Method and means of sensing characteristics of a bath
United States Patent Kiefer, Jr. et al.  
 METHOD AND MEANS OF SENSING CHARACTERISTICS OF A BATH Inventors: Frank I. Kieler, Jr., Beaumont; Billy R. Clark, Groves; James M. Ware, Port Arthur, all of Tex.  
 Texas-US. Chemical Company, Parsippany, NJ.  
 Filed: Dec. 4, I972 Appl. No; 312,198  
 Related US. Application Data Continuation of Ser. No. 84,993, Oct. 29, I970, abandoned, which is a continuation-in-part of Ser. No. 873,I68, Nov. 3, I969, abandoned.  
 Assignee:  
 U.S. CI. 204/1 T, 260/8l5, 260/821 Int. Cl. G0ln 27/46 Field of Search l36/l69; 204/] T, I95 R,  
 204/l95 G, 256, 297 R; 260/78, 8l5, 821  
 References Cited UNITED STATES PATENTS 5/1908 Schoenmehl 136/169 1451 Apr. 1, 1975 973,645 l0/l9l0 Forster l36/l69 2,986,511 5/l96l Digby 204/195 G FOREIGN PATENTS OR APPLICATIONS 903,905 10/1945 France 204 195 0 Primary Examiner-T. Tung Attorney, Agent, or FirmBertram H. Mann; Frank B. Pugsley; Delmar L. Sroufe [5 7] ABSTRACT 4 Claims, 2 Drawing Figures METHOD AND MEANS OF SENSING CHARACTERISTICS OF A BATH RELATED APPLICATIONS This application is a continuation of our application Ser. No 84,993 filed Oct. 29, 1970, now abandoned, which was a continuation in part of our copending application Ser. No. 873,168 filed Nov. 3, 1969, now abandoned.  
 BACKGROUND OF THE INVENTION Where an industrial process involves control or sensing of the characteristics of an aqueous bath containing suspended substance, for instance latex, there is frequently the problem of adhesion of the substance to an immersed part, as a sensing electrode probe and its supporting and protective structures, such that the part becomes less sensitive over a period of use. Inspection, cleaning, and/or replacement of such parts is tedious and expensive and even destructive such that selfcleaning parts, which remain substantially free of suspended material over a longer period of time, would have important economic advantages.  
  One example of this situation occurs in the synthetic rubber industry wherein the polymer in colloidal form (latex) is coagulated by means including careful control of the pH of the aqueous bath. This careful control of the pH of the coagulation bath is secured by means of sensing and control equipment including a sensing electrode or probe which operates immersed in the bath. Materials heretofore used, particularly in constructing the support and protective structures for the electrode, have attracted the tacky polymer crumb so as to become coated and therefore erratic in operation after a relatively short period of use.  
  Accordingly, it is the main object of the present invention to provide a method for preventing buildup of adherent or tacky material on structure, as a sensing electrode, immersed in a bath containing the material.  
 SUMMARY OF THE INVENTION The invention is herein illustrated in connection with the coagulation bath in a synthetic rubber process. An electrode or electrodes for sensing the pH of the bath, electrode protecting tubes, and a support therefor are immersed in the bath. While many materials have been tried for this purpose we have found that certain materials, specifically, nylon 6, nylon 7, nylon 66, nylon 6/10, glass and porcelain exhibit exceptional resistance to accumulation of suspended substance when used in various types of aqueous baths. All of these materials are surface wettable or hydrophilic, that is, receive a protective coating of water in the bath either by absorptive, adsorptive, or electrostatic action, such coating or wetting protecting the support and protective structures from adhesion of the suspended substance. Other wettable or hygroscopic nylons may be used in constructing the self-cleaning probe, protective sleeve, and support body.  
 BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawing which illustrates the invention,  
  FIG. 1 is a schematic, partially exploded representation of a portion of an industrial process illustrating the invention.  
  FIG. 2 is a side view of one form of the novel sensing electrode device, part being in longitudinal center section and part being in elevational and in exploded relationship.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates schematically a coagulation tank 5 and associated parts constituting a part of the apparatus for manufacturing butadiene-styrene synthetic polymers by the emulsion process. The tank is charged through a line 6 with latex, that is, a colloidal dispersion of synthetic polymer particles as a soap stabilized em ulsion. Sodium chloride is added to line 6 through line 7, and dilute sulphuric acid is added as a lto lO-percent solution to the tank through line 8 having a control valve 9 therein. Valve 9 is automatically actuated by means of a fluid or other type of motor 10 driven from a control instrumentality ll. Suspended from instrumentality 11, or a suitable support, is the pH sensing device, generally designated 12, which is normally submerged in the rubber crumb slurry in the tank and is electrically connected to control instrumentality II by wiring and conduit structure 13. An agitating impeller 14 is suspended in the tank at a distance of from l0 to 14 inches below sensor I2 and is driven by motor means 15. It should be understood that the parts just described do not in themselves constitute the present invention, but rather provide an environment in which the method of the invention performs in an exemplary and unexpected fashion.  
  The novel pH sensor device I2 is illustrated in detail in FIG. 2. The device comprises a base or body part 18, a pair of commercial pH sensing probes (electrodes) 19 and 20, protector tubes 21 and 22, and packing and securing bushings 23 and 24.  
  Body 18 has a threaded socket 26 at its upper end for attachment to a support and is continued downwardly in branched passages 27 and 28 with cental restrictions 29 and 30 and enlarged lower portions 31 and 32 terminating in threaded sockets 33 and 34. Snugly but slidably received in passage portions 31 and 32, in the assembly, are the insulating upper extremities 35 and 36 of sensor probes I9 and 20 having basal flanges 37 and 38 and from which project the wires 39 and 40. These wires extend through passages 27, 28, and 26 and support 13 to control instrumentality 11. As will be understood, this wiring extends to conductor means exposed at the bottom extremities 41, 42 of the glass bodies of the probes for passing an electrical current through the ambient fluid, while instrumentality II senses and displays the resistance in the circuit, including the fluid intervening between conductor means 41, 42 as an indicator of the pH rating of such fluid. lnstrumentality II, in turn, controls valve 9 for adjusting the feed of the concentrated acid so as to maintain the pH of the colloidal dispersion in the tank substantially uniform as is necessary for optimum coagulation of the rubber particles therein.  
  Probes 19 and 20 depend from sockets 33 and 34 and are surrounded by protector tubes 21 and 22 having top flanges 43 and 44 which seat upon electrode flanges 37 and 38. The electrode flanges are urged against shoulders 45 and 46 at the upper ends of sockets 33 and 34 by means of packing nuts or bushings 23 and 24 bearing against protector flanges 37 and 38 with the intervention of O-ring seals 47 and 48. The bushings are externally threaded for firm securement in sockets 33 and 34 and have polygonal lower extremities 49 and 50 for engagement by a tool if necessary in threading the bushings in place.  
  While probes l9 and as commercially available are glass encased, glass as a material for constructing body 18 is generally impractical and has not been used. The materials heretofore utilized for this purpose as well as for the protector wall structure-for instance, the plastics Plexiglas and polyvinyl chloride, polyesterglass laminate, and stainless steelhave had substantial affinity for the rubber particles in the slurry. Conse quently, there have been operational periods of buildups of latex on the electrodes and support and of decreasing pH sensitivity so that it has been necessary to withdraw the sensing device from the coagulation tank at intervals to permit removal of the latex adherent. In the case of continuous processes, these removals are particularly undesirable since the quality of the product is affected and the process must be stopped during the cleaning or replacement of the sensor device, or if continued will operate for the replacement period without pH sensor control. Furthermore, the sensor probes themselves are relatively fragile and subject to breakage while being handled.  
  As the result of a substantial test program we have discovered several materials which appear to have a self cleaning effect when immersed in the coagulation tank, that is, resist build-up thereon of coagulum for a much longer period. Some of the materials found to have the self-cleaning effect are ofa glass or glassy nature, or are hygroscopic. Materials found to effectively resist build-up or coating of coagulum thereon for long periods when immersed in the coagulation tank as described above, are porcelain or glazed ceramic, Pyrex glass, Vycor glass, and silica or soft glass. In addition, nylon 6, nylon 7, nylon 66, and nylon 6/l0 plastics also have been found exemplary for the purpose and, because of their mechanical features, are recommended as the body material. All of these nylons are wettable, i.e., hygroscopic. Other wettable or hygroscopic nylons may be used in constructing the support body and/or sensing electrode and its protective sleeve. Protector tubes and attchment bushings also may be constructed ofthis material. However, we have found Pyrex glass as supplied by Corning Glass Works to be particularly ef fective as protector material.  
  Materials tried and found to be unacceptable because ofthe accumulation of solids thereon are polyvinyl chloride, FEP and TFE teflon, polyethylene, Plexiglas, ABS (acrylonitrile-butadiene-styrene plastic), polyester, type 316 stainless steel, and nylon l I. These materials are neither hygroscopic nor absorptive of moisture. Accordingly, it is our belief that wettability is the characteristic which determines the selfcleaning characteristic of the part.  
  As stated, the most desirable materials found for construction ofthe body are the nylon 6, nylon 7, nylon 66,  
 and nylon 6/10 because of their mechanical properties and molding facility, while the glass, particularly Pyrex glass, and porcelains were found to be particularly effective and desirable in construction of the protector tubes. in test service, a pH sensing device with a support body of nylon 6 and a protector tube of Pyrex glass operated substantially coagulum-free for approximately a year, whereas the normal effective life of the commercially obtainable sensors and holders is limited to approximately 300 hours because of gum accumulation on the protector tube and holder. Exemplary selfcleaning results also may be achieved by constructing the entire bath contacting surface portions of the immersed elements of one or more of the special selfcleaning materials. The invention may be modified in various respects as will occur to those skilled in the art and the exclusive use of all modifications as come within the scope of the appended claims is contemplated.  
 We claim:  
  I. The method of resisting the buildup of latex in an aqueous latex bath upon a sensing electrode and its support body immersed in the bath which comprises the step of constructing at least the surface portions of both said immersed electrode and said immersed support body entirely of one or more of the self-cleaning materials of the class consisting of procelain, glass, and wettable nylon.  
  2. In the manufcture of synthetic rubber including coagulation of colloidal latex in an aqueous bath containing a sensing electrode and its support body immersed in the bath, the method of resisting buildup of latex and coagulum on and about said electrode comprising the step of constructing at least the surface portions of both said immersed electrode and said immersed body entirely of one or more of the selfcleaning materials of porcelain, glass, and wettable nylon.  
  3. In the manufacture of synthetic rubber including coagulation of colloidal latex in an aqueous bath containing a sensing electrode and its support body immersed in the bath, the method of resisting buildup of latex and coagulum on and about said electrode comprising the step of constructing at least the surface portions of said immersed electrode and said immersed body entirely of one or more of the self-cleaning materials of the class consisting of nylon 6, nylon 6/6, nylon 6/10, porcelain, and glass.  
  4. The method of sensing the pH of the aqueous latex coagulation bath in a synthetic rubber process comprising the step of immersing in the bath a pH sensing probe and a support body therefor both having their surfaces exposed to the bath constructed of one or more of the self-cleaning materials of the class consisting of porcelain, glass, and wettable nylon to resist the adherence of latex and coagulum thereto.