LUBRICANT COMPOSITION CONTAINING ALKALI METAL BORATE AND POLYALKYLENE SUCCINIC ANHYDRIDE

Abstract: A lubricant composition having a base oil of lubricating viscosity, a dispersed hydrated alkali metal borate, and a polyalkylene succinic anhydride or non-nitrogen derivative thereof.

Description: LUBRICANT COMPOSITION CONTAINING ALKALI METAL BORATE AND POLYALKYLENE SUCCINIC ANHYDRIDE The present invention relates to a lubricant composition having improved compatibility and improved water tolerance. BACKGROUND OF THE INVENTION U.S. Patent No. 3,313,727, "Alkali Metal Borate E.P. Lubricants", issued April 11 , 1967, teaches a lubricant composition having a non-polar lubricating oil and minor amounts of sodium borate and a lipophilic surface-active agent (such as alkenyl succinimides of alkylene amines and nitrogen-containing compounds). U.S. Patent No. 3,819,521 , "Lubricant Containing Dispersed Borate and a Polyol," issued June 25, 1974, teaches a lubricant composition having a non- polar lubricating oil and minor amounts of sodium borate, a lipophilic surface- active agent (such as alkenyl succinimides of alkylene amines), and a C 3 -C 6 polyol. U.S. Patent No. 3,853,772, "Lubricant Containing Alkali Metal Borate Dispersed With a Mixture of Dispersants," issued December 10, 1974, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate, an alkaline earth metal sulfonate, and succinimides. On column 9, lines 18-31 , this patent teaches using a pentaerythritol combined either with a polyolefin and maleic anhydride or with a polyolefin and a phosphorus sulfide. U.S. Patent No. 3,912,643, "Lubricant Containing Neutralized Alkali Metal Borates," issued October 10, 1975, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate and a mixture of nitrogen-containing dispersants. U.S. Patent No. 3,997,454, "Lubricant Containing Potassium Borate," issued December 14, 1976, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate and an anti-wear agent. U.S. Patent No. 4,089,790, "Synergistic Combinations of Hydrated Potassium Borate, Antiwear Agents, and Organic Sulfide Antioxidants," issued May 16, 1978, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate, an anti-wear agent, and an oil- soluble antioxidant organic sulfur compound. U.S. Patent No. 4,163,729, "Synergistic Combinations of Hydrated Potassium Borate, Antiwear Agents, and Organic Sulfide Antioxidants," issued August 7, 1979, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate, an anti-wear agent, and an oil- soluble antioxidant organic sulfur compound. U.S. Patent No. 4,263,155, "Lubricant Composition Containing Alkali Metal Borate and Stabilizing Oil-Soluble Acid," issued April 21 ,1981 , teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate and an oil soluble acid. U.S. Patent No. 4,384,967, "Lubricant Composition Containing an Alkali Metal Borate and a Sulfur-Containing Polyhydroxy Compound," issued May 24, 1983, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate and a sulfur-containing polyhydroxy compound. U.S. Patent No. 4,401 ,580, "Lubricant Composition Containing an Alkali Metal Borate and an Ester-Polyol Compound," issued August 30, 1983, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate and a ester-polyol compound. U.S. Patent No. 4,472,288, "Lubricant Composition Containing an Alkali Metal Borate and an Oil-Soluble Amine Salt of a Phosphorous Compound," issued September 18, 1984, teaches a lubricant composition having a lubricating oil base and minor amounts of hydrated alkali metal borate and an oil soluble phosphate and/or monothiophosphate compound. SUMMARY OF THE INVENTION The present invention provides a lubricant composition having improved compatibility, and improved water tolerance. That lubricant composition comprises a base oil of lubricating viscosity, a dispersed hydrated alkali metal borate, and a dispersant that is either a polyalkylene succinic anhydride or a non-nitrogen containing derivative of the polyalkylene succinic anhydride. We have discovered that polyalkylene succinic anhydrides and non-nitrogen containing derivatives of the polyalkylene succinic anhydrides give far superior compatibility than other possible dispersants. Preferably, the dispersed hydrated alkali metal borate is a dispersed hydrated sodium borate. A preferred dispersed hydrated sodium borate has a sodium to boron metal ratio of about 1 :3. Preferably, the hydrated alkali metal borate contains small amounts of a water soluble oxo anion. Only from 0.001 moles to 0.11 moles of water soluble oxo anion should be present per mole of boron atom. This water-soluble oxo anion can include nitrate, sulfate, carbonate, phosphate, pyrophosphate, silicate, aluminate, germanate, stannate, zincate, plumbate, titanate, molybdate, tungstate, vanadate, niobate, tantalate, uranates, or can include the isopolymolybdates and isopolytungstates, or the heteropolymolybdates and heteropolytungstates, or mixtures thereof. Preferably, the dispersant is a polyalkylene succinic anhydride. More preferably, the polyalkylene succinic anhydride is a polyisobutenyi succinic anhydride. Most preferably, the polyalkylene succinic anhydride is a polyisobutenyi succinic anhydride having a number average molecular weight of at least 500, more preferably at least 900. Preferably, the lubricant composition also comprises a detergent, such as a metal sulfonate. A preferred metal sulfonate is a calcium alkyl aromatic sulfonate. A preferred process for making that lubricant composition comprises mixing, under agitation, (1 ) an aqueous solution of boric acid and alkali metal hydroxide, and (2) a diluent oil containing the polyalkylene succinic anhydride-type dispersant (and any metal sulfonate); then heating the mixture to remove the water. DETAILED DESCRIPTION OF THE INVENTION In its broadest aspect, the present invention involves a lubricant composition having improved extreme pressure properties, compatibility, and improved water tolerance.That lubricant composition comprises a base oil of lubricating viscosity, a dispersed hydrated alkali metal borate, and either a polyalkylene succinic anhydride or a non-nitrogen containing derivative of the polyalkylene succinic anhydride. THE DISPERSED HYDRATED ALKALI METAL BORATE Hydrated alkali metal borates are well known in the art. Representative patents disclosing suitable borates and methods of manufacture include: U.S. Patent Nos. 3,313,727; 3,819,521; 3,853,772; 3,907,601 ; 3,997,454; and 4,089,790, the entire disclosures of which are all incorporated herein by reference. The hydrated alkali metal borates can be represented by the following formula: M 2 0»mB 2 O 3 «nH 2 0 where M is sodium or potassium, m is a number from 2.5 to 4.5 (both whole and fractional), and n is a number from 1.0 to 4.8. Preferred are the hydrated sodium borates because we have found that they have improved water tolerance. Most preferred are the hydrated sodium borates having a sodium- to-boron ratio of about 1 :3. The hydrated borate particles generally have a mean particle size of less than 1 micron. The hydrated alkali metal borates will generally comprise about 10 to 75 weight percent, preferably 25 to 50 weight percent, more preferably about 35 to 40 weight percent of the lubricant composition. (Unless otherwise stated, all percentages are in weight percent.) The hydrated alkali metal borate dispersions have been found to be reactive in the presence of water. The presence of water has been found to alter the size, shape, and composition of the dispersed, amorphous borate particles, which have the overall composition MB 3 O 5 »H 2 0, to ultimately produce a number of crystalline borates which have the compositions MB 3 O 5 «3H 2 O, MB 5 O 8 «4H 2 O, M 2 B 5 O 8 (OH)«2H 2 O, M 2 B 4 O 7 «4H 2 0, and the like. These crystals generally separate out from the oil phase to form deposits in the oil, and can damage the elastomer seals in various engine parts and cause leakage. We have also found that sodium borates give better water tolerance and compatibility than potassium borates. Preferably, the hydrated alkali metal borates contain small amounts of a water soluble oxo anion. Only from 0.001 moles to 0.11 moles of water soluble oxo anion should be present per mole of boron atom. This water-soluble oxo anion can include nitrate, sulfate, carbonate, phosphate, pyrophosphate, silicate, aluminate, germanate, stannate, zincate, plumbate, titanate, molybdate, tungstate, vanadate, niobate, tantalate, uranates, or can include the isopolymolybdates and isopolytungstates, or the heteropolymolybdates and heteropolytungstates, or mixtures thereof. The presence of small amounts of water soluble oxo anions in the alkali metal borates is thought to improve the water tolerance of the alkali metal borates by disrupting the crystal structure of the hydrolysis products. This results in a lower tendency to form crystals or in a reduced rate of crystallization. THE POLYALKYLENE SUCCINIC DISPERSANT The dispersant can be a polyalkylene succinic anhydride or a non-nitrogen containing derivative of the polyalkylene succinic anhydride. Preferably, the dispersant is a polyalkylene succinic anhydride. More preferably, the polyalkylene succinic anhydride is a polyisobutenyi succinic anhydride (PIBSA). Most preferably, the polyalkylene succinic anhydride is a polyisobutenyi succinic anhydride having a number average molecular weight of at least 500, more preferably at least 900. The polyalkylene succinic anhydride is the reaction product of a polyalkylene (preferably polyisobutene) with maleic anhydride. One can use conventional polyalkylene, or high methylvinylidene polyalkylene. One can use thermal, chlorination, free radical, acid catalyzed, or any other process. Examples of suitable polyalkylene succinic anhydrides are thermal PIBSA described in U.S. 3,361 ,673; chlorination PIBSA described in U.S. 3,172,892; a mixture of thermal and chlorination PIBSA described in U.S. 3,912,764; high succinic ratio PIBSA described in U.S. 4,234,435; PolyPIBSA described in U.S. 5,112,507 and 5,175,225; high succinic ratio PolyPIBSA described in U.S. 5,565,528 and 5,616,668; free radical PIBSA described in U.S. 5,286,799, 5,319,030, and 5,625,004; PIBSA made from high methylvinylidene polybutene described in U.S. 4,152,499, 5,137,978, and 5,137,980; high succinic ratio PIBSA made from high methylvinylidene polybutene described in EP 355895; terpolymer PIBSA described in U.S. 5,792,729; sulfonic acid PIBSA described in U.S. 5,777,025 and EP 542 380; and purified PIBSA described in U.S. 5,523,417 and EP 602 863. The number average molecular weight of the polyalkylene tail in the polyalkylene succinic anhydride should be from 300 to 5000, preferably at least 500, more preferably at least 900. Preferably, the polyalkylene succinic anhydride comprises from 2 to 40 weight percent, more preferably 10 to 15 weight percent of the weight of the lubricant composition. We have found that polyalkylene succinimides, such as polyisobutenyi succinimides, generally provide poorer water tolerance and compatibility than non-nitrogen containing polyalkylene succinic anhydride, diacids, mono acid salts and diacid salts. THE DETERGENT There are a number of materials that are suitable as detergents for the purpose of this invention. These materials include phenates (high overbased or low overbased), high overbased phenate stearates, phenalates, salicylates, and sulfonates. Preferably, sulfonates are used, such as high overbased sulfonates, low overbased sulfonates, or phenoxy sulfonates. In addition the sulfonic acids themselves can also be used. The term "metal sulfonate" is intended to encompass the salts of sulfonic acids derived from petroleum products. Such acids are well known in the art. They can be obtained by treating petroleum products with sulfuric acid or sulfur trioxide. The acids thus obtained are known as petroleum sulfonic acids and the salts as petroleum sulfonates. Most of the compounds in the petroleum product which become sulfonated contain an oil-solubilizing group. Also included within the meaning of sulfonates are the salts of sulfonic acids of synthetic alkyl aryl compounds. These acids also are prepared by treating an alkyl aryl compound with sulfuric acid or sulfur trioxide. At least one alkyl substituent of the aryl ring is an oil-solubilizing group. The acids thus obtained are known as alkyl aryl sulfonic acids and the salts as alkyl aryl sulfonates. The sulfonates wherein the alkyl is straight-chain are the well-known linear alkyl sulfonates. The acids obtained by sulfonation are converted to the metal salts by neutralizing with a basic reacting alkali or alkaline earth metal compound to yield the Group I or Group II metal sulfonates. Generally, the acids are neutralized with an alkali metal base. Alkaline earth metal salts are obtained from the alkali metal salt by metathesis. Alternatively, the sulfonic acid can be neutralized directly with an alkaline earth metal base. Alternatively, the sulfonic acid can be used directly, instead of the sulfonic acid salt. Preferably, the metal sulfonate is a calcium alkyl aromatic sulfonate and the metal sulfonate comprises from 0 to 20 weight percent, more preferably 2 to 10 weight percent of the lubricant composition. THE OIL OF LUBRICATING VISCOSITY The lubricating oil to which the borates and the dispersant are added can be any hydrocarbon-based lubricating oil or a synthetic base oil stock. The hydrocarbon-based lubricating oils may be derived from synthetic or natural sources and may be paraffinic, naphthetic or asphaltenic base, or mixtures thereof. The diluent oil can be natural or synthetic, and can be different viscosity grades. The lubricating oil comprises from 30 to 70 weight percent, more preferably from 45 to 55 weight percent of the lubricant composition. FORMULATIONS The borate lubricating compositions of the present invention are generally blended at a level of 20-80% with other additives such as ashless dispersants (1-20%), sulfurized hydrocarbons (0-30%), dialkyl hydrogen phosphates (0- 10%), zinc dithiophosphates (0-20%), dialkyl hydrogen phosphites (0-10%), pentaerythritol monooleate (0-10%), 2,5-dimercapto thiadiazole (0-5%), benzotriazole (0-5%), dispersed molybdenum disulfide (0-5%), overbased sulfonates (0-10%), imidazolines (0-10%), and the like. This gear oil package can then be blended at 5-15% level in an oil of lubricating viscosity, along with a polymethacrylate VII at a level of 2-12%, and 0-1 % pour point depressant to form a gear oil finished oil. A variety of other additives can be present in lubricating oils of the present invention. Those additives include antioxidants, viscosity index improvers, rust inhibitors, corrosion inhibitors, other antiwear agents, and a variety of other well-known additives. EXAMPLES The invention will be further illustrated by the following examples, which set forth particularly advantageous method embodiments. While the Examples are provided to illustrate the present invention, they are not intended to limit it. COMPARATIVE EXAMPLE A PREPARATION OF THE LUBRICANT COMPOSITION USING NITROGEN CONTAINING SUCCINIMIDES To a 2-liter beaker were added 272.8 grams of water, 219.6 grams of boric acid (3.55 moles), and 148.3 grams of 45% potassium hydroxide solution (1.19 moles). The potassium hydroxide solution typically contained about 2% potassium carbonate. The alkali metal/boron charge mole ratio was 1 :3. This was heated with stirring until the ingredients dissolved. Then this solution was divided in half and then each half, 594 grams, was added to a mixture of a mono tetraethylenepentamine succinimide made from 950 molecular weight polyisobutylene (PIB) (30.25 grams), and a low overbased calcium alkylbenzene sulfonate (13.15 grams) dissolved in 136.15 grams neutral diluent oil. The dispersant/boric acid weight ratio was 0.276:1 , and the sulfonate/boric acid weight ratio was 0.121 :1. The two solutions was stirred rapidly for thirty minutes using Waring blenders and then poured together into a 2-liter beaker. This solution was then stirred and heated to 270°C under a stream of nitrogen. Then it was allowed to cool. A total of about 561 grams product was produced. This product was found to contain a total base number of 122 mg KOH/g sample, 6.8%K, 5.9%B, 0.24%N, and had a viscosity (vis) at 100°C of 15.9 cSt. The particle size distribution (PSD) was 90% less than 0.42 micron, and 50% less than 0.33 micron. This data is shown in Table 1. COMPARATIVE EXAMPLES B-D PREPARATION OF OTHER LUBRICANT COMPOSITIONS USING DIFFERENT SUCCINIMIDES A number of other examples of lubricant compositions were prepared using different amounts of dispersants and detergents. Comparative example D also used sodium hydroxide instead of potassium hydroxide. The sodium hydroxide typically contained about 0.6% sodium carbonate. These are summarized in Table 1. EXAMPLE 1 PREPARATION OF THE LUBRICANT COMPOSITION USING PIBSA AS THE DISPERSANT To a beaker was add water, boric acid, and potassium hydroxide. The potassium to boron molar ratio was 0.33:1. This was heated until the boric acid dissolved. Then this was slowly added to a vigorously stirred solution of polyisobutenyi succinic anhydride (PIBSA) made from polyisobutene that had 1000 M n and a low overbased calcium alkylbenzene sulfonate , dissolved in neutral diluent oil. This was stirred for one half hour, the mixture was heated with stirring until the temperature increased to 270° F. The excess water was removed with a stream of nitrogen gas during the heating stage. The levels of dispersant and sulfonate, and chemical and physical properties of this product are reported in Table 1. EXAMPLES 2-12 PREPARATION OF OTHER LUBRICANT COMPOSITIONS We have prepared other lubricant compositions using the general procedure of Example 1. Different amounts of polyisobutenyi succinic anhydrides made from different molecular weight polyisobutenes, were used in these preparations. Also in some cases sodium hydroxide was used instead of potassium hydroxide. These are summarized in Table 1 , where M is Metal and PSD is Particle Size Distribution. Table 1. Chemical and Physical Properties of the Borate Dis ersions. COMPATIBILITY TESTING OF THE BORATE LUBRICATING COMPOSITION The compatibility testing of a number of borate lubricating compositions in the absence of water was carried out at 80°C. This was carried out by the following procedure. We first blended the borate lubricating compositions of the present invention at the 3% level into a typical automotive gear oil formulation comprising ashless dispersant, calcium sulfonate, corrosion inhibitor, EP agent, friction modifier, multifunctional additives, metal deactivator, etc. This gear oil formulation was then added at the level of 6.5% to diluent oil to make an 80W90 formulation. This formulation was then placed in an oven at 80°C and inspected on a regular basis. The results are reported in Table 2. Table 2. Compatibility of Borate Lubricating Compositions at 80°C. These results show that the borate lubricating compositions that used the PIBSA gave better performance (less sediment) than the borate lubricating compositions that used the succinimides. WATER TOLERANCE DATA FOR BORATES In order to measure the water tolerance for the borate lubricating compositions of this invention, we ran the following procedure. We first blended the borate lubricating compositions of the present invention at the 3% level into a typical automotive gear oil formulation comprising, ashless dispersant, calcium sulfonate, corrosion inhibitor, EP agent, friction modifier, multifunctional additives, metal deactivator, etc. This gear oil formulation was then added at the level of 6.5% to diluent oil to make an 80W90 formulation. This formulation was then run in a modified L60 test. This test is a standardized test described in the ASTM Special Technical Publication 512A, "Laboratory Performance Tests for Automotive Gear Lubricants Intended for API GL-5 Service STP 512A". This information is available from ASTM, 1916 Race Street, Philadelphia, PA. 19103. We modified the L60 test by omitting the copper coupon, eliminating air bubbling, and plugging the air holes in the gear case assembly. The gear case assembly was charged with 360mL oil, and kept at 297°F for 100 minutes. Then the oil was cooled to 175°F and 3% water was added. Then the gear case assembly was held at 175°F for 12 hours and then the temperature was increased to 275°F. The oil was kept at 275°F for 12 hours, then the oil was drained. After draining the oil, the deposits were collected, measured, and reported in milliliters. The collected deposits were rinsed with hexane to remove the oily part, and then the deposits were measured again and reported in milliliters. The results from the water tolerance testing of a number of borate additives are shown in Table 3. Table 3. Water Tolerance Testing For Borate Lubricating Compositions. The data in Table 3 shows that better water tolerance (lower amount of deposits) was observed when the metal used in the borate lubricating composition was sodium compared to potassium. Additional water tolerance data for the borate lubricating compositions was obtained by the following procedure. We first blended the borate lubricating compositions of the present invention at the 3% level into a typical automotive gear oil formulation comprising, ashless dispersant, calcium sulfonate, corrosion inhibitor, EP agent, friction modifier, multifunctional additives, metal deactivator, etc. This gear oil formulation was then added at the level of 6.5% to diluent oil to make an 80W90 formulation. Then a mixture of the finished oil and 0.5 weight percent water was placed in an oven that was held at a temperature of 60°C. This was inspected for compatibility. The results of this study are shown in Table 4. Table 4. Water Tolerance Results for Borate Lubricating Compositions With 0.5% Water at 60°C. These results show that the borate lubricating compositions that used the PIBSA gave better performance (less sediment) than the borate lubricating compositions that used the succinimides. EXAMPLE 13-19 PREPARATION OF BORATES THAT CONTAIN OXO ANIONS The procedure for Example A was followed exactly except that different amounts (based on boric acid) of different oxo anions were added to the water solution of the boric acid and potassium hydroxide. The chemical and physical properties of these material are shown in Table 5. TABLE 5. Chemical and Physical Properties of Borates That Include Oxo Anions While the present invention has been described with reference to specific embodiments, this application is intended to cover those various changes and substitutions that may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

Claims: What is claimed is: 1. A lubricant composition comprising: (a) a base oil of lubricating viscosity; (b) a dispersed hydrated alkali metal borate; and (c) a dispersant selected from the group consisting of a polyalkylene succinic anhydride and a non-nitrogen containing derivative of said polyalkylene succinic anhydride. 2. A lubricant composition according to Claim 1 wherein said dispersed hydrated alkali metal borate is a dispersed hydrated sodium borate. 3. A lubricant composition according to Claim 2 wherein said dispersed hydrated sodium borate has a sodium to boron metal ratio of about 1 :3. 4. A lubricant composition according to Claim 1 wherein said dispersant is a polyalkylene succinic anhydride. 5. A lubricant composition according to Claim 4 wherein said polyalkylene succinic anhydride is a polyisobutenyi succinic anhydride. 6. A lubricant composition according to Claim 5 wherein said polyisobutenyi group of the polyisobutenyi succinic anhydride has a molecular weight of at least 900. 7. A lubricant composition according to Claim 1 further comprising a metal sulfonate. 8. A lubricant composition according to Claim 7 wherein said metal sulfonate is a calcium alkyl aromatic sulfonate. 9. A lubricant composition according to Claim 1 further comprising a water soluble oxo anion of up to 30% by weight of weight of borate. 10. A lubricant composition according to Claim 9 wherein said soluble oxo anion is selected from the group consisting of nitrate, sulfate, carbonate, phosphate, pyrophosphate, silicate, aluminate, germanate, stannate, zincate, plumbate, titanate, molybdate, tungstate, vanadate, niobate, tantalate, uranate, isopolymolybdate, isopolytungstate, heteropolymolybdate, heteropolytungstates, and mixtures thereof. 11. A process for producing a lubricant composition, said process comprising the steps of: (a) mixing, under agitation: (1 ) an aqueous solution of boric acid and alkali metal hydroxide, and (2) a diluent oil containing a dispersant selected from the group consisting of a polyalkylene succinic anhydride and a non- nitrogen containing derivative of said polyalkylene succinic anhydride; (b) heating said mixture of step (a) to remove water. 12. A lubricant composition produced by the process according to Claim 11.

Inventors: HARRISON JAMES J, HARRISON, JAMES, J.
Applicants: CHEVRON CHEM CO, CHEVRON CHEMICAL COMPANY LLC
Application year: 2000
Main classification: C10M141
IPC codes: C10M125, C10M129, C10M133, C10M135, C10M141, C10M159, C10M169, C10N10, C10N30, C10N40