Kraton G thermoplastic elastomer gel filling composition for cables

A fast forming, thermally reversible gel for filling cables at selective, specific gel temperatures which comprises a styrene-ethylene-butene-styrene block copolymer and a naphthenic or paraffinc oil or solvent with an oil aromatic content up to 25% by weight.

BACKGROUND OF THE INVENTION 
Cables for power, electronic (telephone) transmission, hydrophone cables 
for oil exploration at sea and other various uses have been filled with 
various substances in order to protect against water intrusion since 1970. 
Intrusion occurs when water penetrates into a localized opening in a cable 
sheath and is free to channel as far as physical processes for water 
spread and transport allow, often hundreds of feet. Not only does this 
upset capacitance balance of the transmission cable line but it introduces 
more potential corrosion sites in proproportion to the length of wire that 
is wetted. The useful life of water-soaked wires is obviously shorter than 
that of dry wires. 
The solution that has been widely adopted is to fill the voids in the cable 
with a water insoluble filling material that simply encapsulates the cable 
components to prevent water intrusion. The filling fluid serves four 
purposes: (1) it provides a sonic couple of the hydrophone with the 
jacket; (2) it protects the electrical wiring from corrosive salt water; 
(3) it protects the environment from oil spills, and (4) it protects a 
vessel crew from the dangers associated with handling harsh solvents and 
oils. However, although this physical function of the cable filling 
material is straight-forward, the choice of the material is not. Among the 
many considerations that are important for materials used in this 
application are the hydrophobic nature of the material, low temperature 
properties, flow characteristics at elevated temperatures, the highest 
temperature at which the encapsulant may be used ("upper service 
temperature"), processing characteristics, handling characteristics, 
dielectric properties, toxicity and cost. In addition, it is desired that 
the material have the capacity to control the gellation or gel dissolution 
temperature by changing the character of the gel. This is so that a 
specific gel dissolution temperature may be selected. 
Materials that satisfy most of these criteria and which have been widely 
used are described in U.S. Pat. Nos. 3,607,487, 3,717,716 issued Sept. 21, 
1971 and Feb. 20, 1973 respectively and U.S. Pat. No. 3,775,548. These 
materials are essentially a petroleum jelly, mixed with a polymer, usually 
polyethylene, to impart consistency and prevent flowing at warm 
temperatures below the upper service temperature. 
Similar hydrophobic encapsulants have been proposed for filling splice 
closures. For example, U.S. Pat. No. 3,879,575 issued Apr. 22, 1975 
describes a mixture of a low viscosity oil gelled by a 
styrene-isoprene-styrene copolymer, again with polyethylene added. The 
polyethylene is used to obtain a high use temperature needed for use with 
power transmission cables which reach high temperatures. U.S. Pat. No. 
4,259,540 discloses the use of a styrene-ethylene butylene-styrene block 
copolymer, polyethylene, and a paraffinic or napthenic oil, where the oil 
has a maximum of 5% aromatic oils, in order to enable the cable 
encapsulant to meet the functional requirements of the cable, i.e., high 
temperature resistance and to provide good handling characteristics that 
petroleum jelly material does not possess. 
However, all of these above-described encapsulants have a predetermined gel 
dissolution temperature which cannot be selectively controlled. Control of 
the gellation (i.e., dissolution) temperature, as well as maintenance of 
the other necessary and desirable factors discussed, is thus highly 
desirable; however; heretofore there has not been found an encapsulating 
material with the necessary advantages, which is also highly selective 
with regard to the gellation temperature desired. For example, one might 
wish a gel dissolution temperature to be fairly high so that the gel would 
form fast upon filling and allow the cable to be used quickly. Or, one 
might desire a gel which forms at a low temperature so that it would be 
slower forming. In addition, in none of these previously used materials in 
the above-described patents may the density be selectively controlled for 
the amount of buoyancy desired, while still retaining gellation 
temperature control, etc. 
In addition, an encapsulant which is thermally reversible has long been 
sought. This means that the encapsulant may be removed and replaced during 
maintenance time and time again at a temperature below the temperature 
that would damage the cables. An encapsulant which is thermally reversible 
can be heated to a liquid and then cooled to a gel over and over again 
without damage to the nature of the filling material, or cable components. 
This is especially true in hydrophone cables that are generally not 
permanently installed but towed at sea where the utility of such invention 
is paramount. 
SUMMARY OF THE INVENTION 
This invention includes a fast forming, thermally reversible gel so that it 
may be heated to a liquid and cooled to a gel over and over again at a 
temperature above the use temperature where the gel may be removed and 
replaced during maintenance. The gellation or gel dissolution temperature 
may be specifically controlled in order to change the character of the 
gel. This may be done by the concentration of polymer in either solvent 
and/or oil, the aromatic content of oil or solvent, and the molecular 
weight of KRATON.RTM. G thermoplastic elastomer. 
In addition, this gel may be formulated so as to be selective for desired 
degree of buoyancy of the cable. 
The gel is based on light hydrocarbon process oils or solvents and 
styrene-ethylene-butylene-styrene block copolymers. The filling material 
(KRATON G thermoplastic elastomer, available from Shell Oil, Houston, 
Tex.) or gel encapsulating compound, comprises from about 2 percent by 
weight to about 15 percent by weight styrene-ethylene-butylene-styrene 
block copolymers and from about 85 percent by weight to about 98 percent 
by weight of a naphthenic or paraffinic oil or solvent with an aromatic 
content of up to 25 percent by weight. The encapsulating compound is 
preferably about 5% by weight of the S-EB-S block copolymer, and 
preferably about 95 percent by weight of a naphthenic or paraffinic oil or 
solvent with an aromatic content of preferably about 15 percent by weight. 
This invention also includes a cable or other conduit requiring water 
protection which contains the encapsulating compound described above.

DETAILED DESCRIPTION OF THE INVENTION 
The encapsulating compound or gel of the present invention has the 
following properties: 
(1) Above the gel temperature the material is a clear, low viscosity fluid; 
(2) Below the gel temperature, the material is a non-conductive, clear 
rubber gel with measurable tensile strength. 
(3) The gel is thermally reversible at a temperature below the temperature 
that will damage the cables so that the gel may be removed and replaced 
during maintenance. 
(4) The gel dissolution temperature may be controlled precisely by the 
polymer concentration or by the aromatic content of the solvent or oil to 
temperatures from 10.degree. C. to above 100.degree. C. 
(5) The gel is hydrophobic and protects the cable from water leakage. 
(6) The gel's hardness and strength increases gradually at temperatures 
increasingly below the gel temperature. 
(7) The specific gravity of the gel can be between 0.76 and 0.90 depending 
on the solvent, to provide desired buoyancy. 
(8) The gel provides as good a sonic couple as the cable fluids in general 
use. 
The gel is based on light hydrocarbon process oils and/or solvents and 
styrene-ethylene-butylene-styrene block copolymers. Because of the 
temperature dependence of their compatibility with the paraffinic oils, 
and solvents, the S-EB-S block polymers' styrene domains dissolve in the 
oils or solvents above the gel dissolution temperature. Once dissolved, 
these styrene blocks exhibit fast phase separation and gel network 
formation from solution as the temperature is lowered. 
The gel dissolution temperature is a function of (1) the concentration of 
polymer in either solvent and/or oil, (2) the aromatic content of oil or 
solvent being less than 25% by weight, and (3) the molecular weight of 
Kraton thermoplastic elastomer. It should be noted that with oils 
containing &gt;20% aromatics concentration one may need to cool the solution 
to below room temperature to reach the gel dissolution temperature. 
EXAMPLE 1 
Kraton G 1652 rubber was dissolved in Sunpar.RTM. 120LW, available from Sun 
Oil Co., at 80.degree. C. so that the solution contained 4 percent S-EB-S 
block copolymer. As the solution temperature was lowered the viscosity 
began to rise sharply at about 62.degree. C. and the solution gelled 
immediately upon reaching 60.degree. C. The gel had a dissolution 
temperature of 60.degree. C. 
EXAMPLE 2 
Kraton G 1652 rubber was dissolved in Shellflex.RTM. 131, which may be 
obtained from Shell Oil Co., Houston, Tex., oil at 30.degree. C. so that 
the solution contained 4 percent S-EB-S block copolymer. The solution 
gelled upon cooling at 15.degree. C. 
EXAMPLE 3 
A clear gel was formed in Norpar.RTM. 13 solvent, available from Exxon, 
Houston, Tex., by adding 4% Kraton G 1652 rubber and allowing the mixture 
to stand at 20.degree. C. for two hours. Upon heating to 29.degree. C. the 
gel dissolved to a low viscosity fluid. Upon cooling, the solution gelled 
at 29.degree. C. Also, 4% Kraton G 1650 was added to Norpar-13, with a 
resulting gel temperature of 38.degree. C. Likewise, 4% Kraton G 1651 was 
added to Norpar-13, with a resulting temperature of greater than 
100.degree. C. The same gel could be formed by dissolving above the gel 
temperature as in Example 1. 
EXAMPLE 4 
A gel was made by mixing 33% Sunpar 120LW oil at 40.degree. C. with 66% by 
weight of a solution of 6% by weight Kraton G 1652 dissolved in Shellflex 
131 oil which has a gel dissolution temperature below room temperature 
(18.degree. C.) so that it could be prepared by stirring at room 
temperature. The resultant solution gelled at 30.degree. C. upon cooling. 
EXAMPLE 5 
The ethylenic comonomer containing the S-EB-S gel of Example 2 is filled 
into a suitable cable before cooling from the solution. The cable is ready 
for use immediately after filling. 
EXAMPLE 6 
The gel may also be selectively made to achieve the amount of buoyancy 
desired in the cable when used in aqueous environments. For example, 
maximum cable buoyancy was achieved by dissolving 6% by weight Kraton G 
1650 rubber in NOR #13. The gel resulted in a specific gravity of 0.78 
and a gel temperature of 42.degree. C. 
EXAMPLE 7 
Minimum buoyancy was achieved by dissolving 4% Kraton G 1652 rubber in a 
50/50 by weight blend of SUN 120LW oil and SHELLFLEX 131 oil. The gel 
resulted in a specific gravity of 0.88 and a gel temperature of 37.degree. 
C. 
It is thought that many hydrocarbon fluids above the molecular weight of 
150 will be gelled by S-EB-S block copolymers. For example, Isopar.RTM. M, 
available from Exxon, Houston, Tex., which has an average molecular weight 
of 191, has been used. Shellflex 371, which has an average molecular 
weight of 400, is also suitable for gel formation. For example, Shellflex 
210 oil has been used which has a 16 percent aromatic content. Shellflex 
131, may also be used as a suitable oil which contains about 24 percent 
aromatic content as well as Sunpar 120 LW, which contains less than 5 
percent aromatic content. 
The S-EB-S block copolymer dissolves in the oils easily especially at 
elevated temperature. The S-EB-S block copolymer dissolves in lower 
molecular weight solvents to form a gel at room temperature in a period of 
several hours. The gel may be homogenized by heating above the gel 
dissolution temperature prior to filling. Because the polymer is low 
molecular weight, it increases the viscosity of the solvent only slightly 
above the gel temperature. Concentrations of S-EB-S block copolymer may be 
from about 2% by weight to about 15% by weight, but preferably about 6% by 
weight. Gels have been made with Kraton G 1650, 1651, and 1652 
thermoplastic elastomer, which range from about 50,000 to about 200,000 
molecular weight of the entire Kraton G molecule with 30% by weight 
styrene. 
Paraffinic solvents include Shell Sol.RTM. 71, available from Shell Oil, 
Houston, Tex., and Isopar M and Nopar #13. Paraffinic oils may also be 
used including Shellflex.RTM. 210 (HVI 100N), Shellflex.RTM. 371 (HVI 
400N) (both available from Shell Oil Co., Houston, Tex.), and Sunpar 
120LW/ Shellflex 131 blends. In order to from a gel at polymer 
concentrations of less than 10%, the oil or solvent must contain less than 
25% aromatics. 
The Kraton G 1652 rubber may be dissolved in the oil at the cable filling 
site at a temperature above the gel dissolution temperature, or dissolved 
earlier and the gel handled in drums, or made in two parts, one consisting 
of a solution of S-EB-S rubber dissolved in a more aromatic oil so that it 
has a gel dissolution temperature below room temperature and the other 
part being a lower aromatic content oil so that when the two parts are 
mixed a gel is formed. 
Applicant's invention encompasses a fast forming gel material which is 
thermally reversible so that if the cable is later punctured and the gel 
material must be released and/or refilled into the cable, it may be heated 
to solution and cooled to the filling temperature over and over again 
without any loss of the gel materials' desirable filling characteristics. 
FIG. 1 shows the triblock network structure of the 
styrene-ethylene-butene-styrene block copolymer. The styrene domains are 
spherical. The solvent is the ethylene-butene molecules (rubber block). 
Upon reaching the gel dissolution temperature, the spherical styrene, 
domains are dissolved and the gel becomes a liquid. Prior to dissolution 
of the styrene domains, the material is a gel. 
FIG. 2 is a graph of the conceptual behavior of the S-EB-S block copolymers 
in solvent. As the temperature increases, the S-EB-S block copolymers 
approach a more true solution. As the temperature decreases, the S-EB-S 
block copolymers approach a gel. 
Various additional modifications and extensions of this invention such as 
to various types of cable or not even to cable at all, will become 
apparent to those skilled in the art. All such variations and deviations 
which basically rely on the teachings through which this invention has 
advanced the art are properly considered to be within the spirit and scope 
of this invention.