Patent Application
20110059879
This invention relates to a lubricating grease composition suitable for industrial and automotive uses, and a process for its manufacture. In particular, the invention relates to a premium multipurpose grease composition exhibiting good water resistant properties, high and low temperature performance, and which is suitable for use in both industrial and automotive applications.
In North America and other northern climates, it is desirable for a lubricating grease to exhibit good performance over a wide range of temperatures. In addition, industrial greases often require good performance in wet environments. Testing methods and performance criteria established by the National Lubricating Grease Institute (NLGI) have become industry-wide accepted standards. These standards include greases for use in automotive applications. It is therefore desirable for lubricating grease to meet NLGI grade classification. Preferably, such greases should be multipurpose, being suitable for industrial applications and meet NLGI grade classification for automotive application.
There is a need to improve the water resistance and oxidation life of commercial premium greases that exhibit good high and low temperature performance. There is a further need to provide enhanced life expectancy and better overall performance in wet applications over current lubricants and improved performance in relation to low temperature torque and fretting wear.
In one embodiment, this invention relates to a premium multipurpose lubricating grease suitable for industrial and automotive uses, and a process for making the same. In this embodiment, a lubricating grease is disclosed comprising:
(a) at least one Group I oil;
(b) at least one Group II oil;
(c) a hydrophilic copolymer; and
(d) a soap thickener,
wherein the thickener is dispersed into the at least one Group I oil during a cooking phase and the at least one Group II oil is introduced during a finishing phase.
In a second embodiment, a method for making a lubricating grease is disclosed. The method comprises: obtaining at least one Group I oil, obtaining at least one Group II oil, obtaining a hydrophilic copolymer, obtaining a soap thickener, and mixing the at least one Group I oil, the least one Group II oil, the polymer and the soap thickener to form a grease wherein the thickener is dispersed into the at least one Group I oil during a cooking phase and at least one Group II oil is introduced during a finishing phase.
The present invention will be described in connection with its preferred embodiments. However, to the extent that the following description is specific to a particular embodiment or a particular use of the invention, this is intended to be illustrative only, and is not to be construed as limiting the scope of the invention. On the contrary, it is intended to cover all alternatives, modifications, and equivalents that are included within the spirit and scope of the invention, as embodied by the appended claims.
In one embodiment, we have invented novel greases that are suitable for use in industrial applications, and at the same time meets NLGI grade classification for use in automotive applications. The compositions of the greases and methods of manufacturing the greases are disclosed herein.
Various lubricating oils can be employed in preparing the grease compositions of the present invention. Applicants have found that using oils of a certain type during the cooking phase of the grease preparation, and oils of a different type during the finishing phase achieved a grease with favorable properties. Another embodiment of the present invention is the inclusion of a polymer that imparts excellent water resistance properties without compromising the low temperature performance of the grease. Applicants have found that using a hydrophilic polymer provided favorable properties.
Groups I, II, III, IV and V are broad categories of base oil stocks developed and defined by the American Petroleum Institute (API Publication 1509; www.API.org) to create guidelines for lubricant base oils. Group I base stocks generally have a viscosity index of between about 80 to 120 and contain greater than about 0.03% sulfur and/or less than about 90% saturates. Group II base stocks generally have a viscosity index of between about 80 to 120, and contain less than or equal to about 0.03% sulfur and greater than or equal to about 90% saturates. Group III stock generally has a viscosity index greater than about 120 and contains less than or equal to about 0.03% sulfur and greater than about 90% saturates. Group IV includes polyalphaolefins (PAO). Group V base stocks include base stocks not included in Groups I-IV. Table 1 summarizes properties of each of these five groups.
In a preferred embodiment, the base stocks include at least one base stock of synthetic oils. Synthetic oil for purposes of this application shall include all oils that are not naturally occurring mineral oils.
In general, lubricating oils will typically comprise between 50-90 wt % of the overall grease composition. These oils will typically combine to provide an overall viscosity of the grease in the range of ISO 100 to ISO 320. The preferred viscosity for the present invention is between ISO 150 to ISO 275, with ISO 220 being the most preferred.
Lubricating oils used during the cooking and finishing phases can be either mineral or synthetic. Mineral oils can be any conventionally refined base stocks derived from paraffinic, naphthenic and mixed based crudes. Synthetic lubricating oils that can be used include esters of glycols such as a C13 oxo acid diester of tetraethylene glycol, or complex esters such as one formed from 1 mole of sebacic acid and 2 moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid. Other synthetic oils that can be used include synthetic hydrocarbons such as polyalphaolefins; alkyl benzenes, e.g. alkylate bottoms from the alkylation of benzene with tetrapropylene, or the copolymers of ethylene and propylene; silicon oil, e.g. ethyl phenyl polysiloxanes, methyl polysiloxanes, etc.; polyglycol oils, e.g. those obtained by condensing butyl alcohol with propylene oxide; carbonate esters, e.g. the product of reacting C8 oxo alcohol with ethyl carbonate to form a half ester followed by reaction of the latter with tetraethylene glycol, etc. Other suitable synthetic oils include the polyphenyl esters, e.g. those having from about 3 to 7 ether linages and about 4 to 8 phenyl groups.
The lubricating oils used as the base stock in the cooking phase of the manufacturing process is preferably selected from Group I and Group V oils. These oils will have a preferred viscosity in the range of 200 to 1400 cSt at 40° C., with a range of 200 to 500 cSt at 40° C. being most preferred. A combination of heavy naphthenic oil and a bright stock was preferred as the base stock during the cooking phase, with 5-15 wt % heavy naphthenic oil and 30-40 wt % bright stock being the preferred amounts. The use of Group II oils during the cooking phase should be limited or avoided altogether. Group II oils may be combined with other lubricating oils during the finishing phase. A combination of 5-10 wt % of an ISO 68 Group 1 and 20-30 wt % of an ISO 100 Group II was preferred during the finishing phase. Various other oils in smaller amounts may also be incorporated during the finishing phase.
The grease composition will also contain a thickener dispersed in the lubricating oil during the cooking phase to form a base grease. The thickener will typically comprise between 5% and 15% of the overall grease composition weight. The particular thickener employed is not critical and can vary broadly provided that it is effectively water insoluble. For example, the thickener may be based on aluminum, barium, calcium or lithium soaps, or their complexes. Soap thickeners may be derived from a wide range of animal oils, vegetable oils and greases, as well as the fatty acids derived therefrom. Carbon black, silica, and clays may be used as well as dyes, polyureas and other organic thickeners. Pyrrolidone-based thickeners can also be used. Preferred thickeners are based on lithium soap, calcium soap, their complexes, or mixtures thereof. Particularly preferred is a lithium or lithium complex thickener derived from reacting a C-18 fatty acid (12-hydroxy stearic acid) and a C-9 dicarboxylic acid (azelaic acid) with lithium hydroxide monohydrate. Canadian Patent 996537 provides a process for making this preferred thickener. Canadian Patent 996537 is hereby incorporated by reference.
In one inventive embodiment, during the cooking phase of a preferred embodiment of the grease preparation, a mixture of Group I and Group V oils and a lithium soap of a C12 to C24 hydroxy fatty acid is first prepared. Then a C2 to C12 aliphatic carboxylic acid is added to that mixture and converted to its dilithium soap under conditions that are suitable for the formation of a complex between the lithium soap of the dicarboxylic acid and the lithium soap of the hydroxy fatty acid. While the lithium soap of the hydroxy fatty acid could be preformed and then dispersed in the lubricating oil medium, it is generally more expedient to prepare that soap in situ in the lubricating oil by neutralizing the hydroxy fatty acid with lithium base. The usual procedure during the cooking phase is to charge into the grease kettle the Group I and Group V oils and to then add the hydroxy fatty acid. The mixture of fatty acid and oil is heated sufficiently to bring about the dissolving action, e.g. at about 180 to 200° F. Then a concentrated aqueous solution of the lithium base is added, usually in an amount slightly in excess of that required to neutralize the acid. The temperature at this stage of the cooking phase is usually between 200 and 210° F. The rate of addition of the lithium base may be varied. It is possible at this stage to proceed with the addition of the dicarboxylic acid and its subsequent neutralization to its dilithium soap, but this will require the neutraliztion to be conducted slowly or stepwise so as to ensure complexing of the two soaps with each other before the complete neutralization of the dicarboxylic acid has been brought about.
Accordingly, before proceeding with the addition of dicarboxylic acid and conversion to its dilithium soap, it is preferred that the temperature of the mixture of the Group I and Group V oils and lithium soap of the hydroxy fatty acid be raised to between 250 and 300° F. This is done in order to bring about a substantial dehydration of the mixture, such as, the removal of 70 to 100% of the water. As noted in Canadian Patent 996537, substantial dehydration at this stage also promotes the subsequent complexing reaction during the neutralization of the dicarboxylic acid. After substantial dehydration has been brought about, the mixture is cooled to between 230 and 240° F. and the dicarboxylic acid is added to the mixture. The mixture is stirred in order to bring about proper dispersion of the acid throughout the mixture and the concentrated aqueous solution of lithium base is then added to convert the dicarboxylic acid to its dilithium soap. Similarly with the neutralization of the fatty acid, the amount of lithium base added at this stage is slightly in excess of the amount required to neutralize both acid groups of the dicarboxylic acid. The temperature during this stage should be maintained between 210 and 230° F., and preferably between 220 to 230° F.
After all of the lithium base has been added to complete the neutralization of the dicarboxylic acid, the temperature of the grease mixture is once again raised in order to bring about dehydration. Usually this will take place at about 280 to 300° F. Following dehydration of the mixture, in order to ensure optimal thickener dispersion, the temperature of the mixture should further be raised to between 380 and 400° F. The soap stock is then cooled during the finishing phase of the grease preparation. Finishing oils, including Group II oils and various other lubricating oils, may be added into the mixture at this point. Mixing may continue until the grease has reached ambient temperatures. When the temperature has been lowered to about 150° F., other grease additives can be introduced as would be understood by persons skilled in the art.
As mentioned previously, one embodiment contemplates the inclusion of a polymer. Various polymers may be used in greases, although the precise impact of any given polymer on a given grease cannot be predicted. Applicants have found that the use of a hydrophilic copolymer was important in achieving excellent water resistance properties. In a preferred embodiment of the present invention, maleic anhydride styrene esterified copolymer is used, with the preferred amount being between 2 and 6 wt % of the overall grease. The polymer may be incorporated during either the cooking phase or finishing phase of the grease preparation.
The preferred styrene maleic anhydride ester (SMAE) copolymer is unique from other polymer examples because it contains oxygen groups. The structure of the SMAE copolymer (shown below) has exposed hydroxyl and carbonyl groups that can act as hydrogen bond donors (former) and acceptors (latter). As a result, the SMAE copolymer is more hydrophilic than strictly hydrocarbon-based copolymers such as styrene isoprene and styrene isobutylene.
Equation 1 shows the chemical structure of the SMA ester and the esterification of styrene maleic anhydride copolymer to form a SMA ester and the resulting chemical structure of the SMA ester. The grease structure is a type of soap. The ability of the soap to dissolve in waters varies. Preferably, the grease soap should not readily dissociate in contact with water.
The grease soap structure is held together with a variety of bonds, including ionic bonds with the metal, hydrogen bonds within the oxygen-rich triglyceride and the ester function of 12-hydroxy stearic acid (once incorporated into the structure) and van der Waals interactions between the C—C side chains. When a grease is exposed to water, bond networks may be disrupted and the grease's structural stability may be compromised. This can result in poor performance in water resistance tests.
A polymer that incorporates or binds water molecules into its structure may enhance the water resistance performance of a grease. Hydrogen bonding capability present in certain copolymers. For example, SMAE can improve their ability to incorporate or bind water molecules into their respective structures. The water resistance performance of a grease may be improved where the copolymer provides preferential binding of the water, such as, the attraction of water to the copolymer, through hydrogen bonding, is stronger than the attraction of water to the grease structure.
The grease may also contain small amounts of supplemental additives, which include antioxidants, anti-wear agents and other additives. Specific antioxidants employed are not critical and can vary broadly to achieve favorable properties. A combination of a Group II oil and diphenylamine antioxidant was found to enhance the oxidation life of the grease, while achieving good high temperature performance. Antioxidants will typically comprise less than 5 wt % of the overall grease composition. The total amount of all additives, including the antioxidant, will typically be between 2-10 wt % of the overall grease. A person skilled in the art will recognize the benefits of adding specific additives to the grease disclosed herein to achieve favorable properties.
This invention will be further understood by reference to the following tables and examples, which describes the preferred embodiment of the “Invention”.
The examples in table 2 below disclose various screening tests for the influence of the base oils and thickener on overall grease performance. The grease performance tests include water spray-off, low temperature torque, fretting wear and wheel bearing life.
The results in Table 2 demonstrate that changes to the oils in either the cooking phase or the finishing phase will not yield a grease meeting all of the necessary NLGI performance criteria for automotive use.
Table 3 discloses screening test for the influence of the polymer selection and concentration on overall grease performance. These tests includes water spray-off, wet roll, water washout, low temperature torque, fretting wear, wheel bearing life and apparent viscosity.
The results in Table 3 demonstrate that using 3 wt % Polymer A or maleic anhydride styrene ester copolymer exhibits excellent water resistance performance and also meets the other key performance parameters.
Table 4 discloses screening tests for the influence of various antioxidants on grease performance for wheel bearing life. The results of Table 4 demonstrate that a combination of an ISO 100 Group II base oil and a diphenylamine antioxidant achieved good high temperature performance and oxidation life.
Non Provisional Application based on U.S. Ser. No. 61/200,965 filed Dec. 5, 2008.
| Number | Date | Country | |
|---|---|---|---|
| 61200965 | Dec 2008 | US |
