Mixture of dithiodiglycol and polyoxyalkylene glycol derivatives as a lubricating additive

A mixture of di-(2-hydroxyethyl)disulfide and a derivative of polyoxyalkylene glycol selected from the group consisting of polyoxyalkylene glycol esters and polyoxyalkylene glycol ethers. The mixture is useful in improving the lubricating characteristics of water based fluids in metal working operations.

This invention relates to a mixture which is useful as a lubricating 
additive for water-based fluids used in metalworking operations. 
In machining operations of metals, such as cutting, drilling, drawing, 
tapping, polishing, grinding, turning, milling and the like, it is 
customary to flood the tool and the work with a coolant for the purpose of 
carrying off heat which is produced during the operation. Such coolants 
are typically water-based or are based on liquid organic compounds. 
It is also customary to employ these coolants in combination with various 
agents having lubricating properties for reducing friction between the 
tool and the work piece. A number of lubricating additives are known. Some 
of these additives are soluble in water and are thus suitable for use in 
water-based fluids used in metalworking operations. However, it is always 
desirable to develop new lubricating additives for water-based fluids used 
in metalworking operations. 
In accordance with the present invention, there is provided a mixture of 
di-(2-hydroxyethyl)disulfide (also called diethanol disulfide or 
dithiodiglycol) and a derivative of polyoxyalkylene glycol selected from 
the group consisting of polyoxyalkylene glycol esters and polyoxyalkylene 
glycol ethers. When the mixture is added to water-based fluids used in 
metalworking operations, the lubricating characteristics of such fluids 
are improved. 
Other objects and advantages of the invention will be apparent from the 
foregoing brief description of the invention and the detailed description 
of the invention which follows as well as the claims. 
Any suitable polyoxyalkylene glycol ester may be utilized in the 
lubricating additive of the present invention. Preferred polyoxyalkylene 
glycol esters are (a) esters of a polyoxyalkylene glycol or a monoether 
thereof and a phosphorus containing acid and (b) esters of polyoxyalkylene 
glycol or a monoether thereof and a carboxylic acid. Of the phosphorus 
containing acids, phosphoric acid is preferred. Of the carboxylic acids, 
aliphatic carboxylic acids are preferred. 
A generic formula for a suitable ester of polyoxyalkylene glycol or a 
monoether thereof and a phosphorus containing acid follows: 
##STR1## 
wherein R=the ethylene (--C.sub.2 H.sub.4 --) group or the propylene 
(--C.sub.3 H.sub.6 --) group; 
n=2 to 30 (preferably 3 to 12); 
n'=2 to 30 (preferably 3 to 12), n and n' are independent of each other; 
m=1 to 3; 
q=0 to 2; 
r=3-(m+q), wherein m+q+r must equal 3; and 
R' and R" are independently selected from H, a straight chain or branched 
alkyl group, cycloalkyl group, aryl group or alkaryl group having from 3 
to 30 carbon atoms (preferably 4 to 18 carbon atoms). It is presently 
preferred that at least one of R' and R" is selected from such alkyl, 
cycloalkyl, aryl or alkaryl group. 
Examples of suitable esters of polyoxyalkylene glycol or a monoether 
thereof and a phosphorous containing acid include those disclosed in U.S. 
Pat. No. 3,005,056, such as the monohydrogen phosphate ester derived from 
an equimolar mixture of nonylphenol polyoxyethylene (12) ether and 
polyoxyethylene (9) glycol; the dihydrogen phosphate ester derived from 
lauryl alcohol polyoxyethylene (4) ether; the tertiary phosphate ester 
derived from lauryl alcohol polyoxyethylene (23) ether; the dihydrogen 
phosphate ester derived from nonylphenol polyoxyethylene (2) ether; and 
the monohydrogen phosphate ester derived from hexyl alcohol 
polyoxyethylene (8) ether (1 part) followed by reaction with 9 parts 
ethylene oxide. A preferred ester is a mixture of mono- and dihydrogen 
phosphate esters of polyoxyethylene (6) decyl ether (as described in 
Example I). 
A generic formula for a suitable ester of polyoxyalkylene glycol or a 
monoether thereof and a carboxylic acid follows: 
##STR2## 
wherein Y is R", preferably hydrogen, or is characterized by the generic 
formula 
##STR3## 
and R", R', n and R are as previously defined. 
Examples of suitable esters of polyoxyalkylene glycol and a carboxylic acid 
are polyoxyethylene glycol 400 distearate, polyoxyethylene glycol 200 
monooleate, polyoxyethylene glycol 400 monococoate, polyoxyethylene glycol 
600 monoisostearate; and polyoxypropylene glycol 1000 monolaurate. A 
preferred ester is a monolaurate of polyoxyethylene glycol having a 
molecular weight of about 600 (i.e., monolaurate of polyoxyethylene glycol 
600). 
Any suitable polyoxyalkylene glycol ethers may be utilized in the 
lubricating additive of the present invention. Ethers of polyoxyalkylene 
glycol and aliphatic alcohols or cycloaliphatic alcohols or 
alkyl-substituted aromatic alcohols are preferred. A generic formula of a 
suitable polyoxyalkylene glycol ether is as follows: 
EQU R'--O--(RO).sub.n --R" 
where R, R', R" and n are as previously defined, except that R' and R" 
cannot both be hydrogen. Preferably R" is hydrogen and R' is alkyl, 
cycloalkyl, aryl, or alkaryl. 
Examples of suitable polyoxyalkylene glycol ethers are dodecyl phenol 
polyoxyethylene (7) ether; nonylphenol polyoxyethylene (8) ether; oleyl 
alcohol polyoxyethylene (10) ether; C.sub.12-15 linear primary alcohol 
polyoxyethylene (6.5) ether; and C.sub.11-15 secondary alcohol 
polyoxyethylene (5) ether. Preferred ethers are a lauryl polyoxyethylene 
ether with 23 oxyethylene repeat units and a stearyl polyoxyethylene ether 
with 20 oxyethylene repeat units. 
Any suitable polyoxyalkylene glycol may be present in the above described 
esters and ethers. However, for both the polyoxyalkylene glycol esters and 
ethers, OR is preferably oxyethylene such that a polyoxyethylene glycol 
ester or ether is preferred. 
Di-(2-hydroxyethyl)disulfide is available commercially from Phillips 
Chemical Company, Bartlesville, OK and Pennwalt Company, Philadelphia, PA. 
The disulfide may also be prepared as described in U.S. Pat. No. 
4,250,046. Since the di-(2-hydroxyethyl)disulfide is commercially 
available or may be prepared by conventional methods and since such 
preparation does not play any part in the present invention, the 
preparation of di-(2-hydroxyethyl)disulfide will not be discussed more 
fully hereinafter. 
As was the case with the di-(2-hydroxyethyl)disulfide, polyoxyalkylene 
glycol esters and polyoxyalkylene glycol ethers are also commercially 
available. Examples of commercially available polyoxyalkylene glycol 
esters are Kessco PEG 600 dilaurate and Kessco PEG 600 monostearate, 
available from Stepan Chemical, Maywood, N.J. Other examples of 
polyoxyalkylene glycol esters are Actrol 628 and Actrafos 110, available 
from Southland Corporation, Summit, IL. Examples of polyoxyalkylene glycol 
ethers are Tergitol 25-L-5 and Tergitol NP-7, available from Union Carbide 
Corporation, Danbury, CT. 
Both the esters and ethers may also be prepared by conventional techniques. 
Examples of the preparation of polyoxyalkylene glycol esters are given in 
U.S. Pat. No. 3,004,056. Examples of the preparation of polyoxyalkylene 
glycol ethers are given in U.S. Pat. No. 2,213,477. 
As was the case with di-(2-hydroxyethyl)disulfide, the preparation of 
either the polyoxyalkylene glycol esters for the polyoxyalkylene glycol 
ethers does not play a part in the present invention and will not be more 
fully described hereinafter. 
The di-(2-hydroxyethyl)disulfide and the derivative of polyoxyalkylene 
glycol selected from the group consisting of polyoxyalkylene glycol esters 
and polyoxyalkylene glycol ethers may be combined in any suitable manner 
and under any suitable conditions. Preferably, the disulfide and 
derivative of polyoxyalkylene glycol are simply mixed together until a 
substantially clear, homogenous mixture is obtained. It is not believed 
that the conditions of mixing such as temperature or pressure have any 
effect on the forming of the mixture. Optionally, water can be present in 
the mixture. 
Any suitable ratio of di-(2-hydroxyethyl)disulfide to the derivative of 
polyoxyalkylene glycol may be used in the lubricating additive mixture of 
the present invention. Preferably the ratio is such that the concentration 
of the disulfide in the mixture is in the range of about 5 weight percent 
to about 95 weight percent based on the weight of the mixture. More 
preferably, the concentration of the disulfide will be in the range of 
about 10 to about 50 weight percent based on the weight of the mixture. 
The lubricating additive of the present invention may be utilized to 
improve the lubricating properties of any suitable water based fluid used 
in metalworking operations. 
Any suitable amount of the lubricating additive may be added to the water 
based metalworking fluid. The amount added would generally be such as to 
result in a concentration of the lubricating additive in the water-based 
metalworking fluid in the range of about 0.01 weight percent to about 10 
weight percent based on the weight of the combination of lubricating 
additive and water. More preferably, the concentration of the lubricating 
additive will be in the range of 0.02 weight percent to about 1 weight 
percent. 
In addition to the lubricating additive of the present invention, the 
water-based metalworking fluid may contain other lubricating additives and 
other conventional additives such as rust preventatives, biocides and pH 
modifiers. However, since these other additives are well known and do not 
play a part in the present invention, such other additives are not more 
fully described hereinafter.

The following examples are presented in further illustration of the 
invention. 
EXAMPLE I 
In this example the preparation of a polyoxyethylene glycol phosphate ester 
is described. The preparation was carried out substantially in accordance 
with the procedure disclosed in U.S. Pat. No. 3,004,056. 42.2 grams of 
C.sub.10 H.sub.21 O(C.sub.2 H.sub.4 O).sub.6 H (polyoxyethylene (6) decyl 
ether; the reaction product of decyl alcohol and 6 equivalents of ethylene 
oxide; marketed as Chemal DA-6 by Chemax, Greenville, S.C.) were added to 
a 250 mL flask that had been flushed with nitrogen. Then, in three 
portions over a 5 minute period, 3.55 grams of phosphorus pentoxide 
(marketed by Aldrich Chemical Company, Milwaukee, Wis.) were added to the 
250 mL flask. The resulting mixture was heated from about 40.degree. C. to 
about 90.degree. C., kept at the latter temperature for about one hour, 
and was then cooled. After 43.2 grams of the product (most likely a 
mixture of mono and di-hydrogen phosphate ethers of polyoxyethylene (6) 
decyl ether were recovered. The product was water-soluble. It is labeled 
PEG-Ester A. 
EXAMPLE II 
This example illustrates the use of PEG Ester A, in combination with 
di-(2-hydroxyethyl)disulfide (HO--C.sub.2 H.sub.5 --S--S--C.sub.2 H.sub.5 
--OH; also called diethanol disulfide or dithiodiglycol; marketed by 
Phillips Chemical Company, Bartlesville, OK), as a lubricating additive in 
aqueous solutions. Several aqueous solutions were tested in a Four-Ball EP 
(extreme pressure) test in accordance with ASTM D-2783. Test data are 
summarized in Table I. 
TABLE I 
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Fail Load.sup.(1) 
Run Solution (Kg) 
______________________________________ 
1 (Control) 1 wt % Dithiodiglycol.sup.(2) 
126 
2 (Control) 2 wt % Dithiodiglycol 
126 
3 (Control) 1 wt % PEG-Ester A 
126 
4 (Control) 2 wt % PEG-Ester A 
126 
5 (Invention) 1 wt % Dithiodiglycol + 
160 
1 wt % PEG-Ester A 
6 (Control) 2 wt % PEG.sup.(3) 
126 
7 (Control) 1 wt % Dithiodiglycol + 
126 
1 wt % PEG 
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.sup.(1) the load at which the movable steel ball "welds" onto one or mor 
of the stationary steel balls and rotation of the first ball ceases 
.sup.(2) also called di(2-hydroxyethyl) disulfide or diethanol disulfide 
.sup.(3) polyoxyethylene glycol having a molecular weight of about 600, 
marketed by Aldrich Chemical Company. 
Test data in Table I show that an aqueous mixture of dithiodiglycol and 
PEG-Ester A exhibits better lubricity than either component alone (compare 
runs 2, 4 and 5). This effect is especially surprising in view of the fact 
that an aqueous mixture of dithiodiglycol and underivatized 
polyoxyethylene glycol did not exhibit a synergistic effect. 
EXAMPLE III 
This example illustrates the use of another polyoxyethylene glycol ester, 
in combination with di-(2-hydroxyethyl)disulfide as a water soluble 
lubricating agent. The polyoxyethylene glycol ester employed was PEG 600 
monolaurate (marketed by Stepan Chemical, Maywood, N.J.). This ester is 
labeled PEG-Ester B. Results of Four-Ball EP tests (ASTM D-2783) are 
summarized in Table II. 
TABLE II 
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Fail Load 
Run Solution (Kg) 
______________________________________ 
2 (Control) 2 wt % Dithiodiglycol 
126 
8 (Control) 2 wt % PEG-Ester B 
126 
9 (Invention) 1 wt % Dithiodiglycol + 
1 wt % PEG-Ester B 
160 
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Data in Table II show that the aqueous mixture of 
di-(2-hydroxyethyl)disulfide and polyoxyethylene monolaurate is a more 
effective lubricant than aqueous solutions of either component alone. 
Falex EP (extreme pressure) and wear tests in accordance with ASTM D-3233 
and ASTM D-2670, respectively, were carried out employing aqueous 
solutions containing 1 weight-% di-(2-hydroxyethyl)disulfide and 1 
weight-% PEG-Ester B. Results of Run 10 (Falex wear) were: cumulative 
teeth wear of 23; an average torque of 34 inch-lb (both determined at a 
constant load of 2000 lb and a run time of 15 minutes). Results of Run 11 
(Falex EP) were: fail load of 3250 lb and a final torque of 39 inch-lb 
(final torque is the torque at a load 250 lb less than the fail load). 
These lubricity data confirm that the above-described mixture is an 
effective EP lubricant (water alone would fail during the break-in period 
at a load of 300 lb or less). 
EXAMPLE IV 
This example illustrates the use of a mixture of polyoxyethylene glycol 
ethers and di-(2-hydroxyethyl)disulfide. The first PEG ether employed, 
labeled PEG-Ether A, was polyoxyethylene (23) lauryl ether (marketed as 
Brij 35 by ICI Americas, Wilmington, Del.). The second PEG ether (labeled 
PEG-Ether B) was polyoxyethylene (20) stearyl ether (marketed as Brij 78 
by ICI Americas). Falex EP test data are summarized in Table III. 
TABLE III 
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Fail Final 
Load Torque.sup.(1) 
Run Solution (lb) (inch-lb) 
______________________________________ 
12 (Control) 1.6 wt % Dithiodiglycol 
1750 112 
13 (Control) 1.6 wt % PEG-Ether A 
500 32.sup.(2) 
14 (Invention) 
0.8 wt % Dithiodiglycol + 
3500 77 
0.8 wt % PEG-Ether A 
15 (Control) 1.6 wt % PEG-Ether B 
750 48 
16 (Invention) 
0.8 wt % Dithiodiglycol + 
3000 67 
08 wt % PEG-Ether B 
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.sup.(1) Torque at a load of 250 lb below the fail load 
.sup.(2) Torque at breakin load (300 lb.) 
Data in Table III show that aqueous mixtures of a polyoxyethylene glycol 
ether and di-(2-hydroxyethyl)disulfide exhibited superior EP lubricity vs. 
aqueous solutions containing only one component. 
EXAMPLE V 
This example illustrates the use of two more polyoxyethylene glycol esters, 
in combination with di-(2-hydroxyethyl)disulfide, as lubricity agents. One 
of the tested esters, labeled PEG-Ester C, is Inversol 170 (marketed by 
Keil Chemical, Hammon, Ind.). NMR and IR spectroscopic data indicated that 
PEG-Ester C is an ester of PEG and a long-chain (about 17C) carboxylic 
acid. Another ester, labeled PEG-Ester D, is EM 705 (marketed by Keil 
Chemical) which, according to elemental analysis, NMR and IR spectroscopic 
data, most probably is a phosphate ester of a PEG derivative of an 
aliphatic alcohol. 
Four-Ball EP test results on aqueous solutions are summarized in Table IV 
and essentially confirm earlier-reported data on other PEG esters (see 
Tables I and II). 
TABLE IV 
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Fail Load 
Run Solution (lb) 
______________________________________ 
2 (Control) 2 wt % Dithiodiglycol 
126 
17 (Control) 2 wt % PEG-Ester C 
160 
18 (Invention) 1 wt % Dithiodiglycol + 
250 
1 wt % PEG-Ester C 
19 (Control) 2 wt % PEG-Ester D 
126 
20 (Invention) 1 wt % Dithiodiglycol + 
200 
1 wt % PEG-Ester D 
______________________________________ 
Falex EP and wear test results employing aqueous solutions of 
dithiodiglycol and PEG-Esters C and D are summarized in Tables V and VI. 
TABLE V 
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Final 
Fail load 
Torque 
Run Solution (lb) (inch-lb) 
______________________________________ 
12 (Control) 1.6 wt % Dithiodiglycol 
1750 112 
21 (Control) 1.6 wt % PEG-Ester C 
3250 69 
22 (Invention) 
0.8 wt % Dithiodiglycol + 
3500 39 
0.8 wt % PEG Ester C 
23 (Invention) 
0.8 wt % Dithiodiglycol + 
3750 46 
0.8 wt % PEG-Ester D 
24 (Control) 0.8 wt % Dithiodiglycol + 
750 43 
0.8 wt % PEG.sup.(1) 
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.sup.(1) See footnote 3 of Table I. 
TABLE VI 
______________________________________ 
Accumu- 
lative Average 
Teeth Torque.sup.(1) 
Run Solution Wear.sup.(1) 
(inch-lb) 
______________________________________ 
12 (Control) 1.6 wt % Dithiodiglycol 
--.sup.(2) 
--.sup.(2) 
25 (Control) 1.6 wt % PEG-Ester C 
226 53 
26 (Invention) 
0.8 wt % Dithiodiglycol + 
93 43 
0.8 wt-% PEG-Ester C 
27 (Control) 1.6 wt % PEG-Ester D 
34 42 
28 (Invention) 
0.8 wt % Dithiodiglycol + 
22 35 
0.8 wt % PEG-Ester D 
29 (Control) 0.8 wt % Dithiodiglycol + 
83 93 
0.8 wt % PEG.sup.(3) 
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.sup.(1) during test run of 15 minutes 
.sup.(2) failed after 1 minute 
.sup.(3) see footnote 3 of Table I. 
Data in Tables V and VI clearly show the advantages of mixtures of 
di-(2-hydroxyethyl)disulfide and either PEG-Ester C or D versus aqueous 
solutions of the single components. In addition, the invention mixtures 
also exhibited lubricity advantages (higher fail loads, less teeth wear 
and lower torque) versus mixtures of dithiodiglycol and underivatized 
polyoxyethylene glycol (runs 24, 29). 
EXAMPLE VI 
In this example metalworking fluids containing common ingredients such as a 
rust inhibitor, a biocide and an amine (for pH adjustment) are described. 
Compositions of these solutions are summarized in Recipe I. 
______________________________________ 
Recipe I 
Run 30 Run 31 Run 32 Run 33 
(Con- (Inven- (Con- (Inven- 
Ingredients trol) tion) trol) tion) 
______________________________________ 
PEG-Ester C (wt %) 
0.8 0.8 -- -- 
PEG-Ester D (wt %) 
-- -- 0.8 0.8 
Dithiodiglycol (wt %) 
-- 0.8 -- 0.8 
Triethanolamine (wt %) 
0.8 0.8 0.8 0.8 
Synkad 500.sup.(1) (wt %) 
0.3 0.3 0.3 0.3 
Bioban P-1487.sup..sup.(2) (wt %) 
0.05 0.05 0.05 0.05 
Water bal- balance balance 
balance 
ance 
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.sup.(1) carboxylic acid salt rust inhibitor, marketed by Keil Chemical. 
.sup.(2) a biocide marketed by Keil Chemical. 
Note: 
all solutions were prepared by first preparing a concentrated solution an 
diluting 1 part by volume of the concentrated solution with 9 parts by 
volume of water. 
Falex EP test results are summarized in Table VII. 
TABLE VII 
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Final 
Run Fail Load (lb) 
Torque (inch-lb) 
______________________________________ 
Run 30 (Control) 2750 54 
Run 31 (Invention) 
3250 48 
Run 32 (Control) 2750 47 
Run 33 (Invention) 
3500 56 
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Data in Table VII are in good agreement with those of Table V employing 
various solutions also containing dithiodiglycol and/or PEG-Esters C and 
D, but without the amine, rust inhibitor and biocide. 
Reasonable variations and modifications are possible within the scope of 
the disclosure and the appended claims to the invention.