Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
  • B65D88/00—Large containers
  • B65D88/54—Large containers characterised by means facilitating filling or emptying
  • B65D88/58—Large containers characterised by means facilitating filling or emptying by displacement of walls
  • B65D88/60—Large containers characterised by means facilitating filling or emptying by displacement of walls of internal walls
  • B65D88/62—Large containers characterised by means facilitating filling or emptying by displacement of walls of internal walls the walls being deformable
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/71—Feed mechanisms
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/71—Feed mechanisms
  • B01F35/714—Feed mechanisms for feeding predetermined amounts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/71—Feed mechanisms
  • B01F35/717—Feed mechanisms characterised by the means for feeding the components to the mixer
  • B01F35/7173—Feed mechanisms characterised by the means for feeding the components to the mixer using gravity, e.g. from a hopper
  • B01F35/71731—Feed mechanisms characterised by the means for feeding the components to the mixer using gravity, e.g. from a hopper using a hopper
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/71—Feed mechanisms
  • B01F35/717—Feed mechanisms characterised by the means for feeding the components to the mixer
  • B01F35/71805—Feed mechanisms characterised by the means for feeding the components to the mixer using valves, gates, orifices or openings

Definitions

• the present invention relates to a method for adding & high consistency compound, such as a high viscosity polydiorganosiloxane, to a mixer and an integrated process for producing catalyst containing silicone rubber compositions using the method.
• & high consistency compound such as a high viscosity polydiorganosiloxane
• high consistency and high viscosity when used herein with respect to a compound are intended to mean a compound which does not or substantially does not flow under its own weight, an example being a high consistency polydiorganosiloxane gum.
• the present method is especially useful when incorporated into an integrated process for producing catalyst containing silicone rubber compositions, resulting in substantially reduced processing time and labour input compared to standard methods for producing such compositions as described in the applicants co-pending unpublished PCT application No US02/15227.
• the integrated process using, for example, an organoperoxide catalyst involves forming a powdered silicone rubber composition comprising a polydiorganosiloxane gum and a reinforcing filler, treating the reinforcing filler with a treating agent at a temperature greater than about 80°C, cooling the powdered silicone rubber composition by means of a bulk solid cooling apparatus, and admixing the cooled powdered silicone rubber with the organoperoxide catalyst either before, during, or after a massing step.
• organoperoxide curing silicone rubber compositions it was common to prepare a polydiorganosiloxane gum having a viscosity of from 1 x l ⁇ 6 to 2 x 10 ⁇ mPa.s at 25°C which was the basic ingredient of the organoperoxide curing silicone rubber composition.
• the gum was then transported to a dough-mixer. Then, there was added to the gum in the dough-mixer the requisite amount of reinforcing fillers or extending fillers, heat stabilizers, flame retardant additives, processing aids, and other types of ingredients that are normally associated or present in silicone rubber compositions.
• the dough-mixer comprises a large tank with two large mixing blades therein which agitate and mix the gum and the other ingredients into a uniform mixture. Normally, it takes a dough-mixer from a minimum of 3 hours to a maximum of 48 hours to form a uniform homogeneous mass of diorganopolysiloxane gum, filler, and other ingredients. After dough mixing has been completed, the composition is cooled for several hours either in the dough-mixer or after removal from the dough-mixer. The resulting mass is then dumped into a cart, cut into pieces, passed through an extruder to screen out particles and is then formed into packageable slabs, for example 50 pound (22.7kg) slabs.
• the resulting slabs are packaged and shipped, or alternatively may be processed through other extruding and forming machines before they are shipped.
• the 50 pound (22.7kg) slabs are processed on a mill at which point a curing catalyst may be added and the resulting milled mass may then be extruded into the desired shape and shipped as such.
• the un analysesd mass may be shipped to the customer for subsequent addition of the catalyst.
• the above described method is both time consuming and labour intensive and requires multiple manual handling of the silicone rubber compositions during compounding and forming into a shippable form.
• the present process significantly shortens the time required to form the catalyst curable silicone rubber compositions and eliminates the manual handling of the silicone rubber compositions during compounding and forming into a shippable product.
• This reduction in time and elimination of manual handling is achieved by an integrated process comprising first forming a free-flowing particulate polymer mixture comprising in situ treated fumed silica and a high consistency polydiorganosiloxane gum, rapidly cooling the free-flowing powder by means of a bulk solids cooling apparatus, and then extruding the cooled free-flowing powder to effect massing, screening, and shaping of the silicone rubber composition into a form suitable for its intended use.
• the catalyst may be added to the silicone rubber composition at any stage after the cooling step, that is to the free- flowing powder, during the massing of the free-flowing powder, or as a separate mixing step, by for example, an in-line distributive mixer attached to the exit of the extruder.
• Bilgrien et al, U.S. Pat. No. 5,153,238, teach storage stable and gel-free organosiloxane compositions in the form of flowable powders prepared by blending a high polydiorganosiloxane into a quantity of fluidised reinforcing filler that is heated to a temperature of from 100°C to 200°C prior to or immediately following introduction of the polydiorganosiloxane.
• the silica filler is typically treated with an anti-creping agent either prior to or during this blending process.
• the resultant mixture is heated while being subjected to shearing forces that reduce its average particle size to achieve a flowable powder.
• a method for adding a high viscosity compound into a mixer comprising inverting a container having a flexible inner liner bag, secured at an open end of the container and containing a high viscosity compound, over a delivery device positioned to deliver the high viscosity compound into a mixer thereby causing the high viscosity compound to transfer from the bag through the delivery device into the mixer.
• the method for adding the high consistency compound, which may for example be a high viscosity polydiorganosiloxane gum, to a mixer comprises inverting a container having a flexible inner liner bag secured at an open top end of the container and containing a high consistency polydiorganosiloxane gum over a delivery device positioned to deliver said high consistency polydiorganosiloxane gum into a mixer thereby causing the high consistency polydiorganosiloxane gum to transfer from the bag through the delivery device into the mixer.
• the tapered delivery device contains one or more control rods positioned therein to control the rate of transfer of the high consistency polydiorganosiloxane gum into the mixer.
• the container containing the inner liner may be any of those containers typically used for holding high consistency polydiorganosiloxane gum.
• the container may be for example, a plastic drum, a metal drum, or fiber pack. It is preferred that the container be straight walled with a full cross-sectional opening, such as an open type drum or fiber pack.
• the container is fitted with a flexible bag-shaped inner liner.
• the liner can be formed from any sufficiently strong impermeable material, such as polyethylene or a flexible plastic or rubber coated fabric liner. A rubber coated fabric liner is preferred.
• the liner is attached at the upper rim of the container only i.e.
• the liner can be attached to the top of the drum by standard methods such as a strap or drum lid clamp.
• the container be vented on the bottom to prevent formation of a vacuum when the container is inverted.
• a vacuum is formed in the space between the liner and the container as the gum and liner move out of the container and no means of introducing air into the space between liner and container is otherwise available.
• a vacuum may hinder the release of the gum from the container when inverted.
• the intention is to transfer the gum relatively quickly into a mixer and as such a sufficiently large vent hole is usually provided in order to ensure that no or substantially no vacuum is created, whilst the gum is being transferred into the mixer, in order so that the gum and liner can freely slide out of the container when the container is inverted.
• the flow of air to this vent may be regulated to help control the rate at which the load of high consistency polydiorganosiloxane gum will drop from the container.
• the vent serves a second purpose in the present invention in that it provides a simple means of retracting the liner back into the container once the gum has been introduced into the mixer by sucking the liner back into the container by applying, for example, a suction cup to the vent hole and extracting the air between the liner and the container with a vacuum. In the absence of this process the mere return of the liner into the container to its starting position requires mechanical or manual reinserted of the liner back into the container prior to its being loaded with gum.
• the delivery device is tapered.
• the tapered delivery device is conically shaped with the diameter of the inlet being greater than the diameter of the outlet.
• the tapered delivery device can be constructed of standard materials such as steel, stainless steel, plastics, and the like.
• the tapered delivery device may be lined with a non- contaminating material such as polyethylene.
• the inside surface of the tapered delivery device or lining therein may be treated with a low viscosity fluid to provide a low friction surface for the high consistency polydiorganosiloxane gum to slide on rather than flowing.
• a preferred low viscosity fluid is a polydiorganosiloxane having a viscosity of from 1 to 10000 mPa.s.
• the size of the tapered delivery device will depend upon the required delivery rate to the mixer into which the siloxane gum is to be delivered. General guidance as to useful size and shape is provided in the example provided herein.
• the choice of a conical delivery device provides a relatively large opening into which the gum is supplied from the container and provides a smaller more precisely located opening into the mixer.
• the reduction in diameter of the gum transferred into the delivery device acts as a means of flow control of the gum. It takes work to deform the gum in a conical delivery device from for example an initial 75cm diameter opening to a 45 cm diameter exit. In the present invention this work is provided at least substantially by gravity.
• the degree of control required for the addition of the high consistency compound can dictate to a large extent, the geometry of the required delivery device. Totally different results are obtained using tapered delivery devices of differing geometries. These differences are generally achieved depending on the difference in diameter between the delivery device opening and exits. In cases where the exit of the delivery device had the same or only a slightly smaller diameter (d 2 ) than the diameter of the opening of the delivery device (d (e.g. where d 2 is >80% of d ) gum substantially slides through the delivery device quickly with only minor deformation and enters the mixer as a slightly elongated lump. It was found that unless the addition of all the gum in a single lump were required this method was typically not desirable as the mixer into which the gum was being introduced was typically overwhelmed by the rapid introduction of such a large volume.
• the material that has passed through the delivery device opening will typically hang above the mixer opening still attached to the material in the delivery device and actually serves to drag that material through the delivery device opening faster than it would otherwise move, thus enabling the rate of flow of the gum to remain more constant than it otherwise would.
• the strand of material hanging from the delivery device opening tends to stretch and flow at a relatively continuous rate into the mixer. However, as the last of the material passes through the delivery device opening, the suspended strand falls all at once into the mixer resulting in a sudden increase in the rate of introduction into the mixer which is a potential problem.
• d 2 is between 50 and 70% of d ⁇ .
• the delivery device contains one or more control rods positioned therein as a means of enhancing flow control of the gum.
• the control rods may be formed from standard materials, such as those used to construct the tapered delivery device.
• the number of control rods and their size and placement in the tapered delivery device is selected to control the flow of the high consistency polydiorganosiloxane gum from the tapered delivery device at a desired rate.
• the rods are preferably utilised when a relatively even distribution of gum is needed to be added into a mixer because whilst for some applications it is acceptable to merely dump the material as a single large lump into a mixer, for others it is or may be important to precisely control the rate of addition.
• the applicants may use a fairly wide range of acceptable flow rates that are substantially less than would be needed to transfer a single lump but not precise enough as to require expensive mechanical metering equipment (i.e. positive displacement pumps).
• control rods as hereinbefore described provides an easy means of changing the flow rate of the gum through the delivery device. Changing the size/diameter of the delivery device opening would normally require the physical replacement of the delivery device with an alternative having a different opening and/or exit diameter.
• the need for swapping the delivery device dependent on the product being introduced into the mixer negates the need for replacing the delivery device but merely requires a change in the size / number of rods.
• the control rods were also found to offer some other advantages. Since the gum actually has to flow around them, they provide substantial drag and yet they have limited surface area to accumulate gum and so after the gum has passed through the delivery device very little residue remains on the control rods. For a given, moderate opening size various combinations of rod size and quantities were evaluated.
• control rods may be formed, for example, from rigid or cable type materials.
• the control rods may be, for example, round, oval, or polygonal in cross-sectional shape.
• the present method is especially useful when incorporated into an integrated process for producing catalyst containing silicone rubber compositions, resulting in substantially reduced processing time and labour input compared to standard methods for producing such compositions.
• an integrated process for forming a catalyst containing silicone rubber composition comprising the steps of (A) adding a high consistency polydiorganosiloxane gum to a mixer by inverting a container having a flexible inner liner bag secured at an open top end of the container and containing a high consistency polydiorganosiloxane gum over a delivery device positioned to deliver the high consistency polydiorganosiloxane gum into the mixer thereby causing the high consistency polydiorganosiloxane gum to transfer from the bag through the delivery device into the mixer,
• composition comprising: i) 100 parts by weight of the high consistency polydiorganosiloxane gum, ii) about 10 to 80 parts by weight of a treated or untreated reinforcing silica filler,
• step (C) directly transferring the flowable organopolysiloxane powder composition to a bulk solids cooling device and facilitating accelerated bulk cooling thereof to a temperature below the decomposition and/or activation temperature of a catalyst added in step (D),
• step (D) feeding the bulk cooled flowable organopolysiloxane powder composition to a massing apparatus and massing the organopolysiloxane composition therein at a temperature below the decomposition and/or activation temperature of a catalyst added in step (D),
• step (E) adding a catalytic amount of a catalyst to the organopolysiloxane composition either prior to, during, or after step (C) at a temperature below the decomposition and/or activation temperature of the catalyst.
• a massing step as referred to in the present invention comprises the conversion of a divided solid or powder into a single piece, or mass, by compression and mastication/kneading.
• the resulting composition may then be recovered as a catalyst containing silicone rubber composition mass by any appropriate means.
• the present process is an integrated process.
• integrated it is meant that steps subsequent to the batch formation of the powdered organopolysiloxane composition in step (B) are conducted in a continuous mode without manual handling of the organopolysiloxane composition until after massing and preferably after addition of a catalyst and massing.
• Step (B) of the present process is conducted by adding at least a portion of the reinforcing silica filler to a high shear mixer and maintaining the filler in a highly turbulent fluidised state at a temperature of from 80°C to about 350°C.
• the temperature of the fluidised silica be maintained at a temperature of 80°C or greater during step (B) both to facilitate treatment of the filler with the treating agent and to reduce the formation of gels. Preferred is when the temperature within the mixer is maintained within a range of from about 90°C to 180°C.
• Any mixing apparatus capable of maintaining the reinforcing filler in a fluidised state while blending the filler with the high consistency polydiorganosiloxane gum and applying sufficient shear to reduce the size of the resultant filler-coated polymer particles to a uniform powder may be used.
• Suitable mixers include but are not limited to Waring ® blenders containing a high speed shearing blade at the bottom of a vertically oriented conical chamber, mixers manufactured by Rheinstahl Henschel AG, Kassel, Germany, and mixer/granulators manufactured by Littleford Bros. Inc. Florence KY.
• Preferred mixers for use in the present process are the mixer/granulators manufactured by Littleford Bros. Inc.
• Such mixers and their use to form powdered silicone compositions are described, for example, in Link et al., U.S. Pat. No. 3,824,208 andBilgrien et al., U.S. Pat. No. 5,153,238 which are hereby incorporated by reference for their teachings regarding such use.
• These mixers are referred to as “plough” or “ploughshare” mixers due to the presence of at least one triangular or "T" shaped "plough” blade located in a horizontally oriented cylindrical mixing chamber. The plough blade rotates on the horizontal axis of the chamber with the edge of the blade close to the perimeter of the chamber.
• the plough blade is also believed to agglomerate the particles produced by the high speed shearing blade(s), also referred to as chopper blades, present in the chamber to achieve the desired final particle size.
• the speed of the plough blade required to maintain the silica in a fluidised form is typically from about 30 to about 200 revolutions per minute (rpm) and is dependent upon the capacity of the mixing chamber and the particle size range desired for the final powder.
• rpm revolutions per minute
• a speed of from 80 to 180 rpm is preferred using a 130 litre capacity mixing chamber. The speed would be proportionately slower for a larger capacity mixer.
• the mixing chamber also contains at least one high speed chopping blade to provide the shearing force required to reduce the particle size of the high consistency polydiorganosiloxane gum to a fine powder.
• the mixing chamber preferably contains at least one conical array of five blades rotating on a single shaft, said blades ranging in diameter from 15 to 23 cm, the smallest diameter blade being located closest to the mixer wall.
• the speed of the chopping blade(s) should be from about 2000 to about 4000 rpm to prepare the powdered silicone rubber composition of step (B), with a processing time of up to 30 minutes.
• the processing time period will vary depending upon the radius of the blade(s) and the volume of material in the mixer. Smaller diameter blades typically must rotate at a higher speed to impart the same level of shear to the mixture present in the mixer.
• To minimize processing time it is preferable to use the longest chopper blades that will not interfere with rotation of the plough blades located on either side of the chopper blades
• filler is added initially, due to the large increase in filler volume during fluidisation. This volume decreases substantially as the silica densifies and coats the high consistency polydiorganosiloxane gum in the mixing chamber.
• the remaining filler is initially placed in a hopper or other suitable dispensing container and allowed to drop into the chamber as the volume of silica initially present in the mixer decreases due to coating of high consistency polydiorganosiloxane gum particles.
• the high consistency polydiorganosiloxane gum is added to the mixer, after at least a portion of the reinforcing silica filler has been added to the mixer and fluidised and the required temperature of the fluidised silica has been established, by means of the method for adding high consistency polydiorganosiloxane gum described above.
• the high consistency polydiorganosiloxane gum is added to the mixer as a single shot of one or more masses weighing up to about 100 kg each, with the rate of addition and size of mass entering the mixer being primarily controlled by the tapered delivery device and any control rods positioned therein.
• the mass of high consistency polydiorganosiloxane gum added to the mixer is rapidly reduced by the shearing action of the mixer, which in the case of the Littleford-type mixer is provided by the chopper blades.
• the blending of the reinforcing silica filler with the high consistency polydiorganosiloxane gum is continued until the shearing force is sufficient to achieve an average particle size of from about 1 to 1000 microns thereby forming an organosiloxane composition in the form of a flowable powder.
• the length of time required to achieve such a particle size can vary from about 2 minutes to about 50 minute after addition of the high consistency polydiorganosiloxane gum, depending at least in part on the capacity of the mixer chamber and the shear force provided by the mixer.
• step (B) the reduction and subsequent increase in the particle size of the high consistency polydiorganosiloxane gum that occurs during step (B) may be monitored by plotting the amount of electrical power consumed by the motor(s) driving the chopper blades as a function of time.
• This method of assessing the particle size of the high consistency polydiorganosiloxane gum is described in Bilgrien et al., U.S. 5,153,238 which is hereby incorporated by reference.
• step (B) after the reinforcing silica filler is fluidised and the required temperature established the treating agent may be added prior to, during, or after addition of the high consistency polydiorganosiloxane gum.
• the treating agent is added during blending of the high consistency polydiorganosiloxane gum with the fluidized reinforcing silica filler.
• the powdered organopolysiloxane composition at a temperature of 80°C or higher is directly transferred to a bulk solids cooling device to facilitate accelerated cooling of the powdered organopolysiloxane composition to a temperature below the decomposition and/or activation of a subsequently to be added catalyst.
• the bulk solids cooling device may be any of those known in the art capable of facilitating the cooling of the powdered organopolysiloxane composition.
• step B of the integrated process according to the present invention is used to distinguish step B of the integrated process according to the present invention from those situations where the bulk powder of high consistency polydiorganosiloxane gum is allowed to cool relatively undisturbed under ambient conditions.
• the powdered organopolysiloxane composition is free-flowing at this point it is somewhat sticky and easily massed if significant compaction occurs. Therefore, in choosing a bulk cooling device to facilitate cooling of the powdered organopolysiloxane compositions it is important to consider these characteristics of the powder.
• Suitable bulk cooling devices include, for example, belt coolers, jacketed mixers such as the above described Littleford-type mixer, fluidised mixers through which cooling air may be blown, and flow-through apparatus having one or more cooling elements positioned therein.
• a preferred bulk solids cooling device is that described in Mueller, U. S. Pat. 5,167,274 which is hereby incorporated by reference.
• a means adapted to eliminate or reduce lumps, large particles and/or agglomerates which could clog or otherwise compromise the capacity of the bulk solids cooling device may be positioned in the flow path between the mixer of step (B) and the bulk solids cooling device.
• Said means may be of any appropriate design, for example a powder mill, chopper or the like.
• One example of such a means useful in the present process is described in Lynch et al, U.S. Pat. No. 4,768,722 which is hereby incorporated by reference.
• the powder of high consistency polydiorganosiloxane gum After the powder of high consistency polydiorganosiloxane gum has been cooled to a temperature below the decomposition and/or activation temperature of the catalyst to be added in subsequent steps, the powder is fed directly to a massing apparatus suitable for forming the powder into a coherent mass.
• the massing apparatus is a single or twin screw extruder capable of massing the powdered high consistency polydiorganosiloxane gum composition without generating significant heat.
• those single screw extruders typically referred to as "cold feed" silicone rubber extruders such as manufactured by National Feed Screw (Massilon, OH) and Davis Standard (Mystic, CT).
• the exit end of such an extruder is fitted with a screen to strain out particulates that may be present in the massed silicone rubber composition.
• the catalyst may be added to the process anytime after the cooling step (C); that is, after step (C) and before step (D), during step (D), or after step (D).
• the catalyst may be proportioned between two or more of the above described addition points. Because the preferred extruders for use in step (D) typically have poor mixing capabilities, it is preferred that the catalyst be added in a mixing step conducted after step (D).
• a mixing device is coupled directly to the exit end of the barrel of the extruder of step (D). Any low temperature distributive-type mixing devices known in the art may be used for this mixing step. Such mixing devices are described, for example, in MIXING IN POLYMER PROCESSING, Ed.
• a preferred mixer for use in the present process is a cavity transfer type mixer as described in the above citations which are hereby incorporated by reference.
• the catalysed silicone rubber composition is shaped into a suitable form for shipping and handling by means of a die positioned at the exit end of the extruder or when a separate mixer is used at the exit end of the mixer.
• a catalyst containing silicone rubber composition mass is obtained from the present process.
• the massed silicone rubber composition is extruded from the mixer into a size and configuration suitable for further processing in moulding and extruding applications.
• the final size and configuration of the material produced by the present process is not critical and will be generally dictated by the requirements of the final use of the composition.
• Step (B) of the present process involves adding about 10 to 80 parts by weight of a reinforcing silica filler for each 100 parts by weight of the high consistency polydiorganosiloxane gum introduced in Step (A).
• a reinforcing silica filler are well known in the art and may be any of those finely divided silicas having a surface area greater than about 50 m ⁇ /g and include fumed silica, precipitated silica, and silica gels.
• the preferred silica is a fumed silica having a surface area within a range of from about 75 m ⁇ /g to 1000 m ⁇ /g.
• the reinforcing silica filler is added to the present process in step (A).
• the reinforcing silica filler is introduced into the mixer in an untreated form but it may alternatively have been pretreated using treating agents as described below prior to introduction into the mixer.
• the high consistency polydiorganosiloxane gum which is the major component of the silicone rubber composition formed by the present process has a viscosity in a range of from about 6 x 10 ⁇ to 1 x 10 ⁇ mPa.s at 25°C. More preferably the high consistency polydiorganosiloxane gum has a viscosity in a range of from about 1 x 10 ⁇ to 1 x
• the high consistency polydiorganosiloxane gum may be represented by the general formula R3(RlR2siO) n R3 where Rl, R ⁇ , and R 3 are each independently selected monovalent substituted or unsubstituted hydrocarbon groups and n, the average number of repeating units in the polymer, is selected to provide a viscosity within the ranges described above.
• the monovalent hydrocarbon groups represented by Rl, R ⁇ , and R 3 include alkyl and substituted alkyl groups containing from 1 to about 20 carbon atoms, alkenyl groups such as vinyl and 5-hexenyl, cycloalkyl groups such as cyclopentyl and cyclohexyl, and aromatic hydrocarbon groups such as phenyl, benzyl and tolyl.
• Rl, R ⁇ , and R 3 may be independently substituted with, for example, substituents such as halogens, alkoxy groups, and cyano groups.
• Preferred monovalent hydrocarbon radicals are selected from the group consisting of alkyl groups comprising from 1 to 4 carbon atoms, alkenyl, phenyl, and 3,3,3-trifluoropropyl. Most preferably each Rl is independently selected from the group consisting of methyl and alkenyl groups comprising from 1 to 5 carbon atoms, R ⁇ is methyl, and R 3 is selected from the group consisting of methyl and alkenyl groups comprising from 1 to 5 carbon atoms.
• the high consistency polydiorganosiloxane gum may be a homopolymer, a copolymer or a mixture containing two or more different homopolymers and/or copolymers.
• the high consistency polydiorganosiloxane gum may be, for example, trimethylsiloxy end-capped polydimethylsiloxane, vinyldimethylsiloxy end-capped polydimethylsiloxane, vinyldimethylsiloxy end-capped polydimethyl/vinylmethylsiloxane copolymer, and trimethylsiloxy end-capped polydimethyl/vinylmethylsiloxane copolymer.
• step (B) also requires the addition of a treating agent for the reinforcing silica filler.
• the treating agent may be any of those typically used to treated reinforcing silica fillers to make them more hydrophobic and to reduce or prevent a phenomena typically referred to as “creping” or “crepe hardening” that often occurs when mixture of such fillers and polydiorganosiloxanes are stored for any appreciable period of time. Creping is characterized by a gradual increase in the viscosity or decrease in the plasticity of such polydiorganosiloxane compositions. Although such crepe hardening may often be reversed by subjecting the composition to shearing forces using a rubber mill or sigma blade mixer, this adds an additional process step in the use of the composition and such step is preferably avoided.
• Compounds which may be used as treating agents for the reinforcing silica fillers include, for example, liquid low-molecular weight silanol or alkoxy-terminated polydiorganosiloxanes, hexaorganodisiloxanes, hexaorganodisilazanes, cyclic diorganosiloxanes, and partial hydrolyzates of such compounds.
• Preferred treating agents for use in the present process are a low molecular weight hydroxy end-blocked polydimethylsiloxane fluid or a reaction product of a low molecular weight (LMW) hydroxy end-blocked polydimethylsiloxane fluid and/or a LMW hydroxy end-blocked phenylmethylsiloxane fluid and/or a LMW hydroxy end-blocked methylvinylsiloxane fluid which reaction may be catalysed using ammonium hydroxide or ammonium carbonate.
• LMW low molecular weight
• the treating agent may be utilized in any appropriate amount that reduces or prevents crepe hardening of the silicone rubber composition prepared by the present method.
• a useful amount of treating agent is about 10 to 45 weight percent based on the weight of the reinforcing silica filler.
• Preferred is when about 15 to 35 weight percent of the treating agent is added in step (B) of the present process, based on the weight of the reinforcing silica filler.
• optional components may be added during step (B) depending upon the properties desired in the cured silicone elastomer prepared from the process.
• Such optional components include extending fillers such as treated and/or untreated quartz, calcium carbonate, hydrated alumina and diatomaceous earth; pigments such as iron oxide and titanium oxide; electrically conducting fillers such as carbon black and finely divided metals; heat stabilizers such as hydrated cerric oxide; flame retardants such as antimony compounds, hydrated aluminium oxide, magnesium compounds and halogenated hydrocarbons; adhesion promoters; internal mould release agents such as zinc stearate and resinous organosiloxane copolymers as reinforcing agents.
• the treated extending fillers are typically treated with the agents described for the treatment of the reinforcing fillers.
• the catalyst added to the present process is preferably either an organoperoxide type catalyst or a hydrosilylation catalyst, but is most preferably an organoperoxide catalyst.
• any suitable organoperoxide which is effective as a catalyst for the curing of silicone compositions may be used.
• the organoperoxide catalyst may be vinyl specific and require the presence of vinyl or other alkenyl groups substituted on the polydiorganosiloxane polymers.
• the organoperoxide may be non- vinyl specific, and react with hydrocarbon groups bonded to silicon atoms of the high consistency polydiorganosiloxane gum to generate a free radical at which cross-linking may be effected.
• the organoperoxide catalyst may include di- tertiary butyl peroxide, tertiary-butyl-triethylmethyl peroxide, tertiary-butyl-tertiary-butyl- tertiary-triphenyl peroxide, t-butyl perbenzoate and di-tertiary alkyl peroxides such as dicumyl peroxide and 2,5-bis(tert-butyl peroxy)-2,5-dimethylhexane.
• organoperoxide catalyst which effect curing through saturated as well as unsaturated hydrocarbon groups on the siloxane chains are aryl peroxides such as tertiary-butyl perbenzoate, chloroalkyl peroxides such as 1,3-dichlorobenzoyl peroxide, 2,4- dichlorobenzoyl peroxide, monochlorobenzoyl peroxide, benzoyl peroxide, bis(ortho- methylbenzoyl) peroxide, bis(meta-methylbenzoyl) peroxide, bis(para-methylbenzoyl) peroxide, or a similar monomethylbenzoyl peroxide, bis(2,4-dimethylbenzoyl) peroxide, or a similar dimethylbenzoyl peroxide, bis(2,4,6-trimethylbenzoyl) peroxide, or a similar trimethylbenzoyl peroxide.
• a preferred organoperoxide catalyst is selected from the group consisting of 2,4
• the catalytic amount of the organoperoxide catalyst is that sufficient to effect cure of the organopolysiloxane composition when heated above the decomposition temperature of the organoperoxide.
• the organoperoxide may be added to the organopolysiloxane composition, based upon the weight of the organopolysiloxane composition.
• curing of the composition made in accordance with the process of the invention may be carried out via an addition curing reaction using a catalyst comprising a platinum catalyst in combination with a polyorganosiloxane having at least two silicon-bonded hydrogen atoms per molecule.
• the platinum catalyst may be exemplified by the following: a fine-powdered platinum, chloroplatinic acid, alcohol-modified products of chloroplatinic acid, platinum chelates, a complex of platinum and diketone, coordination compounds of a chloroplatinic acid and olefins, a complex of a chloroplatinic acid and an alkenylsiloxane,
• the platinum catalysts may optionally be on an appropriate carrier such as alumina, silica, carbon black or may be encapsulated within at least one layer of a thermoplastic polymer selected from the group consisting of organic polymers and polyorganosiloxanes.
• the most preferred platinum catalyst is a complex of a chloroplatinic acid and an alkenyl siloxane having a very high catalytic activity in a hydrosilylation reaction such as the platinum-alkenylsiloxane complex disclosed US 3419593 or a spherical fine-powdered catalyst composed of a thermoplastic resin that contains more than 0.01 wt.% of metal platinum atoms.
• the platinum catalyst is preferably used in an amount of 0.01 to 500 and more preferably 0.1 to 100 parts by weight based on 10 6 parts by weight of the component A.
• Polyorganosiloxanes having at least two silicon-bonded hydrogen atoms per molecule may be exemplified by the following compounds: trimethylsiloxy terminated polymethylhydrogensiloxane, a trimethylsiloxy terminated copolymer of methylhydrogensiloxane and dimethylsiloxane, a copolymer of a dimethylhydrogensiloxy terminated methylhydrogensiloxane and dimethylsiloxane, a copolymer of a methylhydrogensiloxane and a cyclic dimethylsiloxane, an organopolysiloxane composed of siloxane units expressed by the formula (CH 3 ) HSiO 1/2 , together with siloxane units of the formula SiO 4/2 or CH SiO 3 2 and optionally units of the formula (CH 3 ) 2 SiO 2 / 2; a dimethylhydrogensiloxy terminated polydiorganosiloxane, a dimethylhydrogensil
• the viscosity of the polyorganosiloxane having at least two silicon-bonded hydrogen atoms per molecule at 25°C is within a range of 2 to 100,000 mPa.s.
• the polyorganosiloxane having at least two silicon-bonded hydrogen atoms per molecule is added in amount such that the ratio of the total mole number of silicon-bonded hydrogen atoms to the total mole number of alkenyl groups in the component A is in the range of from 0.5 : 1 to 20: 1.
• the polyorganosiloxanes having at least two silicon-bonded hydrogen atoms per molecule may be introduced into the composition during step B prior to, during, or after addition of the high consistency polydiorganosiloxane gum, or any time after the completion of step C.
• the composition preferably also includes one or more cure retarders which are preferably introduced into the composition before and/or simultaneously with the addition of the platinum catalyst.
• suitable cure retarders include alkyne alcohols such as 3-methyl-l-butyn-3-ol, 3,5-dimethyl-l-hexyn- 3-ol, and 3-phenyl-l-butyn-3-ol; ene-yne compounds such as 3-methyl-3-penten-l-yne and 3,5-dimethyl-3-hexen-l-yne; tetramethyltetrahexenylcyclotetrasiloxane, and benzotriazole.
• a means for adding a high viscosity compound into a mixer comprising:- a container having a closed end and an open end, a flexible inner liner bag secured at the open end of the container, which bag is adapted to receive an amount of a high viscosity compound and a delivery device, having an inlet and an outlet, wherein the delivery device is adapted to receive high viscosity compound from the bag when the open end of said container is placed in communication with the inlet of the delivery device and deliver said high viscosity compound into a mixer.
• an apparatus suitable for use in the integrated process as hereinbefore described comprising a means for adding a high viscosity compound into a mixer comprising: -
• a container having a closed end and an open end, a flexible inner liner bag secured at the open end of the container, which bag is adapted to receive an amount of a high viscosity polymer and a delivery device having an inlet and an outlet, wherein the delivery device is adapted to receive high viscosity polymer from the bag when the open end of said container is placed in communication with the inlet of the delivery device and deliver said high viscosity polymer into a high-shear mixer, a. a high -shear mixer, b. a bulk solids cooling device and c. a massing apparatus,
• said mixer having a plurality of inlets, an outlet, a motor and one or more high shear blades, said motor being adapted to provide rotational energy to said high shear blades contained therein, and thereby fluidise powder introduced into the mixer through one or more of said inlets
• the mixer is additionally adapted to receive high viscosity polymer through a polymer feed port from the container by way of the delivery device, for mixing with said fluidised powder to form a flowable powder, and a treating agent through one or more of said inlets
• said bulk solids cooling device has an inlet and an outlet
• the bulk solids cooling device inlet is adapted to receive flowable powder from said mixer, which powder is cooled in the cooler and subsequently transported from said bulk powder cooler exit to said massing apparatus which is adapted to mass any powder which has been cooled in said bulk solids cooling device, said apparatus being adapted to enable the introduction of one or more additives into free flowing powder prepared in mixer before, during or after cooling.
• Figure 1 is a schematic representation of an equipment configuration suitable for delivering a high viscosity polymer into a mixer; and Figure 2 is a schematic representation of an equipment configuration suitable for practising the integrated process of the present invention utilizing the described high consistency polydiorganosiloxane gum delivery method.
• a container in the form of drum 10 which has a vent hole 11 and an inner liner bag 12.
• Inner liner bag 12 is adapted to receive an amount of high viscosity organopolysiloxane and is attached to the top of drum 10 by securing band 14.
• a tapered delivery device 15 having an inlet 20 and an outlet 21.
• the tapered delivery device 15 is conically shaped with the diameter of the inlet being greater than that of the outlet.
• two control rods 16 Positioned in tapered delivery device 15 are two control rods 16 which are both perpendicular to each other and perpendicular to the vertical axis of tapered deliver device 15.
• high consistency organopolysiloxane in drum 10 is retained in inner liner bag 12, such that none of the high consistency polydiorganosiloxane gum is in contact with the drum 10 during storage.
• drum 10 is upturned and placed over or in communication with inlet 20 of tapered delivery device 15.
• the high consistency polydiorganosiloxane gum leaves the drum and passes through inlet 20 of delivery device 15.
• the high consistency polydiorganosiloxane gum subsequently passes through delivery device 15 and out through exit 21 and into a mixer passing control rods 16.
• liner 12 is illustrated exiting drum 10 and peeling away from high consistency polydiorganosiloxane gum 13 thereby effecting delivery of high consistency polydiorganosiloxane gum 13 to tapered delivery device 15.
• the present method is especially useful when incorporated into an integrated process as depicted in Figure 2 for producing catalyst containing silicone rubber compositions, resulting in substantially reduced processing time and labor input compared to standard methods for producing such compositions.
• a preferred equipment configuration suitable for practising the present integrated process for manufacturing a catalyst containing silicone rubber composition in this case an organoperoxide catalyst containing silicone rubber composition comprising the apparatus for adding high consistency polydiorganosiloxane gum to a high shear mixer 1.
• High-shear mixer 1 has attached thereto motor 2 for providing rotational energy to high shear blades contained therein (not shown), silica hopper 3, polydimethylsiloxane feed port 4 to which is fitted delivery device 15 and feed port 5 for feeding the treating agent for the silica filler and optional ingredients as described herein.
• motor 2 for providing rotational energy to high shear blades contained therein (not shown)
• silica hopper 3 polydimethylsiloxane feed port 4 to which is fitted delivery device 15 and feed port 5 for feeding the treating agent for the silica filler and optional ingredients as described herein.
• In the bottom of high-shear mixer 1 is an exit port connected to powder mill 6. Powder mill 6 empties into bulk solids cooling device 7. Bulk solids cooling device 7 feeds into extruder 8 which has attached at its exit end mixer 9.
• Mixer 1 is initially heated to a temperature of above 80°C subsequent to which silica is fed into mixer 1 from hopper 3 and, when required, extending filler is introduced into mixer 1 from feed port 5 and the filler(s) is/are fluidised by means of the high shear blades driven by motor 2. After a short heating and fluidising period the high consistency polydimethylsiloxane is introduced into mixer 1 through feed port 4 by way of delivery device 15 and treating agent is introduced into mixer 1 through feed port 5. After a further predetermined period of time the pressure in mixer 1 was reduced in order to extract any remaining volatile species.
• a 325 liter fiber pack drum fitted with a rubber coated fabric liner was filled with a vinyl-functional polydimethylsiloxane having a viscosity within a range of 1 x 10 6 to 1 x 10 7 mPa.s at 25°C.
• the weight of polydimethylsiloxane placed in the drum is reported in Table 1.
• the drum was inverted over a tapered delivery device.
• the tapered delivery device was formed from sheet metal and was approximately 152 cm tall, 101 cm in diameter at the top, and 43 cm diameter at the bottom.
• the wall of the tapered delivery device was 11 degrees from vertical forming a 22 degree included angle.
• the tapered delivery device was fitted with an extension that extended the length by 28 cm, resulting in a 33 cm bottom opening.
• the tapered delivery device was lined with polyethylene sheets.
• the surface of the polyethylene sheets was sprayed with polydimethylsiloxane fluid having a viscosity of 40 mPa.s at 25°C to provide a low friction surface.
• Holes were placed near the bottom opening of the tapered delivery device to allow control rods to be inserted across the opening to alter the flow of the polydimethylsiloxane therethrough.
• the bottom of the tapered delivery device was positioned about 2 meters above a receiving container.
• Results using various delivery device openings, rod sizes and configurations, and polydimethylsiloxane loadings are given in Table 1.
• Initial time is the elapsed time from when the polydimethylsiloxane was added to the tapered delivery device until it began to enter the receiver container.
• Final time is the elapsed time from when the polydimethylsiloxane was added to the tapered delivery device until delivery to the receiver container was essentially complete.
• the Rate of delivery to the receiver container is given in Kg/h. Residual is the amount of added polydimethylsiloxane retained in the drum and tapered delivery device.

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