BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates to a lubricating oil
composition that displays excellent thermal stability and
lubrication properties, does not damage members used in
working machinery, and is ideal for use in high-temperature
environments.
The present invention relates particularly to a
lubricating oil composition that is ideal as a chain lubricant
for a tenter or the like.
2. DESCRIPTION OF RELATED ART
Lubricating oils containing a polyolester based oil as
the base oil display comparatively long hardening times (the
length of time required for loss of fluidity) and low
evaporation loss, and consequently offer excellent thermal
stability. As a result, these types of lubricating oils have
been widely commercialized as high-temperature lubricating
oils, in lubricants for tenters used for the transverse
stretching of resin films such as polypropylene (PP),
polyethylene terephthalate (PET), polyamide (PA), or
polyethylene (PE), or woven fabric, nonwoven fabric, building
material, or the like in an open system at a temperature of

approximately 200°C.
However, many of these lubricating oils generate large
quantities of oxidation polymers and sludge, meaning they are
not entirely suitable for practical application. In contrast,
those lubricating oils which are deemed to suffer minimal
sludge generation tend to have shorter hardening times, and
larger levels of evaporation loss, meaning their inherent
lubrication properties are inferior.
Furthermore, amongst high-temperature lubricating oils
containing a base oil as described above, the addition of a
phosphorus based compound or a sulfur based compound of a
lubricant as an extreme pressure agent or an anti-wear agent
is a common technique used to impart more favorable
lubrication characteristics (for example, see Japanese
Unexamined Patent Application, First Publication No. 2000-
129279 and Japanese Unexamined Patent Application, First
Publication No. 2001-303086). However, even lubricating oils
containing these conventional additives can suffer problems
during practical application. For example, under working
machinery conditions, these additives can form secondary
products that can cause blockages within the oil supply lines,
or products generated by the decomposition of these additives
can cause elution of those members within the machinery formed
from silicone rubber or the like. (Note, in this description,
the softening and deterioration of silicone based rubbers such

as vinyl methyl silicone (VMQ) caused by a reduction in the
molecular weight resulting from cleavage of the principal
chain is referred to as "elution.")
Accordingly, a lubricating oil that displays favorable
high-temperature stability with no loss of lubrication
properties, and does not effect the members used in working
machinery, even when used in high-temperature open systems
such as tenters, has been eagerly sought.
BRIEF SUMMARY OF THE INVENTION
The present invention takes the circumstances described
above into consideration, with an object of providing a
lubricating oil composition which is resistant to hardening
(oxidation polymerization) and sludge formation, and displays
minimal evaporation loss and superior thermal stability, even
under practical high-temperature open system conditions such
as those found in a tenter.
In order to achieve this object, a high-temperature
lubricating oil composition of the present invention employs
the aspects described below.
A lubricating oil composition according to the present
invention comprises a base oil component containing a
polyolester based synthetic oil, and
a diphenylamine derivative containing an arylalkyl group
with a number average molecular weight of 400 to 800.

Adding the diphenylamine derivative containing an
arylalkyl group with a number average molecular weight of 400
to 800 to this lubricating oil composition enables the
evaporation loss of the composition to be suppressed.
The quantity of the aforementioned diphenylamine
derivative within a lubricating oil composition of the present
invention is preferably within a range from 2 to 8% by weight.
Furthermore, the quantity of the aforementioned
diphenylamine derivative is even more preferably within a
range from 3 to 7% by weight.
Moreover, the quantity of the aforementioned
diphenylamine derivative is most preferably approximately 6%
by weight.
If the quantity of the diphenylamine derivative exceeds
8% by weight, then the evaporation loss becomes constant, and
no additional effect is achievable. Furthermore, if the
quantity of the diphenylamine derivative is too large, then
supersaturation of the derivative itself can actually cause
hardening. Accordingly, the quantity of the diphenylamine
derivative is preferably no more than 8% by weight, and is
even more preferably 7% by weight or less. In contrast, if
the quantity of the diphenylamine derivative amounts to less
than 2% by weight of the total weight of the lubricating oil
composition, then the effect of the additive in suppressing
evaporation loss is inadequate. Accordingly, the quantity of

the diphenylamine derivative is preferably at least 2% by
weight, and is even more preferably 3% by weight or greater.
From the viewpoint of best suppressing evaporation loss
and hardening of the lubricating oil composition, a
diphenylamine derivative quantity of approximately 6% by
weight is the most desirable.
In a lubricating oil composition of the present
invention, the polyolester based synthetic oil may comprise an
ester in which the alcohol component is dipentaerythritol,
pentaerythritol, trimethylolpropane or neopentyl glycol.
In a lubricating oil composition of the present
invention, the diphenylamine derivative may be 4,4-
bis(dimethylbenzyl)diphenylamine.
A lubricating oil composition of the present invention
may comprise a base oil component containing a polyolester
based synthetic oil and a C12 to C72 fatty acid. This fatty
acid may be a straight chain fatty acid, a branched chain
fatty acid, or a mixture thereof.
By employing a C12 to C72 fatty acid as one component of
the base oil, this lubricating oil composition is able to
impart excellent lubrication (with a high load bearing
capacity), without the use of additives that tend to cause
elution of those members within working machinery formed from
silicone rubber or the like.
In a lubricating oil composition of the present

invention, the quantity of the fatty acid described above is
preferably no more than 10% by weight.
Furthermore, in a lubricating oil composition of the
present invention, the quantity of the fatty acid is
preferably at least 1% by weight.
Moreover, in a lubricating oil composition of the present
invention, the quantity of the fatty acid is most preferably
approximately 2% by weight.
If the quantity of the fatty acid within the lubricating
oil composition exceeds 10% by weight, then the lubricating
oil composition suffers an undesirable loss of heat
resistance. Furthermore, in order to ensure satisfactory load
bearing capacity, the quantity of the fatty acid within the
lubricating oil composition is preferably at least 1% by
weight. In terms of the balance between heat resistance and
load bearing capacity, a fatty acid content within the
lubricating oil composition of approximately 2% by weight is
the most desirable.
In a lubricating oil composition of the present invention
comprising the base oil component containing a polyolester
based synthetic oil and a C12 to C72 fatty acid, the
polyolester based synthetic oil may comprise an ester in which
the alcohol component is dipentaerythritol, pentaerythritol,
trimethylolpropane or neopentyl glycol.
In a lubricating oil composition of the present

invention, the fatty acid may comprise an unsaturated fatty
acid.
Furthermore, in a lubricating oil composition of the
present invention, the fatty acid may comprise a saturated
fatty acid.
A lubricating oil composition of the present invention
may comprise a base oil component containing a polyolester
based synthetic oil and a C12 to C72 fatty acid, and a
diphenylamine derivative containing an arylalkyl group with a
number average molecular weight of 400 to 800.
By incorporating both a C12 to C72 fatty acid and a
diphenylamine derivative containing an arylalkyl group with a
number average molecular weight of 400 to 800, this
lubricating oil composition enables the evaporation loss of
the composition to be suppressed, while imparting excellent
lubrication (with a high load bearing capacity), without the
use of additives that tend to cause elution of those members
within working machinery formed from silicone rubber or the
like.
According to the present invention, a lubricating oil
composition is obtained which is resistant to hardening and
sludge formation, and displays minimal evaporation loss and
superior thermal stability, under working machinery
conditions.
Furthermore, according to the present invention, a

lubricating oil composition is obtained which provides
excellent lubrication without damaging members used within
working machinery.
A lubricating oil composition of the present invention is
particularly suited to use as the lubricating oil within high-
temperature open systems, such as the lubricating oil for a
tenter used for the transverse stretching of resin films,
woven fabric, nonwoven fabric, building material, or the like
in an open system at a high temperature of approximately
200°C. Furthermore, in addition to use as a lubricating oil
for tenters, a lubricating oil composition of the present
invention can also be favorably employed as a lubricating oil
for other applications, including use as a chain oil, jet
engine oil, gas turbine oil, compressor oil, hydraulic system
oil, gear oil, or as a base oil for bearing grease.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a graph showing the results of evaporation loss
tests (secondary performance tests) for oil samples from
Examples 1, 2, 9, and 10 and Comparative Examples 1 and 2.
FIG. 2 is a photograph showing the state of oil samples
from Examples 1 and 2, and Comparative Examples 1 and 2 during
the evaporation loss tests (secondary performance tests).
FIG. 3 is a graph showing the results of evaporation loss
tests (primary performance tests) for oil samples from

Examples 1, 3, 4, and 6 to 8.
FIG. 4 is a graph showing the results of Soda four-ball
tests on oil samples of Examples 1, 5 and 11 to 14.
FIG. 5 is a photograph showing the state of a test
specimen following immersion in an oil sample of Comparative
Example 1.
FIG. 6 is a photograph showing the state of a test
specimen following immersion in an oil sample of Comparative
Example 2.
FIG. 7 is a photograph showing the state of a test
specimen following immersion in an oil sample of Example 1.
DETAILED DESCRIPTION OF THE INVENTION
As follow is a description of embodiments of a high-
temperature lubricating oil composition according to the
present invention.
A polyolester based oil is used as the base oil for a
lubricating oil composition of the present invention, as such
polyolester based oils are resistant to hardening, suffer
minimal evaporation loss, and offer excellent high-temperature
stability. The quantity of the polyolester based oil within
the lubricating oil composition is preferably within a range
from 85 to 95% by weight of the total weight of the
composition. If the quantity of the polyolester based oil
exceeds 95% by weight, then the quantities of antioxidants and

lubrication additives within the composition become very low,
causing an increase in evaporation loss and a deterioration in
the load bearing capacity.
In contrast, if the quantity of the polyolester based oil
is less than 85% by weight of the lubricating oil composition,
then the antioxidants can become prone to hardening caused by
supersaturation. The quantity of the polyolester based oil is
even more preferably within a range from 85% to 95% by weight.
The polyolester based oil can use those oils typically
used as the base oils of conventional high-temperature
lubricating oils, and oils in which the alcohol component is
dipentaerythritol, pentaerythritol, trimethylolpropane or
neopentyl glycol are particularly suitable. There are no
particular restrictions on the acid component of the
polyolester based oil, which can be selected on the basis of
achieving a lubricating oil viscosity that falls within a
desired range. Examples of suitable acid components include
straight chain or branched chain, saturated or unsaturated
fatty acids of 6 to 10 carbon atoms. Of these, branched chain
fatty acids are preferred. Specific examples of suitable
acids include octanoic acid, decanoic acid, trimellitic acid,
and isononanoic acid, and of these, isononanoic acid is
particularly suitable from the viewpoint of viscosity.
A diphenylamine derivative of a lubricating oil
composition of the present invention functions as an

antioxidant, and suppresses evaporation loss from the
lubricating oil composition. The quantity of the
diphenylamine derivative within a lubricating oil composition
of the present invention is preferably within a range from 2
to 8% by weight of the total weight of the composition. If
the quantity of the diphenylamine derivative exceeds 8% by
weight, then the evaporation loss becomes constant, and no
additional effect is achievable. Furthermore, if the quantity
of the diphenylamine derivative is too large, then
supersaturation of the derivative itself can actually cause
hardening. In contrast, if the quantity of the diphenylamine
derivative amounts to less than 2% by weight of the total
weight of the lubricating oil composition, then the effect of
the additive in suppressing evaporation loss is inadequate.
The quantity of the diphenylamine derivative is even more
preferably within a range from 3 to 7% by weight, and is most
preferably approximately 6% by weight.
The diphenylamine derivative is a compound with a
structural formula shown below.


In the above structural formula, R1 and R2 each represent
an arylalkyl group with a number average molecular weight (Mn)
within a range from 400 to 800. One specific example of the
groups R1 and R2 is a dimethylbenzyl group. R1 and R2 may be
either identical groups, or different groups.
Any compound with the structural formula described above
can be used as the diphenylamine derivative of the present
invention, although 4,4-bis (dimethylbenzyl)diphenylamine,
represented by a structural formula shown below, is
particularly desirable.

A fatty acid can be added to the polyolester based
synthetic oil as a base oil component to improve the
lubrication properties (the load bearing capacity) of the
lubricating oil composition.
The quantity of fatty acid within the lubricating oil
composition is preferably no more than 10% by weight. If the
quantity of the fatty acid exceeds 10% by weight, then the
lubricating oil composition suffers an undesirable loss of
heat resistance.

Furthermore, although there are no particular
restrictions on the lower limit of the quantity of fatty acid
incorporated within the composition, in order to ensure
satisfactory load bearing capacity, the quantity is preferably
at least 1% by weight.
Examples of suitable fatty acids include the C12 to C72
fatty acids represented by a structural formula shown below.

In the above structural formula, R1 represents a C11 to C71
straight chain or branched chain hydrocarbon group. This
hydrocarbon group may be either saturated or unsaturated.
Representative examples of suitable saturated fatty acids
include lauric acid (C12) , myristic acid (C14) , palmitic acid
(C16) , and stearic acid (C18) , and representative examples of
suitable unsaturated fatty acids include oleic acid and
linoleic acid (both C18) , although the present invention is in
no way restricted to these acids. Furthermore, the fatty acid
may be either substituted or unsubstituted. In addition, the
fatty acid may also comprise a mixture of the different fatty
acids described above.
In addition to the components described above, one or

more known additives typically employed in conventional
lubricating oil compositions may also be blended into a
lubricating oil composition of the present invention to
further improve the performance of the composition. Examples
of such additives include antioxidants, oiliness and friction
modifiers, anti-wear agents, extreme pressure agents, metal-
based cleaning agents, viscosity index improvers, pour point
depressants, metal deactivators, metal corrosion inhibitors,
rust inhibitors, and antifoaming agents.
There are no particular restrictions on the method of
producing a lubricating oil composition of the present
invention, and each of the components described above can
simply be blended together using a typical heated mixing
device.
As follows is a description of specifics of the present
invention based on a series of examples and comparative
examples, although the present invention is in no way limited
to the examples presented below, and many modifications are
possible without departing from the scope of the appended
claims.
(Examples 1 and 2, and Comparative Examples 1 and 2)
Samples of lubricating oil compositions were prepared
with the respective compositions shown in Table 1. In the
table, the quantity of each component is expressed as a weight
percentage. The oil samples of Comparative Examples 1 and 2

were commercially available products.

(Examples 3 and 4)
With the exception of changing the quantity of 4,4-
bis(dimethylbenzyl)diphenylamine from 6% by weight to 3% by
weight and 1% by weight respectively, oil samples of Examples
3 and 4 were prepared using the same components as Example 1.
(Example 5)
With the exception of changing the quantity of fatty acid
to 0% by weight (that is, removing the component), an oil
sample of Example 5 was prepared using the same components as
Example 1.
(Examples 6 to 11)
Lubricating oil compositions were prepared with the
respective compositions shown in Table 2. In the table, the
quantity of each component is expressed as a weight
percentage.

(Examples 11 to 14)
Lubricating oil compositions were prepared with the
respective compositions shown in Table 3. In the table, the
quantity of each component is expressed as a weight
percentage.

(Evaporation loss testing, Secondary performance tests)
Oil samples of approximately 5 g from each of Examples 1,
2, 9, and 10, and Comparative Examples 1 and 2 were placed in
individual heat resistant glass beakers of capacity 10 cc.
2.5 g of iron powder (JIS SCM440) was added to each beaker,
and the beakers were then heated in an oven at 200°C for 720
hours. The variation in evaporation loss over time for each
oil sample is showed in FIG. 1.
Furthermore, the state of four of the oil samples after
heating for 700 hours is shown in FIG. 2.
From FIG. 1 and FIG. 2 it is evident that the oil samples
from Examples 1 and 2 did not harden, but rather retained
excellent fluidity, even after heating for 700 hours, thus
offering far superior heat resistance to the oil samples of
Comparative Examples 1 and 2.
Furthermore, Example 9, which contained no lubrication
additives, and Example 10, which contained no lubrication
additives and no fatty acid, displayed similar results (at 600
hours).
(Evaporation loss testing, Primary performance tests)
Oil samples of approximately 5 g from each of Examples 1,
3, 4, 6, 7, and 8 were placed in individual heat resistant
glass beakers of capacity 10 cc, and the beakers were then
left to stand in an oven at 200°C for 400 hours. The variation
in evaporation loss over time for each oil sample is showed in

FIG. 3.
From the results shown in FIG. 3 it is evident that
whereas Examples 1, 3, 4, and 6 all displayed excellent heat
resistance, the oil sample of Example 1, which contained 6% by
weight of 4,4-bis(dimethylbenzyl)diphenylamine provided the
best heat resistance, followed closely by the oil sample of
Example 3, which contained 3% by weight of 4,4-
bis(dimethylbenzyl)diphenylamine. The oil samples of Examples
7 and 8 displayed similar results to Example 1.
(Soda four-ball testing)
Oil samples from Examples 1, 5, 11, 12, 13, and 14 were
subjected to testing with a Soda four-ball tester, under
conditions including a revolution speed of 200 rpm, and a load
step-up rate of 0.5 kg/min, and the point at which the
coefficient of friction altered (the point where the oil film
became extremely thin, causing metal contact) was measured,
and recorded as the loading capacity. The results are shown
in FIG. 4.
From the results shown in FIG. 4 it is evident that the
oil samples of Examples 11 and 12, which contained a fatty
acid, had a larger loading capacity and offered more favorable
lubrication properties than the oil sample of Example 5, which
contained no fatty acid. The oil sample of Example 1, which
contained 2% by weight of fatty acid provided an increase in
loading capacity of almost three fold over that of the oil

sample of Example 5, which contained no fatty acid.
Furthermore, the oil samples of Examples 13 and 14, from which
the phosphorus based lubrication additive A had been removed,
displayed unchanged lubrication properties from those of
Example 1.
(Immersion testing)
Test specimens formed from vinyl methyl silicone (VMQ)
rubber were immersed in separate oil samples from Example 1,
and Comparative Examples 1 and 2, and were left to stand at
185°C. After 168 hours, the test specimens were removed and
inspected for evidence of elution. The state of the test
specimen following immersion in the oil sample from
Comparative Example 1 is shown in FIG. 5, the state of the
test specimen following immersion in the oil sample from
Comparative Example 2 is shown in FIG. 6, and the state of the
test specimen following immersion in the oil sample from
Example 1 is shown in FIG. 7.
As is evident from FIG. 5 through FIG. 7, whereas no
elution was observed for the test specimen immersed in the oil
of Example 1, elution was observed for the test specimens
immersed in the oil samples of Comparative Examples 1 and 2.

We Claim :
1. A lubricating oil composition comprising a base oil
component containing a polyolester based synthetic oil, such
as herein described, and a diphenylamine derivative, such as
herein described, containing an arylalkyl group with a number
average molecular weight of 400 to 800.
2. A lubricating oil composition as claimed in claim 1,
wherein a quantity of said diphenylamine derivative is within
a range from 2 to 8% by weight.
3. A lubricating oil composition as claimed in claim 1,
wherein a quantity of said diphenylamine derivative is within
a range from 3 to 7% by weight.
4. A lubricating oil composition as claimed in claim 1,
wherein a quantity of said diphenylamine derivative is
approximately 6% by weight.
5. A lubricating oil composition as claimed in claim 1,
wherein said polyolester based synthetic oil comprises an
ester in which an alcohol component is selected from a group
consisting of dipentaerythritol, pentaerythritol,
trimethylolpropane, and neopentyl glycol.

6. A lubricating oil composition as claimed in claim 1,
wherein said diphenylamine derivative is 4,4-
bis(dimethylbenzyl)diphenylamine.
7. A lubricating oil composition comprising a base oil
component containing a polyolester based synthetic oil, such
as herein described, and a C12 to C72 fatty acid.
8. A lubricating oil composition as claimed in claim 7,
wherein a quantity of said fatty acid is no more than 10% by
weight.
9. A lubricating oil composition as claimed in claim 7,
wherein a quantity of said fatty acid is at least 1% by
weight.
10. A lubricating oil composition as claimed in claim 7,
wherein a quantity of said fatty acid is approximately 2% by
weight.
11. A lubricating oil composition as claimed in claim 7,
wherein said polyolester based synthetic oil comprises an
ester in which an alcohol component is selected from a group
consisting of dipentaerythritol, pentaerythritol,

trimethylolpropane, and neopentyl glycol.
12. A lubricating oil composition as claimed in claim 7,
wherein said fatty acid comprises an unsaturated fatty acid.
13. A lubricating oil composition as claimed in claim 7,
wherein said fatty acid comprises a saturated fatty acid.
14. A lubricating oil composition comprising a base oil
component containing a polyolester based synthetic oil, such
as herein described, and a C12 to C72 fatty acid, and a
diphenylamine derivative, such as herein described, containing
an arylalkyl group with a number average molecular weight of
400 to 800.

A high-temperature lubricating oil composition is
provided, which is resistant to hardening and sludge
formation, and displays minimal evaporation loss and superior
thermal stability, even under practical high-temperature open
system conditions such as those found in a tenter. A
lubricating oil composition that provides excellent
lubrication without damaging members used within working
machinery is also provided. The lubricating oil composition
comprises a polyolester based synthetic oil, and a C12 to C72
fatty acid and/or a diphenylamine derivative containing an
arylalkyl group with a number average molecular weight of 400
to 800.