Abstract:
The present invention relates to a polymer composition exhibiting high temperature oil resistance, while having improved modulus and tensile strength, as well as a novel insulated electrical conductor employing such material, said material comprising a polymeric constituent selected from the group consisting of copolymers of ethylene and propylene, polymers of same with other polymerizable materials, and mixtures of the foregoing, said constituent being in intimate mixture with a fully calcined aluminum silicate clay filler containing less than about 0.5 percent by weight water (based on the weight of the clay) having an average particle size less than 1 micron with at least about 80 weight percent of the particles having size finer than 2 microns and with at least about 10 weight percent of the particles being more finely divided than 0.5 microns.

Description:
This is a continuation of co-pending application Ser. no. 638,152 filed on Aug. 6, 1984, and now abandoned 
    
    
     BACKGROUND OF THE INVENTION 
     In the manufacture of electric cables, particularly those having a conductor insulated with a multi-layer covering, for use at elevated temperatures under extreme pressure and exposure to oil and water environments, it has been found useful to employ an insulation comprising a thermosetting rubber containing ethylene and propylene usually referred to as an &#34;ethylene-propylene rubber&#34; or &#34;EP rubbers&#34;. The ethylene- propylene rubber may be a copolymer, though more commonly it is an ethylene-propylene-diene-monomer terpolymer which, in turn, is usually referred to as an &#34;EPDM&#34;. Such cables are disclosed, for example, in U.S. Pat. No. 4,088,830, and typical insulation formulations compounded from such EPDM polymers together with additional constituents, such as suitable processing aids, curing agents and the like, have been shown, for example, in U.S. Pat. No. 3,926,900. 
     In formulating compounds for such ethylene-propylene rubber compositions, it has been necessary to strike a balance between the desire for compounds having better physical characteristics, i.e. modulus, hardness etc., and the counterbalancing highly undesirable changes in other physical properties, such as, for example, an increase in the coefficient of thermal expansion. Thus, it was possible in the past, by employing an EP rubber with a very high ethylene to propylene ratio, to obtain some improvement in modulus and hardness. Unfortunately, such EP rubbers also exhibited a substantially higher coefficient of thermal expansion. When used in cables, the high coefficient of thermal expansion resulted in very high stress levels being placed on the outer lining or jacket of lead, with the result that splits and cracks in the lead could result, allowing well fluids and gases into underlying insulation. 
     Nevertheless, it has long been desired to formulate an EP rubber based compound which would have higher modulus and hardness so that the resulting insulation would be more resistant to mechanical deformation at room temperature. Such insulation deformation frequently occurs during the cable armoring process, as well as when the cable is handled during service. 
     Suitable EP rubbers and EPDM polymers are available from a variety of sources including Uniroyal under the trademark ROYALENE and E. I. Du Pont under the trademark NORDEL. The final formulation or &#34;compound&#34;, however, typically will also include curing agents, processing aids, fillers, pigments and/or cross-linking agents. In general, the selection of a particular curing system, or other additive, is usually a matter of choice for the individual formulator subject to certain well-known characteristics attributable to specific additives. 
     Again, as noted above, these characteristics often involve something of a tradeoff. For example, it is generally accepted in EP rubber compounding that higher modulus compounds can be obtained by using carbon black or precipitated silica fillers. However, these fillers are unsuitable for cable applications because they seriously degrade the electrical properties. In other words, even though it is known that compounds having the desired higher modulus could be obtained using carbon black or precipitated silica fillers, in cable applications, it has been traditional to use surface treated clay as the filler because the electrical properties are the principal properties which must be maintained. 
     It has long been desired to produce a cable with a multi-layer covering over the conductor wherein the thermosetting rubber insulation has not only excellent electrical insulation properties, but also improved physical properties, particularly higher modulus and hardness, so as to provide greater protection against deformation of the insulation during armoring of the cable within a metal shield and/or during handling of the cable in service. 
     Accordingly, it is a principal object of the present invention to provide an electrical cable of the type used in oil and gas wells which has excellent physical and chemical properties. 
     In addition, other objects of the invention will become apparent to those skilled in the art from a reading of the following specification and claims. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention relates to a filled material, e.g., an electrical insulation composition of high temperature oil resistance and improved modulus and tensile strength. The material comprises a polymeric compound containing copolymers of ethylene and propylene, or containing polymers of same with other polymerizable materials, or containing both, the filler in the compound being a calcined aluminum silicate clay having an average particle size less than about 1 micron, with at least about 80 weight percent of the particles having size finer than about 2 microns and with as much as 10 weight percent of the particles being more finely divided than 0.5 microns. 
     In yet another aspect; the present invention is directed to an insulated electric cable having a metallic conductor, an insulating layer of material as hereinbefore described and a tough outer layer. 
     The cable of the present invention is fabricated using conventional techniques, but employing as the thermosetting rubber insulating jacket an EP rubber compound in which the filler is a calcined fine particle size aluminum silicate clay. The clay filler has an average particle size less than about 1 micron with at least 80 weight percent of the particles having a size finer than about 2 micron, and with at least about 10 weight percent of the particles being more finely divided than about 0.5 microns. 
     The EP rubber compounds employed in conjunction with the present invention provide an insulating layer having a modulus and hardness as high or higher than those heretofore possible only with the use of very high ethylene to propylene ratio EP rubbers and/or with the use of carbon blacks or precipitated silica fillers, but without the undesirable tradeoff of a rise in the coefficient of thermal expansion, and/or degradation of the highly essential electrical properties. 
     Insulated and jacketed electrical conductors of the present invention are especially suitable for service in oil field use. This is particularly so, as such compounds can have retarded swelling and deformation when in contact with hot fluids, which contact might otherwise lead to accelerated deterioration of cable insulator and jacketing materials. 
     Cables intended for use in such applications typically contain from about 60 to 100 percent by weight (based on the weight of the rubber) of processing oil to retard swelling, and typically have a 100% modulus value of from about 500 PSI to about 2000 PSI and a hardness of from about 60 to about 90 durometers (Shore A). 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The insulators of the present invention are based upon synthetic rubber. Although the term &#34;rubber&#34; is found useful herein, the expression &#34;polyolefin elastomer&#34; may also be used. The suitable materials will almost always be an EPDM rubber, although the use of EP rubbers are also contemplated. The EPDM rubbers will usually include only a relatively minor proportion of a diene. Suitable dienes can include dicyclopentadiene, the hexadienes, e.g., 1,4-hexadiene and norbornadiene. In compounding the compositions of the present invention, the particular rubber used will typically have a molecular weight of from about 100,000 to about 1,000,000. When considering the ethylene and propylene content of the rubber, for the purposes of the present invention, the rubber should be quite carefully selected so that the ethylene content dominates. Advantageously for enhanced insulation characteristics, the rubber will have a substantially major ethylene content, e.g., greater than 50 weight percent or more ethylene, based on the ethylene plus propylene weight. Furthermore, for best insulator properties, it is preferred that a rubber be selected having a high ethylene content on the order of 80 weight percent or so. Moreover, care should be taken that the rubber also have a high Mooney viscosity, generally in the range of about 40 to about 90 and typically on the order of 78 at 125° C. (ML1+4). 
     It has been conventional to include an antioxidant with the rubber, e.g., typically on the order of about 1 to about 2 weight parts of antioxidant per 100 weight parts of rubber, with polydihydrotrimethylquinoline being most generally employed. In curing, the cross-linking of the polyolefin elastomers may be acceptably affected with an organic peroxide cross-linking curing agent, although other such agents find utility, as is well-known to those skilled in the art. Also, a principal agent often is used in combination with a co-curing agent. Suitable organic peroxide curing agents include di-cumyl peroxide; 2,5-dimethyl-2,5 (t-butyl peroxy) hexane; 2,5-dimethyl-2,5 (t-butyl peroxy) hexyne-3 and similar tertiary diperoxides. Suitable co-agents for curing are m-phenylene diamine, 1,2-polybutadiene homopolymer and trimethylolpropane trimethacrylate. Amounts of curing agent used may vary from on the order of about 1 to 2 weight parts, based on the weight of all other composition ingredients, up to as much as 6 to 8 weight parts or more. 
     The critical constituent for compounding the materials of the present invention is a fine particle size, calcined aluminum silicate clay. By fine particle size is initially meant a clay having an average particle size of less than 1 micron. Moreover, this very finely divided material should have 80 weight percent or more of the particles having size less than 2 microns. Furthermore, the calcined clay should have on the order of at least about 10 weight percent, and more typically about 12 to about 17 weight percent of particles finer than about 0.5 micron. Thus, although average particle size is important, and this may typically be within the range of from about 0.6 to about 0.9 micron, particle size distribution is also important. Virtually all particles will be more finely divided than about 20 microns. Suitable finely divided calcined clays will show on the order of about 60 to about 75 weight percent of particles more finely divided than 1 micron and have 80 to about 90 weight percent finer than 2 microns. 
     It is also important that the clay be a calcined aluminum silicate as opposed to a softer or hydrous clay. A typical chemical analysis of a suitable clay can be expected to show an about 44 weight percent proportion of alumina and an about 52 weight percent proportion of silica. Stated another way, the clay fillers useful herein will be found to be composed of over 95 percent aluminum silicate. Typical chemical analysis will show less than about 0.5 percent by weight water and the balance to be virtually all oxides, such as of titanium, iron, sodium potassium, calcium and magnesium. As these additional oxides behave in the manner of inert materials, they do not detract from the acceptability of the aluminum silicate clay filler. It should, therefore, be understood that the highly calcined aluminum silicate filler useful herein can include up to about 5 weight percent of residual impurities. 
     Such filler finds use when employed in the range of from about 20 weight parts up to about 200 weight parts, or even more, per 100 weight parts of rubber. It is, however, more typical to find the filler used in a proportion more closely paralleling the amount of the rubber. Hence, most usually there is employed from about 60 to about 150 weight parts of filler per 100 weight parts of rubber. Preferably, for best insulation characteristics, the filler is used in an amount within the range of from about 80 to about 120 weight parts, per 100 weight parts of rubber. 
     It is to be understood that additional finely divided hard particulate materials may be present in the composition. Such can be particularly useful in compounds for preparing tough jackets around insulating layers. When such additional material is used, the amount of the clay filler can be cut back without a deleterious effect on compound properties. Moreover, these additional particulates may be used in varied amounts, and such amounts can depend on whether there is being formulated an insulating material or other compound, e.g., an outer jacketing material for an insulated electric conductor. Finely divided silica has been used for the additional particulate, and the addition of titanium dioxide is also contemplated. For example, from about 20 to about 60 weight percent or more (based on the weight of the clay) of finely divided silica has been found to be useful in the preparation of jacketing compound. It is also common practice to add an ingredient, such as zinc oxide, to the formulation, as well as to include red lead oxide, sometimes referred to in the art as a vulcanizing agent. These ingredients can likewise be present as finely divided-particulate ingredients. It is also to be understood that some constituents, e.g., commercially available curing agent, can be available as a mixture with clay other than the calcined, fine particle size clay used in the present invention.. The introduction of small amounts of such clays, e.g., on the order of up to 5 to 10 weight percent or so, basis the weight of the fully calcined clay, is generally acceptable. 
     It is intended that the calcined aluminum silicate filler preferably be present in treated condition in the filled compound. More particularly, this is meant to be a silicone liquid surface treatment of the filler. the surface treatment of aluminum silicate with a silicone liquid, and especially with an organic polysiloxane, has been shown, for example, in U. S. Pat. No. 3,148,169. Typically, a vinyl silane, such as vinyl-tris (2-methoxyethosy) silane, is used. Usually as little as 1 to 2 weight parts of the vinyl silane per 100 weight parts of the clay filler is serviceable, as will be understood by those skilled in the art. For convenience, the term &#34;silicone liquid&#34; has been used herein and is meant to include the use of the silanes, as well a various siloxane compounds. 
     Reference has frequently been made herein to the use of invention compositions for electrical insulation, as well as for use in an insulated electric conductor as a jacketing material. Such jacket and insulation use, which may be integral layers of jacket and insulation materials, can be particularly serviceable in oil well cable and motor lead cable. It is, however, to be understood that materials may be serviceable in non-cable parts, as well as in non-oil field uses, e.g., as packer seals and gasketing materials. 
     As noted earlier, where the composition is intended to be used as an insulator or jacketing material for service in fluid contact, such as in oil well cable, ingredients might be a liquid 1,2 polymerized butadiene to retard swelling in oil, as discussed in U. S. Pat. No. 3,926,900. These further ingredients may also include so called processing oils, e.g., napthenic or paraffinic oils, also known as compounding oils. 
     It is advantageous that where the composition is to be used as an insulator for the electrical conductor that there be used on the order of about 60 to about 100 weight parts of processing oils, per 100 weight parts of the rubber. Jacket compositions will typically include an even higher level of such oils. In many cases, the upper limit of these ingredients is a matter of &#34;compatability&#34;. That is to say, if too much processing oil is added, part of all of the excess will migrate to the surface of the molded end product as &#34;blooming&#34; or even exudation. 
     It is to be understood that a variety of additional constituents, generally present individually in only very minor amounts, e.g., 1 to 2 weight parts per 100 weight parts of rubber, and in the aggregate typically present in amounts of only 5 weight parts or so, basis 100 weight parts of rubber, might nevertheless be useful in compositions of the present invention. Representatives of such useful substituents can be various lubricants. 
     The following examples show ways in which the invention has been practiced but should not be construed as limiting the invention. In the examples, all parts or percentages are parts or percentages by weight unless otherwise clearly designated or obvious from the context. 
     In these examples, ingredients for the compositions are compounded in a suitable manner, such as on a mill or in a Banbury mixer. Generally the ingredients, less curing agent, are intially blended together at a moderate temperature, e.g., 270° F., for on the order of 2 to 3 minutes. Curing agent, usually peroxide curing agent, is added to the admixed ingredients typically at about a half a minute into the final mixing, while this final mixing continues for approximately 3 to 5 minutes. The compounds are then ready for forming into test shapes and curing to a thermoset condition by heat application. 
    
    
     EXAMPLE 1 
     For this example, an ethylene-propylene-diene terpolymer is selected having an ethylene to propylene ratio of 75 to 25 by weight and having a Mooney viscosity (ML 1+4) of 25 at 121° C. This rubber was compounded with various finely divided aluminum silicate fillers to prepare several test batches. The weight proportions of these ingredients in each test batch, unless otherwise further detailed hereinbelow, plus the weight of other substituents used in the compounding of the batches, are as follows: 
     
         ______________________________________INGREDIENT       WEIGHT______________________________________EPDM.sup.1       45.57Filler           45.57Antioxidant.sup.2            0.68Zinc Oxide       2.28Red Lead Oxide   2.28Vinyl Silane.sup.3            1.14Di-cumyl Peroxide.sup.4            2.44______________________________________ .sup.1 Nordel 2722 supplied by DuPont. .sup.2 Polymerized 1,2dihydro-2,2,4-trimethylquinoline .sup.3 Vinyltris (2methoxyethoxy) silane .sup.4 A 40 percent active material, supplied by Hercules under the trade name DiCup 40KE. 
    
     Hercules under the trade name DiCup 40KE. The vinyl silane was used to surface treat the filler prior to compounding of the filler with the other ingredients. 
     In this example, five compositionss were prepared: three &#34;comparative&#34; compositions, which were not representative of the present invention, and two compounds, which were representative of the present invention. For the first comparative composition, a filler was used that was a calcined, white particulate soft clay typically containing 44.48 weight percent Al 2  O 3  (alumina) and 52.41 weight percent Si0 2  (silica) with a balance of residuals including titanium dioxide. This filler had an average particle size above 1 micron, more particularly 1.2 microns, and although having 99 weight percent of the particles passing 20 microns, had only 67 percent finer than 2 microns and only 42 weight percent finer than 1 micron. The second comparative composition contained as a filler of non-calcined, hydrous ultrafine particle size hard clay. Because this clay is hydrous, it was selected for a comparative composition. It, however, was extremely finely divided having 88.5 weight percent of the particles finer than 2 microns with 75 weight percent finer than 1 micron. It had an average particle size of 0.30 micron. 
     One particulate clay filler used to make a compound representative of the present invention had a specific gravity of 2.63, and on typical chemical analysis showed 52 weight percent silica and 44.5 weight percent alumina with a balance of residuals including titanium dioxide. This filler was a fully calcined, hard clay and had 85 weight percent of particles finer than 2 microns with 61 weight percent finer than 1 micron plus 11 percent finer than 0.5 micron. It had an average particle size of 0.88 micron. The second clay filler used in a composition representative of the present invention showed, on typical chemical analysis, 52.41 weight percent silica and 44.48 weight percent alumina, with a residual balance including titanium dioxide. This fully calcined clay has 82 weight percent of particles finer than 2 microns, 69 weight percent more finely divided than 1 micron, and 17 percent finer than 0.5 micron with an average particle size of 0.76 micron. 
     A third comparative composition was prepared with quite similar proportions as described hereinbefore, but containing 46.13 weight percent of the ethylene-propylene- diene rubber and 46.13 weight percent filler. Moreover, in this third control, the filler was available in surface treated condition so that no final silane addition was used. Because of this, the composition was further adjusted to contain 2.30 weight parts of each of zinc oxide and red lead oxide, as well as 0.70 weight parts of antioxidant. The filler used in this comparative composition had an average particle size of 1.60 microns with 58 weight percent finer than 2 microns, 23 weight percent finer than 1 micron, and only 5 weight percent finer than 0.5 micron. 
     Tensile strength results for samples of each compound, as well as 100 percent modulus results, are reported in Table 1 below. 
     
                       TABLE 1______________________________________           TENSILE     100 PERCENTCOMPOUND        STRENGTH    MODULUS______________________________________First Comparative           2136        1469Second Comparative           1990        1461Third Comparative           1811        1231First Invention Compound           2574        1967Second Invention Compound           2610        1972Tensile strength and 100 percent modulus were measuredin pounds per square inch.______________________________________ 
    
     In addition to the highly enhanced physical improvements as noted in the Table, such were achieved without loss in desirable electrical insulating characteristics. 
     EXAMPLE 2 
     This example compares filled materials at a low filler content. The ethylene-propylene-diene terpolymer of Example 1 was again used along with various fillers and other ingredients of Example 1. More particularly, the ingredients, plus their weight proportions used in the compounding of test specimens for this Example, are as follows: 
     
         ______________________________________INGREDIENT      WEIGHT PARTS______________________________________EPDM            100Filler          60Antioxidant     1.5Zinc Oxide      5Red Lead Oxide  6Di-cumyl Peroxide           3.5.sup.1______________________________________ .sup.1 Basis 100 weight parts of all other ingredients. 
    
     In this example, two fillers used in comparative compositions as described in Example 1 were employed. The first filler was the calcined, white particulate soft clay having an average particle size of 1.2 microns. The second filler used to make a comparative sample was the non-calcined, fine particle size hard clay of Example 1. The particulate clay filler used to make a compound representative of the present invention was the filler described in Example 1 having an average particle size of 0.76 micron. 
     Tensile strength results for samples of each compound, as well as 200 percent modulus results, are reported in Table 2 below. 
     
                       TABLE 2______________________________________           TENSILE    200 PERCENTCOMPOUND        STRENGTH   MODULUS______________________________________First Comparative           1160       700Second Comparative           1600       650Invention Compound           1600       900Tensile Strength and 200 percent modulus were measuredin pounds per square inches______________________________________ 
    
     The foregoing examples clearly establish that the novel insulating compositions, and the novel electric cables fabricated using these insulating compositions, exhibit a highly desirable and unexpected improvement resistance in modulus tensile and hardness not heretofore obtainable in low swelling EP rubber insulation. 
     It will be obvious that many changes, substitutions and alterations can be made in the compositions, procedures and devices hereinbefore described without departing from the scope of the invention herein disclosed and it is our intention to be limited only by the appended claims.