Production process for vinyl-based polymer

Details Production process for vinyl-based polymer Production process for vinyl-based polymer

2002-12-16

2003-10-28

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S084000, C526S319000, C526S317100, C526S330000, C526S291000, C526S343000, C526S344100, C526S344000, C526S910000, C526S911000, C526S346000, C526S329200

Reexamination Certificate

active

06639027

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a production process for a vinyl-based polymer, and more specifically to a production process for polymerizing a vinyl-based monomer by a radical reaction with a characteristic method of adding a reaction inhibitor.
2. Description of the Prior Art
In conventional radical polymerization reactions of vinyl-based monomers, reaction inhibitors (also known as reaction retardants or reaction suppressants) have typically been added to the polymerization mixture. Examples of known reaction inhibitors include phenol-based compounds, sulfur compounds, N-oxide compounds, phosphorus compounds, and unsaturated hydrocarbon compounds. Specific examples of the phenol-based compounds include 2,2-di-(4′-hydroxyphenyl)propane, hydroquinone, p-methoxyphenol, t-butylhydroxyanisole, n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl) propionate, t-butylhydroquinone, 2,5-di-t-butylhydroquinone, 4,4′-butylidenebis-(3-methyl-6-t-butyl)phenol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2′-methylene-bis-(4-ethyl-6-t-butyl)phenol, triethyleneglycol-bis [3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], pentaerythrityl-tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenol)propionate], t-butylcatechol, 4,4′-thiobis-(6-t-butyl)-m-cresol, and tocopherol.
The addition of these reaction inhibitors is performed for a variety of reasons, and they may be added to the polymerization mixture prior to commencement of the polymerization reaction in order to reduce the occurrence of fish eyes within the product polymer (Japanese Laid-open publication (kokai) No. 48-49990 (JP48-49990A), Japanese Post-Examination Publication (kokoku) No. 60-50366 (JP60-50366B)), added during the polymerization reaction in order to suppress heat kick, or alternatively added at the completion of the polymerization reaction in order to prevent postpolymerization and prevent deterioration in the anti-initial discoloration property resulting from heat history (U.S. Pat. No. 3,642,756, Japanese Laid-open publication (kokai) No. 57-185302 (JP57-185302A), and Japanese Laid-open publication (kokai) No. 62-503 (JP62-503A)). Furthermore, such reaction inhibitors are also used for halting rapid reactions which occur during abnormal reactions.
Amongst the above reaction inhibitors, 2,2-di-(4′-hydroxyphenyl)propane displays particularly suitable reaction inhibiting properties, enables the production of high quality polymers, and also produces very little adhesion of scale to the polymerization vessel, and has consequently been widely used at the completion of polymerization reactions. However, 2,2-di-(4′-hydroxyphenyl)propane is a solid at room temperature, and unless the material is dissolved in an organic solvent such as methanol prior to use, then the operation of supplying the reaction inhibitor to the reaction vessel via a supply pipe is problematic. However, because this method requires the use of an organic solvent, not only are there associated physical dangers for the operators exposed to the fumes, but these fumes also become a source of potential environmental pollution.
Consequently, in Japanese Post-Examination publication (kokoku) No. 7-113041 (JP7-113041B), a reaction inhibitor represented by a general formula (1) shown below was disclosed as a potential alternative to 2,2-di-(4′-hydroxyphenyl)propane.
(wherein, R represents an alkyl group of 3 or more carbon atoms). Specifically, the compound in which the R group is a sec-butyl group, namely, 2,6-di-t-butyl-4-sec-butylphenol is currently used. This compound exists as a liquid in the supply tank and piping when the external air temperature is between 20 and 25° C., namely room temperature, and so is able to be supplied to the polymerization vessel via the supply piping without requiring the use of a solvent. Furthermore, 2,4-dimethyl-6-(1-methylpentadecyl)phenol and 2,6-di-tert-butyl-4-nonylphenol are also liquids at room temperature, and can also be supplied to a polymerization vessel without the use of a solvent.
However, these type of reaction inhibitors also suffer problems if the external air temperature drops below normal room temperatures. For example, if 2,6-di-tert-butyl-4-sec-butylphenol is used, then because the melting point is from 18 to 20° C., in cases in which the external temperature is low, namely 10° C. or lower, the compound enters a supercooled state, and as a result, the reaction inhibitor is more likely to solidify, thereby blocking the supply piping. In a worst possible case, the reaction inhibitor may solidify inside the storage tank, making the supply operation itself impossible. In addition, in the case of other reaction inhibitors with lower melting points, such as 2,6-di-tert-butyl-4-nonylphenol, the viscosity at 20° C. is approximately 400 mPa·s, and this viscosity exceeds 1000 mPa·s under cooling, which can make the supply operation extremely difficult. Consequently, an organic solvent such as methanol must be used to dissolve the reaction inhibitor, and so these types of reaction inhibitors do not completely resolve the aforementioned problems of physical danger for the operators and environmental pollution.
Furthermore, methods in which a dispersion such as an emulsion or a suspension is first prepared by using a dispersant such as an emulsifier or a suspension agent to disperse the above type of reaction inhibitor in an aqueous medium, and this dispersion is then added to the polymerization mixture can also be effective, although the viscosity of the dispersion may increase markedly, making the operation of supplying the dispersion through the supply piping to the polymerization vessel extremely difficult. Moreover, if the external temperature is less than 0C, then there is a danger of the dispersion solidifying.
In addition, in those cases where cold temperatures result in the reaction inhibitor solidifying and blocking the supply piping, a device for heating the blocked sections to melt the solidified reaction inhibitor and prevent blocking of the piping can be installed, although the heating operation is complex, and not only does melting the reaction inhibitor take considerable time, but there is also some danger associated with the heating process.
SUMMARY OF THE INVENTION
The present invention takes the above factors in consideration, with an object of providing a production process for a vinyl-based polymer in which a reaction inhibitor can be added to a polymerization mixture without the use of an organic solvent, even at low temperatures, and problems such as the solidification of the reaction inhibitor inside the supply tank or piping, and subsequent blocking of the piping do not occur.
As a result of intensive investigations aimed at resolving the above problems, the inventors of the present invention discovered that by heating the reaction inhibitor supply tank and the reaction inhibitor supply piping, and maintaining the reaction inhibitor, with a melting point of no more than 40° C., in a liquid form with a viscosity below a specified level, problems such as the blocking of the supply piping due to solidification of the reaction inhibitor could be resolved, and the inventors were consequently able to complete the present invention.
In other words, the present invention provides a production process for a vinyl-based polymer comprising:
a step for polymerizing a vinyl-based monomer by a radical reaction within an aqueous medium in a polymerization vessel; and
a step for supplying a reaction inhibitor with a melting point of no more than 40° C. from a reaction inhibitor supply tank to the polymerization vessel via a reaction inhibitor supply pipe;
wherein the reaction inhibitor supply tank and the reaction inhibitor supply pipe are heated, and the reaction inhibitor is added to the polymerization vessel in a liquid state with a viscosity of no more than 200 mPa·s without using an organic solvent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As follows is a more detailed description of the present invention.
In the pre

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