Rudnick L. Lubricant Additives: Chemistry and Applications (Присадки, добавки к смазкам)
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514 Lubricant Additives: Chemistry and Applications
Muslim dietary laws require the imposition of halal (meaning lawful versus “haram” which means
unlawful), which means that the facility and the ingredients must meet the following criteria [6]:
Kosher approvals described above except that for animal products Halal laws must be observed and
additionally alcohol must be excluded from any process. The Islamic Food and Nutrition Council of
America, Chicago, Illinois issues Halal certi cates and the process involves a fee as well as annual
inspections.
Neither of these are mandatory, but given the fact that there are about 13 millions Jews and almost
1.6 billion Muslims worldwide, it is something that manufacturers consider to address its potential
customer base.
21.1.5 OTHER FACTORS TO CONSIDER FOR INCIDENTAL FOOD-CONTACT LUBRICANTS
In addition to the considerations indicated earlier, the manufacturer may consider using “good
manufacturing practices” (GMP) or registration against speci c “International Standards Organ-
ization” (ISO) standards such as 9001 and 14001.
GMP involves self-established protocols during manufacture, which can range from cleaning
protocols to analysis for heavy metals. The ISO standards, which are now common, involve annual
audits and fees.
21.1.6 SUMMARY OF CRITERIA FOR INCIDENTAL FOOD-CONTACT LUBRICANTS
The purpose of this section is to summarize the various criteria that are expected for incidental
food-contact lubricants (additives and nished uids or greases). The use of approved components
generally leads to automatic quali cation for registration of the nished uid or grease as an H1
lubricant. This may be done by self-af rmation or through the NSF.
However, the implication of these restrictions is that the development of these products is challeng-
ing, and the entire process adds cost. This is generally re ected in the higher price of these lubricants
when compared to conventional lubricants. An excellent overview of challenges encountered in the
development and manufacture of incidental food-contact lubricants has been published recently [7].
Figure 21.1 provides a summary of various criteria that must be met at the ingredient level, the
nished uid or grease level, or at the plant level.
Ingredients Finished Lubricant
Facility
Additives Lubricating oil
Manufacturing and
Packaging Sites
Components Grease and compounds
Base oils Solid lubricant
21CFR Sections 21CFR Sections Facility
Incidental Food Contact Lubricants Incidental Food Contact Lubricants GMP
178.3570 178.3570 Kosher
GRAS GRAS Halal
182 182 ISO21469
Prior Sanctions Prior Sanctions ISO 9001
181 181
ISO
Other Other
NSF HX-1 NSF H-1
Kosher Kosher
Halal
Halal
ISO 21469
OEM approvals
FIGURE 21.1 Summary of criteria for incidental food-contact lubricants.
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Formulation Components for Incidental Food-Contact Lubricants 515
21.1.7 COMPONENTS USED IN INCIDENTAL FOOD-CONTACT LUBRICANTS
The USDA program classi ed all quali ed additives, base oils and nished lubricants as H1 lubri-
cants as long as the components belonged to 21CFR Section 178.3570, GRAS list, or the prior
sanctions list. Since the NSF took over the program, a new category termed HX-1 has been created
for components that include additives, thickeners, and base oils, whereas nished lubricants are
classi ed in the H1 category.
21.1.8 BASE OILS FOR INCIDENTAL FOOD-CONTACT LUBRICANTS
Whether the lubricant is an oil or grease, the base oil-usually the main ingredient. For mineral oils
to meet the criteria for incidental food contant lubricants, the presence of aromatics in mineral base
oils is not tolerated. This limitation led to the approval and use of technical white mineral oil as
base oil. Although speculative, it could be argued that Group II oils, polyalphaole ns (PAOs) and
polybutenes, were presumably approved due to the fact that they are also free of aromatics. In addi-
tion to hydrocarbon base oils, polyalkylene glycols (PAGs) are also approved. More recently, the
NSF has approved various esters which enhances formulation exibility. Additionally, technology is
available for vegetable oil–based incidental food-contact lubricants and is covered in a U.S. Patent
[8]. Vegetable oils can be used by virtue of their GRAS status. This means that a wide range of base
oils are now available to a formulator (Table 21.2).
21.2 ADDITIVES
21.2.1 T
HICKENERS
The viscosity of a lubricant is dictated by the application. Common viscosity grades for various
lubricants are listed in Table 21.3.
Polyisobutylenes (PIBs; Figure 21.2) are effective thickeners for mineral oil lubricants. The
thickening ef ciency of a commercially available PIB is shown in Figure 21.3 [9]. PIBs are available
TABLE 21.2
Typical Properties of Base Oils
Base Oil
ISO
Viscosity
Range
Pour
Point (ºC)
Antioxidant
Response
Cost Range
($/lb)
a
Group II oils
Technical white mineral oil 32–46 −9 Excellent 0.30−0.35
Group II oils 32–46 −9 Excellent 0.30−0.35
Group IV oils
PAO 32–46 <−30 Excellent 1.00−2.0
Group V Oils
Polyisobutylenes 220 to >1000 0.85−1.20
Polyinternal ole ns
PAG 32–46 −12 Good 1−2
Vegetable oils 32 and 220 −15 Moderate ∼0.60 to 1.0
Esters 46−1000 −45 Good ∼1 to 3
Silicones 46 −50
b
∼2 to 4
Per uoro oils 32 ∼−12
b
∼1 to 3
a
Price will vary based on quantity, customers, suppliers, and market conditions.
b
Most additives are not soluble in these base oils.
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516 Lubricant Additives: Chemistry and Applications
in various viscosity grades. Special handling of PIBs is required for higher viscosity PIBs. PIBs
are soluble in hydrocarbon oils but may be insoluble in water-insoluble PAGs and certain esters.
Vegetable oils have a limited viscosity range between ISO 32 and 46, which limits their usage in
higher-viscosity applications, and PIB is generally incompatible with vegetable oils.
21.2.2 TACKIFIERS
Tacki ers are used to impart, stringiness, to a lubricant, which in turn improves its adherence to
surfaces. An excellent general review on this topic is available [10]. Tacki ers nd use in chain oils
used in the food industries. Traditionally, tack has been qualitatively measured and is often tested
by the sticky nger test. Here, the number of strings between two ngers is counted, and a large
number of strings indicate better tack. A recent publication has reported substantial progress toward
TABLE 21.3
Typical Viscosity Ranges for Incidental
Food-Contact Lubricants
Fluid Type Typical ISO Viscosity Range
Hydraulic uids 32–68
Gear oils 100–460
Air compressor oils 32–100
CH
3
CH
3
CH
3
CH
3
H
3
C
CH
3
H
3
C
n
FIGURE 21.2 Chemical structure of polyisobutylenes (increasing n increases the molecular weight of
polyisobutylene and its thickening ef ciency).
Thickening of ISO-100
technical white mineral oil
y = 103.95e
0
.
066x
R
2
= 1
0
100
200
300
400
500
600
700
800
0 5 10 15 20 25 30 35
4301FG (%)
40 ¼C Viscosity
AGMA 5 (ISO220)
AGMA 6 (ISO320)
AGMA 7 (ISO460)
AGMA 8 (ISO680)
AGMA 4 (ISO100)
FIGURE 21.3 Increasing the ISO grade of incidental food-contact lubricants.
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Formulation Components for Incidental Food-Contact Lubricants 517
quantifying tack using an open siphon method that ultimately measures free jet length (Figure 21.4),
which is correlated to the tackiness [11]. Tack was found to be a result of exudation of solvent from a
swollen gel in dilute polymer solutions of the tacki er in oil. Tack depends on the molecular weight
(MW) and concentration of the polymer and its viscoelastic properties.
One of the approved HX1 tacki ers are high-molecular-weight polybutene tacki ers. These
polymers have the ability to extend and are also oxidatively stable due to their low level of
unsaturation.
21.2.3 POUR POINT DEPRESSANTS
Although low-temperature properties are important in industrial and off-highway applications, most
food manufacturing occurs in controlled conditions of temperature, and low-temperature proper-
ties are not as critical. At the time of writing, there is no pour point depressant that is approved for
use in incidental food-contact lubricants. The best approach to lower pour points is to blend in low
viscosity base oils.
21.2.4 ANTIOXIDANTS
Incidental food-contact lubricants are used in applications such as hydraulic uids, gear oils,
compressor oils, chain oils, and greases. These lubricants are subject to oxidative stresses much
like conventional lubricants but also present additional challenges. First, the approved hydrocarbon
base oils have very low polarity and solubilizing power due to the removal of the aromatic content
in the oil. As a result, by-products of oxidation such as sludge are not easily solubilized, and this
can affect equipment performance. Second, these lubricants can be subject to temperatures as high
as 350°F in oven chain oils and bearing grease. Fortunately, group II base oils and technical white
mineral oils and PAOs, which are commonly used base oils in these applications, respond well to
antioxidants because they have very low unsaturation. Many antioxidants are available for inci-
dental food- contact lubricants. These include hindered phenols to substituted amine antioxidants.
Some natural antioxidants such as tocopherols may also be used. The structures of some of these
antioxidants are shown in Figure 21.5.
FIGURE 21.4 Free jet length resulting from tack. (Devore, D., Private Communication, Functional
Products.)
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518 Lubricant Additives: Chemistry and Applications
Substituted amine antioxidants are very effective in mineral oils although some darkening may
be expected. Hindered phenols such as butylated hydroxyl toluene (BHT) are also very effective
and may not cause as much discoloration. However, BHT may be dif cult to solubilize in a blend,
and therefore, there is a clear need for more soluble antioxidants.
The recent introduction of an antioxidant package offers a product that is in liquid form and is
highly effective in various oils. The results of this package in technical white mineral oil are shown
in Figure 21.6 [9].
H
N
R
R
Substituted diphenyl amine
OH
CH
3
H
3
C
CH
3
CH
3
H
3
C
H
3
C
CH
3
Butylated hydroxyl toluene
O
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
Tocopherol E
FIGURE 21.5 Chemical structures of antioxidants.
0
200
400
600
800
1000
1200
1400
BHT (1) 1%/w Amine
antioxidant (2)
0.5%/w
Commerical
AO package
(3) 1%/w
Minutes to 25 lb O
2
pressure loss
(1) Shown at treat level comparable to the commercial antioxidant package
(2) Shown at maximum permitted level
(3) Shown at half the maximum permitted treat level
Rotating pressurized vessel
oxidation test
(RPVOT ASTM D2272)
FIGURE 21.6 Performance of a commercial antioxidant package. (Devore, D., Private Communication,
Functional Products.)
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Formulation Components for Incidental Food-Contact Lubricants 519
21.2.5 ANTIWEAR AND EXTREME-PRESSURE AGENTS
Antiwear agents are a crucial component of a lubricant. One of the most commonly used antiwear
agent in incidental food-contact lubricants is an amine phosphate salt shown in Figure 21.7. The
amine phosphate salt also provides a degree of rust protection. Other antiwear agents include
glyceryl esters as well as certain fatty acids.
A limited number of extreme-pressure (EP) agents are available. One of the most commonly
used EP components is triphenyl phosphorothionate (TPPT), which is a white crystalline solid.
Soluble versions of this EP agent containing alkyl substitutions on the aromatic rings are also avail-
able (Figure 21.8). Very often, Timken OK load values obtained for mineral oil and PAO-based
incidental food-contact lubricants are in the 15–25 lb range. Although the approval of ingredients
with active sulfur is desirable to obtain conventional EP performance it appears that the industry
has quite successfully managed with the use of EP agents shown in Figure 21.8.
21.2.6 RUST AND CORROSION INHIBITORS
Incidental food-contact lubricants can be exposed to high-moisture conditions, which means that
it is important that the lubricants have adequate rust and corrosion protection. Oleyl sarcosine
(Figure 21.9) is commonly used, and it is highly effective in mineral oils, PAO, and vegetable oils.
A consistent pass test result can be obtained with this additive in both parts of the ASTM D665 rust
test. The maximum treat rate permitted for this additive is 0.5% by weight.
(OR)
2
P
O
(HO)
2
(NHR
2
)
2
FIGURE 21.7 Chemical structure of a
commonly used antiwear agent (phosphoric
acid, mono- and dialkylesters, compounds
with substituted amines).
O
P S
3
R
R = H (solid)
R = t-butyl; or nonyl (liquid)
FIGURE 21.8 Chemical structure of
commonly used EP agent (structure of
TPPT).
H
3
C
H
N
O
O CH
3
8
7
N-methyl-N-(1-oxo-9-octadecynyl) glycine Oleyl sarcosine
N
N
N
R
R
Substituted imidazoline
FIGURE 21.9 Chemical structures of rust inhibitors and metal deactivators.
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520 Lubricant Additives: Chemistry and Applications
21.2.7 DEFOAMERS
Defoamers are used to prevent excessive foaming. Silicon defoamers are approved for use in incidental
food-contact lubricants as long as the molecular weight of the defoamers is > 2000 (Figure 21.10).
They are generally effective in all approved base oils for this application.
21.2.8 ADDITIVE PACKAGES FOR INCIDENTAL FOOD-CONTACT LUBRICANTS
As in conventional lubricants, additive packages simplify operation and can cut development
time. One of the challenges in offering additive packages is to ensure that the limits speci ed for
components must be adhered to. Hydraulic uid additive packages are now offered by two leading
additive suppliers. One of the suppliers offers a product that may be used in hydraulic oils as well
as gear oils, thereby providing additional procurement simplicity. Key performance results for this
additive package are shown in Table 21.4 and performance tests are shown in Table 21.5 [9].
21.2.9 FORMULATION CHALLENGES FOR INCIDENTAL FOOD-CONTACT LUBRICANTS
The formulation of incidental food-contact lubricants is challenging because the formulator has to
abide by many restrictions. These include
Limited list of approved ingredients–base oils and additives
Limitations on the amount of additive that can be used
Limited solubility of additives in technical white mineral oil
A x e d additive database that creates challenges in product differentiation
This is similar to other specialty lubricants that must meet not only performance standards expected
out of a conventional lubricant but also additional criteria [12]. A recently published article summa-
rizes “ ve hurdles to making incidental food-contact lubricants” and addresses some of the aspects
related to the formulation and manufacture of incidental food-contact lubricants in more detail [8].
21.2.10 FUTURE OUTLOOK AND DRIVING FORCES FOR COMPONENTS
U
SED IN INCIDENTAL FOOD-CONTACT LUBRICANTS
Incidental food-contact lubricants constitute a growing area in the mature lubricant market. Several
factors will continue to drive this growth. In the western hemisphere, there is growing awareness
of the need to use this special class of lubricants. Some plants are converting to all H1 lubricants
to reduce complexity and operational errors, which can lead to wastage if food gets contami-
nated by non-H1 lubricants. The growth in population creates direct and increased demand for
food. Furthermore, the increasing af uence in China and India has led to an increased demand
for processed and packaged food. This has resulted in local companies establishing modern food
•
•
•
•
FIGURE 21.10 Chemical structure of a dimethylpolysiloxane defoamer.
OR Si O
CH
3
CH
3
Si CH
3
CH
3
CH
3
3
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Formulation Components for Incidental Food-Contact Lubricants 521
manufacturing, processing, and packaging plants and likewise attracted western food companies
to establish operations in these countries. To maintain their global quality standard, most of these
operations use incidental food-contact lubricants.
On the regulatory front, a key change on the horizon is the introduction of the ISO 21469
standard. Although most of the aspects of this standard pertain to nished lubricants, the standard
could potentially increase the types of additives available since the additives may be included in any
one of the following [13]:
Joint FAO/WHO Expert Committee on Food Additives (JECFA)
Council Directive 95/2/EC on food additives other than colors or sweeteners
United States CFR 21 part 178.3570: Lubricants with incidental food contact and relevant
sections referenced therein
•
•
•
TABLE 21.4
Performance of a Commercial Hydraulic and Gear Oil Additive Package
Test Method
Test Method
(ASTM or Other)
ISO 46 Hydraulic
Fluid (Typical Result)
ISO 220 Gear Oil
(Typical Result)
Performance tests
Air release at 50ºC D3427
Air bubble separation (in minutes) 2.5
Oxidation and seal performance
RBOT (minutes to 25 lb oxygen pressure loss) D2272 571 623
Seals 168 h/100ºC Hydraulic
SRE-NBR28
% volume/hardness change 4.8/−5
% tensile strength/elongation decrease 1.3/−4
Corrosion and wear performance
Copper strip D130
3 h at 100ºC 1B 1A
3 h at 121ºC 1B
Rust test—part A/part B D665 Pass/pass Pass/pass
4-Ball wear test (167°F, 1200 rpm, 20 kg)
Scar diameter (mm) 0.30
Average friction coef cient 0.108
4-Ball wear test (167°F, 1200 rpm, 40 kg) D4172
Scar diameter (mm) 0.37 0.37
Average friction coef cient 0.113 0.117
TABLE 21.5
Pump Test Performance of a Commercial Hydraulic and Gear Oil Package
Test Method
Initial/Final
Flow (gpm)
Total Ring and Vane
Weight Loss (mg)
a
Ring Weight
Loss (mg)
a
Vanes Weight
Loss (mg)
a
Eaton-Vickers V104-C 100 h
at 150F Conestoga
5.3/5.3 42 39 3
Eaton-Vickers 35VQ (50 h) 52 45 7
a
The values indicated in the tables are typical results and are not intended to be speci cations.
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522 Lubricant Additives: Chemistry and Applications
Overall, incidental food contact lubricants are an exiting subset of industrial lubricants. The growing
awareneness regarding use of these lubricants and the evolution of ISO standards could lead to
global harmonization and increased use of incidental food-contact lubricants.
ACKNOWLEDGMENTS
I acknowledge David DeVore, President of Functional Products, Macedonia, Ohio, and Dr. Ken
Lilje of CPI Engineering, Technical Director, CPI Engineering Services, Midland, Michigan.
REFERENCES
1. Raab, M., S. Hamid, Lubricant Additives—Chemistry and Application, Additives Handbook, Ed.
L. Rudnick, Marcel Dekker Publishing, New York, NY, 2003, pp. 453–465.
2. Lawate, S., What you need to know about food-grade lubricants, Machinery Lubrication, 7, 2007.
3. Code of Federal Regulations, Book 21 Section 178.3570, United States.
4. www.nsf.org.
5. Public Broadcasting Service, Belief and practice, Kosher certi cation, July 22, 2005, Episode No 847,
http://www.pbs.org/wnet/religionandethics/week847/belief.html.
6. http://www.ifanca.org/halal/.
7. Lawate, S.R. Pro let, Five hurdles to making food-grade lubes, Compounding, 57(10), 2007, pp. 27, 28.
8. Lawate, S.S., V.A. Carrick, P.C. Naegely, US Patent 5538654, 1996.
9. Lawate, S., Products for incidental food-contact lubricants—Lubrizol 4300FG, Commercial forum
presented by the Lubrizol Corporation, STLE, 2007.
10. Litt, F., Lubricant Additives—Chemistry and Application, Ed. L. Rudnick, Additives Handbook,
Marcel Dekker Publishing, New York, NY, 2003, pp. 355–361.
11. Levin, V.J., R.J. Stepan, A.I. Leonov, Evaluating the Tackiness of Polymer Containing Lubricants by
Open-Siphon Methods: Experimental Theory and Observation, TAE Conference, Stuttgart, Germany,
July 11, 2007.
12. Lawate, S., Environmentally Friendly Hydraulic Fluids in Synthetic Base Oils, Ed. L. Rudnick, Marcel
Decker Publishing, New York, NY, 1999.
13. NSF Steering Committee Meeting presentations and discussions, Ann Arbor, MI, October 2007.
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523
22
Lubricants for the Disk
Drive Industry
Tom E. Karis
CONTENTS
22.1 Introduction ......................................................................................................................... 523
22.2 Recording Disk Lubricants ..................................................................................................524
22.2.1 Properties ............................................................................................................... 525
22.2.1.1 Viscoelastic (Rheological) ....................................................................527
22.2.1.2 Dielectric ............................................................................................... 531
22.2.1.3 Thin Film Viscosity .............................................................................. 534
22.2.1.4 Vapor Pressure ......................................................................................540
22.3 Spindle Motor Lubricants ....................................................................................................546
22.3.1 Ball Bearing Spindle Motor Bearing Grease ........................................................546
22.3.1.1 Yield Stress at Temperature .................................................................. 547
22.3.1.2 Hydrodynamic Film Thickness ............................................................. 550
22.3.1.3 Grease Electrochemistry ....................................................................... 551
22.3.2 Ball Bearing Spindle Motor Ferro uid Seal ......................................................... 554
22.3.3 Fluid Bearing Motor Oil ........................................................................................ 561
22.3.3.1 Viscosity and Vapor Pressure ...............................................................565
22.3.4 Oil Formulation Chemistry ................................................................................... 571
22.4 Conclusions and Future Outlook .........................................................................................577
Ack nowledgment s ..........................................................................................................................580
References ...................................................................................................................................... 581
22.1 INTRODUCTION
When thinking of a disk drive, one picture that comes to mind is that of digital data bits stored on a
spinning disk housed inside a device such as a computer, digital video recorder, or music player. The
outstanding precision and reliability of these high-speed rotating electromechanical devices is, per-
haps, the leading example of microelectromechanical systems and nanotechnology at work today.
For example, the magnetic recording read/write head oats on an air-lubricated bearing just ∼5 nm
away from the disk surface with a relative velocity that is often more than 10 m/s. That is a shear
rate of 2,000,000,000 m/s. As the data track width in the near future is decreased below 200 nm,
the spindle motor on which the disks are mounted must have increasing stiffness with diminishing
vibration amplitudes that are well below the track width to minimize servo seek time and track fol-
lowing. Ball bearing spindle motors used in the past have reached their limit, and current products
incorporate uid dynamic bearing spindle motors. In addition, when there is a high relative velocity
between metallic and insulating components, electrostatic charge generation and dissipation must
be controlled. Lubricants play a vital role in ful lling these requirements for the disk drive industry.
Fundamental understanding of the lubrication mechanism and lubricant chemistry is essential to the
continued advancement of the technology.
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