U.S. patent application number 11/478482 was filed with the patent office on 2008-01-03 for thermal conductive grease.
This patent application is currently assigned to Polymatech Co., Ltd.. Invention is credited to Tsukasa Ishigaki.
Application Number | 20080004191 11/478482 |
Document ID | / |
Family ID | 38877426 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080004191 |
Kind Code |
A1 |
Ishigaki; Tsukasa |
January 3, 2008 |
Thermal conductive grease
Abstract
A thermal conductive grease used for diffusion of heat generated
in electronic appliances is provided. The thermal conductive grease
comprises: (A) a base oil having a viscosity of 112 to 770 mm.sup.2
at 40.degree. C. and comprising a copolymer of an unsaturated
dicarboxylic acid dibutyl ester and an .alpha.-olefin; and (B) a
thermal conductive filler filled in the base oil. The thermal
conductive grease does not include conventionally used silicone oil
so that insulating substances will not be formed in the thermal
conductive grease.
Inventors: |
Ishigaki; Tsukasa;
(Saitama-shi, JP) |
Correspondence
Address: |
CROMPTON, SEAGER & TUFTE, LLC
1221 NICOLLET AVENUE, SUITE 800
MINNEAPOLIS
MN
55403-2420
US
|
Assignee: |
Polymatech Co., Ltd.
|
Family ID: |
38877426 |
Appl. No.: |
11/478482 |
Filed: |
June 29, 2006 |
Current U.S.
Class: |
508/155 ;
508/172; 508/468 |
Current CPC
Class: |
C10M 169/02 20130101;
C10N 2010/04 20130101; C10M 2201/0616 20130101; C10M 2209/0863
20130101; C10N 2040/14 20130101; C10N 2020/04 20130101; C10M 107/28
20130101; C10M 2201/0626 20130101; C10N 2010/06 20130101; C10N
2050/10 20130101; C10M 2201/0876 20130101; C10M 2209/0863 20130101;
C10M 2205/0285 20130101 |
Class at
Publication: |
508/155 ;
508/468; 508/172 |
International
Class: |
C10M 113/08 20060101
C10M113/08 |
Claims
1. A thermal conductive grease comprising: (A) a base oil having a
viscosity of 112 to 770 mm.sup.2 at 40.degree. C. and comprising a
copolymer of an unsaturated dicarboxylic acid dibutyl ester and an
.alpha.-olefin; and (B) a thermal conductive filler filled in the
base oil.
2. The thermal conductive grease according to claim 1 wherein the
viscosity of said copolymer at 40.degree. C. is in a range between
112 and 340 mm.sup.2/s.
3. The thermal conductive grease according to claim 1 wherein said
thermal conductive filler is selected from a group consisting of
zinc oxide, aluminum oxide, boron nitride and combinations
thereof.
4. The thermal conductive grease according to claim 1 wherein said
thermal conductive filler is zinc oxide and filled in the base oil
in a range between 82 and 87.5 weight percent.
5. The thermal conductive grease according to claim 1 wherein said
thermal conductive filler is boron nitride and filled in the base
oil at 47.6 weight percent.
6. The thermal conductive grease according to claim 1 wherein said
thermal conductive filler is aluminum oxide and filled in the base
oil at 87.5 weight percent.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a thermal conductive grease
to be used for effectively radiating heat generated from electronic
components.
[0002] Most of electronic components that are used in electronic
and electric appliances generate heat during use. Accordingly, in
order to obtain their proper functions, the removal of the heat
generated may be required. Thus, heat conductive materials such as
heat conductive greases and heat conductive sheets have been widely
used in the art. For instance, a thermal conductive grease may be
filled inbetween a heat-generating part of an electronic component
and a cooling component or may be applied thereon to transfer the
heat from the electronic component to the cooling component.
[0003] Thermal conductive grease which contains silicone oil as a
base oil and inorganic powder as a thermal conductive filler has
been widely known conventionally (see for example Japanese
Laid-Open Patent Application 10-110179). However, in the case of
using the thermal conductive grease containing silicone oil for the
base oil, the silicone oil could sometimes separate or leach out of
the grease, to thereby contaminate into its surroundings (see for
example Japanese Laid-Open Patent Application 3-162493). In
addition, as described in Japanese Laid-Open Patent Applications
3-106996 and 2002-201483, low-molecular weight siloxane that is
contained in the silicone oil could precipitate as insulating
materials such as silicon dioxide (SiO.sub.2) and silicon carbide
(SiC) by application of heat. Such insulators could malfunction the
electronic appliances. Accordingly, another thermal conductive
grease using oil other than silicone oil as the base oil has been
proposed.
[0004] For improving the thermal conductivity of the thermal
conductive grease, the base oil should be filled with the thermal
conductive filler at high density. On the other hand, it turned out
through a comparison between greases which have the same thermal
conductivity and which are applied between the heat-generating part
and the cooling component, that the thermal conductive grease could
attain less thermal conductivity when the grease is applied with
lower thickness, to thereby increase the thermal conduction.
Therefore, from the viewpoint of thermal conduction, it is
preferable to form a thin film of grease.
[0005] However, when the conventional thermal conductive grease
provided as the base oil is filled with an inorganic powder at high
density, the thermal conductive grease could have higher hardness
to result in difficulty in forming into a thin film. As a result,
the thermal resistance of the thermal conductive grease being
applied was often inferior.
[0006] In particular, the grease that are filled with the thermal
conductive filler at higher density had higher viscosity, and/or
lower cone penetration (see Japanese Industrial Standard (JIS) K
2220), thereby resulting in poor dispensing properties of grease.
In this case, the term "dispensing properties" refers to good
workability for coating grease on a substrate, such as easiness of
spreading the grease across the surface applied, fluidity and
adherence of the grease thereon, and the like. Therefore, when the
dispensing properties of the grease become inferior, it becomes
difficult to discharge the grease from a coating applicator such as
a syringe or it becomes difficult to spread the grease thinly on an
exothermic body. Therefore, the compressibility of grease, which is
an indicator of easiness in making a thin film of grease, decreases
as the dispensing properties of grease decreases in a case where a
fixed volume of grease is discharged on the contact surface and
flattened out with a constant load.
SUMMARY OF THE INVENTION
[0007] Therefore, an object of the present invention is to provide
a thermal conductive grease having excellent dispensing properties
and an excellent compressibility as well as a high thermal
conductivity attained by filling a base oil of a grease with a
thermal conductive filler at high density.
[0008] According to a first aspect of the present invention, a
thermal conductive grease is provided, comprising: (A) abase oil
comprising a copolymer of an unsaturated dicarboxylic acid dibutyl
ester and an .alpha.-olefin and having a viscosity of 112 to 770
mm.sup.2 at 40.degree. C.; and (B) a thermal conductive filler
filled in the base oil.
[0009] In the first aspect of the invention, use of the copolymer
of the unsaturated dicarboxylic acid dibutyl ester and the
.alpha.-olefin provides the thermal conductive grease with more
excellent dispensing properties and compressibility even when the
thermal conductive grease is filled with the thermal conductive
filler at high density. In addition, since silicone oil is not used
as a base oil, troubles such as a contact fault due to scattering
of low-molecular siloxane do not occur.
[0010] The thermal conductive grease can include copolymer that has
a viscosity of 112 to 340 mm.sup.2/s at 40.degree. C. The viscosity
of the grease can be excellently proper in a case where the
viscosity of the base oil falls in the range of 112 to 340
mm.sup.2/s.
[0011] The thermal conductive filler can be at least one or more
selected from the group consisting of: zinc oxide; aluminum oxide;
and boron nitride.
[0012] Further, the thermal conductive filler can be zinc oxide
which is filled in the base oil at a percentage of 82 to 87.5
weight %.
[0013] The thermal conductive filler can be boron nitride which is
filled in the base oil at a percentage of 47.6 weight % with
respect to the base oil.
[0014] The thermal conductive filler can be aluminum oxide which is
filled in the base oil at a percentage of 87.5 weight %.
[0015] According to the constructions described above, there may be
provided with the thermal conductive grease having more excellent
dispensing properties as well as higher thermal conductivity,
compared with those of the conventional one.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention, together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0017] FIG. 1 is a side view showing a schematic configuration of a
thermal resistance measuring device.
DETAILED DESCRIPTION OF THE INVENTION
[0018] It should be apparent to those skilled in the art that the
present invention may be embodied in many other specific forms
without departing from the spirit or scope of the invention.
Particularly, it should be understood that the invention may be
embodied in the following forms.
[0019] A thermal conductive grease as an embodiment of the present
embodiment comprises: (A) a base oil comprising a copolymer of an
unsaturated dicarboxylic acid dibutyl ester and an .alpha.-olefin,
having a viscosity of 112 to 770 mm.sup.2 at 40.degree. C.; and (B)
a thermal conductive filler filled in the base oil.
[0020] The thermal conductive grease of the present invention
contains, as a base oil, 5 to 55 weight % of a copolymer of
unsaturated dicarboxylic acid ester and .alpha.-olefin. Examples of
the unsaturated dicarboxylic acid ester to be used include: esters
of maleic acid, fumaric acid, citraconic acid, mesaconic acid, and
itaconic acid. Among them, ester of maleic acid and fumaric acid is
preferable. It is desirable that the alcohol component of
unsaturated dicarboxylic acid ester has 3 to 10 carbon atoms. It is
preferable that an unsaturated dicarboxylic acid dibutyl ester
correspond to the unsaturated dicarboxylic acid ester because the
thermal conductive grease attains good fluidity. The .alpha.-olefin
preferably has 6 to 16 carbon atoms. In addition, a copolymer
having an unbranched .alpha.-olefin shows a good fluidity even at
low temperatures, so such the copolymer is preferred compared to
one having a branched .alpha.-olefin.
[0021] The viscosity of the copolymer at 40.degree. C. is 100 to
1,000 mm.sup.2/s, preferably 112 to 770 mm.sup.2/s, and more
preferably 112 to 340 mm.sup.2/s, where the measurement is based on
ASTM D-445. If the copolymer provided as a base oil has a viscosity
of less than 112 mm.sup.2/s, the base oil easily separated from the
obtained grease and thus it is not preferable. Furthermore, in the
case where the viscosity is less than 112 mm.sup.2/s, the base oil
is tend to be evaporated at high temperature. Thus, the content of
oil in the grease may decrease so that crack, air layer, or the
like may be formed at the contact surface with a cooling component,
which then result in a decrease in thermal radiation
characteristics. On the other hand, in the case where the copolymer
used in the base oil has a viscosity exceeding 770 mm.sup.2/s, it
becomes difficult to fill the base oil with an inorganic powder as
a thermal conductive filler at high density. In addition, the
dispensing property of the grease is decreased because of an
increase of the viscosity.
[0022] The thermal conductive grease of the present invention as
the thermal conductive filler contains an inorganic powder in an
amount of 45 to 95 weight %. If the amount is less than 45 weight
%, the grease cannot be provided with sufficient thermal radiation
characteristics. In addition, if the amount is more than 95 weight
%, the grease becomes excessively hard, thereby resulting in poor
dispensing properties. Preferably, the inorganic powder is selected
from a group consisting of zinc oxide, aluminum oxide, titanium
oxide, magnesium oxide, silicon oxide, aluminum nitride, boron
nitride, silicon nitride, silicon carbide, diamond, aluminum,
silver, copper, and graphite, and combinations thereof. However, it
is not limited to any of these material. Alternatively, one or more
of other fillers may be used independently or in combination with
any of the materials listed above. In addition, but not
specifically limited to, the inorganic powder has an average
particle size of preferably 20 .mu.m or less, more preferably 5
.mu.m or less. If the average particle size exceeds 20 .mu.m, the
compressibility of grease becomes inferior, thereby causing a
decrease in thermal conductivity. Furthermore, two or more
inorganic powders having different average particle sizes may be
used in combination. In this case, also, the particle size
distribution of the inorganic powder is not specifically limited.
When electrical insulation properties are required in the thermal
conductive grease, inorganic powder having electrical insulation
properties can be generally used.
[0023] The thermal conductive grease of the present invention may
contain a surfactant for improving the filling ability thereof. The
addition of surfactant to the grease improves the filling rate of
inorganic powder, thereby allowing an increase in thermal
conductivity of the grease. Further, the addition of surfactant to
the grease can impart more excellent dispensing properties and
compressibility to the grease. Examples of the surfactant include
non-ionic surfactant, anionic surfactant, cation surfactant, and
amphoteric surfactant. The non-ionic surfactant does not effect on
the electric characteristics of the grease, so it will be
particularly preferable when the grease is expected to have
electrical insulation properties. Examples of the non-ionic
surfactant include polyoxyethylene oleyl ether and polyoxyethylene
alkyl ether.
[0024] Further, if required, the thermal conductive grease may be
mixed with any of various additives, including oxidation
inhibitors, corrosion inhibitors, anticorrosive compositions,
thickeners, puffing agents, pigments, dyes, antifoaming agents,
plasticizers, and solvents.
[0025] The thermal conductive grease of the present invention can
be obtained by mixing (A) a copolymer of unsaturated dicarboxylic
acid ester and .alpha.-olefin, (B) an inorganic powder, and
optionally a surfactant and any of various additives, in a mixer
such as a planetary mixer and a trimix at room temperature or, if
required, at elevated temperatures by heating. Furthermore, for
mixing the mixture uniformly, the mixture may be mixed under
high-shearing forces using a mixing device such as a three-roll
mill or a colloid mill.
[0026] Hereinafter, the above embodiments will be described more
specifically by way of examples and comparative examples, which do
not intend to restrict the scope of the present invention.
EXAMPLE 1
[0027] With respect to: (A) 100 parts by weight (16.4 weight %) of
a copolymer of unsaturated dicarboxylic acid dibutyl ester and
.alpha.-olefin (trade name: Ketjenlube 115, manufactured by AKZO
NOBEL Co., Ltd., having a viscosity of 112 mm.sup.2/s at 40.degree.
C.) as a copolymer of unsaturated dicarboxylic acid ester and
.alpha.-olefin, (B) 500 parts by weight (82.0 weight %) of zinc
oxide (0.4 .mu.m in average particle size) as an inorganic powder
and 10 parts by weight (1.6 weight %) of an non-ionic surfactant
(polyoxyethylene oleyl ether) were introduced into a planetary
mixer, and then stirred for one hour to be mixed, to obtain a
thermal conductive grease.
EXAMPLE 2
[0028] A thermal conductive grease was prepared similarly as that
of Example 1, except that the quantity of inorganic powder was
increased. The weight percentages of copolymer and thermal
conductive filler in a base oil are shown in Table 1,
respectively.
EXAMPLE 3
[0029] A thermal conductive grease was prepared similarly as that
of Example 1, except that the quantity of inorganic powder was
increased. The weight percentages of copolymer and thermal
conductive filler in a base oil are shown in Table 1,
respectively.
EXAMPLE 4
[0030] With respect to 100 parts by weight (16.4 weight %) of a
copolymer of unsaturated dicarboxylic acid dibutyl ester and
.alpha.-olefin (trade name: Ketjenlube 135, manufactured by AKZO
NOBEL Co., Ltd., having a viscosity of 340 mm.sup.2/s at 40.degree.
C.) as a copolymer of a base oil, 500 parts by weight (82.0 weight
%) of zinc oxide (0.4 .mu.m in average particle size) as an
inorganic powder and 10 parts by weight (1.6 weight %) of an
non-ionic surfactant were introduced into a planetary mixer, and
then stirred for one hour to be mixed to obtain a thermal
conductive grease.
EXAMPLE 5
[0031] With respect to 100 parts by weight (16.4 weight %) of a
copolymer of unsaturated dicarboxylic acid dibutyl ester and
.alpha.-olefin (trade name: Ketjenlube 215, manufactured by AKZO
NOBEL Co., Ltd., having a viscosity of 120 mm.sup.2/s at 40.degree.
C.) as a copolymer of a base oil, 500 parts by weight (82.0 weight
%) of zinc oxide (0.4 .mu.m in average particle size) as an
inorganic powder and 10 parts by weight (1.6 weight %) of an
non-ionic surfactant were introduced into a planetary mixer, and
then stirred for one hour to be mixed to obtain a thermal
conductive grease.
EXAMPLE 6
[0032] With respect to 100 parts by weight (16.4 weight %) of a
copolymer of unsaturated dicarboxylic acid dibutyl ester and
.alpha.-olefin (trade name: Ketjenlube 165, manufactured by AKZO
NOBEL Co., Ltd., having a viscosity of 770 mm.sup.2/s at 40.degree.
C.) as a copolymer of a base oil, 500 parts by weight (82.0 weight
%) of zinc oxide (0.4 .mu.m in average particle size) as an
inorganic powder and 10 parts by weight (1.6 weight %) of an
non-ionic surfactant were introduced into a planetary mixer, and
then stirred for one hour to be mixed to obtain a thermal
conductive grease.
EXAMPLE 7
[0033] As a copolymer of a base oil, 100 parts by weight (47.6
weight %) of Ketjenlube 115, which was the same as the one used in
Examples 1 to 3, was used and as a thermal conductive filler, 100
parts by weight (47.6 weight %) of boron nitride (0.3 .mu.m in
average particle size) was used. Further, 10 parts by weight (4.8
weight %) of a non-ionic surfactant was used. The base oil, the
thermal conductive filler, and the surfactant were introduced into
a planetary mixer and then stirred for one hour to be mixed at room
temperature, to obtain a thermal conductive grease.
EXAMPLE 8
[0034] As a copolymer of a base oil, 100 parts by weight (12.3
weight %) of Ketjenlube 115, which was the same as the one used in
Examples 1 to 3, was used and as a thermal conductive filler, 700
parts by weight (87.5 weight %) of aluminum oxide (1 .mu.m in
average particle size) was used. Further, 10 parts by weight (1.2
weight %) of a non-ionic surfactant was used. The base oil, the
thermal conductive filler, and the surfactant were introduced into
a planetary mixer and then stirred for one hour to be mixed at room
temperature to obtain a thermal conductive grease.
COMPARATIVE EXAMPLE 1
[0035] With respect to 100 parts by weight (16.4 weight %) of
liquid polybutene "LV-50" (manufactured by Nippon Petrochemicals
Co., Ltd., having a viscosity of 110 mm.sup.2/S at 40.degree. C.)
as a base oil, 500 parts by weight (82.0 weight %) of zinc oxide
(0.4 .mu.m in average particle size) as a thermal conductive filler
and 10 parts by weight of a non-ionic surfactant were mixed and
introduced into a planetary mixer, and then stirred for one hour to
mix at room temperature, to obtain a thermal conductive grease.
COMPARATIVE EXAMPLE 2
[0036] With respect to 100 parts by weight (16.4 weight %) of
ethylene .alpha.-olefin oligomer "HC-20" (manufactured by Mitsui
Chemicals, Inc., having a viscosity of 155 mm.sup.2/S at 40.degree.
C.) as a base oil, 500 parts by weight (82.0 weight %) of zinc
oxide (0.4 .mu.m in average particle size) as a thermal conductive
filler and 10 parts by weight of a non-ionic surfactant were mixed
and introduced into a planetary mixer. The ingredients were stirred
for one hour to be mixed at room temperature, to obtain a thermal
conductive grease.
COMPARATIVE EXAMPLE 3
[0037] With respect to 100 parts by weight (16.4 weight %) of poly
.alpha.-olefin "PAO10" (manufactured by Chevron Phillips Chemical
Company LLC., having a viscosity of 65.3 mm.sup.2/S at 40.degree.
C.) as a base oil, 500 parts by weight (82.0 weight %) of zinc
oxide (0.4 .mu.m in average particle size) as a thermal conductive
filler and 10 parts by weight of a non-ionic surfactant were mixed
in a planetary mixer, and then stirred for one hour to be mixed at
room temperature, to obtain a thermal conductive grease.
COMPARATIVE EXAMPLE 4
[0038] With respect to 100 parts by weight (16.4 weight %) of
diphenyl ether "LB-100" (manufactured by Matsumura Oil Research,
Co., Ltd., having a viscosity of 102 mm.sup.2/S at 40.degree. C.)
as a base oil, 500 parts by weight (82.0 weight %) of zinc oxide
(0.4 .mu.m in average particle size) as a thermal conductive filler
and 10 parts by weight (1.6 weight %) of a non-ionic surfactant
were mixed in a planetary mixer. The ingredients were stirred for
one hour to be mixed at room temperature, to obtain a thermal
conductive grease.
COMPARATIVE EXAMPLE 5
[0039] With respect to 100 parts by weight (47.6 weight %) of
liquid polybutene "LV-50" (manufactured by Nippon Petrochemicals
Co., Ltd., having a viscosity of 110 mm.sup.2/S at 40.degree. C.)
as a base oil, 100 parts by weight (47.6 weight %) of boron nitride
(0.3 .mu.m in average particle size) as an inorganic filler and 10
parts by weight (4.8 weight %) of a non-ionic surfactant were mixed
in a planetary mixer. The ingredients were stirred for one hour to
be mixed at room temperature, to obtain a thermal conductive
grease.
COMPARATIVE EXAMPLE 6
[0040] With respect to 100 parts by weight (47.6 weight %) of
ethylene .alpha.-olefin oligomer "HC-20" (manufactured by Mitsui
Chemicals, Ltd., having a viscosity of 155 mm.sup.2/S at 40.degree.
C.) as a base oil, 100 parts by weight (47.6 weight %) of boron
nitride (0.3 min average particle size) as an inorganic filler and
10 parts by weight (4.8 weight %) of a non-ionic surfactant were
mixed in a planetary mixer. The ingredients were stirred for one
hour to be mixed at room temperature, to obtain a thermal
conductive grease.
COMPARATIVE EXAMPLE 7
[0041] With respect to 100 parts by weight (12.3 weight %) of
liquid polybutene "LV-50" (manufactured by Nippon Petrochemicals
Co., Ltd., having a viscosity of 110 mm.sup.2/S at 40.degree. C.)
as a base oil, 700 parts by weight (87.5 weight %) of boron nitride
(1 .mu.m in average particle size) as an aluminum oxide and 10
parts by weight (1.2 weight %) of a non-ionic surfactant were mixed
in a planetary mixer. The ingredients were stirred for one hour to
be mixed at room temperature, to obtain a thermal conductive
grease.
COMPARATIVE EXAMPLE 8
[0042] With respect to 100 parts by weight (12.3 weight %) of
ethylene .alpha.-olefin oligomer "HC-20" (manufactured by Mitsui
Chemicals, Ltd., having a viscosity of 155 mm.sup.2/S at 40.degree.
C.) as a base oil, 700 parts by weight (87.5 weight %) of boron
nitride (1 .mu.m in average particle size) as an aluminum oxide and
10 parts by weight (1.2 weight %) of a non-ionic surfactant were
mixed in a planetary mixer. The ingredients were stirred for one
hour to be mixed at room temperature, to obtain a thermal
conductive grease.
[0043] In Comparative Examples 1, 4, 5, and 7 described above, the
thermal conductive greases were prepared by using the oligomers,
which did not contain .alpha.-olefin, as base oils. As thermal
conductive fillers, zinc oxide (Comparative Examples 1 and 4),
boron nitride (Comparative Example 5), and aluminum oxide
(Comparative Example 7), were respectively used.
[0044] In each of Comparative Examples 2, 3, 6, and 8, the thermal
conductive greases were prepared by using the oligomer containing
.alpha.-olefin as a base oil, however, the oligomer was not a
copolymer of unsaturated dicarboxylic acid dibutyl ester and
.alpha.-olefin. In addition, zinc oxide (Comparative Examples 2 and
3), boron nitride (Comparative Example 6), and aluminum oxide
(Comparative Example 8) were also used, respectively, as thermal
conductive fillers.
[0045] The characteristic features of the thermal conductive
greases prepared by Examples 1 to 8 and Comparative Examples 1 to 8
were shown in Tables 1 and 2, respectively. For evaluating the
characteristic features of the thermal conductive greases, the
compressibility, dispensing properties, and thermal resistance were
used as indicators. The compressibility was determined from the
viscosity and one quarter scale penetration (see JIS-K2220; IS02137
"Petroleum products--Lubricating grease and
petrolatum--Determination of cone penetration"; or ASTM D217-02 or
D1403-02 "Standard Test Methods for Cone Penetration of Lubrication
Grease Using One-Quarter and One-Half Scale Cone Equipment"). The
dispensing properties was determined from the results of whether
the grease could be actually discharged from a dispense nozzle (1.6
mm in opening diameter). The thermal resistance was determined by a
method described below. Further details of the respective
measurements for indicators will be described below.
[0046] The viscosity of grease was determined by using a Brookfield
type rotational viscometer and calorific power Q at a rotating
speed of 10 rpm at room temperature. The cone penetration of grease
was determined by the method described in JIS-K2220 and represented
as a numerical value indicated by the depth of grease reached by a
conular probe immersed therein.
[0047] A thermal resistance measuring device as shown in FIG. 1 was
employed for determination of thermal resistance. The detail of a
thermal resistance measurement, which is based on ASTM D5470, is
described below. A sample 10 was discharged onto a copper block 12
of 1 cm.sup.2 in cross section mounted on a thermal insulating
material 11 and then sandwiched with an upper copper block 13.
Subsequently, the sample 10 was flattened by a weight 14 with a
load of 4 kg. The thickness of the sample sufficiently flattened
was measured. In the lower copper block 12, a heater (25 watts in
calorific power, not shown) was installed. The upper copper block
13 is attached to a heat sink 15 with a fan to accelerate heat
release. The heater was allowed to generate heat while the load was
applied on the sample 10. Subsequently, when the temperature of the
heat released has reached to a stationary state, then the
temperatures of the upper copper block 12 and the lower copper
block 13 were measured and the thermal resistance of the sample was
then calculated from the equation (1).
Thermal resistance=(.theta.j1-.theta.j0)/calorific power Q (1)
wherein .theta.j1 represents the temperature of the lower copper
block 12, .theta.j0 represents the temperature of the upper copper
block 13, and caloric power Q is 25 watts.
[0048] In this case, the compressibility of thermal conductive
grease can also be evaluated by using the thickness of a sample
when a given load is applied at the time of carrying out the
thermal resistance measurement.
TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4
Example 5 Example 6 Example 7 Example 8 Base oil (weight %)
Ketjenlube115 16.4 14.1 12.3 47.6 12.3 Ketjenlube135 16.4
Ketjenlube215 16.4 Ketjenlube165 16.4 Inorganic powder filler
(weight %) Zinc oxide 82.0 84.5 87.5 82.0 82.0 82.0 Boron nitride
47.6 Aluminum oxide 87.5 Surfactant 1.6 1.4 1.2 1.6 1.6 1.6 4.8 1.2
(weight %) Viscosity of base oil 112 112 112 340 120 770 112 112
(mm.sup.2/s) (mm.sup.2/s) Viscosity of 82 91 172 91 116 326 331 138
grease (Pa s) 1/4 scale cone 92 86 80 79 89 71 62 86 penetration
Dispensing Excellent Excellent Excellent Excellent Excellent
Excellent Excellent Excellent properties Sample thickness at 12 14
10 13 14 14 16 20 thermal resistance measurement (.mu.m) Thermal
resistance 0.15 0.14 0.13 0.14 0.14 0.14 0.20 0.20 (.degree.
C./W)
TABLE-US-00002 TABLE 2 Comparative Comparative Comparative
Comparative Comparative Comparative Comparative Comparative Example
1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7
Example 8 Base oil (weight %) LV-50 16.4 47.6 12.3 H-20C 16.4 47.6
12.3 PA010 16.4 LB-100 16.4 Inorganic powder filler (weight %) Zinc
oxide 82.0 82.0 82.0 82.0 Boron nitride 47.6 47.6 Aluminum oxide
87.5 87.5 Surfactant 1.6 1.6 1.6 1.6 4.8 4.8 1.2 1.2 (weight %)
Viscosity of base oil 110 155 65.3 102 110 155 110 155 (mm.sup.2/s)
Viscosity of grease 32 154 40 49 482 306 91 650 (Pa s) 1/4 scale
cone 105 73 84 77 59 61 96 46 penetration Dispensing Excellent
Excellent Excellent Excellent Excellent Excellent Excellent Poor
properties Sample thickness at 23 22 22 24 27 32 31 38 thermal
resistance measurement (.mu.m) Thermal resistance 0.22 0.24 0.25
0.28 0.33 0.38 0.30 0.36 (.degree. C./W)
[0049] The characteristic features of the respective thermal
conductive greases represented in Tables 1 and 2 will be described
in details.
[0050] Examples 1 to 6 and Comparative Examples 1 to 4 are
compared, in which zinc oxide is used as a thermal conductive
filler. In each of Examples 1 to 6, the thermal conductive grease
having 0.15.degree. C./W or less in thermal resistance, or
excellent in thermal conductivity, while maintaining the viscosity
and the cone penetration which can provide the grease with
excellent compressibility, is obtained. In this case, the viscosity
of the grease, which can provide the grease with good
compressibility, is in the range of about 50 to 350 Pas in general.
However, such a range is not always recommended and the
compressibility of the grease may vary depending on materials even
though the materials have the same viscosity. In Example 6 where
the viscosity of the base oil is 770 mm.sup.2/s, the viscosity of
the base oil is preferably in the range of 112 to 770 mm.sup.2/s,
more preferably in the range of 112 to 340 mm.sup.2/s, because the
viscosity of grease is higher than any of other examples. On the
other hand, in any of Comparative examples 1 to 4, even though the
grease obtained attains excellent dispensing properties, the
thickness of the sample 10 is higher than any of the examples and
insufficiently compressed. Therefore, it is revealed that the
sample of any of the comparative examples has poor compressibility.
Further, the thermal resistances of the samples of the comparative
examples show 0.22.degree. C./W or more, and the samples of the
comparative examples have poor thermal conductivities in comparison
with those of Examples 1 to 6.
[0051] Next, Example 7 and Comparative Examples 5 and 6 are
compared, in which boron nitride is used as a thermal conductive
filler. Both the examples and the comparative examples show good
dispensing properties. However, in each of Comparative Examples 5
and 6, the compressibility of grease under the conditions in which
the load is applied at the time of thermal resistance measurement
shows poor compressibility, compared with that of Example 7. As a
result, even though the thermal resistance of grease in the
comparative example is higher than that of the comparative example,
the grease having an excellent thermal conductivity with a thermal
resistance of 0.20.degree. C./W or less is obtained in the
example.
[0052] Next, Example 8 and Comparative Examples 7 and 8 are
compared, in which aluminum oxide is used as a thermal conductive
filler. Example 8 shows excellent dispensing properties, while
Comparative Example 8 shows poor dispensing properties. In
addition, each of the comparative examples shows poor
compressibility under the conditions in which the load is applied
at the time of thermal resistance measurement, thereby resulting in
higher thermal resistance. In Comparative Example 8, furthermore,
the viscosity of grease is extremely high.
[0053] Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive and the invention is
not to be limited to the details given herein, but may be modified
within the scope and equivalence of the appended claims.
* * * * *