JP6399592B2 - Aqueous lubricant composition - Google Patents

Description

  The present invention relates to an aqueous lubricant composition.

Lubricants are roughly classified into oil-based lubricants such as engine oil and gear oil based on mineral oil or synthetic oil, and water-based lubricants and solid lubricants based on water.
Among these, water-based lubricants include water-glycol hydraulic fluids used in hydraulic equipment for steel facilities, emulsion-based hydraulic fluids (mainly water) used mainly in low-pressure hydraulic devices with a pressure of 7 MPa or less, or rolling or forging. In addition, there are plastic working lubricants or water-based cutting fluids used for dicing, pressing and the like.
The advantages of using water as a base material are that there is no need to worry about fire, that it has a high specific heat compared to oil and that it has excellent cooling properties, that the base water is cheaper than mineral oil, and that it is easily available. Can be mentioned.

Especially when the machine is operated at high speed and high load, the contact sliding portion is locally heated by frictional heat. The lubricant is responsible for cooling the friction surface and serves to suppress mechanical damage due to local heating. Therefore, water having a high cooling capacity is effective as the lubricant, but the reason why the use scale of the water-based lubricating liquid remains in a very limited range is that the viscosity is extremely low. For example, the kinematic viscosity of mineral base oils and synthetic base oils used in engine oils and hydraulic oils is about 10 to 50 mm ² / s (40 ° C.), whereas the kinematic viscosity of water is 0.66 mm. ^It is extremely low at ² / s (40 ° C.). If the viscosity is low, a lubricating film having a sufficient thickness cannot be formed at the sliding portion. If the lubricating film is thin, it will easily break when sliding, resulting in mechanical damage such as wear and seizure.

  In order to solve such problems, attempts have been made in the past to improve wear resistance by mixing some substance with water. For example, in order to make up for low viscosity, water-soluble polymer compounds (polyalkylene glycol, etc.) are added to water at around 10 mass% to increase the kinematic viscosity at 40 ° C., and fatty acids are added as an anti-wear agent to increase viscosity. This is a technique for functioning as an aqueous lubricant by the effects of both agents.

Thus, when adding a fatty acid or the like to improve lubricity, which is a drawback of water, since it is separated without dissolving even if a fatty acid is simply added to water, usually an alkaline agent such as potassium hydroxide is used. Combined and dissolved in water. The pH serving as a standard for dissolving the fatty acid without being separated is about 8 or more. A lubricating liquid that is generally referred to as a water glycol-based hydraulic fluid is produced based on this concept. Water glycol-based hydraulic fluid is inferior in lubricity compared to oil-based hydraulic fluid, but is widely used because it is effective in special environments such as locations that require special attention to the occurrence of fire.
However, if the water glycol hydraulic fluid is used continuously, the pH closely related to the separation of the additive is lowered. As a countermeasure against this, the present situation is that a pH adjusting agent for increasing the pH is administered into the liquid while ensuring the stability of the liquid.

  In addition, there is a highly hydrous hydraulic fluid that has been actively developed since the 1980s. A high water content hydraulic fluid is a liquid in which about 5% of various additives are blended in about 95% water, and an alkaline agent is blended as a method for dissolving the antiwear agent in water. The same. The reason why this high water content hydraulic fluid did not spread widely in the end is thought to be from the viewpoint of lack of wear prevention and difficulty in ensuring the stability of the fluid after long-term use.

  In addition, water-based lubricants for plastic working are related to the plastic working of non-ferrous metals such as steel and aluminum, in order to prevent seizure of steel, wear on the tool surface, and rough skin, fatty acids, sulfurized fats and oils, esters, disulfide Molybdenum and the like are used.

  However, since these additives have an effect of exerting an effect by physical adsorption / chemical reaction, the additives are gradually consumed over many years of use. Furthermore, the frictional heat in the friction part causes oxidation and thermal decomposition and is consumed. In addition, daily maintenance such as pH control is complicated.

  As a substance for solving these drawbacks, it has been conventionally studied to add solid additive polytetrafluoroethylene (PTFE) particles, carbon-based graphite, mica, or the like (for example, non- Patent Document 1).

  Furthermore, recently, studies are underway to apply nanomaterials such as fullerene C60, carbon nanohorns, and carbon nanotubes, which are theoretically positioned in nanosize, as antiwear agents.

"New Solid Lubrication Handbook", Japan Tribology Society Solid Lubrication Study Group, Yokendo

  However, PTFE particles, graphite, mica, and the like do not have the effect of reducing wear as expected, so that their use is limited and they are rarely used. The reason why the expected effect cannot be obtained is that other than the presence or absence of effectiveness in reducing the wear of the substance itself, the particle size of these substances is as large as several μm or more. Visible boundary lubrication area (partially in a state where metal materials are microscopically contacted with each other), that is, it cannot enter the lubrication area where ultra-thin film of several nm to several tens of nm, and prevents wear sufficiently It is mentioned that an effect and friction reduction cannot be expressed. Moreover, the dispersion state in water is not good and precipitation occurs early.

  In addition, nanomaterials such as fullerene C60, carbon nanohorns, and carbon nanotubes actually exist in the form of agglomerated large aggregates, so it is difficult to enter the friction surface and a great wear reduction effect is expected. Can not. In addition, these substances are not well dispersed in water and cause precipitation at an early stage.

  An object of the present invention is to provide an aqueous lubricant composition that exhibits a high wear reduction effect and is further excellent in dispersion stability.

  As a result of repeated studies aiming to achieve the above object, the present inventors have formulated the above object by blending a graphene-like nanocarbon material having a specific surface functional group into water at a specific ratio. The present inventors have found that it can be achieved, and have completed the present invention based on this knowledge. That is, the following present invention is provided.

<1> Water-based lubrication containing water and a graphene-like nanocarbon having a content of 0.005% by mass to 2.0% by mass with respect to the total amount of the composition and having a hydroxyl group, an epoxy group, and a carboxyl group as surface functional groups Liquid composition.
<2> The aqueous lubricant composition according to <1>, wherein the length of one piece of the graphene-like nanocarbon is in the range of 1 μm to 100 μm.
<3> The aqueous lubricant composition according to <1> or <2>, wherein the glycol is contained in an amount of 5% by mass to 70% by mass with respect to the total amount of the composition.
<4> 5% to 40% by mass of at least one water-soluble polyoxyalkylene polyol selected from water-soluble polyoxyalkylene polyols and alkyl ether derivatives thereof <1> to <3 > The aqueous | water-based lubricating fluid composition as described in any one of>.

  ADVANTAGE OF THE INVENTION According to this invention, the aqueous | water-based lubricating composition which exhibits the high abrasion reduction effect and is further excellent in dispersion stability is provided.

  Hereinafter, the aqueous lubricant composition of the present invention will be described in detail. In addition, in this specification, "-" showing a numerical range represents the range containing the numerical value of the upper limit and the minimum.

  The water-based lubricating liquid composition of the present invention is a graphene-like nano-particle having a content of 0.005% by mass to 2.0% by mass with respect to water and the total amount of the composition, and having a hydroxyl group, an epoxy group, and a carboxyl group as surface functional groups. And carbon.

(A) Graphene oxide-like nanocarbon As a nanocarbon material having no functional group on the surface, sheet-like graphene in which carbon atoms are arranged in a plane in a honeycomb shape is known, but since there is no functional group, it is easy to aggregate, It becomes a large lump in the lubricating base oil, making it difficult to enter the lubricating surface. Therefore, the wear reduction effect cannot be expected so much.

  On the other hand, the aqueous lubricant composition of the present invention is a graphene-like nanocarbon having a hydroxyl group (* -OH), an epoxy group (* -O- *) and a carboxyl group (* -COOH) as surface functional groups (hereinafter referred to as “ It may be referred to as “graphene oxide nanocarbon” or simply “graphene nanocarbon”). “*” In parentheses indicating each functional group represents a bonding position with a carbon atom of a benzene ring constituting graphene. Extreme aggregation in water can be prevented by having a hydroxyl group, an epoxy group, and a carboxyl group as functional groups bonded to carbon atoms constituting the sheet-like graphene. In addition, these functional groups contribute to the reduction of frictional wear.

The content of the graphene oxide-like nanocarbon with respect to the total amount of the aqueous lubricating liquid composition of the present invention is 0.005% by mass to 2.0% by mass, preferably 0.01% by mass to 1.0% by mass. When the content of the graphene oxide-like nanocarbon is less than 0.005% by mass, an appropriate wear reduction effect cannot be obtained, and when it exceeds 2.0% by mass, it is difficult to obtain an effect sufficient for an increase in amount. It becomes more difficult to function as a lubricant.
In addition, from the viewpoint of wear reduction effect, the content of the graphene oxide-like nanocarbon is more preferably 0.1% by mass to 1.0% by mass.

  The graphene oxide nanocarbon used in the present invention has a thickness on the order of nm (less than 1 μm), and the length of one piece is preferably in the range of 1 μm to 100 μm, and more preferably in the range of 5 μm to 75 μm. If the length of one piece of graphene oxide-like nanocarbon is 1 μm or more, it has a wear reduction effect on the lubrication surface, and if it is 100 μm or less, it can intervene on the lubrication surface and exhibit the wear reduction effect. Note that the length of one piece of the graphene oxide-like nanocarbon is the maximum length and can be measured with an atomic force microscope (AFM).

  A method for producing the graphene oxide-like nanocarbon used in the present invention is not particularly limited, and examples thereof include a Brodie method, a Staudenmeier method, a Hummers method, and an improved Hummers method (see Japanese Patent No. 5098064). For example, in the modified Hummers method, first, the raw material graphite is irradiated with microwaves using a microwave oven or the like, and then the irradiated graphite is composed of sulfuric acid, sodium nitrate, and potassium permanganate. It is oxidized by mixing with an aqueous solution containing an oxidizing agent. And the method of producing the graphene oxide-like nanocarbon which has the said surface functional group by exfoliating layered graphite etc. are mentioned.

  Although the present invention is based on water, glycols and thickeners can be blended. For example, when the aqueous lubricant composition of the present invention is used as the hydraulic fluid of the hydraulic device, it is necessary to place importance on the volumetric efficiency of the hydraulic pump. When the viscosity of the liquid is low, there are many leaks inside the pump, and it may be difficult to secure the flow rate and pressure. Therefore, when used as a hydraulic fluid, it is preferable to blend glycols or thickeners for the purpose of increasing the viscosity.

(B) Glycols The glycols are selected from ethylene glycol, diethylene glycol, trimethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, hexylene glycol, dihexylene glycol, and monoalkyl ethers thereof. At least one kind. These glycols may be used individually by 1 type, respectively, and may be used in combination of 2 or more type.
The blending amount of these glycols varies depending on the required viscosity, but in the usual case, it is preferably in the range of 5% by mass to 70% by mass, more preferably 20% by mass to 60% by mass with respect to the total amount of the composition. % By mass. If the content of glycols is less than 5% by mass, the viscosity does not increase so much, and if it exceeds 70% by mass, the advantages for oil-based lubricants are reduced in terms of cooling and nonflammability for the purpose of using an aqueous lubricant. End up.

(C) Thickener As the thickener, at least one water-soluble polyoxyalkylene polyol selected from water-soluble polyoxyalkylene polyols and alkyl ether derivatives thereof can be used.
Specific examples of the water-soluble polyoxyalkylene polyols include polyoxyalkylene glycol, polyoxyalkylene triol, polyoxyalkylene glycol monoether, polyoxyalkylene glycol diether and the like. More specifically, a water-soluble ethylene oxide (hereinafter sometimes referred to as EO) homopolymer, a copolymer of EO and propylene oxide (hereinafter sometimes referred to as PO), polyhydric alcohol and EO. It is obtained by adding a homopolymer, a copolymer of EO and PO, or a copolymer of EO and another alkylene oxide (for example, 1,2-butylene oxide, tetrahydrofuran, and / or α-olefin oxide). Compounds, or alkyl ether derivatives thereof. 1-4 are preferable and, as for carbon number of the alkyl group in the alkyl ether group in an alkyl ether derivative, 1-3 are especially preferable.

Moreover, as a polymer added to said polyhydric alcohol, the copolymer of EO and PO is preferable.
As a copolymer of EO and PO, a copolymer of EO and other alkylene oxides, or a polymer added to a polyhydric alcohol, the molar ratio of EO and PO or EO and other alkylene oxides is It is desirable that it is 25 / 75-80 / 20. The addition mode of the copolymer of EO and PO and the copolymer of EO and other alkylene oxides may be random addition or block addition.
Of these, EO homopolymers and copolymers of EO and PO are preferred.

The weight average molecular weight of the water-soluble polyoxyalkylene polyols is preferably in the range of 3,000 to 20,000, more preferably in the range of 5,000 to 18,000. When the weight average molecular weight is lower than 3,000, the thickening effect is small, and when the average molecular weight exceeds 20,000, the stability may be impaired by heat or shear received during use.
The blending amount of the thickener (water-soluble polyoxyalkylene polyols) is preferably 5% by mass to 40% by mass, and particularly preferably 10% by mass to 30% by mass with respect to the total amount of the aqueous lubricant composition. .

(D) Other components The aqueous | water-based lubricating liquid composition of this invention can mix | blend the following additive according to the objective to be used other than said substances, such as said graphene oxide nanocarbon.

  In order to improve the solubility and dispersibility of the graphene oxide nanocarbon, a surfactant can be blended, and those having a functional group having an affinity for the graphene oxide nanocarbon are preferable. Specific examples include higher fatty acids such as caproic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid, and esters such as fatty acid esters and sorbitan fatty acid esters. In addition, fatty acid amides, fatty acid amines, polyoxyethylene derivatives, glycerin derivatives, castor oil derivatives, ammonium salts and the like are used.

  Moreover, in order to ensure the long-term stability of the aqueous lubricating liquid composition of the present invention and within a range not impairing the effects of the present invention, known additives commonly used in aqueous lubricating liquids, for example, oily agents Further, a metal deactivator, a pH adjuster, a rust inhibitor, an antifoaming agent, a colorant, and the like can be added.

  Examples of the oily agent include saturated fatty acids such as myristic acid, palmitic acid, lauric acid and stearic acid, unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid, aromatic fatty acids and dimer acids. These fatty acids may be used alone or in combination of two or more.

  Examples of the metal deactivator include benzotriazole compounds such as benzotriazole, tolyltriazole, 5-methylbenzotriazole, carboxybenzotriazole, and alkali metal salts or amine salts thereof, mercaptobenzothiazole and alkali metal salts thereof. It is done.

Moreover, a pH adjuster can be mix | blended as needed. Specific examples include alkaline compounds, potassium hydroxide, sodium hydroxide, and the like.
Examples of the rust inhibitor include alkyl morpholines such as methyl morpholine and ethyl morpholine, organic amines such as triethanolamine and N-methyldiethanolamine, and alkali metal salts of carboxylic acids.
Examples of the antifoaming agent include emulsions of silicone compounds, and examples of the coloring agent include alcohol-based coloring agents and metal-based coloring agents.

The preparation method of the aqueous lubricating liquid composition of the present invention includes water as the essential component, graphene oxide nanocarbon having a content of 0.005% by mass to 2.0% by mass with respect to the total amount of the composition, and further necessary Accordingly, various additives may be appropriately mixed, and the mixing order is not particularly limited.
In addition, it does not specifically limit as water to be used, Purified water, such as distilled water and ion-exchange water, tap water, etc. can be used.

  For mixing and stirring for preparation, a propeller type stirrer is preferably used, and in the case of a small amount, an ultrasonic irradiation method can also be used. In addition, the stirring temperature at the time of preparing the aqueous | water-based lubricating liquid composition of this invention may be room temperature normally.

  Next, the present invention will be described more specifically with reference to examples. In addition, this invention is not restrict | limited at all by these examples.

  In Examples and Comparative Examples, water and each component were blended to prepare an aqueous lubricant composition, and the performance of each was evaluated. Each component used for preparing the composition in each Example and Comparative Example is as follows.

(Nanocarbon material)
A nanocarbon material was produced by the following method.
First, as the graphite, graphite powder having an average particle diameter of about 45 μm was used.
<Pretreatment>
As pretreatment, microwave irradiation treatment was performed.
First, graphite was put in a mortar and stirred lightly, and the mortar was put in a microwave oven in a state where there was no graphite aggregated and aggregated.
When the microwave oven was turned on, a spark started to fly in the microwave oven within a few seconds, so the microwave oven was forcibly stopped when the spark began to fly. This microwave oven switch on / off (forced stop) was repeated three times. A total of about 30 seconds of pretreatment with a microwave oven was performed.

<This processing>
3.6 g of pretreated graphite was placed in a beaker, and 92 mL of sulfuric acid was further added and cooled to 4 ° C. to prepare the primary treatment liquid. Next, 4 g of sodium nitrate (NaNO ₃ ) was added in small portions. Furthermore, potassium permanganate (KMnO ₄ ) was added and stirred for 10 minutes.
The temperature of the treatment liquid was set to 35 ° C., and the mixture was stirred for 2 hours while maintaining the temperature. Thereafter, the beaker was cooled with water, and a predetermined amount of 184 mL of water was added dropwise with stirring. This was stirred for 30 minutes, 100 mL of water was added, and 20 mL of hydrogen peroxide (H ₂ O ₂ ) was added in small portions. This liquid was stirred at 90 ° C. for 30 minutes, and centrifuged while adding 300 mL of water to dilute. Centrifugation was repeated until the supernatant was neutral. After centrifuging, the water was removed and then dried to prepare nanocarbon.

The size of the obtained nanocarbon was observed with an atomic force microscope (AFM), and it was confirmed that the length of one piece was about 10 to 50 μm, the thickness was a minimum of 0.8 nm, and the maximum was 20 nm or less.
Further, the surface was analyzed by a Fourier transform infrared spectrophotometer (FTIR) and X-ray photoelectron spectroscopy (XPS), and it was confirmed that a hydroxyl group, an epoxy group, and a carboxyl group were present on the surface (graphene oxide-like nano Carbon) was used.

  In Examples and Comparative Examples, water-based lubricant compositions were prepared under the conditions shown in Table 1 using the components shown in Tables 3 and 4 described later.

The prepared aqueous lubricant composition was evaluated for wear characteristics under the conditions shown in Table 2, and dispersion stability was evaluated by a stationary observation method.
The wear test was a ring-on-block method. First, the test was conducted after a familiar operation. After the test was completed, the wear characteristics were evaluated by measuring the maximum wear depth of the block wear portion using a surface roughness meter.

  In evaluating the friction and wear characteristics, a jig was inserted into the oil tank of the test apparatus, and improvements were made so that the test could be performed at a test oil amount of 30 ml.

  Dispersion stability was measured by immediately collecting 30 ml in a 35 ml glass tube after preparing an aqueous lubricant composition and allowing it to stand at room temperature (about 25 ° C.) for 24 hours. . The evaluation criteria were set to the following three levels of stability A, B, and C, and the level of the sample that was allowed to stand for 24 hours was evaluated.

Stability A; No precipitation is observed. Stability B; Appearance is black and some precipitation is observed at the bottom of the glass tube. Stability C; Appearance is clear and precipitation is observed (all nanocarbons are precipitated).

  Stability A represents a completely dispersed and stable state, and stability B represents a slight precipitation, but the liquid exhibits a nanocarbon black color and is in a practically usable range. The stability levels A and B are acceptable levels. On the other hand, the stability C indicates that almost all of the nanocarbon has been precipitated, which is a rejected level.

Tables 3 and 4 show the blending ratio of each component, the wear characteristics, and the evaluation results of the dispersion stability when preparing the aqueous lubricant composition.
In addition, the nanocarbon in Table 3 and Table 4 is the produced graphene oxide-like nanocarbon, and details of other components are as follows.
・ Water: Purified water ・ Graphite: Made by Chuetsu Graphite Industries Co., Ltd., trade name: Soil graphite AP-6
・ Carbon nanohorn: Commercial product ・ Propylene glycol: manufactured by ADEKA Corporation, trade name: Propylene glycol for industrial use ・ Polyalkylene glycol: manufactured by NOF Corporation, trade name: UNILOVE 75DE-3800

  Moreover, about the comparative example, the abrasion characteristic was evaluated with respect to the aqueous | water-based lubricating liquid composition of Comparative Example 1-4, and the dispersion stability was evaluated with respect to the aqueous | water-based lubricating liquid composition of Comparative Examples 2, 5, and 6. The amount of each component in Tables 3 and 4 is mass%.

The water-based lubricating liquid composition of the example has a smaller wear depth than the composition of the comparative example. Also, the dispersion stability is in a good range.
Thus, it is clear that the aqueous lubricant composition of the present invention has good wear characteristics and dispersion stability.

  Since the water-based lubricating liquid composition of the present invention is excellent in wear prevention and dispersion stability, it can be used in a severely lubricated environment and can maintain its performance for a long time. In addition, pH adjustment during use is unnecessary and can contribute to maintenance reduction. In addition, since the constituent elements are environmentally friendly with carbon, hydrogen and oxygen, they can contribute to environmental conservation.

  The water-based lubricating liquid composition of the present invention is suitable for various lubricating liquids used for the purpose of reducing wear of various mechanical devices. Specifically, water-based hydraulic fluid, bearing lubricant, electric / hybrid vehicle or fuel cell vehicle electric motor cooling and reduction gear lubrication, lubrication / cooling fluid, antifreeze fluid, cutting fluid, rolling fluid, plastic working fluid It is possible to reduce the damage caused by wear of machine parts, and to smoothly operate the machine apparatus over a long period of time. In addition, it is suitable for applications in which the lubricity of the material is improved by applying or circulating a liquid.

Claims (2)

water and,
Graphene-like nanocarbon having a content of 0.005% by mass to 2.0% by mass with respect to the total amount of the composition and having a hydroxyl group, an epoxy group, and a carboxyl group as surface functional groups
Composition comprising at least one glycol selected from ethylene glycol, diethylene glycol, trimethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, hexylene glycol, dihexylene glycol, and monoalkyl ethers thereof. 20 mass% to 60 mass% with respect to the total amount,
10% by mass to 30% by mass of a copolymer of water-soluble ethylene oxide and propylene oxide based on the total amount of the composition;
A water-based lubricating liquid composition comprising:   The aqueous lubricant composition according to claim 1, wherein the length of one piece of the graphene-like nanocarbon is in the range of 1 µm to 100 µm.