Lubricating oil composition that forms a three-layer protective lubricating film

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] This invention relates to a lubricating oil composition. [Background technology]

[0002] In mechanical systems and the like, sliding parts inevitably wear down due to repeated friction, and if lubrication is insufficient in the sliding parts, problems such as a shortened lifespan of metal parts occur. Therefore, lubricants are generally used. Existing lubricants can be broadly classified into two types: those that form a lubricating film through a chemical reaction by incorporating extreme pressure additives (hereinafter referred to as "conventional product 1"), and those that form a lubricating film through physical means by incorporating solid lubricants (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.) is a report of the results of investigating 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)) through load-bearing capacity tests (Shell four-ball test (ASTM D2783) (conducted by Moresco Techno Co., Ltd.)). It was found that Conventional Product 1 and Conventional Product 2 generated wear marks on the sliding parts at a relatively early stage. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-45229

[0005] According to Patent Document 1, it is possible to reduce the coefficient of friction of sliding parts using the lubricating oil composition described in the document. However, from the viewpoint of extending the service life of metal parts and saving energy, even higher lubricity is required. [Overview of the project] [Problems that the invention aims to solve]

[0006] Based on the above, the present invention aims to provide a lubricating oil composition that has excellent lubricity and does not leave wear marks on metal-to-metal contact surfaces (hereinafter referred to as "lubricated surfaces") in the load range (compensated wear mark diameter setting range) most frequently used in practical applications. [Means for solving the problem]

[0007] Conventional product 1 reacts with metal upon heating to form an adhesive substance (fatty acid metal salt). The stronger the product, the stronger the reaction, which can cause wear and discoloration on the lubricating surface. Furthermore, because it is a thermal reaction, high lubrication performance cannot be expected until the lubricated surface reaches the reaction temperature. Conventional products often incorporate micron-sized solid particles into the base oil, and lubrication is achieved through the rolling and disintegration of these particles. However, the stronger the particles, the higher their hardness, which is similar to sanding, increasing the likelihood of wear on the lubricated surface. Therefore, there is a need to form a strong coating that can prevent direct contact with the lubricating surface.

[0008] Conventional product 1 forms a smooth surface using an adhesive substance created by a chemical reaction, but the lack of lubrication that occurs during the process of the substance's consumption causes wear marks, making it difficult to maintain a smooth surface over the long term. Conventional product 2 primarily focuses on maintaining operation through particle rolling rather than forming a smooth surface, and in the case of particularly hard particles, it has the drawback of digging into the lubricating surface and causing wear. It is thought that the irregularities may be filled in by the disintegration of the particles, but the accumulated disintegrated material does not have enough strength to ensure a smooth surface and ultimately suppresses the rolling of the particles. Therefore, in order to obtain efficient operation, there is a need to ensure the smoothness of the lubricating surface.

[0009] Conventional product 1 ensures cushioning through an adhesive substance, but since this substance is generated by a chemical reaction, its lifespan is determined by the amount of extreme pressure additive added. However, considering the impact on the lubricating surface, it is difficult to add a large amount, and therefore a long lifespan cannot be expected. Conventional product 2 maintains cushioning properties on the lubricating surface due to the compounded solid lubricating particles, but the particles catch on the surface roughness of the lubricating surface, creating resistance. In this case, the stress is released by the disintegration of the particles, but if the disintegration continues, the performance deteriorates. It might seem that increasing the hardness of the particles would solve the problem, but increasing the hardness increases the possibility of abrasion and wear on the metal surface. Therefore, there is a need to ensure sufficient cushioning to absorb the load caused by movement.

[0010] Based on the above, there is a need for a lubricating oil composition that does not cause chemical reactions, does not abrade the lubricating surface with particles, and can ensure sufficient cushioning. The inventors of the present invention have discovered that a lubricating oil composition containing specific particles with surface treatment applied to a specific base oil forms a three-layer protective lubricating film on the lubricating surface, thereby satisfying the above requirements and providing excellent lubrication that does not leave wear marks in the compensation wear mark diameter setting region, thus completing the present invention.

[0011] First, it is necessary to form a strong coating that does not chemically react with the metal and prevents direct contact between metals, i.e., a protective layer for the metal surface. Solid lubricating particles are advantageous for forming this layer, but considering the unevenness of the metal surface, conventionally used micron-sized particles are too large to form a film. Therefore, nanoparticles with a particle size of 1 / 1000th of a micron are incorporated. The nanoparticles to be incorporated are rutile-type titanium oxide nanoparticles with a primary particle size of 10 nm to 30 nm. To efficiently adhere the small, lightweight titanium dioxide nanoparticles to the metal surface, the surface is treated with the surface treatment agents AL(OH)3 (aluminum hydroxide) and stearic acid to achieve an oil absorption capacity (g / 100g) of 24-30. Furthermore, zinc dialkyldithiophosphate, an additive that generates an adhesive substance on the lubricating surface, is added to form a strong film that prevents direct contact between metals (Reference: "Effect of alkyl groups on the friction and wear characteristics of primary alkyl-type zinc dialkyldithiophosphate" (Tribologist 2021 (Vol.66) No. 3, p. 220)). This made it possible to coat the metal surface (the layer formed by this function will be referred to as the "coating layer" below).

[0012] Next, to achieve efficient operation, it is necessary to ensure the smoothness of the lubricating surface. However, since the lubricating surface has irregularities on a micron scale, smoothing it requires a function that fills these micron-sized gaps. While nanoparticle titanium oxide can easily penetrate these micron-sized gaps, it is necessary to consider not only penetration but also fixation. Here, the smoothness can be maintained due to the effect of the surface treatment applied to the titanium dioxide nanoparticles and the difference in liquid flow velocity caused by the structure of the lubricating surface. At the interface (relief width) where cushioning is ensured, the particles flow at a faster rate and move while resisting the stress from the lubricating surface. The stress repulsion pushes particles into micron-sized gaps, and the pushed-in titanium dioxide nanoparticles adhere to the coating layer through the surface treatment effect of each other, creating a situation like filling valleys with a stone wall, thus filling in micron-sized irregularities and ensuring smoothness. The layer formed by this function will be referred to as the "nanoparticle layer" below.

[0013] Furthermore, polyalphaolefin (hereinafter referred to as "PAO"), which has a stable molecular structure, is less affected by temperature, and exhibits gradual viscosity changes, is used as the base oil. By blending multiple PAOs of different viscosities to obtain appropriate cushioning properties and forming an appropriate molecular network shape, the nanoparticle titanium dioxide with improved affinity is uniformly dispersed, resulting in a colloidal solution with cushioning properties against load. The dispersed titanium dioxide nanoparticles ride the flow of the oil, moving through it and constantly being delivered to the lubricating surface, preventing direct contact between metals. This ensures sufficient cushioning on the lubricating surface. The layer formed by this function will be referred to as the "colloidal solution layer" below. [Effects 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, which is completely different from the conventional mechanism, and it is possible to provide a lubricating oil composition that forms a protective lubricating film having extremely excellent lubricity without forming wear marks on the lubricating surface in the compensated wear mark 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 nanoscale titanium oxide particles 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 400 mm 2 / s (40°C) was blended to form an appropriate molecular network shape.

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

[0019] For the surface treatment of the nanoscale titanium oxide particles, AL(OH)3 and stearic acid were used, and the oil absorption amount (g / 100g) was set to 24 to 30. Stearic acid was adopted because it adsorbs on the metal surface through 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 Dialkyldithiolyonate> Zinc dialkyldithioionate was chosen because it decomposes upon friction, forming a protective lubricating film called a tribofilm, while simultaneously efficiently and firmly adhering nanoparticle titanium oxide to the metal surface.

[0021] <Ester oil> Ester oil was selected to improve the wettability of the lubricating surface of the smooth nanoparticle layer, thereby enhancing lubrication and balancing its movement with that of the colloidal solution layer.

[0022] <Other ingredients> Other possible ingredients include, for example, rust inhibitors and antioxidants that are commonly used in lubricating oil compositions.

[0023] <<Kinematic viscosity>> The kinematic viscosity of the lubricating oil composition is 87 mm 2 / s (40℃) ~ 107mm 2 A temperature of 40°C is preferred, and 92 mm 2 / s (40℃) ~ 102mm 2 / s (40℃) is even more preferable.

[0024] <<<<Method for producing lubricating oil composition>>> The base oil and other additive components are mixed, and then surface-treated titanium dioxide nanoparticles are uniformly dispersed in the mixture.

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

[0026] <Base oil> PAO10 (Kinematic viscosity 65mm 2 / s (40℃) PAO40IS (Kinematic viscosity 400mm 2 / s (40℃)

[0027] <Napolecules> 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.

[0028] <Others> Ester oil, zinc dialkyldithiophosphate, rust inhibitor, antioxidant

[0029] <<Manufacture>> The blending 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 blended therein. PAO10: 30%, PAO40IS: 33.6%, ester oil: 31.0%, zinc dialkyldithiophosphate: 5.0%, antioxidant: 0.2%, rust inhibitor 0.2%

[0030] 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).

[0031] <<<Evaluation>>> <<Evaluation method>> Load-carrying capacity test (Shell four-ball test (ASTM D 2783), conducted by Moresco Techno Co., Ltd.).

[0032] <Results> No wear scar was confirmed at a load of 40 Kgf to 126 Kgf, and it was also within the compensated wear scar diameter even at 160 Kgf (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. It was found that the lubricating oil composition according to the present invention has very excellent lubricating performance by preventing direct contact between metals with the protective lubricating film having a three-layer structure formed thereby.

[0033] <<<Applications>>> It helps lubrication between all metals, especially preventing wear and scratches on metal surfaces. Ambient temperature: -20℃ to +300℃

Claims

1. A lubricating oil composition comprising PAO10, PAO40IS, ester oil, zinc dialkyldithiophosphate, and nanoparticle titanium dioxide, which forms a three-layer protective lubricating film on one side of the lubricating surface.

2. The lubricating oil composition according to claim 1, which, as a result of a shell four-ball test (load-bearing capacity test) in accordance with ASTM D 2783 (test conditions: rotation speed: 1760 r / m, temperature: room temperature, test time: 10 seconds, steel ball: 1 / 2″ JIS B 1501 material SUJ-2), forms a film that has the function of preventing contact between metal-to-metal lubricating surfaces up to a load of 126 kgf.