is performed. It may be.

The treatment with the electrolytic phosphorylation treatment bath composition of the present invention is preferably used as a coating base. That is, it is preferable to perform the coating treatment after the treatment with the electrolytic phosphorylation treatment bath composition of the present invention. The coating performed is not particularly limited, and examples thereof include electrodeposition coating with a cationic electrodeposition coating. Further, as a pretreatment of water-based paint, powder paint, solvent-based paint, etc., treatment with the electrolytic phosphorylation treatment bath composition of the present invention can also be performed.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to a following example.
The examples are reported in four steps.
The evaluation will focus on the evaluation of corrosion resistance. Then, mention is made of film thickness and glossiness.

Example 1
40 g of water is added to 80 g of phosphoric acid with 85% phosphoric acid (55.7 ml with 85% phosphoric acid), and 30 g of solid zinc oxide (24 g as zinc) is added to this solution while stirring. Dissolved. At that time, heat was generated up to 70 ° C. 200 g of water was added to the gel thus obtained, and 9.5 g of nitric acid (7.5 ml of 70% nitric acid) was further added and dissolved. To the solution thus obtained, zinc nitrate is added to 8 g of zinc and 15.2 g of nitrate ion, nickel nitrate is added to 1.5 g of nickel and nitrate ion of 3.2 g, and water is further added. The electrolytic phosphate chemical conversion bath composition of Example 1 was obtained with 1L as a whole.

(Examples 2-8, Comparative Examples 1-8)
With the same manufacturing method, the electrolytic phosphate chemical treatment bath compositions of Examples 2 to 8 and Comparative Examples 1 to 8 were obtained with the formulations shown in Table 1.

(Corrosion resistance evaluation)
1st stage
Using Zn (ZnO) / H ₃ PO ₄ as an index, the present invention (Zn (ZnO) / H ₃ PO ₄ = 0.30, 0.35) and the prior art (Patent Document 4: Zn (ZnO) / H ₃ PO ₄ = 0.20, Confirm the difference of 0.25).
A bath with a total Zn / H ₃ PO ₄ = 0.4 and a phosphoric acid concentration of 80 g / L is used. In this test, although the stability of the treatment bath cannot be evaluated, it is classified into Examples and Comparative Examples because “(4) Ensuring the stabilization of the electrolytic phosphate chemical treatment bath” is mentioned.
Table 1 shows the treatment bath compositions of Examples 1 to 8 and Comparative Examples 1 to 8.

The difference between the example and the comparative example is the “Zn (ZnO) / H ₃ PO ₄ ” ratio. Examples are 0.3 and 0.35, while comparative examples are 0.2 and 0.25.
As the test material, an aluminum material (A6061) and a cold rolled steel plate (SPCC-SD) were used. The dimensions of the test material are 50 mm × 110 mm × 0.8 t, and the surface area is 110 cm ² .
Degreasing → Washing → Surface conditioning → Electrolytic phosphate treatment → Washing → Pure water washing → Cation electrodeposition coating → Baking was performed.
Degreasing was performed by immersing alkylene F-500Y (Kiwa Chemicals Co., Ltd.) at a concentration of 3% at 60 ° C. for 3 minutes.

For surface preparation, use Grander Finer # 7 (Million Chemical Co., Ltd.), make a solution containing colloidal solid content at 0.3%, and soak at room temperature for about 15 seconds.
In electrolytic phosphating, zinc and nickel are used as the anode, the material to be treated is used as the cathode, a voltage of about 12v is applied for about 15 seconds, and a phosphate conversion coating is applied to the aluminum material and cold-rolled steel sheet (SPCC-SD). Formed. The size of the electrolytic cell is 14 cm (L) × 9 cm (W) × 13 cm (H), and has a capacity of 1.6 L. The temperature is 29-35 ° C.

Cationic electrodeposition was applied with dupont-Shinto Co., Ltd. Saxade v-80 at 245v for 48 seconds. The size of the electrolytic cell is 17 cm (L) × 17 cm (W) × 16 cm (H) and has a capacity of 4.6 L. The painted product was washed with pure water and baked by holding at 170 ° C. for 20 minutes.

Table 2 shows the current at the time of electrolytic phosphating when using a zinc electrode, the thickness of the electrodeposition coating film, the glossiness of the electrodeposition coating film, the tape peeling state of the coating film after the salt water immersion test of the coated product, And the tape peeling state of the coating film after the salt spray test of the coated product is shown.

The current during the electrolytic phosphate treatment is a current per surface area 110 cm ² (1.1 dm ² ) to be processed.
The electrodeposition coating film thickness was measured with an eddy current film thickness meter LH-300J (Kett Science Laboratory Co., Ltd.) for aluminum materials. Steel (SPCC-SD) is a value measured with an electromagnetic induction type film thickness meter LZ-200J (Kett Science Laboratory Co., Ltd.).

The gloss of the electrodeposition coating film was measured with a gloss meter Gloss Checker IG-310 (Horiba, Ltd.). The glossiness indicates the percentage of reflection. The larger the number, the better the reflectivity. It represents the glossiness of the coating film.

In the salt water immersion test, the coating film was scratched (cross cut) reaching the metal surface with a knife, immersed in 5% saline solution (5% NaCl water) at 55 ° C. for 240 hours, then naturally dried and then JIS Z 1522. Applicable 25 mm wide adhesive tape (Nichiban Co., Ltd., trade name “Cellotape”) is applied to the scratched (cross cut) part, and then the peeled state of the coating film is observed. The criterion for judgment is that a peel width of 5 mm is good. The salt water immersion test is a setting of the temperature of salt water for immersing the coated product, and the coating film peeling width after the immersion greatly changes. The set temperature is set to about 40 ° C to 55 ° C. If the temperature setting is high, the action of the salt water penetrating between the coating film and the material metal increases, and the adhesion of the coating film decreases. The set temperature of the salt water immersion test performed by the present invention is 55 ° C. This temperature is a high setting in the salt water immersion test. And it is a test severer than the salt water spray test (spraying 35 degreeC salt water) with respect to the adhesiveness of a coating film.

In the salt spray test, the coating film was scratched (cross cut) reaching the metal surface with a knife, and then placed in a salt spray tester spraying 5% saline solution (5% NaCl water) at 35 ° C. for 1500 hours. After natural drying, JIS Z 1522 compliant 25 mm wide adhesive tape is applied to the scratched (cross cut) part, and then the state of peeling of the coating film at that part is observed. The criterion for judgment is that a peel width of 5 mm is good.

Table 2 shows the results of a coating film obtained by performing electrolytic phosphate treatment using a zinc electrode for 12v for 15 seconds (30-35 ° C.) and then performing cationic electrodeposition.

When a phosphate conversion coating is formed with zinc as the anode and electrodeposition coating is performed on it, the results of the salt water immersion test are all within the specifications for both the comparative example and the example, and the coating corrosion resistance is good. .
In the salt spray test, the examples are good, but some of the comparative examples cannot satisfy the standard.

The results of the salt water immersion test in Table 2 are summarized in FIG. The results of the salt spray test shown in Table 2 are summarized in FIG. In the corrosion resistance results of Comparative Examples 1 to 8 and Examples 1 to 8, it can be said that there is no difference except for a part. However, the stability of the treatment bath is clearly different between the comparative example and the example. That is, in the comparative example containing a large amount of free phosphoric acid, the electrode surface reacts with the treatment bath, and the stability of the treatment bath cannot be ensured. Therefore, the comparative example is disadvantageous for practical use. 3 and 4 show the results of electroless treatment in comparison. The result of the electroless treatment is the technical level that is currently in practical use. The results of the examples are superior to the results of the electroless treatment.

Next, Table 3 shows the result of the same operation as in Table 2 except that the electrode for electrolytic phosphate treatment was replaced with nickel.

In the comparative examples, both the salt water immersion test and the salt water spray test are out of specification. The use of a nickel electrode results in lower quality than when using a zinc electrode. This seems to be due to the fact that both baths are zinc> nickel. Moreover, the results of Comparative Example is inferior is believed to free H ₃ PO ₄ is affecting.
The results of the salt water immersion test in Table 3 are summarized in FIG. The results of the salt spray test shown in Table 3 are summarized in FIG. There is a difference in the corrosion resistance results between Comparative Examples 9-16 and Examples 9-16. The stability of the treatment bath is clearly different between the comparative example and the example. That is, in the comparative example containing a large amount of free phosphoric acid, the electrode surface reacts with the treatment bath, and the stability of the treatment bath cannot be ensured. Therefore, the comparative example is disadvantageous for practical use. 5 and 6 show the results of the electroless treatment in comparison. The result of the electroless treatment is the technical level that is currently in practical use. The results of the examples are superior to the results of the electroless treatment.

Phase 2 Understand the status of electroless coating pretreatment currently in practical use. (Thus, Comparative Examples 17 and 18 can be used as Prior Art Examples 1 and 2.)
In Comparative Example 17, an aluminum material (A6061) was subjected to pre-coating treatment → cation electrodeposition by a conventional electroless treatment method. The pretreatment for coating is performed by forming a zirconium-based film, and the cationic electrodeposition coating is the same as in the above 1-16. At present, no example has been reported in which electrolytic treatment is applied to an aluminum material to form a phosphate conversion coating and then paint.

The coating ground treatment bath used in Comparative Example 17 forms an inorganic film having a nanometer (nm) level on the aluminum material surface. The treatment bath forms a zirconium-based film by electroless treatment. Therefore, a PH2 bath containing zirconium ions, fluorine ions and nitrate ions is maintained at a temperature of 45 ° C., and a zirconium-based film of nm level is formed on the aluminum material surface by immersion for 2.5 minutes. It is presumed that the nanometer level coating is inferior in adhesion to the phosphate chemical coating at the μm level.

Therefore, Comparative Example 17 represents the current level of practical corrosion resistance.
The coating results of Comparative Example 17 are shown in Table 5.

The results of the salt spray test of the coating using the ground treatment of the current aluminum material for electroless treatment are at the same level as the electrolytic treatment product. However, in the salt water immersion test, the peel width is 12 mm, and the level is significantly lower than that of an electrolytic phosphate conversion film-formed product that does not peel. The difference in peel width between the salt spray test and the salt water immersion test in electroless treatment is considered to be due to the effect of temperature. The salt water immersion test is immersed in a 55 ° C. bath, whereas the salt spray test sprays 35 ° C. salt water. In coating film peeling, chlorine ions permeate into the portion, and the coating film is peeled off from the material. However, if the temperature is high, the penetrating action becomes strong. In addition, when immersed in a 55 ° C. bath and when spraying a liquid in an atmosphere of 35 ° C., the effect of temperature is greater when immersed in a 55 ° C. bath. Therefore, it is considered that the difference in temperature has affected the test, resulting in a difference between the two.

Note) As a reference example, Fig. 28 shows a sample that was not subjected to coating surface treatment (T / P) and was subjected to a salt spray test for 1500 hours. Even without the surface treatment, the peeling width by salt spray is 3 mm, which satisfies the standard (5 mm or less).
In addition, the process is (1) a large facility due to the long processing time of 2.5 minutes, (2) a processing temperature of 45 ° C, and (3) a small energy response in terms of containing fluorine in the processing bath, and environmental impact substances. There are challenges. The embodiment of the present invention is a treatment bath process (equipment) having a treatment time of 15 seconds, a treatment temperature of 30 ° C., and no fluorine, and the corrosion resistance is higher than that of the prior art.

Comparative Example 18
In Comparative Example 18, cold-rolled steel (spcc-sd) was subjected to pre-coating treatment → cationic electrodeposition by a conventional electroless treatment method. The pretreatment for coating is an electroless treatment, and the cationic electrodeposition coating is the same as the above 1-16.
Table 6 shows the cold rolled steel sheet (SPCC-SD) coating process (electroless pretreatment) of Comparative Example 18.

Table 7 shows the results of Comparative Example 18.

Both the salt water immersion test and the salt spray test are out of the target standard and are inferior to those applying electrolytic phosphate treatment. The process time (equipment) is 2 minutes, which is inferior to the electrolytic process of 15 seconds.

Stage 3: direction to increase the check total Zn / H ₃ PO ₄ ratio when large as 0.5, 0.6 total Zn / H ₃ PO ₄ ratio, is in a direction to facilitate the formation of the phosphate conversion coating However, the effect on coating corrosion resistance is confirmed, and the upper limit of the total Zn / H3PO4 ratio is estimated.

The coating corrosion resistance is investigated when the total Zn / H ₃ PO ₄ ratio is 0.5 (Comparative Example 19 and Examples 17 and 18).
In Comparative Example 19, Zn (ZnO) = 0.25, Example 17 = 0.3, Example 18 = 0.35.
12v, 15 seconds of electrolytic treatment → electrodeposition coating. The steps other than the electrolytic treatment bath are the same electrolysis conditions as in Example 1. The corrosion resistance was evaluated by a salt water immersion test, and the results are shown in Table 9.

A6061 of Comparative Example 19 is out of specification.

The coating corrosion resistance is investigated when the total Zn / H ₃ PO ₄ ratio is 0.6 (Comparative Example 20 and Examples 19 and 20).
In Comparative Example 20, Zn (ZnO) = 0.25, Example 19 = 0.3, Example 20 = 0.35.
Electrolytic phosphate treatment is performed at 8 v × 15 seconds. After that, electrodeposition coating is performed. Since the total Zn / H ₃ PO ₄ ratio is 0.6, the film formation is easy, so the applied voltage in the electrolytic treatment is lowered. It is presumed that the amount of phosphate conversion film increases too much when 12v is applied.

When the total Zn / H ₃ PO ₄ ratio was increased to 0.6, good corrosion resistance was obtained by adjusting the applied voltage.

Fourth Step The total Zn / H ₃ PO ₄ ratio is 0.6, and the minimum value of the applied voltage is grasped. Example 21 is the same treatment bath (Zn (ZnO) = 0.35) as Example 20. Example 20 was good at an applied voltage of 8v. The applied voltage is further reduced to 6v and the electrolytic treatment is performed for 15 seconds.
Estimate the lower limit of the applied voltage.

Even in 6v electrolytic treatment, the results of the salt water immersion test are good for both the aluminum material (A6061) and the steel material (SPCC-SD). However, the corrosion resistance of the bath of Example 21 could not satisfy the standard at an applied voltage of 4 v.

Fifth stage: Investigation of lower limit concentration of phosphoric acid Dilute the bath of Example 3 and estimate the lower limit of phosphoric acid concentration.
Example 22 dilutes the Example 3 bath to 0.8. Examples 23 and 24 further dilute the Example 23 bath to 0.8. In Examples 23 and 24, the Example 3 bath was diluted to 0.64. (0.8 × 0.8 = 0.64)

Electrolyze in 12v, 15 seconds. Both aluminum material (A6061) and cold-rolled steel plate (SPCC) have good corrosion resistance.

Electrolyze in 8v, 15 seconds. Although the result of the aluminum material (A6061) is bad, the cold-rolled steel sheet (SPCC) is good. At about 50 g / l phosphoric acid, 8v electrolysis is the lowest concentration and constant voltage in this test example. However, cold rolled steel sheet (SPCC) has good corrosion resistance.

Step 6: Confirmation at electrolysis time of 10 seconds: Confirmation at the total Zn / H ₃ PO ₄ ratio of 0.6 When the total Zn / H ₃ PO ₄ ratio is 0.6, 15 seconds (8v applied) is Comparative Example 20. These were confirmed in Example 19 and Example 20. The direction in which the film is formed is easy, and the applied voltage is reduced to 8v. And the shortening of the electrolysis time was investigated. Comparative Example 21, Example 25, and Example 26 use the treatment baths used in Comparative Example 20, Example 19, and Example 20, respectively, and perform electrolytic treatment for 10 seconds by applying 8v to perform electrodeposition coating. Is the result of

The results in Table 15 show that when the total Zn / H ₃ PO ₄ ratio is 0.6, electrolytic treatment for 10 seconds is performed, and the treatment bath in the range of the example: Zn (ZnO) / H ₃ PO ₄ = 0.3, 0.35 If used, the salt water immersion test shows that a coating film peeling width of 5 mm or less can be achieved. In the present invention, the coating pretreatment is performed in 30 seconds or less, but the target coating corrosion resistance is obtained even in the electrolytic treatment for 10 seconds.

The result of the salt water immersion test of Examples 17-26 and Comparative Examples 19-21 (use of a zinc electrode) is shown in FIG. Except for A6061 (aluminum material) of Example 24, the peeling width exceeds the standard of 5 mm, all the examples are within the standard. In Example 24, the lower limit of the phosphoric acid concentration was investigated. And in steel materials, peeling width is within a specification. Example 24 and its bath are within the scope of the present invention because there is no peeling width in steel. On the other hand, the comparative examples often exceed the standard width.
The comparative example is an index of Zn (ZnO) / H ₃ PO ₄ that is out of the scope of the present invention, which indicates that the corrosion resistance evaluation tends to be out of specification.

The typical photograph which showed the peeling condition after salt water immersion test 240hr and salt spray test 1500hr implementation is shown. In the case of using a zinc electrode and electrolyzing at 12 v · 15 seconds, Comparative Example 7 and Example 3 are shown. (Figs. 8-15)

  Comparative Example 15 and Example 11 are shown in the case of using a nickel electrode and performing electrolysis at 12 v · 15 seconds. (FIGS. 16-23) The above comparison is with the electrolytic phosphate treatment method. The current practical technologies are Comparative Example 17 and Comparative Example 18. In order to clarify the current state of corrosion resistance, the results of Comparative Example 17 and Comparative Example 18 are also shown by photographs. (Figs. 24-27)

Evaluation consideration table 16 such as “film thickness and glossiness” shows the film thickness ranges of the examples and the film thicknesses of the electrolessly treated products (Comparative Examples 17 and 18).

The electroless treatment product has an electrodeposition coating time of ~ 2.5 minutes, while all the examples of the present invention perform electrodeposition coating in 48 seconds. The embodiment of the present invention has a film thickness of the same level or more in spite of a short coating time. This is presumed to be related to the phosphate coating produced in the present invention. This is one of the effects of the present invention.

Table 17 shows the glossiness range of the examples and the glossiness of electrolessly treated products (Comparative Examples 17 and 18).

The embodiment of the present invention has a glossiness equivalent to that of the current electroless processed product. This indicates that the product of the present invention is at the current product level in appearance (glossiness).

"State of used zinc electrode"
It was described in the section “Ensuring the stability of electrolytic phosphate chemical treatment bath” that the surface condition of the zinc electrode used in the electrolytic treatment differs between the comparative example and the example. The situation is shown in FIG. 29 (comparative example) and FIG. 30 (example). FIG. 29 and FIG. 30 are external views after the zinc electrode used in the two months of the experiment was left in the atmosphere for two weeks or more after the experiment. The surface of the electrode of the comparative example (FIG. 29) is in a rough state where zinc phosphate crystals are precipitated on the surface. On the other hand, the electrode surface of an Example (FIG. 30) is smooth.

Summary of Examples: Discussion The treatment bath of the present invention is defined by Zn (ZnO) / H ₃ PO ₄ and total Zn / H ₃ PO ₄ in the range of about 40 g / l phosphoric acid to 120 g / L. I can do it. The outline is shown in FIG.

The electrolytic phosphate chemical treatment bath composition of the present invention can be applied to the formation of a phosphate chemical conversion film on materials other than steel and steel.

Claims (4)

Zinc oxide is dissolved or combined in a phosphoric acid solution in the range of zinc / phosphoric acid (weight ratio) = 0.26 to 0.35, and an aggregate of phosphoric acid and zinc: “H ₂ PO ₄ ⁻ −Zn ²⁺ −H ₂ PO ₄ ^- - ... process to form a "(1),
A step (2) of adding nitric acid to the solution containing “associates of phosphoric acid and zinc” obtained in the step (1) to dissolve the solution containing the aggregates;
Obtained by the step (3) in which zinc nitrate is added and dissolved in the solution obtained in the step (2) and the step (4) in which nickel nitrate is dissolved in the solution obtained in the step (3);
An electrolytic phosphate chemical treatment bath composition comprising phosphate ions, zinc ions, nickel ions, and nitrate ions, wherein the total zinc / phosphoric acid weight ratio is in the range of 0.35 to 0.65. 2. The electrolytic phosphate chemical conversion composition according to claim 1, which is used for a coating base having phosphoric acid of 40 to 120 g / L, total zinc of 20 to 78 g / L, nickel of 0.3 to 30 g / l and nitrate ion of 13 to 90 g / L. Treatment bath composition Zinc oxide is dissolved or combined in a phosphoric acid solution in the range of zinc / phosphoric acid (weight ratio) = 0.30 to 0.35, and an aggregate of phosphoric acid and zinc: “H ₂ PO ₄ ⁻ −Zn ²⁺ −H ₂ PO ₄ ^- - ... "electrolytic phosphate chemical treatment bath composition used for coating base according to claim 1 or 2 comprising the step (1) to form a Using the electrolytic phosphate chemical treatment bath according to claim 1, claim 2 or claim 3, using zinc or nickel as an anode, connecting an object to be treated to a cathode via a direct current power source, and energizing for 5 to 30 seconds. An electrolytic phosphating method characterized in that a phosphate film is formed on the surface of an object to be processed.