High performance grease composition

Abstract

The present invention relates to an overbased calcium sulfonate complex grease composition containing antiwear, antifriction, heat stabilizers, oxidation stabilizers and which is formulated without the use of boric acid and alcohol promoters.

Description

[Technical field]

[0001] The present invention relates to the development of a grease composition and process for its manufacture based on an overbased calcium sulfonate complex grease that is prepared without the use of boric acid and without the use of alcohol-based accelerators. [Background technology]

[0002] Overbased calcium sulfonate greases are well established greases in the art. US 9,273,265 teaches that the known manufacturing process for producing such greases is a two-step manufacturing process including an "accelerating" and a "converting" process. Typically, the first step ("accelerating") is the reaction of a stoichiometric excess of calcium oxide (CO) or calcium hydroxide (Ca(OH)2) as a base source with alkylbenzene sulfonic acid, carbon dioxide (CO2), and other components to produce an oil-soluble overbased calcium sulfonate with amorphous calcium carbonate dispersed therein. These overbased oil-soluble calcium sulfonates are typically clear, glossy, and have a Newtonian rheology. They may be slightly hazy in some cases, but such differences do not preclude their use in the preparation of overbased calcium sulfonate greases. Typically, the second stage ("conversion") involves the addition of a converting agent(s), such as propylene glycol, isopropyl alcohol, water, formic acid or acetic acid, to the product of the promotion stage along with a suitable base oil, such as mineral oil, to convert the amorphous calcium carbonate into a very finely divided dispersion of crystalline calcium carbonate. Because excess calcium hydroxide or calcium oxide is used to achieve overbasing, small amounts of residual calcium oxide or calcium hydroxide may be present, which are dispersed. The crystalline form of calcium carbonate is preferably calcite. This very finely divided calcium carbonate, also known as a colloidal dispersion, interacts with calcium sulfonate to form a grease-like viscosity. Such overbased calcium sulfonate greases produced via a two-stage process have become known as "simple calcium sulfonate greases" and are disclosed, for example, in U.S. Pat. Nos. 3,242,079, 3,372,115, 3,376,222, 3,377,283, and 3,492,231.

[0003] Calcium sulfonate (Ca-sulfonate) greases have recently emerged as a potential replacement for lithium greases in many industrial applications. The advantage of calcium sulfonate greases is that they have superior high performance properties over lithium complex greases in areas such as extreme pressure, antiwear, high temperature, rust protection, and water resistance. While calcium sulfonate greases exhibit these superior inherent performance properties, lithium greases require significant additives to match these performance levels.

[0004] Overbased calcium sulfonates were reported in the 1940s, primarily as additives for motor oil corrosion and oxidation prevention. Overbased calcium sulfonates (OBCS) as thickeners for greases were reported in the 1960s and were primarily formulated in conventional mineral oils and / or synthetic base oils such as PAO. These OBCS greases require thickener contents of more than 50% to achieve the desired viscosity, resulting in a shortage of base oils required for lubrication. Such reported greases have low dropping points, limited workability at high temperatures, poor flow in cold climates, and stability problems. As such, the properties of these fully formulated greases were inferior to those of the lithium complex greases that were popular at the time, and they were significantly more expensive, so they did not attract much attention.

[0005] In 1985, Muir et al. (US No. 4,560,489) disclosed a novel process and composition for producing overbased calcium sulfonate complex (OBCSC) based greases, which comprise calcium carbonate colloidally dispersed in the form of crystalline calcite, calcium borate, and a calcium soap of a soap-forming aliphatic monocarboxylic acid containing at least 12 carbon atoms, exemplified as 12-hydroxystearic acid. The grease compositions disclosed in this invention were prepared in mineral oil or a synthetic base oil derived from mineral oil, e.g., PAO. The unique composition and process disclosed in this invention resulted in reduced thickener content due to complexation, high dropping point, extreme pressure, water resistance, and rust inhibition properties. This triggered the widespread use of these (OBCSC) greases in industry, especially in high temperature, high load, water-borne applications. The performance characteristics of this class of OBCSC greases are reported to be superior to the most common lithium complex greases.

[0006] Overbased calcium sulfonate-based greases in the recent past have experienced exponential growth in a wide range of applications (NLGI production survey 2020). A possible reason for the growth of these greases is that the supply of lithium, an essential component in the production of lithium greases, has become unstable due to their ever-increasing use in lithium batteries for electronic devices and electric vehicles. The rising cost of lithium has reduced the price parity between lithium complex greases and calcium sulfonate greases, increasing interest in calcium sulfonate greases. Several recent publications and papers have demonstrated the potential of calcium sulfonate greases as an alternative to lithium greases. Previous studies have also found that changes in the crystal morphology of a grease composition can affect the tribological performance of the composition (Wang et al., Friction 9(5),(2021)). Summary of the Invention

[0007] A high performance overbased calcium sulfonate complex (OBCSC) grease composition prepared without the use of boric acid and without the use of an alcohol-based accelerator has a dispersed portion in the form of crystalline capsules.

[0008] An overbased calcium sulfonate complex grease composition formulated with extreme pressure, antiwear, antioxidants and polymeric additives, which exhibits superior performance in extreme pressure and high temperature environments compared to high performance lithium complex greases and conventional overbased calcium sulfonate complex greases. [Brief description of the drawings]

[0009] [Figure 1] 1 is a graph comparing extreme pressure weld loads of overbased calcium sulfonate complex greases with lithium complex greases and OBCSC greases described herein. [Diagram 2] 1 is a graph comparing extreme pressure Timken OK loads of overbased calcium sulfonate complex greases with lithium complex greases and OBCSC greases described herein. [Diagram 3] 1 is a graph comparing the high temperature life of an overbased calcium sulfonate complex grease with a lithium complex grease and an OBCSC grease. [Figure 4] 1 is a photograph of the crystalline capsule form of the grease described herein. [Diagram 5] Photograph of the crystalline needle morphology of a grease in the art. Description of the Invention

[0010] Described herein are overbased calcium sulfonate complex greases that are prepared without the traditional formulation steps using boric acid and / or the use of alcohol-based accelerators, simplifying the manufacturing process.

[0011] According to one embodiment of the invention, the overbased grease is produced by reacting and mixing certain compounds including: (a) a first overbased material comprising an overbased oil-soluble calcium sulfonate having amorphous calcium carbonate dispersed therein; (b) a suitable base oil in an amount appropriate to provide a final acceptable product viscosity; (c) a stoichiometric excess of finely divided calcium carbonate, as an oil-insoluble solid calcium-containing base, in the presence of a functionalized polymer, which is added to the first overbased material and base oil prior to conversion; and (d) a doping agent in the form of an extreme pressure, antiwear, antioxidant, metal deactivator or polymeric additive, or combinations thereof.

[0012] A further embodiment of the present invention is the presence of a crystalline capsule form in the insoluble portion of the grease composition resulting from the process as described herein. The capsule form in accordance with the invention described herein has a length of 16.4±6.4 nm and a width of 5.7±1.3 nm. The presence of the capsule form in the grease composition described herein is unique and distinguishes it from the state of the art, and has associated beneficial properties over comparative high performance lithium complex greases and conventional overbased calcium sulfonate complex greases in relevant pressure and temperature environments. See Table 2 and Figures 1-3.

[0013] The highly overbased oil-soluble calcium sulfonate used according to the embodiments of the present invention may be any of those typical of those described in the prior art, such as U.S. Pat. Nos. 4,560,489; 5,126,062; 5,308,514; 5,338,467, and EP 2773590 A1. The highly overbased oil-soluble calcium sulfonate may be prepared in situ according to such known methods or may be purchased commercially. Such highly overbased oil-soluble calcium sulfonate has a total base number (TBN) of 200 or more, preferably 300 or more, and most preferably about 400. Commercially available overbased calcium sulfonates of this type include, but are not limited to, Hybase C401 supplied by Chemtura USA Corporation, Syncal OB 400 and Syncal OB405-WO supplied by Kimes Technologies International Corporation, and Lubrizol 75GR, Lubrizol 75NS, Lubrizol 75P and Lubrizol 75WO supplied by Lubrizol Corporation. The amount of highly overbased oil-soluble calcium sulfonate in the final grease according to this embodiment of the invention may vary, but is generally between 10 and 35%. Preferably, the amount of highly overbased oil-soluble calcium sulfonate in the final grease according to this embodiment of the invention is between 18 and 25%.

[0014] Any petroleum-based naphthenic, paraffinic mineral oil or renewable base oil commonly used and well known in the grease manufacturing art can be used as the base oil according to the present invention. Synthetic base oils can also be used in the grease of the present invention. Such synthetic base oils include, but are not limited to, polyalphaolefins (PAOs), diesters, polyol esters, polyethers, alkylated benzenes, alkylated naphthalenes, and silicone oils. Renewable base oils having properties as described in US 11,041,133, which is incorporated herein by reference, are preferred. The total amount of base oil added, including the base oil added initially and any base oil that may be added later in the grease manufacturing process to achieve the desired viscosity, is usually 25% to 80%, preferably 35% to 75%, and most preferably 40% to 70%, based on the final weight of the grease.

[0015] The complexing acid used in this embodiment does not include boric acid, but does include at least one long chain carboxylic acid and may also include short chain carboxylic acids. Long chain carboxylic acids suitable for use according to the present invention include aliphatic carboxylic acids having at least 12 carbon atoms. Most preferably, the long chain carboxylic acid is 12-hydroxystearic acid. The amount of long chain carboxylic acid is 1% to 6%, preferably 1% to 5%, most preferably 2.0% to 3.5%, based on the final weight of the grease.

[0016] As used herein, a "functionalized polymer" is defined as a polymer that acts as a binding medium between the overbased calcium sulfonate complex thickener and the base oil throughout the reaction cycle. Functionalized polymers may include, but are not limited to, those described in US 8,563,488, which is incorporated herein by reference.

[0017] Doping agents, including antioxidants, antiwear agents, metal deactivators, and pressure additives, are typically present in an amount of 0.5-15%, preferably 5-12%, based on the total weight of the grease.

[0018] Method for producing grease composition An embodiment of the invention is described herein for producing a grease composition having the amounts and terminology reflected in Table 1. The overbased natural / synthetic calcium sulfonate is added to the base oil at room temperature along with the sequential addition of calcium hydroxide, calcium carbonate, water, and functionalized polymer to form an initial mixture. The resulting mixture is slowly (<1° C. / min) heated to 45-50° C.

[0019] Once the mixture has reached the aforementioned temperature range, an anionic surfactant is added to form a second mixture. The anionic surfactant is preferably selected from the group consisting of a hydrophilic sulfonate head group and a hydrophobic alkylbenzene tail group. More preferably, the anionic surfactant is an alkylbenzene sulfonic acid. At a temperature below 65°C, 0.25-3.5% acetic acid is gradually added to the second composition to form a third mixture. After a holding time of 15-30 minutes, the temperature of the third mixture is increased to 90±10°C. The entire amount (1.0-4.5 kg) of 12-hydroxystearic acid is added to the heated third mixture to form a fourth mixture, to which an additional amount of water is added.

[0020] The temperature of the fourth mixture is increased to 160±10° C., after which the hydrogenated styrene isoprene polymer is added to form a fifth mixture and mixed at the elevated temperature for 30 to 60 minutes.

[0021] The fifth mixture is cooled to a temperature of 110±10° C. by adding a portion of the finishing base oil to form a sixth mixture, and then the remaining calcium carbonate and tricalcium phosphate are added sequentially to form a seventh mixture. Upon formation of the seventh mixture, the crystalline capsule morphology described herein is presented.

[0022] The remaining additives are added to the seventh mixture at a temperature below 100° C., whereupon the resulting grease composition is milled to the desired specifications. [Table 1]

[0023] Performance data, particularly at extreme pressure and high temperature, was compared to conventional fully formulated lithium complex EP (extreme pressure) and fully formulated calcium sulfonate complex greases (Table 2). The comparative data (Figures 1-3) show superior comparative performance data compared to high performance lithium complex greases and overbased calcium sulfonate complex greases, highlighting the potential synergistic effects of the unique combination of composition, additives and manufacturing process. [Table 2]

Claims

1. 1. A method for producing a high performance overbased calcium sulfonate complex grease composition prepared without the use of boric acid and without the use of alcohol based accelerators, comprising reacting and mixing: (a) a first overbased material comprising an overbased oil-soluble calcium sulfonate having amorphous calcium carbonate dispersed therein; (b) a suitable base oil in an amount suitable to provide a final acceptable product viscosity; (c) a stoichiometric excess of finely divided calcium carbonate, which is added to said first overbased material and base oil as an oil-insoluble solid calcium-containing base prior to conversion in the presence of a functionalized polymer; and (d) a doping agent in the form of an extreme pressure, antiwear, antioxidant, metal deactivator or polymeric additive, or a combination thereof.

2. 10. The method of claim 1, further comprising adding a carboxylic acid selected from the group consisting of long chain carboxylic acids and short chain carboxylic acids between steps (c) and (d).

3. The method of claim 2, wherein the amount of overbased oil-soluble calcium sulfonate is from 10 to 35%.

4. The method of claim 3, wherein said amount of said overbased oil-soluble calcium sulfonate is 18-25%.

5. The method of claim 4, wherein the total loading of base oil is from 25% to 80%.

6. 6. The method of claim 5, wherein the total loading of base oil is from 35% to 75%.

7. 7. The method of claim 6, wherein the total loading of the base oil is from 40% to 70%.

8. The method of claim 5, wherein the amount of long chain carboxylic acid is from 1% to 6%.

9. 9. The method of claim 8, wherein the amount of long chain carboxylic acid is from 2.0% to 3.5%.

10. The method according to claim 8, wherein the amount of doping agent is between 0.5 and 15%.

11. The method of claim 10, wherein the amount of doping agent is between 5 and 12%.

12. 11. The composition of claim 10, wherein the resulting grease composition comprises an insoluble portion in the form of a crystalline capsule.

13. 14. The composition of claim 13, wherein the crystalline capsule form has a length of about 16.4±6.4 nm and a width of about 5.7±1.3 nm.

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