Sealing compositions for electric cables

The present invention relates to a method of manufacturing sealing compositions for electric wires, wherein one mixes together a filler (comprised chiefly of an alkaline earth carbonate), a binder component, and possibly additives of the type common in the art. The binder component is a combination of two binders: binder I is a homopolymer of 1,3-butadiene or a copolymer which is essentially obtained from 1,3-butadiene; and binder II is a polymer based on 1,3-butadiene and having laterally extending succinic anhydride groups. The sealing compositions are distinguished by good processibility and high dielectric strength.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a method of manufacturing sealing compositions for 
electric cables. 
2. Discussion of the Background 
Sealing compositions for electric cables should have the following 
combination of properties: 
(a) One should be able to prepare the composition by simple mixing of 
components which can be obtained readily and at favorable cost (economy). 
(b) The composition should be easily processible, i.e. it should be 
possible to pour the composition at ambient temperature. 
(c) The composition should be characterized by a high dielectric strength 
(high breakdown voltage for a given electrode separation), and accordingly 
by a high electrical insulation value (safety). 
The production of sealing compositions for electric cables by mixing PVC, 
inorganic fillers, and additives is known. Such compositions have 
properties a and b supra. However, they are deficient as to property c. 
Japanese OS No. 56-109,237 discloses sealing compositions for electric 
cables prepared by mixing a binder component, an inorganic filler, and 
additives. The binder component is comprised of a liquid polybutadiene and 
other binding agents. With these compositions as well, the combination of 
properties described supra is unsatisfactory however. 
Accordingly, there remains a strongly felt need both for sealing 
compositions for electric cables and a method of manufacturing such 
sealing compositions, where the compositions can be prepared by simple 
mixing of readily available components, are easily processed, and are also 
characterized by high dielectric strength and a high electrical insulation 
value. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide a novel method 
for manufacturing a sealing composition for electric cables which can be 
prepared by simple mixing of readily available components. 
It is another object of this invention to provide a novel method for 
manufacturing a sealing composition for electric cables which is easily 
processed, i.e. it should be possible to pour the composition at ambient 
temperature. 
It is another object of this invention to provide a novel method for 
manufacturing a sealing composition for electric cables which is 
characterized by high dielectric strength and/or a high electrical 
insulation value. 
It is another object of this invention to provide a novel method for 
manufacturing a sealing composition for electric cables which is prepared 
by simple mixing of readily available components, which is readily 
processed, and which is characterized by high dielectric strength and/or a 
high electrical insulation value. 
It is another object of this invention to provide a novel sealing 
composition for electric cables which meets each of the above objects of 
this invention. 
These and other objects have now surprisingly been satisfied by the 
discovery of the following novel method for preparing sealing compositions 
for electric cables, in which the following components are mixed together: 
(1) a binder component; and (2) an inorganic, water-insoluble, powdered 
filler material. Other additives well known in this art (but not 
vulcanizing agents) may also be added to components (1) and (2) supra. 
The novel method of the present invention is characterized by the following 
features. 
a. The binder component is a combination of two binders--binder I (in an 
amount of 70-97 wt. %), and binder II (in an amount of 3-30 wt. %); 
a.1 Binder I is a homopolymer of 1,3-butadiene or a copolymer based on 
1,3-butadiene (in an amount of .gtoreq.80 wt. %) and at least one other 
copolymerizable 1,3-diene or 1,3-cyclodiene or at least one other 
copolymerizable alpha-olefin (in an amount of .ltoreq.20 wt. %) (with the 
indicated composition of the said copolymer determined by IR analysis). 
The homopolymer or copolymer may be modified by isomerization or partial 
cyclization; its average relative molecular weight (referred to hydrogen), 
Mn, is 500 to 5,000, and its viscosity (at 20.degree. C. according to DIN 
53 015) is 2-80 dPa-sec. 
a.2 Binder II is a polymer based on 1,3-butadiene with laterally extending 
succinic anhydride groups (i.e., a maleinized polymer based on 
1,3-butadiene) with an acid number of 15 to 150 (mg KOH/g); this polymer 
is prepared by adding maleic anhydride to a polymer of the type of binder 
I (feature a.1). 
b. The filler material is comprised of at least 80 wt. % of an alkaline 
earth carbonate which has not been provided with a hydrophobic coating and 
which is capable of reacting with the anhydride groups of binder II. The 
filler is present in an amount of 65-80 wt. % of the total sealing 
composition. 
The present invention also provides a novel sealing composition prepared in 
accordance with the above method. This novel sealing composition is 
characterized by the advantages outlined above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In exploratory experiments, compositions were prepared by simple mixing of 
liquid polybutadiene, finely powdered chalk, and a fatty acid such as 
linoleic acid, soybean oil fatty acid, and castor oil fatty acid (i.e., 
ricinoleic acid). These compositions satisfied requirements a and b supra, 
but not requirement c. 
However, using the method of the present invention, a novel composition 
satisfying all three of requirements a, b, and c has been obtained for the 
first time. 
The method of the present invention thus relates to the preparation of 
sealing compositions for electric cables comprising (1) a binder 
component, and (2) an inorganic, water-insoluble, powdered filler 
material. Other additives (other than vulcanizing agents) which are well 
known in this art may also be added to components 1) and (2) supra. 
The method of this invention is characterized as follows. 
a. The binder component is a combination of two binders--binder I (in an 
amount of 70-97 wt. %), and binder II (in an amount of 3-30 wt. %). 
a.1 Binder I is a homopolymer of 1,3-butadiene or a copolymer based on 
1,3-butadiene (in an amount of .gtoreq.80 wt. %) and at least one other 
co-polymerizable 1,3-diene or 1,3-cyclodiene or at least one other 
copolymerizable alpha-olefin (in an amount of .ltoreq.20 wt. %) (with the 
indicated composition of the said copolymer determined by IR analysis). 
The homopolymer or copolymer may be modified by isomerization or partial 
cyclization, its average relative molecular weight (referred to hydrogen), 
Mn, is 500 to 5,000, and its viscosity (at 20.degree. C. according to DIN 
53 015) is 2-80 dPa-sec. 
a.2 Binder II is a polymer based on 1,3-butadiene with laterally extending 
succinic anhydride groups (i.e., a maleinized polymer based on 
1,3-butadiene) with an acid number of 15 to 150 (mg KOH/g). This polymer 
is prepared by adding maleic anhydride to a polymer of the type of binder 
I (feature a.1). 
b. The filler material is comprised of at least 80 wt. % of an alkaline 
earth carbonate which has not been provided with a hydrophobic coating and 
which is capable of reacting with the anhydride groups of binder II. The 
filler is present in an amount of 65-80 wt. % of the total sealing 
composition. 
Preferably, the method of preparing sealing compositions is further 
characterized as follows. 
c. The binder component is comprised of binder I in an amount of 80-95 wt. 
% and binder II in an amount of 5-20 wt. %. 
c.1 Binder I is a homopolymer of 1,3-butadiene. It has a content of 
.ltoreq.50 wt. % (based on IR analysis) of recurring units obtained by 
1,4-trans polymerization of 1,3-butadiene. It has an average relative 
molecular weight (based on hydrogen), Mn, of 1,000 to 4,000, and it has 
viscosity 6-60 dPa-sec. 
c.2 Binder II has an acid number of 30-100. It is prepared by adding maleic 
anhydride to a polymer which is a homopolymer of 1,3-butadiene with a 
content of .ltoreq.50 wt. % of recurring units obtained by 1,4-trans 
polymerization of 1,3-butadiene. It has an average relative molecular 
weight, Mn, of 1,000 to 3,000, and has viscosity 6-40 dPa-sec. 
d. The filler material is a natural calcium carbonate or calcium magnesium 
carbonate. Its particle size distribution is characterized as follows (by 
sieve analysis): 90 wt. % &lt;5-150 micron, and &lt;35 wt. % &lt;1 micron. The 
filler is present in an amount of 70-78 wt. % (based on the total weight 
of the sealing composition). 
Binder I supra can be prepared in a known fashion by anionic 
polymerization, particularly with an organolithium catalyst. A Lewis base 
may be used as a co-catalyst. Such a Lewis base may be ethers, tertiary 
amines, or mixtures of ethers and tertiary amines. These ethers and 
tertiary amines are well known in the art. 
The content of recurring units obtained by 1,4-trans polymerization of 
1,3-butadiene in binder I is .ltoreq.50 wt. % (as determined by IR 
analysis). Preferably, binder I is prepared by Ziegler polymerization, and 
a nickel catalyst may be preferably used. 
The copolymers, which are an alternative for binder I supra may be based on 
1,3-butadiene and at least one 1,3-diene or 1,3-cyclodiene copolymerizable 
with 1,3-butadiene, e.g., isoprene or cyclopentadiene, and/or at least one 
copolymerizable alpha-olefin, e.g., styrene or ethylene. 
Binder II, supra, is prepared by a known fashion by adding maleic anhydride 
(MA) to a polymer (binder I) corresponding to feature a.1 or c.1 method of 
this invention outlined supra (for method, see, e.g., German No. AS 23 62 
534). 
As a rule, the amount of binder II used is greater the lower its acid 
number, and the greater the surface area of the filler (i.e., the smaller 
the particle sizes of the filler material). 
For reasons of cost, a maximum degree of filler consistent with good 
processibility is generally added to the sealing compositions. In this 
connection, it is advantageous to select a filler with a particle size 
distribution corresponding to the following criteria: 90 wt. % &lt;4.5-300 
microns, and &lt;40 wt. % &lt;1 micron. 
Other additives may include, e.g., fire retardants, smoke inhibitors, 
drying agents (e.g., molecular sieves), and siccatives (e.g., cobalt 
octoate). All of these are well known in this art. 
The invention also provides a novel sealing composition for electric cables 
prepared in accordance with the novel method. The composition comprises a 
binder component and an inorganic, water-insoluble, powdered filler 
material. 
The binder component is a combination of two binders, a binder I in an 
amount of 70-97 wt. %, and a binder II in an amount of 3-30 wt. %. Binder 
I is a homopolymer of 1,3-butadiene or a copolymer based on 1,3-butadiene 
in an amount of at least 80 wt. % and at least one other co-polymerizable 
1,3-diene or 1,3-cyclodiene, or at least one other copolymerizable 
alpha-olefin in an amount of no more than 20 wt. %. 
The homopolymer or the copolymer have an average relative molecular weight, 
Mn, of 500 to 5,000, and a viscosity of 2-80 dPa-sec. 
Binder II is a polymer based on 1,3-butadiene with laterally extending 
succinic anhydride groups and has an acid number of 15 to 150 (mg KOH/g). 
The filler material is comprised of at least 80 wt. % of an alkaline earth 
carbonate which has not been provided with a hydrophobic coating and which 
is capable of reacting with the anhydride groups of binder II. The filler 
is present in the amount of 65-80 wt. % of the total sealing composition. 
In a preferred embodiment, the binder component is comprised of binder I in 
an amount of 80-95 wt. %, and binder II in an amount of 5-20 wt. %. 
Binder I is a homopolymer of 1,3-butadiene and having a content of not more 
than 50 wt. % of recurring units obtained by 1,4-trans-polymerization of 
1,3-butadiene, and having an average relative molecular weight, Mn, of 
between 1000 and 4000 and a viscosity of between 6 and 60 dPa-seconds. 
Binder II has an acid number of 30-100 and is prepared by adding maleic 
anhydride to a polymer which is a homopolymer of 1,3-butadiene with a 
content of not more than 50 wt. % of recurring units obtained by 1,4-trans 
polymerization of 1,3-butadiene and having a molecular weight, Mn, of 1000 
to 3000 and a viscosity of 6 to 40 dPa-sec. 
The filler material is a natural calcium carbonate or calcium magnesium 
carbonate, having a particle size distribution as follows (by sieve 
analysis): 90 wt % &lt;5-150 microns, and 35 wt. % &lt;1 micron. The filler is 
present in an amount of 70-78 wt. % based on the total weight of the 
sealing composition. 
Other features of this invention will become apparent in the course of the 
following description of exemplary embodiment which are provided for 
purposes of illustration and are not intended to be limiting thereof. 
The average relative molecular weights, Mn, reported in the examples below 
were determined from vapor pressure measurements. 
The viscosities were determined at 20.degree. C. according to DIN 53 015. 
The acid numbers were determined according to DIN 53 402. 
The dielectric strengths were determined according to the following 
procedure: A 50 Hz a.c. test voltage was applied via a variable 
transformer (primary side 0-220 V, secondary side 0-30 kV), between two 
spherical electrodes (diameter 12.5 mm, separation 2.0 mm) which were 
immersed in the composition being tested at ambient temperature. The 
voltage was increased slowly, starting at O V and rising continuously 
until breakdown occurred. 
TABLE 1 
__________________________________________________________________________ 
Polymers employed (all commercially available) 
Average relative 
Viscosity 
Microstructure** 
molecular weight* 
(dPa-sec) 
1,4-cis 
1,4-trans 
vinyl 
__________________________________________________________________________ 
Polybutadiene 1 
ca. 1500 7.5 ca. 72 
27 1 
Polybutadiene 2 
ca. 3000 30 ca. 80 
19 1 
Polybutadiene 3 
ca. 1300 11 ca. 10 
45 45 
Polybutadiene 4 
ca. 1150 60 -- -- &gt;85 
Polybutadiene A 
ca. 6200 300 ca. 85 
12 3 
Polybutadiene B 
ca. 2600 100 ca. 10 
45 45 
__________________________________________________________________________ 
*based on the weight of a hydrogen atom, --Mn 
**requiring units obtained by 1,4cis-, 1,4trans, and 1,2polymerization of 
1,3butadiene, as determined by IR analysis, % 
Polybutadienes 1, 2, and A were obtained by Ziegler polymerization with a 
nickel catalyst. 
The binders I1 to I4, IA, and IB correspond to polybutadienes 1 to 4, A, 
and B, respectively. 
TABLE 2 
______________________________________ 
Binders II, obtained by adding maleic 
anhydride to polybutadiene 1. 
Added maleic 
anhydride (wt. % 
Acid number 
of the adduct) 
(mg KOH/g) 
______________________________________ 
Binder II1.1 7.5% ca. 75 
Binder II1.2 3% ca. 30 
Binder II1.C 0.5% ca. 5 
______________________________________ 
Preparation of the Sealing Compositions 
90 parts by weight of binder I and 10 parts by weight of binder II (Table 
3) were mixed together in a mixer (Hobart-Mischer, Type N5D) at room 
temperature. Then 300 parts by weight of a commercially available 
pulverized chalk (not hydrophobicized, i.e. uncoated; comprised of calcium 
carbonate in the amount of ca. 92 wt. % and magnesium carbonate in the 
amount of ca. 1 wt. %; with 90 wt. % comprised of particles &lt;7 micron and 
26 wt. % comprised of particles &lt;1 micron, by sieve analysis) was added in 
portions and mixed in. 
The resulting compositions were characterized (Table 3) via their flow 
properties as determined qualitatively while being poured out of the 
mixer, and via their dielectric strength as determined by the 
above-described method. 
Table 3: Characteristics of sealing compositions. (Examples 1 to 5 
correspond to the invention. Examples a to c are comparison examples not 
in accordance with the invention.) 
TABLE 3 
__________________________________________________________________________ 
Characteristics of sealing compositions 
Binder Dielectric 
Example No. 
Combination 
Flow properties 
strength kV* 
Remarks 
__________________________________________________________________________ 
1 I1-II1.1 
Very good 
20 
2 I1-II1.2 
Good 25 
a I1-II1.C 
Poor 30 See Table 2 - the acid number of 
binder II1.C is too low 
3 I2-II1.1 
Good 19 
b IA-II1.1 
Poor 20 See Table 1 - the viscosity of 
binder IA is too high 
4 I3-II1.1 
Very Good 
21 
c IB-II1.1 
Poor 20 See Table 1 - the viscosity of 
binder is too high 
5 I4-II1.1 
Good 19 
__________________________________________________________________________ 
*(kV, measured at an electrode separation of 2.0 mm) (average of three 
measurements). 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.