Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-10-25
2003-09-02
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C524S459000, C524S503000, C526S319000, C526S344200
Reexamination Certificate
active
06613853
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a vinyl resin having superior productivity, which comprises subjecting a vinyl compound to suspension polymerization by the use of a polymerization tank equipped with a reflux condenser. More particularly, the present invention relates to a method for producing a vinyl resin having a high bulk density, which is superior in antifoaming effect against dry foams generated during the middle period and the latter period of polymerization in a polymerization tank.
BACKGROUND OF THE INVENTION
A typical method for industrial production of a vinyl chloride resin comprises batch type suspension polymerization including dispersing a vinyl chloride monomer in an aqueous medium in the presence of a dispersion stabilizer in a polymerization tank, feeding an oil-soluble polymerization initiator into the tank, and raising the temperature to allow for polymerization.
For an improved productivity, the time spent on one batch of polymerization has been required to be shortened in recent years. To meet the request, a polymerization tank equipped with a reflux condenser may be used to promote removal of polymerization reaction heat, or a previously heated aqueous medium may be used to shorten the temperature elevating time (hot charge method).
When a polymerization tank equipped with a reflux condenser is used, however, wet foams and dry foams occur because of the pressure near the reflux condenser, which decreases as the gas of vinyl chloride monomer is condensed. The wet foams contain, as a main component, water from polyvinyl alcohol. The dry foams contain, as a main component, vinyl chloride resin (particles) and vinyl chloride monomer, and are generated during the middle period and the latter period of polymerization. When the wet foams and dry foams are generated, the effective area in the polymerization tank becomes smaller, which in turn lowers the productivity. When dry foams are generated, moreover, scales adhere to the reflux condenser, thereby making the temperature of the polymerization tank uncontrollable. When the ref lux condenser is not used, dry foams do not occur, but the polymerization time is prolonged and the productivity becomes low.
To deal with these defects, U.S. Pat. No. 5,087,678 discloses a method wherein silicone, such as dimethylpolysiloxane, polyvinyl alcohol having a low degree of hydrolysis, and the like are added when the polymerization reaction heat in a reflux condenser is removed by not more than 10% of the total polymerization reaction heat; (1). JP-A-3-212409 discloses a method wherein a water-insoluble, partially hydrolyzed polyvinyl alcohol (0.002-0.007 part by weight per 100 parts by weight of a vinyl chloride monomer) having a degree of hydrolysis of 20-50 mol % and a polymerization degree of 200-400 and an antifoaming agent (0.001-0.01 part by weight per 100 parts by weight of the vinyl chloride monomer), such as dimethylpolysiloxane, are added when the polymerization reaction heat in a reflux condenser is removed by less than 10% of the total polymerization reaction heat; (2).
JP-A-55-137105 discloses addition of ionized polyvinyl alcohol having a degree of hydrolysis of 60-80 mol %, before the start of polymerization; (3). U.S. Pat. No. 5,502,123 discloses a method wherein water-soluble polyvinyl alcohol having a degree of hydrolysis of 70-85 mol % and a polymerization degree of 700-3,000 is added at a point where the polymerization conversion is 5-50%, and polymerization is performed at a temperature of 58-70° C.; (4). JP-A-7-53607 discloses a method wherein water-soluble polyvinyl alcohol having a degree of hydrolysis of 70-85 mol % and a polymerization degree of 700-3,000 is added continuously or discontinuously at a point where the polymerization conversion is 5-50%; (5). U.S. Pat. No. 5,478,900 discloses a method wherein a water-soluble polyvinyl alcohol having a degree of hydrolysis of 75-85 mol % and a polymerization degree of 1500-2,700 is added at a point where the polymerization conversion is 30-60%; (6).
In addition, U.S. Pat. No. 5,849,831 discloses a method wherein a polyvinyl alcohol having a degree of hydrolysis of not more than 85 mol % is added at a point where the polymerization conversion is 30-90%; (7), and JP-A-11-116630 discloses a method wherein polyvinyl alcohol having a degree of hydrolysis of not more than 85 mol % is added continuously or in two or more portions at a point where the polymerization conversion is 30-90%; (8).
However, the above-mentioned methods (1) and (2) suffer from extensive occurrence of dry foams that frequently decrease the bulk density of vinyl chloride resin. The methods (3) to (6) are associated with the problems in that polymerization requires an extended period of time and the productivity becomes poor, due to the non-use of a reflux condenser.
Moreover, while the methods (7) and (8) show high productivity due to the use of a polymerization tank equipped with a reflux condenser, the antifoaming effect to suppress dry foams is not entirely satisfactory and the problem of scale attachment still remains, leaving room for further improvement required by the recent high development of technology.
SUMMARY OF THE INVENTION
According to the present invention, there is proposed a production method of a vinyl resin having a high bulk density and a superior antifoaming effect to suppress occurrence of dry foams, which comprises suspension polymerization of a vinyl compound by the use of a polymerization tank equipped with a reflux condenser.
It has been further found that, when the above-mentioned suspension polymerization is conducted with the addition of polyvinyl alcohol (A) having a degree of hydrolysis of not less than 65 mol %, a polymerization degree of not less than 700 and satisfying the following formula (1), at a point where the polymerization conversion of the vinyl compound is not less than 30%, the occurrence of dry foams during the production can be suppressed and a vinyl resin having a high bulk density can be obtained:
0.0300≦(3
−Y
)/
X
≦0.0330 (1)
wherein X is a degree of hydrolysis (mol %) and Y is a degree of iodine absorption.
As used herein, by the degree of iodine absorption is meant the absorbance measured at wavelength 490 nm and slit width 1 mm, for a mixture of a 0.1 wt % sample solution (5 ml), pure water (11 ml) and 1/1000[N] iodine solution (4 ml), which has been adjusted to 25° C. and stood for 20 min.
DETAILED DESCRIPTION OF THE INVENTION
The reflux condenser to be used in the present invention is used for efficiently removing a polymerization reaction heat during suspension polymerization of a vinyl compound. That is, an unreacted gaseous vinyl compound generated from a suspension in a polymerization tank is liquidized in a reflux condenser. The vinyl compound liquidized in the reflux condenser takes away the polymerization heat while being sent back to the polymerization tank. The temperature of the cooling water in the reflux condenser is generally about 10-50° C. The temperature of the polymerization tank is controlled by the reflux condenser and also by a jacket or coil of the polymerization tank. The proportion of the heat from the polymerization reaction, which is to be removed by the reflux condenser, is not particularly limited, but it is preferably 10-80%, more preferably 20-60%, of the total polymerization reaction heat.
In the present invention, a vinyl compound is subjected to suspension polymerization in the presence of a dispersion stabilizer for suspension polymerization. Specifically, a vinyl compound is subjected to suspension polymerization, wherein a dispersion stabilizer, and where necessary, a dispersion auxiliary are added to water or hot aqueous medium to disperse the vinyl compound, whereafter polymerization is conducted in the presence of an oil-soluble catalyst.
The vinyl compound to be subjected to the suspension polymerization in the present invention may be vinyl chloride monomer, a monomer mixture mainly containing vinyl chlor
Leydig , Voit & Mayer, Ltd.
Reddick Judy M.
The Nippon Synthetic Chemical Industry Co., Ltd.
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