JP2010196020A - Water-based lubricant composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel water-based lubricant composition being capable of exhibiting lubricity that is equivalent to or better than that of non-aqueous lubricant containing base oil, as well as, exhibiting anti-freezing effect at the predetermined operating temperature. <P>SOLUTION: The aqueous lubricant composition includes an water-based solution containing 20 mass% or more of at least one water soluble inorganic salt selected from the group consisting of a molybdenum acid salt and a tungsten acid salt. In addition, further lubricity can be given to the water-based lubricant composition by dissolving or dispersing at least one selected from the group consisting of moisture absorbers, thickeners, surfactants, and solid lubricants into the aqueous solution. Moreover, by adding suitable amount of these additives, solely or in a suitable combination thereof, to the aqueous solution, a low frictional coefficient which is unrealizable by the non-water-based lubricant composition containing base oil can be provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an aqueous lubricant that contains water and contributes to improving the lubricity of sliding surfaces of various devices.

  In general, tools and molds used in metal processing, sliding parts of various devices, etc. are used in the presence of a lubricant in order to improve low friction, wear resistance, seizure resistance, etc. Many. Most often used are non-aqueous lubricants containing base oils such as mineral oils, synthetic oils, fats and oils. A thin oil film is formed between the solids to support the entire load and to separate the sliding surfaces from each other for lubrication. Show. For example, general non-aqueous lubricants such as hydraulic oil, cutting oil, metalworking oil, and engine oil exhibit desired lubricity such as anti-friction effect by adding various additives to the base oil. However, when these base oils are used at a high temperature, wrinkles are generated, and depending on the material of the member to which the non-aqueous lubricant is supplied, there is a problem that the base oil exhibits corrosivity due to oxidative change. In recent years, water-based lubricants containing water instead of base oil have been demanded from the viewpoint of environmental impact.

  Patent Document 1 discloses a lubricant treatment liquid in which a water-soluble inorganic salt, a metal salt of a fatty acid, a wax, and a surfactant are dispersed in water. A lubricant treatment liquid is attached to the metal material and then dried to form a film on the surface of the metal material, thereby imparting lubricity to the surface of the metal material. Patent Document 2 discloses a lubricant composition obtained by blending 10% by weight or less of a molybdate with an aqueous lubricant such as a water-glycol hydraulic oil. This lubricant composition is used for bearing lubrication. Further, in the examples, water-glycol hydraulic oil (water: glycol = 40: 60) is blended with 1.5% by weight or less of molybdate.

JP 2000-309793 A JP 2005-29622 A

However, since the water-based lubricant contains water, if it is used below freezing point, it solidifies and does not work as a lubricant. For this reason, water-based lubricants that are currently used are mainly assumed to be used at room temperature or slightly higher than that, and are not considered for use in natural environments that are below freezing in winter, for example. . The lubricant treatment liquid described in Patent Document 1 is deposited on the surface of a metal material and then dried to form a film. Therefore, since water is not contained at the time of use, there is no particular problem even if the temperature at the time of use is lowered. On the other hand, in Patent Document 2, the ratio of molybdate to water is not clarified. However, even in Example 5 containing the most molybdate among the examples, K ₂ MoO ₄ excluding glycol was used. The concentration as an aqueous solution is less than 4% by weight. It is known that the freezing point of the solvent is lowered when the solute is dissolved in the solvent (freezing point lowering). However, at such a concentration, it freezes at several degrees Celsius below the freezing point and does not serve as a lubricant. That is, the lubricating oil composition described in Patent Document 2 is not intended for use at low temperatures.

  In view of the above problems, the present inventors have aimed to provide a novel aqueous lubricant composition that exhibits lubricity equivalent to or higher than that of a non-aqueous lubricant and exhibits an antifreezing effect at a predetermined use temperature. And

  In general, it is known that a water-soluble inorganic salt such as molybdate improves the lubricity of the lubricant by being added to the lubricant in an appropriate amount, but when added in excess (for example, 10% by mass or more), On the contrary, it is said that the lubricity is impaired. However, the present inventors have newly found that by using a specific salt as the water-soluble inorganic salt, even a highly concentrated aqueous solution exhibiting a predetermined antifreezing effect exhibits lubricity. That is, the aqueous lubricant composition of the present invention is characterized by comprising an aqueous solution containing at least 20% by mass of a water-soluble inorganic salt selected from the group consisting of molybdate and tungstate.

  Since the water-based lubricant composition of the present invention comprises a high-concentration aqueous solution containing 20% by mass or more of a water-soluble inorganic salt, it exhibits a predetermined antifreezing effect. Further, by using at least one selected from the group consisting of molybdate and tungstate as the water-soluble inorganic salt, excellent lubricity is exhibited even in an aqueous solution containing the water-soluble inorganic salt at a high concentration. Molybdate and tungstate are known as metal passivators because they have a weak oxidizing action. Therefore, the water-based lubricant composition of the present invention has a property of exhibiting a predetermined corrosion prevention performance against the metal used in the presence thereof and not corroding the metal material. That is, the aqueous lubricant composition of the present invention is suitable as a substitute lubricant for non-aqueous lubricants containing a base oil.

  Further, by dissolving or dispersing at least one selected from the group consisting of a hygroscopic agent, a thickener, a surfactant and a solid lubricant in the above aqueous solution, the aqueous lubricant composition of the present invention has further lubricity. Is granted. Further, by adding an appropriate amount of these additives alone or in an appropriate combination to an aqueous solution, a low friction coefficient that cannot be realized by a non-aqueous lubricant composition containing a base oil can be exhibited.

  It should be noted that the predetermined freezing prevention effect can be exhibited by the use of the freezing temperature of the aqueous lubricant composition of the present invention due to the freezing prevention (freezing point depression) effect by the water-soluble inorganic salt in the use environment. It is possible to make the temperature sufficiently lower than the temperature range assumed as the temperature of the environment (usage temperature) that may be generated. That is, it means that it is possible to reliably prevent the aqueous lubricant composition of the present invention from being frozen during use due to the antifreezing effect due to the inclusion of the water-soluble inorganic salt.

It shows the solubility curve of lithium molybdate _(Li 2 MoO _4), and potassium molybdate _(K 2 WO _4). It is sectional drawing which shows a friction test apparatus typically. It is a graph which shows the result of the friction test using ion-exchange water, Comprising: The change of the friction coefficient with respect to test time is shown. It is a graph which shows the result of the friction test using water-system lubricant composition # 01, Comprising: The change of the friction coefficient with respect to test time is shown. It is a graph which shows the result of the friction test using water-system lubricant composition # 02, Comprising: The change of the friction coefficient with respect to test time is shown. It is a graph which shows the result of the friction test using water-system lubricant composition # 03, Comprising: The change of the friction coefficient with respect to test time is shown. It is a graph which shows the result of the friction test using water-system lubricant composition # 04, Comprising: The change of the friction coefficient with respect to test time is shown. It is a graph which shows the result of the friction test using water-system lubricant composition # 05, Comprising: The change of the friction coefficient with respect to test time is shown. It is a graph which shows the result of the friction test using water-system lubricant composition # 06, Comprising: The change of the friction coefficient with respect to test time is shown. It is the result of measuring the surface roughness of the wear scar after the friction test performed using the aqueous lubricant composition # 06. It is a graph which shows the result of the friction test using water-system lubricant composition # 07, Comprising: The change of the friction coefficient with respect to test time is shown. It is the result of measuring the surface roughness of the wear scar after the friction test performed using the aqueous lubricant composition # 07. It is a graph which shows the result of the friction test using water-system lubricant composition # 08, Comprising: The change of the friction coefficient with respect to test time is shown. It is the result of measuring the surface roughness of the wear scar after the friction test performed using the aqueous lubricant composition # 08. It is a graph which shows the result of the friction test using water-system lubricant composition # 09, Comprising: The change of the friction coefficient with respect to test time is shown. It is the result of measuring the surface roughness of the wear scar after the friction test performed using the aqueous lubricant composition # 09.

  Hereinafter, the best mode for carrying out the aqueous lubricant composition of the present invention will be described.

  The aqueous lubricant composition of the present invention comprises an aqueous solution containing a water-soluble inorganic salt. That is, it does not include base oils such as mineral oil, synthetic oil, and fat. The water-soluble inorganic salt is at least one selected from the group consisting of molybdate and tungstate.

The molybdate is preferably an alkali metal salt of molybdic acid. The tungstate is preferably an alkali metal salt of tungstic acid. The alkali metal salt is preferably one of lithium salt, potassium salt and cesium salt. It is also possible to use a sodium salt of molybdic acid and / or a sodium salt of tungstic acid as the water-soluble inorganic salt. However, sodium salts have low solubility at low temperatures compared to lithium, potassium and cesium salts. For this reason, when a sodium salt is employed as the water-soluble inorganic salt in the water-based lubricant composition of the present invention, an insoluble material is generated at a low temperature. As a result, the antifreezing effect is insufficient, and the environmental temperature range in which the aqueous lubricant composition of the present invention can be used shifts to the high temperature side, so that the usable temperature range is limited. Accordingly, suitable water-soluble inorganic salts include lithium molybdate (Li ₂ MoO ₄ ), potassium molybdate (K ₂ MoO ₄ ), cesium molybdate (Cs ₂ MoO ₄ ), lithium tungstate (Li ₂ WO ₄ ), Mention may be made of potassium tungstate (K ₂ WO ₄ ) and cesium tungstate (Cs ₂ WO ₄ ). These water-soluble inorganic salts may be used alone or in combination of two or more. Of these, lithium molybdate (Li ₂ MoO ₄ ) is particularly preferable. This is because Li ₂ MoO ₄ dissolves in water in a sufficient amount even under freezing, and its aqueous solution exhibits an excellent lubricating action.

And the aqueous | water-based lubricant composition of this invention is the aqueous solution (henceforth, only below) which contains 20 mass% or more of at least 1 sort (s) of water-soluble inorganic salt selected from the group which consists of molybdate and tungstate more than usual. It may be described as “aqueous solution”). In addition, in this specification, the quantity of the water-soluble inorganic salt contained in aqueous solution is shown in the ratio when the whole aqueous solution is 100 mass%. If the blending ratio of the water-soluble inorganic salt is less than 20% by mass, sufficient antifreezing effect cannot be obtained. The content of the water-soluble inorganic salt is preferably 35% by mass or more, more preferably 40% by mass or more. If the water-soluble inorganic salt is at least one selected from the group consisting of molybdate and tungstate, the solubility in water is high even at low temperatures, and an aqueous solution having a concentration of 20% by mass or more can be obtained. For example, FIG. 1 is a solubility curve of lithium molybdate (Li ₂ MoO ₄ ) and potassium molybdate (K ₂ MoO ₄ ), which are one of the water-soluble inorganic salts. It is known that an aqueous K ₂ MoO ₄ solution dissolves up to 62% by mass even at a low temperature below 0 ° C. _Then, it is known that the lowest solidification temperature of the K 2 MoO ₄ solution is about -38 ° C.. On the other hand, in Li ₂ MoO ₄ aqueous solution, solubility data at 0 ° C. or lower is not public, but in our investigation, it is confirmed that at least 44% by mass dissolves even at a low temperature below 0 ° C. The solidification temperature at that time is estimated to be −45 ° C. or lower.

  The aqueous lubricant composition of the present invention can be used by diluting with water as necessary depending on the usage environment such as temperature. For this reason, it is preferable that the water-based lubricant composition used for actual use has a blending ratio of the water-soluble inorganic salt. That is, the aqueous lubricant composition of the present invention is preferably used at a concentration containing a water-soluble inorganic salt at a blending ratio of 20% by mass or more. In addition, the amount of water-soluble inorganic salt tends to improve the antifreezing effect as the content increases, but an insoluble matter is generated with a decrease in temperature during use. Since this insoluble matter does not have a good influence on the lubricity, the content of the water-soluble inorganic salt should not exceed the amount that can be dissolved in water at the use temperature (that is, below the solubility).

The water-based lubricant composition of the present invention can have a freezing temperature of −15 ° C. or lower, more preferably −35 ° C. or lower, due to the antifreezing effect of the water-soluble inorganic salt. In addition, if a freezing temperature is -35 degrees C or less, it can be said that there exists an antifreezing effect equivalent to the non-aqueous lubricant composition containing base oil. For example, when lithium molybdate (Li ₂ MoO ₄ ) is employed as the water-soluble inorganic salt, the water-based lubrication of the present invention is achieved by setting the blending ratio of Li ₂ MoO ₄ to 40% by mass or more, further 42% by mass or more. The freezing temperature of the agent composition can be −35 ° C. or lower.

Furthermore, the aqueous lubricant composition of the present invention is preferably used at a pH of 6 to 8, more preferably at a pH of 6.5 to 7.5. The aqueous solution containing the water-soluble inorganic salt theoretically exhibits alkalinity around pH 11. Since the pH value affects the corrosion prevention performance for the metal material, it is preferable to adjust the pH value to be suitable for use by adding a pH adjuster to the aqueous solution. When the pH of the aqueous solution is excessively inclined to alkali, molybdenum oxide and / or tungsten oxide may be used as a pH adjuster. For example, lithium molybdate (Li ₂ MoO ₄ ) is a salt formed by neutralizing molybdic acid (H ₂ MoO ₄ or MoO ₃ .H ₂ O) and lithium hydroxide (LiOH.H ₂ O). Since molybdic acid is a weak acid while lithium hydroxide is a strong alkali, lithium molybdate (Li ₂ MoO ₄ ), which is a salt having a molar ratio of 1.0, has a pH of about 11.5. Shows alkalinity. Therefore, for example, molybdenum oxide (MoO ₃ : anhydride of molybdic acid) may be added as a pH adjuster to adjust the pH of the aqueous solution to pH 6-8.

  There is no particular limitation on the addition amount of the pH adjuster. In particular, when molybdenum oxide and / or tungsten oxide is used, even if it is added in excess, it does not greatly fall below pH 6 and greatly toward the acidic side. On the contrary, since the pH of the aqueous solution may be inclined toward the alkali during use, it is preferable to add the above oxide excessively because the pH adjustment effect of the aqueous solution lasts for a long time. From these viewpoints, when the aqueous solution is 100 parts by mass, the addition amount of the pH adjusting agent is preferably 0.5 parts by mass or more and 25 parts by mass or less, and further 15 parts by mass or more and 20 parts by mass or less. If it is less than 0.5 part by mass, the effect of neutralizing the aqueous solution before use is hardly exhibited. Moreover, since it will become easy to crystallize a water-soluble inorganic salt when it exceeds 25 mass parts, it is unpreferable. Here, the concentration of the aqueous solution after the addition of the pH adjusting agent needs to be blended and prepared in the aqueous solution so as to be the above-mentioned predetermined concentration as molybdate or tungstate.

  In the aqueous lubricant composition of the present invention, in addition to the pH adjuster, at least one selected from the group consisting of a hygroscopic agent, a thickener, a surfactant and a solid lubricant may be dissolved or dispersed in an aqueous solution.

  The hygroscopic agent absorbs moisture in the atmosphere to reduce water evaporation, and suppresses crystallization of water-soluble inorganic salts and the like accompanying a decrease in the amount of moisture in the aqueous solution. As the hygroscopic agent, a known one can be used as long as it is soluble in an aqueous solution, but it is particularly preferable to use a polyhydric alcohol which is an alcohol having two or more hydroxy groups in the molecule. Further, from the viewpoint of water solubility and antifreezing effect, the molecular weight is preferably 30 to 400, more preferably 90 to 200. For example, glycerin, diglycerin, polyglycerin, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol and the like can be suitably used. These polyhydric alcohols may be used alone or in combination of two or more. Among them, ethylene glycol and glycerin are preferable, and glycerin is particularly preferable because a hygroscopic effect can be obtained by addition of a small amount and it is harmless to the human body.

  The amount of the hygroscopic agent added is not particularly limited, but when the aqueous solution is 100 parts by mass, the hygroscopic agent may be contained in an amount of 30 parts by mass or less, and further 20 parts by mass or less. Further, the lower limit of the amount of the hygroscopic agent added is 5 parts by mass, and if it is less than 5 parts by mass, even if the hygroscopic agent is added, the effect of reducing the evaporation of moisture is not sufficiently exhibited. If the amount of polyhydric alcohol added is excessive, the antifreezing effect may be reduced, but depending on the type of polyhydric alcohol, the coagulation temperature may be well below 0 ° C. There is no significant influence on the antifreezing effect of the aqueous lubricant composition of the present invention. However, when the usage environment is an extremely low temperature of −35 ° C. or less, the amount of the hygroscopic agent added is preferably 20 parts by mass or less, more preferably 15 parts by mass or less with respect to 100 parts by mass of the aqueous solution. Moreover, if it prescribes | regulates by the mass ratio with respect to the water | moisture content in aqueous solution, it is good that water: humidifier is 9: 1-7.5: 2.5. In a normal water-glycol hydraulic fluid, water: glycol is 5: 5 to 3: 7 and is rich in glycol.

  The thickener increases the viscosity of the aqueous solution, thickens the liquid film formed on the surface of the member to be lubricated, and increases the force to support the load on the sliding surface. That is, by adding the thickener, the load bearing performance of the aqueous lubricant composition of the present invention is improved. On the other hand, increasing the viscosity of the lubricant leads to increasing the internal friction of the liquid film. Therefore, as the thickener, a thixotropic thickener having thixotropic property that becomes high viscosity when the sliding speed is low may be used. As this thixotropic thickener, a known one can be used as long as it is water-soluble. Specifically, inorganic thickeners such as bentonite, laponite, and montmorillonite, and organic thickeners such as xanthan gum, guar gum, carrageenan, locust bean gum, diyutan gum, and welan gum can be used. These thixotropic thickeners may be used alone or in combination of two or more. In particular, xanthan gum is preferable because a large thickening effect can be obtained by adding a small amount to an aqueous solution, and high thixotropic properties can be stably imparted even when the pH of the aqueous solution changes.

  There are a wide variety of thixotropic thickeners, and the amount added to the aqueous solution is not generally determined. However, when the aqueous solution is 100 parts by mass, the thickener is 0.5 parts by mass or less, 0. It is preferable to contain 3 parts by mass or less, further 0.25 parts by mass or less. Moreover, when the aqueous solution is 100 parts by mass, it is preferable that the thickener is contained in an amount of 0.01 parts by mass or more, further 0.1 parts by mass or more. If it is less than 0.01 parts by mass, thixotropic properties are not sufficiently imparted to the aqueous solution, which is not preferable. The greater the amount added, the better the thixotropic properties. However, if the amount added exceeds 0.5 parts by mass, the viscosity becomes excessive and adversely affects the lubricity, which is not preferable.

In particular, the aqueous lubricant composition of the present invention to which both the hygroscopic agent and the thickener described above are added exhibits a low coefficient of friction of the order of 10 ^{−2 in the} presence thereof, and such a low coefficient of friction is also present. Stable expression. This is considered to be because even when a load is applied to the friction surface, a water film that is a fluid lubricating film that separates the interface is stably formed.

  The surfactant forms an adsorption film on the surface of the member to be lubricated, and suppresses direct contact between the members. Therefore, the aqueous lubricant composition of the present invention preferably further contains a water-soluble silane compound as a surfactant. Examples of water-soluble silane compounds include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropyltriethoxysilane, and N-2 (aminoethyl) 3-aminopropyltri Methoxysilane or the like can be preferably used. These water-soluble silane compounds may be used alone or in combination of two or more.

  Although there is no limitation in particular in the addition amount of a water-soluble silane compound, when an aqueous solution shall be 100 mass parts, it is good to contain a water-soluble silane compound 5 mass parts or less, 3 mass parts or less, and also 1.5 mass parts or less. Further, when the aqueous solution is 100 parts by mass, the water-soluble silane compound is preferably contained in an amount of 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more. If the amount is less than 0.1 part by mass, the effect of forming an adsorbed film due to the addition of the water-soluble silane compound is not sufficiently exhibited, which is not preferable. As the amount of the water-soluble silane compound is increased, the adsorption film is more easily formed. However, when the amount exceeds 5 parts by mass, no further formation effect can be expected.

  Moreover, the aqueous lubricant composition of the present invention may contain a solid lubricant. For example, known solid lubricants such as molybdenum disulfide, tungsten disulfide, graphite, boron nitride, ethylene tetrafluoride, graphite tetrafluoride, fullerene, zinc stearate, lithium stearate, melamine cyanurate can be used. The water-insoluble solid lubricant is used by being dispersed in an aqueous solution. By using a solid lubricant having a specific gravity close to that of the aqueous solution, the solid lubricant can be uniformly dispersed in the aqueous solution. Melamine cyanurate is particularly preferred because its specific gravity is close to that of an aqueous solution. The solid lubricant is preferably used in the form of a powder having an average particle size of about 0.1 to 3 μm.

  Although there is no limitation in particular in the addition amount of a solid lubricant, when an aqueous solution shall be 100 mass parts, it is good to contain a solid lubricant 5 mass parts or less, 3 mass parts or less, and also 1.5 mass parts or less. In addition, when the aqueous solution is 100 parts by mass, the solid lubricant is preferably contained in an amount of 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more. If the amount is less than 0.1 parts by mass, the effect of improving the lubrication performance due to the addition of the solid lubricant is not sufficiently exhibited, which is not preferable. However, when the amount exceeds 5 parts by mass, the solid lubricant particles tend to aggregate and the lubrication performance deteriorates, which is not preferable.

  The aqueous lubricant composition of the present invention is suitable for sliding parts of various devices used at low temperatures. Specific examples of the sliding parts include engine parts, motor parts, various actuator gears, gears, cams, bearings, and the like. The sliding part is preferably made of metal. If it is the water-system lubricant composition of this invention, even if it is metal materials, such as steel, an aluminum alloy, and a copper alloy, corrosion will be suppressed.

  As mentioned above, although embodiment of the aqueous | water-based lubricant composition of this invention was described, this invention is not limited to the said embodiment. Without departing from the scope of the present invention, the present invention can be implemented in various forms with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be specifically described with reference to examples of the aqueous lubricant composition of the present invention.

[Preparation of aqueous lubricant composition]
Commercially available K ₂ WO ₄ and Li ₂ MoO ₄ were prepared as water-soluble inorganic salts. Then, either one of these, a predetermined amount of ion-exchanged water, and dissolved to give a _K 2 WO ₄ solution and _Li 2 MoO ₄ solution. All aqueous solutions had a pH of 11.5.

In addition, as additives, hygroscopic agents (glycerin and ethylene glycol), thickeners (xanthan gum), solid lubricants (melamine cyanurate powder, average particle size 1.5 μm), surfactants (alkoxysilanes) and pH adjusters (MoO ₃ ) was prepared. One or more of these were dissolved or dispersed in a predetermined amount in an aqueous Li ₂ MoO ₄ solution to obtain # 01- # 09 aqueous lubricant compositions.

  Table 1 shows the blending ratios of the # 01 to # 09 aqueous lubricant compositions. In Table 1, the units of the numerical values in the columns of the aqueous solution and the additive are all grams (g). In addition, the pH of the # 01 to # 09 aqueous lubricant compositions was measured. The measurement results are also shown in Table 1.

Here, in # 01, pH was changed from 11.5 to 7.3 by adding 0.8 g of MoO ₃ to the K ₂ WO ₄ aqueous solution. That is, the added MoO ₃ serves as a part of the water-soluble inorganic salt (K ₂ WO ₄ ) in the K ₂ WO ₄ aqueous solution. Assuming that 0.8 g of MoO ₃ functions as a water-soluble inorganic salt, the # 01 water-based lubricant composition substantially converts 62.8 g of the water-soluble inorganic salt into 38 g of ion-exchanged water. It is 100.8 g of K ₂ WO ₄ (partially H ₂ MoO ₄ ) aqueous solution (concentration is 62.3 mass%) obtained by dissolution. Similarly, the Li ₂ MoO ₄ aqueous solution of # 02 is substantially 100.8 g of Li ₂ MoO ₄ aqueous solution (concentration) obtained by dissolving 42.8 g of Li ₂ MoO ₄ in 58 g of ion-exchanged water. Is 42.5% by mass). That, and calculate the concentration of the aqueous solution in consideration of the amount of MoO ₃ was added, significantly not different concentration of the aqueous solution before the addition of MoO _3. That is, MoO ₃ is not taken into consideration, and the amount of K ₂ WO ₄ or Li ₂ MoO ₄ first dissolved in ion-exchanged water may be considered as the amount of water-soluble inorganic salt contained in each aqueous lubricant composition. . The same applies to the additives.

[Evaluation of lubricity]
Friction tests were performed using the # 01 to # 09 aqueous lubricant compositions, and the lubricity of these aqueous lubricant compositions was evaluated by the friction coefficient and the wear scar shape. The friction test apparatus used for evaluation is shown in FIG. The friction test apparatus 2 mainly includes a rotating disk 21 and a ball 22 placed in contact with the surface of the disk 21. Further, a supply nozzle 23 for supplying a lubricant at a predetermined flow rate is provided near the rotation center of the disk 21. The disk 21 has a 3 mm thick SUS440C stainless steel plate (quenched / tempered (Rockwell hardness (HRC): 58 to 62, surface roughness: 10-point average height Rz (JIS) 0.1 μm or less)) Was used. Further, as the ball 22, a SUJ2 steel ball (normal grade) for a ball bearing having a diameter of 6.35 mm was used. The ball 22 is fixed to one end of a rod-shaped support 24. The support 24 is made of metal, and a strain gauge (not shown) is attached. In the friction test, a weight (shown by a white arrow in FIG. 2) is placed on the other end of the support 24, and a tangential stress generated in the support 24 by friction is detected by a strain gauge.

  In the friction test, any one of the # 01 to # 09 aqueous lubricant compositions (hereinafter referred to as “lubricant # 01” or the like) is dropped from the supply nozzle 23 at a flow rate of 5 cc / min and applied to the rotating disk 21. The ball 22 (stationary state) was pressed. At this time, the load was 3 kg (constant). The friction radius r was 5.1 mm, the rotation speed was 380 rpm (constant), and the test was performed for 60 minutes. That is, the friction speed is calculated to be 0.2 m / sec and the friction distance is calculated to be 731 m. The time change of the stress during the test was recorded with a pen recorder, and the time change of the friction coefficient was obtained by the relationship of “friction coefficient = friction stress / load”. Further, after the friction test, the uneven state on the surface of the disk 21 was measured with a surface roughness measuring machine from the inner peripheral side to the outer peripheral side of the wear scar. The results are shown in FIGS.

  First, as a comparative example, the friction coefficient was measured by the above-described procedure using lubricant # C1 made only of ion-exchanged water. FIG. 3 is a graph showing the change of the friction coefficient with respect to the test time. The coefficient of friction during the period from 10 minutes to 50 minutes after the start of the test was approximately 0.5.

Lubricant # 01 is a K ₂ WO ₄ aqueous solution. The result of the friction test using the lubricant # 01 is shown in FIG. Lubricant # 02 is a Li ₂ MoO ₄ aqueous solution. The result of the friction test using Lubricant # 02 is shown in FIG. The coefficient of friction was around 0.1 in the presence of any lubricant. That is, the friction coefficient was reduced even with the lubricant containing a larger amount of K ₂ WO ₄ or Li ₂ MoO ₄ than usual. Lubricants # 01 and # 02 are contained at a high concentration close to the limit amount capable of dissolving the water-soluble inorganic salt in the aqueous solution. However, even when K ₂ WO ₄ and Li ₂ MoO ₄ contained in 100 g of the aqueous solution were reduced to about 20 g, the same results as in FIGS. 4 and 5 were obtained. Lubricant # 02 made of an aqueous Li ₂ MoO ₄ solution had a more stable variation in the friction coefficient in the vertical axis direction than lubricant # 01, and the friction coefficient tended to decrease with time.

In Lubricant # 03, xanthan gum was dissolved as a thickener in Lubricant # 02 made of a Li ₂ MoO ₄ aqueous solution. The result of the friction test using the lubricant # 03 is shown in FIG. Further, in the lubricant # 04, melamine cyanurate powder as a solid lubricant was further mixed and dispersed in the lubricant # 03. In Lubricant # 04, it was visually confirmed that the melamine cyanurate powder was uniformly dispersed. The result of the friction test using Lubricant # 04 is shown in FIG. In the presence of the lubricant # 02 (FIG. 5) made of the Li ₂ MoO ₄ aqueous solution, the friction coefficient was close to 0.1, whereas in the presence of the lubricant # 03 and the lubricant # 04, the friction coefficient was lower. The coefficient of friction is shown.

In the lubricant # 05, ethylene glycol was dissolved as a hygroscopic agent in the lubricant # 02 made of an aqueous Li ₂ MoO ₄ solution. The result of the friction test using the lubricant # 05 is shown in FIG. The friction coefficient in the presence of the lubricant # 02 (FIG. 5) made of the Li ₂ MoO ₄ aqueous solution was around 0.1, whereas in the presence of the lubricant # 05, the friction coefficient was almost 0.1 or less. And showed a lower coefficient of friction. That is, it was confirmed that the addition of tylene glycol to the Li ₂ MoO ₄ aqueous solution does not lower the lubrication performance but rather improves it.

Further, in the lubricant # 06, glycerin was dissolved as a hygroscopic agent in the lubricant # 02 made of a Li ₂ MoO ₄ aqueous solution. The result of the friction test using Lubricant # 06 is shown in FIG. The friction coefficient in the presence of the lubricant # 02 (FIG. 5) made of the Li ₂ MoO ₄ aqueous solution was around 0.1, whereas in the presence of the lubricant # 06, the friction coefficient was almost 0.1 or less. Indicated. Lubricant # 06 exhibited a lower coefficient of friction than when lubricant # 05 was used.

  In addition, FIG. 10 is the result of measuring the surface roughness of the wear scar after the friction test performed using the lubricant # 06. The surface roughness was 0.25 μm at the maximum height Rmax.

  In the lubricant # 07, 3-aminopropyltriethoxysilane was dissolved as a surfactant in the lubricant # 06. FIG. 11 shows the result of the friction test using the lubricant # 07. FIG. 12 shows the results of measuring the surface roughness of the wear scar after the friction test performed using the lubricant # 07. The surface roughness was 0.20 μm at the maximum height Rmax. A comparison of the lubricant # 06 and the lubricant # 07 showed a coefficient of friction that is comparable in both cases. However, in the presence of the lubricant # 07 containing the surfactant, the surface of the disk 21 Wear was reduced.

In the lubricant # 08, MoO ₃ was excessively added as a pH adjuster to the lubricant # 06. Even when MoO ₃ was added in excess, the pH of the solution was 6.9 and was almost neutral. The result of the friction test using lubricant # 08 is shown in FIG. In the presence of the lubricants # 02 to # 07 described above, all showed a low friction coefficient, but the friction coefficient fluctuated in the vertical axis direction. On the other hand, in the presence of the lubricant # 08, the friction coefficient was stabilized, and furthermore, a result of reaching an extremely low friction coefficient of 0.003 was obtained after 30 minutes from the start of the test. FIG. 14 shows the results of measuring the surface roughness of the wear scar after the friction test performed using the lubricant # 08. The surface roughness was 0.23 μm at the maximum height Rmax.

  In lubricant # 09, xanthan gum was added as a thickener to lubricant # 06. The result of the friction test using Lubricant # 09 is shown in FIG. In the presence of the lubricant # 09, the friction coefficient was stabilized similarly to the lubricant # 08, and the friction coefficient was 0.02 or less. FIG. 16 shows the result of measuring the surface roughness of the wear scar after the friction test performed using the lubricant # 09. The surface roughness was 0.14 μm at the maximum height Rmax, and the effect of reducing wear was very high.

[Evaluation of anti-freezing performance]
The freezing point was measured and the antifreezing performance of the # 01 to # 09 aqueous lubricant compositions was evaluated. The results are shown in Table 1. All the lubricants had a solidification temperature of −15 ° C. or lower.

Claims (12)

  An aqueous lubricant composition comprising an aqueous solution containing at least 20% by mass of a water-soluble inorganic salt selected from the group consisting of molybdate and tungstate.   The water-based lubricant composition according to claim 1, comprising 40% by mass or more of the water-soluble inorganic salt.   The aqueous lubricant composition according to claim 1 or 2, further comprising a hygroscopic agent comprising a polyhydric alcohol that dissolves in the aqueous solution.   The water-based lubricant composition according to claim 3, comprising 20 parts by mass or less of the hygroscopic agent when the aqueous solution is 100 parts by mass.   Furthermore, the aqueous | water-based lubricant composition in any one of Claims 1-4 containing the thickener which provides thixotropic property.   The water-based lubricant composition according to claim 5, comprising 0.5 parts by mass or less of the thickener when the aqueous solution is 100 parts by mass.   Furthermore, the aqueous | water-based lubricant composition in any one of Claims 1-6 containing the surfactant which consists of a water-soluble silane compound.   The water-based lubricant composition according to claim 7, comprising 5 parts by mass or less of the surfactant when the aqueous solution is 100 parts by mass.   Furthermore, the aqueous | water-based lubricant composition in any one of Claims 1-8 containing a solid lubricant.   The water-based lubricant composition according to claim 9, comprising 5 parts by mass or less of the solid lubricant when the aqueous solution is 100 parts by mass.   The aqueous lubricant composition according to any one of claims 1 to 10, wherein the molybdate is an alkali metal salt of molybdic acid, and the tungstate is an alkali metal salt of tungstic acid.   The aqueous lubricant composition according to claim 11, wherein the alkali metal salt is a lithium salt, a sodium salt, a potassium salt, or a cesium salt.

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