[0001] Cables for power, electronic (telephone) transmission, hydrophone cables for oil
exploration at sea and other 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 meters. Not only
does this upset the capacitance balance of a transmission cable line but it introduces
potential corrosion sites in proportion to the length of wire that is wetted. The
useful life of water-soaked wires is obviously shorter than that of dry wires.
[0002] 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. 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 the materials to be used in this application are the hydrophobic
nature of the material, low temperature properties, flow characteristics at elevated
temperatures, the highest temperature at which it may be used ("upper service temperature"),
processing characteristics, handling characteristics, dielectric properties, toxicity
and cost.
[0003] Materials that satisfy most of these criteria and which have been widely used are
described in US-A-3607487 and US-A-3717716. 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.
[0004] Similar hydrophobic encapsulants have been proposed for filling splice closures.
For example, US-A-3879575 describes a mixture of a low viscosity oil gelled by a styrene-isoprene-styrene
copolymer, again with polyethylene added to impart consistency and reduce slump.
[0005] US-A-4259540 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 and to provide good handling characteristics that a petroleum jelly material
does not possess.
[0006] However, all of these above described encapsulants must be heated during the filling
process to a temperature above the "upper service temperature" of the encapsulant.
The upper service temperature of the material is the temperature above which the material
cannot be used in the cable. Thus, filling of most materials requires a time consuming
step in order to heat the encapsulant to a pumpable consistency for filling. There
has been long felt need for an encapsulant which meets other filling material requirements
but which could be processed into the cable well below the "upper service temperature"
of the encapsulant. Previously used encapsulants required that they and the cable
be heated to a temperature well above the melting point of the encapsulant (i.e. the
upper service temperature) in order to significantly reduce the viscosity of the encapsulant
to allow filling of the cable. This heating is energy intensive and may be damaging
to some of the electrical components of a cable. It also precludes the use of desirable
cable component materials that may be advantageous, but which cannot tolerate high
filling temperatures.
[0007] 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 such utility is paramount.
[0008] This invention relates to a slow forming, thermally reversible gel which may be heated
to a liquid and cooled to a gel over and over again at a temperature below a temperature
that will damage a cable so that the gel may be removed and replaced during maintenance.
The gel is slow forming, as the viscosity of a clear liquid formed upon heating rises
over a period of several hours to several days to form the gel. It is this length
of time that one has to fill the cables before the gel material becomes too viscous
to flow, or remove the gel during maintenance.
[0009] According to the invention there is provided a gel-forming compound which comprises
(a) from 2 to 8 percent by weight of an isotactic butene-1 polymer containing from
2 to 8 percent by weight of a C
2-C
5 comonomer, (b) from 0 to 10 percent by weight of a styrene-ethylene-butylene-styrene
block copolymer, and (c) from 82 to 98 percent by weight of a naphthenic or paraffinic
oil having an aromatic content of from 0 to 25 percent by weight.
[0010] The gel-forming compound is based on light hydrocarbon process oils and isotactic
butene-1 copolymers and is suitable for use in encapsulating water sensitive cable
components, wires in particular. Preferred compounds comprise (a) from 4 to 7 percent
by weight of a butene-1 copolymer containing from 3 to 8 percent by weight of said
C
2-C
s comonomer, (b) from 4 to 6 percent by weight of said styrene-ethylene-butylene-styrene
block copolymer, and (c) from 87 to 92 percent by weight of a naphthenic or paraffinic
oil having an aromatic content of from 5 to 25 percent by weight. A particularly preferred
compound comprises (a) about 6 percent by weight of a butene-1 copolymer containing
about 6 percent by weight of said C
2-Cs comonomer, (b) about 5 percent by weight of said styrene-ethylene-butylene-styrene
block copolymer, and (c) about 89 percent by weight of a naphthenic or paraffinic
oil having an aromatic content of about 15 percent by weight. The C
2-C
S comonomer is preferably an ethylenic comonomer.
[0011] This invention also provides a cable or other conduit requiring water protection
which contains the gel-forming compound of the invention. Such a cable typically comprises
a wire within a cable body with the wire being protected against water intrusion by
the gel-forming compound of the invention.
[0012] FIG. 1 is a graph which compares the polybutylene gel upper service temperature and
the temperatures at which previously described encapsulants such as waxes or rubbers
("KRATON" G - Registered Trade Mark) had to be filled, as well as the temperature
at which the encapsulating gel compound of the present invention may be filled.
[0013] The encapsulating compound or gel-forming compound of the present invention has the
following properties:
1) Above the gel temperature the material is a clear, low viscosity fluid;
2) after cooling to room temperature the viscosity rises over a period of several
hours to several days to form a gel, rendering the material too viscous to flow.
3) As the gel forms it becomes translucent.
4) 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.
5) The melting temperature, forming temperature and forming time of the gel can be
controlled by the choice and concentration of the butylene copolymeric component in
the base polymer.
6) The gel is hydrophobic and protects the cable from water leakage.
[0014] The gel is based on light hydrocarbon process oils and isotactic butene-1 copolymer.
Because of their compatibility with the oils and crystallinity, the isotactic butene-1
polymers dissolve in the oils above the polymer's melting temperature. Once dissolved,
these polymers exhibit very slow recrystallization and gel network formation from
solution as the temperature is lowered allowing the material to remain fluid at temperatures
much below the gel's melting temperature for a period of approximately 24 to 48 hours.
Eventually, the crystallites form and become connected in a network forming a translucent
gel.
[0015] We have found that the presence of ethylene comonomer in the butylene polymer decreases
both the gel's melting temperature and rate of polymer crystallization.
COMPARATIVE EXAMPLE
[0016] An isotactic butene-1 homopolymer was dissolved in HVI 100 N oil at 120
°C so that the solution contained 6 weight percent isotactic butene-1 homopolymer.
As the solution temperature was lowered the viscosity began to rise sharply at about
40
°C (taken as the minimum filling temperature) and continued to rise to form a firm
gel within one hour of reaching room temperature. The gel formed had a melting point
of about 80
°C.
EXAMPLE 1
[0017] Six weight percent DP 8010 isotactic butene-1 copolymer containing 5.7 percent by
weight ethylene comonomer was dissolved in HVI 100 N oil. The solution was cooled
from 120
°C, the temperature necessary for the dissolving, and the viscosity began to rise at
about 30
°C. The solution material formed into a viscous, usable gel within 24-48 hours after
the initiation of the cooling process. The resulting gel had a melting point of 55-60
°C.
EXAMPLE 2
[0018] The ethylenic comonomer containing polybutene-1 gel of Example 1 was filled into
a suitable cable within 24-48 hours after initial cooling from the solution. The cable
was ready for use within approximately 12 hours after such filling.
[0019] It is apparent that the presence of a C
2-C
5 comonomer, preferably ethylene, and in the range of 2 to 8 weight percent, but preferably
about 6 weight percent comonomer, has a dramatic effect on the properties of the gel.
In addition, it is thought that many hydrocarbon fluids above a molecular weight of
150 will be gelled by isotactic butene-1 homopolymers and copolymers. For example,
HVI 100 N oil has been used which has a 16 percent aromatic content. "Shellflex" 131
(Registered Trade Mark), which may be obtained from Shell Oil Company, Houston, Texas
may also be used as a suitable oil and contains about 24 weight percent aromatic content
as well as "Sunpar" 120 LW (Registered Trade Mark) available from Sun Oil Co. which
contains less than 5 weight percent aromatic content.
[0020] It is also noted that blends of polybutylene with microcrystalline waxes such as
Shellmax 500, available from Shell Oil Company, Houston, Texas produced a firmer,
more opaque gel which forms somewhat more rapidly than that gel claimed by applicants.
[0021] In addition, the addition of from 0 percent by weight to 10 percent by weight of
"KRATON" G (Registered Trade Mark) thermoplastic rubbers, available from Shell Oil
Company, Houston, Texas increases the strength and clarity of the gels, with a slight
decrease in gel formation time.
[0022] In reference FIG. 1, it may be seen that the encapsulating compound or gel-forming
compound of the invention can be used to fill a cable at 55 to 60
°C - well below the polybutene-1 use temperature of 80
°C. The firm gel-forming temperature is at 30
°C and the filling range is thus a 50
°C range between 80
°C and 30
°C. If a filling material of waxes or rubbers were used, such filling material would
have to be filled, as indicated in FIG. 1, at a point above the 80
°C use temperature of the polybutene-1. This would necessitate, of course, a time consuming
and cost inefficient additional heating step prior to filling, as well as a reheating
every time it became necessary to refill the cable because of leaks or other problems.
The use of such materials would also preclude the use of cable components sensitive
to temperatures above 80
°C.
[0023] The invention encompasses a gel-forming material which is not only slow forming to
allow plenty of time to fill a cable without an additional heating step, but is also
thermally reversible so that if the cable is later punctured and the gel-forming material
must be released and/or refilled into the cable, it may be heated to form a liquid
and cooled to the filling temperature over and over again without any loss of the
gel-forming materials' desirable filling characteristics.
1. A gel-forming compound which comprises (a) from 2 to 8 percent by weight of an
isotactic butene-1 copolymer containing from 2 to 8 percent by weight of a C2-CB comonomer, (b) from 0 to 10 percent by weight of a styrene-ethylene-butylene-styrene
block copolymer, and (c) from 82 to 98 percent by weight of a naphthenic or paraffinic
oil having an aromatic content of from 0 to 25 percent by weight.
2. A compound according to claim 1, which comprises (a) from 4 to 7 percent by weight
of a butene-1 copolymer containing from 3 to 8 percent by weight of said C2~Cs comonomer, (b) from 4 to 6 percent by weight of said styrene-ethylene-butylene-styrene
block copolymer, and (c) from 87 to 92 percent by weight of a naphthenic or paraffinic
oil having an aromatic content of from 5 to 25 percent by weight.
3. A compound according to claim 1 or 2 which comprises (a) about 6 percent by weight
of a butene-1 copolymer containing about 6 percent by weight of said C2~Cs comonomer, (b) about 5 percent by weight of said styrene-ethylene-butylene-styrene
block copolymer, and (c) about 89 percent by weight of a naphthenic or paraffinic
oil having an aromatic content of about 15 percent by weight.
4. A compound according to claim 1, 2 or 3 wherein the C2-C5 comonomer is ethylene.
5. Use of a gel-forming compound as claimed in any one of claims 1 to 4 as a filling
material for cables.
6. A cable which comprises a wire within a cable body, the wire being protected against
water intrusion by, as slow forming, thermally reversible encapsulating compound,
a gel-forming compound as claimed in any one of claims 1 to 4.
1. Gel-bildendes Gemisch das (a) 2 bis 8 Gew.-% eines isotaktischen Buten-1 Copolymers
enthaltend 2 bis 8 Gew.-% eines C2-Cs Comonomers, (b) 0 bis 10 Gew.-% eines Styrol/Ethylen/Butylen/Styrol-Blockcopolymers
und (c) 82 bis 98 Gew.-% eines naphthenischen oder paraffinischen Öls mit einem Aromatengehalt
von 0 bis 25 Gew.-% umfaßt.
2. Gemisch nach Anspruch 1, das (a) 4 bis 7 Gew.-% eines Buten-1 Copolymers enthaltend
3 bis 8 Gew.-% des C2-C5 Comonomers, (b) 4 bis 6 Gew.-% des Styrol/Ethylen/Butylen/Styrol-Blockcopolymers
und (c) 87 bis 92 Gew.-% eines naphthenischen oder paraffinischen Öls mit einem Aromatengehalt
von 5 bis 25 Gew.-% umfaßt.
3. Gemisch nach Anspruch 1 oder 2, das (a) etwa 6 Gew.-% eines Buten-1 Copolymers
enthaltend etwa 6 Gew.-% des C2-Cs Comonomers, (b) etwa 5 Gew.-% des Styrol/Ethyl/Butylen/Styrol-Blockcopolymers und
(c) etwa 89 Gew.-% eines naphthenischen oder paraffinischen Öls mit einem Aromatengehalt
von etwa 15 Gew.-% umfaßt.
4. Gemisch nach Anspruch 1, 2 oder 3, wobei das C2-Cs Comonomer Ethylen ist.
5. Verwendung eines Gel-bildenden Gemisches nach einem der Ansprüche 1 bis 4 als Füllmaterial
für Kabel.
6. Kabel, das umfaßt einen Draht innerhalb des Kabelkörpers, wobei der Draht gegen
Eindringen von Wasser geschützt ist durch ein Gel-bildendes Gemisch nach einem der
Ansprüche 1 bis 4 als sich langsam bildendes, thermisch reversibles Umhüllungsmaterial.
1. Composition formant un gel, qui comprend (a) de 2 à 8% en poids d'un copolymère
isotactique de butène-1 contenant de 2 à 8% en poids d'un comonomère en C2-C5, (b) de 0 à 10% en poids d'un copolymère séquencé styrène-éthylène-butylène-styrène,
et (c) de 82 à 98% en poids d'une huile naphténique ou paraffinique présentant une
teneur en composés aromatiques de 0 à 25% en poids.
2. Composition conforme à la revendication 1, qui comprend (a) de 4 à 7% en poids
d'un copolymère de butène-1 contenant de 3 à 8% en poids dudit comonomère en C2-C5, (b) de 4 à 6% en poids dudit copolymère séquencé styrène-éthylène-butylène-styrène,
et (c) de 87 à 92% en poids d'une huile naphténique ou paraffinique présentant une
teneur en composés aromatiques de 5 à 25% en poids.
3. Composition conforme à la revendication 1 ou 2, qui comprend (a) environ 6% en
poids d'un copolymère de butène-1 contenant environ 6% en poids dudit comonomère en
C2~Cs, (b) environ 5% en poids dudit copolymère séquencé styrène-éthylène- butylène-styrène,
et (c) environ 89% en poids d'une huile naphténique ou paraffinique présentant une
teneur en composés aromatiques d'environ 15% en poids.
4. Composition conforme à la revendication 1, 2 ou 3, dans laquelle le comonomère
en C2-C5 est l'éthylène.
5. Utilisation d'une composition formant un gel, conforme à l'une quelconque des revendications
1 à 4, comme matériau de remplissage pour câbles.
6. Câble qui comprend un fil dans un corps de câble, ce fil étant protégé contre l'infiltration
d'eau par, en tant que composition d'enrobage à formation lente et thermiquement réversible,
une composition formant un gel, conforme à l'une quelconque des revendications 1 à
4.