Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-09-27
2004-05-18
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S099000, C524S108000, C524S110000, C524S361000, C524S364000, C524S365000, C524S379000
Reexamination Certificate
active
06737469
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to styrene-butadiene rubber (SBR) latex dispersions and more particularly to methods of adding water insoluble organic chemicals to SBR latex dispersions.
BACKGROUND OF THE INVENTION
Styrene-butadiene rubber (SBR) is the most widely used synthetic rubber in the world. Typically, an SBR latex dispersion is produced in an aqueous emulsion polymerization reaction using ratios of butadiene to styrene of about 3:1. The polymerization of the styrene and butadiene monomers is conducted in a water emulsion that includes a soap or surfactant, an initiator system and typically a molecular weight regulator. To prevent undesired crosslinking of the poly(styrene-butadiene), the Polymerization reaction can be terminated at below 100% monomer conversion by the addition of a shortstop, which reacts with free radicals and oxidizing agents in the initiator system to terminate polymerization. Once polymerization is terminated, unreacted styrene and butadiene monomers are removed by various processes known in the art. The resulting SBR polymer is an elastic rubbery polymer used for a variety of applications.
There are two common methods for producing SBR latex dispersions: a low temperature method (i.e. cold polymerization) and a high temperature method (i.e. hot polymerization). The low temperature method of producing SBR latex dispersions involves polymerizing styrene and butadiene monomers at temperatures typically between 5° C. and 25° C. to produce “cold” SBR polymer. The low temperature method can be used to make high molecular weight polymers without introducing excess crosslinking. The cold SBR polymer is typically produced using a redox initiator system and a natural soap such as the potassium or sodium salt of oleic acid or rosin acid. In the cold polymerization method, the polymerization reaction is typically terminated at well below 100% monomer conversion (e.g. 60-80%) by the addition of a shortstop, which reacts with free radicals and oxidizing agents in the redox initiator system to terminate polymerization and to prevent undesired crosslinking of the poly(styrene-butadiene).
Unlike the cold polymerization method, the high temperature method for producing SBR latex dispersions involves polymerizing styrene and butadiene monomers at temperatures in excess of 50° C., and generally in the range of 50-80° C., in the presence of a natural or synthetic surfactant. The SBR latex dispersions can be produced by the high temperature method using as much as 50% styrene monomers. Moreover, the high temperature method can have up to about 90% conversion of the styrene and butadiene monomers prior to termination of the polymerization reaction.
In addition to the above differences between the cold polymerization and hot polymerization methods, these methods differ in other respects. For example, once cold polymerization is completed, the SBR latex is typically agglomerated and excess water is removed by evaporation to produce a high solids SBR latex (or HSL) having up to 72% solids. As a result, the agglomeration process produces polymer particles with a broad particle size distribution and thus low viscosity dispersions can be produced with high solids contents. Thus, the low temperature method can be used to produce a SBR rubber that can be used in, e.g., passenger tires, asphalt modification, adhesives, latex foam and other types of applications.
The hot polymerized SBR, on the other hand, cannot be agglomerated to increase the solids content because of the high level of crosslinking and because a synthetic surfactant is used in polymerization. As a result, the hot polymerized SBR latex dispersion has a narrow particle size distribution and a solids content below 50%. Accordingly, hot polymerized SBR latex dispersions are generally referred to as “hot polymerized, medium solids SBR latex dispersions.”
Another difference between cold polymerized SBR and hot polymerized SBR is that cold polymerized SBR is often vulcanized to introduce a desired amount of crosslinking into the SBR polymer. In contrast, because of the high level of crosslinking, the hot polymerized SBR latex is typically not vulcanized. In the vulcanization process, additives such as vulcanizing agents, vulcanization accelerators, prevulcanization inhibitors, antireversion agents, and the like can be added to the cold polymerized SBR latex. The cold polymerized SBR latex polymer can then be subjected to elevated temperatures thereby increasing the tensile strength of the SBR without significantly reducing its elongation.
For both cold polymerized SBR and hot polymerized SBR, antidegradant additives such as antioxidants and antiozonants are added to the SBR latex dispersion to prevent oxidation of the double bonds in the SBR polymer. These antidegradant additives and the vulcanization additives often included in cold polymerized SBR latex dispersions are added in the form of organic solids or aqueous dispersions to the latex dispersions and are often water insoluble organic materials. As a result, these additives become dispersed as particles in the latex dispersion under agitation. Furthermore, because these additives are not soluble in the aqueous latex dispersion and because they typically have higher or lower densities than water, the additives tend to separate from the latex during storage or transportation of the latex. These additives will often also separate from the latex when it is diluted. Accordingly, these additives do not produce the desired effect in the SBR latices. Therefore, there is a need in the art to reduce the separation of these water insoluble additives from aqueous SBR latices, and particularly from cold SBR latices.
SUMMARY OF THE INVENTION
It has been discovered that by adding an organic solvent that is miscible in water in small amounts to the SBR latex together with the water insoluble additives that the water insoluble additives are significantly less likely to separate from the latex. In particular, it has been discovered that the water-miscible organic solvent allows the water insoluble additives to partition into the latex polymer thereby producing increased properties in the latex. Alternatively, smaller amounts of the water insoluble additives can be added along with the water-miscible organic solvent to provide the same properties typically provided by comparatively larger amounts of the additives. Furthermore, the SBR latices of the invention are more stable in storage and transportation than conventional SBR latices including these water insoluble additives. The SBR latices of the invention are also stable even when diluted.
The present invention includes a method of incorporating a water insoluble organic chemical into a styrene-butadiene rubber latex dispersion. A styrene-butadiene rubber latex dispersion is provided comprising an aqueous phase and a disperse phase, with the disperse phase including particles of styrene-butadiene rubber. An organic solvent that is miscible in water and the water insoluble organic chemical are added together to the styrene-butadiene rubber latex dispersion. The organic solvent can then be removed if desired from the latex dispersion. The addition of the water-miscible organic solvent allows the water insoluble organic chemical to pass or partition from the aqueous phase into the disperse phase thus limiting separation of the water insoluble organic chemical from the latex dispersion. The water-miscible organic solvent is preferably selected from the group consisting of low molecular weight alcohols (e.g. C1-C3 alcohols such as methanol, ethanol, propanol, and isopropanol), acetone, dioxane, methyl ethyl ketone (MEK), and N-methyl-2-pyrrolidone (NMP). Preferably, the organic solvent is acetone or NMP. When added to the latex dispersion, a substantial portion of the water-miscible organic solvent preferably enters the disperse phase of the latex dispersion.
In accordance with the invention, the water insoluble organic chemical can be added to the water-miscible organic solvent as a solid or as an aqueous dis
Adams Vanessa M.
Golzar Babak
Takamura Koichi
BASF AG
Szekely Peter
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