JP7561345B2 - Metal corrosion inhibitor and method for producing same - Google Patents

Description

The present invention relates to a metal corrosion inhibitor that has excellent stability and metal corrosion inhibition effect, and a method for producing the same.

The most commonly used rust inhibitors for iron-based metals such as steel, and non-ferrous metals such as aluminum and titanium, especially aluminum and its alloys, are phosphorus-based rust inhibitors such as phosphates and phosphoric acid esters, or organic rust inhibitors such as organic acid amine salts and heterocyclic compounds.

However, even if these rust inhibitors are mixed into aqueous lubricants for processing such as cutting, milling, drilling, and polishing metals, satisfactory rust prevention effects may not be obtained. The reasons for this are thought to be as follows. That is, aqueous lubricants for processing such as those described above are usually diluted with water about 10 to 30 times before use, so the concentration is insufficient and the rust prevention effect is not fully exerted. In addition, since the diluted solution is generally alkaline with a pH of 8 or more, the oil-based agent components contained in the aqueous lubricant act as corrosive components, and it is thought that this creates an environment that is particularly prone to corrosion in the case of aluminum and its alloys. In addition, phosphorus-based rust inhibitors have the major problem of promoting the decay and deterioration of the aqueous lubricants mentioned above due to bacteria and mold.

On the other hand, water-soluble alkali silicates, such as sodium silicate, have long been known as rust inhibitors for aluminum alloys and the like. They are very inexpensive and easy to obtain, and when mixed in the right amount into an aqueous lubricant, they provide excellent rust prevention effects. Moreover, because they do not contain phosphorus, they do not promote decay or deterioration of the aqueous lubricant. However, alkali silicates have a serious practical drawback in that they quickly gel in aqueous lubricants, and improvements are needed in terms of stability over time.

On the other hand, Patent Document 1 describes that when a specific silane-based compound is blended into an aqueous lubricant as a metal corrosion inhibitor, corrosion of metal materials such as aluminum alloys can be prevented. Patent Document 2 describes that when an organosilicon compound obtained by hydrolyzing a hydrolyzable silane-based compound or a partial hydrolyzate thereof having an organic group containing a nitrogen atom in the molecule with a hydrolyzable silane-based compound or a partial hydrolyzate thereof is blended into an aqueous lubricant as a metal corrosion inhibitor, it is effective in preventing corrosion of aluminum alloys and the like.

The present inventors have developed a rust inhibitor composition containing an alkali silicate and a specific silane coupling agent (Patent Documents 3 and 4).

Japanese Patent Application Publication No. 9-194872 JP 2003-268396 A JP 2006-299356 A JP 2006-299357 A

As described above, various corrosion inhibitors for aluminum, aluminum alloys, etc. have been developed, but the present inventors have found that some of the conventional metal corrosion inhibitors are insufficient in terms of stability and metal corrosion inhibition effect.
Therefore, an object of the present invention is to provide a metal corrosion inhibitor excellent in stability and metal corrosion inhibitory effect, and a method for producing the same.

The present inventors have conducted extensive research to solve the above problems. As a result, they have found that a co-condensate of a specific silane coupling agent can enhance the stability and metal corrosion inhibitory effect of a metal corrosion inhibitor, particularly one containing an alkali metal silicate, and have completed the present invention.
The present invention will now be described.

［式中、
Ｒ¹～Ｒ⁴は、独立して、Ｃ_1-6二価炭化水素基を示し、
Ｒ⁵とＲ⁶は、独立して、ＨまたはＣ_1-6一価炭化水素基を示し、
ｍとｎは、独立して、０以上、３以下の整数を示し、
ｍおよび／またはｎが２または３である場合、複数のＲ²および／またはＲ⁴は、互いに同一であっても異なっていてもよく、
前記式（Ｉ）において、Ｒ²は末端炭素と結合して環状炭化水素基または環状エーテル基を形成していてもよい。］
［３］ 更に塩基を含む前記［１］または［２］に記載の金属腐食抑制剤。
［４］ 前記塩基がアルカリ金属ケイ酸塩である前記［３］に記載の金属腐食抑制剤。
［５］ 更に溶媒を含み、ｐＨが８以上、１３以下である前記［１］～［４］のいずれかに記載の金属腐食抑制剤。
［６］ 前記金属がアルミニウムまたはアルミニウム合金である前記［１］～［５］のいずれかに記載の金属腐食抑制剤。
［７］ 塩基の存在下、エポキシ基を有するシランカップリング剤とアミノ基を有するシランカップリング剤を共縮合させる工程を含むことを特徴とする金属腐食抑制剤の製造方法。
［８］ 前記エポキシ基を有するシランカップリング剤が下記式（ＩＩＩ）で表されるものであり、前記アミノ基を有するシランカップリング剤が下記式（ＩＶ）で表されるものである前記［７］に記載の金属腐食抑制剤の製造方法。

［式中、
Ｒ¹～Ｒ⁴は、独立して、Ｃ_1-6二価炭化水素基を示し、
Ｒ⁵とＲ⁶は、独立して、ＨまたはＣ_1-6一価炭化水素基を示し、
Ｒ⁷、Ｒ⁸、Ｒ¹⁰およびＲ¹¹は、独立して、Ｃ_1-6アルコキシ基を示し、
Ｒ⁹とＲ¹²は、独立して、Ｈ、Ｃ_1-6アルキル基、またはＣ_1-6アルコキシ基を示し、
ｍとｎは、独立して、０以上、３以下の整数を示し、
ｍおよび／またはｎが２または３である場合、複数のＲ²および／またはＲ⁴は、互いに同一であっても異なっていてもよく、
前記式（ＩＩＩ）において、Ｒ²は末端炭素と結合して環状炭化水素基または環状エーテル基を形成していてもよい。］ [1] A metal corrosion inhibitor comprising a co-condensate containing a structural unit derived from a silane coupling agent having an epoxy group and a structural unit derived from a silane coupling agent having an amino group.
[2] The metal corrosion inhibitor according to [1], wherein the structural unit derived from the silane coupling agent having an epoxy group is represented by the following formula (I), and the structural unit derived from the silane coupling agent having an amino group is represented by the following formula (II).

[Wherein,
R ¹ to R ⁴ each independently represent a C _1-6 divalent hydrocarbon group;
^R5 and ^R6 are independently H or a _C1-6 monovalent hydrocarbon group;
m and n each independently represent an integer of 0 to 3,
When m and/or n are 2 or 3, multiple ^R2s and/or ^R4s may be the same or different from each other;
In the formula (I), ^R2 may be bonded to the terminal carbon to form a cyclic hydrocarbon group or a cyclic ether group.
[3] The metal corrosion inhibitor according to the above [1] or [2], further comprising a base.
[4] The metal corrosion inhibitor according to [3], wherein the base is an alkali metal silicate.
[5] The metal corrosion inhibitor according to any one of the above [1] to [4], further comprising a solvent and having a pH of 8 or more and 13 or less.
[6] The metal corrosion inhibitor according to any one of [1] to [5], wherein the metal is aluminum or an aluminum alloy.
[7] A method for producing a metal corrosion inhibitor, comprising the step of co-condensing a silane coupling agent having an epoxy group and a silane coupling agent having an amino group in the presence of a base.
[8] The silane coupling agent having an epoxy group is represented by the following formula (III), and the silane coupling agent having an amino group is represented by the following formula (IV). A method for producing a metal corrosion inhibitor according to the above [7].

[Wherein,
R ¹ to R ⁴ each independently represent a C _1-6 divalent hydrocarbon group;
^R5 and ^R6 are independently H or a _C1-6 monovalent hydrocarbon group;
R ⁷ , R ⁸ , R ¹⁰ and R ¹¹ each independently represent a C _1-6 alkoxy group;
R ⁹ and R ¹² independently represent H, a C _1-6 alkyl group, or a C _1-6 alkoxy group;
m and n each independently represent an integer of 0 to 3,
When m and/or n are 2 or 3, multiple ^R2s and/or ^R4s may be the same or different from each other;
In the formula (III), ^R2 may be bonded to the terminal carbon to form a cyclic hydrocarbon group or a cyclic ether group.

The "C _1-6 divalent hydrocarbon group" is a divalent hydrocarbon group having 1 to 6 carbon atoms, and examples thereof include a C _1-6 alkanediyl group, a C _2-6 alkenediyl group, a C _2-6 alkynediyl group, and phenyldiyl (phenylene).

The term "C _1-6 alkanediyl group" refers to a linear or branched divalent saturated aliphatic hydrocarbon group having from 1 to 6 carbon atoms. Examples include methanediyl, ethanediyl, methylmethanediyl, n-propanediyl, methylethanediyl, n-butanediyl, methylpropanediyl, dimethylethanediyl, n-pentanediyl, n-hexanediyl, etc. A C _1-4 alkanediyl group is preferred, and a C _1-3 alkanediyl group is more preferred.

The term " _C2-6 alkenediyl group" refers to a straight-chain or branched-chain divalent unsaturated aliphatic hydrocarbon group having one or more carbon-carbon double bonds and having 2 to 6 carbon atoms. Examples include ethenediyl, n-propenediyl, methylethenediyl, n-butenediyl, methylpropenediyl, dimethylethenediyl, n-pentenediyl, n-hexenediyl, etc. A _C1-4 alkenediyl group is preferred, and a _C1-3 alkenediyl group is more preferred.

The term " _C2-6 alkynediyl group" refers to a straight-chain or branched-chain divalent unsaturated aliphatic hydrocarbon group having one or more carbon-carbon triple bonds and having 2 to 6 carbon atoms. Examples include ethynediyl, n-propynediyl, n-butynediyl, methylpropynediyl, n-pentynediyl, n-hexynediyl, etc. A _C1-4 alkynediyl group is preferred, and a _C1-3 alkynediyl group is more preferred.

The "C _1-6 monovalent hydrocarbon group" is a monovalent hydrocarbon group having 1 to 6 carbon atoms, and examples thereof include a C _1-6 alkyl group, a C _2-6 alkenyl group, a C _2-6 alkynyl group, and a phenyl group.

The term "C _1-6 alkyl group" refers to a linear or branched monovalent saturated aliphatic hydrocarbon group having from 1 to 6 carbon atoms. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, n-hexyl, etc. A C _1-4 alkyl group is preferred, and a C _1-3 alkyl group is more preferred.

The term " _C2-6 alkenyl group" refers to a straight-chain or branched-chain monovalent unsaturated aliphatic hydrocarbon group having 2 to 6 carbon atoms and one or more carbon-carbon double bonds. Examples include ethenyl (vinyl), 1-propenyl, 2-propenyl (allyl), isopropenyl, 2-butenyl, 3-butenyl, isobutenyl, pentenyl, and hexenyl. A _C1-4 alkenyl group is preferred, and a _C1-3 alkenyl group is more preferred.

The term " _C2-6 alkynyl group" refers to a straight-chain or branched-chain monovalent unsaturated aliphatic hydrocarbon group having 2 to 6 carbon atoms and one or more carbon-carbon triple bonds. Examples include ethynyl, 1-propynyl, 2-propynyl, 2-butynyl, 3-butynyl, pentynyl, and hexynyl. A _C1-4 alkynyl group is preferred, and a _C1-3 alkynyl group is more preferred.

The term "C _1-6 alkoxy group" refers to a linear or branched saturated aliphatic hydrocarbon oxy group having from 1 to 6 carbon atoms. Examples include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, t-butoxy, n-pentoxy, n-hexoxy, etc., preferably a C _1-4 alkoxy group, more preferably a C _1-2 alkoxy group.

In the formula (I) and the formula (III), " ^R2 may be bonded to the terminal carbon to form a cyclic hydrocarbon group or a cyclic ether group" means that the carbon atom contained in ^R2 , or when there are multiple ^R2s , the carbon atom contained in one ^R2 may be covalently bonded to the terminal carbon opposite to Si in the group containing ^R2 to form a cyclic hydrocarbon group or a cyclic ether group. Examples of the cyclic hydrocarbon group include cyclobutyl, cyclopentyl, and cyclohexyl, and examples of the cyclic ether group include tetrahydrofuranyl and tetrahydropyranyl. For example, the structural unit represented by the formula (I) includes the following structural units.

The metal corrosion inhibitor of the present invention is inhibited from insolubilizing, precipitating, and settling in insoluble components, and does not contain any components that may cause spoilage, so it can be said to have both metal corrosion inhibitory action and storage stability. In addition, metal corrosion inhibitors are sometimes mixed with processing oils during metal processing, which can cause insoluble components to precipitate, whereas the metal corrosion inhibitor of the present invention inhibits the precipitation of insoluble components even when mixed with processing oils. Furthermore, by using the metal corrosion inhibitor of the present invention as a rust-preventive lubricant in processing such as cutting, milling, drilling, and polishing of metals, excellent lubricity can be enjoyed and corrosion of metal materials after processing can be effectively prevented. Thus, the metal corrosion inhibitor of the present invention is extremely useful industrially because of its excellent stability and metal corrosion inhibitory effect.

First, a method for producing a metal corrosion inhibitor according to the present invention will be described. The method for producing a metal corrosion inhibitor according to the present invention includes a step of co-condensing a silane coupling agent having an epoxy group and a silane coupling agent having an amino group in the presence of a base.

The silane coupling agent used in the present invention has an epoxy group or an amino group attached to a silicon atom via a linker group, and also has two or more C _1-6 alkoxy groups.

The linker group has the effect of facilitating the synthesis of the silane coupling agent and increasing the positional freedom of the epoxy group and the amino group. The linker group is not particularly limited as long as it exhibits such an effect, and examples thereof include a C _1-6 alkanediyl group, an ether group (-O-), a thioether group (-S-), a carbonyl group (-C(=O)-), a thionyl group (-C(=S)-), an ester group (-O-C(=O)- or -C(=O)-O-), an amide group (-NH-C(=O)- or -C(=O)-NH-), a urea group (-NH-C(=O)-NH-), a thiourea group (-NH-C(=S)-NH-), a polyalkylene glycol group, and a polyvinyl alcohol group; and groups in which 2 or more and 5 or less of these groups are linked together. Examples of the linked group include a C _1-6 alkanediyl-O—C _1-6 alkanediyl group and a —[C _1-6 alkanediyl-NH—] _m —C _1-6 alkanediyl group (m is an integer of 0 or more and 3 or less).

More specifically, the above-mentioned epoxy group-containing silane coupling agent (III) and amino group-containing silane coupling agent (IV) can be used. During co-condensation, the epoxy group of the epoxy group-containing silane coupling agent (III) is cleaved to generate a 1,2-diol structure. The alkoxy groups R ⁷ , R ⁸ , R ¹⁰ and R ¹¹ in the epoxy group-containing silane coupling agent (III) and the amino group-containing silane coupling agent (IV) are dehydrated and condensed with each other to form a siloxane bond. When R ⁹ and/or R ¹² in the epoxy group-containing silane coupling agent (III) and the amino group-containing silane coupling agent (IV) are alkoxy groups, the co-condensate is extended not only in one dimension but also in two dimensions.

The ratio of the epoxy group-containing silane coupling agent (III) to the amino group-containing silane coupling agent (IV) may be adjusted as appropriate within a range in which good metal corrosion inhibition is exhibited. For example, the molar ratio of the epoxy group-containing silane coupling agent (III) to the amino group-containing silane coupling agent (IV) may be set to 1 or more and 20 or less. If the ratio is 1 or more, the stability of the metal corrosion inhibitor according to the present invention when mixed with processing oil can be more reliably maintained, and if the ratio is 20 or less, the rust prevention performance can be more reliably exhibited. The molar ratio is preferably 2 or more, more preferably 5 or more, and preferably 15 or less.

Examples of epoxy group-containing silane coupling agents (III) include γ-glycidoxymethyltrimethoxysilane, γ-glycidoxymethyltriethoxysilane, γ-glycidoxymethylmethyldimethoxysilane, γ-glycidoxymethylmethyldiethoxysilane, γ-glycidoxymethylethyldimethoxysilane, γ-glycidoxymethylethyldiethoxysilane, γ-glycidoxymethylpropyldimethoxysilane, γ-glycidoxymethylpropyldiethoxysilane, γ-glycidoxymethylbutyldimethoxysilane, γ-glycidoxymethylbutyldiethoxysilane , γ-glycidoxyethyl trimethoxysilane, γ-glycidoxyethyl triethoxysilane, γ-glycidoxyethyl methyl dimethoxysilane, γ-glycidoxyethyl methyl diethoxysilane, γ-glycidoxyethyl ethyl dimethoxysilane, γ-glycidoxyethyl ethyl diethoxysilane, γ-glycidoxyethyl propyl dimethoxysilane, γ-glycidoxyethyl propyl diethoxysilane, γ-glycidoxyethyl butyl dimethoxysilane, γ-glycidoxyethyl butyl diethoxysilane, γ-glycidoxypropyl trimethoxysilane, γ-glycidoxy glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylethyldimethoxysilane, γ-glycidoxypropylethyldiethoxysilane, γ-glycidoxypropylpropyldimethoxysilane, γ-glycidoxypropylpropyldiethoxysilane, γ-glycidoxypropylbutyldimethoxysilane, γ-glycidoxypropylbutyldiethoxysilane, γ-glycidoxybutyltrimethoxysilane, γ-glycidoxybutyltriethoxysilane, γ-glycidoxypropyl Examples of usable compounds include glycidoxybutylmethyldimethoxysilane, γ-glycidoxybutylmethyldiethoxysilane, γ-glycidoxybutylethyldimethoxysilane, γ-glycidoxybutylethyldiethoxysilane, γ-glycidoxybutylpropyldimethoxysilane, γ-glycidoxybutylpropyldiethoxysilane, γ-glycidoxybutylbutyldimethoxysilane, γ-glycidoxybutylbutyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

As the amino group-containing silane coupling agent (IV), for example, N-2-aminoethyl-3-aminopropyltrimethoxysilane, N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, etc. can be used.

In the present invention, a silane coupling agent other than the epoxy group-containing silane coupling agent (III) and the amino group-containing silane coupling agent (IV) may be used. Examples of such silane coupling agents include methyltrimethoxysilane, vinyltrimethoxysilane, N-2-(N-vinylbenzylaminoethyl)-3-aminopropylmethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, phenyltriethoxysilane, tetramethylsilicate, and tetraethylsilicate.

When a silane coupling agent other than the epoxy group-containing silane coupling agent (III) and the amino group-containing silane coupling agent (IV) is used, the ratio of the epoxy group-containing silane coupling agent (III) and the amino group-containing silane coupling agent (IV) to the total silane coupling agents is preferably 60% by mass or more or 70% by mass or more, more preferably 80% by mass or more or 90% by mass or more, and even more preferably 95% by mass or more or 98% by mass or more. The above ratio is 100% by mass, that is, substantially only the epoxy group-containing silane coupling agent (III) and the amino group-containing silane coupling agent (IV) are used as the silane coupling agent, and other coupling agents may not be used.

In the present invention, a base is used as a catalyst for promoting the co-condensation reaction. Examples of the base include alkali metal silicates such as lithium silicate, sodium silicate, and potassium silicate; alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; Group II metal hydroxides such as magnesium hydroxide and calcium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; and alkali metal hydrogen carbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate. The base is preferably an alkali metal silicate, since it has a metal corrosion inhibitory effect by itself. The alkali metal silicate is represented by the formula M ₂ O·pSiO ₂ (M represents an alkali metal, and p represents a positive number greater than 0 and less than 10).

The solvent for the co-condensation reaction in the present invention is not particularly limited as long as it can dissolve the base and the silane coupling agent appropriately and does not inhibit the co-condensation reaction, but since the co-condensation reaction of the silane coupling agent involves a hydrolysis reaction, it is preferable to use an aqueous solvent. The aqueous solvent refers to water and a mixed solvent of water and a water-miscible organic solvent. The water-miscible organic solvent refers to an organic solvent that can be mixed with water without restrictions, and examples of such organic solvents include C _1-3 alcohol solvents such as methanol, ethanol, and isopropanol. In addition, the water-miscible organic solvent is useful for improving the solubility of a silane coupling agent, which has a relatively low solubility in water, in a solvent. The proportion of water in the mixed solvent is preferably 50% by mass or more or 60% by mass or more, more preferably 70% by mass or more or 80% by mass or more, and even more preferably 90% by mass or more. The upper limit of the proportion is not particularly limited, and may be 100% by mass, that is, the solvent may be only water, but the proportion may be 98% by mass or less or 95% by mass or less.

The conditions for the co-condensation reaction may be appropriately adjusted within a range in which at least the epoxy group-containing silane coupling agent (III) and the amino group-containing silane coupling agent (IV) are co-condensed well. For example, the ratio of the total amount of silane coupling agents to the amount of solvent may be 5% by mass or more and 30% by mass or less, and the ratio of base to the amount of solvent may be 10% by mass or more and 40% by mass or less.

Since the co-condensation reaction according to the present invention involves a hydrolysis reaction of the silane coupling agent, it is preferable to heat the reaction solution. The reaction temperature can be, for example, 50°C or higher and 120°C or lower, and the reaction can be carried out under heated reflux. The reaction time can be, for example, 30 minutes or longer and 10 hours or shorter.

The reaction liquid after the reaction may be used as a metal corrosion inhibitor as it is, or may be diluted by adding a solvent. An aqueous solvent may be used as the dilution solvent, and water is preferred. The dilution degree may be appropriately adjusted within a range in which the metal corrosion inhibitory effect is effectively exerted, but it is preferable to adjust the ratio of the co-condensate to the whole to be 0.01% by mass or more and 10% by mass or less, and/or the ratio of SiO ₂ contained in the alkali metal silicate, which is a base having a metal corrosion inhibitory effect, to the whole to be 0.01% by mass or more and 10% by mass or less.

The metal corrosion inhibitor according to the present invention contains a co-condensate containing a structural unit derived from a silane coupling agent having an epoxy group and a structural unit derived from a silane coupling agent having an amino group. From the above reaction conditions, it is considered that the structural units derived from the silane coupling agent having an epoxy group and the structural units derived from the silane coupling agent having an amino group in the co-condensate are arranged randomly, and the ratio of the structural units derived from the silane coupling agent having an epoxy group and the structural units derived from the silane coupling agent having an amino group in the co-condensate is considered to correspond to the ratio of the structural units derived from the silane coupling agent having an epoxy group and the silane coupling agent having an amino group used. In addition, it is possible that some of the silane coupling agent having an epoxy group and the silane coupling agent having an amino group remain without being co-condensed.

Conventional metal corrosion inhibitors have a problem in that, for example, alkali metal silicates are prone to gelation, and it has been found that such gelation can be inhibited by using condensates of silane coupling agents. In response to this, the present inventors have experimentally found that some silane coupling agents are unable to sufficiently inhibit such gelation, insolubility, and precipitation in metal corrosion inhibitors, resulting in insufficient stability, while other silane coupling agents do not have sufficient metal corrosion inhibitory activity. They have also found that a co-condensate containing a structural unit derived from a silane coupling agent having an epoxy group and a structural unit derived from a silane coupling agent having an amino group can further improve the stability and metal corrosion inhibitory activity of metal corrosion inhibitors.

The constituent unit derived from the silane coupling agent having an epoxy group that constitutes the co-condensation product of the present invention is represented by the above formula (I), and the constituent unit derived from the silane coupling agent having an amino group is represented by the above formula (II).

The metal corrosion inhibitor of the present invention may contain a base. In general, the higher the pH of a metal corrosion inhibitor containing a base, the higher the stability and corrosion prevention effect. If the base contains an alkali metal silicate that itself exhibits a metal corrosion inhibitory effect, the metal corrosion inhibitory effect is further enhanced. On the other hand, if the pH is excessively high, non-ferrous metals such as aluminum and aluminum alloys are more likely to corrode. Therefore, it is preferable to adjust the pH of the metal corrosion inhibitor of the present invention to 8 or more and 13 or less. In particular, alkali metal silicate can be made into a stable aqueous solution at a pH of 11 or more, but gels and forms insoluble matter at a pH of less than 11. In contrast, in the present invention, the above co-condensate suppresses gelation and the formation of insoluble matter even at a pH of less than 11, and maintains stability.

The metal corrosion inhibitor of the present invention is excellent in stability and exhibits excellent corrosion inhibition action against metals. Examples of target metals include iron-based metals such as steel, non-ferrous metals such as aluminum and titanium, and alloys thereof, and is particularly effective against aluminum and aluminum alloys. The metal corrosion inhibitor of the present invention is also useful as a lubricant and anticorrosive agent when processing metals such as cutting, milling, drilling, and polishing. In particular, when the metal corrosion inhibitor of the present invention is used for aluminum and its alloys, which are susceptible to corrosion by lubricating oil-based agent components in an alkaline environment, its characteristics are more effectively exhibited, and an excellent lubricant and corrosion inhibition action is exhibited, which is preferable.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is of course possible to carry out the invention with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

Example 1: Preparation of metal corrosion inhibitor 350 g of deionized water and 50 g of γ-glycidoxypropyltrimethoxysilane were stirred at room temperature (25° C.) to obtain a transparent solution. Next, 95 g of approximately 50% by mass potassium silicate aqueous solution and 5 g of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane were added, and the mixture was stirred and mixed at 90° C. for 2 hours to obtain a transparent solution that is a metal corrosion inhibitor.

Comparative Example 1: Preparation of metal corrosion inhibitor 150 g of an aqueous potassium silicate solution was added to 350 g of deionized water and mixed with stirring at room temperature for 1 hour to obtain a transparent solution that was a metal corrosion inhibitor.

Comparative Example 2: Preparation of a metal corrosion inhibitor 350 g of deionized water and 55 g of γ-glycidoxypropyltrimethoxysilane were stirred at room temperature to obtain a transparent solution. Next, 95 g of an aqueous potassium silicate solution was added, and the mixture was stirred and mixed at 90° C. for 2 hours to obtain a transparent solution of a metal corrosion inhibitor.

Comparative Example 3: Preparation of metal corrosion inhibitor 350 g of deionized water and 55 g of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane were stirred at room temperature to obtain a transparent solution. Next, 95 g of potassium silicate aqueous solution was added, and the mixture was stirred and mixed at 90° C. for 2 hours to obtain a transparent solution of the metal corrosion inhibitor.

Test Example 1: Evaluation of stability when added to processing oil In a transparent 100 mL glass container, the metal corrosion inhibitor (5.0 g) of Example 1 or Comparative Examples 1 to 3 and aluminum processing oil (95.0 g) not containing a metal corrosion inhibitor were placed and thoroughly stirred to prepare a test liquid. The appearance of the test liquid immediately after preparation and after being left to stand at room temperature for 2 weeks was visually evaluated according to the following criteria. The results are shown in Table 1.
◯: No turbidity or precipitation ×: Turbidity or precipitation

As shown in Table 1, the metal corrosion inhibitors of Comparative Examples 1 and 3 remained opaque immediately after being mixed with the aluminum processing oil.
On the other hand, the metal corrosion inhibitors of Example 1 and Comparative Example 2 remained transparent and stable even after being allowed to stand for 2 weeks after being mixed with the aluminum processing oil.

Test Example 2: Corrosion Inhibition Test In a 100 mL glass container, the metal corrosion inhibitors (0.03 g) of Example 1 and Comparative Example 2, water-soluble aluminum processing oil (0.47 g) not containing a metal corrosion inhibitor, and tap water (49.5 g) were added and thoroughly stirred to prepare a test solution. The pH of the test solution was measured and found to be 10.2 in both cases. Note that, for the metal corrosion inhibitors of Comparative Examples 1 and 3 in Test Example 1, which showed turbidity and precipitation immediately after the end of stirring, this test was not performed.
An aluminum test piece was prepared by wet polishing an aluminum plate (JIS H 4000 A1050P) of 60×40×1.0 mm with #320 water-resistant emery paper and then washing the plate with deionized water and acetone in that order.
After wetting the entire surface of an aluminum test piece with each test liquid once, about half of the piece was immersed in each test liquid and left to stand at room temperature for one week. The test piece was then removed from the test liquid, washed with water and acetone, and dried, after which the degree of discoloration of the test piece was visually evaluated according to the following criteria.
◎: No discoloration 〇: Slight discoloration △: Slight discoloration ×: Clear discoloration

As the results shown in Table 2 show, in the aluminum test piece treated with the composition (Comparative Example 2) prepared by heating an aqueous solution containing γ-glycidoxypropyltrimethoxysilane and potassium silicate, no discoloration was observed in the immersed area, but discoloration was observed in the non-immersed area. In contrast, in the aluminum test piece treated with the composition (Example 1) prepared by heating an aqueous solution containing γ-glycidoxypropyltrimethoxysilane, potassium silicate, and N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, no discoloration was observed in the immersed area, non-immersed area, or the interface between them. Thus, the metal corrosion inhibitor according to the present invention clearly had an excellent corrosion inhibition effect on aluminum.

Claims (8)

The composition contains a co-condensate including a structural unit derived from a silane coupling agent having an epoxy group and a structural unit derived from a silane coupling agent having an amino group , and an alkali metal silicate ,
A metal corrosion inhibitor characterized in that the structural unit derived from a silane coupling agent having an epoxy group is represented by the following formula (I), and the structural unit derived from a silane coupling agent having an amino group is represented by the following formula (II) .

[Wherein,
R ¹ to R ⁴ each independently represent a C _1-6 divalent hydrocarbon group;
R5 and R6 ^are independently H or a C1-6 _monovalent hydrocarbon group ^;
m and n each independently represent an integer of 0 to 3,
When m and/or n are 2 or 3, multiple R2s ^and /or R4s ^may be the same or different from each other;
In the formula (I), R2 ^may be bonded to the terminal carbon to form a cyclic hydrocarbon group or a cyclic ether group. The metal corrosion inhibitor according to claim 1, wherein the molar ratio of the structural unit derived from the silane coupling agent having an epoxy group represented by formula (I) to the structural unit derived from the silane coupling agent having an amino group represented by formula (II) is 1 or more and 20 or less. The metal corrosion inhibitor according to claim 1 or 2, wherein the proportion of the co-condensate is 0.01 mass % or more and 10 mass % or less. SiO contained in the alkali metal silicate ₂ The metal corrosion inhibitor according to any one of claims 1 to 3, wherein the ratio of is 0.01 mass % or more and 10 mass % or less. The metal corrosion inhibitor according to any one of claims 1 to 4, further comprising a solvent and having a pH of 8 or more and 13 or less. The metal corrosion inhibitor according to any one of claims 1 to 5, wherein the metal is aluminum or an aluminum alloy. The method includes a step of co-condensing a silane coupling agent having an epoxy group and a silane coupling agent having an amino group in the presence of an alkali metal silicate ,
The method for producing a metal corrosion inhibitor, characterized in that the silane coupling agent having an epoxy group is represented by the following formula (III), and the silane coupling agent having an amino group is represented by the following formula (IV) .

[Wherein,
R ¹ to R ⁴ each independently represent a C _1-6 divalent hydrocarbon group;
R5 and R6 ^are independently H or a C1-6 _monovalent hydrocarbon group ^;
R ⁷ , R ⁸ , R ¹⁰ and R ¹¹ each independently represent a C _1-6 alkoxy group;
R ⁹ and R ¹² independently represent H, a C _1-6 alkyl group, or a C _1-6 alkoxy group;
m and n each independently represent an integer of 0 to 3,
When m and/or n are 2 or 3, multiple R2s ^and /or R4s ^may be the same or different from each other;
In the formula (III), R2 ^may be bonded to the terminal carbon to form a cyclic hydrocarbon group or a cyclic ether group. The method for producing a metal corrosion inhibitor according to claim 7, wherein the molar ratio of the silane coupling agent having an epoxy group represented by formula (III) to the silane coupling agent having an amino group represented by formula (IV) is 1 or more and 20 or less.