MILL MIXING PROCESS FOR COMPOUNDING GAS-PHASE PRODUCED ELASTOMERS

Abstract: There is provided a preferred process for continuous mill mixing which comprises: (i) blending a gas-phase produced elastomer and one or more other compounding ingredients in a dry blender (distributive mixing), (ii) feeding the blend to an open roll mill for compounding into sheets or strips (dispersive mixing). A vulcanizing system can be introduced in either the dry blending (i) or mill mixing compounding (ii) step, but is preferably introduced during dry blending.

Description: MILL MIXING PROCESS FOR COMPOUNDING GAS-PHASE PRODUCED ELASTOMERS Field of the Invention This invention relates to a process for mill mixing granular rubbers, especially gas-phase produced elastomers. More particularly, the invention relates to a continuous mill mixing process using a dry blender and an open roll mill to produce compounded gas- phase produced elastomers, especially EPM and EPDM elastomers. Background of the Invention Until recently, commercial elastomers have been produced in emulsion, solution and suspension/slurry processes. Elastomers produced in these processes are supplied in the form of condensed bales. Sometimes, depending on elastomer building block constituents, they are supplied in friable bales by less dense baling or at extra cost in pellets by underwater pelletizing. To obtain a crumb, granular or powdered form, the dense bales must be physically ground or micropulverized and anti-agglomerants have to be added to reduce sticking problems. The compounding of elastomers supplied in condensed bales is a very costly, labor intensive, energy-consuming multi-step process. It requires sturdy mixing equipment such as internal batch mixers for compounding. In charging large rubber bales and compounding ingredients, there is a substantial initial inhomogeneity and risk of poor reproducibility. Differences in bale density throughout a box or pallet also contribute to mixing variation. The present commercial rubber mixing cycle generally comprises an internal mixer with tangential or intermeshing rotors, a slab-off mill with stock-blender and/or a batch-off mill to homogenize the mixed stocks and to cut the compound to sheets or feeding strips, prior to cooling in batch-off equipment. Alternatively, a dump extruder and a roller die may be used. During the incorporation step of rubber and compounding ingredients such as, for example, carbon black fillers, white fillers, processing oils, activators and processing aids, the dense bales will be crushed by the rotors. Thereafter, distribution and dispersion of the recipe components will take place. High shear stress experienced between the rotor tips and the mixer wall will ensure good compound dispersion but also brings about a time and rotor speed related undesirable heat development. To guarantee good compound dispersion without the risks of overheating curing agents, resulting in compound scorching, batch mixing often requires two stage mixing, especially higher hardness or high compound Mooney stocks. Low hardness compounds need extended mixing time and multiple stage mixing to ensure good polymer dispersion. At the end of each mixing cycle, the ready-made compound requires a batch homogenization step on a batch-off mill for at least 5 minutes, followed by cooling of the mixed stock in a cooling bath of the batch-off unit with subsequent wig wag or sheeting on a storage pallet. Desirably, curatives are added in single-stage mixing at a temperature of around 105°C prior to dumping. Otherwise, they are added on the batch-off mill and well distributed by the stock-blender for some 5 minutes. See Figure 1. In two-stage mixing, -the curatives are added directly into the internal mixer, two minutes after the warming-up process of having fed the first-stage mixed sheets into the mixer again. It can readily be seen that the above-described commercial process used to compound conventional elastomer requires a tremendous amount of energy or shear in the mixing and milling steps. There has been a long-felt need for a vastly simplified approach ~ low cost, reduced labor, faster, preferably continuous mixing and/or milling for compounding elastomers, especially without the requirement of buying new, expensive processing equipment. More recently, it has been discovered that many elastomers previously available only from emulsion, solution and suspension processes could be made in gas-phase processes in a fluidized bed reactor. Surprisingly, it has been discovered that gas- phase produced elastomers provide lower cost, reduced labor, continuous mixing and milling capabilities without using additional processing equipment. Summary of the Invention It is an object of the present invention to provide an elastomeric mill mixing process that is fast, simple, dust-free, less labor intensive, uses less energy (e.g., lower shear), and does not require the purchase of additional expensive equipment for the production of compounded elastomeric products and articles. Accordingly, there is provided a mixing process comprising (i) mixing on a milling device (a) at least one elastomer produced in particulate form as it exits a fluidized reactor, thus avoiding the need to physically granulate the elastomer by post reactor processing, (b) one or more additional ingredients, and optionally (c) a vulcanizing agent, and (ii) removing the mixture from said milling device,. In a preferred embodiment, present invention provides a batch or continuous mill mixing process which comprises (i) introducing at least one gas-phase produced elastomer, and one or more compounding ingredients optionally including a vulcanizing system (curatives) into a high speed mixer a fluid mixer with mixing at ambient temperature such that the elastomer and compounding ingredients, and vulcanizing system when employed are uniformly distributed in a dry blend followed by (ii) passing the uniformly distributed dry blend to an open roll mill to form a dispersed compound; and (iii) cutting the dispersed compound into sheets or strips for removal from the open roll mill. Optionally, sheets or strips of step (iii) can be re-fed to the rollers of a second open roll mill equipped with a stock-blender to obtain a continuous mode and enlarge the dispersion and cooling capacity of the mixing. In a preferred embodiment the vulcanizing system is added during the dry blending step (i). Brief Description of the Drawing Figure 1 is a schematic of conventional mixing applied hitherto using an internal batch mixer, batch-off mill and dispersion mill(s) with stock blenders as it has been commercially practiced using baled elastomers. Figure 2 is a schematic of the continuous mill mixing compounding process and apparatus employed in the invention. In Figure 2: l=liquid feeder (e.g., pump); 2=solid feeder; 3=pneumatic vacuum conveying system; 4=hopper; 5=dry blender; 6=dry blend; 7=open roll mill; 8=sheet or strip of compound; 9=open mill with stock- blender; 10=takeoff apparatus; ll=final elastomeric compound. Detailed Description of the Invention When produced in a gas-phase fluidized bed process, the elastomers are granular and free-flowing without the need for additional physical crushing, pulverizing, or pounding to produce a powdered consistency. Granular, free-flowing elastomers made in a gas-phase process which can be employed in the present invention include, for example, copolymers of ethylene and a C3.C12 alpha olefin, particularly including a copolymer of ethylene and propylene and a terpolymer of ethylene, at least one C3.C12 alpha olefin (especially propylene), and a diene (preferably non-conjugated). Such dienes are disclosed, for example, in U.S. Patent No. 5,317,036. Especially preferred ethylene-alpha olefin-diene rubbers are those which employ a C .Cg alpha olefin (particularly, propylene or butene as the alpha olefin), and a diene selected from the group consisting of ethylidene norbornene, octadiene including methyloctadiene (e.g., 1- methyl-l,6-octadiene and 7-methyl-l,6-octadiene), hexadiene, dicyclopentadiene, and mixtures thereof. Other gas-phase produced elastomers which can be employed in the present invention, include, for example, polyisoprene, polybutadiene, a polymer of butadiene copolymerized with styrene, a polymer of isobutylene copolymerized with isoprene, polychloroprene, a copolymer of butadiene and isoprene, and terpolymers of styrene, butadiene, and isoprene. Polyisoprene, polybutadiene, polychloroprene, poly(styrene-butadiene) rubbers are preferred. Of the above-enumerated gas-phase produced elastomers, especially preferred are polyisoprene, polybutadiene, polystyrene- butadiene), and ethylene-propylene copolymers, and ethylene- propylene-diene terpolymers (e.g., ethylene-propylene-ethylidene norbornene and ethylene-propylene-1- or 7-methyl-l,6 octadiene). It is understood that the elastomers that are blended and compounded in accordance with the process of this invention do not have to be chemically distinct, provided that they are substantially different in some aspect of molecular structure. For example, they can be the same elastomer in two substantially different molecular weight grades or contain substantially different amounts or ratios of the respective monomers comprising them. The above-described elastomeric polymers are produced in gas-phase processes taught, for example, in recent patents such as U.S. Patent Nos. 4,994,534; 5,304,588; 5,317,036; and 5,453,471 utilizing a fluidized bed reactor. The gas-phase polymerizations can be conducted in conventional, condensed mode, including induced condensed mode, (U.S. Patent Nos. 4,543,399; 4,588,790; 5,352,749; and 5,462,999), and liquid monomer mode (U.S. Patent 5,453,471; WO 96/04322 and WO 96/04323) processes. In general, the elastomers are produced in a gas- phase fluidized reactor at or above the softening or sticking temperature of the polymer product optionally and preferably in the presence of an inert particulate material selected from the group consisting of carbon black, silica, clay, talc, and mixtures thereof using a polymerization catalyst typically employed to produce the polymer product. Of the inert particulate materials, carbon black, silica, and a mixture thereof are preferred, with carbon black being most preferred. The inert particulate material is employed in the gas-phase polymerization in an amount ranging from about 0.3 to about 80 weight percent, preferably about 5 to about 75 weight percent, most preferably 5 to 50 weight percent based on the weight of the final elastomeric polymer product. The elastomers produced in a gas-phase polymerization are granular, free-flowing, with an average particle size of about 0.01 mm to about 3 mm, preferably about 0.02 mm to 1.5 mm, and most preferably about 0.05 mm to 1.0 mm. When produced in a gas-phase process, particles of the elastomers have a core-shell morphology. That is, the inert particulate material has been incorporated into the final elastomeric polymer product such that a majority of the inert particulate material is concentrated in the shell and a majority of the elastomeric polymer is found in the core of the particle. It is believed that the core-shell morphology of gas-phase produced elastomers plays a significant role in mixing, milling, and properties of the end-use product. The granular, core-shell form of gas-phase produced elastomer allows higher rotor speed and shorter mixing and milling times, even in higher filled compounds, without the risk of undispersed polymer lumps and pockets of unmixed fillers due to poor wettability as occasionally encountered with condensed bales. Gas-phase produced elastomer is compacted instead of crushed as are bale-form elastomers in the initial mixing cycle. This is believed to be due to the small size of its granules and/or its core-shell morphology. Additionally, elastomer produced in non gas-phase solution or suspension processes, can be employed in small amounts (less than 49% of the total amount of elastomer employed in the blend, preferably less than 25%). It is preferred in this invention that most or all of the elastomer employed be produced in the gas-phase as it is the above-described unique properties of the gas-phase produced particles which make it possible to compound according to the process of the invention. For example, liquid ingredients such as oils are absorbed into the gas-phase elastomeric material forming a single, solid dry phase. In contrast, oils are not absorbed in pulverized conventional (bale-form) elastomers produced in suspension and solution processes, but rather, the oil remains as a liquid and the bale-form elastomer the solid for a two phase mixture. Most preferably, in the process of the present invention, all of the elastomers employed have been produced in a gas-phase polymerization process, as this greatly enhances and simplifies mixing procedures. Other Compounding Ingredients. In addition to the gas- phase produced elastomer(s), other raw materials or compounding ingredients employed in the inventive process include fillers (especially carbon black and white filler), oil or plasticizer, and a vulcanizing system. Other additives can include antioxidants, antiozonants, activators, tackifiers, thermoplastic polymers, adhesion promoters, homogenizing agents, peptizers, pigments, flame retardants, fungicides and the like. When employed, the fillers are selected from the group consisting of carbon black; silica, atomite, silicates of aluminum, magnesium, calcium, sodium, potassium and mixtures thereof; carbonates of calcium, magnesium and mixtures thereof; oxides of silicon, calcium, zinc, iron, titanium, and aluminum; sulfates of calcium, barium, and lead; alumina trihydrate; magnesium hydroxide; phenol-formaldehyde, polystryrene, and poly(alphamethyl)styrene resins, natural fibers, synthetic fibers and mixtures thereof. Silanes like polysulphidic organo silane, vinyl tri-beta-methoxyethoxy silane, gamma-methacryloxypropyl-trimethoxy silane and the like. The plasticizers which can be employed in the process of the invention are selected from the group consisting of petroleum oils; polyalkylbenzene oils; organic acid monoesters; organic acid diesters; glycol diesters; trialkyl trimellitates; trialkyl, trialkoxyalkyl, alkyl diaryl, and triaryl phosphates; chlorinated paraffin oils; vegetable oils and esters and epoxidized derivatives thereof; and mixtures thereof. Antioxidants and antiozonants that can be employed are selected from the group consisting of hindered phenols, bisphenols, and thiobisphenols; substituted hydroquinones; tris(alkylphenyl)phosphites; dialkylthiodipropionates; phenylnaphthylamines; substituted diphenyl amines; dialkyl, alkyl aryl, and diaryl substituted p-phenylene diamines; monomeric and polymeric dihydroquinolines; 2-(4-hydroxy-3,5-t-butylaniline)-4,6- bis(octylthio)-l,3,5-triazine; hexahydro-l,3,5-tris-§-(3,5-di-t-butyl-4- hydroxyphenyl)propionyl-s-triazine; 2,4,6-tris(n-l,4-dimethylpentyl-p- phenylenediamino)-l,3,5-triazine; tris-(3,5-di-t-butyl-4-hydroxy- benzyl)isocyanurate; nickel dibutyldithiocarbamate; 2- mercaptotolylimidazole and its zinc salt; petroleum waxes; and mixtures thereof. When employed activators are selected from the group consisting of metal oxides; fatty acids and metal salts thereof; di-, tri-, and polyethylene glycols; triethanolamine; and mixtures thereof. Accelerators employed in the inventive process are selected from the group consisting of sulfenamides, thiazoles, dithiocarbamates, dithiophosphates, thiurams, guanidines, xanthates, thioureas, cyanotodiamines, caprolactams and mixtures thereof. Tackifiers useful in the process of the invention are selected from the group consisting of resins and resin acids, hydrocarbon resins, aromatic indene resins, phenolic methylene donor resins, phenolic thermosetting resins, resorcinol-formaldehyde resins, and alkyl phenol formaldehyde resins such as octyl phenol formaldehyde, coumarone-indene resins, pine tars, and mixtures thereof. Preferred tackifiers for use in the invention are the low melting tackifiers which are liquid above 20°C, typically melting at 30°-80°C, such that there is instantaneous tack for bending. Such tackifiers speed up mill banding. These tackifiers can be used to replace a portion of the oil in the formulation for improve tack for bending and adhesion of the finished product. Examples of thermoplastic polymers which are sometimes included in formulations described herein are polyethylenes and their related copolymers such as butene, propylene, hexene, octene, 4- methyl-1-pentene copolymers; functional grades of polyethylenes such as maleic acid esters, acrylic and metacrylic acid esters, acrylonitrile, vinyl acetate, and derivatives such as chlorinated and sulfonated polyethylenes and copolymers; polypropylenes and their related copolymers; functional grades of polypropylenes such as maleic acid esters, acrylic and metacrylic acid esters; modified grades of polypropylene and copolymers; ionomers; polyvinyl chlorides and their related copolymers, functional and modified grades; polymers of acetal and their related copolymers and modified grades; fluorinated olefin polymers; polyvinylidene fluoride; polyvinyl fluoride; polyamides and their modified grades; polyimides; polyarylates; polycarbonates and their related copolymers and modified grades; polyethers; polyethersulfones; polyarylsulphones; polyketones; polyetherimides; poly(4-m ethyl- 1-pentene); polyphenylenes and modified grades; polysulphones; polyurethanes and their related modified grades; polyesters and their related modified grades; polysterene and their related copolymers and modified grades; polybutylene; polymers of acrylo-nitrile, polyacrylates, mixtures thereof, and the like. Of those, polyethylene and their related copolymers such as butene, propylene, hexene, octene, 4-methyl-l-pentene copolymers, functional grades of polyethylene such as maleic acid esters, acrylic and metacrylic acid esters, acrylonitrile, vinyl acetate, and derivatives such as chlorinated and sulfonated polyethylene and copolymers; polypropylene and their related copolymers, functional grades of polypropylene such as maleic acid esters, acrylic and metacrylic acid esters, modified grades of polypropylene and copolymers; poly( inyl chloride) and their related copolymers, functional and modified grades; polyamides and their modified grades; polyesters and their related modified grades; polysterene and their related copolymers and modified grades; polyurethanes and their related modified grades; polyesters and their related modified grades are preferred. Vulcanizing (Curing) Systems. Vulcanizing agents for use in the invention include sulfur-containing compounds such as elemental sulfur, 4,4'-dithiodimorpholine, thiuram di- and polysulfides, alkyl phenol disulfides, and 2-morpholino- dithiobenzothiazole; peroxides such as di-tertbutyl peroxide, tertbutylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-(tertbutylperoxy) hexane, di- (tertbutylperoxyisopropyl) benzene, tertbutyl peroxybenzoate and 1,1- di-(tertbutylperoxy)-3,3,5-trimethylcyclohexane; co-agents such as triallyl cyanurate, ethylene glycol dimethacrylate, trimethylol propane trimethacrylate and the like; metal oxides such as zinc, magnesium, and lead oxides; dinitroso compounds such as p-quinone dioxime and p,p'-dibenzoylquinonedioxime; and phenol-formaldehyde resins containing hydroxymethyl or halomethyl functional groups. It is understood that mixtures of two or more vulcanizing agents can be employed in the process of the invention. The suitability of any of these vulcanizing agents or mixtures of vulcanizing agents for use in the invention will be largely governed by the choice of elastomers, as is well known to those skilled in the compounding art. For the preferred elastomers of the invention, the sulfur containing compounds and the peroxides are the preferred vulcanizing agents, and the sulfur containing compounds are most preferred. The amount of the vulcanizing agent can range from about 1 to 10 parts by weight based upon 100 parts of the elastomers in the composition. Mill Mixing Procedure. Using Figure 2, continuous mill mixing of the present invention comprises metering wet ingredients for the blend or mixture via one or more liquid feeding pumps (1) and the dry ingredients via one or more feeders (2). Optionally, the dry ingredients are transported from the feeders via a pneumatic vacuum conveying system (3) into a hopper (4). From the hopper (4), the ingredients are placed in a dry blender (5) in which the gas-phase produced elastomer(s) and other desired ingredients are mixed such that the individual component ingredients are evenly distributed in the mixture (6). The elastomer(s) and other desired ingredients are preferably mixed at ambient temperature up to a temperature below the temperature at which the vulcanizing system would begin crosslinking. Next, the mixture (6) from the dry blender (5) is fed onto an open roll mill (7) for dispersion. On the open roll mill, the ingredients are evenly dispersed such that a band, sheet, or strip of the compounded ingredients (8) is formed. While the vulcanizing system can be added at the mill mixing step, it is preferably already added along with the other ingredients in the dry blending step. On the two roll open mill (7), the elastomeric composition, preferably including the vulcanizing system, forms into a sheet or band on the rollers. Strips (8) are cut away from the roll mill using roller knives. The cuttings (8) from the sheet are taken off the mill and transported via a takeoff apparatus (10) to subsequent additional processing such as calendering, sheeting, moulding, and/or extrusion (11). Alternatively, the cut strips or sheets (8) can be refed to a second two roll open mill equipped with a stock-blender (9) for additional extensive and intensive mixing (distributive and dispersive) and to obtain a continuous mode. See Figure 2, (9). As sheets (11) are taken off the roll mill, they can be folded either before and or after subsequent additional processing. Other well known subsequent additional processing can include, for example, A) air cooled stripping and on-line feeding of sheets to a rotocure machine for continuous curing of sheeting; B) air cooled stripping and on-line feeding to a hose extruder; C) air cooled stripping and sheet feeding to a granulator to prepare granules for extruder or injection moulding feeding; and D) air cooled sheet feeding to a calender for roofing and roll covering. High Speed ' Mixer Procedure. The consistency and precision of the mixing process is enhanced by automatic weighing and metering of the gas-phase produced elastomer into the dry blending (high speed) mixer. Bale weight variation associated with inconsistent mixing is eliminated. Bale weight variation is not only dependent on bale weight, but also related to the accuracy and frequency of cutting bales to meet desired polymer weight for each individual mix. Use of gas-phase produced elastomer removes these variables from the mixing procedure. The dry blend prepared in accordance with the present process is free-flowing and remains free-flowing for at least one week, typically up to more than six months depending on recipe constituents. A dry blend is prepared by adding, preferably by metering, the ingredients into a high speed mixer (also known as a dry blender or fluid mixer), for example, a Henschel® mixer or a Papenmeier® are ideal. Other suitable mixers for the present process can include, for example, Littleford® and Lόdige®. Such ingredients can include, for example, carbon black filler, a plasticizer such as a paraffinic oil, gas- phase produced elastomer(s) such as EPDM or EPM, any other desired optional ingredients (e.g., pigments, dyes, fungicides, etc.), and optionally the curing (vulcanizing) system. The high speed mixer containing the ingredients to be mixed is started and run at about 300 to 650 rpm, preferably about 450 to 600 rpm, for about 15 seconds to 60 seconds, preferably about 25 seconds to 45 seconds at ambient temperatures (about 20° to 30° C). After about 30 seconds, the temperature of the mixture in the high speed mixer reaches about 30° C. The rotor speed is increased to about 750 to 2500 rpm, preferably about 900 to 1500 rpm, for about 1 to 2 minutes, preferably about 1 1/2 minutes. The mixture has reached a temperature of about 40° C as it is dumped into a storage hopper. Total mixing time for the free-flowing dry mix is about 5 minutes or less, preferably about 3 minutes during which the rotor speed ranges from about 300 to 2500 rpm. The mixture is transported from the high speed mixer, optionally to a storage silo and by means of a dosing unit (e.g., rotary valve) into the entry pipe of a pneumatic transporting device, or by other means delivered to the open roll mill. Mill Mixing Procedure. The free-flowing dry mix from the storage hopper is introduced batchwise, preferably continuously, to at least one open roll mill. Preferably at least two mills, one of which is fitted with an overhead stock-blender are employed in the inventive process. Suitable roll mills can include, for example, mills with good water cooling capacity, preferably with adjustable roll speed and gap width setting. A stock-blender will increase mixing capacity, improve dispersive and distributive mixing as well as allow cooling or temperature control of the rubber compound. When a second mill is employed it is used to develop a continuous mode and to improve homogeneity and plasticity of a compound for a given mixing time. The stock-blender above the second mill essentially consists of two deflection rolls of the same width as the mixing rolls which are arranged next to each other on the mill frame above the roll nip and two guide rolls which move backwards and forwards. As soon as sufficient dispersion has been accomplished on the first open mill, the rubber is guided to the second mill. As soon as a band is formed, the band is then cut, pulled up and lead back to the roll nip over the deflection rolls of the stock-blender. The driven deflection rolls assure the transport of the band. The band is deformed and uniformly and intensively ix.ed by the forward and backward movements of the guide rolls without any additional activity of the operator. Simple rotating roller knives will strip off the sheet in the required width and guide rolls will pass the strip to the next stage which might be an extruder, calender, etc. for further continuous end- use production. Preferably, the vulcanizing or curing system is added during dry blending operation, or, if not already included then, at the beginning of the open roll milling process step (ii). The open roll mill has a friction ratio ranging from about 0.6:1 to 2:1, preferably about 1.15:1 to 1.35:1. Starting temperature ranges from about 30° to 70° C. A temperature of about 50° to 70° C ensures faster front roll banding and curing system (e.g., accelerator) dispersion. The finished mill compound temperature ranges from about 55° to 85° C, the latter temperature corresponding to a starting temperature of about 70° C. That is, the finished mill compound temperature is about 15° C higher than the starting temperature. The speed of the rollers ranges from about 15 to 22 rpm, preferably about 16 to 20 rpm. In mill mixing, initially the mill nip is closed to prevent the dry blend ingredients from falling through the gap, and to obtain as fast as possible a closed band. At about 50° to 70° C, using a given aliquot or shot of dry blend, the compound forms a band of material on the faster running front roll. Within about 3 minutes or less, preferably in about 2 to 3 minutes, at about 55° to 75° C, smooth, firm front roll banding is accomplished. To allow fast dispersion, minimum cutting, folding and refeeding will take place in the initial mill mixing process. Within 4 to 6 minutes at 60° to 80° C, the batch is then passed to the stock-blender. The compound is stripped-off at about 60° to 85° C in approximately 7 to 10 minutes, preferably about 8 to 9 minutes, according to recipe composition. Use of granular gas-phase produced elastomer provides faster ingredient incorporation along with better dispersion, thereby, resulting in reduced mixing time, entailing lower mixing energy, and dump temperature. And the gas-phase produced elastomer(s) granular, free-flowing form results in significant process simplification in industrial automatic metering and feeding. All patents cited herein are hereby incorporated by reference. The following examples are given to illustrate the invention and are not intended as limitations thereof. Amounts are in weight percent unless otherwise specified. EXAMPLES Three trials, one factory mill mixing compounding, as well as two laboratory mill mixing operations, were conducted in the following manner. Starting formulations were as described in Tables 1, 5 and 8. Table 1 represents a typical roofing recipe, hardness 65 Shore A. Table 5 gives a typical cooling hose recipe, rubber rich, hardness 75 Shore A. Table 8 shows a typical general purpose profile recipe, filler rich, hardness 70 Shore A. All ingredients were put in a Lόdige high speed mixer with a theoretical volume of 75 liter and a capacity of 30 kW at 500 rpm, and 36 kW at 1000 rpm. The average particle size as the gas phase produced resin particles ranged from about 0.06 to 0.08 mm. Since the dry blending process is practically isothermal, the temperature of the ingredients in the mixer was maintained far below the temperature at which the curatives, when present, would have been activated. The resulting well distributed mixture of compounding ingredients was continuously fed to an open roll mill for dispersion resulting in a 3 mm sheet under the conditions set forth below for the factory mill trial and a 2 mm sheet for the laboratory mill operations. The ready mill mixed compound was evaluated by examining tapes of the sheets for properties described below. Table 1; Roofing Recipe for the High Speed Mixer Gas-phase Produced EPDM* 122 Zinc Oxide 5 Stearic Acid 1 FEF N-5501 50 GPF N-6602 58 Paraffinic Oil, Sunpar 2280 75 Escorez 5320 3 ! Sulphur 1.3 CBS 4 2 MBTS5 1 Total 330.3 Rubber Hydrocarbon Content, % 30 *MEGA 6322 from Union Carbide C2 = 65%; ethylidene norbornene (ENB)=2%, Carbon Black (CB)=22 phr, granular. 1 Fast Extrusion Furnace Black 2 General Purpose Furnace Black 3 Hydrogenated Aliphatic Hydrocarbon Resin 4 N-cyclohexyl-2-benzothiazylsulfenamide 5 Benzothiazyl Disulfide Raw Polymer Moonev Viscosity Unmassed as such Massed ML 1+4 - 125°C 95 86 Green Strength of Raw Polymer Green Modulus 50%, MPa 1.5 Green Modulus 100%, MPa 1.7 Green Modulus 300%, MPa 2.4 Green Tensile Strength, MPa 7.3 Green Elongation before break, % 1025 Table 2: Dry Blend** Preparation High speed, fluid mixer, type Lδdige, capacity 75 liter. Time RPM Temp. Procedure 00 23°C fill mixer with carbon black, oil, rubber and other ingredients 30" 500 23°C start 1'30" 1000 30°C increase speed for 1'30" 3'00" 40°C dump in storage hopper ** Dry blend is free-flowing and remained free-flowing after one week check. Table 3: Factory Mill Mixing Conditions Mill: size 1500 x 600 mm fitted with overhead stock- blender Friction ratio 1.15 to 1 Start temperature approx. 50°C. Finished compound temperature 60°-75°C. Sheet or strip thickness 3mm Table 4; Factory Mill Mixing Procedure Time Temp. Procedure 00 30-50°C - close mill nip, to allow sheet thickness of 3 mm - add 20 kg of dry blend in one shot - allow compound to band on front roll 2'00" 40-60°C - smooth, firm front roll banding accomplished - allow dispersion, minimum cutting 5'00" 50-70°C - pass batch on to stock-blender 8'00" 60-75°C - strip off Table 5: Cooling Hose Recipe for the High Speed Mixer (Rubber Rich) Gas-phase Produced EPDM* 119 Zinc Oxide 5 Stearic Acid 1 FEF N-550 101 Paraffinic Oil, Sunpar 2280 60 Sulphur (95%) 0.5 ZDBCl 2 ZDMC2 2 DTDM3 °- 6 Total 291.1 Rubber Hydrocarbon Content, % 34 *MEGA 7265 from Union Carbide C2=70%; ethylidene norbornene (ENB)=4,5%, Carbon Black (CB)=19 phr, granular 1 Zinc Dibutyldithiocarbamate 2 Zinc Dimethyldithiocarbamate 3 4,4'-Dithiodimorpholine Raw Polymer Moonev Viscosity Unmassed as such Massed ML 1+4 - 125°C 90 79 Green Strength of Raw Polymer Green Modulus 50%, MPa 2.5 Green Modulus 100%, MPa 3.3 Green Modulus 300%, MPa 5.8 Green Tensile Strength, MPa 11.3 Green Elongation before break, c , 625 Table β: Laboratory Mill Mixing Conditions/Rubber Rich Mill: size 320 x 150 mm Friction ratio 1.25 to 1 Start temperature approx. 70°C Finished compound temperature 73° - 75°C Sheet or strip thickness 2 mm Table 7: Laboratory Mill Mixing Procedure Time Temp. Procedure 00 70°C close mill nip, to allow sheet thickness of 2 mm add 400 grams of dry blend in one shot 1'30" 70°C compound banding on front roll 3'00" 75°C compound fully mixed (no cutting) remove compound from mill Table 8: General Purpose Profile Recipe for the High Speed Mixer (FillerRich) Gas-phase Produced EPDM* 119 Zinc Oxide 5 Stearic Acid 1 FEF N-550 151 Paraffinic Oil, Sunpar 2280 120 Sulphur (95%) 0.5 ZDBC 2 ZDMC 2 DTDM 0.6 Total 401.1 Rubber Hydrocarbon Content, % 25 *MEGA 7265 from Union Carbide C 2= 70%; ethylidene norbornene (ENB)=4,5%, Carbon Black (CB)=19 phr, granular Raw Polymer Moonev Viscosity Unmassed as such Massed ML 1+4 - 125°C 90 79 Green Strength of Raw Polymer Green Modulus 50%, MPa 2.5 Green Modulus 100%, MPa 3.3 Green Modulus 300%, MPa 5.8 Green Tensile Strength, MPa 11.3 Green Elongation before break, % 625 Table 9: Laboratory Mill Mixing Conditions/General Purpose Profile/Filler Rich Mill: size 320 x 150 mm Friction ratio 1.25 to 1 Start temperature 50 °C Finished compound temperature 53° - 55°C Sheet or strip thickness 2 mm Table 10; Laboratory Mill Mixing Procedure/General Purpose Profile/Filler Rich Time Temp. Procedure 00 50°C - close mill nip, to allow sheet thickness of 2 mm - add 400 grams of dry blend in one shot 45" 52°C - compound banding on front roll 2'15" 55°C - compound fully mixed (no cutting) - remove compound from mill Results. The roofing compound had a hardness of 65 Shore A. The dry mixing followed by factory scale mill mixing was a dust-free operation. In the milling step, there was immediate and instantaneous sheet formation after one passage of loose, free-flowing ingredients of the dry mix through the mill nip with a minimum amount of dry blend ingredients in the mill pan. On the open roll mill, after initial compound splitting from front to back roll and vice versa, firm compound banding on the faster running front roll occurred within about 2 minutes. As those skilled in the art will readily recognize, front roll processing is important in subsequent processing steps such as stock blending, feed stripping to second mill or air cooled stripping into feeding box, and/or online feeding of calender or extruder for continuous processing. The average dispersion (intensive mixing) time was about 5 minutes. The stock blending (extensive mixing) time was about 3 minutes. The resulting homogeneous dispersion of all the mixing ingredients, including curatives, was comparable to internal mixing heretofore employed with bale form elastomers. The total operation of the present process was scorch-free. The mill mixed compound of the present invention was ready for the next downstream processing (e.g. extruding, calendering, moulding) in a total of about 8 minutes. And the milled compound of the inventive process had physical properties comparable to or better than those obtained using conventional internal mixing with bale- form elastomers. The laboratory scale experiments of mill mixing a typical cooling hose recipe (rubber rich), hardness 75 Shore A, and a typical general purpose profile recipe (filler rich), hardness 70 Shore A, confirm the fast dispersion of dry blends based on gas-phase EPDM. The granules have an average particle size of 0.6 to 0.8 mm and are already partially "wetted" with 15 to 25 phr carbon black, depending on polymer composition. This unique morphology (core-shell) and close interaction are produced in the gas-phase process without introducing shear, heat and mixing history. The pre-wetted surface of granular EPDM is expected to have a "seeding" effect due to the carbon black in the outer shell of the polymer particle. Additionally, when this unique core-shell granule is employed in a formulation, the total amount of loose carbon black filler required by the formulation is lower, thus again speeding incorporation of the ingredients. It has also been theorized that having carbon black concentrated in the shell of the granular resin particle imparts a polar character to the polymer particle thereby more readily attracting loose carbon black of the formulation to enhance the mixing process. This form facilitates fast overall distribution of recipe components and minimizes the risk of ingredients segregation during storage of the ready-made dry blends prior to mill mixing. Those recipes with a low rubber content and a high oil/filler ratio (filler rich), see Table 8, are preferably processed on an open mill with a starting temperature of 50°C, to obtain cold green strength to prevent bagging. However, recipes with a high rubber content (rubber rich), see Table 5, should be processed on an open mill with a start temperature of around 70°C to make use of the thermosoftening of the ethylene component resulting in less dry compounds with increased self-tack, facilitating faster mill banding.

Claims: What is claimed is: 1. A mixing process comprising mixing on a milling device at least one elastomer produced in particulate form as it exits a reactor, one or more additional ingredients, and optionally a vulcanizing agent, and removing the mixture from the milling device. 2. The mixing process of Claim 1 which comprises (i) introducing at least one gas-phase produced elastomer, one or more compounding ingredients, and optionally a vulcanizing system into a high speed mixer with mixing at ambient temperature such that the elastomer, compounding ingredients, and vulcanizing system when employed are uniformly distributed in a dry blend followed by (ii) passing the uniformly distributed dry blend to an open roll mill to form a dispersed compound; (iii) cutting the dispersed compound into sheets or strips for removal from the open roll mill. 3. The mixing process of Claim 2 wherein the vulcanizing system is added during the dry blending step (i). 4. The mixing process of Claim 2 wherein the vulcanizing system is added at the beginning of the open roll mill mixing step (ii). 5. The mixing process of Claim 2 wherein the gas- phase produced elastomers are selected from the group consisting of polyisoprene, polybutadiene, polychloroprene, poly(styrene-butadiene) rubber, ethylene-propylene rubber, ethylene-propylene diene rubber, and mixtures thereof; the compounding ingredients are selected from the group consisting of an oil or plasticizer, carbon black and white filler, and mixtures thereof; and the vulcanizing system is selected from the group consisting of a sulfur-containing compound, a peroxide compound, a mixture thereof, and optionally one or more accelerators optionally with inhibitors, and activators. 6. The mixing process of Claim 2 wherein average particle size of the gas-phase produced elastomers ranges from about 0.01 mm to about 3 mm. 7. The mixing process of Claim 2 wherein the process is a continuous process. 8. The mixing process of Claim 3 wherein the elastomer, compounding ingredients, and vulcanizing system are mixed in the high speed mixer at room temperature at a rotor speed ranging from 300 to 2500 rpm for a time period of 2 to 5 minutes followed by passing the blend onto an open roll mill having the following settings: temperature from about 30° to 70°C friction ratio from about 1.35:1 to 1.15:1 gap size from about 2 to 6 mm roll speed from about 15 to 22 rpm mill residence time from about 5 minutes to 15 minutes. 9. The mixing process of Claim 2 wherein the dry blend is fed to the open roll mill by a gravimetric dosing unit and wherein low melting point tackifiers are added to speed up mill banding. 10. The mixing process of Claim 2 wherein the cut sheets or strips of step (iii) are fed to a second open roll mill having a stock blender.

Inventors: ITALIAANDER ERICH THOMAS, ITALIAANDER, ERICH, THOMAS
Applicants: UNION CARBIDE CHEM PLASTIC, UNION CARBIDE CHEMICALS & PLASTICS TECHNOLOGY CORPORATION
Application year: 1998
Main classification: B29B7
IPC codes: B29B7