Process to produce tack-free rubber particles

Abstract

A process to produce a free flowing fine polymer powder is provided. The process comprises the steps of: providing a polymer cement comprising a polymer either melt or dissolved in a solvent to form a polymer cement; dispersing an antiblocking agent within a stream consisting of steam to form atomization steam; atomizing the polymer cement; contacting the atomized polymer cement with the atomization steam; and recovering polymeric particles. Polymeric particles so prepared have an average particle size of between 100 and 1000 microns. In a preferred embodiment, the polymers produced are rubbery polymers which are free flowing.

I claim: 
     
       1. A process to produce a powder of free flowing polymer particles, the process comprising the steps of: (a) dispersing an amount of antiblocking agent, effective to prevent fouling of down stream equipment and to result in free flowing polymer particles, in a stream of steam to form a atomizing steam stream which does not contain polymer cement;   (b) atomizing a polymer cement, comprising polymer dispersed in a solvent and which is discharged from an atomization nozzle creating a mist of fine droplets of polymer cement, by contacting the polymer cement at the discharge of the atomization nozzle for the polymer cement with the stream of atomizing steam, wherein a substantial portion of the solvent is vaporized from the atomized polymer cement; and   (c) recovering a powder of free flowing polymer particles from the steam-atomized polymer cement wherein said polymer particles have an average particle diameter between about 100 and about 1,000 microns withouot grinding the polymer particles.   
     
     
       2. The process of claim 1 wherein the antiblocking agent is a finely divided power. 
     
     
       3. The process of claim 1 wherein the antiblocking agent is selected from the group consisting of aluminum oxide, silicon dioxide, calcinated aluminum, zinc stearate, calcium carbonate, clay, talc, titanium dioxide, high density polyethylene, magnesium carbonate, and combinations thereof. 
     
     
       4. The process of claim 1 wherein the step of recovering powder of free flowing polymer particles is accomplished by a process comprising passing the steam-atomized cement mixture through a cyclone separator. 
     
     
       5. The process of claim 1 wherein the cement is a solution in which the polymer was synthesized by a living polymerization process. 
     
     
       6. The process of claim 1 wherein the antiblocking agent is dispersed in steam by forcing a slurry containing the antiblocking agent through an atomization nozzle in the presence of the steam. 
     
     
       7. The process of claim 1 wherein the polymer is a block copolymer comprising at least one block comprising polymerized vinyl arene monomer units and at least one block comprising polymerized conjugated diene monomer units. 
     
     
       8. The process of claim 7 wherein the block copolymer is hydrogenated. 
     
     
       9. The process of claim 8 wherein the hydrogenated block copolymer is a hydrogenated styrene-butadiene-styrene block copolymer. 
     
     
       10. The process of claim 7 wherein the hydrogenated block copolymer is a hydrogenated styrene-butadiene block copolymer. 
     
     
       11. The process of claim 6 wherein the slurry comprises between about 1 and about 6 parts by weight of an antiblocking based on 100 parts by weight of slurry in a volatile liquid. 
     
     
       12. The process of claim 11 wherein the antiblocking agent is a silica. 
     
     
       13. The process of claim 11 wherein the volatile liquid is predominantly cyclohexane. 
     
     
       14. The process of claim 1 wherein the solvent is selected from the group consisting of hexane, cyclohexane, heptane, benzene, xylene, and mixtures thereof. 
     
     
       15. The process of claim 1 wherein the polymer is an elastomeric thermoplastic. 
     
     
       16. The process of claim 1 wherein the effective amount of antiblocking agent is between about 80 percent and about 300 percent of theoretical coverage for the free flowing polymer particles. 
     
     
       17. In a process for removing solvent from a polymer cement in a cyclone separator wherein the polymer cement is discharged from an atomization nozzle in the cyclone separator and a mist of fine droplets of polymer cement is created, the improvement which comprises producing a powder of free flowing polymer particles having an average particle diameter between about 100 and about 1,000 microns without grinding by dispersing an amount of an antiblocking agent, effective to prevent fouling of downstream equipment and to result in free flowing polymer particles, in a steam of steam to form an atomizing steam stream which does not contain polymer cement and then contacting the polymer cement at the point of discharge from the polymer cement atomization nozzle with the stream of atomizing steam.