Lubricant composition for forming protective lubricant film with three-layer structure

Abstract

To provide a lubricant composition having excellent lubricity and leaving no wear scars on a metal surface within a compensated wear scar diameter setting region.SOLUTION: A lubricant composition is provided in which surface-treated titanium oxide nanoparticles are mixed into a base oil to form a multi-layer lubricating film composed of three layers on a metal surface.

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition.

Background Art

[0002] In a sliding part of a mechanical system or the like, wear is inevitable due to repeated friction. If lubrication failure occurs in the sliding part, problems such as shortening of the service life of metal parts will occur. Therefore, generally, a lubricant is used. Existing lubricants are roughly classified into two types: a type that forms a lubricating film by a chemical reaction by blending an extreme pressure additive (hereinafter referred to as "Conventional Product 1"), and a type that forms a lubricating film physically by blending a solid lubricant (hereinafter referred to as "Conventional Product 2").

[0003] The attached document ("Analysis and Test Results Report" dated December 9, 2022, prepared by Moresco Techno Co., Ltd.) investigated the functions of the lubricating oil composition according to the present invention (Sample Name ▲1▼ (Appendix 1)), Conventional Product 1 (Sample Name ▲3▼ (Appendix 3)), and Conventional Product 2 (Sample Name ▲2▼ (Appendix 2)) by a load-carrying capacity test (Shell four-ball test (ASTM D2783) (conducted by Moresco Techno Co., Ltd.)). As a result, it was found that Conventional Product 1 and Conventional Product 2 generate wear marks on the sliding part at a relatively early stage.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] According to Patent Document 1, it is possible to reduce the friction coefficient of the sliding part by the lubricating oil composition according to the document. However, from the viewpoints of extending the service life of metal parts and energy saving, higher lubricity is required.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Based on the above, an object of the present invention is to provide a lubricating oil composition having excellent lubricity that does not cause wear marks on the contact surface between metals (hereinafter referred to as "lubricating surface") in the load region (compensation wear mark diameter setting region) most frequently used in practice.

Means for Solving the Problems

[0007] Conventional product 1 reacts with metals by heat to form an adhesive substance (fatty acid metal salt). The stronger the product, the stronger the reaction, which may not only cause wear but also affect discoloration and the like on the lubricating surface. Moreover, since it is a reaction by heat, high lubricating performance cannot be expected until the lubricating surface reaches the reaction temperature. Conventional product 2 often contains solid particles with a micron diameter in the base oil, and the lubricating performance is exhibited by the rolling and disintegration of the particles. However, the stronger the particles, the higher the hardness, which is similar to shaving with a file, and the possibility of wearing the lubricating surface increases. Therefore, there is a need to form a strong film that can prevent direct contact of the lubricating surface.

[0008] Conventional product 1 forms a smooth surface with an adhesive substance formed by a chemical reaction. However, the unlubricated state generated during the process of substance consumption generates wear marks, and it is difficult to maintain the smooth surface for a long time. Conventional product 2 focuses on maintaining the operation by the rolling of particles rather than forming a smooth surface. In particular, in the case of particles with high hardness, there is a drawback of biting into and wearing the lubricating surface. Although it is considered that the unevenness is filled by the disintegration of the particles, the deposited disintegration products do not have enough strength to ensure smoothness, and ultimately suppress the rolling of the particles. Therefore, there is a need to ensure the smoothness of the lubricating surface in order to obtain efficient operation.

[0009] Conventional product 1 ensures cushioning properties with an adhesive substance. However, since the substance is generated by a chemical reaction, the life is determined by the blending amount of the extreme pressure additive. Considering the influence on the lubricating surface, it is difficult to blend a large amount, and a long life cannot be expected. In the conventional product 2, the compounded solid lubricating particles maintain cushioning properties on the lubricating surface, but due to the surface roughness of the lubricating surface, the particles cause catching resistance. In this case, the stress is released by the disintegration of the particles, but if the disintegration continues, the performance deteriorates. Although it may be thought that the hardness of the particles should be increased, increasing the hardness increases the likelihood of scraping and wearing the metal surface. Therefore, there is a demand for ensuring cushioning properties to the extent of dissipating the load due to operation.

[0010] From the above, there is a demand for a lubricating oil composition that does not cause a chemical reaction, does not scrape the lubricating surface with particles, and can sufficiently ensure cushioning properties. The inventors of the present invention have found that a lubricating oil composition containing specific particles obtained by subjecting a specific base oil to surface treatment forms a three-layer protective lubricating film on the lubricating surface, thereby satisfying the above requirements and obtaining extremely excellent lubricity without forming wear marks in the compensated wear scar diameter setting region, and have completed the present invention.

[0011] First, it is necessary to form a strong film that does not cause a chemical reaction with the metal and prevents direct contact between the metals, that is, a layer for protecting the metal surface. Solid lubricating particles are advantageous for forming the layer, but considering the unevenness of the metal surface, micron-sized particles generally used in the past are too large to form a film, so nanoparticles having a particle size of 1 / 1000 of a micron are blended. The nanoparticles to be blended are rutile-type titanium oxide nanoparticles having a primary particle diameter of 10 nm to 30 nm. In order to efficiently adhere small and light titanium oxide nanoparticles to the metal surface, the surface is treated with a surface treatment agent AL(OH)3 (aluminum hydroxide) and stearic acid to have an oil absorption amount (g / 100g) of 24 to 30, and further, an additive that generates an adhesive substance on the lubricating surface, zinc dialkyldithiophosphate, is blended to form a strong film to prevent direct contact between the metals (reference document "Influence of alkyl groups on the friction and wear characteristics of primary alkyl-type zinc dialkyldithiophosphate" (Tribologist 2021 (Vol. 66) No. 3, page 220)). As a result, it has become possible to coat the metal surface so to speak (the layer formed by such a function will hereinafter be referred to as the "coating layer").

[0012] Next, in order to obtain efficient operation, it is necessary to ensure the smoothness of the lubricating surface. However, since there are irregularities on the order of microns on the lubricating surface, a function to fill gaps on the order of microns is required for smoothing. In the case of titanium oxide nanoparticles, it is easy to penetrate into gaps on the order of microns, but it is necessary to consider not only penetration but also fixing. Here, the smoothness can be maintained by the effect of the above surface treatment applied to the titanium oxide nanoparticles and the difference in the flow rate of the liquid due to the structure of the lubricating surface. At the interface (clearance width) ensuring cushioning properties, the particles have a fast flow and move while repelling the stress from the lubricating surface. The repulsion of the stress pushes the particles into the micron-sized gaps, and the pushed-in titanium oxide nanoparticles adhere to each other due to the effects of the surface treatments of the titanium oxide nanoparticles forming the coating layer, filling the valleys like retaining walls, filling the irregularities on the order of microns, and ensuring smoothness. The layer formed by such a function will hereinafter be referred to as the "nanoparticle layer".

[0013] Furthermore, polyalphaolefin (hereinafter referred to as "PAO") with a stable molecular structure, hardly affected by temperature, and a gentle viscosity change is adopted as the base oil. By blending a plurality of PAOs with different viscosities to obtain an appropriate molecular network shape, titanium oxide nanoparticles with improved affinity are uniformly dispersed to realize a colloidal solution with cushioning properties against load. The dispersed titanium oxide nanoparticles ride on the flow of the oil, move in the oil, and are constantly carried to the lubricating surface to prevent direct contact between the metals. As a result, sufficient cushioning properties are ensured on the lubricating surface. The layer formed by such a function will hereinafter be referred to as the "colloidal solution layer".

Advantages of the Invention

[0014] According to the present invention, a multilayer lubricating film composed of a coating layer, a nanoparticle layer, and a colloidal solution layer is formed. Different from the conventional mechanisms, it is possible to provide a lubricating oil composition that forms a protective lubricating film having extremely excellent lubricity and not leaving wear marks on the lubricating surface in the compensated wear scar diameter setting region.

Embodiments for Carrying Out the Invention

[0015] The composition, properties, manufacturing method, uses, etc. of the lubricating oil composition are as follows. Note that the present invention is not limited thereto.

[0016] <<Composition of the Lubricating Oil Composition>> The lubricating oil composition according to the present invention is a colloidal solution prepared by blending nanosized titanium oxide with a surface treatment applied to a base oil.

[0017] <Base Oil> For the base oil, PAO with a stable molecular structure, less affected by temperature, and a gentle viscosity change was selected. To obtain appropriate cushioning properties, PAO with a kinematic viscosity of 65 mm 2 / s (40°C) and the same 400 mm 2 / s (40°C) was blended to form an appropriate molecular network shape.

[0018] <Nanosized Titanium Oxide> In consideration of the surface roughness of the lubricating surface, nanosized rutile-type titanium oxide with a primary particle diameter of 10 nm to 30 nm was selected for forming an appropriate lubricating film. The suitability of the particle hardness was also a reason for selecting nanosized titanium oxide.

[0019] For the surface treatment of nanosized titanium oxide, AL(OH)3 and stearic acid were used, and the oil absorption amount (g / 100 g) was set to 24 to 30. Stearic acid was adopted because it adsorbs on the metal surface by carboxyl groups and hydroxyl groups, which are polar groups (forming iron stearate), and the cohesive force acting between long hydrocarbon chains increases the oil film strength of the adsorption film (Reference: "Tribology from the Perspective of Interface Chemistry" by Seiichiro Hirota, February 12, 1991).

[0020] <Zinc dialkyldithiophosphate> Zinc dialkyldithiophosphate was adopted because it is decomposed by friction to form a protective lubricating film called a tribofilm, and at the same time, it efficiently and firmly adheres titanium oxide nanoparticles to the metal surface.

[0021] <Ester oil> Ester oil was selected to improve the wettability of the lubricating surface of the nanoparticle layer with ensured smoothness, improve the sliding performance, and balance the movement with the colloidal solution layer.

[0022] <Other components> As other components, for example, it is possible to incorporate rust inhibitors and antioxidants that are usually blended in lubricating oil compositions.

[0023] <<Kinematic viscosity>> The kinematic viscosity of the lubricating oil composition is preferably 87 mm 2 / s (40 °C) to 107 mm 2 / s (40 °C), and more preferably 92 mm 2 / s (40 °C) to 102 mm 2 / s (40 °C).

[0024] <<<Manufacturing method of lubricating oil composition>>> Mix the base oil and other additive components, and then uniformly disperse the surface-treated titanium oxide nanoparticles in the mixture.

[0025] <<Raw materials>> The raw materials consist of a base oil, surface-treated titanium oxide nanoparticles, and others.

[0026] <Base oil> PAO10 (kinematic viscosity 65 mm 2 / s (40 °C)) PAO40IS (kinematic viscosity 400 mm 2 / s (40 °C))

[0027] <Nanoparticles> Nanoparticle titanium oxide (rutile form, primary particle diameter 10 nm to 30 nm), using AL(OH3) and stearic acid as surface treatment agents, and the oil absorption amount (g / 100 g) was 24 to 30.

[0029] <Others> Ester oil, zinc dialkyldithiophosphate, rust inhibitor, antioxidant

[0030] <<Manufacture>> The formulation of each raw material in 200 L of the base oil mixture before mixing with nanoparticle titanium oxide is as follows, and 600 g of surface-treated nanoparticle titanium oxide is added thereto. PAO10: 30%, PAO40IS: 33.6%, ester oil: 31.0%, zinc dialkyldithiophosphate: 5.0%, antioxidant: 0.2%, rust inhibitor 0.2%

[0031] The density of the lubricating oil composition is 0.86 g / cm 3 ~0.89 g / cm 3 in the range, and the kinematic viscosity is the measured value of 96.6 mm 2 / s (40 °C).

[0032] <<<Evaluation>>> <<Evaluation method>> Load-carrying capacity test (Shell four-ball test (ASTM D 2783) conducted by Moresco Techno Co., Ltd.).

[0033] <Results> No wear scars were observed at loads of 40 Kgf to 126 Kgf, and even at 160 Kgf, it was within the compensated wear scar diameter (Attachment "Analysis and Test Results Report", separate sheet 1). Compared with the test results of Conventional Product 1 and Conventional Product 2, the generation of wear scars is very slow, and it was found that the lubricating oil composition according to the present invention has extremely excellent lubricating performance by preventing direct contact between metals due to the protective lubricating film having a three-layer structure formed thereon.

[0034] <<<Applications>>> It assists lubrication between all metals, and particularly prevents wear and scratches on metal surfaces. Ambient temperature: -20°C to +300°C

Claims

**Claim 1** A lubricating oil composition comprising base oil and titanium oxide nanoparticles, which forms a three-layer protective lubricating film on the lubricating surface (contact surface between metals). **Claim 2** A lubricating oil composition in which titanium oxide nanoparticles are adsorbed on the metal surface to form a protective lubricating film. **Claim 3** A lubricating oil composition that fills the uneven portions on the metal surface to ensure smoothness. **Claim 4** A lubricating oil composition that forms a film to ensure cushioning against the load caused by friction between metals.