U.S. patent application number 11/439342 was filed with the patent office on 2006-11-30 for lubricant composition and mechanical element.
This patent application is currently assigned to Fuji Photo Film Co., Ltd.. Invention is credited to Ken Kawata.
Application Number | 20060270568 11/439342 |
Document ID | / |
Family ID | 37464199 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060270568 |
Kind Code |
A1 |
Kawata; Ken |
November 30, 2006 |
Lubricant composition and mechanical element
Abstract
A novel lubricant composition is disclosed. The lubricant
composition comprises at least one organic compound, and, when
disposed between two surfaces moving at peripheral speeds differing
from each other, is capable of exhibiting a discotic columnar phase
or a discotic lamellar phase in which a plurality of molecules of
said organic compound is assembled.
Inventors: |
Kawata; Ken;
(Minami-ashigara-shi, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Fuji Photo Film Co., Ltd.
Minami-ashigara-shi
JP
|
Family ID: |
37464199 |
Appl. No.: |
11/439342 |
Filed: |
May 24, 2006 |
Current U.S.
Class: |
508/342 |
Current CPC
Class: |
C10M 2207/2895 20130101;
C10N 2040/25 20130101; C10M 2219/0406 20130101; C10N 2040/02
20130101; C10N 2040/04 20130101; C10M 171/00 20130101; C10N 2030/02
20130101; C10N 2050/08 20130101; C10N 2030/06 20130101; C10N
2040/50 20200501; C10M 171/002 20130101; C10M 2207/2845 20130101;
C10M 2219/0406 20130101; C10N 2010/02 20130101; C10M 2219/0406
20130101; C10N 2010/02 20130101 |
Class at
Publication: |
508/342 |
International
Class: |
C10M 135/02 20060101
C10M135/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 24, 2005 |
JP |
150479/2005 |
Claims
1. A lubricant composition comprising at least one organic
compound, being capable of exhibiting a discotic columnar phase or
a discotic lamellar phase in which a plurality of molecules of said
organic compound is assembled when disposed between two surfaces
moving at peripheral speeds differing from each other.
2. The lubricant composition of claim 1, having a
pressure-viscosity coefficient at 40.degree. C. of 20 GPa.sup.-1 or
below.
3. The lubricant composition of claim 1, wherein, when disposed
under shear between said two surfaces moving at peripheral speeds
differing from each other, a plurality of molecules of said organic
compound are aligned with their molecular planes, having a maximum
diffusion sectional area, being parallel to said two surfaces,
thereby to form a molecular assembly.
4. The lubricant composition of claim 1, exhibiting a minimum
traction coefficient under a pressure of 10 MPa or more.
5. The lubricant composition of claim 1, exhibiting a traction
coefficient of 0.05 or below.
6. The lubricant composition of claim 1, wherein said organic
compound has at least two aromatic rings, at least one condensed
ring, or a .pi.-conjugation plane.
7. The lubricant composition of claim 1, wherein said organic
compound exhibits a liquid crystal phase under normal pressure.
8. The lubricant composition of claim 1, comprising two species or
more of said organic compound.
9. A mechanical element comprising two surfaces moving at
peripheral speeds differing from each other, and a lubricant as set
forth in claim 1 disposed between said two surfaces.
Description
[0001] This application claims benefit of priority under 35 U.S.C.
119 to Japanese Patent Application No. 2005-150479 filed May 24,
2005.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to a lubricant composition
applicable to mechanical elements used under frictional sliding,
and in particular to a lubricant composition applicable to
mechanical elements, excellent in a low traction performance under
a condition of elastic-fluid lubrication condition.
[0004] 2. Related Art
[0005] Materials used as being disposed between solid surfaces
under relative motion in machines and apparatuses, aimed at
reducing friction, and preventing or moderating the surface damage
are referred to as lubricant, and among them, oils are most widely
used as lubricant. A lubricating oil generally contains a
hydrocarbon, as a base oil, obtained in a form of fraction of
petroleum, and various additives added thereto depending on
purposes. Although being considerably variable depending on
purposes, average molecular weight of a typical base oil is known
to be 350 or around, being not so largely different from that of
liquid crystal used for display devices. Possibility of using the
liquid crystal as lubricant has, therefore, been investigated, and
in recent years, friction control making use of changes in
characteristics induced by external fields has attracted a public
attention, as described in Tribologist, vol. 41, No. 6, p. 506
(1996). All of these liquid crystals are, however, rod-like liquid
crystals, whereas discotic liquid crystals based on the opposite
concept are generally known to have high viscosity, so that
low-viscosity ones operable as lubricant are not so readily
available.
[0006] In another exemplary study reported on other materials, R.
Eidenschink investigated alkoxytruxene exhibiting a liquid crystal
phase over the temperature range from 67.degree. C. to 293.degree.
C., only to find a friction coefficient still larger than that of
the rod-like liquid crystal, as reported in Liquid Crystals, Vol.
5, pp1517 (1989). In ACS Symp. Ser., (1990) 441 (Tribol. Liq-Cryst.
State), 61-82, Lauer et al. measured IR spectrum of
alkoxytriphenylene exhibiting a liquid crystal phase over the range
from 80.degree. C. to to 120.degree. C. under high shear, and
suggested possibility of alignment of the discotic molecules of
alkoxytriphenylene in this temperature range unlike the rod-like
liquid crystal, but did not mention about magnitude of the friction
coefficient. In Mol. Cryst. Liq. Cryst., 1999, Vol. 330, pp
327-334, R. Eidenschink et al. evaluated friction coefficient over
the range from 60.degree. C. to 120.degree. C. of alkylthiobenzene
exhibiting a liquid crystal phase at -10.degree. C. or below, and
reported that the compound showed a friction coefficient not so
largely different from that of mineral oil after one hour or
around, although some difference was observed in the friction
coefficient with the elapse of time depending on presence or
absence of branching in the alkyl chain.
[0007] On the other hand, there are some disclosures made on that
the discotic liquid crystals show desirable lubricating
performances (see Japanese Examined Patent Publication "Tokkohei"
No. 2-21436, Published Japanese Translation of PCT International
Publication for Patent Application "Tokuhyohei" No. 2-503326,
Japanese Laid-Open Patent Publication "Tokkaihei" No. 10-279973 and
Japanese Laid-Open Patent Publication "Tokkai" No. 2002-69472).
"Tokkohei" No. 2-21436 and "Tokuhyohei" No. 2-503326, however, do
not disclose friction coefficients under standard evaluation
systems. "Tokkaihei" No. 10-279973 discloses a lubricant containing
one or more species of sulfur-containing phthalocyanine or metal
complex, thereby exhibiting an extremely low friction coefficient
under frictional pairing, but friction coefficient of the
lubricants in Examples is 0.07 at minimum, showing a value only
equivalent to or larger than those of long-chain alkyl carboxylic
acids, such as stearic acid, which are general oils. The present
inventors have disclosed in "Tokkai" No. 2002-69472 that triazine
compounds having a plurality of radial long-chain alkyl groups,
wherein all of which were compounds each having a discotic center
skeleton.
SUMMARY OF THE INVENTION
[0008] It is therefore an object of the present invention to
provide a lubricant composition having a low viscosity, and
affording a low traction coefficient under strict extreme-pressure
conditions over a wide temperature range, and to provide a
low-traction mechanical element excellent in friction
resistance.
[0009] In one aspect, the present invention provides a lubricant
composition comprising at least one organic compound, being capable
of exhibiting a discotic columnar phase or a discotic lamellar
phase in which a plurality of molecules of said organic compound is
assembled when disposed between two surfaces moving at peripheral
speeds differing from each other.
[0010] As embodiments of the present invention, the lubricant
composition having a pressure-viscosity coefficient at 40.degree.
C. of 20 GPa.sup.-1 or below; the lubricant composition wherein,
when disposed under shear between said two surfaces moving at
peripheral speeds differing from each other, a plurality of
molecules of said organic compound are aligned with their planes,
exhibiting a maximum diffusion sectional area, being parallel to
said two surfaces, thereby to form a molecular assembly; the
lubricant composition exhibiting a minimum traction coefficient
under a pressure of 10 MPa or more; the lubricant composition
exhibiting a traction coefficient of 0.05 or below; the lubricant
composition wherein said organic compound has at least two aromatic
rings, at least one condensed ring, or a .pi.-conjugation plane;
the lubricant composition wherein said organic compound exhibits a
liquid crystal phase under normal pressure; and the lubricant
composition comprising two species or more of said organic
compound; are provided.
[0011] In another aspect, the present invention provides a
mechanical element comprising two surfaces moving at peripheral
speeds differing from each other, and the lubricant disposed
between said two surfaces.
[0012] According to the present invention, there is provided a
lubricant composition having a low viscosity, and affording a low
traction coefficient under strict extreme-pressure conditions over
a wide temperature range, and there is also provided a low-traction
mechanical element excellent in friction resistance.
[0013] According to the prior art related to lubricating techniques
under extreme-pressure ever adopted, the lack of the strength of an
oil film formed of low-viscosity, low-traction mineral oil or
oil-and-fat-base synthetic lubricant has been compensated by
polymer-base, sulfur-containing, or heavy-metal-base interface
coating agent. According to the invention, such prior technique can
be replaced with a novel technique using a material capable of
exhibiting a discotic columnar phase or a discotic lamellar phase
under extreme pressure and shear, to thereby allow a low viscosity
to exhibit under extreme pressure. The present invention is
successful not only in obtaining an extremely low traction
performance superior to the conventional low traction coefficient,
but also in obtaining a further tough friction resistance by using
the material capable of covering the interface based on a
highly-ordered alignment. In the current situation strictly
demanding reduction in fuel consumption from the viewpoints of
energy saving, prevention of global warming and environmental
preservation, the present invention can therefore provide a novel
technique contributive to solution of these problems ascribable to
the Piezo-viscosity effect, which has been a big wall of scientific
principle. The present invention is in no need of using any
environmentally hazardous sulfur compounds, phosphorus compounds
and heavy metals such as zinc, molybdenum and so forth, and is
capable of providing a high-performance, environment-friendly
lubricant composition by using organic compound(s) only.
BRIEF DESCRIPTION OF THE DRAWING
[0014] FIG. 1 is a graph showing a temperature dependence of
friction coefficient of LUB-1 evaluated in Example 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0015] Paragraphs below will detail the present invention. It is to
be understood, in this patent specification, that the term " . . .
to . . . " is used as meaning a range inclusive of the lower and
upper values disposed therebefore and thereafter.
[0016] The present invention relates to a lubricant composition
used as being disposed between two surfaces moving at peripheral
speeds differing from each other, and a mechanical element which
includes two surfaces moving at peripheral speeds differing from
each other, and the above-described lubricant disposed between two
these surfaces. The peripheral speeds of the two surfaces are not
specifically limited, and assuming now that the larger peripheral
speed as u1 (>0), and the smaller peripheral speed as u2, or
|u1|>|u2|, the average speed (u2+u1)/2 can range from not lower
than zero to infinity, wherein the average speed of the two
surfaces falls on 1000 m/s or below, and preferably falls in the
range from 1 cm/s to 50 m/s, both ends inclusive. Also absolute
value of the specific sliding .SIGMA. defined by
2.times.(u2-u1)/(u2+u1) can range from not lower than zero to
infinity, wherein it is given as -2 for a mechanical element having
a value of u2 of zero which indicates standstill, allowing use
within the range of -2.ltoreq..SIGMA.<0. Most of mechanical
element are, however, used within the range from -2 to -0.01, both
ends inclusive.
[0017] Shear rate defined by (u1-u2)/(film thickness of lubricant
composition between two surfaces) can range from not lower than
zero to infinity, wherein it is generally adjusted to 10.sup.9/s or
below, and preferably in the range from 10/s to 10.sup.7/s, both
ends inclusive. For the case where the lubricant composition shows
liquid crystallinity under normal pressure, only a small shear rate
can maintain a desired highly-ordered alignment, whereas for the
case of non-liquid-crystallinity, the highly-ordered alignment is
attained only under shear, typically needing a shear rate of
10.sup.4/s or more. It is, however, difficult to unconditionally
determine an appropriate range of the shear rate, because it may
vary depending on structures of organic compound contained in the
lubricant composition, pressure, temperature and so forth. The
degree of ordered alignment of the organic compound contained in
the lubricant composition, determined by the general definition for
the degree of ordered alignment, is preferably adjusted to 0.3 to
0.99, both ends inclusive. The film thickness between the two
surfaces is generally 10 nm to 100 .mu.m, both ends inclusive, and
preferably 50 nm to 5 .mu.m, both ends inclusive.
[0018] As for average pressure between the two surfaces, it is
described in K. E. Weale, "Ko-atsu Hanno Kagaku (High-Pressure
Chemical Reaction)", published by Baifukan, Co., Ltd. (1969), p. 1
that the organic compound generally becomes non-compressive under a
pressure of approximately 100 MPa or above where the effect of
"mass action" on the chemical reaction becomes less important, and
that the pressure promotes the reaction overwhelming steric
hindrance of the organic compound. In the mechanical element of the
present invention, the above-described lubricant composition
exhibits a low traction coefficient under a pressure of 10 MPa or
above due to pressure rise, showing a minimum value of the traction
coefficient. It is further preferable to exhibit the minimum
traction coefficient under a pressure of 100 MPa or above. The
lubricant composition preferably exhibits a low traction
coefficient as small as 0.07 or below, and more preferably exhibits
a low traction coefficient as small as 0.05 or below. It has been
known that also glass and steel become affected on the interface
thereof by elastic distortion, after reaching a pressure region of
10 MPa or above. It is therefore preferable that the mechanical
element of the present invention performs its major movement under
a pressure of 10 MPa or above, more preferably 50 MPa or above, and
still more preferably 100 MPa or above. The lubricant composition
is supposed to reach the mixed lubrication region as the pressure
rises, and to cause fracture of the film interface. Lowering of the
traction coefficient of the lubricant composition is therefore
caused by pressure rise within the range from 10 MPa or above, and
to a pressure where the mixed lubrication region appears.
[0019] The traction coefficient herein means a dimensionless
quantity obtained by dividing the tangential force, caused when
rolling is affected by slipping, by the normal force (vertical
load), that is, slipping friction coefficient. As described in
"Toraiborogi (Tribology)" co-authored by Yamamoto and Kaneda,
published by Rikogakusha Publishing Co., Ltd., (1998) p. 129, FIG.
5.18, the traction coefficient is known to increase proportional to
the slipping ratio when the slipping ratio is small, to reach a
plateau thereafter, and to show a tendency of gradual decrease as
being affected by friction heat when the slipping ratio further
increases. The traction coefficient should, therefore, be compared
under a constant temperature, and in a region of a relatively large
slipping ratio where a maximum traction coefficient can be
obtained.
[0020] In general fluid lubrication action, a narrower gap results
in generation of a larger pressure, so that concentrated contact
such as point contact and line contact caused by roller bearing,
gear and cam produces a pressure of several hundred MPa to Gpa. Not
only elastic deformation of the interface per se, but also
viscosity of the lubricating liquid exponentially increase with
pressure. The relation between the pressure and the viscosity of
lubricating liquid is given by the Barus equation below:
.eta.=.eta..sub.0 exp(.alpha.P) (1) wherein logarithmic conversion
of both sides gives: log.eta.=log.eta..sub.0+loge.times..alpha.P
(2) and logarithmic .eta. and pressure P are in a linear relation
with gradient .alpha.. The index .alpha. of pressure dependence of
viscosity is called as pressure-viscosity coefficient.
[0021] The lubricant composition of the present invention
preferably has a pressure-viscosity coefficient at 40.degree. C. of
20 GPa.sup.-1 or below, and preferably exhibits a low traction
coefficient with increase in pressure under a pressure of 10 MPa or
above. The pressure-viscosity coefficient herein can be calculated
according to the method described in Tribologist, Vol. 38, No. 10,
pp 927 (1993). The lubricant composition of the present invention
preferably has a pressure-viscosity coefficient at 40.degree. C. of
13 GPa.sup.-1.
[0022] For any compound existing in a solid form at 40.degree. C.,
the pressure-viscosity coefficients are measured at two or more
temperatures where the compound liquefies, and the obtained values
are extrapolated towards the low temperature side to thereby define
the value at 40.degree. C.
[0023] The lubricant composition of the present invention contains
at least one species of organic compound, and can form a discotic
columnar phase or a discotic lamellar phase in which a plurality of
molecules of the organic compound(s) is assembled when disposed
between two surfaces moving at peripheral speeds differing from
each other. It is to be understood herein that the term "organic
compound" in the present invention is used for any metal complexes
having an organic compound(s) as ligand thereof. In general, it is
not easy to structurally specify molecules which can form a
discotic self-assembly. Various factors such as a steric structural
factor and an inter-molecular interaction may contribute to forming
the discotic self-assembly. A plurality of molecules may interact
with each other based on specific or position-selective,
inter-molecular interaction (a kind of molecular identification
action) such as hydrogen bond or metal-metal interaction, thereby
to form a discotic self-assembly, as if one disc is formed as a
whole. And rod-like molecules, having a specific balance in sizes
and geometries of the non-polar, long-chain portion and the polar
core portion thereof, may form a d a discotic self-assembly. These
phenomena are specifically reported as columnar phase formation by
an oligomer of an oligoethyleneoxy ester-base compound of trialkoxy
gallic acid as described in J. Chem. Soc., Perkin Trans., 2, 1994,
31; columnar phase formation by a tetraalkoxyphenanthridinone dimer
as described in Angew. Chem., Int. Ed. Engl., 1995, 34, No. 15,
1637; columnar phase formation by a glucitol amide-base compound of
trialkoxygallic acid as described in Liquid Crystals, 1997, Vol.
22, No. 4, 427; formation of super-liquid crystal phase of barbitul
acid as described in Crystals, 1997, Vol. 22, No. 5, 579; columnar
phase formation by rhodium- or iridium-containing dicarbonyl
.beta.-diketonate complex described in Chem. Mater., 1998, 10, 438;
and columnar phase formation by a intra-molecular hydrogen bond
complex of triaryl melamine and aromatic carboxylic acid as
described in Liquid Crystals, 1998, Vol. 24, No. 3, 407. Any of
these materials causative of these phenomena, and any materials
analogous to these materials and supposed to be causative of
similar phenomena are applicable to the lubricant composition of
the present invention. It is, however, to be noted that J. Am.
Chem. Soc., 1997, Vol. 119, No. 18, 4097 describes that trialkoxy
stilbazole trimer of trimellitic acid and phthalimide trimer of
melamine cannot readily be formed, suggesting that formation of the
columnar phases of these compounds are based on some delicate
structural factors.
[0024] It is preferred that the organic compound, which can be
employed in the lubricant composition of the present invention, has
at least two aromatic rings (more preferably benzene rings) , at
least one condensed ring (more preferably an aromatic condensed
ring, such as naphthalene ring or phenanthrene ring), or
.pi.-conjugation plane. The organic compound is preferably selected
from materials showing a liquid crystal phase under normal
pressure. Some organic compounds, even being incapable of forming a
discotic columnar phase nor a discotic lamellar phase all by
themselves, may form the phase if mixed with any other organic
compounds, so that the embodiments of the present invention also
include the lubricant composition comprising a plurality of species
of organic compounds, being capable of exhibiting a discotic
columnar phase or a discotic lamellar phase in which molecules of
such plurality of species of organic compounds are assembled.
[0025] It is preferred that, when the lubricant composition of the
present invention disposed under shear between the two surfaces
moving at peripheral speeds differing from each other, molecules of
the organic compound(s) are aligned with their planes, exhibiting a
maximum diffusion sectional area, being parallel to the two
surfaces, thereby to form a molecular assembly film. For the case
of rod-like molecules, they are aligned with their inertial axes or
optical axes being parallel to the two surfaces, thereby to form a
molecular assembly film. For the case of planar or discotic
molecules, they are aligned with their largest molecular planes
being parallel to the two surfaces, thereby to form a molecular
assembly film.
[0026] The organic compound may be selected from discotic organic
compounds having a plurality of radial side chains. This sort of
compound can ensure a large free volume of the side chains even in
the self-assembly structure, and is consequently understood as a
large-free-volume compound, or a low-viscosity compound under high
pressure, and is expected to show a low friction coefficient under
conditions of elastic fluid lubrication. In fact, the present
inventors have confirmed that discotic liquid crystals, having
viscosity values considerably larger than those of general
lubricant base oils under normal temperature and normal pressure,
respectively showed extremely low friction coefficients under
conditions of elastic fluid lubrication, and have measured the
pressure-viscosity coefficient of a triazine-base discotic compound
according to a known method described in Liquid Crystals, 1997,
Vol. 22, No. 4, 427, and have confirmed that the compound showed a
value as small as being comparative to those of oil-and-fat
compounds. It is therefore supposed that, by using such a discotic
compound, a film of a discotic structurally-assembly having side
chains radiating therefrom is formed between the two surfaces, and
that an appropriate level of low friction coefficient, attributed
to the large free volume of its chemical structure, can be obtained
under conditions of elastic fluid lubrication, or high pressure and
high shear.
[0027] Specific examples of the organic compounds, which can be
employed in the present invention, include, however not to be
limited to, compounds listed below. ##STR1## ##STR2## ##STR3##
[0028] In view of ensuring practical performances adaptive to
various applications, the lubricant composition of the present
invention may optionally be added with various additives generally
used for lubricant including bearing oil, gear oil and power
transmission oil, that is, anti-wearing agent, extreme pressure
agent, antioxidant, viscosity index improver, detergent-dispersant,
metal deactivator, anticorrosive, anti-rust agent, defoaming agent
and so forth, within ranges without impairing the purpose of the
present invention. The lubricant composition of the present
invention may contain a medium for the organic compound. The medium
can be selected from any materials so far as they do not inhibit
spontaneous formation of the self-organizing material. For example,
one species, or two or more species may be selected from general
mineral oils and synthetic oils which have conventionally been used
as lubricant base oils. It is to be noted that, in any case of
containing other constituents, such one species or two or more
species of organic compounds preferably account for 50 mol % or
more of the total composition, and more preferably 80 mol % or
more.
[0029] Structure of the mechanical element of the present invention
is not specifically limited so far as it has two surfaces moving at
peripheral speeds differing from each other, and the
above-described lubricant disposed between two these surfaces. It
may be any of mechanical elements incorporated into
conventionally-known frictional sliding portions in need of
lubricant, grease and so forth. The two surfaces moving at
different peripheral speeds may be curved surfaces or flat
surfaces, or may be such as having irregularity over the entire
surface or in a part thereof. Examples of which include frictional
sliding portions of sliding bearing and rolling bearing. The
mechanical element of the present invention may further include
gear, cam, screw or traction drive as a transmission element. The
mechanical component may still further include a contact seal such
as oil seal, mechanical seal, piston ring, or the like, as a
sealing element sealing the lubricant composition.
[0030] Materials of the two moving surfaces can be exemplified by
carbon steel for mechanical structures; alloy steels for mechanical
structures such as nickel-chromium steel,
nickel-chromium-molybdenum steel, chromium steel,
chromium-molybdenum steel, and aluminum-chromium-molybdenum steel;
stainless steel; multi-aging steel; ceramics such as silicon
carbide, silicon nitride, alumina and zirconia; cast iron; copper,
copper-lead, aluminum alloy and castings thereof; white metal;
various plastics including high-density polyethylene (HDPE),
polytetrafluoroethylene resin (PFPE) polyacetal (POM),
polyphenylene sulfide (PPS), polyether ether ketone (PEEK),
polyamide imide (PAI) and polyimide (PI); organic-inorganic
composite materials composed of plastic compounded with fiber such
as those composed of glass, carbon, aramid and so forth; and cermet
as a composite material of ceramic and metal.
EXAMPLES
[0031] Paragraphs below will more specifically explain the present
invention referring to Examples and Comparative Examples, wherein
the present invention is by no means limited to these Examples.
Evaluation of the lubricant composition in Examples and Comparative
Examples was carried out according to the methods below. [0032] 1.
Methods of Evaluation and Measurement Using Reciprocating (SRV)
Friction Wear Test
[0033] Friction coefficient and wear resistance were evaluated
using a reciprocating (SRV) friction wear tester, wherein the
friction wear test was carried out according to the test conditions
shown below.
Test Conditions
[0034] Test piece (friction member): SUJ-2 [0035] Surface
roughness: 0.45 to 0.65 .mu.m [0036] Plate: 24 mm in
diameter.times.7 mm [0037] Cylinder: 15 mm in diameter.times.22 mm
[0038] Temperature: 0 to 150.degree. C. [0039] Load: 100 N (149
MPa) [0040] Amplitude: 1.5 mm [0041] Frequency: 50 Hz [0042]
Preliminary slide time: 2 minutes [0043] 2. Lubricant Composition
using Compound Capable of Forming Discotic Assembly Structure
Example 1
[0044] A lubricant LUB-1 having a composition below was evaluated
by the reciprocating (SRV) friction wear test. Results are shown in
FIG. 1. Composition of LUB-1 and phase transfer temperatures are
shown below.
Composition of LUB-1
[0045] Isomolar mixture of a and b ##STR4## Liquid Crystal Phase
Transfer Temperatures of LUB-1 ##STR5##
[0046] LUB-1 is a composition exhibiting liquid crystallinity under
normal pressure and normal temperature, and showed a property of
being readily aligned under shear. Molecules of discotic compounds
are horizontally aligned with respect to a polar surface, unless
the surface is specifically treated for allowing thereon vertical
alignment. Under the conditions of this experiment, LUB-1 is
therefore supposed to form a molecular assembly film in which
molecules are aligned with their molecular plane, having a maximum
diffusion sectional area, being parallel to the shear plane.
Changes in the phase transfer temperature could otherwise be
observed also under pressure, but alignment property under shear
preferably remains unchanged or evolves into a higher order degree
from the viewpoint of energy, so that LUB-1 is supposed to show a
tendency of being more readily aligned. Exhibition of a low
traction coefficient at a temperature region higher than the
isotropic phase transfer temperature under normal pressure, as
shown in FIG. 1, suggests that LUB-1 is in a highly-aligned state
even at such temperature.
INDUSTRIAL APPLICABILITY
[0047] According to the present invention, it is possible to
provide a mechanical element exhibiting a low traction coefficient
under frictional sliding with elastic fluid lubrication, such as
piston, bearing, cam, gear, transmission, and bone joint in
biological systems, and to provide a lubricant composition
applicable to the mechanical element.
* * * * *