Data storage device with improved roller lubricant characterized by stable viscosity over wide range of temperatures

A data storage device of the type having a rotating member mounted on a shaft, said data storage device comprising a lubricant provided between the shaft and the rotating member, wherein the lubricant comprises (a) a linear, nonpolar polyether base oil having a glass transition temperature (T.sub.g) of about -110.degree. C. or less and an activation energy of flow (E.sub.a) of about 30 kJ/mol or less, and (b) an amount of a thickening agent sufficient to provide the lubricant with a grease-like consistency.

FIELD OF THE INVENTION 
This invention is in the field of belt-driven magnetic recording tape 
cartridges such as are described in U.S. Pat. No. 3,692,255 (Von Behren). 
More specifically, this invention relates to an improved roller lubricant 
for such belt-driven magnetic recording tape cartridges. 
BACKGROUND OF THE INVENTION 
The belt-driven tape cartridges of the Von Behren patent, U.S. Pat. No. 
3,692,255, incorporated herein by reference, are commonly referred to as 
"data cartridges." A data cartridge typically includes a housing defining 
a thin, generally rectangular enclosure. The housing contains a length of 
magnetic recording tape which is wound upon a pair of tape reel hubs. The 
magnetic recording tape is driven by an elastomeric drive belt which, in 
turn, is driven by a single, reversible drive motor. The drive belt 
provides rapid acceleration and deceleration of the recording tape in 
either direction. The drive belt is stretched along a drive belt path 
generally defined by a drive roller, a pair of corner rollers, and part of 
the tape pack wound on each hub. 
The tape, driven by the drive belt, is under a certain amount of tension 
during operation of the data cartridge. The tape tension must not fall 
below a certain level as the tape passes from hub to hub or else contact 
between a read/write head and the tape may be insufficient to allow 
successful data transfer. Conversely, the maximum drive force, i.e., the 
force which must be applied to rotate the cartridge drive roller, must not 
exceed the power rating of the motor in the associated drive. In short, 
data cartridges must meet minimum tape tension specifications while 
simultaneously operating within maximum allowable drive force 
specifications to achieve acceptable performance of a data cartridge in a 
drive. Meeting both specifications may be difficult, especially since 
drive force is at least partially dependent on tape tension, meaning that 
an increase in tape tension has the effect of increasing drive force. 
To further optimize data cartridge performance, it is extremely desirable 
to maintain uniform minimum tape tension and operate within specified 
drive force parameters during recording and playback. Changes in 
temperature, for example, may cause tape tension and drive force 
characteristics to vary considerably. This variability may lead to 
undesirable consequences such as stalling of the drive at low operating 
temperatures or insufficient tape tension at high operating temperatures. 
Therefore, reducing the temperature dependence of tape tension and drive 
force characteristics will improve data cartridge performance. 
SUMMARY OF THE INVENTION 
The present invention concerns an improved roller system that provides 
extremely stable tape tension and drive force characteristics over a wide 
range of temperatures. The advantages of the present invention are 
achieved by a data storage device, such as but not limited to a data 
cartridge, of the type having a rotating member mounted on a shaft. The 
rotating member may be, for example, a corner roller, a drive roller, or a 
tape reel hub. A lubricant is provided between the shaft and the rotating 
member. The lubricant comprises a linear, nonpolar polyether base oil and 
a thickening agent. The base oil has a glass transition temperature, 
T.sub.g, of -110.degree. C. or less and an activation energy of flow, 
E.sub.a, of about 30 kJ/mol or less. The thickening agent is present in an 
amount sufficient to provide the lubricant with a gmase-like consistency. 
The present invention is based in part upon our discovery that the 
variation in tape tension and drive force in the data cartridge with 
changes in temperature is caused, in part, by the temperature dependence 
of the lubricant's viscosity. We have also discovered that the class of 
lubricants whose base oils have a low activation energy of flow (E.sub.a) 
and low glass transition temperature (T.sub.g) as defined herein are 
characterized by extremely stable viscosity over a wide range of operating 
temperatures. Accordingly, the use of such lubricants in a data cartridge 
provides substantially more uniform tape tension and drive force over a 
wide range of operating temperatures as compared to other lubricants 
having higher values of E.sub.a and/or T.sub.g. The lubricants of the 
present invention are particularly suitable for use in a data cartridge at 
the interface between the corner rollers and their corresponding shafts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is shown one example of a belt-driven data 
cartridge 10 according to the present invention. The cartridge 10 is shown 
engaged with a magnetic recording apparatus 12. As used herein, "magnetic 
recording apparatus" means an apparatus for recording or reproducing 
information that is stored on magnetic or optical recording tape. The 
magnetic recording apparatus 12 comprises a support frame 14 including a 
horizontal cartridge support deck 16 supporting a magnetic transducer head 
18. The support deck 16 also supports, in a depending manner, a reversible 
drive motor (not shown), the shaft 20 of which extends through the support 
deck 16. A drive puck 22 is mounted on the shaft 20 above the support deck 
16. Elongate guides 24 define the position of the cartridge 10 on the 
support deck 16. 
The cartridge 10 includes a housing 26 which includes drive access means. 
In FIG. 1, drive access means comprises openings 28 and 30 which are 
located on one edgewall 31 of the housing 26. The opening 28 provides 
access for the drive puck 22. The opening 30 provides access for the 
transducer head 18. The opening 30 is covered by a door 32 which is biased 
by a torsion spring 34 towards a closed position covering the opening 30. 
A pair of tape reel hubs 36 and 38 are rotatably mounted on shafts 37 and 
39, respectively, on parallel axes inside housing 26. A length of magnetic 
recording tape 40 is wound on the hubs 36 and 38 such that a portion of 
the tape 40 extends from one hub to the other hub and across opening 30. 
Means for defining a tape path in the housing to guide the tape 40 from 
one hub to the Other hub and across the opening 30 includes guide pins 44 
and 46. Means for defining a drive belt path includes a drive belt roller 
48 rotatably mounted on a shaft 49, part of the tape 40 wound on each hub 
36 or 38, and belt corner rollers 50 and 52 rotatably mounted on shafts 51 
and 53, respectively. The drive belt 54 of the present invention extends 
along the drive belt path such that the drive belt 54 frictionally engages 
a portion of the magnetic recording tape 40 to cause transport of the tape 
40 from one hub to the other hub. The length of the unstretched drive belt 
54 is less than the length of the drive belt path so that the belt 54 is 
stretched when inserted into the cartridge 10. 
When the cartridge 10 is engaged with the magnetic recording apparatus 12 
as shown in FIG. I, the drive puck 22 contacts the belt drive roller 48 
through the opening 28, and the transducer head 18 contacts the tape 40 
through the opening 30. A belt-contacting portion 55 of the drive belt 
roller 48 is recessed to permit the tape 40 to pass across the drive belt 
roller 48 without touching the drive puck 22. Cartridges such as cartridge 
10 and their operation have been described in U.S. Pat. Nos. 3,692,255 and 
4,581,189. 
FIGS. 2 and 3 show a portion of the inside of a data cartridge which 
includes a corner roller suitable in the practice of the present 
invention. A corner roller 62 is rotatably mounted on a shaft 64. The 
shaft 64 is mounted in a baseplate 66 such that the corner roller 62 
rotates about an axis which is perpendicular to the baseplate 66. As shown 
in FIG. 3, the corner roller 62 includes a body 68 which has an external 
periphery 70 for guiding a drive belt 72 (shown in FIG. 3, but not shown 
in FIG. 2). The corner roller 62 also has a central bore defined by an 
inner periphery 76. The central bore is adapted to receive the shaft 64. 
Generally, configuring the central bore with a diameter approximately 1.1 
mils (0.028 mm) greater than the diameter of the shaft 64 has been found 
to be suitable in the practice of the present invention. For purposes of 
clarity, the space between the shaft 64 and the inner periphery 76 has 
been exaggerated in FIG. 3. We have also found that it is desirable for 
the inner periphery 76 to have a surface roughness (Ra) of 22 microinches 
(0.56 .mu.m) to 38 microinches (0.96 .mu.m), preferably about 28 
microinches (0.71 .mu.m). In the practice of the present invention, 
surface roughness (Ra) is measured using a Taylor-Hobson Talysuff 10 
apparatus. 
As seen best in FIG. 3, the external periphery 70 is configured with a 
slight crown to help prevent the drive belt 72 from shifting away from a 
centered position on the external periphery 70 as the drive belt 72 is 
guided by the corner roller 62. See, e.g., yon Behren et al., "Mechanical 
Design of a Belt-Driven Data Cartridge," Adv. Info. Storage Syst. 1 
(1991), pp. 49-59 for a discussion of this design. FIG. 3 also shows that 
the shaft 64 extends slightly above the top of the central bore. FIG. 3 
also shows a slight sink 78, i.e., concavity, on the inner periphery 76. 
When the corner roller 62 is formed from a polymeric material, the sink 78 
forms naturally as the corner roller cools after being released from its 
mold, because the walls of body 68 of the corner roller 62 are thicker 
around its center than at its ends. Advantageously, the sink forms a 
chamber for holding the lubricant 82. 
The shaft 64 can be made from a wide variety of materials. Preferably, the 
shaft 64 is formed with at least a metal coating or more preferably is 
entirely formed from a metal. A preferred metal material is hardened steel 
(SAE 52100, R.sub.c .gtoreq.60). The corner roller 62 can also be made 
from a wide variety of materials, but is preferably formed from a 
thermoplastic or thermosetting resin such as polytetrafluoroethylene, high 
density polyethylene, polyamide, polyurethane, polyacetal resin, or a 
carbon-fiber reinforced polyacetal resin. 
In order to reduce the temperature dependence of the drag force and tape 
tension, the lubricant 82 according to the present invention is provided 
on the interface between any of the rotating members in the data cartridge 
such as drive rollers, corner rollers, or tape reel hubs and their 
corresponding shafts. Most advantageously, the lubricant is provided on 
the interface between one or more of the corner rollers and their 
corresponding shafts. 
In the practice of the present invention, the lubricant comprises a linear, 
nonpolar polyether base oil and a thickening agent, wherein the base oil 
has an activation energy of flow, E.sub.a, of about 30 kJ/mol or less and 
a T.sub.g of -110.degree. C. or less. Preferably, the E.sub.a of the base 
oil is less than about 25 kJ/mol, and more preferably is less than about 
22 kJ/mol. The T.sub.g of the base oil is preferably in the range from 
-125.degree. C. to -150.degree. C., more preferably -130.degree. C. to 
-135.degree. C. 
While not wishing to be bound by theory, we can present a possible 
rationale as to why a base oil having such E.sub.a values is desirable. 
When flow takes place in a fluid, it is opposed by internal friction 
arising from forces such as intermolecular attractive forces, steric 
hindrance, entanglements between neighboring molecules, and rotational 
energy of flow. The intermolecular attractive forces may include Van der 
Waals forces, dipole-dipole interactions, hydrogen bonding, or 
dipole-induced dipole interactions. Rotational energy of flow refers to 
the energy needed to rotate bonds to conform to and pass steric 
hindrances. The internal friction caused by forces such as those described 
above is the property of the fluid known as viscosity. Molecules must 
overcome this internal friction in order to flow; the required force is 
characterized by a property known as the activation energy of flow 
(E.sub.a). 
We have discovered that the property E.sub.a of the base oil can be 
optimized to minimize the temperature dependence of a lubricant's 
viscosity. For example, the relationship between viscosity as a function 
of temperature and E.sub.a for a base oil is represented quite 
satisfactorily by the Andrade equation: 
EQU .eta.(T)=A.sub.o (e.sup.Ea/RT) (1) 
wherein 
.eta.(T) is the viscosity at a temperature T; 
A.sub.o is a constant; 
E.sub.a is the activation energy of flow; 
R is the gas constant; and 
T is temperature. 
By taking the derivative of this equation with respect to temperature, the 
following equation is obtained: 
EQU d.eta./dT=-A.sub.0 E.sub.a /RT.sup.2 (e.sup.Ea/RT) (2) 
Equation 2 shows that the magnitude of the temperature dependence of 
viscosity grows exponentially with Ea. This means that base oils with 
lower E.sub.a will show more stable viscosity over a range of temperatures 
as compared to base oils with higher E.sub.a values. 
To determine E.sub.a by one preferred method, the logarithm of Equation 1 
is taken to give the following equation: 
EQU 1n .eta.(T)=1nA.sub.0 +E.sub.a /RT (3) 
The viscosity of a base oil is then measured over a range of temperatures 
at a controlled shear rate. After obtaining the viscosity and 
corresponding temperature data, a plot of 1n .eta. versus 1/T is made. We 
have found that this plot yields a substantially straight line. For 
example, the coefficient of correlation of the best fit line is typically 
0.9 or higher for such data. The slope of the resultant line is equal to 
E.sub.a /R as shown by Equation 3. In SI units, R has the value 8.3 
14.times.10.sup.-3 kJ/mol-K. Generally, the slope of the line 1n .eta. 
versus 1/T can be calculated using the least squares method. A steep 
slope, indicating a large E.sub.a, means that the sample has a relatively 
large temperature dependence-of viscosity. On the other hand, a shallower 
slope indicates that the sample has a lower temperature dependence of 
viscosity. 
A particularly preferred technique for obtaining the viscosity and 
corresponding temperature data required for the above analysis includes 
using a Haake Rotovisco RV 100 cup-and-cylinder Searle type viscometer 
with a computer-controlled temperature and shear rate cycle having a 
duration of 255 minutes. To begin the cycle, the lubricant sample is 
maintained at 10.degree. C. while the shear rate is increased at a 
substantially constant rate from zero to 15,000 s.sup.-1 over a period of 
30 minutes. The sample is then maintained at the shear rate of 15,000 
s.sup.-1 for an additional 15 minutes. After the additional 15 minutes 
have passed, the temperature of the sample is increased from 10.degree. C. 
to 60.degree. C. at a substantially constant rate over a period of 120 
minutes while maintaining the shear rate at 15,000 s.sup.-1. The viscosity 
values at various temperatures during this 120-minute period are 
collected. The resultant data for viscosity and temperature can then be 
used to calculate E.sub.a as described above. 
E.sub.a of the base oil is not the only property that can be used to 
characterize the temperature dependence of the lubricant viscosity. 
Molecular flexibility is another such property. Relatively flexible 
molecules tend to have more stable viscosities over wider temperature 
ranges as compared to relatively less flexible molecules. With increasing 
internal friction, the flexibility of the lubricant molecules, i.e. their 
ability to bend or rotate in the bulk, decreases due to increased steric 
hindrance, entanglement and intermolecular attractive forces. We have 
found that glass transition temperature, T.sub.g, is an excellent 
indicator of a lubricant molecule's flexibility. Lubricants characterized 
by a lower T.sub.g tend to be more flexible. Thus, a base oil with a 
relatively low T.sub.g tends to have a relatively low temperature 
dependence of viscosity. Accordingly, the base oil of this invention has a 
T.sub.g of -110.degree. C. or less, preferably in the range from 
-125.degree. C. to -150.degree. C., more preferably -130.degree. C. to 
-135.degree. C. In addition, the proportion of oxygen in a molecule also 
has been observed to be an indicator of molecular flexibility because 
bonds containing oxygen tend to require relatively less rotational energy 
to pass steric hindrances. For example, a polyether containing primarily 
--CH.sub.2 O-- groups would be expected to be more flexible, and therefore 
would have a more stable viscosity, than one containing primarily 
--CH.sub.2 CH.sub.2 O-- groups because of the higher proportion of C--O 
bonds in the polyether containing the --CH.sub.2 O-- groups. 
The glass transition temperature, T.sub.g, of the base oil is typically 
determined using the differential scanning calorimetry (DSC) method, 
although other methods such as thermally stimulated current discharge 
analysis (TSC) are also available. According to one particularly preferred 
technique for determining T.sub.g, a Perkin-Elmer DSC 7 apparatus is used 
with a scanning range from -150.degree. C. to 20.degree. C. and a scanning 
rate of 20.degree. C. per minute. The onset temperature of the glass 
transition is taken to be the T.sub.g. The onset temperature has been 
defined in ASTM method D3418. A method for calculating the onset 
temperature using the Perkin-Elmer DSC 7 apparatus is described in the 
operating manual at pages 7-53 through 7-56. 
In the practice of the present invention, the term "linear" with respect to 
the base oil means that the base oil is characterized by a linear 
molecular chain. Generally, molecules with a linear molecular chain tend 
to be more flexible and therefore are characterized by a lower E.sub.a and 
a lower T.sub.g as compared to branched chain molecules. Thus, the 
temperature dependence of a lubricant's viscosity is reduced by the use of 
base oils with a linear molecular chain. 
The term "polyether" with respect to the base oil means that the backbone 
of the base oil comprises a repeating unit wherein such repeating unit 
contains a C--O bond. The polyethers of the present invention may contain 
one or more different kinds of such repeating units. Preferred embodiments 
of polyethers will be described in more detail below. 
The term "nonpolar" with respect to a base oil means that the end groups of 
the base oil have substantially no hydrogen bonding ability or electron 
withdrawing or donating ability when considered in conjunction with the 
rest of the molecule to which the end groups are attached. Examples of 
nonpolar end groups suitable in the practice of the present invention 
include monovalent lower alkyl moieties of 1 to 10 carbon atoms, 
preferably 1 to 4 carbon atoms; and monovalent lower perfluoroalkyl 
moieties of 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms. 
Preferably, the lower alkyl or lower perfiuoroalkyl moieties are linear. 
Particularly preferred examples of such moieties include CH.sub.3 --, 
CF.sub.3 --, CF.sub.3 CF.sub.2 --, CH.sub.3 CH.sub.2 --, and the like. 
The nonpolar or polar character of an end group may be affected by the 
nature of the moiety adjacent to it on the molecular chain. For example, a 
perfluoroalkyl end group adjacent to an alkyl moiety will be polar, 
whereas the same end group adjacent to a more chemically similar 
peffluoroalkyl or perfluorooxyalkyl moiety will be nonpolar. Similarly, an 
alkyl end group will be polar when adjacent to a peffluoroalkyl or 
perfluorooxyalkyl moiety, but nonpolar if adjacent to an alkyl moiety. 
Generally, base oils with nonpolar end groups have less internal friction 
due to intermolecular attractive forces as compared to base oils with 
polar end groups. Inasmuch as reducing intermolecular attractive forces 
reduces the E.sub.a of a lubricant, the use of nonpolar end groups tends 
to reduce the temperature dependence of a lubricant's viscosity. 
In one preferred embodiment, the base oil of the present invention is a 
polyether represented by the formula 
EQU W--O--(Z).sub.m --W (4) 
Each W is independently a nonpolar, linear alkyl group of 1-10 carbon atoms 
and is preferably CH.sub.3 --. Z comprises at least one linear oxyalkylene 
moiety of the formula --(C.sub.n H.sub.2n O)--. The integer n has a value 
of 2 to 10, preferably 2 to 4, and most preferably 2. The integer m has a 
value such that the number average molecular weight of the polyether is in 
the range from 200 to 2000, preferably about 400. In those instances in 
which Z comprises more than one different kind of linear oxyalkylene 
moiety, e.g., a combination of --(C.sub.2 H.sub.4 O)-- and --(CH.sub.2 
O)-- groups, the different groups may be either randomly distributed or 
grouped in blocks in the chain. Preferably, the polyether of formula (4) 
is a linear polyethylene glycol dimethyl ether having the formula 
EQU CH.sub.3 O(CH.sub.2 CH.sub.2 O).sub.m CH.sub.3 (5) 
wherein m has a value such that the compound has a molecular weight of 
about 400. 
In another preferred embodiment of the present invention, the base oil is a 
perfluoropolyether represented by the formula 
EQU W.sub.f --O--(Z').sub.m --W.sub.f. (6) 
In this formula, each W.sub.f is independently a monovalent, linear, 
nonpolar perfluoroalkyl group having from 1 to 20 carbon atoms, preferably 
1 to 4 carbon atoms, and more preferably is --CF.sub.3. Z' comprises at 
least one linear oxyperfluoroalkylene moiety of the formula --(C.sub.n 
F.sub.2n O)--. The integer n has a value of 1 to 10, more preferably 1 to 
4. The integer m has a value such that the linear perfluoropolyether has a 
molecular weight in the range from 500 to 10,000, preferably 2,000 to 
10,000, and more preferably 4,000 to 8,000. A general discussion of the 
properties and methods of preparation of these materials is found in 
George R. Lappin and Joe D. Sauer, eds., Alpha Olefins Applications 
Handbook (New York: Marcel Dekker, 1989), p. 353. Linear 
perfluoropolyethers are commercially available from Ausimont USA, Inc. 
under the FOMBLIN tradename and Daikin Industries, Ltd. under the DEMNUM 
tradename. 
In those instances of the perfluoropolyethers of Formula (6) wherein Z' 
comprises more than one kind of oxyperfluoroalkylene moiety, e.g., a 
combination of --(CF.sub.2 O)-- and --(CF.sub.2 CF.sub.2 O)-- groups, the 
different groups may be either randomly distributed or grouped in blocks 
in the chain. Specific examples of more preferred linear 
perfluoropolyethers according to Formula (6) include: 
EQU W.sub.f --O--(CF.sub.2 O).sub.p --(CF.sub.2 CF.sub.2 O).sub.q --W.sub.f (7) 
wherein the oxyperfluoroalkylene groups, --CF.sub.2 CF.sub.2 O-- and 
--CF.sub.2 O--, are either randomly distributed or grouped in blocks in 
the chain, p is an integer from 1 to 200, preferably 20 to 80, q is an 
integer of 1 to 200, preferably 20 to 80, each W.sub.f is independently a 
nonpolar end group as described above, and more preferably is CF.sub.3 -- 
or CF.sub.3 CF.sub.2 --. The ratio p/q is preferably in the range from 0.5 
to 100, and most preferably is about 22. This ratio may be determined by 
nuclear magnetic resonance (NMR) spectroscopy. 
The presence of the thickening agent not only tends to provide the 
lubricant with a grease-like consistency, but it also provides the 
lubricant with a lower E.sub.a as compared to the base oil by itself, 
thereby reducing the temperature dependence of viscosity of the resulting 
lubricant as compared to the base oil. Generally, using 1 to 60, 
preferably 10 to 40 and more preferably 20 to 30 parts by weight of the 
thickening agent together with 40 to 99 parts by weight of the base oil 
has been found to be suitable in the practice of the present invention. 
The resulting lubricant preferably has a viscosity less than or equal to 
about 2 Pa-s at 22.degree. C. at a shear rate of 15,000 s.sup.-1. 
A wide variety of thickening agents are suitable in the practice of the 
present invention, including metallic salts of a fatty acid wherein the 
counterion is an ion of Ba, Si, Zn, Pb, K, Na, Cu, Mg, Sr, Ca, Li, Al, and 
the like; clays; polyureas such as those having 2-20 urea bonds and a 
molecular weight of 100 to 50,000; cellulose derivatives; fluorinated 
resin particles; fatty acid esters of dextrin; carbon black; silicon 
dioxide; aluminum complexes; and the like. Thickening agents have been 
described in U.S. Pat. Nos. 4,711,523, 4,507,214, and 4,406,801. 
In preferred embodiments of this invention, the lubricant comprises a 
polyether base oil and one or more thickening agents including fluorinated 
resin particles. In a particularly preferred embodiment, the base oil is a 
linear perfluoropolyether and the fluorinated resin particles are 
substantially spherical and preferably less than one micron in diameter, 
more preferably 0.05 microns to 0.5 microns in diameter, and most 
preferably about 0.1 microns in diameter. The size of individual particles 
is generally measured using a method such as transmission electron 
microscopy (TEM). A relatively smaller fluorinated resin particle size is 
desirable to achieve the proper grease-like consistency without an 
excessively high loading of fluorinated resin particles in the lubricant. 
The fluorinated resin particles act as both a thickening agent and an 
anti-wear agent for the rotating member which the lubricant contacts. In 
addition to providing lubricating properties, the linear 
perfluoropolyether base oil serves as a dispersant for the fluorinated 
resin particles so that no additional dispersing agents are required in 
the lubricant. A preferred lubricant Comprising a linear 
perfluoropolyether and a thickening agent of fluorinated resin particles 
is commercially available under the designation 899-1 from Nye Lubricants, 
Inc. A more preferred lubricant is a modified formulation of 899-1 
lubricant containing 20% by weight fluorinated resin particles. 
Preferred fluorinated resin particles are characterized by a surface energy 
of less than about 30 dyn/cm and a surface area of at least 9 m.sup.2 /g. 
More preferably, the surface area is at least 20 m.sup.2 /g. For the 
purposes of this invention, surface area of the particles is measured by 
nitrogen absorption using a Model 4200 Automatic Surface Area Analyzer 
from Lees & Northrup Instruments. The measured area of the particles 
includes the internal or porous surface area. 
The fluorinated resin particles can be made from any of a variety of 
suitable fluorinated resins. Examples of suitable fluorinated resins 
include polytetrafluoroethylene (PTFE), polyhexafluoropropylene, 
perfluoroalkyl vinyl ethers, and the like. The use of fluorinated resins 
for making fluorinated resin particles has been described in U.S. Pat. 
Nos. 4,724,092 and 4,472,290. Preferably the fluorinated resin is PTFE 
with a number average molecular weight in the range from 2,000 to 100,000. 
Fluorinated resin particles are commercially available either dispersed in 
a solvent or as a dry powder. Preferably, the fluorinated resin particles 
are present in the amount of between 1 and 40 parts by weight per 100 
parts of the lubricant, and more preferably between 1 and 30 parts by 
weight per 100 parts of the lubricant, and most preferably about 20 parts 
by weight per 100 parts of the lubricant. Examples of suitable fluorinated 
resin particles are those which are commercially available from E. I. 
Dupont de Nemours and Co. under the VYDEX and TEFLON tradenames, Ausimont 
USA, Inc. under the ALGOFLON and HALON tradenames, Daikin Industries, Ltd. 
under the POLYFLON tradename, Hoechst AG under the HOS TAFLON tradename, 
and Imperial Chemical Industries, PLC (ICI) under the FLUON tradename. 
Particularly preferred particles are MP 1000 TEFLON particles, MP 1600 
TEFLON particles and VYDEX GT particles, all manufactured by E. I. Dupont 
de Nemours and Co., because of their relatively small particle size. 
The lubricant of the present invention can be applied to the interface 
between any rotating member in the data cartridge and its corresponding 
shaft. For example, referring to FIG. 1, the lubricant can be used between 
one or both corner rollers 50 and 52 and their corresponding shafts 51 and 
53, the drive roller 48 and its shaft 49, and/or one or both tape reel 
hubs 36 and 38 and their corresponding shafts 37 and 39. Preferably, as 
shown in FIG. 3, the lubricant 82 is used between the corner roller 62 and 
its shaft 64. The lubricant of the present invention can be applied 
between a roller and its shaft in a variety of ways. For example, the 
lubricant can be first applied to the shaft after which the roller is 
mounted on the lubricated shaft. Alternatively, the lubricant can be 
applied to the inner periphery of the roller first after which the roller 
is then mounted on the shaft. As another alternative, the lubricant can be 
applied to both the shaft and the roller, after which the roller is 
mounted on the shaft. 
The amount of lubricant applied between the roller and the shaft can be 
varied depending upon the viscosity of the lubricant and the desired level 
of drag force. However, if too little lubricant is used, the drag force 
may become too high or be unstable. If too much lubricant is used, the 
excess lubricant can migrate out from between the corner roller and the 
shaft. Generally using an amount of lubricant sufficient to occupy 60 
percent to 100 percent, more preferably about 100 percent, of the volume 
of the central bore remaining after the roller is mounted on its shaft has 
been found to be suitable in the practice of the present invention. 
The present invention will now be further described with reference to the 
following examples. 
EXAMPLE 1 
A lubricant of this invention, hereinafter referred to as Lubricant 1A, was 
evaluated for performance as a lubricant when used in a data cartridge. 
Lubricant 1A was a grease containing a linear nonpolar perfluoropolyether 
base oil having an E.sub.a of 21.9 kJ/mol and a T.sub.g of -131.3 .degree. 
C., and PTFE particles. Another lubricant was evaluated for comparison. 
The comparative lubricant contained a first synthetic hydrocarbon base oil 
having an E.sub.a of 35 kJ/mol and a T.sub.g of -93.4.degree. C., a second 
synthetic hydrocarbon base oil having an E.sub.a of 43.2 kJ/mol and a 
T.sub.g of -79.1 .degree. C., PTFE particles and a thickening agent. 
Performance of the lubricants was measured as the change in minimum tape 
tension (.DELTA.T) and the change in maximum drive force (.DELTA.D). To 
conduct the test, the lubricant was placed between the corner rollers and 
the corresponding shafts of a standard, commercially available data 
cartridge. The data cartridge was inserted into a magnetic recording drive 
adapted to monitor and record tape tension and drive force levels via 
computer control. Tape tension was measured at the point where the tape 
contacts the head. Each cartridge was first operated continuously at a 
controlled speed of 60 ips (152.4 cm/sec) for about 40% of the total tape 
length, or about 400 ft., while tape tension was recorded. Afterwards, 
drive force was recorded at 120 ips (302.8 cm/sec) for the remaining 
length of the tape (about 600 ft.). The minimum tape tension and maximum 
drive force values were then selected from the resulting data. The test 
was repeated three times for each sample using three different data 
cartridges, and average minimum tape tension and average maximum drive 
force values were calculated from the three tests. 
The testing described above was repeated at three different controlled 
environmental conditions: "HL" (45.degree. C. and 10% relative humidity), 
"RT" (25.degree. C. and 20% relative humidity), and "LL" (5.degree. C. and 
10% relative humidity). 
The change in minimum tape tension (.DELTA.T), which is the difference 
between the average minimum tape tensions at the LL and HL conditions, and 
the change in maximum drive force (.DELTA.D), which is the difference 
between the average maximum drive forces at the LL and HL conditions, are 
shown in the table below. 
______________________________________ 
base oil E.sub.a 
base oil T.sub.g 
Lubricant 
[kJ/mol] [.degree.C.] 
.DELTA.T [oz] 
.DELTA.D [oz] 
______________________________________ 
Lubricant 1A 
21.9 -131.3 0.47 1.67 
Comparative 
37.6 -88.6 0.78 2.72 
lubricant 
______________________________________ 
This data shows that Lubricant 1A, having the lower E.sub.a and T.sub.g, is 
less temperature dependent than the comparative lubricant with regard to 
performance in a data cartridge. 
EXAMPLE 2 
A lubricant, hereinafter referred to as Lubricant 2A, was prepared as 
follows: 495 g of MP 1600 TEFLON fluorinated resin particles (E. I. Dupont 
de Nemours and Co.) were combined with 1755 g of a perfluoropolyether base 
oil having the formula CF.sub.3 O(CF.sub.2).sub.p (CF.sub.2 
CF.sub.2).sub.q CF.sub.3, wherein p/q=1.27 and a molecular weight of about 
9500, the base oil having an E.sub.a of 22.0 kJ/mol and a T.sub.g of 
-131.1.degree. C. (Z15 perfluoropolyether made by Ausimont USA, Inc.). The 
resulting mixture was mixed for 30 minutes to produce a lubricant having a 
viscosity of 0.7 Pa-s at a shear rate of 15,000 s.sup.-1 and a temperature 
of 22.degree. C. 
A lubricant, hereinafter referred to as Lubricant 2B, was prepared as 
follows: 60 g of MP1000 TEFLON fiuorinated resin particles (E. I. Dupont 
de Nemours and Co.) was combined with 300 g of the same base oil used for 
Lubricant 2A. The resulting mixture was mixed to produce a lubricant 
having a viscosity of 0.7 Pa-s at a shear rate of 15,000 s.sup.-1 and a 
temperature of 22.degree. C. 
Lubricants 2A and 2B were then tested for performance by measuring corner 
roller drag force stability at conditions referred to as "HL" (45.degree. 
C., 10% R.H.), "LL" (5.degree. C., 10% R.H.), and "RT" (25.degree. C., 50% 
R.H.). Comer roller drag force stability is measured as the change in 
corner roller drag force over 5000 passes in a drag force tester. Results 
are shown in the following table. 
______________________________________ 
Drag force 
stability [oz.](standard deviation) 
Lubricant HL RT LL 
______________________________________ 
Lubricant 2A 
0.72 (0.02) 0.95 (0.03) 
1.86 (0.41) 
Lubricant 2B 
0.62 (0.03) 0.74 (0.06) 
0.76 (0.10) 
______________________________________ 
Both lubricants exhibited stable drag force at HL and RT conditions, while 
only Lubricant 2B was stable at LL conditions. 
Other embodiments of this invention will be apparent to those skilled in 
the art upon consideration of this specification or from practice of the 
invention disclosed herein. Various omissions, modifications, and changes 
to the principles described herein may be made by one skilled in the art 
without departing from the true scope and spirit of the invention which is 
indicated by the following claims.