MXPA00000142A - A method of producing synthetic rubbers - Google Patents

Abstract

A method for producing an elastomeric mixture based on the steps of mixing the additives and/or fillers of the predetermined composition of the mixture to be produced into a solution of at least one elastomer in one or more solvents, removing the solvent from the mixture thus obtained, and granulating the mixture to produce dry granules of elastomeric mixture.

Description

METHOD FOR PRODUCTfl SYNTHETIC GUMS DESCRIPTION The present invention relates to a method for producing synthetic gums in particular, but not exclusively, for the production of tires. More specifically, the invention relates to a method for producing solvent-free synthetic elastomer blends ready for conventional molding and vulcanization operations, and so-called master batches that have a high content of additives and / or fillers and which are used for conventional way to produce the mixtures mentioned above. Both of these "types" will be referred to in the following description simply as elastomeric mixtures. It is known that synthetic elastomers such as, for example, polybutadiene, polyisopropene, butyl, and styrene-diene rubbers, etc., are produced by catalytic polymerization of the respective monomers in organic solvents. It is also known that the reaction conditions, the operating parameters of the processes, and the catalysts used are strictly selected in relation to the chemical / physical characteristics of the synthetic rubber to be produced. For example, and in particular, it is well known how carefully the catalyst and operating conditions are selected in order to ensure a predetermined weight ratio of cis / trans isomers in the produced elastomer, the modulus of elasticity of the final product being associated. with this relationship. The elastomer produced is recovered from the polymer solution by distilling the solvent in a vapor stream. The elastomer recovered in this manner is free of organic solvent but incorporates up to 50-60% by weight of condensed vapor which is generally removed by a first treatment on web driers and subsequent extrusion through suitable dies. An elastomeric granulate, substantially dry, free of solvent, is obtained in this manner. This extrusion step which is generally provided for the elastomer, in the prior art, constitutes a considerable and recognized mechanical stress which results in an appreciable deterioration of the flexibility properties which are achieved with great difficulty in the polymerization step (a substantial reduction in the original modulus of elasticity) apparently due to an increase in the content of trans isomer. In order to restore the predetermined flexibility values of the final gum, the known technique provides an adequate addition of natural gum (100% cis isomer) to the elastomeric granulate when the mixture is formulated. In addition to the aforementioned disadvantage connected with the extrusion step, an additional technical-economic problem is that at least three separate steps are required to obtain an elastomeric granulate free of solvent and moisture from the elastomeric solution, i.e. : the distillation in a steam stream, the drying, and the extrusion, each of which involves the use of respective apparatus with installation and handling of related costs. The problem on which the present invention is based is provide a method that allows dry, solvent-free synthetic elastomers to be produced, overcoming the aforementioned problems with reference to the prior art, particularly and above all, those caused by the extrusion step. This problem is solved, according to the invention, by a method for producing synthetic elastomers in granular form from a solution thereof in at least one organic solvent, characterized in that it comprises the steps of: - Providing a continuous flow of the solution in a turbo dryer / granulator that has a shaft with blades that rotates to 400/1200 revolutions / minute, - dispersing the solution in the form of particles and centrifuging simultaneously against the inner wall of the turbo dryer / granulator, forming a thin tubular fluid bed, - advancing the fluid bed through the turbo dryer / granulator 20 towards the outlet thereof, - supplying heat to the fluid bed, separating the solvent from the elastomeric solution particles with the simultaneous formation and growth of granules thereof, - separating the dry elastomer granulate from the gaseous solvent stream with the turbo dryer / granulator discharge. In order to supply heat to the fluid bed of elastomeric solution particles, the inner part of the turbo dryer / granulator is heated to temperatures between 80 and 120 °. A stream of hot nitrogen (120-140 °) supplied to the turbo dryer in the same direction as the flow of elastomeric solution is advantageously used to promote evaporation and removal of the solvent from the solution, as well as the formation of the fluid bed of particles. The term "turbo dryer / granulator" is designed to define in the present apparatus that consist of a cylindrical, tubular body, generally arranged with its horizontal axis, closed at opposite ends, and having intake openings for materials and / or substances to be treated and exit openings for the treated material, and also has a heating sleeve to bring the inner wall to a predetermined temperature, a shaft with blades (or turbine), supported for rotation in the cylindrical tubular body, which has blades arranged in a helical arrangement, and which extend radially as for almost touching the inner wall of the body, and drive means being provided to rotate the shaft with blades up to 1500-2000 revolutions / minute. The use of a turbo dryer / granulator produced and marketed by the applicant has been particularly advantageous for the objects of the invention. ^ igjgi The methods of operation, performance and efficiency of the apparatus of the type mentioned above (turbo driers / granulators) are well known. In the specific case to which the present invention refers, a continuous flow of the elastomeric solution is supplied within the cylindrical, tubular body, where it is immediately dispersed, by the shaft with blades, which is rotated at 600-1200 revolutions / minute, in particles that are centrifuged against the heated wall of the body to form a thin, tubular fluid bed, which is dynamic because it is advanced towards the exit opening with a "mode" of advance imposed by the orientation of the blades of the shaft with blades. In the fluidized bed, the mixing particles are maintained in a state of constant high turbulence by the mechanical action of the blades by which they are thrown continuously against the heated wall.

With each impact (thermal shock) the temperature of the individual particles increases until it reaches the evaporation temperature of the solvent which can therefore be removed therefrom. A stream of hot nitrogen (in the same direction) is advantageously used for this purpose. The advantages connected with the use of the method of agreement with the invention are constituted, first of all, by the considerable simplification achieved in the procedure as a whole because it is possible to achieve, in a single step, a result that was achieved by at least three steps of successive operations with the methods of the prior art. &guu - • n-Sa-tat ^ g ^ _a ^ Moreover, the method according to the invention is implemented by extremely compact and versatile apparatuses, the installation and handling of costs of which are considerably less than those of the apparatuses of the prior art. Finally, by completely avoiding the extrusion step to produce the elastomer in granular form, the method according to the invention allows the elastomers produced to have improved flexibility properties due to the alterations in the structure of the polymer chains due to the stress The mechanics imposed by the extrusion mentioned above are completely avoided. The elastomer granulate produced by the aforementioned method is designed to be sent to subsequent conventional molding and vulcanization steps, after the addition of suitable additives and / or fillers. According to the prior art, these steps consist of repeated mechanical treatments, for example, decomposition, homogenization, and chewing, which have the purpose of conferring on the elastomeric mass a plasticity suitable for incorporation therein, in the most homogeneous manner possible, of all the additives and / or fillers typically used to prepare vulcanization mixtures. Among the most commonly used additives and plasticizers are vulcanization agents, accelerators, peptizing agents, antioxidants, extender oils, black carbon and color fillers.

The mechanical treatments mentioned above are carried out in respective devices, for example, extrusion plasticizers (GORDON) and mixers with rollers or closed mixers (BANBURY), and it must be mentioned that the additives are added to the plasticized elastomeric mass in a very precise sequence which is critical for the objects of the final result. In addition to the operational complexity and the difficulties in controlling and executing extemporaneous interventions during the various operations, as well as the substantial consumption of expensive additives, a recognized problem of the prior art is the imperfect and non-homogeneous distribution of the additives and / or fillers in the plasticized elastomeric mass, with the possibility resulting from defects of greater or lesser importance in the final product. Surprisingly, it has been discovered that all of the problems mentioned above are overcome by premixing, in the starting elastomeric solution, all the preselected additives and / or fillers to produce the final mixture. The present invention consequently also relates to a method for producing an elastomeric mixture from a solution of at least one synthetic elastomer in one or more solvents, the mixture having a predetermined composition comprising at least one synthetic elastomer and one or more additives. and / or fillers conventionally used in the gum industry, characterized pyrque consists, basically, of the steps of: - intimately mixing the elastomeric solution with the additives and / or fillers of the predetermined composition of the mixture to be produced, -remove the solvent of the mixture thus obtained, and -granulating the mixture to produce dry, solvent-free granules, each of which has a composition substantially identical to the composition of the predetermined mixture. In this case also, the steps of removing the solvent and granulating the mixture advantageously tplace simultaneously in a turbo dryer / granulator. Because each mixing particle consists of a respective amount of vulcanizing agent in due proportion, the temperature of the particles within the turbo dryer must not reach the vulcanization temperature. It has been discovered that wall temperatures of 80-120 ° and nitrogen temperatures of 120-140 ° are optimal for this object. With the temperature values mentioned above and the speed of rotation of the shaft with knives, it has been discovered that it is possible to treat continuous mixing flows (elastomeric solution / solvents / additives) with flow rates of 5000-8000 kg / hour, with periods 60-90 * * * ^ ¿M ^ g? ^ - ^^ seconds spent in the turbo dryer, and with the production of a granulate which is discharged at a temperature of 30 ° -40 ° C. The composition of the "elastomeric granulate mixture" produced in this way is statistically so satisfactory that it can be sent directly (pneumatically) to the molding and vulcanization presses. The organic solvent discharged from the turbo dryer can be recovered by conventional techniques and reused for the polymerization reaction. The optimum results of the method of the invention are closely related to the manner in which the ingredients and fillers are premixed in the elastomeric solution. The more homogenous and intimate this mixture is, the better the "composition" of each individual blend granule that conforms to the predetermined and desired composition. For this purpose, it has been discovered that it is particularly advantageous to use turbine mixers and, more particularly, those known as TURBOMETERS, which are structurally similar to the turbo driers described above and, like turbo driers, are produced by Applicants and marketed with the trademark TURBOMIXER. The advantages of the invention. - Clearly, both the plant and the operation are greatly simplified. In fact, it is enough to keep in mind that, by carrying out rfHHHaÉ ^ g jittArfM «gU H, * & j ^ &g ^^^ H ^ l ^ j | Fc ^^ ^ 3? ^ J í to only two operative steps (mixing plus drying / granulation), and thus the use of apparatus consisting of only 2-3 small and very efficient machines, for example, Vomm turbomixers and turbo driers / granulators, it is possible to produce rubber mixtures ready for five molding and vulcanization, for which the prior art required the installation of large, complex plants which are not easy to operate and control, and which involve the use of many trained workers. -The premix of the pre-selected additives and / or fillers with the solution of elastomers in organic solvents is carried out in viscous fluid conditions; this ensures optimal homogenization of the one mixture which, when carried out by a TURBOMIXER achieves comparable levels of "intimacy" with the films of the individual particles of fillers and additives with the elastomeric solution. The results in the final product are considerably better than those achieved by the prior art in which, precisely due to the dry mixing, the polymer chains were subjected to fatigue stress and therefore chain breaking due to the powerful mechanical action of Banbury type mixers. - The high degree of homogenization achieved in the premix The aforementioned allows the use and consumption of small amounts of additives, particularly peptizing agents which, in the methods of the prior art, must necessarily be used in ^^! Jg ^^^ ^^^^ s ^ SSÍ¡ Iî Let's ^^^^^^^^^^^^^ Im ^ significant step to facilitate chewing and subsequent incorporation of other additives amounts. - The production of an elastomeric mixture in ready-to-use granular form provides a material that is much easier to handle than the "material" of the prior art; this allows the use of considerably simplified devices, which can be controlled easily and safely to the extent that the need for personnel is reduced or even eliminated. - Surprisingly, the produced elastomeric mixture granules have better flexibility characteristics than those of conventional mixtures. The modulus of elasticity values displayed in many tests performed on granules of the mixture of the invention allows the hypothesis that the length of the chains which are elastomers in the starting solution is not in any way reduced during the steps of removal of solvent and granulation and that its cis isomer content is not only reduced but even increased. Although the chemical-physical mechanism mentioned above is not fully explained, it is thought that this can occur as a result of "supplying" large amounts of mechanical energy, through the shaft with blades, to the mixture of very small particles that make up the bed. Fluid generated by the shaft. This surprising result can also involve, if confirmed, a complete series of advantages for polymerization reactions, ^ sggjj & ^ jggg for the catalysts used and for the operational parameters, as will be apparent to those skilled in the art. The advantages and features of the invention will become clearer from one embodiment of the method of the invention described by way of non-limiting example with reference to apparatuses shown schematically in the appended drawings. In the drawings: Figure 1 shows schematically a drier / granulator used for producing elastomers turbo free granulates solvent according to the method of the invention, and Figure 2 shows apparatus for producing a granulated elastomeric mixture. With reference to Figure 1, a turbo dryer / granulator is used to implement the method according to the invention comprising, basically, a tubular, cylindrical body 1 closed at its opposite ends by walls 2, 3 and having a coaxial heating sleeve 4 through which a fluid, eg, diathermic oil, is designed to flow to maintain the inner wall 1a of the body 1 at a predetermined temperature. The tubular body 1 has inlet openings 5, 6 for the solution of elastomers in at least one organic solvent, and for hot nitrogen, respectively, as well as outlet openings 7 and 8 for granular elastomers and organic solvents. in gaseous state, respectively. A shaft with blades 9 supported for rotation in the tubular body 1 has blades 10 arranged in the manner of a helix and oriented to centrifuge the elastomeric solution and the granulate gradually formed therein and simultaneously drive them towards the outlet. An engine M is provided to drive the shaft with blades 9 at variable speeds of 600 to 1200 revolutions / minute or more.

EXAMPLE 1 150 l / h of a solution of butadiene / styrene copolymer in cyclohexane in a ratio of 1: 1 by weight was continuously supplied in the turbo dryer 1 in which the shaft with blades 9 was rotated at a speed of 1000 revolutions / minute and in which the inner wall 1a was maintained at a temperature of 120 °. At the same time, a stream of nitrogen was supplied through the opening 6, in the same direction, at 140 ° C, with a flow rate of 300 Nm3 / h. Immediately after admission to the turbo dryer 1, the flow of copolymer solution was mechanically divided into particles which were centrifuged against the inner wall 1a of the turbo dryer and formed a thin, annular fluid bed, which was dynamic because was moved continuously to exit 7. The heat supplied to the bed fluid by the internal wall of the turbo dryer and by means of the hot nitrogen attracted the progressive removal of the cyclohexane with the simultaneous formation of increasing granules. After a period of approximately 60 seconds spent in the turbo dryer, a butadiene / styrene copolymer granulate substantially free of cyclohexane having a main temperature of 35-37 ° C was discharged continuously from the opening 7.

EXAMPLE 2 One hundred and thirty kilos / hour of a solution of polyisoprene in N-hexane (ratio 1: 2 by weight) was continuously supplied into a turbo dryer 1 and a stream of hot nitrogen was supplied simultaneously at a temperature of 120 ° C with a flow rate of 250 Nm3 / h. The temperature of the wall was regulated to a value of approximately 100 ° and the shaft with blades 9 was rotated at a constant speed of 800 revolutions / minute. After a period of approximately 60 seconds spent in the turbo dryer, a polyisoprene granulate substantially free of hexane and having a temperature of 32-33 ° C was continuously discharged therefrom.

With reference to Figure 2, the apparatus for producing the granular elastomeric mixture according to the invention consists of a turbine mixer 11 (particularly and vetajosamente a turbo mixer Vomm) with inlet openings 11a, 11 b for mixing additives. and / or fillers and for elastomeric solution, respectively, and an outlet opening 11c connected by means of a pipe 12 to a first turbo dryer / granulator 13. The turbo dryer 13 is exactly the same as the turbo dryer described with reference to the Figure 1. The turbo dryer / granulator 13 is connected, with the interposition of a gas separation cyclone 14, to a second turbo dryer 15 of identical structure, the connections being indicated schematically by pipes 16, 17. A scrubber 18 it is arranged in the gas discharge tube from the cyclone 14 and a second solid-gas separation cyclone 19 is disposed in the discharge tube 20 of the turbo dryer 15. Gas discharged from the cyclone 19 is recycled via a tube 21 to one of the inlet openings of the turbo dryer 13. The hot nitrogen can be supplied to the turbo driers 11 and 15 by means of the respective tubes 22 and 23.

EXAMPLE 3 A flow of a solution of butadiene-styrene copolymer (SPR) in cyclohexane containing the copolymer in a ratio of 1: 2 by 5 weight relative to the cyclohexane was supplied at a flow rate of 4800 kg / hour within the turbo mixer 11 to which a continuous flow consisting of the following additives given in percentage by weight was also supplied simultaneously: 0.67% benzothiazyl-2-cyclohexyl sulfonamide, 0.33% tetramethylthiuram disulfide, 2.5% sulfur, 0.9% paraffin wax, 67.1% black carbon, 6.7% zinc oxide, 16.8% highly aromatic mineral oil, 5% stearic acid. The flow rate of this second flow of additives was 2800 kg / hour. With the discharge from the turbo mixer 11, the highly homogeneous mixture was supplied continuously to the first shot turbo dryer / granulator 13 simultaneously with a stream of nitrogen heated to 120 ° C and having a flow rate of 300 Nm3 / hour. The temperature of the wall of the turbo dryer was regulated to a value of approximately 80 ° C and the speed of the shaft with knives was constantly maintained at 1000 revolutions / minute. Immediately upon admission to the turbo dryer 12, the mixture flow was mechanically divided into very small particles which were centrifuged against the heated inner wall and formed a thin, tubular fluid bed. The blades of the shaft with blades advanced the bed fluid towards the output of the turbo dryer with a predetermined mode of movement. The hot nitrogen stream easily covered the fluid bed, removing the solvent or solvents which gradually evaporated from the mixing particles. Simultaneously with this evaporation, very small "granules" of mixture began to form and these grew gradually as they moved towards the output of the turbo dryer. After a period of approximately 60 seconds spent in the turbo dryer, a solid-gas flow was discharged therefrom and supplied to cyclone 14 where the gas (hot nitrogen plus solvent) was separated from the solid (small mixing granules) . The flow of granules discharged from the cyclone 14 was supplied through the tube 17 to the second turbo dryer / granulator 15 towards which a stream of hot nitrogen was admitted simultaneously at a temperature of 80 ° C and with a flow rate of 300 m3 /hour. The removal of the solvent and the formation of elastomeric mixture granules was achieved in this second turbo dryer 15, in which the conditions of internal wall temperature and rotation speed of the shaft with blades were substantially the same as those of the turbo dryer 13. The gas-free granules were discharged at a temperature of 34-35 ° C from cyclone 19 disposed downstream and could be transported directly to the molding and vulcanization presses, while ^^ jgjj ^^^ g ^ ^ jjSÍjj rc ^^? ^ 8¿mU $ that the hot nitrogen was recycled through tube 21 to the first turbo dryer 13. At the beginning of this nitrogen recycling, the direct supply of nitrogen to the Turbo dryer 13 was automatically stopped. Many variations and modifications may be applied to the implementation of the method of the invention. In this way, for example, the solvent removal step can be carried out under vacuum, avoiding the use of a hot gas stream. Furthermore, the use of a single turbo dryer of adequate size for the removal of the solvent and the simultaneous formation of the mixing granules can be contemplated.

Claims (16)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for producing an elastomeric mixture from a solution of at least one synthetic elastomer in one or more organic solvents, the mixture having a predetermined composition consisting of at least one synthetic elastomer and one or more additives and / or fillers used conventionally in the rubber industry, which comprises the steps of: intimately mixing the elastomeric solution with the additives and / or fillers of the predetermined composition of the mixture to be produced; removing the solvent from the mixture thus obtained, and granulating the mixture to produce dry, solvent-free granules, each of which has a composition substantially identical to the composition of the predetermined mixture; characterized in that the steps of removing the solvent and granulating the mixture take place while the mixture is maintained in a turbulent fluid bed condition simultaneously in at least one turbo dryer / granulator.

2. A method according to claim 1, characterized in that the steps of removing the solvent and granulating the mixture are carried out with the supply of heat to the turbulent fluid bed condition.

3. - A method according to claim 1, characterized in that the steps of removing the solvent and granulating the mixture are carried out under vacuum.

4. A method according to claim 1, characterized in that the turbo dryer / granulator has an internal wall temperature of between 80 and 120 ° C.

5. A method according to claim 2, characterized in that a hot nitrogen stream supplied inside the turbo dryer / granulator is used for the solvent removal step.

6. A method for producing synthetic elastomers in the form of granules from solutions thereof in at least one organic solvent, characterized in that it comprises the steps of: providing a continuous flow of the solution in a turbo dryer / granulator having a shaft with blades rotated at 400/1200 revolutions / minute, - disperse the solution in the form of particles and centrifuge them simultaneously against the inner wall of the turbo dryer / granulator, forming a tubular fluid bed, - advance the fluid bed through the turbo dryer / granulator towards the outlet thereof, - supplying heat to the fluid bed, separating the solvent from the elastomeric solution particles with the simultaneous formation and growth of granules thereof, - separating the dry elastomer granulate from the flow of gaseous solvent with the discharge of the turbo dryer / granulator.

7. An apparatus for producing elastomeric mixtures in granular form from respective elastomeric solutions, characterized "^. ^, ^ | ^^ because it comprises: - a turbine mixer (11) having inlet openings (11a, 11b) for the mixture additives and / or fillers and for the elastomeric solution, respectively, and at least one outlet opening 11c for the mixture produced, - at least one turbo-dryer / granulator (13,15) 5 connected to the mixer (11) by means of a pipe (12) and having inlet openings (5,6) for the materials to be treated and at least one outlet opening (7) for the treated material, - a gas separation cyclone (14) in communication with the outlet opening (7) of the turbo dryer / granulator (13); - A tube (21) for recycling the gas discharged from the cyclone (14) to the outlet 10 of the turbo dryer / granulator (13).

8. An apparatus according to claim 7, characterized in that it consists of a second turbo dryer / granulator (15) supplied by the gas separation cyclone (14) and having an outlet opening (20) in communication with a second separation cyclone 15 gas (19).

9. A method according to claim 5, characterized in that the hot nitrogen stream supplied to the turbo dryer / granulator is used for the solvent removal step.

10. A mixture for the production of synthetic gums comprising at least one synthetic elastomer and one or more additives and / or fillers conventionally used in the rubber industry, characterized in that it is in granular form.

11. - A granular mixture comprising at least one synthetic elastomer and one or more additives and / or fillers conventionally used in the rubber industry, when produced by the method according to claims 3 to 9.

12. An apparatus for producing elastomeric mixtures in granular form from respective elastomeric solutions, characterized in that it consists of: - a turbine mixer (11) having inlet openings (11a, 11b) for the additives and / or fillers of the mixture and for the elastomeric solution, respectively, and at least one outlet opening 11c for the mixture produced, - at least one turbo dryer / granulator (13, 15) connected to the mixer (11) by means of a tube (12) and having openings of inlet (5, 6, 7) for the materials to be treated and at least one outlet opening (8) for the treated material, - a gas separation cyclone (14) in communication with the outlet opening (8) of the turbo dryer / granulate dor (13).

13. An apparatus according to claim 12, characterized in that it consists of a tube (21) for recycling the gas discharged from the cyclone (14) to the inlet of the turbo dryer / granulator (3).

14. An apparatus according to claim 12, characterized in that it comprises a second turbo dryer / granulator (15) supplied by the gas separation cyclone (14) and having an outlet opening (20) in communication with a second gas separation cyclone (19). g ^ * ** & j j | ^ j ^ «| g ^^^^ jgj ^ gd ^ ^

15. - A method for producing synthetic elastomers in the form of granules from solutions thereof in at least one organic solvent, characterized in that it comprises the steps of: - supplying a continuous flow of the solution towards a turbo dryer / granulator having a Shaft with blades rotated at 400-1200 revolutions / minute, - Disperse the solution in the form of particles and centrifuge them simultaneously against the inner wall of the turbo dryer / granulator, forming a thin, tubular fluid bed, - advance the fluid bed through the turbo dryer / granulator towards the outlet thereof, - supplying heat to the fluid bed, separating the solvent from the elastomeric solution particles with the simultaneous formation and growth of granules thereof, - separating the dry elastomer granulate from the flow of gaseous solvent with the discharge of the turbo dryer / granulator.

16. A synthetic elastomer in the form of dry granules, free of solvent produced from a solution of a corresponding elastomer in at least one organic solvent by the method according to claim 15. i | í = HM «fiMßBa attj ^^^^ ji ^ ggj BÍteMM