BACKGROUND OF THE INVENTION A number of compositions have been prepared pursua to prior patented technology which have very superior properties. One such composition is covered by the Pat ents Nos. 4,125,586 and 4,247,446. The composition has excellent properties but does have a relatively hig cost, both in material content and in the processing of the material as well as in the final product as applied as an insulation on wire. One of the cost factors in- volved in the high, quality material of the 4,123,586 and 4,247,446 patents composition is that the processing costs are relatively high, because of the unique combina*- tion of ingredients which are employed to achieve the superior properties and the unique manner in which such ingredients must be combined to achieve the unique set of properties as set forth, in the patents.

Accordingly, it has been an object of the industry to achieve a desirable combination of superior propertie but to do so at a lower cost both in the ingredients or materials employed and in the processing technology as the ease of processing of a material can substantially affect the cost of the final product. For example, as has been pointed out in the 4,123,586 patent, there is

a requirement, deemed essential heretofore, for separate processing and preparation of the flame retardant ingre¬ dient by a method described in the U.S. Patent 4,209,566 The processing of the higher specification material of the 4,123,586 and 4,247,446 patents, including the separate processing of the flame retardant ingredient of the 4,209,566 patent, leads to a lower rate of productio of the compound for a given set of manpower and equipmen and, accordingly, to a higher cost. This production rat is effectively a half of the rate of production accordin to this invention, but is for the relatively higher cost and higher specification materials of the patents 4,123,586 and 4,247,446 and its related processing by U.S. Patent 4,209,566. A further concern of the industry is to find a com¬ position which not only has a lower cost and which is easier to process to a final insulation layer on a wire or cable, but which also meets a very -substantial num¬ ber of industry requirements as, for example, the stan- dard requirements"established by various- testing agencie such as Underwriters Laboratory including, for example, the -l test.

The patents 4,123,586, 4,247,446 and 4,209,566 are assigned to the same assignee as the subject application

OBJECTS OF THE INVENTION It is accordingly one object of the present inventi to provide an insulating composition which has superior flame retardance combined with superior wire insulation properties at a relatively low cost and methods of formin Another object of the present invention is to provi a composition as described in the first object above whi is relatively easy to process and to form into the pelle and into the wire insulation directly on a wire. Another object is to provide a composition at rela¬ tively low cost which not only has exceptional flame re¬ tardant properties and good physical prioerties for incl sion in wire but, in addition, has very desirable elec¬ trical properties for use as a wire insulation. A further object of the present invention is to pro vide a composition which has high, flame retardancy and which has properties suitable for use as a power cable at voltages up to 35 ilovolts and above at suitable wal thicknesses and novel cable products insulated therewith. Another object of the invention is to provide a nove insulating composition suitable for use in wet environ¬ ments and damp environments, and which at the s me time has good flame retardant properties and which has a rela¬ tively low cost. Another object is to provide a wire insulation compo sition which is qualified for use in nuclear applications and, specifically, which will pass the tests specified in IEEE-323 and IEEE-383.

The foregoing object includes the subsidiary object of providing a composition at relatively low cost which passes the LOCA test, which is the worst type of accident which occurs in a nuclear facility and is an accident resulting in or associated with the loss of coolant in the reactor.

Another object of the present invention is to pro¬ vide a composition which is useable under UL specifica¬ tions in applications at up to 105°C and higher in en¬ vironments where, the cable is exposed to petroleum pro- ducts such as in oil well applications or in locomotive applications.

Another object is to provide a composition which performs well at relatively thin wall thicknesses of the order of 5 or 10 mils and which is accordingly suitable for use in electronic wire type applications . and wire products formed therewith.

It is a further object of the present invention to provide an insulating composition having high, dielectric strength, of the order of 1300 volts per mil. Another object is to provide an insulating compo¬ sition which, passes Both, the UL -l test and passes a 100-hour U-bend test as specified in the UL-1072 test¬ ing procedure on an unshielded power cable construction. Other objects will be in part apparent and in part pointed out in the description which follow _t

BRIEF DESCRIPTION OF THE DRAWING The drawing comprises a perspective view of an in¬ sulated conductor comprising a metallic element having a flexible polyolefin insulation thereabout.

O.MPI

W.Σ-Ό

SUMMAR OF THE INVENTION Objects of this invention are achieved by pre¬ paring an insulating composition by first combining polyolefin polymer with a substantial proportion of an organic brominated flame retardant; a substantial proportion of mineral flame retardant, such as antimony oxide; and a substantial proportion of a silicone- treated clay material, and by combining these ingre¬ dients with a relatively smaller proportion of lead stabilizer compound and antioxidant compositions.

After the aforementioned ingredients are first combined, there is then added to this first combination, but at a lower temperature, a second combination of silicone fluid and organic peroxide. Following the second addition, the material is formed into the desired, con¬ figuration as insluation on a wire and the composi¬ tion is heated under pressure to decompose the peroxide and to cause a chemical crosslinking of the material. Optionally, the peroxide component can be omitted and the composition can be crosslinked by radiation as with high voltage electrons.

DESCRIPTION OF A-PREFERRED EMBODIMENT Polyolefin as used herein refers to polyethylene as a preferred component, but the polyolefin may also be co- polymers of ethylene, including but not limited to ethyl- ene ethyl acrylate, ethylene vinyl acetate copolymers, ethylene-propylene copolymers, terpolymers and quatrepoly mers such as EPDM. Also, the polyolefin may be either of the high density or the low density polyethylene or may be polyallomer. The organic halogenated flame retardant may prefer¬ ably be the decabromodiphenyl oxide or decabromodi henyl ether, but may also be ethylene bis (.tetrabromophthali- mide) sold commercially under the designation BT-93 by Saytech Corporation, or a brominated diphenyl oxide of a lover degree of bromination. In a more general se s _^

the stable organic halogenated flame retardant, such as the chlorinated flame retardant available commercially under the trade name Dechlorane of Hooker Chemical Corpor ation, may be employed. The antimony oxide flame retardant used in the prese invention is the conventional or standard powdered compou The silicone-treated clay may be a commercially avai able composition sold under the designation Translink 37 Clay by the Freeport Kaolin Company. Alternatively, it may be a similar clay composition as taught in column 2 of U.S. Patent 3,148,169 assigned to the same assignee as the subject application.

Dibasic lead phthalate composition or ingredient may optionally be used in the composition of this invention and may be any organic lead compound in which the lead pr portion is roughly equivalent to that of the dibasic lead phthalate or greater. For example, other .organic com¬ pounds which have low volatility and which result in suit able stabilization properties may be employed but the di- basic lead phthalate is the preferred compound for this i gredient. By stabilization is meant that the lead compou can scavenge free halogen from the composition.

An antioxidant ingredient preferably includes the lower cost antioxidants such as commercially available Flectol H, commercially available Santowhite Crystals, or the combination as brought out in the specific example of Table I below where the composition cost is desirably kept- at relatively low levels and where the temperature of performance of the composition is also at a relatively low level of about 105°C. However, where higher tempera¬ ture performance is desirable, it is possible to achieve such higher temperature performance by inclusion of anti¬ oxidants as described with reference to Table V.

Considering next the silicone fluid ingredient, the silicone fluid is a reactive silicone such, as is describe

and set forth in the U.S. Patent 4,209,566,

The peroxide curing agent as indicated above may be an organic peroxide which decomposes, i.e., generates free radicals, at the elevated temperatures above the basic mixing temperatures and may be, as in the examples given, dicumyl peroxide. Alternatively, materials sold under the commercial designation Vul-Cup R may be employ although the cost is higher than that of the dicumyl peroxide. Such organic peroxides are known in the art an in the patent literature directed to this art and are described in part in the patents referenced above which patents are incorporated herein by reference,

Silicone gum can be used as an optional ingredient and is accordingly included as such, in Example 1 below, as is the dibasic lead phthalate above. The silicone gu useful in the novel composition of this invention is de¬ scribed in copending application Serial o 196,989 file October 14, 1980 and assigned to the same assignee as the subject application _* The copending application 196,989 is incorporated herein by reference as is copending appli cation. Serial No. (attorney Docket 41WC-2135) filed July 21, 1981. The benefits pointed out in the co¬ pending application will be obtained in reference to the composition of the present invention.

EXAMPLE 1

Referring to Table I, a set of ingredients and pro¬ portions of these ingredients is set forth for both a pre¬ ferred concentration range of ingredients (given in pro- portions of parts by weight) and also for an operable range of concentrations.

The first seven ingredients as described in the Table I are thoroughly mixed in a Banbury mixing apparatus as follows: The seven ingredients are first introduced into a high intensity mixer, such as a Banbury, which has an initial temperature of about 150°F. The mixing action of the high intensity mixer generates heat in the com¬ position and the composition temperature is measured during the mixing. The composition is dropped from the high intensity mixer when the chart or apparatus tempera¬ ture reaches about 270°F. The heat which it has received is heat of mixing and no external heat need be applied for this temperature increase. The batch, of material, which has a probe temperature of about 280 to 290°F, is milled on a plastic mill after removal from the high in¬ tensity mixer. The material on the plastic mill is banded and taken off as sheets.

The sheet product is later blended with a mixture of liquid silicone fluid and a peroxide crosslinking agent, specifically, dicumyl peroxide. This blending is at a lower temperature, below the decomposition temperature of the peroxide crosslinking agent. The composition is blended in the high intensity mixer at a temperature of approximately 220 to 240°F maximum.

Following the introduction of the silicone fluid and the peroxide crosslinking agent to the compound, it is again rolled on a plastic mill into sheet form from which it can be cut into strip and pelletized for later use in an extruder.

TABLE I

INGREDIENTS USEFUL RANGE ^" PREFERRED RANG

Polyethylene 100 100 Decabromodiphenyl oxide 10-50 20-40 Antimony oxide 3-30 10-20 Silicone-treated clay* 5-50 10-30 Dibasic lead phthalate 0-20 5-10 Silicone gum 0-20 0-10 Flectol H** 0-10 1-5 Santowhite Crystals*** 0-5 0-3 Silicone fluid 1-5 1-3 Peroxide crosslinking agent 1-5 2-5 (Dicumyl peroxide)

* Prepared according to teaching of column 2 of U.S. Patent 3,148,169 or similar method,

** Flectol H is a commercial designation for polymerized

1,2-dihydro-2,2,4-trimethyl quinoline. ^■ -kzk Santowhite Crystals is a commercial designation for 4,4'- hiobis-(6 tert-butyl-m-cresol) , ****Silicone fluid as described in U.S. Patents 4,123,586 4,247,446 or similar composition.

_/ ^" BU Z - ^' i

EXAMPLE 2

A composition prepared in this manner was extruded onto a #14 AWG wire as a 30 mil insulating sheath. It was crosslinked by subjecting the wire insulation to heating under pressure.

The crosslinked composition was demonstrated to have exceptionally good physical properties for use as a wire insulation including a high tensile value of over 2100 psi, and a high elongation percentage value of over 400%.

A table of data, Table II, is provided here giving the test results of a series of standard tests performed on the wire insulation formed in accordance with the method of the present invention as set forth above.

TABLE II TEST DATA

Construction: #14 Solid bare, 0.03" wall

Test Specimen Identification: ID-92-44-1

Original Tensile, PSI: 2143

Original Elongation, %: 447

Hot Modulus*: 88.5

Heat Aging according to standard UL testing procedure:

7 days at

121°C, % RTZRD**: 103/98

136°C, % RT/ RE: 100/93

158°C, 1 RT/ RE: 95/72 at 97°C:

30 days, I RT/%RE: 103/98

60 " " " 92/76

QQ 11 M II 105/94

120 " " 102/83

150 " " " 100/82 at 113°C:

30 105/79

60 " 103/85

90 " 98/69

120 " " " 103/71

150 " " " 95/66 θ Index by standard UL test in % oxygen concentration: 29.5

V -1 by standard UL test: PASS

Cold bend at -65°C/1 hour: PASS

4 hrs. at 70°C #2 ASTM Oil:

7- Swell: 4.6

% RT/%RE**: 86/92

* ^' ζt- of oH t-n 1 DC.? -, - r-.ι—i en" n - ^' 1 Λ on crf-V_ β tensile strength in PSI measured. ** ZRT/ RE — Percent of original tensile retained and percent original elongation retained.

TABLE ^" II Ccon'-t) 42 hours Air Bomb, 7. RT/7»RE (standard UL test) 102/87 CONDUCTOR CORROSION by standard UL test

7 days at 121°C _: PASS 7 days at 136°C: PASS

Dielectric Strength, V/mil, by Quick Rise at 500 volts per second c cording to UL and ICEA standard tests 1382 Insulation Resistance "K" Constant by. ICEA standard: 82,765

EM-60 at 75°C Water Test according to UL and ICEA standard test:

1 day: Specific Inductive Capacitance: 2.35

% Power factor at 80V/mil 0.93 Stability factor: 0.04

7 days:Specific inductive Capacitance; 2,34

% Power factor at 80V/mil 0.66

14 days:Specific Inductive Capacitance: 2,35

% Power factor at 80V/πil 0.57 Stability factor 0,02

% Increase in Specific Inductive

Capacitance

1-14 days 0

7-14 days 0.43 IEEE 383 & 323 Qualification: heat aged to simulate 40-year thermal life, then received 220 megarads of gamma radiation prior to a 33-days LOCA cycle and subsequently hipot to 2.4 KV/min. PASS

With reference to the experimental results reported in Table II above, a number of important observations can be made with respect to the efficacy of the cross¬ linked composition as a wire and cable insulation. One such observation is that, to the knowledge of the applicant, no prior composition which displays VW-1 properties (passes the VW-1 test) , also has the capabil¬ ity of passing the U-bend test when employed as an insula tion on an unshielded cable. Prior cables having an insu- lation layer which passed the VW-1 test required a shield¬ ing jacket to pass the U-bend test. Accordingly, the in¬ sulation composition and the cable formed with this com¬ position is quite novel and unique.

In addition to the unique combination of an unshielde cable which passes both the U-bend and VW-1 tests, the

Table II of test results indicates that the novel compo¬ sition of this invention has an oxygen index of 29.5, a value which is quite high for a composition having the other combination of properties. Another observation regarding the data of Table II is that the dielectric strength is quite high for a flame resistant material, particularly for a VW-1 grade material and more particularly for one with an oxygen index .of 29.5 Such a combination of properties makes the novel composi- tion of this invention uniquely suitable for use in power cable. Use in power cable is particularly suitable be¬ cause of the relatively low cost of the novel composition • and-the power cable insulated with this novel composition, In part, the low cost of the novel composition is the result of the simpler processing of this composition. For example, standard equipment and standard processing steps may be employed even though the compound produced is quite unique and novel.

O. Pt

In Table II, it will be observed that the tests of heat aging at 113°C gave results which establish that the loss of physical properties and, particularly, ten¬ sile and elongation properties, as a function of time is unusually slow. The UL test of heat aging to qualify a composition for use at 105°C is the heat aging at 113°C for 30, 60 and 90 days without a major loss of the tested properties. The Table II results evidence that the novel composition of this invention easily passes the UL test but also exceeds it in that the Table II data shows only minor loss of properties beyond 90 days and, in fact, for 120 and 150 days.

From Table II, it is also evident that the high dielectric strength can make possible a thin wall insu- lation of 10 mils or even of 5 mils so that products formed with the insulation of this invention can be used in electronic applications. Noreover, the ease of pro¬ cessing compositions of this invention makes fabrication of such electronic wire feasible,

EXAMPLE 3

A seven conductor control cable was fabricated usin seven strands of the #14 AWG conductor insulated with the 30 mil insulation coating. The individual insulated conductors were the same as that used above in carrying out the tests reported in Table I above. The control cable was then subjected to a burn test and the follow¬ ing data was obtained.

TABLE III 7 conductor control cable con¬ struction subjected to 210,000 BTU IEEE vertical flame test PASS

EXAMPLE 4

The composition prepared as descirbed with reference to the Table I above was employed in preparing a cable article. The cable was formed with a #2 AWG copper con- ductor. An insulating layer having a thickness of 205 mils was formed by compounding and extruding the preferred composition in Table I above, onto the conductor followed by heating the compound at a temperature above the activa¬ tion temperature of the peroxide and subjecting the cable to pressure in a manner known in the art.

The cable product prepared as described here was then subjected to a number of tests and the test results are reported in Table IV below:

TABLE IV TESTS RESULTS

Soak in water at 75°C for 14 days followed by subjecting the cable ^' to a U-bend* test at 15 kilovolts for a period of 350 hours PASS

Sub ect the cable as formed, and without soaking in water, to a dry U-bend test at 20 kilovolts for 100 hours PASS

210,000 BTU vertical flame test on the cable of this example having the 205 mil wall thickness PASS

*The U-bend test is specified as the UL-1072 testing procedure for an unshielded power cable construction.

The foregoing results, particularly those reported with reference to Table II, are reported for an insula¬ ting composition which is used and useable at a basic operating temperature of about 105°C, The actual opera- ting temperature of the composition can be above the

105°C, but reference is made to 105°C because it is the basis of a UL standard which is recognized in the indus¬ try. The composition of the present invention as des¬ cribed above meets the standards of the industry and does function as a 105°C insulating composition.

However, the composition is also inherently capable of functioning at higher temperatures and at higher tem¬ perature ratings. For example, the composition of the present invention will function at a temperature of 125 C and above and this 125°C temperature is again a standard UL temperature grade for an insulating composition. The manner in which the composition as described above is made to serve as a 125 C composition is by incorporating in the composition a combination of antioxidants as follows.

TABLE V

INGREDIENTS WORKABLE RANGE PREFERRED RAN

Polyethylene 100 100

Brominated^aromatic ^{' •} - compound 10-50 20-40

Antimony oxide 3-30 10-20

Silicone-treated clay 5-50 10-30

Dibasic lead phthalate 0-20 5-10

Silicone gum 0-20 0-10 0 2MB-2* 1-10 1-5

Irganox.1010** 1-5 0-3

Silicone fluid 1-5 1-3

Peroxide crosslinking agent

Dicumyl peroxide 1-5 2-5

5 * Zinc salt of a mercapto imidazole

**Sterically hindered di-tertiary butyl phenol

Ingredients marked with * and ** are as set forth in Patent 4,260,661 which is incorporated herein by referenc All other ingredients are as set forth in Table I 20 above.

Where higher temperature insulating compositions are desired, or, in other words, where it is desired to em¬ ploy an insulating composition at a higher use temperatur generally a larger amount of the antioxidant components 25 _. listed in Table V should be employed in the combination of-Table IV for a higher projected use temperature.

To illustrate, if a use temperature of 125°C is sought, then the ratio or proportion of the ZMB-2 ingre¬ dient and also the proportion of Irganox ingredient sub- 30 stantially as set forth in the lower ranges of values in¬ cluded in Table V should be employed. For still higher temperatures of use of the insulating compound prepared pursuant to this invention, employing the ingredients

of Table V in some of still higher conventration ranges set forth for the ZMB and the Irgonox antioxidants will permit such higher use temperatures to be achieved.

As noted above, the peroxide ingredient of the co - position may be omitted and high energy radiation, such as high energy electrons, can be employed to cause cross¬ linking and curing of the coating composition also by methods well known in the art.

In the figure, there is illustrated a central con- ductor 12 about which has been formed an insulating layer 14 prepared pursuant to the present invention. The insulating layer 14 may be in the curable state or may be in the cured state. Also, the cured insulation may be chemically cured or cured by high energy radiation. The product illustrated is an insulated conductor 10, the conductor of which may be solid as. illustrated or stranded.

Although the invention has been described with reference to certain specific embodiments thereof, numer- ous modifications are possible and it is desired to cover all modifications falling,within the spirit and scope of this invention.