Abstract: A polymerization process, comprises a polymerization vessel, a reflux condenser installed outside the polymerization vessel and a pipe connected between the reflux condenser and a wall of the polymerization vessel with an end thereof opening into a gaseous phase region inside the polymerization vessel, for returning the liquid condensate to the polymerization vessel, wherein said end projects from an inner surface of the wall of the polymerization vessel into the gaseous phase region. In polymerizing a monomer having an ethylenically unsaturated double bond using the polymerization apparatus, the quantity of heat removed by the reflux condenser is increased stepwise or continuously with progress of the polymerization, such that not less than 20% of the total reaction heat generated during the whole course of the polymerization is removed by the reflux condenser. With 100 or more repeated polymerization runs, polymer scale deposition inside the vessel is minimal even below the pipe end.

Abstract: An apparatus for producing a vinyl chloride-based polymer which comprises a polymerization vessel for carrying out suspension polymerization of a monomeric material containing at least vinyl chloride dispersed in an aqueous suspension, and a circulating passage extended from said polymerization vessel and through a heat exchanger back to said polymerization vessel for circulating a polymerization reaction mixture, wherein the polymerization reaction mixture returning from said circulating passage into said polymerization vessel is sprayed inside the polymerization vessel so that the inside wall portion of said polymerization vessel in a gas-phase zone is entirely wetted with the polymerization reaction mixture.

Abstract: A polymerization apparatus that is equipped with a circulation path for the flow of a reaction mixture that comprises a polymerization vessel, a heat exchanger arranged outside said polymerization vessel, and a pipeline that is extended from said polymerization vessel, is returned to said polymerization vessel through said heat exchanger, and is provided with a strainer in the course thereof, wherein the surface of a filter provided in said strainer that is located upstream has rodlike projections, and a method of producing a polymer of a monomer having an ethylenically unsaturated double bond by using said apparatus. Scale and polymers in the form of blocks can be prevented from mixing into the reaction mixture. Therefore, where the obtained sheet is molded into a sheet or the like, fish eyes can be reduced and even if the polymerization is repeated, clogging of the tubes of the heat exchanger and dropping in the flow velocity of the reaction mixture can be prevented.

Abstract: A process for producing a vinyl chloride-based polymer by suspension polymerizing vinyl chloride monomer or the like while circulating a reaction mixture in a polymerization vessel by a circulating pump through a circulation line led out from the polymerization vessel to extend through a heat exchanger back to the vessel, wherein the pump comprises a conical hub and an impeller comprised of a spirally shaped single blade provided on the hub, and, during polymerization, the stirring energy (A) applied to the reaction mixture by the stirrer in the polymerization vessel and the circulating energy (B) exerted to the reaction mixture by the circulating pump in the circulation line are controlled so as to satisfy the relationships(A)+(B)=from 1.5 to 4.0 kW/t (1)and(B)/[(A)+(B)]=from 0.1 to 0.6 (2)Polymer scale is prevented from being deposited on inner surfaces of the heat exchanger, circulation piping, circulating pump or the like.

Abstract: A method for preparing powder of a vinyl chloride polymer comprises the steps of polymerizing vinyl chloride monomer or a vinyl monomer mixture mainly comprising vinyl chloride monomer in an aqueous medium and adding, to the polymerization system, a fluorine atom-containing nonionic surfactant in an amount ranging from 0.0001 to 0.5 part by weight per 100 parts by weight of the vinyl chloride monomer or the vinyl monomer mixture mainly comprising vinyl chloride monomer after the rate of polymerization reaches at least 70% or fine powder of at least one inorganic substance having a particle size ranging from 0.001 to 50 .mu.m in an amount ranging from 0.001 to 1.0 part by weight per 100 parts by weight of the vinyl chloride monomer or the vinyl monomer mixture mainly comprising vinyl chloride monomer after the rate of polymerization reaches at least 70%.

Abstract: A process for producing a vinyl chloride polymer comprises subjecting a vinyl chloride monomer or a mixture comprising a major proportion of a vinyl chloride monomer along with at least one co-polymerizable monomer to suspension polymerization in an aqueous medium in the presence of a monomer-soluble polymerization initiator. The monomer-soluble polymerization initiator comprises, in combination, (A) a compound which is free of a benzene ring, a cyclohexyl group and an alkoxy group in the molecule and whose 10 hours half-life temperature at a concentration of 0.1 mole/liter of benzene is in the range of 30.degree. to 50.degree. C. and (B) 1-cyclohexyl-1-methylethyl peroxyneodecanoate.

Abstract: A process for suspension polymerizing vinyl chloride or a monomeric mixture containing the same in an aqueous medium comprising the step of adding a partially saponified polyvinyl alcohol having an average polymerization degree of 600 to 800 and a saponification degree of 65 to 75 mol % to a polymerization system, wherein the partially saponified polyvinyl alcohol is added before start of polymerization, and also after-added continuously or intermittently over the period from the start of polymerization to the time when a polymerization conversion of 10 to 30% is reached. By the suspension polymerization process, it is possible to obtain a vinyl chloride-based polymer having high bulk specific gravity, high gelation rate and a certain level of thermal stability and showing an effectively reduced number of fish eyes when formed into shaped products.

Abstract: The preparation of vinyl chloride-type polymers by suspension polymerization of vinyl chloride monomers in the presence of monomer-soluble polymerization initiators, wherein the monomer-soluble polymerization initiators utilized are a combination of (A) a compound which possesses neither a benzene ring nor an alkoxyl group, and has a half-life of 10 hours at 0.1 mol/l concentration in benzene solution at a temperature of 40.degree.-50.degree. C., and (B) 1-cyclohexyl-1-methylethylperoxy pivalate.This method yields vinyl chloride-type polymers the qualities of which such as an initial colorization and thermal stability are effectively improved, without being affected by the limitations accompanied by the insufficient cooling capacity of the polymerization vessel in general. The preparative method further enables one to effectively avoid scale deposition in the polymerization vessel.

Abstract: A process for producing a vinyl chloride-based polymer, which comprises suspension polymerizing vinyl chloride monomer or a vinyl chloride-containing monomeric mixture in an aqueous medium in the presence of an oil-soluble polymerization initiator, wherein the initiator comprises (A) at least one compound having a 10-hour half-life temperature, at a concentration of 0.1 mol/l in benzene, of not lower than 35.degree. C., and (B) at least one compound having a 10-hour half-life temperature, at a concentration of 0.1 mol/l in benzene, of lower than 35.degree. C., with the amount of the initiator (B) being from 0.01 to 0.07% by weight based on the monomer or monomeric mixture and being from 10 to 30% by weight based on the total amount of the initiators (A) and (B). The process makes it possible to shorten easily the time required for raising temperature, and to produce vinyl chloride-based polymers which have a good particle size distribution and which have few fish eyes when formed into sheets or the like.

Abstract: A polymerizing apparatus for polymerizing a monomer having an ethylenically unsaturated double bond which is equipped with a polymerization vessel having an agitator and a return nozzle to a gaseous phase part and with a circulating pipeline extending from said polymerization vessel and connected to said return nozzle of the polymerization vessel through a heat exchanger, in which said return nozzle is installed such that it discharges a reaction mixture in the direction which is tangential to the circumferential wall of the vessel and in which the agitator is rotated. Scale of a polymer can be prevented from depositing in the polymerization vessel and it is possible to reduce the number of fish eyes of a molded product such as a sheet into which the polymer obtained by the present polymerizing apparatus can be worked.

Abstract: An improved method is proposed for the suspension polymerization of vinyl chloride monomer in an aqueous medium, by which the polyvinyl chloride resin obtained may have an increased bulk density without causing any disadvantages. The improvement can be obtained by controlling the power on the stirrer for the agitation of the polymerization mixture in such a manner that the power at the moment of the start of the polymerization reaction is 100 to 200 kgf.m/s per 1000 kg of the polymerization mixture and the power is subsequently decreased either continuously or step-wise according to a specified schedule down to 60 to 90% of the value at the start of the polymerization reaction at the moment when conversion of the monomer to polymer is 30% along with starting of the operation of the reflux condenser at a specified moment in relation to the stirrer power and the monomer conversion.

Abstract: In a polymerizing apparatus which comprises a polymerization vessel and a circulating line comprising a heat exchanger installed outside said polymerization vessel and a circulating pipeline extending from said polymerization vessel and returning to said polymerization vessel through said heat exchanger, the improvement comprising a strainer installed in the course of said circulating pipeline. Since polymer scale and a polymer in the form of blocks formed in the circulating line can be trapped, the circulating pipeline and tubes of the heat exchanger can be prevented from being blocked up. Further, since they can be prevented from mixing with a reaction mixture in the polymerization vessel, when the obtained polymer is worked into a molded item such as a sheet, fish eyes can be prevented from increasing. Therefore, a polymer can be produced efficiently with high productivity.

Abstract: A process for producing a vinyl chloride-based polymer in which an aqueous suspension of a vinyl chloride-based monomeric material placed in a polymerization vessel equipped with an agitating element is subjected to suspension polymerization by introducing a polymerization initiator to the aqueous suspension at a position located inside the diameter of the agitating element being rotated. By this process it is possible to prevent totally the deposition of polymer scale on the inside wall of the polymerization vessel, particularly in the vicinity of a gas-liquid interface. Therefore, troubles arising from polymer scale formation and labor needed for removing such polymer scale are obviated, and a vinyl chloride-based polymer of high quality can be produced efficiently.

Abstract: An improvement is proposed in the suspension polymerization of vinyl chloride monomer in order to obtain a polyvinyl chloride resin powder having good absorptivity of plasticizers by virtue of the well developed porosity of the resin particles and containing a decreased amount of fish eyes. The improvement comprises adding, to the polymerization mixture, a water-insoluble partially saponified polyvinyl acetate having an average degree of polymerization of at least 1000 and a degree of saponification of 20 to 60% in combination with a conventional water-soluble polymer as the suspending agent such as water-soluble partially saponified polyvinyl acetates and water-soluble cellulose ethers.

Abstract: An apparatus for continuous polymerization of vinyl chloride or a vinyl chloride-based monomeric mixture, comprising a pre-mixer 1 for preparing an aqueous suspension of the vinyl chloride or vinyl chloride-based monomeric mixture, and a polymer slurry tank 5 connected to the pre-mixer 1 through a polymerization passage comprising a piping 3, wherein a pump comprising a conical hub and an impeller mounted thereon comprised of a single spiral blade is used for drawing out the aqueous suspension from the pre-mixer into the polymerization passage and for discharging a polymer slurry formed in the passage into the slurry tank, and the polymerization passage has a length sufficient for permitting the vinyl chloride or vinyl chloride-based monomeric mixture contained in the aqueous suspension flowing through the passage to be polymerized to a predetermined extent while passing through the passage.

Abstract: An improved method for the suspension polymerization is proposed which gives a PVC resin product having an increased plasticizer absorptivity and greatly decreased content of fish eyes. The invention can be achieved by additionally adding a limited volume of water into the polymerization mixture under proceeding of the polymerization reaction within a specified period of 30 to 70% monomer conversion and at such a controlled rate as not to unduly decrease the pressure inside of the reactor.

Abstract: A method for recovering unreacted monomers during preparation of a vinylic polymer comprises the steps of polymerizing a vinyl monomer in an aqueous medium in a polymerizer and then recovering unreacted monomers from the polymerization system, wherein a gas evacuation rate per unit charge weight of the monomer is controlled to the range of from 60 to 300 Nm.sup.3 /hr per ton of the monomer from the initiation of the monomer recovery till the pressure in the polymerizer reaches 2.5 kg/cm.sup.2 G and a superficial gas linear velocity is reduced to a level of not more than 0.008 m/sec when the pressure in the polymerizer reaches 2.5 kg/cm.sup.2 G. The method makes it possible to recover unreacted monomers quickly without causing carrying over of polymer particles formed and is effective to maintain high quality of vinylic polymers produced.

Abstract: An improvement is proposed in the process of suspension polymerizatiopn of vinyl chloride monomer in an aqueous polymerization medium, by which a resin product of high quality relative to the contents of foamy resin and fish-eyes can be produced in a high efficiency with little deposition of polymer scale on the reactor walls. The improvment comprises heating and keeping the surfaces of the polymerization reactor and accessory equipment coming into contact with the gaseous phase above the polymerization mixture at a temperature of 55.degree. C. or higher during a period starting from a moment when the temperature of the polymerization mixture under temperature elevation up to the polymerization temperature is still 45.degree. C. or lower to a moment when conversion of the monomer into polymer is at least 10% so that foaming on the polymerization mixture can be greatly reduced.

Abstract: A process for preparing a vinyl chloride polymer of the present invention comprises initiating suspension polymerization by suspending a vinyl chloride monomer in an aqueous medium in the presence of a first dispersion stabilizer and adding a second dispersion stabilizer at a specified time after the initiation of polymerization. Here, as the first dispersion stabilizer, (A) a partially saponified polyvinyl alcohol with a high saponification degree and (B) a hydroxypropylmethyl cellulose are used in combination, and as the second dispersion stabilizer, (C) a partially polyvinyl alcohol with a low saponification degree is used. According to the process, it is possible to prepare a vinyl chloride polymer with excellent characteristics such as plasticizer take-up, etc.

Abstract: A process for producing a vinyl chloride polymer for matted moldings which comprises performing the suspension polymerization of vinyl chloride monomer or a mixture of vinyl monomers composed mainly of vinyl chloride in an aqueous medium, in the presence of (A) 0.01 to 3 parts by weight of a polyfunctional monomer having two or more ethylenic double bonds in the molecule and (B) 0.00005 to 0.01 part by weight of antioxidant, thereby yielding a vinyl chloride resin composed of 5 to 90% by weight of tetrahydrofuran-insoluble gel fraction, with the remainder being tetrahydrofuran-solubles.