JPH0610165A - Corrosion inhibitor for copper-based materials and lubricating oil containing the corrosion inhibitor - Google Patents

Abstract

(57) [Abstract] [Purpose] Providing a corrosion inhibitor for copper-based materials and a lubricating oil containing the corrosion inhibitor [Structure] Ant nest of copper-based materials caused by a lubricant containing an oxygen-containing organic compound A corrosion inhibitor, which comprises an organic compound having an imidazole group, and a lubricant containing the corrosion inhibitor. [Effect] Effective against ant nest corrosiveness against copper-based materials against lubricating oils containing oxygen-containing organic compounds and susceptible to ant nest corrosion due to reaction with water on copper-based materials It can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ant-nest corrosion inhibitor of a copper-based material and a lubricating oil containing the inhibitor, and more particularly to a copper pipe used for piping of air-conditioning and refrigeration equipment. Regarding ant nest corrosion of copper-based materials caused by lubricating oil used for bending, pipe expanding and stretching
The present invention relates to the corrosion inhibitor and a lubricating oil containing the corrosion inhibitor.

[0002]

2. Description of the Related Art Copper-based materials are used for various purposes because of their workability, thermal conductivity, electrical conductivity, etc. Tubes are widely used. In recent years, a penetration accident of unknown cause has occurred in such a hollow copper pipe, and its countermeasure has become a problem. A survey of copper pipes that had this type of accident revealed that a corrosion caused a penetration accident. The characteristic point of this corrosion is so small that the surface opening of the corrosion hole cannot be visually observed, for example, 10 μm or less, whereas inside the corrosion hole, many corrosion holes are formed like tunnels in the depth direction. This corrosive form looks like an ant nest and is called ant nest corrosion or abnormal morphology corrosion.

Corrosion of copper pipes is generally classified into erosion, pitting, corrosion fatigue and the like, but the ant nest corrosion is a form of corrosion completely different from the conventional forms of corrosion. In the ant nest corrosion, the surface near the corrosion pits was discolored to reddish brown, and no green-blue corrosion product covering the pits like the pitting corrosion formed on the inner surface of the copper pipe was observed on the surface. Conventionally,
The only thing that has been confirmed is that, as a result of X-ray diffraction analysis, etc., it is clear that the corrosion product observed on the wall surface of the tunnel-shaped corrosion hole is cuprous oxide in the cross-section observation of the copper pipe. In the present situation, chlorine, fluorine, and sulfur, which are the substances that cause general corrosion, are not detected and the corrosive medium is not specified. Incidentally, the above ant nest corrosion is not found in the inspection at the time of assembling the air-conditioning equipment, and is often found in the product inspection at the time of shipping after storing the product for a certain period or in the early stage of use by the user. Therefore, it is considered that the ant nest corrosion progresses in a short period after the product is assembled and leads to penetration. For example, there is a case in which a 0.35 mm thick copper tube causes a penetration accident within 3 months.

[0004] As a conventional research on ant nest corrosion of copper pipes, there is a paper "Unusual Morphological Corrosion of Copper Pipes", which was published by Yamauchi et al.
This report points out the possibility of decomposition products of chlorine-based organic solvents, which are degreasing detergents, as a corrosive medium for ant nest corrosion. On the other hand, after that, it was confirmed that formic acid reproduces the ant nest corrosion of the copper tube. However, formic acid is not generated even when a chlorine-based organic solvent reacts with water and is hydrolyzed, and further research by the present inventor shows that even in a copper pipe that is not subjected to a degreasing cleaning step with a chlorine-based organic solvent Penetration accident due to corrosive corrosion has been found.

Therefore, the present inventor considers that a chlorine-based organic solvent is also one of the causative substances of ant nest corrosion, but in addition to this,
We focused on lubricating oil as a common corrosion-causing substance. That is, lubricating oil is widely used for copper pipe processing regardless of the use of chlorine-based organic solvent, and since the lubricating oil is composed of various organic substances, its hydrolysis products cause ant nests. I thought that formic acid, which causes corrosive corrosion, might also be generated.

[0006]

BACKGROUND OF THE INVENTION Dovetail corrosion of copper tubes is often found in heat transfer tubes for air conditioners and refrigerant piping. In particular, it was found from the case analysis of the present inventor that the rate of occurrence of ant nest corrosion is high in a copper tube in a heat exchanger unit equipped with aluminum fins. The copper tube used for this purpose is
The copper tube manufacturer ships the heat exchanger processing manufacturer with a soft material that has undergone tube expansion processing and bright annealing, but the copper tube shipped is
Even if the surface is analyzed with a high-precision microanalyzer such as Auger analysis, only the amount of carbon equivalent to the amount adsorbed in the atmosphere is detected, and it is washed to a level where contaminants such as lubricating oil are not recognized at all. There is. The heat exchanger processing manufacturer applies the lubricating oil to the copper tube received from the copper tube manufacturer, cuts the copper tube, expands the mouth part, expands the balls for fixing the aluminum fins, and then expands the aluminum fins. Is fixed to a copper tube and a heat exchanger is assembled. The lubricating oil used at this time is
Aluminum fin press oil is diverted, machine oil or refrigerating machine oil, etc. Basically, it is not a lubricating oil dedicated to copper-based materials, but a lubricating oil dedicated to copper-based materials is not actually sold. .

The lubricating oil used for assembling the heat exchanger is generally often washed with an organic chlorine solvent, but the copper pipe in the heat exchanger is repeatedly bent into an S shape. Therefore, it is impossible to completely clean the lubricating oil in the copper pipe, and in reality, the lubricating oil remains in the copper pipe to some extent. In addition, the use of chlorine-based organic solvents has recently been regulated to prevent environmental pollution, and as a result, the use of self-volatile lubricants that do not require cleaning instead of the previously used non-volatile lubricants is increasing. I am doing it. Therefore,
The number of cases in which lubricating oil remains on copper pipes is increasing.

The inventor of the present invention has conducted a number of lubricants (7 companies, 20 kinds of products) by the same method as in the examples described later.
An attempt was made to reproduce the ant nest corrosion of a copper tube. As a result, 1
We succeeded in reproducing the above ant nest corrosion for seven kinds of lubricants, and found that the cause of ant nest corrosion was a lubricant. An example of this result is shown in FIG. FIG. 1 is a photomicrograph (magnification: 100 times) showing a metal structure in which a copper pipe was immersed in a commercially available lubricating oil for 3 months to cause ant nest corrosion. In addition, it was confirmed by ion chromatographic analysis that the lubricant that caused the ant nest corrosion reacts with water to form formic acid or acetic acid. Furthermore, it has been clarified by instrumental analysis that all of these lubricants contain oxygen-containing organic compounds as common components, that is, esters, ethers, higher alcohols and the like. It is known that these compounds hydrolyze with water to form low molecular weight alcohols and aldehydes. Therefore, the oxygen-containing organic compounds contained in the lubricant are one of the causative agents of the above-mentioned ant nest corrosion. Was expected.

On the basis of the above findings, the present inventor has found that methyl alcohol, formaldehyde, which is a decomposition product of a lubricant,
Attention was paid to C1 compounds of formic acid and C2 compounds of ethyl alcohol, acetaldehyde, and acetic acid, and an attempt was made to reproduce ant nest corrosion of copper pipes using these single compounds. Corrosion occurred.
An example of this is shown in FIG. FIG. 2 is a photomicrograph (magnification: 200 times) showing a metal structure in which ant nest-like corrosion occurred when a copper tube was immersed in acetaldehyde for 1 month. The relative strength of corrosion based on the erosion depth in the above corrosion reproduction test was as follows. In the case of acetic acid, the corrosion form is pitting corrosion. Formaldehyde> formic acid> methyl alcohol = acetaldehyde> ethyl alcohol> acetic acid

As described above, the main causative substances of ant nest corrosion found in copper-based materials are aldehydes, carboxylic acids, and alcohols, which are decomposition products of oxygen-containing organic substances contained in lubricants. However, it was found that the aldehyde has the strongest corrosiveness. In these substances, for example, alcohol is oxidized to aldehyde, and carboxylic acid is generated by oxidation of aldehyde. Since aldehyde groups (—CHO groups) are involved in these substances, aldehyde nest corrosive reactions are involved. It is clear that the reducibility of the group has a strong influence. Conventionally, the most common cause of corrosion is the presence of acid. However, as mentioned above, the presence of reducing substances such as aldehyde groups has a great influence on ant nest corrosion, and the presence of reducing substances is important, not just the presence of acidic substances. It is very different from the mechanism.

The ant nest corrosion is an oxygen concentration battery type wet corrosion that advances using droplets of water droplets as a medium, and the corrosion proceeds by using dissolved oxygen in the water droplets as an intermediary. Specifically, the tunnel-like erosion inside the corrosion hole, which is peculiar to ant nest corrosion, is because the reducing —CHO group acts on the anode part of the tip of the tunnel-shaped corrosion hole and the tip of the corrosion hole always maintains its activity. It is considered that Cu becomes an anode and Cu is eluted, and as a result of repeating this, tunnel-shaped erosion in which corrosion holes extend in one direction occurs. On the other hand, a thick cuprous oxide film is recognized on the wall surface of the corrosion hole. This is considered to be because the cathode reaction due to the reduction of dissolved oxygen proceeds on the wall surface of the tunnel-shaped corrosion hole. Therefore, as corrosion progresses and the corrosion hole becomes deeper in the tunnel shape, the cathode portion increases and the erosion rate increases at an accelerated rate. It is thought that. Since the above-mentioned corrosion reaction occurs, it is considered that the corrosion progresses at an erosion rate that is unprecedented in other corrosion, and a copper pipe with a wall thickness of 0.35 mm will cause a penetration accident in only about 3 months. In addition, the corrosive medium cannot be specified despite the investigations using various high-precision analytical instruments by many researchers so far, if the corrosive medium is the above-mentioned alcohol, aldehyde, or carboxylic acid, It can be understood from evaporative and water-soluble properties.

[0012]

As described above, the ant nest-like corrosion of the copper-based material is caused by the lubricating oil, but the corrosion mechanism has not been known so far, and therefore a substance effective as a corrosion inhibitor has not been found. It has not been released and the causative substance, the lubricating oil, has not been improved at all. Moreover, as mentioned above, unlike the conventional mere acid corrosion, reducing substances such as aldehydes are greatly involved in ant nest corrosion. Therefore, the substances known as conventional corrosion inhibitors can be diverted as they are. Has almost no corrosion inhibiting effect. For example, conventionally used alcohol-based corrosion inhibitors are rather causative substances in ant nest corrosion and have no effect. Various additives may be added to the lubricating oil for various purposes. For example, a phenol-based antioxidant may be added to prevent decomposition of the lubricating oil, and an anthraquinone-based metal deactivator or sulfonate-based corrosion inhibitor may be added to prevent metal corrosion. Therefore, these substances were tested for their corrosion inhibitory effect against ant nest corrosion under the same experimental conditions as those in Examples described later. 2.6-di-tert-butyl-p-cresol was used as an additive in the test, 1.4-dioxyanthraquinone was used in the anthraquinone system, and Na-sulfonate was used in the sulfonate system. It showed no effect on the inhibition of ant nest corrosion of copper tubes. As described above, the present invention aims to provide an effective corrosion-inhibiting substance for ant nest-like corrosion whose corrosion mechanism is conventionally unknown, and has a corrosion-inhibiting effect on the lubricating oil that causes corrosion. The object is to provide an improved lubricating oil.

The present inventor has pursued the corrosion mechanism of ant nest-like corrosion of copper-based materials and found that reducing substances such as aldehydes, which were conventionally considered to have a corrosion inhibiting effect, are the cause of corrosion. As a result of investigating many compounds based on this finding, a compound having a remarkable corrosion inhibiting effect was found. Further, by adding this compound to the lubricating oil, a lubricating oil having an excellent corrosion inhibiting effect on the ant nest corrosion of the copper-based material was obtained.

[0014]

That is, according to the present invention, an inhibitor for ant nest corrosion of a copper-based material caused by a lubricant containing an oxygen-containing organic compound, which comprises an organic compound having an imidazole group A corrosion inhibitor is provided. Furthermore, according to the present invention, a lubricating oil for processing a copper-based material containing an oxygen-containing organic compound, the corrosion inhibitor comprising an imidazole group-containing organic compound that is an inhibitor against ant nest corrosion of the copper-based material A lubricating oil is provided which comprises:

Particularly preferable organic corrosion inhibitors having the imidazole group are those represented by the following formula.

[Chemical 6]

[Chemical 7]

[Chemical 8]

[Chemical 9]

[Chemical 10]

These organic compounds are preferentially adsorbed on the copper-based surface to prevent local corrosion, suppress the hydrolysis reaction of oxygen-containing organic compounds such as esters and ethers, and form a ant nest shape. Controls the occurrence and growth of corrosion.

Typical specific examples of these organic compounds are shown below.

[Chemical 11]

[Chemical 12]

[Chemical 13]

[Chemical 14]

The amount of the organic corrosion inhibitor having an imidazole group added to the lubricating oil is influenced by the amount of the oxygen-containing organic compound contained in the lubricating oil and is influenced by the environmental conditions in which the lubricating oil is used. It is difficult to determine uniformly, but the range of 0.01 to 50 g / l is preferable. 0.01 g /
Below l, the effect of suppressing ant nest corrosion is small and 50
Even if it exceeds g / l, further improvement effect cannot be expected, and the original function of the lubricating oil is rather deteriorated, which is not preferable.

It is desirable that the organic corrosion inhibitor having an imidazole group should be soluble in lubricating oil, and should be dissolved in the lubricating oil at least 0.005 g / l or more. Also, it is preferable from the viewpoints of decomposition and prevention effects of lubricating oil and adsorption to copper-based materials.

Furthermore, since the ant nest-like corrosion of the copper-based material is the corrosion that occurs in the medium of water, the organic corrosion inhibitor having an imidazole group is also soluble in water. This is preferable from the viewpoint of suppressing ant nest corrosion, and 0.005 g / 10% of water is required in order to exert a sufficient suppressing effect.
It is desirable to have a solubility of 0 ml or more.

The lubricating oil to which the organic corrosion inhibitor having an imidazole group of the present invention is added has the following effects. (1) Since it contains an organic corrosion inhibitor, the stability of the lubricating oil with respect to water is improved, and the formation of low molecular weight alcohols, aldehydes, and formic acid, which are the corrosive media for ant nest corrosion, is suppressed. (2) Organic corrosion inhibitors in lubricating oil are preferentially adsorbed on the active sites on the surface of copper-based materials to prevent the copper-based materials themselves from coming into direct contact with water and improve the surface stability of the copper-based materials. Increase and suppress corrosion. (3) Since the organic corrosion inhibitor has solubility in lubricating oil, it has a high effect of preventing deterioration of lubricating oil. (4) Since organic corrosion inhibitors have solubility in water, the corrosion medium generated by decomposition and deterioration of lubricating oil dissolves out of the lubricating oil into water and participates in the corrosive action. The corrosion inhibitor also dissolves in the water from the lubricating oil and is adsorbed on the surface of the copper-based material to protect the surface and react with the corrosion medium to suppress the corrosion activity.

Some lubricating oils have self-volatility, and evaporative condensation is repeated due to changes in the outside air temperature, and the lubricating oil may agglomerate at a portion different from the originally applied portion. In order to suppress the ant nest corrosion caused by the corrosive lubricating oil, it is preferable that the organic corrosion inhibitor exhibits the same evaporation behavior as the corrosive evaporation part in the lubricating oil, and a certain degree of vaporization at room temperature It is preferable to have. For nonvolatile lubricants, nonvolatile corrosion inhibitors are preferred. The organic corrosion inhibitor of the present invention is appropriately selected according to the above properties of the lubricating oil.

Next, the present invention will be described more specifically by way of examples. As the copper material, a phosphorus deoxidized copper pipe OL material (JISH3300, C1220T-OL) of φ9.52 × 0.35 × 300 mm was used for the corrosion test. The phosphorous deoxidized copper tube was ultrasonically cleaned in acetone, thoroughly cleaned, and then dried to obtain a test material. One end of this cleaned phosphorous deoxidized copper pipe was sealed with a silicon stopper, 1 ml of the corrosive liquid was injected into the copper pipe, and the other end was sealed with a silicon stopper, and the pipe was shaken well to corrode the inner surface of the pipe. The liquid, i.e. the lubricating oil, has adhered.

The method for producing the corrosive liquid is as follows. As the lubricating oil, a self-volatile lubricating oil (trade name OAK50-5) that caused the largest ant nest corrosion in the ant nest corrosion reproduction test conducted by the inventor, or a relatively ant nest corrosion A non-volatile lubricating oil (trade name OAK11-b) that did not easily corrode, and polypropylene glycol was selected as a representative of each constituent of the lubricating oil. Then, a predetermined amount of the organic corrosion inhibitor having an imidazole group shown in Tables 1 to 3 is added to these lubricating oils, and the mixture is thoroughly stirred to dissolve the organic corrosion inhibitor in the lubricating oil, and then the measuring pipette is used. At this time, 0.5 ml of lubricating oil containing an organic corrosion inhibitor was poured into the phosphor deoxidized copper pipe, and then another 0.5 ml of pure water was poured into the phosphor deoxidized copper pipe. The etchant was 1 ml. The corrosive liquid of the comparative example was also prepared by the same method as that of the example except that the organic corrosion inhibitor was not added.

Next, the phosphorous deoxidized copper tube (tube length 300 mm) into which the corrosive liquid was injected was vertically dipped in a constant temperature water tank and half-immersed in water. 40 ° C for 12 hours at 25 ° C in a constant temperature water bath
The temperature was changed under the condition of 1 cycle per day for 12 hours at ℃, and thereby the phosphorus deoxidized copper pipe was heated and cooled to simulate the temperature cycle of day and night, thereby forming an environmental condition in which ant nest corrosion was likely to occur. . Self-volatile lubricating oil (trade name)
OAK50-5) and polypropylene glycol were used for 1 month, and non-volatile lubricating oil (trade name OAK11-b) was used for 3 months.

After completion of the test, the phosphorous deoxidized copper pipe was taken out from the constant temperature water bath, the copper pipe was divided into two in the longitudinal direction, and then the cross-section was polished.
Optical microscope observation was performed to measure the erosion depth of the ant nest corrosion of the copper tube. The results are shown in Tables 1 to 3.
A microscopic cross-sectional photograph of the sample of Comparative Example 1 is shown in FIG. Since the ant nest-like corrosion exists under the red spot-like corrosion portion on the inner surface of the copper pipe, it can be easily found by polishing the cross section of this portion and by a speculum. As shown in Tables 1 to 3, the imidazole group-containing organic corrosion inhibitor of the present invention has a remarkable effect of preventing and inhibiting ant nest corrosion caused by lubricating oil. On the other hand, in the comparative example in which the corrosion inhibitor of the present invention is not used, typical ant nest corrosion occurs as shown in FIG.

Copper-nickel alloy tube (9-1 Cupro JIS C70
With respect to 60), a corrosion test was conducted on the self-volatile lubricating oil (trade name OAK50-5) to which the organic corrosion inhibitor of the present invention was added and not added, by the same method as in the above example. The results are shown in Table 4. As is clear from these results, the lubricating oil containing the organic corrosion inhibitor of the present invention did not cause ant nest corrosion at all even for copper alloys, and excellent corrosion prevention or corrosion inhibition effects were confirmed. .

Further, these organic corrosion inhibitors having an imidazole group are not limited to those used by adding them to a lubricating oil, and even if they are pre-applied to the surface of a copper-based material and then brought into contact with the lubricating oil, they are treated with the lubricating oil. It has almost the same inhibitory effect on the nest corrosion.

[0029]

As described above, according to the present invention, even a lubricating oil containing an oxygen-containing organic compound, which easily causes ant nest corrosion due to a reaction with water on a copper-based material, has an organic compound having an imidazole group. By including the corrosion inhibitor, it is possible to effectively prevent the ant nest-like corrosiveness of the copper-based material. Further, by applying this organic corrosion inhibitor to the surface of the copper-based material, the same corrosion inhibition effect can be obtained.

[Brief description of drawings]

FIG. 1 is a photomicrograph showing a metal structure in which ant nest-like corrosion has occurred by immersing a copper pipe in a commercially available lubricant for 3 months (magnification: 10
0 times).

FIG. 2 is a photomicrograph (magnification: 200 times) showing a metal structure in which a copper tube is immersed in acetaldehyde for 1 month to cause ant nest corrosion.

FIG. 3 is a photomicrograph (magnification: 200) showing a metal structure in which ant nest-like corrosion occurred in Comparative Example 1.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C10N 40:24 Z 8217-4H (72) Inventor Masato Watanabe 1975 2 Shimoishitogami, Kitamoto City, Saitama Prefecture Kitamoto Factory

Claims (7)

[Claims] 1. An inhibitor for ant nest-like corrosion of a copper-based material caused by a lubricant containing an oxygen-containing organic compound, comprising an organic compound having an imidazole group. 2. The corrosion inhibitor according to claim 1, comprising an imidazole group-containing organic compound represented by the following general formula. [Chemical 1] [Chemical 2] [Chemical 3] [Chemical 4] [Chemical 5] 3. A lubricating oil for processing a copper-based material containing an oxygen-containing organic compound, comprising a corrosion inhibitor comprising an imidazole group-containing organic compound which is an inhibitor against ant nest corrosion of the copper-based material. Lubricating oil characterized by 4. A lubricating oil for processing a copper-based material containing an oxygen-containing organic compound, wherein at least one or two kinds of corrosion inhibitors composed of the imidazole group-containing organic compound represented by the general formula of claim 2 are used. A lubricating oil containing the above. 5. The organic corrosion inhibitor is added in an amount of 0.01 to 50 g.
The lubricating oil for processing copper-based materials according to claim 3 or 4, characterized in that the lubricating oil contains / l. 6. The lubricating oil for processing a copper-based material according to claim 3, 4 or 5, wherein the organic corrosion inhibitor is dissolved in the lubricating oil at least 0.005 g / l or more. 7. The copper-based material as claimed in claim 3, wherein the organic corrosion inhibitor has a solubility of at least 0.005 g / 100 ml in water. Lubricating oil for processing.