U.S. patent application number 11/136366 was filed with the patent office on 2005-10-06 for grease composition and rolling apparatus.
This patent application is currently assigned to NSK Ltd.. Invention is credited to Fujita, Yasunobu, Hokao, Michita, Miyajima, Hirotoshi, Nakatani, Shinya.
Application Number | 20050221997 11/136366 |
Document ID | / |
Family ID | 32996186 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050221997 |
Kind Code |
A1 |
Nakatani, Shinya ; et
al. |
October 6, 2005 |
Grease composition and rolling apparatus
Abstract
A grease composition is produced by mixing a thickener
comprising a fluoro resin and a second thickener component (a
metallic soap, a complex metallic soap, an N-substituted
terephthalamic acid metal salt, organic bentonite or a calcium
sulfonate complex) into a base oil. This grease composition is
excellent in heat resistance, load carrying capacity, water
resistance, rust protection, lubricating life and the like. A
rolling apparatus filled with the above grease composition has
excellent lubricating ability and is long-lived under
high-temperature conditions. Moreover, a grease composition is
produced by mixing a thickener comprising a fluoro resin and carbon
black as a second thickener component into a base oil. This grease
composition is excellent in heat resistance, water resistance, rust
protection, lubricating life, electric conductivity and the like. A
rolling apparatus filled with the above grease composition has
excellent electric conductivity and is long-lived under
high-temperature conditions.
Inventors: |
Nakatani, Shinya; (Kanagawa,
JP) ; Fujita, Yasunobu; (Kanagawa, JP) ;
Hokao, Michita; (Kanagawa, JP) ; Miyajima,
Hirotoshi; (Kanagawa, JP) |
Correspondence
Address: |
CROWELL & MORING LLP
INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
NSK Ltd.
Tokyo
JP
|
Family ID: |
32996186 |
Appl. No.: |
11/136366 |
Filed: |
May 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11136366 |
May 25, 2005 |
|
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10378060 |
Mar 4, 2003 |
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Current U.S.
Class: |
508/137 |
Current CPC
Class: |
C10M 169/06 20130101;
C10M 2215/223 20130101; C10M 2213/043 20130101; C10N 2030/68
20200501; C10M 2201/041 20130101; C10M 2207/0406 20130101; C10M
2207/1426 20130101; C10N 2030/10 20130101; C10M 2201/0416 20130101;
C10N 2010/02 20130101; C10N 2010/04 20130101; C10N 2030/02
20130101; C10N 2030/22 20200501; C10N 2050/10 20130101; C10M
2215/064 20130101; C10M 169/02 20130101; C10M 2207/2835 20130101;
C10M 2201/1036 20130101; C10M 2211/066 20130101; C10N 2030/60
20200501; C10N 2030/08 20130101; C10M 2215/065 20130101; C10M
2219/046 20130101; C10N 2030/12 20130101; C10M 2201/1026 20130101;
C10M 2207/1285 20130101; C10M 2215/02 20130101; C10N 2030/26
20200501; C10M 2213/0626 20130101; C10M 2201/1006 20130101; C10M
2205/0285 20130101; C10M 2213/02 20130101; C10M 2211/0213 20130101;
C10M 2219/044 20130101; C10M 119/22 20130101; C10M 2201/083
20130101; C10M 2203/1025 20130101; C10N 2030/06 20130101; C10M
2203/1025 20130101; C10M 2203/1025 20130101; C10M 2213/02 20130101;
C10M 2213/02 20130101 |
Class at
Publication: |
508/137 |
International
Class: |
C10M 169/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2002 |
JP |
2002-062069 |
Mar 15, 2002 |
JP |
2002-073110 |
Aug 30, 2002 |
JP |
2002-252665 |
Sep 30, 2002 |
JP |
2002-286026 |
Claims
What is claimed is:
1. A grease composition comprising a base oil and a thickener,
wherein said thickener comprises a fluoro resin and a second
thickener component, wherein said second thickener component is
organic bentonite.
2. The grease composition according to claim 1, wherein said
thickener comprises 5 to 95% by mass of the fluoro resin and 95 to
5% by mass of the organic bentonite.
3. The grease composition according to claim 2, wherein the content
of said thickener is 3 to 40% by mass based on the total mass of
the composition.
4. A rolling apparatus comprising an inner member having a raceway
surface on the outer surface; an outer member which has a raceway
surface opposed to the raceway surface of said inner member and is
disposed outside of said inner member; and a plurality of rolling
elements which are disposed between said two raceway surfaces so as
to flexibly roll therebetween, wherein a space, which is formed
between said inner member and said outer member and in which said
rolling elements are disposed, is filled with the grease
composition according to claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of patent application Ser.
No. 10/378,060, filed Mar. 4, 2003, the entire disclosure of which
is incorporated herein by reference. Priority is claimed based on
Japanese Patent Application Nos. 2002-062069, filed Mar. 7, 2002;
2002-073110, filed Mar. 15, 2002; 2002-252665, filed Aug. 30, 2002;
and 2002-286026, filed Sep. 30, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to a grease composition, which
hardly disperses and has excellent high-temperature performance.
Moreover, the present invention relates to a rolling apparatus,
which has low torque and excellent acoustic performance and
generates a few dusts, and in particular, the present invention
relates to a rolling apparatus, which is preferably used in
electronic intelligence equipment, semiconductor manufacturing
machines and others.
[0003] Furthermore, the present invention relates to a grease
composition having excellent lubricating ability and heat
resistance. Still further, the present invention relates to a
rolling apparatus, which has excellent lubricating ability and is
long-lived under high-temperature conditions, and in particular, it
relates to a rolling apparatus, which is preferably used as a
rolling or sliding portion of machines used under high-temperature
and high-speed conditions including car electrical components such
as alternators or electromagnetic clutches; auxiliary equipment for
car engine such as idler pulleys; and business machines such as
copying machines or printers.
[0004] Furthermore, the present invention relates to a grease
composition having excellent rust protection, extreme-pressure
property, water resistance and lubricating life, and a rolling
apparatus which is long-lived although it is used under stringent
conditions.
[0005] Furthermore, the present invention relates to a grease
composition having excellent heat resistance, lubricating ability
and rust protection. Still further, the present invention relates
to a rolling apparatus which has excellent lubricating ability and
is long-lived under high-temperature conditions, and it
particularly relates to a rolling bearing, which is preferably used
in electrical machines for a car engine which are required for heat
resistance, load carrying capacity and durability.
[0006] Furthermore, the present invention relates to a grease
composition having excellent lubricating ability and electric
conductivity. Still further, the present invention relates to a
rolling apparatus, which has excellent electric conductivity and is
long-lived under high-temperature conditions, and in particular, it
relates to a rolling apparatus, which is preferably used as a
rolling or sliding portion of machines used under high-temperature
and high-speed conditions including car electrical components such
as alternators or electromagnetic clutches; auxiliary equipment for
car engine such as idler pulleys; and business machines such as
copying machines or printers.
DESCRIPTION OF THE RELATED ART
[0007] (1) A rolling apparatuses (e.g. rolling bearings, linear
guide apparatuses, ball screws, etc.), which are used in electronic
intelligence equipment such as a hard disk drive (hereinafter
referred to as HDD) or laser beam printer (LBP), semiconductor
manufacturing machines and others, are required to have various
performances such that these apparatuses generate a few dusts, have
low torque and excellent acoustic performance, and are
long-lived.
[0008] Moreover, with the development of high-precision electronic
intelligence equipment and semiconductors in recent years, the use
conditions (temperature, speed, etc.) of rolling apparatuses, which
are used in electronic intelligence equipment and semiconductor
manufacturing machines, have become increasingly strict. Under such
strict use conditions, the above stated various types of
performance are required to be excellent.
[0009] For example, in the case of electronic intelligence
equipment such as HDD used under a clean atmosphere, if a gaseous
oil or the fine particles of grease are released from the inside of
a bearing when a rolling apparatus rotates, the fine particles
pollute a recording medium or the like and cause operation errors.
Therefore, it is most important to suppress the amount of dusts
generated.
[0010] As a grease composition enclosed in such a rolling bearing
for HDD, Undock C (Trade name), which is a grease comprising a
mineral oil as a base oil and a sodium complex soap as a thickener,
is well known, and this product has been used over 20 years because
it causes a small amount of dusts.
[0011] When excellent performance of low torque and low noise is
required, a grease comprising a lithium soap as a thickener and an
ester oil as a base oil has been used at times.
[0012] Moreover, Japanese Patent Laid-Open No. 2000-109874
discloses a fluoro grease composition obtained by mixing a silicone
oil into a fluoro grease consisting of a fluoro oil and a
thickener. This fluoro grease composition has a property such that
oil does not leak so much from the grease.
[0013] Furthermore, Japanese Patent Laid-Open No. 2001-187892
discloses a grease composition comprising a silicone oil as a base
oil, polytetrafluoroethylene as a thickener, silica aerogel and an
extreme-pressure additive. This grease composition has a property
such that it has excellent low-temperature flow property, wear
resistance, heat resistance and low torque property at a low
temperature.
[0014] However, in the above sodium complex soap-mineral oil
grease, the dispersibility of the thickener is insufficient and so
it hardly becomes homogenous, and thereby problems regarding
acoustic and vibration performances occur in the early stage of
rotation of the rolling bearing. In addition, since this grease has
strong hygroscopicity and gets hard over time, and thereby the flow
property in the rolling bearing decreases, this grease also has a
problem of causing insufficient lubrication and readily generating
abnormal sounds from the cage.
[0015] Therefore, when excellent performance of low torque and low
noise is required, the above described lithium soap-ester oil
grease has been used at times. However, since this grease easily
disperses (causes a large amount of dusts), there is a great risk
that the grease might pollute a recording medium or the like when
it is used in a rolling bearing for HDD. Moreover, since the
temperature used for the rolling bearing for HDD is more and more
increased, the above described lithium soap-ester oil grease cannot
be applied in some cases.
[0016] Further, the grease compositions as disclosed above in
Japanese Patent Laid-Open Nos. 2000-109874 and 2001-187892 comprise
a very expensive silicone oil or fluoro oil, these grease
compositions are expensive when compared with common greases.
SUMMARY OF THE INVENTION
[0017] Thus, it is a first object of the present invention to solve
the above described problems of the prior art techniques and to
provide a grease composition which is hardly dispersed and has
excellent high-temperature performance. Moreover, it is also the
first object of the present invention to provide a rolling
apparatus, which has low torque and excellent acoustic performance,
and generates a few dusts.
[0018] (2) Cars (passenger cars) tend to be directed towards
downsizing, weight saving and the expansion of the living space,
and therefore cars are forced to reduce their engine room space.
For this reason, the downsizing and weight saving of electrical
components or auxiliary equipment for car engine are increasingly
progressing. In addition, cars are required for silence
improvement, the hermeticity of the engine room is progressing, and
thereby the temperature in the engine room becomes higher.
Accordingly, the above described components or equipment for cars
are also required for high-temperature resistance property. For
example, bearings for electrical fan motors had previously been
used at a bearing temperature of 130.degree. C. to 150.degree. C.,
but in recent years, the same bearings have been required to resist
a high temperature of 180.degree. C. to 200.degree. C.
[0019] As described in Japanese Patent Publication No. 2977624,
bearings used under high-temperature environment of 150.degree. C.
or higher have previously been dealt with by filling the inside of
the bearing with a grease obtained by mixing a lithium soap and a
urea compound into a synthetic oil type lubricating oil. However,
under a high-temperature condition of 160.degree. C. or higher,
even this grease generates seizure in an early stage, and so a
grease having further higher heat resistance is required.
[0020] On the other hand, in OA machines, especially in copying
machines or the like, since color fine particles (toner) consisting
of a thermoplastic resin and a coloring agent is fused by heating
and then fixed on a paper by pressure, a heater is inserted into
the axis of a roller, and therefore the temperature of the rolling
bearing of a bearing portion sometimes rises to 140.degree. C. to
200.degree. C., depending on the models. Therefore, for such
rolling bearings, a grease having excellent heat resistance should
be used.
[0021] For example, a fluoro grease comprising
polytetrafluoroethylene (PTFE) as a thickener and a
perfluoropolyether oil (PFPE oil) as a base oil has excellent heat
resistance, and so a rolling bearing filled with this fluoro grease
can be used under high-temperature environment of 160.degree. C. or
higher.
[0022] However, since it is difficult to add additives that can be
mixed into common greases into the above described fluoro greases,
these greases are likely to have poor lubricating ability, rust
protection and a metallic corrosion preventing property. Moreover,
the fluoro greases have another disadvantage in that these greases
are more expensive than synthetic oil type greases by approximately
5 to 20 times.
[0023] Japanese Patent Laid-Open No. 11-181465 describes a grease
composition, heat resistance of which is improved by blending a
fluoro oil with a urea grease. However, since a mineral oil or
synthetic oil that is a base oil of the urea grease has a poor
affinity for a fluoro oil, the above grease composition has a high
oil separation percentage, and therefore this grease composition
has a disadvantage in that the use of the grease composition is
inappropriate for a bearing used in components which rotate at a
high speed.
[0024] Thus, it is a second object of the present invention to
solve the above described problems of the prior art techniques and
to provide a grease composition having excellent lubricating
ability and heat resistance. Moreover, it is also the second object
of the present invention to provide a rolling apparatus, which has
excellent lubricating ability and is long-lived under
high-temperature conditions.
[0025] (3) With the development of mechanical technology in recent
years, mechanical devices tend to be directed towards downsizing,
weight saving and high-speed rotation. Mechanical portions such as
a bearing and a gear become increasingly exposed at a high
temperature. Therefore, in such mechanical portions, a grease used
at a high temperature is used. Moreover, a grease used at a high
temperature is used also for bearings which are used under
high-temperature conditions, such as bearing integrated into iron
manufacturing machines (e.g. continuous casting machines, rolling
mill for iron and steel, etc.,) various heat processing apparatus
or driers.
[0026] Examples of such a high-temperature grease include a
metallic soap grease which uses, as a thickener, a metallic soap
such as Ca, Al, or Li, and a complex metallic soap; an organic
grease which uses an organic compound such as polyurea, a
terephthalamic acid metal salt or a fluoro resin; and an inorganic
grease which uses an inorganic compound such as bentonite.
[0027] However, each of these greases also has a disadvantage. For
example, the metallic soap grease such as an alminum complex grease
has excellent lubricating ability, but it cannot maintain the
grease structure for a long time under high-temperature conditions.
The grease comprising polyurea is likely to cause hardening
phenomenon, and the grease comprising a terephthalamic acid metal
salt has large oil separation. Further, the grease comprising
bentonite has insufficient rust protection, extreme-pressure
property and water resistance.
[0028] As a grease which solves the above problems, a grease
obtained by adding dibasic acid esthers into organic be itonite to
enhance rust protection is known (Japanese Patent Laid-Open No.
6-200273). There is also known a grease obtained by adding the
metal salt of carboxylic acid with a substitution at condensed ring
into organic bentonite to enhance a metallic corrosion preventing
property (Japanese Patent Publication No. 2711150).
[0029] However, the grease described in the above Patent
Publication still has a problem regarding insufficient
extreme-pressure property and water resistance.
[0030] Thus, it is a third object of the present invention to solve
the above described problems of the prior art techniques and to
provide a grease composition having excellent rust protection,
extreme-pressure property, water resistance and lubricating life.
Moreover, it is also the third object of the present invention to
provide a rolling apparatus, which is long-lived although it is
used under strict conditions.
[0031] (4) As stated above, with the development of mechanical
technology in recent years, mechanical devices tend to be directed
towards downsizing, weight saving and high-speed rotation, and
rolling bearings used in electrical machines surrounding a car
engine also tend to have a high temperature. On the other hand,
resources and power saving efforts are required, and
maintenance-free mechanical devices are also required. Accordingly,
rolling bearings are required not only for heat resistance but also
for reliability and durability.
[0032] Presently, in rolling bearings used under high-temperature
environment over 180.degree. C., a fluoro grease, clay mineral
grease or the like is generally charged. However, although these
greases are excellent in heat resistance, they have a disadvantage
in that they have poor lubricating ability, load carrying capacity
and rust protection.
[0033] As a grease satisfying conditions such as rust protection,
heat resistance and load carrying capacity, a calcium sulfonate
complex grease which comprises, as a thickener, a calcium sulfonate
complex containing calcium carbonate is known (Japanese Patent
Publication No. 5-8760). However, when this calcium sulfonate
complex grease is used under high-temperature conditions over
180.degree. C., it does not have the same level of heat resistance
as a fluoro grease.
[0034] Thus, it is a fourth object of the present invention to
solve the above described problems of the prior art techniques and
to provide a grease composition having excellent heat resistance,
lubricating ability and rust protection. Moreover, it is also the
fourth object of the present invention to provide a rolling
apparatus, which has heat resistance so that it can be used under
high-temperature conditions over 180.degree. C., as well as having
excellent load carrying capacity, durability and rust protection,
and particularly to provide a rolling bearing which is preferably
used in electrical machines surrounding a car engine.
[0035] (5) Cars (passenger cars) tend to be directed towards
downsizing, weight saving and the expansion of the living space,
and therefore cars are forced to reduce their engine room space.
For this reason, the downsizing and weight saving of electrical
components or auxiliary equipment for car engine are increasingly
progressing. In addition, cars are required for silence
improvement, the hermeticity of the engine room is progressing, and
thereby the temperature in the engine room becomes higher.
Accordingly, the above described components or equipment for cars
are also required for high-temperature resistance property.
[0036] At present, as a grease composition used for the rolling
bearing of each of the above components, a grease composition
comprising a synthetic oil as a base oil and a urea compound as a
thickener is mainly used, and this urea compound-synthetic oil
grease has excellent lubricating ability up to a temperature of
170.degree. C. to 180.degree. C. However, under high temperature
conditions of 200.degree. C. or higher, the evaporation of the base
oil, the hardening of the grease associated therewith, and the
softening of the grease by the construction of the thickener occur,
and therefore there is a risk that a rolling bearing filled with
the urea compound-synthetic oil grease might generate seizure in an
early stage.
[0037] Moreover, as described in Japanese Patent Laid-Open No.
11-72120, in the rolling bearing used in each of the above
components, there are some cases where hydrogen generates by water
present in the bearing, and the generated hydrogen enters in a
bearing steel constituting an inner ring, an outer ring and rolling
elements, thereby causing a flaking of formed white structure due
to hydrogen brittleness. This is considered to occur as a result of
the phenomenon that a direct electric current is generated by
metallic contact by vibration or the like at a portion between the
inner and outer rings which becomes isolated by the oil film of a
lubricant, and that hydrogen ions thereby generate from the water
present in the bearing. The generation of hydrogen and the flaking
of formed white structure thereby can significantly be controlled
by the impartation of electric conductivity to a grease.
[0038] On the other hand, in OA machines, especially in copying
machines or the like, since color fine particles (toner) consisting
of a thermoplastic resin and a coloring agent is fused by heating
and then fixed on a paper by pressure, a heater is inserted into
the axis of a roller, and therefore the temperature of the rolling
bearing of a bearing portion sometimes rises to 140.degree. C. to
200.degree. C., depending on the models. Therefore, for such
rolling bearings, a grease having excellent heat resistance should
be used.
[0039] Moreover, as described above, since the inner and outer
rings of a rolling bearing become isolated by the oil film of a
lubricant, static electricity generates by rotation. Since the
radiation noise has adverse effects such as distortion on the
copying screen of a copying machine, as described, for example, in
Japanese Patent Publication No. 63-24038, there is taken a
countermeasure of charging a grease with electric conductivity in a
rolling bearing to electrify the portion between inner and outer
rings, thereby eliminating static electricity.
[0040] For example, a fluoro grease comprising
polytetrafluoroethylene (PTFE) as a thickener and a
perfluoropolyether oil (PFPE oil) as a base oil has excellent heat
resistance, and so a rolling bearing filled with this fluoro grease
can be used under high-temperature conditions of 180.degree. C. or
higher.
[0041] However, since it is difficult to add additives that can be
mixed into common greases into the above described fluoro greases,
these greases are likely to have poor lubricating ability, rust
protection and a metallic corrosion preventing property. Moreover,
the fluoro greases have another disadvantage in that these greases
are more expensive than synthetic oil type greases by approximately
5 to 20 times.
[0042] Japanese Patent Laid-Open No. 11-181465 describes a grease
composition, heat resistance of which is improved by blending a
fluoro oil with a urea grease. However, since a mineral oil or
synthetic oil that is a base oil of the urea grease has a poor
affinity for a fluoro oil, the above grease composition has a high
oil separation percentage, and therefore there is a disadvantage
that the use of this grease composition is inappropriate for a
bearing used in components which rotate at a high speed.
[0043] Thus, it is a fifth object of the present invention to solve
the above described problems of the prior art techniques and to
provide a grease composition having excellent lubricating ability
and electric conductivity. Moreover, it is also the fifth object of
the present invention to provide a rolling apparatus, which has
excellent electric conductivity and is long-lived under
high-temperature conditions.
[0044] (6) As stated above, grease composition are classified into
the following 4 types according to the types of a thickener:
[0045] (i) a metallic soap grease comprising a metallic soap such
as Li, Ca, Na or Al;
[0046] (ii) a complex metallic soap grease comprising a complex
metallic soap such as Li, Ca, Na and Al;
[0047] (iii) an organic grease comprising an organic compound (an
organic thickener) such as polyurea, a terephthalamic acid metal
salt or a calcium sulfonate complex; and
[0048] (iv) an inorganic grease comprising an inorganic compound
(an inorganic thickener) such as bentonite or silica gel.
[0049] However, as described in the "Lubrication Control Manual
Book" edited by the Japan Lubricating Oil Society and the
Lubrication Control Diffusion Task Force (the Japanese Lubricating
Oil Society, published Mar. 20, 1990) and "A Brief History of
Lubricating Greases" written by Arthur T. Polishuk (Llewellyn &
McKane, Inc., published 1998), it has previously been thought that,
when different types of grease compositions are mixed, the
properties of the grease compositions are altered and deteriorated
in many cases. This deterioration naturally occurs when 2 types
from among the above 4 types of grease compositions are mixed, but
it could also occur when 2 types of metallic soap greases are
mixed, in which the type of metals is different.
[0050] When a significant deterioration occurs in a grease, the
grease structure is destroyed, significant softening of the grease
or decrease of the dropping point occurs, and the grease is
liquefied at times. Moreover, there are also cases where additives
which are added to a grease composition, act on one another and
reduce the performance of the grease composition. For these
reasons, it has generally been believed that the mixing of grease
compositions should be prevented as much as possible.
[0051] Grease compositions used in rolling apparatuses such as a
rolling bearing, a ball screw, a linear guide apparatus and a
linear bearing are required to have various performances such as
lubricating performance, load carrying capacity, heat resistance,
water resistance, low torque and few dusts generating property. To
obtain such a grease component having many excellent performances,
a method for mixing grease components each having one of the above
performances is considered to be effective. However, probably
because it has generally been believed that the mixing of grease
components comprising different types of thickener is not good, the
above method has seldom been used.
[0052] A few examples include Japanese Patent Publication No.
6-31375 disclosing the combined use of an N-substituted
terephthalamic acid metal salt and polyurea, Japanese Patent
Laid-Open No. 7-268370 (& U.S. Pat. No. 5,948,737A) disclosing
the combined use of a hydrogen-addition grease and a fluoro grease
or fluoro oil, and Japanese Patent Laid-Open No. 2001-3074
disclosing the combined use of a sodium soap and a lithium
soap.
[0053] Although two types of thickener are used in combination, if
the excellent performances of both thickener consist with each
other, the above described grease component having many excellent
performances can be obtained. Thus, the present invention adopts a
method involving the combined use of two different types of
thickener to achieve the above described first to fifth
objects.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0054] (1) The grease composition of the present invention is a
grease composition in which two different types of thickeners are
used in combination, and the grease composition of the present
invention has many excellent performances. A large number of
combinations of two types of thickeners can be conceived, but in
the present invention, as a first thickener, a fluoro resin is
used. That is to say, the grease composition of the present
invention is a grease composition comprising a base oil and a
thickener, wherein the above thickener consists of a fluoro resin
and a second thickener component.
[0055] As described later, as the second thickener component, a
metallic soap, a complex metallic soap, an N-substituted
terephthalamic acid metal salt, organic bentonite, a calcium
sulfonate complex or carbon black is used.
[0056] It should be noted that a different type of a third
thickener may also be used in combination to such an extent that it
does not impair the purpose of the present invention.
[0057] (2) To achieve the above first object, the present invention
has the following features. That is to say, the grease composition
of the present invention comprises a metallic soap as the above
second thickener component.
[0058] Since this grease composition comprises both a fluoro resin
and a metallic soap as a thickener, it hardly disperses and has
excellent high-temperature performance. Moreover, this grease
composition imparts excellent acoustic performance and torque
performance to a rolling apparatus in which the grease composition
is enclosed.
[0059] The above thickener preferably comprises 10 to 80% by mass
of the fluoro resin and 90 to 20% by mass of the metallic soap.
[0060] If the composition of the thickener is out of the above
range, there is a risk that the grease composition might generate
an increased amount of dusts or have insufficient high-temperature
performance. Moreover, there is also another risk that when the
grease composition is charged in a rolling apparatus, the acoustic
performance of the rolling apparatus might decrease, or torque
might increase.
[0061] In order to decrease the amount of dusts generated from the
grease composition and to enhance the high-temperature performance
so as to enhance the acoustic performance and torque performance of
a rolling apparatus in which the grease composition is enclosed,
the thickener more preferably comprises 20 to 70% by mass of the
fluoro resin and 80 to 30% by mass of the metallic soap.
[0062] Furthermore, the content of the above described thickener is
preferably 10 to 33% by mass based on the total mass of the
composition.
[0063] If the content of the thickener is less than 10% by mass,
the grease composition becomes too soft and thereby the amount of
dust generated increases, and if the content is more than 33% by
mass, the grease composition gets so hardened that it becomes
difficult for the grease composition to exert sufficient
lubricating ability, resulting in a risk of decreasing acoustic
durability. Taking into consideration the amount of dusts
generated, acoustic durability and worked penetration, the content
of the thickener is more preferably 15 to 30% by mass based on the
total mass of the composition.
[0064] The above base oil preferably comprises 20 to 70% by mass of
a perfluoropolyether oil and 80 to 30% by mass of at least one of
either a mineral oil or synthetic oil.
[0065] Since the grease composition of the present invention
comprises the perfluoropolyether oil as a base oil and the fluoro
resin as a thickener, it has excellent high-temperature
performance. Accordingly, a rolling apparatus in which the grease
composition of the present invention is enclosed is long-lived
under high-temperature conditions. Moreover, since the viscosity of
the base oil of the grease composition is controlled at low, the
grease composition is also excellent in low-temperature flow
property.
[0066] The grease composition described in Examples 1 to 4 of
Japanese Patent Laid-Open No. 7-268370 contains a small amount of
fluoro oil, the same high-temperature performance as in the present
invention cannot be obtained.
[0067] Moreover, since the grease composition of the present
invention comprises, as a base oil, at least one of either the
mineral oil or synthetic oil, various additives can be added
thereto, thereby imparting various performances such as lubricating
ability, rust protection and a metallic corrosion preventing
property to the grease composition. Furthermore, since the grease
composition comprises, as a base oil, at least one of either the
mineral oil or synthetic oil, the grease composition of the present
invention is low-priced when compared with the conventional grease
compositions comprising a silicone oil or fluoro oil as a base
oil.
[0068] If the content of at least one of either the mineral oil or
synthetic oil is less than 30% by mass, there is a risk of not
obtaining sufficient additive effects when additives are added to
the grease composition. Moreover, when the content of at least one
of either the mineral oil or synthetic oil is less than 30% by
mass, the content of the perfluoropolyether oil exceeds 70% by
mass, and the grease composition thereby becomes expensive. In
contrast, if the content of at least one of either the mineral oil
or synthetic oil exceeds 80% by mass and that of the
perfluoropolyether oil is less than 20% by mass, the grease
composition has insufficient high-temperature performance.
[0069] Moreover, it is preferable that the above perfluoropolyether
oil has a kinematic viscosity at 40.degree. C. of 20 to 400
mm.sup.2/s, and at least one of either the above mineral oil or
synthetic oil has a kinematic viscosity at 40.degree. C. of 50 to
500 mm.sup.2/s.
[0070] If the kinematic viscosity at 40.degree. C. of each of the
above compounds exceeds the above upper limit, there is a risk that
the low-temperature flow property of the grease composition might
be insufficient and that abnormal sounds might be generated when
the rolling apparatus is activated at a low temperature. To the
contrary, if the kinematic viscosity of each of the above compounds
is less than the above lower limit, it is not appropriate in terms
of evaporation loss or lubricating ability. That is, if the
viscosity of a base oil is too low, it becomes difficult to form
lubricating oil film which is enough to prevent metallic contact
between the raceway surface and the rolling elements when the
bearing is rotated at a high temperature.
[0071] In order to reduce this problem wherever possible, it is
more preferable that the above perfluoropolyether oil has a
kinematic viscosity at 40.degree. C. of 30 to 200 mm.sup.2/s, and
at least one of either the above mineral oil or synthetic oil has a
kinematic viscosity at 40.degree. C. of 70 to 400 mm.sup.2/s.
[0072] Furthermore, it is preferable that the grease composition of
the present invention has a worked penetration of 190 to 250.
[0073] In order to suppress dusts generated from a rolling
apparatus in which the grease composition is enclosed, it is
preferable to harden the grease composition. However, if the grease
composition is too hard, the flow property in the rolling apparatus
decreases, resulting in insufficient lubrication and then ready
generation of abnormal sounds from a cage. Therefore, the worked
penetration of the grease composition is preferably 190 to 250. If
the worked penetration is less than 190, the grease composition is
so hard that the rolling apparatus filled with the grease
composition has decreased acoustic and torque performances. If the
worked penetration exceeds 250, the amount of dusts generated from
the rolling apparatus increases.
[0074] Still further, the rolling apparatus of the present
invention directed towards achieving the above first object is a
rolling apparatus comprising an inner member having a raceway
surface on the outer surface; an outer member which has a raceway
surface opposed to the raceway surface of the inner member and is
disposed outside of the inner member; and a plurality of rolling
elements which are disposed between the two raceway surfaces so as
to flexibly roll therebetween, wherein a space, which is formed
between the inner member and the outer member and in which the
rolling elements are disposed, is filled with the above described
grease composition comprising a metallic soap as the second
thickener component.
[0075] Since the rolling apparatus with the above configuration is
filled with a grease composition comprising both a fluoro resin and
a metallic soap as thickeners, the rolling apparatus has low torque
and excellent acoustic performance, generating a small amount of
dusts.
[0076] Moreover, a grease composition comprising a complex metallic
soap as the above second thickener component can also achieve the
above first object. That is to say, the grease composition of the
present invention comprises a complex metallic soap as the above
second thickener component.
[0077] Since this grease composition comprises both a fluoro resin
and a complex metallic soap as thickeners, it hardly disperses and
has excellent high-temperature performance. Moreover, this grease
composition imparts excellent acoustic performance and torque
performance to a rolling apparatus in which the grease composition
is enclosed. The grease composition comprising the complex metallic
soap as the second thickener component has high-temperature
performance more excellent than the grease composition comprising
the metallic soap as the second thickener component. However,
regarding acoustic performance, the grease composition comprising
the metallic soap as the second thickener component is more
excellent than the grease composition comprising the complex
metallic soap as the second thickener component.
[0078] Moreover, a rolling apparatus filled with this grease
composition can achieve the above first object. That is to say, the
rolling apparatus of the present invention comprises an inner
member having a raceway surface on the outer surface; an outer
member which has a raceway surface opposed to the raceway surface
of the inner member and is disposed outside of the inner member;
and a plurality of rolling elements which are disposed between the
two raceway surfaces so as to flexibly roll therebetween, wherein a
space, which is formed between the inner member and the outer
member and in which the rolling elements are disposed, is filled
with the above described grease composition comprising a complex
metallic soap as the second thickener component.
[0079] (3) To achieve the above second object, the present
invention has the following features. That is to say, the grease
composition of the present invention comprises an N-substituted
terephthalamic acid metal salt as the above second thickener
component.
[0080] The above base oil preferably comprises a perfluoropolyether
oil and at least one of either a mineral oil or synthetic oil.
[0081] Since the grease composition of the present invention
comprises the perfluoropolyether oil as a base oil and a fluoro
resin as a thickener, it has excellent heat resistance. Moreover,
since the viscosity of the base oil is controlled at low, the
grease composition is also excellent in low-temperature flow
property. Furthermore, since the grease composition comprises, as a
base oil, at least one of either the mineral oil or synthetic oil,
various additives can be added thereto. Accordingly, the grease
composition of the present invention is excellent in lubricating
ability, rust protection and a metallic corrosion preventing
property.
[0082] Further, since the grease composition comprises at least one
of either the mineral oil or synthetic oil as a base oil, and the
N-substituted terephthalamic acid metal salt as a thickener, the
grease composition of the present invention is low-priced when
compared with fluoro greases.
[0083] Still further, the above thickener preferably comprises 40
to 80% by mass of the fluoro resin and 60 to 20% by mass of the
N-substituted terephthalamic acid metal salt.
[0084] When the content of the N-substituted terephthalamic acid
metal salt is less than 20% by mass and the content of the fluoro
resin exceeds 80% by mass, it results in the high cost of the
grease composition. To the contrary, when the content of the
N-substituted terephthalamic acid metal salt exceeds 60% by mass
and the content of the fluoro resin is less than 40% by mass, the
heat resistance of the grease composition is insufficient. In order
to reduce this problem wherever possible, it is more preferable
that the thickener comprises 50 to 70% by mass of the fluoro resin
and 50 to 30% by mass of the N-substituted terephthalamic acid
metal salt.
[0085] Moreover, the above base oil preferably comprises 10 to 90%
by mass of the perfluoropolyether oil and 90 to 10% by mass of at
least one of either the mineral oil or synthetic oil.
[0086] If the content of at least one of either the mineral oil or
synthetic oil is less than 10% by mass, sufficient additive effects
cannot be obtained when additives are added to the grease
composition. If the content of at least one of either the mineral
oil or synthetic oil is less than 10% by mass, the content of the
perfluoropolyether oil exceeds 90% by mass, thereby resulting in
the high cost of the grease composition. To the contrary, if the
content of at least one of either the mineral oil or synthetic oil
exceeds 90% by mass and the content of the perfluoropolyether oil
is less than 10% by mass, the heat resistance of the grease
composition is insufficient.
[0087] Moreover, the content of the above thickener is preferably 5
to 40% by mass based on the total mass of the composition.
[0088] If the content is less than 5% by mass, it becomes difficult
to maintain a grease state, but if the content exceeds 40% by mass,
the grease composition gets so hardened that it becomes difficult
for the grease composition to exert sufficient lubricating
ability.
[0089] Furthermore, it is preferable that the above
perfluoropolyether oil has a kinematic viscosity at 40.degree. C.
of 20 to 400 mm.sup.2/s, and at least one of either the above
mineral oil or synthetic oil has a kinematic viscosity at
40.degree. C. of 20 to 400 mm.sup.2/s.
[0090] If the kinematic viscosity at 40.degree. C. of each of the
above compounds exceeds 400 mm.sup.2/s, oil film gets relatively
thick and torque becomes large in a rolling apparatus filled with
the grease composition of the present invention. Further, there is
a risk that the low-temperature flow property of the grease
composition might be insufficient and that abnormal sounds might be
generated when the rolling apparatus is activated at a low
temperature. However, if the kinematic viscosity of each of the
above compounds is less than 20 mm.sup.2/s, it is not appropriate
in terms of evaporation loss or lubricating ability. That is, if
the viscosity of the base oil is too low, it becomes difficult to
form lubricating oil film which is enough to prevent metallic
contact between the raceway surface and the rolling elements when
the bearing is rotated at a high temperature.
[0091] In order to reduce this problem wherever possible, it is
more preferable that the kinematic viscosity at 40.degree. C. of
both parties is set at 30 to 200 mm.sup.2/s.
[0092] Furthermore, the grease composition of the present invention
comprises additives, and the content of the additives is preferably
20% or less by mass based on the total mass of the composition.
[0093] Further, the rolling apparatus of the present invention
directed towards achieving the above second object is a rolling
apparatus comprising an inner member having a raceway surface on
the outer surface; an outer member which has a raceway surface
opposed to the raceway surface of the inner member and is disposed
outside of the inner member; and a plurality of rolling elements
which are disposed between the two raceway surfaces so as to
flexibly roll therebetween, wherein a space, which is formed
between the inner member and the outer member and in which the
rolling elements are disposed, is filled with the above described
grease composition comprising an N-substituted terephthalamic acid
metal salt as the second thickener component.
[0094] Since the rolling apparatus with the above configuration is
filled with a grease composition comprising both a fluoro resin and
an N-substituted terephthalamic acid metal salt as thickeners, it
is long-lived under high-temperature conditions.
[0095] This rolling apparatus, especially a rolling bearing, can
preferably be used in car electrical components, auxiliary
equipment for car engine, or business machines used under
high-speed and/or high-temperature environment.
[0096] (4) To achieve the above third object, the present invention
has the following features. That is to say, the grease composition
of the present invention comprises organic bentonite as the above
second thickener component.
[0097] Since this grease composition comprises the mixture of a
fluoro resin and organic bentonite as a thickener, it has excellent
rust protection, extreme-pressure property, water resistance and
lubricating life.
[0098] The above thickener preferably comprises 5 to 95% by mass of
the fluoro resin and 95 to 5% by mass of the organic bentonite.
[0099] If the composition of the thickener is out of the above
range, there is a risk that the rust protection or lubricating life
of the grease composition might become insufficient. To ensure
sufficient rust protection or lubricating life, it is more
preferable that the thickener comprises 10 to 90% by mass of the
fluoro resin and 90 to 10% by mass of the organic bentonite. Since
the grease composition described in Examples 5 and 6 of Japanese
Patent Laid-Open No. 7-268370 does not contain a fluoro resin, the
same rust protection or lubricating life as in the present
invention cannot be obtained.
[0100] The content of the above thickener is preferably 3 to 40% by
mass based on the total mass of the composition.
[0101] If the content is less than 3% by mass, it becomes difficult
to maintain a grease structure, but if the content exceeds 40% by
mass, the grease composition gets so hardened that it becomes
difficult for the grease composition to exert sufficient
lubricating ability.
[0102] Moreover, the rolling apparatus of the present invention
directed towards achieving the above third object is a rolling
apparatus comprising an inner member having a raceway surface on
the outer surface; an outer member which has a raceway surface
opposed to the raceway surface of the inner member and is disposed
outside of the inner member; and a plurality of rolling elements
which are disposed between the two raceway surfaces so as to
flexibly roll therebetween, wherein a space, which is formed
between the inner member and the outer member and in which the
rolling elements are disposed, is filled with the above described
grease composition comprising organic bentonite as the second
thickener component.
[0103] The rolling apparatus with this configuration is long-lived,
although it is used under stringent conditions.
[0104] (5) To achieve the above fourth object, the present
invention has the following features. That is to say, the grease
composition of the present invention comprises a calcium sulfonate
complex as the above second thickener component.
[0105] Since this grease composition comprises both the fluoro
resin and the calcium sulfonate complex as thickeners, it has
excellent heat resistance, lubricating ability and rust
protection.
[0106] The above thickener preferably comprises 5 to 95% by mass of
the fluoro resin and 95 to 5% by mass of the calcium sulfonate
complex.
[0107] If the composition of the thickener is out of the above
range, there is a risk that the heat resistance, lubricating
ability and rust protection of the grease composition might become
insufficient. In order to reduce this problem wherever possible, it
is more preferable that the above thickener comprises 10 to 90% by
mass of the fluoro resin and 90 to 10% by mass of the calcium
sulfonate complex.
[0108] Moreover, the content of the above thickener is preferably
10 to 40% by mass based on the total mass of the composition. If
the content is less than 10% by mass, it becomes difficult to
maintain a grease state, but if the content exceeds 40% by mass,
the grease composition gets so hardened that it becomes difficult
for the grease composition to exert sufficient lubricating
ability.
[0109] Furthermore, the above base oil has a kinematic viscosity at
100.degree. C. of preferably 3 to 60 mm.sup.2/s, and more
preferably 5 to 40 mm.sup.2/s.
[0110] Still further, the rolling apparatus of the present
invention directed towards achieving the above fourth object is a
rolling apparatus comprising an inner member having a raceway
surface on the outer surface; an outer member which has a raceway
surface opposed to the raceway surface of the inner member and is
disposed outside of the inner member; and a plurality of rolling
elements which are disposed between the two raceway surfaces so as
to flexibly roll therebetween, wherein a space, which is formed
between the inner member and the outer member and in which the
rolling elements are disposed, is filled with the above described
grease composition comprising a calcium sulfonate complex as the
second thickener component.
[0111] The rolling apparatus with this configuration has heat
resistance so that it can be used under high-temperature
environment over 180.degree. C., and the rolling apparatus also has
excellent load carrying capacity, durability and rust protection.
Among rolling apparatuses, a rolling bearing comprising a plurality
of rolling elements which are disposed between an inner ring and an
outer ring so as to flexibly roll therebetween is particularly
preferable.
[0112] (6) To achieve the above fifth object, the present invention
has the following features. That is to say, the grease composition
of the present invention comprises carbon black as the above second
thickener component.
[0113] The above base oil preferably comprises a perfluoropolyether
oil and at least one of either a mineral oil or synthetic oil.
[0114] Since the grease composition of the present invention
comprises the perfluoropolyether oil as a base oil and the fluoro
resin as a thickener, it has excellent heat resistance. Moreover,
since the viscosity of the base oil of the grease composition is
controlled at low, the grease composition is also excellent in
low-temperature flow property.
[0115] Moreover, since the grease composition of the present
invention comprises carbon black as a thickener, it has excellent
electric conductivity.
[0116] Furthermore, since the grease composition comprises, as a
base oil, at least one of either the mineral oil or synthetic oil,
various additives can be added thereto, and the grease composition
is thereby excellent in various performances such as lubricating
ability, rust protection and a metallic corrosion preventing
property.
[0117] Still further, since the grease composition comprises at
least one of either the mineral oil or synthetic oil as a base oil
and carbon black as a thickener, the above grease composition is
low-priced when compared with the conventional fluoro greases.
[0118] The above thickener of the grease composition of the present
invention preferably comprises 40 to 80% by mass of the fluoro
resin and 60 to 20% by mass of the carbon black. If the content of
the carbon black is less than 20% by mass, the electric
conductivity becomes insufficient. When the content of the carbon
black is less than 20% by mass, the content of the fluoro resin
exceeds 80% by mass, resulting in the high cost of the grease
composition. To the contrary, if the content of the carbon black
exceeds 60% by mass and the content of the fluoro resin is less
than 40% by mass, the heat resistance of the grease composition
becomes insufficient. In order to reduce this problem wherever
possible, it is more preferable that the thickener comprises 50 to
70% by mass of the fluoro resin and 50 to 30% by mass of the carbon
black.
[0119] Moreover, the content of the above thickener is preferably 5
to 40% by mass based on the total mass of the composition. If the
content is less than 5% by mass, it becomes difficult to maintain a
grease state, but if the content exceeds 40% by mass, the grease
composition gets so hardened that it becomes difficult for the
grease composition to exert sufficient lubricating ability.
[0120] Furthermore, the above base oil of the grease composition of
the present invention preferably comprises 10 to 90% by mass of the
perfluoropolyether oil and 90 to 10% by mass of at least one of
either the mineral oil or synthetic oil.
[0121] If the content of at least one of either the mineral oil or
synthetic oil is less than 10% by mass, the carbon black easily
coagulates and so it does not become a grease state, and further,
sufficient additive effects cannot be obtained when additives are
added to the grease composition. Moreover, when the content of at
least one of either the mineral oil or synthetic oil is less than
10% by mass, the content of the perfluoropolyether oil exceeds 90%
by mass, and the grease composition thereby becomes expensive. In
contrast, if the content of at least one of either the mineral oil
or synthetic oil exceeds 90% by mass and that of the
perfluoropolyether oil is less than 10% by mass, the grease
composition has insufficient heat resistance.
[0122] Furthermore, it is preferable that the above
perfluoropolyether oil has a kinematic viscosity at 40.degree. C.
of 20 to 400 mm.sup.2/s, and at least one of either the above
mineral oil or synthetic oil has a kinematic viscosity at
40.degree. C. of 20 to 400 mm.sup.2/s. If the kinematic viscosity
at 40.degree. C. of each of both types of the above oils exceeds
400 mm.sup.2/s, oil film gets relatively thick and electric
resistance value increases in the rolling apparatus supplied with
the grease composition of the present invention. Further, there is
a risk that the low-temperature flow property of the grease
composition might become insufficient and that abnormal sounds
might be generated when the rolling apparatus is activated at a low
temperature.
[0123] However, if the kinematic viscosity of each of the above
compounds is less than 20 mm.sup.2/s, it is not appropriate in
terms of evaporation loss or lubricating ability. That is, if the
viscosity of the base oil is too low, it becomes difficult to form
lubricating oil film which is enough to prevent metallic contact
between the raceway surface and the rolling elements when the
bearing is rotated at a high temperature.
[0124] In order to reduce this problem wherever possible, it is
more preferable that the kinematic viscosity at 40.degree. C. of
both base oils is set at 30 to 200 mm.sup.2/s.
[0125] Moreover, it is preferable to set the DBP oil absorption of
the above carbon black at 100 ml/100 g or more, the primary
particle size at 100 nm or shorter, and the specific surface area
at 50 m.sup.2/g or larger.
[0126] Furthermore, the grease composition of the present invention
comprises additives, and the content of the additives is preferably
20% or less by mass based on the total mass of the composition.
[0127] Still further, the rolling apparatus of the present
invention directed towards achieving the above fifth object is a
rolling apparatus comprising an inner member having a raceway
surface on the outer surface; an outer member which has a raceway
surface opposed to the raceway surface of the inner member and is
disposed outside of the inner member; and a plurality of rolling
elements which are disposed between the two raceway surfaces so as
to flexibly roll therebetween, wherein a space, which is formed
between the inner member and the outer member and in which the
rolling elements are disposed, is filled with the above described
grease composition comprising carbon black as the second thickener
component.
[0128] Since the rolling apparatus with this configuration is
filled with the grease composition comprising both the fluoro resin
and the carbon black as thickeners, it has excellent electric
conductivity and is long lived under high-temperature
conditions.
[0129] This rolling apparatus, especially a rolling bearing, can
preferably be used in car electrical components such as alternators
and electromagnetic clutches, or auxiliary equipment for car engine
such as idler pulleys. Moreover, it can preferably be used also for
business machines such as copying machines and printers.
[0130] (7) Examples of the rolling apparatus of the present
invention directed towards achieving the above described first to
fifth object includes various apparatuses such as rolling bearings,
ball screws, linear guide apparatuses and linear bearings.
[0131] The term "inner member" for the rolling apparatus of the
present invention is used to mean a bearing inner ring when the
rolling apparatus is a rolling bearing. Likewise, the term "inner
member" is used to mean a screw shaft when the rolling apparatus is
a ball screw, a guide rail when it is a linear guide apparatus, and
a shaft when it is a linear bearing, respectively. The term "outer
member" is used herein to mean a bearing outer ring when the
rolling apparatus is a rolling bearing. Likewise, the term "outer
member" is herein used to mean a nut when the rolling apparatus is
a ball screw, a slider when it is a linear guide apparatus, and an
outer casing when it is a linear bearing, respectively.
[0132] (8) Each of the components of the grease composition of the
present invention will be explained below.
[0133] Fluoro Resin:
[0134] The type of the fluoro resin used as a thickener in the
present invention is not particularly limited, and preferred
examples include polytetrafluoroethylene (PTFE); a copolymer of
tetrafluoroethylene and another ethylene unsaturated hydrocarbon
monomer, the entire or a part of which is fluorinated (hereinafter
referred to as a tetrafluoroethylene copolymer); and others.
[0135] Examples of the tetrafluoroethylene copolymer include the
following (1) to (4):
[0136] 1) Denatured polytetrafluoroethylene obtained by
copolymerizing one or more types of comonomers selected from a
group consisting of perfluoroalkyl-trifluoroethylene ether,
vinylidene fluoride, hexafluoroisobutene, chlorotrifluoroethylene
and perfluoroalkylethylenes (e.g.perfluoropropene, etc.) with PTFE
at a ratio of 0.01 to 3 mole %, and preferably 0.05 to 0.5 mole
%.
[0137] (2) A tetrafluoroethylene (TFE) thermoplastic copolymer
obtained by copolymerizing at least one type of perfluoroalkylvinyl
ether (wherein the perfluoroalkyl group contains 1 to 6 carbon
atoms) with TFE at a ratio of 0.5 to 8 mole %. Examples of such a
copolymer include a copolymer of perfluoropropylvinyl ether and
TFE, a copolymer of perfluoromethylvinyl ether and TFE, a copolymer
of perfluoroethylvinyl ether and TFE, and others.
[0138] (3) A TFE thermoplastic copolymer obtained by copolymerizing
perfluoro olefin containing 3 to 8 carbon atoms with TFE at a ratio
of 2 to 20 mole %. Examples of such a copolymer include a copolymer
of hexafluoropropene and TFE, and the like. Other comonomers having
a trifluoroethylene ether structure may also be copolymerized with
this copolymer, if the ratio is less than 5 mole %.
[0139] (4) A TFE thermoplastic copolymer obtained by copolymerizing
perfluoromethylvinyl ether (0.5 to 13 mole %) with one or more
types of monomers of fluoride represented by the following formulas
(I) to (III): 1
[0140] wherein R in formula (III) is a perfluoroalkyl group
containing 1 to 5 carbon atoms and it is preferably CF.sub.3. Each
of X.sub.1 and X.sub.2 is independently a perfluoroalkyl group
containing 1 to 3 carbon atoms or F, and it is preferably
CF.sub.3.
[0141] Moreover, RF in Formulas (I) and (II) is at least one of the
following (i), (ii) and (iii):
[0142] (i) a perfluoroalkyl group containing 2 to 12 carbon
atoms,
[0143] (ii) a compound having a chemical structure represented by
the following formula (IV), wherein r in the formula (IV) is an
integer of 1 to 4, and r' is an integer of 0 to 3:
.paren close-st.CF.sub.2CF(CF.sub.3)O.paren
close-st..sub.rCF.sub.2.paren close-st..sub.r'CF.sub.3 (IV)
[0144] (iii) a compound having a chemical structure represented by
the following formula (V):
-ZOCFX.paren close-st..sub.qOCF.sub.2CFY.paren close-st..sub.q'O-T
(V)
[0145] wherein structural units (OCFX) and (OCF.sub.2 CFY) in
formula (V) are statistically distributed along a chain. T is a
perfluoroalkyl group containing 1 to 3 carbon atoms, and it
arbitrarily has one H or Cl. X and Y is F or CF.sub.3, and Z is
--CFX-- or --CF.sub.2 CFY--. Further, each of q and q' is an
integer of 0 to 10, and the values are identical with or different
from each other, wherein the number average molecular weight of the
monomer of a fluoride is 200 to 2,000.
[0146] In (1), (2), (3) and (4) above, the preferred ranges of the
value of the molecular formulas, copolymerization ratio and number
average molecular weight are defined as above described. If these
values are less than the lower limit of the above range, thickening
ability sufficient to convert the grease composition into a grease
state is not imparted to the tetrafluoroethylene copolymer. In
contrast, if these values are more than the upper limit of the
above range, the grease composition gets so hardened that it
becomes difficult for the grease composition to exert sufficient
lubricating ability.
[0147] Specific examples of such a fluoro resin include
polytetrafluoroethylene (PTFE), perfluoroalkoxy alkane (PFA), a
perfluoroethylene propene copolymer (PFEP), an
ethylene-tetrafluoroethyle- ne copolymer (FTFE), polyvinylidene
fluoride (PVDF), a polychlorotrifluoroethylene-perfluoro dioxol
copolymer (ECTFE), a polytetrafluoroethylene-perfluoro dioxol
copolymer (TFE/PDD), polyvinyl fluoride (PVE) and others. Of these,
PTFE is the most preferable because of its excellent mass
productivity.
[0148] Metallic Soap and Complex Metallic Soap:
[0149] An example of a metallic soap used as a thickener (second
thickener component) together with a fluoro resin in the present
invention includes an aliphatic monobasic metal salt which is
synthesized from a 1-, 2- or 13-group metal according to the
periodic table, and higher fatty acid containing 10 or more carbon
atoms or higher hydroxyfatty acid containing one or more hydroxyl
group(s) and 10 or more carbon atoms.
[0150] Examples of the metal include lithium, sodium, calcium,
barium, aluminum and others. Examples of the higher fatty acid
include lauric acid, myristic acid, palmitic acid, margaric acid,
stearic acid, arachidic acid, behenic acid, lignoceric acid, tallow
fatty acid and others. Examples of the higher hydroxyfatty acid
include 9-hydroxystearic acid, 10-hydroxystearic acid,
12-hydroxystearic acid, 9,10-dihydroxystearic acid and others. Of
these aliphatic monobasic acids, 12-hydroxystearic acid is the most
preferable in terms of the stability of the thickener.
[0151] An example of a complex metallic soap used as a thickener
(second thickener component) together with a fluoro resin in the
present invention includes a complex metallic soap which is
synthesized by saponifying a 1-, 2- or 13-group metallic hydroxide
according to the periodic table and the mixture of fatty acid and
dibasic acid. Examples of the metal include lithium, sodium,
calcium, barium, aluminum and others. A grease composition
comprising the above described complex metallic soap has a higher
dropping point than that of a grease composition comprising an
ordinary metallic soap, and it is excellent in heat resistance.
[0152] This metallic soap and complex metallic soap may be
dispersed in a base oil after they are synthesized separately, or
may be dispersed in a base oil by synthesizing them in the base
oil. However, a thickener is better dispersed in a base oil by the
latter method, and so the latter method is advantageous in the
industrial production of a grease composition.
[0153] N-Substituted Terephthalamic Acid Metal Salt:
[0154] An N-substituted terephthalamic acid metal salt used as a
thickener (second thickener component) together with a fluoro resin
in the present invention is represented by the following general
formula (VI): 2
[0155] In the general formula (VI), a substituent R binding to a
nitrogen atom is a straight chain, branched chain or cyclic,
saturated or unsaturated, monovalent hydrocarbon group, M is a
metal, and n denotes a number equivalent to the valence of the
metal.
[0156] When the substituent R is a straight or branched chain
hydrocarbon group, the hydrocarbon group contains 10 to 32,
preferably 12 to 22 carbon atoms, and when the substituent R is a
cyclic hydrocarbon group, the hydrocarbon group contains 6 to 28,
preferably 7 to 22 carbon atoms. If the number of carbon atoms of
the hydrocarbon group is smaller than the above described minimum
value, the thickener is hardly dispersed in a base oil and further
the thickener is likely to separate from the base oil. To the
contrary, if the number of carbon atoms of the hydrocarbon group is
greater than the above maximum value, then the production of the
thickener is industrially unrealistic.
[0157] Examples of the substituent R include a decyl group, a
tetradecyl group, a hexadecyl group, an octadecyl group, a
cyclohexyl group, a benzyl group, a phenyl group, a tolyl group, a
butylphenyl group and others. Examples of the metal M include 1-,
2-, 12- and 13-group metals according to the periodic table, and
examples of such a metal include lithium, potassium, sodium,
magnesium, calcium, barium, zinc, aluminum and others. Of these,
sodium, barium, lithium and potassium are particularly preferable,
and sodium is the most preferable because of its excellent mass
productivity.
[0158] Such an N-substituted terephthalamic acid metal salt may be
synthesized separately and then dispersed in a base oil, or may be
dispersed in the base oil by synthesis in the base oil. However,
since the thickener is better dispersed in a base oil by the latter
method, when the thickener is industrially produced, the latter
method is advantageous.
[0159] Organic Bentonite:
[0160] Organic bentonite used as a thickener (second thickener
component) together with a fluoro resin in the present invention is
one type of colloidal clay which is naturally produced, and it is
obtained by treating bentonite that is ferro silicate (laminar
silicate) such as montmorillonite with a cationic surfactant. When
bentonite is treated with a cationic surfactant, organic molecules
are adsorbed between the crystalline layers of the bentonite so as
to obtain lipophilic organic bentonite which swells well in an
organic liquid in the presence of a polar dispersing agent.
[0161] Bentonite, an important element constituting organic
bentonite, is complicated silicate containing a large amount of
water of crystallization and has a structure containing the layers
of ion alignments laminated in parallel. That is, two silicate
layers are disposed in parallel, and a layer of alkaline metal,
alkaline earth metal or water molecules is interposed between the
silicate layers. More specifically, in the above layer has a
three-layer structure, two tetrahedral layers of Si are disposed in
parallel, with the tetrahedrons opposing to each other on the
vertexes, and an octahedral layer of Al is interposed between the
tetrahederal layers.
[0162] In such bentonite, since the binding strength between the
metal ion locating in the interlamillar portion and the silicate is
relatively weak, an ion exchange reaction occurs, for example,
between a quarternary ammonium salt and the metal ion, by treatment
with a cationic surfactant, and as a result, what is called organic
bentonite is obtained. By this reaction, hydrophilic bentonite is
changed to lipophilic one.
[0163] A production method of organic bentonite and the like are
disclosed in detail, for example, in Japanese Patent Laid-Open Nos.
62-83108 and 53-72792.
[0164] Organic bentonite may be synthesized separately and then
dispersed in a base oil, or may be dispersed in the base oil by
synthesis in the base oil. However, since the thickener is better
dispersed in a base oil by the latter method, when the thickener is
industrially produced, the latter method is advantageous.
[0165] Calcium Sulfonate Complex:
[0166] A calcium sulfonate complex used as a thickener (second
thickener component) together with a fluoro resin in the present
invention comprises calcium sulfonate as an essential component,
and also comprises at least one type of calcium salt (calcium soap)
selected from a group consisting of (a) calcium carbonate, (b) a
higher fatty acid calcium salt such as calcium dibehenate, calcium
distearate and calcium dihydroxystearate, (c) a lower fatty acid
calcium salt such as calcium acetate, and (d) calcium borate.
[0167] It is particularly preferable to use a calcium sulfonate
complex, which comprises calcium sulfonate and calcium carbonate as
essential components and also comprises two or more selected from a
group consisting of calcium dibehenate, calcium distearate, calcium
dihydroxystearate, calcium acetate and calcium borate.
[0168] In terms of thickening effect, the above described calcium
sulfonate preferably has a base number of 50 to 500 mgKOH/g, and
more preferably it is overbased calcium sulfonate with a base
number of 300 to 500 mgKOH/g.
[0169] The calcium sulfonate complex may be dispersed in a base oil
after it is synthesized separately, or the calcium sulfonate
complex may also be dispersed in a base oil by synthesis in the
base oil. However, since the thickener is better dispersed in a
base oil by the latter method, when the thickener is industrially
produced, the latter method is advantageous.
[0170] Carbon Black:
[0171] Carbon black used as a thickener (second thickener
component) together with a fluoro resin in the present invention
acts as an electric conductivity imparting additive as well as a
thickener in the grease composition.
[0172] The type of carbon black to be used is not particularly
limited, but considering ability to impart thickening capacity and
electric conductivity to the grease composition, carbon black
having large oil absorption capacity (DBP oil absorption being 100
ml/100 g or more) is preferable. Moreover, it is preferable to use
carbon black having lipophilic property and a large specific
surface area (the primary particle size being less than 100 nm and
the specific surface area being 50 m.sup.2/g or larger.)
[0173] If the DBP oil absorption, primary particle size and
specific surface area of carbon black are out of the above range,
there is a risk that the thickening capacity and electric
conductivity of the grease composition might become insufficient.
The above specific surface area is determined by e.g. nitrogen
adsorption method.
[0174] Specific examples of the carbon black include acetylene
black, Ketjen black, channel black and others. Of these, acetylene
black is particularly preferable, since it has a developed carbon
structure by thermal decomposition.
[0175] This carbon structure consists of primary particles (the
average particle size being 0.026 to 0.042 .mu.m by electron
microscopy), in which crystallites obtained by the lamination of
net planes of carbons are aggregated. A large number of the primary
particles are connected to construct a chain or resinous structure.
Of these acetylene black, one having a significantly small amount
of hydrogen that is considered to fix the motion of .pi. electrons
is preferable. Of commercially available acetylene black,
easy-to-handle granular acetylene black as well as powder acetylene
black may be used. Not only acetylene black but also other carbon
black such as gas black can be used, as long as they have the
developed carbon structure as described above.
[0176] Base Oil:
[0177] The type of a base oil used in the grease composition of the
present invention is not particularly limited, but the base oil
preferably comprises at least one of either a mineral oil or
synthetic oil and a perfluoropolyether oil. However, other types of
oils may be used in combination to such an extent that it does not
impair the purpose of the present invention.
[0178] The type of the mineral oil is not particularly limited, but
a paraffin mineral oil, a naphthene mineral oil, a mixed oil
thereof, and others, are preferably used. The type of the synthetic
oil is also not particularly limited, a synthetic hydrocarbon oil,
an ether oil, an ester oil, a fluoro oil and others are preferably
used.
[0179] Specific examples of the synthetic hydrocarbon oil include a
poly .alpha.-olefin oil, a cooligomer synthetic oil of
.alpha.-olefin and ethylene, and others.
[0180] An example of the ether oil includes a phenyl ether oil
substituted by an alkyl group(s) containing 12 to 20 carbon atoms
(e.g. a diphenyl ether oil, a triphenyl ether oil, a tetraphenyl
ether oil, etc.). The number of alkyl groups substituted is not
particularly limited, but one or two are preferable. Taking into
consideration the low vaporizability of the base oil, an alkyl
diphenyl ether oil is preferable.
[0181] Examples of the fluoro oil include a perfluoroether oil and
a derivative thereof, a fluorosilicone oil, a
chlorotrifluoroethylene oil, a fluorophosphazene oil and
others.
[0182] Moreover, examples of the ester oil include a diester oil, a
polyol ester oil (e.g. a neopentyl-type polyol ester oil, etc.), a
complex ester oil thereof, an aromatic ester oil, a carbonate oil
and others.
[0183] The diester oil is obtained by a reaction between dibasic
acid and alcohol, and examples of the diester oil include dioctyl
adipate, diisobutyl adipate, dibutyl adipate, dibutyl sebacate,
dioctyl sebacate, methylacetyl ricinolate and others.
[0184] Moreover, the polyol ester oil is obtained by a reaction
between polyol and one or two or more types of monobasic acid. A
complex ester that is oligo ester obtained by a reaction between a
mixed fatty acid of monobasic acid and dibasic acid and polyol may
also be used.
[0185] Examples of the polyol include trimethylolpropane,
pentaerythritol, dipentaerythritol, neopentyl glycol,
2-methyl-2-propylpropane-1,3-diol, and others.
[0186] A preferred example of the monobasic acid includes fatty
acid containing 4 to 18 carbon atoms, and specific examples include
valeric acid, caproic acid, caprylic acid, enanthic acid,
pelargonic acid, capric acid, undecanoic acid, lauric acid,
myristic acid, palmitic acid, tallow fatty acid, stearic acid,
caproleic acid, undecylenic acid, linderic acid, tsuzuic acid,
physeternic acid, myristoleic acid, palmitoleic acid, petroselinic
acid, oleic acid, elaidic acid, asclepinic acid, vaccenic acid,
sorbic acid, linolic acid, linolenic acid, sabinic acid, ricinoleic
acid and others.
[0187] Examples of the aromatic ester oil include trimellitic acid
ester such as trioctyl trimellitate or tridecyl trimellitate, and
pyromellitic acid ester such as tetraoctyl pyromellitate.
[0188] The type of the perfluoropolyether oil used in the grease
composition is not particularly limited, but the perfluoropolyether
oil is preferably comprised of at least one type selected from the
following fluorooxy alkylene structural units. In the following
formulas, X.sub.3 represents CF.sub.3(CF.sub.2).sub.n--, and n
represents an integer of 0 to 4.
CF.sub.2CF.sub.2O.paren close-st., CF.sub.2O.paren close-st.
CF.sub.2CF(CF.sub.3)O.paren close-st.. CF(CF.sub.3)O.paren
close-st.
CF.sub.2CF.sub.2CF.sub.2O.paren close-st.,
CF.sub.2CF(OX.sub.3)O.paren close-st.
CF(OX.sub.3)O.paren close-st.
[0189] When the perfluoropolyether oil is comprised of two or more
types of the above fluorooxy alkylene structural units, each
structural unit is statistically distributed along a chain. The
terminal group thereof is a fluoroalkyl group arbitrarily having an
H and/or a Cl such as CF.sub.3--, C.sub.2F.sub.5--,
C.sub.3F.sub.7--, CF.sub.2Cl(CF.sub.3)CF--, CF.sub.3CFClCF.sub.2--,
CF.sub.2ClCF.sub.2--, CF.sub.2Cl--, CHF.sub.2-- or
CF.sub.3CHF--.
[0190] Each of the above described various base oils may be used
singly, or may be used appropriately in combination of two or more
types. Taking into consideration the lubricating ability and life
of the rolling apparatus under high-temperature and high-speed
conditions into which the grease composition is enclosed, it is
preferable that a synthetic oil is contained in the base oil, and
it is more preferable that at least one type selected from an ester
oil, an ether oil and a fluoro oil is contained in the base oil. Of
the ester oils, a polyol ester oil and an aromatic ester oil are
further preferable, of the ether oils, an alkyldiphenyl ether oil
is further preferable, and of the fluoro oils, a perfluoroether
oil, a derivative thereof and a fluorophosphazene oil are further
preferable.
[0191] Additive:
[0192] Various additives may be added, as desired, to the grease
composition of the present invention so as to improve various
performances of the grease composition. For example, additives such
as an antioxidant, a rust preventive, an extreme-pressure additive,
an oiliness improver and a metal deactivator, which are generally
used for grease compositions, can be used singly or in combination
of two or more.
[0193] Examples of the antioxidant include amine antioxidants,
phenol antioxidants, sulfur antioxidants, zinc dithiophosphate and
others.
[0194] Specific examples of an amine antioxidant include
phenyl-1-naphthylamine, phenyl-2-naphthylamine, diphenylamine,
phenylenediamine, oleyl amide amine, phenothiazine and others.
[0195] Specific examples of a phenol antioxidant include hindered
phenols or the like such as p-t-butylphenyl salicylate,
2,6-di-t-butylphenol, 2,6-di-t-butyl-p-phenylphenol,
2,2'-methylenebis(4-methyl-6-t-octylphenol- ),
4,4'-butylidenebis-6-t-butyl-m-cresol, tetrakis
{methylene-3-(3',5'-di-- t-butyl-4'-hydroxyphenyl)propionate}
methane, 1,3,5-trimethyl-2,4,6-tris(3-
,5-di-t-butyl-4-hydroxybenzyl)benzene,
n-octadecyl-.beta.-(4'-hydroxy-3',5- '-di-t-butylphenyl)propionate,
2-n-octyl-thio-4,6-di(4'-hydroxy-3',5'-di-t-
-butyl)phenoxy-1,3,5-triazine, 4,4'-thiobis(6-t-butyl-m-cresol),
2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole and
others.
[0196] Examples of a rust preventive include petroleum sulfonate,
an organic sulfonic acid metal salt (herein, metal is an alkali
metal, alkaline-earth metal or the like), esters and others.
[0197] Specific examples of an organic sulfonic acid metal salt
include the metal salt of dinonylnaphthalene sulfonic acid or heavy
alkylbenzene sulfonic acid (calcium sulfonate, barium sulfonate,
sodium sulfonate, etc.), and others.
[0198] Specific examples of esters include sorbitan esters such as
sorbitan monolaurate, sorbitan tristearate, sorbitan monooleate and
sorbitan trioleate, which are the partial esters of polybasic
carboxylic acid and polyol; alkyl esters such as polyoxyethylene
laurate, polyoxyethylene oleate and polyoxyethylene stearate; and
others.
[0199] Moreover, alkyl succinic acid derivatives and alkenyl
succinic acid derivatives such as alkyl succinic acid ester and
alkenyl succinic acid ester can also preferably be used as rust
preventives.
[0200] The grease composition of the present invention has a rust
protection property by itself, but the rust protection property is
further improved by adding the above rust preventives.
[0201] Furthermore, examples of an extreme-pressure additive
include phosphorus extreme-pressure additives, zinc
dithiophosphate, organic molybdenum and others.
[0202] Still further, examples of an oiliness improver include
fatty acid such as oleic acid or stearic acid; alcohol such as
lauryl alcohol or oleyl alcohol; amine such as stearylamine or
cetylamine; phosphoric ester such as tricresyl phosphate; animal
and vegetable oils; and others.
[0203] Still further, an example of a metal deactivator includes
benzotriazole or the like.
[0204] The additive amount of these additives is not particularly
limited unless it impairs the purpose of the present invention, but
it is preferably 20% or less by mass based on the total mass of the
grease composition. If the additive amount exceeds 20% by mass, the
additive effects are not improved, and there is also a risk that
the lubricating ability might lower since the amount of a base oil
is relatively reduced.
[0205] The production method of the grease composition of the
present invention is not particularly limited. For example, a
fluoro grease comprising a perfluoropolyether oil as a base oil and
a fluoro resin as a thickener; and a grease composition comprising
at least one of either a mineral oil or synthetic oil as a base oil
and a second thickener component such as a metallic soap or carbon
black as a thickener, are produced separately, and these are then
mixed. Otherwise, the grease composition of the present invention
can also be produced by adding the fluoro resin and the second
thickener component as thickeners into the base oil obtained by
mixing the perfluoropolyether oil and at least one of either the
mineral oil or synthetic oil.
[0206] The former method is a method of mixing the previously
produced grease composition, and therefore the fluoro oil can be
used as a base oil. Moreover, in the latter method, the fluoro oil
can be used, if the amount is within 5 volume % based on the total
volume of the base oil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0207] FIG. 1 is a partial longitudinal sectional view showing the
configuration of a deep groove ball bearing, which is one
embodiment of the rolling apparatus of the present invention;
[0208] FIG. 2 is a schematic diagram showing the configuration of
an apparatus for evaluating the amount of dusts generated from a
bearing;
[0209] FIG. 3 is a schematic diagram showing the configuration of a
torque measuring apparatus;
[0210] FIG. 4 is an oblique perspective view of a continuous
rotating apparatus for evaluating the durability of a bearing;
[0211] FIG. 5 is a partial front view of the continuous rotating
apparatus of FIG. 4;
[0212] FIG. 6 is a graph showing the correlation between the ratio
of PTFE in a thickener, and the amount of dusts generated and
durability of a grease composition, in the case of using a grease
composition comprising a metallic soap as the second thickener
component;
[0213] FIG. 7 is a graph showing the correlation between the
content of a thickener based on the total mass of a grease
composition, and the amount of dusts generated and durability of
the grease composition, in the case of using a grease composition
comprising a metallic soap as the second thickener component;
[0214] FIG. 8 is a longitudinal sectional view showing the
configuration of a ball bearing, which is another embodiment of the
rolling apparatus of the present invention;
[0215] FIG. 9 is a cross-sectional view showing the configuration
of a bearing life test machine for evaluating the seizuring ability
of a grease composition;
[0216] FIG. 10 is a graph showing the correlation between the ratio
of a fluoro resin in a thickener, and the seizuring life of a ball
bearing and the rust protection of a grease composition, in the
case of using a grease composition comprising an N-substituted
terephthalamic acid metal salt as the second thickener
component;
[0217] FIG. 11 is a graph showing the correlation between the ratio
of a fluoro resin in a thickener, and the seizuring life of a ball
bearing and the amount of grease leaked, in the case of using a
grease composition comprising an N-substituted terephthalamic acid
metal salt as the second thickener component;
[0218] FIG. 12 is a graph showing the correlation between the ratio
of organic bentonite in a thickener, and the rust protection and
lubricating life of a grease composition, in the case of using a
grease composition comprising organic bentonite as the second
thickener component;
[0219] FIG. 13 is a graph showing the correlation between the
content of a thickener based on the total mass of the grease
composition and the lubricating life, in the case of a grease
composition comprising organic bentonite as the second thickener
component;
[0220] FIG. 14 is a longitudinal sectional view showing the
configuration of a ball bearing, which is another embodiment of the
rolling apparatus of the present invention;
[0221] FIG. 15 is a partial longitudinal sectional view showing the
configuration of a ball bearing, which is another embodiment of the
rolling apparatus of the present invention;
[0222] FIG. 16 is a schematic block diagram of an apparatus for
measuring the electric resistance value of a bearing;
[0223] FIG. 17 is a graph showing the correlation between the ratio
of a fluoro resin in a thickener, and the seizuring life of a ball
bearing and the rust protection of a grease composition, in the
case of using a grease composition comprising carbon black as the
second thickener component; and
[0224] FIG. 18 is a graph showing the correlation between the ratio
of a fluoro resin in a thickener, and the seizuring life and
electric resistance value of a ball bearing, in the case of using a
grease composition comprising carbon black as the second thickener
component.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0225] The embodiments of the grease composition and the rolling
apparatus of the present invention will be explained in detail,
while referring to figures.
[0226] (A) Grease Composition Comprising Fluoro Resin and Metallic
Soap as Thickener
[0227] Tables 1 to 3 show the compositions of the grease
compositions of Examples and Comparative examples. NLGI worked
penetration of each grease composition is also shown in the tables.
The worked penetration is determined according to JIS K2220.
1 TABLE 1 Example Example Example Example Example Example A1 A2 A3
A4 A5 A6 Type of Li soap.sup.2) 60 30 80 30 30 -- thickener.sup.1)
Ca soap.sup.3) -- -- -- 30 -- 30 Na soap.sup.4) -- -- -- -- 30 30
PTFE.sup.5) 40 70 20 40 40 40 Content of thickener.sup.1) 23 29 19
24 24 25 Type of base POE oil.sup.6) 60 30 80 60 60 60 oils.sup.1)
PFPE oil.sup.7) 40 70 20 40 40 40 Content of base oil.sup.1) 77 71
81 76 76 75 Worked penetration 221 240 210 220 216 222 Amount of
dusts 25.degree. C. 750 400 900 650 550 500 generated in the early
70.degree. C. 3250 2100 4400 3550 3250 2700 stage of
rotation.sup.8) Acoustic performance in the .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. early stage of rotation Torque value in the early
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. stage of rotation Durability (hr)
>3000 >3000 >3000 >3000 >3000 >3000 Amount of
dusts generated 4200 3300 5250 3950 3700 3450 after durability
test.sup.8) .sup.1)Unit of value is % by mass .sup.2)Lithium
12-hydroxystearate .sup.3)Calcium 12-hydroxystearate .sup.4)Sodium
12-hydroxystearate .sup.5)Polytetrafluoroethylene .sup.6)Polyol
ester oil .sup.7)Perfluoropolyether oil .sup.8)Unit is
particles/283 cm.sup.3
[0228]
2 TABLE 2 Example Example Example Example Example Example A7 A8 A9
A10 All A12 Type of Li soap.sup.2) 60 30 80 30 30 --
thickener.sup.1) Ca soap.sup.3) -- -- -- 30 -- 30 Na soap.sup.4) --
-- -- -- 30 30 PTFE.sup.5) 40 70 20 40 40 40 Content of
thickener.sup.1) 23 29 19 24 24 25 Type of base ADPE oil.sup.6) 60
30 80 60 60 60 oils.sup.1) PFPE oil.sup.7) 40 70 20 40 40 40
Content of base oil.sup.1) 77 71 81 76 76 75 Worked penetration 219
235 203 215 207 214 Amount of dusts 25.degree. C. 650 450 800 550
500 450 generated in the early 70.degree. C. 3150 2200 4150 3350
3200 2400 stage of rotation.sup.8) Acoustic performance in the
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. early stage of rotation Torque value in
the early stage .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. of rotation Durability
(hr) >3000 >3000 >3000 >3000 >3000 >3000 Amount
of dusts generated after 4000 3350 5150 3750 3550 3300 durability
test.sup.8) .sup.1)Unit of value is % by mass .sup.2)Lithium
12-hydroxystearate .sup.3)Calcium 12-hydroxystearate .sup.4)Sodium
12-hydroxystearate .sup.5)Polytetrafluoroethylene .sup.6)Alkyl
diphenyl ether oil .sup.7)Perfluoropolyether oil .sup.8)Unit is
particles/283 cm.sup.3
[0229]
3 TABLE 3 Comparative Comparative Comparative Example Example
Example example example example A13 A14 A15 A1 A2 A3 Type of Li
soap.sup.2) 20 60 60 100 -- -- thickener.sup.1) Ca soap.sup.3) --
-- -- -- 100 -- Na soap.sup.4) -- -- -- -- -- -- PTFE.sup.5) 80 40
40 -- -- 100 Content of thickener.sup.1) 30 41 9 15 18 35 Type of
base ADPE oil.sup.6) 20 60 60 100 100 -- oils.sup.1) PFPE
oil.sup.7) 80 40 40 -- -- 100 Content of base oil.sup.1) 70 59 91
85 82 65 Worked penetration 220 170 300 224 217 245 Amount of dusts
25.degree. C. 300 200 1800 2400 3000 150 generated in the early
70.degree. C. 1800 1500 6750 9000 12000 1200 stage of
rotation.sup.8) Acoustic performance in the .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. x early
stage of rotation Torque value in the early stage .smallcircle. x
.smallcircle. .smallcircle. .smallcircle. x of rotation Durability
(hr) 2500 >3000 >3000 >3000 Amount of dusts generated
35000 23000 33000 after durability test.sup.8) .sup.1)Unit of value
is % by mass .sup.2)Lithium 12-hydroxystearate .sup.3)Calcium
12-hydroxystearate .sup.4)Sodium 12-hydroxystearate
.sup.5)Polytetrafluoroethylene .sup.6)Alkyl diphenyl ether oil
.sup.7)Perfluoropolyether oil .sup.8)Unit is particles/283
cm.sup.3
[0230] The compositions of the grease compositions of Examples A1
to A15 and Comparative examples A1 to A3 are as shown in Tables 1
to 3, and each composition comprises a thickener consisting of a
metallic soap and a fluoro resin (PTFE), and a base oil consisting
of a synthetic oil and a perfluoropolyether oil (PFPE oil) (except
Comparative examples A1 to A3). The metallic soap is the lithium
salt, calcium salt or sodium salt of 12-hydroxystearic acid, but a
complex metallic soap can also be used instead of the metallic
soap. The synthetic oil is a polyolester oil (POE oil) or
alkyldiphenylether oil (ADPE oil), and regarding the kinematic
viscosity of each oil at 40.degree. C., the POE oil has 70
mm.sup.2/s, the ADPE oil has 100 mm.sup.2/s, and the PFPE oil has
190 mm.sup.2/s.
[0231] Although not described in each table, each grease
composition comprises, as additives, 1.0% by mass of an amine
antioxidant, 0.5% by mass of a calcium sulfonate rust preventive
and 0.05% by mass of a benzotriazole metal deactivator based on the
total mass of the grease composition.
[0232] It should be noted that the content (% by mass) of the base
oil and the thickener described in each of Tables 1 to 3 is a value
based on that the total mass of the base oil and the thickener is
defined as 100, and that the above additives are not considered.
Moreover, values described in the columns of the type of thickener
and the type of base oil show the mass ratio of each component
constituting the thickener and the mass ratio of each component
constituting the base oil, respectively, in a case where each of
the total mass (% by mass) of the thickener and the total mass of
the base oil is defined as 100.
[0233] Rolling bearings filled with each of the above 18 types of
grease compositions were prepared, and acoustic performance, torque
performance, durability, and the amount of dusts generated
therefrom were evaluated.
[0234] The used rolling bearing was a single-row deep groove ball
bearing 10 (inside diameter: 5 mm, outside diameter: 13 mm, width:
4 mm) completely defatted by organic solvent, and this rolling
bearing was comprised of: an inner ring 1; an outer ring 2; a
plurality of balls 3, which were disposed between the inner ring 1
and the outer ring 2 to flexibly roll therebetween; a cage 4 for
retaining the plurality of balls 3 between the inner ring 1 and the
outer ring 2; and noncontact rubber seals 5, 5 installed in the
seal groove 2a, 2a of the outer ring 2 (refer to the partial
cross-sectional view of FIG. 1). A space portion, which was
surrounded by the inner ring 1, the outer ring 2 and the rubber
seals 5, 5 of the ball bearing 10, was filled with 19 mg of the
above grease composition G, and the rubber seals 5, 5 hermetically
sealed the grease composition in the ball bearing 10.
[0235] Next, methods of evaluating each of the above various
performances will be explained below.
[0236] Method for Evaluating the Amount of Dusts Generated from
Grease Composition:
[0237] As shown in FIG. 2, the inner ring 1 of the ball bearing 10
was mounted on a rotation shaft 21, and the outer ring 2 was
mounted on a container 22. The container 22 comprised an air
introduction port 22a and an air discharge port 22b, and clean air
was flown into the container 22 through the air introduction port
22a, and then the air was flown out of the container 22 through the
air discharge port 22b.
[0238] When the rotation shaft 21 was rotated by a motor which is
not shown in the figure and the ball bearing 10 was thereby
rotated, dusts were generated from the grease composition G
contained in the ball bearing 10, and the particles of the grease
composition were dispersed in the container 22. These particles
were flown out of the container 22 by the air which was flown in
through the air introduction port 22a, and then the particles were
transported to a particle counter which is not shown in the figure.
Thereafter, the number of particles having a particle size of 0.3
.mu.m or greater which were contained in 0.01 cubic feet (283
cm.sup.3) of the air, was counted by this particle counter.
[0239] The ball bearing 10 was mounted on the container 22 under
the condition where a preload of 14.7 N was loaded. Moreover, the
rotational speed of the ball bearing 10 was set at 3,600
min.sup.-1. Under these conditions, the amount of dusts generated
was counted both at 25.degree. C. and at 70.degree. C. for 20
minutes.
[0240] Thus, the amount of dusts generated in the early stage of
rotation of a ball bearing 10, which was counted as above, is also
shown in Tables 1 to 3.
[0241] Method for Evaluating Acoustic Performance:
[0242] The acoustic performance of the ball bearing 10 in the early
stage of rotation (the rotational speed was 1,800 min.sup.-1) was
evaluated using an Anderon Meter. The results are also shown in
Tables 1 to 3. In each table, when the Anderon value is 2 or less,
it is evaluated as satisfactory and shown with the mark
.largecircle., and when the Anderon value is more than 2, it is
evaluated as unsatisfactory and shown with the mark x.
[0243] Method for Evaluating Torque Performance:
[0244] Using a torque measuring device shown in FIG. 3, the torque
value of the ball bearing 10 was determined in the early stage of
rotation. The inner ring of the ball bearing 10 was fixed to an air
spindle 41 via an arbor 42, and the outer ring was fixed to an
aluminum cap 44 which was equipped with an air bearing 43. The air
spindle 41 was rotated at a rotational speed of 3,600 min.sup.-1 at
a room temperature so as to rotate the inner ring of the ball
bearing 10. At the time when the torque value was almost stabilized
(about 10 minutes later), the torque value was determined by a
strain gauge 45 which was connected to the aluminum cap 44. The
obtained value was recorded by a recorder 48 via a strain amp 46
and a low-pass filter 47.
[0245] The obtained results are also shown in Tables 1 to 3. In
each table, when the torque value is 29.4 N.multidot.cm or less, it
is evaluated as satisfactory and shown with the mark .largecircle.,
and when the torque value is more than 29.4 N.multidot.cm, it is
evaluated as unsatisfactory and shown with the mark x.
[0246] Method for Evaluating Durability:
[0247] The ball bearing 10 (not shown) was mounted in the housing
51 of a continuous rotating apparatus having a configuration shown
in the oblique perspective view of FIG. 4 and the partial front
view of FIG. 5, and rotated by a motor 54 via a rubber belt 52 and
a pulley 53. The rotational speed was 3,600 min.sup.-1 and the test
temperature was 70.degree. C. The Anderon value of the ball bearing
10 was determined using an Anderon Meter every 500 hours of
rotation, and the life was defined as a time when the Anderon value
exceeded 2. However, where the Anderon value did not exceed 2 even
after 3,000 hours, the test was terminated.
[0248] As well as the above described evaluation of acoustic
durability, the evaluation of the amount of dusts generated from a
grease composition was also carried out. That is, the amount of
dusts generated from a grease composition at the time of the
completion of the durability test (after rotation at a high
temperature for a long time) was determined by the same method as
described above.
[0249] The evaluation results of the durability and the amount of
dusts generated from a grease composition after rotation at a high
temperature for a long time are also shown in Tables 1 to 3. Where
">3,000" which is described in the column of durability means
that the durability test was terminated after 3,000 hours of
rotation.
[0250] Now, the results of each test will be considered. As
apparent from Tables 1 to 3, the grease compositions in Examples A1
to A12 generated a small amount of dusts in the early stage of
rotation both at an ordinary temperature and at a high temperature,
and even when the grease compositions were subjected to rotation at
a high temperature for a long time, the amount of dusts generated
was not significantly increased. Further, their acoustic
performance and torque value were excellent in the early stage of
rotation, and also their durability was extremely excellent.
[0251] In contrast, since Comparative examples A1 and A2 did not
comprise PTFE as a thickener, a large amount of dusts was generated
in the initial rotation stage. Moreover, the amount of dusts
generated further increased by rotation at a high temperature for a
long time.
[0252] Comparative example A3 generated a small amount of dusts,
but since it did not comprise a metallic soap as a thickener, the
acoustic performance and torque value in the initial rotation stage
were unsatisfactory, and durability was also insufficient.
[0253] Example A13 was excellent in the amount of dusts generated,
acoustic performance and torque value in the initial rotation
stage. However, since the amount of the mineral oil and the
synthetic oil in the base oil was smaller than the case of the
perfluoropolyether oil, it was somewhat poor in durability.
[0254] Example A14 had a small amount of dusts generated and good
acoustic performance in the initial rotation stage, but since the
worked penetration was small, the torque value in the initial
rotation stage was unsatisfactory.
[0255] Example A15 had good acoustic performance, torque value in
the initial rotation stage and durability, but since the worked
penetration was large, it generated a large amount of dusts in the
initial rotation stage both at an ordinary temperature and at a
high temperature, and further, the amount of dusts significantly
increased when rotated at a high temperature for a long time in
comparison with the grease compositions in Examples A1 to A12.
[0256] Next, the ratio between a metallic soap and PTFE in a
thickener was studied. That is to say, grease compositions were
prepared by variously changing the ratio between the metallic soap
and PTFE in the grease composition of Example A1, and the amount of
dusts generated at 70.degree. C. in the initial rotation stage and
durability were evaluated by the same method as described above.
The results are shown in the graph of FIG. 6.
[0257] The graph of FIG. 6 shows that when the ratio of PTFE in a
thickener was 10 to 80% by mass, the grease composition was
excellent in both the amount of dusts generated at 70.degree. C. in
the initial rotation stage and durability, and when the ratio was
20 to 70% by mass, the above both performances were more
excellent.
[0258] Next, the content of a thickener based on the total mass of
a grease composition was studied. That is to say, grease
compositions were prepared by variously changing the content of the
thickener in the grease composition of Example A1, and the amount
of dusts generated at 70.degree. C. in the initial rotation stage
and durability were evaluated by the same method as described
above. The results are shown in the graph of FIG. 7.
[0259] The graph of FIG. 7 shows that when the content of the
thickener was 10 to 33% by mass, the grease composition was
excellent in both the amount of dusts generated at 70.degree. C. in
the initial rotation stage and durability, and when the content was
15 to 30% by mass, the above both performances were more
excellent.
[0260] (B) Grease Composition Comprising Fluoro Resin and
N-Substituted Terephthalamic Acid Metal Salt as Thickener
[0261] FIG. 8 is a longitudinal sectional view showing the
configuration of a ball bearing 101, which is one embodiment of the
rolling apparatus of the present invention. This ball bearing 101
is comprised of an inner ring 110; an outer ring 111; a plurality
of balls 113, which are disposed between the inner ring 110 and the
outer ring 111 so as to flexibly roll therebetween; a cage 112 for
retaining the plurality of balls 113; and contact seals 114,114
installed in the outer ring 111. A space portion, which is
surrounded by the inner ring 110, the outer ring 111 and the seals
114,114, is filled with a grease composition G, and the seal 114
hermetically sealed the grease composition in the ball bearing 101.
This grease composition G lubricates the contact surface between
the raceway surfaces of both rings 110 and 111, and the balls
113.
[0262] The grease composition G comprises 20% by mass of a
thickener and 80% by mass of a base oil. The thickener comprises
50% by mass of an N-substituted terephthalamic acid metal salt and
50% by mass of PTFE, and the base oil comprises 50% by mass of a
polyol ester oil and 50% by mass of a perfluoropolyether oil (PFPE
oil). Since the grease composition G comprises the PTFE and the
PFPE oil, it has excellent heat resistance.
[0263] Since a rolling apparatus such as a ball bearing filled with
this grease composition has excellent lubricating ability and is
long-lived under high temperature conditions, it can preferably be
used as a rolling or sliding portion of machines used under
high-temperature and high-speed conditions including car electrical
components such as alternators or electromagnetic clutches;
auxiliary equipment for car engine such as idler pulleys; and
business machines such as copying machines or printers.
[0264] Next, with regard to 18 types of grease compositions
(Examples B1 to B12, and Comparative Examples B1 to B6) which have
almost the same composition as the above described grease
composition G, a worked penetration determination, a rust
protection test, a copper corrosion test, a seizure test and a
grease leakage test were carried out.
[0265] The compositions of the grease compositions of Examples B1
to B12 and Comparative examples B1 to B6 are as shown in Tables 4
to 6, and each grease composition comprises a thickener consisting
of N-octadecyl terephthalamic acid metal salt (sodium salt or
barium salt) and a fluoro resin (PTFE or a copolymer), and a base
oil consisting of a synthetic oil and a PFPE oil (excluding
Comparative examples B1 and B2). Each grease composition further
comprises, as additives, 1.0% by mass of an amine antioxidant, 0.5%
by mass of a calcium sulfonate rust preventive and 0.05% by mass of
a benzotriazole metal deactivator based on the total mass of the
grease composition.
4 TABLE 4 Example Example Example Example Example Example B1 B2 B3
B4 B5 B6 Type of Terephthalamic acid 50 -- 20 50 60 --
thickener.sup.1) Na.sup.2) Terephthalamic acid -- 50 -- -- -- 50
Ba.sup.3) PTFE 50 50 80 -- -- -- Copolymer.sup.4) -- -- -- 50 40 50
Content of thickener.sup.1) 25 25 30 25 24 25 Type of base POE
oil.sup.5) 50 50 20 50 60 50 oils.sup.1) ADPE oil.sup.5) -- -- --
-- -- -- PFPE oil 50 50 80 50 40 50 Content of base oil.sup.1) 75
75 70 75 76 75 Worked penetration 268 275 270 273 272 279 Copper
corrosion test 1 1 1 1 1 1 Rust protection test #6 #6 #5 #6 #6 #6
Seizure test (for life).sup.7) 1274 1199 1612 1231 1098 1167 Grease
leakage test.sup.1) 3.5 3.6 2.8 3.4 3.5 3.5 .sup.1)Unit is % by
mass .sup.2)N-octadecylterephthalamic acid sodium salt
.sup.3)N-octadecylterephthalamic acid barium salt .sup.4)Copolymer
of vinylidene fluoride and hexafluoroisobutylene (molar ratio 1:1)
.sup.5)Polyol ester oil .sup.6)Alkyl diphenyl ether oil .sup.7)Unit
is hr
[0266]
5 TABLE 5 Example Example Example Example Example Example B7 B8 B9
B10 B11 B12 Type of Terephthalamic acid 50 -- 20 50 60 --
thickener.sup.1) Na.sup.2) Terephthalamic acid -- 50 -- -- -- 50
Ba.sup.3) PTFE 50 50 80 -- -- -- Copolymer.sup.4) -- -- -- 50 40 50
Content of thickener.sup.1) 25 25 30 25 24 25 Type of base POE
oil.sup.5) -- -- -- -- -- -- oils.sup.1) ADPE oil.sup.6) .50 50 20
50 60 50 PFPE oil 50 50 80 50 40 50 Content of base oil.sup.1) 75
75 70 75 76 75 Worked penetration 268 275 270 273 272 279 Copper
corrosion test 1 1 1 1 1 1 Rust protection test #6 #6 #5 #6 #6 #6
Seizure test (for life).sup.7) 1688 1632 1722 1595 1534 1521 Grease
leakage test.sup.1) 3.5 3.4 2.8 3.4 3.5 3.5 .sup.1)Unit is % by
mass .sup.2)N-octadecylterephthalamic acid sodium salt
.sup.3)N-octadecylterephthalamic acid barium salt .sup.4)Copolymer
of vinylidene fluoride and hexafluoroisobutylene (molar ratio 1:1)
.sup.5)Polyol ester oil .sup.6)Alkyl diphenyl ether oil .sup.7)Unit
is hr
[0267]
6 TABLE 6 Comparative Comparative Comparative Comparative
Comparative Comparative example example example example example
example B1 B2 B3 B4 B5 B6 Type of Terephthalamic acid -- 100 50 80
70 -- thickener.sup.1) Na.sup.2) Terephthalamic acid -- -- -- -- --
50 Ba.sup.3) PTFE 100 -- 50 -- -- -- Copolymer.sup.4) -- -- -- 20
30 50 Content of thickener.sup.1) 35 15 3 20 23 42 Type of base POE
oil.sup.5) -- -- -- -- -- -- oils.sup.1) ADPE oil.sup.5) -- 100 50
80 70 50 PFPE oil 100 -- 50 20 30 50 Content of base oil.sup.1) 65
85 97 80 77 58 Worked penetration 293 267 -- 271 272 190 Copper
corrosion test 4 1 -- 1 1 1 Rust protection test #1 #7 -- #7 #6 #6
Seizure test (for life).sup.7) 1743 375 -- 737 891 689 Grease
leakage test.sup.1) 2.3 4.5 -- 3.9 3.6 1.1 .sup.1)Unit is % by mass
.sup.2)N-octadecylterephthalamic acid sodium salt
.sup.3)N-octadecylterephthalamic acid barium salt .sup.4)Copolymer
of vinylidene fluoride and hexafluoroisobutylene (molar ratio 1:1)
.sup.5)Polyol ester oil .sup.6)Alkyl diphenyl ether oil .sup.7)Unit
is hr
[0268] It should be noted that the contents of the base oil and the
thickener described in Tables 4 to 6 are values based on the total
mass of the base oil and the thickener defined as 100, and
therefore the above additives are not considered. Values described
in the columns of the type of thickener and the type of base oil
represent mass ratio (% by mass) of each component based on the
total mass of the thickener and the total mass of the base oil.
[0269] Each component of the grease composition will be explained
below.
[0270] Copolymer: a copolymer of vinylidene fluoride and
hexafluoroisobutylene (the mole ratio being 1:1)
[0271] Polyol ester oil: a kinematic viscosity at 40.degree. C.
being 70 mm.sup.2/s
[0272] Alkyl diphenyl ether oil: a kinematic viscosity at
40.degree. C. being 100 mm.sup.2/s
[0273] PFPE oil: a kinematic viscosity at 40.degree. C. being 190
mm.sup.2/s
[0274] Next, each test method and test results will be explained
below.
[0275] Worked Penetration Determination:
[0276] Worked penetration was determined according to JIS
K2220.
[0277] The results are shown in Tables 4 to 6. The grease
compositions in Examples B1 to B12 had good worked penetration. In
contrast, since the content of the thickener was too large in
Comparative example B6, the worked penetration was small. Moreover,
since the content of the thickener is too small in Comparative
example B3, the grease composition did not become a grease
state.
[0278] Rust Protection Test:
[0279] Each of the grease compositions in Examples B1 to B12 and
Comparative examples B1 to B6 was filled in a deep groove ball
bearing with rubber seals having an inside diameter of 17 mm, an
outside diameter of 47 mm and a width of 14 mm (having the same
configuration as the ball bearing of FIG. 8,) at 50% the volume of
the space portion of the ball bearing.
[0280] After a running-in (rotation) at a rotational speed of 1,800
min.sup.-1 for 30 seconds, 0.5 ml of 0.5% by mass of salt water was
poured in the inside of the bearing, and another running-in was
carried out again at a rotational speed of 1,800 min.sup.-1 for 30
seconds. Then, this ball bearing was left at rest for 48 hours in a
constant temperature and humidity bath which was controlled at
80.degree. C. and 100% RH, and thereafter, the ball bearing was
decomposed and the condition of rust generated on the raceway
surface was observed by the visual test. The rust condition was
evaluated in the following ranks.
[0281] #7: Generation of no rust
[0282] #6: Generation of very slight rust stain
[0283] #5: Generation of punctated rust with a diameter of 0.3 mm
or shorter
[0284] #4: Generation of rust with a diameter of 1.0 mm or
shorter
[0285] #3: Generation of rust with a diameter of 5.0 mm or
shorter
[0286] #2: Generation of rust with a diameter of 10.0 mm or
shorter
[0287] #1: Generation of rust on almost the entire surface of the
raceway surface
[0288] Herein, #7 to #5 were defined as good rust protection, and
#4 to #1 were defined insufficient rust protection.
[0289] The results are shown in Tables 4 to 6. The grease
compositions in Examples B1 to B12 showed good rust protection.
Accordingly, the grease compositions in Examples B1 to B12 can
preferably be used in a bearing, which is used under strict
environment where the bearing readily contacts with rain water or
the like and so readily generates rust. In contrast, since
Comparative example B1 does not contain a mineral oil or synthetic
oil (that is, since it is a common fluoro grease), the rust
protection was insufficient.
[0290] Copper Corrosion Test:
[0291] Copper corrosion test was carried out according to the
method for a copper corrosion test with grease according to JIS
K2220. The test temperature was set at 100.degree. C., and after 24
hours, the condition of color change of a copper plate was observed
by the visual test. According to the color change standard for
copper plates, the condition was evaluated in 4 stages of class 1
to class 4 in which 1 is the best.
[0292] The results are shown in Tables 4 to 6. The color of copper
plates was little changed with the grease compositions in Examples
B1 to B12. In contrast, since Comparative example B1 does not
contain a mineral oil or synthetic oil (that is, since it is a
common fluoro grease), the color change of copper plates was
observed.
[0293] Seizure Test:
[0294] Each of the grease compositions in Examples B1 to B12 and
Comparative examples B1 to B6 was filled in a deep groove ball
bearing with an iron shield having an inside diameter of 8 mm, an
outside diameter of 22 mm and a width of 7 mm (having almost the
same structure of the ball bearing of FIG. 8 with the exception
that it comprises an iron shield instead of contact seals) at 50%
the volume of the space portion of the ball bearing. Thereafter,
the ball bearing was mounted to a tester which was similar to the
bearing life tester of ASTM D 1741 shown in FIG. 9.
[0295] Thereafter, the ball bearing was rotated at a rotational
speed of 3,000 min.sup.-1 under conditions of a bearing temperature
of 180.degree. C. and an axial load of 59 N (other conditions were
set in accordance with ASTM D 1741.) The life was defined as a time
when seizure generated and the temperature of the outer ring was
risen to 190.degree. C. or higher. When the temperature was not
risen t(.about.190.degree. C. or higher even after rotation for
1,000 hours, it was evaluated as satisfactory and the test was
terminated. In this rotation test, 4 bearings were used for one
type of bearing, and the mean value was defined as a test
result.
[0296] The results are shown in Tables 4 to 6. The grease
compositions in Examples B1 to B12 had good life. In contrast,
since Comparative example B2 did not contain a fluoro resin and a
PFPE oil (that is, since it is a common N-substituted
terephthalamic acid metal salt grease), the anti-seizuring ability
at a high temperature of this grease composition was poor.
Moreover, since the contents of the fluoro resin and the PFPE oil
were small in Comparative examples B4 and B5, the anti-seizuring
ability at a high temperature of these grease compositions was
insufficient.
[0297] Grease Leakage Test:
[0298] Each of the grease compositions in Examples B1 to B12 and
Comparative examples B1 to B6 was filled in a deep groove ball
bearing with rubber seals having an inside diameter of 17 mm, an
outside diameter of 40 mm and a width of 12 mm (having the same
configuration as the ball bearing of FIG. 8), at 35% the volume of
the space portion of the ball bearing. Then, the inner ring was
rotated at a rotational speed of 14,500 min.sup.-1 for 20 hours
under conditions of an outer ring temperature of 180.degree. C. and
an axial load of 200 N, the mass of the grease composition leaked
from the bearing during rotation was measured.
[0299] When the amount of grease leaked was 10% or less by mass
based on the total mass of the filled grease composition, it was
evaluated as satisfactory. In this test, 4 bearings were used for
one type of bearing, and the mean value was defined as a test
result.
[0300] The test results are shown in Tables 4 to 6. The leaked
amount of each of the grease compositions in Examples B1 to B12 was
small, and therefore all these grease compositions were evaluated
as satisfactory.
[0301] FIG. 10 and FIG. 11 are graphs showing the results of the
rust protection test, seizure test and grease leakage test, which
were carried out on the grease compositions in Examples B7 to B12
and Comparative examples B1, B2, B4 and B5. The horizontal axis of
each graph represents the ratio of the fluoro resin (PTFE or a
copolymer) in the thickener.
[0302] As is clear from these graphs, when the ratio of the fluoro
resin in the thickener was 40 to 80% by mass (that is, the ratio of
the N-substituted terephthalamic acid metal salt being 60 to 20% by
mass), both the rust protection and the seizuring life were
excellent, and the amount of grease leaked was small.
[0303] (C) Grease Composition Comprising Fluoro Resin and Organic
Bentonite as Thickener
[0304] A grease composition comprising a fluoro resin (PTFE) and
organic bentonite as thickener was produced. When the fluoro resin
is used as a thickener, it is desired to use a fluoro oil such as a
perfluoropolyether oil (PFPE oil) as a base oil. A mixed base oil
of a base oil other than a fluoro oil and the fluoro oil was used,
and the mixing ratio is preferably a mass ratio which depends on
the mass ratio between the fluoro resin and the organic
bentonite.
[0305] The compositions of the grease compositions are as shown in
Tables 7 and 8. It should be noted that the each value described in
the column of "Type of thickeners" in Tables 7 and 8 is the mass
ratio of each component which constitutes the thickener, when the
total mass of the thickener is defined as 100. Each value described
in the column of "Type of base oils" has the same meaning.
Moreover, values described in the columns of "Content of
thickeners," "Content of base oils," and "Content of additives" are
the mass ratio of each of thickeners, base oils and additives, in a
case where the total mass of the grease composition is defined as
100.
7 TABLE 7 Example C1 Example C2 Example C3 Example C4 Type of
thickener.sup.1) Organic bentonite 50 80 30 10 PTFE 50 20 70 90
Content of thickener.sup.1) 25 21 29 33 Type of base Paraffin
mineral oil 50 -- -- 10 oils.sup.1) PAO oil.sup.2) -- 80 -- -- PETE
oil.sup.3) -- -- 30 -- Fluoro oil 50 20 70 90 Content of base
oil.sup.1) 71.5 75.5 67.5 63.5 Content of Naphtylamine.sup.4) 1 1 1
1 additive.sup.1) Calcium sulfonate 0.5 0.5 0.5 0.5 Sodium nitrite
2 2 2 2 Worked penetration 345 322 355 376 Water washout resistance
(% by mass) -1.2 -1.3 -1.0 -0.9 Rust protection property
.smallcircle. .smallcircle. .smallcircle. .smallcircle. Seizure
load (N) 1333 1333 1333 1333 Lubricating life 1.6 2.2 2.3 1.8
.sup.1)Unit is % by mass .sup.2)Poly .alpha.-olefin oil
.sup.3)Pentaerythritol tetraester oil
.sup.4)Phenyl-.alpha.-naphthylamine
[0306]
8 TABLE 8 Comparative Comparative Comparative Comparative example
example example example C1 C2 C3 C4 Type of thickener.sup.1)
Organic bentonite 100 -- -- -- PTFE. -- 100 -- -- Content of
thickener.sup.1) 18 35 -- -- Type of base oils.sup.1) Paraffin
mineral oil 35 -- -- -- PAO oil.sup.2) 65 -- -- -- PETE oil.sup.3)
-- -- -- -- Fluoro oil -- 100 -- -- Content of base oil.sup.1) 80.5
63 -- -- Content of Naphtylamine.sup.4) 1 -- -- -- additive.sup.1)
Calcium sulfonate 0.5 -- -- -- Sodium nitrite -- 2 -- -- Worked
penetration 312 290 271 285 Water washout resistance (% by mass)
-3.7 -0.6 -0.7 -0.7 Rust protection property x .smallcircle.
.smallcircle. x Seizure load (N) 980 980 980 980 Lubricating life
1.0 2.5 1.6 1.9 .sup.1)Unit is % by mass .sup.2)Poly .alpha.-olefin
oil .sup.3)Pentaerythritol tetraester oil
.sup.4)Phenyl-.alpha.-naphthylamine
[0307] A method of producing a grease composition comprising a
fluoro resin as a thickener is not particularly limited, but a
preferred example includes the method described in Japanese Patent
Laid-Open No. 10-273684. The grease compositions in Comparative
examples C1 and C2 are commercially available fluoro grease
compositions.
[0308] With regard to these 8 types of grease compositions
(Examples C1 to C4, and Comparative Examples C1 to C4), worked
penetration and water washout resistance were determined (according
to JIS K2220). In order to determine water washout resistance, a
deep groove ball bearing of bearing designation 6204 was filled
with 4 g of each type of grease composition, and the bearing was
rotated at 600 min.sup.-1 while distilled water with 79.degree. C.
was sprayed thereon at a rate of 5 ml/s. After rotation for 1 hour,
the reduced amount (% by mass) of the grease composition was
defined as water washout resistance. The results are shown in
Tables 7 and 8.
[0309] Moreover, the rust protection, load carrying capacity and
lubricating life of these grease compositions were also evaluated
(refer to Tables 7 and 8 for the results). The evaluation methods
will be explained below.
[0310] Rust Protection Test:
[0311] Each of the grease compositions in Examples C1 to C4 and
Comparative examples C1 to C4 was filled in a deep groove ball
bearing with rubber seals having an inside diameter of 17 mm, an
outside diameter of 47 mm and a width of 14 mm (not shown) at 50%
the volume of the space portion of the ball bearing.
[0312] After a running-in (rotation) at a rotational speed of 1,800
min.sup.-1 for 30 seconds, 0.5 ml of salt water having a
concentration of 0.5% by mass was poured in the inside of the
bearing, and another running-in was carried out again at a
rotational speed of 1,800 min.sup.-1 for 30 seconds. Then, this
ball bearing was left at rest for 48 hours in a constant
temperature and humidity bath which was controlled at 80.degree. C.
and 100% RH, and thereafter, the ball bearing was decomposed and
the condition of rust generated on the raceway surface was observed
by the visual test. The rust condition was evaluated in the
following ranks.
[0313] #7: Generation of no rust
[0314] #6: Generation of very slight rust stain
[0315] #5: Generation of punctated rust with a diameter of 0.3 mm
or shorter
[0316] #4: Generation of rust with a diameter of 1.0 mm or
shorter
[0317] #3: Generation of rust with a diameter of 5.0 mm or
shorter
[0318] #2: Generation of rust with a diameter of 10.0 mm or
shorter
[0319] #1: Generation of rust on almost the entire surface of the
raceway surface
[0320] Herein, #7 to #5 were defined as good rust protection, and
#4 to #1 were defined insufficient rust protection. In a graph
described later, rust protection is represented by each of the
above values, but in each table, good rust protection is
represented by the symbol .largecircle., and insufficient rust
protection is represented by the symbol x.
[0321] Evaluation Method of Load Carrying Capacity:
[0322] Load carrying capacity was evaluated by a four-ball test,
using a four-ball tester based on ASTM. That is, 3 test balls (SUJ2
(the corresponding US Industrial Standard number SAE52100) steel
balls for ball bearings having a diameter of about a half inch)
were disposed and fixed in a regular triangle form so that the
balls were contact with one another, and a test ball was then
placed and held on a hollow, which was formed in the center of the
three balls.
[0323] An evaluation target, grease composition was applied on all
the test balls, and the test ball which was placed and held as
above was rotated at a certain rotational speed (4,000 min.sup.-1)
under load conditions. The above load was set at 98 N for 1 minute
in the initial rotation stage, and then the load was gradually
increased at a rate of 392 N per minute. Seizure load was defined
as a load at the time when rotation torque was sharply increased,
and load carrying capacity was evaluated with this seizure
load.
[0324] Evaluation Method of Lubricating Life:
[0325] Each 5 g of the above 8 types of grease compositions was
enclosed in a rolling bearing separately, and the rolling bearing
was then mounted to a tester which was similar to the bearing life
tester of ASTM D 1741 shown in FIG. 9. Thereafter, the rolling
bearing was rotated at a rotational speed of 1,000 min.sup.-1 under
conditions of a temperature of 150.degree. C., a radial load of 98
N and an axial load of 294 N. Lubricating life was defined as a
time when the motor stopped due to overload or a time when the
temperature of the bearing exceeded 160.degree. C.
[0326] This lubricating life is an L.sub.50 life, which was
obtained by examining 10 tests per one type of bearing and then
using a Weibull distribution curve. The term "lubricating life" is
not used herein to mean the rolling fatigue life of a bearing due
to the generation of flaking, but the term is used herein to mean
the life of a grease determined when a bearing becomes not to
rotate because of the deterioration of a grease composition or the
like.
[0327] The configuration of the rolling bearing used in the test
will be explained below, while referring to a partial longitudinal
sectional view in FIG. 1.
[0328] This rolling bearing (bearing designation 6306VV, inside
diameter: 30 mm, outside diameter: 72 mm, width: 19 mm) is
comprised of: an inner ring 1; an outer ring 2; a plurality of
balls 3, which are disposed between the inner ring 1 and the outer
ring 2 so as to flexibly roll therebetween; a cage 4 for retaining
the plurality of balls 3 between the inner ring 1 and the outer
ring 2; and noncontact rubber seals 5, 5.
[0329] The rubber seal 5 is attached to a seal groove 2a of the
outer ring 2, and the seal covers almost the entire opening portion
located between the outer surface of the inner ring 1 and the inner
surface of the outer ring 2. A space portion, which is formed
between the inner ring 1 and the outer ring 2 and in which the
balls 3 were placed, is filled with a grease composition G, and the
rubber seals 5, 5 hermetically seal the grease composition in the
bearing. This rubber seal 5 may also be a contact type.
[0330] The test results are shown in Tables 7 and 8. The
lubricating life is represented by a relative value in a case where
the lubricating life of the grease composition in Comparative
example C1 is defined as 1.
[0331] As understood from Tables 7 and 8, the grease compositions
in Examples C1 to C4 were more excellent than the grease
compositions in Comparative Examples C1 to C4 in terms of water
washout resistance (water-resisting), rust protection and load
carrying capacity (extreme-pressure property). These grease
compositions were excellent also in lubricating life, and the
bearing was long-lived under high-temperature conditions.
[0332] Next, grease compositions were prepared by diversely
changing the ratio of organic bentonite to the total mass of the
thickener in the grease composition of Example C1. Then, rust
protection and lubricating life were evaluated by the same method
as described above. The results are shown in the graph of FIG. 12.
The lubricating life in the graph is represented by a relative
value in a case where the lubricating life of the grease
composition in Comparative example C1 is defined as 1. The graph
shows that when the content of the organic bentonite is 10 to 90%
by mass, the rust protection and the lubricating life are
excellent.
[0333] Moreover, grease compositions were prepared by diversely
changing the content of thickener to the total mass of the grease
composition in the grease composition of Example C1. Then,
lubricating life was evaluated by the same method as described
above. The results are shown in the graph of FIG. 13. The
lubricating life in the graph is represented by a relative value in
a case where the lubricating life of the grease composition in
Comparative example C1 is defined as 1.
[0334] This graph shows that when the content of the thickener is 5
to 38% by mass based on the total mass of the grease composition,
the lubricating life of the grease composition is excellent. The
graph also shows that, when the content is 8 to 30% by mass, the
lubricating life is more excellent, and when the content is 12 to
23% by mass, the lubricating life is further more excellent.
[0335] (D) Grease Composition Comprising Fluoro Resin and Calcium
Sulfonate Complex as Thickener
[0336] The configuration of a rolling bearing filled with a grease
composition comprising a fluoro resin and a calcium sulfonate
complex as thickeners is not particularly limited, but an example
includes the ball bearing shown in FIG. 14. The ball bearing 201,
as illustrated in the figure, is comprised of an inner ring 210; an
outer ring 211; a plurality of balls 213, which are disposed
between the inner ring 210 and the outer ring 211 so as to flexibly
roll therebetween; and a cage 212 for retaining the plurality of
balls 213, wherein the space portion of the bearing S is filled
with a grease composition described later, and a seal 214 seals the
grease composition in the bearing.
[0337] The present invention is further described in the following
examples and comparative examples. However, these examples are not
intended to limit the scope of the invention.
[0338] Using base oils and thickeners as shown in Table 9, ten
types of grease compositions (Examples D1 to D6 and Comparative
examples D1 to D4) were prepared. The content of the thicker was
set at 30% by mass in any of the grease compositions. Using these
10 types of grease compositions, each of the following tests was
carried out. The results are shown in Table 9.
9 TABLE 9 Comparative Comparative Comparative Comparative Example
Example Example Example Example Example example example example
example D1 D2 D3 D4 D5 D6 D1 D2 D3 D4 Thickener A 50 20 5 50 80 95
100 -- 3 97 (mass ratio) Thickener B 50 80 95 50 20 5 -- 100 97 3
(mass ratio) Base oil A ADE(50) PET(20) DPET(5) ADE DPET + PAO MO
-- PET(3) PAO(97) (mass ratio) MO Base oil B PFPE(50) PFPE(80)
PFPE(95) -- -- -- -- PFPE PFPE(97) PFPE(3) (mass ratio) Seizure
1500 1280 1100 1580 1780 1700 1820 1000 1000 1650 load (N)
Lubricating 1780 1880 2000 1580 1540 1620 1280 2180 2020 1420 life
(hr) Result of rust .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. x .DELTA.
.smallcircle. protection test Thickener A: Calcium sulfonate
complex Thickener B: Polytetrafluoroethylene PFPE:
Perfluoropolyether ADE: Alkyldiphenylether PET: Pentaerythritol
ester DPET: Dipentaerythritol ester PAO: Poly .alpha.-olefin MO:
Mineral oil
[0339] Evaluation Method of Load Carrying Capacity:
[0340] Load carrying capacity was evaluated by a four-ball test,
using a four-ball tester based on ASTM, in the same manner as
described above. That is, 3 test balls (SUJ2 (the corresponding US
Industrial Standard number SAE52100) steel balls for ball bearings
having a diameter of about a half inch) were disposed and fixed in
a regular triangle form so that the balls were contact with one
another, and a test ball was then placed and held on a hollow,
which was formed in the center of the three balls.
[0341] Thereafter, an evaluation target, grease composition was
applied on all the test balls, and the test ball which was placed
and held as above was rotated at a certain rotational speed (4,000
min.sup.-1) under load conditions. The above load was gradually
increased at a rate of 1,800 N per minute. Seizure load was defined
as a load at the time when rotation torque was sharply increased.
Load carrying capacity was evaluated with this seizure load, and
when the seizure load was 1,100 N or more, the grease composition
was evaluated as satisfactory.
[0342] Evaluation Method of Lubricating Life:
[0343] Lubricating life was evaluated, using a tester similar to
the bearing life tester of ASTM D 1741 shown in FIG. 9.
[0344] First, the space portion of a rolling bearing (bearing
designation 6306VV) manufactured by NSK Ltd., was filled with a
grease composition at 35% the volume of the space portion.
Thereafter, the rolling bearing was mounted to the above tester,
and the inner ring was then rotated at a rotational speed of 7,000
min.sup.-1 under conditions of a temperature of 180.degree. C., a
radial load of 98 N and an axial load of 294 N. A cycle of rotating
the inner ring for 24 hours and then stopping it for 4 hours was
repeated. Lubricating life was defined as a time when the motor
stopped due to overload or a time when the temperature of the
bearing exceeded 190.degree. C.
[0345] When the lubricating life was 1,500 hours or longer, the
grease composition was evaluated as satisfactory.
[0346] Rust Protection Test:
[0347] The space portion of a rolling bearing (bearing designation
6202VV) manufactured by NSK Ltd., was filled with each of the
grease compositions in Examples D1 to D6 and Comparative examples
D1 to D4 at 35% the volume of the space portion.
[0348] Thereafter, under load conditions of an axial preload of
39.2 N, the rolling bearing was left for 1 month in a constant
temperature and humidity bath, which was controlled at 80.degree.
C. and at 90% RH. At that time, the rolling bearing was placed in
the constant temperature and humidity bath at an ordinary
temperature without preheating it, so as to cause condensation on
the rolling bearing. One month later, the rolling bearing was taken
out of the constant temperature and humidity bath. The rolling
bearing was then decomposed, and the condition of rust generated
was visually observed. Rust protection was evaluated according to
the following standard:
[0349] No rust: .largecircle. (Satisfactory)
[0350] Punctated rust (1 to 3 spots): .DELTA. (Unsatisfactory)
[0351] Punctated rust (many spots): x (Unsatisfactory)
[0352] As shown in Table 9, the rolling bearing of each Example
filled with a grease composition which comprises, as a thickener, a
calcium sulfonate complex consisting of calcium sulfonate and a
calcium salt and a fluoro resin had a seizuring load which further
exceeded 1,100 N as a satisfactory standard. Moreover, the rolling
bearing of each Example had a lubricating life which further
exceeded 1,500 hours as a satisfactory standard. Furthermore, in
all the Examples, the rolling bearing passed the rust protection
test.
[0353] In contrast, the lubricating life of the rolling bearing of
Comparative example D1 did not reach the satisfactory standard.
Moreover, the load carrying capacity and the rust protection of the
rolling bearings of Comparative examples D2 and D3 did not reach
the satisfactory standard. Furthermore, the lubricating life of the
rolling bearing of Comparative example D4 did not reach the
satisfactory standard.
[0354] (E) Grease Composition Comprising Fluoro Resin and Carbon
Black as Thickener
[0355] FIG. 15 is a partial longitudinal sectional view showing the
configuration of a ball bearing 321, which is one embodiment of the
rolling apparatus of the present invention. This ball bearing 321
is comprised of: an outer ring 322; an inner ring 323; a plurality
of balls 324, which are disposed between the outer ring 322 and the
inner ring 323 so as to flexibly roll therebetween; a cage 325 for
retaining the plurality of balls 324; and noncontact seals 326, 326
installed in the seal groove 322b of the outer ring 322. A space
portion, which is surrounded by the outer ring 322, the inner ring
323 and the seals 326, 326 are filled with a grease composition
327, and the seal 326 hermetically sealed the grease composition
327 in the ball bearing 321.
[0356] This grease composition 327 comprises 20% by mass of a
thickener and 80% by mass of a base oil. The thickener comprises
50% by mass of carbon black and 50% by mass of PTFE, and the base
oil comprises 50% by mass of a poly .alpha.-olefin oil and 50% by
mass of a perfluoropolyether oil (PFPE oil).
[0357] Since the grease composition 327 comprises carbon black, the
grease composition 327 lubricates the contact surface between the
raceway surfaces 322a and 323a of the above both rings 322 and 323,
and the balls 324, and also conducts electricity to the outer ring
322, the inner ring 323 and the balls 324. In addition, the outer
ring 322 or inner ring 323 is grounded (not shown in the figure),
so that static electricity generated by the rotation of the ball
bearing 321 can be eliminated. If the seal 326 is a contact type
seal and is made from conductive rubber so that also the seal 326
obtains electric conductivity, the electric conductivity of the
ball bearing 321 can be better.
[0358] Since the grease composition 327 comprises PTFE and a PFPE
oil, this grease composition has excellent heat resistance.
[0359] A rolling apparatus such as a ball bearing filled with this
grease composition has excellent electric conductivity and is
long-lived under high temperature conditions, and therefore it can
preferably be used as a rolling or sliding portion of machines used
under high-temperature and high-speed conditions including car
electrical components such as alternators or electromagnetic
clutches; auxiliary equipment for car engine such as idler pulleys;
and business machines such as copying machines or printers.
[0360] Next, with regard to 16 types of grease compositions
(Examples E1 to E10, and Comparative Examples E1 to E6) which have
almost the same composition as the above described grease
composition 327, a worked penetration determination, a rust
protection test, a copper corrosion test, a seizure test and an
electric conductivity test were carried out.
[0361] The compositions of the grease compositions of Examples E1
to E10 and Comparative examples E1 to E6 are as shown in Tables 10
to 12, and each grease composition comprises a thickener consisting
of carbon black and a fluoro resin (PTFE or a copolymer) and a base
oil consisting of a synthetic oil and a PFPE oil (except
Comparative examples E1 and E2). Each grease composition further
comprises, as additives, 1.0% by mass of an amine antioxidant, 0.5%
by mass of a calcium sulfonate rust preventive and 0.05% by mass of
a benzotriazole metal deactivator based on the total mass of the
grease composition.
10 TABLE 10 Example Example Example Example Example E1 E2 E3 E4 E5
Type of thickener.sup.1) Carbon black 50 60 20 50 60 PTFE 50 40 80
-- -- Copolymer.sup.2) -- -- -- 50 40 Content of thickener.sup.1)
20 18 28 20 18 Type of base oils.sup.1) PAO oil.sup.3) 50 73 21 50
52 ADPE oil.sup.4) -- -- -- -- -- PFPE oil 50 27 79 50 48 Content
of base oil.sup.1) 80 82 72 80 82 Worked penetration 278 280 270
273 272 Copper corrosion test 1 1 1 1 1 Rust protection test #6 #6
#5 #6 #6 Seizure test (for life) 1.9 1.9 2.3 2.0 1.8 Electric
conductivity test (for 0.09 0.08 0.18 0.10 0.08 bearing's
resistance) .sup.1)Unit is % by mass .sup.2)Copolymer of vinylidene
fluoride and hexafluoroisobutylene (molar ratio 1:1) .sup.3)Poly
.alpha.-olefin oil .sup.4)Alkyldiphenylether oil
[0362]
11 TABLE 11 Example Example Example Example Example E6 E7 E8 E9 E10
Type of thickener.sup.1) Carbon black 50 30 20 50 60 PTFE 50 70 80
-- -- Copolymer.sup.2) -- -- -- 50 40 Content of thickener.sup.1)
20 28 28 20 20 Type of base oils.sup.1) PAO oil.sup.3) -- -- -- --
-- ADPE oil.sup.4) 38 28 20 50 50 PFPE oil 62 72 80 50 50 Content
of base oil.sup.1) 80 72 72 80 80 Worked penetration 268 264 270
276 265 Copper corrosion test 1 1 1 1 1 Rust protection test #6 #5
#5 #6 #6 Seizure test (for life) 2.5 2.6 2.6 2.4 2.4 Electric
conductivity test (for 0.13 0.24 0.25 0.15 0.10 bearing's
resistance) .sup.1)Unit is % by mass .sup.2)Copolymer of vinylidene
fluoride and hexafluoroisobutylene (molar ratio 1:1) .sup.3)Poly
.alpha.-olefin oil .sup.4)Alkyldiphenylether oil
[0363]
12 TABLE 12 Comparative Comparative Comparative Comparative
Comparative Comparative example E1 example E2 example E3 example E4
example E5 example E6 Type of thickener.sup.1) Carbon black -- 100
50 80 70 50 PTFE 100 -- 50 -- -- -- Copolymer.sup.2) -- -- -- 20 30
50 Content of thickener.sup.1) 35 10 3 20 23 42 Type of base
oils.sup.1) PAO oil.sup.3) -- -- -- -- -- -- ADPE oil.sup.4) -- 100
48 75 65 83 PFPE oil 100 -- 52 25 35 17 Content of base oil.sup.1)
65 90 97 80 77 58 Worked penetration 293 267 -- 271 272 190 Copper
corrosion test 4 1 -- 1 1 1 Rust protection test #1 #7 -- #6 #6 #6
Seizure test (for life) 2.8 1 -- 1.2 1.3 1.2 Electric conductivity
test (for 1.00 0.05 -- 0.07 0.07 0.10 bearing's resistance)
.sup.1)Unit is % by mass .sup.2)Copolymer of vinylidene fluoride
and hexafluoroisobutylene (molar ratio 1:1) .sup.3)Poly
.alpha.-olefin oil .sup.4)Alkyldiphenylether oil
[0364] It should be noted that the content of the base oil and the
thickener described in each of Tables 10 to 12 is a value based on
that the total mass of the base oil and the thickener is defined as
100, and that the above additives are not considered. Moreover,
values described in the columns of the type of thickener and the
type of base oil show the mass ratio (% by mass) of each component
based on the total mass of the thickener and the total mass of the
base oil.
[0365] Each component of the grease composition will be explained
below.
[0366] Carbon black: a primary particle size of 30 nm, a DBP oil
absorption with a dibutyl phthalate absorptiometer of 350 ml/100 g,
and a specific surface area by nitrogen adsorption of 800
m.sup.2/g
[0367] Copolymer: a copolymer of vinylidene fluoride and
hexafluoroisobutylene (mole ratio being (1:1)
[0368] Poly .alpha.-olefin oil: a kinematic viscosity at 40.degree.
C. being 60 mm.sup.2/s
[0369] Alkyl diphenyl ether oil: a kinematic viscosity at
40.degree. C. being 100 mm.sup.2/s
[0370] PFPE oil: a kinematic viscosity at 40.degree. C. being 190
mm.sup.2/s
[0371] Next, each test method and test results will be explained
below.
[0372] Worked Penetration Determination:
[0373] Worked penetration was determined according to JIS
K2220.
[0374] The results are shown in Tables 10 to 12. The grease
compositions in Examples E1 to E10 had good worked penetration. In
contrast, since the content of the thickener was too large in
Comparative example E6, the worked penetration was small. Moreover,
since the content of the thickener is too small in Comparative
example E3, the grease composition did not become a grease
state.
[0375] Rust Protection Test:
[0376] Each of the grease compositions in Examples E1 to E10 and
Comparative examples E1 to E6 was filled in a deep groove ball
bearing with rubber seals having an inside diameter of 17 mm, an
outside diameter of 47 mm and a width of 14 mm (having almost the
same configuration as the ball bearing of FIG. 8,) at 50% the
volume of the space portion of the ball bearing.
[0377] After a running-in (rotation) at a rotational speed of 1,800
min.sup.-1 for 30 seconds, 0.5 ml of 0.5% by mass of salt water was
poured in the inside of the bearing, and another running-in was
carried out again at a rotational speed of 1,800 min.sup.-1 for 30
seconds. Then, this ball bearing was left at rest for 48 hours in a
constant temperature and humidity bath which was controlled at
80.degree. C. and 100% RH, and thereafter, the ball bearing was
decomposed and the condition of rust generated on the raceway
surface was observed by the visual test. The rust condition was
evaluated in the following ranks:
[0378] #7: Generation of no rust
[0379] #6: Generation of very slight rust stain
[0380] #5: Generation of punctated rust with a diameter of 0.3 mm
or shorter
[0381] #4: Generation of rust with a diameter of 1.0 mm or
shorter
[0382] #3: Generation of rust with a diameter of 5.0 mm or
shorter
[0383] #2: Generation of rust with a diameter of 10.0 mm or
shorter
[0384] #1: Generation of rust on almost the entire surface of the
raceway surface
[0385] Herein, #7 to #5 were defined as good rust protection, and
#4 to #1 were defined insufficient rust protection.
[0386] The results are shown in Tables 10 to 12. The grease
compositions in Examples E1 to E10 showed good rust protection. In
contrast, since Comparative example E1 did not contain a mineral
oil or synthetic oil (that is, since it is a common fluoro grease),
the rust protection was insufficient.
[0387] Copper Corrosion Test:
[0388] Copper corrosion test was carried out according to the
method for a copper corrosion test with grease according to JIS
K2220. The test temperature was set at 100.degree. C., and after 24
hours, the condition of color change of a copper plate was observed
by the visual test. According to the color change standard for
copper plates, the condition was evaluated in 4 stages of class 1
to class 4 in which 1 is the best.
[0389] The results are shown in Tables 10 to 12. The color of
copper plates was little changed with the grease compositions in
Examples E1 to E10. In contrast, since Comparative example E1 did
not contain a mineral oil or synthetic oil (that is, since it is a
common fluoro grease), the color change of copper plates was
observed.
[0390] Seizure Test:
[0391] Each of the grease compositions in Examples E1 to E10 and
Comparative examples E1 to E6 was filled in a deep groove ball
bearing with an iron shield having an inside diameter of 8 mm, an
outside diameter of 22 mm and a width of 7 mm (having the same
configuration of the ball bearing of FIG. 15) at 50% the volume of
the space portion of the ball bearing. Thereafter, the ball bearing
was mounted to a tester which was similar to the bearing life
tester of ASTM D 1741 shown in FIG. 9.
[0392] Thereafter, the ball bearing was rotated at a rotational
speed of 3,000 min.sup.-1 under conditions of a bearing temperature
of 180.degree. C. and an axial load of 59 N (other conditions were
set in accordance with ASTM D 1741.) The life was defined as a time
when seizure generated and the temperature of the outer ring was
risen to 190.degree. C. or higher. When the temperature was not
risen to 190.degree. C. or higher even after rotation for 1,000
hours, it was evaluated as satisfactory and the test was
terminated. In this rotation test, 4 bearings were used for one
type of bearing, and the mean value was defined as a test
result.
[0393] The results are shown in Tables 10 to 12. The life described
in each of Tables 10 to 12 is a relative value in a case where the
life of Comparative example E2 is defined as 1. The grease
compositions in Examples E1 to E10 had good life. In contrast,
since Comparative example E2 did not contain a fluoro resin and a
PFPE oil (that is, since it is a common carbon black grease), the
anti-seizuring ability at a high temperature was poor. Moreover,
since the contents of the fluoro resin and the PFPE oil were small
in Comparative examples E4 and E5, the anti-seizuring ability at a
high temperature of these grease compositions was insufficient.
[0394] Electric Conductivity Test:
[0395] Each of the grease compositions in Examples E1 to E10 and
Comparative examples E1 to E6 were filled in a ball bearing having
the same configuration as in FIG. 15 at 50% the volume of the space
portion of the bearing, and the ball bearing was then mounted to an
apparatus shown in FIG. 16. Thereafter, electric resistance
(maximum) between the inner ring and the outer ring during rotation
was measured. The ball bearing was first rotated for 100 hours
under the conditions of the above seizure test, and it was then
subjected to this electric conductivity test.
[0396] First, the apparatus for measuring resistance will be
explained, referring to the schematic block diagram of FIG. 16.
[0397] In FIG. 16, a numerical code 401 denotes a ball bearing that
is a measurement target, and the apparatus is configured that a
motor 403 rotates a shaft 402 installed in the inner ring 401a, so
that the ball bearing 401 rotates. A certain constant voltage is
applied between the shaft 402 installed in the inner ring 401a and
an outer ring 401b by a constant-voltage power supply 404. An
electric resistance measuring device 405 is connected in parallel
to the constant-voltage power supply 404.
[0398] The electric resistance measuring device 405 outputs a
measured voltage value (an analog value) to an A/D conversion
circuit 406. The A/D conversion circuit 406 converts the measured
voltage value to a digital value based on a previously established
sampling cycle, and then it outputs the converted digital signal to
a processor 407. In the present embodiment, the sampling cycle is
set at 50 kHz (sampling time interval=0.02 ms).
[0399] The processor 407 is comprised of a maximum resistance
processing unit 407A, a threshold processing unit 407B, and a wave
number counting unit 407C. The maximum resistance processing unit
407A calculates the maximum resistance based on the input digital
signal. The threshold processing unit 407B processes the input
digital signal with a certain threshold value so as to eliminate
noise. The wave number counting unit 407C counts the fluctuation
number per certain time unit, that is, the wave number of waves
regarding pulse counts from the threshold processing unit 407B,
based on the fluctuation of pulse values over time, and then the
unit 407C obtains the mean value of wave numbers per unit time. The
processor 407 outputs the obtained maximum resistance and the mean
value of wave numbers per unit time to a displaying device 408. In
the present embodiment, the unit time for counting the above wave
number is set at 0.328 second. The displaying device 408 is
comprised of a display and others, and it displays the maximum
resistance and the mean value of wave numbers per unit time
obtained by the processor 407.
[0400] Next, a method of evaluating the electric resistance of the
ball bearing 401 using the above configured apparatus will be
explained.
[0401] Under the conditions where the shaft 402, that is, the inner
ring 401a is being rotated at a certain rotational speed by the
motor 403, a certain constant voltage is applied between the inner
ring 401a and the outer ring 401b of the bearing 401 by the
constant-voltage power supply 404. At this time, an electric
current is passed between the inner ring 401a and the outer ring
401b, but the voltage is fluctuated by spark or the like. The
voltage is measured by the resistance measuring apparatus 405, the
measured value is then converted into a digital value by the A/D
conversion circuit 406, and based on the digital signal, the
maximum resistance and the wave number per certain unit time are
obtained by the processor 407, and finally the obtained values are
displayed on the displaying device 408.
[0402] The measurement conditions are as follows:
[0403] Inner ring rotational speed: 100 min.sup.-1
[0404] Radial load (Fr) applied on bearing 401: 19.6 N
[0405] Voltage applied: 6.2 V
[0406] Maximum electric current: 100 .mu.A
[0407] Series resistance: 62 k.OMEGA.
[0408] Atmosphere temperature: 40.degree. C.
[0409] Atmosphere humidity: 50% RH
[0410] The results are shown in Tables 10 to 12. It should be noted
that the bearing electric resistances described in Tables 10 to 12
are relative values in a case where the bearing electric resistance
of Comparative example E1 is defined as 1.
[0411] The grease compositions in Examples E1 to E10 had good
electric conductivity, but the grease composition in Comparative
example E1 had poor electric conductivity because it did not
contain carbon black.
[0412] FIGS. 17 and 18 are graphs showing the results of the rust
protection test, the seizure test and the electric conductivity
test of the grease compositions of Examples E6 to E10 and
Comparative examples E1, E2, E4 and E5. The horizontal axis of each
graph represents the ratio of the fluoro resin (PTFE or a
copolymer) in the thickener.
[0413] As is shown in these graphs, when the ratio of the fluoro
resin in the thickener is 40 to 80% by mass (that is, the ratio of
carbon black being 60 to 20% by mass), the grease composition is
excellent in all of the rust protection, the seizuring life and the
electric conductivity.
[0414] These embodiments are provided for illustrative purposes
only, and are not intended to limit the scope of the invention.
[0415] For example, the types of the base oils, thickeners and
additives used in the present grease composition are not limited to
the above described ones.
[0416] Further, in the present embodiments, a deep groove ball
bearing was used to explain the rolling apparatus of the present
invention. However, the present invention can be applied to other
various types of rolling bearings. Examples of such rolling
bearings include radial rolling bearings such as an angular contact
ball bearing, a self-aligning ball bearing, a cylindrical roller
bearing, a tapered roller bearing, a needle roller bearing and a
self-aligning roller bearing, and thrust rolling bearings such as a
thrust ball bearing and a thrust roller bearing.
[0417] Moreover, the present invention is not limited to a rolling
bearing, but can be applied to other various types of rolling
apparatus. Examples of such rolling apparatuses include a ball
screw, a linear guide apparatus, a linear bearing and others.
* * * * *