Rubber composition improved in anti-static property and pneumatic tire using the same

Provided are a rubber composition improved in an anti-static property and a pneumatic tire using the same for its tread part, wherein the rubber composition comprises natural rubber and/or diene base synthetic rubber and a white filler as a filler, and further comprises an anionic anti-static agent or a polyoxyalkylene glycol compound represented by the flowing formulas (I), (II) or (III): ##STR1## wherein R.sup.1 and R.sup.3 each represent a linear or branched, saturated or unsaturated aliphatic hydrocarbon group having 1 to 21 carbon atoms, or an aryl group; R.sup.4 and R.sup.5 each represent a hydrogen atom, a linear or branched, saturated or unsaturated aliphatic hydrocarbon group having 1 to 21 carbon atoms, or an aryl group; R.sup.1 and R.sup.3 in the above formula (I), R.sup.4 and R.sup.3 in the above formula (II) and R.sup.4 and R.sup.5 in the above formula (III) in one same molecule may be the same as or different from each other; R.sup.2 is a methylene, ethylene, propylene or tetramethylene group, and all R.sup.2 's may be the same or different; and n is an integer of 100 or less.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a rubber composition improved in an 
anti-static property and a pneumatic tire using the rubber composition. 
2. Description of the Related Art 
Natural rubber and synthetic rubber are used in various industrial fields 
including tires. In general, these rubbers are insulating materials and 
substantially have a property to be liable to carry static charge. 
It has so far been carried out as a publicly known technique to reduce a 
volume resistance of rubber and improve the anti-static property by 
blending a rubber composition with carbon black. However, this technique 
is restricted to black color products. 
It is known that carbon black blended into a rubber composition increases 
hysteresis loss even in black color products such as a tire. In recent 
years, it is investigated to decrease the blending amount thereof or to 
substitute a white filler such as silica for carbon black in low fuel 
consumption tires. In this case, conductivity provided by carbon black is 
reduced, which in turn causes a result that static charge is liable to be 
carried. 
If tires carry static charge, concerned are the inconveniences, for 
example, that when passengers get off a car they have an unpleasant 
feeling because of an electric shock, and that radio waves are generated 
when static charge accumulated in tires is discharged, so as to cause 
radio noises. 
A technique of blending nonionic surfactants or phosphoric acid esters is 
known as a conventional anti-static technique for a rubber composition for 
tires, as disclosed in International Patent Application Laid-open No. WO 
95/31888 applied by one of the present inventors. This technique is 
excellent in terms of being capable of reducing a volume resistance of a 
rubber composition but has a problem that an anti-static effect is reduced 
in a relatively short period of time depending on conditions of using the 
tires. 
On the other hand, anionic anti-static agents are already publicly known as 
anti-static agents for plastics, but it is not known that they provide 
rubber compositions capable of maintaining an anti-static performance over 
a long period of time in combination of rubber including diene base rubber 
with a specific filler. 
Although it is known that polyoxyalkylene glycol esters are excellent as a 
low temperature resistant and heat resistant plasticizer for butadiene 
rubber as described in Japanese Patent Publication No. Hei 6-4722 applied 
by one of the present inventors, it is not yet known that they have an 
anti-static performance. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a rubber composition 
capable of maintaining an anti-static performance over a long period of 
time and a pneumatic tire provided with an excellent anti-static 
performance by using the rubber composition. 
Intensive investigations continued by the present inventors in order to 
solve the problems described above have resulted in finding that a rubber 
composition capable of maintaining an anti-static performance over an long 
period of time can be obtained by adding a specific filler and a specific 
additive for rubber to natural rubber and/or diene base synthetic rubber 
and thus coming to complete the present invention. That is, the present 
invention comprises the following constituents (1) to (7): 
(1) A rubber composition improved in an anti-static property comprising 
natural rubber and/or diene base synthetic rubber and a white filler as a 
filler, and further comprising an anionic anti-static agent or a 
polyoxyalkylene glycol compound represented by the following formula (I), 
(II) or (III): 
##STR2## 
wherein R.sup.1 and R.sup.3 each represent a linear or branched, saturated 
or unsaturated aliphatic hydrocarbon group having 1 to 21 carbon atoms, or 
an aryl group; R.sup.4 and R.sup.5 each represent a hydrogen atom, a 
linear or branched, saturated or unsaturated aliphatic hydrocarbon group 
having 1 to 21 carbon atoms, or an aryl group; R.sup.1 and R.sup.3 in the 
above formula (I), R.sup.4 and R.sup.3 in the above formula (II) and 
R.sup.4 and R.sup.5 in the above formula (III) in one same molecule may be 
the same as or different from each other; R.sup.2 is a methylene, 
ethylene, propylene or tetramethylene group, and all R.sup.2 's may be the 
same or different; and n is an integer of 100 or less. 
(2) The rubber composition improved in an anti-static property as described 
in the above (1), wherein the polyoxyalkylene glycol compound represented 
by the formula (I), (II) or (III) described above has a molecular weight 
of 300 to 2600. 
(3) The rubber composition improved in an anti-static property as described 
in the above (1) or (2), wherein the polyoxyalkylene glycol compound 
represented by the formula (I), (II) or (III) described above has an 
amount of etheric oxygen of 12 to 30% by weight in one molecule. 
(4) The rubber composition improved in an anti-static property as described 
in any of the above (1) to (3), wherein R.sup.2 in the polyoxyalkylene 
glycol compound represented by the formula (I), (II) or (III) described 
above is an ethylene group and in the case of the formula (I), R.sup.1 is 
an alkyl group having 1 to 17 carbon atoms, and R.sup.3 is an alkyl group 
having 7 to 17 carbon atoms; in the case of the formula (II), R.sup.4 is a 
hydrogen atom or an alkyl group having 1 to 17 carbon atoms, and R.sup.3 
is an alkyl group having 7 to 17 carbon atoms; and in the case of the 
formula (III), R.sup.4 is a hydrogen atom or an alkyl group having 1 to 17 
carbon atoms, and R.sup.5 is a hydrogen atom or an alkyl group having 7 to 
17 carbon atoms. 
(5) The rubber composition improved in an anti-static property as described 
in the above (1), wherein the anionic anti-static agent contains a 
sulfonic acid group. 
(6) The rubber composition improved in an anti-static property as described 
in the above (1) or (5), wherein the anionic anti-static agent is dialkyl 
sodium sulfosuccinate. 
(7) A pneumatic tire characterized by using the rubber composition improved 
in an anti-static property as described in any of the above (1) to (6) for 
a tread part. 
According to the present invention, there is provided a rubber composition 
improved in an anti-static property, in which the low heat-generating 
property, anti-static performance and durability thereof are 
simultaneously satisfied. 
Further, according to another aspect of the present invention, there is 
provided a pneumatic tire having an excellent low fuel consumption and 
capable of preventing troubles likely to occur with static charge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiments of the present invention shall be explained below in 
detail. 
The rubber composition improved in an anti-static property of the present 
invention (hereinafter referred to merely as the rubber composition of the 
present invention) comprises natural rubber and/or diene base synthetic 
rubber and a white filler as a filler, and further comprises an anionic 
anti-static agent or a polyoxyalkylene glycol compound represented by the 
formula (I), (II) or (III) described previously as an anti-static agent. 
Natural rubber (NR) and/or diene base synthetic rubber can be used as 
rubber used for the rubber composition of the present invention. The diene 
base synthetic rubber includes, for example, styrene butadiene rubber 
(SBR), butadiene rubber (BR), isoprene rubber (IR), butyl rubber (IIR), 
halogenated butyl rubber (X-IIR), ethylene propylene rubber (EPDM) and a 
mixture thereof. 
The white filler used for the rubber composition of the present invention 
includes, for example, silica, aluminum hydroxide (Hygilite), magnesium 
hydroxide, magnesium oxide, titanium oxide, talc and clay. They can be 
used singly or in a mixture of two or more kinds thereof. 
Silica and aluminum hydroxide are particularly preferred as white fillers. 
When these white fillers are used for a rubber composition for a tire 
tread, an improvement of wet performance of the tire is made to be 
compatible with the low fuel consumption performance. 
The blending amount of the white filler shall not specifically be 
restricted and is suitably set up according to uses of a rubber 
composition. 
For example, when the white fillers described above are used for a rubber 
composition for a tire tread, the blending amount of the white filler is 
10 to 60 parts by weight, particularly preferably 30 to 50 parts by weight 
per 100 parts by weight of said rubber component comprising natural rubber 
(NR) and/or diene base synthetic rubber from the viewpoint of improvement 
in a wet performance. 
When the white fillers are used, it is preferable, in general, to add an 
additive called a coupling agent in order to increase an affinity between 
the filler and rubber molecules or in order to chemically combine them to 
raise the abrasion resistance. 
A silane coupling agent is suitably used as a coupling agent. To be 
specific, it includes, for example, 
bis(3-triethoxysilylpropyl)tetrasulfide, 
bis(3-triethoxysilylpropyl)trisulfide, 
bis(3-triethoxysilylpropyl)-disulfide, 
bis(2-triethoxysilylethyl)tetrasulfide, 
bis(3-trimethoxysilylpropyl)tetrasulfide, 
bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 
3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 
2-mercaptoethyltriethoxysilane, 3-nitropropyltrimethoxysilane, 
3-nitropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 
3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 
2-chloroethyltriethoxysilane, 
3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 
3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 
2-triethoxysilyl-ethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 
3-trimethoxysilylpropylbenzothiazole tetrasulfide, 
3-triethoxysilylpropylbenzothiazole tetrasulfide, 
3-triethoxysilylpropylmethacrylate monosulfide, 
3-trimethoxysilylpropylmethacrylate monosulfide, 
bis(3-diethoxymethylsilylpropyl)tetrasulfide, 
3-mercaptopropyldimethoxymethylsilane, 3-nitropropyldimethoxymethylsilane, 
3-chloropropyldimethoxymethylsilane, 
dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 
dimethoxymethylsilylpropylbenzothiazole tetrasulfide. 
The blending amount of the silane coupling agent is variable depending on 
the blending amount of the white filler and is 1 to 15% by weight, 
preferably 1 to 12% by weight based on the weight of the white filler. If 
the blending amount of the silane coupling agent is less than 1% by weight 
based on the weight of the white filler, an effect of adding the silane 
coupling agent is not satisfactory, and if the blending amount exceeds 15% 
by weight, the reinforcing property and the abrasion resistance result in 
being reduced. 
Carbon black can be used in combination as a filler in addition to the 
white fillers described above. 
The blending amount of carbon black shall not specifically be restricted as 
well and is preferably 0 to 50 parts by weight, more preferably 0 to 40 
parts by weight per 100 parts by weight of the rubber component described 
previously. 
If an amount exceeding 50 parts by weight of carbon black is blended, the 
conductivity originating from carbon black increases, and the anti-static 
property contributed by the anionic anti-static agent or the 
polyoxyalkylene glycol compound becomes relatively less significant. On 
the other hand, the hysteresis loss originating from carbon black becomes 
too large. 
The anti-static agent used in the present invention is blended in order to 
provide the rubber composition with an anti-static performance over a long 
period of time. 
The anionic anti-static agent is preferably a compound containing a 
sulfonic acid group. To be specific, it includes dialkyl sodium 
sulfosuccinate, sodium polyoxyethylene alkylethersulfate, sodium 
alkylsulfonate and sodium alkylbenezenesulfonate. Among them, dialkyl 
sodium sulfosuccinate is preferred since it has a high anti-static 
property. 
Next, the polyoxyalkylene glycol compound used in the present invention is 
a polyoxyalkylene glycol compound represented by the following formula 
(I), (II) or (III): 
##STR3## 
wherein R.sup.1 and R.sup.3 each represent a linear or branched, saturated 
or unsaturated aliphatic hydrocarbon group having 1 to 21 carbon atoms, or 
an aryl group which has preferably 6 to 21 carbon atoms; R.sup.4 and 
R.sup.5 each represent a hydrogen atom, a linear or branched, saturated or 
unsaturated aliphatic hydrocarbon group having 1 to 21 carbon atoms, or an 
aryl group which has preferably 6 to 21 carbon atoms; R.sup.1 and R.sup.3 
in the above formula (I), R.sup.4 and R.sup.3 in the above formula (II) 
and R.sup.4 and R.sup.5 in the above formula (III) in one same molecule 
may be the same as or different from each other; R.sup.2 is a methylene, 
ethylene, propylene or tetramethylene group, and all R.sup.2 's may be the 
same or different; and n is an integer of 100 or less. 
Preferably, R.sup.2 in the polyoxyalkylene glycol compound represented by 
the formula (I), (II) or (III) described above is an ethylene group and in 
the case of the formula (I), R.sup.1 is preferably an alkyl group having 1 
to 17 carbon atoms, and R.sup.3 preferably is an alkyl group having 7 to 
17 carbon atoms; in the case of the formula (II), R.sup.4 is preferably a 
hydrogen atom or an alkyl group having 1 to 17 carbon atoms, and R.sup.3 
is preferably an alkyl group having 7 to 17 carbon atoms; and in the case 
of the formula (III), R.sup.4 is preferably a hydrogen atom or an alkyl 
group having 1 to 17 carbon atoms, and R.sup.5 is preferably a hydrogen 
atom or an alkyl group having 7 to 17 carbon atoms. 
The blending amount of the anti-static agent used in the present invention 
shall not specifically be restricted and is preferably 0.5 to 10 parts by 
weight, more preferably 2 to 8 parts by weight per 100 parts by weight of 
the rubber component described previously. 
If the blending amount of the anti-static agent is less than 0.5 part by 
weight, the anti-static effect is not satisfactory, and if it exceeds 10 
parts by weight, the anti-static effect does not increase to such an 
extent as expected therefrom, which results in increasing the cost of the 
rubber composition. 
A mechanism in which the rubber composition is provided with an anti-static 
effect by the anti-static agent of the present invention has not yet been 
made clear. As shown in the examples described later, however, the 
polyoxyalkylene glycol compound has an effect of reducing a volume 
resistance of the rubber composition. Accordingly, it is presumed that the 
anionic anti-static agent and the polyoxyalkylene glycol compound form 
some conductive route in the rubber composition. 
It is said that in a revealing mechanism of an anti-static effect in a 
conventional kneading type anti-static agent for plastics, the anti-static 
agent bleeds out on the surface and is combined with water in the air to 
form a conductive layer on the surface (reduce the surface resistance). In 
this mechanism, however, it is considered to be difficult to apply such 
anti-static agent to uses in which a surface always contacts a road and is 
abraded as is the case with a tire. In that sense, it is considered that 
the anti-static agent of the present invention which is presumed to reduce 
a volume resistance of the rubber composition so as to raise a 
conductivity of the rubber composition itself exerts a particularly 
excellent effect in its application to a tire. 
The polyoxyalkylene glycol compound used for the rubber composition of the 
present invention is characterized by having no alcoholic OH groups. That 
is, a technique of employing a conventional nonionic type surfactant 
having alcoholic OH groups for anti-static use is disclosed in, for 
example, WO95/31888, but the polyoxyalkylene glycol compound used in the 
present invention can improve the durability of an anti-static effect by 
having no alcoholic OH groups as explained in detail by examples described 
later. 
The polyoxyalkylene glycol compound represented by Formula (I) dan be 
obtained, for example, by esterifying polyoxyalkylene glycol with 
carboxylic acids corresponding to R.sup.1 and R.sup.3 in Formula (I) at 
high temperatures. 
Polyoxyalkylene glycol may be either a polymer of a single monomer like 
polyethylene glycol or a copolymer of plural monomers like ethylene oxide 
and propylene oxide, and polyethylene glycol is the most preferable in 
terms of volume-resistance-reducing effect. 
Fatty acids such as butyric acid and caprylic acid, aromatic carboxylic 
acids such as benzoic acid, or mixed fatty acids obtained from animal oils 
and vegetable oils can be used as the carboxylic acids corresponding to 
R.sup.1 and R.sup.3 in Formula (I), and saturated or unsaturated fatty 
acids in which R.sup.1 and R.sup.3 each are alkyl groups having 7 to 17 
carbon atoms is the most preferable from the viewpoint of 
volume-resistance-reducing effect. Saturated fatty acids in which R.sup.1 
and R.sup.3 each are alkyl groups having 7 to 17 carbon atoms include, for 
example, caprylic acid, capric acid, lauric acid, myristic acid, 
pentadecylic acid, palmitic acid and stearic acid. 
The polyoxyalkylene glycol compound represented by Formula (II) can be 
obtained, for example, by esterifying polyoxyalkyl ether with carboxylic 
acid corresponding to R.sup.3 in Formula (II) at high temperatures, 
wherein R.sup.4 is preferably a hydrogen atom or an alkyl group having 1 
to 17 carbon atoms, and R.sup.3 is preferably an alkyl group having 7 to 
17 carbon atoms. 
The polyoxyalkylene glycol compound represented by Formula (III) can be 
obtained, for example, by reacting polyoxyalkylene glycol, KOH or NaOH 
equivalent thereto with alkyl halide corresponding to R.sup.4 and R.sup.5 
in Formula (III), wherein polyoxyalkylene glycol may be either a polymer 
of a single monomer like polyethylene glycol or a copolymer of plural 
monomers like ethylene oxide and propylene oxide, and polyethylene glycol 
is the most preferable in terms of volume-resistance-reducing effect. 
This polyoxyalkylene glycol compound has preferably a molecular weight of 
300 to 2600. If the molecular weight is less than 300, the durability of 
the volume-resistance-reducing effect is reduced since the polyoxyalkylene 
glycol compound is liable to volatilize, and if the molecular weight 
exceeds 2600, there is a tendency of reducing the 
volume-resistance-reducing effect. 
Further, this polyoxyalkylene glycol compound has preferably an amount of 
12 to 30% by weight of etheric oxygen in one molecule. The amount of 
etheric oxygen in the present invention does not include oxygen in an 
ester bond. 
If the amount of etheric oxygen in one molecule is less than 12% by weight, 
the volume-resistance-reducing effect is not satisfactory. On the other 
hand, if the amount of etheric oxygen exceeds 30% by weight, the 
solubility of polyoxyalkylene glycol compound into rubber is deteriorated, 
and said compound bleeds out in an early stage. Accordingly, the 
durability of the volume-resistance-reducing efect is reduced. 
The polyoxyalkylene glycol compound used for the rubber composition of the 
present invention may be a single compound or a mixture as long as it is 
represented by Formula (I), (II) or (III) described previously. In the 
case of the mixture, however, the respective polyoxyalkylene glycol 
compounds constituting the mixture fall desirably in the preferable range 
of the molecular weight and the amount of etheric oxygen described above. 
Further, the anionic anti-static agent and the polyoxyalkylene glycol 
compound used for the rubber composition of the present invention are 
liquid or soft semi-solid in some cases. In those cases, they can be 
adsorbed in advance on silica serving as a white filler so as to improve 
handling. 
In explaining the rubber composition of the present invention described 
above, emphasis has been put mainly on a rubber composition for a tire 
tread, but the rubber composition of the present invention not only is 
used as a rubber composition for a tire tread, but also can be applied to 
various rubber products other than a tire such as conveyor belts and home 
electric appliances as long as they are desired to inhibit from generating 
static charge. 
The rubber composition of the present invention can be prepared by kneading 
the rubber component described above, fillers including the white filler 
and the anti-static agent by means of, for example, a banbury mixer. 
Further, compounding agents usually used in the rubber industry, for 
example, a vulcanizing agent, a vulcanization accelerating agent, a 
softening agent, an anti-oxidant and a processing aid can suitably be 
added. 
The pneumatic tire of the present invention uses the rubber composition of 
the present invention having the excellent anti-static effect described 
above for a tire tread part and inhibits static charge from generating 
while a car is being driven, whereby inconveniences such as an unpleasant 
feeling caused by an electric shock when a passenger get off the car and 
an occurence of a radio noise can be controlled. 
EXAMPLES 
The present invention shall be explained below in further detail with 
reference to examples and comparative examples, but the present invention 
shall not be restricted thereto. 
In the examples and the comparative examples, a heat-generating property 
(index), a volume resistance (VRc), the durability [change (.DELTA.VRc) in 
the volume resistance] of an anti-static performance and a bloom on a 
rubber surface were determined for a rubber sheet obtained for evaluating 
the anti-static agents by the following evaluation methods. 
Evaluation of heat-generating property (index value): 
A visco-elasticity of a rubber sheet was measured at 50.degree. C., 50 Hz 
and a distortion of 1% by means of Rheolograph Solid manufactured by Toyo 
Seiki Mfg. Co., Ltd. 
It is generally known that the heat-generating property of rubber is shown 
by tan .delta.. A value obtained by dividing tan .delta. of each rubber 
sheet by tan .delta. of a rubber sheet of Comparative Example 1 or 4 was 
represented in percentage to obtain a heat-generating index. The smaller 
the value is, the better the heat-generating value is. 
Evaluation of volume resistance: 
Measured at a measuring voltage of 500 V by means of an insulation sample 
chamber and a high-insulation resistance tester both of which are 
manufactured by Advantest Co., Ltd. 
The value shows a volume resistance, and it means that the smaller the 
value is the better the conductivity is and thus no static charge is 
carried. The unit is .OMEGA. cm, and .DELTA...DELTA.E+n represents 
.DELTA...DELTA.X10.sup.+n. 
Evaluation of durability of anti-static performance: 
In order to evaluate the durability of the anti-static performance, each 
rubber sheet was put in a gear oven at 80.degree. C. for 2 weeks to be 
aged. After returned to room temperature, the volume resistance was 
determined. 
The volume resistance before aging was designated as VRc.sub.1, and the 
volume resistance after aging was designated as VRc.sub.2 to calculate a 
change (.DELTA.VRa) in the volume resistance according to the following 
equation: 
EQU .DELTA.VRc=log.sub.10 (VRc.sub.2 /VRc.sub.1) 
The value means that the smaller the value is, the smaller the change in 
the volume resistance is and the better the anti-static performance is and 
that the conductivity can be maintained over a long period of time. 
Evaluation of bloom on rubber surface: 
A rubber sheet after vulcanization was taken out of a vulcanizing mold and 
then left standing at room temperature for one day to evaluate the 
condition of the surface by eyes according to the following three stage 
evaluation criteria: 
.smallcircle.: no bloom 
.DELTA.: a little bloom observed 
X: considerable amount of bloom observed 
Examples 1 to 3 and Comparative Examples 1 to 3 
The anionic anti-static agents used for evaluation are shown in the 
following Table 1. All these anionic anti-static agents used here were 
manufactured by Nippon Oil & Fat Corp. and added so that the effective 
ingredients were 50 parts by weight per 100 parts by weight of the rubber 
component. 
These anionic anti-static agents were blended in the components shown in 
the following Tables 2 and 3 by means of a banbury mixer to prepare rubber 
compositions. 
These rubber compositions were vulcanized at 150.degree. C. for 30 minutes 
to obtain rubber sheets having a thickness of about 2 mm. 
The rubber sheets thus obtained were evaluated for a heat-generating 
property, a volume resistance and the durability [change (.DELTA.VRc) in 
the volume resistance] of an anti-static performance. 
These results are shown in the following Table 3. The relation of the 
volume resistance (common logarithmic value) with the durability [change 
(.DELTA.VRc) in the volume resistance] of the anti-static performance in 
Examples 1 to 2 and Comparative Examples 1 to 3 is shown in FIG. 1. 
TABLE 1 
______________________________________ 
Effective ingredient 
(amount of effective 
No. Brand name Type ingredient %) 
______________________________________ 
A Rabisol B90 Anion Dioctyl sodium sulfosuccinate 
(90%) 
B Persoft EK Anion Sodium polyoxyethylene alkyl 
ether sulfate (30%) 
C New Lex Soft 60 
Anion Sodium dodecylbenzenesulfonate 
(60%) 
D Cation DT Cation Alkylbenzylpropylenediammonium 
dichloride (50%) 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
Parts by 
Component Name of product used for component 
weight 
__________________________________________________________________________ 
SBR SBR 1502 manufactured by Japan Synthetic Rubber Co., 
100.0 
Nipsil AQ manufactured by Nippon Silica Co., Ltd. or 
Filler Asahi #70*.sup.1 manufactured by Asahi Carbon Co., 
50.0 
Coupling agent 
Si69*.sup.2 manufactured by Degussa Japan Co., Ltd.; 
5.0 
addition when the filler is carbon black 
Anti-static agent 
Described in Table 1 5.0*.sup.3 
Stearic acid 
Lunac S-40 manufactured by Kao Corp. 
2.0 
Zinc oxide Zinc oxide No. 1 manufactured by Mitsui Kinzoku 
3.0yo 
Co., Ltd. 
Anti-oxidant IPPD*.sup.4 
Nocrac 810 NA manufactured by Ohuchi Shinko Chemical 
1.0. 
Co. Ltd 
Vulcanization accelerat- 
Nocceller NS-P manufactured by Ohuchi Shinko 
0.5mical 
ing agent TBBS*5 
Ind. Co. Ltd. 
Vulcanization accelerat- 
Nocceller DM-P manufactured by Ohuchi Shinko 
0.5mical 
ing agent MBTS*6 
Ind. Co. Ltd. 
Sulfur Powder sulfur manufactured by Karuizawa Seirensho 
1.5, 
Ltd. 
__________________________________________________________________________ 
*1: HAF carbon back 
*2: Bis(3triethoxysilylpropyl)tetrasulfide 
*3: Amount of effective ingredient 
*4: Nisopropyl-Nphenyl-p-phenylenediamine 
*5: Ntert-butyl-2-benzothiazolyl sulfenamide 
*6: 2,2Dithio-bisbenzothiazolyl 
TABLE 3 
__________________________________________________________________________ 
Comparative Example 
Example 
1 2 3 1 2 3 
__________________________________________________________________________ 
Compo- 
Filler Silica 
Silica 
Carbon black 
Silica 
Silica 
Silica 
nent 
Coupling agent 
Present 
Present 
None Present 
Present 
Present 
Anti-static agent 
None D None A B C 
Evalu- 
Heat-generating index 
100 93 164 112 98 95 
ation 
(the smaller the better) 
Volume resistance (VRc) 
2.3E+14 
1.3E+14 
5.2E+09 
3.5E+11 
8.2E+12 
5.2E+11 
(the smaller the better) 
.DELTA.VRc 0.38 0.73 0.22 0.43 0.32 0.58 
(the smaller the better) 
__________________________________________________________________________ 
Comments on Tables 1 to 3 and FIG. 1: 
As apparent from Table 3 and FIG. 1, it has been confirmed that in Examples 
1 to 3 falling in the scope of the present invention, both the 
heat-generating properties and the volume resistances are low as compared 
with those in Comparative Examples 1 to 3 falling outside the scope of the 
present invention, so that the anti-static performances are excellent and 
that the durability of the anti-static performance is improved as well. 
Observing the individual cases, it has been confirmed that in the case of 
Comparative Example 1 in which the anionic anti-static agent is not 
contained as an anti-static agent, the volume resistance is large and 
static charge is liable to be generated. 
It has been found that in the case of Comparative Example 2 in which the 
cationic anti-static agent (alkylbenzylpropylenediammonium dichloride) is 
blended as an anti-static agent, the effect of reducing the volume 
resistance is small. 
It has been confirmed that in the case of Comparative Example 3 in which 
carbon black is used as a filler, the volume resistance is low and the 
durability of the anti-static performance is excellent without adding the 
anti-static agent but the heat-generating property is inferior to a large 
extent. 
In the case of Examples 1 to 3 in which the anionic anti-static agents of 
the present invention are contained, the low heat-generating properties, 
the anti-static performances and the durabilities thereof all are 
simultaneously satisfied. 
Examples 4 to 12 and Comparative Examples 4 to 6 
The polyoxyalkylene glycol base anti-static agents used in Examples 4 to 12 
and Comparative Examples 4 to 6 are shown in the following Table 4. They 
were synthesized by the following respective methods (1) to (10). 
(1) Synthesis of CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 O).sub.9 H 
Polyethylene glycol #400 (molecular weight: 400) of 400 g (1.0 mole), 
caprylic acid of 72 g (0.5 mole) and dibutyltin oxide of 0.14 g as a 
catalyst were weighed into a four neck flask of 500 ml, and esterification 
reaction was carried out at 225.degree. C. for 5 hours while stirring 
under blowing nitrogen gas. 
After confirming that the acid value became 1.0 or lower, the reaction 
liquid was cooled down to room temperature to take out the content. This 
reaction product was a mixture containing 50% of unreacted polyethylene 
glycol #400, 42% of CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 
O).sub.9 H and 8% of CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 
O).sub.9 CO(CH.sub.2).sub.6 CH.sub.3. 
Unreacted polyethylene glycol #400 was removed from this reaction product 
by washing with water to obtain CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 
CH.sub.2 O).sub.9 H having a purity of 84%, which was used as a sample. 
(2) Synthesis of CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 O).sub.9 
CO(CH.sub.2).sub.6 CH.sub.3 
Polyethylene glycol #400 (molecular weight: 400) of 200 g (0.5 mole), 
caprylic acid of 173 g (1.2 mole) and dibutyltin oxide of 0.19 g as a 
catalyst were weighed into a four neck flask of 500 ml, and esterification 
reaction was carried out at 225.degree. C. for 5 hours while stirring 
under blowing nitrogen gas. 
After confirming that the hydroxyl value became 1.0 or lower, the acid was 
removed under conditions of 200.degree. C. and 0.27 kPa in order to 
distill off excess caprylic acid to obtain a sample. 
(3) Synthesis of CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 O).sub.23 
CO(CH.sub.2).sub.6 CH.sub.3 
Polyethylene glycol #1000 (molecular weight: 1000) of 300 g (0.3 mole), 
caprylic acid of 104 g (0.72 mole) and dibutyltin oxide of 0.20 g as a 
catalyst were used to carry out the synthesis under the same conditions as 
in (2) described above to obtain a sample. 
(4) Synthesis of CH.sub.3 (CH.sub.2).sub.16 COO(CH.sub.2 CH.sub.2 O).sub.34 
CO(CH.sub.2).sub.16 CH.sub.3 
Polyethylene glycol #1500 (molecular weight: 1500) of 225 g (0.15 mole), 
methyl stearate of 115 g (0.36 mole) and dibutyltin oxide of 0.17 g as a 
catalyst were used to carry out transesterification reaction under the 
same conditions as in (2) described above. Then, excess methyl stearate 
was distilled off at 250.degree. C. while introducing steam to obtain a 
sample. 
(5) Synthesis of CH.sub.3 (CH.sub.2).sub.2 COO(CH.sub.2 CH.sub.2 O).sub.23 
CO(CH.sub.2).sub.2 CH.sub.3 
Polyethylene glycol #1000 (molecular weight: 1000) of 300 g (0.3 mole), 
butylic acid of 63 g (0.72 mole) and sulfuric acid of 0.18 g as a catalyst 
were used to carry out esterification reaction at 160.degree. C. for 5 
hours while stirring under blowing nitrogen gas. 
After confirming that the hydroxyl value became 1.0 or lower, excess 
butyric acid was removed under conditions of 160.degree. C. and 0.27 kPa 
to obtain a sample. 
(6) Synthesis of CH.sub.3 (CH.sub.2).sub.16 COO(CH.sub.2 CH.sub.2 O).sub.5 
CO(CH.sub.2).sub.16 CH.sub.3 
Polyethylene glycol #200 (molecular weight: 200) of 80 g (0.4 mole), methyl 
stearate of 307 g (0.96 mole) and dibutyltin oxide of 0.19 g as a catalyst 
were used to carry out the synthesis under the same conditions as in (4) 
described above to obtain a sample. 
(7) Synthesis of CH.sub.3 O(CH.sub.2 CH.sub.2 O).sub.9 CO(CH.sub.2).sub.6 
CH.sub.3 
A methanol-ethylene oxide 9 mole adduct 428 g (1.0 mole), caprylic acid of 
144 g (1.0 mole) and dibutyltin oxide of 0.57 g as a catalyst were weighed 
into a four neck flask of 1000 ml, and esterification reaction was carried 
out at 225.degree. C. while stirring under blowing nitrogen gas to obtain 
a sample. 
(8) Synthesis of CH.sub.3 (CH.sub.2).sub.16 CH.sub.2 O(CH.sub.2 CH.sub.2 
O).sub.45 CO(CH.sub.2).sub.16 CH.sub.3 
A stearyl alcohol-ethylene oxide 45 mole adduct of 562.5 g (0.25 mole), 
stearic acid of 71 g (0.25 mole) and dibutyltin oxide of 0.6 g as a 
catalyst were weighed into a four neck flask of 1000 ml, and 
esterification reaction was carried out at 225.degree. C. while stirring 
under blowing nitrogen gas to obtain a sample. 
(9) Synthesis of CH.sub.3 (CH.sub.2).sub.7 CH.dbd.CH(CH.sub.2 ).sub.8 
O(CH.sub.2 CH.sub.2 O).sub.45 CO(CH.sub.2).sub.7 
--CH.dbd.CH(CH.sub.2).sub.7 CH.sub.3 
An oleyl alcohol-ethylene oxide 45 mole adduct of 674.4 g (0.3 mole), oleic 
acid of 84.6 g (0.3 mole) and dibutyltin oxide of 0.76 g as a catalyst 
were weighed into a four neck flask of 1000 ml, and esterification 
reaction was carried out at 225.degree. C. while stirring under blowing 
nitrogen gas to obtain a sample. 
(10) Synthesis of CH.sub.3 (CH.sub.2).sub.7 O(CH.sub.2 CH.sub.2 O).sub.9 
(CH.sub.2).sub.7 CH.sub.3 
Polyethylene glycol #400 (molecular weight: 400) of 400 g (1.0 mole), KOH 
of 112.2 g (2.0 mole) and tetrabutylammonium bromide of 0.51 g as a 
catalyst were weighed into a four neck flask of 1000 ml, and octyl 
chloride of 297 g (2.0 mole) was dropwise added thereto while stirring 
under blowing nitrogen gas. After further continuing stirring for 5 hours, 
the reaction liquid was cooled down to 70.degree. C., and KCl was removed 
by filtering to obtain a sample. 
The preceding anti-static agents (1) to (10) thus obtained were blended in 
the component shown in the following Table 5 and Table 6 by means of a 
banbury mixer to prepare rubber compositions. 
These rubber compositions were vulcanized at 150.degree. C. for 30 minutes 
to obtain rubber sheets having a thickness of about 2 mm. 
The rubber sheets thus obtained were evaluated for a bloom on a rubber 
surface, a heat-generating property, a volume resistance and the 
durability [change (.DELTA.VRc) in the volume resistance] of an 
anti-static performance. 
These results are shown in the following Table 6. The relation of the 
volume resistance (common logarithmic value) with the durability [change 
(.DELTA.VRc) in the volume resistance] of the anti-static performance in 
Examples 4 to 12 and Comparative Examples 4 to 6 is shown in FIG. 2. 
TABLE 4 
__________________________________________________________________________ 
Number 
Chemical formula of polyoxyalkylene glycol compound 
__________________________________________________________________________ 
(1) CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 O).sub.9 H 
(2) CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 O).sub.9 CO(CH.sub.2) 
.sub.6 CH.sub.3 
(3) CH.sub.3 (CH.sub.2).sub.6 COO(CH.sub.2 CH.sub.2 O).sub.23 CO(CH.sub.2 
).sub.6 CH.sub.3 
(4) CH.sub.3 (CH.sub.2).sub.16 COO(CH.sub.2 CH.sub.2 O).sub.34 CO(CH.sub. 
2).sub.16 CH.sub.3 
(5) CH.sub.3 (CH.sub.2).sub.2 COO(CH.sub.2 CH.sub.2 O).sub.23 CO(CH.sub.2 
).sub.2 CH.sub.3 
(6) CH.sub.3 (CH.sub.2).sub.16 COO(CH.sub.2 CH.sub.2 O).sub.5 CO(CH.sub.2 
).sub.16 CH.sub.3 
(7) CH.sub.3 O(CH.sub.2 CH.sub.2 O).sub.9 CO(CH.sub.2).sub.6 CH.sub.3 
(8) CH.sub.3 (CH.sub.2).sub.16 CH.sub.2 O(CH.sub.2 CH.sub.2 O).sub.45 
CO(CH.sub.2).sub.16 CH.sub.3 
(9) CH.sub.3 (CH.sub.2).sub.7 CH.dbd.CH(CH.sub.2).sub.8 O(CH.sub.2 
CH.sub.2 O).sub.45 CO(CH.sub.2).sub.7 CH.dbd.CH(CH.sub.2).sub.7 
CH.sub.3 
(10) CH.sub.3 (CH.sub.2).sub.7 O(CH.sub.2 CH.sub.2 O).sub.9 (CH.sub.2).sub 
.7 CH.sub.3 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Parts by 
Component Name of product used for component 
weight 
__________________________________________________________________________ 
SBR SBR 1502 manufactured by Japan Synthetic Rubber Co., 
100.0 
Filler Nipsil AQ manufactured by Nippon Silica Co., Ltd. 
50.0 
Asahi #70*.sup.1 manufactured by Asahi Carbon Co., Ltd. 
Coupling agent 
Si69*.sup.2 manufactured by Degussa Japan Co., Ltd.; 
5.0 
addition when the filler is carbon black 
Anti-static agent 
Described in Table 4 5.0 
Stearic acid 
Lunac S-40 manufactured by Kao Corp. 
2.0 
Zinc oxide Zinc oxide No. 1 manufactured by Mitsui Kinzoku 
3.0yo 
Co., Ltd. 
Anti-oxidant IPPD 
Nocrac 810 NA manufactured by Ohuchi Shinko Chemical 
1.0. 
Co. Ltd 
Vulcanization accelerat- 
Nocceller NS-P manufactured by Ohuchi Shinko 
0.5mical 
ing agent TBBS 
Ind. Co. Ltd. 
Vulcanization accelerat- 
Nocceller DM-P manufactured by Ohuchi Shinko 
0.5mical 
ing agent MBTS 
Ind. Co. Ltd. 
Sulfur Powder sulfur manufactured by Karuizawa Seirensho 
1.5, 
Ltd. 
__________________________________________________________________________ 
*1: HAF carbon back 
*2: Bis(3triethoxysilylpropyl)tetrasulfide 
TABLE 6 
__________________________________________________________________________ 
Comparative Example 
Example 
4 5 6 4 5 6 
__________________________________________________________________________ 
Compo- 
Filler Silica 
Silica 
Carbon black 
Silica 
Silica 
Silica 
nent 
Coupling agent 
Present 
Present 
None Present 
Present 
Present 
Anti-static agent 
None (1) None (2) (3) (4) 
Molecular weight of 
-- 540 -- 666 1282 2046 
Anti-static agent 
Amount of etheric 
-- 23.7 -- 19.2 27.5 25.8 
oxygen in 
Anti-static agent 
Evalu- 
Bloom on rubber surface 
.largecircle. 
.DELTA. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
ation 
Heat-generating index 
100 97 168 106 110 107 
(the smaller the better) 
Volume resistance (VRc) 
1.6E+14 
5.1E+10 
4.9E+09 
2.4E+11 
5.8E+10 
7.0E+10 
(the smaller the better) 
.DELTA.VRc 0.45 1.5 0.21 0.18 0.49 0.85 
(the smaller the better) 
__________________________________________________________________________ 
Example 
7 8 9 10 11 12 
__________________________________________________________________________ 
Compo- 
Filler Silica 
Silica 
Silica 
Silica 
Silica 
Silica 
nent 
Coupling agent 
Present 
Present 
Present 
Present 
Present 
Present 
Anti-static agent 
(5) (6) (7) (8) (9) (10) 
Molecular weight of 
1170 770 554 2514 2512 638 
Anti-static agent 
Amount of etheric 
30.1 8.3 26.0 28.6 28.7 25.1 
oxygen in 
Anti-static agent 
Evalu- 
Bloom on rubber surface 
x .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
ation 
Heat-generating index 
112 108 103 101 102 108 
(the smaller the better) 
Volume resistance (VRc) 
3.0E+10 
4.7E+12 
8.2E+10 
6.2E+10 
7.4E+10 
1.3E+11 
(the smaller the better) 
.DELTA.VRc 1.3 0.61 0.69 0.91 0.84 0.37 
(the smaller the better) 
__________________________________________________________________________ 
Comments on Tables 4 to 6 and FIG. 2: 
As apparent from Table 6 and FIG. 2, it has been confirmed that in Examples 
4 to 12 falling in the scope of the present invention, both the 
heat-generating properties and the volume resistances are simultaneously 
satisfied as compared with those in Comparative Examples 4 to 6 falling 
outside the scope of the present invention, so that the anti-static 
performances are excellent and the durability of the anti-static 
performance is improved as well. 
Observing the individual cases, it has been confirmed that in the case of 
Comparative Example 4 in which the polyoxyalkylene glycol compound is not 
contained as an anti-static agent, the volume resistance is large and 
static charge is liable to be generated. 
It has been found that in the case of Comparative Example 5 in which a 
compound obtained by adding one molecule of alcohol to one molecule of 
polyoxyalkylene glycol and having an alcoholic hydroxyl group at a 
terminal is used as an anti-static agent, the initial effect of reducing 
the volume resistance is large but the .DELTA.VRc is large and the 
durability of the anti-static performance is poor. 
It has been confirmed that in the case of Comparative Example 6 in which 
carbon black is used as a filler, the volume resistance is low and the 
durability of the anti-static performance is excellent without adding the 
anti-static agent but the heat-generating property is inferior to a large 
extent. 
In the case of Examples 4 to 12 with an exception of Example 7 in which the 
polyoxyalkylene glycol compounds of the present invention are contained as 
antistatic agents, the low heat-generating properties, the anti-static 
performances and the durabilities thereof and the bloom resistances all 
are simultaneously satisfied. 
In Example 7 which falls in the scope of the present invention, the 
anti-static performance and low heat-generating property are balanced, 
while the bloom resistance is inferior to other Examples. 
Otherwise, all other Examples fulfill the intended purpose. In particular, 
in the case of Examples 4 to 6 and Examples 9 to 12 in which more 
preferable polyoxyalkylene glycol compounds are contained as antistatic 
agents, the low heat-generating properties, the anti-static performances 
and the durabilities thereof and the bloom resistances all are highly 
satisfied simultaneously. 
Next, the following test was further carried out in order to confirm the 
effect of improving the durability by excluding an alcoholic hydroxyl 
group from the polyoxyethylene glycol compound in the present invention. 
That is, the vulcanized rubber sheets prepared in Comparative Example 5 and 
Example 5 were put in a gear oven at 80.degree. C. for 2 weeks to age 
them, and after aging, the vulcanized rubber sheets were cut into fine 
pieces to precisely weight about 1 g of them. 
Ethanol 50 ml was added to it to carry out extraction at room temperature 
for 72 hours. The anti-static agent extracted in the extract was 
determined by means of .sup.1 H-NMR to calculate the recovery rate, 
wherein the amount calculated from the blending amount was set to 100. The 
results thereof are shown in the following Table 7. 
TABLE 7 
______________________________________ 
Comparative 
Example 5 
Example 5 
______________________________________ 
Recovery rate 25.9 47.8 
after aging 
______________________________________ 
Comments on Table 7: 
Since the anti-static agent used in Comparative Example 5 has approximately 
the same etheric oxygen content as that of the anti-static agent used in 
Example 5, it is considered that there is no big difference between them 
in terms of an SP value (solubility parameter), but as apparent from the 
results shown in Table 7, it can be found that the recovery rate is higher 
in Example 5. 
Accordingly, it is considered that the effective anti-static component has 
been increased even after aging by removing the alcoholic hydroxyl group, 
and therefore the durability has been improved.