Pulp insulation repair

A compound for spray application onto pulp insulation on an electrical conductor, the compound comprising between 5 and 9 parts by weight of polyvinylpyrrolidone polyvinylacetate copolymer with 0.5 to 0.9 parts by weight of a copper corrosion inhibitor and 1.0 to 3.0 parts of a plasticizer. The compound is useful either to repair damaged pulp regions or for spraying the pulp during manufacture of an insulated conductor without substantially reducing the electrical insulating characteristics of the pulp.

This invention is concerned with pulp insulation repair on electrically 
insulated conductors but is also concerned with the prevention from 
deterioration of pulp insulation. 
In the manufacture of electrically insulated conductors, pulp insulation is 
sometimes used. One disadvantage found with pulp insulation is that during 
the course of its operational life, it becomes dry and brittle. When a 
splicer handles conductors, during a resplicing operation or to conduct a 
cable throw, dry and brittle pulp insulation will crack or even break away 
to expose the conducting member. In consequence, an electrical "short" may 
be caused between conducting members or between a conducting member and 
some other electrically conducting article in close proximity to it. In 
any case, the dielectric is impaired between conductors. 
Various methods have been tried to repair pulp damage but with limited 
success. For instance coatings of various kinds applied to strengthen the 
pulp have resulted in reduction in dielectric between conducting members. 
Oil has also been used but this tends to make the pulp messy for handling 
purposes. 
The applicant has discovered an efficient method of repairing pulp 
insulation and a compound for enabling the repair to be made. The 
invention also applies to the application of the compound to the pulp 
insulation of a conductor during its manufacture to prevent the 
deterioration of the pulp. 
According to one aspect of the invention, there is provided a fibreless 
compound for use as a spray material, the compound comprising from 5.0 to 
9.0 parts by weight of polyvinylpyrrolidone-polyvinylacetate copolymer, 
from 0.5 to 0.9 parts by weight of copper corrosion inhibitor and from 1.0 
to 3.0 parts by weight of a plasticizer. 
The copper corrosion inhibitor may be tolyltriazone and the plasticizer may 
be dibutyl phthalate. 
It is found that a compound according to the formulation according to the 
invention, when sprayed onto fibrous material, tends to become attracted 
to the surfaces of the fibers so as to cover them with a compound layer 
which strengthens the fibers and the junction between fibers. It is also 
effective in forming new junctions between adjacent fibers so as to repair 
a crack appearing in pulp insulation. Further the compound may be used to 
coat individual pulp coated conductors and after drying of the compound, 
coatings on adjacent individual conductors do not tend to stick together. 
In preferred compounds, one or more ingredients are included to accelerate 
the drying time of the compound after spraying or to increase the flame 
retardancy and reduce the conductivity of the dried compound. As examples 
of these materials, butyl cellosolve may be added to accelerate drying 
time while retarding film forming time towards the end of the drying 
operation. This enables compound to penetrate completely into the pulp 
before setting up. Butyl cellosolve in quantities around 2 parts by weight 
may be used with 10 to 40 parts by weight of methylene chloride which are 
suitable for flame retardance and 44-76 parts by weight of tetrahydrofuran 
which are suitable for reduction of conductivity. Alternatively to 
methylene chloride, 10 to 40 parts by weight of trichlorethylene is a 
suitable substitute. Also the tetrahydrofuran may be successfully replaced 
by 44 to 76 parts of a mixture of tetrahydrofuran and heptance in a ratio 
around 55:45 or a mixture of tetrahydrofuran and kerosene in a ratio 
around 60:40. 
The invention also includes a method of repairing an electrically insulated 
conductor having a layer of pulp insulation overlying a conductor member 
comprising spraying the region to be repaired with the compound as defined 
above, the compound penetrating between and along the pulp fibers while 
avoiding the air spaces formed between fibers. 
Further according to the invention, there is provided an electrically 
insulated conductor having a region of pulp insulation which has been 
repaired by the spray application of the compound as defined above. 
The invention further includes a method of making an electrically insulated 
conductor in which a conducting member is insulated with a covering layer 
of pulp insulation and this is subsequently sprayed with a compound as 
defined above, the compound covering the individual fibers and penetrating 
between the fibers while substantially avoiding air spaces formed between 
the fibers. 
In addition, the invention extends to include an electrically insulated 
conductor having a conducting member insulated with a covering layer of 
pulp insulation and the fibers of the pulp insulated being covered by the 
compound as defined above, the compound penetrating between fibers while 
substantially avoiding air spaces formed between fibers.

In a first embodiment in FIG. 1, a conductor 10 in the form of a 
telecommunication cable is insulated by a layer of pulp insulation 11. 
During use of the conductor, the pulp insulation has become dry and 
brittle, partly because of moisture extraction by the use of dry air in 
the cable pressuring system extracting moisture from the pulp. The result 
of this is that the pulp is broken away and cracked in the region 
generally designated 12 during flexing as a resplicing operation is 
performed further along the cable. 
To repair the region 12 and increase dielectric between the conductors, the 
region and areas of the pulp insulation axially at each side of the region 
are sprayed by a fibreless repair compound. This compound has the 
following formulation. 
______________________________________ 
Parts by Weight 
______________________________________ 
Polyvinylpyrrolidone - Polyvinylacetate 
copolymer (PVP/PVA) 10 
Tolyltriazone 1 
Dibutyl Phthalate 2 
______________________________________ 
The above formulation is admixed with the following further ingredients in 
the following proportions: 
______________________________________ 
Volume per 100 gms. of copolymer 
______________________________________ 
Butyl Cellosolve 
3 cc. 
Methylene Chloride 
64 cc. 
Tetrahydrofuran 
120 cc. 
______________________________________ 
The compound is sprayed as a 5% solution onto the region 12 and surrounding 
areas from a distance of between 5 and 10 inches. It is found that the 
compound has a quality imparted to it by the PVP/PVA that when sprayed 
onto the pulp fibers, it is attracted to the surfaces of the fibers. Thus 
in the areas where pulp is present, the compound upon drying tends to 
strengthen the fibers and regions torn junctions between fibers. Some of 
the air gaps between fibers may still remain depending upon the degree of 
saturation by the compound. The butyl cellosolve, because of its solvent 
characteristics, accelerates the drying time to enable work to be done on 
the sprayed area if desired. A retardancy of film forming time enables the 
compound to penetrate completely into the pulp before setting up. 
Complete penetration of the pulp enables the compound to penetrate into the 
pulp areas lying between pairs of conducting members 13 so as to repair 
any pulp insulation impairment between the conducting members. Hence, 
within the immediate spray area, the pulp is completely saturated, by 
surface coverage, with the compound and because of the flow capabilities 
of the compound the areas of pulp adjacent to the spray area also have 
amounts of the compound with the quantities of compound decreasing as the 
distance extends from the area of spray. As shown in FIG. 1, the thicker 
outlined fibers of the pulp insulation represent the areas infiltrated by 
the compound. 
Also as may be seen from FIG. 1, the region 12 is devoid of pulp insulation 
to cause baring of the conducting members. The compound upon spraying onto 
the conducting members is capable of forming a film 14 over the members 
because no fibers are in the vicinity which may attract the compound and 
prevent it from film forming. The compound has insulating properties which 
satisfactorily increase the dielectric between the conducting members by 
film formation and also reinsulate the members from the outside of the 
cable. The strength properties of the film do not cause rupturing of the 
pulp if the conducting members are subsequently intentionally separated. 
The further properties of the compound are such that it strengthens the 
pulp insulation in the area sprayed and provides this area with a degree 
of flexibility and plasticity which prevents the embrittlement. The 
flexibility also allows for the spray treated area to be used for some 
future splicing operation without fear of the pulp insulation breaking 
away from the conducting members in areas where it is not desired. 
The compound described above and according to the invention is particularly 
useful for use on telecommunications cables where no temperature rise 
takes place as in power cables. Dielectric strength of pulp insulation is 
low and any range of high voltage will cause the breakdown of the 
insulation. The compound sprayed onto certain areas of insulation does not 
decrease the dielectric strength of the pulp to the extent that it will 
cause any significant increase in breakdown in the insulation. It is 
suspected that it may even increase dielectric strength. 
Further, the compound does not interfere with the making of a connection to 
a conductor in the areas in which it is sprayed, by any of the standard 
wire connecting methods such as insulation displacement, piercing, etc. 
In a second embodiment, as shown in FIG. 3 a conducting member 15 is 
insulated during manufacture of a telecommunications cable by passing it 
through a pulp bath 16 in which it is coated with pulp. After being 
subjected to pulp finishing processes as well known in the art, the pulp 
covered conductor 17 is passed through a drying area 18 and then through a 
spray 19 of compound which covers and penetrates between the fibers as 
disclosed for the repair region in the first embodiment. A suitable 
formulation for the compound is as follows: 
______________________________________ 
Parts By Weight 
______________________________________ 
PVP/PVA 10 
Tolytriazone 1 
Dibutyl Phthalate 2 (gms. or cc) 
______________________________________ 
The above formulation is mixed with 30 cc of isopropyl alcohol per 10 gms 
of PVP/PVA and then mixed with 140 cc of water per 10 gms. of PVP/PVA 
before spraying. 
After the sprayed pulp is dried, it is found that the compound has 
infiltrated substantially evenly through the pulp while substantially 
avoiding air spaces to generally strengthen it and give it flexibility and 
plasticity which will prevent the pulp from becoming brittle after a 
period in use. 
In use of the invention the proportions of PVP/PVA may be varied dependent 
upon particular requirements. For instance, where the compound is to be 
used for repair and in which pulp insulation has broken away so as to 
expose conducting members, a high molecular weight copolymer is required 
with a good film strength to provide a permanent covering film or layer 
over the exposed parts. It is also important that for repair work, the 
copolymer should be resistant to water solubility. Such a polymer should 
have a high percentage of PVP compared with PVA. For instance, in the 
first embodiment described, the ratio of PVP:PVA may be in the region of 
60:40. 
For the manufacture of insulated conductors, e.g. as in the second 
embodiment, the film strength requirements are not so important as the 
compound is to be sprayed solely on pulp and there are no exposed 
conducting members. Hence, the copolymer may be of low molecular weight 
with, for instance, the ratio of PVP:PVA lying anywhere between 70:30 to 
30:70. It should be understood that water solubility increases with 
increase in proportion of PVA.