Abstract:
The disclosure of this application relates to compositions based on alkylene-alkyl acrylates and silanol condensation catalysts which are useful in the preparation of water-curable, silane modified alkylene-alkyl acrylate copolymers, capable of extrusion about wires and cables.

Description:
SUMMARY OF THE INVENTION 
     The invention disclosed in this application relates to compositions, based on alkylene-alkyl acrylate copolymers and silanol condensation catalysts, which are useful in the preparation of water-curable, silane modified alkylene-alkyl acrylate copolymers. More particularly, this invention relates to a process of extruding water-curable, silane modified alkylene-alkyl acrylate copolymers and compositions based thereon about wires and cables to provide coverings, such as insulation and jacketing, characterized by improved properties. 
     BACKGROUND OF THE INVENTION 
     Silane modified alkylene-alkyl acrylate copolymers described in U.S. Pat. No. 4,328,323 granted May 4, 1982 and 4,291,136 granted Sept. 22, 1981, are particularly desirable for use in extrusion applications as these polymers and compositions based thereon can be cured by a simple water treatment, as opposed to the more conventional peroxide cure, to crosslinked products of high crosslinked density. As a result, silane modified alkylene-alkyl acrylate copolymers, as described, and compositions based thereon are especially useful in extrusion applications, being capable of extrusion under a wide latitude of processing conditions. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention, in one aspect, relates to compositions, based on alkylene-alkyl acrylate copolymers and silanol condensation catalysts, which are particularly useful in an improved process of extruding water-curable, silane modified alkylene-alkyl acrylate copolymers and compositions based thereon about wires and cables. 
     In the process aspect of this invention, an alkylene-alkyl acrylate copolymer or composition based thereon is admixed with a silanol condensation catalyst, the resultant composition soaked with an organo titanate catalyst and the soaked composition admixed with a polysiloxane or monomeric silane with the result that the alkylene-alkyl acrylate copolymer reacts with the polysiloxane or monomeric silane to form a product, containing a water-curable, silane modified alkylene-alkyl acrylate copolymer, which is then extruded about a wire or cable. 
     The process, as described, results in coverings, such as insulation and jacketing, about wires and cables which are characterized by a number of improved properties, as shown by the data of the examples of this application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing is a schematic view of the preferred system, including the extrusion apparatus for carrying out the process of this invention using a 21/2 inch extruder. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As previously stated, the present invention, in one aspect, relates to compositions based on an alkylene-alkyl acrylate copolymer and a silanol condensation catalyst. 
     The alkylene-alkyl acrylate copolymers are known copolymers, normally solid at ambient temperatures, produced by reacting an alkene with an alkyl acrylate. 
     Suitable alkenes include ethylene, propylene, butene-1, isobutylene, pentene-1, 2-methylbutene-1, 3-methylbutene-1, hexene-1, heptene-1, octene-1, vinyl chloride, styrene and the like and mixtures thereof. 
     The alkylene moiety of the alkylene-alkyl acrylate copolymer generally contains from 2 to 18 carbon atoms inclusive, preferably 2 to 3 carbon atoms inclusive. 
     Suitable alkyl acrylate monomers which are copolymerized with the alkenes fall within the scope of the following formula: ##STR1## wherein R 4  is hydrogen or methyl and R 5  is alkyl having one to 8 carbon atoms inclusive. Illustrative compounds encompassed by this formula are: methyl acrylate, ethyl acrylate, t-butyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate and the like and mixtures thereof. 
     Alkylene-alkyl acrylate copolymers generally have a density (ASTM D 1505, with conditioning as in ASTM D 147-72) of about 0.92 to about 0.94 and a melt index (ASTM D 1238 of 44 psi tested pressure) of about 0.5 to about 500 decigrams per minute. 
     For purposes of the present invention, the preferred copolymer, generally a copolymer of ethylene-ethyl acrylate, has about one to about 50 percent by weight combined alkyl acrylate, preferably has about 2 to about 40 percent by weight combined alkyl acrylate. 
     Silanol condensation catalysts, that is compounds which accelerate the crosslinking of the watercurable, silane modified alkylene-alkyl acrylate copolymers are also well known compounds. Among such compounds can be noted the metal carboxylates such as dibutyltin dilaurate, stannous acetate, stannous octoate, lead naphthenate, zinc octoate, iron-2-ethyl hexoate and the like, organic bases such as ethylamine, hexylamine, dibutylamine, piperidine and the like, and acids such as mineral acids and fatty acids and the like. 
     For purposes of this invention, dibutyltin dilaurate is preferred. 
     Exemplary of organo titanate compounds which catalyze the reaction between the polysiloxane or monomeric silane and the alkylene-alkyl acrylate copolymer, and are used to soak the alkylene-alkyl acrylate compositions, as previously described, are those falling within the scope of Formula II. 
     
         Ti(OR.sup.2).sub.4                                         Formula II 
    
     wherein each R 2 , which can be the same or different, is hydrogen or a hydrocarbon radical having one to 18 carbon atoms inclusive, preferably one to 14 carbon atoms inclusive. By definition of a titanate, one R 2  must be a hydrocarbon radical. 
     Exemplary of suitable hydrocarbon radicals are alkyl radicals such as methyl, ethyl, n-propyl, isopropyl, butyl, octyl, lauryl, myristyl, stearyl and the like, cycloaliphatic radicals such as cyclopentyl, cyclohexyl and the like, aryl radicals such as phenyl, methylphenyl, chlorophenyl and the like; alkaryl radicals such as benzyl and the like. 
     Particularly desirable titanates falling within the scope of Formula II are those wherein each R 2  is alkyl having one to 18 carbon atoms inclusive, preferably one to 14 carbon atoms inclusive, exemplified by tetrabutyl titanate, tetraisopropyl titanate and the like. 
     Other suitable organo titanates are the organo titanium chelates such as tetraoctylene glycol titanium, triethanol amine titanate, titanium acetyl acetonate, titanium lactate and the like. 
     Polysiloxanes, which are suitable for purposes of this invention, contain repeating units of the formula: ##STR2## wherein R is a hydrocarbon radical or oxy substituted hydrocarbon radical, each V, which can be the same or different, is hydrogen, a hydrocarbon radical or a hydrolyzable group; Z is a hydrolyzable group; n is an integer having a value of one to 18 inclusive and x is an integer having a value of at least 2, generally 2 to 1000 inclusive, preferably 5 to 25 inclusive. 
     Illustrative of suitable hydrocarbon radicals for R are alkylene radicals having one to 18 carbon atoms inclusive, preferably one to 6 carbon atoms inclusive, such as methylene, ethylene, propylene, butylene, hexylene and the like; alkoxy radicals having one to 18 carbon atoms inclusive, preferably one to 6 carbon atoms inclusive such as methyloxymethyl, methyloxypropyl, ethyloxyethyl, ethyloxypropyl, propyloxypropyl, propyloxybutyl, propyloxyhexyl and the like. 
     As stated, each V can be hydrogen, a hydrocarbon radical or a hydrolyzable group. Illustrative of suitable radicals are alkyl radicals having one to 18 carbon atoms inclusive, preferably one to 6 carbon atoms inclusive such as methyl, ethyl, n-propyl, isopropyl, n-butyl, n-hexyl and the like; alkoxy radicals having one to 18 carbon atoms inclusive, preferably one to 6 carbon atoms inclusive, such as methoxy, ethoxy, propoxy, hexoxy, dodecyloxy, methoxyethoxy and the like; aryl radicals having 6 to 8 carbon atoms inclusive such as phenyl, methylphenyl, ethylphenyl and the like; cycloaliphatic radicals having 5 to 8 carbon atoms inclusive such as cyclopentyl, cyclohexyl, cyclohexyloxy and the like. 
     Z, as previously stated, is a hydrolyzable group among which can be noted alkoxy radicals as previously described for V and R; oxy aryl radicals such as oxyphenyl and the like; halogens such as chlorine and the like. 
     Polysiloxanes containing repeating units falling within the scope of Formula III can be prepared as described in U.S. Pat. No. 4,328,323 by condensing and polymerizing a silane falling with the scope of Formula IV. ##STR3## wherein R 1  is a hydrocarbon radical, as for example, an alkyl radical having one to 18 carbon atoms inclusive, preferably one to four carbon atoms inclusive such as methyl, ethyl, n-propyl, isopropyl, n-butyl and the like; alkylene radicals having two to 18 carbon atoms inclusive, preferably two to 4 carbon atoms inclusive such as etylene, propylene and the like; aryl radicals having six to ten carbon atoms inclusive such as phenyl, benzyl and the like. Other variables are as previously defined. 
     Exemplary of suitable silanes falling within the scope of Formula IV are the following: ##STR4## 
     Preferred polysiloxanes have a viscosity of about 0.5 poise to about 150 poise, preferably about one to about 20 poise as determined by a Gardner-Holdt bubble viscometer at a temperature of 25° C. 
     As previously stated, monomeric silanes, for instance, silanes falling within the scope of Formula IV can be used in lieu of the polysiloxanes. 
     Referring now to the accompanying drawing, a pelletized mixture of alkylene-alkyl acrylate copolymer and silanol condensation catalyst is fed from resin feed stock bin (3) to a dryer system (5) by means of a vacuum tube (7) and vacuum loader (9), through conveyer line (1). 
     The amount of silanol condensation catalyst admixed with the alkylene-alkyl acrylate copolymer is sufficient to accelerate the water-cure of the silane modified alkylene-alkyl acrylate copolymer. As a rule, this amount is about 0.001 to about 0.5, preferably about 0.005 to about 0.1 percent by weight based on the weight of the copolymer. 
     Admixing of the silanol condensation catalyst, the alkylene-alkyl acrylate copolymer and desired additives is carried out in a compounding system such as a twin screw extruder wherein the ingredients are melted and mixed. The mixture is subsequently pelletized by methods known in the art. 
     The pelletized mixture of alkylene-alkyl acrylate copolymer and silanol condensation catalyst is dried in dryer system (5) to insure that the water content thereof is below about 500 ppm, preferably below about 300 ppm. 
     From dryer system (5), the pelletized mixture is fed through conveyer line (11) and into receiver (13) of vertical blender (15) by means of vacuum loader (17). 
     Vertical blender (15) contains an open helix mixer (19) which aids in dispersing the organo titanate throughout the pelletized mixture. The organo titanate is pumped into the top of vertical blender (15) from reservoir (23). Helix mixer (19), driven by motor (25) through gear reducing driving belt (27) and uplifting agitator (not shown) of vertical blender (15) thoroughly mix the pellets and the organo titanate. 
     Residence time of the pelletized mixture in vertical blender (15) is sufficient to soak the organo titanate into the pellets as evidenced by absence, essentially, of liquid (wetness) on the surface of the pellets. 
     The resultant soaked pellets drop directly into the hopper (2) of an extruder assembly and are contacted therein with polysiloxane or monomeric silane pumped from reservoir (21). 
     The amount of silane &#34;reactant&#34; fed into hopper (2) is generally about 0.05 to about 10, preferably about 0.3 to about 5 percent by weight, based on the weight of the copolymer. 
     The amount of organo titanate used to soak the pelletized mixture, previously defined, is sufficient to inhibit the adverse effects of moisture, present in the composition or generated therein during processing. Generally, the weight ratio of organo titanate to polysiloxane or monomeric silane is at least about 0.1 to 1, generally about 0.5 to about 10 to one, preferably about 1 to about 5 to one, and most preferably about 1 to about 3 to 1. 
     The total reaction mixture containing the alkylene-alkyl acrylate copolymer, the silanol condensation catalyst, organo titanate and silane &#34;reactant&#34; passes into the extruder wherein the reaction mixture is mixed, reacted and extruded out of the extruder onto a wire. 
     In the extruder assembly shown, designed by Geoffrey Brown, the reaction mixture passes through a series of zones of the extruder assembly, being in sequence, a feed zone, a transition zone, a metering zone, a reaction zone defined by a static mixer and is extruded from the extrusion die onto a wire. 
     Feed zone function is to convey the pellets forward to maintain a constant supply of material to the next section. Typical temperatures are about 100° C. to about 180° C. preferably about 140° C. to about 160° C. for this zone. 
     Transition zone function is to compress the pellets into a shallower channel. The tightly packed pellets are deformed, sheared, and for the most part, melted in this section due to a combination of mechanical energy input and thermal energy from the hot barrel. Typical temperatures are about 130° C. to about 200° C., preferably about 150° C. to about 175° C. for this zone. 
     Metering zone function is to complete the melting process, to provide a steady and metered output rate, and to pressurize the melt to force it through the die. Typical temperatures are about 130° C. to about 220° C., preferably about 160° C. to about 190° C. for this zone. 
     Reaction zone function is to allow sufficient time at the metering zone temperature to insure that complete reaction or grafting has occurred. 
     To the silane modified copolymers can be added various additives in amounts well known in the art. This is conveniently accomplished by formulating compositions containing additives, alkylene-alkyl acrylate copolymers and silanol condensation catalysts and processing the compositions as described. 
     Exemplary of such additives are those disclosed in U.S. Pat. No. 4,328,323 and U.S. Pat. No. 4,353,997, among which can be noted halogenated flame retardant additives, antimony oxide, ground calcium carbonate, clay and the like. 
     Also, the compositions of this invention can contain hydrous and/or water-releasing fillers. 
     These fillers, which are generally used in amounts of about 1 to about 250 percent by weight based on the total weight of the copolymer can be exemplified by the following: hydrous fillers such as hydrous clay, non-conductive carbon blacks, conductive carbon blacks such as Ketjen Black EC, zinc borate, talc, and the like; water-releasing fillers such as aluminum trihydrate, magnesium hydroxide, calcium hydroxide, barium hydroxide, zinc hydroxide, precipitated calcium carbonate, basic magnesium carbonate and the like. 
     Particularly desirable compositions contain, as additives, aluminum trihydrate or magnesium hydroxide and a scorch inhibiting compound. 
     Among suitable scorch inhibiting compounds can be noted alcohols, particularly alcohols having a boiling point higher than 100° C. such as octanol, decanol, dodecanol, myristyl alcohol, stearyl alcohol and the like. Also suitable are esters of such alcohols such as dioctyl phthalate, dioctyl adipate, dioctyl succinate and the like. 
     Plasticizers for vinyl resins are also suitable as scorch inhibiting compounds. These plasticizers include cyclic plasticizers such as phthalate plasticizers among which can be noted butyl decyl phthalate, butyloctyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, dicyclooctyl phthalate and the like. Phosphate esters such as cresyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, triphenyl phosphate and the like; trimellitic acid esters such as the n-octyl and n-decyl ester of trimellitic acid and the like; acyclic plasticizers such as the di(2-(2-butoxyethoxy)ethyl) ester of adipic acid, the di(2-ethylhexyl) ester of adipic acid, the diisodecyl ester of adipic acid and the like; oleic acid esters such as butyl oleate, glyceryl trioleate, methyloleate and the like as further disclosed in a publication entitled Vinyl Plasticizers, Report No. 62, April 1970, Stanford Research Institute, Menlo Park, Calif. 
     Suitable scorch inibiting compounds, that is compounds which reduce scorch and do not undergo a crosslinking reaction with the components of the composition to which they are added are used in amounts sufficient to reduce scorch, generally in amounts of about 0.5 to about 20 percent by weight, preferably about 2 to about 10 percent by weight based on the weight of the total composition. 
     The curing or crosslinking of the silane modified alkylene-alkyl acrylate copolymer and compositions based thereon is effected by exposing the copolymer to moisture. The moisture present in the atmosphere is usually sufficient to permit curing to occur over a period of 48 hours. 
     The rate of curing, in a matter of 30 minutes, can be accelerated by exposure to an artificially humidified atmosphere or immersion in water and heating to elevated temperatures or by exposure to steam. 
     Generally, curing is effected at temperatures on the order of about 23° C. to about 180° C., preferably about 70° C. to about 100° C. 
     In Example 1 which follows, the composition was extruded onto a #14 AWG copper wire using a system as shown in the accompanying drawing wherein the extruder had: 
     1. a 30 to 1 length to diameter grooved barrel (grooved at Feed Zone). 
     2. a 20 to 1 polyethylene compression screw, having a 2.5 inch diameter, which was tapered and cored, allowing for control of temperature by feeding water into the core. 
     3. four sets of radial mixing pins equally spaced along the metering zone. 
     4. band or cylindrically cast heaters, providing independent temperature control of each zone. 
     A run, Example 1, was carried out using the system shown in the accompanying drawing wherein the materials used were a pelletized mixture of dibutyltin dilaurate and Formulation I; tetraisopropyl titanate and polysiloxane. 
     
         ______________________________________Formulation I______________________________________               Percent by WeightCopolymer of Ethylene-Ethyl               56.15AcrylateContaining 15% by Weight CombinedEthyl Acrylate-Melt Index 1.6Talc Coated with Zinc Stearate               21.68Antimony oxide      2.50Calcium Carbonate   2.50Ethylene (Bis-tetrabromophthalimide)               16.29(Flame Retardant Additive)Polymerized 1,2-dihydro-               0.582,3,4-trimethylQuinoline (Antioxidant)Vinyl-tris(2-methoxy) Silane               0.30               Percent by Weight Based               On Formulation IDibutyltin Dilaurate               0.04Tetraisopropyl Titanate               0.79Polysiloxane        0.80Weight Ratio of Organo Titanate to               ˜1Polysiloxane______________________________________ 
    
     The polysiloxane used was prepared according to Example 3 of U.S. Pat. No. 4,328,323 with the exception that 235 grams (1.03 moles) of ethyl laurate were substituted for ethyl benzoate. 
     The polysiloxane can be depicted, ideally, as follows: 
     
         ______________________________________ ##STR5## 
    
     
         ______________________________________Moisture content of pelletized mixture                   149     ppmafter dryingSoak time of pelletized mixture of                   10      minutesdibutyltin dilaurate and Formulation Iwith organo titanateScrew speed             94      rpmScrew coolingwater fed into core at a temperature of 53° C.and rate of 75 gallons per hour - temperatureat removal - 68° C.Rate of extrusion       199     lbs. per                           hourWire speed              500     feet per                           minute______________________________________ 
    
     
         ______________________________________Temperature and PressureProfile  Feed Transition                 Metering  Reaction  Zone Zone      Zone      Zone    Die______________________________________Tempera- 154    150       154-171 160      204ture ofHeaters, SetTemperature,(°C.)Material 153    159       166     163-175  191Temper-ature, (°C.)Pressure,    --     3200-4600 5000-5500                             5300-5400                                     5200(psi)______________________________________ 
    
     For purposes of conducting the Rheometer test, described below, insulation was stripped from the wire, placed in a water bath, which was at a temperature of 75° C., for 18 hours and then pressed into 0.150 inch thick plaques under the following conditions: 
     
         ______________________________________Pressure           3 TonsTemperature        125° C.Time of Cycle      5 minutes heating              5 minutes cooling______________________________________ 
    
     
         ______________________________________Tests and Test Results______________________________________ Rheometer-ASTMD-2084-75           reported in inch-lbs and indicates           the level of cureNumber of Voids cross-section of uncured insulation           was examined           under 40× magnification and voids           counted per gridThickness of Insulation           37 milsSpark faults    test described in Underwriters           Laboratories Standard UL-44           &#34;Rubber Insulated Wires And           Cables&#34; as revised January 1, 1982,           paragraphs 70-72. This test           determines if there are any minute           holes in the uncured insulation           which would allow the current to           short to ground. UL specifies that           there be no faults in a completed           cable, but industry standards allow           for a maximum of one per 3000 feet           of cable as made in a commercial           run. The UL requirement is then           met by cutting out the voids or           faults from the cable and splicing           the ends together.Stability       calculated from diameter           fluctuations and expressed as ±           percent of total output. Normal           deviation of extrusion lines is ±           2 percentTest ResultsRheometer       42 inch-lbs.Number of Voids 15 per gridSpark Faults    0 per 13,500 feet of insulationStability       ±1.8 percent______________________________________ 
    
     A second run, Control 1, was carried out in essentially the same manner as Example 1, using the same materials, with the exception that the dibutyltin dilaurate, tetraisopropyl titanate and polysiloxane were admixed and introduced into the system as a mixture at the hopper (2). 
     
         ______________________________________Test Results______________________________________Rheometer       37 inch-lbsNumber of Voids 468 per gridSpark Faults    0 per 16,000 feet of insulationStability       ±9.0 percent______________________________________ 
    
     In order to further show the advantages of adding the silanol condensation catalyst to the alkylene-alkyl acrylate copolymer, three runs were carried out essentially as described with respect to Example 1, using Formulation I and the same extruder system with the following exceptions: 
     1. Smooth barrel extruder was used 
     2. An Acrison Horizontal Blender was used in lieu of the vertical blender shown in the accompanying drawing 
     3. Control 2 was carried out by adding a mixture of organo titanate, polysiloxane and silanol condensation catalyst to Formulation I in the Acrison Horizontal Blender 
     4. Control 3 was carried out by adding a mixture of organo titanate and polysiloxane to a pelletized mixture of silanol condensation catalyst and Formulation I in the Acrison Horizontal Blender 
     5. Example 2 was carried out in a manner similar to Example 1 by combining the silanol condensation catalyst with Formulation I, soaking the pelletized mixture with organo titanate in the Acrison Horizontal Blender and adding the polysiloxane to the soaked composition at the extruder throat as in Example 1 
     
         ______________________________________Percent By Weight Based on Formulation I       Example  Control  Control       2        2        3______________________________________Dibutyltin Dilaurate         0.03       0.05     0.04Tetraisopropyl Titanate         0.41       0.36     0.37Polysiloxane (same as         0.90       1.08     1.12Example 1)Moisture Contentof pelletized mixture         233 ppm    --       --of Formulation I         --         171 ppm  190 ppm______________________________________ 
    
     
         ______________________________________Operating Conditions of Extruder Assembly        Example Control   Control        2       2         3______________________________________Temperaturesset/actualin °C.Feed Zone      138/--    137/--    154/--Transition Zone          149/149   154/156   165/162Metering Zone  179/180   177/180   182/184Reaction Zone  176/183   177/189   182/193Die            204/199   204/199   204/203PressurespsiTransition Zone          1200-2400  400-3000  800-2600Metering Zone  3400-4800 2400-5000 2000-4800Reaction Zone  --        --        --Die            5000      4400      5100Screw Speed, rpm          118       116       116Output Rate, lbs/hr          183       200       200Wire Speed, fpm          500       500       500Screw Cooling,  75        75        75Amount of water, gphTemperature of Water in           81        81        79°C.Temperature of Water out,           88        91        93°C.PropertiesRheometer       40        42        55Voids           5         30        40Spark Faults   0 per     14 per    0 per          9000 ft.  13,500 ft.                              1000 ft.Stability (%)  ±7.6   ±16.8  ±15.3Thickness of Insulation          33.5 mils 37.5 mils 37.5 mils(average)______________________________________ 
    
     If desired mixtures of reactants, catalyst, additives and the like can be used if so desired. 
     Also, it is to be understood that within the essence of the claimed invention, the operating conditions of the extrusion system such as temperatures, pressures and the like can be varied to accommodate the actual composition being extruded, output of the extruder and the like. 
     The disclosures of all patents noted are incorporated herein by reference.