JP3070411B2 - Method for forming water-repellent coating film on iron-based member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a coating layer having high water repellency on an iron-based member.

[0002]

2. Description of the Related Art Various surface treatment methods have been used to improve the durability of iron-based members, for example, steel plates. However, conventional methods, such as chromate treatment, have a temporary rust-preventive action and are not suitable for long-term rust-proofing. Further, the organic resin coating method has a rust-preventing action for a certain period of time. However, pinholes are present in the organic resin coating film, and moisture may enter through the pinholes to corrode the iron-based member. Further, the organic resin coating film has low heat resistance, and therefore cannot be used for iron-based members used in a high-temperature environment, for example, members of an internal combustion engine.

In order to solve such a problem, Japanese Patent Laid-Open No.
-68477, a fluoroalkylsilane and A
It has been proposed to increase the durability and heat resistance of a steel sheet by forming an inorganic oxide coating formed from alkoxides of 1, Zr, Ti, Si, W, Ce, Sn, and Y. This coating is a composite inorganic oxide coating formed by cross-linking by dehydration condensation of the above-mentioned metal, so that it has excellent durability and heat resistance, and also has water repellency derived from a fluoroalkyl group.

[0004]

However, when an iron-based member represented by the above-mentioned steel sheet is formed with the above-mentioned inorganic oxide film, it has a low surface activity and thus low adhesion. In addition, the iron element is easily diffused and precipitates on the surface of the coating,
It covers the fluoroalkyl group that exhibits water repellency. In addition, since iron oxide is generated during the heating process, the water repellency of the coating is reduced, and the adhesion between the coating and the iron-based member is reduced.

The present invention solves the above-mentioned drawbacks of the coating, and provides a method of forming a water-repellent coating film having high adhesion to an iron-based member and having heat deterioration resistance in which a decrease in water repellency is suppressed. The purpose is to provide.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for forming a water-repellent coating film on an iron-based member, comprising a step of adding a hydroxyl group to the surface of the iron-based member, a method for forming a metal alkoxide and a part of an alkoxyl group. A step of applying a mixed solution with a fluoroalkyl group-substituted metal alkoxide substituted by a fluoroalkyl group on the surface of the iron-based member to which the hydroxyl group has been added to form a coating film, and baking the coating film to form a coating film Is formed.

Further, the present invention is a method for forming a water-repellent coating film on an iron-based member, wherein Mn, Z
n, Ni, Cu, Mg, Co, Fe, Ti, Zr, V,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
forming a coating film of an oxide of at least one metal selected from the group consisting of b, Lu, Y, Ba, Sr, and Pb; and a method in which a metal alkoxide and a part of an alkoxyl group are substituted with a fluoroalkyl group. A step of applying a mixed solution with an alkyl group-substituted metal alkoxide on the coating film of the metal oxide to form a coating film, and baking the coating film to form a coating film. It is characterized by becoming.

Further, the present invention is a method for forming a water-repellent coating film on an iron-based member, comprising: a metal alkoxide; a fluoroalkyl group-substituted metal alkoxide in which a part of the alkoxyl group is substituted by a fluoroalkyl group; Mn, Z
n, Ni, Cu, Mg, Co, Fe, V, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, B
a step of applying a mixed solution with an alkoxide of at least one metal selected from a, Sr, and Pb to the surface of the iron-based member to form a coating film, and baking the coating film to form a coating film The process is characterized by comprising the steps of:

Furthermore, the present invention provides a method of forming a water-repellent coating film on ferrous member, the following equation aqueous sulfuric acid solution _{pH3~5 C n H 2n + 1 SO} 4 - · Na + ( above formula Wherein n is 7 to 15).
A solution obtained by dissolving ^-1 to 10 ^-3 M / L is applied to an iron-based member and dried.

[0010]

According to the first aspect of the present invention, the surface of the iron-based member is activated by providing an OH group on the iron-based member as a pre-treatment for forming the water-repellent coating film, and the water-repellent coating film is activated. Improves adhesion. In addition, the presence of the OH group reduces fluoroalkyl groups that decompose and disappear during firing in the formation of the coating film, improves the concentration of fluorine remaining in the coating film after firing, and improves the initial water repellency of the coating film. Improve. further,
The stable and stable formation of the iron oxide film uniformly and densely on the surface of the iron-based member suppresses the subsequent generation of iron oxide on the surface of the coating film, thereby improving the heat resistance of the coating film.

In the invention according to the second aspect, as a pre-treatment for forming a water-repellent coating film, an iron-based member is coated with an oxide of at least one metal selected from the above-mentioned metals, whereby this metal The oxide improves the conformity between the coating film formed thereafter and the surface of the iron-based member. Furthermore, the iron oxide generated from the iron-based member and the metal in the metal oxide coating layer form a stable composite oxide such as spinel, ilmenite, perovskite, garnet, or magnetoplumbite, thereby reducing the iron-based member. Is trapped in the metal oxide layer below the water-repellent coating layer, thereby suppressing precipitation on the water-repellent coating layer. As a result, heat resistance is improved.

According to the third aspect of the present invention, since a metal that forms a stable composite oxide with iron oxide from an iron-based member as described above exists in the water-repellent coating layer, the iron oxide is repelled. It traps in the aqueous coating layer and suppresses deposition on the surface.
As a result, heat resistance is improved.

[0013] In the invention according to claim 4, the surfactant represented by the above formula is adsorbed on the clean surface of the iron-based member, and the surface active agent is dissolved in SO _4.
It forms a salt of Fe and forms a bond with an iron-based member. When the sulfuric acid solution of the above surfactant is applied and dried, the alkyl groups bonded to the adsorbed sulfate groups are arranged and arranged on the surface of the iron-based member. This alkyl group is generally water repellent,
Because it is firmly fixed on the iron-based member surface as described above,
Shows stable water repellency after drying.

[0014]

Supplementary Description of Means for Solving the Problems The method for adding a hydroxyl group to the iron-based member is not particularly limited, and any method may be used. For example, the following method is exemplified. 1. The iron-based member is sufficiently heated in air at a temperature of 200 ° C. or higher and does not require reheat treatment, that is, at a temperature lower than the transformation point, and then cooled in water. 2. Exposing the iron-based member to high-temperature steam. 3. The iron-based member is immersed in an oxidizing acid, for example, nitric acid for a short time, and then sufficiently washed with distilled water. By repeating the above method several times, a large amount of hydroxyl groups can be added on the surface of the iron-based member.

After a hydroxyl group is added to the iron-based member by the above-described method, a water-repellent coating film is coated. This water-repellent coating film is formed by a so-called sol-gel method. This sol-gel method is a method in which an organic or inorganic compound of a metal is made into a solution, a hydrolysis / polycondensation reaction of the compound proceeds in the solution, the sol is solidified as a gel, and an oxide solid is produced by heating the gel. It is. In the present invention, a metal alkoxide and a fluoroalkyl group-substituted metal alkoxide in which part of an alkoxyl group is substituted with a fluoroalkyl group are used as raw materials.

The metal alkoxide is represented by the following formula M (OR) _n , wherein M is a metal, R is alkyl, and n is the oxidation number of the metal M. Various materials can be used as the metal M, and the metal M is to be formed.
A material corresponding to the metal oxide to be used is used. Examples of metals include, but are not limited to, Li, Na, Cu, C
a, Sr, Ba, Zn, B, Al, Ga, Y, Si, G
e, Pb, P, Sb, V, Ta, W, La, Nd and the like. As the alkyl, methyl, ethyl, propyl, butyl and the like can be used. Therefore, as metal alkoxides, LiOCH ₃ , NaOCH ₃ , Cu (O
CH ₃ ) ₂ , Ca (OCH ₃ ) ₂ , Sr (OCH ₃ ) ₂ , Ba (OCH ₃ ) ₂ , Zn (OCH
_{3) 2, B (OCH 3} ) 3, Al (i-OC 3 H 7) 3, Ga (OC 2 H 5) 3, Y (OC 4 H 9)
_{3, Si (OC 2 H 5} ) 4, Ge (OC 2 H 5) 4, Pb (OC 4 H 9) 3, PO (OCH 3)
_{3, Sb (OC 2 H 5} ) 3, VO (OC 2 H 5) 3, Ta (OC 3 H 7) 5, W (OC
_{2 H 5) 6, La (} OC 3 H 7) 3, Nd ((OC 2 H 5) 3 can be exemplified.

The fluoroalkyl group-substituted metal alkoxide is a metal alkoxide in which a part of the alkoxyl group is substituted with a fluoroalkyl group. The presence of this fluoroalkyl group imparts water repellency to the resulting coating. The effect is higher as the amount of the fluoroalkyl group-substituted metal alkoxide is larger, but when the amount is larger, the strength of the coating decreases. Therefore, the amount is preferably 0.3 to 30 mol% of the amount of the metal alkoxide.

Water (for hydrolysis), alcohol (for preparing a homogeneous solution), acid or base (catalysis) is added to these metal alkoxides to prepare a solution. As the alcohol, for example, methanol, ethanol, propanol, butanol and the like are used. Examples of the acid used as the catalyst include hydrochloric acid, sulfuric acid, acetic acid, and hydrofluoric acid.
As the base, ammonia that can be removed by volatilization after the treatment is used. Further, a known additive such as acetylacetone may be added to the solution in the sol-gel method.

The thus prepared metal alkoxide solution is applied to the surface of the iron-based member. As the coating method, a known coating method such as dipping, spin coating, spraying or the like can be used. The thickness of the coating film is not particularly limited, and is usually
It is 50-1000 nm.

Next, the coating film is fired. The firing step may be performed by a general method in the sol-gel method,
It is carried out at 200 to 500 ° C. in the air or in a non-oxidizing atmosphere. When calcination is performed in the air, the calcination is preferably performed at 350 ° C. or lower to prevent decomposition of the fluoroalkyl group.

Mn, Zn, Ni, Cu, M
g, Co, Fe, Ti, Zr, V, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, B
The method of forming the coating film of the oxide of at least one metal selected from a, Sr, and Pb is not particularly limited, and any method can be used. Can be formed.

The above metals react with iron oxide generated from iron-based members to form stable double oxides. For example, Mn,
Zn, Ni, Cu, Mg, Co, and Fe form an oxide (MFe ₂ O ₄ ) having a spinel type (senlite) structure. T
i, Zr, and V form an oxide (MFeO ₃ ) having an ilmenite type (ilmenite type) structure. Sm, Eu, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu and Y are oxides (MFeO ₃ ) having a perovskite type (perovskite type) structure
Or a garnet-type (garnet-type) oxide (M ₃ F)
e ₅ O ₁₂ ). Further, Ba, Sr and Pb form an oxide (MFe ₁₂ O ₁₉ ) having a magnetoplumbite structure.

After forming the above-mentioned metal oxide coating layer, a water-repellent coating layer is formed thereon in the same manner as described above. The thickness of this metal oxide coating layer is preferably 50 to 10
0 nm.

In the above method, an oxide layer of a metal that forms a stable double oxide is formed as a lower layer of the water-repellent coating film. Good. That is, as a water-repellent coating film forming material,
A coating film is formed on an iron-based member by the sol-gel method as described above using an alkoxide of a metal that forms the stable double oxide in addition to the above materials.

[0025] The formula _{C n H 2n + 1 SO 4} - · Na + in surfactant represented are sulfuric acid aqueous solution of pH 3-5, 2 × 10
It is used after being dissolved at a concentration of ^-1 to 10 ^-3 M / L. Sulfuric acid p
If H is less than 3, the formation of sulfate (iron sulfate) becomes excessive,
Iron-based members suffer from excessive corrosion and are not preferred. PH 5
If it is higher, the formation of iron sulfate is not sufficient.

When the concentration of the surfactant is higher than 2 × 10 ^-1 / L, the surfactant forms micelles and agglomerates. Cannot be formed. If this concentration is lower than 10 ⁻³ M / L, sufficient water repellency cannot be obtained in the formed coating film.

This water-repellent coating film forms a bond not only with iron but also with other substances, for example, nickel and aluminum, as long as the sulfate group forms a salt. Water repellency derived from long-chain alkyl can be imparted.

[0028]

EXAMPLE 1 A martensitic stainless steel plate was heated to 300 ° C. in air, immersed in water and cooled. This treatment was repeated three times to add hydroxyl groups to the steel sheet surface. Next, 1 mol of water, 0.01 mol of hydrochloric acid, and 21 mol of ethanol were added to 1 mol of tetraethoxysilane, and the mixture was refluxed at 70 ° C. for 1 hour. Add 2/9 mole of fluoroalkylsilane to this solution
(CF ₃ (CF ₂ ) ₇ C ₂ H ₄ Si (OCH ₃ ) ₃ ) and 8 mol of methoxyethanol were added, and the mixture was stirred at room temperature for 30 minutes. 11 mol of water and 8 mol of methoxyethanol were added to the obtained mixture and left at room temperature for 24 hours. The solution thus obtained was applied to the surface of the steel sheet to form a wet coating film.
Next, this coating film was baked at 250 ° C. for 1 hour to form a coating film. Thus, Sample 1 was manufactured.

Example 2 A martensitic stainless steel plate was exposed to steam at 200 ° C. for 30 minutes.
This was repeated three times to add hydroxyl groups to the steel sheet surface. Next, a coating film was formed on the surface of the steel sheet in the same manner as described above to obtain Sample 2.

Example 3 A martensitic stainless steel plate was immersed in concentrated nitric acid of 1N or more for several seconds, and then sufficiently washed with distilled water. This treatment was repeated three times to add hydroxyl groups to the steel sheet surface. Next, a coating film was formed on the surface of the steel sheet in the same manner as described above to obtain Sample 3.

Samples 1 to 3 manufactured as described above
And an untreated sample produced by directly forming a coating film in the same manner as described above without adding a hydroxyl group to a martensitic stainless steel sheet. The contact angle, which is a measure of the water repellency, was measured. Further, these samples were placed in a furnace at 350 ° C., heated at an isothermal temperature, and the change in the contact angle was examined. The result is shown in FIG. For each sample, the initial contact angle was larger for samples 1-3 than for the untreated sample, and
There was a difference in the decrease in contact angle due to isothermal heating at 350 ° C.
It is clear that Samples 1 to 3 show a smaller decrease as compared to untreated samples, and that the heat resistance is significantly improved by the method of the present invention.

Example 4 1 mol of iron tetraisopropoxide, 5 mol of methoxyethanol and 0.2 mol of 2,4-pentanedione were mixed and the mixture was refluxed at 80 ° C. for 1 hour. Next, 1 mol of water and 5 mol of methoxyethanol were added to this solution, and the mixture was left at 25 ° C. for 24 hours. The iron alkoxide solution thus obtained was applied to a martensitic stainless steel plate to form an iron oxide coating film on the surface. Next, a water-repellent coating film was formed on the iron oxide coating film using tetraethoxysilane and fluoroalkylsilane in the same manner as in Example 1. Thus, Sample 4 was obtained.

Example 5 A martensitic stainless steel having a water-repellent coating on a MnO coating in the same manner as in Example 4 except that manganese diisopropoxide was used instead of iron tetraisopropoxide. A steel sheet sample 5 was obtained.

Example 6 1 mol of tetraethoxysilane was added with 1 mol of water, 0.01 mol of hydrochloric acid, and 21 mol of ethanol, and refluxed at 70 ° C. for 1 hour to prepare a solution of tetraethoxysilane. Also, 1 mol of manganese diisopropoxide, 5 mol of methoxyethanol and 0.2 mol of 2,4-pentanedione were mixed and refluxed at 80 ° C. for 1 hour to produce a solution of diisopropoxymanganese. These solutions were mixed and refluxed at 80 ° C. for 1 hour. Then 2/9 mole of fluoroalkylsilane (CF ₃ (CF ₂ ) ₇ C ₂ H ₄ Si (OCH ₃ ) ₃ ) and 8
After adding mol of methoxyethanol and stirring at room temperature for 30 minutes, 11 mol of water and 8 mol of methoxyethanol were further added and left at room temperature for 24 hours. The solution thus obtained was applied to the surface of the steel sheet to form a wet coating film. Next, this coating film was baked at 250 ° C. for 1 hour to form a coating film. Thus, Sample 6 was manufactured.

Samples 4 to 6 manufactured as described above
And an untreated sample manufactured by forming only a water-repellent coating film on a martensitic stainless steel sheet. The contact angle, which is a measure of the water repellency, was measured. Further, these samples were placed in a furnace at 350 ° C., heated at an isothermal temperature, and the change in the contact angle was examined. The result is shown in FIG. For each sample, the initial contact angle was larger in samples 4 to 6 than in the untreated sample, and the difference in the contact angle was observed due to the isothermal heating at 350 ° C. Samples 4 to 6 were untreated. It is clear that the decrease is smaller than that of the method of the present invention, and that the heat resistance is significantly improved by the method of the present invention.

[0036] Example 7 pH 4.5 for C ₁₁ H ₂₃ SO ₄ in aqueous sulfuric acid ^- dissolving · Na ^+, was prepared the 3.2 × 10 ^-2 mol / l solution.
The SUS 340 substrate whose surface was degreased was immersed in this solution for 1 minute, pulled up by applying ultrasonic waves, washed with distilled water, and dried at room temperature. The contact angle of the obtained sample was measured, and the result is shown in FIG. This sample showed a contact angle of about 100 ° in a dry state, and showed almost the same level of contact angle even when immersed in water and measured. In addition, this sample was rubbed with a dry cloth at a surface pressure of 500 g / cm ² ,
The decrease in the contact angle was investigated. The result is shown in FIG.
A contact angle of about 90 ° is maintained at about 2000 times of friction, indicating that the durability is high.

[0037]

According to the method of the present invention, when a water-repellent coating film is formed after a hydroxyl group is added to the surface of an iron-based member or pretreatment for forming an iron oxide coating film is performed, water repellency and durability are improved. improves. The water repellency and durability of the coating film obtained by adding a specific metal in the matrix of the water repellent coating layer are also improved. Furthermore, by coating with a long-chain alkyl sulfate, water repellency and durability are improved.

[Brief description of the drawings]

FIG. 1 shows samples 1 to 3 manufactured in Examples 1 to 3.
4 is a graph showing the water repellency and durability.

FIG. 2 shows samples 4 to 6 manufactured in Examples 4 to 6.
4 is a graph showing the water repellency and durability.

FIG. 3 is a graph showing water repellency of a sample manufactured in Example 7.

FIG. 4 is a graph showing the durability of a sample manufactured in Example 7.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shoji Yokoishi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 18/00- 18/54

Claims (4)

(57) [Claims] 1. A step of adding a hydroxyl group to the surface of an iron-based member, wherein a mixed solution of a metal alkoxide and a fluoroalkyl group-substituted metal alkoxide in which a part of an alkoxyl group is substituted with a fluoroalkyl group is mixed with the hydroxyl group. A method of forming a water-repellent coating film on an iron-based member, comprising: a step of forming a coating film by applying the film on a surface of an iron-based member to which iron is added, and a step of forming a coating film by baking the coating film. 2. Mn, Zn, Ni, C on the surface of the iron-based member
u, Mg, Co, Fe, Ti, Zr, V, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu,
Forming a coating film of an oxide of at least one metal selected from Y, Ba, Sr, and Pb; a fluoroalkyl group-substituted metal in which a part of a metal alkoxide and an alkoxyl group is substituted by a fluoroalkyl group A step of applying a mixed solution with an alkoxide on the coating film of the metal oxide to form a coating film, and baking the coating film,
A method for forming a water-repellent coating film on an iron-based member, comprising a step of forming a coating film. 3. A metal alkoxide, a fluoroalkyl-substituted metal alkoxide in which part of an alkoxyl group is substituted by a fluoroalkyl group, and Mn, Zn, Ni,
Cu, Mg, Co, Fe, V, Sm, Eu, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu, Ba, S
a step of applying a mixed solution with an alkoxide of at least one metal selected from r and Pb to the surface of the iron-based member to form a coating film, and baking the coating film to form a coating film Forming a water-repellent coating film on an iron-based member. Wherein the following formula in an aqueous solution of sulfuric acid _{pH3~5 C n H 2n + 1 SO} 4 - · Na + ( in the above formula, n a is 7-15) surfactant 2 × 10 represented by A method for forming a water-repellent coating film on an iron-based member, comprising applying a solution in which ^-1 to 10 ^-3 M / L is dissolved to an iron-based member and drying the solution.