Water-based rust inhibiting agent

Abstract

A water-based rust inhibiting agent according to the present disclosure contains a carboxylate, a sorbitan-based surfactant, a silane coupling agent having an epoxy group or a glycol group, and an aqueous medium.

Description

Water-based rust inhibitor

[0001] The present invention relates to a water-based rust inhibitor.

[0002] Metals such as iron-based metals that have not been subjected to rust prevention treatment are very prone to rusting, easily react with moisture in the air, and red rust or black rust occurs. Therefore, a rust inhibitor is used to prevent rusting during storage before or after processing of metals such as iron-based metals.

[0003] When performing rust prevention treatment on metals such as iron-based metals, water-based rust inhibitors using fatty acid amines are widely used. For example, Patent Document 1 discloses a water-based rust inhibitor composition containing a nitro compound, a fatty acid, and an amine.

[0004] On the other hand, from the perspective of health hazards or environmental hazards, the development of water-based rust inhibitors that do not contain amines is desired. For example, Patent Document 2 discloses a metal corrosion inhibitor composition containing a surfactant, an organic acid having 4 or more carbon atoms, a phosphorus-containing compound, and a sulfur-containing compound.

[0005] Japanese Patent Application Laid-Open No. 2016-148095, International Publication No. 2008 / 123453

[0006] Since the water-based rust inhibitor composition of Patent Document 1 contains an amine, it has high harmfulness to the environment, and there are concerns about the safety of workers handling the water-based rust inhibitor composition. The metal corrosion inhibitor composition of Patent Document 2 has concerns in terms of rust prevention performance. In addition, since it contains a phosphorus-containing compound, there are also concerns about the environmental load.

[0007] One aspect of the present invention aims to realize a water-based rust inhibitor having high rust prevention performance and capable of reducing the environmental load.

[0008] As a result of intensive research to achieve the above problems, the present inventor has found that a water-based rust inhibitor containing specific components has high rust prevention performance and can reduce the environmental load, and has completed the present invention.

[0009] In order to solve the above problems, the water-based rust inhibitor according to one aspect of the present invention contains a carboxylate, a sorbitan-based surfactant, a silane coupling agent having an epoxy group or a glycol group, and an aqueous medium.

[0010] According to one aspect of the present invention, a water-based rust inhibitor can be provided that has high rust prevention properties and can reduce environmental impact.

[0011] Embodiments of the present invention will be described in detail below. However, the present invention is not limited thereto, and various modifications are possible within the scope described. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of the present invention. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or greater, B or less".

[0012] [Water-based rust inhibitor] A water-based rust inhibitor according to one aspect of the present invention comprises a carboxylate, a sorbitan-based surfactant, a silane coupling agent having an epoxy group or a glycol group, and an aqueous medium.

[0013] (Carboxylate Salt) Any carboxylate salt can be used as the carboxylate salt contained in the aqueous rust inhibitor according to one aspect of the present invention. The inclusion of a carboxylate salt improves the liquid-phase rust inhibitory properties of the aqueous rust inhibitor. In this specification, liquid-phase rust inhibitory properties refer to the rust inhibitory effect on the portion in contact with the liquid aqueous rust inhibitor. The carboxylic acid may exist as a carboxylate salt in the aqueous rust inhibitor, or it may be dissolved in a dissociated state. Furthermore, the carboxylate salt may be obtained by mixing a carboxylate salt, which is formed by carboxylic acid forming a salt, into an aqueous medium, or by mixing a carboxylic acid and a basic compound in an aqueous medium to form a carboxylate salt.

[0014] The carboxylic acid constituting the carboxylate salt may be a monocarboxylic acid, or a polycarboxylic acid such as a dicarboxylic acid or tricarboxylic acid. Furthermore, the carboxylic acid may be an aliphatic carboxylic acid such as a linear aliphatic carboxylic acid, a branched aliphatic carboxylic acid or an alicyclic carboxylic acid, or an aromatic carboxylic acid. The carboxylate salt contained in the water-based rust inhibitor according to one aspect of the present invention may be one type or two or more types.

[0015] Carboxylate salts may be inorganic or organic salts. Examples of carboxylate salts include alkali metal salts such as sodium or potassium salts; alkaline earth metal salts such as magnesium or calcium salts; and so on. Carboxylate salts are preferably potassium or sodium salts of carboxylic acids because they are easily soluble in aqueous media.

[0016] In terms of achieving higher liquid-phase corrosion prevention, the carboxylic acid constituting the carboxylate salt is preferably a carboxylic acid having 7 or more carbon atoms. Examples of carboxylic acids having 7 or more carbon atoms constituting the carboxylate salt include benzoic acid, p-tert-butylbenzoic acid, isononanoic acid, octicic acid, o-toluic acid, p-toluic acid, m-toluic acid, o-phthalic acid, m-phthalic acid, p-phthalic acid, suberic acid, azelaic acid, sebacic acid, and dodecanediic acid.

[0017] There is no particular upper limit on the number of carbon atoms in a carboxylate salt. For example, the number of carbon atoms in a carboxylate salt may be 20 or less, or 18 or less. The range of carbon atoms in the carboxylic acid constituting the carboxylate salt may be 7 to 20, and preferably 7 to 15.

[0018] In terms of achieving higher gas-phase corrosion prevention, the carboxylate preferably contains at least one carboxylate from among aliphatic carboxylates having 7 or more carbon atoms and aromatic carboxylates having 7 or more carbon atoms, and more preferably contains at least one carboxylate from among dodecane diate and octylate. In this specification, gas-phase corrosion prevention refers to the corrosion prevention effect when a metal is immersed in an aqueous corrosion inhibitor and then exposed to air. It is believed that a film is formed on the metal surface by contacting the corrosion inhibitor, and that this film contributes to gas-phase corrosion prevention.

[0019] In terms of improving gas-phase corrosion prevention, liquid-phase corrosion prevention, and stability, the carboxylate salt is more preferably composed of aliphatic carboxylate salts having 7 or more carbon atoms and aromatic carboxylate salts having 7 or more carbon atoms. Furthermore, it is preferable to include two of dodecane diate, octylate, p-toluylate, and sebacinate, more preferably three, and even more preferably all of them.

[0020] The carboxylic acid content of the carboxylate salt contained in the aqueous rust inhibitor according to one aspect of the present invention is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, based on 100% by mass of the aqueous rust inhibitor. Furthermore, the carboxylic acid content of the carboxylate salt is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 18% by mass or less, based on 100% by mass of the aqueous rust inhibitor. Here, the carboxylic acid content is expressed as the amount of carboxylic acid excluding the salt, because the molecular weight of the carboxylate salt differs depending on the type of salt. When the carboxylic acid content of the carboxylate salt is within the above range, the liquid phase rust prevention performance is further improved.

[0021] When two or more types of carboxylates are included, it is preferable that the carboxylic acid content of each carboxylate is 10% by mass or less relative to 100% by mass of the water-based rust inhibitor.

[0022] (Sorbitan-based surfactant) The sorbitan-based surfactant contained in the aqueous rust inhibitor according to one aspect of the present invention is a sorbitan derivative obtained by the reaction of sorbitan with compounds such as fatty acids and alkylene oxides. The sorbitan-based surfactant is a nonionic surfactant. The inclusion of the sorbitan-based surfactant improves the gas-phase rust inhibitory properties of the aqueous rust inhibitor.

[0023] In terms of achieving higher gas-phase corrosion prevention, sorbitan-based surfactants are preferably those containing fatty acid esters. The fatty acid portion of the fatty acid ester is preferably a saturated or unsaturated fatty acid having 10 to 30 carbon atoms, more preferably a saturated or unsaturated fatty acid having 12 to 20 carbon atoms, even more preferably a saturated or unsaturated fatty acid having 14 to 20 carbon atoms, and even more preferably a saturated or unsaturated fatty acid having 16 to 18 carbon atoms. When the fatty acid portion of the fatty acid ester is a saturated or unsaturated fatty acid having 10 to 30 carbon atoms, gas-phase corrosion prevention and stability are further enhanced.

[0024] In terms of achieving higher gas-phase corrosion prevention and stability, the sorbitan-based surfactant is preferably at least one of sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters. The sorbitan-based surfactant contained in the aqueous corrosion inhibitor according to one embodiment of the present invention may be one type or two or more types.

[0025] Examples of sorbitan fatty acid esters include SPAN® 20 (sorbitan monolaurate), SPAN 40 (sorbitan palmitate), SPAN 60 (sorbitan stearate), and SPAN 80 (sorbitan oleate). Sorbitan unsaturated fatty acid esters are preferred, and sorbitan oleate esters are more preferred, as they offer higher gas-phase corrosion resistance and stability. Sorbitan oleate esters are commercially available, and for example, Ionet S80 (manufactured by Sanyo Chemical Industries, Ltd.) can be used.

[0026] Examples of polyoxyethylene sorbitan fatty acid esters include TWEEN® 20 (polyoxyethylene monolaurate), TWEEN 40 (polyoxyethylene sorbitan monopalmitate), TWEEN 60 (polyoxyethylene sorbitan monostearate), and TWEEN 80 (polyoxyethylene sorbitan monooleate). Polyoxyethylene sorbitan monostearate is preferred among polyoxyethylene sorbitan fatty acid esters because it offers higher gas-phase corrosion prevention and solubility. Polyoxyethylene sorbitan monostearate is commercially available, and for example, TWEEN 60 or LT-221 (manufactured by NOF Corporation) can be used.

[0027] In terms of improving gas-phase corrosion prevention and stability, the content of the sorbitan-based surfactant in the aqueous rust inhibitor according to one embodiment of the present invention is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the aqueous rust inhibitor. Furthermore, the content of the sorbitan-based surfactant is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less, based on 100% by mass of the aqueous rust inhibitor. When the content of the sorbitan-based surfactant is within the above range, gas-phase corrosion prevention and stability are further improved.

[0028] (Silane Coupling Agent) The silane coupling agent contained in the water-based rust inhibitor according to one aspect of the present invention has an epoxy group or a glycol group. By including a silane coupling agent having an epoxy group or a glycol group, the sorbitan-based surfactant becomes more easily soluble in the aqueous medium, and the stability of the water-based rust inhibitor is improved. The silane coupling agent contained in the water-based rust inhibitor according to one aspect of the present invention may be one type or two or more types.

[0029] Examples of silane coupling agents having an epoxy group include 3-glycidoxypropyltrimethoxysilane. 3-glycidoxypropyltrimethoxysilane is commercially available, and for example, KBM-403 (manufactured by Shin-Etsu Chemical Co., Ltd.) can be used.

[0030] Examples of silane coupling agents having glycol groups include polyether-modified alkoxysilanes. A polyether degree of polymerization of 2 to 15 is preferred for the polyether-modified alkoxysilane, as this further improves the stability of the water-based rust inhibitor. Polyether-modified alkoxysilanes are commercially available; for example, AF-1 (manufactured by Momentive) can be used.

[0031] In order to further enhance the stability of the water-based rust inhibitor and suppress its gelation, the content of the silane coupling agent in the water-based rust inhibitor according to one embodiment of the present invention is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, based on 100% by mass of the water-based rust inhibitor. Furthermore, the content of the silane coupling agent is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the water-based rust inhibitor. When the content of the silane coupling agent is within the above range, the stability of the water-based rust inhibitor is further enhanced and its gelation can be suppressed.

[0032] (Aqueous medium) The aqueous medium contained in the water-based rust inhibitor according to one aspect of the present invention is usually water, and examples of aqueous mediums other than water include water-soluble organic solvents. The water may be purified water such as ultrapure water, pure water, or distilled water. Examples of water-soluble organic solvents include lower alcohols having 1 to 4 carbon atoms such as ethanol and isopropanol, polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (#200, #400), and glycerin. When water and other aqueous solvents are used, it is preferable that the water content is greater than the content of the other aqueous solvents.

[0033] (Other components) In addition to the components described above, the water-based rust inhibitor according to one aspect of the present invention may contain any additives such as pH adjusters, known rust inhibitors, and organic titanium, to the extent that they do not impair the effects of the present invention.

[0034] Basic compounds such as inorganic bases can be used as pH adjusters. Including basic compounds can further enhance the effect of the silane coupling agent. In terms of facilitating the solubility of carboxylic acids in aqueous media, alkali metal or alkaline earth metal hydroxides are preferred as basic compounds, alkali metal hydroxides are more preferred, and potassium hydroxide or sodium hydroxide is even more preferred. Examples of known rust-preventive components include tetraethoxysilane (TEOS).

[0035] [Preferred Embodiment of Water-Based Rust Inhibitor] In terms of further reducing the environmental burden, a water-based rust inhibitor according to one embodiment of the present invention is preferably free of amine compounds and phosphorus-containing compounds. Here, "free of amine compounds and phosphorus-containing compounds" means substantially free of amine compounds and phosphorus-containing compounds, and includes not only cases where amine compounds and phosphorus-containing compounds are not present at all (i.e., 0% by mass), but also cases where amine compounds and phosphorus-containing compounds are present at 1% by mass or less.

[0036] In terms of excellent stability, gas-phase corrosion prevention, and liquid-phase corrosion prevention, and the ability to suppress the formation of precipitates, the pH of the water-based rust inhibitor is preferably 7 or higher, more preferably 8 or higher, even more preferably 9 or higher, and even more preferably 10 or higher. Furthermore, in terms of higher stability, gas-phase corrosion prevention, liquid-phase corrosion prevention, and safety, the pH of the water-based rust inhibitor is preferably 13 or lower, and more preferably 11 or lower. The pH of the water-based rust inhibitor can be adjusted with a pH adjusting agent such as a basic compound.

[0037] An example of a water-based rust inhibitor according to a preferred embodiment of the present invention is one in which the carboxylic acid content of the carboxylate salt is 0.1% by mass or more and 20% by mass or less, the sorbitan-based surfactant content is 0.1% by mass or more and 20% by mass or less, and the silane coupling agent content is 0.1% by mass or more and 15% by mass or less.

[0038] [Preferred ratio of each component of the water-based rust inhibitor] The carboxylic acid content of the carboxylate salt in the water-based rust inhibitor according to one embodiment of the present invention is preferably greater than the content of the sorbitan-based surfactant. The carboxylic acid content of the carboxylate salt is preferably 1 or more times the content of the sorbitan-based surfactant, more preferably 1.2 or more times, and even more preferably 1.5 or more times. Furthermore, the carboxylic acid content of the carboxylate salt is preferably 3 or less times the content of the sorbitan-based surfactant, more preferably 2.5 or less times, and even more preferably 2 or less times. When the ratio of the content of the carboxylate salt to the sorbitan-based surfactant is within the above range, the liquid-phase rust prevention performance is further enhanced.

[0039] In one aspect of the present invention, the carboxylic acid content of the carboxylate salt in the water-based rust inhibitor is preferably greater than the content of the silane coupling agent. The carboxylic acid content of the carboxylate salt is preferably twice or more than the content of the silane coupling agent, more preferably 2.2 times or more, and even more preferably 2.5 times or more. Furthermore, the carboxylic acid content of the carboxylate salt is preferably four times or less than the content of the silane coupling agent, more preferably 3.8 times or less, and even more preferably 3.5 times or less. When the ratio of the carboxylate salt content to the silane coupling agent content is within the above range, stability is further enhanced.

[0040] In one embodiment of the present invention, the content of the sorbitan-based surfactant in the aqueous rust inhibitor is preferably greater than the content of the silane coupling agent. The content of the sorbitan-based surfactant is preferably 1 or more times the content of the silane coupling agent, more preferably 1.2 or more times, and even more preferably 1.5 or more times. Furthermore, the content of the sorbitan-based surfactant is preferably 2.2 times or less times the content of the silane coupling agent, more preferably 2 times or less, and even more preferably 1.8 times or less. When the ratio of the content of the sorbitan-based surfactant to the silane coupling agent is within the above range, gas-phase rust prevention, liquid-phase rust prevention and stability are improved, and the generation of precipitates can be suppressed.

[0041] [Method for producing a water-based rust inhibitor] There are no particular limitations on the method for producing a water-based rust inhibitor according to one aspect of the present invention. For example, it can be prepared by mixing and stirring a carboxylate, a sorbitan-based surfactant, a silane coupling agent having an epoxy group or a glycol group, an aqueous medium, and other components.

[0042] In the manufacture of water-based rust inhibitors, carboxylate salts may be formed by reacting a carboxylic acid with a basic compound in an aqueous medium.

[0043] [Use of Aqueous Rust Inhibitor] The aqueous rust inhibitor according to one aspect of the present invention is particularly suitable for use as a rust inhibitor for metals such as iron-based metals. The aqueous rust inhibitor according to one aspect of the present invention can be used, for example, as an additive for cleaning liquids such as mechanical parts or metal parts, water-soluble cutting oils used in metal processing, or heat transfer media. Since the aqueous rust inhibitor according to one aspect of the present invention has vapor-phase rust prevention properties, mechanical parts, metal parts, and metal processed products treated with this aqueous rust inhibitor can be stored as they are for short to long periods.

[0044] [Summary] The aqueous rust inhibitor according to Aspect 1 of the present invention contains a carboxylate, a sorbitan-based surfactant, a silane coupling agent having an epoxy group or a glycol group, and an aqueous medium.

[0045] The aqueous rust inhibitor according to Aspect 2 of the present invention preferably does not contain an amine compound and a phosphorus-containing compound in Aspect 1 above.

[0046] The aqueous rust inhibitor according to Aspect 3 of the present invention preferably contains at least one carboxylic acid of dodecanedioate and octylate in the carboxylate in Aspect 1 or 2 above.

[0047] The aqueous rust inhibitor according to Aspect 4 of the present invention preferably contains at least one sorbitan-based surfactant of sorbitan unsaturated fatty acid ester and polyoxyethylene sorbitan fatty acid ester in any one of Aspects 1 to 3 above.

[0048] The aqueous rust inhibitor according to Aspect 5 of the present invention preferably contains dodecanedioate, octylate, p-toluylate, and sebacate in the carboxylate in any one of Aspects 1 to 4 above.

[0049] The aqueous rust inhibitor according to Aspect 6 of the present invention preferably has a content of the carboxylate of 0.1% by mass or more and 25% by mass or less as the carboxylic acid content, a content of the sorbitan-based surfactant of 0.1% by mass or more and 20% by mass or less, and a content of the silane coupling agent of 0.1% by mass or more and 15% by mass or less in any one of Aspects 1 to 5 above.

[0050] [Materials] Details of the components used in the examples and comparative examples are as follows.

[0051] (Silane coupling agents) KBM-403: 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd. AF-1: Polyether-modified alkoxysilane, manufactured by Momentive Co., Ltd. KBM-803: Silane coupling agent having a mercapto group, manufactured by Shin-Etsu Chemical Co., Ltd. KBE-9007N: Silane coupling agent having an isocyanate group, manufactured by Shin-Etsu Chemical Co., Ltd. KBM-3063: Silane coupling agent having a hexyl group, manufactured by Shin-Etsu Chemical Co., Ltd.

[0052] (Carboxylic acids) p-Toluic acid: Aromatic carboxylic acid with 8 carbon atoms Dodecane dioic acid: Aliphatic dicarboxylic acid with 12 carbon atoms Octylic acid: Branched aliphatic carboxylic acid with 8 carbon atoms Sebacic acid: Aliphatic dicarboxylic acid with 10 carbon atoms

[0053] (Basic compound) KOH water soluble 48%: 48% by mass potassium hydroxide solution

[0054] (Surfactants) Ionet S80: Sorbitan-based surfactant (sorbitan fatty acid ester), manufactured by Sanyo Chemical Industries, Ltd. TWEEN (registered trademark) 60: Sorbitan-based surfactant (polyethylene glycol sorbitan monostearate) Sanhibiter OMA-10: Anionic surfactant, manufactured by Sanyo Chemical Industries, Ltd. KF-6011: Silicone-based surfactant, manufactured by Shin-Etsu Chemical Co., Ltd. Futergent 681: Fluorine-based surfactant, manufactured by Neos Co., Ltd. Fillet L: Anionic amino acid-based surfactant, manufactured by NOF Corporation

[0055] (Other ingredients) TA-21: Organic titanium (Ti(O-nBt) ４ ), manufactured by Matsumoto Fine Chemical Co., Ltd. TEOS: Tetraethoxysilane

[0056] [Evaluation Test of Water-Based Rust Inhibitors] (Evaluation of Rust Inhibition) Rust inhibition (gas-phase rust inhibition and liquid-phase rust inhibition) was evaluated by a semi-immersion test method according to the following procedures (1) to (5). (1) The water-based rust inhibitors prepared in each example and comparative example were diluted to 3% by mass with ultrapure water, and 100 mL of the resulting diluted solution was used as the test solution and placed in a container with a lid. (2) 100 ppm each of chloride ions, sulfate ions, and carbonate ions were added to the test solution obtained in (1). (3) The entire metal test piece (cast iron: FC200) polished with #320 was immersed in the test solution obtained in (2). After shaking for 1 minute, 50 mL of the test solution was discarded, and the test piece was lifted and fixed so that the lower half of the metal test piece was immersed in the test solution and the upper half was in the gas phase. (4) It was left in a sealed state at a 50°C atmosphere for 7 days. (5) The amount of rust on the metal test pieces after being left for 7 days was visually confirmed.

[0057] (Criteria for determining gas-phase and liquid-phase corrosion prevention) Gas-phase corrosion prevention was evaluated based on rust on the surface of metal test pieces that were not in contact with the test solution. Liquid-phase corrosion prevention was evaluated based on rust on metal test pieces that were in contact with the test solution. ◎: No rust occurred on the surface of the metal test piece ○: Rust occurred on 1-20% of the surface of the metal test piece ×: Rust occurred on 21% or more of the surface of the metal test piece -: Not performed

[0058] (Stability Evaluation) The water-based rust inhibitors prepared in each example and comparative example were left to stand at room temperature for one day, and the appearance of the solution was visually inspected. The criteria for judging stability are as follows: ◎: No precipitation or turbidity ○: A small amount of precipitation or turbidity occurs △: Turbidity or precipitation that can be seen with the naked eye occurs ×: A large amount of turbidity or precipitation occurs, or the solution separates into two layers

[0059] (Overall assessment) Water-based rust inhibitors that all have a rating of △, 〇, or ◎ for gas-phase rust prevention, liquid-phase rust prevention, and stability were judged to be superior as water-based rust inhibitors. Water-based rust inhibitors that have a rating of × for at least one of gas-phase rust prevention, liquid-phase rust prevention, and stability were judged to be inferior as water-based rust inhibitors.

[0060] The aqueous rust inhibitors in the examples and comparative examples were adjusted to have a pH of 9 to 11 by adding 48% water-soluble KOH as a pH adjuster.

[0061] (Preparation of Water-Based Rust Inhibitors) Water-based rust inhibitors for the Examples and Comparative Examples were prepared by adding a silane coupling agent, a sorbitan-based surfactant, a pH adjuster, a carboxylic acid, and water in that order while stirring, so that the compositions (mass%) were as shown in Tables 1 to 4. The evaluation results of the prepared water-based rust inhibitors are shown in Tables 1 to 4. In the Examples and Comparative Examples, carboxylate salts were produced by mixing a carboxylic acid with potassium hydroxide, a basic compound, in water. The carboxylate salt content in Example 1 was 18 g as the carboxylic acid content.

[0062]

[0063] [Example 1, Comparative Examples 1-3] As shown in Table 1, the aqueous rust inhibitor of Example 1, which contains a carboxylate salt, a sorbitan-based surfactant, a silane coupling agent having an epoxy group, and water, was found to have excellent gas-phase rust prevention properties, liquid-phase rust prevention properties, and stability.

[0064] On the other hand, the aqueous rust inhibitor in Comparative Example 1, which did not contain a silane coupling agent, had poor stability. The aqueous rust inhibitor in Comparative Example 2, which did not contain a surfactant, had poor rust prevention properties. The aqueous rust inhibitor in Comparative Example 3, which did not contain a carboxylic acid, had poor stability, making it impossible to evaluate its rust prevention properties.

[0065]

[0066] [Examples 2-5, Comparative Examples 4-7] As shown in Table 2, the aqueous rust inhibitors in Examples 2-5, which contain sorbitan-based surfactants, were found to have excellent gas-phase rust prevention, liquid-phase rust prevention, and stability. Furthermore, a comparison of Examples 2-5 and Comparative Examples 4-7 revealed that the inclusion of sorbitan-based surfactants in aqueous rust inhibitors improved gas-phase rust prevention. However, the aqueous rust inhibitors in Comparative Examples 5 and 6 had poor stability, making it impossible to evaluate their rust prevention properties.

[0067]

[0068] [Examples 6-7] As shown in Table 3, the water-based rust inhibitors in Examples 6-7, which contain dodecane dioate or octylate, were found to have excellent gas-phase rust prevention, liquid-phase rust prevention, and stability. A comparison of Examples 6-7 with Comparative Example 3 showed that the water-based rust inhibitors had improved stability and high gas-phase and liquid-phase rust prevention when they contained dodecane dioate or octylate. Furthermore, a comparison of Examples 1, 6-7 showed that the water-based rust inhibitors exhibited improved gas-phase rust prevention, liquid-phase rust prevention, and stability when they contained multiple types of carboxylate salts from among dodecane dioate, octylate, p-toluic acid, and sebacic acid, compared to containing only one type of carboxylate salt.

[0069]

[0070] [Examples 8-9, Comparative Examples 8-11] As shown in Table 4, the aqueous rust inhibitors in Examples 8-9, which contained silane coupling agents having epoxy or glycol groups, were found to have excellent gas-phase rust prevention, liquid-phase rust prevention, and stability. On the other hand, Comparative Examples 8, 10-11, which contained silane coupling agents having mercapto, isocyanate, or hexyl groups, had poor stability and could not be evaluated for rust prevention. Furthermore, Comparative Example 9, which had a low content of silane coupling agent having isocyanate groups, could be evaluated for gas-phase rust prevention, but its gas-phase rust prevention was poor.

[0071] (Summary of Examples) The aqueous rust inhibitors of the examples, comprising a carboxylate, a sorbitan-based surfactant, a silane coupling agent having an epoxy or glycol group, and water, were found to have high gas-phase rust prevention properties, liquid-phase rust prevention properties, and stability. Furthermore, since the aqueous rust inhibitors of the examples do not contain amine compounds or phosphorus-containing compounds, they can reduce the environmental impact.

[0072] A water-based rust inhibitor according to one aspect of the present invention can be used as a cleaning solution for machine parts or metal parts, a water-soluble cutting oil used in metal processing, a heat transfer medium, and the like.

Claims

1. A water-based rust inhibitor comprising a carboxylate, a sorbitan-based surfactant, a silane coupling agent having an epoxy group or a glycol group, and an aqueous medium.

2. The water-based rust inhibitor according to claim 1, which does not contain amine compounds or phosphorus-containing compounds.

3. The aqueous rust inhibitor according to claim 1, wherein the carboxylate salt comprises at least one carboxylic acid selected from dodecane diate and octylate.

4. The aqueous rust inhibitor according to claim 1, wherein the sorbitan-based surfactant comprises at least one sorbitan-based surfactant selected from sorbitan unsaturated fatty acid esters and polyoxyethylene sorbitan fatty acid esters.

5. The aqueous rust inhibitor according to claim 1, wherein the carboxylate salt comprises dodecane diate, octylate, p-toluylate, and sebacinate.

6. The aqueous rust inhibitor according to claim 1, wherein the content of the carboxylate salt is 0.1% by mass or more and 25% by mass or less as carboxylic acid content, the content of the sorbitan-based surfactant is 0.1% by mass or more and 20% by mass or less, and the content of the silane coupling agent is 0.1% by mass or more and 15% by mass or less.

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