Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Patent
1998-07-20
2000-03-07
Seidleck, James J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
528501, 528502, 523328, 526344, C08F 610
Patent
active
060342099
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Method of Recovering Low Boiling Substances from a Polymer Latex
1. Technical Field
This invention relates to a process and an apparatus by which low boiling point substances such as a vinyl chloride monomer and a chain transfer agent can be recovered or removed with high efficiency from a foamable polymer latex such as, for example, a latex of vinyl chloride polymer by using a continuous multi-stage evaporator.
2. Background Art
Polymer latexes such as a vinyl chloride polymer latex, a polystyrene latex and an acrylic rubber latex are widely used as, for example, coating materials, paints and materials to be incorporated with other polymers. As for a polyvinyl chloride resin for paste processing, a vinyl chloride polymer latex is dried to give a powder and the powder is mixed with a plasticizer or the like.
The above-mentioned polymer latexes are in the form of a dispersion comprising minute polymer particles having a particle diameter of 0.1 to 10 .mu.m which are uniformly suspended in an aqueous medium. As typical methods for preparing the polymer latexes by polymerization, there can be mentioned an emulsion polymerization procedure, a seeding emulsion polymerization procedure and a micro-suspension polymerization procedure. In these polymerization procedures, surfactants such as anionic surfactants and nonionic surfactants are usually used.
The thus-prepared polymer latexes contain residual ingredients such as low-boiling-point unreacted monomers, chain transfer agents such as t-dodecyl mercaptan and carbon tetrachloride, and solvents for free-radical initiators, such as n-hexane. Low-boiling point substances having a boiling point lower than that of water which are contained in the polymer latexes should preferably be recovered with high efficiency from the viewpoint of reduction of a raw material cost, quality and hygiene.
As processes for recovering low-boiling point substances, there can be mentioned, for example, a process for recovering unreacted monomers from a vinyl chloride polymer latex, wherein the polymer latex is retained in an evaporator, i.e., an evaporating vessel, in a continuous or batchwise manner where it is heated to evaporate unreacted monomers. However, a polymer latex having polymer particles having an average particle diameter of about 0.1 to 10 .mu.m usually contains a surfactant, and thus, there is a problem such that the polymer latex readily foams from the latex surface within the evaporator with the result that polymer particles easily flow away therefrom through an unreacted monomer-recovering line (suction line). To suppress the foaming of polymer latex from the surface of latex, the amount of polymer latex and the rate of flow thereof are usually controlled, or the suction force through the unreacted monomer-recovering line is weakened. Therefore, other problems arise in that a substantial long time is required for recovering the unreacted monomers, and a polymer is deposited in a polymer latex-feeding line whereby the pipe line occasionally clogs. If the heating temperature in the evaporator is lowered, then the undesirable foaming can be suppressed, but this leads to reduction of recovery of the low-boiling point substances.
To solve the above-mentioned problems, a proposal has been made wherein a rotational disc-type defoaming device is provided inside or outside the evaporator. However, the vinyl chloride polymer contained in foams is deposited and, when the defoaming device is operated for a long period, the deposited polymer adheres onto and builds up on the inside of the defoaming device, which leads to stop of operation of the defoaming device.
A defoaming agent may be used instead of the defoaming device, but it readily thermally degrades the polymer when the polymer is processed at an elevated temperature. Further when the polymer is subjected to expansion molding, residual defoaming agent exerts a harmful influence upon the expansion and hence only a minor quantity of defoaming agent is used which is insufficient for suppressing the undesirable f
REFERENCES:
patent: 4158092 (1979-06-01), Botsch
patent: 4247686 (1981-01-01), Takemoto
Takeyama Youichi
Yoshida Masahiro
Asinovsky Olpa
Seidleck James J.
Shindai-Ichi Vinyl Corporation
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