US 3875323 A
This filling compound for communication cables has a thixotropic promoting material added to petroleum to increase the temperature to which the filling compound can be heated before it will flow and drip from the cable. Colloidal silica in percentages of 6%, and substantially less than 6% raises the drip point of petrolatum to an unexpected degree, as high as 80 DEG C; and at the same time leaves the filler material soft enough to permit installation of the cables at temperatures as low as -30 DEG C.
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Description (OCR text may contain errors)
United States Patent Bopp et a]. Apr. 1, 1975 WATERPROOF TELEPHONE CABLES 3,607.332 9/1971 Wingfield 106/272 x WITH PLIABLE NON FLOWING FILLING 3,683,104 8/1972 Woodland et al. 174/116 COMPOUND 3,717,485 2/1973 Larson 260/28  Inventors: Louis A. Bopp, Fair Haven; Ludwik FOREIGN PATENTS 0R APPLICATIONS Jachi nowicz, Elizabeth; Gertraud 2,018,863 10/1971 Germany 174/23 C A, Schmidt, Long Beach all of NJ, 2,019,074 11/1971 Germany 174/23 C 73 A General Cable Cor oration, I I Sslgnee Greenwkh Conn p Primary Examiner-Arthur T. Grlmley  Filed: Oct. 1, 1973  ABSTRACT  Appl. No.: 402,389
This filling compound for communication cables has a thixotropic promoting material added to petroleum to  US. Cl 174/23 C, 156/48, 174/116. increase the temperature to whi h the filling com- 208/21 252/59 pound can be heated before it will flow and drip from II."- Cl. the bl Colloidal Silica in percentages of 61%,1 and  Flew Search I 174/23 23 25 substantially less than 6% raises the drip point of pet- 174/25 252/59 rolatum to an unexpected degree, as high as 80 C; 156/48; 208/20 21; l06/27O 260/28 and at the same time leaves the filler material soft enough to permit installation of the cables at tempera-  References Cited tums as low as 3 o C.
UNITED STATES PATENTS 0 3.271.177 9/1966 Rumberger 106/272 14 Clams 1 Drawmg Flgule PETROLATUM AND FUMED SILICA '2 METALIC SHIELDS MENIEUIPR H975 PETROLATUM AND FUMED SILICA PLASTIC JACKET METALIC SHIELDS WATERPROOF TELEPHONE CABLES WITH PLIABLE NON-FLOWING FILLING COMPOUND BACKGROUND AND SUMMARY OF THE INVENTION In order to prevent moisture ingress into plastic insulated. buried telephone cables, hydrophobic insulating compounds have been used to fill the spaces in the cables between the separate insulated conductors in the cables.
The most economical filling compound consisted of a mixture of petrolatum (petroleum jelly) and low molecular weight polyethylene in the ratio of 85/l572 by weight, later changed to 92/87( ratio. This modification of petrolatum was intended to prevent the filling compound from becoming liquid enough at 85C (later at 65C) to flow or drip out of the cable when the cable ends are exposed to sunshine at pedestals of buried cables, on storage reels, or in aerial installations.
It was found that after liquid polyethylene and petrolatum are mixed at l C and then cooled, the physical properties of the cooled compound will depend on the rate ofcooling. lfcooling is slow, as when hot compound is poured into storage barrels and allowed to cool off within hours there will be separation between polyethylene and oils in the petrolatum. Slow cooling allows for gradual crystalization of the polyethylene. The crystals are large and agglomerate. Quick chilling, in a matter of seconds, in a thin layer produces very homogeneous compound. In this process there is no time for the crystals of polyethylene to grow, hence a greater number of crystals of smaller dimensions are precipitated. The crystals are suspended in petrolatum. Compounds so prepared will not revert to separate phases until the softening temperature of polyethylene is reached. A cable drip test shows that quick chilled compound does not drip at 85C for the 85/l5 mixture or at 70 C for the 92/87! mixture, while slowly solidified compound drips at 60 and 50 C respectively.
It appeared that the problem with finding a suitable compound and cable filling method were solved. Recent observations of cables indicate, however, that there is instability in the filling compound resulting in separation of the oil and the solids in finished cables.
If the compound is pressed against a fine mesh, or when the finished cable is compressed, as when wound on a reel. the pressure of the weight of upper layers of cable on the reel will induce the compound to be slightly dislocated. In the process, part of the compound is squeezed through narrow slots, for instance between conductors of a cable pair, through closed overlap of the belting tape (Mylar belt insulation) etc. As a result of this movement of the compound, a filtering phenomenon becomes operative. The solids, the crystals of polyethylene and microcrystaline waxes of petrolatum are left behind, and small quantities of oil, liquid at room temperature, flow through capillary passages presented to the compound.
The net result is that free oil in various quantities, depending on the pressure and condition of squeezing, will appear in the cable. This phenomenon is undesirable and can be harmful to the protection of cable against water ingress. Liquid oil will drip at the cable ends. and may leak away when the jacket is damaged,
This invention solves the drip problem encountered with petrolatum in a different way from the addition of polyethylene to the petrolatum. This invention is based on the discovery that the temperature at which petrolatum begins to drip from a cable on be increased by mixing with the petrolatum small amounts of colloidal silica. The colloidal silica of this invention is not to be confused with silica gels, silica aerogels or other precipitated silicas.
Other objections, features and advantageas of the above will appear or be pointed out as the description proceeds.
The drawing is a view of a portion of a communication cable, made in accordance with this invention and shown in section at one end and broken away at the other end to show the various parts in isometric view and description of drawing. The drawing shows a cable 10 having a core 12 made up ofa plurality ofinsulated conductors. Insulation may be polyethylene, polyvinyl chloride or other conventional insulation, compatible with the filling material. The core 12 includes a D shield 16 around half of the pairs of the core, and the core 12 is held together by helical binding 13 which is surrounded by a metal shield 18 whcih may be made of aluminum coated with polyethylene or other corrosion protecting coating. The construction thus far described is conventional.
Cable core 12 is filled with a filling compound of this invention; the compound being designated by stippling and by the reference character 20. This compound 20 fills substantially all of the spaces, exaggerated in the drawing for clearer illustration, within the shield 18 so as to prevent entrance of moisture into the cable. In the illustrated construction, the jacket 22 surrounds the shield 18 and supplies mechanical protection for the cable.
The mechanism by which this invention accomplishes the desirable properties of a cable filling compound is based upon the dispersion of extremely fine particle size silica which has been produced in a vapor phase process and the product will be referred to herein as colloidal or fumed silica. Examples used in the tables in this specification were made by the hydrolysis of silicon tetrachloride at'l,l00 C and such procedure provides a colloidal silica of expectional purity. in particular, a grade of silica designated as Cab-O-Sil EH-S" has been found to be very desirable because its efficiency is greater than other available grades due to its greater surface area. The Ell-5 grade has a surface area of 390 i 40 m /gram and a particle size of 0.007 micron. The particles themselves are spherical and the particles per gram number 2.0 X l0.
The designation Cab-O-Sil EH-S is a trade designation of the Cabot Corporation, High Street, Boston, Mass. EH-S is but one grade of Cab-O-Sil. Other grades differ from EH-S in particle size, surface area, or bulk density, and the net effect of the silica can be achieved from these other grades but the ratios differ somewhat according to the difference in particle size and surface area of the particular grade chosen. Larger particle size and resulting less surface area increases the amount of fumed silica that must be mixed with the petrolatum.
A quote from Cabots literature states: Cab-O-Sil is a submicroscopic particulate silica prepared in a hot gaseous environment (1,100 C) by the vapor phase hydrolysis of a silicon compound. This method of preparation, which is unusual for a silica, results in a product entirely different from other commercial silicon pigments prepared by aqueous precipitation processes."
The action of the fine particle size silica is to impart thickening and thioxtropic control to fluidlike materials, in this case petrolatum or mineral oils. Individual particles group together to form a chain-like structure. When dispersed in a fluid medium, the chain-like formations join each other to form a lattic type structure that entraps the liquid thereby reducing the ability of the liquid to flow and increasing the viscosity. When shear forces are applied. the lattice structure breaks down. lowering viscosity and reforms when shearing is stopped.
Mineral oil and similar petroleum derivations including petrolatum are non-polar, non-hydrogen bonding liquids. Thus, only a relatively small amount of the colloidal silica is needed to form a gel. This is a desirable feature of this invention because the lower amount of silica required results in a filling compound of close to 95% petrolatum which has very good electrical properties.
The silica functions by forming a gel which increases and broadens the melting range of the petrolatum. The degree to which this can be accomplished is directly related to the concentration of silica incorporated. The referenced 65C temperature is the minimum temperature that is acceptable for non-flowing, non-dripping properties of a cable filling compound. Actually temperatures of 80 90 can be achieved.
The grade of colloidal silica used preferably has a particle size that provides from 200 400 square meters per gram surface area. The amount of colloidal silica mixed with the petrolatum is preferably from l.0 to 5.0 percent by weight of the mixture. Wider ranges can be used. for example, between 0.5 and 10.0%.
Two other things control the effective temperature range of the formulations. First is the selection of the petrolatum itself. The lower the oil content, the higher the flow temperature of the untreated material. As the wax content is increased. the low temperature properties are impaired. Depending upon the petrolatum selected. the ultimate working temperature range of the silica/petrolatum composition can be controlled by the percentage silica added.
An important advantage of this invention is that petroleum fractions of narrower distillation range can be used for the petrolatum, and can be stabilized for broader temperature range utility through the use of the colloidal silica.
The selection of the petrolatum cut to be used in filling compounds is generally broad. having both an oil content of relatively low molecular weight hydrocarbons. and paraffin and microcrystaline waxes of high molecular weight. The oils have a tendency to separate and drip at temperatures below the maximum temperatures that are encountered in service, and this is undesirable. The waxes impart high temperature performance, but are responsible for impairment of low temperature performance. Viscosity. being a function of average molecular weight, can be controlled by two approaches, a broad range of molecular weight components, or a relatively narrow one. By selecting a petrolatum with narrow molecular weight distribution and increasing its upper temperature performance by the addition of colloidal silica, it is possible to obtain both the desired high and low temperature performance, while at the same time eliminating the undesirable low molecular weight oils, and the poor low temperature performing waxes.
The petrolatums used in the examples of this invention are commercial products known as Silkolene" and Hydromolol (identified more fully at the end of this specification). The Silkolene is petrolatum of broad cut, and the Hydromolol is a narrower cut having the range of molecular weight components relatively narrow and without the waxes of Silkolene.
The colloidal silica Cab-O-Sil is originally a dry, finely divided solid with an extremely large available surface area. Apparently its physical configurations are long, branched chains, with numerous hydrogenbonding sites. In a liquid system, the CabO-Sil chains tend to join to each other. The result is a network structure, which might be compared to very time chicken wire, that retards or inhibits the flow of the liquid. The more extensive the formation of the network structure, the more efficient the thickening and thioxtropy.
If the petrolatum and colloidal silica are mixed cold, the blends drip more readily than compared with blends that are mixed hot. This invention preferably mixes the petrolatum and colloidal silica by first heating the petrolatum to 120 C and then inserting and starting a mechanical stirrer, and adding the colloidal silica carefully and mixing it for several minutes until the colloidal silica is thoroughly and intimately mixed with the petrolatum. Cold mixing does not sufficiently wet the colloidal silica; but the cold mixed material can be subjected toa heating and sitrring action after mixing which will obtain the desired effects, but require more time.
The mixtures of colloidal silica and petrolatum were subject to aging tests at room temperature and an aging test of thirty days showed no effect on the drip behavior of the blends. The rate of cooling of the mixture of petrolatum and colloidal silica apparently has no noticeable effect on the drip behavior of the mixture. This is in contrast with petrolatum and polyethylene mixtures which have substantial increase in drip temperature when quench cooled.
Tables No. l and No. 2 show the effect obtained by increasing the amount of colloidal silica in the filling compound which consists of principally petrolatum. In the results shown in these tables the petrolatum was mixed with from 1 to b 5 of colloidal silica. In Table No. l the petrolatum is Silkolene; whereas in Table No. 2 the petrolatum is Hydromolol.
The drip behavior of these blends was tested in aluminum cups with a S/8th inch hole at the center of the bottom of each cup; and temperatures of 40 C to C were maintained for'test periods of 24 hours. During the test each aluminum cup was placed on top of a glass beaker. The designation drip" in the tables indicates that the contents of the cup flowed out during the 24 hours and this indicates that drops of the filler compound would escape from a cable at cable ends and through breaks in a cable covering.
The designation partial" means that only the material in the cup directly over the hole dropped through; and all other material in the cup resisted flow. This is improved performance, but not perfect. The designation OK indicates that no material flowed from the cups during the 24 hour test.
TABLE 1 Composition 40C 45C 50C 60C 65C 70C 75C 80C 85C 90C Silkolene 949 (no silica) OK OK Drip +196 Cah-O-Sil OK OK OK Drip +37: Cah-O-Sil OK OK OK OK Partial Cab-O-Sil OK OK OK OK OK OK +3.75% Cah-O-Sil OK OK OK OK OK OK Partial +4.05% Cab-O-Sil OK OK OK OK OK OK Partial TABLE 2 Com position 40C C C C C C C C C C Hydrornolol HM OK OK Drip "+47 Cab-O-Sil OK OK OK OK OK OK OK OK OK OK +5'Ji Cab-O-Sil OK OK OK OK OK OK OK OK OK OK +6$i Cab-O-Sil OK OK OK OK OK OK OK OK OK OK Hydromolol HM +49l Cah-O-Sil and 5'1 Butyl Rubber OK OK OK OK OK OK OK OK OK OK The last composition in Table 2 utilized Butyl Rubber (Exxon 0.35) which was added to tackify the filling compound to promote better adhesion to the insulated conductors in the cable. An example of another tacki-.
fier which would be used in place of the Exxon 035 Butyl Rubber is Vistanex (available and satisfactory for use) polyisobutylene in a wide variety of molecular weights.
The Silkolene used for the tests set forth in Table 1 above is a petrolatum sold under the trade designation Silkolene 949 and it is available from Dalton and Co. Ltd.. Silkolene Oil Refinery, Belpher.
Derby. England The Hydromolol used for the tests of Table 2 is a petrolatum sold under the trade name Hydromolol HM." This material is available from Witco Chemical Co., Sonneborn Div.. 277 Part Avenue, New York, NY. 10017 The preferred embodiments of this invention have been illustrated and described, but changes and modifications can be made. and some features can be used in different combinations without departing from the invention as defined in the claims.
What is claimed is:
l. A filled communication cable including in combination a plurality of insulated conductors assembled in a cable core having an outer shield surrounding the conductors, filler material in the core in spaces between the insulated conductors. the tiller material comprising a mixture of petrolatum and fumed silica, having a particle size that provides about 200 square meters per gram of surface area and having thixotropic properties that raise the drip point of the material.
2. The cable described in claim 1 characterized by the tiller material being in excess of of the space in the cable core between the insulated conductors.
3. The cable described in claim 1 characterized by the tiller material filling space between the insulated conductors and the shield that surrounds the conductors.
4. The cable described in claim 1 characterized by the fumes silica comprising from 0.5 10.0%, by weight. of the filler material.
5. The cable described in claim 4 characterized by the fumed silica being 1.0 5.0%. by weight. of the tiller material.
6. The cable described in claim 1 characterized by the silica having between about 200 and 400 square meters of surface area per gram weight ofthe silica particles.
7. The cable described in claim 1 characterized by the filler material having a drip point in excess of 65 C but being of low enough viscosity at 30 C for handling the cable in overhead installations in cold climates.
8. The cable described in claim 7 characterized by the drip point being at least 80 C.
9. The cable described in claim 8 characterized by the drip point being at least 90 C.
10. The cable described in claim 1 characterized by the filler material also including a tackifier to promote better adhesion of the filler material to the insulated conductors of the cable.
11. The cable described in claim 10 characterized by the tackifier constituting approximately up to 5% of the filler material by weight.
12. A filled communication cable including in combination a plurality of insulated c'onductors assembled in a cable core having an outer shield surrounding the conductors, filler material in the core in spaces between the insulated conductors, the filler material comprising a mixture of a petrolatum having a relatively narrow range of molecular weight ingredients and limited in wax content to decrease the viscosity of the mixture at low temperatures to a flexibility for handling the cable in overhead installations at temperatures as low as 30 C. the mixture being low in oils of low molecular weight, and a thixotropic promoting material intimately mixed with the petrolatum to obtain a drip point in excess of 65 C at which the filling material will drip from ends of the cable.
13. The method of raising the drip point of a petrolatum filling compound in a communication cable which comprises mixing with the petrolatum a quantity of fumes silica before applying the filling compound to the cable, and thereafter filling spaces between the conductors of the cable with the filling compound 14. The method described in claim 13 characterized by mixing the petrolatum and the fumed silica at a temperature as high as about C.