Title:
LUBRICATING COMPOSITIONS
United States Patent 3772196


Abstract:
Lubricating oil compositions for internal combustion engines having unexpectedly wide temperature operating characteristics, contain a combination of 2-block copolymer comprising a first polymer block of an alkenyl arene, e.g., styrene and a second essentially completely hydrogenated polymer block of isoprene and certain pour point depressants in a lubricant base stock having a viscosity index of at least 85. The compositions have excellent shear stability and can be formulated to pass a number of the ASTM and SAE engine oil performance and engine service classifications.



Inventors:
Clair St., David J. (Bethalto, IL)
Evans, Donald D. (Burlington, Ontario, CA)
Application Number:
05/204668
Publication Date:
11/13/1973
Filing Date:
12/03/1971
Assignee:
SHELL OIL CO,US
Primary Class:
Other Classes:
508/591, 585/3, 585/12, 585/13
International Classes:
C10M169/04; C08F8/00; C08F8/04; C08L53/02; C10M157/00; C10M157/04; C10N20/02; C10N20/04; C10N30/00; C10N30/02; C10N40/25; (IPC1-7): C10M1/48; C10M1/16
Field of Search:
252/32
View Patent Images:
US Patent References:
3554911N/A1971-01-12Schiff et al.
3438897ENGINE LUBRICATING COMPOSITIONS1969-04-15Henderson
2889282Lubricating oil compositions1959-06-02Lorensen et al.



Foreign References:
GB769281A
Primary Examiner:
Garvin, Patrick P.
Assistant Examiner:
Metz, Andrew H.
Claims:
We claim as our invention

1. A lubricating oil composition comprising

2. a single polymer block A, at least about 75 percent of which is condensed alkenyl arene units, no more than about 5 percent of the aromatic unsaturation being reduced by hydrogenation, said block A having an average molecular weight between about 10,000 and 55,000;

3. a single hydrogenated polymer block B, said block, prior to hydrogenation, being a polyisoprene block; at least about 95 percent of the olefinic unsaturation of block B being reduced by hydrogenation; said block B having an average molecular weight between about 20,000 and about 100,000; the weight ratio of block A to block B being between about 0.45:1 and about 0.8:1; any remaining blocks in the block copolymer having a total average molecular weight not exceeding about 7,500, being selected from alkenyl arene polymer blocks and conjugated diene polymer blocks each having the monomer identity and hydrogenation limitations recited for blocks A and B.

4. A lubricating oil composition according to claim 1 comprising

5. A is a polymer block comprising at least about 75 percent by weight of condensed styrene units, no more than 25 percent of the aromatic unsaturation in said block being reduced by hydrogenation; and

6. B is hydrogenated polymer block comprising, prior to hydrogenation, at least 75 percent by weight of condensed isoprene units, at least 95 percent of the olefinic unsaturation in said block being reduced by hydrogenation.

7. A lubricating oil composition according to claim 2 wherein the pour point depressant is an oil-soluble copolymer of (1) a monovinyl-substituted pyridine of the group consisting of pyridines substituted on one of the ring carbon atoms with, as the sole substituted substituent, a vinyl group, and derivatives of the afore-described vinyl pyridines having a lower alkyl group substituted on a ring carbon atom and (2) a mixture of a C16 to C20 alkyl ester of an acrylic acid of the group consisting of acrylic acid and methacrylic acid and a C10 to C14 alkyl ester of an acrylic acid of the group consisting of acrylic acid and methacrylic acid in mole ratios varying from 1:4 to 4:1, said copolymer having the monovinyl pyridine and the combined acrylic acid esters in a mole ratio varying from 1:2 to 1:10, respectively, and a molecular weight from 5 × 104 to 2.5 × 106.

8. A lubricating oil composition according to claim 3 wherein the block copolymer has the structure A-B wherein

9. A is a homopolymer block of styrene having an average molecular weight between about 25,000 and about 50,000.

10. B is a hydrogenated homopolyisoprene block having an average molecular weight between about 35,000 and about 80,000; the weight ratio of A:B being between 0.5:1 and 0.7:1.

11. A lubricating oil composition according to claim 3 wherein the pour point depressant is a copolymer of 2-methyl-5-vinyl pyridine, lauryl methacrylate and stearyl methacrylate.

12. A lubricating oil composition according to claim 1 wherein the composition has a viscosity of less than 24 poises at 0°F and more than 58 SUS at 210°F.

13. A lubricating oil composition according to claim 6 wherein the composition has a viscosity more than 85 SUS at 210°F.

14. A lubricating oil composition according to claim 6 wherein the lubricating oil consists essentially of fractions having a viscosity of at least about 95 SUS at 100°F.

15. A composition according to claim 7, which comprises in addition:

Description:
BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to novel lubricating compositions and the like, containing a critically defined combination of certain block copolymers and pour point depressants. Unless otherwise indicated, the terms lubricant, lubricating oil or lubricating composition refer to lubricating oils for internal combustion engines.

2. Description of the Prior Art

The art of lubricating oil formulation has become increasingly complex with the ever more stringent demands made by the developing automotive industry. One of the primary requirements is to provide an economical petroleum lubricant which can be utilized over a wide range of operating conditions, especially insofar as temperature variations are concerned. At the same time, the formulated lubricant must also possess an ability to impart oxidative stability, detergency, dispersancy, wear inhibition and corrosion inhibition during its use as well as during storage. Furthermore, the automotive industry desires lubricants which will stay in their SAE viscosity grades for a substantial length of time again under both use and storage conditions.

By "multi-grade lubricants" is meant lubricants which meet a 0°F viscosity specification and a 210°F viscosity specification, such as is shown for motor oils by the following table derived from SAE, J300a taken from the SAE Handbook for 1969:

SAE Viscosity at SAE Viscosity at Oil Grade 0°F, poises Oil Grade 210°F, SUS Spec. Spec. -- -- 20 45-58 5W 12 maximum 30 58-70 10W 12-24 40 70-85 20W 24-96 50 85-110

according to the table, for example, an SAE 10W/50 oil must have a viscosity at 0°F between 12 and 24 poises and a viscosity at 210°F of between 85 and 110 SUS.

The art has evolved a number of multi-grade oils such as SAE 10W/30 and SAE 20W/40 oils but with few exceptions has not been able to formulate wider multi-grade oils such as SAE 10W/50 having low oil consumption and high shear stability. Commercially, such formulations should be economically feasible, capable of large scale production, versatile in regard to the base stock and preferably resistant to degradation under conditions of high shear.

A large variety of polymeric additives have been employed primarily as thickening agents, viscosity index (VI) improvers and pour point depressants. A common limitation of essentially all of these is shear sensitivity. This is not unexpected, since most of the these polymers are relatively high molecular weight materials and consequently are readily subject to shear degradation. On the other hand, relatively low molecular weight polymeric materials, at least up to the present time, have proven to be relatively ineffective as thickeners or VI improvers in automotive engine lubricants, even though they may have reasonably good shear stability.

A number of styrene diene copolymers have been investigated for possible use in lubricants. For example, Schiff et al. U.S. Pat. No. 3,554,911 issued Jan. 12, 1971, teaches the use of hydrogenated random butadiene-styrene copolymers as viscosity index improvers which are said to the shear stable. However, as will be brought out hereinafter, these have proved to be relatively ineffective, particularly with respect to their response to supplementary pour point depressants and also to their effect upon viscosity index. Shepherd U.S. Pat. No. 3,509,056 issued Apr. 28, 1970, shows the use of styrene-olefin copolymers prepared by Ziegler catalysts as lubricating oil additives. These have proven to be surprisingly ineffective as thickening agents and VI improvers. A number of block polymers of the tapered type have been investigated such as those prepared by copolymerization of alpha methyl styrene and ethylene. For some unexplained reason, as shown in Anderson U.S. Pat. No. 3,290,414, issued Dec. 6, 1966, the tapered or random copolymerization as in the case of styrene-butadiene random copolymerization results in an unsatisfactory composition.

Certain styrene-hydrogenated butadiene block copolymers have been employed as pour point depressants or thermal degradation stabilizers in pertroleum fuels as shown in Streets U.S. Pat. No. 3,419,365 issued Dec. 31, 1968. However, since they were employed as fuel additives, they were used in frictional percentages which were too small to appreciably affect the thickening of the oil or the viscosity index thereof. Moreover, as will be developed later, block copolymers containing hydrogenated polybutadiene blocks show essentially no response to supplementary pour point depressants, especially if the 1,2-content is low.

Fully formulated multi-grade oils of the SAE 10W/30 type are shown in Henderson U.S. Pat. No. 3,438,897 issued Apr. 15, 1969. However, the combination of lubricating oil additives disclosed by this patent, while useful for relatively narrow multi-grade oils, such as SAE 10W/30, does not provide for the possibility of compounding wider multi-grades such as SAE 5W/20, 5W/30, 10W/40, 10W/50 or SAE 20W/50.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide improved lubricating compositions. It is another object of the present invention to provide improved multi-grade lubricants. It is a particular object of the invention to provide wide multigrade compositions which will exhibit lower oil consumption due to volatility than the same viscosity multigrade oil made with conventional VI improvers. Other objects will become apparent during the following detailed description of the invention.

Now, in accordance with the present invention hydrocarbon lubricating compositions are provided comprising the following components:

a. a hydrocarbon lubricating oil having a viscosity index of at least 85;

b. a minor but effective amount of pour point depressant for said oil; and

c. 0.1-10 percent by weight of a block copolymer comprising

1. a single polymer block A, at least 75 percent of which is condensed alkenyl arene units, no more than 5 percent of the aromatic unsaturation being reduced by hydrogenation of the block copolymer, said block A having an average molecular weight between about 10,000 and about 55,000; and

2. a single hydrogenated polymer block B, said block, prior to hydrogenation, being a polyisoprene block; at least 95 percent of the olefinic unsaturation of block B being reduced by hydrogenation of the block copolymer; same block B having an average molecular weight between about 20,000 and about 100,000;

the weight ratio of block A to block B being between about 0.45:1 and 0.8:1;

remaining blocks C, if any, in the block copolymer having a total average molecular weight not exceeding about 7,500 and being selected from alkenyl arene polymer blocks, conjugated diene polymer blocks and copolymer blocks of alkenyl arenes and conjugated dienes, each having the hydrogenation limitations of blocks A and B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with this invention it has been found that block copolymers having the above limitations, when combined with a high viscosity index hydrocarbon lubricant containing a pour point depressant, exhibit outstanding physical characteristics not possessed by any other polymeric thickener investigated to date. Preferably, the block copolymer has the simple structure A-B. However, as pointed out above, it may have the alternative structure A-B-C wherein C is the relatively low molecular weight polymer block referred to above. It is preferred that each of blocks A and B be homopolymeric blocks. Moreover, it is preferred that polymer block A be essentially aromatic, e.g. less than 5 percent hydrogenated while polymer block B be at least 99 percent saturated insofar as its original olefinic unsaturation is concerned.

The monoalkenyl arenes, particularly α-alkenyl arenes, which may be used in the preparation of the subject class of block copolymers comprise styrene and methyl styrenes such as alpha methyl styrene, vinyl toluene and other ring methylated styrenes. Styrene is the preferred monomer. Mixtures of these alkenyl arenes may be used if desired.

Polyisoprene is the conjugated diene employed in preparing the precursor of block B. Preferably the polyisoprene block should have at least about 80 percent 1,4 structure which may be either cis or trans and still more preferably it should have at least about 88 percent 1,4 structure.

The block copolymers may be prepared by conventional methods using lithium-based initiators, preferably lithium alkyls such as lithium butyls or lithium amyls. Polymerization is usually conducted in solution in an inert solvent such as cyclohexane or alkanes such as butanes or pentanes and mixtures of the same. The first monomer to be polymerized (which may be either mono alkenyl arene or isoprene) is injected into the system and contacted with the polymerization initiator which is added in an amount calculated to provide the predetermined average molecular weight. Subsequent to obtaining the desired molecular weight and depletion of the monomer, the second monomer is then injected into the living polymer system and block polymerization occurs, resulting in the formulation of the living block copolymer poly(alkenyl arene)-polyisoprene which is then killed, e.g., by the addition of methanol.

This precursor is then subjected to selective hydrogenation such as by the method shown in Wald et al. U.S. Pat. No. 3,595,942 issued July 27, 1971, to form the block copolymers used in the lubricating compositions of this invention. Preferably hydrogenation is conducted in the same solvent in which the polymer was prepared, utilizing a catalyst comprising the reaction product of aluminum alkyl and a nickel or cobalt carboxylate or alkoxide. A favored catalyst is the reaction product formed from triethyl aluminum and nickel octoate.

The temperatures and pressures employed in the hydrogenation step are adjusted such as shown in the last referred-to patent to cause essentially complete hydrogenation of the polyisoprene block with essentially no effective hydrogenation of the monoalkenyl arene polymer block.

The polymer may be isolated from its solvent after its hydrogenation and dispersed in lubricating oil. This may be effected, for example, by adding a lubricating oil to the solution of hydrogenated polymer and thereafter evaporating the relatively volatile solvent.

It is convenient to prepare concentrates of the hydrogenated block copolymer in lubricating oil. Such concentrates suitably contain up to about 20 percent by weight of the hydrogenated block copolymer and preferably between about 2.5 and 15 percent by weight depending on polymer molecular weight.

Wherein the present specification and claims, reference is made to molecular weights of the block copolymers, these are meant to refer to number average molecular weights as determined, for example, by tritium counting techniques or osmotic pressure methods.

Preparation of the block copolymers by anionic solution polymerization results in the desired relatively very narrow molecular weight spread as contrasted to the broad spectrum of species which results from the use of Ziegler polymerization catalysts. Broad spectrum (Ziegler) polymers, containing a substantial proportion of high molecular weight fractions, exhibit excessive shear degradation.

Preferably the polymer blocks A have molecular weights between about 25,000 and 50,000 and the polymer blocks B have molecular weights between about 35,000 and 80,000. Still more preferably, the weight ratio of A:B is from 0.5:1 to 0.7:1.

The pour point depressants utilized in accordance with the present invention and in conjunction with the block polymers as defined above are employed primarily for their pour point depressing effect although many of them may act as viscosity index improvers or thickeners. However, since they are employed in minor (pour point depressing) amounts, e.g., 0.1-2.5 percent by weight preferably 0.15-0.7 percent by weight, their proportion is normally too small to have an appreciable effect upon oil properties other than pour point. It is essential that the pour point depressant be present, however, since the block copolymers defined above exhibit essentially no effective pour point depressant function. On the other hand, one of the prime characteristics of the above class of block copolymers is their effective response to added pour point depressants such as high molecular weight compolymers of alkyl acrylates or alkyl methacrylates as well as nitrogen containing acrylic esters. By the term "acrylic esters" is meant esters of acids of the acrylic acid series including both acrylic acid and methacrylic acid.

The nitrogen-containing acrylic ester polymers as defined can be prepared by any suitable means such as described in Hughes et al. U.S. Pat. No. 3,215,632 issued Nov. 2, 1965, and can be illustrated by the following examples: Nitrogen-containing polymers, namely, copolymers of vinyl pyridine and C8-30 alkyl methacrylates, having a molecular weight range of from 1,500 to 2,000,000, preferably between 200,000 and 850,000 include (1) copolymer of 25 percent 2-methyl-5-vinyl pyridine and 75 percent stearyl methacrylate, molecular weight 200,000; (2) copolymer of 30 percent stearyl methacrylate, 51 percent lauryl methacrylate, 14 percent methyl methacrylate and 5 percent 2-methyl-5-vinyl pyridine, molecular weight 600,000; (3) copolymer of 14 percent methyl methacrylate, 54 percent lauryl methacrylate, 27 percent stearyl methacrylate and 5 percent 2-methyl-5-vinyl pyridine in weight ratio molecular weight 830,000; (4) copolymer of lauryl methacrylate, stearyl methacrylate and 2-methyl-5-vinyl pyridine in the weight ratio of 60:35:5, molecular weight 810,000; (5) copolymer of 2-methyl-5-vinyl pyridine, lauryl methacrylate and stearyl methacrylate in the weight ratio of 7.5:58:34.5, molecular weight 31,000; (6) N-vinyl pyrrolidone-alkyl acrylate copolymers; and (7) N,N-dimetyl-aminoethyl acrylate-alkyl acrylate copolymers.

The oil component of the lubricating compositions according to the present invention is especially designed for the preparation of multi-grade lubricants although single grade lubricants may be compounded as well. Still more specifically, the present combination of block copolymer and pour point depressant is especially beneficial in Wax-containing lubricating oil cuts such as found in Mid Continent oils, West Texas Ellenburger crudes, East Texas crudes, Oklahoma crudes, Pennsylvania crudes and California crudes and similar waxy crudes which may be referred to as paraffin base crudes, naphthenic crudes or mixed base crudes as distinguished from asphalt base crudes. While lubricating oils of any viscosity may be used as the base for the present compositions, the preferred oils are referred to as High Viscosity Index (HVI) 100 Neutral, HVI 250 Neutral and HVI Bright Stock as well as combinations of the same. Also included in this general term HVI for the purpose of this description, are very high viscosity index (VHVI) oils such as those prepared via hydrocracking of poor quality oils, such as low viscosity index (LVI) oils. More volatile oils may be employed for special purposes such as (HVI) 80N. These neutral oils are produced by well-known refining methods, such as distillation, dewaxing, deasphalting, dearomatizing, etc, as may be needed, dependant largely on the crude oil used. Typical properties of these HVI oils are the following:

PROPERTIES OF BASE OILS

HVI HVI HVI HVI VHVI Designation 80 N 100 N 250 N 150 BS 100 N VIS 210°F (SUS) 38.0 39.8 50.0 157 38.6 VIS 100°F (SUS) 82 107 265 2775 82.7 VI 103 93 93 95 126 Gravity (lb/gal) 7.08 7.20 7.33 7.44 7.21 Pour Point (°F) 5 20 20 15 0 Flash Point (°F) 360 405 430 575 400 Aniline Cloud Point 203 213 220 260 226 (°F) % Aromatics by UV 15 11 14 27-40 5 % w S 0.05 0.09 0.05 0.16 0.05 ASTM Color L0.5 L0.5 L1.0 L4.5 L0.5

the present invention, in part, comprises the discovery that the block polymers as defined hereinbefore are only effective in hydrocarbon lubricants having a viscosity index of at least 85 and preferably of at least 90 as defined by ASTM test D2270-64. Data given hereinafter will establish the criticality of the present invention in this respect by showing the block copolymers of the invention either have little or no effect on VI on low and medium VI oils, or actually reduce the VI in such oils.

One of the primary aspects of the present invention comprises the discovery of the unique capability of these compositions for the provision of wide multi-grade lubricants having relatively low tendency toward oil consumption during use. It has been well-established that oil consumption is directly related to the relative volatility of the lubricant base. With most thickeners and VI improvers as well as most pour point depressants it is essential to formulate an SAE 10W/50 lubricant containing a substantial amount of relatively high volatility oils such as 80N or even lighter. This is due to the basic fact that most polymers alter the viscosity/temperature slope to only a moderate degree. However, as shown by FIG. I forming a part of this specification, it will be seen that the block copolymers of the present invention have an unexpected effect in providing a unique viscosity/temperature slope between 210°F and 0°F. The practical result of this is that multi-grade oils such as SAE 10W/30, 10W/40 and 10W/50 oils may be compounded with the present combination of additives utilizing as the oil base the relatively heavier oils, e.g., fractions having a viscosity at 100°F of at least about 95 SUS such as HVI 100 or heavier, rather than resorting to thinning the composition with the more volatile lubricants. The second commercially important implication of this is that a single mixture of relatively heavy lubricant base stocks may be kept in storage for the preparation of a number of multi-grade oils which may be prepared simply by varying the block copolymer concentration. Thus, by the use of the present invention it is possible not only to simplify manufacturing requirements but also to reduce oil consumption during engine operation.

As will be seen in the working examples which follow, other types of polymers which may provide a certain degree of oil thickening or VI improving at temperature between 100+F and 210°F, do not have the unique and strong effect upon the viscosity/temperature slope between 0°F and 210°F as is experienced with the particular block copolymers of this invention. The unexpectedly low viscosities at 0°F of the SAE 10W/50 compositions of this invention are unique and cannot be achieved with other polymers. The working examples furthermore demonstrate that even within the area of polymers having the structure polystyrene-hydrogenated polyisoprene, the block molecular weights and weight proportions of the two blocks must be within the limits specified hereinbefore if the block copolymer is to impart a substantial increase in viscosity index.

The present invention not only provdes wide range multigrade lubricant compositions but also provides compositions having relatively low ash content, e.g. less than about 1 percent by weight sulfated ash, which are especially suitable for gasoline engines.

The basic composition as described above may be used as such but preferably is modified by the presence of supplementary additives combined with the block copolymer and pour point depressant to provide the necessary stability, detergency, dispersancy,antiwear and anticorrosion properties required of modern lubricants according to increasingly severe automotive specifications.

Among such supplementary additives are polymeric succinic acid derivatives used as detergent-dispersants. These can be made by the process described in U.S. Pat. Nos. to Hughes 3,215,632 issued Nov. 2, 1965; to Rense 3,215,707 issued Nov. 2, 1965; to Stuart et al. 3,202,678 issued Aug. 24, 1965, or Le Suer et al. Canadian 681,235 issued Mar. 3, 1964, and can be illustrated by examples (1) succinimide of mono(poly-isobutylene) succinic anhydride and tetraethylene pentamine, the polyiso-butylene radical having a molecular weight of about 1,000, (2) amine derivative of polyisobutyl monocarboxylic acid and tetraethylene pentamine having a molecular weight of about 1,000, (3) succinimide of mono(polypropylene)succinic anhydride and diethylene triamine, the polypropylene radical having a molecular weight of 800-1,500, (4) diimide of mono(polyisobutylene)succinic anhydride and tetraethylene pentamine, the polyisobutylene radical having a molecular weight of 800-1500.

The most preferred ashless dispersants to be used in the lubricants of the present invention are achieved by providing oil-soluble compositions prepared by reacting under esterification conditions (A) at least one substituted poly carboxylic acid acylating agent containing an average of at least about 30 aliphatic carbon atoms per substituent with (B) at least one polyhydric alcohol in amounts such that there is at least one equivalent of polyhydric alcohol for each equivalent of substituted carboxylic acid acylating agent to form an ester-containing first reaction mixture and thereafter intimately contacting this first reaction mixture with (C) from about 0.025 to about 0.15 equivalent of at least one hydroxy-substituted primary amine per equivalent of (A). These reaction products and their preparation are described in Widmer et al. U.S. Pat. No. 3,576,743, issued Apr. 27, 1971. Still more preferably, (A) is further characterized in that it is a substantially saturated acylating agent produced by reacting ethylenically unsaturated carboxylic acidic reactant of the formula

Ro -- COOH)n

or the corresponding carboxylic acid halides, anhydrides, and esters where Ro is characterized by the presence of at least one ethylenically unsaturated carbon-to-carbon covalent bond and n is an integer of two to six, with an ethylenically unsaturated hydrocarbon or chlorinated hydrocarbon containing at least thirty aliphatic carbon atoms at a temperature within the range of 100°-300°C with the proviso that said acylating agent may contain polar substituents to the extent that such polar substituents do not exceed 10 percent by weight of the hydrocarbon portion of the acylating agent excluding the weight of the carboxylic acid groups. The use of such detergents results in a substantial reduction (e.g., 15-50 percent) in the ash level compared to the use of other detergents which may otherwise be effective and satisfactory, such as the succinimides of high molecular weight mono(polyolefin)succinic anhydride and polyalkylene polyamines.

Alkaline earth metal overbased petroleum sulfonates also may be employed. The highly basic alkaline earth metal (Mg, Ca and/or Ba) petroleum sulfonate can be made by suitable means known in the art such as described in British Patents 790,471 and 818,323 or Ellis et al. U.S. Pat. No. 2,865,956 issued Dec. 23, 1958. The basic calcium petroleum sulfonates (M.W. 300-800) are preferred. By basic sulfonate is meant that the end product has a basicity in excess of 20 percent and up to 1,800 percent and preferably between 40 percent and 1,400 percent in excess of that normally required to neutralize the acid to produce the normal salt. Other types of sulfonic acids in the molecular weight range of 350 to 800 and derived from olefinic polymers, alkyl aromatic compounds, e.g., alkylated benzene, or alkylated naphthalene also can be used in forming the basic magnesium, calcium and/or barium sulfonate salt, such as basic calcium diwax benzene sulfonate, basic diwax naphthalene sulfonate and the like, the basicity being in excess of about 50-180 percent and the molecular weight of the compound between 450 and 750. Similar alkaline earth metal alkyl phenates and alkyl salicylates also are useful.

Furthermore, dithiophosphates may be included as supplementary additives, e.g., Ca, Zn, Pb salts of alkylthiophosphates, as well as their thio derivatives, Zn bis(2-ethylhexyl)dithiophosphate, Zn dioctyl dithio-phosphate Zn bis(alkylphenyl)dithiophosphate, P2 S5 -terpene reaction product, phosphonates such as dibutyl methane phosphate, dibutyl trichloromethane phosphonate, dibutyl monochloromethane phosphate, dibutyl chlorobenzene phosphonate, and the like. The full esters of pentavalent phosphorus acids may be used, such as triphenyl, tricresyl, trilauryl and tristearyl orthophosphates or potassium salt of P2 S5 -terpene reaction products or zinc above, like Zn di(C4-10 alkyl)dithiophosphate, e.g., Zn bis(2-ethylhexyl)-dithiophosphate, Zn bis(alkylphenyl)dithiophosphate. Corresponding dithiocarbamates, preferably zinc salts, also may be employed.

Anti-foaming agents such as silicone polymers, e.g., dimethyl silicone polymer, can also be used.

When desired, additional improvements with respect to oxidation stability and scuffing inhibition can be imparted to the oil compositions of the invention by incorporating small amounts (0.01 %-2%, preferably 0.1%-1%) of phenolic antioxidants such as alkylphenols, e.g., 2-6-ditert.butyl-4-methylphenol or p,p'-methylene bisphenols such as 4,4'-methylene-bis( 2,6-ditert.butylphenol) or arylamines such as phenyl-alphanaphthylamine; dialkyl sulfides and mixtures thereof, e.g., dibenzyl disulfide or didodecyl sulfide. Anti-scuffing agents include esters of metal salts or organic phosphites, phosphates, phosphonates and their thio derivatives, such as C3-18 trialkyl phosphites, or phosphonates, e.g., tributyl-, trioctyl-, trilauryl-, tristearyl-, tricyclohexyl-, tribenzyl-, tricresyl- or triphenyl phosphites or phosphates.

A preferred formulation incorporating the present invention is as follows:

Components % by Weight Block Copolymer 0.1-10 Pour Point Depressant 0.1-5 Oil Soluble Metal Thiophosphate 0.01-0.3 Ashless detergent 0.1-8.5 Overbased alkaline earth metal alkaryl sulfonate (Basis sulfated ash) 0.05-3.5 Oil Balance

EXAMPLE I

Response of Various Block Polymers to Pour Point Depressants

The basic compounded oil in this example was a 10W base oil (47 SUS at 210°F) containing sufficient acrylic pour point depressant to reduce its pour point to -20°F; the VI of the base oil (including acrylic additive) was 117 (Sample A in Table I). The acrylic pour point depressant was a copolymer of cetyl methacrylate (50%w), lauryl methacrylate (25%w) and octyl methacrylate (25%w), used in amount of 0.17%w), based on the oil.

The block polymers tested are identified in Table I. The "polymer" column identifies the types of blocks and the "mol wt" column shows the molecular weight of each block.

When the polymers of Table I were tested in the uncompounded base oil they showed no pour point depressant effect. The polymers must therefore be used in combination with a pour point depressant to be useful as low temperature lubricant compositions.

In the tests recorded in Table I, the amount of each polymer employed was that required to thicken the oil blend from 47 SUS to 65 SUS at 210°F. Table I summarizes the data obtained: ##SPC1##

As the above data show, the only satisfactory polymer was polystyrene-hydrogenated polyisoprene (Sample B). All of the other polymers were deficient in one or more respects. For example, the hydrogenated polystyrene-hydrogenated polyisoprene 2-block polymer (Sample E) which lies outside the A:B ratio range of this invention had only a mediocre effect on VI. All of the samples containing hydrogenated polybutadiene blocks (prepared by about 40 percent 1,2 addition) (Samples C, D, F and G) had substantially higher pour points than that of the compounded base oil without block copolymer. Further data indicate that this pour point problem may be solved by randomly copolymerizing styrene with the butadiene block or by including higher 1,2-content (about 70 percent) in the butadiene block. Both remedies, however, have an adverse effect on the thickening efficiency of the polymer and thus require either higher polymer concentrations to thicken the oil or higher polymer molecular weights.

EXAMPLE II

Comparison of Polymers

In order to determine what type of polymer would provide an optimum combination of properties in lubricating oil compositions, a number of polymers were tested in an oil composition comprising 100 HVI Neutral Mid-Continent oil containing 0.2 percent by weight of a copolymer of 2-methyl-5-vinyl pyridine (5%w), lauryl methacrylate (60%w) and stearyl methacrylate (35%w) as a pour point depressant. The oil containing the pour point depressant was thickened with the amount of polymer required to raise the oil from a viscosity of 45 SUS to 75 SUS at 210°F. Table II below summarizes the data obtained: ##SPC2##

The above screening comparison illustrates several points: Ethylene/propylene random copolymer (Sample J) had poor shear stability. This particular ethylene/propylene copolymer was chosen for investigation because of its moderately good low temperature flow properties. In general, ethylene/propylene random copolymers are very poor in low temperature flow. The hydrogenated block polymer containing a styrene/butadiene random copolymer block (Sample I) had poor thickening efficiency, less than the desired effect on VI and relatively high 0° viscosity. The block copolymer including a hydrogenated polybutadiene block (prepared by 72 percent 1,2 addition) (Sample H) showed virtually no VI enhancement effect. The set of samples having the structure polystyrene-hydrogenated polyisoprene (Samples C-G) show the powerful effects of molecular weight and weight ratio of the two types of blocks on thickening efficiency and VI: If the ratio or polystyrene to hydrogenated polyisoprene is too low (Samples D and E) there is a stong negative effect on VI. If the ratio of polystyrene to hydrogenated polyisoprene is too high (Sample C), the polymer has poor thickening efficiency. However, if both the balance of the two types of blocks and the molecular weights come within the limits specified for this invention (Samples F and G), then the lubricating oil composition exhibits high polymer thickening efficiency and high VI response.

EXAMPLE III

Rheological Properties: Relationship to Base Oil

The viscosity index was determined for lubricating compositions comprising a block copolymer (same as the polymer of Sample F, Table II, of Example II), 0.2%w of a pour point depressant (same as used in Example II), and four lubricating oils differing in VI. Table III presents the results obtained:

TABLE III

Vis- Vis- Polymer cosity cosity Conc., at 210°F, at 100°F, Base Oil %w SUS SUS VI LVI 100N 0 38.2 106 6 LVI 100N 1.0 45.6 214 70 LVI 100N 2.0 55.4 564 19 LVI 100N 3.0 73.5 1698 Negative MVI 100N 0 38.2 100 38 MVI 100N 2.0 59.2 638 35 MVI 100N 3.0 98.2 2092 33 HVI 100N 0 39.2 98 100 HVI 100N 1.0 48.8 182 150 HVI 100N 2.0 75.9 423 176 HVI 100N 3.0 163.9 1246 186 VHVI 100N 0 38.7 84 129 VHVI 100N 1.0 48.8 158 184 VHVI 100N 2.0 80.2 399 205 VHVI 100N 3.0 212.0 1447 200+

as the above data show, the present invention applies to the use of high viscosity index, including very high viscosity index lubricating oils, since the polystyrene-hydrogenated polyisoprene block polymers were either ineffective or even detrimental in low or medium VI oils.

Other block copolymers, e.g., a 3-block copolymer having the structure:

hydrogenated polystyrene-hydrogenated polyisoprene-hydrogenated polystyrene

did not show this critical feature, being about equally effective in all types of lubricants regardless of VI. However, as the Figure shows, such 3-block copolymers requires the addition of a relatively light lubricant (80N) in order to meet broad spectrum multi-grade viscosity requirements, such as SAE 10W/50.

EXAMPLE IV

Oil Base Stock Requirements for Multigrade Oils

The primary objective, as discussed hereinbefore, was to design a multgrade lubricant having relatively low volatility. The Figure shows graphically the effect of a number of types of polymers upon the oil base stock allowable for multigrade oils. All polymers were added to a base blend containing HVI 100N plus a representative additive combination. At a given viscosity at 210°F, the lower the viscosity at 0°F measured in the cold cranking simulator, the heavier may be the oil employed for a given multigrade oil. It is readily apparent from the Figure that the polymers fall into two classes, those containing polystyrene and thos containing hydrogenated polystyrene or no styrene at all. It is also apparent that the polystyrene-containing polymers show a steeper slope in the Figure and thus show superior performance.

These data have been converted into actual polymer concentrations and base oil compositions allowed in SAE 10W/50 motor oils. Results are shown in Table IV. The lettered curves on the Figure refer to the corresponding samples listed in Table IV. It is apparent from these data that polystyrene-hydrogenated polyisoprene is the only polymer which can be used to make an acceptable SAE 10W/50 lubricant. The ethylene propylene random copolymer is much too susceptible to degradation by shear to remain an SAE 10W/50 under normal service. Except with polystyrene-hydrogenated polyisoprene polymers, in order to obtain an SAE 10W/50 lubricant it was necessary to use substantial amounts of HVI 80 oil in the blend or to use higher amounts of polymer. If an 80 neutral oil is required, the ultimate result is high oil consumption during service. If a large amount of polymer is needed, the composition is at an economic disadvantage compared with the more efficient polymers. ##SPC3##

From comparison, an expert in lubricating oil formulation can see that only the polystyrene-hydrogenated polyisoprene block copolymers are the suitable choice: 1) they are effective at relatively low concentrations; 2) they do not require any high volatility (80 neutral) oil; and 3) a range or oils (e.g. SAE 10W/30, 10W/40 and 10W/50) can be made from the same oil base by varying the polymer concentration.

EXAMPLE V

Effect of Partial Hydrogenation of Aromatic Block

To test the possibility of hydrogenating the aromatic block to a small extent, the following comparison was made: A polystyrene (32,000 mol wt)-hydrogenated polyisoprene (55,000 mol wt) polymer was prepared. Two further samples of this polymer were partially hydrogenated in the polystyrene block to the extent of 5 percent and 12 percent. All three polymers were tested as VI improvers in a blend of 75 percent HVI 100N, 25 percent HVI 250N containing 0.2 percent of the same pour point depressant as was used in Example II. The following results were obtained:

TABLE V

% Aromatic Polymer Viscosity Saturation Concentration at 210°F (sus) VI (%w) 1.5 74.4 166 2.0 105.5 172 2.5 163.8 177 5 1.5 71.9 152 5 2.0 99.2 153 5 2.5 142.7 158 12 1.5 62.6 145 12 2.0 72.3 127 12 2.5 89.5 121

Unexpectedly, these data show that even a small degree of aromatic hydrogenation renders the polymer less desirable as a VI improver.

EXAMPLE VI

Performance Features of Fully Formulated SAE 10W/50 Motor Oil

A representative SAE 10W/50 lubricating oil formulation in accordance with this invention is shown herewith:

Component %w HVI 100 neutral oil (Mid-Continent 65.66 HVI 250 neutral oil (Mid-Continent) 21.89 Polystyrene-hydrogenated polyisoprene (29,000-51,000 mol wt) 1.95 Zince dialkyl dithiophosphate 2.00 Polyisobutylene succinimide (0.34% total nitrogen. Basic nitrogen : nil) 7.00 Overbased Ca petroleum sulfonate (1400% excess basicity as CaCO3) 1.00 Copolymer of 2-methyl-5-vinyl pyridine (5%), lauryl methacrylate) (60%) and stearyl methacrylate (35%) 810,000 mol wt) 0.50 Dimethyl silicone, ppm 10

Typical properties for this formulation are the following:

Tested Oil Viscosity at 210°F, SUS 108.8 Viscosity at 100°F, SUS 756.0 Viscosity at 0°F (cold cranking 21.2 simulator), poise Viscosity index 174 Pour Point, °F -30 Flash Point, °F 405 TBN-E Total Base Number electrometric 5.15 TAN-E Total Acid Number electrometric 2.60 Initial pH 7.5 Sulfated Ash, %w 0.89 Gravity, °API 29.1 Zinc, %w 0.18 Phosphorus, %w 0.15 Calcium, %w 0.17 Magnesium, %w None ASTM Foam Test, ml ) Sequence 1 : 0/0 ) Sequence 2 :10/0 (Foam Tendency/Foam Stability ) Sequence 3 ; 0/0

The formulation was subjected to the series of tests designated ASTM-SE, which were set as standard to satisfy automotive requirements. Reference to these tests may be found in the ASTM special Technical Publication No. 315-E. The set of engine tests are those proposed as additions to Technical Report J183 of the 1971 SAE Handbook. The more important results of the tests, all of which were passed by the above formulation, are summarized as follows:

Sequence III C This is an oxidation thickening test, designed to simulate conditions such as those encountered by a car pulling a trailer at 70 mph.

SE Requirement Tested Oil Average Sludge (10= clean) 9.0 min. 9.8 Average Piston Skirt Varnish (10= clean) 9.5 min. 9.8 Average Ring Land Varnish (10= clean) 6.0 min. 8.3 Viscosity Increase at 100°F, % at 40 hours 400 max. -4 at 64 hours Must complete 18 Cam and Lifter Wear, in. Average 0.0010 0.0006 Maximum 0.0020 0.0013

Sequence VC This is a low temperature sludge and varnish test to indicate effect of the oil formulation on engine cleanliness.

SE Requirement Tested Oil Average Sludge (10=clean) 8.5 min. 9.6 Average Varnish (10=clean) 8.0 min. 8.7 Average Piston Skirt Varnish (10=clean) 8.7 Oil Screen Clogging, % 5 max. 0 Oil Ring Clogging, % 5 max. 0 Compression Ring Sticking None None

L-38 this is a high temperature test to indicate copper-lead bearing corrosion under operating conditions.

Bearing weight loss, mg at 40 hours 40 max. 12.2

Sequence IIB This test is designed to establish the rust protection properties of the oil formulation under dynamic operating conditions.

Average Engine Rust (10=clean) 8.9 min. 8.9

Summarizing the above formulation and engine test results, the SAE 10W/50 formulation having low base stock volatility and low oil consumption in service is made possible by the unique thickener, polystyrene-hydrogenated polyisoprene. The low temperature properties are enhanced by the vinyl pyridine-methacrylate copolymer, while oxidation inhibition and anti-wear protection are obtained by the dithiophosphate. Anti-rust and engine cleanliness are promoted by the overbased calcium sulfonate and the ashless dispersant (polybutylene succinimide). The entire formulation typically has only 0.8 percent sulfated ash.

As shown by the engine test results, the above formulation provides excellent sludge, varnish and wear control as indicated by the Sequence IIIC, VC and L-38 tests. The rust rating in the Sequence IIB test assures adequate rust protection under the most severe operating conditions.

In addition to these laboratory engine test results which should assure excellent performance in the field, the oil satisfies current shear stability requirements: that is, it stays within the SAE 10W/50 viscosity grade after (a) 1,000 simulated miles in a Ford 302-CID shear stability test (60 mph for 17 hours) and (b) 10 hours in the L-38 engine test.

An additional advantage of the present invention lies in the ease of hot starting, enabled by the use of, for example, a 10W/50 oil of this invention. It is a fairly common occurrence that cars experience, hot starting problems when, for example, after a high speed trip on a freeway they are stopped to refill the gas tank. A comparison was made between the SAE 10W/50 oil of Example VI and a SAE 10W/30 oil as described in the Henderson patent U.S. Pat. No. 3,438,897. The tests were carried out on a 1972 Chevelle with a 307-CID V-8 engine to determine cranking speed as a function of coolant temperature in the jacket next to the inder wall. Results of this comparison clearly indicated at least a 10°F increase in the temperature at which the engine could be started when using the SAE 10W/50 oil of this invention over the 10W/30 oil of the Henderson patent.

EXAMPLE VII

In order to determine if three-block polymers having terminal polystyrene blocks attached to a hydrogenated rubber center block could be used in the compositions of the present invention, the gelling tendencies of such polymers in lubricating oils were examined.

Polystyrene-hydrogenated polybutadiene-polystyrene polymers having the block molecular weights as shown below, were dispersed in HVI 100 neutral lubricating oil at 2%w concentration and observed at room temperature.

Sample Block Mol Wt×10-3 Room Temp. Gel Results A 3--53--4 no gel B 5--25--5 no gel C 10--50--10 gelled

These results indicate that three block S-EP-S copolymers are operable in the present invention as long as the additional polystyrene block is sufficiently low in molecular weight that gellation does not occur. However, if both polystyrene blocks are small enough that gellation will not occur, they would lie outside the optimum molecular weight range described herein and the polymer would not demonstrate the unique properties of polystyrene-hydrogenated polyisoprene polymers described here.

EXAMPLE VIII

Anti-Rust Characteristics of Formulated Oil

%w 100 HVI neutral 65.24 250 HVI neutral 21.75 Block copolymer 1.85 Zinc dialkyl dithiophosphate 1.5 Polyisobutylene succinimide of trimethylolaminomethane 7.00 Overbased magnesium sulfonates 2.16 Vinyl pyridine-acrylate copolymer 0.50 Dimethyl silicone, ppm +10 Total sulfated ash, %w 1.0

The above SAE 10W/50 formulation was run in the Sequence IIB and gave an engine rust rating of 9.0. The above formulation had essentially the same components in different concentrations as the formulation of Example VI, except that magnesium sulfonates (800 percent overbased) were used in place of calcium sulfonates.

EXAMPLE IX

Diesel Cleanliness of Formulated Oil

%w 100 HVI Neutral 34.0 250 HVI Neutral 29.0 150 HVI Bright Stock 14.0 Polystyrene-hydrogenated polyisoprene Block Copolymer 0.8 Tetraethylene pentamine derivative of polyisobutylene 6.0 Zinc diaryl dithiophosphate 3.4 Overbased calcium salicylate 11.7 Acrylate polymer 0.1 Isooctyl phenoxytetraethoxyl ethanol 1.0 Silicone fluid, ppm +10 Total sulfated ash, %w 1.8

The above SAE 20W/40 formulation was run in the Caterpillar 1-G test for 240 hours. The results were excellent with very little top-ring groove carbon filling (2 percent) and very little lacquer deposit. This performance is almost identical to an SAE 30 oil with the same additive package except without the block copolymer. A comparable oil containing a polymethacrylate polymer gave poorer clenliness ratings with about 25 percent top-ring groove filling.