JP4796320B2 - Rust preventive coating composition using layered double hydroxide that peels off in water - Google Patents

Description

The present invention relates to a nanosheet-dispersed sol obtained by adding a layered double hydroxide capable of causing delamination in water and / or a water-soluble solvent containing water to water and / or a water-soluble solvent containing water. The present inventors have found that when used as a rust preventive film composition, excellent rust preventive properties can be developed, and the present invention relates to the novel rust preventive film composition and its use.

The layered double hydroxide has the general formula: [M 2 ⁺ _1−x M ³⁺ _x (OH) ₂ ] ^{x +} [A ⁿ⁻ _{x / n} · yH ₂ O] ^x− , and is a positively charged basic layer [M ²⁺ _1-X M ³⁺ _X (OH) ₂ ] is a layered compound in which an anion and water of crystallization are encapsulated in an intermediate layer, and is electrically neutral.

Mg, Mn, Fe, Co, Ni, Cu, Zn, etc. are known as divalent metals in the basic layer in the layered double hydroxide, and Al, Fe, Cr, In, etc. are known as trivalent metals. Etc. are known. Moreover, examples of the substance included between the layers include OH ⁻ , F ⁻ , Cl ⁻ , NO ₃ ⁻ , CO ₃ ²⁻ , V ₁₀ O ₂₈ ⁶⁻ , Fe (CN) ₆ ⁴⁻ , CH ₃ COO ^{− and the} like. Anions are known, but other than anions can be included.

Layered double hydroxides are usually chemically synthesized, but are also produced as natural minerals and are called hydrotalcites. The properties, such as Cl in JP-A-11-148029 ^- as a scavenger, and techniques used in conjunction with anticorrosive pigment in anticorrosive paints is disclosed, such as a carboxylic acid in JP 2004-351452 A technique is disclosed in which a composite material in which an organic acid is intercalated between layers is used as a processing agent before plastic working such as metal pressing. However, in any case, there is no description that the layered double hydroxide is separated and dispersed to form a nanosheet-dispersed sol.
Japanese Patent Laid-Open No. 11-148029 Japanese Patent Laid-Open No. 2004-351542

On the other hand, exfoliation phenomena in clay minerals have been known for some time, but there are few reports on exfoliation phenomena of layered double hydroxides. The reason for this is that the charge density of the basic layer of the layered double hydroxide is generally large and the electrostatic attractive force between the basic layer and the intermediate layer is strong. It can be difficult.

However, the peeling phenomenon does not occur at all. For example, JP 2004-189671 A discloses a layered double hydroxide in which an anion of an aromatic aminocarboxylic acid is encapsulated between layers of a layered double hydroxide, such as alcohol. Although it is known that the peeling phenomenon occurs in the polar solvent, there is no description regarding application to rust prevention or the like.
JP 2004-189671 A

As for the exfoliation phenomenon of other layered compounds, JP-A-10-259023 discloses a method of synthesizing flaky titanium oxide by exfoliating lamellar titanic acid powder with an aqueous amine solution and heating it. Japanese Laid-Open Patent Publication No. 2003-138145 discloses a technique in which layered titanic acid swollen and nano-sheeted is added to a synthetic resin to improve the mechanical strength of the resin. It is not intended.
Japanese Patent Laid-Open No. 10-259023 JP 2003-138145 A

Therefore, the present inventor has already studied to solve the above problems, and as a result, the layered double hydroxide obtained by including a specific aliphatic carboxylic acid metal salt in the intermediate layer can be easily peeled off in an aqueous medium. The patent application (Japanese Patent Application No. 2004-370532) has been filed.
Japanese Patent Application No. 2004-370532

On the other hand, as a rust preventive film composition, a rust preventive paint containing a lead-based or chromium-based rust preventive pigment has been generally widely used for rust prevention of metal materials. The use of phosphate-based rust preventive pigments that do not contain harmful lead compounds or hexavalent chromium has increased.

In addition, as a primary rust prevention treatment method for steel materials, chromate treatment containing hexavalent chromium and phosphate treatment such as zinc phosphate and iron phosphate are also performed. Widely used for improving adhesion and rust prevention with paints.

The present inventor has already succeeded in developing a peelable double hydroxide that can be easily peeled off in an aqueous solution, and the present invention uses this peelable double hydroxide as a novel antirust coating composition. It has been found that it can be applied.

The rust preventive coating formed by conventional rust preventive paint or phosphate treatment usually has a film thickness of micrometer (μm) order, and there is a problem that the rust preventive performance is remarkably lowered at a thinner film thickness. . On the other hand, in the chromate treatment, although the film thickness is thinner than the above, since harmful hexavalent chromium is used as a raw material, development of an alternative treatment method has been strongly desired.

Furthermore, as a new rust prevention technology, a method for obtaining a highly transparent rust prevention film by adding metal oxide nanoparticles to an acrylic resin or the like has been proposed, which is said to be good for specific base materials such as magnesium alloys. However, there is no mention of the formation of a single film with nanoparticles, and no mention is made of the effect on a wide range of metal materials.
“Transparent antirust treatment agent and antirust effect by metal oxide-containing film of nanoparticles” Industrial Materials, October 2004 (Vol. 52, No. 10), P36-39.

As a result of studying to solve the above-mentioned problems, the present inventor is obtained by delaminating a layered double hydroxide that has already been found in water and / or a water-soluble solvent containing water. It has been found that an excellent rust-preventing effect is exhibited by treating the nanosheet-dispersed sol on the metal surface as a rust-preventive coating composition, thereby completing the present invention.

That is, a layered double hydroxide composed of a divalent metal and a trivalent metal in which an aliphatic carboxylic acid metal salt is incorporated between layers exhibits high swellability in water and / or a water-soluble solvent containing water. Delamination occurs, resulting in a highly viscous colloidal solution.

Examples of the water-soluble solvent include alcohols such as methanol and ethanol, ketones such as acetone, glycols such as ethylene glycol and diethylene glycol, and a mixed solvent thereof.

In addition, when synthesizing a layered double hydroxide that is exfoliated in water, which is the base of the nanosheet-dispersed sol, the reaction solution obtained by reacting the layered double hydroxide with an aliphatic carboxylic acid metal salt in water is left as it is or centrifuged. The solid content is usually produced by drying up moisture in a dryer at 80 ° C. to 120 ° C., but it can be produced without any problem even at a temperature of 80 ° C. or lower, although the drying time becomes longer. On the high temperature side, a temperature exceeding 350 ° C. is not preferable because the decomposition of the organic functional group of the aliphatic carboxylic acid used to form the nanosheet starts.

Furthermore, when synthesized by a freeze-drying method, although the reason is not clear, it has been confirmed that the peeling time in water is shortened, which is suitable for efficiently obtaining a nanosheet-dispersed sol.

The nanosheet-dispersed sol is considered to have a skeleton component of layered double hydroxide dispersed as a nanosheet as a colloidal solution. For example, when 50 ml of a 1% aqueous dispersion colloid solution is placed in a 100 ml glass beaker and irradiated with visible light (using a red laser pointer with a wavelength of 650 nm) from the side, it shows a Tyndall phenomenon in which the optical path shines, indicating that it is in a colloidal state. .

Since the nanosheet-dispersed sol obtained as described above is in a transparent or translucent aqueous solution state, it can usually be easily coated with various metal materials alone, and as a coating method, spray coating, dipping coating, Brush coating, spin coating, electrodeposition coating, etc. (The surface charge of the nanosheet present in the nanosheet dispersion sol of the present invention is positive and is electrodeposited on the negative electrode: cationic electrodeposition) Is possible.

In addition, since this nanosheet-dispersed sol exhibits neutrality or alkalinity and can form an effective film without corroding the metal material, the metal materials that can be coated include iron and steel materials, aluminum-based materials, galvanizing, etc. It can be used for zinc-based materials, magnesium-based materials, or these alloy-based materials such as duralumin and magnesium alloys. Furthermore, the present invention can also be applied to phosphate-treated surfaces such as zinc phosphate treatment and iron phosphate treatment performed as the surface treatment of steel sheets.

The nanosheet-dispersed sol coated on the metal surface by the various coating methods described above can easily form a layered double hydroxide-based rust preventive coating by directly drying at room temperature or heat treatment.

In addition, the film dried at low temperature like room temperature drying has the property of causing the peeling phenomenon in water in the layered double hydroxide material, so most of it is redispersed in water when it comes into contact with water again. Apparently the film seems to have dissolved and disappeared. However, when the surface of the coated plate that appears to have lost the film in this way is measured by XPS (X-ray surface analysis method), for example, in the case of Mg-Al-based layered double hydroxide / treated Mg acetate, the components of Mg and Al Therefore, it is considered that the nanosheet is firmly attached on the surface of the coated plate, and it is known that the antirust performance is exhibited as shown in Examples described later.

As described above, the rust-preventing effect of the rust-preventing film according to the present invention is exhibited even when drying at room temperature or at a low temperature of 100 ° C. or lower, but heat treatment is more effective in order to exhibit a more advanced rust-preventing effect. It is. The heat treatment temperature is desirably 100 ° C. or higher and 700 ° C. or lower, and more preferably 250 ° C. to 500 ° C.

The heat treatment effect mentioned here means that even when the rust preventive film comes into contact with water, the redispersibility in water is lost and the rust preventive film changes to a strong water resistant film.

When the heat treatment is less than 100 ° C., the water resistance is insufficient, part of the film is re-dispersed, and the film thickness becomes thinner than in the initial stage. Therefore, it is difficult to control the film thickness. This is because, since the characteristics are almost the same as those of the heat treatment at 500 ° C., the energy required for the treatment is wasted. Furthermore, when the temperature exceeds 700 ° C., the chemical structure of the nanosheet is changed, the film becomes brittle, a defect occurs in the film, and the rust prevention effect decreases.

Moreover, it turned out that the hardness of a film | membrane improves by heat-processing. The heat treatment time depends on the film thickness to be coated, but if it is short, it may be about several seconds. Usually, a time of about one hour or less applied to the baking paint is sufficient. Note that there is no problem in quality even if the heat treatment is performed for 1 hour or more.

The film thickness can be controlled from nanometer (nm) size to micrometer (μm) size by changing the concentration of the nanosheet-dispersed sol. The concentration of the nanosheet dispersion sol is preferably 0.01 wt% to 30 wt%, more preferably 0.05 wt% to 15 wt%.

This is because when the content is 0.01 wt% or less, the amount of nanosheets, which are active ingredients for forming a film, is small and an effective film cannot be formed. If it is 30 wt% or more, the viscosity of the dispersed sol becomes high, and the workability at the time of coating film formation becomes difficult.

Usually, at a concentration level of 5 wt% or less, a thin film of 0.1 μm (100 nm) or less is obtained. Since this thin film cannot be measured with an existing electromagnetic film thickness meter, it is judged from a scanning electron micrograph or the like.

Since the film using the nanosheet-dispersed sol forms a strong film, it exhibits excellent rust resistance against various metal materials such as iron, steel, aluminum and zinc. In particular, since the single film has excellent transparency, the base is not concealed. Further, by adding pigments, fillers, and the like that are usually used in paints, it is possible to impart colorability, concealability, film strength, and the like.

It is not always clear why the layered double hydroxide film formed by nanosheet dispersion sol shows excellent rust prevention effect, but nanosheet is laminated on the surface of the object to be coated and effectively covers the surface it is conceivable that. That is, it is presumed that entry of corrosive components such as moisture, oxygen or chlorine ions from the outside into the metal surface is suppressed. Furthermore, the effect of alkali corrosion prevention by holding | maintaining a film | membrane by alkalinity is also considered.

Furthermore, since this film is transparent, it has a feature that the base can be seen. When used as a primary rust preventive film, there is no possibility of hiding a record directly written on a metal substrate. In addition, since it is colorless, there is a feature that there is no influence on the color of the top coating even when the coating is repeated on top.

For example, when the visible light transmittance in a 400 nm to 750 nm region was measured with a spectrophotometer on a film sample having a thickness of 1 μm, the transmittance showed 70% or more, and excellent transparency was confirmed. did it.

As described above, the present nanosheet-dispersed sol forms an excellent rust preventive film even when used alone, but a method of using it as a binder is also possible. In other words, inorganic pigments such as titanium oxide and bengara that are usually used in paints, colored pigments such as phthalocyanine blue, various dyes, extender pigments such as calcium carbonate and barium sulfate, rust preventive pigments such as zinc phosphate, and design properties Aluminum flakes, glass flakes, etc., metal oxide nanoparticles such as fine particle titanium oxide and fine particle zinc oxide used for imparting UV-cutting properties, and various surface treatment pigments considering dispersibility, etc. are used Is possible.

As described above, various commonly used pigments can be used, but as a result of investigating rust prevention characteristics, the rust prevention property of the nanosheet-dispersed sol-based film of the present invention is particularly obtained by using rust prevention pigments and metal oxide nanoparticles. Was found to improve.

As the anti-corrosion pigment, phosphate-based, phosphite-based, molybdate-based, chromate-based, etc. that are usually used in paints can be used. It was found that the addition of zinc acid or aluminum tripolyphosphate anticorrosive pigments further improved the antirust effect.

As the metal oxide nanoparticles, fine particle titanium oxide, fine particle zinc oxide, fine particle silica, fine particle cerium oxide, and the like can be used. However, particularly in fine particle titanium oxide, fine particle zinc oxide and fine particle silica, an improvement in the rust prevention effect is recognized. It was. It is not clear why the metal oxide nanoparticle contributes to the rust prevention effect, but it is presumed that the metal oxide nanoparticle contributes to the formation of a dense film as the same level of the nanosheet of the present invention.

The metal oxide nanoparticle may be difficult to disperse when used in powder form, and is therefore conveniently used in a sol state such as titania sol, alumina sol, silica sol.

However, in the case of a sol, various products have been developed from the acidic side to the alkaline side for dispersion stabilization and the like. However, for this purpose, a strongly acidic sol that dissolves the nanosheet-dispersed sol is not preferable, and usually pH = Any sol of 5 or more can be used.

The metal (M) of the layered double hydroxide used in the present invention is preferably a divalent or trivalent metal. As the divalent metal, Mg, Ca, Zn, Co, Ni, Cu, Mn, Fe, or the like can be used. Among these, Mg and Zn are preferable, and Mg is most preferable.

As the trivalent metal, Ce, Al, Fe, Cr, Co, In, or the like can be used. Among these, Ce and Al are preferable, and Al is most preferable. That is, in the layered double hydroxide used in the present invention, a combination in which the divalent metal is Mg and the trivalent metal is Al is most preferable. These metals may be used alone or in combination of two or more.

And as a saturated aliphatic monocarboxylate (G) used in the layered double hydroxide of the present invention, a fatty acid having up to 5 carbon atoms can be used. In particular, a carbon number of 2, that is, a metal acetate is most preferable.

The metal salt is preferably a divalent or trivalent metal. Mg, Ca, Zn, Co, Ni, Cu, Mn, Fe, or the like can be used as the divalent metal. Among these, Mg and Zn are preferable, and Mg is most preferable.

As the trivalent metal, Ce, Al, Fe, Cr, Co, In, or the like can be used. Among these, Ce and Al are preferable, and Al is most preferable. These saturated aliphatic monocarboxylates may be used alone or in combination of two or more.

Examples of the method for producing an organic-inorganic composite using a layered double hydroxide include a coprecipitation method, an ion exchange method, and a reconstruction method, and the layered double hydroxide forming the nanosheet-dispersed sol of the present invention includes these methods. Although any manufacturing method can be used, a manufacturing method based on a reconstruction method is most preferable.

In the coprecipitation method, an aliphatic carboxylic acid metal salt aqueous solution is first prepared. For example, a mixed aqueous solution of a divalent metal salt such as Mg (NO ₃ ) ₂ and a trivalent metal salt such as Al (NO ₃ ) ₃ is dropped into the aqueous solution. During dropping, the pH is adjusted to 6 to 10, and then ripened to separate the solid product, whereby a layered double hydroxide in which an aliphatic carboxylic acid metal salt is included in the intermediate layer can be obtained.

In the ion exchange method, first, an aqueous solution of an aliphatic carboxylic acid metal salt was prepared, and a layered double hydroxide containing an anion such as OH ⁻ , Cl ⁻ , CO ₃ ⁻ , etc. was added to the intermediate layer and aged. Thereafter, when the solid product is separated, a layered double hydroxide in which an anion containing an aliphatic carboxylic acid metal salt is included in the intermediate layer can be obtained.

In the reconstruction method, first, an aqueous solution of an aliphatic carboxylic acid metal salt is prepared, and then heated in advance at a temperature of 400 ° C. or higher and lower than 800 ° C. for 1 hour or more, and then cooled, carbonated double hydroxide pyrolysis. Add things. After stirring or shaking, the solid product can be separated to obtain the desired layered double hydroxide. In addition, when the reaction is carried out using an acidic aliphatic carboxylic acid solution, a part of the divalent metal and trivalent metal that are components of the layered double hydroxide are eluted, resulting in a reaction as a metal salt of the aliphatic carboxylic acid. A layered double hydroxide can also be obtained.

The layered double hydroxide obtained above is added to water and / or a water-soluble polar solvent containing water, and mixed or stirred to form a layered double hydroxide capable of forming a film having excellent rust prevention properties. A hydroxide nanosheet dispersion sol can be obtained. At that time, it can be easily solated at room temperature, but may be performed at a temperature of 100 ° C. or lower.

(When nanosheet dispersion sol is used as a binder)
As described above, the nanosheet-dispersed sol can be used not only alone but also with components such as pigments and fillers to enhance the effects of coloring, concealing, and improving rust prevention. Although there is no restriction | limiting in particular as a component which can be added, Since a strongly acidic substance may dissolve the layered double hydroxide of a raw material, it is not desirable. In particular, it was found that the addition of zinc phosphate or K-white 105 (produced by Teika Co., Ltd.), which is an aluminum tripolyphosphate anticorrosive pigment, further improves the antirust property.

Furthermore, the effect of improving rust prevention was also observed in ultrafine metal oxide powders such as fine particle titanium oxide, fine particle zinc oxide and fine particle silica. When using ultrafine particles, sol bodies such as titania sol and silica sol are more preferable because they can be easily dispersed.

Hereinafter, specific examples will be shown and the effects of the present invention will be described. However, the present invention is not limited to these examples.

Synthesis of layered double hydroxides that peel in water-1
0.28 mol of Mg-Al-based layered double hydroxide (carbonated double hydroxide DHT-6 manufactured by Kyowa Chemical Co., Ltd.), which was previously heat-treated at a temperature of 700 ° C. for 20 hours to a 0.28 mol / L magnesium acetate aqueous solution. Add After stirring at room temperature for 15 hours, the obtained solid product (gel form) was separated by centrifugation, then dried as it was in a 90 ° C. dryer for 10 hours, and then pulverized to obtain Product 1.

Synthesis of layered double hydroxides that peel in water-2
A product 2 was obtained in the same manner as in Example 1 except that the magnesium acetate was changed to cerium acetate.

Synthesis of layered double hydroxides that peel in water-3
To the 0.28 mol / L aqueous solution of zinc acetate, 0.28 mol of Zn—Al-based layered double hydroxide that has been previously heat-treated at 600 ° C. for 20 hours is added. After stirring at room temperature for 15 hours, the resulting reaction solution was directly dried in a 100 ° C. dryer for 20 hours and then pulverized to obtain Product 3.

Preparation of rust preventive coating composition (a) Nanosheet-dispersed sol obtained by adding a predetermined amount of the powder of product 1 obtained in Synthesis-1 to ion-exchanged water at room temperature is used as a rust preventive coating composition. Used as (a).

Preparation of rust preventive coating composition (b) Nanosheet-dispersed sol obtained by adding a predetermined amount of the powder of product 2 obtained in Synthesis-2 to ion-exchanged water at 50 ° C. to obtain a rust preventive coating composition Used as (b).

Preparation of antirust coating composition (c) The powder of product 3 obtained in Synthesis-3 was placed in ion-exchanged water / ethanol = 0.7 / 0.3 (wt ratio) at room temperature. The nanosheet-dispersed sol obtained by quantitative addition was used as the anticorrosive film composition (c). In addition, this nanosheet dispersion | distribution sol showed a slightly cloudy state, and it was estimated that the nanosheet partially aggregated.

Preparation of anti-rust coating composition (d), (e) A predetermined amount of the powder of product 1 obtained in Synthesis-1 was added to ion-exchanged water at room temperature, and a 10 wt% solution of nanosheet-dispersed sol was obtained. As a binder component, rust preventive coating compositions (d) and (e) were obtained by the following composition.

Preparation of antirust coating compositions (f), (g) and (h) A predetermined amount of the powder of product 1 obtained in Synthesis-1 was added to ion-exchanged water at room temperature, and nanosheet-dispersed sol The 5 wt% solution was adjusted, and using it as a binder component, anti-rust coating compositions (f), (g) and (h) were obtained by the following formulation.

Examples 1 to 14 were prepared under the conditions shown in Table 3 using the antirust coating compositions (a) to (h). In addition, the to-be-coated board for a test used the degreasing process mild steel plate SPCC-SB (JIS G3141) and the degreasing process galvanization board SGCC. The coating was performed by dipping, bar coater and electrodeposition (DC 10V, 3 minutes, counter electrode stainless steel plate).

Comparative Example 1

A commercially available Mg—Al-based layered double hydroxide (carbonated double hydroxide DHT-6 manufactured by Kyowa Chemical Co., Ltd.) was treated as a rust-proof coating composition on the mild steel plate under the same conditions as in Example 4.

Comparative Example 2

A commercially available zinc phosphate treated plate (bonded steel plate # 144: manufactured by Nippon Test Panel Co., Ltd.) was used as it was for rust prevention comparison with zinc phosphate treatment.

[Evaluation methods]
Rust prevention test 1 :
It put into the salt spray test machine maintained at 35 degreeC inside machine temperature, sprayed 5% sodium chloride aqueous solution at 1 kg / cm < ² > for 8 hours and 24 hours, and observed generation | occurrence | production of the rust of the test plate.

Rust prevention test 2 :
The test plate was put into a thermo-hygrostat kept at an internal temperature of 20 ° C. and a relative humidity of 80%, and the occurrence of rust on the test plate after 24 hours was observed.

[Evaluation results]
The evaluation results are shown in Table 4. As is apparent from Table 4, the effect of rust prevention of the examples based on the present invention was confirmed. Regarding the 20 ° C. dry film in Example 7, the redispersibility in water remains, which is apparently worse in a normal salt spray test (rust test 1), which is a severe rust test method. In the rust prevention test 2 performed under mild conditions, a clear rust prevention effect was confirmed.

Moreover, the rust preventive property which was excellent in any evaluation was able to be confirmed in the system which used nanosheet dispersion | distribution sol as a binder like Examples 10-14 and used a rust preventive pigment etc. together.

In Comparative Example 1, since no film was formed, no rust prevention effect was observed. Moreover, although the antirust effect was recognized by the comparative example 2, the Example of this invention showed the antirust property equivalent to or more than it.

In the present invention, the layered double hydroxide rust preventive film composition that peels off in water can form a nano-level transparent rust preventive thin film alone, or can be used in combination with rust preventive pigments, metal oxide ultrafine particles, etc. Therefore, it can be used as a coating material for various metal materials. In particular, since the nanosheet is the main component of the film, it can be used as a primary antirust treatment agent for a metal material as a nanothin film.

Claims (4)

General formula,
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] (wherein M ²⁺ is Mg ²⁺ or Zn ²⁺ , M ³⁺ is Al ³⁺ , and 0.2 ≦ X ≦ 0.33 ) A layered double hydroxide peeled off in water composed of a metal double hydroxide basic layer represented by the following formula: Mg, Zn or Ce acetate intercalated in an intermediate layer of the basic layer and interlayer water A rust preventive coating composition containing, as a film-forming component, a sol that is dispersed in water or a mixture of water and a water-soluble organic solvent and then peeled off. The rust preventive coating composition according to claim 1, comprising fine titanium oxide, fine zinc oxide or fine particle silica in the form of a rust preventive pigment and / or sol . The rust preventive paint composition according to claim 2, wherein the rust preventive pigment is zinc phosphate or aluminum tripolyphosphate .   A method for forming a rust-preventing film, comprising: coating a metal material with the rust-preventive coating composition according to any one of claims 1 to 3, and heating the coating film to 100 to 700 ° C to dry.