US3753906A - Grease thickened with synergistic proportions of bentonite clay and polyethylene - Google Patents

Abstract

GREASE THICKNESS WITH SYNERGISTIC PROPORTIONS OF BENTONITE CLAY HAVING 30-40 CARBON ATOMS AND POLYETHYLENE HAVING A MOLECULAR WEIGHT OF 10,000-30,000 AND CONTAINS SMALL AMOUNTS OF ALKALI METAL NITRITE AND AROMATIC AMINE SELECTED FROM DIPHENYLAMINE, N-OLEYTRIMETHYLENE DIAMINE, AND MIXTURES THEREOF.

Description

United States Patent Office 3,753,996 Patented Aug. 21, 1973 US. Cl. 252-28 4 Claims ABSTRACT OF THE DISCLOSURE Grease thickened with synergistic proportions of bentonite clay having 30-40 carbon atoms and polyethylene having a molecular weight of l0,000-30,00(l and contains small amounts of alkali metal nitrite and aromatic amine selected from diphenylamine, N-oleyltrimethylene diamine, and mixtures thereof.

This invention concerns a novel non-soap thickened brake cylinder lubricant having improved physical properties.

More particularly, this invention concerns lubricants prepared by thickening oils of lubricating viscosities with a critical ratio of polyethylene to a bentonite basic complex containing 30 to 40 carbon atoms.

Technical background of invention The lubrication of brake cylinders, such as railroad brake cylinders, presents special problems. Not only must lubrication be assured, but the composition of the grease must be such that it will not cause swelling of the natural rubber packing cups which have been found to be superior to other types of grease containers. The mineral oil used in the greases must be a compromise insofar as viscosity is concerned. For instance, a high viscosity oil reduces the swelling support on the rubber cups while a low viscosity oil gives better lubrication at low temperatures.

Another difiieulty has been the different types of materials to be lubricated. For example, some of the parts have metal-to-metal contact which formerly required two (2) sets of lubricants, oil based for the piston rings and dry graphite for the slide and graduating valves. However, here problems were encountered for, when suflicient oil was supplied to the piston rings, some reached the slide valve and formed an undesirable gum which not only failed to provide lubrication but formed a gum that caused excess friction.

It has been found that proper oil will lubricate the slide, the graduating valves as well as the rings if it possesses the following requirements:

(1) It must resist aging since it is current practice to have cleaning periods only at relatively prolonged intervals,

(2) It must resist oxidation catalyzed by the brass alloys used in slide valves,

(3) The oil must further be free from impurities such as grit, gum, dissolved solids and water,

(4) It must prevent the washing action when the lubricant is subjected to large amounts of moisture normally encountered under operational conditions. This mixture eventually removes the valve oil from the piston, accelerating corrosion, permitting lead oxide to form in the piston ring groove which may cause binding of the rings.

Until recently these stringent conditions were achieved by the use of a lime (calcium soap based) grease. However, in 1966 the Association of American Railroads (AAR) issued a revised version of their specification which increased their requirements as to low temperature operation, minimal rubber swelling, water tolerance, oxidation resistance and rust resistance. Unfortunately, none of the commercially avialable greases satisfied these more demanding standards for brake cylinder lubricant. The older calcium soap based greases proved to be not fully satisfactory, and revisions of these formulations did not achieve the desired result. In view of the failings of soap based (particularly calcium soap based) greases, work was understaken to develop non-soap thickened lubricants which would meet the latest AAR standards for brake cylinder lubricants and for applications outside the railroad industry which require some or all of the above-mentioned characteristics.

It is an object of this invention to provide a novel process for preparing what is believed to be novel grease composition especially developed for the specific lubrication needs of brake cylinder lubricants. These greases combine several stringest requirements necessary for AAR standards, including good low temperature properties, minimal swelling of the rubber grease cups, high water tolerance, oxidation resistance compared to the closest known prior art lubricant.

These objects among others are achieved by:

(l) the preparation of a non-soap thickened grease containing as thickeners a critical ratio of bentonites (complexed with 30 to 40 carbon containing organic bases) to polyethylene thickener (2) a critical concentration of the bentonite in the finished cylinder lubricant, and

(3) by using a specific and critical sequence of adding the thickeners used in the preparation of the grease.

In the favored practice each 100 parts by weight of finished grease is prepared by admixing in a suitable container provided with stirring, heating, circulating, shearing and cooling means, the following components used in the quantities and sequence described below:

(1) To the above container is charged at least 20% of the to parts by weight of mineral oil ultimately employed and from 1 to 2 parts by weight of water (2) To the stirred oil and water mixture is added from about 5.5 to 10 parts by weight of a bentonite clay (complexed with a nitrogeneous base containing from about 30 to 40 carbon atoms), until a homogeneous dispersion of bentonite, water and oil is formed.

(3) At this time the dispersion is heated to about F. while adding a small portion of the mineral oil component to keep the mixture in the proper consistency.

(4) Then 1 to 2 parts by weight of polyethylene is added to the stirred dispersion while keeping temperature between 280 F. and 350 F. until most of the polyethylene has dissolved or is at least softened. During this time the batch temperature is kept within the above range and the mixture is circulated 1 and sheared in the usual manner until a homogenous grease is obtained.

(5) When the polyethylene in the sheared batch has completely dissolved or softened, the temperature is cut back to about 140-200" F. and any optional additives required are added at this time, including 1 to 2 parts by weight of water and the remaining oil. During this step stirring is continued and the grease milled to the desired consistency.

In the preferred practice each 100 parts by weight of finished grease is prepared by admixing in the above-noted 1 Dispersion is commonly achieved in continuous operations by constantly circulating and shearing.

type of container the following components in the amount designated below:

(1) At least 30% of the 80 to 90 parts by weight of the mineral oil ultimately employed is charged to abovementioned container along with l to 2 parts by weight of water and vigorously stirred,

(2) From 6.5 to 8 parts by weight of bentonite clay amine complex containing 32-36 carbon atoms, until a homogenous dispersion of clay, water and oil is obtained.

(3) Then heating the dispersion to about 155 -165 F. while slowly adding suflicient mineral oil to the stirred dispersion, to keep the mixture in proper consistency.

(4) At this point from 1 to 2 parts by weight of polyethylene is added to the stirred batch allowing the temperature to rise to 300 to 320 F. and maintaining said temperature between said range until the polyethylene has substantially dissolved or softened. Again the mixture is circulated and sheared to a uniform consistency.

(5) When the polyethylene has been completely dispersed, the heat is cut back between 160 'F. to 180 F. and from 1.5 to 2.0 parts by weight of a sodium nitrite dispersion in oil, from 0.5 to 0.75 part by weight of arcmatic amine, from 1 to 2 parts by weight of water as well as the remaining oil are added and the homogeneous grease is milled to the desired consistency.

In order to supplement the instant disclosure, the following additional information is submitted.

(A) Mineral oils of lubricating viscosities-The lubricating oils which are the major component of the invention non-soap thickened brake cylinder oils are selected from paratlinic, napthenic, asphaltic or blends of one or more of these having a viscosity ranging from about Saybolt Universal Viscosities (SUS) of about 100 SUS to about 1000 SUS at 100 F. The viscosity index of the oil or oils can vary from below to about 100 and higher. As indicated earlier, the oil component(s) can comprise between 80 and 90 parts by weight based upon the weight of the finished grease composition. Preferably 85 to 90 parts by weight of oil per 100 parts by weight of the finished grease is employed. While the particular oil employed will depend upon the characteristics of the finished grease, the favored oils are those paraflinic distillate oils having a SUS range of from 325 to 350 at 100 F.

(B) Organophilic bentonites are the name applied to a class of thickeners resulting from cation exchange between organic basis and bentonite or its clay mineral component, montmorillonite. Montmorillonite is a hydrous magnesium silicate of an exceptionally small particle size. Use of organic basis such as quaternary ammonium salts of relatively short alkyl moieties give rise to clay complexes with slight organophilic properties and retention of a large part of the original hydrophilic propertiesuse of a slightly larger base such as a quaternary ammonium salt containing two longer alkyl chains each, 16 to 18 carbon atoms each, gives a. completely organophilic bentonite thickener. The applicants have found that bentonites resulting from the cation exchange of bentonite clay with a quaternary ammonium salt such as the chloride containing 30 to 40 carbon atoms in the alkyl chains give rise to a class of grease thickeners, especially when combined with from about one third /3) to one sixth A) of a medium density polyethylene to be described latter. That is, in the preferred embodiment, when a major amount of mineral oil and ratios of bentonite base complexes ranging from 6.5 parts by weight to 8 parts by weight of the clay complex are combined with 1 to 2 parts by weight of polyethylene, the resultant thickened grease has unusually good properties not obtainable using either thickener alone. The preferred bentonite is that bentonite thickener made by complexing finely particulated montmorillonite in aqueous media with dimethyldioctadecyl ammonium chloride using the techniques described in US. Pats. 2,531,427 and 2,531,440. This product can also be purchased under the 4 coined name "Bentone 34 from the Baroid Sales Division of National Lead.

(C) Water dispersant-Ordinarily, 0.25 to 3 parts by weight of water are required for optimum results.

(D) Polyethylene-The polyethylene used as co-thickener in the instant case is a medium density polyethylene having an average molecular weight ranging from about 10,000 to 30,000 or more. These polyethylenes have characteristics as follows:

Softening point P" 220-230 Viscosity at 266 F 1X 10 Tensile strength, p.s.i.g 1.800 Elongation, percent 550 Yield, p.s.i 1.475

The use of polyethylene to thicken mineral oil to grease consistency is old, as is the combination per se of bentonite complexes with polyethylene (US. Pat. 2,704,27 6). However, applicants have found that three difierent factors differentiate the patentees invention from applicants in vention. They are:

(l) A diiferent sequential addition of the two thickeners.

That is, applicants add the bentonite complex first, disperse it in oil, and then add the polyethylene to the mixture.

(2) The applicants use a basic bentonite complex containing from 30 to 40 atoms (preferably 34 carbon atoms), rather than a basic bentonite complex containing 10 to 20 atoms (3) The applicant was found that when the two thickeners are used in order to pass AAR specification the amount of bentonite in the final grease must not exceed 8% by weight and preferably ranges from about 6.5 to about 8% by weight.

(4) When the basic bentonite complex is used alone (as opposed to using both thickeners together), from 8 to 10 milling passes were required to reduce the concentration of bentonite to a level which enables it to meet both the hardness (penetration) requirements and water stability requirements of the revised AAR specification.

(5) When both thickeners are used together, a bentonite to polyethylene ratio varying between about 3:1 to 6:1 is required to avoid excessive hardening in the Water Stability Test.

(6) Applicants use a small quantity of water as dispersant while the patent uses methanol.

(E) Optional additives-The term additives as used throughout this disclosure is used to describe materials added to the lubricant to impart or enhance desirable properties or to eliminate or minimize deleterious properties. These materials can be of diverse chemical structure and include oxidation inhibitors, EP agents, wear prevention agents, stringiness inhibitors, dropping point improvers, tackiness agents and in the instant formulations, rust inhibitors. When additives are employed, they seldom exceed 1 0% by weight of the finished grease and are added at the expense of the lubricating oil component. In order to meet AAR specifications, an aromatic amine such as diphenylamine, N-oleyltrimethylene diamine or mixtures therein and alkali metal nitriles are added to the grease composition in a ratio ranging from 2 to 5 parts by weight of alkali metal nitrite (particularly sodium nitrite) per part by weight of aromatic amine.

(F) Preferred brake cylinder lubricant composition comprises:

-90 parts by weight of mineral oil,

6.5-8 parts by Weight of a bentonite clay complexed with a quaternary ammonium salt such as dimethyldioctadecyl ammonium chloride whose characteristics are described under (B), column 3, of this application,

2 This product has the following characteristics Color, very light cream form, finely divided powder; specific gravity, 1.80: apparent density, 3.5 lb. 1 gallon; fineness, less than 5% retained on #200 sieve.

1 to 2 parts by weight of medium density polyethylene having an average molecular weight between 10,000 and 30,000, and 0.5 to 2.0 parts by weight of water,

1.5 to 2.0 parts by weight of alkali metal nitrite, particularly sodium nitrite,

.5 to 0.75 part by weight of aromatic amine such as diphenylamine, N-oleyltrimethylene diamine or mixtures thereof.

(G) Preferred preparative process:

(1) A charge comprising from 30 to 35% by weight of a parafi'inic distillate oil and at least 1-2 parts by we1ght of water and 6.5-8 parts by weight of a bentonite nitrogenous complex containing 30 to 40 carbon atoms are stirred, circulated and sheared and heated to 160-180 F. until smooth (no lumps).

(2) Add all of the polyethylene into the vigorously stirred mixture of oil and bentonite complex.

(3) Heat the stirred batch containing oil, bentonite complex water and polyethylene between 300-320 F. for at least 30 minutes until the polyethylene is substantially dissolved or dispersed.

(4) Add slowly from 40 to 50 parts by weight of the paraflinic distillate of (1) over a period of 45 to 120 minutes. At this time, circulation and shearing are used to assure uniformity.

(5) Maintain the batch at 300-320 F. for at least of an hour to 2 hours with circulating shearlng and vigorous stirring to assure freedom from lumps of polyethylene.

(6) Cool batch to 160-180 F. while adding the rust inhibitor combination of alkali metal nitrite and adding from 0.5 to 2 parts by weight of water and the remaining oil.

(7) Stir and circulate the batch with shearing at 160 to 180 F.

(8) Mill the batch to the desired penetration range of 275-285 and allow to cool for removal and future use.

In order to disclose specific embodiments both satisfactory and unsatisfactory, the following illustrative embodiments are submitted.

EXAMPLE 1 Preparation of a suitable brake cylinder lubricant in plant size batches using the inventive process To an appropriate sized kettle equipped with heating, cooling, stirring, circulating means and shearing means is charged 407 gals. (2971 lbs.) of parafiinic distillate oil and 22 gals. (185 lbs.) of water. Stirring is started and an additional 266 gals. (1942 lbs.) of the oil is added while adding 924 lbs. of a commercial bentonite clay complexed with dimethyldioctadecyl ammonium chloride prepared as described in US. Pat. 2,531,427. The batch is heated to 160-180 F. and circulation is commenced using the grease circulation pump. At the same time the batch is sheared using 60 p.s.i.g. pressure. The stirring, circulating and shearing (60 p.s.i.g.) is continued until the batch is smooth without lumps. The circulation of the batch is discontinued and 216 lbs. of polyethylene resin 4 is added while the stirred batch is heated to 300- 320 F. At 300320 F. an additional 700 gals. (5108 lbs.) of the paraffin distillate oil is added at a rate of about 5.5 gal/minute (40 lb./min.) and circulating and shearing the batch at 60 p.s.i.g.-back pressure is resumed. The batch is maintained at 300-320 F. with circulation and shearing for 1 /2 hours to ensure the dis- Whose physical characteristics are as follows: API gravity, 29.3; flash, COC, 450 F.; pour point, 5 F.; viscosity $211602)? 342 SUS; viscosity at 210 F., 54.3 SUS; viscosity 4 Having the following characteristics: softening point (ASTM-ZS), 229 F.; hardness (ASlM-D1321, 100 g./5 see/77 R; acid number, 16; specific gravity at 75 F., 0.94; specific gravity at 245 F., 0.81; viscosity at 284 F. (cps), 160; viscosity at 248 F. (cps), 300.

solution and dispersion of the polyethylene. At the end of this time, the kettle is cooled by circulating cool oil through the jacket. The batch is cooled to 160l8 0 F. and 600 lbs. of a dispersion of 198 lbs. of sodium nitrite in 402 lbs. mineral oil base, described in the footnote 3, col. 5, as well as lbs. of a residuum oil, 60 lbs. of diphenylamine and 7 gals. of water are added. At the end of this time, the batch containing all the additives is stirred, circulated, sheared for an additional 30 minutes and milled to specification.

EXAMPLE 2 Preparation of an unsatisfactory brake cylinder lubricant caused by reversing the sequence of addition of bentonite and polyethylene thickeners to the lubricating oil base As indicated by the procedure of Example 1, the order of addition of the two thickeners is to incorporate the bentonite complex into the mineral oil using water as dispersant; then the polyethylene is dissolved at 300- 320 F. and the oil-thickener mixture is cooled at 180 F. to incorporate additives and milled to finish.

In this example, although the components and the proportions of Example 1 were the same, the sequence of addition of the thickeners is reversed as in US. Pat. 2,704,276, the process being as follows:

The polyethylene was dissolved into the oil at 300- 320 F. and the batch cooled to -180 F. At this time the bentonite complex was added using water as a dis persant and the additives (diphenylamine and sodium nitrite) were incorporated into the mixture and the grease milled to finish. As the data of Table I which follows indicate, although the same proportions of the components were used, worked penetration, water stability (AARM-91469) and yield were poorer when the reverse sequence of adding the thickener is used and additional bentonite complex had to be added. These deficiencies establish the criticality of the sequence of thickeners over the process of US. Pat. 2,704,276.

TABLE I I Brake cylinder lubricant of Example 2 at- Nor- Revers- AAR s e Manufacturing procedure mai 1 ed 1 M-QlE-EQ Composition, percent weight (calculated):

1 Bentone 34 dispersed in oil first, then polyethylene dissolved in batch. l Polyethylene dissolved in oil first, then Bentone 34 dispersed in batch.

Positive change indicates softening, negative indicates hardening.

EXAMPLES 3 TO 8 Preparation of brake cylinder lubricants containing bentonite showing the need for polyethylene as a cothickener In these examples a kettle similar to the one utilized in Example 1 is employed as well as the same components (oil, etc.), their properties and the sequence of addition of all the components. The only difierence of substance is that the polyethylene co-thickener is omitted in two batches (Examples 3 and 4) and varying ratios of ben- As the preceding disclosure and several examples indicate, the process of this invention is both advantageous and novel and produces unexpected results. In addition, the resultant grease compositions meet the recently retonite to polyethylene ranging from 1:1 to 4.25:1 are 5 vised AAR specification for brake cylinder lubricants esshown. tablished in 1969.

As the data of Table 'II establish, a range of from about Quite unexpectedly, it has been found that the process 6% by weight up to not exceeding 8% by weight of benof US. Pat. 2,704,276 which discloses a similar type of tonite is critical to meeting water stability requirements lubricant except for the much lower molecular weights of the AAR specifications as manifested by changes in 10 of the bentonite amine complexes, discloses a preparative worked penetration in the Water Stability Test. process which, as shown in Example 2, produces a grease Similarly Table II establishes that the presence of polyinferior in several characteristics required to meet the ethylene within the ratios of bentonite disclosed supra is newly revised AAR specification. Inasmuch as the most essential to keep milling requirements to a minimum of substantial process difference in the two processes is in one (1). Examples 3 and 4, wherein polyethylene is abthe sequence of adding the two thickeners (applicants add sent from the formulation, requn'e 5 and 10 milling passes the bentonite complex, then the polyethylene, while the to meet specifications of hardness. Since multi-millpatentee teaches the reverse order of sequence), the remg passes ralse the cost of preparing the inventive greases sults are both unobvious and unexpected. Further, the unduly, Examples 3 and 4 would not be practical in the addition of polyethylene co-thickener produced a surprising commercial manufacture of greases. reduction of millings from several to one milling.

TABLE 11 Example- 3 4 l5 6 7 8 AAR spee- Composition, percent by weight:

Bentone s4 7.90 9.00 0.0 0.00 7.05

Polyethylenm. 6.0 1.65 1.80

Paraflinio oil or Example 1--. 88.74 87.00 at. 50 09.25 88.05

Water 1.s0 2.00 1.50 0.50 0.50

Diphenylamine 0. 50 0.50 0.50 0.50 0.50 T sodium nitrite 1.50 1.50 1.50 1.50 1.50

Milling passes .'.1;. r; 10 5 1 1 1 Worked penetration at 77 F- 290 300 320 280 296 Apparent viscosity at 40 F 20 sec poises, 9,500 19,700 33,000 21,300 24,000 100sec.- ,poises------ 3,050 10,500 17,500 10,500 10, 000 Oil separation None None None None None Bomb oxidation, pressure drop, p.s.i. at

100 hours. 5 5, 8 Oil swell test ratio, percent swelling in grease/AS'IM #2 oil 0.98 0.06 0.96

Water stability test: 1

Penetration of grease/water after working 100,000 strokes .2 302 273 277 303 304 273 533x322; Changefrom tiostroke penetrationrange- +12 27 -43 +9 +8 +5 -10-+30 1 Maximum. 1 Test described in AAR M-914-69.

EXAMPLES 9 AND 10 In addition to the above advantages, the subject in- Further examples of the inventive lubricating composition ventmn f l m that i q using lower and higher bentonite to polyethylene ratios changes and modxficanons may be made m the Invention without departing from the inventive concept. The true Using the procedure, apparatus and components of Example l, two more brake cylinder lubricant compositions are prepared using in one instance 7.5 parts by weight of bentonite and 2.5 (3:1 ratio) parts by weight of polyethylene, and in the other composition employing 8 parts by weight of bentonite with 1.32 parts by weight of polyethylene (6:1 ratio). In both instances AAR specifications are met and the change in bentonite and polyethylene composition is compensated for at the expense of the mineral oil component.

EXAMPLES 11 TO 12 Further examples of the inventive brake cylinder lubricant compositions using a lower and higher bentonite complex In these two examples the procedure, apparatus, components and preparations of Example 1 are followed exactly except that bentonite is in one instance complexed with base containing 40 carbon atoms 5 while in the other case the complexing amine contains 30 carbon atoms. The resulting lubricants were comparable in their physical characteristics to the grease produced in Example 1.

This preparation is based upon a. slight modification 0! the process disclosed in U.S. 2,531,427.

metes and bounds of the inventive process can best be seen by a perusal of the specification in light of the claims which follow.

What is claimed is:

1. A process for producing homogeneous brake cylinder, mineral oil based grease containing a small quantity of water having improved characteristics comprising the steps of:

(a) contacting at least 20% of the to parts by weight of the mineral oil employed in the finished grease with from about 1 to 2 parts by weight of water in the finished grease and admixing said oilwater mixture with from 5.5 to 10 parts by weight of bentonite clay complex containing 30 to 40 carbon atoms until a homogenous mixture is obtained,

(b) heating and stirring said admixture of oil-water and bentonite complex to about to F., and

(0) adding from 1 to 2 parts by weight of a polyethylene having a molecular range of from about 10,000 to 30,000, said polyethylene concentration being based upon the finished grease,

(d) raising the temperature of the stirred polyethylene containing admixture to about 300-320 F. until the polyethylene is uniformly dispersed,

(e) cooling the batch to about 160-l80 F. and adding any optional additives and the residuum of the oil, and l to 2 parts by weight of water,

(f) shearing and milling the resultant grease to the desired consistency and hardness.

2. The process of claim 1 wherein the additives added 5 are an aromatic amine selected from the group consisting of diphenylamine, N-oleyltrimethylene diamine, and mixtures thereof and alkali metal nitrite.

3. The process of claim 2 wherein the bentonite is a complex of dimethyldioctadecylammonium chloride.

4. The process of claim 3 wherein the bentonite complex to polyethylene is within the ratio of 3:1 to 6:1.

1 0 References Cited UNITED STATES PATENTS 3/1955 McCarthy et a1. 25228 3/1969 Gimmaria 25228 US. Cl. X.R. 25259