JP5238934B2 - Aqueous zirconium anticorrosive, metal corrosion prevention method using the same, and aqueous zirconium anticorrosive - Google Patents

Description

  The present invention relates to an aqueous zirconium anticorrosive that can be suitably used for anticorrosion of zinc plating, a metal anticorrosion method using the same, and a method for producing an aqueous zirconium anticorrosive.

  The chromate treatment that forms a film on the metal surface using a hexavalent chromate solution is widely used as an anticorrosion treatment for various metal products including galvanized steel sheets because it can easily provide excellent corrosion resistance at low cost. I have been. However, in recent years, the problem that hexavalent chromium contained in discarded chromate-treated products elutes by acid rain and contaminates soil rivers, and the harmfulness of hexavalent chromium contained in the treatment liquid in the chromate treatment process are problems. It has become. Furthermore, in 2007, environmental regulations on hexavalent chromium in automobiles were enforced in Europe, so the development of a chromium-free treatment method has become an urgent issue, and it can be an alternative to chromate for galvanization and is inexpensive and has low toxicity. Moreover, there is an urgent need to develop a non-chromium aqueous treatment agent that can produce a film having high corrosion resistance.

  Approaches to chemical treatment technology free of hexavalent chromium are roughly classified into three types, inorganic coatings, organic coatings, and organic / inorganic composite coatings, depending on the composition of the coatings to be formed. For inorganic coatings, molybdenum-based and phosphate coating-based chemical conversion treatments have been developed, but corrosion resistance comparable to chromate treatment has not been obtained. In addition, organic coatings use resin coatings and silane coupling agents, and organic / inorganic composite coatings use organic resins having functional groups and inorganic substances such as phosphates, silica, and metal salt compounds. Mixed ones have been developed, but none have sufficient corrosion resistance.

  When a resin-based coating agent is used, since the resin swells, in order to obtain high corrosion resistance, a film thickness of several μm or more is required, and thin coating is difficult. In addition, the coating agent itself may be in a suspended state, and it is often difficult to produce a film having excellent smoothness and uniformity in addition to the stability of the solution.

  Many studies have been made on organic / inorganic composite coatings using solutions in which various organic silanes are dissolved in organic solvents, and this is a promising method for forming corrosion-resistant coatings. There is a need for an aqueous coating solution that does not use an organic solvent. Silanol groups formed by hydrolysis of tetraalkoxysilane, which is the least expensive silicon metal alkoxide, exist stably at pH 2 to 5, and an aqueous solution can be easily prepared. The inventors have already changed the composition and concentration of a solution prepared using tetraalkoxysilane, methyltrialkoxysilane and acetic acid using water as a solvent, and developed a high corrosion resistance coating on metals such as galvanizing. An aqueous coating agent that can be formed has been developed (Patent Document 1).

JP2007-284745A

However, in the aqueous coating agent of Patent Document 1, the solution becomes cloudy in about 2 to 3 weeks, and thus it has been a problem to improve its stability.
The present invention has been made in view of the above-described conventional problems, and does not contain heavy metal compounds such as chromium and organic solvents, does not deteriorate the working environment, and forms an anticorrosive film excellent in adhesion and corrosion resistance. It is an object of the present invention to provide an anticorrosive agent that can be manufactured at low cost and excellent in stability and a method for producing the same.

  The inventors have an appropriate pH in coating on galvanizing using zirconium alkoxide and acetic acid, which use water as a solvent, is relatively inexpensive except for silicon, and is expected to improve the corrosion resistance of the produced film. A highly stable aqueous solution was prepared, and the corrosion resistance of the produced film on the metal was evaluated. So far, many treatment solutions for the purpose of rust prevention using zirconium salts have been reported, but zirconium alkoxide is highly reactive with water and difficult to form a uniform aqueous solution. It was never chosen.

  In general, in order to prepare a metal aqueous solution using a metal alkoxide as a starting material, 1) a metal alkoxide having a very low hydrolysis rate is used. 2) a hydroxyl group is chelated to moderately suppress polymerization after hydrolysis. 3) Conditions such as adjusting the pH of the prepared solution so that the resulting metal hydroxide is dissolved must be optimized. Moreover, in order to remove the alcohol produced by hydrolysis of the metal alkoxide by heating, methanol (64.7 ° C.), ethanol (78.3 ° C.), 1-propanol (97.2 ° C.), 2-propanol ( It is desirable to use an alkoxide that generates alcohol having a boiling point lower than that of water, such as 82.3 ° C.) and 2-methyl-2-propanol (82.5 ° C.). Even if these organic components cannot be completely removed, it is possible to reduce the solution to a level that is not flammable.

  Even if zirconium alkoxide is simply added to aqueous acetic acid, the hydrolysis and polymerization reaction rate of zirconium alkoxide is fast, so a uniform aqueous solution cannot be prepared. If strong acid such as sulfuric acid or nitric acid is used, the pH is 1 It becomes the following aqueous solution of strong acid. Therefore, when diligent research was conducted on a method for preparing an aqueous solution from zirconium alkoxide, the pH was adjusted by mixing acetic acid with zirconium alkoxide in advance and then adding water to moderately control the hydrolysis and polymerization rate. 3-4, it discovered that the substantially transparent aqueous solution which had film forming property on the board | substrate by dip coating can be prepared. This aqueous solution is stable without gelation for a long time, but is clearly different from a solution prepared by dissolving water-soluble zirconyl acetate in water. An aqueous solution of the same concentration of zirconyl acetate has no film-forming property on the substrate by dip coating, and exhibits strong acidity with a pH of about 1. It has been discovered that a solution prepared by mixing the zirconium alkoxide and the acetic acid at a predetermined ratio can be suitably used as an aqueous zirconium anticorrosive for galvanization, and has led to the present invention.

  That is, the aqueous zirconium anticorrosive agent of the present invention contains zirconium alkoxide and acetic acid in water as a solvent, and the ratio of (number of moles of the zirconium alkoxide) :( number of moles of the acetic acid) is 1: 1. .6 to 1: 4.

  According to the test results of the inventors, zirconium alkoxide and acetic acid are contained in water as a solvent, and the ratio of (number of moles of the zirconium alkoxide) :( number of moles of the acetic acid) is 1: 1. The aqueous zirconium anticorrosive agent of the present invention of 6 to 1: 4 can form a uniform and dense anticorrosive film when the surface treatment of the metal is performed using this. The ratio of (number of moles of the zirconium alkoxide) :( number of moles of the acetic acid) is particularly preferably in the range of 1: 1.8 to 1: 3, and more preferably 1: 2.0 to 1: The range is 2.4.

  This is presumed to be due to the following reason. When a substantially transparent zirconium hydroxide sol solution having a pH of 3 to 4 which is moderately hydrolyzed and polymerized is used, it is possible to form an anticorrosive film having excellent adhesion and corrosion resistance on the galvanizing. In the composition of the water-based zirconium anticorrosive agent, if the amount of acetic acid added to the zirconium alkoxide is too large, the corrosion resistance of the produced film is lowered, and if it is too small, a large amount of insoluble matter is generated and the sol solution has transparency. Cannot be prepared. Acetic acid is preferably added in an amount of about 2 moles relative to zirconium alkoxide, whereby an aqueous zirconium anticorrosive agent having a pH of 3 to 4 and stable at room temperature for a long time can be prepared.

  The kind of zirconium alkoxide is not particularly limited, and examples thereof include zirconium tetraethoxide, zirconium tetrapropoxide, zirconium tetrabutoxide and the like. Zirconium tetrapropoxide is inexpensive and easily available, and the inventors have confirmed that a dense and uniform film is formed when a coating is applied to a metal, and can be used particularly suitably.

  Since the aqueous zirconium anticorrosive agent of the present invention does not contain heavy metals such as chromium and organic solvents, it has little toxicity and does not deteriorate the working environment. Moreover, it is possible to form the anticorrosion film excellent in adhesiveness and corrosion resistance. Furthermore, since the zirconium alkoxide as a raw material is inexpensive, the manufacturing cost is also low.

  The concentration of zirconium alkoxide contained in the solution is preferably 1.8 to 5.5% by mass in terms of zirconium. If it is like this, it is suitable for formation of a uniform and precise | minute film | membrane in the adhesion process made to adhere to the base materials which consist of metals, such as galvanization.

  The metal anticorrosion method of the present invention comprises an attaching step of attaching the aqueous zirconium anticorrosive agent according to claim 1 or 2 to a metal substrate, and a drying step of drying the substrate to which the aqueous zirconium anticorrosive agent is attached. It is characterized by providing.

  According to the inventors, if the above-mentioned aqueous zirconium anticorrosive agent is adhered to a substrate made of metal and dried, a film having excellent anticorrosion properties can be formed. Although there is no limitation in particular about the adhesion method, methods, such as an immersion method, spraying by spray, and a roll coating method, can be used. After coating, it is desirable to dry at room temperature to about 80 ° C. A single coating is sufficient, but multiple coatings are possible.

  Although the anticorrosion method of the present invention can improve the corrosion resistance of various metals, it can be suitably used for improving the corrosion resistance of zinc and zinc alloys, such as zinc plating, zinc alloy plating, and zinc die casting. it can.

  In the method for producing an aqueous zirconium anticorrosive agent of the present invention, the ratio of (number of moles of the zirconium alkoxide) :( number of moles of the acetic acid) of zirconium alkoxide and acetic acid is 1: 1.6 to 1: 4. A mixing step of mixing so as to have a ratio of, a water addition step of adding water to the mixed solution obtained in the mixing step, and an alcohol removing step of distilling off the alcohol by heating the mixed solution to which water has been added It is characterized by providing.

In the method for producing an aqueous zirconium anticorrosive of the present invention, it is important to add water in the water addition step after previously mixing the zirconium alkoxide and acetic acid in the mixing step. It is important that the solution obtained thereafter is dissolved and reacted by heating at a predetermined temperature in the alcohol removing step. By adding acetic acid in advance, the alkoxide group of zirconium alkoxide is replaced with the acetate group of acetic acid, so that the hydrolysis reaction and the polymerization reaction due to the subsequent addition of water are suppressed. Therefore, a moderately polymerized stable ZrO _{x / 2} (OAc) _y (OH) _4-xy (x + y = 4) An aqueous solution of sol can be prepared. Since the reactivity can be controlled by the amount of acetic acid to be added, the amount of acetic acid that can be used to produce a dense and uniform gloss film on galvanizing was found.

  As mentioned above, it does not contain harmful heavy metal compounds such as chromium, and because it removes alcohol in the alcohol removal process, it does not contain organic solvents, and does not deteriorate the working environment, so that the storage stability of the solution Also good.

  In the mixing step, it is preferable to heat the mixed liquid to which water has been added to 60 to 90 ° C. to distill off the alcohol. If the heating temperature is 90 ° C. or higher, the hydrolysis reaction and polymerization reaction of zirconium alkoxide in the solution are excessively promoted, so that precipitation occurs in the solution and white turbidity occurs. Moreover, if heating temperature is 60 degrees C or less, the hydrolysis reaction and polymerization reaction of zirconium alkoxide in a solution will become inadequate, and the corrosion resistance of the produced film | membrane will fall. Further, since the temperature is not sufficient for distilling off the alcohol in the solution, it is difficult to remove the alcohol.

  Hereinafter, the present invention will be described in detail.

  Examples of the zirconium alkoxide include zirconium tetraethoxide, zirconium tetranormal propoxide, zirconium tetraisopropoxide, zirconium tetraisobutoxide and the like sold by High Purity Chemical Research Laboratories, Wako Pure Chemical Industries, Amax, etc. .

Hereinafter, the present invention will be described in more detail with reference to examples. The blending amounts of zirconium tetranormal propoxide (Wako Pure Chemical Industries) and acetic acid described in the examples are indicated by mol / L in the whole solution. Moreover, the abbreviations of Zr (OnPr) ₄ and AcOH were used as notation for zirconium tetranormal propoxide and acetic acid.

  (Solution concentration) The concentration of the preparation solution was measured with an ICP emission spectrometer.

  (Adhesion evaluation) According to the tape test method, which is one of the peeling test methods in JIS H8504 standard, the tape is adhered to the surface of the film produced on the substrate, and then the tape is peeled off vigorously. The surface condition of was visually evaluated.

  (Measurement of surface state and film thickness of film) The surface state of the obtained film was observed with a scanning electron microscope (SEM). Regarding the film thickness, since the obtained film was a thin film, it was difficult to produce a fracture surface of a sample for film thickness measurement on a galvanized substrate. Therefore, as a reference value, a silicon substrate was coated under the same conditions as those for coating a metal substrate, and a sample obtained after heat treatment at 80 ° C. for 30 minutes was cut to prepare a fracture surface. This was observed by SEM, and the film thickness was estimated from the cross-sectional image of the film.

  (Evaluation of Corrosion Resistance) A JIS Z 2371 standard salt spray tester was used for the corrosion resistance of the film produced on the galvanizing. Spraying of 5 mass% NaCl aqueous solution at 35 ° C, the area ratio of white rust generation after 72 hours is binarized by color extraction using image processing software (Win ROOF, Mitani Corporation) for sample photographs. Measured.

(Solution Preparation) FIG. 1 shows a method for preparing an aqueous zirconium solution. Zr (OnPr) ₄ (about 70%) is added with 1.6 to 4 moles of AcOH in a molar ratio with respect to zirconium, and after stirring uniformly, the concentration is about 0.1 to 0.3 mol / L. Water was added to the. After mixing and dissolving at 60 to 90 ° C., in order to evaporate and remove propanol, the solution was concentrated to a predetermined concentration by heating and stirring to prepare a substantially transparent sol aqueous solution. A small amount of insoluble matter produced by concentration by heating was removed by suction filtration.

  (Coating) Using the above solution, a steel plate that had been galvanized with a thickness of 8 μm was immersed in the solution for 1 minute at room temperature, and then dip-coated at a lifting speed of 6 mm / s. After coating, it was dried in air at room temperature for about 72 hours.

(Results) Zir (OnPr) ₄ hydrolyzed zirconium hydroxide began to form a precipitate at pH 2-3, but it was found that a stable and transparent sol solution can be prepared by coexisting with acetic acid. Although solution preparation was similarly performed using formic acid or propionic acid instead of acetic acid, it was found that a transparent sol solution could not be prepared, and a stable transparent sol solution could be prepared when acetic acid was used. Table 1 summarizes the results of investigations on the properties of solutions prepared by adding 1.6 to 5 molar amounts of acetic acid to Zr (OnPr) ₄ in a molar ratio. When 1.6 mol of acetic acid was added to Zr (OnPr) ₄ , a complete homogeneous sol solution could not be prepared even at a concentration of about 0.1 mol / L. When 1.8 mol of acetic acid is added to Zr (OnPr) ₄ , gelation occurs during concentration, so a uniform sol solution is 0.2 mol / L (1.8% by mass in terms of zirconium). Only to a certain level was obtained. When prepared by adding 2 mol of acetic acid, a uniform and almost transparent sol solution of about 0.5 mol / L could be produced. When 3 mol amount of acetic acid is added, a uniform and almost transparent sol solution of about 0.6 mol / L (5.5% by mass in terms of zirconium) can be prepared, and when 4 mol amount is added, 0.6 mol / L A clear solution of a degree could be produced. The pH values of the solutions that could be prepared uniformly were all 3 to 4, indicating stability without precipitation over a long period of time. Since Zr (OnPr) ₄ has _four propoxy groups that can replace acetate groups, addition of an excess of 4 molar amounts of acetic acid requires more hydrolysis and polymerization reactions due to the subsequent addition of water. It is not preferable because it is suppressed. Therefore, in the preparation of the aqueous zirconium solution, a suitable addition amount of acetic acid is 1.6 to 4 mol by mole with respect to zirconium.

These aqueous zirconium solutions can be formed on a glass substrate, and a water-insoluble transparent film without peeling was obtained by a tape test method. In the film formed on the galvanized film, the concentration of acetic acid added at the time of preparing the solution is 0.36 mol / L or more and less than 1.8 mol / L, that is, the ratio of (number of moles of the zirconium alkoxide) :( number of moles of the acetic acid). However, when it was in the range of 1: 1.8 to 1: 3, a glossy film was obtained by drying a film prepared from the solution at room temperature. When a glossy film is obtained on galvanized plating, it indicates that a uniform and dense film has been formed. In order to form a highly corrosion-resistant film, an aqueous zirconium solution containing a high concentration of zirconium with as little acetic acid content as possible is desirable. Therefore, a solution prepared by adding 2.0 to 2.4 mol of acetic acid in a molar ratio with respect to Zr (OnPr) ₄ that forms a glossy film and is capable of preparing a solution having a high zirconium concentration. It is considered particularly suitable for the production of a corrosion-resistant film.

SEM observation of the surface and cross section of the film formed on the silicon substrate using a 0.5 mol / L solution prepared by adding 2 mol of acetic acid at a molar ratio to Zr (OnPr) ₄ Thus, a film having a film thickness of 260 nm was obtained by one coating.

FIG. 2 shows the results of examining the corrosion resistance of a film produced on galvanizing using this solution by a salt spray test (72 hours). The white rust occurrence rate indicating the corrosion rate was 3.5% in terms of area ratio, and the corrosion resistance was 5% or less. In the film prepared using an aqueous zirconium solution having other composition, no film showing higher corrosion resistance was found. In addition, it was found that a film prepared using a solution having a low zirconium concentration or a film that does not exhibit gloss does not exhibit corrosion resistance, and that the higher the film gloss, the higher the corrosion resistance. Therefore, it was found that the optimal molar ratio of acetic acid added to Zr (OnPr) ₄ is about 2 mol.

  From the above results, it is most preferable to produce a uniform and dense corrosion-resistant film on the galvanizing, in which the ratio of moles of zirconium alkoxide to moles of acetic acid is 1: 2.0 to 1: 2.4. It is considered a range.

  In this way, it was found that an aqueous zirconium solution having high stability can be prepared using acetic acid using a metal alkoxide as a starting material. The coating film produced on the galvanizing using the solution exhibited corrosion resistance with an area ratio of white rust generation of 5% or less by a salt spray test for 72 hours.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the scope of the claims.

The aqueous zirconium anticorrosive agent of the present invention does not contain a heavy metal compound such as chromium, and can produce a film having excellent adhesion and corrosion resistance on galvanizing. Therefore, it can be widely used as an alternative to chromating chromate. it can. It can be used in various industrial fields such as the automobile industry and the electronics industry that use chromate-treated galvanized products.

Preparation of aqueous zirconium solution Photograph after a salt spray test (72 hours) of a sample in which a film was formed on a galvanizing with an aqueous zirconium solution

Claims (3)

It contains zirconium alkoxide and acetic acid in water as a solvent,
The ratio of (number of moles of the zirconium alkoxide) :( number of moles of the acetic acid) is 1: 1.6 to 1: 4, and zirconium alkoxide is contained in an amount of 1.8 to 5.5% by mass in terms of zirconium. , An aqueous zirconium anticorrosive agent for zinc plating containing no alkoxysilane ,
The aqueous zirconium anticorrosive is
A mixing step of mixing zirconium alkoxide and acetic acid so that a ratio of (number of moles of the zirconium alkoxide) :( number of moles of the acetic acid) is 1: 1.6 to 1: 4;
A water addition step of adding water to the mixture obtained in the mixing step;
An alcohol removing step of heating the mixed solution to which water has been added to distill off the alcohol;
An aqueous zirconium anticorrosive agent produced by performing Wherein in the alcohol removal step, an aqueous zirconium anticorrosive as claimed in claim 1, wherein heating the mixture to 60 to 90 ° C. distilling off the alcohol. A method for producing a galvanized member with an anticorrosive coating , comprising: depositing the aqueous zirconium anticorrosive agent according to claim 1 or 2 on a galvanized surface; and drying the zirconium anticorrosive agent on the galvanized surface .